bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron diffraction analysis of a metastable state in ion-irradiated MgAl2O4 spinel
Authors: Devanathan Ram , Yu Ning , Sickafus Kurt E. , Nastasi Michael
Published: June 2020

Magnesium aluminate spinel is considered to be a remarkably radiation resistant material. Single crystal spinel exhibits very little damage when irradiated with fast neutrons or energetic ions. Recently, amorphization of single-crystal MgAl204 was observed, for the first time, following irradiation with 400 keV Xe2+ at about 100 K to a peak dose of 25 dpa. Electron diffraction patterns from spinel subjected to different doses show the extinction of first-order fundamental reflections prior to the occurence of amorphization. This suggests that, enroute to becoming amorphous, ion-irradiated spinel transforms to a metastable crystalline state with a lattice constant that is half that of spinel. In an effort to understand this phase transformation, we have analyzed the structure of the metastable state using electron diffraction.

Spinel belongs to the spacegroup Fd3m (fee Bravais lattice). The unit cell has a lattice constant of about 0.8 nm and is made of two sets of four octants.
Alternative interpretation of electron diffraction patterns from chrysotile asbestos fibers
Authors: Ling P. , Ling H. , Kawayoshi H. , Tsai F. , Gronsky R. , Washburn J.
Published: June 2020

Chrysotile asbestos fibers have been the object of intensive study for many years, and their structure and growth mechanisms have perplexed investigators ever since the original 1930 X-ray diffraction work of Warren and Bragg confused superlattice for fundamental reflections along two of the three unit cell directions. Even after the lattice parameters were accurately found, the origins of the characteristic and plentiful diffuse scattering seen in diffraction patterns challenged the most careful analyses. In 1956, Whittaker performed very detailed calculations of the scattering from fibers that were assumed to adopt the structure of concentric circular cylinders, yet could not obtain agreement with experimental results, especially the intensity distribution of subsidiary maxima(diffuse scattering) bordering Bragg reflections on a single side. It took the beautiful high-resolution electron microscopy of Yada to show that the fibers were actually spiral cylinders rather than circular cylinders, an observation that removed some of the minor discrepancies in Whittaker's model.
In Z-contrast, not all that glistens is high-Z
Authors: Treacy M. M. J. , Bisher M. E. , Jacobson A. J. , Gibson J. M.
Published: June 2020

It is by now a given that high resolution Z-contrast is a useful imaging technique for detecting high atomic number (Z) domains in nanophase materials. However, image intensity also depends on specimen orientation, electron-optical geometry, thickness and local strain fields, as well as local structural ordering. In this paper we will present examples from our materials studies where contrasts from strain and short-range order in hollow-cone dark-field images provide important structural insights. Strain fields were found to be responsible for the unusual "blister' contrasts observed in hollow-cone dark field images of delaminated sheets of calcium sodium niobate layered materials. Wherever two sheets overlap, the average intensity increases and dark disks of diameter ~20 nm, with bright central spots, appear (Fig. 1). For large hollow-cone angles, q1 > 20 nm-1, the blisters vanish, although faint fine-scale features persist. Elasticity analysis and image simulations (Fig. 2) reveal that the blisters are pockets of gas or liquid that became trapped between sheets during the drying stage of the specimen preparation process, when individual sheets come into contact at random mutual angles and reseal (Fig. 3).
Morphological transformations in solution-cast Styrene-Butadiene-Styrene (SBS) triblock copolymer thin films
Authors: Kim Ginam , Marsillo W. , Libera M.
Published: June 2020

The fact that block copolymers can assume a range of morphologies depending upon such variables as relative block length and molecular weight is now well known. In the case of poly(styrene)[PS]-poly(butadiene)[PB]-poly(styrene) (SBS) triblock copolymer, the morphologies range from spheres (roughly ~20% minor component), to cylinders (roughly 20%~35% minor component), to lamellae (roughly equal component fractions) Most recently, there has been increasing interest in transformations between morphologies by thermal annealing. This paper describes initial results studying the effect of solvent evaporation rate and post-casting annealing treatment on the morphology of SBS thin films.

TEM specimens were prepared by solution casting electron transparent films. 50 μl of 0.1 wt% SBS (30% styrene, Mw=14,000, Scientific Polymer Products, Inc.) dissolved in toluene was deposited on a polished NaCl single crystal substrate placed in a small dish. After solvent evaporation the film was cut into small squares, floated from the salt in water, and each square was collected on a Cu grid.
The influence of nitrogen on the stability of nanophase molybdenum disilicide
Authors: Kung H. , Jervis T. R. , Hirvonen J-P , Mitchell T. E. , Nastasi M.
Published: June 2020

The intermetallic compound, MoSi2, has a combination of interesting properties, ranging from a high melting point to superior high temperature oxidation and corrosion resistance, which makes it a potential candidate for high temperature structural applications. It was shown previously that the addition of nitrogen into MoSi2 forms MoSi2Nx (x:3-4). The new phase has a very high crystallization temperature (> 1000°C) and is thermally compatible with both Mo and MoSi2. As suggested by these results, the introduction of nitrogen into MoSi2 may cause significant changes in its properties, yet the role of nitrogen in influencing the structure and phase stability of MoSi2 is still not known. In this study, we have systematically investigated the evolution of structure in MoSi2 in the presence of different nitrogen contents and annealing conditions.

