bluuebunny/crossref_metadata_2025 huggingface dataset:
Lattice Parameter Change of BaSrTiO3 Films Grown by Pulsed Laser Deposition
Authors: Kim W.J. , Chang W. , Qadri S.B. , Horwitz J.S. , Chrisey D.B.
Published: April 2011

Single phase Bao0.5Sro0.5TiO3 films with three different thicknesses (40, 80, and 160 nm) have been deposited onto MgO substrates by pulsed laser deposition (PLD). The lattice parameters for the thin film have been measured using x-ray diffraction. The deposited films all show a significant tetragonal distortion. The in-plane lattice parameters for all film thickness are always larger than surface normal lattice parameters for as-deposited films. Films (80 and 160 nm) annealed at 900, 1100, and 1200 °C for 6 hours after deposition show reduced tetragonal distortion compared to as-deposited films. Further, tetragonal distortion of annealed films with thicknesses of 80 and 160 nm were reduced with decreasing annealing temperature from 1200 °C to 900 °7, while that with a thickness of 40 nm is increased with decreasing annealing temperature. This result indicates that the stress due to lattice mismatch and thermal expansion difference changes as a function of film thickness.
Growth and Characterization of Lithium Niobate Thin Films on Diamond/Si(100) Substrates
Authors: Wang Shunxi , Su Qingxin , Robert Marc A. , Rabson Thomas A.
Published: April 2011

A low temperature metal-organic decomposition process for depositing LiNbO3 thin films on diamond/Si(100) substrates is reported. X-ray diffraction studies show that the films are highly textured polycrystalline LiNbO3 with a (012) orientation. Scanning electron microscopy analyses reveal that the LiNbO3 thin films have dense, smooth surface without cracks and pores, and adhere very well to the diamond substrates. The grain size in the LiNbO3 thin films is in the range of ∼0.2-0.5 μm. The effect of the processing procedures on the surface morphology of the LiNbO3 films is investigated. Possible reasons for the elimination of microcracks in the LiNbO3 films are discussed.
Light-Induced Structural Phase Transition in Confining Gallium and Associated Gigantic Optical Nonlinearity
Authors: Albanis V. , Dhanjal S. , Emelyanov V. , Petropoulos P. , Richardson D. J. , Zheludev N. I.
Published: April 2011

We report a light-induced, surface-assisted structural phase transition from a common orthorhombic phase of crystalline gallium (α-gallium) to a highly reflective, metastable phase of more ‘metallic’ nature. The transition has been observed at the interface of gallium with fused silica at temperatures just below the metal's bulk melting point and affects only several tens of gallium atomic layers. The transition is fully reversible and occurs on a nanosecond/microsecond time scale. The transition appears to show some characteristic features of a second order structural phase transition, including an increase of the transition relaxation times at the critical temperature (of approximately 30°C). The transition has no apparent optical intensity threshold, and is induced by radiation of very low intensity of only 10−4 − 10−5 W/μm2. The two gallium phases involved in the phase transition have significantly different dielectric properties which gives rise to a gigantic cubic optical nonlinearity, χ(3) ∼ 1 esu. The transition can be stimulated by light at any wavelength in the visible and the infrared ranges out to at least 1.55μm. The effect is therefore of great interest for applications requiring light by light control at milliwatt power levels.
Recent Advances in Simulation of Dendritic Polymers
Authors: Çağin Tahir , Miklis Paul J. , Wang Guofeng , Zamanakos Georgios , Martin Ryan , Li Hao , Mainz Daniel T. , Nagarajan Vaidehi , Goddard William A.
Published: April 2011

Dendrimers and hyperbranched polymers represent a revolution in methodology for directed synthesis of monodisperse polymers with enormous possibility of novel architectures. They demonstrate ability to attain micelle-like structures with distinct internal and external character. Furthermore polyfunctional character of dendrimers allows varied response to environment and promise as selective sensors, carrier for drugs, encapsulation of toxic chemicals and metals. One of the key problems are the characterization of the structures. Theory and simulation can be essential to provide and predict structure and properties. Here, we present some recent advances in theory, modeling and simulation of dendritic polymers.
Simulation of Thermal Stability and Friction: A Lubricant Confined Between Monolayers of Wear Inhibitors on Iron Oxide
Authors: Çağin T. , Zhou Y. , Yamaguchi E. S. , Frazier R. , Ho A. , Tang Y. , Goddard W. A.
Published: April 2011

To understand antiwear phenomena in motor engines at the atomic level and provide evidence inselecting future ashless wear inhibitors, we studied the thermal stability of the self-assembled monolayer(SAM) model for dithiophosphate (DTP) and dithiocarbamate (DTC) molecules on the iron oxidesurface using molecular dynamics. The interactions for DTP, DTC and Fe2O3 are evaluated based on aforce field derived from fitting to ab initio quantum chemical calculations of dimethyl DTP (and DTC)and Fe(OH)2(H2O)2-DTP (DTC) clusters. MD simulations at constant-NPT are conducted to assesrelative thermal stabilities of the DTP and DTC with different pendant groups (n-propyl, i-propyl, npentyl.and i-pentyl). To investigate frictional process, we employ a steady state MD method, in whichone of the Fe2O3 slabs maintained at a constant linear velocity. We obtain the time averaged normaland frictional forces from the interatomic forces. Then, we calculated the friction coefficient at theinterface between SAMs of DTP and the confined lubricant, hexadecane, to assess the shear stability ofDTPs with different pendant groups.
Impurity Induced Slowing oF Nucleation in Emulsified Liquids
Authors: Herhold Amy , Ertaş Deniz , Levine Alex J. , King H. E.
Published: April 2011

