Fundamental parameters in quantitative depth profiling and bulk analysis with glow discharge spectrometry

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,

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“…9 in Ref. 18 (and equal to 0.15 for the conditions used). For r.f., OP' and OP are replaced by P'/3 and P/3, where P is the r.f.…”

Section: Methodsmentioning

confidence: 99%

Quantitative analysis with d.c.‐ and r.f.‐glow discharge spectrometry

Payling

Jones

Gower

1993

Surface & Interface Analysis

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“…Now, by combining Eqns (l), (11) and (15) one obtains an equation for intensity where a generalized dependency on the lamp parameters has been included where A = a + 1, B = b + n and C = c. Or, by combining Eqns (l), (12) and (15) one obtains an equation for intensity with a more physical definition of the pressure parameter…”

Section: The Dependence Of Intensity On Lamp Parametersmentioning

confidence: 99%

In search of the ultimate experiment for quantitative depth profile analysis in glow discharge optical emission spectrometry. Part II: Generalized method

Payling

1995

Surface & Interface Analysis

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INTRODUCTIONThe glow discharge lamp used in glow discharge optical emission spectrometry (GDOES) combines a high-speed sputtering source and an intense emission source in one. This gives the lamp its power, compactness and speed to analyse and depth profile practically any solid material compatible with vacuum. Paradoxically, it is this combination of sputtering and emission that makes the technique so difficult to describe theoretically. The sputtering supplies atoms from the sample into the glow region of the source where the optical lines are emitted. The intensity of an emission line therefore varies with the concentration of the element in the sample, with the sputtering rate and with the emission process. It is difficult to know, when the intensity changes, which is the cause of the change : concentration, sputtering or emission.The analyst is therefore left largely with empirical means to obtain quantitative results. These empirical means are complicated by the inter-relatedness of the lamp parameters : current, voltage and pressure.'.' One can fix only one of the these three variables at a time and vary the other two. Hence, one is constantly unsure which of the two varying parameters-or perhaps a combination of both-is responsible for any variation in sputtering or emission.Several empirically based quantitative schemes are now available for GDOES.3-'3 Of particular note here are: (1) the method of Bengston et al., developed at the Swedish Institute for Metals Research (SIMR), of correcting intensities for voltage and current changes in the lamp;" (2) the method developed separately by Cazet and Hocquaux at the Institut de Recherches de la Sid6 rurgie Frangaise (IRSID), of varying the argon flow to ensure that current and voltage do not change with depth;14 and (3) the approach of Payling and Jones at BHP of keeping pressure constant to ensure that the emission yield is ~onstant.''*'~ These methods were discussed in more detail in Part I." The first two methods assume that pressure does not have a significant effect on emission yield but that current and voltage do, while the third method assumes that pressure is the only significant parameter affecting emission yield.The SIMR and BHP models each give a good description of how the intensity of a given emission line from one matrix varies as a function of current or voltage. This is illustrated in Fig. 1 for iron from brass standard 306C. The models work well with one matrix because they are clearly expressing different versions of the same current-voltage-pressure relationship inside the lamp.These varying approaches pose several obvious questions : how does emission yield really vary with current, voltage and pres?ure, and, from that, which quantitative scheme really is the best one? How does one separate the effects of parameters that are correlated with each other? How does one design an experiment, a decisive experiment, that shows precisely how the intensities in the GDOES lamp depend separately on current, voltage and pressure? Deep down these ques...

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“…2 The sputtering process enables GD-OES to be a rapid analytical method for obtaining a depth profile of the sample composition, because it requires only little sample pretreatment without ultra-high vacuum conditions. [3][4][5][6][7] In a conventional measurement system for GD-OES, the emission signal is observed from the axial direction of the plasma when it is collected onto an entrance slit of the spectrometer with a point-focused lens. Therefore, the intensity of an emission line is integrated over a certain area of the plasma, enabling it to be estimated with better precision; however, it cannot give information about the spatial distribution of the emission intensity at different portions of the plasma.…”

Section: Introductionmentioning

confidence: 99%