bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stabilising a Peels spectrometer
Authors: McMullan D. 
Published: June 2020

The resolution of a parallel recording electron energy loss spectrometer (PEELS) depends critically on the stabilities of the power supplies to the microscope column and the spectrometer over the period of the exposure. They may be the limiting factor in a dedicated scanning transmission electron microscope (STEM) with a field-emission electron gun (FEG), and improving them so that they are sufficiently stable can be a difficult task.An alternative approach is to compensate for any drift by deflecting the electron image of the spectrum leaving the spectrometer. The amount of deflection is that required to keep the zero-loss peak at a fixed position relative to the recording system. Such a stabiliser is being developed in the Microstructural Physics (MP) Group at the Cavendish Laboratory and a progress report is given here.The MP STEM is a VG Microscopes HB501 fitted with an Isaacson electron spectrometer. The normal accelerating potential is 100 kV and the FEG has an electron energy spread of about 0.25 eV. The spectrometer gives a dispersion of 1.8 pm per eV at the slit and from the evidence of very short exposures its resolution is adequate to match the FEG energy-spread in the absence of drift. A PEELS system with 3 quadrupoles and a YAG + CCD detector has been added, but the slit has been retained.
HREM image simulation of Ti5Si3TiC/6H-SiC interfaces
Authors: Bow J. S. , Carpenter R. W. , Kim M.J. 
Published: June 2020

Researches on interfacial structures by experimental HREM and computer simulation to the present have concentrated on solving one interface between two phases. Interfaces with a thin third phase interlayer between two major phases are of more recent interest. As the thickness of the interlayer phasedecreases, the strain fields of the bounding interfaces are no longer completely accommodated by the interlayer phase. The structures of both interfaces have to be considered simultaneously. This abstract describes some early work on establishment of a supercell including three phases and two interfaces for HREM simulation.The interface triad, Ti5Si3/TiC/6H-SiC, which was formed during annealing Ti/6H-SiC contacts, is an important example. The TiC thickness observed in the experimental HREM image, Fig. 1, is about 2.5 nm. The interlayer dimension normal to the interfaces is not large, and the size of the required supercell is small enough for computation on a moderately fast workstation.The simplest way to build a supercell including these three phases is to build each individual crystal constituent of the triad in the desired orientation and dimension and then assemble them with suitable translation vectors.
Phase transformation and layer evolution in molybdenum disilicide-silicon carbide nanolayered coatings
Authors: Kung H. , Jervis T. R. , Hirvonen J.-P. , Nastasi M. , Mitchell T. E. , Embury J. D. 
Published: June 2020

MoSi2 is a potential matrix material for high temperature structural composites due to its high melting temperature and good oxidation resistance at elevated temperatures. The two major drawbacksfor structural applications are inadequate high temperature strength and poor low temperature ductility. The search for appropriate composite additions has been the focus of extensive investigations in recent years. The addition of SiC in a nanolayered configuration was shown to exhibit superior oxidation resistance and significant hardness increase through annealing at 500°C. One potential application of MoSi2- SiC multilayers is for high temperature coatings, where structural stability ofthe layering is of major concern. In this study, we have systematically investigated both the evolution of phases and the stability of layers by varying the heat treating conditions.Alternating layers of MoSi2 and SiC were synthesized by DC-magnetron and rf-diode sputtering respectively. Cross-sectional transmission electron microscopy (XTEM) was used to examine three distinct reactions in the specimens when exposed to different annealing conditions: crystallization and phase transformation of MoSi2, crystallization of SiC, and spheroidization of the layer structures.
Structural-property relations in ferroelectric-based materials
Authors: Randall C. A. 
Published: June 2020

