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Intensity-interrogation surface plasmon resonance (I-SPR) provides the fastest imaging speed among various SPR techniques, including wavelength, phase, and angle-based detection. It also integrates easily with other devices and has substantial practical application potential. However, I-SPR's reliance on direct detection of reflected light intensity renders it sensitive to light source fluctuations and detector dark noise, and its dynamic range is relatively limited. To address these challenges, we have developed a multi-channel I-SPR sensing platform featuring rapid wavelength interval selection technology. This system optimizes the sensing wavelength according to the refractive indices of different samples, mitigating issues related to inconsistent SPR signals from various biomolecules. Our improved I-SPR technology enables high-throughput biomolecular detection with a refractive index range size of 2.035 × 10−2 for dynamic monitoring, reaching a leading role among the existing I-SPR technologies. This represents the widest linear dynamic range for I-SPR to date. Experimental results on protein binding kinetic constants KD are consistent with those obtained from commercially available instruments. We believe that this study is expected to accelerate the development of SPR technology toward broader biological applications. [ABSTRACT FROM AUTHOR]

We present a design of an ultrafast spin current emitter utilizing the Au nanoparticles/Co/Pt heterostructures, which facilitate significant enhancement in terahertz radiation. Using Au nanoparticles synthesized by thermal annealing and embedded in Co/Pt bilayers, we show that the Au nanoparticles fulfill surface plasmon resonance conditions under the illumination of femtosecond laser pulses, and enhanced terahertz spin currents are generated in the Co thin film. The terahertz signal amplitude of Au nanoparticles/Co/Pt sample exhibits an enhancement of 70% and 45% compared to that observed in Au thin film/Co/Pt and Co/Pt samples, respectively. By integrating experimental analysis and numerical calculations, we ascribe the enhancement of terahertz emission amplitude to the contribution of spin current generated by surface plasmon resonance in the Co thin film, which may result from the magnetization enhancement induced by surface plasmon-excited electromagnetic fields at the Au nanoparticles/Co interface, and the plasmon-induced spin current density is approximately 1 × 1029 electrons s−1 m−2. This plasmon-induced spin current establishes a connection between the fields of plasmonic and spintronic physics, thereby promoting the development of spintronic terahertz emitters. [ABSTRACT FROM AUTHOR]

This study establishes the accuracy and efficacy of the recently developed radiative transfer with reciprocal transactions (R2T2) method for quickly simulating radiation transfer through concentrated thick suspensions of optically hard nanoparticles featuring a large mismatch in refractive and/or absorption indices compared with their surrounding medium. Concentrated suspensions of optically hard nanoparticles exhibit strong light scattering and dependent scattering effects including both near-field interactions among particles and interferences of scattered waves in the far-field. Concentrated suspensions of metallic nanoparticles also exhibit plasmon coupling effect that leads to widening of absorption peak and red-shift in the peak surface plasmon resonance wavelength. However, predicting these complex interactions between EM waves and particles in thick and concentrated suspensions by explicitly solving Maxwell's equations is computationally intensive, if not impossible. Conventional solutions like Lorenz–Mie theory combined with independent scattering approximation do not account for dependent scattering and plasmon coupling. Furthermore, the dense medium radiative transfer theory is a far-field approximation that does not account for near-field effects, leading to significant errors in predictions, as illustrated in this study. By contrast, the R2T2 method's predictions showed excellent agreement with the solutions of Maxwell's equations obtained using the superposition T-matrix method for thin films containing optically hard particles. The method also rigorously accounted for multiple scattering as well as plasmon coupling in thick concentrated suspensions. These results could facilitate the design of plasmonic suspensions used in various energy and environmental applications. [ABSTRACT FROM AUTHOR]

The requirements of augmented signal contrast provided by nanoparticle tags in biosensor microscopy-based point-of-care technologies for cancer and infectious disease diagnostics can be addressed through metallo-dielectric nanoarchitectures that enhance optical scattering and absorption to provide digital resolution detection of single tags with simple instrumentation. Photonic Resonator Interferometric Scattering Microscopy (PRISM) enables label-free visualization of nanometer-scale analytes such as extracellular vesicles and virions, and its applicability can be extended to biomolecular analyte counting through nanoparticle tags. Here, we present template-free, linker-less cryosoret nano-assemblies fabricated via adiabatic cooling (−196 °C) as plasmonic nano-antennas that provide high scattering contrast in PRISM. Plasmonic Ag and Au nanomaterials and their cryosorets are evaluated through imaging experiments and simulations based on the finite element method to understand the photo-plasmonic coupling effect at the surface of a photonic crystal (PC) interface. The Ag and Au cryosorets provide at most 8.29-fold and 6.77-fold higher signal contrast compared to their singlet counterpart. Through the simulations, the averaged field magnitude enhancements of 2.77-fold and 3.68-fold are observed for Ag and Au cryosorets when interfacing with PCs compared to bare glass substrates. The hybrid coupling between the localized Mie and delocalized Bragg plasmons of cryosorets and the underlying PC's guided mode resonance provides insights for developing nano-assembly-based nano-tags for biosensing applications. [ABSTRACT FROM AUTHOR]

In this paper, a surface plasmon resonance assisted hybrid photodetector (PD) made of a low bandgap covalent polymeric framework material is experimentally demonstrated. The PD demonstrated a broadband photodetection capability ranging between 350 and 1550 nm with subsecond transients. The fabricated hybrid PD offered a remarkable responsivity and external quantum efficiency of 42.87 A/W and 11 873% at 410 nm, respectively. The peak detectivity is recorded to be 7.43 × 10 13 Jones at 400 nm. Up to 1550 nm, the hybrid PD offered a responsivity > 0.4 A/W, thereby showcasing its efficacy even for the near-infrared signals. The time-dependent photoresponse study estimated the rise time and fall time of the fabricated PD to be approximately 0.31 and 0.22 s, respectively. [ABSTRACT FROM AUTHOR]

Chiral edge states are a hallmark feature of photonic Chern insulators, where waves propagate in opposite directions along two parallel edges of a strip sample. Different from the chiral edge states, at recently discovered counterintuitive antichiral edge states, where waves propagate in the same direction on the two edges, the antichiral edge states are modeled by the modified Haldane model. Here, we theoretically propose, experimentally observe the antichiral edge states induced by magnetic surface plasmon resonance, and realize the antichiral edge states in a gyromagnetic photonic crystal with rectangular lattice. Through microwave experiments and photonic band calculations, the unique properties of this antichiral edge states have been confirmed, including edge dispersion without Dirac points frequencies shift, unidirectional transmission without ancillary cladding, and the operating frequency of the edge states that can be flexibly controlled by the external magnetic field. These results extend the scope of antichiral edge states and supplement the current understanding of antichiral edge states. [ABSTRACT FROM AUTHOR]

