bluuebunny/crossref_metadata_2025_split huggingface dataset:
Applications of high-resolution Electron Microscopy to semiconductor interfaces
Authors: Tsai H. L. 
Published: June 2020

Practical applications of high-resolution electron microscopy (HREM) to semiconductor interfaces have been conducted in various areas. Among these are the use of the HREM as a diagnostic technique for interfacial quality, understanding of interfacial interactions, and analysis of misfit dislocations in heterostructures. These studies indicate that the HREM is a useful technique to provide in-depth understanding of interfaces for the process and defect controls.The quality of an interface often plays an important role in the film quality or the performance of a semiconductor device. Figure 1a shows one example illustrating the generation of threading dislocations from particles located at the lattice-mismatched In0.15Ga0.85As/GaAs interface. The HREM image shown in Fig. 1b indicates a particle to be located at a misfit dislocation. This observation suggests that a particle at the heterointerface can promote the nucleation of a dislocation and/or the formation of the misfit dislocation.
Electron-stimulated damage processes in oxides under ultra-high vacuum (UHV) conditions
Authors: Buckett M.I. , Singh S.R. , Fan H. , Wagner T. , Marks L. D. 
Published: June 2020

HREM has recently entered the surface science arena as a complementary technique for studies of electron-stimulated damage of oxide surfaces. The primary advantage offered is the ability to observe in-situ structural changes of the surface, as has been exemplified in the literature for NiO, WO3, V2O5, and TiO2, among other oxide crystals. One major drawback has been the inability to perform experiments under UHV conditions comparable to those used in conventional surface science techniques. Previous HREM reports have not considered the effect of the microscope environment in surface radiation damage.In this study, we compared the surface radiation damage effects of oxides under UHV conditions (l0-10 Torr in a Hitachi UHV-H9000 instrument) to damage effects observed in conventional instruments (operating at approximately 10-7 Torr). A number of oxides were investigated, including NiO, V2O5 , WO3 , MoO3 , TiO2, and Ta2O5. Our results indicate that although the same basic damage mechanisms are operative under both vacuum conditions, subsequent surface alteration due to reoxidation or reaction with surface contamination occurs under non-UHV conditions. WO3, for example, underwent surface-initiated reduction to metallic W under UHV conditions (Fig. 1, 2 ).
In situ High-Resolution Electron Microscopy
Authors: Sinclair Robert 
Published: June 2020

The strength of in situ electron microscopy lies in its ability to observe directly material changes which are pertinent to bulk processes. The most rigorous experiments employ a purpose-built specimen holder to simulate specific testing conditions (e.g. heating, cooling, straining, environment), with the associated microstructural changes deduced from appropriate micrographs, diffraction patterns or video-recordings. The influence of the electron microscope itself must always be taken into account (e.g. thin-foil specimen, large electron flux, high electron energy). However when artifacts are overcome, remarkable insight into the mechanisms of the behavior of solids can be achieved. The purpose of this article is to review our work in extending this capability into the high-resolution regime, so that atomic reactions can be followed. In the right circumstances this allows straightforward interpretation of atomic-scale phenomena.Our studies have employed a Philips EM430ST, 300 kV transmission electron microscope (TEM) with about 0.2 nm resolution. To-date we have carried out only heating experiments, utilizing the standard side-entry, single-tilt specimen holder (model number PW 6592), mainly on reactions at semiconductor interfaces. The zone axis orientation necessary for high-resolution TEM is obtained by careful sectioning of the substrate crystals and judicious positioning in the heating holder. The imaging conditions (including drift) can be optimized at a temperature slightly below that required for the changes of interest, so that recording can be initiated immediately on ramping up.
Structural rearrangements in small gold particles
Authors: Lewis James , Smith David J. 
Published: June 2020

A knowledge of the structure of small metal particles is fundamental to understanding their role in heterogeneous catalysis. It is therefore of much topical interest that structural rearrangements have been found to take place as a result of intense electron irradiation within the electron microscope. Initial observations were of gold particles on supports of carbon and silica-covered silicon, but further studies confirmed that qualitatively similar behaviour also took place for particles of Pt, Ru and Rh. Some of the factors which influence the motion have been noted, including the particle size, the nature of the substrate and, obviously, the current density of the electron beam. Considerable debate has been generated by these observations. It has been suggested, for example, that the structural fluctuations should be dampened by an electrically conducting substrate which would prevent the particles from becoming charged. It was also proposed that the “quasimelting” of gold particles was triggered by Auger decay, in effect heating the particles electronically rather than thermally. The energetics of these fluctuations have also been considered.In this paper, we report our initial efforts to quantify some of the experimental factors involved in this quasimelting process. Three sets of samples were prepared: one was a normal holey carbon support film, the second was a holey silicon support film, and the third was a carbon film upon which graphitised carbon had been deposited.
Electron and ion irradiation-induced dissolution of mechanical twins in the intermetalic U3Si: An in situ HVEM study
Authors: Allen Charles W. , Birtcher Robert C. 
Published: June 2020

