bluuebunny/crossref_metadata_2025 huggingface dataset:
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).
Microscopy in VLSI reliability studies
Authors: Rose J. H. , Shuman R. , Elliott L.
Published: June 2020

Reliability engineering arises from the very practical need to accurately predict the eventual failure of a manufactured component or system. In microelectronics, the failure process is far too complex, even in a simple length of thin film conductor subjected to a constant current, to rely solely onany model for prediction of failure probability. Hence, reliability engineers extrapolate device lifetime predictions from accelerated (via elevated temperature and current) testing of batches of samples. Even this approach requires accurate temperature and current acceleration factors to extend reliability statistics to use conditions. A great deal of work has been performed over the past 25 years onthe behavior of interconnect materials when subjected to current and mechanical stress. To varying degrees, this work has included microstructural evaluations. It has been well demonstrated that voidsandhillocks can arise from electromigration derived grain boundary diffusion. It is also well known that alloying aluminum, notably with small copper additions, greatly slows electromigration damage, though the mechanism of this benefit is yet to be proven. Microscopy used in these studies has generally consisted of simple observations of precipitates and grain boundaries and the defects which lead to failure, voids and hillocks. SEM observations are commonly employed for quick surveys, though as a surface imaging tool, the SEM is very limited in the microstructural view provided (Fig. 1). Recent attempts to study the failure process from a materials (rather than electrical engineering) point of vieware leading to greater insight into the microstructure of failure (see, for example, several articlesin Ref. 1). However, much work is needed to bridge the gap between observation of specific failures and the statistical approach in modeling and testing employed by reliability engineers. Success here could lead to quicker, microstructure based screening of material quality and new processing for optimized microstructure to maximize reliability.
TEM sample preparation and analysis of single-crystalline Si spheres
Authors: Jones Kim M.
Published: June 2020

In parallel with the technological advancements in the field of Transmission Electron Microscopy (TEM), numerous innovations in TEM sample preparation have also transpired. Innovations in polishing techniques, ion etching, and ultramicrotomy have not only expanded the types of materials that are being investigated with TEM, but have also improved the quality of the thin sections that are examined. Described in this paper is a sample preparation procedure that was developed in order to prepare small Si spheres for TEM analysis. Metallurgical-grade Si is the starting material used in the productionof the spheres. The Si spheres are the main components in the Spheral Solar Cell technology developed by Texas Instruments. The solar cell configuration is shown schematically in Fig. 1. The spheresaresubjected to a number of refinement steps, for example: denuding, gettering, and annealing in order to achieve a purity that is suitable for solar cell fabrication. TEM characterization of the Si spheres was performed at various stages in the refinement process. The spherical shape and size (ave. dia.=0.75 mm) of the Si pose a challenge for TEM sample preparation.
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.
Experimental determination of k-factors for grain boundary analysis of alloyed Nb3Sn superconductor wires
Authors: Rodrigues D. , Garratt-Reed A. J. , Foner S.
Published: June 2020

In superconductors the critical current densities are limited by the ability of the pinning centers in the material to pin flux lines. In A15-type superconductor wires, such as Nb3Sn, the pinning centers are the boundaries of A15 grains formed during the reaction heat treatment between the Nb and Sn at 650-750°C. The pinning behavior in these wires usually relates the average grain size and average composition of the A15 phase to the pinning force measured for the same wire. Few publications described the variations of the pinning behavior due to changes in the grain and grain-boundary compositions. In order to better understand the pinning behavior in regular A15 wires or in new wires with artificial pinning centers, the concentrations of elements across the grains and at the grain boundaries must be analyzed. These concentrations change the chemical potential of the region and, consequently, the interaction energy between the flux line lattice and the pinning centers. For our superconductor wires, the Nb3Sn grains could contain Nb, Sn, Cu, and Ta or Ti.
Observations of thick and thin sections in a field-emission SEM
Authors: Wergin W. P. , Roy S. , Erbe E. F. , Murphy C. A. , Pooley C. D.
Published: June 2020

