Phase transformations of the Mo33Si66 powder mixture under different milling conditions have been systematically investigated by x-ray diffraction, and scanning and transmission electron microscopy. The effect of the milling conditions on the Mo/Si solid state reactions (SSR) has been examined in detail. The energy transfer from the milling tools to the powder under processing has been quantified by an already assessed collision model. It has been found that the higher energetic input favors the formation of the room temperature stable phase αMoSi2, while the lower energetic input promotes the formation of the metastable phase βMoSi2. In addition, if the energy transfer is high enough, the Mo/Si reaction proceeds in a form of self-propagating high temperature synthesis (SHS). Thermodynamics and kinetics aspects related to the different SSR's are discussed.

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.

Dense YBa2Cu4O8 (124) ceramics were prepared by the following two-stage sintering: compressed 124 powders were heated to 1203 K for decomposition to YBa2Cu3O7−x (123) and CuO, and then cooled down to 1073 K and annealed for the re-formation of 124 single phase. The relative densities thus obtained were 93–95%, as high as those prepared under high oxygen pressure. The densification was considered to take place due to the liquid phase. In the sintered 124, the island-like fine grains of CuO were observed within the 123 matrix. As a result, it was considered that the re-formation of 124 proceeded in each grain. The geometrical phase distribution in the grains is discussed on the basis of superconducting properties from resistivity measurements.

This paper describes the growth and analysis of cubic boron nitride films in a low-density, supersonic nitrogen/argon plasma flow into which boron trichloride gas was injected. Both hexagonal boron nitride (h-BN) and cubic boron nitride (c-BN) were synthesized using this apparatus. Phase selectivity is obtained by applying a relatively low negative bias voltage to the substrate. All of the films described in this paper were grown on {100} silicon wafers at substrate temperatures varying from 400–700 °C. Boron nitride films with greater than 90% cubic phase were successfully synthesized with this method. The films were analyzed using infrared spectroscopy, x-ray photoelectron spectroscopy, and scanning electron microscopy. The volumetric percentages of the hexagonal and cubic phases were determined from model fits to the infrared transmission spectra of the films. X-ray photoelectron spectroscopy provided qualitative evidence for the presence and/or lack of sp2 bonding through the identification of a π-plasmon feature in the spectra. Infrared reflectance spectra are used to provide insight into the growth mechanisms leading to c-BN formation and have revealed features which are not present in the transmission spectra, specifically the 1305 cm−1 LO mode of c-BN and the 1610 cm−1 LO mode of h-BN. The mean ion energies involved with this bias-enhanced chemical vapor deposition (CVD) process are much lower than the ion energies in traditional physical vapor deposition (PVD) processes; however, the ion fluxes (currents) used in this CVD process are at least an order of magnitude higher, resulting in a total momentum transfer to the deposited atoms through ion bombardment that is at least equal to or greater than that reported for many ion-enhanced PVD processes.

The quantitative description of highly nonequilibrium processes for the preparation of metastable and unstable phases requires the determination of the thermodynamic functions of the system under investigation. However, in systems such as Cu–Cr which are immiscible in the equilibrium states, the determination of the thermodynamic functions over the entire concentration range is often difficult if not impossible because reliable experimental data are not available for the metastable or unstable regime. The present paper demonstrates that such data can be obtained by a combination of thin film deposition techniques and differential scanning calorimetry. It is concluded that the phase formation in such thin films can be described in terms of the thermodynamics of the system, even when the heats of mixing are highly positive. The results indicate that models of the regular solution type still provide a reasonable description of the thermodynamic functions of such alloys.

A two-step heat treatment process has been employed to crystallize low pressure deposited thin films of amorphous germanium. Large grain p-type polycrystalline germanium with a Hall effect hole mobility of greater than 300 cm2/Vs has been obtained. Films with near intrinsic conductivity, necessary for the construction of practical enhancement-mode insulated-gate thin film transistors, were obtained by introducing phosphorus as a compensating dopant. High Hall effect electron mobility of 245 cm2/Vs has been measured on the resulting n-type polycrystalline germanium thin films.

This paper reports a study of microscopic on-chip corrosion on a 17 μm × 17 μm microelectromechanical device. The active atmospheric corrosion occurred only on the Al−Si−Ti components which were connected directly to the TiW components. Adsorbed fluoride ionic species on the microelectromechanical device were found to activate the observed bimetallic corrosion on the Al−Si−Ti/TiW contacts. Water rinse or replacement of TiW by TiAlx completely eliminates the active corrosion. Electrochemical potential data confirm the dissimilar metal corrosion mechanism. Effective prevention of on-chip corrosion was achieved by the judicious design of the device components to avoid dissimilar metal contacts with large galvanic potential differences.