The system investigated is single phase MoSi2Nx. Films were prepared by sputter deposition using a planar magnetron MoSi2 target at a DC power of 100-200 W.
Oxidation and phase identification in silver/iron-oxide nanocomposites
Authors: Bandaru P. , Yamamot T. , Cosandey F.
Published: June 2020

In the last few years, there has been great interest in magnetic nanocomposite materials because of their unique properties such as giant magnetoresistance and enhanced magnetocaloric effects. We have recently synthesized bulk Ag/FeOx nanocomposites by inert gas phase condensation (GPC). In this process, Ag and Fe particles were first formed by co-evaporation followed by vapor phase condensation and collection on a LN2 cooled collector. The particles were then passivated in oxygen, collected and compacted in-situ. Selected samples were then annealed in an inert atmosphere of helium at 250°C for 1h or in an oxidizing atmosphere of 10%-O2/He at 230°C for 15h. These annealing treatments were found to modify the effective magnetic moment size and saturation value of magnetization. For the O annealed sample, a superparamagnetic nanocomposite has been obtained with a transition temperature Tc of 160 °K. In order to understand these magnetization changes, an effort has been made to characterize the microstructure and to identify the oxide phases by combined Mössbauer, X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). In this paper, phase identification by combined selected area diffraction and direct high resolution imaging are presented.
Amorphous silica coating on α-alumina particles
Authors: Mellowes J. W. , Chun C. M. , Aksay I. A.
Published: June 2020

Mullite (3Al2O32SiO2) can be fabricated by transient viscous sintering using composite particles which consist of inner cores of a-alumina and outer coatings of amorphous silica. Powder compacts prepared with these particles are sintered to almost full density at relatively low temperatures (~1300°C) and converted to dense, fine-grained mullite at higher temperatures (>1500°C) by reaction between the alumina core and the silica coating. In order to achieve complete mullitization, optimal conditions for coating alumina particles with amorphous silica must be achieved. Formation of amorphous silica can occur in solution (homogeneous nucleation) or on the surface of alumina (heterogeneous nucleation) depending on the degree of supersaturation of the solvent in which the particles are immersed. Successful coating of silica on alumina occurs when heterogeneous nucleation is promoted and homogeneous nucleation is suppressed. Therefore, one key to successful coating is an understanding of the factors such as pH and concentration that control silica nucleation in aqueous solutions. In the current work, we use TEM to determine the optimal conditions of this processing.
Investigation of irradiation-induced nucleation processes in silicon and germanium
Authors: Atwater Harry A. , Yang C.M. , Shcheglov K.V.
Published: June 2020

Studies of the initial stages of nucleation of silicon and germanium have yielded insights that point the way to achievement of engineering control over crystal size evolution at the nanometer scale. In addition to their importance in understanding fundamental issues in nucleation, these studies are relevant to efforts to (i) control the size distributions of silicon and germanium “quantum dots𠇍, which will in turn enable control of the optical properties of these materials, (ii) and control the kinetics of crystallization of amorphous silicon and germanium films on amorphous insulating substrates so as to, e.g., produce crystalline grains of essentially arbitrary size.

Ge quantum dot nanocrystals with average sizes between 2 nm and 9 nm were formed by room temperature ion implantation into SiO2, followed by precipitation during thermal anneals at temperatures between 30°C and 1200°C[1]. Surprisingly, it was found that Ge nanocrystal nucleation occurs at room temperature as shown in Fig. 1, and that subsequent microstructural evolution occurred via coarsening of the initial distribution.
In Situ microscopy of the anodic etching of silicon
Authors: Ross Frances M. , Searson Peter C.
Published: June 2020

Porous semiconductors represent a relatively new class of materials formed by the selective etching of a single or polycrystalline substrate. Although porous silicon has received considerable attention due to its novel optical properties1, porous layers can be formed in other semiconductors such as GaAs and GaP. These materials are characterised by very high surface area and by electrical, optical and chemical properties that may differ considerably from bulk. The properties depend on the pore morphology, which can be controlled by adjusting the processing conditions and the dopant concentration. A number of novel structures can be fabricated using selective etching. For example, self-supporting membranes can be made by growing pores through a wafer, films with modulated pore structure can be fabricated by varying the applied potential during growth, composite structures can be prepared by depositing a second phase into the pores and silicon-on-insulator structures can be formed by oxidising a buried porous layer. In all these applications the ability to grow nanostructures controllably is critical.
Energy-filtered imaging of interfacial composition in complex Ni-base superalloys
Authors: Hall E. L. , Bentley J.
Published: June 2020

