bluuebunny/crossref_metadata_2025 huggingface dataset:
Light Harvesting Molecular Assemblies in the Design of Highly Luminescent Sol-Gel Derived Glasses
Authors: Dulebohn Joel I. , Van Vlierberge Béatrice , Berglund Kris A. , Lessard Ronald B. , Yu Jeong-a , Nocera Daniel G.
Published: March 2011

Sol-gel derived molecular composites exhibiting intense luminescence, induced from efficient energy transduction processes, have been prepared. The composites are comprised of an Eu3+⊂ 2.2.1 cryptate complex or native Eu3+ ion embedded in sol-gel derived titania glass films. The titania glasses contain interconnected porous networks that permit the diffusion of exogenous substrates, such as the salts of benzoic and 4-tert-butylbenzoic acids, through the film. Interaction of the substrate with the embedded lanthanide complex is indicated by enhanced luminescence from the lanthanide ion. The carboxylic acid salts whose electronic excited states are produced upon capture of incident photons, undergo facile transfer of their electronic energy to the lanthanide ion. By monitoring europium ion luminescence, the diffusion constants of the benzoate and 4-tert-butylbenzoate salts have been measured. Although the diffusion of the 4-tert-butylbenzoate is slower than that of benzoate, the overall higher sensitivity of the former is consistent with hydrophobic guest-host interactions. These new molecular composites relying on the immobilization of an absorption-energytransfer- emission molecular assembly in porous, optically transparent ceramic glasses may be useful in the design of practical sensing devices.
Nmr Spectroscopic Investigations of Pbtio3 Sol-Gel Processing
Authors: Ramamurthi S.D. , Payne D.A.
Published: March 2011

Lead titanate gels were prepared by sol-gel processing from lead acetate and titanium isopropoxide in methoxyethanol. In the present study, 1H, and 13C FTNMR spectroscopic and mass spectrometric techniques were used to identify the structures of lead and titanium precursors formed by refluxing lead acetate and titanium isopropoxide in methoxyethanol, respectively. Lead acetate was found to be partially alkoxylated, whereas, the titanium precursor was identified as a dimer with complete alkoxy group exchange. Similar procedures were applied to identify the lead titanium complex formed from lead and titanium precursors.
Laser Densification Modeling
Authors: Chia Taipau , Hench L. L. , Qin Chaobin , Hsieh C. K.
Published: March 2011

A three-dimensional transient model for heat conduction in silica glass is developed. The model simulates a three-dimensional temperature distribution in a silica glass irradiated by a moving CO2laser. Both the reflectivity of the glass surface and the strong attenuation of the laser energy in the glass medium are accounted for by a detailed radiation analysis. The energy absorbed by the glass is determined to be confined in a 10 μm thickness; the laser irradiation is thus treated as a boundary condition. The heat diffusion equation is solved by an alternating direction-implicit method.
Emulsion Precipitation and Characterization of Zirconia
Authors: Shyu Lieh-Jiun , Cambria Frank M.
Published: March 2011

Zirconia and yttria-stabilized zirconia (YSZ) powders were prepared from water/oil emulsions followed by high temperature calcination. The morphology and particle size were correlated with several variables such as composition of emulsions, concentration of starting materials and surfactants, stirring rate, hydrolysis rate and calcination temperature. The powders were characterized according to crystalline phase, particle size distribution, and flow rate. Emulsion precipitation typically yielded spherical zirconia particles which were either solid or hollow. Particle size could be controlled from submicron to a few hundred microns depending primarily on the composition of the emulsion and stirring rate during hydrolysis. SEM/EDX results showed that yttria was uniformly distributed throughout the zirconia particles. The crystalline phase of the powders after calcination at 800°C was entirely non-transformable tetragonal. The flow rate increased with increasing particle size and with increasing sphericity.
Review of Hydrolysis Behavior of Ions in Aqueous Solutions
Authors: Mesmer R. E. , Baes C. F.
Published: March 2011

The word “hydrolysis,” literally “water splitting,” refers here to those reactions of metallic ions with water that liberate protons and produce hydroxy or oxy complexes in solution and precipitate hydroxide or oxide solids. Over the wide range of pH available in water, the strong tendency of hydroxide to bond to and bridge among cations leads to a multitude of species for many of the metals. Properties of the metal ion such as “hardness” and, especially, charge and size, determine the strength of these interactions and the species formed by each. Over 200 mononuclear species have been identified that predominate in dilute solutions across the pH scale. It is the stability of these species that largely determines the pH dependence of the solubility of the oxide or hydroxide solid formed. Both the tendency of the variety of polynuclear species (those containing more than one metal ion) to form and the solubility of the hydrolytic solid correlate with the stability of the first mononuclear species. Other correlations allow one to predict the enthalpy and entropy of a variety of hydrolysis reactions, and therefore the dependence of the stability of hydrolysis products on temperature.
Synthesis of Superconducting Thin Films by Organometallic Decomposition
Authors: Barbe Christophe , Ring Terry A.
Published: March 2011

The discovery of high critical temperature superconducting oxides 1,2 has stimulated intensive research activities aimed not only at understanding the physical mechanisms of superconductivity, but also developing techniques to produce these ceramics in useful forms. A promising application for superconductors is in electronic components industry which has given rise to an interest in the various ways of producing thin films of superconducting materials.
Soluble and Volatile Precursors for the Preparation of Superconducting Films
Authors: Sauer Nancy N. , Garcia Eduardo , Ryan Robert R.
Published: March 2011

