Optical and microstructural properties of diamond-like carbon films grown by pulsed laser deposition

Diamond-like carbon films have been fabricated using 308 nm excimer laser ablation in vacuum followed by deposition at temperatures between 77 K and 573 K. Optical band gap energies are obtained from UV/optical spectroscopy. Raman spectra and X-ray photoelectron spectra (XPS) show that the sp³/(sp² + sp³) ratio in these films is in excess of 0.7 in films deposited at 77 K and 300 K. This ratio decreases to 0.2 in films deposited at 573 K. It is found that films deposited at cryogenic temperatures consist of a matrix structure assembled from embedded nanometer clusters, while films deposited at 300 K or higher temperature are amorphous and atomically flat. Microstructural features in cryogenic films are discussed in relation to the mechanism of deposition and possible phase transitions during assembly of these films.