In a wide variety of important engineering materials, including structural Ni, Fe, and Al-base alloys, the study of compositional gradients that occur at grain boundaries and other interfaces due to the precipitation of solute-rich second phases is of critical importance. X-ray spectrometry in the analytical electron microscope (AEM) has been used for many years to study solute depletion at interfaces in these alloys. It has been particularly effective at providing accurate, quantitative measurements in cases where the interface precipitates are spaced far apart and where relatively wide compositional gradients result from diffusion-controlled “collector-plate” mechanisms. However, in complex alloys, with heavy grain boundary coverage, multiple precipitate types, and/or multiphase matrices, x-ray microanalysis is more limited due to beam spreading and die associated 5-20nm spatial resolution achieved in these alloys with AEMs equipped with thermionic sources.

Elemental mapping in an AEM equipped with an imaging energy-filter is an alternative method for the study of interface compositional gradients. It has been shown to be effective for this purpose in relatively simple situations in steels.
Delocalization effect in energy-filtered electron images of surfaces and interfaces
Authors: Wang Z. L. , Shapiro A.J.
Published: June 2020

Accurate structure determination is feasible using zero energy-loss images, since image simulations can be done accurately based on elastic scattering theory [1]. Two factors can be assessed from the energy-filtered images: one is the contribution of inelastically scattered electrons to HREM images; and two is the effect of absorption by inelastic scattering on images obtained using 0-loss electrons. In this paper, MgO(l00) surface and Al/Ti interface are used to demonstrate the delocalization effect of valence-excitation in energy-filtered surface and interface images, respectively.

Figure 1 shows a pair of MgO lattice images recorded using all the transmitted (Figure la) and just the elastically transmitted (Figure lb) electrons, respectively. The MgO cube is oriented along [110], so that the contrast variation as a continuous function of the specimen thickness is revealed by a single image. When the specimen is thinner than about 20 nm, no significant differences are seen between the filtered and unfiltered images.
Application of through-focal series restoration for resolution enhancement
Authors: McCartney M. R.
Published: June 2020

Apart from instrumental instabilities, the point resolution for phase contrast imaging is determined by the spherical aberration of the objective lens and the electron wavelength. The 1Å spatial resolution barrier in transmission electron microscopy has recently been broken or very closely approached by several research groups. These efforts have concentrated in two directions; reducing the wavelength and post-correction of the aberration function. The advantage of increasing the accelerating voltage is that images of sufficiently thin specimens are immediately interpretable, with the disadvantages being increased radiation damage and enormous cost. The alternate method involves application of a complex phase plate which is the inverse of the objective lens transfer function. One must then have access to the phase and amplitude of the image wave, rather than the intensity which is normally obtained. Two promising methods for this complex wave retrieval are electron holography, and through-focal-series restoration. This presentation will address practical issues in the use of the “paraboloid” through-focal-series method. This method utilizes the functional form of the Fresnel propagator which relates wave functions modified by different defoci.
Quantitative high spatial resolution microchemical analysis of Fe-Co-Ni transformational-toughened steels
Authors: Lippard H.E. , Dravid V.P. , Olson G.B.
Published: June 2020

Superior strength-toughness combinations can be obtained in Aermet 100 by an austenite→martensite phase transformation of small intralath austenite precipitates. The enhanced toughness in these alloys has been attributed to the presence of “metastable” austenite precipitates, the stability of which is intimately related to the size and composition. The austenite precipitates require high stability to resist transformation under all stress conditions except when in the triaxial stress field of a crack tip. The two primary factors determining austenite stability are size and composition. Thus the microstructureproperty correlations and further alloy development require quantitative microchemical analysis of the 50-150Å austenite precipitates.

Of the two obvious analytical electron microscopy techniques, energy dispersive spectrometry (EDS) is superior for quantitative results. Several artifacts must be considered when performing quantitative EDS, for example; the continuum background, absorption/fluorescence effects, k-factor measurement and peak overlap. The continuum background fitting is elementary due to the high peak/background ratio and extensive research in this area.
Electron optical design of an EFTEM concerning optimum selection of imaging parameters for different sizes of detection systems
Authors: Benner G. , Probst W. , Rilk R.
Published: June 2020

The amount of information which can be gained about an object is considerably improved by the incorporation of an imaging energy filter in a TEM. Besides the conventional modes of operation elastic brightfield (EBF) and darkfield (EDF) imaging or diffraction are provided by an Energy Filtering Transmission Electron Microscope (EFTEM) as well as Electron Spectroscopic Imaging (ESI) or Electron Energy Loss Spectroscopy (EELS). Thus, the demands for carefully designed highly flexible electron optics are much more sophisticated as compared to a CTEM.

