Crystallization behavior, defects, and interface structures of sol-gel derived LiNbO3 films on three kinds of substrates were examined. The nucleation was found to occur epitaxially at the interface between the film and the substrate. The continuous film is formed by coalescence of the island-like crystallites. When sapphire substrate is used, which has large lattice mismatch with the LiNbO3, the resulting film contains a large amount of micropores, twin structures, and misfit dislocations. On the other hand, while LiTaO3 and 5% MgO-doped LiNbO3 substrates with smaller mismatch are used as substrates, the films show no evidence of the formation of dislocations and twins. The film on 5% MgO-doped LiNbO3 substrate shows better optical waveguiding property.

A novel pressureless reaction sintering process is presented for the fabrication of Al2O3-aluminide alloys (3A). Compacts of intensively milled metal oxide-aluminum mixtures are heat-treated in vacuum or inert atmosphere such that the exothermic reactions take place in a controlled manner essentially at temperatures below the melting point of Al. Dense, homogeneous microstructures were obtained with a variety of Al2O3-matrix systems with interpenetrating networks of aluminides of Ti, Fe, Nb, Mo, Zr, Ni, etc. By adding modifiers in the form of oxides or metals, volume and phase composition as well as properties can be tailored in a wide range.

A thermal diffusion process of Ti into a LiNbO3 substrate for optical waveguides has generally been carried out under a wet gas atmosphere in order to prevent undesirable Li outdiffusion. In this work, such thermal decomposition was confirmed to be significantly suppressed for an OH-free LiNbO3 substrate, even after a dry atmosphere annealing. No extra x-ray diffraction peak for LiNb3O8 was detected from the OH-free substrate after 10 h of annealing at 1000 °C in a dry O2. Furthermore, the surface morphology of this sample, and as well an unannealed one, were smooth. In a conventional LiNbO3 substrate containing many OH ions, subjected to a similar dry annealing, the presence of the LiNb3O8 phase and a surface coarsening were observed.

A glass of 47.5BaO · 47.5B2O3 · 5Al2O3 (in mol%) having a shorter optical absorption edge (∼236 nm) and suitable glass formation was selected as the mother glass for studying the surface crystallization of β−BaB2O4 · β−BaB2O4 was not the main surface crystallized phase when only a conventional heat treatment was applied. Crystallization of β−BaB2O4 was stimulated due to ultrasonic surface treatment with an ethanol suspension of β−BaB2O4 particles and subsequent heat treatment. After the ultrasonic treatment, β−BaB2O4 was the main crystallized phase. Transparent and dense β−BaB2O4 thin films/glass showed second harmonic generation. The tensor components of the second-order nonlinear optical susceptibility were estimated.

The influence of microstructure on the abrasive machining and indentation response for a series of dental glass-ceramics was characterized. The experimental materials prepared for this study contained crystalline mica platelets that ranged in diameter from about 1 to 15 μm, while the volume fraction of mica remained essentially constant. Damage formation and material removal behavior were studied as a function of mica platelet size using Vickers indentation, Berkovich instrumented indentation, and abrasive machining. In the instrumented indentation experiments, the energy absorbed in indentation decreased with increasing platelet size when indentations of equal penetration depth are made in each material. To characterize the grinding response, the normal and tangential forces for each material were measured as a function of the depth of cut in surface grinding. The grinding forces and the specific grinding energy at fixed depths of cut decreased with increasing the mica platelet size following the same trend observed in the fixed displacement indentation tests. Since the same microfracture process was observed to occur in both indentation and grinding, the absorbed indentation energy is proposed as a quantity for predicting the machining response of these glass-ceramics.

Results on hydrogenated carbon nitride (CNxHy) thin films grown by reactive magnetron sputtering in a mixed Ar/NH3 discharge are reported. Depending on the growth temperature (Ts) and negative substrate bias voltage (Vs), both the composition and the microstructure were altered. Using nuclear reaction analysis and resonant backscattering spectroscopy, the maximum N and H content were both 15 at. %. Both the hydrogen and nitrogen content of the films was found to decrease with increasing growth temperature. The results also show pronounced chemical resputtering effects, resulting in no net film growth for Vs > 75–100 V. X-ray photoelectron spectroscopy showed no signs of N bound to sp3 hybridized C. Also, the microstructure of the films was found to change with Ts. For Ts < 150 °C, a structure with crystalline clusters embedded in an “fullerene-like” matrix was observed by high-resolution transmission electron microscopy. Power-spectra obtained from the clusters could be identified with the cubic diamond structure. For Ts ≥ 300 °C, no crystalline clusters were found and the films had a homogeneous “fullerene-like” microstructure with strongly bent planes and closed shell-like features resembling bucky-onions. Evaluation of nanoindentation results from the homogeneous “fullerene-like” films gave hardness values between 7 and 11 GPa and elastic recoveries of 55–60%. This should be compared with hardness and elastic recoveries of 40–60 GPa and 85–90%, respectively, previously reported for on nonhydrogenated carbon nitride CNx films grown under the same conditions, but in pure N2 discharges.

