Weixing Yu

Oxygen Vacancy Enhanced Photocatalytic Activity of Pervoskite SrTiO3

A facile and general method has been developed to fabricate oxygen vacancies on perovskite SrTiO3 (STO) nanocrystals through a controllable solid-state reaction of NaBH4 and SrTiO3 nanocrystals. STO samples with tunable color, oxygen vacancy concentration on nanocrystal surface have been synthesized. TEM results reveal that these STO samples have a crystalline core/amorphous shell structure (SrTiO3@SrTiO3-x). XPS and EPR results disclose that the oxygen vacancy concentration increases with the increase of reaction time and temperature. The concentration of oxygen vacancies calculated from TGA data, could reach 5.07% (atom) in this study. UV-vis spectra and photocatalytic results indicate that oxygen vacancies on STO surface play an important role in influencing the light absorption and photocatalytic performance. However, an excess amount of oxygen vacancies leads to a decrease of photocatalytic performance. The optimal photocatalytic activity for H2 production under UV-vis irradiation is up to 2.2 mmol h(-1) g(-1), which is about 2.3 times than the original SrTiO3, corresponding to 3.28% (atom) of oxygen vacancy concentration.

Numerical study of the meta-nanopyramid array as efficient solar energy absorber

Conventional dielectric moth eye structure is well known to be antireflective, but cannot work well in the whole solar spectrum. In addition, it cannot be used as a light absorber. However, in some cases, light absorbing and harvesting are important for energy conversion from light to heat or electricity. Here, we propose a metamaterial-based nanopyramid array which shows near 100% absorbing property in the entire solar spectrum (i.e. 0.2-2.5 m). In addition, the high absorption performance of meta-nanopyramid array retains very well at a wide receiving angle with polarization-independent. Thus, it can dramatically improve the efficiency of the solar light absorbing. The efficient light absorbing property can be explained in terms of the synergetic effects of slow light mode, surface plasmon polariton resonance and magnetic polariton resonance. 2013 Optical Society of America.

High-aspect-ratio metal microchannel plates for microelectronic cooling applications

A new manufacturing process and the characterization of high-aspect-ratio metal microchannel plates for microelectronic cooling applications are reported in this article. A nickel-based microchannel cooling plate, with channels of width 20 µm and aspect ratio up to 3.6:1, has been successfully fabricated using a modified UV-LIGA process. Similar metal microstructures, based on electroplated copper, have also been obtained with a width of 15 µm and an aspect ratio of up to 5:1. In both cases, an over-plate technology was used to electroform the metallic microchannel plates in a single manufacturing step. Hydrodynamic and cooling characteristics of the microchannel plates such as flow rate and heat resistance have been measured. A heat transfer coefficient of 511 W m−2 K−1 for a flow rate of 120 l h−1 has been obtained for the 20 µm wide nickel-based microchannel.

Two-dimensional subwavelength meta-nanopillar array for efficient visible light absorption

We report the extraordinary light harvesting property of a metamaterial-based subwavelength nanopillar array with a periodic arrangement. It is found that the meta-nanopillar array can absorb light efficiently with an average absorptivity of 0.96 over the whole visible waveband with independent of the incoming light polarization state as well as the wide receiving angle of as large as ±60°. We attribute the efficient light harvesting property of meta-nanopillar array to the synergistic effect of the slow light mode and localized surface plasmon resonant effect.

Beam shaping of complex amplitude with separate constraints on the output beam

We present a beam shaping technique in controlling the complex amplitude of an optical beam. The constraint on the amplitude of the output beam in the Gerchberg-Saxton algorithm is replaced with constraints both on the amplitude and phase of the output beam in the proposed method. The total areas of the constrained regions and free regions on the complex amplitude of the output beam in the proposed method are maintained. An output beam with arbitrary complex amplitude can be realized with the proposed method. The computing result from the proposed method is a phase-only distribution, which can be fabricated as diffractive optical element for higher diffraction efficiency. Both simulations and experiments are present and the effectiveness of the proposed method is verified.

Photocatalytic reduction of Cr(VI) by polyoxometalates/TiO2 electrospun nanofiber composites

Polyoxometalates (Ti0.75PW12O40, Ti-PTA)/TiO2 nanofiber composites were fabricated by a simple electrospinning technique and then high temperature calcination. In the structure, Ti-PTA, as an electron relay, can accept the photo-generated electrons from the conduction band of TiO2, which promote the separation of photo-generated charges in TiO2. Then the electrons stored on Ti-PTA further transfer to the Cr(VI) in the solution to realize the removal of Cr(VI). The Ti-PTA/TiO2 nanofiber composites exhibit enhanced photocatalytic performance for photocatalytic reduction of Cr(VI), which might be a potential photocatalyst for Cr(VI) removal in environmental therapy.

