bluuebunny/crossref_metadata_2025 huggingface dataset:
Residual damage after annealing of Be and O implanted GaAs/AlGaAs hetero bipolar transistors
Authors: Wurzinger P. , Oppolzer H. , Pongratz P. , Skalicky P.
Published: June 2020

Beryllium (2.5·1014/cm2 at 40 keV and 7.5·1014/cm2 at 90 keV) and oxygen (1013/cm2 at 380 keV) were implanted into a GaAs/AlGaAs-HBT (hetero bipolar transistor) to facilitate the formation of an ohmic contact with the p-type base using planar technology. The layer sequence and doping levels of the HBT are listed in table 1. Annealing was performed using optical RTA (rapid thermal anneal) equipment, at 860 °C, for 3 s. Technological data as well as SIMS, electrical, and photoluminescence measurements are published in detail elsewhere. This paper focuses on the residual lattice damage in the annealed HBT. TEM investigations were performed at 200 keV beam voltage using cross-sectional specimens.

Fig.l shows a dark-field micrograph taken with a {200} reflection. The different layers are numbered (cf. table 1) and can be distinguished by differences in overall contrast. The residual damage consists of Frank type (b=a/3<111>) and perfect(b=a/2<110>) dislocation loops. The perfect loops are prismatic. Most of them lie in the <110> plane perpendicular to the Burgers vector b. All loops are of interstitial type. Defects are only found in the top three layers of the HBT which corresponds to the depth of the Be implantation. The defect distribution is inhomogeneous (Fig.1): While there are rather large loops (up to 200 nm) together with small ones in the GaAs layers of cap and base, only small loops (up to 30 nm) can be observed in the AlGaAs emitter layer.
A study of the interaction of silver with amorphous chalcogenide films in the Scanning Electron Microscope
Authors: Fitzgerald A.G. , Potrous S.M.
Published: June 2020

The diffusion of silver in amorphous chalcogenides is the basis for high-resolution lithographic applications. Previous studies of the diffusion of silver on contact with chalcogenide films has been studied by Auger depth profiling and the effects of photodoping on chemical bonding have been studied by x-ray photoelectron spectroscopy. Electron lithographic effects have been studied in the transmission electron microscope.

The objective of the investigation described here has been to determine the degree of diffusion of silver in the amorphous chalcogenides, As2S3, As2Se3, GeS and GeSe when these films are in contact with thin silver films. The silver distribution has been determined by x-ray microanalysis of film cross-sections in the scanning electron microscope (SEM). Electron beam induced conductivity (EBIC) at points in these films has also been investigated.
Chemical structure of diamond-like carbon thin films
Authors: Cho N.-H. , Krishnan K.M. , Bogy D.B.
Published: June 2020

Diamond-like carbon (DLC) films have attracted much attention due to their useful properties and applications. These properties are quite variable depending on film preparation techniques and conditions, DLC is a metastable state formed from highly non-equilibrium phases during the condensation of ionized particles. The nature of the films is therefore strongly dependent on their particular chemical structures. In this study, electron energy loss spectroscopy (EELS) was used to investigate how the chemical bonding configurations of DLC films vary as a function of sputtering power densities. The electrical resistivity of the films was determined, and related to their chemical structure.

DLC films with a thickness of about 300Å were prepared at 0.1, 1.1, 2.1, and 10.0 watts/cm2, respectively, on NaCl substrates by d.c. magnetron sputtering. EEL spectra were obtained from diamond, graphite, and the films using a JEOL 200 CX electron microscope operating at 200 kV. A Gatan parallel EEL spectrometer and a Kevex data aquisition system were used to analyze the energy distribution of transmitted electrons. The electrical resistivity of the films was measured by the four point probe method.
A TEM study of discommensurations in K2ZnCl4
Authors: Pan Xiaoqing
Published: June 2020

A number of A2BX4-type compounds are known to have an incommensurate (INC) phase between high temperature paraelectric phase (space group Pcmn) and low temperature ferroelectric commensurate (C) phase (space group Pc21n). In the case of Rb2ZnCl4 the static patterns of discommensurations (DCs) and some information about their kinematic behavior have been revealed by transmission electron microscopy (TEM). More recently the DCs in the C-phase of K2ZnCl have been studied by TEM as well as by replica techique Here we report our observation of DCs in K2ZnCl4

Single crystals of K2ZnCl4 were grown from a stoichiometric mixture of aqueous solutions of KCL and ZnCl2 at about 40°C. The crystal plates were cut using a wet thread, and were further thinned
by Ar ion sputtering. Observations were carried out with a JEOL-200CX electron microscopy at an accellarating voltage of 200kV, using a liquid nitrogen cooling holder.
Effects of dopant concentration on the microstructure of tin- doped indium oxide thin films
Authors: Rauf I. A.
Published: June 2020

To understand the electronic conduction mechanism in Sn-doped indium oxide thin films, it is important to study the effect of dopant atoms on the neighbouring indium oxide lattice. Ideally Sn is a substitutional dopant at random indium sites. The difference in valence (Sn4+ replaces In3+) requires that an extra electron is donated to the lattice and thus contributes to the free carrier density. But since Sn is an adjacent member of the same row in the periodic table, the difference in the ionic radius (In3+: 0.218 nm; Sn4+: 0.205 nm) will introduce a strain in the indium oxide lattice. Free carrier electron waves will no longer see a perfect periodic lattice and will be scattered, resulting in the reduction of free carrier mobility, which will lower the electrical conductivity (an undesirable effect in most applications).

