Effect of heat treatment on the structural and optical characteristics of plasma deposited 2-(diethylamino)ethyl methacrylate thin films by a capacitively coupled glow discharge plasma system

Abstract

This paper reports the effect of post-deposition heat treatment on the optical and structural properties of plasma polymerized 2-(diethylamino)ethyl methacrylate (PPDEAEMA) thin films. SEM confirm that both as-deposited and heat treated PPDEAEMA thin films are uniform and pinhole free. Differential thermal analysis and thermogravimetric analysis demonstrate the decomposition and mass loss of PPDEAEMA, respectively, and PPDEAEMA is stable up to 550 K. The Fourier transform infrared spectroscopic investigation indicates the presence of the –CH2– group in as-deposited PPDEAEMA and heat treated PPDEAMEA. The absorption coefficient, allowed direct transition, Eqd, and allowed indirect transition, Eqi, energy gaps were determined from the ultraviolet–visible absorbance spectra and thus the Urbach energy, steepness parameter and extinction coefficient were calculated. Eqd and Eqi decrease with an increase in thickness and are found to be about 3.25–3.45 and 1.65–1.90 eV, respectively, for as deposited PPDEAEMA thin films of different thicknesses. The effect of heat treatment on the optical properties in relation to structural changes of PPDEAEMA is also discussed. As temperature increases, both Eqd and Eqi decrease. The Urbach energy Eu of the PPDEAMEA thin films increases with the increase in film thickness and heat treatment temperature. The steepness parameter β decreases with thickness and heat treatment temperature.