Position Of Localized Surface Plasmon Resonance Research Articles

Plasmonic hemispherical Ag nanoparticles on silicon substrate: A comprehensive study of optical properties

In this work, we demonstrate a comprehensive study of the optical properties of hemispherical Ag nanoparticles (AgNPs) on a single-crystal (c-Si) wafer. The fabricated method involves a galvanic displacement reaction of Ag on c-Si and annealing in oxygen atmosphere at 500 °C. Substrates with different morphological parameters of AgNPs were obtained by varying the volume ratio of Ag in the deposition solution. Using the quasinormal modes (QNMs) theory formalism, the localized surface plasmon resonance (LSPR) multipole positions were determined as a function of the AgNP size and incidence angle. Also, the effective field approximation and QNMs methods were used to calculate the specular reflectance of the disordered hemispherical array on c-Si. Thus, the experimentally obtained LSPR positions in the reflectance spectra were described. Finally, surface-enhanced Raman scattering (SERS) demonstrated reliable detection of brilliant green triphenylmethane dye (1 nM), methyl red dye (10 nM) and hemoglobin from bovine blood (1 mM). The dependence of the SERS enhancement factor on the LSPR position and the absorption band of the analyte was established, the maximum value of which was 1.1 × 107. In summary, this study suggests that the numerical and experimental investigation of the optical properties of hemispherical AgNPs on c-Si contributes to the field of optical sensing.

The approaches for localized surface plasmon resonance wavelength position tuning. Short review

A unique feature of nanoparticles made from highly conductive materials (plasmonic nanoparticles) is that their localized surface plasmon resonance (LSPR) wavelength position can be tuned by changing the shape, size, composition and environment in accordance with the purpose of the application. In this paper, the main mechanisms of LSPR tuning that are available at the present time are reviewed. In particular, a widely used method for tuning the LSPR wavelength position is based on selecting the type of a plasmonic nanoparticle material such as gold, silver, copper, aluminum and gold-silver alloy. The examples of changing the resonance absorption position by using nanoparticles with different shapes and dimensions have been аlso demonstrated. Furthermore, works with less used LSPR tuning methods, such as controlled regulation of the distance between nanoparticles in one and two dimensions have been considered. The number of works is given, where the LSPR wavelength position can be also controlled by changing the environment in the vicinity of plasmonic nanoparticle: the substrate thickness, the thickness and dielectric parameters of the layer on the surface of the nanoparticle. Examples of active influence on the change in the wave position of LSPR by applying an electric potential and regulating plasma modes have been also discussed.

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.

Simulation and Experimental Studies of Size Effects on Plasmonic Gas Sensing with Nanohole Arrays

Simulation and Experimental Studies of Size Effects on Plasmonic Gas Sensing with Nanohole Arrays

Formation of silver nanoparticles in ion-exchanged glass with nanosecond laser irradiation

We studied the irradiation of silver enriched soda-lime glass slides by 6 nanosecond long laser pulses at the wavelengths of 1064 and 532 nm. The extinction spectra of the irradiated glass regions after the laser exposition and after chemical and reactive ion etching (RIE) were compared. Independently on the wavelength, the irradiation resulted in the formation of silver nanoparticles demonstrating localized surface plasmon resonance (LSPR), which gradually disappeared with the etching of the samples. The dependence of the spectral position of LSPR on the etching time was significantly different for chemical etching and RIE. We relate this to the chemical interaction of silver with the gases used in RIE.

Intriguing branching of the maximum position of the absorption cross section in Mie theory explained.

A potential control over the position of maxima of scattering and absorption cross sections can be exploited to better tailor nanoparticles for specific light-matter interaction applications. Here we explain in detail the mechanism of an appreciable blue shift of the absorption cross-section peak relative to a metal spherical particle localized surface plasmon resonance (LSPR) defined as the maximum of the extinction (and scattering) cross section. Such a branching of cross sections' maxima requires a certain threshold value of size parameter (x≈0.7 for dipole channel) and is a prerequisite for obtaining high fluorescence enhancements, because the spectral region of high radiative rate enhancement becomes separated from the spectral region of high non-radiative rate enhancement. A consequence is that the maximum of the absorption cross section cannot be used as the definition of the LSPR position for x≳0.7.

