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Recent demonstrations of deep- and vacuum-ultraviolet (DUV and VUV) light emission from artificially engineered meta-atoms through nonlinear harmonic signal generation processes have opened up new avenues for fundamental engineering approaches and modern applications. While many different phenomena based on optical metasurfaces have been revealed in linear optics, several studies have reported the observation of various nonlinear optical phenomena in such nanosystems, like, for example, second and third harmonic generation (SHG and THG), multiphoton luminescence, higher harmonic generation, and four-wave mixing. Plasmonic and all-dielectric flatland metasurfaces enable successful manipulation of light–matter interactions on ultradense platforms and provide substantial enhancement of driving fields, which make these architectures promising and attractive to efficiently radiate intense and coherent second and third harmonic radiations. In this focused Review, we highlight and discuss the recent state-of-the-art methods that have been developed and proposed for the generation of nonlinear harmonic signal and high-energy DUV and VUV lights. This contribution not only summarizes the strategies that have been exploited for augmenting the intensity of nonlinear UV signal, but also introduces the novel mechanisms to strongly optimize the conversion efficiency of this principle. We envisage that this understanding allows to compare the performance of versatile nonlinear DUV and VUV metasources and paves the way of designing much more efficient light emitting tools such as lasers, super-resolution imaging nanosystems, and nanolithography apertures.

The context of strong coupling has sparked extensive interest in both the photonics and solid-state physics communities, owing to its exquisite advantages in understanding intriguing phenomena, inc...

We fabricated a full-dielectric three-dimensional photonic-crystal cavity containing an ultrahigh-mobility two-dimensional electron gas. By applying a strong perpendicular magnetic field, we created Landau polaritons originating from the ultrastrong coupling of electrons with cavity modes.

Recent developments in subwavelength localization of light have paved the way of novel research directions in the field of optics, plasmonics, and nanophotonics [...]

This work reviews fundamentals and the recent state-of-art achievements in the field of plasmonic biosensing based terahertz (THz) spectroscopy. Being nonpoisonous and nondestructive to the human tissues, THz signals offer promising, cost-effective, and real-time biodevices for practical pharmacological applications such as enzyme reaction analysis. Rapid developments in the field of THz plasmonics biosensors and immunosensors have brought many methodologies to employ the resonant subwavelength structures operating based on the fundamental physics of multipoles and asymmetric lineshape resonances. In the ongoing hunt for new and advanced THz plasmonic biosensors, the toroidal metasensors have emerged as excellent alternates and are introduced to be a very promising technology for THz immunosensing applications. Here, we provide examples of recently proposed THz plasmonic metasensors for the detection of thin films, chemical and biological substances. This review allows to compare the performance of various biosensing tools based on THz plasmonic approach and to understand the strategic role of toroidal metasensors in highly accurate and sensitive biosensors instrumentation. The possibility of using THz plasmonic biosensors based on toroidal technology in modern medical and clinical practices has been briefly discussed.

Resolving the dynamics of photoexcited d-holes in metallic nanostructures is one step in the rational design of plasmonic photocatalysis. Here, we track the creation and relaxation of charge carrie...

An active hybrid toroidal metasurface is demonstrated based on artificially engineered plasmonic metamolecules deposited on a gate-controlled graphene layer. Our numerical predictions are confirmed by room-temperature time-domain spectroscopy characterizations in the terahertz frequency range. We quantitatively and qualitatively show that the gate-controlled active graphene metamaterial allows for an active tuning of the dynamic nonradiating toroidal dipole by tuning the essential mismatch in the spinning magnetic fields in the strongly coupled resonators. It is demonstrated that this feature can be obtained by varying the resistivity of gate-controlled graphene and tuning the capacitive coupling at the critical openings of the system.

