bluuebunny/crossref_metadata_2025 huggingface dataset:
High-resolution immunogold labeling of cell surfaces: The hypothetical homodimeric nature of the cd5 receptor
Authors: de Harven E. , Christensen H.
Published: June 2020

Molecules exposed on cell surfaces and labeled with colloidal gold markers can be optimally demonstrated using the backscattered electron imaging (BEI) mode of the scanning electron microscope (SEM). Steric hindrance, however, limits labeling efficiency, making it necessary to use gold markers of small size for labeling at the molecular level. Using a JEOL 840 SEM equipped with a lanthanum hexaboride (LaB6) cathode, 13 nm gold particles were demonstrated. This, however, seems to represent the limit of the resolution of this type of instrument in the BEI mode. Fortunately, it has been demonstrated by Walther and Muller that 5 nm gold particles can be seen in the BEI mode, using field emission SEM.

We have confirmed this observation, using the JEOL 890 field emission SEM and a solid state backscattered electron detector. Human peripheral blood lymphocytes prefixed with 0.1% glutaraldehyde, incubated with the murine monoclonal antibody LEU-1 (CD5), were labeled with a goat anti-murine IgG adsorbed on 5 nm gold particles (GAM-G5, Janssen Pharmaceutica, Beerse, Belgium) according to previously described procedures.
Ultrastructural localization of alkaline phosphatase in lactating rat mammary gland
Authors: Farrell Harold M. , Maleeff Beverly E. , Leung Cecilia T.
Published: June 2020

Alkaline phosphatase is found in almost all nucleated mammalian cells as well as in many microorganisms. In animal tissues, it is often found associated with plasma membranes and also has been indirectly implicated in the accumulation of calcium-phosphate in calcifying tissue, osteoblasts and odontoblasts. In the secretion of milk, vesicles accumulate casein and colloidal calcium-phosphate, while in a separate pathway milk fat is secreted and bounded by the apical plasma membrane. Alkaline phosphatase is found in milk, and all milks contain both colloidal calcium-phosphate and fat globule membranes which are derived in part from the plasma membrane. Previous studies had suggested that mammary alkaline phosphatase is limited to nonsecretory myoepithelial cells, but recent work has indicated that intracellular alkaline phosphatase is cryptic. We therefore decided to investigate the cytochemical distribution of alkaline phosphatase in mammary secretory cells, and to determine if it could participate in calcium-phosphate accumulation in milk.
Image analysis of 2-D Na,K-ATPase crystals maintained in vitreous ice
Authors: Misra Manoj , Beall Harry C. , Taylor Kenneth A. , Ting-Beall H.P.
Published: June 2020

The molecular description of the Na,K-ATPase in the native state at high-resolution is required for the detailed description of the mechanism by which the active transport of Na and K ions occurs. Our efforts, therefore, are directed toward obtaining this molecular description by means of electron microscopy of ordered arrays of Na,K-ATPase molecules preserved in the frozen-hydrated state in amorphous ice.

The procedure for crystallization of Na,K-ATPase was similar to that of Mohraz et al. Electron microscope grids for cryo-microscopy were prepared essentially as described by Dubochet et al. Frozen-hydrated specimens were examined in the Philips 420 electron microscope using a Gatan model 626 Cryotransfer system and cooling holder. Micrographs were recorded at 36000X under minimal dose conditions. Electron micrographs of frozen-hydrated membranes were screened initially by optical diffraction and examined for the presence of 4-6 rows of crystal lattice without any discernible visual disorder.
Unbiased estimation of particle number and sizes using the new stereological tools: the disector, the fractionator, the selector, and the nucleator — or just point-sampled intercepts
Authors: Gundersen H.J.G.
Published: June 2020

Previously, all stereological estimation of particle number and sizes were based on models and notoriously gave biased results, were very inefficient to use and difficult to justify. For all references to old methods and a direct comparison with unbiased methods see recent reviews.

The publication in 1984 of the DISECTOR, the first unbiased stereological probe for sampling and counting 3—D objects irrespective of their size and shape, signalled the new era in stereology — and give rise to a number of remarkably simple and efficient techniques based on its distinct property: It is the only known way to obtain an unbiased sample of 3-D objects (cells, organelles, etc). The principle is simple: within a 2-D unbiased frame count or sample only cells which are not hit by a parallel plane at a known, small distance h.

The area of the frame and h must be known, which might sometimes in itself be a problem, albeit usually a small one. A more severe problem may arise because these constants are known at the scale of the fixed, embedded and sectioned tissue which is often shrunken considerably.
Field ion microscopy
Authors: Ehrlich Gert
Published: June 2020

The field ion microscope, devised by Erwin Muller in the 1950's, was the first instrument to depict the structure of surfaces in atomic detail. An FIM image of a (111) plane of tungsten (Fig.l) is typical of what can be done by this microscope: for this small plane, every atom, at a separation of 4.48Å from its neighbors in the plane, is revealed. The image of the plane is highly enlarged, as it is projected on a phosphor screen with a radius of curvature more than a million times that of the sample. Müller achieved the resolution necessary to reveal individual atoms by imaging with ions, accommodated to the object at a low temperature. The ions are created at the sample surface by ionization of an inert image gas (usually helium), present at a low pressure (< 1 mTorr). at fields on the order of 4V/Å.
Adsorbate deformation as a contrast mechanism in stm imaging of biopolymers in an aqueous environment
Authors: Lindsay S.M.
Published: June 2020

