Crystal habit prediction ‐ Including the liquid as well as the solid side

Commercially available methods of morphology prediction utilize molecular dynamics to estimate the crystal growth rates but predominantly consider the solid side. For the extension of these methods to a multi‐component solid‐liquid system the diffusion coefficient is required. Since, the diffusion coefficient enables the calculation of crystal growth rates and the morphology in presence of additives and solvents. Modeling the diffusion coefficient is achieved by conducting MD on a system consisting of the crystal surface and the liquid phase. The achieved results match very well with the calculated diffusion coefficient (Wilke‐Chang). In this case study benzoic acid is used as model substance with water as solvent.     

On the equilibrium crystal habit as predicted by the Gibbs-Curie principle

It is pointed out that there is no physical mechanism for the change, dictated by the Gibbs-Curie principle, from a nonequilibrium habit of a macroscopic faceted crystal to the equilibrium habit. The reason why this principle is inapplicable to such a crystal is established.     

缓冲层ZnPc对有机电致发光器件特性的影响

本文研究了酞菁锌(ZnPc)薄膜的表面形貌及ZnPc薄膜作为缓冲层对有机电致发光器件(OLEDs)光电特性的影响.对比两组样品的AFM图像,ZnPc薄膜相比于ITO薄膜,其表面的岛面积较大,薄膜表面更连续平整,基本上覆盖了ITO膜表面针孔,减少了表面的缺陷.另外,ZnPc薄膜的岛分布均匀有序.使用ZnPc作为缓冲层的器件性能明显好于未使用ZnPc修饰的器件,在7.42V的驱动电压下的最大发光亮度达到1.428kcd/m2,在4.3V电压驱动下时,最大光功率效率为1.411m/W;而未使用缓冲层的器件在8V的驱动电压下达到最大发光亮度达到1.212kcd/m2,在5.5V电压驱动下时,最大光功率效率为0.931m/W.     

Simple crystal forms as the orbits of crystallographic symmetry groups

Simple crystal forms are analyzed as the orbits of point symmetry groups on a set of crystal planes of space. All known polyhedra are described and structurized based on the theory of the orbits of groups, which provided a new, more harmonious approach to this problem. The orbits of groups can be general or particular and characteristic or non-characteristic. All possible versions of all crystallographic groups are listed in the table. The problem of the equivalence of polyhedra as the orbits of point symmetry groups is considered. An analysis of this problem has shown that 32 point crystallographic symmetry groups correspond to 139 symmetrically nonequivalent polyhedra.     

Synthesis of hybrid mesoporous spheres using the chitosan as template

Hybrid mesoporous spheres of Al and Si oxides were synthesized for the mixture of organic material (chitosan) with inorganic material (aluminum and silicon hydroxide). It was observed that chitosan with larger polymerization degree, resulted in a larger mechanical resistance of the spheres. The oxides were characterized by the following: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), as well as, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and adsorption isotherms of N₂ (BET). Highly uniform oxide sphere diameters were obtained (average of 1.0 mm). The results of the adsorption isotherms indicated that the material is mesoporous. The surface area of the materials ranged between 620 and 245 m²/g, and the pore volume varied between 0.82 and 0.28 cm³/g, depending on the molar ratio of the organic and inorganic materials.     

Johari-Goldstein relaxation as the origin of the excess wing observed in metallic glasses

Measurements of the shear loss modulus G″ of amorphous Zr₆₅Al_7.5Cu_27.5 at 5.4 kHz were reported by Rösner, Samwer and Lunkenheimer. They observed that the measured G″ are in excess of the contribution from the α-relaxation, indicating the existence of an ‘excess wing’ in amorphous metals like that found in molecular glass-formers. They speculated that the excess wing found in amorphous metal is due to the presence of an unresolved Johari-Goldstein (JG) secondary relaxation. In this work, the coupling model is used to calculate the temperature T_JG at which the JG relaxation frequency coincides with the experimental frequency of the isochronal measurement. The location of T_JG is well within the temperature range where the excess wing of Zr₆₅Al_7.5Cu_27.5 appears at 5.4 kHz. Hence, the result supports the assertion of Rösner et al. that the excess wing found in the metallic glass originates from the intrinsic JG relaxation.     

The Mechanism as SI GaAs Substrate Influences the Resistivity of the Epitaxial Layer

It is known that it is possible to grow a semi-insulating or, at least, a high resistivity GaAs epitaxial layer without doping on an SI GaAs substrate by VPE. The SI substrate is suspected as the originator of the high resistivity intermediate layer and diffusion and/or out-diffusion are accepted as mechanisms explaining this effect. In this work carrier concentration depth profiles were studied in various GaAs multi-layered epitaxial structures grown on SI GaAs substrates before and after various heat treatment procedures in order to study the diffusion and outdiffusion processes. It is concluded that the role of the diffusion is negligible and the out-diffusion process is insignificant, and the main, i.e. the determining effect in the compensation process is the growth mechanism of the layer. The impurities set free from the substrate by chemical etching processes rebuilt into the growing layer. In addition formation of EL2 centres may be initiated by As rich gas phase composition following the in-situ etching.     