Attempts to identify intermediates in an alkoxide-based solution route to films of the high temperature superconductor YBa2Cu3O7 reported by Fahrenholtz et al.[1] have led to the isolation of the first molecular barium-copper cluster, Ba2Cu2(OR)4(acac)4·2 HOR, R = CH2CH2OCH3. The extension of this route to the preparation of the bismuth superconductors has necessitated the investigation of bismuth alkoxide chemistry. Two separate routes to bismuth alkoxides have been examined: the metathesis of the metal halides with NaOR, (R = t-butyl, and diisopropylphenoxide) and the alcoholysis of bismuth amides, Bi(NR2)3, [R = N(SiMe3)2] The alcoholysis preparation gives high yields of several alkoxides suitable as precursors to the high Tc materials. A monomeric bismuth phenoxide, which is targeted as a volatile precursor, and a bismuth t-butoxide cluster have been isolated and stucturally characterized. Solubility and volatility studies have also been undertaken.
Inorganic-Organic Composites (Ormocers) as Structured Layers for Microelectronics
Authors: Popall Michael , Meyer Henning , Schmidt Helmut , Schulz Jochen
Published: March 2011

Enhanced integration, faster signal transmission and reduced size of mounting devices in components for microelectronics requires new patternable materials. Inorganic-organic copolymers (ORMOCERs = ORganically MOdified CERamics), prepared by sol-gel techniques have been developed for interconnection technologies in microelectronics. Photopolymerization is enabled by unsaturated hydrocarbon or epoxide substituents and UV-sensitive initiators. Using a frequency doubled Argonion laser at 257 nm for direct laser writing, patterned layers with high edge quality have been realized. In combination with high breakthrough voltages, low permittivity constants and high bulk resistivities they open interesting aspects for very large system integration techniques (VLSI).
Investigation of Texture and Stress in Undoped Polysilicon Films
Authors: Huang J. , Krulevitch P. , Johnson G.C. , Howe R.T. , Wenk H.R.
Published: March 2011

Undoped LPCVD polysilicon films deposited on thermal oxide and prepared under various process conditions have been investigated for their texture and stress characteristics. Pole figures measured by X-ray diffraction in reflection geometry were used to determine the orientation. distribution function which provides a quantitative description of the texture. Stresses were determined using wafer curvature measurements. Both texture and stress show substantial variation with deposition condition. Textures typically exhibit axial symmetry and appear to be correlated with the sign and magnitude of the stress. Under certain deposition conditions, the stress varies considerably along the tube, with the stress in the wafers at the upstream end being tensile and at the downstream end being compressive.
Characterization of Polysilicon Thin Films by Variable Angle Spectroscopic Ellipsometry
Authors: Xiong Yi-Ming , Snyder Paul G. , Woollam John A. , Krosche Eric R. , Strausser Yale
Published: March 2011

Variable angle spectroscopic ellipsometry was used to characterize polysilicon multilayer structures. Five different multilayer wafers, each containing a polysilicon layer, were studied. Layer thicknesses and compositions were determined at several locations across each wafer. The thickness measurements obtained by ellipsometry are compared with those determined from cross-sectional transmission electron microscopy (XTEM).
High Performance Polysilicon Thin Film Transistors
Authors: Mitra U. , Khan B.A. , Venkatesan M. , Carlson A. , Vaez-Iravani M.
Published: March 2011

Polysilicon TFT characteristics are shown to be dependent on the nature of the polysilicon film used as well as the TFT fabrication process. Best results were obtained when silicon self-implant and regrowth techniques were used together with plasma hydrogenation. TFTs exhibiting a mobility of 115 cm2/V-sec, subthreshold slope of 0.27 V/decade, leakage current below 0.01 pA/μ;m, and an on-off ratio of 10 orders of magnitude have been fabricated.
Polysilicon High-Voltage TFT with Field-Plate-Controlled Offset Region
Authors: Huang T. Y. , Wu I. W. , Lewis A. G. , Chiang A. , Bruce R. H.
Published: March 2011

An improved polysilicon high voltage thin film transistor (HVTFT) structure with field-plate-controlled offset region (FP-HVTFT) is proposed for eliminating the current-pinching phenomena often observed in the conventional offset-gate polysilicon HVTFTs. The new metal field plate serves, in lieu of ion implantation, to control the conductivity of the offset region. By properly biasing the field plate to distribute the drain electric field at both ends of the offset region, high-voltage operation of up to 100 V, suitable for many large-area applications, is achieved. Good turn-on characteristics without current-pinching effects are consistently obtained. Moreover, the new FP-HVTFT also eliminates the lightly-doped-drain implant normally required in conventional offset-gate HVTFTs, resulting in a simpler and more reproducible process flow.
Comparative Studies of Furnace and Rapid Thermal Passivation for Accumulation and Inversion Mode Polysilicon-On-Oxide Mosfets.
Authors: Batra S. , Park K. , Banerjee S. , Sundaresan R.
Published: March 2011

Carrier transport in the channel region of polysilicon thin film MOSFETs is affected by the presence of grain boundary potential barriers and is further complicated by the modulation of the grain boundary barrier height with gate voltage. Passivation of the trap sites with atomic hydrogen reduces the barrier height and thereby improves the performance of polysilicon transistors. In this paper, we demonstrate the effectiveness of Rapid Thermal Annealing (RTA) using Si3N4 as a solid source of H as a passivation technique for both inversion and accumulation mode polysilicon MOSFETs. ON/OFF ratios of 107 can be obtained by RTA passivation for inversion mode polysilicon MOSFETs compared to 106 after furnace passivation permitting the potential application of these MOSFETs both as load transistors in SRAMs as well as pass transistors in DRAMs. In contrast, the ON&OFF ratio of accumulation mode polysilicon MOSFETs does not show any improvement even though ID and VT improve with passivation. This is because of excessive back channel leakage in accumulation mode MOSFETs which increases with passivation.
TiSi2 Thin Films Formed on Crystalline and Amorphous Silicon
Authors: Xiao Z.G. , Jiang H. , Honeycutt J. , Osburn C.M. , Mcguire G. , Rozgonyi G.A.
Published: March 2011

