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A tribute to the work of

Christian Colliex

9th-11 th June 2010Past, Present and Future of (S)TEM

and its applications

One day in LPS ...

St Tropez 1977 (No comment)

Towards atomic resolution ?

A re al poster !

N ice 1977

Half a microscope is better than nothing

Preface

The idea of holding a celebratory event in Christian’s honour ensued from his

decision to relinquish responsibility for the Orsay group, which he created nearly 40 years ago and has led ever since. Amiable but insistent pressure from many of our colleagues, who considered that such a meeting was clearly indispensable, confirmed our own initial feelings. Once the decision was taken, the format came naturally: it should combine the highest level research with festivities in prestigious locations, accompanied bien sûr by quality cuisine (keywords which Christian would certainly endorse).

To celebrate the contribution of Christian to the field the (S)TEM and EELS, we planned a series of presentations by many of the other principal actors in the history of these techniques, including those with whom Christian has closely collaborated down the years. Thanks to their unanimous participation, the project has taken the form of a very high-level conference with a truly impressive panel of eminent speakers from the scientific elite. We would like to thank them all for their rapid and enthusiastic acceptance.

The conference and social programme will take place in locations recalling Christian’s life and work. First of all the CNRS, within which Christian has spent his entire career, will host the scientific sessions. Then there is the Ecole des Mines, one of the illustrious French «Grandes Ecoles» in which Christian studied, and in whose garden and mineralogical museum we will share a gastronomical buffet

on the first evening. The Conference Banquet will be held at the famous Train Bleu in the Gare de Lyon. This restaurant opened as part of the Grand Exposition in 1900 and the atmosphere is evocative of that period of great scientific progress and general optimism known worldwide as the Belle Epoque. What could be more fitting than a railway station to symbolise the globe-trotting life that Christian has always led (and will continue to lead)?

The meeting could never have been organised without the invaluable aid of the Société Française de Microscopie, which joined its efforts to ours right from the start, offering its financial (and moral) support and much useful advice. The fact that the meeting quickly sold out illustrates the excellence of its advertising skills. We are grateful to the CNRS for providing free use of their headquarters and to the Ecole des Mines for opening their amenities exceptionally for this event. We wish also to express our thanks to the support of Laboratoire de Physique des Solides, METSA and ESTEEM and, of course, our generous sponsors: NION, Orsay Physics, Gatan, FEI, JEOL, Leica, Zeiss, EMS, EDP Sciences, Eloïse and Elexience for their financial support.

Like Christian, we hope you will appreciate both the excellent science which will be presented here and the social programme. And finally, we thank you, Christian’s friends, for your presence, which will make this event unforgettable.

Still a great experimentalist ...

A re al poster !

N ice 1977

Past, Present and Future of (S)TEM Paris - 9th - 11th June 2010

4

Scientific committee

Albert FertUnité Mixte de Physique, CNRS / Thalès, Palaiseau (France)

Colin HumphreysDepartment of Materials Science & Metallurgy, University of Cambridge (Great Britain)

Sumio IijimaDepartment of Materials Science & Engineering, Meijo University, Nagoya (Japan)

Helmut KohlPhysikalisches Institut, Westfälische Wilhelms-Universität Münster (Germany)

Richard LeapmanNational Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda (U.S.A.)

Odile StéphanLaboratoire de Physique des Solides, Université Paris Sud, Orsay (France)

Gustaaf Van TendelooElectron Microscopy for Materials Science - EMAT, University of Antwerp (Belgium)

Paul Ballongue

Nathalie Brun

Marie-France Cozic

Bénédicte Daly

Alexandre Gloter

Mathieu Kociak (coordination)

Katia March

Claudie Mory

Marcel Tencé

Mike Walls

Alberto Zobelli

Organization committee


Paris - 9th - 11th June 2010 Past, Present and Future of (S)TEM

5

Table of contents

Preface .............................................................................................................................................................................................................. 3

Scientific and organization committees ..........................................................................................................................4

EELS session 1 ........................................................................................................................................................................... 7

C.H. Chen ...............................................................................................10S. Pennycook ........................................................................................11A. Howie ................................................................................................12

A. Fert ................................................................................................................ 13

Instrumental session ...................................................................................................................................................15

O. Krivanek ............................................................................................18P. Sudraud .............................................................................................19

Elastic and inelastic coherence session .............................................................................................20

A. Tonomura .........................................................................................24H. Kohl ....................................................................................................25J. Spence ................................................................................................26

EELS session 2 .................................................................................................................................................................................27

A. Craven ................................................................................................29D. Muller ................................................................................................30

C. Bréchignac ....................................................................................................31

Application session 1 ...........................................................................................................................................................33

K. Suenaga .............................................................................................35R. Leapman ...........................................................................................36

Application session 2 ...........................................................................................................................................................37

P. Ajayan .................................................................................................39D. Ugarte ................................................................................................40

S. Iijima ..............................................................................................................41

Presentation of the SFµ ...................................................................................................................................................43

Young researchers ....................................................................................................................................................................44

Poster sessions ..............................................................................................................................................................................46

Participant list ............................................................................................................................................60

Social events ................................................................................................................................................63


6

Sponsors


7

EELS session 1

Wednesday 9th June

Chairman: Philip Batson

10:15 Cheng-Hsuan Chen .......... 10 10:45 Steve Pennycook ............. 1111:15 Archie Howie ................... 12


10

Electron Energy-Loss Spectroscopy for Solid State Physicists: the Early Years at Cornell*

C. H. Chen

Center for Condensed Matter Sciences and Department of Physics, National Taiwan University,Institute of Atomic and Molecular Sciences, and Institute of Physics, Academia Sinica,

Taipei, TAIWAN

Electron energy-loss spectroscopy (EELS) carried out in the past three decades were mostly done in conjunction with scanning transmission electron microscopes (STEM) emphasizing the unmatchable spatial solving power of the technique. Recently, with the aberration-corrected STEM, spectroscopy with spatial resolution at atomic level has been demonstrated by STEM-EELS. The specific momentum (wave-vector) dependence of inelastic scatterings for particular solid state excitations, which is of great significance for solid state physics, is then lost in EELS with high spatial resolution carried out by a highly convergent electron probe. In the early development of EELS, in fact, much attention was focused on the momentum dependence of EELS yielding the so-called dispersion characteristics of related excitations. Small angle scatterings focused on the momentum dependence of optical excitations, such as surface plasmons, surface guided modes, and Cherenkov radiation, were achieved with an extremely parallel electron beam with angular divergence ~8x10-6 rad. On the other hand, dispersion of bulk plasmons and direct non-vertical interband transitions were carried out at much larger scattering angles out to the Brillouin zone boundaries. Anisotropies of these excitations along different crystallographic directions could be easily explored. An example of EELS at large scattering angles is shown in figure 1 for [001] single crystal aluminum where dispersions of bulk plasmons starting from ~ 15 eV and direct non-vertical interband transition from 1.5 to 9 eV along the [100] direction can be clearly seen. In this talk, I’ll revisit some early such activities at Cornell in the seventies which yielded a plethora of fascinating results, some of which still defy our understanding today.

Figure 1 Electron energy-loss spectra showing dispersions of bulk plasmons and direct non-vertical interband transitions along the [100] direction for single crystal aluminum.

* Work done in collaboration with J. Silcox and P. E. Batson.


11

Spectroscopy at the Atomic Level: Past, Present and Future

S. J. Pennycook

Oak Ridge National Laboratory, Materials Science and Technology DivisionPO Box 2008, Oak Ridge, TN 37831-6071, USA

Christian Colliex has been a leader in the field of EELS since my time as a graduate student in the Cavendish Laboratory, Cambridge (1-3). This talk will trace the development of EELS at atomic resolution and look to future directions. The earliest attempt at near atomic resolution spectroscopy was through the spatial difference technique, by which means nitrogen was detected at platelets in diamond (4). With the development of the Z-contrast method for direct imaging of atomic planes (5) or columns (6) it became clear that the Z-contrast image could be used to locate a small probe with atomic precision, enabling EELS to be performed with planar (7, 8) and atomic-column (9) sensitivity. These developments used “home-built” capabilities and were not widely adopted until the availability of TEM/STEM instruments with comparable performance (10).

The success of aberration correction has allowed the spectroscopic identification of a single atom within a single atomic column of a crystal (11), quantitative investigation of delocalization by comparison of experiment with theory, in one (12) and even two dimensions (13) and mapping of fine structure with unprecedented sensitivity (14, 15). The figure shows spectroscopic images (recorded by M. Varela) from a Nion UltraSTEM that not only differentiate the elements in LaMnO3, but also show clearly the octahedral rotations of the O sublattice. A future challenge for simulations is to include both dynamical diffraction of the probe and realistic solid state bonding.

1. P. C. Colliex, B. Jouffrey, Philos Mag 25, 491 (1972).2. C. Colliex, V. E. Cosslett, R. D. Leapman, P. Trebbia, Ultramicrosc. 1, 301 (1976).3. C. Jeanguillaume, P. Trebbia, C. Colliex, Ultramicrosc. 3, 237 (1978).4. S. D. Berger, S. J. Pennycook, Nature 298, 635 (1982).5. S. J. Pennycook, L. A. Boatner, Nature 336, 565 (1988).6. S. J. Pennycook, D. E. Jesson, Phys. Rev. Lett. 64, 938 (1990).7. N. D. Browning, M. F. Chisholm, S. J. Pennycook, Nature 366, 143 (1993).8. N. D. Browning, M. F. Chisholm, S. J. Pennycook, Nature 444, 235 (2006).9. P. E. Batson, Nature 366, 727 (1993).10. E. M. James et al., J. Electron Microsc. 47, 561 (1998).11. M. Varela et al., Phys. Rev. Lett. 92, Art. No. 095502 (2004).12. M. P. Oxley et al., Phys. Rev. B 76, Art. No. 064303 (2007).13. M. Bosman et al., Phys. Rev. Lett. 99, Art. No. 086102 (2007).14. M. Varela et al., Phys. Rev. B 79, 085117 (2009).15. D. A. Muller et al., Science 319, 1073 (2008).

Research sponsored by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, US DOE.


12

Delocalization Effects in the Elastic and Inelastic Scattering of Electrons

Archie Howie

Cavendish Laboratory, University of Cambridge,J.J. Thomson Avenue, Cambridge CB3 0HE UK

Given their obsession with spatial resolution in imaging, electron microscopists are naturally concerned about delocalization effects but overuse of this blanket term has tended to obscure a somewhat complex situation where delocalization can arise from a whole range of causes. Here I suggest therefore that it may be helpful to attach to these different delocalization mechanisms the names of relevant scientists.

Scherzer delocalization arising from lens aberrations and defocus has recently been dramatically reduced with the development of aberration correction. Delocalization due to scattering processes in the specimen is now usually more important. For elastic scattering we must consider Bragg delocalization (e.g. Bloch wave current flow spread in crystals) and Hirsch delocalization (arising from the extended elastic strain field near defects). In quasi-elastic (thermal) scattering there is Debye delocalization (usually included via the Debye Waller factor but sometimes more directly manifest in HREM images of flexural vibrations of nanoscale structures). In an inelastic excitation ΔE = ħω by an electron of velocity v, the Coulomb delocalization is very roughly described by an impact parameter v/ω. The correct description of the excitation also depends on its propagation and the surrounding boundary conditions resulting in various forms of Landau delocalization and including the familiar ELNES effects, the role of a whole nanostructure in defining collective valence excitations, and sometimes even more dramatically Cherenkov delocalization.

With concerns about radiation damage (both ionization damage and knock-on damage) there has been reconsideration of the optimum beam operating energy in electron microscopy. The overall delocalization scenario after aberration correction is clearly an important factor in any decision of this kind. However a familiar and more general conclusion for STEM or SEM imaging is that we have to make maximum use of every available signal. For the secondary electron and cathodoluminescence signals, coincidence detection with the energy loss signal may be important in providing information about the specific initial excitation for every event and hence at least partial knowledge of the associated delocalization.


13

Spintronics: fundamentals and emerging directions

Albert FertUnité Mixte de Physique CNRS/Thales and Université Paris-Sud

Spintronics is a new field of research which exploits the influence of the electron spin on electronic transport. It is well known for the giant magnetoresistance of the magnetic multilayers and its application to the hard disc drives, but it has also revealed many other interesting effects. In my talk I will review some of the most promising directions of today: spin transfer phenomena, spintronics with semiconductors, molecular spintronics, single electron spintronics, Spin Hall Effect (SHE). In a spin transfer experiment, for example, one manipulates the orientation of a nanomagnet by transfusing spin angular momentum from a spin-polarized electronic current to the nanomagnet. This electronic spin transfusion can be used to switch the magnetization (with near applications to the writing of magnetic memories) or to generates oscillations in the radio-wave frequency range (with promising applications in telecommunications). Spintronics with semiconductors aims to some fusion between conventional electronics and spintronics, while molecular spintronics turns out to be a possible way to go “beyond CMOS”, that is beyond conventional silicon electronics. Single electron spintronics and SHE have also very interesting prospects.

Albert Fert

Wednesday 9th June 12:00 - 12:45


14

Nanoscale analysis of a SrTiO3 ÕLa2Õ3Sr1Õ3MnO3 interface

F. Pailloux,1 D. Imhoff,2 T. Sikora,2 A. Barthelemy,1 J.-L. Maurice,1 J.-P. Contour,1 C. Colliex,2,3 and A. Fert1,*1Unite mixte de Physique CNRS/THALES, Domaine de Corbeville, 91404 Orsay Cedex, France

and Universite Paris-Sud, 91405 Orsay Cedex, France2Laboratoire de Physique des Solides, UMR CNRS 8502, Batiment 510, Universite Paris Sud, 91405 Orsay, France

3Laboratoire Aime Cotton, UPR CNRS 3321, Batiment 505, Universite Paris Sud, 91405 Orsay, France�Received 9 October 2001; published 8 July 2002�

The aim of the present work is an atomic scale characterization of the SrTiO3 /La2/3Sr1/3MnO3 interfaceinvolved in Co/SrTiO3 /La2/3Sr1/3MnO3 tunnel junctions. Our high-resolution transmission electron microscopyexperiments show the quality of the pseudo-morphic growth of La2/3Sr1/3MnO3 �LSMO� and SrTiO3 �STO�,but do not allow us to determine the termination of LSMO. On the other hand, we have carried out anenergy-loss near-edge structure study of the Mn2p and O1s edges. The main result is that the valence of Mnkeeps its intrinsic value of the bulk material till the last MnO2 layers at the interface, which is consistent withthe observation of magnetoresistance up to practically the Curie temperature of bulk LSMO in our junctions.These results suggest a La2/3Sr1/3O termination of LSMO.

