bluuebunny/crossref_metadata_2025 huggingface dataset:
Three - dimensional coherent electron microdiffraction applied to oxygen precipitates in silicon
Authors: Kim Y. , Shindo S. , Long N. , Spence J.C.H.
Published: June 2020

The study of the atomic and electronic structure of oxygen precipitates in CZ silicon has a long history. After a long annealing treatment at 600-700°C, two kind of precipitate phases have been observed. One is rod-like defects which have been known as a crystalline silica phase,coesite. The other is small amorphous platelets similar, but smaller than those observed at higher temperatures. We have found new polyhedral shaped, crystalline precipitates with a size of 300A° to 650A° in CZ silicon (oxygen rich, low carbon) annealed for 256 hours at 635°C. Fig.l shows high resolution lattice images of a 300A° diameter particle obtained using a JEOL 200CX at 200kV. Four faces are parallel to the Si﹛111﹜ planes, and two are truncated in Si(100) as for the amorphous octahedral observed at 1100-1200°C. These particles give the diffraction patterns shown in Fig.2 (obtained on a Philips 400 STEM FEG) at 100kV with 50A° probe from a 650A° particle. Our experimental data calibrated using silicon discs and lattice images are consistent with the tetragonal keatite [012] zone axis pattern within the error ranges.
Diffraction effects from interfaces
Authors: Vitek J. M.
Published: June 2020

The ability of electron microscopes to examine the structure and composition of materials on a very fine scale has paved the way for a renewed interest in examining the structure at interfaces and grain boundaries. Complemented by theoretical work on the structure of interfaces, much new information has become available. Among the various techniques available for studying the structure at interfaces, diffraction experiments have proved to be very useful. It has been shown, for example, that a periodic array of defects exists within the plane of the interface, leading to extra reflections in the plane of the interface. More recently, the diffraction behavior in the direction perpendicular to the interface plane has been examined. By considering diffraction effects in this direction only (to be referred to as the z direction in real space and the L direction in reciprocal space), information can be derived on the structural distortions in this direction near the interface without interference from any arrays of defects within the interface plane.
Microstructure of MBE Grown Al/Gaas [100] schottky contacts
Authors: Kiely C. J. , Cherns D.
Published: June 2020

The Aℓ/GaAs contact system is used in microwave field effect transistors, but to date, little systematic TEM characterization of the contact microstructure has been performed. There are three possible epitaxial configurations of Aℓ on GaAs [100].

[100]Aℓ; Aℓ [100] ||GaAs[100], Aℓ [010] ||GaAs[011]
[110]Aℓ; Aℓ [110] ||GaAs[100], Aℓ [110]||GaAs[011]
[110]R Aℓ; Aℓ[110] ||GaAs[100], Aℓ [001] ||GaAs [011]

The interfacial atomic structure of Aℓ[100] ||GaAs[100] has been investigated previously using a CBED technique on plan view specimens. this paper we study the distribution of the various Aℓ orientations as a function of initial GaAs surface reconstruction and film thickness. The misfit dislocation structure of [100] Aℓ/[100] GaAs has been characterized by weak beam microscopy. Also, lattice images from cross-sectional samples are presented. The samples studied were MBE grown and subsequent electrical characterization showed them all to have Schottky barrier heights (SBH) of 0.77eV and excellent rectifying properties over a large temperature range.
Application of WACBED to superlattice structures in compound semiconductors
Authors: McKernan S.
Published: June 2020

Superlattice structures are now routinely grown in compound semiconductors, with superlattice periodicities ranging from a few angstroms to several hundred angstroms. The structures consist of alternating layers of compound semiconductor which have different chemical composition. The composition of the layers may be chosen to provide a relatively large lattice mismatch for a strained layer superlattice, or to provide lattice matching for good epitactic growth. The chemical difference may be large, as in AIAs/GaAs for example or may be represent only a change in concentration of substitutionally doped material. In all of these materials it is important to characterize the material of the individual layers as well as the interface between these layers.

Microscopy of these materials has been performed in real space, using both high resolution and diffraction contrast techniques, and in reciprocal space. The thin cross section specimens used in these investigations are affected by stress relaxation at the interfaces which can result in bending of the atomic planes near the interface.
Evidence for very high order laue zone (VHOLZ) lines in CBED patterns
Authors: Sung C. M.
Published: June 2020

It is well known that High Order Laue Zone (HOLZ) line analysis is a powerful tool to study lattice parameter changes due to local chemical composition and microstrain, in addition to determining crystal symmetry. One of the first approaches described by Ecob et al for indexing the HOLZ reflections does not simulate all the observed HOLZ lines. Therefore a more complete computer program for indexing all the observed HOLZ reflections based on kinematical conditions has been developed using the visibility criterion originally developed for Kossel lines. This approach is easy and more accurate. With this technique we have been able to identify very high order Laue zone lines (>3rd order) in low symmetry orientations and index them.