Near stoichiometric titanium nitride (TiN) was deposited from tetrakis(dimethylamido)titanium (TDMAT) and ammonia using atmospheric pressure chemical vapor deposition. Experiments were conducted in a belt furnace; static experiments provided kinetic data and continuous operation uniformly coated 150-mm substrates. Growth rate, stoichiometry, and resistivity are examined as functions of deposition temperature (190−420 °C), ammonia flow relative to TDMAT (0−30), and total gas-flow rate (residence time 0.3−0.6 s). Films were characterized by sheet resistance measurements, Rutherford Backscattering Spectrometry, and X-Ray Photoelectron Spectrometry. Films deposited without ammonia were substoichiometric (N/Ti, 0.6−0.75), contained high levels of carbon (C/Ti = 0.25−0.40) and oxygen (O/Ti = 0.6−0.9), and grew slowly. Small amounts of ammonia (NH3/TDMAT ≥ 1) brought impurity levels down to C/Ti, 0.1 and O/Ti = 0.3−0.5. Ammonia increased the growth rates by a factor of 4−12 at temperatures below 400 °C. Films 500 Å thick had resistivities as low as 1600 μΩ-cm when deposited at 280 °C and 1500 μΩ-cm when deposited at 370 °C. Scanning electron micrographs indicate a smooth surface and poor step coverage for films deposited with high ammonia concentrations.

The development of a novel Al matrix composite is described based on a simple displacement reaction when an SiO2 particulate preform is brought into contact with liquid Al at temperatures between 1273 and 1373 K. This interaction leads to the wetting of the SiO2 particles by Al and its eventual transformation to a composite with Al2O3/Al particles in an Al matrix. Infiltration of the preform as induced by this reaction takes place with the simultaneous formation of the Al2O3/Al particles in situ. Synthesis of engineered multiphase composites, wherein reinforcements of other materials incorporated into the preform and reacted with liquid Al, is also presented.

In 1993, a new beryllium bearing bulk metallic glass with the nominal composition Zr41.25Ti13.75Cu12.5Ni10Be22.5 was discovered at Caltech. This metallic glass can be cast as cylindrical rods as large as 16 mm in diameter, which permitted specimens to be fabricated with geometries suitable for dynamic testing. For the first time, the dynamic compressive yield behavior of a metallic glass was characterized at strain rates of 102 to 104/s by using the split Hopkinson pressure bar. A high-speed infrared thermal detector was also used to determine if adiabatic heating occurred during dynamic deformation of the metallic glass. From these tests it appears that the yield stress of the metallic glass is insensitive to strain rate and no adiabatic heating occurs before yielding.

The role of aluminum nitride (AlN) as a buffer layer on the nucleation and growth of diamond on silicon and steel substrates during hot filament chemical vapor deposition (HF-CVD) has been investigated systematically. The scanning Auger electron microscopy (AES) is employed to study chemistry and content of carbon on the surface and in subsurface regions of AlN as a function of HF-CVD parameters. It is found that AlN offers an excellent diffusion barrier for carbon over a wide range of temperature and hydrocarbon content of CVD gas environment, with simultaneous inhibition of graphitization. It also facilitates nucleation of diamond phase. The surface reactions between AlN and carbon are discussed in terms of hydrogen-assisted phase transformations. We have developed a two-step procedure to obtain a continuous diamond film on steel substrates. The characteristic features of AlN have been exploited to obtain adherent and graphite-free diamond deposits on various types of steels, including low carbon steel, tool steel, high speed steel, and bearing steel.

The processing of microporous glassy carbon derived from furfuryl alcohol and ethylene glycol mixtures has been studied, with emphasis on understanding and controlling microstructure development. It is shown that this system exhibits a polymerization-dependent miscibility gap, and that the carbon microstructure is determined by phase separation in the liquid state. Variations in carbon microstructure with composition and thermal history can be understood in terms of the time-dependent immiscibility and resulting phase separation.

