Wenli Bai

Design of plasmonic back structures for efficiency enhancement of thin-film amorphous Si solar cells

Metallic back structures with one-dimensional periodic nanoridges attached to a thin-film amorphous Si (a-Si) solar cell are numerically studied. At the interfaces between a-Si and metal materials, the excitation of surface-plasmon polaritons leads to obvious absorption enhancements in a wide near-IR range for different ridge shapes and periods. The highest enhancement factor of the cell external quantum efficiency is estimated to be 3.32. The optimized structure can achieve an increase of 17.12% in the cell efficiency.

Observation of ultra-narrow band plasmon induced transparency based on large-area hybrid plasmon-waveguide systems

We report the observation of an ultra-narrow band plasmon induced transparency resonance which is realized in a large area hybrid plasmon-waveguide system consisting of a gold nanowire array embedded in a slab waveguide. Due to the destructive interference between optical modes supported by the hybrid system, an ultra-narrow plasmon induced transparency resonance with a bandwidth of 8 nm at the wavelength of 966 nm was obtained (i.e., ∼1/120 of the peak wavelength at the incident angle of 60°). The group velocity is estimated to be ∼76, which is promising for miniaturized slow-light components.

Hybrid plasmonic waveguide with gain medium for lossless propagation with nanoscale confinement

In this Letter, we propose a hybrid plasmonic nanosystem consisting of a silver cladding layer with a semicylinder bump on top of InGaAsP nanowire. Because of the coupling between the dielectric waveguide mode and surface plasmon polariton mode, the hybrid plasmonic mode can exhibit low loss with strong field localization. The finite element method numerical simulations are employed to evaluate the performances of the hybrid mode. In order to achieve the lossless propagation of the hybrid mode with the mode area of 0.0058(λ²/4) at 1.55 μm, the material gain of 200 nm × 300 nm InGaAsP nanowire should reach 1223 cm⁻¹.

Slow light at terahertz frequencies in surface plasmon polariton assisted grating waveguide

A subwavelength grating waveguide (GW) consisting of two parallel metallic slabs with periodic corrugations on their inner boundaries is developed to slow down the speed of light at terahertz frequencies. Assisted by a tapered input port, our structure has a transfer efficiency of about 80% over a broad bandwidth and strong confinement in the subwavelength scale. Based on the GW, three graded GWs are designed to demonstrate that the spoof surface plasmon polaritons are slowed down and asymptotically stopped when they tend to the location, where the local cutoff frequency is the same as the frequency of the incident light.

Omnidirectional absorption enhancement in hybrid waveguide-plasmon system

We investigate the omnidirectional absorption enhancement induced by the excitation of the localized surface plasmon in the hybrid system consisting of a gold nanowire array embedded in a slab waveguide. Assisted by the waveguide layer, the hybrid system can support the localized waveguide-plasmon resonances for a wide range of incident angles. Theoretical and experimental results are both presented to demonstrate the omnidirectional absorption enhancement which could find important applications on plasmonic-assisted photovoltaic devices or photodetectors.

Effect of Fe-doping concentration on microstructure, electrical, and magnetic properties of Pb(Zr0.5Ti0.5)O3 thin films prepared by chemical solution deposition

The highly (l00) oriented Pb(Zr0.5Ti0.5)O3 thin films with different Fe3+ doping concentrations were fabricated on LaNiO3-coated silicon substrates by chemical solution deposition. And the microstructure, ferroelectric, leakage, and magnetic properties were investigated. The results indicate that incorporation of Fe3+ into PZT thin films can promote the degree of the lattice distortion and greatly improve the surface roughness. In comparison with the pure PZT sample, the ferroelectric hysteresis loops of Fe-doped PZT samples demonstrate larger and larger polarizations and coercive fields with the increase in Fe3+ doping amount. Moreover, leakage mechanism of present films evolves from the space charge limited conduction to the “modified” space charge limited conduction, and then returns to the space charge limited conduction with increasing Fe3+ doping concentration. The occurrence of exchange bias in these Fe-doped PZT samples implies that the magnetic exchange interaction can be explained by the bound m...

Hybrid waveguide-plasmon resonances in gold pillar arrays on top of a dielectric waveguide.

We propose a hybrid waveguide-plasmon system consisting of gold pillar arrays on top of a dielectric waveguide. The formation of extraordinary transmissions induced by the hybrid waveguide-plasmon resonances is investigated by rigorous coupled-wave analysis. The characteristics of the hybrid resonances can be predicted by introducing the photonic crystal slab theory. Extremely narrow absorption peaks and the electromagnetically induced transparency-like optical property are demonstrated in our hybrid system.

Short-Range Surface Plasmon Polaritons for Extraordinary Low Transmission Through Ultra-Thin Metal Films with Nanopatterns

We provide both experimental and theoretical investigation on extraordinary low transmission through one-dimensional nanoslit and two-dimensional nanohole arrays on ultra-thin metal films. Unambiguous proofs demonstrate that short-range surface plasmon polaritons play a key role leading to this novel phenomenon, which could be useful for creating new polarization filters and other integrated plasmonic components.

Multiple Surface Plasmon Resonances in Compound Structure with Metallic Nanoparticle and Nanohole Arrays

The optical properties of a compound structure with metallic nanoparticle and nanohole arrays are numerically investigated by the means of finite-difference time domain method. We report on the observation of multi-valleys in the reflection spectra due to the excitation of surface plasmon (SP) resonant modes of the compound structure. Simulation results show that multiple SP resonances consist of surface plasmon polaritons on the gold film, localized surface plasmons on the nanoparticles, and coupling mode between them. These findings are important for applications utilizing multiple surface plasmon resonances.

Double plasmonic structure design for broadband absorption enhancement in molecular organic solar cells

Absorption enhancement by a double plasmonic nanostructure in molecular organic photovoltaics (OPVs) is theoretically investigated. The structure consists of a periodic array of metal nanodiscs on one side of the OPV active layers and a thin metal nanohole array on the other side. Excitation of coupled modes of localized surface plasmon polaritons at the nanodiscs and short-range surface plasmon polaritons at the nanohole array causes the electromagnetic field to be highly concentrated within the organic active layers, leading to a polarization-independent, broadband absorption enhancement in the visible and near-infrared portion of the solar spectrum. Calculations show that an optimized double plasmonic structure can enhance the total photon absorption by >125% for molecular OPVs based on a double heterojunction of an electron donor/hole transporter and an electron acceptor/transporter.