Nanoring Arrays Research Articles

Selective MOCVD synthesis of VO2 crystals on nanosharp Si structures

High-quality single VO2 nanocrystals and ordered arrays of VO2 nanorings were selectively synthesized by chemical vapor deposition (CVD) respectively on the tip apices and on the sidewall scallops.

Two-dimensional silicon nanoring array enabled polarization-independent narrow spectral linewidth optical filter

In this paper, we investigate a new, to the best of our knowledge, type of guided-mode resonance optical filter with polarization-independence at normal incidence and relatively narrow spectral linewidth in the near-infrared regime. The new optical spectral filter consists of a 2D array of silicon nanorings on silicon film on silica substrate. Using finite difference time domain (FDTD) simulations, it is found that the spectral linewidth of the optical filter is primarily controlled by nanoring width and is tolerant to the variations of the size and height of silicon nanorings. FDTD simulations also reveal that the excited guided mode is more tightly confined in the nanoring structures with smaller ring widths. It is explained that the narrow spectral linewidth of the nanoring structure filter is due to the smaller scattering cross-section of the silicon nanorings and tighter confinement of the guided mode. Our optimally designed optical reflection filter exhibits a 2.4 nm spectral linewidth with nearly 100% peak reflectance at the resonance wavelength.

Au nanoring arrays as surface enhanced Raman spectroscopy substrate for chemical component study of individual atmospheric aerosol particle

Monolayer-ordered gold nanoring arrays were prepared by ion-sputtering method and used as surface enhanced Raman spectroscopy (SERS) substrates to test the individual atmospheric aerosols particle. Compared to other methods used for testing atmospheric aerosols particles, the collection and subsequent detection in our work is performed directly on the gold nanoring SERS substrate without any treatment of the analyte. The SERS performance can be tuned by changing the depth of the gold nanoring cavity as originating from coupling of dipolar modes at the inner and outer surfaces of the nanorings. The electric field exhibits uniform enhancement and polarization in the ordered Au nanoring substrate, which can improve the accuracy for detecting atmospheric aerosol particles. Combined with Raman mapping, the information about chemical composition of individual atmospheric aerosols particle and distribution of specific components can be presented visually. The results show the potential of SERS in enabling improved analysis of aerosol particle chemical composition, mixing state, and other related physicochemical properties.

Plasmonic-enhanced microcrystalline silicon solar cells

This paper describes the enhanced performance of the microcrystalline silicon (µc-Si) thin-film solar cells due to the incorporation of plasmonic nanostructures. Finite-difference time-domain numerical modeling is used to calculate the optical properties of the solar cells such as the absorption and the short-circuit current density ( J s c ). In this paper, two-dimensional(2D) periodic arrays of various geometries of plasmonic nanostructures such as nano-rings, nano-discs, nano-hemispheres, and nano-cubes are employed on the back side of the solar cells to increase the absorption for the longer wavelengths of the incident light, where most of the photons remain unharvested due to extremely low absorption coefficients of µc-Si material. These plasmonic nanostructures are compared in terms of solar cell performance, and it is found that the 2D periodic arrays of nano-rings show significant absorption enhancement at multiple wavelengths, thereby leading to a substantial enhancement in the J s c . An enhancement of 35% in the J s c is obtained when a 2D periodic array of plasmonic nano-rings is present on the back side of the solar cell, which is higher than that of the µc-Si solar cells having arrays of plasmonic nanostructures of other geometries (i.e., nano-discs, nano-cubes, nano-hemispheres). It is observed that the enhancement in the absorption is attributed to the enhanced electromagnetic fields in the active layer due to several localized surface plasmon modes that are excited in the plasmonic nanostructures at different wavelengths. Moreover, the effect of the thickness of the spacer layer (the layer between the metal back-reflector and plasmonic nanostructure arrays) on the performance of different plasmonic solar cells is examined.

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.