The Scanning Tunneling Microscope (STM) has already been applied to several problems in biology. Examples are imaging of both stained and unstained biopolymers adsorbed on substrates such as graphite in air and in vacuo, AFM images of the surface of a polypeptide crystal and STM images of carbon-platinum replicas. Useful though these methods are, they involve dehydration of the samples and, in the case of adsorbates on graphite, the experiments are not easy to repeat. Sonnenfeld and Hansma have invented a method for operating the STM in conducting solvents'. We have been investigating the mechanism of the STM operated in a non-UHV environment and are using the STM to study aggregates of biopolymers on a metal substrate submerged under a buffer solution. Although formation of the aggregates must modify hydrated biopolymers considerably, repeatable images are obtained relatively easily, and deposition from a biochemically useful environment is straightforward.
TEM studies of amorphization processes and amorphous structures
Authors: Mitchell T. E. , Schwarz R. B.
Published: June 2020

Traditional oxide glasses occur naturally as obsidian and can be made easily by suitable cooling histories. In the past 30 years, a variety of techniques have been discovered which amorphize normally crystalline materials such as metals. These include [1-3]:

Rapid quenching from the vapor phase.

Rapid quenching from the liquid phase.

Electrodeposition of certain alloys, e.g. Fe-P.

Oxidation of crystals to produce amorphous surface oxide layers.

Interdiffusion of two pure crystalline metals.

Hydrogen-induced vitrification of an intermetal1ic.

Mechanical alloying and ball-milling of intermetal lie compounds.

Irradiation processes of all kinds using ions, electrons, neutrons, and fission products.

We offer here some general comments on the use of TEM to study these materials and give some particular examples of such studies.

Thin specimens can be prepared from bulk homogeneous materials in the usual way. Most often, however, amorphous materials are in the form of surface films or interfacial films with different chemistry from the substrates.
The characterization of amorphous Al2O3by extended energy loss fine structure (EXELFS) analysis
Authors: Sklad P. S. , Angelini P. , Sevely J.
Published: June 2020

Amorphous phases have been shown to influence properties of many metallic, semiconducting, and ceramic materials. However, analysis of these phases presents a difficult challenge since most conventional characterization techniques provide only limited qualitative information. Extended Energy Loss Fine Structure (EXELFS) analysis is a technique which is sensitive to both structure and composition within near neighbor distances of specific types of atoms in both crystalline and amorphous materials. The fine structure, which is present in the form of modulations on the core loss edges of electron energy loss spectra, results from diffraction of ejected core electrons by neighboring atoms. The ability to obtain EXELFS measurements with an analytical electron microscope allows direct observation of changes in composition, microstructure, and local atomic environment at a spatial resolution (<100 nm) not attainable by other techniques.

Recently an investigation of the effects of ion implantation on the microstructure and properties of A12O3has revealed differences in the response of various forms of amorphous A12O3to post-implantation annealing.
Early stages of oxygen precipitation in si: morphology and structure
Authors: Bergholz W. , Hutchison J. L.
Published: June 2020

Intrinsic gettering in Si - VLSI technology depends on a controlled initial stage of oxygen precipitation and is characterized by a complicated interaction of growth-induced microdefects, self interstitial (SiI) generation and strain caused by SiO2 precipitate growth and secondary defects, table 1. We address the controversial issues of the identity of ribbon-like defects (RLDs) and of the nature of oxygen precipitate nuclei.

RLDs were initially identified by HRTEM as coesite, a high pressure phase of SiO2. Recently, both Bourret and Reiche et al have interpreted the RLDs as hexagonal Si, or agglomerates of Si. We wish to make the point that the evidence against coesite is, as yet, not conclusive, and present circumstantial evidence in favour of coesite: (1) The loss of interstitial oxygen correlates with the density of RLDs (Fig. 1) at 450 - 485°C.
TEM and cathodoluminescence of precipitates in II-VI semiconductors
Authors: Batstone Joanna L.
Published: June 2020

Interest in II-VI semiconductors centres around optoelectronic device applications. The wide band gap II-VI semiconductors such as ZnS, ZnSe and ZnTe have been used in lasers and electroluminescent displays yielding room temperature blue luminescence. The narrow gap II-VI semiconductors such as CdTe and HgxCd1-xTe are currently used for infrared detectors, where the band gap can be varied continuously by changing the alloy composition x.

