bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurements of white line intensities in 4d transition metals using Electron Energy Loss Spectrometry (EELS)
Authors: Pearson Douglas H. 
Published: June 2020

A feature of considerable interest in the electron energy loss spectra of transition metals is the L23 edge which is composed of two sharp “white lines” superimposed on a broad edge that makes up the trailing background. The white lines are due to the excitations of electrons from filled 2p1/2 and 2p3/2 states to unoccupied 3d or 4d states, and the background intensity is due to continuum excitations. Recent work on the white lines of the 3d transition metals has shown that when normalized to the continuum excitations, the total white line intensity decreases nearly linearly with atomic number (or d band occupancy) across the 3d series. Furthermore, this linear relationship may be used to measure the changes in 3d state occupancy local to specific atoms during alloying and during solid state phase transformations. In the present paper the experimental analysis of the white lines is extended to the 4d transition metals and is then compared to experimental results from the 3d metals.Electron-transparent specimens of the pure 4d metals were prepared by standard electropolishing and evaporation techniques. To prevent oxidation of the Yttrium specimen, however, a 40 nm film of Yttrium was deposited between 15 nm films of Vanadium by direct current ion sputtering in a chamber with a base pressure of < 1.0 × 10−7 Torr. Energy loss spectra were obtained using a Gatan 607 electron energy loss spectrometer attached to a Philips EM 430 electron microscope operating in image mode at 200 kV.
Planar defects in AIN
Authors: McKernan Stuart , Carter C. Barry 
Published: June 2020

Aluminum nitride has recently become the subject of much interest as a technologically useful ceramic. The mechanical strength, high thermal conductivity and large electrical resistivity and a relatively small thermal expansion coefficient, make this material extremely well suited as a semiconductor substrate material. AlN has the hexagonal, wurtzite structure rather than the cubic structure of the more common semiconductors. It is also a polar material. The characterization of microstructural defects in this material is obviously necessary to the understanding of the materials properties.In sintered AlN material, several different planar defects have previously been examined. Anti-phase boundaries (which produce the same configuration as basal twins in this structure) and stacking-faults have been identified in this material. A defect described as a “dome-like defect” has also been reported. The association of oxygen impurities with these extended defects has also been proposed. In this paper we report the observation of a defect (which may be the same as the “dome-like defect”) consisting of a flat, planar, basal fault and a curved, planar fault (rather than a spherical one) which join together to enclose a region of AlN, and separate it from the rest of the grain.
Structural development of solution-derived, monodisperse powders studied using cryo-TEM.
Authors: Bailey J.K. 
Published: June 2020

High quality advanced ceramic materials can be produced by using unagglomerated monodisperse powders for preparation of ceramic pre-forms. Stöber et al. first showed that monodisperse silica particles could be derived from silicon alkoxides, and Bugosh et al. demonstrated the control over particle size and mass fraction that could be obtained. Similarly, Barringer and Bowen produced titania colloids but without using a catalyst. In these preparation procedures, a solution of metal alkoxide monomers undergoes hydrolysis and condensation to form the particles. By the chemical processing of monodisperse powders, one can control the particle size and stabilization. In order to understand and control the influence of the processing conditions on the morphology of these particles, the growth mechanism needs to be understood. As yet, there are no widely accepted growth models for the various materials.Using cryo-microscopy, one can directly observe the development of these particles by freezing the reaction at various stages and observing the products at that time. A thin liquid film of solution is fast frozen, vitrifying the solvent and trapping the particles suspended in solution, thus avoiding potential artifacts, such as agglomeration, that can be caused by drying the sample.
Direct STEM ADF imaging of gold on silicon (111)
Authors: Xu P. , Kirkland E. J. , Silcox J. 
Published: June 2020

Many studies of thin metal film growth and the formation of metal-semiconductor contacts have been performed using a wide range of experimental methods. STEM annular dark field imaging could be an important complement since it may allow direct imaging of a single heavy atom on a thin silicon substrate. This would enable studies of the local atomic arrangements and defects in the initial stage of metal silicide formation.Preliminary experiments were performed in an ultra-high vacuum VG HB501A STEM with a base pressure of 1 × 10-10 mbar. An antechamber directly attached to the microscope for specimen preparation has a base pressure of 2×l0-10 mbar. A thin single crystal membrane was fabricated by anodic etching and subsequent reactive etching. The specimen was cleaned by the Shiraki method and had a very thin oxide layer left on the surface. 5 Å of gold was deposited on the specimen at room temperature from a tungsten filament coil monitored by a quartz crystal monitor.
Microstructure of chromium films grown on glass and silicon substrates
Authors: Duan J.Z. 
Published: June 2020

