The 2nd International Workshop on TEM Spectroscopy in the

Materials Sciences

Uppsala, SwedenMay 18th - 20th, 2015

Conference information

Registration and scientific events The registration desk is located in front of Polhemsalen (see map) and is open from 8:00 on Monday, May 18th. Participants can pick up their badges and booklets at that time.

When registering, please also indicate if you would like to participate in the museum tour on Monday evening.

Talks will be held in the lecture room Polhemsalen at the Ångström Laboratory of Uppsala University. Posters and industry tables will be on display directly outside the lecture hall. Coffee breaks will be served there as well

Lunch Lunch can be purchased at Café Ångström, which is located near the entrance of the laboratory. It can also be purchased at the local restaurants Rullan or Sven Dufva. A full lunch typically costs 80 SEK, but sandwiches and drinks are available for lower prices.

Getting to the workshop The Ångström Laboratory is approximately a 30 minute walk along the river from the city center (see map). Alternatively, the buses 1, 12, and 20 go here from the central station. To take the bus, proceed to the bus stop marked “B3” in front of the central station. Tickets can be purchased on board the bus with a card (not with cash!). Take the bus to the stop named “Polacksbaken.” More information can be found on the website of the travel authorities, UL:

http://www.ul.se

Wi-fi access Wi-fi access is provided through Edu-roam. If your institution does not support Edu-roam, we can provide you with a temporary account within the Uppsala University wi-fi network. Please contact one of the organizers at the registration desk for assistance.

Social Program The workshop includes a dinner on Tuesday, May 19th at Sven Dufva restaurant, about a 10 minute walk from the laboratory. There is also the option of having a guided tour of the museum Gustavianum on Monday evening starting at 18:15. Please sign up for this at registration.

The Ångström Laboratory

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Scientific Program MMonday, May 18, 2015

8:00 – 9:00 Workshop registration, in front of Polhemsalen, Ångström Laboratory

9:00 – 9:05 (welcome) Klaus Leifer, Uppsala University, Sweden

9:05 – 10:35 Session I: Tutorials

9:05 – 9:50 (invited) Helmut Kohl, Universität Münster, GermanyElectron Energy Loss Spectroscopy: Fundamentals and Applications

9:50 – 10:35 (invited) Nestor Zaluzec, Argonne National Laboratory, USAEverything you wanted to know about XES (in an hour or less …)

10:35 – 11:00 Coffee break

11:00 – 12:15 Session II: 3D spectroscopic tomography and data treatment

11:00 – 11:45 (invited)Jo Verbeeck, University of Antwerpen, BelgiumAdvances in model based quantification of EELS spectra

11:45 – 12:00Ling Xie, Uppsala University, SwedenThe analysis of nanostructures and interface in vacuum annealed Si rich SiC film by 3D spectroscopic electron tomography

12:00 – 12:15Thomas Thersleff, Uppsala University, SwedenModel construction for the analysis of Electron Magnetic Circular Dichroism (EMCD) datasets

12:15 – 14:00 Lunch

14:00 – 15:15 Session III: Applications of EELS: Low Loss

14:00 – 14:45 (invited)Michael Stöger-Pollach, Vienna University of Technology, AustriaProbing optical properties using valence EELS

14:45 – 15:00Ed White, Imperial College London, UKMapping nanoscale thermal gradients with plasmon energy shifts

15:00 – 15:15Wei Zhan, University of Oslo, NorwaySTEM-EELS Band Gap Measurement in ZnCdO

15:15 – 15:45 Coffee break & posters

15:45 – 17:00 Session IV: Applications of EELS: ELNES

15:45 – 16:30 (invited)Richard Brydson, SuperSTEM Daresbury, UKNanostructural development in graphitising and non-graphitising carbons probed using TEM/EELS

16:30 – 16:45Markus Neuschitzer, IREC-Fund. Inst., CatalunyaThe effects of tailored surface and grain boundary passivation routes for high efficient kesterites solar cells revealed by advanced transmission electron microscopy techniques

16:45 – 17:00Cheuk-Wai Tai, Stockholm University, SwedenElectron Microscopy and Spectroscopy Study of Porous FexNi1-xMn2O4

17:00 – 17:45 Round table discussions18:15 – 19:00 Tour of Museum Gustavianum

TTuesday, May 19, 2015

9:05 – 10:15 Session V: Applications of EDX Spectroscopy

9:00 – 9:45 (invited) Shunsuke Muto, Nagoya University, JapanApplications of EDX Spectroscopy

9:45 – 10:00Alena Folger, Max-Planck-Institute für Eisenforschung GMbH, GermanyDetailed electron microscopy study on the structural transformation inside rutile TiO2 nanowires upon annealing

10:00 – 10:15

Lisa S. Karlsson, Sandvik Materials Technology, SwedenUnderstanding the oxidation front on coated stainless steels for SOFC interconnects – A time resolved study using STEM-EELS

10:15 – 10:45 Coffee break

10:45 – 12:00 Session VI: Magnetic information in the TEM

10:45 – 11:30 (invited)Juan Carlos Idrobo, Oak Ridge National Laboratory, USAUtilizing the phases in electron probes for chiral spectroscopy

11:30 – 11:45Sebastian Schneider, IFW Dresden, GermanyMagnetic properties of single particles: Classical EMCD on FePt nanocubes

11:45 – 12:00Takeshi Kasama, Technical University of Denmark, DenmarkTransmission electron microscopy of magnetite at low temperature

12:00 – 14:00 Lunch

14:00 – 15:15 Session VII: New instrumentation and its applications

14:00 – 14:20 (sponsor)Meiken Falke, Bruker-Nano GmbH, GermanyQuantitative EDS of Electron Transparent Samples

14:20 – 14:40 (sponsor)Mauro Porcu, FEI Company, The NetherlandsFEI Solutions for Materials Science Applications

14:40 – 15:00 (sponsor)Neil Wilkinson, Gatan UK, UKUltra-Fast data acquisition for EELS and Imaging

15:00 – 15:20 (sponsor)Philipp Wachsmuth, JEOL (Germany) GmbH, GermanyAdvances in analytical transmission electron microscopy

15:20 – 15:40 (sponsor)James Holland, Oxford Instruments NanoAnalysis, UKOpening the Window for Large Solid Angle Silicon Drift Detectors to Enhance EDS Analysis on the TEM

15:40 – 17:05 Coffee break & posters

16:20 – 17:35 Session VIII: Spectroscopy at high spatial and energy resolution

16:20 – 17:05 (invited)Niklas Dellby, Nion Co., USAAdvances in Aberration-corrected STEM and EELS

17:05 – 17:20Lars Hansen, Haldor Topsoe A/S, DenmarkElectron Microscopy studies on MoS2-based nanocatalysts

17:20 – 17:35Jan Rusz, Uppsala University, SwedenTowards atomic resolution magnetic measurements

18:00 – 21:30 Workshop dinner at Sven Dufva

WWednesday, May 20, 2015

9:00 – 10:30 Laboratory Demonstration Session 110:30 – 10:45 Coffee break

10:45 – 12:15 Laboratory Demonstration Session 212:15 – 13:45 Lunch

13:45 – 15:15 Laboratory Demonstration Session 315:15 – 15:30 Coffee break

15:30 – 17:00 Laboratory Demonstration Session 4

Electron Energy Loss Spectroscopy: Fundamentals and Applications

Helmut Kohl

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

The energy loss spectrum taken in a transmission electron microscope contains a wealth of information about the irradiated specimen. Recently very low energy losses (below 1 eV) have been detected to obtain information about the (optical) phonons in the specimen. Slightly larger losses, due to interband excitations, can be used to determine the band gap in semiconductors and insulators. Frequently a large plasmon loss peak occurs at an energy loss, which is related to the electron density in the specimen.

The onset of an inner-shell loss occurs at the binding energy of an inner-shell electron. Therefore it can be used to identify the elements in the irradiated area. Using the integrated intensities under the peak, these features are routinely used to determine the chemical composition of the irradiated area. The fine structure just above the onset of the edge yields important information about the bonding of the excited atom to its neighbors.

The characteristic features in an energy loss spectrum can also be used to obtain images of the local properties with high spatial resolution. This can be done in two different ways:

1) Focussing the incident beam into a small spot and scanning it over the specimen. Thisis the procedure used in a Scanning Transmission Electron Microscope (STEM). Forevery pixel one obtains a complete spectrum.

