Quantitative depth profile analysis by direct current glow discharge time of flight mass spectrometry

Abstract

Three operation modes, based on the “absolute sensitivity factor” concept, were studied in a simple laboratory-made glow discharge ion source coupled to a time of flight mass spectrometer for depth profile quantification of conductive zinc coatings. In method 1 voltage and pressure are fixed, in method 2 constant voltage and electrical current are used and method 3 resorts to using fixed electrical current and pressure. For qualitative depth profiling of steels with a coating of galfan, slightly better results were obtained using method 1. In quantitative depth profiling studies with the GD-TOFMS system, good correlation for absolute sensitivity factors was obtained when a calibration for signal intensities of analytes versus the product “sputtering rates × elemental concentrations” was tried using homogeneous reference materials of different matrices. Therefore, conversion of the experimental emission intensities obtained from the qualitative profiles into elemental concentrations and of erosion times into depths was investigated. In this vein, quantitative profiles have resulted when using the three methods investigated for galfan, electroplated ZnNi and a galvanized coating containing lead. Method 3 provided, in general terms, slightly better results than method 1 for the three coatings, while method 2 proved to be less reliable for in-depth quantitative results.