How to measure velocity correlations from surface diffusion experiments bySTM

We introduce a generalized velocity-correlation function phi (g)(t) for the study of tracer diffusion of interacting particles on surfaces. This funct ion is defined in terms of particle displacement variables that can be obta ined from both scanning tunneling microscopy experiments and simulations. W e demonstrate this approach by considering a simple model adsorption system in which we find phi (g)(t) to decay in a non-exponential fashion that can be well characterized by a power-law phi (g)(t) similar to t(-x) in time t . The decay exponent x provides information of predominant adatom-adatom in teractions and ordering effects as is shown in this work. (C) 2001 Elsevier Science B.V. All rights reserved.