Topographical coloured plasmonic coins

TL;DR

This paper introduces a rapid, scalable laser-based method to produce angle-independent colors on noble metals by controlling nanoparticle distributions, leveraging plasmonic cluster resonances for industrial applications.

Contribution

It presents a bottom-up laser processing technique for large-scale, angle-independent colorization of metals, based on controlling nanoparticle size distributions and plasmonic resonances.

Findings

Colors are controlled by accumulated laser fluence.

Nanoparticle size distributions influence color outcomes.

Finite-difference time-domain simulations confirm plasmonic cluster resonances as the color mechanism.

Abstract

The use of metal nanostructures for colourization has attracted a great deal of interest with the recent developments in plasmonics. However, the current top-down colourization methods based on plasmonic concepts are tedious and time consuming, and thus unviable for large-scale industrial applications. Here we show a bottom-up approach where, upon picosecond laser exposure, a full colour palette independent of viewing angle can be created on noble metals. We show that colours are related to a single laser processing parameter, the total accumulated fluence, which makes this process suitable for high throughput industrial applications. Statistical image analyses of the laser irradiated surfaces reveal various distributions of nanoparticle sizes which control colour. Quantitative comparisons between experiments and large-scale finite-difference time-domain computations, demonstrate that colours are produced by selective absorption phenomena in heterogeneous nanoclusters. Plasmonic cluster resonances are thus found to play the key role in colour formation.