Atomic-resolution spectroscopic imaging in a new generation of electron microscopes is now capable of unraveling bonding details at buried interfaces and clusters, providing both physical and electronic structure information at the Angstrom-level. The sensitivity and resolution can extend to imaging single dopant atoms or vacancies in their native environments. The thousand-fold increase in electron energy loss spectroscopy (EELS) mapping speeds over conventional microscopes allows us to collect data from millions of spectra. Experiments that were previously unthinkable, requiring days of microscope time can now be performed in under an hour. This includes measuring monolayer-level segregation in statistically meaningful ensembles of catalyst nanoparticles,chemical images of defects, and oxygen-bonding maps in complex oxide heterostructures. For core-loss spectroscopy and the proper collection geometry, EELS has achieved atomic-resolution and the spatial resolution is limited by the allowable dose set by radiation limits. By mapping the evanescent electric field of the swift electron to a pulse of virtual photons, the different sensitivities of electrons and x-rays to elastic and inelastic scattering mechanisms and contrast can be compared, and optimal regimes for both methods can be identified. For instance, in radiation-sensitive samples, x-rays tend to be more efficient for inelastic spectroscopies and electrons are more efficient for elastic imaging.

Solid solutions with perovskite-type structure are used as cathodes in solid oxide fuel cells at elevated temperature. During operation of the SOFC the electrodes may undergo severe chemical and microstructural changes which cause de-activation or activation - depending on the electrical load. Here we present a detailed study on the surface processes of LSM (= (La,Sr)MnO3) and LSCrM (= (La,Sr)(Cr,Mn)O3) [1] on zirconia solid electrolyte, studied by µ-ESCA (beamline at ELETTRA synchrotron), HRESEM and ToF-SIMS under operation conditions (high temperature, electrochemical polarization, decreased oxygen partial pressure). During operation the chemical components of the thin film model electrode system (prepared by pulsed laser deposition, PLD) show high mobility and redistribute as a function of the electrochemical polarization. Under certain conditions, the surface composition can be controlled reversibly by applying either cathodic or anodic potentials. These surface kinetic phenomena and the chemical information obtained from the analytical techniques are imaged in situ, and the results have been used to derive microscopic models for electrode activation and de-activation. The quality of the results depends strongly on the preparation of chemically and microstructurally well defined model electrodes in thin film geometry. The perspectives and limitations of the combined use of the analytical tools are discussed. References: A.-K. Huber, M. Falk, M. Rohnke, B. Luerssen, L. Gregoratti, D. Matteo, J. Janek, In situ study of electrochemical activation and surface segregation of the SOFC electrode material La0.8Sr0.25Cr0,5Mn0,5O3-δ, Phys. Chem. Chem. Phys. 14 (2012) 751-758.

The anomalous conductivity at the interface between nominally-insulating polar and non-polar materials, such as LaAlO3/SrTiO3 (LAO/STO), has sparked considerable debate within the oxide community and given rise to multiple hypotheses explaining both the conductivity and the resolution of the polar discontinuity. A possibility that has been suggested is the unintentional doping of either the film or the substrate, as might be caused by imbalanced cation diffusion across the interface. For instance, there have been indications that the extent of the A- and B-site cation interdiffusion are uneven in the LAO/STO interfaces grown by some groups. The interface between similarly structured LaCrO3 (LCO) and STO is investigated to provide additional insight. Contrary to the case of LAO/STO, the LCO/STO system appears to be thoroughly insulating. The extent of the intermixing at the interface is examined using a combination of high resolution Rutherford backscattering (HRRBS) and cross-sectional electron microscopy, including aberration-corrected high resolution TEM, probe-corrected HAADF-STEM, x-ray energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS), and chromaticaberration-corrected energy filtered TEM (EFTEM) imaging, both for a range of La/Cr stoichiometries and film thicknesses from 5-125 unit cells. Cross-sectional TEM/STEM provides a far more local measurement than RBS, illuminating the effects of interfacial non-uniformity, the presence of which appears to affect the average interface width, particularly for thicker LCO films. Aberration-corrected HAADF-STEM enables the formation of a probe fine enough to sufficiently separate intensities from the A- and B-sites, allowing a comparison of the diffusion widths for the two cation sites. LCO/STO is better suited to such analysis than, e.g., LAO/STO, as both the A- and B-site cations are heavier in the film than the substrate. HAADF-STEM analysis suggests roughly equal diffusion for both cation sites, with an interface width that generally increases with film thickness (or growth time). Several analysis methods are considered and,for instance, the full width at a tenth maximum (FWTM) for best-fit curves is for no film thickness less than a few unit cells A- and B-sites in. For all approaches, both the shapes and widths of the profiles are very similar, suggesting even diffusion of A- and B-site cations, with EDS, EELS, and EFTEM confirming similar trends. The interface width trends are in rough qualitative agreement with HRRBS, but HRRBS is more sensitive to small concentrations La than HAADF-STEM, EELS, or EDS, and shows that there are long diffusion tails of the La into the STO. The results together suggest that while there is significant interdiffusion at this interface, there are nonetheless no conclusive indications that there is an imbalance in A- and B-site cation interdiffusion, as would be expected for insulating interfaces.

Atomic-scale spectroscopic imaging of Pt-based materials obtained during electrochemical reactions has been a major challenge in understanding the electrocatalysis process in proton exchange membrane fuel cells (PEMFCs). Able to reach sub-Ångstrom spatial resolution and sub-eV energy resolution, the aberration-corrected scanning transmission electron microscope (STEM) equipped with electron energy loss spectroscopy (EELS) proves to be an invaluable tool to obtain structural, compositional and electronic information of precious metal-based catalyst materials. Here, we show the atomic-resolution spectroscopic imaging of Pt based fuel cell electrocatalyst is achieved with the Cornell NION Ultra STEM. These methods provide insight into how atomic-level engineering could affect the electrocatalytical activity of materials in the oxygen reduction reaction (ORR). We will first present the spectroscopic mapping of PtM (M=Pd, Co, Mn, Fe, Cu) core-shell nanoparticles, resolving even a single Pt monolayer. In a comparative study of two generations of electrocatalysts, we found the differences in particle size, number ratio of core-shell to non-core-shell structured particles, Pt-shell thickness, shell homogeneity, and surface orientation. We also correlated these microstructural features with results of various membrane electrode assembly (MEA) performance tests inside PEMFCs. Secondly, we will illustrate the imaging of low-Pt-mole-fraction intermetallic Cu3Pt nanoparticles with an ordered phase by aberration-corrected STEM-EELS. We controlled the morphology of the nanoparticles by employing two types of dealloying methods: electrochemical and chemical treatments. The spectroscopic imaging reveals that this electrochemical treatment yielded a ~1 nm Pt shell, while this form of chemical leaching gave rise to a spongy structure. We demonstrate the potential of using aberration corrected STEM-EELS to correlate the behavior of electrocatalysts with the morphology and composition of these nano-materials.

