White light generation and anisotropic damage in gold films near percolation threshold

TL;DR

This study investigates enhanced electromagnetic fields and optical damage in gold films near the percolation threshold, revealing super-cubic luminescence dependencies and potential applications in nanotechnology.

Contribution

It demonstrates the strong field enhancement and damage effects in near-percolation gold films, linking optical phenomena to morphological changes, with scalable fabrication methods.

Findings

Maximum two-photon luminescence near percolation threshold

Confined (~30 nm) and enhanced (~100x) electromagnetic fields

Optical damage depends on wavelength and polarization

Abstract

Strongly enhanced and confined electromagnetic fields generated in metal nanostructures upon illumination are exploited in many emerging technologies by either fabricating sophisticated nanostructures or synthesizing colloid nanoparticles. Here we study effects driven by field enhancement in vanishingly small gaps between gold islands in thin films near the electrically determined percolation threshold. Optical explorations using two-photon luminescence (TPL) and near-field microscopies reveals super-cubic TPL power dependencies with white-light spectra, establishing unequivocally that the strongest TPL signals are generated with close to the percolation threshold films, and occurrence of extremely confined (~ 30 nm)and strongly enhanced (~ 100 times) fields at the illumination wavelength. For linearly polarized and sufficiently powerful light, we observe pronounced optical damage with TPL images being sensitive to both wavelength and polarization of illuminating light. We relate these effects to thermally induced morphological changes observed with scanning electron microscopy images. Fascinating physics involved in light interaction with near-percolation metal films along with their straightforward and scalable one-step fabrication procedure promises a wide range of fascinating developments and technological applications within diverse areas of modern nanotechnology, from bio-molecule optical sensing to ultra-dense optical data storage.