Recently, highly oriented WSe2 thin films, with the c axis of the crystallites perpendicular to the substrate, were reproducibly obtained by interposing a Ni/Cr thin layer between the substrate and a WO3 precursor film. In the present work the preparation conditions were varied to elucidate the growth mechanism of such films. A model for the growth mode is proposed. Based upon this analysis, WSe2 thin films with improved crystalline and electronic properties were obtained. The photoresponse spectrum for photoelectrochemical cells with the WSe2 electrode immersed into a selenosulfate solution was measured. Quantum efficiency of 0.1% was calculated from this spectrum.

Neutron powder diffraction methods with Rietveld analysis are utilized to determine GaN lattice parameters from 15 to 298.1 K. Using these measurements and literature data, we calculated the thermal expansion of gallium nitride (GaN) and predicted its higher temperature thermal expansion. The results are compared with available experimental data and earlier work.

Nanosized amorphous alloy powders of Fe25Ni13Co62, Fe38Ni23Co39, Fe40,Ni24,Co36, and Fe69Ni9Co22 were prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO)5, Ni(CO)4, and Co(NO)(CO)3 in decalin, under an argon pressure of 100 to 150 kPa at 273 K. The amorphous nature of these particles was confirmed by various techniques, such as scanning electron microscopy, transmission electron microscopy, electron microdiffraction, and x-ray diffractograms. Magnetic measurements indicated that the as-prepared amorphous Fe–Ni–Co alloy particles were superparamagnetic. The observed magnetization measured up to a field of 1.5 kG of the annealed Fe–Ni–Co samples (75–87 emu g−1) was significantly lower than that for the reported multidomain bulk particles (175 emu g−1), reflecting the ultrafine nature of our sample.

Hillock formation, a stress-induced diffusional relaxation process, was studied in sputter-deposited Al films. The grain sizes in these films were small compared to those in other sputter-deposited Al films, and impurities (O, Ti, W) were incorporated during the preparation of the films. Stress and hardness measurements both indicate that the Al films were strengthened by the small grain size and incorporated impurities. We observed a new type of hillock in these Al thin films after annealing for 2 h at 450 °C in a forming gas ambient. The hillocks were composed of large Al grains created between the substrate and the original Al film with its columnar grain structure, apparently by diffusion from the surrounding area. By modifying the boundary conditions of Chaudhari's hillock formation model [P. Chaudhari, J. Appl. Phy. 45, 4339 (1974)], we have created a new model that can describe the experimentally observed hillocks. Our model seems to explain the experimentally observed abnormal hillock formation and may be applied to other types of hillock formation using different creep laws.

The combustion of zirconium in oxygen was simulated using a two-dimensional finite difference model. The model accounts for heat generation by the oxidation reaction and heat loss due to convective and radiative processes. Using geometric considerations along with the heat transfer conditions, the model was utilized to determine the effect of dilution and particle size on the combustion process. Dilution was examined in regular and random geometries and the results showed a marked influence on the nonlinearity of the wave. The effect of particle size was also examined as a function of the geometry of diluent dispersion.

A transparent magnetic particle/organic film was synthesized from an iron–organic compound. Iron(III) 3-allylacetylacetonate (IAA) was polymerized followed by in situ hydrolysis yielding an iron oxide particle/oligomer hybrid. The sizes of magnetic particles were dependent upon the hydrolysis conditions of the IAA oligomers. A nanometer-sized ferrimagnetic iron oxide particle/oligomer hybrid showed a magnetization curve with no coercive force at 300 K and that with Hc of 200 Oe at 4.2 K, respectively. The magnetization versus H/T curves at 300 and 77 K were superimposed on each other and satisfied the Langevin equation. The transparent hybrid film showed a magnetization curve at room temperature. The absorption spectrum of the film was shifted to higher energy by 0.14 eV compared with that of bulk magnetite. The absorption edge of the film was blue-shifted.

