bluuebunny/crossref_metadata_2025_split huggingface dataset:
Grain Boundary Microstructure Dependent – Intergranular Fracture in Polycrystalline Molybdenum
Authors: Tsurekawa Sadahiro , Watanabe Tadao 
Published: April 2011

ABSTRACTThe intergranular brittleness in polycrystalline materials is a source of serious problem in material processing and practical applications. To obtain a fundamental knowledge of improvement in the brittleness, we have examined the relationship between fracture behaviour and grain boundary (GB) microstructures in polycrystalline molybdenum. Quantitative analyses of GB microstructures were performed by orientation microscopy (OIM), and followed by 4-points bending tests at 77K. Thereafter, crack propagation was analyzed in connection with GB microstructures. We found the fracture stress depends on the grain size in similar manner to the Hall-Petch relation. In addition, the Hall-Petch relation also depends on the grain boundary character distribution (GBCD). The fracture stress increases with increasing the frequency of low σ GBs at constant grain size. Conversely, random GBs seem to act as weak intrinsic defects and the interconnection among them may give rise to premature failure. Therefore, the connectivity of random GBs probably becomes important as well as the GBCD to suppress the intergranular fracture.
Interfacial Engineering for Optimized Adhesion in Polymeric Composite Materials
Authors: Drzal Lawrence T. 
Published: April 2011

ABSTRACTFiber-matrix adhesion is a variable to be optimized so that optimum composite mechanical properties can be achieved in polymer matrix composites. The contemporary view of adhesion rests on an “interphase” model in which not only the actual chemical and physical interactions between fiber and matrix are considered but also the structure and properties of both the fiber and the matrix in the region near the interface. The optimum design methodology starts with the specification of the fiber and matrix from a structural consideration. Once the constituents are selected, the focus is on the creation of a beneficial fiber-matrix “interphase”. This region where the fiber and matrix interact has to be designed for both “processing” and “performance”. Although no quantitative algorithm is available for interphase optimization, various thermodynamic principles coupled with experimental data can be used to qualitatively design the optimum interphase. Examples will be presented to illustrate how this interface can be engineered with surface treatments and sizings or coatings to insure thorough wetting, protection of the fiber, chemical bonding between fiber and matrix, toughness and desirable failure modes.
Inclined Substrate Deposition by Evaporation of Magnesium Oxide for Coated Conductors
Authors: Bauer Markus , Metzger Ralf , Semerad Robert , Berberich Paul , Kinder Helmut 
Published: April 2011

AbstractBiaxially textured MgO buffer layers were deposited on metal substrates using “inclined substrate deposition” (ISD). The influence of the substrate inclination angle, deposition rate, and film thickness on the texture is shown. Scanning electron microscopy reveals columnar growth. We developed a growth model to explain the texturing. To test this model we have carried out 3D Monte-Carlo simulations. We find that the preferred orientation arises from mutual shadowing of the columns and directional surface diffusion due to their initial momentum.YBa2Cu3O7 (YBCO) films deposited on the ISD buffer layers are highly textured. The ab-planes of the YBCO are tilted with respect to the surface by typically 25° towards the direction of MgO vapor incidence. Therefore, the critical current density jc is anisotropic with up to 8 × 105MA/cm2 in one direction and 4 × 105MA/cm2 in the other. For tape coating the MgO deposition direction can be chosen so that the high jc is along the tape.
Ion Beam Induced Growth Structure of Fluorite Type Oxide Films for Biaxially Textured htsc Coated Conductors
Authors: Iijima Y. , Kimura M. , Saitoh T. 
Published: April 2011

AbstractBiaxially aligned film growth by dual-ion-beam sputtering method were studied for fluorite type (Zr0.85Y0.15O1.93(YSZ), Hf0.74Yb0.26O1.87, CeO2), pyrochlore type (Zr2Sm2O7), and rare-earth C type (Y2O3, Sm2O3) oxides on polycrystalline Ni-based alloy substrates. Cube-textured (all axes aligned with a <100> axis substrate normal) films were obtained for fluorite and pyrochlore ones by low energy (<300 eV) ion bombardment at low temperatures (< 300 °C). Besides, cube textured Y2O3 films were obtained in far narrow conditions with a quite low energy (150 eV)-ion bombardment at the temperature of 300°C. The assisting ion energy dependence was discussed in connection with lattice energies for these oxide crystals.
Growth and Structural Characterization of Sr2TiO4: Chemical Control Over the Terminating SrTiO3 Surface.
Authors: Salvador P. A. , Mercey B. , Perez O. , Haghiri-Gosnet A. M. , Doan T.-D. , Raveau B. 
Published: April 2011

