Microscopic mechanisms of initial formation process of graphene on SiC(0001) surfaces

TL;DR

This study uses density-functional theory calculations to elucidate the microscopic mechanisms of initial graphene formation on SiC(0001), highlighting the preferential desorption of Si atoms and the energy dynamics involved.

Contribution

The paper provides the first detailed calculations of desorption pathways and energy barriers for Si and C atoms on SiC(0001), clarifying the initial steps of graphene formation.

Findings

Si desorption barrier is 0.75 eV lower than C desorption barrier.

Si desorption is exothermic, driven by C bond formation.

Selective Si desorption facilitates graphene seed formation.

Abstract

We report total-energy calculations based on the density-functional theory that clarify microscopic mechanisms of initial stage of graphene formation on the SiC(0001) surface. We explore favorable reactions for desorption of either Si or C atoms from the stepped surface by determining the desorption and the subsequent migration pathways and calculating the corresponding energy barriers for the first time. We find that the energy barrier for the desorption of an Si atom at the step edge and the subsequent migration toward stable terrace sites are lower than that of a C atom by 0.75 eV, indicative of the selective desorption of Si from the SiC surface. We also find that the subsequent Si desorption is an exothermic reaction. This exothermicity comes from the energy gain due to the bond formation of C atoms being left near the step edges. This is certainly a seed of graphene flakes.