2) Using an imaging energy filter in a conventional transmission electron microscope toform an image using only the characteristic loss electrons to form an image. SuchEnergy Filtering Transmission Electron Microscopes allow the fast acquisition ofimages with large pixel numbers (e.g. 2k by 2k or 4k by 4k)).

We shall give an overview of the physical principles of these methods and present some recent applications.

Electron Microscopy Center, Argonne National Laboratory, Argonne, IL, USA

Advances in model based quantification of EELS spectra

Jo Verbeeck 1

1 EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium

Acquiring EELS data from a given sample can be considered as a first step in the process of obtaining quantitative information about the sample. Often chemical profiles or stoichiometric ratios are needed and should be accompanied by estimates of the precision of the measurement. In this talk I will briefly review the conventional data treatment of EELS spectra and propose an alternative method based on parameter estimation theory. The theory starts from a model description of the experiment and estimates the parameters via an iterative procedure taking into account a model for the counting noise. The result of this process is an estimate of the parameters which often link to e.g. stoichiometric ratios, an indication of the validity of the used model and an estimate of the precision. Treating the data in this slightly more formal way results in an improvement of the precision of more than a factor 3 over conventional treatment while solving the issue of thickness related bias. The whole process is incorporated in the open source software EELSMODEL [1,2] and the general procedure will be demonstrated.

As a side note, the usefulness of principal component analysis, which is popular to filter noise in EELS spectra, will be discussed and compared against model based fitting of spectra.

Fig. 1 Screenshot of the EELSMODEL program that implements model based fitting of EELS spectra.

References [1] J. Verbeeck and S. Van Aert, “Model based quantification of EELS spectra.,” Ultramicroscopy, vol. 101, no. 2–4, pp. 207–24, Nov. 2004.[2] http://www.eelsmodel.ua.ac.be/[3] S. Lichtert and J. Verbeeck, “Statistical consequences of applying a PCA noise filter on EELS spectrum images.,” Ultramicroscopy, vol. 125, pp. 35–42, Feb. 2013.

The analysis of nanostructures and interface in vacuum annealed Si rich SiC film by 3D spectroscopic electron tomography:

Ling Xie1, Karol Jarolimek2, Rene A. C. M. M. Van Swaaij2, Vancho Kocevski3, Jan Rusz3 and Klaus. Leifer1

1. Uppsala University, Department of Engineering Sciences, Applied Materials Sciences, Box 534, SE-751 21Uppsala, Sweden.

2. Photovoltaic Materials and Devices, Delft University of Technology, P.O. Box 5031, 2600 GA Delft,Netherland.

3. Department of Physics and Astronomy, Ångström Laboratory, Uppsala University, Sweden

Silicon nanopartcles (NPs) embedded in the insulating or semiconducting matrices has attracted much interest for the third generation of photovoltaics, “all-Si” tandem solar cells. In this work, the amorphous silicon carbide (SiCx) with 30% carbon content were deposited using plasma enhanced

[1] The spatial distribution of Silicon NPs embedded in SiCx matrix in three-dimension (3D) is a critical parameter for the operation of “all-Si” tandem solar cells. From 2D EF TEM spectrum imaging dataset, both Si and 3C-SiC NPs were observed. In particular, a-SiC interface was found as an interface between Si and 3C-SiC NPs. The aim of this study is to show how Si NPs, 3C-SiC NPs and a thin a-SiC interface are distributed in 3D using electron tomography technique on transmission electron microscopy (TEM). [2]

References[1] S. Perraud et al., Phys. Status Solidi A, 1–9 (2012). [2] J. Frank, Electron Tomography: Three Dimensional Imaging with the Transmission Electron Microscope, Plenum, New York, London, 1992.

Department of Engineering Sciences, Uppsala University, Uppsala, Sweden Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden

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Probing optical properties using valence EELS

Michael Stöger-Pollach

University Service Centre for Electron Microscopy, Vienna University of Technology, Wiedner Hauptstraße 8-10, 1040 Vienna, Austria

Studying optical properties on the nano-scale is requested in semiconductor science as well as in photonics. Whereas the bulk properties determine the optical behavior in semiconductor science, the dielectric response of surfaces is key for the optical properties requested in photonics. The advent of monochromators in transmission electron microscopy (TEM) was the door opener for studying these optical excitations by means of valence electron energy loss spectrometry (VEELS).

This lecture will give an overview the latest research high-lights in VEELS in terms of semiconducting and photonic devices. A comparison of electron beam techniques with optical measurements will be given in terms of spatial and energy resolution, and momentum transfer. We will discuss the influence of the development of latest generation monochromators on the spectral resolution and discuss the physical limitations like energy losses caused by the

When trying to understand the VEELS spectrum, many excitation processes have to be taken into account: a) excitation of interband transition – whose recombination leads to the excitation of cathodoluminescence (CL) [1] –soon as the swift probe electron travels faster than the phase velocity of light inside the specimen [2], c) excitation of transition radiation (TR) being a dipole radiation caused by the electron – mirror charge dipole at the sample surfaces [3], d) excitation of the volume plasmon (VP) being a longitudinal charge density oscillation, e) surface plasmon excitation (SP) being a transversal charge density oscillation [4], and f) phonon scattering (Phon.) being an electron beam induced thermal vibration of the rystal lattice. Consequently we discuss the respective physical basics and give guide lines under which circumsances these excitations are of importance.

Fig. 1: Inelastic interactions contributing to the low loss spectrum in VEELS

References[1] M. Kociak et al., Comp. Rend. Phys. 15 (2014) 158-175 [2] M. Stöger-Pollach, Micron 39 (2008) 1092-1110 [3] E.T. Arakawa et al., Phy. Rev. 135 (1964) A224-A226 [4] V. Myroshnychenko et al., Nano Lett. 12 (2012) 4172-4180

Session III (invited): Monday, 14:00

Mapping nanoscale thermal gradients with plasmon energy shifts

Edward R. White1,2,3, Matthew Mecklenburg4, William A. Hubbard2,3, Rohan Dhall5, Stephen B. Cronin5, Shaul Aloni6, B. C. Regan2,3

1 Department of Chemistry, Imperial College London, SW7 2AZ London, UK.2 Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA.

3 California NanoSystems Institute, University of California, Los Angeles, CA 90095, USA. 4 Center for Electron Microscopy and Microanalysis, University of Southern California, Los Angeles,

CA 90089, USA. 5 Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089,

USA. 6 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

A better understanding of nonuniform temperature distributions in operating microelectronic devices will lead to more efficient and robust designs. Existing thermometry methods suffer fundamental limitations. Optical thermometers are diffraction-limited and thuscannot measure nanoscale thermal gradients, and contact methods perturb the temperatures of small systems. Here we describe an electron energy loss spectroscopy based non-contact thermometry technique that achieves nanometer-scale resolution with an accuracy of 10% and a statistical precision of 3 K/Hz1/2 [1]. As in a classical mercury thermometer, the temperature is determined by quantifying the density changes resulting from thermal expansion. Relating the bulk plasmon energy to the density, we find that temperature change ΔT is given by:

(1) where α1ΔT + α2ΔT2 describes the material’s thermal expansion per unit length and E is theplasmon energy. We produce a temperature map by rastering the electron beam across thesample and measuring the plasmon energy as a function of position.

Figure 1 shows a temperature map of a Joule-heated aluminum wire. The map reveals that the device reaches its highest temperature (440±40 K in a 66×66 nm2 region) away from the room-temperature electrical contacts. Such temperature maps are possible for many types of devices, as a variety of technologically-important metals (e.g. W, Ag) and semiconductors (e.g.Si, GaN) have sufficiently sharp plasmon resonances to serve as their own thermometers.

Fig. 1 A false-color temperature map of an 80-nm-thick, 100-nm-wide serpentine aluminum wire Joule-heated with 60μW. The histogram indicates the color scale and bins each pixel according to its temperature.

References [1] Mecklenburg et al., Science 347 (2015) 629-32.

