The pronounced anisotropy of shrinkage in the axial and the radial direction, observed in earlier studies on the sintering behavior of cordierite-type glass powder, is investigated in detail. It is shown that a planar orientation of the pore/solid interface exists that gives rise to an oriented shrinkage in the radial direction. The results show that the axial-to-diametral shrinkage ratio increases from a value of 0.3 to approximately 0.7 with increasing density, and that particle size and particle shape of the glass powders have little influence on shrinkage anisotropy.

A well-established stability model for hydrocarbon molecules is reviewed and then applied to organometallic compounds used in the epitaxial growth of HgCdTe films. For hydrocarbon molecules, the strength of carbon-hydrogen bonds is modified by neighboring organic groups. The mechanism for this effect is delocalization of the free radical electronic charge by the neighboring groups. The delocalization effect is present in organometallic compounds and is illustrated for tellurium, mercury, and cadmium compounds. An important application of the delocalization effect is the development of a low-temperature approach for pyrolytic metalorganic growth of HgCdTe.

The crystallization kinetics of thin (35 and 60 nm) amorphous as-deposited Ge films were studied using diffraction limited laser beam irradiation and laser pulses between 30 ns and 1 ms. The recrystallization of crystalline as-deposited films was also studied for similar laser conditions. Crystallization was observed for pulses as short as 50 ns. It was concluded that the irradiation of amorphous thin films with small beam spots (∼ 1μm) gives a very different crystallization morphology from that observed previously for larger beam diameter and same laser pulse length. In the present case for short irradiation times, the nucleation process dominates over crystal growth. Temperature calculations allow the understanding of these results by showing that only the small spot irradiation sustains the material at high temperature for times comparable to the pulse width. Laser irradiation of as-deposited crystalline films produced grains with significantly fewer defects than grains crystallized from as-deposited amorphous films.

Here a-Si:H is prepared by ion bombardment-activated reactive evaporation of Si in a H2O residual gas pressure ranging from 10−9 to 10−7 Torr. The Si+ ions (2.7keV) are bombarding the substrate and the walls during evaporation. Two hydrogen incorporation mechanisms are revealed by H evolution experiments, depending on the H2O residual gas pressure during evaporation. In the first mechanism H is sputtered from the walls of the system by the ion bombardment; this mechanism contributes 10 at. % to the hydrogen content. In a second mechanism Si+ bombardment on the growing layer injects H from H2O molecules adsorbed on the film surface; at least 5 at. % H is incorporated by this process. The second mechanism has a remarkable influence on the microstructure as revealed from the electrical conductivity, electron spin resonance, and infrared transmission. Indeed, Si+ bombardment-induced injection of H changes the conductivity type from variable range hopping to an activated behavior, while the dangling bond density remains low (< 1018 cm −3). The growth of [SiH2]n bundles, observed by the resonance frequency and absorption strength of the stretch mode of the Si–H dipole, is also a consequence of the H injection mechanism. It is concluded that the properties of the a-Si:H, prepared by ion bombardment-activated reactive evaporation, are explained by a microstructure, dependent on the specific hydrogen incorporation mechanism.

Laser-beam-controlled heating appears to be an excellent technique for driving isothermal transformations in a thin solid film on a thick substrate. The transformation is detected by the change in optical properties of the film as it evolves from the initial to the final state. Results are presented for the amorphous-to-crystalline transition in 100 nm thick films of InSb and of some Te alloys on thick glass substrates. Discrimination between interface growth and homogeneous crystallization can be made from the data. The crystallization of InSb films can be desribed by an Avrami equation with a single activation energy of 154 ± 6 kJ/mol over the full range of measured crystallization times between 100μs and 1000s. For low temperatures the results are consistent with differential scanning calorimetry (DSC) measurements. For Te-alloy films, the large temperature interval covered by the experimental method enables clear observation of the curvature of the temperature-time-transmission (T–t–t) plot.

