Metallic Nanorings Research Articles

Direct‐Laser‐Written Polymer Nanowire Waveguides for Broadband Single Photon Collection from Epitaxial Quantum Dots into a Gaussian‐like Mode

AbstractSingle epitaxial quantum dots (QDs) embedded in nanophotonic geometries are a leading technology for quantum light generation. However, efficiently coupling their emission into a single mode fiber or Gaussian beam often remains challenging. Here, direct laser writing (DLW) is used to address this challenge by fabricating 1 µm diameter polymer nanowires (PNWs) in‐contact‐with and perpendicular‐to a QD‐containing GaAs layer. QD emission is coupled to the PNW's waveguide mode, enhancing collection efficiency into a single‐mode fiber. PNW fabrication does not alter the QD device layer, making PNWs well‐suited for augmenting pre‐existing in‐plane geometries. Standalone PNWs and PNWs in conjunction with metallic nanoring devices that have been previously established for increasing extraction of QD emission are studied. Methods that mitigate standing wave reflections and heat, caused by GaAs's absorption/reflection of the lithography beam, and which otherwise prevent PNW fabrication, are also reported. A maximum improvement of ( in a nanoring system with a PNW compared to the same system without a PNW is observed, in line with numerical results, and highlighting the PNW's ability to waveguide QD emission and increase collection efficiency simultaneously. These results demonstrate new DLW functionality in service of quantum emitter photonics that maintains compatibility with existing top‐down fabrication approaches.

Upconversion enhancement based on mode hybridization in metamaterial absorber

Upconversion nanoparticles (UCNPs) can be used to harvest near-infrared (NIR) light and convert it into visible light. Although this improves optical device operating spectral range and efficiency, e.g., solar cells, typical UCNPs conversion efficiency is too low for practical devices. In this paper, we utilize mode hybridization to enhance the upconversion emission in a metamaterial absorber, which consists of metallic nanoring arrays, UCNPs and a metal film. Numerical and theoretical analysis results show that the maximum upconversion enhancement factor of 2.5×106 is achieved due to the mixture of gap plasmonic resonance mode and surface lattice resonance mode. Moreover, the electromagnetic field distribution shows that the anti-crossing behavior strongly impacts the mode distribution, making the mode energy contribute to upconversion. The designed metamaterial absorber is a novel approach in enhancing upconversion and promising for solar cells.

A universal synthesis of ultrathin Pd-based nanorings for efficient ethanol electrooxidation.

Metallic nanorings (NRs) with open hollow structures are of particular interest in energy-related catalysis due to their unique features, which include the high utilization of active sites and facile accessibility for reactants. However, there is still a lack of general methods for synthesizing Pd-based multimetallic NRs with a high catalytic performance. Herein, we develop a template-directed strategy for the synthesis of ultrathin PdM (M = Bi, Sb, Pb, BiPb) NRs with a tunable size. Specifically, ultrathin Pd nanosheets (NSs) are used as a template to steer the deposition of M atoms and the interatomic diffusion between Pd and M, subsequently resulting in the hollow structured NRs. Taking the ethanol oxidation reaction (EOR) as a proof-of-concept application, the PdBi NRs deliver a substantially improved activity relative to the Pd NSs and commercial Pd/C catalysts, simultaneously showing outstanding stability and CO tolerance. Mechanistically, density functional theory (DFT) calculations disclose that the incorporation of Bi reduces the energy barrier of the rate-determining step in the EOR C2-path, which, together with the high ratio of exposed active sites, endows the PdBi NRs with an excellent EOR activity. We believe that our work can illuminate the general synthesis of multimetallic NRs and the rational design of advanced electrocatalysts.

Fabrication of Metallic Nano-Ring Structures by Soft Stamping with the Thermal Uplifting Method

In this study, the unconventional microfabrication method by the combined processes of the chemical soft stamping technique with the thermal uplifting technique to fabricate metal nanoarrays on a glass plate is proposed and their feasibility verified. The gold micro-ring arrays on a quartz glass plate are realized by utilizing a chemical template with the thermal uplifting method. Their optical properties are studied experimentally. First, a plastic mold is made of a Biaxially Oriented Polyethylene Terephthalate (BOPET) via the hot embossing method. Then, the Methanal micropatterns are transferred onto an etched surface of a substrate via a soft stamping process with a BOPET mold. The gold thin film is coated onto the methanol patterned glass plate via the Ar+ sputter coating process. Finally, the metallic micro-ring structures are aggregated on a glass plate via the thermal uplifting technique. The LSPR optical properties as the extinction spectrums of the gold micro-ring structure arrays are investigated experimentally. It is confirmed that this method was able to fabricate plasmonic micro-ring arrays with low cost and high throughput.

