Correlation between scanning tunneling microscopy/spectroscopy images and apex profiles of scanning tips

Abstract

Variations of topographic and current images with bias voltages were examined utilizing the current imagingtunneling spectroscopy (CITS) and dual‐polarity tunnelingimaging (DPTI) techniques. While the CITS and DPTI images of the Si(111)‐(7×7) reconstructed structure at the specimen voltage of +2 V and the DPTI image at −2 V are reliably reproducible exhibiting bright Si adatoms and dark corner holes, the CITS current image at −2 V often showed reversed contrast grey‐scale images with bright corner holes. The observed reversed image is explained as the result of the difference in the effective tunneling barrier and the surface state density of the tip apex and specimen, and also as the effect of the atomic arrangement and composition and profile of the tip apex.