Ag Nanorings Research Articles

Transforming Nature's Bath Sponge into Stacking Faults-Enhanced Ag Nanorings-Decorated Catalyst for Hydrogen Evolution Reaction.

The rational design of cost-effective and efficient electrocatalysts for electrochemical water splitting is essential for green hydrogen production. Utilizing nanocatalysts with abundant active sites, high surface area, and deliberate stacking faults is a promising approach for enhancing catalytic efficiency. In this study, we report a simple strategy to synthesize a highly efficient electrocatalyst for the hydrogen evolution reaction (HER) using carbonized luffa cylindrica as a conductive N-doped carbon skeleton decorated with Ag nanorings that are activated by introducing stacking faults. The introduction of stacking faults and the resulting tensile strain into the Ag nanorings results in a significant decrease in the HER overpotential, enabling the use of Ag as an efficient HER electrocatalyst. Our findings demonstrate that manipulating the crystal properties of electrocatalysts, even for materials with intrinsically poor catalytic activity such as Ag, can result in highly efficient catalysts. Further, applying a conductive carbon backbone can lower the quantities of metal needed without compromising the HER activity. This approach opens up new avenues for designing high-performance electrocatalysts with very low metallic content, which could significantly impact the development of sustainable and cost-effective electrochemical water-splitting systems.

Ultra-narrow-band absorption enhancement of monolayer graphene based on surface lattice resonance modes

AbstarctAn ultra-narrow-band perfect absorber based on collective resonances in an Ag nanoring period array is theoretically proposed for the absorption enhancement of monolayer graphene, where the absorptivity can reach as high as 99.4% with the full-width-half-maximum as narrow as 3.6 nm in the visible band. This outstanding absorptive characteristic can be attributed to the excitation of surface lattice resonance modes by Ag nanoring periodic array. The as-designed structure possesses high refractive-index sensitivity, reaching 557.9 nm RIU−1 with its figure of merit attaining 155 RIU−1. This work provides promising guidance for developing high-performance graphene-based photonic devices.

Clusters-based silver nanorings: An active substrate for surface-enhanced Raman scattering

Plasmonic nanostructures, particularly irregular surfaces of ring-like silver (Ag) nanostructures are promising candidates in surface-enhanced Raman scattering (SERS) spectroscopy. In this work, clusters-based Ag nanorings have been fabricated and characterized as SERS-active substrates. The rim of the as-fabricated Ag nanorings was found neither discontinuous nor linear aggregation of nanoparticles. High-resolution field emission scanning electron microscopy (FESEM) revealed that the individual constituent clusters were different from each other, particularly in terms of size and shape in addition to the cases how such clusters were emerged as the edge of the nanoring. Considering the dimensions of the clusters and the arrangement of such clusters as nanorings, it was speculated that the local electromagnetic (EM) near-field distributions would excel and thus enhanced SERS signals would be achieved. Indeed, the inherent features of the nanorings facilitated to achieve SERS enhancement factors as high as 2.1 × 104. SERS-activity of as-fabricated Ag nanorings was confirmed using Rhodamine 6G (R6G) as Raman-active dyes and the enhancement was compared to those obtained from R6G adsorbed on Ag-ZnO/Glass and ZnO/Glass. To the best of our knowledge, this is the first attempt to explore the impact of localized EM near-field within the segments of nanorings through SERS spectroscopy. A model was designed resembling the nanorings under this investigation to simulate EM near-field distributions by finite difference time domain (FDTD) analysis. The dimensions of the model geometry were chosen according to the observations achieved by FESEM. To simplify the simulations, nanoobjects were considered spherical and organized in a periodic fashion, although the constituent clusters of Ag nanorings were found irregular in shape and arrangement. Since EM near-field distribution highly depends on interparticle gaps, three scenarios were implemented, such as, small gap in between two adjacent nanoobjects and adjacent nanoobjects in touch and overlapped. Each configuration was simulated and EM near-field distribution was extracted for s-, p- and 450 of incident polarizations followed by a plausible correlation to SERS enhancements. Such correlated investigations as well as clusters-based Ag nanorings not only inspire the ones to look for cost-effective SERS-active substrate, but also understand the underlying EM mechanism in SERS enhancements.

