A generalized velocity-correlation function, φ, was introduced into the study of the tracer diffusion of interacting particles on surfaces. This function was defined in terms of particle displacement variables that could be deduced from scanning tunnelling microscopy or simulations. This approach was demonstrated by considering a simple model adsorption system in which φ was found to decay in a non-exponential fashion that could be characterized by a power-law: φ ~ t-x. The decay exponent provided information on predominant adatom–adatom interactions and ordering effects.

How to Measure Velocity Correlations from Surface Diffusion Experiments by STM. T.Hjelt, I.Vattulainen, J.M.Lahtinen, T.Ala-Nissila, S.C.Ying: Surface Science, 2001, 482-485[1], 381-5