Evidence for molecular tungsten ionic species presence in impurity-seeded hydrogen plasma in contact with W surfaces

We performed an investigation of tungsten ionic species presence in hydrogen plasmas in contact with a tungsten surface, both in the presence of air impurities and when injected with argon. The study was carried out in a magnetron sputtering system complemented with mass spectrometry diagnostics. Our findings reveal that these plasmas encompass a diverse range of tungsten molecular ionic species in the mass range of 180-250 amu, broadly described as WHxNyOz+ (x = 0-3; y = 0-2; z = 0-3). The validity of these results was further confirmed through dedicated mass spectrometry investigations involving tungsten sputtering discharges in argon-nitrogen and argon-oxygen mixtures. In hydrogen-dominated plasmas in contact with tungsten surfaces, the material removed from surfaces is found not only as metallic atoms but also as tungsten molecular compounds formed in reactions with hydrogen and with oxygen and nitrogen gaseous impurities. image