Wei-Qing Huang

Novel Ag3PO4/CeO2 composite with high efficiency and stability for photocatalytic applications

A novel Ag3PO4/CeO2 composite was fabricated by in situ wrapping CeO2 nanoparticles with Ag3PO4 through a facile precipitation method. The photocatalytic properties of Ag3PO4/CeO2 were evaluated by the photocatalytic degradation of MB and phenol under visible light and UV light irradiation. The photocatalytic activity of the composite is much higher than that of pure Ag3PO4 or CeO2. The rate constant of MB degradation over Ag3PO4/CeO2 is more than 2 times and 20 times than those of pure Ag3PO4 and CeO2 under visible light irradiation, respectively. The Ag3PO4/CeO2 composite photocatalyst also shows higher photocatalytic activity for the colorless phenol degradation compared to pure Ag3PO4. Moreover, the Ag3PO4/CeO2 sample has almost no loss of photocatalytic activity after five recycles under the irradiation of visible light and UV light, indicating that the composite has good photocatalytic stability. The excellent photocatalytic activity of the Ag3PO4/CeO2 composite is closely related to the fast transfer and efficient separation of electron–hole pairs at the interfaces of the two semiconductors derived from the matching band positions between CeO2 and Ag3PO4. This newly constructed Ag3PO4/CeO2 composite, with promising and fascinating visible light-driven photocatalytic activity as well as good stability, could find potential applications in environmental purification and solar energy conversion.

A wide bandgap plasmonic Bragg reflector.

Surface plasmon polaritons (SPPs) Bragg reflector with more excellent optical properties are investigated numerically. By introducing a finite array of periodic grooves on the two surfaces of metal-insulator-metal (MIM) waveguide, we fulfill the periodical changes of effective refractive index, which leads to the photonic band gap (PBG). And it has been further widened by inserting a dielectric material with higher refractive index in the waveguide with narrow slit width. Finite difference time domain (FDTD) simulation confirms the widened bandgap. In addition, a SPP nanocavity is introduced by breaking the periodicity of our proposed structure.

Theoretical Investigation of Broadband and Wide-Angle Terahertz Metamaterial Absorber

Broadband absorbers have attracted considerable attention due to their great prospect for practical applications. The mechanism is usually a superposition of several sets of structures with different geometrical dimensions. Herein, we numerically investigate an unconventional to existing metamaterial-based broadband terahertz absorber based on the multilayer same-sized square plate structure. Greater than 99% absorption across a frequency range of 300 GHz with the central frequency ~ 1.96 THz can be obtained. The FWHM of this device can be up to 42% (with respect to the central frequency), which is 2.6 times greater than that of the single layer structure. Such a property is retained well at a very wide range of incident angles. The mechanism of the broadband absorber is attributed to longitudinal coupling between layers. The results of the designed metamaterial absorber appear to be very promising for solar cell, detection, and imaging applications.

A novel dual-band terahertz metamaterial absorber for a sensor application

We present a new type of dual-band terahertz metamaterial absorber formed by a patterned metallic strip and a dielectric layer on top of a metallic ground plane. It is found that besides a strong absorption in the fundamental resonance, a prominent high-order resonance with near-unity absorption is also unveiled. The origin of the induced dual-band absorption was elucidated. Importantly, the quality factor (Q) and the figure of merit (FOM) of the high-order resonance are 8.4 and 22.7 times larger than that of the fundamental resonance, respectively, which makes the proposed absorber to have significant potential in biological monitoring and sensing. Moreover, we demonstrate a dual-band and insensitive for two orthogonal polarizations terahertz absorber based on a metallic cross and a metallic ground plane separated by a dielectric layer. The Q and FOM of the high-order resonance are still larger than that of the fundamental resonance. The proposed absorbers appear to be very promising for solar cells, detection, and imaging applications.

Frequency Continuous Tunable Terahertz Metamaterial Absorber

Metamaterial-based perfect absorbers utilize the intrinsic loss, with the aid of appropriate structural design (completely suppress transmission and reflection), to achieve near unity absorption at a certain frequency. The frequency of the reported absorbers is usually fixed and operates over a limited bandwidth, which greatly hampers their practical applications. Active or dynamic control over their resonance frequency is urgently necessary. Herein, we propose a novel approach for efficient tuning of the frequency of the absorber by shifting the movable part of the composite structure composed of the fixed and movable parts. The concept is rather general and applicable to various absorbers as long as the sandwich structure design is valid. The demonstrated continuous tuning of metamaterial absorber can find practical applications in detection, imaging, spectroscopy and selective thermal emitters.

