bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of Phase Diagrams by AEM
Authors: Ayer Raghavan 
Published: March 2011

ABSTRACTDetermination of phase diagrams to understand the equilibria among phases in metallic and ceramic systems has been of paramount interest in many areas of materials research. Traditionally, phase diagrams have been determined by (i) selecting several experimental compositions to map the region in the system of interest, (ii) exposing the alloys to temperature to achieve equilibrium, and (iii) characterizing one or more of the physical properties of the bulk material such as the crystal structure(s), magnetic property, metallography, etc., to determine the number and type of phases present in each alloy. Phase boundaries are then determined by delineating the regions of alloy compositions with respect to the number and types of phases present. The traditional methods suffer from several drawbacks, the major ones being (i) the need for numerous samples, (ii) difficulties in accurately determining multi-phase regions, (iii) assumption that the bulk samples are macroscopically and microscopically homogeneous, and (iv) difficulties in establishing the attainment of equilibrium. The limitations of these traditional methods mainly stem from their inherent inability to characterize the crystal structure and composition of the individual phasesCI). More recently, methods have been developed to determine phase boundaries by x-ray microprobe analysis of bulk diffusion couples (2). Though this approach offers some advantages over the conventional methods, it is still limited by the poor spatial resolution of x-ray microprobe analysis.
Measurement of Equilibrium and Nonequilibrium Segregation by X-Ray Microanalysis
Authors: Kenik Edward A. 
Published: March 2011

ABSTRACTX-ray microanalysis in an analytical electron microscope is a proven technique for the measurement of solute segregation in alloys. Solute segregation under equilibrium or nonequilibrium conditions can strongly influence material performance. X-ray microanalysis in an analytical electron microscope provides an alternative technique to measure grain boundary segregation, as well as segregation to other defects not accessible to Auger analysis. The utility of the technique is demonstrated by measurements of equilibrium segregation to boundaries in an antimony containing stainless steel, including the variation of segregation with boundary character and by measurements of nonequilibrium segregation to boundaries and dislocations in an ionirradiated stainless steel.
The Use of Symmetry in the TEM Analysts of Precipitate Morphologies
Authors: Dahmen U. , Westhacott K. H. 
Published: March 2011

ABSTRACTThis study points out how symmetry properties inherent in precipitation reactions can be exploitet to facilitate and improve the accuracy of a morphological analysis by TEM. A method is given for the simple determination of the direction and distribution of needle precipitates and the habit plane of plate precipitates based on the use of symmetry properties of the matrix crystal. The bicrystal symmetry of different orientation relationships between cubic crystals and its connection with observed and equilibrium shapes is illustrated with examples of high resolution micrographs of Ge precipitates in an Al matrix.
Contributions of Electron Microscopy to the Understanding of Reactions on Compound Semiconductor Surfaces
Authors: Sands T. 
Published: March 2011

ABSTRACTReacted films on compound semiconductor substrates present challenging materials characterization problems which often require the application of transmission electron microscopy (TEM) techniques. In this paper, both the problem - solving potential of the TEM techniques and the limits imposed by preparation of thin film/compound semiconductor TEM specimens are discussed. Studies of the Ni/GaAs, CuCl(aq)/CdS and Pd/GaAs reactions exemplify the role of TEM in identifying and determining the spatial distribution of interface - stabilized polymorphs and new ternary phases (e.g. tetragonal Cu2S, Ni3GaAs and PdxGaAs). These examples also serve to clarify the relationship between TEM and complementary analysis techniques such as Rutherford backscattering spectrometry, Auger electron spectroscopy and glancing-angle x-ray diffraction. In particular, it is argued that a combination of (1) high-spatial-resolution information obtained by TEM and (2) an indication of the “average” behavior provided by data from a complementary characterization technique provide the minimum quality and quantity of data necessary to understand most reactions on compound semiconductor substrates.
EDX and EELS Analysis of Precipitates in HSLA Steels
Authors: Chen Z. , Loretio M. H. , Cochrane R. 
Published: March 2011

