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First-principles study on atomic configuration of electron-beam irradiated C$_{60}$ clusters

A theoretical study proposes the atomic configuration of electron-beam irradiated C$_{60}$ thin films. We examined the electronic structure and electron-transport properties of the C$_{60}$ clusters using density-functional calculations and found that a rhombohedral C$_{60}$ polymer with $sp^3$-bonded dumbbell-shaped connections at the molecule junction is a semiconductor with a narrow band gap while the polymer changes to exhibit metallic behavior by forming $sp^2$-bonded peanut-shaped connections. Conductance below the Fermi level increases and the peak of the conductance spectrum arising from the $t_{u1}$ states of a C$_{60}$ molecule becomes obscure after the connections are rearranged. The present rohmbohedral film, including the [2+2] four-membered rings and peanut-shaped connections, is a candidate to represent the structure of the metallic C$_{60}$ polymer at the initial stage of electron-beam irradiation.