CONTACT ELECTRIFICATION OF C-60

We have used gold-, tungsten-, and copper plates to contact repeatedly a C60 powder sample. We observed the flow of electrons to the sample leading to negative charge accumulation. In repeated-contact experimen ts, we find charge saturation after 15 contacts for gold and copper co ntact partners. This is typical for the behavior of a semiconductor. F or contact with tungsten however, charge accumulation continues even a fter 30 contacts. This unusual behavior is explained by the electron s tate density distribution of C60.