Local work function measurement on Cu(111)-Au and Cu(111)-Pd surfaces

In this paper, we report the local work function measurements on the Cu(111)-Au, and Cu(111)-Pd surfaces with scanning tunneling microscopy (STM). We successfully observed the local work function difference between the Au/Pd overlayer and the Cu substrate, the decreased work function at the step edges. We also found that the work function of the Pd film is larger than that of the bulk Pd(111). The lower work function at step edges can be explained by the dipole moment formation. It is demonstrated that the local work function measurement by STM is a powerful way to identify different elements with nanometer resolution.