Surface Plasmon Resonance Peak Position Research Articles

Effect of wavelength and liquid on formation of Ag, Au, Ag/Au nanoparticles via picosecond laser ablation and SERS-based detection of DMMP.

The present study investigates the effects of input wavelength (1064, 532, and 355 nm) and surrounding liquid environment (distilled water and aqueous NaCl solution) on the picosecond laser ablation on silver (Ag), gold (Au), and Ag/Au alloy targets. The efficacy of the laser ablation technique was meticulously evaluated by analyzing the ablation rates, surface plasmon resonance peak positions, and particle size distributions of the obtained colloids. The nanoparticles (NPs) were characterized using the techniques of UV-visible absorption, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Furthermore, NPs of various sizes ranging from 6 to 35 nm were loaded onto a filter paper by a simple and effective drop-casting approach to achieve flexible surface-enhanced Raman spectroscopy (SERS) substrates/sensors. These substrates were tested using a simple, portable Raman device to identify various hazardous chemicals (malachite green, methyl salicylate, and thiram). The stability of the substrates was also systematically investigated by determining the decay percentages in the SERS signals over 60 days. The optimized SERS substrate was subsequently employed to detect chemical warfare agent (CWA) simulants such as methyl salicylate (a CWA simulant for sulfur mustard) and dimethyl methyl phosphonate (has some structural similarities to the G-series nerve agents) at different laser excitations (325, 532, and 633 nm). A notably higher SERS efficiency for CWA simulants was observed at a 325 nm Raman excitation. Our findings reveal that a higher ablation yield was observed at IR irradiation than those obtained at the other wavelengths. A size decrease of the NPs was noticed by changing the liquid environment to an electrolyte. These findings have significant implications for developing more efficient and stable SERS substrates for chemical detection applications.

Operando UV-vis spectroscopy for real-time monitoring of nanoparticle size in reaction conditions: a case study on rWGS over Au nanoparticles.

We propose the use of surface plasmon resonance (SPR) as a distinctive marker for real-time monitoring in reaction conditions of gold nanoparticles supported on α-Al2O3. The study leverages the SPR shape-and-size dependency to monitor metal nanoparticles in reaction conditions, evidencing an influence of both dimensions and agglomerations on the SPR peak position. Operando measurements, coupling UV-vis spectroscopy and catalytic testing, allows to follow the dynamics during nanoparticle formation (Au3+ to Au0 reduction) and during the reverse water gas shift reaction (CO2 + H2 → CO + H2O). The catalyst structure and stability in reaction conditions was further confirmed by operando X-ray spectroscopy and PXRD data. Overall, this approach enables the direct acquisition of information on the structure-activity relationship of metal-based supported catalysts under actual reaction conditions.

Au-CeO2 composite aerogels with tunable Au nanoparticle sizes as plasmonic photocatalysts for CO2 reduction

Tuning the size of Au nanoparticles is always an interesting task when constructing Au/semiconductor heterojunctions for surface plasmon resonance-enhanced photocatalysis. In particular, the size of Au nanoparticles in the newly emerging “plasmonic aerogel” photocatalyst concept could approach the size of the semiconductor phase. This work provides an alternative route to realize the size tuning of Au nanoparticles in Au-CeO2 composite aerogels to some extent, within the framework of the well-established epoxide addition sol–gel method. The size tuning is achieved by exploiting the multi-functionalities of a mixed organic acid additive containing a thiol group in the gelation step. The obtained aerogel photocatalysts are composed of a porous backbone of interconnected CeO2 nanoparticles and Au nanoparticles, and the size of Au nanoparticles ranges from ∼30 nm to sub-10 nm, while the size of CeO2 remains at ∼15–10 nm. The surface plasmon resonance peak position and intensity contributed by the Au nanoparticles then vary accordingly. Photocatalytic CO2 reduction at the gas–solid interface is chosen as a model reaction to study the effect of Au nanoparticle size on the photocatalytic activity of composite aerogel photocatalysts. The addition of Au nanoparticles undoubtedly enhances the overall activity of the CeO2 aerogel photocatalyst, while the degree of enhancement (in terms of total charge consumption) and product selectivity (CH4 or CO) are different and correlated with the size of the Au nanoparticles. The best performance can be achieved in a composite in which the Au sizes are the smallest.

