Enhanced optoelectronic and non-linear optical performance of plasma polymerized furan-2-carboxaldehyde-n-butylmethacrylate composite thin films via thermal annealing

This research explores the influence of thermal annealing (100 to 300°C) on the morphology, structural, electronic, dielectric, and optical properties of plasma-polymerized thin films synthesized from furan-2-carboxaldehyde and n-butyl methacrylate. The annealed thin films exhibit smoother, more homogeneous surfaces with uniformly distributed nanostructure granules (12.6 – 16.5 nm) and a higher carbon content (up to 77.05%) with a more pronounced C−C/C−H framework, resulting in enhanced structural stability. The fabricated thin films display excellent optical transparency (85 − 96%) in the visible region, except HT-300, while both the direct (3.51 – 3.01 eV) and indirect (2.45 – 1.81 eV) optical band gaps decrease with increasing annealing temperature. The annealed thin films also exhibit increased localized states and free charge carriers (6.8 ×10 57 – 2.28×10 58 m −3 kg −1 ), as evidenced by higher Urbach energy (0.46 – 0.83 eV), optical conductivity, refractive index (2.28 – 2.31), and plasma frequency (2.43×10 15 – 2.62×10 15 Hz). Both the oscillation (2.97 – 1.31 eV) and dispersion (11.29 – 1.8 eV) energies decrease with increasing annealing temperature, which may be attributed to enhanced electron transport between the electronic bands. The real dielectric constant exceeds the imaginary component, while increased optical electronegativity (1.81 – 2.01) after annealing indicates enhanced interaction of the thin films with incident radiation. This strengthened interaction induces a phase transition, leading to a reduction in the first-order (0.30 – 0.11) and third-order (2.67×10 −10 – 4.9×10 −11 esu) nonlinear susceptibilities. Therefore, the optical characteristics of PP(FC-BM) thin films can be effectively tuned by varying the annealing temperature, facilitating their application in sensing, nonlinear, and optoelectronic devices.