Larvae of the nematode, Steinernema carpocapsae Weiser strain All, were cryofixed and freezesubstituted for 3 days in acetone containing 2% osmium tetroxide according to established procedures. Following chemical fixation, the nematodes were brought to room temperature, embedded in Spurr's medium and sectioned for observation with a Hitachi S-4100 field emission scanning electron microscope that was equipped with an Oxford CT 1500 Cryotrans System. Thin sections, about 80 nm thick, similar to those generally used in conventional transmission electron microscope (TEM) studies were mounted on copper grids and stained with uranyl acetate for 30 min and lead citrate for 5 min. Sections about 2 μm thick were also mounted and stained in a similar fashion. The grids were mounted on an Oxford grid holder, inserted into the microscope and onto a cryostage that was operated at ambient temperature. Thick and thin sections of the larvae were evaluated and photographed in the SEM at different accelerating voltages. Figs. 4 and 5 have undergone contrast conversion so that the images would resemble transmitted electron micrographs obtained with a TEM.
Near-field optical microscopy/spectroscopy of discrete quantum emitters
Authors: Betzig E.
Published: June 2020

A subwavelength sized source or detector of visible light can be raster scanned in close proximity to the surface of a sample to generate images at a resolution well beyond the classical diffractional limit. Applications of the resultant technique, near-field scanning optical microscopy (NSOM), include fluorescence imaging of fixed cells, mode profiling of semiconductor lasers, and high density magnetooptic data storage. The focus of this presentation, however, will be on the more recent use of NSOM in the identification and characterization of discrete quantum emitters from within an ensemble.

Two such systems will be discussed. The first involves the detection and characterization of single fluorescent molecules. The usual difficulty with single molecule detection is not the inherently weak luminescence signal from each molecule, but rather the large background from impurity luminescence and Raman scattering within the excitation volume. NSOM greatly reduces this volume and hence the resultant background, yielding sensitivity of 0.005 molecules.
Displacement at the twin boundary in YBa2Cu3O7 superconductor
Authors: Zhu Yimei , Pan M. , Li Z.G. , Suenaga M. , Welch D.
Published: June 2020

A shear displacement at the twin boundary in YBa2Cu3O7 superconductor has been observed by means of High Resolution Electron Microscopy. It was found that the a and b planes across the twin boundary are shifted along the boundary by a distance of (1/3 ∼ 1/2) · 2d110. In order to confirm our observation and give an optimum interpretation of the HREM image, computer simulation of the twin structure in YBa2Cu3O7 was carried out.

A large supercell, 81.72×21.72×11.70 Å, with a total of 1492 atoms was constructed to simulate the twin structure. The twin boundary is modeled not only by a rotation of the planes in one domain with respect to the adjacent domain by an angle of 90° - ϕ (ϕ≈0.967°) but also by a translation (R= 1/3•2d110) along the boundary. In addition, in order to simulate the diffused boundary, boundary steps in and directions as shown in Fig.1(d) were introduced.
HRTEM analysis on phase transitions in Bi-based superconductive oxides
Authors: Horiuchi S. , Shoda K. , Wu X.J. , Nozaki H. , Tsutsumi M. , Matsui Y.
Published: June 2020

It is known for the superconductors in a Bi-Sr-Ca-Cu-O system that there are three phases. Bi2Sr2CuOx, Bi2Sr2CaCu2Ox and Bi2Sr2Ca2Cu3Ox, which are called for simplicity the (2201), (2212) and (2223) phases with the critical temperatures Tc at about 20, 85 and 110K respectively. Their crystal structures are closely related and the phase transition among them often occurs. When the specimen in the partially molten state was quenched to ice-water, it was composed of a Bi-rich, amorphous phase and impurity phases like Ca1−zSrzCuO2. On crystallization the former became the (2201) phase. On further heating at higher temperature firstly the (2212) phase and secondly the (2223) phase were obtained.

