Photoinduced products in a C60 monolayer on Si(111)(√3x√3)-Ag:: An STM study

Irradiation of ultraviolet-visible light onto a C-60 monolayer on Si(111)(root 3 x root 3)R30 degrees-Ag resulted in a chemical reaction between adjacent C-60 molecules, as confirmed by scanning tunneling microscopy (STM) images. The major photoinduced products were double-bonded (two covalent C-C bonds between molecules) C-60 dimers and linear trimers. We also found single-bonded (single covalent bond between molecules) C-60 dimers and linear trimers, and two-dimensional C-60 oligomers as minor products. Observed atomic 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 regarding their axes, is different from that reported between C-60 molecules in three-dimensional C-60 crystals, where there is no interaction with a substrate.