Controlled trapping of light-absorbing nanoparticles with low-power optical tweezers is crucial for remote manipulation of small objects. This study takes advantage of the synergetic effects of tightly confined local fields of plasmonic nanoaperture, self-induced back-action (SIBA) of nanoparticles, and resonant optical trapping method to demonstrate enhanced manipulation of Janus nanoparticles in metallic nanohole aperture. We theoretically demonstrate that displacement of Au-coated Janus nanoparticles toward plasmonic nanoaperture and proper orientation of the metal coating give rise to enhanced near-field intensity and pronounced optical force. We also explore the effect of resonant optical trapping by employing a dual-laser system, where an on-resonant green laser excites the metal-coated nanoparticle, whereas an off-resonant near-infrared laser plays trapping role. It is found that, at the optimum nanoparticle configuration, the resonant optical trapping technique can result in threefold enhancement of optical force, which is attributed to the excitation of surface plasmon resonance in Janus nanoparticles. The findings of this study might pave the way for low-power optical manipulation of light-absorbing nanoparticles with possible applications in nanorobotics and drug delivery. [ABSTRACT FROM AUTHOR]

Plasmons in graphene (Gr) show many fascinating characteristics, such as dynamic tunability, strong field confinement of light-matter interaction, and highly responsive, which has been widely exploited for a number of applications, including photodetectors, optical modulators, and sensors. In this paper, graphene plasmons (GPs) were motivated by implanting Au nanoparticles (Au NPs) into Ta2O5 thin layers adjacent to the Gr film, and the strong localized surface plasmon resonance (LSPR) effect has been proposed and demonstrated by placing the GPs structure on a III–V semiconductor quantum well saturable absorber (SA). It has been substantiated that the heightened interaction between light and Gr via LSPR predominantly occurs through the mechanisms of resonant energy transfer and local electromagnetic field enhancement, rather than direct electron transfer. Significant improvement on the nonlinear characteristics of the GPs modulated III–V semiconductor SA has been observed with a 17.1% large modulation depth and obviously improved working stability. A 1550 nm passive mode-locked laser has been successfully constructed with a pulse width down to 523 fs by integrating the SA into the laser cavity. This work lays the foundation for the development of high-performance mode-locked lasers and also demonstrates the substantial enhancement of nonlinear optical properties of various materials not limited to III–V semiconductors provided by this GPs' modulated structure; hence, these findings offer extensive prospects for applications in various photonics and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Due to the weak birefringence from the intracavity fiber, vector solitons are easily generated in GHz-fundamental-repetition-rate mode-locked fiber lasers, which can exhibit diverse time-varying polarization dynamics. These soliton dynamics can lead to polarization instability of the pulse train, which prevents industrial and scientific applications that require stable and uniform pulse trains. However, it is hard to suppress the polarization instability due to insufficient space for inserting traditional polarizers and difficulties in enhancing the fiber birefringence in the ultrashort fiber laser cavity. To this end, here we propose an alternative method that can effectively transform the vector solitons into scalar solitons by exploring gold nanorod (GNR) film as a polarizer in the laser cavity. First, the theoretical studies of polarization dynamics in ultrashort Fabry–Pérot (FP) fiber lasers with and without intracavity GNR film are conducted. The results indicate that the use of GNR film can significantly suppress the polarization instability and generate scalar solitons. Then, the large-scale preparation of GNRs with longitudinal surface plasmon resonance absorption peak of >1380 nm is realized by a two-step seed-mediated method, and the GNR film with an operation wavelength range covering the C + L band is fabricated by electrospinning. Finally, we apply the GNR film to a 2-cm-long FP fiber laser, and convert polarization rotation vector solitons to linearly polarized solitons (LPSs) at 1.5 μm. The polarization extinction ratio of the improved LPS pulse train is up to 33 dB. [ABSTRACT FROM AUTHOR]

Nanostructured optical field enhancements have become more attractive in recent years. In this work, we proposed a surface electric field enhancement device based on the combined effect of surface plasmons resonance and surface plasmon polariton. By optimizing the relationship between the morphology of the nanostructures and the Z-direction electric field components, the intensity of the surface polarized plasmons of the meta-atom can be further enhanced. The 633 nm left-circularly polarized light excitation for this device was examined and worked well. It was used as the operating wavelength. A comparison of the results obtained from right-circularly polarized and linearly polarized lights demonstrated only a strong optical field enhancement of the structure with left-handed polarized light. The polarization-selective parameters were also considered. Finally, by designing meta-atoms with different arrangements, we achieved electric field enhancements up to 177.5. It is worth mentioning that this method can control the degree of electric field enhancement by controlling the number of meta-atoms that excite surface plasmon polaritons, which means that obtaining the desired electric field amplitude becomes tunable in the design. With the proper format, the enhancement factor of the surface-enhanced Raman spectroscopy can be increased to approximately 109. In the research of surface-enhanced Raman spectroscopy and optical tweezers, it would be a straightforward and effective design method to create the desired optical field enhancements. [ABSTRACT FROM AUTHOR]

In this study, Au nanoparticles were introduced to functionalize hydrogen-terminated diamond (H-diamond) to optimize surface modification and improve the performance of diamond sensor for trace detection of SARS-CoV-2 N-protein. The Au nanoparticles were obtained by an electron beam evaporation system and annealing. Atom force microscope and scanning electron microscope were utilized to characterize the structure, morphology, and distribution of fabricated Au nanoparticles. The concentration of SARS-CoV-2 N-protein was determined by the investigation of transfer characteristics of a diamond solution gate field effect transistor. Sensitivity of this sensor was obtained as 27.43 mV/lg (N-protein concentration), which was higher than a regular H-diamond sensor. In addition, it had a wider linear detection range of 10−15–10−5 mg/ml and a lower limit of detection of 10−15 mg/ml. Accordingly, the detection performance of diamond sensor has been greatly improved due to the functionalization of Au nanoparticles. [ABSTRACT FROM AUTHOR]

Photocatalytic water splitting has attracted significant attention as a low-cost, clean, and green method for the conversion of solar energy into hydrogen, highlighting its potential to solve energy and environmental problems. In this work, we report the coupling of a plasmonic resonator with semiconductor quantum dots (QDs) for enhancement in photoelectrocatalytic water splitting toward hydrogen (H2) production. Specifically, cadmium selenide (CdSe) QDs were deposited on silver nano-gratings (Ag gratings). Plasmonic enhancement was observed in the absorption/emission of QDs using our angle-resolved steady-state optical spectroscopy. Furthermore, angle-resolved absorption spectra helped us to optimize the illumination conditions for resonant excitation using a setup for photoelectrochemical (PEC) experiments. Under the resonant pump, the emission of the QDs has been plasmonically enhanced with a Purcell factor ( F P ) of ∼1.5. Our numerical simulation revealed a strong near-field enhancement due to the excitation of surface plasmon resonances, contributing to F P . A similar enhancement order in the PEC experiments was also observed under resonant pump conditions, indicating the contribution of plasmon resonances to the enhanced photoelectrocatalysis. Switching the excitation's polarization further reinforces this, resulting in an enhanced photocurrent under p-polarization. These findings provide a proof of concept, thus laying the foundation for a practical device for efficient solar-to-H2 conversion. [ABSTRACT FROM AUTHOR]