One of the most important parameters for elastic imaging and ESI is the width of the energy window, which can be selected by a slit aperture of adjustable width according to the particular needs. This energy window defines the size of the transferable specimen area or diffraction pattern, respectively, as well as the acceptance angle of the spectrometer. In order to meet the optimum parameters concerning the energy window and the size of the detection system (e.g. photographic plate, image plate, Slow Scan CCD camera (SSCCD), TV camera, electron detector, etc.) the magnifications of the pre- and of the post-spectrometer projector lens systems has to be independently adjustable.
Point-defect distributions in ceramics by spectrum-line profiling
Authors: Bruley John , Williams David B. , Tseng Ming-Wei
Published: June 2020

Electron energy-loss spectroscopy is well suited to the study of interfaces because the ionization edges can be used to identify the atomic species present and the near edge fine structures on the edges reveal information on the electronic structure surrounding these atoms. This information can be extracted from regions of sample approaching atomic dimensions. A challenge is to be able to map and interpret spectral features with a level of confidence that will allow explanations of physical properties of interest.

The term Spectrum-Line is used here to refer to a linear array of spectra, recorded sequentially along a line traced out by the electron probe and is the 1 dimensional analog of the Spectrum-Image. Processing Spectrum-Lines to generate quantitative profiles can provide a vivid picture of changes in composition, a valence state, or site occupancy across an interface. To aid interpretation and guide further spectrum analysis the near-edge fine structures can be compared to spectra from compounds whose atomic coordinations are well known or modeled using the results of band-structure or molecular orbital calculations of electronic structures.
Quantitative analysis of hole density and lattice parameter at grain boundaries in YBa2Cu3O7-δ
Authors: Zhu Yimei , Zuo J.M.
Published: June 2020

One challenge for high Tc superconductor research is to overcome the low intergranular transport currents which hinder practical applications. Evidence shows that lattice mismatch at the boundaries contributes to the depletion in charge carriers (holes), while the strain fields surrounding the cores of boundary dislocations suppress the superconducting order parameter. Using high-spatial resolution EDX, EELS and CBED techniques with a 20 Å field emission probe, we studied cation segregation, variations in oxygen/hole content, and lattice parameters at and across grain boundaries for various Σ and near-Σ boundaries in bulk YBa2Cu3O7-δ. The geometry of those arbitrary grain boundaries was modeled using the constrained Coincidence Site Lattice (cCSL) theory, which requires c2/a2 being rational for coincidence boundaries in non-cubic crystals.

In this presentation, we report our quantitative and simultaneous measurements of oxygen/hole content (Fig.l) and of lattice parameters (Fig.3) at the boundary regions. The oxygen/hole density was quantified by guassian fitting to the observed oxygen K-edge spectra (Fig.2) and comparing them with those from the same batch which had undergone oxygen reduction process (oxygen content was determined by thermal gravimetric analysis and mass-measurement techniques).
The measurement of thin-film reaction layers with high-resolution FESEM
Authors: Kotula Paul G. , Barry Carter C.
Published: June 2020

Thin-film reactions in ceramic systems are of increasing importance as materials such as oxide superconductors and ferroelectrics are applied in thin-film form. In fact, reactions have been found to occur during the growth of YBa2Cu3O6+x on ZrO2. Additionally, thin-film reactions have also been intentionally initiated for the production of buffer layers for the subsequent growth of high-Tc superconductor thin films. The problem is that the kinetics of ceramic thin-film reactions are not well understood when the reaction layer is very thin; that is, when the rate-limiting step is a phase-boundary reaction as opposed to diffusion of the reactants through the product layer. In this case, the reaction layer is likely to be laterally non-uniform. In the present study, the measurement of thin reaction-product layers is accomplished by first digitally acquiring backscattered-electron images in a high-resolution field-emission scanning electron microscope (FESEM) followed by image analysis. Furthermore, the problem of measuring such small thicknesses (e.g., 20-500nm) over lengths of interfaces longer than 3mm is addressed.
A CVI-processing marker study
Authors: Freeman G. B. , Lackey W. J. , Vaidyaraman S.
Published: June 2020

Fiber reinforced ceramic composites greatly extend the region of application for ceramic materials because the inclusion of a second phase such as fibers helps to prevent catastrophic failure via the mechanisms of crack branching, deflection, bridging and fiber pull-out. While ceramic composites are excellent candidate materials for high temperature structural applications, many conventional manufacturing processes damage the fibers during fabrication and thereby reduce the strength and toughness from what is theoretically possible. Chemical vapor infiltration (CVI) is an effective and versatile technique for fabrication of ceramic matrix composites which promises to reduce fiber degradation.

