Array Of Nanocylinders Research Articles

Plasmonic lasing in highly lossy nanocylinder arrays under optical pumping

Plasmonic lasing in highly lossy nanocylinder arrays under optical pumping

Photonic management of silicon nanocylinder arrays to enhance photovoltaic performance

The light–matter interaction of subwavelength and periodic silicon (Si) nanostructures strongly correlates with their geometrical features, resulting in them being highly unsuitable for the practical development of Si-based photovoltaic applications. In this study, the concepts of effective medium and retrieval methods are needed to deal with the subwavelength periodic dielectric structure. Using finite-difference time-domain simulations, we study the interactions of electromagnetic radiation with a square array of dielectric rods parallel to the incident light, and the effective optical properties such as refractive index, permittivity, and permeability are calculated. Furthermore, the electric field distributions are also plotted for a deeper understanding of the energy changes within Si nanocylinder arrays (SiNCAs) under different incident wavelengths of radiation. By employing calculated optimized SiNCAs for the construction of hybrid solar cells, improved cell performances showing a conversion efficiency of 13.79% are demonstrated, with further estimation by electrical chemical measurements for a better understanding of the carrier transition. These are numerically and experimentally interpreted by the involvement of excellent light-trapping effects, delivering a method to design correlated photovoltaic devices.

Thermochromic performance enhancement by geometric structure optimization of VO2 nanoarrays for smart window application

The localized surface plasmon resonance (LSPR) exhibited by vanadium dioxide (VO2) has expanded its utility in thermochromic smart windows. Here, guided by the absorption characteristics of a single VO2 nanoparticle (NP) with a radius between 10 to 60 nm on a glass substrate, we numerically conducted an extensive analysis of the optical properties of VO2 nano-cylinder arrays. We achieved a significant enhancement in the performance of thermochromic smart windows by optimizing the geometric structure of the VO2 arrays. Such a performance enhancement relies on the on-off switch properties of LSPR in VO2 nano-cylinder arrays. Smaller (r≤ 60) ones with high aspect ratios (> 0.75) shows a higher absorption contribution in their extinction effect and a more energetic LSPR peak located in the near-infrared spectra. Those characteristics significantly improve the thermochromic performance of smart windows via enhancing the transmission contrast between the high-temperature rutile state and the low-temperature monoclinic state of VO2. At a transmittance luminous (Tlum) efficacy of 60.03%, an excellent 20.03% in solar spectrum modulation ability (ΔTsol) can be attained. Compared to flat films with an identical Tlum, ΔTsol of the periodically cylindrical-structured film is raised by 234%.

Inverse design of functional photonic patches by adjoint optimization coupled to the generalized Mie theory

We propose a rigorous approach for the inverse design of functional photonic structures by coupling the adjoint optimization method and the 2D generalized Mie theory (2D-GMT) for the multiple scattering problem of finite-sized arrays of dielectric nanocylinders optimized to display desired functions. We refer to these functional scattering structures as “photonic patches.” We briefly introduce the formalism of 2D-GMT and the critical steps necessary to implement the adjoint optimization algorithm to photonic patches with designed radiation properties. In particular, we showcase several examples of periodic and aperiodic photonic patches with optimal nanocylinder radii and arrangements for radiation shaping, wavefront focusing in the Fresnel zone, and for the enhancement of the local density of states (LDOS) at multiple wavelengths over micron-sized areas. Moreover, we systematically compare the performances of periodic and aperiodic patches with different sizes and find that optimized aperiodic Vogel spiral geometries feature significant advantages in achromatic focusing compared to their periodic counterparts. Our results show that adjoint optimization coupled to 2D-GMT is a robust methodology for the inverse design of compact photonic devices that operate in the multiple scattering regime with optimal desired functionalities. Without the need for spatial meshing, our approach provides efficient solutions at a strongly reduced computational burden compared to standard numerical optimization techniques and suggests compact device geometries for on-chip photonics and metamaterials technologies.

