bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new sulphide Ag8S formed in the early stage of sulfurization of silver
Authors: Yu Y.D. , Guan R. , Kuo K.H. , Hashimoto H. 
Published: June 2020

Metal sulphuration, like oxidation, is a basic problem in metal corrosion. For silver the sulphuration is more important than oxidation in materials engineering such as in microelectronic applications. In the present note, we report the formation of Ag8S prior to Ag2S, like copper and nickel oxidation, in the initial sulphuration stage.A block of 99.99% silver was rolled into sheets of about 50 μm thick and was then electrolytically thinned by the window method in dilute nitric acide. Then these films were sulphurated at 300°C in a tube with some trace sulphur left on the tube wall in a vacuum of about 10”4 Torr. The thin film was somewhat sulphurized and many microcrystallites grew up at the edge of the film. From the electron diffraction patterns it is clear that these crystallites are not silver, nor the Ag2S sulphide, indicating that they may belong to a new silver sulphide. Figure 1 is the low magnification electron microscopic images of these sulphide crystallites. Figure 2 shows its energy dispersive X-ray (EDS) peaks, indicating that it contains sulphur of about 2-3 wt%, which is much lower than the sulphur content (12.9 wt%) in Ag2S. Fig. 3 shows the HREM image in which region B is much thinner than region A and shows a higher resolution. The distance between the imaging spots in region B is half of that in region A. By analysing the EDPs and the HREM images we came to conclusion that the structure of the crystal is body- centered orthorhombic with a=0.59, b=0.64 and c=0.87 nm. Each unit cell has 16 Ag atoms and 2 S atoms. Fig.4 is the [010] projection of the structure. Fig.5a shows the magnified image of region A of Fig.3 and Fig.6a shows that of region B. Figs.5b and 6b show the simulated images which were obtained from the suggested model for Ag8S with thicknesses of 185A and 20A, respectively. The agreement between the observed and the calculated images is rather good indeed. Comparing Figs.5b and 6b with Fig.4, we can see that the imaging spots in Fig.5a correspond to the projected S atoms, while those in Fig.6a to the projected Ag atoms. In the thicker area (region A), only S atoms can be imaged as shown in Fig.5a, while in the thinner area (region B), Ag atoms can be observed as in Fig. 6a. This phenomenon can easily be made clear by the variation of the diffraction amplitudes of (400) and (004) planes with Ag atoms as the dominating scatters, and of (200), (002) and (101) planes with S atoms as the dominating scatters, as shown in Fig.7.
Polymer characterization via FT-IR microspectroscopy
Authors: Wihlborg William T. , Reffner John A. 
Published: June 2020

FT-IR microspectroscopy systems have been used for a wide range of polymer applications. Reffner et al reported a quantitative reflectance technique for the determination of ethylene/vinyl acetate copolymer. Chase, using an infrared polarizer with the microscope, studied single polymer fibers and was able to determine the orientation of functional groups relative to the fiber axis. Brasch and Lustiger also used FT-IR microspectroscopy in conjunction with an IR polarizer to determine the percentage of tie molecules in polyethylene. The relative amount of tie molecules is an important parameter for understanding the mechanical failure of polyethylene and the FT-IR microscope improves the sensitivity of this measurement by confining the analysis to the areas of the sample which undergo the greatest change.In the present study the IRμs™ microanalysis system was used to explore the effects of environmental and mechanical stresses upon the molecular structure of polymers. A sample of polypropylene which was weathered for two years was microtomed and the cross section studied for indications of degradation.
New Direct Methods for Phase and Structure Retrieval in HREM
Authors: Van Dyck D. , Op de Beeck M. 
Published: June 2020

