Occurrence Of Fano Resonances Research Articles

Photoinduced Fano Resonances between Quantum Confined Nanocrystals and Adsorbed Molecular Catalysts.

Interaction of surface adsorbate vibration and intraband electron absorption in nanocrystals has been reported to affect the photophysical properties of both nanocrystals and surface adsorbates and may affect the performance of hybrid photocatalysts composed of semiconductor nanocrystals and molecular catalysts. Here, by combining ultrafast transient visible and IR spectroscopic measurements, we report the observation of Fano resonances between the intraband transition of the photogenerated electrons in CdS and CdSe nanocrystals and CO stretching vibrational modes of adsorbed molecular catalysts, [Fe2(cbdt)(CO)6] (FeFe; cbdt = 1-carboxyl-benzene-2,3-dithiolate), a molecular mimic for the active site of FeFe-hydrogenase. The occurrence of Fano resonances is independent of nanocrystal types (rods vs dots) or charge transfer character between the nanocrystal and FeFe, and is likely a general feature of nanocrystal and molecular catalyst hybrid systems. These results provide new insights into the fundamental interactions in these hybrid assemblies for artificial photosynthesis.

Evidence of Tunable Fano Resonance in a Liquid Crystal‐Based Colloidal Metamaterial

AbstractA colloidal metamaterial composite, realized by dispersing sub‐micrometer‐sized high refractive index dielectric resonators (selenium) in a nematic liquid crystal medium, exhibits electrically tunable Mie resonances in the optical regime. Darkfield hyperspectral imaging reveals that when the nematic liquid crystal (NLC) molecules reorient from the pristine planar state on application of an AC electric field, the scattered image from the particle splits into two, owing to the birefringence of the NLC medium. At higher voltages, a doughnut‐shaped scattering pattern is obtained, indicating the occurrence of Fano resonance. The analysis of the darkfield scattering spectra based on the “Multi‐pole Fano interference model” confirms the presence of Fano resonance arising due to the interference between the broad electric dipolar and narrow electric quadrupolar modes. With increasing voltage, the value of Fano parameter q decreases and approaches unity corresponding to an ideal Fano shape. Thus, the inherent optical anisotropy of the NLC medium and Fano coupling between the Mie resonant modes lead to highly reversible changes in the far‐field scattering pattern with potential applications in refractive index sensing, wave‐guiding, etc.

Mediating Broad Band Light Trapping in Silicon Solar Cell by Aluminum Nanoparticles with Native Oxide Shell

We have investigated the role of a native oxide layer on aluminum nanoparticles (Al NPs) in the light forward scattering into the silicon, with the aim of enhancing silicon solar cell performance. Initially, the NPs’ morphology optimized for maximum light confinement into the silicon wafer. Oxide layer inclusion of 2.2 nm on Al NPs’ surface reduces the reflectance (from ∼25% to ∼21%), and improves the photocurrent enhancement (from ∼27 to ∼30 mA/cm2) due to the better light forward scattering, and reduced parasitic absorption losses, with no occurrence of Fano resonances. Oxide layer growth effect around NPs also calculated using the Bruggeman effective medium theory. A finite-element method is adapted to calculate the peak radiative power, spectral field distributions, and spatial dipole field distributions for experimentally optimized Al NPs size on a silicon substrate for explaining plasmonic device performance enhancement in the localized surface plasmon resonance, and off-resonance regions.

Plasmonic silicon solar cell comprised of aluminum nanoparticles: Effect of nanoparticles' self-limiting native oxide shell on optical and electrical properties

The aluminum nanoparticles' (Al NPs) morphology is optimized initially, for maximum light confinement into a silicon substrate. With self-limiting native oxide shell on the Al NPs after ageing, the maximum photocurrent enhancement (from 26.89 to 29.21 mA/cm2) from a silicon solar cell is observed as compared to the bare cell, in surface plasmon resonance and off-resonance regions due to improved light forward scattering, with no occurrence of Fano resonances. Related to the electrical properties of the plasmonic device, an increase in fill factor (from 56.11 to 62.58) and a decrease in series resistance (from 1.80 Ω to 1.24 Ω) are also observed after the oxide layer formation on Al NPs. The passive partial dielectric oxide layer at the interface helped in electrical passivation by reducing lateral resistance to current flow along the plane of the interface. A finite-element method is also adapted to calculate spatial and angular radiative dipole field distributions for the experimentally optimized Al NPs' size on a silicon substrate, without and with oxide inclusion in NPs for explaining the plasmonic device performance enhancement. With oxide inclusion, Al NPs' dipole field exhibited a large shift towards a silicon due to the modified dielectric environment as compared to without oxide. Bruggeman effective medium theory (for dielectric response) is also used to explain the results with the modification in peak radiative power, spectral field distribution, and spatial and angular radiative dipole field distributions of Al NPs with oxide inclusion in Al.

Quantum dynamics simulation with classical oscillators

In a previous paper [J.S.Briggs and A.Eisfeld, Phys.Rev.A 85, 052111] we showed that the time-development of the complex amplitudes of N coupled quantum states can be mapped by the time development of positions and velocities of N coupled classical oscillators. Here we examine to what extent this mapping can be realised to simulate the "quantum" properties of entanglement and qubit manipulation. By working through specific examples, e.g. of quantum gate operation, we seek to illuminate quantum/classical differences which hitherto have been treated more mathematically. In addition we show that important quantum coupled phenomena, such as the Landau-Zener transition and the occurrence of Fano resonances can be simulated by classical oscillators.

Electronic transmission through a polyacene ladder with a substitutional edge impurity

We provide an analytical and numerical study of the electronic and transport properties of a ladder system composed of two coupled chains, arranged in the ladder polymer and in the polyacene lattice topology, with a single substitutional edge impurity embedded in one of them. We evidence in particular the connection between local density of states, transmittivity, and occurrence of Fano resonances in the transmission spectra. Comparison of the local density of states and charge transmittivity through the two different ladder systems, as the impurity position is varied, contributes to evidence the nature of resonant interactions occurring for electronic energies coinciding with the impurity energy.

Phonon Conductance of Potassium- and Sodium-Doped Transpolyacetylene Chain

A theoretical approach for the study of phonon dynamics and scattering properties of doped transpolyacetylene chain is presented. The coherent reflection and transmission scattering cross-sections for phonons incident on the doped unit cell boundary are calculated in accordance with the Landauer-Buttiker electron scattering description, using the matching procedure with the nearest and next nearest neighbor elastic force constants. This is done for two different dopants, namely, the potassium and sodium atoms. Our numerical results yield an understanding of the transpolyacetylene chain dynamical properties and the effects on phonon conductance due to phonon incident on the doped unit cell boundary. The coherent reflection and transmission coefficients show characteristic spectral features, depending on the cutoff frequencies for the propagating phonons and on the nature of the dopants. They illustrate the occurrence of Fano resonances in the scattering spectra that result from the interactions of propagating elastic waves of the undoped transpolyacetylene chain with the localized modes due to the breakdown of the translation symmetry in the x direction.