Photoemission spectroscopic investigation on the interface formation of a ladder-type poly(para-phenylene) with aluminum

The formation of the interface between a thin film of a ladder-type poly(para-phenylene) $m$-LPPP and aluminum was investigated with x-ray and ultraviolet photoemission spectroscopy. The physical properties of this interface are of actual interest as $m$-LPPP is successfully applied as active material in organic light emitting devices (LED). Almost no changes in the core-level and valence electronic structure of the polymer upon increasing coverage with aluminum (in situ) are found. This gives indication for a weak interaction of Al with $m$-LPPP, ruling out the formation of chemical bonds between the two materials. The rapid occurrence of metallic aluminum at rather low coverage in the presented experiment is an important finding for the understanding of charge injection and the interfacial electronic structure in organic LEDs.