Secondary dielectric relaxation in decahydroisoquinoline–cyclohexane mixture

We report dielectric relaxation measurements of the mixture 25% w/w cyclohexane in decahydroisoquinoline. Cyclohexane is a non-polar liquid that acts as an external parameter influencing relaxation dynamics of pure decahydroisoquinoline. Two different secondary relaxation processes dominate the relaxation dynamics below the glass transition temperature, as previously observed in the pure decahydroisoquinoline. Based on the coupling model analysis we identified the fastest secondary process as the genuine secondary Johari Goldstein process, reflecting the motion of the whole molecule. On the other hand, the microscopic origin of the slowest secondary process still remains unknown.     

Effect of thermodynamic history on secondary relaxation in the glassy state

We investigated by dielectric spectroscopy the effect that the thermodynamic history of a glass has on the secondary relaxation process. In particular we focused our attention to glassy states at the same conditions of temperature and pressure but reached with different combinations of variation of the external parameters. Our analysis shows that the effect of thermodynamic history on the relaxation frequency is related to the activation volume of the process: secondary processes with larger activation volume present a larger effect of the thermodynamic history. This demonstrates an important role of density in determining such behavior in glassy systems.     

铜蒸发温度对共蒸发法制备Cu2ZnSnSe4太阳电池的影响

由于Cu元素的含量对Cu2ZnSnSe4(CZTSe)化合物的薄膜性质及电池性能都有影响,本文主要研究了不同铜蒸发温度对CZTSe薄膜性质及电池性能的影响.研究表明:当铜蒸发温度较低时(1400 ℃),CZTSe薄膜中含有SnSe相,同时薄膜呈N型;随着铜蒸发温度的提高,CZTSe薄膜的结晶质量明显提升.但当铜蒸发温度过高时(1500 ℃),薄膜中含有CuxSey相.二次相SnSe与CuxSey的存在都会使电池失效.最终通过优化铜的蒸发温度,在较合适的1450 ℃ 铜蒸发温度条件下制备出效率为2.63;(有效面积0.34 cm2)的CZTSe太阳电池.     

Metastable zone width for secondary nucleation and secondary nucleation inside the metastable zone

This study presents an evaluation of a new method, called zero growth activation free energy, used to determine the metastable zone width for the secondary nucleation case. It predicts the metastable zone width with a maximum error of 5‐10%. Estimation of the metastable zone width for different isothermal crystallization conditions can be modeled according to a chosen reference set of growth experiments carried out in the volume diffusion regime at different initial supersaturations, using seed crystals of a certain characteristic size. Moreover, the activation free energy of the secondary nucleation was estimated. The role of the enthalpy of immersion in the formation of secondary nucleation events inside the metastable zone was pointed out, as well as its effect in causing extra‐fast growth rate. Furthermore, sucrose crystal surface free energy was estimated. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of Nucleation Conditions on the Structure of Zinc Oxide Films

Crystallography Reports - The temperature conditions of nucleation of ZnO films on surface-oxidized silicon substrates during magnetron sputtering of a cermet ZnO–Zn target in an Ar...     

A 3-D numerical heat transfer model for silica aerogels based on the porous secondary nanoparticle aggregate structure

A 3-D finite volume numerical model based on the porous secondary nanoparticle random aggregate structure was developed to predict the total thermal conductivity of silica aerogels. An improved 3-D diffusion-limited cluster–cluster aggregation (DLCA) method was used to generate an approximately real silica aerogel structure. The model includes the effects of the random and irregular nanoparticle aggregate structure for silica aerogels, solid–gas coupling, combined conduction and radiation, nanoparticle and pore sizes, secondary nanoparticle porosity and contact length between adjacent nanoparticles. The results show that the contact length and porosity of the secondary aerogel nanoparticle significantly affect the aerogel microstructure for a give density and, thus, greatly affect the total thermal conductivity of silica aerogels. The present model is fully validated by experimental results and is much better than the model based on a periodic cubic array of full density primary nanoparticles, especially for higher densities. The minimum total thermal conductivity for various silica aerogel microstructures can be well predicted by the present model for various temperatures, pressures and densities.     

