SBPMat BRAZIL-MRS

2nd Brazilian MRS MeetingOctober 26-29, 2003

Symposium A:

Current trends in Nanostructured Materials and Systems II

Symposium Organizers:____________________________________________________

Fernando Lázaro Freire Jr. (PUC-Rio)

Guillermo Solórzano (PUC-Rio, SBPMat)

Israel Baumvol (UFRGS)

Wander Vasconcelos (UFMG)

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INVITED PRESENTATIONS

A-I1 SELF-ASSEMBLING SYSTEMS AND SURFACE PATTERNING STRATEGIES FOR NANOTECHNOLOGIESGiovanni Marletta, Dipartimento di Scienze Chimiche - University of Catania - Viale A.Doria 6 - I-95125 Catania – Italy

The need for very large scale planar integration of different functions in multifunctional devices including electronic devices, arrays of biosensors, highly integrated optoelectronic devices, etc.., is driving a growing effort towards techniques for surface patterning. Two basically different philosophies of patterning have been extensively developed, respectively exploiting self-organization properties of matter (bottom-up approach), and radiation-based lithography (top-down approach). In the present paper we report a number of case studies dealing with the use of techniques as Langmuir-Blodgett deposition (LB), SPM tip-writing and focused-ion beam activation of surfaces to obtain micro- and nanoscale spatially resolved structures. In particular, we will report specific cases of unusual self-structuring of LB-deposited monolayers on solid surfaces, of tip-induced chemical patterning of organic monolayers on silicon, and spontaneous protein aggregation on ion-irradiated polymer dots. The formation of various structures, as variously shaped domains, stripes, fibers and dots, will be related to the molecular structure of the employed compounds, the deposition parameters, and the substrate composition and properties obtained by Near Field Microscopies (NFM), X-ray Photoelectron Spectroscopy (XPS), Imaging ToF-SIMS, Dynamic Contact angle measurements, Surface Enhanced Raman Spectroscopy (SERS) and theoretical simulations. The perspective of the employed techniques in the context of the developing patterning technologies will be given with respect to the state-of-art of the field.

A-I2 TEACHING “OLD” MATERIALS “NEW” TRICKS: SITE- AND SHAPE-SPECIFIC NANOPATTERNING OF FUNCTIONAL NANOSTRUCTURESVinayak P. Dravid, Professor, Materials Science & Engineering, Director, NUANCE CenterNorthwestern University, Evanston, IL 60208 USA

At Northwestern, we are working towards designing the intricate architecture of functional nanostructures, as well as using them as building blocks for device systems for sensing, diagnostics and therapeutics. Embedded in this scheme are several nanopatterning approaches, some are based on the original invention of Dip-Pen Nanolithography (DPN) developed at Northwestern. The original DPN approach is modified to pattern, at the nanoscale, templates for inorganic and organic-inorganic complexes of arbitrary shape/size on arbitrary substrates, thus extending the efficacy and elegance of DPN. The talk will outline sol-based precursor “inks” as an enabling approach to pattern and characterize magnetic, electronic, chemical- and optical active nanostructures at the nanoscale. Success is already evident for magnetic oxides, inorganic mesoporous structures, ferroelectrics and optically-active nanostructures.The real need for characterizing structure/crystallography/chemistry, as well as unambiguous measurement of their local properties, will be emphasized. The prospects for patterning at single-molecule resolution, especially for bioactive molecules, both by themselves and as templates for inorganics, will also be discussed.

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A-I3 MOLECULAR ORIGINS OF BIO(IN)COMPATIBILITY : MATERIALS DESIGN ISSUES AND CHALLENGES AT THE NANOSCALEC. Ortiz, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA USA

To produce truly bioinert or bioactive surfaces a detailed knowledge of the nanoscale morphology, mechanical properties, physical and chemical interactions with the biological environment is needed. Using the powerful technique of high resolution force spectroscopy (HRFS), we have measured the intermolecular interaction forces between a nanosized probe tip covalently bound with human serum albumin (HSA), the most abundant blood plasma protein in the human body, and various well-defined chemically modified surfaces including; COO - and CH3-terminated alkanethiol self-assembling monolayers and end-grafted poly(ethylene oxide) mushrooms. By varying the solution conditions and using molecular-level theoretical models this net interaction was deconvoluted into the individual constituent interactions including; electrostatic double layer, configurational entropy, H-bonding, and van der Waals forces. A series of chemically advantageous molecular attributes was formulated and based on this information, new glycocalyx-mimetic oligosaccharide-functionalized surfaces were chosen and studied using HRFS.

A-I4 PATTERNED ASSEMBLY OF EPITAXIAL SEMICONDUCTOR NANOSTRUCTURESR. Hull; S. Atha, J.L. Gray, M. Kammler, A. Portavoce, N. Singh, D.M. Elzey, Dept. of Mat. Sci., Univ. of Virginia, Charlottesville, VA 22904, USA; F.M. Ross, IBM Yorktown Heights Research Center, NY, USA; X. Luo, G. Snider, Dept of Elec. Eng., Notre Dame Univ., IN, USA; J.A. Floro, Sandia National Laboratories, NM, USA.

Substantial progress has been described in the literature with respect to the synthesis of ordered semiconductor quantum dot (QD) arrays with single spatial frequencies, through control of elastic interactions during epitaxial growth. For most nano-electronic architectures, more complex patterns are required. For example, in the quantum cellular automata concept, QD quadruplets are charged in bistable configurations, with quadruplet cells arranged in more complex patterns to enable the functions of digital logic. We will describe two experimental approaches for achieving accurate surface placement of quantum dots in the epitaxial Ge(Si)/Si system: 1) Creation of localized topography, chemistry and strain on the substrate surface using focused ion beams for seeding of QD nucleation. 2) Synthesis of QD quadruplet molecules, where molecules self-assemble through cooperative nucleation around nano-scaled surface pits formed during epitaxial growth. Combined focused ion beam / electron beam lithography methods for coupling these QD architectures into nano-electronic test structures will also be presented.

A-I5 MAPPING 3D ALLOYING OF Ge:Si (001) DOMESG.Medeiros-Ribeiro, S. Kycia; LNLS, Campinas, SP; A. Malachias, R. Magalhães-Paniago; Depto. de Física, UFMG, Belo Horizonte, MG; T. I. Kamins, and R. Stanley Williams; Hewlett-Packard Labs, Palo Alto, CA

The issue of Si diffusion into Ge islands grown on Si(100) has been addressed by several independent studies with electron microscopy and x-ray techniques. Alloying is a significant factor in determining the shape and size distribution of an island ensemble. All experiment evidences support the existence of a distinct SiGe vertical composition variation, with most of the Si concentrated at the base of the island. Different growth conditions produce distinct lateral profiles. Hence, the assessment of lateral composition profiles is important to both identify the dominant growth mechanisms and model the confining potential of quantum dots. We report Grazing Incidence Angle X-ray Scattering (GIAXS) measurements on an ensemble of Ge domes with a uniform size distribution. We determined the (average) three-dimensional composition of the domes from an analysis of the anomalous scattering reciprocal space intensity maps near the Ge K absorption edge by first segmenting the domes into a stack of layers and then mapping the lateral concentration of Ge in each layer. Finally, we performed selective-etching experiments and qualitatively confirmed our proposed structural model. The significance of the analysis and procedure presented is key for the realistic modeling of quantum dot confining potentials, as this work presents a solution for imputing lateral composition profiles with its associated strain. This work was funded by FAPESP (contract 98/14757-4) and HP Brazil.

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A-I6 ON THE NATURE OF Mn IN SEMICONDUCTORS*

Adalberto Fazzio, Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970, São Paulo-SP, Brazil

We have performed a systematic study of the nature of Mn in semiconductors, using total energy ab initio calculations within the density-functional theory. We will discuss results for Mn in GaAs and in Si, Ge and SiGe. Our results for Ga1-xMnxAs diluted magnetic semiconductors (DMS) unambiguously show that the effective Mn-Mn coupling is always ferromagnetic, thus non-RKKY, and it is intermediated by the antiferromagnetic coupling of each Mn spin to the holes. We then address the following question: can there be a MnxSi1-x ferromagnetic semiconductor, similarly to MnxGe1-x? Since the main difference between Mn in Si and Ge is the fact that it prefers to be interstitial in Si, whereas it is substitutional in Ge, we investigate the origin of this difference. For that, we study the properties of interstitial and substitutional Mn impurities in both Si and Ge bulk crystals, as well as in the alloy Si1-xGex. We conclude that the main reason behind the different behavior of Mn in Si and Ge has a chemical origin, indicating that a Ge-rich neighborhood will stabilize a substitutional Mn in the Si1-xGex. Assuming that in order to obtain a Si based DMS it is fundamental to have substitutional Mn impurities, we investigate the possibility of incorporating MnSi using some sort of non-equilibrium growth procedure. Studying a variety of interstitial and substitutional sites for a Mn impurity on the Si(100) bare and hydrogenated surface, we find a substitutional Mn surface site with a formation energy similar to the interstitial surface site, suggesting that it might be possible to grow, probably through low temperature MBE, MnxSi1-x

samples with a high enough concentration of substitutional Mn.*This work was done in collaboration with Antônio J. R. da Silva, Raimundo R. dos Santos, Luiz E. de Oliveira, Alex Antonelli and Gustavo M. Dalpian, supported by the Brazilian agencies FAPESP and CNPq.

A-I7 NANOPARTICLES-BASED CHEMICAL GAS SENSORS FOR OUTDOOR AIR QUALITY MONITORING MICROSTATIONS M.-I. Baraton, SPCTS CNRS, University of Limoges, France; L. Merhari, CERAMEC R&D, Limoges, France

Due to the growing concern worldwide about the consequences of urban air pollution on public health, the official organizations in charge of environment protection are strengthening the regulations and have set the maximum authorized concentrations of pollutants at very low levels. Current cost-effective semiconductor sensors used to monitor indoor air quality are not suitable for outdoor air quality monitoring due to their insufficient sensitivity and to their cross-sensitivity to humidity.We present here some of our consolidated results on the optimisation of chemical gas sensors based on metal oxide semiconductors. In order to increase sensitivity and selectivity while keeping fabrication at low cost, three major research directions have been considered: 1) the use of semiconductor nanoparticles in the fabrication of screen-printed gas sensors to increase the sensitivity; 2) the printing of sensitive layers on alumina tiles using a simple mechanical layer-by-layer technique to further increase the sensitivity; 3) the control and tailoring of surface chemistry of nanoparticles proved to be a critical step for further device optimisation. We will finally show how our prototype devices which are capable of detecting O3 and NOx concentrations down to 20 ppb and 50 ppb respectively, and CO concentrations down to 3ppm in air, can be used as sensing elements in novel and cost-effective air monitoring micro-stations. This work has been financially supported by the European Community.

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A-I8 SURFACE CHARGE INDUCED NANOSCALE MANIPULATION OF MOLECULAR FILMSFrancisco Nart and Frederico Cunha, Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador Saocarlense, 400 - 13566-690 - São Carlos, SP – Brazil

The adsorption mechanism of organic molecules on metallic surfaces depends upon several factors that include molecular structure, concentration, temperature and surface charge. The careful control of some of these variables allows one to manipulate the adsorption geometry of these molecules leading to dissimilar packing structures, which can be followed by in situ STM and vibrational spectroscopy. The construction of nanostructured materials following a layer-by-layer approach is the final objective of this work. The molecular probe of choice is a series of derivatives of Uracil. These molecules present a variety of possibilities in adsorption geometries and ready availability. We found that the packing depends on the surface charge on the electrode and on the atom substituted in position 5 of the Uracil base molecule. We used also a silver electrode to investigate the charge induced restructuring of Uracil based molecules by Raman Spectroscopy, since SERS measurements on gold were not possible.

A-I9 SPUTTERED NANOSCALE MAGNETIC MATERIALSAntonio Azevedo, F.M. de Aguiar and S.M. Rezende, Departamento de Física, Univ. Federal de Pernambuco, 50670-901 Recife, PE, Brazil.

New properties and phenomena in magnetism have emerged from the ability to artificially prepare nanoscale magnetic materials. The assembling of nanometer-sized magnetic structures with desired properties have resulted in a forthcoming age for electronic devices, named spintronics. The investigation of the structure and magnetic properties of nanoscale magnetic materials such as thin films, multilayers, particulate and thin film recording media, exchange biased films, GMR spin-valves, magnetic tunneling junctions, and so on has been driven by the demanding requirements of this new area of research. Here, it will be presented a description of some challenging problems and exciting applications envisioned for nanomagnetic materials. Particular attention will be devoted to some activities in this area that are being pursued at the Magnetism and Magnetic Materials group, in Recife. The magnetic properties of multilayers, exchange coupled bilayers, GMR spin-valves and spin injection will be discussed. The correlation between structure, growth conditions and magnetic properties will be emphasized. Dynamic and static properties investigated by Brillouin light scattering, ferromagnetic resonance, ac-susceptibility, dc-magnetometry, etc. are going to be also discussed.Supported by FINEP, CNPq and CAPES (Brazilian agencies)

A-I10 THERMODYNAMICS OF NANOPARTICLESMiguel Jose Yacaman, Texas materials Institute and Chemical Engineering department University of Texas- Austin Austin TX 79705 USA

Metallic particles in the nanosized regime show a thermodynamic behavior, which is very different from that of the macroscopic systems. This is reflected in many properties such as strange minimum energy configurations, shape instabilities, wetting properties and unique alloy structures. This is the result of the complex energy landscape in the nano systems. This is increased when two metals are present .we make a review of recent work by our group in this area and present new data on the alloy behavior of bimetallic systems such as Au-Pd and Au-Cu .we demonstrate both experimentally and theoretically that that the eutectic structure and the core shell structures are favored in nano-alloy systems. In addition we discuss the interactions of nanoparticles of metals and semiconductors with carbon nanotubes and onions new ways to form one-dimensional structures are found.Finally we show that when nanoparticles are in a carbon substrate collective phenomena are produced resulting in new chemical properties at the nanolevel.

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A-I11 SYNCHROTRON RADIATION SAXS STUDIES OF NANOSTRUCTURED MATERIALSAldo F. Craievich, Institute of Physics, University of São Paulo, C. P. 66318, 05315-970 São Paulo, Brazil

A set of recent in situ synchrotron radiation SAXS studies of nano-structured materials will be reviewed. The experiments were carried out at the synchrotron laboratory LNLS, Campinas, Brazil. The first investigation deals with the formation and growth of liquid Bi nano-droplets embedded in a borate glass [Phys. Rev. B, 67, 0854051 (2003)]. Measurements performed in absolute scale allowed us to quantitatively characterize the mechanisms of growth and coarsening, and determine the diffusion coefficient and the activation energy of Bi atoms. The second investigation to be reported concerns the clustering mechanism for the formation of fractal aggregates in several sulfate-zirconia colloidal solutions [J. Phys. Chem. B. 107, 3390 (2003)]. The experimental results lead to a unified model of the clustering process consisting of an initial 1D growth of colloidal chains followed by a 3D cross-linking and further coarsening. Finally, the first results of an on-going study of ordered nanoporous materials and self-organized precursor sols, for applications in catalysis, will be described [in progress (2003)]. This study provided useful insight about the nanostructure of several sols and also about the resulting porous powders, which are expected to mimic the structure of the precursor systems. Since the properties of nanomaterials not only depend on the atomic structure but also, and strongly, on the shape and size of their basic building blocks, SAXS characterizations - such as those reported here - are expected to provide useful information for new materials design.

AI-12 MICRO-RAMAN STUDIES OF CARBON NANOTUBES USING TUNABLE LASERSM. A. Pimenta, A. Jorio, C. Fantini, M. Souza, Departamento de Física – UFMG, Brasil; R. Saito, Tohoku University, Japan; G. Dresselhaus and M. S. Dresselhaus, MIT, USA

Resonant Raman scattering is a very useful tool to investigate carbon nanotubes since it can probe both the phonon spectra and the one-dimensional (1D) electronic structure. We will present results of the Raman spectra of different samples of carbon nanotubes (bundles of nanotubes, isolated nanotubes in aqueous surfactant suspensions, isolated nanotubes deposited on a Si/SiO2 substrate), using tunable lasers in the range of laser energies from 1.5 to 2.7 eV. We will show that the 1D electronic structure formed by van Hove singularities can be obtained from the resonant Raman spectra. We will also present a detailed investigation of the intermediate frequency Raman modes, between 600 and 1100 cm-1. These intermediate frequency modes exhibit a step-like dispersive behavior, that can be explained by a 1D double resonance mechanism, involving acoustic and optical phonons.

A-I13 APPLICATIONS OF ANALYTICAL TRANSMISSION ELECTRON MICROSCOPY IN NANOSCIENCE AND NANOTECHNOLOGYJoachim Mayer, Central Facility for Electron Microscopy, Aachen University, 52074 Aachen, Germany

Nanoscale characterisation and analysis are indispensable to establish the structure/property relationship and thus the scientific basis for nanoscience and nanotechnology. Transmission electron microscopy (TEM), in particular in combination with site-specific focused ion beam (FIB) specimen preparation, has become a more and more important tool with unique capabilities for the study of the chemistry, crystallography and local electronic structure of interfaces and nanoscale features. To highlight the experimental possibilities, recent examples from three areas of application will be discussed: (1) The study of the structure and chemistry of metal/ceramic interfaces, (2) the application of Au quantum dots in nanoelectronic devices based on the Coulomb Blockade effect and (3) the investigation of the tunnel barriers in magnetic tunnel junctions (MTJ) used as MRAM test devices. In all the cases, structural and chemical information from the TEM investigations could directly be linked to the materials and device properties. Furthermore, we will present new ideas of how to employ the focused ion beam technology to create model devices in nanoscience. Finally, we will discuss the needs for future developments in the TEM and FIB area.

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A-I14 UNDERSTANDING DEFECT NUCLEATION THROUGH NANOSCALE EXPERIMENTS AND COMPUTATIONSKrystyn J. Van Vliet, Children's Hospital and Harvard Medical School, Boston, MA USA and Subra Suresh, Massachusetts Institute of Technology, Cambridge, MA USA

Nanoscale contact experiments and atomistic modeling thereof is presented as a means to investigate the onset and early stages of plasticity in metals. Although this work focuses on homogeneous defect nucleation far from grain boundaries, it will enable subseuqent development of heterogeneous nucleation near and at grain boundaries--a key phenomenon in the mechanical deformation of nanocrystalline materials. An energetic, position-sensitive defect nucleation criterion is developed to predict the site and slip character of nucleated defects. This criterion is validated explicitly in the context of dislocation nucleation, using nanoindentation both as a means to concentrate applied force and to measure accurately the onset of dislocation activity.Molecular dynamics (MD) modeling of Bragg-Nye soap bubble raft indentation experiments confirm the accuracy and potential of this appoach. In addition, a new nonlinear finite element approach is developed to guide large-scale computational studies by an intrinsically atomic-scale defect nucleation criterion. With these tools, we demonstrate the effects of microstructural features such as grain size and macrostructural features such as film thickness and line width on the initiation and early stages of plastic deformation.

A-I15 TEM STUDIES OF INDIVIDUAL AND AGGLOMERATED NANOPARTICLESC. Barry Carter*, Christopher R. Perrey, William M. Mook, William W. Gerberich, Siri Thompson1, Ameya Bapat1, Uwe Kortshagen1, Rajesh Mukherjee1, Xiaoliang Wang1, Jami Hafiz1, Peter McMurry1, Joachim Heberlein1, and Steven Girshick1

Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN; 1 Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN; * cbcarter@umn.edu

In the 1-100 nm size regime, the properties of materials can differ significantly from those of their bulk counterparts. Recent work has reported nanospheres of Si with hardnesses much higher than that of bulk Si; other studies have described similarly advantageous electronic and chemical properties of nanoparticles. The unique relationships between nanoscale structure, morphology, chemistry, and crystallography to the properties observed must be understood for successful incorporation into commercial applications. Because of the inherently small size of these nanoscale structures, the transmission electron microscope (TEM) is an essential tool for this analysis of both individual nanoparticles and agglomerated nanoparticles. Using the TEM, nanoparticles from three distinctly different plasma-generation methods have been investigated. Nanoparticles of Si, Ti, and SiC have been observed and led to interesting discoveries on nanoparticle surface structure, formation processes, oxidation, and planar defects in nanoparticles. Similar work involving nanoparticle agglomerates provides the opportunity to observe the behavior of sintering and coagulation at the nanoscale. These observations of nanoparticle systems can then be compared to that of previously studies bulk systems for a greater understanding of these processes across different length scales.

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A-I16 USING NATURE'S TOOLS TO DESIGN NOVEL HYBRID NANOSTRUCTURED MATERIALSAngela M. Belcher*, Brian Reiss*, Seung-Wuk Lee* and Chuanbin Mao; University of Texas at Austin and *Massachusetts Institute of Technology

Peptides capable of specific recognition and nucleation of semiconductor and magnetic materials were isolated and engineered into advanced biological viral templates and long range-ordering viral liquid crystal systems. Peptides selected through an evolutionary screening process that exhibit control of composition, size and phase during nanoparticle nucleation were exploited for these materials-directing structures. The incorporation of specific, nucleating peptides into the generic scaffold of the M13 coat structure provides a viable template for the directed synthesis of semiconducting and magnetic materials. The engineered viruses were exposed to semiconductor precursor solutions, and the resultant nanocrystals that were templated along the viruses to form nanowires were extensively characterized using high resolution analytical electron microscopy and photoluminescence. Removal of the viral template via annealing promoted oriented aggregation-based crystal growth, forming individual single crystal nanowires. We report a virus based scaffold for the synthesis of crystalline ZnS and the first free standing L10 CoPt nanowires. The unique ability to interchange substrate specific peptides into the linear self-assembled filamentous construct of the M13 virus introduces a material tunability not seen in previous synthetic routes. Additionally, liquid crystal systems were used for the fabrication of a highly ordered composite material composed of genetically engineered M13 bacteriophage and inorganic nanocrystals.

A-I17 MECHANICAL PROPERTIES OF BULK METALLIC GLASS-BASED COMPOSITESW.J. Botta F., A.M. Jorge Júnior, C.Bolfarini, C.S. Kiminami, LabNano, DEMa, UFSCar, cp 676, 13565-905, São Carlos, SP, Brazil; A.R. Yavari, Institut National Polytechnique de Grenoble, LTPCM (CNRS umr 5614), BP 75, St-Martin-d’Hères Campus, 38402, France

Despite the large values of elastic strain range (2% as compared with 0.2% for conventional metals) and excellent values of fracture stress, applications of bulk metallic glasses (BMG) are limited by the lack of plasticity since they fail catastrophically by strain softening or a shearing off mechanism. However, more recently, it was discovered that the strain-softening mechanisms that lead to the shear instability and rapid plastic failure of BMGs can be overcome in BMG-based composites of appropriate microstructural length-scales, leading to the emergence of room-temperature ductility and plastic deformations of the order of 10% beyond their usual 2% elastic deformation range. In this paper, the controlled partial crystallisation by direct heating processing of bulk metallic glasses is reported. Fully amorphous Zr55Ti5Cu22Ni8A110 samples have been annealed by a direct electrical current heating system for the formation of nanocrystals, whose transformation is controlled by the analyses of the thermal variation of the bulk sample resistivity. Mechanical properties results are discussed as a function of the presence of crystalline phase and its interaction with the shear bands which penetrate or branch-off when reaching the micro-nano particles in the BMG matrix.

