Sample records for crystal growth mechanisms

  1. The mechanism of protein crystal growth from lipid layers.

    PubMed

    Hemming, S A; Bochkarev, A; Darst, S A; Kornberg, R D; Ala, P; Yang, D S; Edwards, A M

    1995-02-17

    Two-dimensional (2D) crystals of proteins on lipid monolayers can initiate the formation of large three-dimensional (3D) crystals suitable for X-ray diffraction studies. The role of the 2D crystals in this process has not been firmly established. While it is likely that the 2D crystals serve as nuclei for epitaxial crystal growth, other mechanisms, such as non-specific nucleation induced by the high local concentration of the protein at the surface of the lipid layer, cannot be excluded. Using streptavidin as a model system, we have now firmly established that 3D crystal growth from 2D crystals on lipid layers occurs by epitaxy. We show that 2D crystals of streptavidin (space group C222) on biotinated lipid layers nucleate the growth of a 3D crystal form (space group I4I22) that possesses a structural similarity with the 2D crystal, but have no effect on the growth of 3D crystal forms (I222 and P2(1)) that are unrelated to the 2D crystal. At lower pH, a new 3D crystal form (space group P1), unrelated to the previously described 2D crystals, grew from lipid layers. This discovery initially raised concern about the validity of the epitaxial mechanism, but these concerns were alleviated with the subsequent discovery of a structurally related 2D P1 crystal that grew in similar solution conditions. Some parameters affecting epitaxial growth of both the P1 and I4I22 crystals were investigated, revealing several noteworthy features of the epitaxial growth. (1) 2D crystals are very effective nucleating agents; for instance, the P1 2D crystals can direct the growth of P1 3D crystals even under conditions that favour the growth of other crystal forms. (2) The epitaxial 3D crystal grow very rapidly and at amazingly low protein concentrations; P1 3D crystals can be grown from solutions as low as 10 microM streptavidin. (3) There is no obligate requirement for the deposition of pre-formed 2D crystals; lipid layers alone are equally effective at promoting epitaxial crystal growth. PMID:7869382

  2. An assessment of calcite crystal growth mechanisms based on crystal size distributions

    USGS Publications Warehouse

    Kile, D.E.; Eberl, D.D.; Hoch, A.R.; Reddy, M.M.

    2000-01-01

    Calcite crystal growth experiments were undertaken to test a recently proposed model that relates crystal growth mechanisms to the shapes of crystal size distributions (CSDs). According to this approach, CSDs for minerals have three basic shapes: (1) asymptotic, which is related to a crystal growth mechanism having constant-rate nucleation accompanied by surface-controlled growth; (2) lognormal, which results from decaying-rate nucleation accompanied by surface-controlled growth; and (3) a theoretical, universal, steady-state curve attributed to Ostwald ripening. In addition, there is a fourth crystal growth mechanism that does not have a specific CSD shape, but which preserves the relative shapes of previously formed CSDs. This mechanism is attributed to supply-controlled growth. All three shapes were produced experimentally in the calcite growth experiments by modifying nucleation conditions and solution concentrations. The asymptotic CSD formed when additional reactants were added stepwise to the surface of solutions that were supersaturated with respect to calcite (initial ? = 20, where ? = 1 represents saturation), thereby leading to the continuous nucleation and growth of calcite crystals. Lognormal CSDs resulted when reactants were added continuously below the solution surface, via a submerged tube, to similarly supersaturated solutions (initial ? = 22 to 41), thereby leading to a single nucleation event followed by surface-controlled growth. The Ostwald CSD resulted when concentrated reactants were rapidly mixed, leading initially to high levels of supersaturation (? >100), and to the formation and subsequent dissolution of very small nuclei, thereby yielding CSDs having small crystal size variances. The three CSD shapes likely were produced early in the crystallization process, in the nanometer crystal size range, and preserved during subsequent growth. Preservation of the relative shapes of the CSDs indicates that a supply-controlled growth mechanism was established and maintained during the constant-composition experiments. CSDs having shapes intermediate between lognormal and Ostwald also were generated by varying the initial levels of supersaturation (initial ? = 28.2 to 69.2) in rapidly mixed solutions. Lognormal CSDs were observed for natural calcite crystals that are found in septarian concretions occurring in southeastern Colorado. Based on the model described above, these CSDs indicate initial growth by surface control, followed by supply-controlled growth. Thus, CSDs may be used to deduce crystal growth mechanisms from which geologic conditions early in the growth history of a mineral can be inferred. Conversely, CSD shape can be predicted during industrial crystallization by applying the appropriate conditions for a particular growth mechanism.

  3. Mechanisms of protein and virus crystal growth: An atomic force microscopy study of Canavalin crystallization

    SciTech Connect

    Land, T.A.; De Yoreo, J.J. [Lawrence Livermore National Lab., CA (United States); Malkin, A.J.; Kutznesov, Y.G.; McPherson, A. [California Univ., Riverside, CA (United States). Dept. of Biochemistry

    1995-03-10

    The evolution of surface morphology and step dynamics during growth of single crystals of the protein Canavalin and of the cubic satellite tobacco mosaic virus crystals (STMV) have been investigated by in situ atomic force microscopy. These two crystals were observed to grow by very different mechanisms. Growth of Canavalin occurs on complex vicinal hillocks formed by multiple, independently acting screw dislocations. Small cluster were observed on the terraces. STMV on the other hand, was observed to grow by 2D nucleation of islands. No dislocations were found on the crystal. The results are used to determine the growth mechanisms and estimate fundamental materials parameters. The images also illustrate the important mechanism of defect incorporation and provide insight to the processes that limit the growth rate and uniformity of these crystals.

