Plasmónica con materiales nanoestructurados poco convencionales para aplicaciones en el UV

Zusammenfassung

There is a growing interest in extending plasmonics into the UV range due to the new challenges arising in fields such as biosensing, chemistry or spectroscopy. Because common plasmonic materials employed in the visible range (i.e., Au and Ag) present interband transitions above 3 eV, their use in UV plasmonics is inhibited. Therefore, there is an ongoing quest for materials, both metal and high refractive index dielectrics, for plasmonic applications in the UV. Concerning metals, recent studies have presented Mg, Ga and Rh as promising candidates. The work in this dissertation will tackle some of the current problems when applying these metals in real applications. Both Ga and Mg nanoparticles form an oxide shell when exposed to air that critically affect their plasmonic response and hinder their use in certain applications like surface-enhanced spectroscopies or photocatalysis. The oxidation effect is studied thoroughly, not only in these two materials, but also on Al,which also has been presented as a good candidate for UV plasmonics. More in detailed is studied the role of a MgO layer in the H uptake of Mg nanoparticles. This study is of relevance due to the potential role of Mg nanoparticles in the hydrogen-based economy. However, oxidation is not the only surface transformation occurring on the surface of Mg nanoparticles. Here, we report the tarnishing of Mg, a phenomenon already known to occur on Ag surfaces. Gallium nanostructures, whose oxidation process is stopped after the growth of a ≈ 1 nm oxide shell, have been presented as building blocks for plasmonic phase-change devices. It presents a wide polymorphism with at least five solid phases at atmospheric pressure, plus several others at high-pressure. The design of this type of devices has been severely hampered by the lack of information on the dielectric constant of the different Ga polymorphs. In this work, it is presented a comprehensive analysis of the interdependence of the crystal structure, band structure, and dielectric function of some of the different Ga-phases. Conversely to Mg and Ga, Rh do not oxidize. This property along with its inherent catalytic properties and UV plasmonic response, make it an adequate material for photocatalytic applications. In fact, recently it was reported the role of Rh nanocubes in the CO2 catalyzation. In this PhD thesis, it is presented an optimization of these nanostructures’ geometry attending to their ability to produce hot-spots and surface charge distributions. The applicability of high refractive index dielectric materials for plasmonics in the UV range still remains a challenge. In part due to the lack of materials with loss-less behavior above 3 eV with, at the same time, a refractive index high enough to produce the so-called Mie resonances (i.e., the analog in dielectrics to the localize surface plasmon resonances in metals). In this dissertation it is performed a systematic quest for materials that ful ll these conditions along with an analysis of their applicability to UV light guiding and surface-enhanced spectroscopies.