bluuebunny/crossref_metadata_2025 huggingface dataset:
Advantages of FE-TEM for convergent-beam electron diffraction
Authors: Kaneyama T. , Tomita T. , Ishida Y. , Kersker M.
Published: June 2020

Many electron microscopes equipped with a field-emission gun (FE-TEMs) are now used for the purpose of improving the spatial and the energy resolution in energy dispersive x-ray spectroscopy and electron energy loss spectroscopy. For the convergent-beam electron diffraction techniques, FE-TEMs have greater advantages than conventional electron microscopes with a thermal LaB cathode. We discussed these advantages using JEM2010F and JEM2010, which have equivalent specifications except for the electron source and the condenser lens system.

High spatial resolution

The brightness of an FE-gun (∽ 5 × 108A cm-2 sr-1) is about 100 times that a conventional LaB6 cathode. The gun can obtain enough current for taking CBED patterns in an exposure time of a few seconds even with an electron probe less than 1 nm in diameter (FIG. 1). Steep wedge shapes and rapid bends within the illuminated area deteriorate the accuracy of quantitative CBED analysis. Improvement of the spatial resolution by a small probe reduces these inevitable averaging effects.
Quantitative analysis of convergent-beam electron diffraction patterns
Authors: Lin Xiwei , Zhu Jing , Dravid Vinayak P.
Published: June 2020

In recent years, there have been great advances in electron crystallography by quantitative convergent beam electron diffraction (QCBED). From the distribution of dynamical diffraction intensities, QCBED can determine the Fourier components of the crystal potential accurately and completely, enabling direct measurement of phases of crystal structure factors. Given the combination of small probe size in CBED and the high accuracy of the quantitative analysis (e.g. determination of bonding charge distributions in covalent crystals), QCBED is a powerful experimental methods for detection of a small change in the crystal potential of a few nanometer structure (e.g. near grain boundaries/defects).

More recently, interest has shifted towards the possibility of the automated matching of experimental and theoretical CBED patterns by optimization for speed and even higher accuracy. In this work, the combined variable matrix algorithm is used to automate the least-squares refinement. The program was tested by calculated intensities randomized with Gaussian distribution as experimental data.
A photoelectron microscope study of surfaces
Authors: Engel W. , Kordesch M. , Bradshaw A. M. , Zeitler E.
Published: June 2020

Photoelectron microscopy is as old as electron microscopy itself. Electrons liberated from the object surface by photons are utilized to form an image that is a map of the object's emissivity. This physical property is a function of many parameters, some depending on the physical features of the objects and others on the conditions of the instrument rendering the image.

The electron-optical situation is tricky, since the lateral resolution increases with the electric field strength at the object's surface. This, in turn, leads to small distances between the electrodes, restricting the photon flux that should be high for the sake of resolution.

The electron-optical development came to fruition in the sixties. Figure 1a shows a typical photoelectron image of a polycrystalline tantalum sample irradiated by the UV light of a high-pressure mercury lamp.
PHAX-SCAN: Functional integration of a Scanning Electron Microscope and an energy-dispersive x-ray analyser
Authors: Peeters Marc H. , Otten Max T.
Published: June 2020

Over the past decades, the combination of energy-dispersive analysis of X-rays and scanning electron microscopy has proved to be a powerful tool for fast and reliable elemental characterization of a large variety of specimens. The technique has evolved rapidly from a purely qualitative characterization method to a reliable quantitative way of analysis. In the last 5 years, an increasing need for automation is observed, whereby energy-dispersive analysers control the beam and stage movement of the scanning electron microscope in order to collect digital X-ray images and perform unattended point analysis over multiple locations.

The Philips High-speed Analysis of X-rays system (PHAX-Scan) makes use of the high performance dual-processor structure of the EDAX PV9900 analyser and the databus structure of the Philips series 500 scanning electron microscope to provide a highly automated, user-friendly and extremely fast microanalysis system. The software that runs on the hardware described above was specifically designed to provide the ultimate attainable speed on the system.
EM-002B computer control development
Authors: Chang M. , Kamewari T.
Published: June 2020

The EM-002B is an ultrahigh resolution TEM with unique TEM-probe analytical capabilities. In its standard configuration, one set of lens current parameters along with 20 specimen stage XY coordinate sets can be stored in a non-volatile memory. The first stage in implementing computer control of the microscope involves extending the ability to store and recall multiple lens parameter and stage position sets.

This has been accomplished by adding a standard RS-232C communications channel to the EM-002B and developing a state-of-the-art window software package to run on an IBM AT PS2 or compatible computer. This package accepts the commands from a mouse input and allows storage and automatic setting of lens current and stage position sets. After transfer to the computer parameter, sets are assigned a file name and may be stored on a floppy or hard disk. These files are easily modified and transferred via the communications channel to the EM-002B.
Development of 200kV ultrahigh-resolution analytical electron microscope
Authors: Kaneyama T. , Naruse M. , Ishida Y. , Kersker M.
Published: June 2020

In the field of materials science, the importance of the ultrahigh resolution analytical electron microscope (UHRAEM) is increasing. A new UHRAEM which provides a resolution of better than 0.2 nm and allows analysis of a few nm areas has been developed. [Fig. 1 shows the external view] The followings are some characteristic features of the UHRAEM.