ABSTRACTThe sizes and compositions of precipitates in two weldable HSLA steels have been determined using analytical electron microscopy. It has been shown that the balance between the microalloy additions must be carefully controlled if the formation of very large precipitates in the cast slab is to be avoided. These large precipitates are very stable, some having been shown to be stable on reheating to about 1200°C and others are stable up to the melting point of the steel. The significance of these observations is briefly discussed in terms of the influence of these precipitates on the properties of the microalloyed steels.
Commensuration and Discommensuration in the Ag-Mg Alloys
Authors: Fujino Y. , Sato H. , Otsuka N. 
Published: March 2011

ABSTRACTCommensuration and discommensuration characteristics of the long period superlattice in the Ag-Mg alloys near Ag3Mg with short modulation periods (M ≃ 2) are investigated. When quenched from 650°C, the modulation periods M of these alloys is found to take theoretical values determined by the size of the Fermi surface, while upon further annealing at low temperatures, alloys assume the commensurate structure M=2, except for those alloys with theoretical M values substantially different from 2. These alloys approach the periodic discommensuration structures of the type <2j1> or its variants whose average periods M are closest to the theoretical incommensurate values. This behavior leads to the conclusion that the formation of the long period superlattice in these alloys is basically due to the CDW formation and that the commensuration and the discommensuration characteristics are determined by the free energy of the modulation boundaries.
High Resolution Electron Microscopy of Triply Incommensurate Phase of 2H-TaSe2
Authors: Onozuka Takashi , Otsuka Nobuo , Sato Hiroshi 
Published: March 2011

ABSTRACTThe triply incommensurate phase of 2H-TaSe2 obtained by cooling from the normal phase was investigated by TEM between 87K and 113K with the resolution of 3 A. Moire-like patterns observed in this phase were confirmed to be interference fringes due to the first and the second order diffraction beams from the incommensurate structure and were not due to the dark field diffraction contrast of domains of the commensurate structure as interpreted earlier. Lattice fringes (∼9Å) of this modulated phase do not show any discontinuity across the boundaries of regions of different contrasts of the moire-like fringes which is expected from domain boundaries. Instead, a periodic change in the spacing of the lattice fringes (phase slip region) expected from the superposition of split superlattice spots in forming the lattice image is observed. This is the first direct observation of the existence of the phase slip region which is also expected from the discommensuration theory.
The Core Structure of Dislocations in GaAs
Authors: De Cooman B. C. , Kuesters K.-H. , Carter C. B. 
Published: March 2011

ABSTRACTThe structural aspects of dislocations in GaAs which had been plastically deformed at high stress were studied by TEM. The glide of well-defined dislocations in their slip-plane was observed during the recombination-enchanced relaxation of the dislocations from their high-stress configuration. The strong asymmetry of dislocation velocity previously observed by other techniques is confirmed. High-resolution, electron micrographs of dissociated end-on screw dislocations were compared to computer simulated micrographs of model structures of the dislocation core. No definite conclusion regarding the exact core structure could be made due to the movement of the defects during the observation.
Morphological Developments of Nickel Particles in Supported Metal Catalysts
Authors: Dhere A. G. , De Angelis R. J. , Reucroft P. J. , Bentley J. , Ice G. E. , Habenschuss A. 
Published: March 2011

ABSTRACTThe morphology of nickel-containing phases at each stage during the treatment of a 12%Ni/SiO2 catalyst was studied. Liquid impregnated catalyst initially shows nickel nitrate uniformly dispersed on the surface of the silica in the form of a film. After calcining, large rafts of NiO with faceted surface pits are seen. The reduced catalyst contains bunched nickel particles or large rafts on the surface of the silica.
High Resolution Imaging of As-Grown Sapphire Surfaces
Authors: Hsu Tung , Nutt S. R. 
Published: March 2011

