The analysis of the dynamics of equilibrium step fluctuations has been extended to a chemically heterogeneous surface. The multicomponent reconstructed Al/Si(111)-($\sqrt{3}$×$\sqrt{3}$) surface has been studied using variable-temperature scanning tunneling microscopy at elevated temperatures. The temporal correlation functions for both single steps and step arrays follow a $t^{1/2}$ dependence over the entire temperature range (770–1020 K), consistent with a rate limiting mechanism of random attachment and detachment of atoms at step edges. The alternative mechanism, diffusion from step-to-step, is shown to be inconsistent with more detailed analytic approximations to the correlation function for the measured step-step separation. An activation energy of 1.9 eV and the major kinetic parameters that govern surface mass transport and step equilibration processes have been determined.

• Received 14 December 2001

DOI:https://doi.org/10.1103/PhysRevB.66.085327