TiO_2/SrTiO_3核壳结构光阳极制备及其光电化学性能

采用水热法在纳米多孔TiO2光阳极表面包覆一薄层SrTiO3,制得TiO2/SrTiO3核壳结构光阳极,并用X射线衍射、扫描电镜、能谱仪、透射电镜及紫外可见吸收光谱对其进行表征。探讨了水热反应时间对TiO2/SrTiO3光阳极组装的染料敏化太阳能电池(DSSCs)的光电化学性能的影响。结果表明:钙钛矿结构的SrTiO3包覆在纳米多孔TiO2光阳极的表面,形成TiO2为核SrTiO3为壳的光阳极;SrTiO3包覆的样品吸收边有红移;与TiO2光阳极相比,水热反应制备的TiO2/SrTiO3核壳结构光阳极组装的DSSC短路电流密度明显增加,5h时光电性能最优,短路电流密度为13.98mA/cm2,开路电压为0.74V,填充因子为0.45,全光转换效率为4.68%,提高了35.65%。     

氮掺杂SrTiO3/TiO2纳米棒异质结的制备及光催化活性

通过水热反应和直接浸渍法在FTO导电玻璃上制备得到了高度有序的氮掺杂SrTiO3/TiO2纳米棒异质结阵列(N-STO/TNR),利用扫描电子显微镜(SEM),X射线衍射(XRD)和X射线光电子能谱(XPS)对其表面形貌,晶体结构和元素价态进行了分析。同时,采用荧光光谱(FL)、紫外可见漫反射光谱(UV-DRS),电化学阻抗谱(EIS)和莫特肖特基(MS)对异质结的光电性能进行了测试。最后以甲基橙为模拟污染物,考察了异质结材料在可见光下的光催化活性。结果表明,SrTiO3/TiO2异质结构能有效的分离光生载流子,同时N元素的掺杂将异质结的光谱响应范围扩展到可见光区,得益于半导体复合和能级修饰策略的协同增强效应,N-STO/TNR展现出优异的光电性能,N-STO/TNR的光催化效率是未改性的TNR样品的5.7倍。     

二维ReS2/TiO2异质结薄膜的制备及其光电催化性能

本研究利用TiO2的前驱体在FT O上旋涂一层种子溶液,退火后用水热法使TiO2籽晶垂直生长成纳米棒阵列.随后采用液相剥离法(L PE)制得二维ReS2材料,并用滴涂法将二维ReS2滴涂到TiO2纳米棒阵列形成ReS2/TiO2异质结.通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)和光电催化测试等分析表征了所制备材料和结构的晶型,形貌及其光电化学性能.结果表明,当负载量在约0.1 mg/cm2时,ReS2/TiO2异质结有着最强的光电流1.5 mA/cm2,是纯TiO2纳米棒(0.03 mA/cm2)的50倍,强烈的增强来源于ReS2/TiO2异质结构形成能可有效地拓宽TiO2的吸光范围,并且促进光生载流子的有效分离和提高光电催化性能.     

锐钛矿型TiO_2纳米线的水热法制备及其光电性能的研究

利用水热技术制备了锐钛型的TiO2纳米线(TNWs),研究了不同的水热反应时间,水热反应温度以及所用碱的浓度对所制备的纳米线的形貌的影响。采用XRD技术和SEM技术对纳米线的成分及其形貌进行了表征。将TNWs与TiO2(P25)混合分散于水和乙醇的混合溶剂中,制得均匀稳定的浆体,涂敷于不锈钢基体表面,进行光电化学性能的测试,结果表明,当TNWs的掺杂量为5%(w)时,薄膜的光电性能最优。     