The wetting of ceramic surfaces by aluminum alloys has been reexamined using a chemical system where interfacial reactions and oxide film effects could be isolated. The system Al–Mg–O was chosen since it is technologically important and high-purity, well-characterized materials are readily available. Magnesium alloyed with the aluminum sessile drop and silicon picked up from the experimental apparatus cause an initial reduction in contact angle by altering the protective nature of the oxide film formed on the sessile drop. Evidence of spreading is observed as an intermediate process in the reactive sessile drop pairs. Reaction products formed between the Al–Mg alloys and sapphire (Al2O3), spinel (MgAl2O4), or periclase (MgO) can be interpreted with predicted phase equilibria and the measured loss of magnesium from the sessile drop. Only the rate of the periclase alloy interaction was rapid enough to result in a continuous product layer after 24 h at 800 °C. The volatilization of all of the magnesium from the sessile drop resulted in the formation of a true Al–Al2O3 interface. The contact angle for a true Al–Al2O3 interface is 88 ± 5 deg at 800 °C. The liquid-solid interfacial energy is 1688 ergs/cm2.

Antiphase domain-free, monocrystalline β-SiC thin films have been epitaxially grown on off-axis Si (100) substrates. The effects of degree of misorientation and substrate preannealing on the antiphase domain boundaries (APB's) have been investigated. Wet oxidation, optical microscopy, and transmission electron microscopy were used to characterize the defect structures in both β-SiC thin films grown on exact Si (100) and on off-axis Si (100) substrates. The results revealed that many dislocations were included in APB's and that APB's were eliminated in the β-SiC thin films grown on Si (100) substrates that were oriented 2°–4° from [100] toward the [011] direction. Some APB's were observed near the edge of the β-SiC film on the 2° off-axis Si (100) substrates; however, they were eliminated by substrate preannealing. The carrier concentration and electron mobility of these β-SiC films were similar to those of β-SiC films grown on exact Si (100) substrates as determined by differential capacitance-voltage and Hall effect measurements. Au-β-SiC Schottky diodes were also fabricated on the β-SiC thin films on 4° off-axis substrates and had an ideality factor of 1.4. Differential capacitance-voltage measurements and current-voltage characteristics of Au-β-SiC Schottky diodes indicated that APB's caused significant leakage current in the β-SiC thin films.

A new rapid thermal annealing (RTA) procedure has been developed that eliminates the problem of crystallographic slip in 2 in, ion-implanted GaAs wafers. This annealing arrangement is easy to implement and is reliable. A precision machined graphite support structure and guard ring are used to insure uniform cooling across the entire wafer, thus eliminating slip line production. Characteristics of silicon ion implants have been determined using van der Pauw Hall, Polaron C–V profiling, and eddy current resistivity measurements. Characterization showed excellent dopant activation and uniformity can be achieved using this new technique. Low-temperature photoluminescence measurements were performed on samples annealed with and without graphite in the system, and no detectable difference in surface carbon contamination was found.

This paper describes the complexity of the spinel iron oxides in thin-film configuration. First, the experimental deposition conditions are determined for the parameters of substrate temperature and oxygen flow such that only the “Fe3O4” phase is formed. Then a study is made of how the structural (grain size, lattice parameter, texture), magnetic (M), and optical (visible and infrared transmission) properties of the films depend on the deposition and postdeposition (air annealing) conditions. The experimental deposition region is defined where the films have the most similar physical properties to bulk Fe3O4 and subsequently, after annealing, to bulk gamma Fe2O3. Finally, a discussion is presented of a model that accounts for the anomalous, low values of the magnetic moment for the samples deposited at room temperature. The model proposes an overpopulation of the iron tetrahedral A sites.

