bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Soluble Polymer Supported Organic Molecules by Mass Spectrometry
Authors: Enjalbal C. , Lamaty F. , Ribière P. , Varray S. , Suberchicot E. , Yadav-Bhatnagar N. , Martinez J. , Aubagnac J-L.
Published: April 2011

Syntheses carried out on soluble polymers, such as polyethylene glycol (PEG), benefit the advantages of both solution-phase and solid-phase syntheses. The choice of the reaction solvent governs the polymer solubility. Synthetic steps are conducted under homogeneous conditions whereas purifications are performed by filtration after polymer precipitation. This alternative strategy, known as liquid-phase chemistry, has been investigated to prepare combinatorial libraries.

The fact that soluble polymer supported molecules are directly amenable to standard spectroscopic methods, including NMR (1H, 13C) and ESI or MALDI mass spectrometry (ElectroSpray and Matrix Assisted Laser Desorption Ionization) allows to perform to in situ reaction monitoring without the need to release the compound from the polymeric support.

We report a general methodology to characterize step by step soluble polymer supported organic molecules by MALDI and ESI mass spectrometry. High throughput analyses were targeted to fullfil combinatorial chemistry requirements. Data acquisition and interpretation were automated through the design of specific experimental protocols and a data managment software. MALDI mass spectrometry was appropriate to analyze pure supported molecules whereas ESI mass spectrometry coupled to liquid chromatography was required to unravel PEG mixtures.
Nonequilibrium Structures in Codeposited Cr-Fe-Ni Films
Authors: Specht E.D. , Rack P.D. , Rar A. , Pharr G.M. , George E.P. , Hong H.
Published: April 2011

Ternary libraries are prepared by codeposition of Cr, Fe, and Ni on single-crystal Si and Al2O3 (sapphire) substrates at ∼100°C. The varying proximity to the three metal sources produces a spread of compositions in the films, which are analyzed both as-deposited and after annealing in vacuum for 2 h at 500°C. Structural maps are produced using synchrotron radiation and simultaneous detection of 2D diffraction patterns and x-ray fluorescence spectra. Four phases are identified in the as-deposited films. Three phases occur in equilibrium: bcc (α), fcc (γ), and intermetallic (σ). The fourth phase does not correspond to any equilibrium phase in the Cr-Fe-Ni system; it is tentatively identified as isomorphic to the α-Mn (A12) structure. After annealing, the nonequilibrium phase is no longer observed, but the occurrence of the three equilibrium phases is still far from the equilibrium phase boundaries. The particle size measured by x rays is small (9–15 nm), suggesting that higher annealing temperatures are required for the growth of equilibrium phases.
Combinatorial Study and High Throughput Screening of Transparent Oxygen and Moisture Barrier Films
Authors: Grunlan Jaime , Chavira Aaron , Wolfe Timothy J. , Akhave Jay , Hamilton Charles , Mehrabi Ali R.
Published: April 2011

ABSRACT

High throughput screening methods for evaluating oxygen and moisture barriers are described. The screening methods are based on the change in a certain optical property, such as absorbance or fluorescence, due to a chemical reaction with oxygen gas or water vapor. The results of these measurements for several cases are presented and their advantages and disadvantages are discussed.
Synthesis and characterization of combinatorial libraries of semiconductor gas sensors.
Authors: Aronova M. A. , Chang K. S. , Takeuchi I. , Jabs H. , Westerheim D. , Gonzalez-Martin A. , Kim J. , Lewis B.
Published: April 2011

We have fabricated thin-film combinatorial gas sensor libraries based on doped semiconducting SnO2 thin films. The utility of combinatorial libraries is two-fold: one is to search and optimize the compositions for high sensitivity and selectivity of gases, and the other is to make use of the natural array geometry of the libraries with different sensor elements for electronic noses. Combinatorial pulsed-laser ablation was used to deposit compositionally varying arrays of sensor elements onto a pre-patterned device electrode configuration. Using a multiplexing electronics, we have demonstrated detection of chloroform, formaldehyde, and benzene gases at concentrations down to 12.5 ppm through pattern recognition of signals from the arrays of sensors.
The study of luminescence of rare-earth organic complexes sensitized Eu3+ complex in PMMA matrix using combinatorial method
Authors: Ding Jianjun , Jiu Hongfang , Bao Jun , Lu Jiecheng , Gui Wanru , Zhang Qijing , Gao Chen
Published: April 2011

