“激光选择性表面气化”可控合成单分散胶体纳米晶

Monodisperse colloidal nanocrystals have been considered as ideal building blocks for advanced functional nanodevices. As a green, efficient, and room-temperature synthesis technique, laser ablation in liquids (LAL) has been believed promising in nanomaterials synthesis, however, a wide size distribution of as-obtained nanocrystals remains one of the significant problems limiting LAL development. Although there have been some works on size-reduction/uniformity of noble metal nanocrystal via laser fragmentation, the uniformity of nanocrystals is still not good due to lack of elaborate designs. In this project, we take advantage of "selective-surface-evaporation by laser" to make reasonable designs, where the irradiated nonuniform nanocrystals are partially evaporated, thus reduced in size and tends to more uniform, and finally become monodisperse colloidal nanocrystals with a final average size slightly smaller than the critical size for surface-evaporation. By means of the above universal strategy, we will controllably synthesize a number of monodisperse colloidal metal and semiconductor nanocrystals with size dispersion less than 5%, clarify the effects of laser fluence, dielectric constants of liquid media and surfactants on the final average size of nanocrystals, and demonstrate the size evolution of partially evaporated nanocrystals in the nonequilibrium conditions created by pulsed laser irradiation. This project will make a breakthrough in uniform-nanocrystal-synthesis by laser and provide a novel synthesis route towards monodisperse colloidal nanocrystals.

单分散胶体纳米晶是组装先进功能纳米器件的理想单元,激光液相烧蚀法作为一种发展潜力巨大的常温、绿色、高效的纳米材料合成工艺，却仍存在纳米晶尺寸不均匀这一制约其发展的严重问题。虽然研究人员在"激光破碎"使贵金属纳米晶均匀细化方面已开展了一些工作，但由于尚缺少精巧而合理的设计，纳米晶尺寸均匀性仍不甚理想。本项目提出利用"激光选择性表面气化"，通过合理的设计，使被激光辐照的非均匀纳米晶只发生表面气化，尺寸逐渐减小且趋向均匀，最终达到略小于表面气化临界尺寸为止，纳米晶不再气化，形成单分散胶体纳米晶。本项目将利用这一普适思路可控制备各种金属、半导体单分散胶体纳米晶（尺寸分布<5%），阐明激光能量密度、溶剂和表面活性剂的介电常数对纳米晶均衡尺寸的调控作用，及脉冲激光辐照的非平衡条件下，表面气化纳米晶的变化规律。本项目将突破激光法在合成尺寸均匀纳米晶方面的瓶颈，为单分散胶体纳米晶的可控合成开辟一条新途径。

粒径高度均匀的单分散胶体纳米晶往往具有独特的光、电、磁学等性能，是组装先进功能纳米器件的理想单元。而激光液相烧蚀法作为一种发展潜力巨大的常温、绿色、高效的纳米材料合成工艺，却仍存在纳米晶尺寸不均匀这一制约其发展的严重问题。针对以上问题，本项目提出“激光选择性表面气化”可控合成胶体纳米晶的合成策略，并利用这一普适思路可控制备各种金属、半导体单分散胶体纳米晶，阐明激光能量密度、溶剂和表面活性剂的介电常数对纳米晶均衡尺寸的调控作用，及脉冲激光辐照的非平衡条件下，表面气化纳米晶的变化规律。本项目取得重要结果如下：1）采用激光法可控合成了镉、锌等多种单分散非贵金属胶体纳米晶，阐明了“激光选择性表面气化”机制，建立了“尺寸选择性表面逐层气化”模型。2）单分散镉胶体纳米晶具有强烈的深紫外等离激元特性，消光效率高于文献报道的其他金属纳米颗粒。3）以单分散锌纳米晶为模板，利用Kirkendall效应，首次合成出硒化锌纳米空心球，自组装成减反膜，获得近90%的近红外增透性能。4）铝纳米颗粒自组装结构具有大面积、高密度“热点”的等离激元特性，紫外SERS增强因子远远高于已报道的其他铝纳米结构，达到了贵金属水平。5）实现了单分散半导体纳米晶的“自上而下”激光可控合成，揭示了“尺寸选择性气化”机制和“局部拉莫生长”机制。本项目突破了激光法在合成尺寸均匀纳米晶方面的瓶颈，为单分散胶体纳米晶的可控合成开辟一条新途径。