One of the main objectives of the present investigation is to understand the effects of the strain (produced by difference in the ionic radius) on the microstructure of the indium oxide lattice when the doping level is increased to give high carrier densities. Sn-doped indium oxide thin films were prepared with four different concentrations: 9, 10, 11 and 12 mol. % of SnO2 in the starting material. All the samples were prepared at an oxygen partial pressure of 0.067 Pa and a substrate temperature of 250°C using an Edwards 306 coating unit with an electron gun attachment for heating the crucible. These deposition conditions have been found to give optimum electrical properties in Sn-doped indium oxide films. A JEOL 2000EX transmission electron microscope was used to investigate the specimen microstructure.
Inexpensive tin oxide films obtained at several substrate temperatures: A High Resolution Electron Microscopy study
Authors: Acosta Dwight R. , Asoraoza René , Maldonado Arturo
Published: June 2020

Obtention of inexpensive thin films for practical uses is currently a challenge for any research group working in this field. Spray pyrolysis, electrodeposition and screen printing are some of the low-cost non vacuum deposition techniques commonly used for the above purposes In this work we present some results on tin oxide fi1ms-SnO2 - grown using the spray pyrolysis method which consists of spraying a finely atomised solution onto a suitable hot substrate. During the thermal decomposition, the chemicals in the spray solution provide the complexes that will undergo a thermallly activated reaction to yield a thin tin oxide film. Deposition was achieved in this work by keeping the substrate at 350°C, 400°C and 450°C respectively. The initial suspension had a composition of Sn Cl4 5H2O, at 0.2 molar concentration in ethyl alcohol. A solution flux of 3.2 ml/min and air flux of 4 lt/min were used in the process. A deposition rate of 20 A/sec was impinging the hot substrate and a 30 nm average thickness was obtained for the films in all the cases. At this point we recall that droplets size variations and temperature changes in the substrate will give rise to different deposition processes: for large and medium droplet sizes not all the solvent vaporise before reaching the hot surface and many defective zones are obtained. For very small droplet size the precipitated particles melt, grow and diffuse with the consequent nucleation and layer growth.
Electron Microscope contrast mechanisms of doped semiconductor layers
Authors: Perovic D.D. , Weatherly G.C.
Published: June 2020

With the development of crystal growth techniques such as molecular beam epitaxy, it is now possible to fabricate modulation-doped superlattices consisting of alternating, ultra-thin layers of n- and/or p-type material abruptly separated by undoped material. At sufficiently high dopant concentrations it has been found that these atomically abrupt layers can be readily imaged in the transmission electron microscope. This study is concerned with the visibility of boron and arsenic-doped layers in silicon from which a generalized interpretation of the TEM contrast of doped layers can be obtained.

Fig.l is a cross-sectional, two-beam dark field image of a B-doped superlattice consisting of five three-layer sets. Each three-layer set was grown using a different substrate temperature in the range 600 to 800 °C; the boron occupies substitutional positions in the Si lattice at the lower temperatures while at the higher temperatures the boron has precipitated in stable clusters (∽3nm) as observed by direct lattice imaging. The maximum concentration of boron in all layers is ≈ 0.7 at.% which is well above the solid solubility limit at these temperatures. There are several important contrast features to note in Fig. 1. First, in the thicker areas of the foil where anomalous absorption effects are dominant, the B-doped layers appear dark relative to the Si matrix; the same is true in bright field.
Differential phase contrast Lorentz microscopy
Authors: McFadyen Ian R.
Published: June 2020

Transmission electron microscopy can provide high spatial resolution information on domain structures in thin magnetic films provided the interaction between the electron beam and the magnetic sample is correctly utilised: As an electron beam passes through a magnetic sample it suffers a phase shift due to the magnetic induction of the sample and the associated stray fields. The derivative of this phase shift is a direct measure of the in-plane magnetic induction integrated along the electron trajectory, Therefore measurement of this phase derivative would provide the integrated in-plane induction directly. The conventional phase contrast techniques of Fresnel and Foucault Lorentz microscopy provide image contrast which has a very non-linear relationship to the above mentioned phase derivative. Differential phase contrast Lorentz microscopy (DPC), on the other hand, does provide direct, high resolution information on the phase derivative of the electron wave as it leaves tile sample. In this technique a focused probe of electrons is scanned cross the sample and a position sensitive detector in the far field measures two orthogonal components of the probe deflection angle at each point in the scan. This corresponds to the derivative of the phase of the electron wave as it leaves the sample, and thus to the integral of the in-plane induction at each point.
The interaction of electron beams with solids - Some new effects
Authors: Humphreys C J , Bullough T J , Devenish R W , Maher D M , Turner P S
Published: June 2020

It has recently been found that electron beams, of energy typically 100 keV, can damage a very wide range of solids, many of which are normally thought to be stable to electron irradiation. For example, metals, semiconductors and ceramics can all be damaged by electrons having energy less than that required for direct displacement damage. Radiation damage effects are particularly apparent when using intense electron beams from field emission guns in STEM's, TEM's and SEM's, but damage also occurs in materials thought to be stable when using electrons from LaB6, or heated W filaments. Considerable care must therefore be taken in microanalysis, etc, particularly when using field emission guns.

