How an oxide shell affects the ultraviolet plasmonic behavior of Ga, Mg, and Al nanostructures

Abstract

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).

Plasmonics in the Ultraviolet with Aluminum, Gallium, Magnesium and Rhodium

“…As a consequence, plasmonic resonances of Al NPs are spectrally modified. It has been experimentally and theoretically shown that the growth of this oxide layer leads to both a red-shift and a weakening of the resonance peaks in Al NPs with different shapes [22,23,31,34]. On the other hand, the self terminating oxide layer can prevent further oxidation, producing a natural encapsulation.…”

“…However, the oxidation of Mg NPs is more aggressive. The native oxide MgO forms without stopping upon exposure to air as oxygen rapidly diffuses through porous oxide into the metal [15,23]. This process leads to a complete destruction of the plasmonic effects on Mg NPs, unless they are manipulated under controlled atmospheres [49].…”

“…These fabrication methods include molecular beam epitaxy (MBE) [24,56], optically regulated self-assembly [57], thermal evaporation [58], and colloidal synthesis [59]. In addition, unlike either Al or Mg, its very low tendency to oxidation (1-2 nm oxide shell thickness), minimally affects its optical properties, keeping them stable over months or even years [23,24]. Ga NPs form liquid droplets with a melting point of 30 • C, so when deposited on a substrate at room temperature, they produce a close-packed array of smooth truncated spheres whose mean radii and size distributions vary with growth conditions.…”

“…The thickness of this oxide shell can go from 1 nm, as in the case of Ga, to the complete destruction of the metal content of the NP, as in the case of Mg [21]. So, knowing how this oxide shell affects the plasmonic behavior of this type of NPs is a key point for researchers in UV plasmonics [22][23][24]. It will be addressed in the next two sections for the four most significant metals able to sustain UV LSPRs.…”

Nonlinear optical response of Mg/MgO structures prepared by laser ablation method

“…In the recent months, Gutierrez et al reported an investigation of the effect of an oxide shell on the ultraviolet plasmonic behavior of Ga, Mg, and Al nanostructures. They studied the plasmonic response of Mg/MgO nanostructures and effect of oxidation on the UV-plasmonic response of Mg/MgO spherical or hemisphere-on-substrate nanostructures [22].…”