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ORAL PRESENTATIONS

A-O1 SHAPE STABILITY OF SELF-ASSEMBLED InAs/InP NANOSTRUCTURESH.R. Gutiérrez, M.A.Cotta, J.R.R. Bortoleto; IFGW, DFA/LPD, UNICAMP, CP 6165,13081-970 Campinas-SP, Brazil. R. Magalhaes-Paniago; Departamento de Física, Universidade Federal de Minas Gerais, C.P. 702, CEP 30123-970 Belo Horizonte, MG, Brazil

InAs nanostructures in an InP matrix have received much attention in the last years. Recently, we have reported the conditions that determine the InAs shape transition -from wires to dots – for films grown on (100) InP substrates by Chemical Beam Epitaxy. The grown of such self-assembled nanostructures requires a complete understanding and control of the formation mechanisms. In this sense we have obtained a complete picture of the InAs nanostructures formation. InAs growth evolution was monitored by Reflection High Energy Electron Diffraction (RHEED). The samples were analyzed by Atomic Force Microscopy (AFM) and High Resolution Transmission Electron Microscopy (HRTEM). The strain distribution was characterized by grazing incidence x-ray scattering, an accurate method sensitive to both local lattice parameter variations and nanostructure lateral size. These measurements were correlated with Atomic Force Microscopy and Transmission Electron Microscopy data. A remarkable anisotropy was observed for strain distributions parallel and perpendicular to the wires. Here we report the three-dimensional map of the strain distribution in these nanostrucutres, for crystalline directions parallel and perpendicular to the wires.

A-O2 EFFECT OF DISORDER ON OPTICAL BAND EDGE OF RANDOM DOPED GaAs/AlGaAs SUPERLATTICES Yu.A.Pusep, F.E.G.Guimarães, M.B.Ribeiro, H. Arakaki, C.A. de Souza, Instituto de Fisica de São Carlos, Universidade de São Paulo, 13560-970 São Carlos, SP, Brazil; S.Malzer, G.H.Döhler, Institut für Technische Physik I, Universität Erlangen, D-91058 Erlangen, Germany

The optical broadenings studied by the photoluminescence in the intentionally disordered GaAs/AlGaAs superlattices were compared with the broadenings of the individual electron states measured by the Shubnikov-de Haas oscillations. It was shown that the combined effect of the electron and hole energy blurrings is to decrease the optical broadening with respect to the individual state broadenings resulting in very sharp optical edges even in highly disordered superlattices. It was also found that the impurities almost equally influence the electron and hole scattering potentials, contrary to what happens due to the structural superlattice disorder. The anisotropy of the scattering potentials, additional to that one caused by the vertical intentional disorder, was found due to the segregation of impurities near interfaces.

A-O3 HIGH-PRESSURE EFFECTS ON P-PHENYLENEDIAMINE/SILICA AND P-ANISIDINE/SILICA HYBRID XEROGELS S. V. M. de Moraes, M. T. Laranjo, M. Zat, C. C. Moro, T. M. H. Costa, E. V. Benvenutti, Instituto de Química, UFRGS, CP 15003, 91501-970, Porto Alegre, RS, Brazil, M. R. Gallas, Instituto de Física, UFRGS, CP 15051, 91501-970, Porto Alegre, RS, Brazil

The hybrid xerogels p-phenylenediamine/silica and p-anisidine/silica were prepared with different surface area and porosity and they were processed at high-pressure, at 7.7 GPa in a quasi-hydrostatic medium, at room temperature. The morphology of the materials were studied before and after the high-pressure treatment by using N2 adsorption desorption isotherms, scanning electron microscopy and infrared thermal analysis. The porous hybrid p-phenylenediamine/silica presented after the high-pressure treatment, a surface area reduction and an entrapment of organics in closed pores. However the less porous hybrid p-anisidine/silica showed a surprising behavior, a pressure-induced increase in surface area with opening of pores. We propose a mechanism based on the inhibition of the cold sintering process by the organics to explain these results.

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A-O4 ORDERED MESOPOROUS SILICA: MICROWAVE PROCESSM. C. A. Fantini, IF-USP, CP 66318, 05315-970, São Paulo, Brazil; J. R. Matos, L. C. Cides da Silva, L. P. Mercuri, G. O. Chiereci, IQ-USP, CP 26077, 05599-970, São Paulo, Brazil; Mietek Jaroniec, Department of Chemistry, Kent State University, Kent, Ohio 44240, USA.

Triblock copolymers are used as templates for the synthesis of ordered mesoporous silica, due to the fact that they allow the growth of different morphological structures, besides their reasonable commercial cost and biodegradability. These silicas are synthesized at temperatures lower than 550 oC and are useful for applications running from microelectronics to medical diagnosis, opening up a wide variety of utilities beyond the traditional areas of materials for catalysis and absorbers. Depending on the polymers used as template and synthesis process, mesoporous cubic and hexagonal silicas are formed, with pores between 10 nm and 30 nm. The structural differences are suitable for each specific application. In this work we report on FDU-1 type ordered mesoporous silicas, synthesized with the triblock copolymer "B50-6600" [1]. The microwave heating was used, varying the process time, and it was compared with results obtained with hydrothermal treatment. This new procedure succeeded in producing ordered cubic face centered, diamond like, mesoporous structures even at 15 min. of heating. The best result was obtained for 1 h. treatment. The X-ray diffraction, gas adsorption and electron microscopy results were compared to characterize the material. 1. J. R. Matos; L. P. Mercuri; M. Kruk; M. Jaroniec; Langmuir 18 (2002) 884.Acknowledgements: FAPESP, CNPq, CAPES, Brazil.

A-O5 OPTICAL CHARACTERISTICS OF SOL-GEL SILICA GLASSES CONTAINING COPPER N.F. de Sales, V.C.Costa, W.L.Vasconcelos, Dep. de Eng. Metalúrgica e de Materiais, UFMG, 30160-030, Belo Horizonte, Brazil

We evaluated the influence of reagents concentration and temperature on structural properties of sol-gel silica glasses doped with copper nitrate. Optical absorption and transmission were followed using visible-near infrared spectroscopy (VIS/NIR) and Fourier transform infrared spectroscopy (FTIR). The density was obtained via helium picnometry and porosity was measured by nitrogen gas adsorption (BET). The gels analysed were dried at 80C and 120C had molar ratios of TEOS/Cu of 1/0.0084, 1/0.042 and 1/0.084. The molar ratios of TEOS/H2O/EtOH/HNO3 used for the three samples was 1/3.8/3.8/0.005. We observed a increase in the energy of Si-O(H) with the evolution of the drying process and a decrease in the energy with increasy of reagents concentration. The color of the glasses shifted from blue to green between 80C and 120C due to changing on the environment coordination of Cu2+ ions related to the hidroxyl groups.

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A-O6 OBTENTION OF SELECTIVE MEMBRANES FOR WATER AND HYDROPHOBIC LIQUIDS BY PLASMA ENHANCED CHEMICAL VAPOR DEPOSITIONP. Bankovic, MD student, Laboratory of polymers, Department of Metallurgy and Materials Engineering, USP, 2463, Prof. Mello Moraes Av., 05508-900 São Paulo, Brazil, N. R. Demarquette PhD, Associate Professor, Department of Metallurgy and Materials Engineering, USP, 2463, Prof. Mello Morães Av., 05508-900 São Paulo, Brazil, M. L. P. da Silva PhD, Laboratório de Sistemas Integráveis, Department of Electrical Engineering, USP 158, Prof. Luciano Gualberto Av., 05508-900 São Paulo, Brasil

In this work, the possibility of obtaining selective membranes for water and hydrophobic liquids by Plasma Enhanced Chemical Vapor Deposition (PECVD) of Hexamethyldisilasane (HMDS), or double layers of HMDS and n-hexane using a capacitive plasma reactor, on porous substrates was investigated. The porous substrates used were filter paper, diatomite and textiles of polyester, aramide and nylon. The films were characterized by Electron Spectroscopy of Chemical analysis (XPS) and Infrared Spectroscopy (FTIR) and measuring the contact angle formed by drops of water on their surface. The membranes obtained were characterized by mercury porosimetry and Cobb test. Their efficiency to separate hydro carbonates from water was evaluated through filtration experiments and Karl Fisher titration. The reagents used in the filtration experiments were: CHCl3, n-hexane, n-heptane or C6H6. The modified porous substrates were tested with solutions of water and ethanol. The porosity of the different substrates was shown to be unchanged by the deposition of the films. The contact angles formed by drops of water on the film surface and water adsorption measured by Cobb Test for all the substrates were above 12 g.m-2 and reduced to around 15 g.m-2

respectively, showing the hydrophobic character of the modified surfaces. The Karl Fisher titration indicated that between 90 and 500 ppm (depending on the reagent used) of water remained in the hydro carbonate after filtration. Addition of ethanol to water that was retained on the top of the membrane resulted in a change of hydrophobic character of the membrane and resulted in a hydrophilic substrate. The results are explained in light of XPS and FTIR analysis.

A -O7 AB INITIO INTERPRETATION OF PHOTOLUNINESCENCE IN PEROVSKITE STRONTIUM AND BARIUM TITANATEE. Orhan, J. A. Varela, Instituto de Química, Universidade Estadual Paulista, 14801-907, Araraquara-SP, Brazil

C. D. Pinheiro, M. F. C. Gurgel, M. A. dos Santos, F. M. Pontes, Elson Longo, Laboratório Interdisciplinar de Eletroquímica e Cerâmica (LIEC), Departamento de Quimica, Rod. Washington Luis, km 235, Universidade Federal de São Carlos, 13565-905 São Carlos – SP P. S. Pizani, T. M. Boschi, C. E. M. Campos, Departamento de Física, Universidade Federal de São Carlos, Caixa Postal 676, 13565-905, São Carlos – SPFirst principles quantum mechanical techniques, based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and deformed periodic models for Ba0.5Sr0.5TiO3. Electronic properties are analyzed in the light of the measured photoluminescence properties. The presence of localized electronic levels in the band gap, due to the symmetry break, together with the coexistence of a charge gradient between TiO6 and TiO5 clusters in the deformed model would be responsible for the visible photoluminescence of the amorphous compound at room temperature. (FAPESP-CEPID, CNPq, CAPES)

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A -O8 QUANTUM DYNAMICS SIMULATIONS OF INTERFACIAL ELECTRON TRANSFER IN SENSITIZED SEMICONDUCTORS.L.G.C. Rego, Depto. de Física, UFPR, Curitiba, CP 19044, 81531-990; V.S. Batista, Dept. of Chemistry, Yale University, 06520-8107, USA.

Ab initio-DFT molecular dynamics simulations are combined with semi-empirical quantum dynamics calculations of electronic relaxation to study interfacial electron transfer processes in sensitized semiconductor nanostructures. Realistic models are used to investigate the dynamics of electron-injection from the adsorbed catechol molecule to the conduction bands of TiO2 (anatase). This is a fundamental process in surface physical-chemistry, relevant to a broad range of technological applications. It is found that the primary process in the interfacial electron transfer involves an ultrafast (1 6 fs) electron-injection event that localizes the charge in the Ti4+ surface ions next to the catechol adsorbate. The primary event is followed by charge delocalization (i.e., carrier diffusion) through the TiO2 crystal, an anisotropic diffusional process that can be up to an order of magnitude slower along the [-101] direction than carrier relaxation along the [010] and [101] directions in the anatase crystal. It is shown that both the mechanism of electron injection and the time scales for interfacial electron transfer are quite sensitive to the symmetry of the electronic state initially populated in the adsorbate molecule. The thermal effects due to the lattice (nuclear) dynamics are considered in the simulations. Possible applications of this mechanism to molecular electronics are considered. (J. Am. Chem. Soc. 125, 7989 (2003)).

A -O9 INTRABAND TRANSITIONS IN Si/SiO2 QUANTUM DOTSJ. S. de Sousa, V. N. Freire, Universidade Federal do Ceará, Depto. de Física, CX Postal 6030, 60455-970 Fortaleza-CE, Brazil; E. F. da Silva Jr., Universidade Federal de Pernambuco, Depto. De Física, Cidade Universitária, 50670-901 Recife-PE, Brazil

Semiconductor quantum dots (QD’s) have been considered one of the nanotechnology building blocks because their electronic structure can be tailored by controlling their shape, size and charge state. As intraband transitions usually occur in the infrared (IR) spectral range, night vision systems and IR radiation detectors figure among the main applications of this technology, which are important to a variety of fields like military and surveillance. Even though the interest in intraband transitions in quantum dots have recently increased [1], the number of papers in this matter is still small. Moreover, they are limited to few systems like III-V compounds and almost inexistent for the Si/SiO2 systems. Here, we address the investigation of the intraband transitions in Si/SiO2 QD’s, by using a 3D quantum mechanical model, which has the ability to capture the coupling of the Si band structure anisotropy and QD geometry, and different alignment of the Si crystallographic orientation [2]. We observed that Si/SiO2 QD’s have efficient transitions and that QD size, shape and crystallographic orientations strongly affect the oscillator strength of the optical transitions. Moreover, smaller QD’s exhibit a larger energy range of efficient transitions in comparison to larger ones.[1] G. Allan and C. Delerue, Phys. Rev. B 66, 233303 (2002); [2] J. S. de Sousa et al., Appl. Phys. Lett. 82, 2685 (2003)

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A-O10 Fe SPIN STRUCTURE IN Fe/MnF2 EXCHANGE-BIASED BILAYERSW. A. A. Macedo, Lab. de Física Aplicada, Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, Brazil; B. Sahoo, V. Kuncser, W. Keune, Institut für Physik, Universität Duisburg-Essen, Duisburg, Germany; J. Eisenmenger, Ivan K. Schuller, Physics Department, University of California - San Diego, La Jolla, Ca, USA; I. Felner, Racah Institute of Physics, The Hebrew University, Jerusalem, Israel; J. Nogués, Institutió Catalana de Recerca i Estudis Avançats (ICREA) and Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, Spain; K. Liu, Department of Physics, University of California – Davis, Ca, USA.

The spin structure of the ferromagnetic (F) Fe layer at different depths in Fe films exchange-coupled to twinned (110) MnF2 antiferromagnetic (AF) layers has been probed by 57Fe probe layer Mössbauer spectroscopy. Conversion electron Mössbauer spectroscopy (CEMS), above (80 K), and below (18 K) the Nèel temperature of the AF layer (TN = 67 K for MnF2), was carried out in remanence, after applying an in-plane magnetic field of 0.4 T at room temperature, which results in an exchange bias of –54 Oe at 10 K and zero-field cooling. We find that exchange bias induces a significant in-plane rotation of the average orientation of the Fe magnetic moments at the interface and inside the Fe film, consistent either with the onset of an in-plane rotation of the average Fe spin orientation or with an increase of in-plane Fe spin fanning, away from the remanent magnetization direction. Out-of-plane spin canting in the Fe layer is ruled out.

A -O12 PARTICLE SIZE AND DISORDER IN GMR CO-CU SYSTEMS STUDIED BY EXAFSJ.C.Cezar, H.C.N.Tolentino, LNLS, CP 6192, 13084-971 Campinas, SP, Brazil; M.Knobel, LMBT, IFGW, UNICAMP, Campinas, SP, Brazil

Granular magnetic systems are made of small particles of a magnetic material embedded in a non magnetic one. Produced beyond the solubility limit, their properties are controlled by suitable annealing. We have studied the structural, magnetic and transport properties of Co nanoparticles embedded in a Cu matrix using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, magnetization and transport measurements of samples containing 3, 10, 12 and 25 at % Co, annealed under different conditions. We have observed by EXAFS a systematic contraction of the average distance around Co atoms, with the increasing Co content and annealing, related to the growing of small nanoparticles. Based on a simple structural model, we have deduced particle sizes ranging from 1 nm to more than 8 nm. We have found that the particle diameter for the maximum giant magnetoresistance (GMR) is about 4.4 nm. This corresponds to nearly 30 % of the Co atoms at the interface with the Cu matrix, which optimizes GMR because the particles are sufficiently large to change orientation under an applied magnetic field and have a large amount of surface to scatter the conducting electrons responsible for the transport properties. Moreover, we have observed that the disorder is significantly reduced around that size, due to the hardening of Co bonds, further favoring the GMR.Cezar et al., Phys. Rev. B 68, 054404 (2003)

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A -O13 LOCAL DISTORTION AND CHARGE LOCALIZATION IN MIXED MANGANITE THIN FILMS N. M. Souza-Neto, A. Y. Ramos, H. C. N. Tolentino, LNLS, C.P. 6192, 13084-971, Campinas SP, Brazil ; L. Ranno, E. Favre-Nicolin, Laboratoire Louis Néel, Grenoble, France.

Mixed manganite films have received special attention due to their potential application for a new generation of magneto-electronic devices. In these systems the external biaxial strain resulting of epitaxial growth could be used, as cation doping, to tune the magnetism and transport properties. In this context it is important to explicit the consequence of strain-induced distortion on the local structure. We report on an angular resolved X-ray Absorption Spectroscopy study of the local atomic structure around the manganese atoms in La07Sr03MnO3 thin films (25-60nm) grown on tensile and compressive substrates. We derive a model of local biaxial anisotropic distortion of the coordination octahedrum around the manganese atoms, without modification of the tilt angle Mn-O-Mn among the octahedra. This distortion, tending to localize the charge carriers, is the driving parameter in the modifications of the magnetic and transport properties observed in thin films with respect to bulk systems. An additional distortion in the plane of the film suggest that cooperative distortion is still more energetically favorable than isotropic planar expansion of the Mn-O distance.

A -O14 QUANTUM TRANSPORT PROPERTIES OF MAGNETIC NANOWIRESV. Rodrigues, J. Bettini, P.C. Silva, D. Ugarte, Lab. Nac. de Luz Síncrotron, C.P. 6192, 13084-971 Campinas SP, Brazil.

The development of spintronics has rendered the influence of low dimensionality and/or reduced size on the magnetic properties of materials a fundamental issue. There is a large amount of work on metal nanowires, however it is surprising that magnetic nanowires have not yet been studied in detail. In this work, we have analyzed the electronic transport properties of atomic-size metallic wires made of magnetic and non-magnetic metals using an ultra-high-vacuum mechanically controllable break junction system. In addition, the atomic structure of NWs has been studied using independent experiments based on time-resolved high-resolution transmission electron microscopy. We have observed that just before rupture, the ultimate Co wires adopt a suspended chain of atoms configuration, which shows a conductance of half the conductance quantum. Then, our results suggest that a fully spin polarized current is spontaneously generated even at room temperature and zero magnetic field. Similar behavior has been observed for Pd (a quasi-magnetic 4d metal) and Pt (a non-magnetic 5d metal) atom chains. These results open new opportunities to get a deeper understanding of spin effects in nanostructures.

A -O15 FORMATION OF EXTENDED DEFECTS AFTER He+ IMPLANTATION AT ELEVATED TEMPERATURESD.L. da Silva, M.J. Mörsbacher, E. Oliviero, M. Behar, Instituto de Física-UFRGS, Caixa Postal 15051, 91501-970 Porto Alegre, Brasil; P.F.P. Fichtner, Departamento de Metalurgia-UFRGS, Caixa Postal 15051, 91501-970 Porto Alegre, Brasil

In the present contribution we study on the formation of {311} defects in Si(100) which occurs concomitantly with the formation of nano-bubbles during He implantations at 150 and 300°C (implantation energies of 15 and 40 keV and fluences between 1 and 2x1016 He cm-2). The as implanted samples were analyzed using Rutherford Backscattering/ Channeling, Elastic Recoil Detection Analysis and Transmission Electron Microscopy. After the implantation, independently of the energy, spherical-like nano-bubbles (1 to 3 nm in diameter) and {311} type defects are formed. The sizes of the bubbles and the defects increase with the implantation temperature. In addition, the defect morphology depends on the implanted fluence. Single {311} defects are observed for the lower fluences while ribbon-like defects resulting from the agglomeration of the single {311}’s start to appear for the high fluence cases. We propose a mechanism correlating the formation of the defects and the He bubbles and discuss the effects of the implantation temperature on the point defect fluxes. The present results also demonstrate that {311}-type defects can be formed and dissolved at temperatures about 300°C lower that what is know in the literature.

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A -O16 TOWARDS STRAINED SILICON: STRAIN RELAXED Si1-xGex BUFFER LAYERS PRODUCED BY He+ ION IMPLANTATIONB. Holländer, S. Mantl, St. Lenk, D.M. Buca, N. Hüging M. Luysberg, ISG/IFF Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany, Th. Hackbarth, H.-J. Herzog, DaimlerChrysler Forschungszentrum Ulm, D-89013 Ulm, Germany, R. Loo, M. Caymax IMEC, B-3001 Leuven, Belgium, M. Mörschbächer, P.F.P. Fichtner, UFRGS, BR-91501-970 Porto Alegre, BrazilStrain relaxed Si1-xGex layers serve as virtual substrates for the growth of strained Si, a material with superior electronic properties. Strained Si will be used for the fabrication of advanced microelectronic devices in the near future. We report on the strain relaxation of pseudomorphic Si1-

xGex layers (x=0.10 ... 0.30) grown by MBE and CVD on Si(100) and SOI after subsequent He+

implantation and annealing. Implantation with energies between 10 keV and 50 keV and doses between 7x1015 cm-2 and 2x1016 cm-2 promotes the generation of strain relieving misfit dislocations during subsequent annealing. The samples were investigated by Rutherford backscattering and ion channeling, X-ray diffraction and transmission electron microscopy and Raman spectrometry. The amount of strain relaxation and threading dislocation density will be discussed as a function of implantation and annealing conditions. n-MODFETs grown on these relaxed layers showed excellent results comparable to structures grown thick, graded Si1-xGex buffer layers. The alternative use of other light ions for the promotion of strain relaxation will be addressed.

A -O17 EFFECTS OF NITROGEN INCORPORATION INTO Al2O3 FILMS ON Si FOR ADVANCED MOS DEVICES R.P. Pezzi, K.P. Bastos, L. Miotti, G.V. Soares, C. Driemeier, E.B.O. da Rosa and J. Morais Instituto de Física - UFRGS, CP 15051 Porto Alegre 91501-970 – Brazil; I.J.R. Baumvol, Centro de Ciências Exatas e Tecnológicas - UCS Av. Francisco G. Vargas 1130, 95070-560 Caxias do Sul – Brazil.

There is a frenetic search for an alternative material with higher dielectric constant than that of SiO2, which can be able to replace it as the gate dielectric in MOSFET devices. Thermal stability during post- deposition annealings at high temperatures is one of the mandatory requirements this new material, called high-k, must satisfy. Some previous works have shown that the addition of nitrogen into the high-k material can have beneficial effects. In this work we report on the investigation of thermal stability (atomic mobility and chemical reaction) of Al2O3 films deposited on Si substrates by remote plasma-enhanced chemical vapor deposition, followed by remote plasma-assisted nitridation in 15N2. This structure was submitted to thermal annealings in either inert or oxidizing atmospheres. Areal densities and concentration profiles of the species of interest were addressed using ion beam techniques, namely resonant and non-resonant nuclear reaction analysis, while the chemical environment was investigated by X-ray photoelectron spectroscopy.

A-O18 PHOTONIC CRYSTALS FORMATION BY SELF-ASSEMBLE TECHNIQUED. S. Raimundo and W. J. Salcedo, Laboratório de Microeletrônica da Escola Politécnica da USP, Av. Prof. Luciano Gualberto Travessa 3, n.158, Caixa Postal 61548, São Paulo, Brazil.

