Explanation of Effect of Added Water on Dye-Sensitized Nanocrystalline TiO2 Solar Cell： Correlation between Performance and Carrier Relaxation Kinetics

Time-resolved mid-IR transient absorption spectroscopy is employed to explore the mechanism of improving the performance of dye-sensitized TiO2 solar cell （DSSC） when a certain amount of H2 0 is added into the electrolyte. The relaxation kinetics of dye-sensitized TiO2 nanocrystalline film and the corresponding DSSC performance are investigated under different conditions. It is found that the interracial charge recombination is retarded and electron injection efficiency is increased in the water vapour and in the electrolyte when D20 is added. The values of open-circuit photovoltage Voc and the short-circuit photocarrent Jsc of the cells are linearly correlated to the product of the two decay time constants. We also observed that Voc well correlates with electron injection efficiency. It provides a preliminary microscopic account for the function of the added water in improving the performance of DSSCs.     

NO--CO--O2 Reaction on a Metal Catalytic Surface using Eley--Rideal Mechanism

Interactions among the reacting species NO, CO and O2 on metal catalytic surfaces are studied by means of Monte Carlo simulation using the Eley-Rideal （ER） mechanism. The study of this three-component system is important for understanding of the reaction kinetics by varying the relative ratios of the reactants. It is found that contrary to the conventional Langmuir-Hinshelwood （LFI） thermal mechanism in which two irreversible phase transitions are obtained between active states and poisoned states, a single phase transition is observed when the ER mechanism is combined with the LH mechanism. The phase diagrams of the surface coverage and the steady state production of CO2, N2 and N2O are evaluated as a function of the partial pressures of the reactants in the gas phase. The continuous production of CO2 starts as soon as the CO pressure is switched on and the second order phase transition at the first critical point is eliminated, which is in agreement with the experimental findings.     

Formation Mechanisms of Electrical Conductivity and Optical Properties of ZnO:N Film Produced by Annealing Treatment

The effects of annealing on the chemical states of N dopant, electrical, and optical properties of N-doped ZnO film grown by molecular beam epitaxy (MBE) are investigated. Both the as-grown ZnO:N film and the film annealed in N₂ are of n-type conductivity, whereas the conductivity converts into p-type conductivity for the film annealed in O₂. We suggest that the transformation of conductivity is ascribed to the change in ratio of the N molecular number on O site (N₂)_O to the N atom number on O site (N_O) in ZnO:N films under the various annealed atmosphere. For the ZnO:N film annealed in N₂, the percentage content of (N₂)_O is larger than that of N_O, i.e.the ratio >1, resulting in the n-type conductivity. However, in the case of the ZnO:N film annealed in O₂, the percentage content of (N₂)_O is fewer than that of N_O, i.e., the ratio <1, giving rise to the p-type conductivity. There is an obvious difference between low-temperature (80K) PL spectra of ZnO:N film annealed in N₂ and that of ZnO:N film annealed in O₂. An emission band located at 3.358eV is observed in the spectra of the ZnO:N film after annealed in N₂, this emission band is due to donor-bound exciton (D⁰X). After annealed in O₂, the PL of the donor-bound exciton disappeared, an emission band located at 3.348eV is observed, this emission band is assigned to acceptor-bound exciton (A⁰X).     

Fabrication and Characterization of Si Nanocrystals Synthesized by Electron Beam Evaporation of Si and SiO2 Mixture

Silicon nanocrystals synthesized by electron beam （e-beam） evaporation of Si and SiO2 mixture are studied. Rutherford backscattering spectrometry of the as-deposited Si-rich silicon dioxide or oxide （SRO） thin film shows that after evaporation, the Si and SiO2 concentration is well kept, indicating that the e-beam evaporation is suitable for evaporating mixtures of Si and SiO2. The SRO thin films are annealed at different temperatures for two hours to synthesize silicon nanoerystals. For the sample annealed at 1050℃, silicon nanoerystals with different sizes and the mean diameter of 4.5 nm are evidently observed by high resolution transmission electron microscopy （HRTEM）. Then the Raman scattering and photoluminescence spectra arising from silicon nanocrystals are further confirmed the above results.     