While CVI is no longer a truly novel processing technique, it is still difficult to predict the best set of operating conditions for what can be a tedious process. Conventional CVI methods may take up to a week to fully infiltrate a small part and even state-of-theart forced flow-thermal gradient CVI (FCVI) processing takes the better part of a day. It is, more over, difficult to monitor the evolution of deposition within a, for example, woven preform.
Identification of the intermediate phase Bi4Sr4Ca3Cu5O18+δ during Bi/2212 and Bi/2223 conversion
Authors: Bian Weimin , Zhu Yimei , Wang Y.L. , Gillette D. , Suenaga M.
Published: June 2020

Among all the high-temperature superconductors, Bi/2223 is the most promising material as tapes and wires for large-scale and high-current applications. However, synthesizing Bi/2223 as a single phase is extremely difficult because of its relatively poor thermal stability and the narrow ranges of stoichiometry and temperature for its formation. Recently, to understand the formation mechanism and establish the optimum heat treatment conditions for the growth of Bi/2223, we have systematically studied phase transformation of the Bi-based superconductors. In this article, we report our finding of the intermediate phase of Bi4Sr4Ca3Cu5O18+δ (Bi/4435).

Bi/2212 tapes with a Bi/2223 composition, produced by the standard “oxide powder in tube” process, were used in the study. TEM cross-section specimens were prepared from the bulk samples that were quenched or furnace-cooled from different stages during the Bi/2212 and Bi/2223 conversion.

Figure 1 shows a lattice image of the Bi/4435 phase with an alternating narrowly and widely spaced lattice (each black line corresponds to the position of the BiO layer).
Improving soil remediation through characterization
Authors: Buck E. C. , Dietz N. L. , Bates J. K.
Published: June 2020

Operations at former weapons processing facilities in the U. S. have resulted in a large volume of radionuclidecontaminated soils and residues. In an effort to improve remediation strategies and meet environmental regulations, radionuclide-bearing particles in contaminant soils from Fernald in Ohio and the Rocky Flats Plant (RFP) in Colorado have been characterized by electron microscopy. The object of these studies was to determine the form of the contaminant radionuclide, so that it properties could be established [1]. Physical separation and radiochemical analysis determined that uranium contamination at Fernald was not present exclusively in any one size/density fraction [2]. The uranium-contamination resulted from aqueous and solid product spills, air-borne dust particles, and from the operation of an incinerator on site. At RFP the contamination was from the incineration of Pu-bearing materials. Further analysis by x-ray absorption spectroscopy indicated that the majority of the uranium was in the 6+ oxidation state [3].
Petrofabric study using electron channeling patterns of quartzes and hematites in dual-phase banded iron formations
Authors: Lee K. Y. , Robertson B. W.
Published: June 2020

Research in deformation of rocks requires the understanding of structure-property relationship. The study of structure-property relationships requires knowledge of the crystallographic texture on a local scale. Electron Channeling in scanning microscope has been used to analyze textures of local features in a microstructure, misorientations between grains and the spatial arrangement of grains of individual crystallographic orientations can be determined. This information is critical for a mechanical understanding of microstructure evolution during the deformation of rocks. Petrofabric analysis using Electron Channeling Patterns can use normal geological thin sections and mounted sections, which allows relatively fast and easy interpretation and allows one to determine the relationship between a microstructural feature and the individual orientations of its grains. The most efficient and satisfactory way of accomplishing this task is by direct electronic detection and indexing of Kikuchi patterns, which requires modification of the microscope, at considerable cost. This study, however, has been undertaken using only an unmodified SEM with electron channeling capability.
Composition-size distribution diagrams for alloy catalysts
Authors: Lyman C. E. , Lakis R. E. , Stenger H. G.
Published: June 2020

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.
Transmission Electron Microscopy studies of catalytically grown carbon nanostructures
Authors: Baker R. T. K. , Rodriguez N. M.
Published: June 2020

In recent years a great deal of research effort has been devoted to the synthesis of carbon structures possessing extensive crystalline order. Methods used for the preparation of such materials center around arc-discharge procedures, however, separation and purification of the desired product has proven rather difficult. Studies carried out in our laboratory have led to the developement of an alternative approach, which involve the participation of a metal catalyst for the production of various carbonaceous structures. Carbon nanofibers are the product of the catalytic decomposition of selected hydrocarbons and carbon monoxide over metal particles. In this process, the hydrocarbon is adsorbed and decomposed on certain faces of the metal, carbon species diffuse through the particle to precipitate at another set of faces to form graphite as illustrated in Figure 1. The structure of the nanofiber is therefore dependent on the geometric orientation and the number of carbon precipitating faces in the metal particle.
Atom probe studies of catalyst surfaces: structure and chemistry at atomic level
Authors: Smith G.D.W. , Cerezo A. , Poulston S.
Published: June 2020

