Xiao Bing Li

Growth and spectral analysis of ZnO nanotubes

ZnO nanotubes were fabricated by vapor-phase transport using the mixture of ZnO and graphite powders in air. A self-catalyzed growth mechanism was proposed based on microstructure analysis by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Raman scattering, integrated photoluminescence, and time-resolved photoluminescence were employed to explore the optical properties and the dynamic process. Combing with crystal structure and the spectral characteristics of the ZnO nanotubes, the charge carrier transport process was discussed.

Hydrothermally grown ZnO nanorods on self-source substrate and their field emission

Vertically aligned zinc oxide nanorod arrays were grown directly using a zinc foil as both source and substrate in pure water at low temperature by a simple hydrothermal reaction. The morphology and crystal structure of the ZnO nanorod arrays were examined by scanning electron microscopy, transmission electron microscopy and x-ray diffraction, respectively. The nanorods grew along the [0?0?0?1] direction and were 80?nm in diameter and almost 2??m in length. Directly employing the zinc foil substrate as cathode, the field emission (FE) of the ZnO nanorods presented a two-stage slope behaviour in a ln(J/E2)?1/E plot according to the Fowler?Nordheim equation. The FE behaviour was investigated by considering the action of the defects in ZnO nanorods based on the measurement of the photoluminescence.

Graphene plasmon guided along a nanoribbon coupled with a nanoring

The propagation properties of edge mode graphene surface plasmon polaritons (EGSPs) guided along a nanoribbon coplanar waveguide coupled with a nanoring are investigated, both in parallel and serial cascades. Strong coupling of EGSPs between the nanoribbon and nanoring appears at the resonance frequencies. Further investigation shows that EGSPs can be supported by nanorings, even though the radiuses are very small. The resonance frequencies can be tuned by the geometric parameters and the doping level of graphene. A Y-shape switch based on parallel coupled structures is presented as an application. Various potential planar devices are expected to derive from the prototype coupled structures.

Plasmonic metamaterial based on the complementary split ring resonators using graphene

Plasmonic metamaterial based on the graphene complementary split ring resonators is introduced and investigated. The underlying mechanisms of the resonances are explored in detail when such metamaterial is illuminated by horizontal and vertical polarization infrared lights, which provides us with a better understanding of the phenomenon of spectral responses. With its more pronounced spectral response and a tunability that is more conveniently recognized, such a metamaterial has great prospects for being adopted for practical applications in the future.

Terahertz Wavefront Control Based on Graphene Manipulated Fabry–Pérot Cavities

This letter proposes a new approach for controlling the terahertz wavefront using simply constructed equipment, consisting of graphene-based Fabry-Pérot cavities (GFPCs) arranged regularly in one dimension. The reflection spectrum of each cavity can be efficiently tailored by changing the doping level of the graphene. Specifically, more than 270°, 240°, and 180° of phase shifts are produced near the first, second, and third resonances, respectively. With such a significant degree of freedom for the response phases, we demonstrate three different strategies to organize the array, viz., 4, 3, and 2 GFPC cells-based periodic lattices were designed, respectively, to generate particular propagating directions of the reflection waves. Compared with the metal resonant structures, our scheme is convenient for obtaining the multi-scanning angle and multi-frequency properties. The GFPC structure and the associated arrangement approach are a new addition to the wavefront control toolbox, which is promising for future innovative applications in terahertz sensing, communication, and spectrum splitting.

Excitation of topological insulator plasmons by two-dimensional periodic structure

Plasmons induced by topological insulator (TI) Bi2Se3 micro-ribbon arrays have been experimentally observed recently (Nature nanotechnology 2013, 8, 556-560). In this letter, the surface plasmons excited by TI Bi2Se3 micro-disk arrays are investigated by the methods of full-wave numerical simulations. Numerical simulation results show that thin Bi2Se3 micro-disk arrays can support dipolar plasmon resonances in the terahertz (THz) regimes and the absorptions can be tuned by the structure parameters. In addition to the plasmon mode, two phonon-mode responses are also observed, which confirms the experimental results of micro-ribbon arrays. Our work further proves that TI can be a good candidate of plasmonic platform.

Optical function of bionic nanostructure of ZnO

A novel bionic network nanostructure of zinc oxide (ZnO), which is similar to the microstructure of a butterfly wing, was first fabricated by a vapor-phase transport method using zinc powder as a source. These bionic nanostructures are composed of three ordered multi-aperture gratings. Similar to the optical effect of butterfly wings, the diffraction patterns of the bionic network of ZnO were observed. The mechanism of the optical function was discussed based on the physical model of multi-aperture diffraction.

Two-dimensional graphene metasurfaces for wavefront manipulation

Two dimensional graphene metasurfaces working in terahertz regime are proposed to realize dynamical control of wavefront with high efficiency. Each graphene metasurface consists of an array of graphene rectangle patches on square grounded dielectric substrate. The reflection amplitude and phase of graphene rectangle patches are investigated with different patch lengths and widths. It is found that a full phase tuning range from 0 to 2π, together with sufficiently high amplitude (larger than 86%), can be achieved by only changing the geometry size of graphene patches. Different types of wavefront manipulations can be realized by properly arranging these graphene patches. As a proof of principle, 2D anomalous reflection and vortex waves are demonstrated in this paper.

Multiple-Beams Splitter Based on Graphene

Due to its tunability of conductivity, graphene can be considered as a novel epsilon-near-zero (ENZ) material. Based on this property, we propose a wave splitter using graphene. Simulation results show that the circular surface plasmon polariton waves excited by a point source can be transferred to narrow beams through a graphene-based wave splitter, which is formed by a polygonal contour of the ENZ graphene layer. The number of beams can be easily controlled by adjusting the shape of the polygonal ENZ graphene layer, and the operation frequency can also be chosen.

Dual-beam scanning using graphene-based reflectarray

A reflectarray possessing symmetrically dual-beam scanning capability is proposed, which is based on graphene reflective cells operating at Terahertz (THz). Due to the tunability of graphenes conductivity, the phase distribution of the reflectarray can be controlled and then the electromagnetic properties of the surface can be altered. For simplicity, the reflectarray is composed of two types of cells with different phase responses, 0 and pi, which correspond to two different chemical potentials that can be obtained by applying different biased voltages. By designing the sequence of cells, the beam can be steered and the direction can be scanned in a range via switching between different phase distributions of the reflectarray. Simulation results and theoretical calculations agree well, demonstrating the possibility of beam scanning using graphene based reflectarray. This new electronically beam scanning mechanism offer an alternative to a conventional phased array.