The passivation of the nitrogen top-layered (100) surface of cBN by hydrogen was theoretically predicted recently to be related to the difficulty of chemical vapor deposition of cubic boron nitride. The possibility of photochemical depassivation of this surface was suggested by the anti-bonding nature of the surface H–N bonds at the lowest unoccupied molecular orbital; that was demonstrated by AM1 molecular orbital calculations using large cBN clusters such as B30N32H64(2+) and B30N32H62 (2BH3).

We report a novel method for the synthesis of carbon nanotubes: low temperature solid pyrolysis. By pyrolysis of hexamethyldisilazane-derived silicon carbonitride powders in a graphite furnace, we synthesized carbon nanotubes at 1400 °C. This new method has advantages of in situ growth of the carbon nanotubes, is stable in the synthesis process, and is technically simpler than conventional arc-discharge methods.

Differential thermal analysis, in air and argon, in concert with x-ray diffraction, was performed on 2- and 3-component mixtures of Al, B2O3, and TiO2, to foster an understanding of the reaction path involved in the TiB2-forming thermite reaction. In argon, aluminum reacted with B2O3 to form elemental boron, and reacted with TiO2 to form AlTi3. These two products reacted just after boron was made available at ∼1060 °C to form TiB2. Formation of Al18B4O33 by reaction between B2O3 reactant and Al2O3 product attenuated the yield of TiB2, but facilitated its formation by extraction of Al2O3 reaction barriers.

The interfacial characteristics of positive temperature coefficient of resistance (PTCR) BaTiO3-electrode interfaces were studied. Sessile drop wetting experiments in combination with measurements of the contact resistance of the interface were used to establish a fundamental perspective of the electrode-ceramic interface. It was shown that the thermodynamic work of adhesion Wad), which is the sum of the strengths of chemical interactions present at the interface, can be manipulated by the addition of chemically active elements to the electrode metal which enhance adhesion. This same procedure is shown to modify the important electrical interfacial properties such as the contact resistance.

A new method to prepare polycrystalline AlN thin films biaxially oriented on amorphous substrates has been demonstrated. The films were deposited at different angles of incidence with a rf sputtering system. Population-1 crystallites, oriented with their c-axis pointing toward the incoming flux with random orientation in aximuthal directions, predominate at low angle of incidence (near normal). Population-2 crystallites result from non-normal incidence and have their c-axis tilted away from the incoming flux and predominate at high, near glancing, angle of incidence. The alignment of crystallites (population-2) increases with angle of incidence. Crystallites align along the [11*0] channeling direction, characterized by a low sputtering yield, while misoriented crystal grains suffer a higher resputtering and their growth is inhibited. For films deposited at 75°, the FWHM of an x-ray ϕ scan profile is 25°, indicating a high in-plane alignment.

A novel metal salt of TCNQ (tetracyanoquinodimethane) has been synthesized via an electrochemical process using cadmium as donor. Thin films of the same material have been obtained by evaporating under high vacuum the metal and the organic molecule. The electronic properties of a pellet of the powdered material have been investigated by means of standard UV-VIS-IR spectroscopy, x-ray photoelectron spectroscopy, and Auger electron spectroscopy. The complex shows two absorption structures at about 3.4 eV and 1.7 eV due to the in-plane intramolecular transitions and a shoulder at about 1.4 eV probably due to the bond with the metal. The infrared spectrum is dominated by a deep absorption structure distinctive of the charge transfer. The electrical conductivity of the sample shows a semiconductor behavior in the investigated temperature range; the best fit of the transport data provides an activation energy of about 0.12 eV and shows that at low temperature the electrical conductivity is mainly due to a hopping process among differently charged sites.

The strain compensation produced by heavy boron doping in Si1−xGex layers with x = 0.21, 0.26, and 0.34 grown by solid phase epitaxy on (001) Si wafers has been analyzed using high resolution electron microscopy, high resolution x-ray diffractometry, and ion channeling. The structure of the epilayers consists of a defect-free region located next to the layer-substrate interface and a top region which contains strain-relieving defects. In the undoped samples the defect-free layers are partially relaxed and their relaxation increases as the Ge fraction increases. Substitutional boron incorporated to the SiGe lattice to levels of 2.8 ± 0 3 × 1020 cm−3 during the growth process reduces the lattice mismatch between the epilayers and the substrate. The boron-doped, defect-free layers are thicker than the corresponding undoped layers of the same Ge content and their strain relaxation is lower. It has been shown that it is possible to grow at least 27 nm thick defect-free and fully strained heavily boron-doped layers with x = 0.21 by solid phase epitaxy.

