bluuebunny/crossref_metadata_2025 huggingface dataset:
SEM Correlation of Electrical Inhomogeneities and Crystal Defects in Semiconducting Si/Spinel Specimens
Authors: Norris C. B. , Thomas G. J. , Miglionico C. J.
Published: June 2020

The use of SEM to characterize electrically inhomogeneous semiconductor specimens has numerous applications. Previous studies, however, have generally yielded results only when gross features, such as PN junctions, are present in the specimen. Here we report a sensitive technique for detecting electrical inhomogeneities in a semiconductor and establishing their relation to microscopic defects observable through SEM. A result is shown for an epitaxial Si film on a spinel substrate.

Figure 1 describes the apparatus used for these studies. A JSM-II SEM is set to scan rapidly in the Y-direction, but at a much slower rate in the X-direction. The electron-beam-induced transient conductance of the contacted specimen produces a voltage at the input of a lock-in amplifier synchronized to the SEM Y-scan frequency. The demodulated amplifier output drives the Y-axis of an X-Y recorder, on which the X-axis sweep coincides with the slow X-scan of the SEM beam.
Temperature Dependence of Magnetic Domains and Wall Structures
Authors: Tsukahara Sonoko , Taoka Tadami , Nishizawa Hisao
Published: June 2020

The high voltage Lorentz microscopy was successfully used to observe changes with temperature; of domain structures and metallurgical structures in an iron film set on the hot stage combined with a goniometer. The microscope used was the JEM-1000 EM which was operated with the objective lens current cut off to eliminate the magnetic field in the specimen position. Single crystal films with an (001) plane were prepared by the epitaxial growth of evaporated iron on a cleaved (001) plane of a rocksalt substrate. They had a uniform thickness from 1000 to 7000 Å.

The figure shows the temperature dependence of magnetic domain structure with its corresponding deflection pattern and metallurgical structure observed in a 4500 Å iron film. In general, with increase of temperature, the straight domain walls decrease in their width (at 400°C), curve in an iregular shape (600°C) and then vanish (790°C). The ripple structures with cross-tie walls are observed below the Curie temperature.
TEM Analysis of Psuedo-Amorphous and Polycrystalline Silicon Thin Films
Authors: Anderson Ronald M.
Published: June 2020

Thin polycrystalline Si films are used in certain aspects of the fabrication of integrated circuits in the electronics industry. To date, analysis of Si films has been confined to thick films (10-50μ) deposited and/or heat-treated at temperatures over 800°C. The pyrolytic decomposition of silane gas in nitrogen or hydrogen carriers is the most common deposition technique in the industry. In the present work, thin Si films, e-beam evaporated at 300°C onto SiO2 and Si3N4 substrates and subsequently heat-treated at temperatures from 450°C to 1040°C are compared to films deposited onto SiO2, Si3N4 and Al2O3 by the pyrolytic decomposition of silane gas at temperatures from 500°C to 900°C with no further heat-treatment.

The evaporated films are psuedo-amorphous as-deposited and remain so after subsequent heat-treatments up to 600°C for one hour. A psuedo-amorphous diffraction pattern is seen in Fig.1; the first diffuse ring occurs at the Si (111) radius and the second broad diffuse ring spans the radii of the Si (220) and (311) reflections.
The Crystallography and Morphology of Epitaxial PtSi on Si Substrates
Authors: Anderson Ronald M.
Published: June 2020

PtSi is used as an ohmic contact metallurgy and in Schottky Barrier diodes in the electronic component industry. Several points are considered in this paper that were not addressed in an earlier analysis of PtSi on Si due to the early PtSi's inability to grow on a Si substrate with an epitaxial relationship to the Si. These points are: what is the epitaxial relationship of PtSi to Si and why does PtSi not act as a barrier to the easy diffusion of subsequently deposited metals through the PtSi to the Si?

An understanding of the epitaxial relationships of PtSi to Si can only come after the ambiguous SAD pattern of the PtSi is indexed. PtSi has an orthorhombic unit cell which would preclude the normal observation of diffraction symmetries greater than two-fold. However, the diffraction pattern in Fig. 1, of PtSi epitaxial on (001) Si, exhibits anomalous four-fold symmetry.
Electron Microscopical Study of Halloysite Spherules
Authors: McKee Thomas R.
Published: June 2020

The clay minerals comprising the kaolinite subgroup are hydrated aluminosilicates formed by chemical weathering of rock under the appropriate conditions. Kaolinite, halloysite and frequently x-ray amorphous allophane have the general chemical composition 2 SiO2 Al2O3.2H2O Halloysite, which exists in 4H2O form, dehydrates irreversably at 110°C to the 2H2O form. In contrast to the thin platelets of kaolinite, halloysite normally occurs as tubes of mean width 0.08μ and length 0.38μ. In some instances, the tubes have been shown to be polygonal in cross section when studied by both replication (Figure 1) and ultrathin section (Figure 2).
Effect of Diffraction Geometry on Lattice Images of Dislocations
Authors: Phillips Victor A.
Published: June 2020

It was shown recently that the number of terminating fringes and fringe bending at inclined dislocations in germanium were sensitive to the diffraction geometry. The present experiments were designed to explore the situation for dislocations nearly normal to the foil.

