David D. Allred received Alumni Professorship Award

The depth profiles of high dosage Cr-52(+) and V-51(+) ions implanted in (100) crystalline silicon after thermal anneal at temperatures between 300 degreesC and 1000 degreesC are studied by secondary ion mass spectrometry and cross-sectional transmission electron microscopy. At dosages of 1x10(15) ions/cm(2) and above, the surface layer of silicon substrate is amorphorized. During the subsequent thermal annealing, the depth profiles of the implanted ions are strongly coupled with the solid phase epitaxial growth of amorphous silicon. Silicide precipitate formation is important to understand the differences between Cr and V diffusion. After anneal of the 1x10(15) ions/cm(2) implanted samples at 900 degreesC and 1000 degreesC, most of the Cr has left the silicon, but only 10% of the V has escaped. The 1x10(14) ions/cm(2) Cr-implanted sample shows Cr ions exist only near the surface after 1000 degreesC anneal. The V-implanted sample, on the other hand, only shows a narrowing of the V profile after 1000 degreesC anneal. (C) 2004 American Institute of Physics.

We report the preparation and investigation of ferromagnetic La0.67Sr0.33MnO3 (LSMO) thin films with orthogonally (along (110) and (1 (1) over bar0)) distributed nanometer-scale cracks. When the density of cracks reaches similar to10(4) cm(-1), the magnetoresistance MR = (R-H - R-0)/R-0 > - 30% was observed in the magnetic fields less than or equal to200 Oe and temperature range from 5 to > 300 K. The discussion about such unique feature will be done based on the spin-polarized electron tunneling and spin scattering, (C) 2004 Elsevier Ltd. All rights reserved.

Amorphous silica nanowires (a-SiONWs) were produced by direct solid state transformation from silica films. The silica nanowires grow on TiN/Ni/SiO2/Si substrates during the annealing in H-2 or a H-2:CH4 mixture at 1050 degreesC. Titanium nitride (TiN) films were used to induce a solid state reaction with silica (SiO2) films on silicon wafers to provide silicon atoms into growing nanowires. The TiN layers induce the diffusion of silicon and oxygen to the surface by a stress gradient built inside the films. The nickel diffuses to the surface during the TiN deposition and acts as a nucleation site for the a-SiONWs. (C) 2003 Elsevier B.V. All rights reserved.

Free-standing wafers (50 mm diameter) of GaN were grown by halide vapor phase epitaxy on lattice-matched gamma-LiAlO2. We report a transmission electron microscopy study of defects and defect densities in these wafers. The growth direction is [10 (1) over bar0]. Stacking faults in the basal plane are seen when viewing the specimen in the [1 (2) over bar 10] direction with an average spacing of less than 100 nm. Convergent beam electron diffraction measurements show no switch in the polarity and thus the faults are proposed to be ABABACAC changes in the stacking. Threading dislocations are found to have a correlated arrangement with a density of 3x10(8) cm(-2) when viewing the [1 (2) over bar 10] direction and widely varying (depending upon location) when viewing in the [0001] direction. These dislocations act as "seeds" for postgrowth surface features that directly exhibit the correlated nature of these threading dislocations. (C) 2003 American Institute of Physics.

Silica nanowires were synthesized by using silica nanoparticles as a growth catalyst using a gas composed of CH4 and H-2 at 1050degreesC. Silica nanoparticles provide silicon and oxygen atoms for the formation of the nanowires, as well acting as a growth site. The nanowires nucleated on graphitic carbon layers formed around the seed particles, indicating that the nanowires grow by the vapor-solid mechanism. Photoluminescence spectra of the nanowires normally showed strong blue emission peaked at 3.1 and 2.8 eV under 3.8 eV laser excitation. Post-hydrogen annealing resulted in the appearance of longer wavelength photoluminescence band. (C) 2003 Elsevier B.V. All rights reserved.

Nanocrystalline as well as submicron sized, non-agglomerated, spherical ZrO2 particles have been successfully synthesized using the sol-gel technique utilizing hydroxypropyl cellulose (HPC) as a polymeric steric stabilizer. The effect of various parameters such as the ratio of molar concentration of water and alkoxide (R), the molar concentration [HPC] and the molecular weight (MWHPC) of HPC polymer as well as the calcination temperature on ZrO2 nanocrystallites size and their phase evolution behavior is systematically studied. The phase evolution behavior of nanocrystalline ZrO2 is explained and correlated with the adsorption behavior of HPC polymer on ZrO2 nanoparticles surface, which is observed to be a function of R, [HPC], MWHPC and the calcination temperature. Optimum synthesis parameters for obtaining 100% tetragonal phase in nanocrystalline ZrO2 are identified for the present sol-gel method of synthesizing nanoparticles.