Enhancement of light transmission through randomly located copper nano-islands near the percolation threshold

TL;DR

This study investigates how thin copper films with randomly distributed nano-islands near the percolation threshold can enhance light transmission, with implications for sensor applications and comparisons to extraordinary optical transmission phenomena.

Contribution

It demonstrates enhanced light transmission in randomly structured copper films near the percolation threshold and compares effects in different substrate layers, supported by numerical simulations.

Findings

Enhanced transmission observed near percolation threshold on glass

Titanium oxide layers inhibit transmission enhancement

Numerical models replicate experimental optical behavior

Abstract

We report the absorption/transmission properties of thin copper films slightly below the percolation limit produced by laser ablation; these samples show randomly positioned islands. Two types of films are grown: in the first type, copper is deposited on glass, and it is shown that as the amount of deposited copper approaches the percolation limit, the samples show enhanced light transmission; in the second set of samples, made of TiO$_2$/Cu/TiO$_2$ layers, the presence of titanium oxide inhibits light transmission enhancement, even though the same amount of copper has been deposited compared to the samples deposited on glass. We also present numerical calculations based on the discrete dipole method to simulate the optical behaviour of the copper films. The enhanced light transmission of the samples presented in this work resembles the Extraordinary Optical Transmission (EOT) observed in periodic metallic structures. The similarities and differences between experiment and numerical calculations and the possible use of these films as sensors are discussed.