The interaction of aluminum with a methane-substituted polythiophene with electroluminescence applications

The interaction of aluminum with spin-cast films of poly[2(3-thienyl)ethanol n-butoxycarbonylmethylurethane], a polythiophene having a hydrogen-bond-forming urethane side chain, has been studied by X-ray photoelectron spectroscopy (XPS). The aluminum was evaporated in situ under ultra-high vacuum conditions, and changes in the Al(2p), C(1s), O(1s), N(1s) and S(2p) electronic levels were monitored as a function of aluminum coverage. O(ls) and N(ls) shifts to lower binding energies indicate that initially deposited aluminum preferentially bonds with oxygen atoms of the urethane side-chain, transferring electrons to it. Interaction with the side-chain is so strong that it prevents electron donation into the thiophene ring, as evidenced by a lack of aluminum-induced S(2p) features. This is in contrast to reactive metal deposition on aliphatic-substituted polythiophenes, such as poly(3-hexylthiophene). A1(2p) spectra show that the metal in contact with the polymer electronically resembles that of aluminum oxide, but deposition beyond about 4 X 10(15) Al/cm(2) leads to metallic aluminum. Comparison of aluminum intensities on the polymer with aluminum on gold suggest limited diffusion of metal into the bulk. (C) 2000 Elsevier Science S.A. All rights reserved.