八足状PbS树枝晶的水热合成及演变

以Pb(NO3)2和KSCN为原料,水为溶剂,采用水热法制备出了三维的八足状PbS树枝晶.XRD测试表明粉体为面心立方结构,结晶性好;SEM照片显示粉体为八足状的三维超结构,每足的平均长度5 μm,由边长600～800 nm的片状纳米块自组装而成.结合PbS晶体的结构模型和样品SEM照片的跟踪观察,分析了八足状PbS树枝晶的生长演变过程,为超结构微晶的生长机理研究提供有益参考.     

宽吸收带MEH-PPV/PbS量子点复合材料的制备

制备出粒径在3~8nm之间的宽吸收带聚合物MEH-PPV/PbS量子点复合材料。该材料在400~1100nm波长区域内表现出强吸收,能覆盖太阳光谱的大部分。准原位吸收光谱分析表明,MEH-PPV的加入不是获得宽吸收带纳米颗粒的主要因素。     

球状PbS纳米颗粒的室温合成与性能表征

以醋酸铅为铅源,硫代乙酰胺为硫源,在表面活性剂十二烷基硫酸钠(SDS)和十六烷基三甲基溴化铵(CTAB)共同作用下,在常温下合成了PbS纳米晶,利用XRD、紫外分光度计、SEM、TEM对合成产物的结构和形貌以及光学特性进行了表征分析,结果表明,合成的PbS为尺寸均匀的球形纳米晶,对合成的PbS纳米晶的形成机理进行了初探.当反应温度较低时,形成的PbS小颗粒在表面活性剂SDS的烷基链模板和CTAB微胶束软模板共同作用下生成球状PbS纳米晶.     

Compositional effects accompanying near equilibrium vapour growth of solid solution crystals of the types IV‐VI and II‐VI

Near equilibrium evaporation‐condensation in a sealed ampoule leads to almost full compositional reproduction of a solid solution if it consists of components having comparable vapour pressures; this can be qualitatively interpreted by domination of entropy increase. Nevertheless, even vestigial separation requires closer characteristics, since it may prove crucial – particularly for properties of semiconducting solid solutions. Maximum component separation allowed by a small temperature difference is described here in terms of thermodynamics and kinetics of solid‐vapour and vapour‐solid phase transitions. Theoretical models of the determining effects having different character are shortly described, and their applicability areas are determined. Experimental data collected for crystal growth of numerous semiconducting solid solutions of the II‐VI and IV‐VI type support the conclusion drawn from the models that the near equilibrium crystal growth from the vapour in a closed system ensures the highest degree of compositional uniformity. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Shape evolution of detached Bridgman crystals grown in microgravity

Detached (or dewetted) Bridgman crystal growth defines that process in which a gap exists between a growing crystal and the crucible wall. In microgravity, the parameters that influence the existence of a stable gap are the growth angle of the solidifying crystal, the contact angle between the melt and the crucible wall, and the pressure difference across the meniscus. During actual crystal growth, the initial crystal radius will not have the precise value required for stable detached growth. Beginning with a crystal diameter that differs from stable conditions, numerical calculations are used to analyze the transient crystal growth process. Depending on the initial conditions and growth parameters, the crystal shape will either evolve towards attachment at the crucible wall, towards a stable gap width, or inwards towards eventual collapse of the meniscus. Dynamic growth stability is observed only when the sum of the growth and contact angles exceeds 180°.     

pH值对电沉积PbS薄膜结构和性能的影响

采用阴极恒电压法在ITO导电玻璃表面沉积了PbS薄膜,并用X射线衍射仪(XRD)、原子力显微镜(AFM)以及傅立叶变换红外光谱仪(FT-IR)对薄膜的结构和光学性能进行了表征,研究了沉积液pH值对薄膜的相组成、显微形貌以及光学性质的影响.结果表明:在U=3 V,pH=2.4,沉积时间为20 min,加入EDTA作络合剂的情况下,可制备出沿(111)和(200)晶面取向生长的立方相PbS薄膜.薄膜均匀而致密,随pH值增加,薄膜的压应力及禁带宽度呈现先减小后增大的变化趋势.所制备的微晶PbS薄膜的禁带宽度约为0.38～0.39 eV.     

Ethylenediamine inducing growth of {100} facets exposed PbS nanosheets

A simple ethylenediamine‐assisted hydrothermal method was developed for the synthesis of sheet‐like PbS nanostructures. Studies show that ethylenediamine not only provides a weakly basic environment for the reaction system, but also acts as a capping reagent to control the growth habit of cubic PbS. A reasonable growth mechanism for the PbS nanosheet structure has been proposed on the basis of the experimental studies. The structure, morphology, and composition of the nanosheets have been characterized by X‐ray powder diffraction, field‐emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and transmission electron microscopy.     

