Tunability Of Surface Plasmon Resonance Research Articles

Quantifying the optical and thermoplasmonic properties of some bimetallic alloy nanospheres

The bimetallic alloy NPs are ideal objects for a variety of applications like catalysis, nanofluidics, thermo-voltaic and bio-imaging due to their peculiar and adaptable optical response in UV–visible-NIR region of optical spectra. The heating effect of bimetallic alloys involves surface plasmon resonance (SPR) and takes place when the material is illuminated by light. Instead of pure and alloy NPs of Au & Ag, the opto-thermal properties of Au-Cu, Au-Al, Ag-Cu and Ag-Al bimetallic alloy nanospheres for their different compositions with a size radius of 10 nm to 50 nm immersed in water (n = 1.33) using the Mie theory approach are investigated theoretically. In order to determine the heat generation and the temperature distribution by plasmonic nanoparticles in the host medium (water in this study) we have solved the heat transfer equation analytically for steady-state conditions. The great utility of these bimetallic alloy nanoparticles for thermoplasmonic investigation is accompanied with a large extent of SPR tunability which is rarely found in their pure monometallic counterpart. The SPR of Aux-Cu1-x (214 nm to 548 nm), Aux-Al1-x (213 nm to 493 nm), Agx-Cu1-x (214 nm to 539 nm), and Agx-Al1-x (214 nm to 381 nm) bimetallic alloys with compositions of x = 0.25,0.50 and 0.75 have been observed for different size of the nanospheres. Thus, we anticipate that the results of this work will evoke the curiosity of researchers towards the use of bimetallic alloys in thermoplasmonic applications.

Wide range tunability of surface plasmon resonance of nanostructured Ag deposited by off-axis magnetron sputtering

In this work, nanostructured Ag showing size distribution dependent tunable surface plasmon resonance (SPR) are grown on glass substrate using off-axis DC magnetron sputtering at a sputtering power of 74 W. Argon gas pressure is set at 8.0 Pa and the deposition time is varied in the range 5–300 s. The structural, morphological, and optical properties are examined by using X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), and UV–Visible spectrophotometer. XRD patterns of all samples reveal characteristic (111) and (200) peaks of fcc Ag. Broad XRD peaks suggest formation of nanosized Ag crystallites with mean crystallite size of 3 nm. FESEM images depict near spherical Ag grains up to 120 s deposition time and elongated grains with greater substrate coverage with extended deposition time of 300 s. SPR features are well distinct in the optical absorption spectra which are highly sensitive to the deposition time. Within a short deposition time of 5–60 s, nanostructured Ag demonstrates wide range SPR tunability from 438 nm to 530 nm. It is observed that the variations in the size distribution as estimated from FESEM images are crucial to observe systematic red shift of SPR with increasing deposition time. Nanosized Ag produced by off-axis magnetron sputtering may be used as a vital component in plasmonic devices and sensors.

Seed-mediated synthesis of silver nanoparticles: Tunable surface Plasmon and their facile fabrication

Abstract Coating of plasmonic metal nanostructures on glass surfaces is important in designing optical sensor probes for analyte detection. Herein, a facile and quick production of AgNPs (silver nanoparticles) into highly anisotropic structures using a seed-mediated autocatalytic process is reported. The nanocrystal growth can also be initiated on glass surface. AFM studies revealed branched networks of crystal growth as well as dense aggregates. Such facets occur as mediated by hydrogen-bonding short ligands used to passivate the AgNPs surface. Experimental findings indicate the substantial influence of the ligand-to-seed on the crystal growth of anisotropic AgNPs and their tunable SPR (Surface Plasmon Resonance) band. The UV–vis spectroscopic studies indicated that the surface Plasmon of the resulting AgNPs was tunable throughout the visible region of the electromagnetic spectrum further extending into the infrared region. The AgNPs were coated on glass slides through a simple in situ process resulting in optically active thin-films thus increasing the effective applicability of the particles. The SPR tunability and easy fabrication methodology shows potential of the AgNPs reported here to be utilized in thin-film devices as well as in future solar cells for enhanced utilization of the solar spectrum.

ITO induced tunability of surface plasmon resonance of tin thin film

A low-cost tin thin film with different thicknesses was deposited on ITO covered silica substrates via magnetron sputtering. The structure, surface morphology, and optical properties of tin/ITO thin films were investigated via X-ray diffraction (XRD), atomic force microscopy (AFM), UV–VIS-NIR double beam spectrometer, and Raman system, respectively. The results show that by controlling the thickness of the tin thin film with ITO, red shift of the surface plasmon resonance wavelength was achieved and the surface-enhanced Raman scattering (SERS) was enhanced. On the contrary, when no ITO layer was employed in the system, the variation of the tin film thickness did not cause a significant change in the resonance wavelength. Additionally, Finite-Difference Time-Domain (FDTD) was performed for the surface plasmon resonance properties of the samples, and the simulation results were consistent with the experiments.

