TUNNELING BARRIER REDUCTION AND ASYMMETRY IN SCANNING TUNNELING MICROSCOPE DUE TO DYNAMICAL SCREENING

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