Symposium Organizers
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
Session Chairs
G. Botton
Uli Dahmen
Rafal Dunin-Borkowski
J. Silcox
Etienne Snoeck
Jo Verbeeck
Monday PM, November 26, 2007
Back Bay D (Sheraton)
9:30 AM - C1:Analytical I
Opening Remarks by Organizers
Show Abstract9:45 AM - **C1.1
Probing the Chemistry and Bonding of Nanoscale Materials with High-Resolution Electron Energy Loss Spectroscopy.
Gianluigi Botton 1
1 Materials Science and Engineering, BIMR, McMaster University, Hamilton, Ontario, Canada
Show AbstractThe 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
1 Stuttgart Center for Electron Microscopy, Max Planck Institute for Metals Research, Stuttgart, Baden-Württemberg, Germany
Show AbstractWith 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 [1]. Limitations of spatial resolution and possible solutions for improvements will be discussed.[1] 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
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
Show AbstractDuring 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 [001] 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
1 FELMI, Graz University of Technology, Graz Austria
Show AbstractFor 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
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
Show AbstractCompositional 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
1 Materials and London Centre for Nanotechnology, Imperial College London, London United Kingdom
Show AbstractBarium 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
1 Physics, EMAT, University of Antwerp, Antwerp, Antwerpen, Belgium
Show AbstractIn 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 [3] and including prior knowledge from lifetime broadening of the ELNES fine structure will be discussed.[1] J. Verbeeck and S. Van Aert - Model based quantification of EELS spectra - In: Ultramicroscopy, 101-2-4 (2004), p.207-224 [2] 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 [3] 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
Session Chairs
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
1 , AIST, Tsukuba Japan
Show AbstractThe 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 [1]. 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 [2]). 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 [3] 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.[1] L. Reimer, in Physical Aspects of Electron Microscopy and Microbeam Analysis, ed. By Siegel and Beaman, (Wiley New York, 1975)[2] A. Hashimoto, K. Suenaga, A. Gloter, K. Urita and S. Iijima, Nature, 430 (2004) 870[3] Z. Liu, M. Koshino, K. Suenaga, A. Mrzel, H. Kataura and S. Iijima, Phys. Rev. Lett., 96 (2006) 088304[4] M. Koshino, T. Tanaka, N. Solin, K. Suenaga, H. Isobe and E. Nakamura, Science 316 (2007) 853[5] 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
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
Show AbstractSemiconducting 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
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
Show AbstractThe 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
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
Show Abstract4:30 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
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
Show AbstractThe 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
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
Show Abstract5:00 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
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
Show Abstract5:15 PM - C2.8
In-situ Observation of Giant Diffusivity Along Dislocation Cores.
Marc Legros 1
1 , CEMES-CNRS, Toulouse France
Show AbstractDiffusion 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
1 R&D, Hysitron Inc., Minneapolis, Minnesota, United States, 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractBy 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
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
Show AbstractWe 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
Session Chairs
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
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show Abstract9:00 PM - C3.2
Radiolytic Purification of CaO by Electron Beams.
Andre Mkhoyan 1 , John Silcox 1 , Michael McGuire 2 , Francis Disalvo 3
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
Show Abstract9:00 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
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
Show AbstractThe 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
1 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 , University of Nevada, Las Vegas, Las Vegas, Nevada, United States
Show Abstract9:00 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
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
Show Abstract9:00 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
1 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka, Japan
Show AbstractLi1.2Mn0.4Fe0.4O2 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) [1] 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 [2]. 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 [1]. 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 [3]. 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 [3]. 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 [1] M. Tabuchi et al. J. Power Sources (2007) in press; J. Electrochem. Soc. 154, A638 (2007).[2] M. Shikano et al. Abstract of IMLB 2006, #55, (2006).[3] 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
1 Service Centre for TEM, Vienna Univ. of Technology, Vienna Austria, 2 Inst. of Solid State Physics, USTEM, Vienna Univ. of Technology, Vienna Austria
Show AbstractTransmission 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
1 CBME, Stevens Institute of Technology, Hoboken , New Jersey, United States
Show AbstractC4: Poster Session: SEM/LEEM I
Session Chairs
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
1 , Sandia National Laboratories, Livermore, California, United States, 2 , Instituto de Química-Física “Rocasolano”, CSIC, Madrid Spain
Show AbstractWe are developing a new method for measuring the concentration of mobile adsorbates on surfaces using an electron-reflectivity technique [1]. 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 [2], 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.[1] J. de la Figuera, N. C, Bartelt, and K. F, McCarty, Surf. Sci., 600 p.4062 (2006)[2] 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
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Department of Engineering Materials, University of Sheffield, Sheffield United Kingdom
Show AbstractTwo-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
1 Petrology & Mineralogy, CEDEX -- Ministerio Fomento, Madrid, Madrid, Spain, 2 Materials & Construction, Eduardo Torroja Institute for Construccion Science, Madrid, Madrid, Spain
Show AbstractC5: Poster Session: In-situ
Session Chairs
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
1 , The Institute of Scientific and Industrial Research (ISIR), Osaka University, Ibaraki, Osaka, Japan
Show Abstract9:00 PM - C5.2
Overcoming Challenges in Materials Science: Performing in-situ Fatigue Testing in the Large Chamber Scanning Electron Microscope.
Martin Klein 1
1 , VisiTec Microtechnik, Grevesmuehlen, M-VP, Germany
Show AbstractOne 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 community. The Large chamber, which can accommodate samples up to 1000mm in diameter, is also equipped with an innovative positioning system that allows views from different angles by moving the electron gun and detectors, as well as the sample (fig.1) somehow identical to the behaviour of human beings. Besides the investigation of large samples, the LC-SEM also has a great potential for in situ observations of deformation behaviour of materials, as well as for relatively small production processes in the field of micro-system techniques. The Large Chamber SEM also makes it possible to perform “interrupted in-situ” experiments for larger engineering parts. As an example, testing the tribological behavior of highly loaded parts from high-pressure pumps can be investigated by interrupted monitoring. The parts can be in service for a special period of time followed by an investigation of the loaded surfaces in the LC-SEM, bringing them to service immediately after the investigation is completed. This way of monitoring a system will open a vary broad field for engineering applications that will allow to get a closer and more detailed understanding of the running-in and damaging processes. To fulfil the need of evaluating in-situ investigations of deformation behaviour, a new design of the LC-SEM was created, where a servo-hydraulic fatigue-testing frame from MTS was integrated to the chamber creating new possibilities for materials testing, as well as overcoming the challenge of performing fatigue testing in a SEM. The idea of combining these two equipments seemed impossible. Just the integration of hydraulic components inside a vacuum environment was the beginning of many design related challenges to overcome. The combination of the LC-SEM and the Servo-hydraulic Fatigue Testing Machine allows to perform mechanical tests on standard specimen geometries. Moreover, under cyclic loading, all the classic control channels – stroke, stress and strain – of a standard fatigue-testing machine are available.
9:00 PM - C5.3
Oxidation Kinetics of Cu-Ni Alloy Observed by in situ UHV-TEM.
Li Sun 1 , Guangwen Zhou 1 , John Pearson 2 , Judith Yang 1
1 Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show Abstract9:00 PM - C5.4
In-Situ Tensile-Creep Testing of Structural Alloys.
Carl Boehlert 1 , Sara Longanbach 1 , Matthew Nowell 2 , Stuart Wright 2
1 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States, 2 , EDAX-TSL, Draper, Utah, United States
Show AbstractThe recent progress in the development of in-situ scanning electron microscopy techniques for understanding the deformation behavior of materials, combined with the high beam current and stability of a hot Schottkey field emission gun and the latest camera technology for obtaining high-quality electron backscattered diffraction patterns (EBSPs) now allows for a unique capability for imaging surface deformation. It is possible to make unprecedented sub-micron resolved measurements of the local two-dimensional crystal-structure distribution during high-temperature tensile-creep deformation. A technique has been developed to acquire secondary electron (SE) and backscattered electron (BSE) detector images and electron backscattered diffraction (EBSD) orientation maps during tensile-creep deformation at temperatures as high as 760C. The EBSD observations during deformation proved to be useful for quantifying the types of grain boundaries which have preferentially cracked. The EBSD orientation maps were acquired over an approximately 200mmx200mm area using a step size of 0.5mm in 20 minutes (140,000 points were acquired with a speed of 150 points second). The amount of displacement measured by the testing assembly during this 20 minute period was typically 7mm, and this small movement did not significantly disturb the orientation mapping accuracy. Details and limitations of this testing technique and the results obtained on advanced structural alloys (titanium-, nickel-, and cobalt-based) will be presented. For boron-modified Ti-6Al-4V(wt.%), TiB whiskers have been shown to crack at stresses well below the global yield strength of the alloy. For Ti-Al-Nb alloys, grain boundary sliding has been characterized and quantified from local grain boundary measurements. For a cobalt-based superalloy, Udimet 188, grain boundary cracking has been shown to preferentially occur on general high-angle grain boundaries rather than low-angle boundaries or special boundaries.
9:00 PM - C5.5
Nanoscale Characterization of Local Stresses and Dislocation Configurations in Undulated Si1-xGex/Si(100) Thin Films.
Chi-Chin Wu 1 , Eric Stach 2 , Robert Hull 1
1 Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractSurface roughening and misfit dislocation formations are important mechanisms for stress relaxation during heteroepitaxial thin film growth. This work describes how we have used in-situ transmission electron microscopy and numerical simulations to quantitatively analyze nansocale stress variations and equilibrium dislocation configurations in undulated Si1-xGex/Si films, and to correlate these properties to the local surface morphology. The local dislocation propagation velocities in 30 nm strained Si0.7Ge0.3/Si(100) films were measured by in-situ transmission electron microscopy annealing experiments and converted to average lateral stresses using previously established stress-velocity relations. For a film having undulations of 50 ~ 60 nm wavelength and < 5 nm amplitude, at ~ 480 oC the dislocation velocity varied from 0 ~ 30 nm/s at peaks to 160 ~ 240 nm/s at troughs with an average of 82 nm/s, corresponding to periodic variations of the (unresolved) lattice mismatch stress from 3.2 ~ 4.4 GPa under the film troughs to 0.7 ~ 1.2 GPa at the film peaks with a 2.0 GPa average film stress. These inferred stress variations are too large to be attributable to the film morphology; instead we show how the observed variations in dislocation velocity could be explained by variations in kink nucleation rates as a function of the varying stress at different regions of the surface waveform.Because dislocations glide on {111} planes in the Si1-xGex/Si system, the configuration of threading segments was examined under weak beam conditions in <111> zone axes. The dislocations were observed to have relatively complex curved shapes between the interface and the free surface. Numerical calculations were also performed to quantitatively estimate dislocation configurations within a strained film using Fortran 77 computer programs based on dislocation energy equations in isotropic media, and compared to the observed experimental configurations. The equilibrium dislocation configuration on its glide plane depends on the length of threading segment, the image force, the orientation of the dislocation with respect to its Burgers vector, and – of greatest significance for this work - the details of the local stress field.This work has explored new methods for probing nanoscale stress fields and analyzed the configuration of threading dislocations in heteroepitaxial thin films, as well as providing new insight into stress relaxation mechanisms during the growth of these systems. This work is funded by the NSF-MRSEC at UVa: “The Center for Nanoscopic Materials Design” under DMR# 0075116.
9:00 PM - C5.6
Creating Suspended Atomic Chains Composed of Different Atoms from HRTEM Experiments.
Jefferson Bettini 2 , Fernando Sato 1 , Pablo Coura 3 , Socrates Dantas 3 , Douglas Galvao 1 , Daniel Ugarte 1 2
2 , LNLS, Campinas Brazil, 1 Applied Physics, State University of Campinas, Campinas Brazil, 3 Physics Department, Federal University of Juiz de Fora, Juiz de Fora Brazil
Show AbstractMetallic nanowires (NWs) and suspended atomic chains (LACs) generated by mechanical stretching have been object of intense theoretical and experimental investigations in the last years. However most of these works have been carried out for pure metals. It is essential to extend these studies to metal alloy NWs in order to gather information on the mechanical and electrical properties of alloy nanosystems. At the moment rather limited results have been obtained for these structures. In this work we present results for NWs obtained from Au-Ag alloys. NWs were produced in situ in the HRTEM (JEM-3010 URP 300 kV, 0.17 nm point resolution) using the methodology proposed by Kondo and Takayanagi. The Au-Ag alloy thin films (10-30 nm in thickness) were prepared by thermal co-evaporation of both metals in a standard vacuum evaporator (10-7 mbar). A quartz crystal monitor was used to set the evaporation rate of each metal source and, subsequently, to measure the equivalent thickness of the alloy films. In order to obtain more insights about the atomistic aspects associated with the structural evolution of metal alloy NWs, we have also carried out tight-binding molecular dynamics simulations using second-moment approximation (TB-SMA). This methodology has recently proved to be very efficient to study NWs. In general terms our studies of metal alloy NWs revealed that, unlike pure metals, structural defects (mainly twins and stacking faults) are sometimes present at the apexes and very close to the narrowest wire constriction, or even in the NW themselves. Similarly to pure NWs we have observed the existence of LACs. These are the first experimental evidences that LAC formation is possible from metallic alloys [1]. HRTEM data analysis suggests that these atomic chains are composed of atoms of different types (Au and Ag). Molecular dynamics simulations also present these configurations. Another interesting aspect inferred from experiments and simulations is that the atomic-size Au-Ag alloy NWs exhibit a spontaneous gold enrichment of the nanojunction region during the wire thinning process. This leads to a dominant gold-like behavior, even for alloys with minor gold content. This can allow the spontaneous generation of organized Ag core-Au shell structured nanowires or even, in some cases, pure Ag surface enclosing a gold mono-atomic wire. These phenomena open new opportunities to control the stability or length of the atomic chains by a suitable alloy composition. [1] F. Bettini, F. Sato, P. Z. Coura, S. O. Dantas, D. S. Galvao, and D. Ugarte, Nature Nanotechnology 1, 182 (2006)
Symposium Organizers
Etienne Snoeck CEMES-CNRS
Rafal Dunin-Borkowski Technical University of Denmark
Johan Verbeeck University of Antwerp
Ulrich Dahmen Lawrence Berkeley National Laboratory
C6: Grand Challenges for Electron Microscopy I
Session Chairs
Tuesday AM, November 27, 2007
Back Bay D (Sheraton)
9:30 AM - *C6.1
Scanning Transmission Electron Microscopy: A Perspective.
John Silcox 1
1 Applied Physics, Cornell University, Ithaca, New York, United States
Show AbstractC7: Diffractive Imaging and Diffraction
Session Chairs
Tuesday PM, November 27, 2007
Back Bay D (Sheraton)
10:15 AM - **C7.1
Exit Wave Reconstruction from Diffraction Intensities and the Achievement of Sub-Angstrom Resolution Imaging of CdS Quantum Dots without an Aberration Corrector.
Weijie Huang 1 , Jian-Min Zuo 1 2 , Bin Jiang 1 , Kwan-Wook Kwon 1 , Moonsub Shim 1
1 Materials Science, Univ. Illinois, Urbana, Urbana, Illinois, United States, 2 Materials Research Laboratory, University of Illinois , Urbana, Illinois, United States
Show AbstractThe amplitude of electron exit wave function is directly recorded in a diffraction pattern. Compared to imaging, the phase of the wavefunction is lost. The exit wavefunction can not be constructed without the phase. But, the amplitudes recorded in a diffraction pattern are unperturbed unlike the nonlinear imaging process and unlimited by the lens aberrations, defocus and other microscope resolution limiting factors. Sub-Ångstrom signals are thus available beyond the information limit of direct imaging. If the phase problem can be solved, reconstruction of exit wave function from diffraction intensities (diffractive imaging) then avoids numerous difficulties with direct imaging and can provide diffraction-limited atomic resolution. Here we report the realization of such an approach and demonstrate the potential of this new imaging technique by using nanometer-sized CdS quantum dots as examples. The solution of the phase problem is achieved using an iterative phase retrieval algorithm. The diffraction patterns were recorded from individual quantum dots using a nanometer-sized, coherent and parallel, electron beam. Complex wavefunctions of several quantum dots at different orientations are reconstructed from the diffraction intensities. Atoms at sub-angstrom distances are resolved. Significant contrast improvement is obtained compared to high resolution electron micrographs. The issues critical to reconstruction will be discussed in the talk; these include the quality of electron diffraction patterns, the robustness of the reconstruction algorithms in the presence of experimental noises, the object support and its effect on reconstruction, last but not least important, dynamic scattering of electrons.
10:45 AM - C7.2
Intensity Analysis of Parallel Beam Selected Area Nanodiffraction from Metallic Glass Foils.