DOI: 10.1103/PhysRevB.66.014417 PACS number�s�: 75.45.�j, 82.80.Pv, 68.37.Lp, 85.30.Mn

I. INTRODUCTION

Half-metallic ferromagnets are, in principle, ideal materi-als for spin electronics since they are expected to present acomplete spin polarization of their electron states at theFermi level. It is true that record magnetoresistances �MR’s�have been obtained in tunnel junctions with electrodes madeof half-metallic manganites like La2/3Sr1/3MnO3 �LSMO� orLa2/3Ca1/3MnO3 �LCMO�, but, disappointingly, these hugeMR effects decrease as a function of temperature much morerapidly than it could be expected from the value of the Curietemperature (Tc) in bulk materials.1–4 What is actually im-portant in tunnel junctions and other heterostructures is thespin polarization not in the bulk half-metallic ferromagnetbut at its interfaces with other materials. An interesting cor-relation has been found between the temperature dependenceof the junction resistance and the drop of the magnetoresis-tance with temperature in LSMO/STO/LSMO tunnel junc-tions �STO is SrTiO3�.2 As the temperature increases from4.2 K, the junction resistance increases, as normally expectedfrom the decrease of the carrier density in LSMO when themagnetic disorder increases. A resistance maximum, corre-sponding to a carrier density minimum, is expected at theCurie temperature of LSMO �also at the metal-insulator tran-sition�, but, surprisingly, the junction resistance maximum isfound at about 200 K, well below the Curie temperature ofbulk LSMO �around 350 K�. This temperature has been iden-tified to the ‘‘effective’’ Curie temperature5 at the LSMO/STO interface. Quite consistently, the MR vanishes at thistemperature �inset of Fig. 1�. Similar collapses of the MR attemperatures well below Tc

bulk �generally below Tcbulk/2� have

been found in other tunnel junctions with LSMO or LCMOelectrodes,1,2,4 and it is tempting to conclude that this strongreduction of the ‘‘effective’’ Curie temperature at interfacesis an unavoidable intrinsic property of heterostructures withhalf-metallic oxides.

However, this conclusion of unavoidable large reductionof the ‘‘effective’’ Curie temperature at interfaces is in con-tradiction with more recent experiments. The tunnel magne-

toresistance �TMR� vanishes only at 270 K in some junctionsstudied by Noh et al.3 Moreover TMR is still observed atroom temperature in Co/STO/LSMO junctions, and vanishesonly at 320–330 K, practically the Curie temperature of bulkLSMO �around 350 K�. We refer to the work in our labora-tory on Co/STO/LSMO tunnel junctions6,7 in which theSTO/LSMO basis is deposited by laser ablation in the sameconditions as for the LSMO/STO/LSMO junctions2 of thediscussion above, before depositing a Co layer on STO. Thetemperature dependence of the MR in a Co/STO/LSMOjunction7 is shown in Fig. 1: at low temperature the MR�50%� is smaller than in junctions with two LSMO elec-trodes �as expected from the moderate polarization of Co incomparison with LSMO� but, in contrast, the MR decreasesmore slowly with temperature and vanishes only at about330 K, that is practically at Tc

bulk . Consistently the maximumof tunnel resistance is also close to Tc

bulk . This absence of aTc reduction when only a ‘‘bottom’’ STO/LSMO interface isinvolved indicates that the ‘‘effective’’ Curie temperature ofthis ‘‘bottom’’ interface is close to Tc

bulk , and suggests that,in the LSMO/STO/LSMO junctions prepared in the sameconditions,2 only the top LSMO/STO interface presents astrongly reduced Tc and is responsible for the rapid MR dropwith temperature.

The problem of the structure at LSMO/STO �or LCMO/STO� interfaces and the influence of this structure on thephysical properties were already discussed in several publi-cations, for example in Refs. 7 and 8. Strain, presence ofdefects, roughness, departures from stoichiometry can affectthe physical properties and, in the case of superlattices,Izumi et al.8 in particular put forward the influence of thetermination of the manganite at the interface. As will be dis-cussed in more detail in Sec. III and in the following, themost probable terminations at a �001� interface are those rep-resented in Fig. 2. In a type-I termination �Fig. 2�a��, theLSMO layer is terminated by a La2/3Sr1/3O atomic layer, sothat the environment of the Mn atoms in the adjacent MnO2layer is approximately the same as in bulk LSMO. Such a

PHYSICAL REVIEW B 66, 014417 �2002�

0163-1829/2002/66�1�/014417�9�/$20.00 ©2002 The American Physical Society66 014417-1


15

Chairman:

114:00 Ondrej Krivanek ........................18 14:30 Pierre Sudraud ...................... 19

Instrumental session

Wednesday 9th June

Marcel TencÁ


16


18

Focused electrons: sub-Å beams, sub-0.1 eV energy resolutionO.L. Krivanek

Nion Co. 1102 8th St., Kirkland, WA 98033, USA

I first met Christian Colliex at the 1978 Cornell workshop, where he was one of the top experts in the exciting new field of electron energy loss spectroscopy, and I a total novice thinking about switching to EELS from high resolution EM. I liked what I saw at the workshop. Since there was no high-performance commercial EEL spectrometer available back then, I decided to build my own, despite having had zero experience in instrument building. This launched me on an instrumentation development path that has led to many collaborations with the group of Christian, a physicist who has always welcomed the opportunity to build or use new tools to explore new fields. I learned much from Christian and his French colleagues, especially during my two sabbatical stays in his lab.

We started our collaboration by putting a serial EELS spectrometer which I developed on a VG STEM his group had, and the collaboration is still going strong many years later. Our most recent joint effort has involved a new STEM column that is able to produce a 1.2 Å diameter probe at 60 kV primary voltage. This is useful for atomic-resolution annular dark field (ADF) STEM imaging of light-Z materials susceptible to knock-on damage. The chemical type of single light atoms (B, C, N, O) can now be reliably identified by their ADF intensity. Fig. 1 shows an ADF image of monolayer BN in which B, N and individual substitutional atoms were identified using this approach1. The circle in the image marks a single C hexagon incorporated in the BN sheet.

Orsay will soon get a new 50-200 kV CFEG STEM, which will be able to reach probe sizes down to 0.7 Å (Fig. 2). Nion’s next major project is a high-resolution monochromated EELS system2. We are using what we learned building aberration correctors to produce an EELS with an energy resolution hopefully as good as 10 meV. It is the next chapter on the path that Christian helped me start on many years ago, and it promises to be even more exciting than the previous ones.1. O.L Krivanek et al., Nature 464 (2010) 571.2. O.L. Krivanek et al., Phil. Trans. Roy.

Soc. A 367 (2009) 3683-3697.

Fig. 1. a) ADF image of monolayer BN with atomic substitutions. 60 kV, courtesy M.F. Chisholm. b) line profiles identifying the substitutions.

Fig. 2. Sub-area of a 2kx2k ADF image of Au particles. Inserts: FFT and a magnified area showing single atoms. court. N. Dellby.


19

Focused Ion Beams: Birth of a technologyPierre Sudraud

Orsay-Physics, 95 Avenue des Monts Auréliens 13710 Fuveau

Electrostatic energy can strongly modify the equilibrium conditions of a liquid meniscus. Stable conical liquid-air interfaces have been studied, especially in UK with the early works of Gilbert, Rayleigh, Zeleny, Taylor in a purely electro-hydrostatic point of view (1) (2). Such electro-hydrodynamic phenomena are probably involved in storms formation. About five cen-turies after Gilbert’s experiments, they gave rise during years 90s to several major industrial applications like electrospray, ion space propulsion and focused ion beam technology.

In years 1970, encouraged by an idea from R.Castaing, and by C. Colliex and his group, we started a pioneering work on the concept of high brightness point ion sources based on liquid and solid high curvature structures (4) (5). We developed a very compact ion source inclu-ding a sharp needle wetted by a film of liquid metal (Au, Sn, Ga, U etc...) and studied the ion beam physical properties. This was the beginning of “liquid metal ion source (LMIS)”. They had surprisingly better stability and brightness properties than all existing ion sources (6) and ion optics, easily delivering submicrometer spots, with nanoamp range currents. This was the begining of a new family of instruments called “focused ion beam” (FIB). Rapidly there was no getting away from FIB instruments, especially in the area of microelectronics (7), allowing accurate circuits cross-sectionning, editing, TEM sample preparation, nanostructures elabo-ration (8). Spectacular biological applications have recently been validated, like mapping of neuronas wiring and connectics called “brain mapping”. In 1989, with the help of Paris XI Uni-versity and Anvar, we started up a instrumentation company developping mainly focused ion and electron beams for both industrial integrators and laboratories. The company built the first combined FIB/SEM instrument in the world, then the first Leica VP SEM, using a innovative detector. Orsay-Physics is now located near Aix-en-Provence and develops different standard FIB optics (9), and has grouped 40 persons. It maintains strong R&D activities.

In 2010 the best FIB imaging resolution is better than 2nm with 1pA Ga current. It is the only instrument able to perform editing at the 22nm scale of next generation circuits . In the area of FIB instrumentation, current efforts are centered around brighter point ion sources for na-notechnologies research and future industrial “below 22nm” technology. This is why we are working in close collaboration with LAC for ultracold plasma sources and with several labo-ratories including LPN for point sources. The goal is to prepare sharper and sharper ion tools reaching the physical size limits of sputtering process. The other effort ranges in the opposite direction, in order to get focused ion tools able to remove “large” quantities of materials in the 100nm range. This is performed in collaboration with ion source specialists in CNRS. An example of positive exchanges between a small company, large industrial integrators, and pu-blic laboratories, which has definitely kept the philosophy of enthousiasm about physics and instrumentation, initiated by Christian in his research group.

(1) Gilbert, W. (1628) De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure, London, Peter Short(2) Taylor, G. (1969) Electrically Driven Jets. Proceedings of the Royal Society of London A: Mathematical, Physical & Engineering Sciences, 313, 453-475(4) Sudraud P, van de Walle J, Colliex C and Trebia P 1979 J. Physique 40L207(5) P. Sudraud, J. Van de Walle, C. Colliex, and P. Trebbia, Proc. 25th Int. Field. Emission Symp. (Albuquerque, 1978)(6) G. BenAssayag, P. Sudraud, B. Jouffrey, Ultramicroscopy 16 (1985)(7) J. Orloff, J. Scanning Electron Microscopy/1984/IV (1984) 1541.(8) G. Ben Assayag, C. Vieu, J. Gierak, P. Sudraud and A. Corbin, J. Vac. Sci. Technol. B 11/6 (1993), p. 2420.(6) Sudraud P, Ballongue P, Colliex C, Ohawa R and van de Walle JElectron Microscopy 1 1980 96(9)www.orsay-physics.com


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Notes


21

Chairman:

116:00 Akira Tonomura ...................... 24 16:30 Helmut Kohl ...................... 2517:00 John Spence ...................... 26

Elastic and inelastic coherence session

Bernard Jouffrey

Wednesday 9th June


22


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24

Observing vortices in superconductors using electron waves

Akira TonomuraRIKEN, Wako, Saitama, 351-0198, Japan

OIST, 12-22, Suzaki, Uruma, Okinawa, 904-2234, JapanHitachi, Ltd, Hatoyama, Saitama, 350-0395, Japan

Vortices in superconductors were predicted to exist by Abrikosov [1] in 1954. The possibility of the direct observation of the vortices by electron microscopy was investigated by Colliex et al. [2] and others in 1960s. However, the deflection angle of electrons due to a vortex was as small as 1×10-6 rad, the brightness of thermionic electron beams those days was not high enough to produce a highly collimated beam. The development of bright field-emission electron beams [3] has enabled their observation by holographic interference microscopy or by Lorentz microscopy.

I will talk on most recent application results not only on various behaviors of vortices including Josephson vortices in a high-Tc YBCO thin film, but also the nucleation process of the ferromagnetic phase assisted by magnetic fields in colossal magnetoresistance [4].

References[1] A. A. Abrikosov: “On the Magnetic Properties of Superconductors of the Second Group”

Soviet Physics JETP 5 (1957) p. 1174-1182.[2] C. Colliex, B. Jouffrey and M. Kleman: “Sur les Possibilites d’Observation de Lignes de

Vortex en Microscopie Electronique par Transmission” Acta Cryst. A24 (1968) p. 692-696.

[3] A. Tonomura: “Direct observation of thitherto unobservable quantum phenomena by using electrons” Proc. Natl. Acad. Sci. USA. 102 No.42 (2005) 14952-14959.

[4] Y. Murakami, H. Kasai, J. J. Kim, S. Mamishin, D. Shindo, S. Mori and A.Tonomura: “Ferromagnetic domain nucleation and growth in colossal magnetoresistive manganite” Nature. Nanotech. 5, No. 1 (January 2010) 37-41.


25

Image formation by inelastically scattered electronsHelmut Kohl

Physikalisches Institut und Interdisziplinäres Centrum für Elektronenmikroskopie Westfälische Wilhelms- Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany

The invention of the imaging energy filter by Castaing and Henry [1] has opened new possibi-lities for electron microscopy. First, it permits to select only the elastically scattered electrons and thus to enhance contrast and sharpness by eliminating the inelastically scattered electrons from the final image. Second, it is possible to select specific energy loss windows and study the spatial distribution of the corresponding excitations.

In their pioneering publication, Colliex et al. [2] showed, that this method could be used to ob-tain images of the elemental distribution. With these experiments they laid the ground for ele-mental mapping using energy filtered transmission electron microscopy. Furthermore, in these images, acquired using electrons having suffered a Cu-M23 loss, they demonstrated the preser-vation of elastic contrast. In the years to follow, he and his group have continued to investigate both aspects of imaging with inelastically scattered electrons, starting with an imaging energy filter and later on using a scanning transmission electron microscope (STEM) they pushed the detection limit down to a single atom [3].

In our presentation we shall review the theoretical description of image formation by inelasti-cally scattered electrons in the electron microscope based on quantum mechanical scattering theory. This approach yields the coherence properties of the scattered electrons in a straight-forward way. Currently the preservation of the elastic contrast is of great interest for the inter-pretation of atomic resolution chemical maps. To simulate such images the scattering matrix elements have to be calculated between distorted (Bloch) wave states.

References[1] R. Castaing and L. Henry, CR Acad. Sc. (Paris) 255 (1962) 76[2] C. Colliex and B. Jouffrey, CR Acad. Sc. (Paris) 270 (1970) 673[3] K. Suenaga, M. Tencé, C. Mory, C. Colliex, H. Kato, T. Okazaki, H. Shinohara, K. Hirahara, S. Bandow, and S. Iijima, Science 290 (2000) 2280


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Fast (monochromatic ?) electron sources and fast imaging.

J.C.H. SpenceDepartment of Physics, Arizona State University

Tempe, Az 85287-1504 USA and Lawrence Berkeley Laboratory, Ca.

From the beginning [1], Christian Colliex has provided sustained international leadership with a remarkably focussed effort to develop and apply the methods of electron energy-loss spectroscopy (EELS) in STEM. Apart from a brief excursion into liquid ion sources, his research has consistently been at the forefront of instrumentation development and theory in the application of EELS to interfaces, strongly-correlated electron materials, nanoparticles, helium bubbles, elemental mapping, plasmon imaging, STEM lithography and, most recently, nanotubes [2]. We have much to thank him for, including his recently demonstrated organisational abilities.

The brightness of his electron sources is one of the few things that has limited Christian’s enthusiastic efforts over forty years, and this we know , for a FEG STEM, is brighter than a synchrotron [3]. In our lab recently we have been experimenting with a laser-driven pulsed GaAs photo-field emission tip, for use in fast electron imaging, EELS, diffraction, and spectroscopy [4]. It had been suggested that this arrangement would produce a highly monochromatic beam, useful for EELS. The dependance of emission energy width on laser energy, and of electron intensity on laser intensity will be presented and discussed. In order to avoid the Coulomb interactions at crossovers which limit the speed of electron imaging [5], the diverging beam of a low-voltage point-projection image which avoids crossovers, may be useful.

