The SiC(0001)6√3 × 6√3 reconstruction studied with STM and LEED

Abstract

We have used scanning tunneling microscopy (STM) to study the 6√3 × 6√3 reconstruction obtained by heat treatment of 6H-Sic(0001) samples at temperatures above 1100°C. For surfaces showing a well-developed 6√3 × 6√3 low-energy electron diffraction (LEED) pattern, we observe with STM two pseudo-periodic reconstructions with approximate periodicities of 6 × 6 and 5 × 5, respectively, in addition to √3 × √3-reconstructed regions. The fraction of the surface exhibiting the √3 × √3 reconstruction in STM images and the intensity of the √3 × √3 spots in the 6√3 × 6√3 LEED pattern decrease with increasing annealing temperature and time. The 5 × 5 reconstruction is observed on a small fraction of the surface (⪅ 10%) and the 6 × 6 reconstruction becomes dominating upon annealing at temperatures above 1200°C. For the 6 × 6 reconstruction, a Fourier analysis of the STM images reveals an underlying incommensurate 2.1 × 2.1-R30° lattice with long-range order. The features defining the 6 × 6 periodicity have well-defined positions with respect to this lattice. A comparison between the Fourier transforms of the STM images and the 6√3 × 6√3 LEED pattern shows that the LEED pattern can be fully explained by scattering from surfaces with a mixture of the √3 × √3, 5 × 5 and 6 × 6 reconstructions. For surfaces heated above 1250°C, we observe a partial graphitization which results in a modification of the 6 × 6 structure observed in STM.