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Observation of inhomogeneous plasmonic field distribution in a nanocavity
Get PDF等离激元材料和器件中电场的强度分布是等离激元技术及其应用的重要基础。虽然针尖增强光谱成像技术的发展已经实现了亚纳米的横向空间分辨率，并发现了亚纳米级电场的不均匀性，但是迄今人们对电场的纵向场强分布仍然知之甚少。李剑锋教授课题组设计了一种具有~2Å空间分辨率的分子尺，利用金单晶基底和壳层隔绝金纳米粒子来构筑等离激元纳米腔，并通过分子尺的拉曼信号强度，精准地直接表征纳米腔中的纵轴方向上高度不均匀的场强分布。中国科学技术大学罗毅教授课题组利用基于量子场论的局域场光谱理论，精确地模拟得到了与实验相符的等离激元纳腔中的场分布，并发现了因分子自聚焦作用而引起的“等离激元梳”。该工作提供了一种通用有效的定量表征纳腔中场强分布的方法，完善了对等离激元学基础的理解，为超高空间分辨的拉曼光谱成像、光学力调控分子组装、单分子反应操控提供指导。
该工作是在李剑锋教授和中国科学技术大学罗毅教授共同指导下完成的。实验部分主要由李超禹（论文第一作者，已毕业博士）、温宝英（在读博士）、李松波（已毕业硕士）完成，复旦大学段赛研究员（论文共同第一作者）和陈舒（已毕业博士）进行了局域场光谱理论计算。谢立强（已毕业博士）和毛秉伟教授帮助完成了扫描探针显微镜实验。浙江师范大学周小顺教授和王亚浩老师提供了自组装膜表征方面的重要帮助。印度的Kathiresan、叶龙武教授课题组和浙江大学陆展教授课题组在分子合成方面提供了重要帮助。瑞士伯尔尼大学Wandlowski教授和田中群教授为该工作提供了指导。【Abstract】The progress of plasmon-based technologies relies on an understanding of the properties of the enhanced electromagnetic fields generated by the coupling nanostrucutres.Plasmon-enhanced applications include advanced spectroscopies, optomechanics, optomagnetics and biosensing. However, precise determination of plasmon field intensity distribution within a nanogap remains challenging. Here, we demonstrate a molecular ruler made from a set of viologen-based, self-assembly monolayers with which we precisely measures field distribution within a plasmon nanocavity with ~2-Å spatial resolution. We observed an unusually large plasmon field intensity inhomogeneity that we attribute to the formation of a plasmonic comb in the nanocavity. As a consequence, we posit that the generally adopted continuous media approximation for molecular monolayers should be used carefully.The progress of plasmon-based technologies relies on an understanding of the properties of the enhanced electromagnetic fields generated by the coupling nanostrucutres1,2,3,4,5,6. Plasmon-enhanced applications include advanced spectroscopies7,8,9,10, optomechanics11, optomagnetics12 and biosensing13,14,15,16,17. However, precise determination of plasmon field intensity distribution within a nanogap remains challenging. Here, we demonstrate a molecular ruler made from a set of viologen-based, self-assembly monolayers with which we precisely measures field distribution within a plasmon nanocavity with ~2-Å spatial resolution. We observed an unusually large plasmon field intensity inhomogeneity that we attribute to the formation of a plasmonic comb in the nanocavity. As a consequence, we posit that the generally adopted continuous media approximation for molecular monolayers should be used carefully.The Swedish National Infrastructure for Computing is acknowledged for computer time. S.D. is sponsored by Shanghai Pujiang Programme (grant no. 19PJ1400600).
