Resonance Peak Position Research Articles

Colorimetric determination and recycling of Hg2+ based on etching-induced morphology transformation from hollow AuAg nanocages to nanoboxes

Herein, we propose a selective and simple colorimetric sensing approach for the determination of Hg2+ ions based on bimetallic AuAg nanocages with partial hollow cavity and several pinholes on the wall, wherein the residual Ag atoms existing inside this AuAg nanocages can be directly etched by Hg2+ and the generated Hg depositing on inner surface of nanocages induces the morphology transformation from hollow AuAg nanocages to closed nanoboxes which consists of an AuAg shell and Hg core. This morphology transformation of “nanocage-to-nanobox” not only extends the detection range of Hg2+, but also cleans the Hg2+ in solutions by enriching it into the nanoboxes. With increasing Hg2+ concentrations, the blue shift of localized surface plasmon resonance (LSPR) peak position with multicolor changing from light-blue to light-brown is great for colorimetric determination of Hg2+. Under optimal conditions, the colorimetric sensing shows a linear response to Hg2+ ranging from 0.03 to 35 μM with a detection limit of 10 nM. Besides, interference study and real samples detection applying lake and tap water demonstrated that Hg2+ can be specifically and practically detected by utilizing this method.

Nonlinear optical characteristics of an exciton in a GaSb-capped InSb heterodot: role of size control

The optical characteristics of a bound electron-hole quasiparticle inside a GaSb-capped InSb nanodot were investigated using a combination between a density-matrix approach and variational calculations. Our theoretical model considers the electric permittivity mismatch between the core and shell materials via the self-energy term obtained by the means of an image charge approach. Furthermore, the core-to-shell conduction and valence band offsets were modeled by finite-depth confinement potentials. To elucidate the impact of the nanoheterodot spatial parameters on the confined exciton optical properties, we have investigated the change of the refractive index, the optical absorption coefficient, and the 1p–1s exciton transition energy with respect to the nanodot shape. Our numerical results exhibit the great potential for the improvement of the exciton optical properties by tailoring the nanodot size. It was also obtained that, for a fixed core radius, the resonance peak position of the optical absorption coefficient was still constant after a certain shell thickness value. Otherwise, decreasing the shell thickness leads to blue-shifting the 1p–1s transition energy.

Au–Ag alloy nanoparticles with tunable cavity for plasmon-enhanced photocatalytic H2 evolution

Au–Ag alloy nanoparticles with different cavity sizes have great potential for improving photocatalytic performance due to their tunable plasmon effect. In this study, galvanic replacement was combined with co-reduction with the reaction kinetics processes regulated to rapidly synthesize Au–Ag hollow alloy nanoparticles with tunable cavity sizes. The position of the localized surface plasmon resonance (LSPR) peak could be effectively adjusted between 490 nm and 713 nm by decreasing the cavity size of the Au–Ag hollow nanoparticles from 35 nm to 20 nm. The plasmon-enhanced photocatalytic H 2 evolution of alloy nanoparticles with different cavity sizes was investigated. Compared with pure P25 (TiO 2 ), intact and thin-shelled Au–Ag hollow nanoparticles (HNPs)-supported photocatalyst exhibited an increase in the photocatalytic H 2 evolution rate from 0.48 µmol h −1 to 4 µmol h −1 under full-spectrum irradiation. This improved photocatalytic performance was likely due to the plasmon-induced electromagnetic field effect, which caused strong photogenerated charge separation, rather than the generation of hot electrons. Au–Ag hollow alloy nanoparticles with tunable cavity sizes were constructed by regulating reaction kinetics processes and by combining galvanic replacement with co-reduction. This hollow alloy nanoparticle dramatically enhance the photocatalytic performance.

Ambient Ammonia Electrosynthesis from Nitrogen and Water by Incorporating Palladium in Bimetallic Gold–Silver Nanocages

