Two-dimensional transition metal dichalcogenides exhibit strong optical transitions with significant potential for optoelectronic devices. In particular they are suited for cavity quantum electrodynamics in which strong coupling leads to polariton formation as a root to realisation of inversionless lasing, polariton condensation and superfluidity. Demonstrations of such strongly correlated phenomena to date have often relied on cryogenic temperatures, high excitation densities and were frequently impaired by strong material disorder. At room-temperature, experiments approaching the strong coupling regime with transition metal dichalcogenides have been reported, but well resolved exciton-polaritons have yet to be achieved. Here we report a study of monolayer WS2 coupled to an open Fabry-Perot cavity at room-temperature, in which polariton eigenstates are unambiguously displayed. In-situ tunability of the cavity length results in a maximal Rabi splitting of ħΩRabi = 70 meV, exceeding the exciton linewidth. Our data are well described by a transfer matrix model appropriate for the large linewidth regime. This work provides a platform towards observing strongly correlated polariton phenomena in compact photonic devices for ambient temperature applications.

of interest and be as sensitive as possible to small changes in the local environment. While individual particle resonances can be effectively tuned through size, shape and material choice, [ 2,12 ] coupled modes between two or more nanoparticles have been shown to exhibit far greater electric fi eld enhancements and produce more sensitive detectors. [13][14][15][16][17][18] However, these are extremely diffi cult to fabricate, with many top-down lithographic and FIBbased examples being unrealistic for scaling up, and bottom-up techniques that generally produce randomly oriented particle pairs with no control over the alignment, which is key as the resonances of such dimers are highly sensitive to the polarization of incident illumination. Henzie et al. made some important progress in this fi eld by using a gravity-driven technique to assemble nanoparticles in shallow pits in a substrate, which allows excellent control over orientation and positioning of any number of particle sets. [ 19 ] Another elegant solution to the fabrication problem is the placement of a metallic particle above a metal sheet separated by a thin spacer. A "mirror particle" is excited in the metal plane, which produces a strong coupling effect without having to align two separate particles, drastically simplifying the production process. [ 22 ] There is a growing body of work investigating the properties of silver nanocubes (NCs) above metal fi lms, to tune their scattering properties, [ 21 ] produce controlled-refl ectance surfaces, [ 22 ] and to control and enhance the radiative processes of fl uorophores within the spacer material, [ 23,24 ] as well as theoretical studies looking to build a complete description of the structure. [ 25,26 ] This system can be considered an optical patch antenna, where gap plasmon modes are supported between the metal sheet and the NC. [ 21 ] The resonant modes of these antennae are extremely sensitive to the properties of the spacer layer separating the NC and the silver sheet, and any environmental changes that infl uence the refractive index (RI), or more importantly the thickness of the chosen material will produce signifi cant changes in the plasmon resonance. As long as spacer materials which expand in response to a given analyte are available, this design can be utilized to detect any number of chemicals. This forms the basis for a new type of sensor, which can operate equally well in a gaseous or liquid setting (depending on spacer choice) and that is scalable from the sub-wavelength scale (the footprint of one nanocube) up to a large-surface area metamaterial.In this paper, we demonstrate the operation of the nanocube patch antenna system as a gas sensor for the fi rst time, usingThe ability of individual nanocube patch antennas, consisting of a silver nanocube separated from an Ag sheet by a thin fl uoropolymer spacer, to act as subwavelength sensing elements is demonstrated. An increase in relative humidity (RH) causes the spacer to expand, which alters the resonance of the plasmon cavity mode fo...

The use of photothermal sensitizers to facilitate the sintering of polymer powders is rapidly becoming a pivotal additive manufacturing technology, impacting multiple sectors of industry. However, conventional carbon-based sensitizers can only produce black or gray objects. To create white or colorful prints with this method, visibly transparent equivalents are needed. Here, we address this problem by designing resonant photothermal sensitizers made of plasmonic nanoparticles that strongly absorb in the near-infrared, while only minimally interacting with visible light. Gold nanorods were coated with silica before being mixed with polyamide powders to create stable colorful nanocomposite powders. At resonance, these composites showed greatly improved light-to-heat conversion compared with equivalent composites using the industry standard carbon black as a sensitizer and could be sintered using low-power light sources. Furthermore, they appear much whiter and can produce brightly colored 3D objects when mixed with dyes. Our results open a new route to utilize plasmonic nanoparticles to produce colorful and functional 3D-printed objects.

The effect of a thin dielectric film on the plasmonic behaviour of metal nanoparticles (MNPs) above a high refractive index substrate is explored. Using finite-difference time domain simulations, the optical properties of Ag nanoparticles are investigated as a function of film thickness, refractive index, and particle position within the film. We demonstrate that the addition of a film around a MNP at the air interface of a high-index substrate, where n air < n f ilm < n substrate , will always increase the fraction of light coupled to the substrate (F subs ). It is found that placement within a layer that does not conform to n air < n f ilm < n substrate can lead to reduced enhancements in F subs . The principal application for this work is for light-trapping in thin-film solar cells. We show that the inclusion of a thin film can increase the fraction of radiation coupled into the substrate by up to 30% for solar wavelengths. Additional potential benefits of the film structure, such as greater tunability of scattering resonances, an increase in path length of light in the substrate, and some control over the emission pattern are demonstrated. MNPs in a film are found to produce a more finely structured emission pattern than particles at a simple interface, showing potential for this research to be applied to optical nanoantennae. V

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