Kelvin probe liquid-surface potential sensor

The design of a surface potential sensor is described in detail. It uses the Kelvin vibrating-probe principle and is specifically designed to characterize organic overlayers on poorly conducting liquid substrates. A novel manual compensation control allows the systematic measurement offsets originating in the electronics to be nulled. The head is based on a commercially available piezo-driven tuning-fork assembly with a 6 mm diameter gold-plated electrode, and includes a high-gain low-noise preamplifier to maximize sensitivity and minimize parasitic coupling. The input stage of the preamplifier uses balanced junction field-effect transistors mounted in a transimpedance configuration, giving low noise and minimizing phase shifts of the Maxwell-offset signal related to low substrate conductivity. The reproducibility of the measured surface potential is +/- 1 mV.(C) 1999 American Institute of Physics. [S0034-6748(99)02108-5].