The electron transport properties of photo- and electron-beam-irradiated C60 films

The electron transport properties of photo- and electron-beam-induced C-60 polymers, in which the former is a dumbbell-type two-dimensional (2D) polymer and the latter is a new polyhedral structured (peanut-shaped) carbon nanomaterial, have been investigated. Using a four-probe measurement, we found that the 2D photopolymer and the peanut-shaped polymer exhibit semiconducting and metallic characters in air at room temperature, respectively. In order to elucidate the origin of these electron transport properties, we have performed density-functional calculations of the dumbbell-shaped and peanut-shaped C-120 dimers that can be regarded as a basic unit of each polymer. It was found that the HOMO consisting of pi-electrons orbital, which is related to the electron transport property, has a node on the [2 + 2] cyclo-bond for the dumbbell-shaped dimer, while that the HOMO has no node on the cross-linkage and spreads over the peanut-shaped dimer. (C) 2003 Elsevier Ltd. All rights reserved.