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)

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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.