Spectroscopic and structural analysis of precursors to hexagonal close packed phases in C₆₀ thin films

When vacuum deposited C₆₀ thin films are exposed to chlorobenzene solvent vapour, the absorption feactures of C₆₀ shift to the red, most notably the charge-transfer exciton features at ∼475 nm and 525 nm. Microscopic analysis of the surface shows the effect of exposure to the vapour is structural with a number of distinct regions clearly visible. Raman shows that the features of the exposed film have been shifted relative to those of the pristine film and that crystal like deposits seen on the film are stable against the characteristic C₆₀ photo-transformation. The behaviour is reminiscent of that observed in annealed C₆₀ films, which was shown to be the result of a partial conversion of the film to a hcp structure. X-ray diffraction and DSC have been employed to examine the various regions visible on the film surface. It is shown that there is a photostable form of solid C₆₀ whose electronic properties differ significantly from those of fcc films present in small quantities on the film surfaces.