Free radicals, molecules with one or more unpaired electrons, are highly chemically reactive. This high reactivity means that free radicals exert a major influence on the chemistry of any environment in which they are formed, even though they are often not the most abundant species. For example, it is free radical chemistry that controls important atmospheric phenomena such as the ozone hole and the formation of photochemical smog. The interactions of free radicals with surfaces are thought to be vitally important in controlling the chemistry of formation of thin-films from electrical discharges, so called plasma-assisted deposition. Such thin-films have enormous technological importance in fields such as integrated circuits and solar cells. However, the details of the interactions of the radicals with the surfaces in these film formation processes are not well understood. The major hurdle to investigating this surface chemistry of free radicals is that, currently, there is no general technique available to dose a surface with only the free radical of interest, for example CH. Current radical sources generate the radicals from a precursor gas (e.g. CH from C2H2) and the precursor gas molecules always outnumber the radicals. Thus if a surface was dosed from a conventional radical source, the precursor molecules would be the dominant species on the surface, making it almost impossible to study the interactions of the radical with the surface using standard surface science techniques. In this application, we propose the development of a new source of free radicals which will generate "clean" beams of the radical species, uncontaminated by the precursor molecule. The source will work by generating negative ions (e.g. CH-), which can be mass selected to form a clean beam. The radicals are then generated from the negative ions by using a laser beam to knock off the electron. This photo-detachment of negative ions will yield a clean beam of the radical species of interest. Calculations given in the proposal show that a practical flux of free radicals can be generated by this methodology. The clean beams of free radicals can then be used to dose the surface with the radical species, and the surface can be studied using the standard techniques of surface science to reveal the details of the radicals sticking and surface chemistry. We propose to develop the source and then use it to study the radical-surface interactions involved in three technologically important film deposition processes. The chemistry revealed by our investigations will dramatically improve our understanding of what is going on in these industrially relevant surface reactions and allow us to optimize and refine these deposition processes in the light of the chemistry that is occurring.

Untreatable infections are one of the biggest modern-day dangers to society, which the current SARS-CoV-2 pandemic has highlighted. The development of antibiotics has been one of the major medical successes of the last 100 years. However, the capacity of pathogens to evolve and acquire resistance to new antibiotics makes their effectiveness necessarily precarious. Meanwhile, studies on the spread of drug-resistant pathogens such as MRSA, respiratory syncytial virus, norovirus and CoVID-19 suggest that surfaces are a major point of transmission with CoVID-19 remaining infectious on plastic and stainless steel surfaces for up to 6 days. Surfaces with an antimicrobial function that avoid or minimise the use of antibiotics whilst maintaining good efficacy after prolonged use are critically needed in hospitals, living spaces, and on biomedical implants, to reduce healthcare-acquired and public space-acquired infections, reduce healthcare costs, and promote healthier lives. However standard antimicrobial surfaces are not sufficiently robust to withstand the wear and tear encountered in a biomedical implant environment and in public spaces. Sheffield Hallam University and Imperial College London aim to develop superhard nanostructured surfaces with plasmonically-enhanced photocatalysis which will enable microbial inactivation in both illuminated and dark environments whilst retaining their robustness and effectiveness in the long term and which, as a result, will lead to orthopaedic implants and anti-microbial surfaces that are more functional than those produced with the current technologies. The innovative antimicrobial surfaces will be robust due to the use of superhard nanoscale multilayer coatings with wear rates up to 1000 times better than conventional metal alloys. At the same time the robust antimicrobial surfaces will have a dual functionality - (1) active, they will be able to kill microorganisms by photocatalysing the production of highly reactive singlet oxygen - one of the most effective killers of pathogens. The photocatalysis will be activated by visible light from the environment. The light will interact with a carefully prepared coating material to induce plasmonic resonance on its surface and generate high energy electrons which are needed to boost the photocatalytic reaction. (2) passive, mimicking naturally occurring surfaces such as the cicada wing, the surfaces will contain a number of appropriately dimensioned nanopillars which will stretch and mechanically rupture the walls of microorganisms. This functionality is potent in wet, dry, illuminated or dark environments. We have developed a new plasmonic nanoscale multilayer material which activates photocatalysis under standard (visible) light and have developed technology based on high power impulse magnetron sputtering which can produce these materials at room temperature on polymers. We will study the plasma processes needed to produce the materials and nanopillars, their response to light activation and the effect they have on microbials. This will help us to develop a cost-effective manufacturing technology to enable large scale production by upgrading systems which are already available in industry for coating deposition and nanopatterning with a digitalised system control which is driven by artificial intelligence algorithms. Together with the local NHS hospital trust we will trial the material on metal plates for door furniture and polymer sheets to cover surfaces in hospitals (beds, seating areas). When successful we will have some of the most exciting new developments in robust antimicrobial materials and their manufacturing and take a step closer to a world with fully effective infection control.