bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Resolution Imaging of Twin and Antiphase Domain Boundaries in Perovskite KNbO3 Thin Films.
Authors: Rou Shang H. , Hren Philip D. , Hren John J. , Graettinger Thomas M. , Ameen Michael S. , Auciello Orlando H. , Kingon Angus I. 
Published: March 2011

AbstractPerovskite KNbO 3 thin films were heteroepitaxially deposited onto (100) MgO substrates. Twin domains with tetrahedral shape were typically observed. These tetrahedrons were bounded by three {211} twin planes. High resolution transmission electron microscopy (HRTEM) was employed to examine these {211} twin boundaries. Surface steps of {110}<110> type generated by dislocation slip were present on the MgO substrate. The tetrahedral twin domains originate on surface steps, then grow with a stacking fault relationship to the matrix. The strain fields of dislocations near the stacking faults slightly rotate the tetrahedral twin nuclei. This small degree of misalignment between the matrix and the twin domain result in some of the twin boundaries having amorphous boundary regions rather than coherent interfaces.Order-disorder antiphase domains (APD's) were directly imaged with HRTEM. Ultra small APD's ranging from 10 to 30 atomic spacings were observed. The origin of these APD's was either the surface steps of {100} <1 10> type on MgO substrates or the random nucleation of anions at either of two equivalent sites on the MgO substrate.
The Interpretation of HRTEM Images of Partially Amorphized Pyrochlore Structure Types.
Authors: Miller Mark L. , Ewing R. C. 
Published: March 2011

AbstractThe results of image simulations on partially amorphous microlite (Ca2Ta2O7, pyrochlore structure) are presented. Results indicate that HRTEM images are not sensitive to the position of amorphous layers within a crystalline matrix. In addition, it is observed that the limit of detection of amorphous material within a crystalline matrix is dependent upon the total thickness of the sample. In thin crystals (<150 Å), up to 75 volume percent crystalline material can give rise to aperiodic images, yet the addition of a small amount of crystalline material (80 volume percent crystalline) produces a periodic image. Images calculated for isolated spheres of amorphous material distributed within crystalline microlite suggest that isolated domains of amorphization are observable at sample thicknesses less than three times the diameter of the feature. The image contrast of amorphized domains is enhanced by imaging at defocus settings significantly different than Scherzer focus. These results indicate that interpretation of HRTEM images of partially amorphized crystalline materials should be undertaken with caution, and estimates of the volume of damage considered only qualitative.
Metallic Particles Supported in Several Synthetic Zeolitic Materials
Authors: Acosta Dwight R. , Yacaman Miguel J. 
Published: March 2011

AbstractHigh resolution electron microscopy observations were carried out in several zeolitic systems with different supported metallic phases in order to determine besides distributions of metallic particles, possible preferential orientations of metallic phases during impregnation processes and to detect some crystallographic relations between metallic particles and support.
High Resolution Transmission Electron Microscopy of Partial States of Oxygen Order in YBa2Cu3Oz
Authors: Burmester C. P. , Quong S. , Wille L. T. , Gronsky R. , Ahn B. T. , Lee V. Y. , Beyers R. , Gür T. M. , Huggins R. A. 
Published: March 2011

AbstractHigh resolution electron microscopy is used to investigate the effect of electron irradiation induced oxygen loss on the states of partial order in YBa2Cu3Oz. Contrast effects visible in the [001] zone image as a result of the degree of the out-of-plane correlation of these ordered states are investigated. Using statistical simulations to aid in the analysis of the HREM images, an interpretation based on a kinetically limited evolution of the variation of long range [001] ordering is proposed.
An HREM Investigation into the Atomic Structure of an Aluminum Grain Boundary
Authors: Hetherington C. J. D. , Dahmen U. , O'Keefe M. A. , Kilaas R. , Turner J. , Westmacott K. H. , Mills M. J. , Vitek V. 
Published: March 2011

AbstractAn experimental high resolution image of a grain boundary has been compared with images simulated from atomic structures calculated by two theoretical methods. Some of the techniques used in the analysis of the images are presented. A good agreement is found between each theory and the experiment, confirming the validity of calculations of such a boundary.
Hrtem of the Cu/Mno Interface in an Internally Oxidized Cumn Alloy
Authors: Ernst F. 
Published: March 2011

