bluuebunny/crossref_metadata_2025 huggingface dataset:
Grain Growth Simulation of [001] Textured YBCO Films Grown on (001) Substrates with Large Lattice Misfit: Prediction of Misorientations of the Remaining Boundaries
Authors: Rodriguez Julio C. , Ling S. , Tsap J. , Chan Siu-Wai
Published: April 2011

We employed a Monte Carlo technique to simulate the effect of (1) the anisotropic grain boundary energy in the film and (2) the large misfit between the film and substrate on the grain growth of [001] textured Yba2Cu3Ov7-x (YBCO) films. In terms of remaining grain boundaries of certain misorientations, the simulation results concur with the experimental observation of preferred grain orientations of YBCO on various substrates, such as (001) MgO and (001) Yttria stabilized Zirconia (YSZ). Three factors were identified to influence the grain growth of these [001] tilt boundaries in the simulation and could help to elucidate the origin of special misorientations observed experimentally. These are (1) the depth of local minima in boundary energy vs. misorientation curve, (2) the number of possible combinations of coincidence epitaxy (CE) orientations contributing to the exact misorientation for each of the high angle but low energy (HABLE) boundaries, and (3) the number of possible combinations of coincidence epitaxy CE orientations within the angular ranges near each of the HABLE boundaries.
Structure, Mechanical Properties, and Thermal Transport in Microporous Silicon Nitride Via Parallel Molecular Dynamics
Authors: Omeltchenko Andrey , Nakano Aiichiro , Kalia Rajiv K. , Vashishta Priya
Published: April 2011

Molecular dynamics simulations are performed to investigate structure, mechanical properties, and thermal transport in amorphous silicon nitride under uniform dilation. As the density is lowered, we observe the formation of pores below ρ = 2.6 g/cc and at 2.0 g/cc the largest pore percolates through the entire system. Effects of porosity on elastic constants, phonons and thermal conductivity are investigated. Thermal conductivity and Young's modulus are found to scale as ρ1.5 and ρ3.6, respectively.
Ab Initio Investigation of Grain Boundary Sliding
Authors: Payne M. C. , Francis G. P. , Molteni C. , Marzari N. , Deyirmenjian V. , Heine V.
Published: April 2011

We are using total energy pseudopotential calculations to carry out an extensive investigation into grain boundary sliding in a number of different systems, in order to understand, at microscopic level, the fundamental mechanisms responsible for this process.

In this paper we present results for the sliding process at the ∑ = 5(001) twist grain boundary in germanium, chosen as a typical covalently bonded material, and contrast them with preliminary results obtained for the ∑ = 5 (001) twist grain boundary in aluminium, a typical metal.
Defect Structure of β NiAl Using the BFS Method for Alloys
Authors: Bozzolo Guillermo , Amador Carlos , Ferrante John , Noebe Ronald D
Published: April 2011

The semiempirical BFS method for alloys is generalized by replacing experimental input with firstprinciples results thus allowing for the study of complex systems. In order to examine trends and behavior of a system in the vicinity of a given point of the phase diagram a search procedure based on a sampling of selected configurations is employed. This new approach is applied to the study of the/3 phase of the Ni-Al system, which exists over a range of composition from 45–60 at. % Ni. This methodology results in a straightforward and economical way of reproducing and understanding the basic features of this system. At the stoichiometric composition, NiAl should exist in a perfectly ordered B2 structure. Ni-rich alloys are characterized by antisite point defects (with Ni atoms in the Al sites) with a decrease in lattice parameters. On the Al-rich side of stoichiometry there is a steep decrease in lattice parameter and density with increasing Al content. The presence of vacancies in Ni sites would explain such behavior. Recent X-ray diffraction experiments suggest a richer structure: the evidence, while strongly favoring the presence of vacancies in Ni sites, also suggests the possibility of some vacancies in Al sites in a 3:1 ratio. Moreover, local ordering of vacant sites may be preferred over a random distribution of individual point defects.
Monte-Carlo Studies of Bosonic van der Waals Clusters
Authors: Meierovich M. , Mushinski A. , Nightingale M. P.
Published: April 2011

In a previous paper [1], we developed a form of variational trial wave function and applied it to van der Waals clusters: five or less atoms of Ar and Ne modeled by the Lennard-Jones potential. In addition, we tested the trial functions for a hypothetical, light atom resembling Ne but with only half its mass. We did not study atoms such as He4 with larger de Boer parameters, i.e., systems in which the zero point energy plays a more important role relative to the potential energy. This is the main purpose of the present paper. In fact, we study clusters to the very limit where the zeropoint energy destroys the ground state as a bound state. A simple picture of this un-binding transition predicts the power law with which the energy vanishes as the de Boer parameter approaches its critical value and the power of the divergence of the the size of the clusters in this limit. Our numerical results are in agreement with these predictions.
Film Effects On Ductile/Brititle Behavior In Stress-Corrosion Cracking
Authors: Zhang Tong-Yi , Chu Wu-Yang , Xiao Ji-Mei
Published: April 2011

The present work analyzes the effects of a passive film formed during stress corrosion cracking on ductile/brittle fracture behavior, considering the interaction of a screw dislocation with a thin film-covered mode III crack under an applied remote load. Exact solutions are derived, and the results show that the crack stress field due to the applied load is enhanced by a harder film or abated by a softer film. The critical stress intensity factor for dislocation emission from the crack tip is greatly influenced by both the stiffness and thickness of the filn. A dislocation is more easily to be emitted from the crack tip if the covered film has a shear modulus larger than that of the substrate. The opposite is also true, i.e., a softer film makes dislocation emission more difficult. Both phenomena become more significant when the film thickness is smaller.
R-Curve Response Of Silicon Carbide Whisker-Reinforced Alumina: Microstructural Influence
Authors: Sun E. Y. , Hsueh C. H. , Becher P. F.
Published: April 2011

