Periodic Hole Arrays Research Articles

On the extraordinary optical transmission in parallel plate waveguides for non-TEM modes.

Extraordinary transmission has been recently measured in a parallel plate waveguide (PPWG) through a metal strip with a patterned 1-D periodic array of circular holes, the metal strip being embedded inside the PPWG. Wood's anomaly and the extraordinary transmission peak (EOT) were detected for transverse electric (TE) mode excitation at frequencies higher than those found for TEM mode excitation. In this paper we provide an explanation for this frequency shift by decomposing the problem of a TE mode impinging on the 1-D array of holes into two problems of plane waves impinging obliquely on 2-D periodic arrays of holes. By then solving the integral equation for the electric field on the surface of the holes, the origin of the frequency shift is proved both mathematically and physically in terms of the symmetries present in the system.

Extraordinary optical transmission of periodic array of subwavelength holes within titanium nitride thin film

We focused on the optical properties of square array of subwavelength holes created within a titanium nitride (TiN) thin film. The TiN layer was placed on top of the dielectric layer as a surface plasmonic system originated from an intermetallic–dielectric arrangement. The finite-difference time-domain method was used via an Optiwave package to simulate periodic array of square and circular holes within the TiN layer. The effect of geometrical and material parameters such as periodic constant (a), size (S), shape of the holes, and the electric permittivity of the dielectric substrate has been investigated. An extraordinary optical transmission was observed in comparison with the nonhole system. It was shown that the wavelength of plasmonic modes, as a characteristic feature of the system, was affected by changing the periodic constant and electric permittivity. Meanwhile, changing the size as well as the shape of the holes did not affect the position of the peaks. These results are in agreement with the characteristic equation for plasmonic structure, which relates the surface plasmon wavelength (λsp) to the geometrical and material parameters of the system. The intensity of excited peaks was explained by distribution of the z-component of the electric field obtained from simulation, which illustrated the role of the surface plasmon polariton, localized surface plasmon resonance, and waveguide mode in tuning the optical behavior of the system. The results showed that TiN is a promising candidate for replacing metals in a plasmonic application with particular chemical and mechanical features.

Period- and cavity-depth-dependent plasmonic metamaterial perfect absorber at visible frequency: design rule

Plasmonic perfect absorbers are artificially designed metal-dielectric-metal (MDM) structures to realize unity optical absorption (UOA) at the specific spectral wavelength. In the recent past, a variety of structures have been investigated theoretically and experimentally to achieve UOA. However, fabrication of a complex structure often requires sophisticated instruments and skills. A simple structural design may be an alternative solution. An MDM structure consisting of a square array of cylindrical holes in the top layer is proposed, and optical reflection/absorption is studied using 3-D finite-difference time-domain computation to achieve UOA. The structure has three sequential layers: a ground gold plane (100-nm thick) to block the transmission, a spacer layer of typical thickness of 20 nm of constant real value of dielectric permittivity, and a top gold layer structured with periodic square array of cylindrical holes. Numerical results show period- and hole-depth-dependent 100% optical absorption (UOA) at a specific spectral wavelength. A significant influence of hole packing density and refractive index of filled material on the resonant absorption and absorption bandwidth is also observed. Based on the results, a design rule is proposed to achieve UOA at an arbitrarily chosen spectral wavelength in the visible range.

Periodic Arrays of Phosphorene Nanopores as Antidot Lattices with Tunable Properties.

A tunable band gap in phosphorene extends its applicability in nanoelectronic and optoelectronic applications. Here, we propose to tune the band gap in phosphorene by patterning antidot lattices, which are periodic arrays of holes or nanopores etched in the material, and by exploiting quantum confinement in the corresponding nanoconstrictions. We fabricated antidot lattices with radii down to 13 nm in few-layer black phosphorus flakes protected by an oxide layer and observed suppression of the in-plane phonon modes relative to the unmodified material via Raman spectroscopy. In contrast to graphene antidots, the Raman peak positions in few-layer BP antidots are unchanged, in agreement with predicted power spectra. We also use DFT calculations to predict the electronic properties of phosphorene antidot lattices and observe a band gap scaling consistent with quantum confinement effects. Deviations are attributed primarily to self-passivating edge morphologies, where each phosphorus atom has the same number of bonds per atom as the pristine material so that no dopants can saturate dangling bonds. Quantum confinement is stronger for the zigzag edge nanoconstrictions between the holes as compared to those with armchair edges, resulting in a roughly bimodal band gap distribution. Interestingly, in two of the antidot structures an unreported self-passivating reconstruction of the zigzag edge endows the systems with a metallic component. The experimental demonstration of antidots and the theoretical results provide motivation to further scale down nanofabrication of antidots in the few-nanometer size regime, where quantum confinement is particularly important.

