Pushing the High-Energy Limit of Al Plasmonics

The localized surface plasmon resonance of metal nanoparticles allows confining the electromagnetic field in nanosized volumes, creating high-field "hot spots", most useful for a huge variety of applications in photonics and optics.

The most commonly-employed plasmonic metals, Au and Ag, yield resonances only reaching up to the near-UV electromagnetic range. Stretching upwards the energy of plasmon resonances would open new perspectives in the field, but requires exploiting different materials.

Deep-ultraviolet plasmon resonances were theoretially predicted exploting one of the cheapest and most abundant materials available on earth. Aluminum holds the promise of a broadly-tunable plasmonic response, theoretically extending far into the deep-ultraviolet (DUV). However, complex fabrication issues, including the strong Al reactivity, have stood in the way of achieving such an ultimate DUV response.

We report the fabrication of 2-dimensional arrays of ultrafine aluminium nanoparticles with remarkable plasmonic response in the DUV electromagnetic range. Careful nanofabrication allowed to maintain the mean NP size below 20 nm, preserving a purely-metallic core under a few-nm thick native-oxide layer. These systems exhibit a striking high-energy plasmon resonance up to 6.8 eV photon energy , and preserve their DUV plasmon response when exposed to atmosphere [Maidecchi et al., ACS Nano 7 (2013) 5834, Bisio et al., ACS Nano 8 (2014) 9239]. Theoretical calculations allowed to rationalize the plasmonic response of the arrays in terms of dipolar and multipolar plasmonic contributions.

These observations pave the way to the full exploitation of aluminium’s remarkable plasmonic tunability, expanding on the high-energy side the spectral range of plasmonics` numerous applications.

francesco.bisio@spin.cnr.it