Synthesis Of Silver-based Nanostructures Via Laser Chemistry

As a noble metal, silver has excellent electrical conductivity and heat-transferperformance, and silver nanostructures have great potential applications in electronics,optics, catalysis, surface-enhanced Raman scattering and biological tags. So far, avariety of silver-based nanomaterials, such as zero-dimensional silver nanoparticles,one-dimensional silver nanowires, two-dimensional silver dendritic structures, havebeen synthesized via chemical methods. Whereas, few research has been published onthe synthesis of these silver-based nanomaterials via laser technique that has a numberof advantages, such as simple processing, short experimental period, few impurities,green synthesis, etc. In this paper, a liquid target, ethanol solution of silver nitrate,was irradiated by five different types of laser beams. Various laser induced chemicalreactions occurred, and numerous novel silver-based nanostructures were finallyacquired. Meanwhile, the formation mechanisms of these novel nanostructures werediscussed.Abundant Ag-C composite nanowires were successfully synthesized while a1064nm nanosecond pulsed laser was used to irradiate the liquid target. It was found thatirradiation duration, laser fluence, the concentration of silver nitrate and the solventall played important roles in determining the morphology of products. Meanwhile, theas-synthesized Ag-C composite nanowires was proposed to originate from the laserinduced thermal decomposition of the molecules of silver nitrate, and graduallyevolved to silver oxide nanoparticles, silver-silver oxide heterostructures, silver-silveroxide-carbon nano-chains and the final nanowires. The complete process could occuronly if the laser fluence exceeds a threshold.Four other types of laser beams were also used to irradiate the liquid target, andthe findings are as follows:1. Fine silver nanoparticles were synthesized when a1064nm millisecond pulsedlaser with quite low power density was used. The size of silver nanoparticles wasincreased via adding photosensitizer in the solution or using silver nitrate with higherconcentration.2. Self-assembled silver nanoparticles were synthesized when1064nmmillisecond and nanosecond pulsed laser were used one after another. The formationof these self-assembled silver nanoparticles could attributed to a second irradiation of the premier products (the large silver nanoparicles), which were heated and becamesmaller and smaller.3. A variety of silver nanostructures, such as silver-silver oxide heterostructures,sivler nanoparticles, silver tree, were synthesized when a1064nm continuous laserwas used with different irradiation durations. It is believed that as irradiation durationincreases, laser pulse energy becomes higher, and more molecules of silver nitratedecompose to generate more nucleation sites, and the growth direction of theas-formed silver clusters changes from zero-dimensional space to two-dimensionalspace.4. Silver-silver oxide heterostructures were synthesized once again when both a532nm and a266nm nanosecond pulsed laser were used. The former could beascribed to the multi-photon effect while the latter was attributed to the decompositionof silver nitrate under a low laser fluence.