Synthesis of high-entropy alloy nanoparticles by laser ablation in liquids: scalability and monodispersity control by beam shaping

• Applicant: Professor Dr. Bilal Gökce
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 496156402

The research activities on high-entropy alloys (HEA) started less than ten years ago and focused primarily on bulk materials, ignoring HEA nanoparticles (NPs). This is mainly due to the absence of a fully established, scalable and straightforward synthesis method for such NPs. Pulsed laser ablation in liquids (PLAL) has proven to be a simple, flexible and efficient technique for the synthesis of colloidal NPs of various materials including alloy NPs. The PLAL method allows synthesizing stable colloidal alloy NPs without the use of any ligands for stabilization and with properties difficult to achieve by other synthesis methods. In particular, PLAL is capable of synthesizing binary alloy NPs with a homogeneous elemental distribution of controllable composition, a difficult task for (wet) chemical synthesis methods due to element segregation. Besides, the possibility of scaling up PLAL to produce NPs in gram per hour productivities relevant for industrial applications was recently demonstrated.However, even for binary alloys, the mechanisms of NP formation under PLAL are still poorly understood and the generation of monodisperse NPs, desirable for many applications, is a rather unsettled problem. For multicomponent HEA NPs, whose formation mechanisms are more complicated and virtually unexplored, controlling the NP size, as well as a high NP productivity, are a real challenge. One of the most efficient and flexible way to control and tune the laser ablation process is shaping of the utilized laser pulses, both in space and time. The use of double-pulse irradiation with two ultrashort pulses separated in time was demonstrated to be advantageous for material processing, fast ion generation, designing of nanoscale structures, and nanoparticle generation. It was also demonstrated with various non-Gaussian laser beams that spatial pulse shaping improves the quality of laser machining and enables efficient control over the size distribution of laser-generated nanoparticles. Essentially an in depth study of these techniques in PLAL represents an interesting approach for achieving a size distribution control. In this project, we propose a comprehensive study on the generation of HEA nanoparticle by laser ablation in liquids. The main attention will be given to the effects of laser pulse shaping on the size and the yield of the produced colloidal nanoparticles. Irradiation regimes using flat-top and doughnut-shaped pulses as well as using two pulses with a variable delay between them will be investigated. The mechanisms of nanoparticle formation under picosecond laser ablation of multicomponent materials in liquids will be revealed and efficient control over the nanoparticle size and yield is expected to be found. The possibilities of scaling-up the found regimes to increase the synthesis efficiency and to produce HEA nanoparticles in gram per hour amounts will be investigated.

• DFG Programme: Research Grants
• International Connection: Czech Republic
• Partner Organisation: Czech Science Foundation
• Cooperation Partner: Professor Dr. Alexander Bulgakov