Quantitative analysis of the compound layer of plasma nitrided pure iron

Abstract

Pure iron is plasma nitrided in a low pressure triode ion plating equipment. During this process a compound layer, containing different Fe-N phases depending on the plasma process parameters used, is formed at the surface. In this paper, the nitrogen concentration of the different phases is determined by measuring the backscatter yield of the different layers in a cross-sectional sample. Under appropriate instrumental conditions, the backscatter yields of elements and compounds can be determined quantitatively in a scanning electron microscope by measuring the specimen current. A simple relation between the backscatter coefficient of a binary target and those of its constituents is used for a quantitative analysis of the binary Fe-N phases. The strength of the specimen current measurement technique for this kind of application lies in the high spatial resolution which can be obtained using a small spotsize of the primary electron beam. This high resolution is required because the different Fe-N layers are very thin. Because the limitations of photon counting statistics are not involved, meaningful measurements can be performed very rapidly. As compared to X-ray analysis techniques, this is an advantage because in this way carbon contamination during the experiment can be minimised.