Wavelength-Converted/Selective Waveguiding Based on Composition-Graded Semiconductor Nanowires

Compact wavelength-sensitive optical components are desirable for optical information processing and communication in photonic integrated system. In this work, optical waveguiding along single composition-graded CdS(x)Se(1-x) nanowires were systematically investigated. Under a focused laser excitation, the excited light can be guided passively along the bandgap-increased direction of the nanowire, keeping the photonic energy of the guided light almost unchanged during the whole propagation. In comparison, the excited light is guided actively through incessantly repeated band-to-band reabsorption and re-emitting processes along the bandgap-decreased direction, resulting in a gradual wavelength conversion during propagation. On the basis of this wavelength-converted waveguiding, a concept of nanoscale wavelength splitter is demonstrated by assembling a graded nanowire with several composition-uniform nanowires into branched nanowire structure. Our study indicates that composition-graded semiconductor nanowires would open new exciting opportunities in developing new wavelength-sensitive optical components for integrated nanophotonic devices.

Asymmetric light propagation in composition-graded semiconductor nanowires

Asymmetric light propagation is crucial to the development of optical-based functional components in nanophotonics. Diverse configurations and structures have been proposed to allow asymmetrical propagation of photonic signal, but on-chip integration is difficult to achieve due to their complex structure and/or relatively large footprint. Here we report the first design and realization of asymmetric light propagation in single semiconductor nanowires with a composition gradient along the length. We show the asymmetric nanowire waveguides can be synthesized using a simple thermal evaporation and vapor transport approach without involving complicated and costly fabrication processes. Our studies demonstrate the asymmetric nanowire waveguides offer some significant advantages over previous designs, including ultra-low operation power, tunable working wavelength and nanoscale footprint, making them attractive building blocks for integrated photonic circuits.

Ag 3 PO 4 semiconductor photocatalyst: possibilities and challenges

Ag3PO4 as a photocatalyst has attracted enormous attention in recent years due to its great potential in harvesting solar energy for environmental purification and fuel production. The photocatalytic performance of Ag3PO4 strongly depends on its morphology, exposed facets, and particle size. The effects of morphology and orientation of Ag3PO4 on the catalytic performance and the efforts on the stability improvement of Ag3PO4 are reviewed here. This paper also discusses the current theoretical understanding of photocatalytic mechanism of Ag3PO4, together with the recent progress towards developing Ag3PO4 composite photocatalysts. The crucial issues that should be addressed in future research activities are finally highlighted.

Frequency tunable metamaterial absorber at deep-subwavelength scale

Metamaterial-based absorbers utilize the intrinsic loss, with the aid of appropriate structure design, to achieve near unity absorption at a certain frequency. The frequency of the reported absorbers is usually fixed and operates over a limited bandwidth, which greatly hampers their practical applications. Active or dynamic control over their resonance frequency is urgently necessary. Herein, we theoretically present a novel frequency tunable terahertz metamaterial absorber formed by a square metallic patch and a ground plane separated by a strontium titanate dielectric layer. Up to 80.2% frequency tuning is obtained by changing the temperature of the absorber, and there is very little variation in the strength of the absorption. The frequency shift is attributed to the temperature-dependent refractive index of the dielectric layer. Furthermore, the ratio between the lattice period and the resonance wavelength is close to 1/36 at 0.111 THz, which is smaller than the previously reported results. The proposed absorber has potential applications in detection, sensors, and selective thermal emitters.

Coupling effect on phonon thermal transport in a double-stub quantum wire

By using the scattering matrix method, we investigate the thermal conductance in a double-stub quantum wire at low temperatures. The coupling effects between two stubs are analyzed in detail. It is found that the quantum structures exhibit oscillatory decaying thermal conductance with the width between two stubs at low temperature. A comparison between thermal conductances is made when stress-free and hard-wall boundary conditions are applied for acoustic modes, respectively. The result indicates that the behavior of the thermal conductance versus temperature is qualitatively different for the different types of boundary conditions.