In the present study the structural variation during the transition from the (2201) phase to the (2212) phase and further to the (2223) phase was clarified mainly by using a high-resolution transmission electron microscopy (IIRTEM). Thin specimens were prepared by ion-thinning method and observed by a 200kV TEM (JEM 2000EX). The mechanism of the phase transition was discussed from the structural viewpoint.
Origin of superstructure modulations in Bi-Sr-Ca-Cu-O superconductors
Authors: Gai Pratibha L. , Subramanian M.A. , Sleight Arthur W.
Published: June 2020

New insights into the origin of superstructure modulations in Bi-Sr-Ca-Cu-O superconductors with the idealized formulation Bi2Sr2CaCu2O8 (2212) have been obtained primarily from electron microscopy. Systematic investigations of the Bi-Sr-Ca-Cu-O samples annealed in both reducing and oxidizing environments show that the superconducting transition temperature (Tc) decreases for the oxygen-annealed samples containing oxygen interstitials. Electron diffraction has revealed significant local differences in the modulation periodicities depending on the annealing environment. Superstructure modulations have also been found in the samples prepared entirely in reducing nitrogen. Rare-earth doped Bi2Sr2Ca1−xYxOy have also been examined in different environments. High precision microanalysis using quantitative EDX shows that the modulations are insensitive to the concentration of cation point defects.

Proposed models for superstructure modulations include: a rigid rotation of CuO5 polyhedra which may result from small differences in the equilibrium bond lengths between Bi-O and Cu-O layers; ordering of Bi-concentrated and deficient zones;
Microstructural characterization of Y-Ba-Cu-O laser deposited with high deposition rates on SrTiO3
Authors: Ravi T.S. , Ramesh R. , Hwang D.M. , Wu X.D. , Inam A. , Venkatesan T.
Published: June 2020

As the technique of pulsed-laser deposition of YBa2Cu3O7−x (YBCO) matures, it is important to be able to have economically feasible processing conditions for future industrial applications such as microelectronics. Very high quality thin films of YBCO (with excellent Tc and Jc) have been consistently obtained for low deposition rates, such as 0.3Å/sec. However at this rate it takes at least two hours to produce a film 2000Å thick. While the quality of the film grown is of prime importance, it would be economically advantageous if the film can be grown much faster without much loss in quality. The objective of this study is to microstructurally characterize, using a combination of microdiffraction, X-ray microanalysis and HREM, thin films of YBCO prepared with higher deposition rates.
HRTEM study of crystal structures and microstructures of High-Te superconductors YBa2−xSrxCu3Oy (x=0-1.2)
Authors: Matsui Yoshio , Lee Uk , Ono Akira , Horiuchi Shigeo , Tsuruta Chusei
Published: June 2020

High-Tc superconducting oxide YBa2Cu3Oy has an orthorhombic structure (a=0. 382, b=0. 389 and c=1. 17nm) with layer sequences of (..BaO CuOx BaO CuO2 Y CuO2 BaO CuOx BaO..) along the c-axis. It usually has twinned microstructure with twin plane {110}, causing associated splitting of some of the diffraction spots. It is well known that these characteristic structures of YBa2Cu3Oy can be affected by partial substitutions of cation sites. For instance, tetragonal structure with a=b is stabilized in the compounds Ba2−xLa1+xCu3Oy and Ba2−xNd1+xCu3Oy . Formations of 90-degree domain structures are also observed in these compounds. Recently, Ono et al. prepared a series of compounds, YBa2−xSrxCu3Oy (x=0 to 1.2), to study the effects of substituting Ba by Sr and found the gradual decrease of Tc with increase of x. In the present study, change of the crystal structures and the microstructures in a series of compounds are examined by means of high-resolution transmission electron microscopy.
The role of specimen morphology in the preparation of High-TC superconductors for Transmission Electron Microscopy
Authors: Powers M.
Published: June 2020

It is vital in TEM investigations, especially for high resolution studies, that specimen quality be optimized and the information desired in a particular TEM analysis often prescribes the method of specimen preparation required. We have found that the morphology of a bulk superconductor sample can significantly influence the ultimate success of the preparation technique utilized.