TiSi2 thin films were formed on crystalline and amorphous silicon substrates obtained by Ge+ and Ge++B+ implantation and optional subsequent annealing. Transmission electron microscopy, X-ray diffraction and electrical resistivity analysis revealed that the silicide formed on amorphous Si has more tendency to have a C54 structure rather than the metastable C49 structure. Also, the grain size is smaller and the silicide/silicon interface is smoother for silicides formed on amorphous Si. Comparison between implanted and unimplanted, (100) and (111) Si substrates indicated that the origin of the differences can be attributed to the latent energy stored in amorphous silicon, which favors the silicide with fine grains and promotes the transformation to the C54 phase. Non-random distribution of planar defects in C49 grains has been observed by plan-view TEM. A proposal that these defects are transformation stress induced microtwins is presented.
High Resolution Study of CoSi2/Si (111) Interfaces
Authors: Catana A. , Lu Ping , Smith David J.
Published: March 2011

The atomic structure of A- and B-type CoSi2/Si (111) interfaces has been investigated by observations of samples in cross-section using a 400 kV high-resolution electron microscope. The samples were prepared by UHV e–beam evaporation of Co layers followed by annealing at temperatures between 300°C and 500°C. Based upon image simulations for various interface bonding models we have found evidence for 7–fold Co coordination at the A–type CoSi2/Si interfaces and for 7– and 8–fold coordination at the B-type interfaces.
Hrem and Nano-Scale Microanalysis of the Titanium-Silicon Interfacial Reaction
Authors: Kouzaki T. , Ogawas S. , Nakamura S.
Published: March 2011

The interfacial reaction of titanium with single crystal silicon has been characterized using high-resolution electron microscopy(HREM) combined with nano-scale microanalysis. HREM shows that there is an amorphous interdiffused alloy formation at titanium-silicon interfaces. The reacted layer is about 1.7nm thick for single crystal silicon, but is 2.5nm thick for sputter-amorphized silicon. Annealing increases the thickness of the amorphous alloy. We have used high-spatial-resolution microanalysis to obtain energy dispersive spectrometry (EDS) using a 2nm probe size. The results clearly show that reliable composition analysis can be obtained at this level since some of the layers are only about 2nm thick. It was found that the amorphous alloy composition was Ti55Si45for the sputter-amorphized silicon. Futhermore we ascertained no induced reaction by 2nm probe electron beam irradiation.
Hrem Study of α-Si3N4 Precipitates in Silicon
Authors: De Veirman A. , Broddini D. , Van Landuyt J. , Skorupa W. , Voelskow M.
Published: March 2011

Nitrogen and also sequential nitrogen/oxygen implantations at an energy of 330 keV result in the formation of α-Si3N4 precipitates below the buried layer. A particular orientation relation between the α-Si3N4 and the Si lattice was established: the basal (00.1) α-Si3N4 plane is parallel to one of the Si {111} planes. Planar defects with (00.1) habit planes have been identified by HREM as stacking faults with a displacement vector of 1/3<10.0>.
Direct Defect Imaging in the High Resolution Sem
Authors: Joy David C
Published: March 2011

The theory of imaging crystallographic defects in solid specimens through the use of electron channeling contrast is reviewed and the necessary conditions for observation are deduced. It is shown that current high performance field emission scanning electron microscopes can meet these requirements and produce dislocation images from suitable materials.
High-Resolution STEM Observations of Nanometer-Sized Cavities in Rapidly Solidified 304 Stainless Steel
Authors: Kelly Thomas F. , Shin Keesam , Bae Jung Chan , Noll Richard K. , Flinn John E.
Published: March 2011

Based upon coarsening studies of larger cavities (8 nm) in a rapidly solidified 304SS, it was determined that there should be a large number of very small cavities (1–2 nm) in these materials that are too small to observe with out-of-focus imaging techniques on a conventional TEM. Out-of-focus imaging on a high-resolution TEM could also be used but ambiguities would remain in the interpretation of the origin of the image contrast. In order to overcome these problems of ambiguity, the annular dark field (ADF) image on a VG HB501 STEM was employed. Since this signal is proportional to mass thickness and Z3/2, we expected that the change in mass thickness locally associated with a cavity would be detectable in a thin enough region. These images show a clear correlation between features in the BF through-focus series which behave as cavities and features in the ADF image. This combination of imaging modes has provided convincing evidence for existence of the 1 nm cavities.
Solving Defect Structures by Hrtem: Expectations and Limitations
Authors: Barry John C.
Published: March 2011

Most metals have small unit cells, and in small unit-cell materials in low-index zones the strength of the diffracted beams is often greater for lighter metals than it is for heavier metals. The reason for this is that the strong double-diffraction in heavy metals gives rise to weak Bragg diffraction. In this paper it is shown that for small unit-cell materials, light atom precipitates can be easily detected in heavy atom matrices; and that in large unit-cell materials, the breakdown in the weak-phase-object approximation in thick crystals can be used to identify atom type at defects.
Hrem Visualization of Light Atoms: An Application to the Study of Carbon Defects in Ordered Transition Metal Carbides
Authors: Epicier T.
Published: March 2011

