Effect of nanocolloids as an ablation medium on structure and morphology of laser-generated bimetallic Cu-Ni nanoparticles

Abstract We report on the synthesis of bimetallic Cu-Ni nanoparticles (NPs) in deionized water (DIW) adopting two different methodologies: (i) laser ablation of Cu target in laser-generated Ni nanocolloids (abbreviated as M1 henceforth) and (ii) laser ablation of Ni target in laser-generated Cu nanocolloids (abbreviated as M2 henceforth). In both approaches, the resulting NPs show a homogeneous particle size distribution. Structural and morphological analysis using microscopic and spectroscopic techniques reveals the formation of different phases and nanostructures of NP in the samples. The Cu-Ni NPs generated using M2 show the formation of a core-shell (CS) structure in which the Cu reside at the core and the shell is composed of Ni oxide. However, in M1, solid Cu-Ni NP were assumed. The observed differences in morphology are attributed to the relative concentration of Cu and Ni, their interaction during pulsed laser ablation in liquid (PLAL) process, and their differences in nucleation rate and diffusion kinetics. The compositional analysis showed domination of Ni in both sample, which could be assumed due to higher stability of Ni based on its physical and thermodynamic properties. The optical results also confirm the formation of bimetallic Cu-Ni NP in both samples, which is in agreement with the structural analysis of the samples. Based on the experimental findings, a possible growth mechanism for the formation of different structures and morphologies of these NPs during PLAL is systematically discussed. Furthermore, this study evidenced the importance of a chemical interaction between nanocolloids (as ablation medium species) and ablated materials, and their influence on the cavitation bubble (CB) dynamics, which affects the formation mechanism and growth kinetics of NPs.