Synchrotron-based spectroscopic analysis of diamond-like carbon films from different source gases

Diamond-like carbon (DLC) films were deposited using the pulsed plasma-enhanced chemical vapor deposition (PECVD) method with different source gases such as methane (CH4), acetylene (C2H2), acetylene with methane (C2H2:CH4), ethylene (C2H4), and ethylene with methane (C2H4:CH4). The chemical characteristics of these DLC films were investigated using suitable spectroscopic techniques. Raman spectroscopy analysis illustrated decrease of the I-D/I-G ratio with the addition of CH4. Importantly, X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy not only enabled evaluation of the relative content of sp(2) and sp(3), but also clarified the chemical bonding of the films with different source gases. The XPS results showed lower sp(2) content than the NEXAFS results. Moreover, glow discharge optical emission spectrometry (GD-OES) illustrated increase in the hydrogen content, which is in good agreement with increase of the sp(3) content based on Raman, XPS, and NEXAFS analyses. Consequently, the synthesis and characterization indicate a significant role for differences of chemical composition of the films. The study described herein provides useful information for preparing high-quality DLC films, as well as for evaluating appropriately the distribution of the carbon sp(2)/(sp(2) + sp(3)) ratio and the hydrogen content in the films with different source gases.