Spatially resolved spectroscopy of an atmospheric pressure microwave plasma jet used for surface treatment

In this study, the variations of properties of a microwave plasma jet (surfatron) along the discharge axis have been investigated using optical emission spectroscopy. As the argon jet is not enclosed, the spatial distribution of individual species in effluent plasma is the result of rather complicated interplay between energy loss and gradual mixing with the air. Spatial 2D relative intensity profiles of atomic lines and molecular bands at 310 nm, 336 nm, 391 nm and 656 nm are presented in the form of colour maps revealing different positions of maximum emission intensity for 310 nm and 336 nm (in the effluent plasma) and for 391 nm and 656 nm (inside the discharge tube). The plasma jet was used for surface treatment of heat resistant samples (stainless steel, aluminium, silicon wafer) and the effectiveness of the plasma treatment was evaluated by measuring the sessile drop contact angle, with water and glycerol as testing liquids. The optimal position for plasma treatment (close to the tube nozzle) combined with longer treatment time (10 s) lead to hydrophilic properties of samples with contact angles as low as 10°.