Cheng Chun Tang

Defects Induced Room Temperature Ferromagnetism in ZnO Thin Films

Polycrystalline ZnO thin films are prepared by the co-sputtering method under different oxygen partial pressures. Films deposited in pure argon gas exhibit ferromagnetism, whereas other films deposited under different oxygen partial pressures are diamagnetism. XPS results show the presence of Zn interstitial and oxygen vacancy in all of samples. Further analysis indicates that Zn interstitial may play an important role in triggering magnetic order on the undoped ZnO thin films by inducing an alteration of electronic configuration.

The Rietveld Refinement of Thermal Synthesized Rhombohedra Boron Nitride Micro-Rod

We reported on a convenient route to synthesize rhombohedra boron nitride (r-BN) micro-rod using urea (CO(NH2)2) and sodium borohydride (NaBH4) through thermal treatment at 1300 °C. The structure, morphology, and chemical composition of the obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). In order to determine the phase composition and abundance of the as-synthsized simples, Rietveld refinement has been performed to analyze the XRD data using the Rietan-2000 program. The results show that the abundance of r-BN is about 90.6 wt % and h-BN is 9.4 wt % deduced from Reitveld refinement.

Synthesis and Photoluminescence Properties of Two-Bands Excited SrSi2O2N2: Yb2+ Phosphors

The crystal structure and luminescent properties of synthesized SrSi2O2N2: Yb2+ phosphors have been investigated to seek for convention phosphor for white light-emitting diode applications. The Sr1-xYbxSi2O2N2 phosphors have yellow-red luminescence under the exciting of blue light, which is attributed to the 4fn↔4fn-15d transitions of Yb2+. Although the chemical compositions for Sr1-xYbxSi2O2N2 materials are different, no shifts are observed from the excitation and emission spectra.

Enhanced Visible Light Activity of Ag-Loaded TiO2 Nanotube Arrays by AC Electrodeposition

In this work, highly-ordered TiO2 nanotube arrays were prepared by constant-voltage anodization, followed by electrodeposition of Ag to obtain Ag-loaded TiO2 (Ag-TiO2) nanotube arrays via alternating current (AC) process. The results of SEM and XRD show that the morphology and crystal structure of Ag-TiO2 layer depend greatly on the electrodeposition parameters. Ag-TiO2 nanotube arrays prepared in 2.5 mmol/L AgNO3 solution by electrodeposition with applied voltage of 12 V for 1 minute performed the best photoelectrochemical current response and photocatalystic activity. The photocurrent density of Ag-TiO2 is 43.32 μA/cm2 under sunlight irradiation (70 mW/cm2), which is 4.2 times as that of unloaded TiO2 nanotube arrays. Methyl orange (MO) degradation rate with the Ag-TiO2 nanotube arrays achieves 52.13% after 90 min sunlight irradiation which is obvious higher than that of TiO2 nanotube arrays. The mechanism of enhancing photoelectrochemical activity of decorating titania with Ag has also been discussed in the view of energy band theory.

Property of Nanoporous Metal-Organic Frameworks at Different Synthesis Temperature

The nanoporous metal-organic frameworks were synthesized under solvothermal conditions using organic solvent dimethylformamide. The samples were characterized by XRD, SEM, TGA, FT-IR and specific surface area for their properties difference. When the reaction temperature rises, the particle size becomes larger. All TGA curves are the basically same, the framework structure begins to be destroyed from 500°C up to around 600°C. The metal-organic frameworks accepted at reaction temperature 190°C have larger specific surface area and better structure stability.

Property and Research Process of Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are new functional materials, which are developing quickly last years, especially as new hydrogen storage materials. This review introduces concept, characteristics, application, classification, and synthesis and development trend of metal-organic frameworks. Some new problems and difficulties in metal-organic frameworks study and next challenges are also discussed.

The Structure and Photoluminescence Properties of Ca3Si2O7: Eu2+ Phosphor

A series of yellow-emitting phosphors based on a silicate host matrix, Ca3-xSi2O7: xEu2+, were prepared by solid-state reaction method. The structure and photoluminescent properties of the phosphors were investigated. The XRD results show that the Eu2+ substitution of Ca2+ does not change the structure of Ca3Si2O7 host. The SEM images display that phosphors aggregate obviously and the shape of the phosphor particle is irregular. The EDX results reveal that the phosphors consist of Ca, Si, O, and Eu elements. The Ca3-xSi2O7: xEu2+ phosphors can be excited at wavelength of 300-490 nm, which is suitable for the emission band of near ultraviolet or blue light-emitting-diode (LED) chips. The phosphors exhibit a broad emission region from 520 to 650 nm and the emission peak centered at 568 nm. The phosphor for has the strongest excitation and emission intensity, and the energy transfer style between Eu2+ ions is quadrupole-quadrupole interaction for higher concentration Eu2+ doped Ca3Si2O7 phosphor. The Ca3-xSi2O7: xEu2+ phosphors can be used as candidates for white LEDs.

Ab Initio Study on the Structural Stability and Elastic Properties of Tungsten Borides with Hexagonal Structure

In this paper, we have investigated the structural stability and elastic properties of four tungsten borides with the hexagonal structure by the first principle calculations. The results indicated that m-WB2 and c-WB2 were stable in thermodynamics and structure. The stiffness coefficient and modulus of the stable compounds were also calculated and were compared with those of the typical MAX ceramics. The computed ratios of bulk-to-shear-modulus and bulk-modulus-to-c44 showed that m-WB2 and c-WB2 were ductile.

Fabrication and Mechanism of Titania Nanotube Arrays by Anodization in DMSO Electrolyte

Titania nanotube arrays were synthesized via anodic oxidization of titanium foil in dimethyl sulfoxide (DMSO) solution containing 2 wt% HF and 3 wt% H2O at 40 V. The microstructure of the arrays was characterized with scanning electron microscopy (SEM). The results show that morphology of titania nanotube arrays is evidently influenced by the anodization time, and with the extension of oxidation time, the better morphology could be obtained. The possible formation mechanism of titania nanotube arrays has been discussed.