Stephan Hruszkewycz 1 , Takeshi Fujita 2 , Mingwei Chen 2 , Todd Hufnagel 1
1 Department of Materials Science and Engineering, Johns Hopkins Univeristy, Baltimore, Maryland, United States, 2 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan
Show AbstractIt has previously been observed that electron diffraction patterns from small volumes of nominally amorphous materials can display inhomogeneously distributed intensites ("speckle"). This is in contrast to the smooth diffraction halos seen in selected area diffraction patterns from the same materials. In fluctuation electron microscopy (FEM), the variance V(k,Q) in the scattered intensity from a disordered material is statistically quantified as a function either of the magnitude of the scattering vector, k("variable coherence microscopy"), or of the resolution, Q ("variable resolution microscopy"). Structure in the normalized intensity variance as a function of k can be a signature of nanometer-scale structural order in the material. Traditionally, fluctuation electron microscopy has been performed either with a conventional TEM using tilted- or hollow-cone dark field imaging, or in an STEM by collecting nanodiffraction patterns.We approach FEM in a somewhat different way, by collecting diffraction patterns using parallel-beam illumination and a very small (15x15 nm) selected area aperture in a conventional TEM. Diffraction patterns from samples of Pd-Ni-P metallic glasses show considerable intensity variations. We analyze these variations in a method similar to traditional FEM analysis techniques, by considering azimuthal intensity variations in the nanodiffraction patterns at different scattering vectors. These azimuthally collected intensities are used to calculate V(k) curves which are then averaged with similar curves from nanodiffraction patterns taken from other areas of the foil. The V(k) measured from the selected area nanodiffraction patterns correspond well to results obtained from traditional tilted dark field FEM on the same samples. Based on these observations, we conclude that structural order in this amorphous material extends beyond 1.1 nanometers.
11:30 AM - C7.3
Determination of Strain within Si1-yCy Layers Grown by CVD on a Si Substrate.
Nikolay Cherkashin 1 , Adrien Gouye 2 , Florent Houdellier 1 , Martin Hytch 1 , Etienne Snoeck 1 , Vincent Paillard 1 4 , O. Kermarrec 2 , D. Rouchon 3 , M. Burdin 3 , P. Holliger 3 , Alain Claverie 1
1 , CEMES/CNRS, Toulouse France, 2 , ST Microelectronics, Crolles France, 4 , Paul Sabatier University, Toulouse France, 3 , CEA-DRT, LETI/D2NT&DPTS, Grenoble France
Show AbstractTuesday, Nov 27Transferred Poster C11.9 to C7.3 @ 10:30 AMDetermination of Strain within Si1-yCy Layers Grown by CVD on a Si Substrate. Nikolay Cherkashin
11:45 AM - C7.4
Quantitative Convergent Beam Electron Diffraction Measurements of Structure Factors in GaAs.
Jerome Pacaud 1 , Jian-Min Zuo 2
1 Lab de Métallurgie Physique, University of Poitiers, Chasseneuil France, 2 Materials Science and Engineering and Materials Research Laboratory, University of Illinois at Urbana and Champaign, Urbana, Illinois, United States
Show AbstractTuesday, Nov 27Transferred Poster C11.3 to C7.4 @ 10:45 AMQuantitative Convergent Beam Electron Diffraction Measurements of Structure Factors in GaAs. Jerome Pacaud
12:00 PM - C7.5
Surface Atomic Contraction in Nanocrystals Revealed by Coherent Diffraction.
Weijie Huang 1 , Ruoshi Sun 1 , Laurent Menard 2 , Ralph Nuzzo 2 , Jian-Min Zuo 1
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractTuesday, Nov 27Paper Number Changed C7.4 to C7.5Surface Atomic Contraction in Nanocrystals Revealed by Coherent Diffraction. Weijie Huang
12:15 PM - C7.6
Diffraction Microscopy using 20-kV Electron Beam for Multi-Wall Carbon Nanotubes.
Osamu Kamimura 1 , Kota Kawahara 2 , Takahisa Doi 1 , Takashi Dobashi 1 , Takashi Abe 2 , Kazutoshi Gohara 2
1 Central Research Laboratory, Hitachi, Ltd., Kokubunji-shi Japan, 2 Applied Physics, Hokkaido University, Sapporo Japan
Show AbstractTuesday, Nov 27Paper Number Changed C7.5 to C7.6Diffraction Microscopy using 20-kV Electron Beam for Multi-Wall Carbon Nanotubes. Osamu Kamimura
12:30 PM - C7.7
Convergent Beam Electron Diffraction for Strain Determination at the Nanoscale.
Florent Houdellier 1 , Christian Roucau 1 , Marie-Jose Casanove 1
1 , CEMES-CNRS, Toulouse, 31, France
Show AbstractTuesday, Nov 27Paper Number Changed C7.6 to C7.7Convergent Beam Electron Diffraction for Strain Determination at the Nanoscale. Florent Houdellier
12:45 PM - C7.8
Results of a pnCCD Detector for Direct Single-Electron Imaging in the TEM.
Alexander Ziegler 1 , Robert Hartmann 2 , Robert Andritschke 3 , Florian Schopper 3 , Lothar Strueder 3 , Heike Soltau 2 , Juergen Plitzko 1
1 , Max-Planck Institute for Biochemistry, Martinsried Germany, 2 , PNSensor GmbH, Munich Germany, 3 , Max-Planck Institute Halbleiterlabor, Munich Germany
Show AbstractTuesday, Nov 27Paper Number Changed C7.7 to C7.8Results of a pnCCD Detector for Direct Single-Electron Imaging in the TEM. Alexander Ziegler
C8: Electron Tomography and STEM
Session Chairs
Rafal Dunin-Borkowski
P. Midgley
Tuesday PM, November 27, 2007
Back Bay D (Sheraton)
2:30 PM - **C8.1
Towards Quantitative Electron Tomography and 3D Nano-Metrology.
Paul Midgley 1 , Edmund Ward 1 , Alison Harrison 1 , Rafal Dunin-Borkowski 1 , Ana Hungria 1
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractElectron tomography has become an established tool for 3 dimensional visualization and characterisation not only in the life sciences but also in the physical sciences and especially in the study of complex nanoscale materials and structures. There is a need not only to study the morphology of a structure but also its physical and chemical properties in three dimensions. As such, electron tomography in materials science has developed very quickly over the past few years using a wide range of imaging modes to capture this 3D information. These modes include STEM HAADF imaging for 3D visualization of morphology, particle distribution, porosity and so on, through to weak-beam dark-field imaging to study 3D dislocation networks, plasmon imaging to discern different carbonaceous species and electron holography to understand the 3D electrostatic potential distribution in semiconductor devices. However, there is now an increasing desire to make electron tomography more quantitative, to extract meaningful and reliable data from tomograms and to be able to do so with statistical confidence. In this paper, we will show how we have begun to address these issues and to try to obtain accurate measurements from electron tomograms as we move towards true 3D nano-metrology. A number of examples will illustrate how reliable and reproducible quantitative information may be extracted from a variety of different materials specimens.
3:00 PM - **C8.2
3-Dimensional Imaging and Spectroscopy of Nanostructures.
David Muller 1 , Judy Cha 1 , Peter Ercius 1 , Aycan Yurtsever 1 , Matthew Weyland 1 2
1 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 2 Centre for Electron Microscopy, Monash University, Melbourne, Victoria, Australia
Show AbstractAtomic-resolution electron microscopy and spectroscopy is now capable of unraveling bonding details at buried interfaces and clusters, providing both physical and electronic structure information. In some cases the sensitivity and resolution extends to imaging single dopant atoms or vacancies, allowing us to study identify the clusters responsible for electrical deactivation in integrated circuits. In fact, the smallest feature in a modern transistor, the gate dielectric, is already little more than an interfacial layer just over 1 nm thick, and the fundamental physical limits to device scaling are set by the measured electronic structure. However, as integrated circuits have shrunk, conventional electron microscopies have proven inadequate for imaging complicated interconnect structures due to the overlap of features in projection and three-dimensional imaging methods become necessary. A similar challenge exists in imaging densely packed structures or networks of nanoparticles. Here we discuss how both elastic and spectroscopic imaging modes are useful in enhancing contrast or ensuring a monotonic signal for quantitative reconstructions. In particular we explore the limits of plasmon tomography for imaging silicon nanoparticles in SiO2 as well as probing the photonic density of states in gate oxides and waveguide structures. This work was supported by the NSF and the SRC.
3:30 PM - **C8.3
Quantitative Electron Microscopy for Life Science Applications.
Juergen Plitzko 1
1 Dept. of Molecular Structural Biology, Max-Planck-Institute for Biochemistry, Martinsried Germany
Show Abstract4:30 PM - C8.4
3D Morphology of Nanoparticles by Geometric and Quantitative Tomography Modes.
Xiaojing Xu 1 , Zineb Saghi 1 , Ralph Gay 1 , Beverley Inkson 1 , Guenter Moebus 1
1 Engineering Materials, University of Sheffield, Sheffield United Kingdom
Show AbstractElectron tomography is now established as a method for nanoscale three-dimensional (3D) structure retrieval for inorganic nanomaterials using coherent or incoherent transmission electron microscopy (TEM) or scanning transmission electron microscopy (STEM) based methods, including energy filtered TEM (EFTEM, elemental mapping), high-angle annular dark field (ADF) STEM, and bright field TEM (BF). In this paper, we present 3D morphology reconstruction of crystalline CeO2 nanoparticles using BF, EFTEM, and ADF STEM methods. Tomographic tilt series suitable for close comparisons between the three methods have been acquired and are evaluated with respect to various image quality parameters. The origin of artefacts for the methods is traced using profiles from the image acquisition and cross-sections of the reconstructed volume, and systematic trends are shown. Experimental particles are shape-modeled in the computer and reconstructed under ideal and non-ideal conditions, especially under various levels of detector saturation.
4:45 PM - C8.5
Effects of Tilt on High-Resolution ADF-STEM Imaging.
Andre Mkhoyan 1 , Sara Maccagnano-Zacher 1 , Earl Kirkland 1 , John Silcox 1
1 Applied Physics, Cornell University, Ithaca, New York, United States
Show AbstractA study of the effects of small-angle specimen tilt on high-resolution annular dark field images was carried out for scanning transmission electron microscopes with uncorrected and aberration-corrected probes using multislice simulations. The results indicate that even in the cases of specimen tilts on the order of 1 degree a factor of two reduction in the contrast of the high-resolution image should be expected. This effect holds for different orientations of the crystal. Calculations also indicate that as the tilted and untilted specimen gets thicker the contrast reduction increases. Images simulated with a low-angle annular dark field detector show that tilt effects are more pronounced in this case and suggest that these low-angle detectors can be used to eliminate the residual tilt during STEM operation.
5:00 PM - C8.6
STEM Tomography of Dy-doped YBa2Cu3O7 Coated Conductors.
Volkan Ortalan 1 , Miriam Herrera 1 , David Morgan 1 , Martin Rupich 2 , Nigel Browning 1 3
1 Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States, 2 , American Superconductor Corporation, Westborough, Massachusetts, United States, 3 Chemistry, Materials and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
Show Abstract5:15 PM - C8.7
Cation Ordering induced Surface Modifications in Nanocrystalline Ce/Zr Mixed Oxides.
Jose Perez-Omil 1 3 , Ana Hungria 2 , Juan Hernandez 1 , Susana Trasobares 1 , Serafin Bernal 1 , Paul Midgley 2 , Ali Alavi 3 , Jose Calvino 1
1 Materials Science and Inorganic Chemistry, University of Cadiz, Puerto Real, Cadiz, Spain, 3 Department of Chemistry, University of Cambridge, Cambridge, Cambrideshire, United Kingdom, 2 Materials Science and Metallurgy, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom
Show AbstractCerium-zirconium mixed oxides have recently been used as common promoting components of the three way catalysts (TWC) employed for the elimination of toxic exhaust gases in automobiles[1]. The achievement of a high oxygen storage capacity (OSC), related to the particular ability of the CeO2-ZrO2 oxides to undergo rapid reduction/oxidation cycles, has been shown to be of major relevance for the enhancement of the performance in their application as catalysts in TWC and other fields. Therefore, a precise understanding of the redox behaviour is essential to establish optimum synthesis procedures for these materials.In this work, high-resolution electron microscopy, high-angle annular dark field images, electron tomography and density functional theory calculations show the occurrence of significant structural and surface modifications in a nanoparticle Ce-Zr oxide sample upon high-temperature reduction with hydrogen followed by mild oxidation (SR-MO treatment).[2,3] Structural changes are related with the occurrence of a disorder-order transition in the cationic sublattice of the ceria-zirconia mixed oxides resulting in an ordered arrangement of Ce4+ and Zr4+ cations. Fourier transforms obtained from HREM images show the appearance, after the SR-MO treatment, of superstructure spots characteristic of a pyrochlore-related structure.Surface modifications involve a transition from roundedlike crystallites to well-faceted oxide particles with a significant increase of the presence of {111} faces in the SR-MO treated oxide observed in the HREM images. HAADF-STEM tomography reveals that these faceted crystallites have a shape very close to that of an octahedron, in agreement with the observed increase of {111} facets. Furthermore, the close inspection of high-resolution HAADF-STEM images shows an alternating intensity sequence in intensity profiles recorded along lines normal to the {111} fringes, suggesting an alternation of Ce-rich and Zr-rich planes along that direction, being in all the analyzed HAADF images the uppermost surface plane a Zr-rich {111} plane. This particular surface termination of the mixed oxide nanocrystals seems to be at the basis of an enhanced H2 dissociation capacity and, therefore in the increase of OSC observed after the application of SR-MO treatments.Let us also emphasize how TEM-STEM techniques have provided unique information about both the bulk and the surface of oxide nanocrystals that allows us rationalizing their macroscopic redox behaviour. 1 J. Kaspar, P. Fornasiero, N. Hickey., Catal. Today 2003, 77, 419 2 J. C. Hernandez, A.B. Hungria, J.A. Perez-Omil, S. Trasobares, S. Bernal, P.A. Midgley, A. Alavi, J.J Calvino , J of Phys. Chem.C, in press. 3 M.P. Yeste, J. C. Hernandez, S. Bernal, G. Blanco, J.J Calvino, J.A. Perez-Omil, J.M. PintadoChem Mater, 2006, 18, 2750.
5:30 PM - C8.8
Advances in Multi-Dimensional Imaging Techniques for the Modern Scanning TEM.
Ray Twesten 1 , Christopher Booth 1 , Robin Harmon 1 , Steffen Meyer 1 , Paul Thomas 1
1 Research and Development, Gatan Inc., Pleasanton, California, United States
Show AbstractThe last few years have seen significant advances in the acquisition of multi-dimensional data-sets in the modern scanning TEM. With the advent of next generation spectrometers and energy filters, high-speed cameras, advanced microscope control, and the widespread availability of high-brightness electron sources, it is now possible to routinely acquire multi-dimensional high-information density data sets in an automated manner.Continuing advances in computing power and the processing tools now available enable rapid identification and extraction of the elemental, chemical and physical information contained within these data-sets. Such improvements have made these rich data collection and analysis techniques available to nearly all characterization laboratories.To elucidate these advances, we will discuss recent progress in acquisition and analysis techniques for materials characterization at the nanometer scale and beyond. We will reference several case studies that serve to illustrate the strength and potential pit falls of these techniques with particular emphasis on the simultaneous acquisition and analysis of complementary techniques such as EELS and EDS spectrum imaging, spatially resolved diffraction, and electron tomography.
5:45 PM - C8.9
Advanced TEM Sample Preparation Using Low Energy Argon Beams.
David Basile 1 , Arda Genc 2 , Paul Fischione 1 , Hamish Fraser 2 , Krishnamurthy Mahalingam 3 , Frank Scheltens 4 , Robert Wheeler 4
1 , E.A. Fischione Instruments, Export, Pennsylvania, United States, 2 , The Ohio State University, Columbus, Ohio, United States, 3 , Wright Patterson AFRL, Dayton, Ohio, United States, 4 , UES, Inc., Dayton, Ohio, United States
Show AbstractThe recent advent and availability of aberration-corrected and computerized (S)TEM instruments means that more information about our samples are visible, and important aspects of their chemistry, atom locations, surface properties, and microstructure are quantifiable in both 2D and 3D. Surface damage and unintended ion implanted layers incurred during ion beam-assisted TEM sample preparation are being more deeply recognized as artifacts limiting the information that can be obtained using analytical electron microscopy. Both the quality and quantity of scientific and technological results are impacted by artifacts because deleterious surface layers are often a significant fraction of total sample thickness, and also because more samples of more materials are being made by ion beam-assisted techniques. After initially being prepared using conventional broad-beam or focused ion-beam assisted milling, samples that have been post-processed with low voltage argon beams show significant reductions in surface amorphous layer thickness, and also alteration of implanted gallium layers. A number of benefits and examples of the use of low energy argon beam milling, and its enhancement to sample quality and analytical information content are presented.
C9: Poster Session: TOMO
Session Chairs
Wednesday AM, November 28, 2007
Exhibition Hall D (Hynes)
9:00 PM - C9.1
Autofocus of HAADF STEM Images.
