Guang Tao Fei

Large-scale synthesis of single crystalline gallium nitride nanowires

Large-scale synthesis of single crystalline GaN nanowires in anodic alumina membrane was achieved through a gas reaction of Ga2O vapor with a constant flowing ammonia atmosphere at 1273 K. X-ray diffraction, Raman backscattering spectroscopy, scanning electron microscopy, and transmission electron microscopy indicated that those GaN nanowires with hexagonal wurtzite structure were about 14 nm in diameter and up to several hundreds of micrometers in length. The growth mechanism of the single crystalline GaN nanowires is discussed.

Preparation of photonic crystals made of air pores in anodic alumina

Photonic crystals made of air pores in anodic alumina were prepared by electrochemical oxidation of aluminium and subsequent chemical etching. Optical photographs and transmission spectra prove the existence of a photonic band gap in the optical sprectrum for this porous material. The colour of the sample and the diffraction peak position in the transmission spectra could easily be adjusted in the chemical etching process. This method could provide a possible approach to producing large-area optical photonic crystals cheaply and rapidly.

Size-dependent melting behavior of Zn nanowire arrays

The melting behavior of Zn nanowires embedded in the holes of porous anodic alumina membrane with different diameters was studied by using the differential scanning calorimetry. The crystalline structure and morphology of Zn nanowire arrays were characterized by x-ray diffraction and transmission electron microscopy. The melting temperature of Zn nanowire arrays shows the strong dependence on nanowire sizes. The melting temperature was curvilinear with the reciprocal of the diameter of nanowires with the change of the diameter, which was discussed in terms of size-dependent heat of fusion change.

Synthesis of polyaniline micro/nanospheres by a copper(II)-catalyzed self-assembly method with superior adsorption capacity of organic dye from aqueous solution

Hollow and core-shell polyaniline (PANI) micro/nanospheres have been fabricated by a simple copper(II)-catalyzed self-assembly method under different reagent concentrations. In this synthesis system, the copper(II) salt and the template composed of aniline monomers were two key factors in the formation of PANI spherical products. The molecular structure of the PANI prepared by the copper(II)-catalyzed self-assembly method is similar to that of PANI prepared by traditional methods as demonstrated by X-ray diffraction, Fourier-transform infrared and Raman spectroscopy. The synthesized PANI hollow spheres and fiber/sheets were used to adsorb methyl orange from aqueous solution. The results showed that the adsorption/desorption kinetics and isotherms followed pseudo-second-order and Langmuir models. Importantly, the as-synthesized PANI hollow spheres exhibited a superior adsorption capacity (384.62 mg g−1) compared with other absorbents. The excellent adsorption characteristic of the hollow PANI microsphere will render it an ideal candidate for removal of organic dye from wastewater.

Modulation of Transmission Spectra of Anodized Alumina Membrane Distributed Bragg Reflector by Controlling Anodization Temperature

We have successfully prepared anodized alumina membrane distributed Bragg reflector (DBR) using electrochemical anodization method. The transmission peak of this distributed Bragg reflector could be easily and effectively modulated to cover almost any wavelength range of the whole visible spectrum by adjusting anodization temperature.

Porous-ZnO-Nanobelt Film as Recyclable Photocatalysts with Enhanced Photocatalytic Activity

In this article, the porous-ZnO-nanobelt film was synthesized by oxidizing the ZnSe-nanobelt film in air. The experiment results show that the porous-ZnO-nanobelt film possesses enhanced photocatalytic activity compared with the ZnO-nanobelt film, and can be used as recyclable photocatalysts. The enhanced photocatalytic activity of the porous-ZnO-nanobelt film is attributed to the increased surface area. Therefore, turning the 1D-nanostructure film into porous one may be a feasible approach to meet the demand of photocatalyst application.

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.

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.

In situ x-ray diffraction study of the thermal expansion of the ordered arrays of silver nanowires embedded in anodic alumina membranes

Thermal expansion of as-prepared and annealed ordered arrays of silver nanowires embedded in anodic alumina membranes (AAMs) was studied by in situ x-ray diffraction measurement in the temperature range from 25to800°C. The axial thermal expansion coefficient (TEC) for the as-prepared nanowires is 6.35×10−9∕°C and 6.02×10−6∕°C below and above 650°C, respectively. However, the TEC of the annealed sample turns from 2.32×10−6∕°Cto12.06×10−6∕°C when the temperature is above 350°C. The collective effects of the intrinsic expansion, surface pressure, the limit effect of AAM, and the vacancies incorporated into the silver lattice were responsible for the thermal expansion.