Silver Nanograting Research Articles

Holographic silver nanograting formation driven by TE0, TE1, and TE2 mode propagation in an AgCl slab Waveguide: Optical properties and analysis

Holographic silver nanogratings on the surface and within the volume, which have significant potential for data storage applications, are generated in silver chloride (AgCl) waveguides using a single laser beam exposure. This formation process leverages the interference between the polarized incident wave and the TEm modes propagating inside the AgCl waveguide. These plasmonic nanogratings are anisotropic nanostructures, demonstrating intriguing optical traits such as wavelength-specific linear dichroism and birefringence. The observed linear dichroism and birefringence in the holographic silver nanograting can modify the optical rotation and ellipticity of a probe beam traversing this anisotropic medium. Notably, volume holographic nanogratings function as complex nanogratings with a periodicity exceeding that of the incident wavelength. As a result, upon exposure, these complex nanogratings exhibit discernible light diffraction, while the surface holographic nanogratings do not show any diffraction pattern. Additionally, as the AgCl film thickness is increased and more complex nanogratings are formed within the AgCl waveguides, there is a noted reduction in the resulting birefringence.

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.

Relative humidity sensor based on a silver nano-grating made from DVD discs.

A relative humidity sensor based on a silver nano-grating was proposed. By stripping and cleaning commercially available CD and DVD discs, polycarbonate plates with different grating periods are obtained. These plates as templates are coated with a layer of sputtered silver film to form silver nano-gratings, which exhibit refractive index sensing sensitivities of 517nm/RIU and 742.9nm/RIU, respectively. The finite-difference time-domain simulation results conform the excited surface plasmon polariton modes and localized surface plasmon modes on the nano-grating. By spin coating a layer of humidity-sensitive porous silica with optimized thickness, the silver nano-grating shows a relative humidity detection sensitivity of 0.23nm/%RH.

Protein capture and SERS detection on multiwavelength rainbow-trapping width-graded nano-gratings

Surface-enhanced Raman scattering (SERS) substrates with multiwavelength rainbow-trapping properties hold the potential for a one-size-fits-all platform for rapid and multiplexed disease detection. We present the first report on the utilization of rainbow-trapping width-graded nano-gratings, a new class of chirped metamaterials, to detect protein biomarkers. Using cytochrome c (Cc), a charged analyte with inherent difficulty in adsorbing onto sputtered silver films, we investigated methods of binding Cc on the silver nano-grating in order to improve the SERS signal strength at both 532 and 638 nm excitation. Cc was not detectable on the Ag nano-gratings without surface functionalization at 1 μM concentration. Upon charge reversal functionalization of the Ag nano-gratings, 1 μM Cc was detectable albeit not reliably. By further crosslinking 1 μM Cc to the functionalized Ag nano-gratings, the analyte-capture detection scheme greatly improved the SERS signal strength and reliability at both excitation wavelengths and allowed for quantification of their coefficients of variation with values down to 27%.

Photoinduced tunable birefringence and dichroism in silver nanogratings

Silver nanogratings are anisotropic plasmonic nanostructures with potential application in optical components due to their large birefringence and dichroism. We induced linear birefringence and linear dichroism in subwavelength Ag-AgCl films by irradiating with a single low-power linearly polarized laser beam. The laser beam aligns silver nanoparticles in the direction of laser polarization and forms nanograting. We used Stokes parameters to determine linear birefringence and linear dichroism in silver aligned nanostructures. The values of linear dichroism and linear birefringence in silver nanogratings are controllable through manipulating the spatial period of nanogratings. The dispersion characteristic of dichroism and birefringence is also investigated.

Polarization Selective Color Filter Based on Plasmonic Nanograting Embedded Etalon Structures.

In this paper, we propose a polarization-selective color filter that can generate two different color informations simultaneously depending on the polarization direction. The proposed color filter is mainly composed of the etalon structure to generate the color by the structural resonance properties while the upper layer of the etalon is made of plasmonic nanogratings to promote polarization-dependent color properties. When the duty ratio of the silver nanogratings is fixed, the proposed color filter can maintain identical optical properties for orthogonal polarization, while the etalon structure of the proposed color filter can manipulate different color information depending on the cavity height for the horizontal polarization. Finally, we experimentally confirm that polarization-dependent security images can be generated using the proposed color filters with a fixed duty ratio of various nanograting arrays.

