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.     

SiO2 gel-glasses prepared from alkoxide, colloidal and amine-silicate solutions, a comparison

Silica gels were prepared by the alkoxide, collidal and amine-silicate methods. The obtained gels and glasses were characterized by density and Vickers microhardness measurements, thermal analysis and Raman spectroscopy. Differences in physical properties and in the behavior during thermal treatment are discussed and related to the process chemistry and the structure of the products.     

晶体形态一些基本概念的实际意义分析

本文对晶体学中关于晶体形态一些古老的基本概念(单形的正形与负形、左形与右形、一般形与特殊形)进行了深入思考,并从实际晶体形态上发育这些单形的角度,分析了它们的本质区别与内在含义:单形的正形与负形是属于同一几何单形、同一对称型(点群)的两个结晶单形,它们可以相聚;单形的左形与右形也是属于同一几何单形、同一对称型(点群)的两个结晶单形,但它们却具有不同的内部结构,所以它们不能够相聚;单形的一般形与特殊形只有结晶单形意义,无几何单形意义.这些认识阐明了过去我们多年来并没有足够重视的一些理论与实际问题,这有助于晶体形态对称理论的发展,也有助于晶体学教学思路的明确.     

MOMBE GaAs and AlGaAs for microelectronic devices

This paper reviews the state of the art of GaAs and AlGaAs materials and microelectronic devices grown by MOMBE (metalorganic molecular beam epitaxy) and related techniques. FET, HEMT and HBT devices have been grown using MOMBE and in the case of FETs and HBTs excellent device and MMIC power performance has been obtained. For example, MOMBE HBTs show current gains in excess of 100 and MMIC power HBT circuits are delivering 2 W of power at 8.5 GHz. We will examine device behavior and relate this to properties of the GaAs and AlGaAs materials.     

Specific physical and chemical properties of two modifications of poly(N-vinylcaprolcatam)

Two modifications of poly(N-vinylcaprolactam)—PVCL25 and PVCL40 (drying of a PVCL solution at 25 and 40°С, respectively)—as powdered films and their solutions were systematically investigated for the first time. Powders were studied by X-ray diffraction, IR spectroscopy, scanning electron microscopy, low-temperature krypton adsorption, and differential scanning calorimetry. Solutions were studied by smallangle X-ray scattering and dynamic light scattering. It was demonstrated that powders of PVCL25 and PVCL40 differ in the characteristics of the sub- and microstructure and in the water content and the solutions differ in the particle size. The relationships between the characteristics of the systems in the solid and liquid state and between the hydrodynamic diameter of PVCL particles in solution and their coagulation time were found.     

同质外延生长ZnO单晶结构及光电性能的研究

本文报道了同质外延生长氧化锌(ZnO)单晶在高温氧气气氛退火前后的结构及光电特性.利用化学气相输运(CVT)法生长了红棕色的ZnO单晶,且进行高温氧气气氛退火处理后的ZnO单晶呈现无色透明状.通过X射线衍射仪(XRD)、X射线光电子能谱(XPS)、能谱仪(EDS)和拉曼(Raman)光谱测试分析了高温氧气气氛退火前后的...     

Influence of morphology on in vitro compatibility of bioactive glasses

In vitro bioactivity and biocompatibility of fiber and bulk bioactive glasses were studied. After synthesis with tetraethoxysilane, individual bulk and fiber samples were soaked in a simulated body fluid solution and removed at intervals of 5 and 30 days, respectively. Fourier transform infrared spectroscopic analysis showed hydroxyapatite characteristic P–O vibrational bands for simulated body fluid soaked fibers and bulk samples. Osteoblast viability and alkaline phosphatase production were evaluated by cell incubation in the presence of samples and compared to controls. Fiber glass-incubated osteoblasts showed lower viability but the same alkaline phosphatase production when compared to bulk sample and controls.     

Glow curves of flux-grown NaMgF3 crystals

Glow curves and optical absorption spectra of X-irradiated flux grown crystals are studied. Two glow peaks at 370, 585 K and three shoulders at 420, 540 and 610 K are obtained. Optical absorption studies reveal two absorption bands at 405 and 475 nm and a well defined peak at 295 nm. Room temperature annealing and bleaching studies have suggested that the glow peaks at 370 and 585 K may correspond to impurities and F-centers of 295 nm band respectively. The other shoulders at 420, 540 and 610 K are attributed to other F-aggregate centers. The glow peaks are analysed using first order kinetics.     

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.     

