IR spectroscopic and photoluminescence studies of plasma polymerized organic thin films based on tea tree oil

Abstract

Plasma-assisted synthesis of transparent, environment friendly, lightweight, flexible and stable organic thin films from naturally occurring precursors were emerging as potential candidates for organic semiconductor industry. In the present study, tea tree (Malaleuca alternifolia) oil based polymer thin films were deposited on glass and silicon substrate by using radio frequency plasma polymerization technique. The polymer thin films were characterized with atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy techniques. AFM images indicate the formation of homogenous film on the substrate surface. FTIR spectra gives bands related to methyl and methylene groups which confirms the formation of chain branching in the polymer films. Relatively intense infrared (IR) bands obtained from films deposited on glass substrate reveals that glass substrate is more favourable for the growth of polymers than silicon substrate. Optical band gap of the polymerized thin film on glass substrate was estimated using Tauc plot which gives a value of 3.19 eV, indicating the semiconducting nature of the material. Photoluminescence (PL) emission in the yellow region were observed from both the samples and its CIE colour coordinates also matches with yellow emission. Broad visible emission observed in the wavelength range 465-695 nm indicates the presence of multichromophores in the polymer film. Samples also gives IR emission in the wavelength range of 850-1090 nm, upon excitation with a wavelength of 785 nm contributed to polaronic transitions.

Plasma polymerization of biogenic precursors

“…IR spectroscopy showed that band maxima shifted depending on the substrate used, indicating a variation in bond lengths depending on the substrate and showing that amorphous glass substrates are better scaffolds for plasma polymer growth than crystalline silicon substrates. [ 91 ] Bazaka et al were the first to examine the effects of plasma treatment with Ar APPJ on thin films from tea tree oil plasma polymers upon PET substrates. Compared to as‐deposited plasma polymers, APPJ‐treated plasma polymers showed increased surface oxidation, with three potential oxygen sources being: fragments of oxygen moieties from retained precursor molecules, coating exposure to ambient air and reactions between Ar plasma and ambient air.…”