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.