Growth and annealing kinetics of α-sexithiophene and fullerene C₆₀ mixed films

Thin films of α-sexithiophene (6T) and C₆₀ mixtures deposited on nSiO substrates at 303 and 373 K were investigated in real time and in situ during the film growth using X-ray diffraction. The mixtures are observed to contain the well known 6T low-temperature crystal phase and the β phase, which usually coexist in pure 6T films. The addition of C₆₀ modifies the structure to almost purely β-phase-dominated films if the substrate is at 303 K. In contrast, at 373 K the low-temperature crystal phase of 6T dominates the film growth of the mixtures. Post-growth annealing experiments up to 373 K on equimolar mixtures and pure 6T films were also performed and followed in real time with X-ray diffraction. Annealing of pure 6T films results in a strong increase of film ordering, whereas annealing of equimolar 6T:C₆₀ mixed films does not induce any significant changes in the film structure. These results lend further support to theories about the important influence of C₆₀ on the growth behaviour and structure formation process of 6T in mixtures of the two materials.