The imaged (apex) region of a field ion microscope (FIM) specimen is sharply curved and has a radius of less than lOOnm. It is thus a reasonably good "model" for one half of a single particle of a metallic catalyst. FIM images show good detail of steps, ledges and kink site atoms (Fig. 1). When combined with a time-of-flight mass spectrometer to form an atom probe (AP), single atom chemical identification becomes possible. The FIM-AP combination has considerable value for the study of heterogeneous catalysts and catalytic reactions, but there are problems due to the high field acting on the specimens during observation, and the need to work in a vacuum environment. The most important applications to date have involved studies of the surface of the catalyst material, and of relatively non-labile adsorbates. However, new developments in AP instrumentation have opened the prospect of seeing catalytic reactions occurring on the atomic scale, and analysing the intermediate reaction products in both spatially- and time-resolved modes with high precision. Two main lines of development have contributed to this exciting prospect. Block and co-workers in Berlin produced the Pulsed Field Desorption Mass Spectrometer (PFDMS). In this instrument, a high electric field is initially applied to a FIM specimen in the presence of a reactive gas mixture. The specimen apex is cleaned by raising the field to a level sufficient to produce field evaporation, and then the field is dropped to zero to allow gas adsorption and reaction to occur.
Al2O3/CeO2 washcoats for three-way automotive emission catalysts
Authors: Kenik E.A. , More K.L. , LaBarge W. , Beckmeyer R.
Published: June 2020

Platinum-rhodium based three-way-catalysts (TWC) are the primary catalytic system for control of hydrocarbon, CO, and NOx automotive emissions. Mixed Al2O3/CeO2 oxides are often dispersed on a cordierite honeycomb monolith as a washcoat and act as a high-surface-area carrier for the heavy metal catalyst clusters. There are both regulatory and marketplace demands for improved performance, lifetime, cost and reliability of these catalytic converters. The conversion efficiency and lifetime of a converter is determined by the microstructure of the washcoat/monolith and its evolution during high temperature exposure to the exhaust gas stream. Scanning electron microscopy (SEM), electron microprobe analysis, and analytical electron microscopy (AEM) were utilized to characterize these catalysts. Some AEM was performed on crushed washcoat specimens dispersed on holey carbon films. In addition, an innovative technique was developed for the preparation of transverse section specimens from the monolith, which preserves the spatial correlation of microstructure and elemental distribution with respect to position in the washcoat/cordierite.
TEM Study of bonded silicon wafers
Authors: Mulestagno L. , Craven R. , Fraundorf P.
Published: June 2020

The promise of higher speed, radiation hard, high temperature capabilities, and increased device density has made SOI ( silicon - on - insulator) an attractive proposition since its conception several years ago . Until recently the methods for its manufacture had been plagued by low yields, and poor quality . Remarkable advances have been made lately resulting in increasing quantities of SOI wafers being sold commercially.

The two main techniques for making SOI are Separation by Implantation of Oxygen (SIMOX) and direct wafer bonding (Bonded wafers). Little analytical work has yet been performed on the latter by the microscopy community at large, so we studied 2 commercial quality wafers with the intent of looking for particulate defects which might arise during annealing, and studying the oxide layer and oxide-SOI interface quality.

Plane view samples were made from the SOI taking advantage of its chemistry, by dimpling and milling from the back-side, and then dipping in HF which attacks the oxide, and leaves large areas of silicon film suitable for TEM untouched.
Cathodoluminescence studies of materials for use in optical display devices
Authors: Wright P.J.
Published: June 2020

Cathodoluminescence studies have been carried out for many years for the assessment of semiconductor materials such as Gallium Arsenide, Gallium Phosphide and Silicon. These investigations have relied on utilising the focused electron beam of an SEM to excite luminescence. This is subsequently directed through a monochromator to allow spectroscopy and also the acquisition of high resolution images showing the spatial distribution of the optically active centres (≥0.5μm).

The recent growth of research in the production and characterisation of optically active materials and devices such as 3/5 or 2/6 LED's for the use in visible display products has fuelled the use of CL to determine the optical properties on a scale that is superior to that available by PL. In addition characterisation of the optical properties as a function of electron beam characteristics, dosage and at temperatures between 4.2K and 300K are possible.

Results from GaN epilayers will be shown that indicate that two separate phases (alpha and beta) can be identified by the position of the Bound Exiton luminescence and that this luminescence is distributed randomly through the sample. The sites responsible for this luminescence are less than 0.5μm in size.
HREM study of epitaxy in Co-Sm // Cr thin films
Authors: Liu Y. , Robertson B. W. , Sellmyer D. J.
Published: June 2020

In developing Co-based magnetic thin films for high density recording, it is well known that the Cr underlayer plays a critical role in generating large in-plane coercivity. Recently it has been shown that Co-Sm films with a nominal composition from Co4Sm to Co7Sm2 exhibit high coercivity and inplane anisotropy. Transmission electron microscopy studies of Co-Sm films have shown that the microstructure of a Co-Sm thin film is composed of the amorphous matrix and crystallites with a grain size of about 5 nm. The crystallites in the as-deposited Co-Sm films have a close-packed structure . Each crystallite has a particular stacking mode which consists of local random stacking, occasionally a few unit cells of two layer stacking AB, three layer stacking ABC, and four layer stacking ABAC. However, the epitaxy relation between the Co-Sm crystallites and the Cr, if any, remains a mystery. In this paper we report our discovery of a new epitaxial relation between the Co- Sm crystallites and the Cr underlayer.
Investigation of thermochromic polydiacetylenes by AFM
Authors: Shivshankar V. , Sandman Daniel J. , Kumar Jayant , Tripathy Sukant K. , Sung Changmo
Published: June 2020