This paper gives an overview of recent High Resolution Electron Microscopy (HREM) observations of transition metal carbides. The main point is to show how HREM can be used to study a sublattice of light atoms within a complex crystal. General tendencies of this approach will be outlined, which appear, to a large extent, to be common to similar possible studies of other compounds such as nitrides, borides or oxides. Specifically, attention is focused on studies of long-range ordered structures in carbides, due to non-stoichiometry accommodated by metalloid vacancies. Various examples are given for representative compounds, including V8C7, V6C, 5, Nb6C5 and W2C.
Hrtem Observations of Sol-Gel Derived Yag and Alumina/Yag Thin Films
Authors: Hay R. S.
Published: March 2011

Thin films of YAG and YAG/alumina mixtures were prepared by gelling a sol across a TEM grid. The grids were heat-treated to temperatures as high as 1550°C. The resulting ceramic thin films were observed by standard and high resolution TEM techniques. Ion-milling, carbon coating, or other specimen preparation was not necessary. The phase and microstructure evolution, as well as pore structure evolution and spheroidization of film edges could be easily observed. Abnormal grain growth was observed in yttrium-aluminum garnet (YAG) films. Lattice images were taken of the matrix, abnormal grains, and structures that evolved from the abnormal rains at higher temperatures. The grain size preceding abnormal grain growth was 20–50 nm. The abnormal grains were composed of 20–50 nm subgrains with up to several degrees of misorientation. High resolution observations were also made of small (< 0.2 μm) YAG inclusions in alumina. An orientation relationship of (111)[011]alumina//(112)[021]YAGwas observed. This orientation relationship was not observed in large inclusions.
Interdiffusion in Metallic Layers
Authors: Bourret A. , Rouviere J. L.
Published: March 2011

The atomic structure of ion-sputtered Fe/Ti multilayers with an average composition FeTi2 is studied by high resolution electron microscopy. A systematic use of diffractometry is made to measure the local parameter change as well as to recognise the crystalline phase. Local lattice parameter changes are attributed to compositional changes indicating interdiffusion at a scale of 1.8 nm. The phases are very dependent on the multilayer period, Λ. For small periods, Λ < 4 nm, the layers are amorphous. For intermediate periods 4 nm < Λ < 8 nm the Ti-rich layer is crystalline. And for larger periods both the Fe-rich and the Ti-rich layers are crystalline. These observations are explained in terms of a growth model, assuming a constant depth of mixing during sputtering.
High Resolution Transmission Electron Microscopy of Aluminophosphates; Proposed Structure for AlPO4–8
Authors: Ulan Judith G. , Szostak Rosemarie , Sørby Kristin , Gronsky Ron
Published: March 2011

VPI-5 transforms to AlPO4–8 under mild thermal treatment (100 °C, 18 hrs). HRTEM micrographs, oriented normal to the c axis, show extensive defect-free regions in VPI-5, while slip planes normal to the c axis are found in AlPO4–8. Analysis of the HRTEM data, in conjunction with infrared and thermal analysis, adsorption studies and x-ray powder diffraction, has lead to a proposed structure for AlPO4–8. Though the sheets containing the 18 member rings which define the pores in VPI-5 remain intact in AlPO4–8, reduction in the porosity is attributed to blockages created by the movement of these sheets relative to each other.
High-Resolution Electron Microscopy of Process-Induced Defects in Silicon
Authors: Cerva Hans , Oppolzer Helmut
Published: March 2011

Several examples of defect characterization which are of topical inter-est to Si device technology are presented. The results obtained by high-reso-lution electron microscopy (HREM) are discussed in context with the actual defect problem. - Reinvestigation of platelike defects in Si produced by reactive ion etching in hydrogen containing plasmas (CHF3) shows that some of the {111} platelets are of extrinsic nature. The defects contain probably both constituents from the plasma and Si-interstitials created by the impin-ging ions. - A high dose As-implantation forms an amorphous Si surface layer which has a sharply curved amorphous/crystalline (a/c)-interface below the implantation mask edge. Annealing at 900°C leads to formation of vacancy-type defects under the mask edge. This is due to the different regrowth rates on the various lattice planes of the curved a/c-interface. - Metal-silicide pre-cipitation at the SiO2/Si interface reduces the breakdown field strength of thin oxides. The main failure mechanism observed in model experiments is the thinning of the oxide layer thickness. - Additional x-ray peaks which are frequently observed in low-pressure chemical vapour deposited (625 7deg;C) po-lycrystalline Si layers arise from a diamond hexagonal Si phase. Small inclu-sions and bands of this phase were for the first time directly observed by HREM.
Stability of Multilayered Semiconductor Systems
Authors: Kim Y. , Ourmazd A.
Published: March 2011

We have studied the atomic scale relaxation of multilyered semiconductor systems through interdiffusion, and its implications for layer and hence device stability. Our technique combines chemical lattice imaging and vector pattern recognition to measure interdiffusion coefficients as small as 10-20 cm2/s at single AiGaAs/GaAs interfaces. Our results can be summarized as follows. (a) The interdiffusion coefficient and hence layer stability depend strongly on the distance from the top surface. (b) The strong influence of the surface stems from its role as the source of rative point defects (interstitials, vacancies) involved in the diffusion process. (c) The study of the initial transients in the diffusion process can directly yield the migration and formation energies of these defects as a function of their charge state. (d) The non-linear nature of the diffusion process can have serious consequences for the low temperature stability of multilayered materials and devices. We also discuss the implications of our results for the design and fabrication of stable multilayered systems.
Defect Mechanisms in Degradation of Long Wavelength (1.30–1.55 Micron) Laser Diodes
Authors: Chu S. N. G.
Published: March 2011

