Weihua Tang

The structural and biological properties of hydroxyapatite-modified titanate nanowire scaffolds.

Hydroxyapatite-modified titanate nanowire scaffolds as alternative materials for tissue engineering have been developed via a titanate nanowire matrix assisted electrochemical deposition method. The macroporous titanate nanowire matrix on Ti metal was fabricated by a hydrothermal method, and then followed by an electrochemical synthesis of hydroxyapatite nanoparticles on titanate nanowire. The incorporation of titanate nanowire matrix with high oriented hydroxyapatite nanoparticles generates hierarchical scaffolds with highly osteogenic, structural integrity and excellent mechanical performance. As-prepared porous three dimensional interconnected hydroxyapatite-modified titanate nanowire scaffolds, mimicking the natures extracellular matrix, could provide a suitable microenvironment for tissue cell ingrowth and differentiation. The ceramic titanate nanowire core with HA nanoparticle sheath structure displays superhydrophilicity, which facilitates the cell attachment and proliferation, and induces the in vitro tissue-engineered bone. Human osteoblast-like MG63 cells were cultured on the hydroxyapatite-modified titanate nanowire scaffolds, and the results showed that the scaffolds highly promote the bioactivity, osteoconductivity and osteoblast differentiation.

Silver nanoparticles modified reduced graphene oxide wrapped Ag3PO4/TiO2 visible-light-active photocatalysts with superior performance

Silver nanoparticles (Ag NPs) modified reduced graphene oxide wrapped Ag3PO4/TiO2 (Ag3PO4/TiO2/Ag-rGO, Ag-ATG) photocatalysts have been developed through a rational design that combines the optimization of charge generation, separation and transfer in the composites, which helps to increase the photocatalytic performance. The Ag-ATG composites possess novel microstructure, in which TiO2 mesoporous spheres of hundreds of nanometers in size are decorated with dense nano-sized Ag3PO4 to form pinecone-liked Ag3PO4/TiO2 particles, which were further wrapped by rGO sheets that are selectively decorated with Ag NPs. The Ag-ATG composites exhibit improved photocatalytic performance toward degradation of methylene blue (MB) and methyl orange (MO) under visible light compared to bare Ag3PO4 and Ag3PO4/TiO2/rGO (ATG). The underlying mechanism has been studied based on the results of reactive oxygen species capture experiment, photoluminescence (PL) spectra, and photocurrent measurements under visible light and monochromatic lights. The improved photocatalytic performance is mainly ascribed to the efficient spatial separation of photo-induced electrons and holes in Ag-ATG, i.e., the electrons in Ag3PO4 transfer to Ag-rGO, meanwhile the holes in Ag3PO4 transfer to TiO2. Ag NPs play an important role in the hybrid structure owing to the synergistic effect of Ag NPs and rGO, which not only enhance the light harvest but also increase the capacity of electron accepting from Ag3PO4. Meanwhile, active photo-induced electrons at the plasmonic Ag NPs can facilitate the formation of O2˙− radicals for photocatalysis. As a result, both the stability and photocatalytic active of Ag-ATG are significantly improved.

(AlGa)_2O_3 solar-blind photodetectors on sapphire with wider bandgap and improved responsivity

Single crystallinity (AlGa)2O3 solar-blind photodetectors are epitaxially grown on sapphire. Oxygen pressure during the growth has a great impact on the Al composition in (AlGa)2O3, which is investigated utilizing X-ray photoelectron spectroscopy and X-ray diffraction measurements. Measured transmittance spectra and responsivity demonstrate that (AlGa)2O3 photodetectors achieve a wider bandgap compared to a Ga2O3 device. An (Al0.12Ga0.88)2O3 device obtains 10 times higher photocurrent Iphoto than a Ga2O3 photodetector. However, as Al composition increases, significant Iphoto degradation is observed in an (Al0.35Ga0.65)2O3 photodetector. Meanwhile, an (Al0.35Ga0.65)2O3 device exhibits the stronger persistent photoconductivity compared to the Ga2O3 control device. Analysis shows that defect states in a bandgap of (AlGa)2O3 might be associated with the performance change in (AlGa)2O3 photodetectors.

