Etienne Snoeck CEMES-CNRS
Rafal Dunin-Borkowski Technical University of Denmark
Johan Verbeeck University of Antwerp
Ulrich Dahmen Lawrence Berkeley National Laboratory
C1: Mapping of Electronic States and Local Bonding and Elemental Mapping I
Monday PM, November 26, 2007
Back Bay D (Sheraton)
9:30 AM - C1:Analytical I
Opening Remarks by Organizers Show Abstract
9:45 AM - **C1.1
Probing the Chemistry and Bonding of Nanoscale Materials with High-Resolution Electron Energy Loss Spectroscopy.
Gianluigi Botton 1 Show Abstract
1 Materials Science and Engineering, BIMR, McMaster University, Hamilton, Ontario, Canada
The technique of electron energy loss spectroscopy (EELS) in the transmission electron microscope makes it possible to probe the chemical environment of atoms in a solid with a spatial resolution that now approaches the Angstrom level. The main features of interest in EELS are the near-edge fine structures that provide information on the local composition and chemical bonding in the same way as X-ray absorption spectroscopy. In this presentation I will demonstrate examples of applications of near-edge structures in the study of a variety of perovskite based compounds. These materials exhibit fascinating electronic properties that can be tuned by suitable changes in composition of the compounds and, for the case of thin films, the substrates. I will focus my presentation on the application of the monochromators and new generations of electron microscopes to demonstrate the advantages of such technologies for extracting valuable information on the bonding end electronic structure of these materials at high spatial resolution. Examples will cover solid solutions in the BaTiNbO3 series, dielectric materials (relaxor ferroelectrics) that have shown high-dielectric constant and engineering materials such as fuel cells and machining tools.
10:15 AM - **C1.2
Semiconductor Band-gap Measurements Using Electron Energy-loss Spectroscopy.
Peter vanAken 1 , Wilfried Sigle 1 , Lin Gu 1 , Vesna Srot 1 , Christoph Koch 1 Show Abstract
1 Stuttgart Center for Electron Microscopy, Max Planck Institute for Metals Research, Stuttgart, Baden-Württemberg, Germany
With the latest development of monochromators for transmission electron microscopes, electron energy-loss spectroscopy has become a powerful technique to study the band structure of materials with high spatial resolution. The present results are obtained with the Zeiss LIBRA 200FE and SESAM microscopes which are equipped with an electrostatic Omega-type monochromator produced by CEOS and highly dispersive energy filters. The zero-loss spectrum acquired in the SESAM with the smallest energy-selecting monochromator slit and an acquisition time of 10 s exhibits a full width at half maximum of 87 meV. At this resolution after subtraction of the zero-loss peak tail, the onset of electron excitations from the top of the valence band to the bottom of the conduction band in semiconductors and insulators becomes unambiguously visible. Examples were obtained from a series of various semiconductors from the system GaN–AlN, diamond, and Si. Differences are clearly revealed which are due to the different band gaps and the variation of the band structure. The noise level of the spectra is very low because of the long exposure time which allows detection of subtle details.Additional low-loss scattering events like the excitation of Cerenkov radiation, transition radiation, and surface plasmons may overlap with the onset of the band gap and, hence, pose a limitation for the interpretation of the low-loss spectra. In order to reveal the exact band-gap onset, we minimized the influence of these artefacts by varying specimen thickness and detected scattering angles. For the direct semiconductor GaN, we found that below a critical specimen thickness Cerenkov radiation and transition radiation are negligible and also surface losses are small. In the case of the indirect semiconductor Si, we used electrons scattered to large angles. Under these dark-field mode conditions, indirect transitions are strongly enhanced, since the required momentum transfer for indirect transitions is satisfied, and Cerenkov radiation losses are completely removed, because they are limited to a very narrow angular range . Limitations of spatial resolution and possible solutions for improvements will be discussed. L. Gu, V. Srot, W. Sigle, Ch. Koch, P. van Aken, F. Scholz, S.B. Thapa, Ch. Kirchner, M. Jetter, M. Rühle: Band-gap measurements of direct and indirect semiconductors using monochromated electrons. Phys. Rev. B 75 (2007) 195214 – 1-8. Acknowledgements: The financial support for the SESAM project by the German Science Foundation, the Land Baden-Württemberg, and the Max Planck Society is highly appreciated. The authors acknowledge financial support from the European Union under the Framework 6 program under a contract for an Integrated Infrastructure Initiative. Reference 026019 ESTEEM.
10:45 AM - C1.3
The Electronic Structure of the 2D Spin Gap System SrCu2(BO3)2 : EELS Experiments and Ab initio Band Structure Calculations.
