Ablating Boundaries, Sparking the Future of Materials : Engineering of Bimetallic Nanoparticles via Spark Ablation

Bimetallic nanoparticles exhibit unique physicochemical characteristics that often translateinto functional properties surpassing those of their monometallic counterparts. The abilityto precisely tailor these characteristics enables fine-tuning of their properties for targetedapplications. This doctoral thesis investigates the engineering of bimetallic nanoparticlesvia spark ablation, a continuous, solvent-free, gas-phase synthesis method that facilitates theproduction of high-purity nanoparticles. This method allows direct atomic-scale mixing ofelements, even those immiscible in bulk, through rapid vaporization followed by kineticstabilization via quenching. A key advantage of spark ablation is its capacity to modifynanoparticles in-flight, prior to deposition, enabling precise control over size, morphology,elemental composition, and crystal structure within a single-step process.In the synthesis stage, the role of different carrier gases in the production of Co–Ni nanoparticlesis examined. The chemical nature of the carrier gas determines the distribution ofmetallic and oxide phases, thereby influencing the final nanoparticle morphology. Additionally,the effects of electrode diameter, polarity, and composition are explored as meansof tuning the bimetallic ratio in Pd–Hf and Pd–Cu nanoparticles, demonstrating the versatilityof spark ablation for achieving precise elemental control.Following synthesis, in-flight processing is explored as a tool for altering nanoparticle characteristics.Thermal treatment in a tube furnace enables fine-tuning of the morphology,structure, and composition of Au–Sn nanoparticles, inducing a transition from randomlyordered Au-rich alloys at lower temperatures to more Sn-rich intermetallic compounds athigher temperatures. Additionally, applying an external magnetic field during nanoparticledeposition facilitates the self-assembly of FeCo nanoparticles into nanochains, withcontrolled aspect ratios and enhanced magnetic properties due to shape anisotropy.Finally, the insights gained from the carrier gas and magnetic self-assembly studies are appliedto engineer the magnetic properties of Co–Ni nanoparticles. By controlling the synthesisand processing conditions, significant changes in coercivity and remanence magnetizationare achieved, along with the emergence of exchange bias effects. These results highlightthe potential of spark ablation as a flexible and tunable approach for designing advancedmagnetic nanostructures.Overall, this thesis deepens the understanding of spark ablation, emphasizing its capabilityto produce customized nanoparticles with precisely controlled physicochemical characteristicsand magnetic properties. With its highly tunable synthesis and in-flight processingcapabilities, spark ablation emerges as a powerful technique for developing next-generationnanostructures suited to a wide range of applications.