Abstract:
Plasma polymerized N, N, 3, 5 tetramethylaniline (PPTMA) thin films were deposited
on to glass substrates at room temperature by a capacitively coupled parallel plate
reactor. The as-grown PPTMA thin films were characterized by elemental analysis
(EA), infrared (IR) spectroscopy, differential thermal analysis (DTA)/
thermogravimetric analysis (TGA), ultraviolet-visible(Uv-vis) spectroscopy and dc
electrical measurements.
The EA and IR spectroscopic analyses indicate that the PPTMA is chemically and
structurally different from that of the N, N, 3, 5 tetramethylaniline (TMA) monomer.
The empirical formula of the PPTMA film is C7.70HIO,JoN1.5000.80' The structural
investigation reveals that PPTMA thin films may be formed with certain amount of
conjugation. The DTA/TGA analyses shows that the degradation in the structure and
evaluation of gases may occur temperatures between 373 to 873K most probably due
to dehydrogenation and oxidative reactions in the thin films. It is observed that the
PPTMA films are thermally stable up to about 505 K. From the Uv-vis absorption
spectra, allowed direct transition (Eqd),allowed indirect transition (Eqi) energy gaps,
Tauc parameter, B and extinction coefficient were determined. The Eqdand Eqi are
2.80 and 1.44eV respectively. The value ofB is 188cm'l/2 (eVr1l2.
The current density-voltage(J-V) measurements were performed on the PPTMA thin
films of different thicknesses in a aluminium/PPTMA/aluminium configuration over 0
to 13 V and temperature range from 300 to 450 K. The J-V characteristics ofPPTMA
showed a power law dependence, J 00 Vn
, with a lin~ar behavior (n ""I) at the lower
voltage region followed by a non ohmic dependence with an exponent about 2 at
higher voltage region. These results emphasize that the conduction mechanism is
space charge limited (SCL) conduction. Measurements of current density as a function
of temperature at constant applied voltages yielded different activation energies. The
values obtained are 0.81 :t 0.02 and 0.85 :t 0.05 eV for 2(ohmic) and 10 V( non
ohmic) in the high temperature region respectively and 0.19:t 0.01 and O.l9:t 0.02 eV
in the low temperature region respectively. The conduction in PPTMA may be
dominated by hopping of carriers between the localized states at low temperatures and
thermally excited carriers from energy levels within the band gap in the vicinity of
high temperature.
