Structure and phase-change phenomena in evaporated thin films of cobalt phthalocyanine

Abstract

The structures of thin films of cobalt phthalocyanine (CoPc) which have been deposited onto glass substrates at room temperature are investigated. Films of thickness 0.1 μm are primarily of the α-form and show a single Bragg peak indicating a strong preferential orientation in either the [001] or [200] directions, depending on whether the structure is tetragonal or orthorhombic. Films of thickness 1 μm show a slight decrease in the degree of preferential orientation, with the appearance of several additional peaks. After annealing at approximately 300 °C much of the material undergoes a phase transition to the stable β-form, preferentially oriented in the [001] direction, while annealing at lower temperatures produces a mixture of the α- and β-phases. The mean crystallite grain size increases systematically with maximum annealing temperature from approximately 30 nm without annealing to a maximum of approximately 100 nm when annealed at 315 °C.