Electrostatic effect due to patch potentials between closely spaced surfaces

Abstract

The spatial variation and temporal variation in surface potential are important error sources in various precision experiments and deserved to be considered carefully. In the former case, the theoretical analysis shows that this effect depends on the surface potentials through their spatial autocorrelation functions. By making some modification to the quasi-local correlation model, we obtain a rigorous formula for the patch force, where the magnitude is proportional to $\frac{1}{a^2}{(\frac{a}{w})}^{\beta (a/w)+2}$ with $a$ the distance between two parallel plates, $w$ the mean patch size, and $\beta$ the scaling coefficient from $-2$ to $-4$. A torsion balance experiment is then conducted, and obtain a 0.4 mm effective patch size and 20 mV potential variance. In the latter case, we apply an adatom diffusion model to describe this mechanism and predicts a $f^{-3/4}$ frequency dependence above 0.01 $\mathrm{mHz}$. This prediction meets well with a typical experimental results. Finally, we apply these models to analyze the patch effect for two typical experiments. Our analysis will help to investigate the properties of surface potentials.

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