Rh and Au deposited on ultrathin TiO∼1.2 film formed on Rh(111) facets and the effects of CO exposure

Abstract This STM study deals with the structure and reactivity of Rh and Au deposited on a “pinwheel” TiO ~ 1.2 ultrathin film (w-TiO-UTO) formed on Rh nanoparticles supported on TiO 2 (110). The deposition of a monolayer (ML) Au at 500 K disturbed the order of the w-TiO-UTO layer and led to the formation of 3D adparticles. The deposition of Rh (~ 1 ML) at 500 K and annealing up to 900 K led exclusively to the formation of 2D adparticles. It was found that 3D Au nanoparticles are gradually sintering in the range of 500–800 K. Upon a further raise of the temperature, a 3D→2D transformation takes place. The main difference is that on the top facet of the 2D Rh particles a w-TiO-UTO film forms, while the top facets of the 2D Au particles exhibit a clean gold metal structure. CO exposure of max. 10 min at 10 Pa causes no remarkable change of the encapsulated Rh particles, however, the 2D gold nanoparticles change significantly. The disintegration of Au particles and the spillover of Au atoms to the UTO surface accelerate at a CO pressure above 10 − 1  Pa. This morphological process is reversible as an effect of annealing in UHV.