Doping effects induced by potassium ion implantation in solid C60

Ion implantation is presented here as another technique for investigating the electrical properties of doped solid C60. The conductivity and the thermopower have been studied versus the implantation parameters in order to investigate electrical transport phenomena which occur in implanted solid C60, and thus prove doping effects. First results on ion implantation in C60 show a strong competition between damaging (induced by energetic ions) and doping effect (induced by charge transfer). Generally, electron transfers between the potassium atoms and the C60 molecules produce a conducting phase: up to x ⋍ 0.1, metallic K3C60 islands are dispersed in an insulating phase (virgin C60); then, for x > 0.1, damage plays a major role, leading to conduction paths through the samples (the saturation threshold x ⋍ 0.1 is lower than in chemical doping due to the degradations). Potassium ion implantation with low energy (E ⋍ 30 keV) and low fluence (D < 1015 ions/cm2) seems to provide the best implantation parameters for doping. Indeed, small ion size, low energy and low fluence are necessary in order to diminish the degradation effects.