Alloying Pt with 3d transition metals (Fe, Co, Ni, etc.) are strong candidate catalysts for the oxygen reduction reaction (ORR) in fuel cells.1-3 Previous work on well-defined extended surfaces has demonstrated that ultrahigh ORR activity can be achieved for bi-metallic alloys with Pt segregated surfaces, e.g., a Pt-skin layer and a Ni enriched subsurface layer in the case of Pt3Ni.4 Quantitative characterization of such materials in nanoparticle configuration, with a diameter of less than 10nm and with interest features at an atomic scale, however, is of a considerable challenge to most conventional imaging and chemical analysis techniques. Aberration Corrected Scanning Transmission Electron Microscopy (AC-STEM) imaging recently has been considered as one of the ideal techniques to investigate crystalline structures of such nanoparticles.5 The detailed compositional quantification, however, requires the combination of imaging and chemical analysis with a high spatial resolution. The challenges of atomic-scale chemical analysis on such small nanoparticles mainly involve effectively reducing radiation damage and obtaining sufficient signal for quantification. In this work, we will present our recent results on developing a comprehensive microscopy method for characterizing Pt-TM nanoparticles by combining atomic-scale Z-contrast imaging, Electron Dispersive X-ray (EDX), as well as Electron Energy Loss Spectroscopy (EELS). Optimized beam and acquisition conditions, which provide sufficient enough signals for appropriate chemical analysis while maintaining fine probe sizes, will be discussed. In addition, surface stability of such nanoparticles under different accelerating voltages (60, 200 and 300kV) will be compared. Quantifications are further performed on both Z-contrast images and EDX/EELS mapping by combining image simulation and multivariate statistical analysis (MSA). 6 References: 1. Toda, T.; Igarashi, H.; Uchida, H.; Watanabe, M., J. Electrochem. Soc. 1999, 146 (10), 3750-3756. 2. Stamenkovic, V. R.; Mun, B. S.; Mayrhofer, K. J. J.; Ross, P. N.; Markovic, N. M., J. Am. Chem. Soc. 2006, 128 (27), 8813-8819. 3. Stamenkovic, V. R.; Mun, B. S.; Arenz, M.; Mayrhofer, K. J. J.; Lucas, C. A.; Wang, G. F.; Ross, P. N.; Markovic, N. M., Nature Materials 2007, 6 (3), 241-247. 4. Stamenkovic, V. R.; Fowler, B.; Mun, B. S.; Wang, G. F.; Ross, P. N.; Lucas, C. A.; Markovic, N. M., Science 2007, 315 (5811), 493-497. 5. Chen, S.; Ferreira, P.J.; Sheng, W.C.; Yabuuchi, N.; Allard, L.F.; and Shao-Horn, Y.; J. Am. Chem. Soc., 2008, 130, 13818-13819. 6. The microscopy research performed at the ORNL SHaRE User Facility supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

The application of photoelectron spectroscopy (PES) to catalysis and environmental science has long driven the advancement of PES to function at higher pressure. While such systems have been developed for the past 30 years, there has been a resurgence of ambient pressure PES(APPES) in the past decade due to advanced construction of electron analyzers and the exploitation of synchrotron facilities with high brightness, tunable, monochromatic light with small spot size. Other PE based techniques, such as PE microscopy has matured and become powerful tools in materials science and solid state physics over the same period. X-ray PE microscopy, which can be achieved either by focusing the x-ray beam or imaging PEs with a dispersive electron lens system, is able to provide spatial mapping of elemental composition and chemical states. At ALS, we have been working on the design and construction of new APPES systems with high electron transmission and detection efficiency to reduce radiation exposure and data acquisition time. Additionally, one-dimensional imaging spectromicroscopy (~16um resolution) have been developed and tested. These additional features increase our ability to extract more information from detected PEs and study more complex materials under catalytically and environmentally relevant conditions. Merging the rich landscape of PE microscopy with the in situ capabilities of APPES will lead to deeper understanding of materials under working conditions, which is necessary for the rational design of advanced materials with tailored properties. The new APPES systems at ALS are becoming important tools for the discovery and testing of new materials and devices in energy related research. I will give an overview of science projects at ALS BL9.3.2 in heterogeneous catalysis and electro-chemistry using these new systems.

The full-field transmission x-ray microscope (TXM) on beam line 6-2 of the Stanford Synchrotron Radiation Lightsource (SSRL) is capable of imaging at high spatial resolution (down to <30 nm), yet with relatively large field of view (30x30 square microns; larger with raster scanning). These length scales are quite relevant to the operation of hierarchical functional materials such as batteries, fuel cells and catalysts. Here we present the application of full-field TXM to in-operando measurements of dynamic changes in morphology, porosity and chemical composition during operation of battery and catalyst materials. Recent developments in hard- and software enable the combination of TXM with x-ray absorption spectroscopy (XAS) to perform 2D and even 3D chemical speciation of relatively large areas (up to mm^2) or volumes (up to 30x30x30 microns^3), while maintaining the high spatial resolution of the microscope[1]. In addition, battery electrodes can be imaged during operation, to determine changes in morphology over time [2]. These techniques will be presented as applied to in operando imaging of energy materials. [1] Meirer, F. et al. Three-dimensional imaging of chemical phase transformations at the nanoscale with full-field transmission X-ray microscopy. J. Synchrotron Radiat. 18, 773-781 (2011). [2] Nelson, J. et al. In Operando X-ray Diffraction and Transmission X-ray Microscopy of Lithium Sulfur Batteries. JACS 134, 6337-6343 (2012).

High-resolution transmission electron microscopy based on phase contrast is a well-established technique widely used to determine structures at atomic resolution. However, atomic resolution in energy-filtered TEM had not been realized until the recent development of chromatic aberration corrector. In this work, we report atomic resolution energy-filtered TEM not only in the low-loss region but also at high-loss regions enabled through chromatic aberration correction. One of the primary benefits of chromatic aberration correction is that it significantly reduces the focus blurin images formed from electrons with an energy spread. This allows use of a wider energy slit without compromising resolution. Instead, the wider slit increases counts forenergy-filtered TEM images, improving both resolution and S/N. Using LaMnO3/SrTiO3 2x2 superlattice film, we demonstrated that atomic level energy-filtered high-resolution TEM images can be obtained from zero-loss up to 600 eV energy loss. Using BaTiO3/SrTiO3/CaTiO3 1x1x1 superlattice film, we found that 0.4 nm resolution of Ca mapping can be achieved using Ca L2,3 edge. Although image formation in energy filtered high resolution electron microscopy (EF-HREM) is complex, it provides another approach to obtain “Z”-like contrast in atomic resolution images. Since EFTEM is formed using inelastically scattered electrons, atomic resolution EFTEM offers another method to determine structural and chemical information at atomic resolution. *Research sponsored by the U.S. DOE, Office of Science - Basic Energy Sciences under contract DE-AC02-06CH11357.The Electron Microscopy Center at Argonne is supported by the Office of Science.

In situ characterization of the evolution in electronic structure of electrode materials during repeated charge- discharge cycling is fundamentally important for more fully understanding the processes of charge storage and degradation, which, in turn, is essential for the development of new electrical energy storage (EES) materials with tailored properties and improved performance. X-ray spectroscopies provide ideal tools with which to obtain enhanced insight into the origins of electrode behavior in EES systems due to their capabilities for direct, element specific, characterization of the electronic densities of states. To date, in situ studies of EES materials have primarily focused on hard x-ray experiments due to the challenges associated with UHV compatibility and high photon attenuation of cells for soft x-ray measurements. Nonetheless, the use of soft x-ray spectroscopies to EES systems is vital since they provide complementary information that cannot be obtained via hard x-ray studies. We report the development of a cell for in situ soft x-ray emission spectroscopy and x-ray absorption spectroscopy studies of EES materials and will discuss experiments focused upon the x-ray spectroscopy characterization of a series of novel electrode materials. Prepared by LLNL under Contract DE-AC52-07NA27344.

Direct imaging is a powerful means to develop an atomistic understanding of scientific challenges in the chemical, material, biological, and environmental sciences. What science can routinely visualize at a particular length scale it may then use to gain sufficient control and prediction at that same scale. The Chemical Imaging Initiative at PNNL is building just that - a suite of in situ imaging tools with nanometer resolution and element specificity. Specifically we are developing a suite of coupled x-ray, electron, optical, ion, mass and scanning probe microscopies to address challenges in several scientific domains including, materials for energy conversion and storage, microbial systems for fuel synthesis and environmental remediation, and the interplay between aerosol particle chemical morphology and climate effects. We will describe our progress towards development of unique tools in this domain - in particular the coupling of electron and scanning x-ray transmission microscopy - and how they will impact these scientific challenges.