Fast imaging is also possible using the world’s first hard X-ray laser (the LCLS) at Stanford. A continuous single-file jet of protein nanoparticles was fired across the pulsed 2 kV X-ray beam, and single-shot diffraction patterns read-out 30 times per second, one from each particle, lying in a random orientation. For 3 femtosecond pulses, the pulse terminates before radiation damage can begin, and before the sample is vaporized, yet contains enough photons for a useful high-resolution diffraction pattern (about 1012 photons). In this way radiation damage is out-run, breaking the previous nexus between damage and dose. Details of the jet design [6,7], of the electronic excitation times, and of the data analysis [8,9] for the millions of nanocrystal snapshot “stills” will be given. Femtosecond diffraction patterns have been obtained from membrane protein nanocrystals, viruses and live cells, all fully hydrated. Prospects for future pump-probe work, in which diffraction snap-shots are taken after exciting a molecule, will be given, aimed at providing “molecular movies”.

References1. C. Colliex and B. Jouffrey, Phil Mag 25 , 471 (1972)2. A. Gloter et al. Phys. Rev. B80, 035413 (2009).3. J. Spence and M. Howells Ultramic. 93, 213 (2002).4. J. Spence and T. Vecchionne. Phil Mag (2010) In press.5. A. Zewial and J. Thomas. 4D Electron Microscopy. Imperial College Press. 2010.6. J. Spence and R.B. Doak. Phys. Rev. Letts 92, 198102 (2004).7. D. DePonte et al. J.Phys D 41,195505 (2008); D. Shapiro et al J. Synch Rad. 15, 593 (2008)8. R. Kirian et al. Optics Express. (2010). Submitted. 9. J. Spence. Diffractive (lensless) Imaging. Chapter 18 in “Science of Micoscopy”. P. Hawkes and J.C.H. Spence eds. (Springer, New York) 2008.


27

Chairman:

110:00 Alan Craven ........................... 2910:30 David Muller ........................... 30

EELS session 2

Hiroki Kurata

Thursday 10th June


28


29

From apprentice to master – developments in STEM-EELSAlan J. Craven

Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland UK

I first met Christian at a summer school in Erice where he stood in for Raimond Castaing to lecture on SIMS and energy selected TEM. While he was already working in the field of EELS, I was research student in the process of building a FEGSEM based on the pioneering work of Albert Crewe. Some years later, I had moved on to running the VG HB5 in the Cavendish Laboratory when Christian came to the Cavendish on a visiting fellowship. At this point a long lasting friendship and a keen interest in what became know as STEM-EELS started. Key instrumental milestones along the way include the addition of post-specimen lenses, improved serial spectrometers and acquisition systems, parallel detection systems, the concept of spectrum imaging and its rapid development in recent years, methods of acquiring the whole energy range at individual pixels and the introduction of aberration correction. As the instrumentation developed so did the understanding and the data processing. This lead to applications to a wide range of materials systems. At all points, Christian and his group have made major contributions and earned truly international recognition for them.


30

Imaging the Electronic Structure of Interfaces

David A. Muller 1,2,1, Lena Fitting Kourkoutis 1 and John Silcox1

1 School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.2 Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.

In 1968 John Silcox spent a sabbatical at Orsay working with Pierre de Gennes on superconductivity. A meeting with a promising young graduate student performing EELS experiments [1] provided inspiration and motivation for a program in quantitative electron microscopy to probe the physics of materials. Christian’s contributions to STEM EELS serve as important landmarks in the field, which has now progressed to the point that atomic-resolution spectroscopic imaging is now capable of unraveling bonding details at buried interfaces and clusters, providing both physical and electronic structure information [2]. In some cases the sensitivity and resolution extends to imaging single dopant atoms or vacancies in their native environments. The detection and control of interface defects using EELS, closely-coupled with atomically-precise growth methods, has enabled the realization of interface-stabilized states unreachable in their bulk counterparts, including an oxidation-resistant 2D metal [3]; a 2D superconductor between two band insulators [4]; and, by eliminating extended 2D defects, ferromagnetic oxides a few unit cells thick.

[1] C. Colliex, B. Jouffrey, Inelastic-Scattering Of Electrons In A Solid By Excitation Of Deep Atomic Levels .1. Energy-Loss Spectra, Phil. Mag. 25 (1972), 491.

[2] D. A. Muller, L. F. Kourkoutis, M. Murfitt, J. H. Song, H. Y. Hwang, J. Silcox, N. Dellby, O. L. Krivanek, 86. “Atomic-Scale Chemical Imaging of Composition and Bonding by Aberration-Corrected Microscopy”, Science 319, (2008) 1073 .

[3] A. Ohtomo, D. A. Muller, J. L. Grazul, and H. Y. Hwang, “Artificial Charge-Modulation in Atomic-scale Perovskite Titanate Superlattices” Nature 419, 378 (2002).[4] N. Reyren, S. Thiel, A. D. Caviglia, L. F. Kourkoutis, G. Hammerl, C. Richter, C. W. Schneider, T. Kopp, A. S. Ruetschi, D. Jaccard, M. Gabay, D. A. Muller, J. M. Triscone, and J. Mannhart, “Superconducting interfaces between insulating oxides” Science 317 (5842), 1196 (2007).

Figure 1 – John Silcox’s Machinist’s union card during his 1967/8 sabbatical to Orsay. The union had a reputation as the best place to eat lunch.

Figure 2 –Atomic-Resolution EELS map of a LaSrMnO3/SrTiO3 multilayer, showing 1 unit cell of intermixing on the Ti/Mn sublattice.

Figure 3 –Mapping formal valence changes at the atomic scale using EELS – here showing an increased oxidation state for a single layer of Eu atoms at the interface between EuTiO3 on DyScO3.

1 Author to contact : [email protected] – Tel : +1 607 255 4065


31

CatherineBrÁchignac

Thursday 10th June 12:00 - 12:45

Clusters as precursors of nano-objects

Catherine BréchignacLaboratoire Aimé Cotton, CNRS, 91405 Orsay Cedex, France

Investigations of clusters made up from a few atoms, to several thousand atoms, from one to several tens of nanometers in diameter have opened new avenues for explorations of the physical factors and principles that underlie the transition from atomic and molecular regime to the condensed phase regime. The transition of matter from atomic to the solid state implies changes of organization which turn out to be more subtle and complex than was anticipated from scaling law.

The methods of synthesizing small particles based on agglomerating atoms or molecules, form objects whose size is comparable to the nanostructures obtained by sculpting the material microscopically, by nano-lithography or nano-engraving for example. When it is isolated the cluster can be considered as a prototype of small finite system and constitute a tool for exploring the unexpected properties of small finite objects, where each atom counts. When interacting they offer the possibility of use as elementary building blocks for new nano-architectures, making possible the control of matter at nanometer scale.

In the light of several examples this paper will discuss the issues of the electronic excitation, the stability, reactivity of metallic clusters as well as the new architectures made by self-organization of deposited clusters. At sufficiently small sizes when at least one of the dimensions of the material aggregate approaches the length scale characteristic to a physical phenomenon, nano-objects can behave in an unprecedented way.

Associated with new properties is the sensibility of small systems to shape. The fascinating capability that a nano-object has to modify its shape in order to minimize its free energy leads to shape modifications that may be observed on a reasonable time scale. Moreover at such a scale, the instabilities considerably influence the morphological stability of the nano-objects, leading to relaxation dynamics in non-equilibrium complex systems. These new facets of nano-objects lead to the invention of nano-objects yet not imagined.


32The morphology of islands grown on surfaces from soft-landed

clusters has been investigated by electron microscopy. Compact

islands have been observed on amorphous carbon surfaces, whereas

an evolution from compact to ramified shapes occurs on graphite

surfaces as the mean size of deposited clusters increases. Moreover,

by increasing the surface defect density on graphite, a continuous

variation of the island morphology is observed, from extended

ramified shapes to small compact shapes. In order to account for the

island morphologies observed, we propose a crude model involving

a competition between the time for aggregated clusters to coalesce

and the time interval between successive arrivals of clusters to grow

the islands. It shows that there exists a critical island size R0 dividing

island shapes into compact shapes for R<R0 and into ramified shapes

for R>R0. This critical size R0 varies as a function of the incident

cluster size. Relying on our experimental results, we show how the

morphology of the islands can be controlled by the size of the incident

clusters and the presence of surface defects.

Fig. 3. STEM images of antimony islands grown on gra-phite surfaces for different sizes of the incident clusters: (a)

<n>=4, (b) <n>=90, (c) <n>=150, and (d) <n>=500.


33

Chairman:

114:00 Kazumoto Suenaga ................ 3514:30 Richard Leapman ................ 36

Application session 1

Gustaaf Van Tendeloo

Thursday 10th June


34


35

Single molecular imaging and single atom spectroscopy

Kazu Suenaga1, 2

1 Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 305-8565 Tsukuba, Japan

2 JST-CREST

Applications of high-resolution (S)TEM has been mostly restricted to materials with periodic structures by now. Analysis of non-periodic structures with atomic resolution and atomic sensitivity, such as individual molecules, has still remained a challenge.

In the scheme of an international collaboration between Japan and France (1998-2003) (headed by Sumio Iijima and Christian Colliex), we have realized to utilize a carbon nanotube as a specimen cell to support individual molecules. The method is quite beneficial in terms of reducing irradiation damage of molecules because the cross-linking, a major mechanism for damage in molecular crystal, can be largely prevented. Chemical analysis of single molecules (metallofullerene, Gd@C82) has been then demonstrated for the first time by using the Colliex instrument [1].

We now recognize that a (S)TEM dedicated to single molecules or low-dimensional materials requires different specifications from that designed for the bulk (or thin film) crystal structures. The current status of so-called "Triple C project" which aims to build a (S)TEM dedicated to observation of non-periodic, light-element materials without thickness, will be presented.

[1] M. Tencé, M. Quartuccio and C. Colliex, PEELS compositional profiling and mapping at nanometer spatial resolution, Ultramicroscopy 58 (1995) 42-54.


36

Probing biological structures using STEM, EELS and energy filtering

Richard D. Leapman

National Institute of Biomedical Imaging and Bioengineering, NIH, Bethesda, Maryland, USA

Biological researchers performing nanoscale elemental analysis and imaging of biological structures owe a debt of gratitude to the pioneering work of Professor Christian Colliex and his colleagues, who laid down the framework and principles for many of the techniques that have now become the state of the art. This talk will outline a historical perspective of those developments and present up-to-date examples of their use. In the 1970s, Christian Colliex’s group recorded the first comprehensive set of core-edge electron energy loss spectra (EELS) from the first three rows of the periodic table, including the K and L2,3 edges of all of the biologically important elements [1]. Initially, employing a Castaing-Henry filter that had been developed earlier in Orsay, they characterized the core edge shapes and showed how they could be used to quantify elemental composition [2]. Then in the early 1980s the group introduced the VG Microscopes HB501 STEM into their laboratory and showed the possibility of elemental analysis on a nanometer scale with near single atom sensitivity [3, 4]. At about the same time, it was realized that important biological elements such as calcium could be detected at trace levels of parts per million [5]. Collaborating with the Biozentrum in Basel, Colliex’s group also combined the elastic dark-field STEM signal with inelastic signal and developed a theory of Z-contrast imaging to discriminate between different molecular components within cells [6]. Then in a landmark paper Jeanguillaume and Colliex introduced for the first time the concept of STEM ‘spectrum-imaging’, whereby multichannel EELS data are collected at each pixel in a rastered image [7]. This has been a critical development that enables biological nanoanalysis, and we adopted a similar approach in our own laboratory.

We have made use of many of these historic developments at Orsay to address biomedical problems at the NIH. Although radiation damage imposes a fundamental limit to the meaningful spatial resolution that is attainable in biological structures, we have shown the feasibility of measuring trace elemental concentrations [8], and detecting single atoms of elements such as iron and calcium [9]. We have combined electron tomography with energy-filtered imaging to map three-dimensional distributions of DNA in cell nuclei based on the phosphorus signal [10], and we have also developed a bright-field axial STEM tomography technique to image the three-dimensional structure within one-micrometer thick sections [11]. These approaches have recently been applied to diverse fields of research ranging from parasitology to neurobiology [12]. The scientific contributions of Christian Colliex have been essential to realize these objectives in the field of biomedicine.

[1] Colliex C, Jouffrey B. (1972) Phil. Mag. 25: 491-511.[2] Colliex C, Cosslett VE, Leapman RD, Trebbia P. (1976) Ultramicroscopy 1: 301-315.[3] Colliex C, Jeanguillaume C, Mory C. (1984) J. Ultrastruct. Res. 88: 177-206.[4] Colliex C. (1986) Ann. NY. Acad. Sci. 483: 311-325.[5] Shuman H, Somlyo AP (1987) Ultramicroscopy 21: 23-32.[6] Kellenberger E. et al. (1986) Ann. NY. Acad. Sci. 483: 202-226.[7] Jeanguillaume C, Colliex C. (1989) Ultramicroscopy 28: 252-257.[8] Leapman RD et al. (1993) Ultramicroscopy 49: 225-234.[9] Leapman RD (2003). J. Microsc. 210: 5-15.[10] Aronova MA et al. (2007) J. Struct. Biol. 160: 35-48.[11] Hohmann-Marriott MF et al. (2009) Nature Methods 6: 729-732.[12] Fukunaga M et al. (2010) Proc. Natl. Acad. Sci. USA (in press)


37

Chairman:

1

Application session 2

10:00 Pulickel Ajayan ........................ 39 10:30 Daniel Ugarte ........................ 40

Hui Gu

Friday 11th June


38

7. J. Faist, F. Capasso, C. Sirtori, D. L. Sivco, A. Y. Cho, inIntersubband Transitions in Quantum Wells, Semicon-ductor and Semimetal, H. C. Liu, F. Capasso, Eds.(Academic Press, London, 2000), vol. 66, chap. 1, andreferences therein.

8. Reciprocal space mapping along the (113) and (224)Bragg planes was performed.

9. T. Fromherz et al., Appl. Phys. Lett. 68, 3611 (1996).

10. T. Fromherz et al., Phys. Rev. B 50, 10573 (1994).11. P. Kruck et al., Appl. Phys. Lett. 76, 3340 (2000).12. J. Faist et al., Appl. Phys. Lett. 63, 1354 (1993).13. J. Faist et al., Appl. Phys. Lett. 65, 94 (1994).14. S. Blaser et al., unpublished data.15. P. Boucaud et al., Appl. Phys. Lett. 69, 3069(1996).

16. In a recent sample we have also been able to demon-

strate a confinement shift (observed EL energy, 154meV; calculated HH2 3 HH1 transition, 149 meV).

17. Supported by the Schweizerischer Nationalfonds andBundesamt fur Bildung und Wissenschaft Nr 99 0078.We thank M. Kummer, S. Blaser, D. Hofstetter, and S.Stutz for technical and analytical assistance.

