Magnetic-field-induced superconductivity in a two-dimensional organic conductor

The application of a sufficiently strong magnetic field to a superconductor will, in general, destroy the superconducting state. Two mechanisms are responsible for this. The first is the Zeeman effect, which breaks apart the paired electrons if they are in a spin-singlet (but not a spin-triplet) state. The second is the so-called 'orbital' effect, whereby the vortices penetrate into the superconductors and the energy gain due to the formation of the paired electrons is lost. For the case of layered, two-dimensional superconductors, such as the high-Tc copper oxides, the orbital effect is reduced when the applied magnetic field is parallel to the conducting layers. Here we report resistance and magnetic-torque experiments on single crystals of the quasi-two-dimensional organic conductor lambda-(BETS)2FeCl4, where BETS is bis(ethylenedithio)tetraselenafulvalene. We find that for magnetic fields applied exactly parallel to the conducting layers of the crystals, superconductivity is induced for fields above 17 T at a temperature of 0.1 K. The resulting phase diagram indicates that the transition temperature increases with magnetic field, that is, the superconducting state is further stabilized with magnetic field.     

Pressure-induced insulator conductor transition in a photoconducting organic liquid-crystal film

Intermolecular separation determines the extent of orbital overlap and thus the rate of electron transfer between neighbouring molecules in an organic crystal. If such a crystal is compressed, the resistivity decreases owing to a diminishing intermolecular distance. Metal insulator transitions have been observed by applying hydrostatic pressure to, for example, Langmuir films of metal nanoparticles. But previous attempts to observe a clear transition point in organic crystals, such as anthracene and tetracene, were not successful owing to difficulties with electrically insulating the high-pressure cell. Here we report a different approach by using a sample that is photoconductive and forms an organized film. A cylindrical tip (approximately 100 microm in diameter) was used to compress the sample instead of a piston/cylinder structure, entirely eliminating the problem of electrical insulation. Furthermore, by illuminating the sample with a laser, the conductivity of the sample is increased by several orders of magnitude. By monitoring the photocurrent with sensitivity at the 10(-13) A level, changes in resistivity at very low pressure could be monitored. We observe a sharp increase in current that could indicate a transition from hopping to delocalized conduction.     

一种新型有机聚合物的光全息存储

合成了吩噻嗪(Phenothianzine)聚合物,将其掺入聚乙烯咔唑Poly(N Vinylcarbazole)(PVK)和聚丙烯丁酯(Poly butylacrylate)(PBA)的聚合物(PVK PBA)以及三硝基芴酮2,4,7 trinitro 9 fluorenone(TNF)聚合制成有机薄膜器件.样品在双相干光束作用下,可建立光折射率光栅,其衍射效率可超过30%,并考察了样品折射率光栅形成的动力学过程.我们还实现了全息图象存储,并获得了清晰的存储图象.文章并对相关结果形成的机制做出了定性的分析.     

Fluctuating superconductivity in organic molecular metals close to the Mott transition

On cooling through the transition temperature T(c) of a conventional superconductor, an energy gap develops as the normal-state charge carriers form Cooper pairs; these pairs form a phase-coherent condensate that exhibits the well-known signatures of superconductivity: zero resistivity and the expulsion of magnetic flux (the Meissner effect). However, in many unconventional superconductors, the formation of the energy gap is not coincident with the formation of the phase-coherent superfluid. Instead, at temperatures above the critical temperature a range of unusual properties, collectively known as 'pseudogap phenomena', are observed. Here we argue that a key pseudogap phenomenon-fluctuating superconductivity occurring substantially above the transition temperature-could be induced by the proximity of a Mott-insulating state. The Mott-insulating state in the kappa-(BEDT-TTF)2X organic molecular metals can be tuned, without doping, through superconductivity into a normal metallic state as a function of the parameter t/U, where t is the tight-binding transfer integral characterizing the metallic bandwidth and U is the on-site Coulomb repulsion. By exploiting a particularly sensitive probe of superconducting fluctuations, the vortex-Nernst effect, we find that a fluctuating regime develops as t/U decreases and the role of Coulomb correlations increases.     

Photomechanics: directed bending of a polymer film by light

Polymer solutions and solids that contain light-sensitive molecules can undergo photo-contraction, whereby light energy is converted into mechanical energy. Here we show that a single film of a liquid-crystal network containing an azobenzene chromophore can be repeatedly and precisely bent along any chosen direction by using linearly polarized light. This striking photomechanical effect results from a photoselective volume contraction and may be useful in the development of high-speed actuators for microscale or nanoscale applications, for example in microrobots in medicine or optical microtweezers.     