大面积3D有序介孔二氧化钛薄膜光子晶体制备与性能研究

介绍了大面积有序反蛋白石结构介孔二氧化钛薄膜光子晶体制备与性能研究的进展.为了保证二氧化钛骨架结构的稳定性和有序度,从而使氧化钛介孔薄膜达到大面积结构均匀,在介孔薄膜制备过程中采用了几种新的工艺方法,其中包括二氧化硅晶体模板的应用和用NaOH溶液代替常用的HF溶液作为模板去除剂.制备的介孔二氧化钛薄膜光子晶体的面积达到厘米尺寸,二氧化钛骨架的填充率达到17.4%,薄膜制备过程中的收缩率<3%.薄膜透射光谱研究结果表明,这种大面积3D有序的反蛋白石结构介孔二氧化钛薄膜具有非常优良的光子带隙特性,有望成为一类具有非常好的发展和应用前景的光子晶体材料.     

锐钛矿/TiO2（B）异质纳米线制备、表征及其光催化性能研究

通过简单的水热反应,和后续的退火处理得到锐钛矿/TiO2(B)异质结构纳米线。通过XRD、SEM和TEM对其进行表征。并对锐钛矿/TiO2(B)进行甲基橙紫外光降解性能测试,探究和讨论了H2O2对其光催化性能的影响,实验表明当加入1.6mL H2O2时对体系光催化促进效果最优,只需要8min分解率达到99%,降解时间只为无H2O2时的1/5。     

叠层式TiO2/SnO2复合纳米薄膜制备及其光电性能研究

采用溶胶-凝胶法在不同基体表面制备了叠层式TiO2/SnO2复合纳米薄膜.用扫描电子显微镜(SEM)、X射线衍射(XRD)对复合薄膜表面形貌和晶体结构进行表征.采用紫外-可见吸收光谱法和电化学方法来研究复合薄膜光学与光电化学性能特征.结果表明,所制备的叠层式TiO2/SnO2复合纳米薄膜表面连续、均匀、致密;XRD分析表明纳米TiO2为锐钛矿型结构,SnO2为金红石型结构;紫外-可见吸收光谱测试表明叠层式TiO2/SnO2复合纳米薄膜较纯TiO2薄膜的吸收范围拓宽;稳定电位随时间变化曲线(OCP-t)结果表明,叠层式TiO2/SnO2复合纳米薄膜光照下其光电化学性能高于纯TiO2薄膜;同时,光照后叠层式TiO2/SnO2复合纳米薄膜能有效储存TiO2先生电荷,延续对不锈钢基体的光生阴极保护性能.经比较,叠加3层SnO2的TiO2/3SnO2复合纳米薄膜改善光电性能最佳.     

ZnO调制改性染料敏化太阳能电池TiO2光阳极研究

采用丝网印刷的方式制备了染料敏化太阳能电池的TiO2薄膜光阳极、TiO2-ZnO复合薄膜光阳极以及TiO2/ZnO双层薄膜光阳极,研究了ZnO对TiO2薄膜光阳极的调制改性作用。研究结果表明分别以醋酸锌和ZnO直接掺杂制备的TiO2-ZnO复合薄膜光阳极同未掺杂的TiO2薄膜光阳极相比,以醋酸锌为原料制备的复合薄膜光阳极使电池转换效率提高了1倍,而由于微米量级的ZnO的粒径大,用其作原料制得的复合薄膜光阳极反而使电池的转换效率有所降低。以醋酸锌为原料制备的TiO2/ZnO双层薄膜光阳极同TiO2薄膜光阳极相比,电池转换效率提高了13倍,通过性能优化后电池的转换效率达到4.7%。     

微孔结构TiO2薄膜在准固态染料敏化太阳电池上的应用

采用200 nm聚苯乙烯(PS)造孔可以改善TiO2半导体薄膜的散射光性能,提高了准固态染料敏化太阳电池的光电性能。用10%聚苯乙烯造孔制备TiO2半导体组装的染料敏化太阳电池,在100 mW/cm2光强下电池光电转换效率达到2.94%,与不含造孔剂电池相比,光电转换效率提高52%。薄膜光学性能和入射单色光子–电子转化效率(IPCE)研究表明,电池光电性能的提高与薄膜的光散射改善和电池中染料的光捕获效率增大密切相关。     

