Localized or delocalized unoccupied electronic states in polymers

Ikeura, Hiromi*; Sekiguchi, Tetsuhiro  

X-ray absorption spectroscopy (XAS) is commonly used as probing unoccupied electronic states. However, XAS can not distinguish localized and delocalized electronic states. In metal system, plotting the normal Auger yields (in Resonant Auger spectroscopy (RAS)) around the XAS region exhibit unoccupied conduction band state near the Fermi level (EF). In polymer system, RAS spectra can be interpreted based on two competing decay channels: that is, core-hole decay and core-excited resonant electron delocalization. If the resonantly excited electron remains long enough to be localized in the vicinity of a core-hole site during the core-hole decay, the decay process results in final states of two holes with one electron (2h1e), known as "spectator Auger". In contrast, if it delocalizes to the conduction band prior to the core-hole decay, the decay process results in final states of two holes (2h), known as "normal Auger". Thus, If polymer has a delocalized conduction band, an excited electron can delocalize along the polymer chain before core-hole decay. Consequently, the normal Auger yields exhibit the conduction band structure, as similar to the metal system. We show that the localized or delocalized band structure can be probed by the normal Auger yields.