Free-electron-like dispersion in an organic monolayer film on a metal substrate

Thin films of molecular organic semiconductors are attracting much interest for use in electronic and optoelectronic applications. The electronic properties of these materials and their interfaces are therefore worth investigating intensively, particularly the degree of electron delocalization that can be achieved. If the delocalization is appreciable, it should be accompanied by an observable electronic band dispersion. But so far only limited experimental data on the intermolecular dispersion of electronic states in molecular materials is available, and the mechanism(s) of electron delocalization in molecular materials are also not well understood. Here we report scanning tunnelling spectroscopy observations of an organic monolayer film on a silver substrate, revealing a completely delocalized two-dimensional band state that is characterized by a metal-like parabolic dispersion with an effective mass of m* = 0.47m(e), where m(e) is the bare electron mass. This dispersion is far stronger than expected for the organic film alone, and arises as a result of strong substrate-mediated coupling between the molecules within the monolayer.     

有机LED聚合物薄膜的制备工艺研究

采用两次重复的2^3析因实验设计,应用方差分析方法,研究了旋涂工艺中聚合物溶液的浓度,匀胶机的旋涂速度和加速度对旋涂的薄膜厚度和薄膜均匀性的影响。实验和分析的结果表明：溶液浓度和和旋涂速度对膜厚和薄膜均匀具有显著性的影响,而旋涂加速度对它们的影响则不显著。这一结论对于制备优质薄膜、改善聚合物发光器件性能具有重要的指导作用。     

分子印迹聚合物及其在有机合成中的应用

分子印迹技术是近年发展起来的一种新颖的有机合成手段。评述了分子印迹聚合物的制备方法及尚有待深入的关键问题,重点介绍了分子印迹聚合物用作催化剂在有机合成中应用的优势及研究近况,特别是用作手性催化剂不对称合成光学活性物质。并设计将分子印迹聚合物用于催化醛酮不对称还原反应,可获得较高光学产率的手性醇,其％e.e值达95％以上。     

J-aggregates聚合物膜的超快飞秒光克尔效应的研究

实验中研究染料分子J-aggregatcs和聚乙烯醇聚合物膜的超快共振光学克尔现象.测量该聚合物膜的光克尔信号随泵浦光功率的变化关系,得到了相关的泵浦阈值.改变泵浦光的波长,发现该聚合物膜的光克尔信号在泵浦光波长为600 nm时达到最大.     

Intercalation of alkylamines into an organic polymer crystal

Organic solid-state synthesis allows formation of products that are difficult or impossible to produce by conventional methods. This feature, and the high degree of reaction selectivity that can be achieved, is a direct result of the control over the relative orientation of the reactants afforded by the solid state. But as the successful development of 'topochemical reactions' requires the careful design of suitable reactant crystals, the range of both reactions and products amenable to this approach has been limited. However, recent advances in organic crystal engineering, particularly the rational design of complex solid architectures through supramolecular preorganization, have renewed interest in topochemical reactions. Previously, we have orientated muconate monomers--diene moieties with a carboxylate group on each end--using long-chain n-alkylammonium ions, such that the topochemical photopolymerization of the solid-state reactants produces layered crystals of stereoregular and high-molecular-mass polymers. Here we show that these polymer crystals are capable of repeated, reversible intercalation by conversion to the analogous poly(carboxylic acid), followed by transformation into a number of poly(alkylammonium muconate)s upon addition of the appropriate amine. Introduction of functional groups into these crystals may allow the design of organic solids for applications such as molecular recognition, separation and catalysis, thereby extending the range and practical utility of current intercalation compounds.     

纳米微球聚合物膜的构建及其修饰电极性能

将一种核壳结构两亲性聚合物纳米微球修饰到玻碳电极表面,该微球组成是以质子化PDMAEMA大分子为壳以及聚苯乙烯为核（简称PDS）。在最优化成膜条件下,得到的PDS膜电极的电子传导能力明显优于裸电极。考察PDS膜对磷钼杂多酸（PMo12）修饰电极性能的影响。结果表明,PDS膜不仅可以使PMo12修饰电极的稳定性得到改善,而且有助于PMo12在电极表面的电子转移,从而有效提高PMo12的电化学及对103^-的电催化性能。     

溶胶-凝胶法制备有机/无机复合膜的研究

直接从无定型二氧化硅出发,研究了与乙二醇、氢氧化钾反应,生成高反应活性的五配位硅钾化合物,再与2-氯乙醇反应制备双羟基四配位硅化合物,然后通过溶胶-凝胶法制备了双羟基四配位硅/聚乙烯醇复合膜,并分析了膜的热性能,发现改性PVA复合膜的热性能有所降低;但膜的透明性和韧性基本没变;说明四配位硅水解后得到的硅醇基与PVA中的羟基发生了缩合作用.     

