Polyhedral stability ‐ on the growth of flat crystal faces on small molecule and protein crystals

The old standing problem of face morphology is discussed. A special emphasis is put on the macroscopically flat faces, appearing on small molecule crystals mostly during calm growth, under low supersaturations. As distinct, protein crystals are growing with macroscopically flat faces even under surprisingly high supersaturations. Explanations of these facts are suggested by considering the surface micro‐profile of crystal faces which growth is driven by screw dislocations. It is shown that, due to kinetic reasons, the tips of the growth hillocks and the valley between them have to be levelled to some extent (at least on a quasi‐atomic scale) under low enough supersaturations. The amplitude of the surface roughness has to be suppressed also due to the surface energy gain, especially under quasi‐equilibrium. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of inorganic salts from aqueous solutions in a microwave field

The crystallization of some inorganic salts (KH₂PO₄, NaCl, Sr(NO₃)₂, KNO₂, Ca(OH)₂) by the thermal-gradient (with decreasing temperature) and solvent-evaporation methods using microwave heating of solutions is investigated. It is established that the growth rates of single crystals in a microwave field are an order of magnitude higher than obtained in other known techniques at comparable crystallization temperatures and supersaturations. For example, the growth rate of prismatic faces {100} of KH₂PO₄ crystals is as high as 11 mm/day at supersaturations of ～1.2%. The results obtained are discussed in the context of the effect of microwave radiation on the adsorption surface layers of crystals. Fine-grained phases of the salts under study are obtained by evaporation of the solvent.     

Wachstum von Graphitkristallen in Eisen-Kohlenstoff-Werkstoffen

The dependence of the nucleation rate on the supersaturation is calculated for the basic and prismatic faces of graphite crystals growing from a iron-carbon-melt containing a surface active substance (e.g. sulphur). The addition of sulphur causes a reversal in the ratio of the nucleation rates relative to the pure melt. These results make possible to explain the formation of the different kinds of graphite crystals as well in ductile cast iron as in malleable cast iron. This explanation agrees with an earlier hypothesis of HERFURTH .     

Various Growth Shapes of Na2S2O3 5H2O Crystals

The relation between the growth shapes and supersaturations and/or supercoolings was investigated in the Na₂S₂O₃ 5H₂O crystals: (i) The growth shapes changed from a hexagonal prismatic crystal, aggregate of platy crystals and to a spherulite with an increase of supersaturations and/or supercooloings. (ii) The deposition rate suddenly increased at a certain supersaturation and/or supercooling, where the growth shape changed from the hexagonal prism to the aggregate of platy crystals. (iii) The deposition rates of spherulites become higher with increasing the solute concentrations. (iv) The formation process of the spherulites were in situ observed by the Schlieren and/or Mach‐zehnder interferometer methods.     

Growth of filamentary KDP crystals from solution with the addition of Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript> · 9H<Subscript>2</Subscript>O

To elucidate the mechanism of nucleation and growth of filamentary crystals on the bipyramid faces of KH₂PO₄ (KDP) crystals from solution with the addition of Al(NO₃)₃ · 9H₂O, the growth rates and transverse dimensions of the crystals were measured at various supersaturations, temperatures, and impurity concentrations. The dependences obtained can be interpreted with due regard for the competition between the intrinsic and impurity particles in the presence of Cabrera-Vermilyea stoppers.     

Effect of Mn(II) ions on the growth of ammonium oxalate monohydrate crystals from aqueous solutions: I. Growth habit and surface morphology

The effect of concentration of Mn(II) ions on the growth habit and the surface micromorphology of different as‐grown faces of ammonium oxalate monohydrate (AO) single crystals grown from aqueous solutions was studied at a constant temperature of 30 °C and predefined supersaturations up to 20%. It was observed that the growth habit and the surface morphology of the crystals strongly depend on the supersaturation used for growth and the impurity concentration in the solution. The experimental results were analysed in terms of connected nets determined from different projections of the structure of AO crystals. Analysis of the observations revealed that: (1) the directions of connected nets corresponding to basic growth units composed of single (NH₄)₂C₂O₄ · H₂O molecules are in excellent agreement with the low‐index crystallographic directions of the orientations of growth layers, (2) all faces appearing in the growth morphology of AO crystals are F faces, and (3) the {001} face growing from pure aqueous solutions is essentially a kinetically rough face but the presence of Mn(II) impurity leads to their appearance in the morphology due to increase in the strength of bonds of the connected nets composing the surface graph.     

