Photohole induced adsorption of oxygen on CdS

Abstract In the absence of illumination, adsorption of oxygen on clean CdS surfaces is not detected by XPS, nor unequivocally by SIMS, although contact potential measurements indicate that reversible changes in work function do occur. When exposure to oxygen is combined with bandgap illumination however, adsorption takes place at a rate of at least 5 orders of magnitude faster and is accompanied by the formation of sulfur oxyanions. Since this effect is not dependent on dark electron densities, we propose that the availability of holes in these n-type crystal is the rate limiting step for adsorption to occur. This can be reconciled with models formulated in the context of electrical measurements involving the transfer of electrons to the adsorbate.