Energy level alignment between C60 and Al using ultraviolet photoelectron spectroscopy

The energy level alignment between C-60 and Al has been investigated by using ultraviolet photoelectron spectroscopy. To obtain the interfacial electronic structure between C-60 and Al, C-60 was deposited on a clean Al substrate in a stepwise manner. The valence-band spectra were measured immediately after each step Of C-60 deposition without breaking the vacuum. The measured onset of the highest occupied molecular orbital energy level was located at 1.59 eV from the Fermi level of Al. The vacuum level was shifted 0.68 eV toward lower binding energy with additional C-60 layers. The observed vacuum level shift means that the interface dipole exists at the interface between C-60 and Al. The barrier height of electron injection from Al to C-60 is 0.11 eV, which is smaller value than that of hole injection. (c) 2005 Elsevier B.V. All rights reserved.