Rising fracture resistance with crack extension (R-curve response) can lead to improvements in the mechanical reliability of ceramics. To understand how microstructures influence the R-curve behavior, direct observations of crack interactions with microstructural features were conducted on SiC whisker-reinforced alumina. The contribution of the dominant toughening mechanisms to the R-curve behavior of these composites is discussed using experimental and theoretical studies.
Fracture Of Particulate Composites With Strong Or Weak Interfaces
Authors: Lekatou A. , Faidi S.E. , Lyon S.B. , Newman R.C.
Published: April 2011

The tensile fracture of glass-bead/epoxy composites has been studied using a large number of glass volume fractions (q) from 0 to 0.25. Absorption of water from a saturated NaCl solution was used to destroy interface adhesion. The strength of the dry composites decreased up to q = 0.15, then became constant. The strength of the wet composites showed a plateau around q = 0.12, then an abrupt drop between 0.12 and 0.15, then became nearly constant. It is possible that the abrupt drop in strength occurs at the percolation threshold. However, electrical measurements on similar composites prepared with conducting (silver-coated) beads showed that the applicable percolation threshold (qc) was ≥ 0. 16, in agreement with the observation of anomalous water uptake only for q ≥ 0.18. It is concluded that the abrupt drop in strength occurs below qc, and is due to large finite interface clusters (or rather the more planar parts of such clusters) acting as nuclei for a progressive matrix fracture process. The plateau around q = 0.12 is due to favourable fibre-like interactions of smaller interface clusters, and gives the highest normalized (wet/dry) strength of about 0.9.
Micromechanical Behavior Of Polymer Interface Reinforced With Copolymers
Authors: Wang Q. , Chiang F. P. , Guo L. , Rafailovich M. , Sokolov J.
Published: April 2011

The fracture toughness of interface reinforced with dps-b-dpmma copolymer between immiscible polymers of PS and PMMA is tested by asymmetric double cantilever beam. The local deformation field at the interfacial crack tip is determined by the technique of SIEM. Normal and tangential crack opening displacements are calculated. A weak singularity is shown to exist near crack tip. Direct observation on the fracture process inside an environmental scanning electron microscope shows the large effect of mode mixity.
Synthesis And Characterization Of Nine Metal Nitrides
Authors: Wade Travis , Crooks Richard M.
Published: April 2011

We demonstrate a simple electrochemical method suitable for preparing precursors for nine different metal-nitride ceramics. These precursor powders were calcined in flowing NH3 or Ar to yield metal-nitride ceramic powders. This electrochemical synthetic technique was applied to Al, Ga, Mo, Nb, Ni, Ti, V, W, and Zr and resulted in a nitride of each of these metals. The calcination conditions determined the resulting phase, composition, and morphology of the product. The ceramic materials were characterized primarily by powder XRD.
Flame Synthesis Of High Purity, Nanosized Crystalline Silicon Carbide Powder
Authors: Keil D. G. , Calcote H. F. , Gill R. J
Published: April 2011

Self-propagating flames in pure silane-acetylene mixtures produce silicon carbide (SiC) powder and hydrogen as main products. Through precise control of the stoichiometry of the reactant gas mixture, it has been possible to produce white SiC at high yields. Characterization of such powders by TEM has shown that the nascent powder consists of polycrystalline hexagonal plates with a narrow size distribution (40 ± 7 nm diameter). Infrared spectroscopy of powders indicate microcrystalline SiC and little bound hydrogen. Chemical analysis by the ANSI method showed the powder to be >96 wt % SiC with an impurity of silica (3.9 weight %) due to air exposure of the powder. Traces (0.1 to 0.2 weight %) of both free carbon and free silicon were found. Metal impurities detected by SIMS were typically low: less than 10 ppba for aluminum, sodium, titanium and vanadium. Boron was observed at 10 ppma. Like the oxygen, the boron impurities are probably associated with exposure of the powders to the atmosphere.
High-Pressure, High-Temperature Synthesis of Superhard Boron Suboxide
Authors: Hubert H. , Garvie L. A. J. , Leinenweber K. , Buseck P. R. , Petuskeyt W. T. , McMillan P. F.
Published: April 2011

A multianvil device was used to investigate the formation of BxO phases produced in the 2 to 10 GPa pressure range with temperatures between 1000 and 1800 °C.Amorphous and crystalline B and BP were oxidized using B2O3 and CrO3. Using powder X-ray diffraction and parallel electron energy-loss spectroscopy (PEELS), we were unable to detect graphitic or diamondstructured B2O, reported in previous studies. The refractory boride B6O, which has the α-rhombohedral boron structure, is the dominant suboxide in the P and T range of our investigation. PEELS with a transmission electron microscope was used to characterize the boron oxides.
Thermodynamic Modeling of Atomic Bonding in Covalent Cx(BN)1-x Alloys
Authors: Akkerman Z. L. , Efstathiadis H. , Smith F. W.
Published: April 2011

The results of the application of the free energy model (FEM) to the atomic bonding in covalent network Cx(BN)1-x alloys are presented. The high values of C-C and B-N bond energies strongly favors chemical ordering and phase separation of carbon and boron nitride. Only at temperatures of the order of the melting points are equilibrium bonding configurations including CB and C-N bonds expected to be present. Two types of structure based on either sp3 (tetrahedral) or sp2 (trigonal) configurations with different short and long range ordering are possible in the alloys. The tetrahedral structure will consist of separate clusters of diamond-like carbon and cubic boron nitride. For the hexagonal structure planar bonding causes instead two-dimensional clusters to be present. The weak interlayer bonding makes thermodynamically possible the formation of alternating graphite and BN layers. Special physical properties of the alloys connected with this ordering may be expected.
synthesis of crystalline carbon nitride by chemical vapor deposition
Authors: Zhang Yafei , Li Hulin , Xue Qunji
Published: April 2011

