bluuebunny/crossref_metadata_2025_split huggingface dataset:
TEM characterization of reaction zone in a SiC fiber-reinforced titanium alloy
Authors: Das G. , Omlor R. E. 
Published: June 2020

Fiber reinforced titanium alloys hold immense potential for applications in the aerospace industry. However, chemical reaction between the fibers and the titanium alloys at fabrication temperatures leads to the formation of brittle reaction products which limits their development. In the present study, coated SiC fibers have been used to evaluate the effects of surface coating on the reaction zone in the SiC/IMI829 system.IMI829 (Ti-5.5A1-3.5Sn-3.0Zr-0.3Mo-1Nb-0.3Si), a near alpha alloy, in the form of PREP powder (-35 mesh), was used a茸 the matrix. CVD grown AVCO SCS-6 SiC fibers were used as discontinuous reinforcements. These fibers of 142μm diameter contained an overlayer with high Si/C ratio on top of an amorphous carbon layer, the thickness of the coating being ∽ 1μm. SCS-6 fibers, broken into ∽ 2mm lengths, were mixed with IMI829 powder (representing < 0.1vol%) and the mixture was consolidated by HIP'ing at 871°C/0. 28GPa/4h.
SEM measurement of surface roughness of dental filling materials
Authors: Stewart G. P. , Savoca D. E. , Russ J. C. 
Published: June 2020

Composite resin materials for dental restorations are preferred to amalgams for aesthetic reasons, for instance when used in fillings visible on the front teeth. However, the roughness of the filling surfaces is of concern, both for aesthetic and health reasons: the rougher the surface, the greater the accumulation of plaque. The smoothest obtainable surface is produced by allowing the composite to set against a matrix band. However, most restorations require some finishing, and the response of these materials to various polishing techniques is of concern.This study compares surface roughness measurements using profilometry and quantitative measurement of SEM micrographs. Samples were prepared using a representative composite: Concise (3M Dental Products, St. Paul MN). This consists of a polymer matrix (BIS-GMA, a dimethacrylate formed by reacting bisphenol-A and glycidyl methacrylate) with about 78% filler (by weight) in the form of 30 p.m. mean diameter quartz spheres. The filler reduces the shrinkage of the composite during setting, reduces the thermal expansion coefficient in normal service to prevent leakage between the tooth and the restoration, and increases the wear resistance of the restoration. Unfortunately, it also makes it difficult to polish the surfaces smoothly or evenly.
The HVEM-tandem user facility at Argonne National Laboratory
Authors: Allen C. W. , Ryan E. A. , Ockers S. T. 
Published: June 2020

Established in 1981, the High Voltage Electron Microscope-Tandem Ion Accelerator Facility (HVEM-Tandem) is a user-oriented resource for materials research. It is located at Argonne National Laboratory about 20 miles south of O'Hare International Airport near Chicago. The Facility consists of a modified Kratos/AEI HVEM with accelerating voltages ranging continuously from 0.1-1.2 MeV, interfaced to a 2 MV tandem and a 0.65 MV ion implanter-type accelerator. This combination of instruments offers capability, unique in the western hemisphere, for a wide range of in Situ experiments involving ion irradiation and ion implantation with simultaneous microscopy. During 1987 approximately 75% of microscope time was devoted to this type of experiment (Fig. 1) including studies of solid state phase transformations, such as amorphization, radiation damage and defect structures and the implantation of noble gas and metal ions.In situ experiments of various types account for nearly 90% of usage of the HVEM. In addition to the radiation effects studies, this includes experiments performed in the microscope involving deformation, annealing and environmental effects.
Single atom visibility on (111) silicon in simulated ADF STEM images
Authors: Loane R. F. 
Published: June 2020