If the incident electron beam is focussed to nanometre-scale diameter, then nanometre-scale surface and volume structures (e.g. indentations, holes and lines) can be produced in a variety of specimens. It is also possible to cut a specimen to a desired shape with nanometre precision and to remove surface steps from surfaces, leaving them atomically smooth.
Electron-beam damage and analysis at low temperature
Authors: Bando Yoshio , Kitami Yoshizo , Yokoyama Masato
Published: June 2020

Elemental analysis for beam-sensitive materials is limited by radiation damage due to inelastic scattering of electrons. The amorphization and the mass loss often occure during the observation under a focused electron beam. It has been so far understood that the electron beam damage is effectively reduced by decreasing the specimen temperature. The cryo-electron microscope using liquid helium colled specimen holder is useful to minimize the radiation damage of the beam-sentitive materials. In the present paper, we have studied the radiation damage of various insulating inorganic materials in terms of the rate of the amorphization and the selective mass loss, which are observed at a room temperature (300K) and a low temperature (20K). All measurements are performed on a JEM-4000FX high-resolution analytical electron microscope with full analytical system. The specimen fragments placed on a holey carbon supporting grid are cooled down to about 20K. using a liquid helium specimen holder attached with a Be retainer.
Some examples of ruthenium tetroxide staining technique for TEM of polymers
Authors: Heckmann W.
Published: June 2020

Staining is essential for examination of polymers under the electron microscope. Organic polymers consist exclusively of light atoms, e.g. carbon, oxygen, hydrogen and nitrogen, with the consequence that natural contrast is faint and completely inadequate. The aim of staining is to treat the polymer molecules with chemical substances, which must contain heavy atoms, and thus to modify them so that the electron density is drastically increased on the molecular site. Frequently, a hardening and structure-stabilizing effect is also achieved.

In the last few years, ruthenium tetroxide staining has developed into a very useful method. Ruthenium tetroxide (RuO4) is a very strong oxidizing agent that can react not only with unsaturated, but also with many saturated polymers. For this reason, the method is less selective than others, yet it attracts interest for some polymer systems, because it allows differences in the rate of reaction and reaction intensity between various polymers to be exploited. This will be explained in the light of a few examples.
Correlative STM, FESEM, and TEM studies of fibrillar structures in liquid crystalline polymers
Authors: Musselman I. H. , Russell P.E. , Chen R.T. , Jamieson M.G. , Sawyer L.C.
Published: June 2020

Hierarchical fibrillar structures have been reported to be present in liquid crystalline polymer (LCP) extrudates such as fibers and tapes. Using conventional scanning and transmission electron microscopy (SEM, TEM), the smallest fibrils were shown to be about 50 nm wide and 5 nm thick. With the emergence of higher resolution imaging techniques such as scanning tunneling microscopy (STM) and field emission SEM (FESEM), we have been able to further explore the ultrastructures in the LCP fibrils and extend the LCP structural model.

The LCP materials investigated consist of copolyesters of 4-hydroxybenzoic acid (HBA) and 2- hydroxy-6-napthoic acid (HNA) in the form of melt-spun fibers and extruded tapes. These materials exhibit unidirectionally-oriented structures as revealed by x-ray diffraction and microscopy studies. For STM and FESEM, samples were prepared by a peel-back method which reveals the internal structures of fibrils. In addition, ultrasonication was used to disintegrate the LCP fibers and tapes to provide fine “fibrillar” samples for STM, FESEM, and TEM studies. The original tape and fiber surfaces were also examined by STM and FESEM. Thin Pt coatings (ca. 5 nm) were deposited on the LCP samples using ion beam sputtering to provide a conducting surface for STM and FESEM imaging. These coatings have been shown to introduce minimal topography to the original sample surface.
Impurity-controlled contrast in secondary-electron images of reaction-bonded silicon carbide
Authors: Youngman R.A.
Published: June 2020

Reaction-bonded SiC is formed by the high temperature (>2100°C) heat treatment of a mixture of alpha-SiC powder and organic binders in the presence of elemental Si. The bonding occurs by the in-situ formation of beta-SiC from the reaction of the pyrolyzed binder and the Si. Substantial microstructural characterization of these materials has been carried out in the past. A particular feature of these analyses is the so-called trace-impurity-controlled contrast of secondary electron (SE) images of uncoated specimens. This report describes further attempts to elucidate the origin of this contrast mechanism.

