bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of mesoscopic structures by co-assembly
Authors: McGehee M. D. , Gruner S. M. , Yao N. , Chun C. M. , Navrotsky A. , Aksay I. A.
Published: June 2020

Synthesis of materials with nanoscale (1-100 nm) organization is of utmost importance in various applications. Recently, scientists at Mobil described a surfactant-based procedure which yields mesoporous silicate/aluminosilicate materials with pores up to 10 nm in size and lamellar, hexagonal, and bicontinuous cubic structures. Two models were proposed to explain the formation of these materials. The first model assumes that silica polymerizes around a water-surfactant liquid crystal phase while the second model contends that the polymerization of the silica determines the ordering of the surfactants in a co-assembly fashion. Our time-resolved x-ray diffraction studies show that transitions between structures occur during synthesis, supporting the co-assembly model.

The procedure for synthesizing cubic surfactant-silicates was as follows: 10.41 g of TEOS (tetraethoxy silane, Alpha Chemicals) was added to 35.86 g of Arquad (29% by weight C16TMAC1 in water, Akzo Chemicals), 25 ml of 1M NaOH, and 5.34 mL of deionized water. This mixture was stirred for 30 min with a magnetic stir bar, causing the TEOS to disperse with the surfactant solution and hydrolyze.
X-ray image compression: 16 bit counts into 8 bit space
Authors: Engle P. D. , Herrington C. R. , Geller J. D.
Published: June 2020

One way to improve upon the detection limits for digital images involves increasing the number of counts per pixel. Eight bits, or 1 byte (256 counts), per pixel is most commonly used for monochrome optical, electron and x-ray imaging. This number is well matched to the human eye which can discern approximately 128 gray values, while photographic and some laser printer outputs have the capability of displaying nearly 256 gray values. When the counts exceed 8 bits/pixel the recorded image file size will likely double to 16 bits/pixel.With the better imaging detection limits we are faced with the technical problem of how to view more than 256 gray levels. One solution to both problems is to store and display the square root of the image intensity. While the compressed data cannot be reconstructed exactly to match the original numbers it will be shown that no statistically significant data will be lost.This compression scheme reduces storage requirements by eliminating the statistical variations in the data. The square root display of the data into 256 levels also enhances low concentration visibility since the brightness change per gray level is greatest at low concentrations.
Rotating specimen stage for angle-indexed videotape microscopy of automotive water-pump seals and ring-shaped specimens
Authors: Laurion Tristan A. , Dolson Richard L.
Published: June 2020

Videocameras and electronic image storage devices have given new vigor and potential to optical microscopy and parts inspection, as well as a powerful means of recording microscopic motion in live-time biological studies. Video and electronic techniques permit fast exploratory examinations simultaneous with extensive archiving, and allow the option of deferring hard copy printing to the time when reports may be needed. These capabilities aid in improving the quality of scanning electron microscopy (SEM) and other analyses that may follow and have great value in communicating with the customer.

Our modular system was conceived to permit the imaging of the entire surface of ring-type objects as well to certify that features later characterized in more detail by SEM have been well chosen. The system uses the Nikon SMZ-U optical microscope equipped with a current technology video camera used in combination with a commercial frame grabber device, a dye transfer printer, and VHS videotape recorder.
Compact back-scattered electrons' energy analyzer for standard SEM
Authors: Likharev S. , Kramarenko A. , Vybornov V.
Published: June 2020

At present time the interest is growing considerably for theoretical and experimental analysis of back-scattered electrons (BSE) energy spectra. It was discovered that a special angle and energy nitration of BSE flow could be used for increasing a spatial resolution of BSE mode, sample topography investigations and for layer-by layer visualizing of a depth structure. In the last case it was shown theoretically that in order to obtain suitable depth resolution it is necessary to select a part of BSE flow with the directions of velocities close to inverse to the primary beam and energies within a small window in the high-energy part of the whole spectrum.

A wide range of such devices has been developed earlier, but all of them have considerable demerit: they can hardly be used with a standard SEM due to the necessity of sufficient SEM modifications like installation of large accessories in or out SEM chamber, mounting of specialized detector systems, input wires for high voltage supply, screening a primary beam from additional electromagnetic field, etc. In this report we present a new scheme of a compact BSE energy analyzer that is free of imperfections mentioned above.
The application of electronspectroscopic imaging (ESI) in biological studies
Authors: Wei Sheng Jun , Smith Nancy R.
Published: June 2020

Electronspectroscopic imaging (ESI) offers a means of filtered imaging of specimens resulting in high resolution and depth of field with optimum constrast. Using an integrated imaging electron energy spectrometer (integrated prism/mirror/prism) in a Zeiss-902A transmission electron microscope (TEM), it is possible to select unscattered electrons (ΔE=OeV) or inelastically scattered electrons (ΔE>OeV) to observe biological structures of interest. The contrast in biological specimens is enhanced bythis technique and unstained, ultrathin sections and thick sections can be imaged with optimum contrast and high resolution. This technology can solve many of the problems encountered with staining biological samples (e.g. precipitates or poor contrast) and has proven to be superior to the conventional TEM (CTEM) in many aspects. Virus particles in cultured cells are clearly observed without post-staining. Unstained lipsome and other drug delivery systems can be viewed and measured without negative staining and subsequent deformation and as a result, more accurate sizing information can be obtained. Granules and enzyme reacted precipitates inside unstained cells and tissues can also be observed without staining. Sections that are stained yield finer details than those imaged by CTEM. Figures 1 through 8 obtained with the Zeiss-902A show the quality of ESI and the advantages of using this system of imaging biological specimens.
A new approach to the study of solid-state reactions in oxide ceramics
Authors: Kotula Paul G.
Published: June 2020

