A study of volatile organic compounds diffusion in thin plasma polymerized TEOS thin film

A sensor based on quartz crystal microbalance (QCM) coated by TEOS film has been developed for the detection of volatile organic compounds (VOCs), such as methanol, ethanol, acetone and chloroform vapors. Plasma polymerized tetraethoxysilane (ppTEOS) thin films deposited on quartz crystal microbalance (QCM) electrode were used as sensitive layer. The measured isotherms on modified QCM electrode showed a good reproducibility and reversibility. The frequency shifts (Δf) of the QCM were found to be linearly correlated with the concentration of VOC vapor. The ppTEOS film is found to be highly sensitive and selective to methanol vapor than other vapors. The diffusion process of different alcohols vapor was studied and diffusion coefficients (D) were calculated. It is concluded that the diffusion of the vapors into the ppTEOS film follows Fickian kinetics. Fourier transform infrared spectroscopy (FTIR) analysis revealed the presence of CH
_n
and OH groups in the film structure, which suggests the formation of porous and low dense structure, resulting in the promotion of VOC vapor diffusion into the film.