Titanium films were mixed, using excimer laser radiation, into the surface of bulk Si3N4 materials. The tribological and mechanical properties of these surfaces were then evaluated using pin-on-disk and nanoindenter techniques, respectively. Reduced friction and a change in the wear mechanism that resulted in a more benign failure mode were observed. These results are interpreted as resulting from the establishment of a transfer film, changes in the compliance of the surface which reduces instantaneous stresses in the surface, and toughening of the surface, all results of the laser process.

The authors completed a 3 MeV proton irradiation test on a terbium gallium garnet crystal sample. The main goal was to determine the proton dose required to reduce the fluorescence intensity to half its original value (half-brightness dose) at ambient temperature. The 3 MeV proton half-brightness dose was found to be 1.25 × 1015 p/cm2 using the Birks and Black relation. This decay is comparable to other fluors irradiated by the authors. The sample exhibited a yellow glow when irradiated in a 3 MeV beam. The fluorescence spectrum was composed of four peaks at wavelengths of 487.2 nm, 542.4 nm, 589.92 nm, and 624.1 nm.

A two-dimensional model of oxygen-deficit layer of superconducting material YBa2Cu3O7 has been simulated by the molecular-dynamics technique in order to study the influence of the impurities in the site of copper on the low-temperature microstructure. The microstructure pattern arises as a result of quenching the system from a high-temperature tetragonal phase to the low-temperature orthorhombic one and subsequent annealing. The potential of the impurity is modified in such a way that it promotes occupation of opposite nearest-neighbor sites around impurity by an oxygen and vacancy simultaneously. The simulations of the annealing processes showed that the domain pattern becomes very tiny with increased concentration of randomly distributed impurities. Domains of larger sizes would appear if the impurities were able to diffuse to the domain walls. This is confirmed by annealing the sample containing linear chains of impurities. The tweed microstructure depends on the magnitude of the force constants of the elastic subsystem, and at too large coupling the randomly distributed impurities are not able to pin the stiff domain walls. The results resemble the electron-microscope photographs made for cobalt in YBa2(Cu1−xCox)3O7−δ.

Defects in Bi2Sr2Can-1CunOy superconducting thin films annealed in an oxygen atmosphere are examined by high-resolution electron microscopy (HREM). In addition to the majority 2212 (n = 2) phase, subsequent slabs of other homologous phases with n values up to n = 10 are found intergrown in the films. Large-angle tilt grain boundaries and various secondary phases such as CuO, Sr-Cu-O oxides are formed in the films. The occurrence of these defects is attributed to an inhomogeneous Sr, Ca, and Cu distribution induced by the post-annealing. Superconducting transition temperature (Tc) is increased by the annealing under suitable conditions.

Starting from a glassy precursor, Bi2Sr2Ca1−xDyxCu2O8−y (for x = 0.2) was recrystallized under a 0.6 T magnetic field. After splat quenching, the samples were heated and sintered at different temperatures T1, then slowly cooled. X-ray diffraction data, sometimes showing 00l peak splitting and electron scanning microscopy pictures, were collected. The results showed that the magnetic field could orient the grains and led to a magnetically textured growth process. Secondary phases formed in the system during this process were identified by EDX analysis. The optimum T1 for texturing was found to be between 930 °C and 950 °C.

Amorphous silicon germanium (a-SiGe) films, deposited on silicon substrates at room temperature in a molecular beam epitaxy system, were transformed into a single-crystal film and doped with phosphorus by exposure to KrF laser pulses. Electron channeling patterns showed that laser exposure resulted in crystallization of the undoped a-SiGe films. The SiGe films were doped by laser irradiation, using a phosphorus spin-on-dopant. The sheet resistance of the doped films decreased with increasing numbers of pulses, reaching a value of about ∼ 5 × 104 ohms/□ after 15 pulses. I-V data from mesa-type n-SiGe/p-Si diode devices were used to determine the effect of laser processing on the quality of the SiGe films.