Enhancing Near-Field Radiative Heat Transfer with Si-based Metasurfaces.

We demonstrate in this work that the use of metasurfaces provides a viable strategy to largely tune and enhance near-field radiative heat transfer between extended structures. In particular, using a rigorous coupled wave analysis, we predict that Si-based metasurfaces featuring two-dimensional periodic arrays of holes can exhibit a room-temperature near-field radiative heat conductance much larger than any unstructured material to date. We show that this enhancement, which takes place in a broad range of separations, relies on the possibility to largely tune the properties of the surface plasmon polaritons that dominate the radiative heat transfer in the near-field regime.

Electromagnetic local density of states in graphene-covered porous silicon carbide

Surface phonon polariton supported by silicon carbide (SiC) can be strongly coupled with graphene plasmon in the graphene-covered SiC bulk. The spectrum of the electromagnetic local density of states exhibits two peaks whose positions can be tuned by the chemical potential of graphene. In this work, we study the electromagnetic local density of states in the proximity of a graphene-covered SiC with periodic hole arrays. The well-known peak from the coupling of surface polariton supported by SiC and graphene plasmon splits into two. With increased volume ratio of holes, one of the split peak shifts towards high frequencies, whereas the other moves towards low frequencies. The dependence of split-peak positions on the chemical potential and permittivity of filling materials in the holes are also investigated. This study offers another method of modulating the electromagnetic local density of states.

The Use of Phononic Crystals to Design Piezoelectric Power Transducers.

It was recently proposed that the lateral resonances around the working resonance band of ultrasonic piezoelectric sandwich transducers can be stopped by a periodic array of circular holes drilled along the main propagation direction (a phononic crystal). In this work, the performance of different transducer designs made with this procedure is tested using laser vibrometry, electric impedance tests and finite element models (FEM). It is shown that in terms of mechanical vibration amplitude and acoustic efficiency, the best design for physiotherapy applications is when both, the piezoceramic and an aluminum capsule are phononic structures. The procedure described here can be applied to the design of power ultrasonic devices, physiotherapy transducers and other external medical power ultrasound applications where piston-like vibration in a narrow band is required.

Dynamic transition from Mott-like to metal-like state of the vortex lattice in a superconducting film with a periodic array of holes

We show that under an a.c. magnetic field excitation the vortex lattice in a superconductor with periodic array of holes can undergo a transition from a Mott-like state where each vortex is localized in a hole, to a metal-like state where the vortices get delocalized. The vortex dynamics is studied through the magnetic shielding response which is measured using a low frequency two-coil mutual inductance technique on a disordered superconducting NbN film having periodic array of holes. We observe that the shielding response of the vortex state is strongly dependent on the amplitude of the a.c. magnetic excitation. At low amplitude the shielding response varies smoothly with excitation amplitude, corresponding to elastic deformation of the vortex lattice. However, above a threshold value of excitation the response shows a series of sharp jumps, signaling the onset of the Mott to metal transition. Quantitative analysis reveals that this is a collective phenomenon which depends on the filling fraction of vortices in the antidot lattice.

周期性孔阵列金属表面附近的局域态密度

周期性孔阵列金属表面附近的局域态密度

Retraction: Effect of localized surface plasmon and surface plasmon polariton modes on properties of metamaterials

We present the effects of localized surface plasmon (LSP) and surface plasmon polariton (SPP) modes on transmission peaks and resonance frequency of a compound structure metamaterial consisting of periodic metallic particle and hole arrays. During simulation, the lateral interval (Lx) between the metal particle and hole arrays is increased but the longitudinal interval (L) remains unchanged. Simulated results indicate that the main transmittance peak is enhanced and the resonant frequency red-shifted when Lx is increased, while the high-frequency transmittance peak is reduced and its resonance frequency is unchanged. We find that the increase in the intensity of SPP modes leads to the variation of the main transmittance peak, and the increase of the intensity of LSP modes results in the reduction of the high-frequency transmittance peak with increasing Lx.

Stress field in a porous material containing periodic arbitrarily-shaped holes with surface tension

In the mechanical analysis of a structure/composite with periodic holes/inhomogeneities based on analytic techniques, the holes/inhomogeneities are usually assumed to be circular. In this paper, we develop an efficient method (based on complex variable techniques) to calculate the surface tension-induced stress field in a porous material containing a periodic array of unidirectional holes of arbitrary shape. In this method, we use conformal mapping and Faber series techniques to address a finite representative unit cell (RUC) consisting of a single arbitrarily-shaped hole with a constant surface tension imposed on the hole’s boundary and periodic deformations imposed on the edge of the RUC. Several numerical examples are presented to verify the accuracy of our method and to study the influence of the shape and volume fraction of the periodic holes on the stress concentration in the structure. We show that the maximum hoop stress around periodic holes of some shapes (such as triangle, pentagon or hexagon) may appear exactly at the point(s) of maximum curvature when the hole volume fraction exceeds a certain value. Moreover, when the hole volume fraction falls below about 7%, it is found that the surface tension-induced stress concentration around periodic holes can be treated approximately as that around a single hole with the same hole shape and size in an infinite plane.

