Silicon nitride films are grown by plasma enhanced chemical vapor deposition from tetrakis(dimethylamido)silicon, Si(NMe2)4, and ammonia precursors at substrate temperatures of 200-400 °C. Backscattering spectrometry shows that the films are close to stoichiometric. Depth profiling by Auger electron spectroscopy shows uniform composition and no oxygen or carbon contamination in the bulk. The films are featureless by scanning electron microscopy under 100,000X magnification.

Self-limited growth of InAs at 480 °C is achieved by a rotating substrate method with a specially designed susceptor. The residual precursors and the boundary layer are removed by the mechanical shear-off. Prevention of the precursor carryover and the gas-phase decomposition are thought to result in the self-limited growth of InAs at temperatures as high as 480 °C.

Monophasic β-SiC powder has been synthesized in a commercial microwave oven operating at 2450 MHz and power levels up to 980 W. This simple method of solid-state synthesis involves a direct reaction between silicon and charcoal powder at temperatures lower than 1250 K.

Rare-earth huntite-borates R(Al, Ga)3(BO3)4, where R = Yb, Er, and/or Nd, were grown by spontaneous crystallization from fluxes based on Bi2O3-B2O3. Crystals were removed from the melts and selected to different size fractions using meshes. It was found that dependence of weight for each size fraction on size in double logarithm coordinates was close to a symmetrical function. The dependence of logarithm of crystal amount on size was almost linear.

A fully oxygen-compatible ion-beam sputter deposition process (IBS) has been implemented for investigation of four film/substrate couples: (103)/(110)YBCO on (110)SrTiO3 (STO) and on (100)NdGaO3 (NGO), and (100)/(010)YBCO on (110)NGO and on (100)STO. For comparison, some (103)/(110)YBCO films have also been prepared by off-axis rf-magnetron sputtering. Below about 600 °C semiconducting, sub-nm flat, and perfectly single-crystalline YBCO films crystallize on these substrates with a crystallographic unit cell of about 1/3 of the Cu-O subcell of YBCO and perfect registration with the Ti4+-O and Ga3+-O sublattice of STO and NGO, respectively. At higher temperature superconducting YBCO films grow coherently epitaxially in the first ∼100 nm thickness; in thicker films the lattice-misfit strain relaxes to the “free” lattice constants. Above ∼680 °C a faceted (103)YBCO orientation grows on (110)STO and (100)NGO substrates with uniform in-plane orientation of the [010]YBCO direction parallel to [001]STO and [001]NGO. Along [010]YBCO the (103)YBCO films exhibit high crystalline perfection and intrinsic superconducting properties approaching those of (001)YBCO films in the plane; i.e., Tc,0 > 88 K, ΔTc,0 < 0.6 K, R300/R100 > 2.9, ρ100 > 250 μ°Cm, and jc (77 K) ⋚106 A/cm2. Practical use of (103)YBCO films is hampered by the large surface roughness. Above ∼680 °C a mixed (100)/(010)YBCO orientation grows on (110)NGO substrates, exhibiting a very smooth surface but less attractive superconducting properties; typically, Tc,0 ⋚ 80 K, ΔTc,0 ∼ 1 K, R300/R100 ∼ 1.2, ρ100 > 3 m°Cm, and jc (77 K) ⋚105 A/cm2. On (100)STO substrates the YBCO film orientation varies from pure (100)YBCO between ∼580 and ∼630 °C and mixed (100)/(010)YBCO below ∼660 °C to pure (001) YBCO above ∼670 °C. With rising temperature the surface roughness increases from <2 to ∼6 nm-rms, while the other parameters continuously improve to state-of-the-art values for c⊥-oriented films. Specifically, mixed (100)/(010)YBCO films reach Tc,0 > 86 K, δc,0 ∼ 1 K, R300/R100 > 2.8, ρ100 < 3 m°Cm, and jc (77 K) > 105 A/cm2. (100)/(010)YBCO films on (100)STO are a promising candidate for sandwich-type SIS-JJ.

