Ag Gratings Research Articles

Bilateral passive thermal management for dynamical temperature regulation

Space heating and cooling of buildings account for ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim $$\\end{document} 30% of energy consumed globally. As a result, efforts to reduce the carbon footprint associated with building temperature regulation are crucial to achieving sustainability goals. Passive radiative cooling and sun heating are two promising innovations that can help reduce the energy consumption associated with building temperature regulation. However, these methods are constrained by factors such as climate zones and seasonal changes. In this work, we demonstrate numerically that bilateral photonic metamaterials enabled by vanadium dioxide (VO2) nanoparticles embedded into polyethylene nanogratings can achieve dynamically modulate solar absorptance at one side in winter and achieve radiative cooling on another side. In cold weather, the solar absorptance of this metastructure can change from 0.93 to 0.2 at a critical temperature when VO2 changes from a metallic to an insulating state. This metastructure consists of broadband transparent polyethylene (PE) gratings on the reflective silver (Ag) gratings with the same period and filling ratio. These gratings are deposited on top of the Polydimethylsiloxane (PDMS) thin film. The VO2 nanoparticles enable dynamic solar absorptance modulation for winter space heating, while the PDMS with strong infrared emittance derived from molecular vibrations over the atmospheric window for summer radiative cooling. Temperature response simulations validate that this bilateral design achieves 6 °C subambient temperature drop at noontime in the summer and stabilizes its temperature around 22 °C during the daytime in the winter. This passive dynamical thermal regulation technique can be deployed for energy-saving targets of buildings, vehicles, and greenhouses in areas with large temperature fluctuations.

Optical transparent metamaterial with multi-band compatible camouflage based on inverse design.

Infrared (IR) thermal camouflage and management are deeply desirable in the field of military and astronomy. While IR compatible with laser camouflage technology is extensively studied to counter modern detection systems, most existing strategies for visible light camouflage focus on color matching, which is not suitable for scenarios requiring transparency. In this work, we propose an optically transparent metamaterial with multi-band compatible camouflage capability based on the inverse design. The metamaterial consists of Ag grating, Si3N4 dielectric spacer layer, Ag reflection layer, and Si3N4 anti-reflective layer. An ideal multi-band compatible spectrum is involved in the inverse design algorithm. Calculated results demonstrate high transmittance (T0.38-0.78µm = 0.70) in the visible region, low reflectance (R1.55µm = 0.01) in laser working wavelength, high reflectance (R3-5µm = 0.86 and R8-14µm = 0.92) in the dual-band atmospheric window, and high emissivity (ɛ5-8µm = 0.61) for the non-atmospheric window. The radiative heat flux in the detected band is 31W/m2 and 201W/m2 respectively. Furthermore, the incident and polarized insensitivity of the proposed metamaterial supports applicability for practical situations. This work, emphasizes an effective strategy for conducting optically transparent design with compatible IR-laser camouflage as well as radiative cooling properties by an automated design approach.

Plasmonically coupled semiconductor quantum dots for efficient hydrogen photoelectrocatalysis

Photocatalytic water splitting has attracted significant attention as a low-cost, clean, and green method for the conversion of solar energy into hydrogen, highlighting its potential to solve energy and environmental problems. In this work, we report the coupling of a plasmonic resonator with semiconductor quantum dots (QDs) for enhancement in photoelectrocatalytic water splitting toward hydrogen (H2) production. Specifically, cadmium selenide (CdSe) QDs were deposited on silver nano-gratings (Ag gratings). Plasmonic enhancement was observed in the absorption/emission of QDs using our angle-resolved steady-state optical spectroscopy. Furthermore, angle-resolved absorption spectra helped us to optimize the illumination conditions for resonant excitation using a setup for photoelectrochemical (PEC) experiments. Under the resonant pump, the emission of the QDs has been plasmonically enhanced with a Purcell factor (FP) of ∼1.5. Our numerical simulation revealed a strong near-field enhancement due to the excitation of surface plasmon resonances, contributing to FP. A similar enhancement order in the PEC experiments was also observed under resonant pump conditions, indicating the contribution of plasmon resonances to the enhanced photoelectrocatalysis. Switching the excitation's polarization further reinforces this, resulting in an enhanced photocurrent under p-polarization. These findings provide a proof of concept, thus laying the foundation for a practical device for efficient solar-to-H2 conversion.