Electrosynthesis of ammonia using nitrogen and water provides a potential alternative to the thermochemical process (Haber-Bosch) in a clean, sustainable, and decentralized way when electricity is generated from renewable sources. To enable the widespread commercialization of this technology, an electrocatalyst to convert nitrogen (N2) to ammonia (NH3) with high selectivity and activity must be developed. Here, we report our findings in the investigation into the role of incorporating palladium (Pd) in bimetallic Au-Ag nanocages on the electrocatalytic activity of the nitrogen reduction reaction (NRR) under ambient conditions. The localized surface plasmon resonance (LSPR) peak position of the resulting trimetallic nanoparticles is tuned with Pd concentration, achieving the highest electrocatalytic NRR activity (NH3 yield rate = 5.80 μg cm−2 h−1, Faradaic efficiency = 48.94%) using Au-Ag-Pd-850 nanoparticles at −0.3 V vs RHE. This activity corresponds to the production energy efficiency of 28.9% with an electrical energy input of 19.1 MWh / ton NH3. The enhanced NRR activity is attributed mainly to the formation of a highly porous Pd layer with remarkably high surface area active for NRR. In addition, operando surface-enhanced Raman spectroscopy (SERS) is used to probe the mechanism of NRR on the trimetallic nanostructures and to identify the intermediate species at the electrode-electrolyte interface.

Silk fibroin a bio-template for synthesis of different shaped gold nanoparticles: Characterization and ammonia detection application

A simple environmentally friendly method for the synthesis of different shaped gold nanoparticles (AuNPs) using silk fibroin (SF) as a reducing, shape tailoring, chapping and subsequent stabilizing agent is reported. In this study, neither external reducing agents nor high temperature are used for the synthesis of nanoparticles. The nanoparticles formed in SF solution was probed by considering the changes in position and intensity of the localized surface plasmon resonance (LSPR) peak using UV–Visible spectroscopy (UV–Vis). Nano crystalline structure and FCC crystal family was established by X-ray diffraction (XRD) measurement. The size and shape evolution of the nanoparticles was inspected using transmission electron microscope (TEM) which confirmed the formation of different shaped nanoparticles. The average particles size of AuNPs in colloidal solution was scrutinized using dynamic light scattering (DLS) experiment. Synthesized gold nanoparticles were sense as potential ammonia detector.

Tunable plasmonic properties of elongated bimetallic alloys nanoparticles towards deep UV-NIR absorbance and sensing

Combining magnetic nanoparticles with noble metallic nanoparticles to construct multifunctional alloy nanostructures has become a powerful tool for imaging sensing, medicine, biology, and cancer treatment and photothermal therapy. This work reports a study regarding the plasmonic properties of Co-Ag and Co-Au bimetallic alloys nanostructures on the electromagnetic spectrum. In this paper, the optical properties of magnetic and plasmonic nanoparticles (NPs) with different shapes, sizes, compositions, and surrounding medium are investigated by using the discrete dipole approximation (DDA) technique. The absorption and scattering localized surface plasmon resonance (LSPR) peak positions are found between 211–964 nm wavelengths ranges and can be tuned in the deep UV-NIR region of the EM spectrum in accordance with the desired application. Further, we calculate the refractive index sensitivity (S) and figure of merit (FOM) of LSPR based nanosensors. Although, LSPR based sensors undergo low FOM as compared to conventional surface plasmon resonance (SPR) sensors due to high losses from the radiative damping of localized surface plasmons (LSPs) waves. However, LSPR based sensors have potential applications in gas and bio-sensors technology viz. medical and environmental monitoring applications. In this work, the main feature of LSPR peak is dependent on nanoparticle shapes, sizes, compositions, and ambient medium and have ordered as prolate < sphere < cube < rectangular shape NPs. These results suggest that the nanostructures of Co-Ag and Co-Au alloys associated with LSPR tunability and sensitivity can be used in biomedical and sensing environment technology such as detection of chemical and catalytic events.

A theoretical study on the optical properties of a quantum well with short-range bottomless exponential potential

The effects of external applied fields on the electron-related optical nonlinear properties in a short-range bottomless exponential potential quantum well are investigated. The potential profile behaves as inverse square root in the vicinity of the origin and vanishes exponentially toward infinity, supporting a finite number of bound states whose energies and wave functions are determined within the effective-mass approximation. The linear, third-order nonlinear and total optical absorption coefficients (TOACs) as well as the coefficient of relative refractive index changes (RRICs) of the system are calculated from the expressions derived in the framework of the compact density matrix approach. The results obtained after numerical calculations show that with the effect of the static electric and magnetic fields (high-frequency THz laser field), the resonant peak position of the optical response shifts toward higher (lower) energies and the magnitude of the peak increases.

