Conformational isomers of stilbene on Si(100)

Stilbene (1,2-diphenylethylene) has shown an intriguing isomerisation behavior and may serve as a model system for ‘‘molecular switches’’ incorporating a C=C double bond. To evaluate the possible use of such molecules as molecular switches on semiconductor surfaces, the adsorption of cisand trans-stilbene on Si(100) has been investigated. Identification of both isomers is achieved by differences in adsorption geometry as revealed by NEXAFS, and differences in electronic structure in the occupied and unoccupied molecular orbitals. For both isomers, bonding takes place via the C=C double bond to the Si dimer atoms allowing for free movement of the aromatic rings, a necessary prerequisite for photoinduced isomerisation on the surface. Our experimental results agree well with theoretical calculations.