Methods employed for the production of electron transparent foils of ceramic oxide superconductors include mechanical grinding, cleavage, jet polishing, ultramicrotomy and ion milling. Grinding and cleavage are both low cost, quick and easy specimen preparation techniques. However, because of the layered crystal structures of these materials, they display a marked tendency to cleave along (001) planes, and hence the range of crystallographic orientations available with these methods is restricted. With grinding in particular, mechanical deformation can be a problem while with cleavage, transparent areas are confined to the vicinity of particle edges.
Correlation of electrical properties of Bi-Sr-Ca-Cu-O superconductor with changes in microstructure and composition caused by rapid heating and cooling
Authors: Duan Q. , Dash J.
Published: June 2020

Samples of Bi2Sr2CaCu2Ox were prepared from a mixture of reagent-grade Bi2O3, SrCo3, CaCo3, and CuO. After mixing and grinding, the powder was sintered for 24 h at 800 C. Then the sinter was again ground and then pressed into pellets about 12.5 mm dia.

The pellets were heated at 880 C in air for 20 h and then quenched rapidly in liquid nitrogen. In this condition the surface had a granular structure, as shown by the SEM image, Fig. 1. The average surface composition of this area is indicated by the EDS spectrum, Fig. 2.

The pellets were then exposed to pure argon at about 1000 C and 1000atm pressure in a ballistic compressor. The time of exposure to hot, dense argon was about 10−3 sec. The samples were then cooled at a rate of about 105 C per second. After this treatment, the granular surface texture was completely gone, Fig. 3.
Xenon ion irradiation of superconducting YBa2Cu3O7 thin films
Authors: Watanabe H. , Kabius B. , Roas B. , Urban K.
Published: June 2020

Recently it was reported that the critical current density(Jc) of YBa2Cu2O7, in the presence of magnetic field, is enhanced by ion irradiation. The enhancement is thought to be due to the pinning of the magnetic flux lines by radiation-induced defects or by structural disorder. The aim of the present study was to understand the fundamental mechanisms of the defect formation in association with the pinning effect in YBa2Cu3O7 by means of high-resolution electron microscopy(HRTEM).

The YBa2Cu3O7 specimens were prepared by laser ablation in an insitu process. During deposition, a substrate temperature and oxygen atmosphere were kept at about 1073 K and 0.4 mbar, respectively. In this way high quality epitaxially films can be obtained with the caxis parallel to the <100 > SrTiO3 substrate normal. The specimens were irradiated at a temperature of 77 K with 173 MeV Xe ions up to a dose of 3.0 × 1016 m−2.
A model for the modulation in Bi2−xPbxSr2CaCu2O8+δ with large x
Authors: Zandbergen H. W. , van Tendeloo G.
Published: June 2020

Compounds with composition Bi2−xPbxSr2CaCu2O8+∂ show to have two different kinds of incommensurate superstructures. The first one (Bi-type) occurs for x being small and for the pure Bi compound. This superstructure is reported by many authors, which all reports shifts of all atoms. The modulation is directed along the b axis and the modulation vector was found to vary between about 3.5b and 5.0b for Ca completely replaced by Y and Bi2−xPbxSr2CaCu2O8+∂ with x being 0.1 respectively. A model for the modulation was proposed by Zandbergen et al, based on the interpretation of HREM images and structural chemistry arguments. This model, assuming the introduction of extra oxygen in the BiO layers to decrease the mismatch between the BiO layers and the perovskite blocks with which the BiO layers are sandwiched, has been proven to be basically right and is schematically represented in Figure 1.

For x being larger than about 0.2 the amplitude of the Bi type of modulation starts to decrease and another type of modulation (Pb-type) is occurring. A number of authors have reported this type of of modulation but up till now no explanation has been given. The modulation vector is mostly reported to be close to 7.5b but also a variation with x is reported. When x is between 0.2 and 0.5 both types of modulation are present and Pierre et al report that when both modulation are present the ratio of both modulation vectors is 3/2. Similarly to the Bi type of modulation, the Pb type of modulation is accompanied with a periodicity of 0.54 nm along the a axis, as is shown in Figure 2.
Structures and crystallization of vacuum-deposited amorphous Se and Sb films
Authors: Shiojiri Makoto , Isshiki Toshiyuki , Fudaba Tetsuya , Hirota Yoshihiro
Published: June 2020

In hexagonal Se crystal each atom is covalently bound to two others to form an endless spiral chain, and in Sb crystal each atom to three others to form an extended puckered sheet. Such chains and sheets may be regarded as one- and two- dimensional molecules, respectively. In this paper we investigate the structures in amorphous state of these elements and the crystallization.

