Tunneling Current and Surface Potential Simultaneous Measurement Using a Scanning Probe

A new simultaneous measuring system for tunneling current and surface potential has been developed. The distance (d) between a sample and an electrochemically etched tungsten tip is changed sinusoidally with high precision. The tunneling current flows periodically in accordance with the vibration of the tip when d becomes as small as a few nm. The surface potential is measured using the principle of the Kelvin method in which the displacement current due to the presence of surface potential and the change in capacitance difference between the tip and the sample is detected. Simultaneous measurement of the tunneling current and the displacement current has been attained by utilizing their phase difference in tip vibration. The method for determining the tip radius and d is also presented.