Shape evolution and thermal stability of Ag nanoparticles on spherical SiO2 substrates

In this paper, the shape evolution and thermal stability of Ag nanoparticles (NPs) on spherical SiO2 substrates were investigated by means of in situ transmission electron microscopy (TEM) imaging and differential scanning calorimetry (DSC). The initial Ag NPs at room temperature were semispherical-like, with an average size of 9 nm in half-height width, well-dispersed on spherical SiO2 substrates. No obvious shape change was observed when the semispherical NPs of Ag were heated at temperature lower than 550 °C. The shape of the semispherical Ag NPs changed gradually into a spherical one in the temperature range of 550–700 °C, where surface diffusion and surface premelting took place. When the heating temperature was increased up to 750 °C, the spherical Ag NPs were found to desquamate from the substrates due to the decreases of the contact area and the binding force between Ag NPs and SiO2 substrates. A possible mechanism for the desquamation of Ag NPs from the SiO2 sphere surface is proposed according to the results of in situ TEM observation and DSC analysis.