Tong Fu

Plasmonic chirality of L-shaped nanostructure composed of two slices with different thickness

A concise method is proposed to fabricate L-shaped Ag nanostructures (LSANs) for generating chirality. Prepared by glancing angle deposition, the LSAN composed of two slices with different thickness is stacked on self-assembled monolayer polystyrene nanosphere arrays by controlling substrate azimuth and deposition time. The strong optical chirality of LSANs is achieved in visible and near-IR regions by measurement. For the circular dichroism spectrum of LSANs, the intensity is enlarged, and its peaks red-shift with increasing thickness difference. When LSANs are stacked on polystyrene spheres of different diameters, enlargement and red-shift are also observed in their circular dichroism spectra with increasing thickness difference. The numerical calculations of finite element method show that the two slices composing LSAN provide cross-electric dipoles and their thickness difference provides phase difference for generating optical chirality. This study not only provides a concise and scalable method for fabricating chiral plasmonic nanostructures but also contributes to understand the knowledge of the mechanism of circular dichroism.

Broadband Extraordinary Optical Transmission Through a Multilayer Structure With a Periodic Nanoslit Array

Extraordinary optical transmission (EOT) of metallic film perforated by a periodic array of subwavelength holes is significant in photoelectric devices. In this paper, a multilayer structure with periodic nanoslit arrays is proposed to achieve broadband EOT in infrared. The optical transmission properties of such structure are simulated through the finite-element method. Greatly enhanced transmissions over a broad spectral range are observed in near-infrared wavelengths, and many enhanced electric fields occur in the narrower slit. In addition, the effects of structural parameters on transmission properties are also investigated. All these findings could guide the design of devices with broadband-enhanced transmission and high electric-field concentration.

Circular dichroism of a tilted U-shaped nanostructure

The circular dichroism (CD) effect plays an important role in biological detection, analytical chemistry, and plasmonic sensing. Tilted 3D structures can generate CD signals under normal illumination. However, fabricating tilted 3D structures is complex and expensive. In this study, we fabricate a tilted U-shaped nanostructure (TUSN) on a polystyrene (PS) nanosphere through the glancing angle deposition method. One branch of the U-shaped nanostructure is tilted by raising a sheet of SiO2 on the PS nanosphere. And the CD signal of the TUSN is enhanced because the phase difference increases with increasing thickness of the SiO2 sheet. This work proposes a method for fabricating tilted nanostructures and elucidates the mechanism of the CD effect for future research.

Direct and indirect coupling mechanisms in a chiral plasmonic system

Artificial chiral plasmonic nanostructures (ACPNs) are widely studied and used in biological monitoring, analytical chemistry, and negative-refractive-index media. The mechanism of direct coupling between two twist metal nanorods has been obtained in usual ACPNs. In this work, we proposed a nanosystem of twist nanorods separated by a metal film (TNMF). By analyzing the charge distributions, a new indirect coupling mechanism is found. According to the equivalent LC resonant circuits, gold nanorods on the two sides of the gold film can be regarded as a receiver and an emitter. These components enhanced transmittance and provided direct and indirect coupling mechanisms for the circular dichroism (CD). The direct coupling mode cannot be explained by impedance matching and can be tuned monotonously by monotonously varying geometric dimensions. However, the CD signal of indirect coupling can be explained by impedance matching and can be tuned to its maximum by varying geometric dimensions when the impedances of both sides of the gold film match. These results can help design novel chiral optical structures and promote combined applications between photons and electrons when a gold film is powered on.

Active control of optical chirality with graphene-based achiral nanorings.

A strong chiral near-field is crucial for the detection of chiral molecules. Active tuning of the chiral near-field can shorten the detection process. In this study, a graphene-based achiral nanoring (GAN) that can actively control chiral near-fields is presented. The GAN is composed of three identical graphene pieces. The handedness and strength of the chiral near-fields can be actively controlled by adjusting the Fermi levels of these three graphene pieces. The optical chirality of the GAN near-field is 500 times that of circularly polarized light. In addition, the GAN enhances the chiral response of the chiral material by a factor of 250. This work provides opportunities for the ultrasensitive detection and location of molecules through the active control of chiral near-fields.