Two major sources of precipitation can be identified in II-VI materials; (i) dopant introduction leading to local variations in concentration and subsequent precipitation and (ii) Te precipitation in ZnTe, CdTe and HgCdTe due to native point defects which arise from problems associated with stoichiometry control during crystal growth. Precipitation is observed in both bulk crystal growth and epitaxial growth and is frequently associated with segregation and precipitation at dislocations and grain boundaries. Precipitation has been observed using transmission electron microscopy (TEM) which is sensitive to local strain fields around inclusions.
SEM and microdiffraction study of the reduction of metal oxides in a STEM instrument
Authors: Liu J. , Cowley J. M.
Published: June 2020

It has been reported that under electron beam irradiation maximally valent metal oxides can be reduced to lower oxides and under some circumstances even to metals due to the preferential loss of oxygen. The electron beam induced reactions can be conveniently studied in a STEM instrument equipped with a field emission gun and a chamber vacuum pressure about 5x10-9 Torr.. Microdiffraction patterns obtained from areas about 1.0-1.5 nm in diameter can be used to deduce the structural information of the reduction products. The recently attached SE detector in our HB5 STEM instrument can collect secondary electrons at the exit surface of the sample and the image resolution is better than 1 nm3. Since SE signals carry information about the surface and sub-surface of the studied material and SE emission is sensitive to surface modifications (both geometric and electronic) such as the change of work function due to the formation of new phases on the specimen surface, high resolution SE imaging can provide additional information about the reduction processes of metal oxides under electron beam bombardment. The combination of SE imaging with the microdiffraction technique proves to be a powerful tool for studying surface reactions.
Background modeling alternatives in EELS and their implications on microanalysis
Authors: Krishnan Kannan M. , Stampfer M. T.
Published: June 2020

With the advent of parallel detectors, electron energy-loss spectroscopy (EELS) is expected to be employed increasingly in the routine microanalysis of light elements. The quantitation formulae that are used are relatively simple and straightforward and require only a measurement of the integrated core-loss intensity over a particular energy window beyond the ionization edge (Δi) and most often, a calculated ionization cross-section. Even though the hydrogenic cross-sections that are used routinely for microanalysis can be a source of error, it is observed that the procedure that largely determines the accuracy of quantification is the removal of the contribution of the background below the ionization edge. Based on empirical observations, an inverse power law function of the form I = AE-r, where the exponent ‘r’ takes values from 2 to 6, is now commonly used for the background. A background fitting region preceding the ionization edge (Δb) is chosen, the constants A and r determined by least squares refinement and the background extrapolated beyond the ionization edge for the required energy window (Δi).
Microstructural characterization of inconel alloy 690
Authors: Burke M. G. , Hyatt B. Z.
Published: June 2020

Inconel 690 is a nickel-base superalloy which, because of its superior corrosion resistance, is being considered as a substitute for Inconel 600. The composition of Alloy 690 is nominally 30wt.%Cr-10wt.%Fe-0.3wt.%Ti-bal Ni. This alloy is generally used in the thermally treated condition: solution anneal in the range 1030-1120*C for ∼0.07-lh followed by a thermal treatment (∼550-875*C for ∼10h) [1,2]. The purpose of this study is to characterize the microstructure during the post-annealing thermal treatment by scanning/transmission electron microscopy (STEM/TEM). Of particular importance is the identification of precipitates and the documentation of Cr depletion at grain boundaries and precipitates. Specimens were examined in the 1) annealed, and 2) annealed and thermally treated conditions.

TEM examination of the annealed alloy revealed that the conventional annealing treatment did not result in the complete dissolution of the M23C6 precipitates. Numerous coarse matrix carbides were visible in the alloy. In addition, notable intergranular precipitation of M23C6. occurred during cooling from the annealing temperature (Fig. 1.).
Microstructural characterization of a rapidly solidified Al-Fe-V-Si alloy for elevated temperature applications
Authors: Franck R. E. , Hawk J. A. , Shiflet G. J.
Published: June 2020

Rapid solidification processing (RSP) is one method of producing high strength aluminum alloys for elevated temperature applications. Allied-Signal, Inc. has produced an Al-12.4 Fe-1.2 V-2.3 Si (composition in wt pct) alloy which possesses good microstructural stability up to 425°C. This alloy contains a high volume fraction (37 v/o) of fine nearly spherical, α-Al12(Fe, V)3Si dispersoids. The improved elevated temperature strength and stability of this alloy is due to the slower dispersoid coarsening rate of the silicide particles. Additionally, the high v/o of second phase particles should inhibit recrystallization and grain growth, and thus reduce any loss in strength due to long term, high temperature annealing.

The focus of this research is to investigate microstructural changes induced by long term, high temperature static annealing heat-treatments. Annealing treatments for up to 1000 hours were carried out on this alloy at 500°C, 550°C and 600°C. Particle coarsening and/or recrystallization and grain growth would be accelerated in these temperature regimes.
Effect of inert gas on the structure/property relations in rapidly solidified 304 stainless steel
Authors: Chan Bae Jung , Kelly Thomas F. , Flinn John E.
Published: June 2020

Recent research reported that significant amounts of helium (about 8 appm) are entrained in extruded Type 304 stainless steel powder that has been rapidly solidified by centrifugal atomization with helium cooling gas. The entrained helium was reported to be directly related to a desirable improvement in properties of materials such as a notable resistance to grain growth, improved room temperature tensile properties with little reduction in ductility and improved creep properties.