Research in magnetism is motivated by the scientific curiosity to understand and control spins on a nanoscale and thus to meet future challenges in terms of speed, size and energy efficiency of spin driven technologies. Imaging magnetic structures and their fast dynamics down to fundamental magnetic length and time scales with elemental sensitivity in emerging multi-element and nanostructured materials is highly desirable. Magnetic soft X-ray microscopy is a unique analytical technique combining X-ray magnetic circular dichroism (X-MCD) as element specific magnetic contrast mechanism with high spatial and temporal resolution [1]. Our approach is to use Fresnel zone plates as X-ray optical elements providing a spatial resolution down to currently 10nm [2] thus reaching out into fundamental magnetic length scales such as magnetic exchange lengths. The large field of view allows to investigate both the complexity, but also the stochasticity of magnetic processes, such as nucleation or reversal, which occur on a mesoscale. Utilizing the inherent time structure of current synchrotron sources fast magnetization dynamics such as current induced wall and vortex dynamics in ferromagnetic elements can be performed with a stroboscopic pump-probe scheme with 70ps time resolution, limited by the lengths of the electron bunches. In this talk I will review recent studies of magnetic vortex structures, where we found a stochastic character in the nucleation process, which can be described within a symmetry breaking DM interaction [3]. I will also present time resolved studies of dipolar coupled magnetic vortices, where we found an efficient energy transfer mechanism, which can be used for novel magnetic logic elements [4]. This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05-CH11231. [1] P. Fischer, Exploring nanoscale magnetism in advanced materials with polarized X-rays, Materials Science & Engineeering R72 81-95 (2011) [2] W. Chao, P. Fischer, T. Tyliszczak, S. Rekawa, E. Anderson, P. Naulleau, Optics Express 20(9) 9777 (2012) [3] M.-Y. Im, P. Fischer, Y. Keisuke, T. Sato, S. Kasai, Y. Nakatani, T. Ono, Nature Communications (2012) in print [4] H. Jung, K.-S. Lee, D.-E. Jeong, Y.-S. Choi, Y.-S. Yu, D.-S. Han, A. Vogel, L. Bocklage, G. Meier, M.-Y. Im, P. Fischer, S.-K. Kim, NPG - Scientific Reports 1 59 (2011)

Gaining simultaneously structural and elemental information at the nanometer scale is a challenge that has kept surface scientists on the run for the past decade. Hence, it was a logical step to combine two of the most powerful analytical methods: Scanning Probe Microscopy (SPM) and Mass Spectrometry (MS). On one hand, SPM is a powerful surface analysis tool to access non-destructively local properties of surfaces. Not only can topography be measured down to atomic resolution, properties as various as electrical, magnetic and tribological are accessible as well. However, identifying unambiguously elements or molecules remains a tedious task that was only achieved in very specific cases. Furthermore, the tool is confined to surface analysis. On the other hand, MS has developed into a work horse of analytical instrumentation, being able to measure molecular weights from hundreds of kD down to atoms and isotopes with sensitivities down to ppt. Among the established MS methods, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is the best complementary method to SPM due to its very high sensitivity, mass resolving power and spatial characterization. A combined measurement of ToF-SIMS and SPM gives access to both topographical and chemical information of the surface and even below it. However, the technical challenges for such a set-up are very significant. Several key tasks have to be tackled, besides building a ToF-SIMS and a SPM in an UHV environment, both instruments have to be integrated into a reference frame that allows positioning a sample back and forth between the two measurement points with an accuracy comparable to the ToF-SIMS and SPM precision. Further, the controllers of both instruments have to be integrated to match measurements together. The EU-project “3D-NanoChemiscope” united the know-how of 6 research institutions and 2 industrial partners to combine the strengths of both analytical methods. The presentation will show first results of this set-up and discuss new measurement methods developed to match SPM analysis at the nanometer scale to ToF-SIMS ranges at the sub-millimeter scale.

Transmission electron microscopy is unique in its ability to obtain both image and spectroscopy data from catalytic nanoparticles at high spatial resolution. Environmental TEM - wherein the sample is exposed to both high atmospheric pressures and elevated temperatures - can be used to understand the structure and chemical modifications taking place in nanoparticle systems, under near-reactor conditions. We will describe how this approach can be used to investigate changes in the structure, chemical composition and electronic configuration of supported Cu and bimetallic Cu nanoparticles on polycrystalline oxides during reaction. Scanning transmission electron microscopy combined with parallel electron energy loss spectroscopy is used to investigate changes in the Cu L2,3 edge in reaction conditions, and compared with “bulk” x-ray absorption spectroscopy (XAS) measurements. We will present quantification of the valence state from a large number of nanoparticles in different states of reduction and oxidation and correlate this with XAS observations at equivalent conditions. Notably, we find significant compositional heterogeneity by probing individual nanoparticles, which in turn affects and informs the measurements of electronic structure on both the local and global levels. This material is based upon work supported as part of the Institute for Atom-efficient Chemical Transformations (IACT), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Work at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

Scanning electron microscopy (SEM) has been widely used in materials science research. A new generation of SEMs with field-emission gun and in-lens secondary electron (SE) detector enables nano-resolution SE imaging at low accelerating voltages (30V to 3 kV). We installed a Protochips heating stage in a Zeiss Merlin SEM, and evaluated the chemical imaging capabilities by energy-dispersive X-ray spectroscopy (EDS) using a Bruker solid-state EDS detector. In-situ heating in an SEM - wherein the sample is exposed to elevated temperatures - can be used to understand the structure and chemical modifications taking place in nanoparticle systems or films as thick as 20 microns. We will describe how this approach can be used to investigate changes in the structure and chemical composition during heating reactions in (1) BiFeO3/LaAl O3 films and (2) Ni/NiAl2O4 particles. Scanning electron microscopy combined with EDS mapping is used to investigate changes during heating up to 1200 C. We will present X-ray maps from Fe L-edge collected at 3kV during in-situ heating. Notably, we find that the high processing rate of the SDD detector can tolerate the large dose of photon leak, which makes in-situ X-ray mapping during heating in an SEM a reality. This microscopy work was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, with funding support by the Office of Basic Energy Sciences, Materials Sciences and Engineering Division.

3-D atom probe tomography (3-D APT) measures the mass and position of atoms that have been field-ionized from a needle-shaped specimen, offering a powerful method for the 3-D characterization of all atoms within a volume. However, the resulting 3-D model is produced by reconstruction of the acquired data, and this process is subject to aberrations due to deviation of the specimen from an idealized tip shape, often large differences in the field-evaporation rates of the constituent elements, crystalline orientation effects, etc. To account for such artifacts, complimentary techniques can be employed in order to independently assess the structural and chemical distribution within the sampled volume and provide a baseline with which to compare the APT reconstruction. One method for achieving this is to combine electron tomography (ET) techniques with hyperspectral analysis. In a traditional ET analysis, a series of two-dimensional projection images acquired from a specimen over a range of orientations is used to produce a 3-D model of the density variations present at nanoscale resolution. This technique has been applied most widely to amorphous (mainly biological) specimens, since non-uniform changes in image intensity with orientation due to Bragg diffraction render the technique unsuited to crystalline materials. However, these effects are less pronounced for the hyperspectral image techniques available in the analytical electron microscope (AEM) such as X-ray energy-dispersive and electron energy-loss spectroscopies (XEDS and EELS, respectively). Herein, we highlight progress in the development of quantitative 3-D chemical imaging using spectroscopic tomography in the AEM. Needle-shaped specimens were fabricated from a model multilayer thin film consisting of alternating layers of Ni and Cr. Two sets of samples were fabricated: one in which the layer modulation direction was parallel to the needle axis and another where it was perpendicular. A series of both high-angle annular dark-field (HAADF) images and hyperspectral image signals were collected over a range of specimen orientations using a high-tilt tomography holder to eliminate missing-wedge related artifacts from the resulting reconstructions. Quantifying the resulting elemental distribution is problematic, since the orientation of the specimen with respect to the detector changes with tilt, and thus so are the conditions for absorption, fluorescence, etc. The geometric simplicity of the multilayer specimen, and the ability to examine it in differing orientations, makes it ideal for assessing the limits to quantification in such measurements and the possibilities for extending them to more ‘realistic&’ samples which exhibit complex geometries. We will discuss approaches for data processing, including alignment, reconstruction, and quantification, as well as comparisons of experimental data to simulations which allow for optimization of the acquisition parameters.