AbstractThin films of Sr2TiO4 were grown using pulsed laser deposition (PLD) and laser-MBE on [100]-SrTiO3single crystal substrates. Films grown by standard PLD display only a single peak in the X-ray diffraction spectra, corresponding to the (006) peak of the K2NiF4 parent structure. Using a Laser-MBE, controlled two-dimensional growth and RHEED intensity oscillations can be routinely obtained. The period of the RHEED intensity oscillations was confirmed to correspond to the deposition of one-half the unit cell. In contrast to PLD-grown films, the (004) and (006) peaks are observed in XRD spectra for the Laser-MBE-grown films. The intensity of the (004) peak is discussed and modeled with respect to in-plane disorder arising from substrate step-edges and out-of-plane film-substrate structural mismatches. That a single, half unit-cell can be deposited allows one to "flip" the terminating surface of SrTiO3 in a controlled and simple manner from a pure TiO2 layer to a SrO layer. Experimental evidence of the importance of such surface control is given for the SrCuO2 structural stability.
Instabilities and Point Defects at Step-Free Si(001) and (111) Terraces During High Temperature Annealing
Authors: Lee Doohan , Blakely Jack M. 
Published: April 2011

AbstractIn this paper we describe observations on the stability of extremely large Si(001) and (111) terraces that are formed by a technique described previously. Following annealing at high temperature and quenching, a series of concentric pits of monoatomic depth are observed with spacing between successive pits of the order of several microns; pits do not form on (111) until the terraces get extremely large. The occurrence of small islands or small pits on the terraces of quenched samples gives information on the majority point defect at the annealing temperature. On (001) samples that are slowly cooled from the annealing temperature, it is observed that pairs of atomic steps have formed on the large terrace; we believe that these result from the tendency of the surface to minimize the strain energy associated with the (2 × 1) reconstruction.
Structural and Electrical Characterization of Si-Modfet Structures Grown at High Rates by Lepecvd
Authors: Rosenblad C. , Kummer M. , Müller E. , Dommann A. , Künel H. Von 
Published: April 2011

AbstractStrain relaxed graded SiGe buffer layers have been grown by low energy plasma enhanced chemical vapour deposition (LEPECVD). Due to the low ion energies involved in LEPECVD, exceptionally high plasma intensities can be applied without any ion damage of the epitaxial layers. Transmission electron microscopy and X-ray reciprocal space mapping show that relaxed buffer layers grown at rates exceeding 5 nm/s are of a comparable quality to buffer layers grown by standard techniques at much lower rates. Low temperature electric transport measurements on remotely doped tensilely strained Si quantum wells synthesized by LEPECVD show that also good electrical quality is achieved.
SPM Characterization of Substrate Surfaces Prepared for Carbon-Related-Film Deposition
Authors: Narumi Kazumasa , Yamamoto Shunya , Naramoto Hiroshi 
Published: April 2011

AbstractsVariation of surface steps on sapphire (0001) and (1120) substrates processed with thermal annealing in air or a reducing environment at 1000 to 1400°C for 1 to 10 hours were investigated with an atomic force microscope (AFM). The annealed (0001) surfaces consist of atomically smooth and large terraces and atomic-height steps, whose configurations strongly depend on annealing conditions. On the (1120) surfaces, where crystallographic misorientation is almost an order of magnitude larger than that of the (0001) surfaces, step height and terraces increase in size with the longer annealing time and higher annealing temperature. Characteristic step figures due to the symmetry of atomic arrangement were observed on the (0001) surface.
Porous SiC Substrate Materials for High-Quality Epitaxial and Bulk Growth
Authors: Mynbaeva M. , Savkina N. , Zubrilov A. , Seredova N. , Scheglov M. , Titkov A. , Tregubova A. , Lebedev A. , Kryzhanovski A. , Kotousova I. , Dmitriev V. 
Published: April 2011