A study was made of the thermal properties of low pressure chemical vapor deposition (LPCVD) silicon thin films with amorphous and polycrystalline microstructures, produced by varying the substrate temperature. Thermal diffusivity measurements were conducted using a thermal wave technique. The thermal diffusivity of the polycrystalline films was found to be about three times that of the amorphous films, but about one eighth that of bulk silicon single crystals. There was also an indication that the diffusivity increased with deposition temperature above the transition temperature from the amorphous to the polycrystalline state. The relationships between the thermal properties and microstructural features, such as grain size and grain boundary, are discussed.

This paper reports on the formation of metastable π phase on mechanical alloying of elemental Ag and Te powders in the composition range of 50 to 75 at. % Te. Contrary to the reported results in vapor-deposited thin films, no amorphous phase could be detected during mechanical alloying. The extent to which the π phase forms on milling is restricted, compared to rapid solidification. Formation of the metastable π phase coincides with the achievement of nanometric grain size and is preceded by the formation of intermetallic compound Ag2Te. An approximate estimation of the free energies of the competing phases has been attempted to provide insight into the phase selection process. It is suggested that tellurium diffusion through the nanoscale grain boundaries plays an important role in the formation of the metastable π phase.

The quasicrystalline (qc) alloy Al65Cu20Cr15, unlike its Ru- and Fe-bearing counterparts like Al65Cu20Ru15 and Al65Cu20Fe15, is a metastable phase. This qc alloy has been shown to possess several structural variants and curious structural characteristics. We have investigated the qc alloy Al65Cu20Cr15 with special reference to the possible occurrence of new structural variants. TEM exploration of the as-quenched qc alloy has indeed revealed the existence of several new phases. These are (i) body-centered cubic (bcc) (a = 12.60 Å, disordered) and simple cubic (s.c.) (a = 12.60 Å, ordered), which are the 1/1 approximants of the primitive icosahedral phase (i phase); (ii) a twice order-induced modulated cubic phase (bcc, a = 25.20 Å) which has been shown to correspond to 1/1 approximant of the ordered i phase [i.e., face-centered icosahedral (FCI)]; and (iii) real crystalline bcc (a = 8.90 Å) and face-centered cubic (fcc) (a = 17.98 Å) phases possessing a specific orientation relationship with the icosahedral matrix phase. Tentative structural models showing the interrelationships between the bcc/fcc phases have been outlined.

Structure factors of μ-TiAl equiaxed grain in TiAl duplex intermetallic compound before and after V-alloying were measured by the quantitative electron crystallography method. Then the structure factors were transferred into charge-density distributions of real space. Comparing the charge-density distributions in γ-TiAl with those in V-alloyed γ-TiAl, it was found that V-alloying with the optimum amount decreases the electronic charge density in the Ti-Ti interatomic bond, and increases the electronic charge density in the Al-Al interatomic bond and Ti-Al interatomic bond. Thus, the anisotropy of charge-density distribution in γ-TiAl equiaxed grain is reduced.

The structure and the thermal stability of the Fe0.89B0.11 rapidly quenched alloy have been investigated. Transmission Mössbauer measurements were carried out as a function of temperature in the range from 148 K to 513 K. Room temperature x-ray diffraction and transmission and conversion-electron Mössbauer experiments, as well as 4.2 K spin-echo nuclear magnetic resonance measurements, were also performed after some selected thermal treatments for one hour between 523 K and 1273 K. Based on these experiments it is suggested that the alloy is inhomogeneous at nanoscopic scale and consists of a fine dispersion of a defective boride phase with an o-Fe3B-like short-range order, embedded in an α-Fe matrix. This result gives support to the models which indicate phase separation in the amorphous phase with o-Fe3B short-range order prevailing in the hypereutectic iron concentration range. This phase was found to be less stable than the undefective one present in the less boron concentrated alloys. The transformation into the equilibrium phases, analyzed with an Arrhenius-type temperature dependence for the increase of the relative fraction of Fe2B, led to an activation energy Ea = 1.38 ± 0.68 eV/atom.