Plasmonically Enhanced Upconversion Luminescence via Holographically Formed Silver Nanogratings.

Greatly enhanced upconversion luminescence was demonstrated by integrating the core-shell upconversion nanorods with the Ag nanogratings. Both the Ag nanogratings and upconversion nanorods were fabricated/synthesized in a facile, cost-effective, high-throughput way. Experimental results showed that the upconversion luminescence intensity of Er3+ in the core-shell upconversion nanorods can be well tuned and enhanced by changing the shell thickness and the period of the Ag nanograting. The underlying physical mechanism for the upconversion luminescence enhancement was attributed to the plasmonically enhanced near infrared broadband absorption of the periodic Ag nanograting and the localized surface plasmon resonance of Ag nanocrystals. The maximum enhanced factors of 523 nm, 544 nm (green emission), and 658 nm (red emission) of Er3+ ions excited at 980 nm are 3.8-, 5.5-, and 4.6-folds, respectively. Our fabrication approach and results suggest that such a simple integration is potentially useful for biosensing/imaging and anti-counterfeiting applications.

Impact of silver nanogratings for enhanced light absorption in plasmonic based photodetector

Recent era has witnessed a wide interest of researchers for the development of nano scale high speed photodetectors. Now days, optical communication systems demand these detectors with light enhancement along with high gain and bandwidth. Plasmonics based photodetectors with gold nanogratings are employed in literature for high responsivity and miniaturization. However, these devices need to be explored for other metals as gold being very costly. In this work, plasmonic based photodetector is designed with silver nanogratings and analyzed over varying shapes like rectangular, trapezoidal, ellipse and parabolic taper. Enhanced light absorption with quenching factor of 73.96% is achieved with rectangular grooves in near infrared region as compared to other shapes.

High-Quantum Efficiency of the Plasmonic Photodetectors-Based on Coupling Between Ag Nanoparticles and Ag Nanograting Electrodes

The plasmonic effects due to the coupling of silver spherical nanoparticles with silver nanograting electrodes on active medium of the photo detector are investigated. Calculations show that the coupling of nanoparticles and nanograting electrodes at the surface of active medium lead to reflection wave into the active medium, and electrodes can participate in the absorption and quantum efficiency. Calculations show that the addition of nanograting electrodes to the structure can lead to increase the absorption coefficient up to 120% respect to the plasmonic structure containing only nanoparticles and about 4.5 times that of conventional (metal-semiconductor -metal ) MSM photo detectors.

A voltage-controlled silver nanograting device for dynamic modulation of transmitted light based on the surface plasmon polariton effect.

An active-controlled plasmonic device is designed and fabricated based on the index-sensitive properties of surface plasmon polaritons (SPPs). We utilize a one-dimensional silver nanograting with a period of 320 nm overlayered with a liquid crystal (LC) layer (50 μm in thickness), to transmit selectively the surface plasmon resonance (SPR) wavelength. This device realizes the active, reversible and continuous control of the transmitted light wavelength by modulating the external voltage signal applied to the LC layer. This voltage-controlled plasmonic filter has a dynamic wavelength modulation range of 17 nm, a fast respond speed of 4.24 ms and a low driving voltage of 1.06 V μm(-1). This study opens up a unique way for the design of tunable nanophotonic devices, such as a micro light sources and switches.