HRTEM and ED images of vacuum-deposited amorphous Se and Sb films were taken with a JEM-200CX electron microscope (Cs=1.2 mm). The structure models of amorphous films were constructed on a computer by Monte Carlo method. Generated atoms were subsequently deposited on a space of 2 nm×2 nm as they fulfiled the binding condition, to form a film 5 nm thick (Fig. 1a-1c). An improvement on a previous computer program has been made as to realize the actual film formation. Radial distribution fuction (RDF) curves, ED intensities and HRTEM images for the constructed structure models were calculated, and compared with the observed ones.
TEM study of amorphization of Cu and Ti foils by cold-rolling
Authors: Chiou W. A. , Jeon N. L. , Xu Genbao , Meshii M.
Published: June 2020

For many years amorphous metallic alloys have been prepared by rapid quenching techniques such as vapor condensation or melt quenching. Recently, solid-state reactions have shown to be an alternative for synthesizing amorphous metallic alloys. While solid-state amorphization by ball milling and high energy particle irradiation have been investigated extensively, the growth of amorphous phase by cold-rolling has been limited. This paper presents a morphological and structural study of amorphization of Cu and Ti foils by rolling.

Samples of high purity Cu (99.999%) and Ti (99.99%) foils with a thickness of 0.025 mm were used as starting materials. These thin foils were cut to 5 cm (w) × 10 cm (1), and the surface was cleaned with acetone. A total of twenty alternatively stacked Cu and Ti foils were then rolled. Composite layers following each rolling pass were cleaned with acetone, cut into half and stacked together, and then rolled again.
Cross-section TEM observations of amorphous nickel-titanium thin films formed by solid state reaction
Authors: Cook Russell E.
Published: June 2020

There have been conflicting results concerning solid state amorphizing reactions (SSAR) in thin films consisting of alternating multiple layers of nickel and titanium. Clemens first reported evidence for SSAR in Ni-Ti using X-ray diffraction, Auger depth-profiling, and electrical conductivity measurements. The thickness of the Ni and Ti layers was 200 close-packed atom planes each in those samples in which SSAR was observed, although the reaction did not go to completion. Meng, et al. made plan-view TEM observations of films consisting of 10nm layers of Ni and Ti (about 50 atom planes) which had been vacuum- annealed for five hours at 250°C and 300°C. They observed that an intermetallic compound had formed as a result of the anneal, rather than amorphous material. The present study was initiated to explore the apparent conflict and to examine the kinetics of the SSAR if it occurred.
Transmission Electron Microscopy analysis of ion implantation-induced NiTi amorphization
Authors: Delage J. , Moine P.
Published: June 2020

Amorphization mechanisms are studied through the variation (with the ion fluence Φ) of the amorphous volume fraction C which is estimated from an average surface measurement of the amorphous regions (or crystalline regions) observed in the transmission electron microscopy (TEM) images, following an analysis used and described by Brimhall et al (1). Two ions with different ballistic and chemical characteristics have been used : Ni and N. Low ion currents were used to prevent heat effects. TEM samples were mechanically thinned to 100 μm then electropolished to electron transparency, and observed in a JEOL 200CX TEM, before and after ion implantation. The initial structure of the samples is martensitic (B19 distortion (2)) (fig.l). Before becoming amorphous under ion irradiation, the martensite transforms into austenite (B2 structure) (fig.2). We present for two implantation temperatures (77 and 293K), the results of this investigation in the form of a plot of log [-ln (1-C)] versus log Φ (fig.4).
Formation process of periodic non-conservative antiphase boundary structure in L-Pd5Ce
Authors: Itakura Masaru , Kuwano Noriyuki , Oki Kensuke
Published: June 2020