Germanium was selected since dislocations are immobile at room temperature A (110) oriented crystal slice was chemically thinned in a 95/5 mixture of nitric and hydrofluoric acids. Foils were examined in the high resolution stage of a Philips EM300 microscope modified to give a maximum magnification of one million. The specimen was oriented to give a strong zone of {111} systematic reflections, and {111} lattice images (3.27Å spacing) produced by the 2-beam tilt technique. The electromagnetic beam deflector was set-up so that the tilt switch could be used to switch from the +g to -g image. It was found possible to do this at one million magnification without appreciable change in image quality, field or focus, permitting pairs of images (Fig. 1) to be recorded.
Compensation of Lens Aberrations by Single-Sideband Holography
Authors: Downing Kenneth H.
Published: June 2020

Single-sideband holography has been suggested as a method for extending the resolution of the electron microscope, since it produces contrast for all object spacings simultaneously and avoids the oscillations of the contrast transfer function characteristic of normal imaging. Image processing is still required to compensate for the effects of spherical aberration and defocus, which now show up in lateral shifts of image components. The method involves use of a semicircular objective aperture to stop out half of the scattered electrons. One finds, however, that a charge builds up on or around the aperture soon after it is positioned, introducing still another image defect.

In order to compensate for the image defects, one needs to determine the wave aberration corresponding to the point spread function or contrast transfer function. In the case of normal (double-sideband) imaging one can determine the transfer function from measurements of the oscillations of the fourier transform of the micrograph (Fig. 1e).
Contrast and Resolution in Alfresco Microscopy and Thick Specimens
Authors: Sellar J. R. , Cowley J. M.
Published: June 2020

Current interest in high voltage electron microscopy, especially in the scanning mode, has prompted the development of a method for determining the contrast and resolution of images of specimens in controlled-atmosphere stages or open to the air, hydrated biological specimens being a good example. Such a method would be of use in the prediction of microscope performance and in the subsequent optimization of environmental cell design for given circumstances of accelerating voltage, cell gas pressure and constitution, and desired resolution.

Fig. 1 depicts the alfresco cell of a focussed scanning transmission microscope with a layer of gas L (and possibly a thin window W) between the objective O and specimen T. Using the principle of reciprocity, it may be considered optically equivalent to a conventional transmission electron microscope, if the beams were reversed. The layer of gas or solid material after the specimen in the STEM or before the specimen in TEM has no great effect on resolution or contrast and so is ignored here.
Phase Transformation In Ti-6al-4v Alloys
Authors: Fujishiro Shiro
Published: June 2020

The Ti-6 wt.% Al-4 wt.% V commercial alloys have exhibited an improved formability at cryogenic temperature when the alloys were heat-treated prior to the tests. The author was interested in further investigating this unusual ductile behavior which may be associated with the strain-induced transformation or twinning of the a phase, enhanced at lower temperatures. The starting materials, supplied by RMI Co., Niles, Ohio were rolled mill products in the form of 40 mil sheets. The microstructure of the as-received materials contained mainly ellipsoidal α grains measuring between 1 and 5μ. The β phase formed an undefined grain boundary around the a grains. The specimens were homogenized at 1050°C for one hour, followed by aging at 500°C for two hours, and then quenched in water to produce the α/β mixed microstructure.
Characteristics of an Electrostatic Phase Plate
Authors: Krakow William , Siegel Benjamin
Published: June 2020

Unwin has used a metallized non-conducting thread in the back focal plane of the objective lens that stops out a portion of the unscattered beam, takes on a localized positive charge and thus produces an additional phase shift to give a different transfer function of the lens. Under the particular conditions Unwin used, the phase contrast image was shifted to bright phase contrast for optimum focus.

We have investigated the characteristics of this type of electrostatic phase plate, both analytically and experimentally, as functions of the magnitude of charge and defocus. Phase plates have been constructed by using Wollaston wire to mount 0.25μ diameter platinum wires across apertures ranging from 50 to 200μ diameter and vapor depositing SiO and gold on the mounted wires to give them the desired charging characteristics. The net charge was varied by adjusting only the bias on the Wehnelt shield of the gun, and hence the beam currents and effective size of the source.
Reduction of Contamination Rates in Electron Microscopes
Authors: Greene G. M. , Sprys J. W. , Melvin C. D.
Published: June 2020

In scanning and transmission electron microscopes anti-contamination coldfingers at the specimen are usually limited in design or use because of available space. An anti-contamination device has been developed which takes advantage of the space provided by the long evacuation pipes employed on many SEMs and TEMs. This device consists of a long U shaped copper tube inserted into the vacuum line used to evacuate the emission chamber and column. Liquid nitrogen is circulated through the copper tube for cooling. The cooled tube provides a trapping surface for contamination with a minimum restriction to gas flow. A “top hat” configuration, as shown in the figure, was used to prevent freezing of-the o-ring. The purpose of the cup is to increase the heat conduction path between the feed-thru and the o-ring.

Two such devices were installed in electron microscopes; one in a JSM II SEM and one in a Philips EM 200 TEM.
Refinements to a Polyvinyl Alcohol Replication Technique
Authors: Plummer H. K.
Published: June 2020

Many techniques for the replication of polymer fractures for study in the transmission electron microscope have evolved through the years. If the surface of interest is to be retained for further study a two stage replication technique, which does not alter the original surface, must be used.

