bluuebunny/crossref_metadata_2025_split huggingface dataset:
Devitrification Mechanisms in Al-Y-Ni Glasses
Authors: Vasiliev A. L. , Aindow M. , Blackburn M. J. , Watson T. J. 
Published: April 2011

ABSTRACTCrystallization of gas atomized Al-Y-Ni alloy powder during consolidation has been studied ex-situ using high-resolution lattice imaging, diffraction and energy-dispersive X-ray spectrometry experiments in a transmission electron microscope. In the as-atomized powder amorphous particles occur but others show some evidence of decomposition. On the application of heat and pressure two types of decomposition product are formed initially; equiaxed nanoscale α-Al grains embedded in an amorphous matrix, and dendritic aluminum structures with veins of amorphous and micro-crystalline phases between the aluminum-rich regions. Complex ordered structures were identified in the α-Al: thin sheets of solute rich material were formed on the {100} and {110} aluminum planes with ordered cubic symmetry. Precursors for the Al19Ni5Y3 and Al3Y phases are formed in the vein regions. The second and third stages of crystallization involve the conversion of these ordered phases and embryonic precipitates to the better-known binary and ternary compounds.
Solidification Modeling of Bulk Amorphous Alloys
Authors: Lee Sang Bok , Kim Nack J. 
Published: April 2011

ABSTRACTClassical heterogeneous nucleation theory coupled with DTA data has been used to closely estimate the crystallization behavior of continuously cooled bulk metallic glass (BMG) alloys. Continuous cooling transformation and time temperature transformation diagrams of three BMG alloys, Zr41.2Ti13.8Cu12.5Ni10Be22.5, Cu47Ti33Zr11Ni6Si1Sn2and Mg65Cu25Y10alloys, have been calculated. The critical cooling ratesRcof three alloys were calculated to be 1.7 K/s, 242 K/s and 36 K/s for Zr41.2Ti13.8Cu12.5Ni10Be22.5, Cu47Ti33Zr11Ni6Si1Sn2and of Mg65Cu25Y10alloys, respectively, which match well with the experimental values. We conclude that heterogeneous nucleation is more favorable than homogeneous nucleation for the formation of crystals during cooling of BMG alloy liquids. Our approach can be applied to the analyses of crystallization kinetics of BMG alloys with a wide range of critical cooling rates during continuous cooling as well as isothermal annealing.
Microstructure And Ternary Phases In Al-rich Al-Y-Ni Alloys.
Authors: Vasiliev A. L. , Aindow M. , Blackburn M. J. , Watson T. J. 
Published: April 2011

ABSTRACTThe results of a transmission electron microscopy study on the crystal structures and morphologies exhibited by each of the phases in a set of four Al-rich Al-Y-Ni alloys which contain 1.7–4.5 at. % Y and 3.5–10.1 at. % Ni are presented. It is shown that each alloy contains fcc-Al, a binary Al3Ni or Al3Y phase (depending on alloy composition), and a ternary phase. The same ternary phase was found in each alloy and this was found to correspond to a new phase Al19Ni5Y3 (Cmcm, a=0.4025 nm, b=0.799 nm and c= 2.689 nm, Al19Ni5Gd3 structure type). In many cases, the ternary particles also contain embedded slabs of the equilibrium Al23Ni6Y4 phase. This phase mixture did not decompose even after extended annealing.
Non-equilibrium Technology of Obtaining Nanoamorphous Metals
Authors: R.T. Malkhasyan 
Published: April 2011

ABSTRACTA new non-equilibrium technology of obtaining structureless amorphous nanosize metals (not alloys) is presented in the given paper. The new content of definition of amorphous metals is discussed with an example of synthesized nanosize amorphous metals: W* and Mo*, with the grain size of less than 5 nm.A comparison of some properties of these metals with those of nanosize but crystalline ones (Wcr and Mocr) are presented. It is shown that they are much more reactive than the crystalline metals of analogous size.
Viscous Flow of Glass-forming Liquids: A Cluster Approach
Authors: Fan G. J. , Lavernia E. J. , Fecht H. J. 
Published: April 2011

