bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical Loss Associated with Stress Anomaly in Ni3Al and Ni3(Al, Ta) Single Crystals
Authors: Carreno-Morelli E. , Cheng B.L. , Demura M. , Schaller R. , Baluc N. , Bonneville J. 
Published: April 2011

AbstractThe mechanical loss and shear modulus behaviors of Ni3Al and Ni3(Al, Ta) single crystals have been investigated in the temperature range 100 K – 1300 K. The mechanical loss spectra exhibit two temperature regimes, which are separated by a relaxation peak at nearly 950 K for a frequency of 1 Hz. This relaxation peak has been interpreted by the stress re-orientation of Al-Al elastic dipoles in the (111) octahedral plane [1, 2]. In the low temperature regime, corresponding to the anomaly domain of the flow stress, the mechanical loss of pre-deformed specimens exhibit a strong positive dependence on both the oscillation amplitude and the amount of pre-strain.Pre-deformations, which were performed either at room temperature or at 100 K, yield a broad maximum in the mechanical loss that extends from nearly 100 K up to 550 K. This maximum is observable for only strain amplitudes larger than 10−4 and entirely vanishes after heating the specimens above 550 K. The increase in mechanical loss has been attributed to the bowing of the superkinks under the action of the applied stress. The gradual and irreversible decrease in damping above 300 K is interpreted in terms of pinning of the screw dislocation segments by a thermally activated process leading to the formation of Kear-Wilsdorf locks.
Crystallization Behaviour of Amorphous Si0.5Ge0.5 Films Observed by Positron Annihilation
Authors: Edelman F. , Börner F. , Krause-Rehrberg R. , Werner P. , Weil R. , Beyer W. , Butz R. 
Published: April 2011

ABSTRACTThe crystallization behavior (ordering) of undoped and boron-doped Si0.5Ge0.5 films, deposited on SiO2/Si(001) substrate by molecular beam epitaxy in hish vacuum at room temperature, were studied by XRD, HRTEM and in situ by Doppler broadening spectroscopy using monoenergetic positrons. Some decomposition features of SiGe solid solutions were demonstrated via splitting the XRD peaks at high temperatures. The SiGe decomposition was detected in the precrystalline state of the SiGe undoped and doped films in the temperature range from 450 to 600 K by compaering S- and W-parameters of SiGe with that of amorphous silicon and germanium. In conclusion, we discuss model of internim ordering states before crystallization.
ARC Discharge for the Synthesis of Monoclinic Ga2O3 Nanowires
Authors: Choi Young Chul , Bae Dong Jae , Lee Seung Mi , Park Young Soo , Lee Young Hee , Park Gyeong-Su , Choi Won Bong , Lee Nae Sung , Kim Jong Min 
Published: April 2011

ABSTRACTMonoclinic gallium oxide (β-Ga2O3) nanowires were catalytically synthesized by electric arc discharge of GaN powders mixed with a small amount (less than 5 %) of transition metals under a pressure of 500 Torr (80 %-Ar + 20 %-O2). Scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM) images showed that the average diameter of the wires were about 30 nm and their lengths were as long as up to one hundred micrometer, resulting in extremely large aspect ratio. Fourier diffractogram was indicative of single crystalline nature of the β-Ga2O3 wire. HRTEM image also showed β-Ga2O3 with twin defects at the center of the wire which might play as nucleation seeds. Both X-ray diffraction (XRD) patterns and FT-Raman spectra of the wires identified the observed nanowires as monoclinic crystalline gallium oxides.
Preparation of Highly Ordered Mesoporous Thin Film with Alkyltrimethylammonium(CnTMA+)
Authors: Goto Y. , Sugimoto N. , Fukushima Y , Imada Y. , Kubota Y. , Sugi Y 
Published: April 2011

ABSTRACTWe synthesized the highly ordered mesoporous thin films with alkyltrimethyl-ammonium (CnTMA+). The arrangement of mesopores was depend on the Si/surfactant ratio. The hexagonal(P6mm) arrangement was observed, when Surfactant/Si ratio was 1/10. Increasing the Surfactant/Si ratio to 1.6/10, the cubic (Pm3n) arrangements were observed. A steel vessel for the measurement of the nitrogen adsorption isotherms of thin film on the substrate was designed. It was found that mesopore arrangements in the film is more regular than that in the powder samples prepared by the same acidic synthesis conditions.
Sintering Behavior of Nano-Ceramic Coatings
Authors: De Hosson J.Th.M. , Popma R. , Hooijmans J. 
Published: April 2011

