Structural and thickness-dependent optical parameters of plasma polymerized 2-vinylpyridine thin films

Plasma polymerized 2-vinylpyridine (PP2VP) thin films have been synthesized under glow discharge using a capacitively coupled system. In the scanning electron microscope images, surface morphology of the PP2VP thin films is observed to be very smooth and crack free. Fourier transform infrared spectra of the thin films clearly indicate that structural change occurs during the polymerization process. The information about the electronic structure and the existence of both direct and indirect optical transitions in the PP2VP thin films have been ascertained by the ultraviolet– visible spectroscopic studies. The band gaps for the allowed indirect and direct transitions of the as-deposited PP2VP thin films are obtained as 1.82 ± 0.10 and 3.30 ± 0.03 eV, respectively. To understand the optical response of the PP2VP thin films elaborately, different optical parameters, such as extinction coefficient, Urbach energy, refractive index, steepness parameter, optical conductivity, etc. are estimated. (author)