Samples of reaction-bonded SiC (Hexoloy KT, The Carborundum Co.) were prepared for multiple-technique analysis. This was accomplished by preparing an optical thin section for reflected and transmitted optical microscopy. Regions of interest were diamond-scribed on the optical microscope (Leitz, Orthoplan) and then SE and backscattered electron (BE) microscopy (CamScan, Series IV) of the same areas (both coated and uncoated with evaporated carbon) was conducted. Finally, the same areas were imaged in a secondary ion mass spectrometer (SIMS) (Cameca, IMS3F) to detect trace and major impurity levels.
Effect of refractory elements on microstructure and fracture of rapidly solidified nickel base alloys
Authors: Adeva P. , González-Carrasco J.L. , Ibáñez J. , Aballe M.
Published: June 2020

In order to evaluate the effect of refractory elements on the microstructure and properties, and especially on ductility of nickel- base rapidly solidified materials, three rapidly solidified alloys have been obtained by melt spinning under helium atmosphere of 0.04 Pa at linear speed of 47 ms-1 in the form of smooth 20 ∼30 ∼m thick and ∼1 mm wide ribbons. Starting materials were inert gas induction melted alloys with 12 at.% Cr and 20 at.% A1, with additions of 1.5 at.% Nb, 1.5 at.% Ta or 1.9 at.% Mo respectively, balance nickel. Samples were observed by AEM and EPMA in the as-cast condition, and by SEM-EPMA after mechanical testing at temperatures between 300 and 773K. Tensile specimens were suitable ribbon lengths with gauge length 16 mm, and initial strain rate was 10-4s-1. Results were compared with those previously obtained on a similar alloy not containing refractory elements (Ni - 15 at.% Cr - 20 at.% Al).

Longitudinal sections show columnar through thickness grains (Fig.l) and in some cases equiaxed grains in the region close to the gas side. The free surface shows grains and cells with an average area in the prepared section of ∼3 μm2 and 0.8 μm2 approximately, as measured by quantitative metallography.
Microstructure of mechanically alloyed and hot-pressed Al5CuZr2
Authors: Mitchell T. E. , Desch P. B. , Schwarz R. B.
Published: June 2020

Al3Zr has the highest melting temperature (1580°C) among the tri-aluminide intermetal1ics. When prepared by casting, Al3Zr forms in the tetragonal DO23 structure but by rapid quenching or by mechanical alloying (MA) it can also be prepared in the metastable cubic L12 structure. The L12 structure can be stabilized to at least 1300°C by the addition of copper and other elements. We report a TEM study of the microstructure of bulk Al5CuZr2 prepared by hot pressing mechanically alloyed powder.

MA was performed in a Spex 800 mixer using a hardened steel container and balls and adding hexane as a surfactant. Between 1.4 and 2.4 wt.% of the hexane decomposed during MA and was incorporated into the alloy. The mechanically alloyed powders were degassed in vacuum at 900°C. They were compacted in a ram press at 900°C into fully dense samples having Vickers hardness of 1025. TEM specimens were prepared by mechanical grinding followed by ion milling at 120 K. TEM was performed on a Philips CM30 at 300kV.
An Electron Microscope study of structure of high damping capacity Ti - 644 casting titanium alloy during the quenching and aging
Authors: Guozhao Xu , Jianke Sun , Yuli Fan , Guilan Cheng
Published: June 2020

Ti-6A1-4V-4Mo casting titanium alloy is a new high damping capacity α + β martensitic titanium alloy, which suits for the manufacture of rotating blades particularly of large sizes or for highspeed operations. It was found that a remarkable improvement in damping capacity is made possible by rapidly cooling the alloy from a proper temperature in the α + β phase temperature range after heating a predetermined time. Especially the alloy will have the highest damping capacity when heating in the 850-900°C temperature range.

Fig. 1 Shows the relation between the damping capacity of the alloy and solution treatment temperatures. It also was found that damping capacity of the alloy decreases when the specimens were reheated at, 150-300 ° C temperature range for a certain time after solution treatment, the results show in Fig. 2.
Dislocation structures in titanium aluminides deformed at 815°C
Authors: Donlon W.T. , Dowling W.E. , Allison J.E.
Published: June 2020

Ordered (L10) intermetallic γ-TiAl alloys are candidates for high temperature structural applications in the automobile industry because of their low density and high strength at elevated temperature. The major drawback of these materials is their low ductility at ambient temperature. Improvements in low temperature ductility may be achieved without sacrificing the desired high temperature performance by optimizing the microstructure through thermomechanical processing. This investigation measured the tensile and fatigue properties of an “as-cast” and cast plus heat treated Ti-48A1-1V-0.2C (at%) alloy at 25 and 815°C.

The microstructure of both samples consisted of primary γ grains with an average intercept size of 100 μm, and regions of a γ matrix with α2 lathes. The vol% of the primary γgrains was 40% and 85% in the “as-cast” and cast plus heat treated samples, respectively. Figure 1 shows the microstructure of the “as-cast” material.
Intensity distribution of electron diffraction pattern from Ti-14Wt%Mo alloy containing ωphase plate crystal
Authors: Awaji Mitsuhiro , Hashimoto Hatsujiro , Sukedai Eiichi , Akao Fumio
Published: June 2020