Ferroelectric and related materials are gaining importance owing to the wide variety of phenomena associated with ferroelectricity. This includes high dielectric permittivity, electrostriction, pyroelectricity, and piezoelectricity. Applications using these properties are continually requiring higher performance of the materials. Therefore, there exists a need to understand the structuralproperty relations of ferroelectrics as a means to optimize their design.Transmission electron microscopy (TEM) techniques are beginning to provide quantitative and qualitative information on the mesoscopic structures, local crystallography, and chemistry of ferroelectric materials. This paper will consider three examples in which TEM methods have been successfully used to prepare higher performance materials and/or a deeper understanding of the role of mesoscopic structures on the physical dielectric characteristics.The first example demonstrates the importance of intermediate scale B-site chemical ordering within the complex lead perovskite lattice and the associated observation of relaxor behavior. Figure 1 shows a typical dark field electron micrograph of B-site order domains in Pb(Mg1/3Nb2/3)O3.
Determination of crystal polarity in the Electron Microscope
Authors: Mader W. , Recnik A. 
Published: June 2020

A few methods were proposed for the determination of crystal polarity using electron diffraction. The method by Taftø and Spence is based on the coupling between ZOLZ and FOLZ reflections, requiring exact tilting to excite weak high- and odd-indexed reflections. The method by Spellward and James relies on the comparison of experimentally observed and calculated CBED patterns of fairly thick crystals, where the features in the CBED discs are compared. In this paper we present a method for polarity determination readily evident from ZOLZ reflections in zone-axis microdiffraction patterns. The method is based on zero-layer interactions from thin crystals with thickness t smaller than the extinction length of the primary beam. Then the diffraction discs appear homogeneous, and the breakdown of Friedel's law is noticable in a difference of the intensities of the reflections g and -g which are not related to a mirror plane (Bijvoet-related reflections).The method can be applied using any transmission electron microscope which is designed for obtaining convergent-beam microdiffraction patterns and in principle, specimen-cooling is not necessary. The crystals have to be oriented to a low-indexed zone axis, where the diffraction plane contains a polar crystal axis.
Orientation imaging of microstructures
Authors: Adams B. L. 
Published: June 2020

The complexity of microstructures characteristic of polycrystalline materials presents the serious investigator with many challenges. The materials engineer hopes to associate the important technological properties of these materials with specific (quantifiable) attributes of the microstructure; however, microscopy presents an overwhelming myriad of details over a wide range of scales of inquiry. Thus, the persistent question becomes: What is important in the microstructure relative to a specific property or aspect of material performance? One particular viewpoint, which stems from the modern atomistic interpretation of the structure of solids, is that for polycrystalline materials it is the spatial placement of lattice orientation that is of essential interest.The past decade has seen some remarkable progress in microdiffraction technique in conjunction with the scanning electron microscope. This progress now makes it possible to vigorously pursue the aforementioned lattice-orientational viewpoint. Since 1987 modern SIT (silicon intensified target) vidicon and CCD (charge-coupled device) cameras have been used to capture the backscattered Kikuchi diffraction (BKD) formed in stationary spot mode in the scanning electron microscope.
Applications of microtexture analysis for materials characterization using SEM and TEM techniques
Authors: Weiland H. , Liu J. 
Published: June 2020

Research and development in material science require the understanding of structure and property relationship. In many instances, such a relationship at a local microstructural scale is crucial for a mechanistic insight. Spatially-resolved microtexture analyses based on both scanning and transmission electron microscopy have now become powerful tools for these studies. By these techniques, not only can a linkage be established between morphological and crystallographic components of the microstructure, grain boundary details can be obtained as well. The choice of the SEM- or TEM-based microtexture technique for a study, however, depends on the specific needs. Several industrial examples of applied and basic work will be used for illustration.Industrial deformation processes such as extrusion, rolling and forging are generally inhomogeneous. As a result, strain gradients, and consequently, microstructure gradients, are intrinsic to most industrial products. For example, a laboratory-produced plane strain extrusion of an Al-Zn-Mg-Cu alloy exhibits a range of complex grain structures (Fig. 1a).
Characterization of SiC fiber-reinforced SiC composites by TEM
Authors: Park K. , Sung C. 
Published: June 2020

