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Abstract

In situ heating experiments were performed in a transmission electron microscope (TEM) to monitor the thermal stability of silver nanoparticles. The sublimation kinetics from isothermal experiments on individual nanoparticles was used to assess the actual temperatures of the nanoparticles by considering the localized heating from the electron beam. For isolated nanoparticles, beam heating under normal TEM operating conditions was found to increase the temperature by tens of degrees. For nominally isothermal experiments, the observed sublimation temperatures generally decreased with decreasing particle size, in agreement with the predictions from the Kelvin equation. However, sublimation of smaller nanoparticles was often observed to occur in discrete steps, which led to faceting of the nanoparticles. This discrete behavior differs from that predicted by conventional theory as well as from experimental observations in larger nanoparticles where sublimation was continuous. A hypothesis that explains the mechanism for this size-dependent behavior is proposed.

Impact Statement

In this report, TEM electron beam effects on nanoparticles was investigated. The electron beam, especially on nanoparticles and at high current density, can have non trivial effects on samples. The authors used silver nanoparticles as a representative material, and showed that sublimation temperatures depend on nanoparticle/substrate contact geometry, intensity of the electron beam and size of the particle. Observations backed up this claim, where nanoparticles of a similar size sublimated at different temperatures indicating different contact geometries. Other observations included stepwise sublimation of particles when the particles were faceted, which were usual particles 30 nm in diameter, and larger particles that were nearly spherical
sublimated continuously.