Investigations of curved graphite crystals for the use as X-ray monochromators

X-ray investigations on curved graphite crystals for focusing monochromators for X-ray powder diffractometers are performed. The reflection power, avertences of crystal blocks, and radius of curvature of these crystals were determined by measuring rocking curves in dependence on the crystal position. The favourable application of curved graphite crystals as monochromators is shown by comparative X-ray measurements of selected reflexes.     

Minerals as advanced materials

A resume is given on relationships between minerals and materials. It is shown that Nature has many advantages over technology which can be profitably exploited for finding new materials with useful properties. However, Nature has also inherent limitations. Therefore, it seems advisable to use the knowledge of minerals as a treasure which can be tapped for getting inspired on the way to finding new materials. Several examples are given, including those of zorite/ETS‐4/ETS‐10, boracites, zircon, kesterite, a natural quasicrystal, opals, ultramarine and mayenite. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the role of the β process as precursor of the α relaxation in aromatic polyesters

By performing broad band dielectric spectroscopy measurements in a series of amorphous aromatic polyesters we show that different fast modes, contributing to the β relaxation, appear at temperatures below the glass transition temperature, T_g. At high temperatures, (T > T_g) the different β modes tend to merge and the data have to be described by a single β peak. We tentatively assign a molecular origin to each of the different β modes. But also we find a strong connection among the merged β processes and the precursor of the structural α relaxation, implying that this relaxation may posses an important degree of intra-segmental cooperativity.     

Interpretation of the switching effect in amorphous semiconductors as a recombination instability

For an explanation of the switching effect appearing on thin layers of amorphous semiconductors, a double-injection model is developed where the presence of diffusion currents in front of the electrodes is assumed in the high-resistance state. In the diffusion regions recombination takes place. The cause of the switching effect is seen in a recombination instability. Because of a saturation of the recombination current the life time of the free carriers becomes long enough for the diffusion length to extend over the full length and the high-resistance state to collapse.     

The Search for Prospective Media for the Application as Active Laser Elements

On the basis of an earlier methodology for assessing the quality of laser materials wellknown chemical compounds are considered and among them emphasis is given to those, the single crystals of which can successfully be used as active media in solid-state lasers. Possible directions of the search for new chemical compounds are shown, the single crystals of which can without doubt be expected to be of interest for quantum electronics.     

Packing motifs as predictors of the propensity of antibody fragments to crystallize

A recurring theme in the crystallization of antibody fragments in our laboratory has been a packing pattern involving formation of intermolecular, antiparallel β-pleated sheets across two-fold axes. The most common motif is the antiparallel stacking of constant (C) domains of light (L) chain dimers or Fab molecules. Here, cross-molecule six-stranded sheets are produced by hydrogen-bonding interactions of three-residue polypeptide segments (triads), in the i, i+2 and i+4 positions of the final strands (designated 3–3) of the three-chain layers from two adjacent molecules. In the variable (V) domains the triads are supplied by the first strands (4–1) of the four-chain layers and the resulting cross-molecule sheets contain eight strands. The latter type of packing is more likely to be seen in crystals of Fv fragments (V domains only) than in those of L chain dimers or Fabs. Amongst the triads from either the V or C domains, there are on average four sets of backbone carbonyl and amide groups within hydrogen bonding distance (<3.2 Å) of each other. In at least one example, the adjacent antiparallel strands are sterically aligned, but only two of the appropriate sets of atoms are sufficiently close to meet the distance criteria for intermolecular hydrogen bonding. These observations have been used to construct a list of rules for predicting which types of L chain dimers, Fab and Fvs are likely to crystallize in these packing patterns.     

Neuromorphic elements and systems as the basis for the physical implementation of artificial intelligence technologies

The instrumental realization of neuromorphic systems may form the basis of a radically new social and economic setup, redistributing roles between humans and complex technical aggregates. The basic elements of any neuromorphic system are neurons and synapses. New memristive elements based on both organic (polymer) and inorganic materials have been formed, and the possibilities of instrumental implementation of very simple neuromorphic systems with different architectures on the basis of these elements have been demonstrated.     

Different morphologies of the dry physical gels as a function of the sample preparation method

Xerogels obtained by drying the gels formed by glucofuranose derivatives with organic solvents were studied. The xerogels were characterized using the SEM, XRD, DSC and OPM techniques. The morphology of a xerogel observed by SEM may change from ‘amorphous, fibrillar’ to ‘crystal-like’, which may be caused by time or temperature. The results suggest that a similar transition may take place when the xerogel is being prepared. Thus SEM pictures of xerogels should be treated with great caution as they may not reflect the gelator network morphology in the bulk gel.     

Tetrabutylphosphonium Cation as Template in the Kinetics of Crystallisation of ZSM-5

Zeolite ZSM-5 was synthesised using ethyl silicate ester 40 and sodium aluminate so as to get the gel mix with SiO₄/Al₂O₃ = 90 employing TBPCl and TPABr templates separately (for comparison) at temperatures 423 K, 448 K, and 473 K. Nucleation and crystallisation processes were kinetically analysed. Activation energies for nucelation and crystallisation and the geometric factors have been evaluated. Correlations were found between the kinetic characteristics and the habits of the crystals formed. The study of the composition and morphology of the intermediates, with the support of SEM pictures, reveal the different mechanisms operating in the templating action of TBPCl and TPABr molecules.