Monolayer semiconductors with spin-dependent contrasting phenomena at K and K’ valleys feature addressable valley degree of freedom for valleytronic applications. Herein, we demonstrate that chiral Purcell effects can versatilely control the relaxation of targeted valley excitons at monolayer semiconductors, allowing the actively tunable modulation of valley dynamics at room temperature. We achieve the tunable valley modulation by embedding a monolayer WSe2 in our model system, known as a moiré chiral metamaterial, with actively controllable chiral plasmonic modes. Our work provides advanced understanding on mechanisms to distinguish the effects of spin-dependent excitation and near-field-controlled relaxation on valley emission in hybrid systems of valley excitons and plasmonic cavities. We have also shown that large room-temperature valley modulation can be achieved outside of strong-coupling regime with active tunability.
We have developed microbubble-assisted rapid concentration and ultrahigh-sensitive detection of multiple chiral metabolites. Through the strong Marangoni convection, the drag force can efficiently drag and print the biomolecules with hundreds of molar masses on the plasmonic substrates for chiral analysis, breaking the limit of conventional electrophoresis and thermophoresis in the manipulation of molecules. We show that we can detect and differentiate 100 pM D/L pure glucose solution, which shows 107 times greater sensitivity than the state-of-the-art chiral sensing techniques. Finally, we successfully detect the enantiomer excess in purified urine and therefore push the label-free lab-on-a-chip detection of chiral biomarkers for diabetes mellitus detection.
We demonstrate a novel moiré chiral metamaterial (MCM) with actively tunable and reversible optical chirality, which is enabled by the tunable Fano coupling and a solvent-controllable dielectric spacer in the MCM. Using an ultrathin MCM that is only 1/5 of the working wavelength in thickness, we have achieved the active spectral shift over more than one full width at half maximum and the sign inversion of the circular dichroism spectra. We have further applied the plasmon-enhanced chiral near-fields in the MCM to actively modulate the valley excitons in a monolayer semiconductor. With the large and controllable tunability in both far-field and near-field chiroptical responses, our metamaterials are promising for applications in chiral light modulators, ultrasensitive solvent sensors, and active valleytronic devices.
Controlling light scattering and emission at subwavelength scale has significant implications for solar energy conversion, sensing, and nanophotonic devices. Plasmonic nanopatch antennas (PNAs), which consist of plasmonic nanoparticle coupled with metallic films, have shown directionality of radiation and large emission rate enhancement due to the strong plasmonic waveguide modes within the spacer layer. Herein, we comparatively study the light scattering and emission behaviors of a series of plasmonic nanopatch antennas (PNAs) with different plasmonic nanoparticles (i.e., nanosquare, nanotriangle, nanorod, and nanodisk) to develop the design rules of the PNAs. Using finite-difference time-domain (FDTD) simulations, we show that the shape and size of plasmonic nanoparticles can be tuned to control the resonance peak, intensity, directionality, and spatial distribution of the scattering light as well as the directionality, spatial distribution, spontaneous emission rate, quantum efficiency, and radiation enhancement factor of light emission. For example, high radiative quantum efficiency (0.74) and radiation enhancement factor (>20) can be achieved by disk PNA, while triangle PNA shows remarkable spontaneous emission rate enhancement of over 2,500. The effects of locations of emitters relative to the PNAs on the emission properties are also examined. Our results pave the way towards the rational design of PNAs for the optimal light scattering and emission as required by targeted applications.
Nanosphere lithography (NSL) uses self-assembled layers of monodisperse micro-/nano-spheres as masks to fabricate
plasmonic metal nanoparticles. Different variants of NSL have been proposed with the combination with dry etching
and/or angled-deposition. These techniques have employed to fabricate a wide variety of plasmonic nanoparticles or
nanostructures. Here we report another promising extension - moiré nanosphere lithography (MNSL), which
incorporates in-plane twisting between neighboring monolayers, to extend the patterning capability of conventional
NSL. In conventional NSL, the masks, either a monolayer or bilayer, are formed by spontaneous self-assembly.
Therefore, the resulted colloidal crystal configurations are limited. In this work we used sequential stacking of
polystyrene nanosphere monolayers to form a bilayer crystal at the air/water interfaces. During this layer-by-layer
stacking process, a crystal domain in the top layer gains the freedom to positon itself in a relative angle to that in the
bottom layer allowing for the formation of moiré patterns. Subsequent O2 plasma etching results in a variety of complex
nanostructures that have not been reported before. Using etched moiré patterns as masks, we further fabricated the
corresponding gold nanostructures and characterized their scattering optical properties. We believe this facile technique
provides a new strategy to fabricate novel and complex plasmonic nanostructures or metasurfaces.
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