CdS量子点敏化纳米TiO_2异质薄膜的制备和表征

以异丙醇钛(C12H28O4Ti)为主要原料合成氧化钛(TiO2)前驱体溶胶,并结合230℃水热处理得到TiO2溶胶,利用电流体动力学(EHD)技术在掺氟氧化锡导电(FTO)玻璃基片上镀膜,450℃高温煅烧制备具有多级结构锐钛矿TiO2纳米薄膜。以硝酸镉(Cd(NO3)2)及硫化钠(Na2S)分别为镉源和硫源,采用化学浴沉积技术在TiO2薄膜上沉积制备了量子点敏化的异质薄膜。采用X射线衍射(XRD)、电子扫描电镜(SEM)、电子透射电镜(TEM)以及紫外-可见吸收光谱(UV-Vis absorbance spectra)对薄膜结构和性能进行表征。结果表明,纳米TiO2薄膜具有亚微米球簇堆积结构,球簇之间形成尺寸连续分布的微纳通道,便于溶液的浸润和离子的表面吸附。敏化制备异质薄膜中硫化镉以量子点状态存在,晶粒尺寸为3～5nm范围内。UV-Vis吸收光谱证实量子点的量子限域效应,吸收发生蓝移现象。     

Toughness enhancement in TiAlN-based quarternary alloys

Improved toughness in hard and superhard thin films is a primary requirement for present day ceramic hard coatings, known to be prone to brittle failure during in-use conditions. We use density functional theory calculations to investigate a number of (TiAl)_1 − xM_xN thin films in the B1 structure, with 0.06 ≤ x ≤ 0.75, obtained by alloying TiAlN with M = V, Nb, Ta, Mo and W. Results show significant ductility enhancements, hence increased toughness, in these compounds. Importantly, these thin films are also predicted to be superhard, with similar or increased hardness values, compared to Ti_0.5Al_0.5 N. For (TiAl)_1 − xW_xN the results are experimentally confirmed. The ductility increase originates in the enhanced occupancy of d-t_2g metallic states, induced by the valence electrons of substitutional elements (V, Nb, Ta, Mo, W). This effect is more pronounced with increasing valence electron concentration, and, upon shearing, leads to the formation of a layered electronic structure in the compound material, consisting of alternating layers of high and low charge density in the metallic sublattice, which in turn, allows a selective response to normal and shear stresses.     

A novel single-phased white light emitting phosphor of Eu ions-doped Ca2LaTaO6

A novel single-phased white light emitting phosphor, Ca₂(La_1−xEu_x)TaO₆ (x = 0.001–0.7), was synthesized using a vibrating milled solid state reaction. The results indicate that the emission spectra of Ca₂LaTaO₆:Eu³⁺ samples exhibit a series of shaped peaks assigned to the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions under an excitation of 395 nm. The characteristic peaks of Eu³⁺ ion intra-4f transitions from excited states to lower levels include ⁵D₃ → ⁷F_J (J = 1, 2, 3), ⁵D₂ → ⁷F_J (J = 0, 1, 2, 3), ⁵D₁ → ⁷F_J (J = 1,2,3), and ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions. The higher level ⁵D_J (J = 1, 2, 3) emission depends on the concentration of Eu³⁺ ions. The emission spectra shows a completely different ratio between the ⁵D_3,2,1 blue-green emission and ⁵D₀ red emission for lower and higher Eu³⁺ concentrations. For lower Eu³⁺ ion concentrations, the dominant transition of Ca₂(La_1−xEu_x)TaO₆ phosphors are ⁵D_3,2,1,0 → ⁷F_J emissions, whereas the dominant transitions are ⁵D₀ → ⁷F_J emissions for higher Eu³⁺ ion concentrations. The chromaticity coordinate of the Ca₂(La_1−xEu_x)TaO₆ phosphor varies with the Eu³⁺-doped concentrations from white, to reddish orange, and red. Thus, this type of phosphor may be potentially applicable as a white light emitting phosphor for ultraviolet light-emitting diodes.     