We report detailed nucleation studies on the liquid -to -solid transition of hexadecane using nearly monodisperse hexadecane -in -water emulsions. A careful consideration of the kinetics of isothermal and nonisothermal freezing show deviations from predictions of classical nucleation theory, if one assumes that the emulsion droplet population is homogeneous. Similar deviations have been observed previously [3]. As an explanation, we propose a novel argument based on the dynamic generation of droplet heterogeneity mediated by mobile impurities. This proposal is in excellent agreement with existing data.
Plasma Deposition of Diamond-Like Carbon and Carbon-Nitride Films in an Electron Cyclotron Resonance-Radio Frequency Discharge
Authors: Turban Guy , Zarrabian Marjan , Hong Junegie
Published: April 2011

Hydrogenated and nitrogenated amorphous carbon films, a-C:H and a-C:H:N, were elaborated by Plasma Enhanced Chemical Vapor Deposition (PECVD) in a dual Electron Cyclotron Resonance - Radio Frequency (ECR-RF) discharge of methane and/or nitrogen. The use of a low pressure plasma (2.6 mTorr) and a capacitive coupling of the substrate, separately from the electrical power of the ECR source, leads to reach new conditions of preparation. The ions and radicals fluxes, Φi and ΦR, determined respectively from the Langmuir probe measurements and the Mass Spectrometry (MS) give a ratio ΦR/Φi of order of 20. The CH3 radicals were identified and their concentration was measured from the technique of threshold ionization. It is shown that, even at low pressure, numerous ion-molecule reactions take place in the gas phase which explain the formation of major ions CH5+. and C2H5+.
The plasma-surface interaction is studied by in-situ kinetic ellipsometry and by ex-situ X-ray Photoelectron Spectroscopy (XPS) measurements of deposited films. The role of the impact energy of ions, during the growth of films, is studied by Ultra-Violet-Visible spectroscopic ellipsometry.
A new technique of deposition by alternating sequences of «C H4 deposition - treatment by N2, plasma » is described in this paper. The resulted a-C:H:N films are compared to those elaborated from CH4-N2 plasmas. The aim of the discussion on the presented results is to better understand the mechanism of the growth of amorphous carbon films by PECVD.
Surface Immobilization of Synthetic Proteins Via Plasma Polymer Interlayers
Authors: Griesser Hans J , McLean Keith M , Beumer Gerrit J , Gong Xiaoyi , Kingshot Peter , Johnson Graham , Steele John G
Published: April 2011

Coatings of biologically active molecules on synthetic ”bulk“materials are of much interest for biomedical applications since they can in principle elicit specific, predictable. controlled responses of the host environment to an implanted device. However, issues such as shelf life. storage conditions, biological safety, and enzymatic attack in the biological environment must be considered; synthetic proteins may offer advantages. In this study we investigated the covalent immobilization onto polymeric materials of synthetic proteins which possess some properties that mimic those of the natural protein collagen, particularly the ability to form triple helical structures, and thus may provide similar bio-responses while avoiding enzymatic degradation. In order to perform immobilization of these collagen-like molecules (CLMs) under mild reaction conditions, the bulk materials are first equipped with suitable surface groups using rf plasma methods. Plasma polymer interlayers offer advantages as versatile reactive platforms for the immobilization of proteins and other biologically active molecules. Application of a thin plasma polymer coating from an aldehyde monomer is particularly suitable as it enables direct immobilization of CLMs by reaction with their terminal amine groups, using reductive amination chemistry. An alternative route is via plasma polymer layers that contain carboxylic acid groups and using carbodiimnide chemistry. A third route makes use of alkylamme plasma polymer interlayers, which are less process sensitive than aldehyde and acid plasma coatings. A layer of poly-carboxylic acid compounds such as carboxylic acid terminated PAMAM-starburst dendrimers or carboxymethylated dextran is then attached by carbodiimide chemistry onto the amine plasma layer. Amine-terminated CLMs can then be immobilized onto the poly-carboxylic acid layer. Surface analytical methods have been used to characterize the immobilization steps and to assess the surface coverage. Initial cell attachment and growth assays indicate that the biological performance of the CLMs depends on their amino acid sequence.
Highly Transparent Arcproof Films for Space Applications
Authors: Adorjan A. J. , Alexander C. , Blanchard T. L. , Bruckner E. , Ferrante R. , Gajdos S. M. , Mayer K. , Pal A. M. , Walters P. A. , Hambourger P. D. , Dever J. A. , Rutledge S. , Fu Henry
Published: April 2011

Highly transparent films with tailorable sheet resistivity were prepared by ion-beam sputtering of indium tin oxide (ITO) with MgF2or SiO2in the presence of high-purity air. Sheet resistivities of 103−101ohms/square (ω/–) and visible transmittances as high as 92% (not corrected for substrate absorption) were obtained in films ∼30 nm thick. Resistivity increased by as much as two orders of magnitude in the first year after preparation; however, thicker films (e.g. 80 nm) were much more stable but somewhat less transparent. Preliminary data from exposure of film samples to atomic oxygen in a plasma asher indicate minimal degradation in optical properties. Heat-treating pure ITO in air produced transparent, slightly conductive films but with poorer stability of sheet resistivity in air than co-deposited ITO with either SiO2, or MgF2. Electrical transport measurements yielded new information on the electronic properties of ITO and related materials. These films show promise as low-absorption static bleedoff coatings for space photovoltaic arrays as well as CRT faceplates and other commercial applications.
Rare Earth Doped Yttrium Aluminium Garnet (YAG) Selective Emitters
Authors: Chubb Donald L. , Pal AnnaMaria T. , Patton Martin O. , Jenkins Phillip P.
Published: April 2011

