bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and chemistry of diffusion-bonded metal/ceramic interfaces
Authors: Rühle Manfred
Published: June 2020

The application of modern engineering materials often requires that two different materials be bonded. The resultant interfaces must typically sustain mechanical and/or electrical forces without failure. Consequently, interfaces exert an important and sometimes controlling, influence on performance in such applications as composites, electronic packaging systems, thin film technology and joining.

During joining by a diffusion-bonding process, surfaces of the two materials are brought into contact by applying a small load and temperature. During the bonding and the subsequent cooling cycle chemical reactions may occur leading to chemical gradients or chemical reactions. The actual reaction and diffusion paths depend on the activities of the diff erent elements present near the interface.

Bonds of bulk Nb/Al2O3 and Ni/Al2O3 were formed (for details of bonding conditions, see Elssner et al. ) and structure of the interface as well as chemical gradients near the interfaces were studied by TEM, HREM and SEM.
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.
Digital phase analysis in interference electron microscopy
Authors: Hasegawa S. , Kawasaki T. , Endo J. , Futamoto M. , Tonomura A.
Published: June 2020

Interference electron microscopy enables us to record the phase distribution of an electron wave on a hologram. The distribution is visualized as a fringe pattern in a micrograph by optical reconstruction. The phase is affected by electromagnetic potentials; scalar and vector potentials. Therefore, the electric and magnetic field can be reduced from the recorded phase. This study analyzes a leakage magnetic field from CoCr perpendicular magnetic recording media. Since one contour fringe interval corresponds to a magnetic flux of Φo(=h/e=4x10-15Wb), we can quantitatively measure the field by counting the number of finges. Moreover, by using phase-difference amplification techniques, the sensitivity for magnetic field detection can be improved by a factor of 30, which allows the drawing of a Φo/30 fringe. This sensitivity, however, is insufficient for quantitative analysis of very weak magnetic fields such as high-density magnetic recordings. For this reason we have adopted “fringe scanning interferometry” using digital image processing techniques at the optical reconstruction stage. This method enables us to obtain subfringe information recorded in the interference pattern.
Automatic measurement of SAED patterns from asbestos minerals
Authors: Russ J. C. , Taguchi T. , Peters P. M. , Chatfield E. , Russ J. C. , Stewart W. D.
Published: June 2020

Conventional SAD patterns as obtained in the TEM present difficulties for identification of materials such as asbestiform minerals, although diffraction data is considered to be an important method for making this purpose. The preferred orientation of the fibers and the spotty patterns that are obtained do not readily lend themselves to measurement of the integrated intensity values for each d-spacing, and even the d-spacings may be hard to determine precisely because the true center location for the broken rings requires estimation. We have implemented an automatic method for diffraction pattern measurement to overcome these problems. It automatically locates the center of patterns with high precision, measures the radius of each ring of spots in the pattern, and integrates the density of spots in that ring. The resulting spectrum of intensity vs. radius is then used just as a conventional X-ray diffractometer scan would be, to locate peaks and produce a list of d,I values suitable for search/match comparison to known or expected phases.
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.
Interlayer mixing in GaAs/AlxGa1-xAs heterostructures as a result of Se+ ion implantation
Authors: Bithell E.G. , Stobbs W.M.
Published: June 2020

It is well known that the microstructural consequences of the ion implantation of semiconductor heterostructures can be severe: amorphisation of the damaged region is possible, and layer intermixing can result both from the original damage process and from the enhancement of the diffusion coefficients for the constituents of the original composition profile. A very large number of variables are involved (the atomic mass of the target, the mass and energy of the implant species, the flux and the total dose, the substrate temperature etc.) so that experimental data are needed despite the existence of relatively well developed models for the implantation process. A major difficulty is that conventional techniques (e.g. electron energy loss spectroscopy) have inadequate resolution for the quantification of any changes in the composition profile of fine scale multilayers. However we have demonstrated that the measurement of 002 dark field intensities in transmission electron microscope images of GaAs / AlxGa1_xAs heterostructures can allow the measurement of the local Al / Ga ratio.
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.
Imaging, representation and analysis of 3-dimensional biological structures by confocal microscopy
Authors: Brakenhoff G.J. , van der Voort H.T.M.
Published: June 2020

