Fullerenes superconducting films

Tens of conductive LB films have been developed so far, including metallic and superconductive LB films. These LB films are classified into the categories anion radical salt, charge-transfer complex, cation radical salt, conducting polymer, and transition metal complex in this section. The LB films, with metallic temperature dependences of conductivity, and the fullerene LB films, which exhibit a superconducting transition, are discussed separately. 

Potassium-doped LB film prepared from 50 layers of fullerene (C60) and deposited on a polyethylene terephtphalate substrate Microwave absorption or low-field signal Superconductivity was observed at or below 8.1 K 121... 

The synthesis of macroscopic amounts of C o and C70 (fullerenes) has stimuiated a variety of studies on their chemical and physical properties. We recently demonstrated that C o and C70 become conductive when doped with alkali metals. Here we describe iow-temperature studies of potassium-doped both as films and bulk samples, and demonstrate that this material becomes superconducting, Superconductivity is demonstrated by microwave, resistivity and Melssner-effect measurements. Both polycrystalline powders and thin-flim samples were studied. A thin film showed a resistance transition with an onset temperature of 16 K and essentially zero resistance near 5 K. Bulk samples showed a well-defined Meissner effect and magnetic-field-dependent microwave absorption beginning at 18 K. The onset of superconductivity at 18 K is the highest yet observed for a molecular superconductor. 

Small amounts of the individual fullerenes ( 0.5mg) were placed in quartz tubes with alkali metals and sealed under vacuum. These samples were subjected to a series of heat treatments and tests for superconductivity by 9-GHz microwave-loss experiments. Preliminary tests indicated that only the K-doped Cfto showed a response consistent with a superconducting transition (Fig. 1). For this reason, together with the fact that K Cgo showed the highest film conductivity, we focused our studies on the K-doped compound. 

At cooling films formed from fullerene, which was doped by potassium, and possess a K3C60 structure, at Tj =18 K a transition into a superconductive state was detected [13]. Then for materials doped by Rb and Cs, a Tc of 33 K was achieved [6]. Currently, the maximum reporting temperature of a transition into a superconducting state amounts to 45 K [14] for fullerite doped by Rb and Ta. These values of Tc concede only to ceramic superconductors, but in comparison with the latter, doped fullerite has considerably higher values of critical currents. 

A series of anionic derivatives of backminsterfullerene have been also obtained as phases of type A Ceo (x = 1 — 6) by exposing the fullerene films to alkali-metal vapor. Since some of these phases lead to conducting and superconducting solids, they are therefore promising as new materials and they will be discussed separately later in this section. 

Interest in the superconductivity of alkali metal doped 60 [18-21] provided an impetus to begin electrochemical studies of solid and immobilized fullerenes. Depending on the thickness of the fullerene film or the crystallite size, one may distinguish three different categories of samples for electrochemical studies ... 

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