Plasmonic Nanolenses Produced by Cylindrical Vector Beam Printing for Sensing Applications

Interaction of complex-shaped light fields with specially designed plasmonic nanostructures gives rise to various intriguing optical phenomena like nanofocusing of surface waves, enhanced nonlinear optical response and appearance of specific low-loss modes, which can not be excited with ordinary Gaussian-shaped beams. Related complex-shaped nanostructures are commonly fabricated using rather expensive and time-consuming electron- and ion-beam lithography techniques limiting real-life applicability of such an approach. In this respect, plasmonic nanostructures designed to benefit from their excitation with complex-shaped light fields, as well as high-performing techniques allowing inexpensive and flexible fabrication of such structures, are of great demand for various applications. Here, we demonstrate a simple direct maskless laser-based approach for fabrication of back-reflector-coupled plasmonic nanorings arrays. The approach is based on delicate ablation of an upper metal film of a metal-insulator-metal (MIM) sandwich with donut-shaped laser pulses followed by argon ion-beam polishing. After being excited with a radially polarized beam, the MIM configuration of the nanorings permitted to realize efficient nanofocusing of constructively interfering plasmonic waves excited in the gap area between the nanoring and back-reflector mirror. For optimized MIM geometry excited by radially polarized CVB, substantial enhancement of the electromagnetic near-fields at the center of the ring within a single focal spot with the size of 0.37λ2 can be achieved, which is confirmed by Finite Difference Time Domain calculations, as well as by detection of 100-fold enhanced photoluminescent signal from adsorbed organic dye molecules. Simple large-scale and cost-efficient fabrication procedure offering also a freedom in the choice of materials to design MIM structures, along with remarkable optical and plasmonic characteristics of the produced structures make them promising for realization of various nanophotonic and biosensing platforms that utilize cylindrical vector beam as a pump source.

Broadband visible light absorber based on ultrathin semiconductor nanostructures**Project supported by the Natural Science Foundation of Guangdong Province, China (Grant Nos. 2018A030313854 and 2016A030313851).

It is desirable to have electromagnetic wave absorbers with ultrathin structural thickness and broader spectral absorption bandwidth with numerous applications in optoelectronics. In this paper, we theoretically propose and numerically demonstrate a novel ultrathin nanostructure absorber composed of semiconductor nanoring array and a uniform gold substrate. The results show that the absorption covers the entire visible light region, achieving an average absorption rate more than 90% in a wavelength range from 300 nm to 740 nm and a nearly perfect absorption from 450 nm to 500 nm, and the polarization insensitivity performance is particularly great. The absorption performance is mainly caused by the electrical resonance and magnetic resonance of semiconductor nanoring array as well as the field coupling effects. Our designed broadband visible light absorber has wide application prospects in the fields of thermal photovoltaics and photodetectors.

A High-Sensitivity Methane Sensor with Localized Surface Plasmon Resonance Behavior in an Improved Hexagonal Gold Nanoring Array.

This paper proposes a methane sensor based on localized surface plasmon resonance (LSPR) of a hexagonal periodic gold nanoring array. The effects of structural parameters on the extinction spectrum and refractive index (RI) sensitivity are analyzed to obtain optimal parameters. In particular, the RI sensitivity can reach 550.08 nm/RIU through improvement of the sensor structure, which is an increase of 17.4% over the original value. After coating a methane-sensitive membrane on the inner and outer surfaces of the gold rings, the methane concentration can be accurately measured with a gas sensitivity of −1.02 nm/%. The proposed method is also applicable to quantitative analyses of components concentration and qualitative analyses of gas composition.

Numerical investigation on dielectric-metal based dual narrowband visible absorber

We propose a dual narrowband perfect visible absorber using periodic dielectric nanoring arrays on aluminum film. This nanostructure can reduce the oxidation problem that noble metal nanostructure is facing. In the designed structure, the resonance peak I corresponds to the first order grating mode, and the resonance peak II is due to the combination of SPP mode, SLR mode and the guide mode. For the application as refractive index sensor, the sensitivity of the two resonance modes is almost the same, and the figure of merit (FOM) of the resonance I and II are 21.8/RIU and 3.5/RIU, respectively. The narrowband perfect absorber has potential applications in sensing application.

