bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural evolution of an iron silicate catalyst with thermal and hydrothermal treatments
Authors: Csencsits Roseann
Published: June 2020

Iron silicate analogs of the zeolite ZSM-5 may be directly synthesized from iron silicate gels in a manner which differs slightly from the alumino-silicate ZSM-5. The resultant white, crystalline iron silicate is referred to as FeZSM-5 in the as-synthesized form. Thermal treatment removes the organic crystal-directing agent and moves some of the framework iron into non-framework sites producing the calcined form of the molecular sieve FeZSM-5. Subsequent hydrothermal treatment moves more of the iron out of the molecular sieve framework. This iron-rich second phase and the ZSM-5 pore structure can be used to convert synthesis gas (CO and H2) to “gasoline range” hydrocarbons and water (Fischer-Tropsch synthesis). To optimize the Fischer-Tropsch catalyst, homogeneity in the particle size distribution and in the distribution of catalytic iron throughout the particles is desired.

Scanning electron microscopy (SEM) was used to characterize the overall molecular sieve particle sizes and morphologies as a function of preparation conditions.
X-ray emission spectroscopy study of iron silicate catalyst FeZSM-5
Authors: Csencsits R. , Lyman C.E. , Gronsky R.
Published: June 2020

Iron silicate analogs of the zeolite ZSM-5 may be directly synthesized from iron silicate gels in a manner which differs slightly from the alumino-silicate ZSM-5. The resultant white, crystalline iron silicate is referred to as FeZSM-5 in the as-synthesized form. Thermal treatment removes the organic crystaldirecting agent and moves some of the framework iron into non-framework sites producing the calcined form of the molecular sieve FeZSM-5. Homogeneity in the distribution of catalytic iron throughout the particles is desired in an optimal catalyst. Distribution of the iron throughout the framework in the assynthesized forms would affect the final distribution of catalytic iron in the calcined and steamed forms; thus, the iron distribution throughout the as-synthesized and calcined forms of FeZSM-5 were studied using the high spatial resolution of the analytical electron microscope.

X-ray emission spectroscopy (XES) performed in the transmission electron microscope (TEM) and the scanning transmission electron microscope (STEM) was used to determine the inter- and intra-particle composition variations for FeZSM-5.
Interfacial phenomena in the fracture resistance of interfaces
Authors: Evans A. G.
Published: June 2020

In composite systems, the mechanical response of interfaces to the approach of cracks that initially form either in the matrix or in the fiber dominates the mechanical performance. In particular, in brittle matrix composites, the interface must have a sufficiently low fracture resistance compared with that of both the fiber and matrix that the crack diverts into the interface and debonds the fiber, Thereafter, the debonded fiber must be able to slide against the matrix with a low friction stress in order to inhibit fiber failure and thus enhance pull-out. These processes are schematically illustrated in Fig. 1. Mechanics investigations have established requirements concerning debonding and sliding that must be satisfied in order to achieve good composite properties. At the simplest level, these studies reveal that the fracture energy of the interface should be less than about one-third that of either the fiber or the matrix.
What may theoreticians and electron microscopists learn from each other about phase transformations?
Authors: Russell K.C.
Published: June 2020

Plenty! Unfortunately theoreticians and experimentalists generally live in separate worlds, if not universes, and are oftentimes happier that way. Dealing with the other party requires work, both to master unfamiliar concepts and to develop one's research in the direction and to the point that the other can understand and deal with it. More usually the theorists make predictions on what pleases them while the experimentalists measure the quantities which please them. The overlap between the two sets is often minimal, and sometimes nil.

Real cooperation and learning occurs when each develops his research product to the point that it is useful to the other, and in addition can explain his needs to the other.

Unfortunately, sometimes in spite of the best of efforts common ground cannot be found. I refer in particular to early attempts in solid state phase transformation studies to relate nucleation theory and experiment. The theorist typically views the progress of a phase transformation as starting with an incubation period after which steady state nucleation conditions are established and the particle number density increases linearly with time. Then nucleation ceases and the particles grow at constant number density. Finally coarsening occurs and the number density decreases with time while the remaining particles get bigger.
The Center for Microanalysis of Materials
Authors: Eades J.A.
Published: June 2020

The main purpose of the Center for Microanalysis of Materials is to serve the 250 or so people, from the materials-science research community on the Urbana campus of the University of Illinois, who use its facilities each year. (This represents about 80% of all researchers in this field on campus.) However, there is also a continuing interest in working with scientists from other institutions via collaborative research programs.

The Center houses a large number of state-of-the-art instruments in almost all aspects of microanalysis: electron microscopy, x-ray diffraction, backscattering spectroscopies and several techniques in surface microanalysis. This equipment is operated and maintained by a team of full-time professional staff. Staff members also train users and collaborate in their research.

