Optical study of low energy ion-beam-assisted deposited diamond-like carbon films

Diamond-like carbon (DLC) films were prepared on single crystal silicon wafers by low energy ion-beam-assisted deposition (IBAD). The microstructure characteristics, thickness, optical band gap, sp3 fraction and so on, of these DLC films have been analyzed by infrared reflection, Raman and ultraviolet-visible optical spectroscopy experiments. It was found that the infrared reflectivity of the as-deposited DLC films depends on both the wave number and deposition conditions. The measured infrared reflection spectra were fitted by a Bruggeman effective medium approximation (EMA) method. The calculated spectra coincided very well with the experimental data, and it was demonstrated that the as-deposited DLC films were mainly composed of sp3 bonded carbon atoms. The Raman spectra showed a broad asymmetric band in the range of 1500-1580 cm-1, which is a typical characteristic of an amorphous diamond-like structure. The optical band gap of the DLC films was determined to be 0.54-1.0 eV from UV transmittance spectra. (orig.)