Since the materials of interest in our laboratory were polymethyl methacrylate and polystyrene, a water soluble replicating material, such as gelatin, polyvinyl acetate, or polyvinyl alcohol had to be used. Organic solvents commonly used for other replicating materials have swollen or dissolved the fracture surfaces.

Because of the excellent results reported in the literature for polyvinyl alcohol (PVA) with rough fracture surfaces it was decided this technique would best fit our needs.

According to Prestridge (E. M. S.A., 1962, p. 278) the supernatant liquid from a saturated solution of PVA (approx. 13%w/v) was placed on the fracture surface and allowed to dry.
Relative Intensities in ED Patterns From Thin Gold Films
Authors: Morriss R. H. , Peng J. D. C. , Melvin C. D.
Published: June 2020

Although dynamical diffraction theory was modified for electrons by Bethe in 1928, relatively few calculations have been carried out because of computational difficulties. Even fewer attempts have been made to correlate experimental data with theoretical calculations. The experimental conditions are indeed stringent - not only is a knowledge of crystal perfection, morphology, and orientation necessary, but other factors such as specimen contamination are important and must be carefully controlled. The experimental method of fine-focus convergent-beam electron diffraction has been successfully applied by Goodman and Lehmpfuhl to single crystals of MgO containing light atoms and more recently by Lynch to single crystalline (111) gold films which contain heavy atoms. In both experiments intensity distributions were calculated using the multislice method of n-beam diffraction theory. In order to obtain reasonable accuracy Lynch found it necessary to include 139 beams in the calculations for gold with all but 43 corresponding to beams out of the [111] zone.
Contrast Effects at Grain Boundary Ledges in 304 Austenitic Stainless Steel
Authors: McDonald R. C. , Ardell A. J.
Published: June 2020

Grain boundary ledges and/or dislocations have been observed in a wide variety of materials by a number of investigators using transmission electron microscopy (TEM) techniques. These defects can be expected to have interesting implications in terms of grain boundary precipitation reactions and creep behavior. In this paper we describe some of our TEM observations of grain boundary ledges in a specimen of type 304 stainless steel which was solution treated at 1040°C, quenched, cold worked 2%, and aged for 15 minutes at 850°C.

The configuration of the ledges can be observed in Fig. 1. For the diffracting conditions in Fig. 1 both bright and dark contrast effects are associated with many of the ledges. Strong contrast of this sort has been observed by other investigators. This strong contrast is not typical, however, as can be seen on comparison with Figs. 2 and 3, which show the same grain boundary under different diffracting conditions.
Temperature Coefficient for Twin Boundary Free Energy in 304 Stainless Steel: An Electron Microscope Study
Authors: Murr L.E. , Horylev R.J.
Published: June 2020

It has been recently shown that, as generally assumed, the coherent twin boundary free energy and the intrinsic stacking fault free energy in fee pure metals are approximately related by a factor of 2 at constant temperature, i. e.,

In the case of pure metals, the temperature coefficient assumes a simple Gibbs form for a general interface (stacking fault or twin boundary):

where S is the interfacial entropy per unit area of interface. It is noted in Eq. (2) that the temperature coefficient for an idealized pure metal is always negative. Thus, in the absence of interfacial adsorption of vacancies or impurities [assumed in Eq. (2)], the stacking fault and twin boundary free energies will increase with increasing temperature, and will be related by Eq. (1).

In the case of multicomponent (alloy) systems, the temperature coefficient becomes a complex function of component entropy contributions, surface adsorption and desorption, and their temperature dependence:
The Analysis of Dislocations Using a Symmetry Criterion
Authors: Ingram J. C. , Strutt P. R. , Tzeng Wen-Shian
Published: June 2020

The invisibility criterion which is the standard technique for determining the nature of dislocations seen in the electron microscope can at times lead to erroneous results or at best cause confusion in many cases since the dislocation can still show a residual image if the term is non-zero, or if the edge and screw displacements are anisotropically coupled, or if the dislocation has a mixed character. The symmetry criterion discussed below can be used in conjunction with and in some cases supersede the invisibility criterion for obtaining a valid determination of the nature of the dislocation.

The symmetry criterion is based upon the well-known fact that a dislocation, because of the symmetric nature of its displacement field, can show a symmetric image when the dislocation is correctly oriented with respect to the electron beam.
Fractographic Studies of Fatigue Fracture of Metals
Authors: Koterazawa Ryoichi
Published: June 2020

1. Correlation between crack growth rate and fracture surface topography.

This section describes a part of the result of a co-operative investigation of Subcommittee on Fractography of Japan Society of Mechanical Engineers which is now under way with the aim of correlating microscopic fracture surface topography of different materials to macroscopic parameters. Materials studied are carbon steels, low alloy steels, stainless steels, cast steels, aluminum alloys, titanium alloys, copper alloys, bearing steels, case hardening steels and sintered alloys. Roughly speaking, fairly good correlation was obtained between spacing of fatigue striations and macroscopic crack growth rate with ductile materials in the range of growth rate around 0.03--3 microns/cycle (Fig.1). There was a tendency of striation spacing being larger than macroscopic rate in the range of lower growth rate and smaller in the range of higher growth rate. Above this range, dimples or stretched surfaces were predominant and, below this range, irregular striation-like markings(Fig.2) were main feature of the fracture surface, cleavage-like markings or grain boundary fracture being found occasionally.
The Effects of Impurities on Void Formation in α-Iron
Authors: Sprague J. A.
Published: June 2020

A number of previous observations of the void formation induced in a variety of metals by fast neutrons or other bombarding particles have indicated that the degree of metal purity can have a significant effect on the void production rate. Increasing impurity content seems, in general, to reduce void formation, but some cases have been reported in which low concentrations of certain impurities significantly increased void production over that seen for the pure metal.

