In Situ Transmission Electron Microscopy Study On The Structural Evolution Of Nanoparticles Under Thermal Field

With the further miniaturization of microelectromechanical systems(MEMS),metal and semiconductor materials for building devices are facing new challenges.At the nano scale,the electrical,mechanical,and thermal properties of materials often no longer follow the laws of macroscopic materials.Therefore,the design and manufacture of smaller-sized MEMS requires reconsideration of the specific structure and properties of materials at the nano scale.In this paper,based on in-situ transmission electron microscopy,semiconductor and metal alloy nanoparticles are taken as examples to study the structural evolution under thermal field.The main results are summarized as follows:1.In-situ study on the structural evolution of CdSe/CdS nanoparticles under thermal field.(1)A novel domain-confined growth strategy was proposed to prepare individual hollow nanostructure.The sublimation and regrowth of CdSe/CdS core/shell nanoparticles were controlled by changing the heating temperature and electron beam irradiation parameters to obtain individual hollow CdSeS nanostructures.(2)Electron beam irradiation plays a dominant role in the domain-confined growth process.Moreover,the regrowth of hollow CdSeS nanostructures is strongly dependent on the volume ratio of the residual volume of partially sublimed CdSe/CdS nanoparticles to the carbon shell.Only when CdSe/CdS nanoparticles with a volume ratio of about 0.2-0.8 can successfully form hollow CdSeS nanostructures.2.In-situ study on the structural evolution of copper-silver nanoparticles under thermal field.(1)In-situ heat treatment of CuAg nanoparticles with different sizes under high vacuum conditions was performed.For sub-10 nm particles,the CuAg heterostructures preferentially show a unique Cu(100)/Ag(100)interface,differing from the traditional Cu(111)/Ag(111)interface in large particles.(2)Size-effect was considered by whether to involve the contribution of surface energy(depending on the surface to volume ratio),to determine the preferential orientation relationship of the interface.When the particle sizes down to sub-10 nm,owing to surface to volume ratio increases rapidly,the effect of surface energy related to the particle size becomes increasingly dominant and plays a major role in determining the final interface structure.(3)Finally,a resonable atomic motion mechanism is discussed to explain the effect of particle size on the formation of different heterogeneous interfaces.For sub-10 nm particles,due to large surface/volume ratio,surface diffusion is a major mechanism for driving mass transport,which determines the type of heterogeneous interface.3.Non-in-situ study on the structural evolution of copper-nickel nanoparticles under thermal field.(1)The thermal stability of spherical Cu/Ni core/shell nanoparticles under thermal field was studied in the atmosphere.It was found that the spherical Cu/Ni core/shell nanoparticles were transformed into hollow truncated cubic nickel oxide nanostructures.(2)In-situ heating experiments of Cu/Ni core/shell nanoparticles in transmission electron microscopy indicated that oxygen is a necessary condition for the formation of hollow truncated cube structures...