DC discharge

Figure 1 Schematic of DC glow-discharge atomization and ionization processes. The sample is the cathode for a DC discharge in 1 Torr Ar. Ions accelerated across the cathode dark space onto the sample sputter surface atoms into the plasma (a). Atoms are ionized in collisions with metastable plasma atoms and with energetic plasma electrons. Atoms sputtered from the sample (cathode) diffuse through the plasma (b). Atoms ionized in the region of the cell exit aperture and passing through are taken into the mass spectrometer for analysis. The largest fraction condenses on the discharge cell (anode) wall.

Mass-spectrometric research on silane decomposition kinetics has been performed for flowing [298, 302-306] and static discharges [197, 307]. In a dc discharge of silane it is found that the reaction rate for the depletion of silane is a linear function of the dc current in the discharge, which allows one to determine a first-order reaction mechanism in electron density and temperature [302, 304]. For an RF discharge, similar results are found [303, 305]. Also, the depletion and production rates were found to be temperature-dependent [306]. Further, the depletion of silane and the production of disilane and trisilane are found to depend on the dwell time in the reactor [298]. The increase of di- and trisilane concentration at short dwell times (<0.5 s) corresponds to the decrease of silane concentration. At long dwell times, the decomposition of di- and trisilane produces... 

For frequencies below 5 kHz the discharge has the characteristics of a pulsating dc discharge. On each half cycle the electrode acting as the cathode is subjected... 

Direct current plasma (DCP) this is produced by a dc discharge between electrodes. DCPs allow the analysis of solutions. Experiments have shown that although excitation temperatures can reach 6000 K, sample volatilisation is not complete because residence times in the plasma are relatively short (this can be troublesome with samples containing materials that are difficult to volatilise). A major drawback is the contamination introduced by the electrodes. 

FIGURE 7.16 DC discharge plasma formed in a chamber (1000 x 350 x 150 pm) at 750 Torr, 500 V, and 60 pA. (A) Original image. (B) False-color image of the same plasma [718]. Reprinted with permission from the Royal Society of Chemistry. 

Fig. 10.2 Different types of plasma reactors employing the use of an IL (a) DC dis charge with the IL as an integral part of a serial set-up, (b) DC discharge with the IL as optional part of a parallel set-up, (c) in-...

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