How to measure velocity correlations from surface diffusion experiments by STM

We introduce a generalized velocity-correlation function φg(t) for the study of tracer diffusion of interacting particles on surfaces. This function is defined in terms of particle displacement variables that can be obtained from both scanning tunneling microscopy experiments and simulations. We demonstrate this approach by considering a simple model adsorption system in which we find φg(t) to decay in a non-exponential fashion that can be well characterized by a power-law φg(t)∼t−x in time t. The decay exponent x provides information of predominant adatom–adatom interactions and ordering effects as is shown in this work.