The metallicity of aluminum and gold in contact with thin films of a urethane-substituted polythiophene

The metallic natures of aluminum and gold deposited in ultrahigh vacuum on a urethane-substituted polythiophene, poly[2-(3-thienyl)ethanol n-butoxycarbonylmethylurethane], have been studied by x-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) and electron energy loss spectroscopy (ELS). XPS demonstrates that initially deposited aluminum exists as oxide, similar to Al2O3 in character, up to a metal dose of about 4.0x10(15) atoms/cm(2). Higher metal doses result in metallic aluminum. UPS valence electronic spectra and ELS show, respectively, the existence of a band gap and an absence of plasmons. These indicate that interfacial aluminum is not metallic. In contrast, gold is metallic even for doses as small as 1.0x10(15) atoms/cm(2). In situ photoluminescence measurements of the polymer as a function of metal dose have also been performed to assess the ability of interfacial metal to quench photoluminescence. Deposited gold results in significantly more quenching than aluminum per deposited metal atom. However, the fact that nonmetallic aluminum facilitates some photoluminescence quenching indicates that factors, in addition to the existence of a nearby metallic layer, may lead to nonradiative decay of electronic excitations. (C) 2003 American Institute of Physics.