AbstractThe structure of the Cu/MnO interface has been studied using high resolution electron microscopy (HRTEM). Interfaces were formed by internal oxidation of a CuMn alloy. In the course of the reaction, MnO particles precipitate in several special orientations relative to the Cu lattice: “parallel” topotaxy, “twin” topotaxy, and a 55°[110] rotation yielding (111)Cu∥(002)MnO. Each of the three Cu/MnO orientation relationships has a characteristic particle morphology reflecting thermodynamically favourable interface structures. In parallel topotaxy MnO particles preferentially form flat {111}Cu/{111} MnO interfaces with a lattice mismatch of 21%. Although this mismatch is large, the existence of coherence strains in the Cu cannot be excluded. MnO particles in the 55°[110] orientation form regions of semi-coherent Interface where {200}MnO planes face a set of parallel {111} Cu planes with a mismatch of only 6%. This interface variant exhibits equally spaced steps, every 16 to 18 Cu {111} planes. Parallel to every step there is a misfit dislocation in the Cu at a stand-off distance of about 2 Cu {111} spacings. The relationship between structure and energy of the Cu/MnO interface is discussed.
Aplications of Image Processing Techniques on the Structural Characterization of Decagonal Phases
Authors: Reyes-Gasga J. , Perez R. , Jose-Yacaman M. 
Published: March 2011

AbstractImage processing techniques applied to HREM images of decagonal quasicrystalline phases are carried out. A comparison between these processed images, simulated images based on the multislice method and density wave techniques and also experimental STM images of the decagonal phase [9] suggest some insights on their structure.
Interface Structure and Layer Synthesis Modes in Mesotaxial Si/CoSi2/Si Structures
Authors: Hull R. , Hsieh Y. F. , Short K. T. , White A. E. , Cherns D. 
Published: March 2011

AbstractWe report observations of interfacial structure and consequences for layer synthesis modes in mesotaxial Si/CoSi2/Si structures, as deduced from high resolution transmission electron microscopy (HRTEM). It is argued that relative crystal misalignments arising from the lattice parameter mismatch between the Si and CoSi2 may render classic rigid shift measurements of interfacial structure inaccurate. An alternative method for determining interfacial structure at threedimensional precipitates by analyzing crystal stacking sequences is demonstrated.
Low - Temperature Defect - Induced Aging of GaAs Grown by Molecular Beam Epitaxy
Authors: Szafranek I. , Stockman S. A. , Szafranek M. , McCollum M. J. , Plano M. A. , Miller W. R. , Stillman G. E. 
Published: March 2011

ABSTRACTDegradation in optical and electrical properties has been observed for high-purity and high-mobility p-type GaAs layers which contain significant concentrations of an unidentified shallow acceptor-like defect, labeled “A”, that is frequently incorporated in crystals grown by molecular beam epitaxy. Low-temperature photoluminescence and variable temperature Hall-effect measurements were employed to monitor the aging process in samples stored for about one year at room temperature. Profound changes in the exciton recombination spectra, indicative of increasing concentration of the “A” defect, have been accompanied by a decrease in hole mobility and an increase in carrier concentration. These results are discussed in the context of the acceptor-pair defect model, originally proposed by Eaves and Halliday [J. Phys. C: Solid State Phys. 17, L705 (1984)].
Degradation Mechanism in GaAs Led
Authors: Jicheng Zhou , Zhiping Fu , Qianbao Zhan , Shuifu Feng 
Published: March 2011

ABSTRACTA series of experiments have been performed to verify the nature of hole trap A and B in GaAs proposed by Zou and revised by Zhou (one of the present authors). The relative concentration of these two Craps is responsible for the degradation behavior of the diodes. Accordingly, the degradation mechanism in GaAs LED can be reasonably deduced based on thermodynamic consideration.
Effects of Neutron Irradiation and Post-Irradiation Annealing on the Radiant Output Power of Infrared Light Emitting Diodes
Authors: Hajghassem H. S. , Brown W. D. , Yeargan J. R. , Williams J. G. 
Published: March 2011

