Position Of Surface Plasmon Resonance Research Articles

Investigation of microstructural, micromorphology, and surface plasmon resonance characteristics in Ni/Al, Ni/Cu, and Ni/SS thin films.

As the first boundary between the environment and the material, the surface plays an important role in their interaction with each other, therefore, the use of appropriate tools and analysis to examine the mechanical properties and morphology of surfaces has particular importance in industry and research. In this research, a thin film of nickel was deposited on metal substrates made of aluminum, copper, and steel by using the RF magnetic cathode. Then, using a non-contact atomic force microscope, the morphological properties of the nickel film with static parameters, Minkowski functionals (MF's), fractal, and multifractal were extracted to be analyzed and studied. After that, using parameters such as root mean square (RMS) roughness, skewness, and kurtosis, it was determined how the surface roughness, distribution, and probability density of particles on the film surface alters with the change of the substrate. Next, by examining and analyzing the Δα and Δf parameters obtained from the multifractal section, the morphology of the produced film on the metal substrates was investigated. Then, the change in the surface plasmon resonance (SPR) peak position is changed for the prepared film in the range of the absorption spectrum due to the substrate effect and the microstructural properties of the formed film. HIGHLIGHTS: Ni film has been deposited by Rf magnetron sputtering. The effect of metal substrates on the topography, fractality, and optical properties was studied. Minkowski functionals were used to investigate the surface morphology of the samples. Substrate's material and the topography of the formed film can changed the surface plasmon resonance position.

Biosynthesis of Ag@Au bimetallic nanoparticles from Hymenaea courbaril extract (Jatobá) and nonlinear optics properties

Green synthesis of metal nanoparticles (NPMs) has been considered an innovative and sustainable alternative to produce metallic nanoparticles, due to the use of biological structures or parts thereof as reducing and stabilizing agents. This study reports, for the first time, the use of leaf extract from Hymenaea courbaril (Jatobá) as a reducing and stabilizing agent in the synthesis of bimetallic nanoparticles (Ag@AuNPs) in different proportions. Also, the nonlinear optical properties were investigated with continuous laser excitation at 532 nm by Thermal lens spectroscopy and Z-scan technique. The leaf extract is composed of chemical groups such as tannins, flavonoids, and others, confirmed by infrared spectroscopy, responsible for the process of chemical reduction. The UV–VIS spectra confirmed the formation of nanoparticles, through the presence of typical Surface Plasmon Resonance (SPR) bands characteristic of these nanostructures, ranging from 433 nm to 508 nm, depending on the proportion of silver and gold precursors. The nanostructures have an average hydrodynamic radius value of 48 nm and all exhibit a negative surface charge. TEM analysis shows that the Ag@AuNPs were spherical-like shape. The thermo-optical properties were investigated using thermal lens spectroscopy and showed thermal diffusivity values in the range of (8–10) × 10−4 cm2/s, depending on the SPR position. The Z-scan technique shows that the nonlinear refractive index is negative, and we observe the reverse saturable absorption. The results obtained indicate that these nanostructures have potential for nonlinear optics and photothermal applications.

Thermal dewetting as a method of surface modification of the gold thin films for surface plasmon resonance based sensor applications

Here, we report a quick and simple approach with low, optimized production costs to obtain surface plasmon resonance (SPR) based sensors fabricated through a time- and resource-effective method based on thermal dewetting of thin Au films. From the applicative point of view, the method of detection presented here should be easier to implement, since light transmission measurements seems to be much less challenging than light refractive index changes measurements conducted by many authors. Metallic films with nanometric thickness were deposited by magnetron sputtering method on a Corning 1737 glass substrates. Plasmonic nanostructures were formatted as a result of thermal annealing of the films. The detection repeatability, selectivity, and sensibility of manufactured devices were investigated. For this purpose, many verification tests were performed. The quality of the plasmonic nanostructures used for the detection was examined by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and ultraviolet-visible spectroscopy (UV–VIS). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) spectra showed the absence of any signs of structure degradation after several cycles of detection in the liquid environment. The surface plasmon resonance position of the achieved sensors was linearly changeable in correlation with the ethanol concentration, which translates into their high robustness. Such a simply prepared sensing device showed key features desired in the detection in the liquids area, which opens up the possibility of large-scale commercial production.