Strong coupling with directional scattering features of metal nanoshells with monolayer WS2 heterostructures

Realizing and manipulating strong light–matter coupling in 2D monolayer semiconductors are of the utmost importance in the development of photonic devices. Hollow nanostructures of noble metals are particularly interesting because of their stronger local electromagnetic field compared with solid nanoparticles, which facilitate the strong coupling of single metal nanostructures. Here, the tunable single nanocavity plasmon–exciton coupling was demonstrated at room temperature in hybrid systems consisting of Ag@Au hollow nanocubes (HNCs) and monolayer WS2 underneath, where a large vacuum Rabi splitting of 131.3 meV was observed. Mode splitting can be clearly observed from the dark-field scattering spectrum of the single hybrid nanocavity, which is ascribed to the strong coupling between the nanocavity mode and the excitonic mode. Then, we used the finite difference time domain method to simulate these hybrid systems. By changing the thickness of the shell of the Ag@Au HNC, we can tune the surface plasmon resonance peak position of HNCs to match the exciton energy of the monolayer WS2. The strong couplings were realized via the calculated scattering spectra. The calculated results were consistent with the experimental results. Furthermore, the mode volume of different nanostructures was discussed, and the mode volume of HNCs is smaller than other solid ones at the same plasmonic resonance wavelength, which also indicates that its ability to restrict an electromagnetic field is stronger. This study provides an ideal platform for the strong coupling of a single nanocavity at room temperature and has broad application prospects in the field of single-photon devices.

Synthesis of bimetallic AuAg nanoparticles by sequential ion implantation for modifying surface-plasmon-resonance properties

Bimetallic AuAg (Au (80%) and Ag (20%)) nanoparticles (NPs) have been synthesized in fused quartz matrix using sequential ion implantation and post-annealing in air at 600 °C, 700 °C, 800 °C and 900 °C. X-ray diffraction (XRD) results confirm the formation of crystalline Au80Ag20 bimetallic NPs after annealing. Transmission electron microscopy (TEM) investigations have confirmed presence of spherical AuAg alloyed and few AuAg alloy core- Ag shell/satellite NPs. Rutherford backscattering spectra, along with fittings, revealed the mixing of Au and Ag atoms after annealing and movement of elements towards the surface. The peak position of the surface plasmon resonance (SPR) feature of Au has been shifted towards higher energy after sequential Ag implantation. The SPR peak position and intensity is further modified after annealing of Au80Ag20 NPs. The mechanism of modified SPR properties is mechanistically discussed by considering the diffusion, alloying, segregation and redistribution of Au/Ag in the host matrix.

Study of plasmonic properties of copper monosulfide nanoparticles depending on their dielectric constant

The object of research is plasmonic properties copper of monosulfide nanoparticles. One of the most problematic areas is that there is still no unambiguous answer to which main copper monosulfide nanoparticles parameters have a decisive effect on their resonance absorption, scattering or electric field enhancement. It is necessary to study the plasmonic properties of copper monosulfide nanoparticles depending on their main parameter, namely the dielectric constant. The principle of dipole equivalence and Mee-Gans theory for the modeling of the optical nanoparticle characteristics is used. It is found that dielectric constant is a crucial parameter determining the resulting optical response of such nanoparticles. The surrounding medium refractive index affects the position and magnitude of the nanoparticles maximum plasmonic absorption. The nonspherical nanoparticles are characterized by two plasmon peaks corresponding to transverse and longitudinal localized surface plasmon resonance if the ratio between the axes is higher than 1.5. The ellipsoidal nanoparticles exhibit higher sensitivity to changes in the refractive index of the surrounding medium in comparison to the spherical ones. The obtained research results are primarily the basis for further comprehensive research of plasmonic copper monosulfide nanoparticles for their specialized applications. Second, knowledge of the influence of the nanoparticle dielectric constant on their resulting spectral characteristics allow tuning of the localized surface plasmon resonance peak position in a wide wavelength range, from 500 to 1200 nm, using the nanoparticle synthesis technique. Thus, the material under study is promising for sensor applications in a wide spectral range.

