Scanning tunneling potentio-spectroscopic microscope and a data

Abstract

A bias voltage U.sub.B including a sine-wave voltage U.sub.T sin.omega. .sub.o t and an off-set voltage U.sub.REG is applied to an electrode on a sample. A potential U.sub.1 of the electrode is represented by: U.sub.1 =U.sub.REG +U.sub.T sin.omega. .sub.o t. A voltage including the bias voltage U.sub.B and a voltage .DELTA.U is applied to an electrode on the sample. A probe is approached to the sample by several nm, and a tunnel current I.sub.T flows therebetween. And the probe scans the surface of the sample. During the scan, the position of the probe is servo-controlled in the z-direction, to make constant the average absolute value of the tunnel current. The servo voltage is recorded thereby obtaining an STM image. Given that the potential difference between the electrode and a surface portion facing the probe is U.sub.S (x), the average of U.sub.1 +U.sub.S (x) becomes zero when the average of the tunnel current I.sub.T is zero. Accordingly, <U.sub.S (x)+U.sub.REG +U.sub.T sin.omega. .sub.o t>=0, that is, U.sub.S (x)=-U.sub.REG. Thus, by recording-U.sub.REG the potential distribution U.sub.S (x) on the sample surface is determined. Spectroscopic data is obtained by an analog operation unit, on the basis of a differential conductance .differential.I.sub.T /.differential.U.sub.T calculated from the tunnel current signal I.sub.T and the bias voltage U.sub.T.