STEM-EELS Band Gap Measurement in ZnCdO

Wei Zhan1,2, Vishnukanthan Venkatachalapathy1,2, Ingvild Julie Thue Jensen3, Cecilie S.Granerød1,2, Espen Flage-Larsen3, Augustinas Galeckas1,2, Andrej Yu. Kuznetsov1,2 and

Øystein Prytz1,2

1 Department of Physics, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo, Norway 2 Centre for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1126 Blindern, N-

0318 Oslo, Norway 3 SINTEF Materials and Chemistry, P.O. Box 124 Blindern, Forskningsveien 1, N-0314 Oslo, Norway

ZnO can be alloyed with CdO resulting in band gap tuning from UV to the visible range as shown by recent optical measurements of ZnCdO, see e.g [1]. Concurrently, there is an unresolved debate on the limitations of the single phase ZnCdO alloying, because of different crystallographic structures of its binary components, calling for applications of high resolution techniques and cross-methodological interpretations. In this work, the band gap measurements obtained by STEM-EELS were compared to the results obtained by photoluminescence (PL) and ab-initio calculations, as well as experimental observations of valence band shift by X-ray photoelectron spectroscopy (XPS).

ZnCdO samples were prepared by metal organic vapour phase epitaxy (MOVPE) on c-Al2O3 substrates buffered with a ZnO film. In these samples, in accordance with our initial x-ray diffraction measurements, Cd was successfully incorporated into the wurtzite ZnO matrix with concentrations up to 25%. Further, for TEM studies, samples were prepared by mechanical cutting, grinding/polishing, and ion beam thinning. The band gap studies with high spatial resolution were performed in an FEI Titan 60-300 probe-corrected and monochromated STEM. The critical voltage for generation of Cerenkov radiation in ZnO is 79 kV, so the microscope was operated in low-voltage mode with a high-tension of 60 kV. At this high tension, a spatial resolution better than 1.4 Å can be achieved for probe-corrected STEM imaging. The energy resolution for our monochromated EELS measurements was approximately 0.15 eV.

As a result, the assessments of the ZnCdO band structure obtained by various methods (STEM-EELS, PL, XPS, as well as ab-initio calculations) were interpreted in a combination, providing new arguments for the ZnCdO alloying debate.

References [1] V. Venkatachalapathy, et al., Phys. Rev. B 83 (2011), 125315.

Nanostructural development in graphitising and non-graphitising carbons probed using TEM/EELS

R. Brydson1, H. Freeman1, B. Miranov1, F, Hage2

1 School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, U.K.2 SuperSTEM, STFC Daresbury Laboratories, Keckwick Lane, Daresbury WA4 4AD, U.K.

Carbon materials are highly versatile owing to the strong dependence of their physical properties on the ratio of sp2 (graphitic) to sp3 (adamantine) bonds. Graphitic carbons have avariety of forms with various degrees of ordering ranging from microcrystalline graphite to glassy carbons. Amorphous carbons can have any mixture of sp3, sp2 and, in some cases, sp1

bonded carbon sites with the additional possible presence of hydrogen, nitrogen or boron. The structure of amorphous or poorly crystalline carbon materials are difficult to study using conventional characterisation tools; techniques which have been successfully applied include neutron scattering, nuclear magnetic resonance, (uv) Raman spectroscopy and EELS.

This work represents a comprehensive study of a large set of both graphitizing and non-graphitising carbons as a function of heat treatment from a few hundred degrees Centigrade up to 3000 oC using a combination of density measurements, X-ray and electron diffraction, highresolution TEM and low loss and core loss EELS [1,2]. Of interest is the variation in plasmon energy with heat treatment temperature and its relationship to density as well as the ratio of sp2 to sp3 bonded carbon species derived from the carbon K-edge using a heavily revisedanalytical procedure [2]. Of particular interest is the suggestion that the intrinsic structure of non-graphitising carbons is based on the inclusion of fullerene-like units and this hypothesis is tested against this present dataset and a fullerene or non-planar sp2 contribution is identified.

Overall using these techniques an insight into the nanostructural development of these two very different classes of carbon materials is obtained and this had very wide applicability to many engineering problems ranging from nanomaterial synthesis, coating deposition, catalysis and combustion. A number of specific examples are given: firstly, the analysis of new types of porous carbon derived from the pyrolysis of biomass that are used as chromatographic stationary phase materials [3], and secondly the analysis of radiation damage in nuclear graphites [4].

References [1] H. Daniels et al., Phil. Mag. 87 (2007) 4073. [2] Z. Zhang et al., Carbon. 49 (2011) 5049.[3] A Marriott et al., Carbon 67 (2014) 514.[4] B Mironov et al., Carbon 83 (2015) 106.

The effects of tailored surface and grain boundary passivation routes for high efficient kesterites solar cells revealed by advanced transmission electron microscopy techniques

Markus Neuschitzer1, Thomas Thersleff2, Sergio Giraldo1, Yudania Sánchez1, Simon López-Marino1, Marcel Placidi1, Klaus Leifer2, Alejandro Perez-Rodriguez1,3, and Edgardo Saucedo1

1 Catalonia Institute for Energy Research- IREC, Jadins de les Dones de Negre 1, Barcelona, Spain 2 The Ångström Laboratory, Department of Engineering Sciences, Uppsala University, Uppsala, Sweden 3 IN2UB, Departament d’Electrònica, Universitat de Barcelona, C. Martí i Franquès 1, Barcelona, Spain

Kesterite Cu2ZnSn(Sy-1Sey)4 (CZTSSe) is a promising candidate to replace chalcopyrite (CuIn1-

xGaxSe2 – CIGS) as absorber layer in thin film solar cells due its composition of more earth abundant materials. However, the main limitation of this technology so far is the lack of open circuit voltage (Voc) compared to CIGS. The reasons for this high Voc deficit are not totally clear yet. In polycrystalline thin film absorber material a benign passivation of grain boundaries and interfaces is crucial to achieve high device performance because grain boundaries and interface can act as highly active recombination paths.[1,2] In this work we show that low temperature post deposition annealings (PDA) after a specific surface etching can increase device performance of pure selenide CZTSe based solar cells from around 2% power conversion efficiency to over 8%, and further increase Voc of almost 100 mV. Combining this PDA with a tailored surface modification of the CZTSe absorber power conversion efficiency could be further increased to over 10% with a remarkable Voc of up to 450 mV; one of the highest values reported so far. Prior X-ray photoemission spectroscopy studies show that the 200ºC PDA promotes a Cu diffusion towards the bulk together with an Zn enrichment of the surface, thus creating a Cu poorer and Zn richer surface, which is crucial for the formation of a benign junction with the n-type CdS buffer and i-ZnO/ ITO window layers normally used in this technology. TEM microstructural investigations of the CZTSe/CdS interface combined with EELS shows an increased Cu content inside the CdS layerwhich further helps the formation of a Cu-depleted surface and seems to play an important role in the formation of the pn-heterojunction. Furthermore, EELS elemental maps reveal that the beneficial PDA and surface modification not only changes the CZTSe absorber surface, however, also the grain boundaries are largely affected. Before PDA Cu rich grain boundaries are observed.After PDA this is not evident, thus indicating grain boundary passivation, since Cu rich grain boundaries are reported to be detrimental to device performance.[3] Understanding the beneficial effects of post deposition annealing together with surface modifications on device performance thanks to this detailed study using TEM and EELS helps to further develop tailored surface and grain boundary passivation strategies to improve device performance of this promising technology.

0.0 0.1 0.2 0.3 0.4 0.50

10

20

30

200ºC

PDA

+ surf

. mod

.200

ºC PDA

Voc= 453 mVeff. = 10.2%

Voc= 320 mVeff. = 2.2%

not annealed

Voc= 412 mVeff. = 8.3%

curre

nt d

ensi

ty [m

A/cm

2 ]

voltage [V]

Fig. 1 Device performance before/after PDA + surface modification; elemental maps using EELS of CZTSe/CdS interface CZTSe absorber.

[1] M. Gloeckler et al., J. Appl. Phys. 2005, 98, 113704. [2] J. Li et al., ACS Nano 2011, 5, 8613.[3]A. Kanevce et al., Sol. Energy Mater. Sol. Cells 2015, 133

Electron Microscopy and Spectroscopy Study of Porous FexNi1-xMn2O4

Yue Ma 1, Cheuk-Wai Tai 2, Reza Younesi 1, Torbjörn Gustafsson 1, Jim Yang Lee 3 and Kristina Edström 1

1 Ångström Advanced Battery Centre (ÅABC), Department of Chemistry-Ångström Laboratory, Uppsala University, Box 538, SE-75121, Uppsala, Sweden.

