Macroscopic variations of surface potentials of conductors

The surface potential variations of the following conductors have been measured over a 0.7 cm2 area: bronze, NiP, conducting polymer (polyaniline), Al, Cu, Au, and graphite. The measurements were performed with a Kelvin probe of spatial and potential resolution of 1.5 mm and 1 mV, respectively. Subjecting the surfaces to no cleaning procedure other than a low temperature ultrahigh vacuum bake, we find a wide spectrum of variation in surface potential uniformity, with alloys typically the least uniform and nonreactive surfaces such as gold and graphite the most uniform (no fluctuations above the 1 mV probe sensitivity). Application of these results to the Los Alamos antiproton gravity experiment is discussed.