Optimization of 1D Plasmonic Grating of Nanostructured Devices for the Investigation of Plasmonic Bandgap

Plasmonics - The present work investigates the effect of geometrical parameters of 1D nanograting on surface plasmon resonance (SPR) and plasmonic bandgap (PBG). The use of plasmonic grating device...     

Coupled SPP Modes on 1D Plasmonic Gratings in Conical Mounting

Plasmonics - Plasmonic nanostructures exhibit a variety of surface plasmon polariton (SPP) modes, with different characteristic properties. While a single metal dielectric interface supports a...     

Coupling Efficiency of Surface Plasmon Polaritons for 1D Plasmonic Gratings: Role of Under- and Over-Milling

This paper reports the successful excitation of surface plasmon polaritons (SPPs) through 1D metallic grating on higher refractive index GaP substrate. Coupling efficiency (η) of a free-space transverse-magnetic (TM) plane-wave mode into a SPP mode is crucial for many plasmonic devices. This η predominantly depends on the fabrication (milling) parameters and the factors (under- and over-milling) affecting the η is investigated experimentally and numerically. First of all, η is estimated by measuring the transmission spectra obtained through the plasmonic grating structures by varying the slit width (a) for a fixed period (Λ) and the thickness (t) of the gold (Au) film in which the grating is formed. The wave vector of the incident light is tuned to match the wave vector of the SPP, to get maximum η. For an optimum Au film thickness, a slit width of half of the periodicity of 770 nm in the grating device yields a maximum η. Such grating devices support only a fundamental plasmonic mode because the profile/shape of the slit in the grating device is more like a sinusoidal nature. Furthermore, such grating offers intermediate scattering to the incident light and the SPP as well which in-truns couple more incident energy to the SPPs. Moreover, over-milling results in decreased η where the crystalline plane of the substrate is disturbed. Finite element method (FEM) in COMSOL modeling is used to understand the underlying physics. This study is very useful for the development of the device application in real word.     

Curved Gratings as Plasmonic Lenses for Linearly Polarised Light

The ability of curved gratings as sectors of concentric circular gratings to couple linearly polarised light into focused surface plasmons is investigated by theory, simulation, and experiment. The experimental and simulation results show that increasing the sector angle of the curved gratings decreases the width of the lateral distribution of surface plasmons resulting in focusing of surface plasmons, which is analogous to the behaviour of classical optical lenses. We also show that two faced curved gratings, with their groove radius mismatched by half of the plasmon wavelength (asymmetric configuration), can couple linearly polarised light into a single focal spot of concentrated surface plasmons with smaller depth of focus and higher intensity in comparison to single curved gratings. The major advantage of these structures is the coupling of linearly polarised light into focused surface plasmons with access to, and control of, the plasmon focal spot, which facilitate their potential applications in sensing, detection, and nonlinear plasmonics.     

Colloidal Synthesis of Plasmonic Metallic Nanoparticles

Solutions of Ag and Au nanoparticles are strongly colored because of localized surface plasmon resonance in the UV/visible spectral region. The optical properties of these nanoparticles may be tuned to suit the needs of the application. This article summarizes our work in recent years on the solution synthesis of nanoparticles with tunable optical properties. The systems of interest include zero-dimensional bimetallic Ag–Au nanoparticles with different structures, one-, two-, and three-dimensional anisotropic monometallic Ag or Au nanoparticles. All of these nanosystems were prepared from colloidal synthesis through simple changes in the synthesis conditions. This is a demonstration of the versatility of colloidal synthesis as a convenient scalable technique for tuning the properties of metallic nanoparticles. Zhang, Tan, and Xie contributed equally to this article     

Plasmonic Band Gap: Role of the Slit Width in 1D Metallic Grating on Higher Refractive Index Substrate

This paper reports the excitation of surface plasmon polaritons (SPPs) and associated plasmonic band gap (PBG) while using TM plane wave interacting with 1D metallic grating on higher refractive index GaP substrate. A simple method is introduced to estimate the PBG which is crucial for many plasmonic devices. The PBG is estimated by measuring the transmission spectra obtained through the plasmonic grating structures when slit width is varied while periodicity and the thickness of the gold (Au) film remained fixed. The PBG is observed for the grating devices whose slit width is less than one third of the periodicity which is caused by the presence of a higher plasmonic mode. The PBG is absent for the grating device whose slit width is slightly less than half and greater than one third of the periodicity. Such grating devices support only a fundamental plasmonic mode because the profile/shape of the slit in the grating device is more like a sinusoidal nature. Furthermore, such grating offers intermediate scattering to the incident light and the SPP as well which in turn couple more incident energy to the SPPs. Far-field modelling results also support the results obtained through experiment.

