Amorphous fluorohydrogenated carbon layers are deposited on silicon and glass substrates using an expanding thermal are plasma, burning on argon with a fixed flow (3 standard cm(3) s(-1)) of acetylene and a varying Bow (0-2.9 standard cm(3) s(-1)) of tetrafluoromethane. The layers deposited are analyzed in situ by means of ellipsometry and ex situ by means of Fourier transform infrared spectroscopy, transmission of visible light, scanning electron microscopy and atomic force microscopy. It is found that the growth rate of the layers is independent of the CF4 flow added to the plasma. No dramatic variation in the refractive index, extinction coefficient and optical bandgap is observed with changing CF4 flow. The molecular bonding structure is influenced by the addition of CF4, suggesting that the layers are modified by the addition of CF4.