The present work reports the 2-D and 3-D photonic crystals formation by self-assemble process of the polymeric micro-spheres (polystyrene). These photonic crystals were fabricated from dispersible solution of polystyrene micro-spheres. The glass substrates were immersed into the solution in vertical configuration after that, the cell was heated at temperature of 50 oC in order to have a controllable evaporation process of the solvent. At these conditions, the hydrodynamic forces drove the formation of self-assemble structure. The Scanning Electron Microscopy imagines of samples showed the hexagonal compact periodic array with lattice constant of ca. 0.666 m in agreement with the minimum of Gibbs energy as reported in the literature. The 2-D photonic crystals were obtained preferentially when glass surface was in hydrophilic condition. However, hydrophobic surface condition drove to 3-D photonic crystal formation preferentially. The optical transmittance spectra of the samples showed the existence of band gaps in 1376 nm to 1517 nm (near infrared region).

A -O20 STRESS CONTROL IN DIAOMONDLIKE CARBON FILMS BY ENERGETIC IONS.Othon R. Monteiro(1) and Marie-Paule Delplancke-Ogletree(2); (1)Lawrence Berkeley national

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Laboratory, University of California, Berkeley, Berkeley, CA 94720; (2) Universite Libre de Bruxelles , Brussels, Belgium

High level of intrinsic stresses has prevented, to a large extent, the use of such films to applications where thick coatings are required. The magnitude of intrinsic stresses in diamondlike carbon (DLC) films is directly related to the sp3 content in the films, which bears a strong dependence on the energetics of the deposition process. We have used in-situ monitoring of the stress to determine its evolution during deposition of DLC films, and to guide us in altering process conditions so that thick DLC films are produced with virtually no intrinsic stresses, while maintaining a high fraction of sp3 bonding. Stress measurements was carried out by using the laser deflection technique. The process parameter used for relaxation was the energy of the depositing ions. Deflection of the laser beam induced by changes in the radius of curvature of the substrate was measured with a position sensitive detector (PSD). The mechanisms of stress-relaxation in DLC are discussed in view of the results obtained.

A-O21 NANOMANIPULATOR FOR IN-SITU STUDIES IN A FEG-SEMD. Nakabayashi, P. C. Silva, V. Rodrigues, D. Ugarte, LNLS – Laboratório Nacional de Luz Síncrotron, C.P. 6192, 13084-971, Campinas, SP, Brazil; H. Gutiérrez, M.A. Cotta, UNICAMP - IFGW - DFA/LPD, C.P. 6165, 13081-970, Campinas, SP, Brazil.

Nanosystems are attracting a huge interest; nevertheless the controlled characterization and manipulation are still a challenge. High-resolution capabilities of electron microscopy techniques render them a preferred tool for studying nano-objects, however electron microscopy methods are usually static. Here, we describe the development of manipulation system operating inside a FEG-SEM; the nanomanipulator has three independent axes, each one with coarse and fine movements. The coarse movements are driven by picomotors and piezo elements slabs are responsible by precise displacements. We have already used the manipulator to measure the mechanical properties of individual nanosystems showing a high aspect ratio by measuring resonance vibration modes excited by AC voltages. We have also produced Atomic Force Microscopy (AFM) tips based on carbon nanotubes in a controlled way. These tips have shown a high performance, allowing a significant improvement of the AFM image quality.

A-O22 SYNTHESIS OF CARBON NANOTUBES BY CVDS. A. Moshkalyov, J. W. Swart, UNICAMP, CCS, C.P. 6061, Campinas, SP, Brazil

Results of carbon nanotubes (CNTs) synthesis, employing methane and acetylene based gas mixtures, are presented. Two different catalytic high-temperature (up to 900 C) CVD techniques were used: microwave plasma-enhanced low-pressure CVD and atmospheric-pressure thermal CVD. Multi-walled CNTs with tube diameters from ~ 10 to 100 nm were obtained and analyzed using high-resolution SEM. Thin Ni films (1-40 nm) were used as a catalyst material. After deposition, the films were thermally treated (~700 C) in a N2 or H2 atmosphere to provide formation of separate catalyst nanoparticles. The CNTs growth process depends critically on the catalyst thickness. For thicker films, large diameter (up to 100 nm) tubes, apparently with high content of amorphous carbon were grown. For thin films, it was possible to grow long (up to 30 m) and small diameter (~10 nm) CNTs. The study of CNTs CVD using another catalysts is in progress.

A-O23 PHOTOCURRENT AND PHOTOLUMINESCENCE STUDIES OF RESONANT TUNNELING DIODES

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L.F. dos Santos, A. Vercik, Y. Galvão Gobato, Universidade Federal de São Carlos , CP 676, São Carlos - SP, 13560-970 ; M. J. S. P. Brasil, Universidade de Campinas, CP 6165, Campinas-SP, 13083-970, Brazil.

In this work, we have investigated the transport and optical properties of a GaAs/GaAlAs double-barrier diode. Current-voltage (I-V) characteristics and photoluminescence (PL) spectra were measured as a function of applied voltage, laser intensity and temperature on symmetric GaAs/Al0.35Ga0.65As double barrier resonant tunneling diodes. We have observed an unexpected enhancement of the photoluminescence intensity with increasing temperature, which depends on applied voltage and laser intensity. This enhancement is followed by a decrease of PL intensity at higher temperatures, associated to more effective nonradiative mechanisms and a consequent decrease of radiative recombination, reducing the quantum efficiency. The integrated PL spectra versus temperature curves present a peak, whose position depends on the applied voltage in the structure. We have observed a similar temperature-dependent behavior of the photocurrent, measured in the same voltage and temperature range. This effect is associated to the transport of holes in the collector contact which controls the minority carrier supply for tunneling into the well

A-O24 HARDNESS AND ELASTIC MODULUS MEASUREMENTS BY NANOINDENTATION OF ALUMINUM IMPLANTED WITH CARBONC.E. Foerster, F.C. Serbena, A. Assmann, Defis, UEPG, 84030-900, Ponta Grossa, PR, Brazil, C.M. Lepienski, Defis, UFPR, CP 19044, 81531-990 ,Curitiba, PR, Brazil, T. Fitz, E. Richter, W. Moeller, Institute of Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf, GermanyIn this work the mechanical properties of pure Al samples implanted with C+ ions at 25 keV and fluences ranging from 1 x 1017 to 20 x 1017 C+.cm-2 at room temperature were measured. The near surface region after low C+ fluence revealed a structure of Al4C3 as embedded precipitates in addition to C-C clusters that changed to an amorphous Al4C3 structure together the C-C clusters at higher C+ fluences. To measured the surface mechanical properties, load/unload curves were performed using a nanoindenter and from the Oliver and Pharr method, the hardness and elastic modulus profiles were determined. The results showed a hardening process due to the presence of Al4C3 and C-C clusters. The hardness increased from 0.3 GPa for the bulk Al up to 9 GPa at the highest C+ fluence. At same time, the elastic modulus increased from approximately 70 GPa (bulk Al) to 100 GPa. Subsequent annealing at 500°C produced a little decrease in these values, meaning that hardness and elastic modulus are determined by the presence of Al4C3 and C-C clusters. The surface morphology and structure were previously analyzed by elastic recoil detection analysis (ERDA), Raman spectroscopy, grazing incidence X-Ray diffraction analysis (GIXRD) and high resolution electron microscopy (HRTEM).Financial support: CAPES

A-O25 SPECTROSCOPIC CHARACTERISTICS OF DOPED ALUMINUM OXIDE NANOPOROUSW. M. de Azevedo, D. D. de Carvalho, Departamento de Química Fundamental, UFPE-PE 50670-901, Recife, Brasil; H.J. Khoury Departamento de Energia Nuclear UFPE-PE 50740-540, Recife,

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Brasil;E.F. da Silva Júnior, Departamento de Física UFPE-PE 50670-901, Recife, Brasil

In nanotechnology research, fabricating functional nanoscale structures and devices in a well-controlled way represents one of the most difficult challenges facing today’s researchers and engineers. The means to organize nanoelements into device structures to realize their desired functionalities using inexpensive fabrication techniques is essential from a technological point of view. Aluminum anodization is one of the most controllable self-assembly processes, and nanoporous anodic aluminium oxide has been employed to synthesize a variety of nanoparticles and nanowires through a template-mediated approach. From the point of view of luminescent properties, it is interesting to note that colloidal Al2O3 does not exhibit any photoluminescence whereas polymeric aluminum oxide exhibit photoluminescence at 420 nm. In this work we present the luminescence characterization of porous aluminum oxide synthesized by anodization process in several solvents. We found that the luminescence of porous aluminum doped with rare earth ions strongly depends on the synthesis medium, in inorganic acid only rare earth luminescence is found, whereas aluminum oxide synthesized in organic solvent presents two strong unexpected luminescence emission, one at 4200 A and the second at 4900 A when excited in the UV region, with quit long decay time, it is worthwhile to mention that porous aluminum oxide synthesized in inorganic acid presents no fluorescence at all

POSTER PRESENTATIONS

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A-P01 THE ROLE OF COMPOSITIONAL MODULATION IN INGAP LAYER SURFACE PROPERTIESJ.R.R.Bortoleto, H.R.Gutiérrez, M.A.Cotta, and M.M.G.de Carvalho; Instituto de Física Gleb Wataghin, DFA/LPD, UNICAMP, CP 6165,13081-970 Campinas-SP, Brazil. J.Bettini; Laboratório Nacional de Luz Síncrotron, C.P. 6192, 13084-971 Campinas-SP, Brazil

In this work, we investigate InGaP layer properties leading to preferential nucleation sites to Stranski-Krastanov dot overgrowth. Our experimental results indicate that a periodic strain field can be formed within the InGaP layer via surface processes. We have investigated the presence of CuPt ordered regions and compositional modulation phenomena in our samples, since these bulk properties are both surface-activated. TEM plan-view images from InGaP layers shows bright domains organized into a bidimensional pattern. Such patterns have been extensively credited to compositional modulation on InGaP films. On the other hand, cross-sectional TEM micrographs with g=(½,½,½) shows random, weak CuPt domains for our samples. This fact rules out any correlation between CuPt phenomena and the periodic strain field. But, cross section TEM images with g=(2,-2,0) show a clear correlation between InP dots positioning with the contrast modulation in the InGaP buffer layer. Thus the compositional modulation indeed gives rise to preferential sites to dot nucleation, allowing the in situ formation of InP dot arrays. We have extended this concept to create a bidimensional array of InAs/GaAs quantum dots using the InP array as a template for lateral ordering .

A-P03 PRESSURE-INDUCED CHANGES ON THE OPTICAL PROPERTIES AND MICROSTRUCTURE OF SILICA-GEL MATRICES DOPED WITH RHODAMINE 6G T. M. H. Costa, H. S. Hoffmann, E. V. Benvenutti, V. Stefani, Instituto de Química, UFRGS, CP 15003, 91501-970, Porto Alegre, RS, Brazil, M. R. Gallas, Instituto de Física, UFRGS, CP 15051, 91501-970, Porto Alegre, RS, Brazil

Sol-gel method and the high-pressure technique were associated to produce rhodamine 6G doped silica compacts with a very low porosity. It was studied the state of R6G dye molecules in the silica sol-gel monolith/powder and in the compacted powders obtained at 7.7 GPa and room temperature. The excitation-emission fluorescence spectra were measured, in order to investigate pressure-induced changes in the optical properties of R6G embedded in closed pores of the silica matrix. Measurements of surface areas and pore size distribution, using the N2 isotherms were performed, showing a great reduction in surface area and porosity. The dye entrapped in the compacted silica maintain its optical properties similar to that in ethanolic solutions, which means that the dye is dispersed in a molecular level. Additionally, these samples are optically transparent, hard and resistant to dye leaching and to chemical attacks, being a promising material to be used in optical devices.

A-P04 NANOSTRUCTURAL EVOLUTION OF STRUCTURAL BRICKSJ. Calabria, W. L Vasconcelos; Laboratório de Materiais Cerâmicos – UFMG, Rua Espírito Santo, 35, sala 206, 30160-030,Belo Horizonte, Brazil

In this work we studied the nanostructure of clay and two types of bricks. One brick was made using the same clay analysed and the material was fired at around 900C. The second brick was kept in a non-fired condition, becoming similar to an adobe. We evaluated the nanostructure of the particles using X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy and chemical adsorption. We described the evolution of the nanostructure, associating it to different conditions of processing.

A-P05 PROCESSING AND CHARACTERIZATION OF α-SILICON CARBIDE NANOPOWDERSM. A. P. Santos, Grupo de Materiais, IPqM, Ilha do Governador, Rio de Janeiro, Brazil; C. A. Costa, Centro de Tecnologia, Bl. F/210, Cidade Universitária, CEP 21945-970, Rio de Janeiro,

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Brazil

The use of nanopowders in sintering process has been increasing very fast and the resulting products possess very good mechanical properties. Brazil process -silicon carbide (SiC) powders with mean particle size around 5 m, which is very large for sintering application.In this study, the national -SiC was comminuted by high energy milling process and the mean particle size was reduced to nanometer size. The analysis of the powders milled for ½, 2, 4 and 6 hours were conducted by sedigraphy, BET, laser and X-ray diffraction methodologies. The results showed that precise measurement was not achieved, but the size range was in between 0,1 and 0,5 m. The difficulty in measuring fine particles is that they tend to cluster very fast and strongly.

A-P06 VIBRATIONAL PROPERTIES OF OXIDATED SINGLE-WALL CARBON NANOTUBE BUNDLESE.B. Barros, and V. Lemos, Departamento de Física, UFC, C.P. 6030, Fortaleza, CE, M. Herbst, , Instituto de Física, FRJ, Rio de Janeiro, RJ, C.A. Luengo, Instituto de Física “Gleb Wataghin”, UNICAMP, Campinas, SP, J.G Huber, 501 N. Boulevard, #7 Richmond, VA 23220, USA

Single-wall carbon nanotubes, SWNTs, prepared by arc discharge using Zr(Fe0.5Ni0.5)2 as catalyst, were oxidated and filtered. Both samples, before and after the treatment, were analyzed by using Raman scattering and Scanning Electron Microscopy. The raw material was found to consist of bundles of SWNTs in an heterogeneous, nearly uniform distribution of nanoparticle clusters. In the treated material the SWNTs seemed less abundant but the bundles appear in small regions quite defect free. Raman spectra reveal that nanotubes are present in the raw as well as in the treated sample. The spectra, however, differ in several aspects. The radial breathing mode, RBM, structure for the treated material is upshifted by a few wavenumbers. Two additional higher frequency peaks appear in the spectrum for the raw material. As no nanotube Raman feature is expected in the position of those features they are supposed to be due to vibrations involving metal particles. As they do not appear in the treated sample spectrum it is possible to infer that the metal particles are quite removed from the bundles. After treatment the tangential modes, besides upshifted, appear with two shoulders at lower and higher wavenumber sides of the band. The overall Raman modifications are typical of intercalation of HNO3 molecules into the bundles.

A-P07 HELIUM REDISTRIBUTION IN AS-IMPLANTED SILICON AND Si0.8Ge0.2/Si HETEROSTRUCTUESM.J. Mörschbächer, D.L. da Silva, E. Oliviero, M. Behar, F.C. Zawislak, Instituto de Fisica-UFRGS, C.P. 15051, 91501-970 Porto Alegre, RS, Brasil; P.F.P. Fichtner, Departamento de Metalurgia-UFRGS, Porto Alegre, RS, Brasil; M. Luysberg, Institut für Festkörperforschung, Forschungszentrum Jülich, Jülich, Germany; B. Holländer, S. Mantl, Institut für Schichten und Grenflächen, Forschugszentrum Jülich, Jülich, Germany; R. Loo, M. Caymax, IMEC, Leuven, Belgium.

In the present contribution we report experimental results on the retention of implanted He atoms in Cz (100) Si wafers and in 80 nm thick Si0.8Ge0.2 pseudomorphic heterostructures, grown by CVD on a Si(100) wafer, as a function of the implantation energy. The implantations were performed at room temperature using energies from 5 to 60 keV and fluences within 1 to 4x1016 cm-2. The implanted samples were analyzed by Elastic Recoil Detection (ERD), Rutherford Backscattering/Channeling Spectrometry (RBS/C) and Transmission Electron Microscopy (TEM). The fraction of the implanted He fluence that is retained increases from 5% at 5 keV to 100% for E 40 keV. The retained He fraction is independent of the implanted fluence, of the accumulated lattice damage or of the presence of TEM observable bubbles. The present results are applied to optimize the He assisted strain relaxation process of pseudomorphic ultra thin SiGe/Si (100) buffer layers with low threading dislocation densities.

A-P08 NANOCAVITIES FORMATION IN ION IMPLANTED SILICONE. Oliviero, S. Peripolli, L. Amaral, Instituto de Física, Universidade Federal do Rio Grande do Sul, P.O. Box 15051, 91501-970 Porto Alegre, RS, Brazil; P. F. Fichtner, Departamento de Metalurgia,

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Universidade Federal do Rio Grande do Sul, P.O. Box 15051, 91501-970 Porto Alegre, RS, Brazil.

The formation of nanocavities in Si is considered as a microstructure engineering tool to form very efficient gettering sites for metallic impurities thus improving device performance. This is usually achieved by room temperature He implantation at sufficiently high fluences followed by thermal annealings, thus allowing the formation of a nano-bubble system which interact and modify the point defect fluxes in the matrix and therefore affect the obtained extended defects. In the present contribution we have expanded our previous studies to the case of Ne implanted into (100) Cz silicon wafers. The Ne ions were implanted at 50 keV with fluences ranging from 1x1015 cm-2 to 5x1016 cm-2. The implantations were carried out at a temperature of 250°C to avoid target amorphization. As implanted and annealed samples were investigated by Rutherford Backscattering Spectrometry under channeling conditions (RBS/C) and by Transmission Electron Microscopy (TEM) to quantify and characterize the lattice damage. In the as implanted samples we observe the formation of a continuous buried layer containing a high density of Ne nano-bubbles (1 to 5 nm in diameter) as well as small clusters of interstitials. Upon annealing at temperatures higher than 400 C, the bubbles coarsen and extended defects of {311} type are formed. The results are discussed in comparison to the case of He, accounting for the distinct diffusivity, solubility as well as and implantation damage of Ne in Si. On the basis of the present results we propose a method to significantly reduce the thermal budget required for the formation of local impurity gettering layers in Si matrix.

A-P09 METAL LAYER MASK PATTERNIG BY FORCE MICROSCOPY LITHOGRAPHYH.D. Fonseca Filho, C.R. Ponciano, R. Prioli, Depto. de Física, PUC-Rio, Caixa Postal 38071, Cep 22452-970, Rio de Janeiro, Brazil; M.H.P.Maurício, Depto. de Ciência dos Materiais, PUC-Rio, Caixa Postal 38008, Cep 22453-970, Rio de Janeiro, Brazil

In this work a nanolithography process is developed with the use of an atomic force microscope equipped with a diamond tip while operated in contact mode. The presented process starts with a deposition of an a-As2S3 thin film by PVD on a Si substrate. A metallic layer is then deposited on the top of the a-As2S3 surface. The AFM is used to draw a pattern, in a controlled way, on the surface of the metallic layer with the use of a nanoscript program, leaving the As2S3 surface exposed. The photosensitive surface of the a-As2S3 film is illuminated and chemically etched. This leaves now the Si surface exposed with the pattern draw by the tip. A final layer is then deposited, filling the lithographed pattern. A last chemical etching is performed in order to remove all the remaining a-As2S3 from the substrate, leaving only the desired pattern on the substrate surface. An analysis of the As2S3 surface roughness as a function of film thickness is presented and it is shown that films with thickness of 40nm are suitable to the lithography. The influence of the tip-surface normal force on the lithography process is also presented. It is shown that the depth of the lithographed pattern increses with the rise of the applied normal force. Furthermore, the scanning velocity have influence on the AFM patterning process. As the scanning velocity increases the pattern depth decreases. The possible use of the presented process to create nanostructures are discussed.

A-P10 NANOINDENTATION STUDIES OF NATURAL RUBBERMariselma Ferreira, Ciência e Engenharia de Materiais-USP, Caixa Postal 369, São Carlos, SP, Brazil; Luiz Henrique Capparelli Mattoso, Embrapa Instrumentação Agropecuária, Caixa Postal

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741, São Carlos, SP, Brazil; Christine Ortiz, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA

In recent years, the importance of natural rubber has increased due to the need for environmentally friendly materials and improved properties relative to synthetic materials. In this context, Embrapa Agricultural Instrumentation, in collaboration with Agronomic Institute of Campinas, has initiated a research program to study the mechanical, chemical, and physical properties and to assess the quality of the natural rubber in São Paulo State, which is the largest rubber producer in Brazil. As one component of this program, the technique of nanoindentation has been employed to characterize the compressive normal load versus displacement properties of natural rubber in nm thick films yielding information on nanomechanical properties such as viscoelasticity and energy of dissipation. The nanoindentation force curves show forces near to 50 nm and displacements up to 500 nm and reveal a huge amount of mechanical hysteresis indicating viscoelastic deformation. This novel technique has great potential to yield insights into the molecular origins of macroscopic mechanical properties and material performance. FUNDING: FAPESP, CAPES, CNPQ

A-P11 INVESTIGATION OF DOMAIN STRUCTURE AND GRAINS IN Pb(Zr 1-x Tix)O3

FERROELECTRIC THIN FILMS BY PIEZORESPONSE MICROSCOPYV.B.Nunes1, S.I.Zanette1, A.O.Caride1, E.B. Araújo2, J.A.Eiras3 M.P.Albuquerque1, M.P.Albuquerque1 and A.G.Mello1; 1Centro Brasileiro de Pesquisas Físicas, Rua Dr.Xavier Sigaud, 150-Urca, 22290-180, Rio de Janeiro, RJ – Brazil; 2Universidade Estadual Paulista, Dpto.de Física e Química, Caixa Postal 31, Ilha Solteira, São Paulo – Brazil; 3Universidade Federal de São Carlos, Dpto de Física, Grupo de Cerâmicas Ferroelétricas, Caixa Postal 676, 13565-670, São Carlos, SP – Brazil

Ferroelectric Pb(Zr 1-x Tix)O3 (PZT) thin films were prepared by rapid thermal annealing and investigated by piezoresponse (PFM) using a commercial atomic force microscope (AFM, TopoMetrix, Discoverer TMX 2010) connected to a lock-in amplifier (EG&G Instruments, 7265). The AFM tips were made of Si3N4 coated with TiO2 . Standard Si cantilevers were used with spring constant k=2 N/m and resonant frequency of 105 kHz. Topography and piezoresponse images were taken simultaneously across the PZT thin films. An ac modulation voltage of 10 Vpp at 10 kHz was applied to the tip during imaging. Regions of dark and white contrast show opposite directions of polarization. The films also show a structure with grains of different sizes depending on the crystallization temperature. The image processing of ferroelectric domains consists in grain delimitation by watershed technique, entropic segmentation and histogram computation of dark and white regions. This analysis quantifies the ferroelectric domain distribution for each grain.