The performance of hybrid organic-inorganic photovoltaic cells is highly dependent on both the morphology of the active layer and the chemical composition of the internal interfaces in this layer. Here we show that the combination of transmission electron microscopy (TEM) and energy filtered TEM (EFTEM) can be used to characterize the nanostructure and molecular level composition of various metal oxide-conjugated polymer photovoltaic (PV) cells. In a first example, the active electrode of a solid-state dye sensitize solar cell (DSSC) was analyzed to determine the efficiency of conjugated polymer infiltration into the pre-formed 2.5 µm thick mesoporous titania electrode (fabricated from 20 nm TiO2 nanoparticles, 60% porosity). EFTEM investigation was used to determine the location of the polymer after infiltrated and revealed that despite the small size of the pores and the polymer stiffness, polythiophene infiltrated through the entire mesoporous TiO2 and is evenly distributed in the film. The high performance of the solid-state photovoltaic devices based on this layer is attributed to the successful infiltration of the polythiophene polymer. In a second and more complex example, hybrid PV films were prepared by the co-assembly of a surfactant, titania precursor and opto-electronically active organic species: conjugated polymer and/or ruthenium based dyes. TEM revealed the self-assembly of the surfactant resulted in the formation of a continuous highly ordered titania scaffold with a Im3m cubic mesostructure and ~15 nm periodicity. Furthermore, combining conventional TEM and EFTEM measurements in a single location enabled to determine that the distribution of the conjugated species across the sample is in specific domains, which were identified as the surfactant domains. Moreover, these domains are distributed homogenously through the entire film thickness (200 nm- 1µm), creating controlled, interpenetrating and continues networks of the conjugated species which are considered to be the ideal structure for efficient charge generation, transfer, and transport to the electrodes in hybrid photovoltaic cells.

Morphological and surface characteristics of γ-Al2O3 are topics of high relevance in the field of catalysis. Using tomography and high-resolution aberration corrected S/TEM imaging, we have studied the surface characteristics of model γ-Al2O3 synthesized in the shape of platelets and macroscopically defined by (110)Al2O3 and (111)Al2O3 surface facets. The electron microscopy observations were performed on an FEI Titan 80-300 equipped with a CEOS Cs -probe corrector operated at 300kV, and the surface characteristics were studied under ex-situ conditions and in-situ heating conditions with a Aduro Protochips heating holder. The TEM analysis shows that the dominant (110)Al2O3 surface of the synthesized γ-Al2O3 is not atomically flat but shows a significant reconstruction, forming nanoscale (111)Al2O3 terraces. Apart from the (110) surface, the general (111) surface was studied at the atomic level and compared with presently available models in the literature. In addition to high resolution imaging, tomographic analysis was carried out, enabling an examination of the pores/voids which were found to be exclusively defined by (100)Al2O3 and (111)Al2O3 facets. In the current system, the majority of pores are enclosed within the bulk and inaccessible to gasses or metals. The importance of these findings is discussed in the context of relative surface energies, ethanol desorption characteristics, and the possible impacts on catalytic activity.

Understanding structural order at solid-liquid interfaces is important for both fundamental science and for many technological processes. Due to contrast delocalization in conventional transmission electron microscopy (TEM), past investigations of ordering phenomena required detailed and time-consuming image simulations to understand the experimental results. As a result, ordering in liquid aluminum adjacent to (0006) α-alumina was only recently confirmed not to be an experimental artifact. In the current study, ordering in liquid Al adjacent to additional terminating planes of crystalline α-alumina and ordering in liquid Al partially confined by crystalline alumina was studied. Experiments were conducted using two techniques: in-situ aberration-corrected high resolution TEM (HRTEM) and in-situ electron energy loss spectroscopy (EELS). Heating experiments were conducted using a monochromated and spherical aberration (Cs) corrected FEI Titan 80-300 S/TEM. The use of Cs corrected HRTEM enabled direct and quantitative analysis of the ordering phenomenon at different terminating alumina facets. The energy of Al bulk plasmons was found to be sensitive to local ordering of the liquid at the interface with alumina, which provided a second independent method for the quantification of structural ordering by in-situ EELS. Enhancement of the ordering phenomenon in liquid Al partially confined by crystalline alumina was found. Comparison of the data obtained from in-situ EELS with the results from Cs-corrected HRTEM provided information regarding preferential oxygen segregation to the ordered liquid at different alumina facets. The ordering phenomenon is described using a modified Gibbs adsorption equation. The role and importance of facet intersections as nucleation sites for solidification will be discussed.

Simultaneously probing the electronic structure and morphology of materials at the nanometer or atomic scale while a chemical reaction proceeds is significant for understanding the underlying reaction mechanisms and optimizing a materials design. This is especially important in the study of nanoparticle catalysts, yet such experiments have rarely been achieved. Utilizing an environmental transmission electron microscope (ETEM) equipped with a differentially pumped gas cell, we are able to conduct nanoscopic imaging and electron energy loss spectroscopy (EELS) in situ for cobalt catalysts under reaction conditions. Analysis revealed quantitative correlation of the cobalt valence states to the particles&’ nanoporous structures. The in situ experiments were performed on nanoporous cobalt particles coated with silica while a 15 mTorr hydrogen environment was maintained at various temperatures (300-600 degree C). When the nanoporous particles were reduced, the valence state changed from cobalt oxide to metallic cobalt and concurrent structural coarsening was observed. In situ mapping of the valence state and the corresponding nanoporous structures allows quantitatively analysis necessary for understanding and improving the mass activity and lifetime of cobalt-based catalysts, i.e., for Fischer-Tropsch synthesis that converts carbon monoxide and hydrogen into fuels, and uncovering the catalyst optimization mechanisms. This work was supported by the Office of Basic Energy Sciences, Chemical Science Division of the U.S. DOE under Contrast No. DE-AC02-05CH11231. The in situ environmental TEM experiments were carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886. We performed ex situ TEM experiments at National Center for Electron Microscopy (NCEM) of the Lawrence Berkeley National Laboratory (LBNL), which is supported by the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231. EAP thanks Trevor Ewers and Prof. Paul Alivisatos for providing guidance and the access to the synthesis laboratory. HL Xin thanks Peter Ercius for helping with the tomography setup and Robert Hovden for the development of the Cornell e-Tomo reconstruction software. H Zheng thanks the funding support from DOE Early Career Research Program.

The role of aberration-corrected scanning transmission electron microscopy (STEM) in materials characterization is examined in regards to Al(x)Ga(1-x)N nanowires. Wires were graded from x=0 to x=1 and then from x=1 to x=0 with a small active quantum disc region located between the two gradations. This configuration is the basis for previously reported UV light emitting diodes. However, to assist subsequent growth processes while striving for optimum efficiency, both structural and chemical characterization methods are necessary, which can be provided at sufficiently high resolutions by advanced STEM instruments. Specifically, structural characterization will focus on determining layer thicknesses and wire polarity, as well as visualizing any short-range ordering and/or stacking faults that may be present. Chemically, both energy dispersive X-ray (EDX) and electron energy loss (EELS) spectroscopies will be discussed in various capacities, ranging from quantum well composition (EDX) to N K-edge fine structure of both GaN and AlN (EELS).

