A SCANNING TUNNELING POTENTIOSPECTROSCOPIC MICROSCOPE AND A DATA DETECTING METHOD

摘要

A bias voltage UB including a sine-wave voltage UTsin omega ot and an off-set voltage UREG is applied to an electrode (14) on a sample (10). A potential U1 of the electrode (14) is represented by: U1 = UREG + UTsin omega ot. A voltage including the bias voltage UB and a voltage DELTA U is applied to an electrode (16) on the sample (10). A probe (12) is approached to the sample (10) by several nm, and a tunnel current IT flows therebetween. And the probe (12) scans the surface of the sample. During the scan, the position of the probe (12) 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 (14) and a surface portion facing the probe (12) is US(x), the average of U1 + US(x) becomes zero when the average of the tunnel current IT is zero. Accordingly, = 0, that is, US(x) = - UREG. Thus, by recording - UREG the potential distribution US(x) on the sample surface is determined. Spectroscopic data is obtained by an analog operation unit (32), on the basis of a differential conductance DIFFERENTIAL IT/ DIFFERENTIAL UT calculated from the tunnel current signal IT and the bias voltage UT.