Antimicrobial and Aging Properties of Ag-, Ag/Cu-, and Ag Cluster-Doped Amorphous Carbon Coatings Produced by Magnetron Sputtering for Space Applications.

Inside a spacecraft, the temperature and humidity, suitable for the human crew onboard, also creates an ideal breeding environment for the proliferation of bacteria and fungi; this can present a hazard to human health and create issues for the safe running of equipment. To address this issue, wear-resistant antimicrobial thin films prepared by magnetron sputtering were developed, with the aim to coat key internal components within spacecrafts. Silver and copper are among the most studied active bactericidal materials, thus this work investigated the antibacterial properties of amorphous carbon coatings, doped with either silver, silver and copper, or with silver clusters. The longevity of these antimicrobial coatings, which is heavily influenced by metal diffusion within the coating, was also investigated. With a conventional approach, amorphous carbon coatings were prepared by cosputtering, to generate coatings that contained a range of silver and copper concentrations. In addition, coatings containing silver clusters were prepared using a separate cluster source to better control the metal particle size distribution in the amorphous carbon matrix. The particle size distributions were characterized by grazing-incidence small-angle X-ray scattering (GISAXS). Antibacterial tests were performed under both terrestrial gravity and microgravity conditions, to simulate the condition in space. Results show that although silver-doped coatings possess extremely high levels of antimicrobial activity, silver cluster-doped coatings are equally effective, while being more long-lived, despite containing a lower absolute silver concentration.

Durable infrared optical coatings based on pulsed DC-sputtering of hydrogenated amorphous carbon (a-C:H).

Optical properties of low-temperature pulsed DC-sputter deposited ($ {\le} {70° {\rm C}}$≤70°C) hydrogenated carbon are presented. Increasing hydrogen incorporation into the sputter deposited carbon significantly decreases infrared optical absorption due to a decrease in deep absorptive states associated with dangling bonds. Hydrogen flow is optimized (hydrogen flow 3 sccm), achieving the best compromise between increased infrared transmittance and hardness for durable coating performance. Optical, environmental, and durability performance of pulsed DC-sputtered carbon incorporated in multilayer (a-C:H/Ge) infrared antireflective coatings indicates suitability as a durable infrared optical coating for commonly used infrared substrates, including temperature sensitive chalcogenide glass.

Bacterial attachment and removal properties of silicon- and nitrogen-doped diamond-like carbon coatings.

Si- and N-doped diamond-like carbon (DLC) coatings with various Si and N contents were deposited on glass slides using magnetron sputter ion-plating and plasma-enhanced chemical vapour deposition. Surface energy analysis of the DLC coatings revealed that with increasing Si content, the electron acceptor gamma(s)(+) value decreased while the electron donor gamma(s)(-) value increased. The antifouling property of DLC coatings was evaluated with the bacterium, Pseudomonas fluorescens, which is one of the most common microorganisms forming biofilms on the surface of heat exchangers in cooling water systems. P. fluorescens had a high value of the gamma(s)(-) component (69.78 mN m(-1)) and a low value of the gamma(s)(+) component (5.97 mN m(-1)), and would be negatively charged with the zeta potential of -16.1 mV. The experimental results showed that bacterial removal by a standardised washing procedure increased significantly with increasing electron donor gamma(s)(-) values and with decreasing electron acceptor gamma(s)(+) values of DLC coatings. The incorporation of 2%N into the Si-doped DLC coatings further significantly reduced bacterial attachment and significantly increased ease of removal. The best Si-N-doped DLC coatings reduced bacterial attachment by 58% and increased removal by 41%, compared with a silicone coating, Silastic T2. Bacterial adhesion strength on the DLC coatings is explained in terms of thermodynamic work of adhesion.