Spectral-distortion-free light extraction from organic light-emitting diodes using nanoscale photonic crystal

Despite their generally good performance, photonic crystal (PC)-based organic light-emitting diodes (OLEDs) encounter a serious spectral distortion problem. In this study, we obtained spectral-distortion-free PC-based OLEDs by lowering the pitch (period of the PC) to less than a half the emission wavelength, using a simple and scalable nanoscale process of laser interference lithography. The demonstrated OLEDs with 200 nm pitch-size nanoscale periodic hole arrays exhibited negligible changes in the Internal Commission on Illumination 1931 color coordinate of Δ (0.0104, 0.0078) and a peak wavelength of Δ0 nm (relative to the reference), while maintaining the function of the internal light extraction layer, manifested as a 23% enhancement of the external quantum efficiency (EQE). The enhancement of the EQE reached 85% after incorporating a micro-lens array. The improved light extraction, spectral-distortion-free characteristic, and excellent color stability over a broad range of viewing angles were successfully derived by performing finite difference time domain simulations.

Optically-rough and physically-flat TCO substrates for superstrate-type thin-film solar cells: sol-gel Zn1−xMgxO coating on nanoimprint patterned glass substrates

Novel optically-rough and physically-flat transparent conductive oxides (TCO) substrates were developed for thin-film solar cells with superstrate configuration. These substrates consist of a widegap Al doped Zn1−xMgxO (AZMO) transparent conductive thin film prepared by sol-gel process and glass substrates with periodic hole array pattern formed by a nanoimprinting technique. These substrates showed low optical absorption, low surface roughness, strong light-diffraction behavior, and moderate sheet resistance, simultaneously. The number of AZMO coating layers and the dimension of the hole feature on the pattern influenced the surface roughness and diffraction behavior of these substrates significantly. A substrate with 40 AZMO coating layers on a hole pattern (diameter=2µm, pitch=2.2µm, and depth=1µm) showed a root-mean-square surface roughness of 5.5nm, a sheet resistance of 34.3Ω/sq, and a haze ratio of 11.2% at the wavelength of 700nm. These TCO substrates enabled hydrogenated amorphous Si single junction solar cells with large open-circuit voltage (Voc=0.92V) and good spectral response through acting as the front electrode. These substrates would enable an efficient light management and the growth of high quality photoactive materials, simultaneously.

Size Effect and Aperture Configuration Dependence of Extraordinary Optical Transmission through Penrose Metal Hole Arrays in the Terahertz Region

SUMMARYExtraordinary optical transmission (EOT) through Penrose metal hole arrays (PMHA) in the terahertz region is investigated numerically by using coupled‐mode analysis. Spectral change of the transmittance is studied at resonant frequencies by increasing the number of holes and comparing the spectra of PMHA and a periodic metal hole arrays (MHA). While the resonant mode of MHA is excited in periodic order along one direction, the resonant mode on PMHA has a complicated shape. It seems that the propagating length of surface wave of PMHA is shorter than that of the MHA. Therefore, when the number of holes is increased, increasing rate of the resonant transmittance through PMHA is smaller than that through MHA. In addition, the transmission spectra for three kinds of generalized PHMA are analyzed numerically. Although the distributions of holes in these PMHA are different from each other in real space, the transmission spectra have almost the same shape. Consequently, the structure given by the aperture configuration of PMHA in reciprocal lattice space has stronger effects on EOT through metal hole arrays, rather than that in real space.

Novel aluminum plasmonic absorber enhanced by extraordinary optical transmission.

We report a theoretical and experimental study on a novel type of aluminum super absorber which exhibits a near perfect absorption based on the surface plasmon resonance in the visible and near-infrared spectrum. The absorber consists of Ag/SiO2/Al triple layers in which the top Al layer is patterned by a periodic nano hole array. The absorption spectrum can be easily controlled by adjusting the structure parameters including the radius of the nano hole and the maximal absorption can reach 99.0% in theory. We completely analyze the SPP and LSP modes supported by the metal-dielectric-metal structure and their contribution to the ultrahigh absorption. On this basis, we find a novel method to enhance the absorption via the simultaneous excitation of SPP at different interfaces theoretically and experimentally. Moreover, for the first time we clarify the EOT caused by the nano hole array can enhance the absorption by experiment, which is not reported in previous works. This kind of absorber can be fabricated by low-cost colloidal sphere lithography and the use of stable Al overcomes the disadvantages brought by the noble metal, which make it a more appropriate candidate for photovoltaics, spectroscopy, photodetectors, sensing, and surface enhanced Raman scattering.

