Tunneling barrier reduction and asymmetry in scanning tunneling microscope due to dynamical screening

Abstract

We find the three-dimensional potential barrier in the scanning tunneling microscope (STM), by calculating the interaction of the tunneling electron with surface plasmon oscillations (SPO) in the coupled tip-sample system with different metals. The barrier is lowered in the region near the tip apex which leads to focusing of the tunneling current and increased lateral STM sensitivity. We also explain the asymmetrical current-voltage (I–V) curves arising from the difference in curvatures and bulk plasmon frequencies of the tip and sample.