衬底温度对碲化镉薄膜结构及光学性能的影响

碲化镉(CdTe)因具有良好的光电性能和吸收性能经常被作为太阳电池的吸收层材料.以纯度为99.99;的CdTe陶瓷靶为靶材在玻璃衬底上采用射频磁控溅射的方法制备了一系列的CdTe薄膜,研究了衬底温度对样品薄膜的厚度、结构和光学性能的影响.结果表明:随着衬底温度的增加薄膜的厚度在逐渐地减少;制备的薄膜都是立方闪锌矿结构且具有高度的(111)面择优取向;薄膜对可见光有较好的吸收性能,随衬底温度的增加而减小.     

移动加热器法生长碲锌镉晶体的组分输运与界面形貌研究

移动加热器法(THM)生长碲锌镉晶体时,界面稳定性对晶体生长的质量有很大影响。本文基于多物理场有限元仿真软件Comsol建立了THM生长碲锌镉晶体的数值模拟模型,讨论了Te边界层与组分过冷区之间的关系,对不同生长阶段的物理场、Te边界层与组分过冷区进行仿真研究,最后讨论了微重力对物理场分布的影响,并对比了微重力与正常重力下的生长界面形貌。模拟结果表明,Te边界层与组分过冷区的分布趋势是一致的,在不同生长阶段,流场中次生涡旋的位置会发生移动,从而导致生长界面的形貌随着生长的进行发生变化,同时微重力条件下形成的生长界面形貌最有利于单晶生长。因此,在晶体生长的中前期,对次生涡旋位置的控制和对组分过冷的削弱,是THM生长高质量晶体的有效方案。     

Optical Properties of Thick Zinc Oxide Films Doped with Gallium and Gold

Crystallography Reports - Samples of thick (30–32 µm) films of pure and gallium- and gold-doped zinc oxide obtained by magnetron sputtering using an uncooled target have been...     

Characteristics of sputtered amorphous carbon films prepared by a closed-field unbalanced magnetron sputtering method

We discuss the tribological performance of sputtered amorphous carbon (a-C) films deposited by closed-field unbalanced magnetron (CFUBM) sputtering with a graphite target using a mixture of helium (He) and argon (Ar) as sputtering gases. We investigated the effects of the graphite target power density on the micro-structural and physical properties. In the Raman spectra, the G-peak position moved to the higher wavenumbers. The I_D/I_G ratio increased with the increase of target power density in the fixed DC bias voltage. This was the result of the structural change in the a-C film that resulted with the increase in sp² bonding fraction. Also, the maximum hardness of the a-C film was 23 GPa, the friction coefficient was 0.1, and the critical load was 25.9 N on the Si wafer. In addition, the compressive residual stress of the film increased a little with increasing target power density. Consequently, the various properties of a-C films, with an increase of the target power density, were associated with the increase of cross-linked sp² bonding fraction and the cluster size. The tribological properties of a-C film showed clear dependence on the energy of ion bombardment with the increase of plasma density during film growth.     

Leaching behavior of a polyphase glass–ceramic containment matrix

In order to understand the alteration mechanisms affecting a glass matrix comprising a secondary phase dispersed in a durable encapsulating glass, a simplified conservative model was used to estimate the expected normalized mass loss variation during a Soxhlet leach test. The model showed that once the secondary phases directly exposed to water have been fully altered, the overall behavior of the glass matrix corresponds to the behavior of the durable encapsulating glass. The additional release due to the secondary phase depends essentially on the dimensions of the dispersed phase and on its volume fraction within the matrix. The model was applied to a glass–ceramic containing several secondary phases dispersed in a durable borosilicate glass. Some of the secondary phases are rich in boron, and thus of a lower chemical resistance compared to the major encapsulating glassy phase. In order to compile the parameter data necessary for applying the model to these glass–ceramics, their microstructure was analyzed and the dimensional characteristics and composition of the secondary phases were determined by scanning electron microscopy coupled with image analysis and electron microprobe analysis. The model was then compared with the results of leach tests of the same samples in Soxhlet mode at 100 °C.     

