Influence of Ne sputtering gas on structure and properties of diamond-like carbon films deposited by pulsed-magnetron sputtering

The key process in diamond-like carbon (DLC) film deposition is the formation of sp3-C hybridized bond, which is believed to significantly link to the ionization degrees of the carbon atoms. Ne has a high ionization energy and can facilitate the ionization degree of sputtered carbon. In this paper, Ne and Ar gas mixture was used as the sputtering gas to prepare DLC film by using a pulsed-magnetron sputter. The influences of the Ne fraction in the sputtering gas mixture on the growth character, carbon bond structure, residual stress and mechanical properties of the as-deposited DLC films were studied carefully by using scanning electron microscope, Raman spectroscopy, stress tester and nano-indentation, respectively. The results reveal that the introduction of Ne in sputtering gas mixture can induce the structure densification of the coatings, and significantly increase the sp3 fraction of the DLC films. However, it was found that the sp3 fraction of the films increased little as the Ne fraction exceeded 25%. This phenomenon might be attributed to the reduction of the electron density of the plasma due to the increase of the Ne fraction in the sputtering gas mixture. The residual stress of the DLC films was believed to depend on the sp3 fraction of the films, and thus exhibited a similar changing trend to sp3 fraction as a function of Ne fraction. However, the hardness and elastic modulus of the films increased continuously as the Ne fraction increased. The structure densification and the increase of the sp3 fraction caused by the addition of Ne may be the main factors contributed to the increase of the hardness and elastic modulus of the films.