Rough gold films as broadband absorbers for plasmonic enhancement of TiO2 photocurrent over 400–800 nm

Recent years have witnessed an increasing interest in highly-efficient absorbers of visible light for the conversion of solar energy into electrochemical energy. This study presents a TiO2-Au bilayer that consists of a rough Au film under a TiO2 film, which aims to enhance the photocurrent of TiO2 over the whole visible region and may be the first attempt to use rough Au films to sensitize TiO2. Experiments show that the bilayer structure gives the optimal optical and photoelectrochemical performance when the TiO2 layer is 30 nm thick and the Au film is 100 nm, measuring the absorption 80–90% over 400–800 nm and the photocurrent intensity of 15 μA·cm−2, much better than those of the TiO2-AuNP hybrid (i.e., Au nanoparticle covered by the TiO2 film) and the bare TiO2 film. The superior properties of the TiO2-Au bilayer can be attributed to the rough Au film as the plasmonic visible-light sensitizer and the photoactive TiO2 film as the electron accepter. As the Au film is fully covered by the TiO2 film, the TiO2-Au bilayer avoids the photocorrosion and leakage of Au materials and is expected to be stable for long-term operation, making it an excellent photoelectrode for the conversion of solar energy into electrochemical energy in the applications of water splitting, photocatalysis and photosynthesis.

Functional nanostructured surfaces in hybrid sol–gel glass in large area for antireflective and super-hydrophobic purposes

We demonstrate the modification of substrate surfaces by the fabrication of thin layer sub-wavelength nanostructures in sol–gel glass in large area on their surfaces. Compared with the traditional methods, the sol–gel method eliminates the etching step and therefore becomes more convenient. It is found that 90% of the height of nanostructures in the master can be transferred into the hybrid SiO2–TiO2 sol–gel glass in our experiment, while the horizontal size of the nanostructures can be replicated precisely. The optical characterization results show that the light reflectivity can be reduced by about 1% over a wide waveband ranging from 400 nm to 800 nm for ARS with a height of 32.4 nm. In addition, it is found that the contact angle of the substrate surface with sol–gel nanostructures has been significantly improved from about 47° to 108°. Therefore, it can be concluded that with a thin layer sol–gel glass sub-wavelength nanostructures, the substrate surface can be effectively modified to have the function of both anti-reflectivity and super hydrophobicity, which can find applications in the area of photovoltaic concentrating lenses for enhancing light transmission, antifogging purposes and others.

A novel thermal reflow method for the fabrication of microlenses with an ultrahigh focal number

In this paper, we demonstrate a novel thermal reflow method with an additional near ultraviolet (UV) flood exposure and upside-down reflow configuration for the fabrication of microlenses with an ultrahigh focal number. By using this method, microlenses with a focal number (F#) as high as 9.7 have been successfully obtained, which is about four fold higher than that can be fabricated with a conventional reflow method. The final profile of the microlenses can be flexibly and accurately tuned by controlling the flood exposure dosage and adopting the appropriate reflow configuration, which enables fabrication not only of spherical microlenses but also of more complex aspheric lenses. The fabricated microlens is characterized by measuring the point spread function (PSF) and the measurement result indicates that the diffraction limited optical performance of the microlens can be achieved. The method developed in this work can be used for the mass and cost-effective fabrication of high performance microlenses with ultrahigh focal numbers, which can find applications such as in accurate optical testing, integration imaging, and laser beam collimating.

TiO2 nanosheet array thin film for self-cleaning coating

A simple hydrothermal method is developed to directly grow TiO2 nanosheets on a bare glass substrate. By tuning the reaction conditions, the thickness of the TiO2 nanosheet layer can be tuned from tens to hundreds of nanometers. This TiO2 nanosheet layer exhibits good transparency due to the air pocket existing inside the thin film layer between nanosheets. On the other hand, the TiO2 layer has a good hydrophilic surface and good wettability, especially under UV light illumination. The degradation of dye (rhodamine B) results indicate that the TiO2 nanosheet coating has excellent photocatalytic activity. All these results demonstrate that the TiO2 nanosheet coating could be a highly transparent self-cleaning coating.