14 September 2000; accepted 15 November 2000

Element-SelectiveSingle Atom Imaging

K. Suenaga,1,3* M. Tence,1 C. Mory,1 C. Colliex,1,2 H. Kato,4

T. Okazaki,4 H. Shinohara,4 K. Hirahara,3 S. Bandow,3 S. Iijima3,5

Electron energy-loss spectroscopy (EELS) is widely used to identify elementalcompositions of materials studied by microscopy. We demonstrate that thesensitivity and spatial resolution of EELS can be extended to the single-atomlimit. A chemical map for gadolinium (Gd) clearly reveals the distribution of Gdatoms inside a single chain of metallofullerene molecules (Gd@C82) generatedwithin a single-wall carbon nanotube. This characterization technique thusprovides the “eyes” to see and identify individual atoms in nanostructures. Itis likely to find broad application in nanoscale science and technology research.

Advances in nanotechnology increasinglyrely on characterization tools with atomicresolution. Chemical information on hetero-geneous nanostructures in particular is moreand more crucial for diagnosing and predict-ing properties of nanodevices. Electron mi-croscopies have long been able to image in-dividual atoms (1, 2) but cannot be used toidentify elements, because all scattered elec-trons are collected for imaging. For elementalidentification of individual atoms in an elec-tron microscope, only the inelastically scat-tered electrons that suffer element-specificenergy loss must be counted. It has beenpredicted that the detection limit of EELSshould be a single atom (3). However, con-vincing experimental evidence has been lack-ing because of the absence of fully adaptedtest objects (4 ).

Here, we demonstrate single-atom spec-troscopy by means of EELS. For this pur-pose, a perfectly suited specimen exhibiting asequence of individual atoms positioned atregular intervals has been selected. It is foundin a recently synthesized hybrid nanomate-rial, a single-walled carbon nanotube(SWNT) encapsulating a chain of metal-lofullerenes (5). A scanning transmissionelectron microscope ( VG HB501) that pro-vides a tiny electron beam with a high current

flux (�650 pA in a probe 0.5 to 0.6 nm indiameter) and a high-efficiency charge-cou-pled device–based detector after an electronspectrometer (modified Gatan PEELS 666)were used for the experiment. The focusedincident probe can scan the object under in-vestigation with accurate step increments onthe order of angstroms, allowing a wholeEELS spectrum to be recorded within a fewmilliseconds at each probe position. Hence,the intensity of characteristic energy-lossedges can be derived with highly accuratespatial information, and consequently themapping of the searched element is feasible(6 ).

A chain of endohedral Gd-metallofullereneswas recently generated inside a SWNT bythis research group (5). Such a material isideal for demonstrating single-atom spectros-copy, because this structure involves isolatedGd atoms separated by 1 to 2 nm (Fig. 1). Themetallofullerene molecules (Gd@C82) arealigned within a SWNT. The dark spots seenon each fullerene structure in the high-reso-lution image are suspected to be the encap-sulated Gd atoms (7). The interval betweenthe adjacent Gd atoms is large enough with

respect to the smallest probe size (�0.5 nm)accessible with our current electron optics.Element-selective imaging has been per-formed on a structure similar to that in Fig. 1.A set of 128 � 32 spectra was recorded witha 3 Å step (consequently, the scanned areacorresponds to �40 � 10 nm). Each spec-trum was acquired in as little as 35 ms withenough counting statistics. Intensities of theGd N45 edge and carbon K edge were extract-ed pixel per pixel from all the individualspectra (8), and chemical maps for both ele-ments were constructed (Fig. 2).

The bright spots in Fig. 2A are alignedalong the nanotube direction, which indicatesthat they correspond to the Gd atoms. Com-parison with the simultaneously obtained car-bon map (Fig. 2B) shows that the Gd atomsare located inside the carbon nanotube. Thisis further confirmed in Fig. 2C, which dis-plays the Gd map (smoothed by convolutionwith a 3 � 3 pixel matrix) superposed on thecarbon map. Therefore, we can confirm thatdoping the carbon nanotubes with metal-lofullerenes has been successful and that thedark spots seen in the high-resolution image(Fig. 1) explicitly correspond to the Gd atoms.

The arrows in Fig. 2B indicate the approx-imate positions of the individual Gd atoms.The interval between them is about 1 to 3 nm,and some of the Gd atoms are missing. Thisis probably because the Gd atoms tend tomove around from the original positions and,under the intense electron beam, make anaggregate of one to three (or four) atomsassociated with a fusion of the adjacent met-allofullerenes. Such coalescence processesbetween the metallofullerenes under the elec-tron beam have also been observed in situduring high-resolution electron microscopyobservations. Note that our present spatialresolution (�0.5 nm) is not sufficient to re-solve the carbon layer spacing (�0.34 nm)between the adjacent fullerenes and nano-

1Laboratoire de Physique des Solides (CNRS UMR8502), 2Laboratoire Aime Cotton (CNRS UPR 3321),Universite Paris-Sud, Orsay 91405, France. 3JapanScience and Technology Corporation, “Nanotubulites”project, Meijo University, Nagoya 468-8502, Japan.4Department of Chemistry, Nagoya University,Nagoya 464-8602, Japan. 5NEC Corporation, Tsukuba305-8501, Japan.

*To whom correspondence should be addressed. E-mail: [email protected]

Fig. 1. A conventionalhigh-resolution image(A) and a schematicpresentation (B) of asimilar structure. Achain of endohedralGd-metallofullerenes(Gd@C82) is encapsu-lated in a SWNT. TheGd atoms are shownin yellow in (B). Scalebars, 3 nm.

R E P O R T S

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Element-selective images for gadolinium (A) and carbon(B) and a constructed color image (Gd, red; carbon, blue) (C).

The Gd atoms are clearly identiÞed within thecarbon nanotube and distributed along the

nanotube axis. Scale bar, 3 nm


39

Microscopy for Materials Scientists: Carbon Nanotubes and Beyond

Pulickel M. AjayanMechanical Engineering and Materials Science Department

Rice University, Houston, Texas 77005, USA

With the advent of nanotechnology the utility of microscopy techniques have acquired new dimensions. The need to resolve every single atom in a structure and the hierarchical organization of atomic structure present in materials make characterization challenging, both from the spatial resolution as well as chemical discrimination perspectives. In addition, in situ dynamic events are important to determine stability in these materials as nanostructures often behave differently from their bulk counterparts.

Here I will describe excerpts from work done over nearly two decades, where microscopy has served as a guiding light in understanding as well as development of materials at the nanoscale. The bulk of the work will relate to the history of carbon based nanostructures, starting with the early work on carbon nanotubes. Carbon, in its various nanoscale morphologies has fascinated the scientific community in recent times and the talk will discuss the challenges and excitement that microscopy has offered materials scientists in deciphering the structure-property correlations in carbon based structures.

In particular, the case of different carbon nanostructures will be used to highlight the state of the art. Various organized architectures from carbon fabricated using relatively simple processes and the work in attaining control on the directed assembly of these structures will be discussed. The story extends from carbon nanotubes to graphene. Some of these structures offer excellent opportunity to probe novel nanoscale behavior; and some of our contributions in understanding this will be highlighted. The challenges in creating and characterizing heterogeneous and complex nanostructures and composites will be discussed.


40

Manipulation and characterization of individual nanosystems by in-situ electron microscopy experiments in a tropical environment

Daniel Mario Ugarte Inst. de Física “Gleb Wataghin”-UNICAMP, Campinas SP, Brazil

[email protected]

Nano-systems are attracting a great deal of interest as one of the most promising alternatives to continue miniaturization of electronic devices. Despite the huge importance of this field, both from the basic physics and, nanodevice viewpoints, many essential questions remain open. The high spatial resolution of electron beam instruments has transformed electron microscopy (EM) into an essential tool of cutting edge research in nanoscience and technology. The activities developed in the Orsay STEM Group have certainly helped to create, build and consolidate the major role of EM in current science. We must keep in mind that, well before “nanofashion”, many physical and instrumental aspects were addressed and worked out in Orsay with visionary insight.

During 2010, several events will focus the attention of EM researchers; firstly, in June, a workshop will honor the role of Christian Colliex (CC) in fostering excellence in science and friendship. Secondly, the major EM meeting (ICM 17) will take place in Rio de Janeiro-Brazil in September; finally, the football world cup will start in June. Maybe, some people may think that this last, but not least, shindig provides an explanation for the presence of a South-American contribution at this workshop (Vamos Messi!!!!!).

In fact, the Brazilian National EM Facility in Campinas has benefited from the active engagement of CC in Brazil (everybody knows that he likes to travel, especially to fancy places!) through discussions on research, funding and scientific policy. The creation of this lab certainly became a reality due to his energetic support and clarifying ideas. The subsequent lab operation tried humbly to mirror the Orsay group’s essential aspects: scientific quality, deep understanding of sample and instrument physics and, all this within a motivating friendly ambiance (…food and wine welcome; unfortunately in

Brazil, French cheese is only available to us by smuggling after scientific missions to Paris).

Finally, talking about scientific results, we have focused our activities on the elongation and rupture of atomic–size metal wires, in particular the ultimate metal conductor: a one-atom-thick one (see Fig 1a). We have studied the correlation between atomic structure and quantum conductance behavior for different metals (Au, Ag, Cu, Pt, etc.) and alloys (AuAg, AuCu). But, we have also been recently influenced by the artistic nature of Orsay/Paris’s rich and varied intellectual ambiance and, we were involved in a project with Institute of Arts graduate students for the transcription (or new representation) of poetry, or to coin a new word “Nanopoetry” (see Fig. 1b). Briefly, a sculpture/one-word-poem was sculpted on a semiconductor (InP) nanowire using the latest FEG-TEM/STEM in our lab. This experiment obviously did not yield a high impact journal paper, but it got half a page of the main Brazilian newspaper.

Fig. 1. a) HRTEM image of a suspended atom chain generated by the elongation of an Ag-Au alloy nanowire; atomic positions appear dark. b) Nanowriting on an InP nanowire; reinterpretation of the original poem-sculpture “Infinitozinho” (small infinity) from Arnaldo Antunes (Brazilian artist). Idea from Giuliano Tosin (Inst.- Arts/UNICAMP), execution L.H.G. Tizei, management DU.


41

The 40 Years of High Resolution Transmission Electron Microscopy of Materials Science

Sumio IijimaMeijo University, National Institute of Advanced Industrial Science and Technology /Nanotube Research Center,

SAINT and NEC

On-ko-chi-shin. It is an old Chinese saying by Confucius. It means that to explore a new thing we should go back sometime to the old things from time to time. Electron microscope is meant to be an instrument to characterize atomic structures of materials and toward this goal so many researchers devoted their effort to see more details of the materials. The efforts still have been going even after its invention in the 1930s. We will see the latest achievements of electron microscopy studies of materials in this symposium in the happy occasion of Prof. Christian Colliex retiring from his lifelong devotion to the electron microscopy. But I would like to draw your attentions in looking back my personal achievements in the HRTEM works in terms of materials science point of view. By doing so I would like to convince you that one of my discoveries in materials science, that is, the carbon nanotubes is a consequence of my ample experiences with many different types of materials in Three Dimension (bulk), Two-D (surfaces), One-D (filaments or nanotubes) and Zero-D (individual atoms and molecules). I have looked at all of these structures in my carrier for 40 years. I will emphasize on the fact that surprisingly all of these experiences are related to the discovery of carbon nanotubes in many ways.

1) S. Iijima, Jpn. J. Appl. Phys., 8, 1377-1389 (1969)2) S. Iijima, J. Appl. Phys., 42, 5891-5893 (1971).3) P. R. Buseck and S. Iijima, Am. Mineral., 59, 1-21 (1974).4) S. Iijima, Optik, 48, 193-214 (1977).5) M. A. O’Keefe, P. R. Buseck and S. Iijima, Nature, 274, 322-324 (1978).6) S. Iijima, Chemica Scripta, 14, 117-123 (1978-9).7) S. Iijima, J. Cryst. Growth, 50, 675-683 (1980).8) S. Iijima, J. Solid State Chem., 42, 101-105 (1982).9) S. Iijima and T. Ichihashi, Phys. Rev. Lett., 56, 616-619 (1986).10) M. Murakami, S. Iijima and S. Yoshimura, J. Appl. Phys., 60, 3856-3863 (1986).11) S. Iijima, J. Phys. Chem., 91, 3466-3467 (1987).12) M. Haruta, N. Yamada, T. Kobayashi and S. Iijima, J. Catal., 115, 301-309 (1989).13) S. Iijima, Yumi Aikawa and Kazuhiro Baba, Appl. Phys. Lett., 57, 2646-2648 (1990).14) S. Iijima, Nature, 354, 56-58 (1991).15) Z. Liu, et al., PRL, 102, 015501 (1)-(4) (2009).16) C. H. Jin, et al., PRL, 102, 195505 (1)-(4) (2009).

Sumio Iijima

Friday 11th June 11:45 - 12:30


42


43

SociÁtÁ Fran�aise de Microscopie

The French Electron Microscopy Society was created on June 6, 1959. The aims were and are to “contribute to progress in electron microscopy, electron optics and diffraction, as well as related science in industry”. In 1996, the name was changed to the “French Microscopies Society (SFµ)” to reflect an expansion towards the new kinds of microscopy (STM, AFM,…).The principal aims of the SFµ are the gathering and dissemination of scientific knowledge, the training of microscope users, and cooperation with commercial companies. The scientific conference of the society is organised every two years. Special emphasis is placed on student support, with the “Pierre Favard prize” rewarding the best PhD dissertation of the last two years, and the provision of grants to young researchers to attend international conferences.Christian Colliex, as a student of the first president Raimond Castaing, has always been strongly involved in SFME and Sfµ activities; he was, in particular, president of the SFµ from 1990 to 1991 and editor of Microscopy, Microanalysis, Microstructures, published by the SFME from 1990 to 1997.At this conference the Sfµ will be represented by Virginie Serin, the current president. Bernard Jouffrey, president in 1978-1979, will give an overview of some scientific aspects of Christian Colliex’s career, and Françoise Livolant, an expert in cryomicroscopy for biological applications will give a presentation on the study of biological nano-objects by electron microscopy.

Virginie Serin

Presentation of the Sfµ, Christian Colliex’s contributions

Bernard Jouffrey Christian Colliex’s career: an overview of the scientific aspects

Françoise LivolantBiological nano-objects and electron microscopy

Thursday 10th June 16:00 - 17:00


44

Figure 1: From catalyst deactivation towards Chemi-cal Atomic Resolution information of nanostructures.

Cadiz-Paris Train Line: Catalysts, Nanostructures and EELS Spectroscopy

S. Trasobares1, M. López-Haro1, J.A. Pérez-Omil1, J.C.Hernandez1, J.J Calvino1, O Stephan2,M. Kociak2 and C Colliex2.1Universidad de Cadiz, Campus Universitario Rio San Pedro, 11510 Puerto Real, Spain

1Laboratoire de Physiques des Solides, Université Paris Sud, 91405 Orsay, France.

