Shao Hui Xu

Fano resonance in anodic aluminum oxide based photonic crystals

Anodic aluminum oxide based photonic crystals with periodic porous structure have been prepared using voltage compensation method. The as-prepared sample showed an ultra-narrow photonic bandgap. Asymmetric line-shape profiles of the photonic bandgaps have been observed, which is attributed to Fano resonance between the photonic bandgap state of photonic crystal and continuum scattering state of porous structure. And the exhibited Fano resonance shows more clearly when the sample is saturated ethanol gas than air-filled. Further theoretical analysis by transfer matrix method verified these results. These findings provide a better understanding on the nature of photonic bandgaps of photonic crystals made up of porous materials, in which the porous structures not only exist as layers of effective-refractive-index material providing Bragg scattering, but also provide a continuum light scattering state to interact with Bragg scattering state to show an asymmetric line-shape profile.

A facile and universal way to fabricate superlattice nanowire arrays

A facile and universal synthetic approach for preparing superlattice nanowire (SLNW) arrays is developed. In this method, two kinds of elements are alternately electrodeposited into the holes of the anodic alumina oxide (AAO) template, automatically in separate electrolytes by a programmed device. This method is not restricted by the relative values of the reduction potentials of the elements, and the deposition of each element can be controlled independently. Three kinds of representative SLNW arrays containing noble-metal material (Ag/Ni), thermoelectric material (Bi/Sb) and magnetic material (Ni/Cu) with adjustable segment length are fabricated successfully.

Necklace-like NiO-CuO Heterogeneous Composite Hollow Nanostructure: Preparation, Formation Mechanism and Structure Control

Composite hollow nanostructure composed by transition metal oxides are promising materials in electrochemistry, catalyst chemistry and material science. In this contribution, necklace-like NiO-CuO heterogeneous composite hollow nanostructures were synthesized by annealing Ni/Cu superlattice nanowires in air. Two kinds of morphologies including CuO nanotube linked core-shell structures and CuO nanotube linked hollow structures were obtained. The structure can be tuned easily by adjusting the relative length of Cu segments in Ni/Cu superlattice nanowires and the annealing temperature. The relative diffusion amount of Cu to Ni segments was proved to be the key factor to influence the annealed sample morphology. The formation mechanism was discussed in detail based on Kirkendal effect and high temperature oxidation of alloy. We demonstrated that hollow structure or core-shell structure is related to whether the oxidation exists only in external sites or co-exists in external and internal sites during annealing.

Controllable fabrication of nickel nanoparticle chains based on electrochemical corrosion

The magnetic nanoparticle (NP) chain has attracted great concern due to its potential applications in magnetic recording, electron nano-devices, micro-mechanical sensors, and drug delivery. Here, we demonstrate the controllable preparation of magnetic Ni NP chains using electrochemical corrosion methods. Ni/Cu multi-segmented nanowires (NW) were prepared by alternately depositing Ni and Cu into the pores of an anodic aluminum oxide (AAO) template, then highly uniform Ni NP chains were obtained by immersing Ni/Cu NWs/AAO composite membrane in a 15 wt% NaOH solution for about 50 min. The reaction mechanism is proposed based on electrochemical corrosion, in which Cu serviced as the anode is corroded and Ni serviced as the cathode are retained in the NaOH electrolyte solution. Particle size and separation of the Ni NP chains can be easily adjusted and the smallest particle size and particle spacing reached to 6 nm and 15 nm, respectively. This strategy developed herein can be expected to be general route for the controllable fabrication of metallic NP chains.

Tunable broadband wavelength-selective enhancement of responsivity in ordered Au-nanorod array-modified PbS photodetectors

Herein, we report an enhanced tunable broadband wavelength-selective lead sulfide (PbS) film detector integrated with Au-nanorod arrays that were obtained by using an ultrathin open-ended porous titanium dioxide membrane (UOP-TM) as a mask. The responsivity of the PbS films with periodic Au-nanorods exhibits a drastic enhancement by up to 125%–175% due to the enhancement of the localized electromagnetic fields around the gold nanorods. Notably, the location of the strongest enhancement peak of photocurrent shifted from 450 to 980 nm as the height of the Au-nanorods increased from 30 to 120 nm. In addition, the responsivity and detectivity of the hybrid PbS film modified with 90 nm Au-nanorod arrays under laser illumination of 980 nm are as high as 944 mA W−1 and 1.72 × 1010 cm Hz1/2 W−1, respectively. These excellent figures-of-merit of the tunable broadband plasma-enhanced PbS films could be a promising candidate in future wavelength-selective photodetector applications.

Controlled solvothermal synthesis of single-crystal tellurium nanowires, nanotubes and trifold structures and their photoelectrical properties

Uniform tellurium nanowires (NWs), nanotubes (NTs) and trifold nanorods (NRs) were synthesized using a facile, environmentally benign solvothermal method with ethylene glycol as solvent, polyvinylpyrrolidone as surfactant and non-hazardous ascorbic acid as a reducing agent. By adjusting the amounts of the surfactant and the reducing agent, Te NWs, NTs and trifold NRs were prepared. The diameter of the Te NWs and NTs are 30–40 nm and 120–150 nm, respectively. A morphology evolution diagram based on different amounts of polyvinylpyrrolidone and ascorbic acid aqueous solution are presented. The effects of temperature are also investigated meticulously. The growth mechanism of the Te NTs and trifold Te NRs are discussed based on the crystallization law. The photoelectrical properties of the Te NWs and trifold Te NRs were measured. The photocurrent and responsivity of the photodetector based on Te NWs are 0.17 mA and 25.8 A W−1, respectively.

Noble-metal Ag nanoparticle chains: annealing Ag/Bi superlattice nanowires in vacuum.

One-dimensional noble-metal Ag nanoparticle chains have been prepared by electrodepositing Ag/Bi superlattice nanowires in a porous anodic alumina oxide (AAO) template and following an annealing process in vacuum. It is found that Bi, as a sacrificial metal, can be removed completely after annealing at 450 °C with a vacuum degree of 10(-5) Torr. The regulation of particle size, shape and interparticle spacing of Ag NP chains has been realized by adjusting the segment length of the Ag/Bi superlattice nanowires and the annealing condition. With an extension of the annealing time, it is observed that Ag particles display the transform trend from ellipsoid to sphere. Our findings could inspire further investigation on the design and fabrication of metal nanoparticle chains.

Alternative radiative and dark mode-induced multi-broadband transmission in asymmetrical metallic grating

The phenomenon of extraordinary and multi-broadband optical transmission through sub-wavelength metallic grating with symmetry breaking has been theoretically investigated. Under normal incident light, the radiative and dark modes appear in adjacent slits of the grating with asymmetric heights. Through the destructive interference of alternative radiative and dark modes, multiple broadband transmission and enhanced light propagation is realized. The counter-propagating light circulation results in sharp dips in the transmission spectrum. These characteristics of the asymmetric grating could provide highly controllable ways to design novel devices.