ABSTRACTThis paper concentrates on the densification of sol gel derived thin nano-ceramic coatings by laser radiation and by furnace treatment. Deposition of the film is done by means of spin coating of Zirconia. The sintering of the layer is observed using a number of different measuring techniques. Especially, attention is paid to the densification behavior and the grain growth in the layer, investigated by scanning electron microscopy and ellipsometry. Also the different crystal phases observed are addressed. During sintering at a constant temperature a change in the sintering behavior with time is observed. This change is observed for most temperatures. Both the initial fast sintering of the process (for all sintering temperatures), and the final slow sintering (only at the higher sintering temperatures) are explained.
CuPt Ordering Signatures of Phonons in GaInP2
Authors: Alsina F. , Cheong H. M. , Mestres N. , Pascual J. , Mascarenhas A. 
Published: April 2011

AbstractWe present a comprehensive overview of the large spectroscopic evidence on the influence of ordering on the Raman and infrared spectra of partially ordered GaInP2. Our phonon mode calculation within the adiabatic bond charge model describes the appearance of new phonons and also the optical anisotropy.
Evolution of the Shape and Size of Ingaas Selforganized Quantum Dots
Authors: Xie Qianghua , Brown J. L. , Jones R. L. , Nostrand J. E. Van 
Published: April 2011

AbstractWe have found a shape transformation of InGaAs quantum dots formed via a fractional monolayer deposition technique on GaAs (001) surfaces. This is evidenced by the bimodal quantum dot height (peaked at 8.5 nm and 14.5 nm) and aspect ratio (peaked at 0.18 and 0.26) distributions. The lateral size, height, and aspect ratio all become convergent, suggesting a simultaneous quantum dot size equalization and shape stabilization. Photoluminescence peaks red shift as a consequence of dot growth, and their line-widths become smaller due to dot shape stabilization and size equalization. A record low inhomogeneous broadening of 18.4 meV at a wavelength of 1180 nm (4 K) is obtained for vertically-aligned, shape-stabilized, and size-equalized InGaAs dots.
Real-Time Observation of Pt-Si Micro-Droplet Migration by Photo-Electron Emission Microscopy
Authors: Yang W. , Ade H. , Nemanich R. J. 
Published: April 2011

AbstractThe formation and dynamics of Pt-Si liquid droplets on Si (001) substrates have been investigated by Photo-electron Emission Microscopy (PEEM). After ambient deposition of a 10nm Pt film, a uniform PtSi layer was transformed into an island structure at ∼ 800°C. The PtSi islands of micrometer size began to melt and were transformed into molten Pt-Si alloy islands below the melting point of PtSi. At ∼1100°C surface migration of the micro-droplets was observed. The moving droplets coalesced with nearby islands and grew in size. The motion was related to the temperature difference across the substrate, and droplet migration was observed from the cold to the hot regions of the surface. The migration velocity was measured as a function of temperature and droplet size. The driving force for migration is related to material diffusion, equilibrium at the solid-liquid interfaces, and surface energetics.
Computer Simulation of Nucleation on Patterned Surfaces
Authors: Kuronen A. , Nurminen L. , Kaski K. 
Published: April 2011

AbstractWe have studied qualitatively the effect of patterned substrate surface on adatom nucleation using Kinetic Monte Carlo simulations and solid-on-solid model. The inhomogeneity in the activation energies of adatom diffusion was incorporated into the simulations using two models: a) periodic variation of the adatom–substrate interaction energy as a function of the adatom lateral position and b) adding a direction dependent and periodically varying diffusion barrier energy to the adatom diffusion activation energy. The effect of the patterned surface was clearly manifested as a confinement of nucleated islands and, consequently, narrowing the island size distribution. The effect was strong in a narrow temperature range.
Structural Evolution During the Initial Epitaxial Growth of Moon on Sapphire
Authors: Ryan P. A. , Tsui F. 
Published: April 2011

