Plasma-Enhanced Pulsed Laser Deposition of metal oxynitride thin films for photoelectrochemical water splitting

Plasma-enhanced pulsed laser deposition (PE-PLD) is a novel thin film deposition method
which employs radio-frequency plasmas and laser-ablated plasma plumes to produce semiconductor thin films. A high-powered, pulsed laser ablates material from a metal target into a plasma plume, which interacts with non-metal inductively-coupled plasma species to form metal compound material that deposits onto a substrate. PE-PLD has been shown to produce high-quality metal oxide thin films with many applications, including photocatalysts which use solar energy to produce hydrogen fuel from water splitting. PE-PLD remains an active area of research, particularly elucidating its underlying plasma physics and chemistry, such that thin films can be created according to specific criteria rather than empirical observation. This work centres around the suitability of PE-PLD in producing metal oxynitride thin films for photocatalysis.

This thesis presents results from modelling the laser ablation of different photocatalytic
metals using the code POLLUX, showing the electron temperature and mass density of the plasma plume both increased with the atomic number of the material, whilst the mass density of the material had no observed effect on the electron temperature or particle density of the plume.

Additionally, the TALIF diagnostic provided absolute measurements of ground-state
atomic O and N densities for a range of low-pressure oxygen/nitrogen plasma mixtures, showing the relative flow input of oxygen and nitrogen had the greatest control over the O:N atomic density ratio, allowing it to change by up to a factor of 100.

Finally, the structure and chemical composition of deposited metal oxynitride thin films
were analysed with different diagnostics, showing a consistent lack of nitrogen present on the films and lack of visible light absorption, highlighting many areas of improvement for PE-PLD in producing oxynitride films, such as understanding interactions between oxygen/nitrogen plasma species and their effect on deposition.