Soft organic and metal-organic frameworks with porous architecture: From wheel-and-axle to ladder-and-platform design of host molecules

The family of wheel-and-axle host molecules is reviewed and the approaches to the creation of new host geometries for supramolecular materials based on weaker interactions are discussed. The combination of bulky groups (or platforms) and spacers yields various host geometries including humming-top molecules (Werner complexes, metal dibenzoylmethanates and other bis-chelates, dimeric metal carboxylates and macrocyclic complexes), wheel-and-axle and dumb-bell shaped molecules and their modifications, ladder-and-platform, shish-kebab, multi-decker, stair-case and double-strand ladder-and-platform oligomeric and polymeric structures. The host shapes are compared with cyclic and trifoil (trityl) host types. The use of metal centers, chelating and macrocyclic ligands (β-diketones, carboxylic acids, Schiff bases, porphyrins, phthalocyanines, corroles, annulenes and their analogs), bridging ditopic ligands and other building elements in the engineering of host molecules is illustrated. The role of such factors as size and nuclearity of the platforms, rigidity/flexibility of the spacers and hydrogen bonding is discussed. The relation between porosity and packing efficiency, predisposition to self-inclusion, parallel alignment and interdigitation, dimensionality and secondary assembly of host molecules in the crystal is examined. Clathration and sorption abilities and other important qualities and functionalities of the new host materials are elucidated.     

熔体法生长大尺寸有机晶体

大尺寸有机晶体在太赫兹波产生、中子探测、微波激射等多个关系国计民生、涉及国家安全的领域具有重要应用前景。但大尺寸有机单晶生长一直是国际公认的难题,无论是在生长理论、生长方法还是生长设备方面都远远落后,在整个人工晶体领域相对小众;而且有机晶体硬度低、脆性高、易解理等本征特性为加工和后期应用带来了很多困难,制约了相关领域的发展。有机分子晶体的物化性质决定了其生长方法多采用溶液或气相方法,熔体生长方法在结晶质量控制方面难度更大;但针对上述应用所需的大尺寸单晶和掺杂要求,熔体生长方法相比溶液和气相方法更具优势。本文对熔体法生长大尺寸有机晶体进行分类总结,对影响生长过程和晶体质量的原料提纯、籽晶生长、安瓿设计、固液界面控制、生长及降温速度调控、加热温区等因素进行分析,结合本课题组近年来利用熔体法生长大尺寸有机晶体的实际经验,旨在为大尺寸有机晶体的生长研究提供理论基础和实践经验,突破高质量、大尺寸有机单晶生长的国际难题。     

硒化铟材料的发展及其光电器件应用

自2004年发现石墨烯以来,二维材料以其丰富的带隙结构、独特的光电特性和无悬挂键的范德瓦耳斯表面等,极大地拓宽了半导体电子、光电子器件的设计维度。其中二维硒化铟材料成为最具竞争力的未来高迁移率光电子器件用候选材料,被诺贝尔奖获得者Andre Geim认为是“硅和石墨烯的‘黄金分割点’”。但人们对二维硒化铟材料的研究仅有不到十年的时间,对其制备及应用的认识仍然不足。本文综述了二维硒化铟材料及其光电器件的研究现状。另外,考虑到目前绝大多数二维硒化铟材料的研究是基于块状单晶体材料的机械剥离开始的,因此本文首先回顾了硒化铟晶体结构的认识及其制备方法的发展历程,在此基础上综述了二维硒化铟材料制备及其性能表征的前沿研究结果,探讨了器件结构、材料制备方法等因素对二维硒化铟场效应晶体管和光探测器电学输运特性的影响,最后分析了未来硒化铟材料及器件应用面临的机遇与挑战。     

Methods for studying the coherent 4D structural dynamics of free molecules and condensed state of matter