TiO2-based powders doped with a small amount of SiO2 were prepared by a sol-gel method and subsequently were heated to precipitate fine anatase crystals. Although the obtained powders have large specific surface areas (≈200 m2 · g−1), they showed poorer activity in a photocatalytic property than the undoped TiO2 powders which have the area of 50 m2 · g−1. The SiO2-doped TiO2 powders were treated chemically with aqueous NaOH. Infrared reflection spectra showed that the treatment reduced the amount of SiO2 in the powders. The photocatalytic property of the powders was extremely improved by the treatment, and the powders showed higher activity than the undoped TiO2 powders.

The mechanical properties of ion-implanted Al–Si alloy were studied using disk samples of alloy irradiated with Ar+, B+, and N2+ ions. Knoop hardness of ASTM 336.0 disks increased from 117 to 165 kgf/mm2 upon N2+ ion implantation. To measure tribological properties, lubricated ball-on-disk tests were performed using steel balls. The coefficients of friction of ion-implanted disks were higher than those of unimplanted ones. Ion implantation improved the wear resistance of the disks, and in the case of N2+ ion-implanted disks, the worn volume was smaller than 10−4 mm3. XPS analysis for the N2+ ion-implanted samples revealed the formation of aluminum and silicon nitride on the sample surface. On the other hand, the cross-sectional image of the ion-implanted surface showed precipitated Si which is held under the implanted N2+ ions.

Barium and potassium hydroxide have been investigated as fluxes for the growth of cuprate single crystals. The relatively high solubility of transition metals and lanthanoids in these salt fluxes at moderate temperatures allows significant lowering of the growth temperatures required for many phases. Also, phases not stable at high temperatures become accessible. Two new cuprates have been prepared in the Ba–Ca–Cu–O and Ba–Y–Cu–O systems from a Ba(OH)2 · H2O flux. The compounds Ba3(Y0.23Cu0.77)2O5.78 and Ba3(Ca0.24Cu0.76)2O4.43 crystallize in a tetragonal (space group I4/mmm) oxygen deficient Sr3Ti2O7-type structure with lattice parameters a = 4.069(2) Å, 4.022(1) Å and c = 21.61(2) Å, 21.63(2) Å, respectively. The compound (Ba0.92Sr0.08) (Ca0.38Cu0.62)O2.1 crystallizes with a doubled perovskite unit cell along all three axes, a = 8.116(4) Å. In addition, single crystals of Ba2Ycu3O7–δ have been prepared from a KOH flux at 750 °C.

A new varistor composition based on SnO2 doped with Co, Al, and Nb has been successfully synthesized by a chemical route. It exhibits excellent nonlinear current-voltage (I-V) characteristics with α ≈ 72 and E1mA ≈ 1820 V/mm.

Much of the conductor development effort in the last decade has focused on optimizing the processing of (Bi, Pb)2Sr2Ca2Cu3Ox oxide-powder-in-tube conductors and (Bi, Pb)2Sr2CaCu2O8 (Bi-2212) and TlBa2Ca2Cu3Ox thick film conductors. It is demonstrated that in each of these conductors, critical current densities are dictated by the grain boundary misorientation distributions (GBMD's). Percolative networks of low-angle boundaries with fractions consistent with the active cross-sectional area of the conductor exist in each of these conductors. Further enhancements in the properties require increased numbers of small-angle grain boundaries. Given the processing methods used to fabricate these materials, no clear route employing a simple modification of the established processing method is apparent. To address this need, conductors with controlled or predetermined GBMD's are necessary. Development of biaxial texture appears to be the only possible way to increase the number of small-angle boundaries in a practical and controllable manner. We summarize in this paper recent results obtained on epitaxial superconducting films on rolling-assisted-biaxially-textured-substrates (RABiTS). This technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield structurally and chemically compatible surfaces. Epitaxial YBa2Cu3O7–δ films grown using laser ablation on such substrates have critical current densities exceeding 106 A/cm2 at 77 K in zero field and have a field dependence similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of the next generation high temperature superconducting (HTS) wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