Angle-resolved and time-resolved spectroscopic study on large-area silver gratings fabricated via optical interference lithography

Plasmonic resonators, which can enhance the near-field due to plasmon excitation, have attracted extensive research interest due to their significant potential in photodetection, photocatalysis, photovoltaics, and other applications. Here, we experimentally present spectroscopic results of plasmonic resonances on large-area nanoscale silver (Ag) gratings, fabricated by optical interference lithography based on angle-resolved optical absorption spectroscopy and femtosecond transient absorption spectroscopy (TAS). Specifically, we have measured plasmon resonances as a function of azimuthal angles and detection angles under p- and s-polarization. TAS reveals the non-radiative decay of plasmon resonances by transferring energy to nearby species, including exciting plasmonic hot electrons, which can be harvested by coupled semiconductors through a metal-semiconductor Schottky barrier. Our numerical simulation provides insight into the near-field analysis and quantifies the density of plasmonic hot electrons excited in our Ag-gratings.

Multidimensional structural coloration from hierarchically designed plasmonic structures

We propose a photonic strategy for multidimensional structural coloration that responds to varying illumination conditions. Both theoretical and experimental results verified that the combination of a metal/dielectric/metal cavity with a one-dimensional (1D) metal grating can increase the degree of freedom of structural coloration. We fabricated Ag/MgF2/Ag cavities coupled to 1D Ag gratings (pitches of 400, 570, and 800 nm) and obtained their photonic band dispersions (i.e., angle-resolved reflectance spectra) to unravel their mode characteristics. The 1D Ag grating and Ag/MgF2/Ag cavity induced surface plasmon polariton (SPP) and Fabry–Perot cavity modes, respectively. Notably, only a cavity mode emerged in the s-polarization and gradually blueshifted with increasing angle, whereas in the p-polarization, both SPP and cavity modes appeared and shifted oppositely with changes in the angle, leading to intricate color patterns at different wavelengths, angles, and polarizations. To further understand the effect of each mode upon structural coloration, we obtained the distribution of electric field intensity using rigorous coupled-wave analysis simulation, which identified multiple photonic bands in the p-polarization as various SPP-mediated hybrid modes.

Beam manipulation for quantum dot light-emitting diode with an Ag grating and a phase-gradient metasurface.

The quantum dot (QD) light-emitting diode (LED) is a robust scheme for single photon source. However, the spontaneous emission of a QD LED has arbitrary directions and polarizations, which is disadvantage for photon collection and manipulation. We propose a QD LED integrated with an Ag grating and a phase-gradient metasurface. The circular patterned Ag grating is adopted to collimate the emission beam with right phase and improve its spatial coherence, therefore a phase-gradient metasurface can work for beam manipulation. The 10°, 20°, and 30° angle deflection as well as doughnut-pattern generation are demonstrated by numerical simulation. A small metasurface with the width of 6 µm can provide a collection efficiency of 25.9% at the deflection angle of 10°. Furthermore, only one single QD can be selected from a QD assembly with a low-density.

Enhanced Reflection of GaAs Nanowire Laser Using Short-Period, Symmetric Double Metal Grating Reflectors.

Owing to the high contrast of the refractive indices at the end facets of a nanowire, lasing emission can be achieved in an individual nanowire without external, reflected feedback. However, the reflection provided by the end facet is not high enough to lower the threshold gain, especially for nanowires with smaller diameters. This work proposes a novel structure of nanowire laser partially sandwiched in double Ag gratings. Compared to a nanowire with a single metal grating or without a grating, the parallel double metal gratings play the reflector role with higher reflectivity to enhance the round-trip feedback and reduce the threshold gain. The reflective properties are calculated using the finite elements method. Simulation results show that a high reflectivity of more than 90% can be achieved when the number of periods is more than 8. The reflectivity of double gratings is 2.4 times larger than that of the nanowire end facet for large nanowire diameters. When the nanowire has a small diameter of 150 nm, the reflectivity of double gratings is 17 times larger than that of the nanowire end facet. Compared to a single grating, the reflective performance of double gratings is much better. Owing to the highly reflective properties of the double gratings, nanowires partially sandwiched in the double gratings can realize lasing emission at a very low threshold gain, and the period of the grating can be very short to benefit on-chip interconnection systems.

