Energy level alignment at C_(60)/Hf interface by using x-ray and ultraviolet photoelectron spectroscopy

摘要

We report the characterization of the interface formation of fullerene (C_(60)) on hafnium (Hf) using x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). The valence band, C 1s and Hf 4f spectra were measured during the deposition of C_(60) on a clean Hf surface in a stepwise manner. After enough deposition of C_(60) layers on Hf, XPS measurements indicate that there is no chemical reaction between C_(60) on Hf, and band bending exists at the C_(60)/Hf interface. From UPS measurements, the energy level difference between Fermi level of Hf and the onset of the highest occupied molecular orbital of C_(60) is 2.01 eV. The vacuum level of Hf was shifted toward low binding energy (0.95eV) as the Ceo deposition. These valence spectra results indicate that there exist an interface dipole and small electron injection barrier at the C_(60)/Hf interface. We provide the complete energy band diagram of the C_(60)/Hf interface and confirm that a small electron injection barrier can be achieved by inserting a low work function metal in a C_(60) field-effect transistor.