Electron Energy Loss Spectroscopy in the context of a Scanning Transmission Electron Microscope has demonstrated to be a perfect tool to characterise complex structures as metal nanoparticles (Rh, Pt, Au) supported on cerium oxides. In these catalytic materials, the substrate composition and electronic structure are crucial parameters which are directly related to the catalytic properties of the system. It is also important to remark that these nanostructures present an active substrate whose oxygen storage capability is directly related to Ce3+/Ce4+ exchange. As it will be demonstrated in this work the “Cadiz-Paris train line” has provided information about the structure and chemistry of individual nanocrystals. Since the inauguration of this “transport line” in 1997 many problems and questions have been solved. EELS has been successfully used to identify the catalyst deactivation, metal-support interaction, surface modifications etc… Recently, aberration corrected microscopy combined with EELS spectroscopy has also provided the first direct chemical evidence of a cationic order in a Ce-Zr mixed oxide nanocrystal and chemical atomic resolution maps have been used to refine the structure of a phase of this material.

Young researchers

Susana TrasobaresWednesday 9th June 15:00 - 15:15

Gianluigi BottonThursday 10th June 11:45 - 12:00

Alexandre GloterThursday 10th June 15:00 - 15:15


45

High-Resolution EELS imagingGianluigi Botton, Sorin Lazar, David Rossouw, Yang Shao, Lina Gunawan, Karleen Dudeck and Martin Couillard 1

1 McMaster University, Canada,

The field of electron microscopy has drawn upon from the many contributions of Christian Colliex and his research team. From energy loss near-edge structures, and low-loss spectroscopy to atomic resolution chemical analysis, the Orsay group has always been at the forefront of EELS analysis. Christian has also been a great promoter of the new generation of researchers irrespective of their research base. In this presentation, I will thus highlight some research work done at McMaster in the areas that have overlapped with Christian’s contributions and influence.

Experiments were done on an aberration-corrected (probe and image) microscope (Titan 80-300^3) equipped with a high-resolution energy loss spectrometer and a high brightness electron source. This system recently demonstrated atomic resolved elemental map-ping [1] and shallow core-loss imaging that clearly highlighted the presence of the collection-angle-dependent predicted volcano structure [2]. We also demonstrated the detection of near-edge structures variations in inequivalent sites of a layered perovskite unit cell. In low-loss imaging, we have also recently demonstrated the detection of contrast at atomic resolution arising from the phonon-mediated losses [2]. As example, low-loss images normally exhibit contrast dominated by the zero-loss image features. When large

collection angles are used, however, reversal of contrast has been observed (figure 1). Further examples will highlight the application of high-resolution analysis and the major challenges.

Figure 1 HAADF image of LaB6 in the <100> orientation (La-La spacing of 4.15Å), Zero-Loss images and energy filtered STEM images at 3 and 18eV loss obtained at two spectrometer collection angles: 110mrad (top row), and 27 mrad (bottom row).[1]GA Botton, S Lazar, C Dwyer, In press Ultramicroscopy[2] Lazar et al, Accepted Microsc.& Microanalysis

Electron Energy-Loss Spectroscopy of transition metal-based materials: from high energy p-d excitations to low energy d-d excitations

A. Gloter1, L. Bocher1, F.T. Huang1, A. Torres-Pardo1, M. Walls1, D. Imhoff1, O. Stephan1 and C Colliex1.1Laboratoire de Physiques des Solides, Université Paris Sud, CNRS UMR 8502, F-91405 Orsay, France.

Transition metal-based materials are widely and extensively studied by electron energy-loss spectroscopy (EELS). The energy range of their 2p excitations (spanning from 400eV to 950eV) is particularly convenient for EELS analysis. The diversity of properties and contexts (photo-catalysis, magnetism, transport, environment...) in which transition metals can be encountered has also contributed to this popularity. In the early ‘90s, C. Colliex and coworkers [1] produced a series of articles on the L edges of iron and manganese oxides that are still a reference for current studies of nanomaterial valences. Starting from these pioneering works, we will present some recent results concerning the electronic structure of TM-doped nanostructures [2] and interfaces [3] and their elucidation using the fine structures of the EELS TM 2p excitations.We will also show that among the various spectral domains which have been probed for studying strongly correlated materials, the low energy region (<5eV) is of increasing interest. In particular, d-d excitations, which correspond to transitions within the open d shell, have been investigated and can provide information on the ground state properties [4].

Figure 1 : Ti 2p-3d excitations for reference TiO2 and tri-titanate nano-tubes.

[1] H. Kurata and C. Colliex PRB 48 2102 (1993); H. Kurata et al. PRB 47 13763 (1993) ; C. Colliex et al. 44 11402 (1991). [2] L. Catala et al., Angewandte Chemie 48, p183-187 (2009) ; S-Y Chen et. al., PRB 79, 104103 (2009) ; A. Gloter et al PRB 80, 035413, (2009).[3] L. Bocher et al. In preparation. [4] A. Gloter et al., Ultramic. 109, 1333 (2009)


46

Postersessions

Figure 1: CL Spectra acquired on selected areas: bulk GaN and GaN Quantum discs.

A cathodoluminescence study of a UV photodetector based on GaN/AlN Quantum Discs

in a single nanowireL. F. Zagonel1, M. Tchernycheva2, L. Rigutti2, F. H. Julien2,

R. Songmuang3 O. Stephan1 and M. Kociak1

1Laboratoire de Physique des Solides, U. Paris Sud, France; 2Institut d’Electronique Fondamentale,U. Paris Sud, France ;

3Nanophysique et Semiconducteurs, Institut Néel, France

In order to explore optical properties of objects belonging to the nano-world, experimental techniques are facing the challenge of high efficiency associated with high spatial resolution and high energy resolution. Modern Electron Microscopes readily reach the required spatial resolution while cathodoluminescence (CL) can directly provide the optical response of the sample to the electron beam excitation. A Scanning Transmission Electron Microscope (STEM) equipped with a High Brightness Cold Field Emission Gun (C-FEG) is well suited to support this technique. We have developed a optimized CL system which can work simultaneously with the parallel EELS system. This apparatus is capable of acquiring CL spectral imaging in parallel acquisition mode (a full spectrum for each pixel of the image) with high spatial sampling (1 nm) and high spectral resolution with a relatively fast acquisition. The microscope is also equipped with a cryogenic sample stage operating at liquid nitrogen temperatures.

Here we will discuss preliminary results obtained in the study of a UV photodetector based on a stack of GaN/AlN quantum discs (QD) in a single nanowire. The CL spectra shown here, Figure 1, were obtained by use of selected area spectroscopy corresponding to zones on the bulk and on the QD’s. The stronger line at ~3.5 eV corresponds to the strained bulk GaN signal. Peaks at higher energies correspond to small QD with a pronounced quantum confinement effect.

STEM-CL – Cathodoluminescence studies using fast electrons

Duncan Alexander 1, Anas Mouti 1, Pierre Stadelmann 1 and Cécile Hébert 1

1 Centre Interdisciplinaire de Microscopie Électronique,EPFL, Switzerland.

An 80–200 kV JEOL 2200FS (scanning) transmission electron microscope equipped with a Gatan XiClone cathodoluminescence (CL) spectrometer is being used to explore the possibilities and benefits of CL detection in STEM mode. A high-contrast pole piece allows insertion of a large, 3 mm parabolic mirror for efficient light collection, which can either be detected in pan or monochromatic mode on a Peltier-cooled PM-tube, or with a liquid nitrogen cooled CCD camera for parallel (para-CL) acquisition. The in-column W-filter, an array of STEM detectors (BF, ADF, HAADF, SE, BSE), and a CCD camera give flexibility for simultaneous acquisition of other signals, such as electron energy-loss spectrum, diffraction and Z-contrast images, and STEM diffraction patterns.

Investigations are underway on a variety of samples (e.g. semiconducting oxides and nitrides, luminescent and photonic crystals, plasmonic and geological samples). Results show that a balance clearly exists between the operating conditions and the physics of the signal generation. For instance, study of nitrides is found to depend critically on the greater e-h formation density, and thus CL signal, generated at lower beam energies. With use of 80 keV electrons, a CL signal spatial resolution of 1 nm is then realised on quantum wells. Meanwhile, in a silicon photonic tile structure, fast 200 keV electrons can be used to stimulate Čerenkov radiation, which is in turn backward detected using the CL mirror. As seen in Figure 1, this allows mapping of Bloch modes with a spatial resolution of some nm, compared to a few mm for conventional optical characterization tools. Such results illustrate the potential of STEM-CL for analysis of optical properties on the nano-scale.

Figure 1. CL maps of Čerenkov radiation-generated Bloch modes in a photonic tile structure for wavelength windows 499–507 nm (left) and 655-663 nm (right).


47

Postersessions

Two versatile TEM specimen holders for in situ illumination of photoactive materialsM. Kobylko1, G. Divitini1 , and C. Ducati 1 ,

1 HREM Group, Department of Materials Science and Metallurgy, University of Cambridge, UK

Understanding the photon-induced modification in the electronic structure of nanosized particles of photoactive materials can contribute to the development of more efficient photovoltaic devices for the conversion of sunlight into electricity.

Therefore, we have designed and constructed two in situ illumination TEM specimen holders for Philips and FEI TEMs which allow suitable materials to be irradiated with photons of a chosen wavelength under the electron beam. This has been achieved by incorporating commercial home-processed light emitting diodes (LEDs) into existing TEM biasing holder designs and by modifying the specimen fixation mechanisms.

The first design we demonstrate is based on a single tilt Philips EM300 heating holder. It has the advantage of being able to accommodate specimens of different geometries, in particular also thicker and/or larger specimens, e.g. silicon oxide or silicon nitride membranes.

The second design, based on the Fischione electrical biasing tomography holder [1] is best suited for traditional copper grids.

As in this design the LED is placed on a home-made removable cartridge and can thus be very quickly and easily exchanged for another LED, this design allows to easily change the illumination wavelength. Furthermore, the second design is capable of high-resolution imaging under photon irradiation, as verified using a FEI Tecnai F20.

Both holders are compatible with the Philips CM300, the FEI Tecnai and the FEI Titan TEM [2].

[1] R.E. Dunin-Borkowski et al., Microscopy and Microanalysis (2004), 10 (Suppl 2), 1012-1013

[2] We want to thank Professor P. Midgley for fruitful discussions, and Dr R. Broom for help in manufacturing the first design holder. We thank the Royal Society and EPSRC for funding.

Valence Electron Energy-Loss Spectroscopy characterization of Ti2AlN/TiN multilayers.

M. Bugnet , V. Mauchamp, F. Pailloux, T. Cabioc’h and M. Jaouen

Institut P’, CNRS-Université de Poitiers, UPR 3346, Bd M.&P. Curie, 86360 Futuroscope-Chasseneuil

Ti2AlN belongs a family of layered ternary nitrides or carbides: the MAX phases. These compounds combine the best properties of ceramics and metals which make them very attractive both fundamentally and for applications (structural materials, electrical contacts …). Ti2AlN/TiN multilayers were, for instance, shown to exhibit strong damage tolerance to light ion irradiations.a

Ti2AlN/TiN multilayers were synthesized by dual ion beam sputtering of TiN/TiAl multilayers followed by high temperature nitriding. The low-loss region of a bulk Ti2AlN sample was first fully analyzed combining VEELS experiments and Density Functional Theory calculations. The two main peaks were respectively shown to correspond to a plasmon excitation and an interband transition characteristic of the Ti-d N-p hybridization.b

The multilayer was then analyzed by HAADF and Energy Filtered TEM using energy windows of 2 eV around the Ti2AlN

or TiN plasmon energies (at 16.5 and 25.5 eV respectively). The multilayer structure of the Ti2AlN/TiN sample was confirmed: images show 15 nm Ti2AlN polycrystalline layers separated by 3 nm TiN layers. The micrographs also reveal the presence of an epitaxial layer. STEM-EELS experiments (fig a and b) performed on this layer show that it consists in two phases: a TiN layer epitaxially grown on the Al2O3 substrate and a Ti2AlN layer epitaxially grown on this TiN layer. Epitaxy is then lost in the remaining of the multilayer.

(a) HAADF micrograph of the epitaxial layer showing the probed areas in STEM-EELS. (b) plasmon losses fingerprints corresponding to the different probed areas.

a M. Bugnet et al., J. of Material Science, submittedb V. Mauchamp et al., Phys. Rev. B 81, 035109 (2010)


48

Postersessions

Investigation of advanced gate stacks dedicated for microelectronics coupling HRTEM/ STEM-

EELS with electrical or optical methodsS. Schamm-Chardon 1, J. Groenen 1, L. Lamagna 2 and

C. Wiemer 2,

1 CEMES-CNRS, Université de Toulouse, nMat group, France,2 MDM, IMM-CNR, Agrate Brianza, Italy.

Downscaling in microelectronics raises big challenges concerning the choice of new materials and their successful integration in MOS structures. At CEMES, we particularly aim at establishing structure-property relationships based on TEM/EELS nano-analytical methods using an image aberration corrected microscope and their connection with other physical methods. We propose here to illustrate two case studies dealing with a coupling with C-V measurements and Raman experiments respectively.

The first case concerns high permittivity (k) oxides based on transition and rare-earth metals dedicated for replacing SiO2 in MOS gate stacks. Maximizing performances of these stacks requires strategies to minimize the overall effective oxide thickness particularly aiming at obtaining the highest k value for the gate oxide and the thinnest but passivating interfacial

layer (IL) that forms unavoidably at the semiconductor/gate oxide interface. Beyond the demonstration of a structural and/or chemical IL formation, the dielectric properties of each layer in the stack (IL and high-k above) is determined combining HRTEM/STEM-EELS and electrical C-V results with a multi-layers capacitor model approach [1,2].

The second case concerns the support that HRTEM/STEM-EELS experiments bring to the development of a non-destructive method for optical spectrometry measurements based on Raman-Brillouin scattering. Velocities of light and sound can be measured locally. For example, determining the elastic constant is a prerequisite to assess the local stress that impact on the mobility of carriers in devices. The method is based on the comparison of Raman-Brillouin spectra to models. In this procedure, HRTEM/STEM-EELS help to fix structural and chemical parameters in the model in order to be able to determine the contributions of only optical/acoustical effects.

[1] S. Schamm et al., J. Electrochem. Soc., 156 (2009) H1. [2] L. Lamagna et al., Appl. Phys. Lett., 95 (09) 122902.

Theoretical analysis of q-dependent dielectric properties of Ag and Au

C. Hébert1, A. Alkauskas1, S. D. Schneider1, S. Sagmeister2, and C. Ambrosch-Draxl2

1Ecole Polytechnique Fédérale de Lausanne (EPFL), LSME, Institute of Condensed Matter Physics, CH-1015 Lausanne, Switzerland. 2Chair of Atomistic Modelling and Design of

Materials, Montanuniversität, Leoben, Franz-Josef-Strasse18, A-8700 Leoben, Austria

In this work we perform a comparative theoretical study of dielectric properties, the loss function in particular, of Ag and Au in the energy range 0-60 eV. The dielectric functions were calculated in the linear response regime within the RPA. At q=0 for energies >15 eV the inclusion of local-field effects is crucial to bring the calculated loss functions in a good agreement with experiment.

Given this good agreement for q=0, we have then studied the q-dependence of the loss function. In the case of Ag, the 3.8 eV plasmon peak shows a parabolic dispersion. When the single-particle spectrum of Ag is corrected for many-body effects within the approximate GW scheme, the energy and the parabolic dispersion coefficient of this plasmon are in excellent agreement with experiment. Higher-lying peaks are caused by

intra-band transitions. Their energy changes little, but their intensity reduces for larger q. In the case of Au the low-energy plasmon is completely damped already at q=0. Higher-lying peaks caused by intra-band transitions show analogous behavior to the case of Ag.

