Abstract: Washcoat loading on automotive exhaust catalysts is normally determined, in production, by a weight gain procedure, which gives an accurate measure of washcoat weight present on an individual catalyst but does not address such parameters as uniformity of washcoat loading and geometric surface area within the monolith. Both issues are important factors that affect the catalytic activity (especially during catalyst lightoff) and catalyst cost (due to a thick, less functional washcoat) in an automotive exhaust system. Washcoat loading also plays a role in post-use analysis to determine possible reasons for changes (i.e., loss) in catalytic activity. For the post-use examinations weighing techniques are not useful since the washcoat cannot be preferentially removed and part of the weight gain is due to contamination from the combustion process. In the present work a combination of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) X-ray mapping, light microscopy, and digital image processing was used. Two methods have been demonstrated for the determination of the density of calcined alumina washcoats. Additionally, a method has been developed to determine catalyst washcoat loading, either on a sampling basis after manufacture or in studies of catalysts after use. Methods also have been developed to determine other important parameters such as monolith wall thickness, percent open area in a catalyst monolith, geometric surface area, and hydraulic diameter. A linear correlation has been shown between hydrocarbon conversion efficiency and measured geometric surface area, with a coefficient of determination (r2) of 0.84.

Abstract: High-resolution transmission electron microscopy (HRTEM) images of the [1–10] zone of cubic SiC layers grown by molecular beam epitaxy (MBE) often reveal regions of material exhibiting an unusual threefold periodicity. The same contrast was found in earlier works of Jepps and Page, who attributed this contrast in HRTEM images of polycrystalline SiC to the 9R-SiC polytype. In this report we demonstrate by HRTEM image simulations that the model of the 9R polytype and an alternative twinning model can fit qualitatively the experimental HRTEM images. However, by comparing the fast Fourier transform (FFT) patterns of the experiments and the simulations, as well as by using dark-field imaging, we show unambiguously that only the model of overlapping twinned 3C-SiC crystals fully agrees with the experiments.

Convergent-beam electron diffraction and Z-contrast imaging are used to study oxygen-associated defects, flat inversion domain boundaries, dislocations, and interfaces in sintered AlN ceramics. The structures of these defects are directly derived from atomic-resolution Z-contrast images. The flat inversion domain boundaries contain a single Al-O octahedral layer and have a stacking sequence of . . .bAaB-bAc-CaAc. . , where -cAb- indicates the single octahedral layer. The expansion at the flat inversion domain boundaries is measured to be 0.06 (±0.02) nm. The interfaces between 2H- and polytypoid-AlN are found to be also inversion domain boundaries but their stacking sequence differs from that of the flat inversion domain boundaries.

Materials science requires the use of increasingly powerful tools in materials analysis. The last 20 years have witnessed the development of a number of analytical techniques. However, among these techniques, only a few allow observation and analysis of materials at the nanometer level. The tomographic atom probe (TAP) is a three-dimensional atom-probe (3-DAP) developed at the University of Rouen. In this instrument, the specimen is field evaporated, atomic layer by atomic layer, and the use of a position-sensing system makes it possible to map out the chemical identity of individual atoms within each field-evaporated layer on a nearly atomic scale. After analysis, the volume of matter removed from the specimen can be reconstructed atom by atom in the three dimensions of real space. The main advantages of the 3-DAP is its single-atom sensitivity and very high spatial resolution. In addition to 3-D visual information on chemical heterogeneity, 3-D images give an accurate measurement of the composition of any feature without any convolution bias. This study first describes the history of the 3-DAP technique. Its main features and the latest developments of the TAP are then detailed. The performance of this instrument is illustrated through two recent applications in materials science. Possible ways to further improve the technique are also discussed.

This study provides a quantitative validation of qualitative automated three-dimensional (3-D) analysis methods reported earlier. It demonstrates the applicability and quantitative accuracy of our method to detect, characterize, and count Feulgen stained cell nuclei in two tissues (hippocampus and testes). A laser-scanned confocal light microscope was used to record 3-D images i which our algorithms automatically identified individual nuclei from the optical sections given an estimate of minimum nuclear size. The hippocampal data sets were also manually counted independently by five trained observers using the STERECON 3-D image reconstruction system. The automated and manual counts were compared. A nucleus-by-nucleus comparison of the manual and automated counts verified that the automated analysis was accurate and reproducible, and permitted additional quantitative analyses not available from manual methods. The algorithms also identified subpopulations of nuclei within the hippocampal samples, and haploid and diploid nuclei in the testes. Our methods were shown to be repeatable, accurate, and more consistent than manual counting.