The uranium silicides, including U3Si, are under study as candidate low enrichment nuclear fuels. Ion beam simulations of the in-reactor behavior of such materials are performed because a similar damage structure can be produced in hours by energetic heavy ions which requires years in actual reactor tests. This contribution treats one aspect of the microstructural behavior of U3Si under high energy electron irradiation and low dose energetic heavy ion irradiation and is based on in situ experiments, performed at the HVEM-Tandem User Facility at Argonne National Laboratory. This Facility interfaces a 2 MV Tandem ion accelerator and a 0.6 MV ion implanter to a 1.2 MeV AEI high voltage electron microscope, which allows a wide variety of in situ ion beam experiments to be performed with simultaneous irradiation and electron microscopy or diffraction.At elevated temperatures, U3Si exhibits the ordered AuCu3 structure. On cooling below 1058 K, the intermetallic transforms, evidently martensitically, to a body-centered tetragonal structure (alternatively, the structure may be described as face-centered tetragonal, which would be fcc except for a 1 pet tetragonal distortion). Mechanical twinning accompanies the transformation; however, diferences between electron diffraction patterns from twinned and non-twinned martensite plates could not be distinguished.
The derivation of Bloch waves in the reflection case: Analytical solutions and numerical calculations
Authors: Gjønnes K. , Peng L.-M. , Gjønnes J. 
Published: June 2020

The Bloch wave description of electron diffraction was originally derived with reflection experiments in mind, but has since been applied mainly to the transmission case, where the neglect of back scattering leads to an eigenvalue equation for the anpassung, γ, and eigenvectors (Bloch waves). In the reflection case such an approximation can not be made, γ will appear in second order. A general solution was formulated in terms of 2N Bloch waves which are obtained as non-orthogonal eigenvectors of a non-Hermitian matrix by Colella and Moon. Due to this added complexity there has been little discussion of Bloch wave solutions and properties pertaining to reflection electron diffraction – most calculations are based on integration procedures normal to or parallel to the surface.We have studied the derivation of Bloch wave solutions in the reflection case by starting from the equation for scattering ,using one greens function operators for forward scattering (Z>Z’)
Elemental mapping with a parallel-detection Electron Energy-Loss Spectrometer
Authors: Krivanek Ondrej L. , Meyer Chris E. , Tencé Marcel 
Published: June 2020

Elemental maps, that is images showing the concentration of different elements in a sample, can be obtained in an electron microscope equipped with an electron energy-loss spectrometer (EELS) by acquiring and processing data in three dimensions: spatial coordinates x and y, and the energy loss ΔE. Since the electron detector is necessarily at most a two-dimensional one, acquiring all the required data at the same time is not possible. Instead, one can either use an imaging electron spectrometer and acquire a series of whole images at one energy at a time, or use a small probe in a scanning-transmission electron microscope (STEM), and acquire the data image-point by image-point. With a serial-detection spectrometer the data at each image-point must be recorded sequentially, while with a parallel-detection spectrometer a whole spectrum can be recorded at the same time.The two approaches are illustrated schematically in figure 1. The individual sampling points in the three- dimensional volume have been called voxels (by analogy with two-dimensional pixels).
The microstructure of a TiB2/Ti-47 Al composite material
Authors: Popoola O. , Heuer A.H. , Pirouz P. 
Published: June 2020

The addition of fibres or particles (TiB2, SiC etc.) into TiAl intermetallic alloys could increase their toughness without compromising their good high temperature mechanical and chemical properties. This paper briefly discribes the microstructure developed by a TiAl/TiB2 composite material fabricated with the XD™ process and forged at 960°C.The specimens for transmission electron microscopy (TEM) were prepared in the usual way (i.e. diamond polishing and argon ion beam thinning) and examined on a JEOL 4000EX for microstucture and on a Philips 400T equipped with a SiLi detector for microanalyses.The matrix was predominantly γ (TiAl with L10 structure) and α2(TisAl with DO 19 structure) phases with various morphologies shown in figure 1.
High-resolution transmission electron microscopic study of highly oxygen doped silicon layer
Authors: Takaoka H. , Tomita M. , Hayashi T. 
Published: June 2020