Improving range of SPR tunability and extinction efficiency of spheroidal silver nanostructures in graphene environment

In photovoltaics, the materials having ability to manipulate the optical fields and coupling of energy flow inside the device play a crucial role. In this article, we report the role of graphene environment on spheroid-shaped Ag nanoparticles (NPs) with various shapes and sizes. This study confirms the tunability of surface plasmon resonances (SPRs) and an enhancement in extinction efficiency, derived numerically using discrete dipole approximation (DDA). We have chosen oblate- and prolate-shaped Ag NPs for the numerical experiment and analysed their optical signatures in terms of extinction efficiency and SPR tunability against the quasi-static approximation. The excitation of longitudinal and transversal resonances was also observed because of the asymmetric shape of Ag NPs. All optical responses have been analysed by varying the effective radii and aspect ratio of Ag NPs, and the thickness of graphene monolayer (from 0.1 to 0.5 nm). Tunability of longitudinal resonances has been observed in the 600–833 nm wavelength region, while for transversal resonances, the tunability is in the 450–505 nm wavelength range. The results represent the effect of graphene environment on the tunability of SPRs with enhanced extinction efficiency. This study could lead to the development of a photovoltaic device with wide range of tunability and enhanced efficiency.

Mediating broadband light into graphene–silicon Schottky photodiodes by asymmetric silver nanospheroids: effect of shape anisotropy

Designing thinner, more efficient and cost-effective 2D materials/silicon Schottky photodiodes using the plasmonic concept is one of the most recent quests for the photovoltaic research community. This work demonstrates the enhanced performance of graphene–Si Schottky junction solar cells by introducing asymmetric spheroidal shaped Ag nanoparticles (NPs) embedded in a graphene monolayer (GML). The optical signatures of these Ag NPs (oblate, ortho-oblate, prolate and ortho-prolate) have been analyzed by discrete dipole approximation in terms of extinction efficiency and surface plasmon resonance tunability, against the quasi-static approximation. The spatial field distribution is enhanced by optimizing the size (aeff = 100 nm) and aspect ratio (0.4) for all of the utilized Ag NPs with an optimized graphene environment (t = 0.1 nm). An improvement of photon absorption in the thin Si wafer for the polychromatic spectral region (λ ~ 300–1100 nm) under an AM 1.5 G solar spectrum has been observed. This resulted in a photocurrent enhancement from 7.98 mA cm−2 to 10.0 mA cm−2 for oblate-shaped NPs integrated into GML/Si Schottky junction solar cells as compared to the bare cell. The structure used in this study to improve the graphene–Si Schottky junction’s performance is also advantageous for other graphene-like 2D material-based Schottky devices.

Superplastic Formation of Metal Nanostructure Arrays with Ultrafine Gaps.

Laser shock compression of plasmonic nanoarrays results in ultrafine tunable line-gaps at sub-10 nm scale by collaborative superplastic flow. From molecular dynamics analysis, the metal nanostructures change from crystalline to liquid-like metals, expanding quickly but never fusing together, even when they are very close. This technique enables good tunability of surface plasmon resonances and significantly enhanced local fields.

A Study of Metal@Graphene Core–Shell Spherical Nano-Geometry to Enhance the SPR Tunability: Influence of Graphene Monolayer Shell Thickness

Graphene, new generation advance material of two dimensional hexagonal lattice having extraordinary optical signatures, is used as coating material to enhance the surface plasmon resonance (SPR) effect of core@shell metal nanospheres. In a core@shell nanosphere, we have chosen metal as a core and graphene monolayer (GML) as a shell. We have analysed optical signature of coated and non-coated nanospheres in terms of extinction efficiency (Q ext) and tunabilty of surface plasmon resonances using electrostatic model, where particle size is much smaller than the wavelength of incident light. We analysed this model over different metals (silver, gold and aluminium) core, coated with different thickness of GML (d = 0.1 to 0.5 nm). These core@shell nanospheres are embedded in refractive index media of air (n em = 1), SiO2 (n em = 1.47) and TiO2 (n em = 2.79). The Q ext has been calculated by varying both the core radii as well as the GML shell thickness. Graphene-coated metal nanosphere exhibits SPRs that have wide range tunability from 300 to 1500 nm. In the presenting work, we also analysed that extinction efficiency for metal@GML is higher in TiO2 than others. The optimum value of GML shell thickness is 0.4 nm for TiO2, the magnitude of extinction efficiency is maximum for the optimum thickness. The tunability of these plasmonic resonances is highly dependent on the core@shell material, thickness of Graphene shell and surrounding environment while non-coated metal nano-spheres do not show appropriate SPR tunability.

