Adhesion of Amorphous Carbon Nanofilms on Ferrous Alloy Substrates Using a Nanoscale Silicon Interlayer: Implications for Solid-State Lubrication

The low adhesion of amorphous carbon (a-C) films on ferrous alloys has restricted massive industrial application since their development, restricting application to mechanical and electromechanical components. Although different mechanisms have been raised to describe the a-C film adhesion, the chemical affinity and the role of oxygen at the interfaces are the key issue. Nevertheless, a quantitative approach considering the oxygen adsorption and the adhesion strength/base pressure relationship is still not proposed, which would be of special interest in industry. In this study, we analyze the influence of the base pressure on the adhesion of amorphous carbon (a-C) films onto a ferrous alloy intermediated by a nanometric silicon interlayer. The different base pressure deposition resulted in different adhesion of the films. By means of structural and chemical techniques, the oxygen content at the interfaces was quantified and correlated with the base pressure before thin film deposition. We propose a quantitative physicochemical model that correlates the a-C film adhesion with oxygen located at the interfaces, which is indirect evidence of its previous presence in the deposition chamber, as a fraction of the residual gases from the base pressure. As adhesion depends on oxygen content, we used the Langmuir isothermal law to evaluate this dependence with good agreement. This model may be of potential interest in plasma surface engineering and process automatization not only for carbon-related materials deposited on metals, mainly in its potential use as a solid lubricant.