Interplay of Strain Relaxation and Chemically Induced Diffusion Barriers: Nanostructure Formation in 2D Alloys

TL;DR

This study investigates how strain relaxation and chemically induced diffusion barriers jointly influence nanostructure formation in 2D alloys, using kinetic Monte Carlo simulations to replicate experimental stripe patterns.

Contribution

It demonstrates that both strain relaxation and diffusion barriers must be combined in models to accurately reproduce observed nanostructures in 2D alloy systems.

Findings

Neither mechanism alone explains experimental patterns.

A combined model reproduces stripe formation and island ramification.

Quantitative relationships between parameters and structures are established.

Abstract

We study the formation of nanostructures with alternating stripes composed of bulk-immiscible adsorbates during submonolayer heteroepitaxy. We evaluate the influence of two mechanisms considered in the literature: (i) strain relaxation by alternating arrangement of the adsorbate species, and (ii) kinetic segregation due to chemically induced diffusion barriers. A model ternary system of two adsorbates with opposite misfit relative to the substrate, and symmetric binding is investigated by off-lattice as well as lattice kinetic Monte Carlo simulations. We find that neither of the mechanisms (i) or (ii) alone can account for known experimental observations. Rather, a combination of both is needed. We present an off-lattice model which allows for a qualitative reproduction of stripe patterns as well as island ramification in agreement with recent experimental observations for CoAg/Ru(0001) [R. Q. Hwang, Phys. Rev. Lett. 76, 4757 (1996)]. The quantitative dependencies of stripe width and degree of island ramification on the misfit and interaction strength between the two adsorbate types are presented. Attempts to capture essential features in a simplified lattice gas model show that a detailed incorporation of non-local effects is required.