A re-examination of scanning tunneling spectroscopy for its practical application in studies of surface electronic structures

In this paper we present a re-examination of the merits of scanning tunneling spectroscopy (STS) based on a detailed mathematical analysis and computer simulations. The analysis shows an intrinsic restriction in the technique due to the tunneling barrier transmission probability, which exponentially attenuates the low-lying electronic states in the energy band of a sample when composing the tunneling current. The results emphasize that a STS measurement is suitable for detecting the localized empty (conduction band) electronic states of a solid surface, whereas its ability to detect the filled (valence band) electronic states is limited. Tip material selection may be an option to circumvent this limitation to some extent, which is supported by our computer simulation results using delta function-like and flat band tip electronic structures.