Fabrication of nanorings from ultrathin layer of silver on zinc oxide-coated glass substrate

Fabrication of ring-like nanostructures of noble metal, particularly silver (Ag) nanostructures are challenging but long expected and suitable for various applications. Here, in this work, a strategy has been reported to fabricate Ag nanorings from ultrathin layer of the same. The edges of as-fabricated Ag nanorings were found continuous in nature rather than linear aggregation of adjacent nanoclusters as confirmed by high-resolution scanning electron microscope (SEM) micrographs. Interestingly, none of the Ag nanorings was found broken or cracked. Such clues led ones to a plausible hypothesis in demonstrating the fabrication mechanism. In this context, an in-depth morphological investigation and quantitative analysis have been carried out to understand the evolution of nanorings. SEM micrographs captured at the intermediate stage of Ag nanorings formation revealed that ultrathin layer of Ag turned into spherical nanoparticles before ending at the formation of such nanorings. High-resolution SEM micrographs confirmed that Ag nanoparticles were mostly spherical along with dark sheds at the center. A detailed morphological investigation of such Ag nanoparticles confirmed average estimated outer diameter of 376.74 ± 37.24 nm and average wall thickness of 102.89 ± 18.10 nm. Further estimation indicated Ag nanorings of 213.58 nm edge height which was verified in high-resolution SEM investigations. An attempt was taken to slice an individual Ag nanoparticle with SEM-aided focus ion beam (FIB) facility. A small deviation in heights was observed by high-resolution SEM micrographs of such SEM-aided FIB treated nanoparticles. Silver nanorings of different sizes and shapes (background) along with fractal features at the rim (inset) and plausible formation mechanism thereof (right).

Self-assembly 2D plasmonic nanorice film for surface-enhanced Raman spectroscopy* *Project supported by the National Natural Science Foundation of China (Grant No. 11974067), Natural Science Foundation Project of CQ CSTC (Grant Nos. cstc2019jcyj-msxmX0145, cstc2019jcyj-bshX0042, and cstc2019jcyj-msxmX0828), and Sharing Fund of Chongqing University & Large-scale Equipment.

As an ultrasensitive sensing technology, the application of surface enhanced Raman spectroscopy (SERS) is one interesting topic of nano-optics, which has huge application prospectives in plenty of research fields. In recent years, the bottleneck in SERS application could be the fabrication of SERS substrate with excellent enhancement. In this work, a two-dimensional (2D) Ag nanorice film is fabricated by self-assembly method as a SERS substrate. The collected SERS spectra of various molecules on this 2D plasmonic film demonstrate quantitative detection could be performed on this SERS substrate. The experiment data also demonstrate this 2D plasmonic film consisted of anisotropic nanostructures has no obvious SERS polarization dependence. The simulated electric field distribution points out the SERS enhancement comes from the surface plasmon coupling between nanorices. And the SERS signals is dominated by molecules adsorbed at different regions of nanorice surface at various wavelengths, which could be a good near IR SERS substrate for bioanalysis. Our work not only enlarges the surface plasmon properties of metal nanostructure, but also exhibits the good applicationprospect in SERS related fields.

Plasmon coupling nanorice trimer for ultrahigh enhancement of hyper-Raman scattering

A new tactic that using Ag nanorice trimer as surface-enhanced hyper Raman scattering substrate is proposed for realizing maximum signal enhancement. In this paper, we numerically simulate and theoretically analyze the optical properties of the nanorice trimer consisting of two short nanorices and a long nanorice. The Ag nanorice trimer can excite Fano resonance at optical frequencies based on the strong interaction between the bright and the dark mode. The bright mode is attributed to the first longitudinal resonance of the short nanorice pair, while the dark mode originates from the third longitudinal mode resonance of the long nanorice. The electric field distributions demonstrate that the two resonances with the largest field strength correspond to the first-order resonance of the long nanorice and the Fano resonance of the trimer, respectively. Two plasmon resonances with maximum electromagnetic field enhancements and same spatial hot spot regions can match spectrally with the pump and second-order Stokes beams of hyper Raman scattering, respectively, through reasonable design of the trimer structure parameters. The estimated enhancement factor of surface-enhanced hyper Raman scattering can achieve as high as 5.32 × 1013.

Synthesis of morphology controlled PtAu@Ag nanorings through concentric and eccentric growth pathways.

We report the synthetic methodology for silver nanorings with controlled nanoscale morphology. The morphology of Ag nanorings was kinetically controlled by electrochemical potential tuning of Ag deposition using halide counter-ions, which resulted in concentric PtAu@Ag nanorings (i.e., Ag homogeneously wrapped around the Pt nanorings) and eccentric PtAu@Ag nanorings (i.e., Ag selectively deposited at the inner boundary of the Pt nanorings). The resulting high quality of each Ag nanoring allowed us to systematically investigate their corresponding localized surface plasmon resonance (LSPR) profiles as a function of their geometrical parameters. Additionally, we evaluated the application of the samples as surface-enhanced Raman spectroscopy (SERS) substrates composed of 2D monolayers of varied compositions of Ag and Au nanorings, which showed a different extent of enhancement depending on the adsorption characteristics of the analytes.