ABSTRACTThis paper presents results of a study of the degradation of commercially available GaAs and AlGaAs light emitting diodes subjected to neutron bombardment at a TRIGA reactor. Devices were characterized using current-voltage and light output measurements prior to and following a sequence of neutron irradiations and after high temperature annealing. A model is derived which can be used to determine the lifetime damage constant product, τoK, if the light output measurements as a function of IMeV equivalent neutron fluence are made at a fixed operating current. For current levels smaller than approximately 1 ma, τoK and operating current is logarithmic with τoK decreasing as current increases. Annealing at temperature up to 275°C recovers some of the neutroninduced damage but does not affect the validity of the model.
Reliability of Ohmic Contacts for AlGaAs/GaAs HBTs
Authors: Jackson G. S. , Tong E. , Saledas P. , Kazior T. E. , Sprague R. , Brooks R. C. , Hsieh K. C. 
Published: March 2011

ABSTRACTThe reliability of ohmic contacts to thin, heavily doped layers of GaAs is investigated. Pd/Ge/Au contacts to n-type GaAs display excellent electrical stability over extended periods of thermal stress. The contact resistance stays below 0.50Ω-mim during a 2500h, 280°C bake. Reactive ion beam assisted evaporation of Ti with N forms TiN which is introduced as a barrier layer in Pt/TiN/Ti/Au contacts to a thin p+ layer. The TiN layer allows greater process latitude in the sintering process and improves long term stability of the ohmic contact. The microstructure of the p-type contacts is examined with TEM and Auger profiling at different instances of the 2500h, 280°C bake and compared to the contact resistance measurements.
Pd-Ge-Au Ohmic Contacts to GaAs: Reliability and Failure Analysis
Authors: Kazior T. E. , Hieslmair H. , Brooks R. C. 
Published: March 2011

ABSTRACTWe report on experiments that were performed to evaluate the temperature stability and long term reliability of non-alloyed Pd-Ge-Au ohmic contacts on N-type GaAs. Low resistance contacts (≈1×10−6 Ωcm2) were obtained for samples that were sintered in a conventional furnace or flash sintered in a graphite susceptor. Elevated temperature storage (≈4000 hours at 280°C) showed improved contact stability when compared to Ni-AuGe-Ni-Au control samples. Gateless MESFETs subjected to bias temperature stress measurements (Ids ≈300–350mA/mm, 2000–4000 hours at 200°C) showed no significant change in device current. This result is in contrast to devices with Ni-AuGe-Ni-Au ohmic contacts which exhibited a 6–27% decrease in current under the same test conditions. Failure analysis reveals significant electromigration and Au diffusion in the drain fingers of devices with Ni-AuGe-Ni-Au contacts. In contrast, devices with Pd-Ge-Au contacts show no elect romigration or Au diffusion in the GaAs.
Making Reliability Estimates when Zero Failures are Seen in Laboratory Aging
Authors: Nash Franklin R. 
Published: March 2011

ABSTRACTTo estimate the probability of failure for a deployed population, when the laboratory aging of a sample certified population produces zero failures, an appropriate model is required. The widely used exponential (constant hazard rate) model, and a declining-hazard-rate Weibull model are contrasted. On balance the use of the Weibull model seems preferred because: (i) It is consistent with laboratory aging studies on many types of electronic components; (ii) It is less sensitive to the choices for parameters (e.g., thermal activation energy) whose values are not known accurately; and, (iii) It may yield more conservative (i.e., larger) values for the relevant hazard rate than the exponential model. The unavoidable uncertainties connected with the use of either model are discussed. An example is given of a plausible, but in fact mistaken, use of the exponential model that leads to disastrously incorrect reliability predictions.
Electroluminescence from Gunn Domains in GaAs MESFETS as a Means of Defect Detection
Authors: Zappe Hans P. , Jantz Wolfgang 
Published: March 2011

ABSTRACTThe emission of visible light from the high-field region near the drain of GaAs/AlGaAs MESFETs has been used to study the quality of fabricated transistors. Inhomogeneities or bright spots in the emission have proven to indicate the presence of defects in the gate/drain spacing or surface contaminants, such as re-deposited gate material. Processing abnormalities of 0.5 μm diameter are easily seen. The time-variation of emission from the brightest spots is characteristic of the formation of microplasmas the location of which will often predict the site of destructive device breakdown.
Degradation of Hydrogen-Passivated p-Type Layers in GaAs by Minority Carrier Injection and Reverse Bias Annealing
Authors: Tavendale A. J. , Pearton S. J. , Williams A. A. , Alexiev D. 
Published: March 2011

