Surface cleaning with atmospheric pressure plasma jet investigated by in-situ optical emission spectroscopy and laser-induced breakdown spectroscopy

• Surface cleaning by Argon plasma jet investigated by optical emission spectroscopy. • Metal surfaces cleaned for different atmospheric pressure plasma jet parameters. • Cleaning efficiency (CE) quantified using measured spectroscopic signals. • Dependence of CE and optical intensities on process parameters determined. • Thermal and non-thermal processes in APPJ surface cleaning categorized. Cleaning of surfaces with atmospheric pressure plasma jet (APPJ) is investigated by in-situ optical emission spectroscopy (OES) and laser-induced breakdown spectroscopy (LIBS). The APPJ device operates a spark discharge of kW power in Argon gas flow resulting in a powerful plasma jet expanding into air. For cleaning experiments samples are coated with lubricant layers of 1.1 to 7.1 µm thickness. Light collected at the sample surface during APPJ treatment is analyzed spectroscopically and used to monitor the cleaning process. LIBS chemical imaging delivers spatial cleaning profiles of plasma treated surfaces. From measured emission intensities of CN molecular band and Na atomic line the cleaning efficiencies for carbon and Na containing contaminants are determined. The power of APPJ plasma generator, distance between sample and jet nozzle, scan speed, and Argon gas flow are varied to optimize the surface treatment. Thermal and non-thermal processes contribute to cleaning. For the carbon containing contaminant thermal processes are dominating (∼90 %) while also non-thermal processes (∼30–45 %) are relevant for the Na containing component. A cleaned surface area per time from 0.3 to 10 cm 2 /s is investigated. Cleaning efficiency up to 95 % is obtained highlighting the potential of APPJ surface cleaning under ambient conditions.