Dielectric metamaterials rationally engineered in both bulk and quasi-infinite planar fashions with optical properties beyond natural materials have emerged as promising platforms for the development of resonant architectures with sub-wavelength dimensions. The main criterion that distinguishes all-dielectric metamaterials from their plasmonic counterparts is that they exhibit negligible losses in the infrared and visible spectral regions, possessing an immense potential to be employed in the development of ultradense and efficient devices [1] , [2] . Advances in the nanofabrication and design of dielectric metamaterials enabled the miniaturization of photonic metadevices for coming generation technologies. In particular, dielectric-metamaterial coatings possess strategic applications in diverse technologies through controlling the characteristic reflection/transmission responses. In this study, multi-layer metamaterials were produced by coating with e-beam thermal evaporation system, which is one of the highly developed micro fabrication techniques, sequentially without vacuum breaking. Beyond that, the design, fabrication and characterization of Al 2 O 3 /Ge/ITO on Soda Lime Glass planar dielectric metamaterial and absorber platform as a novel and exquisite composite for multi-spectral absorption at infrared frequencies are presented. This includes the semi-infinite media, finite thickness dielectric layers and lossy dielectric layers. In the nanocavity architecture with three planar layers, the ITO layer acts as a reflective metal by providing a high absorption in the MWIR band. Moreover, in this configuration, the Al 2 O 3 layer performs as an antireflective coating (ARC) that matches air impedance with the impedance of Ge layer to reduce the reflection losses from the top surface, thus further enhancing the absorption [3] . To that end, extensive numerical and experimental assessments were conducted to illustrate multiple spectral absorption across the infrared spectrum across the mid-wave infrared (MWIR) to long-wave infrared (LWIR). Besides, the mechanism behind the absorption properties is demonstrated and argued. To further investigate the spectral behavior of the proposed structure, we performed numerical studies using finite-difference time-domain (FDTD) modelling. The influence of the thickness of the Al 2 O 3 layer on the spectral properties of the entire structure was analyzed and evaluated. Ultimately, the experimentally achieved electromagnetic wave propagation results using Fourier Transform Infrared System (FTIR) is verified by numerical calculations.

The self-assembled plasmonic nano-enabled photonic crystals (PCs)have been studied as promising platforms to develop next-generation photonic and opto-electronic devices. In this review, we attempt to describe the fundamentals of self-assembled colloidal plasmonic nanostructures and various applications of such devices. Different important aspects, such as interaction between metal NPs (MNPs) and non-metal 3-D crystals, effect of NPs on the spectral properties of materials, the mechanism of plasmonic based PCs, and related challenges and their possible solutions have been demonstrated crucially. The advancements in the self-assembly based plasmonic PCs and their applications are discussed carefully. We believe that nano-enabled self-assembled plasmonic crystals are better candidates of nanostructures to advance photonic technologies with reduced form factor and high performance.

The emission of photons from metal-insulator-metal (MIM) nanojunctions through inelastic tunneling of electrically driven electrons is a well-acknowledged approach to develop miniaturized light sources and ultradense photonic instruments. Generally, the existing research in the optimization of electromigrated tunneling junctions is principally centered on the generation of visible and near-infrared lights. This study reports on the near-ultraviolet (NUV, λ ≈ 355 nm) light emission from enhanced tunneling of electrons using aluminum nanoelectrodes. Compared to conventional noble metals, the high electron density and low screening of aluminum enable supporting of pronounced local fields at high energies (i.e, ultraviolet (UV)). As the color of light can be straightforwardly determined by the properties of tunneling structures, the exquisite features of aluminum have empowered the fashioning of tunneling devices that are able to effectively sustain plasmons at short wavelengths and emit UV light with high photon yield. This demonstration is a breakthrough in the generation of high-energy beams using electrically excited aluminum tunneling platforms, which promisingly accelerates the implementation of electrically tunable and ultradense UV light sources.

Toroidal moments in artificial media have received growing attention and considered as a promising framework for initiating novel approaches to manage intrinsic radiative losses in nanophotonic and plasmonic systems. In the past decade, there has been substantial attention on the characteristics and excitation methods of toroidal multipoles—in particular, toroidal dipole—in 3D bulk and planar metaplatforms. The remarkable advantages of toroidal resonances have thrust the toroidal metasurface technology from relative anonymity into the limelight, in which researchers have recently centered on developing applied optical and optoelectronic subwavelength devices based on toroidal metaphotonics and metaplasmonics. In this focused contribution, the key principles of 3D and flatland toroidal metastructures are described, and the revolutionary tools that have been implemented based on this topology are briefly highlighted. Infrared photodetectors, immunobiosensors, ultraviolet beam sources, waveguides, and functional modulators are some of the fundamental and latest examples of toroidal metadevices that have been introduced and studied experimentally so far. The possibility of the realization of strong plexciton dynamics and pronounced vacuum Rabi oscillations in toroidal plasmonic metasurfaces are also presented in this review. Ultimate efficient extreme‐subwavelength scale devices, such as low‐threshold lasers and ultrafast switches, are thus in prospect.

