Surface atomic structure of reconstructedVC0.8(111) studied with scanning tunneling microscopy

Abstract

Scanning tunneling microscopy has been performed on the reconstructed polar surface of substoichiometric ${\mathrm{VC}}_{0.80}$(111). A mixture of (8×1) and (√3 × √3 )R30° reconstructed areas was found. The (8×1) periodicity could be determined to be the result of a square-lattice surface layer superimposed on the hexagonal substrate. As this square lattice must have its origin in strong and directed in-plane bonds with the relatively large length of about 2.9 Å, it can be deduced to consist of vanadium atoms. Lateral positions of these vanadium surface atoms with respect to the substrate are suggested from the measured surface corrugation. The (√3 × √3 )R30° structure was found in small triangular areas which can, due to the measured step heights between the two reconstructions, be believed to be carbon terminated. The occurrence of a reconstructed surface with a reduced atomic concentration is in contrast to what is known for TiC(111) and NbC(111), both having stable (1×1) surfaces. A qualitative explanation for this difference is suggested.