Objective lens (OL)

Two types of OL polepieces (URP for ±10' specimen tilt and ARP for ±30' tilt) have been developed. The optical constants shown in the table on the next page are figures calculated by the finite element method. However, Cs was experimentally confirmed by two methods (namely, Beam Tilt method and Krivanek method) as 0.45 ∼ 0.50 mm for URP and as 0.9 ∼ 1.0 mm for ARP, respectively. Fig. 2 shows an optical diffractogram obtained from a micrograph of amorphous carbon with URP under the Scherzer defocus condition. It demonstrates a resolution of 0.19 nm and a Cs smaller than 0.5 mm.
Electron-beam damage and the 3-D structure of negatively stained ompF porin
Authors: Dorset Douglas L. , Massalskl Andrew K.
Published: June 2020

A 20Å resolution 3D electron microscopic structure analysis of negatively-stained crystalline sheets of ompF porin was instrumental in demonstrating the existence of a physical water-filled pore which spans the membrane bilayer. It also suggested that the three separate channels in a trimer actually converge near the interface of two stacked membranes to form a single cylindrical outlet. Immediately this structure was criticized in terms of its probable transport properties.An additional inconsistency was found with the 3D structure of the genetically related phoE porin, which revealed no such convergence of the negative stain-filled pores. The possible role of radiation damage in this discrepancy will be shown.

Electron micrographs of the small hexagonal porin sheets (a=79Å, plane group p3) stained with 2% uranyl acetate had been photographed with “normal” beam doses and the images of specimens tilted ±45° were digitized so that the phases and amplitudes of the Fourier transforms could be used to construct a 3D representation of the structure.
An epi-fluorescent spinning-disk confocal microscope
Authors: Cheng P. C. , Chen V. K.-H. , Kim H. G. , Pearson R. E.
Published: June 2020

The confocal microscope offers a number of advantages over the conventional light microscope in improvement in spatial resolution optical sectioning by rejecting out-of-focus signals. The applications of confocal microscopy in biology will be greatly expanded if real-time imaging can be achieved.

A real-time epi-fluorescent confocal microscope based on a spinning disk design has been constructed at our laboratory (Fig. 1). Different from Petran's tandem scanning configuration, but similar to Kino's, our microscope has both the illumination and the detection rays sharing the same pinholes (Fig. 2). As a result, the optical arrangement is simpler and much easier to align. The spinning “Nipkow disk” used in our microscope has 194,400 pinholes (25х25μm) arranged in 90 interleaved spirals (Fig. 3). The minimum and maximum spacing between adjacent pinholes are 90μm and 207μm respectively. When the disk is spun at 1000rpm, we achieved a frame rate of 1500f/sec with 1440 lines/frame. The disk is spun by a simple mechanism mounted on a X-Y linear slide (Fig. 4). The disk was fabricated by lithography on a 4 inch glass substrate (Fig. 5). At the present time, a 5W Argon ion laser or a 200W high pressure mercury arc lamp is used as the light source. By a set of mechanical slides, the microscope operates not only in epi-fluorescent and reflective confocal modes, but also in conventional epi-fluorescent and transmitted modes (i.e. bright field, phase contrast etc.). The low intensity confocal fluorescent image is amplified by the use of a TV-coupled second generation image intensifier. Then, the TV signal from the video camera is digitized and processed by a frame store interfaced to a 80386 microcomputer. In addition, the fine focus control of the microscope is driven by a stepping motor via the same computer.
3-D image analysis of serial focal sections from confocal scanning laser microscopy
Authors: Russ J. Christian , Russ John C.
Published: June 2020

The Confocal Scanning Laser Microscope (CSLM) is used in two quite different imaging modes: reflection and transmission. Most instruments maintain their confocal optics only when operated in reflection mode, in which light reflected or emitted from points in the sample or on its surface, lying in the focal plane of the microscope, is detected to form an image. Point elevations can be measured by scanning through a range of focal distances. Recording in memory the maximum brightness at each pixel forms an image containing the “in-focus” information for the entire irregular surface or object (Figure 1). These are powerful capabilities and account for much of the current use of confocal microscopes for metrology of rough surfaces, and for use with fluorescent dyes.

True transmission confocal imaging can be achieved by passing the light from the source through the specimen to a mirror, reflecting it back through the specimen again (maintaining the focus in the same plane), and thence to the detector. This is shown schematically in Figure 2. This is only possible with monochromatic light, because of sample-induced chromatic aberrations.
Ordered Structures in Gd2CuO4 and isostructural cuprates
Authors: Mitchell T. E. , Roy T. , Fisk Z. , Cheong S-W , Thompson J. D. , Cheng T. T.
Published: June 2020

INTRODUCTION.

