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Underwater produced plasmas and synthesis of nanoparticles by dual pulse laser ablation

Nanoparticles of various materials are today implemented in wide variety of industrial, scientific and medical applications. Biocompatible nanoparticles are used for cell treatment ; as nanobiomarkers, for therapy and diagnostics. Nanoparticles can be synthesized conventionally either using wet chemistry methods or gas phase processes. The colloid solutions of nanoparticles synthesized by wet chemistry are often characterized by impurities which are reaction products of additives and precursors. The nanoparticles synthesized by gas phase processes are often agglomerated and hardly redispersible into the solution. Such drawbacks make those techniques of nanoparticles synthesis very limiting. In the past decade the laser ablation in liquids appeared to be a solution for many of those problems. It is recognised as simple and versatile technique and there are almost no limitations in a selection of materials for the nanoparticle synthesis. The remarkable advantages of this technique over other techniques are absence of impurities in the final product (free of contaminating processes, chemical precursors not required), possibility of preparation of multicomponent nanoparticles, weak agglomeration, relatively narrow size-distribution of nanoparticles, etc. Anyway, over a time nanoparticles produced by laser ablation in liquids may aggregate (if not charged) and precipitate thus making theirs properties limiting. In this work we will consider synthesis of nanoparticles of Ag and Au by dual-pulse laser ablation underwater (no surfactants or other chemicals were added to avoid undesired agglomerations). The main parameter is time delay between pulses for ablation and it was varied from 0 to 50 ms thus making the second laser pulse to interact with the primarly created NP’s in various stages of their formation and evolution. The comparison between orthogonal and parallel configuration of the laser pulses is studied. The experiment was performed with Nd:YAG lasers irradiating at 1064 nm and 10 Hz. The results were discussed in terms of time delays between pulses, size-distributions based on TEM figures and DLS measurements, mass and crater volumes after ablation, Z-potential measurements and measurements of extinction curves (monitoring during experiment and after treatment) extracting data on precipitation and agglomeration of NP’s. The dual pulse laser synthesis of NP’s is compared to conventional post-treatment synthesis.

laser synthesis of nanoparticles underwater; dual pulse laser ablation; underwater laser produced plasmas

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