Patterning of polyoxometalate rings on gold nanorods.

We report a facile method for the self-assembly of various polyoxometalates (POMs) on cetyltriethylammonium bromide-covered gold nanorods (GNRs) into an ordered array of POM rings along their long axis. The periodic distance of POM rings can be tuned by the POM charge and the transverse curvature of GNRs.

Theoretical investigation of a plasmonic substrate with multi-resonance for surface enhanced hyper-Raman scattering

Because of the unique selection rule, hyper-Raman scattering (HRS) can provide spectral information that linear Raman and infrared spectroscopy cannot obtain. However, the weak signal is the key bottleneck that restricts the application of HRS technique in study of the molecular structure, surface or interface behavior. Here, we theoretically design and investigate a kind of plasmonic substrate consisting of Ag nanorices for enhancing the HRS signal based on the electromagnetic enhancement mechanism. The Ag nanorice can excite multiple resonances at optical and near-infrared frequencies. By properly designing the structure parameters of Ag nanorice, multi- plasmon resonances with large electromagnetic field enhancements can be excited, when the “hot spots” locate on the same spatial positions and the resonance wavelengths match with the pump and the second-order Stokes beams, respectively. Assisted by the field enhancements resulting from the first- and second-longitudinal plasmon resonance of Ag nanorice, the enhancement factor of surface enhanced hyper-Raman scattering can reach as high as 5.08 × 109, meaning 9 orders of magnitude enhancement over the conventional HRS without the plasmonic substrate.

Rutin detection using highly electrochemical sensing amplified by an Au–Ag nanoring decorated N-doped graphene nanosheet

The novel Au–Ag nanorings/NG modified electrode was found to have a wide linear range from 0.05 μM to 241.2 μM (S/N = 3) with a low detection limit of 0.01 μM when it was employed for rutin detection.

Plasmon mode excitation and photoluminescence enhancement on silver nanoring

We demonstrate a simple and high-performance laser-assisted technique for silver nanoring fabrication, which includes the ablation of the Ag film by focused nanosecond pulses and subsequent reactive ion polishing. The nanoring diameter and thickness can be controlled by optimizing both the pulse energy and the metal film thickness at laser ablation step, while the subsequent reactive ion polishing provides the ability to fabricate the nanoring with desirable height. Scattering patterns of s-polarized collimated laser beam obliquely illuminating the nanoring demonstrate the focal spot inside the nanoring shifted from its center at a distance of ~0.57Rring. Five-fold enhancement of the photoluminescence signal from the Rhodamine 6G organic dye near the Ag nanoring was demonstrated. This enhancement was attributed to the increase of the electromagnetic field amplitude near the nanoring surface arising from excitation of the multipole plasmon modes traveling along the nanoring. This assumption was confirmed by dark-field back-scattering spectrum of the nanoring measured under white-light illumination, as well as by supporting finite-difference time-domain simulations.

Dipole, Quadrupole, and Octupole Plasmon Resonance Modes in Ag Nanoring Structure: Local Field Enhancement in the Visible and Near Infrared Regions

Here, we provide a simulation based on finite-difference time-domain (FDTD) way of the properties of surface plasmons on Ag nanoring and study their electric field distribution in order to identify different multiple surface plasmon resonances. We can obtain the symmetric field distribution that parallels to the orientation of direction of incident light. We find their propagation can be controlled. And we discuss some of the parameters that influence the optical response of the Ag nanoring. Adjustment of nanoring radius (inner radius and outer radius) and height can change the absorption intensity and the resonance peaks. The simulation of the field distribution also displays that the location of the field enhancement is specified by the different resonance patterns. Dipole, quadrupole, and octupole plasmon resonance modes can be found in the Ag nanoring at resonance wavelength. This is an important step toward a thorough understanding of plasmon resonance in Ag nanorings.

Study of strong dipole and quadrupole plasmon resonance in Ag nanorings antenna

Self-organized Ag nanorings antenna were formed on quartz glass wafers by a simple chemistry reaction without any template. By using absorption measurements and three-dimensional finite-difference time-domain (3D-FDTD) calculations, the dipole and quadrupole plasmon resonances of Ag nanorings antenna were investigated experimentally and theoretically. Calculations have shown that large electric fields are confined at the quadrupole of the Ag nanoring, leading to quadrupole plasmon resonances. Compared the electric enhancement factor of the exterior surfaces of Ag nanoring, the electric enhancement factor of the interior surface is about six times excited by an incident light with 514.5 nm wavelength. Furthermore, the highest electric-field intensity of Ag nanorings is around four times larger than that for Ag nanodome with the same condition. These results pave the way to design plasmonic nanostructures for practical applications that require metallic nanoparticles with enhanced electric fields.