Catalysis of Au nano-pyramids formed across the surfaces of ordered Au nano-ring arrays

Gold (Au) is a noble metal that has been widely researched due to its high catalytic performance-to-cost ratio. The catalysis could be improved by fabrication of nanostructured arrays on Au thin film with a large area. In the present paper, a facile NSL-RIE approach comprising of nanosphere lithography followed by oxygen plasma reactive ion etching has been developed to fabricate ordered Au nano-ring arrays with almost 100% substrate coverage. The preferential etching of {1 1 1} lattice planes of Au gives rise to the formation of a number of Au nano-pyramids across the entire surface of the nano-ring arrays. The sharp tips along with the Au atoms around the edges of these nano-pyramids provide active sites that perform strong catalysis. Meanwhile, Moiré fringes are observed over the etched Au surface which is caused by the rotation of the partial Au lattice with respect to the original Au lattice. This lattice distortion provides high surface energy allowing the significant improvement of the catalysis of Au nano-ring arrays. The direct evidence is proven by the enhanced electrochemical properties of the as-produced Au nano-ring array, which has high efficiency in ethanol oxidation reactions (EORs) with low energy input requirement. Electrochemical testing with varying physical parameters shows that the detecting limit of ethanol is ∼5.0 mM and strong signals come with high concentrations of mobile charge carriers at extreme pH values. Long continuous CV scans reveal that in alkaline medium, C1 pathway could become increasingly preferential over C2 pathway, and thus making the Au nano-ring array structure useful in the field of direct ethanol fuel cell.

Ordering, flexibility and frustration in arrays of porphyrin nanorings

The regular packing of atoms, molecules and nanoparticles provides the basis for the understanding of structural order within condensed phases of matter. Typically the constituent particles are considered to be rigid with a fixed shape. Here we show, through a combined experimental and numerical study of the adsorption of cyclic porphyrin polymers, nanorings, on a graphite surface, that flexible molecules can exhibit a rich and complex packing behaviour. Depending on the number of porphyrin sub-units within the nanoring we observe either a highly ordered hexagonal phase or frustrated packing driven by directional interactions which for some arrangements is combined with the internal deformation of the cyclic polymer. Frustration and deformation occur in arrays of polymers with ten sub-units since close packing and co-alignment of neighbouring groups cannot be simultaneously realised for nanorings with this internal symmetry.

Numerical investigation of a tunable metamaterial perfect absorber consisting of two-intersecting graphene nanoring arrays

In this paper, we report a numerical investigation of tunable dual-band metamaterial perfect absorber (MMPA) consisting of two-intersecting graphene nanorings arrays. The optical absorption performance of absorber is dominated by the inner/outer radius of nanorings and center distance between the two nanorings. For the resonance modes λ1 and λ2, the sensitivity of probing the surrounding refractive index can reach 7.97 μm/RIU and 13.27 μm/RIU respectively. The absorption performance of the under-study graphene nanorings can be flexibly adjusted by modulating the Fermi level of graphene with voltage. Due to excellent wavelength selectivity and high refractive-index sensitivity, the presented tunable dual-band MMPA has great application prospects as sensors in biopharmaceutical, environmental monitoring.

Design of aluminum-based nanoring arrays for realizing efficient plasmonic sensors

In this work, for the first time to our knowledge, an aluminum-based plasmonic nanoring array has been employed to present a practical approach for design of efficient optical sensors. Applying aluminum for this design benefits from cost-effectiveness, CMOS-compatibility, and ease of fabrication, while offering tunable and selective optical characteristics. Utilizing surface plasmon resonances of the proposed nanostructure, an effective refractive index sensor at visible wavelengths has been achieved. The simulation results show a high sensitivity up to 408 nm/RIU with a figure of merit of 5.88, which is comparable to those of gold-based plasmonic sensors and even outperforms some of them.