Although numerous studies of high-energy, ball-milled metal powders have been conducted, to date few studies have characterized the mechanical processing of identical elemental compositions of prealloyed powders and of powder blends. This study reports on the mechanical processing (attritor ball milling) in argon and nitrogen gas environments of (a) iron powder and prealloyed iron–2 wt.% aluminum powder, and (b) iron-aluminum, iron-aluminum nitride, and iron-iron nitride powder blends. When nitrogen was milled into iron particles either from nitride powder or by gas infusion, the nitrogen dissolved interstitially in bcc-Fe (principally at the grain boundaries) or was present as bct-Fe nanoparticles at the bcc-Fe nanograin boundaries. The resulting nitrogen distribution was independent of how the nitrogen was added. Milled blends of iron and aluminum powder and prealloyed iron-aluminum powder resulted in similar microstructures: micrometer size particles with similar nanograin size. The aluminum in the blended powder mixture developed an ultrafine distribution on the grain boundaries, but it did not become uniformly distributed within the bcc-Fe grains. In contrast, the aluminum in prealloyed Fe–Al powder remained in solid solution during the mechanical milling

Stoichiometric composition and formation process of the icosahedral phase in the Zn–Mg–Y system have been studied. The icosahedral phase exhibit a stoichiometric composition in the vicinity of Zn60Mg30Y10. During cooling, (Zn, Mg)5Y phase primarily crystallizes from the melt at ∼960 K and then undergoes a peritectic reaction with the residual Mg-enriched melt (∼820 K) to form the icosahedral phase. The melt with a constant composition close to Mg7Zn3 is in equilibrium with the (Zn, Mg)5Y phase above the peritectic temperature in a wide compositional range.

Semiconductor ZnSe microcrystal-doped SiO2 glass thin films were prepared by the RF-magnetron sputtering method. The particle size of ZnSe microcrystals in the films depended on sputtering conditions such as input power, substrate temperature, and relative surface area ratio (ZnSe/SiO2) in the target. The blue shift of the optical absorption edge was observed in these glass films. This blue shift energy was explained in terms of the independent confinement of electrons and positive holes, Coulomb force and the influence of a collapsed exciton and the dielectric constant of the matrix glass being taken into consideration.

The effects of thermal cycling through the martensitic transformation have been studied in three Cu–Al–Ni–Mn–B high temperature shape memory alloys. An increase of the martensitic transformation temperatures with the number of cycles (up to ∼7 K after 60 cycles) has been generally observed by DSC measurements. The microstructure of these alloys is rather complicated, with the presence of big manganese or aluminum boride particles and small boron precipitates, as well as the formation of dislocations during thermal cycling. By means of aging experiments, it has been shown that the evolution of transformation temperatures during cycling is mainly due to the step-by-step aging in parent phase accompanying the thermal cycling, and that the dislocations formed during cycling have only a very small effect, at least up to 60 cycles.

Microelectromechanical systems (MEMS) devices are made of doped single-crystal silicon, LPCVD polysilicon films, and other ceramic films. Very little is understood about tribology and mechanical characterization of these materials on micro- to nanoscales. Micromechanical and tribological characterization of p-type (lightly boron-doped) single-crystal silicon (referred to as “undoped”), p+-type (boron doped) single-crystal silicon, polysilicon bulk, and n+-type (phosphorous doped) LPCVD polysilicon films have been carried out. Hardness, elastic modulus, and scratch resistance of these materials were measured by nanoindentation and microscratching using a nanoindenter. Friction and wear properties were measured using an accelerated ball-on-flat tribometer. It is found that the undoped silicon and polysilicon bulk as well as n+-type polysilicon film exhibit higher hardness and elastic modulus than the p+-type silicon. The polysilicon bulk and n+-type polysilicon film exhibit the lowest friction and highest resistance to scratch and wear followed by the undoped silicon and with the poorest behavior of the p+-type silicon. During scratching, the p+-type silicon deforms like a ductile metal.

Electromigration damage in Al-based interconnects with three compositions (pure Al, Al–1%Si–0.5%Cu, and Al–2%Cu) was studied quantitatively. Using scanning electron microscopy, the spacings between more than 1000 voids and hillocks were measured. The distribution of the spacings was found to be a function of the composition, the applied current density, and the linewidth. The measurements confirm the existence of a threshold product of current density and diffusion length. In particular, a dependence of this threshold product on the Cu content was found. The results of the analysis show that there are clear correlations between the details of the microscopic damage processes and the lifetime of the conductor lines.

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.

We present experimental measurements of the accessible pore fraction in ceramic matrix composites during consolidation by vapor phase infiltration. For two topologically distinct filament architectures, the accessible pore fraction decreased during consolidation with a power law decay and a critical scaling exponent of 0.41 (R2 = 0.97). A three-dimensional analysis of the percolating pores revealed that the structures became topologically equivalent and simply connected near the critical density.