In situ x-ray photoelectron spectroscopy studies of interactions of evaporated metals with Poly(⁠$p$-phenylene vinylene) and its ring-substituted derivatives

The results obtained from the in situ analysis by angle resolved x-ray photoelectron spectroscopy (XPS) of the interactions between thermally evaporated metals (aluminum and indium) and conjugated electroluminescent polymer films, such as poly(⁠$p$-phenylene vinylene) and its soluble derivative, $poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]$ (MEH-PPV), are reported. The changes in the carbon and metal core-level spectra and the chemical stoichiometries of polymer–metal interfaces with progressive deposition of the metal atoms were monitored. The interactions of the Al and In atoms with the polymer surfaces were compared. For both metals, a simple electrical contact was not formed. From the XPS studies, it was deduced that chemical reactions had occurred between the polymer and the metal, leading to the formation of an interfacial layer of metal oxides and complexes. The interfacial reactions were promoted by the surface oxidation states of the polymer, the migration of bulk adsorbed oxygen to the polymer surface upon metal deposition, and also in the case of MEH-PPV, by the oxygen from the alkoxy side chains.