Mechanism Study On Galvanic Replacement Reactions Of One-dimensional Metal Nanometerials By In-situ Liquid Cell Transmission Electron Microscopy

The structure,size and morphology of metal nanomaterials are key factors to determining their physical and chemical properties.These parameters of metal nanomaterials can be tailored by galvanic replacement reaction,which is a versatile tool,especially for hollow structures.Based on galvanic replacement,several progress have been made in tuning the morphology and structure of nanomaterials.However,many complicated behaviors during galvanic replacement have not been well understood.This is because it is difficult to directly monitor the dynamic reaction process of metal nanomaterials based on conventional chemical methods.Liquid cell electron microscopy is a rapidly developing and powerful technique that is capable of achieving sub-nanometer resolution of structure and components.The understand of galvanic replacement can be greatly improved via liquid cell TEM technique.We used in-situ liquid cell electron microscopy to study the dynamic process of galvanic replacement between silver nanowire and HAucl₄ or H₂Ptcl₆ solution.Real-time observations were performed to trace the continuous evolutions of microstructures from solid nanowires to hollowed nanotubes.Based on experimental observations,galvanic replacement reaction mechanism was proposed.The whole process can be described as follows.Pits firstly appear on the surface of nanowire due to the dissolution of silver atoms.The dissolution starts from the pits,penetrates into the nanowires and extends along the axis,till to form tubular structures.The five-fold twinned structure of silver nanowires may cause the anisotropic oxidative etching behavior.The compositions of the nanotube were characterized by scanning transmission electron microscopy?STEM?,which revealed the deposition of metal atoms continuous among the reaction on the surface of silver nanowires result in alloy of silver.The influence of different alloy forming abilities on the reactions was analyzed by comparing the galvanic replacement reactions of silver nanowires with different solutions.The result presented here will serve as an important reference to tuning the structures of metal nanomaterials for wide applications.