Electron Beam Induced Enhancement and Suppression of Oxidation in Cu Nanoparticles in Environmental Scanning Transmission Electron Microscopy

We have investigated the effects of high-energy electronirradiationon the oxidation of copper nanoparticles in environmental scanningtransmission electron microscopy (ESTEM). The hemispherically shapedparticles were oxidized in 3 mbar of O-2 in a temperaturerange 100-200 & DEG;C. The evolution of the particles was recordedwith sub-nanometer spatial resolution in situ in ESTEM. The oxidationencompasses the formation of outer and inner oxide shells on the nanoparticles,arising from the concurrent diffusion of copper and oxygen out ofand into the nanoparticles, respectively. Our results reveal thatthe electron beam actively influences the reaction and overall acceleratesthe oxidation of the nanoparticles when compared to particles oxidizedwithout exposure to the electron beam. However, the extent of thiselectron beam-assisted acceleration of oxidation diminishes at highertemperatures. Moreover, we observe that while oxidation through theoutward diffusion of Cu+ cations is enhanced, the electronbeam appears to hinder oxidation through the inward diffusion of O2- anions. Our results suggest that the impact of thehigh-energy electrons in ESTEM oxidation of Cu nanoparticles is mostlyrelated to kinetic energy transfer, charging, and ionization of thegas environment, and the beam can both enhance and suppress reactionrates.