Confocal scanning laser microscopy is a new technique capable of visualizing the three-dimensional structure in suitable objects. As further explained in fig. 1 the basic aspect of this type of microscopy is that one and the same object point in the specimen is both optimally illuminated from a laser illuminated pinhole as well as optimally imaged on a detector pinhole. Due to the specific properties of this optical arrangement not only the lateral resolution is substantially improved, but also an excellent optical sectioning property comes available. The latter means that only information from a chosen plane in the specimen will contribute to the image, while the influence of the layers above and below is suppressed. The important advantage over elec- tronmicroscopy, apart from the speed of the technique, is that to make the 3-D information accessible in a specimen no mechanical sectioning of the material is necessary.
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 by

U being the initial voltage applied to the electron beam and γ the path distance from the optical axis Z.
Noise and energy broadening in field emission systems
Authors: Smith K.C.A. , Cumming A.D.G.
Published: June 2020

To improve the performance of the field emission electron gun requires that greater total currents are drawn from the field emission cathode. This involves various practical difficulties associated with the vacuum environment, and in addition, the Boersch effect energy broadening may become important at high currents and for certain applications, for example in pulsed transmission microscopy (Smith and Cleaver, 1976). As part of a study of field emission guns under high current conditions we have measured the energy spreads in a pulsed triode gun system. Positive going pulses on the control electrode, or Wehnelt, were used to draw peak currents of up to 2 mA for 10 μS durations, the pulses being of 4 kV amplitude. A (111) orientated single crystal tungsten cathode was used, of 150 mm tip radius, and the energy of the emitted electrons measured in an analyser due to Brack (1962). This consists of a three electrode einzel lens with a superimposed axial magnetic field, and is designed to have a high coefficient of chromatic aberration.
Image converters for the high-voltage electron microscope
Authors: Vernon King Murray , Parsons Donald F.
Published: June 2020

One of the major concerns of biological electron microscopists has been that of obtaining images of biological specimens with minimal radiation damage. The problem of designing more sensitive imaging devices and materials for the high-voltage electron microscope (HVEM) becomes pressing because: 1) the relative insensitivity of conventional photographic materials to 1-MeV electrons requires inordinately long exposures unless measures are taken to enhance the sensitivity of photographic recording; 2) the relative insensitivity of conventional viewing screens requires excessive beam intensities for scanning the specimen and focusing the image unless means are found to obtain a visible image at lower beam current densities; 3) an increasing part of the practice of high-voltage electron microscopy has involved taking multiple images from the same specimen area, as in taking stereo pairs or more extensive tilt series for three-dimensional reconstruction --- this feature is inherent in high-voltage electron microscopy, and it is occasioned by the wealth of detail offered by semithin sections, which requires three-dimensional methods for decipherment
Transverse sections of multifilamentary Nb3Sn superconductor wires in TEM
Authors: Koch Edward F.
Published: June 2020

New devices using fine multifilament superconducting wires are becoming more important, since these wires now have better thermal stability, lower losses and better current carrying capacity. The multifilament Nb3Sn superconductor wires reviewed in this report were made by the solid state diffusion method developed by Kaufman and Pickett. In this process, a niobium rod in a bronze jacket is extruded into an hexagonal shape, this rod is then cut into lengths, which are packed together in a bronze jacted and extruded again. This process is continued until the total reduction ratio for the niobium is a billion to one. At this point the wires are still ductile and can be fabricated into their final shape. The Nb2-bronze composite is then heat treated, and the tin from the bronze diffuses into the Nb, forming Nb3Sn. This heat treatment is important, since it controls both the amount of Nb3Sn formed and the grain size, which affects flux-pinning.
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 by

where 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.
Diffraction contrast and defect symmetry
Authors: Katerbau K.-H.
Published: June 2020

Symmetry rules for the bright-field images of lattice defects were derived by Howie and Whelan /1 /, and for the dark-field images by Pogany and Turner /2/. In both cases, only one of the N diffracted beams is considered, and no statement is made on how the intensities of the other beams are affected by defect symmetry. This question is studied in the present paper.

