Electroluminescence from Multilayered Diamond/CeF3/SiO2 Films

We report a thin film electroluminescent device with a three-layer structure （diamond/CeF3/SiO2 films）, which has a luminance of 1.5 cd/m^2 at dc voltage 215 V. The electroluminescence spectrum at room temperature shows that the main peaks locate at 527 and 593nm, which are attributed to isolated emission centers of Ce^3＋ ions.     

Effects of Interfacial Polarization on Voltage Tunability of Pb(Fe1/2Nb1/2)1-xTixO3 Single Crystals

The voltage tunability of Pb(Fe_1/2Nb_1/2)_1-xTi_xO₃ single crystals is investigated at a low electric field (<130 V/cm) in a low frequency range (<1 MHz). The results show that the capacitance is strongly suppressed by the applied dc biases for both the rhombohedral sample and the tetragonal sample. A negative voltage tunability is only detected in the tetragonal sample. The origin of the giant tunability and the negative tunability is discussed based on the multipolarization-mechanism model and the equivalent circuit model, respectively. It is ascribed to the interfacial polarization at the interface of electrode/sample.     

Vector Coherent State Representations of SO5 SU2 SU2 U1 U1 and SO5 U1 U1

VCS representantions of SO₅ SU₂ SU₂ U₁ U₁ and SO₅ U₁ U₁ are discussed.Reduced matrix elements for SO₅ SU₂ SU₂ are derived.The multiplicity of a weight for SO₅ is determined by using the K-matrix technique.     

高压下SiO_2的第一性原理计算

基于密度泛函理论(DFT)的第一性原理,采用Hartree-Fork(HF)方法,分别计算了Si O2的α-石英结构、金红石结构以及氯化钙结构的总能量随体积的变化关系。利用Murnaghan状态方程,通过能量和体积拟合,得到了3种结构的体变模量及其对压强的一阶导数。计算结果表明,随着压强的增加,Si O2会从α-石英结构转变为金红石结构,与实验结果和其它理论结果一致;金红石结构与氯化钙结构之间不存在相变,可以共存。此外,对具有α-石英结构的Si O2的晶格常数、电子态密度和带隙随压强的变化关系进行了计算和分析,结果表明:加压作用下,能带向高能方向移动,Si─O键缩短,电子数转移增加,带隙展宽,电荷发生重新分布。     

First-Principles Study of Defects in CuGaO2

Using the first-principles methods, we study the electronic structure, intrinsic and extrinsic defects doping in transparent conducting oxides CuGaO₂. Intrinsic defects, acceptor-type and donor-type extrinsic defects in their relevant charge state are considered. The calculation result show that copper vacancy and oxygen interstitial are the relevant defects in CuGaO₂. In addition, copper vacancy is the most efficient acceptor. Substituting Be for Ga is the prominent acceptor, and substituting Ca for Cu is the prominent donors in CuGaO₂. Our calculation results are expected to be a guide for preparing n-type and p-type materials in CuGaO₂.     

500 MHz LiNbO3 2×2光开关/调制器

本文描述一种采用铬-金电极的Ti:LiN_bO₃型2×2光开关/调制器。给出了该器件的设计参数,工艺条件,带单模尾纤的器件性能为:总插入损耗<8dB,开关电压<10V,串音<-15dB(λ=1.3μm)。本文讨论了器件的高频特性,测得器件的调制频率>500MHz。     

Photovoltaic Cells with TiO2 Nanocrystals and Conjugated Polymer Composites

Various compositional photovoltaic cells based on the blend of poly(3-hexylthiophene) (P3HT) as donors and TiO₂ nanocrystals as acceptors are fabricated and investigated. It is demonstrated that the blend ratio of P3HT and TiO₂ nanocrystals could greatly influence the performance of the photovoltaic cells. The maximum of 0.411% in power conversion efficiency under AM 1.5, 100mW/cm², and 44.4% of fill factor are obtained in the solar cell with the blend weight ratio 1:1 of P3HT and TiO₂ nanocrystals. The function of nanocrystal composition is discussed in terms of the results of photoluminescence spectroscopy, atomic force microscopy, transmission electron microscopy, and charge transport I-V curve.     

Electrical and material characterization of tantalum pentoxide (Ta2O5) charge trapping layer memory

In this experiment, tantalum pentoxide (Ta₂O₅) was used in a metal/oxide/high-k Ta₂O₅/oxide/silicon (MOHOS) novel nanocrystal memory as a trapping layer. Post-annealing treatment, which can passivate defects and improve the material quality of the high-k dielectric, was applied to optimize device performance for a better memory window and faster P/E (program/erase) cycle. Material and electrical characterization techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and electrical measurements were performed to analyze the device under different annealing conditions. The Ta₂O₅ charge trapping layer memory annealed at 900 °C had a higher window of 3.3 V in the current-voltage (C-V) hysteresis loop, and a higher charge retention capability than the samples prepared under various annealing conditions. These higher levels were due to the higher probability of deep-level charge trapping and lower leakage current.     

