Sodium-doped dimer rows on Si(001)

The stability and electronic structure of a nanowire are studied by first-principles calculations. The wire consists of a single depassivated silicon dimer row on the hydrogen passivated Si(001) $2\times 1$ surface. We predict that sodium atoms evaporated onto this surface stick preferentially at the depassivated row and partially fill the empty one-dimensional states of this row. This leads to a thin metallic wire of atomic size dimensions. At room temperature the sodium atoms are mobile along the depassivated row; they become immobile at temperatures below $\sim 120$ K.