  4. Growth mechanism of NaBrO 3 crystals from aqueous solutions

    Microsoft Academic Search

    V Surender; K Kishan Rao

    1995-01-01

    To study the growth mechanism of {111} faces of NaBrO3, crystals were grown at different supersaturations ranging from 2% to 8%. The growth mechanisms were investigated based on\\u000a the growth rate versus supersaturation relation and from the surface features observed on {111} faces. The growth mechanism\\u000a of these crystals appear to be due to 2D nucleation. The growth rate curve

  5. VO{sub 2} (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms

    SciTech Connect

    Rao Popuri, Srinivasa [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara (Romania); Artemenko, Alla [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); Labrugere, Christine [CeCaMA, University of Bordeaux 1, ICMCB, 87 Avenue du Dr. A. Schweitzer, F-33608 Pessac (France); Miclau, Marinela [National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara (Romania); Villesuzanne, Antoine [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); Pollet, Michaël, E-mail: pollet@icmcb-bordeaux.cnrs.fr [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France)

    2014-05-01

    Well crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal reaction in the presence of V{sub 2}O{sub 5} and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO{sub 2} (A) micro rods. The structural and electronic transitions in VO{sub 2} (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversible intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO{sub 2} (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO{sub 2} (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO{sub 2} (M1) are described. - Graphical abstract: Using a single step and template free hydrothermal synthesis, well crystallized VO{sub 2} (A) microrods were prepared and the P4/ncc space group was assigned to the room temperature crystal structure. Reversible and irreversible phase transitions among different VO{sub 2} polymorphs were identified and their progressive nature was highlighted. Attempts to increase the microrods size, involving layer by layer formation mechanisms, are presented. - Highlights: • Highly crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal process. • The P4/ncc space group was determined for VO{sub 2} (A) at room temperature. • The electronic structure and progressive nature of the structural phase transition were investigated. • A weak coupling between structural and electronic phase transitions was identified. • Different crystallite morphologies were discussed in relation with growth mechanisms.

  6. Deducing growth mechanisms for minerals from the shapes of crystal size distributions

    USGS Publications Warehouse

    Eberl, D.D.; Drits, V.A.; Srodon, J.

    1998-01-01

    Crystal size distributions (CSDs) of natural and synthetic samples are observed to have several distinct and different shapes. We have simulated these CSDs using three simple equations: the Law of Proportionate Effect (LPE), a mass balance equation, and equations for Ostwald ripening. The following crystal growth mechanisms are simulated using these equations and their modifications: (1) continuous nucleation and growth in an open system, during which crystals nucleate at either a constant, decaying, or accelerating nucleation rate, and then grow according to the LPE; (2) surface-controlled growth in an open system, during which crystals grow with an essentially unlimited supply of nutrients according to the LPE; (3) supply-controlled growth in an open system, during which crystals grow with a specified, limited supply of nutrients according to the LPE; (4) supply- or surface-controlled Ostwald ripening in a closed system, during which the relative rate of crystal dissolution and growth is controlled by differences in specific surface area and by diffusion rate; and (5) supply-controlled random ripening in a closed system, during which the rate of crystal dissolution and growth is random with respect to specific surface area. Each of these mechanisms affects the shapes of CSDs. For example, mechanism (1) above with a constant nucleation rate yields asymptotically-shaped CSDs for which the variance of the natural logarithms of the crystal sizes (??2) increases exponentially with the mean of the natural logarithms of the sizes (??). Mechanism (2) yields lognormally-shaped CSDs, for which ??2 increases linearly with ??, whereas mechanisms (3) and (5) do not change the shapes of CSDs, with ??2 remaining constant with increasing ??. During supply-controlled Ostwald ripening (4), initial lognormally-shaped CSDs become more symmetric, with ??2 decreasing with increasing ??. Thus, crystal growth mechanisms often can be deduced by noting trends in ?? versus ??2 of CSDs for a series of related samples.

  7. Synthesis, crystal growth, structural, thermal, optical and mechanical properties of solution grown 4-methylpyridinium 4-hydroxybenzoate single crystal.

    PubMed

    Sudhahar, S; Krishna Kumar, M; Sornamurthy, B M; Mohan Kumar, R

    2014-01-24

    Organic nonlinear optical material, 4-methylpyridinium 4-hydroxybenzoate (4MPHB) was synthesized and single crystal was grown by slow evaporation solution growth method. Single crystal and powder X-ray diffraction analyses confirm the structure and crystalline perfection of 4MPHB crystal. Infrared, Raman and NMR spectroscopy techniques were used to elucidate the functional groups present in the compound. TG-DTA analysis was carried out in nitrogen atmosphere to study the decomposition stages, endothermic and exothermic reactions. UV-visible and Photoluminescence spectra were recorded for the grown crystal to estimate the transmittance and band gap energy respectively. Linear refractive index, birefringence, and SHG efficiency of the grown crystal were studied. Laser induced surface damage threshold and mechanical properties of grown crystal were studied to assess the suitability of the grown crystals for device applications. PMID:24184578

  8. VO2 (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms

    NASA Astrophysics Data System (ADS)

    Rao Popuri, Srinivasa; Artemenko, Alla; Labrugere, Christine; Miclau, Marinela; Villesuzanne, Antoine; Pollet, Michaël

    2014-05-01

    Well crystallized VO2 (A) microrods were grown via a single step hydrothermal reaction in the presence of V2O5 and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO2 (A) micro rods. The structural and electronic transitions in VO2 (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversible intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO2 (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO2 (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO2 (M1) are described.

  9. User's Guide to Galoper: A Program for Simulating the Shapes of Crystal Size Distributions from Growth Mechanisms - and Associated Programs

    USGS Publications Warehouse

    Eberl, Dennis D.; Drits, V.A.; Srodon, J.

    2000-01-01

    GALOPER is a computer program that simulates the shapes of crystal size distributions (CSDs) from crystal growth mechanisms. This manual describes how to use the program. The theory for the program's operation has been described previously (Eberl, Drits, and Srodon, 1998). CSDs that can be simulated using GALOPER include those that result from growth mechanisms operating in the open system, such as constant-rate nucleation and growth, nucleation with a decaying nucleation rate and growth, surface-controlled growth, supply-controlled growth, and constant-rate and random growth; and those that result from mechanisms operating in the closed system such as Ostwald ripening, random ripening, and crystal coalescence. In addition, CSDs for two types weathering reactions can be simulated. The operation of associated programs also is described, including two statistical programs used for comparing calculated with measured CSDs, a program used for calculating lognormal CSDs, and a program for arranging measured crystal sizes into size groupings (bins).

  10. New AFM Techniques for Investigating Molecular Growth Mechanisms of Protein Crystals

    NASA Technical Reports Server (NTRS)

    Li, Huayu; Nadarajah, Arunan; Konnert, John H.; Pusey, Marc L.