AbstractThe main unsolved problem in SiC technology is a high density of defects in substrate materials (micropipes and dislocations) propagating into device structures and causing device failure. Recently, significant progress in defect density reduction in semiconductor materials has been achieved using epitaxial lateral overgrowth techniques. In this paper, we describe a novel technique, which shows a high potential for defect reduction in epitaxial and bulk SiC. This technique is based on nano-scale epitaxial lateral overgrowth (NELOG) method, which employs porous substrate materials. Usually, the pores are from 50 to 500 nm in size and epitaxial material overgrowing these pores, forms continues high-quality layer. It is important that the NELOG method does not require any mask. This technique may be easily scaled for large area substrates.In this work, SiC layers were grown on porous SiC by sublimation method, which is widely used for both epitaxial and bulk SiC growth. Porous SiC substrates were formed by surface anodization of SiC commercial wafers. It was shown that SiC layers grown on porous SiC substrates have smooth surface and high crystal quality. The surface of overgrown material was uniform and flat without any traces of porous structure. X-ray topography indicated significant defect density and stress reduction in SiC grown on porous material. Photoluminescence measurements showed a reduction of deep level recombination in SiC.
Micro-Raman Characterization of Arsenic-Implanted Silicon: Interpretation of the Spectra
Authors: Lavine James P. , Tuschel David D. 
Published: April 2011

AbstractRaman spectra were measured on arsenic-implanted silicon with micro-Raman spectroscopy in the backscattering mode and with macro-Raman spectroscopy. A peak is observed between 505 and 510 cm−1 with 488 and 514.5 nm excitation. This peak and a related peak from the substrate at about 520 cm−1 are seen in selected regions of the implanted samples when the implant dose is above 2 × 1014 As/cm2. These features may be due to a long room temperature anneal, as they are absent in recently prepared samples. Possible explanations for the features are presented.
Scanning Tunneling Microscope-Induced Luminescence Studies of Defects in GaN Layers and Heterostructures
Authors: Evoy S. , Harnett C. K. , Keller S. , Mishra U. K. , DenBaars S. P. , Craighead H. G. 
Published: April 2011

AbstractWe present the scanning tunneling microscope-induced luminescence (STL) imaging of defects in optoelectronic materials. Resolution is first discussed using cross-sectional images of InGaAs/GaAs quantum dots. Proof of concept is then provided through the nanometer-scale imaging of GaN layers and quantum wells. The expected λ=356±25 nm range dominates the low temperature STL of GaN. Mapping of luminescence shows circular non-emitting areas around threading dislocations. Extent of dark areas suggests a hole diffusion length of Ld=30–55 nm, in agreement with reported values. The expected λ=450±35 nm range dominates the STL from a buried InGaN/GaN multiple quantum well. Imaging reveals 30–100 nm wide smooth fluctuations of luminescence.
Optical Absorption and Luminescence Study of the Effect of Thermal Treatments on the Porous Silicon Surface
Authors: Plugaru R. , Craciun G. , Bercu M. , Rams J. , Piqueras J. 
Published: April 2011

AbstractThe evolution of the cathodoluminescent emission bands of porous silicon at 420–480 nm, 540 nm and 640 nm under oxidizing and inert atmosphere annealings has been investigated and correlated to the structural reconstruction of the porous silicon surface during the treatments. Dry oxidation at low temperature of 450°C determines a less defected bonding interface structure of the growing oxide matrix comparatively with an oxidation treatment at 1000°C. The optical absorption band at 883 cm−1 observed in the 1000°C oxidized porous silicon is correlated to the presence of the interface defect centers. The quenching of the 540 nm and 640 nm emission bands in the high temperature oxidized porous silicon results from nonradiative transitions in the associated defect levels.
Confocal Micro-Raman Characterization of SiC Epilayers
Authors: Liu Ran 
Published: April 2011

AbstractThe large visible optical penetration depth makes it difficult to isolate the Raman signals of SiC epilayers from those of the substrates such as SiC, sapphire and Si when visible laser lines are used. In this work, confocal micro-Raman was used to characterize 3C, 4H and 6H SiC layers on different substrates with enhanced lateral resolution (˜ 0.8 μm) and depth resolution (˜ 2 μm). Both lateral and depth variation of the free electron concentration and scattering time were measured from n− SiC epi layers on n+ SiC substrates and from H+ implanted SiC. A defect mode induced by oxidation process was also analyzed as function of the depth and the lateral position.
Internal Spatial Modes and Local Propagation Properties in Optical Waveguides Measured Using Near-Field Scanning Pptical Microscopy
Authors: Goldberg Bennett B , Ünlü M. Selim , Rhodes Greg Vander 
Published: April 2011