Ultrafast modulation of valley dynamics in multiple WS2\u2009\u2212\u2009Ag gratings strong coupling system

Strong light-matter interactions in two-dimensional transition metal dichalcogenides (TMDCs) with robust spin-valley degrees of freedom open up the prospect of valleytronic devices. A thorough understanding on the dynamics of the valley polarizations in the strong coupling regime is urgently required. Here, multiple polarized TMDCs-SPPs hybrid systems were constructed by combining monolayer WS2 flakes to linear, circular, and spiral Ag gratings, resulting in linear and circular polarized modulation on the coherent hybrid states, respectively. Particularly, valley polaritons can be tailored asymmetrically by chiral strong coupling regime. Furthermore, the dynamics of the polarized polaritons were directly analyzed by transient absorption (TA) measurement. Both of the linear and circular polarization difference in the TA spectra can be retained for a remarkable long time, leading to a polarized PL even at room temperature. More importantly, in the chiral strong coupled WS2-spiral Ag grating devices, the mechanism of the asymmetrical valley-polarized PL (p σ+ = 14.9% and p σ- = 10.8%) is proved by the opposite valley polarization dynamics in the circularly polarized TA spectra. The multiple polarization modulation in monolayer TMDCs-SPPs strong coupling devices could provide a viable route toward multiple polarization polaritonic devices.

Surface-Enhanced Raman Scattering on Silver Sinusoidal Nanograting: Impact of Interactions of Grating-Coupled Surface Plasmon Polaritons

In this study, we reported a silver sinusoidal nanograting used in microchannels, forming H2O/Ag/NOA/SiO2 heterostructure and studied the impact of interactions of grating-coupled surface plasmon polaritons (SPPs) on surface-enhanced Raman scattering (SERS). There are two modes of \(E_{x} (z)\) in the Ag grating, namely, the anti-symmetric mode (AM) at the high SPP resonance frequency and the symmetric mode (SM) at the low-SPP resonance frequency. When the refractive indices of the upper and lower dielectrics of the thin Ag grating are close, there will be a strong coupling between the SPPs of the two interfaces, which will increase the transmittance but reduce the maximum electromagnetic (EM) of the SERS substrate. Additionally, the thinner the Ag grating, the stronger the coupling, accompanied by the frequency shift of the two coupling modes. Our experimental results are supported by FDTD calculations, which have corroborated the importance of the interactions of grating-coupled SPPs in the design of SERS substrate.

High-Performance Laterally Oriented Nanowire Solar Cells with Ag Gratings

A laterally oriented GaAs p-i-n nanowire solar cell with Ag gratings is proposed and studied via coupled three-dimensional optoelectronic simulations. The results show that the gratings significantly enhance the absorption of nanowire for both TM and TE polarized light due to the combined effect of grating diffraction, excitation of plasmon polaritons, and suppression of carrier recombination. At an optimal grating period, the absorption at 650–800 nm, which is an absorption trough for pure nanowire, is substantially enhanced, raising the conversion efficiency from 8.7% to 14.7%. Moreover, the gratings enhance the weak absorption at long wavelengths and extend the absorption cutoff wavelength for ultrathin nanowires, yielding a remarkable efficiency of 13.3% for the NW with a small diameter of 90 nm, 2.6 times that without gratings. This work may pave the way toward the development of ultrathin high-efficiency nanoscale solar cells.

Ultra-Narrow SPP Generation from Ag Grating.

In this study, we investigate the potential of one-dimensional plasmonic grating structures to serve as a platform for, e.g., sensitive refractive index sensing. This is achieved by comparing numerical simulations to experimental results with respect to the excitation of surface plasmon polaritons (SPPs) in the mid-infrared region. The samples, silver-coated poly-silicon gratings, cover different grating depths in the range of 50 nm–375 nm. This variation of the depth, at a fixed grating geometry, allows the active tuning of the bandwidth of the SPP resonance according to the requirements of particular applications. The experimental setup employs a tunable quantum cascade laser (QCL) and allows the retrieval of angle-resolved experimental wavelength spectra to characterize the wavelength and angle dependence of the SPP resonance of the specular reflectance. The experimental results are in good agreement with the simulations. As a tendency, shallower gratings reveal narrower SPP resonances in reflection. In particular, we report on 2.9 nm full width at half maximum (FWHM) at a wavelength of 4.12 µm and a signal attenuation of . According to a numerical investigation with respect to a change of the refractive index of the dielectric above the grating structure, a spectral shift of can be expected, which translates to a figure of merit (FOM) of about 1421 . The fabrication of the suggested structures is performed on eight-inch silicon substrates, entirely accomplished within an industrial fabrication environment using standard microfabrication processes. This in turn represents a decisive step towards plasmonic sensor technologies suitable for semiconductor mass-production.