该研究工作得到国家自然科学基金、国家重点研发计划、安徽省量子信息技术引导专项等的资助和支持
Electrochemical Performance Improvement of Li2MnO3 Cathode Materials by MgF2 Coating
No full textLi2MnO3正极材料具有较高的理论容量（459 mAh·g -1）,不仅安全无毒还能够大大降低电池的制造成本,从而受到越来越多的关注. 然而,较低的首圈库仑效率和较差的循环性能妨碍了其在锂电池中的实际应用. 在此,作者研究了MgF2涂层对Li2MnO3正极材料的电化学性能. 结果表明,MgF2涂层诱导部分层状Li2MnO3向尖晶石相转化,从而降低了首圈不可逆容量,提高库仑效率. 重量比为0.5%、1.0%和2.0%的MgF2涂层电极的初始库仑效率分别为70.1%、77.5%和84.9%,而原始电极仅为57.7%. 充放电曲线表明,1.0wt.%MgF2涂层改性的Li2MnO3具有最高的充放电容量和最佳的循环稳定性. 40个循环后1.0wt.%MgF2涂层样品的容量保持率为81%,远高于原始样品的容量保持率（53.6%）. 电化学阻抗谱结果表明MgF2涂层减少了不利成分的快速沉积,并改善了电极的循环稳定性.Cathode material Li2MnO3 has received more and more attention owing to its high theoretical capacity (459 mAh·g -1). However, the low initial coulombic efficiency and the poor cycle stability hamper its practical application in lithium-ion batteries. Herein, we investigated the crystal structure and electrochemical performance of Li2MnO3 by introducing MgF2 coating layer. The results indicated that the conversion of partial layer Li2MnO3 to spinel phase induced by MgF2 coating could reduce the initial irreversible capacity and improve the first cycle efficiency. The initial coulombic efficiencies of the 0.5wt.%, 1.0wt.%, and 2.0wt.% MgF2-coated electrodes were 70.1%, 77.5% and 84.9%, respectively, compared with 57.7% of the pristine cathode. The charge-discharge curves showed that the 1.0wt.% MgF2-modified Li2MnO3 delivered the highest charge and discharge capacities, and exhibited the best cycle stability. The capacity retention rate of the 1.0wt.% MgF2-coated sample was 81% after the 40th cycles, which was much higher than that of the pristine sample (53.6%). The electrochemical impedance spectroscopic data revealed that the MgF2 coating reduced the rapid deposition of the resistive component and improved the cycle stability of the electrodes.通讯作者:陈康华E-mail:[email protected]:CHENKang-huaE-mail:[email protected]. 中南大学轻合金研究院,湖南 长沙 4100832. 中南大学粉末冶金研究院,湖南 长沙 4100831. Light Alloy Research Institute, Central South University, Changsha 410083, Hunan, China2. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, Hunan, Chin
Recent Progress on Enhancing Effect of Nanosized Metals for Electrochemical CO2 Reduction
No full text将二氧化碳通过电化学方法转化为化工原料再利用,不仅可以有效缓减温室效应,而且可以实现自然界的碳循环,对绿色化学与可持续发展意义重大. 本文简要地介绍了二氧化碳电还原的优势及其基本反应原理并综述了近年来基于纳米金属催化剂的一系列活性增强策略的研究进展. 重点探究了合金效应、界面工程、协同效应、缺陷工程以及载体效应等对纳米金属电催化还原二氧化碳性能的影响及相关反应机理. 基于以上策略,提出未来开发面向工业化应用的二氧化碳电还原催化剂面临的挑战与前景.The electrochemical conversion of CO2 to chemical raw material for further utilization shows promising future to alleviate global warming and realize carbon cycle in nature, which is of great significance to the green chemistry and sustainable development. This review briefly introduces the advantages of CO2 electrochemical reduction (CO2ER) and its basic reaction principles, and summarizes the recent progress in a series of activity enhancement strategies based on nanosized metal catalysts. The influences of alloy effect, interface engineering, synergistic effect, surface defect engineering and support effect on the catalytic performance of nanosized metals for CO2ER and the related reaction mechanisms are mainly reviewed. Based on the above strategy, the challenges and prospects for the future development of CO2ER catalysts for industrial applications are proposed.国家自然科学基金项目资助(21972042)通讯作者:钮东方,张新胜E-mail:[email protected];[email protected]:NIUDong-fang,ZHANGXin-shengE-mail:[email protected];[email protected]华东理工大学化工学院,化学工程联合国家重点实验室,上海 200237State Key Laboratory of Chemical Engineering, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, Chin