A-P12 SYNTHESIS OF MoS2 NANOTUBESO.P. Ferreira, O.L. Alves, Laboratório de Química do Estado Sólido LQES, IQ–UNICAMP, Campinas, SP, Brazil. http://lqes.iqm.unicamp.br

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The discovery of carbon nanotubes in 1991 has stimulated intense experimental and theoretical studies in such tubular structures. A great deal of effort has also been dedicated to the synthesis of different kinds of nanotubes. Metal sulfide nanotubes (MSN) are the most studied inorganic nanotubes due to their promising electronic, catalytic and mechanical properties. In this work we report the synthesis of MoS2 nanotubes by thermal decomposition of thiomolybdates [(NH4)2MoS4

and (NH4)2Mo2S12] under argon flow. Different conditions of decomposition were investigated such as heating temperature (250-1100oC), heating rate and annealing time (0.5-8h). The reaction products were characterized by SEM, TEM, XRD and Raman. The XRD patterns of the as prepared samples showed the presence of reflections characteristic of 2H-MoS2. The SEM and TEM images showed nanotubes with outer diameter in the range of 50-100 nm. The MSN showed inner diameter about 10 nm. Nanorods and spherical nanoparticles were also observed in TEM images. The Raman spectra obtained for MoS2, prepared in this work, showed bands with frequencies similar to the bulk MoS2, whose spectrum is characterized by bands at 380, 405 and 450 cm -1. To our knowledge this is the first time MoS2 nanotubes were prepared by solid reaction under inert atmosphere. [CNPq and Millennium Institute of Complex Materials]

A-P13 QUANTUM CONDUCTANCE OF COPPER NANOWIRESJ. C. González, V. Rodrigues, J. Bettini, D. Ugarte, Laboratório Nacional de Luz Síncrotron, C.P. 6192, 13084-971 Campinas, SP, Brazil; A. R. Rocha, Department of Physics, Trinity College Dublin, Dublin 2, Dublin, Ireland; L. G. C. Rego, Departamento de Física, Universidade Federal do Paraná, Curitiva, PR, Brazil.

In this work, we present a study of the correlation between atomic structure and quantum conductance of atomic size Cu nanowires (NWs). Time resolved high resolution transmission electron microscopy was used to study the formation, elongation, and rupture of Cu NWs produced by mechanical stretching. One-atom-thick chains were observed for NWs generated along [111], [100] and [110] directions. Rod-like NWs that evolve to one-atom-thick chains were also observed for NWs generated along the [100] and [110] directions.Quantum conductance of Cu NWs was studied using a mechanically controllable break junction (MCBJ) system operating at room temperature in ultra high vacuum. MCBJ experiments showed conductance values around 1 G0, 2.4 G0 and 4.5 G0. Molecular orbital calculations were implemented to calculate the quantum conductance of Cu NWs with face centered cubic (fcc) structure. These calculations revealed that one-atom-thick chains display conductance close to 1 G0, regardless of NWs direction. Rod-like [100] and [110] NWs show conductance at 4.5 G0 and 2.4 G0, respectively. However in order to explain all the conductance evolution observed in the MCBJ experiments [110] NWs with pentagonal structure (none fcc) must also be considered. Quantum conductance calculations of these NWs explain our experimental results, demonstrating the formation of relaxed atomic arrangements in Cu NWs.

A-P14 SYNTHESIS AND CHARACTERIZATION OF FREE-STANDING SEMICONDUCTOR NANOWIRESJ. C. González, J. Bettini, D. Zanchet, D. Ugarte, Laboratório Nacional de Luz Síncrotron, Caixa

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Postal 6192, 13084-971 Campinas SP, Brazil; H. R. Gutiérrez, M.A. Cotta, Instituto de Física Gleb Wataghin, DFA/LPD, UNICAMP, CP 6165, 13081-970 Campinas-SP, Brazil; F. M. Matinaga, Departamento de Física, UFMG, CP 702, 30123-970, Belo Horizonte, MG, Brazil.

In this work, we report the synthesis and characterization of free-standing semiconductor nanowires. III-V wires were grown by the Vapor-Liquid-Solid (VLS) method in a Chemical Beam Epitaxy (CBE) reactor. Au nanoparticles (NPs) were used as seeds to catalyze the growth process. Using this method nanowires of InP, GaP, GaAs and InAs were grown with diameters around 50 nm and several microns long. The wires may also be generated to include heterostructures (ex. InP/InAs/InP).The morphology, crystal structure and chemical composition of the wires were characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Electron Diffraction (ED) and Energy Dispersive X-ray Spectroscopy (EDS). The nanowires were found to be stoichiometric, single crystal with a tapered morphology and mainly oriented along the [100] and [110] crystallographic directions.Low temperature Photoluminescence (PL) experiments in undoped and Si doped InP NWs revealed a small quantum confinement in the wires and confirmed the good crystalline quality of the wires, as observed by TEM.

A-P15 MORPHOLOGICAL CHARACTERIZATION OF NANOPARTICLES OF SnO2 WITH ADDITIVES Ni AND FePilar Hidalgo 1 , Douglas Gouvêa1, Daniela Zanchet2, Jefferson Bettini2; 1 Department of Metallurgical and Materials Engineering- USP, Av. Professor Mello Moraes, 2463, 05580-900. S.P. Brazil; 2 National Synchrotron Light Laboratory (LNLS), Campinas, SP, Brazil. Recently studies on ceramic powders have shown that microestrutural modifications take place when the system reaches the lowest surface energy. Indirectly this decrease is related to the segregation of the additive onto the surface powder. This work intends to study the segregation of additives in two interesting system: F2O3-SnO2 and NiO-SnO2, prepared by Pechini´s method. Morphological characteristics were performed using Transmission Electron Microscopic (TEM), X-ray diffraction (XRD), Specific Surface Area (SBET) and Mössbauer Spectroscopy. The segregation of ions Fe or Ni on the surface the matrix phase (SnO2) was observed even in specimens with 30 mol% of additive. After, with increasing of ions Fe or Ni (50 and 80 mol %) has been observed nucleation of second phase: magnetite (Fe3O4) and NiO respectively. Perhaps SnO2

has persuaded epitexial growing for these phase. This was confirmed better joining EDX results and TEM.

A-P16 NANOMECHANICAL PROPERTIES OF THE SUPERCONDUCTORS JOINTSP. R. JUNIOR, Universidade Estadual de Ponta Grossa – DEFIS, Ponta Grossa, Brazil; C. M. LEPIENSKI, A. S. DUBIEL, Universidade Federal do Paraná - DEFIS, Centro Politécnico, Caixa Postal 19044, CEP 81531-990, Curitiba, Brazil

The determination of the mechanical properties of nanostructured material is a new and very interesting area. In the present work the nanomechanical properties of the superconductors joints from YBCO system were studied. The samples processed had YBCO-123, YBCO-211 and Ag particles. The YBCO with silver was used as solder agent because its melting point is lower than YBCO-123. The method to obtain hardness and elastic modulus by load-displacement curves with a load and depth-sensing indentation consists in using a diamond indenter, with triangular base to penetrate some few nanometers into the material surface. In these samples the Berkovich indenter applied a peek load of 400 mN and its maximum penetration into material was 1600 nm. The hardness and the elastic modulus obtained were 16-10 GPa and 200 GPa respectively. In displacements until 400 nm the hardness was 16 GPa decreasing to a constant value of 10 GPa. The elastic modulus value was constant in all displacements. The difference on the hardness value can be an effect of the mechanical polishing on the sample before the indentation test.

A-P18 STUDY OF CARBON NANOTUBES GROWTH BY MICROWAVE PLASMA WITH NICKEL AND IRON CATALYSTE.F.Antunes, E.J.Corat, A.F.Beloto, V.J.T.Airoldi, Instituto Nacional de Pesquisas Espaciais –

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INPE, Laboratório Associado de Sensores e Materiais – LAS, Grupo de Diamantes e Materiais Relacionados – DIMARE, Avenida dos Astronautas, 1758, Jd. da Granja -  São José dos Campos/ SP- Brasil CEP 12.245-970, Caixa Postal 515, ericafa@las.inpe.br

Carbon nanotubes have been investigated by many research groups of around the world due its greats properties, mainly about field emission capacity. In this work, we have studied the morphology of carbon nanotubes thin films produced by microwave plasma chemical vapor deposition. For this, nickel and iron thin film (5nm) have been used as catalyst, deposited by electron beam evaporator on silicon substrates covered by silicon oxide (50nm). Microwave plasma has been used to promote island formation of diameter of tens of nanometers on the metallic films, and in a further step the carbon nanotubes have been nucleated. In the step of island (clusters) formation only N2 and H2 are inserted in the plasma chamber and then CH4, which is the carbon source to form the nanotubes. The plasma conditions are studied (pressure, power, gas mixture). External heating is necessary to control substrate temperature. Cluster and nanotubes have been characterized by AFM (atomic force microscopy), SEM (scanning electron microscopy) and Raman spectroscopy.[1] Ph. Mauron , Ch. Emmeneger, A. Züttel, Ch. Nützenadel, P. Sudan, L. Schlapbach. Carbon 40 (2002)1339-1344 [2] U. Kim, R. Pcionek, D. M. Aslam, D. Tománek. Diamond and Related Materials 10 (2001)1947-195 [3] Qing Zhang, S. F. Yoo, J. Ahn, B. Gan ,Rusli , M.-B. Yu. J. of Physics and Chemistry of Solids 61(2000)1179-1183 [4] J. H. Huang, C. C. Huang, C. H. Tsai. Microelectronic Engineering 1(2003) 000-000 [5] S. G. Wang, Qing Zhang, S. F. Yoon, J. Ahn. Scripta Materialia 48 (2003) 409-412 [6] C. H. Lin, H. L. Chang, M. H. Tsai, C. T. Kuo. Diamond and Related Materials 11 (2002) 922 -926

A-P19 CARBON NANOTUBES PRODUCTION BY ARC DISCHARGE IN AQUEOUS SOLUTIONR. C. Z. Lofrano, L. A. Montoro and J. M. Rosolen. Depto. de Química da FFCLRP - USP Avenida dos Bandeirantes, 3900 CEP 14 040-901 Ribeirão Preto/SP, Brasil

A lot of progress has been reported in the synthesis of carbon nanotubes (CNT) in recent years. Different authors have successfully produced carbon onions and nanotubes in large quantities by arc discharge in water. They have shown that arc discharge in water technology simplifies the traditional. We have studied the products of pyrolise of graphite in an arc-discharge reactor in metavanadic acid solutions. The graphite bars were filled with a mixture of Ni/Co powder and the arc was formed in DC conditions (25V, 60A). The samples were characterized using Raman and microscopy techniques (SEM and HRTEM). The carbon produced is presents bundles interconnected by many segments of solid materials like foil. The length and diameter of bundles is in the range 1.0 – 2.0m and 10-50nm, respectively. The Co, Ni and V are presents in these structures, inside the bundles and solid materials. Vanadium oxide traces was detected in the samples. The Raman spectra show that the composite carbon present features of multi-wall carbon nanotubes. Acklowledments LME/LNLS and FAPESP.

A-P20 STRUCTURAL AND NANOSCALE FRICTION MODIFICATIONS INDUCED BY NITROGEN INCORPORATION INTO HARD AMORPHOUS FLUORINATED CARBON FILMS

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C.M.T. Sanchez, M.E.H. Maia da Costa, R.R.M. Zamora, R. Prioli , F.L. Freire Jr. and L.G. Jacobosohn* ; Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Caixa Postal 3807, Rio de Janeiro, RJ 22453-970, Brazil; *- Los Alamos National Laboratory, P.O.Box 1663 Los Alamos, NM 87545, USA

Plasma enhanced chemical vapor deposition (PECVD) technique was used to study the nitrogen incorporation into fluorinated amorphous carbons films by decomposition of CH4-CF4-N2 mixtures. The gas mixture was (CH4-CF4)1-x (N2)x where x was varied from 0 to 0.6. The CH4:CF4 ratio was fixed at 1:2. All the films were deposited at 10 Pa. The structural and chemical characterizations of the films were performed by ion beam analysis (RBS, ERD and NRA), Raman spectroscopy and X-Ray photoelectron spectroscopy. The results show that nitrogen incorporation occurs at the expense of the carbon contents of the films. It results in an increase of the size and the number of the graphictic domains. The nitrogen was incorporated into aromatic rings and as terminator radicals, as observed in XPS measurements. The nanofriction behavior of the films was investigated by atomic force microscopy. The direct correlation of the nitrogen incorporation with the contact angle and the friction coefficient were was investigated.

A-P21 ENHANCEMENT OF THE HYDROPHOBICITY OF POLYPROPYLENE AND TEFLON BY SF6 PLASMA TREATMENTRita C. C. Rangel, Elidiane C. Rangel, Nilson C. Cruz , Laboratório de Plasmas, Av. Dr. Ariberto Pereira da Cunha, 333, Guaratinguetá / SP, Brazil DFQ/FEG/UNESP

Low water affinity materials are interesting in many scientific and technological areas. In biomaterial field, for instance, abdominal wall prostheses are made from hydrophobic materials to avoid bowels adherence onto the implant surface. In this work, polypropylene and Teflon have been exposed to SF6 plasmas in order to enhance their hydrophobicity. It has been investigated the influence of exposure time, applied power and discharge pressure on the contact angle, , of such polymers. Plasmas were generated by applying radiofrequency power (13.56 MHz) to two metallic electrodes external to a cylindrical glass vacuum chamber. Contact angles were evaluated using an automated goniometer comprised by a CCD camera which digitizes the image of a water drop, of about 0.2 l in volume, placed onto the polymer surface by micro-syringe. A dedicated software analyzes that image and determines . We have observed that the treatments resulted in considerable enhancement in . For instance, under certain conditions the contact angle of polypropylene increased from 93, as measured in the pristine material, to about 125.

A-P22 LATERAL FORCE MICROSCOPY OF HYDROPHILIC SURFACESR.R.M.Zamora , R.Prioli, Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Cx. Postal 38071, 22452-970 Rio de Janeiro Brasi.

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In the quantitative measurement of friction with AFM, it is important to take into account the calibration of the lateral photodiode and the cantilever spring constants. In this work we present a procedure for the AFM cantilever and photodetector calibration. The proposed calibration procedure is focused on the calculation of the cantilever normal and lateral spring constants as a function of the cantilevers dimensions. The relationship between the torsion signal (lateral force) and the normal bending signal (normal force) is obtained by an analysis of the AFM optical detection system. It is shown here that the position of the laser on the cantilever strongly influences the lateral force measurement. To analyze the reproducibility of the lateral force data, we have measured the lateral force between the Si3N4 and SiO2 for ten cantilevers in a first set and ten independent measurements with the same cantilever in a second set. We show that, in spite of the fact that both sets presents the same lateral force, the error in the first set of measurements is up to 50% higher then for the second set. The calibrated microscope was used to study the influence of the humidity in the adhesion and lateral forces between the AFM tip and an hydrophilic sample. It is shown that at very low humidities, the Van der Waals forces are responsible for the tip-surface adhesion, while at humidities higher than 10% the capilary condensation of water is responsible for the adhesion. The lateral forces are shown to be strongly dependent on the environmental conditions. At low humidities a multiasperity regime is observed wihle at higher humidities a single asperity friction is observed. The friction coeficient is shown to decrease with the increase of humidity.

A-P24 WEAR OF AMORPHOUS FLUORINATED CARBON FILMS IN NANO AND MICROSCALESP. Ayala, M.E.H. Maia da Costa, R. Prioli, F.L. Freire Jr.; Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Caixa Postal 3807, Rio de Janeiro, RJ 22453-970, Brazil.

Amorphous fluorinated carbon films were deposited by plasma enhanced chemical vapor deposition (PECVD) to study the wear in nanoscale and microscale. For nanoscale wear, an atomic force microscopy was used and for microscale a sliding sphere test. The films microstructure and chemical composition were also investigated. Density measurements, Raman and x-ray photoelectron spectroscopy showed that films became polymeric-like upon fluorine incorporation. It was shown that the wear marks produced with a microscope diamond tip are strongly related to the film hardness and microstructure. The wear depth on a polymeric-like film was greater than that obtained from hard amorphous carbon and carbon fluorinated films. At nanometer scale, the minimum force necessary to scratch the films increased with the film hardness, while the wear rate decreased. Similar behaviors were observed in both nano and microscale wear experiments

A-P25 STRUCTURAL CHARACTERIZATION, MECHANICAL PROPERTIES AND THERMAL STABILITY OF HARD AMORPHOUS CARBON-FLUORINE FILMS DEPOSITED BY PECVD USING C2H2-CF4 GAS MIXTURES

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M. E. H. Maia da Costa and F.L.Freire Jr. , Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Caixa Postal 3807, Rio de Janeiro, RJ 22453-970, Brazil.

Fluorinated amorphous carbon films (a-CF) were deposited by PECVD in C2H2-CF4 gas mixtures at a pressure of 10 Pa. The first series of samples were prepared fixing the self-bias voltage at -350V and changing the ratio of the partial pressure of C2H2 and CF4. The idea is to investigate the effects of the fluorine incorporation on the film properties. The acetylene partial pressure was varied from 100% to 20% of the total pressure. The second series of samples was deposited at a fixed self-bias voltage (–350V) and partial pressure ratio of C2H2-CF4 of 1:2. Films deposited in pure acetylene atmosphere were also deposited. In order to investigate the thermal stability of a-CF films, samples of these second series were annealed in vacuum without any kind of sequential annealing for 30 minutes. The range of temperature was 200oC to 600oC. Ion beam techniques (RBS and ERD) were used to determine the chemical composition and, when combined with the film thickness, the atomic density of the films. Structural modifications were investigated by Raman spectroscopy, while X-ray Photoelectron Spectroscopy probed the chemical bonds. The internal stress and the hardness were also measured. Contact angle measurements were made to evaluate the hidrophobicity of the samples. Films with hidrophobicity comparable to that of the polytetrafluoroethylene (PTFE) were obtained for films with high fluorine content. However, the film hardness is much higher compared to PTFE. The films were thermally stable up to 300 oC. For higher annealing temperatures, strong fluorine loss and structural changes were observed.

A-P26 PRODUCTION AND CHARACTERIZATION OF HYDROGENATED AMORPHOUS CARBON THIN FILMS DEPOSITED IN METHANE PLASMAS DILUTED BY NOBLE GASES G. Capote and F.L. Freire Jr. ; Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente, 225 – Gávea, Caixa Postal 38071, Rio de Janeiro, 22452-970, Brazil.

The effects of the dilution of the precursor methane atmosphere by three noble gases (Ar, Ne and He) on the mechanical properties and the microstructure of hydrogenated amorphous carbon films (a-C:H) are presented. The influence of the precursor atmosphere and the variation of the self-bias voltage are studied. The influence of the substrate temperature also is studied for three temperatures 250 K, 300 K and 420 K for films deposited in atmospheres of 100% CH4 and 2% CH4 + 98% Ar. The films were deposited by Plasma Enhance Chemical Vapor Deposition (PECVD). The mechanical and structural properties were investigated with the use of the nuclear techniques (Rutherford backscattering and elastic recoil detection analysis), infrared and Raman spectroscopies, atomic force microscopy, contact angle measurements, internal stress and hardness measurements. The results shown that the precursor atmosphere dilution by noble gases did not induce substantial modifications in the microstructure or in the mechanical properties of the films. On the other side, the composition, the microstructure and the mechanical properties of the films are strongly dependent on the ion bombardment regime. The dependence of the mechanical and structural properties of the films as a function of the substrate temperature was also investigated. Experimental results had been obtained from the film roughness measurements using atomic force microscopy. These results suggest the transition from predominantly adsorption/diffusion mechanisms to the predominance of the ballistic processes in the formation mechanisms of the a-C:H films.

A-P27 SURFACE MODIFICATION OF PLASMA POLYMERIZED THIN FILMS BY PLASMA IMMERSION ION IMPLANTATIOND. C. R. Santos, R. P. Mota, R. Y. Honda, M. E. Kayama, E. C. Rangel, FE-UNESP, Av. Ariberto

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P. da Cunha, 333, Guaratinguetá, 12516-410, SP, Brazil.

Surface modification of metal, ceramic and polymeric materials is a study of great interest for several engineering and biomedical areas. Improvements of the surface properties can increase the lifetime and the functionality of those materials. Plasma Immersion Ion Implantation (PIII) is an effective method to do it. It is relatively cheaper than the conventional ion implantation and, furthermore, it overcomes the difficulties of that technique. In this work, we investigated the PIII effect in plasma polymer films, varying the exposure time from 1800 to 9000 s. The films were deposited from the mixture of acethylene and argon gas, submitted to radiofrequency plasma (RF, 13.56 MHz, 100 W) in low pressure regime. Then, the films were polarized by high voltage negative pulses (10 kV, 30 Hz) and bombarded by ions created from RF nitrogen plasmas (13.56 MHz, 70 W). Contact angle measurements were performed to evaluate the wettability and surface energy. Age of the films was accompanied by periodical measurements of the contact angle after the treatment. Etching rate was evaluated after exposing the films to oxygen reactive plasmas. After the implantation, the contact angle droped for all samples. However, there was not stability of them. In spite of that, the films showed better oxidation resistance.

A-P28 AMORPHOUS CARBON FILMS WITH VERY LOW HYDROGEN CONTENT PREPARED BY RF PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION E. F. Motta and I. Pereyra Departamento de Engenharia de Sistemas Eletrônicos, Escola Politécnica, Universidade de São Paulo, CP: 61548 CEP: 05424-970, São Paulo, SP, Brazil

Research on tetrahedral amorphous carbon (taC), is still at a young stage, in the sense that film preparation and characterization as well as practical applications have yet to be proven. In this way, the relationship between the deposition conditions, the growth mechanisms, the microstructure and the electronic density of states of films prepared by PECVD from hydrocarbon gaseous precursors are not fully understood [1-3]. Therefore, in this work, we perform a systematic study by means of several complementary characterization techniques to determine the correlation of the material microstructure and optical properties with the deposition conditions for taC samples deposited by radio-frequency glow discharge from methane and argon gaseous mixtures at 25 degrees C. The studied deposition parameters were the plasma Rf power, the deposition pressure and the argon flow rate. Raman scattering and FTIR results indicate that high argon flows and optimized intermediate chamber pressure favor the deposition of tetrahedral amorphous carbon films with low hydrogen content. On the other hand high deposition pressure and low flows induce the growth of diamond like films with much higher hydrogen incorporation.

A-P29 PRE-IRRADIATION EFFECTS ON THE PHOTOLUMINESCENCE AND CLUSTER COARSENING PROPERTIES OF GE-IMPLANTED SIO2 LAYERS J. M J. Lopes, F.C. Zawislak, M. Behar, Instituto de Física – UFRGS, Porto Alegre, Brazil;

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P.F.P. Fichtner, Escola de Engenharia - UFRGS, Porto Alegre, Brazil; L. Rebohle, Nanoparc GmbH, Dresden, Germany; W. Skorupa, Rossendorf e.V. , Dresden, GermanySiO2/Si(100) films were irradiated with He+, Si+, Au+ and Kr++ ions as function of the amount of electronic and nuclear deposited energy density by the beams. After the irradiation, the SiO 2 layers were implanted with 120 keV Ge+ ions at a fluence of 1.2 1016 cm-2. Thermal annealings in the 400800C temperature range were performed to allow the formation of a Ge-nanoclusters, characterized by transmission electron microscopy. The photoluminescence (PL) and PL excitation properties of the pre-irradiated Ge-implanted layers were investigated and compared with those from non pre-irradiated samples. The results showed that, in both situations, PL emissions are observed in the blue-violet and ultra-violet spectral regions. At 800C the blue-violet PL intensity of the Ge-implanted layer pre-irradited with Si+ ions is about 65% higher than in the non-irradiated Ge-implanted layer while for the Au-irradiated layer a decrease by a factor of 6 was observed. Furthermore, we also observe that the mean cluster sizes are affected by the pre-irradiation. For the Au+ irradiation case, the Ge mean cluster size is 2 times smaller than to the non pre-irradiated sample. These results indicate a pre-irradiation memory effect on the PL intensity and on the cluster growing. The results are discussed in terms of a new model correlating the formation of PL luminescent centers with the cluster coarsening behavior.

