The practical efficacy of technologically promising metals for use in ultraviolet plasmonics (3−6 eV) is assessed by an exhaustive numerical analysis. This begins with estimates of the near-and far-field electromagnetic enhancement factors of isolated hemispherical and spherical metallic nanoparticles deposited on typical dielectric substrates like sapphire, from which the potential of each metal for plasmonic applications may be ascertained. The ultraviolet plasmonic behavior of aluminum, chromium, copper, gallium, indium, magnesium, palladium, platinum, rhodium, ruthenium, titanium, and tungsten was compared with the well-known behavior of gold and silver in the visible. After exploring this behavior for each metal as a function of nanoparticle shape and size, the deleterious effect caused by the metal's native oxide is considered, and the potential for applications such as surface-enhanced Raman spectroscopy, accelerated photodegradation and photocatalysis is addressed.

Abstract:The ultraviolet (UV) range presents new challenges for plasmonics, with interesting applications ranging from engineering to biology. In previous research, gallium, aluminum, and magnesium were found to be very promising UV plasmonic metals. However, a native oxide shell surrounds nanostructures of these metals that affects their plasmonic response. Here, through a nanoparticle-oxide core-shell model, we present a detailed electromagnetic analysis of how oxidation alters the UV-plasmonic response of spherical or hemisphere-on-substrate nanostructures made of those metals by analyzing the spectral evolution of two parameters: the absorption efficiency (far-field analysis) and the enhancement of the local intensity averaged over the nanoparticle surface (near-field analysis).

Since the first studies made by Kerker in the 1970s stating the conditions for null light scattering in certain directions by particles, such conditions have remained unquestioned. The increasing interest in scattering directionality by tuning the optical properties of materials demands a new analysis of this problem. In addition, as has been shown recently, one of Kerker's statements does not comply with the optical theorem. We propose corrected expressions for the null-scattering conditions that satisfy the optical theorem.

We have studied the problem of light scattering by an ensemble of dipoles with both electric and magnetic polarizabilities. Using the coupled electric and magnetic dipole method as the formal base, we have generalized the eigenvector decomposition of the local dipole moments previously derived for purely electric particles to the case of both electric and magnetic dipoles. We have analyzed the properties of eigenvalues and eigenvectors in the most elementary case of two particles. In the purely electric case, the eigenvalues correspond to the resonance modes of the system due to the electromagnetic coupling of its components. For a two-dipole system with both electric and magnetic responses, purely electric, purely magnetic, and mixed states can be distinguished. The resonance spectrum is analyzed as a function of the magnetic permeability, and it is shown that the latter can be fitted quite accurately by the eigenmode decomposition.

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.