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

Bimetallic nanoparticles exhibit unique physicochemical characteristics that often translate
into functional properties surpassing those of their monometallic counterparts. The ability
to precisely tailor these characteristics enables fine-tuning of their properties for targeted
applications. This doctoral thesis investigates the engineering of bimetallic nanoparticles
via spark ablation, a continuous, solvent-free, gas-phase synthesis method that facilitates the
production of high-purity nanoparticles. This method allows direct atomic-scale mixing of
elements, even those immiscible in bulk, through rapid vaporization followed by kinetic
stabilization via quenching. A key advantage of spark ablation is its capacity to modify
nanoparticles 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 nanoparticles
is examined. The chemical nature of the carrier gas determines the distribution of
metallic and oxide phases, thereby influencing the final nanoparticle morphology. Additionally,
the effects of electrode diameter, polarity, and composition are explored as means
of tuning the bimetallic ratio in Pd–Hf and Pd–Cu nanoparticles, demonstrating the versatility
of 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 randomly
ordered Au-rich alloys at lower temperatures to more Sn-rich intermetallic compounds at
higher temperatures. Additionally, applying an external magnetic field during nanoparticle
deposition facilitates the self-assembly of FeCo nanoparticles into nanochains, with
controlled aspect ratios and enhanced magnetic properties due to shape anisotropy.
Finally, the insights gained from the carrier gas and magnetic self-assembly studies are applied
to engineer the magnetic properties of Co–Ni nanoparticles. By controlling the synthesis
and processing conditions, significant changes in coercivity and remanence magnetization
are achieved, along with the emergence of exchange bias effects. These results highlight
the potential of spark ablation as a flexible and tunable approach for designing advanced
magnetic nanostructures.
Overall, this thesis deepens the understanding of spark ablation, emphasizing its capability
to produce customized nanoparticles with precisely controlled physicochemical characteristics
and magnetic properties. With its highly tunable synthesis and in-flight processing
capabilities, spark ablation emerges as a powerful technique for developing next-generation
nanostructures suited to a wide range of applications.