SiC fiber-reinforced SiC composites have been accepted to have considerable potential as an engineering structural ceramic for numerous high-temperature applications, such as various heat engine components. In this study, the microstructure of matrix, fiber, and matrix/fiber interface of SiC fiber (SCS-6, Textron)-reinforced nitrogen-treated SiC composites was characterized using transmission electron microscopy (TEM). Cross-sectional TEM samples were prepared by mechanical grinding, dimpling, and ion-milling. The samples were analyzed using a Philips EM400T TEM and a Noran ultrathin window Micro-Z detector.The α-Si3N4 was formed in the porous SiC matrix by nitriding (Fig. 1(a)). The porous SiC matrix can permit easy and continuous penetration of the nitriding gas and rapid escape of the reaction and volatilization products, thus favoring vapor-phase reactions. In the case of huge SiC grains, the α-Si3N4 was formed at the surface of the huge SiC grains. Rod-shaped Si2N2O phase was often observed in the porous matrix. Figs. 1(b), (c), and (d) show electron diffraction patterns obtained from the α-SiC, α-Si3N4, Si2N2O phases, respectively.
Microstructure of intermetallic-matrix composites produced in situ by self-propagating high-temperature synthesis
Authors: Doğan C. P. , Alman D. E. 
Published: June 2020

Self-propagating, high-temperature synthesis (SHS) is one method of material production in which elemental constituents are ignited, initiating a self-sustaining, exothermic reaction that results in their transformation into intermetallic and ceramic compounds. In addition, several reactions can be initiated within a single body to form intermetallic-intermetallic, intermetallic-ceramic, or ceramic-ceramic composites in situ. The driving force for the reactions is the negative heats of mixing of the forming compounds, which results in the liberation of heat. The obvious advantages of SHS processing are that it presents an opportunity to produce near net-shape advanced materials and composites with a high level of purity in a relatively low-cost and energy efficient manner.At the U.S. Bureau of Mines, we are actively involved in the SHS processing of a wide range of singlephase intermetallic and intermetallic-matrix composites: TiAl, TiAl+TiB2, TiAl+TiC, TiAl+Ti5Si3, MoSi2+SiC. One key element of our study is a thorough understanding of the effect of processing variables, such as composition, temperature, pressure, time, powder morphology, etc., on the microstructure, and hence the properties, of these materials.
Toward quantitative defect analysis using HREM
Authors: Smith David J. 
Published: June 2020

The electron microscope has evolved to the level where it is now straightforward to record highresolution images from thin samples (t∼10 to 20nm) that are directly interpretable in terms of atomic arrangements. Whilst recorded images necessarily represent two-dimensional projections of the structure, many defects such as dislocations and interfaces may be linear or planar in nature and thus might be expected to be amenable to detailed characterization. In this review, we briefly consider the recent significant progress that has been made in quantitative defect analysis using the high-resolution electron microscope and then discuss some drawbacks to the technique as well as potential scope for further improvements. Surveys of defect modelling for some small-unit-cell materials and interfaces have recently been published, and reference should be made to other papers in this symposium for further examples.The technique of structure imaging originated in the early '70s with observations of large-unit-cell block oxides.
Quantitative analysis by reconstruction of HREM focal series
Authors: Coene W. , Thust A. , Op de Beeck M. , Van Dyck D. 
Published: June 2020

Compared to conventional electron sources, the use of a highly coherent field-emission gun (FEG) in TEM improves the information resolution considerably. A direct interpretation of this extra information, however, is hampered since amplitude and phase of the electron wave are scrambled in a complicated way upon transfer from the specimen exit plane through the objective lens towards the image plane. In order to make the additional high-resolution information interpretable, a phase retrieval procedure is applied, which yields the aberration-corrected electron wave from a focal series of HRTEM images (Coene et al, 1992).Kirkland (1984) tackled non-linear image reconstruction using a recursive least-squares formalism in which the electron wave is modified stepwise towards the solution which optimally matches the contrast features in the experimental through-focus series. The original algorithm suffers from two major drawbacks : first, the result depends strongly on the quality of the initial guess of the first step, second, the processing time is impractically high.
HRTEM: White-atom images versus black-atom images
Authors: Clancy J. P. 
Published: June 2020