High resolution transmission electron microscopy (HRTEM) is the effective technique for characterization of detailed structure of semiconductor materials. Oxygen is one of the important impurities in semiconductors. Detailed structure of highly oxygen doped silicon has not clearly investigated yet. This report describes detailed structure of highly oxygen doped silicon observed by HRTEM. Both samples prepared by Molecular beam epitaxy (MBE) and ion implantation were observed to investigate effects of oxygen concentration and doping methods to the crystal structure.The observed oxygen doped samples were prepared by MBE method in oxygen environment on (111) substrates. Oxygen concentration was about 1021 atoms/cm3. Another sample was silicon of (100) orientation implanted with oxygen ions at an energy of 180 keV. Oxygen concentration of this sample was about 1020 atoms/cm3 Cross-sectional specimens of (011) orientation were prepared by argon ion thinning and were observed by TEM at an accelerating voltage of 400 kV.
Morphological studies on poly(ethylene oxide)/hydroxypropyl cellulose blends
Authors: Gerroir P. J. , Sundararajan P. R. , Bluhm T. L. , Piché Y. 
Published: June 2020

The studies of polymer blends for industrial applications is widespread owing to the possible diversity of such blends. In addition to binary blends in which both components are amorphous, blends that consist of a crystalline and an amorphous polymer have received particular attention. One such system studied in detail in the literature is that of blends of poly(ethylene oxide) (PEO) and poly(methylmethacrylate) (PMMA). These two are vinyl-type polymers having similar skeletal chain cross-sections. The subject of the present study is the physical characterization of blends of PEO and hydroxypropyl cellulose (HPC). While the studies on PE0/PMMA blends involved melt blending or nonaqueous solutions, in the present case, both PEO and HPC are water soluble. In addition, the skeletal chain cross-sections of PEO and HPC differ appreciably.Aqueous solution of PEO and HPC (1% wt/v) were prepared. Blends of varying composition were made from these solution by mixing for one hour using a magnetic stirrer.
Scanning tunneling microscopy of metal particles on graphite
Authors: Bailey J. M. , Schmidt L. D. 
Published: June 2020

Supported metal catalysts are typically 10 to 100Å diameter particles on inert supports such as Al2O3 or graphite. The shape of catalytic particles determines the number and type of active sites on which a reactant can adsorb. The particle morphology can be studied by TEM which gives atomic resolution, but little information about the surface topography, or by SEM which yields topographic information but only at resolutions of >20Å. However, Scanning Tunneling Microscopy (STM), a surface analysis technique developed in 1981, is a very sensitive surface probe with vertical resolution of >0.1Å. In this work, catalytic systems of small platinum and rhodium particles supported on graphite substrates have been studied using STM to determine the surface morphology of the particles.The supported particle samples were prepared by first evaporating approximately 20Å of metal film on an Highly Oriented Pyrolitic Graphite (HOPG) substrate. A typical platinum sample was then placed in a tube furnace and annealed in hydrogen at 850°C for 4 hours; a typical rhodium sample was annealed in hydrogen at 750°C for 2 hours.
Topographical signaling for cell differentiation in the plant pathogenic fungus, Uromyces
Authors: Hoch H.C. 
Published: June 2020

Fungal plant pathogens invade host cells with a variety of specialized infection structures, however, for most fungi the appressorium is developmentally the first and most important structure to be formed in preparation for host colonization. It must be positioned at an appropriate site on the host in a timely way so that subsequent infection can be assured. For fungi which cause rust diseases of plants, positioning the appressorium is the most critical stage because invasion of the host can occur only via the stomata. Uredospores of these fungi (e.g.,Uromyces appendiculatus) germinate and grow, directed by the leaf (bean) surface topography toward stomata where they cease growth and develop appressoria directly over the stomatal openings. Development of the appressorium is accompanied by ameboid-like migration of the cytoplasm into the ballooning hyphal tip, DNA synthesis and nuclear division, synthesis of several “differentiation” proteins, and a rearrangement of the cytoskeleton. An orderly succession of subsequent infection structures (e.g., infection pegs, vesicles) follow in a preprogrammed sequence once the initial developmental process has been started.My research goals have been to determine what feature(s) of the host plant signals infection structure formation and how the fungus perceives these signals.
Ultrastructural analyses of local circuits in the olfactory system
Authors: Greer C.A. , Kaliszewski C.K. , Cameron H.A. 
Published: June 2020

