Giant Enhancement Research Articles

Giant Photoluminescence Enhancement of Monolayer WSe2 Using a Plasmonic Nanocavity with On-Demand Resonance.

Monolayer transition metal dichalcogenides (TMDs) are considered promising building blocks for next-generation photonic and optoelectronic devices, owing to their fascinating optical properties. However, their inherent weak light absorption and low quantum yield severely hinder their practical applications. Here, we report up to 18000-fold photoluminescence (PL) enhancement in a monolayer WSe2-coupled plasmonic nanocavity. A spectroscopy-assisted nanomanipulation technique enables the assembly of a nanocavity with customizable resonances to simultaneously enhance the excitation and emission processes. In particular, precise control over the magnetic cavity mode facilitates spectral and spatial overlap with the exciton, resulting in plasmon-exciton intermediate coupling that approaches the maximum emission rate in the hybrid system. Meanwhile, the cavity mode exhibits high radiation directivity, which overwhelmingly directs surface-normal PL emission and leads to a 17-fold increase in the collection efficiency. Our approach opens up a new avenue to enhance the PL intensity of monolayer TMDs, facilitating their implementation in highly efficient optoelectronic devices.

Giant Modulation of Refractive Index from Picoscale Atomic Displacements.

It is shown that structural disorder-in the form of anisotropic, picoscale atomic displacements-modulates the refractive index tensor and results in the giant optical anisotropy observed in BaTiS3, a quasi-1D hexagonal chalcogenide. Single-crystal X-ray diffraction studies reveal the presence of antipolar displacements of Ti atoms within adjacent TiS6 chains along the c-axis, and threefold degenerate Ti displacements in the a-b plane. 47/49Ti solid-state NMR provides additional evidence for those Ti displacements in the form of a three-horned NMR lineshape resulting from a low symmetry local environment around Ti atoms. Scanning transmission electron microscopy is used to directly observe the globally disordered Ti a-b plane displacements and find them to be ordered locally over a few unit cells. First-principles calculations show that the Ti a-b plane displacements selectively reduce the refractive index along the ab-plane, while having minimal impact on the refractive index along the chain direction, thus resulting in a giant enhancement in the optical anisotropy. By showing a strong connection between structural disorder with picoscale displacements and the optical response in BaTiS3, this study opens a pathway for designing optical materials with high refractive index and functionalities such as large optical anisotropy and nonlinearity.

Light-induced giant enhancement of nonreciprocal transport at KTaO3-based interfaces

Nonlinear transport is a unique functionality of noncentrosymmetric systems, which reflects profound physics, such as spin-orbit interaction, superconductivity and band geometry. However, it remains highly challenging to enhance the nonreciprocal transport for promising rectification devices. Here, we observe a light-induced giant enhancement of nonreciprocal transport at the superconducting and epitaxial CaZrO3/KTaO3 (111) interfaces. The nonreciprocal transport coefficient undergoes a giant increase with three orders of magnitude up to 105 A−1 T−1. Furthermore, a strong Rashba spin-orbit coupling effective field of 14.7 T is achieved with abundant high-mobility photocarriers under ultraviolet illumination, which accounts for the giant enhancement of nonreciprocal transport coefficient. Our first-principles calculations further disclose the stronger Rashba spin-orbit coupling strength and the longer relaxation time in the photocarrier excitation process, bridging the light-property quantitative relationship. Our work provides an alternative pathway to boost nonreciprocal transport in noncentrosymmetric systems and facilitates the promising applications in opto-rectification devices and spin-orbitronic devices.

Giant enhancement of positive and negative Goos-Hänchen shifts in two-dimensional grating waveguide structures supporting Fano resonances

We propose a two-dimensional grating waveguide structure based on guided-mode resonance (GMR) to greatly enhance the Goos-Hänchen (GH) shift due to the asymmetric Fano peak. In addition, the enhancement of the GH shift is located at the peak of the reflectivity, which enables a more accessible measurement compared to the conventional GH shift enhancement based on Brewster angle or transmission-type resonance. In particular, such structure supports four channels for the GH shift enhancements, with a maximum value of 4.8×104λ0 for the positive one and -6000 λ0 for the negative one. Our results benefit the potential applications for optical sensors, optical filters, optical absorbers and surface plasmon resonators, etc.

Giant enhancement of second harmonic generation via merging bound states in the continuum for vacuum ultraviolet radiation

Vacuum ultraviolet (VUV) light plays a crucial role in various scientific and technological fields, such as nanolithography and biomedical treatments. However, the inherent nonlinear optical coefficient of nonlinear optical crystals is typically very low, and increasing the action length is often necessary to improve the nonlinear conversion efficiency. This makes it challenging for these materials to achieve high-density optoelectronic integration at the micro-/nano-scale. In this study, we propose a design for generating coherent VUV radiation close to 175 nm using second harmonic generation (SHG) with an absolute efficiency exceeding 1.2‰ mW−1. This is achieved by merging multiple bound state in the continuum modes in a free-standing photonic crystal slab. Even with fabrication imperfections at a level lower than 10% disorder, the SHG efficiency of the samples remains robust, maintaining an efficiency of at least 2‰. This research provides a beneficial platform for generating efficient VUV light in the nanoscale.