ABSTRACTWe detail experiments showing that acceptor passivation by atomic hydrogen in p-type GaAs is unstable to either illumination, forward bias annealing or reverse bias annealing. The long-term stability of operation of devices employing hydrogen in or near the active region of FETs or quantum-well lasers is therefore questionable. The systematics of acceptor reactivation during minority carrier injection or reverse bias annealing are presented.
Ordering Energy of B2 Alloys Calculated in the Frozen Potential and Harris Approximations
Authors: Shelton W. A. , Nicholson D. M. , Stocks G. M. , Pinski F. J. , Johnson D. D. , Sterne P. , Temmerman W. M. 
Published: March 2011

AbstractIt has been established that the coherent potential approximation can successfully describe the energy of random alloys [1]. It has also served as the basis of generalized perturbation method [2] and concentration wave [3] xscalculations of the energy of short range ordered alloys. The multisublattice coherent potential, (MCPA) is the natural extension of the CPA with which to address long range order (LRO). Using the recently developed multisublattice coherent potential approximation Korringa Kohn Rostoker [4], (MCPA-KKR) code the elgenvalue sum can be calculated as a function of LRO. This allows the evaluation of the ordering energy by either of two approximations. The frozen potential approximation (FPA) [5] assumes that the muffintin single site potentials do not change as the long range order is varied; the Harris Approximation, (HA) [6], as applied in this work, assumes that the single site charge densities do not change as the long range order is changed. These two methods of calculating the ordering energy will be compared with each other and to experiment for several systems including CuZn, NiAl, and NiAl with zinc additions.
Thermodynamic Stability of Ordered Intermetallic Compound Phases
Authors: Chang Y. Austin , Neumann Joachim P. , Chen Shuang-Tin 
Published: March 2011

AbstractThe Wagner-Schottky model was used to describe the thermodynamic behavior of ordered intermetallic compound phases. To demonstrate the utility of the approach, the models developed for triple-defect B2 (and B32) and anti-structure L10phases were used to describe the thermodynamic properties of β-AlLi and γ-TiAl respectively. Since any potential engineering materials to be developed on the basis of intermetallics will be multi-component systems, the methodology was extended to describe the thermodynamic properties of ternary intermetallics. The ternary Ti-Mo-Al system was used as an example for discussion. It is believed that the general topologies concerning the phase equilibria of Ti-M-AI with M being V, Nb, Ta, Mo and W are similar. The relative stabilities of the competing phases, i.e. BCC and HCP, in the mid-composition region of Ti-M-AI were discussed.
Kinetics of Ordering in Fe3Al: Experiment
Authors: Fultz Brent , Gao Zheng-Qiang , Anthony Lawrence 
Published: March 2011

AbstractAlloys near the Fe3Al stoichiometry were prepared far from thermodynamic equilibrium by rapid solidification methods. These highly disordered materials were then annealed at low temperatures to develop B2 and D03 order. Both shortrange and long-range order (SRO and LRO) were measured by Mössbauer spectrometry and by x-ray diffractometry, respectively. The SRO was found to evolve in two stages: an initial quick growth of the SRO alone, followed by a slower growth of SRO along with LRO. As expected, at lower temperatures the absolute rates of growth of order were suppressed, but more interestingly, the relative rates of growth of B2 and D03 long-range order parameters were different at different temperatures of annealing. When the B2 order parameter is graphed against the D03 order parameter, at lower temperatures the “kinetic path” through this graph shows that B2 order evolves relatively more rapidly than D03 order.
Morphological and Structural Characterization of the Spinodal Decomposition of FE-CR Alloys.
Authors: Cerezo A. , Hetherington M.G. , Hyde J.M. , Miller M.K. 
Published: March 2011

AbstractThe position sensitive atom-probe (POSAP) is capable of extremely high resolution (subnanometer) microanalysis. Its 3-dimensional capabilities are unique and offer a new opportunity to study the topology and structure of materials. This paper is an initial overview of the new types of parameters and analysis that this technique makes possible.
The Measurement of Composition During the Early Stages of the Spinodal Decomposition of Fe-Cr Alloys
Authors: Hetherington M.G. , Hyde J.M. , Miller M.K. 
Published: March 2011

AbstractThe properties of many advanced alloys are derived from extremely fine-scale microstructures. This poses interesting questions about the measurement of composition on this scale. The phase separation of model Fe-Cr alloys has been been studied with the atom-probe. Statistical techniques have been used to estimate the composition and compare the results with the predictions of linear and non-linear theories of spinodal decomposition and the distributions obtained from Monte-Carlo calculations.
Dislocation Core Structures in Nial.
Authors: Pasianot R. , Farkas D. 
Published: March 2011

