Electronic Structure of Surfaces and Interfaces in Conjugated Polymers

Abstract

A description of the electronic and chemical structure of polymeric and condensed molecular solid systems is an important ingredient in the field of organic polymeric and molecular materials in modern electronics applications. The investigation of the interaction between conjugated polymer materials and various metals has become an important issue, both for interfacial characteristics as well as for doping-induced effects. Studies on the interface characteristics are of significant importance in the connection with various device applications. Investigations of initial stages of both metal-on-polymer and polymer-on-metal interface formation are of importance in the context of how the interfaces may affect the actual device performance. In other words, when a few isolated atoms of an active metal are applied in some way to a polymer surface, they will react in a very different way compared to the case where an isolated polymer chain is applied in some way to the clean surface of an otherwise three dimensional metal substrate, with or without the presence of an oxide layer [1]. In this context, the single most useful experimental tool has turned out to be photoelectron spectroscopy (PES) [2]. Also, it has been shown that use of the results of appropriate quantum-chemical calculations [3] in interpreting PES data in many cases provides a level of information output which is larger than the sum of the two [4]. In this chapter, the principles involved in the study of the electronic and chemical structure of conjugated polymer surfaces and interfaces are reviewed. Examples of materials system are included which demonstrate information obtainable from photoelectron spectroscopy on both pristine and doped conjugated polymers as well as the modification of the electronic and chemical structure of conjugated systems induced upon interaction with different metals such as aluminum and calcium. Also, the usefulness of the combination of photoelectron spectroscopy and quantum-chemical calculations is demonstrated with some examples. The theoretical models most commonly used are only briefly outlined. More theoretical details are to be found in, for example, Ref. [3].This chapter is organized as follows: the experimental and theoretical techniques are presented briefly in Sections 5.2 and 5.3. In Section 5.4 some materials aspects and concepts are introduced, where trans-polyacetylene is used as an illustrative example. A series of illustrative examples on surfaces and interfaces Semiconducting Polymers: Chemistry, Physics and Engineering. Edited by G. Hadziioannou and P. F. van Hutten

Fundamentals of Organic Semiconductor Devices

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