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No full text厦门大学化学化工学院College of Chemistry and Chemical Engineering, Xiamen Universit
Identifying the Conformational Isomers of Single-Molecule Cyclohexane at Room Temperature
Get PDF构象异构是化学中的基本问题。然而对于环己烷等柔性分子，由于其在室温下极快的互变异构过程，基于系综的表征方法（如核磁等）只能得到所有构象平均贡献的结果。为了应对这一挑战，化学化工学院洪文晶教授与夏海平教授课题组为在室温条件下对柔性分子构象的定量分析与表征这一挑战，课题组成功实现了在室温条件下对环己烷两种椅式构象的电学表征与比例识别。同时，通过纳米电极间隙对分子的限域作用，发现在宏观尺度下极不稳定的扭船式中间体得以在单分子尺度稳定存在，这为不稳定中间体的研究提供了重要表征方法。
这一研究工作是在化学化工学院洪文晶教授、夏海平教授共同指导下完成的，iChEM直博生唐淳与化工系研究生唐永翔为论文共同第一作者。师佳副教授与刘俊扬副研究员为该工作提供了指导，博士后陈志昕、博士研究生陈李珏以及研究生叶艺玲、严哲玮、张珑漪共同参与了该工作。【Abstract】Isomerism reflects the ubiquitous nature that molecules with the same molecular formula show different structures. The interconversion between conformational isomers of flexible molecules is quite fast owing to the low barriers of around 10 kcal mol−1, leading to average signal contributed by all the possible isomers characterized by ensemble methods. On this account, identifying the conformational isomers of flexible molecules at room temperature has a substantial challenge. Here, we develop a single-molecule approach to identify the conformational isomers of cyclohexane at room temperature through the single-molecule electrical characterization. By noise analysis and feature extraction of the conductance of single-molecule junctions, we quantificationally identified two chair isomers of cyclohexane at room temperature, while such identification is only feasible at low temperatures by ensemble characterization. The strategy to apply the single-molecule approach to identify conformational isomers paves the avenue to investigate the isomerization of flexible molecules beyond the ensemble methods.This work was supported by the National Natural Science Foundation of China (nos, 21722305, 21673195, 21703188, and U1705254), the National Key R&D Program of China (2017YFA0204902), China Postdoctoral Science Foundation (no. 2017M622060), and the Fundamental Research Funds for Xiamen University (20720190002).该工作获得了科技部国家重点研发计划、国家自然科学基金等项目的资助，也得到了固体表面物理化学国家重点实验室、能源材料化学协同创新中心的支持
Research Progress of High-Safety Phosphorus-Based Electrolyte
No full text随着锂离子电池的市场拓展,安全性问题已成为电动汽车、大规模储能等应用领域关注的首要问题. 目前商品化的锂离子电池普遍采用低沸点碳酸酯类电解液,其易燃性成为电池不安全性的主要隐患. 为了提高锂离子电池的本征安全性,阻燃或不燃性电解液成为近年来研究的热点,其中以磷酸酯为溶剂的阻燃型或不燃型电解液受到广泛关注. 本文主要介绍磷酸酯阻燃和不燃电解液的研究状况,分析了这类电解液与锂离子电池正负极的兼容性问题,讨论了改善磷酸酯电解液电化学兼容性的途径,提出了发展高效、安全、稳定的不燃电解液的一些思路.Lithium-ion batteries (LIBs) have emerged as the most widely used energy storage devices owing to their high energy density and excellent cycling stability. However, safety issues have become a critical obstacle for the large-scale applications of LIBs in the energy storage systems and electric vehicles (EVs). Currently, LIBs use a low flash- and boiling-point organic carbonate as the electrolyte, which is extremely likely to cause firing or explosion. Although some flame-retardant additives can inhibit the combustion of electrolyte to a certain extent, it brings little effect in practical application. Therefore, the development of nonflammable electrolytes is an essential solution to eliminate the safety hazards of LIBs. The phosphorus-based electrolytes seem to be a good choice for flame-retardant or nonflammable electrolytes because of their low viscosity, high solubility, and low cost. In this paper, the problems and solutions of phosphate-based solvents as a safe electrolyte for LIBs are reviewed. Firstly, the feasibility and existing problems of phosphate ester as a solvent of electrolyte are introduced, and then the flame-retardant mechanism, flame-retardant or nonflammable phosphorus-based electrolytes are described by classifications, with emphasis on the electrochemical compatibility of such an electrolyte and its countermeasures. On this basis, we prospect the future research directions in high safety phosphorus-based electrolytes.