Wouter Van den Broek 1 2 , Jo Verbeeck 1 , Dominique Schryvers 1 , Paul Scheunders 2
1 EMAT, University of Antwerp, Antwerp Belgium, 2 Vision Lab, University of Antwerp, Wilrijk Belgium
Show AbstractIn High Angle Annular Dark Field (HAADF) STEM the image forming is an approximately incoherent process, and the image intensities are a function of the object’s thickness and the atom number Z, with typically I ~ Zn. Therefore it is suitable for electron tomography because it more closely fulfils the projection requirement as compared with bright field TEM. For this, typically 50 to 100 images have to be taken and focussing each of them is an important bottleneck. To significantly reduce acquisition time and radiation dose automating this step is necessary. Because of the incoherent image forming, automatic focussing can be done by maximizing the contrast of the image f. We compared two contrast measurements: the variance s2, and the autocorrelation difference D. For an image of N by N pixels D is defined as:D = ∑(∑fi,j fi,j-1 - ∑fi,j fi,j-2)/N2.An evaluation of the contrast transfer function shows two frequency intervals I1 and I2 to be maximally transmitted at Scherzer defocus, with the dependence on defocus being largest in I2. So the third criterion is a Fourier filter F that transmits I2. This is based on [1].s2 and D were tested on focus series of ceramic nanoparticles and a ceramic multilayer, with magnifications below the High Resolution (HR) regime, subsequently denoted as Low Resolution (LR). They both found the best focus value, but generally D was more peaked, smoother and had less local maxima. F was not tested because of the large undersampling in the LR regime. An online optimization routine using D reaches focus in 10 to 15 iterations, faster than a human operator.In the HR regime all three criteria were tested on focus series of a LaAlO3/SrTiO3 multilayer with a pixel size of 0.028nm. None of the images contained an amorphous region, only atom columns were visible. All functions have maxima in each others vicinity, the average difference between the two outer maxima is 7.0nm. This proves autofocus of HR images of crystalline materials is possible, without need for a separate amorphous region. [2,3][1] Boddeke F R, van Vliet L J, Netten H, Young I T, Bioimaging 2 (1994) 193.[2] Van den Broek W. is supported by a Concerted Action project, University of Antwerp, 2002/1, “Characterization of nanostructures by means of advanced electron energy spectroscopy and filtering”.[3] 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
9:00 PM - C9.2
Determination of the L10 FePt Phase Fraction of Annealed FePt Thin Films Using Dynamical Conical Annular Dark Field Transmission Electron Microscopy.
Bo Yao 1 , Kevin Coffey 1
1 Advanced Materials Processing and Analysis Center, and Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, Florida, United States
Show AbstractThe chemically ordered L10 FePt phase has stimulated research interest because of its potential applications as magnetic recording media and a permanent magnet material due to its large magnetocrystalline anisotropy energy density. However, mixtures of ordered L10 and disordered A1 phases commonly occur in annealed FePt thin films, and the fraction of the L10 phase strongly determines film magnetic properties. Measurement of the L10 fraction by X-ray diffraction is difficult due to the confounding effect of the extent of chemical order within each grain on the relative intensity of L10 X-ray diffraction peaks. This paper describes a method using the dynamical conical annular dark field (ADF) transmission electron microscopy to quantify the L10 FePt phase fraction of annealed FePt films. Specifically, the ratio of the illuminated area of an ADF image from the 001 diffraction ring (scattered solely from L10 phase) and that from the 002 ring (scattered from both A1 and L10 FePt phases) is used to calculate the fraction of L10 phase to A1 phase present in the film. The complicating factors which may influence the results are analyzed in detail and solutions are provided. The technique is demonstrated for several FePt film samples.
9:00 PM - C9.4
Si Ultra Shallow Junctions Dopant Profiling with ADF-STEM.
Andrea Parisini 1 , Damiano Giubertoni 2 , Massimo Bersani 2 , Vittorio Morandi 1 , Pier Giorgio Merli 1 , Jaap van den Berg 3
1 , CNR-IMM Sezione di Bologna, Bologna Italy, 2 , Fondazione Bruno Kessler-IRST, Povo (TN) Italy, 3 Joule Physics Laboratory, Institute of Materials Research, University of Salford, Salford United Kingdom
Show AbstractThe huge scaling down of the electronic devices nowadays attained, requires both ultra shallow junctions and high levels of dopant concentration and activation. In these conditions, the presence of surfaces or interfaces assumes a very important role in the determination of the dopant distribution during post-implantation annealing. In this work, we show how the Z-contrast annular dark field scanning transmission electron microscopy (ADF-STEM) technique, pionereed by Pennycook and co-workers [1], can be adapted, with some modifications, to give reliable dopant profiles at a sub-nanometer scale thus satisfying some of the new needs of the ultrashallow implants characterization.
The cases of low energy (3 and 5 keV) 2x1015 As+/cm2 implantations in Si are considered following the dopant distribution evolution with the annealing time at a temperature of 600° C. The ADF-STEM Z-contrast profiles indicate that As is pushed towards the sample surface during the sample recrystallization, indicating that its incorporation into the advancing recrystallization front is a relatively slow process. This confirms previously reported secondary ions mass spectroscopy, SIMS, and medium energy ion scattering, MEIS, results [2]. For an annealing at 800 °C for 30 min the ADF-STEM Z-contrast profiles indicates that the As peak has reached the sample surface [3,4]. These ADF-STEM Z-contrast results indicate that this technique appears to be an effective complementary technique to SIMS and MEIS for the determination of the dopant localization at a subnanometer level.
[1] S. J. Pennycook, S. D. Berger, and R. J. Culbertson, J. Microsc., 1986, 144, 229.
[2] D. Giubertoni, M. Bersani, M. Barozzi, S. Pederzoli, E. Iacob, J.A. van den Berg, M. Werner, Appl. Surf. Sci. 2006, 252, 7214.
[3] M. Ferri, S. Solmi, A. Parisini, M. Bersani, D. Giubertoni and M. Barozzi, J. Appl. Phys., 2006, 99, 113508-1-113508-7.
[4] A. Parisini, D. Giubertoni, M. Bersani, M. Ferri, V. Morandi and P. G. Merli, Proceedings of the 8th Multinational Congress on Microscopy, Prague, 18-21 june 2007, p. 43.
9:00 PM - C9.5
Quantitative Morphology Characterization of Polymer Nanocomposites through Electron Tomography.
Lawrence Drummy 1 2 , Y. Wang 3 , Keith May 1 4 , Mike Jackson 1 5 , Hilmar Koerner 1 6 , Benji Maruyama 1 , Richard Vaia 1
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States, 2 , UES Inc., Dayton, Ohio, United States, 3 , FEI Company, Hillsboro, Oregon, United States, 4 , Triune Group, Beavercreek, Ohio, United States, 5 , IMTS, Dayton, Ohio, United States, 6 , Universal Technology Corporation, Dayton, Ohio, United States
Show AbstractPolymer nanocomposites often display a complex hierarchical structure that can be accurately described only through the combination of quantitative results from multiple complimentary characterization techniques. Here we compare quantitative analysis of electron tomography results with results from small angle X-ray scattering (SAXS) techniques. Nanocomposites were processed by mixing of organically modified montmorillonite, a layered silicate material functionalized with a octadecylammonium surfactant, and epon 862 epoxy monomer. Several processing techniques (stirring, sonication, high-shear mixing, or low temperature compounding), with a subsequent thermal curing cycle of the epoxy, produced a range of morphologies. HAADF-STEM was shown to provide more than adequate contrast between the MMT layers and the epoxy matrix, as demonstrated by an experimental analysis of the MMT contrast as a function of layer tilt angle from the beam direction. Tomographic reconstruction by simultaneous iterative reconstruction techniques (SIRT) and the application of several three dimensional image filters produced a fully segmented 3D data set. A 3D power spectrum of the fast Fourier transform (FFT) was calculated, radially integrated, and compared with the one dimensional SAXS from the same sample. The analysis revealed good agreement between the techniques from the sub-nm regime up to a length scale of 1 micron. These results are expected to provide a basis for quantitative morphology analysis of nanocomposites and should be applicable to a wide range of materials.
9:00 PM - C9.6
Quantitative S/TEM Studies on Metallic Nano-Catalysts.
Long Li 1 , Edward Magee 1 , Laurent Menard 2 , Joo Kang 2 , Qi Wang 3 , William Alley 4 , Kim Heck 5 , Michael Wong 5 , Richard Finke 4 , Anatoly Frenkel 3 , Ralph Nuzzo 2 , Judith Yang 1
1 Mechanical Engineering and Materials Science Department,, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Department of Physics, Yeshiva University, New York, New York, United States, 4 Chemistry Department, Colorado State University, Fort Collins, Colorado, United States, 5 Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas, United States
Show AbstractThe synthesis of variety of exceptionally small metallic particles of a few nanometers with various shapes and structures is being actively pursued because of the potential to design promising catalysts with novel physical and catalytic properties. A grand challenge is the unequivocal characterization of such tiny particles, especially when they are deposited on oxide supports. Structural information, for example their sizes, shapes, and interfacial structures between the functional parts (particle/support or boundary of bimetallic phases), is of paramount importance. We have utilized quantitative scanning transmission electron microscopy (Q-STEM) and high-resolution transmission electron microscopy (HRTEM) combined with extended X-ray absorption fine structure (EXAFS) spectroscopy for quantitative analyses of the three-dimensional structures of several catalytic systems. The Q-STEM technique provides the number of atoms in each metallic cluster, based on high-angle annular dark-field (HAADF) imaging (inner acceptance angle > 95 mrad). EXAFS allows the measurement of ensemble-average coordination numbers and pair-distances of nearest neighbors to an X-ray absorbing atom. Specifically, we have examined Au on TiO2, in which the Au13 precursor, Au13[PPh3]4[S(CH2)11CH3]4, was treated with heat, ozone and atomic oxygen to form Au particles without ligands. Both reactive oxygen species, ozone and atomic oxygen, produced significantly less agglomeration of the Au clusters compared to annealing at 400 °C (2.7 ± 0.6 nm, 324 ± 264 atoms); ozone produced the smallest clusters (1.2 ± 0.5 nm, 40 ± 49 atoms). The exposure to 5 eV atomic oxygen produced Au particles with a broad size distribution (2.1 ± 0.7 nm, 72 ± 98 atoms) with a variety of structures including bilayer rafts, faceted hemispheres and spherical shapes as observed by HRTEM. A second system that we have studied is Ir nanoparticles that serve as commercial model catalysts for Ziegler-type hydrogenation catalysis. While HRTEM observations showed relatively few features due to the weak image contrast from small Ir clusters (<1 nm) containing only a few atoms, our STEM measurements determined the Ir size distribution (from 0.22 nm to 1.43 nm) with an average size of 0.50 ± 0.22 nm. Importantly, these results are consistent with the EXAFS measurements that indicated the Ir nanoclusters contained approximately 3-4 atoms and of the same average size (0.4 nm) as measured by STEM. We are currently expanding the application of the combined Q-STEM, HRTEM and EXAFS approach to bimetallic systems (Au-Pd, Au-Pt and Ir-Pt), to study their compositional (random nanoalloys, core-shells, etc.) as well as structural habits.
C10: Poster Session: Aberration Correction I
Session Chairs
Wednesday AM, November 28, 2007
Exhibition Hall D (Hynes)
9:00 PM - C10.1
Aberration-corrected HRTEM of the Incommensurate Misfit Layer Compound (PbS)1.14NbS2.
Magnus Garbrecht 1 , Erdmann Spiecker 1 , Wolfgang Jaeger 1 , Karsten Tillmann 2
1 Mikrostrukturanalytik, Institute of Material Science, Christian Albrechts University, Kiel Germany, 2 Ernst Ruska-Centrum and Institut für Festkörperfoschung, Forschungszentrum Jülich, Jülich Germany
Show AbstractThe development of spherical aberration (Cs) imaging correctors for medium-voltage transmission electron microscopes offers new opportunities for atomic-scale investigation of materials. One advantage of Cs-corrected HRTEM over conventional HRTEM is that the delocalization of the image contrast can be reduced below the typical separation of atomic columns in low-index crystal projections by tuning the spherical aberration to small values. This is particularly important for the investigation of crystal defects and interfaces where the translation symmetry of the perfect crystal is broken and a range of spatial frequencies contribute to the image contrast. We have investigated the misfit layer compound (PbS)1.14NbS2 which consists of an alternating stacking of two atomic sheets of cubic PbS and a sandwich layer of hexagonal NbS2. Two structural features make the HRTEM investigation of this compound particularly interesting and challenging. First, the two layers are incommensurate in one in-plane direction, i.e. different periodicities meet at the interfaces. Secondly, light atomic columns (S) and heavy atomic columns (mixed Pb/S) occur on opposite sides of each interface. We demonstrate that direct imaging of the complete projected crystal structure including the atomic columns at the interfaces becomes possible by applying Cs-corrected HRTEM in a Titan 80-300 instrument under imaging conditions with negative Cs values (NCSI-contrast). Evaluation of such images allows us to locally study structural phenomena, like layer distortion and stacking disorder, which so far could only be investigated by spatially averaging X-ray diffraction methods. An even more precise investigation of atomic column positions is achieved when we combine Cs-corrected HRTEM with exit-wave reconstruction from defocus series.M. Garbrecht acknowledges a travel grant sponsored by the European Microscopy Society (EMS).
9:00 PM - C10.2
Compositional Analysis of Tailored Interfaces in Short-Period InAs-GaSb Heterostructures Using Exit-Plane Wave Retrieval in High-Resolution Transmission Electron Microscopy.
Krishnamurthy Mahalingam 1 , Heather Haugan 1 , Gail Brown 1 , Kurt Eyink 1
1 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Show AbstractEmploying exit-plane wavefunction (EPWF) reconstruction in high-resolution transmission electron microscopy (HRTEM) we have developed an approach to atomic scale compositional analysis of quaternary III-V semiconductor interfaces with intermixing in both cation and anion sublattices. In this approach, we initially use the focal series reconstruction (FSR) technique, which retrieves the complex-valued EPWF from a thru-focus series of HRTEM images. Quantitative analysis using linear multivariate statistical analysis is then performed on the EPWF-phase image, which enables independent determination of the interface composition profiles along the cation and anion sublattices. We have used this approach to investigate interfaces in short-period InAs-GaSb superlattices (individual layer thickness ranging from 1-3 nm) with nominal and precisely tailored interfaces. Specifically, we examine a variety of heterostructures in which the bonding at each interface is either not controlled, or is intentionally tailored to be either “InSb-like” or “GaAs-like.” A comparison of the In-Ga and As-Sb composition profiles for the different interface types reveals an asymmetric broadening in the profiles corresponding to the tailored interfaces, that is consistent with an Ga-into-In exchange reaction at the GaSb-on-InAs interface, and similarly, an As-into-Sb exchange at the InAs-on-GaSb interface. Further results correlating the observed profiles to the photoluminescence spectra will be presented. Finally, the validity of our results is verified based on image simulations performed on simple atomistic models with graded and abrupt interfaces, explicitly taking in to account the role of interfacial strain.
C11: Poster Session: Diffraction
Session Chairs
Wednesday AM, November 28, 2007
Exhibition Hall D (Hynes)
9:00 PM - C11.1
Plasticity Mechanism of Indium Antimony (InSb) in the Brittle Regime: Combined Study with Conventional TEM and LACBED.
Bouzid Kedjar 1 , Ludovic Thilly 1 , Jean-Luc Demenet 1 , Jacques Rabier 1
1 Lab. Metallurgie Physique, University of Poitiers, Futuroscope France
Show AbstractThe study of plasticity of semiconductors (SCs) in the brittle regime is still of great interest for fundamental reasons and technical applications. In this temperature domain, the mechanical behaviour of many SCs has been studied in compression via pre-deformation at high temperature or under solid confinement (Griggs apparatus, multi-anvils): it usually appears that the observed mechanisms are radically different from the high temperature ones: dislocations are non dissociated in weak beam conditions (Si, SiC, GaAs) with sometimes exotic orientations (Si). Therefore, the study of low temperature mechanisms is of importance to understand the origin of the brittle-to-ductile transition (BTDT).In this context indium antimony (InSb) has been chosen for its low BTDT temperature and deformed in compression in the [20°C-400°C] range under gaseous confining pressure (Paterson apparatus) to prevent untimely fracture of specimen. Thin foils have been prepared from the macroscopic compression samples and dislocations were characterized with conventional TEM as well as LACBED.This paper will focus on the room temperature deformation microstructures which appeared to be extremely complex with the observation of very well arranged network of perfect and partial dislocations. In such case, the traditional dislocation extinction conditions were extremely difficult to analyze and only the use of the LACBED technique uncovered the nature of the observed dislocations and gave further insight to their interactions, revealing in particular the presence of partial dislocation dipoles. These original observations will be discussed within the framework of plasticity of brittle materials under the BTDT temperature.
9:00 PM - C11.10
Convergent Beam Electron Diffraction Experiments on Thermoelectric Skutterudites.
Ragnhild Saterli 1 , Oystein Prytz 2 , Per Erik Vullum 1 , Knut Marthinsen 3 , Randi Holmestad 1 , Johan Tafto 2
1 Department of Physics, NTNU, Trondheim Norway, 2 Department of Physics, University of Oslo, Oslo Norway, 3 Department of Materials Science and Engineering, NTNU, Trondheim Norway
Show Abstract9:00 PM - C11.2
Factors Influencing the Study of Charge Distribution in Layered Oxides Using Parallel Beam Quantitative Nano Electron Diffraction.