Guillaume Radtke 1 , Andres Saul 2 Show Abstract
1 Laboratoire TECSEN - CNRS, Université Paul Cézanne Aix Marseille III, Marseille France, 2 Centre de Recherche en Matière Condensée et Nanosciences - CNRS, Campus de Luminy, Marseille France
During the last decade, a lot of theoretical and experimental work has been devoted to the study of the magnetic properties of SrCu2(BO3)2. This compound crystallizes in a tetragonal structure where layers of CuBO3 alternate with planes of Sr atoms along the  direction. Due to this unusual structure where Cu2+ atoms are arranged in the layers to form a network of orthogonal dimers, SrCu2(BO3)2 appears as the first realization of a 2D Heisenberg model known as the Shastry-Sutherland model and exhibits a number of unique features such as a spin gapped behavior, unusual magnetic excitations or magnetization plateaux. Solid-state magnetism is always intimately related to the underlying electronic structure of solids. Electron energy loss spectroscopy and in particular, energy loss near edge fine structure (ELNES) is one of the most powerful solid state spectroscopies allowing the investigation of the electronic structure of materials. When combined with ab initio band structure calculations, this technique provides an efficient way to determine the energy position and the character of the unoccupied states in a solid.In this work, we present an experimental and theoretical study of the O-K edge recorded in SrCu2(BO3)2. In a first part, we will show that under specific experimental conditions of illumination and collection, the conventional TEM can be used to determine the spatial orientation of the electronic states in such an anisotropic material. In a second part, we will show how a careful analysis of the O-K edge fine structure can be used to estimate the on site Cu-3d Coulomb and exchange interactions (U). These interactions not only play a crucial role in the electronic structure of this compound, leading to the creation of a correlation gap, but also scale to superexchange coupling constants appearing in the Shastry-Sutherland model. Therefore, electron energy loss spectroscopy can provide relevant and quantitative information when studying the magnetic properties of strongly correlated systems such as cuprates compounds.
11:30 AM - **C1.4
Chemical Mapping on a Nanometer Length Scale.
Werner Grogger 1 , Bernhard Schaffer 1 , Gerald Kothleitner 1 , Ferdinand Hofer 1 Show Abstract
1 FELMI, Graz University of Technology, Graz Austria
For many years performing nanoanalysis in the transmission electron microscope (TEM) has helped to solve numerous material science problems. Typically, energy dispersive X-ray spectrometry (EDXS) and electron energy-loss spectrometry (EELS) have been used extensively to explore the chemical composition of specimens on the atomic scale. Complementary to “point analyses”, where a finely focused electron beam defines the analyzed specimen area, mapping techniques are nowadays widely used as a means of visualizing the specimen’s chemistry in an illustrative manner.Based on EELS, energy-filtering TEM (EFTEM) is a quick and easy way of chemical mapping. Thus EFTEM nicely complements TEM image information in terms of elemental information about the specimen on a nanometer length scale. On the other hand, a finely focused beam in a scanning TEM (STEM) provides the possibility of recording several analytical signals simultaneously (STEM spectrum imaging). Spectrum imaging actually yields three dimensional data sets from which two dimensional maps can be created using for instance the EDXS, and/or EELS signals. In the case of EELS, the three dimensional data set can also be obtained in a slice-by-slice way by using EFTEM (EFTEM spectrum imaging).Spectrum imaging techniques can provide excellent data, both in terms of spatial and – in the case of EELS – energy resolution. For instance, by closing down the energy selecting slit for the acquisition of an EFTEM spectrum image can yield an energy resolution of the extracted spectra of 0.8 eV, which is comparable to that of a conventional 200 kV FEG-TEM. Working in the low energy-loss regime, the high dynamic range of the signals usually imposes an acquisition problem. However, an automatically adjusting acquisition procedure for an EFTEM spectrum image can help to overcome this problem. This way, subtle differences, like a shift of the plasmon peak by just less than 0.2 eV, can be detected and used for mapping at a very good spatial resolution. On the other hand, the high quality data may also be used for sophisticated data processing techniques (e.g. multiple least squares fitting) improving the mapping capabilities of EFTEM significantly.In this paper we will present some of our results in terms of chemical mapping using conventional EFTEM as well as spectrum imaging methods. Issues like obtainable spatial and energy resolution, artifact correction techniques, and optimized acquisition and data processing schemes will be discussed.
12:00 PM - C1.5
EELS Quantitative Analysis of AlGaN and GaN Nanowires Grown by Ni Promoted MBE on Sapphire Substrate.
Leonardo Lari 1 , Robert Murray 1 , Mhairi Gass 2 , Timothy Bullough 1 , Paul Chalker 1 , Caroline Chreze 3 , Lutz Geelhaar 3 , Henning Riechert 3 Show Abstract
1 Engineering, University of Liverpool, Liverpool United Kingdom, 2 , SuperSTEM Laboratory, STFC Daresbury, WA4 4AD, Daresbury United Kingdom, 3 , Qimonda D-81730, Munich and NaMLab, D-01099 , Dresden Germany
Compositional analysis of nitride-based nanowires grown by radio frequency plasma assisted Molecular Beam Epitaxy on c-sapphire is reported. Two types of nanowire were examined: a uniform gallium nitride one; and one with a uniform AlGaN composition of nominally 10% Al atomic weight. In particular, examination of the composition of nickel seeds used to promote the nanowire type growth has been made with the aim of understanding the growth mechanism. Electron microscopy analysis was performed using the aberration-corrected Scanning Transmission Electron Microscope at the SuperSTEM Laboratory in UK. This instrument is based on a 100 keV VG HB501 with a cold-field emission source, equipped with a Gatan Enfina parallel channel Electron Energy Loss Spectrometry (EELS) system and a Nion Mark II spherical aberration corrector. The semi-angular range of the high angle annular dark field (HAADF) detector is from 70 to 210 mrad. Bright field and HAADF images of the growth tip at the end of nanowires revealed the presence of seed particles which is characteristic of either a vapor-liquid-solid or a vapor-solid-solid type of growth mechanism. The lattice spacing measured in the GaN nanowire body yielded a value of 2.59±0.02Å in good agreement with GaN (0002) spacing. Measured values of lattice spacing from the seed area of 2.084±0.016 Å are attributable to the lattice spacing of either (002) NiO or (111) GaNi3. EELS analyses of the same nanowires was performed to elucidate the phase of nickel based seeds. Line scans and spectrum images were quantified assuming a single power law decay for the background subtraction. The electronic partial cross sections for inelastic scattering were calculated using the Hartree-Slater model for each specific core loss feature. Mean free path (MFP) for all inelastic scattering was calculated in the materials under investigation verifying the fulfilling of the condition t/λ ≤ 0.3, where t is sample thickness and λ is the MFP, allowing plural scattering to be neglected. This analysis yielded the expected 1:1 ratio for the Ga and N elemental compositions within the nanowire body. Compositional analysis of the nickel seed ‘catalysts’ exhibited two general types of characteristics according to their size. Larger seeds showed metallic cores contained gallium and nickel concentrations consistent with the presence of the equilibrium phase α’ GaNi3. Virtually no nitrogen was observed within the seeds, which is consistent with a thermodynamic consideration of the stability of the Ni3N and Ni4N phases that are unstable at the MBE growth temperature of 730°C. The larger nickel seeds also consisted of a gallium-doped nickel oxide shell which is attributed to oxidation in the ambient, following removal from the MBE growth system. Smaller seeds showed no indication of a metallic core but instead overlapping of nickel and oxygen signals indicating the complete oxidation of the seed arising from its relatively small volume-to-surface ratio.Acknowledgements: EMS sponsorship for the participation to this conference and financial support under the MRTN-CT-2004-005583 “PARSEM” project are gratefully acknowledged
12:15 PM - C1.6
HRTEM and STEM-EELS Studies of Ba1-xSrxTiO3 Multilayered Films.
