Formation of Highly Ordered Organic Molecular Thin Films on Deactivated Si Surfaces Studied by Scanning Tunneling Microscopy and Low Energy Electron Diffraction

Abstract

Growing organic molecular films on inorganic substrates is crucial for organic electronics applications; however, it still remains a significant challenge to achieve long-range molecular ordering. Here we report the formation of highly ordered zinc phthalocyanine (ZnPc) thin films on the deactivated Si(111)-B √3 × √3 R30° surface characterized by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). We find that for the initial submonolayer growth, access to the anisotropic step-flow growth mode yields a reduction in the substrate symmetry resulting in two dominant mirror-reflected domains. Upon further deposition, the ZnPc molecules are able to maintain a highly ordered configuration both laterally and vertically up to 40 monolayers even though the molecule–substrate interaction decreases as evidenced by the diminished moiré pattern and a mild relaxation in the molecular packing. We attribute the formation of highly ordered organic molecular thin films to the delicate balance between the molecule–molecule and molecule–substrate interactions. These findings pave the way for the integration of functional organic materials into silicon-based electronics.