Fracture surfaces of a recently developed Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 (at.%) bulk metallic glass were investigated using a three-dimensional surface reconstruction technique. Stereoscopic scanning electron microscopy of both fatigue and overload fracture surfaces permitted the creation of digital elevation models that were used to quantify important fracture surface features. Characterization of the surfaces revealed striations of nearly constant spacing on fatigue surfaces and a vein morphology characteristic in amorphous metals on the overload fracture surfaces. Additionally, at the onset of critical failure, crack-tip openings of ˜16 μm were observed that were consistent with measured values of fracture toughness. Interestingly, at the onset of fracture, deformation was confined to one side of the fracture plane, possibly because of the asymmetric emission of shear bands from the crack tip, consistent with the highly inhomogeneous nature of deformation in this alloy.

Dense p-type and n-type SiGe thermoelectric conversion units were fabricated with a double-layer electrode of W/TiB2 or W/MoSi2 by using glass encapsulation hot-isostatic-pressing process. The TiB2 and MoSi2 layers were used to prevent the chemical reaction between the tungsten and SiGe materials. Si3N4 ceramic particles were added into the electrode materials to reduce the mismatch of the thermal expansion between the electrode and the SiGe. Finite element analysis showed that the addition of 40 vol% Si3N4 into the TiB2 layer and 55 vol% Si3N4 into the MoSi2 layer reduced the thermal residual stress to a much lower value than the strength of individual layer. Sintered units had electrical resistivities of (1.5–2.0) × 10−3 Ω cm in the SiGe zone and 10−4 Ω cm in the electrodes. The comparison of the thermoelectric properties of the SiGe sintered with and without electrodes confirmed that the electrodes did not deteriorate the Seebeck coefficient of the SiGe alloys.

The use of an electric field to activate the combustion synthesis of chromium silicides was investigated. Despite their relatively low adiabatic temperatures, all four silicides were synthesized by field-activated combustion synthesis. However, although self-propagating synthesis reactions were initiated, the products were not pure but contained other silicides and reactant phases. The purity of the samples increased with increasing field strength, and under the highest field, the products contained the desired silicide as the major phase with minor amounts of other stoichiometries. Observation of microstructural evolution in quenched reactions revealed the key role played by the liquid phases in the propagation of the combustion front. The phase Cr5Si3 was the first product of the interaction between the reactants when either solid–solid or solid–liquid processes were involved. These results were confirmed by isothermal solid–solid and solid–liquid diffusion couple experiments.

Bimodally porous titania powders with controlled phase composition and porosity were made by hydrolysis of titanium tetraisopropoxide (TTIP) and calcination. The extent of calcination was followed by thermogravimetric differential thermal analysis and Fourier transform infrared spectroscopy. The specific surface area (SSA) of the powders ranged from 10 to 500 m2/g as determined by nitrogen adsorption. The SSA increased by decreasing either the water concentration during hydrolysis or the calcination temperature. The pore size distribution was bimodal with fine intraparticle pore diameters at 1–6 nm and larger interparticle pore diameters at 30–120 nm as determined by nitrogen adsorption isotherms. The particle phase composition as determined by x-ray diffraction ranged from amorphous to crystalline anatase and rutile largely proportional to the calcination temperature and to a lesser extent on the initial H2O/TTIP molar ratio.

The behavior of Au in the course of the primary crystallization process of Fe87Zr7B5Au1 amorphous alloy was examined by use of atom probe field ion microscopy and transmission electron microscopy. In the early stage of crystallization, Au atoms were still distributed uniformly in the amorphous matrix. Au atoms form clusters at a later stage when more α–Fe particles are present. The Au clusters were observed to be separated from α–Fe particles, indicating that Au clusters do not stimulate nucleation of α–Fe particles. During the growth of α–Fe grains, cosegregation of Au and Zr occurred without any influence on the α–Fe grain growth. We conclude that Au addition has no effect on nanocrystallization of Fe–Zr–B amorphous alloys.