The local order in a single crystal of YBa2Cu2.53Co0.47O7.13 has been studied with anomalous diffuse x-ray scattering. (For such a Co concentration the compound is nonsuperconducting.) Intensity measurements were carried out at two energies below the Co edge. The difference data could then be expressed in terms of the local structure around a Co atom. The short-range order parameters (α's) indicate that the Co and Cu atoms are nearly randomly distributed on the Cu1 sites. The estimated size of the Co-free “domains” is 5-7 Å. The first neighbor in-plane Co-Co distances are significantly shortened, indicating that the Co atoms are displaced from their average positions. The data also show a significant decrease of the Co-O1 distance, leading to an increase of the Cu2-O1 distance. The lengthening of the Cu2-O1 distance implies a lowering of the Cu2 formal valence. The Co substitution also affects the in-plane Cu2 positions. The present study shows that the Cu-O2 structural coherence is altered on a scale smaller than the superconducting coherence length. As far as the superconductivity is concerned, the Cu2 valence remains one of the most important parameters in determining the superconducting properties of the Co-doped 123 compounds. On the other hand, there is some evidence that in order for superconductivity to occur in this and other doped cuprate compounds, the size of dopant-free regions in the basal plane may have to exceed the superconducting coherence length.

The composition and microstructural evolution of nonsuperconducting phases during the course of formation of (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) in a silver sheath have been investigated by x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and digital image analysis. Wire samples fabricated by the oxide-powder-in-tube technique were heat-treated under a variety of conditions (time, temperature, and oxygen pressure). Backscattered images taken on polished but unetched transverse cross sections were subjected to computerized image processing, which allowed determination of the stoichiometry and quantification of microstructural characteristics (such as area fraction, size distribution, position, and orientation) of each nonsuperconducting particle. The dominant nonsuperconducting phases observed by SEM/EDX were CuO, (Ca,Sr)2CuO3 (2/1), and (Ca, Sr)14Cu24O41 (14/24) in amounts that varied depending on the annealing temperature, time, and oxygen partial pressure. Time evolution studies performed at 825 °C in 0.075 atm O2 showed that the area fraction of 2/1 decreased with reaction time, while that for 14/24 increased. In all cases, a substantial amount (>10% area fraction) of nonsuperconducting phases was detected even after all the Bi2Sr2CaCu2Oy (Bi-2212) in the as-rolled composite conductor was fully converted to Bi-2223, as determined by XRD. High aspect ratio nonsuperconducting particles were initially randomly oriented in the composite conductor core but gradually aligned parallel to the silver/(Bi,Pb)-Sr-Ca-Cu-O interface after extended annealing. They tended to segregate and exhibited a much broader size distribution when processing was carried out at temperatures and oxygen partial pressures on the high end of the normal processing range, most likely as a result of the occurrence of partial melting in the system.

Transmission electron microscopy and powder x-ray diffraction methods have been used to investigate the evolution of two-phase (L12 + DO22) microstructures from the quenched fcc phase of the Ni-5Al-20V (at. %) alloy. The microstructure after annealing in a temperature range from 650 to 900 °C differs from the eutectoid structure which might be expected for the alloy according to the eutectoid-type phase diagram of the Ni3Al-Ni3V section. This structure results from fast kinetics of ordering in the fcc → L12 and fcc → DO22 phase transitions. Four main stages in the microstructural evolution were observed. Stage I is the formation of spheroidal coherent L12 clusters in a disordered fcc matrix. During stage II the L12 clusters transform into cuboidal precipitates, and the fcc matrix orders into three DO22 variants (which may have interfaces that are wetted by thin fcc layers). In stage III accommodation of misfit (elastic energy) between different phases and variants occurs by formation of (110) twins or a single variant of the DO22 phase and tetragonally strained lamellae of the L12 phase. Stage IV is a discontinuous coarsening process in which a coarse incoherent two-phase structure replaces the fine coherent one. Grains of the coarse structure are nucleated on high-angle boundaries of primary fcc or other surfaces. Many of the grains are found twinned.

Diamond films exhibiting contiguous epitaxial crystallites (∼3-4 μm) have been grown on single crystal (100) silicon by 2.45 GHz microwave plasma deposition. The diamond films were deposited by a three-step process. In the initial stage the silicon wafer was pretreated for 3 h in a 1.8% methane in hydrogen plasma at low pressure. The subsequent nucleation stage was performed, under identical processing conditions, except that a dc bias of −340 V was applied for 25 min. During this period the current increased from 38 mA at the start to 102 mA at the end of the bias. The final growth stage was performed, with an earthed substrate, utilizing a carbon monoxide/methane/hydrogen gas mixture whose composition is conducive to uniformly faceted (100) diamond growth. Scanning electron micrographs showed that a large fraction of the (100) faces of the diamond crystallites are aligned with the (100) plane of the underlying silicon lattice with the crystallite edges parallel to the (110) direction. Raman scattering was used to confirm this finding by measuring the angular dependence of the Raman backscattering intensity at 1332 cm−1 using plane polarized excitation of individual crystallites within the diamond films.