The virtue of having microanalytical resources organized this way is that each research group can call on a very broad range of techniques. It can use Auger spectroscopy this week, EXAFS next and a combination of SIMS and TEM the week after that. This possibility is not available in universities where each instrument is acquired and run by one particular group.
Enhancement of structure of interstellar diamond microcrystals by image processing
Authors: O'Keefe Michael A. , Blake David , Freund Friedemann , Hetherington Crispin , Turner John
Published: June 2020

Since the discovery of 0.5-7.5 nm diamond crystals in oxidized acid residues of carbonaceous chondrites much speculation has centered on the mechanism of their origin. Indeed; there is even some difference of opinion regarding the presence of “amorphous low-atomic number phases” intimately associated with the diamond crystallites. While the diamond-containing residue from the meteorites comprises only 50-200 ppm of the total meteorite mass, theories regarding the genesis of the diamonds have far-reaching consequences since noble gas isotopic data indicate that they predate the solar system and are from an interstellar source. Lewis et al. propose that the diamonds formed under low pressure conditions by processes similar to those used in recent low-pressure CVD laboratory syntheses. Blake et al. propose a second mechanism of formation, within the stability field of diamond, due to particle-particle collisions behind supernova shock waves. At the present time, no data exist which unequivocally support one model over the other.
Geometry and formation of twins in YBa2Cu3O7-x
Authors: Sarikaya Mehmet , Kikuchi Ryoichi , Aksay I. A.
Published: June 2020

Geometry and formation of twins in the orthorhombic YBa2Cu3O7-x phase are studied by transmission electron microscopy and modeling. Samples with bulk superconductivity at 90K are produced by heating the stoichiometric 1:2:3 proportions of metal oxides with a single heat treatment schedule involving a heating rate of 5°C/min to 950°C (1 hr) and 1°C/min cooling to room temperature. Powder mixtures were formed by colloidal mixing of oxide powders or by molecular mixing techniques.

Twinned domains with {110} twin boundaries, parallel to [001] of the orthorhombic lattice, usually form with both variants occurring in a single grain (Fig. 1). The twin boundary separation λ (Fig. 2) is dictated by energetic and geometrical requirements which are both related to Δa = b — a, where b and a are lattice parameters of the orthorhombic phase. Geometrical requirements lead to the estimate that the stable values of λ are integer values of the basic distance d.
An in situ and ex situ TEM study of the formation of thin cobalt silicide films by molecular beam epitaxy on the silicon (100) surface
Authors: Loretto D. , Gibson J. M. , Yalisove S. M. , Tung R. T.
Published: June 2020

The cobalt disilicide/silicon system has potential applications as a metal-base and as a permeable-base transistor. Although thin, low defect density, films of CoSi2 on Si(111) have been successfully grown, there are reasons to believe that Si(100)/CoSi2 may be better suited to the transmission of electrons at the silicon/silicide interface than Si(111)/CoSi2. A TEM study of the formation of CoSi2 on Si(100) is therefore being conducted. We have previously reported TEM observations on Si(111)/CoSi2 grown both in situ, in an ultra high vacuum (UHV) TEM and ex situ, in a conventional Molecular Beam Epitaxy system.

The procedures used for the MBE growth have been described elsewhere. In situ experiments were performed in a JEOL 200CX electron microscope, extensively modified to give a vacuum of better than 10-9 T in the specimen region and the capacity to do in situ sample heating and deposition. Cobalt was deposited onto clean Si(100) samples by thermal evaporation from cobalt-coated Ta filaments.
Angular correlation between grains of metastable TiSi2
Authors: Pico C.A. , Lagally M.G.
Published: June 2020

TiSi2 is the primary silicide candidate as interconnect material in very largy scale integrated (VLSI) devices because of its low resistivity (15μΩ-cm) and relatively low processing temperature. While formation of TiSi2 from Ti-on-Si reaction couples can be accomplished easily and quickly at anneal temperatures above 550°C, below ∽650°C TiSi2 forms in the metastable C49 (base-centered orthorhombic; a=3.62Å, b=13.76Å, and c=3.605Å) 12-atom-per-unit-cell crystal structure with a characteristic resistivity of 65μΩ-cm. To achieve the low-resistivity C54 (face-centered orthorhombic; a=8.24Å, b=4.78Å, and c=8.54Å) phase, anneals above ∼650°C are required. It has been suggested that the decrease in resistivity of TiSi2 from the C49 phase to the C54 phase is a result of the reduced number of microstructural defects (defect separation changes from ∼30Å to 5μm) associated with the change of crystal structure. An understanding of the arrangement of the microstructural defects in C49 is needed to correlated the electrical properties of C49 and C54 correctly.
Microtwin morphology and density for silicon on sapphire
Authors: Twigg M. E. , Richmond E. D.
Published: June 2020

In order to understand the influence of various growth and processing procedures on the quality of silicon grown on sapphire (SOS), one needs a way to measure microtwin density as a function of distance from the interface. In previous studies, however, the technique best suited for determining such a density profile, transmission electron microscopy (TEM), has been applied to this problem in a relatively qualitative manner. We have chosen to apply TEM in a more quantitative fashion to this problem by keying our observations to microtwin morphology as determined by trace analysis and stereomicroscopy (Fig.1). These observations indicate that the microtwins occuring in SOS grown by chemical vapor depostition (CVD) are faceted and grow contiguously from the interface. The volume fraction of silicon occuring as microtwins does not decrease away from the interface at as large a rate as indicated by previous TEM studies (Fig.2). Instead, the decrease in the number of twins away from the interface appears to be balanced by an increase in twin size.
Computer systems in microscopy: The big, the small and the ugly
Authors: Rez Peter
Published: June 2020