The room temperature mechanical properties of a mixed conducting perovskite Sm1?xSrxCo0.2Fe0.8O3 (x = 0.2 to 0.8) were examined. Density, crystal phase, and microstructure were characterized. It was found that the grain size increased abruptly with increasing Sr content. Mechanical properties of elastic modulus, microhardness, indentation fracture toughness, and biaxial flexure strength were measured. Young's modulus of 180–193 GPa and shear modulus of 70–75 GPa were determined. The biaxial flexure strength was found to decrease with increasing Sr content from ∼70 to ∼20 MPa. The drop in strength was due to the occurrence of extensive cracking. Indentation toughness showed a similar trend to the strength in that it decreased with increasing Sr content from ∼1.1 to ∼0.7 MPa m1/2. In addition, fractography was used to characterize the fracture behavior in these materials.

A huge magnetic hardening (i.e., increase of coercivity from 5 A/m up to 4.4 kA/m) was reported for Fe75Si11B10Nb3Sn alloy ribbons during their very first stage of crystallization from an initial amorphous state. In contrast, Fe78Si11B10Sn1 showed no such hardening, while a moderate hardening was observed for Fe76Si11B10Nb3. This outstanding change was ascribed to the generation of metastable nanocrystallites that disappear upon heating at higher temperatures. A noticeable softening was then recovered (with a decrease of coercivity down to 0.8 kA/m) once the optimum homogeneous conventional nanocrystalline phase was achieved. Both structure and magnetic evolutions are followed by different techniques.

Carbonate precursors of Y3Al5O12 (YAG) were synthesized from a mixed solution of alum and yttrium nitrate using ammonium hydrogen carbonate as precipitant. Precipitation method (normal-strike or reverse-strike) and aging were found to have dramatic effects on cation homogeneity of the precursor, which in turn influenced the formation temperature of the YAG phase. Reactive YAG powders were produced from the reverse-strike-derived, as-synthesized precursors at temperatures ≤1200 °C. These powders densified to >98.0% of the theoretical density up to 1500 %C at a constant heating rate of 8 %C/min or to transparency by vacuum sintering at 1700 %C for 1 h without additives.

Commercially useful multiphase alloy Inconel 783 is made up of Ni(28%), Fe(25%), and Co(35%) with smaller amounts of Cr, Al, Nb, Mo, Ti, C, and Si. In this work, relative temperature variations of the lattice constants a(T)/a0 of the gamma (face-centered-cubic) and beta (body-centered-cubic) phases of this alloy are determined from 97 to 773 K using analyses of their x-ray diffraction (XRD) patterns. Plots of a(T)/a0 for the two phases vary from 1.0 at 97 K to 1.012 at 773 K and show that (i) for T = 500 K, thermal expansion of the β phase is larger than that of the = phase; and (ii) an abrupt jump is observed near 300 K. The appearance of new lines above 700 K in XRD representing Co2CrO4 and CoCr2O4 is interpreted in terms of the oxidation of the γ phase, whereas the β phase is oxidation resistant. The anomalous change in a(T)/a0, observed near 300 K and accompanied by a similar change in the temperature variation of the initial magnetic susceptibility, is not well understood. A brief discussion on the implications of these results is presented.

It is known that diamond films display poor adhesion on metals such as copper and steel. One solution to overcome the poor adhesion is to use interlayer materials. In this study we report results of an investigation of the adhesion behavior of diamond on pure chromium (Cr) and titanium (Ti) substrates. Cr and Ti are promising interlayer materials for adhering diamond to stainless steel. The coating adhesion was studied using indentation tests combined with acoustic emission signals during loading. It was found that a 105-N load indentation caused the film to delaminate from the Cr substrate, while the diamond film remained attached to the titanium even after the indentation at 180 N. Micro-Raman spectroscopy was used to monitor the film stress. The diamond films grown on Ti substrates were found to be less stressed than the films grown on Cr substrates. Therefore, Ti was used in thin-film form to obtain adherent diamond coatings on steel.