The study of ω-phase in various alloys such as Ti-Mo, Ti-Cr, Zr-Nb etc. have been carried out so far by electron diffraction and electron microscopy. However, the shape of ω-phase particles has not been fully clarified yet. This is due to the facts that ω-phase is formed in ω-phase crystal, and rather difficult to obtain isolated crystal particles and also that w-phase is produced only by the displacement of atoms in characteristic directions which makes no contrast in the electron microscope images projected along this directions and hence the crosssectional shape can not be studied. Since the intensity of electron diffraction patterns is very sensitive to the amount of ω-phase existing in β-phase, its thickness dependence has been studied in the present paper by using multi-slice dynamical theory of electron diffraction for the various thickness combination of the ω- and β-phases so that the thickness and location of ω-phase can be seen.
Intergranular phase in Nd-Fe-B permanent magnets
Authors: Chu Tsung-Yao , Rabenburg L. K.
Published: June 2020

Even though the significance of the intergranular phase in the Nd-Fe-B magnets in terms of sintering aid and domain wall pinping has now been recognized, its exact nature has not yet been conclusively determined. This is so because the Nd-rich intergranular phase has been reported to stabilize in a variety of structures instead of the equilibrium hexagonal α-Nd structure as the ternary phase diagram suggests. This study is directed toward obtaining detailed crystal structure of the intergranular phase by means of transmission electron microscopy.

Magnet ribbons with a starting composition of Nd13.5Fe80B6.5 were prepared by melt-spinning; the ribbons were subsequently hot pressed into fully dense magnets. Electron transparent samples, prepared from the hot-pressed magnets by mechanical grinding and ion beam milling, were examined in a JEOL 1200EX scanning transmission electron microscope.
Microstructural characterization of CaO-doped AlN substrate material
Authors: Bischoff E. , Ruckmich S. , Kranzmann A. E.
Published: June 2020

AIN ceramics are candidates for substrate materials in electronic circuits. In spite they are insulators they exhibit a very high thermal conductivity. Impurities and the unavoidable sintering additives usually degrade the thermal conductivity. With a special heat treatment it was possible to improve the thermal properties. Microstructural characterization with analytical transmission electron microscopy (TEM) on sintered and purified AIN samples was conducted to understand the reason for this behavior.

AIN powder contaminated with 1 wt% oxygen and doped with 1.4 wt% CaO was pressureless sintered in a N-atmosphere to more than 98.1 % relative density. Additional annealing at 2100 K yielded a translucent product with a high thermal conductivity. With annealing for less than 24 h in a reducing or non reducing atmosphere thermal conductivity increased slowly from 41 Wm-1K-1 to 75 Wm-1K-1. This could be attributed to microstructural changes like grain growth and change in fractal dimension via SEM. A drastic increase was achieved after 44 h in a reducing atmosphere, where a thermal conductivity of 219 Wm-1K-1 was reached, approaching that of pure aluminum. Thin specimen for TEM were prepared in the usual manner from a 23.5 and 44 h annealed sample and examined in a Jeol 2000 FX. Analytical work was done with a Tracor Northern energy dispersive x-ray system (EDS) and a Gatan serial electron energy loss spectrometer (EELS).
Observing the relaxation of molecular orientation in sheared liquid crystalline polymer solutions
Authors: Putnam Wendy , Viney Christopher
Published: June 2020

Liquid crystalline polymers (solutions or melts) can be spun into fibers and films that have a higher axial strength and stiffness than conventionally processed polymers. These superior properties are due to the spontaneous molecular extension and alignment that is characteristic of liquid crystalline phases. Much of the effort in processing conventional polymers goes into extending and aligning the chains, while, in liquid crystalline polymer processing, the primary microstructural rearrangement involves converting local molecular alignment into global molecular alignment. Unfortunately, the global alignment introduced by processing relaxes quickly upon cessation of shear, and the molecular orientation develops a periodic misalignment relative to the shear direction. The axial strength and stiffness are reduced by this relaxation.

Clearly there is a need to solidify the liquid crystalline state (i.e. remove heat or solvent) before significant relaxation occurs. Several researchers have observed this relaxation, mainly in solutions of hydroxypropyl cellulose (HPC) because they are lyotropic under ambient conditions.
Study of silver-bearing filler metal diffusion in copper metal base by SEM and EDXA, in the brazing
Authors: Traveria A. , Tura J.M. , Camps X. , de Castellar M.D. , Saulό J.
Published: June 2020

The brazing is a joint process between two or more metallic parts, by using a nonferrous filler metal, having a melting point below that of the Base Metal. The filler metal is distributed between the closely fitted surface of the joint by wettability and capillarity attraction.

In the present work the filler metal (FM) was DIN 8513: L-Ag30Cd and the base metal (BM) was electrolytic Cu (Figure 1). In the rod of the filler metal the following phases were identified: αZn(Cu), ordered β’(CuZn) and brittle β(Cu2Cd). The larger part of the matrix was composed by βCd(Ag). In this research two brazed structures were studied, obtained in the same experimental conditions, with the single exception of the post-brazing cooling cycle. Probe I suffered a slow solidification process at room temperature. Probe II was rapidly cooled by immersion in cold water.

