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.