Linear and nonlinear optical properties of donors inside a CdSe/ZnTe core/shell nanodot: Role of size modulation

The optical absorption coefficient (OAC) and the refractive index (RI), related to a confined donor, were theoretically investigated by the mean of the density matrix formalism. In order to obtain the 1s-1p donor transition energy a variational calculation, within the context of the effective-mass approach, was deployed. Our numerical results exhibit the possibility to modulate the electronic and optical properties of confined donors by tailoring the inner and outer radii of the core/shell heterodot. Further, we have obtained that the nanodot size shrinking leads, for very small values of core radius, to reduce the magnitude of the total absorption coefficient resonance peak. It was also obtained that the resonance peak position of the absorption coefficient is redshifted with increasing the core radius for a fixed shell thickness. The same situation occurs when reducing the thickness of the shell material for a fixed core size.

Nonlinear optical properties of morse quantum well modulated by THz laser fields

In this study, the influence of structure parameter (η) and intense laser field (ILF) on the optical properties such as the nonlinear optical rectification (NOR) coefficient, second and third harmonic generation (SHG and THG) coefficients related to intersubband transitions in a quantum well with Morse confinement potential are theoretically studied. The energy levels and corresponding wave functions of the system are obtained by solving the one-electron Hamiltonian within the framework of the effective-mass, parabolic-band approximations and Kramers-Henneberger (KH) transformation. The optical properties of the structure are calculated through the compact density matrix approach. Numerical calculations are brought out for a typical GaAs quantum well. The results unveil significant influences of ILF and structure parameters of Morse confinement potential on resonant peak position and peak intensity of the NOR, SHG and THG coefficients.

Tuning the optical properties of Fe-Au core-shell nanoparticles with spherical and spheroidal nanostructures

Present research interest is to highlight on the manufacturing of core-shell nanoparticles because of core activity with unique properties and surface modification by a shell in the diverse fields (e.g. optoelectronic, catalysis and magneto-optics). In addition, the combined optical properties of magnetic-plasmonic core-shell NPs make them ideal candidates for many applications in biomedical fields. The influence of Fe-core and Au-shell for the formation of the core-shell viz. spherical and spheroidal nanostructures is studied using the discrete dipole approximation method. DDA is an approximation method and its accuracy is compared to Mie theory results for spherical core-shell NPs as Mie theory gives the exact solution to spherical targeted NPs. DDA calculations are further extended to spheroidal core-shell nanostructures. It is observed that the localized surface plasmon resonance (LSPR) peak position in considered core-shell nanostructures is enhanced by changing the cores and shell thickness in the core-shell spherical nanostructures and aspect ratio as well as shell thickness in spheroidal core-shell nanostructures. The absorption spectra are found between 363–788 nm wavelength ranges and can be tuned into UV-visible-near-infrared region of the electromagnetic (EM) spectrum in accordance with desired applications. It has been found that the Fe@hollow@Au and prolate core-shell nanostructures show enhancement to LSPR peaks, bandwidth and their corresponding intensities in comparison to other considered spherical and spheroidal core-shell nanostructures. Tunability in core size, shell thickness, aspect ratio, and configuration will open new potential uses of suitable magnetic-plasmonic core-shell nanostructures in cancer therapy, tissue engineering, drug delivery, and many more of biomedical fields.

The Role of Oxidation of Silver in Bimetallic Gold-Silver Nanocages on Electrocatalytic Activity of Nitrogen Reduction Reaction.

Electrochemical ammonia synthesis from nitrogen and water provides an alternative route to the thermochemical process (Haber-Bosch) in a clean, sustainable, and decentralized way if electricity is generated from renewable sources. We have previously demonstrated the use of bimetallic hollow Au-Ag nanocages as an effective electrocatalyst for electrosynthesis of ammonia in an aqueous solution. The stability of the electrocatalyst during electrochemical nitrogen reduction reaction (NRR) is of paramount importance when considering the feasibility of electrochemical NRR for industrial applications. Here, the role of oxidation of silver in bimetallic Au-Ag nanocages with various localized surface plasmon resonance (LSPR) peak positions on electrocatalytic activity of NRR is studied by oxygen treatment of Ag through the simple oxidation process to form Ag2O-Au nanocages. Electrocatalytic NRR activity with an NH3 yield rate of 2.14 µg cm-2 h-1 and Faradaic efficiency of 23.4% has been achieved at -0.4V vs. RHE using Ag2O-Au-719. This electrochemical performance is a substantial reduction to our previously reported NRR activity using Ag-Au-715 nanocages (3.74 µg cm-2 h-1 and 35.9% at -0.4V vs. RHE). This work highlights the importance of an O2-free environment in electrochemical NRR for the stable N2 electrolysis operation and discerns the role of Ag on the selectivity and activity of bimetallic Au-Ag nanocages toward NRR.