David McComb 1 , Yiqian Wang 1 , James Perkins 1 , Peter Petrov 1 , Neil Alford 1 Show Abstract
1 Materials and London Centre for Nanotechnology, Imperial College London, London United Kingdom
Barium strontium titanate Ba1−xSrxTiO3 (BST) thin films have potential applications in a range of microelectronic devices that utilise the properties of BST films, such as a high dielectric permittivity, reasonably low dielectric loss and high tunability. The cubic paraelectric phase of bulk BST transforms to a tetragonal ferroelectric phase at the Curie temperature. In BST thin films the observed transition temperatures and phase stability depend on the microstructure and strains in the films. More significantly the peak in the temperature dependence of the dielectric permittivity is broader than that observed in bulk BST. A broad peak in the dielectric response is desirable as the performance of the devices becomes less sensitive to temperature variations. This improvement in temperature stability can be improved further by using multilayer superlattice films of SrTiO3 (STO) and BaTiO3 (BTO) with the thickness of the layers tuned to give the desired BST composition.In this work, we report the results of an investigation into thin-film STO/BTO multilayers deposited by pulsed laser deposition on LaAlO3. Oxygen relaxation was used during the PLD growth to ensure the films were not oxygen deficient. The multilayer formed has an overall composition of Ba0.75Sr0.25TiO3. The dielectric properties of the multilayer were investigated as a function of temperature and these were correlated with microstructural studies of the epitaxial relation between the layers, crystal defects and strain distribution in the film. Energy-loss spectroscopy was carried out in a monochromated scanning transmission electron microscope (STEM) to investigate the influence of changing in local electronic structure on the dielectric properties.
12:30 PM - C1.7
Quantification Of EELS Spectra: Converting Spectra To Numbers.
Jo Verbeeck 1 , Giovanni Bertoni 1 , Sandra Van Aert 1 Show Abstract
1 Physics, EMAT, University of Antwerp, Antwerp, Antwerpen, Belgium
In this contribution we discuss the use of model based quantification as a novel approach to EELS quantification problems [1,2]. We show that realistic models describing the shape of an EELS spectrum can be constructed. These models are used in a maximum likelihood iterative procedure to estimate the unknown parameters taking into account the noise properties of the detector. The result of this approach is firstly a set of estimated parameters that could present the concentration of a certain element. Secondly the precision on these parameters can be estimated, and finally an indication on the validity of the model is given. Experimental examples show that the attainable precision, which can theoretically predicted, is attained in real life experiments, and statistically valid models can be constructed. Moreover, it will be shown that the estimated concentrations of elements are often also very accurate as opposed to conventional quantification routines. A comparison with conventional quantification shows that an improvement in precision of about a factor of three is obtained for the same experimental data. Moreover the technique has a broader area of application because it can handle spectra from thicker samples and with overlapping excitation edges.An overview of the working principle of model based quantification will be given as well as a set of examples that show the real life performance of this method. Recent developments dealing with correlated noise from the detector  and including prior knowledge from lifetime broadening of the ELNES fine structure will be discussed. J. Verbeeck and S. Van Aert - Model based quantification of EELS spectra - In: Ultramicroscopy, 101-2-4 (2004), p.207-224  J. Verbeeck, S. Van Aert and G. Bertoni - Model based quantification of electron energy loss spectroscopy: including the fine structure - In: Ultramicroscopy, 106-11-12 (2006), p.976-980  J. Verbeeck and G. Bertoni - Model-based quantification of EELS spectra: Treating the effect of correlated noise - In: Ultramicroscopy, available online doi:10.1016/j.ultramic.2007.03.004-(2007)The authors acknowledge financial support from the Fund for Scientific Research-Flanders and the European Union under the Framework 6 program under a contract for an Integrated Infrastructure Initiative. Reference 026019 ESTEEM.
C2: In-situ Measurements of Properties, Reaction Rates and Mechanisms
Monday PM, November 26, 2007
Back Bay D (Sheraton)
2:30 PM - **C2.1
Imaging Individual Organic Molecules by High-contrast Microscopy.
