Guo Liang Shang

Fabrication of one-dimensional alumina photonic crystals with a narrow band gap and their application to high-sensitivity sensors

In this study, alumina photonic crystals (PCs) were fabricated by applying a sine-wave current in the anodization of aluminum. The effect of periodic time and peak–peak value of the current on the photonic band gap (PBG) were discussed. By selecting the appropriate experimental conditions, a full-width at half maximum (FWHM) of the PBG of only 18 nm was achieved. The experimental results show that the central position of the PBG was proportional to the periodic time of the current signal in the anodization process. A short periodic time allowed the formation of alumina PCs with a narrow band gap. By changing the peak–peak value of the current, the position of the PBG with a narrow FWHM could also be tuned artificially. The as-prepared alumina PCs showed a linear shift of PBG position and transmittance with the increase of refractive index of the analytes infiltrated into the pores, indicating their potential application in chemical sensing or bio-sensing.

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.

Anodic alumina photonic crystal heterostructures

Anodic alumina photonic crystal heterostructures (PCHs) consisting of two photonic crystals with different lattice constants are fabricated under the combination of two periodic oxidation voltage waves with similar voltage waveforms but different upper and lower bound values. The optical properties of these PCHs are studied. The anodic alumina PCHs with controllable photonic bandgaps (PBGs) offer an ability to tailor the PBGs. Three different combinations of band structures—overlapped, staggered, and split PBGs—are introduced. These may provide a broad range of possibilities for optical device development.

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.

Preparation of large scale and highly ordered vanadium pentoxide (V2O5) nanowire arrays towards high performance photodetectors

Large scale and highly ordered vanadium pentoxide (V2O5) nanowire arrays were successfully prepared. The nanowires were arranged parallel in the same direction and formed into a uniform and compact structure by using the improved self-assembly method. The V2O5 nanowire arrays were obtained from the in situ high temperature treatment of VO2(A) nanowire arrays. The as prepared V2O5 nanowire arrays show an excellent light response under visible light irradiation at room temperature. Experimentally, when the incident light intensity is 105 mW cm−2, the arrays exhibit a high responsivity of 160.3 mA W−1, a high detectivity of 6.5 × 108 Jones and a fast response time. These results pave the way for an effective approach to fabricate large-scale ordered semiconductor nanowire arrays and promising photoelectric detectors.

LiTaO3 microcubes: the layered structure and the increased Curie temperature

Lithium tantalate (LiTaO3) is a very important material with various outstanding properties. In this paper, a LiTaO3 microcube has been successfully synthesized using a hydrothermal method at 220 °C. The microcube is about 1 μm in diameter. The structure is characterized by FESEM, TEM and Raman investigation, and the results suggest that the microcube is constructed by nanolayers. To clarify the growth mechanism of the layered microcube, a time-dependent FESEM investigation is performed. Further investigation of PL, dielectric and ferroelectric properties indicate that there are lots of oxygen related defects among the layers, which is helpful for increasing the Curie temperature. The LiTaO3 microcubes show application potential to be used as a pyroelectric detector material with high performance.

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.