| Research Abstract |
1. How the behavior of a Si adatom or a Ge adatom deposited on the Si substrate and the morphology of the deposited layers in the initial period depend on the substrate temperature was investigated by the molecular-dynamics simulations with the Stillinger-Weber potential and the Tersoff one. For Si/Si homo-deposition processes, it was concluded that (1) the deposited layers form an amorphous structure at 300K and 400K, (2) the deposited atoms construct the alternately perpendicular dimer rows in the successive atomic layers to form an epitaxial structure at 700K and 1000K, which agrees with experimental results, (3) the ranges of the trajectories of a single deposited atom at 300K and 400K do not extend beyond, those at 500K are of the order of, and those at 700K and 1000K extend beyond the length between the nearest-neighbor atoms at the substrate surface, which corresponds with the different morphologies of the deposited layers at the temperatures. For Ge/Si hetero-deposition process
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es, it was elucidated that (4) at 1000K, the deposited layers with the deposition energy 0.2eV grow in the layer-by-layer mode until the initial two to four monolayers are deposited, and then the growth mode changes into the amorphous one while the deposited layers form amorphous stractures in the other conditions.
2. The temperature dependence of the strain distributions within Si/Ge/Si quantum dot structures was investigated using the molecular-dynamics simulation with the Tersoff potential, and the phonon densities of states for the optical mode were obtained. It was concluded that (1) the strain distributions within quantum dots computed by the molecular-dynamics method, at finite temperatures qualitatively agree with those computed by the conjugate-gradient method although the normal strain components perpendicular to the base of the quantum dots to the former are larger than those in the latter, and that (2) the positions of the peaks of the phonon densities of states for the optical mode in the quantum dots shift from those in bulk crystals
3. The mechanical properties of carbon naotubes were investigated by the molecular-dynamics simulation. The interaction between carbon atoms were calculated by using the Brenner potential. The Poisson's ratios and the Young's modulus were obtained for the naotubes models with the same diameter and with six chiral angles. It was conluded that (1) the Poisson's ratios of naotubes depend on their chiral angles, (2) the Young's modulus of nanotubes does not depends on their chiral angles, and (3)the elastic region in the deformations of nanotubes are extremely broad. Less
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