Influence of space charge on the performance of the Kelvin probe

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Abstract
Measurement using a Kelvin probe depends vitally on the acquisition of a zero field between the probe and the sample. The charges in the space significantly affect the measurement of the work function change via the Kelvin probe due to the induced electric field between the probe and the sample, which adds uncertainty to the probe output. A simple model is presented in this article to depict the origin of the measurement errors. Then a solution, error deduction method, is suggested to effectively eliminate the influence due to charging by introducing a reference sample. The solution is also valid to cancel the error due to the change in the work function of the probe. The experimental results verified the feasibility of the method. Also discussed are other factors that affect the state of charging within a vacuum chamber. Careful shielding is necessary even if a stable reference sample is available. In the case where no stable reference samples are available, the use of insulating materials should be kept at a minimum. Once the insulating materials are used, they should be protected from being charged as much as possible. Any charge-generating components should be isolated by appropriate shielding, if possible, to avoid any leakage of charge into the space.

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