Surface Plasmon Resonance Frequency Research Articles

Cherenkov terahertz surface plasmon excitation by an electron beam over an ultrathin metal film

The mechanism of Cherenkov excitation of terahertz (THz) surface plasma wave (SPW), by a relativistic electron beam propagating over an ultrathin metal film deposited on glass, is investigated. The SPW field falls off exponentially in vacuum as well as glass, while the surface plasmon resonant frequency is lowered by the reduction of film thickness. The SPW field causes density bunching of the beam leading to current modulation and generation of THz radiation via the Cherenkov interaction. The frequency of the THz decreases with the energy of the beam, whereas the growth rate increases.

Magnetic circular dichroism of thiolate-protected plasmonic gold nanoparticles: separating the effects of interband transitions and surface magnetoplasmon resonance

Magneto-optical activity is demonstrated in thiolate-protected Au nanoparticles with magnetic circular dichroism (MCD) spectroscopy. The samples examined are decanethiolate-protected Au nanoparticles with the mean diameters ranging from 2.0 to 4.7 nm. The nanoparticles larger than 2.4 nm in diameter exhibit a derivative-like MCD signal, indicating the presence of two circular modes of surface magnetoplasmon, but the spectral shape is so asymmetric that its identification is rather difficult. This is due to the contribution of interband transitions occurring at around the localized surface plasmon resonance (LSPR) frequency. We then develop an efficient method to phenomenologically separate the effects of magnetoplasmonic intraband (= Drude) and interband transitions in the measured MCD spectra using an approximation that the optical response of the Au nanoparticle with a critical size (∼2.0 nm) for the disappearance of LSPR, which is also experimentally obtainable, is substantially dominated by the interband transitions. The consistency of the method is ensured for tiopronin-protected Au nanoparticles, and a very small bisignate magnetoplasmonic response hidden in the total MCD spectrum can be extracted. The practical advantage of the proposed method is that we can intuitively and effectively evaluate the characteristic features of the surface magnetoplasmon of thiolate-protected Au nanoparticles without performing complicated Mie or quasielectrostatic calculations.

Tunable ultrasensitive terahertz sensing based on surface plasmon polariton of doped monolayer graphene

We reported the surface plasmon resonance (SPR) on doped monolayer graphene (MLG) for terahertz (THz) sensing of refractive index of testing samples using a prism‐coupling attenuated total reflection configuration. The theoretical detection range and sensitivity of the THz plasmonic sensor were investigated. The sensor performance in terms of variation of detection accuracy with different refractive index was explored. It was demonstrated that the Fermi level energy of MLG and also the gap distance between the prism base and the MLG had great effects on the performance of THz sensing. The gap distance not only caused the coupling resonance frequency shift in the reflection spectrum, but also affected the full width at half maxima (FWHM) of the SPR curve. The incident angle of THz radiation was also the key impact factor of the detection accuracy of the sensor. The effective SPR frequency could be tuned by controlling the incident angle or the Fermi level energy. The results revealed the maximum sensitivity of the THz plasmonic sensor up to 6.65 THz RIU−1 with a figure of merit (FOM) of 1187 RIU−1 for Fermi level energy ranges from 0.4 to 1.2 eV, making the sensor potential for ultra‐sensitive SPR sensing in the terahertz regime.

Systematic control of edge length, tip sharpness, thickness, and localized surface plasmon resonance of triangular Au nanoprisms

Triangular gold (Au) nanoprisms of various sizes were synthesized in a controlled way using a modified three-step seed-mediated method with different volumes of starting seed solution and subsequent first step’s growth solution. The structures and optical properties of the triangular Au nanoprisms were investigated using transmission electron microscopy (TEM), atomic force microscopy, and UV–Vis–NIR spectrophotometry. The Au nanoprisms synthesized also varied in optical response frequency of localized surface plasmon resonance (LSPR) owing to electric dipole polarizations of the Au nanoprisms. This variation depended nonlinearly on the volume of the seed solution. From optical extinction spectra and careful TEM observations, the dipole LSPR peak frequency was found to be linearly proportional to the edge length of the Au nanoprisms. Consequently, it was experimentally shown that the LSPR optical response frequency of their colloidal solutions could be controlled in the near-infrared region (700–1200 nm), corresponding to an edge length of 40–180 nm of the Au nanoprisms. It was also demonstrated that the tip sharpness of triangular Au nanoprisms was improved by using fine Au seeds instead of coarse Au seeds, and the resulting Au nanoprisms were smaller and thinner. A formation mechanism of triangular Au nanoprisms shall also be discussed with a prospect of synthesizing very tiny Au nanoprisms.

