关键词: 低电压, 电化学沉积, 类金刚石碳膜, 不锈钢, 二甲基亚砜

Abstract:

Diamond-like carbon (DLC) films are receiving a lot of attention from the scientific community, thanks to the promise of DLC films for applications in microelectronics and optoelectronics. Usually, electrodeposition is the preferred common technique because of low cost, large deposition area and simplicity of the setup. However, when carbon films are electrodeposited on a stainless steel, high cell voltages (≥1000 V) are required owing to the low electric conductivity of the organic solvents. This work has developed a new electrolyte system that could achieve carbon deposition on a stainless steel under a low applied cell voltage. The DLC films were electrodeposited from 230 g·L^-1 formic acid and 17 g·L^-1 sodium formate in 1:1 (v/v) water-dimethyl sulfoxide mixture with the applied voltages ranged from 4.0 V to 8.0 V on the stainless steel substrate. The effects of the applied voltage on film morphology have been investigated. Dimethyl sulfoxide (DMSO) can broaden the electrochemical window of the solvents, inhibit hydrogen evolution and improve current efficiency. Nevertheless, the current efficiency was still low. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, probe surface profiler, and four-point probe resistivity tester were employed to analyze the structure, morphology, surface chemical composition, film thickness, and electric conductivity of the DLC films. It was found that the dense and uniform hydrogenated DLC films were successfully prepared on the stainless steel substrate. The film thickness was sensitive to the cell voltage and decreased with the increase in cell voltage. The Raman spectra of these films indicated the three broad peaks. Presences of D and G peaks near 1330 cm^-1 and 1570 cm^-1, respectively, revealed that the as-deposited films were typical DLC films. The average grain size and sp³ carbon content of the film increased with the increase in deposition voltages. The FTIR results showed that the peaks observed at 2850 cm^-1, 2920 cm^-1 and 2960 cm^-1 were related to the C-H symmetric and asymmetric stretching of CH₂ and CH₃ groups. Because of deionized water added in the solution, the infrared spectroscopic measurements supported that the DLC films were hydrogenated carbon films. The XPS results demonstrated that the two peaks for C1s at 284.5 eV and 285.2 eV with the comparatively lower intensity corresponded to C=C and C-C, respectively. The third peak at 288.5 eV may be associated with ester or carboxyl groups. The electric conductivity of the DLC film decreased with the increase in deposition voltage, falling between those of metal and semiconductor.

Key words: low voltage, electrochemical deposition, diamond-like-carbon films, stainless steel, dimethyl sulfoxide