Glow discharge as analytical tool: influence of secondary electron emission coefficient on its features

Glow Discharge Optical Emission Spectrometry (GD-OES) is commonly used for the spectrochemical analysis of materials and has become a standard tool for analyzing depth profile composition of multi-layer materials. This technique allows also quantification based on the number of photons emitted by sputtered atoms and depends only on Z, the impedance of the discharge used for analysis. This approach is based on the analysis of metals, without theoretical foundation, and its extension to the analysis of non-conductive materials is not yet validated. For a fixed geometry, Z depends mainly on the plasma gas pressure and gamma, the secondary electrons emission coefficient of the cathode material. Thus, to validate the quantification, it is necessary to know gamma of different materials and to classify them. An 'effective' gamma was determined from the Paschen curves for various conductor materials and non-conductors. The study showed that this coefficient depends strongly on the physico-chemical state of the electrode surface; these variations (up to 50%) make the results hard to use. However, the determination of the variation of Z with the pressure, allowed a classification of materials according to their gamma: a high Z corresponds to a low gamma. Moreover, these studies have shown that a variation of the pressure of plasma gas can compensate the gamma effect on the impedance of the discharge, which is essential for the quantification process. To validate the process, we analyzed a thin organo-metallic (LiPON) and shown that quantification is applicable to complex materials in thin layers. (author)