退火温度对TiO2/CdSe纳米片异质结薄膜光电性能的影响

采用水热法在FTO上制备（001）高活性晶面主导的TiO₂纳米片薄膜,利用循环伏安法在TiO₂纳米片薄膜上沉积CdSe颗粒,制备了TiO₂/CdSe纳米片异质结薄膜。分别在150、250、350、450 ℃,氩气保护气氛中对样品进行退火。利用X射线衍射仪（XRD）、场发射扫描电镜（FESEM）、X射线光电子能谱分析仪（XPS）、紫外-可见（UV-Vis）分光光度计以及电化学工作站对不同温度退火后的TiO₂/CdSe纳米片异质结薄膜的微观形貌、晶体结构、光电化学性能进行表征和测试。结果表明：六方相CdSe纳米颗粒均匀包覆在TiO₂纳米片表面,直径30 nm左右;随着退火温度的升高CdSe纳米颗粒长大,形成光滑的CdSe薄膜,且晶化程度提高;TiO₂纳米片表面的Se元素与Cd元素发生氧化;TiO₂/CdSe纳米片异质结薄膜对可见光的吸收光谱发生红移,禁带宽度逐渐减小。光电化学性能测试表明随着退火温度的升高,TiO₂/CdSe纳米片异质结薄膜的光电流密度显著提高,开路电压减小,但由于SeO2和CdO的出现,导致填充因子减小,影响光电转换效率的提高。在本实验条件下,TiO₂/CdSe纳米片异质结薄膜的最佳退火温度为150 ℃,填充因子为0.77,光电转换效率达到3.12%。     

骨架结构多孔TiO2薄膜增强染料敏化太阳能电池性能

以空心球状TiO₂为基体、以片状TiO₂为骨架,采用刮刀法制备了染料敏化太阳能电池的多孔TiO₂光阳极薄膜。光电转化效率测试结果表明,当作为骨架支撑材料的片状TiO₂含量为20wt%时,光阳极薄膜组装成太阳能电池的光电转化效率达到最高值4.53%,比商业P25制备的无孔无骨架TiO₂薄膜电池(4.06%)及无骨架结构的多孔TiO₂薄膜电池(4.17%)的性能均有显著提高。当片状TiO₂的最佳含量为20wt%电池薄膜厚度为33 μm时,太阳能电池光电转化效率进一步提升为7.06%。光电性能增强的原因是骨架结构有利于快速传输电子并增大染料吸附量。本研究通过设计制备具有骨架结构的多孔TiO₂薄膜为提高染料敏化太阳能电池性能提供了新的思路。     

Study of the Molecular Mobility in Polymers with the Thermally Stimulated Recovery Technique—A Review

Thermally stimulated recovery (TSR) is a non‐conventional mechanical spectroscopy technique that allows to analyse in detail the relaxation processes of polymeric systems in the low frequency region. This work reviews the main aspects and potentialities of this technique. The different kinds of TSR experiments that can be performed, global and thermal sampling (TS) experiments, are described and illustrated with several examples. Also, the different methods for the determination of the thermokinetic parameters (activation energy and pre‐exponential factor) of the thermal sampling (TS) procedure are explained and compared. In this context, the compensation phenomenon, which always appears in TSR results when the studies are performed in the glass transition region of a given system, is discussed. Examples of the application of this technique to different polymeric systems during the last 20 years are provided. An emphasis will be made on the analysis of the effect of crystallinity degree and crosslink density on the TSR response. A comparison between the results (characteristic times and activation energies) obtained by different techniques, namely TSR, dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC), is made.     

Concentration induced the interfacial self‐assembly polymorphism of 4, 4′‐dihexadecyloxy‐benzophenon by scanning tunneling microscopy

The concentration effect on a two‐dimensional (2D) self‐assembly of 4, 4′‐dihexadecyloxy‐benzophenon (DHB) has been investigated by scanning tunneling microscopy. The self‐assembly of DHB at the phenyloctane/graphite interface was concentration dependent. Under low concentration, the DHB molecules were adsorbed intactly on the graphite surface. With the increasing of concentration, one of side chains connecting the conjugated moiety stretched into the liquid phase. The coexistence of two self‐assembled structures was observed in a moderate concentration. The result indicated that the van der Waals interactions between the molecules and the graphite lattice were decreasing with the increasing concentration. After the samples were placed in ambient conditions over 24 h, a different self‐assembled structure was obtained on the gas/solid interface, in which the DHB molecules were adsorbed on the surface with only one of the side chains. Both the benzophenon core and the other side chain were extended to the gas phase. The results demonstrated that concentration played an important role in forming the 2D molecular self‐assembly and provided an efficient approach for the control of the DHB molecular nanostructure. Copyright © 2013 John Wiley & Sons, Ltd.     