As a result of their electron structure, rare earth ions in crystals at high temperature emit radiation in several narrow bands rather than in a continuous blackbody manner. This study presents a spectral emittance model for films and cylinders of rare earth doped yttrium aluminum garnets. Good agreement between experimental and theoretical film spectral emittances was found for erbium and holmium aluminum garnets. Spectral emittances of films are sensitive to temperature differences across the film. For operating conditions of interest, the film emitter experiences a linear temperature variation whereas the cylinder emitter has a more advantageous uniform temperature. Emitter efficiency is also a sensitive function of temperature. For holminum aluminum garnet film the efficiency is 0.35 at 1446K but only 0.27 at 1270 K.
Artificial Effects on Cryogenic Fracture Toughness of the Main Structural Alloy for the Super Light Weight Tank
Authors: Chen P.S. , Stanton W.P.
Published: April 2011

At Marshall Space Flight Center (MSFC), a new aging technique has been developed that can significantly enhance the cryogenic fracture toughness (CFT) of Alloy 2195, as well as reducing the statistical spread of fracture toughness values. This technique improves cryogenic properties by promoting T1 nucleation and growth in the matrix, so that T1 nucleation and growth can be suppressed in the subgrain boundaries. It also minimizes mechanical property scatter due to unavoidable variations in thermomechanical processing parameters and alloy chemistry.
Fatigue-Crack Propagation in Gamma-Based Titanium Aluminide Alloys at Large and Small Crack Sizes
Authors: Kruzic J. J , Campbell J. P , Ritchie R. O.
Published: April 2011

Most evaluations of the fracture and fatigue-crack propagation properties of γ + α2titanium aluminide alloys to date have been performed using standard "large-crack" samples, e.g., compact-tension specimens containing crack sizes which are on the order of tens of millimeters, i.e., large compared to microstructural dimensions. However, these alloys have been targeted for applications, such as blades in gas-turbine engines, where relevant crack sizes are much smaller (<500 µm) and where the small-crack fatigue threshold may be the most relevant design parameter. In this study, we compare and contrast the cyclic crack-growth behavior of both large (a > 5 mm) and small (c ∼ 25–300 µm) cracks in a γ-TiAl based alloy, of composition Ti-47A1–2Nb-2Cr-0.2B (at%), specifically for duplex (average grain size ∼17 µm) and refined lamellar (average colony size ∼150 µm) microstructures. It is found that, whereas the lamellar microstructure displays far superior fracture toughness and fatigue-crack growth resistance in the presence of large cracks, in small-crack testing the duplex microstructure exhibits a better combination of properties. The reasons for such contrasting behavior are examined in terms of the intrinsic and extrinsic (i.e., crack bridging) contributions to cyclic crack advance.
Solute Partitioning and Interfacial Segregation in TiAl-Based Alloys
Authors: Larson D. J. , Miller M. K.
Published: April 2011

Atom probe microscopy has been used to investigate elemental partitioning and segregation behavior in a TiAl-based alloy with a variety of alloying additions including Cr, Nb, W and B. These results indicate that in a stress-relieved state (2 h at 900°C) and a reheated state (2 h at 900°C, 2184 h at 800°C and 2 h at 1210°C) chromium, and to a lesser extent tungsten, is partitioned to the α2phase. However, in an annealed state (2 h at 900°C and 720 h at 800°C), these elements are partitioned to the, γ phase. Segregation of chromium and tungsten to lamellar interfaces is observed in the stress-relieved material, but significant segregation was not observed in material subjected to the other heat treatments. A W- and B-enriched precipitate was observed in the reheated material and provides a possible explanation for the low tungsten concentrations measured in the matrix phases.
Deformation of Polysynthetically Twinned TiAl Single Crystals with Near-Hard Orientations
Authors: Kim Min-Chul , Nomura M. , Vitek V. , Pope D. P.
Published: April 2011

Compression tests were performed on specially-oriented PST TiAl crystals to which strain gages were attached in order to precisely measure the three axial strains in the samples during deformation. It was found that all samples deform by plane strain except when the compression axis is nearly perpendicular to the lamellar planes. This measurement technique was used to determine the orientations in which the various slip systems are operative in PST samples, and this, in turn was employed to explain the shape of the flow stress vs. orientation curve. An important component of this explanation is the fact that slip of ordinary dislocations and twinning are closely coupled in this material, implying that the twinning must occur relatively slowly-at about the same rate that ordinary dislocations move. Atomistic calculations have shown that a slow twinning process is to be expected in this material at low temperatures, perhaps even by a thermally activated process.
Processing and Properties of FeAl Sheets Obtained by Roll Compaction and Sintering of Water Atomized Powder
Authors: Deevi S. C. , Hajaligol M. R. , Sikka V. K. , McKernon J. , Scorey C. R.
Published: April 2011