Vikas Kumar 1 , Qiang Xu 1 , Tyrel McQueen 2 , Jouk Jansen 1 , Henny Zandbergen 1
1 Nanoscience, Technical University of Delft, Delft Netherlands, 2 Chemistry, Princeton University, Princeton, New Jersey, United States
Show AbstractElectron Diffraction in comparison with X-ray/Neutron Diffraction has the added advantage that it can be used as a means to find the distribution of valence electrons in the structure as shown by CBED [1] [2]. The reason is that the electron beam interacts with the electrostatic potential of the crystal which includes the contribution from both the nuclei and the electron distribution. It can be seen that X-ray/Neutron data are quite insensitive to the positions of the charges specially for the class of oxides represented by Nb12O29. Nb12O29 exists in two different polymorphs: Monoclinic and Orthorhombic. There short range structure is quite similar and they differ only due to the rearrangement of nanometer length scale structural building blocks of NbO6 octahedras. Monoclinic Nb12O29 shows a very interesting feature in a way that it is both a metallic as well as anti ferromagnetic with the Neel temperature at about 12K [3]. Magnetic susceptibility and zero field muon spectroscopy clearly shows the low dimensional long range anti ferromagnetic ordering at 12K .The magnetic ordering is attributed to the charge ordering wherein half of the unpaired electrons contribute to the localization of the charge on a specific site or a group of sites (charge ordering) and the other half as being itinerant leading to the metallic nature [3]. However the orthorhombic Nb12O29 shows similar magnetic moments and exchange interactions but does not show any magnetic ordering at all. In this contribution we tried to determine the charge distribution in both phases to allow understanding of the different magnetic ordering and thus show the effectiveness of quantitative PBED.Refinement of experimental Parallel Beam Electron Diffraction (PBED) data using Multi Slice Least Squares (MSLS) algorithm [4] for models differing in ionic positions point towards a particular charge ordering. PBED refinements for charges depend on many factors which have to be taken into account very precisely, i.e., nuclei positions (structure), thickness (in combination with misorientations), selection of reflections, absorption, Debye Waller factors, degree of parallel beam and so on. Further the kinematic approximation that lower order reflections are more sensitive to ions than higher order ones needs to be interpreted in detail. MSLS refinement results on PBED data shouldn’t be accepted blindly because of the complex nature of the scattering i.e., dynamic. [1] Taftu, J.; Zhu, Y.; Wu, L.; Acta Cryst. 1998.A 54, 532-542 [2] Zhu, Y.; Wu, L.; Taftu, J.; J. Microscopy, Vol 194, Pt 1, April 1999, pp. 21-29[3] Waldron et al., Journal of Phy and Chem. of solids, 2004, 65, 79[4] Jansen, J.; Tang , D.; Zandbergen, H.W.; Schenk, H.; Acta Cryst. 1998 A54, 91-101
9:00 PM - C11.4
Electron Diffuse Scattering Characterization of Perovskite Thin Films.
Jerome Pacaud 1 , Frederic Pailloux 1
1 Lab de Métallurgie Physique, University of Poitiers, Chasseneuil France
Show AbstractSrTiO3 (STO) has generated great interest in recent years due to its large potential for technical applications in electronic devices, due to the similarity of structure between STO and other perovskite materials showing high temperature superconductivity, colossal magnetoresistance or ferro-electromagnetism, it can be used for the design of complex new microelectronic devices involving such materials especially in the field of the spintronic. Moreover, STO is a model system for the perovskite family and the detailed study of its behavior can give insight to the properties of the more complex materials of similar structure. The main requirement for many devices is the growth of a high purity and high structural quality thin film. The perovskite structure is extremely sensitive to the deposition condition and particularly to the temperature and the partial pressure of oxygen. Changes in deposition conditions may lead to a large deviation of the dielectric properties of thin films from those of bulk materials. The chemistry of defects is often proposed as an explanation of this deviation. Beside the oxygen deficiency, the cation stoichiometry seems to play a major role on the structure and properties of the grown film as it might induce the nucleation of structural defects (dislocation loops, stacking fault, Ruddlesden-Popper faults...).Another important parameter for thin perovskite films is the geometrical constraint imposed by the substrate. Most of the time, perovskite exhibit excellent epitaxy on each other and the films are tied to the substrate so the in-plane parameters are not free to reach their bulk equilibrium values (as a consequence the c-axis also differs from the bulk value). For materials as sensitive to phase transition as perovskite this effect and the associated relaxation processes can be extremely important for the fine tuning of the physical properties of the film.The goal of this study is to characterize, through diffuse scattering in electron diffraction, the structure of defects in the epitaxial layers of perovskite structure and more specifically its influence on the dynamic of the lattice (lattice vibrations, structural fluctuations and continuous phase transition due to phonon softening). Experiments are performed at both room temperature and 120K.For perfect crystal, diffuse scattering is mostly inelastic due to phonons, plasmons and other processes. Thermal diffuse scattering or phonon scattering can lead to large effects in the electron diffraction pattern especially near second order phase transition where phonon softening occurs. Additionally, elastic diffuse scattering comes from structural deviations from a periodic lattice. These structural deviations can be defects, partial ordering of otherwise disordered structure or structural fluctuations. By studying diffuse scattering we can obtain information about the crystal imperfections and dynamics which can not be obtained from other characterization methods.
9:00 PM - C11.5
EFTEM Spectral Imaging of Ceria Nanoparticles Using the LACSBI Method.
Jonathan Winterstein 1 , Ian Anderson 2 , Joysurya Basu 1 , Divakar Ramachandran 3 , C. Carter 1
1 Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Microanalysis Research Group, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 Phys. Metallurgy Sect., Metallurgy and Materials Grp., Indira Gandhi Centre for Atomic Research, Kalpakkam, TN, India
Show AbstractCerium oxide nanoparticles have many applications in fields as varied as catalysis and abrasion. The functional (electrochemical, mechanical, etc.) properties of such nanoparticles can be altered by the presence of dopant atoms in the ceria, or by a variation in the oxidation state of the cerium cations. Previous studies have indicated that these point defects are inhomogeneously distributed in commercially obtained lanthanum-doped ceria particles of ≈ 100 nm diameter. In the present study, lanthanum-doped ceria nanoparticles of ≈ 2 nm – 20 nm diameter were synthesized by a hydrothermal process by dissolution of cerium and lanthanum nitrates in an aqueous solution containing hexamethylenetriamine (HMTA). Nanoparticles were collected on carbon films at various times after the start of the reaction to examine the time evolution of particle size, shape, and chemical homogeneity. The structure and chemistry of the as-synthesized particles were examined using a combination of conventional transmission electron microscopy (TEM) techniques. Lattice imaging of the nanoparticles was performed by high-resolution TEM (HRTEM). The spatial distributions of dopant atoms and cerium oxidation state were characterized by energy-filtered TEM (EFTEM) spectral imaging, in conjunction with the large angular convergence scanned-beam illumination (LACSBI) method. LACSBI effectively removes most of the diffraction and phase contrast from conventional TEM images, permitting quantitative spectroscopic analysis of the resulting largely incoherent signal. An alternative methodology for performing dark-current subtraction and gain normalization, which was explored to remove point blemishes from the EFTEM image series, will also be discussed.
9:00 PM - C11.7
Critical Role of Inelastic Scattering in Quantitative Electron Microscopy.
Andre Mkhoyan 1 , Sara Maccagnano-Zacher 1 , Mick Thomas 1 , John Silcox 1
1 Applied Physics, Cornell University, Ithaca, New York, United States
Show Abstract9:00 PM - C11.8
Characterization of Local Strain Relaxation after Mesa Isolation for Global Strained-Substrates Using NBD and FFTM Methods.
Koji Usuda 1 , Toshifumi Irisawa 1 , Tsutomu Tezuka 1 , Yoshihiko Moriyama 1 , Norio Hirashita 1 , Shin-ichi Takagi 2 3
1 MIRAI Project, Association of Super-Advanced Electronics Technologies (ASET), Kawasaki Japan, 2 MIRAI Project, AIST, Tsukuba Japan, 3 , Univ. of Tokyo, Tokyo Japan
Show AbstractStrained-channel MOSFETs are one of very promising devices for high-speed CMOS. Thus, evaluation of strain in strained layers is mandatory. Particularly, in order to employ global strained substrates for advanced CMOS, strained layers are isolated into active areas with sub-µm to sub-100 nm sizes. Therefore, an extremely fine strain probe with the resolution of sub-100 nm order is needed. We have developed a nano-electron beam diffraction (NBD) method in transmission electron microscopy technique to quantitatively evaluate the local strain variation within a strained layer. The advantage of NBD is a high lateral resolution of 10 nm order and a high strain resolution, Δd/d, of 0.1%. In order to investigate the strain relaxation of a strained layer in a global strained substrate after isolation, we utilized following typical strained substrates: 40-nm-thick strained SiGe (x=0.23) on Si and 15-nm-thick SSOI substrates. The mesa isolation was carried out by using a conventional reactive-ion-etch (RIE) process. Finally, direct strain measurements using NBD were performed for both the strained SiGe layers, and the SSOI layers. As a result, full strain relaxation at the edges of the isolated strained layers was observed for both the substrates. Furthermore, the relaxation was enhanced around 200 nm from the edge, while it extended to almost 1 µm from the edge. In order to evaluate the spatial strain distribution over large areas in the strained layers, we employed the fast Fourier transform mapping (FFTM) method. This method is capable of mapping the variation in lattice parameters with a lateral resolution of 5 nm and a strain resolution, Δd/d, of 0.5%. It was confirmed from the 2-dimensional strain mapping by the FFTM that the strain relaxation of the strained SiGe layers was accompanied by local strain variations at the interface between the SiGe layers and the Si substrates. If the strained layers were relaxed by the introduction of dislocations in the layer, variations in the strain would be observed around the dislocations by the FFTM mapping. However, the strain variations were not observed, suggesting that elastic relaxation in the strained layers occurred. Another characteristic of FFTM is the capability to statistically analyze the lattice variations using histograms of characterized areas. The FFTM histogram has clearly revealed that strain relaxation accompanied the lattice inclination for the strained SiGe layers on Si, while no inclination for the SSOI layers. This fact means that the relaxation mechanism is different and dependent on the substrate structure, although the amounts of the strain relaxation in the strained layers were similar. In conclusion, it was found that combination of NBD and FFTM methods provides unique information of strain characterization, because NBD is a useful tool for quantitative local strain measurement and FFTM allows 2-dimensional characterization of lattice variations. This work was supported by NEDO.
9:00 PM - C11:diffraction
C11.9 Transferred to C 7.3
Show Abstract9:00 PM - C11:diffraction
C11.3 Transferred to C7.4
Show Abstract
Symposium Organizers
Etienne Snoeck CEMES-CNRS
Rafal Dunin-Borkowski Technical University of Denmark
Johan Verbeeck University of Antwerp
Ulrich Dahmen Lawrence Berkeley National Laboratory
C12: Grand Challenges for Electron Microscopy II
Session Chairs
Wednesday AM, November 28, 2007
Back Bay D (Sheraton)
9:30 AM - *C12.1
Options for Pump-probe Electron Microscopy.
Archie Howie 1
1 Physics, University of Cambridge, Cambridge United Kingdom
Show AbstractCombining the high spatial resolution provided by electrons with the high spectral selectivity and precision of photons is an attractive prospect for microscopy. It is already exploited under steady state illumination conditions in X-ray microanalysis and cathodolumenescence (CDL) operation. Inverse CDL,resulting in energy gain to the electron beam, has also been demonstrated. Greater sensitivity and additional information about dynamic response can be obtained with the use of periodically modulated or chopped beams and phase sensitive detection. The incident electron flux sets an upper limit of perhaps 10 GHz on these methods but pump-probe pulse techniques can go beyond this.Sub-picosecond electron pulses can now be combined with ultrashort optical pulses to yield high spatial resolution with precision timing or spectroscopy in pump-probe operation. Repeated pulsing will allow dynamic imaging of resettable, repeatable phenomena. Possible operational schemes will be described including electron pump / optical probe and optical pump / electron probe. Here STEM operation may be advantageous since a relevant (eg defect-containing) specimen area can be preselected. Purely optical pump-probe microscopy could be carried out with high spatial resolution in scanning probe microscopy using the tip field enhancement effect.
C13: Mapping of Electronic States and Local Bonding and Elemental Mapping II
Session Chairs
Wednesday PM, November 28, 2007
Back Bay D (Sheraton)
10:15 AM - **C13.1
Mapping Composition and Chemistry in the Nanoanalytical Microscope.
Alan Craven 1 , Maureen MacKenzie 1 , Sam McFadzean 1
1 Physics and Astronomy, University of Glasgow, Glasgow, Scotland, United Kingdom
Show AbstractMany modern materials and devices require a well-defined structure on the atomic or near-atomic scale. Such materials range from advanced semiconductor devices through to high strength low alloy steels. To optimise performance, knowledge of the local composition and chemistry is crucial. Electron energy loss spectroscopy (EELS) in the nanoanalytical electron microscope is a very powerful technique for providing such information. The ionisation edge energy, the edge intensity and the edge shape identify the element, the concentration and the chemistry, respectively. Other information, including the local thickness and the dielectric function, is also available.With computer control of both the probe position and the data acquisition, spectrum imaging is a powerful technique. In its simplest form, a spectrum is acquired at each pixel of a spatial array, allowing detailed analysis of the spectrum at each pixel. Many of the systems of interest contain a wide range of atomic numbers e.g. hafnia high-k dielectrics on silicon, gallium gadolinium oxide high-k dielectrics on GaAs, lead zirconate titanate (PZT) thin films and magnetic multilayers. Examples of the application of spectrum imaging to such systems will be demonstrated.The spectrum imaging technique can be extended to collect any signal available at a pixel provided suitable computer control of the microscope system is available. In Glasgow we have a system that collects the low loss region and up to two different energy ranges of the core loss region of the EELS spectrum, allowing complete processing of the EELS data. The energy dispersive x-ray spectrum and the image detector signals can also be collected, allowing exact registration of the information collected. The sub-pixel scanning and drift correction facilities can also be used with the system. The application of this system to the analysis of precipitation in vanadium microalloyed steels will be presented to demonstrate the benefits and potential of having a full data set.
10:45 AM - C13.2
(S)TEM Characterization on the Refractory Minerals from Comet 81P/Wild-2.
Miaofang Chi 1 2 , Nigel Browning 1 3 , Hope Ishii 2 , Zurong Dai 2 , John Bradley 2
1 Department of Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States, 2 Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, California, United States, 3 Materials Science and Technology Division, Lawrence Livermore National Laboratory, Livermore, California, United States
Show Abstract11:30 AM - **C13.3
Recent Progress of Quantitative X-ray Analysis of Thin-Film Specimens in Transmission Electron Microscopy.
Masashi Watanabe 1
1 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show Abstract12:00 PM - C13.4
Tomographic Reconstruction of the EELS Data Cube; Experimental Results.
Wouter Van den Broek 1 2 , Jo Verbeeck 1 , Steve De Backer 2 , Paul Scheunders 2 , Dominique Schryvers 1
1 EMAT, University of Antwerp, Antwerp Belgium, 2 Vision Lab, University of Antwerp, Wilrijk Belgium
Show AbstractThe EELS data cube combines spatial and spectral information because it has an EELS spectrum in each pixel of a spatial image. The two major methods of acquiring it are image-spectroscopy (or an Energy Filtered Series or EFS) and spectrum-imaging. In [1] we showed that a proper defocus of the energy filter induces a mixing of spatial and spectral information that can be proven equivalent to a projection of the data cube onto the CCD camera. The projection angles are directly related to the defocus value and all angles between 0° and 180° are possible in principle. The projections are then used to reconstruct the data cube by tomographic techniques. In [1] we concluded that the method needs a lower electron dose than EFS to acquire a data cube with the same resolution and mean signal-to-noise ratio.Experiments are conducted on a Jeol 3000F TEM equipped with a Gatan post-column energy filter (GIF). We aim at recording a data cube measuring 50 pixels in the energy direction (1.1eV/pixel) and 90 by 90 pixels in the spatial directions (1.1nm/pixel). By defocusing the Q3 lens of the GIF in imaging mode, projections through angles ranging from 0° to 74° and from 109° to 180° are possible. An EELS spectrum is equivalent with a projection through 90°. Defocusing in spectroscopy mode yields angles ranging from 72° to 90° and from 93° to 110°. This leaves a negligible missing wedge of 3°. To obey the projection requirement the data cube needs to be bounded in both the spatial and the spectral directions, so the 0.6mm entrance aperture of the GIF is inserted as well as a 50eV wide energy slit. 87 projections were made, 66 in imaging mode and 21 in spectroscopy mode, and they were fed into an algebraic reconstruction technique.The sample is a CeO2 particle with an N4,5 peak. It is recorded with the method proposed here and with an EFS for comparison, both with approximately the same electron dose. Visual inspection shows that the data cube is faithfully reconstructed and exhibits lower noise than an EFS. This already is a strong proof of concept that demonstrates the method is experimentally feasible. The energy resolution is slightly lower than predicted. This is probably due to the projections in spectroscopy mode, where the defocus also significantly shrinks the image, thus increasing the relative size of the point spread function of the CCD camera. Preliminary experiments suggest this can be compensated for by also exciting other lenses. [2,3][1] Van den Broek W., Verbeeck J., De Backer S., Scheunders P., Schryvers D., Ultramicroscopy, 106 (2006) 269. [2] Van den Broek W. is supported by a Concerted Action project, University of Antwerp, 2002/1, “Characterisation of nanostructures by means of advanced electron energy spectroscopy and filtering”.[3] 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.
12:15 PM - **C13.5
WITHDRAWN ON-SITE EMCD: Magnetic Chiral Dichroism in the Electron Microscope.