The use of nanophotonics for optical manipulation has continuously attracted interest in both fundamental research and practical applications, due to its significantly enhanced capabilities at the nanoscale. In this work, we showed that plasmonic particles can be trapped at off-axis location in Gaussian beams assisted by surface plasmon resonance. The off-axis displacement can be tuned at the sub-wavelength scale by the incident light beams. Based on these, we propose that a superfast orbital rotation of particles in a continuous-wave laser beam can be realized in tightly focused circularly polarized Gaussian beams. The rotation has a tunable orbital radius at the sub-wavelength scale and a superfast rotation speed (more than 1 0 4 r/s in water under common laboratory conditions). Our work will aid in the development of optically driven nanomachines and find applications in micro-/nano-rheology, micro-fluid mechanics, and biological research at the nanoscale. [ABSTRACT FROM AUTHOR]

A higher detection performance and stability are always pursued in the development of photoelectric or photo-electrochemical devices, critical for their further commercial application. Here, we report a CsPbBr3-based photodetector engineered from a multilayer Si/Ag islands/CsPbBr3/PMMA system, showing an evidently enhanced photosensitization and breaking the absorption edge of CsPbBr3. On the one hand, the photocurrent contribution from plasmonic hot-electron injection effectively extends the detection limit of our photodetectors much below the band edge of CsPbBr3, depending only on Schottky barrier. On the other hand, the surface plasmons on nanoscale silver islands can considerably improve the light harvesting ability of the CsPbBr3 layer, ascribed to the confinement of light in the adjacency of silver islands. Numerical simulations show the localized enhancement of light near silver islands, corresponding to the excitation of localized surface plasmon resonances. It shows a higher light intensity distribution inside the CsPbBr3 layer of the photodetector consisting of Si/Ag islands/CsPbBr3/PMMA with the photodetector with only Ag islands in accordance with their current–voltage(I–V) characteristics. Ultimately, our plasmonic CsPbBr3-based photodetector presents a >10-fold increase in the photocurrent and a doubling of the operating lifetime. Our work provides important insight into the realization of the performance and stability of optoelectronic devices based on plasmonics. [ABSTRACT FROM AUTHOR]

Owing to the extraordinary physical and chemical properties, and the potential to couple with nanoplasmonic structures, two-dimensional (2D) transition metal dichalcogenides are promising materials for next-generation (opto-)electronic devices. Targeting the application stage, it is essential to understand the mechanisms of photoluminescence (PL) quenching and enhancement at the nanoscale. In this work, using monolayer MoSe2/hBN heterostructure on Au nanotriangles (NTs) as an example, we report on the local PL quenching and enhancement in the quantum tunneling regime at MoSe2/hBN/plasmonic nanostructure interfaces. By exploiting tip-enhanced photoluminescence spectroscopy, we were able to resolve and image the nanostructures locally. Moreover, by studying the different near-field emission behavior of MoSe2/SiO2, MoSe2/hBN, MoSe2/NT, and MoSe2/hBN/NT, we investigate the localized surface plasmon resonance, electron tunneling, and highly localized strain as the three competing mechanisms of local PL quenching and enhancement in the quantum tunneling regime at the nanoscale. [ABSTRACT FROM AUTHOR]

Ferrell and Berreman modes are absorption resonances in thin metal films and polar-dielectric media that arise from radiative bulk plasmon-polariton and phonon-polariton excitations. Compared to surface polaritons, Ferrell and Berreman modes occur due to volume charge oscillations across the medium and provide a unique pathway for light–matter interactions. Though the resonances are studied individually, stringent polarization and material requirements have prevented their observation in one host medium. Here, we show simultaneous excitation of Ferrell and Berreman absorption resonances in refractory epitaxial TiN/Al0.72Sc0.28N plasmonic metal/polar-dielectric hyperbolic metamaterials in the visible and far-infrared spectral ranges. The nanoscale periodicity of the superlattices enables the coupling of bulk plasmons (and longitudinal optical phonons) across different TiN (and Al0.72Sc0.28N) layers and allows polarization matching with free-space light that results in Ferrell (and Berreman) mode excitations. Ferrell and Berreman absorption resonances can be used for strong light confinement in radiative cooling, thermophotovoltaics, and other dual-band applications. [ABSTRACT FROM AUTHOR]

Surface plasmons resonance is a promising way to improve the luminescence efficiency of light-emitting materials including InGaN/GaN-based quantum wells; however, it has rarely been used for GaN epilayer with metal nanoparticles (NPs). We demonstrated in enhancing the bandgap emission from GaN epilayer by localized surface plasmon resonance (LSPR) in a quadrupole oscillation mode using Ag NPs fabricated on the GaN. The shapes of the Ag NPs fabricated on the GaN substrates gradually changed over time and were eventually destroyed completely. This should be the reason why previous studies of enhancement of GaN-based materials by using Ag NPs have not performed as good results as expected. This problem was solved by employing oxide thin films to protect the Ag NPs from destruction or aggregation and obtain enhanced photoluminescence of the GaN epilayer. The localized and enhanced electric fields have been calculated by the finite difference time domain (FDTD) method to elucidate the enhancement mechanism. However, it has been still difficult to use this method to reproduce the enhanced emissions caused by the quantum interaction between the surface plasmons and excitons. We reproduced the highly efficient emissions attributed to the Purcell effect by evaluating the nanoantenna effect using the FDTD method. This technique confirmed that an oxide thin film between the GaN substrate and Ag NPs played an effective role in the local enhancement of the electromagnetic field and light extraction from the LSPR mode when several types of oxide thin films were considered. [ABSTRACT FROM AUTHOR]

In this Letter, we present long-wavelength microdisk lasers based on five stacks of self-assembled InAs/InAlGaAs quantum dots as the active medium, which were grown on InP (001) substrate by solid-source molecular beam epitaxy. The 8.4-μm-diameter quantum dot microdisk laser is operated at room temperature under pulsed optically pumping conditions. Multi-wavelength lasing emissions at ∼1.6 μm were achieved with a low lasing threshold of 30 μW and a quality factor of ∼1336. The lasing behavior was verified by the "S" shape L–L curve, linewidth narrowing effect, and strong speckle patterns of the collected near field intensity profile. The demonstrated long-wavelength lasers with low threshold and ultracompact footprint can find potential applications in integrated gas detection and highly localized label-free biological and biochemical sensing. [ABSTRACT FROM AUTHOR]