The multislice method has been adapted to simulate annular dark field (ADF) scanning transmission electron microscope (STEM) images. In the STEM image simulation, a highly focused electron probe is scanned across a specimen and the scattered intensity, accumulated over an annular detector, is recorded as a function of probe position. Each pixel in the STEM image is determined by an entire multislice calculation for a particular position of the incident probe. This N4 process is very computationally expensive and currently requires the use of a supercomputer to achieve runtimes of less than a day.The simulated specimen consisted of a (111) silicon crystal substrate, which was a multiple of 94 Å (30 slices) thick, followed by an additional slice containing a single gold atom. Slice potentials were 38.4 Å x 39.9 Å (256 x 256 pixels) in size, which set the maximum included scattering angle to 79 mrad.
Chromatic imaging effects in hvem: an avenue to partial energy filtering
Authors: Fotino Mircea 
Published: June 2020

In transmission electron microscopy the normal image is formed by elastic and inelastic electrons that have interacted with the specimen. Their relative contributions to image formation depend on beam accelerating voltage and on angular acceptance determined by the objective-lens aperture.Inelastic scattering occurs primarily within small scattering angles while elastic scattering extends to wider angles. Consequently, the beam accepted by small objective-lens apertures contains a higher proportion of inelastic electrons than the beam accepted by larger apertures. By varying the size of the objective-lens aperture it is thus possible to modify the composition of the imaging beam and thereby the image quality: better resolution and higher image quality are obtained with larger apertures. It is necessary, however, to make sure that the acceptance angle is both larger than the lower limit imposed by diffraction and smaller that the upper limit imposed by spherical aberration.
Local entropy edge detection in digital images
Authors: Martin David C. 
Published: June 2020

Detection of edges in digital images is an important task for feature recognition and interpretation. Typically, edge detection schemes involve difference operators such as the gradient or Laplacian which depend on the rate of change of brightness in an image. Recently, Shiozaki has shown that a local entropy operator can be useful for edge detection in digital images. This method is simple, rapid, and the resulting image can be interpreted as a measure of the local “information” content of the original data. Here, we investigate the applicability of this approach to digital electron micrographs.The definition of the entropy for a probability distribution pi is S=-Σ pi in Pi. For an image, the conditional probabilities pi are defined as the fraction of total flux which is in a given pixel. If the intensity of the image at a pixel i is fi, then pi=fi/Σfi. The entropy has a maximum when all the Pi's are equal, corresponding to the case of least configurational information.
Incommensurate ordering in Ca-Sr-Bi-Cu oxide superconductors
Authors: Zaluzec N. J. , Hinks D. G. , Capone D. W. , Shi D. , Soderholm L. , Dabrowski B. , Liu J. Z. , Downey J. W. , Lam D. J. 
Published: June 2020

High temperature superconductivity in non-rare earth ceramic oxides has been recently reported, however the structure and composition of the phase(s) has yet to be unequivocally identified. In the Ca-Sr-Bi-Cu Oxide system onset transition temperatures as high as 120 K have been reported, in both single and multiphase specimens. In this work we report on preliminary AEM-based studies of single and polycrystalline specimens of Ca-Sr-Bi-Cu Oxide superconductors.The superconducting material was prepared by mixing powders of Bi2O3, CaCO3, SrCO3, and CuO; and then processed by repeated grinding, heating in either flowing oxygen or air followed by furnace cooling as described in detail elsewhere. The superconducting phase(s) in the powder (∽0.5 x 20μm) specimens are dark, elongated layered crystals which exhibit pronounced basal plane cleavage similiar to graphite or clay based minerals. Larger nominally single crystal specimens (∽0.5 - 2 mm) are less regular in shape, however, all other macroscopic characteristics are essentially the same.
HREM observation of dislocations near room temperature fractures in silicon
Authors: Rhee M. H. , Coghlan W. A. 
Published: June 2020

