Study of optical and electrical properties of plasma polymerized 1,2-diaminocyclohexane thin films synthesized by AC and RF power source

Abstract

Smooth, transparent plasma polymerized (1,2-diaminocyclohexane) (PPDACH) thin films have been prepared on to glass substrates under AC (50 Hz) and RF (13.56 MHz) plasma using a capacitively coupled reactor. RF plasma deposited PPDACH thin films are observed smoother compared to AC plasma deposited thin films, which is confirmed from the atomic force microscopy images. However, mosaic-like structure is observed in the AC plasma deposited films, which are thermally more stable (up to ~280 C) compared to RF deposited thin films. The at% of C and N in the thin films increases with increasing film thickness. Appearance of new absorption peaks in the FTIR spectra confirms structural changes in the plasma polymer owing to the degradation or re-organization of the monomer molecules during the plasma polymerization. The direct band gap values of the PPDACH (AC) thin films increase from 3.02 to 3.15 eV with the increase of film thickness, while nearly equal (~ 4.04 eV) for the RF PPDACH thin films. Schottky type electrical conduction mechanism is observed to be dominant in the PPDACH (AC) thin films, whereas space charge limited conduction is operative in the PPDACH (RF) thin films. Other optical parameters such as refractive index, extinction coefficient, Urbach energy, steepness parameter are also calculated to understand their applicability in different electronic and optoelectronic devices like optical coating, photovoltaic cells, etc.