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(100) and GeS(001)). 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. (c) 2006 Elsevier B.V. All rights reserved.