THE SOUND OF ONE-ATOM HOPPING - ATOMIC MANIPULATION ON SILICON SURFACES BY STM

We report time-resolved studies of the vertical tip displacement of a scanning tunnelling microscope during atomic-scale modification of silicon surfaces induced by voltage pulses. In a previous investigation, it was found that the majority of modification events occur either at the onset of the pulse or after the pulse. Here, we show that by suitably shaping the voltage pulse and varying the tunnelling conditions after the pulse, the temporal distribution of modification events can be controlled. In particular, modification events occurring at the pulse onset or after the pulse can be selectively suppressed. We also observe that voltage pulses sometimes generate bistable fluctuations in the tunnel junction resistance. It is suggested that these fluctuations share a common origin with the modification events occurring after pulses, namely both effects are the result of the diffusive motion of an atom hopping between absorption sites on the tip or surface.