Understanding the growth mechanism of CuI crystals during gel growth experiments

Cuprous iodide crystals have been grown with decomplexation method in silica gel. Various crystal morphologies, such as polycrystalline aggregate, skeletal, dendrite, hopper crystals and regular tetrahedron crystals, were observed in different growth regions with an optical microscope. Their surfaces were photographed using a binocular metallographic microscope and the results were explained with the crystal growth mechanism which was determined by supersaturation. These observations support the general hypothesis that the concentration of reactant affects the relative growth rate by controlling the nucleation and diffusion. The mutual influence of the crystals grown in different regions was also discussed. Additionally, the suitable condition for getting regular tetrahedron crystals or large hopper crystals was obtained by changing the concentration of CuI·HI complex in the later period of crystal growth. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

沉积温度对电沉积PbS薄膜结构和性能的影响

采用电沉积法在ITO导电玻璃表面沉积了PbS薄膜,并用X射线衍射仪(XRD)、原子力显微镜(AFM)以及傅立叶变换红外光谱仪(FT-IR)对薄膜的结构和光学性能进行了表征,研究了沉积温度对薄膜的相组成、显微形貌以及光学性质的影响.结果表明:在U=3 V,pH=2.5,T=60 ℃,沉积时间为20 min,加入EDTA作络合剂的情况下,可制备出沿(111)和(200)晶面取向生长的立方相PbS薄膜.薄膜显微结构均匀而致密,随着反应温度从20 ℃增加到60 ℃,薄膜内的压应力逐渐减小,禁带宽度也随着变小.所制备的微晶PbS薄膜的禁带宽度约为0.39 eV.     

Effects of anions on rapid growth and growth habit of KDP crystals

The synthesis of KDP from its raw material has been found exist in the growth solution. In the crystal growth experiment, significant extension of specific faces was observed at low dopant concentration. At high doping concentration, the growth rate of the whole crystal decreased with no significant habit modification. The inhibiting effects of phosphite and other H-bonding anionic ions on the growth of pyramidal faces are discussed. Rapid growth rate experiments have been carried out with purified material and an averaged growth rate of 18.6mm/day was obtained.     

Synthesis via an organic molten salt solvent route and characterization of PbS nanocrystals

In this paper, four petals flowers‐like and quasi sphere‐like PbS nanostructures were successfully synthesized by an environment friendly organic molten salt solvent (OMSS) route at 200 °C, with different sulfur sources, e.g. thiourea and sodium thiosulfate, respectively. The as‐synthesized products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), UV–vis absorption spectrum and photoluminescence (PL) spectrum, respectively. It was shown that four petals flowers‐like and quasi sphere‐like PbS nanocrystals were formed. It was also demonstrated that the morphologies of PbS nanocrystals were significantly influenced by different sulfur sources. The ultraviolet‐visible absorption peaks of PbS nanocrystals exhibited a large blue‐shift and the luminescence spectra had strong and broad emission bands centered at 488 nm and 492 nm. The possible formation mechanisms of the PbS nanostructures were discussed. The organic molten salt solvent (OMSS) method is preferable for synthesizing high‐quality PbS nanocrystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Connection between electrical and deformation characteristics of PbS crystals

The influence of plastic deformation on temperature dependence of carrier concentration n and mobility μ in PbS crystals has been studied. Comparison of the results obtained with selective etching patterns from original and deformed crystals makes it possible to conclude that during the plastic deformation there takes place a dissolution of precipitates by passing of dislocations through them. As a results, rows of point defects appear along the path of dislocation movement which may be the cause of a change in n and μ due to deformation. A change in the electron scattering mechanism below 110 K has been discovered.     

