A.S. Perel

C60 thin film transistors

N‐channel field effect transistors with excellent device characteristics have been fabricated by utilizing C60 as the active element. Measurements on C60 thin films in ultrahigh vacuum show on‐off ratios as high as 106 and field effect mobilities up to 0.08 cm2/V s.

Electrical resistivity and stoichiometry of BaxC60 films

Electrical resistance measurements show that uniform intercalation of Ba into C60 films is much more difficult to achieve than in the case of the other alkaline earths (AE), Ca and Sr. BaxC60 films studied after annealing at 220°C show a resistivity minimum between 1 <x <2, and another weak minimum at x = 5. The activation energies for the conduction process show a minimum at Ba1C60. The resistivities are γmin (x ≈ 1.5) = 0.2 Ω cm and γmin (x = 5) = 3 × 10−3 Ω cm. This latter value is the lowest yet reported in a adoped granular C60 thin (≈ 200 A) film and Ba5C60 exhibits a metallic (positive) temperature coefficient of resistivity. There is a maximum in the resistivity at x = 3. The results suggest that the conductivities observed in (AE)xC60 films (AE = Ca, Sr, Ba) between 0 <x < 3 are associated with the population of bands derived from the t1u LUMO levels of C60, whereas the most conducting phases have the composition x = 5 and involve energy bands derived from the t1gLUMO+1 levels of C60.

Electrical resistivity and stoichiometry of KxC60, RbxC60, and CsxC60 films

Electrical resistance measurements as a function of stoichiometry have been carried out on KxC60, RbxC60 and CsxC60 thin films for 0<x<6. The annealed films show global resistance minima at K3C60, ϱmin=4×10−3 Ω cm (60°C), Rb3C60, ϱmin=4 × 10−3 Ω cm, and Cs1C60, ϱmin=7 × 10−2 Ω cm. All of the annealed films show additional features in the vicinity of x=4, but the manifestation of the A4C60 phase (A=K, Rb, Cs), in transport studies is dependent on the metal and the annealing conditions. The A6C60 phase is apparent for all of the metals studied and shows a relatively high resistivity. The activation energies of the conduction process show well defined stationary points at K3C60 (not activated), Rb3C60 (not activated). Cs1C60 (minimum), Cs4C60 (maximum), with less distinct features between 4 <x < 6 in all cases.