Figs, la and lb are computer simulations which show the indexed HOLZ reflections for the second order (SOLZ) and fourth order Laue zone (FOROLZ) in the <116> zone axis. The corresponding defect HOLZ lines in the transmitted disk from pure Al are shown along with computer-simulated patterns for both the SOLZ and FOROLZ in Figs. 2a and 2b respectively.
Study of segregation in La1.8Sr0.2CuO4 superconductor by STEM-EDS microanalysis
Authors: Kelly T. F. , Lee P. J. , Hellstrom E. E. , Larbalestier D. C.
Published: June 2020

Recently there has been much excitement over a new class of high Tc (>30 K) ceramic superconductors of the form A1-xBxCuO4-x, where A is a rare earth and B is from Group II. Unfortunately these materials have only been able to support small transport current densities 1-10 A/cm2. It is very desirable to increase these values by 2 to 3 orders of magnitude for useful high field applications. The reason for these small transport currents is as yet unknown. Evidence has, however, been presented for superconducting clusters on a 50-100 nm scale and on a 1-3 μm scale. We therefore planned a detailed TEM and STEM microanalysis study in order to see whether any evidence for the clusters could be seen.

A La1.8Sr0.2Cu04 pellet was cut into 1 mm thick slices from which 3 mm discs were cut. The discs were subsequently mechanically ground to 100 μm total thickness and dimpled to 20 μm thickness at the center.
Developments in the processing of electron energy-loss spectra
Authors: Egerton R.F.
Published: June 2020

Because the total-inelastic mean free path is generally comparable to the specimen thickness, energy-loss spectra recorded in a TEM contain appreciable contributions from plural (or multiple) scattering, which imparts no additional information but may distort or submerge characteristic features. Happily, the single-scattering spectrum S(E) can be derived from a recorded spectrum by the method of Fourier-log deconvolution; if j(f) and z(f) are the Fourier transforms of the recorded data J(E) and of the zero-loss peak Z(E), the Fourier transform s(f) of the single-scattering distribution S(E) is given by:

s(f) = r(f) loge [j(f)/z(f)] (1)

Here, r(f) is the Fourier transform of a bell-shaped reconvolution function R(E); if r(f) were omitted from Eq.(l), s(f) would correspond to an ‘ideal’ single-scattering distribution, unbroadened by the instrumental resolution △E.
Computer system architecture for image and spectral processing
Authors: Rez Peter , Fathers D.J.
Published: June 2020

In this paper we shall discuss digital imaging and spectroscopy systems from the perspective of a system designer and we shall concentrate on those design choices that limit performance in microscopy and analysis applications. The hardware of a computer system can be broken down into three main components. These are the processor which performs arithmetic and logical operations, the memory for storing data and instructions and the peripherals for long term data storage (disks, tapes) and communication with the outside world. Linking these components is a data highway or bus for passing digital information from one section of the machine to another. A good definition of a bus is a set of interconnections with a defined procedure (protocol) for information transmission. In many small systems the bus is not only a set of electrical connections but is also an enclosure (a backplane) into which the different modules (processor, memory, peripheral controllers) are added.
Image processing of nonperiodic electron micrographs
Authors: McKernan S.
Published: June 2020

The information contained in transmission electron microscope (TEM) images originates from many sources. It is the aim of image processing to extract those details of the image that arise from features of interest in the specimen, and to supress the remaining details. For periodic micrographs (lattice images of perfect crystals for example) this has been accomplished typically by either averaging over many unit cells in real space or through the use of Fourier filtering techniques in reciprocal space. Both of these techniques rely on the fact that useful information occurs periodically (i.e. at each lattice position) so that departures from this periodicity are a result of image degradation only. Obviously if there are departures from perfect regularity in the image, as at a stacking fault or a twin boundary for example, supressing the non-periodic information will not reveal much about the nature of the faults.
Enhancing the contrast of defects in lattice images
Authors: Fan Gary
Published: June 2020

The technique used in processing HREM images to locate atomic positions in defective area of crystal, such as grain boundaries and GP zones which often have poor contrast in a HREM image due to strain fields and, worse yet, lack of atomic columns in the projection, has been the application of ring filters in Fourier space to get rid of both high and low frequency components. There is no doubt that such technique is capable of providing useful results, but only if practiced with caution. Enough bandwidth must be kept to guarantee the claimed resolution which, one has to remember, is not simply determined by the larger diameter of the ring filter. As pointed out, a compromise, between effectively removing ‘noise’ and creating spurious atoms, exists which probably depends on specific case. Improper use can give impressive, but not necessarily reliable, results.
On convenient use of nanoprobe and scanning without a stem unit in an EM-420
Authors: Christenson K. K. , Eades J. A.
Published: June 2020

One of the strengths of the Philips EM-400 series of TEMs is their ability to operate under two distinct optical configurations: “microprobe”, the normal TEM operating condition which allows wide area illumination, and “nanoprobe”, which gives very small probes with high angular convergence for STEM imaging, microchemical and microstructural analyses. This change is accomplished by effectively turning off the twin lens located in the upper pole piece which changes the illumination from a telefocus system to a condenser-objective system. The deflection and tilt controls and alignments are designed for microprobe use and do not function properly when in nanoprobe. For instance, in nanoprobe the deflection control gives a mix of deflection and tilt; as does the tilt control.
Studies of the scanning ion beam sputter-cleaned MgO crystal surface by scanning reflection electron microscopy
Authors: Ou H.-J. , Cowley J. M. , Higgs A. A.
Published: June 2020

A scanning ion gun system has been installed on the specimen preparation chamber (pressure ∼5xl0-8 torr) of the VG-HB5 STEM microscope. By using the specimen current imaging technique, it is possible to use an ion beam to sputter-clean the preferred surface region on a bulk sample. As shown in figure 1, the X-Y raster-gate control of the scanning unit for the Krato Mini-Beam I is used to minimize the beam raster area down to a 800μm x800μm square region. With beam energy of 2.5KeV, the MgO cleavage surface has been ion sputter-cleaned for less than 1 minute. The carbon film or other contaminant, introduced during the cleavage process in air, is mostly removed from the MgO crystal surfaces.

