Kazuhito SHINTANI (新谷 一人)

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: competitive_research_funding, Overall Grant Amount: - (direct: 3600000, indirect: 0)
1. Simulations of coalescence of a Au cluster and a Cu cluster were performed. Clusters of fcc and icosahedral structures were created. How the structure, temperature, and size of the clusters before coalescence affect the structure of the coalesced cluster was investigated. It was concluded that an isolated cluster of fcc or icosahedral structure preserves its original shape and remains in the quasi-stable state, that the process of coalescence of clusters consists of spread of Au atoms over the Cu cluster, transfer of the surface energy to the kinetic energy, and progress of alloying at the internal Au/Cu interface, and that an alloyed cluster is created if a Cu cluster and a Au cluster are of about the same size while a core-shell cluster is created if the size of a Au cluster is smaller than that of a Cu cluster.
Next, deposition of an icosahedral Cu cluster on a Cu substrate in Ar gas was simulated. The effect of Ar gas on the deposition and on the structural properties of the deposited cluster was investigated. It was concluded that clusters deposited at room temperature become epitaxial, and that since the kinetic energy of a cluster is dissipated by Ar gas, the cluster arrives at a substrate surface without damage and undergoes a nondispersive structural transformation.
2. Simulations of formation of a Co/Cu/Co multilayer were performed. A Co(0001) substrate was created, and 6ML of Cu atoms and 6ML of Co atoms with the velocities corresponding to ones in experiments were deposited on it. The quality of a created multilayer was evaluated by calculating its surface roughness and intermixing. It was concluded that Cuatoms form two-dimensional islands on a Co(0001) substrate, that the higher the incident energy of deposited atoms, the flatter the surface of the deposited atoms, that the best interface is obtained by the deposition of atoms with the energy 5eV among the energies leV, 5eV, and 10eV, and that the usage of the smaller incident energy of Co atoms deposited on a Cu film diminishes the interface roughness and intermixing.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: competitive_research_funding, Overall Grant Amount: - (direct: 3200000, indirect: 0)
(1) Deposition of Si atoms on a Si substrate was investigated by means of molecular-dynamics simulation. It was concluded that at low temperatures, the initial three or four monolayers of deposited adatoms grow epitaxially while the subsequent layers form an amorphouslike structure, which is consistent with the limited-thickness epitaxy identified in experiments, that the mechanism of epitaxy at nanoscale can be understood by considering repetition of the breaking and renewal of dimer rows on transient growing surfaces, and that the dimer bonds become gradually stabilized as deposition proceeds, and breakdown of epitaxy occurs if the breaking and renewal of dimer rows are interrupted.
(2) The molecular-dynamics analysis of morphological evolution of a Au cluster softly-deposited onto a Au substrate was performed. It was concluded that both the clusters in a crystalline state and in a liquid state succeed in epitaxially accommodating themselves to the substrate, that in the accommodation of a crystalline cluster to the substrate at low temperatures, an energy barrier exists, and the cluster becomes finally a facetted epitaxial island, that in the accommodation of a liquid cluster to the substrate at low temperatures, no energy barriers exist, and the cluster becomes an epitaxial island smoothly, and that the morphology of such deposited nanostructures can be controlled by changing the state of free clusters and the substrate temperature.
(3) Elongation of Au nanowires was simulated by the molecular-dynamics method. It was concluded that the Young's modulus of a Au nanowire with a helical multi-shell structure is smaller than the Young's modulus of a Au nanowire of the fcc structure with a <110> center axis and with {111} surfaces, that with the increase of temperature, the former decreases more rapidly than the latter, and that a Au nanowire with a helical multi-shell structure can be elongated to produce a single-atom chain of Au atoms.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: competitive_research_funding, Overall Grant Amount: - (direct: 2100000, indirect: 0)
1 The anisotropic linear stability analysis of surface undulations of semiconductor heteroepitaxial layers was performed. Numerical results for SiィイD21-xィエD2GeィイD2xィエD2/Si systems show that the free energy change for the <100> surface undulations is greater than for the <110> undulations, which means surface undulations are likely to be formed in the <100> directions, that the present theory predicts the critical wavelength for the SiィイD20.82ィエD2GeィイD20.18ィエD2/Si system at 444nm which is in good agreement with the experimental value 44Onm, and that the main mechanism of the strain relaxation is the formation of surface undulations at the Ge fraction greater than 0.5 while it is the misfit dislocation generation at the Ge fraction less than 0.5.
2 The molecular dynamics simulations were performed for the dislocation generation from the surface of Si thin films. The Stillinger-Weber potential was used. The effects of surface steps and temperature on the change of the atomic structures are investigated. The simulation results show that at the temperatures 500K and 1000K, the energy decrease always occurs if the strain of the system exceeds a critical value whether there exists a surface step or not and whether the strain is compressive or tensile, that the energy decrease occurs due to the formation of (111) stacking faults either at an arbitrary point on the surface if there is no step or at the surface step if there is one, and that both the SィイD2AィエD2 and SィイD2BィエD2 steps can become generation points of stacking faults and the critical strain for the former is smaller from 1% to 2% than for the latter.
3 The atomistic calculations of the strain profiles within GaAs/InAs/GaAs pyramidal quantum dot structures were performed. The most stable atomic structures were obtained by the conjugate gradient minimization of the system energy expressed in terms of the Stillinger-Weber potential. The results show that there arises tensile strain just above the top of the island, which causes the vertical self-ordering of the stacked dots, that the larger the thickness of the wetting layer, the greater the magnitude of the tensile strain, and that the present results are in good agreement with those obtained by the inclusion theory.