Multistable rippling of graphene on SiC: A Density Functional Theory study

TL;DR

This study uses Density Functional Theory to clarify the ambiguous rippling patterns of graphene on SiC, revealing how van der Waals interactions stabilize different corrugation states and enabling potential applications in nano-electronics.

Contribution

It provides a realistic model including full symmetry and substrate effects, demonstrating the importance of vdW interactions in stabilizing graphene's rippling patterns.

Findings

Accurate vdW treatment is crucial for pattern stabilization.

Low temperature favors buffer-layer-like topography.

Environmental factors can induce switching between states.

Abstract

Graphene monolayer grown by Si evaporation from the 0001 surface of SiC displays a moir\'e pattern of corrugation whose structure is ambiguous: different measurements and theoretical studies show either protruding bumps surrounded by valleys, or, reversely, wells surrounded by crests. Here we address the fine structure of monolayer graphene on SiC by means of Density Functional Theory, using a model including the full symmetry of the system and the substrate (1648 atoms) and therefore realistically reproducing the experimental sample. We find that accurate treatment of the vdW interactions between monolayer and the underlying substrate-bound buffer layer is crucial in stabilizing one or the opposite corrugation pattern, which explain the different results and measurement available in the literature. Our study indicates that at low temperature a state more closely following the topography of the underneath buffer layer is stabilized, while others are metastable. Since environmental conditions (e.g. temperature or doping) can influence the vdW forces and reduce the energy differences, this system is prone to externally driven switching between different (opposite) corrugation states. In turn, corrugation is related to local reactivity and to electronic properties of graphene. This opens to potentially interesting applications in nano-electronics or tailored graphene chemical functionalization.