Low energy lamellar interfaces in the directionally solidified eutectic (DSE) NiO-ZrO2(CaO) have been investigated using transmission electron diffraction and imaging. The symmetry of this bicrystal and an aspect of interfacial relaxations in the form of symmetry lowering in-plane rigid body translation (RBT) have been explored by performing convergent beam electron diffraction (CBED) experiments of plan-view bicrystals. Edge-on interfaces have also been studied by conventional and high resolution transmission electron microscopy (CTEM and HRTEM respectively), and electron diffraction fine structure analysis. Despite certain experimental difficulties due to interfacial defects and strain, plan-view CBED patterns offered valuable information concerning bicrystal symmetry and indicated no symmetry lowering RBT in this bicrystal. The suitability of plan-view CBED is briefly discussed in view of its potential as a technique to determine bicrystal symmetry and RBT.

The microstructural basis of the strength of borosilicate glass-to-Kovar alloy joints has been investigated where the alloy was preoxidised at 750°C for 10min in air. X-ray diffraction revealed that the oxide scale consisted of hematite and magnetite. Glass was bonded to the alloy by melting at 1000°C for 15min under two conditions: (a) ambient atmosphere and (b) vacuum (360mbar). Scanning and transmission electron microscopy revealed an iron oxide interlayer in the joint bonded under normal atmosphere. Dendritic fayalite nucleated on the iron oxide interlayer and grew into the glass. In the joint made under vacuum, neither the interlayer nor the fayalite phase was observed. In both cases, Co and Ni in the alloy were not involved in the chemical bonding. The joint formed under vacuum had a higher bonding strength of 4.3MPa, compared to 3.6MPa for the joint bonded under ambient atmosphere.

Extract HTML view is not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button. Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

Journal Article Composition-Size Diagrams of Supported Pt-Sn Catalysts Get access L Bednarova, L Bednarova Norwegian University of Science and Technology, Department of Chemical Engineering, Sem Saelands vei 4, N-7491 Trondheim, Norway Search for other works by this author on: Oxford Academic Google Scholar C E Lyman, C E Lyman Lehigh University, Department of Materials Science and Engineering, 5 East Packer Ave., Bethlehem, Pennsylvania, USA Search for other works by this author on: Oxford Academic Google Scholar E Rytter, E Rytter Norwegian University of Science and Technology, Department of Chemical Engineering, Sem Saelands vei 4, N-7491 Trondheim, Norway Search for other works by this author on: Oxford Academic Google Scholar A Holmen A Holmen Norwegian University of Science and Technology, Department of Chemical Engineering, Sem Saelands vei 4, N-7491 Trondheim, Norway Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 8, Issue S02, 1 August 2002, Pages 1150–1151, https://doi.org/10.1017/S1431927602103825 Published: 01 August 2002

The effect of various concentrations of water and chlorine on the formation of bimetallic particles on commercial Pt-Re/Al 2 O 3 reforming catalysts has been investigated. STEM combined with EDX has been used to directly measure the degree of “alloy” formation in the metal particles. XANES/EXAFS analysis was employed to further elaborate the effect of drying prior to reduction. As an indirect measure of bimetallic particles, chemical characterization techniques such as cyclopentane hydrogenolysis and hydrogen chemisorption were used. The beneficial effect of water on the formation of bimetallic particles has been confirmed. No significant effect of the level of chlorine content prior to reduction was found.

Quantitative analysis of particles less than 10 nm in diameter requires a focused electron beam to isolate individual particles for X-ray emission spectrometry. Effects such as phase separation among particles and surface segregation within particles can only be determined by this technique. This analysis can be made quantitative with minimal use of the usual correction factors provided the small particles are supported on ceramic materials about the same thickness as the particles themselves. Two alloy nanoparticle systems are examined here: Pt-Rh and Pt-Re. In each case the catalytic properties resulting from various processing procedures have been correlated with the microstructure within and among individual particles.

Standard Reference Material (SRM) 482 of the National Institute of Standards and Technology is a set of 6 gold/copper wires, ranging in concentration from 0 to 100% Cu in 20% steps, intended for calibration studies of electron beam microanalyzers. This is an appropriate standard to test the accuracy of energy dispersive x-ray spectrometry (EDS) in the Environmental Scanning Electron Microscope (ESEM). While the presence of the gas in the sample chamber gives the ESEM its unique capabilities, it also is the source of complications to x-ray spectrometry. The gas can spread the primary electron beam into a wide skirt of electrons with the consequent production of x-rays many micrometers from the target location of the beam. The six wires (∼ 500 jam in diameter) were embedded and polished in one epoxy mount. The mount was carbon coated in one set of experiments. The coating was removed and the sample retested.

