Nanoindentation load-displacement curves provide a “mechanical fingerprint” of a materials response to contact deformation. Over the last few years, much attention has been focused on understanding the factors controlling the detailed shape of unloading curves so that parameters such as true contact area, Young's modulus, and an indentation hardness number can be derived. When the unloading curve is well behaved (by which we mean approximating to linear behavior, or alternatively, fitting a power-law relationship), then this approach can be very successful. However, when the test volume displays considerable elastic recovery as the load is removed [e.g., for many stiff hard materials and many inhomogeneous systems (e.g., those employing thin hard coatings)], then the unloading curve fits no existing model particularly well. This results in considerable difficulty in obtaining valid mechanical property data for these types of materials. An alternative approach, described here, is to attempt to understand the shapes of nanoindentation loading curve and thus quantitatively model the relationship between Young's modulus, indentation hardness, indenter geometry, and the resultant maximum displacement for a given load. This paper describes the development and refinement of a previous approach by Loubet et al1 originally suggested for a Vickers indenter, but applied here to understand the factors that control the shape of the loading curve during nanoindentation experiments with a pointed, trigonal (Berkovich) indenter. For a range of materials, the relationship P = Kmδ2 was found to describe the indenter displacement, δ, in terms of the applied load P. For each material, Km can be predicted from the Young's modulus (E) and the hardness (H). The result is that if either E or H is known, then the other may be calculated from the experimental loading curve. This approach provides an attractive alternative to finite element modeling and is a tractable approach for those cases where analysis of unloading curves is infeasible.

Diphenylborosiloxane (PBS), an organometallic compound with Si–O–B bonds, was compounded with carbon fiber (CF) to form CF/ceramic composite. Three types of PBS with different molar ratios (Si/B) in the materials were used. On the PBS obtained, specific gravity, Si content, molecular weight, melting point, and infrared absorption spectrum were measured. On the basis of these results, structures of PBS were examined, which clarified that the PBS thus synthesized consisted of several components with different molecular weights. Mechanical properties and oxidation resistivity of the CF/ceramic composites obtained differed with the Si/B ratios of PBS. Mechanical strength of the CF/ceramic composites increased with increase of Si content of PBS. It was also found that, when PBS with high boron content was used, compact vitreous film consisting mainly of B2O3 was formed over the composite. Due to the formation of this film, oxidation resistivity of the composite was improved.

The effects of plasma cycle and TiO2 doping on sintering kinetics during plasma activated sintering (PAS) of γ−Al2O3 have been studied in the temperature range of 1473–1823 K. Multiple plasma cycle leads to higher densification. Also, TiO2 doping enhances the sintering kinetics during PAS. In TiO2 doped specimens, near full density was obtained at 1673 K in less than 6 min using multiple plasma cycle. It is suggested that the dielectric properties of a material are critical for the success of the PAS process.

Laser physical vapor deposition (LPVD) has been used to grow titanium nitride films on hydrogen-terminated silicon(100) substrates at deposition temperatures ranging from room temperature to 600 °C. A pulsed KrF excimer laser (λ = 248 nm, τ = 25 ns) was used with the deposition chamber maintained at a base pressure of 10−7 Torr prior to deposition. Different properties of the films were investigated by x-ray diffraction, Auger electron spectroscopy, Raman spectroscopy, optical, scanning, and high resolution transmission electron microscopy, and measurement of electrical resistivity. When the substrate temperature was low (at and below 500 °C), oxygen atoms from the residual gases were incorporated in the films. The microstructures and resistivities of TiN films were found to be strongly dependent on the temperature of the silicon substrates. The TiN films deposited at 600 °C were oxygen-free, as observed from Auger analysis, and the room temperature resistivity was found to be 14–15 μΩ-cm. Raman spectroscopy of the films showed that the nitrogen-related optical phonon peak increased with deposition temperature in comparison with the titanium-related acoustic peak. Transmission electron microscopy and x-ray diffraction analyses showed that the films were polycrystalline at low temperature with grain size ranging from 300–600 Å, depending on the temperature of the substrate. At 600 °C, the films were found to be single crystals with occasional presence of dislocation loops. The spacing of Moiré fringes in TiN/Si samples deposited at 600 °C established the nearly periodic elastic strain field extending into the TiN and Si at the interface. Although there exists a large misfit between TiN and Si (24.6%), the epitaxial growth of TiN films on Si(100) substrates was explained by means of domain-matched epitaxy with a 4-to-3 match in unit cells for TiN/Si structure, giving rise to a residual lattice misfit of only 4%.

