Abstract:
Plasma polymerized o-methoxyaniline (PPOMA) thin films of different
thickness were prepared in glow discharge plasma using a parallel plate capacitively
coupled polymerization reactor. The PPOMA thin films shows smooth, flawless and
homogeneous surface together with the content of carbon (63 %) oxygen (24 %),
nitrogen (8 %) and others (5 %). Fourier transform infrared spectrum reveals a decrease
of absorption intensity and disappearance of some absorption peaks for PPOMA as
compared to that of OMA, indicating the polymer formation from the monomer. The
differential thermal analysis showed a peak at around 350 and 700 K which may be due
to the removal of water content and the breaking of bonds in the PPOMA respectively.
The thermogravimetric analysis shows the onset of weight loss from 540 K, which may
be due to the loss of low molecular mass hydrocarbon gases. The ultraviolet-visible
spectroscopy shows that the allowed indirect and direct band gaps for as deposited
PPOMA thin films of 100 – 300 nm thickness have the values in the range 1.65-1.76
eV and 2.94-3.30 eV, respectively. Both the energy gaps showed a slight increase for
100 – 125 nm and above this range the gaps remain almost constant. From the plot of
alternate current electrical conductivity (σac) versus frequency, the value of ‘n’ is
calculated using the relation n
ac () A . In the low frequency range (0.1-1 kHz) the
value of ‘n’ is 1 which indicates Debye type conduction and in the higher frequency
range (1- 100 kHz) ‘n’ is > 1 which indicates non-Debye type conduction. The
observed mechanism of carrier conduction in PPOMA films at low frequencies is due
to hopping of carriers between the localized states. At the low frequency region (0.1 -
20 kHz), the change of dielectric constant, ′ at low temperature exhibits the nature of
‘static’ dielectric constant and the decrease of ′ at higher temperature may be due to
the interfacial polarization. The loss factor, tan increases with the increase in
frequency having a peak above 100 kHz for all the PPOMA films of different
thickness. Cole-Cole plot between real and imaginary dielectric constant exhibits single
relaxation mechanism in PPOMA thin films and the sample become more resistive with
the increase in film thickness and temperature.