High performance photodetectors operating in the mid-wavelength infrared spectral range are of great significance in many applications such as defense, surveillance, gas sensing, and night vision. A key parameter in the design of infrared detectors is the thickness of the absorber layer; reaching high absorption with a thin absorber layer can significantly enhance the performance of the device. In this work, we demonstrate the enhancement of InAs-base infrared detectors using surface plasmon nanostructures. Experimental results show that our device exhibits broadband enhancement compared to the reference with an increase in peak responsivity of about 50%. Further analysis shows that the enhancement of the device is attributed to the near-field localization effect of the plasma structure, which is well demonstrated by the experimental dual-peak spectrum. Such mechanisms provide valuable insight into the plasmon-enhanced infrared photodetector. [ABSTRACT FROM AUTHOR]

Niobium carbide (Nb2CTx), a type of MXene with high optical transparency, large specific surface area, and good electrical conductivity, is expected to perform as an excellent medium in the field of optical fiber biosensing. Here, we fabricated double S-tapered fiber sensors functionalized with gold nanoparticles/graphene oxide/tyrosinase (AuNPs/GO/tyrosinase) and AuNPs/Nb2CTx/tyrosinase, respectively. The double S-tapered structure can provide more evanescent wave leakage and enhance light–matter interaction. By implementing transmittance experiment, the sensitivity of the two probes were tested to be 17 and 34 pm/μM over 0–300 μM tyramine concentrations. The comparative results demonstrate that Nb2CTx-enhanced localized surface plasmon resonance (LSPR) sensor has more excellent performance due to the existence of surface functional groups and large specific surface area of Nb2CTx. Our work provides a research platform for improving the sensitivity of LSPR sensors. [ABSTRACT FROM AUTHOR]

We present ultrafast spectroscopic investigations of the coherent acoustic vibrations of Au/SiO2 and Au/TiO2 core–shell nanoparticles (NPs) upon excitation of the Au surface plasmon resonance. The oscillations are detected in the region of the interband transitions of Au in the deep-ultraviolet, where they appear in the form of intensity modulations with no changes in the spectra. For the Au/SiO2 NPs, the oscillation period (typically ∼10 ps) is similar to that of bare Au NPs having a size identical to that of the core, implying a negligible coupling of the core with the shell. For Au/TiO2 NPs, significantly slower (∼20 ps) oscillations appear, whose period is identical to that of a bare gold NP having the same total diameter, implying that the Au/TiO2 NPs can be treated as a single object. This may due to the strong chemical interaction at the gold/TiO2 interface. Finally, the amplitude modulations are a consequence of the modifications of the band structure of the Au NP, resulting from the strain due to the phonons, which may affect the joint density of states. [ABSTRACT FROM AUTHOR]

Plasmonic metal nanostructures have been widely applied in photodetectors for the enhanced light response range and sensitivity. In contrast, photodetection based on surface plasmon effect of the emerging plasmonic nonmetals has not been investigated. Here, single nonmetal plasmonic WO3−x nanosheets were used as the sensing material for UV–Vis–NIR broad spectral photodetectors. The plasmonic WO3−x nanosheets were synthesized by solvothermal and follow-up thermal treatment in a hydrogen-containing atmosphere, which exhibited a localized surface plasmon resonance (LSPR) band centered at 899 nm with broad spectral absorption spanned from UV to NIR. Then photodetectors fabricated facilely by depositing Au electrodes on a film of WO3−x nanosheets showed sensitive response for the regulation of conductance through the plasmonic hot free charge carriers. The responsivity and detectivity were 52 mA/W and 1.46 × 108 Jones under an incident light with a wavelength of 980 nm with an ultralow bias of 0.01 V, and went up to 538 mA/W and 4.75 × 108 Jones under 0.1 V. The results demonstrate the great potential of nonmetal plasmonic materials for photodetection. [ABSTRACT FROM AUTHOR]

Based on frequency-domain optical measurement using single nanoparticle plasmon sensors (NanoSPR), a versatile multiplex molecular affinity kinetics detection method is proposed. To improve the detection precision and throughput, a single-color imaging NanoSPR method (SI-NanoSPR) is used to obtain the light scattering signals of thousands of gold nanorod sensors over time under the configuration of a total internal reflection dark-field microscope. The frequency-domain power spectral density analysis of the fluctuation signal extracts the characteristic frequency fc, by which the molecular affinity kinetics manifest the identifiable measurand. By measuring the kinetics of two different aptameric affinity systems in the same microscope field of view, the obtained equilibrium dissociation constants (KD values) are demonstrated to be in agreement with previous studies, which were measured by traditional techniques. We expect that our NanoSPR method may pave the way for a deeper understanding of the physiological essence of biological affinity systems by accurately quantifying multiple affinity constants. The high-throughput biosensing potential is of great significance in further biomedical and pharmaceutical applications. [ABSTRACT FROM AUTHOR]

Incorporating metallic nanostructures into a cesium lead halide [CsPbX3 (X = Cl, Br, I)] perovskite system has attracted considerable attention for improving the performance of amplified spontaneous emission (ASE) and lasing. However, the ASE/lasing threshold is normally quite high since the photophysical properties of pristine CsPbX3 quantum dots (QDs) are limited and the traditionally utilized metal nanoparticles suffer from a weak localized surface plasmon resonance within a narrow spectral range. Herein, a configuration of a silica coated CsPbBr3 QDs (CsPbBr3@SiO2 QDs) film incorporated with the deposition of gold nanorods (AuNRs) underneath has been proposed for high-performance ASE. In this configuration, SiO2 coating not only serves as an insulation layer to avoid the large Ohmic loss between CsPbBr3 and Au but also contributes to improved photoluminescence quantum yield and stability against water, heat, and ultraviolet light compared to the counterparts of pristine CsPbBr3 QDs. As a result, the fabricated CsPbBr3@SiO2-AuNRs hybrid film yields a low-threshold ASE (23.6 μJ/cm2) with excellent photostability owing to efficient exciton–plasmon coupling effect, which is only 23% of the pristine CsPbBr3 QDs film (102 μJ/cm2). The demonstration of metallic NRs coupled perovskite QDs not only provides a strategy for realizing strong light–matter interactions but also paves the way for improving the performance of perovskite-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Plasmons associated with zero-dimensional (0D) metal nanoparticles and their synergistic interactions with excitons in two-dimensional (2D) semiconductors offer opportunities for remarkable spectral tunability not otherwise evident in the pristine parent materials. As a result, an in-depth study elucidating the nature of the plasmonic and excitonic interactions, jointly referred to as plexcitons, is critical to understanding the foundational aspects of the light–matter interactions in hybrid 0D–2D systems. In this work, our focal point is to examine the plexcitonic interactions of van der Waals (vdWs) hybrid structures composed of 2D WSe2 and 0D Au nanoparticles (Au-NPs) in their spherical (Au-Sp) and bi-pyramidical (Au-BP) architectures. The geometry-dependent surface plasmon resonance (SPR) peaks in Au-Sp and Au-BP nanoparticles were deciphered using ultraviolet-visible (UV-Vis) optical absorption spectroscopy, while photoluminescence spectroscopy revealed the excitonic behavior in the vapor synthesized monolayer (1L) WSe2 as well as the Au-Sp/WSe2 and Au-BP/WSe2 hybrids. Furthermore, our temperature-dependent and wavelength-dependent optoelectronic transport measurements showed a shift in the spectral response of 1L WSe2 toward the SPR peak locations of Au-Sp and Au-BP, mediated via the plexciton interactions. Models for the plexcitonic interactions are proposed, which provide a framework to explain the photoexcited hot charge carrier injection from AuNPs to WSe2 and their influence on carrier dynamics. Our findings demonstrate that geometry-mediated response of the AuNPs provides another degree of freedom to modulate the carrier photodynamics in WSe2, which can also be useful for tailoring the optoelectronic performance of the broader class of semiconducting 2D materials. [ABSTRACT FROM AUTHOR]