Wavelength-Dependent Super-resolution Images of Dye Molecules Coupled to Plasmonic Nanotriangles

The emission properties of fluorescent molecules are strongly affected by proximal plasmonic nanoparticles that act as optical nanoantennas. In particular, fluorescence intensity can be greatly increased by enhancing both the excitation and emission rates of a fluorophore, and the angular and spatial emission pattern from a dye coupled to a plasmonic nanoantenna will be altered. Here, we use single-molecule imaging to measure this shifted emission pattern based on the super-resolution image of cyanine dye molecules coupled to gold nanotriangles. To compare the relative effects of excitation versus emission enhancement on the emission pattern, we vary laser excitation wavelengths, dye emission and absorbance spectra, and local surface plasmon resonance frequency. We demonstrate that the emission pattern is dramatically changed when coupling occurs and that coupling between the dye and gold nanotriangle happens even in the absence of intensity enhancement.

Gold nano-ripple structure with potential for bio molecular sensing applications

We introduce a simple and cost-effective scheme for bio-sensing using nano-ripple structures. One dimensional metallic nano-ripple structures formed by gas cluster ion beam irradiation have shown polarization of light as well as localized surface plasmon resonance. These localized surface plasmon resonance based bio sensors not only are capable of label free real time analytical detection but also show high sensitivity. The nano-surface morphology determines the changes in the plasmonic properties of nano-structures hence the plasmonic response is tunable. By adsorbing a mono-layer of thiolated organic compound on the surface of these substrates we identified the shift in the localized surface plasmon resonance peaks triggered by the change of dielectric function in the neighborhood of the structures. These plasmonic nano-metallic structures can be utilized to observe the change of localized surface plasmon resonance frequency due to the cycle of adsorption, re-adsorption and reactions taking place on the surface that can potentially be mapped in to reaction mechanics. The bio-sensor has monolayer molecule-coating sensitivity and specific selectivity. This study can be extended to sensing biological molecules such as proteins, DNAs, antibodies and antigens.

Localized surface plasmon resonance frequency tuning in highly doped InAsSb/GaSb one-dimensional nanostructures

We report a detailed analysis of the influence of the doping level and nanoribbon width on the localized surface plasmon resonance (LSPR) by means of reflectance measurements. The plasmonic system, based on one-dimensional periodic gratings of highly Si-doped InAsSb/GaSb semiconductor nanostructures, is fabricated by a simple, accurate and large-area technique fabrication. Increasing the doping level blueshifts the resonance peak while increasing the ribbon width results in a redshift, as confirmed by numerical simulations. This provides an efficient means of fine-tuning the LSPR properties to a target purpose of between 8–20 μm (1250−500 cm−1). Finally, we show surface plasmon resonance sensing to absorbing polymer layers. We address values of the quality factor, sensitivity and figure of merit of 16 700 nm RIU–1 and 2.5, respectively. These results demonstrate Si-doped InAsSb/GaSb to be a low-loss/high sensitive material making it very promising for the development of biosensing devices in the mid-infrared.

One-step Solution Processing of Ag, Au and Pd@MXene Hybrids for SERS.

We report on one-step hybridization of silver, gold and palladium nanoparticles from solution onto exfoliated two-dimensional (2D) Ti3C2 titanium carbide (MXene) nanosheets. The produced hybrid materials can be used as substrates for surface-enhanced Raman spectroscopy (SERS). An approximate analytical approach is also developed for the calculation of the surface plasmon resonance (SPR) frequency of nanoparticles immersed in a medium, near the interface of two dielectric media with different dielectric constants. We obtained a good match with the experimental data for SPR wavelengths, 440 nm and 558 nm, respectively for silver and gold nanoparticles. In the case of palladium, our calculated SPR wavelength for the planar geometry was 160 nm, demonstrating that non-spherical palladium nanoparticles coupled with 2D MXene yield a broad, significanlty red-shifted SPR band with a peak at 230 nm. We propose a possible mechanism of the plasmonic hybridization of nanoparticles with MXene. The as-prepared noble metal nanoparticles on MXene show a highly sensitive SERS detection of methylene blue (MB) with calculated enhancement factors on the order of 105. These findings open a pathway for extending visible-range SERS applications of novel 2D hybrid materials in sensors, catalysis, and biomedical applications.