Phase-field simulations of Te-precipitate morphology and evolution kinetics in Te-rich CdTe crystals

Te precipitates are one of principal defects that form during cooling of melt-grown CdTe or CZT crystals when grown Te-rich. Many factors such as the kinetic properties of intrinsic point defects (vacancy, interstitial, and antisite defects); stresses associated with the lattice mismatch between precipitate and matrix; temperature gradients and extended defects (dislocations, twin and grain boundaries); non-stoichiometric composition; thermal treatment history all affect the formation and growth/dissolution of Te precipitates in CdTe. A good understanding of these effects on Te precipitate evolution kinetics is technically important in order to optimize material processing and obtain high-quality crystals. This research develops a phase-field model capable of investigating the evolution of coherent Te precipitates in a Te-rich CdTe crystal undergoing cooling from the melt. Cd vacancies and Te interstitials are assumed to be the dominant diffusing species in the system, which is in two-phase equilibrium (matrix CdTe and liquid Te inclusion) at high temperatures and three-phase equilibrium (matrix CdTe, Te precipitate, and void) at low temperatures. Using available thermodynamic and kinetic data from experimental phase diagrams and thermodynamic calculations, the effects of Te interstitial and Cd vacancy mobility, cooling rates and stresses on Te precipitate, and void evolution kinetics are investigated.     

Amorphous polystyrene-block-polybutadiene and crystallizable polystyrene-block-(hydrogenated polybutadiene) solutions in compressible near critical propane and propylene – Hydrogenation effects

Polystyrene, polybutadiene, hydrogenated polybutadiene, and styrene diblock copolymers of these homopolymers can form homogenous solutions in compressible solvents, such as propane and propylene, which separate into two bulk phases upon reducing pressure. The cloud and micellization pressures for homopolymer and diblock copolymers are generally found to be higher in propane than in propylene, except for hydrogenated polybutadiene and polystyrene-block-(hydrogenated polybutadiene). Hydrogenated polybutadiene homopolymers and copolymers exhibit relatively pressure-independent crystallization and melting observed in both propane and propylene solutions.     

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。     

Nanoscale characterization of silica soots and aluminium solution doping in optical fibre fabrication

Visual and microanalytical studies have been made of the nanostructures and mechanisms involved in aluminium solution doping of silica soot generated by Modified Chemical Vapour Deposition used in the fabrication of silica optical fibres. Three aspects were studied – the nature of the soot particles, the structures in thermophoretically deposited soot layers and the way aluminium bonds to the surface of the soot particles. Soot particles were shown to be non-crystalline using both X-ray diffraction and electron diffraction. Particle size distributions, particle morphologies and deposited soot layer structures were characterised by electron microscopy and microprobe analysis. Atomic distributions of aluminium on surfaces of soot particles soaked in aluminium chloride solution were studied by high resolution transmission electron microscopy. The surface of solution doped particles was shown to have high aluminium content and nanoscale crystalline regions were identified amongst the mainly amorphous material. Soot layer structures and porosity were examined by electron and optical microscopy and distribution of the aluminium impregnation was mapped across the thickness of the deposited soot layer. Heterogeneous porosity distributions were observed and the effect of different types of pores, holes and cavities in the silica soot layer are discussed with regard to efficiency of deposition and solution doping.     

Studies of vapour transport reactions for III–V compounds

Although the III-V compounds and their alloys are increasingly important in the ever widening range of electronic and electro- optic devices, fundamental thermodynamic and chemical kinetic data for the chemical transport reactions used for their preparation is sparse, with few exceptions. The modified entrainment method developed by Faktor, Garrett and co-workers can be used to study chemical transport reactions and to obtain thermodynamic and chemical kinetic data. The direct analogy between the results of these experiments and corresponding crystal growth experiments is emphasised. Results from the systems GaAs-HCl, GaAs-HBr, AlAs-HBr, InSb-HCl, GaP-HBr, and InAs-HCl are discussed and used to illustrate the effects of competing transport reactions and the interplay between gas transport and surface reaction kinetics. Some of the pitfalls in simplistic calculations relating crystal growth rates to thermodynamic data are pointed out.     

Analysis of SiC crystal sublimation growth by fully coupled compressible multi-phase flow simulation

A fully coupled compressible multi-phase flow solver was developed to effectively design a large furnace for producing large-size SiC crystals. Compressible effect, convection and buoyancy effects, flow coupling between argon gas and species, and the Stefan effect are included. A small and experimental furnace is used to validate the solver. First, the essentiality of 2D flow calculation and the significance of incorporating buoyancy effect and gas convection, the Stefan effect, and flow interaction between argon gas and species were investigated by numerical results. Then the effects of argon gas on deposition rate, growth rate, graphitization on the powder source, and supersaturation and stoichiometry on the seed were analyzed. Finally, the advantages of an extra chamber design were explained, and improvement of growth rate was validated by the present solver.     