The purpose of this work was to study the effect of inert gases on the microstructure of powder-metallurgy (P/M) Type 304 stainless steel with different preconditioning heat treatments. The heat treatments performed on the specimens include 1 hour anneals at 900,1000,1100, and 1200C followed by water quenching. In addition, the 1100 and 1200C annealed specimens were subjected to aging treatments at 600C for 1000 hours. The TEM specimens were thinned by electropolishing at 13C using a solution of 5% perchloric acid in acetic acid.
Fibrous and columnar grain structures in chromium films
Authors: Jiang-zhong Duan , Hetherington Crispin , Fisher R.M.
Published: June 2020

Vapour-deposited and sputtered thin films are widely used in optical and microelectronic components. The optical, electrical and mechanical properties of such films depend primarily on microstructural features such as grain size, shape and crystallographic orientation, defect and impurity content, and substrate surface topology. The microstructure is determined by deposition conditions and especially substrate temperature andinclination relative to the source, metal deposition rate, and residual gaspressure in the chamber. These parameters affect the transition fromirregular, defect-laden, fibrous grains and rough film surfaces to smooth, highly reflecting surfaces and well-formed columns with little void space between them.

Factors affecting the adherance of thin films to substrates are under study as part of a broad program on interfacial adhesion. Important parameters are internal stresses that drive spontaneous delamination and the fracture energy of the interface that resists crack growth. Internal stress levels in Cr films can be exceptionally high, so this metal is being studied extensively to determine the origin of tensile stresses in relation to microstructure.
Analytical TEM study of a yttria stabilized zirconia/glass composite
Authors: Lin Yung-Jen , Angelini Peter , Mecartney Martha L.
Published: June 2020

Yttria stabilized zirconia is a versatile ceramic material. It can be used for structural components or as a solid electrolyte. Its properties (such as high toughness) are strongly affected by the microstructure. In partially stabilized zirconia, the high toughness is mainly due to the toughening effect of a tetragonal (t) to monoclinic (m) phase transformation in the vicinity of a crack. Retention of tetragonal zirconia at room temperature is important for fabricating transformation toughened materials. To completely retain tetragonal zirconia at room temperature the grain size of the material must be less than a critical size. In yttria stabilized zirconia this critical grain size depends on the yttria concentration. Grain growth of yttria stabilized zirconia is also influenced by the amount of yttria in the grains. These previous studies, however, have focused on the behavior of materials with minimal glassy grain boundary phases. In contrast, in commercial polycrystalline zirconia often a significant amount of glassy grain boundary phase is present. This current research seeks to elucidate the effects of these grain boundary phases on the grain growth in yttria stabilized zirconia ceramics.
Microstructural characterization of AIN sintered with Y2O3
Authors: Chiang S-K.
Published: June 2020

Aluminum nitride's high thermal but low electrical conductivity make it a potential ceramic packaging material. Processing history, however, can have significant effects on these properties and studies aimed at correlating them to the processing and microstructure are sparse.

Pure AIN cannot be readily sintered without additives. Addition of Y2O3 significantly improves its densification behavior and the results presented here concern microstructural analysis of AIN sintered with Y2O3.

High-purity AIN powder (containing 1.24% oxygen impurity) with 3 or 9 weight% Y2O3 added was sintered in N2 at 1850°C for 1 hour followed by a further 3 hours at 1900°C. Samples made using this treatment were >95% dense. Specimens for microstructural investigation were prepared using standard techniques and examined using a JEOL 200 CX AEM.

The general microstructure of all specimens consists of AIN grains with pockets of intergranular phase(s) located at triple points and some grain boundaries (FIG. 1).
TEM studies of line defects in interfaces
Authors: Pond R.C.
Published: June 2020

Line defects are ubiquitious features in interfaces, and have important structural and mechanistic role. Recently, a crystallographic theory of such defects has been presented which appears to offer a comprehensive framework for their classification. The object of the present paper is firstly to outline the characterisation and classification of defects according to this treatment. Secondly, we illustrate examples of defects in the distinctive classes observed using tern, and discuss the various imaging techniques which have been employed.

In the absence of a rigorous treatment of line defects in single crystals and interfaces, which would require the development of a discrete field theory, approximate methods of defect characterisation are used. The most popular method involves mapping a contour, initially constructed around a defect of interest, into a reference space. For defeats in single crystals this Burgers circuit method, introduced by Frank, is very helpful, but suffers from certain procedural inconveniences in the case of interfacial defects.
Grain boundary structure in Ni3Al
Authors: Mackenzie R.A.D. , Vaudin M.D. , Sass S.L.
Published: June 2020

Ni3Al is a potentially useful high temperature alloy. In its single crystal form it exhibits good ductility, however in polycrystalline form the pure alloy is highly prone to intergranular failure. It has been seen that in slightly nickel-rich alloys the addition of small amounts of boron has the effect of dramatically increasing the material ductility and of changing the failure mode from intergranular to transgranular. In alloys which have been ductilitized by boron addition, atom probe investigation has shown the boron to be segregated to grain boundaries. This segregation may induce a change in the boundary structure as has been seen by Sickafus and Sass in gold doped iron bicrystals.

