Surface Heterogeneity and Diffusion in the Desorption of Methanol from WO3(001) Surfaces

We have investigated the role of intermolecular interactions, surface site heterogeneity, and surface diffusion on the desorption of methanol from the oxidized and reduced surfaces of (001) oriented, epitaxially grown WO 3 films on Al 2 O 3 (1̄102) substrates. Ultraviolet photoelectron spectroscopy (UPS) showed that methanol adsorbed molecularly on the oxidized WO 3 surface but dissociatively on the reduced surface. On both surfaces, calibrated thermal desorption spectroscopy (CTDS) showed the desorption of methanol as an asymmetric peak that shifts to lower temperature with increasing coverage, behavior that is typical of water and alcohols on other oxide surfaces. X-ray photoelectron spectroscopy (XPS) was used to characterize the surface by monitoring the W4f and valence-band region; STM studies indicate that the surface is heavily stepped. Monte Carlo simulations including surface heterogeneity and rapid diffusion effects are consistent with the observed desorption spectra.