Optical and electrical properties of plasma polymerized cedar wood oil thin films

Abstract

Plasma polymerized organic thin films have recently attained considerable attention due to their widespread applications in the fields of electronics, optics, etc. The aims of the thesis are to study the optical and electrical properties of plasma polymerized Cedar Wood Oil (PPCWO) thin film. The uniform and pinhole-free PPCWO thin films were deposited at room temperature onto glass substrates by a parallel plate capacitively coupled glow discharge reactor. The thicknesses of the films were measured by a Multiple Beam Interferometric method. The thermal behavior has been investigated by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The TGA/DTA measurements indicate that the materials exhibit single-stage weight loss and thermal stability up to 505 K. The FTIR analysis reveals that the heat treated sample of PPCWO thin film does not have the chemical structure to that of the CWO monomer and the presence of carbon double bond group is detected. Ultraviolet-visible spectroscopic studies have been carried out on the as deposited and heat treated PPCWO thin films of different thicknesses. The effect of heat treatment on the optical properties of PPCWO thin films is significant. It is seen that the absorbance increases with the increase of the thickness and heat treatment temperature. An incresing trend is observed in the values of band gap. Thus it can be attributed that the band gap of the PPCWO thin films is dependent of thickness. The direct band gap of the PPCWO thin film decreases gradually with increasing heat treatment temperature used. The alternating current (AC) capacitance and conductance of PPCWO thin films in Al/PPCWO/Al sandwich structure were measured as functions of frequency (103<f<106 Hz) and of temperature (300<T<400 K). The AC conductivity, •ac, increases as frequency increases with a lower slope in the high frequency (above 1x105 Hz) region at all temperatures. The •ac is more dependent on temperature in the low frequency region than that in the high frequency region. The dielectric constant, ε′, decreases slowly with increasing frequency up to 20 kHz and then decreases very sharply in the high frequency region. The variation of ε′ and dielectric loss tangent with frequency which is related with multicomponent contribution of polarizability of the polar materials, as more or less all thin polymer films deposited by plasma polymerization technique.