The morphologies of ZrSi2 on Si(111) and TiSi2 on Si(111) and (100) have been investigated, and the results compared and contrasted. Films were prepared by UHV deposition of Ti or Zr onto clean, reconstructed Si(100) or (111) substrates, and reacted by in situ annealing. The sheet resistivity of the ZrSi2 was measured and found to be 33-42 μΩ-cm. The morphologies were examined by transmission and scanning electron microscopy. In particular, the islanding properties were studied; both the temperature of the onset of islanding and the island characteristics were measured. The surface and interface energies have been determined from the contact angles of the silicide islands, according to a solid-state capillarity model. The system of ZrSi2 on Si(111) was found to have surface and interface energies lower than those of the system of TiSi2 on Si(100), but higher than those of the system TiSi2 on Si(111). ZrSi2 on Si(111) was found to island at a higher temperature than TiSi2 on either substrate, a result attributed to kinetic effects. Areal coverage of the islands was measured, and the results were consistent with the solid-state capillarity model. For both TiSi2 and ZrSi2, increasing faceted structure was observed with increasing anneal temperature. Preferred faceting planes were found to be of Si(111) and (100) type for TiSi2 islands and of Si(111) type for ZrSi2. Faceted islands were apparently epitaxial. As the solid-state capillarity model does not directly apply to islands with a faceted structure, an observation of the percentage of faceted islands produced by different annealing temperatures was used to suggest the processing conditions in which the model is applicable.

The electrical conductivity of 3Y-TZP ceramics containing SiO2 and Al2O3 has been investigated by complex impedance spectroscopy between 500 and 1270 K. At low temperatures, the total electrical conductivity is suppressed by the grain boundary glass films. The equilibrium thickness of intergranular films is 1-2 nm, as derived using the “brick-layer” model and measured by HRTEM. A change in the slope of the conductivity Arrhenius plots occurs at the characteristic temperature Tb at which the macroscopic grain boundary resistivity has the same value as the resistivity of the grains. The temperature dependence of the conductivity is discussed in terms of a series combination of RC elements.

The role of aluminum as dopant in gas phase synthesis of titania powders was experimentally investigated in an aerosol flow reactor between 1300 and 1700 K. Titania was produced by vapor phase oxidation of titanium tetrachloride in the presence of dopant aluminum trichloride vapor. The presence of aluminum altered the particle morphology from polyhedral to irregular crystals. Energy dispersive analysis and transmission electron microscopy indicated that the powders were mixtures of crystalline titania and amorphous alumina. Analysis by XPS indicated significant enrichment of aluminum on the particle surface. Some aluminum titanate (up to 17% by volume) was formed at 1700 K when a high concentration of AlCl3 was used (AlCl3/TiCl4 ≥ 0.07). Measurements of lattice parameters by x-ray diffraction indicated that aluminum formed a solid solution in titania. While titania synthesized in the absence of aluminum was about 90% anatase, the introduction of aluminum resulted in pure rutile at AlCl3/TiCl4 = 0.07. The effects of aluminum on titania phase composition and morphology are explained by the creation of oxygen vacancies in the titania crystallites and by the enhancement of the sintring rate of titania grains.

Rheotaxial growth and thermal oxidation (RGTO) for depositing thin films is a recognized technique in preparing gas sensitive semiconducting oxides. This paper presents a study performed by x-ray diffraction and scanning Auger microscopy of the mechanisms of growth and formation of the thin films of the new ternary compound Sn1−xFexOy with an iron content in the range O < x < 25 at. %. A structural model of this compound, which is found to be stable over a very large range of Sn/Fe ratios, can be derived by partially substituting Fe3+ ions in Sn4+ sites. This is an easy substitution in view of the similar values shown by the ionic radii (Fe3+ = 0.64 Å, Sn4+ = 0.71 Å) and the Pauling electronegativity (Fe3+ = 1.8, Sn4+ = 1.8) of these two ions. Experimental data, showing that this material is an excellent CO sensor, are reported.

