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Abstract:
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Nanoparticles possess unique physical , chemical , optical and electronic properties stemming from their nanoscale dimensions and are currently used in catalysis , microelectronics , drug delivery , as well as other applications . However , due to their large surface area -to -volume ratio , nanoparticles have a strong tendency to coalesce and sinter during processing or usage over short time scales and at low temperatures , which lead to significant changes in behavior and performance . In this work , in -situ transmission electron microscopy (TEM ) heating has been used to investigate the effects of particle size , temperature and carbon capping layers on sintering in face -centered cubic (FCC ) metallic nanoparticles . For the first time , we make direct and real -time measurements of nanoparticle size , neck growth , dihedral angle and grain boundary motion during sintering , which are then used to calculate fundamental material transport parameters such as surface diffusivity and grain boundary mobility . We observe that carbon surface coatings typically present on most commercial nanoparticles can significantly inhibit sintering in nanoparticles . Also , a new mechanism for coalescence in nanoparticles is shown where small clusters on the support can initiate neck growth by forming a bridge between the nanoparticles consisting of individual atoms or small clusters of atoms . In -situ TEM experiments provide critical and valuable real -time dynamic information for direct investigation of the link between the evolution of sintering and controlling mechanisms , which conventional experiments such as post -mortem TEM observations are not capable of conveying . |