Broadband Scattering With Strong Electric Field Coupling Between Metal Nanostructures Using DDA Simulation: Role of Different Organic Environments

A numerical model to study the optical properties of silver and gold nanoparticles surrounded by various organic media using a discrete dipole approximation method has been considered. The overall extinction and scattering (including forward and backward) efficiency with respect to wavelength has been analyzed to obtain optimized parameters for metal nanoparticles (MNPs) embedded in different organic matrices. P3HT:PCBM blend (Poly (3-hexyl thiophene))-(phenyl-C61-buryricacid methyl ester), P3HT (poly (3-hexyl thiophene)), and PEOPT (1”, 4”, 7”-trioaoctyl) phenyl) theophany) are taken as organic media in present calculation, where the Ag and Au nanoparticles of different sizes are embedded in it. MNPs support surface plasmon resonance having a wide range of tunability in the wavelength domain 300–700 nm. The tunability of surface plasmon resonances is highly sensitive to the particle size, as well as surrounding media. The numerical model is simulated for the spherical-shaped MNP of size 10–160 nm. The analysis of electric field intensity has been done for selective sizes of MNP. The magnitude of field intensity is highly sensitive to parameters associated with the metal structure and surrounding media. The entire numerical experiment has been replicated for the multiparticle system, in which the interaction between the nanoparticles has been considered. This gives an extra degree of freedom and wide tunability. Overall results are very encouraging and show better photon absorption in P3HT:PCBM blend for the 300–700-nm spectral range, as well as enhanced overall performance, as shown by the J–V curve.

Broadband tunability of surface plasmon resonance in graphene-coating silica nanoparticles**Project supported by the National Natural Science Foundation of China (Grant Nos. 11204365 and 11434017) and the National Basic Research Program of China (Grant No. 2013CB632704).

Graphene decorated nanomaterials and nanostructures can potentially be used in military and medical science applications. In this article, we study the optical properties of a graphene wrapping silica core–shell spherical nanoparticle under illumination of external light by using the Mie theory. We find that the nanoparticle can exhibit surface plasmon resonance (SPR) that can be broadly tuned from mid infrared to near infrared via simply changing the geometric parameters. A simplified equivalent dielectric permittivity model is developed to better understand the physics of SPR, and the calculation results agree well qualitatively with the rigorous Mie theory. Both calculations suggest that a small radius of graphene wrapping nanoparticle with high Fermi level could move the SPR wavelength of graphene into the near infrared regime.

Numerical Simulation of Broadband Scattering by Coated and Noncoated Metal Nanostructures Using Discrete Dipole Approximation Method

We suggest numerical method to study the optical response of metal nanostructures. The analysis of optical properties such as scattering and absorption by coated and noncoated nanogeometry has been done using discrete dipole approximation (DDA) method. The core-shell nanogeometry supports surface plasmon resonances, which are highly tunable from 400 to 1100 nm. The tunability of surface plasmon resonance (SPR) highly depends on the structural anisotropy and chosen core-shell material. Further, we have observed that aspect ratio is one of the key parameter to decide the nature and position of the plasmonic peaks and magnitude of optical cross section. We have also shown that coated nanospheroid is a more appropriate geometry as compared to coated nanosphere and noncoated nanospheroid in terms of wide tunability of surface plasmon resonance. The wide tunability in SPR is observed for the effective radii 90 nm core-shell (Au@SiO2) nanospheroid with aspect ratio 0.1.

ITO induced tunability of surface plasmon resonance of silver thin film

A series of silver films with various thicknesses were deposited on ITO covered silica substrates by magnetron sputtering at room temperature. The tunability of the surface plasmon resonance wavelength was realized by varying the thickness of silver thin film. By adjusting the silver layer thickness from 5 to 40nm, the resonance wavelength shows a blueshift, which is due to a change in the electromagnetic field coupling strength from the localized surface plasmons excited between the silver thin film and ITO layer. In contrast, when the ITO layer is absent from the system, no noticeable shift in the resonance wavelength is observed upon varying the silver thin film thickness.

Tunable Dipole Surface Plasmon Resonances of Silver Nanoparticles by Cladding Dielectric Layers.