In recent years, Polydiacetylenes (PDAs) have attracted a great deal of attention owing to their extremely large third order non-linear optical susceptibilities, which are believed to result from their molecular arrangement. It is also known that a specific sub-class of these PDAs, namely, the urethane - substituted PDAs such as ETCD (Bis ethyl urethane of 5,7 dodecadiyn 1,12 diol) and IPUDO (Bis isopropyl urethane of 5,7 dodecadiyn 1,12 diol) exhibit thermochromism. This is the underlying principle behind the potential use of such PDAs in optical devices such as holographic elements, spatial light modulators etc. The surface properties of these PDA materials are critical to their performance as optical devices. There are several indications from Raman Spectroscopy that PDA crystals have surface features distinct from the bulk. Also PDA - IPUDO has been identified as a material with a variable surface. We have investigated the free standing single crystals of the monomeric and polymeric forms of PDA - ETCD and IPUDO by Atomic Force Microscopy (AFM). Large scale as well as molecular resolved images were obtained.
Multitechnique characterization of polysulfone gas permeation membranes
Authors: Behrens M. A. , Jois Y. H. R. , Dahlstrom P. L.
Published: June 2020

Integrally thin skinned asymmetric polysulfone membranes developed for gas separation applications were prepared by casting a dope solution on a glass plate. A dry/wet phase inversion process with a forced convective evaporation step is then used to form a skin. The membrane is immersed in water before undergoing a solvent exchange and drying process. The thin skin of these membranes allows gas to selectively diffuse through the membrane when the surface is without defects. The gas transport properties (selectivity and flux) are measured using standard techniques and are reported on Table II.

Scanning electron microscopy is an important method of examining the cross-sections and surfaces of these membranes to determine the surface integrity, skin thickness, and porosity of the supporting substructure. The ideal integrally thin skin thickness is 1000 Å or less. We further characterized these membranes using Atomic Force Microscopy to image the membrane surface and X-ray Photoelectron Spectroscopy to obtain chemical information about the polysulfone surface.
Parallel EELS of polymers in a TEM: energy calibration of the carbon-K-edge
Authors: Heckmann W.
Published: June 2020

Electron energy loss spectroscopy (EELS) measures the loss in energy of the primary electrons caused by inelastic scatter at the electron shell. The energy loss can be detected with magnetic spectrometers operating in parallel (PEELS) and with imaging magnetic/electrostatic Castaing or magnetic omega filters. To detect EEL-spectra of radiation sensitive polymers a PEEL-spectrometer is useful, because it allows a very fast detection of the spectrum. Dynamic measurements that show the changes in the PEEL spectra during irradiation, yield additional information.

An important part of recording the spectrum at high energy resolution is the energy calibration. In parallel detection, the spectrum is displayed on a diode array with a finite number of diodes (1,024). So at high energy resolution (0.05 eV/ch) it is in general only possible to observe a narrow section of about 50 eV of the total spectrum. At higher energy losses that do not allow simultaneous measurement of the elastic peak, it is only possible to give a very approximate value in terms of eV units as the primary radiation energy can drift during the measurement. It is therefore impossible to compare spectra with one another as the absolute energy scale is not known. But, as the chemical shifts of interest have an order of magnitude ranging from fractions of an eV to several eV, it is essential to know the absolute energy scale.
Thin foil preparation for AEM study of small metal particles in stony meteorites
Authors: Yang Cheol-Woong , Williams David B. , Goldstein Joseph I.
Published: June 2020

The phase transformation processes and phase equilibria of the Fe-Ni and Fe-Ni-S system at low temperature can be better understood by characterizing the microstructure and chemistry of metallic particles in stony meteorites using analytical electron microscopy (AEM) techniques. However stony meteorites have a composite nature consisting of metal particles embedded in an inherently brittle silicate matrix, which causes a differential thinning rate. The thin foil preparation of the metal particles for AEM has proved to be very difficult, and we report on the first successful specimen preparation.

Materials of this type present particular difficulties in the preparation of thin foil specimens because the area of interest is limited to specific regions within the metal particles. The metal particles are usually less than 500 μm in size and the silicate matrix is inherently brittle. Moreover, the interfaces between metal particles and silicates are weak because of corrosion, depending on cooling, etc.
Quantitative defect studies in semiconductor TEM samples prepared by low angle ion milling
Authors: Mulestagno L. , Holzer J.C. , Fraundorf P.
Published: June 2020

Due to the wealth of information, both analytical and structural that can be obtained from it TEM always has been a favorite tool for the analysis of process-induced defects in semiconductor wafers. The only major disadvantage has always been, that the volume under study in the TEM is relatively small, making it difficult to locate low density defects, and sample preparation is a somewhat lengthy procedure. This problem has been somewhat alleviated by the availability of efficient low angle milling.