A-P30 CHARACTERIZATION OF Si1-xCx:H THIN FILMS DEPOSITED BY PECVD ON Si AND Si/INSULATOR SUBSTRATESN. A. E. Forhan and I. Pereyra, Escola Politécnica da USP - PEE – LME, Av. Prof. Luciano Gualberto, 158, Trav. 3 - CEP05508-900, São Paulo - SP - Brazil In this work we investigate the structural properties of amorphous hydrogenated silicon carbide thin films (-Si1-xCx:H) deposited by PECVD on silicon and silicon covered with an insulator layer substrates, before and after thermal annealing for crystallization. The SiC-on-insulator heterojuntion allows its use in high temperature, high power, high frequency, smart-sensors, and micromechanical applications. Here, we analyze -Si1-xCx:H films deposited on silicon covered with different kind of insulator capping layer: high temperature (1100oC) thermal SiO2, low temperature (300oC) PECVD SiO2, SiOxNy, and Si3N4. These insulators were chosen due to their great interest for optoelectric and microelectronic applications. The infrared studies have shown that samples deposited on silicon covered with an insulator layer have a better coordination among Si and C atoms. Post-growth thermal annealing leads to the crystallization for all the amorphous films. Raman scattering spectroscopy measurements exhibit a weak C-C bond vibration, after annealing, only for samples deposited on PECVD insulator. The structural properties and the mechanical internal stress of the -Si1-xCx:H films are studied, before and after thermal annealing, by X-Ray Diffraction and Stoney method, respectively.

A-P31 ANNEALING OF DEFECTS AND NANOPORES PRODUCED ON SiO2 THIN FILMS BY MEANS OF ION BOMBARDMENTC.Milanez1 , J.M.J.Lopes2 , P.F.P.Fichter3 , R.M.Papaléo1

1Faculdade de Física, PUCRS, Av Ipiranga 6681, 90619-900 Porto Alegre; 2Instituto de Física,

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UFRGS; 3Dep. Metalurgia, Escola de Engenharia, UFRGS, Cx Postal 15051, 91501-970 Porto Alegre-RS.

Nanometer-sized conical pores of high aspect ratio were produced on SiO2 thin films thermally grown on Si (100) wafers by irradiation with Au MeV ions followed by chemical etching. Such holes are formed because of the enhanced etching rate around the site of ion penetration, as compared to undamaged zones of the material. The number of defects produced by the MeV ions and their spatial distribution are key to the final shape and size of the pores. Thermal annealing of the bombarded oxide was performed at temperatures Ta ranging from 150˚C to 900˚C for 30 min under dry N2 flux, before pore opening by etching in aqueous HF solution. Thermal treatment results in a substantial decrease in the pore size, even at Ta as low as 150˚C. For example, while pore diameters were around 150nm on unannealed samples, their average values decrease to 50nm for Ta = 250˚C and to 25nm for Ta = 500˚C. Pores are not seen on samples annealed at 900˚C, probably because of a complete recovery of the defects in the ion track. We note that the pore dimensions on the etched SiO2 films are unchanged even after annealing at 800˚C for 1h, i.e. once formed the pores show an excellent thermal stability.

A-P32 EVIDENCE OF CLUSTERS SIZE DEPENDENT PHOTOLUMINESCENCE ON SILICON-RICH SILICON OXYNITRIDE FILMSR.A.R. Oliveira, M. Ribeiro, I. Pereyra and M.I. Alayo; University of São Paulo, CP 61548, CEP 5424-970, São Paulo, SP, Brazil

In recent years, photoluminescent materials for optical and microelectronic integration have received great attention. Among these, silicon nanocrystals in a SiOx matrix is considered very promising due to its stability and high luminescence intensity after annealing at high temperatures [1,2].This work reports on the growth of silicon clusters within silicon oxynitride (SiOxNy) matrices by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. The films were characterized by Fourier transform infrared spectroscopy (FTIR), Raman scattering and photoluminescence before and after thermal annealing at various temperatures. The results indicate the presence of silicon clusters in as-deposited and the evolution of clusters size after annealing. Also, the photoluminescence measurements, show that as-deposited films already present high luminescence intensities. These results are in accordance with soft X-ray absorption spectroscopy (XANES) measurements at Si K-edge which demonstrate the silicon phase segregation on these films.[1] M. Ribeiro, I.Pereyra, M.I. Alayo, Thin Solid Films 426 (2003) 200.[2] L. Pavesi et. al., Nature 408 (2000) 440.

A-P33 STUDY OF PECVD MATERIALS FOR TFT APLICATIONK.F.Albertin; I.Pereyra and M.N.P.Carreño, LME, EPUSP, University of São Paulo, CEP 05508-900, CP 61548, São Paulo,SP, Brazil

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The application of thin film transistors (TFT’s) in image sensors and displays is widespread and the amorphous silicon technology has shown to be mature and thus a-Si:H TFTs are widely used for individually switched display elements (pixels) in flat panel displays[1]. However the mobility of amorphous silicon is in the 0.5-1.0 cm2.V-1.s-1range and higher values are needed for some applications, such as: high resolution large area displays, requiring complementary metal – insulator – semiconductor operation (CMOS). CMOS operation however is out of reach for a-Si:H since its hole mobility is insufficient for p channel operation. In this way research is now directed to semiconductors materials with higher mobilities than amorphous silicon, as nanocrystaline (nc-Si), microcrystaline (uc-Si) and policrystaline (Poly-Si) silicon films. In this work we fabricate TFT’s utilizing a-Si:H and c-Si:H as active layer and with insulating layer of SiOxNy and a-SiC:H all obtained by the PECVD technique at low temperatures (~300oC). The TFT’s are caracterized by Ids xVds and Ids x Vgs measurements, and these results are correleted with the physical properties of the materials which are characterized by Raman, XRD and FTIR measurements.[1] R.E.I Schropp, B.Stannowski, J.K. Rath. Journal of Non-Crystalline Solids 299 – 302 (2002) 1304.

A-P34 STRUCTURAL ANALYSIS OF SILICON OXYNITRIDE FILMS DEPOSITED BY PECVDD. Criado, M.I. Alayo, I. Pereyra, M.C.A. Fantini ; University of São Paulo, CEP 5424-970 CP 61548, São Paulo, SP, Brazil

Silicon oxynitride films have nowadays assumed great importance for the development of various microelectronic and optical devices, such as: waveguides, TFT transistors, and micro-electro-mechanical systems (MEMS) [1]. The main characteristic of these materials is the possibility of tuning the physical and optical properties when adequate growth parameters are varied [2]. This work reports on the deposition and characterization of silicon oxynitride films deposited by Plasma Enhanced Chemical Vapor Deposition at low temperatures from different N2, N2O and SiH4

gaseous flow ratio. Fourier Transform Infrared Spectroscopy, Rutherford Backscattering Spectroscopy and Soft X-Ray Absorption Near Edge Structure (XANES) performed at the Si-K edge show that depending on the deposition parameters it is possible to grow materials with a homogeneous structure between silicon dioxide and silicon nitride obeying a Random Bonding Model (RBM). Furthermore, analysis of XANES at N-K edge demonstrate two edges which are attributed to the different nitrogen neighborhoods, nitrogen in a Si3N4 matrix and nitrogen substituting the O in a SiO2 matrix.[1] K.C. Mohite et. al. Materials Letters 4494 (2003) 1; [2] M.I. Alayo et. al. Thin Solid Films 402 (2002) 154.

A-P35 PECVD-SILICON OXYNITRIDE FILMS FOR FABRICATION OF OPTICAL WAVEGUIDESM.I. Alayo, M.N.P. Carreño, D. Criado, I. Pereyra; University of São Paulo, CEP 5424-970, CP 61548, São Paulo, SP, Brazil

Silicon oxynitride films have nowadays assumed great importance in the fabrication of optical devices mainly due to that this material permits the integration of optical and microelectronic devices in a single chip because the same infra-structure is used by the fabrication of both devices [1]. Furthermore, the properties of these materials are strongly dependent on the deposition parameters, so tunability of the refractive index over a wide range can be obtained (n = 1.46 - 2) resulting in a large degree of freedom for integrated optics design [2]. In this work were fabricated optical waveguides with different compositions PECVD silicon oxynitride films and optical attenuation measurements in these devices were realized. On the other hand, in order to correlate the optical characteristics of these devices with the optical, physical and chemical characteristics of the films utilized as core and cladding, materials characterization such as: Fourier Transform Infrared Spectroscopy (FTIR), Ellipsometry and Rutherford Backscattering Spectroscopy (RBS) were realized.[1] M. Modreanu et. al. Optical Materials 17 (2001) 145; [2] M.I. Alayo et. al. Thin Solid Films 402 (2002) 154.

A-P36 ELECTRICAL PROPERTIES OF LOW-TEMPERATURE PECVD SiC/c-Si HETEROSTRUCTURESA.R. Oliveira*, M.N.P. Carreño and I. Pereyra; Department of Electronic Systems, Polytechnic School of the University of São Paulo - CP 61548, CEP 05424-970, São Paulo – SP, Brazil

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The electrical properties of the SiC/Si heterostructure based on stoichiometric a-SiC:H thin films grown by r.f. plasma chemical vapor deposition at low-temperature (320 ºC) on Si(100) substrates have been investigate. Films deposited with different chemical and structural orders and annealed at 550 ºC for 2 hours were obtained in the so-called “silane starving plasma” condition, from SiH4, CH4 and H2 gaseous mixture. In order to assess the applicability of these films, the electrical properties were evaluated from current-voltage and capacitance-voltage characteristics curves. It was found that electrical properties of the heterojunction formed with optimized deposition condition and subsequent annealing step show the better electrical performance, exhibiting good rectifying properties.

A-P37 MICRO-RAMAN STRESS CHARACTERIZATION OF POLYCRYSTALLINE SILICON FILMS GROWN AT HIGH TEMPERATURE R. C. Teixeira; I. Doi, M. B. P. Zakia, J. A. Diniz, and J. W. Swart; School of Electrical and Computer Engineering (FEEC), and Center for Semiconductor Components (CCS), State University of Campinas (UNICAMP), C.P. 6101, 13083-970 Campinas-SP, Brazil

Polycrystalline Silicon (poly-Si) is widely used in microelectronics and micro-electro-mechanical systems (MEMS). In MEMS, poly-Si is used as structural material for a variety of applications such as pressure transducers and micro-switches. The performance and control of the dimensions of the micro-structural elements are critically dependent on the mechanical stress in the films. The stress is controlled during deposition process, as the processing parameters affects significantly the mechanical and electrical characteristics of devices. Poly-Si obtained by low pressure chemical vapor deposition (LPCVD) is used in surface micromachining applications, however, a high residual stress are inherent in as-deposited poly-Si, requiring further annealing steps to achieve minimum residual stress. In this paper we present the residual stress characterization and analysis of the poly-Si grown at high temperature in a vertical pancake type LPCVD reactor by Micro-Raman spectroscopy. The samples were prepared on Si (100) substrates coated with 50nm of SiO2

at pressure of 5 and 10 Torr in the temperature range between 750°C to 900°C. The results show that residual stress decreases with temperature, thus with crystalline amount of the films. All the samples exhibited less than 250 Mpa tensile stress at temperatures above 800°C. These results indicate that a high quality, low strained, and highly crystalline poly-Si films, can be obtained in this type of reactor at high temperature.

A-P38 STRUCTURAL AND OPTICAL CHARACTERIZATION OF SILICON NANOCRYSTALS OBTAINED BY ÍON IMPLANTATIONS. N. M. Mestanza, J. E. C.Queiroz, H. R. Gutierrez, A. A. R. Neves, G. O. Dias, I. Doi and J. W. Swart; Centro de Componentes Semicondutores CCS/FEEC-UNICAMP, CP6165, 13083-970 Campinas, SP, Brazil; nilo@led.unicamp.br

In spite of high efficiency emitter devices can be obtained from III-V semiconductor compounds; its integration in the current Si planar technology is very complex and often ineffective. On the other hand silicon is a very poor emitter due to it indirect bandgap. However, in nanocrystal form (Si-nano), silicon properties change drastically presenting a direct bandgap with emission in the wavelength range of 600-1000 nm, depending on the nanocrystal size distribution. In this work, different samples with Si nanocrystals were prepared by implantation and annealing. Thermal silicon oxides with 300nm, were grown on (100) n-Si and p-Si wafers. 28Si+ implantation was performed with energies of 100Kev. The implantation energies were chosen from Monte Carlo simulation, using the TRIM code. Conventional photoluminescence (PL) spectra were obtained at room temperature, showing a broad luminescence band in the red region for all the samples. We have studied the behavior of PL emission peak and full wide at half maximum (FWHM) with the annealing time. The nanocrystal size distribution was determined by cross-section Transmission Electron Microscopy measurements.

A-P39 THERMAL STABILITY OF Hf-BASED HIGH-K FILMS ON SILICON FOR ADVANCED CMOS DEVICESK.P. Bastos, R.P. Pezzi, L. Miotti, G.V. Soares, C. Driemeier and J. Morais, Instituto de Física - UFRGS, CP 15051 91501-970 Porto Alegre – Brazil; I.J.R. Baumvol, Centro de Ciências Exatas e

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Tecnológicas – UCS, Av. Francisco G. Vargas 1130, 95070-560 Caxias do Sul – Brazil

The use of metal oxide and silicate films with higher dielectric constant than that of silicon oxide (high-k materials) as a substitute for SiO2 as gate dielectric presents several difficulties. Some of them include chemical and structural instabilities in further thermal processing following gate deposition, such as oxidation of the Si substrate, migration of metallic species into the active semiconductor region, transport of Si into the high-k film, and crystallization of the initially amorphous film. This work reports on the thermal stability investigation of HfO2/SiOxNy/Si, HfSiO/Si and HfSiON/Si structures submitted to various combinations of rapid thermal annealings in either inert or oxidizing atmospheres. The areal densities and the concentration profiles of the species of interest were determined before and after rapid thermal annealings by resonant and non-resonant nuclear reaction analysis and Rutherford backscattering spectrometry. The incorporation of nitrogen into hafnium oxide and hafnium silicate films, either during deposition or during post-deposition thermal treatments, provided substantial improvements in the thermal stability of the films.

A-P40 ANNEALING STUDIES IN JVD HIGH-K OXIDE SYSTEMSE. A. de Vasconcelos, J. A. A. Fotius, J. B. Oliveira Jr., E. F. da Silva Jr., Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife, PE, Brazil; H. Boudinov, Instituto de Física, Universidade Federal do Rio Grande do Sul, 91501-970 Porto Alegre, RS, Brazil; T. P. Ma, Department of Electrical Engineering, Yale University, New Haven, CT 06520, USA.

High-k oxides are promising materials for ultra-thin gate dielectrics in advanced MOS technologies and the development of their fabrication techniques has been actively investigated in the last few years. The Jet-Vapor-Deposition (JVD) process is one of the methods proposed for fabrication of these materials. In this work, we report on the effects of gaseous, ultra-violet and ion-irradiation annealing on the interfacial and bulk properties of Jet-Vapor-Deposited high-k oxides. MOS capacitors with high-k oxides (HfO2, HfAlO) were fabricated and I-V, C-V, voltage and current stress tests have been performed. The results indicate that it is possible to improve significantly the oxide properties by an appropriate selection and combination of the annealing techniques above. We will discuss the details of the techniques and discuss the mechanisms involved.

A-P41 MORPHOLOGY AND STRESS STUDY OF NANOSTRUCTURED POROUS SILICON AS A SUBSTRATE FOR PbTe THIN FILMS GROWTH BY ELECTROCHEMICAL PROCESSC.R.B. Miranda1,2, P.G. Abramof1,3, F.C.L. Melo2, N.G. Ferreira2; 1Instituto Nacional de Pesquisas Espaciais INPE/LAS, CP 515, 122245-970, São José dos Campos, SP, Brasil; 2Centro Técnico Aeroespacial – Divisão de Materiais - AMR/IAE /CTA, 12228-904, São José dos Campos, SP, Brasil ; 3Centro de Desenvolvimento de Tecnologia e Recursos Humanos - CDT, 12242-800, São José dos Campos, SP, Brasil

Porous silicon layers (PSL) were produced by stain etching using a solution of HF:HNO3 500:1 with etching time varying from 1 up to 10 min. The samples have presented nanometric porosity as a function of etching time, characteristic of heavily doped p type silicon. The residual stress and the correlation length of the layers were obtained through the analysis of the micro-Raman spectra using a phonon confinement model including a term to account for the amorphous phase. The correlation length, which corresponds to the crystallite size, is found to decrease as the etching time increases, and agrees with the values obtained by Atomic Force Microscopy (AFM) analysis. The residual compressive stress tends to increase with etching time, as expected by the smaller crystallite size. PbTe thin films were electrodeposited on PSL from aqueous alkaline solutions of Pb(CH3COO)2, disodium salt of ethylendiaminetetraacetic acid (EDTA) and TeO2 by galvanostatic and potentiostatic method. It was also obtained nanostructured PbTe thin films with polycrystalline morphology evidenced by X-Ray Diffraction (XRD) spectra. Scanning Electron Microscopy (SEM) analysis has demonstrated good films reproducibility with an average grain size of 100 nm.

A-P42 EXPERIMENTAL AND THEORETICAL STUDY OF POROUS SILICON ELASTIC PROPERTIESA. B. S. Camussi, R. J. M. da Fonseca, Grupo de Ótica e Propriedades Físicas de Materiais – DEQ, Instituto de Física, UERJ, R. São Francisco Xavier, 524 sala D-3030, 20550-013 Rio de Janeiro,

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Brazil; J. Attal, Laboratoire d’Analyse des Interfaces et de Nanophysique – URA CNRS 1881 - Université Montpellier II 34095, Montpellier CEDEX 05 – France

Porous silicon (PS) has been extensively studied since it exhibits strong visible luminescence at room temperature, suggesting promising applications in silicon-based optoeletronic devices, dielectric isolation of integrated circuits and epitaxial growth of heterostructures on Si substrate. Great part of this research has been focussed in the investigation of optical and electronic properties of PS layers. However, for many pratical applications, it is important to characterize the mechanical behaviour of them. For this purpose, we apply the scanning acoustic microscopy (acoustic imaging and V(z) signature) to measure the acoustic wave velocities and elastic characteristics of this material (Young’s modulus and Poisson coefficient) with different porosity. This is a powerful technique for non-destructive and non-contact measurements, specially when small volumes are involved. The investigated samples have a porosity range of 20% to 60% and thickness of 30 µm to 120 µm. So, in this work, we present V(z) curves and acoustical images and a comparision between theoretical and experimental results using Biot’s theory which describes the propagation of elastic waves in a system composed of a porous elastic solid saturated by a fluid.

A-P44 STRUCTURAL CHARACTERIZATION OF Ge NANOCRYSTALS IN SILICAG. de M. Azevedo 1,2 , A. Cheung2, M. C. Ridgway2, C. J. Glover2, D. J. Llewellyn2, R.G. Elliman2, G. J. Foran3; 1Laboratório Nacional de Luz Síncrotron, Campinas-SP, Brazil; 2Australian National University, Research School of Physical Sciences and Engineering, Canberra, Australia; 3Australian Nuclear Science and Technology Organisation, Menai, Australia

Germanium nanocrystals encapsulated in silica display size-dependent photo luminescence, with possible applications in the fabrication of optical devices. Given the influence of nanocystal size and structure on the optical properties, characterization of the geometrical structure as a function of the preparation conditions is crucial to fully understand and exploit their optical properties. In this contribution, ion implantation followed by annealing was utilized synthesize nanocrystals in the near surface region of 5 micron-thick silica layers. Samples were produced with a variety of ion doses and annealing temperatures. The resulting size distributions were estimated by transmission electron microscopy (TEM) and the local environment surrounding Ge atoms was investigated with EXAFS. The highest dose and annealing temperatures resulted in samples containing nearly spherical nanocrystals with average diameter of 14 nm. Simulations with the FEFF8.0 code indicate precipitates of such a size with bulk like parameters should yield bulk-like spectra. Our experimental results indicate the first nearest neighbor shell in the annealed sample is essentially identical to that of the bulk standard. None-the-less, the amplitudes of the second and greater nearest neighbor shells are considerably reduced. We attribute this reduction to distortions in both bond-length and bond-angle distributions relative the bulk phase. The potential causes of the observed perturbations will be discussed.

A-P45 TRANSPORT VIA EXCITONIC COMPLEXES IN RESONANT TUNNELING STRUCTURES. A. Vercik, Y. Galvão Gobato, Universidade Federal de São Carlos, CP 676, São Carlos - SP, 13560-970, Brazil; M. J. S. P. Brasil, Universidade de Campinas, CP 6165, Campinas-SP, 13083-970, Brazil.

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The Coulomb interaction can bind an electron to a hole forming a neutral exciton. When a second electron is involved, negatively charged excitons are formed, also known as trions. These systems have attracted much interest and their properties continue to be subject of intense debate. These complexes can participate in charge transport, creating an intermediate state in the quantum well of a double barrier structure, through which electrons can tunnel resonantly. Because of the binding energy of the excitons or trions, the excitonic intermediate level must be located at a lower energy than the resonant level. In this work we study the formation of neutral and negatively charged excitons in double barrier diodes under bias, and how they contribute to transport. We observe a pre-resonance shoulder in the current-voltage curve, which is associated to trion-assisted tunneling of electrons. We analyze this phenomenon by measuring also the quantum-well photoluminescence emission. This trion-assisted mechanism is terminated when trion complexes are dissociated either by thermal excitation or by scattering with free carriers in the quantum well. A simple phenomenological rate equation model allows us confirming the hypothesis of charge transport via a trion state and the proposed methods of termination.

A-P46 RELAXATION OF NANODEFORMATIONS PRODUCED ON PMMA THIN FILMS NEAR THE GLASS TRANSITION R. Leal , R. M. Papaléo; Faculdade de Física, PUCRS, Av Ipiranga 6681, 90619-900 Porto Alegre; -RS, Brasil.

Individual heavy ions impacting polymers and other organic materials at high energies leave at the surface nanometer-sized craters often surrounded by a raised region of displaced material (rims). In this work, we report on measurements of relaxation times of such features near the glass transition. PMMA thin films were bombarded by 20 MeV Au ions at grazing angles at different temperatures (75, 84, 91, 93, 95 and 100°C) and low fluences (~109 ions/cm-2). The targets are kept at the irradiation temperature for a certain period of time before the samples are quenched to room temperature (where PMMA is a glass and structural relaxation of the chains is virtually stopped). By irradiating a series of samples at a fixed temperature, each annealed during a different time, the average dimensions of the crater and rims can be extracted from SFM images and plotted as a function of annealing time, t. The relaxation of the protusions follows roughly an exponential law ( exp(-t/), where is identified as an average characteristic relaxation time. Extracted values of were smaller than 2s at 100°C and around 48h at 75°C, in accordance to what is expected for macroscopic deformations in PMMA. Some parts of the rims surrounding the middle of craters relax much more slowly, probably because of the severe chemical modification of the chains in the core of the impact.