The transmission electron microscope has now reached a stage of maturity such that the differences between different models are in the details rather than the fundamental design. Although the early computer systems in microscopy appeared only as adjuncts to X-ray multichannel analyzers newer, more powerful systems have become available at relatively low cost and there is an increasing demand for image acquisition, processing and analysis. There is still no agreement as to what is the right design for a microscope computer system. The answer depends not only on the planned applications but also on the organization of the microscopy lab.

For spectroscopy there is a need to acquire spectra both by multichannel scaling (EELS) and multichannel analysis (EDX) and process the results for quantitative analysis. In imaging the requirement can be for either capture of TV camera images or direct scanning of a focussed probe across the specimen with digitization of an appropriate signal (bright field, secondary electron).
The ultrastructure of a dental composite resin
Authors: Laffoon J.E. , Jensen M.E.
Published: June 2020

Methacrylate has been used as a resin with exceptional cutting quality for electron microscopy, but suffers from problems of stability in the electron beam. On the other hand, one of the areas it is used is as a synthetic resin where it is increasingly becoming a factor in the restoration of missing tooth structure in dentistry. All the resins used in dental procedures are produced by “addition polymerization”, that is once the polymer is produced it consists of a sequence of identical monomers. The resin is then “filled” with particulate matter to increase it's strength and stability, such as silica. Of the many available resin systems used presently in dentistry, three were chosen for this study. One is a Type II composite, and the other two are classified as microfilled. The aim of this study is to compare some methacrylate based composite at the ultrastructural level and in items of microstructure and topography, and to determine the elemental composition.
SEM analysis of DC magnetron sputtered beryllium films
Authors: Lindsey E. F. , Price C. W. , Pierce E. L. , Hsieh E. J.
Published: June 2020

Columnar structures produced by DC magnetron sputtering can be altered by using RF biased sputtering or by exposing the film to nitrogen pulses during sputtering, and these techniques are being evaluated to refine the grain structure in sputtered beryllium films deposited on fused silica substrates. Beryllium is brittle, and fractures in sputtered beryllium films tend to be intergranular; therefore, a convenient technique to analyze grain structure in these films is to fracture the coated specimens and examine them in an SEM. However, fine structure in sputtered deposits is difficult to image in an SEM, and both the low density and the low secondary electron emission coefficient of beryllium seriously compound this problem. Secondary electron emission can be improved by coating beryllium with Au or Au-Pd, and coating also was required to overcome severe charging of the fused silica substrate even at low voltage. The coating structure can obliterate much of the fine structure in beryllium films, but reasonable results were obtained by using the high-resolution capability of an Hitachi S-800 SEM and either ion-beam coating with Au-Pd or carbon coating by thermal evaporation.
Reflection monolayer scattering and RHEED diffraction conditions
Authors: Peng L.-M. , Cowley J.M.
Published: June 2020

In an infinite crystal, when the fast electrons are transmitted through the crystal, the effects of the periodic potential distribution on the incident electron wave can be best described by expanding the electron wavefunction in terms of propagating Bloch waves having the same periodicity as that of the crystal. The requirement for a three dimensional translation symmetry excludes the existence of evanescent Bloch waves with imaginary component of wave vector. With the presence of external surfaces, as in the case of reflection high energy electron diffraction (RHEED), the translation symmetry in the surface normal direction is broken. Bloch waves which are confined to the surface region in the form of damping waves in the surface normal direction are then allowed.

In an ideal two-beam case, when the Bragg reflection condition is exactly satisfied, the incident electrons are totally reflected back into the vacuum from the surfaces of crystal, giving rise to an evanescent wave in the crystal and a standing wave outside in the vacuum.
PC based diffraction pattern analysis programs
Authors: Jackson A. G. , Rowe M.
Published: June 2020

The analysis of electron diffraction patterns can be done automatically using image techniques for collecting the diffraction pattern. This is useful if the material is well known. The alternative when the material is not well known is to do hand measurements on the plate and then enter that data into a program, or do the entire analysis by hand. We have developed a small software package called CRYSTAL, for a PC/AT which is an intermediate point between the fully automated approach and the approach by hand. These programs were written to be used in conjunction with the EMS programs in order to compare theoretical patterns with those obtained experimentally.