Optical degradation of long wavelength (1.30–1.55 micron) laser diodes during normal operation or accelerated aging test caused by lattice structural deterioration of the active region materials and mirror facet damage were investigated in detail. Extrinsic dislocation loops of 1/2<100>{010) types were observed in gradually degraded channeled-substrate-buried-heterostructure (CSBH) lasers. These dislocation loops, originated at the sidewall interfaces outside the active region, grew into the active region in the direction of minority carrier injection. A great enhancement of the loops' growth rate was observed after they entered the active region, indicating a nonradiative recombination enhanced defect reaction under the strong optical field. Furthermore, the <100> oriented extrinsic dislocation loops were confirmed to be dark-line-defects (DLDs). On the other hand, strong nonradiative recombination centers, created by mirror facet damage, or pre-existed internally inside the cavity, resulted localized melting on the {111} planes. The propagation of the localized melt-patch along the laser beam direction created a wormlike defect along the laser cavity, which degraded the laser device catastrophically. Various types of grown-in defects for CSBH and etched-mesa-buried-heterostructure (EMBH) laser devices are described and their effects on the device performance are demonstrated.
Properties of DX Centers in AlxGa1−xAs and Effects on Heterojunction Devices
Authors: Mooney P. M.
Published: March 2011

In this paper the effects of DX levels on the properties of AlxGa1−xAs and certain heterojunction device structures are summarized. Studies of alloy effects, variations of the local atomic environment near the donor, are reviewed and microscopic models of the DX center are discussed in terms of these and other recent experimental results.
DX Centers and III-V Device Performance
Authors: Muñoz-Merino Elias
Published: March 2011

The properties of deep donor states (DX's centers) in III-V alloys are reviewed in relation to their influence on the device characteristics and limitations. Because of the systematic research being performed on AlGaAs, most of the information presented refers to such material. The electron thermal emission and capture properties of the DX's are then related to the DC and noise characteristics in heterojunction transistors. The optical properties of DX centers indicate a clear difference between unipolar and bipolar device performance at low temperatures. The technical efforts to avoid DX centers will also be described.
Phase Stability in Binary Ti-Al
Authors: Anderson C.D. , Hofmeister W.H. , Bayuzick R.J.
Published: March 2011

Binary Ti-Al samples containing from 46 to 54 at.% Al were solidified while undercooled by various amounts using electromagnetic levitation techniques. A detailed thermal history of these samples was obtained with sampling rates as high as 500 KHz during recalescence. This very high sampling rate was essential to resolve the thermal events. Primary α solidification was observed in samples containing from 51 to 54 at.% Al that were undercooled less than about 100 K at solidification. Primary β solidification was found for all undercoolings tested in samples containing less than 51 at.% Al and for undercoolings greater than about 100 K in samples containing 51 to 54 at.% Al. These first two observations are in agreement with results from Valencia et al. for Ti-45 at.% Al and Ti-50 at.% Al, respectively [4]. However, the third observation of β as the primary solidification structure at high undercooling and 54 at.% Al differs from Valencia's interpretation for Ti-55 at.% Al. The results in this study are consistent with the proposed McCullough Ti-Al phase diagram.
Amorphous Phase Formation in NiTi During Cold Rolling
Authors: Koike J. , Parkin D. M. , Nastasi M.
Published: March 2011

The intermetallic compound NiTi was cold rolled at room temperature. Amorphous bands were formed within the finely twined crystalline matrix after thickness reduction of 60%. Striking similarities were observed in microstructural morphology between amorphous bands and shear bands that are generally observed in heavily cold-rolled pure metals. We suggest from the present observations together with the reported results in other solid-state amorphization experiments that the amorphous bands are produced in the shear bands, and that amorphization is caused by mechanical instability against the shear stress.
Atom Probe Analysis of the Compositions of γ′ AND γ″ Intermetallic Phases in Nickel-Based Superalloy 718
Authors: Miller M. K. , Burke M. G.
Published: March 2011

An atom probe field ion microscopy and transmission electron microscopy characterization has been performed on the intragranular precipitates that are formed in a niobium-modified nickel-base superalloy 718 after the various stages of a multistage heat treatment. Atom probe results indicate that there is a wide variation in the compositions of the DO22-ordered γ″, the Ll2-ordered γ′ precipitates and the γ matrix with heat treatment and with position in the microstructure.
First Principles Study of Phase Stability in The Al-Ti System
Authors: Asta M. , Sluiter M. , Singh Prabhakar P. , Fontaine D. de , Hong T. , Freeman A.J.
Published: March 2011

Due to its technological importance, the Al-Ti system has received much attention lately. For example, TiAl3 (as well as TiAl) has a low density and very high elevatedtemperature strength. However, this compound forms in the tetragonal D022 structure which has low ductility. Recent studies [1,2] have tried to understand the role of tetragonal distortion and the effect of ternary additions [3] in stablizing the D022 relative to the L12.
Fracture Toughness and the Effects of Stress State on Fracture of Nickel Aluminides
Authors: Lewandowski John J. , Michal Gary M. , Locci Ivan , Rigney Joseph D.
Published: March 2011

