Simulations of rectification in a laser-illuminated scanning tunneling microscope

Asymmetry of the barrier in a STM, due to differences in the shapes of the tip and sample electrodes, would cause a small rectified current to be produced by the direct interaction of tunneling electrons with optical fields. We have simulated this model for rectification using two different numerical methods in which the potential was approximated using the multiple-image barrier for a hemispherical tip and planar sample. The results of these simulations suggest that the rectified currents would be much less than those which have been observed experimentally. Thus, we conclude that it is unlikely that the observed STM diode effects are caused by the direct interaction of tunneling electrons with the fields set up by a laser.