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In this work, an active screen plasma discharge system based technology was incorporated in a PECVD reactor for DLC films growth, making it a new development in DLC films deposition. In this case, the active screen system is used to seek better electrons confinement, which might result in high ions density due to the collisions number increase, leading to a possible increase in ionization. DLC films were grown on steel substrates, using two variations of this system. In order to enhance adhesion between coating and substrate, a silicon interlayer was deposited, using different bias voltages. Morphological and structural characterization was performed by scanning electron microscopy, optical profilometry and Raman scattering spectroscopy. Tribological tests were performed by nanohardness, scratch and wear tests. Results showed that the plasma confinement promoted good films adhesion, which may be related to a high sub-implantation. This might be a consequence of the pressure decrease, as well as, to the ions energy distribution narrowing.

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This paper reports the efficacy of nonthermal plasma (NTP) as a biocidal agent to treat 304 stainless steel (SS304) covered with a diamond-like carbon (DLC) film contaminated with Candida albicans biofilms. The association of two techniques using electric plasma was used. The first was plasma-enhanced chemical vapor deposition (PECVD) used to deposit a DLC film on the SS304. The second was NTP used on the surface of the SS304 with and without the DLC film. The combination of the SS304 surface with the DLC film was demonstrated to be effective when using the DLC film as corrosion protection. Comparing the proliferation of Candida species on the DLC film and SS304 surface, it was possible to conclude that Candida species stays longer in the DLC film than in SS304. The reduction of colony numbers was visible after 5 min using plasma on both surfaces; in addition, 99% of Candida species were eliminated after 15 min. Three C. albicans microorganisms were used. Two were from samples of urine and tracheal secretion, and one was from the American Type Culture Collection (ATCC #90028). Characterization of the plasma chemical species was performed using optical emission spectroscopy in order to understand the nature of the chemical species that inactivated the microorganisms. The DLC film was analyzed using profilometry, Raman spectroscopy, scanning electron microscopy, and tribocorrosion tests. The tribocorrosion tests were used to evaluate the effectiveness of the DLC film in protecting the SS304 surface against corrosion in simulated body fluid because corrosion species from the SS304 could interfere in biofilm growth and mask the effect of the plasma. The results of the factorial analysis of variance confirmed the statistical significance (p > 0.05) of the plasma as a biocidal agent, considering the reduction of colony-forming units of C. albicans. It was found that exposure of the samples to the plasma for only 5 min resulted in reductions ranging from 96.4 to 100.0% for all the microorganisms studied.

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