Giant enhancement of high-order rotational and rovibrational transitions in near-field spectroscopy in proximity to nanostructures

Giant enhancement of high-order rotational and rovibrational transitions in near-field spectroscopy in proximity to nanostructures

Giant enhancement of third harmonic generation via guided mode resonances in notched silicon waveguides

We report a giant enhancement of the third harmonic generation (THG) at 343 nm by periodically notched silicon waveguide arrays supporting guided mode resonances (GMRs) at 1030 nm. Maximum efficiency of the third harmonic generation η = 7.71 × 10−5 is achieved with a peak pump power density of 5.31 GW/cm2. The enhancement factor of the THG from the GMR metasurface reaches up to 1.3 × 107 compared to a flat silicon film with the same thickness. This observation demonstrates a promising approach to design high-efficiency nonlinear optical metasurfaces.

Revisiting anapoles in a single high-index dielectric structure

High-index dielectric structures support electric and magnetic Mie resonance. Through careful manipulation of geometric parameters, destructive interference can be induced between electric multipole moments and toroidal multipole moments. This leads to the formation of anapoles, which are characterized by quenched scattering in the far field and giant enhancement in the near field. Here, we revisit the formation mechanism of anapole states in a single dielectric structure with a high refractive index from an eigenmode perspective. We find that scattering efficiency is mainly determined by the intrinsic phase governed by the leaky mode of the structure and the extrinsic phase induced by the frequency deviation from resonance. It is also demonstrated that the anapole modes in a two-dimensional cylinder and a three-dimensional sphere can only occur in the following two situations: (1) when only one mode is involved, the combined phase of intrinsic and extrinsic phase should be equal to 2π at a certain frequency (anapole frequency), which is very close to the resonance frequency. Generally, these types of anapoles are low-order anapoles since low-order resonant modes (i.e., magnetic (electric) dipole and quadrupole) are well separated. (2) If two or more leaky modes are involved, the combined phase for each mode must be 2π at the same frequency located between the two resonances. This corresponds to the high-order anapoles. It is also found that more anapole states will emerge with increasing refractive index. Our results may provide new perspectives for designing high-order anapoles with more freedom.

Giant enhancement of fluorescence resonance energy transfer based on nanoporous gold with small amount of residual silver

Fluorescence resonance energy transfer (FRET) was found strongly enhanced by plasmon resonance. In this work, Nanoporous Gold with small amount of residual silver was used to form nanoporous gold/organic molecular layer compound with PSS and PAH. The ratio of its specific gold and silver content is achieved by controlling the time of its dealloying. Layered films of polyelectrolyte multilayers were assembled between the donor–acceptor pairs and NPG films to control distance. The maximum of FRET enhancement of 80-fold on the fluorescence intensity between the donor–acceptor pairs (CFP-YFP) is observed at a distance of ∼10.5 nm from the NPG film. This Nanoporous Gold with small amount of residual silver not only enhanced FRET 4-fold more than nanoporous gold of only gold content almost, but also effectively realized the regulation of FRET enhancement. The ability to precisely measure and regulate the enhancement of FRET enables the rational selection of plasmonic nanotransducer dimensions for the particular biosensing application.

The effect of property contrast in two-component piezoelectric composites

A Mori - Tanaka model of piezoelectric composites is used to study the effect of property contrast between the components of a two-component composite. The composite comprises a piezoelectric matrix and piezoelectric inclusions whose property values are scaled from those of the matrix. The scaling method allows a wide range of material combinations to be approximated without using explicit properties of specific materials. Additionally, the aspect ratio and volume fraction of inclusions is varied to seek optimum values of the piezoelectric coefficients in the composite. It was found that scaling the properties in the electroelastic moduli reveals significant results for the piezoelectric performance coefficients dhgh, κ33, g33 and kt. By varying the material scaling factors alongside the inclusion aspect ratio it is demonstrated that giant enhancements of the transducer figure of merit dhgh could potentially be achieved through composite design. This approach identifies some novel opportunities for optimised piezoelectric composites.