AbstractNear-field scanning optical microscopy has been used to measure the internal spatial modes and local properties controlling optical wave propagation in glass/silica buried waveguides. The period of the observed standing modes provides a direct measure of the effective index, which combined with the measured transverse modal shape and decay constants, determines the values of all spatial components of the wave vector.Typically, small fluctuations in the material properties of structures can prevent proper operation as well as accurate diagnostic device modeling. The NSOM local probe measurements provide a means of detailed characterization, and defects in processing and their affects on performance are readily identified. We have also developed a technique that can obtain information about the locations of remote dielectric interfaces based upon the rate of change in the phase of the standing wave as a function of wavelength. Finally, experimental results addressing the issue of perturbation of the NSOM probe on the measurement of the local field shows a weak but measurable perturbation, and the dependence on aperture and material parameters will be discussed.
Characterization of Mixed-Metal Oxides Using Synchrotron-Based Time-Resolved x-ray Diffraction and x-ray Absorption Spectroscopy
Authors: Rodriguez José A. , Hanson Jonathan C. , Brito Joaquín L. , Maiti Amitesh 
Published: April 2011

ABSTRACTExperiments are described showing the utility of synchrotron-based time-resolved x-ray diffraction (TR-XRD) and x-ray absorption near-edge spectroscopy (XANES) for characterizing the physical and chemical properties of mixed-metal oxides that contain Mo and a second transition metal (Fe, Co or Ni). TR-XRD was used to study the transformations that occur during the heating of a FeMoO4/Fe2(MoO4)3 mixture and the α⇒β phase transitions in CoMoO4 and NiMoO4. The Mo LII- and O K-edges in XANES are very useful for probing the local symmetry of Mo atoms in mixed-metal oxides. The results of XANES and density-functional calculations (DMo13, DFT-GGA) show large changes in the splitting of the empty Mo 4d levels when going from tetrahedral to octahedral coordinations. XANES is very useful for studying the reaction of H2, H2S and SO2 with the mixed-metal oxides. Measurements at the S K-edge allow a clear identification of S, SO2, SO3 or SO4 on the oxide surfaces. Changes in the oxidation state of molybdenum produce substantial shifts in the position of the Mo LII- and MIII-edges.
Anomalous Ultra-Small-Angle X-ray Scattering From Evolving Microstructures during Tensile Creep
Authors: Jemian P. R. , Long G. G. , Lofaj F. , Wiederhorn S. M. 
Published: April 2011

ABSTRACTUltra-small-angle x-ray scattering provides quantitative and statistically significant information on the size distribution of electron density inhomogeneities with dimensions between ≈100 Å and ≈5 μm. All sizes are sampled simultaneously with a single experiment, removing the possibility of observational bias. In a material such as commercial silicon nitride, where the inhomogeneities are due to populations of intergranular secondary phases and voids of similar dimensions, the scattering contains contributions from each individual population. A single USAXS scan cannot separate overlapping populations of scatterers due to the different contrasts of the microstructural components. Anomalous USAXS (A-USAXS) is an elementspecific contrast variation method to vary the scattering contribution from one of the populations while holding that of the other populations fixed. To follow the size evolution under tensile creep of both the cavities and the Yb disilicate secondary phases, A-USAXS data was measured near the Yb LIII absorption edge. Creep cavity and disilicate size distributions were each determined as a function of deformation.
Attenuation- and Phase-Contrast Microtomography Using Synchrotron Radiation for the 3-D Investigation of Specimens Consisting of Elements With Low and Medium Absorption
Authors: Beckmann F. , Bonse U. 
Published: April 2011

ABSTRACTAttenuation- and phase-contrast microtomography using synchrotron radiation is applied to different samples demonstrating the advantages and limits of the two different contrast mechanism. Photon energies in the range of 8-25 keV and 60-100 keV are used. Scanning techniques employing a 2-dim. x-ray detector allow for investigation of larger specimens at high spatial resolution.
X-ray Topography Study of Surface Damage in Single-Crystal Sapphire
Authors: Black D. , Polvani R. , Medicus K. , Burdette H. 
Published: April 2011