ABSTRACTAn accurate description of the structure of a glass-forming liquid has eluded investigators, partly due to the dynamic behaviour that is inherent to liquids. The free volume concept provides a useful descriptor of a structural parameter that can be applied to glass-forming liquids. In previous work, we developed a cluster model to account for the viscous flow of glass-forming liquids (G. J. Fan and H. J. Fecht, J. Chem. Phys. 116, 5002 (2002)). In this work, we found that the kinetic fragility of a glass-forming liquid is quantitatively connected with its entropy of fusion ΔSf, the value of its melting point Tm, and the structures of interfaces between clusters. We will demonstrate that the proposed cluster model is consistent with an energy landscape model of the glass transition. On the basis of this suggestion, glass-forming liquids, consisting of nanometer-sized clusters, may be responsible for the observed similarity in the mechanical properties between metallic glasses and nanostructured metals.
TEM Studies Of Devitrification Products in Al-Gd-Ni-(Fe) Alloys.
Authors: Vasiliev A. L. , Aindow M. , Blackburn M. J. , Watson T. J. 
Published: April 2011

ABSTRACTMetallic glasses can form in certain Al-Gd-Ni alloys. Devitrificaion occurs on subsequent heating to intermediate temperatures and although some phases form as expected the crystal structures of others are less certain. This paper presents a summary of transmission electron microscopy (TEM) data acquired from four devitrified Al-Gd-Ni(-Fe) alloys. It is shown that the alloys exhibit nanocrystalline microstructures consisting of face-centered-cubic α-Al, binary Al3Gd, and ternary phases. An Al-(Gd,Fe)-Ni phase forms as rods and exhibits the orthorhombic Al19Ni5Gd3 structure. Plates of the rhombohedral phase Al23(Ni,Fe)6Gd4 are also present. Complex faulting is observed in both ternary phases.
Transient Fatigue Crack-Growth Behavior and Damage Zones in Zr-Based Bulk Metallic Glass
Authors: Hess Peter A. , Dauskardt Reinhold H. 
Published: April 2011

ABSTRACTFatigue crack propagation mechanisms of bulk metallic glasses (BMGs) are not well understood, limiting their use in safety-critical structural applications particularly where complex fatigue loading may occur. Accordingly, the present study examines the effects of variable amplitude fatigue loading associated with block loading and tensile overloads on fatigue crack-growth rates in a Zr-based BMG. Crack growth studies were conducted on compact tension specimens using computer control of the applied stress intensity range, ΔK. Fatigue crack closure loads, which represent the initial contact of mating crack surfaces during the unloading cycle, were continuously monitored during testing. Abrupt drops in ΔK were found to significantly decrease fatigue crack-growth rates far below equilibrium values, arresting growth completely at a ΔK twice the nominal fatigue threshold ΔKTH. Conversely, an abrupt increase in ΔK was found to accelerate fatigue crack-growth rates. The effects of roughness-induced crack closure were assessed and found to be consistent with the suppression or acceleration of growth rates. However, in order to fully explain the observed transient growth rate response, other mechanisms that may be related to the fatigue mechanism itself were also considered. Specifically, the nature of the fatigue crack tip damage zone was also investigated. As BMGs lack distributed plasticity at low temperatures, the plastic zone differs greatly from that seen in ductile crystalline materials, and its role in fatigue crack propagation mechanisms is examined.
Plasticity in Nanocrystalline and Amorphous Metals: Similarities at the Atomic Scale
Authors: Lund Alan C. , Schuh Christopher A. 
Published: April 2011

ABSTRACTFor metallic alloys, the amorphous state is often regarded as the limiting structure as grain size is reduced towards zero. One interesting consequence of this limit is that the properties of the finest nanocrystalline metals must begin to resemble those of metallic glasses. In this work we focus upon the nature of the plastic yield mechanisms in these material classes, and seek to identify commonalities and disparities in the nature of plastic yield in glasses and nanocrystals. The discussion is presented with reference to static atomistic simulations of (i) an amorphous binary alloy, and (ii) a nanocrystalline Ni specimen with grain size of 3 nm. We show that both these materials deform by the operation of fine atomic shearing events, and both exhibit asymmetric yielding as a consequence.
Infiltration Processing of Tungsten-Reinforced Bulk-Amorphous Metal Matrix Composites
Authors: Kecskes Laszlo J. , Szewczyk Steven T. 
Published: April 2011