Enhanced Performance of Quantum Dot-Based Light-Emitting Diodes with Gold Nanoparticle-Doped Hole Injection Layer.

In this paper, the performance of quantum dot-based light-emitting diodes (QLEDs) comprising ZnCdSe/ZnS core-shell QDs as an emitting layer were enhanced by employing Au-doped poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) hole injection layer (HIL). By varying the concentration and dimension of Au nanoparticle (NP) dopants in PEDOT:PSS, the optimal devices were obtained with ~22-nm-sized Au NP dopant at the concentration with an optical density (OD) of 0.21. Highly bright green QLEDs with a maximum external quantum efficiency (EQE) of 8.2 % and a current efficiency of 29.1 cd/A exhibit 80 % improvement compared with devices without Au NP dopants. The improved performance may be attributed to the significant increase in the hole injection rate as a result of the introduction of Au NPs and the good matching between the resonance frequency of the localized surface plasmon resonance (LSPR) generated by the Au NPs and the emission band of QD layer, as well as the suppressed Auger recombination of QD layer due to the LSPR-induced near-field enhanced radiative recombination rate of excitons. These results are helpful for fabricating high-performance QD-based applications, such as full-color displays and solid-state lighting.Graphical 80 % enhancement of efficency of quantum dot-based light-emitting diodes with gold nanoparticle doped hole-injection-layer.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1573-8) contains supplementary material, which is available to authorized users.

Tuning the Resonance Frequency of Surface Plasmons Localized in Au-Ag Bimetallic Hollow Nanorods In-situ in a Transmission Electron Microscope

Tuning the Resonance Frequency of Surface Plasmons Localized in Au-Ag Bimetallic Hollow Nanorods In-situ in a Transmission Electron Microscope

Analysis of Photothermal Release of Oligonucleotides from Hollow Gold Nanospheres by Surface-Enhanced Raman Scattering

The photothermal release of single-stranded DNA (ssDNA) from the surface of gold nanoparticles of different shapes and sizes is a promising mode of delivering DNA for gene-therapy applications. Here, we demonstrate the first targeted photothermal release of ssDNA from hollow gold nanospheres (HGNs) and analyze the release of the ssDNA using quantitative surface-enhanced Raman scattering (SERS). The HGNs used demonstrate a tunable localized surface plasmon resonance (LSPR) frequency while maintaining size consistency, allowing for selective ssDNA release based on matching the excitation frequency to the plasmon resonance. It is shown that HGNs with resonances at 760 and 670 nm release significant amounts of ssDNA when excited via 785 and 640 nm lasers, respectively. When excited with a wavelength far from the LSPR of the particles, the ssDNA release is negligible. This is the first demonstration of SERS to analyze the amount of ssDNA photothermally released from the surface of HGNs. In contrast to traditio...

Time-resolved Z-scan investigation of photoheating effect in aqueous suspensions of gold nanorods

In this paper, we study photothermal effects in suspensions of gold nanorods in water. The heating occurs owing to the light absorption and it is especially effective when the light frequency is close to the frequency of the localised surface plasmon resonance (LSPR). We use the time-resolved Z-scan method to monitor the time-dependent temperature profile in the liquid under Gaussian beam illumination. Using the experimentally measure parameters we determine the conditions for vapour generation for different concentrations of gold nanorods.