The purpose of this study is to evaluate the variable pressure correction technique (VPCT) as a solution to the problem of extraneous x-ray peaks due to electron beam broadening in the chamber gas of the ESEM. The basis of VPCT is the observation that target x-ray counts decrease with increasing chamber pressure; whereas, x-ray counts due to beam broadening increase. If data are collected at two or more chamber pressures, the number of x-ray counts for an element can be corrected to that expected at zero gas pressure (high vacuum). Tests of NIST SRM 482 have shown EDS x-ray analysis in the ESEM (within the chamber pressure range of 1 to 8 torr) to have comparable accuracy and precision values to those of EDS in the traditional SEM. The samples used in the these studies, however, were quite large (ca. 500 μm in diameter) and so extraneous EDS peaks, due to the electron beam broadening effect of the chamber gas, were minimized. The 60% Au / 40% Cu wire of SRM 482 was pressed into a hole in the surface of an Al specimen stub so as to produce a flat surface with a sharp interface between the wire and the stub. Spectra were collected at 5 and 150 μm from the junction of the wire and the Al stub at chamber pressures of 2, 4, and 8 torr.

Standard Reference Material (SRM) 482 of the National Institute of Standards and Technology is a set of 6 gold/copper wires, ranging in concentration from 0 to 100% Cu in 20% steps, intended for calibration studies of electron beam microanalyzers. This is an appropriate standard to test the accuracy of energy dispersive x-ray spectrometry (EDS) in the Environmental Scanning Electron Microscope (ESEM). While the presence of the gas in the sample chamber gives the ESEM its unique capabilities, it also is the source of complications to x-ray spectrometry. The gas can spread the primary electron beam into a wide skirt of electrons with the consequent production of x-rays many micrometers from the target location of the beam. In spite of the difficulties, at least two methods have been proposed to correct high pressure data to that expected at low pressures.

Solid phase synthesis (SPS) is used for the discovery and optimization of biologically active substances for the pharmaceutical and agricultural industries. Large numbers of novel organic compounds are generated by successively adding functional groups onto a solid substrate - usually polystyrene. Several techniques have been applied to the qualitative and quantitative analysis of these polymer-bound compounds with varying success. Environmental scanning electron microscopy (ESEM) with energy dispersive x-ray spectrometry (EDS) offers a unique approach to the qualitative analysis of SPS resins. Heteroatoms (such as Cl, Br, and S) are added either as a part of the synthesis or as a marker for analysis. Heavier atoms, such as these, are easily detected by EDS. The advantages of EDS are speed, sensitivity, and small required weight of the sample. The advantages of the ESEM are that it eliminates the need for a conductive coating and the vacuum conditions are not as severe on the specimen as with a conventional SEM.

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Catalyst microstructure and catalytic properties can be directly correlated using a composition-size distribution diagram that maps the phases of small alloy particles by composition and size. The application of this diagram given here concerns Pt-Rh/alumina catalysts for reduction of NO in hydrogen at low temperatures. The composition-size diagram provides an understanding of why some alloy catalysts perform worse than pure Pt in the NO reduction reaction, while other preparations exhibit the several times the activity of pure Pt. The composition-size diagram can be used to "fingerprint" active and less active alloy catalysts. Analytical electron microscopy (AEM) has been used to determine the Pt-Rh particle composition-size distribution.Catalysts were prepared by aqueous impregnation of platinum chloride into gamma-alumina particles with a 4 nm average pore size. After impregnation and air drying, the catalyst was calcined in air at 500°C for 3 hr. Subsequently, rhodium was impregnated from its chloride into the same support material, and the preparation was air-dried.

A major goal of analytical electron micrsocopy (AEM) is to detect small amounts of an element in a given matrix at high spatial resolution. While there is a tradeoff between low detection limit and high spatial resolution, a field emission electron gun allows detection of small amounts of an element at sub-lOnm spatial resolution. The minimum mass fraction of one element measured in another is proportional to [(P/B)·P]-1/2 where the peak-to-background ratio P/B and the peak intensity P both must be high to detect the smallest amount of an element. Thus, the x-ray detection performance of an analytical electron microscope may be characterized in terms of standardized measurements of peak-to-background, x-ray intensity, the level of spurious x-rays (hole count), and x-ray detector performance in terms of energy resolution and peak shape.This paper provides measurements of these parameters from Lehigh’s VG Microscopes HB-603 field emission AEM. This AEM was designed to provide the best x-ray detection possible.