AbstractStructural evolution during initial epitaxial growth of Mo (111) and (110) on Al2O3 substrates has been studied using real-time reflection high energy electron diffraction and in-situ scanning tunneling microscopy. The Mo (111) growth on sapphire (0001) is initiated by the formation of small mound-like 3-dimensional (3D) islands that are correlated with unique length scales. The observed surface length scales depend on growth temperature and rate, and they coarsen as the thickness increases. The initial growth of Mo (110) on sapphire (1120) begins with layer-by-layer growth for the first monolayer, and subsequently the growth is 3D with mound-like features that are larger than those corresponding (111) counterparts. In both orientations lattice relaxation occurs within the first 2 – 3 monolayers.
Enhancement of the Adhesion of Cordierite Glass-Ceramic Coatings on Molybdenum by the Deposition of Metallic Interlayers on the Substrate
Authors: Calata Jesus Noel , Lu Guo-Quan , Kuhr Thomas A. 
Published: April 2011

ABSTRACTSintered coatings of cordierite-base glass-ceramic do not adhere readily on bare molybdenum substrates. This is due to the absence of a stable metal oxide film on the substrate that serves as a suitable transition layer between the glass-ceramic and the substrate. To address this problem, dual layers of either chromium/nickel or chromium/copper were deposited by electroplating on the molybdenum substrates. Glass powder in slurry form was then cast on the substrates using a doctor blade and sintered in a helium-hydrogen atmosphere at 950°C. The metallic interlayer structure was found to produce an excellent bond between the coating and the substrate. The adhesion of the coatings was observed to be sensitive to the thickness of the deposited metal layers. Quantitative chemical analysis of the interface region was performed to explain the difference in adhesion quality. In all instances, the fracture surface was found to occur at the chromium oxide/chromium boundary providing a clear indication that the chromium oxide layer plays an important role in enhancing the adhesion. The superior adhesion in samples with the Cr-Cu interface was attributed to Cu acting as an effective diffusion barrier to Mo. Cr however, was able to diffuse through the Cu layer enhancing the bond between Mo and Cu by alloying with the Mo. Ni was not as effective as Cu in preventing the diffusion of Mo towards the glass-ceramic coating but a thicker Cr layer still produced a strong bond. In samples where the distinct Cr layer was either too thin or non-existent, adhesion was poor possibly because the Cr oxide does not bond well to the Ni-Cr alloy layer that formed after firing.
Near-Interface Crack Initiation in Thermal Barrier Coatings
Authors: Zhang Z. , Bloomer T. E. , Kameda J. , Sakurai S. 
Published: April 2011

ABSTRACTThe delamination behavior of thermal barrier coatings (TBC) in transition ducts of inservice used combusters has been characterized using a protruded four-point bending testing technique recently developed by the authors. A reinforced protruded TBC specimen allowed the formation of TBC cracks adjacent to the TBC/alumina interface in a similar mode to inservice TBC failure. Finite element stress analysis showed that a peak transverse stress appeared in a protruded TBC part away from the interface and a large principal tensile stress operated on planes inclined to the interface. It was found that the onset of near-interface TBC cracks in the protruded TBC specimen did not occur under the high transverse and principal tensile stresses. The critical local tensile stress for the onset of TBC cracks near the interface, estimated to be 127 MPa, was lower than that of the near-center TBC. The near-interface TBC cracking behavior in the protruded TBC tests is discussed in light of the residual stress distribution and stressed volume effect.
Modelling the Effect of Composition on the Stability of Equilibrium Intergranular Films with Diffuse Interfaces
Authors: Bishop C. M. , Carter W. C. 
Published: April 2011

ABSTRACTCurrent understanding of the equilibrium thickness of interfacial films derives from models which balance a steric repulsion against an attractive force between abutting crystals such as the van der Waals forces [1]. Recent experimental observations indicate that, a) film thickness is a non-monotonic function of additions of impurities and b) impurities are non-uniformly distributed in the interfacial phases and triple junctions [2]. We have developed a model which couples the steric terms which affect the equilibrium thickness with composition for a semi-infinite film in equilibrium with a chemical reservoir at a fixed composition.
Dewetting of Reactive CaMgSiO4 Glass Films on Single-Crystal MgO(001) Substrate
Authors: Yanina S. V. , Carter C. B. 
Published: April 2011