The lanthanide cuprates Ln2CuO4 (Ln = Pr, Nd, Eu, Gd, etc.), have a a triple perovskite unit cell.The structure is tetragonal, 14/mmm, a ∼ 0.39nm, c ∼1.19nm, with layered nets of [CuO4] squares. By contrast, the structure of La2CuO4, which also has a triple perovskite cell, contains layers of [CuO6] octahedra. La2CuO4 becomes superconducting by doping with SrO while Ln2CuO4 becomes superconducting by doping with CeO2 for Ln = Pr, Nd and Sm. Both La2CuO4 and YBa2Cu3O7 have a tetragonal-to-orthorhombic transformation while Ln2CuO4 remains tetragonal.The present study was undertaken to investigate microstructures in the lanthanide cuprates.

EXPERIMENTAL. The Ln2CuO4 single crystals were grown as plates from a PbO or CuO flux. Specimens for TEM were prepared by ion milling using a liquid nitrogen specimen cooler. High resolution electron microscopy (HREM) was performed on either a Philips CM3OST at 300kV or a JEM4000FX at 400kV.
Scanning Electron Microscope Study of Superconducting Transport in a YBa2Cu3O7-δ thin film
Authors: Farrow R. C. , Monroe Don , Brocklesby W. S. , Hong M.
Published: June 2020

By combining electron probing with current biasing at low temperatures a map of the transport characteristics of a mixed phase thin film superconductor can be obtained. The electron beam of a scanning electron microscope (SEM) acts as a local heat source. Under the proper conditions of temperature, bias current, and beam current, variations in the superconducting state can be mapped and compared to microstructure and chemical phase information. This method has recently been applied to high Tc superconductors to map critical currents and to identify weak links in superconducting paths. We discuss here the possible application of the technique to identify the superconducting phase within a matrix of non-superconducting material.

The sample was an ∼1 μm thin film that was grown by sputtering from a YBa2Cu3O7-δ target onto a [001] SrTiO3 substrate. A more detailed description of the growth procedure is given elsewhere. The morphology, crystallinity, and stoichiometry of the samples were characterized in the SEM. The film had several chemical phases and a morphology consisting of large rectangular platelets (typical size 200х50 μm), covering ∼20-30% of the surface.
Electron radiation damage in YBa2Cu3O7
Authors: Roy T. , Sickafus K. , Clinard F. W. , Mitchell T. E.
Published: June 2020

Some potential applications of high temperature superconductors involve radiation environments with possible deleterious effects on properties. In addition, radiation introduces point defects and defect clusters which could possibly pin flux lines and raise the critical current density. The present research was undertaken to characterize the damage produced by electrons in situ by TEM.

Thin specimens of YBa2Cu3O7 were prepared either by crushing or by ion-milling. Irradiations and observations were performed in either a Philips EM400T at 120kV, a Philips CM30 at 300kV, or a JEM2000EX at 200kV.

The main effect of electron irradiation is to cause the fading of the twins which are ubiquitous in YBa2Cu3O7 (Fig. 1). The twins themselves are the result of the tetragonal-to-orthohombic phase transformation and represent regions in which the Cu-O chains (and oxygen vacancies) are ordered along either of the a axes of the original tetragonal cell.
Magnetic-history-dependent critical currents in granular high-temperature superconductors: Dependence on defect structures and morphology
Authors: Maley Martin P. , McHenry Michael E. , Willis Jeffrey O.
Published: June 2020

Critical current densities, Jc’s, in conventional low temperature superconductors are controlled by defect structures that provide pinning for the magnetic flux lattice. High critical current densities and strong pinning have been observed in single crystals of the new oxide, high temperature superconductors (HTS) and have been ascribed to the presence of twin planes and to stoichiometry variations in the YBCO compound. Neutron irradiation studies have shown that intragranular Jc’s in YBCO can be strongly enhanced by the point defects introduced by irradiation. However, transport Jc’s determined by intergranular current transfer have remained dissappointingly low in bulk ceramic HTS materials. This has suggested a model of strongly superconducting grains separated by “weak links” that behave as Josephson tunnel junctions.The extraordinarily small superconducting coherence length ζo ∼ 10 A° in the HTS make them considerably more sensitive to small scale defects. Grain boundaries that act as pinning centers in conventional superconductors thus become barriers to current flow in the HTS.
Strain measurement by means of bend contour microscopy
Authors: Hren Philip D.
Published: June 2020

The pattern of bend contours which appear in the TEM image of a bent or curled sample indicates the shape into which the specimen is bent. Several authors have characterized the shape of their bent foils by this method, most recently I. Bolotov, as well as G. Möllenstedt and O. Rang in the early 1950’s. However, the samples they considered were viewed at orientations away from a zone axis, or at zone axes of low symmetry, so that dynamical interactions between the bend contours did not occur. Their calculations were thus based on purely geometric arguments. In this paper bend contours are used to measure deflections of a single-crystal silicon membrane at the (111) zone axis, where there are strong dynamical effects. Features in the bend contour pattern are identified and associated with a particular angle of bending of the membrane by reference to large-angle convergent-beam electron diffraction (LACBED) patterns.
High-resolution observations of nanometer-sized cavities in rapidly solidified 304 stainless steel
Authors: Kelly Thomas F. , Shin Keesam , Bae Jung Chan , Flinn John E.
Published: June 2020

Recent theoretical work by Wolfer and Adams has predicted, and experimental work by Bae et al. has confirmed, that void-like cavities are produced in rapidly solidified materials during post-melting heat treatment. Studies of a 304 stainless steel using conventional TEM have shown that 8 nm voids are present in a material that wgs consolidated from centrifugally atomized powder by hot extrusion at 900°C. After heat treating the material at 900° C for one hour, 1 × 1021m−3of the 8 nm voids are found. When heat treated at 1200° C for one hour, however, there is a large increase in the number density of 8 nm voids to 5 × 1021m−3.

