Modifying argon glow discharges by hydrogen addition: effects on analytical characteristics of optical emission and mass spectrometry detection modes

An overview of the effects produced by the presence of hydrogen in a glow discharge (GD), generated either in argon or in neon, is given. Extensive work related to the addition of hydrogen to GDs, coupled with optical emission spectrometry (OES) and mass spectrometry (MS), has been published in the last few years in an attempt to explain the processes involved in the discharge of mixed gases. Although numerous experimental results have already been explained theoretically, a complete understanding of the effects brought about by mixing hydrogen with argon (or another discharge inert gas) has not been reported yet. The use of theoretical models implemented using a computer has allowed the importance of some collisional and radiative processes in the inert gas plasma when hydrogen is present to be evaluated. This review shows, however, that both experimental work and theoretical work are still needed. The influence of small quantities of hydrogen on discharge parameters, such as electrical current or dc bias voltage, on crater shapes and on sputtering rates is thoroughly reviewed along with the effect on the analytical signals measured by OES and MS. Also, hydrogen-effect corrections needed to carry out proper calibrations for direct solid quantitative analyses are discussed.