ABSTRACTThe early stages of dewetting of a reactive silicate (CaMgSiO4) film on a ceramic (MgO) substrate were studied by scanning probe microscopy. Subsequent interactions between the glass phase and an underlying single-crystal substrate, such as dissolution/re-precipitation of substrate material at the glass-ceramic interface and evaporation of silicate phase, were investigated by observing selected areas of the specimens through a series of annealing-quenching cycles. Implications deduced from the CaMgSiO4-MgO equilibrium phase diagram on the process of dissolution/re-precipitation of MgO are briefly discussed.
Solid Phase Epitaxial Recrystallization of AlN Films on Sapphire (0001): A Novel Substrate Approach for GaN Epitaxy
Authors: Vispute R. D. , Patel A. , Sharma R. P. , Venkatesan T. , Zheleva T. , Jones K. A. 
Published: April 2011

AbstractHigh quality and lattice matched buffer layers are needed for the growth of device quality GaN thin films on sapphire for optoelectronic applications. In this context, we report the fabrication of AlN thin films having low defect densities through a novel process called solid phase epitaxial recrystallization (SPER). In this process, as-grown crystalline AlN thin films, having a large defect concentration (such as threading dislocations due to a large lattice mismatch between AlN and sapphire and low angle grain boundaries), were thermally annealed in an inert atmosphere at various temperatures ranging from 1200-1600° for 30 min. The as-grown and annealed samples were characterized using x-ray diffraction, transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and UV-visible spectroscopy. The ion channeling/RBS and TEM results clearly indicate a substantial reduction in the defect density for the recrystallized AlN films. The surface morphology of the SPER AlN films was smooth with a surface roughness close to the unit cell height. The optical bandgap was sharp as compared to as-grown films, with a bandgap of 6.2 eV. The recrystallized films having smooth surface morphology and low defect densities may be useful for the growth of device quality GaN films on sapphire.
Characterization of Si, SiGe and SOI Structures Using Photoluminescence
Authors: Higgs V. 
Published: April 2011

AbstractA new Photoluminescence (PL) method has been developed to detect defects in the near surface region of Si wafers and Si-on-insulator (SOI) structures. Wafer maps (up to 300 min diameter) can be readily acquired and areas of interest can be scanned at high resolution (≈1 μm). The excitation laser beam is modulated to confine the photogenerated carriers; defects are observed due to the localised reduction of the carrier lifetime. Si p-type (10 Ohm.cm) wafers were intentionally contaminated with various levels of Ni and Fe (1×109−5×1010atoms/cm2) and annealed. The PL intensity was observed to decrease due to the metal related non-radiative defects. Whereas in contrast, for Cu, (1×109−5×1010atoms/cm2) the PL intensity actually increased initially and reached a maximum value at 5×109atoms/cm2. It is suggested that during contamination the Cu related defects have complexed with existing defects (that have stronger recombination properties) and increased the PL. Further Cu contamination (1×1010−5×1010atoms/cm2) produced a reduction in the PL intensity. PL mapping of strained SiGe epilayers showed that misfit dislocations can be detected and PL can be used to evaluate material quality.PL maps of SOI bonded wafers revealed that the non-bonded areas, voids or gas bubbles could be detected. This was confirmed using defect etching and polishing, voids as small as ≈30 μm in diameter could be detected. SOI wafers fabricated using the separation by implanted oxygen (SIMOX) technique were also analysed, variations in the recombination properties of the layer could be observed. Further inspection using transmission electron microscopy (TEM) revealed that the defects were non-uniformities of the buried oxide covering several microns and containing tetrahedral stacking faults. Focused ion beam (FIB) milling and secondary ion mass spectrometry (SIMS) showed that these defects were at the Si/SiO2interface and were chemically different to the surrounding area.
High real-space resolution structure of materials by high-energy x-ray diffraction
Authors: Petkov V. , Billinge S. J. L. , Heising J. , Kanatzidis M. G. , Shastri S. D. , Kycia S. 
Published: April 2011

ABSTRACTResults of high-energy synchrotron radiation experiments are presented demonstrating the advantages of the high-resolution atomic Pair Distribution Function technique in determining the structure of materials with intrinsic disorder.
Charge Transfer and Local Structure in Thermoelectric Germanium Clathrates
Authors: Palmqvist A.E.C. , Iversen B.B. , Furenlid L.R. , Nolas G.S. , Bryan D. , Latturner S. , Stucky G.D. 
Published: April 2011

