Ultraviolet plasmonics (UV) has become an active topic of research due to the new challenges arising in fields such as biosensing, chemistry or spectroscopy. Recent studies have pointed out aluminum, gallium, magnesium and rhodium as promising candidates for plasmonics in the UV range. Aluminum and magnesium present a high oxidation tendency that has a critical effect in their plasmonic performance. Nevertheless, gallium and rhodium have drawn a lot of attention because of their low tendency of oxidation and, at the same time, good plasmonic response in the UV and excellent photocatalytic properties. Here, we present a short overview of the current state of UV plasmonics with the latest findings in the plasmonic response and applications of aluminum, gallium, magnesium and rhodium nanoparticles.

Reconfigurable plasmonics constitutes an exciting and challenging new horizon in nanophotonics. This blooming field aims at providing plasmonic nanostructures that present a dynamic and active plasmonic response that can be switched or manipulated by external stimuli to induce a controllable change in the optical properties. Most common plasmonic materials, such as the noble metals gold and silver, cannot deliver this type of behavior. Therefore, significant effort is being invested in developing alternative materials whose optical properties can be controllably modified to provide a reconfigurable plasmonic response. In this perspective, several materials including non-noble metals, transition metal oxides and nitrides, and chalcogenide compounds will be analyzed. The selected materials share interesting characteristics like low cost, good chemical and thermal stabilities, and CMOS compatibility while presenting a reconfigurable plasmonic response governed by different phase-change mechanisms.

Interest in layered van der Waals semiconductor gallium monosulfide (GaS) is growing rapidly because of its wide band gap value between those of two-dimensional transition metal dichalcogenides and of insulating layered materials such as hexagonal boron nitride. For the design of envisaged optoelectronic, photocatalytic and photonic applications of GaS, the knowledge of its dielectric function is fundamental. Here we present a combined theoretical and experimental investigation of the dielectric function of crystalline 2H-GaS from monolayer to bulk. Spectroscopic imaging ellipsometry with micron resolution measurements are corroborated by first principle calculations of the electronic structure and dielectric function. We further demonstrate and validate the applicability of the established dielectric function to the analysis of the optical response of c-axis oriented GaS layers grown by chemical vapor deposition (CVD). These optical results can guide the design of novel, to our knowledge, optoelectronic and photonic devices based on low-dimensional GaS.

Interest in gallium (Ga) is growing rapidly, thanks in part to its wide spectral tunability and its intriguing temperature‐dependent polymorphism. In order to exploit and control phase‐change plasmonics in the liquid and solid phases of Ga, an accurate understanding of the dielectric functions for each Ga phase is needed. A comprehensive analysis of the interdependence of the crystal structure, band structure, and dielectric function of the several Ga phases (liquid, α, β, γ, δ) is presented, showing that the selective presence of flat bands in the vicinity of the Fermi energy is crucial to understand the metallicity of each phase. The dielectric function obtained through first principles calculations is compared with experimental measurements obtained by spectroscopic ellipsometry. Cooling liquid Ga always produces a mixture of phases, and how the volume fraction of each phase may be deduced from these pure phase dielectric functions and an analysis of the measured spectra using a Bruggeman effective medium approximation is demonstrated. Figures of merit are presented, and applications of Ga polymorphism are discussed for propagating and localized surface plasmon resonances in Ga thin films and nanostructures, respectively. This research can have important implications on the phase change control for plasmonics/photonic applications with gallium.