A combinatorial approach has been utilized for researching the luminescence of rare-earth ions complexes (RE(DBM)3·Phen, RE=Dy3+, La3+, Gd3+, Sm3+, Y3+) sensitized Eu3+ complex in PMMA matrix. The results show that the La3+ complex has the maximum sensitization efficiency among these sensitization ions. The luminescent intensities increase as the Eu content increase in PMMA matrix. The La3+ complex exhibits higher sensitization efficiency at lower Eu content in PMMA matrix. At a content of 5% Eu complex, the maximum sensitization efficiency of La3+ is more than 20 times.
Effects of Oxygen on Meta-stable Phase Formation in Zr80Pt20 Melt Spun Ribbons
Authors: Sordelet Daniel , Yang Xiaoyun , Rozhkova Elena , Besser Matthew , Kramer Matthew
Published: April 2011

This report continues previous studies that show melt spun Zr80Pt20 ribbons having oxygen contents ranging from <200 to approximately 5000 mass ppm form various meta-stable phases during quenching. In the presence of sufficient oxygen, a big cube Zr6Pt3O phase forms, but this structure is de-stabilized towards an icosahedral quasicrystalline structure at lower oxygen levels. Further reduction of oxygen promotes increasingly stable Zr-Pt bonds, and a meta-stable β-Zr(Pt) structure is formed.
Crystal Chemistry and Electronic Structure of Magnesium based Mackay Icosahedron Type Approximants
Authors: Makongo Julien Pierre Amelie , Moguilnikov Yuri , Kudla Christian , Grüner Daniel , Schäpers Melanie , Kreinery Guido
Published: April 2011

In order to obtain reliable experimental information on the long-range order, the role of the valence electron concentration and the type of disorder for Mackay icosahedron type quasicrystals we have studied binary and ternary Mg based approximant phases. An overview is presented on the crystal structures, homogeneity ranges, physical properties, and electronic structures of the following intermetallic phases: Mg6Pd, Mg57Pd13, Mg56.4Pd13.5, Mg306Pd77, Mg3Pd, Mg5Pd2, Mg2Pd, Ga30-xMg32+xPd21-y, Ga15-x-yMg38+yPd13+x, GaMg3Pd2, Ag17Mg54, Ag7Mg26, and AgMg4.
Chemical Bonding and Pseudogap in Zn- and Cd-based Compounds with Complex Hexagonal Structures
Authors: Ishii Y. , Nozawa K. , Fujiwara T.
Published: April 2011

Electronic structures of hexagonal Zn-Mg-Y and Cd58Y13 compounds are studied by first-principles calculations. Both of the systems show deep pseudogap in the electronic density of states near the Fermi level and considered to be stabilized electronically. To illustrate bonding nature of electronic wavefunctions, the crystal orbital Hamilton population (COHP) is calculated for neighboring pairs of atoms in the unit cell. It is found that the bonding nature is changed from bonding to anti-bonding almost exactly at the Fermi level for Zn-Zn and Cd-Cd bonds. On the contrary, for Zn/Cd-Y bonds, both of the states below and above the pseudogap behave as bonding ones. Possible effects of the p-d hybridization are discussed.
Stability and Icosahedral Transformation of Supercooled Liquid in Metal-Metal type Bulk Glassy Alloys
Authors: Inoue Akihisa , Zhnag Wei , Louzguine Dmitri V. , Saida Junji , Matsubara Eiichiro
Published: April 2011

