Interplay of geometric and electronic structure in thin films of diindenoperylene on Ag(1 1 1)

Abstract

Using the example of Diindenoperylene (DIP) a strong dependence of ionization potential, electron affinity and transport gap on the growth conditions of an organic molecular thin film is demonstrated. DIP single crystals show a remarkable polymorphism as single crystals as well as crystalline films on weakly interacting substrates like Au or SiO2 surfaces. We have investigated DIP thin films on Ag(111) substrates and found a strong dependence of the photoemission and inverse photoemission spectra as well as of the low energy electron diffraction (LEED) patterns on the substrate temperature. Three different temperature regions could be identified with distinct reproducible signatures in the structural data as well as in the valence level spectra. Peak positions, line widths, and relative intensities directly correlate with the degree of order and with the molecular orientation. Moreover, we identified a systematic change of the structural quality ranging from high mosaicity at low temperature (<150K) via small ordered domains (150–250K) to a high degree of order at elevated temperature (>350K).