9.2.1.4 Tunneling spectroscopy

This chapter provides information on tunneling spectroscopy measurements. Tunneling spectroscopy measurements provide new insight into both the scanning tunneling spectroscopy (STM) imaging process and the local electronic structure of surfaces and have been widely employed on a number of semiconductor surfaces. Tunneling I-V measurements were not able to directly correlate the I-V characteristics with the sample topography. This limitation was overcome using a multiplexing technique known as current imaging tunneling spectroscopy (CITS), in which complete tunneling I-V curves are recorded at each tip location during a complete raster-scan of the surface. The goal of tunneling spectroscopy is to measure the tunneling current I as a function of applied voltage V, measured at fixed sample-tip separation at some well-defined location(s) on the surface. As an example of the kind of information which can be obtained using this technique is, tunneling spectroscopy results for the silicon (Si) (111)7 x 7 surface, compared with the results of photoemission and inverse photoemission spectroscopy is shown. Tunneling spectroscopy results on defected Si(001) surface, demonstrating the metallic nature of the defects and the spatial extent of the metallic behavior is illustrated.