The glassy structure and the primary precipitation phase from supercooled liquid were examined in metal-metal type Zr-, Hf- and Cu-based alloy systems by various advanced analytical techniques. The icosahedral phase precipitates as the primary phase from supercooled liquid for all the metal-metal type glassy alloys examined in the present study. The icosahedral phase has a rhombic triacontahedra type for the Zr-Al-Ni-Cu-NM (NM=Ag, Pd, Au, Pt), Zr-Cu-NM, Hf-Al-Ni-Cu-NM, Cu-Zr-Ti-Pd and Cu-Hf-Ti alloys. In addition, the short-range atomic configurations in their glassy alloys have the features of highly dense packed atomic configuration, new local atomic configurations and long-range homogeneity with attractive interaction. It is therefore concluded that the high glass-forming ability of the metal-metal type alloys is due to the self-formation of the unique glassy structure with the above-described three features which are consistent with the formation of short-range icosahedral atomic configuration.
Structural Relationships between QC and Meta-stable Crystalline Phases in Melt Spun Zr80Pt20 Ribbons
Authors: Yang X. Y. , Kramer M. J. , Rozhkova E. A. , Sordelet D. J.
Published: April 2011

Two competing meta-stable crystalline phases, a bcc hyperstoichiometric β-Zr(Pt) (Im3m) superstructure and a non-stoichiometric fcc ε-Zr6Pt3O (Fd3m) phase, have been observed to coexist with a quasicrystalline (i) phase, respectively, in as-spun Zr80Pt20 ribbons with low oxygen content (184ppm mass O) and high oxygen content (4737 ppm mass O). Transmission electron microscopy (TEM) results show that the β-Zr(Pt) superstructure and i phase have a well defined orientational relationship, good crystallographic match and nearly identical stoichiometry. Icosahedral two-fold axes coincide with <110>, <111>, <112> and <113> axes in β-Zr(Pt); {110}β-Zr planes register with icosahedral {211111} fivefold or {221001} twofold planes. The observed orientational relationship and the space group (Im3m) preclude β-Zr(Pt) as a cubic approximant to the i phase. Both β-Zr(Pt) and the i phase are distorted; β-Zr(Pt) maintains a basic β-Zr Bravais lattice with an aperiodic superlattice. Morphologies suggest that the i phase forms first, followed by an easy nucleation of the β-Zr(Pt) on the surfaces of the i phase. Also, a similar orientational relationship and lattice match between ε-Zr6Pt3O and i phase has been revealed by TEM.
Electrical Properties of Ag-In-(Yb,Ca) Quasicrystals and Their Approximants
Authors: Tetsuka Daisuke , Tamura Ryuji , Takeuchi Shin
Published: April 2011

We report the electrical resistivity of the ternary Ag-In-(Yb,Ca) quasicrystals (QCs) together with those of their 1/1 and 2/1 cubic approximants. The temperature coefficient of the resistivity (TCR) is negative and nearly the same for the QCs and the 2/1 approximants suggesting that the coherence length of the conduction electrons in the QCs is comparable to the lattice parameter of the 2/1 approximants, i.e., ∼2.5 nm. On the other hand, both positive and negative values of TCR are observed for the 1/1 approximants depending on the annealing temperature. Taking into consideration the occurrence of positive TCR in the binary Cd-(Yb,Ca) 1/1 approximant, the latter phenomenon suggests that the negative TCR of the ternary 1/1 approximants is due to chemical disorder between Ag and In, and the chemical disorder is possibly reduced when annealed at low temperatures.
Wetting and friction on quasicrystals and related compounds
Authors: Dubois Jean Marie , Fournée Vincent , Belin-Ferré Esther
Published: April 2011

Reduced wetting and friction are two essential surface properties that to a large extent currently embody the technological potential of quasicrystalline coatings. By quasicrystalline compounds, one considers here the whole family of complex Al-(Cu or Pd)-(Fe, Cr or Mn) intermetallics, which comprises true quasicrystals, their approximants and some crystalline materials of related composition.

