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Plasmonic hyperbolic metasurfaces have emerged as an effective platform for manipulating the propagation of light. Here, confined modes on arrays of silver nanoridges that exhibit hyperbolic dispersion are used to demonstrate and model a super-resolution imaging technique based on structured illumination microscopy. A spatial resolution of ~75 nm at 458 nm is demonstrated, which is 3.1 times better than an equivalent diffraction limited image. This work emphasizes the ability to engineer the properties of confined optical modes and to leverage those characteristics for applications in imaging. The results of this work could lead to improved approaches for super-resolution imaging using designed sub-wavelength structures., Comment: 9 pages, 7 figures

Colloidal nanocrystals are a promising fluorescent class of materials, whose spontaneous emission features can be tuned over a broad spectral range via their composition, geometry and size. However, towards embedding nanocrystals films in elaborated device geometries, one significant drawback is the sensitivity of their emission properties on further fabrication processes like lithography, metal or oxide deposition, etc. In this work, we demonstrate how bright emitting and robust thin films can be obtained by combining nanocrystal deposition from solutions via spin2 coating with subsequent atomic layer deposition of alumina. For the resulting composite films, the layer thickness can be controlled on the nanoscale, and their refractive index can be finely tuned by the amount of deposited alumina. Ellipsometry is used to measure the real and imaginary part of the dielectric permittivity, which gives direct access to the wavelength dependent refractive index absorbance of the film. Detailed analysis of the photophysics of thin films of core-shell nanocrystal with different shape and different shell thickness allow to correlate the behavior of the photoluminescence and of the decay life time to the changes in the non-radiative rate that are induced by the alumina deposition. We show that the photoemission properties of such composite films are stable in wavelength and intensity over several months, and that the photoluminescence completely recovers from heating processes up to 240$^\circ$C. The latter is particularly interesting, since it demonstrates robustness to the typical heat treatment that is needed in several process steps like resist-based lithography and deposition by thermal or electron beam evaporation of metals or oxides., Comment: 20 pages, 4 figures, SYNOPSIS TOC

Metal/Insulator/Metal nanocavities (MIMs) are highly versatile systems for nanometric light confinement and waveguiding, and their optical properties are mostly interpreted in terms of surface plasmon polaritons. Although classic electromagnetic theory accurately describes their behavior, it often lacks physical insight, letting some fundamental aspects of light interaction with these structures unexplored. In this work, we elaborate a quantum mechanical description of the MIM cavity as a double barrier quantum well. We identify the square of the imaginary part of the refractive index of the metal as the optical potential, and find that MIM cavity resonances are suppressed if the ratio n/\k{appa} exceeds a certain limit, which shows that low n and high \k{appa} are desired for strong and sharp cavity resonances. Interestingly, the spectral regions of cavity mode suppression correspond to the interband transitions of the metals, where the optical processes are intrinsically non-Hermitian. The quantum treatment allows to describe the tunnel effect for photons, and reveals that the MIM cavity resonances can be excited by resonant tunneling via illumination through the metal, without the need of momentum matching techniques such as prisms or grating couplers. By combining this analysis with spectroscopic ellipsometry on experimental MIM structures, and by developing a simple harmonic oscillator model of the MIM for the calculation of its effective permittivity, we show that the cavity eigenmodes coincide with low-loss zeros of the effective permittivity., Comment: 33 pages, 7 figures

The coupling between multiple nanocavities in close vicinity leads to hybridization of their modes. Stacked Metal/Insulator/Metal (MIM) nanocavities constitute a highly versatile and very interesting model system to study and engineer such mode coupling, since they can be realized by lithography-free fabrication methods with fine control on the optical and geometrical parameters. The resonant modes of such MIM cavities are epsilon-near-zero (ENZ) resonances, which are appealing for non-linear photophysics and a variety of applications. Here we study the hybridization of ENZ resonances in MIMIM nanocavities, obtaining a very large mode splitting reaching 0.477 eV, Q factors of the order of 40 in the visible spectral range, and fine control on the resonance wavelength and mode linewidth by tuning the thickness of the dielectric and metallic layers. A semi-classical approach that analyses the MIMIM structure as a double quantum well system allows to derive the exact analytical dispersion relation of the ENZ resonances, achieving perfect agreement with numerical simulations and experiments. Interestingly, the asymmetry of the mode splitting in a symmetric MIMIM cavity is not reflected in the classical model of coupled oscillators, which can be directly related to quantum mechanical tunneling for the coupling of the two cavities. Interpreting the cavity resonances as resonant tunneling modes elucidates that can be excited without momentum matching techniques. The broad tunability of high-quality ENZ resonances together with their strong coupling efficiency makes such MIMIM cavities an ideal platform for exploring light-matter interaction, for example, by integration of quantum emitters in the dielectric layers., Comment: 24 pages, 4 figures

Directing and polarizing the emission of a fluorophore is of fundamental importance in the perspective of novel photonic sources based on emerging nano-emitter technologies. These two tasks are usually accomplished by a sophisticated and demanding structuring of the optical environment in which the emitter is immersed, or by non-trivial chemical engineering of its geometry and/or band structure. In this paper, the wavelength and polarization selective spontaneous emission from a dye-embedded in a Metal/Insulator/Metal (d-MIM) nanocavity is demonstrated. A push-pull chromophore with large Stokes shift is embedded in a MIM cavity whose resonances are tuned with the spectral emission band of the chromophore. Angular and polarization resolved spectroscopy experiments reveal that the radiated field is reshaped according to the angular dispersion of the nanocavity, and that its spectrum manifests two bands with different polarization corresponding to the p- and s-polarized resonances of the cavity. The d-MIM cavities are a highly versatile system for polarization and wavelength division multiplexing applications at the nanoscale, as well as for near-field focused emission and nanolenses., Comment: 18 pages, 4 figures

Colloidal core/shell nanocrystals are key materials for optoelectronics, enabling control over essential properties via precise engineering of the shape, thickness, and crystal lattice structure of their shell. Here, we apply the growth protocol for CdS branched nanocrystals on CdSe nanoplatelet seeds and obtain bone-shaped heterostructures with a highly anisotropic shell. Surprisingly, the nanoplatelets withstand the high growth temperature of 350 {\deg}C and we obtain structures with a CdSe nanoplatelet core that is overcoated by a shell of cubic CdS, on top of which tetrahedral CdS structures with hexagonal lattice are formed. These complex core/shell nanocrystals show a bandedge emission around 657 nm with a photoluminescence quantum yield of ca. 42 % in solution, which is also retained in thin films. Interestingly, the nanocrystals manifest simultaneous red and green emission, and the relatively long wavelength of the green emission indicates charge recombination at the cubic/hexagonal interface of the CdS shell. The nanocrystal films show amplified spontaneous emission, random lasing, and distributed feedback lasing when the material is deposited on suitable gratings. Our work stimulates the design and fabrication of more exotic core/shell heterostructures where charge carrier delocalization, dipole moment, and other optical and electrical properties can be engineered., Comment: 26 pages, 6 figures, 1 table