Kelvin probe liquid-surface potential sensor

The design of a surface potential sensor is described in detail. It uses th e Kelvin vibrating-probe principle and is specifically designed to characte rize organic overlayers on poorly conducting liquid substrates. A novel man ual compensation control allows the systematic measurement offsets originat ing in the electronics to be nulled. The head is based on a commercially av ailable piezo-driven tuning-fork assembly with a 6 mm diameter gold-plated electrode, and includes a high-gain low-noise preamplifier to maximize sens itivity and minimize parasitic coupling. The input stage of the preamplifie r uses balanced junction field-effect transistors mounted in a transimpedan ce configuration, giving low noise and minimizing phase shifts of the Maxwe ll-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].