Although covered by a layer of native Al2O3oxide, wetting by water on these materials exhibits a clear correlation between the reversible adhesion energy of water and the bulk density of states at the Fermi energy. Similarly, in high vacuum, the friction coefficient measured in contact against a hard-steel rider is characteristically smaller than the one measured against conventional metallic alloys (including steel). Observing that wear is nearly non existent under such friction conditions, experiment allows us for the first time to derive a fair estimate of the true surface energy of quasicrystals and related complex metallic alloys. Similarly to wetting, the electronic density of states seems to determine the friction characteristics of these compounds.
Debye Temperature at the Fivefold- and Threefold-Symmetry Surface of the Al-Pd-Mn Quasicrystal.
Authors: Lüscher R. , Flückiger T. , Erbudak M. , Kortan A. R.
Published: April 2011

Specular-beam intensity profiles are measured in low-energy electron diffraction as a function of temperature for the fivefold- and threefold-symmetry surfaces of the icosahedral quasicrystal Al-Pd-Mn. The resulting shifts of the Bragg-peaks to lower energies are accounted for mainly by a lattice expansion perpendicular to the surface and allow us to determine the thermal expansion coefficient of atomic layers to be (24.5 ± 2.0) × 10−6 K−1 for both surfaces. As a result of several measurements, a surface Debye temperature of 298 ± 7 K is found for the pentagonal and 301 ± 10 K for the threefold-symmetry surface. This similarity implies comparable bonding forces for the atoms at these surfaces. Additionally, the derived thermal expansion coefficient supports a layer-based structural model for both surfaces investigated here.
Electrochemical Reactivity of Zirconium-Based Bulk Metallic Glasses
Authors: Gebert Annett , Kamachi Mudali U. , Eckert Jürgen , Schultz Ludwig
Published: April 2011

Amorphous Zr-(Ti)-(Nb)-Al-Cu-Ni alloy samples were prepared by melt-spinning and copper mould casting in an argon atmosphere and characterized regarding their microstructure and thermal behavior. Their anodization behavior in aqueous environments with pH= 0.5 – 13 was studied by electrochemical polarization techniques in combination with surface analytical investigations, i.e. SEM/EDX, AES. In chloride-containing solutions the macroscopic corrosion resistance of bulk amorphous alloys is affected by the presence of heterogeneities, such as concentrated cluster zones of selected components or crystalline defects. Pitting phenomena are studied in neutral and acidic chloride solutions and as a result a local corrosion mechanism is proposed. The cathodic reactivity of alloy samples at different microstructural states and after pre-etching in fluoride solutions was investigated. After pre-etching melt-spun amorphous samples exhibit a significant increase in surface reactivity as expressed by a drastic increase in electrochemical capacities and in cathodic current densities as well as by a significant reduction of overpotentials for the hydrogen reduction reaction. The hydrogen sorption behavior was studied on samples galvanostatically charged at various cathodic current densities by means of XRD, DSC, TEM and thermal desorption analysis TDA. At room temperature Zr-based alloys absorb hydrogen up to H/M=1.65 mainly by interstitial solution of hydrogen atoms in the amorphous structure. The effect of absorbed hydrogen on the thermal stability and the crystallization behavior is described.
Bulk metallic glasses for industrial products; New structural and functional applications
Authors: Nishiyama Nobuyuki , Amiya Kenji , Inoue Akihisa
Published: April 2011

By use of excellent properties of bulk metallic glasses, some industrial products were practically prepared and their performances were investigated. Linear actuator constructed by a set of Fe-based BMG yokes generates large Lorentz force due to the large permeability and saturation magnetization of the BMG. Ni-based BMG microgear prepared by injection casting exhibits nano-imprintability against the surface roughness of mold. The newly developed alloy with a nominal atomic composition of Ti52Cu23Ni11Mo7Fe7 exhibits high yield strength of 1250 MPa, high fracture strength of 2740 MPa and large plastic elongation of over 20 %. These results for the industrial products made of BMGs are promising for future developments as industrial materials with high performance.
Increased, Directed Osteoblast Adhesion at Nanophase Ti and Ti6Al4V Particle Boundaries
Authors: Webster Thomas J. , Ejiofor Jeremiah U.
Published: April 2011

