Annealing temperatures induced optical constant variations of methyl violet 2B thin films manufactured by the spin coating technique

Spin coating technique has been successfully applied to deposit uniform methyl violet 2B (MV2B) thin films. X-ray diffraction and Fourier-transform infrared techniques were used to study the crystal and molecular structure of MV2B. The optical properties of the films have been studied by spectrophotometer measurements of transmittance and reflectance at normal incidence of light in the spectral range of 200–2500 nm. The absorption and refractive indices are independent of the film thickness. The absorption parameters such as molar extinction coefficient, oscillator strength and electric dipole strength have been reported before and after annealing. The type of electronic transition is indirect allowed transition with onset energy gap of 1.82 eV and optical energy gap of 3.65 eV. Annealing temperatures reduce structure disorder, remove trap level, increase values of the onset and optical energy gaps and decrease refractive index. The single oscillator model has been applied for calculating the dispersion parameters. The oscillator energy, the dispersion energy, the high frequency dielectric constant, the lattice dielectric constant and the ratio of free charge carriers' concentration to its effective mass were evaluated before and after annealing. The dielectric properties of the films were also determined.