In the current investigation, zone-refined iron and five low-concentration alloys of zone-refined iron were studied following irradiation with 8.8 × 1020 neutrons per cm2 < 0.18 MeV at 280°C. The five alloys contained 0.3 at-% Cu, 0.3 at-% Ni, 0.3 at-% V, 0.3 at-% P, and 0.1 at-% C, respectively. Since the voids produced by these irradiation conditions were very small, the out-of-focus observation technique suggested by Ruhle was employed in this study.
Radiation Damage Study of Type 304 Austenitic Stainless Steel by High Voltage Electron Microscopy
Authors: Das Gopal , Mitchell Terence E.
Published: June 2020

In recent years high voltage electron microscopy has found widespread application to simulate the kind of damage produced by neutrons in potential nuclear reactor materials and to study ‘in-situ’ the nucleation and growth of defect clusters, such as dislocation loops and voids.

In this investigation AISI Type 304 stainless steel has been used as a prototype to study electron irradiation damage as a function of accelerating voltage, irradiation time and temperature. A preliminary result on such studies will be reported here. 0.4 mm thick discs were cut from as-received 3 mm rods. They were sand-ground to 0.2 mm and most of them were encapsulated in a quartz tube under a vacuum of 10−5torr and subsequently annealed at 1100°C for 7 hours. Electron transparent foils were made from annealed and as-received discs by a two-step process of jet dimpling and electropolishing.
A Field Ion Observation of a Grain Boundary Node
Authors: Eaton H. C.
Published: June 2020

In recent years there has been considerable interest in relating the structure of high angle grain boundaries to the properties of polycrystalline materials. It has been firmly established that these interfaces exhibit a highly complex, and often regular structure on the near atomic scale which can control the chemical or mechanical macro-behavior of the aggregate. However, unlike external surfaces, which can be probed by conventional surface spectroscopic and diffraction techniques, the internal structure of the grain boundary is usually only accessible with the transmission electron microscope. Interpretation of such images is at best complex and oftentimes the fine-scale structure is not observed due to resolution limitation of conventional imaging modes. The field ion microscope (FIM), on the other hand, offers both high resolution and a more direct imaging process. The FIM has been used in numerous grain boundary observations and more recently the results have been improved by computer reconstruction techniques providing detailed topographies of the interface. Presented in the present work is a computer reconstruction of the point of junction between three grains and two of the associated grain boundaries (see Figure 1).
Three Surface TEM Observations of Cold Rolled 1100 Aluminum
Authors: Rohr D. L. , Hecker S. S.
Published: June 2020

As part of an on-going study of 1100 Al at large plastic strains, we have examined cold-rolled samples from three orientations; through the sheet surface, and in the thickness direction along the rolling direction (RD) and transverse to the RD. Cell and subgrain sizes were determined in the same manner as for the earlier work.

The starting plates of 1100 Al were annealed at 500 C and then rolled at room temperature to various thicknesses. These rolled plates were used to produce final samples rolled to 0.5 mm thickness with 62, 80, and 90% reductions. Thin foils were produced by lapping and jet electropolishing. A method was developed to make thin foils perpendicular to the sheet by lapping small pieces of sheet (1 mm wide) edgewise from both edges. This produces sheet 0.25 mm thick by 0.5 mm wide which were mounted between two 0.25-mm-thick 1100 Al disks 3 mm in dia. These disks had been slitted in the center to have slits ≪ 0.5 mm wide.
Comparison of Substructures Between Uniaxial and Biaxial Deformation in 1100-0 Aluminum
Authors: Rohr D. L. , Hecker S. S.
Published: June 2020

As part of a comprehensive study of microstructural and mechanical response of metals to uniaxial and biaxial deformations, the development of substructure in 1100 A1 has been studied over a range of plastic strain for two stress states.

Specimens of 1100 aluminum annealed at 350 C were tested in uniaxial (UT) and balanced biaxial tension (BBT) at room temperature to different strain levels. The biaxial specimens were produced by the in-plane punch stretching technique. Areas of known strain levels were prepared for TEM by lapping followed by jet electropolishing. All specimens were examined in a JEOL 200B run at 150 and 200 kV within 24 to 36 hours after testing.