Peter Schattschneider 1 2 6 , Stefano Rubino 1 , Michael Stoeger-Pollach 2 , Cecile Hebert 3 , Jan Rusz 4 , Lionel Calmels 6 , Benedicte Warot-Fonrose 6 , Florent Houdellier 6 , Virginie Serin 6 , Pavel Novak 5
1 Inst. of Solid State Physics, Vienna Univ. of Technology, Vienna Austria, 2 Service Centre for TEM, Vienna Univ. of Technology, Vienna Austria, 6 Nanomatériaux, CEMES-CNRS , Toulouse France, 3 SB-CIME Station 12, EPFL, Lausanne Switzerland, 4 Deptmt. of Physics, Uppsala University, Uppsala Sweden, 5 Institute of Physics, Academy of Sciences, Prag Czech Republic
Show Abstract12:45 PM - C13.6
New Electron Energy Loss Magnetic Chiral Dichroism (EMCD) Configuration Using an Aberration-corrected Transmission Electron Microscope.
Benedicte Warot Fonrose 1 , Florent Houdellier 1 , Christophe Gatel 1 , Lionel Calmels 1 , Virginie Serin 1 , Peter Schattschneider 2 , Martin Hytch 1 , Etienne Snoeck 1
1 CEMES, CNRS, Toulouse France, 2 , Technische Universität, Wien Austria
Show AbstractX-Ray magnetic circular dichroism (XMCD) is a powerful technique for studying magnetic properties at the atomic level. The signal originates from the absorption difference between left and right circularly polarized X-ray beam in a magnetic material. XMCD is chemically and orbitally selective and allows a quantitative determination of the size and direction of atom spin and orbital magnetic moments from sum rules applied to experimental spectra. The technique, however, requires the use of a synchrotron source and has a spatial resolution limited to about 100 μm2. Recently, a technique has been proposed to measure the magnetic circular dichroism in a Transmission Electron Microscope (TEM) [1, 2]. Analogous to XMCD, the energy loss spectrum shows a dichroic signature - magnetic chiral dichroism (EMCD) - with much higher spatial resolution. The dichroic signal is measured at two precise positions of the diffraction pattern where the imaginary part of the Mixed Dynamical Form Factor (MDFF) has opposite sign in magnetic samples. In the original configuration proposed, the EMCD signal remains weak and difficult to exploit in practice.Using the SACTEM-Toulouse, a Tecnai F20 (FEI) equipped with an objective lens aberration corrector (CEOS), rotatable biprism and imaging filter (Gatan Tridiem), we have improved both the diffraction condition and the detection method of the inelastic signal. This has been achieved by increasing the inelastic signal in the diffraction pattern using the newly developed LACDIF configuration which combines properties of LACBED and Cs-correction, and by using spatially resolved EELS techniques. The asymmetry of the imaginary part of the MDFF can be mapped across the diffraction pattern using Energy Spectroscopic Imaging (ESI), which helps to visualize the most significant dichroic positions [3]. A systematic quantitative comparison between the different diffraction and detection techniques has been realised to determine the optimal configuration. We have also analysed the evolution of the EMCD signal using ferromagnetic and non-magnetic material such as Fe, Co, Cu, Fe304, … with the thickness and the orientation.Using new holographic configuration called EMCD holography, we will also show how to control the intensity of the EMCD signal.References [1] C. Hébert, P. Schattschneider, Ultramicroscopy 96 (2003) 463.[2] P. Schattschneider, S. Rubino, C. Hébert, J. Rusz, J. Kunes, P. Novak, E. Carlino, M. Fabrizioli, G. Panaccione, G. Rossi, Nature 441 (2006) 486[3] B.Warot-Fonrose, F.Houdellier, M.J.Hÿtch and E.Snoeck Ultramicroscopy - in press
C14: Grand Challenges for Electron Microscopy III
Session Chairs
Wednesday PM, November 28, 2007
Back Bay D (Sheraton)
2:30 PM - *C14.1
Ultimate Resolution Limits for Electron Microscopy?
David Smith 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractThis talk will consider the grand challenge of ultimate resolution limits in terms of the complex and closely inter-related issues of beam-specimen interactions and trends in instrumental performance.
C15: SEM/ LEEM II
Session Chairs
Wednesday PM, November 28, 2007
Back Bay D (Sheraton)
3:15 PM - C15.1
Secondary Electron Doping Contrast: Theory Based on Band Bending and Electron Affinity Measurements.
Irina Zhebova 1 , Michel Molotskii 1 , Iris Magid 1 , Guilia Meshulam 1 , Enrique Grunbaum 1 , Yossi Rosenwaks 1 , Zahava Barkay 2
1 School of Electrical Engineering- Department of Physical Electronics, Faculty of Engineering, Tel Aviv University, Tel-Aviv Israel, 2 Wolfson Applied Materials Research Center, Tel Aviv University, Tel Aviv Israel
Show AbstractThe secondary electron emission (SEE) flux in a high-resolution scanning electron microscope has already shown to be a powerful tool for delineation of electrically active dopant concentration, built-in potentials and surface electric fields in semiconductors. However, the quantitative interpretation of the SE contrast and their energy distribution is limited by the presence of surface states (and consequent band bending) and changes in the electron affinity due to surface adsorbed charges (1,2,3). We present a quantitative theory of SEE doping contrast in the p- and n-sides of a pn junction. It is found that the contrast is governed by the difference in the secondary electrons escape length on both sides of the junction. The internal electric field on the junction p-side increases exponentially the SE escape length, while it is exponentially decreased on the n-side of the junction. In addition, the surface barrier for electron escape, due to different electron affinities on the n- and p-type semiconductors, increases the contrast and also causes an energy shift of the SE distributions towards higher energy. The calculated contrast is based on band bending and electron affinities extracted from our Kelvin probe force microscopy (KPFM) measurements. The SE contrast measured on the same passivated Si pn junctions measured by the KPFM was found to be in a reasonable agreement with our calculations. The effect of oxide layers and carbon contamination is discussed.1. C P Sealy, M R Castell and P R Wilshaw, J. Electron Microsc. 49, 311, (2000).2. A. Schwarzman, Th Glatzel, E. Grunbaum, E. Strasburg, E Lepkifker, A Boag, Z Barkay, M. Mazzer, K Barnham, and Y. Rosenwaks, J. Appl. Phys. 98, 084310, (2005).3. K.W.A.Chee, C.Rodenburg and C.J.Humphreys, Micr. Semicond.Mat.XV Conf,Cambridge (2007) (to be published).
3:30 PM - C15.2
Helium Ion Microscope Imaging and Analysis of Nanomaterials; Nanowires, Nanoparticles and Composites.
David Bell 1 , Louis Stern 2 , Lou Farkas 2 , Billy Ward 2
1 School of Enginnering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 ALIS Corporation, Carl Zeiss SMT Company, Peabody , Massachusetts, United States
Show AbstractThe helium ion microscope (Orion microscope) offers some unique abilities in terms of imaging and analytical capabilities of nanomaterials and composite materials. Due to the interaction of the relatively low energy helium ion with the surface of the material the resultant secondary electron arises from a surface regime interaction volume resulting in superb resolution and image fidelity. One reason for the enhanced image fidelity is due to the ion source causing no high energy backscattered electrons contributing to imaging focus issues. Further imaging and analytical capability are possible using a RBS type detector in the system. The helium ion source has proven to be very stable and offers high brightness, low virtual size and low energy spread as compared to a conventional FEG type SEM. With this source the sputtered target atoms occur at a rate of 100 times less than Gallium ions in a conventional FIB system, meaning long imaging times and no electrically active ion implantation. The converse idea of using the slow spluttering rate is also useful in the application to materials modification. Materials that would be termed sensitive in a Ga FIB can be gently milled or sputtered in the He+ microscope without contamination effects as normally seen in FIB system.A wide variety of nanomaterials have now been examined using the helium ion microscope, these include; Nanotubes, nanowires, nanoparticles and composite materials and structures such as polymers and multi-layer fabricated devices. There is a wealth of surface information available in the images obtained, interpretations of the images and a complete understanding of the physical processes is the current focus of our ongoing investigations. RBS imaging allows grey level determination of atomic number over a range of elements, the image in essence becoming a real time spectral map of materials constituents. Current results to be presented using this new microscope system of materials imaging and analysis.
3:45 PM - C15.3
Imaging Oxide-Covered Doped Silicon Structures Using Low-Energy Electron Microscopy.
M. Anderson 1 , G. Kellogg 1 , C. Nakakura 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractOwing to the increasing complexity of integrated circuits, quantitative 2D techniques that analyze the dopant characteristics of state-of-the-art devices have become a necessity. Traditionally, the low-energy electron microscope (LEEM) has been employed to achieve high resolution surface and interface analysis, yet little work has been done to exploit its unique capabilities for device applications. The sensitivity of LEEM to surface morphology, differences in work function, and surface charge variations make this an ideal instrument for studying devices. In this talk, we will present recent work on imaging doped Si devices in the LEEM, with the purpose of creating an analytical technique to image and quantify dopant concentrations in devices. Diode test structures were fabricated by implanting As and/or B into Si(100) p-type substrates to construct n+/p junctions. Oxide thickness above the Si substrate ranged from ~15 Å (native oxide) to ~50 Å. When imaging these diodes we found that there is significant contrast between the n- and p-type regions, even with a 50 Å oxide on the surface and minimal sample preparation. This is in contrast to photoelectron emission microscopy (PEEM) reports, where contrast decreases rapidly as a function of oxide thickness [1]. The intensity from the n- and p-type regions decreases rapidly and then slowly increases as a function of increasing sample bias relative to the electron beam (“start voltage”). The start voltage at which the intensity begins to decrease depends on the dopant type and concentration. Thus, strong contrast can be achieved by “tuning” the start voltage. We measured time-dependent oxide charging effects that are more pronounced on samples with thicker oxides. Contrast effects induced by external biasing are also observed on these diode test structures when forward and reverse biased. The LEEM measurements were compared to atomic force microscopy and scanning capacitance microscopy in order to make quantitative comparisons between step height and dopant type. Although the source of LEEM image contrast is not exclusively due to work function differences between heavily/lightly doped n- and/or p-type regions, the contrast is also not strictly due to topography (height differences) inherent to oxides on doped Si surfaces. Contrast mechanisms for biased and unbiased test structures will be detailed in the presentation. These experiments show promise for LEEM-based device imaging because it is capable of characterizing pn junctions without complicated sample preparation, allowing for rapid, non-destructive imaging of devices. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.[1] V. W. Ballarotto, M. Breban, K. Siegrist, R. J. Phaneuf, and E. D. Williams, J. Vac. Sci. Technol. B, 20, 2514 (2002).
4:00 PM - C15:SEM/LEEM
BREAK
C16: Aberration Correction II
Session Chairs
Wednesday PM, November 28, 2007
Back Bay D (Sheraton)
4:30 PM - **C16.1
Applying Aberration Corrected STEM and EELS.
Andrew Bleloch 1
1 , SuperSTEM Laboratory, Warrington, Cheshire, United Kingdom
Show AbstractThe first aberration corrected instruments have been operating for around 10 years. These instruments however were existing columns with correctors retrofitted to them. Nion Co. has recently installed a new microscope at the SuperSTEM laboratory that is designed from scratch around the aberration corrector with a number of novel design elements. These include a new stage design, modular lens system and highly modular electronics. Here we report initial results from this instrument together with some insights from the existing retrofitted VG STEM (with a Nion quadrupole-octupole corrector).Imaging and spectroscopy of single atoms represents in one sense at least the ultimate characterisation of a material. Single atom characterisation will be shown in several systems including supported platinum group metal catalysts and doped nanotubes. Significantly, the additional brightness available from a cold field emission source together with the fifth order Nion corrector, allows a 0.2nm beam to be formed with around 1nA of beam current. This is an order of magnitude more than the current previously available at this resolution and allows larger EELS maps at higher losses to be usefully acquired.In addition, the conventional multislice approach to simulating images has been straightforwardly extended to include all aberrations up to and including 5th order. A comparison of simulated and experimental STEM images using measured aberration coefficients demonstrates the precision to which (especially the low order) aberrations need to be set and measured. Quantitative checking of the self-consistency of the aberration coefficients in this way needs to become routine because it is possible to acquire images with significant artefacts unless care is taken to reconcile the aberration measurements with the images. This is a most exciting time in electron microscopy in which the promise of aberration correction is being realised and explored across a wide range of material systems.
5:00 PM - C16.2
Effects of Amorphous Layers on ADF-STEM Imaging.
Sara Maccagnano-Zacher 1 , Andre Mkhoyan 1 , Earl Kirkland 1 , John Silcox 1
1 Applied Physics, Cornell University, Ithaca, New York, United States
Show AbstractA study of high-resolution ADF imaging in uncorrected and aberration-corrected STEMs was carried out by multislice simulation. The presence of amorphous layers at the surface of a crystalline specimen is shown to significantly alter the visibility of the atomic columns. An amorphous layer at the beam entry surface has a much bigger effect than that of an amorphous layer at the exit surface. After propagating through an amorphous layer a portion of the beam passes without any alteration while scattered electrons introduce a Gaussian background. The dependence of the image contrast on the crystal structure, orientation and the types of the atoms present in the crystal was studied. In the case of uncorrected probes an amorphous layer thicker than 20 nm is necessary to achieve considerable reduction of the visibility of the atomic columns, but with aberration-corrected probes only 6 nm is necessary. With changes in defocus the crystalline specimens with amorphous layers on the top can also be imaged and high-resolution ADF images can be obtained.
5:15 PM - C16.3
Direct Imaging of Surfaces on Platinum Nanocatalysts using Aberration-Corrected TEM.
Lan-Yun Chang 1 , Lionel Cervera Gontard 3 , Dogan Ozkaya 4 , Angus Kirkland 1 , Rafal Dunin-Borkowski 2 3
1 Department of Materials, University of Oxford, Oxford United Kingdom, 3 Centre of Electron Nanoscopy, Technical University of Denmark, Kongens Lyngby Denmark, 4 , Johnson Matthey Technology Centre, Reading United Kingdom, 2 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractThe active components of heterogeneous catalysts are often small metallic particles, whose reactivity and selectivity depend on the structure of their surfaces [1]. The roles of different active sites, such as steps and kinks and the inter-atomic distances, on the extended surfaces of model catalysts can be identified using techniques such as scanning probe microscopy and low energy electron diffraction, respectively [2, 3]. However, for the industrial catalyst applications, it is even more important that the detailed structures on the surfaces of catalytic nanoparticles are well characterized at atomic resolution, as similar analysis can not be performed on individual nanoparticles.High-resolution electron microscopy is a powerful technique to study the atomic structures of nanoparticles. However, conventional high-resolution images suffer from aberrations introduced by the objective lens, and these images are generally not directly interpretable. Recent successful development of the aberration corrected microscopes [4] has greatly reduced the spherical aberration and hence the image delocalisation. The phase (of the specimen exit plane wavefunction) restored [5] from a series of differently aberrated images gives a directly interpretable representation of the atomic structures. In the present work, we examined a powder of Pt nanoparticles on carbon black, which had been heated to 900 degree C in a N2-rich atmosphere. These particles are used to both electro-oxidize H2 and electroreduce O2 at the anode and cathode, respectively, of a polymer electrolyte membrane fuel cell. The phase restoration from a focal series acquired using an aberration-corrected transmission electron microscope (JEM-2200FS) provides direct imaging of the local topologies of active sites at atomic resolution on the commercial platinum nanoparticles. Furthermore, the analysis of the atomic column positions at sub-pixel resolution, in conjunction with the multislice simulations, allows us to directly observe the surface distortions on these nanoparticles. A comparison will also be presented between our study on catalytic platinum nanoparticles and other existing measurements and first principle calculations.
5:30 PM - C16.4
A Phenomenological Approach to Quantify the Composition of Semiconductor Materials from High-resolution Z-contrast Images.
Sergio Molina 1 2 , Maria Varela 1 , David Sales 2 , Pedro Galindo 3 , David Fuster 4 , Yolanda Gonzalez 4 , Benito Alen 4 , Luisa Gonzalez 4 , Stephen Pennycook 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory (ORNL), Oak Ridge, Tennessee, United States, 2 Departamento de Ciencia de los Materiales e I.M. y Q.I., Universidad de Cádiz, Puerto Real, Cadiz, Spain, 3 Departamento de Lenguajes y Sistemas Informáticos, Universidad de Cádiz, Puerto Real, Cadiz, Spain, 4 Instituto de Microelectrónica de Madrid, CSIC, Tres Cantos, Madrid, Spain
Show AbstractC17: Poster Session: QHRTEM
Session Chairs
Thursday AM, November 29, 2007
Exhibition Hall D (Hynes)
9:00 PM - C17.1
Melt Growth and Effect of Monovalent Alkaline Metals (M+ = Li+, Na+ and K+) on the Optical Properties of Yb3+-doped CaF2 Laser Crystals.