Dark plasmon in asymmetric nanoring arrays on conducting substrates and related applications

We put forward a theoretical analysis of the optical properties of an asymmetric nanoring array on a gold metal layer. We show that for normal incidence, the spectrum of the symmetric system is characterized by a general dipolar ring resonance. For the asymmetric nanoring with an offset inner surface, obviously both dark monopolar and quadrupolar ring resonances can be generated under a normal incidence, which depends sensitively on the asymmetry of the structure. Meanwhile, the symmetry breaking of the structure provides the desirable near-field characteristics for biosensing. As a result, monopolar and multipolar modes reveal ultrahigh refractive sensitivities as large as 792 nm/RIU and 742 nm/RIU, respectively. Furthermore, due to their subradiant features, the resulting FOM is 72 RIU−1 for the monopolar mode and the record high value of 137.4 RIU−1 for the quadrupolar mode in a wide refractive index range of 1.33-1.38. These results indicate that an asymmetric ring system could be promising for biosensing applications with high performance.

Design of semiconductor surface pits for fabrication of regular arrays of quantum dots and nanorings

We report a systematic computational study on the formation of complex nanostructures consisting of quantum dots and nanorings on surfaces of coherently strained thin films grown epitaxially on pit-patterned substrates. The analysis is based on self-consistent dynamical simulations according to a film surface evolution model that has been validated experimentally by comparison of its predictions with experimental observations on Ge films grown on Si pit-patterned substrates and is supported by linear stability theory that explains the film surface nanopattern formation as the outcome of a Stranski-Krastanow instability. Emphasis is placed on the design of conical pit patterns and the effects on the resulting film surface nanopattern of varying geometrical design parameters including film thickness, pit-pattern period, pit depth, pit opening diameter, and pit wall inclination. We demonstrate that varying the pit opening diameter and the pit wall slope leads to formation of complex nanostructures inside the pits of a regular pit pattern on the film surface, which include quantum dots, as well as single nanorings and multiple concentric nanorings that may or may not surround a central quantum dot inside each pit. Our simulation predictions demonstrate that the ordered nanostructure patterns forming on the film surface can be controlled precisely by tuning the geometrical parameters of the pits on the pit-patterned substrate. Our findings have important implications for designing optimal semiconductor surface patterns toward enabling future nanofabrication technologies.

Highly ordered 3D-silver nanoring arrays (3D-AgNRAs) for refractometric sensing

Multistep colloidal lithography-fabricated 3D-silver nanoring arrays were optimized by regulating their structural parameters and accomplished improved refractometric sensing performance.

Nanostructures of functionalized zinc phthalocyanines prepared with colloidal lithography: Evaluation of surface orientation and dimensions using scanning probe microscopy

Patterned arrays of nanoholes and nanorings were prepared using colloidal lithography combined with steps of solution immersion and vapor deposition of organosilanes. Samples prepared with colloidal lithography exhibit millions of reproducible test structures with a periodic arrangement throughout areas of the surface according to the dimensions and spacing of the particle mask. Views of the size and morphology of nanopatterns obtained with atomic force microscopy (AFM) can provide information of progressive steps of chemical reactions as nanostructures are grown within spatially confined areas surrounded by a resist film. A surface mask of colloidal latex or silica spheres was used to protect discrete areas of a Si(111) substrate from the deposition of organosilanes. When the mask was removed, the uncovered areas of the surface revealed regularly-shaped, small sites of uncovered substrate available for further reaction steps to build hierarchical surface structures. Nanostructures of zinc phthalocyanines (ZnPcs) were constructed using amine-terminated nanopatterns as sites for binding. Spatial selectivity was achieved for directing the attachment of ZnPcs to the surface using resist films of 2-methoxy(polyethyleneoxy)propyl]trichlorosilane (PEO-silane) and also with octadecyltrimethoxysilane (OTMS). The molecule chosen as a linker was (3-aminopropyl)triethoxysilane (APTES) which presents an amine group at the interface. In general, phthalocyanine molecules tend to bind in a coplanar orientation by physisorption to the surface and can stack together through pi-pi interactions between adjacent macrocycles. However, the nature of the substituents will also influence whether the molecules assemble on surfaces in a side-on orientation or with the macrocycle oriented in a coplanar arrangement. Hydroxyl and isothiocyanate pendant groups were attached to the macrocycles of ZnPcs chosen for this study, to investigate conformational differences when attached to APTES nanopatterns. The size and morphology of nanostructures was visualized and sensitively measured with tapping-mode AFM. The elastic response of samples patterned with ZnPc was mapped with force modulation AFM. Changes in the height of nanostructures indicate whether the macrocycles are oriented upright or parallel to the surface plane, or if multilayers were formed.