    1998-01-01

    Atomic Force Microscopy (AFM) has emerged as a powerful technique for investigating protein crystal growth. Earlier AFM studies were among the first to demonstrate that these crystals grew by dislocation and 2D nucleation growth mechanisms [1]. These investigations were restricted to the micron range where only surface features, such as dislocation hillocks and 2D islands are visible. Most AFM instruments can scan at higher resolutions and have the potential to resolve individual protein molecules at nanometer ranges. Such scans are essential for determining the molecular packing arrangements on crystal faces and for probing the growth process at the molecular level. However, at this resolution the AFM tip influences the image produced, with the resulting image being a convolution of the tip shape and the surface morphology [2]. In most studies this problem is resolved by deconvoluting the image to obtain the true surface morphology. Although deconvolution routines work reasonably well for simple one- dimensional shapes, for complex surfaces this approach does not produce accurate results. In this study we devised a new approach which takes advantage of the precise molecular order of crystal surfaces, combined with the knowledge of individual molecular shapes from the crystallographic data of the protein and the AFM tip shape. This information is used to construct expected theoretical AFM images by convoluting the tip shape with the constructed crystal surface shape for a given surface packing arrangement. By comparing the images from actual AFM scans with the constructed ones for different possible surface packing arrangements, the correct packing arrangement can be conclusively determined. This approach was used in this study to determine the correct one from two possible packing arrangements on (I 10) faces of tetragonal lysozyme crystals. Another novel AFM technique was also devised to measure the dimension of individual growth units of the crystal faces. Measuring these units was not attempted before and most studies have assumed that the growth unit consisted of individual protein molecules. The linescan mode of AFM instruments allows the crystal surface to be scanned along a single line. By scanning across a growth step an image showing the motion of the step is obtained. Normally such an image shows a straight line for continuous and constant step velocity. In this study by increasing the scan rate and by decreasing the step velocity (by decreasing the supersaturation), we were able to capture images of individual growth events, shown by jump discontinuities in the step line. By suitable integration of the image the growth unit dimension in the scanned direction can be obtained. Since multiple units can be involved in the growth process it is necessary to collect a statistically relevant sample before drawing conclusions about the growth mechanism. This technique was successfully employed to obtain the dimensions of growth units for the (110) face, showing that they consisted of various aggregates corresponding to the 43 helices in the crystal structure.

  11. Crystal growth mechanisms and morphological control of the prototypical metal-organic framework MOF-5 revealed by atomic force microscopy.

    PubMed

    Cubillas, Pablo; Anderson, Michael W; Attfield, Martin P

    2012-11-26

    Crystal growth of the metal-organic framework MOF-5 was studied by atomic force microscopy (AFM) for the first time. Growth under low supersaturation conditions was found to occur by a two-dimensional or spiral crystal growth mechanism. Observation of developing nuclei during the former reveals growth occurs through a process of nucleation and spreading of metastable and stable sub-layers revealing that MOFs may be considered as dense phase structures in terms of crystal growth, even though they contain sub-layers consisting of ordered framework and disordered non-framework components. These results also support the notion this may be a general mechanism of surface crystal growth at low supersaturation applicable to crystalline nanoporous materials. The crystal growth mechanism at the atomistic level was also seen to vary as a function of the growth solution Zn/H(2)bdc ratio producing square terraces with steps parallel to the <100> direction or rhombus-shaped terraces with steps parallel to the <110> direction when the Zn/H(2)bdc ratio was >1 or about 1, respectively. The change in relative growth rates can be explained in terms of changes in the solution species concentrations and their influence on growth at different terrace growth sites. These results were successfully applied to the growth of as-synthesized cube-shaped crystals to increase expression of the {111} faces and to grow octahedral crystals of suitable quality to image using AFM. This modulator-free route to control the crystal morphology of MOF-5 crystals should be applicable to a wide variety of MOFs to achieve the desired morphological control for performance enhancement in applications. PMID:23055448

  12. Growth, mechanical, thermal and dielectric properties of pure and doped KHP single crystal

    NASA Astrophysics Data System (ADS)

    M, Lakshmipriya.; Babu, D. Rajan; Vizhi, R. Ezhil

    2015-06-01

    L-Arginine doped potassium hydrogen phthalate and L-Histidine doped potassium hydrogen phthalate single crystals were grown by slow evaporation method at room temperature. The grown crystal crystallizes in orthorhombic system which is confirmed by single crystal XRD analysis. The grown crystals are subjected to thermal, mechanical and dielectric analysis.

  13. Spiral crystal growth

    NASA Astrophysics Data System (ADS)

    Smereka, Peter

    2000-04-01

    We numerically study the spiral mode of crystal growth using a theory developed by Burton, Cabrera and Frank using a level set method. This method is novel in that it can handle not only closed curves but open curves as well. We use our method to compute interacting spirals and make estimates of growth rates. We also propose a possible coarsening mechanism for a large number of interacting spirals.

  14. Morphology and growth mechanism of multiply twinned AgBr and AgCl needle crystals

    NASA Astrophysics Data System (ADS)

    Bögels, G.; Buijnsters, J. G.; Verhaegen, S. A. C.; Meekes, H.; Bennema, P.; Bollen, D.

    1999-06-01

    In this study the morphology and growth mechanism of AgX (X=Cl, Br) needle crystals will be revealed. The silver halide needles are grown by two different techniques. AgBr needles are grown with an extractive crystallization in a dimethylsulfoxide-water mixture and AgCl needles are grown from the vapor phase. All needles contain nonparallel twin planes. The morphology of the AgBr needles grown from dimethylsulfoxide is the same as the needles grown in the industrial precipitation process in water. The side faces of these solution grown needles are built up of relatively slowly growing {1 1 1} faces. Both needle tops are composed of three relatively fast growing {1 0 0} faces making a ridge structure. The vapor-grown needles have two different morphologies. For both types the side faces consist of four {1 1 1} and two {1 0 0} faces. All {1 1 1} faces are linked via twin planes to a fast growing {1 0 0} face. The preferential unidirectional growth of all needles is caused by cross-twinning. The preferential growth occurs along the intersection line of the twin planes. Between the twin planes a rough growing face appears on the needle top. This face is capable of increasing the growth rate of the other top faces owing to the substep mechanism.

  15. AFM studies of the nucleation and growth mechanisms of macromolecular crystals

    NASA Astrophysics Data System (ADS)

    Kuznetsov, Yu. G.; Malkin, A. J.; McPherson, A.