Kazu Suenaga 1 Show Abstract
1 , AIST, Tsukuba Japan
The most of the past structural studies of organic molecules by TEM have been based on diffraction analysis of their films or thin crystals because it has long been considered difficult to observe individual organic molecules by HR-TEM. There are presumably two major reasons for that; (i) the phase contrast of individual organic molecules is intrinsically quite low, and (ii) the organic molecules are radiation-sensitive and therefore they are supposed to strongly suffer the electron irradiation damage.The destruction of the electron-diffraction pattern indicates the critical dose of polyethylene for 100keV electron as 0.01 C/cm2 . It seems a priori not at all possible to obtain a HR-TEM image of this molecule with higher dose (since a dose around 1 C/cm2 is typically required for carbon atom imaging ). Despite this discouraging prediction, we have attempted the individual molecular imaging of small organic molecules inside carbon nanotubes by HR-TEM. The successful imaging of pyrolidine-type functional groups  and single carbon chains will be presented [4, 5]. The carbon nanotube acts as a specimen protecting cell to prevent the cross-linking by isolating the molecules from their neighbors.Supports from JST-CREST and JST-ERATO are acknowledged. L. Reimer, in Physical Aspects of Electron Microscopy and Microbeam Analysis, ed. By Siegel and Beaman, (Wiley New York, 1975) A. Hashimoto, K. Suenaga, A. Gloter, K. Urita and S. Iijima, Nature, 430 (2004) 870 Z. Liu, M. Koshino, K. Suenaga, A. Mrzel, H. Kataura and S. Iijima, Phys. Rev. Lett., 96 (2006) 088304 M. Koshino, T. Tanaka, N. Solin, K. Suenaga, H. Isobe and E. Nakamura, Science 316 (2007) 853 Z. Liu, K. Yanagi, K. Suenaga, H. Kataura and S. Iijima, Nature Nanotechnology 2 (2007) July issue
3:00 PM - **C2.2
Quantifying Nucleation Processes During the Growth of Semiconducting Nanowires and Carbon Nanotubes.
Eric Stach 1 , Bong Joong Kim 1 , Jerry Tersoff 2 , Sueng Min Kim 1 , Suneel Kodambaka 3 2 , Dmitri Zakharov 1 , Benji Maruyama 4 , Frances Ross 2 Show Abstract
1 School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 2 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States, 3 Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States, 4 Materials and Manufacturing Directorate, Wright Patterson Air Force Research Laboratory, Dayton, Ohio, United States
Semiconducting nanowires and carbon nanotubes are two of the primary 'new' materials of interest in the field of nanotechnology. This is because their small dimensions and unusual structures allow for new technologies to be established that exploit their unique electronic properties. We have been focused on understanding the mechanisms and kinetics associated with their nucleation and growth, in an attempt to provide a scientific framework for controlling their structure. Through the use of in-situ chemical vapor deposition in both ultra-high vacuum and at elevated pressures, we can observe the mechanisms of nucleation and quantitatively characterize the kinetics of these processes. In the case of vapor-liquid-solid silicon nanowire growth, we have found that the dissociative desorption of disilane is the rate limiting step. Additionally, after nucleation, we find that the nuclei undergo a rapid growth in size, driven by the supersaturation of silicon in the host gold-silicon liquid alloy drop. We will present a theoretical framework to describe this behavior which balances the roles of supersaturation, pressure and interface energies. In the case of carbon nanotube growth, we utilize a unique catalyst approach wherein the catalysts are firmly embedded in a silicon dioxide support film, so as to permit high resolution images of their surface structure at the onset of nanotube growth via the alcohol catalytic chemical vapor deposition process. We will report quantitative measurements of catalyst coarsening, and discuss how this process plays a controlling role in nanotube nucleation and subsequent growth. In each case, we will emphasize the power of the in-situ approach in providing quantitative data for discovering unique information regarding fundamental growth processes.
3:30 PM - C2.3
Fractal Aspects Related to the Oxidation of Cu(111).
Guangwen Zhou 1 , Xidong Chen 2 3 , Judith Yang 4 Show Abstract
1 Mechanical Engineering, State University of New York at Binghamton, Binghamton, New York, United States, 2 Department of Science and Mathematics, Cedarville University, Cedarville, Ohio, United States, 3 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 4 Mechanical Engineering and Matierials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
The growth dynamics of oxide thin films and the mechanisms governing the selection of their morphology during metal oxidation are subjects of substantial fundamental interest because of their practical importance in many fields including corrosion, heterogeneous catalysis, and oxide thin film processing. In situ surface science studies such as scanning tunneling microscopy (STM) have provided elegant insights into the atomic mechanisms of oxygen adsorption but are limited to a few atomic monolayers. In situ ultrahigh vacuum (UHV) transmission electron microscopy (TEM) is an ideal tool to investigate the growth dynamics of oxide films from nucleation, growth and coalescence of oxide islands by performing in situ measurements of the structures and kinetics in real time as the reaction progresses. Choosing (111)Cu as a model system, we perform an in situ TEM study on the spatiotemporal aspects of oxide films as a function of oxidation time at different temperatures and oxygen pressures. Unlike (100) and (110)Cu, (111)Cu does not show faceted oxide island growth, instead discontinuous film growth, which resembles fractal growth. The geometrical features of the oxide films are analyzed in terms of both the scaling theory of percolation and fractal geometry. It is shown that the perimeter of the non-faceted oxide islands is linearly proportional to area. The time evolution of the topologic parameters of the oxide films such as mean size of clusters, correlation length and fractal dimension are obtained from the in situ TEM observation. These observations are explained in terms of fractal diffusion of oxygen on a disordered Cu(111) surface induced by oxygen chemisorption. This in situ TEM study allows us to demonstrate that the geometric and scaling interpretations can be extended to metal oxidation.