The low ductilities of FeAl alloys led us to explore powder metallurgical processing technology to obtain sheets of 0.2mm thickness as opposed to manufacturing processes based on hot rolling of cast FeAl alloys. In our approach, water atomized FeAl powders were roll compacted to 0.66mm with a polymeric binder using two counter rotating rolls to a green density of 3.1 g/cc. Roll compacted green sheets were then de-bindered in nitrogen in the temperature range of 300 to 600°C for several hours prior to sintering the sheets in vacuum. Sintered sheets were rolled down from 0.66 to 0.20 mm in three different stages resulting in a total reduction of 69% Vacuum annealing of the sheets was carried out between each stage of the reduction process to eliminate edge cracking associated with the work hardening of the FeAl. The properties of the FeAl sheets depend on the Al content, annealing temperature and time in a vacuum furnace. The fine microstructure of FeAl sheets led to tensile elongations of 4 to 6%. The sheets are formable at room temperature, and possess excellent mechanical properties both at room and high temperatures.
Directional Solidification of Mo5Si3-MoSi2 Eutectic
Authors: Borowicz S. M. , Heatherly L. , Zee R. H. , George E. P.
Published: April 2011

The Mo-Si phase diagram exhibits a Mo5Si3-MoSi2 eutectic at the 54% Si composition. Since the terminal phases have comparable melting points and are equidistant from the eutectic composition, there is the possibility of obtaining lamellar microstructures in this system. In addition, if the alloys are directionally solidified, there is the further possibility of obtaining aligned lamellae. In this study, a high temperature (xenon-arc-lamp) optical floating zone furnace is utilized to directionally solidify Mo-Si alloys of the eutectic composition. Growth conditions are systematically varied to investigate their effects on the solidification microstructure. Growth rates and rotation speeds are identified that result in lamellar microstructures.
Point Defect Behavior in B2-Type Intermetallic Compound FeAl
Authors: Haraguchi T. , Kogachi M.
Published: April 2011

Point defect behavior in B2-type FeAI alloys is investigated from a thermodynamic point of view, based on the Bragg-Williams method. The model is developed by taking new defect formation mechanisms, random vacancy distribution (RVD), and antisite atom recovering (ASAR), into consideration, which were proposed based on the current findings in in situ neutron and X-ray diffraction studies for the B2 FeAl. The condition for appearance of the RVD and ASAR states is given. Application of this model to B2 FeAl alloys shows that the RVD-like behavior is reproduced in the Ferich composition region and also a rapid increase in vacancy concentration observed in the Al-rich region can be interpreted by the ASAR process by antisite Al atoms.
Processing and Properties of Mo5Si3 Single Crystals and Alloys
Authors: Chu F. , Thoma D. J. , McClellan K. J. , Peralta P. , Li F. X. , Fodran E.
Published: April 2011

Among the high-temperature intermetallic systems, transition-metal silicides are attractive because of their high melting temperatures (many greater than 2273 K) and potential oxidation resistance. In particular, Mo5Si3 exhibits a very high melting point (2453 K) and also has a solubility range of 2 – 3 atomic percent, which can aid in processing and alloy design strategies. The focus of this study is to evaluate the processing and properties of Mo5Si3 and Mo5Si3-base ntermetallics. For the optimal baseline comparison, high-purity single crystals have been fabricated, and thermal and elastic properties have been experimentally measured. Although Mo5Si3 has a strong thermal expansion anisotropy, ts elastic anisotropy factors and the Poisson's ratios indicate that Mo5Si3 is less anisotropic in elasticity. The combination of the thermal and elastic properties has been employed to calculate the thermal residual stress and to explain the potential for grain boundary cracking during processing. Room temperature Vickers indentation tests of Mo5Si3 have been performed. The orientation dependence of hardness and fracture toughness of Mo5Si3 single crystals have been obtained. The corresponding deformation and fracture modes have been revealed by microscopy studies. Finally, micro- and macroalloyed Mo5Si3 with aluminum and boron will be briefly explored with property assessments.
Deformation of Two-Phase Alloys Based on C15 Laves Phase HfV2 + Nb
Authors: Kimura Yoshisato , Luzzi D. E. , Pope D. P.
Published: April 2011

To investigate the deformation behavior of the C15 HfV2+Nb Laves phase, compression tests were conducted on the C15/bcc two-phase alloys at very low temperatures down to 4.2 K. Transmission electron microscopy revealed that substantial mechanical twinning takes place in the C15 Laves phase at room temperature and 77 K. A deep minimum in the flow stress, with a drop of nearly 500 MPa, appears at around 77 K for the C15/bcc two-phase alloy. Since no such anomaly is seen in the bcc phase, we believe that the cause of this can be attributed to mechanical twinning in the C15 Laves phase. A high density of ultra-fine twin bands is the characteristic feature of twinning in the C15 matrix. We also investigated the phase relations between the C15 HfV2 Nb and bcc (V, Nb) solid solution in the Hf-V-Nb ternary system in an attempt to understand why we were unsuccessful in our attempts to grow single crystals of the Laves phase.
Nature of Slip in γ-Titanium Aluminide Above the Yield Stress Anomaly Temperature
Authors: Jiao S. , Bird N. , Hirsch P. B. , Taylor G.
Published: April 2011

