The transition from 3C SiC (1 1 1) to graphene captured by Ultra High Vacuum Scanning Tunneling Microscopy

Abstract

In this paper we clarify the transformation mechanism of 3C-SiC into graphene upon thermal decomposition, by a combination of high resolution Scanning Tunneling Microscopy (STM) images and first principle calculations. We studied the transition from 3C-SiC to graphene by high temperature annealing of C-terminated 3C SiC(111)/Si(111) samples in Ultra High Vacuum. By using STM we were able to observe very clear atomic resolution images of the transition from SiC (√3×√3)R30° to a new intermediate stage SiC 32×√3R30° (very close to the graphene (2×2) reconstruction) after annealing at 1250°C. We also obtained images of the transformation of the intermediate structure into a (1×1) monolayer graphene, caused by further sublimation of atoms in the subsurface layer. We have interpreted the results by using Density Functional Theory – Local Density Approximation calculations, which give full account of the SiC (√3×√3)R30° reconstruction, but fail to describe the SiC 32×√3R30° structure due to its incommensurability with the 3C-SiC(111) lattice.