Direct Quantification of Heat Generation Due to Inelastic Scattering of Electrons Using a Nanocalorimeter

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 electron irradiation on the oxidation of copper nanoparticles in environmental scanning transmission electron microscopy (ESTEM). The hemispherically shaped particles were oxidized in 3 mbar of O2 in a temperature range 100-200 °C. The evolution of the particles was recorded with sub-nanometer spatial resolution in situ in ESTEM. The oxidation encompasses the formation of outer and inner oxide shells on the nanoparticles, arising from the concurrent diffusion of copper and oxygen out of and into the nanoparticles, respectively. Our results reveal that the electron beam actively influences the reaction and overall accelerates the oxidation of the nanoparticles when compared to particles oxidized without exposure to the electron beam. However, the extent of this electron beam-assisted acceleration of oxidation diminishes at higher temperatures. Moreover, we observe that while oxidation through the outward diffusion of Cu+ cations is enhanced, the electron beam appears to hinder oxidation through the inward diffusion of O2- anions. Our results suggest that the impact of the high-energy electrons in ESTEM oxidation of Cu nanoparticles is mostly related to kinetic energy transfer, charging, and ionization of the gas environment, and the beam can both enhance and suppress reaction rates.

Effect of electron beam irradiation on the temperature of single AuGe nanoparticles in a TEM

Knowledge of the actual temperature of nanoparticles under electron beam irradiation is of growing demand for in situ TEM studies. In this work, we addressed the problem with an experimental study of the temperature increment of single AuGe nanoparticles in a TEM and a STEM. The two-phase hemispherical AuGe nanoparticles were formed by the dewetting of an Au/Ge film on a SiNx substrate. The nanoparticles were thermally cycled in an electron microscope in the 293-653 K temperature range, under a wide range of electron beam currents. The jump-like change of the morphology of the AuGe nanoparticles at melting was used as a temperature label. The melting-crystallization process in binary alloy nanoparticles is fully reversible, with a large temperature hysteresis. It could be repeated on the same nanoparticle, providing a simple and robust way to measure the local temperature increment induced by the electron beam. It was shown that the temperature of the AuGe nanoparticles rose linearly with the e-beam current density J, and the temperature increment reached 25 K at J ∼ 1.8 × 106 A/m2 in the TEM. Given a fully known specimen geometry, the temperature increment was calculated when using theoretical approaches and compared with the experimental observations. As a result, recommendations for the assessment of real temperature in similar configurations were provided. In the STEM mode, no change in the temperature of the nanoparticles was registered at conventional parameters of the electron beam and the raster scans, which makes this mode preferable for in situ studies of metal and alloy nanoparticles.