Atomistic Mechanisms of Nonlinear Graphene Growth on Ir Surface

TL;DR

This study combines first principles calculations and kinetic Monte Carlo simulations to elucidate atomistic mechanisms of nonlinear graphene growth on Ir(111), revealing the importance of cluster attachment and substrate effects.

Contribution

It provides a detailed atomistic understanding of graphene growth on Ir(111), highlighting the role of cluster attachment and substrate-induced inhomogeneity in nonlinear growth kinetics.

Findings

Growth rates vary with graphene orientation.

Cluster attachment is the rate-limiting step at difficult sites.

Inhomogeneity due to lattice mismatch influences growth behavior.

Abstract

As a two-dimensional material, graphene can be naturally obtained via epitaxial growth on a suitable substrate. Growth condition optimization usually requires an atomistic level understanding of the growth mechanism. In this article, we perform a mechanistic study about graphene growth on Ir(111) surface by combining first principles calculations and kinetic Monte Carlo (kMC) simulations. Small carbon clusters on the Ir surface are checked first. On terraces, arching chain configurations are favorable in energy and they are also of relatively high mobilities. At steps, some magic two-dimensional compact structures are identified, which show clear relevance to the nucleation process. Attachment of carbon species to a graphene edge is then studied. Due to the effect of substrate, at some edge sites, atomic carbon attachment becomes thermodynamically unfavorable. Graphene growth at these difficult sites has to proceed via cluster attachment, which is the growth rate determining step. Based on such an inhomogeneous growth picture, kMC simulations are made possible by successfully separating different timescales, and they well reproduce the experimentally observed nonlinear kinetics. Different growth rates and nonlinear behaviors are predicted for different graphene orientations, which is consistent with available experimental results. Importantly, as a phenomenon originated from lattice mismatch, inhomogeneity revealed in this case is expected to be quite universal and it should also make important roles in many other hetero-epitaxial systems.