Fluorescence Hydrogen Peroxide Probe Based on a Microstructured Polymer Optical Fiber Modified with a Titanium Dioxide Film

A highly sensitive microstructured polymer optical fiber (MPOF) probe for hydrogen peroxide was made by forming a rhodamine 6G-doped titanium dioxide film on the side walls of array holes in an MPOF. It was found that hydrogen peroxide only has a response to the MPOF probe in a certain concentration of potassium iodide in sulfuric acid solution. The calibration graph of fluorescence intensity versus hydrogen peroxide concentration is linear in the range of 1.6 x 10(-7) mol/L to 9.6 x 10(-5) mol/L. The method, with high sensitivity and a wide linear range, has been applied to the determination of trace amounts of hydrogen peroxide in a few real samples, such as rain water and contact lens disinfectant, with satisfactory results.

Development of durable carbon black/titanium dioxide supported macrocycle catalysts for oxygen reduction reaction

Carbon black and titanium dioxide supported iron tetraphenylporphyrin (FeTPP/TiO2/C) catalysts for oxygen reduction reaction (ORR) were prepared by sol-gel and precipitation methods followed by a heat-treatment at temperatures of 400-1000 degrees C. The FeTPP/C and TiO2/C were also studied for comparison. The FeTPP/TiO2/C pyrolyzed at 700 degrees C exhibits significantly improved stability while maintaining high activity towards ORR in comparison with the FeTPP/C counterpart. The electrochemical study combined with XRD, XPS, and SEM/EDX analyses revealed that the appropriate dispersion of TiO2 on the surface of FeTPP/TiO2/C catalysts, which depending on heat-treatment temperature, plays a crucial role in determining the activity and stability of catalysts.

Investigation on microstructure and optical properties of titanium dioxide coatings annealed at various temperature

TiO2 coatings were prepared on fused silica with conventional electron beam evaporation deposition. After TiO2 thin films were annealed at different temperatures for 4 h, several properties were investigated by X-ray diffraction (XRD), spectrometer.. photoelectron spectroscopy (XPS) and AFM. It was found that with the annealing temperature increasing, the transmittance of TiO2 coatings decreased, and the cutoff wavelength shifted to long wavelength in near ultraviolet band. Especially, when coatings were annealed at high temperature, the optical loss is very serious, which can be attributed to the scattering and the absorption of TiO2 coatings. XRD patterns revealed that only anatase phase was observed in TiO2 coatings regardless of the different annealing temperatures. XPS results indicated that the fine chemical shift of TiO2 2p(1/2) should be attributed to existence of oxygen vacancies around Ti+4 ion. The investigation on surface morphology by AFM showed that the RMS of titania thin films gradually increases from less than 0.40 nm to 5.03 nm and it should be ascribed to the growth of titanium dioxide grain size with the increase of annealing temperature. (C) 2005 Elsevier B.V. All rights reserved.

Photoluminescence properties of nitrogen-doped ZnSe epilayers

The photoluminescence (PL) properties of nitrogen-doped ZnSe epilayers grown on semi-insulating GaAs(100) substrates by MBE using a rf-plasma source for N doping were investigated. The PL peak which can be related to N acceptor was observed in the PL spectra of ZnSe:N smaples. At 10K, as the excitation power density increases, the energy of donor-acceptor pair(DAP) emission shows a blue-shift and its intensity tends to saturate. As the temperature increases over a range from 10K to 300K, the relative PL intensity of donor bound exciton to that of the acceptor bound exciton increases due to the transfer between two bound excitons.

Quantitative analysis of excitonic photoluminescence in nitrogen-doped ZnSe epilayers

We have investigated the photoluminescence (PL) properties of nitrogen-doped ZnSe epilayers grown by molecular beam epitaxy using a nitrogen radio frequency-plasma source. The PL data shows that the relative intensity of the donor-bound exciton (I-2) emission to the acceptor-bound exciton (I-1) emission strongly depends on both the excitation power and the temperature. This result is explained by a thermalization model of the bound exciton which involved in the capture and emission between the neutral donor bound exciton, the neutral acceptor bound exciton and the free exciton. Quantitative analysis with the proposed mechanism is in good agreement with the experimental data. (C) 1999 American Institute of Physics. [S0021-8979(99)09102-1].

Dislocation movement in nitrogen-doped Czochralski silicon

Dislocation movement in N-doped Czochralski silicon (Cz-Si) was surveyed by four point bend method. Dislocation movement velocities in Cz-Si doped with nitrogen, with both nitrogen and antimony, and with only antimony were investigated. The order of measured dislocation movement velocities, at 700 degrees C less than or equal to T less than or equal to 800 degrees C and under resolved stress sigma=4.1 kg/mm(2), was V-Sb.O > V-n.Sb.O>V-N.O. The experiments showed that nigtrogen doping could retard the movement of dislocations.

A mechanism for enhanced photocatalytic activity of silver-loaded titanium dioxide

In this paper, silver-loaded TiO2 photocatalyst was prepared by photochemical impregnation method and characterized by transmission electron microscopy (TEM), diffuse reflectance spectra (DRS), photooxidation of phenol and photoreduction of Cr(VI). Electron paramagnetic resonance (EPR) was used to detect photoproduced paramagnetic radicals. The correlation of photocatalytic activity and photogenerated reactive species was discussed, and the mechanism of silver-loaded TiO2 for enhancement of photocatalytic activity was elucidated. The results show that deposited silver on TiO2 Surface acts as a site where electrons accumulate. The better separation between electrons and holes on the modified TiO2 surface allowed more efficiency for the oxidation and reduction reactions. The enhanced photocatalytic activity was mainly attributed to the increased amounts of O-2(.-) reactive species and surface Ti3+ reactive center on silver-loaded TiO2 photocatalyst. (C) 2004 Published by Elsevier B.V.

