PHOTOINDUCED PRODUCTS IN A C60 MONOLAYER ON ${\rm Si}(111) (\sqrt{3}\times \sqrt{3})\hbox{-}{\rm Ag}$: AN STM STUDY

Irradiation of ultraviolet-visible light onto a C60 monolayer on resulted in a chemical reaction between adjacent C60 molecules, as confirmed by scanning tunneling microscopy (STM) images. The major photoinduced products were double-bonded (two covalent C–C bonds between molecules) C60 dimers and linear trimers. We also found single-bonded (single covalent bond between molecules) C60 dimers and linear trimers, and two-dimensional C60 oligomers as minor products. Observed atomic geometry of the nonbonding contact between a C60 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 C60 molecules in three-dimensional C60 crystals, where there is no interaction with a substrate.