3:45 PM - C2.4
Transient Cellular Structure is Revealed using Nanosecond in situ TEM.
Judy Kim 1 2 , Thomas LaGrange 1 , Bryan Reed 1 , Nigel Browning 1 2 , Geoffrey Campbell 1 Show Abstract
1 Chemistry, Materials, & Life Sciences, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Chemical Engineering & Materials Science, Univ. of California, Davis, California, United States
4:30 PM - C2.5
In situ TEM Study of Site-specific Deposition of Au and Ag on Reconstructed m-plane Sapphire.
Joysurya Basu 1 , Divakar Ramachandran 3 , N. Ravishankar 4 , C. Carter 1 Show Abstract
1 Chemical, Materials Science & Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 3 Metallurgy & Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam India, 4 Materials Research Centre, Indian Institute of Science, Bangalore India
The patterned assembly of nanoparticles is not only important from an application point-of-view but also presents interesting possibilities for performing fundamental studies on, e.g., the role of the surface on the growth process. Several different approaches can be used to produce ordered structures. Most of the techniques rely on fabricating a pattern or transferring a pattern onto a particular substrate and then assembling nanoparticles onto the substrate. Transport of metal atoms through the vapor phase and subsequent deposition on a substrate provides a facile synthesis route for nanopatterning. In most practical experimental scenarios nucleation is a heterogeneous process. Nucleation at specific sites on a substrate is a particularly important bottom-up approach to nanostructure synthesis. In the present study, we have observed site-specific nucleation of metal nanostructures via vapor-phase transport onto the reconstructed sapphire surface. The growth has been carried out in the TEM using a heating holder with a specially designed TEM sample. Using this approach, the physical vapor deposition process of Au and Ag near the melting point has been observed in situ. Observations indicate that the electron beam influences local deposition of the metal.
4:45 PM - C2.6
In-situ Studies of Martensitic Phase Transformations using the Dynamic Transmission Electron Microscope.
Thomas LaGrange 1 , Geoffery Campbell 1 , Patrice Turchi 1 , Bryan Reed 1 , Nigel Browning 1 2 , Judy Kim 1 , Mitra Taheri 1 , J. Brad Pesavento 1 , Wayne King 1 Show Abstract
1 Chemistry Materaials and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States
5:00 PM - C2.7
The Dynamic TEM for Controlled Ultrafast Studies of the Structural Evolution of Nanoscale Electronic and Catalytic Materials.
Mitra Taheri 1 , Bryan Reed 1 , Thomas LaGrange 1 , Nigel Browning 1 2 Show Abstract
1 Chemistry, Materials & Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Department of Chemical Engineering and Materials Science, University of California-Davis, Davis, California, United States
5:15 PM - C2.8
In-situ Observation of Giant Diffusivity Along Dislocation Cores.
Marc Legros 1 Show Abstract
1 , CEMES-CNRS, Toulouse France
Diffusion of atoms in a crystalline solid can be strongly enhanced by diffusion short circuits such as grain boundaries and dislocations. When dislocations are concerned, the mechanism is called "pipe diffusion" and has a potential effect on many other processes such as climb, aging, Ostwald ripening... This effect is however more often conjectured than directly evidenced. Here, we present real-time observations of in-situ TEM experiments in which Si precipitates present in an Al thin film dissolve through a single dislocation. The driving force for this flow of matter from small precipitates to larger ones is their Gibbs free energy. We will show that it is then possible to calculate rather directly the diffusivity of the dislocation. The pipe diffusivity is, as expected, orders of magnitude larger than its bulk counterpart. Finally experiments carried out at different temperatures also allowed the calculation of the activation energy of pipe diffusion.
5:30 PM - C2.9
Measuring the Mechanical Response of Individual Nano Structures through in situ, Quantitative TEM Deformation Tests.
Zhiwei Shan 1 2 , Andy Minor 2 , S.A. Syed Asif 1 , Oden Warren 1 Show Abstract
1 R&D, Hysitron Inc., Minneapolis, Minnesota, United States, 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States
By incorporating a miniature capacitive force and displacement transducer into a TEM holder, we have recently developed a novel in situ TEM device (termed PicoIndenter) which provides the ability to accurately measure the force vs. displacement relationship during the deformation of individual nanostructures while simultaneously monitoring their microstructure evolution. This presentation will report on the current progress in applying our unique in situ TEM device (displacement resolution of ~1 nm and load resolution of ~0.3 micro newton) for mechanical measurement of individual nanoparticles. As an example we will show that nanocrystalline CdS synthesized into a spherical shell geometry not only achieves ultra-high strength (approaching its ideal value), but also exhibits considerable deformation to failure (up to 20%) while simultaneously reducing the average density of the material by up to 50%. This raises the expectation of achieving both ultrahigh strength and deformability in nanocrystalline materials by taking into account structural hierarchy. Considering the small volume involved, our technique of fully quantitative in-situ TEM deformation shows great promise for narrowing the gap between experimental nanomechanics and computer simulations of material deformation, a truly exciting occurrence indeed.
5:45 PM - C2.10
In situ TEM Observation of Brownian Motion of Au Nanocrystals in Liquid Thin Films.
