Porous Diamond-Like Carbon Nanolayers with Excellent Anti-Corrosion and Barrier Performance

Keywords:
DLC, corrosion, density, Si-incorporation

Abstract:
We investigated the surface modification of Al2O3-TiC substrates using Si-incorporated hydrogenated amorphous carbon coatings (Si-aC:H) synthesized by radio frequency plasma enhanced chemical vapor deposition (PECVD). The precursor gas was a mixture of C2H2/Ar plasma and tetramethylsilane (TMS). We have demonstrated that TMS-incorporation causes a massive reduction in the density and a complete elimination in of the films’ residual-stress. Also, a hydrogenation process was established by ERDA technique. The increased hydrogen concentration associated with the TMS precursor was responsible for a rise in density of voids and an associated reduction in the connectivity (i.e., porosity) and stress release of the carbon network. In contradiction to the dramatic reduction in density and increase density of voids in the films, TMS-incorporation also led to significant improvements in the corrosion resistance of Al2O3-TiC substrates. The electrochemical impedance spectroscopy (EIS) showed an increase in the charge transfer resistance and reduction in the anodic current of the polarization curves. The reason for the enhanced corrosion resistance is thought to be related to the formation of charge-denuded layer that forms by a reaction between the porous Si-aC:H and either air or the aqueous solution. In summary our results contradict the concept that high density coatings are expected to display good corrosion and gas barrier performance.

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Nanotech 2006 Conference Program Abstract