Simulated and Experimental Studies of Size Effects on Plasmonic Gas Sensing with Nanohole Arrays

Simulated and Experimental Studies of Size Effects on Plasmonic Gas Sensing with Nanohole Arrays

Predicting the Size of Silver Nanoparticles from Their Optical Properties

In this study, localized surface plasmon resonance (LSPR) of the spherical silver nanoparticles (AgNPs) was evaluated based on experimental and theoretical viewpoints. In the experimental phase, a facile seed-mediated method was employed to synthesize spherical AgNPs with different sizes. As expected, an increase in the size of AgNPs resulted in a red-shift in LSPR peak position from 390 to 460 nm. Besides, the theoretical LSPR peak position of AgNPs was derived from Mie theory using different refractive indices databases. A comparison between the experimentally obtained data and the theoretical predictions indicated that “Palik” database can lead to a more reliable data regarding the size of AgNPs. Finally, a relation was established for the prediction and estimation of AgNPs’ size through a simple measurement of LSPR position with a UV-Vis spectrometer.

Localized Surface Plasmon Resonance in Gold Nanocluster Arrays on Opaque Substrates

We report on the investigation of the localized surface plasmon resonance (LSPR) in periodical Au nanostructures. The arrays of Au nanoclusters and dimers were fabricated on Si and Si/SiO2 surfaces by electron beam lithography. Diameters and periods of nanoclusters with disk shape vary in the range of 30–150 and 130–200 nm, respectively. Because of the opaque nature of the substrates, optical reflection spectroscopy was chosen to probe the plasmonic properties of the metal nanostructures. From a comparison of experimental reflection spectra with those numerically simulated by the Finite Difference Time Domain (FDTD) method, we determined the model structural parameters of the plasmonic nanostructures. These parameters were further used for the calculation of absorptance spectra of the plasmonic structures for which absorptance in the substrate was subtracted. LSPR positions were determined from the maxima of the absorptance spectra. This study reveals a strong dependence of the LSPR position on nanocluster size, distance between nanoclusters, as well as on the SiO2 layer thickness in the nanometer range. In the case of dimer arrays, the plasmon anisotropy in the dimers leads to a splitting of the LSPR plasmon into two modes with orthogonal polarizations. The absorptance spectra reveal a transverse LSPR mode corresponding to the excitation of plasmons in nanoclusters induced by scattered fields from the neighboring ones. This research provides a pathway for a fast and cost-effective determination of the LSPR position from optical reflection spectra. A broad field of potential applications of metal structures with well-controlled plasmonic properties includes surface-enhanced infrared absorption, photoluminescence, and Raman scattering as well as signal transmission in silicon photonics.

Electrochemical Synthesis of Ammonia from N2 and H2O under Ambient Conditions Using Pore-Size-Controlled Hollow Gold Nanocatalysts with Tunable Plasmonic Properties.

An electrochemical nitrogen reduction reaction (NRR) could provide an alternative pathway to the Haber-Bosch process for clean, sustainable, and decentralized NH3 production when it is coupled with renewably derived electricity sources. Developing an electrocatalyst that overcomes sluggish kinetics due to the challenges associated with N2 adsorption and cleavage and that also produces NH3 with a reasonable yield and efficiency is an urgent need. Here, we engineer the size and density of pores in the walls of hollow Au nanocages (AuHNCs) by tuning their peak localized surface plasmon resonance (LSPR); in this way, we aim to enhance the rate of electroreduction of N2 to NH3. The interdependency between the pore size/density, the peak LSPR position, the silver content in the cavity, and the total surface area of the nanoparticle should be realized for further optimization of hollow plasmonic nanocatalysts in electrochemical NRRs.

Plasmonic Properties of Aluminum Nanocylinders in the Visible Range

Plasmonic and surface enhanced Raman scattering (SERS) studies have been performed on aluminum nanocylinders arrays of different diameters. We observed sharps localized surface plasmon resonance (LSPR) peaks that can be tuned on the whole visible range and having the same behavior than gold nanocylinders. The near-field enhancement was measured by SERS on probe molecules as well as on the indium tin oxide (ITO) substrate using two excitation wavelengths: 660 and 785 nm. No SERS signal of the probe molecules was detected. Using the ITO substrate SERS signal, we were able to measure a small near-field enhancement largely lower than the one reached with gold nanocylinders indicating that this kind of structure in not usable for SERS in this spectral range. A spectral shift is also observed between the SERS measurement and the LSPR position. All the experimental results are compared to DDA simulation in order to provide interpretation of the data.

