Growth at high substrate coverage can decrease the grain boundary roughness of 2D materials

TL;DR

High substrate coverage during 2D material growth can lead to smoother grain boundaries by promoting rapid relaxation of roughness, offering a new method for producing high-quality 2D materials.

Contribution

This study introduces a high coverage growth regime that reduces grain boundary roughness, supported by kinetic Monte Carlo simulations and theoretical analysis.

Findings

High coverage growth forms uncorrelated, smoother grain boundaries.

This regime accelerates roughness relaxation compared to near-equilibrium growth.

Simulations extrapolated to micrometer scales confirm faster smoothing.

Abstract

Grain boundary roughness can affect electronic and mechanical properties of two-dimensional materials. This roughness depends crucially on the growth process by which the two-dimensional material is formed. To investigate the key mechanisms that govern the roughness, we have performed kinetic Monte Carlo simulations of a simple model that includes particle attachment, detachment, and diffusion. We have studied the closure of the gap between two flakes during growth, and the subsequent formation of the grain boundary (GB) for a broad range of model parameters. The well known near-equilibrium (attachment-limited) and unstable (diffusion-limited) growth regimes are identified, but we also observe a third regime when the precursor flux is sufficiently high to fully cover the gap between the edges. This high coverage regime forms GBs with spatially uncorrelated roughness, which quickly relax to smoother configurations. Extrapolating the numerical results (with support from a theoretical approach) to edge lengths and gap widths of some micrometers, we confirm the advantage of this regime to produce GBs with minimal roughness faster than near-equilibrium conditions. This suggests an unexpected route towards efficient growth of two-dimensional materials with smooth GBs.