Characterization of diamond-like carbon by Raman spectroscopy, XPS and optical constants

Crystalline diamond coatings and, increasingly, diamond-like amorphous carbon (DLC) films are used for tribological and protective layers for their hardness and chemical inertness. They are also under investigation for their electron emitting properties, with possible applications in field emission displays. In this study, hydrogen-free DLC films were deposited by laser ablation using a KrF excimer laser and fluences between 0.5 and 2 J/cm2. Information about the disorder and short range order in the films was gained via Raman spectra. As the ratio of graphitic and diamond bonds (sp2 and sp3) is often hidden in these measurements, other analytical methods have to be included. XPS spectra exhibit for certain films the presence of sp3 bonds or graphitic growth. For a better determination of the sp3-content, a correlation with optical properties in the near IR to near UV region was established. These values depended strongly on the substrate temperature and the laser fluence. DLC formation with large sp3 contents could be demonstrated without substrate heating. Vickers hardness values and measurements on the electron emissivity of the films are strongly correlated to the sp3 content and the preparation method of the films.NRC publication: Ye