ABSTRACTSurfaces of commercially grown edge-defined film-fed growth sapphire (EFG α-Al2O3) were studied in the electron microscope using both reflection electron microscopy (REM) and conventional transmission electron microscopy (TEM). The as-grown sapphire surface, ostensibly {1120}, was characterized by “rooftop” structures which were often locally periodic. These rooftop structures consisted of alternating {1120} facets and additional facets inclined a few degrees. The crystallography of the surface facets was analyzed using REM imaging of bulk specimens, and trace analysis of back-thinned plan section TEM specimens. Surface roughness was measured by stylus profilometry. and these measurements were compared to the electron microscopy observations. Fine structural features parallel to <0110> directions were also observed in both REM and TEM experiments, and these were attributed to surface steps of atomic scales.
Electron Microscopy of Ion Deposited Thin Films of the Oxides of Titanium
Authors: Harker A. B. , Howitt D. G. , Hood P. J. , Kobrin P. 
Published: March 2011

ABSTRACTThe reactive ion beam deposition of ceramic films onto unheated substrates can produce amorphous films with essentially molecular mixing. The annealing and hot isotatic pressing (hipping) of these films to produce crystalline phases have reproducable effects which are sensitive to the temperature and the density of the film. Experiments with titanium oxides indicate that it is principally the equilibrium phases that are formed and that hipping can be used to encourage the same transformations at lower temperatures.Thin films of titanium oxide close to the stoichiometry of TiO2 were deposited onto unheated substrates of sodium chloride. Some of the films were removed from the substrate by floating them off in water and the remainder were either annealed or hipped to induce crystallization. The anneals were performed either in air or argon and the hipping was done under an argon pressure of about twenty thousand pounds per square inch. Several of the free standing films were annealed in the same atmospheres on nickel grids. All the specimens were prepared for transmission electron microscopy by the same floating technique and were examined in a Philips 400 T.E.M. at 125 keV. The as deposited films were amorphous and showed no visible texture other than that derived from a small amount of porosity. The films were sufficiently conductive that they could be examined directly in the T.E.M. without carbon coating provided they were supported on a grid of fairly fine mesh. One specimen was also examined in the Kratos 1.5 MeV high voltage electron microscope at the National Center for Electron Microscopy. The specimen was annealed in vacuum using an in-situ hot stage to directly observe the behavior of the film.The post deposition annealing and hipping of these films reproducibly induced the crystallization of anatase below 800°C. This is the equilibrium phase [1] and the extent to which the films transformed and the morphology of the growing crystallites were determined principally by the film thickness. There was little difference between the responses of free standing films and films left on the salt substrate. They tended to transform at about the same temperature, which was reproduced in the in-situ hot stage experiment and the microsructures which formed were very similar. The dependence upon thickness was also reflected in all the microstructures of the different post deposition treatments and it was possible to complete the transformations that were very sluggish in some of the films by hipping them at the same temperatures.
Defect and Microstructural Analyses in Ferromagnetic Material
Authors: Horton L. L. 
Published: March 2011

ABSTRACTTransmission electron microscopy (TEM) of ferromagnetic materials requires special and often time-consuming procedures to obtain good images. Tilting and high resolution experiments are particularly difficult. A survey of several investigations of microstructures in ferromagnetic materials ranging from pure iron to commercial magnet materials is presented. The topics of these investigations include determination of Burgers vectors and interstitial/vacancy character for dislocation loops, cavity shape analyses, magnetic domain/microstructure correlations, and characterization of structures resulting from isotropic spinodal decomposition. Problems encountered during these studies as they relate to magnetic materials and the modifications to standard microscope operating procedures required to overcome these problems are presented. This discussion includes specimen requirements, specimen loading and insertion, and alignment corrections required during specimen tilting.
Identification of Growth Induced Planar Defects in Silicon
Authors: Strunk H. P. , Kessler A. , Bauser E. 
Published: March 2011

