Strong optical anisotropies of F16CuPc thin films studied by spectroscopic ellipsometry

We have used spectroscopic ellipsometry to measure the optical functions of F16CuPc (copper-hexadecafluoro-phthalocyanine, C32F16N8Cu) films grown by organic molecular beam deposition simultaneously onto MgO(001), SiO2/Si, and A-plane (11 (2) over bar0) sapphire substrates. The latter allows one to produce, under suitable conditions, highly ordered films with interesting anisotropic optical properties. These films are shown to be oriented with two principal axes of the dielectric tensor on the film surface, with one of them almost aligned with the c axis of the substrate. The main spectral features, corresponding to the strong Q- and B-band absorptions of phthalocyanines, are polarized along the other in-plane axis which is perpendicular to c. The Q band contains a particularly sharp excitonic peak near 1.55 eV whose intensity variations point to different molecular stackings in the films. (C) 2003 American Institute of Physics.