Mutation scanning analysis of genetic variation within and among Echinococcus species: Implications and future prospects

Adult tapeworms of the genus Echinococcus (family Taeniidae) occur in the small intestines of carnivorous definitive hosts and are transmitted to particular intermediate mammalian hosts, in which they develop as fluid‐filled larvae (cysts) in internal organs (usually lung and liver), causing the disease echinococcosis. Echinococcus species are of major medical importance and also cause losses to the meat and livestock industries, mainly due to the condemnation of infected offal. Decisions regarding the treatment and control of echinococcosis rely on the accurate identification of species and population variants (strains). Conventional, phenetic methods for specific identification have some significant limitations. Despite advances in the development of molecular tools, there has been limited application of mutation scanning methods to species of Echinococcus. Here, we briefly review key genetic markers used for the identification of Echinococcus species and techniques for the analysis of genetic variation within and among populations, and the diagnosis of echinococcosis. We also discuss the benefits of utilizing mutation scanning approaches to elucidate the population genetics and epidemiology of Echinococcus species. These benefits are likely to become more evident following the complete characterization of the genomes of E. granulosus and E. multilocularis.     

Synthesis and thermotropic studies of a novel series of nematogenic liquid crystals 2-(6-alkoxynaphthalen-2-yl)-5-cyanopyridines

A novel series of highly birefringent liquid crystalline compounds, 2-(6-alkoxynaphthalen-2-yl)-5-cyanopyridines (nO-NpPyCN, n?=?2–8) that have potential as commercially useful, were synthesised using a short two-step reaction with overall yields between 55% and 85%. Spectral analyses were in accordance with the expected structures. Their thermotropic behaviours were investigated by polarising optical microscopy and differential scanning calorimetry. It was found that the desymmetrised core results in a nematic phase with a broad mesophase range.     

The optimal cell gap determination of a liquid crystal wavefront corrector from a single photoelectric measurement

It has been a crucial technique to improve the dynamic response characteristics of a liquid crystal wavefront corrector (LCWFC) with optimal cell gap since the LCWFC needs at least 2π (or π) phase modulation in adaptive optics systems (AOSs). We have given a complete process for obtaining the optimal cell gap accurately from a single photoelectric measurement, which can be conducted with a liquid crystal (LC) cell of any known thickness. This method has been analysed theoretically and confirmed experimentally by using a wedge-shaped cell; the experimental results match very well with the theoretical analysis. The response time of an optimal gap cell can be a novel evaluation method of response performance of LC materials.     

Photosensitive cholesteric copolymers with spiropyran-containing side groups I. Phase behaviour and photo-optical properties

A number of terpolymers were synthesized by copolymerization of nematogenic, chiral and photochromic monomers with different contents of spiropyran photosensitive side groups. The synthesized copolymers possess selective light reflection in the visible region of the spectrum. Action of UV light on planarly-oriented films of the copolymers leads to the formation of the merocyanine form of the dye with a maximum of absorbance coinciding with the selective light reflection peak. The 'degeneration' of the selective light reflection is observed during this process. It was shown that such types of material can be used for reversible information storage; the principal scheme for the processes of optical data recording and reading is suggested.     

Blue phase III widening in CE6-dispersed surface-functionalised CdSe nanoparticles

The phase transition behaviour of the chiral liquid crystal CE6 doped with spherical surface-functionalised CdSe nanoparticles has been examined by means of high-resolution adiabatic scanning calorimetry and polarising microscopy. The addition of nanoparticles results in an essentially stabilised blue phase III. The phase diagram is displayed upon heating and cooling and the enthalpy changes involved in the conversion between the blue phases are determined. The dispersion of functionalised nanoparticles is prominent for the stabilisation of blue phase III, which is potentially useful for applications, especially if applied on liquid crystals that exhibit blue phases close to room temperature.     

Synthesis,characterisation and mesomorphic properties of ester containing aroylhydrazones and their nickel(II) complexes

A new series of mesogenic aroylhydrazone-based ligands, N-[4-(4′-alkoxy)benzoyloxybenzylidene]-N′-[4″-alkoxybenzoyl]hydrazine with either the same or different peripheral alkyl chains, and nickel(II) complexes of some of them have been synthesised. They were characterised by elemental analyses, Fourier transform infrared, proton and carbon nuclear magnetic resonance and ultraviolet-visible spectroscopy. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry and polarising optical microscopy. All the aroylhydrazones, except those with no lateral chains on either end of the molecule and where m?=?n?=?14, 16, exhibit a monotropic or enantiotropic smectic C mesophase, which are almost insensitive to the peripheral alkoxy chain length. The square planar nickel(II) complexes of the ligands show only an isotropic phase at higher temperature (>175°C) and no mesogenic nature is observed. Density functional theory calculations have been performed using the GAUSSIAN-03 program at the Becke, three-parameter, Lee–Yang–Parr level to obtain the stable electronic structure of the ligand.