Silicon is believed to be an almost perfectly brittle material with cleavage occurring on {111} planes. In such a material at room temperature cleavage is expected to occur prior to any dislocation nucleation. This behavior suggests that cleavage fracture may be used to produce usable flat surfaces. Attempts to show this have failed. Such fractures produced in semiconductor silicon tend to occur on planes of variable orientation resulting in surfaces with a poor surface finish. In order to learn more about the mechanisms involved in fracture of silicon we began a HREM study of hardness indent induced fractures in thin samples of oxidized silicon.Samples of single crystal silicon were oxidized in air for 100 hours at 1000°C. Two pieces of this material were glued together and 500 μm thick cross-section samples were cut from the combined piece. The cross-section samples were indented using a Vicker's microhardness tester to produce cracks. The cracks in the samples were preserved by thinning from the back side using a combination of mechanical grinding and ion milling.
Microcomputerized stereographic projection
Authors: Kosel T.H. 
Published: June 2020

Stereographic projection is a well-known and frequently used technique for representing crystal orientations and solving crystallographic problems. Graphical techniques for preparation of stereo projections on paper are especially time-consuming for non-cubic crystals since the angles between planes and/or directions must be calculated and depend on crystal lattice parameters. A computer program has therefore been developed which permits the construction and manipulation, in a matter of seconds, of projections of any crystal structure in any orientation. The program has applications both in research and in teaching, and runs on the Macintosh™ series of microcomputers. The purpose of this paper is simply to briefly describe the capabilities of the program for the interest of electron microscopists.Johari and Thomas described a computer program which generated stereo projections of any crystal system. Since great circles, small circles and rotation of a pole or the crystal are commonly used in stereo projection problems, Kosel developed the mathematical basis for more complete computer algorithms which could perform virtually any basic operation normally done on paper.
Thin film x-ray analysis quantification program for the Macintosh
Authors: Carr M. J. , Romig A. D. 
Published: June 2020

We have written a program which implements a Cliff-Lorimer quantitative thin film x-ray analysis on Apple Macintosh computers. The original FORTRAN algorithm developed by Romig was translated to Turbo Pascal for the Macintosh. The new implementation adheres to the guidelines for the standard Macintosh user interface, while retaining and expanding the analytical capabilities of earlier implementations for VAX and IBM-PC computers.The program opens with a window displaying general instructions and accumulated user comments. The Help window may be bypassed without being read. The user next opens a NEW analysis file or re-OPENs an existing file for editing and re-analysis. This is done either with the mouse or with command-key macro-instructions. Input data is entered through a series of dialog windows requesting detector characteristics, experimental conditions, k-factors, and measured peak intensities at one or more points. The program performs interactive error-checking and a final check for completeness.
Computers for data, control and simulation
Authors: Joy David C. 
Published: June 2020

Personal computers (PCs) are a powerful resource in the EM Laboratory, both as a means of automating the monitoring and control of microscopes, and as a tool for quantifying the interpretation of data. Not only is a PC more versatile than a piece of dedicated data logging equipment, but it is also substantially cheaper. In this tutorial the practical principles of using a PC for these types of activities will be discussed.The PC can form the basis of a system to measure, display, record and store the many parameters which characterize the operational conditions of the EM. In this mode it is operating as a data logger. The necessary first step is to find a suitable source from which to measure each of the items of interest. It is usually possible to do this without having to make permanent corrections or modifications to the EM.
Characterization of multi-component polymer blends by multi-step staining techniques
Authors: Kramer Vivian , Reimschuessel Annemarie 
Published: June 2020

Morphology is one of the important parameters that affects polymer properties and performance. A standard procedure used when characterizing the morphology of many polymer blends by TEM is to stain one of the components with a heavy element rendering it opaque to the electron beam. Among the more common stains used are phosphotungstic acid (PTA) for nylon and OSO4 for unsaturated rubbers. Although these stains work well for simple two component systems, innovative techniques are often essential when the material contains three or more phases, as necessitated by ever expanding industrial demands. This paper describes two such techniques used in characterizing three multi-phase polymer systems.One multi-component system consisted of a polybutadiene-polymer blend, nylon, and a saturated rubber. OSO4 reacts with the double bonds of the butadiene rendering it opaque while slightly darkening its matrix. PTA reacts with the amine groups of nylon rendering it opaque.
HVEM and high resolution SEM of polyurethane bulk and surface structure
Authors: Goodman S. L. , Li C. , Cooper S. L. , Albrecht R. M. 
Published: June 2020