Information processing within the mammalian olfactory bulb, following transduction of odor stimuli by the receptor cells of the epithelium, occurs at two distinct levels. First, in the glomerular layer dendrodendritic synapses from a subpopulation of interneurons onto projection neurons (mitral and tufted cells) modulate the influence of arriving sensory information. The second level of processing occurs within the external plexiform layer where a second population of interneurons, granule cells, form reciprocal dendrodendritic synapses with mitral and tufted cells to modulate the flow of information out of the olfactory bulb. This second population of interneurons has been of interest, in part, due to the recent recognition that subpopulations form microcircuits preferentially with either the mitral or the tufted cell projection neurons, thus supporting the notion of parallel processing pathways. As part of a continuing effort to characterize the properties of these neurons and their dendritic circuits we have been utilizing light microscopy of selectively stained neurons and both conventional and high voltage electron microscopy of selectively stained neurons to study the geometry and synaptology of the olfactory bulb granule cells.Sprague-Dawley rats, 12 - 60 days postnatal, were perfused with 1% paraformaldehyde and 1% glutaraldehyde followed by immersion in the fixative for 8-12 hrs. After washes in 0.1M phosphate buffer the tissue was passed through a conventional dehydration series, embedded in EPON and routinely stained with uranyl acetate and lead citrate following sectioning. In addition, littermates were processed for Golgi-EM. Tissue examined utilizing conventional EM (60 - 100kV) was cut at approximately 70 nm and mounted on formvar slotted grids. Tissue examined utilizing high voltage EM (800 - 1000 kV) was cut at 1 - 5 um and mounted on mesh grids prior to carbon coating. Serial sections studied with conventional EM were reconstructed and morphometrically assessed utilizing a PC based 3D reconstruction program.
Molecular analysis of the tight junction
Authors: Stevenson Bruce R. , Heintzelman Matthew B. , Anderson James Melvin , Citi Sandra , Braun I. Deborah , Mooseker Mark S. 
Published: June 2020

The tight junction (zonula occludens) constitutes a selectively permeable barrier in the paracellular pathway of most epithelia. It is also thought to play a role in the maintenance of the cell surface compositional asymmetry characteristic of epithelial cells. The identification of ZO-1 and cingulin, the first two proteins found to be exclusively associated with the tight junction, permits novel investigations of this important epithelial cell structure at the biochemical level.ZO-1 is a high molecular weight polypeptide (>200 kD) found at the tight junctions of a variety of epithelia as well as endothelia, and ultrastructural localization studies on isolated liver plasma membranes indicate that this molecule is clustered at the points of membrane contact on the cytoplasmic surface of the junction. Physical analysis demonstrates ZO-1 to be an elongated, monomeric, phosphorylated protein, peripherally associated with the junctional membrane. Cingulin was originally isolated from chicken intestine, and, like ZO-1, is a peripheral membrane component of the junction which exhibits an elongated shape. Antibodies directed against this molecule show two primary bands at 140 kD and 108 kD on immunoblots of several epithelial tissues, although the relationship between these two elements remains undefined. Little information currently exists regarding the relationship of ZO-1 and cingulin to each other or to tight junction structure or function. We report here a comparison of the immunocytochemical properties of these junctional components as well as an examination of the phosphorylation state of ZO-1.
Nuclear magnetic resonance microscopy
Authors: Lauterbur Paul C. 
Published: June 2020

Nuclear magnetic resonance imaging can reach microscopic resolution, as was noted many years ago, but the first serious attempt to explore the limits of the possibilities was made by Hedges. Resolution is ultimately limited under most circumstances by the signal-to-noise ratio, which is greater for small radio receiver coils, high magnetic fields and long observation times. The strongest signals in biological applications are obtained from water protons; for the usual magnetic fields used in NMR experiments (2-14 tesla), receiver coils of one to several millimeters in diameter, and observation times of a number of minutes, the volume resolution will be limited to a few hundred or thousand cubic micrometers. The proportions of voxels may be freely chosen within wide limits by varying the details of the imaging procedure. For isotropic resolution, therefore, objects of the order of (10μm) may be distinguished.Because the spatial coordinates are encoded by magnetic field gradients, the NMR resonance frequency differences, which determine the potential spatial resolution, may be made very large. As noted above, however, the corresponding volumes may become too small to give useful signal-to-noise ratios. In the presence of magnetic field gradients there will also be a loss of signal strength and resolution because molecular diffusion causes the coherence of the NMR signal to decay more rapidly than it otherwise would. This phenomenon is especially important in microscopic imaging.
The role of cell-extracellular matrix interactions in neural crest cell migration
Authors: Bronner-Fraser Marianne 
Published: June 2020

The formation of the embryo involves intricate cell movements, cell proliferation, and differentiation. The neural crest has long served as a model for the study of these processes because these cells: 1. migrate extensively along characteristic pathways during embryogenesis. 2. give rise to diverse and numerous derivatives, including pigment cells, adrenal chromaffin cells, and the ganglia of the peripheral nervous system; and 3. are accessible to surgical, immunological, and biochemical manipulations during both initial and certain later stages in their development. We are in the process of identifying factors that influence cell migration and differentiation in the neural crest system.Neural crest cells follow two primary migratory pathways in the trunk: a dorsolateral route underneath the skin, and a ventral route through the somite. Within the somites, neural crest cells preferentially migrate through the rostral half of each sclerotome but are absent from the caudal sclerotome. The regions through which neural crest cells migrate are lined with extracellular matrix (ECM) molecules. Because of the intimate relationship between neural crest cells and the surrounding matrix, it has been proposed that the ECM plays an important role in the initiation, guidance, and cessation of neural crest cell movement.