Steady-state motion of silicon islands driven by a DC current

The understanding and control of structures at the surface of crystals is a fashionable topic nowadays. The role of an electric heating current in sha ping the morphology of vicinal (111) and (001) silicon surfaces during subl imation in ultra-high vacuum is well known. Less known is the behaviour of surface features when the crystal is in contact with its own saturated vapo ur, and thus at equilibrium. We report here the observation by reflection e lectron microscopy of two-dimensional, micrometre-sized silicon islands on a resistively heated Si(001) substrate held at equilibrium (vanishing super - and undersaturation) at temperatures between 1000 and 1100 degrees C. Sur prisingly, the islands are seen to perform a gliding motion at a constant v elocity in or against the current direction, depending on the island recons truction. The value of the velocity is, on the contrary, independent of isl and reconstruction and size. A simple model based on adatom electromigratio n is discussed, that allows us to account for all observed features. (C) 19 99 Elsevier Science B.V. All rights reserved.