Fluorine Substitution of Hexa-peri-hexabenzocoronene : Change in Growth Mode and Electronic Structure

We have studied the effect of fluorine substitution on growth mode and electronic structure of hexa-peri-hexabenzocoronene (C42H18, HBC). Fluorinated-HBC, 2,5,8,11,14,17-hexafluoro-hexa-peri-hexabenzocoronene (C42F6H12, 6F-HBC), grew epitaxially on a Cu(111) single-crystal surface, similar to HBC. Higher crystalline films with rather flat surfaces were obtained for 6F-HBC than for HBC due to the attractive intermolecular C−H···F−C interaction. Electron spectroscopy measurements of HBC and 6F-HBC films indicated that fluorination causes energy shifts of molecular orbitals to higher binding energies and increase of the work function. Thickness dependence spectroscopic measurements revealed that the interface dipole and the ionization potential are drastically increased in 6F-HBC/Cu(111), which is favorable for n-type electric conduction through the decrease of electron injection barrier to LUMO.