Abstract:
Plasma polymerized organic thin films have recently attained considerable attention due to
their extensive application in the fields of electronics, optics. Our present investigation aims
at to study the dc electrical conduction mechanism (rom the ~oltage, thickness and
temperature dependent current density measurements and structure-property relation of
plasma polymerized 2, 6, diethylaniline (PPDEA) thin film. The uniform, pinhole-free
PI'DEA thin films were deposited at room temperature onto glass substrates by a parallel
plate capacitive!y coupled glow discharge reactor. The thicknesses of the films were
measured by Multiple Beam Interferometric method. The structure, surface morphology,
and compositions ofl'l'DEA thin tilms were characterized hy scanning elcctron microscopy
(SEM), encrgy dispersive X-ray (EOX) analysis, and Infrared (lR) spectroscopy. The
optical properties of the thin films were investigated by Ultraviolet visible (UV-vis)
absorption spectroscopic analysis.
In SEM analysis, a smooth, flawless and pinhole free surface was observed for PPOEA thin
films. No significant changc •• vas observed in PPOEA thin films of different thicknesses.
The EOX analysis indicated the presence of C, Nand 0 in the samples. The presence of 0
in PPDEA which is not prescnt in DEA implies incorporation of carbonyl and hydroxyl
groups through the reaction of the free radicals. IR analysis reveals that the PPDEA thin
film deposited by plasma polymerization technique does not exactly resemble to that of the
OEA monomer and the presence of carbonyl group is detected. The absorption coefficient
a, at various wavelengths was calculated using the UV-vis data. The direct transition energy
Eg(d)and indirect transition energy Eg(j) were obtained by extrapolating the linear portion of
the plots of (uhyi vs hv and (a:hy)1!2vs hv respectively to intercept the photon energy axis.
The current density-voltage (J-V) characteristics ofPPDEA thin films of difTerent thickness
havc been studied at different temperatures. In the low voltage region, the conduction
current obeys Ohm's law while the charge transport phenomenon appears to be electrode
limited Schottky type conduction in the higher voltage region. The temperature dependence
of the current density for different bias voltages was also investigated. From the arrhenius
plots of J vs. 1fT, it is found that the activation energies (ilE) decrease as the bias voltage
increases. The activation energies are about 0.10:t 0.03 eV and 0.20:l: 0_05 cV at the lower
temperature region and about 0.69:t 0.06 eV and 0.63:l: 0.03 cV at the higher temperature
region for 8 and 14 V respectively. The low activation energy in the low tempcralllre region
and the higher activation energy in the higher temperature region may be attributed to a
transition from a hopping regime to a regime dominated by distinct energy levels.