Heating devices (e.g. Aduro^TM, Protochips Co.) based on MEMS microfabrication technology are gaining acceptance for in situ heating studies in both TEM and SEM instruments, with heating and cooling rates of ~10⁶°C/s. Aduro technology has recently been incorporated into a closed-gas-cell holder compatible with the 2-mm-gap objective lens pole piece of the JEOL 2200FS ACEM. The unique features of Aduro devices permit construction of a reactor with a narrow gas gap that allows imaging with virtually no loss of signal, and the ability to achieve atomic resolution at up to atmospheric pressure. Most work to date has been conducted with the gas cell in a ''static gas” (i.e. no flow) configuration, but reactor capability has recently been extended to allow gas flow at controlled rates; imaging examples of catalytic reactions in both static and dynamic flow conditions will be presented. The unique capability for high-precision control of the heating rates using the Aduro technology will also be demonstrated, with examples that capture the formation of catalytic species on support surfaces with very short reaction times. This research at the Oak Ridge National Laboratory's High Temperature Materials Laboratory was sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program.

When gold is supported in the form of nanoparticles on crystalline metal oxides, gold shows remarkable catalytic activity for CO oxidation even below room temperature. We intend to contribute toward elucidating the mechanism of gold nanoparticulate (GNP) catalysts. Environmental TEM (ETEM) has advanced greatly with aberration correctors and improved operation systems. Using recently developed ETEMs, we performed operando studies of GNP catalysts by systematic and statistical acquisition and analyses of ETEM data. By quantitative ETEM, one can convincingly determine the structures of catalysts including adsorbed gas molecules at reaction environments. Here we report the ETEM analyses with novel in-situ high resolution ETEM movies. GNP catalysts, Au/CeO2 and Au/TiO2 were prepared by the deposition precipitation method. The conversion of CO to CO2 reached 100% at room temperature. Details of the catalyst samples were described in our previous paper [1, 2]. ETEM observation was performed using a 200 kV ETEM (based on FEI Tecnai F20) and a 80-300 kV ETEM with the spherical aberration (Cs) corrector (based on FEI Titan 80-300 kV). In real GNP catalysts, the structures of supported GNPs are not identical at atomic scale. Hence, we examined a large number of GNPs by ETEM and, after numerical and statistical analyses we established the morphology phase diagram [1] that represented the morphology of GNPs as a function of the partial pressures of CO and O2. We found that the majority of GNPs changed the morphology systematically, depending on the partial pressures of CO and O2. We also examined electron irradiation effects on the structure of supported GNP systematically by ETEM. We established the structure evolution diagram [2] that represented the structures as a function of electron flux and electron dose. Establishing the diagrams, we concluded that the morphology change correlated with the catalytic activity of supported GNPs and could also determine the intrinsic catalytic structure of supported GNPs in reaction environments [2]. Furthermore, using a newly developed Cs-corrected ETEM, we found that CO gas made the {100} facets of a GNP reconstructed in reaction environments [3]. CO molecules were adsorbed at the on-top sites of gold atoms in the reconstructed surface. The stability of the adsorbate-induced structure was confirmed by ab initio calculations. The pressure gap and high energy electron irradiation were thought to be critical issues in applying ETEM especially to catalysis chemistry. However, they can be overcome by the quantitative data acquisition and analyses as shown in this study. The atomic-scale visualizing method combined with the quantitative analyses by ETEM can be most probably applied to various fields in chemistry. References [1] T. Uchiyama, et al., Angew. Chem. Int. Ed. 50, 10157 (2011). [2] Y. Kuwauchi, et al., to be published (2012). [3] H. Yoshida, et al., Science 335, 317 (2012).

Ceria-titania based powder catalysts have yielded noteworthy activity in the water-gas shift (WGS) reaction and the visible light driven photocatalytic splitting of water. The performance metrics of these mixed oxide materials are dependent on physical parameters such as particle size, morphology and electronic properties. Growth of ceria nanoparticles onto titania has been shown to provide unique structure and selectivity towards the aforementioned reactions considerably better than their individual counterparts. Studies of these catalysts using aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) provides insight into the physical origins of the observed enhancement. The structure and oxidation state of ceria strongly depends on the processing conditions for synthesis. High-angle annular dark-field imaging reveals that the ceria takes on a plethora of morphologies and exists over different size-regimes ranging from atom clusters, atomically thin wires to nanoparticles. Because the ceria grows epitaxially on the titania this introduces strain and defects in the ceria as well as dictating the growth mechanics and hence the morphology. EELS measurements of the ceria-titania interface reveal the presence of intermixing while examination of the EELS fine structure identifies both Ce⁴⁺ and Ce³⁺ states can be present. These results elucidate the origins behind the improved performance and provide crucial insights on how to further tailor growth conditions for optimal structure and catalytic performance. The utilization of environmental transmission electron microscopy will subsequently provide insight into the catalytic reaction dynamics of this material system.

Combining plasmonic and optical antenna concepts with ultrafast and shaped laser pulses allows for the precise control of an optical excitation on femtosecond time and nanometer length scales. I will present several new concepts extending tip-enhanced spectroscopy into the nonlinear and ultrafast regime for nano-scale imaging and spectroscopy of surface molecules and nano-solids. Examples include the adiabatic nano-focusing on a tip for background free tip-enhanced Raman nano-spectroscopy, and spatio-temporal superfocusing with optical control at the 10 nm-10 fs level. Furthermore, the combination of ultrafast mid-IR femtosecond pulses with scattering-scanning near-field optical microscopy (s-SNOM) allows for the control of the ultrafast free-induction decay of infrared molecular vibrations with an increase in sensitivity of IR surface spectroscopy by 10⁹ compared to conventional IR micro-spectroscopy, reaching the single molecule limit.

Often nanomaterials are characterized at the nanoscale with a variety of high resolution imaging techniques (i. e. AFM, SEM,hellip;), that provide detailed morphological information but their chemical composition is usually assessed at a larger scale (micron scale for diffraction limited FTIR), thus resulting in an average over several nanoobjects. Determining the chemical/physical properties at the nanoscale is the key for optimizing nanomaterials&’ performances towards their technological applications. Photo Thermal Induced Resonance (PTIR), is a new technique that attracted great interest for enabling chemical identification and imaging with nanoscale resolution. PTIR uses a tunable pulsed laser for sample illumination in ATR configuration and an AFM tip in contact mode to measure the sample instantaneous thermal expansion induced by light absorption. Infrared spectra are obtained by plotting the amplitude of the tip deflection with respect to the laser frequency. Our set up requires placing the sample over an optically transparent prism. PTIR was previously used for nanoscale chemical characterization under the assumption that the PTIR signal is proportional to the energy absorbed. However, this assumption was not previously verified experimentally, nor was proved that PTIR can be used for quantitative chemical analysis at the nanoscale. In this work, electron beam nano-patterned polymer samples were fabricated directly on ZnSe prisms using customized adaptor pieces to evaluate the PTIR lateral resolution, sensitivity and linearity. The samples analyzed here can be grouped into 2 categories: samples with constant thickness patterned with features of various size and samples with variable height patterned with lines. Results shows that PTIR lateral resolution for chemical imaging is comparable to the lateral resolution obtained in the AFM height images, up to the smallest feature measured (100 nm). Spectra and chemical maps were produced from the thinnest sample analyzed (40 nm). Additionally, we demonstrate, for the first time, that the intensity of the PTIR spectra of thin films (< 1 µm) depends linearly on the sample thickness. This is arguably the most important contribution of this work since it proves that PTIR spectra and imaging can be effectively used for quantitative analysis at the nanoscale. Finally, by analyzing samples with an extended range of thicknesses we demonstrate that the PTIR signal is proportional to the local energy absorbed, to the thermal expansion and to persistence time of the thermal excitation in the sample, as previously predicted theoretically. We believe that our findings provide experimental evidence of PTIR usefulness, allowing its use for quantitative characterization in a variety of nanotechnology applications.

