A NEW METHOD TO DETECT GEOMETRICAL INFORMATION BY THE TUNNELING MICROSCOPE

A new method for the detection of the geometrical information by the s canning tunneling microscope is proposed. In addition to the bias volt age, a small ac modulation is applied. The nonlinear dependence of the transmission coefficient on the applied voltage is used to generate h armonics. The ratio of the harmonics to the dc current is found to giv e the width between the sample and the probe, i.e., the geometrical in formation. This method may be useful to measure materials, where the l ocal-spatial-density of states may change notably from place to place. (C) 1997 American Institute of Physics. [S0021-8979(97)05621-1].