Thus far, we showed that toroidal excitations exist in free space as spatially and temporally confined electromagnetic pulses propagating at the velocity of light and interacting with matter. In this Chapter, we presented an exhaustive study on the theoretical and experimental observation of toroidal excitations in both bulk and quasi-infinite artificially structured media, also known as metamaterials. Using the established framework to analyze the toroidal electrodynamics, we discussed the strategies that have been utilized to efficiently excite toroidal modes in well-engineered subwavelength architectures. We initially argued the formation of the toroidal resonances in 3D metamaterials, and later, we revealed that how the flatland metaphotonics successfully addressed the fabrication, simulation, and inherent losses in bulk metastructures.

This Chapter presents a complete electromagnetic multipole expansion, effective for all point sources in space, including the presence of toroidal moments. To that end, in light of the provided information in Chap. 2, we utilized the solution of inhomogeneous Helmholtz equations to evaluate the electromagnetic field due to alternating poloidal currents in a toroidal solenoid. This solution was obtained through the use of Green’s functions and Debye potentials for point sources and fields. The achieved results enabled us to show the physical meaning of unconventional toroidal moments, in comparison to the classical electric and magnetic moments. Besides, the analysis in the long wavelength limit clearly demonstrates that the toroidal moments were neglected previously in the multipole expansion.

In this chapter, we presented a set of calculations for the radiation intensity, angular momentum loss, and recoil force of the most general type of source, in terms of electric, magnetic, and toroidal multipole moments. In these calculations, we considered a set of studies based on radii of any multipolarity and an arbitrary time dependence. The results are articulated in terms of time derivatives of the multipole moments and mean radii of the associated distributions. To that end, we recalled the equations for the description of electromagnetic multipoles as well as dynamic toroidal moments from Chap. 2. Besides, we employed the classical electrodynamics framework to obtain the rate of angular momentum loss of a time-dependent toroidal dipole, which was derived by Radescu and Vlad (Phys Rev E 57(5):6030, 1998); Radescu and Vaman (Phys Rev E 65:046609, 2002), in connection with a forced precession of the toroidal dipole around a particular axis.

Photoinduced light emission from plasmonic nanoparticles has attracted considerable interest within the scientific community because of its potential applications in sensing, imaging, and nanothermometry. One of the suggested mechanisms for the light emission from plasmonic nanoparticles is the plasmon-enhanced radiative recombination of hot carriers through inter- and intraband transitions. Here, we investigate the nanoparticle size dependence on the photoluminescence through a systematic analysis of gold nanorods with similar aspect ratios. Using single-particle emission and scattering spectroscopy along with correlated scanning electron microscopy and electromagnetic simulations, we calculate the emission quantum yields and Purcell enhancement factors for individual gold nanorods. Our results show strong size-dependent quantum yields in gold nanorods, with higher quantum yields for smaller gold nanorods. Furthermore, by determining the relative contributions to the photoluminescence from inter- and intraband transitions, we deduce that the observed size dependence predominantly originates from the size dependence of intraband transitions. Specifically, within the framework of Fermi's golden rule for radiative recombination of excited charge carriers, we demonstrate that the Purcell factor enhancement alone cannot explain the emission size dependence and that changes in the transition matrix elements must also occur. Those changes are due to electric field confinement enhancing intraband transitions. These results provide vital insight into the intraband relaxation in metallic nanoconfined systems and therefore are of direct importance to the rapidly developing field of plasmonic photocatalysis.