Crystals of γ-TiAl, containing ∼54.5 at% Al, with various orientations were deformed at different temperatures and examined by transmission electron microscopy (TEM). It was found that while in many cases slip and climb of ordinary dislocations tend to predominate, slip by [001] dislocations can be important also. The occurrence of [001] slip has not been reported before. The values of critical resolved shear stress were determined and strong locks on [001] dislocations have been identified as local segments of ½ ⟨112] dislocations arising from interactions between [001] and ½⟨110] dislocations.
High-Resolution Electron Microscopy of Dislocation Cores in NiAl
Authors: Stöckle D. , Sigle W. , Seeger A.
Published: April 2011

The atomic structure of dislocation cores in NiAl is studied by high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) calculations. Results are presented on dislocations with Burgers vectors b=a<100> and a<111>. A comparison with HRTEM image simulations indicates that the core of a 45° a <100> dislocation consists of Al atoms. The Burgers vector distribution shows a width of 2.2b. This corresponds very closely to MD results and is consistent with the relatively low Peierls stress of this dislocation. By detailed image analysis the angular dependence of the shear stress components of the dislocation are made visible. MD results obtained from 45° dislocations with opposite screw components suggest, that the helicity of the screw component might be discernible from high-resolution electron micrographs. A a<111> dislocation with <110> line direction is shown which exhibits a rather wide dissociation, probably into two a/2<111> partials.
Atom Clusters In A 2/1 Cubic Approximant Phase For Understanding The Structures Of Icosahedral Phases
Authors: HIRAGA K.
Published: April 2011

Two types of atom clusters found in the β-(A1PdMnSi) cubic phase, referred to as a 2/1 crystalline approximant, with a composition of approximately Al70Pd23Mn6Si1which is near to the composition Al72Pd20Mn8of the icosahedral phase, are discussed in detail for understanding the structure of the Al-Pd-Mn icosahedral phase. A large dodecahedral atom cluster located at the body-centered position can be divided into 19 atom shells with approximately icosahedral symmetry, and a dodecahedron of the 12th shell internally touches the surface of the cubic unit cell with a lattice constant of 2.0211 nm. At each vertex of the dodecahedron, a small icosahedral atom cluster consisting of 12 Al atoms surrounding a central Pd atom is located. The dodecahedron is connected to each other by edge-sharing, namely by sharing two small icosahedral atom clusters, along the twofold rotational direction, and forms a simple-cubic packing of the atom cluster in the β-(AlPdMnSi) cubic phase. Another atom cluster located at the origin fills up gaps of the simple-cubic packing of the large dodecahedral atom cluster. By using the dodecahedral and bridging atom clusters, the structure of the Al-Pd-Mn icosahedral quasicrystal is discussed.
The Atomic Structure Of The Zn-Mg-Rare-Earth Quasicrystals Studied By High-Resolution Electron Microscopy
Authors: Abe Eiji , Tsai An Pang
Published: April 2011

High-resolution transmission electron microscopy has been applied to study the real atomic structure of the decagonal (d-) quasicrystal in the Zn-Mg-rare-earth (RE) system, which is the first d-phase based on Frank-Kasper phase. We show that the phase has a novel structure in which the atomic arrangement in the tenfold symmetry plane can simply be interpreted as the Penrose tiling decorated by individual atoms - the simplest realization of the Penrose tiling as a real atomic structure. This is supported by the fact that a similar local atomic configuration exists in the Zn7Mg4crystal structure. This simple structural model is in sharp contras to the idea of atomic clusters, which has been successfully used to describe the structure of quasicrystals in Altransition metal alloys. The present results strongly suggest that the symmetric atomic clusters are not an essential factor for formation of quasicrystals. Instead, a new idea ofquasi-unit-celland itscoveringis applied for structural description. The atomic structure of the Zn-Mg-RE icosahedral phase is also implied to follow the present concept, based on the fact that its related crystalline phases with hexagonal lattices are not built of giant atomic clusters with icosahedral symmetry.
Numerical Simulations Of Plasticity And Fracture In Quasicrystals
Authors: Trebin Hans-Rainer
Published: April 2011

Dislocation motion and crack propagation are studied in model quasicrystals both by geometrical considerations and large scale molecular dynamics simulations. It turns out that two characteristic features of quasicrystals govern plasticity and the rough appearence of cleavage planes: the phason degree of freedom and the cluster structure.
Electronic Structure Of Quasicrystals
Authors: Belin-Ferré E.
Published: April 2011

The study of the electronic structure of quasicrystals is still a matter of investigations to date. The paper will report several significant experimental results obtained through spectroscopic techniques which involve the bulk material as well as the surface. Comparison is made with data from related crystalline alloys, densities of states calculations and structural models available for icosahedral quasicrystals.
Containerless Solidification Studies Of The 1/1 Phase IN TI-(MN, CRFE)-SI-O Alloys
Authors: Croat T. K , Kelton K. F. , Holland-Moritz D. , Rathz T. J. , Robinson M. B.
Published: April 2011

The nucleation behavior of the 1/1 quasicrystal approximant phase was investigated in Ti-TMSi- O (TM=Mn, Cr, Fe) alloys made near the stoichiometric composition. Containerless solidification studies were performed using electromagnetic (rf) levitation and drop-tube techniques. The solidification microstructures indicate that α-Ti nucleated first in Ti-Cr-Si-O and β-Ti in Ti-Mn-Si-O alloys; the 1/1 phase nucleated and grew on these titanium oxide dendrites. In Ti-Fe-Si-O alloys, the 1/1 phase nucleated and grew directly from the liquid, allowing information on the nucleation rates to be obtained from undercooling data.
Ti/Zr-Based Quasicrystals - Formation, Structure And Hydrogen Storage Properties
Authors: Kelton K. F.
Published: April 2011