    1999-01-01

    Atomic force microscopy (AFM) has been used to visualize events arising from the formation of intervening metastable phases at the surfaces of macromolecular crystals growing from solution. Crystals investigated were of the proteins canavalin, thaumatin, lipase, xylanase, and catalase, crystals of transfer RNA, and crystals of satellite tobacco mosaic virus. The appearance of aggregates on crystal surfaces was observed. The aggregates we infer to originate from liquid-protein droplets. These were particularly evident in freshly mixed mother liquor solutions. Droplets, upon sedimentation, have two possible fates. In some cases they immediately restructured as crystalline, multilayer stacks whose development was guided by, and contiguous with the underlying lattice. These contributed to the ordered growth of the crystal by serving as sources of growth steps. In other cases, liquid-protein droplets formed distinct microcrystals, somehow discontinuous with the underlying lattice, and these were subsequently incorporated into the growing substrate crystal. Scarring experiments with the AFM tip indicated that, detached from the crystal, molecules do not dissolve in the fluid phase but form metastable liquid-protein droplets with a potential to rapidly crystallize on the crystal surface. The molecular structure of the growth steps for thaumatin and lipase protein crystals were deduced. There is no step roughness due to thermal fluctuations, and each protein molecule which incorporated into the step edge remained. Growth steps propagate by addition of individual molecules which form subkinks of different size on the step edge.

  16. Crystal growth and dielectric, mechanical, electrical and ferroelectric characterization of n-bromo succinimide doped triglycine sulphate crystals

    Microsoft Academic Search

    Chitharanjan Rai; K. Byrappa; S. M. Dharmaprakash

    2011-01-01

    Single crystals of triglycine sulphate (TGS) doped with n-bromo succinimide (NBS) were grown at ambient temperature by the slow evaporation technique. An aqueous solution containing 1–20mol% of n-bromo succinimide as dopant was used for the growth of NBSTGS crystals. The incorporation of NBS in TGS crystals has been qualitatively confirmed by FTIR spectral data. The effect of the dopant on

  17. Crystal structure and growth mechanism of unusually long fullerene (C60) nanowires.

    PubMed

    Geng, Junfeng; Zhou, Wuzong; Skelton, Paul; Yue, Wenbo; Kinloch, Ian A; Windle, Alan H; Johnson, Brian F G

    2008-02-27

    Exceptionally long C60 nanowires, with a length to width aspect ratio as large as 3000, are grown from a 1,2,4-trimethylbenzene solution of C60. They have been formed to possess a highly unusual morphology, with each nanowire being composed of two nanobelts joined along the growth direction to give a V-shaped cross section. The crystal structure of these nanowires is found to be orthorhombic, with the unit cell dimensions of a = 10.2 A, b = 20.5 A, and c = 25.6 A. Structural and compositional analyses enable us to explain the observed geometry with an anisotropic molecular packing mechanism that has not been observed previously in C60 crystal studies. The nanowires have been observed to be able to transform into carbon nanofibers following high-temperature treatment, but the original V-shaped morphology can be kept unchanged in the transition. A model for the nanowire morphology based upon the solvent-C60 interactions and preferential growth directions is proposed, and potentially it could be extended for use to grow different types of fullerene nanowires. PMID:18251467

  18. Growth, optical, thermal and mechanical studies of methyl 4-hydroxybenzoate single crystals

    NASA Astrophysics Data System (ADS)

    Vijayan, N.; Ramesh Babu, R.; Gunasekaran, M.; Gopalakrishnan, R.; Ramasamy, P.

    2003-08-01

    Bulk single crystals of methyl 4-hydroxy benzoate have been successfully grown by slow evaporation solution growth technique at room temperature. The grown crystals have been subjected to spectroscopic studies like FT-IR and FT-Raman. The hardness of the crystal was measured by Vicker's microhardness tester. The lattice parameters have been calculated by X-ray diffraction technique and the values are in good agreement with the reported JCPDS file.

  19. Liquid encapsulated crystal growth

    NASA Technical Reports Server (NTRS)

    Morrison, Andrew D. (Inventor)

    1989-01-01

    Low-defect crystals are grown in a closed ampoule under a layer of encapsulant. After crystal growth, the crystal is separated from the melt and moved into the layer of encapsulant and cooled to a first temperature at which crystal growth stops. The crystal is then moved into the inert gas ambient in the ampoule and further cooled. The crystal can be separated from the melt by decanting the melt into an adjacent reservoir or by rotating the ampoule to rotate the crystal into the encapsulant layer.

  20. Crystal growth and mechanical characterization of ZrMo2O8

    NASA Astrophysics Data System (ADS)

    Ahmad, Md. Imteyaz; Mohanty, Gaurav; Rajan, Krishna; Akinc, Mufit

    2014-10-01

    We report a fluxing technique for ZrMo2O8 single crystal growth. The volatility of MoO3 coupled with the limited temperature range of its stability with the liquid phase makes the single crystal growth of ZrMo2O8 a formidable challenge. Single crystal growth of ZrMo2O8 was carried out in a horizontal tubular furnace using a platinum boat and utilizing Li2MoO4 as a fluxing agent. The synthesized faceted crystals were up to 3 mm along the maximum dimension. Laue and single crystal X-ray diffraction confirmed the monoclinic crystal structure having a space group C 1 2/c 1 (S.G#15), and a single crystallographic domain within the crystals. Reduced elastic modulus and hardness were determined to be 108±4 GPa and 6.4±0.2 GPa respectively using nanoindentation. Appearance of additional peaks in Raman spectra of the indented region when compared with the fresh crystal indicated a possible pressure induced phase transformation during indentation.

  1. Mercury iodide crystal growth

    NASA Technical Reports Server (NTRS)

    Cadoret, R.

    1982-01-01

    The purpose of the Mercury Iodide Crystal Growth (MICG) experiment is the growth of near-perfect single crystals of mercury Iodide (HgI2) in a microgravity environment which will decrease the convection effects on crystal growth. Evaporation and condensation are the only transformations involved in this experiment. To accomplish these objectives, a two-zone furnace will be used in which two sensors collect the temperature data (one in each zone).

  2. Determining the Molecular Growth Mechanisms of Protein Crystal Faces by Atomic Force Microscopy

    NASA Technical Reports Server (NTRS)

    Nadarajah, Arunan; Li, Huayu; Pusey, Marc L.