The Role of Oxidation of Silver in Bimetallic Gold–Silver Nanocages on Electrocatalytic Activity of Nitrogen Reduction Reaction

Electrochemical ammonia synthesis from nitrogen and water provides an alternative route to the thermochemical process (Haber-Bosch) in a clean, sustainable, and decentralized way if electricity is generated from renewable sources. We previously demonstrated the use of bimetallic hollow Au–Ag nanocages as an effective electrocatalyst for electrosynthesis of ammonia in an aqueous solution. The stability of the electrocatalyst during electrochemical nitrogen reduction reaction (NRR) is of paramount importance when considering the feasibility of electrochemical NRR for industrial applications. Here, the role of oxidation of silver in bimetallic Au–Ag nanocages with various localized surface plasmon resonance peak positions on electrocatalytic activity of NRR is studied by oxygen treatment of Ag through the simple oxidation process to form Ag2O–Au nanocages. Electrocatalytic NRR activity with an NH3 yield rate of 2.14 μg cm–2 h–1 and Faradaic efficiency of 23.4% was achieved at −0.4 V versus reversible hydroge...

Resonance Absorption of Electromagnetic Radiation in a Phosphorene Single Layer

The absorption coefficient of the electromagnetic radiation in a phosphorene single layer placed in a magnetic field is found. A degenerate and nondegenerate electron gas is considered. The resonant dependences of the absorptance on the radiation frequency and applied magnetic field are found. Taking into account electron scattering at an ionized impurity leads to oscillation dependences of the absorption coefficient on the radiation frequency and external magnetic field. The resonance character of the absorption curve is shown. The conditions of resonances and position of resonance peaks are found.

Резонансное поглощение электромагнитного излучения в монослое фосфорена

AbstractThe absorption coefficient of the electromagnetic radiation in a phosphorene single layer placed in a magnetic field is found. A degenerate and nondegenerate electron gas is considered. The resonant dependences of the absorptance on the radiation frequency and applied magnetic field are found. Taking into account electron scattering at an ionized impurity leads to oscillation dependences of the absorption coefficient on the radiation frequency and external magnetic field. The resonance character of the absorption curve is shown. The conditions of resonances and position of resonance peaks are found.

Local dielectric environment-dependent plasmonic optical sensitivity of gold nanocage: from nanobox to nanoframe

In this study, a gold nanobox with 40 nm edge length has been transformed into nanoframe gradually by increasing the square-hole length in each {100} facet of the hexahedron. The local dielectric environment-dependent plasmon spectra and refractive index sensitivity of this face-holed single gold nanocage were investigated based on the discrete dipole approximation method. Both the redshift of the resonance peak position and the sensitivity factor increased near exponentially with increasing hole length, which could be attributed to the changing of hot regions of plasmonic field coupling. Moreover, the shift of their resonance peak position to the refractive index of environmental medium increased linearly, and the face-holed nanocage-based sensor shows an excellent sensitivity factor of 955.7 nm/RIU [figure of merit (FOM) = 3.58]. It was also noticed that the non-monotonic transform of the local field enhancement factor (|E/E0|) with a maximum of 80.9 is also extremely affected by the refractive index. The physical mechanism discussed herein may be that the polarized field in local dielectric environment becomes intense as the refractive index increases, resulting in an improvement of field enhancement factor on the corners. We therefore believe that the square-hole length of {100} facets could enhance the plasmonic optical sensitivity of nanocage-based nanoparticles.

Tuning the surface plasmon resonance in gold nanocrystals with single layer carbon nitride

The introduction of colloidal single-layer carbon nitride (SLCN) nanosheets at the stage of the formation of Au nanocrystals (NCs) in aqueous solutions allows the surface plasmon resonance peak position of gold/SLCN composites to be tuned in a relatively broad range of 520–610 nm. The effect is believed to originate from a strong electronic interaction between Au NCs and SLCN nanosheets attached to their surface as capping ligands and resulting in a decrease of the effective electron density on the Au NC surface. The SLCN nanosheets suppress direct interparticle interactions between Au NCs prohibiting additional plasmonic features typical for the Au NC associates. Species similar to SLCN in terms of functionalities but having no conjugated aromatic system, such as polyethyleneimine, only induce aggregation of Au NCs but do not allow the main surface plasmon resonance of the NCs to be tuned demonstrating the crucial role of electronic interaction between the NC surface and the aromatic SLCN sheets for the surface plasmon resonance tuning.