Construction of GaN/Ga2O3 p–n junction for an extremely high responsivity self-powered UV photodetector

A self-powered ultraviolet photodetector was constructed with GaN/Ga2O3 p–n junction by depositing n-type Ga2O3 thin film on Al2O3 single crystals substrate covered by p-type GaN thin film. The fabricated device exhibits a typical rectification behavior in dark and excellent photovoltaic characteristics under 365 nm and 254 nm light illumination. The device shows an extremely high responsivity of 54.43 mA W−1, a fast decay time of 0.08 s, a high Ilight/Idark ratio of 152 and a high detectivity of 1.23 × 1011 cm Hz1/2 W−1 under 365 nm light with a light intensity of 1.7 mW cm−2 under zero bias. Such excellent performances under zero bias are attributed to the rapid separation of photogenerated electron–hole pairs driven by built-in electric field in the interface depletion region of GaN/Ga2O3 p–n junction. The results strongly suggest that the GaN/Ga2O3 p–n junction based photodetectors are suitable for applications in secure ultraviolet communication and space detection which require high responsivity and self-sufficient functionality.

A self-powered deep-ultraviolet photodetector based on an epitaxial Ga2O3/Ga:ZnO heterojunction

A deep-ultraviolet photodetector (DUV PD) which can function independently of an external power supply is urgently desired for the next-generation photodetection applications from the viewpoint of being diminutive, convenient, and power saving. In this work, by introducing a lattice compatible semiconductor Ga:ZnO, a high quality β-Ga2O3/Ga:ZnO heterojunction based DUV PD is achieved using laser molecular beam epitaxy. The obtained device could operate in a self-powered mode with an excellent wavelength selectivity, a high ON/OFF ratio, a high DUV/visible rejection ratio, and a high stability under 254 nm light illumination. The physical mechanism responsible for the observation is discussed based on the photogenerated electron–hole pairs separated in the depletion region under the built-in electric field. Our work may provide a new insight into further high performance self-sufficient DUV PD applications.

Growth and characterization of α-phase Ga2−x Sn x O3 thin films for solar-blind ultraviolet applications

Ga2−x Sn x O3 thin films on m-plane (300) sapphire substrates were deposited by laser molecular beam epitaxy technology. Corundum-structured α-phase Ga2−x Sn x O3 thin films with different Sn content were obtained at 850 °C in vacuum pressure of 5 × 10−5 Pa. The band-gap energy of the α-phase Ga2−x Sn x O3 thin films, determined from the absorption spectrum, decreases linearly with increasing Sn content. A metal–semiconductor–metal structured solar-blind photodetector based α-phase Ga2−x Sn x O3 thin films was fabricated, and excellent solar-blind ultraviolet characteristics were demonstrated. The ratio of I 254/I dark was up to 1.40 × 102 and the responsivity increased to 9.55 × 10−2 A W−1. The results suggest that α-phase Ga2−x Sn x O3 thin films are promising candidates for use in solar-blind photodetectors.

Propeller-shaped ZnO nanostructures obtained by chemical vapor deposition: photoluminescence and photocatalytic properties

Propeller-shaped and flower-shaped ZnO nanostructures on Si substrates were prepared by a one-step chemical vapor deposition technique. The propeller-shaped ZnO nanostructure consists of a set of axial nanorod (50 nm in tip, 80 nm in root and 1 µm in length), surrounded by radial-oriented nanoribbons (20-30nm in thickness and 1.5 µm in length). The morphology of flower-shaped ZnO nanostructure is similar to that of propeller-shaped ZnO, except the shape of leaves. These nanorods leaves (30nm in diameter and 1-1.5 µm in length) are aligned in a radial way and pointed toward a common center. The flower-shaped ZnO nanostructures show sharper and stronger UV emission at 378nm than the propeller-shaped ZnO, indicating a better crystal quality and fewer structural defects in flower-shaped ZnO. In comparison with flower-shaped ZnO nanostructures, the propeller-shaped ZnO nanostructures exhibited a higher photocatalytic property for the photocatalytic degradation of Rhodamine B under UV-light illumination.

Growth and Characterization of Sn Doped β-Ga2O3 Thin Films and Enhanced Performance in a Solar-Blind Photodetector

Ga2−xSnxO3xa0thin films were deposited on c-plane Al2O3 (0001) substrates with different Sn content by laser molecular beam epitaxy technology (L-MBE). The Sn content x was varied from 0 to 1.0. (

Decrease of oxygen vacancy by Zn-doped for improving solar-blind photoelectric performance in β-Ga2O3 thin films

bar{2}01