Thin-film heterostructures experience structural relaxation when subjected to post-deposition thermal heat treatment. The rate of relaxation, elastic effects, and inelastic effects on the stress and deformation of the structure are determined by the physical properties of the materials, in particular, the solid-phase viscosity. During relaxation, movement of defects causes an increase of viscosity with time at a constant rate as these defects are annihilated. Experimental anneals have been performed on structures with polycrystalline silicon films on (111) germanium substrates, in which the substrate relaxes during thermal annealing. A numerical analysis of the experimental results has determined values for the viscosity and viscosity rate of (111) germanium wafers. In addition, four zones of the relaxation process have been identified, and results indicate that the increasing viscosity with time has a larger effect at lower furnace ramp-up rates.

We have performed resistivity and magnetoresistance measurements down to 0.3 K, and under fields up to 37 T of boron carbonitride and BC3 films prepared by chemical vapor deposition. The turbostratic structure of the as-deposited materials favors a 2D weak localization effect which is invoked to explain the negative magnetoresistance (MR) as well as the log T variation of the resistivity. However, at very low temperature a positive component is superimposed on the negative MR. At high fields, the total MR is positive and almost isotropic. Usual theories are unable to account for the observed phenomenon. Increasing heat treatments up to 1800 °C increase the 2D character of the deposits, which show an increasingly negative magnetoresistance. For still higher treatments, the change of the films to a 3D graphitic-like structure leads to a vanishing of the negative magnetoresistance.

Amorphous Si (a–Si) films, sputter deposited under lower Ar pressure conditions, include numerous Ar atoms and exhibit high refractive indices, higher even than that of crystalline Si (c–Si), notwithstanding their lower Si densities. Such behavior in the refractive indices of the films was inconsistent with the conventional explanation considering only the density term in the Clausius–Mossotti relation. In the present study, the contribution of the polarizability changes of the films is proposed in order to account for the result in the refractive index. The molecular orbital (MO) calculations and experiments reveal that the polarizability of the a–Si film is sensitive to change in the angular distortion of the Si–Si bonds brought on by changing deposition conditions. The incorporated Ar atoms are found to cause the distortion in the Si network, leading to higher refractive indices for the less densified films.

The recovery of lattice damage in ion implanted 6H-SiC single crystals by thermal annealing has been investigated in the temperature range 200–1000 °C by Rutherford backscattering spectrometry-channeling and by optical measurements in the UV-visible wavelength. The damage was produced by implantation at room temperature of 60 keV N+ at fluences between 1014 and 5 × 1015 ions/cm2. At low fluences a partially damaged layer with defects distributed over a depth comparable to the projected ion range was obtained. At higher fluences a continuous amorphous layer was formed. The defect annealing behavior depended on the initial damage morphology: an almost total defect recovery occurred in partially damaged layers with kinetics depending on the initial damage degree. If the defect concentration is smaller than 20 at.% the annealing rate is independent of temperature. Amorphous layers were stable in the investigated temperature range and no epitaxial regrowth occurred. After annealing, a strong change in the optical properties of the amorphous phase was observed indicating a recovery of the electronic properties of the material, suggesting the existence of several amorphous states and the relaxation of the amorphous that evolves toward thermodynamic states characterized by lower free energy values.

The reaction between shape-memory TiNi thin films and silicon has been characterized by conventional, analytical, and high-resolution transmission electron microscopy. A reaction layer is formed during the 525 °C post-deposition crystallization anneal of the sputter-deposited TiNi, and consists of several phases: Ti2Ni, a nickel silicide, and a ternary titanium nickel silicide. The mechanism for the interlayer formation is discussed.

A model based on mosaic pattern analysis is shown to have the potential to describe the complex shapes and spatial distribution of phases in the microstructures of multiphase materials. Several characteristics of both micrographs of portland cement pastes and images generated using the few parameters of the model are determined and, for the most part, agreement is good. The advantage is that spatial features of the microstructures can be captured by a few parameters.

A near-surface thin layer is melted when alumina is pulsed-laser-irradiated in an Ar–4% H2 atmosphere or in air. A thin layer of amorphous phase forms when the substrates are irradiated in Ar–4% H2 at 1 to 1.3 J/cm2 with multiple laser pulses. Amorphous phase is also found in samples laser-irradiated in air and oxygen. After a laser pulse at an energy density of 1.6 J/cm2 or higher the melt solidifies epitaxially from the unmelted substrate with a cellular microstructure. There is a decrease in the cooling rate of the melt as the laser energy density is increased because more heat must be dissipated. The amorphous phase forms when the heat input due to the laser pulse produces a superheated melt that cools down sufficiently fast to avoid crystallization. Very small particles of aluminum in the laser-melted and subsequently solidified layer are observed only in samples laser-irradiated in an Ar–4% H2 atmosphere. In this reducing atmosphere, the alumina is possibly reduced to metallic aluminum which is mixed into the melt by the turbulence provoked by the laser pulses. The effects of these metallic particles on copper deposition when the irradiated substrates are immersed in an electroless bath are discussed.

