On the coexistence of different polymorphs in organic epitaxy: α and β phase of PTCDA on Ag(1 1 1)

The structure and epitaxy of thin films of PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride, C24H8O6) grown at 180°C on Ag(1 1 1) have been studied in situ using grazing-incidence X-ray diffraction. An extensive map of Bragg reflections has been recorded. A pronounced peak splitting is found, which provides evidence for the coexistence of α and β-like polymorphs,