Reliable interpretation of high resolution electron micrographs is only possible by comparison with computer simulations. However, simulation is a tedious trial and error technique which can only be successful if the experimental parameters are known and if the number of plausible structure models is small. For instance the interpretation of images of amorphous objects by simulation is hopeless. This makes the power of HREM very much dependent on the amount of prior information available from other techniques such as X-ray diffraction. HREM would be much more powerful and independent if a direct method could be established to retrieve the structural information of the object directly from the electron micrographs.We present a new “focus variation method” in which the phase is retrieved in the image plane in a deterministic way from a combination of images at closely spaced focus values, as inspired on the method proposed in [1] [2]. In a sense the whole information is used in the 3D image area of the electron microscope. The method allows to correct for chromatic aberration, spherical aberration and focus and is robust against noise. In a second stage we retrieve the projected structure of the object directly from the knowledge of the wavefunction at the exit face, using the channelling theory proposed in [3]. The first results are very promising.
High-Resolution Electron Microscopy Study of Enamel Crystal Growth in Human Foetus
Authors: Cuisinier F.J.G. , Steuer P. , Voegel J.C. , Frank R. M. 
Published: June 2020

The mineral component of human dental enamel is formed by nonstoichiometric carbonated hydroxyapatite crystals. The presence of relatively large amounts of impurities in mature enamel crystals as well as their external shape are related to their growing mechanism. Enamel crystal growth was investigated previously directly with low resolution electron microscopy or by comparison with synthetic apatite crystal growth. The growing process of enamel crystals is still unknown and the aim of this study was to investigate foetal enamel growth during secretory stage by high resolution transmission electron microscopy.Developing enamel from 5 month-old human foetuses was fixed for 3 hours in a 2% glutaraldehyde and 2% paraformaldehyde solution in 0.1 M sodium cacodylate buffer. After 2 hour postfixation in 1% OsO4in the same buffer and embedding in Epon, non decalcified ultrathin sections were obtained with a Sorvall-Porter MT-2C microtome equipped with a diamond knife and floated on demineralized water saturated against hydroxyapatite (200mg/l). The sections were observed in a Philips EM 430 transmission electron microscope operating at 300 kV equipped with a double tilt specimen holder. This microscope possessed a Sherzer resolution of 0.19 nm and the absence of drift and astigmatism was checked for each micrograph by an optical diffraction.
Evolutionary Developments in X-Ray and Electron Energy Loss Microanalysis Instrumentation for the Transmission Electron Microscope
Authors: Zaluzec Nestor J. 
Published: June 2020

Developments in instrumentation for both X-ray Energy Dispersive and Electron Energy Loss Spectroscopy (XEDS/EELS) over the last ten years have given the experimentalist a greatly enhanced set of analytical tools for characterization. Microanalysis have waited for nearly two decades now in the hope of getting a true analytical microscope and the development of 300-400 kV instruments should have allowed us to attain this goal. Unfortunately, this has not generally been the case. While there have been some major improvements in the techniques, there has also been some devolution in the modern AEM!In XEDS, the majority of today's instruments are still plagued by the hole count effect, which was first described in detail over a fifteen years ago. Figure 1 shows that the magnitude of this problem can still reach the 20% level for medium atomic number species in a conventional off-the-shelf intermediate voltage AEM. This is an absurd situation and the manufacturers should be criticized, however, part of the blame here also rests on the AEM community for not having come up with a universally agreed upon standard test procedure. Fortunately, such a test procedure is in the early stages of refinement. On the quantitative side, after corrections for the hole count, we understand the effects of the higher voltage to the intensity variation and hence to quantification (figure 2). Windowless x-ray detector systems have opened up the low-energy, light-element regime to the x-ray analyst (figure 3), however, spectral overlaps are a recurring problem in complex systems.
Stem Holography
Authors: Leuthner Thomas , Lichte Hannes , Herrmann Karl-Heinz , Sum Jürgen 
Published: June 2020

