How transparent is graphene? A surface science perspective on remote epitaxy

TL;DR

This paper critically examines the fundamental assumptions of remote epitaxy on graphene, proposing new analysis methods to quantify substrate potential and re-evaluate experimental evidence for the mechanism.

Contribution

It introduces Fourier and beating analysis to decompose lattice potentials and reassesses the validity of remote epitaxy compared to alternative mechanisms.

Findings

Weak remote potential challenges the assumption of graphene transparency.

Proposed analysis methods can distinguish substrate, graphene, and surface reconstruction effects.

Experimental evidence for true remote epitaxy remains inconclusive due to competing mechanisms.

Abstract

Remote epitaxy is the synthesis of a single crystalline film on a graphene-covered substrate, where the film adopts epitaxial registry to the substrate as if the graphene is transparent. Despite many exciting applications for flexible electronics, strain engineering, and heterogeneous integration, an understanding of the fundamental synthesis mechanisms remains elusive. Here we offer a perspective on the synthesis mechanisms, focusing on the foundational assumption of graphene transparency. We identify challenges for quantifying the strength of the remote substrate potential that permeates through graphene, and propose Fourier and beating analysis as a bias-free method for decomposing the lattice potential contributions from the substrate, from graphene, and from surface reconstructions, each at different frequencies. We highlight the importance of graphene-induced reconstructions on epitaxial templating, drawing comparison to moir\'e epitaxy. We highlight the role of the remote potential in tuning surface diffusion and adatom kinetics on graphene, which are crucial for navigating the competition between remote epitaxy and defect-seeded mechanisms like pinhole epitaxy. In light of this weak remote potential, we re-evaluate the current state-of-the-art experimental evidence, highlighting why it remains challenging to experimentally validate a ``remote'' epitaxy mechanism that cannot be explained by alternatives, such as pinhole-seeded epitaxy or serial van der Waals epitaxy. We end with one experimental example that, to out knowledge, cannot be explained by competing mechanisms: a different long-range epitaxial relationship for GdPtSb films grown on graphene/sapphire, compared to direct epitaxy on sapphire. We suggest for future experiments that directly measure the remote potential and impact of tunable growth kinetics.