Atomic scale microscopy unveils the growth mechanism of 2D-like CuO nanoparticle agglomerates produced via electrical discharges in water

In this paper we describe the growth mechanism leading to the selective synthesis of 2D-like CuO nanoparticle agglomerates via pulsed electrical discharges in water. By adjusting the voltage and pulse width, we selected four experimental conditions: 5 kV/100 ns, 5 kV/500 ns, 20 kV/100 ns and 20 kV/500 ns. In these conditions, we obtained agglomerates with dimensions ranging between 40 and 100 nm, formed of CuO nanoparticles having sizes of few nm. While the morphology of the agglomerates and their composition do not change in all the four conditions, the size, the shape and the crystal properties of the CuO nanoparticles can be finely tuned by choosing the coupling between voltage and pulse width. Moreover, the nanoparticles are more densely agglomerated at longer pulse width. Based on our observations, we infer the growth mechanism of the CuO nanoparticle agglomerates. We demonstrate that CuO nanoparticles are formed during the discharge, while their agglomeration can be mainly due to the pressure gradients existing within the plasma formed by the discharge, which encourage nanoparticle agglomeration on one plane.