Effects of Helium and Oxygen Common Implantation in Silicon Wafer

Defect engineering for SiO2 precipitation is investigated using He-ion implantation as the first stage of separation by implanted oxygen （SIMOX）. Cavities axe created in Si by implantation with helium ions. After thermal annealing at different temperatures, the sample is implanted with 120 keV 8.0 ×1016 cm 2 0 ions. The Q ion energy is chosen such that the peak of the concentration distribution is centred at the cavity band. For comparison, another sample is implanted with O ions alone. Cross-sectionM transmission electron microscopy （XTEM）, Fourier transform infrared absorbance spectrometry （FTIR） and atomic force microscopy （AFM） measurements are used to investigate the samples. The results show that a narrow nano-cavity layer is found to be excellent nucleation sites that effectively assisted SiO2 formation and released crystal lattice strain associated with silicon oxidation.     

Surface Emitting THz Wave Parametrical Oscillator Using MgO：LiNbO3

Room-temperature operation terahertz （THz） wave source is demonstrated using three MgO：LiNbO3 crystals which have a noncollinear arrangement. The experimental results show that the THz wave can be tunable from 0.8 THz to 3.0 THz, and the peak energy output is 103 pJ/pulse at 1.5 THz. The noncoilinear cavity configuration makes the THz beam have Gaussian-like spatial distribution, small divergence angle, perpendicularly eradiated from the crystal surface. The beam quality factor M2 is measured to be Mx^2 = 1.15, Mx^2 = 1.25 for characterizing the THz wave beam. Experiments also show that the THz beam can be focused by using a polyethylene lens, and the focal spot size is close to the diffraction limit.     

Room-Temperature Ferromagnetism in Zn1-xMnxO Thin Films Deposited by Pulsed Laser Deposition

Zn1-xMnxO （x = O.Olq3.1） thin films with a Curie temperature above 300K are deposited on Al2O3 （0001） substrates by pulsed laser deposition. X-ray diffraction （XRD）, ultraviolet （UV）-visible transmission and Raman spectroscopy are employed to characterize the microstructural properties of these films. Room temperature ferromagnetism is observed by superconducting quantum interference device （SQUID）. The results indicate that Mn doping introduces the incorporation of Mn^2＋ ions into the ZnO host matrix and the insertion of Mn^2＋ ions increases the lattice defects, which is correlated with the ferromagnetism of the obtained films. The doping concentration is also proven to be a crucial factor for obtaining highly ferromagnetic Zn1-xMnxO films.     

定义在分形集上函数的H-导数

 分形的生成含有降维与升维两种形式,采用适当的方式总可以对分形集加以定向化,分形的内禀测度是Hausdorff测度。因此,定义在分形集上的函数可以看作是在Hausdorff测度下定义在区间[0, h]。在函数图像也是分形的前提下,依函数的Hausdorff测度的定义,给出了定义在分形集上的函数f(p)关于Hausdorff测度p的导数以及一些性质。     

Effect of TiO2 Nanotubes on Polymer-Fullerene Bulk Heterojunction Solar Cells

We investigate the photovoltaic properties of hybrid organ/c solar cell based on the blend of poly[2-methoxy-5-（2- ethylhexoxy-l,4-phenylenevinylene） （MEH-PPV）, C60 and titanium dioxide （TiO2） nanotubes. In comparison of the composite devices with different TiO2：[MEH-PPV ＋C60] weight ratios of lw$.% （D1-1）, 2wt.% （D1-2）, 3wt.% （D1-3）, 5wt.% （D1-4）, 10wt.% （D1-5） and 20wt.% （D1-6）, it is found that the device Dl-a exhibits the best performance. The conversion efficiency is improved by a factor of 3 compared with the MEH-PPV：C60 device.     

Realization of Ultraviolet Electroluminescence from ZnO Homojunction Fabricated on Silicon Substrate with p-Type ZnO:N Layer Formed by Radical N2O Doping

ZnO homojunction light-emitting diodes are fabricated on Si（100） substrates by plasma assisted metal organic chemical vapour deposition. A p-type layer of nitrogen-doped ZnO film is formed using radical N2O as the acceptor precursor. The n-type ZnO layer is composed of un-doped ZnO film. The device exhibits desirable rectifying behaviour with a turn-on voltage of 3.3 V and a reverse breakdown voltage higher than 6 V. Distinct electrolumineseence emissions centred at 395nm and 490nm are detected from this device at forward current higher than 20mA at room temperature.     

