Ellipsometric study of an organic template effect: H2Pc/PTCDA

A key prerequisite for fabricating opto-electronic devices with organic molecules is to control the molecular growth mode. In this work we present an ellipsometric study of the templating effect of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on the growth mode of metal free phthalocyanine (H2Pc). The difference in the anisotropic dielectric function between the H2Pc films grown on bare glass or silicon substrates compared to the anisotropic dielectric function of H2Pc films grown on PTCDA indicates a drastic change in molecular orientation. From the strong in-plane/out-of-plane anisotropy the average molecular tilt angle of H2Pc was found to be around 52° for the films grown on bare substrates and around 25° for H2Pc films grown on PTCDA. A splitting in the H2Pc Q-band was observed for the H2Pc films grown on PTCDA which indicates a deviation from the perfect H2Pc α-phase crystal.