Fundamental aspects of VLS growth

The kinetics and the mechanism of the vapor-liquid-solid (VLS) growth are discussed. Emphasis is placed on the dependence of the growth rate on the whisker diameter. It is found that the rate decreases abruptly for submicron diameters and vanishes at some critical diameter d_c ? 0,1 μm according to the Gibbs-Thomson effect. A new method for simultaneous determination of kinetic coefficients and of supersaturations has been developed. The method can be used to measure the coefficients of some materials as well as the temperature dependence of the coefficient for silicon and the activation energy of the process. From the dependence of supersaturation on the diameter we conclude that whiskers grow by a poly-nuclear mechanism. The periodic instability of the diameter is discussed and the rate-determining step is analysed. We conclude that phenomena on the liquid-solid interface are the decisive ones. In determining the role of liquid phase in vapor growth we measured the “liquid phase effectivity coefficient” as a function of crystallization condition; the coefficient typically was about 10²?10³. It is stressed that the liquid phase reduces the activation energy both on vapor-liquid interfaces (for chemical reactions) and on liquid-solid interfaces (for nucleation). The liquid phase ensures growth rates as high as 1 cm/sec, provided there are no barriers between the interfaces. The growth mechanism of the side faces was studied, and it was observed that the faces grow mainly by a chain mechanism rather than by two-dimensional nucleation. In work on surface diffusion in the VLS whiskers growth by CVD, we found that the whiskers grow mainly by direct deposition rather than by diffusion on the side faces. It is concluded that the VLS mechanism is important also for the vapor growth of platelets, films, and bulk crystals.     

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)     

Yb∶YAl3(BO3)4晶体形貌与生长速度的关系

观察测量了不同生长速度(相应于不同降温速度)自发成核生长的Yb∶YAl3(BO3)4晶体形貌。粒度较大(>2mm)的晶体不管降温速度快慢形态都很简单,只发育六方柱｛1120｝和菱面体｛1011｝;粒度较小(<2mm)的晶体形态随降温速度增快而变复杂,发育一些罕见的高指数晶面。说明在生长速度较快的条件下,在晶体生长早期,一些高能面发育,在晶体生长后期已尖灭了,晶体生长的大部分时间是在低能面｛1120｝和｛1011｝上进行的。对比了不同生长条件下晶面的粗糙度,随着降温速度的增快,六方柱面｛1120｝和菱面体面｛1011｝由光滑变粗糙,顶面｛0001｝永远是粗糙的。从晶体结构上定性地探讨了3种晶面的杰克逊因子α及生长机理     

Some observations of growth hillocks and growth layers on potassium hydrogen tartrate crystals

Some observations of growth hillocks and growth layers on the as-grown surfaces of potassium hydrogen tartrate (KHT) crystals obtained at 30 °C from aqueuos solutions of different supersaturations are reported and discussed. It is found that macrospirals, isolated growth hillocks, and growth layers are typical features observed on these crystals. Bunching of rectilinear growth layers originating from growth hillocks produced parallel macrosteps on the {010} faces. In certain cases, interaction of thick rounded layers of unequal height, emitted from neighbouring strong sources, gave rise to residual steps (pseudo-interlaced steps). Isolated growth hillocks produced by microbes were also observed.     

Morphology and growth mechanism of vapor grown Cd crystals as affected by Bi impurity

The effects of Bi impurity on the morphology and growth mechanism of (physical) vapor-deposited Cd crystals were investigated. Scanning electron microscopic observation revealed, for the first time, hexagonal prismatic Cd crystals which were grown on the Bi contaminated pyrex glass tube wall. This kind of morphology does not appear in the case of pure Cd without the impurity Bi. The top of the hexagonal prismatic crystal was usually rounded hemispherically. X-ray microprobe investigations showed that the tip of the crystals contained about 57 wt% Bi. It was concluded that the Cd hexagonal prismatic crystals grow by the mechanism of vapor-liquid-solid with the impurity Bi.     

一水甲酸锂晶体生长界面过饱和度的测量

本文采用激光全息相衬干涉显微术研究了有机非线性光学晶体一水甲酸锂晶体的生长,计算了晶体生长的界面过饱和度.我们的研究结果表明,晶体生长的界面过饱和度随体过饱和度的增加而非线性增加;不同晶面的界面过饱和度不同;当体过饱和度增加到一定程度时,不同晶面的界面过饱和度趋于相同.     