Thin metal films are widely used in microelectronics and this has stimulated a great deal of research about their microstructures and related properties. During the past two years, chromium microstructures and internal stresses generated during e-beam evaporation Cr film growth have been researched by us. Many relationships between Cr columnar microstructures and internal stresses have been discovered. In this paper, the results of studies of the dependance of Cr columnar microstructures on Si and glass substrates are reported. They have been found to be very useful for analyzing the internal stresses in Cr films and understanding the atomistic mechanism of their growth.It is well known that microstructures and properties are closely related to the processing conditions, so in our experiments, all experimental parameters are kept constant except for factor whose influence on on microstructure and internal stress is under study.
Geometrical explanation of parabolas and resonance in electron diffraction
Authors: Gajdardziska-Josifovska M. , Cowley J. M. 
Published: June 2020

Reflection electron microscopy (REM) relies on the surface resonance (channeling) conditions for enhancement of the intensity of the specular reflection from a flat surface of a single crystal. The two most frequently cited geometries for attaining surface resonance conditions are: i) tilting the incident beam such that the specular beam in the RHEED pattern falls on an intersection of a K-line parallel to the surface with some oblique K-line; ii) positioning the specular beam on an intersection of a K-Iine parallel to the surface with some of the surface resonance regions bound by parabolas. Parabolas are also observed in the transmission diffraction patterns and have been explained as Kikuchi envelopes. Recent studies indicated a similarity between the CBED transmission and reflection patterns. We will describe a simple geometry which can be used to interpret the above observations.A parabola is by definition a curve of equal distance from a point (called focus) and a line (called directrix; see Fig.1 ).Simple previously unnoticed facs are that the zone axis is a focal point of all the parabolas belonging to a given zone, and that the directrix of each parabola corresponds to a K-line.
Using crystallographic symmetry in diffraction and contrast analysis
Authors: Dahmen U. , Westmacott K.H. 
Published: June 2020

Despite the increased use of convergent beam diffraction, symmetry concepts in their more general form are not commonly applied as a practical tool in electron microscopy. Crystal symmetry provides an abundance of information that can be used to facilitate and improve the TEM analysis of crystalline solids. This paper draws attention to some aspects of symmetry that can be put to practical use in the analysis of structures and morphologies of two-phase materials.It has been shown that the symmetry of the matrix that relates different variants of a precipitate can be used to determine the axis of needle- or lath-shaped precipitates or the habit plane of plate-shaped precipitates. By tilting to a special high symmetry orientation of the matrix and by measuring angles between symmetry-related variants of the precipitate it is possible to find their habit from a single micrograph.
Annealing effects on the sapphire (0001) surface
Authors: Ndubuisi G. C. , Liu J. , Cowley J. M. 
Published: June 2020

The techniques of RHEED, REM and SREM have proven to be important in the study of surface structures. Since these techniques are sensitive to surface perturbations at nanometer scale they can be used to study surface structures as well as surface interactions such as metal surface oxidation processes, metal substrate interactions, etc. The study of the as-grown and the cleaved sapphire surfaces have benn reported. This paper intends to reports some preliminary results on the study of annealed sapphire (0001) surface structures and possible interactions with deposited small metal particles.The sapphire rod, with c-axis parallel to the rod, was purchased from Saphikon, Inc. A 2.0 mm disc was cut, thinned, oriented to the (0001) face and polished to 2.8х 1.0х0.2mm strips. Some of the strips were examined by Laue back reflection to ensure preservation of the [0001] orientation, then cleaned and transported to the furnace. The specimens were annealed in pure oxygen at high temperatures with a vacuum pressure a little above atmospheric. The experiments were performed both in a Philips 400T TEM with a vacuum pressure around 10-7 to 10-6 Torr. and in a VG HB5 STEM microscope with a vacuum pressure of about 5×10-9.
Seashells as a natural model to study ceramic-polymer composites
Authors: Sarikaya Mehmet , Gunnison Katie L. , Aksay Ilhan A. 
Published: June 2020

Interests in ceramic/polymer composites are increasing mainly because of their superior physical properties for structural and electronic applications. Naturally produced composites, such as seashells, are ideal to study the formation, microstructure, and physical properties of these composites as these materials have far superior properties with well-defined microstructures than man-made ones which require complex fabrication techniques. In this paper, a summary of a recent study on the microstructure of abalone shell (Haliotis refuscens) will be described in conjunction with its mechanical properties.A longitudinal cross-section of abalone shell displays two types of microstructures: outer prismatic layer and inner nacreous layer. Two forms of CaCO3, calcite (rhombohedral,
) and aragonite (orthorhombic, Pmcn) constitute the inorganic component of the organic/ceramic composite in the prismatic and nacreous layers, respectively. The structure and properties of the nacreous will be described here as this is the part which provides a good combination of mechanical properties for the seashell.
Interface reactions in a high-temperature metal-matrix composite
Authors: Allard L. F. , Coffey D. W. , Ohriner E. K. , Sikka V. K. 
Published: June 2020

