Limited Elemental Mixing in Nanoparticles Generated by Ultrashort Pulse Laser Ablation of AgCu Bilayer Thin Films in a Liquid Environment: Atomistic Modeling and Experiments
Limited Elemental Mixing in Nanoparticles Generated by Ultrashort Pulse Laser Ablation of AgCu Bilayer Thin Films in a Liquid Environment: Atomistic Modeling and Experiments
复制标题
液体环境中 AgCu 双层薄膜超短脉冲激光烧蚀产生的纳米颗粒中的有限元素混合：原子建模和实验
DOI：
10.1021/acs.jpcc.0c09970
复制
发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Zhigilei, Leonid V.
中科院分区：
文献类型：
--
作者：
Shih, Cheng-Yu;Chen, Chaobo;Rehbock, Christoph;Tymoczko, Anna;Wiedwald, Ulf;Kamp, Marius;Schuermann, Ulrich;Kienle, Lorenz;Barcikowski, Stephan;Zhigilei, Leonid V.
液体脉冲激光烧蚀（PLAL）是一种很有前途的制备胶体合金纳米颗粒的技术，在催化、增材制造和生物医学等广泛领域都有很高的需求。许多应用对纳米颗粒的组成和尺寸分布有严格的要求，只有在明确纳米颗粒形成机制的指导下，通过PLAL技术的创新才能满足这些要求。在这项工作中，我们进行了计算和实验相结合的银/铜和铜/银双层薄膜的超短PLAL纳米颗粒形成机制的研究。对单个纳米粒子组成的实验探测和大规模原子模拟的预测提供了一致的证据，证明PLAL双层膜中两种成分之间的混合有限。纳米粒子组成的模拟和实验分布表明，富银和富铜纳米粒子的丰度增加，而混合良好的合金纳米粒子的数量明显减少。令人惊讶的是，双层膜中两种组分的纳米级相分离表现为胶体纳米颗粒中完全定量混合的急剧偏离，这可以用烧蚀过程初始阶段模拟中揭示的烧蚀羽流和液体环境之间复杂的动态相互作用来解释。模拟结果表明，液体环境对烧蚀羽流的快速减速会导致在羽流前部形成一个短暂的热金属致密区，这阻碍了两种成分的混合，同时也会导致羽流在空化泡中分层。因此，在烧蚀过程的第一个纳秒内，在出现的空化泡的不同部位产生了不同尺寸和成分的纳米颗粒。值得注意的是，在烧蚀过程初始阶段模拟中产生的最大纳米颗粒的直径比原始双层膜的厚度大两倍以上。这一观察结果为实验中观察到的大纳米颗粒的形成提供了一个合理的场景。在不同空间顺序的Cu和Ag双分子层的模拟中，证实了纳米颗粒中元素混合有限的结论，尽管这两个体系表现出一些显著的数量差异，这主要与Cu和Ag中电子-声子耦合强度的不同有关。总的来说，本研究结果为超短PLAL中双金属纳米颗粒的形成机制提供了新的见解，并表明具有明显元素偏析的目标可能会阻碍非混相元素形成合金纳米颗粒。
Pulsed laser ablation in liquids (PLAL) is a promising technique for the generation of colloidal alloy nanoparticles that are of high demand in a broad range of fields, including catalysis, additive manufacturing, and biomedicine. Many of the applications have stringent requirements on the nanoparticle composition and size distributions, which can only be met through innovations in the PLAL technique guided by a clear understanding of the nanoparticle formation mechanisms. In this work, we undertake a combined computational and experimental study of the nanoparticle formation mechanisms in ultrashort PLAL of Ag/Cu and Cu/Ag bilayer thin films. Experimental probing of the composition of individual nanoparticles and predictions from large-scale atomistic simulations provide consistent evidence of limited mixing between the two components from bilayer films by PLAL. The simulated and experimental distributions of nanoparticle compositions exhibit an enhanced abundance of Ag-rich and Cu-rich nanoparticles, as well as a strongly depressed population of well-mixed alloy nanoparticles. The surprising observation that the nanoscale phase separation of the two components in the bilayer films manifests itself in the sharp departure from the complete quantitative mixing in the colloidal nanoparticles is explained by the complex dynamic interaction between the ablation plume and liquid environment revealed in the simulations of the initial stage of the ablation process. The simulations predict that rapid deceleration of the ablation plume by the liquid environment results in the formation of a transient hot and dense metal region at the front of the plume, which hampers the mixing of the two components and, at the same time, contributes to the stratification of the plume in the emerging cavitation bubble. As a result, nanoparticles of different sizes and compositions are produced in different parts of the emerging cavitation bubble during the first nanoseconds of the ablation process. Notably, the diameters of the largest nanoparticles generated in the simulations of the initial stage of the ablation process are more than twice larger than the thickness of the original bilayer films. This observation provides a plausible scenario for the formation of large nanoparticles observed in the experiments. The conclusion on limited elemental mixing in the nanoparticles is validated in simulations of bilayers with different spatial order of Cu and Ag layers, even though the two systems exhibit some notable quantitative differences mainly related to the different strength of electron–phonon coupling in Cu and Ag. Overall, the results of this study provide new insights into the formation mechanism of bimetallic nanoparticles in ultrashort PLAL from thin bilayer targets and suggest that the formation of alloy nanoparticles from immiscible elements may be hampered for targets featuring distinctive elemental segregation.