Formation of Graphene atop a Si adlayer on the C-face of SiC

TL;DR

This study investigates the surface structures of SiC(000-1) in a gaseous environment, revealing Si adlayers and graphene formation, with insights into stable surface configurations under various conditions.

Contribution

It demonstrates the formation of Si adlayers and graphene on SiC(000-1) surfaces, using experimental and ab initio thermodynamic methods to identify stable surface structures.

Findings

Graphene spontaneously forms at high temperatures.

Surface contains 1.4-1.7 ML of Si under graphene.

Stable Si-rich surfaces with ~1.3 ML Si exist above 400 K.

Abstract

The structure of the SiC(000-1) surface, the C-face of the {0001} SiC surfaces, is studied as a function of temperature and of pressure in a gaseous environment of disilane (Si2H6). Various surface reconstructions are observed, both with and without the presence of an overlying graphene layer (which spontaneously forms at sufficiently high temperatures). Based on cross-sectional scanning transmission electron microscopy measurements, the interface structure that forms in the presence of the graphene is found to contain 1.4 - 1.7 monolayers (ML) of Si, a somewhat counter-intuitive result since, when the graphene forms, the system is actually under C-rich conditions. Using ab initio thermodynamics, it is demonstrated that there exists a class of Si-rich surfaces containing about 1.3 ML of Si that are stable on the surface (even under C-rich conditions) at temperatures above about 400 K. The structures that thus form consist of Si adatoms atop a Si adlayer on the C-face of SiC, with or without the presence of overlying graphene.