Adatom diffusion characteristics from STM noise: theory

Adatoms moving along the substrate surface under an STM tip cause a random time dependence of the current, J(t). We have obtained simple expressions for the average current 〈J(t)〉 and the temporary current correlation function 〈J(t +τ)J(τ)〉_τ - 〈J(t)〉² through the diffusion coefficients of the adatoms and a few parameters of the tunneling gap. The results offer a way to study the local diffusion of adatoms by treatment of experimentally measured J(t) dependencies.