In-situ Tailoring The Surface/Interface Structures And Observing Its Dynamic Process Of Nanomaterials

When the size of the material drops to the nanometer scale,the surface/interface effect becomes more and more significant.Precisely tailoring the surface/interface structure of nanomaterials and elucidating the relationship between structure and properties are of great significance for understanding the working mechanism of nanomaterials in various applications,exploring novelty properties,and designing nano-functional devices.Based on the in-situ transmission electron microscopy method,we study the in-situ regulation mechanism and structure-property relationship of the surface/interface structure of semiconductors under different external fields.The main achievements are summarized as follows:1.In-situ regulation of sulfide heterostructure interface by electric field.?1?An electrically driven cationic exchange method has been developed.Using this method,it is possible to completely control the interface structure of individual nanocrystals.?2?The formation process of CdS/Cu₂S hetero interface structure has been observed in situ,including sublimation of cadmium,electro-dissolution of copper,migration of copper ions,and formation of CdS/Cu₂S core-shell structure.?3?The reaction mechanism strongly supports the fact that the inwardly migrating cations?here,Cu⁺and Li⁺?originate from metal active electrodes and are driven by the electric field force,whereas the outward migration of cations(here,Cd²⁺)occurs due to evaporation into the gas phase and is actuated by Ohmic heating.2.In-situ regulation of Cu2S/W interface by electric field.?1?The reversible copper extraction-reinsertion at the Cu₂S/W interface has been monitored in situ and the pseudoelectroelasticity of monocrystalline Cu₂S nanowires has been reported for the first time.The atomic scale details including phase transformation,migration and redox reactions of Cu⁺ions,nucleation,growth,as well as spontaneous shrinking of Cu protrusion.?2?The microscopic mechanism demonstrates that the extraction of Cu⁺ions is driven by the external electric field and the cation diffusion barriers are dominated by Joule heat,whereas the oxidation and reinsertion of Cu in the absence of bias is due to the chemical potential difference.?3?The pseudoelectroelasticity behavior of Cu₂S nanowires was successfully applied to nanoelectromechanical systems.The Cu₂S nanowire electric actuator can be used to drive the movement of tiny objects with nanometric or subnanometric precision,and it has better repeatability.3.In-situ regulation of the surface structure of silver peroxide nanoparticles by electron beam irradiation.?1?Two distinct etching processes of Ag₂O₂ nanoparticles with clean surface and Ag₂O₂nanocrystals with Ag surface adsorbers have been observed.The anomalous shape evolution of Ag₂O₂ nanocrystals modulated by the surface adsorbates of Ag clusters,and the process includes three stages:a sphere-to-a cube transformation,side etching of a cuboid,and bottom etching underneath the surface adsorbates.?2?After detailed analysis,we find the Ag adsorbates modify the Ag₂O₂ nanocrystal surface configuration by selectively capping the junction between two neighboring facets and thus they prevent the edge atoms from being etched away and block the diffusion path of surface atoms.In this thesis,the in-situ regulation mechanism of the surface/interface structure and the structure-property relations in semiconductor are stuied at atomic scale,which provides a theoretical basis for the preparation of materials with complex surface/interface structure and the design of multifunctional devices.