The development of the substructure with deformation is shown in Fig. 1 for both stress states. Initial deformation produces dislocation tangles, which form cell walls by 10% uniaxial deformation, and start to recover to form subgrains by 25%. The results of several hundred measurements of cell/subgrain sizes by a linear intercept technique are presented in Table I.
Microstructural Evolution in Reduced TiO2
Authors: Donlon W. T. , Shinozaki S. , Logothetis E. M. , Kaizer W.
Published: June 2020

Since point defects have a limited solubility in the rutile (TiO2) lattice, small deviations from stoichiometry are known to produce crystallographic shear (CS) planes which accomodate local variations in composition. The material used in this study was porous polycrystalline TiO2 (60% dense), in the form of 3mm. diameter disks, 1mm thick. Samples were mechanically polished, ion-milled by conventional techniques, and initially examined with the use of a Siemens EM102. The electron transparent thin foils were then heat-treated under controlled atmospheres of CO/CO2 and H2 and reexamined in the same manner.

The “as-received” material contained mostly TiO2 grains (∼5μm diameter) which had no extended defects. Several grains however, aid exhibit a structure similar to micro-twinned grains observed in reduced rutile. Lattice fringe images (Fig. 1) of these grains reveal that the adjoining layers are not simply twin related variants of a single TinO2n-1 compound. Rather these layers (100 - 250 Å wide) are alternately comprised of stoichiometric TiO2 (rutile) and reduced TiO2 in the form of Ti8O15, with the Ti8O15 layers on either side of the TiO2 being twin related.
Application of the Analytical Electron Microscope to the Characterization of Protective Coatings on Nickel-Base Superalloys
Authors: Lin L. S. , Walsh J. M.
Published: June 2020

The combined chemical and structural analysis capabilities of the analytical electron microscope (AEM) make it an important tool for understanding the nature of protective coatings on nickel-base superalloys. One of the important coating systems for protecting turbine blades from oxidation and hot corrosion is a MCrAlY alloy applied by electron beam physical vapor deposition (where M = Ni, Co, or Fe). In the as deposited condition this coating consists of a fairly open, generally columnar structure. A post-coating heat treatment on the order of 2 to 4 hours at approximately 1100°C is normally given to the coating. The major coating constituents are a β[(Ni,Co)Al] intermetallic phase and a γ[Co,Cr,Ni] solid solution phase. This heat treatment results in the formation of a ∼ 10 μm interdiffusion zone of phase transformation products at the coating/substrate interface and a thin protective layer (< 1 μm) of Al2O3 at the coating surface (Fig. l). While the coating contains just a few tenths of a percent yttrium, this yttrium plays an important role in improving the adherence of the protective Al2O3 layer. It has previously been proposed that the yttrium causes oxide pegs to develop at the Al2O3/coating alloy interface and that these pegs improve oxide adherence by mechanically keying the Al2O3 to the coating alloy.
Study of Faulting in Laves Phase TiCr2 Alloys
Authors: Kolar H. R. , Allen C. W. , Spence J.C.H.
Published: June 2020

The Laves phases TiCr2 have shown polytypism dependent on temperature. TiCr2 is 2H (C14, MgZn2 structure) above 1100°C (C15, MgCu2 structure) at lower temperatures with 4, 6, and 12 layer variants occurring as intermediate structures. Of particular interest are the phase transformations which presumably proceed by a shear mechanism.

Laves phase structures and their stacking variants can be described in terms of the stacking sequence of six similar compound layers. These layers form topologically close packed structures of AB2 composition in which the metallic radius of the A atom is approximately 1.22 times larger than that of the B atom. Fig. 1 shows the atomic arrangement within a single compound layer. Similar layers are then stacked as in close packed structures. In TiCr2 the most common transition structures seem to be the 4H, 6H1, and 6H2 with the latter being less prominent. It is possible to form all these structures by the glide of arrays of Shockley type partial dislocation dipoles which are highly mobile at practical transformation temperatures. Models for each of the transformations have been proposed but have not been confirmed by direct observation. The partial dislocation dipoles may arise from the dissociation of perfect dipoles, emission from grain boundaries (or interfaces), or by nucleation from perfect crystal.
Lattice Image Analysis of the Metamict Transformation in Synthetic Quartz
Authors: Pascucci M. R. , Hobbs L. W. , Hutchison J. L.
Published: June 2020

The irradiation-induced crystalline-to-amorphous transformation in quartz and other silicates has been investigated because of its importance to nuclear waste storage ard frequency control. The transformation to an amorphous (metamict) state is accompanied by up to 14% decrease in density.

Recent in-situ electron damage studies of synthetic α-quartz using transmission electron microscopy have shown that the metamict transformation occurs in two stages at different rates: first, a rapid, heterogeneous nucleation of well-defined amorphous inclusions; and second, a more gradual, homogeneous loss of correlation in the surrounding matrix. The first stage initiates at doses less than ten times the second. Experiments at different electron energies have established that both stages can result from the ionizing component of the radiation alone. The proposed radiolytic damage mechanism involves localization of excitations resulting in bond breakage which provides the necessary topological freedom for reorientation of SiO4 tetrahedra. Water has been implicated in the first-stage heterogeneous nucleation.
High Resolution Study of the Metamict State in Zircon
Authors: Headley T. J. , Ewing R. C. , Haaker R. F.
Published: June 2020

