Factors affecting the formation of the radiation pre-peak at the operation of a Grimm-type source in pulsed DC mode

Abstract

The plasma emission pre-peaks of many atomic and ionic spectral lines of Cu and Ar were systematically investigated in a Grimm-type pulsed glow discharge (PGD). To register the pre-peaks with sufficient time resolution, a monochromator with photomultiplier detection was used. When the applied power exceeded a specific threshold, pre-peaks were found in all spectral lines investigated, and it was revealed that the electrical pre-peak was the cause of the atomic emission pre-peak. The form and intensity of the pre-peak radiation were, however, found to be different for different atomic emission lines. The excitation energy of the upper energy level of the atomic line transition, and factors related to recombination and self-absorption, were found to affect the emission pre-peak. Pre-peaks observed when using pulsed DC and pulsed radio-frequency power were compared. This investigation provides insight into best practice when selecting spectral lines most suitable for analytical spectrometry using PGD.

Spatio-temporal dynamics of a microsecond pulsed Grimm-type glow discharge

“…For these lines self-absorption is commonly obtained in pulsed discharges. 13,15,53 In our discharge, intensity of Cu I 324.75 nm line (which has the same upper level as Cu I 510.55 nm line) reaches a prominent peak at 3rd ms, and aer that continually decreases during steady-state phase, see Fig. 13b.…”

“…I pp /I ss ) is observed for the atomic copper lines with upper levels of relatively low energy. 13 Analyzing the graph, one can conclude the same i.e., that I pp /I ss decreases with increasing energy of the upper level, and that it is valid for all applied voltages. For the higher voltage the decreasing is steeper.…”

“…That enables complete separation of the power source from the discharge plasma, without discharging of the capacitors through the plasma during the aerglow phase and without parasitic capacitance, which is not taken into account by most of the studies, see e.g. 13,14 Pulse frequency, pulse width and the off-time were controlled separately by programable signal generator Tektronix MDO 3032.…”

“…All measurements obtained here are recorded using argon (Messer, 99.999% purity) as a working gas, at constant gas flow of 80 ml min −1 and at the gas pressure of 6 mbar, conditions that is typical for optical-emission spectrometry analysis with the Grimm-type GD source. 13 To run the discharge, a laboratory made pulsed voltage power supply with capability to ensure up to 300 W per pulse was used (Fig. 1).…”

“…Which of the three phases will be the most prominent in the line intensity distribution depends on the particular spectral line: its energy levels and excitation processes. It has been generally observed that in the pre-peak phase the lines with upper levels of relatively low energy have higher intensities, 13 while in the aerglow phase the higher intensities belongs to upper levels with higher energy. 30,31 In this section we present the spatio-temporal distributions of the spectral lines that, following the mentioned general rule, are selected in a such way that rst line has low energy upper level and the second line has lower energy level identical or close to upper energy level of the rst line.…”