Band Gap Energies and Refractive Indices of Epitaxial Pb1-xSrxTe Thin Films

Pb1-x Srx Te thin films with different strontium （St） compositions axe grown on BaF2 （111） substrates by molecular beam epitaxy （MBE）. Using high resolution x-ray diffraction （HPLXRD）, we obtain Pb1-xSrxTe lattice constants, which vary in the range 6.462-6.492 A. According to the Vegard law and HRXRD data, Sr compositions in Pb1-xSrxTe thin films range from 0.0-8.0%. The Pb1-xSrxTe refractive index dispersions are attained from infrared transmission spectrum characterized by Fourier transform infrared （FTIR） transmission spectroscopy. It is found that refractive index decreases while Sr content increases in Pb1-xSrx Te. We also simulate the Pb1-xSrxTe transmission spectra theoretically to obtain the optical band gap energies which range between 0.320 e V and 0.449 e V. The simulated results are in good agreement with the FTIR data. Finally, we determine the relation between Pb1-xSrx Te band gap energies and Sr compositions （Eg = 0.320＋0.510x-0.930x^2 ＋184x^3 （eV））.     

Influence of Different Substrates on Laser Induced Damage Thresholds at 1064nm of Ta2O5 Films

Ta2O5 films are prepared on Si, BK7, fused silica, antireflection （AR） and high reflector （HR） substrates by electron beam evaporation method, respectively. Both the optical property and laser induced damage thresholds （LIDTs） at 1064 nm of Ta2O5 films on different substrates are investigated before and after annealing at 673 K for 12 h. It is shown that annealing increases the refractive index and decreases the extinction index, and improves the O/Ta ratio of the Ta2O5 films from 2.42 to 2.50. Moreover, the results show that the LIDTs of the Ta2O5 films are mainly correlated with three parameters： substrate property, substoichiometry defect in the films and impurity defect at the interface between the substrate and the films. Details of the laser induced damage models in different cases are discussed.     

Electrostatic surface guiding for cold polar molecules: experimental demonstration

We demonstrate an electrostatic surface guiding for cold polar molecules over a long distance of 44.5 cm, 0.85 mm above a dielectric substrate, and measure the transverse distribution of the guided supersonic D2O/CH3Br beam and its longitudinal velocity one. Also, we study the dependence of the relative guiding efficiency and the transverse temperature of the guided molecular beam on the guiding voltage, and show that the absolute guiding efficiencies from the Monte Carlo simulation and theoretical calculation multiplied by 3 are about equal to the measured relative one.     

Measurement of isotope shifts,fine and hyperfine structure splittings of the lithium D lines

The lithium D lines were studied using a diode laser that was frequency modulated by an electro-optic modulator, to excite an atomic beam. The transmission of part of the laser beam through an etalon was monitored to correct for the nonlinearity of the laser scan. The results for the ^6,7Li 2 S _1/2 and 2 P _1/2 hyperfine splittings agree very well with the best existing data while those for the D1 isotope shift and ^6,7Li fine structure splittings disagree significantly from data obtained by a previous laser atomic beam experiment. Our result for the D1 isotope shift is very close to the latest value computed using Hylleraas variational theory. Received 8 April 2002 / Received in final form 26 June 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: wvw@yorku.ca     

Reversible Resistance Switching Effect in Amorphous Ge1Sb4Te7 Thin Films without Phase Transformation

We demonstrate a reversible resistance switching effect that does not rely on amorphous-crystalline phase transformation in a nanoscale capacitor-like cell using Ge1Sb4Te7 films as the working material. The polarity and amplitude of the applied electric voltage switches the cell resistance between low- and high-resistance states, as revealed in the current-voltage characteristics of the film by conductive atomic force microscopy （CAFM）. This reversible SET/RESET switching effect is induced by voltage pulses and their polarity. The change of electrical resistance due to the switching effect is approximately two orders of magnitude.     

