Combination of in situ functionalization and transient ultrashort-time spectroscopy for the mechanistic elucidation of laser fragmentation mechanisms and the associated growth kinetics of colloidal gold nanoparticles (Ultra frag)

基于激光的高纯度胶体金属、合金和氧化物纳米颗粒的合成及其随后在载体上的静电吸附使材料设计变得灵活，在生物医学、能源技术、催化和添加剂制造中有广泛的应用。在UDE和KIT结合实验实验室和同步加速器方法的联合研究中，我们对液体中激光烧蚀过程中超短时间尺度上的颗粒形成和生长机制有了基本的见解。因此，激光烧蚀过程中存在的广泛的粒度分布问题被归因于内在的、难以避免的机制。脉冲激光破碎是唯一已知的基于激光的方法，可以获得颗粒尺寸远低于3 nm的高纯度纳米颗粒，其重要性迫在眉睫。然而，碎片的相变、碎裂、热传递和随后的生长是以叠加的方式进行的，并且在从超短到微秒乃至更长的时间尺度上进行，抑制了可预测性。因此，基于激光的材料合成仍然严重依赖于经验配方。人们提出了各种破碎机制。然而，由于叠加碎裂和纳米颗粒成熟的分级能量和时间尺度，它们的验证仍然是一个挑战。在申请者的初步研究中，在选定的激光强度范围内，用脉冲X射线衍射仪(100ps)分别研究了金胶体的单脉冲破碎和随后的成熟。本项目现在打算独立地跟踪和绘制碎裂机制和随后成熟的情况。为此，将结合瞬变结构分析、瞬变光学光谱和扩散延迟的原位生长抑制碎片。确定的膨胀过程将与机制的预测相关联，并进行定量建模。基于已确定的激光辐照与胶体稳定性的相互作用机理，本研究将最终为高通量、高能效的激光基纳米粒子的合成提供指导。

The laser-based synthesis of high-purity colloidal metal, alloy, and oxide nanoparticles and their subsequent electrostatic adsorption on supports allows a flexible material design with a wide range of applications in biomedicine, energy technology, catalysis, and additive manufacturing. In a joint study by UDE and KIT combining experimental laboratory and synchrotron methods, fundamental insights into the particle formation and growth mechanism occurring on ultra-short time scales during laser ablation in liquids have been developed. Therefrom, the broad particle size distribution that is a known issue during laser ablation was attributed to intrinsic, hardly avoidable mechanisms.With pulsed laser fragmentation being the only known laser-based method to access high-purity nanoparticles with particle sizes well below 3 nm its importance is imminent. Yet, phase transitions, fragmentation, heat transfer and subsequent growth of the fragments proceeds in superposition and on timescales ranging from ultrashort to microsecond and longer timescales, inhibiting predictability. Accordingly, laser-based material synthesis still relies heavily on empirical recipes. Various fragmentation mechanisms were proposed. Yet, their verification is still a remaining challenge due to the hierarchical energy and time scales of the superimposed fragmentation and nanoparticle ripening.In a preliminary study by the applicants the single-pulse fragmentation and subsequent ripening of gold colloids after fragmentation were separately investigated with pulsed X-ray diffraction (100 ps) for a selected range of laser intensities. The present project now intends to follow up and map the fragmentation mechanisms and subsequent ripening independently. To that end, transient structure analysis, transient optical spectroscopy, and diffusion-delayed in-situ growth suppression of the fragments will be combined. Identified swell processes will be correlated with predictions of mechanisms and modeled quantitatively. Based on the identified mechanistic interplay of the laser irradiation and colloidal stability this study will ultimately provide a guideline for high-throughput and energy-efficient laser-based nanoparticle synthesis in future applications.