Molecular orientation of substituted phthalocyanines: Influence of the substrate roughness

We compare the molecular orientation of differently alkyl-substituted metal phthalocyanines on polycrystalline gold and on single crystalline substrates (Au(1 0 0) and GeS(0 0 1)). In both cases we observe a high degree of molecular ordering for ultrathin films (1–3 monolayers), the molecules are oriented parallel to the substrate surface (lying). However, the molecular orientation can be different for 5–30 nm thick films: we observe “standing” molecules on relatively ill defined polycrystalline substrate surfaces whereas almost disordered films were found on single crystalline surfaces. The growth mode is discussed in terms of different molecule–molecule and molecule–substrate interactions.