Collective diffusion of dense adsorbate at surfaces of various geometry

TL;DR

This paper develops a variational approach to calculate the collective diffusion coefficient of dense adsorbates on lattices with various geometries, accounting for particle interactions and coverage effects.

Contribution

A new variational formula for collective diffusion is introduced, applicable to arbitrary lattice geometries and coverage levels, including real systems like GaAs surfaces.

Findings

Diffusion transitions from isotropic to anisotropic with increased coverage.

Inter-particle correlations significantly affect the diffusion coefficient at higher coverages.

Application to GaAs surfaces demonstrates the method's practical relevance.

Abstract

Convenient variational formula for collective diffusion of many particles adsorbed at lattices of arbitrary geometry is formulated. The approach allows to find the expressions for the diffusion coefficient for any value of the system's coverage. It is assumed that particles interact via on-site repulsion excluding double site occupancy. It is shown that the method can be applied to various systems of different geometry. Examples of real systems such as GaAs with specific energetic landscapes are also presented. Diffusion of Ga adatoms on GaAs(001) surface reconstructed in two different symmetries is studied. It is shown how increasing Ga coverage changes the character of diffusion from isotropic two-dimensional into highly anisotropic, almost one-dimensional. It is shown how important the role of the inter-particle correlations is, which influence the value of the collective diffusion coefficient at higher coverages.