High-Q Fano Resonances in Asymmetric and Symmetric All-Dielectric Metasurfaces

We present high-quality (high-Q) Fano resonances in all-dielectric metasurfaces consisting of a periodic array of air holes on silicon (Si) film, deposited on the top of quartz substrate. With the control of the radius difference Δr and center distance Δd between the air holes, two asymmetric all-dielectric metasurfaces are proposed to achieve extremely high-Q Fano resonances. Numerical method with finite difference time domain and equivalent circuit model is employed to analyse the excitation mechanism of the sharp Fano resonances. It is shown that the high-Q Fano resonances come from the interference of two Fabry-Perot resonances, resulting in an extremely narrow window. Moreover, we also demonstrate that the high-Q Fano resonances can also be realized as electromagnetic wave is obliquely incident on the symmetric all-dielectric metasurface. Finally, we show the high-Q Fano resonances caused by asymmetric configurations can coexist with the Fano resonances in the symmetric configuration induced by oblique incidence. As a result, a tri-band Fano resonance is obtained. It is expected that our results will provide important mechanisms for tuning and switching a wide variety of optical devices such as angular sensors, filters, switches, and modulators.

Bottom-Up Fabrication of Hybrid Plasmonic Sensors: Gold-Capped Hydrogel Microspheres Embedded in Periodic Metal Hole Arrays.

The high potential of bottom-up fabrication strategies for realizing sophisticated optical sensors combining the high sensitivity of a surface plasmon resonance with the exceptional properties of stimuli-responsive hydrogel is demonstrated. The sensor is composed of a periodic hole array in a gold film whose holes are filled with gold-capped poly(N-isoproyl-acrylamide) (polyNIPAM) microspheres. The production of this sensor relies on a pure chemical approach enabling simple, time-efficient, and cost-efficient preparation of sensor platforms covering areas of cm2. The transmission spectrum of this plasmonic sensor shows a strong interaction between propagating surface plasmon polaritons at the metal film surface and localized surface plasmon resonance of the gold cap on top of the polyNIPAM microspheres. Computer simulations support this experimental observation. These interactions lead to distinct changes in the transmission spectrum, which allow for the simultaneous, sensitive optical detection of refractive index changes in the surrounding medium and the swelling state of the embedded polyNIPAM microsphere under the gold cap. The volume of the polyNIPAM microsphere located underneath the gold cap can be changed by certain stimuli such as temperature, pH, ionic strength, and distinct molecules bound to the hydrogel matrix facilitating the detection of analytes which do not change the refractive index of the surrounding medium significantly.

Conversion of the optical orbital angular momentum in a plasmon-assisted second-harmonic generation

We experimentally demonstrate the plasmon-assisted second-harmonic generation of an optical orbital angular momentum (OAM) beam. Because of the shape resonance, the plasmons in a periodic array of rectangular metal holes greatly enhance the nonlinear optical conversion of an OAM state. The OAM conservation (i.e., 2l1 = l2 with l1 and l2 being the OAM numbers of the fundamental and second-harmonic waves, respectively) holds well under our experimental configuration. Our results provide a potential way to realize nonlinear optical manipulation of an OAM mode in a nano-photonic device.

Planar modes free piezoelectric resonators using a phononic crystal with holes

By using the principles behind phononic crystals, a periodic array of circular holes made along the polarization thickness direction of piezoceramic resonators are used to stop the planar resonances around the thickness mode band. In this way, a piezoceramic resonator adequate for operation in the thickness mode with an in phase vibration surface is obtained, independently of its lateral shape. Laser vibrometry, electric impedance tests and finite element models are used to corroborate the performances of different resonators made with this procedure. This method can be useful in power ultrasonic devices, physiotherapy and other external medical power ultrasound applications where piston-like vibration in a narrow band is required.

Experimental demonstration of a dual-band metamaterial absorber

We present the design, simulation and fabrication of a dual-band metamaterial absorber. The designed structure consists of periodic composite metallic holes array and dielectric layer. The availability of absorption enhancement is verified by our measured results. Cavity and electrical resonances lead to these two absorption peaks at λ1=1.8μm and λ2=4.3μm. Effects of structural parameters on absorption and resonant wavelengths have been experimentally surveyed. The average absorption can be increased by optimizing the structural parameters of the designed metamaterial absorber.