    1999-01-01

    A high resolution atomic force microscopy (AFM) study had shown that the molecular packing on the tetragonal lysozyme (110) face corresponded to only one of two possible packing arrangements, suggesting that growth layers on this face were of bimolecular height. Theoretical analyses of the packing also indicated that growth of this face should proceed by the addition of growth units of at least tetramer size corresponding to the 43 helices in the crystal. In this study an AFM linescan technique was devised to measure the dimensions of individual growth units on protein crystal faces as they were being incorporated into the lattice. Images of individual growth events on the (110) face of tetragonal lysozyme crystals were observed, shown by jump discontinuities in the growth step in the linescan images as shown in the figure. The growth unit dimension in the scanned direction was obtained from these images. A large number of scans in two directions on the (110) face were performed and the distribution of lysozyme growth unit sizes were obtained. A variety of unit sizes corresponding to 43 helices, were shown to participate in the growth process, with the 43 tetramer being the minimum observed size. This technique represents a new application for AFM allowing time resolved studies of molecular process to be carried out.

  3. Crystal growth of semiconductor bulk crystals

    SciTech Connect

    Kakimoto, Koichi [Research Institute for Applied Mechanics, Kyushu University, 6-1, Kasuga-Koen, Kasuga, 816-8580 (Japan)

    2010-07-22

    This course is aimed at showing how to grow bulk crystals by using several methods. The course involves the following points. The growth methods of Bridgman and Czochralski will be introduced. The course also focuses on the mechanism of some processes with consideration of the basic phenomenon. Experimental and numerical examples of the methods will also be introduced.

  4. Studies on growth, spectral, optical and mechanical properties of new organic NLO crystal: guanidinium L-glutamate (GuGL).

    PubMed

    Arumanayagam, T; Ananth, S; Murugakoothan, P

    2012-11-01

    Good optical quality single crystal of guanidinium l-glutamate is grown by slow evaporation solution growth technique. The cell parameters and crystallinity are determined from the single crystal and powder X-ray diffraction analysis. The formation of synthesized compound was confirmed by FT-IR and FT-Raman spectroscopic analysis. Wide band gap of 4.98eV with high transmittance up to 2000 nm is observed for the grown crystal in UV-Vis-NIR spectral analysis. The optical constants such as refractive index and extinction coefficient of the grown crystal are obtained as 2.1 and 8.64×10(-6) respectively. The nonlinear optical study reveals that the second harmonic generation efficiency of guanidinium l-glutamate is 2.8 times that of potassium dihydrogen phosphate (KDP). The mechanical stability of the grown crystal was analyzed by Vickers microhardness test and the results are discussed. PMID:22902572

  5. Investigation on growth, structural, optical, thermal, dielectric and mechanical properties of organic L-prolinium trichloroacetate single crystals

    SciTech Connect

    Boopathi, K.; Rajesh, P. [Centre for Crystal Growth, SSN college of Engineering, Kalavakkam 603 110 (India)] [Centre for Crystal Growth, SSN college of Engineering, Kalavakkam 603 110 (India); Ramasamy, P., E-mail: ramasamyp@ssn.edu.in [Centre for Crystal Growth, SSN college of Engineering, Kalavakkam 603 110 (India)

    2012-09-15

    Graphical abstract: L-Prolinium trichloroacetate is an organic nonlinear optical crystal has been grown from the aqueous solution by slow evaporation solution growth technique. Single crystal X-ray diffraction analysis reveals that L-PTCA crystallizes in trigonal crystal system. The optical band gab is found to be 4.26 eV. Second harmonic conversion efficiency of L-PTCA has been found to be half that of KDP. Highlights: ? It deals with the synthesis, growth and characterization of L-PTCA an organic NLO crystal. ? Wide optical transparency window between 260 nm and 1100 nm. ? Thermal study reveals that the grown crystal is stable up to 127 °C. ? L-PTCA crystal exhibits the second order nonlinear optical properties. -- Abstract: A new organic nonlinear optical material L-prolinium trichloroacetate (L-PTCA) single crystal has been synthesized and grown by slow solvent evaporation technique at room temperature using water as solvent. Single-crystal X-ray diffractometer was utilized to measure unit cell parameters and to confirm lattice parameter. The powder X-ray diffraction pattern of the grown L-PTCA has been indexed. The modes of vibration of different molecular groups present in the sample were identified by the FTIR spectral analysis. The optical transmittance window and the lower cutoff wavelength of the L-PTCA have been identified by UV–vis–NIR studies. Thermal stability of the L-prolinium trichloroacetate was determined by TGA/DTA measurements. Dielectric measurements were carried out at various temperatures at frequency range 10–1 MHz. The mechanical properties of the grown crystals have been analyzed by Vickers microhardness method. The chemical etching studies were carried out on the grown crystals. Its SHG efficiency has been tested by Kurtz powder method.

  6. Polymorphic polytypic transition induced in crystals by interaction of spirals and 2D growth mechanisms

    NASA Astrophysics Data System (ADS)

    Aquilano, Dino; Veesler, Stéphane; Astier, Jean Pierre; Pastero, Linda

    2003-01-01

    The relationship between crystal polymorphism and polytypism can be revealed by surface patterns through the interlacing of the growth spirals. Simple high-symmetry structures as SiC, ZnS, CdI2 and more complex low-symmetry layered structures as n-paraffins, n-alcohols and micas are concerned with polymorphic-polytypic transition. In this paper, we will show for the first time, through in situ AFM observations and X-ray diffractometry, that a protein polymorph (P2 12 12 1?-amylase) locally changes, during growth, to a monoclinic P2 1 polytype, thanks to the screw dislocation activity. The interplay between spiral steps and 2D nuclei of the polytypes coexisting in the same crystalline individual allows to foresee the consequences on the crystal quality. The discussion is extended to other mineral and biological molecules and a new general rule is proposed to explain the interactions between surface patterns and the bulk crystal structure.

  7. The Influence of Low Frequency Mechanical Vibrations on the Growth of Single Crystals

    NASA Technical Reports Server (NTRS)

    Feigelson, R. S.; Elwell, D.

    1985-01-01

    The optimum conditions for crystal growth are usually achieved either by suppressing convective fluid flows (e.g., by the use of a low-gravity environment) or by over-riding thermal and solutal convection by the use of a strong stirring action. A novel stirring technique has been developed which involves subjecting a vertical crucible to a circle in a horizontal plane (without rotation). Use of an amplitude of 3 mm at a frequency of approx 6 Hz produced complete mixing of a non-uniform aqueous liquid in a few seconds. The mixing action involved the downward flow of liquid in the outer annulus of the liquid, driven by surface waves. When the downward flowing liquid reaches the bottom of the crucible, it is reflected in a central, upward flowing spiral. This flow pattern should be beneficial for crystal growth by the Bridgman method since it will sweep impurities away from the walls and produce a more convex solid-liquid interface. Initial attempts to apply the new stirring technique to CdTe crystal growth did not show significant improvement in the number of crystals nucleated, but the interface shape appeared to be close to that predicted.