Crystalline carbon nitride films have been synthesized in a rf plasma assisted hot filament chemical vapor deposition system. Large crystalline grains up to ∼10 μm in size as well as film-like regions are observed in the morphology of the films. β-C3N4with two groups of lattice parameters ( one is consistent with the theoretical value and the other is 3% smaller) in the deposited films on polycrystalline Ni substrate has been revealed by x-ray diffraction spectrum (XRD). No Raman shift peaks have been found evidently by Raman scattering measurement, but some presently unknown diffraction peaks appeared in the XRD spectrum. It is proposed that there are possible unknown structures of crystalline C-N in the films. Heteroepitaxial growth of crystalline β-C3N4has also been tried via a buffer layer of α-SiC on Si (100) substrate. The XRD pattern of a film show that there are only two main peaks at 2.79 Å and 1.87 Å corresponding to the (200) and (300) crystalline planes of the theoretical β-C3N4The two main peaks indicate heteroepitaxial growth along the (100) direction of β-C3N4.
Adhesion Evaluation of TiN and (Ti, Al)N Coatings on Titanium 6Al-4V
Authors: James R. D. , Paisley D. L. , Gruss K. A. , Parthasarthi S. , Tittmann B. R. , Horie Y. , Davis R. F.
Published: April 2011

To assess the adhesion of nitride coatings on metals, titanium 6% aluminum 4% vanadium substrates were coated with titanium nitride (TiN) using both cathodic arc and electron beam evaporation. Titanium aluminum nitride ((Ti, Al)N) was also deposited using cathodic arc evaporation. The interfaces of the coated samples were loaded in tension using a high speed shock wave which caused spallation either at the interface, in the coating or in the metal. Scanning acoustic microscopy analysis of the spalled samples detected delaminations at the interface in the samples deposited by cathodic arc evaporation. DYNA2D modeling of plate impact spallation experiments revealed the tensile adhesion strength for TiN deposited by both techniques was ≈ 2.0 GPa. The tensile adhesion strength for (Ti, Al)N was less than 1.5 GPa.
Synthetic, Characterization and Decomposition Studies of Indium Sulfide Precursors
Authors: Schluter Rodney D. , Luten Henry A. , Rees William S.
Published: April 2011

The synthesis, characterization and decomposition of several indium thiolates containing the bulky substituted aryl ligand 2,4,6-i-Pr 3C6H2 (Ar′) or the internally chelating ligands 2-CH3O,5-CH3C6H3 (Ar″) and o-C6H4CH2N(CH3)2 (Ar"‘) are described. Two synthetic methods have been utilized: metathesis reactions between lithium thiolates and the appropriate metal halides and the addition of elemental metal to diaryl disulfides. The thermal decomposition of each indium precursor results in the formation of 1n2S3, based on thermogravimetric data. The homoleptic compound In(SAr′)3 can be isolated as a yellow oil. This liquid precursor has been derivatized by the reversible formation of acetonitrile and tetrahydrofuran adducts. Although, the molecule exists as a monomer in both adducts, the coordination number of the metal and he orientation of the ligands are markedly different. The internally chelating In(SAr″)3 and In(SAr.″′)3 adopt contrasting dimeric and monomeric structures respectively.
A Carbon Drug Delivery System for Lithium
Authors: Maleki H. , Ila D. , Zimmerman R. L. , Jenkins G. M. , Poker D.
Published: April 2011

Lithium was introduced into pyrolyzed phenolic resins by dissolving lithium nitrate (5, 10, and 15% by mass) in a resol precursor. Impregnated specimens were pyrolyzed at 500°C, 575°C, and 650°C in inert atmosphere. After pyrolysis, samples were placed in 5 ml of phosphate buffered saline solution, refrigerated at 5°C, for various Li release times. Inductively coupled plasmaatomic spectroscopy was used to analyze these solutions, which were tested every 24 hours for 5 days; another set was tested after 60 days. Samples containing 5% lithium salt, fired to 500°C, released Li+at a lower rate than those fired at higher temperature. At the early stages of exposure to saline, samples fired at 575°C and 650°C released Li+at a higher rate, which fell to that of 500°C samples after many days. After leaching, nuclear reaction analysis using alpha radiation, with an exposure time of I hour, allowed us to analyze [Li+] and gradient up to 121μm below the surface. This indicates that a smaller [Li+] remains in 650°C samples than in those fired at 575°C and 500°C. For 500°C samples, [Li+] near the surface was lower than that for samples fired at 575°C and 650°C. This indicates that 500°C samples release Li+from near the surface, whereas samples fired at higher temperature release Li+from deep below the surface, probably because of higher permeability. Li+release rates of samples fired at 500°C and below 650°C follow a simple diffusion law, with diffusivities between 1017and 10-18m2/s. Li+rate may controlled over long time by a multilayered sprayed precursor with variable concentration.
Prediction of New Fingerprints of Ordering in GaInP2 Alloys
Authors: Franceschetti Alberto , Wei Su-Huai , Zunger Alex
Published: April 2011

