In situ TEM observation of liquid-state Sn nanoparticles vanishing in a SiO2 structure: a potential synthetic tool for controllable morphology evolution from core-shell to yolk-shell and hollow structures

In situ TEM investigation of nucleation and crystallization of hybrid bismuth nanodiamonds

Despite great progress in the non-classical homogeneous nucleation and crystallization theory, the heterogeneous processes of atomic nucleation and crystallization remain poorly understood. Abundant theories and experiments have demonstrated the detailed dynamics of homogeneous nucleation; however, intensive dynamic investigations on heterogeneous nucleation are still rare. In this work, in situ transmission electron microscopy (TEM) at the atomic scale was carried out with temporal resolution for heterogeneous nucleation and crystallization. The results show a reversible amorphous to crystal phase transformation that is manipulated by the size threshold effect. Moreover, the two growth pathways of Bi particles can be mainly assigned to the atomic adsorption expansion in the amorphous state and effective fusion in the crystal contact process. These interesting findings, based on a real dynamic imaging system, strongly enrich and improve our understanding of the dynamic mechanisms in the non-classical heterogeneous nucleation and crystallization theory, providing insights into designing innovative materials with controlled microstructures and desired physicochemical properties.

Synthesis of Au@Cu2O Core-Shell Nanoparticles with Tunable Shell Thickness and Their Degradation Mechanism in Aqueous Solutions

Metal@semiconductor core-shell nanoparticles (NPs) are widely used in photocatalysts, sensors, and optical applications owing to their unique metal-semiconductor interface and the integration of the properties from both core and shell materials. Although many efforts have been made toward the precise synthesis of Au@Cu₂O core-shell structures, the chemical stability of Au@Cu₂O aqueous suspensions, which is of great significance in many related applications, is not mentioned in any published research. Herein we report the synthesis of Au@Cu₂O core-shell NPs with small shell thickness from 2 to 40 nm through a wet-chemistry method. The UV-vis absorption properties are found to be tunable with Cu₂O thickness in the range of 2-40 nm. Furthermore, the chemical stability of Au@Cu₂O core-shell nanoparticle suspensions in water/ethanol mixed solvents is investigated. It is found that water/ethanol mixed solvents with a larger amount of water are more likely to deteriorate the stability of Au@Cu₂O NPs by oxidizing Cu₂O to CuO. The results from this work may provide useful information for the preparation of metal@Cu₂O water-based suspensions that are expected to be used for SERS, photocatalyst, or photothermal applications.