Nanoporous metallic networks are endowed with the distinctive optical properties of strong field enhancement and spatial localization, raising the necessity to map the optical eigenmodes with high spatial resolution. In this work, we used cathodoluminescence (CL) to map the local electric fields of a three-dimensional (3D) silver network made of nanosized ligaments and holes over a broad spectral range. A multitude of neighboring hotspots at different frequencies and intensities are observed at subwavelength distances over the network. In contrast to well-defined plasmonic structures, the hotspots do not necessarily correlate with the network morphology, emphasizing the complexity and energy dissipation through the network. In addition, we show that the inherent connectivity of the networked structure plays a key optical role because a ligament with a single connected linker shows localized modes whereas an octopus-like ligament with multiple connections permits energy propagation through the network.
Bibliographical noteFunding Information:
R.R. thanks the Charles Clore Foundation for a fellowship for Ph.D students. This work was supported by the Energy and Water Resources Ministry of Israel (Grant 016-11-216) and the Israel Science Foundation (ISF) (Grant 1231/19).
- 3D nanoporous metals
- light localization
- random optical system