Photoinduced products in a C-60 monolayer on Si(111)(root 3x root 3)-Ag: An STM study

Irradiation of ultraviolet-visible light onto a C-60 monolayer on Si(111)(r oot 3 x root 3)R30 degrees-Ag resulted in a chemical reaction between adjac ent C-60 molecules, as confirmed by scanning tunneling microscopy (STM) ima ges. The major photoinduced products were double-bonded (two covalent C-C b onds between molecules) C-60 dimers and linear trimers. We also found singl e-bonded (single covalent bond between molecules) C-60 dimers and linear tr imers, and two-dimensional C-60 oligomers as minor products. Observed atomi c geometry of the nonbonding contact between a C-60 dimer (or a trimer) and a neighboring dimer (or a trimer), which are parallel to each other regard ing their axes, is different from that reported between C-60 molecules in t hree-dimensional C-60 crystals, where there is no interaction with a substr ate.