Quantum Chemical Cluster Models for Chemi- and Physisorption of Chlorobenzene on Si(111)-7×7

Quantum chemical models for the absorption of endohedral clusters on Si(111)-(7 × 7): a subtle balance between W–Si and Si–Si bonding

The absorption of endohedral clusters on Si(111)-7 × 7 generates a new bond between W and a surface silicon adatom.

Mapping the site-specific potential energy landscape for chemisorbed and physisorbed aromatic molecules on the Si(1 1 1)-7 × 7 surface by time-lapse STM

We present a scanning tunnelling microscope study of site-specific thermal displacement (desorption or diffusion) of benzene, toluene, and chlorobenzene molecules on the Si(1 1 1)-7 × 7 surface. Through time-lapse STM imaging and automated image analysis we probe both the chemisorbed and the physisorbed states of these molecules. For the chemisorption to physisorption transition there are distinct site-specific variations in the measured rates, however their kinetic origin is ambiguous. There is also significant variation in the competing rates out of the physisorbed state into chemisorption at the various surface sites, which we attribute to differences in site-specific Arrhenius pre-factors. A prediction of the outcome of the competing rates and pre-factors for benzene over three hours matches experiment.

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.