ABSTRACTHigh-density tungsten (W)-reinforced bulk amorphous metal (BAM) matrix composites have been fabricated by a pressure infiltration methodology. A hafnium (Hf)-based BAM with a density of 11 g/cm3, glass transition temperature, Tg, of 495 °C, and liquidus temperature, Tliq, of 1,050 °C has been used to infiltrate open-porosity W-wire preforms to create W-Hf-BAM composites. Because of the considerably higher Tliq of Hf-based BAM alloys than those based on Zr, the interaction of the BAM with the fixture components, reaction with the W perform, and the formation of undesirable intermetallic phases in the composite were of primary interest. The roles of infiltration pressure, soak temperature, and time at temperature on the composite structure were examined. The structure and quality of the composites were determined with simple fracture tests, scanning electron microscopy, X-ray diffraction, and differential thermal analysis. The fabrication procedure steps and the characteristics of the composites are described.
Microstructure, thermal stability and mechanical properties of slowly cooled Zr-based composites containing dendritic bcc phase precipitates
Authors: Radtke Nicolle , Eckert Jürgen , Kühn Uta , Stoica Mihai , Schultz Ludwig 
Published: April 2011

ABSTRACTWe report on the microstructure, the thermal stability and the mechanical properties of slowly cooled Zr-Nb-Cu-Ni-Al alloys with ductile bcc phase precipitates embedded in a glassy or nanocrystalline matrix. The samples were prepared in form of rods by injection casting into a copper mold. The phase formation and the microstructure of the composite material were investigated by X-ray diffraction, EDX analysis and scanning and transmission electron microscopy. The thermal stability was examined by differential scanning calorimetry and the mechanical behavior was investigated by compression tests under quasistatic loading at room temperature. The formation of bcc phase dendrites and a glassy or nanocrystalline matrix is strongly governed by the alloy composition and the actual cooling rate during solidification. Besides, changes in composition and cooling rate lead to different volume fraction and size of the bcc phase precipitates and, hence, to different values of yield strength, elastic and plastic strain. The samples with nanocrystalline matrix show a homogeneous distribution of the bcc phase precipitates over the whole cross-section and exhibit higher yield strength and plastic strain than the samples containing an amorphous matrix. Illustrated by the presented results we show the possibility of obtaining tailored mechanical properties by control of composition and solidification conditions.
Strained Channel Transistor Using Strain Field Induced By Source and Drain Stressors
Authors: Yeo Yee-Chia , Sun Jisong , Ong Eng Hong 
Published: April 2011

ABSTRACTWe perform a theoretical evaluation of the strain field in a p-channel transistor with silicongermanium (Si1−yGey) stressors in the source and drain regions. The strain field comprises a lateral compressive strain component and a vertical tensile strain component. The lateral strain component is larger in magnitude and more uniformly distributed as compared to the vertical strain component. The impact of transistor design parameters, such as the Ge mole fraction y in the stressors, the spacing L between stressors, the stressor depth, and the raised stressor height, on the strain field are investigated. Hole mobility enhancement larger than 30% is achievable wth L = 50 nm and y = 0.15. More aggressive mobility enhancement targets may be achievable by reducing the stressor spacing and employing a stressor with a larger lattice mismatch with the Si channel.
Fabrication of Strained Silicon on Insulator (SSOI) by Direct Wafer Bonding Using Thin Relaxed SiGe Film as Virtual Substrate
Authors: Lee J.J. , Maa J.S. , Tweet D. J. , Hsu S.T. 
Published: April 2011

ABSTRACTNMOS devices have been successfully fabricated on SSOI wafers. The SSOI wafer fabrication is by direct wafer bonding and wafer transfer by splitting of the strained Si on thin SiGe virtual substrate to an oxidized wafer. The thin SiGe virtual substrate is fabricated by strained SiGe deposition, H2+ implantation, and SiGe lattice relaxation anneal. This relaxation process creates a confined defect zone at the SiGe to Si substrate interface that ensures low defect strained Si growth. 10 μm by 10 μm NMOS SSOI devices show an improvement of 100% in drive current and 115% in transconductance. A near ideal subthreshold swing was observed on NMOS devices with channel length as short as 0.1 μm.
Analysis of junctions formed in strained Si/SiGe substrates
Authors: Eneman G. , Simoen E. , Lauwers A. , Lindsay R. , Verheyen P. , Delhougne R. , Loo R. , Caymax M. , Meunier-Beillard P. , Demuynck S. , Meyer K. De , Vandervorst W. 
Published: April 2011

