Doping DLC coatings for tailored technical solutions

Abstract

Diamond-Like Carbon (DLC) films have been extensively applied in different fields due to their attractive mechanical, chemical, and tribological properties. The characteristics of the DLC films can be significantly enhanced by the presence of other elements in their structure, with the expansion of its applicability in the space and health areas. In this work the films were grown via two different systems, a Plasma-Enhanced Chemical Vapor Deposition (PECVD) modified with an additional cathode and a combined PECVD/Physical Vapor Deposition (PVD) process. For the incorporation of other elements into the film matrix, a suspension of the particulate material in water or hydrocarbon liquids was used for the PECVD process, and a metal target was used for the PECVD/PVD depositions. The unique properties of the film made it possible to study several application possibilities for this material. Thus, diamond nanoparticles, B, Zn, Cu, Ag, and Ni-based materials were incorporated into the DLC structure to tailor the properties of the films to be applied as a sensor material, antimicrobial, and tribological coating. Therefore, the piezoresistive, antimicrobial, cytotoxicity, tribological, and mechanical properties of the films were studied and analysed as a function of different parameters. In the sensors field, sputtered strain gauges have several advantages in comparison with the classic strain gauges, such as the direct application of the sensor to the component and better measurement accuracy. Particularly, incorporating metals into DLC films ensures thermal compensation combined with high sensitivity. Herein, DLC films with Ni-based materials were studied to be applied as strain gauges and different process parameters were investigated, such as working pressure, substrate bias voltage, and film composition. The results indicated that the incorporation of metals in the DLC structures showed a high strain sensibility and a zero crossing of the Temperature Coefficient of Resistance (TCR). Furthermore, in the biomedical area, the addition of metals in the DLC (Me-DLC) matrix has been investigated to obtain a material with antimicrobial properties and biocompatible. Thus, Zn, Cu, and Ag were incorporated in the DLC matrix via a High-Power Impulse Magnetron Sputtering (HIPIMS)/PECVD process to be applied as an antimicrobial coating on textile surfaces. In addition, the antimicrobial effectiveness of the material was studied against a Gram-negative bacterium (Escherichia coli), a Gram-positive bacterium (Staphylococcus aureus), and a fungus (Candida albicans). The films showed excellent results against all microorganisms, with 100% effectiveness in some cases. However, the pure extracts obtained from all the samples with metals were cytotoxic. Despite that, the cell viability after contact with some Me-DLC diluted extracts (10%) was not different from that observed in the uncoated group. Besides, the influence of the incorporation of diamond nanoparticles, boron, and metals into the DLC was investigated. Therefore, the coefficient of friction and wear resistance of the films as a function of their composition was studied. Thus, this work shows the incorporation of metallic and non-metallic materials in the DLC structure to tailor the properties of the films to different industrial application fields.