The effect on dislocation density of elastic anisotropy (relation of growth direction to elastic stiffness tensor of cubic symmetry) and of plastic anisotropy (relation of growth direction to crystallographic slip systems of {111} ≪110≫ type) is investigated for the growth from the melt of shaped, single-crystal semiconductors of III–V compounds (typically GaAs, InP) by the Czochralski method. The thermal stresses are determined numerically by using three-dimensional finite element techniques for growth along the ≪100≫, ≪111≫ or ≪110≫ directions. The equivalent shear stress is calculated and it is assumed that the dislocation density is proportional to the sum over all slip systems of the excess of the resolved thermal shear stress over the crystal's yield stress in shear. It is shown that proper account of both elastic and plastic anisotropy is necessary in order to correlate numerical estimates of dislocation density to experimentally determined patterns. In particular, it is shown that the effect of elastic anisotropy is to produce significantly higher dislocation densities, especially for the case of ≪111≫ and ≪110≫ growth. For moderate levels of elastic anisotropy, the dislocation density levels during ≪111≫ and ≪110≫ growth become significantly larger than density, during ≪100≫ growth, at specific locations within the crystal. The correlation between dislocation density and equivalent shear stress is presented, and the effect of plastic anisotropy is thus discussed. It is shown that the assumption of elastic isotropy leads to dislocation density levels that considerably underestimate the levels but, for a given growth direction, are qualitatively similar to the dislocation density patterns corresponding to the three-dimensional numerical solutions in which elastic anisotropy is accounted in full.

An elementary-reaction mechanism of diamond growth by a vapor deposition process is proposed. The central postulate is that the main monomer growth species is acetylene. The mechanism basically consists of two alternating steps: surface activation by H abstraction of a hydrogen atom from a surface carbon and the addition of one or two acetylene molecules. During the addition reaction cycle a number of solid C–C bonds is formed and hydrogen atoms migrate from a lower to an upper surface layer. The mechanism is in general agreement with the macroscopic views of the Russian researchers and is consistent with the numerous experimental observations reported in the literature.

Zinc oxide films were deposited using the reactants dimethyl zinc and tetrahydrofuran. Growth kinetics were determined from the dependence of the growth rate on substrate temperature and reactant partial pressure. A complex temperature dependence was observed over the temperature range of 300–500 °C. For a deposition temperature of 400 °C, the growth kinetics were modeled using a bimolecular surface reaction rate-limited mechanism. The layers were characterized using x-ray diffractometer and Auger spectroscopy measurements.

The solid-phase epitaxial regrowth of a III–V compound semiconductor by a two-stage reaction between a two-layer metallization and a compound semiconductor substrate is described. The regrowth process begins with a low-temperature reaction between a metal M (e.g. Ni, Pd, or Pt) and a compound semiconductor substrate, AB, to produce an intermediate M, AB or MB, phase. A subsequent reaction at a higher temperature between an overlayer of Si, Ge, Al, or In and the intermediate phase results in the decomposition of the intermediate phase and the epitaxial regrowth of a layer of the compound semiconductor. This regrowth mechanism is verified experimentally for the specific case of the Si/Ni/GaAs system. Rutherford backscattering spectrometry and transmission electron microscopy data show that the ternary phase Nix GaAs, formed during the initial stage of the reaction, decomposes toNiSi and GaAs by reaction with the Si overlayer. The incorporation of the overlayer element into the regrown semiconductor layer is proposed as a mechanism to explain the formation of Ohmic contacts in Si/Pd/n-GaAs, In/Pd/n-GaAs, In/Pt/n-GaAs, and similar two-layer metallization systems on n-GaAs.

Different Raman experiments on structural relaxation of a-Si and a-Ge are reviewed and discussed in relation to calorimetric measurements on a-Ge. On the basis of the correlation found between results from Raman spectroscopy and results from calorimetry in the case of a-Ge and of the strong similarity between a-Si and a-Ge in terms of their Raman spectra, it is suggested that the strain energy in a-Si may vary considerably with preparation conditions and subsequent treatments. Under this assumption the a-Si Gibbs free energy versus temperature has been constructed for material in different initial states of relaxation. It is shown that the melting temperature of amorphous silicon should increase when relaxation occurs during the heating phase prior to melting. Thus differences in apparent melting temperature, as observed under different laser heating conditions, may be explained.