A modeling framework to quantify the intermediate layer impact in III–V//Si multijunction solar cells

Multijunction solar cells (MJSCs) are capable of converting sunlight to electricity more efficiently than single-junction solar cells. The intermediate scattering layers between the individual junctions contribute to high efficiency by impacting the generated currents, photon recycling (PR), as well as luminescent coupling (LC) in the device. The MJSC efficiency can be simulated using expressions that involve a simplified and idealized intermediate layer structure but cannot accurately reflect its actual performance. This work, however, aims to establish a systematic optical model for MJSCs with complicated intermediate layers. It begins with incorporating the LC and PR effects into the developed model, emphasizing requirements for the cut-off wavelength and long-wavelength transmission of the intermediate layer. Furthermore, a three-dimensional metallic nanocylinder array is designed as the intermediate layer to improve device performance. With the model, high-performance MJSCs can be designed and optimised by quantifying the impact of PR and LC on device parameters.

Ultra-broadband and tunable infrared absorber based on VO2 hybrid multi-layer nanostructure

We propose an ultra-broadband near- to mid-infrared (NMIR) tunable absorber based on VO2 hybrid multi-layer nanostructure by hybrid integration of the upper and the lower parts. The upper part is composed of VO2 nanocylinder arrays prepared on the front illuminated surface of quartz substrate, and VO2 square films and VO2/SiO2/VO2 square nanopillar arrays prepared on the back surface. The lower part is an array of SiO2/Ti/VO2 nanopillars on Ti substrate. The effects of different structural parameters and temperature on the absorption spectra were analyzed by the finite-difference time-domain method. An average absorption rate of up to 94.7% and an ultra-wide bandwidth of 6.5 μm were achieved in NMIR 1.5–8 μm. Neither vertical incident light with different polarization angles nor large inclination incident light has a significant effect on the absorption performance of the absorber. The ultra-broadband high absorption performance of this absorber will be widely used in NMIR photodetectors and other new optoelectronic devices.

Polarization-independent 3D metasurface with complex amplitude modulation.

Metasurfaces, which possess unprecedented capabilities in manipulating electromagnetic wavefronts, are promising for accurate complex amplitude modulation with a compact device. However, current strategy of complex amplitude modulation based on metasurfaces focuses on anisotropic unit design which is intrinsically constrained of polarization states. In this study, we propose a design methodology of polarization-independent metasurface which comprises an array of nanocylinders with various radii and heights. The effectiveness of the proposed scheme is verified using an optical vortex generator and a complex-amplitude hologram device. The straightforward, cost-effective, and polarization-independent design can provide robust and reliable solutions for wavefronts modulation in various optical applications.

Vapor Condensation on Bioinspired Hierarchical Nanostructured Surfaces with Hybrid Wettabilities.

Vapor condensation on bioinspired hierarchical nanostructured surfaces with hybrid wettabilities has been investigated using molecular dynamics simulations. A series of hierarchical surfaces consisting of nanocylinder arrays with hydrophilic top and hydrophobic nanopillar arrays are constructed. The results manifest that the condensed nanodroplets undergo three states in the whole water vapor condensation process, and the total condensed atom number on surfaces increases with the increase of nanocylinder diameter (D), which indicates that the introduction of hydrophilic nanocylinders is conducive to improving the condensation performance compared with that on the hydrophobic surface patterned with homogeneous nanopillars. However, the nucleation sites on hierarchical nanostructured surfaces are covered by the condensed nanodroplets at the end of condensation, which suppresses the further enhancement of condensation performance. To solve these problems, we add a collection region close to the edge of the nanostructured surface. It is noticed that the condensed nanodroplets can roll into the collection regions gradually during the condensation process, which keeps the nucleation sites on nanostructured surfaces exposed effectively, especially for the cases of 20 Å ≤ D ≤ 40 Å. Moreover, the cluster number, the total condensed atom number, and the condensation enhancement efficiency on hierarchical nanostructured surfaces with collection regions at 20 Å ≤ D ≤ 40 Å are higher obviously compared with those on surfaces without collection regions. Our study demonstrates that the bioinspired hierarchical nanostructured surface with the collection region is beneficial to boost the vapor condensation performance, which can bring new insights into water vapor condensation.

