Scanning tunneling microscopy and spectroscopy of electron-irradiated thin films of C60 molecules

We have used scanning tunneling microscopy and spectroscopy to determine the effect of electron irradiation on thin films of C60 molecules. Upon the irradiation of electrons with an energy of 100 eV or 2 keV, clusters of molecules are created in the C60 films as the initial products. The molecules in the clusters exhibit different electronic structures from that of pristine C60 molecules; the molecule at the center of the cluster exhibits a metallic or semimetallic nature and the other molecules exhibit an additional density of states in the filled states. C60 thin films are covered with clusters upon continuous electron irradiation for a longer duration, changing the electronic structure of the films. We consider that the electron-induced polymerization between C60 molecules is responsible for the observed alteration of the C60 thin films.