Pulsed-laser deposition of Ta-doped PZT ferroelectric films for memory applications using conductive oxide La0.25Sr0.75CoO3 and SrRuO3 electrodes

New methods for fabricating highly 𘚡¢-oriented and complete 𘜏¢-textured Pb(Ta_0.05Zr_0.48Ti_0.47)O₃ (PTZT) films on Pt/TiO₂/SiO₂/Si(001) substrates by pulsed-laser deposition have been developed using conductive oxide La_0.25Sr_0.75CoO₃ and SrRuO₃ electrodes. The 𘚡¢-preferred orientated PTZT ferroelectric capacitor was not subjected to loss of its polarization after 1᎒¹⁰ switching cycles at an applied voltage of 5 V and a frequency of 1 MHz, and the 𘜏¢-textured PTZT film capacitor retains 94.7% of its polarization after 1.5᎒¹⁰ switching cycles at 5 V and 50 kHz. The PTZT capacitors using these conductive oxide electrodes have low leakage current dominated by Schottky field emission mechanism.     

Role of TiO2 Nanotube on Improvement of Performance of Hybrid Photovoltaic Devices

The performance of TiO₂ nanotubes in bulk heterojunction of poly (2-methoxy-5-(2'-ethylhexyloxy)-1, 4-phenylenevinylene) (MEH-PPV)/TiO₂ nanotubes is investigated. The transport properties are studied by using the time-of-flight technique (TOF). The carrier mobilities of both holes and electrons are not improved for the MEH-PPV:TiO₂ composites compared with the pristine MEH-PPV. However, photoluminescence under the influence of the electric field indicates that the dissociation of excitons in the MEH-PPV:TiO₂ composites, which is facilitated by photoinduced charge transfer, only requires a smaller electric field.     

Ferroelectric Properties of Bi3.25La0.75Ti3O12 Thin Films Crystallized inDifferent N2/O2 Ambients

Bi3.25La0.75 Ti3O12 （BLT） ferroelectric thin films are deposited by sol-gel method and annealed for crystallizaion in total l eccm N2/02 mixed gas with various ratio at 750℃ for 30rain. The effect of crystallization ambient on the structural and ferroelectric properties of the BLT films is studied. The growth direction and grain size of BLT film are revealed to affect ferroeleetric properties. Alter the BLT film is annealed in 20%O2, the largest P~ value is obtained, which is ascribed to an increase of random orientation and large grain size. The fatigue property is improved with the concentration of oxygen in the ambient increasing, which is ascribed to annealing in the ambient with high concentrated oxygen adequately decreasing the defects related to lack of oxygen.     

Viscous flow and MOS properties of CaF2-B2O3-GeO2-SiO2 glasses with ionic bonds

The capacitance and voltage (C-V) characteristics of Metal-Oxide-silicon (MOS) capacitors passivated by CaF₂-B₂O₃-GeO₂-SiO₂ glasses with OH^m ions, water and fluoride contents were investigated. As the OH^m absorption coefficients of the glass increased, adverse effects on the recovery of hysteresis C-V curve shifts was observed. The content of OH^m ions is closely related to the fluoride content in the CaF₂-B₂O₃-GeO₂-SiO₂ glass. The viscous-flow point of the glass was lowered with increasing degree of ionic character obtained from Hannay's equation.     

Preparation and Luminescence Characteristics of Ca3Y2（BO3）4：Eu^3＋ Phosphor

Ca3Y2 （BO3）4：Eu^3＋ phosphor is synthesized by high temperature solid-state reaction method, and the Iuminescence characteristics are investigated. The emission spectrum exhibits two strong red emissions at 613 and 621 nm corresponding to the electric dipole ^5 Do- ^7F2 transition of Eu^3＋ under 365 nm excitation, the reason is that Eu^3＋ substituting for Y^3＋ occupies the non-centrosymmetric position in the crystal structure of Ca3 Y2 （BO3）4. The excitation spectrum for 613 nm indicates that the phosphor can be effectively excited by ultraviolet （UV） （254 nm, 365nm and 400nm） and blue （470nm） light. The effect of Eu^3＋ concentration on the emission intensity of Ca3 Y2 （BO3）4 ：Eu^3＋ phosphor is measured, the result shows that the emission intensities increase with increasing Eu^3＋ concentration, then decrease. The CIE colour coordinates of Ca3Y2 （BO3）4：Eu^3＋ phosphor is （0.639, 0.357） at 15mol% Eu^3＋.     

