Characterization of a versatile low-pressure plasma treatment unit for steel surfaces

This study presents a thorough characterization of a low-pressure plasma treatment applied to low-carbon steel surfaces conducted in a simple and versatile plasma treatment unit. Optical emission spectroscopy (OES) and retarding field energy analyzer (RFEA) measurements are utilized to investigate plasma parameters and sample surface interactions. OES confirms sputtering of the sample surface, while the energy and ion flux can be independently tuned by varying the voltage of the plasma generator and adjusting the supportive plasma discharge sustained by a thermionic electron emitter. The study measures electron temperatures ranging from T_e = 1 eV to 2 eV and ion flux densities up to J_i = 7 A/m². Mapping of the ion flux density on the sample surface reveals a distribution consistent with the geometry of the anode tube implemented. Plasma treated steel surfaces are investigated via contact angle measurements and X-ray photoelectron spectroscopy. Results indicate an increase in surface free energy following short plasma treatment at an energy density of approximately E_A ≈ 5 J/cm². This can improve adhesion in coatings or bonding processes, making low-pressure plasma treatment highly suitable for various industrial applications. Additionally, the effective reduction of carbon compounds and oxides on steel surfaces suggests potential uses in manufacturing sectors that require clean, reactive metal surfaces for improved performance and longevity.