DOPING EFFECTS INDUCED BY POTASSIUM-ION IMPLANTATION IN SOLID C-60

Ion implantation is presented here as another technique for investigat ing the electrical properties of doped solid C-60. The conductivity an d the thermopower have been studied versus the implantation parameters in order to investigate electrical transport phenomena which occur in implanted solid C-60, and thus prove doping effects. First results on ion implantation in C-60 show a strong competition between damaging ( induced by energetic ions) and doping effect (induced by charge transf er). Generally, electron transfers between the potassium atoms and the C-60 molecules produce a conducting phase: up to x similar or equal t o 0.1, metallic K3C60 islands are dispersed in an insulating phase (vi rgin C-60); then, for x > 0.1, damage plays a major role, leading to c onduction paths through the samples (the saturation threshold x simila r or equal to 0.1 is lower than in chemical doping due to the degradat ions). Potassium ion implantation with low energy (E similar or equal to 30 keV) and low fluence (D < 10(15) ions/cm(2)) seems to provide th e best implantation parameters for doping. Indeed, small ion size, low energy and low fluence are necessary in order to diminish the degrada tion effects.