A-P47 PHOTOLUMINESCENCE OF NANOCRYSTALLINE TUNGSTEN DOPED ZT Rubens S.G.1, Zaghete M.A2, Sidey J.L.R.3, Santos D. M.4, Paiva_Santos C.O2 , Siqueira J. R.R4, Varela J.A.2, Longo E.6

1Department of Mechanical and Material (DMM) - Centro Federal de Educação Tecnológica do

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Maranhão (CEFET-MA) - São Luís, MA, Brazil; 2 Centro Multidisciplinar de Desenvolvimento de Materiais Cerâmicos (CMDMC) - Instituto de Química- UNESP, C.Postal 355,14801-970 Araraquara,SP, Brazil; 3 Departamento de Química Geral e Inorgânica - Instituto de Química- UNESP, Araraquara,SP, Brazil; 4 Universidade Federal do Maranhão (UFMA); São Luís, MA, Brazil ; 5 Universidade Estadual de Mato Grosso do Sul (UEMS), Brazil; 6 Centro Multidisciplinar de Desenvolvimento de Materiais Cerâmicos (CMDMC) - Department of Chemistry, Universidade Federal de São Carlos, C.Postal 676 13565-905, São Carlos, SP, Brazil.

Photoluminescence studies of tungsten doped ZT powders are presented. The polymeric precursor method was used to synthesize the ZT powders. The polyester precursor was decomposed at low temperature to obtain the “amorphous” phase. The experimental results suggest that the visible photoluminescence emission, at room temperature, could be related to the disorganization of the atoms in the structure. Which is in the interface between amorphous and crystalline state. The photoluminescence properties were investigated and correlated with amount of dopant and annealing temperature. The optical gap and the energy constant were calculated using the Wood and Tauc method whereas the absorption coefficient,, was obtained Kubelka-Mulk model. Both constants were calculated using the UV_vis data. The powders were also characterized by DRX, IR.Keywords: none structured, ZT, Photoluminescence, amorphous structure, optical gap

A-P48 STUDY OF NiFe/WTi MULTILAYERS BY XMCD V. P. Nascimento, 1A. D. Alvarenga, M. Morales, E. Baggio Saitovitch, Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, RJ, 22290-180; A. Biondo, Depto. de Física do CCE/UFES, Av. Fernado Ferrari, Campus de Goiabeira, Vitória, ES, 29060-900; A.R.B. de Castro, LNLS, Rua Giuseppe Máximo Scolfaro 10000, Campinas, SP, 13083-100; Universidade Estadual de Campinas – UNICAMP, Campinas, SP, Brazil.

The investigation of spin-dependent phenomena in magnetic materials has being intensively enhanced by the use of circularly polarized synchrotron radiation. Here we report investigations on the magnetism of NiFe/WTi multilayers prepared by Magnetron Sputtering. These multilayers have great interest for magnetoresistive devices based on antiferromagnetic coupling and giant magnetoresistance, which depend sensitively on interface structure and film morphology. XMCD measurements were performed in order to study the interfacial spin configuration. The XMCD experiments gives a magnetic depth profile; few layers of material are removed by in situ sputtering, followed by XMCD measurements at the Fe and Ni L2, 3 edges. For complementary analysis X-ray diffraction, magnetization (VSM), magnetoresistance and ferromagnetic resonance (FMR) measurements are also discussed. The results give evidence of a NiFe dead layer at the interface.

A-P49 NEW ELECTRODE MATERIAL FOR THE ELECTROCHEMICAL DETERMINATION OF 2,4 DICLOROPHENOXYACETIC ACID HERBICIDE (2,4D)*F. R. Simões1,2, 1Programa Interunidades em Ciência e Engenharia de Materiais- IFSC-USPCaixa Postal: 369. 13560-970 São Carlos, SP, Brasil. C. M. P. Vaz2, 2Embrapa Instrumentação

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Agropecuária Caixa Postal:741, CEP:13560-970 São Carlos, SP, Brasil.

Conducting polymers have been used in many technological and scientific research applications. Due to the necessity of active materials and great demand for different applications, the conducting polymer allows an increasing of versatility for the construction of sensors. In agriculture, in particular, the uncontrolled use of pesticide has been causing a great environmental impact, as for example the groundwater and surface water contamination. The most popular methods of pesticide analysis are the chromatographics mainly the HPLC and gas chromatography. These methods are sensible and selective, but they are laborious and expensive. Electroanalytical techniques have also been used as methods for pesticides determination in natural waters, soils, vegetables, fruits and other matrices. The main advantage of this method is the possibility of determining its concentration without previous treatments or separations. This work presents a new modified electrode for the determination of the herbicide 2,4 diclorophenoxyacetic acid (2,4D). This compound is known as not electroactive in electrodes as mercury, platinum and carbon (glassy, fiber or paste), but a new composite material consisting of carbon paste electrode and the conducting polymer polyaniline (PANI) was prepared, showing electroactivy and therefore, the possibility of the pesticide determination using electrochemical techniques. The analyses of the herbicide was carried out through cyclic voltammetry (C.V) in different pHs. The results showed good sensitivity and selectivity.*Correspondências devem ser enviadas no endereço abaixo:R. Carlos S. Rodrigues n.75 apto 21. CEP 13574-580 São Carlos, SP, Brasil.

A-P50 POLYMER-LIGHT EMITTING DIODES IN ITO/MEH-PPV/Al STRUCTURESJ. A. R. Neves, E. A. T. Dirani, F. J. Fonseca, A. M.Andrade; Av. Luciano Gualberto, travessa 3, nº 158, Cidade Universitária, São Paulo/SP, CEP 05424-970, jrocha@lme.usp.br

This work, is aimed to study and develop electroluminescence polymeric devices, such as polymer light emitting diodes (PLEDs). These devices are of interest because of their comercial application, for example, in the manufacturing of large area, slim, light and flexible displays. They can also offer potential low cost compared to the present available technology. All devices presented in this work were processed in matricial shape, using photolithography techniques, in order to study and develop procedures for displays production. The polymer used as emissive coating of the device was the poly (2-methoxy 5-(2’-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) and the process of coating deposition was made by spin casting of liquid solution on substrate. For the device manufacturing, it was necessary to study the characteristic of the various coating components through optical and electrical measurements. The process variables analysed were the polymeric film thickness, deposition uniformity, polymeric solution concentration, superficial roughness of the hole injector electrode and device packaging. In these processed devices, the best obtained electrical characteristics for the structure formed by ITO/MEH-PPV/Al were the operation voltage about 7 volts with currents close to 0.2 mA. These results show that the improvment in the PLED’s characteristics is associated to the uniformity and thickness of the polymeric coating (MEH-PPV), carrier injection and device packaging.

A-P51 IONENE-MODIFIED BENTONITE AS A TOOL IN THE ADSORPTION OF ORGANIC POLLUTANTSA.P.Costa Filho*1,2; A.S.Gomes; and F.E.Lucas. 1Instituto de Macromoléculas, Centro de Tecnologia, Universidade Federal do Rio de Janeiro, Bloco J, Ilha do Fundão, Rio de Janeiro, C. P.

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68525, CEP 21945-570, Brasil. 2Tecnologia Química, Universidade Federal do Maranhão-CT, Campus do Bacanga S/N, São Luís, Maranhão, Brasil.* araofilho@terra.com.br

The adsorption of organic pollutants in polycation-modified clays is a well known technique. In this work, a sodium bentonite, (having CEC= 96 meq/100 g clay as determined by X-Ray fluorescence) was treated with ionene-like polycations containing different spacers, those being synthesized according to the Menshutkin reaction. Those polymers were characterized using FT-IR, NMR 1H, 13C and UV visible (for assessing the molecular weight), TGA and elemental analysis.The modified clays were analyzed by FT-IR, TGA, fluorescence and X-Ray diffraction. Data confirm polymer intercalation in the clay, configuring a polymeric net between the mineral interlamellar spaces. These materials find potential application in the absorption of organic pollutants such as benzene, toluene, p-nitrophenol, and the like.Acknowledgments:CAPES/UFMA/FINEP/CTPETRO, CNPQ/RENAMI

A-P52 SIMULATION ENVIRONMENT FOR INVESTIGATING ADSORPTION MECHANISMS IN LAYER-BY-LAYER FILMS.Linder C. DaSilv a , Osvaldo N. Oliveira Jr. and Luciano da F. Costa. IFSC – USP , Caixa Postal 369, São Carlos, SP, 13570-970 Brazil

A computational environment is described which is aimed at simulating adsorption processes in layer-by-layer films obtained via physical adsorption of charged polymers. Consistent with experimental data, the mechanism of adsorption is treated at the nanoscopic level, with adsorption of polymer aggregates as they appear in an aqueous solution. Simulations can be made for aggregates of any shape and with a generic polydispersity for circular particles. When the ballistic deposition is applied, interpenetration between adjacent layers occurs, which may explain adsorption data for polyelectrolytes. The morphological characteristics of simulated films such as porosity, degree of interpenetration and roughness are obtained by defining the film/air interface with the Euclidean distance transform. These features allow the verification of scaling laws. Correlation can also be made between the morphological properties of the aggregates and the shape functionals of individual particles as a means to predict the overall properties of the film. The system is generic and may be extended to any process of surface growth. The tools are developed under the Scilab environment incorporating C routines for the bottleneck processing. A graphic-interactive interface will be developed to foster collaboration with material scientists.

A-P53 ELECTRICAL PERCOLATION DURING GELATION OF LITHIUM-DOPED SILOXANE-POLY(OXYETHYLENE) HYBRIDSA.P Sacco, Instituto de Química, UNESP, C.P 355, Araraquara-SP, Brazil; K. Dahmouche, Instituto de Química, UNESP, C.P 355, Araraquara-SP, Brazil; C.V Santilli, Instituto de Química, UNESP, C.P 355, Araraquara-SP, Brazil; S.H Pulcinelli, Instituto de Química, UNESP, C.P 355, Araraquara-SP, Brazil

Gelation mechanisms of lithium-doped Siloxane-Poly(oxyethylene) (PEO) hybrids containing polymer of two different molecular weight (500 g/mol and 1900 g/mol) were investigated through the evolution of the electrical properties of the materials during the sol-gel transition. The electrical investigation, performed by in-situ complex impedance spectroscopy, was correlated with the local coordination and the dynamical properties of the lithium ions during the process performed by 7Li NMR measurements. For both hybrids sols, a decrease of the conductivity is observed at the initial gelation stage, due to the existence of an inverted percolation process consisting of the progressive separation of solvent molecules containing conducting species in isolated islands during the solid network formation. An increase of conductivity occurs at more advanced stages of gelation and aging, attributed to the increasing connectivity between PEO chains promoted by the formation of crosslinks of siloxane particles at their extremities, favoring hopping motions of lithium ions along the chains.

A-P54 NYLON-6 / CLAY (NANO)COMPOSITES PREPARED BY MELT INTERCALATIONT. J. A. Mélo; E. M. Araújo; M. P. Baracuhy, L. H. Carvalho, Departamento de Engenharia de Materiais, Universidade Federal de Campina Grande, Av. Aprígio Veloso, 882, Bodocongó, Caixa Postal 10034, 58109-970 Campina Grande, Brazil. tomas@dema.ufcg.edu.br

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Nanocomposites of nylon-6 were prepared by melt blending the polymer with imported Na+ montmorillonite and montmorillonite modified by quaternary ammonium salt. The nanocomposites were obtained by mixing in a Haake closed mixer at 240°C and 60 rpm for 10min, with 3wt% of clay. The effects of the incorporation of clay were observed by X-ray diffraction, Fourier transform infrared (FTIR) analysis and mechanical properties. The results from X-ray and FTIR suggest that has occurred intercalation of the salt but the mechanical properties no showed significant changes. This might be due the processing conditions are not enough to provide an appropriate nanometric dispersion of clay layers and an homogeneous distribution of the clay in the samples.

A-P55 INFLUENCE OF ORGANO-BENTONITE CLAY ON THE PROCESSING AND MECHANICAL PROPERTIES OF NYLON 6 AND POLYSTYRENE COMPOSITESE.M. Araújo 1; T.J.A. Mélo 1; L.N.L. Santana 1; G.A. Neves 1; H.C. Ferreira1; H.L. Lira 1; L.H Carvalho1; M.M. A’vila Jr.,2; M.K.G. Pontes, 2; I.S. Araújo,2; 1DEMa/CCT/UFCG – C.Postal 10034, CEP 58109-970, Campina Grande, PB edcleide@dema.ufcg.edu.br; 2 Students of the Materials Engineering/UFCG

The development and characterisation of nanostructured polymer-clay composites has received special attention in recent years. Organoclays consist of a clay that has been modified with quaternary amine cations. Influence of organoclay on the processing and mechanical properties of nylon 6 and polystyrene was investigated. A bentonite sample from Boa Vista/PB, Northeast of Brazil, was treated by ion exchange with alkyldimethylbenzylammonium chloride quaternary ammonium salts. After the modifying, the powder was characterised by infrared spectroscopy, analysis chemistry, thermal analysis and X-ray diffraction. Composites were prepared using a Haake Blucher Torque Rheometer. The results evidence the effective intercalation of quaternary ammonium salt in the structure of bentonite and show that the organo-bentonite produced significant changes on the processing of the nylon 6 with increase in the viscosity and rigidity. However, the mechanical properties of polystyrene/organoclay system no showed significantly changes.

A-P56 CHARACTERISTICS OF ELECTRICAL TRANSPORT IN SOL-GEL DIP-COATING SnO2

EXCITED BY ULTRAVIOLET SOURCESV. Geraldo 1, T. J. Pereira2, L. V. A. Scalvi 2, P.B. Miranda 1 and C. V. Santilli3 ; 1 I. Física de S. Carlos–USP, C.P. 369, 13560-970 S. Carlos SP; 2 D.Física – Fac. Ciências, UNESP, C. P. 473, 17033-360 Bauru SP; 3 I. Química -UNESP, C. P. 355, 14801-970, Araquarara SP,Brazil Technological interest on tin dioxide has grown due to large application in devices. Our films are deposited via sol-gel with nanocrystalline grains (3-7 nm), and present n-type conduction, due to oxygen vacancies and/or Sb doping, and interesting nanoscopic transport properties. In this communication we report photoconductivity of SnO2 film, excited in the range 70-200 K, by using the fourth harmonic of a Nd:YAG laser (266nm). The conductivity increases up to 40 times under laser irradiation until practically saturates. After removing the illumination, the conductivity remains unchanged as long as the temperature is kept constant. Film conductivity only changes when the temperature is increased. The return to original values after a few hours discharge possibilities of local structural effects such as laser induced burns. The photocurrent spectra in the range 200-400nm, obtained by using a deuterium source, yields a band around 240nm, which is temperature dependent. The explanation for these results is related to optical absorption of SnO 2 in conjunction with recombination of photogenerated electron-hole pairs with grain boundary adsorbed oxygen. Adsorbed oxygen recombines with holes and the resulting gaseous specimen is continuously eliminated from the system by the vacuum pumping.

A-P57 EFFECT OF GAMMA IRRADIATION ON OPTICAL PROPERTIES OF POLY(P-PHENYLENEVINYLENE) SOLUTIONSEric A. B Silva.;. C F. O. Graeff.; . P Nicolucci;. T. G Netto; Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Univ. São Paulo, Avenida Bandeirantes 3900, Ribeirão Preto- SP/Brazil

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R. F Bianchi; R. M. Farias, D. T. Balogh; Instituto de Física de São Carlos, Univ. São Paulo, São Carlos-SP, Brazil

Conjugated polymers have nowadays a vast field of technological applications, however there are still few applications of them in medicine as sensors and detectors of ionizing radiation, for example. In this work we use a conducting polymer: poly[2-methoxy,5-(2-ethyl-hexyloxy – p - phenylenevinylene] (MEH-PPV) for the detection of ionizing radiation, by means of spectroscopic methods such as: (Uv-vis) absorption, photoluminescence (PL) and (FTIR) infrared absorption. The samples have being prepared in films, deposited by spin-coating as well as in solution dissolved in CHCL3. We have found that oxygen plays an important rule in the process of photo-degradation of the material exposed to ionizing radiation. It was found a displacement in the absorption band proportional to radiation dose absorbed from 493 nm up 467 nm for a dose between 0 and 45Gy. This displacement is followed by other changes in the UV-VIS absorption spectra, attributed to the replacement of C=C by C=O bonds. Both FTIR absorption and photoluminescence spectroscopy confirmed this substitution. These results suggest the potential of this material as ionizing radiation detectors.

A-P58 ORGANO-INORGANIC NANOCOMPOSITE ALTERNATING -GERMANIUM HYDROGENPHOSPHATE LAYERS AND NYLON-6 CHAINS R. Romano, O. L. Alves, Laboratótio de Química do Estado Sólido, Instituto de Química, UNICAMP, CP 6154, 13083-970, Campinas, SP, Brasil.

A two-dimensional organo-inorganic nanocomposite was obtained by direct intercalation and polymerization of the monomer -aminocaproic acid inside the interlayer spaces of -germanium hydrogenphosphate. The inorganic host was prepared by refluxing germanium oxide and phosphoric acid during 125 hours, giving rise to a layered material showing an interlayer distance of 7,8 Å. The intercalation reaction was performed by sealing the host and the monomer inside an ample and heating the mixture firstly above the melting point of the later (230 oC), and then to the polymerization temperature (300 oC). The product presented a brown flocculated aspect suggesting external polymerization of the monomer. The solid was washed with formic acid, an acid capable of dissolving the external polymer, leading to a white powder. The removed polymer was characterized as nylon-6 by FTIR spectroscopy, while the white powder showed a new interlayer distance of 11,2 Å. The increment of 3.4 Å was consistent with the intercalation of a single chain of this polymer. The FTIR spectroscopy confirms the presence of intercalated chain of nylon-6 by detecting characteristic bands and the maintenance of the chemical nature of the layered phosphate.

A-P59 THE INFLUENCE OF SOLVENT ANNEALING TIME TO PULLING DOWN OF ADSORBED CYLINDRICAL MICELLES.M. A. Pereira-da-Silva, IFSC/USP, CP 369, 13560-970, São Carlos SP Brasil; S. S. Sheiko, Univ N Carolina, Dept Chem, CB 3290, Chapel Hill, NC 27599 USA

Block copolymers form micelles which shape depends on the relation between the degree o polymerization of the two components. The adsorption of micelles to a solid substrate and the atomic force microscopy visualization technique give the possibility to image and 3D measure the micelle shape evolution during pulling down process under influence of solvent annealing. In this work it was used a block copolymer composed by polystyrene and polyisoprene being different polymerization degree(PD): PDPS=404 for polystyrene and PDPI=147 for polyisoprene. To obtain a micelle from a copolymer solution it is needed to find a solvent that is a good solvent for only one of the two parts of block copolymer. For this work it was chosen the N-heptane, which is a good solvent for polyisoprene and a bad solvent for polystirene. Therefore, the formed micelle should show a central portion of polystyrene and a polyisoprene corona. In the present work, PD PS/PDPI = 2.75, we verified that formed micelles are cylinder shaped. This work shows the quantitative shape evaluation during pulling down process under influence of solvent annealing

A-P60 PALLADIUM-SILICA AND PALLADIUM-TITANIUM COMPOSITES PREPARED BY THE SOL-GEL METHOD: EFFECT OF THE SUPPORT AND OF THE THERMAL TREATMENT ON THE CATALYTIC ACTIVITY E. V. Gusevskaya; José Aílton Gonçalves, Departamento de Química, UFMG, Belo Horizonte,

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MG; P.A. Robles-Dutenhefner; D. L. Nunes, V. K. Moreira; M. G. Speziali and E. M. B. Sousa, Centro de Desenvolvimento da Tecnologia Nuclear, CDTN/CNEN, R. Mario Werneck s/n, Campus Universitário, 30123-970, Belo Horizonte, MG.

Composites of silica and titanium doped with palladium were prepared by the sol-gel method. The materials were characterized by a powder X-Ray diffraction, nitrogen adsorption and scanning electronic microscopy. Catalytic behavior of the gels was investigated in the oxidation of limonene with dioxygen, in acetic acid solutions. For the sample treated at 300 and 1100oC, the XRD patterns showed the presence of metallic palladium dispersed in amorphous matrix of the silica.The XRD patterns for the sample treated at 500 and 900oC showed the presence of the palladium oxide phase. The catalysts treated at 500 and 900oC showed a catalytic activity in the limonene oxidation. The main products are cis and trans- carveyl acetate. The relation between cis/trans carveyl acetate is influenced by the support. (CNPQ, FAPEMIG)

A-P61 PALLADIUM-TITANIUM COMPOSITES OBTAINED BY SOL-GEL METHOD: CATALYTIC ACTIVITY IN THE CICLOOCTADIENE (COD) HYDROGENATIONP. A. Robles-Dutenhefner, D. L. Nunes, V. K. Saraiva, M. G. Speziali and E. M. B. Sousa, Centro de Desenvolvimento da Tecnologia Nuclear–CDTN/CNEN. Rua Professor Mário Werneck, s/n. Campus Universitário – Belo Horizonte – MG, CEP 30.123-970, Brazil

In this work, composites of palladium were prepared via sol-gel method. The samples were obtained from tetraethylorthosilicate (TEOS) or from tetraisopropylorthotitanate (TIOT) and the palladium was added in the proportions 1 and 3% (w/w). Gels samples were dried at 110 C and then thermally treated at 300, 500, 900 and 1100 C. The structural characteristics were studied by scanning electronic microscopy (SEM), X-ray diffraction (XRD) and nitrogen gas adsorption (BET). The catalytic activity of these materials was tested in the hydrogenation of ciclooctadiene as a model of polyunsaturated olefin. The samples treated at 300 and 1100oC showed catalytic activity due the presence of metallic palladium phase according to the XRD patterns. Although, the selectivity to ciclooctadiene (monohydrogenated product) have been affected by morphology of the catalyst.

A-P63 EFFECT OF PRESENCE OF AN ACID CATALYST ON STRUCTURE AND PROPERTIES OF IRON-DOPED SILOXANE-POLYOXYETHYLENE NANOCOMPOSITES PREPARED BY SOL-GELL. A. Chiavacci, Instituto de Química, UNESP, Araraquara-SP, Brazil; K. Dahmouche, Instituto de Química, UNESP, Araraquara-SP, Brazil; N.J.O. Silva, Departamento de Física, Universidade de Aveiro, Aveiro, Portugal; L. D. Carlos, Departamento de Física, Universidade de Aveiro, Aveiro, Portugal; C.V. Santilli, Instituto de Química, UNESP, Araraquara-SP, Brazil; V. Briois, LURE, Université Paris-Sud, Orsay, France, A.F. Craievich, Instituto de Física, USP, São Paulo-SP, Brazil.

In this work we investigate the effect of addition of hydrochloric acid (HCl) on the structure and on the thermal and magnetic properties of iron-doped siloxane-polyoxyethylene (POE) hybrids prepared by sol-gel route. X-ray powder diffraction (XRD) and X-ray absorption near edge structure (XANES) results reveal the predominance of ferrihydrite nanoparticles and a mixture of this phase with FeCl4

- species in the hybrid prepared without and with HCl, respectively. Thermal analysis reveals the existence of two polymeric crystalline phases in the hybrid prepared with HCl, whereas hybrids prepared without HCl are amorphous. The existence of 105 and 60 Å sized ferrihydrite nanoparticles was detected by small-angle X-ray scattering (SAXS) analysis of the composites prepared without and with HCl, respectively. The magnetic results suggest that in both samples antiferromagnetic nanoparticles coexist with small clusters/isolated ions. In the sample without HCl addition, larger particles dominate the magnetic behaviour, while the opposite occurs for the sample prepared using HCl catalyst.