Time-reversal-symmetry breaking and chiral quantum state manipulation in plasmonic nanorings

The chiral transfer of quantum information in a metal nanoring network is presented. A system of three metal nanorings coupled to a two-level quantum dot enables the chiral transport of quantum states by breaking the time-reversal symmetry, which provides a platform for chiral quantum information processing in nanorings. The direction of the chirality can be controlled by preparing the quantum dot in its ground or excited state. We show that the system dynamics can be controlled such that one can achieve a perfect or a partial chiral transfer of the excitation. The synthetic magnetic field that enables the chirality in the system makes the generation of specifically tailored entangled nanoring states possible. As particular examples, we show that in this platform the generation of a two-excitation NOON state and entangled coherent states among nanorings can be realized.

Broadband, efficient extraction of quantum light by a photonic device comprised of a metallic nano-ring and a gold back reflector

To implement quantum light sources based on quantum emitters in applications, it is desirable to improve the extraction efficiency of single photons. In particular, controlling the directionality and solid angle of the emission are key parameters, for instance, to couple single photons into optical fibers and send the information encoded in quantum light over long distances, for quantum communication applications. In addition, fundamental studies of the radiative behavior of quantum emitters, including studies of coherence and blinking, benefit from such improved photon collection. Quantum dots grown via Stranski–Krastanov technique have shown to be good candidates for bright, coherent, indistinguishable quantum light emission. However, one of the challenges associated with these quantum light sources arises from the fact that the emission wavelengths can vary from one emitter to the other. To this end, broadband light extractors that do not rely on high-quality factor optical cavities would be desirable, so that no tuning between the quantum dot emission wavelength and the resonator used to increase the light extraction is needed. Here, we show that metallic nano-rings combined with gold back reflectors increase the collection efficiency of single photons, and we study the statistics of this effect when quantum dots are spatially randomly distributed within the nano-rings. We show an average increase in the brightness of about a factor 7.5, when comparing emitters within and outside the nano-rings, in devices with a gold back reflector, and we measure count rates exceeding 7 × 106 photons per second and single photon purities as high as 85% ± 1%. These results are important steps toward the realization of scalable, broadband, easy to fabricate sources of quantum light for quantum communication applications.

Active Graphene Plasmonic Tweezers: Size Based Nanoparticle Trapping and Sorting

In this article, a novel graphene based Optical tweezer (OT) and size based particle sorter is proposed and numerically investigated by finite difference time domain (FDTD) method and Maxwells stress tensor (MST) analysis. Each unit cell of the structure is composed of a graphene layer on top a metallic nano-ring which is embedded in SiO2. Strong hotspots with field enhancements reaching values as high as 140 are obtained inside the rings with no need to sharp edges conventional in plasmonic structures. Size based trapping can be achieved by controlling the fermi energy of the graphene through a gate. By cascading several unit cells, each operating at a different gate voltage, a particle size based sorter is designed which can effectively sort Polystyrene particles with their diameter in the range of smaller than 10 nm to 100 nm. The structure is illuminated by a laser beam in the mid-IR frequency range of 4-8 m and its wavelength and intensity are kept constant even for sorting functionality. Instead, tunable plasmonic characteristics of graphene is utilized for active particle sorting. The fermi level-particle size-gate voltage relationship of the proposed OT is fully investigated at the article. Moreover, it is shown that the proposed structure is capable of sorting particles according to their refractive indices as well.

