Internal photoemission in polyaniline revealed by photoelectrochemistry

After self-assembling a p-aminothiophenol (PATP) monolayer on bare Au elect rode, polyaniline (PANI) films were prepared by electropolymerization on th e modified Au electrode and three forms of PANI (the emeraldine salt, the l eucoemeraldine and the pernigraniline) were obtained by electrochemical met hod. The cyclic voltammograms of the probe (K3Fe(CN)(6)/K4Fe(CN)(6)) for th e three forms of PANI show that three different oxidized forms can be found and all of them are stable under our experiment conditions. The potential dependence of magnitude and the spectra of the photocurrent of the PANI fil ms were observed. When the spectra of photocurrent are displayed in a Fowle r plot (the square-root of the incident photon-to-current efficiencies vers us the photon energy), the functional form appears linear, which is interpr eted as indication of internal photoemission of holes or electrons from met al into the appropriate electronic band of the semiconductor or insulator, The band gap energy of insulating matrix in the emeraldine salt is determin ed as 3.33 eV by the Fowler plots. The flat-band potential, in the order of 0.63 V versus SCE, is obtained from Mott-Schottky plots. A photoelectroche mical process based on internal photoemission in the emeraldine salt, which agrees with the model of granular metal island that assumes metallic polym er particles are embedded in the insulating matrix, is proposed. (C) 2001 E lsevier Science B.V. All rights reserved.