WP 2: experimental studies on glow discharge processes

The objective of work package 2 on experimental studies on glow discharge processes is the examination of effect of molecular gases in terms of the individual excitation processes. Investigation of the optical signal from a dc GD source running in pure noble gases and mixtures with molecular gases and their relation to physical parameters (voltage, current, gas pressure etc.). Measurement of high resolution FT spectra from pure and mixed gases for various cathode materials for comparison with modelling predictions and the development of correction procedures in the presence of hydrogen and nitrogen and to assess gas temperature via line width measurements.

Situation at mid-term:

Sohail Mushtaq in Imperial College has undertaken preliminary investigations, for the first time over a wide spectral range including many spectral lines, of the effect of oxygen as an impurity (0.05-2 %V/V) in argon glow discharge plasma with pure iron sample. Initial results show marked differences for oxygen impurities compared with the effect of hydrogen and nitrogen molecular gases as impurities in GD. Controlled experiments investigating the change in sample sputtering rate with level of oxygen concentration in the glow discharge have also been undertaken, and the resulting crater profiles have been measured. The most important result is that the sputtering rate for a given oxygen-argon gas mixture is not proportional to current, usually the correct assumption in GDS work. This appears to be due to the formation of an oxide layer on the cathode (sample), and will be investigated in the future.

Dr Petr Šmíd in ULMET studied the effects produced by small amounts of hydrogen and nitrogen on the optical emission of the argon plasma using the IC FTS instrument. Asymmetric charge transfer (ACT) excitation of ionic states with total excitation energy close to 13.6 eV is already well established, as is the suppression by hydrogen of ionic states excited by argon ACT. Dr Šmíd also observed clear intensity trends in the atomic spectra of titanium (Ti I) when small amount of hydrogen is added to discharges in argon, however, such effects are not observed when nitrogen is added. This effect was attributed to a hitherto unreported interaction leading to the dissociation of the ionized hydrogen molecule.

Dr Peter Horvath had a 4.5 months temporary appointment at ULMET. He recommissioned the microwave boosted glow discharge source at ULMET and did preliminary studies on the use of the boosted GD source for depth profiling, using zinc and nickel coated aluminium samples. To aid the identification of spectral lines, he also recorded the full Grimm source spectrum of nickel using the IC FT spectrometer, and this has revealed some very complex line profiles which require further investigation and explanation.


Viktoria Weinstein in ULMET is continuing investigations on the effects produced by hydrogen and nitrogen, and already showed that there are some errors in the earlier results. She is also carrying out an extensive comparison between plane and deep hollow cathode spectra for copper and iron samples. As the spectral changes are linked with changes in the excitation processes, these experiments shed further light on the possible changes produced by traces of molecular gases.

At the University of Belgrade, Vasilka Steflekova took part in setting up two experiments, one with a low-pressure hollow cathode discharge and the other with a Grimm type glow discharge source. At this moment, the experiment with Grimm discharge is set up and detailed study of hydrogen and hydrogen-argon DC discharge interaction with different cathode materials is in progress. Studies are carried out by observing hydrogen Balmer line shapes under different discharge conditions. Ms Steflekova also spent one month at both Imperial College and the Metropolitan University in London and used Fourier Transform Spectrometer (FTS) to analyse Fulcher band spectral lines of molecular hydrogen in Grimm glow discharge source operated with inert gas (Ar, Ne) -hydrogen mixtures.