With the ultrahigh vacuum variable-temperature scanning tunneling microscope (UHV-VT-STM), atomic-level observation has been achieved. An ultrahigh vacuum atomic force microscope (UHV-AFM) has also been developed, with success in obtaining atom images where observation in noncontact (NC) mode with a frequency modulation (FM) detection method was attempted. Using the FM detection method in the constant oscillation amplitude of the cantilever excitation mode, we have obtained atomic-resolution images of Si(111) 7 × 7 structures and Si(100) 2 × 1 structures and other structures together with STM images in an ultrahigh vacuum environment. Also shown here are contact potential difference (CPD) images using the NC-AFM method.

Abstract: We compare here multi-photon excitation microscopy and tandem scanning reflected light confocal microscopy for the microscopic observation of human skin in vivo. Multi-photon excitation is induced by a 80-MHz pulse train of femtosecond laser pulses at 780 nm wavelength. This nonlinear microscopic technique is inherently suitable for tissue fluorescence imaging because of its deeper penetration depth and lower specimen photodamage. This technique has noninvasively obtained tissue structural information in human epidermis and dermis. Alternatively, tandem scanning confocal light microscopy based on a white light source can provide video-rate image acquisition with high resolution and high contrast. Reflected light confocal methods have been used to obtain images from the skin surface to the epidermal–dermal junction. The relative merits of these two techniques can be identified by comparing three-dimensionally resolved images obtained from the forearm skin of the same volunteer.

The High Temperature Materials Laboratory (HTML, Fig. 1) is a national resource for materials characterization sponsored by the Department of Energy’s Office of Transportation Technology, Assistant Secretary for Energy Efficiency and Renewable Energy. The HTML comprises six principal user centers: Materials Analysis, Thermophysical Properties, X-ray and Neutron Diffraction, Mechanical Characterization and Analysis, Residual Stress, and Machining and Inspection Research. Instruments available at the user centers have extensive capabilities for characterizing the microstructure, microchemistry, and physical and mechanical properties of materials over a wide range of temperatures. Details of all the capabilities of the various user centers are available on the World Wide Web at http://www.ms.ornl.gov/htmlhome/default.htm.http://www.nice.org.uk/page.aspx?o=43210

To date, more than 300 different institutions, evenly divided between university and industry, have formal research agreements with the HTML. Three separate programs are available to meet the needs of these users as well as those from federal agencies wishing to gain access to the HTML.

Abstract: Static and dynamic grain boundary potential barrier effects are directly observed at high spatial resolution for a varistor of model structure and chemistry. Grain boundary mechanisms for nonlinear electrical behavior are investigated for Nb-doped SrTiO3 bicrystals by in situ high-resolution electron holography under applied current coupled with electrical measurements. For the static case, holography reveals a positive grain boundary barrier of about 0.45 V, which is indicative of positive grain boundary charge adjoined by negative space charge regions. Under high applied current, in situ holography records the breakdown of this grain boundary barrier in accord with the macroscopic varistor effect, which is reflected in bulk I-V experiments.

Previous work on microstructural characterization has shown variations in terms of defects and organization of nanostructures in the two polymorphs of calcium carbonate, calcite, and aragonite in mollusc shells. Large variations in mechanical properties are observed between these sections which have been attributed to variations in composite microstructure as well as intrinsic properties of the inorganic phases. Here we present local low-loss electron energy-loss spectroscopic (EELS) study of calcitic and aragonitic regions of abalone shell that were compared to geological (single-crystal) counterpart polymorphs to reveal intrinsic differences that could be related to organismal effects in biomineralization. In both sets of samples, local dielectric function is computed using Kramer-Kronig analysis. The electronic structures of biogenic and geological calcitic materials are not significantly different. On the other hand, electronic structure of biogenic aragonite is remarkably different from that of geological aragonite. This difference is attributed to the increased contribution from single electron excitations in biogenic aragonite as compared to that of geological aragonite. Implications of these changes are discussed in the context of macromolecular involvement in the making of the microstructures and properties in biogenic phases.

