bluuebunny/crossref_metadata_2025_split huggingface dataset:
Composition of uranium oxide surface layers analyzed by μ-Raman Spectroscopy
Authors: Siekhaus Wigbert J. 
Published: April 2011

AbstractOxide thickness and composition averaged over a few square millimeter have been measured with nm thickness resolution by diffuse reflectance Fourier transform infrared (FTIR) spectroscopy. μ-Raman spectroscopy has been done on powders and bulk samples in the past, and can now be done on surfaces layers with μm lateral and depth resolution using con-focal microscopy. Here we apply con-focal-microscopy-based μ -Raman spectroscopy to a freshly polished/lightly oxidized and to heavily oxidized uranium to determine its sensitivity. The spectra show that μ-Raman spectroscopy does detect oxide thickness and oxide composition with high sensitivity.
High-Throughput Screening of Thermoelectric Materials; Application of Thermal Probe Method to Composition-Spread Samples
Authors: Yamamoto Atsushi , Kukuruznyak Dmitry , Ahmet Parhat , Chikyow Toyohiro , Ohuchi Fumio S. 
Published: April 2011

ABSTRACTIn this paper, we demonstrate the use of thermal probe method that is capable of mapping Seebeck coefficient, thermal conductivity and contact resistance on a micrometer scale. We show the successful screening example on pseudo binary (Bi1−xSbx)2Te3 (0.5<x<1) bulk composition-spread sample prepared by conventional powder metallurgy process. Another demonstration is a novel attempt to combine the combinatorial PLD and the thermal probe method. A pseudo ternary diagram of nickel-copper-manganese oxides fabricated on Nb doped STO substrate was used for the screening. The mapping of electrical resistance over the ternary diagram yields a lot of information, which is essential for materials researches on complex, multi-composition systems.
Development of High-Throughput substrates for Generating Two-Dimensional Nanoparticles Assemblies and for Screening Protein Adsorption
Authors: Bhat Rajendra R. , Genzer Jan 
Published: April 2011

ABSTRACTWe discuss methods leading to the fabrication of orthogonal substrates comprising surface-anchored polymer brushes, in which the polymer brush grafting density and molecular weight vary independently in two mutually perpendicular directions. We demonstrate that these orthogonal polymer substrates can be used as intelligent combinatorial platforms that facilitate the spatial distribution of nanoparticles and allow screening of protein adsorption on surfaces.
Ab Initio Structure Determination of Quasicrystals via Single Crystal X-Ray Diffraction
Authors: Takakura Hiroyuki , Yamamoto Akiji , Boissieu Marc de , Sato Taku J , Tsai An Pang 
Published: April 2011

ABSTRACTA standard approach for structure solution of ordinary crystals begins with solving the phase problem. We show that a similar procedure can be taken even in the case of quasicrystals using single crystal X-ray diffraction by applying anab initiostructure determination method called the low density elimination method. The first picture of the occupation domains, which must be specified in a higher-dimensional structure determination of quasicrystals, is obtained from a phase-reconstructed density. We present six-dimensional densities determined by this method and give their interpretation for several different types of icosahedral quasicrystals.
Low temperature plasticity of an AlPdMn quasicrystal
Authors: Mompiou Frédéric , Caillard Daniel 
Published: April 2011

ABSTRACTTEM observations have been performed in AlPdMn single-grain quasicrystal deformed at low temperature. They show that dislocation motion has occurred by climb associated with vacancy diffusion. At room temperature, deformation also occurs by crack followed by re-healing.
From Crystalline to Glassy: Crack Propagation Modes in Decagonal Quasicrystals
Authors: Rudhart Christoph , Gumbsch Peter , Trebin Hans-Rainer 
Published: April 2011

ABSTRACTThe propagation of mode-I cracks in a two-dimensional decagonal model quasicrystal is studied by molecular dynamics simulations. The samples are endowed with an atomically sharp seed crack and a temperature gradient. Subsequently the crack is loaded by linear scaling of the displacement field. The response of the crack running into regions of increasing temperature is monitored.For low temperatures below 30% of the melting temperature Tm the model-quasicrystal fails by brittle fracture. We observe that the crack follows the path of dislocations nucleated at its tip. The crack propagates along well defined planes and circumvents tightly bound clusters. In the medium temperature regime from 30% to 70% Tm the crack is blunting spontaneously by dislocation emission. In the range of 70%-80% Tm the quasicrystal fails by nucleation, growth and coalescence of micro-voids. This gradual, dislocation-free crack extension is caused by plastic deformation which is mediated by localized rearrangements comparable to so-called shear transformation zones in amorphous solids.
Medium-Range Order and Crystallization in Zr59Cu20Al10Ni8Ti3 and Zr57Cu20Al10Ni8Ti5 Metallic Glasses Investigated by NMR
Authors: Breitzke Hergen , Lüders Klaus , Scudino Sergio , Eckert Jürgen , Kühn Uta 
Published: April 2011