Thin-film reactions have potential applications for the production of buffer layers in heterojunctions and for the reaction bonding of materials. The main drawback to these applications at present isthat the effect of interface morphology on the initial kinetics of solid-state reactions is not well understood. In order to study the kinetics and mechanisms of thin-film reactions in oxide ceramics, a new method has been developed. The approach relies on the production of a well characterized high-quality oxide thin film on a single-crystal oxide substrate which makes up the idealized reaction couple-a ‘single-crystal’ thin film in intimate contact with a single crystal substrate. The thin-film approach localizes the reaction near the surface of the specimen so that conventional cross-sectioning techniques can be utilized. Additionally, the scale of the reaction is of the order of tens of nanometers or less which is ideally suited to high-resolution SEM or conventional TEM.

NiO/α-Al2O3is a model system for the study of solid-state reactions.
Electron holography of ferroelectric materials
Authors: Joy David. C. , Zhang Xiao
Published: June 2020

Electron holography gives to the electron microscope the ability the visualize, and measure, electric and magnetic fields at high spatial resolution . The principle of the method is shown in figure (1). Some fraction of a coherent electron beam, typically produced from a cold field emission electron gun, is incident on the specimen while the rest passes through vacuum, or through some other region of the sample, to form a reference wave. An electrostatic bi-prism converges these two components to form an interferogram or ‘hologram’ at the viewing screen. The hologram consists of a fringe pattern, with a spacing determined by the potential on the bi-prism, modulated by the intensity variations of the transmitted bright-field signal. Variations in the phase of the transmitted signal are stored as shifts in the fringe pattern. The hologram can then be reconstructed, either optically or by using a computer and appropriate software, to yield two images, one - the 'Amplitude Image' - containing normal intensity contrast (bright field) information, and a second- the 'Phase Image'- which displays variations in the relative phase of the signal as changes in grey level. The phase of the transmitted beam will be shifted by an amount proportional to the mean inner potential of the specimen multiplied by the thickness, and also by the potential that the electron encounters as it travels through the sample.
Applications of electron holography to ferromagnetic and superconductive materials
Authors: Tonomura Akira.
Published: June 2020

Electromagnetic fields are not observable with conventional electron microscopy: The fields deflect an incident electron beam but no contrast is produced in the electron micrograph for the fields since all the electrons deflected at an object point are focused into a single image point through the electron lens. The information about the electomagnetic fields is included in the deflection distribution or the phase distribution of an electron beam, which is lost in electron micrographs. Electron interferometry has been carried out since 1950s using a transmission electron microscope equipped with an electron biprism to make ultra-fine measurements. The advent of a "coherent" field-emission electron beam has greatly expanded the range of applications and possibilities: Electric and magnetic fields are directly observed as equipotential lines and magnetic lines of force in an electron-holographic interference micrograph. Precision in phase measurement has increased to 2π/50 thanks to a phase amplification technique peculiar to holography.

In magnetic field observation, contour fringes in an interference micrograph directly indicate projected magnetic lines of force in h/e flux units. An example of a magnetic field micrograph is shown in Fig. 1.
HREM study of ferroelectric domain wall in barium titanate
Authors: Normand Laurent. , Thorel Alain. , Montardi Yvan.
Published: June 2020

This study focuses on High Resolution Transmission Electron Microscopy of barium titanate in its tetragonal ferroelectric phase, and especially on the structure of domain walls. This phase is stable between about 0 °C and 130 °C. During cooling, at 130 °C barium titanate changes from a cubic parraelectric phase to a tetragonal ferroelectric phase. In this phase the spontaneous polarisation is along one of the six [001] pseudo-cubic directions. Two types of domains can be formed during the phase transition :90° and 180° domains. In 90° domains the polarisation is at 90° from the polarisation of the next domain (exactly 2* ArcTan(a/c) if a and c are the lattice parameters). For these domains the domain walls are <110< type planes ; In 180° domains the polarisation is at 180° from the one in the next domain. 180° domain walls are <100< type plane and are assumed to be purely ferroelectric.
The role of excess Pb and PbO overpressure on the microstructural development in polycrystalline PZT thin films
Authors: Lefevre M. J. , Dimos D. B. , Speck J. S.
Published: June 2020