  8. The secrets of crystal growth

    SciTech Connect

    De Yoreo, J.; Land, T. [Lawrence Livermore National Lab., CA (United States)

    1996-11-01

    Lawrence Livermore researchers are using the atomic-force microscope (AFM) to elucidate the growth mechanisms and three-dimensional structures of widely different solution-based crystals on the nanometer (billionth-of-a-meter) scale. Much of the AFM work has been in support of the Laser Programs` need to better understand KDP (potassium dihydrogen phosphate) crystal growth because of its direct impact on advanced lasers such as the National Ignition Facility. A second avenue of research has focused on the growth of solution-based crystals of biological macromolecules, specifically the protein canavalin and the satellite tobacco mosaic virus. The AFM images have revealed how solution-based crystals grow and how they are affected by impurities, defects, and solution conditions. The results are likely to affect many disciplines and technologies, from pharmaceuticals to materials synthesis.

  9. Protein crystal growth

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Atomic force microscopy uses laser technology to reveal a defect, a double-screw dislocation, on the surface of this crystal of canavalin, a major source of dietary protein for humans and domestic animals. When a crystal grows, attachment kinetics and transport kinetics are competing for control of the molecules. As a molecule gets close to the crystal surface, it has to attach properly for the crystal to be usable. NASA has funded investigators to look at those attachment kinetics from a theoretical standpoint and an experimental standpoint. Dr. Alex McPherson of the University of California, Irvine, is one of those investigators. He uses X-ray diffraction and atomic force microscopy in his laboratory to answer some of the many questions about how protein crystals grow. Atomic force microscopy provides a means of looking at how individual molecules are added to the surface of growing protein crystals. This helps McPherson understand the kinetics of protein crystal growth. McPherson asks, How fast do crystals grow? What are the forces involved? Investigators funded by NASA have clearly shown that such factors as the level of supersaturation and the rate of growth all affect the habit [characteristic arrangement of facets] of the crystal and the defects that occur in the crystal.

  10. Shaped Crystal Growth

    NASA Astrophysics Data System (ADS)

    Tatartchenko, Vitali A.

    Crystals of specified shape and size (shaped crystals) with controlled defect and impurity structure have to be grown for the successful development of modern engineering. Since the 1950s many hundreds of papers and patents concerned with shaped growth have been published. In this chapter, we do not try to enumerate the successful applications of shaped growth to different materials but rather to carry out a fundamental physical and mathematical analysis of shaping as well as the peculiarities of shaped crystal structures. Four main techniques, based on which the lateral surface can be shaped without contact with the container walls, are analyzed: the Czochralski technique (CZT), the Verneuil technique (VT), the floating zone technique (FZT), and technique of pulling from shaper (TPS). Modifications of these techniques are analyzed as well. In all these techniques the shape of the melt meniscus is controlled by surface tension forces, i.e., capillary forces, and here they are classified as capillary shaping techniques (CST). We look for conditions under which the crystal growth process in each CST is dynamically stable. Only in this case are all perturbations attenuated and a crystal of constant cross section grown without any special regulation. The dynamic stability theory of the crystal growth process for all CST is developed on the basis of Lyapunov's dynamic stability theory. Lyapunov's equations for the crystal growth processes follow from fundamental laws. The results of the theory allow the choice of stable regimes for crystal growth by all CST as well as special designs of shapers in TPS. SCG experiments by CZT, VT, and FZT are discussed but the main consideration is given to TPS. Shapers not only allow crystal of very complicated cross section to be grown but provide a special distribution of impurities. A history of TPS is provided later in the chapter, because it can only be described after explanation of the fundamental principles of shaping. Some shaped crystals, especially sapphire and silicon, have specified structures. The crystal growth of these materials, and some metals, including crystal growth in space, is discussed.

  11. Studies on the growth, structural, optical, mechanical properties of 8-hydroxyquinoline single crystal by vertical Bridgman technique

    SciTech Connect

    Prabhakaran, SP. [Crystal Growth and Thin Film Laboratory, Department of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu (India)] [Crystal Growth and Thin Film Laboratory, Department of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu (India); Babu, R. Ramesh, E-mail: rampap2k@yahoo.co.in [Crystal Growth and Thin Film Laboratory, Department of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu (India); Velusamy, P.; Ramamurthi, K. [Crystal Growth and Thin Film Laboratory, Department of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu (India)] [Crystal Growth and Thin Film Laboratory, Department of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu (India)

    2011-11-15

    Highlights: {yields} Growth of bulk single crystal of 8-hydroxyquinoline (8-HQ) by vertical Bridgman technique for the first time. {yields} The crystalline perfection is reasonably good. {yields} The photoluminescence spectrum shows that the material is suitable for blue light emission. -- Abstract: Single crystal of organic nonlinear optical material, 8-hydroxyquinoline (8-HQ) of dimension 52 mm (length) x 12 mm (dia.) was grown from melt using vertical Bridgman technique. The crystal system of the material was confirmed by powder X-ray diffraction analysis. The crystalline perfection of the grown crystal was examined by high-resolution X-ray diffraction study. Low angular spread around 400'' of the diffraction curve and the low full width half maximum values show that the crystalline perfection is reasonably good. The recorded photoluminescence spectrum shows that the material is suitable for blue light emission. Optical transmittance for the UV and visible region was measured and mechanical strength was estimated from Vicker's microhardness test along the growth face of the grown crystal.

  12. Crystal Growth Control

    NASA Technical Reports Server (NTRS)

    Duval, Walter M. B.; Batur, Celal; Bennett, Robert J.

    1997-01-01

    We present an innovative design of a vertical transparent multizone furnace which can operate in the temperature range of 25 C to 750 C and deliver thermal gradients of 2 C/cm to 45 C/cm for the commercial applications to crystal growth. The operation of the eight zone furnace is based on a self-tuning temperature control system with a DC power supply for optimal thermal stability. We show that the desired thermal profile over the entire length of the furnace consists of a functional combination of the fundamental thermal profiles for each individual zone obtained by setting the set-point temperature for that zone. The self-tuning system accounts for the zone to zone thermal interactions. The control system operates such that the thermal profile is maintained under thermal load, thus boundary conditions on crystal growth ampoules can be predetermined prior to crystal growth. Temperature profiles for the growth of crystals via directional solidification, vapor transport techniques, and multiple gradient applications are shown to be easily implemented. The unique feature of its transparency and ease of programming thermal profiles make the furnace useful for scientific and commercial applications for the determination of process parameters to optimize crystal growth conditions.