Probe I. In order to estimate the thickness of the diffusion zone in the braze-metal interfaces the specimen was arranged with its joint clearance not completely refilled ( Fig.2). As it may be observed one clear gap between the affected zone and the unaltered base metal appears.
Contribution of Atomic-Level TEM to Resolution of Structure
Authors: Hashimoto Hatsujiro
Published: June 2020

Atomic Resolution Electron Microscopes are now producing useful results in many fields of science and technology. This success was obtained not only by the improvement of resolution of TEM but also through the developments of theories and experiments of diffraction crystallography, image formation and recording technique over the past 44 years. Boersch (1946-47) discussed the image of atoms and crystals by the phase object approximation; the image contrast is due to the phase shift of electron waves passing through them. Scherzer (1949) discussed the effect of the phase shift by the electron lens and proposed the phase contrast transfer function. He pointed out that the key to observe images of single atoms is by contrast enhancement, which might be possible by dark field images if resolution is improved. This proposal was attempted by improving the resolution using tilted-beam dark fields (Th atoms, Hg & Pt atoms 1971). Crystal lattice fringes were observed by Menter in 1956 who discussed the contrast by kinematical theory. The interpretation of lattice images by dynamical theories were carried out by Hashimoto et al. (Bethe theory) and Cowley (Multi-slice theory) in 1958-60 and noted the correct position of atoms is in neither black fringe regions nor white ones when the images are taken in the Bragg reflecting position. However Miyake et al in 1964, showed that black or white contrast peaks appear at atom positions if the crystal is in symmetry position. Two dimensional lattice structure images were first photographed in 1970-71, which stimulated strongly the application of electron microscopy to materials science, crystallography and engineering at many laboratories such as the National Center at Berkeley. For the identification of correct position of atoms, two types of image contrast calculation have been proposed (e.g. multi-slice 1972, Bethe method 1975). The partially coherent theory originally developed in optics was introduced into the contrast calculation in 1979-80. Around this time, many observations of defect structures have been carried out, some of which are shown in Table 1. In situ observation of moving atoms and atom columns in molecules and crystals have been carried out in 1978 by using a TV system, which enable us to see the transition phenomena with a speed of 1/30 or 1/60 seconds. More recently atomic imaging at 1.8 A-1.6 A played an important role in the structure research of new materials and phenomena such as superconducting materials (metallic A15, 1989, ceramic high Tc, 1988), metal ceramic interface (Nb/Al2O3 1984), superstructure (GaAs/AlAs/GaAs 1985) quasi crystals (1987) etc. Many subsequent observations are presented in this congress. In spite of these developments, there are still some problems to be solved, e.g. imaging of atoms in the correct positions and the identification of different kinds of atoms in the materials especially with unknown crystal structure.
The Structure of Thin Gold Films at the Early Stage of Continuous Film Growth
Authors: Krakow William
Published: June 2020

The use of a transmission electron microscope to observe surface structure of thin films has been demonstrated in recent years by diffraction contrast imaging to ∼ 10Å resolution using the forbidden reflections of [111] Au and at atomic resolution using bright-field phase contrast on both [001] and [111] oriented Au films. It has also been possible to demonstrate that beyond a minimum thickness, these films can be free standing and viewed in the microscope without significant modification due to the incident electron beam generating sputtering events at high beam currents. It is therefore now possible to obtain free standing [001] Au films which exhibit various types of surface topography. These films were obtained by varying the growth parameters with a microprocessor controller attached to a UHV deposition system. The deposition of Au was precisely controlled onto a thick Ag substrate which was initially deposited upon NaCl single crystals.

Fig. 1 shows a low magnification image ∼ 40Å thick [001] Au film grown at a vacuum level of 5 × 10-9 Torr, 50° substrate temperature and a deposition rate of ∼ 1/20 ML/sec. Clearly defined atomic step regions are visible as demonstrated by the terrace-like contrast variations over extended regions i.e. a step-ledge growth regime. Regions between these terrace areas represent coalescence of individual grains which were not attached at an earlier stage of growth. These regions exhibit finer scale terraces and ledges which follow either <100> or <110> directions as evidenced by comparing their directions to stacking faults and twins occasionally observed in the field of view. Small holes are also present which have crystallographic edge facets and anomalous contrast bands also occur which represent the lack of tracking of the upper surface layer growth to steps which exist at the lower surface. Fig. 1 was obtained by diffraction contrast from the direct beam alone. It was not necessary to use the forbidden reflections here since they produced too drastic a contrast change.
Interpretation of the Contrast of High-Resolution Electron Microscopy Images of Ni4Mo by Means of Simulated Image Maps
Authors: Thust A. , Urban K.
Published: June 2020

The alloy of composition Ni4Mo develops, at temperatures below 860 °C, an ordered Dla-structure which is based on the fcc-lattice. This alloy has been widely investigated with respect to its physical properties and its ordering behaviour. High resolution studies are rare and concentrated mainly on its short-range order structure. The aim of the present work was to develop a detailed understanding of image contrast and to apply the results to antiphase-boundary studies in ordered Ni4Mo by means of a JEOL 4000 EX electron microscope.

