[论文解读] Controlling the size distribution of nanoparticles through the use of physical boundaries during laser ablation in liquids

Kaushik Roy Choudhury, Rajesh Kumar Singh+4 more|arXiv (Cornell University)|Nov 4, 2018

Laser-Ablation Synthesis of Nanoparticles参考文献 46被引用 6

一句话总结

本研究提出一种新颖方法，通过在烧蚀位点附近引入物理边界，控制液体中激光烧蚀的纳米粒子尺寸分布。通过限制电浆喷云，热化时间延长，导致纳米粒子尺寸增大；在水和异丙醇中对铜和钛进行的实验表明，与开放式靶面配置相比，平均尺寸显著增加，尤其是铜粒子。

ABSTRACT

A simple, yet effective method of controlling the size and size distributions of nanoparticles produced as a result of laser ablation of target material is presented. The method employs the presence of physical boundaries on either sides of the ablation site. In order to demonstrate the potential of the method, experiments have been conducted with copper and titanium as the target materials that are placed in two different liquid media (water and isopropyl alcohol). The ablation of the target material immersed in the liquid medium has been carried out using an Nd:YAG laser. Significant differences in the size and size distributions are observed in the cases of nanoparticles produced with and without confining boundaries. It is seen that for any given liquid medium and the target material, the mean size of the nanoparticles obtained with the boundary-fitted target surface is consistently higher than that achieved in the case of open (flat) targets. The observed trend has been attributed to the plausible role(s) of the confining boundaries in prolonging the thermalisation time of the plasma plume. In order to ascertain that the observed differences in sizes of the nanoparticles produced with and without the presence of the physical barriers are predominantly because of the prolonged thermalisation of the plasma plume and not due to the possible formation of oxide layer, select experiments with gold as the target material in water have also been performed. The experiments also show that, irrespective of the liquid medium, the increase in the mean size of the copper-based nanoparticles due to the presence of physical boundaries is relatively higher than that observed in the case of titanium target material under similar experimental conditions.

研究动机与目标

• 开发一种简单方法，精确控制液体中激光烧蚀过程的纳米粒子尺寸及其分布。
• 研究烧蚀位点附近的物理边界如何影响电浆喷云动力学及纳米粒子形成。
• 确定观察到的尺寸变化是由于热化时间延长，还是氧化层形成所致。
• 比较不同材料（铜、钛、金）和液体介质（水、异丙醇）在受限条件下的影响。

提出的方法

• 在靶材两侧设置物理边界以限制电浆喷云的膨胀。
• 使用Nd:YAG激光在水或异丙醇中对浸没的铜和钛靶材进行烧蚀，分别在边界受限和开放式（平面）靶面条件下进行。
• 采用透射电子显微镜（TEM）分析所合成纳米粒子的尺寸及其分布。
• 在水中进行金的对照实验，以隔离等离子体受限效应与表面氧化的影响。
• 测量并比较边界受限与开放式烧蚀设置下的平均粒子尺寸及尺寸分布宽度。
• 通过关联受限条件与观察到的尺寸增加，分析热化时间在纳米粒子生长中的作用。

实验结果

研究问题

• RQ1 物理边界的引入如何影响激光烧蚀纳米粒子的尺寸及其分布？
• RQ2 尺寸控制的主要物理机制是什么——电浆热化时间延长，还是表面氧化？
• RQ3 不同靶材材料（铜、钛、金）在受限条件下对纳米粒子尺寸增强的响应如何？
• RQ4 液体介质（水与异丙醇）在受限条件下如何影响尺寸控制效果？
• RQ5 通过此基于边界的调控方法，平均纳米粒子尺寸可调节到何种程度？

主要发现

• 与开放式靶面配置相比，物理边界的引入始终显著增加了激光烧蚀纳米粒子的平均尺寸。
• 在相同条件下，铜纳米粒子的平均尺寸在受限条件下增加幅度明显大于钛。
• 对于铜和钛靶材，水中的尺寸增加效应均强于异丙醇，表明存在溶剂依赖性影响。
• 在水中对金进行的对照实验确认，尺寸增加是由于电浆热化时间延长，而非表面氧化。
• 在受限条件下，尺寸分布宽度保持较窄，表明具有良好的单分散性控制能力。
• 观察到的趋势支持该假设：物理边界可延长电浆喷云的热化时间，从而促进纳米粒子的增强生长。