Excitation mechanism for nickel and argon lines emitted by radio-frequency glow discharge plasma associated with bias current introduction

The introduction of d.c. bias current to an r.f. glow discharge plasma led to enhancement in the intensity of particular emission lines. In order to investigate the excitation mechanism, a large number of nickel emission lines was measured with and without the bias-current introduction. Emission intensities of nickel atomic lines were predominantly elevated by conducting bias current, especially when the emission lines have an excitation energy of approximately 5 eV. This phenomenon could be explained from the additional excitation through collisions with the introduced electrons having kinetic energies favorable for the excitation of such nickel atomic lines. However, this additional excitation mechanism was less effective for excited states of nickel ion, argon atom and argon ion, because their excitation energies were fairly high compared with the excitation energies of Ni atomic lines.