AbstractSince the early studies on bcc materials, computer simulation of dislocation core structures has been recognized as a valid means of understanding yield behavior with temperature. Many of today's high temperature ordered alloys do have yield anomalies and computer simulation of core structures is a basic ingredient in the corrent theories for the anomalous yield behavior in Ll2alloys. In the case of B2 type alloys there are very few of these studies. The present work deals with computer simulation of core structures in B2 NiAl. An embedded atom type potential is used to simulate interactions and several slip systems are considered, particularly those having [100] and [111] slip vcctors that are the experimentally observed.
The Electronic Structure And Phase Stabilities Of Metallic Alloys
Authors: Györffy B.L. , Barbieri A. , Jolnsoni D.D. , Nicholson D.M. , Pinski F.J. , Shelton W.A. , Stocks G.M. 
Published: March 2011

AbstractCondensed matter consists of positively charged atomic nuclei and the electron glue which holds them together. Although it is attractive to attempt to oilodl it by nentral atoms interacting via. relatively weak pairwise ‘effective interactions’ in genbreak down the predictive and inter;retative power of the analysis. Hence, there is no substitute to forging a parameter-free and quantitative theory of the complex degenerate Fermi liquid ‘glue’ to complement phenomenological calculations. Such theory is the general aim of ’first-principles’ calculations of the electronic structure. This talk will concern past present and future first-principles calculations relevant it the state of compositional order in metallic alloys. Special attention will be paid to phaase insta bilities induced by Fermi Surface effects.
Microstructure and Compressive Properties of Fe-Modified L12-TYPE Al3Ti
Authors: Pak H.R. , Wayman C.M. , Favrow L.H. , Cooper C.V. , Pak J.S.L. 
Published: March 2011

AbstractThe microstructures and mechanical properties of an Fe-modified L12 alloy containing 7.5 at.% Fe have been investigated. This alloy has been determined to be essentially single phase following a homogenization heat treatment (HHT) at 1100°C for 100h, with a very small volume fraction of precipitates having been observed to form along dislocations. Conversely, in the case of the as-cast (AC) condition, the alloy has been determined to contain band-like precipitates, which have also formed along dislocations. In addition, a high density of very thin plate-like precipitates have formed parallel to {001} planes of the L12 matrix. Although these plate-like precipitates appear to exhibit lattice tetragonality, their crystal structure cannot be explained by assuming D022 and D023 structures. Five different <110>-type dislocations havfe been activated within a small region of a matrix grain during deformation at 1100°C, some of which cross slipped from {111} to {001} planes. Specimens in both AC and HHT conditions were deformed in compression to approximately 0.5% without fracture at both 22 and 1 100°C, the yield stress for the HIT condition having been determined to be 192 MPa at 22°C and 98 MPa at 1100°C.
Mechanical Properties, Fracture Behavior, and Grainboundary Chemistry of B-Doped Nial
Authors: George E. P. , Liu C. T. , Liao J. J. 
Published: March 2011

AbstractThis paper summarizes the results of our work aimed at overcoming the intrinsic grainboundary weakness of NiAI by microalloying with boron. In previous work we have shown that 300 wppm boron is very effective in suppressing intergranular fracture in NiAI [1]. It does this by segregating strongly to the grain boundaries and strengthening them. Despite this dramatic effect on the fracture mode, however, boron is unable to improve ductility because it is a potent solid solution strengthener, more than doubling the yield strength relative to that of undoped NiA1. The present work attempts to decrease this deleterious hardening effect by lowering the bulk concentration of boron in NiA1. Our results show that if the boron concentration in the bulk is lowered to 30 wppm, the yield strength of boron-doped NiA1 is only about 30% higher than that of undoped NiAI. In addition, there is enough boron at the grain boundaries of this alloy to suppress intergranular fracture. Under these conditions, boron-doped NiAI has a tensile ductility of 2%, which is essentially identical to that of undoped NiA1. This result, namely that the strengthening of grain boundaries by boron does not by itself improve ductility, indicates that although grain boundaries might well be the weakest links in NiAI, cleavage planes are not much stronger. In other words, even though boron additions serve to strengthen the grain boundaries and suppress intergranular fracture, ductility is not improved, because the next brittle fracture mode, namely transgranular cleavage, takes over before significant plastic deformation can occur.