Nanoparticles produced via laser ablation of microparticles

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Henneke, Dale Edwin

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Several different nanoparticle synthesis techniques exist. One synthesis method uses the laser ablation of microparticles (LAM) entrained in an aerosol technique to produce charged nanoparticles. Here, we discuss nanoparticles made using the LAM process. Since nanoparticles made in this fashion are charged in the ablation process, they are not overly susceptible to agglomeration. The synthesized particles appear to have diameters that are dependant on background pressure, but are relatively insensitive to gas type. Once the particles have been made, they must be collected in a capping solution to prevent agglomeration from occurring. Two distinct methods of collection have been devised. The first collection scheme uses an impactor to remove any large (>300 [nm]) unablated material. The charged nanoparticle aerosol is then supersonically impacted directly into a surfactant capping solution. The suspension is then gathered for subsequent processing. In the second collection method, the charged nature of the nanoparticles is utilized to deflect the aerosol in an electric field. The electric field drives the particles onto a surfactant laden electrode. Size distributions for silver were determined using a transmission electron microscope; the mean particle diameter was found to be 5 [nm]. The collected nanoparticles were found to be flocculated; this can be explained by inadequate coverage of the capping molecule. For this reason, an annealing step to provide better surface coverage of the cap is performed. As the suspensions are heated, the size of the flocculents decreases. The decrease in flocculent size indicates that nanoparticles are leaving the main group and going into suspension.



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