ABSTRACTJunctions were formed in thin SiGe/strained Si substrates with a thickness of 250-350 nm to assess the effect of different buffer layer parameters (bandgap, dislocations, thickness) on the junction leakage density that can be expected in MOSFET devices. The implantations used are standard well, channel and Highly Doped Drain (HDD) implants. Both p+/n and n+/p junctions were evaluated. The total thickness of the buffer layers was varied to compare the effect of different structural layers on the diode leakage. This investigation shows that the effect of an increased defect density is dominant at room temperature for the strained Si samples, resulting in 4-5 orders of magnitude increase in leakage. However, there is a different gradation in leakage dependence for thick and thin buffer layers, especially at higher temperatures.
High Mobility SiGe/Si n-MODFET Structures and Devices on Sapphire Substrates
Authors: Mueller Carl , Alterovitz Samuel , Croke Edward , Ponchak George 
Published: April 2011

ABSTRACTSiGe/Si n-type modulation doped field effect structures and transistors (n-MODFETs) have been fabricated on r-plane sapphire substrates. Mobilities as high as 1380 cm2/Vs were measured at room temperature. Excellent carrier confinement was shown by Shubnikov-de Haas measurements. Atomic force microscopy indicated smooth surfaces, with rms roughness less than 4 nm, similar to the quality of SiGe/Si n-MODFET structures made on Si substrates. Transistors with 2 μm gate lengths and 200 μm gate widths were fabricated and tested. An IDS of 9 mA was obtained by operating the transistor in an enhancement mode (positive VGS) and the maximum transconductance (gm) was 37 mS/mm at a VDS of 2.5 V. The transducer gain (Gt) measured with a loadpull system was 6.4 dB at 1 GHz for a VDS of 2.5 V and VGS=-0.4 V.
Modeling Dopant Diffusion in SiGe and SiGeC alloys
Authors: Pakfar Ardechir , Holliger Philippe , Poncet Alain , Fellous Cyril , Dutartre Didier , Schwartzmann Thierry , Jaouen Hervé 
Published: April 2011

ABSTRACTA unified diffusion model is developed, valid for all usual substitutional atoms in SiGe and strained SiGeC layers, in accordance with all published experimental data and predicting the enhancement of Arsenic diffusion in SiGe and SiGeC strained layers. Using a new SIMS methodology, the study of As intrinsic diffusion in SiGe and SiGeC layers is performed, at low concentration and under equilibrium annealing conditions. Arsenic diffusivity in fully-strained SiGe and SiGeC layers on Si substrates was successfully compared to the unified diffusion model.
Fin Sidewall Microroughness Measurement by AFM
Authors: Gondran Carolyn F. H. , Morales Emily , Guerry Angela , Xiong Weize , Cleavelin C. Rinn , Wise Rick , Balasubramanian Sriram , King Tsu-Jae 
Published: April 2011

ABSTRACTThe sidewalls of etched Si lines will be the carrier channel surfaces in FinFET devices. These surfaces must be as smooth as possible for optimal device performance. Thus, the ability to quantitatively measure sidewall roughness is essential to process development. A methodology to quantitatively measure Fin sidewall roughness by AFM is presented. The samples were prepared for measurement by cleaving along the length of the Fins or dense-line test structures and by FIB polishing to bring the edge of the sample close to the sidewall of the etched feature. The cleaved and FIB-polished sample was mounted 17 degrees shy of normal. This exposes the sidewall on the top surface while preventing shadowing of the lower part of the sidewall due to contact between the side of the probe support and the cleaved or polished edge. Quantitative AFM measurements taken by this method show meaningful differences in the sidewall roughness for samples that have seen different sidewall smoothing treatments. The average observed rms roughness values for various surface-smoothing treatments range from 0.8 to 1.8 Å for a 50 nm square area.
Highly-Insulating Ultra-Thin SiO2 Film Grown by VUV Photo-Oxidation
Authors: Fukano Atsuyuki , Oyanagi Hiroyuki 
Published: April 2011

ABSTRACTInsulating performance of high-density SiO2 films on Si(100) wafer grown by VUV irradiation in oxygen atmosphere at low-temperatures (300 ∼ 400°C) is reported. Comparing the SiO2 films grew with various wavelength irradiation, i.e., 126, 172 and 222nm, we found a strong wavelength dependence in density and insulating performance. The results suggest that electrical characteristics are highly correlated with film density. Higher density films are formed by shorter wavelength photo-oxidation whereas higher breakdown voltage and lower leakage current are achieved by the dense films. This shows that lower density of defects, dangling bonds, existing at the Si-O interface strongly affects the insulating performance. VUV photo-oxidation is a promising silicon oxide growth technique with greater insulating performance beyond the conventional limit for thermally oxidized films.
Determination of Hydrogen in Semiconductors and Related Materials by Cold Neutron Prompt Gamma-ray Activation Analysis
Authors: Paul Rick L. 
Published: April 2011