Electron optical imaging is a wave optical process. Therefore, to obtain the whole information about the object structure, one must record both amplitude and phase of the electron in the detector plane, e.g. in the Fourier plane or in the image plane. In the general case, an electron image detected only by its intensity is in principle incomplete [1]. This is true in particular in face of the lens aberrations which scramble amplitude and phase hence limit resolution and interpretability of an electron image.Following Gabor’s proposal of electron holography, these problems are being solved in the TEM [2], and in the STEM we try to tackle them in the following way [3] (fig.l): Two coherent waves, produced by means of the Mollenstedt electron biprism, are focused in the object plane. One of them is transmitted through the object and modulated in amplitude a(x,y) and phase φ(x,y) whereas the other one instead goes through empty space. Subsequently they are superimposed and give rise to an interference pattern (spatial frequency Rc) in the detector plane (coordinate u ) as
Structural Studies on the Eukaryotic Ribosome
Authors: Verschoor Adriana , Milligan Ronald , Srivastava Suman , Frank Joachim 
Published: June 2020

We have studied the eukaryotic ribosome from two vertebrate species (rabbit reticulocyte and chick embryo ribosomes) in several different electron microscopic preparations (Fig. 1a-d), and we have applied image processing methods to two of the types of images. Reticulocyte ribosomes were examined in both negative stain (0.5% uranyl acetate, in a double-carbon preparation) and frozen hydrated preparation as single-particle specimens. In addition, chick embryo ribosomes in tetrameric and crystalline assemblies in frozen hydrated preparation have been examined. 2D averaging, multivariate statistical analysis, and classification methods have been applied to the negatively stained single-particle micrographs and the frozen hydrated tetramer micrographs to obtain statistically well defined projection images of the ribosome (Fig. 2a,c). 3D reconstruction methods, the random conical reconstruction scheme and weighted back projection, were applied to the negative-stain data, and several closely related reconstructions were obtained. The principal 3D reconstruction (Fig. 2b), which has a resolution of 3.7 nm according to the differential phase residual criterion, can be compared to the images of individual ribosomes in a 2D tetramer average (Fig. 2c) at a similar resolution, and a good agreement of the general morphology and of many of the characteristic features is seen.Both data sets show the ribosome in roughly the same ’view’ or orientation, with respect to the adsorptive surface in the electron microscopic preparation, as judged by the agreement in both the projected form and the distribution of characteristic density features. The negative-stain reconstruction reveals details of the ribosome morphology; the 2D frozen-hydrated average provides projection information on the native mass-density distribution within the structure. The 40S subunit appears to have an elongate core of higher density, while the 60S subunit shows a more complex pattern of dense features, comprising a rather globular core, locally extending close to the particle surface.
High Resolution Scanning Electron Microscopy of Surfaces
Authors: Cowley J.M. 
Published: June 2020

Electron beams of small diameter, generated with field emission guns may be used to investigate surfaces in many different ways. Images may be formed in the scanning mode by use of the elastically, or quasi-elastically scattered electrons or by the detection of secondary radiation including low energy secondary electrons, Auger electrons and X-rays. Except in the case of low-energy secondary electrons, high spatial resolution has not yet been achieved by detection of the secondary radiations so these imaging modes will not be discussed here.The scanning modes used with the detection of elastic or quasi-elastic electrons in a dedicated STEM instrument are analogous to those used in conventional TEM instruments for surface studies, such as profile imaging and reflection electron microscopy. In each case, the practical limitations of current STEM systems tend to limit the quality of the imaging but the flexibility of the STEM detector system has provided several important advantages. In scanning reflection microscopy (SREM) the resolution attained is comparable with that for REM. The important advantage over REM is that microdiffraction patterns may be obtained from any surface features as small as the resolution limit for imaging. Also it is relatively easy to make use of the surface channelling conditions in order to enhance the contrast of surface steps or other surface features.
Comparison of Low-and High-Voltage SEM Images of Beryllium
Authors: Price C. W. 
Published: June 2020

