Patch effect is important for ultra-sensitive experiments involving closely spaced conducting surfaces. A scanning probe equipped torsion pendulum is an experimental apparatus for measuring spatial resolved patch potential on conductive surfaces. An effective approach to improve its measurement precision is by the optimization on the amplitude and frequency of the injected signal in the probe. In this paper, a method based on single- and double-frequency signal injection modes is proposed. The analysis results demonstrate that the potential resolution could achieve the level of 2–4 μV/Hz1/2. In the same integration time, the surface potential precision in the double-frequency mode is twice better than that in the single-frequency mode. In addition, when achieving the same measurement precision, the double-frequency mode takes less time than the single-frequency mode, which improves the measuring efficiency.

The physical mechanism of the patch effect is still an open question. Thus, a high-precision surface potential mapping facility based on a specially designed electrostatically-controlled torsion pendulum is proposed in this paper. The facility not only features high sensitivity and a two-dimensional mapping function but also adapts to various measurement requirements for centimeter-sized samples. The sensitivity of the torsion pendulum reaches about 2.0 × 10−14 N m/Hz1/2 in a frequency range of 1–8 mHz. The temporal variation of the surface potential can be detected at a level of 30 μV/Hz1/2 with a probe whose surface area is 7 mm2. The potential spatial distribution resolution comes to 0.1 mm2 at a level of 40 μV with 1 h integration time.

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