Diffusion versus Desorption: Complex Behavior os H Atoms on an Oxide Surface

X.-L. Yin, M. Calatayud, H. Qiu, Y. Wang, A. Birkner, C. Minot, Ch. Wöll

ChemPhysChem, 9, 2 (2008) 253-256

The interaction of hydrogen atoms with a well defined oxide surface, single crystalline rutile TiO2(110)-(1 × 1), has been investigated by scanning tunneling microscopy, high resolution electron energy loss spectroscopy and thermal desorption spectroscopy in parallel with density functional theory calculations. Adsorption of atomic hydrogen at room temperature leads to the formation of ordered H adlayers with a (1 × 1) periodicity exhibiting a significant amount of vacancies. Upon annealing the sample to above 600 K, surprisingly, no H2 (or H2O) molecules were found to desorb from the surface. An explanation for this unexpected behaviour is provided by ab-initio calculations: the activation energy for H-atoms migrating into the bulk, 1.11 eV, is significantly smaller than that for recombinative desorption of H2 (or H2O).