Study on rapid growth of highly‐deuterated DKDP crystals

Highly‐deuterated potassium dihydrogen phosphate (DKDP) crystals were grown rapidly from point seeds under high supersaturation in a temperature range of 40‐60 °C. The growth rate was about 1‐2 order of magnitude higher than that of the traditional temperature reduction method. It was found that highly pure raw materials, overheating at high temperature, ultrafine filtration and supersaturation stability were needed to keep the solution from spontaneous nucleation at high overcooling. The effect of growth conditions on pyramid faces was different from that of prismatic faces. The tetragonal to monoclinic phase solubility transition scarcely occurred in our experiments even though the overcooling of monoclinic phase was as high as 10 °C in some cases. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vapour growth and morphology of PbBr2 crystals

In this paper, the vapour transport of PbBr₂ under vacuum during vacuum distillation refining and its condensation on the wall of the vessel were described. The macro‐ and micro morphologies of PbBr₂ crystals grown in the vessel (glass tube) were studied. The crystal shape changed dramatically depending on the positions of condensation in the vessel, i.e., the crystal shape varied from an isometric polyhedron to columnar crystals with facets, and to a massive crystal without facets with a rise in the wall temperature. These results were interpreted in terms of the concentration gradient of the molecules in the vessel, surface roughening and/or surface melting of the crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology of struvite crystals as an evidence of bacteria mediated growth

Influence of Proteus mirabilis on the growth, morphology and size of struvite crystals in artificial urine has been studied. The growth in the presence of Proteus mirabilis shows formation of struvite crystals of more regular habits compared with that in the absence of bacteria. This implies that in the presence of Proteus mirabilis, struvite crystals grow with relative growth rates within smaller range of variability compared to the absence of bacteria. The results show that bacteria affect size and struvite morphology while the habit remains almost unchanged. It is suggested that the changes in struvite crystal morphology are induced by the presence of Proteus mirabilis. Microorganism's negatively charged residues interact electrostatically with positive ions which outcrop given surfaces and lead to an enhanced expression of these surfaces. This means that microorganisms actively mediate in growth processes. Therefore, the investigations provide evidence for the importance of biological regulation in crystallization process.     

PbS量子点/MoO3纳米带复合材料的低温气敏性能研究

采用液相法制备PbS量子点修饰MoO3纳米带复合材料.利用XRD、FESEM、TEM、EDS等表征手段分析样品组成、结构与形貌,分别将MoO3纳米带、PbS量子点、PbS量子点/MoO3纳米带组装成陶瓷管气敏元件并测试其对NH3的气敏性能.结果表明,在低温(20~100 ℃)下PbS量子点/MoO3纳米带复合材料对NH3具有良好检测能力,最低测试限为10 ppm.由于PbS量子点均匀分布在MoO3纳米带表面可形成异质结界面,这可有助于电子、空穴的分离,从而显著改善电子传输性能和气敏特性.     

Crystal growth and defects in Ga3PO7 crystals

Crystals with a non‐centrosymmetric structure are of great interest owing to their properties such as ferroelectricity, piezoelectricity, dielectric behavior and optical properties. In this letter, Ga₃PO₇ crystals are grown by the top‐seeded solution growth (TSSG) method from a Li₂O‐3MoO₃ flux. It crystallizes in a non‐centrosymmetric trigonal crystal system with space group R3m within point group 3m. The growth defects are investigated by means of chemical etching method. The results reveal hot concentrated phosphoric acid to be a good etchant for Ga₃PO₇. The main defects are cracks, inclusions, dislocations and twin. In the meantime, the effective measures for reducing the defects are proposed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solution growth of new ferroelectric glycine phosphite unidirectional single crystals at room temperature

Glycine phosphite [NH₃CH₂COOH₃PO₃], abbreviated as GPI is the second hydrogen bonded ferroelectric crystal combination of phosphorous acid and amino acid following βnine phosphite crystals abbreviated as BPI. Sankaranarayanan and Ramasamy‐Technique was adopted to prepare the ferroelectric glycine phosphite unidirectional single crystal. The growth orientation was imposed by the pre‐grown 〈010〉 seed. As water was the solvent, transparent, colourless crystal with cylindrical shaped ingot of sized 20mm‐diameter was grown. Powder X‐ray diffraction, HRXRD, FTIR, dielectric and mechanical studies were carried out. The results are discussed in detail. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling analysis of liquid encapsulated Czochralski growth of GaAs and InP crystals

The results of three‐dimensional unsteady modeling of melt turbulent convection with prediction of the crystallization front geometry in liquid encapsulated Czochralski growth of InP bulk crystals and vapor pressure controlled Czochralski growth of GaAs bulk crystals are presented. The three‐dimensional model is combined with axisymmetric calculations of heat and mass transfer in the entire furnace. A comprehensive numerical analysis using various two‐dimensional steady and three‐dimensional unsteady models is also performed to explore their possibilities in predicting the melt/crystal interface geometry. The results obtained with different numerical approaches are analyzed and compared with available experimental data. It has been found that three‐dimensional unsteady consideration of heat and mass transfer in the crystallization zone provides a good reproduction of the solidification front geometry for both GaAs and InP crystal growth.