Collaborative Research: Ultrafast Laser-Driven Phase Transitions in Nanoparticles near their Melting

合作研究：纳米颗粒熔化附近的超快激光驱动相变

基本信息

批准号：
1708486
负责人：
Leonid Zhigilei
金额：
$ 9万
依托单位：
University of Virginia Main Campus
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-08-01 至 2021-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1708486&HistoricalAwards=false
关键词：
Collaborative Research Ultrafast Laser Driven

项目摘要

Non-Technical AbstractAlthough the melting of solids is the most ubiquitous of phase transitions, its atomistic mechanism is still not well understood. Experimental observations show that melting nucleates at surfaces and extended defects. Besides their technological applications, nanoparticles provide interesting opportunities to study the melting phase transition since their properties can be dominated by their surfaces. The study of melting is complicated by the ultrafast nature of the transition. In this project, ultrafast electron diffraction is used to resolve the atomistic dynamics for nanoparticles heated with a short laser pulse. The electron diffraction maps the structural evolution of the nanoparticles while they melt. Modeling using an accurate description of atomic bonding simulates the electron diffraction results. Improved understanding of nanoparticle response to the laser excitation is likely to make a strong impact on the development of biomedical, nano-electronics, and sensing applications. A post-doc, two Ph.D. students, and undergraduates are actively involved in this research and contribute to outreach activities to high school students and the general public.Technical AbstractThe main objective of this project is to understand the mechanisms of the rapid phase transitions in metal nanoparticles driven up to their melting by femtosecond laser irradiation. Ultrafast electron diffraction (UED) is used to map the structural dynamics of the laser-irradiated nanoparticles. Molecular dynamics (MD) simulations with a realistic description of the laser energy coupling and partitioning in the nanoparticles complements the UED studies and provide atomic-level insights into the laser-induced phase transitions. Since melting and diffusionless solid-solid phase transitions can occur on a picosecond time scale, ultrafast measurements are needed to probe transient states along the transition pathways. Ultrafast laser melting of well-characterized, size-selected metal nanoparticles (In, Pb, and Bi) will be studied. The low vapor pressure of these nanoparticles enables structural studies near their melting point without affecting their size. The experiments are conducted on nanoparticles fabricated in an ultrahigh vacuum on substrates with weak surface van der Waals forces. The experiments are designed to study the structural pathways through which the phase transitions occur and their dependence on heating rate; electronic excitation effects; electron-phonon coupling; limits of superheating and supercooling; and interface and substrate effects on melting and solid-state transitions. MD simulations include the effect of the thermal pressure from the excited electrons, which is parameterized based on the predictions of ab initio calculations and the UED results.

非技术抽象，尽管固体的融化是最普遍的相变，但其原子机制仍未得到充分了解。实验观察结果表明，在表面和扩展缺陷的表面融化成核。除了技术应用外，纳米颗粒还提供了有趣的机会来研究熔融相变的熔点，因为它们的特性可以由其表面主导。过渡的超快性质使熔化的研究变得复杂。在这个项目中，超快电子衍射用于解析用短激光脉冲加热的纳米颗粒的原子动力学。电子衍射在纳米颗粒融化时绘制了纳米颗粒的结构演化。使用原子键的准确描述进行建模可以模拟电子衍射结果。对纳米颗粒对激光激发的反应的了解可能会对生物医学，纳米电子和感应应用的发展产生强烈的影响。博士后两位博士学位学生和本科生正在积极参与这项研究，并为高中生和公众提供宣传活动。技术摘要该项目的主要目标是了解金属纳米颗粒快速过渡的机制，从而通过Femtosoctecond laser iradiation驱动其融化。超快电子衍射（UED）用于绘制激光辐照的纳米颗粒的结构动力学。分子动力学（MD）模拟对激光能量耦合和纳米颗粒中的分配具有现实描述，可以补充UED研究，并为激光诱导的相变点提供原子级别的见解。由于可以在皮秒时间尺度上发生熔融和无扩散的固体相变，因此需要超快测量来探测沿着过渡途径的瞬态状态。将研究良好的，尺寸选择的金属纳米颗粒（IN，PB和BI）的超快激光熔融。这些纳米颗粒的低蒸气压力可以在其熔点附近的结构研究而不会影响它们的大小。实验是在在弱表面范德华力的底物上制成的纳米颗粒上进行的。实验旨在研究发生相变发生的结构途径及其对加热速率的依赖。电子激发效应；电子 - 音波耦合；过热和过冷的极限；以及界面和底物对熔化和固态过渡的影响。 MD模拟包括激发电子的热压力的影响，该仿真是根据AB始于从头计算和UED结果的预测进行参数化的。