ADSORPTION AND ANGLE-RESOLVED ELECTRON-STIMULATED DESORPTION OF CCL4 ON RU(0001)

The adsorption and electron-stimulated desorption of CCl4 on Ru(0001) have been studied at 100 K using a variety of surface analytical techniques, including thermal desorption spectroscopy, Auger electron spectroscopy, low-energy ion scattering, and mass and angle-resolved electron-stimulated desorption (ESDIAD). CCl4 is found to dissociate partially for fractional monolayer coverages, and to adsorb molecularly above a coverage of 13%. Upon electron bombardment, Cl+ ions are found to desorb with their angular distribution directed along the surface normal; this implies that CCl4 orients with one C-Cl bond normal to the surface. The total yield of Cl+ increases linearly with increasing molecular CCl4 coverage up to one monolayer, which implies that Cl+ stems mainly from molecular CCl4 and that interadsorbate quenching is not significantly affecting the desorption yield. Beyond a coverage of 1 ML, the Cl+ yield continues to increase, and starts leveling off after 2 ML. We estimate the yield from a thick layer of CCl4 to be of the order of 3 x 10(-8) ions/electron. The angular distribution of the desorbing Cl+ ions widens with increasing CCl4 exposure. Besides Cl+, higher mass fragments of CCl4, such as CCl+, CCl2+ and CCl3+ are also found to desorb from multilayers upon electron bombardment.