Ceramic waste forms are being developed as solid hosts for radioactive waste disposal, Of concern is the effect of long-term radiation damage on crystalline integrity and subsequent leachability of the waste form. In preparation for understanding radiation damage effects, we have performed a high resolution study of the metamict state in natural zircons (ZrSiO4). Metamict minerals are a class of “amorphous” minerals, originally crystalline which have suffered extensive structural degradation over time from decay of internal radioactive impurities, principally U and Th. From x-ray diffraction evidence it is widely believed that the metamict state is amorphous in the sense of an isotropic glass. However, an electron microscope study performed some 15 years ago suggested that metamict zircons possess a structure composed of slightly misoriented crystallites about 100 Å in size, a structure indistinguishable from an isotropic glass by x-ray diffraction. We felt that high resolution electron microscopy could clearly delineate between the isotropic glass and misoriented microcrystalline concepts.
Preparation of Particulates for Transmission Electron Microscopy: An Update
Authors: Lauf R. J. , Rawlston S. S.
Published: June 2020

A method for preparing fragmented or particulate ceramic materials for transmission electron microscopy (TEM) by embedding in a solid metal matrix such as aluminum, using vacuum hot-pressing at about 550°C, followed by mechanical thinning and ion milling, has been published. This technique is useful for most high-melting ceramic materials but may introduce thermal damage to low-melting materials or to hydrated minerals. We describe here two relatively simple techniques that can be carried out at room temperature and that do not require vacuum hot-pressing equipment.

The first technique disperses the sample in a dental amalgam. Premeasured capsules contain the silver alloy powder and mercury in separate compartments. The capsule is opened and a small amount of sample is added. The capsule is then closed and compressed to release the mercury and agitated for 1 to 2 min. The material is removed from the capsule and tightly packed into a 3-mm-diam cylindrical mold for hardening overnight. The resulting pellet is then sliced and thinned as in the earlier method. Figure 1 shows a coal fly ash particle prepared by this technique.
Pulsed Ion Beam Induced Silicide Formation
Authors: Chen L. J. , Hung L. S. , Mayer J. W.
Published: June 2020

Metal silicides have found increasing use in microelectronic industry as contact material as well as interconnect between devices. Silicide formation is based on the reaction between metal film and substrate silicon. Thermal, laser, electron beam and ion-mixing induced silicide formation have been widely studied. Recently both scanning and pulsed ion beams have been used to anneal semiconductors. In this presentation, we report pulsed ion beam induced silicide formation.

Ni films, 300 and 400 Å thick, were e-gun deposited on (001) oriented, 2 Ω-cm, n-type silicon with substrate temperature maintained at 150°C. A magnetically insulated diode driven by a Marx generator, constructed and run by J. Neri and D. Hammer of Laboratory for Plasma Studies at Cornell in conjunction with J. E. E. Baglin of IBM Research was used to produce pulsed proton and barium beams. Samples were irradiated with about 200 nsec, 200-300 keV, 10-100 A/cm2 ion pulses. A Gaussian-type radial profile was generally obtained. Thin foils for transmission electron microscope study were then chemically polished from silicon side. JEOL 100B and Siemens 102 electron microscopes were used to investigate microstructural changes.
Electron Channeling of Single Crystal Lithia-Disilicate
Authors: McCracken W. J. , Madden M. C.
Published: June 2020

Electron beam channeling has been primarily applied to metals, which both conduct electrons and have cubic crystal structures. Ceramic materials are usually nonconductive and noncubic. However, determining the orientation of a single crystal ceramic is often necessary for subsequent materials analysis. This is the case with lithia-disilicate, the crystalline phase found in some technical glass-ceramics. To study lithia-disilicate single crystals with polarized infrared spectroscopy, it is required to know the crystallographic orientation of the sample.

Lithia-disilicate has an orthorhombic crystal structure with a space group of Ccc2. The structure contains three cleavage planes perpendicular to the primary axes. The plane perpendicular to the (010) axis is micaceous. These features can be seen in Fig. 1, where the top surface is the 010 plane.
An EXELFS Analysis System and Preliminary Orientation Dependence Results
Authors: Disko M. , Krivanek O. , Spence J.C.H.
Published: June 2020

A Fourier analysis of the core electron excitation Extended Electron Energy Loss Fine Structure (EXELFS) has been shown to yield information concerning the radial distribution of atoms about the ionized species. Theoretical descriptions of the EXELFS have been based to date on similarities with the Extended X-ray Absorption Fine Structure (EXAFS) for electron scattering within the dipole approximation. Differences between the EXELFS and the EXAFS phenomena have been stated, and remain to be investigated.