The program menu is displayed by typing “CRYSTAL”. There are five choices available from the menu: 1) enter diffraction pattern data using the digitizer, 2) analysis of the zone and planes associated with the measured planes, 3) plot the theoretical diffraction pattern and/or the measured planes, either on the CRT or the plotter, 4) calculate x-ray planes and 20 angles, 5) return to DOS.
Development of a conical anode Fe-gun for low voltage SEM
Authors: Miyokawa T. , Norioka S. , Goto S.
Published: June 2020

Field emission SEMs (FE-SEMs) are becoming popular due to their high resolution needs. In the field of semiconductor product, it is demanded to use the low accelerating voltage FE-SEM to avoid the electron irradiation damage and the electron charging up on samples. However the accelerating voltage of usual SEM with FE-gun is limited until 1 kV, which is not enough small for the present demands, because the virtual source goes far from the tip in lower accelerating voltages. This virtual source position depends on the shape of the electrostatic lens. So, we investigated several types of electrostatic lenses to be applicable to the lower accelerating voltage. In the result, it is found a field emission gun with a conical anode is effectively applied for a wide range of low accelerating voltages.

A field emission gun usually consists of a field emission tip (cold cathode) and the Butler type electrostatic lens.
Orientation relationships and morphologies in the MBE growth of CrSi2 films on (III) Si surfaces
Authors: Chang K.T. , Mazur J.H. , Fathauer R.
Published: June 2020

Chromium disilicide is a semiconductor with a 0.3 eV bandgap. It has potential for applications in Si based infrared detectors. The CrSi2/Si system is a good candidate for epitaxy because of the low 0.1% lattice mismatch between the basal plane of CrSi2 and the (111) Si surface. Previous studies have reported that the growth of CrSi2 on (111) Si occurs as islands with orientation relationship. The work reported here is an extension of this previous study.

In the present experiments, both (111) Si and 4°-off (111) Si were used as a substrates. After co-deposition of Cr and Si at room temperature in a MBE chamber, the deposited films was annealed in the same chamber at temperatures up to 720°C. Transmission electron microscopy diffraction and imaging were used to study the structure and morphology of the deposited films.
The relevance of local lattice parameter measurements using CBED
Authors: Fraser Hamish L.
Published: June 2020

Since the development of transmission electron microscopes in which the electron beam may be caused to be incident on the sample in the form of a convergent probe, much work has been aimed at the use of convergent beam electron diffraction (CBED) in materials science. One of the techniques afforded by CBED permits the measurement of lattice parameters on a scale more or less defined by the diameter of the probe at the sample, and so a powerful means of determining local distortions has become available. While this technique appears to be very exciting, as is shown below, the necessary use of thin foils results in the possibility of surface relaxations modifying the stress fields of a given distortion, and this raises the question of the relevance of measurements made in thin foils to the physical situation in the bulk. This question is the subject of this paper.
Transmission electron microscopy of composite materials
Authors: Lagerlof K.P.D.
Published: June 2020

Although most materials contain more than one phase, and thus are multiphase materials, the definition of composite materials is commonly used to describe those materials containing more than one phase deliberately added to obtain certain desired physical properties. Composite materials are often classified according to their application, i.e. structural composites and electronic composites, but may also be classified according to the type of compounds making up the composite, i.e. metal/ceramic, ceramic/ceramie and metal/semiconductor composites. For structural composites it is also common to refer to the type of structural reinforcement; whisker-reinforced, fiber-reinforced, or particulate reinforced composites [1-4].

For all types of composite materials, it is of fundamental importance to understand the relationship between the microstructure and the observed physical properties, and it is therefore vital to properly characterize the microstructure. The interfaces separating the different phases comprising the composite are of particular interest to understand. In structural composites the interface is often the weakest part, where fracture will nucleate, and in electronic composites structural defects at or near the interface will affect the critical electronic properties.
Combined CTEM and STEM using a condenser-objective lens and 100kv LaB6 gun
Authors: Beaumont S.P. , Ahmed H.
Published: June 2020

In order to study the differences in contrast that are observed in conventional and scanning transmission electron microscopy, a new microscope has been designed and constructed to examine the same area of a specimen in either mode of operation at a resolution of lnm or better.

A schematic diagram of the instrument is shown in Fig.1 for each of its modes of operation. It operates at voltages of up to 100kV and uses an LaB6 gun that provides a 10 micron source which may be aligned using the coils marked A1. In the STEM mode this source is demagnified by two strong condenser lenses Cl & C2 (fp,min = 1.75mm) and finally by the prefield of a saturated condenser-objective lens (CO) in the centre of which the specimen is immersed. These lenses were designed with the aid of magnetic vector potential programs. A further program was written to calculate the characteristic trajectories and aberration coefficients of the condenser-objective.
A new analytical electron microscope
Authors: Parker N.W. , Crewe A.V. , Isaacson M.S. , Mankawich W.
Published: June 2020

In recent years there has been increasing interest in the ability to perform electron energy loss analysis of areas approaching 20Å in size. We have initiated a program to study the electronic structure of small particles (≳ 10Å diameter) of grain boundaries and to perform EXAFS-type analysis of a variety of materials. For all of these studies, it is necessary to have reasonably high energy resolution (≲ .5 eV) and to focus large current electron beams down to spot diameters of 20Å or less (1). For EXAFS this is important since one is interested in few percent modulations of signals due to inner shell excitations (which by themselves are many orders of magnitude weaker than the signals due to plasmon or valence shell excitations). In the analysis of small particles, the signals are weak due to the small number of atoms within the probe, so high current densities are needed to avoid extremely long counting times.
Magnetic spectrometers with corrected second-order aberrations
Authors: Parker N.W. , Utlaut M. , Isaacson M.
Published: June 2020