Fano-like resonances in the binary elliptical nanoring resonator array

In this paper, we design and investigate a binary elliptical nanoring resonator array on a gold conducting layer, which can generate two optical Fano-like resonant modes in the visible light range under normal incidence. The gold conducting layer underneath the nanoring resonator array strongly enhances the coupling and hybridization among different resonant modes. These two distinct Fano-like resonances originate from the interactions of dipolar antibonding and bonding modes, and dipolar bonding and propagating surface plasmon modes, respectively, which provide as high a refractive index sensitivity as 620 nm/RIU, and achieve high figures of merit, 78 and 154, separately in a refractive index range of 1.33~1.40. Compared to the circular nanoring array, the elliptical structure we demonstrate here can generate shaper resonant modes that can be used for high sensitivity measurement. The designed binary elliptical nanoring resonator array is very promising for dual-channel biosensing application.

Design and development of aluminum nanoring arrays for realization of dual-mode operation plasmonic color filters

In this paper, engineering the optical characteristics of aluminum nanoring arrays has been investigated with the aim of achieving a practical design approach to the realization of dual-mode plasmonic color filters. In addition to designing a set of subtractive and additive color filters with appropriate properties, an improved approach has also been proposed in order to design different additive/subtractive filters at arbitrary wavelengths. The proposed structures show great optical efficiencies while offering narrowband characteristics and a good color purity. They are CMOS-compatible, cost-effective, easy to fabricate, highly tunable, and polarization insensitive. Moreover, they offer potential applications in displays, CMOS image sensors, color printing, and multispectral imaging.

Comparative investigation of sensing behaviors between gap and lattice plasmon modes in a metallic nanoring array.

Plasmonic nanostructures have become the most promising candidates for biosensing applications because of their miniature sizes, ease of integration, and high-throughput detection. Both propagating and localized surface plasmon modes in the nanostructures have been used for sensing and biomolecular detection. However, to maximize the biosensing potential of nanostructures, the choice of an optimized sensing detection strategy among two plasmon modes depends on the relationship between the biomolecule sizes and field decay length of plasmon modes. Here, we propose and investigate plasmonic coupling on a single-crystalline gold film, wherein there are two distinct optical modes, a gap mode (localized surface plasmon) originating from the parallel coupling of a nanoring and a surface lattice mode (propagating surface plasmon) originating from the anti-parallel coupling of a nanoring in an array. The sensing performances of the above two modes are thoroughly investigated and compared by considering two aspects, i.e., bulk and surface sensitivities. It is demonstrated that there is a reciprocal relationship between bulk and surface sensitivities for two modes, which also illustrates that the surface sensitivity is indispensable to fully describe the sensing performance of nanostructures. Furthermore, due to their different decay lengths, the gap and surface lattice modes on a single optical substrate can achieve simultaneous detection of target analytes with various sizes. Therefore, we can provide a high performance sensing platform based on a metallic nanoring array for a broad range of biomolecules with various sizes.