Small angle boundaries in polycrystals and fabricated bicrystals have been examined using transmission electron microscopy. The bicrystals were produced by hot pressing misoriented single crystals of either pure or doped Ni3Al. Boundaries have been observed in a variety of fabricated bicrystals.
Studies of segregation by Z-contrast STEM
Authors: Pennycook S. J.
Published: June 2020

A STEM annular detector has been used to form spectacular images of single heavy atoms on thin carbon films by collecting over a wide angular range. Collecting only those electrons scattered through high angles would increase the Z contrast toward the full Z2 dependence of Rutherford scattering, but reduce the efficiency and signal-to-noise ratio. For crystalline samples, however, it is essential to exclude diffracted electrons which obscure the Z contrast and the high-angle annular dark field image (HAADF) has proved useful for catalyst studies and has also allowed the imaging of dopant distributions in Si. Figure 1 compares a conventional cross-section image of Sb-implanted Si following pulsed laser annealing with a Z-contrast image obtained on a VG Microscopes HB-501 STEM. Excess Sb has segregated into a cell structure in the near-surface region. The concentration remaining between the cells is the solubility limit under these regrowth conditions (an order of magnitude greater than the equilibrium solubility limit) and is directly visible in the Z-contrast image.
Are major instrumental developments in TEM still to be Expected?
Authors: van der Mast K.D. , Koster A.J.
Published: June 2020

In general instrumental developments are caused either by new application demands or by the availability of new technologies. If we investigate the trends in application demands, some predictions can be made safely: More and more the TEM will be used as an analytical instrument. The number of desired signals (detectors) will increase and the quality of the signals must be improved in terms of noise and electron efficiency. Examples are parallel collection EELS and Auger detectors (Kruit and Venables, 1988).

The first experiments on coincidence techniques are also promising (Kruit et al, 1984) and exciting new ideas are investigated today. Besides this, another area of applications will probably become more important: surface science in situ experiments. Especially for this type of experiments it is difficult to transfer the specimen to another system without spoiling the experiment. So these applications will lead to an ultra high vacuum specimen environment - constructed in a way that many accessories necessary for surface experiments can be added: Ion guns, preparation chamber, knudsen cells etc.
Toward improved z-contrast imaging
Authors: Bunn R. D. , Dunlap J. R. , Joy D. C.
Published: June 2020

The electron microscope is an essential tool for the study of microstructure, and with the appropriate hardware can also provide chemical information about the sample. The ideal situation is one in which both types of information are collected with each pass of the electron beam across the sample. The Z-contrast imaging technique (Crewe et al. 1) is potentially capable of providing such information at high spatial resolution. In order for this technique to be quantitative it is imperative that signal transfer and manipulation be linear, under full operator control and appropriately monitored. To often, collection transfer and processing electronics are set by the manufacturer to some standard condition which may or may not be applicable to the other hardware with which it will ultimately be interfaced. This sort of black box technology may then result in information loss or the introduction of artifacts as the signal is passed through the system. In particular, it is difficult to track various signals from detector to processor.
A compact, digital, optically isolated control and support system for a field-emission source on the 200 kV STEM
Authors: Mooney P. E.
Published: June 2020

In the third order corrected STEM, optimization of the probe subject to the limits of fifth order spherical aberration and chromatic aberration leads to a choice of 200 KY for the accelerating potential. In order to obtain sufficient stability at this voltage it Is necessary to house the accelerator, high voltage pover supply and electron beam source in a dry N2 pressure vessel and to cover the source housing vith a polished corona discharge shield. All support electronics for the the beam source must be mounted vlthin this shield. The field emission tip beam source requires a stable extraction voltage, a tip chamber high vacuum system, and a flashing circuit. A compact, optically isolated, digitally controlled system has been built which provides these primary functions along with support functions such as tip alignment, current and voltage monitoring and pover storage.

The major concerns in design of the control system were pover conservation, transient protection, acoustic isolation and compactness.
A system for fast digital image processing of asynchronous SEM signals
Authors: Osten Evariste F. , Schultz John C.
Published: June 2020

The time required to examine a specimen's features with an SEM before photographically recording representative images is related to the amount of visual information about that specimen that is available from the SEM's viewing CRT. In a laboratory that examines several thousand specimens each year, many in low signal-to-noise situations, the accumulated examination time can be significant. Image processing to increase the information content of the viewed image can reduce the time needed to examine the specimen. Digital frame integration can be used to improve an image's signal-to-noise ratio and color processing of the observed image can be used to provide enhanced visual perception. Using a passive interface with the SEM for image processing has the advantage that it doesn't interfere with the SEM scan electronics nor does it affect normal SEM operation. A difficulty in image processing arises when using asynchronous SEM signals - video signals that lack synch pulses and therefore do not conform to standard RS-170 video.
The effects of surface absorbed monolayer microdiffraction patterns
Authors: Pan M. , Cowley J.M.
Published: June 2020

Electron microdiffraction patterns, obtained when a small electron probe with diameter of 10-15 Å is directed to run parallel to and outside a flat crystal surface, are sensitive to the surface nature of the crystals. Dynamical diffraction calculations have shown that most of the experimental observations for a flat (100) face of a MgO crystal, such as the streaking of the central spot in the surface normal direction and (100)-type forbidden reflections etc., could be explained satisfactorily by assuming a modified image potential field outside the crystal surface. However the origin of this extended surface potential remains uncertain. A theoretical analysis by Howie et al suggests that the surface image potential should have a form different from above-mentioned image potential and also be smaller by several orders of magnitude. Nevertheless the surface potential distribution may in practice be modified in various ways, such as by the adsorption of a monolayer of gas molecules.
Electron-beam-induced 3-D epitaxy Of TiO on TiO2
Authors: McCartney M. R.
Published: June 2020