Nanoscale flexible Ag grating/AuNPs self-assembly hybrid for ultra-sensitive sensors

In this paper, Au nanoparticles (AuNPs) are prepared using wet chemical reduction transfer of dense AuNPs film by self-assembly to the surface of Ag grating, which is inverted from the inner DVD after evaporation. The Ag grating/AuNPs self-assembly hybrid substrate commonly used in surface-enhanced Raman scattering (SERS) research is produced. The coupling effect between AuNP-AuNP and AuNPs-Ag slugs can evidently enhance the local electric field. Experimental results show that the hybrid SERS substrate can detect 10−9 M Rh6G, and the enhancement factor reaches 4.4 × 105. This small, cheap hybrid substrate has enormous potential in the field of SERS sensing.

Tunable narrowband metamaterial perfect absorber with single absorption peak

A tunable narrowband metamaterial perfect absorber (NMPA) with single absorption peak at both normal incidence and oblique incidence is proposed. The spectral responses of the designed NMPA are calculated using finite-difference time-domain (FDTD) method. By using an Ag guided-mode resonance grating layer with great fill factor, the designed NMPA exhibits single resonance peak, which is converted to heat due to the strong surface plasmon resonance around the Ag grating and the Ag substrate. An NMPA sample is fabricated and the spectral responses are measured to verify the theoretical results. The experimental results are consistent with the theoretical ones.

Coupling of quantum-well emission to waveguide–plasmon polaritons in rolled-up microtubes

We study the coupling of GaAs quantum wells to waveguide–plasmon polaritons supported by a thin InAlGaAs-based slab waveguide and a Ag grating. The hybrid photon–plasmon modes are excited in a freestanding emitter–waveguide–plasmon structure realized by rolling-up strained InAlGaAs-based layers and nanopatterned Ag structures. By varying the grating’s bar width, we tune the plasmonic resonance of the system. We observe by means of spatially, spectrally, and temporally resolved photoluminescence measurements, a coupling of the quantum-well emission to the waveguide–plasmon system for a specific grating’s bar width. Supported by finite-element simulations, we can assign the coupling to the excitation of a waveguide–plasmon polariton.

Design of a Surface Plasmon Resonance-Enhanced ZnO Ultraviolet Photodetector Based on a Sub-wavelength Metal Grating Covered with a High-Refractive-Index Medium

To realize a surface plasmon resonance-enhanced zinc oxide (ZnO) ultraviolet photodetector based on a sub-wavelength metal grating, we take advantage of the sensitivity of the resonance condition of a sub-wavelength metal grating to the refractive index of the surrounding medium. We theoretically design a sub-wavelength Ag grating covered with a high-refractive-index medium layer and apply it to a ZnO ultraviolet photodetector. By optimizing the parameters (angle of incidence, grating period, grating spacing, grating thickness, high-refractive-index medium layer thickness, refractive index of the covering), the optical field is localized at the interface of the sub-wavelength Ag grating and the ZnO thin film; that is, surface plasmon resonance is realized within the device. Compared with the device without a high-refractive-index medium layer, the maximum absorption enhancement factor of the designed device can reach up to 108. This work will provide theoretical guidance to realize a surface plasmon resonance-enhanced ZnO ultraviolet photodetector with a sub-wavelength metal grating.

Surface plasmon based 1D-grating device for efficient sensing using noble metals

This study presents the design and optimization of device with 1D nanostructured grating modeled on gold (Au), silver (Ag) and copper (Cu) for sensing a minor variation in refractive index (RI). This small change in the adjacent media to metallic grating is detected quite effectively using the unique characteristic of the surface plasmon polaritons (SPPs). The electric field (E-field) of the SPPs penetrates into the nearby media which is very sensitive to slight change in RI. The grating devices has been simulated by using COMSOL Multiphysics 5.3a with periodicity 700 nm, film thickness 50 nm and optimum slit width 300 nm in correspondence with fundamental plasmonic mode. The 0th order transmission spectra have been extracted from each grating device by illuminating (through the substrate side) with p-polarized light at normal incidence. The change in RI of analyte studied to have a significant effect on the resonance wavelength. The sensitivity has been calculated as 700, 731 and 722 nm/RIU for Au, Ag and Cu grating devices respectively which is remarkable. The stability and quick sensing of Au-device make it suitable for application besides some other deficiencies (e.g. slightly less sensitivity as compared to Ag) which should be compromised. Near field analysis has been performed to apprehend the underlying physics connected with each resonance. The highest value of electric and magnetic fields (E-field and H-field) are obtained in the case of Au grating indicating the most efficient excitation of SPPs. This confirms the reasoning behind the efficient sensitivity of Au grating device and finds applications in medicine.

