Low-temperature synthesis of highly transparent carbon nitride thin films

Highly transparent carbon nitride thin films have been prepared on transpar ent plastic substrates at low temperatures by radio frequency reactive magn etron sputtering of a graphite target in the plasmas of pure nitrogen and n itrogen-hydrogen gas mixtures. The amorphous films thus obtained have been characterized for their optical transmittance by spectrophotometry, reveali ng a very high transparency in the visible region of the spectrum. The chem ical composition and bonding states of a sample studied by x-ray photoelect ron spectroscopy (XPS) showed that nitrogen has been predominately bonded t o sp(3)-hybridized carbon, in addition to a small amount of sp(2)-hybridiza tion. The elemental concentration was measured to be C=51.1 at.%, N=43.2 at .%, and O=5.7 at.%. The N/C ratio for the N-sp(3)C component is calculated to be 1.29, close to the expected stoichiometric value of 1.33 for beta-C3N 4. Compared to the unhydrogenated C-N thin films, the hydrogenated samples exhibited increased optical transmittance, about 90% in the whole of the vi sible spectrum. Such transmittance characteristics of the hydrogenated C-N films closely matched those exhibited by the plastic substrate.