Surface Plasmon Resonance of an Individual Nano‐Object on an Absorbing Substrate: Quantitative Effects of Distance and 3D Orientation

Modification of the plasmonic response of a metal nano‐object due to interaction with a substrate is experimentally investigated measuring the quantitative optical extinction spectra of individual nano‐objects with various elongated shapes (bipyramids and rods) deposited on a dielectric (silica) or absorbing (carbon) membrane. Apart from the expected dependence of the nanoparticle surface plasmon resonance (SPR) frequency on the nature of the substrate, large substrate and particle shape dependent modifications of its SPR width are demonstrated. These dependencies are ascribed to strong localization of the electromagnetic field associated with the longitudinal SPR of an elongated nano‐object around its tips, leading to different interaction with the substrate depending on the particle shape and 3D orientation relative to the substrate. Both parameters have been precisely determined by electron tomography, permitting excellent reproduction of the experimental data. Experiments performed on silver‐encapsulated bipyramids, whose shape evolves from a pyramidal one towards a cylindrical one, further confirm this effect.

B12-P-11In-situ observation of Au thin film dewetting on SiO2glass substrate during quantum beam irradiation

Noble metal nanoparticles dispersed on dielectric substrates have been extensively studied to apply to advanced optical devices based on surface plasmon resonance (SPR). The SPR frequency could be tuned by morphology and distribution of Au nanoparticles. Therefore, in order to establish a method to control the morphology and distribution of nanoparticles, it is important to understand fully mechanism of nanoparticles formation. In this study, to investigate the mechanism of the Au nanoparticles formation on Au thin film/SiO 2 glass substrate during quantum beam irradiation, we carried out in-situ experiments using multi quantum beam high-voltage electron microscope (MB-HVEM). TEM samples of SiO 2 glass substrates were prepared by a back thinning method using a precision ion polishing system (PIPS; JEOL AT-12310). A thin Au film was deposited on the front surface of TEM samples at room temperature by using a vacuum evaporator. For the in-situ observation, MB-HVEM (JEOL, JEM-ARM1300) equipped with three kinds of laser was used. In this study, the laser was irradiated to the surface of the Au thin film at an angle of 44 degree with a linearly polarized Nd-YAG nanosecond-pulsed laser (wavelength: 532 nm, average laser energy density of per pulse: 50 mJ/cm 2 , pulse repetition rate: 2Hz). In situ observation was recorded by a CCD camera at 10 frames per second.

Vertical dipole above a dielectric or metallic half space: Energy-flow considerations.

The emission pattern from a classical dipole located above and oriented perpendicular to a metallic or dielectric half space is calculated for a dipole driven at constant amplitude. Emphasis is placed on the fields in the metal or dielectric. It is shown that the radial Poynting vector in the metal points inwards when the frequency of the dipole is below the surface plasmon resonance frequency. In this case, energy actually flows out of the interface at small radii and the power entering the metal can actually oscillate as a function of radius. The Joule heating in the metal is also calculated for a cylindrical volume in the metal. When the metal is replaced by a dielectric having permittivity less than that of the medium in which the dipole is immersed, it is found that energy flows out of the interface for sufficiently large radii, a result reminiscent of the Goos-Hänchen effect.

The effect of surface plasmon resonance on optical response in dielectric (core)–metal (shell) nanoparticles

In this work, we present the effect of refractive index of an embedding medium, core and shell having various sizes of metallic nanoshells on the surface plasmon resonance (SPR) properties in the spherical dielectric–metal core–shell nanoparticles based on the quasistatic approaches and Mie theory. For the metallic nanoshell with dimensions comparable to the wavelength of light, the quasistatic approximation shows good agreement with the Mie theory results. However, for large nanoparticles the quasistatic approximation is not appropriate and Mie theory illustrates SPR due to dipole and quadrupole in extinction cross-section. The typical cross-section calculations show two peaks that related to inner and outer surfaces. The dimensional dependence of optical constant in the Drude model leads to a decrease in plasma absorption in metal core–shell. By increasing the shell radius and therefore increasing the metal content the SPR at the outer surface shifts to higher energy and the weaker peak (at inner surface) shifts to lower energy. Also, depending on the metal shell materials SPR occurs in different energy regions and therefore can be tuned the SP frequency at higher energy by changing the shell materials. In addition, SPR frequency is sensitive to variation in refractive index of the environment of core-shell.

Surface plasmon resonance-induced stiffening of silver nanowires.