Growth of faces of K2Co x Ni1 – x(SO4)2 · 6H2O mixed crystals

Data on the morphology and normal growth rate of the (110) and (001) faces, velocities of step motion, and slopes of dislocation hillocks on the (001) face of K₂Co _x Ni₁– _x (SO₄)₂ · 6H₂O crystals at different supersaturations of solutions with a Co/Ni ratio equal to 1: 1 or 1: 2 have been obtained using a Michelson interferometer. The morphology of the (110) faces is found to be the same for solutions of both compositions. Powerful dislocation sources with large Burgers vectors dominate on the (001) face. The morphology of the (001) surface is rougher than that of (110), especially in a 1: 2 solution at high supersaturation. The (110) faces grow more slowly as compared with (001). The kinetic coefficients of steps on the (001) face are identical in the 1: 1 and 1: 2 solutions. The influence of the kinetic and morphological characteristics of (001) faces on the single-crystal quality is analyzed.

     

Growth,Structural and Microtopographical Studies of Calcium Iodate,Monohydrate Crystals Grown in Silica Gel

Single crystals of calcium iodate, monohydrate [Ca(IO₃)₂, H₂O] have been grown by gel technique. Prismatic, prismatic pyramidal, needle shaped and hopper crystals were obtained. These crystals were also grown by doping impurities such as copper and iron. Kinetics of growth parameters was investigated. Structural analysis was carried out by using X‐ray powder diffraction method. Microtopographical study of the habit faces, such as prismatic and pyramidal, of as grown crystals was carried out. Some surface structures are reported. These crystals were etched by various etchants and appropriate etchant is reported.     

Fluctuations in growth rate of gypsum crystals

Growth of needlelike gypsum crystals from highly supersaturated aqueous solutions has been studied by the methods of the optical and electron microscopies. The average growth rates of the end faces and their fluctuations are determined. It is shown that the fluctuations in the growth rates of end faces are described by the Fokker-Planck equation and that the end faces of gypsum crystals grow by the layer mechanism with the layer nucleation in the vicinity of one of the crystal vertices.     

Na+对KDP晶体生长的影响

本文利用传统的降温法和"点籽晶"快速生长法在不同Na+掺杂浓度的溶液中生长KDP晶体,定量研究了Na+对KDP晶体生长的影响.实验发现:Na+的存在降低了溶液的稳定性,致使KDP晶体柱面容易扩展.Na+的存在对KDP晶体的光学性能基本没有影响.     

Growth morphology of potassium bichromate crystals from aqueous solutions

The results of a systematic study of growth morphology of potassium bichromate single crystals on seeds and by self-nucleation at different temperatures and supersaturations are presented. The observed growth morphology is analysed in the light of theoretical predictions. An increase in both growth temperature and supersaturation leads to a symmetrical morphology, and the transition from asymmetrical to symmetrical morphology is monotonous. The predicted sequence of morphological importance agrees only in the case of crystals grown at low temperatures and supersaturations.     

原料对DKDP晶体生长习性及光学性能的影响

通过传统降温法,利用不同原料从氘化程度为85;的溶液中生长DKDP晶体并对加工样品进行了相关测试.研究了不同原料对DKDP晶体的生长和光学性能的影响.实验表明:采用高纯原料所得DKDP晶体的光学性能提高,但其晶体生长容易出现外扩现象.     

利用全息相衬干涉显微术研究EDTA对KDP晶体生长习性的影响

利用全息相衬干涉显微术(HPCIM)研究了EDTA对KDP晶体(100)柱面和(101)锥面生长习性的影响.通过界面边界层宽度的变化,可以直观地观测到在溶液中添加少量的EDTA后,促使KDP晶体沿柱面和锥面的生长,特别是对柱面的影响更为显著,并对此作了解释.最佳的EDTA浓度范围有待于进一步研究.     

Iso-epitaxial growth of n-octacosane crystals

Iso-epitaxial(epilayer)growth of n-octacosane crystals is reported. The morphology of the epilayers is in the form of triangular growth islands with or without truncature. Epilayer growth precedes spiral growth mechanism which occurs at medium and low supersaturations, respectively. The occurrence of triangular and truncated rhombic platelets is found to be a manifestation of growth at medium supersaturations.