The detection of photons by plasmonic subwavelength devices underpins spectroscopy, low-power wavelength division multiplexing for short-distance optical communication, imaging, and time-gated distance measurements. In this work, we demonstrate infrared light-sensing using toroidal dipole-resonant plasmonic multipixel meta-atoms. As a key factor, the toroidal dipolar mode is an extremely localized electromagnetic excitation independent of the conventional multipoles. The exquisite behavior of this mode enables significant enhancements in the localized electromagnetic field and absorption cross-section, which boost the field confinement at the metal-dielectric interfaces. The proposed novel approach offers an advanced photodetection of the incident light based on substantial confinement of electromagnetic fields in a tiny spot, giving rise to the generation of hot carriers and a large photocurrent. Using both n- and p-type silicon (Si) substrates, we exploited the free-carrier absorption advantage of p-type Si to devise a high-responsivity device. Our findings show an unprecedented performance for infrared plasmonic photodetectors with low noises, high detectivity and remarkable internal quantum efficiency (IQE). Moreover, the tailored photodetection device provides a significant linear dynamic range of 46 dB and a fast operation speed. Our narrowband infrared light sensing photodevice offers a promising approach for further research studies over the optoelectronic and plasmonic tools and paves a viable route for low-dimensional photonic systems.

Smart multifunctional nanoparticles with magnetic and plasmonic properties assembled on a single nanoplatform are promising for various biomedical applications. Owing to their expanding imaging and therapeutic capabilities in response to external stimuli, they have been explored for on-demand drug delivery, image-guided drug delivery, and simultaneous diagnostic and therapeutic (i.e. theranostic) applications. In this study, we engineered nanoparticles with unique morphology consisting of a superparamagnetic iron oxide core and star-shaped plasmonic shell with high-aspect-ratio gold branches. Strong magnetic and near-infrared (NIR)-responsive plasmonic properties of the engineered nanostars enabled multimodal quantitative imaging combining advantageous functions of magnetic resonance imaging (MRI), magnetic particle imaging (MPI), photoacoustic imaging (PAI), and image-guided drug delivery with a tunable drug release capacity. The model drug molecules bound to the core-shell nanostars were released upon NIR illumination due to the heat generation from the core-shell nanostars. Moreover, our simulation analysis showed that the specific design of the core-shell nanostars demonstrated a pronounced multipolar plasmon resonance, which has not been observed in previous reports. The multimodal imaging and NIR-triggered drug release capabilities of the proposed nanoplatform verify their potential for precise and controllable drug release with different applications in personalized medicine.

This review article describes the state-of-art methodologies, mainly self-assembly routes, which are in practice to fabricate photonic crystals (PCs) for advanced applications. The self-assembly of colloidal building blocks is an effective, affordable, and tunable approach to fabricate varieties of photonic materials of desired shapes and surface areas. Because of easy fabrication and controlled performance factors, PCs emerged as a potential platform for designing and developing optical devices with desired features such as photonic bandgap, high reflectance/transmittance, low loss, and lasing in the visible range of wavelengths. To develop next-generation optoelectronics and optical system, significant efforts are being made to explore novel and cost-effective fabrication methods to design and develop 3D-PCs platform, which is covered in this mini-review. The challenges, potential alternatives, and prospects of self-assembled 3D PCs are also discussed in this review.

Substantial enhancement of nonlinear high-order harmonics generation based on Fano-resonant nanostructures has received growing interest due to their promising potential for developing integrated and advanced next-generation nanophotonic devices. In this study, going beyond conventional subwavelength structures, we propose an optothermally functional hetero-metallodielectric asymmetric eight-member octamer cluster composed of a central silicon nanodisk and peripheral disks with a phase-change material (Ge2Sb2Te5). Using full electromagnetic calculations, we show that in the amorphous phase of the surrounding nanoparticles, the oligomer acts as an all-dielectric cluster, while in the crystalline regime, the octamer turns into a hybrid metallodielectric assembly. Exploiting the exquisite ability of supporting distinct Fano lineshapes at different wavelengths depending on the phase of Ge2Sb2Te5, we showed the generation of both second and third harmonics at amorphous and crystalline phases of GST nanodisks, respectively with the produced harmonic wavelengths of 425 nm and 317 nm, respectively. Our calculations for the corresponding conversion efficiencies revealed significant enhancements as ηSHG = 0.0081% and ηTHG = 0.012% for SHG and THG, respectively. Such an exquisite feature of multiresonant optothermally tunable cluster allows generation of several harmonics with substantial intensities using a single system for future photonics applications.