The evolution of microstructure in a cast, extruded, and aged eutectoid Zn-Al-Cu alloy is described based on x-ray diffraction an micrographic observations. Whereas the three phases α′, β′, and η′ were found in the as-cast state, the three phases α, T′, and η′E were observed in this alloy after extrusion at 250 °C. The Al-rich fcc α phase appeared as isolated particles with clear boundaries. The Zn-rich η′E phase decomposed upon aging into α, T′, and η phases. It was found possible to control the phase makeup of the alloy by controlling extrusion temperature. At extrusion temperatures greater than 268 °C, α, E, and η′E were detected, whereas temperatures below this, the phases α, T′, and η′E were found. After prolonged aging, the phase makeup of the alloy was found to be the same regardless of prior treatment routes. Early shrinkage of the extruded alloy occurred after aging at 91 and 150 °C and was related to precipitation of aluminum from the η′E phase during its decomposition to α, T′, and η products.

Solute-atom segregation is studied by Monte Carlo simulations for three high-angle symmetrical (002) twist boundaries in Au-1 at. % Pt and Pt-1 at. % Au alloys at T = 850 K. It complements our previous study, that focused mainly on low-angle boundaries in the same alloys. Solute enhancement occurs on the Pt-rich side of the phase diagram, while on the Au-rich side net depletion in solute is observed. Following the trend observed for low-angle boundaries, Au as a solute prefers the structural units of the perfect crystal type, while Pt as a solute is depleted at those sites. The solutc concentration at structural units depends on the planar fraction of those units in the boundary.

This paper deals with the growth by molecular beam epitaxy of semimetallic (rare-earth group V element) compounds on III-V semiconductors. Results are presented, first on the Er-Ga-As and Er-Ga-Sb ternary phase diagrams, second on the lattice-mismatched ErAs/GaAs (δa ≈ +1.6%), YbAs/GaAs (δa/a = +0.8%), and ErSb/GaSb (δa/a ≈ +0.2%) heterostructures, and third on the lattice-matched Sc0.3Er0.7As/GaAs and Sc0.2Yb0.8As/GaAs systems (δa/a < 0.05%). Finally the growth of YbSb2 on GaSb(001) is reported. The studies made in situ by reflection high-energy electron diffraction (RHEED) and x-ray photoelectron diffraction and ex situ by x-ray diffraction, transmission electron microscopy, He+ Rutherford backscattering, and photoelectron spectroscopy are presented. We discuss the atomic registry of the epitaxial layers with respect to the substrates, the appearance of a mosaic effect in lattice-mismatched structures, and the optical and electrical properties of the semimetallic films. The problems encountered for III-V overgrowth on these compounds (lack of wetting and symmetry-related defects) are commented on, and we underline the interest of compounds as YbSb2 which avoid the appearance of inversion defects in the GaSb overlayers.

The activation energies, Ea's, for Pt2Si and PtSi formation were determined using in situ resistance measurements with ramp rates ranging from 0.4 °C/m to 100 °C/s. Measurements were performed using both conventional furnace and rapid thermal annealing (RTA). Pt films were evaporated on undoped polycrystalline Si and single-crystal Si on sapphire substrates. The Ea's determined from Kissinger plots were 1.63 ± 0.05 and 1.61 ± 0.06 eV for Pt2Si formation and 1.83 ± 0.06 and 1.83 ± 0.07 eV for PtSi formation with polycrystalline Si and silicon on sapphire substrates, respectively. These are the first reported measurements of Ea's for Pt2Si and PtSi formation over such a wide range of heating rates (greater than four orders of magnitude) and at such high heating rates. The phase formation sequence remained the same for the range of heating rates examined.

