Size-controlled growth of nanoparticles and clusters during pulsed laser ablation into an ambient wave induced plasma

Abstract

The interaction of a laser plasma plume with aluminum (Al) targets in an ambient microwave induced plasma is investigated. The expanding metallic laser plasma plume interacts with the gaseous wave induced plasma resulting in the formation of nanoparticles and clusters. The ambient plasma is obtained in molecular and atomic gases of different atomic weights such as hydrogen (H2), argon (Ar) and krypton (Kr), keeping the gas pressure in the range 0.04–0.15 Pa. The plasma is well confined and uniformly distributed within a radius of ∼3 cm in a twelve-pole magnetic multicusp (MC, surface magnetic field ∼0.4 T). The electron temperature (Te) and density (ne) of the ambient plasma are ∼7–10 eV and ∼1010 cm−3 respectively at 200 W of microwave power. The growth and size distribution of the nanoparticles (NPs) formed are investigated. The mean size of the NPs is found to depend directly on Te and gas species of ambient microwave induced plasma. The largest NP size (∼55 nm) is obtained in H2 plasma while the minimum size (∼5 nm) is achieved in Kr plasma. As the atomic weight of the ambient gas increases, the plasma ion thermal velocity decreases and so does the size of the NPs.