The low temperature phase of Pd5Ce (L-Pd5Ce) has a one-dimensional long period superstructure (1D-LPS) derived from Ll2. The periodic antiphase boundaries (APBs) are parallel to (110) planes and have a shift vector of 1/2[110]. Hereafter, the indices are referred to the basic lattices of Ll2 As insertion of the APB causes a change in composition, such an APB is called “non-conservative”. Then, a domain size M depends upon the Ce concentration in the alloy. It was found that M increases also with temperature. The temperature dependency of M is attributed to a change of the degree of order within the antiphase domains. In this work, morphology of the non-conservative APBs is observed to clarify the formation process of the 1D-LPS.

The alloy of Pd-16.7 at%Ce was prepared by arc melting in argon atmosphere. Disc specimens made from the alloy ingot were first held at 985 K for 260 ks and quenched in iced water to obtain the state of M=∞ or Ll2, followed by annealing for various lengths of time. The annealing temperature was 873 K where the equilibrium value for M is about 3 in unit of (110) lattice spacing of Ll2. Observation was carried out using microscopes JEM-2000FX, JEM-4000EX (HVEM Lab., Kyushu Univ.) and JEM-2000EX (Dept. of Mater. Sci. Tech., Kyushu Univ.).
Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4
Authors: Yamamoto Naoki , Kikuchi Makoto , Atake Tooru , Hamano Akihiro , Saito Yasutoshi
Published: June 2020

BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.

At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.
HREM observation of stacking faults in Guinier-Preston zones for Al-Ag alloys
Authors: Schwander P. , Dubey Ph.A. , Kostorz G.
Published: June 2020

The decomposition of Al-rich Al-Ag-alloys quenched from the solid solution (α) and aged within the metastable miscibility gap, follows the sequence GP zones → γ' → γ (Ag2Al). Nearly spherical GP zones (Guinier-Preston zones) coherent with the fee matrix are formed by homogeneous nucleation and growth, whereas γ' plate-like precipitates with an hdp structure — lying on {111}-planes of the fee matrix — nucleate heterogeneously at dislocations after a certain incubation time. In the present work HREM was used to investigate the internal structure of the GP zones.

Single crystals of Al-3 at.% Ag grown by strain-annealing were cut along (110) by spark erosion. The samples were homogenized for 2 h at 580°C prior to ageing for 43 h at 160°C. They were electrolytically thinned at −30°C in a methanol-HNO3 (2:1) solution. The TEM work was performed on a Philips CM 30 fitted with a Super Twin Lens and a double tilt holder. To bring the electron beam parallel to the optical axis the coma-free alignment was used. At 300 kV the instrumental point resolution was determined to be 1.9 Å using the Young’s fringes method.
Microstructural analysis of fiber coatings and reaction zones in Ti-14Al-21Nb/SiC composites
Authors: Hall Ernest L. , Ritter Ann M. , Lewis Nathan
Published: June 2020

Titanium and titanium aluminide fibrous composites are currently under consideration for use in aircraft engine and other applications, and their fabrication, microstructure, and properties are under active investigation. These composites can exhibit enhanced strength relative to the unreinforced matrix alloy, but ductilities are often limited, especially at room temperature. This limited ductility may be related to the formation of brittle reaction zones between the fiber and the matrix during fabrication, heat treatment, or use. In this study, the reaction zones formed during fabrication of a Ti-14 wt. pet. Al-21 wt. pet. Nb (Ti- 142l)/SiC composite were studied using analytical electron microscopy (AEM). The composites were fabricated by plasma-spraying Ti-1421 powder onto a drum wound with SCS-6 SiC fiber obtained from Textron Specialty Materials. The tapes were then stacked and consolidated into 4-ply composites by hot isostatic pressing. After fabrication, samples were prepared for AEM analysis by ion milling.
A high-Voltage electron microscopical investigation of interphase precipitation in high-carbon copper-bearing steels
Authors: Fourlaris G. N. , Baker A.J.
Published: June 2020