Since this increase in void volume cannot be explained as void swelling because there is insufficient gas present, there must be a source of additional void volume in the material. Conventional TEM out-of-focus imaging can be used to image voids down to about twice the point resolution of an instrument. It was reasoned, then, that the extra void volume might then be present as small voids that were to small to be detected in the conventional TEM. In order to image these small voids, we decided to use a high-resolution TEM so that the smallest possible void could be imaged.
Detection of oxygen by PEELS in ribbon-like defects of thermally aged CZ-Si
Authors: Chen Y. L. , Carpenter R. W. , Barry J. C
Published: June 2020

Oxygen precipitation during post growth thermal annealing of CZ-Si has been a subject of practical and fundamental interest for several decades. Precipitation in the lower temperature part of the range, below about 1000K, where the products are small and metastable. is of highest interest at present. The recent general availability of HREM instruments with interpretable resolution limits of ∽0.25nm facilitated many imaging and diffraction investigations of low temperature precipitation reaction products during the past three years. Many metastable reaction products were observed, including ribbon-like defects (RLD’s) extended along [011] Si with habit plane variable between {001} and {311} Si. loopites. blobs, decorated dipoles and small features visible only in strain contrast thought to be nuclei for the larger amorphous SiOx precipitates observed after aging at higher temperature. The RLD’s contained a crystalline phase along their cores differing in structure from Si. This phase was first identified as coesite, a phase of SiO2 stable only under high pressure, but later the HREM results were reinterpreted as hexagonal Si. not involving oxygen. This controversy remains unresolved, and it was suggested that independent determination of the presence or absence of oxygen in RLD’s by electron energy loss spectroscopy may be the most useful method for its resolution. This note presents our first results.
Analytical Electron Microscopy study of two vehicle-aged automotive exhaust catalysts having dissimilar activities
Authors: Kim Sooho , D’Aniello M. J.
Published: June 2020

Automotive catalysts generally lose-agtivity during vehicle operation due to several well-known deactivation mechanisms. To gain a more fundamental understanding of catalyst deactivation, the microscopic details of fresh and vehicle-aged commercial pelleted automotive exhaust catalysts containing Pt, Pd and Rh were studied by employing Analytical Electron Microscopy (AEM). Two different vehicle-aged samples containing similar poison levels but having different catalytic activities (denoted better and poorer) were selected for this study.

The general microstructure of the supports and the noble metal particles of the two catalysts looks similar; the noble metal particles were generally found to be spherical and often faceted. However, the average noble metal particle size on the poorer catalyst (21 nm) was larger than that on the better catalyst (16 nm). These sizes represent a significant increase over that found on the fresh catalyst (8 nm). The activity of these catalysts decreases as the observed particle size increases.
Phase stability of a manganese-stabilized austenitic stainless steel
Authors: Kenik E.A. , Maziasz P.J. , Klueh R.L.
Published: June 2020

Development of manganese-stabilized stainless steels has been prompted by two objectives: (1) replacement of nickel, normally used to stabilize austenitic stainless steels, since it is an expensive, strategic material, and (2) reduction of long-term induced radioactivity of neutron-irradiated stainless steels by replacing nickel, molybdenum, and nitrogen. Klueh et al. have shown that in Fe-Cr-Mn alloys a single-phase austenite exists near Fe-12Cr-20Mn-0.25C (wt %) at high temperatures. Development of more complex alloys based on this composition with other minor alloying additions is underway. The aim is to develop alloys with improved mechanical properties, while minimizing the formation of embrittling second phases such as sigma or Laves. The stability of these alloys during thermal aging and the influence of the other alloying additions was studied in the current work for both solution-annealed and cold-worked conditions.

Seven alloys based on Fe-12Cr-20Mn-0.25C were made with additions of W, Ti, V, P, and B, either singly or in combination. The alloys were hot-worked and subsequently cold-worked to sheet with intermediate anneals at 1150°C. Materials were aged at 600°C for 5000 h in both 20% cold-worked and annealed (1 h, 1050°C) conditions.
Quasicrystal structures in submicron spheres of pure nickel and nickel-chromium alloys
Authors: Lin Hong-Ming , Kelly Thomas F.
Published: June 2020

The icosahedral quasicrystal with a fivefold rotation symmetry was first reported in Al-M (M = Cr, Mn, Fe) alloys. Later, quasicrystals with eightfold, tenfold, and twelvefold rotation symmetries were also reported. A twelvefold symmetry has been found in a Ni-70.6 at%Cr alloy and an eightfold symmetry has been found in a Cr-Ni-Si alloy. This indicates a potential for nickel-chromium alloys to form the quasicrystal phase.

