Concerted Thermal-Plus-Electronic Nonlocal Desorption of Chlorobenzene from Si (111)-7×7 in the STM

The rate of desorption of chemisorbed chlorobenzene molecules from the Si(111)-7 × 7 surface, induced by nonlocal charge injection from an STM tip, depends on the surface temperature. Between 260 and 313 K, we find an Arrhenius thermal activation energy of 450 ± 170 meV, consistent with the binding energy of physisorbed chlorobenzene on the same surface. Injected electrons excite the chlorobenzene molecule from the chemisorption state to an intermediate physisorption state, followed by thermal desorption. We find a second thermal activation energy of 21 ± 4 meV in the lower temperature region between 77 and 260 K, assigned to surface phonon excitation.