Production and control of K-C-60 plasma for material processing

An ultrafine-particle plasma including large negative fullerene ions is produced by introducing fullerene particles into a low-temperature (approximate to 0.2 eV) potassium plasma column confined by a strong axial magnetic field. The density ratio of the negative fullerene to positive potassium ions is controlled by changing the oven temperature for fullerene sublimation and the plasma density being varied in the range from 0 to 0.97 in the central region of the plasma cross section. Since the electrons are well confined in the central region, the ratio increases radially and is more than 0.9999 in the radial edge region. A thin film consisting of the potassium and fullerene particles is formed on a metal end plate which terminates the plasma column. Depending on the end plate potential and radial position, the film is verified to contain metal-doped fullerenes with the potassium atom in the endohedral cavity, which are formed as a result of the potassium-atom insertion into the stable cage of fullerene particles. (C) 1996 American Vacuum Society.