Understanding the enhancement of the optical and electronic attributes of iodine-doped vacuum deposited tetramethylaniline (PPTMA) thin film coatings

Highlights: • I-doped plasma polymerized N, N, 3, 5 tetramethylaniline (PPTMA) thin films were coated onto glass substrates. • I-doping did not alter the amorphous nature of the as-coated PPTMA thin films. • The surfaces of the I-doped PPTMA thin films were found much smoother than as-coated PPTMA thin films. • Structural reorientations observed were occurred in the as-coated PPTMA thin films owing to the I-doping. • I-doping reduced the E_g and E_U, while the steepness parameter of the PPTMA thin films was increased. -- Abstract: This article presents a comprehensive analysis on vacuum deposited Iodine-doped plasma polymerized monomer N, N, 3, 5 tetramethylanilin (PPTMA) thin film coatings to comprehend the structural, morphological, chemical, optical, and electronic properties. The as-deposited PPTMA thin film coatings were characterized by means of X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), energy dispersive X-ray (EDAX) spectroscopy, and ultraviolet-visible spectrophotometry, respectively. The amorphous nature of the PPTMA thin film coatings was established via XRD analysis. The surfaces of the PPTMA thin film coatings were observed to be smooth and uniform. The IR studies pointed out that the I-atoms get connected to amine nitrogen sites of the TMA structure. The absorption peaks detected at 1683 and 1577 cm⁻¹ indicated the existence of aromatic ring stretching, and the CC stretched vibrations due to the I-doping into the PPTMA thin film coatings. It was further noticed that the iodine doping resulted the NH, CN stretching vibrations shifting towards higher wave number sides of 3384 cm⁻¹, and 1384 cm⁻¹ respectively. In a similar fashion, the optical absorption peaks were also shifted towards the longer wavelength sides (from 300 nm to 380 nm). The direct energy band gaps of the PPTMA coatings were decreased 3.20–3.04 eV with increasing I-content. Similar types of behaviors were also observed for the indirect energy band-gaps and Urbach energy values of the PPTMA thin film coatings. However, the refractive index, high frequency dielectric constant, and static dielectric constant were gradually increased with the monotonic increase of coatings thickness due to subsequently enhanced I-content.