Giant thermal enhancement of upconversion photoluminescence in Y2W3O12:Nd phosphor under 808 nm excitation

Luminescent materials usually suffer from thermal quenching at high temperature due to the aggravation of nonradiation relaxations. Herein, a giant enhancement of up conversion (UC) luminescence is observed in negative thermal expansion (NTE) Y2W3O12:Nd phosphor upon increasing the temperature from 310 to 790 K. In addition, the temperature-dependent UC emission is reversible. To penetrate into the mechanisms, the temperature-dependent luminescence intensity and lifetime are investigated for Nd doped negative and positive thermal expansion (PTE) phosphors. Based these investigation, we infer that the underlying mechanism of the giant enhancement for Y2W3O12:Nd phosphor are due to combined effects of phonon assisted absorptions and contraction of NTE crystals. Moreover, the observation of temperature-dependent near-infrared spectra (NIR) can support the mechanism from the other side. The present findings pave the way to overcome thermal quenching of Nd3+ ions and explore new thermal enhancement materials sensitized by Nd3+ ions.

Giant enhancement of third harmonic generation in an array of graphene ribbons using amplification of surface plasmon polaritons by optical gain

In this paper, we theoretically study the enhancement of third-harmonic generation in a plasmonic structure composed of an array of trilayer graphene ribbons sandwiched between two CaF2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$CaF_{2}$$\\end{document} layers. In fact, we suggest a new method for more enhancement of nonlinearity in plasmonic structures using incorporation of optical gain into graphene ribbons. As the pump intensity increases, the maximum output intensity of third harmonic generated (THG) wave versus fundamental frequency is blue-shifted while its value enhances. Our analysis indicates that the enhancement factor of THG in our proposed structure is 1.1 × 107 without occurring an electric breakdown compared to case at which an optically pumped trilayer graphene sheet sandwiched between two CaF2 layers. Therefore, only presence of optical gain is not sufficient for significant enhancement of output intensity of THG wave and excitation of SPPs through the structure is also essential. On the other hand, our results demonstrate that the output intensity of THG wave from the proposed structure under optical pumping enhances by 105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{5}$$\\end{document} times compared to the plasmonic structure without optical gain which confirms the role of optical gain for THG enhancement in the plasmonic structure. This is because the gain in graphene ribbons amplifies the SPPs waves leading to the more field enhancement along the graphene ribbons which results in significant enhancement of THG wave in the plasmonic structure in comparison with one without gain. Therefore, we reveal that both SPPs and optical gain contribute to the strong output intensity of THG in our proposed structure compared to the trilayer graphene sheet inserted between two CaF2 layers.

Hundred-Fold Enhancement in the Anomalous Hall Effect Induced by Hydrogenation.

The anomalous Hall effect (AHE) is one of the most fascinating transport properties in condensed matter physics. However, the AHE magnitude, which mainly depends on net spin polarization and band topology, is generally small in oxides and thus limits potential applications. Here, we demonstrate a giant enhancement of AHE in a LaCoO3-induced 5d itinerant ferromagnet SrIrO3 by hydrogenation. The anomalous Hall resistivity and anomalous Hall angle, which are two of the most critical parameters in AHE-based devices, are found to increase to 62.2 μΩ·cm and 3%, respectively, showing an unprecedentedly large enhancement ratio of ∼10000%. Theoretical analysis suggests the key roles of Berry curvature in enhancing AHE. Furthermore, the hydrogenation concomitantly induces the significant elevation of Curie temperature from 75 to 160 K and 40-fold reinforcement of coercivity. Such giant regulation and very large AHE magnitude observed in SrIrO3 could pave the path for 5d oxide devices.

Giant enhancement of anti-quenching upconversion luminescence in Sc2W3O12:Er3+/Yb3+ phosphors for temperature sensing

Although negative thermal expansion (NTE) materials provide a new strategy to overcome the thermal-quenching phenomenon in rare earth doped luminescent materials, the overall weak upconversion luminescence still restrict their application...

Defect Engineering of 2D Semiconductors for Dual Control of Emission and Carrier Polarity.

2D transition metal dichalcogenides (TMDCs) are considered as promising materials in post-Moore technology. However, the low photoluminescence quantum yields (PLQY) and single carrier polarity due to the inevitable defects during material preparation are great obstacles to their practical applications. Here, an extraordinary defect engineering strategy is reported based on first-principles calculations and realize it experimentally on WS2 monolayers by doping with IIIA atoms. The doped samples with large sizes possess both giant PLQY enhancement and effective carrier polarity modulation. Surprisingly, the high PL emission maintained even after one year under ambient environment. Moreover, the constructed p-n homojunctions shows high rectification ratio (≈2200), ultrafast response times and excellent stability. Meanwhile, the doping strategy is universally applicable to other TMDCs and dopants. This smart defect engineering strategy not only provides a general scheme to eliminate the negative influence of defects, but also utilize them to achieve desired optoelectronic properties for multifunctional applications.