  13. Bridgman crystal growth

    NASA Technical Reports Server (NTRS)

    Carlson, Frederick

    1990-01-01

    The objective of this theoretical research effort was to improve the understanding of the growth of Pb(x)Sn(1-x)Te and especially how crystal quality could be improved utilizing the microgravity environment of space. All theoretical growths are done using the vertical Bridgman method. It is believed that improved single crystal yields can be achieved by systematically identifying and studying system parameters both theoretically and experimentally. A computational model was developed to study and eventually optimize the growth process. The model is primarily concerned with the prediction of the thermal field, although mass transfer in the melt and the state of stress in the crystal were of considerable interest. The evolution is presented of the computer simulation and some of the important results obtained. Diffusion controlled growth was first studied since it represented a relatively simple, but nontheless realistic situation. In fact, results from this analysis prompted a study of the triple junction region where the melt, crystal, and ampoule wall meet. Since microgravity applications were sought because of the low level of fluid movement, the effect of gravitational field strength on the thermal and concentration field was also of interest. A study of the strength of coriolis acceleration on the growth process during space flight was deemed necessary since it would surely produce asymmetries in the flow field if strong enough. Finally, thermosolutal convection in a steady microgravity field for thermally stable conditions and both stable and unstable solutal conditions was simulated.

  14. Quartz crystal growth

    DOEpatents

    Baughman, Richard J. (Albuquerque, NM)

    1992-01-01

    A process for growing single crystals from an amorphous substance that can undergo phase transformation to the crystalline state in an appropriate solvent. The process is carried out in an autoclave having a lower dissolution zone and an upper crystallization zone between which a temperature differential (.DELTA.T) is maintained at all times. The apparatus loaded with the substance, solvent, and seed crystals is heated slowly maintaining a very low .DELTA.T between the warmer lower zone and cooler upper zone until the amorphous substance is transformed to the crystalline state in the lower zone. The heating rate is then increased to maintain a large .DELTA.T sufficient to increase material transport between the zones and rapid crystallization. .alpha.-Quartz single crystal can thus be made from fused quartz in caustic solvent by heating to 350.degree. C. stepwise with a .DELTA.T of 0.25.degree.-3.degree. C., increasing the .DELTA.T to about 50.degree. C. after the fused quartz has crystallized, and maintaining these conditions until crystal growth in the upper zone is completed.

  15. Protein crystals and their growth

    Microsoft Academic Search

    Alexander A. Chernov

    2003-01-01

    Recent results on the associations between protein molecules in crystal lattices, crystal–solution surface energy, elastic properties, strength, and spontaneous crystal cracking are reviewed and discussed. In addition, some basic approaches to understanding the solubility of proteins are followed by an overview of crystal nucleation and growth. It is argued that variability of mixing in batch crystallization may be a source

  16. Crystal Growth from the Melt: A Review

    Microsoft Academic Search

    R. Jeuss Knrpnrnrcr

    This paper reviews four aspects of crystal growth theory: the nature of the rate-controlling process, the mechanism controlling molecular attachment onto the growing crystal surface, the nature of the crystal-melt interface, and the stability of planar interfaces relative to cellular interfaces. The rate-controlling process may be diffusion in the melt, heat flow, or the reaction at the crystal-melt interface. Diffusion

  17. Single crystal growth and mechanical properties of MoSi2 and WSi2

    Microsoft Academic Search

    T. Hirano; M. Nakamura; K. Kimura; Y. Umakoshi

    1991-01-01

    A floating zone (FZ) furnace was modified into a high vacuum type furnace in order to grow high-purity single crystals of MoSi2 and WSi2. The impurity levels of the grown MoSi2 single crystals were very low and the residual resistivity ratio was large, indicating that the grown crystals were of good quality. Compression tests of MoSi2 and WSi2 single crystals

  18. Crystal Shape Evolution in Detached Bridgman Growth

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Mazuruk, K.

    2013-01-01

    Detached (or dewetted) Bridgman crystal growth defines that process in which a gap exists between a growing crystal and the crucible wall. Existence of the gap provides several advantages, including no sticking of the crystal to the crucible wall, reduced thermal and mechanical stresses, reduced dislocations, and no heterogeneous nucleation by the crucible. Numerical calculations are used to determine the conditions in which a gap can exist. According to crystal shape stability theory, only some of these gap widths will be dynamically stable. Beginning with a crystal diameter that differs from stable conditions, the transient crystal growth process is analyzed. In microgravity, dynamic stability depends only on capillary effects and is decoupled from heat transfer. Depending on the initial conditions and growth parameters, the crystal shape will evolve towards the crucible wall, towards a stable gap width, or towards the center of the crucible, collapsing the meniscus. The effect of a tapered crucible on dynamic stability is also described.

  19. Crystal Shape Evolution in Detached Bridgman Growth

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Mazuruk, K.

    2013-01-01

    Detached (or dewetted) Bridgman crystal growth defines that process in which a gap exists between a growing crystal and the crucible wall. Existence of the gap provides several advantages, including no sticking of the crystal to the crucible wall, reduced thermal and mechanical stresses, reduced dislocations, and no heterogeneous nucleation by the crucible. Numerical calculations are used to determine the conditions in which a gap can exist. According to crystal shape stability theory, only some of these gap widths will be dynamically stable. Beginning with a crystal diameter that differs from stable conditions, the transient crystal growth process is analyzed. In microgravity, dynamic stability depends only on capillary effects and is decoupled from heat transfer. Depending on the initial conditions and growth parameters, the crystal shape will evolve towards the crucible wall, towards a stable gap width, or towards the center of the crucible, collapsing the meniscus. The effect of a tapered crucible on dynamic stability is also described

