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.