Interplaying Role of Particle Size and Polymer Layer Thickness on the Large Tunable Optical Response of Polymer-coated Silver Nanostructures

The interplaying role of particle size and polymer layer thickness on the tunable optical response of polymer-coated Ag nanoparticles (NPs) has been studied experimentally and theoretically. A large redshift ( $$\sim$$ 38 nm) of surface plasmon resonance (SPR) peak position has been observed experimentally for Ag NPs of sizes in the range of 8−18 nm synthesized by polyol process with the varying concentration of metal precursor (AgNO $$_{3}$$ ) and using a surfactant (PVP) as a stabilizer. The observed large redshift of the SPR peak position of Ag NPs coated with PVP has been argued due to mainly change of NP size as well as change of local dielectric environment in the vicinity of the Ag NPs. The experimentally observed SPR peak shift has been explained by considering the system as a metal-core polymer-shell nanostructure. The change of local dielectric environment of the surrounding of the NPs is due to the change in the PVP layer on the NPs. Such observation has been confirmed through the theoretical studies considering the changes of NP size as well as the effective thickness of the PVP layers on the NPs. The SPR peak of the system with core-shell nanostructure has been found to vary linearly with the increase in radius of core and thickness of shell together. However, it changes exponentially with particle size alone. It has been found from a detailed study that the change in the ratio of radius of core and thickness of the shell is responsible for the observed redshift. Thus, the redshift of SPR peak position of Ag NPs cannot be justified by only considering the increase in particle size. Rather shell thickness has been found to play a prominent role in the SPR peak shift. This study can be used to understand the optical response of noble metal NPs coated with organic polymers.

Initial Study of Thin-Film Derived Gold Nanoparticles (Au NPs) Surface Plasmon Resonance (SPR) Based Prostate-Specific Antigen (PSA) Detection

The gold nanoparticles (Au NPs) localized surface plasmon resonance (LSPR) based detection of prostate-specific antigen (PSA) biomarker was carried out in this work. Au NPs on Si and quartz substrates were synthesized by DC magnetron sputtering method followed by conventional annealing protocol. The functionalization of antibody and PSA with Au NPs was evaluated using a simple drop-cost method. The SPR peak intensity was found to be proportional to the PSA concentration. The redshift in SPR peak position might be owing to the change in refractive index around the Au NPs with the conjugation of antibody and further additional binding of specific PSA at different concentrations.

Green Synthesized Ag Nanoparticles for Bio-Sensing and Photocatalytic Applications.

In this work, sensing and photocatalytic activities of green synthesized silver nanoparticles (Ag NPs) are investigated. Ag NPs have been synthesized by the reduction of silver nitrate (AgNO3) using different leaf extracts. An optimum surface plasmon resonance (SPR) behavior is obtained for neem leaf extracts because of the presence of a high concentration of diterpenoids, as evidenced from gas chromatography mass spectroscopy results. The underlying mechanism for the formation of Ag NPs is highlighted. The Ag NPs are in spherical shape and exhibit the hexagonal crystal phase and also show a good stability. The biosensing property of the Ag NPs is evaluated using mancozeb (MCZ) agro-fungicide, and the SPR peak position exhibited a linear response with MCZ concentration. The sensitivity is found to be 39.1 nm/mM. Further, the photocatalytic activity of Ag NPs is tested using 0.5 mM MCZ solution as a model under UV–visible illumination. It is observed that photocatalytic activity is caused by the formation of reactive oxygen species. Therefore, the green synthesized Ag NPs are potential candidates for biosensing and photocatalytic applications.

