Extracting adsorbate diffusion dynamics from an STM experiment: a Monte Carlo study of flicker noise

The flicker noise produced by adatoms diffusing underneath a static STM tip has been simulated via a Monte Carlo simulation of surface diffusion. The need to approximate details of the tunnelling process inherent in the use of the autocorrelation function has been avoided bq returning to the method of analysis originally proposed by Binnig et al. [Surf. Sci. 169 (1986) L295]. This method of analysis. however, is shown to be valid only at low coverages. A new method of analysis is proposed which allows diffusion activation energies to be extracted From such an experiment at a wide range of coverages, since the error in the analysis scales with the coverage, rather than the coverage squared. The inherent problems associated with adatom-adatom and adatom-tip interactions have also been investigated. In addition, it is shown that an analysis of the hopping probability gives, as expected, direct access to the diffusion constant of the surface diffusion process. An experimental method of measuring this quantity is proposed. (C) 1998 Elsevier Science B.V.