2 Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-10691, Stockholm, Sweden

3 Department of Chemical and Biomolecular Engineering, National University of Singapore, 119260, Singapore, Singapore.

Ternary spinel oxides (mMn2O4, m = Co, Ni, Zn) attract extensive interests in the Li-ion battery applications due to their natural abundance, low lithiation potential, richer redox reactions from multiple cations and better electrical conductivity than manganese oxides [1-3]. In our study, Fe-doped spinel NiMn2O4 with a 3D macro/mesoporous network was fabricated by a nanocasting method. The hierarchical porosity and the cation distribution on preferential sites can be tailored. Figure 1a shows the distribution of Mn, Ni and Fe in a selected region of the sample obtained by EFTEM. Fe-dopant preferentially occupied in the tetrahedral sites in the spinel structure to prevent the migration of Mn3+ and hence stabilized the cubic structure. This was proofed by the valence-changing trend obtained from the combined XPS and EELS characterization. Cation and oxygen edges are shown in Figure 1b. The valence of the cations can be determined by the near edge features. FexNi1-xMn2O4 has a good cycle life stable for 1200 cycles at a high current density. This good Li+ storage performance could be attributed to the improved electrical conductivity by Fe-doping and the macro/mesoporous network composed by nano-crystals.

(a) (b)

Fig. 1. (a) TEM image and thickness map of a selected region and the EFTEM Mn, Ni and Fe maps. (b) EELS spectrum of the Fe-doped NiMn2O4.

Acknowledgements: This work has been funded by the Swedish Strategic Research Foundation (SFF) within the project Road to load, Swedish Research Council and The Swedish Energy Agency. The Knut and Alice Wallenberg Foundation is acknowledged for an equipment grant for the electron microscopy facilities at Stockholm University.

References [1] R. Patrice et al., Chem. Mater. 16 (2004) 2772-2782. [2] G. Zhang et al., Adv. Mater. 24 (2012) 4609-4613. [3] J. Li et al., Nanoscale 5 (2013) 2045-2054. [4] W. Kang et al., Nanoscale 7 (2015) 225-231.

ABSTRACT CODE (Please do not remove this line )

Applications of EDX spectroscopy

Shunsuke Muto 1, Masahiro Ohtsuka2

1 EcoTopia Science Institute, Nagoya University, Nagoya 464-8603, Japan 2 Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan

The current state-of-the-art aberration-corrected scanning transmission electron microscope (STEM) equipped with electron/X-ray detectors allows us handy for atomic scale imaging and elemental/electronic structural analysis, due to its high-brightness electron source and highly focused subatomic probe size available. In this tutorial talk, we start with the basic concept of energy dispersive X-ray (EDX) spectroscopy, followed by introducing its several advanced application examples.

The atomic column-by-column STEM-EDX spectral imaging (SI) technique inevitably leads to several drawbacks associated with a high density of focused electron probe and its small illuminating area (i.e., a small number of sampling points), so that the probe can drill the sample or otherwise the obtained data may contain high level noise accordingly. In addition, the obtained elemental distribution is not always a simple projection map of the structure for the sample thicker than a certain thickness, because of the spread of electron waves propagating through the sample.

We hence propose an alternative site-selective microanalysis method, instead of exploiting the atomic resolution in real space, using inelastic scattering by channeled electrons in a crystal. The method takes advantage of the high angular resolution in reciprocal space intrinsic to TEM [1].

The concept of the present element/site selective microanalysis is based on the scheme where the incident electron beam is rocked about a pivot point on a sample, acquiring the spectroscopic data as functions of the diffraction condition with respect to the incident beam direction. The sample orientation and diffraction condition is monitored by the beam rocking pattern recorded by the annular dark-field (ADF) or backscattered electron (BSE)detector. The present method is an extension of ALCHEMI/HARECXS [2,3], thereby exploiting element/site selective chemical information of the material associated with the different electron densities propagating along the specific atomic planes/columns by varying Bloch wave symmetry excited in the crystalline sample even from nanoscale areas. The acquired datasets of fluorescent x-ray intensities bear information on the site occupancies ofthe excited elements of interest, which can be quantitatively analyzed by comparing with theoretical simulations, based on the dynamical elastic/inelastic electron diffraction theories [4,5].

We will show several examples where the site occupancies of trace elements are quantitatively determined, which are not accessible by the atomic resolution STEM-EDX-SI.

References[1] S. Muto et al, AMTC Letters, 4 (2014) 248.[2] J. C. H. Spence and J. Taftø, J. Microsc. 130 (1983) 147.[3] K. Yasuda et al., Nucl. Instr. and Meth. B 250 (2006) 238. [4] M. P. Oxley and L. J. Allen, J. Appl. Crystallogr. 36 (2003) 940.[5] M. Ohtsuka and S. Muto, in preparation.

Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany

et al., Crystal Growth & Design 14et al Advanced Functional Materials

Understanding the oxidation front on coated stainless steels for SOFC interconnects – A time resolved study using STEM-EELS

Lisa S Karlsson 1, Mats W Lundberg2

1 Physical Metallurgy, AB Sandvik Materials Technology, 81181 Sandviken, Sweden 2 Surface Technology, AB Sandvik Materials Technology, 81181 Sandviken, Sweden

Interconnects for solid oxide fuel cells (SOFC) has been a part of the research conducted at Sandvik Materials Technology (SMT) for more than a decade. In this study Ce/(Co-Mn) coated AISI 441/0C365 strip steel has been characterized by scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS), in collaboration with the Kelvin Nanocharacterisation Centre at Glasgow University, in order follow the oxidation process. After only 30 s heat treatment at 800˚C (Figure 1) we have been able to identify an upper oxide (UO) layer that is a fully developed (Co,Mn)-spinel containing Mn3+ and to 1/3Co2+ + 2/3 Co3+ based on the white line ratios of Co L3/L2 and Mn L3/L2 [1-2]. The oxidationfront on the other hand is dominated by Co2+ and Mn2+. This difference was also confirmed bythe fine structure of the O K-edge where the first peak, characteristic for the trivalent species in spinels [3], was completely missing at the oxidation front.

Cr

CoO

MnO2

CeO2

Fig. 1 Multiple linear least squares (MLLS) fit coefficient maps of Cr, MnO2, CoO and CeO2 for the entire coated stainless steel after 30 s heat treatment. The upper oxide (UO) formation has started at the top of the coating with protrusions into the underlying layers.

References[1] Daulton et al., Ultramicroscopy 106 (2006) 561.[2] Wang et al., Micron 31 (2000) 571.[3] Eustace et al., Micron 41 (2010) 547.

Pt SSMn-CoUO Ce

Utilizing the phases in electron probes for chiral spectroscopy

Juan Carlos Idrobo Center of Nanophase Materials Sciences, Oak Ridge National Laboratory, TN 37831, USA

Until now, the goal of aberration-correction in scanning transmission electron microscopy has

been to produce electron probes with no phase. Phases increase the size of electron probes and

result in images and spectra with lower spatial resolutions. Here, I will show that phases in

electron waves, produced by aberrations in the lenses, can actually be beneficial when probing

the symmetry of materials. I will present calculations that show that lens aberrations are intrinsic

generators of angular momentum in waves. I will discuss how aberrations can be used to probe

the symmetry of materials at the atomic scale by showing experiments of chiral magnetic signals

in materials. This work was supported by the Center for Nanophase Materials Sciences (CNMS),

which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division,

Office of Basic Energy Sciences, U.S. Department of Energy.

Magnetic properties of single particles: Classical EMCD on FePt nanocubes

Sebastian Schneider1,2, Darius Pohl1, Stefan Löffler3, Peter Schattschneider3,4, LudwigSchultz1,2 and Bernd Rellinghaus1

1IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany. 2TU Dresden, Institute for Solid State Physics, D-01062 Dresden, Germany.

3Vienna University of Technology, USTEM, A-1040 Vienna, Austria.4Vienna University of Technology, Institute of Solid State Physics, A-1040 Vienna, Austria.