Designing of 3D Sensor Chamber for Plasmonic-based Toxic Sensor Detection

Plasmonic sensor implementing an optical phenomenon called Localized Surface Plasmon Resonance (LSPR) resulting from the interaction of free electron with electromagnetic field of light at the metal nanoparticles surface. In this study, the plasmonic sensor has been developed for toxic detection in solution form. This system consists of five components which are the light source, duplex fiber optic, sensor chamber, spectrometer and computer. The sensor chamber has been specially designed using SolidWork software and printed using 3D printer with polylactic acid (PLA) material. The sensing activity was done in the sensor chamber with a sliding drawer which is used to place the sensing material or sample. OceanView software was used to analyze the recorded spectrum from the spectrometer. For this project, the experiment of the plasmonic sensor was carried out using targeted analyte namely chlorpyrifos with deionized (DI) water was set as a reference medium. Gold nanoparticles with nanospheres shape used as sensing materials. The sensing parameters are based on changing its intensity and resonance peak position. This plasmonic sensor was compared with UV-VIS spectrometer data to make sure it standardize and function correctly. Besides, the sensing process toward different concentrations of chlorpyrifos from 7.15 mM to 28.60 mM have been done. As a conclusion, the plasmonic sensor was successfully developed for toxic detection in solution form.

Sensitive real-time monitoring of refractive indices and components using a microstructure optical fiber microfluidic sensor.

Based on the surface plasmon resonance of metal and anti-resonant principles of hole-core microstructure optical fiber (MSF), in this Letter, we demonstrate a MSF microfluidic sensor that combines silver film and hole-core MSF to achieve the sensitive real-time monitoring of refractive indices and components. The large hole core is a common channel for guiding light and flowing measured liquid. Because of the interaction between light and continuous flow measured liquid, the component and refractive indices can be simultaneously monitored by the characteristic absorption wavelength and the surface plasmon resonant peak position, respectively. These results indicate that the MSF microfluidic sensor is an ideal multi-parameter measurement optical sensor.

Tunable high Q-factor terahertz complementary graphene metamaterial

Based on the complementary graphene asymmetric double bars patterns, the tunable Fano resonances with large Q-factors have been investigated in the terahertz regime, including the effects of Fermi levels, structural parameters and operation frequency. The results reveal that compared with existed graphene tunable devices, the Fano resonant curve is very narrow and indicates a large Q-factor of about 60. The strong Fano resonant curves can be convenient tailored. As Fermi level increases, the amplitude of the Fano dip decreases, and the resonant peak position shifts to high frequency. The amplitude modulation depth (MD) of the Fano curve is more, about 90%, if the Fermi level changes in the scope of 0.2–1.0 eV. With the increase of the sample refractive index, the resonant Fano dip shifts low frequency, and the dip amplitude MD can reach more than 40%. The results are very helpful to understand the tunable mechanisms of graphene based Fano systems and to design high sensitivity functional devices, e.g. sensors, modulators, and antenna.

Optical Properties Simulation of Magneto-Plasmonic Alloys Nanostructures

The optical properties of magneto-plasmonic nanostructures are a current subject of research with fast-growing experimental and theoretical activities. The coexistence of iron (Fe) and noble metal (Ag/Au) nanoparticles in the same nanostructure is interesting for biomedical applications, as well as low-cost photonic devices. In this article, we investigated the optical response of Ag–Fe, Au–Fe, and Ag–Fe–Au bimetallic and trimetallic alloy nanostructures as a function of size, shape, and composition by using discrete dipole approximation (DDA) method. We observed that the localized surface plasmon resonance (LSPR) peak position in considered alloy nanostructures is enhanced by changing the particle size and shape, further strongly affected by rectangular shape in comparison to prolate, cube, triangular, and spherical shapes. The absorption and scattering spectra are found between 200 and 647 nm wavelength ranges and can be tuned in UV-visible-near-infrared region of the electromagnetic spectrum in accordance with desired applications. It has been found that the rectangular shape nanostructure show enhancement to LSPR peaks and their corresponding efficiencies in comparison to prolate, cube, triangular, and spherical shapes. The effect of size and shape on relative efficiency has also been studied. An increasing number of peaks appear in the optical spectra of considered nanostructures with higher gold concentration and show a broadening of LSPR peaks. Furthermore, it has been found that the optical response of alloys can be enhanced by varying the metal composition. The comparison of the considered nanostructure of different shape and size shows the LSPR at λmax have the ordering as rectangular > prolate > cube > triangular> spheres. The obtained results indicate the potential use of suitable magnetic-plasmonic nanostructures in medical diagnostics and biological imaging.