ABSTRACTMedium-range order and quasicrystal formation in Zr57Cu20Al10Ni8Ti5 and Zr59Cu20Al10Ni8Ti3 metallic glasses are investigated by means of nuclear magnetic resonance (NMR). The samples are prepared by rapid solidification and annealed to induce primary quasicrystal formation. 27Al and 63Cu NMR spectra and spin relaxation curves are recorded before and after the annealing process. The spectral width of 27Al and 63Cu NMR spectra is relatively small and can be taken as a proof for the presence of medium-range order in these metallic glasses. By simulations of 27Al and 63Cu NMR second moments in various binary Al and Cu compounds the medium-range orders L12 AlZr3 and C11b CuZr2 can be identified in both as-quenched metallic glasses. After heat treatment both metallic glasses show considerable changes in the 63Cu NMR second moments, whereas the 27Al NMR second moments show only relatively small changes. Furthermore, the 63Cu NMR second moment after heat treatment in Zr57Cu20Al10Ni8Ti5 is about half as large as in Zr59Cu20Al10Ni8Ti3 indicating different types of crystallization during heat treatment.
Amorphous Alloy Formation in Immiscible Cu-Ta and Cu-W Systems by Atomistic Modeling and Ion-Beam Mixing
Authors: Gong H. R. , Kong L. T. , Liu B. X. 
Published: April 2011

ABSTRACTFor the immiscible Cu-Ta and Cu-W systems, realistic n-body potentials are derived under an embedded-atom method through fitting the cross potentials to some physical properties obtained from ab initio calculations for a few possible metastable Cu-Ta and Cu-W crystalline phases, respectively. Based on the derived potentials, molecular dynamics simulations reveal that in the Cu-Ta system, 30 at. % of Ta in Cu is the critical composition for the crystal-to-amorphous transition in the Cu-rich Cu-Ta solid solutions, and that in the Cu-W system, amorphous alloys can be formed within the composition range of 20–65 at. % of W. Interestingly, amorphous alloys are indeed obtained by ion-beam mixing in properly designed Cu70Ta 30, Cu65Ta35, Cu60Ta 40, and Cu50Ta 50 multilayered films, while crystalline Cu and Ta remain in Cu75Ta25 multilayered sample, which matches well with the critical composition of 30 at. % of Ta predicted by simulation. Moreover, there have been experimental data, which are in support of the predicted composition range of the Cu-W system by simulations.
On the Fragility of Nb-Ni Based and Zr55-x Tix(CuNi)18.25+yBe26.25-y Bulk Metallic Glasses
Authors: Shadowspeaker Ludi A. , Busch Ralf 
Published: April 2011

ABSTRACTThe heating rate dependencies of the glass transition temperature of the Ni65Nb35, Ni60Nb35Sn5, Ni59.35Nb34.45Sn6.2, Ni60(Nb40Ta60)34Sn6, and Ni57Fe3Nb35Sn5 metallic glass forming alloys were investigated with a differential scanning calorimeter (DSC). The relaxation time for each DSC experiment was plotted versus inverse temperature and a Vogel-Fulcher-Tamman (VFT) type relation was fitted to the data. The fragilities of the alloys were characterized with the fragility parameter, D*, and the VFT temperature, T0, which are the fit parameters from the VFT relation. It was found that for the binary alloy D* = 6.2, for the ternary alloys D* = 11.0, and that for the quaternary alloys D* was between 16.4 and 19.0. The D* increases monotonically as the number of components in the alloy is increased. This trend is also seen in Zr based alloys.
Molding of fine surface features into bulk metallic glass
Authors: McCracken Ivan , Busch Ralf 
Published: April 2011

ABSTRACTMolding of fine surface features into a bulk metallic glass (BMG) from the molten state was investigated. It was studied down to which a feature size in a mold could be reproduced in the BMG. A new casting apparatus was designed and built to carry out the experiments. The BMG used was Vitreloy 1™, Zr41.24Ti13.75Cu12.5Ni10Be22.5, and it was observed to replicate mold features down to several nanometers. This has been verified with SEM photographs of both the mold surfaces and the BMG parts. Processing variables, including the injection temperature of the molten BMG and the atmosphere, in which it is molded, appear to have a great effect on the ability to reproduce the fine features on the mold surface.
Medium-Range Order in High Al-content Amorphous Alloys Measured by Fluctuation Electron Microscopy
Authors: Stratton W. G. , Hamann J. , Perepezko J. H. , Voyles P. M. 
Published: April 2011

