Coadsorption of oxygen and chlorine on Pt(111)

Abstract

The coadsorption of oxygen and chlorine is studied on the Pt(111) surface, using line-of-sight desorption mass spectrometry, LEED and work function measurements to characterize the resulting adlayers and to determine the uptake and desorption kinetics. Preadsorbed chlorine reduces the sticking probability of oxygen to a similar extent, as does an equal concentration of adsorbed oxygen atoms. Chlorine adsorption proceeds in the whole range of possible oxygen precoverages (≤0.25) with a similar sticking coefficient as on the clean surface and leads to a high density adlayer with a total concentration of 11.3×10 14 (O+Cl) atoms cm −2. Starting with a complete (2×2) oxygen adlayer, the ordered structure vanishes during chlorine dosing only at a total coverage (chlorine plus oxygen) of 0.5. Increasing the total concentration further leads to the buildup of a (3 3 ×3 3 ) R30° structure at 9.3×10 14 (O+Cl) atoms cm −2. Temperature-programmed desorption yields oxygen molecules, chlorine molecules and chlorine atoms. The two adsorbed species destabilize each other, and the molecule peaks are shifted to lower temperatures, in the case of oxygen up to 70 K. With high initial coverages, this trend is not continued but reversed.