Spectral Tuning of Plasmon Resonances of Bimetallic Noble Metal Alloy Nanoparticles Through Compositional Changes

The optical absorption properties of the bimetallic noble metal alloy (viz. Au-Ag, Au-Cu, and Ag-Cu) nanoparticles (NPs) of radii of 10 nm and 20 nm embedded in silica glass have been studied theoretically using a simple model based on the effective medium theory. Our study reveals that the spectra of the above bimetallic alloy NPs exhibit single but composition-sensitive surface plasmon resonance (SPR) peak which indicates the successful formation of alloys. The position of the SPR peak that appeared corresponding to alloy NPs is different from that of the component metals. The study further reveals that the Ag-Au and Au-Cu alloy systems are completely miscible over the entire concentration range but Ag-Cu is miscible up to a certain extent, although, their SPR peak shows a linear shift with molar concentration. It has been further observed that the phase of the Ag-Au alloy system changes with concentration of Au during the alloy formation but no such change is seen in the other two systems. Thus, our study shows that the Ag-Cu system which otherwise does not form alloy in bulk may form alloy in nanoscale with limited miscibility. A shift of the SPR peak positions from ~ 405 to ~ 535 nm for Au-Ag, from ~ 535 to ~ 590 nm for Au-Cu, and from ~ 405 to ~ 436 nm for Ag-Cu NP systems has been observed for different composition of constituent monometals. The compositional changes lead to a spectral tuning of the SPR of the system under studies.

SYNTHESIS AND OPTICAL PROPERTIES OF NANOCOMPOSITES BASED ON LIQUID CRYSTAL WITH BIMETALLIC Au + Ag NANOPARTICLES OF ALLOY TYPE.

In this work, we have carried out a research which aimed to obtain complex nanoparticles of noble metals Au + Ag in the form of bimetallic alloys. Bimetallic nanoparticles were synthesized directly in a liquid-crystalline cadmium caprylate melt in an argon atmosphere in the temperature range of mesophase existence by the simultaneous chemical reduction of cations of gold (Au3+) and silver (Ag+) from their compounds, tetrachloroaurate acid (H[AuCl4]×3Н2О) and silver nitrate AgNO3, respectively.
 The effect of synthesis duration (3 and 5 hours) on the spectral behavior of binary nanoparticles have been studied. It has been shown that when the synthesis duration is 3 h, mainly homogeneous bimetallic alloys are obtained, and when it is 5 h, both homogeneous and gradient alloys can be obtained. The absorption spectra of homogeneous alloys are characterized by the presence of one surface plasmon resonance (SPR) peak, which occupies an intermediate position relative to the SPR peaks for monometallic nanoparticles, i.e. between 425 and 560 nm. When forming heterogeneous alloys, which are formed in the molar ratio range where the amount of silver ions predominates, the absorption spectra exhibit two SPR peaks which relate to nanoparticles with different metallic silver content. The formation of metallic nanoparticles containing different metals may be due both to the different mobility of noble metals ions in the liquid crystal matrix and to the different rate of rearrangement of metals in the new formed heteronanoparticle.
 It has been found by electron spectroscopy and transmission electron microscopy that the nanoparticles in this matrix have mostly a spherical shape with a mean diameter of 15 nm. The possibility of the fine control of the position of SPR peak of bimetallic nanoparticles in a liquid crystal matrix over a wide optical range of 422–580 nm is shown.

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...

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.

