Detailed investigation of optoelectronic and microstructural properties of plasma polymerized cyclohexane thin films: Dependence on the radiofrequency power

Abstract

Optical properties of polymerized cyclohexane films deposited by radiofrequency plasma enhanced chemical vapor deposition technique at different radiofrequency powers onto glass and silicon substrates, are studied and correlated with the microstructure of the films, using a combination of atomic force microscopy, Raman and Fourier Transformer Infrared spectroscopy and optical measurements. The optical constants such as refractive index n, dielectric permittivity ε and extinction k and absorption α coefficients, are extracted from transmission and reflection spectra through the commercial software CODE. These constants lead, by using common theoretical models as Cauchy, Lorentz, Tauc and single effective oscillator, to the determination of the static refractive index ns and permittivity εs, the plasma frequency ωp, the carrier density to effective mass ratio N/me*, the optical conductivity σoc, the optical band gap Eg and the oscillation and dispersion energies E0 and Ed, respectively. We find that n, εs, ωp, N/me*, Ed, increase with radiofrequency power, while Eg and E0 decrease in the same range of power. These results are well correlated with those obtained from atomic force microscopy, Raman and infrared measurements. They also indicate that the increase of the radiofrequency power promotes the fragmentation of the precursor and increases the carbon C-sp2 hybridization proportion, which results in an improvement of the optoelectronic properties of the films.