Jianliang Xie

Characterization and microwave resonance in nanocrystalline FeCoNi flake composite

To explore the resonance mechanism of nanocrystalline FeCoNi flake composites, characterization of the flakes was investigated. The structural and magnetic properties of flakes manifestly tailored the features of microwave permeability spectrum of flake composites, relating to the physical effects of nanograins. The exchange mode with a few modifications was used to explain the origin of composite microwave performance, and the computed results were close to the experiment. It is believed that the exchange energy, dominating in the microwave resonance of spherical nanoparticles, plays an equally important role in nanocrystalline flakes.To explore the resonance mechanism of nanocrystalline FeCoNi flake composites, characterization of the flakes was investigated. The structural and magnetic properties of flakes manifestly tailored the features of microwave permeability spectrum of flake composites, relating to the physical effects of nanograins. The exchange mode with a few modifications was used to explain the origin of composite microwave performance, and the computed results were close to the experiment. It is believed that the exchange energy, dominating in the microwave resonance of spherical nanoparticles, plays an equally important role in nanocrystalline flakes.

Electromagnetic and absorption properties of urchinlike Ni composites at microwave frequencies

In this paper, nearly monodispersed urchinlike Ni powders were synthesized by a simple hydrogen-thermal reduction method. Electromagnetic and absorption characteristics were then investigated at 0.5–18 GHz. The permeability spectra present four resonance peaks over the whole frequency range. The resonance absorption property was discussed by fitting the permeability spectrum using the well-known Landau-Lifshitz-Gilbert equation and Maxwell-Garnett mixing rule. Correspondingly, the magnetic loss of the first band observed is attributed to the natural resonance, while the other three bands are considered to originate from non-uniform exchange resonance in the permeability spectra. The maximum reflection loss can reach −43 dB at about 10 GHz with 2 mm in absorber thickness.

Dual-band absorption of mid-infrared metamaterial absorber based on distinct dielectric spacing layers

We present the simulation, fabrication, and characterization of a dual-band metamaterial absorber in the mid-infrared regime. Two pairs of circular-patterned metal-dielectric stacks are employed to excite the dual-band absorption peaks. Dielectric characteristics of the dielectric spacing layer determine energy dissipation in each resonant stack, i.e., dielectric or ohmic loss. By controlling material parameters, both two mechanisms are introduced into our structure. Up to 98% absorption is obtained at 9.03 and 13.32 μm in the simulation, which is in reasonable agreement with experimental results. The proposed structure holds promise for various applications, e.g., thermal radiation modulators and multicolor infrared focal plane arrays.

The hierarchical architecture effect on the microwave absorption properties of cobalt composites

The effect of hierarchical architecture on the electromagnetic properties of microwave absorber candidates is important for absorption design. This work prepares dendritic cobalt powders by a simple hydrothermal reduction method. The study of microwave electromagnetic properties reveals that dielectric polarization relaxation dominates over the power loss owing to the superstructure with a large volume of branches. Compared with the conventional spherical filler, a composite consisting of dendritic filler shows an improved electromagnetic absorption performance in low frequencies due to the enhancement of both the impedance match to free air and the loss induced by interfacial polarization and Ohmic resistance.

Achieving Ultrafast Hole Transfer at the Monolayer MoS2 and CH3NH3PbI3 Perovskite Interface by Defect Engineering

The performance of a photovoltaic device is strongly dependent on the light harvesting properties of the absorber layer as well as the charge separation at the donor/acceptor interfaces. Atomically thin two-dimensional transition metal dichalcogenides (2-D TMDCs) exhibit strong light-matter interaction, large optical conductivity, and high electron mobility; thus they can be highly promising materials for next-generation ultrathin solar cells and optoelectronics. However, the short optical absorption path inherent in such atomically thin layers limits practical applications. A heterostructure geometry comprising 2-D TMDCs (e.g., MoS2) and a strongly absorbing material with long electron-hole diffusion lengths such as methylammonium lead halide perovskites (CH3NH3PbI3) may overcome this constraint to some extent, provided the charge transfer at the heterostructure interface is not hampered by their band offsets. Herein, we demonstrate that the intrinsic band offset at the CH3NH3PbI3/MoS2 interface can be overcome by creating sulfur vacancies in MoS2 using a mild plasma treatment; ultrafast hole transfer from CH3NH3PbI3 to MoS2 occurs within 320 fs with 83% efficiency following photoexcitation. Importantly, our work highlights the feasibility of applying defect-engineered 2-D TMDCs as charge-extraction layers in perovskite-based optoelectronic devices.