H. Zheng 1 2 3 , S. Claridge 3 , A. Minor 1 2 , P. Alivisatos 1 2 3 , U. Dahmen 1 2 Show Abstract
1 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Materials Sciences Divsion, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Department of Chemistry, University of California, Berkeley, California, United States
We designed and fabricated a self-contained liquid cell, which allows us to study particles in liquid solution using a transmission electron microscope. The liquid solution is confined between silicon nitride windows and forms a thin liquid layer that can be as thin as a few nanometers. This liquid cell design has been used to observe the thermally induced motion of gold nanocrystals in aqueous solution inside a 300kV TEM. Surprisingly, we were able to track the motion of individual Au particles with sizes of 5 - 20nm, demonstrating a considerable reduction in diffusivity (over six orders of magnitude) of Au particles in the liquid thin films compared to that in the bulk liquid. The mean square displacements of single-particle trajectories were found to display power-law characteristics. In addition to single-particle motion, we have also examined the interaction among multiple particles. The effects of various parameters including electron beam heating, liquid thickness, proximity of the solid windows, etc. on the motion of the particles have been considered. The dynamics of nanocrystals confined in a liquid thin film will be discussed in light of existing models.
C3: Poster Session: Analytical TEM
Tuesday AM, November 27, 2007
Exhibition Hall D (Hynes)
9:00 PM - C3.1
Verifying the Presence of Low Levels of Neptunium in a Uranium Matrix with Electron Energy-Loss Spectroscopy.
Edgar Buck 1 , Richard Wittman 1 Show Abstract
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
9:00 PM - C3.2
Radiolytic Purification of CaO by Electron Beams.
Andre Mkhoyan 1 , John Silcox 1 , Michael McGuire 2 , Francis Disalvo 3 Show Abstract
1 Applied Physics, Cornell University, Ithaca, New York, United States, 2 Physics Department, Cornell University, Ithaca, New York, United States, 3 Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
9:00 PM - C3.3
Segregation versus Precipitate Chemistry: Activities at Work in Polycrystalline Ceramics.
Ceren Ozaydin 1 , Oguz Armagan 1 , Aysun Karaoglu 1 , Mehmet Gulgun 1 , Saso Sturm 2 , Vesna Srot 3 , Manfred Ruhle 3 , Peter van Aken 3 Show Abstract
1 FENS, Sabanci University, Istanbul Turkey, 2 Department for Nanostructured Materials, Josef Stefan Institute, Ljubljana Slovenia, 3 StEM, Max Planck Institute for Metals Research, Stuttgart Germany
The equilibrium phase diagram between Al2O3 and Y2O3 indicates three yttrium aluminate phases in the binary: Y4Al2O9 (YAM), YAlO3 (YAP), and Y3Al5O12 (YAG). When the yttrium concentration in polycrystalline alumina reaches solubility limit, the first yttrium aluminate phase expected to precipitate is the garnet phase, Y3Al5O12 (YAG). However, our x-ray diffraction and electron microscopy studies shown that the first phase to form at saturation in the system is the perovskite phase, YAlO3 (YAP). We followed this non-equilibrium precipitation behavior of yttrium in saturated polycrystalline alumina with and without additional Si-impurity as a function of temperature and heat treatment time at ambient pressures. Using X-ray and electron diffraction, high angular annular dark field imaging (HAADF), energy dispersive x-ray spectroscopy (EDS), and electron energy loss spectroscopy/electron energy loss near-edge structures (EELS/ELNES) techniques the precipitates were identified. Segregation level of Y at the grain boundaries (gb) at saturation was quantitatively measured. At lower temperatures (1300C≤ T ≤1500C) and short heat treatment times YAP precipitates form. Their sizes vary from 50 nm to 500 nm. At higher temperatures (1400≤ T) or longer annealing times YAG precipitates form with sizes on the order of 500 nm to 2 micrometers. This kinetically constrained, non-equilibrium precipitation behavior allowed us to verify one of the oldest postulates in thermodynamics. The activities (a) of species in different features of the microstructure determine the partitioning of the chemical species among the features of the microstructure, i.e. (aY)bulk = (aY)gb = (aY)precipititate = (aY)surfaceIf the activity of one feature could be changed the others should adjust the concentrations accordingly. TheY gb-segregation level was 5.5±0.9 Y-atoms/nm2 when only YAP was present in the microstructure. In samples where YAP and YAG co-existed Y-excess at gbs was 4.2±1.2 Y-atoms/nm2. Using temperature, heat treatment time and the molar ratio of the yttrium ions to aluminum ions a first attempt is made to establish a TTT diagram for the precipitation behavior of yttrium aluminates in Y-doped alumina. Additional trace amount of Si-impurity appeared to facilitate earlier formation of YAG.
9:00 PM - C3.4
Quantitative Analysis of Nano-Particulates in Fully Radioactive Hanford Tank Sludges
Edgar Buck 1 , Kathryn Draper 1 , Richard Wittman 1 , Ken Czerwinski 2 Show Abstract
1 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 , University of Nevada, Las Vegas, Las Vegas, Nevada, United States
9:00 PM - C3.5
The Estimation of Magnetic Energy Distribution in Polycrystalline Sputtered CoCrTa Magnetic Thin Films from EFTEM Data.
Jafar Al-Sharab 1 , James Wittig 2 , James Bentley 3 , Neal Evans 3 Show Abstract
1 Ceramic and Material Science, Rutgers University, Piscataway, New Jersey, United States, 2 Electrical and Engineering, Vanderbilt University, Nashville, Tennessee, United States, 3 Materials Science and Engineering, Oak Ridge National Lab, Oak Ridge, Tennessee, United States
9:00 PM - C3.6
Origin of High Specific Capacity in Li1.2Mn0.4Fe0.4O2 Positive Electrode Materials for Lithium-ion Batteries Studies by STEM-EELS, HRTEM and NBED.
