Characterization of AgxAuy nano particles by TEM and STEM

The size and chemical composition of bimetallic nano particles (2-20 nm) ha ve an important effect on their catalytic activity. It appears, in particul ar, that alloyed bimetallic nano particles can have extreme catalytic power . Therefore, a method was developed to distinguish between monometallic and bimetallic particles on the one hand, and between alloyed and segregated p articles on the other. A transmission electron microscope equipped with an energy-dispersive X-ray (EDX) detector was used for the determination of th e Ag concentration in single AgxAuy nano particles. An extensive study was performed in order to achieve optimum sample preparation, to obtain quantit ative results, to minimize and determine analytical errors and to estimate the detection limit. A dedicated scanning transmission electron microscope equipped with an EDX detector and an ultra-fine electron beam allowed the d etection of variations in the internal composition of a nano particle.