Order on disorder: Copper phthalocyanine thin films on technical substrates

We have studied the molecular orientation of the commonly used organic semi conductor copper phthalocyanine (CuPC) grown as thin films on the technical ly relevant substrates indium tin oxide, oxidized Si, and polycrystalline g old using polarization-dependent x-ray absorption spectroscopy, and compare the results with those obtained from single crystalline substrates [Au(110 ) and GeS(001)]. Surprisingly, the 20-50 nm thick CuPC films on the technic al substrates are as highly ordered as on the single crystals. Importantly, however, the molecular orientation in the two cases is radically different : the CuPC molecules stand on the technical substrates and lie on the singl e crystalline substrates. The reasons for this and its consequences for our understanding of the behavior of CuPC films in devices are discussed. (C) 2001 American Institute of Physics.