Direct current electrical conduction mechanism and optical properties of plasma polymerized o-methoxyaniline-N,N,3,5-tetramethylaniline composite thin film

Abstract

Plasma Polymerized O-Methoxyaniline-N,N,3,5-Tetramethylaniline (PP(OMATMA)) composite thin films of different thicknesses were prepared by a capacitively coupled glow discharge plasma reactor at room temperature. The composite liquid material was prepared by mixing equal volume ratio of Ortho-methoxyaniline and N,N,3,5-tetramethylaniline monomers. Under a suitable condition, the composite monomer vapor was produced and introduced into the reactor. During polymerization the power of the glow discharge was kept constant and deposition time was varied to get thin films of different thicknesses. The thickness of the plasma polymerized films deposited on chemically cleaned glass substrates was measured by using multiplebeam interferometric method. The differential thermal analysis (DTA) trace showed an exothermic increase up to about 575 K and then levels off where the TGA shows a decrease in weight (%) in 3 stages. Thus the thin films are observed to be stable up to about 575 K. The gradual fall of TGA may be a cause of thermal breakdown of PP(OMA-TMA) structure and expulsion of oxygen containing compounds. The dependence of absorption coefficient () on the photon energy indicates that the absorption edge starts increasing around 2.25 eV and there is a rapid rise in  from 2.80 eV. The indirect and direct band gap of the PP(OMA-TMA) thin films in the range 2.13 to 2.80 eV and 3.13 to 3.73 eV respectively for samples of different thicknesses. As the thickness of the films increases electronic transition occurs from more depth of the samples which need more energy. It is found that the peak wavelength shifts to lower wavelength for thin films with higher thickness. It is observed in the current density - voltage (J-V) characteristics of PP(OMA-TMA) thin films that the current density increases nonlinearly with the applied voltage. It is found that the current density ohmic in the low voltage region and in the high voltage region the current density is nonohmic. The slope of the J-d plot ascertains in the higher voltage region that the type of charge conduction in PP(OMA-TMA) composite thin films is SCLC. Temperature dependence of J shows that there is hopping conduction in the lower temperature region and that is thermally activated in the higher temperature region.