Plasmonic properties of nanohybrids made of metallic nanoring and benzene molecules

AbstractPlasmon‐molecule coupling has recently been attracted great research interest in material science and quantum optics with a multitude of potential applications. In this work, using the linear combination of atomic orbitals real‐time‐propagation rt‐time dependent density functional theory (TDDFT) technique (LCAO‐rt‐TDDFT) and transition contribution maps, we investigate the optical and plasmonic features of a hybrid nanosystem comprising an elliptical‐shaped metal nanoring (ENR) and a couple of benzene molecules (located in close proximity at both sides of the ENR short axis and/or long axis). We find that pristine ENR exhibits localized surface plasmon resonances (LSPRs) and plasmon‐molecule coupling in hybrid nanosystems is highly sensitive to the location of the molecules. More specifically, when benzene molecules are placed at both sides of the ENR short axis, the dominant peak in the photoabsorption spectrum sustains its LSPR features with a significant enhancement in intensity. On the other hand, in an alternative situation where benzene molecules are placed at both sides of the ENR long axis, the dominant peak in the photoabsorption spectrum splits into three with diminishing LSPR features.

Plasmons and magnetoplasmon resonances in nanorings

Plasmonic sensors based on metallic nanorings benefit from resonances covering a wide spectral range and homogeneous cavity fields. Here, we explore the potential for nanorings in active plasmonics by examining the tunability of plasmon resonances due to external magnetic fields. Within the electrostatic approximation, we compute plasmon resonances and their shifts in magnetic fields for both solid and planar nanorings. In particular, solid nanorings of circular, elliptical, and disk-shaped cross sections are critically examined and compared to planar rings. Overall, we find that magnetoplasmon shifts in nanorings are greatly reduced compared to standard nanoparticles. However, flat geometries are found to be preferable and allow for relatively large shifts.

Quantum Hamiltonian for the surface charge density on a ring torus and radiative decay of plasmons

Photon scattering and the ensuing excitation of surface plasmons in single rings, single composite rings, and many-ring systems was recently shown to provide dispersion and field distributions [K. V. Garapati et al., J. Phys. Commun. 2, 015031 (2018)] of potential for specific applications in particle and molecular trapping [R. Alaee et al., Appl. Phys. Lett. 109, 141102 (2016); M. Salhi et al., Phys. Rev. A 92, 033416 (2015)], in addition to metamaterials and sensing. Following photon or electron interactions with metallic nanorings, both radiative and nonradiative decay channels are important in the consideration of the nanoparticle as a photon or phonon source, and in related applications. Here, we quantize the electronic normal modes of the ring torus and obtain the radiative decay of plasmons. Due to a geometry-related complexity, we employ a perturbation approach to obtain analytical expressions for the radiative decay channel for a vacuum bounded single solid nanoring. In quantizing the fields, the frequency spectrum of the charge density normal modes of the nanoring is obtained and shown to agree with the exact quasistatic plasmon dispersion relations. Higher-order corrections beyond the presented zero- and first-order calculations may be obtained following the presented results. The results are of potential interest in quantum sensing such as entangling photons and plasmons, or plasmons and trapped molecules.

Protein Assisted Fabrication of Metallic Nanorings and Spherical Nanoparticles for Electrocatalytic and Organocatalytic Applications

Inspiration from nature has driven the development and application of greener nanomaterials prepared using biotemplates in the field of nanoscience. Compared to traditional chemical routes, bioinspired nanomaterial synthesis has the advantage of mild synthetic conditions such as aqueous environment, ambient temperature, and no requirement for organic capping agent. In addition, the structures of some biomolecules make it possible to fabricate nanomaterials with complex and interesting morphology that are difficult to achieve through chemical methods. In this study, tobacco mosaic virus coat protein (TMV cp) was investigated as a versatile template to mediate the synthesis of nanorings and spherical nanoparticles under neutral and alkaline conditions, respectively. While the prepared silver nanorings displayed superior selectivity (95% Faradaic Efficiency) and stability of catalyzing CO2 electroreduction (CO2 RR) compared to free silver nanoparticles prepared by chemical methods, the platinum nanorings showed excellent electrocatalytic activity for hydrogen evolution reaction (HER). Spherical nanoparticles synthesized under alkaline conditions (Pt, Pd and Au NPs) were also investigated for their catalytic behavior towards organic transformations such as 4-nitrophenol reduction and alkyne hydrogenation.

Localized surface plasmon resonances of a metal nanoring.