An intermediate state between crystalline and quasicrystalline states is also discussed by Li, Teng, et. al. in an Al-Cu-Mg alloy due to the coexistence of micro-quasicrystal and micro-crystal grains. When regions larger than 1 nm are measured, a coherent boundary is found between micro-quasicrystal and micro-crystal grains.

A diffraction pattern with seemingly twelvefold symmetry is found in pure nickel and Ni-20at%Cr sphere of about 25 nm diameter as shown in Figure 1. The diffraction patterns do not have true twelvefold symmetry but the first diffraction ring is found to have twelve diffracted spots. Similar structures are found in Ni-10at%Cr and shown in Figure 2 with a series of diffraction patterns.
Peritectic solidification and precipitation of α-Re in β-NiAl Alloys containing Re additions
Authors: Webber J. G. , Van Aken D.C.
Published: June 2020

Recently it has been shown that solidification of β-NiAl alloys which contain additions of Re will produce eutectic microstructures. The microstructure of the eutectic was determined to be composed of a matrix of β-NiAl with fibers of α-Re. It was thus concluded that a eutectic quasi-binary isopleth between β-NiAl and α-Re was present. Electron microprobe analysis of the eutectic areas showed a eutectic composition (in atomic percent) of 47.5 Ni, 51 Al and 1.5 Re.

The fracture of these eutectic structures has been the primary interest in studying these materials. It appears that the α-Re may improve the fracture toughness of β-NiAl by a fiber pull-out mechanism, see Fig. 1. Careful examination of the α-Re fibers will reveal that each fiber exhibits plastic deformation. Indeed if the eutectic structure could be produced by directional solidification, the fracture toughness of this composite structure could be determined. The purpose of the present study is to further clarify the nature of this quasi-binary phase diagram.
The deformation and fracture of a dual-phase intermetallic alloy
Authors: Larsen Michael
Published: June 2020

Ordered intermetallic alloys possess many attractive properties, yet their use as a structural material has been severely limited by a general lack of low temperature ductility. The beta/gamma-prime dual-phase Ni50Fe30A120 (atomic percent) intermetallic alloy has shown remarkable ductility, exhibiting fracture strains in excess of 20% in both tension and compression. This behavior is yet unexplained, thus an investigation was conducted to study the deformation and fracture behavior of this alloy.

The material studied was a Ni50Fe30A120 (nominal composition) directionally solidified alloy. TEM specimens were made from the as cast material in an unstrained condition and with a 1% strain in compression. The foils were hand ground to a thickness of about 75 um and electrothinned in a Tenupol twin jet polisher with a methanol-based solution containing 2% perchloric acid and 35% butyl cellosolve at -20C. A JEOL 2000 FX AEM was used to examine the strained and unstrained foils. STEM microanalysis was performed on the unstrained foil with a Phillips CM-12 AEM to determine the composition of the two phases. Finally, the compression fracture surface was studied using a Hitachi S520 SEM.
Scanning tunneling microscopy of polymers: A status report
Authors: Russell P.E. , Musselman I.H.
Published: June 2020

Scanning tunneling microscopy (STM) has evolved rapidly in the past few years. Major developments have occurred in instrumentation, theory, and in a wide range of applications. In this paper, an overview of the application of STM and related techniques to polymers will be given, followed by a discussion of current research issues and prospects for future developments. The application of STM to polymers can be conveniently divided into the following subject areas: atomic scale imaging of uncoated polymer structures; topographic imaging and metrology of man-made polymer structures; and modification of polymer structures. Since many polymers are poor electrical conductors and hence unsuitable for use as a tunneling electrode, the related atomic force microscopy (AFM) technique which is capable of imaging both conductors and insulators has also been applied to polymers.

The STM is well known for its high resolution capabilities in the x, y and z axes (Å in x andy and sub-Å in z). In addition to high resolution capabilities, the STM technique provides true three dimensional information in the constant current mode. In this mode, the STM tip is held at a fixed tunneling current (and a fixed bias voltage) and hence a fixed height above the sample surface while scanning across the sample surface.
Liquid crystalline polymer textures near the resolution limit of the light microscope
Authors: Viney C.
Published: June 2020

The “texture” of a liquid crystal (LC) is the image obtained when thin specimens are viewed between crossed polars with a transmitted light microscope. Observation of textures, and of the way in which their appearance changes as the crossed polars are rotated, has long served as the basis for deducing the point-to-point variation of the average molecular orientation in low molecular weight LCs. Hence, the technique has been used as a means of identifying LC phases, and of elucidating their structure.

Polymeric LCs show textures that are qualitatively similar to those formed by low molecular weight LCs, so it is tempting to interpret contrast in the same way in both cases . The textures of polymeric LCs are often quenchable: by means of rapid cooling, the molecular ordering characteristic of high temperatures can be preserved to room temperature. This is a consequence of the relatively slow kinetics of phase transformations in polymers, and is convenient because it allows the microscopist to work at magnifications and resolutions that are inaccessible while specimens are enclosed in a heating stage.
Surface effects in imaging uncoated polymers in low-voltage, high-resolution Scanning Electron Microscopy
Authors: Krause S.J. , Adams W.W. , Joy D.C.
Published: June 2020