We report the results of a computational, atomistic electrodynamics study of the effects of electromagnetic waves on the mechanical properties, and specifically the Young’s modulus of silver nanowires. We find that the Young’s modulus of the nanowires is strongly dependent on the optical excitation energy, with a peak enhancement occurring at the localized surface plasmon resonance frequency. When the nanowire is excited at the plasmon resonance frequency, the Young’s modulus is found to increase linearly with increasing nanowire aspect ratio, with a stiffening of nearly 15% for a 2 nm cross section silver nanowire with an aspect ratio of 3.5. Furthermore, our results suggest that this plasmon resonance-induced stiffening is stronger for larger diameter nanowires for a given aspect ratio. Our study demonstrates a novel approach to actively tailoring and enhancing the mechanical properties of metal nanowires.

A facile synthesis of AgxAu1−x/TiO2 photocatalysts with tunable surface plasmon resonance (SPR) frequency used for RhB photodegradation

A series of AgxAu1−x/TiO2 photocatalysts with tunable surface plasmon resonance (SPR) frequencies were successfully prepared via a facile photoreduction combined with a simple replacement reaction between Ag and Au3+ ions. These two reactions react synergistically, resulting in the formation of Ag–Au alloy on TiO2. The as-prepared AgxAu1−x/TiO2 plasmonic photocatalysts exhibiting different colors absorb the visible light with different wavelengths, improving the utilization efficiency of the incident light with distinct frequencies. For RhB degradation, these catalysts containing Ag–Au alloy show much higher visible light-responsive photocatalytic activity than the commercial P25 and the single supported Ag or Au catalysts. By mixing the catalysts AgxAu1−x/TiO2 with different SPR frequencies, the photocatalytic activity can be further improved due to the widened visible light absorption range.

Extreme blueshift of surface plasmon resonance frequency in graphene nanodisk stacks

The extraordinary properties of graphene surface plasmons like strong field confinement, long propagation distance and tunability have made graphene an attractive alternative to noble metals. However, it is still experimentally challenging to increase the resonance frequency in graphene nanostructures beyond the mid-IR limit. In this work, we investigate the blueshift of surface plasmon resonance frequency via plasmon hybridization in graphene disk stacks. Based on a nonretarded approach, we study the plasmon hybrid modes in graphene disk stack structures, considering the optical coupling between the uncouple eigenmodes of each disk. Through this methodology we were also able to extract the scattered and absorbed fields. We find that due to plasmon hybridization in an N-disk stack, each uncoupled mode splits into N hybrid modes. When the distance between disks is close to the strong coupling limit, we observe that for each uncoupled mode there is only one hybrid mode that is blue-shifted compared with the resonance frequency of its respective uncoupled mode. Analysis of the hybridization by reducing the distance between disks shows that in the transition between the weak and strong coupling regimes the interaction is mainly driven by the coupling of edge plasmons. For a stack with 25 graphene disks having a Fermi level of 1.0eV and a 50nm disk diameter, we observe that surface plasmon hybridization can effectively blueshift the resonance frequency up to 0.69eV (1.8μm). In addition, compared to a single graphene disk with the same diameter, the 25-disk stack can increase the peak of absorption and scattering cross sections by 12 and 38 times, respectively, opening up a wide range of applications for graphene surface plasmons in the near-infrared regime.

Numerical study of the effects of polymeric shell on plasmonic resonance of gold nanorods

Gold nanorods (GNRs) have great potential widespread applications in biomedical imaging, drug delivery and photothermal therapy due to unique surface plasmon resonance (SPR) ranging from visible to near infrared (NIR) region, facile synthesis and easy functionalization. The frequency of SPR is not only determined by the nature of the metal, but also by a number of other parameters, such as particle size and shape, the presence of a capping shell on the particle surface, or the dielectric properties of the surrounding medium. In this study, use is made of finite element method (FEM) for the calculation of the complex effective permittivity of the gold-core nanorod coated with polymer shells. Such a permittivity allows the determination of the absorption spectrum of these clothed nanoparticles. A simple scheme based on FEM is developed, which enables us to compute the optical properties, such as the effective dielectric function and absorption cross-section of coated-GNRs which are embedded in a dielectric matrix. The influences of the aspect ratio, shell thickness and dielectric constant of the shell on the longitudinal and transversal resonances modes are investigated.