SURFACE DIFFUSION WITH A REALISTIC DAMPING COEFFICIENT

摘要

We study the diffusion of a particle in a two-dimensional external potential. Simulation results show that, in the underdamped limit, the average jump length <λ> scales with the damping coefficient η as <λ> ∝ η~(-σλ) with 1/2 ≤σλ ≤2/3, so that the diffusion coefficient behaves as D ∝ η~(-σ) with 0 ≤σ≤ 1/3. We then introduce a realistic friction coefficient for the phonon damping mechanism. The study of diffusion in this model shows that long jumps play an essential role for diffusing atoms of small masses, especially in two limiting cases: a large substrate Debye frequency, when the rate of phonon damping is low, and a small Debye frequency, when the one-phonon damping mechanism is ineffective. As an application, we consider the diffusion of a dimer adsorbed on the crystal surface.