Recent years have seen tremendous advances in analytical electron microscopy and increased interest in electron energy loss spectroscopy has been especially prominent. Due to these developments there have been many discussions in the literature of the use of magnetic spectrometers in energy analysis. The aberrations of magnetic prisms have also received numerous treatments [1-4] although not specifically emphasizing energy analysis in the electron microscope. The importance of the objective and post-specimen lenses on the effective spectrometer resolution, however, has been discussed in recent papers by Crewe [5,6]. To our knowledge, the correction of those aberrations of importance in an electron microscope spectrometer have not been adequately delineated. Recent work of H. Shuman, et al. [7] has demonstrated whole sets of uniform field magnetic prisms with curved pole faces which simultaneously eliminate the main second-order aberrations affecting the energy resolution in addition to making the focal plane perpendicular to the central ray (useful for parallel recording of spectra).
A versatile spectrograph for a STEM
Authors: Engel W.
Published: June 2020

Recently, spectrographs have been considered for the analysis of energy losses in a STEM [1,2]. Contrary to spectrometers, they permit simultaneous recording of the energy loss spectrum over a large range within which the resolution remains nearly constant. This yields two inherent advantages: First, during the recording of the entire spectrum in a spectrograph, the object is bombarded by less radiation. Second, for image formation several signals from the loss spectrum can be utilized in parallel by suitable detector electronics.

Fig. 1 shows the set-up of the proposed spectrograph, which is under construction. It consists of a transfer lens, a sector magnet which is not double-focusing, and a projective. The projective has a system of interchangeable pole pieces to permit various enlargements of the spectrum, yet with minimum aberration.

Table 1 contains the essential data of the spectrograph as they pertain to the various projective magnifications and also to the use without the projective (dashed optical path).
Hydrated form of some clay minerals observed using a film sealed environmental cell
Authors: Kohyama N. , Fukushima K. , Fukami A.
Published: June 2020

Since the interlayer or adsorbed water of some clay minerals are quite easily dehydrated in dried air, in vacuum, or at moderate temperatures even in the atmosphere, the hydrated forms have not been observed by a conventional electron microscope(TEM). Recently, specific specimen chambers, “environmental cells(E.C.),” have been developed and confirmed to be effective for electron microscopic observation of wet specimen without dehydration. we observed hydrated forms of some clay minerals and their morphological changes by dehydration using a TEM equipped with an E.C..

The E.C., equipped with a single hole copper-microgrid sealed by thin carbon-film, attaches to a TEM(JEM 7A) with an accelerating voltage 100KV and both gas pressure (from 760 Torr to vacuum) and relative humidity can be controlled. The samples collected from various localities in Japan were; tubular halloysite (l0Å) from Gumma Prefecture, sperical halloysite (l0Å) from Tochigi Pref., and intermediate halloysite containing both tubular and spherical types from Fukushima Pref..
A light optical diffractometer for electron microscopical images operating in line
Authors: Bonhomme P. , Beorchia A.
Published: June 2020

We have already described (1.2.3) a device using a pockel's effect light valve as a microscopical electron image converter. This converter can be read out with incoherent or coherent light. In the last case we can set in line with the converter an optical diffractometer. Now, electron microscopy developments have pointed out different advantages of diffractometry. Indeed diffractogram of an image of a thin amorphous part of a specimen gives information about electron transfer function and a single look at a diffractogram informs on focus, drift, residual astigmatism, and after standardizing, on periods resolved (4.5.6). These informations are obvious from diffractogram but are usualy obtained from a micrograph, so that a correction of electron microscope parameters cannot be realized before recording the micrograph. Diffractometer allows also processing of images by setting spatial filters in diffractogram plane (7) or by reconstruction of Fraunhofer image (8). Using Electrotitus read out with coherent light and fitted to a diffractometer; all these possibilities may be realized in pseudoreal time, so that working parameters may be optimally adjusted before recording a micrograph or before processing an image.
The theory of improved resolution in stroboscopic SEM for EBIC-mode
Authors: Komolova L.F. , Obyden S.K. , Saparin G.V. , Spivak G.V.
Published: June 2020

Idea of istrohoscopic principle in electron microscopy for the first time was described by ref. Now that is widely used in scanning electron microscopy(SEM)for the studies of dynamical effects caused by exciting electron beam in real materials. It was shown that the stroboscopic principle can be also used to improve the, spatial resolution in the SEM. This possibility was realized for CL-mode. In the present work the quantitative account of resolution inhancement of the EBIC SEM is given.