Studies in the coupled 4D spatial and temporal continuum are necessary for understanding the dynamic features of molecular systems with a complex profile of the potential energy surface. The introduction of time sweep into diffraction methods and the development of principles for studying coherent processes have revealed new approaches to the analysis of the dynamics of wave packets, the intermediate products and the transition state of the reaction center, and short-lived compounds in gaseous and condensed media. The use of picosecond and femtosecond electron probe pulses, synchronized with excitation laser pulses, determined the development of ultrafast electron crystallography, time-resolved X-ray diffraction, and dynamic transmission electron microscopy (DTEM). One of the most promising applications of the developed diffraction methods is the characterization and visualization of the processes occurring upon the photoexcitation of free molecules and biological objects and the analysis of surface and thin films. The whole set of spectral and diffraction methods based on different physical principles, which are complementary and make it possible to perform the photoexcitation of nuclei and electrons and carry out diagnostics of their dynamics at ultrashort time sequences, reveal new possibilities for studies with the necessary integration of the “structure-dynamics-function” triad in chemistry, biology, and materials science.     

多孔硅制备研究进展及其在锂离子电池方面的应用

多孔硅具有比表面积大、发光性能良好等特点,目前对于多孔硅的研究已经涉及到生物与化学传感器、药物递送、光催化、能源等领域。多孔硅中的孔隙可有效缓解硅在锂化时的体积膨胀,缩短锂离子从电解液向硅本体扩散的距离,促进高电流密度下的充放电过程。因此,多孔硅在储能领域得到了广泛研究与发展。但是一些挑战仍然存在,如制备成本、刻蚀机理、多孔结构的调控、多孔硅的电化学性能等还不能满足商业化应用的要求。本文对目前国内外多孔硅制备方法的研究进行了综述,并详细介绍了多孔硅在锂离子电池领域的应用。最后,对多孔硅材料在储能领域的发展进行了展望。     

锂-二氧化碳电池关键材料的研究进展

可充式锂-二氧化碳电池为捕获CO₂和能量存储提供了一种新方法。尽管该技术从发展之初至今取得了很大进步,但它们在实际应用中还面临着许多限制和挑战。其中,在充放电机理方面的研究,虽然取得了显著的成就,但仍存在一些争议。目前,大部分的锂-二氧化碳电池研究在提高电池性能方面,主要针对的是阴极催化剂的制备,例如,碳基催化剂、贵金属基催化剂、过渡金属基催化剂、可溶性催化剂等。上述催化剂虽显著提高了电池性能,但少有同时满足价格低廉、制备方法简单和催化性能优异等优点的催化剂,这也是限制锂-二氧化碳电池走向实际应用的因素之一。由于锂-二氧化碳电池属于半开放式系统,液态电解液存在泄露、蒸发和锂枝晶等问题,导致电池的安全性和性能的降低。采用准固态电解质可有效解决上述问题,并为柔性可穿戴锂-二氧化碳电池的实现提供了可能。本文归纳了锂-二氧化碳电池关键材料的研究进展,分别对锂-二氧化碳电池的充放电机理、阴极催化剂、准固态电解质和阳极锂保护四部分进行了介绍,对其发展的现状和面临的挑战以及未来发展的趋势作出了归纳和总结。为开发高效可逆的锂-二氧化碳电池提供参考。     

Arsenides-and related III-V materials-based multilayered structures for terahertz applications: Various designs and growth technology

The fabrication and investigation of single and multilayered structures have become an essential issue in the past decades since these structures directly define valuable properties and efficiency of widely used terahertz (THz) emitters and detectors. Since the development of molecular-beam epitaxy, as well as other crystal growth techniques, a variety of structural designs has appeared and has been proposed. Since that, an enormous progress has been achieved beginning from the pioneering work on photoconductivity in silicon toward different multilayered heterostructures. The last are now commonly utilized as base components in photoconductive THz emitters/detectors, quantum-cascade lasers for pulsed and continuous-wave THz spectroscopic and imaging systems providing critical fundamental and practical applications at the forefront of scientific knowledge (sensors, flexible electronics, security systems, biomedicine, and others). This review summarizes the developments in different approaches and crystal growth techniques, emphasizing the importance of using single and multilayered arsenides-and related III-V materials-based (phosphides, antimonides, bismuthides) structures to accomplish the needs of modern and existing instruments of THz science and technology.     