Developing Quantum Dots and Plasmonic Nanostructures for Solar Cell Applications

I present our recent work on two types of nanomaterials, near-infrared (NIR) quantum dots (QDs) and plasmonic nanostructures, developed for energy-related applications (including solar cells) [1-10].Harvesting NIR photons represents an attractive approach to improve the energy conversion efficiency of photovoltaics. Most solar cells are only able to strongly absorb "visible" photons, while leaving great amounts of solar energy in the NIR untapped. To harvest the lost NIR photons, PbS QDs and PbS@CdS core-shell QDs are very promising. Herein I present some of our most recent development in these QDs and their application in photovoltaics. In particular, we have recently developed a two-step route for the synthesis of high-quality PbS@CdS core-shell QDs with tunable shell thicknesses and absorption properties. These core-shell QDs show higher photoluminescence efficiency and significantly improved photo- and thermal-stability compared to uncoated PbS QDs only capped with ligands. The CdS shell provides protection to the PbS core and also passivates its surface defects, that may otherwise serve as charge carrier trap sites. The charge transfer behavior of these core-shell QDs has further been studied for different core sizes and shell thicknesses. As for QD-based solar cells, one example is about the controlled hybridization of NIR PbS QDs with carbon nanotubes (CNTs) and their further integration into poly(3-hexylthiophene), which is a hole-transporting polymer. The nanohybrid cells show considerably enhanced power conversion efficiency, which is attributed to the significantly extended absorption in NIR by PbS QDs and the effectively enhanced charge transportation due to CNTs. Solution processed heterojunction inorganic solar cells based on TiO2 nanorods and PbS QDs or PbS@CdS core-shell QDs will be also be briefly introduced. On the other hand, plasmonic nanostructures have recently been explored for enhancing the efficiency of solar cells. Our recent work on some interesting plasmonic nanostructures (such as Ag nanorice and nanocarrots) that have strong resonances in the NIR regime, and their application in solar cells will also be briefly highlighted. References (selected) 1. D. Wang, J. K. Baral, H. Zhao, B. A. Gonfa, V. V. Truong, M. A. El Khakani, R. Izquierdo, D. Ma, Adv. Funct. Mater , 21, 4010 (2011).2. H. Liang, D. Rossouw, H. Zhao, S. K. Cushing, H. Shi, A. Korinek, H. Xu, F. Rosei, W. Wang, N. Wu, G. A. Botton, D. Ma, J. Am. Chem. Soc .,135, 9616 (2013).3. H. Zhao, H. Liang, B. A. Gonfa, M. Chaker, T. Ozaki, P. Tijssen, F. Vidal, and D. Ma, Nanoscale , 2014, accepted (Back Cover). 4. I. Ka, V. Le Borgne, D. Ma, M. A. El Khakani, Adv. Mater . 24, 6289 (2012); Frontispiece Cover. 5. H. Zhao, M. Chaker, N. Wu, D. Ma, J. Mater. Chem ., 21, 8898 (2011); highlighted at http://blogs.rsc.org/jm/.6. H. Zhao, D. Wang, T. Zhang, M. Chaker, D. Ma, Chem. Commun . 46, 5301 (2010). 7. D. Wang, H. Zhao, N. Wu, M. A. El Khakani, D. Ma, J. Phys. Chem. Lett . 1, 1030 (2010).8. F. Ren, H. Zhao, F. Vetrone, D. Ma, Nanoscale,5, 7800 (2013).9. H. Liang, H. Zhao, D. Rossouw, W. Wang, H. Xu, G. A. Botton, D. Ma, Chem. Mater . 24, 2339 (2012).10. B. A. Gonfa, H. Zhao, J. Li, J. Qiu, M. Saidani, S. Zhang, R. Izquierdo, N. Wu, M. A. El Khakani, D. Ma, S olar Energy Materials and Solar Cells, 2014, In press.

Nanoparticle attachment on Ag nanorings and nanoantenna for large increases of surface-enhanced Raman scattering

A simple and inexpensive approach based on the heat-treatment of Ag+/PVA/PVP composite film on quartz glass has been developed for fabricating large-area Ag nanorings attached small nanoparticles.