Various copper salts have been irradiated with the help of a continuous wave CO2 laser. In other experiments the same salts have been decomposed under a controlled heating rate, in a thermal balance, and copper oxide crystallites have been detected as the final product of both types of experiment. The measurements of crystallites performed with the help of x-ray diffraction exhibited differences between the two types of oxides: those obtained by laser irradiation as compared with the oxides obtained by thermal heating. The magnitude of this difference seems to depend on the laser quanta absorptivity of the initial salts. The results are consistent with those obtained previously on nickel oxides.

A microstructural characterization of the La2−xSrxNiO4+δ (0 ⋚ x ⋚ 1) system, prepared with accurate control of the oxygen content, has been performed. The electron diffraction study shows the evolution of the accommodation of compositional variations as a function of δ. For δ > 0.06, interstitial oxygens are ordered, leading to new K2NiF4 superstructural types. Samples with δ < 0.06 accommodate the nonstoichiometry by means of random distribution of anionic vacancies.

Thin films of potassium tantalate niobate (KTN) were prepared by means of pulsed excimer-laser deposition and investigated with a number of analytical techniques, including electrical and electro-optical measurements. For applications in longitudinal electro-optic modulators, a transparent electrode is required between substrate and electro-optic layers. Suitable electrode materials, which at the same time permit epitaxial growth of KTN, were identified and prepared. The resulting layered samples were not only of good epitaxial and optical quality, but also exhibited the expected maximum of the longitudinal electro-optic effect at temperatures between the phase transitions from cubic to tetragonal and from tetragonal to orthorhombic. However, the maximum achievable electro-optic phase shift was found to be limited to roughly τ/100 for KTN films in the thickness range around 1 μm. Therefore, much thicker films are probably necessary for most practical applications, which requires significant improvements in the long-term stability and homogeneity of the deposition process.

We have studied the effects of the kinetic energy of mass-separated O+ beams on the growth of CuO thin films deposited on unheated MgO(001) and at 510 °C, in energy ranging from 10 to 200 eV by x-ray photoemission spectroscopy, x-ray diffraction, reflection high-energy electron diffraction, and scanning electron microscopy. The films deposited at 510 °C show a full width at the half maximum (FWHM) of 0.06°for the rocking curve through the (111) peak, regardless of the kinetic energy of oxygen ions. CuO has been epitaxially grown on MgO(001) without heating it in a vacuum of 4 × 10−7 Pa. The x-ray diffraction intensity of the CuO(111) increases with an increase in the kinetic energy of O+, and its FWHM approaches that of the CuO film grown at 510 °C. The surface morphology is improved for the films deposited on unheated substrates.

Amorphous calcium phosphate coatings on the order of 1 μm thick were deposited onto titanium and silicon substrates using an ion-beam sputtering technique. The target material utilized for sputter deposition was plasma-sprayed fluorapatite [Ca10(PO4)6F2; FA]. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to analyze the coatings. The amorphous as-deposited coatings were annealed in air (at 500 °C or 600 °C) to a crystalline state consisting of a polycrystalline FA matrix with a small amount of microcrystallites of a different composition. The higher annealing temperature (600 °C) tended to produce coarser FA and microcrystallite grains; however, the coatings buckled on the titanium substrates as a result of the heat treatment. Attempts to form the FA phase by in situ annealing in the vacuum chamber at a substrate temperature of 500 °C were not successful. The average bond strength for the as-deposited and 500 °C post-annealed coatings was comparable, while the lowest bond strength was observed in the 600 °C post-annealed coatings. The results suggest that the 500 °C post-annealed coatings have a suitable structure and possess sufficient adherence to be acceptable for use in certain medical and dental implant applications, and further tests under physiologic conditions will be conducted.

High strength can be achieved in high alumina cement (HAC) through the incorporation of phosphate-based additions at levels of 10 and 20 wt. %. In order to establish the mechanism that results in higher strength, the effects of a variety of condensed sodium phosphates (NaPO3)n, (NaPO3)n · Na2O, Na5P3O10, and (NaPO3)3 were studied. The influence of these additions on the kinetics of hydration was studied using isothermal calorimetry. The phosphatic additions enhanced reactivity, but x-ray diffraction analyses did not reveal evidence of new crystalline phosphate-containing hydration products. Microstructural evolution was examined in real time using environmental SEM, and hydration products exhibiting distinct morphologies were observed. The features exhibited ranged from amorphic to polygonal shapes, plates, and fibers. These frequently formed between crystalline calcium aluminate hydrate grains and by doing so appear to provide a means to enhance the strengths of these cements. In spite of the morphological variations, companion energy dispersive x-ray analysis showed that the compositions of these products did not vary widely. Their ranges of compositions are 52-60 wt. % Al2O3, 20-26 wt. % P2O5, and 20-24 wt. % CaO.