Polyurethane materials are ubiquitous as materials of construction for a number of applications, from medical devices to electrical materials to consumer products. These materials have stability issues associated with soft and hard segments that will impact the mechanical stability. While infrared spectroscopy has been used extensively to study these materials, most experiments reported in the literature examine macro samples (a minimum of a few millimeters in diameter). In some cases infrared microspectroscopy has been used but due to experimental limitations, each sample examined is no smaller than approximately 15 microns on a side. Collection of one spectrum of that area usually takes 5 minutes per point making the detailed point by point examination of a sample that is 300 microns on a side time prohibitive. Since the complex chemistry of urethanes is impacted by the soft segment, the hard segment, and the hydrogen bonding, chemical examination of the material on a much higher spatial resolution scale would be valuable. A relatively new technique, Attenuated Total Reflection Fourier Transform Infrared Spectrochemical Imaging, has been used to examine polyester urethanes that have been hydrolytically degraded. The technique has three key components that differentiate it from prior approaches. The interferometer is coupled to a two dimensional array detector providing not one but thousands of spectra collected simultaneously. In addition, by using a germanium prism to contact the sample, a magnification effect (approximately a factor of four) is produced resulting in a significantly higher spatial resolution (~2 microns). The net output of the analysis is a hypercube of high resolution infrared data showing the changes in chemistry of the samples on a much smaller scale than was previously possible. The paper will describe the instrumentation and its use to examine the changes in chemistry as a polyester urethane degrades. We will provide examples of new and failed samples illustrating how the technique is used to examine the degradation. One immediate result of this approach is the differentiation of the urethane carbonyl in the sample from the amide carbonyl, which appears to be a hallmark of degradation.

A scanning angle total internal reflection (SA-TIR) Raman microscope has been developed for tuning the depth over which Raman spectra are collected to study interfacial phenomena with chemical specificity. Controlling the incident angle of the laser upon a prism/sample interface allows precise control of the penetration depth of the evanescent wave, and in turn the depth over which Raman spectra are collected. Depths up to 1500 nm can be profiled with 30 nm axial resolution perpendicular to the focal plane. This is at least one order of magnitude better than confocal Raman measurements. Sub-monolayer detection limits have been demonstrated using near infrared excitation wavelengths. Polystyrene films of varying thickness were coated onto a substrate and Raman spectra were collected across a range of incident angles. Models of the Raman signal at varying incident angles were developed that enable polymer thickness, structure and chemical content to be measured. Molecular orientation at the interface was determined by measuring the polarization dependence of the Raman scatter. Polymer Raman spectra were collected at three interfaces: sapphire, sapphire/gold or sapphire/gold/silica. The smooth metal films and plasmon waveguides enhance the collected Raman scatter in a reproducible and well-modeled fashion. More complex block copolymers were analyzed to determine film homogeneity at different depths from the interface. Furthermore, buried interfaces within multi-layers were also measured using scanning angle total internal reflection Raman spectroscopy. The work demonstrates the ability to nondestructively collect qualitative and quantitative information about thin polymer films and will be applied to measure interfaces relevant to energy harvesting and storage devices.

Poly(lactic acid) (PLA) is an organic polymer that degrades in water, a property that is useful for some applications related to oil and gas production. The rate of PLA degradation depends on the rate of ester hydrolysis. This rate is significantly lower at temperatures below the glass transition temperature (Tg = 60 ^oC) of PLA, which effectively limits the use of PLA to applications above T_g. Here we report the ability of ZnO nanoparticles to accelerate ester hydrolysis of PLA, permitting rapid degradation below the T_g. The kinetics of PLA degradation were studied using a novel method based on ¹H T2 NMR relaxation. By quantitatively monitoring changes in the confined water (proton) peak over time in pure PLA and PLA-ZnO nanocomposite systems, we obtained apparent rate constants and activation energies of ester hydrolysis for both systems. Our results indicate that the activation energy of ester hydrolysis in PLA is reduced by the presence of the ZnO nanoparticles.

Geologic sequestration of CO₂ has become an emerging enterprise for reduction of greenhouse gas emissions. Because CO₂ will be injected and stored in host rock at depths >800m, lithostatic pressure will cause the CO₂ to remain in supercritical fluid state (scCO₂). Knowledge of mineral-fluid chemical transformation rates at geologically relevant temperatures and pressures is expected to be an important aspect of predicting reservoir stability. Many mechanisms of mineral transformation reactions where scCO₂ is the dominant phase and water availability is low have so far remained unstudied. We have developed an atomic force microscope capable of observing in-situ mineral transformations under supercritical conditions (i.e., >72.8 atm and >304K) in real time. This talk will focus on the development of the instrument as well as technical considerations associated with building an AFM head capable of imaging in scCO₂.¹ We will also discuss first of a kind experiments that include the observation of the disappearance of a 1.5nm layer on the surface calcite in anhydrous scCO₂. These results are suggestive of the dehydration of a hydrated calcium carbonate layer and are consistent with measurements from piezoelectric force microscopy.² We have also followed the formation of a water film on the surface of geologically more relevant forsterite, which is deemed to be essential in the transformation of this silicate mineral into a carbonate, and have related film thickness to water content in the scCO₂. ¹A.S. Lea et al., Rev. Sci. Instrum. 82, 043709 (2011). ²T.A. Kendall and S.A. Martin, J. Phys. Chem. A 111, 505 (2007).

In the polymer industry, materials processing methods such as laminating, micro-scale compositing, organic inking and polymer coating are the most common ways to search for new material functions and/or improve performance. These are processes in which various heterogeneous material interfaces are formed and nanoscale chemical information at these interfaces are important for material design. However, this cannot be done with traditional IR or Raman spectroscopy due to fundamental diffraction limitations associated with their applied wavelengths. In our recent work, atomic force microscopy (AFM) and IR spectroscopy have been combined in a single instrument (AFM-IR) that is capable of producing 50-nm spatial resolution IR spectra and absorption images. This new capability enables spectroscopic characterization of polymer blends at resolutions of over two orders of magnitude better than conventional IR. Three polymer materials for different applications were analyzed and their results are discussed. One was a multi-component blend of (PC/ABS). These results suggest that alloying AS domains with PC reinforces material strength and the dispersion of small soft PC precipitates in AS-PC alloyed domains can better absorb impacts, resulting in superior impact strength for 60PC/40ABS blend ratios. The second material was a cross-laminated multilayer film of PE/PET. Results suggest that the binding layer was an ethylene vinyl alcohol adhesive, which is capable of binding the chemically stable PE layer with the thermally stable PET layer. The third material was a biodegradable polymer film of P(HB-co-HHx), [poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)], which was melted and annealed at the nanoscale using a heated AFM tip to generate crystalline microdomains of different sizes. Dramatic differences in the room temperature nano-IR spectra were observed in the 1200-1300 cm-1 range as a function of the position on a spatial scale of 200 nm. Using this spectral region, it is possible to monitor the development of polymer crystalline structures at varying distances from a nucleation site generated by bringing the heated AFM tip close to a specific location to locally anneal the sample.