Determining the three-dimensional atomic structure of grain boundaries is a crucial first step toward understanding how these defects control the overall bulk properties of materials. In this report we discuss the correlation of experimental atomic resolution Z-contrast images and electron energy loss spectrometry (EELS) to achieve this goal. Initial structural analysis is afforded through empirical bond-valence potentials. This structure is then refined using multiple scattering analysis of the energy loss spectra. These techniques are demonstrated in the analysis of a 27° MgO [001] tilt grain boundary. Through this analysis, we were able to determine specific atomic locations of Ca dopants found present at this grain boundary.

The effectiveness of applying a high-frequency, low-energy, reactive gas plasma for the removal of hydrocarbon contamination from specimens and components for electron microscopy has been investigated with a variety of analytical techniques. Transmission electron microscopy (TEM) analysis of specimens that have been plasma cleaned shows an elimination of the carbonaceous contamination from the specimen. With extended cleaning times the removal of existing carbon contamination debris due to previously conducted microanalysis is shown. Following plasma cleaning, specimens may be examined in the electron microscope for several hours without exhibiting evidence of recontamination. The effectiveness of plasma cleaning is not limited to applications for TEM specimens. Scanning electron microscopy (SEM) specimens that have been plasma cleaned likewise show an elimination of carbonaceous contamination. Furthermore, other electron microscopy parts and accessories, such as aperture strips, specimen clamping rings, and Wehnelts, among others, can benefit from plasma cleaning.

X-ray cone-beam reconstruction from incomplete projection data has important practical applications, especially in microtomography. We developed expectation maximization (EM)-type and algebraic reconstruction technique (ART)-type iterative cone-beam reconstruction algorithms for metal artifact reduction and local reconstruction from truncated data. These iterative algorithms are adapted from the emission computerized tomography (CT) EM formula and the ART. A key step in our iterative algorithms is introduction of a projection mask and computation of a 3-D spatially varying relaxation factor that allows compensation for beam divergence and data incompleteness. The algorithms are simulated with projection data synthesized from mathematical phantoms. In simulation, the EM-type and ART-type iterative algorithms are demonstrated to be effective for metal artifact reduction and local region reconstruction. They perform similarly in terms of visual quality, image noise, and discrepancy between measured and reprojected data. The EM-type and ARTtype iterative cone-beam reconstruction algorithms have potential for metal artifact reduction and local region reconstruction in X-ray CT.

Abstract: A set of uranium compound particles relevant to contaminated soils and other environmental concerns surrounding uranium bioavailability were studied by electron energy-loss spectroscopy (EELS). Core-loss EELS results suggest that uranium 4+ compounds have an energy loss resolvable from 6+ compounds. Shoulders on the uranium O4,5 edge further distinguish UO2 from UF4. Low-loss characteristics distinguish carbon-free uranium oxide specimens on holey substrates. In the presence of carbon, correction techniques must be applied. Uranium oxides, fluorides, and minerals show a tendency toward reduction of uranium toward 4+ under the beam. The electron dose required to achieve the transformation from 6+ to 4+ is more severe than that usually required to obtain satisfactory spectra, but the possibility for reduction should be considered. The conditions for low-loss analysis need not be as vigorous as those for core losses, and can be done without altering the valence of most oxides.

A new method for transmission electron microscope (TEM) specimen preparation using a focused ion beam (FIB) system that results in a lower rate of gallium (Ga) implantation has been developed. The method was applied to structural and analytical studies of composite materials such as silicon (Si)-devices and magneto-optical disk. To protect the specimens against Ga ion irradiation, amorphous tungsten (W) was deposited on the surface of the specimen prior to FIB milling. The deposition was quite effective in reducing the Ga implantation rate, and energy-dispersive X-ray (EDX) analysis of these specimens detected 0.3Ð1.5% Ga incorporated in the thinned area. FIB milling times for these specimens were 1.5Ð2 hr. Although the milling rate was high, all the materials were properly prepared for TEM study, and clear crystal lattice images were observed on all specimens.