Growth of quaterrylene thin films on a silicon dioxide surface using vacuum deposition

Quaterrylene molecules, which have a planar and highly π-conjugated chemical structure, were deposited on a SiO₂ surface, and their thin film structures, including surface morphology and molecular orientation, were examined by atomic force microscopy (AFM) and X-ray diffractometry (XRD). AFM observations revealed the grain size and surface roughness to be closely dependent on the substrate temperature in the range from 27 °C to 200 °C. Particularly at a substrate temperature of 140 °C, grain sizes of up to 6 μm and low surface roughness of 1.67 nm were successfully obtained in the 8 ML-thick film. XRD measurements of the quaterrylene thin film revealed (0 0 l) Bragg reflections, corresponding to a spacing of 1.89 nm. This value coincides with the average height of the terraces of the stepped structure observed in the AFM images. These results clearly demonstrate the quaterrylene molecules to have an upright orientation and that thin films grow as layered structures on the surface. From the full width of half maximum (FWHM) of the XRD rocking curve, the degree of alignment of the molecular planes (mosaicity) was estimated to be 0.09°, which shows that the film has a highly ordered structure.