Metal-chalcogenide semiconductor nanocrystals of 3-4 nm in diameter were characterized by matrix-assisted laser de-sorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry. The MALDI-TOF mass spectra were obtained for ZnS, CdS, CdSe, and PbS quantum dots capped with laurate and dodecanethiolate. Of the porphyrin matrices used to desorb and ionize quantum dots with a UV laser, tetrakis(pentafluorophenyl)porphyrin (TPFP) was most effective in MALDI of all four quantum dots. The mass spectral distribution was in line with the size distribution obtained from transmis-sion electron microscopy images. Surface ligands also affected the mass spectra: dodecanethiolate-capped quantum dots resulted in higher m/z values than laurate-capped quantum dots. TPFP is highly recommended for MALDI-TOF detection of semi-conductor nanocrystals.

In order to fully understand the atomic scale chemistry and structure of engineered interfaces, advanced characterization techniques beyond electron microscopy are necessary. Atom probe tomography has opened up a new realm of atomic scale structural and chemical characterization that is proving to be very useful to semiconductor electronics and optoelectronics. Quantum structured materials can be analyzed with dopant level chemical accuracy across the periodic table and including Hydrogen. In order to attain atomic level structural information, improvements to the atom probe reconstruction have been of considerable interest, and several different methods are being evaluated. Cross-correlative microscopy between atom probe tomography and transmission electron microscopy has been suggested as a method for improving atom probe reconstructions. As a first example, the specimen diameter and shank angle, or rate at which the specimen diameter changes with depth, can be directly ascertained from both BFTEM as well as STEM-HAADF images. When dealing with materials that have an unknown evaporation field or tend to evaporate in clusters (common in laser pulsed atom probe of semiconductors and oxides), the estimation of the evaporation field can significantly miscalculate the specimen geometry. Post-analysis quantification of the specimen geometry allows for the determination of magnification, detector efficiency, and image compression factor, all of which can be used to tune the reconstruction volume. In addition to specimen geometry, HRTEM and diffraction data give crystallographic orientation information with relation to the analysis direction, and thus allow for correct depth scaling. In order to facilitate rapid data collection and in-situ experiments, a combined STEM and APT system is being constructed at CSM. The instrument enable sub-ns temporal resolution laser-pump / electron diffraction-probe experiments to be conducted along with the atomic scale chemistry and structure analysis of traditional APT. The combined instrument, dubbed the Dynamic Atom Probe, will allow for the atomic scale investigation of phase transitions, interface formation, and interface movement with nanosecond time resolution. Examples of enabled experiments and potential materials systems are proposed.

Electron energy-loss magnetic chiral dichroism (EMCD) probes the chirality of electronic transitions on the nanometer scale [1, 2]. EMCD is the electron microscopical equivalent of XMCD (X-ray Magnetic Circular Dichroism), giving atom-specific magnetic moments in ferromagnetic materials. An overview is given over the current situation in EMCD, stressing recent results such as nanometric resolution and spin maps of individual atomic columns [3]. One of the intriguing consequences of EMCD is that the outgoing probe electrons have topological charge with quantum number m. Such electrons exhibit a phase singularity and carry nonzero orbital angular momentum (OAM) mh/2π, quite similar to optical vortex beams, or to the recently discovered vortex electrons [4, 5]. Free electrons with a helical wavefront can now be produced routinely in the electron microscope using computer generated holograms. This technique opens an avenue for the practical use of electron vortex beams. They could serve as electron tweezers to move single atoms and molecules. Transfer of angular momentum from vortices could be used in EMCD, and also for the acceleration of nanoparticles to high rotation frequencies. The magnetic moment m associated with a vortex of topological charge m couples to the magnetic field of target atoms carrying magnetic moment. In order to better understand the physics of electron vortices their propagation in fieldfree space [6], in a magnetic field, and in matter is studied. Rich behaviour is found, showing unusual rotation of the beam superimposed on the Larmor rotation in the lens field [7], and transfer of angular momentum to the specimen. References [1] P. Schattschneider et al., Nature. 441 (2006), 486. [2] S. Rubino et al., J. Mat. Res. 23 (2008), 2582. [3] P. Schattschneider et al., PRB 85 (2012), 134422. [4] M. Uchida, A. Tonomura, Nature 464 (2010), 737. [5] J. Verbeeck et al., Nature 469 (2010), 301. [6] P. Schattschneider, J. Verbeeck, Ultramicrosc. 111 (2011), 1461. [7] K. Bliokh et al. arXiv:1204.2780

As the feature sizes in material science continue to decrease to nanometer regime, the techniques solely based on 2-dimensional (2D) imaging fail to provide a full characterization of the nanoscale materials and devices with complex microstructure and architecture. Therefore 3D tomography techniques have been of considerable interest and increasingly employed by electron microscopists to resolve the 3D microstructures. Computed tilt tomography has been utilized based on bright field (BF) TEM or high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) techniques. However neither technique provides direct 3D chemical information. due to the origin of the signal collected. 3D tomography using spectrum imaging or mapping by electron-energy-loss spectrometry (EELS) and X-ray energy dispersive spectroscopy (XEDS) have also been pursued but with significant limitations originating from the signal generation and processing of these techniques; strong dependence of EELS signal to TEM foil thickness and poor collection efficiency and geometry of the single detector systems in XEDS [1-4]. To overcome these problems, we employed a new tomography technique for STEM XEDS which utilizes the combination of a four silicon drift detector (SDD) system and a high brightness electron gun (XFEG) optimized for high X-ray collection efficiency via its windowless design of the detector, fast XEDS mapping and improved tilt response under all tilt angles due to the symmetric design. [5] Three dimensional tomograms are obtained when the sample is tilted and images and EDS maps are acquired from all angles. This data series contains the 3D structural information and the 3D structural and chemical image is obtained through the use of post-processing software. The EDS signal can be processed like normal z-contrast images since the EDS signal increases monotonously with the concentration of the element like z-contrast signal increases monotonously with the mass thickness. Examples of 3D chemical mapping using XEDS are given on (InGa)N Nanopyramid LEDs, NiAl3 super alloy material for aircraft turbine blades, high-k dielectric transistor and catalytic particles. In summary, this new technique enables a larger field of view and reduces the acquisition time of a complete XEDS mapping tilt series to hours instead of days, which were impractical before. The benefits of the high P/B ratio and its insignificant change with sample thickness in XEDS also permits the use of conventionally prepared FIB foils for 3D chemical mapping and overcomes the difficulties related to background changes with thickness increase known in EELS. [1] M.A. Aronova et al., J. Struct. Biol.161 (2008) 322-353. [2] K. Jarausch et al., Ultramicroscopy 109 (2009) 326-337. [3] T. Yaguchi et al., Ultramicroscopy 108 (2008) 1603-1615. [4] D. Huber et al., Late Breaking Poster, Microscopy and Microanalysis (2010) [5] P. Schlossmacher et al., Microscopy Today 18(4) (2010) 14-20.

Activated chemisorption plays a critical role in heterogeneous catalysis, chemical vapor deposition, chemical dry etching and electron image contrast in chemical imaging. We present an in-situ electron microscopy method for characterizing chemisorption by temperature-resolved, gas-mediated electron beam induced processing. Activated chemisorption is incorporated in rate kinetics models of electron beam induced deposition (EBID). The modified model is verified experimentally and used to characterize the rates and energy barriers that govern adsorption of tetraethoxysilane (TEOS) on silicon oxide, and interactions between oxygen radicals and TEOS adsorbates. Electron beam induced deposition and etching (EBIE) entail electron dissociation of precursor adsorbates into fragments that react with a solid surface. Etching is caused by fragments that react to form volatile species which desorb, thereby removing surface material. Deposition occurs when the reaction products are non-volatile, resulting in the addition of surface material comprised of precursor molecule constituents. EBID is typically performed at or close to room temperature by injecting a precursor gas into a high- or an ultra-high vacuum electron microscope while a substrate is irradiated by an energetic (1-300 keV) electron beam. EBID and EBIE growth kinetics are modeled by rate equations that account for precursor transport, adsorption, desorption, surface diffusion and electron dissociation rates. However, to date, adsorption has been described by a single physisorbed state and chemisorption has been neglected in models of EBID and electron induced etching. Here we present a model of EBID rate kinetics that preserves mass balance, accounts for activated (as well as spontaneous) chemisorption, is applicable to both EBID and EBIE, and reduces to existing models in the absence of chemisorbed surface states. It yields the correct, well known temperature dependence of EBID in the absence of chemisorption, and novel behavior arising from thermally activated transitions from physisorbed to chemisorbed states that dominate precursor coverage at elevated temperature. The model is verified by experimentally by the temperature dependence of EBID performed using TEOS precursor, and used to characterize TEOS adsorption kinetics. The combined modeling and experimental method used here illustrates the utility of this approach in characterizing activated chemical processes at surfaces. It will complement and aid interpretation of in-situ electron microscopy studies of chemical processes at surfaces.

