Development Of The In Situ Liquid Cell TEM Chips And Investigation Of The Growth And Etching Process Of Noble Metal Nanocrystal In The Liquid Ceil TEM

Noble metal nanocrystals have gained lots of attention in future applications in optics, electricity, magnetics, catalysis, energy storage and conversion research fields, due to their unique optical, electrical, magnetic, mechanical properties, in contrast to their bulky counterpart. To understand the growth mechanism of the noble metal nanocrystals plays a key role towards the size-, morphology-and electrical structures-controllable synthesis. In the past two decades, nanocrystals with a variety of predesigned shapes including sphere, cube, cuboctahedron, octahedron, etc. have been achieved. However, there are still many issues to be clarified, partly due to the lack of a powerful tool to probe the dynamic processes during the nucleation and growth of nanocrystal with high spatial and temporal resolution, which can be performed in situ along with these dynamic processes.As a result of the advances in electron microscopy and microfabrication, a new experimental platform, so called liquid cell TEM, has emerged in recent years, which has made it possible to directly observe nanocrystal growth in real time with a very high spatial resolution. So far, liquid cell TEM has been successfully applied to study different kinds of nanocrystals, where the trajectories of the nanoparticle growth can be rigidly observed. Here, our main goal is to develop a method to fabricate liquid cell chips firstly, and then investigate the growth and oxidative etching process of noble metal nanocrystal. The main innovative results are summarized as following:(1) Based on the MEMS (Micro-Electro-Mechanical System), we have successfully fabricated two kinds of liquid cell chips:one was used in a commercially available liquid cell holder (Hummingbird Inc.), the other one was compatible with the glue assisted sealed technique. Both of which are marketable.(2) A novel and highly reproducible method that enables atomic resolution transmission electron microscopy investigation of the dynamics of nanoparticles in liquid was proposed. It enabled the formation of ultrathin liquid layers a result of formation of bubbles that was initiated and could be tuned by the electron beam irradiation. Based on this method, we further investigated the growth of two-dimensional (2D) palladium dendritic nanostructures (DNSs) inside the TEM. Detailed in situ and ex situ high-resolution scanning TEM (S/TEM) characterization and fractal dimension analyses reveal that the diffusion-limited aggregation and direct atomic deposition are responsible for the growth of palladium dendritic nanostructures.(3) The etching was realized with oxidative radiation reactants from electron-water interaction in the presence of Br- ions. Dissolution dynamics of mono-dispersed and aggregated nanocrystals were both investigated and compared.