Growth-dependent optical properties of 3,4,9,10-perylenetetracarboxylicacid-dianhydride (PTCDA) films on Ag(1Â 1Â 1)

We measured photoluminescence (PL) and photoluminescence excitation (PLE) spectra of thin films of 3,4,9,10-perylenetetracarboxylicacid-dianhydride (PTCDA) grown by vacuum sublimation on the Ag(1 1 1) surface. Our aim was to study the influence of the film structure and growth morphology on the optical properties. PTCDA films grown on Ag(1 1 1) at low temperatures correspond to the β bulk phase, whereas films grown at high temperatures consist of clusters corresponding to the α bulk phase of PTCDA. Hence, films with a thickness of 30 ML were grown for preparation temperatures ranging from 180 to 420 K. For the films grown at the ends of this temperature interval, we find similar spectra, indicating a small influence of the different structures of two phases. In the transition range, however, considerable intensity changes and new blue-shifted (in PL) and red-shifted features (in PLE) are detected. The significant changes are attributed to the formation of intermediate phases or structural defects (e.g., stacking faults) perhaps involving self-trapped excitons.