ABSTRACTX-ray diffraction topography was used to investigate the relationship between subsurface damage, near-surface microstructure, and fracture strength in a series of sapphire modulus of rupture (MOR) bars which had been fabricated to proof test fabrication processes. The strength of the bars was determined by failure in four point bending. The tensile surface of the bars was also examined using optical microscopy and non-contacting surface profilometry. Both show that the bars have good surface finish, with a typical RMS roughness of 0.7 nm. No correlation was found between RMS surface finish and fracture strength. Although the bars appeared to be indistinguishable, topographs taken prior to fracture testing revealed that they are of two distinct types. Type 1 has an oriented microstructure consisting of a pattern of linear features running the length of the bars. Type 2 was typical of well-polished sapphire, containing individual dislocations and occasional damage from handling. We attribute the Type 1 microstructure to fabrication damage that was not removed by subsequent processing and/or polishing. Fracture strength data showed that the Type I (damaged) bars had strengths less than 70 % of the bars without damage. Topography is sensitive to near-surface damage that can be correlated to fracture strength. Neither low magnification optical microscopy nor conventional surface finish statistics could be correlated to strength.
Dislocation motion around loaded notches in ice single crystals
Authors: Cullen D. , Hu X. , Baker I. , Dudley M. 
Published: April 2011

ABSTRACTSynchrotron X-ray topography has been used to study dislocation behavior around a notch in single crystal ice during in-situ deformation at a constant strain-rate of 1 × 10−8s−1 and a temperature of -8 °C. During deformation a dislocation depleted zone (DDZ) formed above the notch. Modeling the interaction between basal plane dislocation loops and the notch stress field suggested that this DDZ arose from dislocations gliding completely through the specimen.
X-ray Spectro-Microscopy and Micro-Spectroscopy in the 2100 eV to 12000 eV Region (Invited)
Authors: Mölders N. , Schilling P.J. , Schoonmaker J.M. 
Published: April 2011

ABSTRACTAn x-ray microprobe beamline was recently developed and commissioned at the Center for Advanced Microstructures and Devices (CAMD), Louisiana State University. It achieves a moderate horizontal and vertical focal spot size of 18.8 µm × 7.0 µm (σ), respectively. The beamline and end-station are designed and optimized to perform (i) spatially-resolved x-ray fluorescence spectroscopy (spectro-microscopy) using the broad intense spectrum of the white synchrotron radiation, and (ii) spatially-resolved x-ray absorption spectroscopy (micro-spectroscopy) in the energy region of 2100eV to 12000 eV. These dual capabilities enable K-edge measurements and mapping, in non-vacuum conditions, of low-Z elements down to Cl, S, and P that are of both environmental interest and technological importance. In this paper, an application of this novel synchrotron tool to elucidate the elemental distribution (microstructure) and chemical state (speciation) of Mn, Cl, S, and P-containing particulates emitted from automobile engines burning methylcyclopentadienyl manganese tricarbonyl- (MMT-) added fuel will be discussed in detail. Future opportunities of this microbeam technique in materials science and materials characterization will also be outlined.
Extracellular Iron-Sulfur Precipitates From Growth ofDesulfovibrio desulfuricans
Authors: Antonio Mark R. , Tischler Monica Lee , Witzcak Dana 
Published: April 2011

ABSTRACTWe have examined extracellular iron-bearing precipitates resulting from the growth ofDesulfovibrio desuyfuricansin a basal medium with lactate as the carbon source and ferrous sulfate. Black precipitates were obtained whenD. desulfuricanswas grown with an excess of FeSO4. WhenD. desulfuricanswas grown under conditions with low amounts of FeSO4, brown precipitates were obtained. The precipitates were characterized by iron K-edge XAFS (x-ray absorption fine structure),57Fe Mössbauer-effect spectroscopy, and powder x-ray diffraction. Both were noncrystalline and nonmagnetic (at room temperature) solids containing high-spin Fe(III). The spectroscopic data for the black precipitates indicate the formation of an iron-sulfur phase with 6 nearest S neighbors about Fe at an average distance of 2.24(1) Å, whereas the brown precipitates are an iron-oxygen-sulfur phase with 6 nearest O neighbors about Fe at an average distance of 1.95(1) Å.
Giant Magnetoresistance Imaging for NDE of Conductive Materials
Authors: Boltz E. S. , Albanna S. G. , Stallings A. R. , Spooner Y. H. , Abeyta J. P. 
Published: April 2011

ABSTRACTTraditional coil-based eddy-current sensors are severely limited in their ability to detect small buried defects, defects under fasteners and deeply buried cracks and corrosion. TPL has developed eddy-current sensors and arrays based on the use of Giant Magnetoresistance (GMR) sensor elements. GMR offers high sensitivity, very wide bandwidth and low noise from DC to over 1 GHz. Coupled with the ability to fabricate GMR sensors with micron-level dimensions, these new eddy-current sensors offer an ideal technology for inspections requiring high spatial resolution and low-frequency, deeply-penetrating fields.