Using ab initio all-electron methods, we investigate the evolution of effective masses, deformation potentials and pressure coefficients with the degree of long-range order in spontaneously ordered Ga0.5In0.5P alloys. We find that (i) the electron effective mass in the ordering direction increases significantly with the degree of order, while the effective mass in the perpendicular direction decreases; this produces a strong anisotropy of the electron effective mass which is not present in the disordered alloy; (ii) the band-gap deformation potential for (001) epitaxial strain decreases with increasing degree of order, reflecting the extent of the ordering-induced Γ - L coupling; (iii) the band-gap pressure coefficient decreases from 8.4 meV/kbar in the disordered alloy to 6.6 meV/kbar in the ordered CuPt structure; interpolation to partial degrees of order leads to good agreement with recent high-pressure experiments.
Pattern Formation by Changing V/III Ratio During Growth of GaAs by Movpe
Authors: Paul Shashi , Shivashankar S. A.
Published: April 2011

Rode pointed out that periodically-disturbed surface morphology can occur on epilayers grown on slightly misoriented substrates. Johnson and Legg investigated Rode's prediction in Metalorganic Vapour Phase Epitaxy (MOVPE) of AIGaAs at fixed V/III ratio, but no report is available on the faceting as a function of V/III ratio in epilayers of GaAs grown by MOVPE. We have therefore investigated faceting, as function of V/III ratio, during the growth of GaAs by MOVPE at atmospheric pressure, and have found that faceting in epilayers, grown by MOVPE, is not only dependent on misorientation angle but also on the V/III ratio. These layers have characterized by optical microscopy, SEM, photoluminescence(PL), and Hall ineasuremwnts. Direct correlation between surface morphology and near-band-edge PL has been observed. Mirror-like smooth morphology was obtained at a relatively low V/Ill ratio (≈ 15); faceting occur as a ratio is gradually is increased to about 25 and beyond. On the basis of our study, we believe the dimensions of faceting on micrometer scale can be tailored by varying the V/III ratio. These patterns can be utilized in the fabrication of optoelectronic and transferred electron devices, large scale integration of the later being possible.
Growth Rate Enhancement in Selective Area Movpe
Authors: Fujii Takuya , Ekawa Mitsuru , Tanahashi Toshiyuki
Published: April 2011

We investigated the growth rate enhancement in selective area metalorganic vapor phase epitaxy with a new surface boundary condition for the vapor phase concentration of source materials. In our model, the growth rate is proportional to the vapor phase concentration at a distance of the vapor phase mean-free path of source materials from the substrates, and the vapor phase concentration is laterally uniform at the top of the stagnant layer. This model predicts that the growth rate modulation produced by mask-patterning disappears at a specific pressure at which the vapor phase mean-free path reaches the stagnant layer thickness. We controlled the vapor phase mean-free path of trimethylindium in InP growth by varying the growth pressure from 6 to 180 Torr with a fixed total inlet gas flow rate to the reactor. Experiments showed a great reduction of the growth rate enhancement with the decrease in the growth pressure and the growth rate enhancement virtually disappeared at the lowest pressure. We also investigated the dependence of the stagnant layer thickness on the mask design. The experimental stagnant layer thickness related to the typical surface length, such as the period of mask-patterning.
Formation of Quantum Wires by Strain-Induced Lateral-Layer Ordering Process: Growth Mechanism and Device Applications
Authors: Cheng K. Y. , Hsieh K. C.
Published: April 2011

GaxIn1−xAs and GaxIn1−xP quantum wire (QWR) arrays were grown by a single-step molecular beam epitaxy. Lateral Ga(In composition modulation perpendicular to the growth direction occurs spontaneously during the growth of (GaAs)m/(InAs)n or (GaP)m/(InP)n shortperiod superlattices on InP or GaAs substrates, respectively, by the strain-induced lateral-layer ordering (SILO) process, producing lateral quantum wells. This straightforward method employs standard on-axis (001)-oriented substrates, and requires no pre-growth substrate patterning, nor does it involve post-growth processing for the formation of QWRs. Both GaxIn1−xAs infrared (1.7 μm) lasers and GaxIn1−xP visible (0.7 μm) lasers with QWR active regions have been successfully fabricated. These lasers showed many unique features that have never been observed in quantum well lasers.
Compositional Modulation and its Optoelectric Properties of Zn(S,Se,Te) Crystals Grown by Hydrogen Radical-Enhanced CVD
Authors: Fujiwara Hiroyuki , Ii Toshihiro , Shimizu Isamu
Published: April 2011

High-quality (ZnS)n(ZnSe)12n and (ZnSe)n(ZnTe)11n (n=1∼4) crystals were grown at a low temperature of 200°C by hydrogen radical-enhanced chemical vapor deposition. From satellite peaks in x-ray diffraction spectra, these periodic structure crystals were confirmed to be grown coherently on substrates, in spite of large lattice mismatches between the grown layers and the substrates (͛=4∼7%). In photoluminescence (PL) spectra of these films, strong band-edge emissions were predominantly observed, resulting from a suppression of deep-level emissions. We found that the PL peak energy of (ZnSe)n(ZnTe)11n shifts systematically to lower energy by 200 meV with changes in the number of ZnSe layers (n), while relatively small shift of 13 meV was observed in (ZnS)n(ZnSe)12n. These discrepancy can be attributed to the difference of band-lineups or chemical natures of constituent atoms in these crystals.
AlInAs Band Gap Modulations Observed by Tem and Optical Measurements
Authors: Bearzi E. , Benyattou T. , Bru-Chevallier C. , Guillot G. , Harmand J. C. , Marty O. , Pitaval M.
Published: April 2011

At a low MBE growth temperature (400°C), an anisotropic composition modulation has been observed by Transmission Electron Microscopy (TEM) on AIlnAs layers. Optical measurements have been performed on these samples and compared with classical AllnAs grown at 530°C. We show the clustering “organization” on the low temperature layers and we propose some hypothesis to explain the composition modulation effects on the AlInAs optical properties.
Ordering in GaxIn1−xAsyP1−y Detected by Diffraction Methods
Authors: Rechenberg I. , Oster A. , Knauer A. , Richter U. , Menniger J. , Weyers M.
Published: April 2011

