Stress release drives growth transition of quaterrylene thin films on Sio₂ surfaces

The growth process of quaterrylene thin films was examined by atomic force microscopy and in-plane and out-of-plane X-ray diffraction (XRD). Quaterrylene thin films on the SiO₂ surface exhibit the Stranski-Krastanov (SK) growth mode; the films initially formed two-dimensional (2D) layers (<4 monolayers (ML)) followed by three-dimensional (3D) island growth. Grazing incidence X-ray diffraction (GIXD) measurement revealed that the first few layers were subjected to compressive stress along the b axis of the unit cell, resulting in expansion of the a- and c-lattice constants. This result revealed that compressive stress generated in the 2D layers drives the change of the growth mode to 3D. An understanding of the transition mechanism in early growth has important implications for the improvement of carrier transport in organic field-effect transistors.