A-P64 SYNTHESIS OF THIOL FUNCTIONALIZED TITANIA-SILICA WITH NANOPORES BY USING POLYMERIC SPHERES AS TEMPLATERobson Fernandes de Farias 1 and Cláudio Airoldi 2; 1 Departamento de Química, UFRR 69310-270 Boa Vista, RR; 2 Instituto de Química, UNICAMP

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The sol-gel process have been successfully employed to the preparation of a series of doublé oxides with regular nanostructure [1-4], including titânia, due to its many applications, such as photocatalyst. In this work is reported the synthesis of a titania-silica inorganic-organic hybrid matrix, functionalized with thiol groups. Such matrix exhibits a porous nanostructure, with pores from 200 to 500 nm. The matrix is obtained through sol-gel process, by using titanium and thiol functionalized silicon alkoxydes. The porous nanostructure is achieved by using polymeric spheres as template. The main purpose of such preparations is to obtain a hybrid matrix with several functions, able to act as photocalalyst, as well as soft metals sequestrating agent.[1] R. de Faria, et al., J. Phys. Chem. Solids, in press. [2] R. F. de Farias, Int. J. Inorg. Mater., 2001, 3, 825. [3] R. F. de Farias, J. Non-Cryst. Solids, 2001, 288, 218, [4] R. F. de Farias, C. Airoldi, J. Solid State Chem., 2001, 158, 134.

A-P65 MAGNETIC PROPERTIES OF ACICULAR Fe1-XREX (RE = Nd, Sm, Eu, Tb; x = 0, 0.05, 0.15) METALLIC NANOPARTICLES.L.C. Varanda, M. Jafelicci Jr, Instituto de Química, UNESP, CP 355, Araraquara, 14801-970 SP, Brazil; G.F. Goya, Instituto de Física, USP, CP 66318, São Paulo 05315-970 SP, Brazil; M. Imaizumi, Depto de Física FC, UNESP, Av. Luiz Edmundo Carrijo Coube, s/n, Bauru 17033-360 SP, Brazil; M.P. Morales, C.J. Serna, Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco 28049, Spain.

Acicular monodispersed Fe1-xREx (RE= Nd, Sm, Eu, Tb; x = 0, 0.05, 0.15) metallic nanoparticles 60±5 nm in lenght and axial ratio ~6 have been obtained by reduction of alumina-coated goethite nanoparticles containing the RE elements under hidrogen flow at 450 oC/10 h. Metallic nanoparticles were protected against synthering by alumina thin layer on particle surface and stabilized against surface oxidation with nitrogen-containing ethanol vapor atmosphere at room temperature. Al and RE additions were obained by sucessive heterocoagulation reactions. Narrow particle size distribution was observed by TEM and the presence of Al and RE elements were confirmed by ICP analysis. X-ray diffraction, Mössbauer and magnetization data are in agreement with the nanosized -Fe core, having a spinel structure, -Fe2O3, on particle surface. Main magnetic parameters show decreasing in the saturation magnetization and significative increasing in the coercivity with the increase in the RE compositions. Magnetic properties of the particles, ~40% smaller than those commercially available, suggest a decrease in the bit-size for high density magnetic or magneto-optic recording media application. Fapesp

A-P66 MAGNETIC AND STRUCTURAL PROPERTIES OF NANOESTRUCTURED FeAlNiMn QUATERNARY ALLOY OBTAINED BY HIGH-ENERGY MECHANICAL MILLING J.F.M. Borges, Departamento de Física - UEPG, Av. Carlos Cavalcanti, 4748, Uvaranas, Ponta Grossa, PR, Brazil,CEP:84030-900, fborges@uepg.br; C.Larica, Departamento de Física- UFES,

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Av.Fernando Ferrari, Campus Goiabeiras, Vitória, ES, Brazil, A. Paesano Jr., Departamento de Física - UEM, Av. Colombo, 5790 – CEP: 87.020-900, Maringá – PR – Brazil. Due to a high degree of structural complexity, quaternary alloys present an interesting field for investigation of phase formation and magnetic behaviour. On the other side, the high-energy ball-milling is a powerful method to prepare supersaturated or granular alloys, amorphous materials and metastable phases. This technique also provides the conditions for the formation of disordered crystalline phases with grain size of some nanometers. In this sense, this work shows preliminary results of a structural and magnetic characterization of a FeAlNiMn quaternary alloy obtained by high-energy ball-milling. The samples were prepared with high purity iron, aluminum, nickel and manganese powders, with nominal composition of 25 at.% for each element, and manipulated inside a glove box under high purity argon atmosphere. At regular intervals during the milling process, small amounts of the milled samples were collected from the vial. The structural, hyperfine and magnetic characterizations of the milled materials were performed by X-ray Diffraction, Vibrating Sample Magnetometry and Mössbauer Spectroscopy, at room temperature. It can be observed, from the X-ray diffractometry results, a possible interdiffusion of aluminum in the iron-nickel alloy. In addition, the broadening of the FeNi diffraction peaks suggests a grain size reduction with increasing milling time. From the Mössbauer spectra, it was also identified a paramagnetic contribution, which suggests an interdifusion of aluminium in the iron clusters.

A-P67 UNIDIRECTIONAL ANISOTROPY AND COERCIVITY ENHANCEMENT IN NANOCRYSTALLINE POWDERS OF MnO/-FeCoEduardo Padrón Hernández, Daniel R. Cornejo , Sergio M. Rezende; Laboratório de Magnetismo e Materiais Magnéticos, Departamento de Física, UFPE, 50670-901, Recife, PE, Brasil, Pós-Graduação em Ciência de Materiais, UFPE CEP 50670-901, Recife, PE, Brasil

Isotropic nanocrystalline heterogeneous magnetic powders of MnO + FeCo were obtained by mechanical alloying in normal atmosphere from high-purity Mn, Fe and Co elements. After to milling, the material consists of micrometric particles with exchange-coupled nanocrystalline grains of MnO and -Fe40Co60 as determined by x-ray diffraction and Mössbauer spectroscopy. The hysteresis loop obtained by VSM in the as-milled powder showed clear unidirectional anisotropy phenomena when the temperature of the sample is smaller than the Néel temperature of the MnO, approximately 120 K. The as-milled powders were cold pressed and annealed at 700 K for different times in vacuum. Although the exchange-bias field is smaller in the annealed materials, samples with times of annealing below to three hours show a noticeable improvement of the coercivity, even to room temperature. The mechanism for this coercivity enhancement effect can be linked to the substantially high anisotropy field produced by the unidirectional anisotropy, and the favorable fine structure originated during the milling process. Also, a strong effect the spin wave stiffness constant of the ferromagnetic FeCo, induced by the antiferromagnetic ordering of the MnO at 120 K was observed. A modified Preisach model was implemented in order to describe the hysteresis behavior of these exchange-biased materials.

A-P68 DIPOLAR MAGNETIC INTERACTIONS AMONG MAGNETIC WIRESR. Piccin, A. E.P. de Araújo and M. Knobel, Universidade Estadual de Campinas, C.P. 6165, 13.083-970 Campinas, São Paulo, Brazil

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In an amorphous magnetic wire produced by quenching melt technique, the magnetic domain configuration consists of an axial core in a remnant state and an outer shell with a bamboo-like structure. In the axial direction these wires present single and large Barkhausen jump. Such characteristics allow us to use several ferromagnetic wires as an analogous of an array of spins. The stray fields couple the magnetizations of the wires, affecting their magnetic state. Although this system seems to be rather simple, it displays a variety of interesting aspects that apply to magnetic systems. In this work, we present a study of the magnetic properties of arrays formed by Fe77.5Si7.5B15 wires. The array presents jumps and plateau on their hysteresis loops due the dipolar interaction among the wires [1]. The jumps correspond to the inversion of the core magnetization in each wire. Theoretical calculations were also performed applying a single model concerning the effective field, applied field plus the dipolar field produced by the neighbor wires, during the magnetization process. Such results are discussed in comparison with experimental data. The authors thank to FAPESP by the financial support.1 - L.C. Sampaio, E.H.C.P. Sinnecker, G.R.C. Cernicchiaro, M. Knobel, M. Vazquez and J. Velazquez, Phys. Rev. B 61 (13) 8976 (2000).

A-P69 STRUCTURAL AND MAGNETOTRANSPORT PROPERTIES OF Co/SiO2 GRANULAR MULTILAYERSJ.C. Denardin, L. M. Socolovsky, M. Knobel, Unicamp, PO Box 6165, Campinas (SP) 13083-970 – Brazil; L.S. Dorneles, L.F. Schelp, Departamento de Física, CCNE, UFSM, Santa Maria, RS, Brazil

The increase of density requirements in the magnetic data storage has motivated the research of nanostructured magnetic devices. Granular films consisting of magnetic nanoparticles in an insulating matrix could present promising features for ultrahigh density magnetic recording media, respecting the superparamagnetic limit and the effect of dipolar interactions. Cosputtering or coevaporation is a common method to fabricate these granular solids. It usually results in a random distribution of clusters in the matrix, with a large dispersion of grain sizes and distances. We have used an alternative method to fabricate granular multilayer, consisting of successive planes of nanosized cobalt clusters embedded in SiO2 and produced by sequential deposition. Varying the nominal thickness of Co and SiO2 layers we obtained several different samples, ranging from insulating to metallic. Transmission electon microscopy (TEM) images show that the most insulating samples are composed of periodicaly arranged, and almost monodisperse, Co nanoparticles with 3nm in diameter. Measurements of resistivity vs. temperature, Hall effect, magnetoresistance and magnetization were made in the temperature range of 5 - 300 K, and fields up to 7 T. Relationships between the nanostructure and magnetotransport properties are discussed and compared with previous results obtained in cosputtered films.

A-P70 PRODUCTION OF MAGNETIC NANOSTRUCTURED MATERIALS USING HOLOGRAPHIC LITHOGRAPHYL.M. Socolovsky, A.E.P. de Araújo, W. O. Rosa, M. Knobel, E.J. Carvalho and L. Cescato, IFGW UNICAMP Cx. Postal 6165 CEP 13085-970 Campinas, SP.

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The study of the magnetic interactions of the structures in the nanometric scale gives important contributions to improvement of the nanotechnologies. In this work we present the development of a technique to grow magnetic periodic patterns using holographic lithography. An advantage of this technique is the large area of the pattern which can has an aspect ratio smaller than 30 nm in an area up to of the order of 1000 cm2 [1]. It is based on the selective exposing of a resistive layer to an interference pattern from two coherent lasers. For Usually to produce metallic samples we need to combine this technique with electroplating. The idea is to use the fotoresistent resin as the building block for the magnetic patterned material. We prepared two kinds of samples, one using Nd-Fe-B powder and the other one with Fe-Cu powder. For the Nd-Fe-B we obtained powder of 500 nm and in the case of iron we use an additional Cu powder to obtain grains smaller than 50 nm. These powders were mixed with the fotoresine and deposited in a glass substrate using a spinner. After this we characterize the distribution of the grain dimensions with an electronic scanning microscope, and the transport and magnetization measurements were made using a SQUID magnetometer. The effect of the grain size in the line-patterned material on the magnetic properties will be discussed. The authors thank to FAPESP by the financial support. [1] J.I. Martín et al, J. Magn. Magn. Mater. 256 (2003) 449.

A-P71 FLASH EVAPORATED PbTe THIN FILMS IN DIFFERENT STOICHIOMETRY FOR THERMAL INFRARED SENSORS APLICATIONSJ. M. K. Assis1,2, S. Guimarães1; F. C. L. Melo1, N. G. Ferreira1; 1) Instituto Nacional de Pesquisas Espaciais INPE/LAS, CP 515, 12245-970, São José dos Campos, SP, Brazil; 2) Centro Técnico Aeroespacial CTA/IAE/AMR, Pça Marechal Eduardo Gomes, 50, Cep 12228-904, São José dos Campos, SP, Brazil.

Flash Evaporation is an easer and cheaper method for depositing compound such as GaAs and PbTe when compared to Hot Wall Epitaxy or Molecular Beam Epitaxy techniques. In this process the constituents have a high vapor pressure and where it is important to maintain the deposit stoichiometry. PbTe thin films were deposited on silicon and porous silicon substrates. Porous samples were obtained by stain etching technique on (100) p+- type boron doped wafer, which produces a nanostructured surface with a lower stress. This procedure is important for relaxing the natural stress between PbTe films and monocrystalline silicon, mainly due to the lattice mismatch. Semiconductors PbXTeX-1 stoichiometry in the range of x= 0.504 up to 0.508 are flash evaporated by keeping evaporation pressure of around 10-5 torr. Similar films were also evaporated on Si wafer with high resistivity (103 to 6 x 103 .cm) in order to characterize the type of epilayer using Hall Effect measurements. Film morphology and crystalline quality were also analyzed by Scanning Electron Microscopy (SEM) and X-Ray Diffraction, respectively. Film thickness may be estimated with the weigh of the evaporated material and is confirmed by using Fourier Transformed Infrared (FTIR) and Perfilometry techniques.

A-P72 ACCURATE MEASUREMENT OF Ag+/K+ ION-EXCHANGED GLASS WAVEGUIDES BY EDS, M-LINE AND DNS-B METHODS UP TO THE NEAR-SURFACE REGIONM.B. Pereira, F. Horowitz, PGCIMAT and Instituto de Física, UFRGS, Campus do Vale, CP 15051, 91501-970 Porto Alegre, RS, Brasil

In the description of the refractive index profile of ion-exchanged waveguides, we evaluate the accuracy of the standard m-line method (micro-probing range) by comparing its results with those from Energy Dispersion Spectroscopy (EDS) and Direct Near-Surface/Extended Brewster-Pfund (DNS-B) Method (nano-probing range). Looking at single and double-exchange processes, the comparison shows three major situations: (i) the m-line accuracy is validated by the other two methods; (ii) discontinuity of ion-concentration does not allow the assumption of a continuous refractive index profile; or (iii) although the overall m-line profile is compatible with results from the other two methods, these may significantly depart by a near-surface inflection – in which case, the DNS-B Method can be used with the m-line experimental data to produce a more accurate index profile, including the nanometric near-surface region.

A-P73 GROWTH OF METALLIC Ag PARTICLES IN FLUOROBORATE GLASSESLuz P. N. Riano 1 , Marcos A. Couto dos Santos4, Fred Cunha4, Oscar L. Malta2, Petrus Santa Cruz2

and Cid B de Araújo3; 1Programa de Ciência dos Materiais / Universidade Federal de Pernambuco,

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50670-901, Recife, PE, Brazil; 2Departamento de Química Fundamental / Universidade Federal de Pernambuco, 50670-901, Recife, PE, Brazil; 3Departamento de Física / Universidade Federal de Pernambuco, 50670-901, Recife, PE, Brazil; 4Departamento de Física/UFS, 49100-000, São Cristóvão, SE, Brazil. Ag-Eu and Ag-Pr doped fluoroborate glasses have been prepared following the procedure of powder fusion and thermal annealing. The presence of the Ag species and thermal annealing at 550 and 650 °C originate the growth of metallic Ag particles. The thermal-annealing time and corresponding particles sizes are different for each doped glass. Optical absorption, excitation and fluorescence were used for analysis of the plasmon band formation. Electronic microscopy was used to determine the particle concentration and their size distributions. The techniques used allowed to identify the presence of silver particles with diameter in the range of 70-200 nm.

A-P74 EVOLUTION OF THE CRYSTALLINITY Ni DOPED ZTSantos D.M1, Paiva_Santos C.O2, Siqueira J. R.R1, Rubens S.G4, Zaghethe M.A2, Varela J.A2, Longo E2; 1Universidade Federal do Maranhão (UFMA); São Luís, MA, Brazil; 2 CMDMC - Instituto de Química- UNESP, C.Postal 355,14801-970 Araraquara,SP, Brazil. Departamento de química, UFSCars, C.P.676, 13565-905 São Carlos, São Paulo, Brazil; 3 DMM - CEFET-MA - São Luís, MA, Brazil

Abstract. Recently, pure and doped zirconium titanate, ZrTiO4, ceramics have attracted great interest as dielectric resonators for satellite telecommunication ranging from cellular telephones to global positioning systems and as precursor for synthesis of lead zirconium (PZT). The effects of Ni concentration on powder of ZT prepared by polymeric precursor method have been studied. X-ray diffraction (XRD) and thermogravimetric analysis (TG) showed that powders with high crystallinity (>90%) are obtained after calcination at 750oC for 3 h. At 550oC, the XRD pattern shows a broad peak indicating nucleation of the ZT phase. With increasing calcination temperature, an increase in ZT crystallinity is observed. The Rietveld method was applied to determine significant variation in the crystallite size and microstrain of Ni doped ZT samples.Key words: ZT, dielectric, chemical synthesis, XRD, nanostructures.

A-P75 NIOBATE EXFOLIATION: A PROMISING ROUTE FOR HOLLOW TUBES SYNTHESISA. L. Shiguihara, M. A. Bizeto and V. R. L. Constantino, Departamento de Química Fundamental - Instituto de Química, Universidade de São Paulo, CP 26077, 05513-970, São Paulo – SP, Brazil

We have been studying the exfoliation of the layered phase H2K2Nb6O17 promoted by alkyl amines. The exfoliated lamellas can coil producing an hollow tubes depending on the pH and ionic strength of the medium. These tubes have interesting promising applications such as template for porous mesostructures, nanocasting, membranes for separation etc. In this work, the niobate exfoliation process was evaluated in aqueous solution of propylamine, n-butylamine and n-hexylamine at different concentrations. For each experiment two fractions were isolated: a solid fraction that remains seated after the exfoliated process and an aqueous dispersion of niobate particles. The characterization of each one of these systems was performed by x-ray diffraction, thermal analysis, electronic spectroscopy and scanning electron microscopy.It was observed that the formation of the exfoliated niobate particles dispersion is close related to the amine / H+-niobate ratio and carbon chain length. For each amine used, there is an optimal ratio where the exfoliation is more favorable than the intercalation process. The amine also seems to play an important role in the dispersion stabilization.Acknowledgments: FAPESP and CNPq

A-P76 AB INITIO CALCULATION OF THE PHOTOLUMINES-CENCE PROPERTIES OF SrO-DEFICIENT STRONTIUM TITANATEM. A. dos Santos, E. Orhan, F. M. Pontes C. D. Pinheiro, M. F. C. Gurgel, E. Longo, Laboratório

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Interdisciplinar de Eletroquímica e Cerâmica (LIEC), Departamento de Química, Universidade Federal de São Carlos, São Carlos-SP, Brazil. A Beltrán, J. Andrés, Departamento de Ciències Experimen-tals, Universitat Jaume I; PO Box 6029, Castelló, Spain

SrO-deficient Sr1-xTiO3-x powders (ST) was synthesized using polymeric precursor method and its photoluminescence (PL) properties were measured. The samples present an intensive PL at room temperature, due to a combinated radiative and non radiative decay process. First principles quantum mechanical technics were used to calculate the electronic structure of two ST periodic models in the light of the PL results. The first model stands for the crystalline stoichiometric phase, the second for the deficient one. The comparison of the DOS and band diagrams for both models gives keys to understand the PL of those deficient ST compounds. (FAPESP-CEPID, CNPq, CAPES)

A-P77 PREPARATION OF POROUS GLASS-CERAMICS WITH CALCIUM ORTHOVANADATE SKELETON USING VANADIUM PHOSPHATE GLASS AS PRECURSORI.O. Mazali, O.L. Alves, Laboratório de Química do Estado Sólido – LQES, IQ – UNICAMP, Campinas, SP, Brazil http://lqes.iqm.unicamp.br

The aim of this work was the preparation and characterization of porous glass-ceramics with skeleton of Ca3(VO4)2. This material has ferroelectric and luminophoric properties. Porous materials are important in several fields (catalysis, separation sciences, sensors) showing cooperative interactions when reactions are performed in confined porous ambient. Glass-ceramics (GC) were prepared by controlled crystallization of the glass system Li2O-V2O5-CaO-P2O5. The production of the porous glass-ceramic (PGC) involves the acid leaching of the soluble phases, to achieve a porous structure formed by the insoluble phase. The XRD data suggested the presence of the -Ca2P2O7 (-CPP), -Ca2V2O7 (-CPV) and LiCaPO4 phases. The acid leaching of the -CPP and -CPV phases was confirmed by the absence of bands at 725 cm-1 (IR) and at 880 cm-1 (Raman), respectively. The PGC exhibit bright green color due to residual -CPV. The IR and Raman data indicate that the skeleton of the PGC is constituted of Ca3(VO4)2, due to the presence of a very strong band at 898 cm-

1, attributed to (V-O) stretching mode of the VO43- groups and, additionally, vanadyl phosphate, as

minor phase. The SEM/EDX micrographs confirmed the porous structure of the monolithic Ca3(VO4)2. [This is a contribution of Millennium Institute of Complex Materials]

A-P78 MORPHOLOGICAL AND STRUCTURAL CHARACTERISTICS OF DIAZODYES AT THE AIR-WATER INTERFACE. IN-SITU BREWSTER ANGLE MICROSCOPY AND POLARIZED UV/VIS ANALYSISYamaki, S. B.; Andrade, A. A.; Mendonça, C. R.; Oliveira Jr., N. O.; Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, CEP 13560-970, São Paulo, SP, Brazil. +550162713616; Atvars, T. D. Z.; Instituto de Química, Unicamp, Caixa Postal 6154, Campinas, 13084-971, SP, Brazil

The morphological analysis of Langmuir films from the diazodyes Sudan 4 (S4), Sudan 3 (S3) and Sudan Red (SR), using Brewster angle microscopy (BAM), indicates that stable non-monomolecular structures are formed at the air/water interface which is denoted as a plateau in the pressure-area isotherms. Monolayer domains are formed even before the pressure starts to rise, which grow in size until reaching a condensed monolayer with a contrastless image in the beginning of the plateau. This behavior resembles that of Langmuir films from simple aromatic fatty acids. The films from all the azodyes display similar features, according to the surface potential isotherms and in situ polarized UV/VIS. spectroscopy. The only exception was in the larger area per molecule occupied by S4 and SR, which is attributed to the presence of CH 3 groups that cause steric hindrance, and in the organization of diazodye molecules at the air/water interface. UV/VIS polarized absorption spectroscopy showed that S4 and S3 have a preferential orientation on the water surface while SR molecules lie isotropically. For the three diazodyes, film absorption was negligible at very large areas per molecule, only becoming non-zero at a critical area that coincides with the onset of surface potential. This is attributed to the formation of a H-bonded network between water molecules and headgroups of the diazodyes.

A-P79 NANOSTRUCTURAL EVOLUTION AND SPECTRAL IMAGING OF Cu-Al2O3

NANOCOMPOSITES PREPARED BY IN-SITU REDUCTION AND THERMO-MECHANICAL PROCESSED

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M. Motta, I.G. Solórzano, E.A. Brocchi, and P.K. Jena , Department of Materials Science and Metallurgy, Catholic University of Rio de Janeiro (PUC-Rio), Brazil

The uniform dispersion of Al2O3 particles in a copper matrix provides unique characteristics to the material, enabling its use in high temperature applications. In recent years, it has been experienced that the physical and mechanical properties of these composites are improved significantly if the dispersion of the constituents is homogeneous and the particle sizes are in nano-scale. Previous results have shown that the microstructure of the nanocomposites is formed by a copper matrix, with grains in the sub-micron scale, and a homogeneous dispersion of Al2O3 particles in nano-scale size. HRTEM observations have show that the Al2O3 particles are in the range of 10 to 60/70 nm, but mostly in the lower range up to 30 nm. By comparing a computer generated X-Ray STEM elemental mapping with experimental ones taken at very high magnifications it is possible to achieve a better understanding of the real composition of the Cu/Al2O3 interface and also to assess the formation of a third phase in the consolidated material. Finally, studies on thermo-mechanical processing have shown that, even after cold-rolling down to 50% of reduction in thickness and annealing at 900oC for one hour, a high density of dislocations and sub-grain boundaries have still remained in the microstructure. This is an important information about the structural stability of the composite when considering possible future technological applications.

