Hexagon versus Trimer Formation in In Nanowires on Si(111): Energetics and Quantum Conductance

The structural and electronic properties of the quasi-one-dimensional $\mathrm{In}/\mathrm{Si}(111)$ surface system are calculated from first principles. It is found that the symmetry lowering of the In chains is energetically favorable, provided neighboring nanowires are correlated, giving rise to a doubling of the surface unit cell both along and perpendicular to the chain direction. The recently suggested formation of hexagons within the In nanowires [C. González, F. Flores, and J. Ortega, Phys. Rev. Lett. 96, 136101 (2006)]—in clear contrast to the trimer formation proposed earlier—drastically modifies the electron transport along the In chains, in agreement with experiment.

Figure 1

Side and top views of the ideal, unreconstructed $\mathrm{In}/\mathrm{Si}(111)\mathrm{\text{−}}(4\times 1)$ surface (upper two panels) and the hexagon formation within $8\times 2$ translational symmetry (lower panel). The dimerization and shear movements as well as trimer and hexagon orientation are indicated by arrows and shaded polygons, respectively.

Figure 2

Calculated (see text) energy change, for formation of hexagons, per $4\times 1$ unit cell vs configurational coordinate involving (a) the “double” phase transitions $4\times 1\to 4\times 2\to 8\times 2$ and (b) two “single” $4\times 1\to 8\times 2$ or $4\times 1\to 4\times 2$ transitions. A linear scaling between initial and final coordinates has been used to generate the intermediate geometries.

Figure 3

Quantum conductance spectrum for electron transport along the chain direction calculated for $\mathrm{In}/\mathrm{Si}(111)$ model structures; see text.