The tunability of surface plasmon resonance can enable the highest degree of localised surface plasmon enhancement to be achieved, based on the emitting or absorbing wavelength. In this article, tunable dipole surface plasmon resonances of Ag nanoparticles (NPs) are realized by modification of the SiO2 dielectric layer thicknesses. SiO2 layers both beneath and over the Ag NPs affected the resonance wavelengths of local surface plasmons (LSPs). By adjusting the SiO2 thickness beneath the Ag NPs from 5 nm to 20 nm, the dipole surface plasmon resonances shifted from 470 nm to 410 nm. Meanwhile, after sandwiching the Ag NPs by growing SiO2 before NPs fabrication and then overcoating the NPs with various SiO2 thicknesses from 5 nm to 20 nm, the dipole surface plasmon resonances changed from 450 nm to 490 nm. The SiO2 cladding dielectric layer can tune the Ag NP surface charge, leading to a change in the effective permittivity of the surrounding medium, and thus to a blueshift or redshift of the resonance wavelength. Also, the quadrupole plasmon resonances were suppressed by the SiO2 cladding layer because the dielectric SiO2 can suppress level splitting of surface plasmon resonances caused by the Ag NP coupling effect.

Plasmonic Properties of the End-to-End and Side-by-Side Assembled Au Nanorods

Well-defined assemblies of Au nanorods (NRs) exhibit outstanding optical and electric properties, including surface plasmon resonance (SPR) of an individual nanorod and the coupling SPR among the assemblies. We present a direct approach for end-to-end (E-E) and side-by-side (S-S) assembly of Au NRs using poly (ethylene glycol) dithiol (HS-PEG-SH) and cysteine (Cys), respectively. The coupling SPR properties between the neighboring Au NRs are studied through experimental measurements and finite-different time-domain (FDTD) simulations. The simulated SPR tunability over the assembly agree with that of the experimental results, and both of the longitudinal SPR shifts for E-E and S-S assemblies are well fitted with the exponential function. The present assembled method provides a way for directing anisotropic nanostructures into well-defined orientations, and will be potentially useful in optoelectronics and biomedical engineering.

Tunable surface plasmon resonance of silver nanoclusters in ion exchanged soda lime glass

Silver (Ag) nanoclusters embedded in soda lime glass were synthesized by Ag ion exchange followed by thermal annealing. The effects of annealing temperature, time and atmosphere on the plasmonic response, structural and optical properties of silver-glass nanocomposites have been investigated using UV–visible absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). As exchanged sample exhibits surface plasmon resonance (SPR) band around 420nm which showed regular red shift with increase in annealing temperature. A significant red shift of 176nm (from 420 to 596nm) and broadening of the SPR peak was observed for annealing in air at 450°C. XPS studies on air annealed samples confirmed the presence of Ag2O in addition to Ag. Subsequent annealing at 250°C in reducing atmosphere resulted in increase in intensity, narrowing and blue shift of the SPR peak to 398nm. Our observations suggest that SPR tunability is mainly due to the formation and dissolution of Ag2O nanoshells around Ag nanoclusters in the near-surface region of glass during annealing in oxidizing and reducing atmosphere, respectively.

Surface plasmon resonance and field enhancement in #-shaped gold wires metamaterial

A #-shaped gold wires metamaterial is designed for surface enhanced Raman spectroscopy (SERS) and sensing. The tunability of surface plasmon resonance (SPR) excitations, hotspots distribution, localized field enhancement and sensitivity of the structure are investigated. In contrast to most metamaterial, the #-shaped structure exhibits two pronounced SPRs that are insensitive to the polarization of excitation light. Pure electromagnetic Raman enhancement factors of about 10(6) are achieved on the symmetrically distributed field hotspots. It is possible to break the usable wavelength range of conventional gold SERS substrates via higher order excitations of the #-shaped metamaterial. In addition, the sensitivity and the figure of merits are found to be comparable or even higher than those of conventional SERS substrates. All these factors together with the high reproducibility nature of metamaterial and its simple planer structure suggest that this structure is very promising for surface enhanced spectroscopy and sensing applications.

Thermal induced tunability of surface plasmon resonance in Au–VO2 nano-photonics

A new class of nano-photonics for possible χ3(ω) applications have been synthesized by pulsed laser ablation and optically characterized. Compared to standard nano-composites exhibiting an exalted effective χ3(ω) due to the enhancement of the local electric field, these Au–VO2 nano-composites display an additional reversibly tunable surface plasmon frequency under external temperature stimuli. This is due to the semi-conducting/metallic first order transition of the host VO2 matrix. The nano-gold surface plasmon wavelength shifts reversibly from 645 to 598nm when the Au–VO2 nano-composites temperature varies from 25 to 120°C. Even if the spectral shift is not extensively large, such a tunability is positively genuine.