This paper presents an x-ray diffraction and transmission electron microscopy analysis of Al1−xInxAs grown by molecular beam epitaxy. Two samples grown on (001) InP at temperatures of 370 and 400 °C are characterized. The first, which contains a high density of twin lamellae, exhibits triple-period short-range ordering with a rather short correlation range normal to the (111) planes. Within these (individual) planes, the concentration, however, is uniform over a considerably greater distance, leading to a highly anisotropic scattering. This is the first observation of triple-period short-range ordering in a sample that exhibits 2 × 1 surface reconstruction. The second sample exhibits CuPt-type short-range ordering with scattering that is significantly streaked, suggestive of lamellar-shaped ordered domains. Both samples contain high densities of stacking faults leading to additional sharp streaking along symmetry-allowed 〈111〉 directions.

The properties of nonequilibrium face-centered-cubic (fcc) and body-centered-cubic (bcc) Fe–Cu alloys were studied using the first-principles full-potential linearized augmented plane wave method within the generalized gradient approximation. The ab initio calculation results are compared quantitatively with the magnetic moment and atomic volume observed for mechanically alloyed FexCu100–x (x = 0 to 100) supersaturated bcc and fcc solid solutions. The calculations show that Cu alloying leads to a small enhancement of the magnetic moment of bcc Fe. The fcc Fe moment, on the other hand, experiences a more pronounced increase into a high-spin state upon alloying with Cu. It reaches approximately the same value as that in the bcc alloys for all Cu concentrations where fcc solutions are obtained in experiments, corroborating previous ab initio calculations using different methods. The magnetic moment increases are accompanied by an atomic volume expansion. Both the calculated moment and volume behavior are in good agreement with those measured for fcc and bcc Fe–Cu solutions. The magnetovolume expansion upon magnetic interaction between the alloyed Fe and Cu, rather than the positive heat of mixing, constitutes the primary reason for the atomic volume increase observed.

The isothermal reduction of synthetic CoTiO3 and NiTiO3 in hydrogen (1 atm) was investigated using thermogravimetric analysis technique in the temperature range, 928–1287 K (CoTiO3) and 884–1387 K (NiTiO3). Shallow beds of fine titanate powders were reduced by hydrogen at a high flow rate. Quenched samples were analyzed by scanning electron microscopy. The rates of the reaction of the titanates with H2 were very fast during the reduction of Co2+, Ni2+, or Fe2+ ions into metals. The reduction of the remaining titanium oxide was very slow. The activation energy for the reduction of CoTiO3 by hydrogen to Co and TiO2 was evaluated to be 151 ± 1 kJ/mol, and the activation energy for the reduction of NiTiO3 by hydrogen to Ni and TiO2 was evaluated to be 153 ± 1 kJ/mol. The study was complemented by hydrogen reduction of synthetic TiO2 (rutile). The results were also compared with the hydrogen reduction of FeTiO3.

Nanophase elemental Fe powders prepared by mechanical milling were sinter forged to full density with an average grain size in the nanophase range (below 100 nm). If Cu additions are introduced during milling to form supersaturated solid solutions (Fe85Cu15 and Fe60Cu40), grain sizes can be easily controlled to below 50 nm after consolidation. For Fe–Cu, it was observed that atomic level alloying between the two elements during milling was very helpful for obtaining a homogeneous microstructure and nanocrystalline grain/domain sizes in the consolidated product. The advantages of using sinter forging (upset die forging), as well as the role of the Cu addition, in the retention of nanocrystalline grain sizes are discussed. The consolidated Fe alloys exhibit very high strength under compression, further demonstrating that low populations of flaws and nanophase grain structures were attained in the consolidated products.