Most common in Al-3d transition metal(TM) alloys, icosahedral quasicrystals (i-phase) are also found frequently in Ti/Zr-TM alloys. The Ti-TM-Si-O quasicrystals are metastable, produced only by rapid quenching, and are extremely disordered. In contrast, Ti-Zr-Ni i-phases are well ordered and stable, produced by relatively low temperature annealing, nearly 300°C below the melting temperature. Important for both basic and practical reasons, Ti/Zr-based quasicrystals can absorb significant quantities of hydrogen, up to two hydrogen atoms for each metal atom. The formation and structures of these quasicrystals and closely related complex crystal phases are discussed. The hydrogenation properties of these quasicrystals are presented and shown to be competitive with materials in current use for hydrogen storage and battery applications. Results from recent studies using hydrogen as a probe of the local structure of the quasicrystal and crystal approximant are presented.
Determination of Local Fiber Texture in Liquid Crystal Polymer by Electron Diffraction
Authors: Taylor J. , Libera M. , Greeley M.
Published: April 2011

The rigid chain microstructure of thermotropic liquid crystal polymers (TLCPs) permits an ordered morphology to form consequently giving these materials exceptionally high strength. X-ray and neutron scattering techniques effectively determine the semi-crystalline structure of TLCP but lack the spatial resolution needed to detect morphological changes occurring on sub-micron length scales. This research develops an electron optical technique to resolve the local orientation of LCP fibers at resolutions on the order of 100-300 nm. This paper outlines the essential elements of this technique and presents preliminary results showing systematic morphological changes of LCP fiber as a function of position across the fiber diameter.
Microstructure and Morphology of Thermotropic Amphiphilic Liquid Crystalline Materials
Authors: Jung Hee-Tae , Hudson Steven D. , Percec Virgil
Published: April 2011

Electron microscopy methods have been used to investigate the structure and morphology of a hexagonal columnar mesophase, formed by novel amphiphilic and dendrimeric liquid crystals. Alignment of the columns is examined by a surface condition that is suitable for the molecular architecture. For all the materials investigated, columns aligned perpendicular to an evaporated carbon surface. In the case of asymmetric amphiphilic compounds, planar alignment of asymmetric compounds was induced by a water surface. However, planar alignment on water was not possible for a symmetric dendrimer. Based on analysis of electron diffraction and images, the dimension and the stiffness of columnar assemblies is found to depend on molecular architecture.
Liquid Crystalline Zinc Chloride
Authors: Martin J. D. , Thornton T.A.
Published: April 2011

The templated syntheses of our zeolite-type frameworks of metal halides frequently result in the formation of glassy phases or viscous liquids that might be described as ambient temperature molten salts. Having discovered that certain of these materials exhibit remarkable birefringence, we have investigated the structure of both the glass and liquid forms of alkylammonium templated zinc chloride materials by neutron and X-ray diffraction, as well as DSC and polarizing microscopy techniques. Further template control using alkylammonium surfactants as directors has yielded an entire family of liquid crystalline materials with up to 90% inorganic content. The compositional dependence of the structure of these liquid crystalline phases suggests that these materials are best described as “solvent-free” lyotropic liquid crystals.
Role of the Cholesteric Phase In The Formation Of Twisted Smectic Structures
Authors: Suh S. W. , Campbell A. L. , Patel J. S.
Published: April 2011

The smectic structure obtained by cooling the material from the cholesteric phase often produces different structures in the twisted ferroelectric configuration, which depends not only on the nature of the material, but also on the rate of cooling. In this paper, we have investigated the origin of this behavior and have concluded that the twist in the cholesteric phase is responsible for the apparent unpredictability. Furthermore, we show that for a given chirality of material and the same rubbing condition at the surface, two possible smectic domains are produced. While the electro-optic properties of both these domains show gray-scale capabilities, these domains have different optical properties. This comparison was made possible by using a specially prepared sample in which we rubbed two glass plates, each with two areas in which the rubbing direction was both horizontal and vertical. Using this sample, we have been able to show that the presence of pitch inversion close to the cholesteric to smectic phase transition is the apparent reason the results can not be reproduced. Furthermore, our experiments clarify the importance of sample cooling rate. If rapidly cooled during the fabrication from the cholesteric to the smectic phase, the sample retains a memory of the non-equilibrium pitch, providing us with a means to capture the desired pitch. This important discovery will aid us in modifying the material as well as carefully tailoring its pitch in order to insure that cooling of the cholesteric material leads naturally to the twisted smectic structure.
Microstructural Development of Dispersion Strengthened Cu Thin Films
Authors: Weiss D. , Kraft O. , Arzt E.
Published: April 2011

The internal oxidation method is applied for the first time to produce a fine dispersion of second phase particles in thin films. A processing route is presented which includes ultra-high vacuum magnetron sputtering of about 1 μm thick alloy films onto Si substrates followed by in situ annealing and oxidation. Two different Cu-base alloys are examined, Cu-Y and Cu-Al, in which the extent of miscibilitiy differs significantly. This has considerable influence on the grain growth behavior. Nanoindention and wafer-curvature experiments show a drastic improvement of both room-temperature and high-temperature strength. Phenomena well known from bulk oxide-dispersion strengthened (ODS) alloys are found to appear in the thin films as well: Results on abnormal grain growth and the formation of creep voids are presented and discussed in terms of particle effects.
Magnetic and Structural Properties of Laser-Ablated Planar and Cylindrical Co Thin Films
Authors: Madurga V. , Vergara J. , Ortega R. J. , de Landazabal I. P. , Favieres C.
Published: April 2011

