Figure 1

(a) Si lattice viewed along the [110] axis shows the dark and light atoms displaced by $a/2$ in the axial direction, so that the slanted off-plane bonds appear shorter than the in-plane bonds; arrows indicate dimerization of surface atoms. Five prisms outlined by the triangle can join in pentagonal wire with the surface dimer rows either parallel (b) or perpendicular (c) to the wire axis; shown are 12-layer thick $P_{\parallel }$ and 11-layer thick $P_{\perp }$. (d) Energy dependence on nanowire thickness computed with classical EP (circles) and TB (crosses). The inverse-linear curve (dotted) is fitted to the sample points at 7 and 17 layers. The inset is for carbon.Reuse & Permissions

Figure 2

Hexagonal wire with four $\{111\}$ and two $\{100\}$ unreconstructed (a) and reconstructed (b) facets. Size-dependent energy (c) of different types of wires obtained as extrapolation based on several sample-point large-scale computations. The lowest energy line (solid pentagons) makes the ground state for $d<6\mathrm{n}\mathrm{m}$ evident as $P_{\parallel }$ structure, shown in (d). Added here for completeness, $P_{\perp }$ plot (open pentagons) differs from $P_{\parallel }$ due to significant edge-energy, $E_e=4.3\mathrm{e}\mathrm{V}$. Curves with open hexagons, squares, and diamonds denote, respectively, $H$, $S_{\square }$, and $S_{◊}$ wires. The shaded circle corresponds to the chain of fullerenelike ${\mathrm{S}\mathrm{i}}_{20}$ clusters, whose energy is the lowest among this variety; see Fig. 5(c) in Ref. 4.Reuse & Permissions

Figure 3

Potential energy and structural changes of eight-layer $P_{\parallel }$ wires in MD simulations at $T=1000\mathrm{K}$. The insets show the final structures of relatively stable Si (top) and of C transforming into $s{p}^2$ tubular-graphitic foam (bottom).Reuse & Permissions