High-Q collective Mie resonances in monocrystalline silicon nanoantenna arrays for the visible light

Dielectric optical antennas have emerged as a promising nanophotonic architecture for manipulating the propagation and localization of light. However, the optically induced Mie resonances in an isolated nanoantenna are normally with broad spectra and poor Q-factors, limiting their performances in sensing, lasing, and nonlinear optics. Here, we dramatically enhance the Q-factors of Mie resonances in silicon (Si) nanoparticles across the optical band by arranging the nanoparticles in a periodic lattice. We select monocrystalline Si with negligible material losses and develop a unique method to fabricate nanoparticle arrays on a quartz substrate. By extinction dispersion measurements and electromagnetic analysis, we can identify three types of collective Mie resonances with Q-factors ∼ 500 in the same nanocylinder arrays, including surface lattice resonances, bound states in the continuum, and quasi-guided modes. Our work paves the way for fundamental research in strong light-matter interactions and the design of highly efficient light-emitting metasurfaces.

Organic Anisotropic Excitonic Optical Nanoantennas.

Optical nanoantennas provide control of light at the nanoscale, which makes them important for diverse areas ranging from photocatalysis and flat metaoptics to sensors and biomolecular tweezing. They have traditionally been limited to metallic and dielectric nanostructures that sustain plasmonic and Mie resonances, respectively. More recently, nanostructures of organic J‐aggregate excitonic materials have been proposed capable of also supporting nanooptical resonances, although their advance has been hampered from difficulty in nanostructuring. Here, the authors present the realization of organic J‐aggregate excitonic nanostructures, using nanocylinder arrays as model system. Extinction spectra show that they can sustain both plasmon‐like resonances and dielectric resonances, owing to the material providing negative and large positive permittivity regions at the different sides of its exciton resonance. Furthermore, it is found that the material is highly anisotropic, leading to hyperbolic and elliptic permittivity regions. Nearfield analysis using optical simulation reveals that the nanostructures therefore support hyperbolic localized surface exciton resonances and elliptic Mie resonances, neither of which has been previously demonstrated for this type of material. The anisotropic nanostructures form a new type of optical nanoantennas, which combined with the presented fabrication process opens up for applications such as fully organic excitonic metasurfaces.

Optical properties and far field radiation of periodic nanostructures fed by an optical waveguide for applications in fluorescence and Raman scattering

Various systems based on nanostructures built on optical waveguides have recently appeared in literature, since this configuration guarantees an efficient optical feeding to nano-elements and/or the possibility to manipulate guided signals. In this work, we present the analysis of the optical scattering properties of such type of structures, more specifically a periodic array of Au nano-cylinders or nano-domes fabricated upon an ion-exchanged waveguide, an integrated system considered for fluoroscopy and Raman spectroscopy. Absorption, scattering and extinction were calculated by means of Finite Difference Time Domain (FDTD) simulations and Scattering Theory. We took advantage of some particular adaptations to apply the classical scattering theory to this context, and used it to extract the far-field radiation pattern. We show that the rectangular periodicity allows to obtain highly collimated beams and negligible irradiation in a wide angle range, which enables the possibility to steer away the undesirable excitation signals from the detectors, avoiding a mixing with emitted photons from molecules. Our analysis suggests that, in the context of this setup and applications, the modeling of the nanostructures, which aims at the tuning of the plasmonic enhancement of the emission, can be relatively separated from the definition of spatial filtering through the periodic array. Our results add new considerations to the list of potentialities of this configuration for the development of efficient integrated surface enhanced spectroscopic setups.