A-P80 CRYSTALLOGRAPHIC PROPERTIES OF THE KSr2Nb5O15 SOLID SOLUTIONM. A. L. Nobre, C. X. Cardoso, S. Lanfredi, Faculdade de Ciências e Tecnologia – FCT, Universidade Estadual Paulista- UNESP, C. P. 467, CEP 19060-900, Presidente Prudente, SP, Brazil

The rapid progress in microwave telecommunications satellite broadcasting and other related devices has demanded the search of new ferroelectric materials for industrial applications. This work presents the synthesis and structural characterization of a lead-free ferroelectric ceramic derived from KSr2Nb5O15. Nanostructured KSr2Nb5O15 oxide was synthesized by the polymeric precursor method, a chemical synthesis route derived from Pechini’s method. The thermal decomposition of the precursor was followed by differential analysis (DTA) and differential scanning calorimeter (DSC). The XRD pattern of the calcined powder at 1000 oC were performed over the angular range 5 2 120o with a 0.02o step and a fixed counting time of 30 s. The XRD data were analyzed by Rietveld refinements using the software FullProf. The data obtained showed a tetragonal system with the tetragonal tungsten bronze structure – TTB type (a = 12.4577 (3) Å and c = 3.9403 (9) Å, V = 611,52 (2) Å3. The refinements were determined on the basis of a polar group P4bm. The best refinements were provided with pentagonal site occupied by equal quantities of K+ and Sr2+ ions and square site occupied by Sr2+ ion.

A-P81 NANOSIZED BaSO4 POWDER FOR Ba2Ti9O20 CERAMICS FABRICATIONYu. Koldayeva, M. C. A. Nono, C. Kuranaga, S. T. Fonseca, Associated Laboratory of Sensors and Materials (LAS), National Institute for Space Research (INPE), São José dos Campos, SP, C.P. 515

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- 12201-970, Brazil, (P. J. Castro, Associated Laboratory of Plasma (LAP), São José dos Campos, SP, C.P. 515 - 12201-970, Brazil.)

Barium nanotitanate (Ba2Ti9O20) ceramic is good to be used as dielectric resonators (DRs) for microwave applications because of it high quality factor, high dielectric constant, and a low temperature coefficient of resonant frequency. It is complicate to obtain Ba2Ti9O20 stable crystalline phase near the room temperature due to the narrowness of it phase-pure stability region. As usual the BaCO3 and TiO2 powders are used to obtain barium nanotitanate ceramics but the size and shape anisotropy of BaCO3 particles difficult phase formation as well. In this work the BaSO4 and TiO2 powders were mixed in estequiometric proportions to obtain the Ba2Ti9O20 ceramic and the influence of different sintering temperatures and times on the phase formation and microstructure were studied. BaSO4 powder was obtained from BaCO3 by precipitation. The result was a drastic reduction of medium size of particles from 10 m to less than 500 nm. BaSO4 and TiO2 dried mixture was pressed on uniaxial and isostatic press to form cylindrical pellets and then they were synthesized and sintered at the same stage in air atmosphere. This raw material substitution permits diminish of the sintering temperature and time. The finished ceramics were characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD).

A-P82 MICROSTRUCTURES AND MECHANICAL PROPERTIES OF CE-TZP CERAMICS FROM MIXTURES OF NANO AND MICROSIZED POWDERSM. C. A. Nono Associated Laboratory of Sensors and Materials (LAS), National Institute for Space Research (INPE), São José dos Campos, SP, C.P. 515 - 12201-970, Brazil

The fabrication of a nanostructured ceramic materials will undoubtedly involves preparing of a nanosized ceramic powder, which may then then be consolidated to a high sintered density at a relatively lower sintering temperature. Many of desirable microstructural features may therefore be realized, including the improved sintered density, refined grain size, narrow grain size distribution and minimized degree of structural defects. In this work are reported and discussed the microstructures and mechanical properties of a tetragonal ceria-zirconia (Ce-TZP) ceramics prepared from mixtures of nanosized and microsized powders. These mixtures These powders were obtained from dehydratation with isopropilic and ethylic alcohols of zirconium an cerium coprecipitated sulphates (liquid-liquid extraction). Sintered ceramics were fabricated from powder mixtures containing different CeO2 content (8 to 16 mol %). The microstructures of the sintered ceramic was analysed by SEM and X-rays diffraction. The mechanical properties of the sintered ceramic were measured by Vickers indentation to obtain the surface microhardness and fracture toughness, and 4-point bending test to get the rupture strength values. These results were correlated with tetragonal (t) to monoclinic (m) phase transformation. These results were discussed and compared to those published in international literature.

A-P83 ORGANOMETALLIC CHEMICAL VAPOR DEPOSITION OF COMPOUND SEMICONDUCTORSM. Grassi1, A.A.A. de Queiroz 1 , A .H. A .Bressiani2, J.C. Bressiani2 1DFQ/ICI, Universidade

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Federal de Itajubá, alencar@efei.br; 2CCTEM, Instituto de Pesquisas Energéticas e Nucleares.

The organomethallic chemical vapor deposition (OMCVD) of compound semiconductors represents the one of the most important research area of nanotechnology. It provides an efficient synthetic rout for the production of materials in nanometric scale with desirable physical properties, which are often inaccessible by conventional materials synthesis. In this work, we report the development of sulfonated polystyrene (PSSO3H) as a new precursor to OMCVD techniques. The mechanisms of the interaction macromolecule-metal complex were investigated using quantum chemistry calculations. Semiempirical calculations for the PSSO3H and PSSO3H:M (M= Ni+2,Zn+2,Cu+2) charge transfer complexes using the PM3 parametrization were performed with the program MOPAC 2000. The PSSO3H:M structures were obtained by direct minimization of the total energies in a classical molecular mechanic methods with respect to all geometrc variables, i.e. bond lengths and angles. The experimental results suggest a growth mechanism that involves transfer of hydrogen from the polymeric ligand to surface resulting in the oxide crystal growth at polymeric interface (SEM, Phillips XL30) micrograph. The quantum chemical calculations indicate that the stability of the polymer-metal complexes increase in the order Zn+2>Cu+2>Ni+2. This results leads to the known of the decomposition chemistry on the surface leading to a better control of impurities and providing the tools necessary to quantify OMCVD reaction mechanisms.

A-P84 SYNTHESIS AND CHARACTERIZATION OF NANOSTRUTURED THIN FILMSP.S. Gouveia1, N.L.V. Carreño1, M. Mescote1, G.F. Goya2, R.F. Jardim2, E.R. Leite1, E. Longo1; 1 CMDMC-LIEC, Department of Chemistry, UFSCar, Via Washington Luiz, km 235, São Carlos, SP, Brazil; 2 institute of Physics, USP, SP, Brazil; P.S. Gouveia, CMDMC-LIEC, Department of Chemistry, UFSCar, Via Washington Luiz, Km 235, CP 13565-905, São Carlos, SP, Brazil This work describes a new route for the preparation of Ni-nanoparticles embedded in a SiO2 matrix thin film. We have produced Ni-SiO2 films with 3% and 6% wt of Ni by the polymeric precursor method, which were deposited on Si(100) substrates by spin coating, and annealed at a temperatures of 550 oC in a N2 atmosphere. X-Ray Diffraction, Scanning Electron Microscopy, Atomic Force Microscopy and Magnetization characterization were performed in these films.The microstructural characterization suggested that these films display Ni-nanoparticles with an average diameter of ~3nm. Magnetization measurements (ZFC and FC processes) revealed a blocking temperature, TB close to 7.2 K for the most diluted sample. Also, magnetization data showed the expected scaling of the M/Ms vs. H/T curves for superparamagnetic particles.

A-P85 INFLUENCE OF HEAT TREATMENT ON CERAMIC POWDERS OF COBALT FERRITESN. D. S. Mohallem, Laboratório de Materiais, Depto de Química, UFMG, 31270-901, Belo Horizonte, MG, Brazil; Walter de Brito, CDTN/CNEN, 31270-901, Belo Horizonte, MG, Brazil, Juliana B Silva, CDTN/CNEN, 31270-901, Belo Horizonte, MG, Brazil. 

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Nanosized crystalline CoFe2O4 powder was synthesized by a coprecipitation process using metallic nitrates in aqueous media as precursors and NH4OH as precipitant. The as-prepared powder was washed, dried at 80°C and heat-treated at various temperatures for 2 hours for crystallization of the material. The influence of heat treatment on the structure, texture and saturation magnetization was studied. The average crystallite size of the powders varied from 17 to 100 nm with annealing temperature and the corresponding saturation magnetization (Ms) values ranged from 20 to 60 emu/g. The material obtained under optimal condition by this process reached a value of spontaneous magnetization around of 90% (80 emu/g) of the theoretical magnetization of a stoichiometric ferrite.

A-P86 CORRELATION BETWEEN TEXTURAL AND MORPHOLOGICAL PROPERTIES OF ALUMINA PREPARED BY VARIOUS PROCESSESCristina Fontes Diniz, Laboratório de Materiais, Depto de Química, UFMG, 31270-901, Belo Horizonte, MG, Brazil; N. D. S. Mohallem, Laboratório de Materiais, Depto de Química, UFMG, 31270-901, Belo Horizonte, MG, Brazil. 

Alumina (Al2O3) is a well-known ceramic material used as refractory, coating material, and ceramic composite matrix, among others. Recently, porous alumina has attracted much attention due to its potential use in nanotechnology. In this work, we synthesized porous alumina by coprecipitation and sol-gel processes, using variations in the drying procedures (liofilization, controlled, and hypercritic drying) and temperatures. The structural, textural and morphological changes in the obtained material were studied by powder X-ray diffraction, infrared spectroscopy, scanning electronic microscopy, nitrogen adsorption, and thermal analysis.

A-P87 PREPARATION OF SiO2-TiO2 FILMS CONTAINING CdS NANOPARTICLESCosta, V. C., Santos, A.M., Lameiras F. S., Center of Nuclear Technology Development, CP 941, Belo Horizonte, MG, Brazil, 30123-970; Sansiviero, M. T. Department of Chemistry, UFMG, Pampulha, Belo Horizonte, Brazil; Simões, A. B., Vasconcelos, W. L. Mettalurgical and Materials Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil Titania-silica materials have been extensively used as catalysts and supports for a wide variety of reactions. In the present work, silica-titania thin films containing up to 20 mol% TiO 2 were prepared by sol-gel process. The solutions were prepared through a two-stage hydrolysis, where tetraethoxysilane (TEOS) and titanium isopropoxide (Ti(OPr)4) were used as precursors. Small sized CdS particles were incorporated in the silica-titania films by a complex formation reaction using cadmium acetate and thiourea, SC(NH2)2. The films were thermally treated at 300-400 oC. The preparation process and properties of the films were investigated through UV-Visible absorption, IR and Raman spectroscopy, X-ray diffraction and atomic force microscopy (AFM)

A-P88 HIGH-PRESSURE ANNELING EFFECT ON THE STRUCTURAL PROPERTIES OF NANOSTRUCTUREDPbTiO3 COMPOUNDS M. T. Escote, E. R. Camargo, E. R. Leite, and E. Longo, CMDMC – LIEC, Depto. De Química, UFSCar, São Carlos, SP, Brazil; R. F. Jardim, Instituto de Física, USP , São Paulo, SP, Brazil. 

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We have produced polycrystalline PbTiO3 (PT) by the called oxidant peroxo method (OPM). These compounds were heat-treated at temperatures varying from 450 to 700 °C in air and under oxygen pressure of PO2 ~ 60 bar. The structural and microstructural properties were characterized by X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HR-TEM). The XRD and Raman spectroscopy revealed that the oxygen pressure annealing enhances the thermal stability of the amorphous solids. In fact, a comparison among the XRD data shows that the application of the external pressure results in increase of the crystallization temperature. Moreover, HR-TEM images, carry out after each heat treatment, suggested that we have produced nanostructured PT compounds with size particles of the order of 7 to 14 nm. Through these images, we believe that these samples displayed two different crystalline phases: (a) pyroclore Pb2Ti2O6 meta-stable phase for the samples heat-treated at low temperature (T ~ 450 °C); and (b) the PT for sample annealed at 700 °C.

A-P89 LACTOSE INTERCALATION IN THE NANOMETRIC INTERLAYER SPACE OF A SMECTITIC CLAY MINERAL

L. C. Morais, Departamento de Engenharia Química-Escola Politécnica-USP, Rua do Lago250, Prédio Semi-Industrial, Cidade Universitária, São Paulo, Brazil, leandro.morais@poli.usp.brF.R. Valenzuela Díaz, Laboratório de Matérias-Primas Particulados e Sólidos Não-Metálicos, PoliUSP, São Paulo, Brazil.: e-mail: frrvdiaz@usp.br; J. Dweck, Laboratório de Análises Térmicas, Bloco E do CET – DPI, Fundos, Escola de Química, UFRJ, Rio de Janeiro, Brazil.: e-mail: dweck@eq.ufrj.br; P. M. Büchler, Departamento de Engenharia Química(PQI-USP), PoliUSP, São Paulo, Brazil. e-mail: pedro.buchler@poli.usp.br

The treatment of the effluents of dairy product industries containing lactose is done by a biological process, which reduces considerably the original amount of that sugar. Although the final residual content of lactose after treatment is small, it may cause the eutrophication and/or the superfertylization of the water, which provokes vegetation growth on the water surface, hindering the navigability of the rivers where the treated effluent is thrown, and decreasing significantly the content of the dissolved oxygen necessary to the life of the fishes therein. The objective of this paper is to present a study of the intercalation of lactose in the nanometric interlayer space of a smectitic clay, and to compare these results with those of the adsorption of the residual lactose in aqueous solutions by an organophylic clay, which was prepared from a sodium bentonite, after an ion exchange procedure with an organic cation of a quaternary ammonium chloride. This chemical modification transforms the originally hydrophilic clay to an organophilic one, as well as it changes the characteristics and sorption properties of the nanometric interlayer space of the clay structure. The equilibrium lactose concentrations after organophilic clay sorption are measured by the change of the total organic carbon (TOC) present in the original aqueous solution . The characterization of the lactose, the original clay and the organophilic clay is done by thermal analysis techniques and X-ray diffraction.

A-P90 BRAZILIAN ORGANOCLAYS AS NANOSTRUCTURED SORVENTES OF PETROLEUM DERIVED HIDROCARBONSK. R. O. Pereira1, R. A. Hanna 1, M. M. G. Ramos Vianna 1, M. G. F. Rodrigues 2, F. R. Valenzuela-Díaz 1; 1 Laboratório de Matérias-Primas Particuladas e Sólidos Não Metálicos, Rua do Lago, 250, Cidade Universitária, São Paulo, Brazil; 2 Laboratório de Novos Materiais, Rua Aprígio

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Veloso, 882, Campina Grande, Brazil

Smectitic clays, also known as bentonites, find several different industrial uses, being the largest group in terms of utilization and the most interesting group of clays minerals. However, it is necessary to submit them to chemical treatments to develop their real potentialities. Polluted areas by organic pollutants are of great concern in terms of environmental control. Several types of sorvent materials have been studied to remediate these areas. Among them, organoclays obtained from smectitic clays and quaternary ammonium salts, containing at least a 12-carbon chain between their layers, represent a featured promising material. For the preparation of the organophilic clays was used a smectitic clay from Boa Vista city, Paraíba State, and two quaternary ammonium salts. The obtained materials were characterized by X-ray diffraction and infrared spectroscopy. The results showed good capability for the adsorption of gasoline, toluene, diesel fuel and kerosene.

A-P91 MOKE STUDY OF Fe MONOLAYERS ON ZnSe(001)/GaAs(001)M. D. Martins, P. L. Gastelois, L. H. F. Andrade, W.A.A. Macedo, Lab. de Física Aplicada, Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, Brazil; V. H. Etgens, LMCP, Universitè Paris VI-VII, Paris, France.

Hybrid ferromagnetic/semiconductor materials have attracted great attention to new spintronic devices. The Fe-ZnSe is one promising system due to the good quality of epilayers and absence of reactivity at the interface. We have studied the structural and magnetic properties of ultrathin Fe films, from the submonolayer regime up to 10 monolayers thick grown by molecular beam epitaxy on ZnSe(001). Fe monolayers have been deposited at 180 oC on c(2x2) Zn-rich ZnSe/GaAs(001) surfaces. The substrate, growth and structure of the Fe films were well characterized by reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy, and low energy electron diffraction (LEED). The magnetic properties were determined by magneto-optical Kerr effect (MOKE), in situ, in ultrahigh vacuum. We have studied the thickness dependence of the MOKE hysteresis loops in the longitudinal geometry, at 150 K and under magnetic fields up to 0.1 T applied along the [110] and [1-10] directions of the ZnSe(001). Clear hysteretic loops were obtained only starting from ~4 monolayers (ML) Fe. The onset of an uniaxial magnetic anisotropy with [110] magnetic easy axis has been observed at ~ 7 ML Fe. Our results suggest that the in-plane magnetic anisotropy develops after partial relaxation of the in-plane structural anisotropy, as determined by RHEED.

A-P92 IMPEDANCE SPECTROSCOPY ANALYSIS OF BIMEVOX SOLID ELECTROLYTESC. H. Hervoches and R. Muccillo, Centro Multidisciplinar para o Desenvolvimento de Materiais Cerâmicos, CCTM - Instituto de Pesquisas Energéticas e Nucleares, Av. Lineu Prestes 2242, Cidade Universitária, São Paulo, SP, 05508-900, Brazil

The so-called BIMEVOXes are a group of fast oxide ion conductors at fairly low temperature. They are structurally related to the Aurivillius materials consisting of perovskite blocks sandwiched between fluorite-like (Bi2O2)2+ sheets. The parent compound Bi4V2O11 has three structural domains , and , the last one presenting high ionic conductivity between 840 and 1150 K. Here we present results about several BIMEVOX materials prepared by the citrate and combustion techniques. These methods present the advantage over solid state reaction of lower processing temperature and the formation of materials with finer grains size. Different sintering processes allowed us to synthesize materials with various grains size. The physical properties of the BIMEVOX materials prepared have been studied using impedance spectroscopy (IS) and compared with results obtained by other methods of synthesis. The influence of grain size on the conductivity and relative influence of the bulk and grain boundaries have been analyzed.

A-P93 EXPERIMENTAL AND THEORETICAL STUDY OF POROUS SILICON ELASTIC PROPERTIESA. B. S. Camussi, R. J. M. da Fonseca, Grupo de Ótica e Propriedades Físicas de Materiais – DEQ, Instituto de Física, UERJ, R. São Francisco Xavier, 524 sala D-3030, 20550-013 Rio de Janeiro, Brazil; J. Attal, Laboratoire d’Analyse des Interfaces et de Nanophysique – URA CNRS 1881 -

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Université Montpellier II 34095, Montpellier CEDEX 05 – France

Porous silicon (PS) has been extensively studied since it exhibits strong visible luminescence at room temperature, suggesting promising applications in silicon-based optoeletronic devices, dielectric isolation of integrated circuits and epitaxial growth of heterostructures on Si substrate. Great part of this research has been focussed in the investigation of optical and electronic properties of PS layers. However, for many pratical applications, it is important to characterize the mechanical behaviour of them. For this purpose, we apply the scanning acoustic microscopy (acoustic imaging and V(z) signature) to measure the acoustic wave velocities and elastic characteristics of this material (Young’s modulus and Poisson coefficient) with different porosity. This is a powerful technique for non-destructive and non-contact measurements, specially when small volumes are involved. The investigated samples have a porosity range of 20% to 60% and thickness of 30 µm to 120 µm. So, in this work, we present V(z) curves and acoustical images and a comparision between theoretical and experimental results using Biot’s theory which describes the propagation of elastic waves in a system composed of a porous elastic solid saturated by a fluid.

A-P94 MORPHOLOGICAL CHARACTERIZATION OF NANOPARTICLES OF SnO2 WITH ADDITIVES Ni AND FePilar Hidalgo 1 Douglas Gouvêa1 Daniela Zanchet2, Jefferson Bettini2 ; 1Department of Metallurgical and Materials Engineering- USP. Av. Professor Mello Moraes, 2463, 05580-900. S.P. Brazil; 2

Brazilian Synchrotron Light Laboratory (LNLS), Campinas, SP, Brazil. Recently studies on ceramic powders with additives have shown that microestrutural modifications take place when the system reaches the lowest surface energy. It has been suggested that this decrease is related to the segregation of the additive onto the surface powder. This work presents the study of segregation of additives in two interesting system: Fe2O3-SnO2 and NiO-SnO2, prepared by Pechini´s method. Morphological analysis was performed using Transmission Electron Microscopic (TEM), X-ray diffraction (XRD), Specific Surface Area (SBET) and Mössbauer Spectroscopy. The segregation of Fe or Ni ions to the surface of the matrix phase (SnO2) was observed in specimens with 30 mol% of additive. Above that (50 and 80 mol %), it has been observed for both Fe and Ni the nucleation of a second phase: Fe3O4 and NiO respectively. The analysis revealed that SnO2 has a strong influence on the structure of the second phase, suggesting an epitaxial process.

A-P95 PREPARATION OF POROUS GLASS-CERAMICS WITH CALCIUM ORTHOVANADATE SKELETON USING VANADIUM PHOSPHATE GLASS AS PRECURSORI.O. Mazali, O.L. Alves, Laboratório de Química do Estado Sólido – LQES; IQ – UNICAMP, Campinas, SP, Brazil http://lqes.iqm.unicamp.br

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The aim of this work was the preparation and characterization of porous glass-ceramics with skeleton of Ca3(VO4)2. This material has ferroelectric and luminophoric properties. Porous materials are important in several fields (catalysis, separation sciences, sensors) showing cooperative interactions when reactions are performed in confined porous ambient. Glass-ceramics (GC) were prepared by controlled crystallization of the glass system Li2O-V2O5-CaO-P2O5. The production of the porous glass-ceramic (PGC) involves the acid leaching of the soluble phases, to achieve a porous structure formed by the insoluble phase. The XRD data suggested the presence of the -Ca2P2O7 (-CPP), -Ca2V2O7 (-CPV) and LiCaPO4 phases. The acid leaching of the -CPP and -CPV phases was confirmed by the absence of bands at 725 cm-1 (IR) and at 880 cm-1 (Raman), respectively. The PGC exhibit bright green color due to residual -CPV. The IR and Raman data indicate that the skeleton of the PGC is constituted of Ca3(VO4)2, due to the presence of a very strong band at 898 cm-

1, attributed to (V-O) stretching mode of the VO43- groups and, additionally, vanadyl phosphate, as

minor phase. The SEM/EDX micrographs confirmed the porous structure of the monolithic Ca3(VO4)2. [This is a contribution of Millennium Institute of Complex Materials]

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