The effects of stress state on the fracture behavior of Ni3Al, Ni3Al + B, and NiAl were determined using either notched, or fatigue-precracked bend bars tested to failure at room temperature, in addition to testing specimens in tension under superposed hydrostatic pressure. Although Ni3AI is observed to fail in a macroscopically brittle intergranular manner in tension tests conducted at room temperature, the fracture toughnesses (i.e. K IC presently obtained on Ni3Al exceeded 20 MPa1m and R-curve behavior was exhibited. In-situ monitoring of the fracture experiments was utilized to aid in interpreting the source(s) of the high toughness in Ni3Al, while SEM fractography was utilized to determine the operative fracture modes. The superposition of hydrostatic pressure during tensile testing of NiAl specimens was observed to produce increased ductility without changing the fracture mode.
Ground State Properties of the Ai-Ti System
Authors: Singh Prabhakar P. , Asta Mark , deFontaine Didier , Schilfgaarde Mark van
Published: March 2011

Ground state structural energies and lattice constants of Al-Ti system have been studied using the linear muffin-tin orbital (LMTO) method. In particular, we examine the effects of various approximations for the potential on the structural energies of low-symmetry compounds such as Al3Ti. In order to stabilize Al3Ti, in the atomic sphere approximation, the Muffin-Tin correction is essential although the resulting c/a is 10% too large. The lattice constants calculated with the full-potential LMTO method are in complete agreement with experiments, indicating the importance of non-sphericity of the potential for low-symmetry systems.
Ab Initio Calculation of the Cu-Pd One-Dimensional Long Period Superstructure Phase Diagram.
Authors: Ceder G. , Huang P. , Menon S. , Fontaine D. de , Nicholson D.M. , Stocks G.M. , Gyorffy B.L.
Published: March 2011

The FCC superstructure phase diagram for Cu-Pd is calculated by means of isotropic effective interactions derived from an ab initio KKR-CPA electronic structure calculation. We prove the existence of a region in which one-dimensional long period superstructures are stable. This region is composed of several single phase fields in which the modulation period is constant. The value of the modulation period is in close agreement with results from High Resolution Electron Microscopy. Adding oxygen to Cu-Pd is found to sharpen the antiphase boundaries. This experiment enables us to clarify the role of the Fermi surface in these alloys.
Electronic Structure and Phase Stability Properties of Ai-Li Alloys
Authors: Gonis Antonios , Turchi Patrice E.A. , Sluiter Marcel , Pinski Frank J. , Johnson Duane D.
Published: March 2011

Recently, the phase diagram of AI-Li alloys was calculated with the use of the Connolly-Williams method. In an effort to test the validity and to supplement the results of that study, equilibrium lattice constants and effective cluster interactions have been obtained using the generalized perturbation method within the first-principles multiple-scattering formalism of the Korringa-Kohn-Rostoker coherent-potential approximation. The implication of these effective interactions to the phase stability of these alloys is discussed.
Characterization of Silicon and Indium Redistribution in InxGa1−xAs/n+-GaAs(100) Heteroepitaxial Layers Fabricated Using Pulsed Laser Melting
Authors: Chang Y. , Sigmon T.W. , Marshall A.F. , Weiner K.H.
Published: March 2011

Heteroepitaxial InxGa1−xAs/GaAs structures have been formed by pulsed laser induced mixing of molecular beam deposited In films (˜200Å) on Si doped n+-GaAs (100) substrates. The Si dopant and deposited In are redistributed in a rapid melt-solidification process driven by a XeCl pulsed excimer laser. It is found, from high resolution cross-sectional transmission electron microscopy, that the epitaxial layers are crystalline and lattice matched to the substrate except for the misfit dislocations lying along the InxGa1−xAs/GaAs interface. These interfacial dislocations are used to identify the laser melted and unmelted regions. The dip and pile-up regions in the Si SIMS profiles are attributed to a segregation effect. Numerical simulation based on the liquid-solid interface velocity dependent segregation coefficient is used to investigate this effect and has approximated the trends in the measured characteristic In and Si profiles.
Boron Diffusion in Bulk Cobalt Disilicide
Authors: Gas P. , Zaring C. , Svensson B.G. , Östling M. , Whitlow H.J. , Barge T.
Published: March 2011

The lattice diffusion of boron in bulk cobalt disilicide has been studied at temperatures between 450 and 950°C. Two different diffusion sources, a deposited surface layer of boron and an implanted boron distribution, were used. The lattice diffusion coefficient has been deduced from the boron profiles measured by secondary ion mass spectrometry (SIMS); in the studied temperature range the coefficient varies between 6.2×10−17 and 3.0× 10−11 cm2/s with an activation energy of 2.0 eV. These values reveal a very rapid lattice diffusion and agree with results reported previously in the literature concerning redistribution of boron implanted in thin films of CoSi2, and it also emphasizes the important role played by interfaces during the boron redistribution.
Oxidation Kinetics of Metastable Electrodeposited and Sputtered Nickel Thin Films Via Thermogravimetric Analysis
Authors: Herrmann Ann C. , Brower D William E. , Lalvani Shashi
Published: March 2011

The effetzct of the amorphous state and the disordered sputtered state on the oxidation kinetics of nickel films was investigated by a comparison with annealed films and with pure nickel foil and powder. Specimens were exposed to oxygen in a thermogravimetric analyzer (TGA) in the temperature scan mode. An electrodeposited amorphous Ni-P alloy and sputtered pure nickel films were annealed in situ in argon and then oxidized in the same manner as the as deposited films. The as sputtered films oxidized faster at 500%C than pieces of the same film first annealed in argon. Conversely, the as deposited Ni-P film was more oxidation resistant below its crystallization temperature than the annealed Ni-P films.
Chemical Vapor Deposition of Binary Metal Germanides
Authors: Hampden-Smith M.J. , Garvey J. , Lei D. , Huffman J.C.
Published: March 2011

