Relative stability of $6H$-SiC$\{0001\}$ surface terminations and formation of graphene overlayers by Si evaporation

TL;DR

This study uses DFT calculations to analyze the stability of 6H-SiC surfaces and the formation of graphene overlayers via Si evaporation, revealing different bonding types and electronic effects depending on surface orientation.

Contribution

It provides a detailed comparison of surface stabilities and predicts the nature of graphene overlayers formed on different SiC surface terminations.

Findings

Different surface orientations favor distinct graphene bonding types.

A highly strained, chemically bonded overlayer forms on (0001).

A vdW bonded overlayer is preferred on (000\bar1) with doping effects.

Abstract

We present density functional theory (DFT) calculations for 6H-SiC$\{0001\}$ surfaces with different surface stackings and terminations. We compare the relative stability of different $(0001)$ and $(000\bar1)$ surfaces in terms of their surface free energies. Removing surface and subsurface Si atoms, we simulate the formation of graphene and graphene-like overlayers by Si evaporation. We find that overlayers with a different nature of bonding are preferred at the two non-equivalent surface orientations. At $(0001)$, a chemically bonded, highly strained and buckled film is predicted. At $(000\bar1)$, a van der Waals (vdW) bonded overlayer is preferred. We quantify the vdW binding and show that it can have a doping effect on electron behavior in the overlayer.