圆筒式柱面磁控溅射靶的磁场设计与仿真研究

为探究一种可实现向心溅射的圆筒式柱面磁控阴极靶,需要对靶装置内的磁场分布进行研究,进一步讨论靶结构参数对其磁场分布的影响规律。本文根据磁控靶的结构与工作原理,利用COMSOL Multiphysics有限元分析软件中AC/DC接口,对靶进行三维模型构建、划分网格和仿真计算。通过改变靶内磁体形状尺寸、磁轭形状以及结构排布,对靶面磁场的分布进行规律探究。最终确定新型圆筒式柱面磁控溅射阴极靶内的磁场结构参数,结果表明结构靶面磁场分布均匀且大小满足溅射要求的磁感应强度(20~50 mT),平行靶面均匀磁场区域达35%~40%左右。通过这类靶磁场结构的研究,为设计优化磁控阴极靶提供依据。     

Cover Picture: Cryst. Res. Technol. 1/2012

The cover picture shows a secondary electron image of the fracture surface of an as‐extruded YCu sample after tensile deformation at ambient temperature. (see pages 13–18) (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Secondary dynamics in glass formers: Relation with the structural dynamics and the glass transition

In this paper, we study secondary relaxations in a neat glass former close and below the glass transition. The pressure and temperature dependences of the characteristic relaxation frequencies were investigated to find a connection between structural and secondary relaxations and the microscopic mechanism at the basis of the latter. We found that the ratio between the relaxation time of the structural and secondary processes is almost constant when considered at different values of temperature and pressure corresponding to the glass transition (same value of structural relaxation time). This result is also related to the finding of a constant broadness of the structural peak. We propose to use such dynamic relation between the two processes to distinguish between intramolecular secondary relaxation, reflecting the local motion of molecular subgroups, and intermolecular secondary relaxation, called also Johari–Goldstein process, originating by a local motion of the whole molecule.     

Crystallization mechanisms of acicular crystals

In this contribution, we present an experimental investigation of the growth of four different organic molecules produced at industrial scale with a view to understand the crystallization mechanism of acicular or needle-like crystals. For all organic crystals studied in this article, layer-by-layer growth of the lateral faces is very slow and clear, as soon as the supersaturation is high enough, there is competition between growth and surface-activated secondary nucleation. This gives rise to pseudo-twinned crystals composed of several needle individuals aligned along a crystallographic axis; this is explained by regular over- and inter-growths as in the case of twinning. And when supersaturation is even higher, nucleation is fast and random.In an industrial continuous crystallization, the rapid growth of needle-like crystals is to be avoided as it leads to fragile crystals or needles, which can be partly broken or totally detached from the parent crystals especially along structural anisotropic axis corresponding to weaker chemical bonds, thus leading to slower growing faces. When an activated mechanism is involved such as a secondary surface nucleation, it is no longer possible to obtain a steady state. Therefore, the crystal number, size and habit vary significantly with time, leading to troubles in the downstream processing operations and to modifications of the final solid-specific properties.These results provide valuable information on the unique crystallization mechanisms of acicular crystals, and show that it is important to know these threshold and critical values when running a crystallizer in order to obtain easy-to-handle crystals.     