Ferroelectric thin films have recently received considerable attention because of their potential in a range of device applications including both volatile and non-volatile memories, optical data storage, and other electrooptic applications (e.g. waveguides, switches, and modulators). The Pb-based perovskites, such as Pb(Zr,Ti)O3, have many properties that make them attractive for such applications because of their high switchable remanant polarization. In addition, many applications require integration of the ferroelectric with semiconductors. In our work we are studying the crystallization sequence of PZT 40/60 (PbZr0.40Ti0.60O3) grown on platinized silicon substrates, with an overall structure given as PZT/Pt/Ti/SiO2Si. The Ti and Pt are sequentially evaporated onto the oxidized Si substrate. Alkoxide-derived films are spun onto these substrates to form a dry amorphous gel2. The crystallization of the sol-gel film proceeds upon heating to temperatures in the range of 400-700°C. Lead volatility is one of the critical issues in the crystallization of Pb-based perovskite thin films. We have carried out a systematic study on the role of a lead atmosphere in crystallization for PZT (40/60). When heat treated the film forms a transitory pyrochlore phase at intermediate temperatures before transforming to the perovskite phase. This non-ferroelectric pyrochlore phase may stabilize if lead stoichiometry is not maintained, leading to poor optical and ferroelectric properties in the thin films.
In situ TEM crystallization of sol-gel derived BaTiO3 thin films
Authors: Mecartney Martha L. , Gust M. C. , Evans N. D.
Published: June 2020

BaTiO3 thin films made by the sol-gel process require a crystallization heat treatment to transform the amorphous gel into a crystalline material. This work used a Ba-Ti methoxypropoxide precursor in a 0.25M solution of methoxypropanol which was spin coated as 5 (each -600 nm thick) layers on (100) Si (FIG. 1). The {100} planes of perovskite BaTiO3 have a good lattice match with {110} Si; d110 of Si = 0.38 nm, and d100 of BaTiO3 = 0.4 nm. Consequently, it should be possible to grow heteroepitaxial films of (100) BaTiO3 on (100) Si. Such samples pyrolized at 350.C and then annealed in a conventional furnace at 750°C for one hour, however, did not crystallize heteroepitaxially with the substrate. Rather, crystallization occurred by a nucleation and growth process from within the gel. Furthermore, the gel layer at the Si/BaTiO3 interface remained amorphous. In-situ hot stage experiments were conducted in a transmission electron microscope (TEM) to determine the nucleation and crystallization behavior.
Automatic idexing of electron-backscatter diffraction patterns
Authors: Wright S. I.
Published: June 2020

A typical Backscatter Kikuchi Diffraction pattern (BKD, also referred to in the literature as an EBSP or a BEKP) is shown in figure 1. Since the bands in the pattern represent planes in the diffracting volume, the lattice orientation can be determined from their geometrical arrangement. The task of correctly orienting a BKD can be broken into two parts: 1) finding the salient features in the pattern (either the diffraction bands or the intersections of the bands) and 2) using these features to determine the lattice orientation. Recent advances in feature detection in BKDs along with methods for digital image enhancement will be described in some detail. The determination of orientation from a set of detected bands (or intersections of bands) will also be discussed.

Dingley has demonstrated that lattice orientation can be practically obtained from BKDs by imaging the diffraction patterns using a low light level video camera and indexing the patterns with the aid of an online computer.
Slip traces caused by plastic deformation during recrystallization of thin metal sheets
Authors: Lin H. , Pope D. P.
Published: June 2020

During a study of mechanical properties of recrystallized B-free Ni3Al single crystals, regularly spaced parallel traces within individual grains were discovered on the surfaces of thin recrystallized sheets, see Fig. 1. They appeared to be slip traces, but since we could not find similar observations in the literature, a series of experiments was performed to identify them. We will refer to them “traces”, because they contain some, if not all, of the properties of slip traces. A variety of techniques, including the Electron Backscattering Pattern (EBSP) method, was used to ascertain the composition, geometry, and crystallography of these traces. The effect of sample thickness on their formation was also investigated.

In summary, these traces on the surface of recrystallized Ni3Al have the following properties:

1.

The chemistry and crystallographic orientation of the traces are the same as the bulk. No oxides or other second phases were observed.

2.

The traces are not grooves caused by thermal etching at previous locations of grain boundaries.

3.

The traces form after recrystallization (because the starting Ni3Al is a single crystal).

4.

For thicknesses between 50 μm and 720 μm, the density of the traces increases as the sample thickness decreases. Only one set of “protrusion-like” traces is visible in a given grain on the thicker samples, but multiple sets of “cliff-like” traces are visible on the thinner ones (See Fig. 1 and Fig. 2).

5.

They are linear and parallel to the traces of {111} planes on the surface, see Fig. 3.

6.

Some of the traces terminate within the interior of the grains, and the rest of them either terminate at or are continuous across grain boundaries. The portion of latter increases with decreasing thickness.

7.

The grain size decreases with decreasing thickness, the decrease is more pronounced when the grain size is comparable with the thickness, Fig. 4.

8.