It has recently been shown that there are numerous advantages in imaging both coated and uncoated polymers in scanning electron microscopy (SEM) at low voltages (LV) from 0.5 to 2.0 keV compared to imaging at conventional voltages of 10 to 20 keV. The major disadvantages of LVSEM of degraded resolution and decreased beam current have been largely overcome with the new generation of field emission gun SEMs. In imaging metal coated polymers in LVSEM beam damage is reduced, contrast is improved, and charging from irregularly shaped features (which may be unevenly coated) is reduced or eliminated. Imaging uncoated polymers in LVSEM allows observation of the surface with little or no charging and with no alterations of surface features from the metal coating process required for higher voltage imaging. This is particularly important for high resolution (HR) studies of polymers where it is desired to image features 1 to 10 nm in size. Metal sputter coating techniques produce a 10 - 20 nm film that has its own texture which can obscure topographical features of the original polymer surface. In examining uncoated insulating samples at low voltages the effect of sample-beam interactions on image formation and resolution will differ significantly from the effect at higher accelerating voltages. In this study we discuss the nature of sample-beam interactions in uncoated polymers at low voltages and also present results on HRSEM of polymer samples which show some of these effects.
Characterization of machined polystyrene foam
Authors: Price C. W. , Lindsey E. F. , Franks R. M. , Lane M. A.
Published: June 2020

Diamond-point turning is an efficient technique for machining low-density polystyrene foam, and the surface finish can be substantially improved by grinding. However, both diamond-point turning and grinding tend to tear and fracture cell walls and leave asperities formed by agglomerations of fragmented cell walls. Vibratoming is proving to be an excellent technique to form planar surfaces in polystyrene, and the machining characteristics of vibratoming and diamond-point turning are compared.

Our work has demonstrated that proper evaluation of surface structures in low density polystyrene foam requires stereoscopic examinations; tilts of + and − 3 1/2 degrees were used for the stereo pairs. Coating does not seriously distort low-density polystyrene foam. Therefore, the specimens were gold-palladium coated and examined in a Hitachi S-800 FESEM at 5 kV.
Fine structure of inner shell electron energy loss edges of manganese oxides
Authors: Paterson James H. , Krivanek Ondrej L. , Poppa Helmut R.
Published: June 2020

Rask et al. showed that electron energy loss spectroscopy (EELS) may be used to identify oxidation states of polyvalent cations. For the case of manganese, differences in oxidation state are reflected in the shape and position of the edges in the EELS spectrum due to inelastic scattering of incident electrons by the inner shells of manganese and oxygen. We have used a scanning transmission electron microscope (STEM) with a cold field emission gun (FEG) and a parallel-detection EELS system to re-investigate the variations in energy loss fine structure of EELS spectra of various manganese oxides with a significantly improved energy resolution.

Spectra were recorded at 100 kV using a VG HB501 STEM with post-specimen lenses, and a Galan Model 666 parallel-detection electron energy loss spectrometer. The operation and performance of this system are discussed elsewhere in these proceedings. For the inner shell edges, the energy dispersion produced by the spectrometer was set to give 0.05 eV per channel. so that a complete spectrum of 1024 channels sampled a range of energy loss of 50 eV. The energy resolution, of the order of 0.4 eV, was therefore not limited by the spatial resolution of the photodiode array in the spectrometer. The oxygen K and manganese L2,3 edges were recorded separately.
Electron energy loss spectroscopy of nanometer-sized Cr crystallites in MgO single crystals
Authors: Tanaka N. , Mihama K. , Graham R. J. , Weiss J. K. , Cowley J. M.
Published: June 2020

Conposite films including nanometer-sized metal crystallites and atomic clusters in ceramics or insulators are currently of great interest from the points of view of basic science and technology. We have developed new single crystalline composite films of magnesium oxide(MgO) and nanometer-sized metal crystallites. The crystalline structures were studied in detail by HREM and nanometer-area diffraction. In the present study, electron energy loss spectroscopy(EELS) of Chromium(Cr)-MgO composite films was performed to study the oxidation state of the Cr crystallites in the MgO matrix.

Preparation methods of the composite films were described in detail in a previous paper. Cr and MgO were simultaneously deposited on a (001) cleaved surface of sodium chloride in UHV conditions of 10−6 Pa, the mean thickness of Cr and MgO being 3 nm and 30 nm, respectively. The composite films were separated from the substrate in water and mounted on a perforated carbon film. The EELS was carried out at 100 kV by using an electron microscope with a field emission gun (Philips FEG 400ST) equipped with a parallel detection spectrometer (Gatan 666).
Electron spectroscopic imaging and analysis of electron energy loss spectra with an energy filtering Electron Microscope
Authors: Godleski John J. , Stearns Rebecca C. , Millet Emil J.
Published: June 2020

The Zeiss CEM902, energy filtering electron microscope, can be used to image the structure of unstained 30 nm sections of biologic materials, to image the distribution of selected elements in such sections, and to determine electron energy loss spectra (EELS) of elements in areas as small as 10 nm. Although the integrated computer in the latest version of the CEM902 can collect and display signals from the scintillation detector for recording EELS, our instrument did not have this capability. Therefore, we have added a Leading Edge Model D personal computer with a 20 Mbyte hard disk, Hercules compatible graphics display adapter, and a programmable gain analog to digital converter board (Metrabyte DAS16-G1) to collect and analyze voltage signals corresponding to changes in accelerating voltage and changes in the signal from the photomultiplier tube (PMT) of the scintillation detector. With this board, the gain on the PMT channel is dynamically adjusted for optimal resolution. Software is designed to monitor and display voltages, store data on the hard disk, display spectra with adjustable axes, as well as subtract spectra and determine areas beneath regions of interest.

