Regulating of bias voltage of a r.f.-powered glow discharge excitation source and the emission characteristics

A method to control the bias voltage of r.f.-powered glow discharge plasmas was investigated to improve the detection power in optical emission spectrometry. D.C. voltages applied with an external power supply can induce greater voltage drops at the cathode sheath, thus leading to an increase in the sputtering rate. Further, the voltages also help promote excitation and ionization processes occurring in the plasma; therefore, the emission intensities excited by the plasma are elevated. The detection limit, which was defined as the sample concentration corresponding to three-times the standard deviation of the background intensity, was estimated to be 2.6 x 10(-5) m/m% Cu in Fe-Cu binary alloys for Cu I 327.40 nm, when the Ar pressure, the r.f. power, and the d.c. external voltage were set at 800 Pa (6 Torr), 70 W, and 450 V, respectively.