Metal-matrix composites are currently of interest for application in high-temperature, elevated-stress environments. Of a number of such materials currently being investigated in our laboratory, nickel aluminides reinforced with ceramic whiskers or fibers have shown promise in that the maximum operating temperature of the alloy has been extended from 800°C to 1100°C. The microstructure of the fiber/matrix interface in a nickel aluminide strengthened with ceramic fibers is detailed in this paper.The composite material was fabricated by mixing gas-atomized −100 mesh IC-50 powder (11.7 Al, 1.76 Hf, 0.025 B wt %, bal. Ni) with Nextel 440 fiber (3M Co., nominally 70 A12O3, 28 SiO2 and 2 B2O3 wt %) to give a composite with about 20 vol % fiber. The material was placed in a heavy-walled stainless-steel can which was evacuated while being heated to 600°C to remove fiber sizing. The can was subsequently sealed and preheated at 1100° C for 2 h, then hot consolidated at high pressure for 30 s to produce a fully dense material.
Precipitation and dislocation decoration via extrinsic gettering of Co, Au and Pt by misfit dislocations in Si/Si-2%Ge epitaxy
Authors: Lee D. M. 
Published: June 2020

Previous work on the gettering activity of a well defined array of buried interfacial misfit dislocations (MDs) showed that the amount of nickel gettered by MD is dominated by the strong temperature-dependent solubility. Precipitation occurs on or in the immediate vicinity of MDs due to nucleation enhancement by strain effects. High temperature 〈1000°C〉 diffusion of gold resulted in the planar colony precipitates on two {111} planes associated with stacking fault formation. In this contribution, we discuss our continuing research pertaining to cobalt, gold (at low temperature), and platinum gettering by MDs which involves studying the nature of dislocation decoration and impurity precipitation in the Si/Si-2%Ge epitaxial system.All the samples used in this study have a buried Si-2%Ge epitaxial layer of ∼ 2 μm thickness.Co, Au and Pt were deliberately diffused into the wafer. The details of the sample structure and preparation are described in a preceding paper. Two-beam bright field and weak-beam dark field imaging techniques were performed on cross-section TEM specimens.
In Situ Electron Microscopy in catalysis research and related surface reactions
Authors: Gai Pratibha L. 
Published: June 2020

Catalysis plays a major role in the modern oil and chemical industries. Solid state catalysts are most common, whilst the reactants are commodity gases and liquids. The performance of the catalysts depends strongly on their microstructure, chemistry and surface structures on a fine (nanometer) scale and electron microscopy (EM) plays an increasingly important role in the characterization. In-situ EM with an environmental cell permits direct observations of chemical reactions under near operating conditions and in conjunction with HREM and AEM can provide in favorable cases, significant atomic level information about the surface/microstructural changes and about possible reaction with substrates. In this paper, examples of catalyst materials in chemical technology and the nature of catalysis in alloy steels with applications in nuclear reactors are shown to elucidate this.A variety of supported metallic catalysts were examined: Ni/carbon, Cu/alumina and bimetallic Cu-Pd/C (both of interest in methanol synthesis), Cu-Ru/C (incyclohexane conversions) and Cu-Ni/alumina.
The decomposition of praseodymium carbonate, carbonate hydrate, and hydroxy carbonate: An in situ study by High-Resolution Electron Microscopy
Authors: Sharma R. , Hinode H. , Eyring L. 
Published: June 2020

High resolution electron microscopy (HREM) has been successfully used to study electron-induced chemical decompositions in the past few years. With HREM having near-atomic resolution, atomic-level details can provide insight into the mechanisms of solid state reaction. In this work the in situ decomposition of Pr2(CO3)3, Pr2(CO3)3·8H2O and PrCO3OH has been studied.The starting materials were prepared as described elsewhere. Samples for HREM were prepared by crushing the crystal fragments in an agate mortar and placing a drop of the suspended powder in absolute alcohol on a holey carbon film supported on a copper grid to provide a distribution of fine crystal flakes. The samples were then studied by using a JEOL 4000EX microscope operated at 400KV and fitted with double-tilt-lift stage. The current density on the specimen was varied by changing the size of condenser aperture and spot providing various amounts of irradiation and heat transfer.The decomposition reaction was rapid, hence it was not possible to get good HREM images of the starting material. Fig. 1a shows the diffraction pattern of the starting materials. Fig. 1b presents a sequence of images showing crystallization of (PrO)2CO3 (type II), growing from the edge inward.
Transmission Electron Microscopical studies of chemical rearrangements in bismuth uranium oxide
Authors: Parkinson G M , Billyard P D , Goringe M J , Long N J 
Published: June 2020

