Characterization of hydrogenated diamond-like carbon films electrochemically deposited on a silicon substrate

Diamond-like carbon (DLC) films were deposited on a Si substrate by electrolysis in a methanol solution at ambient pressure and low temperature. The morphology and microstructure of the resulting DLC films were analysed using atomic force microscopy, Raman spectroscopy, Fourier transformation infrared spectrometry, x-ray photoelectron spectroscopy (XPS), and x-ray excited Auger electron spectroscopy (XAES). The surface energy and mechanical properties of the DLC films were examined, and the growth mechanism of the DLC films in liquid phase electro-deposition is discussed as well. The results of the study show that the hydrogenated diamond-like carbon films are smooth and compact. The percentage of sp(3) carbon in the DLC films is determined as 55-60%, based on the corresponding XPS and first-derivative XAES spectra of graphite, diamond, and the tested films. The DLC films show low surface free energy, good mechanical properties, excellent friction-reduction and wear-resistance. It is suggested that methanol dissociates to generate the active species of CH3+ and C2H4 at high voltage applied to the electrode, followed by the generation of the alkyl chain [-CH2-CH2-](n) whose C-C and C-H bond lengths and C-C-C and H-C-H bond angles are close to that of diamond. Subsequently, a diamond-like structure was formed by the ordered dehydrogenation of a short-chain [-CH2-CH2-](n) in the electrolysis process.