Enhanced Plasmonic Light Absorption for Silicon Schottky-Barrier Photodetectors

Quantum efficiency of the silicon Schottky-barrier photodetector is limited by the weak interaction between the photons and electrons in the metal. By engineering the metal surfaces, metallic groove structures are proposed to achieve strong light absorption in the metal, where most of the energy is transferred into hot carriers near the Schottky barrier. The proposed broadband photodetector with a bi-grating metallic structure on the silicon substrate enables to absorb 76 % of the infrared light in the metal with a 200-nm bandwidth, while staying insensitive to the incident angle. These results pave a new promising way to attain high quantum efficiency silicon Schottky-barrier photodetectors.     

Ultrabroadband Mid-infrared Light Absorption Based on a Multi-cavity Plasmonic Metamaterial Array

We present a broadband plasmonic metamaterial absorber in the infrared region based on localized surface plasmon polaritons (LSPPs). The unit cell of the proposed metamaterial absorber consists of a multi-cavity structure, in which absorption resonances can be tuned independently through the modification of the width and shift of metallic walls. In order to avoid the degeneration between two contiguous resonances, which dramatically reduces the bandwidth, we introduce a zigzag design rule to arrange the cavities within a compact unit. Thus, the possible number of resonances is greatly increased, enabling an ultrabroadband absorption. A broadband absorber is demonstrated with only a few-layer structure and it also has an incident-angle-insensitive feature. Our results have potential applications in photovoltaic devices, emitters, sensors, and camouflage systems.     

Improve the Effective Resonance Light Scattering of Three-Layered Plasmonic Au@Dielectric@Ag Bimetallic Nanoshells

Plasmonics - The strong light scattering from SPR has received an extraordinary attention due to the useful applications in photodetectors and cell and biomedical imaging. However, the applications...     

Tunable Ultrahigh Order Surface Plasmonic Resonance in Multi-Ring Plasmonic Nanocavities

Optical properties of multi-ring with spatial symmetry breaking are investigated theoretically. Tunable ultrahigh order surface plasmonic resonance is achieved, which is found to be sensitive to geometric parameters. Certain high-order surface plasmonic resonances can be either suppressed or enhanced when geometrical parameters are adjusted. Moreover, more than one quadrupolar-dipolar, octupolar-dipolar, and hexadecapolar-dipolar mode of the surface plasmonic resonance can be achieved. The asymmetry also allows the generation of strong electric field enhancement with these nanostructures that can be applied in the field of surface-enhanced spectroscopy and biosensing.     

Electromagnetic-Induced Transparency and Slow Light in Plasmonic Metasurfaces

Plasmonics - We report numerically electromagnetic-induced transparency (EIT) and Fano resonances in simple plasmonic metasurfaces consisting of gold nanobars arranged in pi, H, and four-shaped...     

Tuning Plasmonic Near-Perfect Absorber for Selective Absorption Applications

In this study, we present a high-performance tunable plasmonic absorber based on metal-insulator-metal nanostructures. High absorption is supported over a wide range of wavelengths, which is retained well at a very wide range of incident angles too. The coupling process occurs with high absorption efficiency of ∼ 99% by tuning the thickness of the dielectric layer. In addition, a complex trapezoidal nanostructure based on simple metal-insulator-metal structures by stacking different widths of Cu strip-nanostructures in the vertical direction has been put forward to enhance light absorption based on selective absorption. A trapezoidal sample has been designed with a solar absorption as high as 95% at wavelengths ranging from 300 nm to 2000 nm for different operating temperatures. Furthermore, the optical absorber has a very simple geometric structure and is easy to integrate into complex photonic devices. Perfect absorption and easy fabrication of the metal-insulator-metal structure make it an attractive device in numerous photonic applications.

     

Plasmonic Behaviors of Two-Dimensional Ag/SiO2 Nanocomposite Gratings: Roles of Gap Diffraction and Localized Surface Plasmon Resonance Absorption

Two-dimensional Ag/SiO₂ nanocomposite gratings of 400 and 600 nm in grating constant are fabricated by etching the SiO₂ slabs implanted with Ag ions, and their plasmonic extinction, absorption, and reflection behaviors are investigated. Our results indicate that no scattering light fields can exist near the localized surface plasmon (LSP) resonance wavelength (about 405 nm) of Ag nanoparticles (NPs) due to the intense LSP resonance absorption. Especially, when the gaps between nanocomposite veins have a width close in value to the LSP resonance wavelength of Ag NPs, the local light fields in the grating plane can be slightly enhanced due to an in-phase addition of the incident light fields and the diffractive light fields induced by the gap diffraction, leading to a slight red shift of LSP resonance mode of Ag NPs. Moreover, in the LSP resonance absorption region, although the grating diffraction can still occur, the diffractive light fields are extremely weak, and thus, the local light fields in the grating plane cannot be modified by coherently adding these extremely weak diffractive light fields to the incident light fields. As a result, the LSP resonance mode of Ag NPs will keep its position unchanged even though the grating constant is set to make the first grating order rightly change from evanescent to radiative character.

     

Formation of Self-organized Silver Nanocup-Type Structures and Their Plasmonic Absorption

The present work reports on the formation of extremely low volume, silver nanocup-type structures on the surface by annealing of ultra-thin silver film on quartz in inert environment. Atomic force microscopy studies together with scanning electron microscopy confirmed the formation of Ag nanocup-type structures at the surface. A basic physical model for the formation of nanocups in terms of buckling and Oswald ripening due to surface-induced morphological instability and diffusional mass transport under thermal treatment is demonstrated. Surface plasmon resonance absorptions of nanocup structures are studied and preliminary experiment for observing the surface-enhanced Raman scattering of fullerene C₇₀ molecules has been shown.     