Physical consideration of EBIC-processes in the material demonstrates the time-inertial properties of this processes. The above fact obliges to, work in the conventional scan case at bad resolution. Real method supposes the usage as a videosignal under pulse excitation of specimen by electron beam only the initial phase of rising induced current into the material. To solve this problem the induced current must be determined as a function of time at the condition of nonstationary excitation.
TEM examination of dislocations generated in GaAS photocathode structures
Authors: Fletcher J. , Titchmarsh J.M. , Booker G.R.
Published: June 2020

Basic studies have been performed on GaAs epitaxial multilayer structures of the type used for transmission photocathodes. The substrates were horizontal Bridgman (100)GaAs, and the layers either GaAs or GaAlAs grown by the LPE method and Zn-doped. TEM examinations were made to determine the nature and distribution of dislocations present in the structures, deduce how they were formed and suggest how they might be eliminated. Special attention was given to those dislocations formed by surface stresses generating 60° dislocations with at the specimen surface and moving down on inclined {1ll} slip planes to form a network at an underlying interface. One feature of the work was the TEM examination of ∽ 1° angle-lap and 90° cross-section thinned specimens to determine the three-dimensional distribution of the dislocations. Results are reported for three different aspects of the work.

First, when GaAs layers are grown by the LPE method.
Representation of information in SEM by equal signal lines
Authors: Rau E. , Karelin N. , Dukov V. , Kolomeytsev M. , Gavrikov S. , Sedov N.
Published: June 2020

There are different methods and devices for the increase of the videosignal information in SEM. For example, with the help of special pure electronic [1] and opto-electronic [2] systems equipotential areas on the specimen surface in SEM were obtained. This report generalizes quantitative universal method for space distribution representation of research specimen parameter by contour equal signal lines. The method is based on principle of comparison of information signal value with the fixed levels.

Transformation image system for obtaining equal signal lines maps was developed in two versions:

1)In pure electronic system [3] it is necessary to compare signal U (see Fig.1-a), which gives potential distribution on specimen surface along each scanning line with fixed base level signals εifor obtaining quantitative equipotential information on solid state surface. The amplitude analyzer-comparator gives flare sport videopulses at any fixed coordinate and any instant time when initial signal U is equal to one of the base level signals ε.
Morphology and coalescence growth of metal oxide smoke particles prepared by gas evaporation technique
Authors: Shiojiri M. , Kaito C. , Sasaki H. , Fujita K.
Published: June 2020

The crystal habit and growth of metal oxide smoke particles which were prepared by burning component metals in a mixture gas of 80 % Ar and 20 % O2 at a pressure of 100 Torr are studied by electron microscopy.

Figure 1 shows SEM and TEM images and ED patterns of a single-crystal In2O3 particle, which grew in an octahedron bounded by eight {111} planes of the cubic bixbyite structure. The particle in (a) and (b) is oriented with the [001] and directions parallel to the incident electron beam, respectively. The determination of crystal habit has so far been done only by TEM observations of a single particle which is placed in different orientations with a tilting goniometer stage, considering thickness contours in the images and fine structures due to double refraction effect as shown in the ED patterns. It is, however, laboursome and sometimes ambiguous. Since the SEM images reveal not only the crystal external form but also surface structure, SEM observations are very useful for the study of fine particles whose sizes are several tens of nanometers or less.
Analytical contrast calculations in the two-beam case
Authors: Katerbau K.-H.
Published: June 2020

The image of a lattice defect in a crystalline specimen depends on a variety of different parameters, describing the material, the experimental conditions and the lattice defect itself. In a two-beam case the material parameters are the extinction length ξg and the anomalous absorption length ξ'g, the experimental parameters are the specimen thickness t, the depth zo of the defect in the foil and the excitation error w (as usual w = s.ξg). Till now, most calculations of the diffraction contrast of lattice defects were done numerically. Analytical calculations can be performed, however, and lead to a much better insight into the dependence of the contrast on the different parameters.

We consider the two-beam case and use the column approximation. A coordinate system (x,y,z) is introduced with its origin in the centre of the lattice defect and the z- axis parallel to the electron beam. x,y are the column coordinates.
Electron beam scattering in an organic specimen
Authors: Adesida Ilesanmi
Published: June 2020

The understanding of electron-solid interactions is of prime importance to both conventional transmission and scanning electron microscopists. Monte Carlo simulation of electron beam scattering in various target samples has made fundamental contributions to this understanding, especially in scanning electron microscopy where primary electron beams of a few to many kilovolts are utilized. A significant example is the understanding of energy dissipation patterns of incident electrons in an organic sample (polymethylmethacrylate-PMMA) which is very useful in electron beam lithography (1). Furthermore, with the close similarity between the organic sample and a biological specimen, a Monte Carlo approach is also very useful for the study of energy dissipation in biological specimens (2).

To enhance our knowledge of these dissipation processes, a more comprehensive Monte Carlo simulation program has been developed. The program is based on the semi-direct technique of simulating individual inelastic scattering and elastic scattering with probabilistic weightings.
Surface structure of (001) Au films by high resolution transmission electron microscopy
Authors: Krakow William
Published: June 2020

In nonprimitive lattices, surface layers corresponding to partially filled unit cells give rise to reflections forbidden in the bulk structure. These reflections allow detailed studies of the surface layer by high resolution transmission electron microscopy and computer modeling experiments.

