Temperature Dependent Epitaxial Growth of C₆₀ Overlayers on Single Crystal Pentacene

Heteroepitaxy of one material onto another molecular single crystal surface is one promising route for resolving questions about formation criteria of molecular heterojunction structures as well as for the development of next-generation organic electronic devices allowing efficient intermolecular charge carrier exchange. In the present work, the in-plane and out-of-plane crystallinity of an epitaxial molecular p–n heterojunction, C₆₀ (acceptor) overlayers formed on the single crystal surface of pentacene (donor), and its evolution, depending on the growth temperature, are systematically elucidated. It is demonstrated that the crystallinity of the C₆₀ on pentacene is dominated by the temperature during the growth rather than the postannealing of the sample. The mean crystallite size in the in-plane directions grows from 50 to 150 nm proportionally to the growth temperature in a range of 125–370 K. The present results suggest that the formation mechanisms of the C₆₀/pentacene heterojunction are kinetically controlled, by diffusion processes at the molecular interface, rather than by the thermal equilibrium conditions.