In high-resolution electron microscopy, depending on defocus and foil thickness, a large variety of different images is obtained. Only a few of these allow a direct interpretation concerning the location and the type of the atoms. By computing a through-focus/through-thickness map (TFTT map) before starting experimental work it is possible to determine the proper conditions at which images can be obtained which are closely related to the projected potential.
Algorithms for Composition Determination from HREM Images of Substitutional Alloys
Authors: de Jong A.F. , Van Dyck D.
Published: June 2020

In a substitutional alloy the positions of the lattice sites are fixed, but they may be randomly occupied by two or more different atom types. An example is the semiconductor Alx Ga1-x As, which has the group III sites arranged in columns at a (projected) distance of 0.28 nm when imaged in the [100] direction. The determination of compositions at atomic resolution would enable the study of roughness and interdiffusion at epitaxial interfaces such as GaAs/Alx Ga1-x . With high-resolution electron microscopy (HREM) it is possible to image the different columns, but it is difficult to image differences in composition. One method has been proposed so far to measure compositions from HREM images. We derive a linear relationship between deviations in composition and image contrast, and propose and test two new image processing algorithms to measure compositions in atomic columns.

Consider a substitutional alloy with one atomic position occupied by either type A or type B atoms, and assume that the z -dependence of the potential can be disregarded. For the average composition an average potential V0 (dependence on (x,y ) implicit) results in an average electron wavefunction ϕo (z ) at the exit plane of the sample. Locally (e.g. in one atomic column) the composition may deviate from the average by y , causing a small deviation from the average potential of y(VA – VB ). VA and VB are the potentials when the crystal would contain only type A or type B atoms, respectively. The wavefunction can be calculated using perturbation theory, yielding formally to first order:
HREM Studies of Some Phases in the ZrO2-Nb2O5 System
Authors: Sundberg Margareta , Marinder Bengt-Olov
Published: June 2020

High resolution electron microscopy and x ray powder diffraction techniques were used to study samples of various compositions in the Nb2O5-rich part of the ZrO2-Nb2O5 system at 1500°C. A large number of fragments were also characterized by electron diffraction in combination with EDS analysis. Some HREM results concerning block structures formed in the above region have previously been reported.

The x ray powder pattern of a ZrO2.9Nb2O5 sample indicated a phase isotypic with T-Nb2O5. The micrograph in Fig. 1, of a thin crystal fragment from that sample, illustrates a phase related to the UVO5 (m=2) structure type. The electron diffraction patterns showed an ordered commensurate phase (m=8) with unit cell dimensions similar to those reported for T-Nb2O5 and Ta30W2O81. The structure models of these two compounds are rather similar and differ mainly in the oxygen content.
Structure Determination at Atomic Resolution by Electron Crystallography
Authors: Zou Xiaodong , Hovmöller Sven
Published: June 2020

Structure determination by electron microscopy is emerging as a serious competitor to the classical methods of X-ray diffraction. The main advantage of EM is that the phase information is restored in the image, whereas with X-ray diffraction it is lost.

The structure determination of an inorganic crystal by electron microscopy would be trivial if the micrograph was just a magnified image of the electron density in the crystal. Unfortunately it is not. A limited number of non-linear effects distort the image. These effects can be divided into two parts; those arising already in the crystal and those that are due to optical distortions. For a crystal one unit cell thick the wave front at the exit surface of the crystal is a linear function of the electron density within the unit cell. As the crystals become thicker more and more of the diffracted electrons will have been doubly diffracted, making the image no longer a linear function of the electron density. For crystals thinner than half the mean free path for electrons most of the scattered electrons are still scattered only once, making the image interpretable.
A Simple Real-Space Channelling Theory for Electron Diffraction and HREM
Authors: Van Dyck D.
Published: June 2020

The computation of the many beam dynamical electron diffraction amplitudes or high resolution images can only be done numerically by using rather sophisticated computer programs so that the physical insight in the diffraction progress is often lost. Furthermore, it is not likely that in this way the inverse problem can be solved exactly, i.e. to reconstruct the structure of the object from the knowledge of the wavefunction at its exit face, as is needed for a direct method [1]. For this purpose, analytical expressions for the electron wavefunction in real or reciprocal space are much more useful. However, the analytical expressions available at present are relatively poor approximations of the dynamical scattering which are only valid either for thin objects ((weak) phase object approximation, thick phase object approximation, kinematical theory) or when the number of beams is very limited (2 or 3). Both requirements are usually invalid for HREM of crystals. There is a need for an analytical expression of the dynamical electron wavefunction which applies for many beam diffraction in thicker crystals. It is well known that, when a crystal is viewed along a zone axis, i.e. parallel to the atom columns, the high resolution images often show a one-to-one correspondence with the configuration of columns provided the distance between the columns is large enough and the resolution of the instrument is sufficient. This is for instance the case in ordered alloys with a column structure [2,3]. From this, it can be suggested that, for a crystal viewed along a zone axis with sufficient separation between the columns, the wave function at the exit face does mainly depend on the projected structure, i.e. on the type of atom columns. Hence, the classical picture of electrons traversing the crystal as plane-like waves in the directions of the Bragg beams which historically stems from the X-ray diffraction picture, is in fact misleading.
Characterization of Modulated Structure Through Structure Images and their Computer Simulation
Authors: Nakai Kiyomichi , Isobe Yusuke , Kinoshita Chiken , Shinohara Kazutoshi
Published: June 2020

Induced spinodal decomposition under electron irradiation in a Ni-Au alloy has been investigated with respect to its basic mechanism and confirmed to be caused by the relaxation of coherent strain associated with modulated structure. Modulation of white-dots on structure images of modulated structure due to high-resolution electron microscopy is reduced with irradiation. In this paper the atom arrangement of the modulated structure is confirmed with computer simulation on the structure images, and the relaxation of the coherent strain is concluded to be due to the reduction of phase-modulation.