Plasmons associated with zero-dimensional (0D) metal nanoparticles and their synergistic interactions with excitons in two-dimensional (2D) semiconductors offer opportunities for remarkable spectral tunability not otherwise evident in the pristine parent materials. As a result, an in-depth study elucidating the nature of the plasmonic and excitonic interactions, jointly referred to as plexcitons, is critical to understanding the foundational aspects of the light–matter interactions in hybrid 0D–2D systems. In this work, our focal point is to examine the plexcitonic interactions of van der Waals (vdWs) hybrid structures composed of 2D WSe2 and 0D Au nanoparticles (Au-NPs) in their spherical (Au-Sp) and bi-pyramidical (Au-BP) architectures. The geometry-dependent surface plasmon resonance (SPR) peaks in Au-Sp and Au-BP nanoparticles were deciphered using ultraviolet-visible (UV-Vis) optical absorption spectroscopy, while photoluminescence spectroscopy revealed the excitonic behavior in the vapor synthesized monolayer (1L) WSe2 as well as the Au-Sp/WSe2 and Au-BP/WSe2 hybrids. Furthermore, our temperature-dependent and wavelength-dependent optoelectronic transport measurements showed a shift in the spectral response of 1L WSe2 toward the SPR peak locations of Au-Sp and Au-BP, mediated via the plexciton interactions. Models for the plexcitonic interactions are proposed, which provide a framework to explain the photoexcited hot charge carrier injection from AuNPs to WSe2 and their influence on carrier dynamics. Our findings demonstrate that geometry-mediated response of the AuNPs provides another degree of freedom to modulate the carrier photodynamics in WSe2, which can also be useful for tailoring the optoelectronic performance of the broader class of semiconducting 2D materials. [ABSTRACT FROM AUTHOR]

Polaritons can provide strong optical field enhancement allowing them to boost light–matter interaction. Here, we experimentally observe enhancement in mid-infrared second-harmonic generation (SHG) using grating-coupled surface phonon polaritons of the 6H-SiC surface. In our experiment, we measure the SHG along the polariton dispersion by changing the incidence angle of the excitation beam. We observe hybridization between the propagating surface phonon polaritons and localized plasmon resonances in the gold grating, evidenced by the modification of the polariton dispersion as we change the area ratio of grating and substrate. Design options for engineering the plasmon–phonon polariton hybridization are discussed. Overall, we find a rather low yield of polariton-enhanced SHG in this geometry compared to prism-coupling and nanostructures and discuss possible origins. [ABSTRACT FROM AUTHOR]

Polaritons in two-dimensional van der Waals (vdW) materials possess extreme light confinement, which have emerged as a potential platform for next-generation biosensing and infrared spectroscopy. Here, we propose an ultra-thin and electric tunable graphene/hexagonal boron nitride/graphene metasurface for detecting molecular fingerprints over a broad spectrum. The vdW metasurface supports hybrid plasmon–phonon polariton resonance with high-quality factor (Q > 120) and electrically controlled broadband spectra tunability from 6.5 to 7 μm. After coating a thin layer of bio-molecular (e.g., CBP) on top of the metasurface, the molecular absorption signatures can be readout at multiple spectral points and, thus, achieve broadband fingerprint retrieval of bio-molecules. Additionally, our electric tunable metasurface works as an integrated graphene-based field-effect transistor device, without the need of multiple resonance generators such as angle-resolved or pixelated dielectric metasurfaces for broadband spectra scanning, thereby paving the way for highly sensitive, miniaturized, and electrically addressed biosensing and infrared spectroscopy. [ABSTRACT FROM AUTHOR]

Realizing and manipulating strong light–matter coupling in 2D monolayer semiconductors are of the utmost importance in the development of photonic devices. Hollow nanostructures of noble metals are particularly interesting because of their stronger local electromagnetic field compared with solid nanoparticles, which facilitate the strong coupling of single metal nanostructures. Here, the tunable single nanocavity plasmon–exciton coupling was demonstrated at room temperature in hybrid systems consisting of Ag@Au hollow nanocubes (HNCs) and monolayer WS2 underneath, where a large vacuum Rabi splitting of 131.3 meV was observed. Mode splitting can be clearly observed from the dark-field scattering spectrum of the single hybrid nanocavity, which is ascribed to the strong coupling between the nanocavity mode and the excitonic mode. Then, we used the finite difference time domain method to simulate these hybrid systems. By changing the thickness of the shell of the Ag@Au HNC, we can tune the surface plasmon resonance peak position of HNCs to match the exciton energy of the monolayer WS2. The strong couplings were realized via the calculated scattering spectra. The calculated results were consistent with the experimental results. Furthermore, the mode volume of different nanostructures was discussed, and the mode volume of HNCs is smaller than other solid ones at the same plasmonic resonance wavelength, which also indicates that its ability to restrict an electromagnetic field is stronger. This study provides an ideal platform for the strong coupling of a single nanocavity at room temperature and has broad application prospects in the field of single-photon devices. [ABSTRACT FROM AUTHOR]

Photoacoustic spectroscopic analysis allows for evaluating biological microscopic features, such as morphology and viscoelasticity, which offers the opportunities of comprehensively understanding the biological specimens. However, an ongoing challenge arises from inadequate response to the photoacoustic impulses owing to limited bandwidth of the piezoelectric transducer. Here, we develop spectroscopically resolved optical-resolution photoacoustic microscopy (OR-PAM) by incorporating a broadband surface plasmon resonance sensor (∼169.5-MHz bandwidth) as the ultrasonic detector. The photoacoustic spectra from polystyrene and polymethyl methacrylate microspheres represent the close dependence upon the density and sound speed in addition to the diameter. The photoacoustic structural images of the two types of microspheres with the same morphology manifest the nearly identical appearances, while the photoacoustic spectroscopic analysis permits them to be clearly distinguished because of the different densities and sound speeds. The results suggest that, by simultaneously revealing the anatomic structures and acoustic spectra, our spectroscopically resolved OR-PAM system is potentially valuable in characterizing the microscopic features of biological samples at a cellular level. [ABSTRACT FROM AUTHOR]

