Study on Localized Surface Plasmon Coupling with Many Radiators

Localized surface plasmon (LSP) coupling with many radiators are investigated. The LSP is generated by excitation of laser or electron beam on the random Ag nano particles (NPs) and arrayed ones embedded in the p-GaN of green LEDs. They couple with the excitons or radiative recombination in the quantum well (QW) and electron beam, which enhance or suppress the luminescence of the radiators. The photoluminescence (PL) intensity of periodic Ag NPs can get as much as 4.5 times higher than that of bare LED. In addition to the periodic structure, the morphology of Ag NPs also affects the localized SP (LSP) resonance intensity and light scattering efficiency. In the finite difference time domain (FDTD) simulation, five x-polarized dipoles are approximated to five quantum wells. Considering the interaction between the five dipoles and their feedback effect on LSP, the enhancement effect of SP dipole coupling with Ag NPs is amplified and the energy dissipation is reduced. The enhancement of cathodoluminescence (CL) was also found in green LEDs with Ag NPs. The three-body model composed of two orthogonal dipoles and an Ag NP is used for 3D FDTD simulation. The LSP-QWs coupling effect is separated from the electron beam (e-beam)-LSP-QW system by linear approximation. Under the excitation of electron beam, the introduction of z-dipole greatly reduces the energy dissipation. In the cross-sectional sample, z-polarized dipoles in QWs show more coupling strength to the dipole and quadrupole modes of LSP. The perturbation theory is used to separate the LSP coupling effects to x-dipole and z-dipole. At last, the resonator and the antenna effects are discussed for LSP coupling at different positions to the Ag NP.

Structure-selected graphene/metallic surface plasmon coupling regime and infrared modulation application

Here we present a graphene-based long-wavelength infrared modulator characteristic of extra-high contrast, where the frequency detuning degree of magnetic and electric surface plasmons (SPs) is controllable by the gated graphene Fermi energy. If the device is designed to work in a strong SP-coupling regime by selecting an appropriate low-lossy gate dielectric thickness, a modulation depth (MD) up to ~100% but insertion loss (IL) as low as ~-0.37 dB is achievable. Moreover, a compromised MD >90% with IL <-1.0 dB is still retainable in two broadband ranges. The disclosed underlying mechanism to the device working state in the strong, electromagnetic-induced transparency (EIT), or weak SP-coupling regime, indicates the coupling regime shows a strong dependence on the dielectric thickness, which is related to the magnetic-SP mode volume, while the working wavelength can be selected in a broader spectral range by scaling the device geometry. These findings are helpful to construct those optoelectronics for infrared absorption enhancement, EIT, and strong coupling spectral characteristic itself.

Silver-Nanowire-Based Localized-Surface-Plasmon-Assisted Transparent Conducting Electrode for High-Efficiency Light-Emitting Diode

Silver nanowire (Ag NWs) networks with high transparency and low resistivity are widely used as promising candidates for the replacement of indium tin oxide (ITO)-based transparent conducting oxides (TCOs) in light-emitting diodes (LEDs). However, LEDs with Ag NW electrodes are less efficient than those with ITO electrodes because of their low electrical properties, such as high contact resistance and strong absorption in the visible region. In this work, we tried to improve the efficiency of LEDs with transparent conducting electrodes of Ag NWs networks via localized surface plasmons (LSPs) by adopting silver nanoparticles. We studied the effect of the thickness of the p-GaN layer on surface plasmon coupling. When a 45 nm thick p-GaN layer was used, the internal quantum efficiency was improved by LSP coupling between a dipole of QW and Ag NW/NP, and the light extraction was improved because the NPs afforded a leakage mode and acted as scattering centers.

Ag-Yb Alloy-Novel Tunable Plasmonic Material

Metals are commonly used in plasmonic devices because of their strong plasmonic property. However, such properties are not easily tuned. For applications such as spatial light modulators and beam steering, tunable plasmonic properties are essential, and neither metals nor other plasmonic materials possess truly tunable plasmonic properties. In this work, we show that the silver alloy silver–ytterbium (Ag-Yb) possesses tunable plasmonic properties; its plasmonic response strength can be adjusted as a function of Yb concentration. Such tunability can be explained in terms of the influence of Yb on bound charge and interaction of its dielectric with the dielectric of Ag. The change in transition characteristics progressively weakens Ag’s plasmonic properties. With a spectral ellipsometric measurement, it was shown that the Ag-Yb alloy thin film retains the properties of Ag with high transmission efficiency. The weakened surface plasmon coupling strength without dramatic change in the coupling wavelengths implies that the tunability of the Ag-Yb alloy is related to its volume ratio. The principle mechanism of the plasmonic change is theoretically explained using a model. This work points to a potential new type of tunable plasmonic material.