国家重点研发计划课题(2016YFB000200);国家自然科学基金(21972108)通讯作者:曹余良E-mail:[email protected]:CAOYu-liangE-mail:[email protected]武汉大学化学与分子科学学院,湖北 武汉 430072College of Chemistry and Molecular Science, Wuhan University, Xiamen University,Wuhan 430072, Hubei, Chin
The Research of the Particularity of the Higher Education System in China
No full text邬大光，厦门大学教育研究院教授、博士生导师，教育学博士。【中文摘要】高等教育学是我国人文社会科学领域最年轻的学科之一，也是一个较为特殊的学科。厘清高等教育学产生的历史背景，反思高等教育学形成与发展的基本特征，对认识高等教育学的“特殊性”以及建构具有本土特色和国际影响的理论体系具有重要意义。构建具有中国特色的高等教育学，需要在分析我国高等教育学产生和发展“特殊性”的基础上，深入研究高等教育学学科体系的特殊性、高等教育学学术体系的特殊性和高等教育学话语体系的特殊性。
【Abstract】Higher education is one of the youngest disciplines in the field of humanities and social sciences in China，and it is also a relatively special academic discipline. The development of humanities and social sciences in our country is about to enter an era in which disciplinary，academic and discourse systems with national characteristics will be built. To clarify the historical background of the emergence of higher education and to reflect on the basic characteristics of the formation and development of higher education is of great significance for understanding the “particularity” of higher education and for constructing a theoretical system with national characteristics and international influence. To construct higher education with Chinese characteristics，we need to recognize the “particularities”of the emergence and development of higher education in our country，as well as the particularities of the disciplinary，academic and discourse systems
Literary Research in Digital Humanities:Based on a Comparison between English and Chinese Classical Literatures
No full text李天，厦门大学中文系讲师，文学博士。【中文摘要】从早期人文计算的单纯量化研究，到数字人文背景下跨学科的研究视野，文学研究随着数字技术的发展不断呈现出新的态势。由于语言和文化的差异，数字人文在英语古典文学和中国古典文学的研究中呈现出不同的发展倾向。在英语古典文学研究中，文学数据库的庞大与检索技术的成熟，使其研究方法突破传统的风格辨析与著作权判断，呈现出多样化与大跨度的特性，并能与读者接受结合，发展出互联网时代特色。中国古典文学也显现出跨学科（如GIS等）特性，但受制于语言契合度与技术发展，在研究方法上仍有待开拓。
【Abstract】From the purely quantitative research in early humanities computing to the interdisciplinary research perspective in digital humanities，literary research has taken on new characteristics with the advancement of digital technology. Because of the difference between languages，digital humanities in English and Chinese classical literatures have different development trends.In the research of English classical literature，these massive literary databases and the maturity of retrieval techniques enable research methods to break through the traditional judgement of style and authorship，exhibiting the characteristics of diversity and large spans. By integrating readers’reception，it has acquired an Internet feature. The research of Chinese classical literature also displays an interdisciplinary feature like GIS ；nevertheless，confined by language fitness and technique，its research methods call for further development.国家社会科学基金重大项目“新时代中国特色美学基本理论问题研究” (18VXK010)；中央高校基本科研业务费专项资金资助项目“后现代语境下的影像美学研究”（ZK1112);教育部人文社会科学研究规划基金“3R视角下视觉艺术的媒介与观念研究”（19YJCZH086
Solving Euler equations via two-stage nonparametric penalized splines