Kyoung Jin Kim 1 , Anis Jouini 2 , Sana Hraeich 3 , Georges Boulon 3 , Akira Yoshikawa 1
1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan, 2 Leti-MINATEC, CEA-Grenoble, Grenoble France, 3 Physical Chemistry of Luminescent Materials, Claude Bernard/Lyon 1 University, Villeurbanne France
Show AbstractVarious Yb3+-doped crystals have been investigated as a candidate for producing a stable laser in the near-IR spectral range in order to replace the conventional Nd:YAG laser. Among many kinds of host materials, CaF2 has also been considered as a candidate. It has attractive features such as low phonon energy, high thermal conductivity and optically uniaxial. Moreover, the Yb3+ ion is interesting because of its strong IR luminescence that can be easily pumped with conventional 940 and 980 nm laser diodes.It is well known when trivalent Yb3+ is introduced into CaF2 crystal, it is substituted for Ca2+, resulting in the creation of Yb3+ surrounded by eight F− ions. This replacement by Yb3+ gives a contribution to the creation of charge compensation, i.e., interstitial F- ions in various sites, such as the nearest neighbor (C4v), next nearest neighbor (C3v) or nolocal site (Oh), and various clusters. Moreover, Yb3+ introduced into CaF2 lattice could be partly in divalent state because of the tendency to complete the full 4f shell. Thus we thought codoping monovalent alkaline metal ions (M+ = Li+, Na+, K+) with Yb3+ as charge compensator in CaF2 would break the Yb3+ ions clusters, and suppress the formation of Yb2+ ions.This study is mainly based on CaF2 single crystals co-doped by Yb3+-M+ covering a broad range of alkaline metal ion concentration. Single crystals were grown by the micro-pulling-down method with precise atmosphere control system. Graphite crucible is surrounded by refractory carbon and inductively heated using a radio-frequency generator. Growth orientation was controlled by [111] CaF2 seed. Phase identification and structural characterization was done by powder X-ray diffraction for all samples at room temperature. Their spectroscopic characteristics were analyzed by absorption and emission in the near-IR between fundamental 2F7/2 and excited state 2F5/2 and by focusing on the variation of the emitting level 2F5/2 life time with concentration of the M+ ions (up to 20 mol%) and temperature (12 to 300 K), in the aim to understand the nature of the formed Yb3+ sites in CaF2.
9:00 PM - C17.10
Lattice-Fringe Fingerprinting: Structural Identification of Nanocrystals Employing High-Resolution Transmission Electron Microscopy.
Ruben Bjorge 1 , Peter Moeck 1 2 , Philip Fraundorf 3
1 Department of Physics, Portland State University, Portland, Oregon, United States, 2 , Oregon Nanoscience and Microtechnologies Institute, Portland, Oregon, United States, 3 Department of Physics and Astronomy & Center for Molecular Electronics, University of Missouri-St. Louis, St. Louis, Missouri, United States
Show AbstractLattice-fringe fingerprinting is a novel method of identifying nanocrystals on the basis of the Fourier transforms of high-resolution transmission electron microscopy (HRTEM) images. The spacings between lattice fringes and the interfringe angles, measured when nanocrystals show crossed lattice fringes in HRTEM images, are used to initially “fingerprint” the nanocrystal. The two-dimensional space group symmetry of the projected electrostatic potential can also be used within the range of the validity of the weak phase-object approximation (and probably also somewhat beyond) for fingerprinting purposes. Lattice-fringe fingerprinting is demonstrated on two different crystal systems: iron oxide and simulated images of gallium nitride. The majority of the iron oxide nanocrystals showing crossed lattice fringes are oriented close to the [211] orientation. The analysis of simulated images of gallium nitride demonstrates the prospective possibility of using the phases of the Fourier coefficients of HRTEM images in identifying a crystal structure. These phases could in the future be compared directly to calculated structure factor phases for a range of candidate structures in order to make lattice-fringe fingerprinting more discriminative. Here, only the phase restrictions and phase relations due to the projected space group symmetry are used as another component of lattice-fringe fingerprinting. Lattice-fringe fingerprinting requires a comprehensive database of crystallographic information combined with search-match algorithms to be employed for the identification of an unknown nanocrystal out of a range of candidate structures. Such crystallographic information is freely available from the Crystallography Open Database (http://crystallography.net) and its mainly inorganic subset at Portland State University's research servers (http://nanocrystallography.research.pdx.edu/CIF-searchable).
9:00 PM - C17.11
Nanoscale Bend of Crystal Lattice in CaCu3Ti4O12.
Sung-Yoon Chung 1 , Si-Young Choi 2 , Takahisa Yamamoto 3 , Yuichi Ikuhara 2
1 Dept. of Materials Sci. & Eng., Inha University, Incheon Korea (the Republic of), 2 Institute of Engineering Innovation, The University of Tokyo, Tokyo Japan, 3 Dept. of Adv. Mater. Sci., The University of Tokyo, Tokyo Japan
Show AbstractPerovskite-type oxides have been recognized as crucial materials for many novel applications in electronics because of the variety of electronic and optical properties they offer. A number of studies have particularly been conducted on the perovskite titanates and their solid solutions in efforts to elucidate the origin of unique electronic behavior. CaCu3Ti4O12 (equivalently, Ca1/4Cu3/4TiO4) is one of the titanates that has attracted much attention over the past several years following the discovery of its extraordinarily high dielectric permittivity of ~100,000 in 2000 [1, 2]. Some earlier studies proposed local dipole moments as a possible cause for the gigantic dielectricity as in other ferroelectrics. However, recent experimental observations, including strong nonlinear current-voltage behavior [3], directly demonstrated that the inhomogeneous electrical configuration with conductive grains and insulating internal interfaces plays a critical role in the peculiar dielectric behavior of CaCu3Ti4O12. Therefore, in order to attain a thorough understanding of the unusual electrical properties in CaCu3Ti4O12, there is a strong need for fundamental nanoscale investigations on the crystal lattice in a single grain on the basis of crystal physics [4, 5].Among the various approaches for the characterization of materials, transmission electron microscopy (TEM) is now an essential tool to show variation in physical structure and chemical composition at a nanometer scale. Recent development in high-resolution electron microscopy (HREM) and Z-contrast imaging in scanning transmission electron microscopy (STEM) offers direct visualization at an atomic level with respect to the architecture of nanomaterials, and lattice defects. In particular, since high-resolution phase contrast images of crystalline solids can provide diverse information on the defect structures as well as the crystallographic relationship between crystallites, HREM-based analysis is necessary to identify any variation in crystal structure of solids. In this presentation, we show that the crystal lattice is inherently bent at a nanometer scale without being separated by a domain wall in Fe-doped polycrystalline CaCu3Ti4O12 via HREM and electron diffraction. Combining lattice image simulation with HREM, we investigate the crystal distortion at a nanoscale. HREM images were obtained in a JEOL JEM-4010 microscope operated at 400 kV as well as in a Topcon EM-002BF microscope with a field emission-type gun operated at 200 kV. Lattice image simulations based on the multislice method were performed for comparison with the experimentally obtained images. (References)1. M. A. Subramanian et al, J. Solid State Chem. 151, p.323 (2000). 2. C. C. Homes et al, Science 293, p.673 (2001). 3. S.-Y. Chung et al, Nature Mater. 3, p.774 (2004). 4. S.-Y. Chung, Appl. Phys. Lett. 87, p.052901 (2005). 5. S.-Y. Chung et al, Appl. Phys. Lett. 89, 121903 (2006).
9:00 PM - C17.12
Manganites Thin Films Patterned by FIB: a Transmission Electron Microscopy Study.
Mauro Porcu 1 , Henny Zandbergen 1
1 , Delft Technical University, Delft Netherlands
Show Abstract9:00 PM - C17.13
Imaging of Boundaries in MgO Nanocubes.
Jonathan Winterstein 1 , Julia Nowak 2 , Joysurya Basu 1 , C. Carter 1
1 Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractEngineering ceramic materials requires an in-depth knowledge of microstructure evolution. Thus, a basic understanding of boundaries in ceramics is crucial for designing processing techniques for producing ceramics of a specified microstructure. Described in their classic 1970 paper, Chaudhari and Matthews investigated the misorientation between small particles of MgO. In this well-known experiment, Mg metal was burned in air to produce MgO smoke, which was then collected on a grid with an amorphous carbon support film. Assuming that the interface plane is (100), TEM analysis of the boundaries indicated that for rotations between 0° and 50°, Σ1, 5, 13, and 15 grain boundaries are of lowest energies. In the present study, particles of crystalline MgO smoke were produced in the same manner and collected on electron transparent membranes of (100) MgO for observation in the TEM. The substrates were prepared by one-sided dimpling and ion milling. Dimpling was followed by chemical cleaning and heat treating to remove amorphized material, ideally leaving a flat, single crystal (100) surface. By using a (100) MgO membrane rather than a carbon support film, the collected smoke particles form twist boundaries with the substrate. The misorientation of the particle can then be determined by diffraction or moiré imaging techniques. Diffraction-contrast and high-resolution TEM imaging was performed to examine strains and dislocations associated with the interfaces. The MgO substrate with attached smoke particles was also heated in situ in the TEM to examine changes in the boundary structure with time. Variation of the means by which the smoke particles are collected also provides insight into coincidence boundary formation. The possibility of extending this sample preparation technique to other materials is also discussed.
9:00 PM - C17.14
TEM and STEM Study of the Au Nano-particles Supported on Metal Oxides.
Tomoki Akita 1 3 , Koji Tanaka 1 , Masanori Kohyama 1 3 , Masatake Haruta 2 3
1 , National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka, Japan, 3 , JST, CREST, kawaguchi, Saitama, Japan, 2 , Tokyo Metropolitan University, Hachioji, Tokyo, Japan
Show Abstract9:00 PM - C17.15
Cationic Migration in Thin La2/3Ca1/3MnO3 Layers Depending on Substrate Orientation.
Sonia Estrade 1 , I. Infante 2 , V. Laukhin 3 2 , F. Sanchez 2 , M. Wojcik 4 , E. Jedryka 4 , J. Fontcuberta 2 , J. Arbiol 1 , F. Peiro 1
1 , university of barcelona, Barcelona Spain, 2 , Institut de Ciència de Materials de Barcelona , Barcelona Spain, 3 , Institut Català de Investigació i Estudis Avançats, Barcelona Spain, 4 , Institute of Physics, Polish Academy of Sciences, Warszawa Poland
Show AbstractSome perovskite-type manganites, such as La2/3Ca1/3MnO3 (LCMO), are usually employed as electrodes in magnetic tunnel junctions (MTJ) in spin manipulation devices. Nevertheless, elastic strain due to lattice parameter mismatch, plastic strain relaxation, and deviations from stoichiometry through interdiffusion or segregation of the species at the heterostructure interface may affect the physical properties of the device. It has been observed that thin films of those materials used in MTJs exhibit a Curie temperature which is clearly bellow that of the bulk values, and that this behaviour depends on the growth direction of the layers. In the present work we show a comparative study of thin (about10 nm) LCMO layers simultaneously grown on (001) and (110) SrTiO3 (STO) substrates, by RF-sputtering. The structures are characterized through High Resolution Transmission Electron Microscopy (HRTEM) and Electron Energy Loss Spectroscopy (EELS); close attention is paid to the quality of the LCMO/STO interfaces, and the chemical homogeneity of the epitaxial layers. The high resolution XTEM images exhibit abrupt interfaces and no evidence of misfit dislocations across the examined region for both layer orientations. Quantitative EELS analysis reveals a significant variation of the Ca/Mn and La/Mn ratios along the layer for (110) oriented substrate sample, with much higher La signal near free surface, whereas no differences are detected in (001) sample. A shift towards lower energies of the Mn L2,3 peaks as well as a variation of the intensity ratio of these two peaks as the distance to the interface increases is observed, specially for the (110) sample, in good agreement with the proposed La enrichment near free surface for (110) sample. Integration ranges were chosen by quantification of LCMO bulk reference samples with controlled stoichiometry.XRD lattice parameters measurements have shown that, for the sample grown on (001) substrate, the layer is completely adapted while for sample grown on (110) substrate, the XRD measurements indicated a 5% of strain relaxation. As the partially relaxed (110) sample does not exhibit plastic deformation, it seems that stress accommodation has occurred via A cation migration. It has been usually reported that elastic strain accommodation in LCMO films occurs by 2+ valence cation migration in tensile strained films. Although 3+ valence cation migration is an unusual result, other authors have also reported an initial La enrichment as layer thickness increases up to 100 nm when analysing thick (410 nm) LSMO films. These results on thin films will be discussed in comparison with thicker films also grown on (001) and (110) SrTiO3 (STO) substrates in terms of the variation of cell volum, strain relaxation and magnetic behaviour.
9:00 PM - C17.16
The Atomic, Electronic and Defect Structure of the Dynamically Formed Cu2O/Cu Interfaces.
Xuetian Han 1 , Long Li 1 , John Pearson 2 , Judith Yang 1
1 Materials Science and Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Materials Science Divsion, Argonne National Laboratory , Argonne, Illinois, United States
Show AbstractClassical theories of oxidation assume uniform film growth with migrating ions, defects and charged species. Our previous work on Cu oxidation by in situ ultra high vacuum transmission electron microscope (UHV-TEM) demonstrated that oxide islands, not uniform film, form during the initial stages of oxidation where surface diffusion of oxygen is the primary mechanism of transport, nucleation and growth [1-3]. However, the detail of how the metal and oxygen atoms convert to oxide along the interface is missed in this simplistic description. To understand the kinetics of this transformation requires examining the dynamically formed metal/oxide interface at the nanometer scale and below. Also, the precise description of the interface will be directly correlated with electronic structure (ES) theoretical modeling of the interface, where the correct ES description of the interface will provide interface energies and the dynamic charge distribution across the interface needed for the potentials that will be used in molecular dynamic (MD) simulations of oxidation. Experimental determined interface structure is the critical first step of the theoretical model of oxidation mechanisms.The Cu2O/Cu interface was formed by oxidation of 500nm (001) Cu films on STO substrates at P(O2) =5 X10-4 torr at 350 °C and 750 °C where triangular and square-in-cross-section Cu2O islands formed with cube-on-cube orientation with respect to the Cu film, respectively. JEOL SMI-3050SE dual beam (DB) focused ion beam (FIB) instrument was utilized to select an oxide island, slice through it, and thin the interface. Details of the structure and oxidation states of the Cu2O/Cu interface are being probed by conventional TEM, high-resolution TEM (HREM) and electron energy loss spectrum (EELS). HREM observations from the oxidation of 350 °C revealed an interfacial zone (~2 nm thick). Within this transition zone it is found that the interplanar spacing parallel to Cu2O {110} decreases while that along Cu2O {100} increases apart from the Cu-O/Cu interface. Initial EELS investigations revealed an interfacial zone of 3 nm thickness where the oxidation states changed continuously from Cu0 to Cu+1, indicating the existence of metastable Cu oxides. Previously metastable copper oxides such as Cu4O, Cu8O, Cu16O, Cu64O were reported in 1980s [4]. Implication of these results on the oxidation kinetics will be discussed. The analysis of defect structure, including dislocation climb behavior in the vicinity of the interfacial zone can provide insights into the formation mechanism of these metastable Cu oxides.References[1]G. Zhou, and J.C. Yang, Applied Surface Science, 210, 165 (2003).[2]Yang, J.C., M.D. Bharadwaj, G.W. Zhou, and L. Tropia, Microscopy and Microanalysis, 7(6), 486(2001).[3]Yang, J.C., D. Evan, and L. Tropia, Applied physics letters, 81(2), 241(2002).[4] R. Guan, H. Hashimoto, and T. Yoshida, Acta Crystallographica, B40, 109 (1984)
9:00 PM - C17.17
Strain Analysis of Non-polar GaN Quantum Nanostructures from Quantitative High Resolution Electron Microscopy.
Catherine Bougerol 1 , Benoit Amstatt 2 , Sebastien Founta 1 2 , Henri Mariette 1 , Bruno Daudin 2
1 , CNRS/Néel Institut, Grenoble France, 2 , CEA/DRFMC, Grenoble France
Show AbstractThe efficiency of nitride based optoelectronic devices is limited, first of all by a huge amount of dislocations due to the lattice mismatch of AlN and GaN with the substrates available (SiC, Al2O3), but also by the very high piezoelectric constants of these materials and a spontaneous polarization appearing when the heterostructures are grown along the c-axis of the wurtzite-type structure (the most stable one). In order to reduce the latter effect which creates an electric field detrimental to the optical properties, we have grown, by Molecular Beam Epitaxy (MBE), GaN quantum nanostructures along two non-polar directions of the wurtzite structure, namely [11-20] and [1-100] (ref 1,2). Because of the well-known dependence of the band gap value, and therefore optical properties, on the strain state of the nanostructures, we have undertaken, at the atomic scale, a detailed and quantitative analysis of their structure and of their deformation state by high resolution electron microscopy. For both [11-20] and [1-100] growth directions, the quantum nanostructures present a strongly anisotropic morphology. The strain profile of the GaN dots and of the AlN layers separating successive GaN dots planes has been deduced by using the Geometrical Phase Method (ref 3). For QDs grown along [11-20], a relaxation of the strain from the bottom to the top of the plane is observed. Furthermore, dislocations observed in the [1-100] zone axis are consistent with a partially plastic relaxation mechanism in this orientation whereas the relaxation would be fully elastic in the [0001] orientation. These results show a good agreement with the deformation profiles of uncovered QDs obtained from Middle Energy Ion Scattering (MEIS) experiments that we have carried out on similar samples (ref 1). When grown along [1-100], QWs or QDs can be obtained depending on the AlN buffer layer strain state. In both cases, the [1-100] nanostructures are less high than [11-20] QDs and no significant strain variation between the bottom and the top was observed. Stacking faults are visible when the heterostructures are viewed along the [11-20] zone axis, but no misfit dislocations were observed. 1 : S. Founta, J. Coraux, D. Jalabert, C. Bougerol, F. Rol, H. Mariette, H. Renevier, B. Daudin, R.A. Oliver, C.J. Humphreys, T.C.Q. Noakes, P. Bailey, J. Appl. Phys. 101, 063541 (2007)2 : B. Amstatt, J. Renard, C. Bougerol, E. Bellet-Amalric, B. Gayral and B.Daudin, submitted to J. Applied Physics3 : M.J. Hytch, E. Snoeck, R. Kilaas, Ultramicroscopy 74, 131, (1998)
9:00 PM - C17.18
A Finite Element Inverse Problem Approach to the Identification of Defaults from TEM Data.
