Alternate heteroepitaxial growth of highly oriented organic multilayer films

The heterostructure, a basic active unit applied in the device level, plays an important role in traditional inorganic optoelectronics. In the organic field, although the requirement for the heterostructure is crucial, achievement and understanding on the growth and functionality of organic heterostructure are still finite, especially for ordered crystalline organic multilayers with smooth interfaces. Here a series of highly ordered crystalline heterostructures with molecule-level smoothness were obtained from single layer to alternate multilayer with a phthalocyanine molecule and a perylene derivative. Well-defined epitaxy relationship and crystal alignment were evidenced from the atomic force microscopy (AFM), X-ray diffraction (XRD), and transmission electron microscope (TEM) results. The evolution of the films reveals that, for organic-organic alternate multilayer growth, along with the intrinsic properties of organic molecules such as the packing and preferred growth direction, the soft matter properties of organic films contribute to well-defined heteroepitaxy despite that the lattice mismatch between the two materials' bulk phases is large. Thin film phases of the first few layers benefit the grain coalescence and thus the formation of smooth films. Potential application is implied from the heterojunctions' good transport ability.