     

Graphene Plasmonic Crystal: Two-Dimensional Gate-Controlled Chemical Potential for Creation of Photonic Bandgap

Plasmonics - A new design of graphene-based plasmonic waveguide is presented and its transmission properties are studied. The transmission channel is such designed that the chemical potential of...     

Experimental Study of Metallic Elliptical Nano-Pinhole Structure-Based Plasmonic Lenses

An elliptical nano-pinhole structure-based plasmonic lens was designed and investigated experimentally by means of focused ion beam nanofabrication, atomic force microscope imaging, and scanning near-field optical microscope (NSOM). Two scan modes, tip scan and sample scan, were employed, respectively, in our NSOM measurements. Both the scan modes have their characteristics while probing the plasmonic lenses. Our experimental results demonstrated that the lens can realize subwavelength focusing with elongated depth of focus. This type of lens can be used in micro-systems such as micro-opto-electrical–mechanical systems for biosensing, subwavelength imaging, and data storage.     

Enhancement of Extraordinary Optical Transmission in a Double Heterostructure Plasmonic Bandgap Cavity

In this paper, a novel plasmonic bandgap cavity inducing the enhancement of extraordinary optical transmission is presented. Numerical simulations have been performed to model a free-standing structure made of a one-dimensional periodic arrangement of gold strips. Two different values of the lattice constant have been properly chosen to realize a double heterostructure-like cavity to accomplish extraordinary optical transmission assisted by the formation of a plasmonic bandgap in the adjacent regions. Numerical results prove the capability of this optical device to efficiently transmit input light beams with far-field transmission values close to 100% due to the excitation of surface plasmon polariton resonant modes.     

Design of a Plasmonic Photocatalyst Structure Consisting of Metallic Nanogratings for Light-Trapping Enhancement

Plasmonics - In this paper, a novel SPP-based photocatalytic system with high photocatalytic performance consisting metallic nanograting elements is proposed and simulated numerically with...     

Microbial Specificity of Metallic Surfaces Exposed to Ambient Seawater

High-molecular-weight materials associated with the extracellular matrix and film found on titanium and aluminum surfaces after exposure to flowing coastal seawater were isolated. This material was purified by hydroxylapatite chromatography and subsequently employed to produce antibodies in the toad, Bufo marinus. The antibodies were immobilized on a solid support and employed to isolate adhesion-enhancing, high-molecular-weight materials from the laboratory culture media of bacterial strains recovered from the respective metallic surfaces during the course of their exposure to seawater. The adhesion-enhancing materials produced by the surface-associated bacterial strains were immunologically related to the extracellular biofouling matrix material found on the surfaces from which these bacteria were isolated. The surface selectivity of these bacterial strains appeared to be based on the specificity of the interaction between adhesion-enhancing macromolecules produced by these bacteria and the surfaces in question.     

Synchronous Tuning of Twined Resonance Modes with Controllable Spectral Separation in Plasmonic Gratings

We investigated angle-resolved tuning performance of the double resonance modes of waveguide metallic grating structures, where the incident angle was changed in the plane formed by the extending direction of the grating lines and the wave vector with the grating plane tilted with respect to the vertical axis. Double resonance modes were observed due to tilting of the grating, which were tuned simultaneously to the blue with increasing the angle of incidence. The spectral separation between the resonance modes can be adjusted simply by changing the tilting angle of the grating. Such a double resonance device is important for exploring multichannel optical filters, optical switching device, or sensors.     