Fig. 1. The calculated (solid line) and measured ([1], dots) loss functions of Ag and Au. The calculated functions are presented both with and without local-field effects. Their inclusion brings the theoretical loss functions in a good agreement with experiment.

We acknowledge the support of the Swiss SNF Project 200021 120308


49

Postersessions

Low-Loss Simulation with a Discrete Dipoles Model

Luc Henrard and Nicolas Geuquet PMR, University of Namur, Belgium

The recent instrumental and experimental advances in low-loss EELS has led to the study of surface plasmon excitations of nanoparticules in the optical range, with an obvious link with plasmonic and the numerous associated scientific and technological challenges [1].

We have developed a discrete dipole approximation (DDA) for the simulation of low loss EELS in non-penetrating geometry. If DDA has been widely developed in classical electromagnetism [2] and applied to metallic nanoparticles [3], the simulation of EELS response has been rather restricted [4,5]. We present in this communication a few recent contributions of our approach to a better understanding of experimental EELS data on plasmonic devices.

First, we compare EELS data and optical properties of a silver triangular nanoprism and show that the spatial variation of surface plasmon excitation probabilities could help to discriminate modes of similar energies. We also emphasized the importance of the substrate polarization effect to correctly

describe experimental data. We demonstrate the importance of the surface plasmon coupling inside the nanoparticle (interface plasmon) for the understanding of the local optical properties [5,6]

Second, we discuss the localization of plasmonic modes with the example of cubic particles. Local modification of the environement is shown to locally modify the surface plasmon response and then to destroy the global optical response.

[1] J. Nelayah et al. Nature Physics 3 (2007) 348[2] B.T. Draine et al. J. Opt. Soc. Am. A 11 (1994) 1491[3] K.L. Kelly et al. J. Phys. Chem. B 107 (2003) 668[4] L. Henrard et al. J. Phys. B 29 (1996) 5127[5] N. Geuquet and L. Henrard. Ultramicroscopy. In Press[6] J. Nelayah et al. NanoLett. 10 (2010) 902

Theoretical Calculations of EELSJ. J. Rehr , K. Jorissen, J. Vinson, and J. Kas

Dept of Physics, Univ. of Washington, USA

There has been significant progress in recent years in theories and ab initio calculations of core-level electron energy loss spectra (EELS). Here we review two complementary approaches. First a relativistic, real-space approach based on an extension of the real-space Green’s function (RSGF) approach [1], and second, a reciprocal space approach based on an impurity KKR formalism [2]. Both are implemented in the FEFF9 spectroscopy code [3] which builds in the dominant many body effects in core-spectra, namely a screened core-hole, inelastic losses, and Debye-Waller factors.

Our reciprocal space approach is applicable to periodic systems but without the need for a supercell. The approach is uses a hybrid scheme incorporating reciprocal space calculation of the KKR multiple-scattering equations, together with a local, real-space calculation of the excitation spectrum in the presence of a statically screened core-hole. The approach accounts for core-hole effects in deep core spectroscopies while circumventing the supercell convergence issues encountered with conventional band structure codes. The relativistic approach is especially important in calculations of the EELS of anisotropic systems, and explains the observed deviation of the magic angle in EELS

from non-relativistic estimates. These approaches are illustrated with a number of applications. We also compare the results with accurate GW/BSE calculations of EELS using the recently developed core-level x-ray and EELS code OCEAN [4].

Acknowledgement: We thank M. Jaouen, G. Hug, E. Shirley, A. Sorini, and F. Vila for comments and other contributions to this effort. This work was supported by the US DOE BES Grant DE-FG03-97ER4562 and was facilitated by the DOE Computational Materials Science Network.

[1] K. Jorissen, J. J. Rehr, and J. Verbeeck, Phys. Rev. B 81, 155108 (2010).[2] K. Jorissen, PhD Thesis, U. Antwerp (2008).[3] J. J. Rehr et al., Comptes Rendus Physique 10, 548 (2009).[4] J. Vinson, E. L. Shirley, J. J. Kas and J. J. Rehr,UW Preprint (2010).


50

Postersessions

EELS assessment of chemical and electronic properties of (001) and (110) SrTiO3/

La2/3Ca1/3MnO3 interfaces

S. Estradé 1,2, J.M. Rebled 1, M.G. Walls 3, F. de la Peña 3, R. Córdoba 4, I.C. Infante 5, G. Herranz 5, F. Sánchez 5, J.

Fontcuberta 5, F. Peiró 1, 1 LENS, MIND-IN2UB, Departament d’Electrònica, Uni-

versitat de Barcelona, Spain, 2 TEM-MAT, SCT, Universitat de Barcelona, Spain, 3 Laboratoire de Physique des Solides,

Université Paris-Sud, France, 4 Instituto Universitario de Investigación en Nanociencia de Aragón (INA), Spain, 5

Institut de Ciència de Materials de Barcelona -CSIC, Spain.

SrTiO3 (STO) capping layers were grown on (001) and (110) La2/3Ca1/3MnO3 (LCMO) electrodes. XRD reciprocal space maps show the (001) LCMO electrode remains fully strai-ned, whilst the (110) is partially relaxed. Curie temperature of the bare electrodes is clearly dependent on the subs-trate orientation, being higher for the (110) one (256 K) than for the (001) electrode (180 K). When depositing 4 nm thick capping layers, the magnetization of the (001) samples is clearly reduced after the capping. On the contrary, no re-levant decrease on magnetization is observed for the (110) samples.

In the present work we will show the results of the compara-tive characterization by (S)TEM – EELS of the STO/LCMO bilayers and corresponding LCMO bare electrodes grown on STO, for both orientations, and we will correlate them with their magnetic properties.

Experiments were carried out in a Jeol J2010F (S)TEM mi-croscope operating at 200 keV, coupled with a GIF spectro-meter, and in a Nion UltraSTEM 100 aberration corrected dedicated STEM.

MnOx/MnOy nanoparticles characterized by EELS

S. Estradé1,2, A. López-Ortega3, M. Estrader3,G. Salazar-Alvarez3,4, M.D. Baró5, J. Nogués3,6, F. Peiró1,

1 LENS, MIND-IN2UB, Departament d’Electrònica, Universitat de Barcelona, Spain, 2 TEM-MAT, SCT,

Universitat de Barcelona, Spain, 3 ICN-CSIC, Spain, 4

Materials Chemistry Group, Dept. of Physical, Arrhenius Laboratory, Sweden, 5 Departament de Física, Universitat

Autònoma de Barcelona, Spain, 6 ICREA, Spain.

Bi-magnetic core-shell systems in which the core is ferroma-gnetic (FM) and the shell antiferromagnetic (AFM) have been widely investigated both theoretically and experimentally. However, studies of “inverse” core-shell nanoparticles with AFM cores are rather scarce. In this work we present the com-plete characterization of inverted MnOx(AFM)/MnOy(FiM) core/shell nanoparticles with different sizes, by means of (S)TEM-EELS.

HRTEM does not allow distinguishing between the core and the shell in these nanoparticles, as the shell grows epitaxially on the core, and HAADF imaging does not yield any different contrast for the two manganese oxides.

In this sense, quantitative EELS was applied to assess the local composition of the MnOx/MnOy nanoparticles, through a direct evaluation of Mn oxidation state, allowing to tell the core from the shell in the nanoparticles and to determine the nature of the involved manganese oxides. Mn oxidation state was estimated based on the Mn L3/L2 peak intensity ratio and from the Mn L3 peak onset using the home-made program MANGANITAS.

EELS analyses reveal that while the core corresponds to MnO phase the shell can be either Mn2O3 or Mn3O4 depending on the size of the nanoparticles: the smallest particles have a pure Mn2O3 shell whereas larger ones have increasing amounts of Mn3O4.


51

Postersessions

EMCD measurements: application to iron-cobalt films and comparison with XMCD experiments

B.Warot-Fonrose1, C.Gatel1, L.Calmels1, V.Serin1, S.Cherifi2, E.Snoeck1

1 CEMES-CNRS 29 rue Jeanne Marvig 31055 Toulouse, France2 IPCMS, CNRS and UdS, 23 rue du Loess BP 43

67034 Strasbourg Cedex 2, France

Local magnetic properties can be studied in a transmission electron microscope allowing the combination of a local probe and the extraction of quantitative data on the material. Some techniques are derived from imaging ones, like electron holography or Lorentz imaging, and some others rely on electron energy loss spectroscopy where intensities in the spectra can be linked to magnetic information. For instance, the energy-loss magnetic chiral dichroism (EMCD) has been proposed recently [1].

For a magnetic material, the absorption cross section will be different for right and left handed circular polarisation inducing a magnetic dichroism as demonstrated for x-ray magnetic circular dichroism (XMCD) [2]. This dichroic signal has been related to a quantitative value of the magnetic moment [3].

The parallel between XMCD and EMCD relies on the fact that the x-ray polarisation vector can be considered as equivalent to the diffusion vector, noted q, in a TEM and measured in the diffraction plane. Different combinations of two diffusion vectors give rise to 2 virtual photons, one right handed polarized, the other left handed polarized. These combinations correspond to two locations in the diffraction pattern, where the energy-loss signal will be measured and from which the difference, corresponding to the EMCD signal, will be extracted.

We have chosen to use this technique on different iron-cobalt alloys, for which the magnetisation depends on the alloy composition whereas the crystalline structure remains the same. Details will be given on the acquisition and the data post-treatments [4]. EMCD and XMCD results obtained in the same measurement geometry for these samples will be discussed.

[1] P. Schattschneider et al., Nature 441, 486 (2006)[2] G. Schutz et al., Phys. Rev. Lett. 58, 737 (1987)[3] B. T. Thole et al., Phys. Rev. Lett. 68, 1943 (1992)[4] C.Gatel et al., Ultramicroscopy, 109, 1465 (2009)

ELNES Fine Structure of Transition Metal Oxides Recorded by HR-EELS

H.K. Schmid 1, S. Irsen 2 and T. Walther 2,3

1INM Saarbrücken/Germany, 2Caesar Research Center Bonn, 3now with University Sheffield/UK.

Zinc oxide (ZnO) doped with 3d transition metals (TM) show novel combinations of properties – seen as promising candidates considered for spintronic applications. Materials properties may be tailored if atomic and electronic structures are known and correlations with spin state transitions are under-stood. It is well known that the energy-loss near-edge fine structure (ELNES) measured in electron energy-loss spectroscopy (EELS) is correlated to the local atomic environment such as coordination, valence state, chemical bonding and spin state. White-line intensities in EEL spectra from tran-sition metals and oxides with partially filled 3d or 4d orbitals show valence sensitivity due to excita-tions of 2p core electrons into unoccupied d-like states. In recent years considerable progress has been made in obtaining high-quality EELS data. Energy-resolution < 0.2 eV is now attainable in Cs-corrected TEM/STEM systems equipped with monochromator and HR-EELS spectrometer, thus approaching natural line widths in these materials.

Experiments were carried out on a new type of 200kV FEG TEM/STEM system (Zeiss Libra 200 MC) equipped with monochromator, Cs corrector in the illumination system, and aberration-corrected in-column Omega type imaging filter. HR-EELS spectra were acquired from TM oxides with formal cation oxidation states Fe2+, Fe3+, Mn2+, Mn3+and Mn4+. The t2g – eg splitting due to crystal field interaction is clearly resolved in HR-EELS (e.g. Fig.1). Thus, information on valence states, atomic coordination, ligand field strength, spin state and Jahn-Teller distortion can be obtained by consider-ing all ELNES features accessible by HR-EELS such as white-line intensity ratios, spin-orbit and crystal-field splitting.

Fig.1: ELNES features in HR-EEL spectrum from Fe2O3. Splitting of t2g – eg energy levels is clearly resolved.


52

Postersessions

Revisiting Li K-edge in LiFePO4

Philippe Moreau and Florent Boucher Institut des Matériaux Jean Rouxel, France.

Amongst the materials to be used in the near future as a positive electrode in lithium batteries, LiFePO4 leads the way. In order to indentify reasons for performance decrease with cycling, EELS in a TEM microscope has been used to identify crystals containing lithium ions and those without lithium.[1, 2] The obvious solution for this analysis is to measure the lithium K edge (54 eV in Li metal). Unfortunately, the M2,3 iron edge is situated at approximately the same energy (54 eV in Fe metal),[3] which creates some confusion on the real attribution of the peaks in this energy region.

Figure 1: EELS spectra of FePO4, LiFePO4 and NaFePO4 in the Li K / Fe M2,3 edges region.

In particular, authors seem to link the large prepeak at 56 eV in LiFePO4 (Figure 1) to the presence of the lithium K edge. Even if the absence of such a prepeak in FePO4 suggests precisely that, the change of Fe oxidation state could also be responsible for such a difference.

In order to answer the question, we have performed electronic structure calculations on these compounds as well as precise EELS experiments. We have specially synthesized a new phase, namely NaFePO4, presenting the same structure (and oxidation state for iron) as LiFePO4, but with the obvious omission of lithium.

As can be observed in Figure 1, the EELS spectrum obtained on NaFePO4 clearly demonstrates that the prepeak around 56 eV is due to the iron +2 configuration and not to the lithium edge. Using DFT calculations, we could obtain the theoretical lithium K edge and compare it to that experimentally extracted from spectra in Figure 1. Agreement experiment/theory is reasonable and further proves our interpretation of this complex region of the LiFePO4 spectrum.

[1] Sigle, W., et al., Electrochem. Solid-State Lett., 12 (2009) A151.

[2] Moreau, P., et al., APL, 94 (2009) 123111.[3] Miao, S., et al., J. Phys. Chem. A, 111 (2007) 4242.

Red-ox speciation and mixing state of iron in African dust by analytical microscopy.

Karine Deboudt1, Alexandre Gloter2, Alexandre Mussi3, Pascal Flament1 and Christian Colliex 2,

1 Laboratoire de Physico-Chimie de l’Atmosphère, Université

du Littoral Côte d’Opale, France, 2 Laboratoire de Physique des Solides, Université Paris-Sud,

France, 3Unité Matériaux et Transformations, Université de Lille1,

France.

The atmospheric deposition of iron in High Nitrate Low-Chlorophyll (HNLC) ocean regions has an important implication for CO2 budget. Desert dust aerosol constitutes a large iron source in these regions. It contains on average 3.5% iron, essentially as ferric iron (Fe3+) in a poorly soluble aluminosilicate form. The interest for the fraction of iron that would become biologically available, once the aerosol particle is deposited in the ocean, is particularly important. It is notably related to the red-ox speciation and the iron repartition in atmospheric particles.

The size, morphology and elemental composition of 12672 individual atmospheric particles, collected at the western African coast (Senegal), were determined by automated Scanning Electron Microscopy combined with Energy Dispersive X-ray spectrometry (SEM-EDX). Mineral dust counts for more than 87.5% of all analysed particles. Considering the air mass trajectories and the literature data on soil types in African source regions, the chemical composition of dust indicate a

north-western Sahara origin, with a very low fraction of pure iron oxides particles (about 1% of dust particles). The mean Fe content in aluminosilicates particles highlights an unexpected Fe enrichment compared to aluminosilicates derived from the soil, indicating probably the presence of iron oxide nodules inside aluminosilicates particles.

