Analytical potential of a glow discharge chamber coupled to a time of flight mass spectrometer for qualitative in-depth profile analysis

Abstract

A simple home-made glow discharge (GD) ion source developed to be coupled to a time-of-flight (TOF) mass spectrometer (MS) for direct solid analysis is characterized here in terms of several parameters of interest for in-depth profiling. First, the three possible operating modes of a dc-GD for coated sample analysis, differing in a pair of parameters (from among pressure, voltage and electrical current), which are maintained constant during analysis, have been critically assessed, comparing the precision and resolution obtained for different coated materials. Crater shapes and sputtering rates, using the GD chamber prototype developed coupled to the (TOF)MS analyzer, have been evaluated for different types of Zn coatings on steel samples. Good crater shapes, with walls “perpendicular to” and base “parallel to” the sample's surface, were obtained. Time-intensity profiles obtained with the GD-(TOF)MS system developed were compared with those obtained with a rf-GD-OES commercial instrument and a good correlation between them was observed. Sputtering rates were found to be about two or three times lower than those obtained with a commercial rf-GD-OES system maintaining in-depth resolution. Finally, the capability of the developed GD-(TOF)MS system for the analysis of thin coatings (below 1 µm thick) containing trace elements has been evaluated.