Effect of p-toluene sulphonic acid doping on the properties of plasma polymerized aniline thin films

The plasma polymerization is the process commonly used for the deposition of the polymers in thin films with specific properties for applications ranged from low k-dielectrics to membranes, light emitting electrochemical cells, anticorrosion and metallic polymers. Usually, the plasma polymers have extremely low electrical conductivity (>10(-12) S/cm) and only by chemical doping, the conductivity can be increased with few orders but the results are not concluded for applications. The usual methods in the plasma polymerization are not appropriate for doping such as the electrochemical and chemical one. To avoid these inconveniences a special design is proposed to induce doping simultaneous with plasma deposition of the polymers. This method has many similarities with electrospray ionization. This study reports the results in plasma polymerization of aniline (PPAni) close to emeraldine base and doped with p-toluene sulphonic acid (PPAniPTS) during the deposition. As-polymerized PPAni shows an electrical conductivity similar to2 x 10(-9) S/cm. The doping with p-toluene sulphonic acid (in very small amount) shows considerable changes in I-V characteristics and the electrical conductivity increases to similar to10(-7) S/cm. The conduction mechanism is space charge limited conduction (SCLC) and is governed by shallow and deep traps originated from sulphonic groups. The films have been characterized by FT-IR, Raman and AFM. (C) 2004 Elsevier B.V. All rights reserved.