The Fe-containing particles were manually analyzed by Trans-mission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS). The Fe3+/SFe ratios inside alumi-nosilicates particles are deduced from the EELS Fe L2,3 edges. A heterogeneous distribution of the iron oxidation state inside these particles is frequently observed, with a dominance of Fe3+. Three-dimensional reconstruction of the local shapes and posi-tions of Fe oxide regions inside aluminosilicates particles were observed by combining Energy Filtered Transmission Electron (EFTEM) and tomography.


53

Postersessions

STEM and EELS study on SrTiO3-x:Ny single crystal obtained by microwave NH3 plasma

Myriam H. Aguirre1, Andrey Shkabko1, Laura Bocher1, Anke Weidenkaff1, Peng Wang2, Bernhard Schaffer2,

Mhairi Gass2, Ursel Bangert3

1 Solid State Chemistry and Catalysis, Empa, Switzerland.2SuperSTEM Daresbury Laboratory. UK

3 School of Materials. The University of Manchester. UK.

Perovskite oxides have been the subject of intense research regarding their ferroelectric and dielectric properties, which can be used effectively in a wide range of applications, such as non-volatile ferroelectric and high-density dynamic random access memory devices. Phenomena like 2D-Electron Gas or resistivity switching have been recently discovered in perovskite materials. From the perovskite material knowledge area, the oxynitride-perovskites AB(O,N)3 are a growing class of materials with prospective optical and catalytic properties. One method to introduce N into SrTiO3 (STO) perovskite structure is by mean of microwave induced NH3 plasma procedure. In this two step treatment, the following modifications of the chemical composition are used to change the electronic structure and properties of STO: i) formation of oxygen vacancies, and ii) an anionic substitution N-3 → O-2. Substitution of O2- with N3- in perovskites is possible due to the similar ion size of both elements. However,

due to the charge compensating mechanism complete anionic substitution of O-2 by N-3 keeping the perovskite type structure can not be realized without the presence of anionic vacancies (collapsed in dislocations, stacking faults and new structures or superstructures). With the reduction scaling of microelectronic devices, lattice defects in these materials become increasingly important. Therefore, it is extremely demanding the careful characterization of defects produced during the ammonia plasma treatment. Several questions arise in this work such as the defect type, how the lattice distortion is around the defect, the local change in composition, and where the N is inserted in the structure. The composition changes around the defects can be better studied by Z-contrast image and mapped with sub-nanometer spatial resolution utilizing EELS in scanning transmission electron microscopy. On the basis of these results atomic model of the defects and the SrTiO3-x:Ny structure will be suggested.

Single atom imaging and spectroscopy in carbon nanostructures in an aberration

corrected STEMU Bangert 1 , A Seepujak1, M H Gass 2 and A L Bleloch 2

1 School of Materials, The University of Manchester, Manchester, UK, 2School of Engineering, University of

Liverpool, Liverpool, UK

Monitoring the ‘fate’ of individual impurity atoms in nanostructured materials, whether unintentionally present or introduced for purposes of electronic functionalisation, is hugely desirable. We examine residual impurity atoms occurring due to various fabrication processes on graphene as well as impurities introduced via ion implantation as dopants into graphene and carbon nanotubes. The latter method is being tested as a possible clean, efficient and site-selective route for large-scale production, whereby uniform impurity atom densities with spatial- and dose-control can be achieved. The technique is demonstrated for a range of dopants, including silver as a likely candidate for optical enhancement, and boron, which is predicted to introduce an interband plasmon within the visible frequency regime. Core loss electron energy-loss spectroscopy performed in an aberration-corrected scanning transmission electron microscope, in combination with high-angle-annular-dark-field imaging, is used to pinpoint and identify the bonding configuration of single foreign species in the

materials. Experimental spectra were characterized using density functional theory calculated EELS spectra, enabling the bonding configuration of single dopant atoms to be ascertained.

EEL spectrum imaging was furthermore performed in the core loss and the low loss regime to monitor spatial distri-butions of impurities and plasmon. Introduction of foreign species into the CNT matrix is shown to provide a potential method for modifying the optical response of CNTs: new plasmons in the vis/uv regime were observed in heavily doped tubes and their existence confirmed by density func-tional theory calculations.


54

Postersessions

HAADF study of the relationship between intergranular defects structure and yttrium segregation in an alumina grain boundary

Sylvie Lartigue-Korinek1, Danièle Bouchet 2, Andrew Bleloch3 and Christian Colliex 2

1 Institut de Chimie et des Matériaux Paris Est, UMR 7182 CNRS- Université Paris 12, 2-8 rue H. Dunant,

94320 Thiais – France 2 Physique des Solides UMR CNRS 8502, Bât 510,

Université Paris-Sud, 91405 – Orsay, France 3 UK SuperSTEM Laboratory, Daresbury Laboratories,

Cheshire, Warrington, WA4 4AD, UK

Z-Contrast (HAADF) imaging in a scanning electron microscope reveals the distribution of yttrium segregation in the core of intergranular dislocations, namely disconnections, in a rhombohedral twin in alumina. The defects present a large step height, the dislocations being dissociated into partials that delimit grain boundary segments with alternating structure. Strong yttrium segregation appears along the step, extending on several planes normal to the twin plane. Yttrium is segregated in the faulted part of the defect. Moreover, it appears segregated

in the partial disconnection cores. It does not simply adapt the alumina structure but form a new structure close to a YAlO3 compound. The general aim of the study is to understand the benefit role of yttrium on creep of alumina. The formation of an ordered compound at the GB dislocation core strongly supports the hypothesis that a reduced creep rate results from a decrease in dislocation mobility and accommodation at triple junctions during GB sliding.

STEM of Dy36 Super Metal-Organic Frameworks: SMOFs

Sharali Malik 1, Christian Kübel 1 and Annie K. Powell 1,2. 1 Karlsruhe Institute of Technology (KIT),

Institute of Nanotechnology, Germany. 2 KIT, Institute of Inorganic Chemistry, Germany.

About 10 years ago the term “metal-organic framework” or MOF was coined to label coordination polymers which are compounds built from classical coordination compound units (termed “Secondary Building Units” or SBUs) containing from one to about four metal centres joined together by organic linker molecules. Because of the way they are constructed, these compounds can have large pores which usually accommodate solvent molecules. If these solvent molecules can be removed without destroying the framework structure, then these mesoporous materials could, for example, be used to play host to and thus store other molecules such as hydrogen or else to perform catalysis, as exemplified by the porous inorganic zeolites. However, a difficulty with this approach is that the extra space offered by using such long linkers tends to favour the interpenetration of multiple frameworks, in accord with the principle that Nature abhors a vacuum, resulting in compounds which are tightly-knit with hardly any accessible volume. Figures 1 and 2 show a realisation of the inverse synthetic concept to access the desired porous materials - SMOFs - porous frameworks where large coordination clusters are joined by short linkers.

Figure 1. 3-D network of Dy36 aggregates.

Figure 2. STEM of Dy36 aggregates


55

Postersessions

Bending of Nanotubes Grown in the ETEMP. Rez 1 , M.M.J. Treacy 1 and R Sharma 1,2

Arizona State University, USA1 ,NIST, USA2.

Catalytic chemical vapor deposition (CVD) is frequently used to grow nanotubes. In recent years it has been possible to observe the growth process at near atomic resolution in the environmental TEM (ETEM). In our earlier work1 on nanotube growth from Ni nanoparticles using acetylene as the precursor gas we showed that bent multiwall tubes were more likely to grow at lower temperatures (480°C) and higher pressure (> 3 mTorr), while straight single wall nanotubes formed more easily at higher temperatures (>550°C) and lower pressures (0.6 Pa <). When a tube bends the different segments have different chirality, and the bend is accommodated by 5- and 7-member rings. A reasonable hypothesis would be that these defects, which form randomly during the tube growth, are annealed out at higher temperatures. It is therefore of interest to see how the energies of 5-7 defects in nanotubes and graphene compare with thermal energies.

A model system for a bent nanotube was constructed from a section of a 5,5 nanotube sandwiched between sections of 9,0 nanotubes each capped with bucky hemispheres. The system has 312 C atoms and was initially relaxed with the Brenner potential. The structure was further relaxed using the VASP code to determine the minimum energy configuration. This energy

was then compared with the fully relaxed total energies for a straight nanotube with 2 5x7 defects and a straight nanotube with no defects. Various bend configurations were also explored.

The energy to introduce the pair of 5,7 defects was 2.94 eV, and an additional energy of about 1.67 eV was needed to bend the tube. It is interesting to note that the energy to introduce a Stone-Wales defect (2 5,7 rings) in graphene is much higher, approximaetly 8 eV. The curvature of the nanotube accommodates some of the strain from the defects.

[1] R. Sharma et al, Nanotech, 18, 125602, 2007.

Analysis of the carbon nanotube – catalyst particle interface

D. Pohl 1 , F. Schäffel 1 , E. Mohn1 , C. Täschner1, M.H. Rüm-meli 1, C. Kisielowski 2, L. Schultz 1 and B. Rellinghaus 1,

1 IFW Dresden, P.O. Box 270116, Dresden, D-01171, Germany.2 National Center for Electron Microscopy, Lawrence Berkeley

National Laboratory, Berkeley, CA 94720, USA.

Although carbon nanotubes are in the focus of intensive world-wide research since almost two decades, details of the growth process are still far from being fully understood. The experiments and modelling efforts presented in the present study aim at determining nature’s choice for the type of internal interface between the concentric graphene layers of a carbon nanotube and the metallic FePt catalyst particle it is grown from [1].

State-of-the-art aberration-corrected electron microscopy (TEAM 0.5, Berkeley) is used to determine the structure of the interface of with atomic resolution. A detailed analysis of the magnification of the interface area in Fig. 1c reveals a systematic increase of the lattice spacing upon approaching the particle-CNT interface, rising in a segregation of platinum towards the interface. The second main feature of the carbon-metal interface is the onset of the concentric graphene sheets at the {111} particle facets. A comparison of the experimental results with molecular dynamics simulations reveals that the minimisation of the desorption energy of carbon is a physical guiding principle for the choice of the metal facet at this internal metal-carbon interface.

[1] F. Schäffel et al. APL 94, 193107 (2009)

Figure 1. (a) HRTEM image of a multiwall CNT with a FePt-catalyst particle at the end inside the tube. (b) Blow-up of the area marked in fig. (a). Dashed lines highlight the measured layers. (c) Lattice variation from interface to particle core.

ba

c


56

Postersessions

Heteroatomic Single-Walled Nanotubes Studied by STEM-EELS

R. Arenal1*, O. Stephan2, A. Loiseau1, C. Colliex2

1 Laboratoire d’Etude des Microstructures, CNRS-ONERA, 92322 Châtillon, France

2 Laboratoire de Physique des Solides, CNRS-U. Paris XI, 91405 Orsay, France

Heteroatomic nanotubes (NTs) based on boron, carbon and nitrogen (B-C-, C-N-, B-C-N- and BN-NTs) have generated intense interest due to their novel properties which make them an attractive alternative to undoped carbon counterparts (C-NTs). As a matter of fact, they could offer a possible route to control their opto-electronic properties in a well defined way: the band gap of these NTs can be tuned in the visible range and, for pure BN-NTs, even in the UV spectral range. The investigation of the atomic configuration, the composition and the properties of such nano-materials at the nanometer scale is a very important and challenging aspect. In this sense, spatial-resolved (SR-) EELS in a TEM is an essential and powerful technique to perform such studies, making therefore possible the inspection of individual nanostructures.

In this contribution, we will present the most significant SR-EELS works developed on these single-walled (SW) heteroatomic NTs using the dedicated STEM VG-HB501. These works have been done in the framework of our fruitful collaboration (ONERA-LPS).

Concerning the core-losses studies, we have investigated the composition and atomic structure of BN- and CNx-SWNTs via the analysis of K edges of B, C and N, and focusing on the study of the fines structures near these edges (ELNES) [1-3]. One of the most significant results was the extraction of the chemical bonding maps at the nano-meter scale using fitting methods (MLS) for retrieving the information contained in the ELNES. We have applied this technique for studying the spatial distribution of B bonds in BN-SWNTs samples [1].

We also measured the dielectric properties of BN-NTs via low loss EEL spectroscopy. These experiments constitute the first measurement of the optical gap of an individual semiconducting nanostructure using aloof EELS spectroscopy. We found a homogeneous value around 5.8 eV for individual BN-NTs, independent of their number of walls or diameter [4].

[1] R. Arenal, F. De la Pena, O. Stephan, M. Walls, M. Tence, A. Loiseau, C. Colliex, Ultramicros. (2008)[2] R. Arenal, O. Stephan, J.L. Cochon, A. Loiseau, J. Am. Chem. Soc. (2007)[3] H. Lin, R. Arenal, S. Enouz-Vedrenne, O. Stephan, A. Loi-seau, J. Phys. Chem. C (2009) and J. Phys, Stat. Solidii B (2008)[4] R. Arenal, O. Stephan, M. Kociak, D. Taverna, A. Loiseau, C. Colliex, Phys. Rev. Lett. (2005) and Microsc. & Microanal. (2008)

Rh and Ti on Carbon Nanotubes

Chris Ewels 1, Irene Suarez-Martinez 1, Xiaoxing Ke2, Gustaaf Van Tendeloo2, Sebastian Thiess3, Wolfgang Drube3, Alexander Felten4, Jean-Jacques Pireaux4, Jacques Ghijsen4

and Carla Bittencourt5

1Institute of Materials, CNRS, Nantes, France2EMAT, Belgium, 3HASYLAB, Germany, 4FUNDP, Belgium,

5University of Mons, Belgium

X-ray photoelectron spectroscopy at 3.5 keV photon energy, in combination with high-resolution transmission electron micros-copy are used to follow the formation of the interface between Rhodium / Titanium and carbon nanotubes. Rh nucleates at de-fect sites, whether initially present or induced by oxygen plasma treatment. More uniform Rh cluster dispersion is observed on plasma-treated CNTs. Experimental results are compared to DFT calculations of small Rh and Ti clusters on pristine and de-fective graphene. While Rh interacts as strongly with the carbon as Ti, it is less sensitive to the presence of oxygen, suggesting it as a good candidate for nanotube contacts.

[1] I. Suarez-Martinez et al, ACS Nano 4 (3), 1680 (2010)[2] A. Felten et al, Chem. Phys. Chem. 10 (11) 1799 (2009)

Figure 1: HRTEM image Formation of small ordered fullerene-like protrusions attached to Rh particles.

Figure 2 : Single Rh atom (a) above a hexagon site (b) bonded to a vacancy-O2 defect. (c) Rh reacts with O2 giving RhO2 which sits further from the graphene sheet


57

Postersessions

The formation of hollow nanospheres in Sm-Fe(Ta)-N system

S. Šturm1*, K. Žužek Rožman1, B. Markoli2, E. Sarantopou-lou3, Z. Kollia3, A. C. Cefalas3, and S. Kobe1

1Jožef Stefan Instiute, Slovenia, 2University of Ljubljana, Slovenia, 3National Hellenic Research Foundation, Greece

A new synthesis method for fabrication of metallic hollow nanospheres from gas-saturated molten droplets is presented. Sm-Fe(Ta)-N system was used to produce molten droplets, which were examined using a STEM/TEM Jeol 2010F equipped with an EELS spectrometer (Gatan PEELS 667).