Beryllium has a low secondary electron (SE) coefficient that produces a low signal-to-noise ratio, and in the past, this deficiency caused many workers to routinely coat beryllium with a high-Z material such as Au/Pd and examine the specimens at high voltage (HV). In principle, beryllium should be an ideal candidate for improved imaging with low voltage (LV), because its low atomic number permits excessive electron-beam penetration during HVSEM imaging — the use of LVSEM to analyze beryllium films was demonstrated previously. Unfortunately, low SE emission can seriously compromise LVSEM images from uncoated beryllium specimens, even with the improved LVSEM imaging capability of a SEM equipped with a field-emission gun (FESEM). This work demonstrates that some beryllium structures yield improved results with LVSEM imaging in a FESEM, particularly at low magnifications, while structures that require high magnification often yield better results with HVSEM.Specimens selected for this study include craters formed by a Cs+ ion beam in specimens that had been analyzed in an ion microanalyzer by secondary-ion mass spectroscopy (SIMS), machined surfaces, and fracture surfaces. SE images were obtained for this study with a Hitachi S-800 FESEM equipped with a cryogenic vacuum pumping system.Surface structure in a sputtered SIMS crater is shown at 2.0 kV in Fig. 1a and at 20 kV in Fig. 1b. This specimen was from commercial grade beryllium sheet. Prominent microtwins are visible in several grains in Fig. 1, and because of the excessive beam penetration at HV, the microtwins are better defined at LV in Fig. 1a than they are at HV in Fig. 1b. In addition, a fine faceted microstructure was formed by the ion beam that could be observed at intermediate magnifications, and it also was better defined at LV than at HV. The dark contamination film that is visible around some of the particles in Fig. 1a also is significant; this film was not apparent at voltages of 5 kV and higher, as demonstrated in Fig. 1b. SIMS ion images revealed that this material contained particles of several different compositions including carbides; since beryllium carbide hydrolyzes when exposed to moist air, the films are suspected to have formed by the decomposition of carbides when the specimen was removed from the ion microanalyzer after the SIMS analysis. This example demonstrates the excellent sensitivity of LVSEM to detect thin films, and it also suggests that contamination and the thin oxide film that forms on beryllium may impair SE imaging.
Generalized C-Means Algorithms for Medical Image Analysis
Authors: Bezdek James C. 
Published: June 2020

Diagnostic machine vision systems that attempt to interpret medical imagery almost always include (and depend upon) one or more pattern recognition algorithms (cluster analysis and classifier design) for low and intermediate level image data processing. This includes, of course, image data collected by electron microscopes. Approaches based on both statistical and fuzzy models are found in the texts by Bezdek, Duda and Hart, Dubes and Jain,and Pao. Our talk examines the c-means families as they relate to medical image processing. We discuss and exemplify applications in segmentation (MRI data); clustering (flow cytometry data); and boundary analysis.The structure of partition spaces underlying clustering algorithms is described briefly. Let (c) be an integer, 1<c>n and let X = {x1, x2, ..., xn} denote a set of (n) column vectors in Rs. X is numerical object data; the k-th object (some physical entity such as a medical patient, PAP smear image, color photograph, etc.) has xk as its numerical representation; xkj is the j-th characteristic (or feature) associated with object k.
Industrial Applications and Future Directions
Authors: Labun P.A. 
Published: June 2020

In recent years the industrial community has become increasingly aware that in order to understand complex materials they require both high resolution imaging (<.2nm) and high spatial resolution microanalysis (≤2.0nm). In working with the members of the Industrial Associates Program at Arizona State University, we have come to recognize and acknowledge these needs and to accept that such needs are on the increase. Each new project has involved complex and difficult analyses, pushing the limits of available technology. The following outlined examples highlight some of the work currently in progress.Zeolites (molecular sieve materials): Of primary importance in utilizing these materials is structural determination of many of the new compounds that are being synthesized. In order to ascertain the complete structure, high-resolution images approaching .2nm are necessary. Considering the severe beam sensitivity of these materials, it is extremely difficult to acquire images that are close to optimum defocus, without drift and damage. Recently, however, with on-line image acquisition systems becoming available, an image can be captured in 1/30th of a second with very low beam doses and effectively no drift present. Contrast enhancement and band filtering (a ring filter cutting off low and high frequencies; the ring is the same in all directions) make it possible to greatly improve the image detail and thus improve the prospects of developing a crystal structure model, (see Fig. 1a,b).
High Resolution Cryo-Electron Microscopy Sheds A New Light Upon Biomembrane Architecture
Authors: Nahoaki Kume P. , Akiko Yuba D. , Akiyasu Yoshizawa C. , Satoshi Sato B. , Yoshinori Fujiyoshi 
Published: June 2020

