FIELD-EFFECT STUDIES OF C-60 THIN-FILMS BEFORE AND AFTER IMPLANTATIONWITH POTASSIUM

We report measurements of the held-effect mobility in thin films of th e fullerene C-60, before and after implantation with potassium ions at 30 keV. Potassium ion implantation is known to produce reductive dopi ng in C-60 at low implantation doses, and was used to raise the bulk c onductivity of the C-60 layer. Devices were fabricated on doped silico n wafers, using thermally grown oxide to provide the insulator layer, and gold source and drain contacts. C-60 was deposited by vacuum subli mation Field-effect mobilities prior to implantation of about 7 x 10(- 7) cm(2) V-1 S-1 were obtained, and at the lowest implantation dose (1 0(10) ions cm(-2)), this was raised by about 50%. We attribute this im proved mobility to the presence of extra bulk charge carriers. At high er implantation levels, however, the mobility decreased, falling to 1. 4 x 10(-7) cm(2) V-1 s(-1) at a dose of 2 x 10(11) ions cm(-2). We pro pose that this is due to an increase in disorder in the C-60 lattice c aused by the implantation process.