Optical and DC electrical properties of plasma polymerized quinoline thin films

Abstract

Plasma polymerized quinoline (PPQ) thin films were deposited onto glass substrate at room temperature by a capacitively coupled plasma polymerization system. The aims of the study are to explore the dc conduction mechanism, optical characteristics and structure-property relation of PPQ thin film. The thickness of the films was measured by Multiple Beam Interferometric method. The SEM investigation shows smooth, uniform, flawless and fracture free surface of the PPQ thin films. The differential thermal analysis (DTA) shows that a peak which reaches a maximum at around 673 K may be due to the removal of water content and the breaking bonds in the PPQ. The thermogravimetric analysis(TGA) shows the mass loss starts from 312 K. Major degradation occurs above 673 K. So it is seen from TGA, PPQ is observed to be stable up to about 600 K. The Fourier transform infrared spectroscopy (FTIR) observations show that the sharpness of the absorption bands decreases significantly in the PPQ thin films compared to that of Q because of hydrogen loss. Also there are shift of bands in the FTIR spectrum of PPQ. It is found that the chemical nature of the PPQ thin films deposited by plasma polymerization technique is departed to some extent from that of the monomer Q. From UV-vis spectroscopy it is found that indirect energy gap varies from 2.20 to 2.00 eV and direct energy gap varies from 3.50 to 3.30 eV with film thickness. The current density-voltage characteristics of PPQ thin films of different thicknesses have been studied at different temperatures. In the low voltage region, the conduction current obeys Ohm’s law and that in the higher voltage region the conduction mechanism in the PPQ thin films is Schottky/PF. For applied voltage 10 V (Ohmic), the activation energies are observed to be around 0.15 ± 0.07eV at the low temperature region and that at the higher temperature region is 0.75 ± 0.02 eV. While for applied voltage 30 V (Non-ohmic), the activation energies are observed to be around 0.18 ± 0.02 eV at the low temperature region and 0.86 ± 0.07 eV at the higher temperature region.