The Formation And Evolution Of Twins In Nanoporous Gold And Copper Nanoparticles Under An External Field

Twins and dislocations are an important part of crystal defects,especially in metal crystals.The existence of twins or dislocations will greatly affect the strength,toughness,plasticity,electronic band structure and other physical and chemical properties of the metal.However,in the now research,because the changes of twins and dislocations are extremely rapid and have great sensitivity to the external environment,the evolution process under actual specific external field conditions is only through theoretical calculations and simulations,there is no direct observe.We analyz the evolution process of twins and dislocations under different external fields in real time by in-situ transmission electron microscopy with high temporal and spatial resolution,and then combined with direct evidence of actual atomic scale,and a new evolution mechanism is proposed.In this paper,we used in-situ transmission electron microscopy to study the evolution of dislocations and twins in nanoporous gold with the gas phase and copper nanoparticles during the annealing process.(1)A large amount of stress is stored in the nanoporous gold ligament prepared by the dealloying method.We found through in-situ gas-phase electron microscopy that these stresses will be released along with the evolution of the ligament structure during the catalytic reaction of nanoporous gold.A large number of dislocations,twins,and lattice distortions are formed in the ligaments.This provides a new idea for the research on the source of the high catalytic activity of nanoporous gold.(2)Copper nanoparticles have a large amount of internal stress after melting and solidification.During the annealing process,these internal stresses will drive a large number of Burst vectors to a/6<112>Shockley partial dislocations emitted,from grain boundaries or distortion regions multiple twin boundaries in different directions are formed in the nanoparticle,and then these twin boundaries move closer to each other to form five-fold twins that are stable in structure and energy.The five-fold twins emit a large number of Shockley's partial dislocations in the lattice distortion area formed by the fluctuations in energy and structure,driving each twin boundary irreversibly away from each other to complete the disintegration.We propose a new mechanism of the formation and disintegration of five-fold twins by Shockley partial dislocations driving the migration of twin boundaries.