ABSTRACTWe have used fluctuation electron microscopy (FEM) to measure nanoscale mediumrange order in amorphous Al92Sm8. Samples of this amorphous alloy formed by rapid quenching (melt-spinning) show a high density of pure Al nanocrystals (>1020 m-3) after low temperature (< 250 °C) devitrification. In samples amorphized by deformation (cold-rolling), primary Al-crystallization does not occur. This difference in devitrification behavior suggests an underlying structural difference in the amorphous state. FEM is a quantitative microscopy technique for determining nanoscale medium-range order in amorphous materials. Our measurements show that amorphous alloys formed by melt-spinning and cold-rolling have significant structural differences, and that annealing melt-spun alloy under conditions previously shown to modify the devitrification thermodynamics also changes the medium-range structure.
Ultra-thin strain relaxed SiGe buffer layers with 40% Ge
Authors: Lyutovich Klara , Kasper Erich , Oehme Michael 
Published: April 2011

ABSTRACTVirtual substrates with ultra-thin SiGe strain relaxed buffers have been grown on Si substrates by a method employing point defect supersaturation in the growing layers. A concept of the point defect influence on the strain relaxation and on defect interactions in layers has been proposed. A method is developed to increase the degree of relaxation in sub-100 nm SiGe buffer layers and to provide a smooth surface morphology. Layer growth has been realized by solid source molecular beam epitaxy in a chamber equipped with an in situ monitoring system. One of the growth stages, performed at a very low temperature, serves the generation of point defects. Strain relaxation tunable up to the high degree and a crosshatch-free surface morphology are demonstrated in 40nm thick SiGe buffers which contain 40-45% Ge.Growth monitoring enables the control of the process window and the layer crystallization by a chosen mechanism.Virtual substrates produced by the described method were successfully tested in nMODFET structures.
The use of ion implantation and annealing for the fabrication of strained silicon on thin SiGe virtual substrates
Authors: Buca D. , Mörschbächer M.J. , Holländer B. , Luysberg M. , Loo R. , Caymax M. , Mantl S. 
Published: April 2011

ABSTRACTStrain relaxed Si1−xGex layers are attractive virtual substrates for the epitaxial growth of strained Si. Tensile strained Si has attracted a lot of attention due its superior electronic properties. In this study, the strain relaxation of pseudomorphic Si1−xGex layers grown by chemical vapor deposition (CVD) on Si(100) substrates was investigated after He+ ion implantation and thermal annealing. The implantation induced defects underneath the SiGe/Si interface promote strain relaxation during annealing via preferred nucleation of dislocation loops which form misfit dislocations at the interface to the substrate. The amount of strain relaxation as well as the final threading dislocation density depend on the implantation dose and energy. Si1−xGex layers with thicknesses between 75 and 420 nm and Ge concentrations between 19 and 29 at% were investigated. The strain relaxation strongly depends on the layer thickness. Typically the structures show ≈70 % strain relaxation and threading dislocation densities in the low 106 cm−2 range. AFM investigations proved excellent surface morphology with an rms roughness of 0.6 nm. The samples were investigated by Rutherford backscattering spectrometry, ion channeling, transmission electron microscopy and atomic force microscopy.
Effect of Carbon on Diffusion of Boron in SiGe between 940 – 1050 °C
Authors: Karunaratne Mudith S. A. , Bonar Janet M. , Zhang Jing , Willoughby Arthur F. W. 
Published: April 2011

ABSTRACTThe effect of carbon on boron diffusion was studied in Si and strained SiGe. Several types B containing matrices were grown: (i) Si, (ii) Si containing 0.1% C peak, (iii) SiGe with 11% Ge and (iv) SiGe with 11% Ge and with a 0.1% C peak, using gas-source molecular beam epitaxy (MBE). The combination of Si, Si with C, SiGe and SiGe with C matrices allowed us to separate the effects of Ge and C on B diffusivity. To ensure non-injection surface conditions, low temperature silicon dioxide (LTO) and silicon nitride layers were deposited on top of samples in that order. These samples were then rapid thermal annealed (RTA) at 940, 1000 and 1050°C in an O2 ambient.Diffusion coefficients of B in each type of matrix were extracted by computer simulation, using SIMS profiles obtained from samples before and after the RTA treatment. Diffusion coefficient is reduced by both Ge and C, the suppression by C being more profound. The results are compared to and found to be in reasonable agreement with limited data available in literature.
Optimizing SiGe HBTs technology using small-signal and high frequency noise device's modeling
Authors: Tartarin J.G , Cibiel G. , Monroy A. , Goascoz V. Le , Graffeuil J. 
Published: April 2011