It is well-known that the surfaces of maximally-valent transition-metal oxides should be particularly susceptible to electron-stimulated desorption of oxygen under the conditions prevailing in high-resolution electron microscopy (HREM). Indeed, it has been observed that lattice fringes corresponding to TiO have developed on the surfaces of crystals of rutile, TiO2. Fig. 1a shows the modified surface of a rutile crystal tilted to (001)-projection with extensive regions of disorder and small crystallites of reduced (metallic) oxide at the edge; fig. 1b shows TiO2 in a [010]-projection with crystals of TiO in -projection. By combining the techniques of high-resolution imaging, optical diffractogram (ODM) analysis, and computer modeling of crystal structure, a three-dimensional epitaxy for the growth of TiO on TiO2 can be proposed.
Measurement of particle sizes in the STEM using high-angle annular detector image intensities
Authors: Rice S. B. , Treacy M. M. J.
Published: June 2020

We describe a STEM technique that permits the volume and thickness of small particles to be estimated from intensities collected in a high angle annular detector (HAAD). This technique provides a convenient method for detecting and measuring catalyst particles when supported on low atomic number substrates. This method is based on the Z contrast technique of Crewe et al. However, in this study, an annular detector with a large central hole is used so as to avoid strong Bragg reflections from the sample. In this configuration, the signal is predominantly Rutherford scattering, which is proportional to ∼Z2 and to the number of atoms intercepted by the probe. Contrasts arising from electron channeling are greatly reduced by the convergence of the incident probe. The HAAD has proven to be of great use for the detection of small catalyst clusters when they are not readily visible in conventional bright field images.
Reactivity and structure of nickel-cobalt bimetallic catalysts
Authors: Woo Ho K. , Srinivasan R. , Rice L. , Reucroft P.J. , De Angelis R.J.
Published: June 2020

Ni and Co catalyst systems have been extensively dealt with in the catalyst research literature but investigations on Ni/Co alloy systems have been relatively sparse. An early study attempted to correlate catalysed hydrogenation activity with metal/alloy lattice parameter. Matsuyama et al. investigated catalytic hydrogenation of ethylene by nickel alloys as a function of surface and bulk composition. The activity increased as the proportion of Ni increased but decreased from 90 to 100%Ni. A study has been initiated to relate catalytic activity to the structure of Ni/Co bimetallic catalyst particles.

Silica supported catalysts were prepared by the incipient wetness (impregnation) technique. Nickel, and cobalt nitrate in the desired proportions were dissolved in the impregnating solution. The wet catalyst samples were dried overnight at 120C after impregnation,. Catalysts were reduced by heating at 400C in flowing hydrogen for 18 hrs. Reactivity was determined by passing a 3/1 mixture of hydrogen and carbon monoxide over the catalyst and analyzing the effluent stream at hourly intervals by gas chromatography for hydrocarbon products.
Characterization of BN-coated ceramic fibers
Authors: Freeman G. B. , Lackey W. J. , Starr T. L.
Published: June 2020

It is well known that ceramic materials possess excellent thermal properties for use at high temperatures but are subject to brittle failure. The incorporation of a suitable second phase (powder or fiber) can mitigate that brittle character and result in a composite material which actually possesses mechanical properties superior to those of competitive traditional materials. It has been shown that the remaining tendency toward brittle failure can be further reduced if the incorporated fiber exhibits a weak rather than strong bond with the matrix. This encourages debonding, crack deflection and fiber pull-out which all contribute to fracture toughness. It was the goal of this project to coat commercial Nextel type 312 fibers (composition: 3 moles Al2O3, 2 moles SiO2, and 1 mole B2O3) with an approximately 0.1 μm thin film of boron nitride (BN) for inclusion in a slip-cast sintered silica matrix.
Effects of compression during formation on the microstructure of composite hydroxylapatite/plaster implants for bone reconstruction
Authors: Hanker J. , Cowden K. , Noecker R. , Yates P. , Georgiade N. , Giammara B.
Published: June 2020

Composites of plaster of Paris (PP) and hydroxylapatite (HA) particles are being applied for the surgical reconstruction of craniofacial bone defects and for cosmetic surgery. Two types of HA particles are being employed, the dense sintered ceramic (DHA) and the porous, coralline hydroxylapatite (PHA) particles. Excess water is expressed out of the moistened HA/PP mixture prior to implantation and setting by pressing it in a non-tapered syringe against a glass plate. This results in implants with faster setting times and greater mechanical strengths. It was therefore of interest to compare samples of the compressed versus noncompressed mixtures to see whether or not any changes in their microstructure after setting could be related to these different properties.