Fig. 1a shows an ADF-STEM image of a typical sphere, with a dark contrast in its central region. Electron diffraction and EELS analysis confirmed that sphere was amorphous and oxidized. The compositional fluctuations, which were measured in this sphere, could not explain such contrast difference in the associated ADF-STEM images. Measurements of relative thickness (t/λ) variations between the central dark and adjacent bright regions revealed that the dark regions are consistently thinner than adjacent brighter regions. This fact was attributed to the formation of voids. In addition, a detailed EELS analysis showed the presence of nitrogen only in the central dark region of the sphere. N-K ionization edge is presented by a sharply-peaked edge at 401 eV (Fig. 2b). The shape of N-K edge, i.e. white-line peak followed by a broad continuum is consistent

with molecular nitrogen [1], which signifies that these hollow spheres are filled with N2 gas. The formation of hollow spheres can be explained by the melt-solidification mechanism and could be in principle applied in various metallic systems.

This work was financially supported by the EU as part of the FP6 under a contract for an Integ. Infra. Init. Reference 026019 ESTEEM.

Fig 1. (a) ADF-STEM image of hollow sphere and the corresponding (b) N-K background subtracted ionization edges.

[1] S. Trasobares et al.,Eur.Phys.J.B, 22 (2001) 117. (a)

(b)(a)

Radial Chemical Homogeneity of III-V Semiconductor Nanowires: InAsxP1-x

and InxGa1-xPLHG Tizei1,2,3 , T Chiaramonte1, MA Cotta1, LF Zagonel3,

O Stephan3 and D Ugarte1,

1IFGW, Universidade Estadual de Campinas, CP: 6165, 13083-970, Campinas, SP, Brazil, 2LNLS, Laboratório Nacional de Luz Síncrotron, CP 6192, 13083-970, Campinas, SP, Brazil,

3Laboratoire de Physique des Solides, CNRS, UMR 8502, Université Paris-Sud, F-91405 Orsay Cedex, France

The finite radial dimension of Nanowires (NWs) allows the growth of defect free interfaces between highly mismatched materials. This permits the integration of, for example, InAsxP1-x segments of different composition, and, hence, different gaps. However, the exact electronic properties depend on the chemical homogeneity of these ternary alloys.

NWs have been grown routinely by the Vapor-Liquid-Solid (VLS) method, which uses a metal nanoparticle (NP) as catalyst. Moreover, it is known that a thin film grows laterally on NWs, resulting on conical shapes.

Thus, there are two questions concerning the chemical homogeneity of ternary alloy NWs: 1) are alloys grown by the Vapor-Liquid-Solid radially homogeneous? Are the compositions of the thin film and of the VLS grown material the same ?

We have grown InAsP and InGaP NWs by VLS on a Chemical Beam Epitaxy (CBE) machine using Au NPs as catalyst.

Initial HAADF/EDS analysis of the InAsP sample (Figures 1a) show that the NWs are core-shells, with the core 5% richer in P. Plasmon shift measurements of the InGaP samples show radial dependence (Figure1b), which could be related to a compositional change and a core-shell structure. In both cases the core region has a size similar to typical NPs. This would imply a difference in composition between the VLS and the thin film growth. Moreover, the core of InGap NWs display contrast variations, both in TEM (Figure 1c) and STEM images, for regions whose radius is smaller than the metal nanoparticle. This may suggest a possible radial inhomogeity also inside the material whose growth was catalytically induced (VLS).


58

Postersessions

Structure of toroidal DNA collapsed inside bacteriophage capsids

Amélie Leforestier, Françoise LivolantLaboratoire de Physique des Solides, CNRS UMR 8502,

Bât 510, Université Paris-Sud, 91405 Orsay, France

In the presence of multivalent cations (spermine4+, Co(NH3)6

3+, …) DNA chains collapse to form toroids or rods [1]. DNA toroids attracted much attention from biologists, polymer physicists and theoreticians because of their interest in unders-tanding condensed states of DNA, but there are still little data on their fine structure. A few years ago, high resolution images of DNA toroids obtained by cryoelectron microscopy (cryoEM) [2], have revealed the local hexagonal packing of DNA, but these spectacular images raised many questions on the internal structure of the toroids that are still pending.

Using bacteriophages, we obtain isolated monomolecular toroids. Upon interaction with their bacterial receptor, the bacteriophages are let to eject partially their DNA. The segment kept in the capsid (1-20 mm in length) is collapsed by addition of spermine at a concentration required to obtain a local hexagonal packing. The toroids, confined in the volume of the capsid, are analysed by cryoEM. We show that DNA organisation is more complex than a simple hexagonal packing. The bundle is twisted and the toroid can be seen as a series of hexagonal domains separated by twist walls. At this high packing density,

DNA helices are correlated, as predicted by theoretical models [3]. These correlations combined to the strong curvature of the confined toroid imposes variations of the DNA helical pitch. We present a geometrical model of this complex 3D-ordered structure [4].

DNA toroids confined in the T5 capsid (80 nm). On side views (left), the hexagonal packing is directly visible. On top views (right), the layers correspond to the reticular planes of the hexagonal lattice (d= 25 Å).

[1] Gosule & Schellman (1978) J.Mol.Biol.121, 311.[2] Hud & Downing (2001) PNAS USA 98, 14925.[3] Kornyshev, Lee, Leikin, Wynveen (2007) Rev. Modern Phy-sics 79, 943.[4] Leforestier & Livolant (2009) PNAS,106, 9167.

Nanostructuration in Soft Matter: Transmission Electron Microscopy for Structure-Properties

Relationship in Polymer BlendsC. Boutin, S. Norvez and S. Tencé-Girault

Matière Molle et Chimie, CNRS-UMR 7167, ESPCI ParisTech, 75005, Paris, France

Polymer blends provide new routes to the design of materials with improved properties compared to the ones of the constituents. However, poor final properties are obtained when macrophase separation occurs between the blend components. To circumvent this, block or graft copolymers were used to produce nanostructured materials. Microphase separation in domains of nanometric size highly improves mechanical, thermal and optical properties, as well as permeability or conductivity properties of the resulting materials. Nanometric charges incorporated in the polymer matrix may also provide new and unique interesting properties.

Transmission electronic microscopy is an essential tool to visualize the structuration of the materials at the nanometer scale and thus to provide a better understanding of the structure-properties relationship.

In our laboratory, we are interested in the properties of compatibilized blends of semi-crystalline or amorphous polymers, obtained by melt or reactive blending, as well as in

the properties of nanostructured polymers charged with carbon nanotubes. To observe the morphologies, thin sections of the samples are cut using ultra-cryomicrotomy and stained prior to imaging. We present here a few images showing how the intimate blending of incompatible materials may produce nice and useful morphologies.


59

Postersessions

FIB tomography of γ’ and γ” nanoparticles in IN718 superalloy

A. Kruk, G. Cempura, B. Dubiel, A. Czyrska-FilemonowiczAGH University of Science and Technology, PL-30-059

Kraków, Al. Mickiewicza 30, Poland

The aim of this work was 3D visualisation of γ’ (Ni3Al) and γ” (Ni3Nb) ordered nanoparticles precipitated in Ni-base g solid solution in the IN718 superalloy using FIB tomography. Identification of γ’ and γ” particles by conventional TEM or HRTEM is not straightforward because of the similarity of unit cell parameters of g, γ’ and γ” phases [1]. The promising results were achieved using 3D mapping of nanoparticles with high Z-resolution by serial FIB slicing and SEM imaging. Ga ion beam at 30 kV was used to perform a precise in-situ milling. The SEM images were taken with SE detector. The distance between slices was about 5 nm. Filtering and shift correction performed using cross-correlation method allowed for 3D visualization of the reconstructed volume (Fig 1). 3-dimentional reconstruction and visualization confirmed that two types of precipitates are present in the γ matrix: spherical-like and disc-like. The results achieved confirm the ability of FIB tomography to reconstruct 3D structures with dimensions in the range of 100 nm or even smaller.

B.Dubiel, A.Kruk, E.Stępniowska, G.Cempura, D.Geiger, P.Formanek, J.Hernandez, P.Midgley, A.Czyrska-Filemonowicz, J. Microscopy, 236 (2009) 149–157.

Figure 1. 3D visualization of FIB serial slicing and SEM imaging stack after surface rendering of γ’ and γ” particles, a-c) 3D visualization of different reconstructed volumes and d, e) morphology of γ” nanoparticle.

The authors acknowledge the Pratt and Whitney, USA for providing the material for investigation. We would like also to thank Prof. Midgley and his team for introducing us to electron tomography. This work was supported by the European Union under the Framework 6th Program, contract for an Integrated Infrastructure Initiative. Reference 026019 ESTEEM.

Nanostructured sapphire vicinal surfaces as templates for the growth of self-organized oxide

nanostructuresE. Thune1, A. Boulle1, D. Babonneau, F. Pailloux2, and

R. Guinebretière1

1Laboratoire Sciences des Procédés Céramiques et de Traitements de Surface (UMR CNRS 6638), France,

2Institute P’ (UPR 3346 CNRS), France

Nanostructured systems based on heteroepitaxial islands (noble metals, transition magnetic metals, functional oxides, etc.) grown onto oxide surfaces (MgO, ZnO, Al2O3, etc.) are attracting intensive interest due to both the fundamental significance and potential application in optics, electronics, spintronics, and magnetic data storage. In such nanosystems, the control of the atomic structure, the shape, and the size of the islands is of prime importance in determining the overall physical properties. In addition, many of the applications so far envisaged also require precise arrangement of these structures into ordered arrays.

In the present work, we aim at producing self-organized nanostructures in a two-step process. The first step consists in the preparation of suitable templates by thermally activated surface diffusion on vicinal surface of oxide single-crystals. Such templates should be chemically and structurally stable over long periods of time and in various environments (air, vacuum, high temperatures...) so as to be compatible with various deposition processes. In the second step, nanoparticles will be grown on

these templates using different techniques (sol-gel, chemical vapor deposition (CVD) and sputtering).

A thermal treatment at 1250°C allows to stabilize a surface made of periodically spaced nanosized step-bunches (see figure 1). Such stepped surfaces were used as template to grow self-patterned epitaxial oxide nanoparticles by thermal annealing of yttria-stabilized zirconia thin films produced by sol-gel dip-coating. Grazing Incidence Small Angle X-ray Scattering and High-Resolution Transmission Electron Microscopy were used to study the morphology of the nanoparticles and their epitaxial relationships with the substrate.

Figure 1: Surface vicinal of Al2O3 annealed at 1250°C

during 32h.


63

60 boulevard Saint Michel75006 Paris

Metro : Luxembourg, Odéon

Gare de Lyon Place Louis-Armand

75012 ParisMetro : Gare de Lyon

Your are welcome on Wednesday 9th June 2010at 7:00 pm

for a buffet-dinner in the garden of

the prestigiousécole des Mines(included in the registration fees)

∫

Exceptional opening of the Mineralogy Museum, with an

optional guided tour

the conference-banquet will be held on

thursday 10th June 2010 at 8:00 pm

at the restaurant

Past, P

rese

nt a

nd

Fu

ture

of (S

)TEM

an

d its a

pp

licatio

ns

A trib

ute

to th

e w

ork

of C

hristia

n C

ollie

x

■■ Wednesday 9

th June 2010 ■■

09.30 – 10.00 R

egistration at the CN

RS

headquarter

10.00 – 10.15 O

pening speech and introduction

10.15 – 11.45 EELS Session 1

10.15 – 10.45 C

heng-Hsuan C

hen E

ELS

for the solid-state physicist

10.45 – 11.15 Steve Pennycook S

pectroscopy at the Atom

ic Level : P

ast, Present and Future

11.15 – 11.45 A

rchie How

ie D

elocalization Effects in the Elastic and Inelastic S

cattering of Electrons

11.45 – 12.00 B

reak

12.00 – 12.45 E

xtended talk by Albert Fert,

Physics N

obel Prize 2007

Spintronics: fundam

entals and emerging directions

12.45 – 14.00 Lunch

14.00 – 15.00 Instrumental Session

14.00 – 14.30 O

ndrej Krivanek

Focused electrons: sub-Å beams, sub-eV

energy resolution

14.30 – 15.00 Pierre Sudraud Focused ion beam

: birth of a technology

15.00 – 15.15 Young researcher: Susana Trasobares

15.15 – 16.00 B

reak/Poster S

ession

16.00 – 17.00 Elastic and inelastic coherence Session

16.00 – 16.30 H

elmut K

ohl Im

age formation by inelastically scattered electrons

16.30 – 17.00 John Spence Fast electron sources and fast im

aging Free Tim

e

19h C

ocktail in Ecole des Mines

■■ Thursday 10th June 2010 ■■

09.30 – 10.00 R

eception at CN

RS

headquarter

10.00 – 11.00 EELS Session 2

10.00 – 10.30 A

lan Craven

From apprentice to m

aster – developments in S

TEM

-EE

LS

10.30 – 11.00 D

avid Muller

Imaging the E

lectronic Structure of Interfaces

11.00 – 11.45 B

reak/Poster S

ession

11.45 – 12.00 Young researcher: G

ianluigi Botton

12.00 – 12.45 E

xtended talk by Catherine B

réchignac on C

lusters as precursors of nano-objects 12.45 – 14.00

Lunch

14.00 – 15.00 Applications Session 1

14.00 – 14.30 K

azutomo Suenaga

Single m

olecular imaging and single atom

spectroscopy

14.30 – 15.00 R

ichard Leapman

Probing biological structures using S

TEM

, E

ELS

and energy filtering

15.00 – 15.15 Young researcher: A

lexandre Gloter

15.15 – 16.00 B

reak/Poster S

ession

16.00 – 17.00 Virginie Serin, Bernard Jouffrey, Françoise Livolant P

resentations by the French Society of E

lectron M

icroscopies

17.00 – 17.30 E

xtended talk by Christian C

olliex

Free Time

20h B

anquet in Le Train Bleu

■■ Friday 11th June 2010 ■■

09.30 – 10.00R

eception at CN

RS

headquarter

10.00 – 11.00 Applications Session 2

10.00 – 10.30Pulickel A

jayan M

icroscopy for Materials Scientists: C

arbon Nanotubes and Beyond

10.30 – 11.00D

aniel Ugarte

Manipulation and characterization of individual nanosystem

s by in-situ electron m

icroscopy experiments in a tropical environm

ent

11.00 – 11.45B

reak

11.45 – 12.30E

xtended talk by Sumio Iijim

a The 40 Y

ears of High R

esolution Transmission E

lectron M

icroscopy of Materials S

cience

a journ

ey on

the work

s of C. C

olliex

9th- h u n 0 Past, Present and C156 heaGTuarter rue 0iFhel ... · An example of EELS at large...

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Transcript of 9th- h u n 0 Past, Present and C156 heaGTuarter rue 0iFhel ... · An example of EELS at large...