Ab initio calculation of stressed cesium iodide lattices and resulting surface plasmon resonance peak shifts

Alkali halides have received attention due to their potential application as detector coating. This is due to the appearance of Surface Plasmon Resonance (SPR) absorption peaks in their absorption spectrum. The formation of SPR peaks is due to the formation of cesium metal clusters within the cesium halide matrix. Experimental work on cesium iodide explained the formation of cesium clusters in cesium iodide films. It was experimentally seen that when iodine atom escapes from the cesium iodide unit cell, then the newly created cubic unit cell of cesium exerts force on neighboring cesium iodide unit cells. This force results in cesium iodide taking up a tetragonal lattice structure. The aim of this paper is to theoretically investigate the tetragonal cesium iodide’s band structure and dielectric constant using ab initio calculations. The results indicate that both the band structure and the dielectric constant of cesium iodide in tetragonal phase show a systematic variation with changes in the lattice constant. This alteration in dielectric constant or variation in refractive index of cesium iodide, which acts as the surrounding media for the cesium metal clusters, induces a shift in the SPR peak position. The calculated dielectric constants were used for Gan model calculations of the extinction coefficient and evaluation of SPR peak position ([Formula: see text]). A redshift in [Formula: see text] was seen with increasing dielectric constant that appears with stress acting on cesium iodide’s lattice. These results were found to be in agreement with experimental results reported earlier by us.

Scrutiny of Surface Plasmon Resonance Bands of Colloidal Cu and Cu-Ag Nanoparticles in Different Reaction Media for Stability Evaluation

The copper nanoparticles (CuNPs) were developed in two different reaction media (distilled water (DW) and ethylene glycol (EG)) by chemical reduction method using two different stabilizers (polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP)). We carried out a careful examination of the time evolution of surface plasmon resonance (SPR) bands (specifically, peak positions and intensities) of colloidal CuNPs so as to evaluate their stability. In addition, the changing pattern of SPR peak positions and intensities during the stability time period was also investigated. Effects of stabilizer materials, stabilizer concentration, Ag capping and reaction medium on the stability of CuNPs colloids have been highlighted. The maximum stability of CuNPs is 4 hours with stabilizer PEG and is 4 days with PVP in DW. They, with PVP, extend up to 10 days in the different reaction medium (EG). The stability time of CuNPs in EG is further lengthened to 20 days in the presence of Ag capping (Cucore AgshellNPs). Thus a proper selection of the stabilizing/capping agent and the reaction medium is critical in determining the stability of CuNPs colloids. The benefits of stabilization of CuNPs for real world applications are immense and this study would help in examinning the stability of other novel plasmonic metal nanostructures.

Effect of core-shell structure on optical properties of Au-Cu2O nanoparticles

Solid Au-Cu2O core-shell nanoparticles were synthesized using gold nanoparticles of 16.6nm in size as the core. The core-shell structure of the synthesized particles was confirmed and characterized by TEM and HRTEM images. Due to their similar crystal structure, the (111) planes of Cu2O are nucleated and grown epitaxially on the {111} facets of Au nanoparticles with the lattice mismatch of about 4.3% resulting in a polycrystallized Cu2O shell covering the Au nanocore. Due to the quantum confinement effect, the band gap energy Eg of the synthesized Cu2O shells is blue-shifted from 2.35 to 2.70eV as the shell thickness decreases from of 24.6±3.6 to 9.0±1.7nm. The localized SPR (Surface Plasmon Resonance) peak of the Au nanocore undergoes a large red shift of the order of a hundred of nm due to both the high refractive index and the increase of the thickness of Cu2O shell. Theoretical models within the Drude framework significantly underestimate the experimental data and predict a wrong rate of change of the SPR peak position with respect to the shell thickness.

