Spatially resolved optical emission analysis of spokes in HiPIMS utilising Al, Cr, Cu, Ti, and W targets

Investigating spokes in high-power impulse magnetron sputtering discharge requires non-invasive diagnostic methods to characterise accurately spoke properties. A fast photodiode and a cylindrical Langmuir probe were employed to synchronise the moment of acquisition of the optical emission spectrum with the position of a passing spoke. This study provides statistical data analysis to bring insights into spoke characteristics in a non-reactive argon atmosphere, employing aluminium, chromium, copper, titanium, and tungsten targets. Utilising different target materials, the objective is to describe basic parameters such as shape, length, and propagation velocity of spokes and also analyse spoke inner parameters such as floating potential and spectral emission, under nearly identical experimental conditions. From the optical emission, the most prominent species within the spoke were determined. Additionally, the mechanism governing spoke movement was described using a phenomenological model.