Gas-phase and film analysis of hydrogenated amorphous carbon films: Effect of ion bombardment energy flux on sp² carbon structures

Hydrogenated amorphous carbon (a-C:H) films comprise nanoclustering graphites (nc-G), fused aromatic rings (nR), and olefinic chain clusters (nC) of sp²-bonded carbons in an sp³ matrix. In this study, the sp² composition of the nc-G, nR and nC in a-C:H films is found to be determined by the ion bombardment energy flux (Γ_Ei), which can be estimated as the product of ion bombardment energy and ion flux onto the deposited surface, in plasma-enhanced chemical vapor deposition using a plasma mixture of H₂ and CH₄ gases with the H radical injection method. The sp² composition is analyzed using Raman spectroscopy and near-edge X-ray absorption structure spectroscopy. a-C:H becomes increasingly graphitized with increasing Γ_Ei. The precise control of the sp² C structure composition can be achieved by controlling the very-high-frequency input power and radio frequency input bias power via the ion flux and ion bombardment energy.