Investigation of the energy level alignment of C ₆₀ and Co by using UV photoelectron spectroscopy

The energy level alignment between C ₆₀ and Co has been investigated by using ultraviolet photoelectron spectroscopy. To obtain the interfacial electronic structure between C ₆₀ and Co, we deposited C ₆₀ on a clean Co 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 1.44 eV from the Fermi level of Co. The vacuum level was shifted 0.39 eV toward lower binding energy with additional C ₆₀ layers. The observed vacuum level shift means that an interface dipole exists at the interface between C ₆₀ and Co. The barrier height for electron injection from Co to C ₆₀ is 1.16 eV, which is smaller value than that of hole injection.