We make use of the column approximation and assume a centro-symmetric crystal and N reflections gn (n=o,...N-1 with go=o), lying in the same reciprocal lattice plane.A cartesian coordinate system (x,y,z) is introduced with the x- and y-axes in this plane and the origin in the centre of the lattice defect, located at a distance zo below the upper foil surface, t is the foil thickness, R(x,y,z) the displacement field of the defect with the abbreviation. R(z) for the displacement field at the column (x,y), and k = (kx, ky ) is the component of the wave vector of the incident electron beam in the (x,y)- plane. k=-gj/2 means that g. is in the Bragg reflecting position.
On the optimisation of methods for the computation of many-beam structure images
Authors: Van Dyck D.
Published: June 2020

The necessity to calculate structure images for the interpretation of high-resolution electron micrographs has often been emphasized However, when large unit cells and/or heavy atoms are involved, the number of beams used for the calculations has to be increased to the order of 1000-10000, whereas an accurate simulation of the beam divergence drastically augments the computing time [11], For these reasons the computational techniques used hitherto, require fairly high computer facilities.

On the other hand because of the availability of mini laboratory computers [≤32k words] in most laboratories nowadays, an image calculation program that could be performed on such a computer with sufficient speed to allow direct feedback, would be very welcome. We searched in this work for optimal computational techniques that meet these requirements without loss of generality. The investigation was carried out in four distinct steps.

1. Basic expression

It was previously shown [5,6] that, when backscattered electrons are neglected, which is a valid assumption [7], all the existing dynamical diffraction formulations can be reduced to a formal expression for Φ[z], the vector of the diffraction amplitudes

as a function of the crystal depth:

with the boundary condition Φ(o) =

T represents the diagonal propagation matrix with components T, where s is the excitation error.
Computer simulation of phase of contrast of cluster atoms on support film made by sputter deposition
Authors: Oikawa Tetsuo , Ishigaki Fumiko , Fukuyama Shuhei , Wakizaka Haruo , Hojou Kiichi , Kanaya Koichi
Published: June 2020

Based on the image formation theory, the wave function of a single atom consisting of the complex scattering amplitude |f(0)|exp{-inj(0)} and phase shift γj of spherical aberration is rigorously obtained by the Kirchhoff diffraction integral in the Fraunhofer approximation as a function of defocus. Using of the wave function w(υj,γj) of a group of atoms, which is extended the wave function of a single atom, variations of imaging phase contrast of tungsten support film in through focal series made by sputter deposition are simulated. The contrast of tungsten support film and a gold cluster atoms on the substrate made by sputter depposition, which are very close with the experiment, are calculated by the Monte-Carlo method with the aid of the inter-atomic size distribution measured by electron diffraction pattern.

The contrast g for cluster atoms has been calculated by integrating the scattering wave for coherent waves, and for incoherent waves the amplitude scattered outside the limiting angle α set by the aperture respectively,
Structural systematics in B2O3Nb2O5 complexes
Authors: Gai P.L. , Anderson J.S.
Published: June 2020

Phase equilibria in the systems B2O3-Nb2O5 and structure and ordering have been investigated by high resolution electron microscopy. Electron energy loss analysis using electron spectrometry techniques (Gai et al. 1977) employed to assist the observations. Compounds of 3OB2O370Nb2O5, 27B2O373Nb2O5 and 17.1B2O3 82.9Nb2O5 were prepared and annealed respectively at 1000°C for 80hrs, 930°C for 14 days, and 900°C for 12 days, with a view to study the structure of the various phases occurring in the phase equilibrium diagram of this particular system. The phase equilibrium diagram deduced from quenching experiments (Levin, 1965) was used as a reference. X-ray Guinier patterns were recorded for the compounds. A JEM 100B electron microscope fitted with a pointed filament and double tilt goniometer stage with modified specimen holder were used for high resolution TEM. The material 30B203:70Nb205 with shorter annealing times showed a structure which appeared to be predominantly a two-phase mixture, one consisting of "3x3" blocks (Figure 1(a)) and the other, H-Nb2O5.
The composition and structure of guinier-preston zones in lunar orthopyroxene
Authors: Nord G. L.
Published: June 2020

