Charge localization on a polymer surface measured by triboelectrically induced x-ray emission

The means by which charge is exchanged between two surfaces that have been brought into contact is perhaps the longest standing unsolved problem in physics. To this day, it is debated as to whether charging is due to electrons or ions. Contact electrification is such a singular process that it lies beyond the scope of density functional theory and other ab initio theories of material structure. We present a new method for studying the fundamental processes that underlie triboelectrification, based upon the structure of x-ray emission from the interface of separating surfaces. Our measurement of the x-ray spectrum emitted from lead rolling against various thicknesses of unplasticized polyvinyl chloride (uPVC) on top of a grounded conductor indicate that triboelectrification, like turbulence, extends over a broad range of length scales. We observe millimeter-scale charge-patching, which indicates the feasibility of building MEMS x-ray sources.