To produce a homogeneous composite of silicon carbide whiskers in a silicon nitride matrix, the whiskers were formed in situ. The resulting bulk density was higher than that obtained by a physical mixing of the components using a dispersion procedure. Bending strength at room temperature of the in situ formed composite was about the same as that for the physically mixed composite when the small amount of carbon remaining in the in situ formed composite was removed.

The hardness of aluminum films on silicon are measured as functions of depth of the indenter. The films have thicknesses of 0.25,0.5, and 1.0μm. The adhesion between one film and the substrate has been reduced through the prior deposition of a 10 nm layer of carbon. In each case the hardness is found to increase as the indenter approaches the film-substrate interface, but the rate of increase is greater for a film with good adhesion than for one with poor adhesion. It is suggested that this increase results from the constraint on deformation of the film by the substrate. A physical model is proposed whereby the yield stress of the film, σo, and an average effective shear strength τ of the indenter-film and film-substrate interfaces, may be determined from the data.

A nominally γ-Fe2O3 thin film (oxidized from an Fe3O4 film) has been structurally depth profiled using x-ray scattering in a grazing incidence, asymmetric Bragg geometry. By varying the grazing incidence angle, the x-ray penetration depth is varied from tens of Angstroms to several thousand Angstroms, slightly larger than the film thickness. At small incidence angles a diffraction pattern characteristic of α-Fe2O3 is observed, while at larger angles the pattern is predominantly from γ-Fe2O3, showing that there is a surface layer of α-Fe2O3. These results are quantified and the thickness of the α phase found to be 90 Å. The presence of the α phase explains a nonferromagnetic layer observed previously. These data together with magnetic and chemical data suggest that the nonferromagnetic layer forms during oxidation of the Fe3O4 film due to outward diffusion of Fe ions and their subsequent oxidation to form α-Fe2O3

The ion-bombardment-induced reversible movement of a planar amorphous/crystalline interface in silicon has been studied between 100 and 400 °C. The temperature dependence of the ion dose rate at which there is zero interface movement has an activation energy of 1.2 eV, the dissociation energy of divacancies. Scaling of this dose rate for different ion species exhibits a quadratic dependence on the density of displaced atoms in the collision cascade of individual ions, giving further evidence for divacancy control of the interface movement.

A low-resistance nonspiking Ohmic contact to n-GaAs is formed via solid-state reactions utilizing the Si/Pd/GaAs system. Samples with Si to Pd atomic ratios greater than 0.65 result in specific contact resistivity of the order of 10−6 Ω cm2, whereas samples with atomic ratios less than 0.65 yield higher specific contact resistivities or rectifying contacts. Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy, and electron diffraction patterns show that a Pd, Si layer is in contact with GaAs with excess Si on the surface after the Ohmic formation annealing. This observation contrasts with that on a previously studied Ge/Pd/GaAs contact where Ohmic behavior is detected after transport of Ge through PdGe to the interface with GaAs. Comparing the Ge/Pd/GaAs system with the present Si/Pd/GaAs system suggests that a low barrier heterojunction between Ge and GaAs is not the primary reason for Ohmic contact behavior. Low-temperature measurements suggest that Ohmic behavior results from tunneling current transport mechanisms. A regrowth mechanism involving the formation of an n+ GaAs surface layer is proposed to explain the Ohmic contact formation.

The ZnO varistor degradation has been attributed to the field-assisted, temperature-activated diffusion of interstitial zinc in the depletion layer. To improve stability, one approach is to reduce the formation of interstitials, and then further, to prevent their migration through empty interstitial sites. Based on this concept, an amphoteric dopant, such as Na or K, has been incorporated in the ZnO varistor grain boundary wherein a dopant is substituted both in the lattice and in the interstitial sites. A grain boundary defect model has been developed for this dual mode of substitution, with the dopant acting as an acceptor at the lattice site and as a donor at the interstitial site. Under these conditions, and given a desired neutrality range, the concentration of zinc interstitial is indeed shown to be reduced and stability greatly improved. The experimental data presented here validate the grain boundary defect model presented in this and in an earlier paper [J. Mater. Sci. 20, 3487 (1985)].