Get PDF动态随机一般均衡（DSGE）和资本资产定价模型是近年来在宏观经济学和宏观金融市场研究中广泛采用的模型方法。DSGE模型要求对未知政策函数（比如价格红利比率等）进行计算求解，从而得到模型结论和政策建言。然而，现有的经济、金融文献大多在金融数据服从某些特定概率分布的假设下，依赖数值方法来对DSGE模型做近似求解，而这会带来模型误设和近似误差问题。这种模型误设和近似误差可能会严重影响到求解动态均衡结果的有效性和可信度。该文首次提出运用非参数估计方法对DSGE模型中的政策函数进行求解，从而替代传统的近似求解法，这克服了过去文献存在的模型误设和近似误差的问题。该文是洪永淼教授牵头，以厦门大学为依托单位，联合中国科学院数学与系统科学研究院共同立项的“计量建模与经济政策研究”国家自然科学基础科学中心项目的阶段性成果。【Abstract】This study proposes a novel estimation-based approach to solving asset pricing models for both stationary and time-varying observations. Our method is robust to misspecification errors while inheriting a closed-form solution. By representing the Euler equation into a well-posed integral equation of the second kind, we propose a penalized twostage nonparametric estimation method and establish its optimal convergence under mild conditions. With the merit of penalized splines, our estimate is less sensitive to the spline setting and we also design a fast data-driven algorithm to effectively tune the key smoother, i.e. the penalty amount. Our approach exhibits excellent finite sample performance. Using the US data from 1947 to 2017, we reinvestigate the return
predictability and find that the estimated implied dividend yield significantly predicts lower future cash flows and higher interest rates at short horizons.Hong's research is supported by National Science Foundation of China (NSFC) (No. 71988101), which is the Basic Scientific Center Project entitled as Econometric Modelling and Economic Policy Studies. Cui’s research is supported by the Research Grants Council of Hong Kong, China (No. 11500119 and 21504818) and NSFC (No. 71803166). Li’s research is supported by NSFC (No. 71571154 and No. 71631004)
Liquid Metal Electrodes for Electrochemical Energy Storage Technologies
No full text液态金属电极电导率高,电极界面容易构建,在充放电过程中可有效避免电极结构形变、枝晶生长等问题,在储能电池领域具有重要应用价值. 本文主要讨论了液态金属电极在液态金属电池、钠硫电池和ZEBRA电池中的应用进展,重点介绍了液态金属电池关键材料体系、充放电机制及电池构型等,评述了液态金属电极储能应用中涉及的熔盐电解质、固态陶瓷隔膜、多场影响因素等方面的重要研究进展,分析了高温密封、腐蚀防护等关键问题,明确了液态金属电极在储能电池应用中的发展方向.Electrochemical energy storage technologies (ESTs) with low cost, long lifespan and high safety are of great importance for efficient integration of renewable energy into the grid. Liquid metal electrodes (LMEs) possessing the merits of high electronic conductivity, easy manufacture and amorphous structure is of great application value in the field of energy storage batteries. During charge-discharge processing, the LMEs could avoid the issues of structural deformation and dendrite growth in solid metal electrodes, which could effectively extend the cycle life of the LME based batteries. Moreover, LME based batteries are easy to be scaled up and less expensive, which are well-positioned to satisfy the demands of grid-scale energy storage. In this paper, the state-of-the-art overview of LMEs in batteries including liquid metal batteries (LMBs), sodium-sulfur (Na||S) and ZEBRA (Na||NiCl2) batteries is presented. The materials systems, reaction mechanisms and novel designing in LMBs are emphatically discussed. Besides the LMEs, the developments of the molten salts electrolytes and solid state electrolytes, and the multi-field coupled flows inside LMBs are summarized. The challenges for the applications of LMEs in the batteries, such as high temperature sealing and corrosion, are discussed. Finally, the prospects of the application of LMEs in the field of the ESTs are also described.国家重点研发计划(2018YFB0905600);国家自然科学基金项目(U1766216);国家自然科学基金项目(51774148);国家自然科学基金项目(51804128)通讯作者:蒋凯E-mail:[email protected]:JIANGKaiE-mail:[email protected].华中科技大学电气与电子工程学院,湖北 武汉 4300742.华中科技大学材料科学与工程学院,湖北 武汉 4300741. School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China2. School of Materials Science and Engineering Huazhong University of Science and Technology, Wuhan, 430074, Chin