Denis Aubry 1
1 , Ecole Centrale Paris, Chatenay Malabry France
Show Abstract9:00 PM - C17.2
Growth and Characterization of TeO2+x Film.
Namrata Dewan 1 , Konepudy Sreenivas 1 , Vinay Gupta 1
1 Physics and Astrophysics, University of Delhi, Delhi, Delhi, India
Show Abstract9:00 PM - C17.3
A Simple and Effective Route to Annihilate Defects in Nanocrystalline SnO2 Thin Films Prepared by Pulsed Laser Deposition.
Zhiwen Chen 1 , C. M. Lawrence Wu 1 , Chan-Hung Shek 1 , Joseph K. L. Lai 1
1 Phys. & Materials Sci., City University of Hong Kong, Hong Kong China
Show AbstractThe microstructural defects of nanocrystalline SnO2 thin films prepared by pulsed laser deposition have been investigated using transmission electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. Defects inside nanocrystalline SnO2 thin films could be significantly reduced by annealing the SnO2 thin films at 300°C for 2h. High-resolution transmission electron microscopy showed that stacking faults and twins were annihilated upon annealing. In particular, the edges of the SnO2 nanoparticles demonstrated perfect lattices free of defects after annealing. Raman spectra also confirmed that annealing the specimen was almost defect-free. By using thermal annealing, defect-free nanocrystalline SnO2 thin films can be prepared in a simple and practical way, which holds promise for applications as transparent electrodes and solid-state gas sensors.
9:00 PM - C17.4
Optimal Noise Filter that Really Works at the Nanoscale.
Kazuo Ishizuka 1 , Paul Eilers 2 , Toshihiro Kogure 3
1 , HREM Research Inc., Higashimatsuyama Japan, 2 , Utrecht University, Utrecht Netherlands, 3 , University of Tokyo, Tokyo Japan
Show AbstractNoise filtering based on a Wiener filter or a background subtraction filter was discussed by Kilaas [1]. Here, we are thinking of a noise from non-periodic materials. Then, contributions from a noise and signal may be separated in Fourier space. The contribution from non-periodic materials, we call it a background, is estimated as a radial average of the Fourier transform of the image by assuming that the background varies slowly. Then, the estimated background is subtracted from intensity of a Fourier transform of an observed image in a Wiener filter or from amplitude in a background subtraction filter. Here, we set a filter to zero, when an estimated background is stronger than an observed Fourier transform. This is a mechanism of noise suppression. However, the radial average background does not work for non-ideal crystals, such as nano-crystals and cylindrical crystals, which only show translation symmetry within a nanometer scale. This is because the signal from such materials appears at equidistant from the origin in Fourier transform, and it becomes difficult to discriminate a noise from a signal when estimating the background.
We propose here two techniques that make these filters applicable even for such materials with nanoscale periodicity. Firstly, we developed a novel approach to estimate a smoothed two-dimensional background based on P-spline fitting [2]. A filtered image using a two-dimensional background estimated from the whole image substantially improves a visibility of nanoscale materials. However, an optimal noise filtering does not result for nanoscale materials, when we treat the whole image at the same time. This is because nanoscale materials usually orient randomly, and thus a local Fourier transform is different from an average Fourier transform calculated from the whole image. Thus, secondary, we developed a procedure to use a set of two-dimensional backgrounds estimated from different small areas, say 64x64 pixels. Then, the difference between the original image and its filtered image becomes featureless. The filters based on this local 2D background are also effective for cylindrical crystals.
References
[1] R. Kilaas, J. Microscopy 190 (1997) 45-51.
[2] P.H.C. Eilers et al, Computational Statistics and Data Analysis 50 (2006) 61-76.
9:00 PM - C17.6
Quantitative Characterization of Carbon Nanotube Composites.
Peter Lillehei 1 , Jae-Woo Kim 2 , Luke Gibbons 2 , Cheol Park 2 , Emilie Siochi 1
1 Advanced Materials and Processing Branch, NASA LaRC, Hampton, Virginia, United States, 2 , National Institute of Aerospace, Hampton, Virginia, United States
Show AbstractRevolutionary design concepts in future aerospace systems will depend on the utilization of materials with extraordinary properties, permitting a significant reduction of component mass and size. Single walled carbon nanotubes (SWNTs) are expected to enable this paradigm shift in design concepts due to their remarkable structural and multifunctional properties. The most important aspect in translating the exceptional properties of SWNTs into functional polymer composites is their effective dispersion in the host matrix. In order to realize the potential benefits of nano-composites, a method to consistently characterize the dispersion of the SWNT network within the polymer matrix must be established. The measured dispersion of SWNT must subsequently be correlated to the known properties of the nano-composite. In this talk, we will present the framework for a systematic study to assess SWNT dispersion in polymer matrices and a quantification method of SWNT dispersion through simple data processing using a Fast Fourier-Transform. In order to quantify the dispersion of the SWNTs it is necessary to image the nanotube network within the polymer matrix using a new imaging protocol. This new method allows one to see the SWNT network deep within the composite through the polymer matrix as if it is invisible. Using this method, it is possible to generate three-dimensional images of the SWNT network to aid construction of three-dimensional models.
9:00 PM - C17.7
Chemical Analysis of As near Si Defects.
Keith Thompson 1 , David Larson 1 , Roger Alvis 1 , Thomas Kelly 1
1 , Imago Scientific, Madison, Wisconsin, United States
Show AbstractThe chemical composition of defects in Si after ion implantation and annealing have been characterized by Transmission Electron Microscopy (TEM), Local Electrode Atom Probe (LEAP) and Secondary Ion Mass Spectroscopy (SIMS). TEM imaging of implantation of <100> Si by As+ ions at 50 keV, followed by annealing, showed a layer of spheroidal defects 5-10 nm in diameter at a depth of 35 nm below the wafer surface. SIMS analysis and 1D LEAP both indicate a perturbation in the As concentration, which is associated with the end-of-range damage. Further annealing removes the end-of-range damage and forms dislocation loops with a {111} habit. LEAP revealed that both defect types are As rich and surrounded by As atmospheres. The spheroidal defects contained 4.8 atomic % As over an As background of 1.2 at.%, and a defect binding energy of 0.1 eV. The dislocation loops imaged in the atom probe had an As peak concentration of 3.7 at.% over a 0.8 at.% As background, and a defect binding energy of 0.17 eV. The As atmospheres around the spheroidal defects and dislocation loops are mathematically described by a numerical model: As(r) = 4.8 exp(-0.86r) and As(r) = 3.7 exp(-0.8r) , respectively.
9:00 PM - C17.8
Ab-initio Structure Determination of Microcrystalline Materials using Correlated Methods, with Mg10Ir19B16 as an Example.
Qiang Xu 1
1 Nano Science, Delft Univ.of Tech., Delft Netherlands
Show Abstract9:00 PM - C17.9
Partial Structural Transitions in GaN during CuO Calcination at 500 C.
Peter Moeck 1 , Chunfei Li 1 , Rolf Erni 2 3 , Nigel Browning 2 , Amita Gupta 1 4 , K Venkat Rao 4
1 Physics, Portland State University, Portland, Oregon, United States, 2 Chemical Engineering and Materials Science, University of California at Davis, Davis, California, United States, 3 EMAT Research Group, University of Antwerp, Antwerp Belgium, 4 Materials Science, Royal Institute of Technology, Stockholm Sweden
Show AbstractC18: Poster Session: HOLO
Session Chairs
Thursday AM, November 29, 2007
Exhibition Hall D (Hynes)
9:00 PM - C18.1
HREM and Electron Holographic Characterization of Au Nano Particles Deposited on TiC Low Index Planes.
Satoshi Ichikawa 1 , Seiji Takeda 2 , Tomoki Akita 3 , Koji Tanaka 3 , Masanori Kohyama 3
1 Organization for the Promotion of Research on Nanoscience and Nanotechnology, Osaka University, Toyonaka, Osaka, Japan, 2 Department of Physics, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan, 3 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka, Japan
Show AbstractGold nano-hetero catalysts exhibit the support dependence and the size dependence. In the previous study, we found that the mean inner potential of Au nano particles supported on TiO2 depends on the size of Au particles and also the stoichiometry at the interfaces. The stoichiometry at the nano-hetero interface affects the electronic structure of Au particles and should have a close relation with the mechanism of the catalytic activities in particular. It is important for the material design of gold catalysts to control not only the size distribution and but also the stoichiometry at the interfaces between gold and support material. The crystal structure of TiC is NaCl structure which is considered to be good matching with Au at the interface and there are both polar planes and non-polar planes in low index planes of TiC.We made Au/TiC nano-hetero model catalysts by vacuum evaporation method (VE) and characterized the interface structure of Au/TiC nano catalysts using high-resolution electron microscopy and electron holography.In the case of Au nano particles supported on TiC (001) plane which is the non-polar plane, Au particles with the size below 2nm have an orientation relationship as (001)[010]Au//(001)[010]TiC. Although the mismatch of the lattice constant between Au and TiC is no less than about 6%, it was found that the interfaces between Au particles and TiC supports have coherent and the strain is relaxed both Au particles and TiC supports. In the case of Au nano particles supported on TiC (111) plane which is the polar plane, the orientation relationship as (1-11)[110]Au//(-111)[110]TiC was observed with high frequency.The mean inner potential of the Au nano particles on TiC(001) and (111) planes also exhibit the size dependence. When the size of Au particle is smaller than 3nm, the mean inner potential of Au increased gradually as the size decreases. When the size is smaller than 2nm, the mean inner potential of the Au is over 30V. This tendency is similar to that of Au/TiO2 catalysts prepared by VE which is considered to have Ti rich interface. Au nano particles should be deposited on Ti rich planes of both TiC(001) and TiC(111) planes.
9:00 PM - C18.2
WITHDRAWN 11/19/07 Charging of Dielectric Materials under Focused Ion Beam (FIB) Irradiation.
Shay Yogev 1 2 , Michele Molotskii 1 , Alex Schwarzman 1 , Jacob Levin 2 , Yossi Rosenwaks 1
1 Dept. of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel-Aviv University, Tel-Aviv Israel, 2 , Applied Materials, Rehovot Israel
Show Abstract9:00 PM - C18.3
Off-Axis Electron Holography of Self-Assembled Co Nanoparticle Rings.
Takeshi Kasama 1 , Rafal Dunin-Borkowski 1 2 , Michael Scheinfein 3 , Steven Tripp 4 , Alexander Wei 4
1 Dept. of Materials Science, Univ. of Cambridge, Cambridge United Kingdom, 2 Center for Electron Nanoscopy, Technical Univ. of Denmark, Kongens Lyngby Denmark, 3 Dept. of Physics, Simon Fraser Univ., Burnaby, British Columbia, Canada, 4 Dept. of Chemistry, Purdue Univ., West Lafayette, Indiana, United States
Show AbstractThe development of a full understanding of the magnetic properties of closely-spaced ferromagnetic nanocrystals is of great importance for the development of high-density magnetic information storage and magnetic random access memory materials. Ring-shaped elements are of particular interest because they can form magnetic states, which exhibit flux closure (FC) and cannot be supported in disk-shaped elements of similar size [1]. Here, we use off-axis electron holography and micromagnetic simulations to study FC states in self-assembled Co nanoparticle rings that contain between four and eleven 20-nm-diameter crystals. Holograms were obtained at room temperature in zero-field conditions after applying chosen magnetic fields to the samples in situ in the electron microscope by partially exciting the conventional microscope objective lens. Mean inner potential contributions to the phase shift were determined by turning the samples over [2], and subsequently subtracted from each recorded phase image to obtain magnetic induction maps. Our results show that most nanoparticle rings form FC remanent states, with larger rings occasionally exhibiting onion-like states. Although the chiralities (the directions of magnetization) of the FC states are determined by the shapes, sizes and positions of the constituent nanoparticles, reproducible magnetization reversal of each ring can be achieved by using an out-of-plane magnetic field of between 1600 and 2500 Oe. Micromagnetic simulations are used to understand the magnetization reversal mechanism, which is highly complex.References[1] Zhu, J-G, Zheng Y. & Prinz, G.A. (2000) J. Appl. Phys. 87, 6668-6673.[2] Dunin-Borkowski, R.E., McCartney M.R. & Smith, D.J. (2003) In Volume 3 of the “Encyclopedia of Nanoscience and Nanotechnology”, edited by H.S. Nalwa, pp. 41-100 (American Scientific Publishers, Stevenson Ranch, California).
Symposium Organizers
Etienne Snoeck CEMES-CNRS
Rafal Dunin-Borkowski Technical University of Denmark
Johan Verbeeck University of Antwerp
Ulrich Dahmen Lawrence Berkeley National Laboratory
C19: Grand Challenges for Electron Microscopy IV
Session Chairs
Thursday AM, November 29, 2007
Back Bay D (Sheraton)
9:30 AM - *C19.1
Automated Electron Nanocrystallography.
John Spence 1 , Joe McKeown 2 , Haifeng He 3 , Jinsong Wu 4
1 Physics, Arizona State University, Tempe, Arizona, United States, 2 Physics, Arizona State University, Tempe, Arizona, United States, 3 NCEM, LBNL, Berkeley, California, United States, 4 NUANCE, Northwestern University, Evanston, Illinois, United States
Show AbstractAn urgent need exists for rapid methods of solving the host of new nanocrystalline structures which are being synthesised, for example in support of combinatorial material synthesis. This work aims to provide an automated method of solving structures in real time, and to present a 3D charge-density map at the electron microscope. (Newly synthesised nanocrystals prepared in-situ using environmental stages would also benefit from this capability). Much progress has been made (for example with catalyst particles) by combining HREM images with powder X-ray and TED patterns (1). Recent dramatic advances in solving structures by the electron precession method will also be reviewed (2). This approach works best for micron-sized areas of layer structures, and, as first shown by Blackman, provides some reduction in multiple-scattering artifacts. We discuss the possibility of using a kinematic convergent beam method (3), combined with a new STEM mode for particle alignment and search, to solve smaller crystals with less symmetry (4). This approach solves the dynamic range problem of TED by allowing the central beam to be recorded with others so that data is normalised correctly, and in addition allows use of the smallest STEM probes. The central pixel of each CBED disk nevertheless provides the same information as an SAD pattern. One may switch conveniently to STEM imaging mode to bring the particle back onto the optic axis. The distribution of intensity across the disks gives an indication of the severity of multiple scattering, independent of sample structure. The optimum strategy for data collection is reviewed, and preliminary results presented for MgO cubes. By not assuming knowledge of their symmetry, this test then applies to any nanoparticle. The thickness of the cubes is exactly known, so that multiple scattering artifacts can be estimated from simulation. The relatively poor quality of electron diffraction data makes it a good candidate for the new charge-flipping method for solving the phase problem. Examples of this iterative method, which does not require knowledge of the space-group, will be given as applied electron and powder X-ray diffraction (5) data.References.1. S. Che et al. Nature 429, 281 (2004)2. Ultramic Vol 107, issue 6 is devoted to this topic.3. J. Wu and J. Spence. Micros and Microan. 9, p.428 (2003).4. H. He and J. Spence. Submitted to Micron. 2007. H. He and C. Nelson. Ultramic 107, 340 (2007)5. J. Wu, J. Spence, M.O'Keeffe and K. Leinenweber. Nature Materials. 5, 647 (2006)Supported by DOE award DE-FG03-02ER45996
C20: HRTEM and Quantitative Comparison of Experiment and Theory I
Session Chairs
C. Boothroyd
M. Hytch
A. Rosenauer
Thursday PM, November 29, 2007
Back Bay D (Sheraton)
10:15 AM - **C20.1
Quantitative Estimation of Unknown Structure Parameters from Electron Microscopy Images.
Sandra Van Aert 1 , Sara Bals 1 , Jo Verbeeck 1 , Arnold-Jan den Dekker 2 , Dirk Van Dyck 1 , Gustaaf Van Tendeloo 1
1 , Electron Microscopy for Materials Science (EMAT) - University of Antwerp, Antwerp Belgium, 2 , Delft Center for Systems and Control (DCSC) - Delft University of Technology, Delft Netherlands
Show AbstractIn principle, electron microscopy can provide accurate and precise values for the unknown structure parameters of the material under study. For example, atom column positions can be determined with an accuracy and precision that is orders of magnitude better than the resolution of the microscope. This requires, however, a quantitative, model-based method. In our opinion, the maximum likelihood (ML) method is the most appropriate one since it has optimal statistical properties. This contribution aims to explain the basic principles of the method and to demonstrate its practical applicability and usefulness by some recent experimental examples.The key to successful application of the ML method is the availability of the joint probability density function of the observations (the image pixel values) and its dependence on the structure parameters to be estimated. This dependence is established by the availability of an expectation model, which describes the expectation values of the observations. In fact, the expectation model includes all the ingredients needed to perform a computer simulation of the images and it is parametric in the quantities of interest, such as the atom column positions. A thus parameterized joint probability density function can be used to obtain ML estimates of the parameters. A comprehensive report of this model-based method can be found in [1-2].In one of the experimental examples which will be shown, the atom column positions of a new ceramic compound, Bi4Mn1/3W2/3O8Cl, have been determined with a precision in the picometer range [3]. Therefore, the phase of a reconstructed exit wave has been used as a starting point for quantitative refinement of the atom column positions. Furthermore, a good agreement has been found when comparing these results with X-ray powder diffraction data. It is also observed that projected distances beyond the information limit of the microscope (110 pm) can be determined with picometer range precision. Another recent example demonstrates the present possibilities for quantitative interface characterization. A SrTiO3/LaAlO3 multilayer system has been quantified from a high angular annular dark field scanning transmission electron microscopy image. Although the intensity difference between the La and Sr atom columns is visually apparent, the proposed model-based method is used to distinguish the Ti and the Al atom columns [4].[1] Ultramicroscopy 104 (2005): 83-106.[2] Ultramicroscopy 104 (2005):107-125.[3] Physical Review Letters 96 (2006):096106-1 - 096106-4.[4] Nature Materials 5 (2006):556-560.S. Van Aert and S. Bals gratefully acknowledge the financial support of the Fund for Scientific Research – Flanders. The authors acknowledge financial support form the European Union under the Framework 6 program under a contract for an Integrated Infrastructure Initiative. Reference 026019 ESTEEM.
