Tunneling current between two nonplanar surfaces

Abstract

The tunneling current between two nonplanar electrodes is treated as a model for scanning tunneling microscopy (STM) in which the tip is nonspherical. One electrode is bounded by a perfect infinite plane with a small protuberence, representing the tip, while the other has a corrugated surface, representing the sample. We calculate the tunneling current for this system and obtain an expression explicitly dependent on both tip and surface profiles. The contours of constant current for a Gaussian shaped tip are compared to our previously calculated contours of constant local density of states (LDOS), corresponding to a spherical tip, and in both cases the image resolution is discussed. We also discuss the effect of an asymmetric tip, such as a double tip, in which the probe structure can significantly influence the STM image. Finally, the current and isocurrent contours for the case of a graphite sample probed by a nonspherical tip are also discussed.