Adsorption and epitaxial growth of benzene on ZnO(1010) studied by thermal desorption spectroscopy,LEED and UPS

The adsorption and condensation of benzene on ZnO(101̄0) was investigated by thermal desorption spectroscopy and LEED. The first monolayer shows an ordered c(2 × 2) super-structure. First order desorption is observed. The desorption energy and frequency factor decrease from 73 to 56 kJ mole^?1 and from ~10¹⁵ to ~10¹² s^?1, respectively, with coverage increasing to 0.85. The second layer is more weakly bound. Two-dimensional (2D) island formation is deduced from peak shape analysis. Near completion, the second layer converts to a more tightly bound configuration as deduced from a sudden shift of the desorption peak and the formation of an additional c(4 × 3) LEED pattern. This pattern which can be identified as a property of bulk benzene is preserved upon epitaxial growth of the 3D benzene crystal. Angular resolved UPS measurements indicate the benzene molecules of the first layer to be arranged in an oblique position of low symmetry.