Journal of Physical Chemistry B, Vol.110, No.32, 15645-15649, 2006
Edge-on bonding of benzene molecules in the second adsorbed layer on Cu(110)
The bilayer of benzene on Cu(110) was studied with temperature-programmed desorption (TPD), time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD), and scanning tunneling microscopy (STM). TPD spectra show that three well-defined adsorption states exist. The alpha layer corresponds to the first layer containing flat-lying benzene molecules. As coverage increases, the, layer forms on top of the beta layer, and eventually, a multilayer, gamma, forms. TPD measurements show that the number of benzene molecules in the alpha layer is equal to the number of benzene molecules in the R layer. ESDIAD measurements establish that the orientation of the benzene molecules in the beta layer is edge-on, with two C-H bonds directed toward the surface. STM images of the beta layer reveal closely spaced edge-on benzene molecules arranged in repeating hexagons, as well as loosely spaced benzene molecules with greater apparent height, which are also edge-on species. Correlation between the different measurements suggests a structural model for the benzene bilayer.