Electron beam induced transformations in metal oxides have been the subject of a number of TEM studies, including, recently, transition metals (eg 1), lanthanides and actinides (eg 2). In this paper we present preliminary results of a high resolution TEM study of bismuth uranium oxide (Bi2UO6), in which several unusual electron beam induced phenomena have been observed. Samples exhibit one of four different types of behaviour in the electron beam. Although in each case the onset of the phenomena is dose-rate dependent, differences in dose-rate do not seem to be solely responsible for the observed differences in behaviour. Although all the samples are nominally of the same chemical stoichiometry, microscopic inhomogeneities in composition may result in differing decomposition behaviour. In this respect, the known ability of Bi2UO6 to give up large proportions of its lattice oxygens (3) without apparently changing crystal structure may be directly relevant.The observed types of behaviour are as follows:
a) The sample remains unchanged, apparently indefinitely, under periods of continous electron irradiation.
b) The sample remains unchanged for a period, after which it suddenly “explodes”, depositing crystalline material on the surrounding carbon support film.
Directional disordering prior to amortization in electron-irradiated Cu-Ti intermetallic compounds
Authors: Luzzi D.E. 
Published: June 2020

At temperatures below approximately 265 K, intermetallic compounds in the Cu-Ti binary alloy system undergo an amorphizat ion transformation when irradiated by high energy electrons. Previous in-situ experimental studies revealed that the irradiation first induces chemical disordering in the compound (seen as a reduction in superlattice reflection intensity) which is followed by the crystalline-amorphous (C-A) transition. However, the actual structural evolution of the material during the C-A transition was not addressed in the previous study.In the present study, the structural evolution of the compound Cu4Ti3 was studied by ex-situ diffraction experiments in irradiated material that had not received a sufficient electron dose for amorphization. Cu4Ti3 has a Frank-Kasper-type tetragonal crystal structure composed of seven stacked body-centeredtetragonal sublattices.In Fig. 1, a diffraction pattern of the (017) systematic reflections is shown prior to complete amorphization. The double arrows mark the location of intersections of the first-order amorphous halo with the second-order halo arising from the (017) reflections and the Ewald sphere.
Observation of tweed microstructures in Ni-Al-Fe alloys
Authors: Munroe P. R. , Baker I. 
Published: June 2020

Ni-Fe-Al alloys are currently being considered for structural applications in the aerospace industry. Two compositions in particular Ni-30Al-20Fe and Ni-20Al-30Fe (in at. %) have generated the most interest. The former alloy is a single phase ordered body-centered cubic or B2 structure and the latter alloy has a B2 + Ll2 (ordered face-centered cubic) two-phase microstructure. X-ray microanalysis performed on Ni-20Al-30Fe has shown that the compostion of the B2 phase is Ni-30Al-20Fe, the same composition as the single phase alloy, and the compostion of the Ll2 phase is Ni-12Al-40Fe. This paper reports upon the observation of tweed microstructures in both alloys.The alloys were cast, canned in mild steel, extruded to rod at 1000°C and then cooled in sand. Details of thin foil preparation conditions have been reported before . Foils were examined in a JEOL 100CX operating at 100kV.Selected area diffraction (SAD) patterns from the B2 phase in Ni-20Al-30Fe(fig.1) exhibited streaking <110> directions, similar to the SAD patterns obtained from the B2 phase in Ni-37at%Al where a tweed microstructure was also observed.
The effect of embedding resins on ultramicrotomed polymer membrane morphology
Authors: Dietz N. L. 
Published: June 2020

A variety of microporous polymeric membranes are used in separation processes. Because the unique chemical and physical properties of these membranes affect performance, determining the membrane ultrastructure is essential to understanding how the structure and performance are related.TEM examination of ultramicrotomed membrane cross-sections is the most appropriate means of observing the thin active edge where the critical separation process occurs. Observation and interpretation of the image, however, is often difficult due to the low electron scattering of the polymer and alteration of the ultra-structure by the embedding resin. To solve the problem of low contrast in polymer thin sections, heavy metal stains such as osmium tetroxide and ruthenium tetroxide are used to selectively increase mass at specific locations. These stains, however, have limited application and carry the potential for creating artifacts. When staining is effective or unnecessary, there is the other concern of how the embedding resin has effected polymer morphology. Previous work with biological material has shown the effect of different epoxies on contrast and the correlation between the mechanical properties of various resins and sectioning dynamics, but the potential alteration of polymer ultrastructure has largely been ignored.