Real-time observation of epitaxial graphene domain reorientation

TL;DR

This study uses low-energy electron microscopy to observe how graphene islands on Ir(111) reorient during thermal annealing, revealing mechanisms that promote alignment and suggesting ways to improve 2D material epitaxy.

Contribution

It provides real-time insights into graphene domain reorientation mechanisms and models the energy landscape influencing alignment during growth.

Findings

Graphene islands reorient through ripening, boundary motion, and lattice rotation.

The driving force for alignment is approximately 0.1 meV per C atom.

A model based on moiré corrugation explains the orientation-dependent energy.

Abstract

Graphene films grown by vapor deposition tend to be polycrystalline due to the nucleation and growth of islands with different in-plane orientations. Here, using low-energy electron microscopy, we find that micron-sized graphene islands on Ir(111) rotate to a preferred orientation during thermal annealing. We observe three alignment mechanisms: the simultaneous growth of aligned domains and dissolution of rotated domains, i.e., "ripening"; domain-boundary motion within islands; and continuous lattice-rotation of entire domains. By measuring the relative growth velocity of domains during ripening, we estimate that the driving force for alignment is on the order of 0.1 meV per C atom and increases with rotation angle. A simple model of the orientation-dependent energy associated with the moir\'e corrugation of the graphene sheet due to local variations in the graphene-substrate interaction reproduces the results. This work suggests new strategies for improving the van der Waals epitaxy of 2D materials.