Canine alveolar macrophages with ingested cobalt oxide particles were fixed with 2.5% glutaraldehyde in 0.164M phosphate buffer, post-fixed in 1% OsO4 in 0.lM Na cacodylate buffer, dehydrated through alcohols, embedded in araldite, and sectioned at 30nm. Sections were assessed with our CEM902 as described above. The spectral range of 500 to 900 electron volts while focused on acobalt oxide particle at 20,000x is illustrated in Figure 1 .
Microstructure of sputter deposited Ni-Sb ohmic contacts on GaAs
Authors: Yegnasubramanian S. , Kannan V.C. , Dutto R. , Sakach P.J.
Published: June 2020

Recent developments in the fabrication of high performance GaAs devices impose crucial requirements of low resistance ohmic contacts with excellent contact properties such as, thermal stability, contact resistivity, contact depth, Schottky barrier height etc. The nature of the interface plays an important role in the stability of the contacts due to problems associated with interdiffusion and compound formation at the interface during device fabrication. Contacts of pure metal thin films on GaAs are not desirable due to the presence of the native oxide and surface defects at the interface. Nickel has been used as a contact metal on GaAs and has been found to be reactive at low temperatures. Formation Of Ni2 GaAs at 200 - 350C is reported and is found to grow epitaxially on (001) and on (111) GaAs, but is shown to be unstable at 450C. This paper reports the investigations carried out to understand the microstructure, nature of the interface and composition of sputter deposited and annealed (at different temperatures) Ni-Sb ohmic contacts on GaAs by TEM. Attempts were made to correlate the electrical properties of the films such as the sheet resistance and contact resistance, with the microstructure. The observations are corroborated by Scanning Auger Microprobe (SAM) investigations.
HRTEM simulation of interfacial structure in amorphous multilayers
Authors: Sattler Margaret L. , O'Keefe Michael A.
Published: June 2020

Multilayered materials have been fabricated with such high perfection that individual layers having two atoms deep are possible. Characterization of the interfaces between these multilayers is achieved by high resolution electron microscopy and Figure 1a shows the cross-section of one type of multilayer. The production of such an image with atomically smooth interfaces depends upon certain factors which are not always reliable. For example, diffusion at the interface may produce complex interlayers which are important to the properties of the multilayers but which are difficult to observe. Similarly, anomalous conditions of imaging or of fabrication may occur which produce images having similar traits as the diffusion case above, e.g., imaging on a tilted/bent multilayer sample (Figure 1b) or deposition upon an unaligned substrate (Figure 1c). It is the purpose of this study to simulate the image of the perfect multilayer interface and to compare with simulated images having these anomalies.
On the determination of enanttomorphs from non-systematic many-beam effects in CBED patterns
Authors: Marthinsen K. , Høier R.
Published: June 2020

A convergent beam electron diffraction (CBED) method which makes it possible to determine structure factor magnitudes and phases with high accuracy has recently been suggested. It is based on detailed simulations of non-systematic many-beam diffraction effects in the disks. Basis for the phase determination is an asymmetry which may appear in a line h with respect to the Bragg condition of the coupled reflection g near a three-beam condition. Approximate analytical three-beam solutions show that the sign and size of this asymmetry depends on the structure factor phases Θh of the reflections h involved through a term cos(Φ) where Φ is the three phase structure invariant, Φ = Θh + Θg + Θh-g. The magnitude of the phase invariant is thus in principle available, but not the sign. The aim of the present work has been to discuss the origin of the sign problem and the possibilities of distinguishing +/−Φ.
Bonding charge densities of Al and Cu determined by electron diffraction
Authors: Fox A.G. , Tabbernor M.A. , Fisher R.M.
Published: June 2020

As discussed by Zuo et al, the small magnitude of the energy which determines a crystal's structure has long provided a severe challenge for both theoreticians and experimentalists who have attempted to accurately calculate and measure the crystal structure factors of many materials. In particular the f.c.c. elements copper and aluminum have received considerable attention both theoretically and experimentally, where attempts have been made to accurately measure the atomic scattering (form) factors by a variety of means other than the traditionally inaccurate X-ray diffraction methods. Smart and Humphreys recognized that the accuracy of the low-angle form factors of Cu and Al determined by the critical voltage effect (Vc) in electron diffraction should be good enough to give bonding information about these two elements. Unfortunately, they failed to analyze the problem of the higher angle form factors correctly, and thus produced erroneous deformation charge density maps.
Symmetry relationship in electron beam induced phase transitions
Authors: Zhang J. P. , Marks L. D.
Published: June 2020

