Thin Films and Bulk Phases Conucleate at the Interfaces of Pentacene Thin Films

Pentacene deposited on silica adopts two different packing arrangements. The kinetically favorable thin-film phase (TFP) occurs at lower substrate temperatures and thinner deposition thicknesses relative to the thermodynamically stable bulk phase (BP). Both phases orient in a tilted edge-on motif, where the BP is tilted further from the perpendicular, identifiable using X-ray diffraction (XRD) techniques. Different types of growth on SiO2 have been proposed. One is that deposition at the interface begins with the TFP, independent of substrate temperature, while the BP deposits over it after a temperature-dependent critical deposition thickness is reached. Others have found both phases to begin their temperature-dependent growth at the interface. Using an interfacial spectroscopic technique, vibrational sum frequency generation, paired with Fourier transform infrared spectroscopy and XRD, we determine that conucleation of both phases at the interface takes place during pentacene thin-film growth.