It is well established that in certain types of low alloy steels the precipitation of alloy carbides occurring on the moving ferrite-austenite interphase boundaries accompanies the growth of proeutectoid ferrite. In other ferrous alloys containing copper or gold but carbon free, the precipitation of discrete particles or particles with fibrous morphology, on the moving ferrite-austenite interphase boundaries has also been observed. In order to describe these phenomena the term interphase precipitation has been used. Although considerable research has been carried out, especially in low carbon copper-bearing steels, interphase precipitation of ε-Cu in high carbon copper steels is not yet fully understood. In this study, high carbon copper-bearing steels were used to assess the interphase precipitation characteristics in the various microconstituents of these steels.
Understanding complex phase chemistry in a Ni-base superalloy: A combined AEM/APFIM approach
Authors: Burke M.G. , Miller M.K.
Published: June 2020

Alloy 718 is a Nb-modified Ni-base superalloy widely-used for gas turbine and related applications which require microstructural stability and good mechanical properties at elevated temperatures (≈ 650°C). In order to achieve the desired properties, the alloy is given a multi-step thermal treatment during which a complex multiphase microstructure is developed. The primary strengthening phases in this alloy are DO22-ordered γ" and Ll2-ordered γ'. A variety of other phases such as Laves, MC-type carbides, and δ (Ni3Nb) have been observed in this material. In this study, the techniques of analytical electron microscopy (AEM) and atom probe field-ion microscopy (APFIM) have been successfully applied to characterize the microstructure of Alloy 718.

The nominal bulk composition of the material examined in this investigation is listed in Table 1 together with the heat treatment schedule. Specimens for AEM characterization were examined in a Philips EM400T analytical electron microscope operated at 120kV and equipped with a Link LZ5/AN10-85S analyzer system.
Computer-Aided TEM- and SEM-based individual orientation techniques for recrystalllzation studies in commercial aluminum alloys
Authors: Weiland Hasso , Liu John
Published: June 2020

Commercial production of aluminum alloy sheet for beer and beverage cans critically depends on the control of plastic anisotropy which affects earing behavior. The final cold rolling texture is responsible for the 45° earing. Plastic anisotropy of the product is minimized by promoting the {001} <100> cube texture during upstream hot rolling and annealing. Hence, the origin of cube texture in light of the nucleation and growth aspects of the recrystallization process has been the subject of research for several decades. Since recrystallization is a local event, electron microscopy has been used in this investigation to shed light on its mechanism. In particular, computer-aided analysis of Kikuchi patterns from the TEM and Backscattered Kikuchi Patterns from the SEM have been used for studying the crystallographic nature of recrystallization nuclei and their orientation relationship to the deformed matrix from which they originate.
Fractal formation in Al/Ge bilayer films after annealing
Authors: Wu Zi-Qin , Zheng Bin
Published: June 2020

The temperature of crystallization of amorphous semiconductor films contacted with metal film is much lower than that of isolated amorphous films. This phenomenon is called metal-enhanced crystallization. In our previous works many fractals were formed after crystallization in bilayer films Pd/Si, Au/Ge and Ag/Ge. Based on TEM observation a mechanism of random successive nucleation was proposed to simulate the fractal formation in Pd/Si films. In this paper the fractal formation in Al/Ge films with different thickness ratios of Al and Ge is reported.

At first Ge and then Al were evaporated onto fresh cloven NaCl in ordinary high vacuum without breaking the vacuum. Thicknesses of Ge and Al were obtained from masses of Ge and Al used according to the formula of point evaporation source as follows:
Use of ultra-microtomy to study phase relationships in industrial alumina particles
Authors: Antonovsky Ari
Published: June 2020

Production of smelting grade alumina relies on the transformation at high temperature (1200°C) of aluminium hydroxide (Al2(OH)3) to alumina (A12O3). In this process, a number of poly-morphic transformations occur which are related to the thermal conditions experienced by particles as they pass through a calcination furnace. TEM is required to study the effect of these transformations on the internal morphology of industrial alumina particles. The information from this can then be related to performance within the smelting operation. Cross-sections of whole particles (up to 70μm diameter) can only be obtained by ultra-microtomy of resin-embedded alumina.