Photocatalytic degradation of CI Acid Blue 80 in aqueous suspensions of titanium dioxide under sunlight

The dye C.I. Acid Blue 80 (AB80) was easily degraded by TiO2-P25 assisted photocatalysis in aqueous dispersion under irradiation of sunlight. The optimal reaction conditions were [TiO2] = 2.0 g/L, pH = 10, [H2O2] = 5 mmol/L. The photocatalytic reaction followed pseudo-first order kinetics. The adsorption of AB80 onto TiO2 was in accord with Langmuir equation.

射频磁控溅射法制备TiO2-xNX薄膜的结构性能研究

利用射频磁控溅射法室温下在Si（100）衬底上制备了N掺杂的TiO2薄膜，并且采用x射线衍射（XRD）、X射线光电子能谱（XPS）和透射光谱对薄膜进行了表征。XRD结果表明在纯Ar和N2（33．3％）／Ar气氛下制备的TiO2-xNx薄膜均为单一的金红石相，薄膜结晶性良好，呈高度（211）择优取向，而在N2（50．0％）／Ar下制备的薄膜结晶性明显变差；对于N掺杂的TiO2薄膜，XPS表明部分N原子进入TiO2晶格，并且以N—Ti—O、N—O键以及间隙式N原子形式存在；透射光谱表明掺N后的TiO2薄膜吸收边发生了红移。

First-principles study of the electronic structures and magnetic properties of 3d transition metal-doped anatase TiO2

We study the electronic structures and magnetic properties of the anatase TiO2 doped with 3d transition metals (V, Cr, Mn, Fe, Co, Ni), using first-principles total energy calculations based on density functional theory (DFT). Using a molecular-orbital bonding model, the electronic structures of the doped anatase TiO2 are well understood. A band coupling model based on d-d level repulsions between the dopant ions is proposed to understand the chemical trend of the magnetic ordering. Ferromagnetism is found to be stabilized in the V-, Cr-, and Co-doped samples if there are no other carrier native defects or dopants. The ferromagnetism in the Cr- and Co-doped samples may be weakened by the donor defects. In the Mn-, and Fe-doped samples, the ferromagnetism can be enhanced by the acceptor and donor defects, respectively.

Heavily doped polycrystalline 3C-SiC growth on SiO2/Si(100) substrates for resonator applications

3C-SiC is a promising material for the development of microelectromechanical systems (MEMS) applications in harsh environments. This paper presents the LPCVD growth of heavily nitrogen doped polycrystalline 3C-SiC films on Si wafers with 2.0 mu m-thick silicon dioxide (SiO2) films for resonator applications. The growth has been performed via chemical vapor deposition using SiH4 and C2H4 precursor gases with carrier gas of H-2 in a newly developed vertical CVD chamber. NH3 was used as n-type dopant. 3C-SiC films were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and room temperature Hall Effect measurements. It was shown that there is no voids at the interface between 3C-SiC and SiO2. Undoped 3C-SiC films show n-type conduction with resisitivity, Hall mobility, and carrier concentration at room temperature of about 0.56 Omega center dot cm, 54 cm(2)/Vs, and 2.0x 10(17) cm(-3), respectively. The heavily nitrogen doped polycrystalline 3C-SiC with the resisitivity of less than 10(-3) Omega center dot cm was obtained by in-situ doping. Polycrystalline SiC resonators have been fabricated preliminarily on these heavily doped SiC films with thickness of about 2 mu m. Resonant frequency of 49.1 KHz was obtained under atmospheric pressure.

Effect of dopant concentration on photocatalytic activity of TiO2 film doped by Mn non-uniformly

The thin films of TiO2 doped by Mn non-uniformly were prepared by sol-gel method under process control. In our preceding study, we investigated in detail, the effect of doping mode on the photocatalytic activity of TiO2 films showing that Mn non-uniform doping can greatly enhance the activity. In this study we looked at the effect of doping concentration on the photocatalytic activity of the TiO2 films. In this paper, the thin films were characterized by UV-vis spectrophotometer and electrochemical workstation. The activity of the photocatalyst was also evaluated by photocatalytic degradation rate of aqueous methyl orange under UV radiation. The results illustrate that the TiO2 thin film doped by Mn non-uniformly at the optimal dopant concentration (0.7 at %) is of the highest activity, and on the contrary, the activity of those doped uniformly is decreased. As a comparison, in 80 min, the degradation rate of methyl orange is 62 %, 12 % and 34 % for Mn non-uniform doping film (0.7 at %), the uniform doping film (0.7 at %) and pure titanium dioxide film, respectively. We have seen that, for the doping and the pure TiO2 films, the stronger signals of open circuit potential and transient photocurrent, the better photocatalytic activity. We also discusse the effect of dopant concentration on the photocatalytic activity of the TiO2 films in terms of effective separation of the photon-generated carriers in the semiconductor. (C) Versita Warsaw and Springer-Verlag Berlin Heidelberg. All rights reserved.