RESUMO
In this study, we used an in situ transmission electron microscopy (TEM) heating system to investigate the sublimation-induced morphological changes of cubic Ag nanoparticles (NPs) and Ag-based core-shell structures and the influence of shell coverage on the thermal stability. In contrast to previous research performed with small Ag nanoparticles (<30 nm), here we found that large-particle Ag NPs (>50 nm) underwent a three-stage sublimation-induced morphological change at 800 °C, in the sequence uniform (I)-nonuniform (II)-uniform (III) sublimation. The (110) and (100) planes were the main sublimation planes during stages I and II. When the reaction reached stage III, the sublimation rate decreased as a result of an increase in the sublimation energy barrier. For core-shell NPs, the sublimation process began with stage II. For Ag NPs presenting TiO2 shells, the sublimation process was initiated at a relatively low temperature (700-750 °C) because of a local heating effect; for Ag NPs with carbon shells, the reaction was suppressed through surface atom passivation, thereby enhancing the thermal stability.