Ga0.54In0.46As0.12P0.88 lattice matched to GaAs and grown by metal organic vapor phase epitaxy (MOVPE) shows an anomalous temperature behaviour of its cathodoluminescence (CL) emission. Using high resolution x-ray diffraction (HRXRD) and transmission electron diffraction (TED), ordering in this quarternary alloy can be identified as the reason for this behaviour. The ordering follows the same trends with respect to misorientation that are known for InGaP. In addition to ordering, compositional fluctuations related to a miscibility gap are found in this material. In contrast, layers with a higher As-content (y=0.5; y=0.76) do not show properties related to ordering.
Texture and Related Phenomena of Copper Electrodeposits
Authors: Lee D. N.
Published: April 2011

The texture of copper electrodeposits changes from the orientation that places the lowest energy crystal facets parallel to the substrate under a condition of low ion concentration adjacent to the deposit, to the orientation that places the higher energy crystal facets parallel to the substrate as the ion concentration adjacent to the deposit increases. The copper electrodeposits have peculiar surface morphologies and microstructures depending on their textures, which in turn may affect their mechanical properties even when they are obtained in similar electrolysis conditions. The electrodeposits undergo recrystallization, when annealed. The recrystallization texture may be different from the original deposit texture. These phenomena have been discussed.
Sub-Half Micron Electroless Cu Metallization
Authors: Dubin V. M. , Shacham-Diamand Y. , Zhao B. , Vasudev P. K. , Ting C. H.
Published: April 2011

Electroless Cu metallization has been fabricated by blanket electroless Cu deposition into the trenches in SiO2 dilectric layer on sputtered Cu seed layer with Ta diffusion layer and Al protection layer. Chemical-mechanical polishing of copper has been used to planarize the structure. Selective electroless CoWP layer has been deposited to protect inlaid Cu metallization.
Mocvd of Copper from New and Liquid Precursors (hfac)CuL, Where L = 1-Pentene, Atms, and Vtmos
Authors: Shin H. K. , Shin H. J. , Lim S. J. , Yoo D. J. , Oh N. Y. , Yoo H. J. , Baek J. T. , Jun C. H. , Kim Y. T.
Published: April 2011

Liquid and volatile (hfac)CuL compounds where hfac = 1,1,1,5,5,5-hexafluoro- 2,4-pentanedionate and L = 1-pentene (1), acetyltrimethylsilane (2), and vinyltri- methoxysilane (3) were newly developed for reproducible copper deposition. During CVD processes, no premature decomposition of the precursor was observed in the source reservoir that contained the mixture of (hfac)CuL and excess free ligand L. Pure Cu films were deposited in the deposition temperature range 180°C ˜ 220°C
Impact of Rapid Thermal Annealing of Ti/Tin Bilayers On Subsequent Chemical Vapor Deposition Of Tungsten
Authors: Mourouxt A. , Palmans R. , Keinonen J. , Zhang S. -L. , Maex K. , Petersson S.
Published: April 2011

The influence of rapid thermal annealing (RTA) of Ti/TiN on the stress in the subsequently deposited tungsten (W) films and on the impurity contents at the TiN-W interface was investigated for two types of Ti/TiN bilayers sputter-deposited at 300 °C and 550 °C. A post treatment of the Ti/TiN bilayers resulted in a substantially decreased stress in the W films. It also led to a considerable reduction of the fluorine contents at the TiN-W interface. Both effects were more pronounced for the W deposited on the low-temperature Ti/TiN bilayers and/or annealed in the NH3 atmosphere, than on the high-temperature Ti/TiN bilayers and/or annealed in the N2 atmosphere. Annealed in N2, the interfacial oxygen at the TiN-W interface increased slightly, which can be attributed to the presence of trace amounts of O2 in the N2 atmosphere. A slight increase in the W film resistivity was thus found for the W films deposited on the N2 annealed Ti/TiN bilayers, while the resistivity decreased somewhat for the W films deposited on the NH3 annealed Ti/TiN bilayers. After the post treatment, a large amount of nitrogen was found incorporated in the Ti layer forming TiNx (× < 0.3). However, the post treatment led to a considerable increase in the tensile stress in the Ti/TiN bilayers, and then an increase in the total stress of the whole Ti/TiN/W system. This stress increase could be controlled by using moderate anneal temperatures (e.g. < 550 °C) for the post treatment.
Interdiffusion and Phase Formation During Thermal Annealing of Ti/Mo Bilayers on Si Substrates
Authors: Mouroux A. , Zhang S.-L. , Kaplan W. , Nygren S. , Östling M. , Petersson C. S.
Published: April 2011

The formation of TiSi2 from deposited Ti layers on Si and the subsequent transformation of TiSi 2 from the C49 to the C54 phase have long been of concern, particular for the silicide formation on heavily doped, narrow polycrystalline Si lines. In this work, phase formation during rapid thermal annealing of Ti/Mo bilayers sequentially deposited on blanket Si wafers and on narrow polycrystalline Si lines (0.6 μm width) is studied. The Mo layer is always 0.5 nm thick, and the Ti either 45 nm or 60 nm. It is shown that the initial physical separation of Ti from Si by the interposed Mo layer leads to complete prevention of the formation of the C49 phase. Instead, a Mo-bearing silicide phase of hexagonal structure forms first, and the C54 phase nucleates and then grows on top of it via Si diffusion through the growing silicide layers. The significance of this finding is that the usual sequence for the formation of TiSi2,. e. the C49 phase forms as a result of the Ti-Si interaction and the C54 phase forms as the product of phase transformation, is altered by the interposition of a thin refractory metal layer, here Mo. The difficulties involved in nucleation and growth of the C54 phase are then overcome, yet by a different approach than the usually employed ones which rely on ion implantation to enhance the formation of the C49 phase and the subsequent transformation to the C54 phase.
Dependence of Crystallographic Texture of C54 Tisi2 on Thickness and Linewidth In Submicron Cmos Structures
Authors: Svilan V. , Rodbell K. P. , Clevenger L. A. , Cabral C. , Roy R. A. , Lavoie C. , Jordan-Sweet J. , Harper J. M. E.
Published: April 2011