Transient analysis of the cooling process and influence of bottom insulation on the stress in the multicrystalline silicon ingot

Directional solidification is one of the most popular techniques for massive production of multicrystalline silicon. After growth and annealing, the ingot is cooled down by a designed cooling process, which is initialized by descending bottom insulation, and then is controlled both by power ramp‐down rate and by motion of the bottom insulation. Thermal stress is piled up during cooling, and associated crystal defects, such as dislocation and micro‐cracks, may generate and propagate in the ingot. In the paper, transient modeling is applied to study the effect of bottom insulation on the cooling process. Temperature, velocity and thermal stress fields are obtained with linear, parabolic and sinusoidal motions of the insulation. The measured and predicted temperatures at two points of the ingot are found consistent. Distributions of von Mises stress in the ingot at different cooling time are obtained, and the maximum von Mises stresses are presented as a function of the cooling time. Specifically, dislocation‐free regions, evaluated by the critical resolved shear stress model, at certain cooling time, and area fractions of the regions as a function of the cooling time are proposed. The linear motion is further discussed with different moving rates, considering its wide applications in the current industry and convenient realization in control.     

多铁性材料的应变调控

多铁性材料是一种同时具有铁电、铁弹、铁磁等两种或者两种以上“铁性”的材料,可以通过多种序参量的耦合产生新的效应,在电子信息、传感、存储、无线网络等领域具备广阔的应用前景。当前在室温下具有强磁电耦合效应的多铁性材料仍然是学者们研究的重点,但基于多铁材料的器件还没有实现应用。应变工程是一种可以有效影响多铁材料物理性质的调控手段,通过晶格与电子、自旋、轨道等的相互作用来影响材料的电、磁、光、声等物理特性,因此通过应变调控多铁性薄膜结构和性能,受到了研究人员的广泛关注。本文通过调研多铁性材料中应变工程的研究,总结了应变调控手段及其对材料物理性能的影响,期望为多铁性材料的研究和发展提供研究思路。     

硅基Ⅳ族SiGeSn三元合金晶格结构、电子结构和光学性质的第一性原理

SiGeSn三元合金由于具有较二元合金更大的晶格和能带性质调控范围,是当前用于制作硅基激光器的热点材料。为全面且精确地研究其晶格结构、电子结构和光学性质,本文采用基于密度泛函理论(DFT)的第一性原理方法,并结合准随机近似和杂化泛函带隙修正,首先研究SiGeSn晶格常数及其弯曲系数的变化规律,并给出了解决GeSn二元晶格失配和压应变问题的方案。其次比较研究了SiGeSn与GeSn合金的能带结构,并通过态密度计算分析了Si的引入对合金带隙变化的物理机制。最后比较研究了SiGeSn与GeSn合金的介电函数谱、吸收系数、消光系数、反射率、折射率和发射率等光学性质。结果表明,SiGeSn晶格常数弯曲系数的变化与合金电负性差值的变化规律一致,Si-p电子态是SiGeSn合金带隙变化的最主要贡献。相比于同Sn浓度的GeSn合金,SiGeSn能保持直接带隙特征,且其带隙值和光吸收波长呈现更宽的变化范围。因此在拓宽硅基高效光源和光电探测器应用波段方面,SiGeSn相较于GeSn合金具有更大的应用潜力和优势。     

4H碳化硅单晶中的位错

4H碳化硅(4H-SiC)单晶具有禁带宽度大、载流子迁移率高、热导率高和稳定性良好等优异特性,在高功率电力电子、射频/微波电子和量子信息等领域具有广阔的应用前景。经过多年的发展,6英寸(1英寸=2.54 cm)4H-SiC单晶衬底和同质外延薄膜已得到了产业化应用。然而,4H-SiC单晶中的总位错密度仍高达10³~10⁴ cm^-2,阻碍了4H-SiC单晶潜力的充分发挥。本文介绍了4H-SiC单晶中位错的主要类型,重点讲述4H-SiC单晶生长、衬底晶圆加工以及同质外延过程中位错的产生、转变和湮灭机理,并概述4H-SiC单晶中位错的表征方法,最后讲述了位错对4H-SiC单晶衬底和外延薄膜的性质,以及4H-SiC基功率器件性质的影响。     

