Photoelectron spectroscopy of conjugated polymers

Photoelectron spectroscopy (PES) is a technique based on the photoelectric effect, which was first documented in 1887 by Hertz and explained in 1905 by Einstein. The use of soft x-ray sources led to the development of x-ray photoelectron spectroscopy (XPS), originally known as electron spectroscopy for chemical analysis (ESCA) [1], indicating the applicability of the method to studies of chemical properties. In parallel with the development of XPS, ultraviolet photoelectron spectroscopy (UPS) [2], i.e., PES based on ultraviolet photon sources, emerged as a tool for studying the valence electronic structure of gaseous and solid samples. However, the increasing use of the continuous spectral distri-bution of synchrotron radiation [3,4] as a photon source has made the historical terminology less meaningful. At present, PES has become a widely used technique for studying the chemical and electronic structure of solid matter and gases. Particularly, the method is very useful for studies on conjugated polymers and their interfaces because (1) it provides maximum amount of chemical and electronic information within a single technique, (2) it is essentially nondestructive to most organic systems, and (3) the method is extremely surface sensitive. Recently, the range of photoelectron spectro-scopies has been extended to include resonant processes occurring near the x-ray absorption threshold. Resonant photoemission (RPE) associated with these processes provides additional information on local electronic structure and charge vibrational coupling.