Papers by Keyword: Growth Mode

Abstract: The single helix type carbon nanocoils were formed under the low temperature (550°C) condition. For the formation of the carbon nanocoils, C₂H₂ was used as a source gas and SF₆ was used as an additive gas under the thermal chemical vapor deposition system. The morphologies of as-grown carbon materials at the low temperature (550°C) and the mass ratios of product/catalyst were investigated according to the ratio of C₂H₂/ SF₆ flow and the injection times of SF₆ and C₂H₂ flows. The conversion efficiency from the carbon source gas (C₂H₂) to the as-grown carbon materials was estimated using the mass ratios of product/catalyst. The sample having the ratio of C₂H₂/SF₆ flow = 50 had the highest conversion efficiency. For the dominant formation of the single helix type CNCs, the optimal ratio of C₂H₂/SF₆ flow was determined to be around 10. As the growth aspect of the single helix type CNCs under the optimal ratio of C₂H₂/SF₆ flow, the formation of the CNCs was understood to be initiated within the reaction time of 5min after the formation of the carbon nanofilaments. The detailed growth mode of the CNCs was proposed.

Abstract: Nano size (2 - 10 nm) metal particles were formed and accumulated on powder substrate by conventional physical vapor deposition (PVD) process, in which the powder were a non-volatile in vacuum, such as Al₂O₃ powder. The neutral nuclei which were formed on the substrates from vaporized or sputtered metal atoms at an initial thin film growth were not grown up to coalescence and island stage with arrival atoms and ad-atom migration in the continuous deposition process, when the powder in vessel were continuously stirred during the deposition. Nano sized particles on the polymer chips (diameter: 1-2mm) easily dispersed into the polymer matrix by heating the chips, and on non-soluble powder, g-Al₂O₃, were stuck on the supporters stably in air. The nanoparticles on sucrose directly formed colloid with water solvents without dispersive agents. Most of the nano sized particles appear their own characteristic colors due to plasmon effect. Concentration and size of the nanoparticles are controlled by physical parameters in the PVD and the stirring speed of the powder. Surface phenomena on the substrate have been discussed with TEM, SEM, EDX, UV spectroscopy, etc. comparing with the conventional thin film growth.

Abstract: Morphology and crystal-quality of InAs/In0.53Ga0.47As/InP quantum dots (QDs) grown by metal-organic vapor phase epitaxy (MOVPE) in N2 ambient using different growth modes have been studied. It is found that the morphology and crystal-quality of InAs QDs are dependant on the growth modes. After optimizing the dots’ growth modes, dots’ size dispersion and crystal-quality are both improved greatly, resulting in the enhancement factor of ∼ 2.9 in the photoluminescence (PL) peak-intensity from single QD. When the dots are buried, the dot size decrease compared with the free-standing dots due to the soon capping layer deposition during dots’ being buried. The thermal activation energy measured is comparable to the valence-band offset in the QD system calculated by 8 kp theory model. This indicates the PL quenching induced by the interface defects is suppressed due to the defect density lowering in the QDs grown by such optimized growth mode.

Abstract: The initial GaN growth mode on stepped sapphires by plasma enhanced metal organic molecular beam epitaxy (PEMOMBE) has been analyzed using in-situ, real time synchrotron x-ray diffraction and x-ray absorption. The sapphire substrate annealed at high temperature had flat terraces and regular atomic steps. The crystal quality and the vicinal angle of sapphire substrate had an effect on the width of terraces and the step arrangement. The initial growth mode of the GaN film on the regular atomic step (AS) surface was the layer-by-layer mode and changed to the 3D growth mode within 2 bilayer thickness. In the meanwhile, the growth mode of the GaN film grown on the sapphire with random roughness (RR) surface made the flat surface in the early stage and changed the 3D growth mode. As increasing the film thickness, the nucleation layer grows strain-free hexagonal GaN on stepped sapphires