Tuning of C60 energy levels using orientation-controlled phthalocyanine films.

The interface electronic structure of C₆₀/CuPc and C₆₀ 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 C₆₀ 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 F₁₆CuPc films, which can be attributed to the rearrangement of underlying F₁₆CuPc molecules. With the use of orientation-controlled CuPc and F₁₆CuPc 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 F₁₆CuPc film. [ABSTRACT FROM AUTHOR]