Structure Evolution and Corresponding Electrical Properties in Weakly Bound Co-C60 Mixture

Mixture films of Co and C60 with various compositions were fabricated by co-evaporation under UHV condition. As for the saturation composition with C60-based phase, Co5C60 is deduced from the systematic Raman analysis. It is reasonably interpreted that the C60-based phase can be realized by less than one electron transfer per a Co atom into C60 and the contribution of a covalent bonding which induces a differently coordinated structure of the C60 molecules from the fcc-C60. The electrical conduction features are dependent on the Co content. In the C60-based phase up to Co5C60, the conduction mechanism seems to be described by the band concept modified with the disorder, followed by the hopping conduction through the precipitated Co clusters or particles and then, by the metallic one with increasing Co content.