Diffusion dynamics of laser-ablated noble-metal nanoparticles in liquids

Abstract

The diffusion dynamics in water of Brownian particles constituted by noble-metal nanoclusters has been treated by a transport model across a limiting surface that separates two layers of the same fluid, having different values of density and temperature. This model, developed by Parrondo and adapted by Streater, has recently been shown to be useful in several situations like ours by the work of Grillo et al. By this approach, which introduces a one-dimensional vertical adiabatic potential produced by density gradients governing the net current of particles across the limiting surface, we are able to explain the mass and thermal energy transport, which rapidly restores the equilibrium conditions when they are perturbed by laser ablation of a noble-metal target vertically submerged in water. Experimentally, the laser ablation of noble-metal targets has been performed by irradiating pure metal sheets submerged in water with a pulsed Nd:YAG laser at 500 mJ cm⁻² fluency for 5 min and pulses of duration on the nanosecond timescale.

Keywords:

• laser ablation
• Brownian particles
• thermal gradients
• liquids
• local density approximations

Acknowledgements

The authors are very grateful to Ministero dell’Università e della Ricerca, Rome, for having financially supported this research. Stimulating discussions with Professor Orazio Puglisi, Department of Chemical Sciences, University of Catania, Italy, are acknowledged.