InGaN/GaN multi-quantum well (MQW) structures are extensively used in light emitting diodes (LEDs) as the active region. As the constituent materials are all piezoelectric, lattice misfit strain at the InGaN/GaN hetero-interfaces inevitably induces the piezoelectric polarization. Such a piezoelectric polarization is coupled to the spontaneous polarization in each layer due to the lack of inversion symmetry of the wurtzite structure. If the net polarization is not zero, polarization charges build up in a form of two-dimensional sheet against the interface, consequently, which result in a strong electric field along the [0001] growth direction across the MQW. This local built-in field has been regarded as major cause of degradation of the internal quantum efficiency of LED devices. As the net polarization is determined by vector sum of the two contributions, a concept of nullifying the net polarization by controlling the lattice strain at InGaN/GaN interface has been suggested as a promising way to improve the internal quantum efficiency. This task, of course, requires an accurate measurement of piezoelectric polarization induced by local strain and the associated charge distribution. Until now, TEM-based off-axis electron holography method has been a tool of choice for the mapping of internal potential and charge density distribution in semiconductor materials. However, the off-axis method has some limitation for practical application as it requires a reference wave passing through the vacuum, necessitating the use of an electrostatic biprism. In contrast, a recently developed inline electron holography extracts the internal potential distribution directly from a through-focal series of bright-field images. Moreover, dark-field inline electron holography (DIH) using a specific diffracted beam enables the determination of local lattice strain with high precision, low noise, sub-nm spatial resolution and large field-of-view of greater than 1 mu;m. In the present study, we directly obtained the 2-D strain map and total charge density distribution across the InGaN/GaN MQW with sub-nm spatial resolution using the DIH. The obtained strain maps were in good agreement with the simulation results by finite element method. It is shown that total charge density can be determined accurately, which includes the polarization charges bound to the interface as well as the free charges by intentional doping. By comparative analysis of the total charge density map with the polarization charge map, we were able to even detect the asymmetric screening effect of the polarization charges, particularly the positive polarization charges by the free electrons in the n-doped GaN quantum barrier. Successful application of inline holography proved that this technique is very powerful in 2-D mapping of strain and charge density with sub-nm resolution, which can further pave a way to explore unexpected phenomena occurring at semiconductor hetero-interfaces.

Energy dispersive X-ray spectroscopy (EDS) in the electron microscope uses characteristic X-rays for element identification, which are generated during the interaction of electrons with the sample. The sample can be bulk material or electron transparent. EDS is predestined particularly for cases where many elements at once have to be identified quickly and other complementary techniques suffer from peak overlaps and further ambiguities. The smaller the structure to be investigated and thus, the higher the necessary spatial resolution of the microscope, the more difficult it can be to get sufficient beam current into a small electron probe to interact with the sample. Measures such as low dose techniques and low voltage to avoide sample damage or the demand for very fast analysis of large material amounts make this problem even more severe. To detect fast, with no shadowing effects and/or to detect enough of the X-rays generated by a small amount of matter using a small electron probe current are the present challanges for EDS technology. One part of the solution is to increase the solid angle of X-ray detection. Various approaches have been implemented so far, reaching from single large detector areas, via different kinds of multi detector systems to ring-shaped and a Pi-steradian detector [1]. The better a sphere around the sample can be resembled, the more X-rays can be captured. Data from single and multiple chip EDS systems where the solid angle of the detectors is increased up to 1.2sr without necessary changes of the SEM or TEM, will be presented. Another solution for chemical analysis is to combine the EDS-system development by respective adjustments in pole piece and port geometry as well as in beam current and sample holder. We will demonstrate that this enables single atom X-ray spectroscopy even at a relatively low solid angle of 0.1sr using 60keV accelerating voltage to avoid sample damage of beam sensitive materials such as graphene [2]. [1] Nestor Zaluzec, Microsc. Microanal. 15, (2009) 93-98 and Microscopy Today (2009) pp. 56-59 [2] T. C. Lovejoy et al., Appl. Phys. Lett.100, 154101 (2012)

#9675;H. Takamizawa¹,*, Y. Shimizu¹, Y. Nozawa¹, T. Toyama¹, H. Morita², Y. Yabuuchi², M. Ogura², and Y. Nagai¹¹ The Oarai Center, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan ² Panasonic Corporation, Moriguchi, Osaka 570-8501, Japan * Phone: +81-29-267-3181, Fax: +81-29-267-4947, E-mail: takami@imr.tohoku.ac.jp Keywords: atom probe, Fin-FET, dopant Fin field-effect transistors (Fin-FETs) have attracted much attention as a promising structure for next generation of silicon electronic devices beyond the scaling-down of transistors.[1] In general, the device performance of Fin-FETs relies on dopant distribution in the near surface sidewall of Fins.[2] Self-regulatory plasma doping (SRPD) method was recently developed to achieve conformal doping on the surface of Fin structure,[3] however, the actual dopant distribution was not clarified by conventional methods due to the complicated structure. In order to precisely understand the dopant distribution in near surface regions, three-dimensional characterization with sub-nanometer spatial resolution is required. Laser-assisted atom probe tomography (APT) is a powerful method for observing dopant distribution in metal-oxide-semiconductor FETs and related materials with sub-nanometer resolution.[4-5] In APT measurement of Fin-structure samples, it is required that the trenches between the Fin arrays be filled with a material with an evaporation field similar to that of the Fin itself. Though, the conventional deposition techniques frequently lead to specimen fracture at the interface between the Fin and the embedded materials during APT measurements due to the low adherence of the interfaces. In this work, we performed APT analysis of silicon-based p-type (boron-doped) Fin structures prepared by the SRPD technique. To suppress the specimen fracture, the trenches between Fin-arrays were embedded by low-energy focused ion beam direct deposition (FIBDD) of silicon in an off-line process.[6] Even after the samples were exposed to air, the dopant distribution at near the surface of Fin-structures was clearly observed. The peak boron concentrations at the top, sidewall, and bottom regions reached 2.6×10²¹, 3.0×10²⁰, and 2.9×10²¹ atoms/cm³, respectively, which were close to or higher than the activation level achieved by spike and rapid thermal annealing.[7] This combination of FIBDD and APT analysis can be applied to quantitative characterization of dopant distribution in more complicated structures for future electronic devices. References [1] International Technology Roadmap for Semiconductors 2011 Edition. [2] N. Collaert et al. Proceedings of ICICDT, pp.187 (2005). [3] Y. Sasaki et al., IEDM Tech. Dig., pp.917 (2007). [4] K. Inoue et al., Ultramicroscopy 109, 1479 (2009). [5] H. Takamizawa et al., Appl. Phys. Lett. 99, 133502 (2011). [6] S. Nagamachi et al., J. Vac. Sci. Technol. B 16, 2515 (1998). [7] H. Takamizawa et al., Appl. Phys. Lett. 100, 093502 (2012).