Chromatic annuli formation and sample oxidation on copper thin films by femtosecond laser

TL;DR

This study explores how femtosecond laser pulses induce the formation of chromatic copper oxide annuli and nanoparticles on copper thin films, revealing new insights into laser-assisted oxidation processes in air and water.

Contribution

It demonstrates the formation of chromatic copper oxide annuli and nanoparticles using high repetition rate femtosecond laser irradiation, with detailed analysis of effects in different environments and immersion times.

Findings

Chromatic copper oxide annuli are generated on copper films.

Cuprous oxide nanoparticles (~20 nm) and nanocubes (~30-60 nm) are produced.

Color of annuli depends on immersion time after irradiation.

Abstract

We report an experimental investigation on the irradiation of copper thin films with high repetition rate femtosecond laser pulses (1040 nm, 50 MHz), in ambient air and liquid water. We observe a novel, striking phenomenon of chromatic copper oxides (cupric oxide and cuprous oxide) annuli generation. The characteristic features of the chromatic copper oxide annuli are studied by exploiting micro-Raman Spectroscopy, Optical and Scanning Electron Microscopies. In the case of irradiation in water, the seldom investigated effects of the immersion time, after irradiation with a fixed number of pulses, is analyzed, and an intriguing dependence of the color of the chromatic annuli on the immersion time is observed. This remarkable behavior is explained by proposing an interpretation scenario addressing the various processes involved in the process. Our experimental findings show that cuprous oxide nanoparticles (size of ~20 nm) and cuprous oxide nanocubes (nanocube edges of ~30, ~60 nm) with extremely fine sizes can be effectively generated by exploiting high repetition rate laser-assisted oxidation.