Chemical vapor deposition (CVD) using gold nanoparticles as the catalyst to grow high-quality single-crystal gallium nitride nanowires was developed. This method enables control over several important aspects of the growth, including control of the nanowire diameter by using monodispersed gold clusters, control of the nanowire location via e-beam patterning of the catalyst sites, and control of the nanowire orientation via epitaxial growth ona-plane sapphire substrates. Our work opens up new ways to use GaN nanowires as nanobuilding blocks.

The diffusion of oxygen in sapphire was accelerated by heating in a 28 GHz microwave furnace as compared with heating in a conventional furnace. Tracer diffusion experiments were conducted using 18O. Single crystal sapphire wafers with a (1 0 1 2) rhombohedral planar orientation were used as the substrate. Concentration depth profiling was done by proton activation analysis using a 5 MeV Van de Graaff accelerator. The diffusion of 18O was greatly enhanced by microwave heating as compared with conventional heating in the 1500–1800°C range. The apparent activation energy for 18O bulk diffusion was determined to be 390 kJ mol-1 with microwave heating and 650 kJ mol-1 with conventional heating.


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Sapphire crystals, 140 mm in diameter and 90 mm in height, have been grown by temperature gradient techniques (TGT). The growth direction of the boule was fixed by means of Laue X-ray diffraction. A prominent 204 nm absorption band in TGT-Al2O3, which does not appear in single crystals grown by Czochralski method has been studied. Analysis further substantiates the F-center model of this band. Two relatively weaker bands absorbing at 232 nm and 254 nm were ascribed to F+ centers. F-type centers concentration was determined using Smakula's equation.

CdTe crystals were obtained using a vapour phase method, where the crystal is grown on a monocrystalline seed without contact with a heat-conducting supporter. Some different agents filling the tube during the growth process were used and it was found that the growth rate depends strongly on the agent.


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The world's largest sapphire boules up to 340-mm diameter are produced by the Heat Exchanger Method (HEM). In order to meet all applications, the highest purity crackle is used so the product has impurity levels very near the detectability limit of Glow Discharge Mass Spectroscopy (GDMS). The charge size of production 340-mm diameter sapphire boules was increased from 55-kg to 70-kg, and larger 380-mm diameter, 84-kg boules were produced. These boules were used to produce 315-mm diameter, 132-mm high sapphire cylinders to meet customer requirements. Efforts have been taken to produce a nearly flat top surface of HEM-grown boules with minimal undulations along the sidewalls to allow fabrication of larger sapphire pieces for production boules.Up-scaling of the gradient furnace technique has resulted in the growth of large monocrystals of Al2O3 up to 15 cm in diameter, 6.8 cm in height, and 4.5 kg in weight.

The technique was developed to detect the crystallization of the upper-central surface of sapphire crystals grown in crucibles. This technique takes advantage of the large difference in optical absorption coefficients of molten and solid sapphire at the melting point, and is based on the recording of pyrometer readings throughout the course of growth. At the point of solidification of the observed sapphire surface, a knee occurs on the recorded graph. The accumulated data enable the optimization of growth rates at the end of the growth as well as the duration of the growth by proper timing of the beginning of crystal cool-down. It is also possible to detect and terminate unsuccessful growth runs at an early stage.


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The etching of sapphire substrates using H2SO4, H3PO4, and a 3:1 H2SO4:H3PO4 mixture, as a function of temperature and etching time, was systematically studied using atomic force microscopy. The sapphire preparation by liquid-based etchings was compared with H2 etching at 1100°C and air-annealing at 1400°C. In liquid-based treatments, the smoothest, pit-free surface was obtained by etching in pure H2SO4 at 300°C for 30 min. Sulfuric acid etching at higher temperatures or for longer periods generated an insoluble mixture of Al2(SO4)3 and Al2(SO4)3⋅17H2O crystalline deposits on the surface.

Phosphoric acid and the 3:1 H2SO4:H3PO4 mixture, which is the routinely employed chemical treatment for sapphire preparation, etched the sapphire preferentially at defect sites and resulted in pit formation on the surface. Sapphire treatment using H2 at 1100°C did not remove the surface damage. Air annealing the sapphire at 1400°C for 1 h produced an atomically smooth surface consisting of a terrace-and-step structure. The results of this study were described in terms of the chemistry of the sapphire etching process.


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