The explosive reactions or self-propagating high temperature synthesis (SHS) take place during milling Ni20Ti50C30 and Ni50Ti30C20 elemental powder mixtures. The coexistence of agglomerates and powders in products indicates the occurrence of melting and solidification. TiC phase and NiTi compound were obtained during millingNi20Ti50C30, while no compound of nickel and titanium was observed when milling Ni50Ti30C20, the final product of which is TiC and Ni. It is suggested that the explosive reaction is ignited by the heat releasing from initial formation of TiC through heavy collisions of milling balls, and the reaction between Ni and Ti, as well as the existence of Ni–Ti liquid, make the following reaction self-sustained. The variation of the addition of nickel did not affect the reaction time in both compositions, but made the reaction temperature different due to the difference of composition of Ni and Ti. It is estimated that the temperature during the reaction in Ni20Ti50C30 rises above 1112 °C, while in Ni50Ti30C20, it might rise above 1349 °C. However, no phenomenon suggests the melting of pure elemental Ti; the formation of TiC is mainly controlled by the diffusion mechanism in SHS.

Carbon-filled polyethylene composites were fabricated and tested to establish the practical lower limit of their electrical resistivity at room temperature and to investigate the trade-offs between low resistivity and the magnitude of the resistance anomaly (i.e., a large positive temperature coefficient of resistivity) that appears when such composites are heated through the polyethylene crystalline melting transition. Carbon blacks with large particle size and low surface area provided low-resistivity composites having large resistance anomalies. The largest resistance anomalies were found in composites that were well mixed, but the room-temperature resistivity also increased in composites that were cycled repetitively through the crystalline-melting transition. A mixture of carbon blacks of two different sizes provided a lower resistance than was found in a material with the same fill of only the coarser black. By controlling the composition and the processing, composites were made with room-temperature resistivities lower than 0.2 ohm cm and resistance changes of at least 2 orders of magnitude. A resistance change of as much as 5 orders of magnitude was obtained for composites with room-temperature resistivities of only 1 ohm cm.

The Nb/α−Al2O3 system has been used as a model study for investigating the stability of different MBE grown epitaxial Nb films on α−Al2O3 substrates. The films were grown at 800 °C in ultrahigh vacuum. The growth process was monitored in situ by reflection high energy electron diffraction (RHEED). After deposition the structure of the film was investigated by x-ray diffraction (XRD) and conventional transmission electron microscopy (CTEM) which encompasses also selected area diffraction (SAD). Both techniques revealed the following orientation relationship between the Nb film and the α–Al2O3 substrate: (0001)α–Al2O3‖ (111)Nb; [2110]α–Al2O3‖ [110]Nb. The stability of the niobium films was investigated by annealing the Nb-film/α–Al2O3 system to temperatures up to 1500 °C for different periods of time. Surprisingly, the orientation relationship between the Nb film and the substrate changed to (0001)α–Al2O3‖ (110)Nb; [0110]α–Al2O3‖ [001]Nb. A model will be developed which shows that above a critical film thickness the growth orientation is metastable with respect to its crystallographic orientation. Furthermore, high resolution transmission electron microscopy (HREM) was performed to investigate the defect structure of the annealed Nb/α–Al2O3 interface.

Recognizing that speed, size, reliability, and cost are the principal driving forces for advanced electronic packages, this review article describes the much needed development of a new, phase transformation-free, single-phase silica dielectric with a dielectric constant (k) of about 4, the lowest among the inorganic oxides, and a coefficient of thermal expansion (CTE) of about 3 ppm/°C, similar to that of Si. This dielectric, consisting largely of SiO2, represents a gain in media speed by about 50% over alumina dielectric, combined with an improvement in reliability of the package by a factor of about 1000. The feature size and system cost can also be drastically reduced by using this dielectric. It is made from a mixture of binary borosilicate glasses that normally exhibit an undesirable characteristic of precipitating cristobalite during sintering that severely weakens the structure. The most important aspect of this article is the design and development of a strategy that prevents the cristobalite growth by incorporating a crystal growth inhibitor in the binary mixture of glasses. Since kinetics, not thermodynamics, are shown to be the key to success of this strategy, the roles of rate-controlling parameters are deliberately emphasized. A working model is delineated to identify compositions that yield a cristobalite-free silica dielectric with values of CTE that match those of Si and GaAs. Critical issues of co-firing between metals and this dielectric are addressed within the context of multilayer packaging fabrication. Finally, a list of measured properties is presented that clearly shows new opportunities for this silica dielectric.

