Analysis of the NbC(111)-( sqrt 3 x sqrt 3 )R30 degrees-Al surface structure by impact-collision ion-scattering spectroscopy.

Abstract

The structure of the NbC(111) clean surface and the aluminum adsorption system at room temperature have been studied by impact-collision ion-scattering spectroscopy, reflection high-energy electron diffraction (RHEED), low-energy electron diffraction, and computer simulation. It has been found that the clean surface exhibits a 1\ifmmode\times\else\texttimes\fi{}1 RHEED pattern and no reconstruction occurs. The outermost layer consists of Nb atoms and relaxes inward by 0.20\ifmmode\pm\else\textpm\fi{}0.05 \AA{}, which is equal to 15.5\ifmmode\pm\else\textpm\fi{}3.9% of the space between the first and second layers of the bulk. The carbon atoms in the second layer also shift inward by 0.05\ifmmode\pm\else\textpm\fi{}0.05 \AA{}. The Al-adsorbed surface has a (\ensuremath{\surd}3\ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3)R30\ifmmode^\circ\else\textdegree\fi{} structure with slight modulation. The Al atoms occupy two-thirds of the threefold-hollow sites, under which a Nb atom of the third layer is situated. Adsorbed Al atoms make a honeycomb pattern. The distance between the Al atom and the surface has been determined to be 2.25\ifmmode\pm\else\textpm\fi{}0.05 \AA{}. The Al-Nb bond length is 2.90\ifmmode\pm\else\textpm\fi{}0.05 \AA{}.