Traces also formed during the recrystallization of cold-rolled polycrystalline Cu thin sheets, Fig. 5.
High-resolution Transmission Electron Microscopy studies of microstructures in blended cement pastes
Authors: Lu Yun , Joy D.C.
Published: June 2020

In providing high resolution analysis of morphology, composition and crystal structure in cement-based pastes, TEM has played an important role and some essential features of the materials have been observed. Because of both improved properties and economic advantages, blended cement materials have been widely developed. However, there is relatively little report with respect to the microstructures in the blended systems containing more than two source materials. In an effort to derive a more complete picture of structural development in hydration products of blended grouts and to have a better understanding of effects of source materials on the resulting products, we applied TEM/EDXA techniques to study the microstructures of cement/fly-ash/slag/limestone blended grout samples. Four starting materials and hydrating products were evaluated. The grout samples at various hydration stages were quenched into acetone solution to stop the hydration reaction. The thin sections for TEM/EDXA were prepared by using an ultramicrotome thinning technique.
Effect of alloy grain size on oxidation resistance of silica-coated stainless steel
Authors: McDowell C. S. , Basu S. N.
Published: June 2020

Oxidation resistance of stainless steels, which rely on the formation of a Cr2O3 (chromia) scale, can be further improved through minor alloying additions such as Al or Si, or by application of coatings to the exposed surfaces. Although, additions of Si to austenitic steels have demonstrated an improvement in oxidation resistance, high Si contents can be detrimental to the mechanical properties of these alloys. The application of a silica coating on the surface of the stainless steel provides improved oxidation resistance without detrimental effects on the mechanical properties. This study examines the effect of the grain size of the stainless steel on the effectiveness of a silica coating as an oxidation barrier.

Fully austenitic stainless steel of composition Fe-18(wt%)Cr-20Ni-1.5Mn was produced in both coarsegrained and fine-grained form. The coarse-grained alloy, with a grain size of approximately 100 μm, was produced by casting and hot rolling. The fine-grained alloy, with a grain size of approximately 5 μm, was produced by rapid solidification powder processing, followed by consolidated by hot isostatic pressing and swaging.
Nano-probe x-ray analysis and high-resolution imaging on planar defects in high-pressure synthesized infinite-layer superconductor
Authors: Wang Y. Y. , Zhang H. , Dravid V. P. , Zhang H. , Marks L. D. , Han P. , Payne D. A.
Published: June 2020

Azuma et al. observed planar defects in a high pressure synthesized infinitelayer compound (i.e. ACuO2 (A=cation)), which exhibits superconductivity at ~110 K. It was proposed that the defects are cation deficient and that the superconductivity in this material is related to the planar defects. In this report, we present quantitative analysis of the planar defects utilizing nanometer probe xray microanalysis, high resolution electron microscopy, and image simulation to determine the chemical composition and atomic structure of the planar defects. We propose an atomic structure model for the planar defects.

Infinite-layer samples with the nominal chemical formula, (Sr1-xCax)yCuO2 (x=0.3; y=0.9,1.0,1.1), were prepared using solid state synthesized low pressure forms of (Sr1-xCax)CuO2 with additions of CuO or (Sr1-xCax)2CuO3, followed by a high pressure treatment.

Quantitative x-ray microanalysis, with a 1 nm probe, was performed using a cold field emission gun TEM (Hitachi HF-2000) equipped with an Oxford Pentafet thin-window x-ray detector. The probe was positioned on the planar defects, which has a 0.74 nm width, and x-ray emission spectra from the defects were compared with those obtained from vicinity regions.
Transmission Electron Microscopy of Pb-doped Bi2Sr2Ca2Cu30x /Ag composite conductors prepared by the two-powder process: The effect of lead addition on critical current and microstructure
Authors: Luo J. S. , Dorris S. E. , Lanagan M. T. , Maroni V. A.
Published: June 2020

Recent studies indicate that a more uniform and more fully reacted Pb-doped Bi2Sr2Ca2Cu3Ox (Bi-2223)phase can be reproducibly obtained within silver sheaths using a two-powder precursor in which the formation of Bi-2223 primarily involves reaction between lead-doped Bi2Sr2CaCu2Oz (Bi-2212) and other non-superconducting phases. In particular, the specific method of introducing lead was reported to significantly influence the phase evolution and superconducting properties of Bi-2223/Ag composite conductors.2 Composites made from lead-doped Bi-2212, where lead is fully incorporated into the Bi-2212 phase prior to its conversion to Bi-2223, exhibit sharper transition temperatures and higher critical current densities than those where lead is added in the form of non-superconducting PbO or Ca2PbO4 phases (Fig. I).2 In this paper, we present a combined investigation by transmission electron microscopy(TEM) and energy dispersive x-ray spectroscopy (EDX) of the composition and microstructure of the (Bi-2223)/Ag composite conductors. The observed differences are discussed with respect to the measured electrical properties.
Surface morphology change induced by bulk order-disorder transition in Cu3Au alloy
Authors: Huang Y. , Gajdardziska-Josifovska M. , Cowley J. M.
Published: June 2020

In recent years the surfaces of Cu3Au, a typical ordering alloy, have attracted interest from many aulhors[l-6], because the surface is a good example for testing general theories of the 2-D order-disorder phase transition, and also because it is a good material for studying the behavior of bimetallic alloy surfaces and their reactions with surface impurities. Previous work on Cu3Au surface mostly used macroscopic techniques and provided only information averaged over a largearea. In this work the microscopic imaging and diffraction methods are used to study the (111) surface on a more localized scale. Reflection Electron Microscopy (REM) was used to directly image the surface, and the selected-area RHEED was used to determine the local surface crystal structure and orientation.