ABSTRACTPlanar defects have been detected by transmission electron microscopy in silicon epitaxial layers that have been grown from Ga solutions below 500 °C. According to fringe contrast analysis, this defect can be modelled by a plane of Ga atoms within the Si lattice. This plane forms during crystal growth due to local preferential incorporation of Ga atoms at crystallographically defined sites, that occur repetitively in the trains of monomolecular growth steps at the liquid/solid growth interface.
Microstructure of Rapidly Solidified Al-Si Exhibiting Enhanced Superconducting Properties
Authors: Noack M. A. , Drehman A. J. , Pelton A. R. 
Published: March 2011

ABSTRACTTsuei and Johnson previously reported significantly enhanced superconducting transition temperatures for rapidly solidified Al-Si alloys. Here we report a microstructural study of melt spun Al80Si20ribbons to determine the mechanism responsible for this enhancement.Results of this investigation revealed three distinct microstructures from the top surface to the more rapidly cooled bottom surface (which was in contact with the melt-spinning wheel). Near the top, the microstructure is of hypoeutectic morphology even though this is a hypereutectic alloy. The predominant microstructure is cellular. A 1 to 3Wmthick layer at the bottom of the ribbon was found to be responsible for the largest enhancement. This layer is composed of fine-grained supersaturated fcc Al containing densely distributed dc Si precipitates. Microdiffraction analysis revealed a cube/cube orientation relationship between the precipitates and the matrix. These results provide insight into the possible mechanism for the enhancement.
Materials in Sports a New Concept for the Teaching of Materials Science and Engineering
Authors: Ebert Lynn J. , Michal Gary M. 
Published: March 2011

ABSTRACTMost sports equipment in common use today represents highly developed engineering structures. Many of the equipment items have evolved empirically, but nonetheless can be used to illustrate basic principles of materials engineering, applied mechanics and kinetics. Using the most common items of sports equipment (footballs, tennis racquets, vaulting poles, etc.), a new course has been developed which introduces first year science and engineering students to materials science and engineering, as well as basic engineering, using a medium they can relate to personally—sports. Emphasis is placed upon the factors which make the equipment functional. These factors include both the basic materials from which the equipment is made and its fundamental design. Detailed treatment is given to the origin of the various species of materials. The processing used to produce the full spectrum of properties required of the various equipment items and the important structure-property relations in the equipment's use are presented. “Hands-on” experiments, guest lectures by world authorities in several fields of sporting activities and equipment use demonstrations compliment the lecture-recitations of the course.
The Metals/Materials Dichtomy: Real or Apparent?
Authors: Bernstein I. M. 
Published: March 2011

ABSTRACTSome of the reasons for and the developing impact of the rapid broadening of the field of materials are presented and the impact of the concomitant shift away from the domination of metals on education and research is assesed. Both the opportunities presented by this view of the materials spectrum and the inherent dangers of over reaction and hyperbole are presented.
Pedagogical Theories and Strategies in Education for Materials Research: A Hierarchical Approach
Authors: Roy Rustum 
Published: March 2011

ABSTRACTThe topic of education optimized for materials research is treated In sequence at four hierarchical levels starting with the most general.Materials Research is the earliest and best developed example within the physical sciences and engineering of an integrative field (discipline?). Yet very little thought and no research (including the relevant cognitive science) has addressed the subject of how best one can educate a cadre of materials researchers. The author will adduce Inductive and anecdotal data to point some fruitful directions in reorganizing the approach to education in integrative knowledge fields.The first important thesis of this paper is that we have failed to analyze correctly the appropriate hierarchical relationships among individual scientific disciplines, engineering departments, and technological research groupings.The second major point is that education for materials research is done is several departments (materials science, physics, electrical engineering, chemical engineering, etc.) and Indeed that some mix of disciplinary roots is desirable for the materials research cadre. Improvements will be proposed in four areas: (1) Optimum content of MSE curriculum, (2) the widespread introduction of MSE minors, (3) under-representation of electronic materials, pol ymers, ceramics.The third aspect deals with the modularization of the content and teaching materials to allow adaptation to local needs in a field like materials research. The international materials community has done rather well by establishing the Materials Education Council and the Journal of Materials Education, for producing and disseminating print media. The status and usage of JME will be described.
Ceramic Engineering Education
Authors: Readey D. W. 
Published: March 2011