Planar and cylindrical Co thin films have been obtained by pulsed laser ablation. X-ray diffractograms have shown no crystalline structure for the as-deposited samples, while the 450 °C annealed samples exhibit Co fcc crystalline peaks. The Scanning Tunnelling Microscopy has revealed a small increase of the surface roughness for the annealed films. The Hall effect has been used to determine the value of the spontaneous magnetization, Ms, at room temperature; Ms ≈ 14 kgauss for the as-deposited sample and Ms ≈ 17.6 kgauss for the 450 °C annealed sample. From transverse magnetooptic Kerr effect, it has been found that the as-deposited samples exhibit magnetic bistability, with a coercive field, Hc, °C. Besides, it has been observed an increase of H, up to ≈ 50 Oe, when the annealing temperature increases. The vibrating sample magnetometry has confirmed these results, showing that the magnetization participating in the magnetooptic effect for these low fields is the total spontaneous magnetization of these samples. Moreover, the cylindrical films exhibit magnetoelastic behavior when they are subjected to angular deformation. It has been found that the saturation magnetostriction constant is negative.
Structure and Magnetic Properties of Fe-N Thin Films Grown by ECR Deposition
Authors: émeth Š , Akinaga H. , Boeve H. , Bender H. , de Boeck J. , Borghs G.
Published: April 2011

The growth of FexNy thin films on GaAs, In0.2Ga0.8As, and SiO2/Si substrates using an ultra high-vacuum (UHV) deposition chamber equipped with electron cyclotron resonance (ECR) microwave plasma source is presented. The structural properties of the deposited films have been measured using various techniques as x-ray diffraction (XRD), Auger electron spectroscopy (AES), and transmission electron microscopy (TEM). The results of XRD measurements show that the films consist of a combination of α-Fe, α'-Fe, y-Fe4N, and α”- Fe16N2 phases. The depth profiles, calculated from the Auger peak intensities, show a uniform nitrogen concentration through the films. The TEM reveals a columnar structure of these films. The properties of the different Fe-N layers have been exploited in the fabrication of Fe(N) / FexNy / Fe trilayer structures, where Fe(N) means a slightly nitrogen doped Fe film. The magneto-transport properties of this trilayer structure grown on In0.2Ga0.8As substrates are presented.
Structure, Electrical and Magnetic Properties of Thin Films of La1−xMxMnO3 on Si
Authors: Mateeva N. N. , Hogan P. C. , Dahmen K. H.
Published: April 2011

Thin films of lanthanum manganates doped with Ca2+, Sr2+, Ba2+ and Pb2+ have been deposited on Si(100) substrate and their electrical and magnetic properties were discussed with respect to the composition, structure and nature of the dopant. Buffer layers of YSZ and La0.8Al0.2O3 were employed and their effect on the materials was studied. Interesting magnetotransport properties were found in some of the films, where there is a large difference between the insulator-metal transition temperature and a ferromagnetic transition temperature.
Film Thickness Monitor for CMP Processing
Authors: Kondo Noriyuki , Hayashi Takahisa , Atsuta Hitoshi , Horie Masahiro , Yoshida Masao , Kimura Norio , Tsujimura Manabu , Yano Hiroyuki , Okumura Katsuya
Published: April 2011

In the CMP planarization process, detecting the final polishing point is extremely important for maintaining high yield rates. Therefore, various methods for detecting the final polishing point have been developed.

We consider it vital that the SiO2 film thickness across a representative area be measured extremely precisely at high speed in the final stages to accurately control film polishing. However, up until now there has not been any wholly satisfactory method to achieve this.

In order to measure a fine representative film area (test pattern) both rapidly and accurately, we concluded that the non-contact, non-destructive and highly reliable methods of spectrometric analysis were most promising.

Based on these considerations, we developed a compact spectrometric film thickness measurement system which can accurately inspect test patterns at high speeds and installed it adjacent to the CMP equipment's polishing table. Using this system as a film thickness monitor, we can now measure film thickness while rinsing away slurry contaminants, halt polishing at any stage, and calculate the remaining polishing time from the current and desired thicknesses.

This system's pattern identification function can automatically measure the film thickness with very fine test patterns (as small as 40 square microns). When used with SiO2 single layer films, the experimental prototype's measurements proved reliably reproducible (showing a deviation of less than 4 nm at 3 σ over repeated trials), and required thirty seconds or less per wafer (including time for pre-alignment and five-point measurement). The system's theoretical basis and actual operations are described below.
Mechanism of a New Post CMP Cleaning for Trench Isolation Process
Authors: Miyashita N. , Mase Y. , Takayasu J. , Minami Y. , Kodera M. , Abe M. , Izumi T.
Published: April 2011