Rapid Colorimetric pH-Responsive Gold Nanocomposite Hydrogels for Sensing Applications.

Surface functionalization of metallic nanoparticles (NPs) with external groups can be engineered to fabricate sensors that are responsive to various stimuli like temperature, pH, and numerous ions. Herein, we report the synthesis of gold nanoparticles (GNPs) functionalized with 3-mercaptopropionic acid (GNPs-MPA) and the doping of these nanoparticles into hydrogel materials using the breathing-in/breathing-out (BI-BO) method. MPA has a carboxyl group that becomes protonated and, thus, ionized at a pH below its pKa (4.32); hence, the GNPs-MPA solutions and gels were mostly pH-responsive in the range of 3–5. Optical properties were assessed through ultraviolet-visible (UV-Vis) spectroscopy, namely: transmission and absorption, and the parameters used to quantify the pH changes were the full width at half maximum (FWHM) and position of surface plasmon resonance (SPR). The solutions and gels gradually changed their colors from red to indigo with pH decrementation from 5 to 3, respectively. Furthermore, the solutions’ and doped gels’ highest FWHM sensitivities towards pH variations were 20 nm and 55 nm, respectively, while the SPR’s position sensitivities were 18 nm and 10 nm, respectively. Also, transmission and scanning electron microscopy showed synchronized dispersion and aggregation of NPs with pH change in both solution and gel forms. The gel exhibited excellent repeatability and reversibility properties, and its response time was instantaneous, which makes its deployment as a colorimetric pH-triggered sensor practical. To the best of our knowledge, this is the first study that has incorporated GNPs into hydrogels utilizing the BI-BO method and demonstrated the pH-dependent optical and colorimetric properties of the developed nanocomposites.

Smart design of high‐performance surface‐enhanced Raman scattering substrates

AbstractSurface‐enhanced Raman scattering (SERS) spectroscopy has renowned its fame for the ultra‐high sensitivity and single‐molecule detection ability, and listed as a fingerprint spectrum representative in various trace detection fields. Considerable efforts have been made by researchers to design high‐sensitive SERS‐active substrates ranging from noble metals to semiconductors. This review summarizes the fundamental theories for SERS technique, that is, the electromagnetic enhancement mechanism and chemical enhancement mechanism and the state‐of‐the‐art design strategies for noble metal and semiconductor substrates. It also sheds light on the effective approaches to improve the SERS activity for noble metal substrates, that is, tuning the localized surface plasmon resonance position, the assembling of hot spots, and precise controlling of nanogaps. Although charge transfer is considered as the main reason for the enhancement mechanism for semiconductors at the present stage, the underlying theoretical basis remains mysterious. This review summarized the critical points for SERS‐active substrates design and prospected the future development direction of SERS technology.

Layer-by-layer Functionalization of Gold Nanorods by Polyelectrolytes to Control Surface Spacer and Precisely Tune the Surface Plasmon Resonance Position

We present a layer-by-layer functionalization of gold nanorods (GNRs) by polyelectrolytes in order to control precisely the spacer surrounding the metallic nanoparticles but also to modulate its plasmonic properties. Alternate functionalization with negatively and positively charged polyelectrolytes ensures a 2 nm step control of the spacer from 0 nm up to 10 nm, depending on the number of layers. Such process changes the local refractive index and thus induces a red shift of the surface plasmon resonance. Both solution and solid samples were studied.