ABSTRACTCeramic Engineering or Ceramics has existed as a separate academic discipline in the United States for over ninety years having been founded to ensure the application of the principles of chemistry to the fabrication of ceramic products. With the maturation of the traditional ceramic industries, including refractories and glass, and the growth markets of high technology ceramics for electronic and structural applications, the requirements of a ceramic engineering education are undergoing rapid change. The current status of the ceramic industry and its impact on education and the ceramic education infrastructure are reviewed. Within this framework and the property and structure emphasis unique to ceramics, a model undergraduate degree curriculum is presented.
Materials Science in the Electrical Engineering Curriculum
Authors: Cochran David R. 
Published: March 2011

ABSTRACTMaterials properties are crucial to the operation of electron devices. Based on this fact, the inclusion of the study of material science as an integral part of an electrical engineering curriculum is examined. The trends in the curriculum over a period of time are considered with respect to the growth of technology. A nationwide sampling of the electrical engineering curriculum over ten year periods is cataloged. Tabulated results are presented. Based on these results, a view of future curriculum that incorporates material aspects is presented.
Energy Distribution of Ions in Plasma Etching Reactors
Authors: Briaud P. , Turban G. , Grolleau B. 
Published: March 2011

AbstractThe energy distributions of the positive ions bombarding the ground electrode in a parallel plate plasma etcher have been measured by means of an electrostatic analyzer after extraction through a 50 μm orifice.Three gases were studied; Ar, CF4 and SF6, with pressures varying from 5 mtorr to 200 mtorr as a function of the discharge frequency.In the low frequency regime (25–125 kHz) the maximum energy of the ions is close to the applied potential (i.e., 500–600 eV).A secondary ion peak is observed and attributed to the secondary electron ionization.SF6 plasma exhibits a behaviour different to that of Ar and CF4 plasmas because of the high electron attachment of the molecule.
OES, LIF, and MS Studies of Silane, Disilane, and Chlorosilane Plasmas
Authors: Lee H. U. , Ross R. C. , De Neufville J. P. 
Published: March 2011

AbstractUsing optical emission spectroscopy (OES), mass spectrometry (MS), and laser-induced fluorescence (LIF), we are investigating a number of glow-discharge reactions as a function of RF power, flow rates, partial pressures, and H2 dilution under realistic thin-film deposition conditions.In this paper we report on the preliminary results of two studies:
1)The formation of radical and polymeric species in SiH4 and Si2H6 plasmas, and2)The characterization of SiF4 + H2 plasmas and the detection of HSiCl and HSiF in the plasmas of SiH2Cl2 and SiH2F2, respectively.
A Mechanistic Study of CC12F2/02 RIE for Bipolar Trench Isolation
Authors: Danner David A. , Petrillo Edward J. , Polcari Michael R. 
Published: March 2011

AbstractThe etching of 1.25×3.5 micron trenches in silicon for use in bipolar device isolation using chemistries based on CC12F2 (freon-12) and 02 has been investigated.It was found that competitive reactions in the trench favor deposition of a Si02-like material on the sidewalls and promote lateral etching of the N+ subcollector under conditions necessary for high selectivity.In addition thermally activated processes were investigated by direct measurement of the sample surface temperature during etching.The temperature threshold for the initiation of subcollector undercut was determined to be 70C and the vertical etch rate exhibited an inverse activation indicating adsorption-limited etching.Results are discussed in the context of a qualitative model, based on the etchant-unsaturate model, which describes the contribution of several phenomena to the trench shape.These include sidewall passivation, species transport, deposition, N+ doping enhancement, Si loading, and ion scattering.