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.
In other words, detailed control of the plasma chemistry is essential for success in plasma-enabled applications, both existing and emerging.

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. In traditional low-pressure plasma applications, tailoring of the EEDF through e.g. multi-frequency applied voltages or magnetic fields, has proven to be a viable method for plasma chemistry control.

However, the same cannot be said in the fast emerging field of atmospheric-pressure plasma (APP) science. Where 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. Given the reliance on plasma chemistry in many APP applications, establishing a viable technique to control the EEDF is an even more pressing challenge than in low-pressure systems. Success in this endeavour would have a profound impact across the entire application space of APPs, which includes activities such as high-value materials processing, renewable chemistry and healthcare technologies.

In this proposal, we bring together expertise from the University of York and the University of Liverpool in state-of-the-art pulsed power technology, the latest plasma diagnostic techniques and novel multiscale numerical modelling to address the challenge of plasma chemistry control for atmospheric-pressure plasmas. We aim to develop an 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 plasma diagnostics and numerical modelling will enable us to understand the underpinning mechanisms of the observed changes in chemistry for different pulse shapes, leading to a new capability for atmospheric-pressure plasma technologies: flexible, tailored plasma chemistry. This would be an international first and deliver user-controlled tunability of well-defined plasma chemistries without changing background gas or plasma source design.