High-order plasmon resonances in an Ag/Al2O3 core/shell nanorice

Using numerical simulation, we investigate the high-order plasmon resonances in individual nanostructures of an Ag nanorice core surrounded by an Al2O3 shell. The peak positions of localized surface plasmon resonances (LSPRs) are red-shifted exponentially with the increase of the dielectric shell thickness. This is due to the exponential decay of electromagnetic field intensity in the direction perpendicular to the interface. This exponential red-shift depends on the wavelength of the resonance peak instead of the resonance order. In addition, we find that the LSPRs in an Ag nanorice of 60-nm width can be perfectly described by a single linear function. These features make nanorice an ideal platform for sensing applications.

Self-Organized Ag Nanorings Antenna Substrates for Surface-Enhanced Raman Spectroscopy

We investigate the surface-enhanced Raman spectroscopy of Ag nanorings antenna in both experiment and simulation. Self-organized Ag nanorings antenna were formed on quartz glass wafers by a simple chemistry reaction without any template. The three-dimensional finite-difference time-domain simulation calculations indicate that the electric field enhancement of Ag nanoring antenna is strongly dependent on the gap distance. A very strong surface plasmon coupling in the gap region of Ag nanoring antenna is observed, whose field intensity is enhanced four times compared to that for Ag nanodomes antenna with the same gap distance. Surface-enhanced Raman scattering (SERS) measurements have shown that the SERS intensity acquired from the Ag nanoring antenna is about 16 times stronger than that obtained from Ag nanodomes antenna. These results pave the way to design plasmonic nanostructures for practical applications that require coupled metallic nanoparticles with enhanced electric fields.

Comprehensive investigation of noble metal nanoparticles shape, size and material on the optical response of optimal plasmonic Y-splitter waveguides

With the purpose of guiding and splitting of optical power at C-band spectrum, we studied Y-shape splitters based on various shapes of nanoparticles as a plasmon waveguide. We applied different configurations of Gold (Au) and Silver (Ag) nanoparticles including spheres, rods and rings, to optimize the efficiency and losses of two and four-branch splitters. The best performance in light transportation specifically at telecom wavelength (λ≈1550nm) is achieved by nanorings, due to an extra degree of freedom in their geometrical components. In addition, comparisons of several values for offset distance (doffset) of examined structures shows that Au nanoring splitters with feasible lower doffset have high quality in guiding and splitting of light through the structure. Finally, we studied four-branch Y-splitters based on Au and Ag nanorings with least possible offset distances to optimize the splitter performance. The power transmission as a key element is calculated for examined structures.

Broad comparison between Au nanospheres, nanorods and nanorings as an S-bend plasmon waveguide at optical C-band spectrum

The integration of optical devices demands the fabrication of waveguides for electromagnetic energy below the diffraction limit of light. In this work, we have investigated the possibility of utilizing specific chains of closely spaced noble metal nanoparticles for waveguides beyond diffraction limit. Accordingly, we have employed Au and Ag nanorings in order to transport the optical energy through the plasmon waveguide at optical C-band spectrum (λ≈1550 nm). In proposed waveguides, we try to select the best structure via comparison between their transmission losses and group velocities of propagated energy. Three-dimensional simulations based on finite-difference time-domain algorithm (FDTD) are used to determine the related geometrical values. It is shown that nanoring’s geometrical tunability and extra degree of freedom (DoFs) in its geometry can cause the optical energy to transport at 1550 nm with higher efficiency and lower losses in comparison with those of the other shapes of nanoparticles such as nanospheres and nanorods.

Finite-Difference Time-Domain Calculation of Light Scattering Efficiency for Ag Nanorings

Enhancement of light trapping in solar cells is becoming increasingly urgent for the development of next generation thin film solar cells. One of the possible candidates for increasing light trapping in thin film solar cells that has emerged recently is the use of scattering from metallic nanostructures. In this study, we have investigated the effects of the geometric parameters of Ag nanorings on the light scattering efficiency by using three dimensional Finite Different Time Domain (FDTD) calculations. We have found that the forward scattering of incident radiation from Ag nanorings strongly depends on the geometric parameters of the nanostructures such as diameter, height, etc. The forward scattering to substrate direction is increased as the outer diameter and height of the nanorings decrease. In particular, for nanorings larger than 200 nm, the inner diameter of Ag nanorings should be optimized to enhance the forward scattering efficiency. Light absorption and scattering efficiency calculations for the various nanoring arrays revealed that the periodicity of nanorings arrays also plays an important role in the absorption and the scattering efficiency enhancement. Light scattering efficiency calculations for nanoring arrays also revealed that enhancement of scattering efficiency could be utilized to enhance the light absorption through the forward scattering mechanism.