ABSTRACTThe rapid expansion of SiGe technologies during the last decade essentially due to civil telecommunication's applications have led Si/SiGe based heterojunction bipolar transistors (HBTs) to excellent performance levels, allowing high frequency low noise circuit designs such as linear low noise amplifiers( RF noise) or also low-phase noise oscillators (LF noise). Among these technologies, the SiGe BiCMOS one integrates digital and RF functions on the same chip. Fast improvements of the technological process have been performed thanks to large efforts allowed to characterization and modeling of the devices. We have investigated on the influence of technological parameters such as Germanium profile, doping level and thickness of the base layer (5 different wafers) on the dynamic and high frequency noise performances to converge towards the optimum technological process (now available with the BiCMOS6G processed by ST microelectronics). We made use of scattering parameters [S] measurements on the devices to extract the electrical parameters of our small signal model. The high frequency noise parameters based on the electrical model (with noise sources added to the junction, resistances) are simulated and compared with the measured noise parameters of the devices. The four noise parameters (Fmin, Rn, and complex Γopt) measurements have been performed from 1 GHz to 12 GHz, and the dynamic S parameters measurements have been realized in the 40 MHz-40 GHz range. These models have been used to enable the identification of the limiting parameters on the dynamic performances and on the high frequency noise parameters.
Evaluation of AlOx in Co/AlOx/Co spin tunneling junctions by XPS
Authors: Otaka Yuki , Kaiju Hideo , Nishiyama Mao , Sakaguchi Naoki , Shiiki Kazuo 
Published: April 2011

ABSTRACTOxidation states of AlOx in Co/AlOx/Co spin tunneling junctions were studied using X-ray photoelectron spectroscopy. Co(10nm)/AlOx/Co(50nm) spin tunneling junctions were fabricated on glass substrates by ion-beam mask sputtering. The Al layers were deposited in various thicknesses and were oxidized in pure O2 gas for 24-48 hours at room temperature. Co/AlOx bilayers simultaneously fabricated were analyzed by XPS. The thicker the Al layer is deposited, the more the unoxidized Al remains. MR ratio of the junctions increasedas the unoxidized Al decreased, and this result is qualitatively in agreement with the LMTO calculation result. The O/Al ratio of AlOx layer is about 1.9-2.0, which means existence of the higher order oxides than Al2O3. XPS depth profiles showed that the unoxidized Al remains not only near the interface with Co but also near the surface when the deposited Al layer thickness isthick.
Characterization and Mapping of Crystal Defects in Silicon Carbide
Authors: Emorhokpor E. , Kerr T. , Zwieback I. , Elkington W. , Dudley M. , Anderson T. , Chen J. 
Published: April 2011

AbstractA method is presented for detecting, counting and mapping micropipes and dislocations in n+, undoped, and semi-insulating Silicon Carbide wafers. The technique is based on etching in molten Potassium Hydroxide (KOH), and it employs image processing that automatically detects etch pits, discriminates between micropipes and dislocations, and generate micropipe and dislocation density maps. We demonstrate a novel way of detecting and mapping dislocations and micropipes in semi-insulating SiC. This is achieved by combining a properly tuned etching technique that reliably produces well defined etch pits with image processing that enables quick and accurate analysis of the etch pit contrast. We show that the results of optical evaluation are close to those obtained using the Synchrotron White Beam X-Ray Topography (SWBXT) technique.
Structural characterization of 3C-SiC films grown on Si layers wafer bonded to polycrystalline SiC substrates
Authors: Myers R.L. , Hobart K.D. , Twigg M. , Rao S. , Fatemi M. , Kub F.J. , Saddow S.E. 
Published: April 2011

AbstractSingle crystal 3C-SiC epitaxial layers have been grown on SOI substrates using low-pressure chemical vapour deposition (LPCVD). The SOI substrates consist of nominally 150 Å Si layers bonded to 100 mm poly 3C-SiC substrates using direct wafer bonding and SOI film transfer techniques. Miscut Si(100) films were incorporated into the wafer bonding process for the first time in an effort to further reduce anti-phase domain formation in the 3C-SiC films. The Si films were transferred from Si(100) wafers miscut 4° toward the (110) direction. For growth of 3C-SiC layers, a two-step process is needed. First the Si is carbonized using propane mixed in a hydrogen carrier gas to convert the surface to SiC at atmospheric pressure. Next SiC growth is conducted by the addition of silane into the gas mix and a reduction of the process to 150 Torr. Previous characterization of these films via SEM and XRD indicated that the films were single crystal and oriented with respect to the starting Si bonded film. In this work we present results of TEM analysis of these films which show details of the atomic structure at the 3C-SiC/poly-crystalline SiC interface where a thin (6 nm thick) amorphous region has been detected, likely due to SiO2 used to wafer bond the Si film to the poly substrate. A detailed study of this material system is presented with the aim of providing feedback for possible improvements in the 3C-SiC growth process.
Thermoplastic Deformation and Residual Stress Topography of 4H-SiC Wafers
Authors: Okojie Robert. S. , Zhang Ming 
Published: April 2011