Energy-loss magnetic chiral dichroism (EMCD) is the electron wave analogue of X-ray magnetic circular dichroism (XMCD). It offers the possibility to study magnetic properties at the nanoscale in a transmission electron microscope (TEM) [1]. In a ‘classical’ EMCD setup, the sample is illuminated with a plane electron wave and acts as a beam splitter. Although this method is meanwhile well established, only very few EMCD spectra were so far obtained from individual nanoparticles [2, 3].

We report on EMCD measurements on individual FePt nanocubes (cf. Fig. 1) with a size of roughly 30 nm and compare our experimental findings with simulations. The dichroic signals at the L3 and L2 edges are expected to be as small as 10 % of the total scattering intensity. Our experiments are supported by simulations utilizing the WIEN2k program package [4], based on which FePt cubes with a thickness, that should provide maximal EMCD signals [5], are chosen for the experiments. The experiments indeed reveal a small but reproducible dichroic signal (cf. Fig. 2) that agrees well with the results of the theoretical calculations.

Fig. 1 TEM image of a FePt nanocube with a thickness of approximately 30 nm.

Fig. 2 EEL spectra of the nanoparticle in Fig. 1 at the Fe L3 and L2 edges for the two detector positions in EMCD geometry.

References [1] P. Schattschneider et al., Nature 441 (2006) 486. [2] J. Salafranca et al., Nano Letters 12 (2012) 2499. [3] Z.Q. Wang et al., Nature Communication 4 (2013) 1395. [4] K. Schwarz and P. Blaha, Computational Materials Science 28 (2003) 259. [5] S. Löffler and P. Schattschneider, Ultramicroscopy 110 (2010) 831.

Transmission electron microscopy of magnetite at low temperature

Takeshi Kasama1, Richard J. Harrison2, Masahiro Nagao3, Nathan S. Church4, Joshua M. Feinberg5, Yoshio Matsui3 and Rafal E. Dunin-Borkowski6

1 Center for Electron Nanoscopy, Technical Univ. of Denmark, Kongens Lyngby, Denmark 2 Dept. of Earth Sciences, Univ. of Cambridge, Cambridge, U.K.

3 Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki, Japan 4 Dept. of Geology and Mineral Resources Engineering, Norwegian Univ. of Science and Technology,

Trondheim, Norway 5 Institute for Rock Magnetism, Dept. of Geology and Geophysics, Univ. of Minnesota,

Minneapolis, U.S.A. 6 Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute,

Research Centre Jülich, Jülich, Germany

The Verwey transition in magnetite is associated with an order-of-magnitude increase in magnetocrystalline anisotropy and a change in easy axis from cubic <111> to monoclinic [001] below ~120 K [1]. Numerous studies have suggested that magnetic domain walls in magnetite can interact with the ferroelastic twin walls that form at low temperature because the monoclinic [001] direction can lie along any cubic <100> direction. However, the nature of these interactions remains controversial and the crystal structure, Fe2+/Fe3+ distribution and magnetic properties of magnetite at low temperature are poorly understood.

We have used conventional and convergent-beam electron diffraction in the transmission electron microscope (TEM) to show that the space group of magnetite below the Verwey transition temperature is monoclinic Cc with a small distortion from cubic symmetry [2]. We find that the choice of monoclinic c-axis is affected by the strength of the magnetic field of the microscope objective lens.

We have also used off-axis electron holography and Lorentz imaging to study the nucleation and motion of magnetic domain walls and transformation twins in synthetic multi-domain magnetite during cycling through the Verwey transition [2,3]. We observe clear interactions between magnetic domain walls and twin domain walls. Most of the twin domains have uniaxial magnetic domains along the monoclinic [001] direction. Whereas most 180˚ magnetic domain walls that intersect ferroelastic twin walls are mobile, some are pinned at the tips of needle twins. Zigzag magnetic domains, which are associated with ab-plane twinning along the c-axis and caused by slight deviations of the magnetic moments from the c-axis towards the intermediate b-axis, are observed only in thinner regions of specimens, suggesting that the specimen thickness may influence their formation. We also find magnetic domains formed by “strain-contrast-free” twins, which are not visible in conventional TEM images. Such submicron-sized magnetic domains with uniaxial anisotropy are observed widely and may have a strong influence on the low temperature magnetic properties of magnetite.

References [1] Walz, F., J. Phys. Cond. Matter. 14 (2002), R285. [2] Kasama et al. Phase Trans. 86 (2013), 67. [3] Kasama et al. Earth Planet Sci. Lett. 297 (2010), 10.

Quantitative EDS of Electron Transparent Samples

Meiken Falke 1, Ralf Terborg1, I. Nemeth, T. Salge1, A. Käppell, W. Hahn1, M. Rohde1,K. Bustillo2, Z. Gainsforth3,

G. Corbin4, P. Hrnciric4, T. Lovejoy4, N. Delby4, O. Krivanek4

1 Bruker-Nano GmbH, Am Studio 2D, 12489 Berlin, Germany.2 National Center for Electron Microscopy, Lawrence Berkeley Lab, Berkeley, CA 94720

3 Space Sciences Laboratory, University of California Berkeley, 7 Gauss Way, Berkeley, CA, 947204 Nion Company, 1102 8th St., Kirkland, WA 98033, USA

Quantitative chemical characterization of mixtures of light and heavier elements using EDS at high spatial resolution in the electron microscope is a challenge. While quantitative bulk analysis by EDS in SEM has been developed extensively, quantitative EDS of nanostructures and in transmission is still being explored. Complicating factors are e.g. absorption effects, radiation damage and preparation artefacts. Various single and multiple detector arrangements providing high solid angles of up to 1.1sr and high take-off angles between 20° and 70° are available now for electron microscopes. Multiple detector systems allow fastest data acquisition, which is suitable to analyze large or 3D samples in a reasonable amount of time and to avoid extended sample exposure in case of beam sensitivity. Additionally, in SEM, the analysis of complex bulk topography becomes possible, limiting the need for sample preparation. Our contribution reports on ways to exploit the available technology for quantitative EDS on the nanoscale using electron transparent samples in STEM and SEM.

In STEM small solid angles of 0.1sr in combination with high beam current and aberration correction allow the identification of single atoms in graphene by EDS [1]. The Cliff-Lorimer method, widely used for the quantification of electron transparent objects larger than that, can provide data on the accuracy level of a few at%. Using high solid and take-off angles as mentioned above, even the ppm level (e.g. 0.02 at% for Rb in an Orthoclase mineral standard [2]) can be accessed. The results of the Cliff-Lorimer quantification method are only valid relative to a suitable standard of similar thickness and composition though, which is often difficult to obtain. An alternative is the Zeta-factor method [3]. It additionally includes information on the beam current and accommodates the use of any standard with known thickness, density and composition. The Zeta-factor method can deliver absolute quantification while accounting e.g. for absorption effects. The implementation, further development options and the combination [4] with electron energy loss (EELS) spectroscopy will be discussed. To correctly interpret STEM-EDS element maps on the atomic scale,simulations of relevant scattering and radiation effects are necessary [5].

EDS of electron transparent samples in SEM can be combined with other emerging complementary SEM-based techniques: micro-XRF allows trace analysis for higher Z elements at low spatial resolution and Transmission Kikuchi Diffraction offers crystallographic analysis on the nm-scale [6].

References[1] Lovejoy T C et al., Appl. Phys. Lett. 100 (2012) 154101. [2] Gainsforth Z et al., Microsc. Microanal. 20 (Suppl. 3) (2014) 1682-1683. [3] Watanabe M & Williams D B, J. of Micr. 221 (2006) 89-109. [4] Kothleitner G et al., Microsc. Microanal. 20 (2014) 678-686 . [5] Forbes B D et al., Phys. Rev. B 86 (2013) 024108. [6] Keller R R & Geiss R H, J. Microscopy 245 (2012) 245.

FEI Solutions for Materials Science Applications

Mauro Porcu 1, Anna Carlsson1

1 FEI Company, Achtseweg Noord 5, Eindhoven, The Netherlands

For researchers in metallurgy, energy storage or functional nano-materials, where elemental distribution is crucial to performance and function, full structural and chemical characterization is made more difficult by decreasing feature sizes and increasingly complex architectures. Aberration correction has of course helped the TEM users to reach resolution in the order of 70 pm in commercially available microscopes. However, the knowledge of the chemical and electronic properties has even more relevance. The capabilities of the FEI Talos and FEI Titan Themis allow for through characterization of structural, chemical and electronic properties of any material. The presentation will illustrate the analytical performances which are currently available on the mentioned microscopes, with focus on EDS and EELS. Additional information will be given on the dynamic experiments enabled by a new class of holders developed by FEI and on the way we overcome the typical limitations of 2D imaging in the TEM.