The immediate SREM inspection of this as-cleaned MgO surface, within the adjacent STEM microscope, has revealed the detailed surface structures of atomic steps, which were difficult to observe on the as-cleaved MgO surfaces in the previous studies.
Identification of a new phase in the Ai-C-B ternary by high-resolution transmission electron microscopy
Authors: Sarikaya M. , Laoui T. , Milius D. L. , Aksay I. A.
Published: June 2020

The purpose of this note is to report the identification of a ternary (XI) phase which has been observed as a reaction product during the processing of B4C-Al composites. These ceramic-metal composites (cermets) have the unique potential for structural applications because of their low density (> 2.6 g/cc) and a desirable combination of mechanical properties. Guidelines for the processing of B4C-Al have been successfully established; and now it is possible to produce tailored microstructures with varying amounts of constituent phases.

The samples for the analysis were prepared by the following procedure. First, it was necessary to heat the B4C powder compacts in excess of 2000°C to attain an interconnected B4C skeletal structure. Liquid aluminum was then infiltrated into this B4C network at 1170°C.
“Stm” Scanning Tunneling Microscopy
Authors: Kubby J. A.
Published: June 2020

Scanning Tunneling Microscopy is a recently developed technique within the area of Scanned Image Microscopy that is based on tunneling between two conducting electrodes. This method offers, for the first time, the possibility of direct, real space determination of surface atomic and electronic structure in three dimensions on an atomic length scale, including nonperiodic structures.

In this technique a sharp metal tip, mounted on a piezoelectric tripod that forms an orthogonal coordinate system, is brought to within a few Angstroms of the sample surface without “touching” the region to be scanned. A tunneling current I, on the order of 0.1 to 1 nA, is established by applying a bias between the tip and sample. The tunneling current is given to first order by;
Analytical Electron Microscopy of Automotive Catalysts
Authors: Chen Y. L. , Powell B. R.
Published: June 2020

The automotive industry uses catalytic converters to reduce the amounts of regulated emissions that are released to the atmosphere from engine exhaust gases. However, given the presence of catalyst poisons in the exhaust gases and operating temperatures in the converter that frequently exceed 700 °C, durability is a major concern for the catalyst. A detailed understanding of the catalyst deactivation mechanisms (poisoning and particle growth of noble metal particles) is essential to the development of more durable catalysts.

Most studies of catalyst deactivation have relied on bulk analytical characterization techniques such as chemisorption, chemical analysis, and x-ray diffraction. Unfortunately, these conventional techniques yield ambiguous and incomplete information about the catalyst because they fail to give a description of the catalyst at the microscopic level where catalysis occurs.
Microstructures of Ni3Al alloyed with iron
Authors: Horton J.A. , Liu C.T. , Santella M.L.
Published: June 2020

The nickel aluminide, Ni3Al, is an ordered intermetallic alloy that exhibits an increase in yield stress with an increase in temperature. Recent efforts have alleviated the inherent grain boundary brittleness by microalloying with boron. Alloying additions such as iron can be used to further increase the high temperature yield stress.

Microstructures and phase relationships in the aluminides were studied by transmission electron microscopy. A Ni3Al alloy with 10 at.% iron was single phase with the ordered Ll2 structure. Two alloys with 15% iron were found to contain a two-phase, γ + γ', cellular structure that consisted of small islands of crystallographically aligned ordered γ', surrounded by a “web” of disordered γ, Fig. 1. At 20% iron, the cellular structure encompasses nearly the entire specimen. Figure 2, a bright-field, dark-field pair of micrographs, shows the dislocation-cell structures (2a) and the ordered cellular structure (2b) present after tensile deformation at 600°C.
surface crystallization of the metallic alloy Fe78B13Si9
Authors: Marti J. , Reidinger F. , Signorelli A.J.
Published: June 2020

The crystallization that occurs in amorphous metallic alloys after isothermal annealing has been studied in a number of reports. Under certain conditions however, a surface crystalline layer may be present in an otherwise amorphous ribbon. Such crystalline structures at the surface of the ribbons may result from isothermal annealing below the normal crystallization temperature or they can result if improper casting conditions are used, which could decrease the thermal contact with the casting wheel. In either case, the presence of a surface crystalline layer has a detrimental effect on the magnetic properties of the ribbons. Thus, it is important that the nature of these structures be better understood. We have used transmission electron microscopy and x-ray diffraction to characterize the crystalline surface structures which can result if quenching conditions during casting are not adequate.
A combined Tem/Apfim study of precipitation in ion-nitrided ultra-low carbon bainitic steel
Authors: Burke M.G. , Palmiere E.J. , DeArdo A.J.
Published: June 2020

Ion-nitriding represents an attractive and cost-effective process for improving the surface properties (hardness, wear resistance) and fatigue behavior of ultra-low carbon bainitic (ULCB) steels (1). Although the improvements in mechanical properties of nitrided steels are well-documented, precipitation in these steels during the nitriding process has not been studied extensively. The precipitation in ULCB steels is complex due to the presence of Mo, Mn, and Ni. Therefore, to investigate nitride precipitation in these steels, we have employed both TEM and APFIM in order to characterize the ultra-fine precipitates.

