On the work function dependency on molecular oxygen coverage for cesiated molybdenum surfaces

DFT-D method aimed at describing the pathways of surface mechanisms of reaction toward stable chemical systems and correlating the resulting structures of the adsorbates to the effects on the work function of the cesiated surface in presence of impurities, i.e. when ultra-high vacuum conditions aren’t met. We set up a computational procedure to mimic the O2 chemical reaction over the cesiated surface, at increasing concentrations of the impinging gas species, and to calculate the work function for each of the many adsorbates’ structures resulting from the gas-surface interaction. As a result, the estimated work function appears strongly dependent on the molecular oxygen coverage with a marked decrease, reaching its minimum variation value of 􀀀 0.80 eV, for medium oxygen coverage degree, with respect to the bare cesiated surface, for the assumed simulation conditions. From a structural analysis we have highlighted the formation of stable molibdate-like structures for few O2 molecules, while in the limit of many molecules these are unbound. This finding has been also confirmed by evaluating projected density of states, band structures, electronic density difference and surface dipole moments.