Study On Size Effect Of Dealloying

Both Nano-porous materials and nanoparticles are widely used in catalysis,sensing,Raman enhancement and other fields due to their large specific surface area.Therefore,nanoparticle-nanoporous structure is expected to displace better performance.Through dealloying,however,nanoparticles were found size effect,i.e.,particles with quiet small size cannot form nanoporous structure during dealloying,the reason is not clear yet,therefor,this work,the Au-Ag alloy nanoparticles were used as model system to study the size effect of metallic nanoparticles dealloying.Firstly,Au-Ag alloy film were deposited on SiO₂ substrate by co-sputtering,then annealing in vacuum.Then the film was dewetting in vacuum with a size distribution.The effect of film composition,film thickness,thermal annealing time and temperature on the morphology,size and composition of nanoparticles were studied.The result showed that the dewetting temperature is high,the nanoparticles are spherical.The increase of Au content in the film,in contrast,can significantly slow down the particle forming.Dealloying was performed under Au-Ag alloy nanoparticles with different sizes on SiN substrate was observed by transmission electron microscope.The Au_0.2Ag_0.8nanoparticles showed size effect during dealloying at–28℃.When the nanoparticle size is less than 15 nm,nanoporous structure cannot form,dealloying only lead to shrinkage of the nanoparticles.When the nanoparticle size is in the range of 15 nm-30nm,morphology can be divided into two different forms,including doughnut-like structure after dealloying,with hole in the center,and nanoparticle with irregular shrinkage.When the size of nanoparticle is larger than 30 nm,porous structure can be formed in the particles after dealloying.The size effect also displaced strong composition sensitivity.When the Au content is 30%or higher than 30%,nanoporous cannot be formed with the size ranging from 10 nm-60 nm even at temperature as low as-28℃。Finally,the Surface Raman Enhancement on nanoporous nanoparticles were studied.When rhodamine is the probe,the un-dealloyed nanoparticles that the average size is 15 nm have the best performance;However,if the crystal violet was the probe,the dealloyed nanoparticles which size is 45 nm have the best performance...