Three kinds of typical structures, hemi-/spherical nanoparticles/nanoparticle dimers on the substrate and spherical nanoparticles/nanoparticle dimers half-buried into the substrate, are used for FDTD simulation to theoretically discuss the influence of the substrate to the localized surface plasmon (LSP) coupling when the metal nanoparticles/nanoparticle dimers are locating near a substrate. Simulated results show that the dependencies between the LSP coupling wavelength and the refractive index of the substrate for different structures are not the same, which can be attributed to the different polarization field distributions of LSPs. When light is incident from different directions, the LSP coupling strength are not the same as well and the ratios of the scattering peak intensities depend on the position of the metal nanoparticles or nanoparticle dimers. These phenomenon can be explained by the difference of the local driving electric field intensities which is modulated by the interface between the air and the substrate.
We perform a systematic investigation of MnPSe3/CrBr3 two-dimensional (2D) van der Waals heterostructures through first-principles calculations. The most stable stacking configuration of MnPSe3/CrBr3 heterostructures is found to have an indirect type-II band structure. Biaxial tensile strain is employed to tailor the spin–valley properties of the heterostructures in terms of the momentum, energy and spin components of the valleys. A novel opposite spin splitting evolution appears at the K and K′ valleys of the top valance band (TVB) with increasing tensile strain. A change from an indirect to a direct band gap is found at 7% tensile strain. A maximum spin splitting of 34.7 meV at the K′ valley is produced simultaneously with valley polarization under a tensile strain of 10%. The spin components distributed at the TVB are found to be controlled by strain-related competition between direct exchange interaction and indirect superexchange interaction of Se (px + py ) and Se pz orbitals. Spin polarization precisely regulated by strain can facilitate the manipulation of valley and spin degrees of freedom in MnPSe3/CrBr3 heterostructures, which opens up great potential for novel applications, such as strained sensor, spintronic and valleytronic devices.
Lasers with small size have demonstrated great potential in numerous applications including communication, optical computing, detection, displays, and optical logic circuits. In this study, hybrid plasmonic nanolasers with metal pad structures based on the InGaN/GaN nanorod are designed and fabricated to investigate the lasing modes and polarization modulation. Dominant coupling of the surface plasmon mode has been achieved by optimizing the hybrid nanolaser structures, which significantly enhances the electric field concentration, leading to an ultralow threshold (∼1.19 W cm −2 ) plasmonic multimode lasing. Based on the theoretical and experimental results, it is proposed that the suitable plasmonic structural parameters could provide wave-vector matching and phase compensation to form a strong plasmon resonator, yielding a low radiative loss and high gain for the laser. These InGaN/GaN nanorod arrays for the hybrid nanolaser not only provide a solution to the ultralow-threshold nanorod-based plasmonic lasers but also advocate the prospect of the greater potential of nanoscale arrays for luminescence and displays. These findings and understandings provide vital insights into the developments of electrically driven plasmonic nanolasers and may contribute to the realization of nanolaser-based display arrays and optical on-chip integration for the next generation of logic circuits.
Coupling localized surface plasmons (LSPs) in Au nanostructure arrays to Fabry-Pérot cavity modes, both peak splitting and peak locking behaviors can be observed when light is incident normally into the cavity from different directions. These phenomena can be quantitatively described by a model based on modified Fresnel equations, and thus be interpreted as an extended Fano resonance effect. Both the peak splitting and peak locking behaviors arise from the interference between localized surface plasmon resonance and cavity modes with different initial phase difference. When the phase difference of the cavity state and the LSP state is π or 0, the superposition between a cavity resonance mode and a localized surface plasmon mode can result in the peak splitting or peak locking. Experimental results demonstrate that the separation energy between the split peaks changes with the volumes and densities of the Au nanoparticles and agree with the numerical calculation results quite well.
The asymmetric light reflectance behavior arising from the Fano interference between Fresnel reflection and localized surface plasmons (LSPs) is investigated. Finite-difference time-domain (FDTD) simulation results demonstrate that, when light is incident from air, reflectance spectra show peaks at the LSP resonance wavelength regardless of the metal nanoparticle density. When light is incident from the substrate, reflectance spectra show typical Fano profiles. This phenomenon can be attributed to different reflectance phase shifts induced when light is incident from different directions. Experiments are conducted with Ag-nanoparticle-coated quartz wafers. The measured spectra are in good agreement with the simulated results.
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