Preferential crystal orientation of low-resistance C54 TiSi2 formed in the reaction of polycrystalline and single crystal silicon with titanium was investigated for Ti thicknesses ranging from 15 to 44 nm. Using in situ synchrotron x-ray diffraction during heating of 15 nm of Ti on single crystal Si, we observed that the C54 TiSi2 silicide film showed predominantly <040> grains oriented normal to the sample. In thicker silicide films the <311> orientation dominated or film was randomly oriented. An ex situ four circle diffractometer was used to investigate the strong <040> texture in narrow line arrays of C54-TiSi2 formed on polycrystalline silicon with linewidths from 0.2 to 1.1 μm. We observed that the angular distribution of <040> Ti Si2 grains is dependent on the line direction, where the majority of grains had their (100) planes oriented parallel with the line direction. These findings support a model of the C49 to C54 TiSi2 transformation involving rapid growth of certain orientations favored by the one-dimensional geometry imposed by narrow lines.
Structural Evolution in Carbon Aerogels as a function of Precursor Material and Pyrolysis Temperature
Authors: Gross J. , Alviso C. T. , Pekala R. W.
Published: April 2011

Several organic reactions that proceed through a sol-gel transition have been identified at LLNL. The most-studied reaction involves the aqueous polycondensation of resorcinol (1,3- dihydroxybenzene) with formaldehyde. Recently, we have shown that phenol can be added to this polymerization as a comonomer. The resultant crosslinked gels are supercritically dried from carbon dioxide (Tc=31°C, Pc = 7.4 MPa) to give resorcinol-phenol-formaldehyde (RPF) aerogels. Because RPF aerogels are composed of a highly crosslinked aromatic polymer, they can be pyrolyzed in an inert atmosphere to form vitreous carbon monoliths (CRPF). The resultant aerogels are black in color and no longer transparent, yet they retain the high porosity (40–98 %), ultrafine cell/pore size (< 50 nm), high surface area (600–800 m2/g), and interconnected particle (˜10 nm) morphology of their organic precursors. In this study, we examine the acoustic and mechanical properties of these materials as a function of precursor material and pyrolysis temperature. It is shown that the elastic moduli of RPF and CRPF is higher than that of pure RF / CRF aerogels at a given density. Upon pyrolysis RPF aerogels tend to shrink to a larger extent.
Preparation of Supported Zeolite Films and Layers: Processing of Zeolite Suspensions and In Situ Growth from Homogeneous Solutions
Authors: Lovallo Mark C. , Boudreau Laura , Tsapatsis Michael
Published: April 2011

The influence of microstructure on the properties of zeolite films and means of controlling the former (film thickness, crystal orientation) are the theme of this report. Firstly, the formation of thin silicalite films from regrowth of nanocrystalline silicalite/alumina composite films is presented. The crystallites at the intergrown top layer are oriented with their straight channels parallel to the substrate film. The membranes show H2/N2 selectivities of about 60 at 150 °C.This high selectivity is attributed to the orientation of the separating layer. Secondly, the formation of oriented multilayers of zeolite L crystallites by alternating dippjpg of a glass substrate in a bohemite and a “plate-like” zeolite L suspensions is illustrated. Finally, continuous films of zeolite NaA are prepared on various substrates (glass, porous and nonporous alumina) using in situ growth from homogeneous solutions. The films exhibit good adhesion to the substrates. The films prepared on porous alumina disks show He/N2 and O2/N2 selectivities of 10 and 0.4 respectively at 120 °C.
Characterization of Porous AlN Separators for Batteries
Authors: Thorsland Brett N. , Giesche Herbert , Mroz Thomas J. , Martin Michael
Published: April 2011

A ceramic membrane of porous, sintered aluminum nitride (AIN) is under consideration for use as a separator in a Lithium-Metal Sulfide battery due to the corrosion resistance and thermal stability of AlN. The pore structure and electrolytic permeability of the membrane must be appropriate if AlN is to be used. Commercialization of these membranes can occur only after repeatability in the processing conditions can be assured. In this study, extensive permeability and porosity testing was performed on membranes prepared under various processing conditions. Attempts to correlate processing conditions with permeability were made in order to determine the optimum method for fabrication of the membranes. It was determined that membranes produced with a lower molecular weight binder will have a higher permeability, higher porosity, and a larger pore structure than membranes produced with a higher molecular weight binder.
Fabrication of InAs Wires in Nanochannel Glass
Authors: Berry A. D. , Tonucci R. J. , Nguyen P. P.
Published: April 2011

Indium arsenide wires have been fabricated in a glass host consisting of a high density array of uniformly shaped channels in a matrix glass. Reactions between organoindium compounds and arsine have produced polycrystalline InAs with crystallite sizes of approximately 10 nanometers when annealed at 400°C. At higher annealing temperatures, the wires exhibit an increase in surface porosity and grain size.
The Influence of Precursor Structure on the Development of Porosity in Polymer-Derived Sic
Authors: Nebo J. F. , Scotto C. S. , Bennett C. A. , Brinker C. J.
Published: April 2011