Enhancement of Fluorescence and Photostability Based on Interaction of Fluorescent Dyes with Silver Nanoparticles for Luminescent Solar Concentrators

For luminescent solar concentrators (LSCs), it is important to enhance the fluorescence quantum yield (FQY) and photostability. Our measurements have demonstrated that the addition of silver nanoparticles to dye solution causes broadening of absorption bands, so the spectral range of sunlight absorbed by LSC has increased. Silver nanoparticles (NPs) were characterized by X-ray diffraction (XRD) and UV-Vis absorption spectra. UV-Vis spectrum showed a single peak at 442 nm due to the surface plasmon resonance (SPR). The position of SPR peak exhibited a red shift after the sample was exposed to UV irradiation (unfiltered light). The optical band gap values have a reduction from 2.46 to 2.37 eV after irradiation for 960 minutes. Such reduction in optical band gap may be due to change in particle size calculated using Mie theory. The photostability of organic dyes used was improved after adding silver nanoparticles. The area under fluorescence spectra of dyes with silver NPs increased by 41–31% when compared with identical dye concentrations without silver nanoparticles as a result of interaction of the species with silver NPs.

Study of Surface Plasmon Resonances of Core-Shell Nanosphere: A Comparison between Numerical and Analytical Approach

An investigation of the wavelength dependent extinction spectra of coated sphere with different core@shell compositions based on discrete dipole approximation technique has been presented in this paper. We have used combinations of A g, A u, and S i O 2 for this analysis. Specifically, we study the impact of spherical core-shell thickness on its surface plasmon resonance (SPR) peak positions and corresponding spectral widening in distinct regimes of the spectrum. We observe that SPR peak of core-shell nanoparticle(CSNP) can be tuned over the visible to near-infrared spectrum region by manipulating the core/shell ratio and composition of core and shell. Specifically, for dielectric@metal (core@shell) nanoparticle, SPR peak position shifted towards lower wavelength as we increase the shell thickness, which is opposite to the SPR behavior of metal@dielectric. The extinction spectrum shows linear relation between SPR position and thickness of the shell. Further, we observed two resonant peaks for the case of metal@metal CSNP. The SPR peak of Au@Ag (a eff 100 nm with shell thickness 8 nm) reveals two resonant peak corresponding to Au (594 nm) in red domain, while the peak in blue domain corresponds to Ag (402 nm). We also observe that optical resonance of CSNP can be tuned across the near-infrared region by changing the surrounding medium of higher refractive index. Further, near field pattern of core@shell geometry at resonance wavelength is also shown in the present study. We have also compared the numerical and analyticalmethod for smaller size CSNP with varying thickness and the results show good agreement.

SPR sensitivity of silver nanorods in CsBr-Ag nanocomposite thin films

We have investigated the optical and morphological properties of CsBr-Ag complex thin films deposited by thermal evaporation on glass substrate. By varying the thickness of the film with fixed mass ratio of cesium bromide and silver, we observed a broad absorption peak in the visible region from 350 to 450 nm corresponding to the transverse and longitudinal surface plasmon resonance (SPR) mode. Red shift is observed, with varying film thickness, in SPR peak position corresponding to longitudinal mode with no significant change in transverse mode due to variation in the aspect ratio of the silver nano crystalline grains. Scanning electron microscope and EDX revealed the formation of silver nanorods in film samples. Such, stable and tunable CsBr-Ag films can be used in optical filters.

Surface plasmon resonance-enhanced light interaction in an integrated ormocomp nanowire

An integrated ormocomp nanowire coated with gold metal layer is proposed and its optical characteristics with the effect of surface plasmon resonance (SPR) are studied. The integrated rib-like nanowire has a trapezoidal shape with sidewall angles of 75°. It is coated with 50 nm gold layer to introduce the SPR and enhance the evanescent field in the sensing region located at the dielectric/metal interface. The possible field modes, the normalized power confinement, and the SPR peak position of the nanowire are studied over the wavelength and the metal thickness by using the full-vectorial H-field FEM in quasi-TM mode. The attenuation coefficient of the nanowire, the SPR peak wavelength, and the wavelength shift is experimentally extracted for three different cladding materials. The redshift of the supermode coupling between the dielectric mode and the anti-symmetric supermode is observed with the higher cladding-index and larger metal thickness. The improvement of the power confinement in the sensing region with the SPR effect is ten times (10×) better than a previous similar study.