Pyroxenes (Ca,Mg,Fe)2Si2O6 are common rock-forming minerals containing both equilibrium and nonequilibrium precipitation products, the distribution, structure and occurrence of which present information necessary for deciphering the mineral1s thermal and mechanical history. One such feature is small zones of calcium-enrichment identified in both terrestrial and lunar orthorhombic pyroxene (Mg,Fe)2Si2O6 (Champness and Lorimer, 1974; and Nord et al.,1977). The zones are disc-shaped parallel to (100). Dark field lattice images obtained utilizing the hll reflections (Fig.l) indicate that the zones are coherent with the host and have similar lattice constants (d100=18.2Å for orthopyroxene). The maximum width of the zones in the terrestrial occurrences is 18Å (one-unit-cell wide) and have therefore been termed G.P. zones by Champness and Lorimer (1973). The lunar orthopyroxene ( from an olivine-anorthite rock, 76535), however, contains G.P. zones identical in all the above characteristics except that the zones are 5 to 6 unit cells wide (∼100Å, Fig. 2).
Optical filtering of images of dislocation core
Authors: Desseaux J. , D'anterroches C. , Penisson J.M. , Renault A.
Published: June 2020

The optical analysis of images obtained with electron microscopes has been widely developed for structural determination of periodic biological objects and for microscope aberration correction in images of periodic or non periodic objects.

Our present purpose is to improve the signal to noise ratio of high resolution micrographs of crystal defects recorded at the Scherzer focalus with the 500 kV Kyoto electron microscope. It is not necessary to correct for sign reversals since the microscope transfer function has the same sign over the 0.13 Å-1 - 0.4 Å-1 spatial frequency domain. Our images are noisy due to photographic or electron processes and to object contamination. Thus a simple binary amplitude filter is placed in the optical Fourier transform plane of the object to remove the noise. As the mask shape has a great influence on the information contained in the reconstructed image we have tested the restoration of two nearly similar dislocation cores with two different masks.
Determination of the Burgers vector of a dislocation in a Fe-Mn alloy by weak-beam image in HVEM
Authors: Ishida Y. , Ishida H. , Kohra K. , Ichinose H.
Published: June 2020

Introduction

A simple and accurate technique to determine the Burgers vector of a dislocation has become feasible with the advent of HVEM. The conventional image vanishing technique(1) using Bragg conditions with the diffraction vector perpendicular to the Burgers vector suffers from various drawbacks; The dislocation image appears even when the g.b = 0 criterion is satisfied, if the edge component of the dislocation is large. On the other hand, the image disappears for certain high order diffractions even when g.b ≠ 0. Furthermore, the determination of the magnitude of the Burgers vector is not easy with the criterion. Recent image simulation technique is free from the ambiguities but require too many parameters for the computation. The weak-beam “fringe counting” technique investigated in the present study is immune from the problems. Even the magnitude of the Burgers vector is determined from the number of the terminating thickness fringes at the exit of the dislocation in wedge shaped foil surfaces.
A method for burgers vector characterization in minerals
Authors: Gandais M. , Willaime C.
Published: June 2020

In some minerals, little is known about slip systems ; then the characterization of dislocation Burgers vector is important in the study of their deformation. However, the classical method which involves extinction conditions = 0 with is often unrelevant : the diffracting vectors with a high structure factor which are used for two-beam case images, generally correspond to high indices so that in = 0 cases, the values are high (about 2 or 3), then the dislocation contrasts remain important.

