Influence of O 2-induced surface roughening on the chemistry of water on TiO 2(1 1 0)

Abstract

The impact of oxygen induced regrowth of TiO 2 on the reduced rutile TiO 2(1 1 0) surface has been studied using temperature programmed desorption (TPD) of adsorbed water multilayers. Pre-exposure of UHV annealed TiO 2(1 1 0) surfaces to O 2 at temperatures from 300 to 850 K induced changes in subsequent water TPDs that were interpreted in terms of the rougher surface morphologies resulting from the regrowth process. Water TPD from TiO 2(1 1 0) previously oxidized at 300 K exhibited a new peak at ∼312 K due to reaction of water with O adatoms. These O adatoms were produced by dissociative adsorption of O 2 at O-vacancy sites. Additionally, oxygen reacted (slowly) with surface Ti 2O 3 strands at RT. Water TPD from surfaces pre-oxidized at higher temperatures (⩾500 K) exhibited features reflective of desorption from rough surfaces, namely loss of peak resolution and eventual merger of the second layer and ice peaks, formation of a high temperature tail on the second layer peak, and broadening of the first layer TPD peak. The multiplicity of kinetically different adsorption sites on the roughened TiO 2(1 1 0) surfaces contributed to the widening of the desorption features.