Estimating surface diffusion coefficients

General guidelines for correlating surface diffusion parameters have existed up to now only in loose form and for specialized cases. Based on a survey of over 500 systems (the largest currently in existence), we propose new correlations for the activation energy E_diff and pre-exponential factor D_o for thermally activated surface diffusion on metals, semiconductors and some types of insulators. Physical bases rationalizing these correlations are provided. The highlights of these results follow, concerning two basic modes of surface diffusion: intrinsic, where the number of mobile particles remains constant with temperature, and mass transfer, where the surface releases mobile particles as the temperature increases. For intrinsic diffusion, E_diff on metals depends most strongly on whether or not the adsorbate is metallic. On semiconductors and insulators with directional bonding, the most important system property is the number of bonds an adsorbate forms with the substrate. For mass transfer self-diffusion at lower temperatures, kinks act as sources of adatoms, whereas at higher temperatures the terraces serve as the primary source. Consequently, two regimes exist for E_diff and D_o, arising from the enthalpy and entropy for adatom creation in each process. Related effects can sometimes exist for mass transfer heterodiffusion. A clear increase in E_diff and D_o appears in the higher temperature regime in progression from metals to semiconductors to insulators. For predictive purposes, semiquantitative estimates may be made for the enthalpy and entropy by analogy with bulk vacancy behavior. Diffusion in general does not seem to be perturbed significantly by the presence of an aqueous ambient. The present work represents the most comprehensive overall picture for surface diffusion yet available.