The structure and evolution of semiconducting buffer graphene grown on SiC(0001)

TL;DR

This study investigates the atomic structure and bonding of the semiconducting buffer graphene layer on SiC(0001), revealing limited covalent bonding, interface depletion, and structural changes upon additional graphene layer growth.

Contribution

It provides a detailed structural analysis of the buffer layer on SiC(0001) and how it evolves with the formation of an additional graphene layer, using advanced x-ray techniques.

Findings

Less than 26% of buffer carbon covalently bonded to Si.

The top SiC bilayer is Si depleted.

Buffer layer becomes less corrugated with an additional graphene layer.

Abstract

Using highly controlled coverages of graphene on SiC(0001), we have studied the structure of the first graphene layer that grows on the SiC interface. This layer, known as the buffer layer, is semiconducting. Using x-ray reflectivity and x-ray standing waves analysis we have performed a comparative study of the buffer layer structure with and without an additional monolayer graphene layer above it. We show that no more than 26\% of the buffer carbon is covalently bonded to Si in the SiC interface. We also show that the top SiC bilayer is Si depleted and is the likely the cause of the incommensuration previously observed in this system. When a monolayer graphene layer forms above the buffer, the buffer layer becomes less corrugated with signs of a change in the bonding geometry with the SiC interface. At the same time, the entire SiC interface becomes more disordered, presumably due to entropy associated with the higher growth temperature.