Ultra-Thin Organic Solar Cells Incorporating Dielectric-Coated Comb Silver Nanogratings

Although coating engineering on metallic nanostructures has been frequently applied in organic solar cells (OSCs) for improving the device performance by preventing the possible exciton quenching and charge recombination at the metal surface, there have been few theoretical researches addressing how the dielectric-coating of metal nanostructures influences the optical performance of OSCs. Here, we theoretically investigate the effect of coating a comb silver nanograting by a dielectric film on the absorption performance of OSCs. It is found that, under transverse-magnetic (TM) polarization, when the refractive index or thickness of the dielectric-coating is tuned, different orders of plasmonic waveguide modes are excited by the P3HT:PC61BM/coating/Ag triple-layered system. The dispersion relationship of such a plamsonic waveguide mode is solved and analyzed for clarifying the physical mechanism of the induced light trapping effect. It shows that for optimizing the light absorption in active layer under TM polarization, it is more favorable to coat a thin dielectric film (of 1 nm thick) with a suitable refractive index. While under transverse-electric (TE) polarization, the higher refractive index of dielectric-coating, the better the effect of light trapping.

Investigating the characteristics of TM-pass/TE-stop polarizer designed using plasmonic nanostructures.

Plasmonics-based polarizers are important for many photonic devices and applications. In this paper, we design and investigate the characteristics of a new TM-pass/TE-stop polarizer using silver nanograting of exponentially tapered slit sidewalls. Performance of the designed polarizer is determined through monitoring the modification of its insertion loss, return loss, extinction ratio, and far-field transform due to changing its structural parameters. We find that the structural parameters of the reported polarizer such as a slit sidewall tapering coefficient and slit opening widths have a significant impact on tuning the polarizer characteristics.

Plasmon enhancement mechanism for the upconversion processes in NaYF4:Yb(3+),Er(3+) nanoparticles: Maxwell versus Förster.

Rare-earth activated upconversion materials are receiving renewed attention for their potential applications in bioimaging and solar energy conversion. To enhance the upconversion efficiency, surface plasmon has been employed but the reported enhancements vary widely and the exact enhancement mechanisms are not clearly understood. In this study, we synthesized upconversion nanoparticles (UCNPs) coated with amphiphilic polymer which makes UCNPs water soluble and negatively charged. We then designed and fabricated a silver nanograting on which three monolayers of UCNPs were deposited by polyelectrolyte-mediated layer-by-layer deposition technique. The final structures exhibited surface plasmon resonance at the absorption wavelength of UCNP. The green and red photoluminescence intensity of UCNPs on nanograting was up to 16 and 39 times higher than the reference sample deposited on flat silver film, respectively. A thorough analysis of rate equations showed that the enhancement was due entirely to absorption enhancement in the strong excitation regime, while the enhancement of both absorption and Förster energy transfer contribute in the weak excitation regime. The Purcell factor was found to be small and unimportant because the fast nonradiative decay dominates the relaxation process. From the experimentally observed enhancements, we concluded 3.1× and 1.7× enhancements for absorption and Förster energy transfer, respectively. This study clearly shows the plasmon enhancement mechanism and its excitation power dependence. It provides the basis for comparison of the enhancements of various plasmonic UCNP systems in the literature. It also lays the foundation for rational design of optical plasmonic structures for upconversion enhancement.

The Optical Response of Trapezoidal Comb-Like Nanostructures

Metal nanostructures can be used to control light transmission on the nanometer scale. In this paper, we propose a ladder-type comb-like metal nano-grating structure, based on optical filtering properties of the comb-like nanostructures and surface plasmon resonance effect of the metal nano-structures. The comb part of the structure is the silver nano-grating with the width of 20nm and a depth difference of 5nm between the adjacent gratings. We use the 532nm CW laser as the incident light source to study the reflective properties of the P polarized light and calculate the reflected power spectrum of the structure in three different parameters, which are the silver nano-grating, the silver-air nano-grating (silver grating are separated by air) and silver-SiO2 nano-grating. The experimental results show that the light wave oscillation modes are closely related to the comb-like structure parameters (including the depth and width) on the power spectrum. Meanwhile, we also draw conclusions that different intervention media does not change the position of the light wave oscillation modes, but only a significant effect on the reflection intensity of the different modes. Furthermore, we also noted that the depth of silver nano-gratings can affect the position of the resonance peak. As the waveguide depth of the silver nano-gratings increasing, the spacing of different modes’ oscillation peak is becoming larger. Based on the finding, we can modulate the light wave oscillation modes in a very wide spectral range. The results of this paper will promote the development of the optical filter, light wave mode selection and random laser excitation.