Polymer-based routes to ceramic oxides take advantage of precursor chemistry and structure to produce materials with a range of pore sizes. Polymer precursor routes to nonoxide ceramics offer products with superior thermal and chemical stability in many cases. Polymethylsilane (PMS), a versatile cross linked SiC precursor, [(MeHSi)x(MeSi)y], was synthesized using published procedures to yield fluid precursors with a low (20–40%) degree of cross linking. Unique, highly cross linked (60–70%), solid polymers were produced under reaction conditions which carefully conserve the volatile monomer. These two polymers were converted to SiC to determine the relative importance of the various contributions to porosity, and to assess the role of precursor structure on porosity development in non-oxides. Initial results indicate that precursor structure has little effect on porosity. The development of the porosity appears to be dominated by high temperature thermochemistry and/or microstructural changes.
Formation and Properties of Porous GaAs
Authors: Schmuki P. , Lockwood D. J. , Fraser J. W. , Graham M. J. , Isaacs H. S.
Published: April 2011

Porous structures on n-type GaAs (100) can be grown electrochemically in chloridecontaining solutions. Crystallographic etching of the sample is a precursor stage of the attack. Polarization curves reveal the existence of a critical onset potential for pore formation (PFP). The PFP is strongly dependent on the doping level of the sample and the presence of surface defects. Good agreement between the PFP and the breakdown voltage of the space charge layer is found. Surface analytical investigations by EDX, AES and XPS show that the porous structure consists mainly of GaAs and that anion uptake in the structure can only be observed after attack has been initiated. Photoluminescence measurements reveal – under certain conditions – visible light emission from the porous structure.
Nanoporous Polyimide Films from Polyimide-Aliphatic Polyester or Polyimide-Aliphatic Polycarbonate Copolymers
Authors: Carter K. R. , Hedrick J. L. , Richter R. , Furuta P. T. , Mecerreyes D. , Jérôme R.
Published: April 2011

We have explored polyimide foams created using a block copolymer approach as part of our research efforts to obtain thin film dielectric layers with very low dielectric constants for use in microelectronic devices. In these systems the pore sizes are in the nanometer range thus the term “nanofoam”, The polyimide foams are prepared from phase separated block copolymers consisting of thermally stabile and thermally labile blocks, the latter being the dispersed phase. Foam formation is effected by thermolysis of the labile block leaving pores the size and shape corresponding to the initial copolymer morphology. Polyimide nanofoams generated from thermolysis of polyimidealiphatic polyester and polyimide-aliphatic polycarbonate copolymers were investigated. The aliphatic co-blocks were synthesized by ring opening polymerization of the cyclic monomers, such as E-caprolactone, valerolactone, trimethylene carbonate, and L-lactide. The aliphatic blocks were designed in such a way as to allow for incorporation into polyimide copolymers. The foams were characterized by a variety of techniques including, TEM, SAXS, WAXD, DMTA, density and refractive index measurements.
Synthesis and Characterization of Ln/Al Pillared Clays
Authors: López-Ortega A. , Domínguez J. M. , Rojas-Hremández A. , Benitez-Patricio A. , Salmón M.
Published: April 2011

La3+ −Al3+ and Ce3+ −A13+ pillar precursors were synthesized and intercalated in swelling montmorillonite type clays. 27Al-NMR and 139La-NMR spectra do not confirm chemical interaction between Al and La ions in solution, but after pillaring and calcination (400°C) d-spacings in the range 18.5 Å−20.5 Å indicate indeed a strong interaction between the Al-La species. Also, Ce4+ (Sulfate) cations do interact with Al3+ in the pillar-precursor-solution, into the pH interval 2.78≤p.H ≤3.99.
Immobilization of Cobalt Complexes on Mesoporous MCM-41 Support Materials
Authors: Diaz J. F. , Bedioui F. , Briot E. , Devynck J. , Balkus K. J.
Published: April 2011

The pore surface of mesoporous MCM-41 type materials have been functionalized with silanes to yield surface bound chelate ligands that include ethylenediamine (ED), diethylenetriamine (DET) and ethylenediaminetriacetic acid salt (EDT). Additionally, The grafted DET ligand was reacted with salicylaldehyde to generate the supported tetradentate Schiff base ligand designated as DES. The MCM-41 bound ligands were used to prepare a series of covalently attached cobalt(II) complexes that potential as oxygen carriers and catalysts. These materials were characterized by FTIR and cyclic voltammetry as well as elemental analysis.
Synthesis and Colloidal Processing of Nanocrystalline (Y2O3-Stabilized) ZrO2 Powders by a Surface Free Energy Controlled Process
Authors: Burgard Detlef , Nass Rüdiger , Schmidt Helmut
Published: April 2011

Using the controlled growth technique, nanocrystalline ZrO2 powders have een prepared from solution. By variation of the Y-content (0-8 mol %), redispersable monoclinic, tetragonal or cubic ZrO2 powders with particle sizes between 5 and 10 mn were obtained after crystallization at elevated temperature and pressure. Nanodisperse suspensions of the powders have been used for colloidal processing techniques such as tape casting, slip casting or extrusion. The resulting green bodies with densities of 55 % and average pore sizes of 5 nm could be sintered at temperatures below 1100 °C leading to monoclinic, tetragonal or cubic ZrO2 ceramics.
Exafs Spectroscopic Studies of Uranium (VI) Oxide Precipitates
Authors: Allen P.G. , Shuh D.K. , Bucher J.J. , Edelstein N.M. , Palmer C.E.A. , Marquez L. N.
Published: April 2011