Ultraclean surface restoration and giant photoresponse enhancement of violet phosphorus

Violet phosphorus (VP), a recently developed kind of layered material, features exotic in-plane anisotropy, alluring thickness-dependent bandgap, and better thermal stability than its phosphorus allotropes. Such a broad variety of functionalities indicates VP is a promising candidate for advanced nanophotonics. However, its hydrophilic surface-induced air instability hinders further exploration and extensive device integration for photodetection and beyond. Herein, we report the successful restoration of the clean VP surfaces through nitrogen plasma combined with vacuum thermal annealing. Via manipulation of plasma excitation power, we can also achieve thickness etching and nondestructive p-doping to VP, paving the way for fabrication and engineering of VP photodetectors. As a proof-of-concept, plasma-treated VP photodetectors have been fabricated. Stemming from the plasma treatment-induced p-doping and hole trapping centers, the VP photodetectors exhibit giant photoresponse enhancement, reaching a high responsivity of 1.923 A/W, and is dramatically improved by 1300% compared with that before plasma treatments, which envisions high-sensitivity photodetection for next-generation more-than-Moore optoelectronics.

All-optically controlled holographic plasmonic vortex array for multiple metallic particles manipulation

Due to the sub-diffraction-limited size and giant field enhancement, plasmonic tweezers have a natural advantage in trapping metallic particles. However, the strict excitation condition makes it difficult to generate an arbitrary plasmonic field in a controllable manner, thus narrowing its practical applications. Here, we propose an all-optical plasmonic field shaping method based on a digital holographic algorithm and generate plasmonic vortex arrays with controllable spot numbers, spatial location, and topological charge. Our experimental results demonstrate that multiple gold particles can be stably trapped and synchronously rotated in the vortex arrays, and the particles’ kinestate can be dynamically switched. The proposed holographic plasmonic vortex tweezers are suitable for a broadband particle trapping, and this method can be generalized to other surface electromagnetic waves like Bloch surface wave.

Novel Nano-Electroplating-Based Plasmonic Platform for Giant Emission Enhancement in Monolayer Semiconductors.

Two-dimensional semiconductors such as monolayer MoS2 have attracted considerable attention owing to their exceptional electronic and optical characteristics. However, their practical application has been hindered by the limited light absorption resulting from atomically thin thickness and low quantum yield. A highly effective approach to address these limitations is by integrating subwavelength plasmonic nanostructures with monolayer semiconductors. In this study, we employed electron beam lithography and nanoelectroplating techniques to develop a gold nanodisc (AuND) array plasmonic platform. Monolayer MoS2 transferred on top of the AuND array yields up to 150-fold photoluminescence enhancement compared to a gold film without normalization with respect to plasmonic hot spots. In addition, the unique protocol of nanoelectroplating helps to get flat-top cylindrical discs which enable less tear during the delicate wet transfer of monolayer MoS2. We explain our experimental findings based on electromagnetic simulations.

Brightening and Directionality Control of Dark Excitons through Quasi-Bound States in the Continuum

Thanks to their long lifetime, spin-forbidden dark excitons in transition metal dichalcogenides are promising candidates for storage applications in opto-electronics and valleytronics. To date, their study has been hindered by inefficient generation mechanisms and the necessity for elaborate detection schemes. In this work, we propose a new hybrid platform that simultaneously addresses both challenges. We study an all-dielectric metasurface with two symmetrically protected quasi-bound states in the continuum to enhance both the excitation and emission of dark excitons in a tungsten diselenide monolayer under normal light incidence. Our simulations show a giant photoluminescence signal enhancement (∼520) along with directional emission, thus offering distinct advantages for opto-electronic and valleytronic devices.

Gate-readout and a 3D rectification effect for giant responsivity enhancement of asymmetric dual-grating-gate plasmonic terahertz detectors

Abstract We experimentally investigated the asymmetric dual-grating-gate plasmonic terahertz (THz) detector based on an InGaAs-channel high-electron-mobility transistor (HEMT) in the gate-readout configuration. Throughout the THz pulse detection measurement on the fabricated device, we discovered a new detection mechanism called the “3D rectification effect” at the positive gate bias application, which is a cooperative effect of the plasmonic nonlinearities in the channel with the diode nonlinearity in the heterobarrier between the InGaAs channel layer and the InAlAs spacer/carrier-supply/barrier layers, resulting in a giant enhancement of the detector responsivity. We also found that an undesired long-tail waveform observed on the temporal pulse photoresponse of the device is due to trapping of carriers to the donor levels in the silicon δ-doped carrier-supply layer when they tunnel through the barrier to the gate and can be eliminated completely by introducing the so-called inverted-HEMT structure. The internal current responsivity and noise-equivalent power are estimated to be 0.49 A/W (with the equivalent voltage responsivity of 4.9 kV/W with a high output impedance of 10 kΩ) and 196 pW/√Hz at 0.8 THz. These results pave the way towards the application of the plasmonic THz detectors to beyond-5G THz wireless communication systems.