AbstractWe have measured thermoplastic deformation in as-received, single-side polished, 4H-SiC wafers and also residual stresses in homoepitaxially grown epilayers on wafers by radius curvature measurements. The wafers studied had n-type resistivities of 0.010-0.011 ω-cm and p-type resistivities of 4.42, 4.72, 9.57 ω-cm. In a first thermal excursion to 900 °C in vacuum, the bow height of the bare substrates in all cases decreased with temperature. Upon cooling down, however, the bow heights remained largely unchanged from their values at 900 °C. A second cyclic excursion to 900 °C did not yield any significant change in the curvature, thus indicating that the substrates had thermoplastically deformed in the first heating cycle. Epilayers having nitrogen doping between 5 × 1017 and 2 × 1019 cm−3 grown on the n- and p-type substrates resulted in compressive stresses ranging between 190 and 400 MPa in the epilayers. Transmission electron microscopy (TEM) examination of the n-type epilayer (with doping levels of 5 × 1017 cm−3 and 5 × 1018 cm−3) on the n-type substrate, revealed bands of stacking faults (SFs) confined within the epilayers after the bicrystals were further annealed at 1150°C in nitrogen for thirty minutes. These doping levels are approximately one and two orders of magnitude below the reported threshold value of 3 × 1019 cm−3 previously suggested for the onset generation of SFs in annealed n-type 4H-SiC epilayers. The calculated residual stresses in all the epilayers were above the critical stress for the motion of dislocations above 1000 °C in 4H-SiC. Thus the SFs that form by glide of pre-existing partial dislocations may actually be stress induced and occur across a much wider range of doping levels. Therefore, it is possible that a significant mechanism for formation of the stacking faults and 3C bands observed in thermally treated 4H-SiC wafer is stress relief via the generation and motion of new and pre-existing partial dislocations on the basal planes of 4H-SiC.
Reliability of Nitrided Oxides in N- and P-type 4H-SiC MOS Structures
Authors: Krishnaswami Sumi , Das Mrinal K. , Agarwal Anant K. , Palmour John W. 
Published: April 2011

AbstractTDDB measurements of NMOS capacitor fabricated with 1200°C dry oxide with 1300°C N2O anneal were performed at 175°C and 300°C under high positive bias stress. The devices are biased into strong accumulation mode such that the field in the oxide is high enough to collect breakdown data in a reasonable period of time. We observe that at 175°C, a 100-year Mean Time to Failure (MTTF) is obtained at an electric field of 3 MV/cm in the oxide. The TDDB measurement has also been performed at 300°C where lifetime has been reduced by a few orders of magnitude, but with an acceptable 100-year MTTF. Recent reliability results on similarly oxidized MOSFETs have shown failures along the same trend as the n-type capacitors, indicating that MOSFETs and MOS capacitors can have similar reliability despite inherent processing and structural differences. PMOS capacitors fabricated with the aforementioned dry + N2O process as well as capacitors fabricated using the low DIT nitridation techniques show acceptable MTTF of 100 years at the nominal operating electric field of 3 MV/cm.
Comprehensive Study of Impact Ionization Coefficients of 4H-SiC
Authors: Hatakeyama T. , Watanabe T. , Kojima K. , Sano N. , Shinohe T. , Arai K. 
Published: April 2011

AbstractThe electric field dependence and anisotropy of the impact ionization coefficients of 4H-SiC are investigated by means of the avalanche breakdown behavior of p+n diodes. The breakdown voltages as a function of doping density and the multiplication factors of a leakage current are obtained using p+n diode fabricated on (0001) and (1120) 4H-SiC epitaxial wafers. The obtained impact ionization coefficients show large anisotropy; the breakdown voltage of a p+n diode on (1120) wafer is 60% of that on (0001) wafer. We have shown that anisotropy of the impact ionization coefficients is attributable to the anisotropy of saturation velocity originated from the electronic structure of 4H-SiC.