The samples used for observation are single crystal spheres prepared by melting a small piece of Cu3Au suspended on a thin Mo wire. The actual compositions of the samples are about Cu0.7Au0.3. The (111) facets on these spheres were then cleaned by the conventional ion-milling-heating method in a UHV environment.
Shadow imaging of surface topography of oxide thick films in the SEM
Authors: Baba-Kishi K. Z.
Published: June 2020

The method of shadow imaging with diffusely scattered electrons in a conventional scanning electron microscope (SEM) has been used to image surface topography of TiO2 and Pb0.88La0.08(Zr0.70Ti0.30)O3 (PLZT) oxide thick films. To produce a shadow image, a simple detector system was used. Figure 1 shows the imaging system, which comprises a phosphor screen, a detector aperture, a YAG scintillator, afibre optic rod and a photomultiplier. The entire system is mounted on a purpose-built stage, which fits into the SEM through a spare port and allows both the azimuth and translational movements of the specimen. The specimen is oriented at the grazing angle of about 3° relative to the electron beam. Toform a shadow image, diffusely scattered electrons are passed through the detector aperture, whose diameter is about 0.5mm. The phosphor which has a small hole at its centre and is aligned with both thedetector aperture and the scintillator, is used to select the brightest part of the scattered electrons, which is found close to the specimen shadow edge. Backscattered diffracted and secondary electrons may also enter through the detector aperture, but their intensities are too weak compared with the intensity of diffusely scattered electrons to form shadow images. Lowloss electrons may contribute to shadow image formation, but their role has not yet been established.
Reflection electron microscopy (REM) of NaCl crystals
Authors: Hsu Tung
Published: June 2020

NaCl and other alkaline halide crystals are unstable under the electron beam and therefore have seldom been examined with the various electron beam techniques. Surfaces of these crystals, however, are of fundamental and application interests. There has been a considerable effort in studying these surfaces using the replica methods.

Reflection high energy electron diffraction (RHEED) and reflection electron microscopy (REM) have been successfully applied to the study of stable insulators. Since direct observation on an uncoated surface is always desirable, we tried RHEED and REM on cleaved NaCl(100) surfaces.

The experiment was carried out on a JEOL JEM-200CX electron microscope with a high tilt side-entrystage. The accelerating voltage of lOOkV was used throughout the experiment. There is no special protection to the specimen except the standard anti-contamination cold finger. The initial effort of doing ordinary REM on NaCl was a failure: When the electron beam and the specimen were properly tilted toget a good RHEED pattern, the bright pattern remained for only a couple of seconds and then turned into a pattern of weak spots and high diffuse background. The bright REM image also lost its contrast in a few seconds.
Auger and TEM analysis of multilayer IC contacts
Authors: Buttry R. W. , Hills C. R. , Nelson G. C. , Tribble T.
Published: June 2020

With the continued shrinkage of the dimensions (both laterally and in depth) of integrated circuits (IC), knowledge of the interactions that occur over nanometer scale distances becomes increasingly important. This requirement has pushed the capabilities of the tools used to analyze these structuresto their maximum. Two techniques which are frequently used to analyze thin layer structures are AugerElectron Spectroscopy (AES) and Transmission Electron Microscopy (TEM).

AES combined with ion beam sputtering is used to measure the elemental composition as a function of sputter time. With suitable calibration, the sputter time scale can be converted to a depth scale. Theprofiles can also be used to study the interfacial reactions for thin layers. TEM is frequently used to accurately measure layer thicknesses and the layer elemental constituents can be identified byEnergy Dispersive Spectroscopy (EDS). When the layer thicknesses approach a few tens of A there are problems associated with interpreting the data from both of these techniques, particularly the data obtained near the interfaces.
Structural and chemical analysis of Pd-Ge ohmic contacts to epitaxially lifted-off GaAs
Authors: Rajesh R. , Liu J. , Fathollahnejad H. , Carpenter R. W. , Maracas G. N.
Published: June 2020

For the past decade, there has been considerable focus on low resistance Pd-Ge ohmic contacts to GaAs. One approach toward achieving thermodynamically stable ohmic contacts is to consider solid-phasereactions for contacts, rather than the liquid phase interactions that occur upon ohmic alloying of Au-Ge-based systems. The two classifications to this approach are: low temperature annealing (<500°C), mainly using Pd, and high temperature annealing (<500°C), mainly using In. The low temperature annealing class is more compatible with existing GaAs technology, hence the attention to Pd-based systems, particularly Pd-Ge. There has also been tremendous interest in hybrid GaAs-on-Si technology. As an alternative to direct lattice-mismatched growth of GaAs on Si, the epitaxial lift-off (ELO) technique has been used, wherein GaAs devices grown on GaAs substrates can be removed and bonded to any substrate regardless of orientation and/or lattice matching criteria. This process yields high quality dislocation-free GaAs-based devices for hybrid applications.

