Smoluchowski Formulation for Simulation of Nano Core-Shell Structure Creation in Nanoparticle Fabrication by Laser Ablation in Liquid Media Process

Abstract

The nano core-shell can be generated in a proper liquid medium under controlled laser ablation condition. In this work, the formation of core-shell structure by laser ablation of two different targets was modeled based on the Smoluchowski approach. In this model, the movement and aggregation of the ablated fragments ejected from the targets were investigated based on Brownian motion, hydrodynamics considerations and coulomb's interactions. The nano core-shell could be generated in the water under controlled exposure conditions using Q-SW Nd:YAG laser shots at 1064 nm. This work addresses a simple numerical modeling of the formation of core-shell nanoparticles in water by laser ablation. The late stage of nanoparticleformation by collisional aggregation was considered avoiding hydrodynamic calculations. Each collision is assumed to be effective in aggregate formation. The rate constants are simply expressed through the diffusion coefficient depending on the temperature and viscosity of the liquid and the aggregation time was estimated. Moreover, Smoluchowski approach was used to describe the step between laser ablation and nano core-shell creation. This proves to be a suitable method for modeling of nanoparticle formation in liquid by laser ablation. The model could be applied to both the nanoparticle and the core-shell formation; however the latter is emphasized here. At first, the gold target was irradiated in water to generate nano particles. Then, the silver target was immersed into water-gold suspension. It was irradiated by multiple laser shots subsequently. The nano core-shells (Ag-Au) are created in the water having 30-50 nm size. The formation of core-shell using laser ablation of metallic targets was modeled based on the Smoluchowski approach. The movement and aggregation of the ablated fragments ejected from the targets were investigated based on Brownian motion, hydrodynamics considerations and coulomb's interactions. For investigation of validation of the model, the results obtained by the model for the nano core – shell (Ag-Au) generation were comprised with reported experimental results.Modeling was based on the irradiation on gold target in water to generate Au nano particles. Then, thesilver target was immersed into water-gold suspension. It was irradiated by multiple laser shots subsequently in the liquid medium. The predicted sizes of the nano core-shells (Ag-Au) by the model were 30-50 nm which were in good agreement with experimental reported results.