Hafnium oxide nanoparticles fabricated by femtosecond laser ablation in water

We report the fabrication of colloidal hafnia nanoparticles (NPs) and nanoribbons (NRs) in deionized water achieved by femtosecond laser ablation. The average size of NPs and NRs varied in the range 13.5-18.0 nm and 10-20 nm, respectively, with varying input laser energy. At lower energies, the NPs were observed to be in pure monoclinic phase of HfO₂. However, at higher input energies, interestingly, both monoclinic and hexagonal phases corresponding to HfO₂ and Hf₆O were observed. Hf₆O is otherwise expected only at high pressures. (orig.)