Fabrication of high-demensional nano-structures by laser ablation in liquids

激光辐照金属纳米粒子是修饰纳米粒子形状的基本技术之一。以往的研究表明，通过化学合成得到的纳米粒子只能得到尺寸减小或增大的球形纳米粒子，而我们揭示了在纯水中激光照射制备的银纳米粒子可以得到纳米线。本研究对纳米线的形成机理进行了探讨。首先，我们研究了辐照强度对产物形状的影响，发现纳米线和纳米片是在高辐照强度下产生的。这一发现表明，纳米线将通过银纳米粒子的融合而产生。此外，还发现在低激光强度下会产生纳米管和纳米棒，这表明存在另一种形状转变。其次，我们研究了作为杂质的离子对纳米线形成的影响。随着氯化钠浓度的增加，线状颗粒的形成效率和尺寸增大。这一发现可以用离子介导的金属纳米颗粒的自组装来解释。此外，还发现加入氯化钠可以促进纳米管和纳米棒的形成。这一发现是从氯离子对银纳米颗粒的氧化刻蚀效应和光还原作用来解释的。在未来的研究中，我们将进一步研究纳米管和纳米棒的形成机理。

Laser irradiation onto metal nanoparticles is one of a essential technique to modify the shape of the nanoparticles. While former studies using nanoparticles obtained by chemical synthesis have shown that only size-decreased or -increased spherical nanoparticle were obtained, we revealed that nanowires were obtained by laser irradiation onto silver nanoparticles prepared by laser irradiation in pure water.In this study, the formation mechanisms of the nanowires have been explored. First, we have investigated the influence of the irradiation intensity on the shape of products, and have revealed that nanowires and sheets were produced at high irradiation intensity. This finding indicates that nanowires will be produced via fusion of silver nanoparticles. In addition, nanoprisms and nanorods were found to be produced at low laser intensity, indicating that another type of shape conversion presents.Second, we have investigated influences of ions contained as impurities on the formation of nanowires. The formation efficiency and size of wire-like particles increased with increase in the concentration of NaCl. This finding can be explained in terms of the ion-mediated self-assembly of metal nanoparticles. In addition, it was found that the formation of nanoprisms and nanorods were enhanced by addition of NaCl. This finding was explained in terms of the oxidative etching effect by chloride ions on silver nanoparticles followed by photo-reduction.In the future study, we will carry out further investigation on the formation mechanism of nanoprisms and nanorods.