Contrast simulations of inclined dislocations through crystal foils, derived from HEAD method were performed. The determination of can be achieved through comparisons between a set of several -micrographs and a set of corresponding -simulations assuming different hypothesis upon . If the method is used without any crue, a lot of simulations are needed due to the generally strong dependance of contrast features upon parameters which cannot be measured with a good accuracy.
A new dissociation mode for dislocations in silicon
Authors: Ourmazd A. , Booker G.R. , Humphreys C.J.
Published: June 2020

A (111) phosphorus-doped Si specimen, thinned to give a TEM foil of thickness ∼ 150nm, contained a dislocation network lying on the (111) plane. The dislocation lines were along the three <211> directions and their total Burgers vectors,ḇt, were of the type , each dislocation being of edge character. TEM examination under proper weak-beam conditions seemed initially to show the standard contrast behaviour for such dislocations, indicating some dislocation segments were undissociated (contrast A), while other segments were dissociated to give two Shockley partials separated by approximately 6nm (contrast B) . A more detailed examination, however, revealed that some segments exhibited a third and anomalous contrast behaviour (contrast C), interpreted here as being due to a new dissociation not previously reported. Experimental results obtained for a dislocation along [211] with for the six <220> type reflections using (g,5g) weak-beam conditions are summarised in the table below, together with the relevant values.
Electrochemical nucleation and growth of copper on iron and aluminum: A TEM study of industrial copper cementation
Authors: Murr L.E. , Annamalai V.
Published: June 2020

Georgius Agricola in 1556 in his classical book, “De Re Metallica”, mentioned a strange water drawn from a mine shaft near Schmölnitz in Hungary that eroded iron and turned it into copper. This precipitation (or cementation) of copper on iron was employed as a commercial technique for producing copper at the Rio Tinto Mines in Spain in the 16th Century, and it continues today to account for as much as 15 percent of the copper produced by several U.S. copper companies.

In addition to the Cu/Fe system, many other similar heterogeneous, electrochemical reactions can occur where ions from solution are reduced to metal on a more electropositive metal surface. In the case of copper precipitation from solution, aluminum is also an interesting system because of economic, environmental (ecological) and energy considerations. In studies of copper cementation on aluminum as an alternative to the historical Cu/Fe system, it was noticed that the two systems (Cu/Fe and Cu/Al) were kinetically very different, and that this difference was due in large part to differences in the structure of the residual, cement-copper deposit.
Surface study by UHV electron microscope
Authors: Yagi K. , Takayanagi K. , Kobayashi K. , Osakabe N. , Tanishiro Y. , Honjo G.
Published: June 2020

Recent advances of UHV techniques, LEED, RHEED and AES, arose a surge of interest on the surface of solids. These techniques reveal structures and chemical compositions at the mono-atomic or mono-molecular level. All of them, however, are devoid of detailed topographic informations, although some efforts to introduce the scanning techniques have been done[l]. Transmission electron microscopy of high resolution should play a complementary role to these techniques. No attempt, however, has been done previously to use it to such a purpose. This was because it was difficult to get and keep clean surfaces in the poor vacuum at 1x10-5Torr level of the conventional electron microscope.

The present paper reports observations of surface phenomena of one or two atomic layer level using a UHV JEM 100B electron microscope (10-8-10-10Torr), recently developed for insitu thin film growth studies[2]. Atomically flat (111) surfaces of Ag, Pd, Au and Cu were prepared by in- situ deposition at 150-350°C on M0S2, graphite and MgO. Air Cleaved thin films of MoS2 and graphite were preheated to 800°C to get clean surfaces[3].
Elucidation of block boundaries as the dissolution channels in hydrated cement
Authors: Belov N.V. , Papiashwili U.I. , Yudovich B.E.
Published: June 2020

It has been almost universally adopted that dissolution of solids proceeds with development of uniform, continuous frontiers of reaction.However this point of view is doubtful / 1 /. E.g. we have proved the active role of the block (grain) boundaries in the main phases of cement, these boundaries being the areas of hydrate phases' nucleation / 2 /. It has brought to the supposition that the dissolution frontier of cement particles in water is discrete. It seems also probable that the dissolution proceeds through the channels, which serve both for the liquid phase movement and for the drainage of the incongruant solution products. These channels can be appeared along the block boundaries.

In order to demonsrate it, we have offered the method of phase-contrast impregnation of the hardened cement paste with the solution of methyl metacrylahe and benzoyl peroxide. The viscosity of this solution is equal to that of water.