Study of the optical and DC electrical properties of plasma polymerized thin films of diethylaniline

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.