Efficacy of ion irradiation in strengthening the surface plasmon resonance effect of Au nanoparticles

Au-Fullerene nanocomposite thin films synthesized by thermal co-evaporation method are irradiated by low energy (2.6 MeV) Ar ions at fluence ranging from 1 × 1014 ions-cm−2 to 3 × 1016 ions-cm−2. To avoid the retrogression of attributes of fullerene subjected to presence of Au, selected concentration and thickness of gold film is kept very small. UV–visible spectroscopy demonstrates the surface plasmon resonance (SPR) peak at 677 nm for the pristine film and at 590 nm after irradiation at fluence of 1 × 1014 ions-cm−2, displaying a shift of 87 nm towards lower side. This confirms that the refractive index of fullerene decreases as an influence of exposure to Ar beam irradiation. Shift in refractive index is explained on the basis of Mie theory which is established by the existence of D and G band after irradiation as displayed in the results of Raman Spectroscopy. A slight increase in the size of Au nanoparticles in irradiated films is observed which is illustrated by TEM images. Atomic Force Microscopy (AFM) images indicate the varying roughness of thin films after irradiation and morphology is determined by SEM images. I-V characterization shows the conductive behavior of Au-fullerene nanocomposite film before and after irradiation at different fluence. There are two phenomena occurring simultaneously with the increase in ion irradiation fluence; one is increase in the size of metal nanoparticle and another is transformation of fullerene in amorphous carbon. This leads to the change in the SPR position of metal fullerene nanocomposite thin film, making ion irradiation as an effective tool to enhance and optimize the optical properties of metal fullerene nanocomposite thin film.

Effect of CTAB on the surface resonance plasmon intensity of silver nanoparticles: Stability and oxidative dissolution

Stable silver nanoparticles (AgNPs) were prepared from the reduction of silver ions by sodium borohydride in presence of shape controlling cationic cetyltrimethylammonium bromide (CTAB) at room temperature. The intensity and position of surface plasmon resonance (SRP), morphology depends on the concentrations of CTAB. The complex forming tendency of CTAB with positive head group of surfactant and borohydride anion (BH4−) was responsible for pre-, and post-micellar effect. The values of BH4−-CTAB binding constant (Ks = 33.6 × 104 mol−1 dm3) and rate constant in micellar pseudo phase (km = 5.5 × 10−5 s−1) were calculated. Catalytic role of CTAB discussed in term of pseudo-phase model. The silver soles were unstable at higher [BH4−] (≥14.0 × 10−5 mol/L). Transmission electron microscopic images indicate that the AgNPs are roughly spherical and poly dispersed. The oxidative dissolution of silver nanoparticles was very slow. The [BH4−] has significant impact on the sensing properties of AgNPs. The dissolution rate increases drastically by adding hydrogen peroxide. Scavengers quenched the oxygen radical reactive species (hydroxy radical and superoxide) and decreased the hydrogen peroxide catalyses rate of AgNPs.

Influence of surfactant, particle size and dispersion medium on surface plasmon resonance of silver nanoparticles

Clear influence of particle size, surfactants and dispersion medium on surface plasmon resonance (SPR) features of Ag nanoparticles (NPs), synthesized in thermal decomposition method, in the broad range of ultraviolet (UV) radiation, critical for many potential applications such as a photocatalyst, UV-sensor and detector, has been demonstrated here. It involves adsorbate coverage, interparticle distance or agglomeration, surface charge density and solvent refractive index (µ). NP agglomeration and surface charge density in solvents of varying µ have been studied systematically through zeta-potential (ζ) and hydrodynamic diameter (HD) using dynamic light scattering (DLS). The main SPR feature found at 316 nm in 31.5 nm NPs shifts to 320 nm in 15.1 nm NPs. The peak at 320 nm in air shifts to 259, 261 and 277 nm in polar solvent methanol, deionized water and ethanol, respectively and to 255, 275 and 282 nm in non-polar solvent n-hexane, benzene and toluene, respectively. In general, the decrease in particle size and increase in µ of solvents show red-shift. Curiously, a number of peaks up to seven in these solvents that are attributed to charge-transfer mechanism and change in inter-particle interaction of the NPs turning from a single peak of SPR in air has been observed for the first time. A model for re-adjustment of Fermi level (EF) of Ag NP and the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) to explain them has also been used. Moreover, the Drude model for shift in the position of SPR in these NPs is only applicable in non-polar solvents, not in polar solvents. Such novel features will be potential candidates for various applications.

Sensitive detection of voltage transients using differential intensity surface plasmon resonance system.