Bowlics: history,advances and applications

There are three types of liquid crystals (LCs) in the world: rodics, discotics and bowlics, corresponding to one-, two- and three-dimensional molecules, respectively. The rodics were discovered by the Austrian, F. Reinitzer, in 1888 and is the material behind the LC display industry of $100 billion annually. The discotics were discovered by S. Chandrasekhar’s team in India, in 1977. The third type, bowlics, was proposed by a Chinese, LIN Lei (Lui LAM), in 1982 while working at the Institute of Physics, CAS, Beijing. Distinguished from the rodic and the discotic, a bowlic molecule breaks the up–down symmetry, and bowlic LCs are one of excellent candidates for switchable ferroelectrics with great potential applications in ultrahigh-density memory devices. The importance of strategic bowlic materials has recently attracted increasing attention of scientists from multiple disciplines and engineers from different backgrounds. In this review, the history of bowlics and their recent advances in molecular design, synthesis and applications are discussed.     

Glass foams: formation, transport properties, and heat, mass, and radiation transfer

Energy efficiency, environmental impact, and quality of the final product in glass manufacturing depend, to a large extent, on foams formed on the surface of the molten glass and of the batch due to entrapment of gas bubbles generated by the batch fusion and refining chemical reactions during the melting process. Hence, understanding the mechanisms of foam formation as well as development of theoretical models for thermophysical and transport properties and heat, mass, and radiation transfer in glass foams are not only a problem of significant fundamental interest but also of tremendous practical impact. In this paper, the review of the current state-of-the-art in our understanding of glass foams is provided, including some of our recent results in modeling the dynamics of the foam growth and its steady-state thickness, prediction of gas diffusion through glass foams, and thermal radiative properties of glass foams. In addition, the new results on simulation of combined conduction and radiation heat transfer in glass foams and radiative transfer in primary (batch) foams are presented and discussed in some detail. The paper also presents practical means available for reducing foaming in glass melting and concludes with the discussion of unresolved problems and summary of the directions for the future work in the area.     

半导体辐射探测材料与器件研究进展

自从1895年伦琴发现X射线以来,辐射探测技术快速发展,被广泛应用于医疗影像、安检安防、工业无损检测、核安全监测、资源勘探、基础科学和空间科学等诸多领域。从探测材料和工作原理划分,辐射探测器主要可分为气体探测器、闪烁体探测器和半导体探测器。本文从各类射线与半导体材料的相互作用以及半导体探测器工作原理和信号处理过程入手,探讨了不同辐射类型、不同应用需求对半导体辐射探测器的性能要求以及探测器设计要点,并按照元素族序的顺序对半导体材料在辐射探测领域的性能表现和研究进展进行了综述。     

TGA-CdTe量子点在荧光探针方面应用

以巯基乙酸(TGA)为稳定剂,在加热回流氮气保护条件下制备CdTe量子点,用荧光分光光度计、透射电子显微镜和X射线粉末衍射仪对CdTe量子点进行表征.以该量子点为荧光探针,完善荧光淬灭法测定Cu2+、Hg2和Ag+等重金属离子的方法.考察缓冲溶液的pH值、反应时间、量子点浓度、量子点的稳定性和干扰离子等多种因素对重金属离子测定的影响.在pH值为6.2的三羟甲基氨基甲烷(tris)-盐酸缓冲溶液中,当量子点的浓度为4.2×10-2 μg/L和反应时间为30 min时,测得Cu2、Hg2+和Ag+的线性区间分别为2.3 ～250 μg、3.2～300 μg和4.3～ 150μg,检测下限分别为0.28 μg/L、0.53 μg/L和0.35 μg/L.并发现只有当所测量的重金属离子能与所采用的量子点能生成更难溶于水的沉淀才能引起量子点的荧光淬火,从而可以对此类重金属离子进行定量检测.     

