Search

Grain boundary migration effects on hillock formation in AI thin films is examined.

Plane view and cross-section transmission electron microscopy (TEM) images were used to compare the density, character, and curvature of dislocations developed during metalorganic vapor phase epitaxy (MOVPE) of GaN on planar c-plane sapphire with those developed during growth on nano-patterned c-plane sapphire. Scanning electron microscopy (SEM) characterization of GaN films at different stages of growth for both types of substrates complemented the TEM investigation. GaN growth on wafers patterned with an array of submicron sapphire bumps exhibited relatively uniform nucleation and initial growth, as well as early island coalescence. It is suggested that this coalescence results in a relatively small fraction of dislocations with partial screw character at the surface of the films grown on the patterned substrate, and that this may be responsible for the improvements in carrier lifetime and device efficiency seen in earlier studies on similar sapphire substrates. [ABSTRACT FROM AUTHOR]

To explore alternatives to the use of pure Au in Ohmic contact RF microelectromechanical switches, we have measured changes in the electrical resistivity and nanoindentation hardness of a series of sputter deposited Au–V and Au–V2O5 thin films. Increasing V content in the Au–V alloys increases resistivity and hardness, which is consistent with solid solution strengthening. In the Au–V2O5 films, the increase in resistivity is greatly reduced and the hardness is further increased as expected for dispersion strengthening with V2O5 particles. These two phenomena are explained in terms of solute and particle effects on electron scattering and bowing of dislocations, respectively. [ABSTRACT FROM AUTHOR]

Cu nanowires with widths ranging from 110 to 300 nm were fabricated on a c-plane sapphire substrate using E-beam lithography and lift-off processes. Thermal annealing of these polycrystalline metal nanowires at 700 °C in an inert (nitrogen) atmosphere showed that for lines of width 160 nm or less, there was complete breakdown into widely spaced, individual beads in a short time (1 h). It was shown that the morphological changes were driven by reduction in the surface energy, with surface diffusion as the predominant transport mechanism. The spacing between the beads was approximately 1.8 times greater than the values predicted by Rayleigh instability theory for a free standing rod with equivalent radius. Based on thermodynamic and kinetic considerations, discrepancies between the experimental observations and the predictions of Rayleigh instability theory were attributed to the stabilization effect of the substrate. [ABSTRACT FROM AUTHOR]

The electrical and mechanical properties of Au-V and Au-V[O.sub.x] alloys are examined. The electrical resistivity and nanoindentation hardness are described in terms of solute and particle effects on electron scattering and bowing of dislocations.

Thermal annealing of Cu nanowires fabricated on a c-plane sapphire substrate by using E-beam lithography and lift-off process is studied. The discrepancies between the experimental observations and the predictions of Rayleigh instability theory are attributed to the stabilization effect of the sapphire substrate.

Materials in single crystal form are often sought after because the absence of grain boundaries can result in unique properties relative to the polycrystal, but producing these materials is typically a slow and complex process. In this work, pseudo single crystals of the pseudobrookite compound CoTi2O5 were synthesized by solid‐state reaction from a duplex grain mixture of CoTiO3 and TiO2. The size of the crystallites was >250 µm. The transformation and subsequent microstructural evolution of the CoTi2O5 was studied by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and X‐ray diffraction (XRD). A novel growth mechanism was identified whereby a single crystal CoTi2O5 front advances simultaneously along multiple CoTiO3/TiO2 diphasic boundaries. The single crystal domains were composed of subgrains approximately 5 µm in diameter; differences in the subgrain size and misorientation were related to the growth mechanism and the initial grain size of the duplex CoTiO3–TiO2 mixture. CoTi2O5 is a little characterized compound, and this study represents the most significant microstructural study of CoTi2O5 to date. The findings may be applied to similar pseudobrookite compounds such as MgTi2O5 and Al2TiO5. [ABSTRACT FROM AUTHOR]

Metal-ceramic composites exhibit desirable combinations of materials properties, but are limited by the complexity of processing, particularly for metal-ceramic nanocomposites. The in situ partial reduction technique is a simple processing method that can be used to produce tailorable metal-ceramic composite microstructures. In this work, in situ partial reduction was utilized to generate novel Co-TixOy composites, including nanocomposites, through the reduction of CoTiO3. By modifying the temperature (800-1400 °C) and time (1-8 h) of reduction, composites with varying cobalt particle size and cobalt grain size were fabricated. Differences in the cobalt crystal structure and nature of the titanium oxide phase were also observed. The lowest-temperature heat treatments resulted in metal-ceramic nanocomposites. The Co-TixOy composites were characterized through scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction. The effect of processing variables on the properties of the composites was evaluated through nanoindentation of the embedded cobalt particles, and it was found that cobalt particle hardness is strongly correlated with grain size. The many useful properties of cobalt and titanium oxide, in conjunction with the range of controllable microstructures, demonstrate that the in situ partial reduction technique has excellent potential for metal-ceramic composite production. [ABSTRACT FROM AUTHOR]