Structural evolution of Ni/NiO nanostructures synthesized by pulsed laser ablation in water

We report on the structural analysis of nickel (Ni)/nickel oxide (NiO) nanoparticles (NPs) synthesized in deionized water (DI) using the pulsed laser ablation in liquid (PLAL) technique. The laser-generated NPs exhibit a bimodal size distribution. The structural analysis of the as-produced NPs using microscopic techniques reveals the formation of a core–shell structure along with three distinct features of Ni/NiO nanostructures, namely, nanosheet, hollow, and chain-like formations. The formation of these structures is attributed to the physical properties of the liquid medium and the cavitation bubble (CB) dynamics that occur during the PLAL process. The formation of nanosheet-like structures in the nanocolloid is attributed to the deformation of the CB and the presence of high pressure at the bubble-target interface during collapse. The formation of the hollow NPs is attributed to the Kirkendall effect, while nanochain-like structures result from the post-ablation effects and localized reheating and melting during the PLAL process. The selected area electron diffraction pattern analysis reveals the presence of both Ni and NiO phases, indicating that the synthesized NPs are polycrystalline. Furthermore, based on the experimental findings, the possible growth mechanisms for the formation of different Ni/NiO nanostructures in DI are discussed.