Electrical and optical properties of plasma polymerized 2-furaldehyde thin film

Abstract

Monomer 2-furaldehyde (FDH) was used to obtain plasma polymerized 2-furaldehyde (PPFDH) thin films of different thicknesses on to glass substrates in optimum condition through glow discharge using a capacitively coupled parallel plate reactor. The thickness of the plasma polymerized films deposited on glass substrates was measured by using multiple-beam interferometric method. The surface morphology of the PPFDH thin films was found to be smooth, flawless and homogeneous. The PPFDH thin films showed highest percentage of Carbon (C) with small percentage of Oxygen (O) in the energy dispersive analysis of X-Ray spectrum. The structural analysis of PPFDH by Fourier transform infrared spectroscopy indicate that structural rearrangements occur may be due to the removal of bonds and it contains certain amount of conjugation. The thermogravimetric analysis (TGA) of PPFDH shows that the PPFDH is stable up to 520 K. The differential thermal analysis shows an exothermic broad band which has a maximum centered around 600 K indicating a gradual change of its original properties. The corresponding TGA trace shows a uniform weight loss up to 760 K. Ultraviolet visible (UV-vis) spectral of PPFDH thin films showed that the absorbance increases with the increase. From the Uv-vis absorption spectra, absorption co-efficient (•), allowed direct (Eqd) energy gap, allowed indirect (Eqi)energy gaps, Urbach energy (EU The current density (J)-voltage (V) characteristics at different temperature (T) follow a power law of the form J • V) and steepness parameter (σ ) were determined and found to be between 3.23-3.31 eV, 2.09-2.30 eV, 0.51-0.61 eV and 0.042-0.050 respectively for PPFDH thin films of different thicknesses. n . In the low voltage region the values of n are 0.80 ≤ n ≤ 1.12 and that in the high voltage region lies between 1.91 ≤ n ≤ 2.58, indicating Ohmic conduction in the low voltage region and non-Ohmic conduction in the high voltage region. Theoretically calculated and experimental results of Schottky (βs) and Poole-Frenkel (βPF) coefficients show xiii that the most probable conduction mechanism in PPFDH thin films is Schottky type. From the Arrhenius plots of J vs. 1/T for the applied voltages 5 and 35 V, the activation energies (Δ E) were calculated. For 5V, it is about 0.13 ± 0.02 and 0.50 ± 0.05 eV in the low and high temperature region respectively. For 35V, it is found to be around 0.11 ± 0.01 eV and 0.55 ± 0.02 eV, respectively in low and high temperature region.