Magneto-optical Goos-Hänchen effect in a prism-waveguide coupling structure

We report a theoretical study of the enhanced Goos-Hänchen (GH) effect in a prism-waveguide coupling system with a magneto-optic thin film of Ce doped Y(3)Fe(5)O(12) (CeYIG). By magnetizing the CeYIG thin film along different directions, a variation of the GH shift can be observed, which is named as the MOGH (magneto-optical Goos-Hänchen) effect. The applied magnetic field direction is found to cause MOGH effect for light with different polarizations. As example systems, enhanced GH shift and MOGH effect is observed in both prism/Air/CeYIG/SiO(2) and prism/Au/CeYIG/SiO(2) structures, by applying opposite magnetic field across the CeYIG layer in a transverse magneto-optical Kerr effect (TMOKE) configuration. The GH and MOGH effect as a function of layer thicknesses, material refractive indices and magneto-optical properties are systematically simulated and discussed. It is observed that the coupling layer and MO layer thickness plays an important role of controlling the MOGH effect in the prism/Au/CeYIG/SiO(2) plasmonic waveguide structure. The MOGH effect shows high sensitivity to applied magnetic field and index variations, making it promising for applications such as optical switches, modulators, and chemical or biomedical index sensors.

Pantoscopic and polarization-insensitive perfect absorbers in the middle infrared spectrum

We have engineered numerically perfect absorbers based on a square ring pattern. The mono- and the multiband perfect absorption were presented in the whole midinfrared region. The characteristic dimension of the single square ring absorber (SSRA), i.e., lattice constant a, can be smaller than 0.1 times the operating wavelength so that the absorber could be viewed as continuous medium. This should be attributed to the high reactance of the patterns, as depicted in an extended equivalent circuit model of our structure. The model can accurately make a prediction of the operating wavelength of the SSRA, and the relative errors can be less than 5%. A crude numerical model of effective permeability was also deduced to account for the magnetic property of the absorbers in the optical spectrum. The multiband perfect absorber exhibited a good stability of polarization, incident angle, and azimuth.

ZrO 2 -TiO 2 thin films: a new material system for mid-infrared integrated photonics

Mid-infrared (MIR, 2 - 6 μm wavelength) transparent metal oxides are attractive materials for planar integrated MIR photonic devices and sensing applications. In this report, we present reactive sputtering deposited ZrO2-TiO2 (ZTO) thin films as a new material candidate for integrated MIR photonics. The material structure and optical properties were systematically studied as a function of Ti concentration. The thin film index of refraction monotonically increases with Ti concentration, while the film crystallinity decreases. Fully amorphous ZTO films were achieved with 40 at.% Ti doping on various substrates. MIR micro-disk resonators on MgO substrates were demonstrated using Zr0.6Ti0.4O2 strip-loaded waveguides with a loaded quality factor of ~11,000 at 5.2 μm wavelength.

Numerical study of a dualband negative index material with polarization independence in the middle infrared regime

We engineered numerically a dualband negative index metamaterial exhibiting polarization independence based on a double square ring pairs array and thin wire net pairs. The mechanism accomplishing the negative refractive index was interpreted using retrieved optical constants together with monitored field distribution. The influence of the substrate on the effective material parameters has also been analyzed qualitatively at the end of this work.

High-frequency magnetic properties of [FeCo/FeCo-SiO2]n multilayered films deposited on flexible substrate

A series of 120 nm [FeCo/FeCo-SiO2]n multilayer thin films with different FeCo layer thicknesses (T = 10–40 nm) and fixed FeCo-SiO2 layer thickness (20 nm) were deposited on flexible substrate (Mylar) by controlling the sputtering time under applied magnetic field. The magnetic properties of the multilayer thin films were investigated. The experimental results showed that the multilayer thin films had obvious in-plane uniaxial magnetic anisotropy, which can be adjusted in a broad range by changing the thickness of FeCo layer. In addition, good soft magnetic performance was obtained. The coercivity in the easy axis H c e of the multilayer films with the T = 10 nm, 20 nm, 30 nm, and 40 nm was 5 Oe, 25 Oe, 10 Oe, and 8 Oe, respectively. In frequency-dependent permeability spectra measurement, two resonance peaks of complex permeability spectrum were observed, especially for T = 20 nm, which can be attributed to the complicated magnetic structure of FeCo and FeCo-SiO2 layer. By introducing multilayers with different effect anisotropy field, one can broaden the absorption peak while maintaining the high permeability, which would open the way for their potential applications as wide-band microwave absorber.