Water coadsorbed with oxygen and potassium on thin NiO(100) films

The coadsorption of H2O with O and K on epitaxial NiO films on Ag(100) was studied by TPD, XPS and UPS. The TPD monolayer signal of H2O with a peak around 200 K on the unperturbed NiO surface decreases after creation of surface defects by ion etching. Oxygen does not adsorb on a well-ordered NiO surface at 120 K, but does on a NiO surface with sputter-induced defects. With preadsorbed oxygen, the monolayer state of molecular water on the defected surface is bound more strongly, yielding minor changes in UPS but a completely changed desorption kinetics. Potassium dosed onto NiO at 300 It leads to a decrease of the work function, and a mixed oxide is formed. From the UP spectra, it can be deduced that water adsorbs molecularly on a potassium precovered NiO surface but with an orientation different from that on clean or oxygen-precovered NiO. (C) 1998 Elsevier Science B.V. All rights reserved.