Efficiency Enhancement of Ultra-thin CIGS Solar Cells Using Bandgap Grading and Embedding Au Plasmonic Nanoparticles

The objective of this study is to enhance the efficiency of copper indium gallium selenide (CIGS) solar cells. To accomplish that, composition grading of absorber layer was carried out by using SILVACO’s technology aided computer design (TCAD) ATLAS program. Results showed a meaningful improvement of output parameters including open-circuit voltage (V_oc), short-circuit current (I_sc), fill factor (FF), and power conversion efficiency (η). For further performance improvement of the cell, Au plasmonic scattering nanoparticles were loaded on the top of the ZnO window layer. Plasmonic nanoparticles can restrict, absorb, navigate, or scatter the incident light. By using the spherical Au nanoparticles, a very good increase in the light absorption in the cell over the reference planar CIGS solar cell was observed. The highest η = 19.01% was achieved for the designed ultra-thin bandgap-graded CIGS solar cell decorated by Au nanoparticles.

     

Controllable Mode Hybridization and Interaction Within a Plasmonic Cavity Formed by Two Bimetallic Gratings

We theoretically study mode hybridization and interaction among surface plasmon polariton Bloch wave mode, Fabry–Perot cavity mode, and waveguide mode within a plasmonic cavity composed by two parallel planar bimetallic gratings. Four hybridized modes result from mode hybridization between surface plasmon polariton Bloch wave modes on the two gratings are observed. By changing the dielectric environment, mode hybridization behavior can be manipulated. Importantly, waveguide-plasmon polariton mode due to hybridization between grating supported surface plasmon polariton Bloch wave mode and cavity supported waveguide mode is observed. We demonstrate that surface plasmon polariton Bloch wave mode and Fabry–Perot cavity mode with the same mode symmetry can interact by presenting an anticrossing behavior, which can be controlled by laterally shifting one grating with respect to the other that causes a phase difference shift of the two involving modes. The proposed plasmonic cavity offers potentials for subwavelength lithography, tunable plasmonic filter, and controllable light-matter interaction.     

Investigation of the Plasmonic Interaction of Gold Nanoparticles Toward Plasmonic Photothermal Therapeutics

Plasmonic interaction of nanoparticles located in close proximity, embedded in breast tissue, is simulated for estimating the optical characteristics like optical absorption cross-section, plasmonic wavelength as well as full-width half maxima (FWHM). The computations are done for the monomers, homodimers, and heterodimers of spherical and rod-shaped gold nanoparticles considering various interparticle spacings for gold nanospheres and the interparticle spacing as well as the orientation for gold nanorods (GNRs). The results indicate that for the spherical dimer, with the change in interparticle spacing from 1 to 20 nm, the peak absorption cross-section decreases by 43%. Whereas for the GNRs, the absorption cross-section increases/decreases, within 9–18%, depending on the homodimer or heterodimer configuration. Furthermore, secondary peaks for the absorption cross-section are obtained within wavelengths of 630–940 nm due to antibonding modes for GNR heterodimers. For GNR heterodimer located end-to-end, this secondary peak for the absorption cross-section appears at 780 nm irrespective of interparticle spacing within 1–5 nm. The absorption coefficient is considerably dependent on the configuration and proximity of GNRs located within the tissue. While FWHM is not significantly influenced by GNRs configuration and interparticle spacing. For interparticle spacing from 1 to 20 nm, the plasmonic wavelength shifts by 38 nm for the spherical dimer and by 35–86 nm for various GNR dimers. The findings of this study are useful for plasmonic photothermal therapeutics as the heat generation is governed by the resulting absorption cross-section due to plasmonic coupling of the closely spaced and different orientations of the nanoparticles.

     

Polarization and Filter Properties Investigation of Metal Gratings and Rings

We demonstrated the near-field optical transmission properties of nanogratings with spoke and rings structures through a near-field scanning optical microscope, and the far-field optical transmission properties with different polarization angles are investigated with an optical microscope. Our experimental results verified the polarization properties of the nanograting structures and further demonstrated the experimental results are supported by the finite difference time domain theoretical simulation. The optical microscope imaging of the spoke and ring structures also show that the grating structures can disperse visible light of different wavelengths.