INVESTIGATIONS OF A JET-ASSISTED GLOW-DISCHARGE LAMP FOR OPTICAL-EMISSION SPECTROMETRY

Jet-assisted sputtering was performed in a conventional Grimm-type glow discharge source (GDS) equipped with a floating restrictor (internal diameter: 8 mm). The source was modified by reversing the gas flow and adding six symmetrically located channels in the restrictor; the channels were directed at an angle of 45-degrees onto the sample surface. The conditions for stable operation were found to not differ from those of a conventional GDS. At power levels below 60 W, the current-voltage characteristics were studied for steel and copper samples; the burning voltages were found to increase by 50 to 300 V when the jet diameters were reduced from 0.5 to 0.2 mm. The resulting burning spots on the sample display the gas-jet pattern. When jets of 0.5-mm diameter were used, electron-microprobe line scans across the burning spots on brass samples revealed no changes in the intensity ratio of Cu/Zn; in contrast, when 0.2-mm jets were employed, composition changes were found, which might be due to analyte redeposition. Under conditions for stable operation, the ablation rates for copper are maximum at 4.77 mg/min with a gas-jet diameter of 0.5 mm, a power of 60 W, a gas flow of 210 ml/min and a pressure of 532 Pa. In the case of brass, the intensities of copper and zinc lines were found to increase with the sample ablation rate except for the Cu I 324.7 nm resonance line, which presumably suffers self-reversal. Noise power spectra obtained from analyte emission show that in the jet-assisted GDS white noise is predominant. Frequency-dependent components at 10-20 Hz and 60 Hz stemming from the pump and the line, respectively, also occur and are similar to those for a conventional GDS. For the intensities of major element lines the relative standard deviations (RDS) measured at 0.1 s are lower than 0.4%.