Using a PIPS® variable angle ion -mill, manufactured by Gatan, we have been consistently obtaining planar specimens with a high quality thin area in excess of 5 × 104 μm2 in about half an hour (milling time), which has made it possible to locate defects at lower densities, or, for defects of relatively high density, obtain information which is statistically more significant (table 1).
High-resolution EM study of submicrometer-grained Al-Mg solid solution alloys
Authors: Horita Z. , Smith D. J. , Furukawa M. , Nemoto M. , Valiev R. Z. , Langdon T. G.
Published: June 2020

It is possible to produce metallic materials with submicrometer-grained (SMG) structures by imposing an intense plastic strain under quasi-hydrostatic pressure. Studies using conventional transmission electron microscopy (CTEM) showed that many grain boundaries in the SMG structures appeared diffuse in nature with poorly defined transition zones between individual grains. The implication of the CTEM observations is that the grain boundaries of the SMG structures are in a high energy state, having non-equilibrium character. It is anticipated that high-resolution electron microscopy (HREM) will serve to reveal a precise nature of the grain boundary structure in SMG materials. A recent study on nanocrystalline Ni and Ni3Al showed lattice distortion and dilatations in the vicinity of the grain boundaries. In this study, HREM observations are undertaken to examine the atomic structure of grain boundaries in an SMG Al-based Al-Mg alloy.

An Al-3%Mg solid solution alloy was subjected to torsion straining to produce an equiaxed grain structure with an average grain size of ~0.09 μm.
Microstructure of roughened surface in metal rolling
Authors: Lee W. M. , Meshii M. , Wilson W. R. D. , Chiou W. A. , Lin C. S.
Published: June 2020

Flat rolled aluminum products have a $25 billion market worldwide annually. The topography of the rolled surface is a key measure of surface quality. A dull surface finish can be generated by non-homogeneous surface deformation when the sheet is rolled under conditions of hydrodynamic lubrication. This is undesirable for some applications where high reflectivity is required, though it improves paintability. Wilson and Schmid have investigated the influence of lubrication conditions on roughening. Although the texture evolution during the hot and cold rolling of aluminum has been studied, the basic mechanisms of the roughening process are not fully understood. The purpose of the present research is to explore the microstructural changes associated with the evolution of surface roughness and to use this information to develop mathematical models which can accurstely describe the surface roughening evolution process.

A TEM study of cross-sectional microstructure evolution of aluminum alloy Al 5052-0 material during cold rolling in the presents of a thick lubricant film has been conducted. Commercial aluminum alloy AL 5052-0 as-received was used in the experiments.
Microanalysis and characterization of protective coatings used in metal-matrix composites
Authors: Heffelfinger Jason R. , Kieschke Robert R. , Barry Carter C.
Published: June 2020

Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and parallel-aquistion electron-energy loss spectrometry (PEELS) have been used to investigate various coating schemes used in alumina-fiber reinforced titanium alloys. The high-temperature properties of metal-matrix composites (MMC's) depend greatly on the interface between the ceramic fiber and metal matrix. The chemical and mechanical properties of this interface may be tailored by coating the alumina fibers with various materials. In this work, emphasis has been placed on the chemical aspect of the coatings and their role in inhibiting the reaction between the alumina fiber and the titanium matrix. The brittle nature of the reaction products, Ti3Al and TiAl, weakens the composite and thus leads to its ultimate failure.

The composites are made of α-alumina fibers (Nextel 610 with a mean diameter of ~12 mm) which are first coated with thin protective layers such as Y2O3 and Nb followed by a coating of β-titanium alloy (TIMETAL 21S Ti -15Mo -3A1 -2Nb -0.2Si.) Several thousand fibers are then placed together inside a glass tube and HIP-ped (Hot Isostatic Press) at temperatures of ~900°C and times of ~2 hours to attain a dense composite.
Microstructure of plasma-deposited iron-nitride films
Authors: Siriwardane H. , Polly C. , Sago A. , Fraundorf P. , Pringle O.A. , Newkirk J. W. , James W.J.
Published: June 2020

Iron nitride films are potential candidates for information storage media. In order to use the films as a perpendicular magnetic recording media, it is necessary to know about the micro-, crystal, and magnetic structures, physical properties, and processing of these thin films. Here we describe the micro- structure of plasma-deposited iron nitride films.

The microstructure of films deposited on glass and carbon support films on copper grids were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Auger electron Spectroscopy (AES). According to XRD, single phase Fe3N was successfully produced on glass substrates at temperatures 200, 275, 400, & 500 °C, and flow ratios between 0.4 to 15.3 of Fe(CO)5, and NH3. Electron diffraction peak positions of films were compared with Fe3C, Fe7C3, Fe2N, Fe3Nγ-Fe4N, Fe5N2 and Fe3O4 crystal structure d-spacings. The presence of a carbide satellite peak in AES data and by matching all d-spacings in the JCPDS Fe3C card file with every experimental diffraction pattem, enabled us to confirm the presence of Fe3C in these films at all deposition temperatures.