Oxide mediated spectral shifting in aluminum resonant optical antennas

Abstract

Abstract:As a key feature among metals showing good plasmonic behavior, aluminum extends the spectrum of achievable plasmon resonances of optical antennas into the deep ultraviolet. Due to degradation, a native oxide layer gives rise to a metal-core/oxide-shell nanoparticle and influences the spectral resonance peak position. In this work, we examine the role of the underlying processes by applying numerical nanoantenna models that are experimentally not feasible. Finite-difference time-domain simulations are carried out for a large variety of elongated single-arm and two-arm gap nanoantennas. In a detailed analysis, which takes into account the varying surface-to-volume ratio, we show that the overall spectral shift toward longer wavelengths is mainly driven by the higher index surrounding material rather than by the decrease of the initial aluminum volume. In addition, we demonstrate experimentally that this shifting can be minimized by an all-inert fabrication and subsequent proof-of-concept encapsulation.

Tailoring Electromagnetic Hot Spots toward Visible Frequencies in Ultra-Narrow Gap Al/Al2O3 Bowtie Nanoantennas

“…Moreover, the expected EM field enhancement factor | E |/| E 0 | rapidly increases with gap narrowing (Figure b,c, bottom panels), up to a value of about 300 at 1150 nm for d = 0.5 nm gap (Figure a, bottom panel). Such value is about 20× larger than one estimated in a recent theoretical work for Al nanorectangular dimers with 20 nm gap working at optical frequencies. Therefore, an extremely reduced interparticle distance in this sub-5 nm range for dimer nanostructures plays a crucial role to get large EM field enhancement and localization in a very small volume.…”

“…When two individual metallic NPs are brought into close proximity with each other, their single surface plasmons couple electromagnetically in the nonradiative near-field region. Besides the generation of hot spots, this leads to many interesting modifications of their plasmonic behaviors, such as the evolution of hybridized plasmon modes and the shift of the LSPRs. , The local EM field enhancement in gap structures is strongly correlated to the gap size narrowing starting from an enhancement factor | E max |/| E 0 | of 15 with 20 nm gap which increases to 150 for gap reduction down to 1 nm for nanosphere dimers . Further downscaling to the subnanometer scale introduces detrimental electron tunneling across the metallic dimer junction or charge transfer plasmons, − and nonlocal responses should be taken into account .…”

Hybrid Graphene-Supported Aluminum Plasmonics

“…There is, however, a ∼10 nm thick amorphous aluminum oxide (AlO x ) layer covering the surface of metallic aluminum (Figure S10). This oxide layer induces a red-shift in the LSPRs of the nanocavity, but it also acts as a protective layer for the metallic Al surface. , Close-up HRTEM images of the plasmonic hotspot at one of the tetramer nanocavities are shown in Figures h,i. The small black dots appearing at the hotspot area are Pt NCs on hydrocarbon contamination at the graphene surface (Figure h).…”

Reflective Coloration from Structural Plasmonic to Disordered Polarizonic

“…However, it is oxidized promptly in air, and its oxide layer redshifts the resonance. [123,124] Thus, finding a suitable plasmonic material for reflective structural coloration is still a challenge and needs further research.…”