SSL Seminar Series 2001 No. 12
Combined talks (two speakers) on SiC (0001) reconstruction surfaces.

Time: July 18, 2001, 5:00-6:00pm
Venue: Physics Resource Room, S13, 02-16

Speaker I: Xie Xianning (Chem. Dept. NUS)
Title: The evolution of 3x3, 6x6, sqrt(3) x sqrt(3)R30° and 6sqrt(3)x6sqrt(3)R30° superstructures on 6H-SiC(0001) surfaces studied by reflection high energy electron diffraction (RHEED)

Abstract
The studies of surfaces and interfacial structures on SiC have received a lot of attention recently due to the distinctive electronic properties of the various superstructures and their importance in the homoepitaxial growth of SiC. RHEED has several advantages over LEED in qualitative structural analysis. In particular, the grazing incidence angle and long probing length of RHEED electron beam renders the technique especially sensitive to surface asperities and topographical variation. In this work, we present high quality RHEED patterns of 3x3, 6x6, sqrt(3) x sqrt(3)R30° and 6sqrt(3) x 6sqrt(3)R30° superstructures obtained on the Si-enriched SiC(0001) surfaces by careful annealing in vacuum. A well-defined 6x6 superstructure was detected by RHEED for the first time following annealing the 3x3 phase. All the superstructures were further characterized by AES, UPS and EELS. Based on the twisted Si-adlayer 3x3 model, we proposed a structural model for the 6x6 metastable phase.

Speaker II: Ong Wei Jie (SSL, Phys. Dept. NUS)
Title: Phase transition of SiC (0001) 3X3 to Si rich 6X6 surface reconstruction

Abstract
There has been little observation of the phase transition mechanism of SiC(0001) 3x3 to Si rich 6x6 reconstruction. Pseudomorphic 6X6 superstructures were first observed using RHEED by Dr KP Loh and Xie XN. The diffraction technique is complemented by the STM to proposed a possible structural model of the 6x6 reconstruction as well as the mechanism preceding its formation. We have managed to capture STM images of the 3x3 to 6x6 phase transition, which would allow us to discuss the mechanics of the surface structural change in greater detail.