Ultra-Fast data acquisition for EELS and Imaging

Neil Wilkinson

Gatan UK, 25 Nuffield Way, Abingdon, UK

The use of CCD and other non - film based cameras have transformed TEM and STEM data acquisition since their introduction in 1990. As the technology has advanced, so too have the application areas possible.

The modern TEM based digital camera can capture not only high resolution images in normal TEM mode, but images from extremely Low illumination conditions as used for Cryo Low Dose - less than 1e/Å2. The Low Dose Cryo technique has been well established for many years, but the older CCD technology (and film) imaging had reached its absolute limits in terms of achievable resolution and sensitivity. However, recent massive improvements have been made in the resolution of 3D reconstruction of protein and virus samples from data collected in cryo mode using new Direct Detection imaging devices.

TEM Digital cameras have been extensively used for the collection of Video images of live events in the TEM. Once again, CCD technology limits what is practical and possible, and frame rates of 30 per second are too slow for may in-situ experiments.

Direct Detection has not only revolutionized cryo applications, but also the in-situ area too. With acquisition frame rates of 1600 per second, in-situ now has come into a new era. Direct Detection looks set to change the kind of experiments we are able to do in the TEM.

Increased sensitivity and fast - 400 frames per second - readout mean that we no longer take a single acquisition, but capture many frames - so called Dose Fractionation. By cross-correlation and subsequent alignment of the image data stack, we can capture higher resolution images from samples that may be drifting. Dose fractionation also allows the rejection of image frames where the specimen is damaging in the beam.

The CCD camera also has a place in the Image filter for the collection of Electron Energy Loss spectra. Developments in CCD and associated hardware now allow acquisition rates of up to 1000 EELS spectra per second. This camera technology and modern TEM and STEM microscopes mean that Atomic resolution EELS mapping is now more commonplace.

From the imaging of delicate protein samples, to fast high resolution movies of crystal formation in the TEM, and fast atomic STEM EELS acquisition - new Detector technology has transformed what we can expect to visualize in a modern TEM/STEM.

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Advances in analytical transmission electron microscopy

Philipp Wachsmuth

1 JEOL (GERMANY) GmbH, Oskar-von-Miller-Str. 1A, 85386 Eching, Germany

With more than 60 years of experience in research and development, JEOL is today one of the largest manufacturers of electron optical systems.

Building on the success of the JEM-ARM200F, with more than 100 installations world wide, JEOL recently introduced the first 300kV transmission electron microscope (TEM) developed from the ground up. Aiming for an optimal integration of modern aberration correctors, the JEM-ARM300F, or GRAND ARM, comes with JEOLs own Cs-Correctors, is highly stable and guarantees a HAADF STEM resolution of 63pm. Furthermore, it is equipped with an optimized cold-field emission gun (cFEG), which routinely provides both a high beam brightness and high energy resolution, ideal for high resolution imaging as well as advanced EELS applications. To further improve the energy resolution for high-end applications JEOL also offers a double-Wien-Filter monochromator which can push the resolution by an order of 10 down if compared with the cFEG.

In order to increase the analytical capabilities of its TEMs JEOL launched the WIN EDS-system an improved energy dispersive x-ray spectrometer system consisting of two silicon drift detectors (SDD). This dual EDS system offers a large collection angle and significantly reduces the dependency on specimen tilt. Due to the increased sensitivity of this system a high throughput analysis is guaranteed.

With these high-end structural and analytical characterization methods, JEOL provides solutions for the investigation and characterization of materials down to the sub-Angström level.

Opening the Window for Large Solid Angle Silicon Drift Detectors to Enhance EDS Analysis on the TEM

James Holland 1, Neil Rowlands2

1 Oxford Instruments NanoAnalysis, Halifax Road, High Wycombe, UK 2 Scientific Consultant, Amesbury, Massachusetts, USA

Ultra high resolution TEMs are now capable of imaging atomic lattice structures. When combined with X-ray energy dispersive spectroscopy (EDS) it is possible to provide elemental analysis of these structures. However, the analytical conditions for such atomic resolution experiments in the TEM are very challenging for current windowed X-ray silicon drift detectors (SDD), due to the low X-ray count rates generated by the samples.

A new generation of X-ray SDD detectors has been designed that maximizes the X-ray signal collected from the sample by increasing the detector’s solid angle. This has been achieved by employing a large area silicon drift sensor without a detector window in front of it. Such a design has been realized in the X-MaxN 100 TLE, which has a sensor with an activearea of 100 mm2.

These detectors can significantly reduce analysis times and windowless technology increases sensitivity to low energy X-rays. Analyses of 15 minutes or less can show distributions of light elements, such as nitrogen, and structures less than 5 nm in size in a microprocessor section (Figure 1). Due to the increased solid angle, these detectors can now credibly be used for EELS + EDS analyses.

Fig. 1 EDS X-ray maps of a microprocessor collected in 15 mins: Nitrogen (yellow) and Hafnium (cyan)

The installation of 2 X-MaxN 100 TLE SDDs on a Hitachi High-Tech HD2700 STEM hasgenerated X-ray maps, in 12 minutes, to reveal GaAs atomic column structures (Figure 2).

Fig. 2 ADF STEM image of GaAs atomic lattice (left). Filtered EDS layered image of GaAS atomic column:based on Ga (red) and As (green) X-ray maps (right). Data courtesy of Hitachi High-Tech

Nion Co. 11515 NE 118th St., Kirkland, WA 98034, USA

An electron microscope for the aberration-corrected era

Dedicated STEM for 200 to 40 keV operation,

Vibrational spectroscopy in the electron microscope

Atomic-scale chemical imaging of composition and bonding by aberration-corrected microscopy

Electron microscopy studies on MoS2-based nanocatalysts

Lars P. Hansen1, Quentin M. Ramasse2, Christian Kisielowski3, Yuanyuan Zhu1, Poul G.Moses1, Michael Brorson1, Stig Helveg1

1 Haldor Topsoe A/S, Haldor Topsøes Allé 1, DK-2800 Kgs. Lyngby, Denmark 2 SuperSTEM Laboratory, STFC Daresbury, Keckwick Lane, Daresbury WA4 4AD, UK

3 Joint Center for Artificial Photosynthesis (JCAP), Lawrence Berkeley National Laboratory 1 Cyclotron Road, Berkeley, CA 94708, USA

New environmental legislation for clean fuels demands an enhanced removal of sulfur and other impurities from mineral oil. Production of transport fuels with ultra-low sulfur contents in oil refineries requires very efficient catalytic hydrodesulfurization processes, and attention is currently being devoted to understand the catalysts’ structure-activity relationships.

In oil refineries, the hydrodesulfurization catalysts are based on highly anisotropic MoS2 nanocrystals as the active component [1]. It is well-known that the catalytic reactivity of the MoS2 nanocrystals is associated with their exposed edges, size and morphology. Moreover, the catalytic effect can be boosted by the incorporation of secondary transitional metals such as Co or Ni [1,2]. However, although MoS2-based catalysts are synthesized at a very large scale in the refining industry, insight into the catalyst’s nanostructure and in particular the nature of the atomic-scale active sites has remained a challenge to unveil.

Recent advancements have made (scanning) transmission electron microscopy (S/TEM) a powerful technique for studying individual (supported) nanoparticles at the atomic-level [3-5]. In this presentation, we demonstrate the application of such advancements for single atom sensitivity electron microscopy of MoS2-based hydrodesulfurization catalysts. Specifically, high-resolution S/TEM imaging combined with electron energy loss spectroscopy (EELS) enable detection of the catalytic active edge structures at the single atom levels (Fig. 1). In combination with information about structure-sensitive catalytic functionality, obtained from scanning tunneling microscopy or density functional theory calculations, the electron microscopy observations provide information that can help establish new, improved structure-functionality relationships of the technological relevant hydrodesulfurization catalysts.