10:45 AM - C20.2
Mapping Strain at Nanometre Spatial Resolution in MOSFET Transistors by Quantitative High-resolution Electron Microscopy.
Florian Hue 1 , Martin Hytch 1 , Florent Houdellier 1 , Hugo Bender 2 , Alain Claverie 1
1 CEMES, CNRS, Toulouse France, 2 , IMEC, Leuven Belgium
Show AbstractStrain improves performance in MOSFET devices by increasing carrier mobility and by reducing inter-valley scattering. To fully quantify the relationship between mobility and strain and to evaluate the process techniques for introducing strain in devices, there is a need for accurate strain measurement techniques at the nanoscale. We will show how strains can be mapped in real devices using high-resolution transmission electron microscopy (HRTEM) combined with geometric phase analysis (GPA). Thin specimens are prepared by focussed ion beam (FIB) to be uniformly thick (about 80 nm). Particular care is taken to reduce bending of the lamella and the thickness of surface damage layers. Observations are carried out using the SACTEM-Toulouse, a Tecnai (FEI) 200kV TEM equipped with objective lens aberration corrector (CEOS) and 2k CCD camera (Gatan). Image analysis is performed using DigitalMicrograph (Gatan) and GPA Phase software (HREM Research). Corrections are applied for geometrical distortions due to the projector lenses and the fibre-optic array of the CCD camera. The components of the 2D strain tensor will be mapped out with nanometre resolution across a MOSFET device including the source, drain and channel region. The experimental results will be compared with finite-element modelling to evaluate the impact of thin foil relaxation on strain measurements. Finally, we will discuss implications for device performance in terms of the strain distribution in the channel.
11:30 AM - **C20.3
Image Contrast in Quantitative HREM.
Chris Boothroyd 1
1 , IMRE, Singapore Singapore
Show Abstract12:00 PM - **C20.4
Measuring Stress and Strain in Nanostructures by Quantitative High-resolution Electron Microscopy.
Martin Hytch 1
1 , CEMES-CNRS, Toulouse France
Show AbstractWe will present the current state of the art in strain mapping at the nanoscale by a combination of high-resolution electron microscopy (HRTEM) and geometric phase analysis (GPA). We will show how the 2-dimensional strain tensor can be measured to an accuracy of 0.1% across relatively large areas of specimen (100s nm) with nanometer spatial resolution. The different steps of the process will be described, including calibrations and optimum experimental conditions. For example, we will show how geometric distortions from the microscope lenses and detector system can be calibrated and removed. We will also show how finite-element modeling (FEM) coupled with full atomistic image simulations taking into account the 3-dimensional strain distribution, can be used to address the problem of relaxation of the thin samples used for microscopy observations. The conversion of strains into stresses will also be discussed along with current limitations and future developments. In particular, we will show the considerable advantages that can be obtained by using the latest generation of electron microscopes equipped with aberration correctors, such as the SACTEM-Toulouse, and preparing samples with focused ion beams (FIB). Examples will be given from studies of nanosystems for which strain is particularly important, such as semiconductor thin films, MOSFET transistors using strained-silicon technology, and strained nanocrystals used in plasmonics.
12:30 PM - **C20.5
Recent Progress Towards a Quantitative Evaluation of HRTEM Experiments.
Andreas Thust 1 , Juri Barthel 1 , Lothar Houben 1 , Chunlin Jia 1 , Markus Lentzen 1 , Karsten Tillmann 1
1 Institute of Solid State Physics, Forschungszentrum Juelich, Juelich Germany
Show AbstractC21: HRTEM and Quantitative Comparison of Experiment and Theory II
Session Chairs
Thursday PM, November 29, 2007
Back Bay D (Sheraton)
2:30 PM - **C21.1
On the Value of Deep Sub-Angstrom Resolution for Materials Science Applications.
C. Kisielowski 1
1 LBNL, National Center for Electron Microscopy, Berkeley, California, United States
Show Abstract3:00 PM - **C21.2
Ab-inito Methods as Tools for Quantitative High-Resolution Transmission Electron Microscopy.
Andreas Rosenauer 1 , Marco Schowalter 1 , Knut Mueller 1 , John Titantah 2 , Dirk Lamoen 2 , Peer Kruse 3 , Dagmar Gerthsen 3
1 , University of Bremen, Bremen Germany, 2 , Universiteit Antwerpen, Antwerpen Belgium, 3 , Universität Karlsruhe, Karlsruhe Germany
Show AbstractHigh-resolution transmission electron microscopy (HRTEM) is chemically sensitive as the scattering probability depends on the atomic number. However, strong interaction of an electron beam with matter gives rise to dynamical diffraction so that quantitative interpretation requires comparison with e.g. Multislice or Bloch wave simulations. These methods base on atomic scattering amplitudes which need to be known accurately. In the first Born approximation, atomic scattering amplitudes are obtained by a Fourier transform of the scattering Coulomb potential, conventionally computed in the isolated atom approximation. However, this is not sufficient in special cases. For low-index reflections, redistribution of electrons in chemical bonds leads to significant deviations. As an example, chemically sensitive 002 reflections in sphalerite type materials are used for measuring chemical composition in ternary semiconductor nanostructures from dark-field or two-beam lattice fringe images with the CELFA-method. In our contribution, we will show that redistribution of electrons can accurately be taken into account with DFT methods, leading to a shift of measured In-concentrations of more than 20 %. Chemical composition can also be measured at high spatial resolution by electron holography. The mean inner crystal Coulomb potential (MIP) causes a phase shift of the undiffracted electron beam, directly correlated with specimen thickness, chemical composition averaged along the electron beam direction, and volume of crystal unit cells. Measurement of specimen thickness or composition with electron holography requires accurate values of the MIP. We will present computation of MIPs for a variety of technological important III-V, II-VI, Si and Ge semicondutors with a DFT method, in comparison with experimental measurements using electron holography. Another scarcely known material parameter is the Debye-Waller (DW) temperature factor. Together with structure factors, DW factors determine intensities of reflections in diffraction patterns and diffractograms of HRTEM images. We have computed DW factors for a variety of semiconductors with DFT. In rare cases (e.g. for GaAs), where accurate experimental data are available, our theoretical results are compared with measured DW factors. These results are also important for simulation of Z-contrast scanning TEM experiments. The electron intensity on an HAADF detector is mainly caused by thermal diffuse scattering. Quantitative interpretation requires comparison with simulations which can be performed with our STEMsim program using the frozen lattice approximation or absorptive potentials together with the Multislice or Bloch-wave methods. Density functional theory methods yield dynamical matrices which we use to generate realistic displacement models for the frozen phonon method, taking into account correlation effects which are neglected in the Einstein approximation.
C22: Mapping of Magnetic and Electric Fields and Electron Holography
Session Chairs
Thursday PM, November 29, 2007
Back Bay D (Sheraton)
4:00 PM - **C22.1
Nanoscale Imaging of Electrostatic and Magnetic Fields by Off-axis Electron Holography.
Martha McCartney 1
1 Physics, Arizona State University, Tempe, Arizona, United States
Show AbstractElectron holography allows electrostatic and magnetic fields to be characterized down to the nanometer scale. The most common experimental arrangement is off-axis electron holography, where the hologram is formed by overlapping part of the electron wave that has traveled through vacuum with the sample wave, using a positively charged electrostatic biprism in the selected-area aperture plane. The Philips CM200-FEG instrument at ASU is equipped with an additional ‘Lorentz’ mini-lens below the lower pole-piece of the objective lens, allowing magnetic samples to be examined in a field-free environment at magnifications of up to 70kX with the objective lens turned off. This electron-optical arrangement is also advantageous in terms of providing a convenient field-of-view for imaging dopant depletion regions in current and next generation semiconductor devices. Electric potentials associated with electrically active heterojunctions have also been analyzed using this technique.The most significant contributions of TEM techniques derive from their inherent localized and two-dimensional imaging capabilities. Medium resolution electron holography has been shown to be capable, both in principle, and in practice, of providing high resolution (~3nm), high sensitivity (0.1V) 2-D maps of electrostatic potential in semiconductor devices. Such two-dimensional potential maps of transistor structures at the nanometer scale provide essential information that is needed for accurate device modeling by semiconductor engineers.Magnetic applications of electron holography include imaging of superconducting fluxons, and characterization of e-beam-lithographed magnetic nanostructures. The potential applications of ferromagnetic nanostructures for high density recording devices and magnetic sensors have stimulated much interest in their micromagnetic states. Reduction in the lateral dimensions of magnetic elements induces unexpected complications in magnetization states and reversal processes. Correlation of the magnetic response of nanostructures with their size and shape is an issue of central importance that has been actively investigated in recent years. As element dimensions decrease, the magnetic microstructure is expected to consist of simple domain patterns rather than the multi-domain patterns present in larger structures. Off-axis electron holography can be used to determine remanent states and to follow hysteresis cycles in situ with spatial resolutions on the order of 5 nm or better.
4:30 PM - **C22.2
Quantitative Atomic Resolution Electron Holography: Modeling and Experiment.
Michael Lehmann 1
1 Institut fuer Optik und Atomare Physik, Technische Universitaet Berlin, Berlin Germany
Show AbstractBecause of the inverse problem of scattering, only reliable computer simulations of dynamical scattering and imaging of the electron wave in forward-propagation allows the determination of the atomic structure at least in projection by means of high-resolution transmission electron microscopy (HRTEM). In the past, qualitative image matching has successfully solved many structure and interface problems. However, not only for solving materials related questions but also for understanding the physics of scattering and imaging, it is necessary to have a modeling, which sufficiently describes the interaction of the electron wave with the object such that also a good quantitative match is achieved. Here, a still unsolved problem is the fact that the experimental image contrast is typically a factor of 3 to 5 (“Stobbs-Factor”) less than predicted by image simulations. Many possible causes for this discrepancy are still in discussion such as insufficient knowledge of scattering factors, of imaging by the objective lens, and of registration by the CCD-camera. No single cause can currently explain the contrast mismatch, although a combination of many factors could. Additionally, subtle effects like migration of adatoms, excitations of surface oscillations, and phonon losses are discussed, which would destroy coherence due to energy transfer >10^-15 eV not discernible by usual energy filters. The concept of most image simulation programs to discard ("absorb") inelastically scattered electrons can be related to the formation of an off-axis electron hologram: By interfering the object-modulated wave with an unmodulated reference wave, only these electrons are contributing to the interference fringes, which are coherent to the reference wave. This implies that these electrons have only been elastically scattered hence they have not changed the quantum mechanical state of the object. Electrons, which have been inelastically scattered (even phonon losses), are discarded before contributing to the interference fringe. Consequently, the reconstructed and aberration-corrected object exit-wave is almost perfectly zero-loss energy filtered, and the process of non-considering inelastically scattered electrons is comparable to most image simulation programs. Experimental finding suggest that electron holography provides a much better dataset than conventional imaging. Since only scattering factors are used, conventional image simulation programs do not take into account internal electrical fields, which are important e.g. in ferroelectrics. An approach for considering these fields is the application of Density Functional Theory for calculating the electron charge density distribution, from which the potential distribution is determined by application of the Poisson equation. These subtle effects can be observed by electron holography.The close cooperation with Prof. Lichte's group at the Triebenberg Laboratory of the TU Dresden is gratefully acknowledged.
5:00 PM - **C22.3
3-D Dopant Profiling Using Holographic Tomography.
Alison Harrison 1 , Paul Midgley 2 , Rafal Dunin-Borkowski 3
1 London Centre for Nanotechnology at Materials Science, Imperial College London, London United Kingdom, 2 Materials Science, University of Cambridge, Cambridge United Kingdom, 3 Center for Electron Nanoscopy, Technical University of Denmark, Kongens Lyngby Denmark
Show AbstractDopant profiling of semiconductor devices using off-axis electron holography has become more widely used in recent years, with many examples of the successful visualisation of dopant-related electrostatic potentials. Electrically biased holography experiments have also been carried out in-situ in the electron microscope in order to ensure that the device is examined under conditions that are as close to working conditions as possible [1]. Although electron holography promises to provide fully quantitative results, the measured potential is a two-dimensional projection along the electron beam direction through the semiconductor membrane thickness, thereby including all surface potential effects. These surface contributions are of particular interest when using electron holography to examine semiconductor device structures because focused ion beam (FIB) milling is required for site-specific membrane preparation of current generations of devices. This preparation technique is known to generate substantial amorphous and electrically altered surface layers. A three-dimensional characterisation of the electrostatic potential within a transmission electron microscope (TEM) membrane is required to reveal such surface effects, information which can be obtained through the use of electron tomography [2]. Electron tomography involves the use of a high angle tilt series of images to reconstruct three-dimensional information about a sample, and has been applied successfully to the examination of small particles such as catalysts. By using a custom-built electrical biasing holder [3], electron tomography and electron holography experiments have been combined to investigate the three-dimensional potential distribution in semiconductor devices. Experimental results obtained from a range of device structures including MOSFETs and diodes will be presented. [1] A. C. Twitchett et al., J. Microsc. 214, 3, 287-296 (2004)[2] A. C. Twitchett-Harrison et al., Nanoletters, in press[3] R. E. Dunin-Borkowski et al., Paper presented at Microscopy and Microanalysis (2004)
5:30 PM - C22.4
Lorentz Microscopy Study of Domain Wall Motion During Magnetization Process.
Aurelien Masseboeuf 1 , Christophe Gatel 2 , Alain Marty 1 , Pascale Bayle-Guillemaud 1
1 DRFMC/SP2M/LEMMA, CEA-Grenoble, Grenoble France, 2 CEMES, CNRS, Toulouse France
Show AbstractThis paper will present investigations of magnetization configuration evolution during in-situ processes in different materials with planar and perpendicular magnetic anisotropy. Transmission electron microscopy has been used to performed magnetic imaging and in particular Lorentz Transmission Electron Microscopy (LTEM) which is a powerful tool to observe magnetization evolution in thin magnetic layers. The technique is sensitive to magnetic induction perpendicular to the beam and different modes give access to a mapping of magnetic induction distribution with a resolution of the order of ten nanometers. Differential Phase Contrast (DPC) and the phase imaging using Transport of Intensity Equation (TIE) are multiple acquisition series techniques which are complementary for quantitative Lorentz Microscopy. LTEM has been carried out on a JEOL 3010 and a FEI Titan 300kV (equipped with a dedicated Lorentz Lens). In one hand we present the switching process and the domain wall motion in continuous thin foils of CoFe (coupled to antiferromagnetic NiMn) and the observation of this phenomenon in dedicated lithographed nanostructures. We’ll then present detailed mapping of out of plane magnetic anisotropy thin film of ordered FePt in different geometries (cross section and plane view). We’ll show how the magnetization process can be described in terms of magnetic dimensions and chirality of domain wall in FePd alloys. All this studies based on phase reconstruction are completed with Lorentz image simulations for validation and analysis of the observed contrasts.
5:45 PM - C22.5
Interlayer Exchange Coupling in Single Crystal Magnetic Tunnel Junctions Studied by Electron Holography.
Etienne Snoeck 1 , Gerard BenAssayag 1 , Coriolan Tiusan 2 , Fanny Greullet 2 , Alain Schuhl 3
1 CEMES, CNRS, Toulouse France, 2 , Université Henri Poincaré-CNRS, Nancy France, 3 SPINTEC, CEA-CNRS, Grenoble France
Show AbstractAntiferromagnetic coupling between two ferromagnetic layers separated by a thin insulating barrier was previoulsy evidenced at the macroscopic scale by using VSM magnetometry on Fe/MgO/Fe/MgO(001) epitaxial magnetic tunnel junctions. We present here nanoscopic holographic measurements showing local evidence of this interlayer exchange coupling (IEC). The strength of IEC have been then been modulated by irradiating the samples with N+ ions at 150keV. For tuning the IEC coupling nature and strength we control the Fe/MgO interface quality by playing with the irradiation dose. In non-irradiated samples the coupling is antiferromagnetic with a dominant bilinear term. A gradual increase of the bilinear and the biquadratic coupling has been measured when the ion dose increases with a significant increase of the biquadratic term for larger doses. The biquadratic coupling is explained here by the superposition between antiferromagnetic and ferromagnetic contributions. Finally, for the larger doses used in our experiments, the net coupling becomes purely ferromagnetic, corresponding to a strong structural intermixing of the MgO barrier with the adjacent Fe layers