Spectral Study of Effects of Aluminium Nanoparticles on Fast Reaction of Nitromethane

Fast reactions between nitromethane and aluminium nanoparticles are studied using transient spectral methods. In comparison with species produced by pure nitromethane, the emergence time for species produced by nitromethane after addition of 1 g of aluminium nanoparticles decreases by 46-58% and the emission intensity increases by 13-100%. The results demonstrate that aluminium nanoparticles have positive effect on accelerating the decomposition rate of nitromethane and that the explosion efficiency of nitromethane is greatly improved. Fast reactions carried out between nitromethane and aluminium nanoparticles in different environments （CO2, H2O and O2） reveal that O2 and an appropriate amount of H2O improve the explosion efficieney of nitrornethane, whereas CO2 has the weakest effect on improving this parameter. The investigations provide insights into the process occurring in actual systems involving propellants and fuel-air explosives.     

Numerical Simulations on the Formation of Speckles in Nanofluids Illuminated by a TEM00 Laser Beam

On the basis of a Rayleigh scattering model for a single nanoparticle illuminated by a TEMoo laser beam, we theoretically and numerically study the speckle formation when nanofluids are illuminated by a TEMoo laser beam. The results show that the laser speckles possess a Gaussian distribution, which are in agreement with the experimental results. The results may be useful for using a laser speckle velocimetry to determine the velocitiies of nanoparticles in nanofluids.     

Laser Molecular Beam Epitaxy of Multilayer Heterostructure SrNb0.05Ti0.95O3/La0.9Sr0.1MnO3 in 10000 Unit-Cell Layers

Ten thousands of unit-cell multilayer heterosturctures, [SrNb0.05 Ti0.95O3/La0.9 Sr0.1MnO3]3 （SNTO/LSMO）, have been epitaxial grown on SrTiO3 （001） substrates by laser molecular beam epitaxy. The monitor of insitu. reflection high-energy electron diffraction demonstrates that the heterosturctures are layer-by-layer epitaxial growth. Atomic force microscope observation indicates that the surface of the heterosturcture is atomically smooth. The measurements of cross-sectional low magnification and high-resolution transmission electron microscopy as well as the corresponding selected area electron diffraction reveal that the interfaces are of perfect orientation, and the epitaxial crystalline structure shows the orientation relation of SNTO（001）//LSMO（001）, and SNTO[100]//LSMO[100].     

Microstructure and Optical Properties of AgxO Prepared by Direct-Current Magnetron-Sputtering Method

Two series of AgxO films are prepared on glass substrates by dc magnetron-sputtering method at room temperature and 90℃ under different oxygen to argon gas ratio （OAR） conditions. The mierostrueture is investigated by XRD and SEM in order to obtain the information on the component evolution of AgO＋Ag2O to Ag2O. Its optical properties are investigated by reflectance and absorption spectroscopy to extract the information on metallic and dielectric behaviour evolution of Ag2O, AgO and silver particles and the interband transition. The results indicate that the AgxO film prepared at room temperature is mainly made up of AgO and Ag2 O clusters while Ag2O is the primary component of AgxO prepared at 90℃. The AgxO film mainly consisting of the primary component shows indirect interband transition structure occurring at 2.89eV. Combination of increasing OAR and substrate temperature is an effective method to lower the threshold of thermal decomposition temperature of AgxO and to deal with the bottleneck of short-wavelength optical and magneto-optieM storage.     

温度对PSⅡCP4 7/D1/D2/Cytb559复合物荧光光谱特性的影响

采用激励光源为514.5 nm的分幅扫描单光子计数荧光光谱装置对经20℃、42℃和48℃不同温度处理后的反应中心复合物CP47/D₁/D₂/Cyt b559的荧光光谱特性进行了研究.经解析,获得不同温度处理后,CP47/D₁/D₂/Cyt b559复合物最大峰值未发生变化,均在682 nm,说明Chla670的能量都由Chla682接收,但损耗愈来愈小,在48℃时,损耗程度最小,而其荧光百分比未发生多大变化.振动副带～700 nm和～740 nm的中心波长都发生蓝移,在不同温度下分别为:20℃ 703 nm,749 nm;42℃ 697 nm,744 nm;48℃ 694 nm,740 nm.因此可以推测温度的升高,影响了CP47/D₁/D₂/Cyt b559色素蛋白的二级结构以及色素分子的空间位置,使最大峰值处的荧光强度逐渐降低,振动副带逐渐蓝移.42℃的温度已造成影响,48℃影响较大.