Fig. 1 HAADF-STEM image and EELS maps of a single-layer Co-Mo-S nanocatalyst on graphite. From [5].

References [1] H. Topsøe et al., Hydrotreating Catalysis, vol. 11, Springer, Berlin (1996). [2] F. Besenbacher et al., Catal. Today, 130 (2008) 86. [3] C. Kisielowski et al., Angew. Chem., Int. Ed. 49 (2010) 2708. [4] L. P. Hansen et al., Angew. Chem., Int. Ed. 50 (2011) 10153. [5] Y. Zhu et al., Angew. Chem. Int. Ed. 53 (2014) 10723.

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Elastic Scattering of Electron Vortex Beams in Magnetic Matter

Alexander Edström1, Axel Lubk2, Vincenzo Grillo3, Jan Rusz1

1 Dept. of Physics and Astronomy, Uppsala University, Uppsala, Sweden2 Technische Universität Dresden, Dresden, Germany

3 CNR-Instituto Nanoscienze, Italy

Recently, electron vortex beams, i.e. electron beams carrying orbital angular momentum (OAM), have gained much attention as a promising route to measure magnetic properties of materials with high resolution in inelastic electron scattering experiments. Technical challenges, such as poor signal to noise ratio, still remain to be overcome. Due to recent progression in producing beams with very high OAM (in the order of 100 ) [1, 2], a new route to overcome this could potentially be elastic scattering of high OAM vortex beams. In order to investigate this possibility, we derive a real-space multislice [3] based model to describe the magnetic interaction of vortex beams with magnetic matter. This model provides a two-component Pauli spinor alternative to fully relativistic four-component Dirac simulations [4]. Based on this model, we present simulations evaluating this potential route to a novel method of magnetic measurements. Initial results indicate the possibility of feasible experiments.

References[1] B. McMorran et al., Science 331 (2011). [2] V. Grillo et al., Phys. Rev. Lett. 114, 034801 (2015). [3] C. Y. Cai et al., Micron 40, 313-319 (2009).

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Can We Use Ferrocene as a Rapid Charge Regenerator?

Ahmed M. El-Zohry*, and Burkhard Zietz

Department of Chemistry, Ångström Laboratories, Uppsala University, Box 523, SE-751 20 Uppsala, Sweden

Charge recombination is a limiting process in dye-sensitized solar cells. Assuming an efficient charge injection from the excited dye to the conduction band of the low band gap semiconductor, such as TiO2, the electron in the semiconductor suffers many deactivation processes, reducing the cell’s efficiency. One of these deactivation processes is charge recombination, where the electron returns to the adsorbed oxidized dye on the semiconductor surface, lowering the voltage of the cell. Ideally, the oxidized dye has to be reduced by the electrolyte in the cell, such as iodide/tri-iodide mixture, this process is known as charge regeneration. Due to different reasons, starting from the slow diffusion coefficients of the used electrolytes, reaching to the mechanism of the charge regeneration that rely on the structure of the used dye, the charge recombination can compete with the charge regeneration leading to a poor efficiency. The charge recombination rate is decreased when increasing the distance between the negative electron in the semiconductor and the positive hole on the surface for stiff molecules [1]. Aiming to reduce the unwanted charge recombination process, two modified new dyes have been synthesized. The first one was connected covalently to one ferrocene (L1Fc), and the second one to two ferrocenes (L1Fc2) [2]. Ferrocene is expected to reduce the oxidized dye directly after charge injection that would lead to a longer distance for the charge separation. The original dye L1 (without the ferrocene) was also studied for comparison.

Fig. 1: Chemical structures of L1, L1Fc, and L1Fc2 dyes.References[1] Abrahamsson, M.; Johansson, P. G.; Ardo, S.; Kopecky, A.; Galoppini, E.; Meyer, G. J. JPCL, 2010, 1,

1725-1728.[2] The Samples were obtained from Prof. Lars Kloo (HKT).

In situ characterization of intermetallic Pd2Ga/SiO2 nanoparticles for low

pressure CO2 hydrogenation to methanol

E. M. Fiordaliso*,1, I. Sharafutdinov2, H. W. P. Carvalho3, J. -D. Grunwaldt3, T. W. Hansen1,

I. Chorkendorff2, J. B. Wagner1, C. D. Damsgaard1,2

1Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Lyngby, Denmark.

2Center for Individual Nanoparticle Functionality, Department of Physics,

Technical University of Denmark,DK-2800 Lyngby, Denmark.

3Institute for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology,

Engesserstr. 20, D-76131 Karlsruhe, Germany.

A combination of complementary in situ and ex situ techniques are used to investigate intermetallic Pd2Ga/SiO2 catalyst tested for CO2 hydrogenation to methanol at ambient pressure. The catalyst is prepared by simple impregnation of Pd and Ga nitrates into industrially relevant high surface area SiO2, followed by drying, calcination and reduction in a H2. The catalytic tests show that at ambient pressure, the intrinsic activity of the Pd2Ga/SiO2catalyst is higher than that of the conventional Cu/ZnO/Al2O3, while the production of the undesired CO is lower. In situ XRD and in situ EXAFS show that the Pd2Ga intermetallic phase is formed upon reduction and is stable during CO2 hydrogenation. TEM images of identical locations acquired ex situ show that nanoparticle size and dispersion are determined upon calcination with no significant changes observed after reduction and methanol synthesis. Similar conclusions can be drawn from electron diffraction patterns and images acquired at the Environmental TEM (ETEM) at 4 mbar, indicating that ETEM results are representative for the catalyst treated at ambient pressure. The chemical composition and the crystalline structure of the nanoparticles are identified by STEM/EDX, selected area electron diffraction patterns and atomic resolved TEM images (see Fig.1).

Fig. 1 Atomic resolved TEM image of a Pd2Ga nanoparticle acquired at ETEM under reduction conditions.

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Characterization of Mo2BC thin films by transmission electron microscopymethods

Stephan Gleich1, Soundes Djaziri1, Hamid Bolvardi2, Jochen M. Schneider2, Christina Scheu1

1 Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, 40237 Düsseldorf, Germany2 RWTH Aachen, Lehrstuhl für Werkstoffchemie, Kopernikusstraße 5, 52056 Aachen, Germany

The designing of a material which combines the properties of both, metals and ceramics,is favorable since then it shows a ductile behavior and is also stiff. This ambivalent nature of properties can be realized in nanolaminated structures. The investigation and understanding of their unique properties is very important regarding a continuing optimizing of the materials and finally to benefit from their advantageous properties in the future. An example of this class of material is Mo2BC.

We focus on the investigation of Mo2BC thin films on copper and silicon substrateswhich are synthesized by high-power pulsed magnetron sputtering deposition technique.[1]While the electronic structure and the mechanical properties of the material has been investigated in detail, electron microscopy investigations are rare.[2, 3] Therefore, we set our main focus on the characterization of the micro- and nanostructure especially by transmission electron microscopy (TEM) methods. Our first results show that the material consists of polycrystalline islands embedded in an amorphous matrix (see Fig. 1). For further investigations we want to perform electron energy loss spectroscopy (EELS) to get more information on the crystalline and amorphous regions in the material.

Fig. 1: TEM micrographs of a Mo2BC thin film (top view). Left: high-angle annular dark field image in scanning TEM mode; right: high resolution TEM image

References[1] H. Bolvardi et al., Thin Solid Films 542 (2013), 5-7. [2] J. Emmerlich et al., Journal of Physics D-Applied Physics 42 (2009), 1-6. [3] H. Bolvardi et al., Journal of Physics-Condensed Matter 25 (2013), 1-6.