Jun Kikkawa 1 , Tomoki Akita 1 , Mitsuharu Tabuchi 1 , Masahiro Shikano 1 , Kuniaki Tatsumi 1 , Masanori Kohyama 1 Show Abstract
1 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka, Japan
Li1.2Mn0.4Fe0.4O2 is an attractive positive electrode material for large-scale lithium-ion batteries such as electric vehicles since it has high specific capacity (>200 mAh/g) and high voltage (~3 V)  at 60 degree C. Especially, the initial charge capacity reaches about 300 mAh/g. Previous 57Fe Mössbauer and X-ray studies showed that part of trivalent Fe ions are oxidized to the tetravalent states at the initial stage of the first charge process, while inactive tetravalent Mn ions do not contribute redox reactions. Nevertheless, the origin of the high specific capacity in this material cannot be explained only by the Fe redox reactions . In this study, we performed comprehensive transmission electron microscopy (TEM) studies to elucidate the novel mechanism underlying the first charge process, i.e., extraction process of lithium ions. Li1.2Mn0.4Fe0.4O2 nanoparticles were prepared through coprecipitationm, mixed-alkaline hydrothermal and firing processes . Local composition and valence states of transition-metal ions are investigated by electron energy-loss spectroscopy combined with scanning TEM (STEM-EELS). Chemical mapping was carried out utilizing spectrum-imaging technique with an electron probe of 1 nm in diameter. Crystal-lattice and cation arrangements were studied by high-resolution TEM (HRTEM) and nanobeam electron diffraction (NBED). We found that Mn-rich and Fe-rich nanodomains coexist in each single Li1.2Mn0.4Fe0.4O2 particle with a common ccp oxygen sub-lattice . Imperfect stacking of lithium layers and transition-metal rich layers in HRTEM images demonstrated that Li1.2Mn0.4Fe0.4O2 is a mixture of layered rock-salt (Fe-substituted Li2MnO3) and cubic rock-salt (Mn-substituted LiFeO2) structures suggested by previous XRD analysis. We also found that Fe-rich nanodomains contain trivalent Mn ions which should contribute to the redox reaction in spite of previous inactive tetravalent Mn ions . Analogous analyses were also applied to delithiated Li1.2-xMn0.4Fe0.4O2 nanoparticles to examine changes in local crystal structures, compositions and valence states. We discuss the origin of the high specific charge capacity in the first cycle of the Li1.2-xMn0.4Fe0.4O2/Li cell system.References  M. Tabuchi et al. J. Power Sources (2007) in press; J. Electrochem. Soc. 154, A638 (2007). M. Shikano et al. Abstract of IMLB 2006, #55, (2006). J. Kikkawa et al. submitted to publication.
9:00 PM - C3.7
The Determination of Optical Properties of Semiconductors Using EELS.
Michael Stoeger-Pollach 1 , Anita Laister 2 , Peter Schattschneider 2 1 Show Abstract
1 Service Centre for TEM, Vienna Univ. of Technology, Vienna Austria, 2 Inst. of Solid State Physics, USTEM, Vienna Univ. of Technology, Vienna Austria
Transmission electron microscopes (TEMs) with monochromators provide an energy resolution of better than 0.2 eV full width at half maximum in the elastic peak. After a long period of relatively small activity in the field this has attracted interest for valence electron energy loss spectrometry (VEELS) again. However, due to the fact that the acceleration voltages of conventional TEMs are in the range of 100-300 kV retardation effects become important. The condition for Cerenkov radiation is fulfilled if v > c/n, with the speed of light c, v as the speed of the probe electron and n as the refractive index of the material. For 200 kV instruments this means that materials with a refractive index of higher than 1.438 cannot be examined without taking Cerenkov losses into account.For determination of optical properties Kramers-Kronig Analysis (KKA) is applied after an iterative removal of relativistic effects and surfce plasmons. Conventional software does not take relativistic effects into account. Our method therefore gives more precise information on the optical properties of materials. Moreover faint differences of the optical response function between similar layers can be probed with high accuracy.We present the result on two similar SiN:H layers with different hydrogen concentration. The difference in the optical refractive index is 2% and can be identified with an accuracy of less than 1%.
9:00 PM - C3.8
Extending the Resolution Limits for Quantitative Electron Spectroscopic Imaging of Radiation-Sensitive Soft Materials.
Sergey Yakovlev 1 , Matthew Libera 1 Show Abstract
1 CBME, Stevens Institute of Technology, Hoboken , New Jersey, United States
C4: Poster Session: SEM/LEEM I
Tuesday AM, November 27, 2007
Exhibition Hall D (Hynes)
9:00 PM - C4.1
Quantitative, Local Measurements of Surface Adsorbate Concentrations using Low-energy Electron Microscopy.
