Bias voltage influence on the shape of cobalt-silicide nanowires

We have fabricated cobalt-silicide nanowires on silicon by removing hydrogen from a passivated Si(001)2×1 surface with a scanning tunnelling microscope, followed by evaporation of cobalt. The apparent shape of the wires depends on the bias applied to the tip. This is due to the Fermi level pinning close to the valence edge by the high work function Pt–Ir tips, and the Co acceptor levels 0.35 eV above the valence band. Moreover, the decrement in the image contrast with increasing bias voltage is related to decrement in the local density of states, which is in qualitative agreement with former studies of nanosized cobalt disilicide islands.