The observed intensity under phase-contrast imaging conditions is a complicated function of the microscope and the thin solid. The important parameters of the microscope are the beam divergence, the energy spread of the fast electrons, and the objective lens excitation. From these parameters, a transfer function is defined that operates on the scattered wavefunction. The important parameters of the thin solid are the thickness, the atomic coordinates, and the scattering strength of the atoms. These parameters define the phase and amplitude of the Bloch waves excited in the crystal. As a result of these complexities, image interpretation is quite often problematic. Moreover, for those models that do accurately predict the experimental intensity, uniqueness is still in question. Since the indicated parameters limit the resolution capability of the microscope and this limit can not be overcome, the task at hand is to exploit the consequences of these parameters.There are two imaging conditions that produce interpretable data for periodic crystals: those where the intensity maxima correspond to atomic columns (white-atom images), and those where the intensity maxima correspond to atomic tunnels (black-atom images.)
Production of novel carbon nanoclusters by catalytic arc discharge
Authors: Zhou D. 
Published: June 2020

Carbon nanoclusters are realizing step by step their technological promises. The initial spherical fullerenes were followed by tubular configurations, and foreign materials were encapsulated into their hollow cores. When catalysts were introduced into the arc-discharge process, a large variety of novel growth phenomena were observed in their presence. We report here on a new type of cluster assembly - a string of carbon nanobeads attached to each other and to a catalytic particle - prepared in the presence of Ni. We also report on the preparation of single-walled carbon nanotubes catalyzed by Ni, Fe, and their mixtures, as well as on their densities observed in different locations in the reaction chamber.The initial material was generated by the catalytic arc-discharge method developed by Kratschmer and Huffman, with pure Ni introduced to a hollow graphite anode which was consumed during the evaporation. After the catalytic arc-discharge, black carbon soot was collected from the inner surface of the reaction chamber; then carbonaceous deposit (slag) was retrieved from the initial flat cathode; and finally a rubber-like deposit was obtained from the periphery of the slag.
Field-assisted ionization theory for microscopists
Authors: Camus Patrick P. 
Published: June 2020

The theory of field ion emission is the study of electron tunneling probability enhanced by the application of a high electric field. At subnanometer distances and kilovolt potentials, the probability of tunneling of electrons increases markedly. Field ionization of gas atoms produce atomic resolution images of the surface of the specimen, while field evaporation of surface atoms sections the specimen. Details of emission theory may be found in monographs.Field ionization (FI) is the phenomena whereby an electric field assists in the ionization of gas atoms via tunneling. The tunneling probability is a maximum at a critical distance above the surface,xc, Fig. 1. Energy is required to ionize the gas atom at xc, I, but at a value reduced by the appliedelectric field, xcFe, while energy is recovered by placing the electron in the specimen, φ. The highest ionization probability occurs for those regions on the specimen that have the highest local electric field. Those atoms which protrude from the average surfacehave the smallest radius of curvature, the highest field and therefore produce the highest ionizationprobability and brightest spots on the imaging screen, Fig. 2. This technique is called field ion microscopy (FIM).
Direct measurement of the coating thickness on spherical particles
Authors: Admon U. , Coakley K. , Dariel M. P. , Giuseppetti A. A. , Hagwood C. , Lashmore D. S. , Vangel M. G. 
Published: June 2020

