Interface Dipole and Growth Mode of Partially and Fully Fluorinated Rubrene on Au(111) and Ag(111)

Thin films of fully and partially fluorinated rubrene deposited on Au(111) and Ag(111) were investigated using ultraviolet and X-ray photoelectron spectroscopy. We demonstrate that fluorination of the molecules is an efficient way for tuning the metal–organic interface dipole and the hole injection barrier. Moreover, the results indicate that the pronounced electrostatic dipole moment of partially fluorinated rubrene (F14-RUB) has a strong impact on the growth mode of these molecules. Most notably, we infer that the first layer of F14-RUB on Au(111) and Ag(111) is formed by molecules with alternating orientation of their dipole moments whereas the second layer shows a nearly uniform orientation.