Ablation of CdTe with 100 µs Nd:YAG laser pulses: dependence on target preparation method

The results of experimental studies of the ablation of CdTe with a pulsed Nd:YAG laser (wavelength 1064 nm) performed with 100 µs pulses and repetition time of 35 Hz are presented for the pulse energy range from 0.13 to 0.25 J. The main goal is to elucidate the dependence of the ablation process on the target preparation method. The investigation of the vapour stream intensity and chemical composition and their evolution with time are performed with a quadrupole mass spectrometer synchronized with the laser pulses. These studies are performed for three kinds of targets: a target made of CdTe bulk crystal (BC target), a target made of CdTe fine powder pressed under the pressure of 700 atm (PP target), and a target made of loose CdTe powder (N‐PP target). The applicability of these targets for obtaining high quality CdTe thin films is determined. The best chemical composition of the vapour stream can be obtained with the BC target. A major drawback of this target is the energetic threshold for ablation with Nd:YAG laser and resulting delay in the ablation process above the threshold. The advantage of powder targets over BC target is the lack of any ablation threshold or delay. Weaker angular dependence of the particle emission (associated with the surface roughness), if confirmed in further experiments, can be the most important advantage of PP and N‐PP targets. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of virtual screening and molecular dynamics for the analysis of selectivity of inhibitors of HU proteins targeted to the DNA-recognition site

DNA-Binding HU proteins are essential for the maintenance of genomic DNA supercoiling and compaction in prokaryotic cells and are promising pharmacological targets for the design of new antibacterial agents. The virtual screening for low-molecular-weight compounds capable of specifically interacting with the DNA-recognition loop of the HU protein from the mycoplasma Spiroplasma melliferum was performed. The ability of the initially selected ligands to form stable complexes with the protein target was assessed by molecular dynamics simulation. One compound, which forms an unstable complex, was eliminated by means of a combination of computational methods, resulting in a decrease in the number of compounds that will pass to the experimental test phase. This approach can be used to solve a wide range of problems related to the search for and validation of low-molecular-weight inhibitors specific for a particular protein target.     

The Growth of KDP Crystals and its Mechanism by Splicing Misoriented in Aqueous Solution

The growing characteristics of splicing misoriented KDP seeds of both bulk and thin pieces were investigated. The chemical etching method was used to determine the prismatic and Z-plate surfaces of the crystals grown by splicing bulk KDP seeds. The X-ray Lang topography method was employed to measure original thin platy crystals grown by splicing thin pieces of KDP seeds. From the results it can be concluded that when the misorientation of two seeds on the Z-axis direction was about 1.5°, the crystal was grown successfully if the secondary capping was controlled properly. In comparison with the growth of splicing “parallel” seeds, the misorientation of both seeds increases such that the secondary capping becomes difficult, the sub-grain boundary stretches longer, the stress field around the secondary cap enlarges and the crystals grown crack easily.     

Batch Precipitation of Potash Alum Crystals by Mixing Aqueous Solutions of the Component Salts

The effects of temperature, supersaturation, excess of reacting component salts and method of precipitation on the batchwise precipitation of potash alum crystals, by mixing aqueous solutions of potassium sulphate and aluminium sulphate, have been investigated. From the primary characteristics of the process (crystal size, size distribution and yield) relative crystal growth rates and relative nucleation rates are calculated and interrelation of these rates with the corresponding supersaturation leads to a value of the nucleation order. It is concluded that secondary nucleation plays an important role in the batch precipitation of potash alum crystals.     

The secondary relaxation in the dielectric loss of glucose–water mixtures

We studied dielectric relaxation phenomena of glucose–water mixtures in the supercooled and glassy states at frequencies ranging from 0.1 Hz to 10 MHz. We clearly observed that as the water content or temperature decreased, the relaxation time difference between the α and the secondary relaxations increased and the relative relaxation strength between the α and the secondary relaxation decreased. We found that the effects of adding water or increasing temperature on the secondary relaxation are qualitatively similar to that of decreasing the rotation–translation (RT) coupling constant in the schematic mode-coupling theory [W. Götze, M. Sperl, Phys. Rev. Lett. 92 (2004) 105701].