The main puzzle in oxidation of hexagonal SiC is the slower rate of the Si-terminated surface as compared to the C-terminated surface, which is blamed on an unknown interface compound. ARXPS is a unique method to identify minor amounts of interface compounds, especially for smooth surfaces. Our ARXPS analysis of oxidized Si-(001) and C-(001) surfaces of 6H SiC reveals the interface oxide Si4C4−xO2 (x < 2), likely a reaction product of a peroxidic O2-bond to a SiC double layer. Si4C4−xO2 occurs in larger thickness (≃1 nm) at the slowly oxidizing Si-(001) surface, whereas the C-(001) surface shows smaller amounts, diminishing fast with oxidation above 1000 K. Evidence is presented that with increasing amount of Si4C4−xO2 the oxidation of SiC to SiO2 is reduced. ARXPS is consistent with a layer of SiO2 containing less than 3% Si4C4O4 being an oxidation product of Si4C4−xO2. At the surface of SiO2, graphite and some Si4C4O4 exist, aside from standard adsorbates.

Xenon and krypton have been implanted into muscovite mica at room temperature and at liquid nitrogen temperature. The behavior of the implanted Xe and Kr was followed by low-temperature transmission electron microscopy and energy dispersive x-ray analysis. An electron diffraction pattern of diffuse bands is observed at room temperature due to the presence of fluid rare gas and to noncrystalline mica. Visible cavities with diameters 10–300 nm formed in the Xe-implanted mica. Visible cavities in room-temperature Kr-implanted mica ranged from 5–50 nm in diameter. The gas pressures at room temperature in the cavities are estimated, assuming all of the implanted gas precipitated in cavities to be ∼10 MPa for Xe and ∼20 MPa for Kr. These pressures are considerably lower than found for rare gases implanted in metals and ceramics, but sufficient to liquefy the rare gases at room temperature. The Xe and Kr were observed by dark-field microscopy to form fcc crystalline solids within the cavities at temperatures below their triple points, with lattice parameters of a(xe) = 0.630 ± 0.0015 nm and a(Kr) = 0.565 ± 0.005 nm. The solid Xe within bubbles was unstable under the electron beam of the transmission electron microscope at temperatures above 80 K, while the solid Kr within bubbles was unstable at temperatures as low as 35 K. The crystalline mica matrix undergoes a transformation from a crystalline structure to an amorphous structure as a result of implantation.

Epitaxial films of single-layer SnO2 and PbTiO3/SnO2 heterostructures were obtained on (0001) sapphire (α-Al2O3) substrates by metal-organic chemical vapor deposition. X-ray diffraction and transmission electron microscopy were used to characterize the structural properties of these films. The epitaxial relationship for the heterostructure PbTiO3/SnO2/sapphire was found to be (111) [011]PbTiO3 ‖ (100) [001]SnO2 ‖ (0001) [1100]α-Al2O3. The fact that epitaxial ferroelectric films were obtainable in such a structurally highly heterogeneous system suggests that a wide range of material selection is possible in exploring the kind of applications that need to utilize epitaxial ferroelectric films in a multilayered heterostructure.

The solid-state epitaxial-regrowth kinetics of ion-beam-amorphized SrTiO3 surfaces annealed in water-vapor-rich atmospheres have been studied using time-resolved reflectivity (TRR). For this material, the conversion of the reflectivity-versus-time data obtained from the TRR measurements to recrystallized depth-versus-time data is more complicated than in systems such as silicon, where the reflectivity can be fit by assuming that the refractive index N (N = n + ik) in the amorphous layer is constant. In SrTiO3, agreement between measurements made directly with Rutherford backscattering spectroscopy (RBS) and those made using TRR can be obtained only when N is permitted to vary within the amorphous layer, with nonzero values for both the real and imaginary components. In some cases, the roughness of the amorphous/crystalline interface must also be considered. Additionally, a model for H2O-enhanced epitaxial regrowth is presented, which is in good agreement with the shape of the depth-versus-time profiles that are obtained from the TRR data.