Cathodoluminescence (CL) spectroscopy in a scanning electron microscope was used to identify and to map the spatial distribution of luminescent defects in a synthetic diamond single crystal. Several defect CL bands were observed in the 1.5-3.5 eV region: (i) a band with a zero-phonon line at 2.156 eV, attributed to a center containing nitrogen and atomic vacancies; (ii) a broadband centered at ∼2.2 eV, tentatively attributed to a boron-containing center; (iii) a doublet line at 2.33 eV, attributed to a nitrogen-containing center; (iv) a zero-phonon line at 2.555 eV, attributed to a nickel-containing center; (v) a broadband centered at ∼2.85 eV, attributed to a dislocation-related center; and (vi) a zero-phonon line at 3.188 eV, attributed to a center containing nitrogen and a carbon interstitial. Lines due to free and acceptor-bound excitons were observed in the 5.0-5.4 eV region. The spatial variation of the CL was examined in the vicinity of regions of relatively high dislocation density (∼106 dislocations cm−2), which had been found in a previous x-ray diffraction imaging experiment. A quantitative analysis was made of the spatial variation of the band intensities. Upon moving from a relatively defect-free region to the center of a high dislocation density region, the intensities of defect bands (i) and (v) increased by very large factors (these bands were observed only within the high dislocation density regions); the intensity of defect band (vi) increased by a factor of ∼2; the acceptor-bound exciton intensity increased by a factor of 1.3; the intensities of defect bands (ii)-(iv) decreased by a factor of ∼2; and the free exciton intensity decreased by a factor of ∼7.5.

A simple model for the size-dependent amplitude of the atomic thermal vibrations of a nanocrystal is presented which leads to the development of a model for the size dependent melting temperature in nanocrystals on the basis of Lindemann's criterion. The two models are in terms of a directly measurable parameter for the corresponding bulk crystal, i.e., the ratio between the amplitude of thermal vibrations for surface atoms and that for interior ones. It is shown that the present model for the melting temperature offers not only a qualitative but even an excellent quantitative agreement with the experimentally observed size-dependent superheating, as well as melting point suppression in both the supported and embedded metallic and semiconductor nanocrystals.

The impact code EPIC was employed to study the relationship between the applied force and the penetration depth in a micrometer-scale indentation experiment with oxygen free high conductivity (OFHC) copper. EPIC is an elastic-plastic finite element code that uses a Lagrangian formulation and triangular mesh, which can accommodate large deformation without the need to remesh during the computation process. By fitting the force-penetration curves for a triangular indenter with second degree polynomials, it was demonstrated that the fit changed with two material constants in the constitutive equation. A systematic procedure for determining the material constants is described that is based on matching either the slope or the curvature of the force penetration depth curves from numerical simulation and experiments. It is concluded that material constants can be determined from indentation data obtained using pyramidal or spherical indenters as well as a flat-ended indenter.

We recently performed a series of experiments on Nb-doped lead-zirconate-titanate ceramic to investigate the influence of constant shear stresses on the displacive, first-order rhombohedral/ferroelectric → orthorhombic/antiferroelectric polymorphic transformation. In a previous paper and report we demonstrated that increasing shear stresses lowers the mean stress and confining pressure at which the transformation occurs, but we did not identify a criterion by which the transformation could be predicted to take place under nonhydrostatic stress. In this paper we use the dielectric anomaly which accompanies the transformation as an indicator of onset of the transition, and correct for the effects of high-pressure-seal friction on measurement of the maximum compressive stress applied to the test specimens during deviatoric loading. We show that a convincing case can be made that the transformation occurs when the maximum compressive stress equals the hydrostatic pressure at which the transformation would otherwise occur.

“Heteroepitaxy of rare-earth hexa-aluminates on sapphire” [J. Mater. Res. 9, 410-419 (1994)]