Structure images of three-dimensional modulated structure along <100> were taken with the JEM-4000EX high-resolution electron microscope at the HVEM Laboratory, Kyushu University. The transmitted beam and four 200 reflections with their satellites from the modulated structure in an fee Ni-30.0at%Au alloy under illumination of 400keV electrons were used for the structure images under a condition of the spherical aberration constant of the objective lens, Cs = 1mm, the divergence of the beam, α = 3 × 10-4 rad, underfocus, Δf ≃ -50nm and specimen thickness, t ≃ 15nm. The CIHRTEM code was used for the simulation of the structure image.
Electron Microscopy/Diffraction Study of the Ternary Mn-Er-S System
Authors: Landa Canovas A. R. , Otero Diaz L.C. , White T. , Hyde B.G.
Published: June 2020

X-Ray diffraction revealed two intermediate phases in the system MnS+Er2S3,:MnEr2S4= MnS.Er2S3, and MnEr4S7= MnS.2Er2S3. Their structures may be described as NaCl type, chemically twinned at the unit cell level, and isostructural with CaTi2O4, and Y5S7 respectively; i.e. {l13} NaCl twin band widths are (4,4) and (4,3).

The present study was to search for structurally-related (twinned B.) structures and or possible disorder, using the more sensitive and appropiate technigue of electron microscopy/diffraction.

A sample with nominal composition MnEr2S4 was made by heating Mn3O4 and Er2O3 in a graphite crucible and a 5% H2S in Ar gas flow at 1500°C for 4 hours. A small amount of this material was thenannealed, in an alumina crucible, contained in sealed evacuated silica tube, for 24 days at 1100°C. Both samples were studied by X-ray powder diffraction, and in JEOL 2000 FX and 4000 EX microscopes.
Staphylococcus aureus α-Toxin Crystals on Lipid Layers: Effects of Trypsin Treatment
Authors: Olofsson Anders , Hebert Hans , Kavéus Urban , Thelestam Monica
Published: June 2020

α-toxin is a lethal, dermonecrotic, cytotoxic, and hemolytic protein which is secreted by most strains of Staphylococcus aureus . The biological effects are brought about by pertubation of membrane structures making them permeable to ions and small molecules. The structural basis for the mode of action is not known in detail. One hypothesis is that an oligomeric form of the toxin, observed both biochemically and by electron microscopy, circumscribe a hydrophilic pore through which transport can occur. Recent functional studies have demonstrated that oligomerization is a necessary but not a sufficient criterion for permeabilization. For example, trypsin treated α-toxin was, despite its lack of membrane damaging activity, able to form 200 kDa aggregates on mouse adrenocortical (Yl) tumor cells. In this work we have compared the structure of trypsin treated α-toxin with that of the intact toxin.

α-toxin was purified from S. aureus strain wood 46 by isoelectric focussing and gel filtration. Tryptic toxin fragments (18 and 17 kD as determined by SDS-PAGE) were generated by digestion of native α-toxin (1 mg in 1.5 ml Tris buffered saline) with 30μg trypsin for 4 h at 37°C, pH 8.0. The reaction was terminated by the addition of 30μg lima beam trypsin inhibitor. Toxin specimens were applied to lipid layers pre-formed on carbon support films. Electron microscopy was performed after negative staining either with 1% Na-PTA (pH 7.0) or with a mixture of Na-PTA and glucose. Subsequent image processing of large coherent crystalline arrays produced correlation averaged projection maps. A three-dimensional model was obtained by collecting and combining data from tilted views.
Performance of A Laser-Pulsed Thermal Electron Gun
Authors: Bostanjoglo O. , Heinricht F. , Wünsch F.
Published: June 2020

High-speed electron microscopy strongly demands a high-brightness electron gun in order to increase the number of image forming electrons. A few years ago, a laser-pulsed high-brightness electron gun was introduced. Fig.1 shows the experimental set-up, A standard triode system was supplemented with a Nd:YAG laser, focussing optics and a modified anode, which incorporates the laser deflection mirror. The frequency doubled laser pulse (τ =5 ns, λ = 532 nm) is focused through a window onto the tip of the tungsten hairpin emitter. The laser treated area (≈ 100 μm diameter) is heated well above the melting point, which results in a strong thermal electron emission. Due to rapid heat-up and fast cool-down of the tungsten surface short electron pulses with a duration of 20 ns and a maximum current of 20 mA at 80 kV are emitted. A destruction of the tungsten wire is avoided, too. Laser energies used for the generation of electron pulses are in the range of 100 μJ. Due to these minor modification, the DC operation of the electron gun is not disabled, which allows a convenient adjustment in the DC mode and then switching into the pulsed operation mode. Fig.2 shows a typical electron pulse emitted by the gun. Shorter electron pulses up to 5 ns can be generated by a beam blanking unit.