Ultrafine titania particles were synthesized from titanium tetraethoxide (TEOT) dissolved in ethanol. The concentration of water and of the soluble polymer hydroxypropylcellulose (HPC) were varied to control particle size. The HPC adsorbed onto the titania particles during growth, providing a steric barrier to aggregation. Electron microscopy showed that particles smaller than 70 nm were formed at high water concentrations (R > 120 where R is the molar ratio [H2O]/[TEOT]) and in the presence of HPC. The annealing-induced, phase-transformation behavior of these particles (amorphous → anatase → rutile) from 100 to 1000 °C was characterized by x-ray, Raman, and infrared techniques. The conversion of anatase to rutile occurred more readily for particles made at high water concentrations and with HPC. For particles formed by premixing TEOT with HPC prior to hydrolysis at R = 155, an 800 °C anneal yielded a rutile fraction exceeding 95%; particles made at R = 5.5 with no HPC showed negligible conversion at this temperature.

Ion-irradiation was observed to transform MgAl2O4 spinel first to a metastable crystalline phase and then to an amorphous phase at cryogenic temperatures. Elastic stiffening of 15% occurred upon formation of the metastable crystalline phase. A second transformation from the metastable crystalline spinel to an amorphous state was accompanied by elastic softening of 25% relative to unirradiated spinel. This phase transformation behavior in spinel appears to be different from that in intermetallic compounds where only elastic softening associated with radiation damage accumulation is observed. A two-stage radiation damage model is proposed to explain the observed phase transformations.

The response of ferroelastic crystals on an applied stress is considered, and a distinction is seen between the reorganization of the domain structure within a grain at low stress and the reorientation of whole grains at high stress. The procedures are modeled in the framework of defect theory, i.e., by twinning dislocations and deformation twinning. The reorganization is controlled by the motion of pre-existing twinning dislocations. Since the Peierls stress of the twinning dislocations is very small, domain reorganization occurs under a very small load. The process of grain reorientation involves the nucleation of dislocations and, therefore, it requires a much higher stress. This concept is confirmed by comparison with experiments.

The abnormal aging behavior, i.e., severe aging in the electric field induced piezoelectric coefficient while very weak dielectric aging, observed in the relaxor ferroelectric lead magnesium niobate-lead titanate (PMN-PT) ceramics under a dc electric bias field, can be significantly reduced by hot isostatic pressing (HIP) treatment on presintered samples. The aging can also be reduced by doping suitable amounts of either La (donor) or Mn (acceptor). We suggest that the reduction in the aging is due to the introduction of additional random fields into the material, which reduces the probability of the growth of micropolar regions into metastable and/or stable macropolar domains. The abnormal aging behavior and the effectiveness of HIP in reducing it indicate the importance of the elastic energy in controlling the aging and relaxor behavior in PMN-PT relaxor ferroelectrics.

In this paper we demonstrate a novel liquid-exchange process to replace a secondary silicon phase in reaction-bonded siliconized silicon carbides (RBSC's) with a ductile metal reinforcement phase. When RBSC is exchanged with pure Al or Al–Si liquid, secondary phase silicon is dissolved and is substituted by Al or Al–Si alloy. The resulting composites show improvements in fracture toughness (single-edge precracked beam technique), with KIC value up to 8.6 Mpa · m1/2, compared to 3–4 MPa · m1/2 in otherwise similar siliconized silicon carbide. Increased fracture strength (four point flexure) was also observed after the liquid exchange process. The processing furthermore allows the coefficient of thermal expansion to be adjusted, and the thermal conductivity increased, for electronic packaging applications.

The structures of interfaces in NiAl-matrix in situ composites reinforced by TiC particulates were studied by means of high-resolution electron microscopy (HREM). No consistent orientation relationship between TiC particles and the NiAl matrix was found. In most cases, TiC particles bonded well to the NiAl matrix free from any interfacial phases. However, in some cases, an interfacial amorphous layer with a thickness of about 3 nm was found. The annealed NiAl–TiC composite showed a good chemical compatibility between the TiC particles and the NiAl matrix, though, some interfacial layers between TiC and NiAl, which were determined to be C-deficient TiC, were found. NiAl precipitates were observed in the TiC particles of the annealed specimens.