Spectrum analysis and its application of tunneling current in Scanning tunneling microscopy

By spectra analysis of tunneling current, a novel technique for the simultaneous measurement of tip-sample force interactions in scanning tunneling microscopy (STM) is developed. Frequency spectra of the tunneling current of highly oriented pyrolitic graphite (HOPG) is measured in air with a mechanically cut probe from a wire of Pt-Ir alloy. A frequency peak at about 40 kHz presented to the spectra, which is demonstrated to relavant to the vibration mode perpendicular to the length direction of the STM probe and to its eigenfrequency under tip-sample force interactions. The characteristics of the eigenfrequency for various experimental conditions are also presented. Quantative relationship between the eigenfrequency and the force gradient of tip-sample interactions is acquired. The spectrum analysis technique provides a novel method for simultaneous measurement of force interactions under true STM conditions.