In this study, we demonstrate a low resistance non-alloyed Pd-Ge ohmic contact to epitaxialiy lifted-off n-type GaAs.
Quantitative footprints, in size & number density, of a TEM search for defects in VLSI silicon
Authors: Siriwardane H. , Fraundorf P.
Published: June 2020

Electron (and scanning tip) microscopes permit the study of objects over a wide dynamic range of size and number density. When reporting results, null or otherwise, of a microscope search to colleagues wishing to fill in blanks in their image of what is and is not there, a few words or numbers oftendoes not convey what really can and cannot be inferred by the technique. We show here some plots which provide a quantitative picture of what was and was not seen, in the context of what might and mightnot be further investigated. Moreover, we illustrate how the format can provide contextual information on the material system under study, using oxygen precipitates in single crystal Czochralski silicon as the example.

A microscope observing session usually involves examination (or recording) of Ni fieldsof view of width Wi on a specimen, where the index i runs over the number of different magnifications (or field widths) used by the microscopist. Each field of view might allow one to discernobjects whose largestdimension is no more than DiμWi, where μ is a constant typically between 0.01 and 0.001, dependingon the nature of the contrast mechanisms and the geometry of the objects of interest. The region of size & number density space thus investigated byNi fields of view can be marked on a plot of maximum dimension versus number per unit area(see Fig. 1) as the region both to the right of a vertical lineat l/(NiWi),and above a horizontal line at maximum dimension μWi. The region investigated by a larger number of fields of view at that magnification simply extends the examined region further to the left.
Visualizing emulsion polymer particles with an Scanning Electron Microscope equipped with transmission detector
Authors: Charaf U. K.
Published: June 2020

It is difficult to obtain good images of small emulsion polymer particles with an older model SEM which necessitates sputter coating and high accelerating voltage. For the purpose of screening a large number of samples before selecting some for TEM imaging off site, a transmission detector was fitted below the sample holder of an Amray 1600 (Turbo) SEM.

Emulsion polymers with particle sizes from 10 to 100 μm were diluted in 1 % phosphotungstic acid (or other negative stain) and applied to Formvar and carbon coated grids. Lacking sophisticated freeze drying equipment, the grids with the sample films were cooled by immersing the stem of the grid holder in liquid nitrogen. They were then freeze dried in vacuo in an old sputter coater

Inspite of some inherent difficulties, (such as high beam sensitivity), reasonably good resolution was obtained at 30 KV to magnifications of 150,000x.. Image processing was used, where applicable, to sharpen the images.
Massively parallel Monte Carlo simulations of images and analytical data for Electron Microscopy
Authors: Romig A. D. , Michael J. R. , Plimpton S. J.
Published: June 2020

Monte Carlo electron trajectory simulations have been adapted to run on massively parallel supercomputers. An nCUBE2 parallel supercomputer with 1024 processors has been used in these studies. The advantage of the parallel architecture is the great increase in computational speed and the fact that few changes in the standard serial Monte Carlo algorithms are required. The temporal performance of the massively parallel Monte Carlo electron trajectory simulation run on 1024 nodes has been compared with Monte Carlo codes run on other types of supercomputers (CRAY-YMP). It was found to be as much as 100 times faster than the CRAY-YMP and over 2000 times faster than a VAX 785. This increase in computational speed allows the exploration of problems, in particular those involving small probability events, which are not normally amenable to solution by traditional serial Monte Carlo simulations due tothe time intensive nature of the calculations. For example, the calculation of 1,000,000 electrons at 100 kV through a thin foil takes about 6 seconds on the nCUBE.
Visualization of compositional data in microscopy: Representation schemes and software tools
Authors: Bright David S.
Published: June 2020

Consider quantitated x-ray maps as micrographs which are displayed as gray level images where the gray level of each pixel represents useful quantitative information. Although the gray levels correspond to elemental concentrations, well known illusions or response characteristics of the human visualsystem interfere with matching the gray levels of the image to the accompanying numerically annotatedgray scale. The effect of different backgrounds or surrounds is illustrated in Fig. 1. More subtle effects due to an abrupt transition in gray level is shown in Fig. 2. In Fig. 2, the squares appear differently if the brightness ‘edge’ in the center is covered with a pencil: for example, the lower squares appear to be uniform and equally bright.

Similar effects also occur for color images. Visual perception effects aside, interpreting colors quantitatively by matching is more difficult than for black and white images, as will be shown in the talk. Color imaging methods can display only three elements at a time, whereas the phases of interest might depend on the interrelationships of four or more elements. Intensity profiles, such as in Fig. 2, do display values unambiguously, but they represent only a small fraction of the data. An appropriately labeled scatter diagram or two dimensional histogram can represent all of the data.
The extended Fourier algorithm: Application in discrete optics and electron holography
Authors: Voelkl E. , Allard L. F.
Published: June 2020