CMP has been revealed as an attractive technique to poly Si of trench planalizing process. Major issues of process integration for that purpose have been post-CMP cleaning process. A new post CMP cleaning process which employed special organic surfactant has been reported in this paper. In general, wafers after CMP process are contaminated by particles and metallic impurities in the case of conventional cleaning method. The contamination introduce the defects into the wafers after oxidation. The contamination was removed by new cleaning method. using DI water containing special organic surfactant and silica particles. The experimental work has focused on critical problems that had to be solved, using AFM, EDX and VPDICP/MS.
Atomically Smooth Ultrathin Oxide Layers on SI(113)
Authors: Müssig H.-J. , Dabrowski J. , Hinrich S.
Published: April 2011

We report the first direct observation of dissociative chemisorption of oxygen molecules on a silicon surface at room temperature via a molecular precursor state. We link this to the fact that smooth oxide layers can be grown easily on Si(113). The process of initial oxidation is discussed in terms of surface diffusion paths and surface stress. First ab initiocalculations help elucidate the favored adsorption sites and the oxidation mechanism. Experimental evidence was found for bond geometries resulting in the quasi-epitaxial growth of a chemisorption layer on the substrate at elevated temperatures (600°C). In contrast to the first stages of Si(001) oxidation, neither defects nor the ejection of Si atoms plays a significant role during the initial oxidation of Si(113).
Bonding Constraints at Interfaces Between Crystalline Si and Stacked Gate Dielectrics
Authors: Lucovsky G. , Phillips J.C.
Published: April 2011

This paper discusses chemical bonding effects at Si-dielectric interfaces that are important in the implementation of alternative gate dielectrics including: i) the character of interfacial bonds, either isovalent with bond and nuclear charge balanced as in Si-SiO2, or heterovalent, with an inherent mismatch between bond and nuclear charge, ii) mechanical bonding constraints related to the average number of bonds/atom, Nay, and iii) band offset energies that are reduced in transition metal oxides due to the d-state origins of the conduction band states. Applications are made to specific classes of dielectric materials including i) nitrides and oxide/nitride stacks and ii) alternative high-K gate materials.
Ultrathin Silicon Dioxide Formation By Ozone On Ultraflat Si Surface
Authors: Kurokawa A. , Maeda T. , Sakamoto K. , Itoh H. , Nakamura K. , Koike K. , Moon D.W. , Ha Y.H. , Ichimura S. , Ando A.
Published: April 2011

We prepared an atomically flat silicon substrate which had a step-terrace structure and observed the topography of the ozone-oxidized surface to clarify whether homogeneous oxidation occurs with ozone. The oxide was formed with high-concentration ozone gas with a thickness of 2.5nm at a temperature of 350°C. The oxide surface still maintained the same step-terrace structure as observed before oxidation, which revealed that ozone-oxidation occurs layer-by-layer and produces an atomically flat oxide. XPS and MEIS analyses show that the stoichiometry of ozone oxide grown at 350°C is the same as that of an oxide grown thermally at 750°C.
Self-Consistent Mosfet Tunneling Simulations—Trends in the Gate and Substrate Currents and the Drain-Current Turnaround Effect with Oxide Scaling
Authors: Massoud H. Z. , Shiely J. P. , Shanware A.
Published: April 2011

This paper discusses the simulation needs of deep-submicron MOSFETs beyond the 100 nm technology generation where the tunneling of carriers through the gate dielectric will become a vital issue in device design, optimization, and characterization. We present simulation results of Tunnel-PISCES, a MOSFET device simulator where tunneling in the gate dielectric is implemented in a self-consistent manner with the device equations in the substrate. Simulation results of trends in the gate, substrate, and drain currents with oxide scaling are presented. The drain-current turnaround effect is explained by considering the role of the voltage drop across the polysilicon gate resistance in determining the device gate tunneling conditions.
Ultrathin Gate Oxide Prepared by Oxidation in D2O for Mos Device Applications
Authors: Kim Hyojune , Hwang Hyunsang
Published: April 2011

We present a novel gate oxidation process using D2O (deuterium oxide) as an oxidizing gas. The electrical and reliability characteristics of ultrathin gate oxide grown in D2O ambient have been investigated. Compared with a control oxide grown in H2O, a oxide grown in D2O exhibits a significant reduction of charge trapping and interface state generation. Based on a secondary ion mass spectroscopy (SIMS) analysis; we found a deuterium rich-layer at the Si/SiO2 interface. The improvement of electrical and reliability characteristics can be explained by the deuterium incorporation at the Si/SiO2 interface.
Spectroscopic Ellipsometry of Ta2O5 ON Si
Authors: Richter C.A. , Nguyen N.V. , Alers G.B.
Published: April 2011

In this paper, we present the results of spectroscopic ellipsometry (SE) studies of Ta2O5 films on Si. Based on these results, we have experimentally determined an effective method for analyzing SE measurements of Ta2O5. A set of CVD-grown Ta2O5 films on silicon – with thicknesses ranging from below 10 nm to approximately 60 nm thick – was investigated by SE in an effort to improve optical film thickness metrology for Ta2O5. The samples were measured across the spectral range 1.5 eV to 6.0 eV by using a well-characterized, high-accuracy rotating-analyzer-type ellipsometer. We present an analysis method, based upon a Tauc-Lorentz parameterization of the optical properties of Ta2O5, that properly describes the SE data. We also demonstrate how optical properties are affected by the presence of an interlayer at the Si/Ta2O5 interface. Our results show small, but meaningful variations in optical parameters resulting from variations in deposition processes and annealing conditions. This work demonstrates that SE can be used successfully to characterize this category of alternate gate dielectrics.