In I(V) Spectroscopy (or Current Imaging Tunneling Spectroscopy, CITS) a normal topographic image is acquired at fixed Io and Vo. At each point in the image feedback loop is interrupted and the bias voltage is set to a series of voltages Vi and the tunneling current Ii is recorded. The voltage is then returned to Vo and the feedback loop is turned back on. Each I-V spectra can be acquired in a few milliseconds so there is no appreciable drift in the tip position. This procedure generates a complete current image Ii(x,y) at each voltage Vi in addition to the topographic image z(x,y)|VoIo.
CITS data can be used to calculate a current difference image DIViVj(x,y) where Vi and Vj bracket a particular surface state, producing an atomic resolved, real space image of a surface state. This technique, for example can be used in UHV to image filled ad-atom states or the dangling bond states for silicon reconstructions.
- G. Binnig and H. Rohrer: Surf. Sci. 126 (1983) 236. Rep. Prog. Phys. 55, 1165-1240 (1992).