Characterization of AgxAuy nano particles by TEM and STEM

Abstract

The size and chemical composition of bimetallic nano particles (2-20 nm) have an important effect on their catalytic activity. It appears, in particular, 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 particles on the other. A transmission electron microscope equipped with an energy-dispersive X-ray (EDX) detector was used for the determination of the Ag concentration in single Ag _x Au _y nano particles. An extensive study was performed in order to achieve optimum sample preparation, to obtain quantitative 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 detection of variations in the internal composition of a nano particle.