The conventional discrete Fourier transform can be extended to a discrete Extended Fourier transform (EFT). The EFT allows to work with discrete data in close analogy to the optical bench, where continuous data are processed. The EFT includes a capability to increase or decrease the resolution in Fourier space (thus the argument that CCD cameras with a higher number of pixels to increase the resolution in Fourier space is no longer valid). Fourier transforms may also be shifted with arbitrary increments, which is important in electron holography. Still, the analogy between the optical bench and discrete optics on a computer is limited by the Nyquist limit. In this abstract we discuss the capability with the EFT to change the initial sampling ratesiof a recorded or simulated image to any other(final) sampling rate sf.
Stopping-power determination for compound by EELS
Authors: Joy David C. , Luo Suichu , Dunlap John R. , Williams Dick , Cao Siqi
Published: June 2020

In Physics, Chemistry, Materials Science, Biology and Medicine, it is very important to have accurate information about the stopping power of various media for electrons, that is the average energy loss per unit pathlength due to inelastic Coulomb collisions with atomic electrons of the specimen along their trajectories. Techniques such as photoemission spectroscopy, Auger electron spectroscopy, and electron energy loss spectroscopy have been used in the measurements of electron-solid interaction. In this paper we present a comprehensive technique which combines experimental and theoretical work to determine the electron stopping power for various materials by electron energy loss spectroscopy (EELS ). As an example, we measured stopping power for Si, C, and their compound SiC. The method, results and discussion are described briefly as below.

The stopping power calculation is based on the modified Bethe formula at low energy:

where Neffand Ieffare the effective values of the mean ionization potential, and the number of electrons participating in the process respectively. Neffand Ieffcan be obtained from the sum rule relations as we discussed before3 using the energy loss function Im(−1/ε).
Quantiative x-ray microanalysis at higher voltages
Authors: Lyman C. E.
Published: June 2020

The advantages of analytical electron microscopy (AEM) at accelerating voltages of 200 kV and above have been discussed for years. However, the practical realization of significant improvements in spatial resolution, elemental detectability, and quantitative elemental measurements have awaited the combination of higher kV with field emission sources, more efficient EDS x-ray detector systems, and system stabilities that allow longer counting times. Improved spatial resolution of analysis is the reason quantitative x-ray microanalysis is sought from thin specimens rather than bulk specimens. With a 100kV field emission source, producing a 2nm probe of 0.3 nA, spatial resolution across a chemically distinct phase boundary can be on the order of 2-3 run in a foil 20nm thick. Michael et al. have predicted that such a thin specimen would not show an improvement in spatial resolution at 300 kV versus 100 kV because beam spreading is small compared to the beam diameter; whereas, specimens 100 times thicker would exhibit the expected 3-fold improvement in spatial resolution at 300 kV.
Grain-boundary compositional measurements in complex high-temperature Ni-base alloys using x-ray spectroscopy
Authors: Hall E. L. , Blankenship C. P. , Henry M. F.
Published: June 2020

Thermal treatment of advanced Ni-base alloys used in critical aircraft engine components can have a significant effect on both the microstructure and properties of these alloys. One important property that can be strongly affected by heat treatment is the time-dependent fatigue crack propagation rate along grain boundaries. It is possible for heat treatments to affect the morphology, chemistry, andphase distribution along the grain boundaries in these complex multiphase alloys. Structure-property correlations require the measurement of each of these parameters. By far, the least tractable of these is the measurement of grain boundary chemistry.

X-ray spectroscopy in the AEM has been shown to be a very powerful method for measuring grain boundary chemistry in single-phase Fe and Ni-base alloys, among others. In the case of a singlephase Ni-base alloy such as IN600, heat treatments in the range of 500-750&C cause precipitation of Crrich carbides at grain boundaries and the depletion of Cr from the grain-boundary segments between precipitates via a collector-plate mechanism. Measurement of Cr-depletion at the grain boundaries and Cr-depletion profiles across boundaries is straightforward.
Nanoscale encapsulation of Fe crystallites within a protective graphite cage
Authors: Yao N. , Navrotsky A. , Leinenweber K.
Published: June 2020

Since the discovery of carbon fullerene nanotubules by Iijima using high resolution transmission electron microscopy, there has been a great deal of interest in the properties of tubules and related structures. Recently, it was reported that in the presence of transition-metal catalyst particles, abundant single-shell carbon nanotubes or graphite-encapsulated metal nanocrystals can be produced in a carbon-arc synthesis chamber using electrodes containing both carbon graphite and metal. The vaporization of metal from anode in an inert gas environment takes place simultaneously with the production of soot from the carbon cathode. In this paper, we report that the graphite-encapsulated iron nanocrystals can be made by electron beam irradiation of iron particles on an amorphous carbon support in situ.