We have investigated the structures of U(VI) oxides precipitated from room temperature aqueous solutions at low ionic strength as a function of pH. Using the uranium LIII - edge extended x-ray absorption fine structure (EXAFS) as a probe of the local structure around the uranium, a trend is observed whereby the axial oxygen bond lengths from the uranyl groups increase from 1.80 Å at pH=7 to 1.86 Å at pH=11. A concomitant decrease in the equatorial oxygen and nearest-neighbor uranium bond lengths also occurs with increasing pH. Expansion of the linear O=U=O group is seen directly at the L111 absorption edge where multiple scattering resonances systematically shift in energy. EXAFS curve-fitting analysis on these precipitates and a sample of synthetic schoepite indicate that the structure of the species formed at pH=7 is similar to the structure of schoepite. At pH=11, the precipitate structure is similar to that of a uranate.
Synthesis and Characterization of Akaganeite-Like Ferric Oxyhydroxides
Authors: Linehan J.C. , Darab J. G. , Matson D. W. , Chen X. , Amonette J. E.
Published: April 2011

Akaganeite, β-FeOOH, a natural ferric oxyhydroxide mineral, has a structure containing tunnel-like cavities in which chloride ions reside. Analogs of akaganeite in which carbonate or sulfate groups replace the chloride ions have also been synthesized. Both akaganeite and its substituted analogs are known to be precursors for active hydrocracking catalysts. We present powder X-ray diffraction (XRD) and X-ray absorption fine-structure spectroscopy (XAFS) data confirming the synthesis of new ferric oxyhydroxides having structures similar to akaganeite, but contain molybdate and tungstate oxy-anions. We also present a new hydrothermal method to prepare this family of materials.
Hematite Nano Cubes and the Prototypes of Their Self Assembly Investigated Using Tem
Authors: Yu San , Kan Shihai , Zou Guangtian , Peng Xiaogang , Li Dongmei , Sun Haiping , Zhang Xingtong , Xiao Liangzhi , Li Tiejin
Published: April 2011

Monodisperse hematite cubes about 30nm in size have been prepared by aging a refluxing acidified aqueous solution of FeCl3 in an open vessel. The as grown nano cubes were determined to be single crystalline hematite in perfect cubic shapes using transmission electron microscope and electron diffraction. The nano cube is one of the equilibrium shapes of hematite, which is resumed to be formed by preferential growth in certain crystallographic directions through the species diffusion in the aqueous solutions.

Some self-assembly prototypes have been observed, such as the short range ordered buildup consisting of several brick-like hematite nano cubes and the nano box consisted of square plates of hematite nanocrystals. The drive force for the formation of the above assemblies is assumed to be the unique magnetic feature of the single crystalline hematite nano cubes.

The perfect shape and the self-assembly feature give a possibility to fabricate bulk ceramics orderly assembled using hematite nano cubes.
Hydroxyapatite Ceramics From Powders Prepared by Precipitation Method
Authors: Silva Viviane V. , Fernandes Rosana Z. D.
Published: April 2011

Hydroxyapatite (HA), specifically, calcium hydroxyapatite, is the main inorganic compound of human bone and teeth. The utilization of synthetic powders of this material in dental and medical implants has increased in the recent days.

In this paper, synthetic hydroxyapatite powder was prepared by a precipitation method, compacted and sintered at 800, 900, 1000, 1100, 1200 and 1300° C. The powder and its ceramics were analysed by X-ray diffraction, infra-red spectroscopy and scanning electron microscopy. The influence of experimental conditions on the microstructure and densification is discussed.

Some measurements of the hydroxyapatite ceramics obtained in this work were compared with those of the hydroxyapatite ceramics produced from a commercial powder. It was shown that calcium hydroxyapatite is probably the only phase present for the precipitated samples sintered below 1100° C.
Corrosion Resistant Coatings for Aluminum by Hydrothermal Film Formation in Alkaline Li-Salt Solutions
Authors: Buchheit R.G. , Martinez M.A. , Cooper C.B.
Published: April 2011

New methods of forming corrosion resistant inorganic coatings on Al and Al alloys are required due to environment and work safety hazards associated with the currently used Cr-based coatings technologies. In this paper we report on certain specific aspects of Al surface film formation that can be exploited to form highly corrosion resistant coatings. The aspects discussed include: formation of hydrotalcite surface films, Li2[Al2 (OH)6]2 CO3nH2O, by exposure to Li-salt solutions, elimination of unwanted Cu compounds that accumulate surface films formed on Cubearing Al alloys, and generation of high corrosion resistance by precipitating transition metal oxides on to alkaline hydrotalcite coated surfaces.
Chemical, Hr-Xrd and Spectroscopic Approaches to Short-Time Dissolution Behavior of Kaolin1tic Soils
Authors: Malengreau N. , Sposito G.
Published: April 2011

Batch experiments were conducted at varying proton concentrations on a representative tropical soil in order to investigate its dissolution behavior over a 12h period. The release kinetics of Al, Fe, Si and C were investigated over a 2 to 6 pH range. The pH-dependence exhibited a “point of minimum dissolution” at pH ≈ p.z.n.c. Light scattering measurements on supernatant solutions indicated that colloids were dispersed mainly at pH > p.z.n.c. These results suggested a two-pathway dissolution process, with organic matter playing a role in both pathways. High-resolution X-ray diffraction as well as electron spin resonance and diffuse reflectance spectroscopies, were applied to characterize solid-phase transformations in the course of dissolution. With the exception of quartz, all mineralogical phases (kaolinite, and minor phases such as Fe-, Al- and Ti-oxides) remained unchanged or were slightly affected. A significant loss of quartz (about 10% by mass) was observed after a 12h dissolution at pH 2. Minor phases might have played an important role in stabilizing kaolinite, and dissolved silica may have hindered the dissolution of minor phases.