Scanning Volta potentials and polarization measurements of metals in irradiated air

A method for direct dc measurement of the Volta potential is presented. A high intensity synchrotron X-ray beam 20 μm in diam was used to locally irradiate the atmosphere adjacent to the metal surface and produce a conducting path between a sample and a reference probe. The direct measurements of potential compared favorably with traditional Kelvin probe measurements. The direct measurements have a poorer spatial resolution but the measurements could be made at probe heights of around 1 mm compared to less than 0.1 mm for the Kelvin probe. In contrast to the Kelvin probe methods, the approach described allows observation of the current as a function of impressed voltage. Hence, it can be used as an active probe for electrochemical measurements in the gaseous phase.