喷淋式MOCVD反应器中AlN的生长速率和化学反应路径的数值模拟研究

利用数值模拟方法,结合反应动力学和气体输运过程,研究喷淋式MOCVD反应器中AlN的生长速率和气相反应路径与反应前体流量(NH3和H2)、进口温度、压强、腔室高度等参数的关系.研究发现:薄膜生长前体和纳米粒子前体的浓度决定了不同的生长速率和气相反应路径.在低Ⅴ/Ⅲ比(2000)、高H2流量(12 L/min)、高进口温...     

Threshold switching and the on-state in non-crystalline chalcogenide semiconductors: An interpretation of threshold-switching research

Experimental research on chalcogenide glasses is reviewed and an interpretation concerning the cause of threshold switching and the basis of the low-impedance on-regime is presented. Observed behavior is consolidated in terms of a single conductivity mechanism and two conducting species governing the off- and on-state electrical characteristics. Phenomenological equations and their consequences are given which are shown to be capable of successfully describing both in functional form and accurate magnitude a very wide variety of experimental data including current — voltage transient characteristics, the Haberland condition, delay time, maximum allowable interruption times, rise and decay characteristics and negative capacitance. Recent research is presented concerning two types of non-thermal radiative emission during the on-regime of a threshold switching event. Various switching models are described and critically discussed in terms of the experimental data and phenomenological equations.     

Parity violation and parity conservation in unstirred crystallization: Effect of first crystals

Statistics of nucleation of chiral forms was studied to establish the effect of the number of first crystals and their handedness on distributions of enantiomers. Various bimodal, trimodal and unimodal distributions are obtained in unstirred crystallization, depending on the number of initial crystals and growth conditions. The binomial distribution satisfactorily describes experimental distributions of enantiomeric excess and may be used to predict distributions and probabilities of nucleation of enantiomers. The first nucleated crystals determine the handedness of secondary crystals, and number of initial crystals governs statistics of chiral nucleation. According to the binomial distribution if single crystals nucleate as the first, the bimodal distributions result with D and L peaks. If LD, LL, and DD pairs are nucleated as first, trimodal distributions with D, R, and L peaks are created, and if groups of crystals of various handedness nucleate as the first the unimodal distributions of enantiomeric excess with racemate R peaks are formed. Chiral nucleation experiments on sodium bromate were the basis for the theoretical considerations and verifications of predictions resulting from binomial distributions on probabilities of the creation of L and D crystals, and racemates, and the presence of D, L, and R peaks in the distributions. Growth conditions affect the number of the first crystals and effectiveness of cloning, and as a result, the distributions of enantiomers. Formation of pure enantiomers and/or racemates proves that the conservation of chiral symmetry, and the breakage of chiral symmetry can occur in unstirred crystallization. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

退役三元锂离子电池正极材料高效清洁回收技术研究进展

锂离子电池因其能量密度高、循环性能好、自放电低等优势在各个领域得到了广泛的应用.近年来,退役三元锂离子电池数量急剧增长,从保护环境和节约资源的角度来看,开展退役锂离子电池回收再生工艺研究是必要的.本文综述了退役三元锂离子电池回收再生技术的研究现状,指出对衰减程度不同的锂电池正极材料需采取灵活的梯级回收工艺路线,并详细介...     

Growth and Optical Absorption of Photorefractive Bi12SiO20 Crystals Doped with Zn and Cd and Co-doped with P

Single crystals of Bi₁₂SiO₂₀ (BSO) Zn- and Cd-doped and co-doped with P have been grown by Czochralski technique and optimum conditions for producing optically homogeneous crystals were established. The transmission and reflection spectra have been measured in the range 0.38–0.85 μm and absorption coefficients have been determined. The Zn dopants have been found to bleach the crystals and decrease the transmission shoulder, whereas Cd dopant increases the absorption and makes the shoulder well pronounced. P-doping strongly decreases the transmission shoulder and shifts absorption to shorter wavelengths. The absorption Coefficient of BSO doped with P has been found to decrease with dopant concentration increase up to 3 mol% P and above it increases with P concentration in the whole studied range. Zn + P- and Cd + P-co-doping (P concentration in the crystal less than 3 mol%) decreases strongly the absorption coefficient and shifts the spectra to short wavelengths.