The crossover from collective motion to periphery diffusion for 2D adatom-islands on Cu(111)

TL;DR

This study uses self-learning Kinetic Monte Carlo simulations to analyze how 2D adatom islands on Cu(111) transition from collective motion to periphery diffusion as their size increases, revealing a crossover point and scaling behaviors.

Contribution

It introduces a detailed size-dependent analysis of diffusion mechanisms for adatom islands on Cu(111) using SLKMC, identifying a crossover from collective to periphery diffusion.

Findings

Crossover from collective to periphery diffusion occurs between 13 and 19 atoms.

Diffusion scaling exponent is approximately 1.5 for islands with 19 to 100 atoms.

Diffusion barriers increase linearly with island size for 2 to 13 atoms.

Abstract

The diffusion of two dimensional adatom islands (up to 100 atoms) on Cu(111) has been studied, using the self-learning Kinetic Monte Carlo (SLKMC) method [1]. A variety of multiple- and single-atom processes are revealed in the simulations, and the size dependence of the diffusion coefficients and effective diffusion barriers are calculated for each. From the tabulated frequencies of events found in the simulation, we show a crossover from diffusion due to the collective motion of the island to a regime in which the island diffuses through periphery-dominated mass transport. This crossover occurs for island sizes between 13 and 19 atoms. For islands containing 19 to 100 atoms the scaling exponent is 1.5, which is in good agreement with previous work. The diffusion of islands containing 2 to 13 atoms can be explained primarily on the basis of a linear increase of the barrier for the collective motion with the size of the island.