The influence of tip-sample interaction on step fluctuations on Ag (111)

The fluctuations of the position of monatomic steps on Ag (111) are investigated by Scanning Tunneling Microscopy (STM). We analyze the influence of tip-sample interact~on by varying the gap ~mpedance over more than two orders of magnitude. For tunneling tips providing a weak tip-sample interact ion, we show that the step position au~ocorrelation function remains essentially unaltered. In this unperturbed case, the kinetlcs of step fluctuations are found to be dominated by one-dimensional mass uansport. For larger variations of tip-sample distance or for less favorable tip configurations we observe a tip-induced increase of the s ~ c p fluctuations. Ow measurements suggest that this effect is rather caused by short-range forces than by the electric field in the. tunneling gap.