2Strong interactions between surface plasmons in ultra-compact nanocavities and excitons in two dimensional materials have attracted wide interests for its prospective realization of polariton devices at room temperature. Here, a continuous transition from weak coupling to strong coupling between excitons in MoS2 monolayer and highly localized plasmons in ultracompact nanoantenna is proposed. The nanoantenna is assembled by a silver nanocube positioned over a gold film and separated by a dielectric spacer layer. A 1570-fold enhancement in the photoluminescence is observed at weak coupling regime in hybrid nanocavities with thick spacer layers. The interaction between excitons and plasmons is then directly prompted to strong coupling regime by shrinking down the thickness of spacer layer. Room temperature formation of polaritons with Rabi splitting up to 190 meV is observed with a fair polariton loss around 165 meV. Numerical calculations quantify the relation between coupling strength, local density of states and spacer thickness, and reveal the transition between weak coupling and strong coupling in nanocavities. The findings in this work offer a guideline for feasible designs of plasmon-exciton interaction systems with gap plasmonic cavities.

Infrared photodetectors have been used extensively in biomedicine, surveillance, communication and astronomy. However, state of the art technology based on III-V and II-VI compounds still lacks excellent performance for high-temperature operation. Surface plasmon polaritons (SPPs) have demonstrated their capability in improving the light detection from visible to infrared wave range due to their light confinement in subwavelength scale. Advanced fabrication techniques such as electron-beam lithography (EBL) and focused ion-beam (FIB), and commercially available numerical design tool like Finite-Difference Time-Domain (FDTD) have enabled rapid development of surface plasmon (SP) enhanced photodetectors. In this review article, the basic mechanisms behind the SP-enhanced photodetection, the different type of plasmonic nanostructures utilized for enhancement, and the reported SP-enhanced infrared photodetectors will be discussed.

All inorganic cesium lead halide perovskite semiconductors exhibit great potential for nanolasers, light-emitting diodes, and solar cells, because of their unique properties including low threshold, high quantum efficiency and low cost. However, the high material refractive index of perovskite semiconductors hinders light extraction efficiency for photonic and illumination applications. In this paper, we demonstrate high light extraction efficiency achieved in CsPbBr 2.75 I 0.25 two-dimensional photonic crystals. The perovskite photonic crystals exhibit both emission rate inhibition and light energy redistribution simultaneously. We observed a 7.9-fold reduction of spontaneous emission rate with a slower decay in CsPbBr 2.75 I 0.25 photonic crystals, because of the photonic bandgap effect (PBG). We also observed a 23.5-fold PL emission enhancement, as a result of light energy redistribution from 2D guided modes to vertical direction in perovskite photonic crystals thin films, indicating a high intrinsic light extraction efficiency. Such a combination of inhibiting undesirable emission with redistributing light energy into useful modes offers a new promising approach in various applications for perovskite, including solar cell, displays, and photovoltaics.

Metamaterials provide a good platform for biochemical sensing due to its strong field localization at nanoscale. In this work, we show that electric and magnetic resonant modes in split-ring-resonator (SRR) can be efficiently excited under unpolarized light illumination when the SRRs are arranged in fourfold rotationally symmetric lattice configuration. The fabrication and characterization of deep subwavelength (~λ/15) gold-based SRR structures with resonator size as small as ~ 60 nm are reported with magnetic resonances in Vis-NIR spectrum range. The feasibility for sensing is demonstrated with refractive index sensitivity as high as ~ 636 nm/RIU.

No abstract

Ultrahigh density nanostructure arrays with controlled size and position have promised a variety of potential applications. However, their practical realization is often hindered by the amount of resources required for large-scale fabrication. Using an ultrahigh contrast electron beam lithography process, we show ultrahigh resolution and high aspect ratio patterning capability which can be done at an exposure dose lower than 100 μC cm(-2). In particular, the high aspect ratio of dot arrays on 110 nm thick resist is confirmed by a standard lift-off process of 20 nm thick gold nanodots at sub-15 nm feature size and 40 nm pitch. The smallest gold nanodot size from our experiment is 11 nm.

Optics-based sensing platform working under unpolarized light illumination is of practical importance in the sensing applications. For this reason, sensing platforms based on localized surface plasmons are preferred to their integrated optics counterparts for their simple mode excitation and inexpensive implementation. However, their optical response under unpolarized light excitation is typically weak due to their strong polarization dependence. Herein, the role of rotational symmetry for realizing robust sensing platform exhibiting strong optical contrast and high sensitivity is explored. Specifically, gammadion and star-shaped gold nanostructures with different internal and external rotational symmetries are fabricated and studied in detail, from which their mode characteristics are demonstrated as superposition of their constituent longitudinal plasmons that are in conductive coupling with each other. We demonstrate that introducing and increasing internal rotational symmetry would lead to the enhancement in optical contrast up to ~3x under unpolarized light illumination. Finally, we compare the sensing performances of rotationally symmetric gold nanostructures with a more rigorous figure-of-merit based on sensitivity, Q-factor, and spectral contrast.

Room temperature plasmon-enhanced InAs0.91Sb0.09-based heterojunction n-i-p mid-wave infrared photodetector. Applied Physics Letters, 113(1), 011110-.