Doping and defect inhomogeneities of polypyrrole tosylate films as revealed by mu-NEXAFS

The photoemission electron microscope (PEEM) based techniques micro-near-ed ge X-ray absorption fine structure (mu-NEXAFS) and micro-photoelectron spec troscopy (mu-PES) have been recently installed at the BESSY-I HE-TGM beam l ines as novel techniques for material analyses. In the PEEM microscope, pho toemitted electrons are imaged by electrostatic lenses having a lateral res olution of 40 nm. Images with a field of view between 800 and 20 mu m are o btained. NEXAFS enables the simultaneous recording of the near-edge fine st ructures of the absorption coefficient while varying the incident photon en ergy. For mu-PES, at a fixed photon energy, core level and valence band spe ctra can be recorded by an electrostatic energy analyser to fit in the opti cal axis of the PEEM microscope. Spectra are recorded by analysing all the electrons of the PEEM image or by selecting segments of the image with a co ntinuous iris aperture. The minimum size of the analysed spot is in the ord er of a few micrometers. Here, we use these techniques to determine the ele ctronic structure of polypyrrole films within a well defined surface area. We found surface structures of such polypyrrole films which are corrugated in the micron range as well as areas that appear almost smooth. In addition , the PEEM microscope gives patterns due to a non-homogeneous surface poten tial distribution. In such patterns bright irregular stripes appear between dark patches. The stripes have a typical width in the order of several mic rometers. (C) 1999 Elsevier Science S.A. All rights reserved.