Laser Ablation

Because everything happens fast — plasma formation, cooling, and condensation occur within microseconds — the nanoparticles are formed far from thermodynamic equilibrium. The liquid acts as a "cage" that confines the process, favouring the appearance of metastable phases and structures that don't naturally form under standard, slow, equilibrium chemistry. This makes PLAL a powerful route to nanoparticles with unusual crystal structures, or with compositions that are otherwise hard to reach — properties that matter a lot for catalysis, where the surface structure of a nanoparticle directly controls its reactivity.

Another advantage: because there's no chemical precursor or reducing agent involved, PLAL naturally produces clean, ligand-free nanoparticle surfaces — every atom at the surface is available for a chemical reaction, rather than blocked by a stabilizing molecule. This is a real asset for catalysis, where surface accessibility is everything.

But PLAL isn't limited to bare particles. By ablating in a liquid that already contains molecules or ions of interest — a doping salt, or a ligand — it's possible to functionalize the nanoparticles during their formation itself, in a single step. In one of my projects, I ablated an undoped target directly in an aqueous solution containing dopant ions, and showed that the dopant becomes incorporated into the core of the nanoparticles as they form — with the doping level directly tunable through the concentration of the solution. So, depending on the liquid you ablate into, you can produce colloidal nanoparticles that are bare and ligand-free, or already doped and functionalized — all from the same simple setup.

Understanding what happens inside that first microsecond — the plasma expansion, the shockwave, the cavitation bubble — is key to controlling the whole process. During my PhD, I studied the shockwaves generated by laser ablation using time-resolved shadowgraphy, comparing their propagation in air and in water, to better link the laser energy delivered to the pressure reached at the ablation point. This kind of measurement helps connect the very first instants of the process — violent, out-of-equilibrium, and over almost before it starts — to the final structure and phase of the nanoparticles it leaves behind.