Using the linear combination of atomic orbitals real-time-propagation rt-TDDFT technique (LCAO-rt-TDDFT) and transition contribution maps, we study the optical and plasmonic features of a metal nanoring (made up of sodium atoms) with respect to the modulation in the ring thickness from a sharp edge (one-atom-thick) to a flat edge (four-atoms-thick). The birth of the localized surface plasmon resonance was accessed by many factors including the number of contributing electron-hole transitions, the relative strengths of these contributions, and the nature of the induced charge density oscillation. We reveal that the occurrence of a large number of contributing electron-hole transitions to an absorption peak cannot be treated as an indicator of plasmonicity. Nonetheless, plasmonicity can be accessed from the transition contribution map (occurrence of many spots with strong contributions and distributed on a large domain of energy) and from the profile of the induced charge density. Our results are useful for designing ultra-small plasmonic devices based on metal nanorings as building blocks.

Bio‐Assisted Tailored Synthesis of Plasmonic Silver Nanorings and Site‐Selective Deposition on Graphene Arrays

AbstractThe spontaneous interaction between noble metals and biological scaffolds enables simple and cost‐effective synthesis of nanomaterials with unique features. Here, plasmonic silver nanorings are synthesized on a ring‐like protein, i.e., a peroxiredoxin (PRX), and used to assemble large arrays of functional nanostructures. The PRX drives the seeding growth of metal silver under wet reducing conditions, yielding nanorings with outer and inner diameters down to 28 and 3 nm, respectively. The obtained hybrid nanostructures are selectively deposited onto a solid‐state 2D membrane made of graphene in order to prepare plasmonic nanopores. In particular, the interaction between the graphene and the PRX allows for the simple preparation of ordered arrays of plasmonic nanorings on a 2D‐material membrane. This fabrication process can be finalized by drilling a nanometer scale pore in the middle of the ring. Fluorescence spectroscopic measurements in combination with numerical simulations demonstrate the plasmonic effects induced in the metallic nanoring cavity. The prepared nanopores represent one of the first examples of hybrid plasmonic nanopore structures integrated on a 2D‐material membrane. The diameter of the nanopore and the atomically thick substrate make this proof‐of‐concept approach particularly interesting for nanopore‐based technologies and applications such as next‐generation sequencing and single‐molecule detection.

Dynamics of quantum discord between two quantum dots placed near a nanoring surface plasmons

We investigate the dynamics of quantum discord between two colloidal quantum dots placed in the vicinity of nanoring with surface plasmons (SPs). We also analytically solve the corresponding master equation and show the influence of coupling strength and interdot distance on the dynamics of quantum discord. It is found that for an initial separable state, maximum quantum discord can be generated at a suitable interdot distance by the scattering of SPs in the metal nanoring resonator. Furthermore, for the initial correlated state, we observe that the decay and revivals of the quantum discord can be controlled by properly choosing the interdot distance and coupling strengths.

Plasmon mediated entanglement dynamics of distant quantum dots**Project supported by the National Natural Science Foundation of China (Grant Nos. 11274132 and 11550110180).

We investigate the time evolution of entanglement between two quantum dots in an engineered vacuum environment such that a metallic nanoring having a surface plasmon is placed near the quantum dots. Such engineering in environment results in oscillations in entanglement dynamics of the quantum dots systems. With proper adjustment of the separation between the quantum dots, entanglement decay can be stabilized and preserved for longer time than its decay without the surface plasmons interactions.

Coupling of Fluorophores in Single Nanoapertures to Tamm Plasmon Structures.

Metal nanostructures (such as plasmonic antennas) have been widely demonstrated to be excellent devices for beaming and sorting the fluorescence emission. These effects rely on the constructive scattering or diffraction from different elements (such as metal corrugations or nanorings) of the nanostructures. However, subwavelength-size nanoholes, without nearby nanoscale features, results in an angularly dispersed emission from the distal surface. Herein, we demonstrate for the first time the emission redirection capabilities of a single isolated nanoaperture milled in a thick silver film deposited on a dielectric multilayer. Specifically, we show that a dye dissolved in ethanol filling in the nanoaperture can couple to Tamm Plasmon Polariton (TPP) modes of the structure. Due to the small in-plane wavevectors of the TPPs, the fluorescence from Tamm-coupled dyes within the nanoaperture is emitted normally to the sample surface, with a minimum angular width of about 12.54°. This kind of fluorescence manipulation has proven to be effective with various nanoaperture shapes, such as circles, squares, and triangles. Our work is also the first experimental demonstration of lateral coupling of fluorophores with TPPs in nanoholes, with potential applications in bioanalysis and biosciences.