Synthesis and mechanical properties of high-purity Cr2AlC ceramic

High-purity and dense Cr₂AlC has been successfully fabricated by hot-pressing, using Cr, Al and graphite as raw materials. Delamination, kink bands, monolamellar kink, transgranular crack and transgranular fracture of bulk Cr₂AlC are found during the room-temperature test. The density, Vickers hardness, flexural strength, Young's modulus, compressive strength and fracture toughness of the Cr₂AlC are 5.17 g/cm³, 4.9 GPa, 469 ± 27 MPa, 282 GPa, 949 ± 22 MPa and 6.22 ± 0.26 MPa m^1/2, respectively. The strength of Cr₂AlC could be greatly improved by second phase of Cr₇C₃. And the slipping of basal planes and slip system cold be hindered by Cr₇C₃, thus resulting in a lower toughness.     

Dynamic Inhomogeneities in the La2CuO4-Based Superconductors

Polarization-dependent X-ray-absorption fine-structure (XAFS) measurements on the local structure of the La₂CuO₄-based high-T _c superconductors La_2–x Sr _x CuO₄, La_2–x Ba _x CuO₄, and La_1.6–x Sr _x Nd_0.4CuO₄ find, among others, orientation disorder induced in the Cu–O₂ planes by doping Sr, Ba, and alloying Nd atoms, all such atoms residing in La-sites. The orientation disorder is of two types: mostly static-buckling disorder, and dynamic disordering of the tilt angles of the Cu–O₆ octahedra correlated in nanoscale regions, with respect to neighboring nanoscale regions. Buckling disorder in the Cu–O₂ planes has the greatest detrimental effect on T _c and conductivity for such foreign atoms.     

Influence of Mn-site doped with Ru on the high-temperature thermoelectric performance of CaMnO3−δ

Thermoelectric properties were measured from room temperature to 1000 K to study the effects of doping of Ru for Mn-site on the thermoelectric performance of CaMnO_3−δ. The electrical resistivity shows a sharp decrease upon Ru doping. The Seebeck coefficients of all the samples are negative, and their absolute values remain fairly large even after Ru doping. Among the samples of CaMn_1−xRu_xO_3−δ (x=0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.15, 0.18), CaMn_0.96Ru_0.04O_3−δ has the largest power factor, 1.85×10⁻⁴ W/mK² at 1000 K. An increase or a decrease of x value results in a marked decrease of the power factor. The thermal conductivity and the figure of merit Z of CaMn_0.96Ru_0.04O_3−δ is 2.88 W/mK and 0.64×10⁻⁴ K⁻¹ at 1000 K, respectively.     

A comparative study of the properties of thermally evaporated CuIn2n + 1S3n + 2 (n = 0, 1, 2 and 3) thin films

CuInS₂, CuIn₃S₅, CuIn₅S₈ and CuIn₇S₁₁ compounds were synthesized by the horizontal Bridgman method using high-purity copper, indium and sulphur elements. Crushed powders of these ingots were used as raw materials for the vacuum thermal evaporation. So, CuIn_2n + 1S_3n + 2 (n = 0, 1, 2, and 3) thin films were deposited by single source vacuum thermal evaporation onto glass substrates heated at 150 °C. The structural, compositional, morphological, electrical and optical properties of the deposited films were studied using X-ray diffraction (XRD), energy dispersive X-ray, atomic force microscopy and optical measurement techniques. XRD results revealed that all the films are polycrystalline. However, CuInS₂ and CuIn₃S₅ films had a chalcopyrite structure with preferred orientation along 112 while CuIn₅S₈ and CuIn₇S₁₁ films exhibit a spinel structure with preferred orientation along 311. The absorption coefficients of the all CuIn_2n + 1S_3n + 2 films are in the range of 10⁻⁴ and 10⁻⁵ cm⁻¹. The direct optical band gaps of CuIn_2n + 1S_3n + 2 layers are found to be 1.56, 1.78, 1.75 and 1.30 eV for n = 0, 1, 2, and 3, respectively. CuIn₃S₅ and CuIn₅S₈ films are p type with electrical resistivities of 4 and 12 Ω cm whereas CuInS₂ and CuIn₇S₁₁ are highly compensated with resistivities of 1470 and 1176 Ω cm, respectively.     