The material employed in this study was a fully bainitic ULCB steel (0.021C- lMn- 1.4Ni- 1.5Mo- 0.016Ti- 0.05 2Nb -0.001B). Ion-nitriding was performed at 466°C for 14 hours using a mixture of 75% H2 - 25% N2 at a pressure of 2500 millitorr.
Application of Analytical Electron Microscopy to design of creep-resistant advanced austenitic stainless steels
Authors: Maziasz P.J.
Published: June 2020

Analytical electron microscopy (AEM) has been used for the last ten years to study precipitation produced in reactor-irradiated austenitic stainless steels, such as AISI type 316. These studies have provided the insight to design irradiation resistant steels based on control of precipitiation. More recently, similar insight into precipitation effects in steels allowed the design of advanced austenitics that also exhibit outstanding thermal creep resistance at 700°C. These steels have direct application for superheater/ reheater tubing materials that will withstand higher temperatures and stresses in advanced steam cycle fossil power plants.

Fine particles (<10 nm in diam) on extraction replicas have been studied by AEM using a high brightness electron source to provide sufficient probe currents for reliable analyses. These studies allowed alloy compositional modifications to be selected that produced stable, fine precipitates for creep strength.
Electron microscopy of TMT Al-Li-Cu alloys
Authors: Radmilovic V. , Nelson C. , Thomas G.
Published: June 2020

The Al-Li series of alloys are now receiving broad and intensive research attention due to their attractive strength-weight and elastic modulus properties. Their disadvantages center around inadequate fracture toughness and corrosion properties unless complex thermal mechanical treatments (TMS) are employed so as to make the microstructures more uniform. In this regard there are similarities to the Al-Zn-Mg alloys for which also special TMT treatments have been successful.

Thus the present research work is concerned with characterizing the microstructure following various TMT procedures of an A1-2.35%Li-2.49%Cu- 0.13 %Zr alloy prepared by Alcoa as part of a broad research program on these alloys. The specific treatment to be reported on here is as follows:- (i) Solution treat 550°C 2 hrs. ice brine quench, (ii) Aged 175°C for 1 hr. (iii) 10% cold rolling, (iv) Re-age 175°C for 15 hrs.
Transition alpha structure in beta-isomorphous Nb-Hf alloys
Authors: Carpenter R.W. , Li Changhai , Smith David J.
Published: June 2020

Binary Nb-Hf alloys exhibit a wide bcc solid solution phase field at temperatures above the Hfα→ß transition (2023K) and a two phase bcc+hcp field at lower temperatures. The β solvus exhibits a small slope above about 1500K, suggesting the possible existence of a miscibility gap. An earlier investigation showed that two morphological forms of precipitate occur during the bcc→hcp transformation. The equilibrium morphology is rod-type with axes along <113> bcc. The crystallographic habit of the rod precipitate follows the Burgers relations: {110}||{0001}, <112> || <1010>. The earlier metastable form, transition α, occurs as thin discs with {100} habit. The {100} discs induce large strains in the matrix. Selected area diffraction examination of regions ∼2 microns in diameter containing many disc precipitates showed that, a diffuse intensity distribution whose symmetry resembled the distribution of equilibrium α Bragg spots was associated with the disc precipitate.
Defect structure and mechanical twinning in rolled and annealed tantalum
Authors: Chatterjee T. K. , Feng C.
Published: June 2020

Twinning, in association with martensitic shear has been extensively discussed in the literature for high carbon steel. This paper describes similar twinning operations observed in as rolled and annealed tantalum plate. The study was performed at 12øKV in a Philips electron microscope. As rolled and rolled/annealed tantalum plate, 8mm thick were first cut into 25ø um thin sections using a slow speed diamond saw, then ion milled to a thickness of 5ø-1øø um and electropolished in a 90 H2Sø4:1øHF solution.

High density dislocation tangles forming the cell wall of the subgrain can be seen in the representative area of the rolled tantalum specimen shown in figure 1. The dislocation density within the matrix of the subgrain is about 1ø11/cm2. Dislocation loops, identified by the letter A, are present within the subgrains. Similar dislocation arrays have been reported in other b.c.c. metals.
Direct structure images of 30° partial dislocation cores in silicon
Authors: Barry J. C. , Alexander H.
Published: June 2020