Three-Dimensional Electrochemical Axial Lithography on Si Micro- and Nanowire Arrays.

A templated electrochemical technique for patterning macroscopic arrays of single-crystalline Si micro- and nanowires with feature dimensions down to 5 nm is reported. This technique, termed three-dimensional electrochemical axial lithography (3DEAL), allows the design and parallel fabrication of hybrid silicon nanowire arrays decorated with complex metal nano-ring architectures in a flexible and modular approach. While conventional templated approaches are based on the direct replication of a template, our method can be used to perform high-resolution lithography on pre-existing nanostructures. This is made possible by the synthesis of a porous template with tunable dimensions that guides the deposition of well-defined metallic shells around the Si wires. The synthesis of a variety of ring architectures composed of different metals (Au, Ag, Fe, and Ni) with controlled sequence, height, and position along the wire is demonstrated for both straight and kinked wires. We observe a strong enhancement of the Raman signal for arrays of Si nanowires decorated with multiple gold rings due to the plasmonic hot spots created in these tailored architectures. The uniformity of the fabrication method is evidenced by a homogeneous increase in the Raman signal throughout the macroscopic sample. This demonstrates the reliability of the method for engineering plasmonic fields in three dimensions within Si wire arrays.

One-Pot Synthesis of Pd Nanorings Using a Soft Template of Spindle-Shaped Amphiphilic Molecular Assembly

Metallic nanorings have attracted much attention of researchers owing to their unique optical, electrical, and magnetic properties, and now, simple and large-scale synthesis methods must be developed for their practical application in various fields. Here, we report the one-pot synthesis of ultrathin Pd nanorings through a simple and novel soft-template approach based on wet-chemical synthesis. A spindle-shaped assembly of a long-chain amidoamine derivative (C18AA) served as the soft template of Pd nanorings that were prepared in an aqueous solution containing the Pd precursor and a suitable amount of C18AA and toluene, and the chemical reduction of the Pd precursor in the aqueous solution produced an array of almost circular Pd nanorings covering the assembly. Pd nanorings that were parallel to the amine group, which is the head group of C18AA, appeared on the assembly surface. The amount of toluene strongly affected the formation of the spindle-shaped assembly and Pd nanorings. Furthermore, transmission...

Entanglement generation among quantum dots and surface plasmons of a metallic nanoring

We study the systems of two and three quantum dots positioned near a metallic nanoring having a surface plasmon in a particular mode. Interaction of surface plasmon with quantum dots generates entanglement between quantum dots as well as among the incident and reflected modes of the surface plasmons. We show that the maximum amount of entanglement is generated among two initially unentangled quantum dots separated by distance and with interaction parameter , while entanglement among two counter-propagating modes of the surface plasmons can be generated with interdot distance and interaction parameter , where k and μ are the propagation vector and coupling constant, respectively. In case of three quantum dots, the maximum entanglement among the quantum dots is obtained at kd = mπ/3 and Finally, the scheme is straightforwardly generalized to generate quantum entanglement among N quantum dots as well as among two counter-propagating modes of the surface plasmon due to their interactions with quantum dots.

Combined metallic nano-rings and solid-immersion lenses for bright emission from single InAs/GaAs quantum dots

Solid-state single-photon emitters are key components for integrated quantum photonic devices. However, they can suffer from poor extraction efficiencies, caused by the large refractive index contrast between the bulk material they are embedded in and air: this results in a small fraction (that can be as low as ∼0.1%) of the emitted photons reaching free-space collection optics. To overcome this issue, we present a device that combines a metallic nano-ring, positioned on the sample surface and centered around the emitter, and an epoxy-based super-solid immersion lens, deposited above the ring devices. We show that the combined broadband lensing effect of the nano-ring and the super-solid immersion lens significantly increases the extraction of light emitted by single InAs/GaAs quantum dots into free space: we observe cumulative enhancements that allow us to estimate photon fluxes on the first collecting lens approaching 1 × 106 counts per second, from a single quantum dot in bulk. The combined broad-band enhancement in the extraction of light can be implemented with any kind of classical and quantum solid-state emitter and opens the path to the realisation of scalable bright devices. The same approach can also be implemented to improve the absorption of light, for instance, for small-area broadband photo-detectors.