The energetics of intermediate phases in the Ca2Fe2O5-CaTiO3 pseudobinary system was determined by high temperature solution calorimetry. The results suggest that both the intermediate compounds Ca3Fe2TiO8 and Ca4Fe2Ti2O11 are entropically stabilized because their enthalpies of formation are positive with respect to a mixture of Ca2Fe2O5 and CaTiO3. At high temperatures, the configurational entropy of the random distribution of Fe and Ti ions on the octahedral sites appears sufficient to stabilize the intermediate phases. The enthalpies of formation from the oxides at 1073 K of Ca2Fe2O5, Ca3Fe2TiO8, and Ca4Fe2Ti2O11 are −45.0 ± 3.8, −123.7 ± 8.0, and −192.7 ± 11.2 kJ/mol, respectively. Their enthalpies of formation from the elements at 298 K are −2139.8 ± 4.4, −3798.4 ± 8.6, and −5447.3 ± 12.2 kJ/mol, respectively.

Polyxylylene thin films grown by chemical vapor deposition (CVD) have long been utilized for uniform, pinhole-free conformal coatings. Homopolymer films are highly crystalline and have a glass transition temperature around room temperature. We show room temperature copolymerization with previously untested comonomers during the CVD process. Samples were studied with wavelength dispersive analysis, FTIR, scanning variable angle ellipsometry, and x-ray diffraction. Copolymerizing chloro-p-xylylene with perfluoro-octyl methacrylate results in dielectric constants at optical frequencies as low as 2.19, compared to 2.68 for the homopolymer. Copolymerizing p-xylylene with 4-vinylbiphenyl resulted in films whose onset of weight loss in TGA measurements was 450 °C, compared to 270 °C for the homopolymer.

The mechanical properties of compositionally modulated Au-Ni films were investigated by submicrometer depth-sensing indentation and by deflection of micrometer-scale cantilever beams. Films prepared by sputter deposition with composition wavelengths between 0.9 and 4.0 nm were investigated. Strength was found to be high and invariant with composition wavelength. Experimental and data analysis methods were developed to provide more accurate and precise measurements of elastic stiffness. Large enhancements in stiffness (the “supermodulus effect”) were not observed. Rather, relatively small but significant minima were observed at a composition wavelength of about 1.6 nm by both techniques. These variations were found to be strongly correlated with variations in the average lattice parameter normal to the plane of the film. Both structural and mechanical property variations are consistent with a simple model in which the film consists of bulk-like Au and Ni layers with interfaces of constant thickness.

The stresses that arise in compositionally modulated Au-Ni thin films as a result of the constraint of the substrate were determined from the curvatures of micrometer-scale bilayer cantilever beams consisting of a silicon dioxide layer upon which the metal film had been deposited. These substrate interaction stresses were found to vary strongly with the wavelength of the composition modulation. Simulations of the bulge test show that such stresses can account for the major features of the “supermodulus effect” as artifacts of the analysis method.

In a new approach to sinter Al/AlN composites in an overpressure environment of Al, the effects of sintering temperature and Al content on the microstructure, density, shrinkage, and mass gain were investigated. Fracture behavior and toughness were correlated with microstructure and composition of Al/AlN composites.

It is well known that mechanical properties of commercial stainless steel are improved by alloying with nitrogen. In this study a series of nitrogenated commercial 201 stainless steel alloys with nitrogen levels as high as 2.6 wt. % were obtained by melting in a hot-isostatic-pressure furnace using nitrogen as the pressurizing gas. Nitrogen concentrations in excess of 1.25 wt. % formed a series of different chromium nitride precipitates and morphologies depending upon the nitrogen concentration. Five different nitrogen levels were fabricated using the same processing conditions recommended for 201 stainless steel including hot-and cold-working, and heat-treating at two different temperatures. Tensile strength of the nitrogenated materials at each processing step was related to the interstitial nitrogen concentration and the presence or absence of precipitates. The presence of chromium precipitates did reduce the fracture ductility and changed the fracture features. This U.S. Bureau of Mines study shows that increasing the nitrogen concentration in commercial steels above their current level has positive effects on mechanical properties as long as the nitrogen solubility level is not exceeded and chromium nitride precipitates begin to form.

When liquid S is heated above 159 °C, the S8 rings (which are the dominant structural units below this temperature) break open and polymerize into helical chains (S∞). Therefore, samples quenched from liquids at temperatures above or below 159 °C would be different in various properties by the difference in the amount of S∞. The present ultrasonic study of liquid-quenched S in the temperature range from room temperature to 200 °C has revealed this difference. It has been demonstrated that ultrasonics is as powerful as a conventional thermal analysis in dealing with the variation of a material with increasing temperature, even though both techniques were found to be relatively insensitive to the polymerization process.