Investigating the Electronic Properties of a Composite Dielectric under an Applied Electric Field by Muon Spectroscopy

The development of a new technique using implanted 100% spin polarized positive muons to probe the behaviour of charge carriers within dielectrics is described. Muons are a well-established method for probing materials at the atomic level. They offer a local probe sensitive both to bound molecular charges and to free charge carriers in materials. A muon study to investigate the charge distribution within a composite dielectric - consisting of epoxy, mica and glass fibre components- as a function of the externally applied electric field strength (E-field) is reported. Implanted muons react with the host epoxy molecule, undergo chemical addition at specific locations and probe the local electronic structure. Muon spectra are interpreted through a comparison with the electronic structure calculated using Density Functional Theory.It is shown that the application of an external E-field modifies the form of the observed spectra. It is believed that the effect of an E-field on identified bound charges within the molecule is being observed, suggesting muons are an excellent probe for understanding local charge redistributions in polymeric dielectrics.