Investigation of pulsed laser induced dewetting in nanoscopic metal films

TL;DR

This study explores how pulsed laser melting induces dewetting in nanoscopic metal films, enabling the creation of ordered nanoparticle arrays with predictable size and spacing, guided by hydrodynamic theory and heat transfer models.

Contribution

It demonstrates the first detailed correlation between laser parameters, film thickness, and nanoparticle pattern formation in nanoscopic metal films, validated by theoretical models.

Findings

Dewetting occurs only above a threshold energy E_m dependent on film thickness.

Nanoparticle spacing scales with h^2, and diameter scales with h^{5/3}, consistent with hydrodynamic theory.

Theoretical models incorporating reflectivity accurately predict experimental threshold energies.

Abstract

Hydrodynamic pattern formation (PF) and dewetting resulting from pulsed laser induced melting of nanoscopic metal films have been used to create spatially ordered metal nanoparticle arrays with monomodal size distribution on SiO_{\text{2}}/Si substrates. PF was investigated for film thickness h\leq7 nm < laser absorption depth \sim11 nm and different sets of laser parameters, including energy density E and the irradiation time, as measured by the number of pulses n. PF was only observed to occur for E\geq E_{m}, where E_{m} denotes the h-dependent threshold energy required to melt the film. Even at such small length scales, theoretical predictions for E_{m} obtained from a continuum-level lumped parameter heat transfer model for the film temperature, coupled with the 1-D transient heat equation for the substrate phase, were consistent with experimental observations provided that the thickness dependence of the reflectivity of the metal-substrate bilayer was incorporated into the analysis. The spacing between the nanoparticles and the particle diameter were found to increase as h^{2} and h^{5/3} respectively, which is consistent with the predictions of the thin film hydrodynamic (TFH) dewetting theory. These results suggest that fast thermal processing can lead to novel pattern formation, including quenching of a wide range of length scales and morphologies.