ABSTRACTGermanium clathrates have recently received attention as potential highly efficient thermoelectric materials based on the phonon glass electron crystal (PGEC) concept [1-4]. A combined EXAFS and XANES study has been performed in order to investigate the local structure and the degree of charge transfer between the guest atoms and the framework atoms. Analysis of the Sr, Ga, and Ge K-edge XANES spectra of a Sr8Ga16Ge30 clathrate reveals that the atoms are close to neutrally charged and that the degree of charge transfer is low in agreement with recent theoretical predictions and charge density distribution measurements [3,5].
Nonlinear Ultrasonic Parameter in Precipitate-Hardened Steels
Authors: Hurley D. C. , Balzar D. , Purtscher P. T. 
Published: April 2011

ABSTRACTWe have investigated several specimens of ASTM A710 steel containing copper-rich precipitates with variations in the final aging treatment. X-ray diffraction line-broadening and small-angle neutron-scattering experiments revealed the existence of the precipitates and associated coherency strain. We determined the nonlinear ultrasonic parameter β for each specimen by harmonic-generation experiments and measured the ultrasonic longitudinal velocity νL and attenuation αL. Although νL and αL showed no consistent trends, β increased with increasing strain. This correlation is compared to a microstructural model for harmonic generation that includes a contribution from precipitate-pinned dislocations.
Scanning Acoustic Microscopy and x-ray Diffraction Investigation of Near Crack Tip Stresses
Authors: Sathish S. , Martin R. W. 
Published: April 2011

ABSTRACTScanning Acoustic Microscopy has been used to measure and map the Rayleigh wave velocity and the Surface Skimming Longitudinal wave velocities near a crack tip in a sample of Ti-6AI-4V. X-ray diffraction measurements have been performed to map the stress in the same region of the sample. The differences in the contrast between the two acoustic velocity images and their sensitivity to stress are examined. Similarities between x-ray stress images and acoustic velocity images are discussed.
Nondestructive Characterization of Corrosion Protective Coatings on Aluminum Alloy Substrates
Authors: Hoffmann J. , Sathish S. , Khobaib M. , Meyendorf N. , Netzelmann U. , Matikas T.E. 
Published: April 2011

ABSTRACTThis paper describes the initial phase of the development of a nondestructive, multisensor approach for detecting, quantifying and monitoring degradation of organic coatings applied to aluminum surfaces. Descriptions of the purposes and chemical compositions of layered coatings used on aircraft structures are provided. The discussion then concentrates on ultrasonic thickness measurements. One is the well-established pulse/echo scanning acoustic microscopy and, as a proposed alternative, continuous acoustic waves measurements with a probe in contact to the sample. Advantages and disadvantages of the two methods and their potential as in field applications are discussed.
Photoluminescence Characterization of Defects in Thermal Oxide
Authors: Nishikawa Hiroyuki , Stathis James H. 
Published: April 2011

ABSTRACTDefects in thermal oxides were investigated by a photoluminescence technique. Thermal oxides with a thickness of 100 nm grown either by dry or wet oxidation were studied. A broad PL band at 2-4 eV was observed for both dry and wet oxides. Effects of annealing under vacuum or in atmospheres of Ar or N2 on the PL were also examined. The PL intensity was enhanced for the case of wet oxide by vacuum annealing at 700 °C. High-temperature anneal above 750 °C without O2 further generated PL centers for both dry and wet oxides. The formation mechanism of the PL centers will be discussed in terms of the decomposition of oxide at Si/SiO2 interface.
Microstructural Evolution in Copper Films Undergoing Laser Pulsing at High Pressures
Authors: Jakkaraju R. , Dobson C. D. , Greer A. L. 
Published: April 2011

AbstractA novel process of pulse-heating copper films under high pressure has been developed for filling high-aspect-ratio vias and contact holes with copper. A copper film is sputter-deposited on to an oxidised silicon substrate containing an array of via holes with varied aspect ratios. The film, which is thick enough to bridge over the via holes, is then subjected to laser pulse heating under selected pressures of inert gas. Via filling has been achieved, up to an aspect ratio of 6 for 0.35 μm diameter holes. The microstructure of the pulse-heated copper films has been investigated by X-ray diffraction, and by focused ion beam microscopy (FIB) including sectioning. The FIB images of the film over a via pattern show a ‘chequer-board’ pattern of grains corresponding to the square pattern of via holes underneath. This pattern can be explained by transient melting of the film under pulse-heating and subsequent solidification in which each via hole acts as a nucleation site and has a crystal associated with it. Even though the as-deposited films are fine-grained and have (111) texture, the treated films can show (111) or (100) texture, depending on processing conditions. The origins of the final film texture and the possibilities for microstructural control are discussed.