Semi-transparent silver electrodes for flexible electronic devices prepared by nanoimprint lithography

The preparation of mechanically flexible and optically transparent electronic circuits plays a key role in the development of next-generation display technologies. Silver nano-gratings are of particular interest due to their excellent conductivity and adjustable transmittance. Printed on polymeric substrates they are suitable for an application in flexible opto-electronic devices. Here, we present the preparation of a smart silver precursor system combining both the ability of cheap and scalable nanoimprint patterning and simple thermal silver reduction. Homogeneous silver line and grid patterns with line widths down to 400 nm are prepared using poly(dimethylsiloxane) stamps in a thermal nanoimprint lithography process. Relatively low process temperatures allow the film formation on polymeric substrates. Semi-transparent silver electrodes with a resistance of 2.8 ohm are patterned on polyimide foils to prepare flexible electro-luminescence devices. A detailed investigation of the precursor's thermal decomposition behaviour as well as the resulting electrical and optical properties of the films is offered.

Selective electroless plating of silver nanograting patterns with no lateral growth for the fabrication of polarizers

Metal patterning has been useful for fabricating many optical and electronic devices. Among all the patterning methods, selective electroless plating in combination with micro-contact printing (μCP) is a simple process compatible with roll-to-roll processing. However, this process suffers from the difficulty to avoid lateral growth during the electroless plating of metal. That will place a limitation on the fabrication of nanoscale patterns, such as the metal wire grid polarizer. In this study, we launch a new approach to restrict the lateral growth of metal by depositing metal selectively in the grooves of a three-dimensional template. The template was first treated with a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) only on the protrusion surface using μCP, and then treated in SnCl2 solution to activate the surface of the trenches for the selective electroless plating (ELP) of silver inside the trenches. A wire-grid polarizer was thus fabricated by selectively depositing 70nm-thick silver in the trenches of a nanograting template with a trench width of 100nm and a pitch of 180nm. The maximum extinction ratio of the polarizer thus obtained was about 130 in the wavelength range of 635–650nm.

Dual Plasmonic Nanostructures for High Performance Inverted Organic Solar Cells

Dual plasmonic metallic nanostructures in organic solar cells are demonstrated by simultaneously incorporating gold nanoparticles (NPs) into the active layer and fabricating the silver nanograting electrode by means of a vacuum-assisted nanoimprinting method. Apart from the waveguide modes and diffraction, hybridized surface plasmonic resonances (SPRs, from the Ag nanograting) and localized plasmonic resonances (LPRs, from the Au NPs) are simultaneously introduced to successfully achieve a high power conversion efficiency (PCE). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Efficient Inverted Polymer Solar Cells with Directly Patterned Active Layer and Silver Back Grating

We have investigated the effects of a directly patterned active layer together with silver nanograting arrays as the anode of inverted polymer solar cells (PSCs). The patterned nanostructure not only greatly enhances the light absorption of the active layer through both light diffraction and coupling to surface plasmon polariton (SPP) modes but also obviously promotes the fill factor of the patterned device. The absorption spectrum shows improvement over a broad wavelength range, especially around the 400 nm region and the near-infrared region surrounding 700 nm, which can also be reconfirmed from Incident Photon to Electron Conversion Efficiency (IPCE) and zeroth-order reflection spectra. Most importantly, our physical study shows that the absorption peak of 400 nm is due to the resonant waveguide mode, and the absorption peak of 700 nm is attributed to the excited SPP mode induced by the metallic back grating. Besides, another splitting SPP mode, called plasmonic band edge, around 800 nm is clarified from our detailed model. Consequently, on one hand, our work offers the fundamental physical understanding of plasmonic band edge resonances in periodic grating nanostructures for enhancing the optical absorption of thin-film photovoltaics. On the other hand, the study contributes to improving the power conversion efficiency of inverted PSCs by about 19% through incorporating grating structures that can be a potential candidate for improving the performances of other PSCs.