Glow discharge spectrometry (GDS) is a technique for rapid depth profiling and bulk analysis of materials. The latest instruments can be operated in either d.c. or r.f. modes. The dc. mode provides analysis of conductive materials only, while the r.f. mode allows analysis of both conductive and non-conductive samples. Until now, no theory for r.f.-GDS has been available. The recently proposed d.c. theory, which assumes that emission yield depends only on pressure, is extended to r.f.-GDS and is shown to be valid for the r.f. mode as well. A key to the success of the theory is that, in support of Duckworth and Marcus, the two modes are shown to have similar analytical characteristics, e.g. in comparing the two modes most elements examined had similar sensitivity factors and background equivalent concentrations. This will facilitate calibration of the light elements hydrogen, oxygen and nitrogen for use in the d.c. mode. Recommended procedures for bulk analysis, in either d.c. or r.f. modes, are presented and illustrated for manganese in steel. Both modes provide calibration curves of high linearity. Quantitative depth profiles of three commercial metalliccoated steel samples are compared in dc. and r.f. modes and the similarity of the quantitative profiles, given the very different lamp parameters operating between the modes, coafirms that the theory works for both d.c. and r.f. Tbe theory is then applied to data from a commercial prepainted metallic-coated sample to provide the first quantitative GDS depth profile of a non-conductive material,
This is the first part of our search for an experiment that will show definitively which is the best method for quantitative glow discharge optical emission spectrometry (GDOES). Three empirical methods for producing quantitative depth profiles from GDOES data are examined: the SIMR method, the IRSID method and the most recent BHP method. AU three methods give worthwhile quantitative depth profiles of thin films and coated materials. The first two methods assume that pressure does not have a significant effect on emission yield, while the third method assumes that pressure is the only significant parameter affecting emission yield. The different approaches therefore imply very different physical processes inside the lamp and it is essential for further develop ment of quantitative GDOES that the best approach be determined. Depth profiling in GDOES is, in principle, simply bulk analysis repeated over and over as a function of depth. The three methods are therefore tested here in their ability to do bulk calibration in a range of steels and zinc-aluminium alloy standards, all at constant current. All methods worked well for steel, while the best calibration curves in zinc-aluminium alloys were obtained with pressure-corrected IRSID and SIMR methods or a voltage-corrected BHP method. The results suggest that emission yields depend on both voltage and pressure (and presumably current, which was not tested here in Part I).
INTRODUCTIONGlow discharge optical emission spectrometry (GDOES) is an important analytical tool for the direct analysis of solids and for depth profiling coatings of industrial interest, i.e. coatings in the range of 0-50 pm in thickness. The theory of the instrument is still in development. Quantitative analysis of bulk materials with GDOES has been available for over 15 years and is a relatively straightforward process if the materials to be analysed have similar matrices to the standards used for calibration, because GDOES generally produces very linear calibration curves for such samples. Glow discharge optical emission spectrometry is much less straightforward if the matrix varies significantly during calibration or analysis, predominantly because the sputtering rates of different materials are very matrix dependent. The different matrices can also produce significant changes in the operating parameters inside the glow discharge, which in turn can affect both the sputtering rate and the emission yields of the elements.The situation of changing matrices is usually most evident in depth profiling, where the coating(s) is usually a very different matrix from the substrate, e.g. zinc on steel, in galvanized steel. In sputtering through the coating into the substrate the sputtering rate and lamp parameters can change dramatically and unless the quantitative method can account for such dramatic changes then the quantitative depth profiles of such coatings will be grossly in error.The glow discharge is responsible for both the sputtering of the s a m p l e a s a means of supplying material into the ...
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