Studies of the DC electrical conduction mechanism and optical properties of plasma polymerized o-methoxyaniline thin film

Abstract

Plasma polymerized o-methoxyaniline (PPOMA) thin lms of di erent thicknesses were synthesized at room temperature on to glass substrates using a capacitively coupled plasma polymerization reactor. The thicknesses of the PPOMA lms were measured by multiple-beam interferometric method. A smooth and awless surface of PPOMA thin lms was observed from the surface morphology observation through the Field Emission Scanning Electron Microscopy. The topological information through the Atomic Force Microscopy analyses revealed that the surface roughnesses of PPOMA thin lms were reasonably low ( 1 nm). The chemical analyses through the Energy dispersive X-ray Spectroscopy report con rmed that the PPOMA thin lms consisted of a dominant proportion of carbon along with a small portion of oxygen and nitrogen. The structural analyses through the Attenuated Total Re ectance Fourier Transform Infrared analyses showed changes in the chemical structure (bonds) of PPOMA thin lms compared to those in o-methoxyaniline. Di erential Thermal Analyzer (DTA) and Thermogravimetric Analyzer (TGA) were used for the thermal analyses of the PPOMA thin lms in oxygen and nitrogen environments. The DTA curve showed the two-stage degradation reaction in oxygen environment indicating the maximum weight loss at the temperature of 790 K, whereas a single-step reaction in nitrogen environment showed the maximum weight loss at the temperature of 683 K. The TGA curves showed that the PPOMA was thermally stabler up to the temperature of around 507 K in both the environments. It also revealed that the weight loss (around 70%) of PPOMA is signi cantly larger in oxygen environment compared to that (around 27%) in nitrogen environment, up to the temperature of 823 K. The optical analyses were carried out through the Ultraviolet-visible spectroscopic analyses. The average values of direct and indirect transition energies were obtained as 3.25 ( 0:10) eV and 1.70 ( 0:20) eV respectively. The direct current electrical measurements of PPOMA thin lms indicated that the conduction current obeys Ohm's law in the low voltage region (< 10 V) while it shows non-ohmic nature at the high voltage region (> 10 V). The dominant type of conduction mechanism was found as the space charge limited conduction type through the analysis of the dependence of current densities on thicknesses of the PPOMA thin lms. The activation energies were calculated for low and high applied voltages, at low and high temperatures in both cases. Finally, the possible applications of the PPOMA thin lms are brie y suggested.