Step fluctuations onAg(111)surfaces withC60

Abstract

STM has been used to characterize fluctuation properties of segments of step edges partly covered by ${\mathrm{C}}_{60}$ on $\mathrm{Ag}(111)$ at room temperature. The distribution of ${\mathrm{C}}_{60}$ at step edges exhibits a step orientation dependence: Low-symmetry step edges are more favorable for ${\mathrm{C}}_{60}$ binding. The temporal correlation functions of step segments between ${\mathrm{C}}_{60}$-covered step regions scale as a power law, with an average exponent of $0.23\ifmmode\pm\else\textpm\fi{}0.02$, indicating that fluctuations of these ``confined'' steps are consistent with step-edge diffusion limited fluctuations. Parameters extracted from temporal correlation and autocorrelation analysis consistently indicate that close-packed steps have smaller fluctuation magnitude and higher step mobility than low-symmetry steps. The measured effective system sizes of step segments with different lengths show at most a weak step-length dependence. Fluctuation features thus yield the surprising conclusion that ${\mathrm{C}}_{60}$ molecules are not acting as pinning points that constrain mass transport along the step edges.