Structure and compositional studies of multi-component nanoparticles

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Malyavanatham, Gokul

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The laser ablation of microparticle (LAM) process was used to study nanoparticles of multi-component materials. The production process utilized laser ablation of a continuously flowing aerosol of micron-sized particles under a gas ambient. An aerosol generator entrained microparticles into a gas flow and directed them through a nozzle into a laser interaction cell. After plasma breakdown, the shock wave propagated through the microparticles and the nanoparticles condensed behind this shockwave. Two methods were developed to collect nanoparticles; the first method used supersonic impaction on substrates at room temperature to enable direct writing of thick films and the second method used electric fields to deflect and collect charged, individual nanoparticles. Two methods for generating multi-component nanostructured materials were studied. The first method involved feeding single-phase microparticles containing the desired composition. Lead Zirconate Titanate (PZT) microparticles were used to generate nanoparticles that were then impacted onto substrates to produce thick films. Quality, morphology, crystallization and composition variations of these thick films were analyzed using material characterization techniques. Segregation of elements and an overall deficiency in Zr and Ti were observed in the deposited thick films as a result of the agglomerated state of the PZT microparticles. However, the analysis for this material system was complicated by the presence of multiple compounds. To develop a further understanding of how segregation occurs in multicomponent systems during the LAM process, a second method for generating multicomponent nanoparticles by feeding mixtures of single component microparticles was studied. Nanoparticles generated by ablation of Cu and Au microparticle mixtures were collected electrostatically and analyzed. Interactions between exploding microparticles resulted in condensation of nanoparticles that were non-equilibrium solid solutions of Au and Cu. The chemical composition of the individual nanoparticles varied over a wide range suggesting that the overlap in plumes from individual microparticles was not complete.



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