This paper describes theoretical and experimental study of the fundamentals of using surface plasmon resonance (SPR) for label-free detection of voltage. Plasmonic voltage sensing relies on the capacitive properties of metal-electrolyte interface that are governed by electrostatic interactions between charge carriers in both phases. Externally-applied voltage leads to changes in the free electron density in the surface of the metal, shifting the SPR position. The study shows the effects of the applied voltage on the shape of the SPR curve. It also provides a comparison between the theoretical and experimental response to the applied voltage. The response is presented in a universal term that can be used to assess the voltage sensitivity of different SPR instruments. Finally, it demonstrates the capacity of the SPR system in resolving dynamic voltage signals; a detection limit of 10mV with a temporal resolution of 5ms is achievable. These findings pave the way for the use of SPR systems in the detection of electrical activity of biological cells.

Tuning Plasmonic Properties of Truncated Gold Nanospheres by Coating

The influence of TiO2 coating on resonant properties of gold nanoisland films deposited on silica substrates was studied numerically and in experiments. The model describing plasmonic properties of a metal truncated nanosphere placed on a substrate and covered by a thin dielectric layer has been developed. The model allows calculating a particle polarizability spectrum and, respectively, its surface plasmon resonance (SPR) wavelength for any given cover thickness, particle radius and truncation parameter, and dielectric functions of the particle, the substrate, the coating layer, and the surrounding medium. Dependence of the SPR position calculated for truncated gold nanospheres has coincided with the measured one for the gold nanoisland films covered with titania of different thicknesses. In the experiments, gold films with thickness of 5 nm were deposited on a silica glass substrate, annealed at 500 °C to form nanoislands of 20 nm in diameter, and covered with amorphous titania layers using atomic layer deposition technique. The resulting structures were characterized with scanning electron microscopy and optical absorption spectroscopy. The measured dependence of the SPR position on titania film thickness corresponded to the one calculated for truncated sphere-shaped nanoparticles with the truncation angle of ~50°. We demonstrated the possibility of tuning the SPR position within ~100 nm range by depositing to 30 nm thick titania layer.

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.

Plasmonic properties of metal nanoislands: surface integral equations approach

The surface integral equations method is used to analyse the surface plasmon resonance position in a metal island film formed by non-interacting axisymmetrical prolate/oblate hemispheroids placed on a dielectric substrate. The approach is verified via the comparison of results obtained for a hemisphere on a substrate with the ones obtained using the multipole expansion method. The preference of the integral equations method is in obtaining a simple final analytical expression for a particle polarizability in which any dielectric function of a metal can be substituted. Such simple formulae for the hemispherical particle on the substrate and calculated dependences of the hemispheroid resonant wavelength on its aspect ratio are presented.

Surface enhanced Raman spectroscopy of Rhodamine 6G on agglomerates of different-sized silver truncated nanotriangles

This reported study investigated the use of agglomerates fabricated from different-sized Ag truncated nanotriangles in highly sensitive surface enhanced Raman scattering (SERS) by employing Rhodamine 6G dye as the probe molecule. It was found that the SERS intensity of R6G was enhanced as the size of the Ag truncated nanotriangles increased. It was postulated that this phenomenon resulted from the generated hot spots and the roughness of the surface of the agglomerates. In addition, the results exhibited an independent feature on the surface plasmon resonance position. The experimental results showed that the prepared SERS substrate was able to detect R6G over a wide concentration range of 10⿿5⿿10⿿11M and could be used as an effective SERS substrate in trace detection.

Electric Properties of Hemispherical Metal Nanoparticles: Influence of the Dielectric Cover and Substrate

We described the distribution of electric potential and field generated by a planar electromagnetic wave in the vicinity of a hemispherical metal nanoparticle deposited on a dielectric substrate and covered with a dielectric layer of arbitrary thickness using the solution of the Laplace equation. The developed solution is applied to calculate the position of surface plasmon resonance and the distribution of electric field near a hemispherical silver nanoparticle placed on a soda–lime glass surface and covered with titania layer. The position of the surface plasmon resonance as a function of the thickness of TiO2 cover of the silver hemisphere is computed and compared with corresponding experimental data. Developed approach can be applied to evaluate the efficiency of Raman scattering enhanced by metal island films with a protective dielectric spacer.