The toroidal dipole is an exquisite and untraditional electromagnetic mode, categorizing separately from the well-known conventional multipole group which can be robustly localized and squeezed in an extremely tiny spot. In optical subwavelength systems, such a dynamic mode, which can be particularly distinguished as a nonradiating charge-current configuration, manifests in a head-to-tail fashion. Here, going beyond conventional toroidal dipoles, we explained the possibility of the excitation of directional toroidal dipoles in plasmonic meta-atoms driven by controlling the oblique magnetic field and poloidal fluxes. This was done by utilizing an antisymmetric multipixel unit cell with strong toroidal response across the near-infrared band. We showed that the unique structural properties of the proposed asymmetric nanostructure lead to the formation of multiple directional toroidal modes with opposite oblique magnetic fields and reverse poloidal current flows. We envision that this understanding paves nove...

Plasmonic hot-carrier-based photodetectors detect light at frequencies below the semiconductor bandgap with room temperature operation and can exhibit spectrally narrowband behavior, potentially el...

Tunable plasmonic resonances across the visible and near infrared spectra have provided novel ways to develop next-generation nanophotonic devices. Here, by utilizing optothermally controllable phase-changing material (PCM), we studied highly tunable charge transfer plasmon (CTP) resonance modes. To this end, we have designed a two-member dimer assembly including gold cores and Ge2Sb2Te5 (GST) shells in distant, touching, and overlapping conditions. We successfully demonstrated that toggling between amorphous (dielectric) and crystalline (conductive) phases of GST allows for achieving tunable dipolar and CTP resonances along the near-infrared spectrum. The proposed dimer structures can help forming optothermally controlled devices without further morphological variations in the geometry of the design, and having strong potential for advanced plasmon modulation and fast data routing.

Functional and reversible plasmonic resonances across the visible and near-infrared spectrum have opened new avenues for developing advanced next-generation nanophotonic devices. In this study, by using optothermally controlled phase-change material (PCM) for plasmonic nanostructures, we successfully induced highly tunable charge transfer plasmon (CTP) resonance modes. To this end, we have chosen a two-member dimer assembly consisting of gold cores and Ge2Sb2Te5 (GST) shells in distant, touching, and overlapping regimes. We show that switching between amorphous (dielectric) and crystalline (conductive) phases of GST allows for achieving tunable dipolar and CTP resonances and enables an effective interplay between these modes along the near-infrared spectrum. By analyzing electromagnetically calculated spectral responses for the dimer antenna in tunneling and direct charge transfer regimes, we confirmed that the induced CTPs in touching and overlapping regimes are highly controllable and pronounced in comparison to the quantum tunneling regime. We also use the precise, fast, and controllable switching between dipolar and CTP resonant modes to develop a telecommunication switch based on a simple metallodielectric dimer. The proposed structures can help designing optothermally controlled devices without morphological variations in the geometry of the design, and having strong potential for advanced plasmon modulation and fast data routing.

The study of the highly tunable plasmonic spectral features has received growing interest in recent years because of broad range of potential applications in the next generation photonics technologies. Here, we developed a four-member nanoparticle cluster composed of gold nanodisks, where two of the nanodisks are connected by a metallodielectric bridge composed of Ge2Sb2Te5 and gold sections. We showed that the optothermal functionality of the Ge2Sb2Te5 allows for excitation of Fano resonances and charge transfer plasmons in a single system. This feature opens new paths for developing highly tunable nanophotonic devices.

Plasmonic waveguides are strategic compact structures consisting of nanoscale components and/or particles to carry the light. Here, by proposing a systematic and artificial configuration of fused nanoparticle assemblies, we develop an optothermally controllable plasmonic waveguide with high and tunable decay length for propagation of both single- and multimode waves. Using symmetric nanoplasmonic clusters based on phase-change material, here Ge2Sb 2Te5, allowed us to efficiently control the beam propagation length and quality at the global telecommunication bands (λ $\approx$ 850 nm and λ $\approx$ 1550 nm). Employing both finite-difference time-domain and finite element method as numerical tools, we accurately computed the critical components of the proposed multifunctional plasmonic light carrier. We believe that the tailored subwavelength optical waveguide paves new approaches to develop practical advanced next-generation nanophotonic technologies.