The role of surface plasmon polaritons (SPPs) in nanohole array optical extinction spectra is explored using a time-resolved technique capable of isolating the air/metal interfacial SPP contribution to the typical Fano profile in optical transmission curves. A pair of interferometrically locked broad-band femtosecond pulses is used to launch SPPs from lithographically patterned plasmonic nanohole arrays. SPPs launched in the co- and counter-propagating directions are probed using a third probe pulse in a photoemission electron microscope. Using this approach, we record interferometric SPP–SPP linear autocorrelations that selectively report on the resonances of SPPs launched from arrays of varying pitches and hole diameters. Aside from advancing an approach to selective SPP spectroscopy, we illustrate that resonant coupling in the counter-propagating direction may be exploited to control the spatial, temporal, and spectral characteristics of SPPs. For the counter-propagating direction, we show that tuning the array pitch near the fundamental plasmon resonance generates color-tuned (∼770–820 nm), narrow bandwidth SPPs, and the bandwidth may be controlled by changing the ratio of pitch to hole diameter. The SPP resonances we recover through Fourier transforms of the interferometric autocorrelations shed light on the classical problem of Fano interference in nanohole array extinction spectra. [ABSTRACT FROM AUTHOR]

By placing high-index dielectric resonators on surfaces supporting surface plasmons in the near field, strong magnetic resonance can be observed in the high-index dielectric resonators with appropriate heights around the surface plasmon resonance frequencies. The strong magnetic resonance allows strong thermal photon tunneling across a 1 μm gap, which is one order longer than the previous demonstrations of near field radiation with surface plasmons. The thermal photon tunneling happens when the horizontal wavenumber is k x ∼ 4 π w with w is the width of the high-index resonators. The height of the high-index dielectric resonators should provide enough retardation of the electric field between the top and bottom of the resonator to form a displacement current loop. Therefore, similar magnetic field resonance occurs in the resonator when we triple rather than double the height of the high-index dielectric resonators. The usage of dielectric resonators to amplify the thermal electric field in the near field domain can be a potential method to increase the quasi-monochromatic radiation distance of an emission domain by one order or more at the frequencies of the surface waves. [ABSTRACT FROM AUTHOR]

Localized surface plasmon resonance (LSPR) has drawn much interest in photocatalysis due to the advantages in extending light-absorption and improving charge-separation efficiency. In this work, Au nanocubes with exposed {100} facets and Au nanotrioctahedrons with exposed {221} facets are synthesized via the seed-growth method with the aim of demonstrating the photocatalytic performance under the LSPR effect using a typical TiO2 photocatalyst. The modification of Au nanocrystals results in accelerated charge separation in the TiO2 photocatalyst, which is attributed to the synergetic effect of local electromagnetic field enhancement from the LSPR effect and the Schottky junction established in Au and TiO2. Consequently, the photocatalytic hydrogen-production from the TiO2 photocatalyst is greatly improved. Moreover, Au nanotrioctahedrons modified TiO2 exhibits superior photocatalytic performance due to the stronger local electromagnetic field of the LSPR and the more efficient electron trapping originated from the unique morphology with exposed {221} facets. [ABSTRACT FROM AUTHOR]

An optical refractive index (RI) nanosensor with a high sensitivity and figure of merit (FOM), good stability, and biocompatibility is of great significance for biological detection and sensing in narrow spaces. However, the current optical RI nanosensors are mainly fabricated using metals, semiconductors, and quartz, which are not biocompatible and are even biotoxic, and often face a trade-off between a high sensitivity and a high FOM. Moreover, the sensors are mainly based on surface plasmon resonance, photonic crystals, fiber grating, etc., and, thus, most of them usually require a laser source with a specific optical wavelength or harsh excitation conditions, which are likely to cause photodamage and are unfavorable for biological applications. Hence, polylactic acid (PLA), a flexible dielectric material with good biocompatibility, is functioned by doping high refractive index quantum dots (QDs) and fabricated as a nanowire RI sensor. Doping the QDs into a PLA nanowire can improve the light confinement ability and then enhance Mie resonant scattering of the PLA nanowire, which is very beneficial to obtain a higher quality factor and then a higher-performance nanowire sensor. Under irradiation of a white light source, a high sensitivity with 833.78 nm/RIU (per refractive index unit) and the highest FOM of 9.64 RIU−1 are obtained. The good reliability and reproducibility of the sensors are further demonstrated. By choosing a proper diameter, the scattering peak of the nanosensor can be tuned into a biofriendly spectral range (600–900 nm), which predicts that the PLA nanowire RI sensors have a great potential in biological microenvironment monitoring, biosensing, and biomedical treatment. [ABSTRACT FROM AUTHOR]

The surface plasmon resonance (SPR) effects of metal nanoparticles prove versatile in terms of equipping wideband-gap photocatalysts, such as TiO2, with visible-light responsiveness. In this regard, Au is the most frequently used material for its SPR, but alternative materials are also being actively developed to effectively utilize solar light from the visible to the near-infrared region. In this work, we found that Pt particles loaded on TiO2 were also active in effecting SPR-induced photocatalysis. Time-resolved absorption measurements confirmed that visible-light irradiation induces electron transfer from Pt to TiO2, and the efficiency of this electron injection increases as the wavelength of the incident light decreases from 660 to 450 nm. Observations of the peak shift of the vibrational frequency of adsorbed CO on Pt confirmed that the Fermi level of Pt decreases as the electron transfer from Pt to TiO2 proceeds. These results imply that Pt nanoparticles can act as sensitizers to induce electron transfer from Pt to TiO2, although Pt is a well-known cocatalyst that enhances H2 evolution by collecting electrons from TiO2. However, as the intensity of the irradiated light increased beyond 50 mW cm−2, a portion of the Pt particles started to capture the injected electrons from TiO2, suggesting that the electron transfer from one Pt particle to the other Pt particles via the conduction band of TiO2 proceeds under visible light illumination. These opposing roles may be ascribed to the variation in the size of Pt particles as well as density of electrons injected into TiO2. [ABSTRACT FROM AUTHOR]