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Solution based organolead tri-iodide Perovskite Crystal Formation

Malin B. Johansson1, Stefan Bitter1, Wubeshet Sahle2, Erik M. Johansson1, Mats Göthelid2,Gerrit Boschloo1

1 Div. Physical Chemistry, Dept. Chemistry, The Ångström Laboratory, Uppsala, Sweden2 KTH- Royal Institute of Technology, Div. Materials and Nano Physics, Stockholm, Sweden

Perovskite-absorber solar cells have become a research area with high interest for their efficientenergy conversion. A clue to the high performance of the material is the long diffusion length of charge carriers, which depend on crystallinity and morphology. However, still the main difficulty is to gain reproducible performance which address questions to the functions originating from the crystal chemistry in these materials. The first crystallographic information is commonly X-ray diffraction fororgano-metal halide perovskites, but scattering is dominated by higher atomic elements, and is relatively insensitive to the organic component that controls the phase and crystal formation [1]. By combining TEM and EDX we study perovskite crystals formed from a mixture of methyl ammoniumiodide and lead iodide in an II-propanol solution. A comparison of different crystals with itsdiffraction pattern gained knowledge in how the material is built up. It is seen how the atoms organize from small perovskite quantum dots, Fig.1 (a), to larger single crystals, Fig. 1 (b). The size and structure of the crystals can further be controlled by molar ratio, additives and temperature. Here we try to illuminate and explain the crystal structure birth and its organized growth of the perovskite grains. The results give new insight into the crystal chemistry of the perovskite solar cell material.

(a) (b)

Fig. 1 (a) TEM image of a perovskite quantum dot (b) Single crystal diffraction pattern from PbI2

References[1] T. Baikie et al., J. Mater. Chem. A. 1 (2013) 5628

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On the medium range order in amorphous FeZr alloys using FEM

Vancho Kocevski1, Tao Sun2, Jan Rusz1, Klaus Leifer3, Ling Xie3, Björgvin Hjörvarsson1,Moritz to Baben4, Nestor J. Zaluzec2

1 Department of Physics and Astronomy, Ångström Laboratory, Uppsala University, Sweden2 Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois, USA

3Department of Engineering Sciences, Ångström Laboratory, Uppsala University, Sweden 4Institute für Werkstoffchemie, Kopernikusstr. 10, RWTH Aachen University, Germany

Fluctuation Electron Microscopy (FEM) is imaging/diffraction technique used in characterizing the medium range order (MRO) [1], i.e. ordering regime within ~0.5–2 nm.The main idea of the technique is correlating the FEM signal spatial variance (V(k,q)) of the nanodiffraction intensity (I(k,q)) with the ordering in the material, where V(k,q) is defined as:

1),(

),(),( 2

2

qkI

qkI=qkV (1)

The averaging is over all sampling positions, k is the magnitude of the scattering vector, and qis the diameter of the objective aperture at which the image was acquired (calculated).

We combine dynamical diffraction calculations and classical molecular dynamics (MD) simulations to have an understanding of the MRO in Fe0.81Zr0.19 alloys. The MD is used to make models of the amorphous alloy, in which the MRO is simulated by inserting crystalline nanoparticles (NPs). We consider randomly oriented NPs with two different sizes, and two different volume occupations–crystallinity of the system. To study the influence of the disorder in the NPs on the variance, we calculated the micro-diffraction patterns of systems with relaxed (disordered) and unrelaxed (crystalline) NPs. The micro-diffraction patterns were calculated using real space multislice method [2], where the response of an electron wave propagating through the sample is calculated.

(a) (b) (c)

Fig. 1 Averaged micro-diffraction patterns of 8x8x10 nm amorphous Fe0.81Zr0.19 alloy and 30 % crystallinity, with: (a) relaxed NPs; (b) unrelaxed NPs. (c) Comparison between the variance, as a function of k, of the models with relaxed and unrelaxed NPs. The diffraction patterns are calculated using probe size of 17.5 Å.

References[1] M. M. Treacy, J. M. Gibson, Acta Crystallogr. Sect. A 52 (1996) 212.[2] C. Y. Cai et al., Micron 40 (2009) 313, and references therein.

Microscopic characterisation of nanocrystalline silicates

MSc. Angela P. Moissl 1,3, Prof. Dr. Martin Ebert1 ,Prof. Dr. Ute Kolb1,2

1 Department of Applied Geosciences, Technische Universität, Schnittspahnstraße 9, 64287 Darmstadt , Germany

²Institute of physical Chemistry, Johannes Gutenberg Universität, Duesbergweg 10-14, 55128 Mainz, Germany

3 Now at: Department of Earth Sciences, Villavägen 16, 75236 Uppsala, Sweden

Various nanocrystalline silicates were studied in a new approach by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and automated diffraction tomography (ADT). The samples were collected at the Jungfraujoch Sphinx Observatory (Switzerland) with an impactor system behind an ICE-CVI (Counterflow Virtual Impactor). The atmospheric particles, placed on a carbon coated copper TEM grid, were roughly pre-classified by their chemical composition via Energy Dispersive X-ray Spectrometry (EDX) with the Scanning Electron Microscope (SEM). This chemical analysis delivered a large number of different groups each still covering a large range of minerals possible. In order to clarify the structural nature of the particles further, a Transmission Electron Microscope (TEM) was used for electron diffraction experiments. Particles showing diffraction, which all turned out to be members of the classes SiAl and SiAl+Fe, were selected and used for further investigation with Automated Diffraction Tomography (ADT). Determined cell-parameters and space groups supported with the chemical composition determined by EDX measurements lead to the conclusion that the investigated silicate particles are sheet silicates. ADT data from a muscovite single crystal, investigated as a model compound, delivered a complete “ab- initio” structure solution. ADT data taken from the investigated ice residuals showed significantly more disorder and polycrystallinity but the majority of the particles were identified unambiguously as members of the mica group. A detailed investigation of atmospheric particles by combining the above mentioned methods is time consuming and restricted as well as somehow biased by several factors, such as particle agglomeration, morphology and crystallinity. Nevertheless the further investigation with ADT allows an in-depth look on particles, which is not achievable with the classic electron microscopic single particle analysis.

References:

[1] Vali, G., 1996, Ice nucleation - A review: Nucleation and atmospheric aerosols,, p. 271–279

[2].Gorelik, T.E., Schlitt, S., and Kolb, U., 2011, Introduction to ADT / ADT3D ADT experiment: cryst.

ressearch technology, v. 46, no. 6, p. 542–554.

[3] Zimmermann, F., Weinbruch, S., Schütz, L., Hofmann, H., Ebert, M., Kandler, K., and Worringen, A., 2008,

Ice nucleation properties of the most abundant mineral dust phases: Journal of Geophysical Research, v. 113, p.

D23204.

EELS-SI reveals nanoscale composition inhomogenity of IN-718 surface case built up via carburization in gas atmosphere at low temperature

Corneliu Sârbu

Laboratory of Atomic Structures and Defects in Advanced Materials, National Institute of Materials Physics, 105B Atomistilor street, RO-077125, M gurele-Bucharest, Romania

We employed the JEM-ARM200F t.e.m. to get direct evidence of microstructure and for testing the atomic scale theory of interstitial carbon super-saturation LTCSS [1], currently accepted as supporting the surface parameters enhancement in stainless alloys carburized in low temperature (LT) gas atmosphere (via the processing invented by Swagelok Co. [2]). We did investigate the Inconel-718 (IN-718) Ni base superalloy, prone for surface parameters enhancement through this technology, as reported [3]. The Z-contrast analysis in connection with line EELS-SI revealed the nanoscale inhomogeneous distribution of major alloy elements Ni, Cr, Fe and of C (introduced by carburization), Fig-1. The high Cu contamination grown during ion milling interferes with the final result. No preservation of initial alloy grains and no colossal concentration of interstitially diffused C atoms inside coarse grains were evidenced. A fragmentation down to nano-sized austenite crystals intermixed with an amorphous phase and the preference of C to accumulate mainly into the amorphous phase were revealed.

References [1] Cao Y, Ernst F, Michal G, Acta.Mater. 51 (2003) 4171 [2] Williams PC, Collins SR, JOM 60 (2008) 27 [3] Sharghi-Moshtaghin R et al, Metall.Mater.Trans. 41A (2010) 2022

(h)

(g)

(c) (f)b

(a)

(b) (e)b)

(d)

FIG-1. EELS-SI analysis of: (b) C, (d) Ni, (e) Cr, (f) Fe, (g) O and of contaminant Cu (h) areal density distributions [atoms/nm**2] in parallel with Z contrast brightness (a), evaluated in 200 equidistant points along the rectilinear segment AB.

The relative thickness variation along AB is also shown in graph (b), in units of , and is variable between 0.468 and 0.583 . All graphs were smoothed.

Dresden Center for Nano analysis, Technical University of Dresden, Germany Fraunhofer Institute for Ceramic Technologies and Systems (IKTS), Dresden, Germany