葡萄糖改性有机硼交联剂在水基聚乙烯醇压裂液中的应用

为验证聚乙烯醇作为水基冻胶压裂液的可行性,提出葡萄糖改性有机硼交联剂的压裂液体系.采用实验室自制葡萄糖改性有机硼交联剂,得出原料最佳配比n(硼砂):n(葡萄糖)=1∶1.5.葡萄糖改性有机硼交联剂对聚乙烯醇有很好的延时性和耐高温性,其交联时间可以控制在60～500 s之间,耐热温度在70℃左右.以聚乙烯醇为稠化剂的水基冻胶压裂液的最低有效浓度可达1.1%.     

No mixing of superconductivity and antiferromagnetism in a high-temperature superconductor

There is still no universally accepted theory of high-temperature superconductivity. Most models assume that doping creates 'holes' in the valence band of an insulating, antiferromagnetic 'parent' compound, and that antiferromagnetism and high-temperature superconductivity are intimately related. If their respective energies are nearly equal, strong antiferromagnetic fluctuations (temporally and spatially restricted antiferromagnetic domains) would be expected in the superconductive phase, and superconducting fluctuations would be expected in the antiferromagnetic phase; the two states should 'mix' over an extended length scale. Here we report that one-unit-cell-thick antiferromagnetic La2CuO4 barrier layers remain highly insulating and completely block a supercurrent; the characteristic decay length is 1 A, indicating that the two phases do not mix. We likewise found that isolated one-unit-cell-thick layers of La1.85Sr0.15CuO4 remain superconducting. The latter further implies that, on doping, new electronic states are created near the middle of the bandgap. These two findings are in conflict with most proposed models, with a few notable exceptions that include postulated spin-charge separation.     

Unconventional superconductivity in PuCoGa5

In the Bardeen-Cooper-Schrieffer theory of superconductivity, electrons form (Cooper) pairs through an interaction mediated by vibrations in the underlying crystal structure. Like lattice vibrations, antiferromagnetic fluctuations can also produce an attractive interaction creating Cooper pairs, though with spin and angular momentum properties different from those of conventional superconductors. Such interactions have been implicated for two disparate classes of materials--the copper oxides and a set of Ce- and U-based compounds. But because their transition temperatures differ by nearly two orders of magnitude, this raises the question of whether a common pairing mechanism applies. PuCoGa5 has a transition temperature intermediate between those classes and therefore may bridge these extremes. Here we report measurements of the nuclear spin-lattice relaxation rate and Knight shift in PuCoGa5, which demonstrate that it is an unconventional superconductor with properties as expected for antiferromagnetically mediated superconductivity. Scaling of the relaxation rates among all of these materials (a feature not exhibited by their Knight shifts) establishes antiferromagnetic fluctuations as a likely mechanism for their unconventional superconductivity and suggests that related classes of exotic superconductors may yet be discovered.     

Boosting superconductivity in organic-inorganic superlattices

Recently,great research efforts have been made to study the superconductivity in 2D systems,especially in 2D transitional metal dichalcogenide (TMD) materials [...     

有机薄膜电致发光器件的研究进展（综述）

对近几年来有机薄膜电致发光（ＥＬ）器件的研究进展进行了综合评停和分析,有机薄膜ＥＬ器件是近年来国际上研究的一个热点,该器件具有可与集成电路相匹配,直流电压低,发光亮度高,以及它与无机薄膜相比较易实现多色显示等优点。     

渗硼金刚石薄膜电极用于有机废水降解的实验

为了研究渗硼金刚石薄膜电极电化学性能以及用于含有机污染物的废水处理的可行性,采用循环电解的方法,对含苯酚的废水进行了电化学氧化实验,同时与活性涂层钛阳极进行了对比实验研究,考察了阴极的可替代性,最后用两种电极对含苯胺的工业废水进行了对比实验。实验结果表明,金刚石电极不仅具有优越的电化学性能和优异的电化学指标,而且可以用于电化学废水处理;同时,用钛电极代替金刚石作阴极经济可行。     

林产化工专业有机高分子合成创新教学探索

林产化工专业是应用性较强的专业,将理论教学与实验教学相结合,是实现创新人才培养目标的重要教学环节。针对有机高分子合成化学课程中存在的问题,结合林产化工专业发展的现状,为了深化教学改革,从添加最新的相关教学内容、引入科技研究前沿动态、采用现代教育理念,引导学生自主学习入手,并在观念上重视实验课程,进行实验课程改革,新开设了研究设计性实验课,考核评定上要合理灵活,才能使本科生有机高分子合成化学教学符合我国现有林产化工的发展趋势,为全面培养学生严谨的科学态度、良好的实验素质的创新能力提供新思路。