THE ELECTRONIC-STRUCTURE OF ALKALI DOPED ULTRA-THIN SEXIPHENYL FILMS

The formation and evolution of the gap states formed with increasing C s concentration in thin 6P films are followed with ultraviolet photoem ission spectroscopy (UPS) and indirectly with energy loss spectroscopy involving electronic transitions (EELS). Two distinct doping regimes are apparent, in the lower doping regime bipolaron-like (dianionic) st ates are formed 0.8 and 2.9 eV above the valence band maxima. In the h igher doping regime, approaching Cs saturation, a 0.5 eV splitting in the gap states is observed which is attributed to interacting bipolaro n states, and as such is a precursor to bipolaron band formation.