In the course of the development of an coating process of metallic powders, the dependence of the coated layer thickness on the process variables and on the initial particle size had to be determined. The initial, atomized powder particles in the 5-80 μm size range, were perfect spheres to a good approximation.We chose to employ a “particulate” approach according to which individual powder particles were repeatedly cross-sectioned and examined at known intervals, sufficiently close to allow the same spheres to be cross-cut more than once. Micrographs of selected particles were taken at each stage. Simple chord measurements taken from the micrographs, which provide two-dimensional information, and the measured spacing between the corresponding cross-sections, giving the third dimension, allows to calculate both the particle diameter and the coating thickness. The accuracy of the results depends critically on the accuracy of the spacing measurement. The present communication describes a simple, practical, and precise method for this measurement, eliminating the necessity for precision alignment and dedicated tools.
Local thickness determination by Electron Energy Loss Spectroscopy
Authors: Luo Suichu , Dunlap John R. , Williams Richard W. , Joy David C. 
Published: June 2020

In analytical electron microscopy, it is often important to know the local thickness of a sample. The conventional method used for measuring specimen thickness by EELS is:where t is the specimen thickness, λiis the total inelastic mean free path, ITis the total intensity in an EEL spectrum, and I0is the zero loss peak intensity. This is rigorouslycorrect only if the electrons are collected over all scattering angles and all energy losses. However, in most experiments only a fraction of the scattered electrons are collected due to a limited collection semi-angle. To overcome this problem we present a method based on three-dimension Poisson statistics, which takes into account both the inelastic and elastic mixed angular correction.The three-dimension Poisson formula is given by:where I is the unscattered electron intensity; t is the sample thickness; λiand λeare the inelastic and elastic scattering mean free paths; Si(θ) and Se(θ) are normalized single inelastic and elastic angular scattering distributions respectively ; F(E) is the single scattering normalized energy loss distribution; D(E,θ) is the plural scattering distribution,
Quantitative energy-filtered electron diffraction
Authors: Vincent R. 
Published: June 2020

Microanalysis and diffraction on a sub-nanometre scale have become practical in modern TEMs due to the high brightness of field emission sources combined with the short mean free paths associated with both elastic and inelastic scattering of incident electrons by the specimen. However, development of electron diffraction as a quantitative discipline has been limited by the absence of any generalised theory for dynamical inelastic scattering. These problems have been simplified by recent innovations, principally the introduction of spectrometers such as the Gatan imaging filter (GIF) and the Zeiss omega filter, which remove the inelastic electrons, combined with annual improvements in the speed of computer workstations and the availability of solid-state detectors with high resolution, sensitivity and dynamic range.Comparison of experimental data with dynamical calculations imposes stringent requirements on the specimen and the electron optics, even when the inelastic component has been removed. For example, no experimental CBED pattern ever has perfect symmetry, departures from the ideal being attributable to residual strain, thickness averaging, inclined surfaces, incomplete cells and amorphous surface layers.
On-line diffraction pattern analysis and phase identification using a JEM 2000FX AEM with a macintosh-based program
Authors: Hills C. R. , Poulter G. A. 
Published: June 2020

A number of computer programs have been written to aid in the indexing of transmission electron diffraction pattcrns. These programs are useful for determining crystallographic orientation and for phase identification and often simplify the analysis of complex patterns. Over the last few years there has been a trend toward automated electron microscopy. It is natural to extend this automation to real time diffraction pattern analysis and phase identification using A/D data acquisition boards and computer software to interface the modern AEM with an electron diffraction database (EDD). This paper describes a real-time Macintosh-based system (hardware and software) for automated electron diffraction pattern analysis and phase identification developed for the JEM 2000FX AEM. Crystallographic analysis with this system is attractive because of the rapid analysis time, ease of implementation, and it is inexpensive compared to buying a digitizing board and video system.Computer-aided diffraction pattern-indexing programs typically require the user to input reciprocal lattice point spacings (r-spacings) and the interplanar angle measurements for at least three non-colinear lattice points in the pattern. It is also necessary to know the crystal structure and lattice constants of the sample.