Plasmonics: The future is ultrafast and ultrasmall

Abstract

Plasmonics has been a flourishing field since the late ‘80s of the last century. Given the number of outstanding developments even without resorting to metrics–it is straightforward to address the 2 decades crossing the new millennium as the golden era of Plasmonics. The unique capabilities of plasmonic nanostructures to collect, direct and enhance light at length scales much below the operating wavelength granted them the name “antennas for light”. These features were crucial for the vast deployment of Plasmonics to a variety of tasks, spanning from light harvesting (Atwater and Albert 2010) to molecular sensing (Homola 2008; Saha et al., 2012), bioimaging (Meola et al., 2018; Bocková et al., 2019; Wu et al., 2019) and plasmonenhanced spectroscopy (Zhang et al., 2013, Ding et al., 2016). Another recently growing field is that of plasmon-enhanced catalysis, which could be of crucial importance for hydrogen synthesis (Ezendam et al., 2022) with significant consequences for sustainability. Despite its indisputable key role in basic and applied research, the disruptive fallout of Plasmonics in life and society is still mainly restricted to medical diagnostic tools, as demonstrated by the antigenic lateral flow test employed to detect SARS-CoV-2, which is massively employed during this last pandemic. The first clinical pilot study of a device for prostate cancer treatment, carried out by Prof. Halas using photothermal ablation via gold nanoshells (Rastinehad et al., 2019), represents another major landmark in nanomedicine. The main hindrances to technological application of classical metal-based Plasmonics are the sizeable ohmic losses at visible wavelengths and the non-trivial integration in semiconductor-based technology. With the aim of targeting a higher technological readiness level, and thanks to the recent advancement in nanofabrication, semiconductor-based Plasmonics has rapidly emerged (Taliercio and Biagioni 2019). Indeed, heavily-doped semiconductors display a sizeable plasma frequency, which can be tuned chemically, optically, or electrically over a broad spectral range. These platforms are extremely appealing for their facile integration in low-cost, mass-fabricated devices, but their operation is yet limited to the midinfrared range. Yet, Plasmonics endures among the liveliest branches in the field of Photonics, thanks to the extreme light confinement achievable and the ultrafast dynamics of the underlying processes. A major technological task still remains, i.e., the improvement of reliability and reproducibility in plasmonic-based devices and techniques (i.e., plasmon-enhanced Raman spectroscopy, sensing). This will require a major effort in nanofabrication in the coming years to control subOPEN ACCESS