USG Medical Grade Calcium Sulfate Hemihydrate (which has the lowest mortar consistency of any known plaster) was mixed with an equal weight of Interpore 200 particles (a commercial form of PHA). After moistening with a minimum amount of water, disc-shaped noncompressed samples were made by filling small holes (0.339 in. diameter x 0.053 in. deep) in polypropylene molds with a microspatula.
Movement of the spinel-wustite interface in thin films
Authors: Summerfelt Scott R. , Carter C.B.
Published: June 2020

The wustite-spinel interface boundary can be thought of as a model interface since wustite and spinel share a common f.c.c. oxygen sublattice with only the cations changing across the interface. However, a wide variety of spinel precipitate morphologies has been experimentally observed and ranges from flat plates parallel to {001} planes in the MgAl2O4-MgO system, to coherent ellipsoids parallel to the {001} planes in the NiCr2O4-NiO system, to large coherent particles having “arms” in the <001> direction bounded by {111~ and {110~ planes in the NiFe2O4-NiO system. The particle morphology is determined by a combination of the interfacial energy and the strain energy which results from the lattice misfit between the wustite matrix and the spinel precipitate. In this study, a TEM sample was made containing spinel particles precipitated in the bulk. Individual precipitates were then characterized between a series of anneals.
Microstructure in soft magnetic E3 (S1, Al) (Sendust) alloys
Authors: Kim June D.
Published: June 2020

Iron-base alloys containing 8-11 wt.% Si, 4-8 wt.% Al, known as “Sendust” alloys, show excellent soft magnetic properties. These magnetic properties are strongly dependent on heat treatment conditions, especially on the quenching temperature following annealing. But little has been known about the microstructure and the Fe-Si-Al ternary phase diagram has not been established. In the present investigation, transmission electron microscopy (TEM) has been used to study the microstructure in a Sendust alloy as a function of temperature.

An Fe-9.34 wt.% Si-5.34 wt.% Al (approximately Fe3Si0.6Al0.4) alloy was prepared by vacuum induction melting, and homogenized at 1,200°C for 5 hrs. Specimens were heat-treated in a vertical tube furnace in air, and the temperature was controlled to an accuracy of ±2°C. Thin foils for TEM observation were prepared by jet polishing using a mixture of perchloric acid 15% and acetic acid 85% at 10V and ∼13°C. Electron microscopy was performed using a Philips EM 301 microscope.
Vanadia-induced transformations in yttria-stabilized zirconia
Authors: Susnitzky D.W.
Published: June 2020

Thermal-barrier coatings for jet-engine components are typically composed of Y2O3-stabilized ZrO2 (YSZ) since this material provides improved ceramic-to-metal bonding, thermal-stress resistance and stability. One problem associated with YSZ thermal barriers is the increased rate of coating failures encountered when trace amounts of impurities, such as 50ppm vanadium, are present in the jet fuel. V2O5 reacts with YSZ to form YVO4 and a monoclinic ZrO2 phase. Although coating failures are attributed to the 3-5% volume change associated with the tetragonal- to-monoclinic transformation, the exact mechanism of V2O5 attack has been unclear. The present study addresses the deleterious effects of V2O5 on YSZ at 810°-950°C by directly exposing perforated TEM specimens of single-crystal YSZ to the vapor produced by a small quantity of V2O5 powder. The experimental details of this thin-film reaction technique have been described elsewhere.

Fig.l shows a bright-field (BF) image recorded from a (100)-oriented YSZ (9mol% Y2O3) specimen which was exposed to V2O5 vapor for 30 min at 810°C.
TEM sample preparation of superconducting oxides
Authors: Sarikaya Mehmet , Thiel B. L. , Bradley J. P.
Published: June 2020

The preparation and observation of high Tc superconducting TEM samples deserves a great deal of care since, as when characterizing any new material, mistreatment can bring about extrinsic features leading to erroneous conclusions. In dealing with materials such as these, where the structural origins of the electromagnetic properties are tantamount, this is especially true. The three most common practices of sample preparation are suspending crushed powder, ultramicrotomy, and ion-beam milling. The illustrations will be made with YBa2Cu3O7-x samples.

The powder suspension technique requires grinding the material with a suitable mortar and pestle (e g., agate) to a size which will allow electron transparency. Dispersing the particles in a suitable solvent such as water or acetone prevents aggregation. If the sample has large amounts of extraneous phases, the choice of medium is crucial as reactions will occur. Ni or Ti grids (50 to 75 mesh) with carbon films are used to fish out the suspended particles.
Characterization of Y-Ba-Cu-O films grown on silicon substrates by sequential evaporation
Authors: Hall E. L. , Mogro-Campero A. , Turner L. G. , Lewis N.
Published: June 2020

There is great interest in the growth of thin superconducting films of YBa2Cu3Ox on silicon, since this is a necessary first step in the use of this superconductor in a variety of possible electronic applications including interconnects and hybrid semiconductor/superconductor devices. However, initial experiments in this area showed that drastic interdiffusion of Si into the superconductor occurred during annealing if the Y-Ba-Cu-O was deposited direcdy on Si or SiO2, and this interdiffusion destroyed the superconducting properties. This paper describes the results of the use of a zirconia buffer layer as a diffusion barrier in the growth of thin YBa2Cu3Ox films on Si. A more complete description of the growth and characterization of these films will be published elsewhere.

Thin film deposition was carried out by sequential electron beam evaporation in vacuum onto clean or oxidized single crystal Si wafers. The first layer evaporated was 0.4 μm of zirconia.
Characterization of intergranular cuprous oxide in polycrystalline YBa2Cu3O7-x
Authors: Thiel Bradley L. , R. P. Chan Han , L. C. Hutter Kurosky , Aksay I. A. , Sarikaya Mehmet
Published: June 2020

The identification of extraneous phases is important in understanding of high Tc superconducting oxides. The spectroscopic techniques commonly used in determining the origin of superconductivity (such as RAMAN, XPS, AES, and EXAFS) are surface-sensitive. Hence a grain boundary phase several nanometers thick could produce irrelevant spectroscopic results and cause erroneous conclusions. The intergranular phases present a major technological consideration for practical applications. In this communication we report the identification of a Cu2O grain boundary phase which forms during the sintering of YBa2Cu3O7-x (1:2:3 compound).