Plasmonic nanostructures are widely applied to couple with quantum emitters (QEs), so as to improve the optical performances of QE and obtain advanced photonic devices, such as the quantum photon source, quantum circuit. However, the huge loss of plasmonic nanostructures greatly hinders the future development of plasmon–QE hybrid systems. Herein, we propose the hyperbolic nanorods (HNR) which are built by alternate Au and SiO2 thin layers. The size of HNR discussed in this paper is mainly around 40 × 50 × 60 nm3, which is a subwavelength size benefiting for device miniaturization and integration. The photonic resonant mode of HNR can be tuned by simply changing its length/width ratio. Due to the hybridization of the surface plasmon polariton resonances associated with each metal–dielectric interface, the HNR possesses the advantage of small mode volume (V) as the Au plasmonic nanorod (PNR) with similar size, and its mode quality factor (Q) can be larger due to the lower loss. Therefore, when coupled with a resonant QE, the Purcell factor in HNR/QE is ∼20 times larger than that in the PNR/QE system. Furthermore, the HNR/QE hybrid also demonstrates obvious superiority over the PNR/QE in generating strong coupling and quantum entanglement. With the features of small V and low loss, it is believed that the HNR can not only greatly improve the optical properties of QE, but also be a powerful nanostructure for studying light–matter interactions. [ABSTRACT FROM AUTHOR]

We investigate the lasing performance of different composite gain materials consisting of small organic molecules, gold nanoparticles, and a polymer matrix mixed on a nanoscale within a spin-coated thin film. We experimentally demonstrate that the localized surface plasmon resonances of randomly distributed gold nanoparticles can oscillate in phase with the standing wave of the surrounding microcavity resonator and contribute to a lower lasing threshold. [ABSTRACT FROM AUTHOR]

A linear triple quantum dot (TQD) integrated with a quantum dot (QD) charge sensor is realized. The TQD and the charge sensor are built from two adjacent InAs nanowires by the fine finger gate technique. The charge state configurations of the nanowire TQD are studied by measurements of the direct transport signals of the TQD and by detection of the charge state transitions in the TQD via the nanowire QD sensor. Excellent agreement in the charge stability diagrams of the TQD obtained by the direct transport measurements and by the charge-state transition detection measurements is achieved. It is shown that the charge stability diagrams are featured by three groups of charge state transition lines of different slopes, corresponding to the changes in the electron occupation numbers of the three individual QDs in the TQD. It is also shown that the integrated nanowire QD sensor is highly sensitive and can detect the charge state transitions in the cases where the direct transport signals of the TQD are too weak to be measurable. Tuning to a regime, where all three QDs in the TQD are close to being on resonance with the Fermi level of the source and drain reservoirs and co-existence of triple and quadruple points becomes possible, has also been demonstrated with the help of the charge sensor in the region where the direct transport signals of the TQD are hardly visible. [ABSTRACT FROM AUTHOR]

We present an experimental technique adapted to characterize individual metallic nanostructures in terms of differential reflectivity spectroscopy. We analyze gold patch nanoantennas holding different morphological properties. Our experimental methodology shows steady and reliable results consistent with classical analytical approximations and simulation methods. This technique allows us to identify absorption properties of metallic nanostructures commonly associated with surface plasmon resonances. By contrasting the light absorbed solely by the metallic antenna with respect to a surrounding reference medium, we found that some antennas show absorption of almost 50% of the incident light across the range of the visible spectrum. Plasmonic patch nanoantennas are promising systems in which the confinement of the electromagnetic field inside the dielectric gap strongly modifies the local density of states. [ABSTRACT FROM AUTHOR]

The use of metal nanoparticles (NPs) that can trigger localized surface plasmon resonance (LSPR) is an effective method for improving the performance of organic photovoltaics (OPVs). Currently, most plasmonic NPs are based on noble metals, including gold and silver; their high cost limits their commercial applications in the cost-effective OPVs. Herein, copper (Cu) NPs, which are more abundant and cheaper, are adopted to fabricate OPVs. To avoid oxidation of Cu NPs, they are positioned at the cathode interface, so that their fabrication could be implemented in an inert environment. The resulting OPVs exhibited improved power conversion efficiencies (PCEs) under illumination at 1 sun, and the device enhancement could be attributed to the LSPR effects of Cu NPs. Further, their potential to enhance the performance of OPVs under indoor lighting conditions is evaluated. The enhancement factor of PCEs was higher, while the light source had a lower color temperature. It could be due to the fact that the main plasmonic band of the Cu NPs is localized in the red spectral range. The results reveal the consideration of matching between the LSPR spectral range and the emission spectra of the artificial light sources is very critical for indoor applications. [ABSTRACT FROM AUTHOR]

Periodically patterned sculptured plasmonic thin films, consisting of forests of nanocolumns of metals like silver on a periodic grating, offer a very rich landscape for light–matter interactions. Multiple light scattering, plasmonic resonances, anisotropy, hyperbolic dispersions, and Bragg scattering: a plethora of effects come together in these systems to offer various possibilities. We realize an efficient random laser by infiltrating a laser dye into such a grating of silver nanocolumns and optically pumping the system. The densely packed plasmonic nanocolumns provide feedback through efficient scattering, while the optically pumped dye solution in the voids provides for amplification. The periodicity and anisotropy provide for an angle and polarization selective enhanced coupling of the pump laser via the propagating surface plasmon resonances in the system. [ABSTRACT FROM AUTHOR]

A photodetector with a controllable response spectrum and high responsivity shows great potential in practical photoelectric applications. Here, we design and experimentally demonstrate a visible and near-infrared (NIR) dual-band photodetector by integrating the out-of-plane Au gratings and n+-Si groove substrate metamaterial (ASGM). Simulation, experimental, and calculation results indicate that the absorption spectrum can be tailored by surface plasmon resonances (SPRs) of different interfaces and Si-groove resonance. Visible-light absorption is caused by Si-groove resonance, SPRs of the Au–air interface, and high-frequency mode SPRs of the Au–Si interface. NIR absorption is induced by the SPRs of the Au–Si interface. Moreover, out-of-plane coupling between upper and lower Au gratings gives rise to an enhanced electric field and broadened SPR absorption. The respective photoresponsivity in the visible and NIR band is more than 7 and 3 mA/W without an external bias, with a maximum responsivity of 13 mA/W at 535 nm. The photoresponse of such ASGM-based dual-band photodetectors can be modulated so that they may be used in various fields like medical imaging, optical communication, and aerography. [ABSTRACT FROM AUTHOR]

The longitudinal surface plasmon resonance of light-irradiated gold nanorods (Au NRs) is generated to enhance the local electric fields of Au NR-based nano-dumbbells (NDs), tailored specifically by coating mesoporous silica at two poles of Au NRs and embedding photosensitizer indocyanine green (ICG) into the mesopores. The assembled NDs possess a superior uniformity and water dispersity with a strong plasmonic absorption around 800 nm. Time-domain finite-difference calculations indicate that the enhanced local electric field of NDs is predominantly distributed in the dumbbells at two poles of Au NRs, which improves the photonic performance of ICG significantly. Illuminated by an 800 nm laser, the fabricated NDs demonstrate an enhanced combination of photothermal and photodynamic effects in comparison to either Au NRs or ICG alone. Synergistic damaging of photothermal and photodynamic combination to nasopharyngeal carcinoma cells has been corroborated experimentally, thus causing substantial cell death under a lower incident near-infrared laser power. This study concludes that the plasmonic NDs combined synergistically with efficient photothermal and photodynamic effects are highly promising in cancer therapy. [ABSTRACT FROM AUTHOR]