Synergetic effects of a front ITO nanocylinder array and a back square Al array to enhance light absorption for organic solar cells.

Efficient light management is critical to obtain high performance for organic solar cells (OSCs), which aims to solve the contradiction between limited carrier extraction and light absorption for the normally employed photoactive layers generally having both short exciton diffusion lengths and low extinction coefficients. In this study, we introduce a simple and efficient light management structure consisting of a front indium tin oxide nanocylinder (ITO-NC) array and a back square Al array. Thanks to the synergetic effects of antireflection and light scattering induced by the ITO-NC array, together with the secondary scattering and localized surface plasmon resonance because of the square Al array, remarkably enhanced light absorption in a broad spectral range can be achieved. Taking the most investigated photoactive layer of the P3HT:PC61BM blend as an example, simulation results reveal that, compared with the planar control device of the ITO/PEDOT:PSS/P3HT:PC61BM(80nm)/ZnO/Al, the short-circuit current density and power conversion efficiency can be enhanced by 36.58% and 38.38% after incorporating the light management structure with the optimal structural parameters. Furthermore, good omnidirectional light management can be achieved for the proposed device structure. Given the excellent performance and simple structure, we believe that this study would provide a meaningful exploration of developing light management structures applicable for thin film-based optoelectronic devices.

Plasmonic Lasing in Lossy Nanocylinder Arrays Under Optical Pumping

Plasmonic Lasing in Lossy Nanocylinder Arrays Under Optical Pumping

Two-dimensional array of iron-garnet nanocylinders supporting localized and lattice modes for the broadband boosted magneto-optics

Abstract We demonstrate a novel all-dielectric magnetophotonic structure that consists of two-dimensional arrays of bismuth substituted iron-garnet nanocylinders supporting both localized (Fabry–Perot-like) and lattice (guided-like) optical modes. Simultaneous excitation of the two kinds of modes provides a significant enhancement of the Faraday effect by 3 times and transverse magneto-optical Kerr effect by an order of magnitude compared to the smooth magnetic film of the same effective thickness. Both magneto-optical effects are boosted in wide spectral and angular ranges making the nanocylinder array magnetic dielectric structures promising for applications with short and tightly focused laser pulses.

Perfect absorption in free-standing GaAs nanocylinder arrays by degenerate critical coupling

Enhancing absorption in optically thin semiconductors is the key in the development of high-performance optical and optoelectronic devices. In this paper, we resort to the concept of degenerate critical coupling and design an ultra-thin semiconductor absorber composed of free-standing GaAs nanocylinder arrays in the near infrared. The numerical results show that perfect absorption can be achieved through overlapping two Mie modes with opposite symmetry, with each mode contributing a theoretical maximum of 50% in their respective critical coupling state. The absorption also shows the polarization-independent and angle-insensitive robustness. This work, together with the design concept, opens up great opportunities for the realization of high-efficiency semiconductor devices, including optical emitters, modulators, detectors, and sensors.

SERS fluctuations of NAD molecules adsorbed on arrays of Au nanocylinders

Detection of a single molecule is a highly fluctuating event in surface-enhanced Raman scattering (SERS) measurements. Explaining these dynamic blinking events remains a challenge. To investigate this fluctuating behavior, we manufactured Au nanocylinder arrays. A monolayer of nicotinamide adenine dinucleotide (NAD) on the nanocylinder array exhibited intense and fluctuating Raman lines. Persistent Raman lines were not observed over time. These fluctuations were discussed within the dynamic back-action parametric interaction between the plasmon mode and vibrational modes. The results suggest that the highly efficient SERS structure promotes the formation and destruction of protuberances smaller than 2 nm at random on the nanocylinder surface.

