Electron-stimulated desorption of F+ and F- from SF6 on Ru(0001):: structure and bonding

The adsorption properties and bonding geometry of octahedrally coordinated SF6 molecules are studied on Ru(0 0 0 1) for coverages less than 1 ML. Temperature programmed desorption reveals predominantly molecular adsorption of SF6 at 25 K; desorption occurs below 100 K. Electron stimulated desorption ion angular distributions of both F+ and F- ions demonstrate halo-like patterns: Heating the substrate to similar to90 K results in transformation of the halo-like patterns into hexagonal angular distributions for both ions. Electron-stimulated desorption of the ions occurs via different mechanisms, but from the same chemical states. SF6 appears to be adsorbed via three F atoms, with the other three pointed away from the surface. At low temperatures, the S-F bonds have a random azimuthal orientation, while upon annealing, lateral ordering occurs in two complementary domains. Low energy electron diffraction reveals no evidence of long, range order in the adsorbed layer. (C) 2002 Elsevier Science B.V. All rights reserved.