The initial aim of our experiments was to study the microstructure and defects of a new calcium iron (II) titanate, CaFeTi2O6, compound, which was synthesized at 12-15 GPa and 1200-1400°C. This material contains a few iron particles in addition to the major oxide phase.
Momentum-resolved low-loss EELS in oxide superconductor
Authors: Wang Y. Y. , Cheng S. C. , Dravid V. P.
Published: June 2020

Valence band EELS spectra can be analyzed in terms of dielectric theory by Kramers-Kronig analysis. While dielectric function can also be obtained by optical techniques with higher energy resolution, EELS offers several advantages over the optical techniques: (i) transmission EELS is a bulk sensitive techniques and can provide dielectric function in a wide energy range (from infrared to soft x-ray); (ii) a large momentum (q) transfer in EELS, under favorable condition, can give rise to optical forbidden transitions; (iii) such q-resolved EELS spectra can be used to determine the localized (or otherwise) nature of excitations. In addition to that, a cold field emission gun (cFEG) electron microscopy (TEM) equipped with a parallel electron energy loss spectrometer provides a reasonable energy resolution (~0.5 eV), a small beam probe and a high counting rate, which eases conditions of sample preparation and makes certain EELS measurements more feasible to do, such as crystal orientation dependent dielectric function and dispersion of excitations in solids without acquiring a large size single crystal.
FEISEM of the cell nucleus: A consideration of parameters
Authors: Allen T. D. , Goldberg M. W. , Reipert S.
Published: June 2020

The wider usage of field emission scanning instruments over recent years has demonstrated their potential to provide useful information on internal cell structure without the necessity to prepare thin specimens in such a way that allows transmission of the electron beam. Resolution of these instruments at around lnm is comparable to that routinely achieved by TEM of biological samples, allowing high resolution surface imaging of intracellular structure. Over the past five years we have been investigating structural organisation of cell nuclei using a Topcon ABT DS130F instrument with a Schottky field emission system which incorporates a Tungsten/Zirconium oxide tip of 0.4μm radius, maintained at 1800°C and 10−8 torr with an extraction voltage of 4,800 volts which generates an emission current of around 60-80 microamps. Specification resolution of this instrument is 1nm at 30kV and 4nms at 1.0kV, using the top stage ‘in lens’ specimen position.

After chemical fixation and critical point drying (optimised by maintaining absolute alcohols over molecular sieve and in line filtration of high purity CO2).
Measurement of Scanning Electron Microscope resolution
Authors: Bentley J. , Evans N. D. , Kenik E. A.
Published: June 2020

The resolution performance of a scanning electron microscope (SEM) is a primary specification of the instrument. For a high-resolution SEM (HRSEM) equipped with a field emission gun (FEG), image resolutions of less than 2 nm are commonly claimed. Generally, both manufacturers and customers identify image resolution as the single most important performance criterion. It is traditionally determined with specimens such as gold islands on bulk carbon supports, where the minimum apparent separation of two islands is claimed as the resolution. This procedure is highly subjective since the spacings are not known independently. Dodson and Joy have pointed out the paradox implicit in this approach-that “the resolution of a given instrument can be verified only after a better instrument is available to characterize the structure spacing.” By analogy to the now standard approach for high-resolution transmission electron microscopes (TEMs), Dodson and Joy investigated the use of Fourier Transforms (FT) of high-resolution SEM images for measuring resolution.
Surface roughness characterization of various ceramic fibers using AFM and low-voltage SEM
Authors: More K. L. , Lara-Curzio E. , Lowden R. A.
Published: June 2020

The effect of interfacial properties in fiber-reinforced ceramic matrix composites is critical to the overall mechanical behavior of the composite material. The creation of a relatively weak fiber/matrix interface allows for the beneficial actions of debonding and fiber pull-out to occur, thus improving the fracture toughness and, in many cases, the ultimate strength of the composite. To date, the best room temperature interfacial properties have been achieved by coating the fibers with either carbon or boron nitride. There are several factors which contribute to the interfacial properties of a composite, including the residual stress (clamping stress) present at the fiber/matrix interface, which is a result of differences in thermal expansion, and the fiber surface roughness. In this study, the surfaces of several ceramic fibers have been characterized qualitatively using a Hitachi S-4500 FEG SEM operated at low voltages and quantitatively using a Topometrix atomic force microscope (AFM). This study is part of an overall program relating fiber surface roughness to the interfacial shear stress.
Production and characterization of high-aspect-ratio probes for use in resonance-mode AFM
Authors: Jarausch K. F. , Mooney C. B. , Griffis D. P. , Shedd G. M. , Russell P. E.
Published: June 2020

Applications of atomic force microscopy (AFM) for the characterization and metrology of technologically-important objects (e.g. x-ray lithography masks) has led to the development of special-purpose, high-aspect-ratio probes. Measuring objects that have deep, narrow trenches requires a controlled probe geometry. The probe radius and aspect ratio determine the congruence of the acquired AFM image to the true profile of the sample. As is illustrated schematically in Figure 1(a), the usual batch-fabricated AFM probe cannot reach down into deep or narrow trenches. Highaspect- ratio AFM probes that can overcome this limitation (Figure lb), have been developed. Probes of ≤100 nm shaft diameter, and up to microns in length, can be grown by electron-beam contamination writing. Focused ion beams have also been used to sharpen conventional probes by rastering a circular pattern around the highest point, removing the“shoulders” by sputtering, and thereby improving the aspect ratio. Previous work has demonstrated the use of such probes in standard, contact-mode AFM. This paper extends the application of these techniques to the creation of probes for resonance-mode AFM, and characterizes the performance of the resulting probes.