In-situ Tem Study Of The Nucleation And Growth Of Perovskite And The Self-assembly Of Cobaltosic Oxide Nanoparticles In Liquid

With the development of liquid environment transmission electron microscopy?LETEM?,it is possible to observe the physicochemical phenomena of materials in liquids at the nanoscale and even atomic scale.This technology is achieved by encapsulating the liquid in a closed liquid chamber,so that the chemical reaction in liquid can be observed under the transmission electron microscope,which is beneficial to reveal the scientific mechanisms of the nucleation/growth and the self-assembly of the nanomaterials.In this paper,the nucleation and growth of organic-inorganic hybrid perovskite in precursor liquids and the self-assembly of Co₃O₄ nanorods driven by electron beam have been studied in liquid environment transmission electron microscopy.The specific research contents and results are as follows:1.Using the lead iodide powder as raw material,lead iodide films with homogeneous amorphous and crystalline coexistence were prepared by vapor deposition on ultra-thin carbon film and silicon nitride?Si₃N₄?film,which were used to perform ex-situ and in-situ LETEM experiment.2.By using ex-situ transmission electron microscopy,the observations of MAPbI3perovskite prepared by two-step method were carried out at different stages,and the morphological evolution of lead iodide and the nucleation and growth process of perovskite were studied.The results showed that there is a recrystallization process of lead iodide at the early stage of the reaction,and then the MAPbI₃ perovskite is formed.Small particles of perovskite are formed firstly during the reaction,then the large particles of lead iodide begin to react inward from the outside.3.By using liquid environment transmission electron microscopy,the reaction growth process from lead iodide to MAPbI₃ perovskite by two-step method was further studied in situ.We found that the lead iodide,which provides the growth of perovskite particles at the beginning of the reaction,was not derived from the crystalline lead iodide.Combined with the surface morphology of the sample film and the results of the ex-situ experiment,we concluded that it was derived from amorphous lead iodide.It was also found that the formation of nanowires was closely related to the coalescence of nanoparticles on the film.On the other hand,we found that the perovskite ripening process conforms to the LSW theory during the experiment.This study is helpful to understand the nucleation and growth mechanism of the perovskite under the two-step method,and to have a new understanding of the preparation of perovskite film in the perovskite solar cell.4.A self-assembly process of Co₃O₄ nanorods in water was observed in situ by liquid environment transmission electron microscopy.By the electron beam irradiation,the dielectric constant of water was changed and the electrical conductivity was increased in the irradiated water.The movement of nanorods was initiated and self-assembled into longer nanorods at last.By characterizing the morphology of the Co₃O₄nanorods,we believe that the polarity of the surface residual charge plays a decisive role in the intelligent assembly between nanorods.This work can offer people a deeper understanding of the incomplete nature of surface charge compensation on polar crystal surfaces,and may provide important experimental data and theoretical reference for artificially regulating the metal oxide self-assembly process.