Tuning of C60 energy levels using orientation-controlled phthalocyanine films

Abstract

The interface electronic structure of C60 /CuPc and C 60 heterojunctions on SiO2 and highly oriented pyrolytic graphite has been studied using ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, and synchrotron based photoelectron spectroscopy. Fermi level pinned to the negative integer charge transfer state of C 60 molecules on the standing CuPc film has been observed, while nearly vacuum-level alignment is observed for C60 on the lying CuPc film. We also found small vacuum-level shifts for C60 on both standing and lying F16 CuPc films, which can be attributed to the rearrangement of underlying F16 CuPc molecules. With the use of orientation-controlled CuPc and F16 CuPc thin films, C60 highest occupied molecular orbital energy levels relative to the substrate Fermi level can be tuned from 1.9 eV for C60 on the standing CuPc film to 1.0 eV on the standing F16 CuPc film. © 2010 American Institute of Physics.