Surface structure of Si(100) with submonolayer coverages of C

We report a combined STM, LEED and AES study of Si(100) surfaces prepared by coevaporation from two MBE-sources with Si and SiC, respectively. The flux from the SiC source contains 10% C, enabling studies of deposited layers with C-concentrations in the range 0–10%. After room temperature deposition, the structures have been annealed at 600 °C to generate a c(4×4) reconstruction. This has previously been reported to contain from 0.0 to 0.5 monolayers (ML) of C. Annealing at 800 °C irreversibly transforms the c(4×4) surface to a 2×1-reconstructed surface that contains precipitates of SiC. Since only 0.07 ML of C is needed to have 98% of the surface covered with the c(4×4) reconstruction, we conclude that the c(4×4) reconstruction is impurity-induced rather than having C-atoms in well defined positions within each unit cell. The c(4×4) reconstruction is attributed to a basic structure containing buckled parallel ad-dimers, which in approximately 50% of the reconstructed unit cells is decorated with perpendicular dimers.