Study of the formation process and mechanical properties of nanoscale materials by means of atomistic simulation

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(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.