Energy level alignment of C60/Co using x-ray and UV photoelectron spectroscopy

The energy level alignment at the interface between fullerene (C60) and Co has been determined by x-ray and ultraviolet photoelectron spectroscopy. To investigate the interfacial electronic structure, a C60 layer was deposited on a clean Co surface in a stepwise manner. The measured onset of the highest occupied molecular orbital energy level was at 1.54 eV from the Fermi level of Co. The vacuum level was shifted 0.41 eV toward lower binding energy with the additional C60 layers, which means that an interface dipole exists at the interface between C60 and Co. The C 1s spectra show that band bending occurs at the interface between C60 and Co. These results indicate that the barrier height of the hole injection from Co to C60 is 1.14 eV, which is a smaller value than that for electron injection (1.46 eV).