Increased functions of osteoblasts (bone-forming cells) have been demonstrated on nanophase compared to conventional ceramics (specifically, alumina, titania, and hydroxyapatite), polymers (such as poly-lactic-glycolic acid and polyurethane), carbon nanofibers, and composites thereof. Nanophase materials are materials that simulate dimensions of constituent components of bone since they possess particle or grain sizes less than 100 nm. However, to date, interactions of osteoblasts on nanophase compared to conventional metals remain to be elucidated. For this reason, the objective of the present in vitro study was to design, fabricate, and evaluate osteoblast adhesion on nanophase metals (specifically, Ti and Ti6Al4V). Results of this study provided the first evidence of increased osteoblast adhesion on nanophase compared to conventional Ti-based metals. Moreover, directed osteoblast adhesion was observed preferentially at metal particle boundaries. It is speculated that since more particle boundaries were created through the use of nanophase compared to conventional metals, increased osteoblast adhesion resulted. Because adhesion is a necessary prerequisite for subsequent functions of osteoblasts (such as deposition of calcium-containing mineral), the present study suggests that Ti-based nanophase metals should be further considered for orthopedic implant applications.
Devitrification Mechanisms in Al-Y-Ni Glasses
Authors: Vasiliev A. L. , Aindow M. , Blackburn M. J. , Watson T. J.
Published: April 2011

Crystallization 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

Classical 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

The 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

A 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

An 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

Metallic 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

Fatigue 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

For 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

High-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

We 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

We 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

NMOS 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

Junctions 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

SiGe/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

A 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

The 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

Insulating 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

An 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

The 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

The 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

A 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

We 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.
Formation of deuterium-related shallow donors in boron-doped diamond.
Authors: Chevallier Jacques , Teukam Zéphirin , Saguy Cécile , Kalish Rafi , Cytermann Catherine , Bailly Francis , Jomard Frančois , Kociniewski Thierry , Ballutaud Dominique , Barbé Michel , Butler James E. , Baron CÉline , Deneuville Alain
Published: April 2011

It is well known that diffusion of deuterium in boron-doped diamond results in the passivation of boron acceptors with the formation of (B,D) complexes. In this work, we show that deuteration of boron-doped diamond can induce a p-type to n-type conversion under certain conditions. The n-type conductivity is governed by the ionization of shallow donors with a ionization energy of 0.34 eV. This is well below the lowest ionization energy of donors found up to now in diamond (0.6 eV for phosphorus donors). The electrical conductivity and the electron mobility can be as high as 6 S/cm and 430 cm2/Vs at 300 K. The reversibility of the effect under thermal annealing and the necessity of excess deuterium to trigger the n-type conductivity suggest that deuterium is involved in the formation of the shallow donors. The present status concerning the understanding of their origin is discussed. In addition, we have found that, contrary to previous conclusions, deuterium can diffuse in type Ib diamond. The conditions where this diffusion is observed are presented.
Pressure Dependence of Aluminum Doping in SiC Vapor Phase Epitaxy
Authors: Schöner Adolf , Gustafsson Malin
Published: April 2011

The dependence of the aluminum incorporation on the total pressure in a hot wall vapor phase reactor for SiC homoepitaxial growth has been investigated. It was found that in the doping concentration range from 1·1017 cm−3 to 1·1019 cm−3 the incorporated aluminum concentration varies by the factor 3 to 4, when the reactor pressure is changed from 150 mbar to 250 mbar. Lower reactor pressure gives lower aluminum concentration. Periodically changing reactor pressure results in aluminum concentration periodically changing with depth in the epilayer. All results were measured electrically by capacitance-voltage measurements on nickel Schottky contacts. Additional experiments have been performed for n-type nitrogen doped SiC epilayers for comparison. The nitrogen doping concentration was found to be independent of the reactor pressure within the accuracy of the applied C-V measurements and the doping profile analysis method.
4H-SiC MIS structures using oxidized Ta2Si as high-k dielectric
Authors: Pérez-Tomás A. , Godignon P. , Mestres N. , Tournier D. , Montserrat J. , Millán J.
Published: April 2011