A series of transition metal substituted germacyclopent-3-ene compounds containing transition metal-germanium bonds have been prepared with supporting ligands which are designed to be easily removed either thermally or photochemically. In solution, model thermal decomposition experiments show that either the geramanium or the transition metal substituents may be removed, depending on the nature of the metal. Preliminary hot-wall CVD experiments using manganese and cobalt derivatives result in films with small grain size.
On the Formation of Amorphous and Metastable PVD-Coatings
Authors: Knotek O. , Barimani A. , Löffler F.
Published: March 2011

By using differing target materials and admitting reactive atmospheres, thin protective coatings having an amorphous and/or metastable character such as sialon, (Ti, Al)N and (Ti, Zr)N are deposited. Phase formation, crystalline structure, morphology and mechanical properties of these films are investigated by X-ray analysis, transmisison electron microscope (TEM), scanning electron microscope, Auger electron spectroscopy (AES) and metallographic measurements. The thermal stability of the coating systems are examined and corrosion and wear test carried out.
Epitaxy of Ni on Si(111) by Ion Beam Assisted Deposition
Authors: Grabowski K. S. , Kant R. A.
Published: March 2011

Epitaxial growth of Ni (111) on Si (111) has previously been obtained at room temperature by 25-keV-Ni ion beam assisted deposition, where both ion and vapor fluxes were incident at 45° to the specimen normal. This work explores the effect of a wider range of deposition conditions on epitaxial film quality. Nominally 300-nm-thick films were deposited at room temperature on Si (111) and other substrates. The substrates were sputter cleaned by the Ni ion beam immediately prior to deposition. Ion energies of 25 to 175 keV, relative ion to vapor fluxes R from 0 to 0.1, and vapor deposition rates of 0.05 to 0.5 nm/s were examined. Bragg-Brentano symmetric x-ray diffraction evaluated film quality while Ni (220) grazing-incidence x-ray diffraction rocking curves verified film epitaxy. Film quality changed gradually over these deposition parameters, with an optimum at 25 keV and an R of about 0.01. At higher energies and R values sputtering and radiation damage destroyed the film epitaxy
Structures of Silver/Chromium Metallic Superlattice
Authors: Kaneko Takeo , Kyuno Kentabo , Niikura Osamu , Hara Shigeki , Yamamoto Ryoichi
Published: March 2011

Ag/Cr metallic superlattices with bilayer thickness in the range of 17–136Å were prepared by metal-MBE method. X-ray diffraction measurements indicated that the thickness fluctuations of each layer were rather small. The lattice matching at the interface between Ag(100) and Cr(100) is almost perfect. But, the interplanar spacings of Ag(100) and Cr(100) changed as a function of bilayer thickness. Surface wave velocities have been measured using Brillouin spectroscopy. In contrast to Au/Cr superlattices which show a hardening, a plot of surface wave velocities as a function of the bilayer thickness in Ag/Cr superlattices showed a distinct dip.
Structures of Silver/Cobalt Metallic Superlattice and Changes Due to Annealing
Authors: Kingetsu T. , Sakai K. , Kaneko T. , Yamaguchi A. , Yamamoto R.
Published: March 2011

Ag/Co metallic superlattices were grown onto Ag buffer layers pre-deposited on sapphire or MgO substrates by ultrahigh vacuum alternate deposition technique. In-situ RHEED observations during superlattice growth and ex-situ XRD measurements revealed that structures of the superlattices were strongly affected by the condition of Ag buffer layer preparation. In case where the Ag buffer layers were single crystals with smooth (111) surfaces, Co layers were epitaxially grown on the buffer layers even in the presence of large lattice mismatch, and whole the superlattices were grown with an epitaxial relation. Interface smoothness was strongly related to the growth temperature. Spotty RHEED patterns of Co layers for a low growth temperature indicated that the Co layers had an FCC structure. Post-annealing of the samples, in some cases, destroyed a superlattice structure completely. From relations between magnetic anisotropy and Co-layer thickness obtained with VSM measurements, it was found that Ag/Co superlattice exhibited in-plane magnetic anisotropy down to a Co thickness of 4A and that the anisotropy was correlated with roughness of the interfaces.
Anomalous Small Angle X-Ray Scattering Studies of Metal-Germanium Alloys
Authors: Rice Marybeth , Wakatsuki Soichi , Bienenstock Arthur
Published: March 2011

The tunability of synchrotron radiation was used to perform anomalous small angle x-ray scattering (ASAXS) experiments on amorphous metal-germanium (a-Mx Ge1−x) alloys with the aim of detecting and characterizing compohitioK modulation and phase separation. Small angle x-ray scattering is sensitive to electron density fluctuations on a scale of tens to thousands of Angstroms. The combination of SAXS with the anomalous dispersion effect allows one to distinguish composition modulation from density fluctuations arising from voids and defects. Data gathered from a-FexGe1−x and a-WxGe1−x samples in the low metal concentration regime show nanometer scale composition modulation. In these samples the density of Ge atoms is uniform throughout the sample. The small angle x-ray scattering arises from fluctuations in the density of metal atoms.
Microstructure and Stability Comparison of Nanometer Period W/C, Wc/C, and Ru/C Multilayer Structures
Authors: Nguyen Tai D. , Gronsky Ronald , Kortright Jeffrey B.
Published: March 2011