Directional Nanoplasmonic Antennas for Self-Referenced Refractometric Molecular Analysis

Localized surface-plasmon resonance (LSPR) sensors are typically based on tracing resonance peak shifts that precisely follow changes in the local refractive index. Such measurements usually require a spectrometer, a stable light source, and an accurate LSPR position tracing technique. As a simple but efficient alternative, we investigated a self-referenced single-wavelength sensing scheme based on angle-dependent and highly directional radiation patterns originating from a monolayer of asymmetric gold nanodimers. We found that one could easily trace a model biotin–neutravidin recognition reaction as well as minute bulk refractive index changes, by measuring the intensity ratio between the light scattered in two different directions with respect to the dimers. The refractometric resolution of the methodology was estimated to be on the order of Δn ≈ 10–5 RIU. These results may be particularly useful for label-free biosensing applications that require a combination of simple and cost-effective optical readout with a reasonable sensitivity.

SPECTROSCOPIC STUDIES ON Ag/PVA NANOCOMPOSITE THIN FILMS PREPARED BY THERMAL ANNEALING PROCESS

In this paper, a systematic spectroscopic analysis on silver–polyvinyl alcohol ( Ag /PVA) nanocomposite thin films is reported. Ag /PVA nanocomposite thin films fabricated by thermal annealing process are shown to exhibit a strong localized surface plasmon resonance (LSPR) at wavelength around 400 nm. The effects of different fabricating parameters on the absorbance and spectral position of LSPR are also investigated. The particle sizes calculated from Mie light scattering theory are found to agree with the values obtained from SEM characterization.

Silver-doped TiO 2 prepared by microemulsion method: Surface properties, bio- and photoactivity

A series of Ag-TiO 2 photocatalysts were obtained in microemulsion system (water/AOT/cyclohexane), using several Ag precursor amounts ranging from 1.5 to 8.5 mol.%. The photocatalysts’ characteristics by X-ray diffraction, STEM microscopy, UV–vis spectroscopy, X-ray photoelectron spectroscopy, BET methods showed that a sample with the highest photo- and bioactivity had anatase structure, about 90 m 2/g specific surface area, absorbed light over 400 nm and contained 1.64 at.% of silver (0.30 at.% of Ag 0 and 1.34 at.% of Ag 2O) and about 13 at.% of carbon in the surface layer. The photocatalytic activity of the catalysts was estimated by measuring the decomposition rate of phenol in 0.21 mM aqueous solution under visible and ultraviolet light irradiation. The bioactivity of silver-doped titanium dioxide nanocomposites was estimated using bacteria Escherichia coli and Staphylococcus aureus, yeast Saccharomyces cerevisiae and pathogenic fungi belonging to Candida family. All modified powders showed localized surface plasmon resonance (LSPR) in visible region with almost the same position of LSPR peaks indicating that similar sizes of silver, regardless of used amount of Ag, is deposited on titania particles during microemulsion method. STEM microscopy revealed that almost 50% of observed silver nanoparticles deposited at the TiO 2 surface are in the range from 5 to 10 nm.

Wavelength-Scanned Surface-Enhanced Resonance Raman Excitation Spectroscopy

We explore the correlation between localized surface plasmon resonance (LSPR) of triangular Ag nanoparticles, molecular resonance, and the surface-enhanced resonance Raman excitation profile of molecules adsorbed on these nanostructures. Ag nanoparticles with various LSPRs were fabricated with nanosphere lithography (NSL). A monolayer of tris(2,2′-bipyridine)-ruthenium(II) (Ru(bpy)32+) was introduced to the NSL Ag nanoparticles, and its effect on the LSPR was monitored by UV−vis spectroscopy. Wavelength-scanned surface-enhanced resonance Raman excitation spectroscopy (WS SERRES) profiles of Ru(bpy)32+ adsorbed on Ag nanoparticle arrays were measured for excitation wavelengths in the range of 400−500 nm. The WS SERRES profiles are correlated, both spatially and spectrally, with the corresponding LSPR spectra of the nanoparticle arrays and with the solution absorption spectrum of Ru(bpy)32+. The WS SERRES profile peak position depends on the relative spectral position of LSPR and the molecular resonance. Quasi-static electrodynamics modeling was applied to simulate the WS SERRES profiles, and the calculations are in agreement with the experimental results, demonstrating that the WS SERRES profiles involve multiplicative electromagnetic and resonance Raman enhancements.