Electric properties of hemispherical metal nanoparticles: influence of the dielectric substrate

We calculated surface plasmon resonance position for gold and silver hemispheres placed on a dielectric substrate and covered with a thin dielectric layer. The results are applicable in metal islands film enhanced Raman spectroscopy.

Investigating the Plasmon-Mediated Catalytic Activity of AgAu Nanoparticles as a Function of Composition: Are Two Metals Better than One?

The surface plasmon resonance (SPR) excitation by visible light in plasmonic nanostructures can be put to work to mediate catalytic processes. However, the role of composition in bimetallic nanoparticles over the SPR-mediated catalytic activity remains unclear. We investigated herein the SPR-mediated catalytic activity of AgAu nanoparticles as a function of composition toward the oxidation of p-aminothiophenol to p,p′-dimercaptoazobenzene. Our results showed that a “volcano-type” relationship between composition and product conversion was observed, with a maximum activity observed for Ag0.19Au0.81 nanoparticles. The variations in catalytic activity could be explained by the balance between the matching of the excitation wavelength with SPR position and the plasmonic damping due to interband transitions above 500 nm. These data suggest that the precise control over composition allows the fine-tuning of catalytic activity in SPR-mediated catalytic processes.

Anisotropic effective medium properties from interacting Ag nanoparticles in silicon dioxide.

Films containing a layer of Ag nanoparticles embedded in silicon dioxide were produced by RF magnetron sputtering. Optical transmittance measurements at several angles of incidence (from normal to 75°) revealed two surface plasmon resonance (SPR) peaks, which depend on electric field direction: one in the ultraviolet and another red-shifted from the dilute Ag/SiO₂ system resonance at 410 nm. In order to investigate the origin of this anisotropic behavior, the structural properties were determined by transmission electron microscopy, revealing the bidimensional plane distribution of Ag nanoparticles with nearly spherical shape as well as the filling factor of metal in the composite. A simple model linked to these experimental parameters allowed description of the most relevant features of the SPR positions, which, depending on the field direction, were distinctly affected by the coupling of oscillations between close nanoparticles, as described by a modified Drude-Lorentz dielectric function introduced into the Maxwell-Garnett relation. This approach allowed prediction of the resonance for light at 75° incidence from the SPR position for light at normal incidence, in good agreement with experimental observation.

Synthesis of Ag nanoparticles with tunable sizes using N,N-dimethyl formamide.

Ag nanoparticles (NPs) were fabricated using N,N-Dimethyl formamide (DMF) as a solvent and reducing agent together with polyvinyl pyrrolidone (PVP) through a solvothermal method. The position of surface plasmon resonance (SPR) band of as-prepared Ag NPs changed with the chain length of PVP and red shifted with increasing the molecular weight of PVP. The concentration of PVP and reaction time affected the position of absorption peaks. The selective adsorption of PVP on the {100} and {111} facets of Ag depended on the kinds of solvents, which determined the driving force of the growth process of nanostructures. For comparison, ethylene glycol, water, and ethanol was added serving as solvents in the presence of PVP. The result indicates that DMF is a vital factor to kinetically control the formation of Ag NPs. Therefore the favorable facets of Ag nanostructures are {111} facets in a DMF solution. Ag nanoplates together with nanowires were observed in the system of ethanol and water, respectively.

Monitoring plasma treatment of thin films by surface plasmon resonance

We report the surface plasmon resonance (SPR) measurements during plasma treatment of thin films by an indigenously designed setup. From the measurements on Al (6.3 nm)/Ag (38 nm) bi-layer at a pressure of 0.02 mbar, the SPR position was found to be shifted by ~20° after a plasma treatment of ~7 h. The formation of oxide layers during plasma oxidation was confirmed by glancing angle x-ray diffraction (GXRD) measurements. Combined analysis of GXRD and SPR data confirmed that while top Al layer enables controlling plasma oxidation of Ag, the setup enables monitoring the same. The setup designed is a first of its kind for in situ SPR studies where creation of low pressure is a prerequisite.