Epitaxial PbTiO3 thin films were produced from a mixed Pb–Ti double-alkoxide precursor by spin-coating onto single crystal (001) SrTiO3 substrates. Heat treatment at 800 °C produces a dense and continuous, epitaxial lead titanate film through an intermediate Pb-Ti fluorite structure. A microstructural instability occurred when very thin single crystal films were fabricated; this instability caused the films to become discontinuous. Scanning electron microscopy and atomic force microscopy observations show that single crystal films with a thickness less than ∼80 nm developed holes that expose the substrate; thinner films broke up into isolated, single crystal islands. The walls of the holes were found to be (111) perovskite planes. A free energy function, which considered the anisotropic surface energies of different planes, was developed to describe the microstructural changes in the film and to understand the instability phenomenon. The function predicted that pre-existing holes greater than a critical size are necessary to initiate hole growth, and it predicted the observed morphological changes in the current system. Morphological stability diagrams that explain the stability fields for different film configurations, i.e., either completely covered, with holes, or single crystal islands, can be calculated for any film/substrate system.

Based on results from chemical kinetic model calculations, a method to improve diamond film growth in a dc arcjet chemical vapor deposition reactor has been developed. Introducing the carbon source gas (CH4) into an Ar/H2 plasma in close proximity to the substrate produced diamond films exhibiting simultaneous improvements in quality and mass deposition rates. These improvements result from a reduced residence time of the methane in the plasma which inhibits the hydrocarbon chemistry in the gas from proceeding significantly beyond methyl radical production prior to encountering the substrate. Improvements in growth rate were modest, increasing by only a factor of two. Optical emission actinometry measurements indicate that the flux of atomic hydrogen across the stagnation layer to the substrate is mass diffusion limited. Since diamond growth depends upon the flux of atomic H to the substrate, these results suggest that under the conditions examined here, a low atomic H flux to the substrate poses an upper limit on the attainable diamond growth rate.

A new phenomenon in the field of Sialon ceramics is reported which may lead to applications based on their optical or electronic properties in combination with their mechanical and thermal properties. For the first time a colored α′-Sialon ceramic has been synthesized, with relatively high optical transparency by careful control of the sintering atmosphere, and adding suitable rare earths as stabilizing cations. This compares with normal Sialons and silicon nitrides which are grey-black in color and are opaque. Oxidation/reduction mechanisms have been identified as an influence on the valence of the stabilizing cation, which is responsible for the unusual optical properties.

Dislocation loops and stacking fault formation mechanism in α–Si3N4 have been studied by annealing α–Si3N4 powders at 1500 °C and 1750 °C. Thermally activated vacancies and the structural vacancies generated with replacement of nitrogen by oxygen have been tentatively suggested to be two sources of vacancies in α–Si3N4. From the point of view of mechanism, incorporation of these vacancies is believed to lie at the building-up stage of α–Si3N4 lattice. As a result of the vacancies agglomeration, dislocation loops and stacking faults seem to be a distinctively structural feature of α–Si3N4 fabricated by different routes [chemical vapor deposition (CVD), silicon nitridation, silica carbothermal reduction, and imide decomposition]. A general discussion has been extended to the historical controversy over the oxygen and vacancy stabilization of α–Si3N4 lattice arisen from the fact that the observed unit cell dimension of α–Si3N4 has a wide variation, and also to some related phenomena in processing of Si3N4.

The effect of BaSnO3 on the phase formation and the dielectric properties of Ba2Ti9O20 was investigated as a function of the amount of BaSnO3 in the temperature range of 20 °C to 80 °C at 7 GHz. In the reaction of 2BaCO3 + 9TiO2 → Ba2Ti9O20 + 2CO2↑, the batch with the addition of BaSnO3 enhanced the reactivity compared to the batch with the addition of SnO2. The enhancement of reactivity caused single phase Ba2Ti9O20 to form effectively with less amounts of BaSnO3. As the amount of BaSnO3 increased up to 0.03 mol, the unloaded Q increased due to an increase of the Ba2Ti9O20 phase; for further addition of BaSnO3 over 0.3 mol, the unloaded Q decreased due to the increase of rutile and BaTi4O9 phases. The dielectric constant increased with increasing BaSnO3. As single phase Ba2Ti9O20 was present in the specimen, the Q·ƒ0 value, the dielectric constant, and the TCF were approximately 37,900, 38.7, and 1.7 ppm/°C, respectively.