阴离子掺杂钨酸铅晶体的生长与发光性能研究

本文报道了阴离子F~-, Cl~-, I~- 和S~(2-)掺杂的PbWO_4晶体的生长与发光性能.通过对掺杂PbWO_4晶体的X射线粉末衍射、紫外可见区的透过光谱、光致激发、光产额和发光衰减特性进行了测试表征,结果表明:F~-掺杂能使PbWO_4晶体在短波方向的透过率明显提高,显著提高PbWO_4晶体的发光强度,但增加的发光强度主要来自于慢发光的贡献.而随着掺杂阴离子半径和电荷数的增加,PbWO_4晶体的发光强度逐渐降低,并且PbWO_4晶体吸收截止边逐渐向长波方向移动.     

Structural characteristics of peroxo complexes of group IV and V transition metals. Review

Structural characteristics of peroxo complexes of transition metals of Groups IV and V (Ti, V, Nb, and Ta) with the ratios M: O₂ = 1: 1, 1: 2, 1: 3, and 1: 4 and alkyl peroxo complexes of Ti, Hf, and V have been considered. The structural manifestation of the trans effect of η²-coordinated peroxo ligand in pseudooctahedral Ti, Nb, and V monoperoxo complexes is characterized. The structural manifestations of the trans effect of multiply bonded peroxo and oxo ligands in monooxomonoperoxo complexes of vanadium(V) are compared.     

化学气相沉积(CVD)金刚石研究现状和发展趋势

化学气相沉积(CVD)技术的发展使得金刚石优异的综合性能得以充分发挥,在诸多领域获得应用,并有可能实现跨越式的发展。色心使得金刚石量子加速器初步显示了巨大可行性,包括紫外激光写入窗口等诸多应用场景将金刚石的光、电、热和力学综合优势发挥到了极致,超宽禁带金刚石半导体应用将很快实现,金刚石的散热应用也在不断拓展。本文在总结CVD金刚石的制备方法和性能特点的基础上,根据金刚石的本征特点和应用领域,将其分为量子级、电子级、光学级、热学级和力学级五类,对各类金刚石的研究和应用状况进行了详细阐述,进一步明晰CVD金刚石目前的发展状态,对研判其未来发展趋势有重要意义。     

Epitaxial growth of ZnO films

After summing up the main physical properties of ZnO and its subsequent applications the aim of this article is to review the growth of ZnO epitaxial films by PLD, MBE, MOCVD and sputtering under their various aspects, substrates, precursors, reaction chemistry, assessment of the layers etc. …, keeping constantly in mind some key issues for the device applications of ZnO in optoelectronics, surface acoustic filters and spintronics, amongst which the growth of high quality epitaxial layers of both n- or p-type conductivity, the possibility of dissolving transition elements in the layers, the growth of ZnO related alloys and heterostructures are of major significance.     

Theoretical and experimental study of excess quantities in glass-forming systems

The present work deals with the correlation among a macroscopic quantity, i.e. kinematic viscosity, and some microscopic quantities, namely the mean-square displacement and the free volume. In primis, some definitions of ‘fragility’, a quantity which allows to rank different liquids on the basis of the temperature dependence of kinematic and/or thermodynamic quantities, are recalled. Successively, the temperature dependence of viscosity, mean-square displacement and free volume is taken into account for three glass-forming systems and is analyzed in order to highlight the linear relationships between the logarithm of viscosity and the excess mean-square displacement and between the logarithm of viscosity and the excess free volume. Finally, on the basis of the observed correlations, two ‘fragility’ parameters, operatively evaluated by elastic neutron scattering and positron annihilation lifetime spectroscopy, are discussed and compared.