Electric field effects on surface dynamics: Si ad-dimer diffusion and rotation on Si( [formula omitted])

Density functional calculations show that the electric field effect on Si ad-dimer diffusion on Si(0 0 1) is largely a reflection of the position dependence of the ad-dimer’s dipole moment. Surface diffusion barriers’ dependence on perpendicular electric fields can be used to discriminate between diffusion mechanisms. Since the previously accepted mechanism for ad-dimer diffusion on Si(0 0 1) has the opposite field dependence to what is observed, it cannot be the one that dominates mass-transport. We identify an alternate process, with a similar barrier at zero electric field and field dependence in agreement with measurements. For rotation, calculations to date show linear field dependence, in contrast to experiments.