The most important experimental EXELFS problem involves the difficulty of obtaining a sufficiently good EXELFS signal to noise ratio out to large postedge energy. The solution of this problem requires the correct combination of the convergence angle α, the collection angle β, the specimen thickness, and an efficient spectrometer system. Energy resolution is not a crucial limiting factor; 5eV resolution at the edge is sufficient. A computer program for EXELFS analysis has been developed that is versatile, and yet sufficiently compact to run on an LSI-11 minicomputer.
The Effect of Specimen Configuration on the Periodicity of a Lattice Image
Authors: Hibbs M. K.
Published: June 2020

One of the most controversial issues in the application of the lattice fringe imaging technique concerns the interpretation of the local fringe spacing. It is well-known from the work of Hashimoto et. al. that the specimen configuration may cause the fringe spacings in an image to deviate from the true interplanar spacings of the crystal. Their paper qualitatively described the effects on fringe spacings of variations in specimen thickness, t, and deviation from the Bragg condition, s, and illustrated their results with the first experimental fringe images of Menter. In this paper an explicit formula for spacings in a fringe image is presented and applied to various specimen configurations and materials currently being studied by high resolution techniques which have much closer lattice spacings (∼2 Å) than have previously been considered.
Interfacing of Computers to a STEM
Authors: Statham P. J.
Published: June 2020

There are many STEM applications where computer monitoring and control can enhance or provide new analytical capabilities. While x-ray detector systems have been available for many years, it is only recently that the system computer has had the capabilities extended to provide serial acquisition facilities suitable for EELS data and even scan control suitable for basic image processing requirements. The addition of a frame store opens up new possibilities for S/N improvement and is a useful intermediate stage toward quantitative image processing. With on-line processing of an image, automatic focussing and stigmation is a possibility and analysis of diffraction patterns can be faster and more convenient with computer assistance. A computer can co-ordinate the simultaneous acquisition of several signals, thus increasing the information gathered in an interval limited by contamination, drift or specimen damage and can supervise sequential, multi-signal analyses at pre-programmed points in the field of view. Where lens currents and alignment have to be specially adjusted for particular applications, settings can be recorded to enable conditions to be reproduced immediately under computer control.
Computer Control of STEM for X-Ray and Energy Loss Imaging
Authors: Rez Peter , Ahn Channing
Published: June 2020

It has long been recognised that the point by point imaging in the STEM (Scanning Transmission Electron Microscope) is suitable for computer control and image processing. Instrument designers will be interested in computer control as it can make the instrument easier to use and provide automation. For reserachers there is no case to be made for computer control if it is just going to be a substitute for existing analog systems which give perfectly adequate results. The purpose of computer control is to manipulate signals or to perform experiments that would otherwise have been impossible or very difficult. The ability to ‘redesign’ the experiment by making software changes also gives added flexibilty. Energy Dispersive X-Ray Spectroscopy (EDX) and Energy Loss Spectroscopy are cases where digital manipulation is useful. In EDX it would be desirable to subtract the background from the peak or to display a ratio of two peak heights for elemental images or line scans. Controlling the dwell time per pixel (picture point) so that time is not wasted on uninteresting regions would also be useful.
Simultaneous Collection and Processing of Energy-Filtered Images in Stem Using a Fast Digital System
Authors: Butler J. H.
Published: June 2020

Hardware and software have been developed allowing concurrent acquisition of up to three electron energy-loss images formed by monitoring three separate regions of the energy-loss spectrum. This imaging mode provides display of three elemental contour maps or, after some digital image processing, an elemental contour map stripped of its spectrum background.

Other systems proposed for simultaneous collection of these signals have not been realized because of the difficulties involved in manufacture of multiple parallel detectors consistent with the physical dimensions of the energy-loss spectrum. The technique described here requires just the single standard bright-field detector. The experimental apparatus consists of a Vacuum Generator's HB5 Scanning Transmission Electron Microscopy (STEM) under the control of a Fast Digital Acquisition System (FDDAS). A PDP11/34 minicomputer controls the electrostatic deflectors at the spectrometer exit so the spectrum can be shifted across the detector slits (Fig. 1). Circuitry enabling this has been incorporated directly into the FDDAS as an expansion device resident on the system bus.
Effect of a Complex Heat Treatment on the Structure of 300M Steel
Authors: Padmanabhan R. , Wood W. E.
Published: June 2020

Intermediate high temperature tempering prior to subsequent reaustenitization has been shown to double the plane strain fracture toughness as compared to conventionally heat treated UHSLA steels, at similar yield strength levels. The precipitation (during tempering) of metal carbides and their subsequent partial redissolution and refinement (during reaustenitization), in addition to the reduction in the prior austenite grain size during the cycling operation have all been suggested to contribute to the observed improvement in the mechanical properties. In this investigation, 300M steel was initially austenitized at 1143°K and then subjected to intermediate tempering at 923°K for 1 hr. before reaustenitizing at 1123°K for a short time and final tempering at 583°K. The changes in the microstructure responsible for the improvement in the properties have been studied and compared with conventionally heat treated steel. Fig. 1 shows interlath films of retained austenite produced during conventionally heat treatment.
Applications of Convergent Beam Electron Diffraction to the Study of Precipitate Structure
Authors: Shaw M.P. , Pcrter A.J. , Ecob R.C. , Ralph B.
Published: June 2020

Convergent Beam Electron Diffraction (CBED) is a technique that has become widely available in recent years with the advent of modern analytical transmission electron microscopes designed to allow the formation of small electron probes on the specimen surface. It can be used in a number of ways to investigate local crystal structure (see e.g. 1) and is complementary to the analytical information obtainable from spectroscopic accessories. The specific application discussed in the present paper involves the use of high order Laue zone (holz) lines, which form part of the fine structure within individual discs in the diffraction pattern. These have been used to investigate small symmetry variations accompanying changes in ordering of γ' precipitates in a nickel base superalloy (Udimet 720) (e.g. 2,3). Examination is made of the symmetry associated with holz patterns from suitably related crystallographic poles, and these are compared with computer simulated patterns in order to establish unit cell shape and symmetry.
Determination of Exact Orientation Relationships between Martensite and Austenite in Steels by Microdiffraction
Authors: Sarikaya M.
Published: June 2020