Dislocations in silicon produced by plastic deformation are generally dissociated into partials. 60° dislocations (Burgers vector type 1/2[101]) are dissociated into 30°(Burgers vector type 1/6[211]) and 90°(Burgers vector type 1/6[112]) dislocations. The 30° partials may be either of “glide” or “shuffle” type. Lattice images of the 30° dislocation have been obtained with a JEM 100B, and with a JEM 200Cx. In the aforementioned experiments a reasonable but imperfect match was obtained with calculated images for the “glide” model. In the present experiment direct structure images of 30° dislocation cores have been obtained with a JEOL 4000EX. It is possible to deduce the 30° dislocation core structure by direct inspection of the images. Dislocations were produced by compression of single crystal Si (sample preparation technique described in Alexander et al.).
Precipitation in silicon-on-insulator material during high- temperature annealing
Authors: Krause S. J. , Jung C. O. , Wilson S.R.
Published: June 2020

Silicon-on-insulator (SOI) structure by high dose oxygen implantation (SIMOX) has excellent potential for use in radiation hardened and high speed integrated circuits. Device fabrication in SIMOX requires a high quality superficial Si layer above the buried oxide layer. Previously we reported on the effect of heater temperature, background doping, and annealing cycle on precipitate size, density, and location in the superficial Si layer. Precipitates were not eliminated with our processing conditions, but various authors have recently reported that high temperature annealing of SIMOX, from 1250°C to 1405°C, eliminates virtually all precipitates in the superficial Si layer. However, in those studies there were significant differences in implantation energy and dose and also annealing time and temperature. Here we are reporting on the effect of annealing time and temperature on the formation and changes in precipitates.
Structure of grain boundaries in hexagonal close-packed metals
Authors: King A.H. , Chen Fu-Rong
Published: June 2020

The structures and behaviors of grain boundaries in cubic materials have been studied extensively by electron microscopists for almost two decades, and much of this work has been related to the geometrical theories of Bollmann. Grain boundaries separating crystals that are close to coincident site lattice (CSL) misorientations have received extensive attention because they appear to have unusual properties and they also have relatively easily resolved structures which can be described in terms of dislocation arrays embedded in low-energy atomic configurations. When we start to deal with materials of lower than cubic symmetry, however, new problems arise and considerable difficulties beset the electron microscopist: in order to tackle some of these problems, we have begun by studying grain boundaries in hep metals.
The wustite-spinel interface
Authors: Summerfelt S.R. , Carter C.B.
Published: June 2020

The wustite-spinel interface can be viewed as a model interface because the wustite and spinel can share a common f.c.c. oxygen sublattice such that only the cations distribution changes on crossing the interface. In this study, the interface has been formed by a solid state reaction involving either external or internal oxidation. In systems with very small lattice misfit, very large particles (>lμm) with coherent interfaces have been observed. Previously, the wustite-spinel interface had been observed to facet on {111} planes for MgFe2C4 and along {100} planes for MgAl2C4 and MgCr2O4, the spinel then grows preferentially in the <001> direction. Reasons for these experimental observations have been discussed by Henriksen and Kingery by considering the strain energy. The point-defect chemistry of such solid state reactions has been examined by Schmalzried. Although MgO has been the principal matrix material examined, others such as NiO have also been studied.
The nucleation of cavities at grain boundaries
Authors: Goodhew P. J.
Published: June 2020

Cavity nucleation and growth at grain and phase boundaries is of concern because it can lead to failure during creep and can lead to embrittlement as a result of radiation damage. Two major types of cavity are usually distinguished: The term bubble is applied to a cavity which contains gas at a pressure which is at least sufficient to support the surface tension (2g/r for a spherical bubble of radius r and surface energy g). The term void is generally applied to any cavity which contains less gas than this, but is not necessarily empty of gas. A void would therefore tend to shrink in the absence of any imposed driving force for growth, whereas a bubble would be stable or would tend to grow. It is widely considered that cavity nucleation always requires the presence of one or more gas atoms. However since it is extremely difficult to prepare experimental materials with a gas impurity concentration lower than their eventual cavity concentration there is little to be gained by debating this point.
Diffraction from arrays of antiphase boundaries in ordered III-V alloys
Authors: Kuan T. S.
Published: June 2020

Recent electron diffraction studies have found ordered phases in AlxGa1-xAs, GaAsxSb1-x, and InxGa1-xAs alloy systems, and these ordered phases are likely to be found in many other III-V ternary alloys as well. The presence of ordered phases in these alloys was detected in the diffraction patterns through the appearance of superstructure reflections between the Bragg peaks (Fig. 1). The ordered phase observed in the AlxGa1-xAs and InxGa1-xAs systems is of the CuAu-I type, whereas in GaAsxSb1-x this phase and a chalcopyrite type ordered phase can be present simultaneously. The degree of order in these alloys is strongly dependent on the growth conditions, and during the growth of these alloys, high surface mobility of the depositing species is essential for the onset of ordering. Thus, the growth on atomically flat (110) surfaces usually produces much stronger ordering than the growth on (100) surfaces. The degree of order is also affected by the presence of antiphase boundaries (APBs) in the ordered phase. As shown in Fig. 2(a), a perfectly ordered In0.5Ga0.5As structure grown along the <110> direction consists of alternating InAs and GaAs monolayers, but due to local growth fluctuations, two types of APBs can occur: one involves two consecutive InAs monolayers and the other involves two consecutive GaAs monolayers.
Microstructure studies of tungsten silicide schottky contacts on Gaas
Authors: Shih Yih-Cheng , Wilkie E. L.
Published: June 2020