The ability to disperse metallic nano-objects in a given matrix material is an important issue for the design and fabrication of functional materials. A means to monitor the spatial distribution of the nano-dopants is highly desirable but often possible only a posteriori and with destructive techniques. Here we present a spectroscopic characterization based on different plasmonic responses of silver nanoparticles, their agglomerates, and finally the percolated silver film. We demonstrate its usefulness for the specific case of their dispersion in layer-by-layer polymeric films but the method is extendable to any other host material transparent in the visible/near UV range. Individual silver nanoparticles display the well-known localized surface plasmon resonance around 400 nm, which is red-shifted upon inter-particle coupling. The transition regime between weakly coupled particles and fully percolated metal films is, however, much harder to evidence unambiguously. We show here how to monitor this transition using the so-called Ferrell plasmon, a plasmonic mode of the thin film in the mid-UV, and excitable only under oblique irradiation but without specific coupling precautions. We can thus follow the entire transition from isolated to coupled and finally to fully agglomerated nanoparticles by optical spectroscopy. [ABSTRACT FROM AUTHOR]

We demonstrate high-frequency (>3 GHz), high quality factor radio frequency (RF) resonators in unreleased thin film gallium nitride (GaN) on sapphire and silicon carbide substrates by exploiting acoustic guided mode (Lamb wave) resonances. The associated energy trapping, due to mass loading from gold electrodes, allows us to efficiently excite these resonances from a 50 Ω input. The higher phase velocity, combined with lower electrode damping, enables high quality factors with moderate electrode pitch and provides a viable route towards high-frequency piezoelectric devices. The GaN platform, with its ability to guide and localize high-frequency sound on the surface of a chip with access to high-performance active devices, will serve as a key building block for monolithically integrated RF front-ends. [ABSTRACT FROM AUTHOR]

In this study, we propose a hybrid black phosphorus (BP)/Au nanoparticle (NP)-based photodetector, which greatly enhances the performance of photodetectors compared to BP-only photodetectors. By integrating Au NPs onto the BP surface, the light absorption was greatly enhanced owing to the localized surface plasmon resonance induced by the Au NPs, and the dark current of the photodetector was suppressed because the holes were withdrawn from the BP to the Au NPs due to the difference in the work function. After optimizing the density of the Au NPs, the responsivity of the BP/Au-NP photodetector reached 6000 and 500 A/W for 655 and 980 nm wavelengths, respectively, which are 60 and 500 times higher than those of BP photodetectors, respectively. The proposed hybrid photodetector, a two-dimensional (2D) semiconductor with noble metal NPs, opens up the possibility of realizing highly sensitive optoelectronic devices in the future. [ABSTRACT FROM AUTHOR]

An effective method to improve the photoresponse of MoTe2 phototransistors by decorating with Au nanoparticles (Au NPs) is demonstrated. The Au NPs can concentrate a strong electromagnetic field around them by localized surface plasmon resonances. As a result, the light absorption of MoTe2 films could be enhanced significantly. After optimized design with Au NPs, a more than 200 times increase in the photocurrent is observed under illumination of both 365 and 405 nm light. Furthermore, the responsivities are changed from 0.61 to 398 A/W under 365 nm light illumination and from 0.43 to 220 A/W under 405 nm light illumination after decorating Au NPs onto the MoTe2 phototransistors. These findings offer an avenue for practical applications of high performance MoTe2 optoelectronic devices in the future. [ABSTRACT FROM AUTHOR]

Recognizing special molecules is crucial in many biochemical processes, and thus, highly enhanced sensing methods are in high demand. In this work, we designed a microrod array metasurface with a SiO2-loaded subwavelength lithium niobate waveguide as a unique platform for enhanced experimental fingerprint detection of lactose. The metasurface could lead to strong surface wave modes due to the near-field coupling of the spoof localized surface plasmon, which also could provide a stronger interaction length between light and matter. The selectivity was remarkable in the transmission spectrum at an intrinsic characteristic frequency of 0.529 THz with a thin layer of lactose, while it was faint while transmitting terahertz (THz) waves normally through a lactose layer of the same thickness. Together with the ability to freely design the shape of the metasurface and the electromagnetic properties, we believe that this platform can function as an elegant on-chip-scale enhanced THz sensing platform. [ABSTRACT FROM AUTHOR]

In this paper, a high-responsivity terahertz quantum well photodetector based on plasmonic resonance is proposed and investigated theoretically and experimentally, and the polarization-discriminating detection of the device is demonstrated. With a one-dimensional metallic grating structure integrated on the top of the detector, a 6-fold enhancement of the peak responsivity about 0.82 A/W at 46 μm compared to that of the standard device has been achieved. The physical mechanism behind the enhanced responsivity can be attributed to the enhancement of the intersubband absorption resulting from the surface Plasmon polariton mode, which can be explored from the theoretical simulation results. The polarization extinction ratio of the plasmonic-enhanced device reaches 56, and the measured signal intensity at each polarization angle satisfies Malus' law. In addition to the above advantages, the structure is simple in fabrication and compatible with the preparation process of the focal plane array. The results open up an effective method for the application of surface plasmon in terahertz detection. [ABSTRACT FROM AUTHOR]

Nanoscale inhomogeneities, such as defects and wrinkles, in atomic layers of transition-metal dichalcogenide (TMDC) semiconductor materials deteriorate the remarkable physical and optoelectronic properties of these materials, precluding their use in optoelectronic devices. Such inhomogeneities can be investigated using vibrational spectroscopic analysis methods, such as Raman spectroscopy, because the deformations in a sample could be identified by the changes in the Raman vibrational energies of the sample. However, it has been challenging to characterize structures localized on the nanoscale in TMDC layers, because such characterization requires a nanoscale high spatial resolution. Here, we present tip-enhanced Raman spectroscopy (TERS) of molybdenum disulfide (MoS2) in the form of monolayers and a few layers to investigate nanoscale inhomogeneities. TERS enables Raman analysis with the nanoscale spatial resolution, using the near-field light generated at a metallic nano-tip through plasmon resonance. TERS imaging, which demonstrates spatially varying Raman spectral features on the nanoscale, allows one to elucidate the existence of nanoscale inhomogeneities. Using this method, defects and wrinkles within MoS2 layers were characterized with a spatial resolution better than 20 nm. This study provides important insights into unique optical and electronic properties of TMDCs for the development of future optoelectronic devices. [ABSTRACT FROM AUTHOR]