Theoretical studies have been made of K-edge x-ray absorption near edge structure (XANES) of Co in CoO, Co(OH)2, CoTiO3, Co3O4, and CoAl2O4. Correlations of experimental near edge features with site symmetry, local geometry, local electronic structure, i.e., atomic configuration, charge transfer, and backscattering from neighboring atomic potentials are interpreted. The self-consistent Discrete Variational Xa Method (DV-Xα) within an embedded cluster technique has been used to generate the crystal potential. A multiple scattering (MS) approach is then used to solve for the final state wave function. The ground state DV wave functions are analyzed in terms of the projected density of states, whereas the final state MS continuum wave functions are analyzed through the concept of photoelectron trapping time.

The growth of amorphous hydrogenated silicon nitride (a-SiN:H) films by plasma enhanced chemical vapor deposition (PECVD) of SiH4−NH3−N2 reactive gas mixtures has been studied. Films were deposited at low temperature (T < 250 °C) in a commercial PECVD system commonly used to grow a-SiN: H for semiconductor integrated circuit passivation. It has been observed that the stress of the a-SiN: H film can be controlled through dilution of the film precursors with an inert gas. Experiments indicate that the influence of the inert gas on the process extends from growth kinetics and plasma chemistry to hydrogen bonding, elemental composition, and biaxial elastic modulus. The stress in films deposited without dilution is tensile. When argon is added to the plasma, Si–Hx plasma chemistry and film hydrogen bond density change producing a reduction in the amount of tensile stress. Dilution with helium can be used to shift the film stress from tensile to compressive with minimum change in growth rate. The observed helium/film stress relationship is associated with helium-based Penning ionization processes, which create metastable reactive gas species. In turn, the metastables influence nitrogen and hydrogen incorporation into the film. Nitrogen incorporation produces volume expansion of the film, increasing the compressive character of the film stress. This effect is similar to that observed when the RF power is varied or when low or multifrequency plasma excitation is used during PECVD growth of a-SiN: H.

The effect of substrate bias voltage on the properties of arc ion-plated TiN films onto high speed steels has been investigated. The high density structure with a large crystallite size grew at the high bias voltage. TiN films deposited by higher bias exhibited strong preferential (111) orientation from XRD. The internal stress of TiN films increased at first with increasing substrate bias voltage; however, it decreased as the bias voltage increased over 100 V. The coating adhesion measured by the scratch tester increased with increasing bias voltage, and this is coupled with a cohesion of films. Cutting performance of TiN coated drills, which increased markedly with increasing substrate bias, has been studied in relation to the physical and chemical properties of deposited films.

The formation processes of epitaxial nickel silicides, resulting from the interaction of nickel silicide films (10 nm–100 nm) on (111) silicon (Si) substrates after furnace annealing, have been studied using transmission electron microscopy (TEM) and x-ray diffraction (XRD) techniques. The formation of type-A epitaxial grains (i.e., grown with the same orientation of the underlying Si substrate) and type-B epitaxial grains (i.e., rotated by 180± around the surface normal) in “thick” epitaxial films (i.e., greater than 35 nm) is proposed to be linked to the formation of a fluorite-based CuPt (L11)-like NiSi phase. This phase is found to be a metastable phase and is believed to be a transitional phase toward the formation of the equilibrium NiSi2 phase in both type-A and type-B orientations. In addition, we have found that a fluorite-based CuPt-like NiSi may even coexist with a fluorite-based CuAu I-like structure. The interrelationship between these two structures is discussed in the context of a displacive transformation process in fcc structures as originally proposed by Hansson and Barnes [Acta Metall. 12, 315 (1964)] and Pashley et al. [Philos. Mag. 19, 83 (1969)].

Several electrorheological (ER) materials systems composed of amorphous ceramic powders dispersed in light paraffin oil were developed to determine if relationships among ER activities, dielectric properties, compositions, porosities, and oxide species could be identified. The results of the studies suggested that trends among ER activity, dielectric phenomena, and alkali metal species existed. The aluminosilicate powders developed with various alkali metals showed that the ER activity increased as the activation energy decreased. The sodium aluminosilicate appeared to have the greatest ER activity and the lowest activation energy, while the cesium aluminosilicate displayed the weakest ER response, but had the highest activation energy. The thermodielectric responses of the different oxide materials systems developed with sodium showed that the mechanisms contributing to the dielectric dispersions had similar activation energies; however, the magnitudes of the recorded ER activities varied, and thus a direct correlation was not apparent. In addition, studies conducted with ER materials composed of sodium aluminosilicate powders of varying porosities showed that ER activities increased with increasing porosity. Furthermore, the analysis of the results of the thermodielectric and rheological studies of the different amorphous materials ER systems suggested that these materials may have an optimal stimulus frequency/temperature for ER activity.