Segmented polyurethanes (PUs) are composed of alternating blocks of crystalline or glassy urethane “hard segments” and rubbery “soft segments.” Chemical incompatability between hard segment (HS) and soft segment (SS) blocks produces a two-phase structure, which accounts for the elastomeric properties of these polymer systems. Polyurethanes are prepared with different HS and SS components, and HS:SS ratios, for various applications. Knowledge of the 3D morphology is necessary to understand polyurethane structure-property relationships. Although conventional transmission electron microscopy can image some polyurethanes, high voltage electron microscopy (HVEM) causes less radiation damage and images thicker samples at higher resolution, thus a sample region may be imaged at multiple tilt angles to provide 3D information. High resolution scanning electron microscopy (HR-SEM) provides complementary information, and at low accelerating voltages (1-3 keV), images near surface structures.Polyurethanes were examined with hard segments of methylene diphenylene diisocyanate (MDI) and 2000 MW soft segments of polytetramethylene oxide (PTMO), polybutadiene (PBD) and polydimethysiloxane (PDMS).
A scanning electron microscope study of defects in PTC materials
Authors: Smith James W. 
Published: June 2020

BaTiO3 and its solid solutions with PbTiO3 and SrTiO3 are normally insulators but, when doped with small amounts of trivalent ions, they become semiconducting. Materials in this family also possess a positive temperature coefficient of resistance (an increase in resistance with increasing temperature) over a limited temperature range and are often referred to as PTCs. The temperature where the PTC region begins is determined by the Ba/Pb/Sr ratio.The materials are generally prepared by solid state reaction of a mixture of oxides and carbonates which is subsequently sintered into a solid form. The electrical properties of such a body, in particular properties such as inrush current capability and voltage breakdown, are critically affected by microdefects in the materials which often originate during processing. The SEM is an ideal tool for studying such defects since they generally manifest themselves as localized variations in resistance.
Electron microscopic evaluation of radioactive particles collected near the Chernobyl nuclear reactor
Authors: Finch G.L. , Cuddihy R.G. , Rothenberg S.J. , Hahn F.F. 
Published: June 2020

In April, 1986, an accident at a nuclear reactor near Chernobyl, USSR, resulted in a substantial release of radioactivity into the environment. Characterization of the release is essential to permit estimates of health risks to exposed individuals. This study was conducted to characterize the nature of particles released during the accident and deposited on nearby surfaces.We obtained a sample of wood that was near the reactor at the time of the accident. Autoradiography of the bulk sample (surface area ≈ 125 cm2) showed the presence of about 30 radioactive particles. After microdissection of small areas of the wood matrix, mounting on carbon stubs, and evaporative carbon coating, samples were examined in a scanning electron microscope (SEM; JEOL JSM-35; operated at 20-30 kV in both backscattered [BSE] and secondary electron [SE] modes) equipped with an energy-dispersive x-ray microanalysis system (EDXA; Kevex 5100C). After EDXA, samples were recoated with gold for improved SE imaging.
Microstructure of graphite fibre reinforced aluminum matrix composites
Authors: Chang K.-T. , Mazur J.H. 
Published: June 2020

The mechanical properties of fiber reinforced materials are determined by the mechanical properties of the individual components (i.e., the fiber and the matrix) and by the nature of the interface between these components. The interface is responsible for the transfer of the stress between the fiber and the matrix and, consequently, an understanding of the microstructure is essential in order to predict the performance of the composite system.In this work we report our preliminary investigations of the microstructure of graphite fiber reinforced 6061 aluminum alloy matrix composite material. The composite material was prepared in the form of a wire 0.65 mm in diameter from mesophase pitch base graphite fiber embedded in 6061 aluminum alloy matrix (A1 97.87%, Si 0.6%, Cu 0.28%, Mg 1.0%, Cr 0.2%, other trace elements 0.05%). Observations of the microstructure were performed on longitudinal and transverse sections of the composite material wire using light microscopy, scanning electron microscopy and transmission electron microscopy.
Electronic, mechanical and electron-optical engineering design features of the cambridge university 600 KV high resolution electron microscope
Authors: Nixon W.C. , Ahmed H. , Catto C.J.D. , Cleaver J.R.A. , Smith K.C.A. , Timbs A.E. , Turner P.W. 
Published: June 2020