Cryo-electron microscopy, together with the rapid cryo-fixation technique, has made it possible to observe chemically unfixed unstained specimens under a transmission electron microscope. Aoki et al. constructed a new cryo-stage in order to reduce irradiation damage upon biological specimens further by cooling them with liquid helium. It was also designed to eliminate shaking of specimens as much as possible by the sophisticated mounting and the refined cooling mechanism of the stage. The stage has proved to achieve a higher contrast and higher resolution of images than a commonly-used cryo-stage cooled solely by liquid nitrogen does. This high resolution cryo-electron microscope (HiRCEM) was originally developed aiming at the improvement of resolution in structural analysis of proteins or nucleic acids, but it has turned out to be quite useful for detecting the architecture of biomembranes as well. This is due to the existence of phosphorus atoms of phospholipids which are heavier than C, H, O, N atoms abundant within biomembranes, and also due to the great optical depth of the membrane where it is aligned parallel to the electron beams.We have examined several kinds of biomembranes as well as the synthesized liposomes under HiRCEM. Among them were the plasma membrane of human erythrocytes (ghosts), the nuclear membrane of chicken erythrocytes, the endoplasmic reticular membrane of rat nerve cells, the chromatophore membrane of a photosynthetic bacterium Chromatium vinosum , the thylakoid membrane of spinach chloroplasts and the envelope of influenza type A virus (PR8 & X31). Liposomes we employed were synthesized from the 2:1 mixture of phosphatidylcholine and cholesterol.
From Static Images To Dynamic Structures: The Use of Image Analysis and Video In Deriving Dynamical Information From Electron Microscopy
Authors: Egelman Edward H. 
Published: June 2020

Advances in computer graphics and numerical processing, in video technology, and in image acquisition have enabled us to extend the power of the electron microscope in the analysis of macromolecular structures, particularly helical protein polymers. Three applications of this technology will be described:1) There are frequently times where the static images acquired from fixed, stained or frozen specimens leads to a loss of information about the dynamical properties of the molecules or structures being studied. We have been using computed image analysis, graphics and animation to recover the dynamical information that can be obtained from electron microscopic images.Using the RecA protein of E. coli , we have been able to capture different biochemical states as a function of time through the use of a slowly hydrolyzable ATP analog, ATP-γ-S. Threedimensional reconstruction of these helical structures, combined with computer-generated animation between different structures, have enabled us to directly visualize the motions within the protein polymer associated with the hydrolysis of the nucleotide analog. Modifications of the RecA protein, achieved through either proteolysis or mutation, have allowed us to use the same techniques to visualize domain-domain movements within the RecA filament which occur over a range of 5-10Å. The methods of analysis, graphics and animation which have been used will be discussed. The general applicability of these procedures to other systems will also be addressed.
Processing Video Images of Chemical Reactions
Authors: LeRoy Eyring , de Ruijter W.J. 
Published: June 2020

The high-resolution transmission electron microscope is unique in its capacity to provide direct images of bulk matter at the atomic level. This suggests the electron microscope as a nanochemical laboratory in which elementary reaction mechanisms can be observed and deciphered. The nature, disposition, and evolution of defects, the agents of chemical change, must be studied intimately if the fundamentals of chemical reactivity in solids are to be understood fully. Chemical change during microscopical observation is inevitable since alterations in the electronic associations of the atoms are produced by the electron beam. For a chemist this presents an extraordinary opportunity for investigating the atomic-level mechanism of a chemical reaction.Chemical reactions observed at near atomic resolution can be recorded on videotape at the rate of 30 images per second. Since the onset, extent and rapidity of a reaction varies over many orders of magnitude and is not predictable it is sometimes necessary to record for hours. The videotape provides a convenient storage medium for this immense quantity of information. The tapes can then be edited for those stretches bearing pertinent information and can be processed as needed. The purpose may simply be clear communication of scientific information to peers or more extensive processing may be desired for pedagogical use.