IMPROVED QUANTIFICATION OF GRAIN-BOUNDARY SEGREGATION BY EDS IN A DEDICATED STEM

The segregation of impurities at grain boundaries is a well known phen omenon in materials science. In some cases the grain boundary segregat ion causes embrittlement of the material. The effect depends on the am ount of impurity coverage of the grain boundaries. A suitable techniqu e for the quantification of the grain boundary segregation of impuriti es is energy dispersive X-ray spectroscopy in a dedicated scanning tra nsmission electron microscope. We have investigated a model system, th e segregation of bismuth at grain boundaries in copper, and have found inconsistent quantitative results from the energy dispersive X-ray sp ectroscopy measurements under different experimental conditions. The i nconsistencies were caused by beam broadening in the specimen which de pends on the specimen thickness, A new method is proposed to quantify impurity segregation. An effective scanwidth is calculated for the sca nning transmission electron microscope, depending on specimen thicknes s, as determined by electron energy loss spectroscopy. This approach t akes beam broadening into account. The application to different grain boundaries in Cu doped with Bi yields quantitative results which are i ndependent of experimental conditions.