1. Introduction.The Cambridge University 600 kV high resolution electron microscope has been developed as a joint programme between the Department of Engineering and the Department of Physics. The shorter electron wavelength at 600 kV when compared to 100 kV gives a potential improvement in resolution that can only be realised in practice if the engineering design and construction are also correspondingly improved. Many aspects of this microscope have been developed specifically for this attempt at very high resolution. Some of these aspects were reported in September 1977 at the time when the microscope was first operated (Nixon et al. 1977). After three months operation the present resolution is better than 3 Å with no indication that any fundamental design limit has been approached.The following three items have been purchased outside. All other aspects of the microscope have been designed and constructed in Cambridge University. The high voltage generator and accelerator, as described by Reinhold and Gleyvod (1974), has been supplied by Haefely, Switzerland
On the magnetic electron lens of minimum sphrical aberration
Authors: Suzuki S. , Ishikawa A. 
Published: June 2020

For the development of the electron microscope, in which high resolving power is demanded, it is important to construct an electron objective lens with minimum spherical aberration.In 1943, one of the authors published the paper on the approximate calculation of the electromagnetic field to give a minimum spherical aberration and also published the papers on small spherical aberration lens design based on this calculation.We will speak a comparison between the experimental results and the numerical calculations in practical cases.The following line shows the method to get more strictly minimum spherical aberration of magnetic lens.In a space charge free electron optical system, where a pure magnetic lens is concerned, differential equation for paraxial electron path is given byU being the initial voltage applied to the electron beam and γ the path distance from the optical axis Z.
EM contrast transfer functions for tilted illumination imaging
Authors: Krivanek Ondrej L. 
Published: June 2020

The transfer theory of electron microscopy has now been firmly established, at least for the case of axial illumination. Tilted illumination introduces slight complications, but even so the theoretical description of the contrast transfer remains essentially quite simple. Experimentally, the existence of the main "achromatic circle" and the subsidiary circles due to plasmon scattering has been well demonstrated, but the theoretical predictions for the change in the apparent defocus and astigmatism,as determined from the image modified by tilting, has not been confirmed. This paper aims to close the gap.With coherent illumination, the contrast transfer from a weak phase object and for tilted illumination is described by including the beam tilt in the familiar axial expressions:where h(q) is the contrast transfer function (CTF), X(q) the aberration function, and the remaining symbols have their usual meaning. The derivation is algebraically lengthy, but the results can be summarised as follows.
The role of differential phase contrast in electron microscopy
Authors: Waddell E.M. , Chapman J.N. , Ferrier R.P. 
Published: June 2020

Dekkers and de Lang (1977) have discussed a practical method of realising differential phase contrast in a STEM. The method involves taking the difference signal from two semi-circular detectors placed symmetrically about the optic axis and subtending the same angle (2α) at the specimen as that of the cone of illumination. Such a system, or an obvious generalisation of it, namely a quadrant detector, has the characteristic of responding to the gradient of the phase of the specimen transmittance. In this paper we shall compare the performance of this type of system with that of a first moment detector (Waddell et al.1977).For a first moment detector the response function R(k) is of the form R(k) = ck where c is a constant, k is a position vector in the detector plane and the vector nature of R(k)indicates that two signals are produced. This type of system would produce an image signal given bywhere the specimen transmittance is given by a (r) exp (iϕ (r), r is a position vector in object space, ro the position of the probe, ⊛ represents a convolution integral and it has been assumed that we have a coherent probe, with a complex disturbance of the form b(r-ro) exp (iζ (r-ro)). Thus the image signal for a pure phase object imaged in a STEM using a first moment detector is b2 ⊛ ▽ø. Note that this puts no restrictions on the magnitude of the variation of the phase function, but does assume an infinite detector.