Large-area all-dielectric metasurface fabricated by an anodized aluminum oxide template

Transmissive metasurfaces formed by high-index dielectric materials have received great attention due to its potential in holograms, deflectors, beam converters, and flat lenses. However, a key challenge of all-dielectric metasurfaces is the limited scale and high cost in fabrication, such as electron beam lithography (EBL) and focused ion beam (FIB) lithography. In this paper, for the first time to our knowledge, an anodized aluminum oxide (AAO) template is combined with titanium dioxide (TiO2) metasurface fabrication with advantages of large area (>2cm2) and low cost. Using the ordered anodized aluminum oxide (AAO) as an evaporation mask, a TiO2 nanocylinder array is deposited through the AAO mask onto the SiO2 substrate. Electric and magnetic dipole resonances of TiO2 metasurface appear in the visible spectrum. Furthermore, we demonstrate the interaction of the CsPbBr1.5I1.5 quantum dot (QD) emission with magnetic dipole (MD) resonance of TiO2 metasurface. Our results reveal that the metasurface exhibits remarkable photoluminescence (PL) enhancement of 25%. Up to now, a TiO2 metasurface with 2.25-cm2-large area using AAO template method has never been attempted. Different from the metasurfaces fabricated by FIB and EBL, our method offers great ease for large-area metasurface fabrication, which is convenient for metasurface researchers and avoids costly facilities.

On-off near-infrared absorbance based on thermal-responsive plasmonic coupling in vanadium dioxide arrays for thermochromic windows.

Vanadium dioxide (VO2) emerges as an attractive plasmonic material due to its unique reversible thermal-responsive phase transition and the promising application in energy-saving smart windows. Here, by optimizing the geometry of VO2 nano-cylinder arrays, we demonstrate a significant performance enhancement for energy-efficient thermochromic windows. Such a performance enhancement relies on the on-off behavior of plasmonic resonance in the extremely high packing density of VO2 nano-cylinder arrays. Different from the typical plasmonic material, silver, VO2 nano-cylinders are characterized to have strong absorbance in near-infrared spectrum with significantly weaker plasmonic coupling to their neighbors, making them suitable to be arranged with a high packing density. The VO2 nano-cylinder arrays exhibit a 160% luminous transmittance increment, comparing to a flat film with the same solar modulation of ∼10%. The work provides a better understanding of the plasmonic behavior on phase-change VO2 and an efficient method to enhance smart window performance.

Strong coupling between in-plane photonic modes and out-of-plane plasmonic modes in 2D metal–dielectric–metal nanocylinder arrays

Arrays of metal–dielectric–metal (MDM) multilayer nanostructure can support various kinds of plasmonic modes including in-plane (IP) localized/delocalized surface plasmons or lattice resonances, photonic waves, as well as out-of-plane (OP) plasmon modes. Hybridization between different modes offers rich physics such as lasing, sub- and super-radiant modes, and efficient light absorption. While interplays between different sets of in-plane modes have been intensively investigated, the interaction between in-plane and out-of-plane modes is rarely explored. Here, we propose a MDM nanostructure with 2D nanocylinder array and study in detail the strong coupling between the in-plane photonic modes at the dielectric layer and the out-of-plane plasmon modes excited at the cylinder sidewalls. We demonstrate the strong coupling between the localized second-order IP mode and the first-order OP mode with a Rabi splitting up to 250 meV in the near-infrared region. A new IP mode arising from the radiative field can induce another kind of strong coupling with OP modes as the cylinder radius is larger than 98 nm. The underlying physics within this plasmon–photon system is quantitatively revealed by the coupled oscillator model and calculated E-field distribution. The proposed MDM system provides a good platform for investigating multimode coupling and nano-optics devices.

Formation of Perpendicularly Aligned Sub-10 nm Nanocylinders in Poly(N-dodecylacrylamide-b-ethylene glycol) Block Copolymer Films by Hierarchical Phase Separation

Thin polymer films with perpendicularly aligned nanocylinder arrays were fabricated from block copolymers of poly(N-dodecylacrylamide) and poly(ethylene glycol) (pDDA-b-PEG). Reversible addition–fr...