Plasmonic Resonance Excited Extinction Spectra of Cross-Shaped Ag Nanoparticles

Plasmonic properties of cross-shaped Ag nanoparticles are investigated theoretically using finite-difference time-domain algorithm. Electric field (E-field) distribution of a single cross-shaped Ag nanoparticle with different shape parameters and patterned nanoparticles with different periods were presented. Both red shift and blue shift of the extinction spectra were observed. The simulation results demonstrated that the strong E-field intensity is located at sharp corner of the nanoparticles. And E-field intensity of the nanoparticle array is much stronger than that of a single Ag nanoparticle. Enhancement of the large localized E-field originating from the nanoparticles was analyzed. Corresponding influence of “hot spots” effect on enhancing Raman scattering was discussed as well.     

Large Plasmonic Resonance Shifts from Metal Loss in Slits

Plasmonics - The impact of loss on the plasmonic resonances in metal–insulator–metal slits is analyzed, particularly the significant effect of loss on the reflection phase. The...     

Fabrication Friendly Plasmonic Metasurface Sensing and Switching Configuration Based on Plasmonic Induced Absorption: Analytical and Numerical Evaluation

Plasmonics - Optical sensing and switching characteristic for a novel plasmonic metasurface structure are verified based on numerical and analytical evaluations for the proposed structure formed by...     

Investigation of Resonance Modulation of a Single Rhombic Plasmonic Nanoparticle

Optical extinction resonant properties of the silver rhombic plasmonic nanoparticles in visible regime were investigated by means of finite difference time domain method algorithm-based computational numerical calculation. Considering aspect ratio (a/b) of the x- and y-axes of the rhombic particles, the polarization in different angles of the incident light, and the index of the surrounding medium, we studied the extinction properties of a single rhombus. The simulation results show that there is only one clear resonance peak in the visible regime, and the corresponding plasmon mode is a dipolar plasmon mode. Along the direction of the light polarization, with the increase of the aspect ratio (a/b), red shift of the resonant peak occurs and the extinction efficiency increases accordingly. With the polarization angle varying from 0° to 90°, the resonance peaks show a small blue shift and the corresponding extinction efficiency varies slightly consequently. The tailoring ability of the resonance frequency is shown to be improved due to a unique interaction of local geometry with surface charge distributions.     

Tuning Triangular Prism Dimer into Fano Resonance for Plasmonic Sensor

We theoretically investigate the plasmonic Fano resonance in a triangular nanoprism dimer. By adjusting the geometry parameters, we have observed a Fano line shape in the scattering spectra, which is induced by the competence of bonding and antibonding modes in the triangular nanoprism dimer. The Fano line shape can be well described by a theoretical model of two harmonic oscillators. A figure of merit value as high as 16.1 is achieved in the triangular nanoprism dimer, which is caused by the Fano resonance. The electric field at the corner of the triangular prisms is the highest among the circular cylinder dimer and square rod dimmers, which shows that the triangular prism dimer is more suitable for the detection of biomolecules. The triangular prism dimer may also used in plasmonic circuits.     

Plasmonic Sensors Based on Funneling Light Through Nanophotonic Structures

We present a refractometric sensor realized as a stack of metallic gratings with subwavelength features and embedded within a low-index dielectric medium. Light is strongly confined through funneling mechanisms and excites resonances that sense the analyte medium. Two terminations of the structure are compared. One of them has a dielectric medium in contact with the analyte and exploits the selective spectral transmission of the structure. The other design has a metallic continuous layer that generates surface plasmon resonances at the metal/analyte interface. Both designs respond with narrow spectral features that are sensible to the change in the refractive index of the analyte and can be used for sensing biomedical samples.

     

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.     

Absorption Enhancements in Plasmonic Solar Cells Coated with Metallic Nanoparticles

We find that three mechanisms lead to the absorption enhancements of light in a thin-film amorphous silicon solar cell coated with a periodic array of silver nanoparticles on the rear surface according to our simulation. They are localized surface plasmon modes of the silver nanoparticles, Fabry–Pérot resonant cavity modes and waveguide effects. Each enhancing mechanism can yield a maximum absorption enhancement of over two times at the corresponding resonant wavelengths when the nanoparticles cover 20 % of the solar cell surface, and an average absorption enhancement of up to 57 % can be achieved in the AM 1.5 G solar spectrum. The absorption enhancements can also be tuned in spectrum to optimize the total absorption in a plasmonic solar cell.     

Broadband Absorption Enhancement of Refractory Plasmonic Material with Random Structure

We demonstrate a broadband absorber using random structures on refractory plasmonic material. The random microstructure is fabricated by femtosecond laser on tungsten and characterized with surface roughness which described by root mean square (RMS) and correlation length. Results show that the absorption efficiency of random microstructure with RMS of 0.8 μm and correlation length of 0.55 μm is over 90 % in the wavelength range from 200 to 1100 nm. However, the sample with surface structure RMS of 0.08 μm has much lower absorption (less than 70 % for λ > 600 nm). Numerical simulations agree well with the experimental results and illustrate that the structure with 0.8-μm RMS and 0.55-μm correlation length has the cut-off wavelength of 2400 nm which prevents mid-infrared emission. The possibility of realizing broadband absorption by using random structures presents a flexible and efficient way for solar cell, thermophotovoltaics, and energy harvesting.

     

Perfect Plasmon-Induced Absorption and Its Application for Multi-Switching in Simple Plasmonic System

Plasmonics - The perfect plasmon-induced absorption (PIA) effect is achieved in a simple plasmonic system, composed of two rectangle cavities side-coupled to the metal-insulator-metal (MIM)...