Tungsten silicides (WSix) have been successfully used as the gate materials in self-aligned GaAs metal-semiconductor-field- effect transistors (MESFET). Thermal stability of the WSix/GaAs Schottky contact is of major concern since the n+ implanted source/drain regions must be annealed at high temperatures (∼ 800°C). WSi0.6 was considered the best composition to achieve good device performance due to its low stress and excellent thermal stability of the WSix/GaAs interface. The film adhesion and the uniformity in barrier heights and ideality factors of the WSi0.6 films have been improved by depositing a thin layer of pure W as the first layer on GaAs prior to WSi0.6 deposition. Recently WSi0.1 has been used successfully as the gate material in 1x10 μm GaAs FET's on the GaAs substrates which were sputter-cleaned prior to deposition. These GaAs FET's exhibited uniform threshold voltages across a 51 mm wafer with good film adhesion after annealing at 800°C for 10 min.
Transmission electron microscopy of epitaxial gallium arsenide grown on a variety of silicon substrates by metallorganic chemical vapor deposition
Authors: Brown J. M. , Pearton S. J. , Caruso R. , Stavola M. , Short K. T. , Malm D. L. , Vernon S. M. , Hobson W. S.
Published: June 2020

The growth of GaAs layers on silicon substrates is under extensive investigation with a view to achieving the integration of GaAs-based optoelectronic devices with Si integrated circuit technology. The large lattice mismatch between Si and GaAs (-4%) together with the differences in the thermal expansion coefficients between the two materials results in a highly stressed interface. Several different approaches have been undertaken in attempts to reduce the dislocation density of the GaAs layer. The inclusion of graded composition GaAsP ‘buffer’ layers, intermediate Ge layers and the inclusion of strained layer superlattices in the growth regime have been reported by many workers. Growth of GaAs directly on Si has been reported to yield GaAs heteroepitaxial films suitable for electronic applications such as FETs and low threshold AlGaAs/GaAs double heterostructure injection lasers.
Enhancement of Atomic Number Contrast for Image Analysis of Highly Strained Materials
Authors: Lee P. J.
Published: June 2020

In order to produce high current density NbTi multifilamentary superconductors a complex thermo-mechanical processing route is followed. The composites are initially cold drawn to strains of 5-7 and heat treated to produce α-Ti precipitates at grain-boundary triple points. Subsequent drawing and heat treatment cycles (typically 3-6) increase the volume of precipitate and refine the homogeneity and scale of the microstructure. A final strain of 3-4 distorts the α-Ti precipitates (initially equiaxed in cross-section) into ribbons less than 4nm in thickness. The thickness and distribution of these “normal” α-Ti ribbons in the superconducting β-NbTi matrix is thought to play an important part in the flux pinning properties of the microstructure. The thickness and distribution of the ribbons are related to the diameter and distribution of the α-Ti precipitates after the final heat treatment. Measurement of these parameters is clearly useful and has been successfully,
A computer system for HREM image processing and simulation
Authors: O'Keefe Michael A.
Published: June 2020

A facility for electron microscope image analysis and interpretation has been established at the National Center for Electron Microscopy (NCEM) as a support for the electron microscopes. The main component of the facility is a computer system designed to assist the experimenter in both “real time” and post-recording image analysis. Real-time includes operator-controlled enhancement of the video-rate TV signal coming from the microscope, and the presentation of diffractograms as required by the microscope operator. Post-recording analysis includes post-processing of the experimental image as well as image simulation from model structures. Our chosen system is based on two host computers (Fig. 1): one host controls the post-recording workstations and the other runs the real-time stations. MicroVAX II minicomputers running the VMS operating system were chosen for both the main and real time hosts because the VMS system is multi-user and has virtual memory capability; in addition, it is the operating system most familiar to outside users of the facility.
Preparation of cross-sectional samples for near-surface TEM studies
Authors: Dickenson R.C. , Lawless K.R.
Published: June 2020

In thermal oxidation studies, the structure of the oxide-metal interface and the near-surface region is of great importance. A technique has been developed for constructing cross-sectional samples of oxidized aluminum alloys, which reveal these regions. The specimen preparation procedure is as follows: An ultra-sonic drill is used to cut a 3mm diameter disc from a 1.0mm thick sheet of the material. The disc is mounted on a brass block with low-melting wax, and a 1.0mm hole is drilled in the disc using a #60 drill bit. The drill is positioned so that the edge of the hole is tangent to the center of the disc (Fig. 1) . The disc is removed from the mount and cleaned with acetone to remove any traces of wax. To remove the cold-worked layer from the surface of the hole, the disc is placed in a standard sample holder for a Tenupol electropolisher so that the hole is in the center of the area to be polished.
Nanometer-scale structures produced in oxide films
Authors: Hollenbeck J. L. , Buchanan R. C.
Published: June 2020

Rapid material removal has been found to occur in a number of metal halide and oxide films at the point of exposure to a high intensity electron beam. As a result, 3-dimensional, nanometer scale (1-100 nm) structures have been produced in these materials. Possible applications of these systems include substrates for high density E-beam data storage and E-beam resist materials for mask fabrication. Other potential applications would include processes where controlled patterning on a nanometer scale is desirable. In this study amorphous thin films of ZrO2, Y2O3 and AI2O3 were deposited onto coated Cu-grid substrates and the mechanism whereby E-beam interaction promoted rapid material removal on a nanometer scale was explored.