A significant number of investigations have been performed on the determination of orientation relationships (OR) in high carbon, plate-martensitic steels. However, very little is known on the exact nature of ORs in technologically important lath martensitic steels. In the present study, in a series of low alloy steels with carbon contents between 0.1-0.4 wt%, the existence of retained austenite as thin films (∼200 Å thick) around the martensite lath boundaries, makes it possible to do direct crystallographic analysis between martensite and austenite by microdiffraction.

The most commonly observed orientations for lath martensite-retained γ are <111>α'//<110>γ//<100>α'. Fig. 1 shows an example of a highly symmetric SAD pattern which was interpreted as follows: Considering only one martensite lath at a time, the α' and <110>γ combination corresponds to Kurdjumov-Sachs (K-S) OR, and <110>α and <100>γ corresponds to Nishiyama-Wassermann (N-W) OR. The coexistance of these two relationships may be taken as evidence that as many variants as necessary occur to provide maximum flexibility for martensite nucleation.
Design of a Parallel-Detection System for EELS
Authors: Egerton R.F.
Published: June 2020

Electron detectors based on a semiconductor-diode array offer the possibility of considerably greater collection efficiency and consequently an improved signal/noise ratio, compared to the scanning method normally used to record electron energy-loss spectra. Some of the design options are shown in Fig. 1. Relative to charge-coupled devices, linear photodiode arrays have the advantage of being available with a relatively large active width (e.g. 430 μm) perpendicular to the length of the array, which helps in obtaining maximum output signal and high collection efficiency. In the direct-exposure method, the array is exposed directly to the electron beam at the exit of a spectrometer; this has the advantage of simplicity, but involves some risk of radiation damage to the device (although this might be overcome by periodically annealing the array). In the indirect- exposure method, a transmission or reflection screen converts the fast electrons into visible light, which is focussed onto the array by a lens or fibre-optics.
A Photodiode, Parallel Detection System for Energy Loss Spectrometry
Authors: Johnson D.E. , Csillag S. , Monson K.L. , Stern E.A.
Published: June 2020

The advantages of parallel detection systems for energy loss spectometry are certainly clear. A variety of approaches are possible ranging from simple film recording to elaborate intensified television cameras. We are in the process of evaluating one approach to such a parallel detection system, which consists of; a magnetic post-spectrometer lens to increase dispersion, a phosphor conversion plate, glass coupling lenses, a dual channeltron image intensifier, and a cooled photodiode array (Reticon RL256C/17). A schematic diagram of the system is shown in Fig. 1.

The post-spectrometer lens is an RCA-3G intermediate lens which typically magnifies (∼15x) the dispersion to ∼25μm/ev with a rotation of ∼90°. Although the dispersion plane of the straight edge sector magnet used is tilted at 30° from the beam axis, pre-spectrometer optics reduce the angular divergence of the beam entering and leaving the spectrometer to ∼1 mr and the consequently large depth of focus assures that the dispersed beam is in focus across the conversion plate, perpendicular to the beam axis.
Results from a New Analytical Electron Microscope
Authors: Parker N. W. , Utlaut M. , Crewe A. V.
Published: June 2020

A new analytical electron microscope has been completed and is now in full operation in our lab. As described earlier, this microscope contains many new design features all of which have now been extensively tested. We report here on the success of each of these design experiments.

The optical design utilized a magnetic lens above the accelerating gun, shielded from HV by a spool-shaped machinable glass insulator. While this system worked very well optically, some HV problems occurred which we are attempting to cure by minor design changes. The beam-defining aperture is contained within a differentially pumped Faraday cage and has worked very well, showing a vacuum differential (outside/inside) of 4 to 5 while allowing quick changes among the eight different apertures available.

The specimen stage temperature control has demonstrated an attainable range of 98°K to above room temperature with no effect on either specimen mobility or microscope vacuum.
Enhanced Projections in Electron Micrographs of 40S Ribosomal Subunits from HeLa Cells
Authors: Boublik M. , Frank J. , Tesche B. , Verschoor A.
Published: June 2020

Direct visualization by electron microscopy is of obvious advantage for conformational analysis of ribosomes. However, low contrast, small size, high degree of hydration, susceptibility to beam damage, recrystallization of the contrasting solution (usually uranyl acetate), and random structure of the support film are responsible for high noise level of the conventional electron micrographs of the ribosomes. Structural asymmetry and the fact that ribosomes do not normally form regular arrangements (exception cf. /l/) preclude the application of crystallographic averaging techniques. These conditions make interpretation of the morphologic parameters of ribosomes and topographic mapping of their constituents - proteins and rRNAs - challenging and controversial.

In our efforts to interpret electron micrographs of ribosomal particles we have used two different techniques - filtering of arrays of images in reciprocal space (FAIRS) /2/ and computer alignment and averaging /3/ - to obtair averaged views of the particles.