Plasma technologies already form a key part of many of today's multi-billion pound industries such as the nanoscale fabrication of microprocessors, energy efficient lighting, production of solar cells and the deposition of advanced functional coatings. Underpinning the effectiveness of these essential technologies is the unique non-equilibrium environment created within the plasma; including a mix of reactive neutral particles, ions and energetic electrons. Many applications rely on the synergistic interaction between the mix of species created in the plasma and a sample surface; however one of the fundamental challenges in plasma science is tailoring the mixture of reactive plasma species such that they have the desired effect on a target.
Novel cold atmospheric-pressure plasmas can operate into open air, remain at room temperature, and still have the selective desired reactivity characteristics. They have many novel applications ranging from plasma medicine to adhesion enhancement of plastics to green chemistry. As with many plasma applications, key for the effectiveness of these devices is the plasma chemistry, i.e. exactly what mix of reactive species are delivered to a substrate by the plasma.
The chemistry in these plasmas is largely controlled by the electrons; more precisely the distribution of energies that the electrons have. Different electron energy distribution functions (EEDF) drive differences in the plasma chemistry and therefore in the observed effect on a surface, making the EEDF, and especially control over the EEDF of key importance.
Compared to traditional low-pressure plasmas, atmospheric-pressure plasmas are generated at much higher pressure (in open air), meaning there are many more collisions between plasma particles, severely hindering existing low-pressure EEDF control methods. This project aims to take advantage of a newly developed extremely agile high-voltage pulsed power technology, in which pulse characteristics such as rise time, duration and repetition rate can be varied by the user. With this flexibility, the electrical excitation of the discharge can be used to modify the EEDF and therefore control and tailor the plasma chemistry of the APP. Sophisticated (laser-based) plasma diagnostics and numerical modelling will enable us to understand the underpinning mechanisms of the observed changes in chemistry for different pulse shapes. Air-based chemistries, in particular reactive species such as OH, NO, O3, O and N play key roles in many applications and are the focus of this project.
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