Crack initiation and progression have been studied in nanoscale brittle/ductile multilayers of Cu and Si. Variations in the interface debond energy on the cracking behavior have been examined by using thin interlayers comprising either Cr (strong interface) or Au (weak interface). For strongly bonded Cr interfaces, it has been found that cracks forming in the Si invariably extend through the Cu layers, despite the ductile rupture characteristics of the Cu. This behavior occurs even when the Cu layers comprise more than 70% of the multilayer volume. It also contrasts with the crack arrest capabilities exhibited by relatively thick ductile layers (∼10-100 μm). The disparity in behavior is attributed to the relatively large cracking strain required for the thin brittle layers. Weak Au interfaces result in debonding which, in turn, can suppress the propagation of cracks into adjacent layers. However, when the interface includes strongly bonded sections, the debond arrests, and often kinks into the attached Si. In this case, cracking still progresses sequentially through the Si layers. Careful control of the interface debond energy is needed to fully suppress crack progression in nanoscale multilayers.

PAN-based activated carbon fibers were saturated by dye adsorption and then were regenerated by thermal treatment in carbon dioxide and in air. The dye adsorption and the regeneration were carried out in several cycles. The changes in fiber physical properties and the capacity of dye adsorption will be discussed. Activated carbon fibers regenerated in air had greater dye adsorption and weaker mechanical properties than those regenerated in carbon dioxide. The preferred orientation changed slightly during air reactivation, but it decreased gradually after carbon dioxide regeneration. The regeneration processes led to a decrease in the weight and degradation of mechanical properties, but the processes increased the capacity of dye adsorption. After the second regeneration, the dye adsorption capacity of activated carbon fibers that were recycled by air regeneration was 15% higher than those that were recycled by carbon dioxide regeneration. But, after the third regeneration, the fibers recycled by air regeneration lost their mechanical properties. For carbon dioxide regeneration, fibers retained satisfactory mechanical properties even after the fourth regeneration. This study indicates that multiple effective applications can be accomplished with carbon dioxide treatment in place of air regeneration. The structural changes of activated carbon fiber during different regenerations are proposed.

A novel method to synthesize “clean” carbon nanotubes with relatively high yield in a hydrogen arc discharge has been developed. The quality and yield of the tubes depend sensitively on the gas pressure in the arc discharge. Sharp, open-ended nanotubes with clear lattice fringes at the edges and empty interiors have been observed. The existence of these frozen-open-ended tubes as part of nanotube-bundles provides evidence for an open-ended growth model for nanotubes. Using time of flight mass spectrometry, it was found that fullerenes, such as C60 and C70, are almost absent from the soot collected in the hydrogen arc discharge. The effect of hydrogen on the formation of fullerenes, both in the laboratory and in space, will be discussed.

A this paper the influence of surface roughness on contact angles in the system of liquid Al wetting solid surfaces of Al2O3 has been studied. It was observed that contact angles of liquid Al vary significantly on different rough surfaces of Al2O3. A model is proposed to correlate contact angles with conventional roughness measurements and wavelengths by assuming a cosine profile of rough grooves with a Gaussian distribution of amplitudes. In comparison with the experimental results, the model provides a good estimate for describing the influence of surface roughness on contact angles of liquid Al on Al2O3.

A simplified model of a direct current arcjet-assisted diamond chemical vapor deposition reactor is presented. The model is based upon detailed theoretical analysis of the transport and chemical processes occurring during diamond deposition, and is formulated to yield closed-form solutions for diamond growth rate, defect density, and heat flux to the substrate. In a direct current arcjet reactor there is a natural division of the physical system into four characteristic domains: plasma torch, free stream, boundary layer, and surface, leading to the development of simplified thermodynamic, transport, and chemical kinetic models for each of the four regions. The models for these four regions are linked to form a single unified model. For a relatively wide range of reactor operating conditions, this simplified model yields results that are in good quantitative agreement with stagnation flow models containing detailed multicomponent transport and chemical kinetics. However, in contrast to the detailed reactor models, the model presented here executes in near real-time on a computer of modest size, and can therefore be readily incorporated into process control models or global dynamic loop simulations.