Benzene/Si(100): metastable chemisorption and binding state conversion

Scanning tunneling microscopy (STM) has been used to investigate the adsorption of benzene on the Si(100)(2×1) surface. At room temperature two types of bonding configurations are observed; on-top of a single Si dimer and bridging two dimers. Upon dosing the single dimer state is populated preferentially but is seen to be metastable with respect to the bridging configuration, in agreement with semi-empirical quantum cluster calculations. The single dimer to bridge conversion is activated, with a barrier of 0.95 eV. The single dimer state can be re-populated via a process assisted by the STM tip.