Multilayer structures of W/C, WC/C, and Ru/C, of various periods were prepared and studied by high-resolution transmission electron microscopy. Comparison of the phases in the layered structures is made for as-prepared and annealed samples. Both as-prepared and annealed WC/C multilayers are predominantly amorphous, while the phases in the W/C depend on the periods. The 2 nm period W/C multilayer remains amorphous after annealing, and the longer periods recrystallize to form W2C. The layered microstructures of W/C and WC/C are stable on annealing at all periods, while the amorphous Ru-rich layers in the 2 nm period Ru/C multilayer agglomerate upon annealing to form elemental hexagonal Ru crystallites. Larger period Ru/C multilayers show stable layered structures, and indicate hexagonal Ru in the Ru-rich layers. X-ray measurements show that the multilayer periods expand on annealing for all metal-carbon multilayers studied.
Superconductivity in Nonsymmetric Epitaxial YBa2Cu3O7−δ - PrBa2Cu3O7−δ Superlattices Grown by Pulsed Laser Ablation
Authors: Lowndes Douglas H. , Norton David P. , Budai J. D. , Pennycook S. J. , Christen D. K. , Sales B. C. , Feenstra R.
Published: March 2011

Pulsed KrF (248 nm) excimer laser ablation has been used to grow nonsymmetric epitaxial YBCO/PrBCO superlattices containing 1-, 2-, 3-, 4-, and 8-unit-cell-thick YBCO layers, separated by N-cell-thick insulating PrBCO layers (N = 1–16). The 1×N and 2×N structures exhibit a rapid initial decrease of Tco with increasing PrBCO layer thickness, followed by saturation of Tco at a nonzero value, as the YBCO layers' separation is increased further. The limiting Tco values for 1-, 2-, 3-, 4-, and 8-cell-thick YBCO layers isolated in a PrBCO matrix are ∼19 K, ∼54 K, ∼71 K, ∼80 K, and ∼87 K, respectively. Single-cell-thick YBCO layers are found to be superconducting even when separated by ∼19 nm in a PrBCO matrix. These results are discussed in terms of possible Josephson and/or proximity effects coupling the YBCO layers, and the possibility that PrBCO modifies the electronic structure and depresses Tco in YBCO cells that are immediately adjacent to the PrBCO layers. Finally, high-temperature postannealing studies show that these superlattice structures are stable and that little diffusion occurs along the c-axis direction of compositional modulation.
Effect of Substrate on the Early Stages of the Growth of YBa2Cu3O7-δ Thin-Films
Authors: Norton M. Grant , Carter C. Barry
Published: March 2011

The fabrication of high-quality thin-films often depends on the early stages of the growth process during which epitaxy is established. The substrate structure and orientation generally play a critical role at this stage through epitaxy and interaction or reaction. Many different materials are being used as substrates to support thin-films of the YBa2Cu3O7-δ superconductors. In this study the early stages of the growth of YBa2Cu3O7-δ thin-films have been investigated using transmission electron microscopy (TEM). Using pulsed-laser ablation, ultra-thin films were formed directly onto self-supporting, ion-thinned, single-crystal ceramic substrates. The substrates used were (001)-oriented MgO, (001)-oriented SrTiO3 and (001)-oriented LaAlO3.
Laser-Ablation of Various Oxide Materials Over Large Areas
Authors: Greer James A. , Hook H. Jerrold Van
Published: March 2011

Laser-Ablation (LA) had received little attention prior to the first published report of depositing Y1Ba2Cu3O7-x) (YBCO) thin films with this novel method.[1] However, LA has been used to produce films of infrared materials for some time[2], and the recent discovery of 1-igh Temperature Superconductors (HITS) has sparked considerable interest in this relatively obscure Physical Vapor Deposition (PVD) technique. Over the past three years, a variety of in-situ LA processes for producing films of HTS compounds, as well as other materials, have been reported in the literature.[3,4,5,6,7] Like any other PVD technique, LA has its own unique advantages anid disadvantages. The main advantages of LA include: 1) its ability to accurately replicate the stoichiometry of the ablation target within the laser-deposited film; 2) the high energy of the ablated species which may enhance the quality of film growth; 3) it does not require hot filaments which allow a number of reactive gases to be present in the chamber during deposition; and 4) a wide array of complex chemical compounds can be deposited. Two of the main problems facing this emerging PVD technique have been: 1) it has been applied mostly to small area deposition (<6 cm2) with poor uniformity, and 2) the ablated films typically display a large number- of particles ranging in size from 0.5 μm to over 10 μm, whose presence may significantly hamper a number of microelectronic device applications.
High Rate Growth of YBa2Cu3O7-x Thin Films using Pulsed Excimer Laser Deposition
Authors: Muenchausen R. E. , Wu X. D. , Foltyn S. , Estler R. C. , Dye R. C. , Garcia A. R. , Nogar N. S. , England P. , Ramesh R. , Hwang D. M. , Ravi T. S. , Chang C. C. , Xi X. X. , Li Q. , Inam A. , Venkatesan T.
Published: March 2011

We report here on the pulsed laser deposition of high quality, superconducting, 200 nm thick films of YBa2Cu3O7-x at rates approaching 15 nm/s. Film crystallinity and electrical properties were studied as a function of deposition rate from 0.1 to 14.5 nm/s. Though some degradation in the film crystallinity is observed by RBS channeling and X-ray rocking curve measurements, critical current densities (Jc = 4 × 106 A/cm2, 77 K, B = 0) are effectively unchanged in going to the higher deposition rates.