We report a quantitative low-temperature scanning tunneling spectroscopy (STS) study on the Ag(111) surface state over an unprecedented range of currents (50 pA to $6\mu \mathrm{A}$) through which we can tune the electric field in the tunnel junction of the microscope. We show that in STS a sizable Stark effect causes a shift of the surface-state binding energy $E_0$. Data taken are reproduced by a one-dimensional potential model calculation, and are found to yield a Stark-free energy $E_0$ in agreement with recent state-of-the-art photoemission spectroscopy measurements.

• Received 29 January 2003

DOI:https://doi.org/10.1103/PhysRevLett.91.196801