The exotic plasmonic properties of highly doped graphene monolayer have opened new doors to develop advanced nanophotonic devices. It has been successfully experienced that the incident field can become substantially intense enough to convert the fundamental laser frequency into both even and odd high-order harmonics via a nonlinear phenomenon. In this work, using highly doped graphene nanorings with semimetallic behaviour, we analyzed the formation of high-harmonic generation using both finite-element method (FEM) and finite-difference time-domain (FDTD) calculations. Employing the inherent anharmonic charge-carrier dispersion of graphene and choosing accurate geometrical sizes for the atomic scale nanorings allow for the generation of third-harmonic (∼730 nm) with high intensity, substantial quality factor ( Q -factor), and significant conversion efficiency up to η THG ∼0.0014%. By realizing the hybridization of excited plasmons, we showed that the unique spectral response of graphene allows for the generation of gate-tunable and efficient higher order harmonic formation along the visible spectrum. We believe that the proposed atomic-scale platform has a strong potential to be used for advanced and integrated photonic devices.

In this letter, we propose a terahertz (THz) plasmonic metamaterial based on planar metamolecule arrays with strong polarization sensitivity and large-modulation-depth for potential switching applications. Using both numerical and experimental studies, we analyzed the spectral features of the plasmonic unit cells. Employing bimetallic resonators, we showed that the proposed metamolecules can be efficiently tailored to support strong toroidal dipole resonant mode across the THz spectrum with high quality factor. The photo-induced toroidal moment with ultrasharp linewidth is used to design a polarization sensitive structure. This approach is the first utilization of toroidal metamaterials for switching applications, possessing strong potential to be used for advanced integrated photonic devices.

We present a systematic study for a metallodielectric nanoplasmonic unit cell to support both Fano and toroidal resonances in the near-infrared region. Using full electromagnetic computations, we show that a combination of phase-changing and metallic materials allows for designing a unit cell with different spectral responses at different phases of the phase-changing material (here Ge2Sb2Te5 or simply GST). This phenomenon of switching between toroidal response and Fano resonant mode is confirmed using both finite-element and finite-difference time-domain methods. Having active control over the interplay between narrow and tunable Fano and toroidal modes at different wavelengths with fast transition would allow for developing efficient and practical photonic devices for communication and imaging applications.

Unconventional characteristics of magnetic toroidal multipoles have triggered researchers to study these unique resonant phenomena by using both 3D and planar resonators under intense radiation. Here, going beyond conventional planar unit cells, we report on the observation of magnetic toroidal modes using artificially engineered multimetallic planar plasmonic resonators. The proposed microstructures consist of iron (Fe) and titanium (Ti) components acting as magnetic resonators and torus, respectively. Our numerical studies and following experimental verifications show that the proposed structures allow for excitation of toroidal dipoles in the terahertz (THz) domain with the experimental Q-factor of ∼18. Taking the advantage of high-Q toroidal line shape and its dependence on the environmental perturbations, we demonstrate that room-temperature toroidal metasurface is a reliable platform for immunosensing applications. As a proof of concept, we utilized our plasmonic metasurface to detect Zika-virus (ZIKV) envelope protein (with diameter of 40 nm) using a specific ZIKV antibody. The sharp toroidal resonant modes of the surface functionalized structures shift as a function of the ZIKV envelope protein for small concentrations (∼pM). The results of sensing experiments reveal rapid, accurate, and quantitative detection of envelope proteins with the limit of detection of ∼24.2 pg/mL and sensitivity of 6.47 GHz/log(pg/mL). We envision that the proposed toroidal metasurface opens new avenues for developing low-cost, and efficient THz plasmonic sensors for infection and targeted bioagent detection.

There have been extensive researches on terahertz (THz) plasmonic structures supporting resonant modes to demonstrate nano and microscale devices with high efficiency and responsivity as well as frequency selectivity. Here, using antisymmetric plasmonic fractal Y-shaped (FYS) structures as building blocks, we introduce a highly tunable four-member fractal assembly to support charge transfer plasmons (CTPs) and classical dipolar resonant modes with significant absorption cross section in the THz domain. We first present that the unique geometrical nature of the FYS system and corresponding spectral response allow for supporting intensified dipolar plasmonic modes under polarised light exposure in a standalone structure. In addition to classical dipolar mode, for the very first time, we demonstrated CTPs in the THz domain due to the direct shuttling of the charges across the metallic fractal microantenna which led to sharp resonant absorption peaks. Using both numerical and experimental studies, we have investigated and confirmed the excitation of the CTP modes and highly tunable spectral response of the proposed plasmonic fractal structure. This understanding opens new and promising horizons for tightly integrated THz devices with high efficiency and functionality.