The occurrence of fractional unit cells at the surface of (001) oriented Au films can be demonstrated by assembling the fcc lattice by the alternate stacking of planar {100} type layers such that the atoms of,each atomic layer are embedded in the depressions of neighboring planes above and below. The stacking sequence is of the ABABAB….type with the B layers shifted an amount ao/2 in the [100] direction (Fig. 1a). The presence of an excess A or B layer gives rise to additional reflections with mixed odd and even Miller indices which are forbidden in the fcc lattice, e.g., (110). In obtaining diffraction patterns from ∼100Å thick Au films the forbidden reflections were approximately 2% of the corresponding bulk lattice reflections and easily identified (see Fig. 1b).
Long period structure in the Cu-Sn system
Authors: Van Sande M. , De Ridder R. , Van Tendeloo G. , Van Landuyt J. , Amelinckx S.
Published: June 2020

High resolution electron microscopy and electron diffraction were used to study the Cu-Sn system in the composition range 3:1. Two different long period superstructures have been reported before as ordening phases with respect to the HCP structure. It was the purpose of this study to eliminate this ambiguity and investigate the influence of slight additions of a third element with respect to the Cu3Sn composition.

Molten alloys were homogenized, quenched and annealed prior to electrolytical thinning of trepanned discs by jet polishing. The Cu3Sn-structures as described in the literature are derived from the Cu3Ti-orthorhombic basic structure which itself is a superstructure of the hexagonal close packed structure. As a confirmation of the structure model the derived phases should present the orientation and translation variants associated with the symmetry reduction fromfor the HCP structure tofor the Cu3Ti. From group theoretical considerations one expects three orientation variants and four translation variants;_the latter are then related by the three displacement vectors[100],[120] and[120].

Our electron diffraction data and structure images confirm the structure proposal of Schubert and his description as a long period antiphase boundary structure with a periodicity of 10 times the b spacing of the orthorhombic cell.
Features of the subboundary structure in deformed molybdenum single crystals
Authors: Myshlyaev M.M. , Khodos I.I. , Senkov O.N. , Romanov Yu.A.
Published: June 2020

The subboundary structure corresponding to the high temperature steady-state creep of molybdenum single crystals is formed by both regular sites of dislocation nets and walls, various in structure and composition, (the nets are formed by two, three, five and six dislocation sets having different values of the angles between the Burgers vector Ḇ and the dislocation line ū ; the walls are formed by one, two and three sets of edge and mixed dislocations; the Burgers vectors of the dislocations are I/2  and, ) and by the sites of a more complex and less regular structure. Several of these are considered below.

Fig.I represents a subboundary formed by five dislocation sets.Its regular sites (nets) can be formed by means of interaction of dislocations I and 4 with dislocations 2 (fig.2a). In several irregular sites (fig.I and 2b) no dislocations 2 are seen to be present, and neither dislocations 3 and 5 arisen from the reactions of dislocations 2 with dislocations I and 4.
Observation of faint contrast at planar faults in alloys
Authors: Kuroda K. , Tomokiyo Y. , Kumano T. , Eguchi T.
Published: June 2020

The contrast in electron microscopic images of planar faults in a crystal is characterized by a phase factor , where is the reciprocal lattice vector of the operating reflection, and the lattice displacement due to the fault under consideration. Within the two-beam theory a planar fault with an integer value of is invisible, but a detectable contrast is expected when the many-beam dynamical effect is not negligibly small. A weak fringe contrast is also expected when differs slightly from an integer owing to an additional small displacement of the lattice across the fault. These faint contrasts are termed as many-beam contrasts in the former case, and as ε fringe contrasts in the latter. In the present work stacking faults in Cu-Al alloys and antiphase boundaries (APB) in CuZn, FeCo and Fe-Al alloys were observed under such conditions as mentioned above, and the results were compared with the image profiles of the faults calculated in the systematic ten-beam approximation.
TEM examinations of ion implanted silicon using cross-section specimens
Authors: Fletcher J. , booker G.R
Published: June 2020

Basic work is being performed on the damage structures resulting from ion implantation of (111) Si slices. Specimens were implanted at room temperature with either 60keV Ne+ in the dose range 1 x 1014 to 5 x l015 cm-2, or 150keV As+ in the range 3 x 1014 to 7.5 x 1015 cm-2, and subsequently annealed in an inert atmosphere at temperatures up to 1000°C. These were thinned for 100kV TEM examination to give both ‘plan’ and ‘90° cross-section' specimens. Results are described for four different aspects of the work.