A Numerical Treatment of the rf SQUID: II. Noise Temperature

We investigate rf SQUIDs (Superconducting QUantum Interference Devices), coupled to a resonant input circuit, a readout tank circuit and a preamplifier, by numerically solving the corresponding Langevin equations. The quantity of interest is the noise temperature T _N . We use an analytical expression T _N0,opt, which is already optimized for the parameters of the input circuit, and vary the model parameters of the remaining circuit to minimize T _N0,opt. We also compare T _N0,opt to numerical simulations of the full circuit and find good agreement. The best device performance is obtained when β′ _L ≡2π LI ₀/Φ ₀ is in the range 0.5–0.9; L is the SQUID inductance, I ₀ the junction critical current and Φ ₀ the flux quantum. For a tuned input circuit we find an optimal noise temperature T _N0,opt≈3Tf/f _c , where T, f and f _c denote temperature, signal frequency and junction characteristic frequency, respectively. This value is close to the optimal noise temperatures obtained by approximate analytical theories carried out previously in the limit β′ _L ≲1. We study the dependence of T _N0,opt on various model parameters away from their optimum values, and often find much lower values of T _N0,opt than predicted by the analytical theory. We finally discuss implications for devices that can be implemented experimentally.      

Fabrication and Characterization of Cross-Connected Microchannel Porous Mesh Plates (CCMPMPs) by Multi-Cutter Milling

A new method for fabricating CCMPMPs, namely multi-cutter milling, is proposed and the fabrication principle is discussed. Then, a study of three microchannel parameters, the microchannel depth H_c, width W_c, and interval W_s, and two CCMPMP parameters, the porosity P and the total surface area per unit volume S_V, is presented. Furthermore, 3D FEM has been adopted to study the effective stress distribution, the metal flow velocity distribution, and the cutting forces. The results show that CCMPMPs can be successfully machined. H_c, W_c, and W_s can be controlled by the radial depth of cut a_e, the slotting cutter thickness E_t, and the gasket thickness E_g, while P and S_V can be changed by adjusting H_c, W_c, and W_s. Moreover, as a_e increases, the average resultant force increases, and the friction between chip and the side face of the machined microchannel, and between chip and the rake face, plays an increasingly important role in it.     

An improved technique for the solution of edge crack problem for finite plate

This paper provides a detailed examination for the edge crack problem of finite plate. The Williams expansion for the crack problem is used first. Secondly, the complex potentials for the central crack problem are used in the present study, which is called the improved technique hereafter. In both techniques, the eigenfunction expansion variational method (EEVM) is used for evaluating the undetermined coefficients in the expansion form. The ratio of height versus width of plate (h/w) is varying from 1.5, 1.0, 0.75, 0.5, 0.4, 0.3 to 0.25. The ratio of edge crack length versus width of plate (a/w) takes two sets: (1) a/w = 0.1, 0.2, … to 0.9, (2) a/w = 0.01, 0.02, … to 0.09. The detailed computation proves that for moderate cases of the a/w ratio, for example, 0.2 < a/w < 08, the deviations for SIFs and T-stress from two techniques are minor. However, for the case of short edge crack length, for example, a/w < 0.05, the deviations for SIFs and T-stress from two techniques are significant. It is found that the Williams expansion may not be suitable for the short edge crack, for example, a/w < 0.05.