Advanced X-Ray Imaging Study on the Mechanism of Nanoparticle Formation during Laser Ablation in Liquid

虽然脉冲激光烧蚀合成液体中的胶体是一个国际上正在发展的领域，但对粒子的形成和尺寸控制机制仍然只有部分了解。在第一个项目阶段，我们率先对气泡和烧蚀过程进行了X射线成像，揭示了气泡振荡过程中非常有趣的现象。原位SAXS测量证实了气泡内部发生了尺寸猝灭，非原位方法证实了颗粒性质的变化。在拟议的12个月的项目完成阶段，我们计划继续探索激光产生的空化气泡内粒子在液体中尺寸猝灭时的时空分布。特别是，宽的，通常是双峰的尺寸分布，我们可以在纳秒消融时澄清，在皮秒消融时变得更加突出，后者有望增加产量。我们试图通过一系列时间和空间分辨方法来分析这一点，其中包括X射线成像和小角散射作为补充工具。我们引入了一种多模X射线全场成像来区分吸收、相位和暗场对比度，后者对大颗粒组分特别敏感。这使得能够研究分层消融过程中的时空分布，特别是在配体作用期间。这种方法的效率将通过首次在时间分辨X射线成像中引入Shack-Hartmann掩模来提高。

Although pulsed laser ablation synthesis of colloids in liquids is an internationally growing field, particle formation and size control mechanisms are still only partially understood. In the first project phase we pioneered X-ray imaging of the bubble and ablation process, revealing very interesting phenomena during bubble oscillation. In situ SAXS measurements proved that size quenching happens inside the bubble, with particle property changes confirmed by ex situ methods. Within the proposed 12 month project finalization phase we plan to continue to explore the spatiotemporal distribution of the particles inside the laser-generated cavitation bubble during size quenching in liquid. In particular, the broad, often bimodal size distribution, which we could clarify for nanosecond ablation, becomes even more prominent for picosecond ablation, the latter promising to increase the yield. We seek to analyze this with a portfolio of time- and space resolving methods, amongst them X-ray imaging and small angle scattering as complementary tools. We have introduced a multi-mode X-ray full-field imaging to discern between absorption, phase and dark-field contrast, the latter being sensitive in particular on the large particle size-fraction. This allows studying the spatiotemporal distribution during the hierarchical ablation process, in particular during the action of ligands. Effciency of this approach will be improved by introducing a Shack-Hartmann mask for the first time in time-resolved X-ray imaging.