Films less than 200 nm in thickness were prepared in a Perkin-Elmer Randex 3140-6J sputtering system. Deposition of films directly onto 20 mesh formvar coated TEM grids facilitated handling and allowed immediate analysis by EM techniques.
Polymer decoration : Principle and uses in surface science
Authors: Lotz B. , Wittmann J. C.
Published: June 2020

The vaporization and condensation of gold particles introduced by G. A. Basset has become a classical method in surface investigation by electron microscopy. The “gold decoration” of small drops reveals steps of atomic diameter on the surface of alkali halides.

Recently, an original decoration technique has been introduced, which is similar in its principle and experimental set up to gold decoration, but uses polymer molecules rather than gold as the marker. The vaporized polymer (typically polyethylene) has a molecular weight of ∼ 1300, i.e. is an elongated cylinder about 100 Å long and 5 Å diameter; this shape makes it a directional marker, in sharp constrast to gold atoms. The molecules build up small rods (in essence, polymer lamellae seen edge on) visible by conventional electron microscopy. The pattern of these rods (the “polymer decoration“) reveals some of the substrate structural features and can be used to analyze polymer-substrate interactions.
The structure of sunlight-degraded polypropylene textile fibers
Authors: Barish Leo
Published: June 2020

Most investigations relating to the miorostructure of light-degraded polypropylene have been made on film or bulk polymer. Some studies have been made in monofilaments but little on fine textile-grade fiber.

Sunlight-degraded polypropylene fibers were obtained from the top surface of an automobile seat cover that had been in service for about five years. The degraded fibers were taken from an area at the top of the back cushion beneath the non-tinted rear window; an area not subject to abrasion but very susceptible to direct sunlight. The origin of these fibers is unknown as is the possible presence of photoinhibitors. From a shaded, undamaged part of the seat cover, undegraded fibers were obtained and examined; they appeared to be round, slightly crimped, bright with little pigmentation, and measured 31.8 μm in diameter, which corresponds to a nominal 0.72 tex or 6.5 denier.
Cryo-Transmission Electron Microscopy of latex systems
Authors: Talmon Yeshayahu
Published: June 2020

Transmission electron microscopy is the most suitable method for the study of latex systems, because it provides direct images of these particles, typically 20 to 500 nm in diameter. As latex preparations contain large amounts of water, methods must be used to make the specimen vacuum compatible, and to arrest any supramolecular motion in it. The most common techniques for latex specimen preparation involve drying of a large drop, a thin liquid layer or atomized droplets. Although suitable for some systems, drying may strongly affect the microstructure of a latex. Particle collapse, aggregation, and coating by concentrated solutes are some of the most common artifacts introduced by drying techniques. An alternative to these are cryo-microscopy methods, that involve fast freezing of the latex aqueous dispersion. The frozen sample is either examined directly, or it is fractured, a metal-carbon replica of the fracture surface is then prepared and examined at room temperature.
TEM analysis of core/shell latex morphology
Authors: Shaffer O.L. , El-Aasser M.S. , Vanderhoff J.W.
Published: June 2020

Transmission electron microscopy is an excellent method to study particle size and particle morphology of latexes. Special sample techniques are utilized in the study of latexes and often more than one technique is needed to answer questions concerning the structure of the particle. If the latex is of a core/shell type the study becomes more complex. Sample preparation for studying latexes include staining with osmium tetroxide to crosslink and stain unsaturated polymers, cold stage if the latex is too soft to examine at room temperature, negative staining to increase contrast shadowing to determine the sag of the particle at room temperature, ultramicrotoming, cryoultramicrotoming or a combination of techniques such as staining and cold stage.

The latex investigated was the first stage seed latex of poly (butylacrylate - butadiene) and the final latex a core-shell of poly(butylacrylate - butadiene)/poly(methyl methacrylate). Because of its unsaturation, poly(butadiene) can be preferentially stained with osmium tetroxide.
LVSEM: A new way of seeing biology
Authors: Pawley J.B.
Published: June 2020

When dried, soft tissue biological samples have a density of .3 to .02 g/cm3. In such material, the range of electrons having an energy of 20-30 keV can be tens or hundreds of microns, and electons emitted from any surface of the sample within this range can contribute to the detected secondary electron signal. However, only those originating from the immediate vicinity of the beam contribute useful topographic information. Those emerging farther away contribute not only a slowly varying noise signal, but the statistical variations in this signal constitute an important noise source. In many cases, it may be so great as to totally mask the signal variations due to topographic contrast. In biology, the limitations caused by this fact are usually ameliorated by coating the outer surface of the sample with 10-20 nm of a heavy metal such as gold (density = 19 g/cm3).
Extracellular matrix morphogenesis: HVEM analysis
Authors: Birk David E. , Trelstad Robert L.
Published: June 2020

Matrix morphogenesis requires the synthesis, assembly and deposition of collagen molecules in a tissue specific manner. Collagen fibrillogenesis is a multistep process involving both intracellular and extracellular assembly reactions. Collagen synthesis, molecular assembly and formation of supramolecular aggregates occurs within a series of well defined cytoplasmic compartments while the assembly and deposition of the newly synthesized collagen fibrils, fibril bundles and tissue specific collagen macroaggregates occurs within a series of extracellular compartments defined by the fibroblast.

