Growth conditions for the formation of thin films (100-300 Angstrom) of potassium-doped superfullerides (KxC60, x > 6) are examined. Thin films of these compounds are formed by depositing C-60 Onto a potassium precovered single crystal quartz substrate maintained at 200 K or lower, in a proportion of K:C-60 >12:1, followed by annealing the surface to the K-sublimation temperature (300 K). In situ measurements of electrical and optical properties are used to identify the compounds. The formation of superfullerides is confirmed by C-60 doping of these phases to check for the formation of insulating K6C60 With a characteristic absorption spectrum. The absorption spectrum of the superfullerides shows distinct features corresponding to the filling of the t(1g) band. The presence of two superfulleride phases is suggested, a near-metallic superfulleride KxC60 (x approximate to 11.2) and a more insulating KxC60 (x approximate to 8-9).