Carbon-carbon composites, if not suitably protected, suffer from the problem of oxidation of the surface in normal atmospheres at temperatures above 350 °C. For this reason they need to be protected from oxidizing environments by either using an impermeable coating, or using a sacrificial protective coating of a suitable material, and/or doping of an oxidation inhibitor in the carbon. In this study we have used a new family of materials with tailorable thermal expansion characteristics, namely, the [NZP] family as the materials for developing a suitable coating material for C-C composites. The candidates selected for matching thermal expansion with that of carbon are Ca0.5Sr0.5Zr4P6O24, SrZr4P6O24, and Ba1.175Zr4P5.65Si0.35O24. They can be sintered in inert atmosphere without decomposition of the phases, and can be hot-pressed in inert atmosphere with C-C composites at 1250 °C without decomposition or chemical interaction. They are stable in the presence of carbon up to 1200 °C for at least a period of 4 h. They also do not show any weight loss after exposure to various temperatures up to 1200 °C for 4 h.

Structural characteristics of CeO2–Al2O3–SiO2 glasses have been studied by infrared and x-ray absorption near edge structure (XANES) spectroscopies, and the Kramers-Kronig analysis of IR reflection data was performed. Results of IR spectra show that ceria is the network modifier and favors the formation of [SiO4] tetrahedron with nonbridging oxygens. The high frequency Si–O–Si stretching vibrational peak near 1100 cm−1 shifts toward the lower frequency as ceria content increases and alumina content is constant. XANES data of the cerium LIII edge show that the majority of cerium ions in cerium aluminosilicate glasses are Ce3+ ions. The ratio of Ce4+/Ce3+ increases with increasing the ratio of Ce/(Al + Si). However, the ratio of Ce4+/Ce3+ decreases with increasing the ratio of Al/(Al + Si).

A hexacarbonyl of chromium and molybdenum [(Cr, Mo) (CO)6] was used as an oxycarbide source for the coating on stainless steel 304 (SS304) at temperatures from 175 °C to 450 °C. Hardness of the films was determined from a microindentation technique through a similar calculation after Thomas (1987). Intrinsic hardnesses of the films formed at low and medium temperatures were determined to be 8.61 and 2.75 GPa, respectively. Both of them are larger than that of SS304 substrate, 1.75 GPa. Adhesive strength of the films was measured by the scratching test. The results reveal that the adhesive strengths of the films formed at low, medium, and high temperatures are 2.8 N, 37.6 N, and 36.0 N, respectively. Two different fracture modes after scratching were found for the films obtained at various temperature regions. A spalling-off type or a deformation failure with many cracks and deformation bands beside the striation was found.

Heteroepitaxial diamond has been successfully deposited on a Si(110) substrate by the microwave plasma chemical vapor deposition method. The pretreatment consisted of carburization and bias-enhanced nucleation steps. Cross-sectional transmission electron microscopy reveals that diamond can be in the cube-on-cube epitaxial relationship with the Si substrate. Various orientation relationships between diamond and Si substrates have also been observed, depending on the location where the plasma applied. Near the center of the plasma, twins were rarely observed in cube-on-cube epitaxial regions. Away from the center of the plasma ball, Σ3 twins are seen first, and then additional Σ9 and Σ27 twins occur near the edge of the plasma. In general, defect density in the epitaxial films is less than that observed in polycrystalline ones. No interlayer could be observed between diamond and silicon. In addition, 2H-type hexagonal diamond has also been found, and is in epitaxy with the Si substrate.

The chemical interaction between two β′–O′ Si–Al–O–N ceramics and a number of iron-based alloys is studied by means of static interaction couple experiments at 1100 and 1200 °C. The onset temperature of reaction of Si3N4 with pure iron was found to be at 1095 °C, which is in good agreement with a calculated temperature of 1033 °C. During the interaction, silicon and nitrogen from the ceramic dissolve and diffuse into the iron alloy, whereas the remaining aluminum and oxygen form Al2O3 particles. The interaction between ceramic and iron alloy is reaction controlled. In the initial stage of the interaction, the dissociation rate of the ceramic is the rate-controlling step. After the ceramic/metal interface is isolated from the furnace atmosphere, the nitrogen solution rate into the iron alloy becomes rate controlling. The influence of alloying elements on the reactivity could be related to their effect on the nitrogen solubility in the iron alloy. Ni, Si, and C decrease the nitrogen solubility and decrease the reactivity with the sialon ceramic. Cr and Mo have the opposite effect. The thickness of the interaction layer on the ceramic side of the interaction couple was found to be a function of the calculated nitrogen solubility in the iron alloy at 1 atm nitrogen pressure, making it possible to predict the relative chemical reactivity of a number of iron-based alloys with the same sialon ceramic.