Multilayer adsorption of water on rutile (110).

Abstract

The adsorption of water on the (110) surface of rutile is investigated by recording Thermal Desorption spectra, and characterizing the substrate using Low Energy Electron Diffraction. The sample is sputtered and annealed according to a previous flattening study of the same surface. After cooling to T $\approx$ 110K, the surface is dosed with H$\sb2$O. The adsorbate/substrate system is heated at 1K/s, and the H$\sb2$O partial pressure is measured with a shrouded quadrupole mass spectrometer. Three desorption peaks are observed below room temperature, two monolayer peaks: one at 310-260K (coverage dependence) and another at 175K, and one multilayer peak at 150K. A fourth peak, representing a coverage of the order of a few percent of a monolayer, is observed at T $\approx$ 500K; this peak is associated with an adsorption state that is more strongly bound than the other three. Analysis of the first three adsorption states provides information on the kinetics of the system, and the bond energies at these adsorption sites.