Imaging of elemental distributions on a fine scale is one of the triumphs of electron microscopy. Compositional imaging frees the operator from the necessity of making decisions about which features contain the elements of interest. Elements in unexpected locations, or in unexpected association with other elements, may be found easily without operator bias as to where to locate the electron probe for compositional data collection. This technique may be applied to bulk or thin specimens using a variety of composition-sensitive signals as shown in Figure 1.Cosslett and Duncumb obtained the first such compositional image in an electron microprobe modified to scan the electron beam and collect a characteristic x-ray signal as a function of beam position. Early images of this type were called x-ray “dot maps” and provided a qualitative indication of the location of elements on a flat polished bulk specimen to a spatial resolution of about 1 μm.

Analytical electron microscopy (AEM) was well served by the original hole count test that prompted microscope manufacturers to reduce, by an order of magnitude, spurious x-ray generation in the specimen. This spurious x-ray signal is caused by hard x-rays or uncollimated electrons from the illumination system and is typically generated over the entire specimen regardless of where the electron probe is placed for analysis. The original test was performed on an ion-milled thin foil disk specimen of Ag or Mo, but the absolute value of hole count was dependent upon both specimen and operator. To make progress in die reduction of spurious xrays at intermediate voltages (if the problem is present), a hole-count test on a standard specimen that does not require operator judgement would be useful. The ultimate goal would be to reduce spurious x-rays to a level that would not affect any experiment on any specimen.

The concept of interfacial width is often invoked in many materials science phenomena which relate to the structure and properties of internal interfaces. The numerical value of interface width is an important input parameter in diffusion equations, sintering theories as well as in many electronic devices/processes. Most often, however, this value is guessed rather than determined or even estimated. In this paper we present a method of determining the effective structural and electronic- structural width of interphase interfaces using low- and core loss fine structure effects in EELS spectra.The specimens used in the study were directionally solidified eutectics (DSEs) in the system; NiO-ZrO2(CaO), NiO-Y2O3 and MnO-ZrO2(ss). EELS experiments were carried out using a VG HB-501 FE STEM and a Hitachi HF-2000 FE TEM.

Interphase interfaces in the directionally solidified eutectic (DSE) NiO-ZrO2(CaO) have been investigated using transmission electron microscopy (TEM) techniques. Arguments are presented, based on extensive experimental results, to show that the observed interface plane, (111) NiO//(100) ZrO2, corresponds to a minimum in interface energy. The possible relaxation events associated with this interface are identified with the aid of imaging and diffraction analyses. A recently introduced technique of convergent beam electron diffraction for a plan-view bicrystal is attempted in order to identify rigid body translation associated with this interface. Some of the difficulties associated with this technique are discussed.

The major advantage of performing x-ray microanalysis in the analytical electron microscope (AEM) is the high compositional spatial resolution and the chemical analysis sensitivity. The spatial resolution (R) is dependent on the size of the focused electron probe (d) and the amount of electron beam broadening (b). The spatial resolution across a discrete interface is:The amount of beam broadening is directly proportional to the thickness (t) to the 3/2 power and inversely proportional to the beam voltage (E). Optimizing d and b involve a consideration of the minimum x-ray intensity necessary for analysis since the x-ray intensity is decreased by minimizing d and t. To obtain the optimum spatial resolution one should use the thinnest possible specimen, a high kV AEM and a high brightness field emission gun (FEG). Figure 1 shows a Ni composition profile across a planar lOnm precipitate in the plessite region of the Grant iron meteorite. A spatial resolution of 2.5nm was obtained from a 20nm thick sample analyzed in a VG Microscopes, Ltd. HB 501 FEG AEM (probe diameter 1.8nm (FWTM)).

RESUMEDes interfaces lamellaires dans I'eutectique obtenu par solidification dirigee (ESD) Ni0-Zr02(Ca0) ont ete etudiees par des techniques optiques electroniques.Plusieurs defauts caracteristiques a ['interface ont 6te analyses et interpretes I'aide de considerations geometriques.Une attention particuliere est portbe aux defauts topographiques et a leurs caracteristiques structurales et fonctionnelles.