Kelvin probe force microscopy without bias-voltage feedback

A variation of Kelvin probe force microscopy that does not require bias-voltage feedback for contact potential difference (CPD) detection was proposed. Two independent lock-in amplifiers were used to measure the first- and second-order derivatives of the electrostatic force exerted on the cantilever, and CPD was deductively determined from these signals. The application of this technique to the unsaturated Au/Si(111)-5 x 2 system confirmed that the instability of the measurement system resulting from bias-voltage feedback can be completely eliminated and that CPD measurement at a finite bias voltage is possible.