Control of in-plane orientation of phthalocyanine molecular columns using vicinal Si(001)-(2×1)-H

In-plane crystal orientation of copper phthalocyanine (CuPc) films formed by organic molecular-beam epitaxy have been successfully controlled by using vicinal Si(001)-(2×1)-H as a substrate, containing atomic steps of an approximately 4 nm period. A continuous film was grown at 60 °C and the film thickness ranged between 5 and 8 molecular layers. By observing a frictional force image of the film, 90% of the molecular columns were found to align across the substrate step rows. The preferential orientation is considered to be induced by artificial surface lattices, which result from the striped effective contact area between the rigid CuPc crystals and the stair-like surfaces. The anisotropic optical properties of the film have been also confirmed by polarized reflection measurements.