Kevin McCarty 1 , Juan de la Figuera 2 , Norman Bartelt 1 Show Abstract
1 , Sandia National Laboratories, Livermore, California, United States, 2 , Instituto de Química-Física “Rocasolano”, CSIC, Madrid Spain
We are developing a new method for measuring the concentration of mobile adsorbates on surfaces using an electron-reflectivity technique . When performed in a low-energy electron microscope (LEEM), the approach can determine local adsorbate concentrations on heterogeneous surfaces. Our method is motivated by the fact that the rates of many surface processes are determined by the concentrations of mobile adsorbed species. Quantitative measurements of adsorbate concentrations are challenging for several reasons. First, the concentrations frequently are low. For example, the metal adatoms that diffuse on metal surfaces have low densities in thermal equilibrium or even during crystal growth. Second, the adsorbates can be highly mobile, making direct concentration measurements by proximal probe microscopies like STM very difficult. Finally, the techniques known to be sensitive to thermal adatom concentrations, work function and helium scattering, are not spatially resolved.We demonstrate our electron-reflectivity-based method using two model systems, Ag on W(110) and C on Ru(0001). The intensity of the low-energy electrons reflected from the surface decreases linearly with the adatom concentration as adatoms are deposited from the vapor. Using this simple relationship, the adatom concentrations are easily determined from electron-reflectivity changes. The intensity change is usefully large - a Ag adatom density at least as small as 10e-3 ML can be measured in a micron-size region at video rates. We use the technique’s imaging basis to measure the adatom concentration in equilibrium with condensed-phase Ag islands. Our results are in quantitative agreement with a previous work-function measurement , albeit with considerably better accuracy.We also demonstrate the method’s ability to measure the temperature-dependent concentration of C adatoms in equilibrium with C impurity atoms in bulk Ru. We use the method to understand how C segregates from the bulk and condenses into single layers of graphitic C (“graphene”). The C adatom supersaturation present before graphene island nucleation is easily observed and is surprisingly large. We will discuss the relationship between the graphene growth rate, bulk diffusion, and the time and spatial dependence of the C adatom concentration.This research was supported by the Office of Basic Energy Sciences, Division of Materials Sciences, USDOE under Contract No. DE-AC04-94AL85000, the Spanish Ministry of Science and Technology, and Spanish Ministry of Education and Science. J. de la Figuera, N. C, Bartelt, and K. F, McCarty, Surf. Sci., 600 p.4062 (2006) J. Kolaczkiewicz and E. Bauer, Surf. Sci. 155 p.700 (1985)
9:00 PM - C4.2
Engineering a Quantitative Dopant Profiling Technique in the SEM.
Augustus Chee 1 , Conny Rodenburg 2 , Colin Humphreys 1 Show Abstract
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Department of Engineering Materials, University of Sheffield, Sheffield United Kingdom
Two-dimensional dopant mapping using secondary electrons (SEs) in a FEG-SEM is a potentially useful technique for studying dopant distributions in semiconducting materials at high spatial resolution. A secondary electron energy-filtering attachment to the through-the-lens detector on our SEM has enabled quantification of dopant profiles to be developed more readily from SE imaging, allowing a non-destructive and rapid in-situ characterisation technique for semiconductor devices. However, the reason that it has not yet found widespread application is the lack of an accurate and robust quantification procedure. Although it is known that the SE dopant contrast observed across a semiconductor p-n junction is a function of the built-in potential across the junction, surface band-bending and external local fields (patch fields) above the specimen, the lack of understanding of the relative contributions from all of these factors has hampered accurate quantification. To analyse this problem, we have performed experiments involving the passivation of Si samples using an ammonium fluoride (NH3F) surface treatment procedure and have compared the SE emission yields from Si p-n junctions having passivated and unpassivated surfaces. Striking differences are observed as a result. Measurements were obtained of the SE emission energy spectra across the sample using our modified through-the-lens SE detector system and they provide useful information on surface states and surface potentials. We have also supported our findings with detailed computer modelling using finite-element analysis of Poisson’s equation for the semiconductor to investigate the effects of surface charges and doping concentration on surface band-bending, surface junction potentials and external patch fields. Our experimental measurements were compared with these calculations. The results described in this work develop our understanding of the physical mechanisms responsible for SE dopant contrast and therefore will help to enable the accurate quantification of dopant mapping in semiconductors using SE detection in the SEM.
9:00 PM - C4.4
Digital Image Processing and MEB (BSE) Techniques in the Identification and Quantification of Minerals Phases Present in Cement and Concrete.
Nicanor Prendes 1 , Esperanza Menendez 2 Show Abstract
1 Petrology & Mineralogy, CEDEX -- Ministerio Fomento, Madrid, Madrid, Spain, 2 Materials & Construction, Eduardo Torroja Institute for Construccion Science, Madrid, Madrid, Spain
C5: Poster Session: In-situ
Tuesday AM, November 27, 2007
Exhibition Hall D (Hynes)
9:00 PM - C5.1
In situ TEM Study on the Formation Process of Iron Silicide Nanoparticles on Si Substrate.
Jonghan Won 1 , Andras Kovacs 1 , Manabu Ishimaru 1 , Yoshihiko Hirotsu 1 Show Abstract
1 , The Institute of Scientific and Industrial Research (ISIR), Osaka University, Ibaraki, Osaka, Japan
9:00 PM - C5.2
Overcoming Challenges in Materials Science: Performing in-situ Fatigue Testing in the Large Chamber Scanning Electron Microscope.
Martin Klein 1 Show Abstract
1 , VisiTec Microtechnik, Grevesmuehlen, M-VP, Germany
One of the most confronted challenges in materials science when using scanning electron microscopy is the limitation of the size of the sample tested, as well as the versatile nature of the application that can be used; normally, only small samples in the order of ten to the hundred millimetres in diameter can be investigated. Also until now, fatigue testing inside a scanning electron microscope (SEM) seemed impossible. Nevertheless, SEM testing is a very valuable method in the fields of materials and biological science as well as in quality control and failure analysis. The first step in overcoming the challenges, specifically the size limitation, was taken by VisiTec Microtechnik in Germany, when in 1994 the Large Chamber SEM was introduced and very well accepted within the scientific