Tunneling behavior of electrified interfaces

The distance dependence of the tunneling current has been measured for the Au(1 1 1)/0.1 M H2SO4 interface over a wide potential range. From these data an effective barrier height (EBH) for the tunneling process through the electrochemical double layer has been determined, the distance dependence of which shows a marked potential dependence. An oscillatory behavior of the EBH with distance s between electrode surface and tip is observed only for the charged interface, while at the potential of zero charge a monotonous increase in the EBH with s is found until a plateau is reached, similar to the situation in UHV, and almost identical to the behavior of Au(1 1 1) in air. Absolute values for the tunnel gap have been obtained with the help of DFT calculations. A detailed DFT-derived model of the negatively charged interface is presented, which allows for a direct correlation between charge densities and EBH extrema.