The addition of BaTiO3 to Pb(Ni1/3Nb2/3)O3 has been confirmed to vary the formation kinetics of the perovskite solid solutions of Pb(Ni1/3Nb2/3)O3-BaTiO3, and to suppress the generation of the pyrochlore phase. A semiquantitatively calculated reaction conversion verified that increasing the BaTiO3 content significantly accelerated the formation of the perovskite solid solutions. The formed solid solutions of Pb(Ni1/3Nb2/3)O3-BaTiO3 (up to 90 mol% of BaTiO3) exhibited a cubic symmetry at room temperature. The lattice parameter monotonously decreased with an increase in the BaTiO3 content. The structural stability of the perovskite phase was found to be enhanced by the addition of BaTiO3 as well. The formed solid solutions were able to maintain the perovskite structure without decomposition when heated up to 1250 °C. The frequency dependence of the apparent Curie temperature and the diffuseness of the dielectric peak of sintered specimens were increased with increasing the BaTiO3 content up to 50 mol%. Whereas with further addition, the relaxor characteristics in the specimens became obscure, associated with lower frequency dependence and less broadening of the dielectric maximum. The largest broadening of the dielectric peak occurred at x = 0.5, implying that this composition exhibited the most disordered structure, which is probably related to the most random arrangement of B-site cations in oxygen octahedran.

The operation of the process of chemical vapor infiltration using a combination of pressure pulsing and thermal gradients is theoretically investigated in this study. Past studies had shown that pulsing of the pressure in the gas phase can lead to a dramatic reduction of the density gradients in the densifying structure, in comparison to those seen in isobaric diffusion-driven Pinfiltration, with significant gradients present only in the vicinity of the external surface of the preforms. Using a detailed model for chemical vapor infiltration under unsteady nonisothermal conditions, we show that temperature gradients, created in our study through microwave heating, can, in conjunction with pressure pulsing, eliminate the density gradients in the final product. Moreover, appropriate tuning of the operational parameters can lead to a situation where densification proceeds from the interior of the preform toward the external surface.

A Pd–Si–Cu bulk nanocrystalline material was prepared by quenching the melted Pd78Si16Cu6 alloy at a cooling rate of 200 K/s under 2–6 GPa. It was found that the nanocrystalline material consists of Pd(Cu) disordered solid solution and a metastable phase-II, Pd4Si. The grain size was found to decrease with increasing pressure. The influence of high pressure on the grain size of bulk nanocrystalline material is discussed, and a possible formation mechanism is proposed.

α–ZrP whiskers have been prepared from ZrCl4 + PCl3 + H2 + Ar gas mixtures at 1050–1250 °C using the mixed metal impurity-activated chemical vapor deposition process. The growth conditions, morphology, growth mechanism, and some properties were examined. The mixed impurities of Si + Pt and Si + Pd were very effective for the ZrP whisker growth with 8–12 mm (avg. 10 mm) long whiskers being obtained at 1300 °C for 1 h. The growth direction of the whiskers having hexagonal and square cross sections were along the c-axis and a-axis, respectively. The whiskers were very stable to an 80 min immersion in a concentrated HCl solution.

A special form of the Debye formula for calculating the powder x-ray diffraction of a turbostratically stacked layer system is derived, and calculated diffraction patterns for turbostratically stacked graphite and MoS2 layers are presented. Single-molecular-layer MoS2, prepared by exfoliation of lithium-intercalated MoS2 in water or alcohols, has been deposited on various supports, and x-ray diffraction patterns show that the restacking of the MoS2 layers can be perfectly turbostratic. The restacked MoS2 may or may not have water or organic bilayers between them, depending on the deposition conditions.

This study investigates the use of the environmentally benign precursor tri(dimethylamino)silane (TDMAS) with NH3 to synthesize silicon nitride films by low pressure chemical vapor deposition. The growth kinetics are investigated as a function of deposition temperature, total pressure, and NH3/TDMAS flow ratios. The deposits are found to be essentially stoichiometric and to contain ∼5 at. % carbon when appropriate NH3 concentrations are present. The films are found in all cases to be amorphous and highly tensile. For optimized processing conditions, values of the refractive index are close to those reported for Si3N4. The film density is observed to increase with higher deposition temperatures up to 800 °C and then decrease due to the onset of gas phase nucleation effects. This behavior is readily reflected in the etch rate of those films. FTIR spectra reveal the presence of hydrogen even at high deposition temperatures (900 °C). Hardness and Young's modulus of the films are seen to increase with higher deposition temperatures, reaching saturation values near 20 and 185 GPa, respectively, above 800 °C.