Study on the broad spectral absorption property of monolayer MoS2 based on hybrid structures

The poor light absorption property in monolayer MoS2 limits its applications such as in photonics, optoelectronics and energy utilizations. Here, we propose a hybrid structure, consisting of a Fabry-Perot (F-P) cavity, plasmonic silver (Ag) gratings and an Ag/Al2O3/Al gap-plasmon resonator, to improve the light absorption of monolayer MoS2 in the wavelength region from 400 to 700 nm. We theoretically investigate the spectral absorption of monolayer MoS2 placed on top of different hybrid structures by FDTD simulations. The simulation results show that monolayer MoS2 in the MoS2/Ag grating/Al2O3/Al structure can absorb about 27.6% of the incident solar light integrated from 400 to 700 nm. The absorption peaks can be tuned in a wide spectral range by changing the geometrical parameters of the structure. We further design Ag gratings with interlaced stripes to enhance the absorption from 500 to 700 nm. The proposed structures in this study also can be applied to other two-dimensional semiconductors to achieve strong absorption in the visible spectral region.

Light-trapping schemes for silicon thin-film solar cells via super-quadratic subwavelength gratings.

We systematically investigate the light-trapping schemes of crystalline silicon thin-film solar cells (TFSCs) for three common grating layouts via one-dimensional super-quadratic subwavelength gratings. The effects of antireflective coating, absorber layer thickness, and grating geometry on the light-trapping performance of TFSCs are numerically studied using the finite-difference time-domain method. The results suggest that the conformal aluminum-doped zinc oxide (AZO) coatings have better optical properties than the plane AZO coatings. For the case of only top Si gratings, the grating geometry of degree $n={4}$n=4 can achieve a good trade-off between the shape-dependent light-trapping and antireflection properties, showing the best light-trapping effect; for the case of only bottom Ag gratings, the optical performance of TFSCs is significantly degraded as the degree $n$n increases from $n={1}$n=1 to $n\to\infty$n→∞. The above findings are analyzed and demonstrated in detail from the optical and electrical perspectives, and they can be utilized to guide the design of light-trapping structures for TFSCs.

Dual broadband infrared absorptance enhanced by magnetic polaritons using graphene-covered compound metal gratings.

A dual broadband perfect absorber based on a graphene-covered compound silver (Ag) grating structure working in the infrared (0.8-2.1 µm) regime is proposed and investigated numerically. Two distinct absorption peaks approximately 1.0 are achieved by the excitation of magnetic polaritons over a large range of incident angles from 0 to 70 degrees. The physics underlying the structure is also explained by computing interactions of electromagnetic fields with the graphene and the Ag grating. In addition, it has shown that the absorption peaks can be tuned by changing geometric parameters of the structure; however, their spectral shape and absorption remain unchanged. Furthermore, the proposed compound grating with a graphene overlay provides potential applications for infrared absorbing devices.

Narrow-band and high-contrast asymmetric transmission based on metal-metal-metal asymmetric gratings

A narrow-band and high-contrast asymmetric transmission (AT) device based on metal-metal-metal (M-M-M) asymmetric grating structure is proposed and investigated. Significantly distinct from previous reports, the upper and lower metallic silver (Ag) gratings are connected by a very thin metallic Ag film, without any dielectric spacer layer or subwavelength slit. Under forward incidence, the M-M-M structure supports efficient surface plasmon polaritons (SPPs) excitation and tunneling, more importantly, it promotes direct and thus high-efficiency SPPs decoupling, enabling high forward transmittance. While under backward incidence, the M-M-M structure offers not only high reflection by the Ag film but also a strong near-field coupling effect between the upper and lower gratings, which further suppresses backward transmittance, leading to near-zero backward transmittance. In addition, the M-M-M structure is optimized for narrow-band operation by employing grating groove depth effect and multiple interference effect. Numerical simulation results demonstrate that high-performance AT with high-quality factor (Q≈91), narrow-bandwidth (6.7 nm) and high contrast ratio is achieved, with forward transmittance of 0.72 and backward transmittance of 0.0015 at visible light (610 nm). Our work provides an alternative and simple way to high-performance AT devices.