Surface atomic structure of reconstructed VC0.8(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\ifmmode\times\else\texttimes\fi{}1) and (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} reconstructed areas was found. The (8\ifmmode\times\else\texttimes\fi{}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 \AA{}, 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 (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} 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\ifmmode\times\else\texttimes\fi{}1) surfaces. A qualitative explanation for this difference is suggested.