ABSTRACTAn instrument for prompt gamma-ray activation analysis (PGAA) at the NIST Center for Neutron Research has proven useful for the measurement of hydrogen and other elements in a variety of materials. The sample is irradiated by a beam of low energy neutrons. Gamma-rays emitted by atomic nuclei upon neutron capture are measured and elemental concentrations determined by comparison with appropriate standards. The detection limit for hydrogen is < 5 mg/kg in most materials, and 2 mg/kg for hydrogen measured in silicon. The instrument has been used to measure hydrogen mass fractions of < 100 mg/kg in high purity germanium, and < 10 mg/kg in quartz. More recently PGAA has been used to measure hydrogen in 1 μm thick porous thin films on a silicon substrate, and in crystals of silicon carbide and cerium aluminate.
Hydrogen Intercalation Sites in Rutile Predicted from Ab Initio Calculations
Authors: Koudriachova Marina V. , Harrison Nicholas M. , Leeuw Simon W. de 
Published: April 2011

ABSTRACTThe geometry of hydrogen intercalation sites in rutile TiO2 has been examined with first principles calculations. The calculations predict a new intercalation site, which is consistent with current experimental data. The apparent contradictions between spectroscopic, diffraction and magnetic resonance data are resolved by taking into account the strong local distortions of the structure induced by localization of charge donated by hydrogen. In particular the predicted OH vibrational frequency is in excellent agreement with the experimentally measured value. A similar local geometry is predicted in the presence of trivalent counter ions but with a preferential site occupancy consistent with the local symmetry implied by spectroscopic measurements of aluminium substituted titania.
Effect of Hydrogen Treatment on Room -Temperature Electric-Field Induced Properties in Narrow-Gap ZnCdHgTe Thin Films
Authors: Khlyap Galina M. , Sydorchuk Petro G. , Polit Jacek 
Published: April 2011

ABSTRACTThe effect of hydrogen treatment on room temperature electric properties of narrow-gap semiconductor thin films ZnxCdyHg1−z−yTe (0 < x < 0.50, 0.20 < y < 0.40) is investigated for the first time. ZnCdHgTe films of 2 – 5 [.proportional]m thickness were grown on glass substrates by pulsed laser deposition technique. As-grown films were thermally treated in the flow of molecular H2 at 200°C during 24 hours. Comparison between electric characteristics measured before and after hydrogenation showed sufficient changes of the film resistance and appearance of photosensitivity in the visible wavelength range. Study of current-voltage characteristics of the films revealed appearance and significant change of diode-like properties.
On the Mechanism of Hydrogen Diffusion in Si Solar Cells Using PECVD SiN:H
Authors: Sopori B.L. , Zhang Y. , Reedy R. , Jones K. M. , Yan Y. , Al-Jassim M. M. , Kalejs J. , Bathey B. 
Published: April 2011

ABSTRACTA mechanism for transport and diffusion of H in a silicon solar cell by PECVD SiN:H process is proposed. Plasma-induced surface damage “stores” H during the nitride deposition, which is driven into the bulk of the solar cell during metal-contact firing. Theoretical and experimental results are given that verify this mechanism.
Comparative Study of Electronically Controlled Motion of Hydrogen around Carbon and Platinum Atoms in Silicon
Authors: Kamiura Yoichi , Bao Namula , Sato Kimihiro , Fukuda Kazuhisa , Iwagami Yasuyuki , Yamashita Yoshifumi , Ishiyama Takeshi 
Published: April 2011

ABSTRACTWe have studied the local motion of hydrogen in the neighborhood of carbon and platinum impurities by observing the stress-induced reorientation and subsequent recovery of two H-related (H-C and Pt-H2) complexes in Si, using deep-level transient spectroscopy (DLTS) under uniaxial compressive stress. We notice two interesting differences in hydrogen motion around carbon and platinum atoms. The first one is a difference in the temperature where stress-induced reorientation occurs. That of the H-C complex occurs at high temperatures above 250 K, while it occurs at low temperatures around 80 K for the Pt-H2 complex. The second difference is the effect of charge state of the complexes on their stress-induced reorientation and subsequent recovery. It occurs preferentially when an electron occupies the level of the H-C complex, but the Pt- H2 complex has the reverse effect of level occupancy. These differences are discussed from viewpoint of different atomic configurations and electronic states of two H-related complexes.