Superconductivity in Hole-Doped （S1-xKx）Fe2As2

A series of layered （Sr1-xKx）Fe2As2 compounds with nominal x = 0-0.40 are synthesized by solid state reaction method. Similar to other parent compounds of iron-based pnictide superconductors, pure SrFe2As2 shows a strong resistivity anomaly near 210 K, which was ascribed to the spin-density-wave instability. The anomaly temperature is much higher than those observed in LaOFeAs and BaFe2As2, the two prototype parent compounds with ZrCuSiAs- and ThCr2Si2-type structures. K-doping strongly suppresses this anomaly and induces superconductivity. Like in the case of K-doped BaFe2As2, sharp superconducting transitions at Tc ～ 38 K is observed. We perform the Hall coefficient measurement, and confirm that the dominant carriers are hole-type. The carrier density is enhanced by a factor of 3 in comparison to F-doped LaOFeAs superconductor.     

Giant Static Dielectric Constant of Strained PbTiO3

First-principles density functional perturbation calculations are employed to study the dielectric and piezoelectric properties of strained tetragonal PbTiO3. Lattice distortion, static dielectric constant, Born effective charge, zone-centre phonons, and piezoelectric constant are obtained. For the strained tetragonal PbTiO3, we obtain a giant static dielectric constant （3600） under a strain 0. 77%. Moreover, the calculated piezoelectric constant e15 of strained PbTiO3 reaches about 203 C/m^2 which is about 20 times of that of unstrained system. The giant static dielectric constant is mainly due to the softening of the lowest-frequency phonon mode and the reduce of Ti-O bond length. This work demonstrates a route to a giant static dielectrics for electrically microwave and other devices.     

Strongly Correlated Effect in TiS2

The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-site Coulomb interaction correction （＋U）. The Seebeck coefficient of TiS2 is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300K shows that Coulomb interaction U in the range of 4.97-5.42eV is important to reproduce the experimental data. The obtained energy gap Eg around 0.05 eV indicates that TiS2 is an indirect narrow-gap semiconductor.     

Properties of a New Nonlinear Optical Crystal CdZn2B2O6

Cadmium dizinc diborate （CdZn2B2O6） single crystals have been grown for the first time. The crystal structure of CdZn2B2O6 is the same as that of the Cd3Zn3B4O12. The x-ray diffraction, infrared and Raman spectra, differential scanning calorimetry analysis and density indicate that the physical and chemical properties of both crystals are very similar. Especially, the nonlinear optical coefficients of CdZn2B2O6 and Cd3Zn3B4O12 crystals are 2.6 and 2.4 times as large as that of KH2PO4 crystal respectively. Chemical etching experiments indicated that these crystals are very stable in neutral solution and not hygroscopic in air at room temperature.     

Influences of Bi2O3/V2O5 Additives on the Microstructure and Magnetic Properties of Lithium Ferrite

Lithium ferrite materials with different concentrations of Bi2O3 and V2O5 additives are prepared by the conventional ceramic technique. The x-ray diffraction analysis proves that the additives do not affect the final crystal phase of the lithium ferrite in our testing range. Both Bi2O3 and V2O5 additives could promote densification and lower sintering temperature of the lithium ferrite. The average grain size first increases, and then gradually decreases with the Bi2O3 content. The maximal grain size appears with 0.25 wt% Bi2O3. The average grain size first increases, and then is kept almost unchanged with the V2O5 content. The maximal average grain size of the samples with V2O5 additive is much smaller than that of the samples with Bi2O3 additive. Furthermore, the V2O5 additive more easily enters the crystal lattice of the lithium ferrite than the Bi2O3 additive. These characteristics evidently affect the magnetic properties, such as saturation flux density, ratio of remanence Br to saturation flux density Bs, and coercive force of the lithium ferrite. The mechanisms involved are discussed.     

Improved Resistive Switching Characteristics of Ag-Doped ZrO2 Films Fabricated by Sol-Gel Process

Ag-doped and pure ZrO₂ thin films are prepared on Pt/Ti/SiO₂/Si substrates by sol-gel process for resistive random access memory application. The highly reproducible resistive switching is achieved in the 10% Ag-doped ZrO₂ devices. The improved resistive switching behaviour in the Ag doped ZrO₂ devices could be attributed to Ag doping effect on the formation of the stablefilamentary conducting paths. In addition, dual-step reset processes corresponding to three stable resistance states are observed in the 10% Ag doped ZrO₂ devices, which may be implemented for the application of multi-bit storage.     

A Two-Parameter Deformed Two-Dimensional Interacting Boson Model With Uqp(U3)Uqp(U2)Uqp(SO2) Symmetry

A two-parameter deformed two-dimensional interacting boson model with U_qp(U₃) U_qp(U₂) U_qp(SO₂)symmetry is constructed.It is found that the energy spectrum and transition matrix elements depend very sensitively on the second parameter of deformation.