Samples of aluminium hydroxide and alumina were embedded in resin blocks (EPON or L.R. White - Hard Grade). Ultra-thin sections (∽50nM) were cut from the blocks using a MICRO-STAR diamond knife and an LKB IV ultra-microtome. Sections of particles were examined using a TEM to identify the different forms of alumina present, and characterise their relative distribution in a sample.
HREM studies of modulated structures of the monoclinic (B) phase in CaO-Dy2O3 solid solutions
Authors: Kim Y. J. , Kriven W. M.
Published: June 2020

Dysprosia (Dy203) undergoes a monoclinic (B) to cubic (C) transformation on cooling through 1860°C, which is accompanied by an 8% volume increase and shattering. Minor additions of CaO combined with rapid quenching, however, are able to stabilize the high temperature phase at room temperature, which is incommensurately modulated. TEM studies revealed the existence of three different modulations: q1 (001-type; λ ≈ 9.0 Å), q2 (200-type; λ ≈ 7.5 Å), and q3 (λ ≈ 40 Å). HREM studies on modulated specimens have been conducted to search for the origin of these modulated microstructures.

Fig. 1 shows characteristic modulations in the [010]B orientation. Whereas both q1 and q2 look like normal lattice fringes in moderate resolution TEM images, HREM images indicate that they are actually not strictly linear but somewhat displaced. This discontinuity is more obvious in the HREM images displaying separate q1 and q2 modulations such as q1 in the [110] orientation (Fig. 2) and q2 in the [011] orientation (Fig. 3).
The structure of small metal crystallites on cerium dioxide
Authors: Cochrane Heather D. , Hutchison John L. , White Donald
Published: June 2020

Many important catalyst systems involve small metal particles supported on ceramics. The development of such catalysts requires an understanding of the structures of the particles and their relationship with their supports. There have been several studies of the dynamic behaviour of metal particles on apparently inactive supports, an example being the work by Iijima on gold particles supported on silicon.

The high resolution microscopy technique of surface profile imaging has been used to study ceria by itself and various ceria supported metal particles including platinum and gold. Electron Microscopy was carried out using two JEOL 4000EX electron microscopes with 1.67 and 1.6 angstrom resolution respectively. Real and model catalysts were prepared as described elsewhere to produce metal particles up to 4nm in diameter, on well-crystallised ceria.
Evidence for the bimodal distribution of Pt metal crystallites on a zeolite support using XRD and HREM
Authors: Allen F.M. , Levine S.M. , Amand J.R. , Khare G.P.
Published: June 2020

Zeolites are of interest as supports for reforming catalysts because of their high selectivity and because they provide a means of achieving and maintaining high dispersion of noble metals. This translates into high activity and also the maintenance of activity for an extended period of time. One of the goals of catalyst characterization in general is to measure those properties assumed to be responsible for performance in a given reaction. In this study, we have applied powder x-ray diffraction (XRD) and high-resolution electron microscopy (HREM) techniques to determine the size, shape, distribution, and location of Pt metal crystallites on a synthetic zeolite support in an attempt to explain CO chemisorption results.
Electron Microscopy in hydrodesulfurization catalysts
Authors: Cruz-Reyes J. , Avalos-Borja M. , Farias M. H. , Fuentes S.
Published: June 2020

Applications of transition metal sulfides for hydroprocessing catalysts have included a variety of reactions. It is generally believed that an interaction between the active phase (Mo or W) and the promoter (Co or Ni) takes place. Several models have been suggested to explain the enhanced catalytic activity. The catalytic properties of the unsupported sulfides are dependent on the catalyst preparation methods . In this work we study by electron microscopy two sets of unsupported samples ranging from molybdenum sulfide to cobalt sulfide. The specimens were prepared by the following methods, a slight variation of the classical homogeneous sulfide precipitation (HSP) method, and a new method called impregnated thiosalt decomposition (ITD).