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  • Author: W. T. Chang x
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Abstract

Pressure-volume X-ray diffraction data were collected at eight pressures to 17.2 GPa for synthetic single-crystal forsterite, Mg2SiO4. Birch-Mumaghan equation-of-state param­eters were determined to be K0 = 125(2) GPa and Kʹ0 = 4.0(4). To ensure hydrostatic conditions, we monitored the diffraction-peak shapes while the sample was in different pressure med.ia: 4:1 methanol-ethanol, He, and Ar. The diffraction peaks for forsterite in 4:1 methanol-ethanol at 12.2 GPa were broadened to such an extern that we believe that any data collected at similar pressures and in this medium may be suspect and should be examined critically. The diffraction-peak profiles for the sample in He were Sharp and well-formed, suggesting He provides an excellent medium at pressures ≤ 17.2 GPa. However, upon decompression, the diffraction peaks of the sample in He also showed significant broadening. This broadening suggests that with increasing pressure He diffused into the crystal, but with the release of pressure the He was unable to diffuse out quickly. The diffraction peaks regained their sharpness after several months.

Abstract

In this paper we present the methods to chemically synthesize the Sb2Se3 nanorods and study the electrical and optical properties of a single Sb2Se3 nanorod with an average size of 70 nm in diameter and a length of about 1 μm to 2 μm. The techniques we devised can immobilize and allocate a single nano-object on an electron beam (E-beam) patterned smart substrate. It can also overcome the limitation of the spatial resolution of conventional optical techniques (∼ 1 mm) to obtain optical spectroscopy in an individual nano-object less than 100 nm in size. We also demonstrate the techniques in using E-beam defined metallic coordination markers as electrodes to measure the conductance of a single Sb2Se3 nanorod.

Abstract

Effects of growth conditions and buffer structures on crystal quality of 1.9-eV In0.5G0.5P, 1-eV In0.3Ga0.7As, and 0.75-eV In0.52Ga0.48As materials on misoriented GaAs substrate for inverted metamorphic solar cell grown by metalorganic chemical vapor deposition have been studied. Large lattice mismatch issue between the two lower bandgap 1.0-eV In0.3Ga0.7As and 0.75-eV In0.52Ga0.48As epilayers and the substrate has been resolved by using optimized step-graded buffer layers. Threading dislocation blocking mechanisms have been studied and discussed. It was indicated that threading dislocations have been significantly blocked in the designed InGaAs buffer layers through annihilation reactions between threading dislocations or through the formation of misfit dislocations. As a result, smooth surface In0.3Ga0.7As and In0.52Ga0.48As epifilms with threading dislocation density of about 1 × 106 cm−2 were obtained. For the growth of InGaP, the surface morphology, crystal quality, ordering parameter, and InGaP composition were significantly affected by growth temperature, V/III ratio, and III/III ratio. The almost lattice match to the substrate, high crystal quality, and smooth surface of In0.495Ga0.505P were obtained at growth temperature of 675°C and V/III ratio above 150. The ordering parameter was strongly dependent on growth temperature. Photoluminescence measurement indicated that the bandgap of the InGaP epilayer is 1.89 eV, indicating that the solid composition in the InGaP film is more disordered.