We report for the first time on the growth of a homogeneous radial p–n junction in the ZnO core–shell configuration with a p-doped ZnO nanoshell structure grown around a high-quality unintentionally n-doped ZnO nanorod using sonochemistry. The simultaneous decomposition of phosphorous (P), zinc (Zn), and oxygen (O) from their respective precursors during sonication allows for the successful incorporation of P atoms into the ZnO lattice. The as-formed p–n junction shows a rectifying current–voltage characteristic that is consistent with a p–n junction with a threshold voltage of 1.3 V and an ideality factor of 33. The concentration of doping was estimated to be NA = 6.7 × 1017 cm–3 on the p side from the capacitance–voltage measurements. The fabricated radial p–n junction demonstrated a record optical responsivity of 9.64 A/W and a noise equivalent power of 0.573 pW/√Hz under ultraviolet illumination, which is the highest for ZnO p–n junction devices.

We report on the study of magnetic responses of azimuthally and radially excited all-dielectric symmetric and antisymmetric nanoassemblies. Our studies show that magnetic Fano resonances (FRs) in the optical wavelengths can be excited in silicon nanoparticle assemblies when illuminated by cylindrical vector beams. We present the underlying mechanism by investigating the generation of hot and coldspots in the gap regions between silicon particles. This work proposes promising methods to induce various types of magnetic resonant modes in all-dielectric nanostructures with high efficiency and without breaking the symmetry under the illumination of cylindrical vector beams.

Dimers, two closely spaced metallic nanostructures, are one of the primary nanoscale geometries in plasmonics, supporting high local field enhancements in their interparticle junction under excitation of their hybridized "bonding" plasmon. However, when a dimer is fabricated on a metallic substrate, its characteristics are changed profoundly. Here we examine the properties of a Au dimer on a Au substrate. This structure supports a bright "bonding" dimer plasmon, screened by the metal, and a lower energy magnetic charge transfer plasmon. Changing the dielectric environment of the dimer-on-film structure reveals a broad family of higher-order hybrid plasmons in the visible region of the spectrum. Both of the localized surface plasmons resonances (LSPR) of the individual dimer-on-film structures as well as their collective surface lattice resonances (SLR) show a highly sensitive refractive index sensing response. Implementation of such all-metal magnetic-resonant nanostructures offers a promising route to achieve higher-performance LSPR- and SLR-based plasmonic sensors.

Above-threshold light emission from plasmonic tunnel junctions, when emitted photons have energies significantly higher than the energy scale of the incident electrons, has attracted much recent interest in nano-optics, while the underlying physical mechanism remains elusive. We examine above-threshold light emission in electromigrated tunnel junctions. Our measurements over a large ensemble of devices demonstrate a giant material dependence of photon yield (emitted photons per incident electrons), as large as four orders of magnitude. This dramatic effect cannot be explained only by the radiative field enhancement effect due to the localized plasmons in the tunneling gap. Emission is well described by a Boltzmann spectrum with an effective temperature exceeding 2000 K, coupled to a plasmon-modified photonic density of states. The effective temperature is approximately linear in the applied bias, consistent with a suggested theoretical model in which hot carriers are generated by non-radiative decay of electrically excited localized plasmons. Electrically driven hot-carrier generation and the associated non-traditional light emission could open new possibilities for active photochemistry, optoelectronics and quantum optics., 23 pages, 5 figures + supplementary information

Plasmon excitations in metallic nanostructures can decay directly into dynamic electron–hole pairs, exploitable for photocurrent generation. This approach has extensively been employed to develop nanoplasmonic light-sensing devices with significant responsivity and quantum efficiency. Among the devices, infrared plasmonic photodetectors have gained particular interest for their wide range of technological applications, including spectroscopy, biosensing, and surveillance. This Review discusses the fundamentals, recent advances, and trending mechanisms in the understanding and applications of plasmon-enhanced photocurrent generation in nanostructures across the infrared spectrum. By highlighting and comparing the developed techniques, we demonstrate the newly introduced directions toward achieving high photon yield infrared plasmonic photodetection tools. As a promising concept in modern metaphotonics, we present the emergence of toroidal meta-atoms as plasmon-induced carrier generators with unconventionally exquisite properties for designing advanced, rapid, and next-generation plasmonic photodetectors with significantly high responsivity and photocurrent.