Island growth kinetics during the vapor deposition of gold onto TiO 2(110)

Abstract

Vapor deposition of Au on the TiO 2(110) surface at 150–300 K has been examined using X-ray photon spectroscopy and low energy ion scattering. Two-dimensional islands are initially formed up to a certain average critical coverage ( θ cr). At coverages above θ cr, added Au mainly goes on top of these, forming three-dimensional islands. Even though thermodynamically the islands would prefer to form three-dimensional islands from the onset of growth, kinetic limitations constrain the growth initially to two-dimensional islands. The critical coverage is found to decrease with temperature, showing an apparent activation energy of −2.2 kJ mol −1, but is independent of Au vapor flux. The critical coverage was also seen to increase with the defect density of the TiO 2 surface. This behavior is explored using a kinetic model which includes surface energetic parameters for Au atom migration.