Improved quantification of grain boundary segregation by EDS in a dedicated STEM

The segregation of impurities at grain boundaries is a well known phenomenon in materials science. In some cases the grain boundary segregation causes embrittlement of the material. The effect depends on the amount of impurity coverage of the grain boundaries. A suitable technique for the quantification of the grain boundary segregation of impurities is energy dispersive X-ray spectroscopy in a dedicated scanning transmission electron microscope. We have investigated a model system, the segregation of bismuth at grain boundaries in copper, and have found inconsistent quantitative results from the energy dispersive X-ray spectroscopy measurements under different experimental conditions. The inconsistencies were caused by beam broadening in the specimen which depends on the specimen thickness, A new method is proposed to quantify impurity segregation. An effective scanwidth is calculated for the scanning transmission electron microscope, depending on specimen thickness, as determined by electron energy loss spectroscopy. This approach takes beam broadening into account. The application to different grain boundaries in Cu doped with Bi yields quantitative results which are independent of experimental conditions.