Toluene adsorption on Si(1 1 1)7×7 studied by synchrotron-radiation photoemission

The toluene adsorption on Si(1 1 1)7×7 was studied by valence band synchrotron-radiation photoemission at room temperature as a function of exposure and time. We found that the adsorption process occurs preferentially on rest atoms and that toluene adsorption is time dependent, since the adsorption features disappear and the rest atoms related feature re-appears as a function of time. The features time evolution is quadratic, hinting at a thermal desorption process. The high desorption rate allows us to rule out a dissociative adsorption involving the methyl group. Our conclusion is that toluene is molecularly π-bonded through the aromatic electrons on silicon rest atoms.