Samples are prepared using a mixture of Y2O3. CuO, and BaO2 powders dispersed in ethanol for complete mixing. The pellets pressed at 20,000 psi are heated to 950°C at a rate of 5°C per min, held for 1 hr, and cooled at 1°C per min to room temperature. The samples show a Tc of 91K with a transition width of 2K. In order to prevent damage, a low temperature stage is used in milling to prepare thin foils which are then observed, using a liquid nitrogen holder, in a Philips 430T at 300 kV.
High resolution STEM imaging study on high Tc superconductor YBa2CuaO7-x
Authors: Ou H.-J. , Cowley J. M.
Published: June 2020

Using the dedicate VG-HB5 STEM microscope, the crystal structure of high Tc superconductor of YBa2Cu3O7-x has been studied via high resolution STEM (HRSTEM) imaging and nanobeam (∽3A) diffraction patterns. Figure 1(a) and 2(a) illustrate the HRSTEM image taken at 10' times magnification along [001] direction and [100] direction, respectively. In figure 1(a), a grain boundary with strong field contrast is seen between two crystal regions A and B. The grain boundary appears to be parallel to a (110) plane, although it is not possible to determine [100] and [001] axes as it is in other regions which contain twin planes [3]. Following the horizontal lattice lines, from left to right across the grain boundary, a lattice bending of ∽4° is noticed. Three extra lattice planes, indicated by arrows, were found to terminate at the grain boundary and form dislocations. It is believed that due to different chemical composition, such structure defects occur during crystal growth. No bending is observed along the vertical lattice lines.
TEM characterization of Ge films grown On GaAs (111) and Ge (111) by RPECVD
Authors: Posthill J.B. , Vitkavage D.J. , Rudder R.A. , Hattangady S.V. , Parikh N.R. , Fountain G.G. , Markunas R.J.
Published: June 2020

The fabrication of a Ge/GaAs heterostructure presents several attractive possibilities for device applications. The formation of a 2-D electron gas due to the difference in bandgaps between the two materials, and the increased hole mobility in Ge may allow a practical HMT-CMOS technology to be developed. Before this structure can be realized; however, it is essential to have a clean, low temperature growth process for the formation of electronic-quality Ge epitaxy. Remote plasma-enhanced chemical vapor deposition (RPECVD) in an ultrahigh vacuum compatible growth chamber is currently being investigated for this purpose. This paper addresses the ex-situ characterization of Ge/GaAs(111) heteroepitaxial structures grown by RPECVD at different temperatures and subsequent comparison with Ge/Ge(111) homoepitaxial material.

Nominal GaAs(111) wafers that had been Ga-face polished and Ge(111) wafers were chosen for this study. Individual wafers were cleaned, loaded into the growth chamber and baked at 200°C for ∼ 10 hours.
Investigation of dislocation propagation and confinement in GaAs epilayers grown on Si substrates using InGaAs-GaAsP strained layer superlattices
Authors: Tarn J.C.L.
Published: June 2020

The heteroepitaxial growth of GaAs on Si has been recognized as a viable technology towards achieving the monolithic integration of III-V compound based optoelectronic components and Si devices. Both metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) growth techniques have been widely employed to achieve heteroepitaxial growth However, as a result of the lattice and coefficient of thermal expansion mismatch that exists between the Si substrate and GaAs epilayer, a high density of defects propagate into the GaAs epitaxial film. In an attempt to reduce the density of these defects to a acomparable level for device fabrication (< 104 cm-2), the use of a strained layer superlattice (SLS) has been advocated as an appropriate defect confinement layer. A judicious choice of SLS is InxGa1-xAs-GaAs1-yPy (y=2x)2 whose average lattice constant is lattice matched as a whole to the GaAs epilayer. Indeed, by using this particular SLS structure, a high level of elastic strain and an infinite number of semiconductor layers can be selected to force the dislocations to glide to the edge of the substrate.
TEM studies of dislocations in deformed Ga1-xInxAs single crystals
Authors: Rai R. S. , Guruswamy S. , Faber K. T. , Hirth J. P.
Published: June 2020

The perfection of GaAs single crystals can be controlled by doping the GaAs with In, at a level of about 5x1019-1x1020/cm3, in single crystals grown by the LEC process. It has been observed that In doping at this level reduces the grown in dislocation density from 104-l05 to ≤ 102/cm2 and results in a large increase in high temperature strength . However, the role of In in dislocation density reduction is not clearly understood. Therefore, a systematic study has been performed with the help of high temperature deformation of In-doped and undoped GaAs single crystals followed by dislocation structural characterization by transmission electron microscopy of the deformed specimens. Here, some results of dislocation studies performed by TEM are descri bed.

Samples were examined in a JEOL JEM 200CX transmission electron microscope equipped with a double tilt goniometer stage. The standard g.b criterion was employed for characterization of dislocations. Dark-field weak beam pictures were taken for characterization of partial dislocations and dipoles.