In the studies described here we will focus our attention on the cellular influences involved in the assembly of collagen molecules into fibrils, fibril bundles and tissue specific macroaggregates. The chick tendon and corneal fibroblasts partition the extracellular space during morphogenesis, forming at least three compartments. These extracytoplasmic compartments have been described using high voltage electron microscopy of thick sections and serial thick sections as well as by conventional transmission electron microscopy.
High-voltage electron microscopy of patch-clamped membranes
Authors: Sachs F. , Song M. J.
Published: June 2020

Cellular electrophysiology has been revolutionized by the introduction of patch clamp techniques. The patch clamp records current from a small patch of the cell membrane which has been sucked into a glass pipette. The membrane patch, a few micons in diameter, is attached to the glass by a seal which is electrically, diffusionally and mechanically tight. Because of the tight electrical seal, the noise level is low enough to record the activity of single ion channels over a time scale extending from 10μs to days. However, although the patch technique is over ten years old, the patch structure is unknown. The patch is inside a glass pipette where it has been impossible to see with standard electron microscopes. We show here that at 1 Mev the glass pipette is transparent and the membrane within can be seen with a resolution of about 30 A.
Combining HVEM and computer-assisted reconstructions to elucidate the three-dimensional structure of taste buds
Authors: Kinnamon John C.
Published: June 2020

The vertebrate taste bud contains 50 to 150 spindle-shaped cells assembled in an onion-shaped structure approximately 60 μm wide and 80-100 μm tall. Located on the tongue and other portions of the oral epithelium, taste buds are always in a state of flux, with new cells continually entering the bud and moving from the periphery to the core as they mature. During the developmental process, young taste cells form afferent synaptic connections with sensory nerve fibers which enter the taste bud at the base and course tortuously throughout the bud. As taste cells age and become senescent, they lose their synaptic connections with the nerve fibers, degenerate, and eventually disappear. All of the processes described above result in the complete turnover of the cells within a taste bud in a period of from 10 days to two weeks in the rat.
Cell morphology, volume, and surface area determinations from multilevel contouring within HVEM micrographs of serial sections and whole-cell mounts
Authors: Marko M. , Leith A. , Parsons D.
Published: June 2020

The use of serial sections and computer-based 3-D reconstruction techniques affords an opportunity not only to visualize the shape and distribution of the structures being studied, but also to determine their volumes and surface areas. Up until now, this has been done using serial ultrathin sections.The serial-section approach differs from the stereo logical methods of Weibel in that it is based on the Information from a set of single, complete cells (or organelles) rather than on a random 2-dimensional sampling of a population of cells. Because of this, it can more easily provide absolute values of volume and surface area, especially for highly-complex structures. It also allows study of individual variation among the cells, and study of structures which occur only infrequently.

We have developed a system for 3-D reconstruction of objects from stereo-pair electron micrographs of thick specimens.
Electron microscopy of endomyocardial biopsies: Diagnostic and research applications
Authors: Ferrans V. J.
Published: June 2020

The development of safe techniques for obtaining right and left ventricular endomyocardial biopsy specimens with a bioptome catheter has provided the opportunity to examine the ultrastructural changes that occur in myocardium in a variety of disease states, particularly in the cardiomyopathies.

The most prominent microscopic abnormalities in hypertrophic cardiomyopathy are: a marked degree of myocyte enlargement, extensive foci of disarray of the myocytes (involving more than 5% of the cells), variable degrees of interstitial fibrosis, and fibromuscular intimal and medial thickening of small intramural coronary arteries. The myocytes have enlarged nuclei, increased numbers of mitochondria, which often accumulate in the perinuclear regions, and irregularly located intercellular junctions, which make extensive contacts not only at the ends of the cells but also along their sides. The disarray of the myocytes is accompanied by disarray of the myofibrils and myofilaments, which often form crisscrossing patterns.
Immunoelectron microscopy in normal and diseased elastic tissues
Authors: Fanning J. C. , White J. F. , Kumaratilake J. , Gibson M. A. , Cleary E. G.
Published: June 2020

Elastic tissue is recognised to be composed of a major amorphous component (consisting of the protein elastin) and a lesser microfibrillar component (complex structures containing at least two glycoproteins). The study of the components of elastic fibers in developing tissues has been hampered by the difficulty of establishing that the amorphous component is distinguishable from other amorphous structures. This is particularly a problem when the elastic material is deranged, so that the amorphous component is atypical in appearance. We have developed, in rabbits, and then affinity-purified, polyclonal antibodies to each of elastin (the amorphous component), “reductive guanidine extracts” of fetal bovine nuchal ligament and to a microfibril-associated glycoprotein (MAGP) isolated from these extracts.

Samples of fetal and adult bovine tissues, including aorta, skin and nuchal ligament; and human tissues; including skin, aorta and breast cancers, were fixed for 4 h in 4% paraformaldehyde and 0.2% glutaraldehyde in phosphate buffered saline, pH 7.4, containing 4% sucrose and 5% polyvinyl pyrolidine;