In this work we present a symmetry rule for the phase transitions in transition metal oxides driven by DIET of oxygen in an electron microscope. The phase transitions are to a structure with a higher point group symmetry. The new phase with a lower oxygen content is either one with a supergroup symmetry with respect to the original phase, or an amorphous intermediary. If a possible lower oxygen content phase does not have the correct supergroup symmetry, it is not formed. Of this type are the phase transitions in TiO2, MoO3, WO3, V2O5 and Ta2o5 of which the experimental results are listed in the first section of Table 1. It is also found that the point group is conserved during the phase transition if the oxide belongs to the highest groups Oh or D6h, for instance NiO, CoO and ZnO. This symmetry selection rule can therefore be used to predict the route of the phase transition. The selection rule is:
Metastable ordered austenite in rapidly solidified Fe-Al-C alloys
Authors: Sarreal J. A.
Published: June 2020

Conventionally cast Fe-Al-C alloys are extremely brittle containing combinations of ferrite, carbide and other phases. Rapid solidification has the potential of altering the microstructure to subsequently change the resulting mechanical properties. An apparent conflict exist concerning the effect of rapid solidification on the resulting microstructure of these alloys. Inoue and co-workers, using transmission electron microscopy (TEM) and electron diffraction analyses, reported the presence of several non-equilibrium phases including austenite (fcc - γ) and ordered austenite (Ll2-γ') structures on alloys containing 1.7 to 2.1 C and 6 to 12 Al in weight % (w/o) on melt spun ribbons 30 μm in thickness. Han and Choo, using x-ray diffraction analysis on 30-48 μm thick melt spun ribbons concluded that this ordered fee phase is rather an austenitic phase in which phase decomposition accompanied by sideband phenomenon had occured.

Single roller melt spinning technique was used to make ribbons 35-70 μm thick and 0.5-5 mm wide. X-ray diffration analysis showed single phase austenite for samples 2-6 w/o AI and 2 w/o C. Samples with 8-10 w/o AI and 2 w/o C also showed several superlattice lines in addition to the fundamental fcc peaks.
A novel technique for studying interface abruptness in a STEM
Authors: Gajdardziska-Josifovska M. , Cowley J. M.
Published: June 2020

The distribution of the electric charges in a solid is such that the volume average of the electrostatic potential, known as the mean inner potential, is positive of the order of a few volts. Incident electrons are accelerated at the surface of the material and noticeable refraction occurs at glancing angles of incidence. At an interface between two materials, a refraction effect may also occur because of the difference in their mean inner potentials. This effect has recently been observed and gives rise to a faint streaking in the spots of a selected area diffraction pattern. Low-angle dark-field images formed with the streak on the undiffracted beam show the interface region as a bright line. We have observed the same effect in a field emission STEM on the interface of polycrystalline Mo and amorphous Si. A preliminary study suggests that this technique can give information on the abruptness of interfaces.
SREM imaging of copper (110) vicinal surfaces
Authors: Liu J. , Cowley J. M.
Published: June 2020

Scanning reflection electron imaging technique is sensitive to surface perturbations at nano-meter scale. Single atom high steps and defects on crystal surfaces can be observed with high contrast. Microanalysis of surface areas can be performed to study surface reaction problems. One advantage of SREM over conventional REM imaging is that by changing the objective lens current synchronously with the frame speed one can manage to keep more of the scanned areas in focus. This dynamic focusing is important for observing less flat surfaces such as the vicinal surface areas. We take this advantage to study the copper (110) vicinal surface structures by SREM technique. All the SREM images reported here are obtained with dynamic focusing conpensation. RHEED study of clean and oxygen adsorbed copper surfaces revealed that most of the vicinal surfaces will be faceted upon oxygen adsorption. Real space observations of these faceted surface areas by SREM imaging may yield some information about the vicinal surface structures with high resolution. The copper surfaces were obtained by melting copper wire in air with careful control to reduce high temperature oxidations on Ihe crystal surfaces. Reasonably flat copper crystal surfaces can be obtained by this preparation method and some of the surface areas are oxidized. The experiment was performed in a VG HB5 STEM instrument with a probe size of about 0.5 nm in diameter and a vacuum pressure of about 5×10-9 Torr.
Microstructural characterization of plasma-processed Ti-Al metal matrix composites
Authors: Burke M. G. , Gungor M. N. , Burke M. A.
Published: June 2020

Intermetallic matrix composites are candidates for ultrahigh temperature service when light weight and high temperature strength and stiffness are required. Recent efforts to produce intermetallic matrix composites have focused on the titanium aluminide (TiAl) system with various ceramic reinforcements. In order to optimize the composition and processing of these composites it is necessary to evaluate the range of structures that can be produced in these materials and to identify the characteristics of the optimum structures. Normally, TiAl materials are difficult to process and, thus, examination of a suitable range of structures would not be feasible. However, plasma processing offers a novel method for producing composites from difficult to process component materials. By melting one or more of the component materials in a plasma and controlling deposition onto a cooled substrate, a range of structures can be produced and the method is highly suited to examining experimental composite systems. Moreover, because plasma processing involves rapid melting and very rapid cooling can be induced in the deposited composite, it is expected that processing method can avoid some of the problems, such as interfacial degradation, that are associated with the relatively long time, high temperature exposures that are induced by conventional processing methods.