First, Fig.l shows the damage for different Ne+ doses (800°C anneal). For 2.5 x 1014( cm-2, the damage consists of a band of loops and rods, with a defect-free zone close to the surface. For 1 x 1015 cm -2, there are two separate damage layers. The upper layer comprises mainly micro-twin lamellae, and the lower layer loops and rods similar to those in Fig.la.
Surface craters induced by displacement cascades in heavy metals
Authors: Jäger W. , Merkle K. L.
Published: June 2020

Past investigations of the erosion of surfaces under bombardment by energetic particles have mainly focused on the measurement of integral sputtering yields and the examination of surface structural changes by scanning electron microscopy. Both types of observations generally require the use of rather high particle doses (≳1015cm-2) and provide only indirect information on the primary sputtering mechanisms. For more direct information, transmission electron microscopy (TEM) was applied to study the interaction of individual displacement cascades with surfaces in thin Au films. First results from low dose (1010 - 1012cm-2) Bismuth ion irradiation revealed the existence of small craters where cascades intersect a surface. In the present paper it will be shown that this surface crater formation strongly depends on cascade energy and cascade energy density. Also, details of the observed crater contrast will be discussed in view of its implications in regard to crater formation mechanisms.

Thin Au films, prepared by vacuum evaporation, were bombarded with Bismuth ions.
Observations of dislocations near θ' precipitates in neutron-irradiated Al-4% Cu by WBDF
Authors: Carpenter R. W. , Loretto M. H. , Remag
Published: June 2020

In this paper some observations of dislocation structure in a neutron-irradiated Al—4% Cu alloy containing θ' precipitate are reported. Both weak-beam dark-field and strong-beam bright-field methods were used. During irradiation, coherency loss begins to occur, and swelling resistance decreases. The WBDF method is necessary to resolve dislocation configurations near the matrix/precipitate interfaces.

The microstructure of the alloy after a neutron fluence of 2.8 x 1025 n/m2(E>0.1 MeV,T ∼ 330 K) is shown in WBDF (Fig. 1). The main features of the irradiated microstructure are the θ' precipitates, faulted and unfaulted loops with diameter ∽30 nm in the matrix, a few long dislocations lying in the precipitate/matrix interfaces, and some small (< 10 nm) contrast features in the background. The latter may be a result of the small amount of Si formed during irradiation by transmutation of the Al. Of primary present interest are dislocations in and near the interfaces.
Alignment of small He-Bubbles during in situ deformation of Al-foils
Authors: Ruedl E. , Schiller P.
Published: June 2020

The low Z metal aluminium is a potential matrix material for the first wall in fusion reactors. A drawback in the application of A1 is the rel= atively high amount of He produced in it under fusion reactor conditions. Knowledge about the behaviour of He during irradiation and deformation in Al, especially near the surface, is therefore important.

Using the TEM we have studied Al disks of 3 mm diameter and 0.2 mm thickness, which were perforated at the centre by double jet polishing. These disks were bombarded at∽200°C to various doses with α-particles, impinging at any angle and energy up to 1.5 MeV at both surfaces. The details of the irradiations are described in Ref.1. Subsequent observation indicated that in such specimens uniformly distributed He-bubbles are formed near the surface in a layer several μm thick (Fig.1).

After bombardment the disks were deformed at 20°C during observation by means of a tensile device in a Philips EM 300 microscope.
Grain boundary structure observed by T.E.M
Authors: Goodhew P.J.
Published: June 2020

This paper reports some observations on gold by TEM which imply that the dissociation of a high angle grain boundary into two lower energy boundaries may occur extensively.

It is well established that grain boundaries of any desired geometry can be created in gold by the welding together of thin single crystals. The resultant thin bicrystal specimens are ideally suited for immediate examination by TEM and many aspects of grain boundary structure and behaviour in such specimens have been studied or discussed. One particularly useful specimen configuration can be achieved if the bicrystal is annealed until its boundary migrates (lowering its total area) until it is perpendicular to the surface of the thin specimen. This specimen geometry has been used to study, inter alia, the faceting of grain boundaries.

During a study of the behaviour of coincidence high angle boundaries (i.e. those special boundaries whose geometry is such that a fraction 1/Σ of the lattice sites in both crystals coincide) it was noticed that the boundary under observation was no longer a single planar defect.
STEM/X-ray microanalysis across α/γ interfaces in Fe-Ni meteorites
Authors: Williams D. B. , Goldstein J. I.
Published: June 2020

Fe-Ni meteorites have cooled at rates ∼1-10°C/106 years giving rise to a characteristic microstructure of Widmanstatten bcc α plates that have nucleated and grown from the parent fcc γ phase. This transformation results in rejection of Ni into the remaining γ, which also exhibits a variety of internal precipitation reactions. The Ni concentration at the α/γ interface should be close to the equilibrium value between the two phases and this has been determined in several meteorites, using a Philips EM300 TEM/STEM equipped with X-ray microanalytical facilities. The sharp α/γ interface also permits a practical determination to be made of the spatial resolution of the technique. This has been performed and the result compared with the predictions of two theoretical models describing the spatial resolution in terms of the spreading of the electron beam within specimens of finite thickness.

Specimens of the meteorites were sectioned such that the α/γ interface was normal to the surface, then 3mm discs were spark machined, ground to ∼100 μm thick, then ion beam thinned to electron transparency