Control of d.c. bias current in radio-frequency glow discharge source and its emission characteristics II - the analytical application

In a radio-frequency-powered glow discharge lamp, a d.c. bias current which is driven by the self-bias voltage can be introduced by connecting an electric circuit comprising a low-pass filter and a variable resistor. The bias current promotes the emission excitations occurring in the plasma, thus leading to an improvement of the detection power in the optical emission spectrometry. At a bias current of 33 mA, the emission intensities of the Al I 396.15-nm line were approximately 20 times larger than those obtained with the conventional plasma. In Fe-Al alloy samples, the detection limit for the Al I 396.15-nm line was 1.1 × 10^-3 mass% and was improved by a factor of 14, when the r.f. power and the Ar pressure was selected to be 80 W and 330 Pa, respectively.