In situ XPS study of the interactions of evaporated copper atoms with poly(p-phenylene vinylene) and its ring-substituted derivatives

Abstract

Angle-resolved X-ray photoelectron spectroscopy was employed for the in situ study of the interactions between thermally evaporated copper atoms and conjugated electroluminescent polymer, such as poly(p-phenylene vinylene) and its soluble derivative, poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV). Quantitative changes in the C 1s and Cu 2p core-level spectra, the Cu LMM Auger line shapes, and the chemical stoichiometries of polymer-metal interfaces with progressive deposition of the copper atoms were carefully monitored. Chemical interactions had occurred between each polymer and the copper atoms, resulting in the formation of an interfacial layer of metal complexes. There appeared to be no significant migration of bulk absorbed oxygen to the polymer surface upon copper deposition unlike that observed during the deposition of metals of lower work function. Diffusion of Cu atoms into the near-surface region of the polymer was observed for PPV and MEH-PPV films. The interactions of the Cu atoms with the polymer surfaces were also compared with the results obtained for the Al/PPV and Al/MEH-PPV interfaces.