Ta2Si silicide has been deposited by sputtering and thermally oxidized on 4H-SiC and Si substrates. A mixture of SiO2 and Ta2O5 insulator films has been obtained after oxidation in dry O2. Among the high-k dielectrics, tantalum pentoxide (Ta2O5) could be a valuable alternative due to its high dielectric constant. Atomic force microscopy (AFM), C-V measurements along with x-ray diffraction analysis have been carried out in order to study the feasibility of this material as gate dielectric for 4H-SiC MOS devices. Electrical characteristics of deposited and oxidized Ta2Si on 4H-SiC and Si samples have been obtained and compared. At the range of oxidation temperatures considered (850°C-950°C), the influence of diffusion processes between the Si substrate and Ta2Si layer during oxidation strongly influences the dielectric properties of the resulting insulator layer on Si substrates.
Aluminum-Ion Implantation into 4H-SiC (11-20) and (0001)
Authors: Negoro Y. , Kimoto T. , Matsunami H.
Published: April 2011

High-dose aluminum-ion (Al+) implantation into 4H-SiC (11-20) and (0001) has been investigated. Surface morphologies of implanted (0001) samples were improved by annealing with a graphite cap. Implant-dose dependence and annealing-time dependence of electrical properties are examined by Hall-effect measurements. A low sheet resistance of 2.3 kΩ/sq. was obtained in (0001) by high-dose Al+ implantation at 500 °C with a dose of 3.0 × 1016 cm−2 and high-temperature annealing at 1800 °C for a short time of 1 min. In the case of (11-20), even room-temperature implantation brought a low sheet resistance below 2 kΩ/sq. after annealing at 1800 °C.
Characterization and Comparison of 4H-SiC(1120) and 4H-SiC(0001) 8° Off-Axis Substrates and Homoepitaxial Films
Authors: Bishop S.M. , Preble E.A. , Hallin C. , Henry A. , Sarney W. , Chang H.-R. , Storasta L. , Jacobson H. , Reitmeier Z.J. , Wagner B.P. , Janzén E. , Davis R.F.
Published: April 2011

Homoepitaxial films of 4H-SiC(1120) and 8° off-axis 4H-SiC(0001) have been grown and characterized. The number of domains and the range of full-width half-maxima values of the x-ray rocking curves of the [1120]-oriented wafers were smaller than the analogous values acquired from the (0001) materials. Hydrogen etching of the former surface for 5 and 30 minutes reduced the RMS roughness from 0.52 nm to 0.48 nm and to 0.28 nm, respectively; the RMS roughness for a 30 μm (1120) film was 0.52 nm. Micropipes in the substrates did not thread beyond the film-substrate interface. The separation distance between stacking faults was determined to be 10 μm by transmission electron microscopy. Hall mobilities and carrier concentrations of 12,200 cm2/Vs and 3.1×1014 cm−3 and 800 cm2/Vs and 7.4×1014 cm−3 were measured at 100°K and 300°K, respectively. Photoluminescence indicated high purity. 4H-SiC(1120) PiN devices exhibited average blocking voltages to 1344 V and a minimum average forward voltage drop of 3.94 V.
Characterization of Defects Generated During Boron Diffusion in SiC
Authors: Lin Xue-feng , Smith Stephen P. , Ma Xianyun , Wang Liang , Sudarshan Tangali S. , Zhang Qingchun , Chang Hsueh-Rong
Published: April 2011

The defects associated with the implantation and diffusion of boron in silicon carbide have been studied using secondary ion mass spectrometry (SIMS) and photoluminescence (PL) imaging and spectroscopy. An n-type epitaxial SiC (1000) substrate was implanted with 2×1014 atoms/cm2 B and annealed to 1700°C. PL data was acquired before and after annealing, and following removal of various thicknesses of the sample by mechanical polishing. Thermal annealing generated a B diffusion profile measured by SIMS to extend to about 3 microns depth. After removing the diffused B layer, a PL spectral feature at 415nm disappeared, which is consistent with its previous identification as arising from donor-acceptor pairs (DAP). The D1 spectral features survived polishing, supporting previous suggestions that these features are intrinsic defects due to the di-interstitial (Ic-Ic or Isi-Isi) or di-vacancy (Vc-Vc or Vsi-Vsi) defects.