Research in the use of organic polymers as the active semiconductors in light-emitting diodes has advanced rapidly, and prototype devices now meet realistic speci®cations for applications. These achievements have provided insight into many aspects of the background science, from design and synthesis of materials, through materials fabrication issues, to the semiconductor physics of these polymers.

In this Review, we summarize recent work on modeling of organic/metal and organic/organic interfaces. Some of the models discussed have a semiempirical approach, that is, experimentally derived values are used in combination with theory, and others rely completely of calculations. The models are categorized according to the types of interfaces they apply to, and the strength of the interaction at the interface has been used as the main factor. We explain the basics of the models, their use, and give examples on how the models correlate with experimental results. We stress that given the complexity of organic/metal and organic/organic interface formation, it is crucial to know the exact way in which the interface was formed before choosing the model that is applicable, as none of the models presented covers the whole range of interface interaction strengths (weak physisorption to strong chemisorption).

We have studied the work function and density of states (DOS) of multiwall carbon nanotubes (MWNTs) using ultraviolet photoelectron spectroscopy (UPS). Raw MWNTs were purified by successive sonication, centrifugation, sedimentation, and filtration processes with the aid of a nonionic surfactant. The purified MWNTs showed a slightly lower work function (4.3 eV) than that of highly oriented pyrolytic graphite (4.4 eV). Effects of three different oxidative treatments, air-, oxygen plasma-, and acid-oxidation, have also been studied. It was found that oxidative treatments affect the DOS of valence bands and increase the work function. X-ray photoelectron spectroscopy (XPS) measurements have suggested that gas-phase treatment preferentially forms hydroxyl and carbonyl groups, while liquid-phase treatment forms carboxylic acid groups on the surface of MWNTs. These surface chemical groups disrupt the π-conjugation and introduce surface dipole moments, leading to higher work functions up to 5.1 eV. We expect the information on the work function of the MWNTs to be of importance to the development of electronic or optoelectronic applications.