Initial Structures

The nanostructures we studied have two supporting layers that are connected with both ends of the nanobridges. The last layers at both supporting ends are rigid; all the atoms in these layers are kept fixed during the MD simulations. These fixed layers at both ends are assumed to be connected to the external agent. Atoms in the following two layers adjacent to the fixed atoms and those of the nanobridges are identified as dynamic atoms and are fully relaxed during the MD steps. We considered eight different structures, which are described in Table 1. D and L in Table 1 and Fig. 1 denote the diameter and the length of the nano-bridges, respectively. The nanowires with a face-centered cubic (fcc) structure have been observed in a previous work[23] and the ultrathin nanowires also have a type of cylindrical multishell (CMS) struc-ture.[24,30] Therefore we have selected nanobridges with fcc or CMS-type structures. The supporting layers have the same structures as those of the nanobridges. To describe CMS-type nanowires, we use the notation n — n' — n" — n" introduced by Ohnishi, Kondo, and Takayanagi[11] when the nanowire consists of coaxial tubes with n, n0, n00, n000 helical atom rows (n > n' > n'' > n'''). Because the structures of the CMS-type nanobridges are closely related to the {111} plane,[24] they are connected to the supporting layers with {111} planes. Nanobridges with different diameters were simulated under conditions of the same structure and the same length.

Fig. 1 Oscillation of the D1 nanobridge.
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