  20. Growth, spectral, thermal, optical, mechanical and etching studies of l-lysine semi-maleate (l-LSM) single crystals.

    PubMed

    Vasudevan, V; Renuka, N; Ramesh Babu, R; Ramamurthi, K

    2014-10-31

    Organic nonlinear optical material, l-lysine semi-maleate (l-LSM) single crystals were grown by slow cooling solution growth technique. The crystal system of grown l-LSM was confirmed by single crystal and powder X-ray diffraction analyzes. Functional groups of the grown crystal have been identified by Fourier Transform Infrared spectral analysis. The proton and carbon NMR spectral studies confirm the presence of hydrogen and carbon in the grown l-LSM. The melting and thermal decomposition temperatures of the crystal were determined using thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses. Optical transparency, second harmonic generation efficiency, micro hardness, dielectric constant and loss, refractive index and birefringence have also been measured. Further, the growth patterns and dislocations present in the grown crystal are studied. PMID:25467679

  1. Growth, spectral, thermal, optical, mechanical and etching studies of L-lysine semi-maleate (L-LSM) single crystals

    NASA Astrophysics Data System (ADS)

    Vasudevan, V.; Renuka, N.; Ramesh Babu, R.; Ramamurthi, K.

    2015-02-01

    Organic nonlinear optical material, L-lysine semi-maleate (L-LSM) single crystals were grown by slow cooling solution growth technique. The crystal system of grown L-LSM was confirmed by single crystal and powder X-ray diffraction analyzes. Functional groups of the grown crystal have been identified by Fourier Transform Infrared spectral analysis. The proton and carbon NMR spectral studies confirm the presence of hydrogen and carbon in the grown L-LSM. The melting and thermal decomposition temperatures of the crystal were determined using thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses. Optical transparency, second harmonic generation efficiency, micro hardness, dielectric constant and loss, refractive index and birefringence have also been measured. Further, the growth patterns and dislocations present in the grown crystal are studied.

  2. Modular design of locally ordered tetrahedral structures: III. Structural mechanism of nonequilibrium fibrous and rough-layer normal growth of diamond crystals

    NASA Astrophysics Data System (ADS)

    Bul'enkov, N. A.; Zheligovskaya, E. A.

    2015-05-01

    Structural mechanisms of nontangential nonequilibrium normal growth of natural and synthetic diamond crystals with a fibrous or layered structure, formed under particularly nonequilibrium conditions, are proposed. It is shown that their growth is based on strained noncrystalline structures rapidly growing in length: 30/11 and 40/9 helices. The fibrous growth of diamond crystals along the <111> and <100> directions occurs according to the helicoidal mechanism, with helicoid axes in the form of 30/11 and 40/9 helices, respectively. Stacks of rough {110} lamellae can be formed via branching of 30/11 helices, which are then overgrown by a crystalline layer. Lamellae with orientation {100}, formed during the growth of diamond and silicon from vapor phase, also grow according to the helicoidal mechanism based on 40/9 helices via the aggregation of helicoids into these lamellae. Due to the complicated internal structure of these diamond crystals, their physical properties differ from those of diamond single crystals grown according to the tangential growth mechanism.

  3. Protein crystal growth in space

    NASA Technical Reports Server (NTRS)

    Bugg, C. E.; Clifford, D. W.

    1987-01-01

    The advantages of protein crystallization in space, and the applications of protein crystallography to drug design, protein engineering, and the design of synthetic vaccines are examined. The steps involved in using protein crystallography to determine the three-dimensional structure of a protein are discussed. The growth chamber design and the hand-held apparatus developed for protein crystal growth by vapor diffusion techniques (hanging-drop method) are described; the experimental data from the four Shuttle missions are utilized to develop hardware for protein crystal growth in space and to evaluate the effects of gravity on protein crystal growth.

  4. Growth, optical, luminescence, thermal and mechanical behavior of an organic single crystal: 3-Acetyl-2-methyl-4-phenylquinolin-1-ium chloride.

    PubMed

    Nirosha, M; Kalainathan, S; Sarveswari, S; Vijayakumar, V

    2014-04-01

    A single crystal of 3-acetyl-2-methyl-4-phenylquinolin-1-ium chloride has grown by slow evaporation solution growth technique using ethanol as solvent. The structural, thermal, optical and mechanical property has studied for the grown crystal. Single crystal XRD revealed that the crystal belongs to monoclinic system with space group P21/c. The presences of Functional groups in the crystallized material have confirmed using the FTIR vibrational spectrum. The optical absorbance spectrum recorded from 190 to 1100nm shows the cut-off wavelength occurs at 371nm. The material shows its transparency in the entire region of the visible spectrum. The photoluminescence spectrum shows the ultraviolet and blue emission in the crystal. Thermogravimetric and differential thermal analysis reveal the thermal stability of the grown crystal. Etching study shows the grown mechanism and surface features of the crystal. Vickers microhardness studies have carried out on the (01-1) plane to understand the mechanical properties of the grown crystal. The hardness of the title compound increases on increasing the load. The Meyer's index number (n), and the stiffness constants for different loads has calculated and reported. PMID:24389003

  5. What Variables Affect Crystal Growth?

    NSDL National Science Digital Library

    Students investigate variables that may influence the growth of crystals which they have learned to make. There are two options for implementing this activity. The first is open-ended, with the students deciding what variables affect crystal growth and then deciding on the manipulating variables they would like to study. The second is prescriptive and explains to students how to test three variables in making crystals: temperature, method of mixing (such as shaking or stirring), and concentration.

  6. Protein crystal growth in space

    NASA Technical Reports Server (NTRS)

    Delucas, Lawrence J.; Bugg, Charles E.

    1991-01-01

    Studies of protein crystal growth in the microgravity environment in space are described with special attention given to the crystal growth facilities and the techniques used in Space Shuttle experiments. The properties of large space-grown crystals of gamma interferon, elastase, lathyros ochrus lectin I, and few other proteins grown on various STS flights are described. A comparison of the microgravity-grown crystals with the bast earth-grown crystals demonstrated that the space-grown crystals are more highly ordered at the molecular level than their earth-grown counterparts. When crystallization conditions were optimized, the microgravity-grown protein crystals were larger, displayed more uniform morphologies, and yielded diffraction data to significantly higher resolution than their earth-grown counterparts.

  7. Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-chloro 4-nitrostilbene (CONS): a potential NLO material.

    PubMed

    Dinakaran, Paul M; Kalainathan, S

    2013-07-01

    4-Chloro 4-nitrostilbene (CONS) a new organic nonlinear optical material has been synthesized. Employing slow evaporation method, good optical quality single crystals (dimensions up to 6×2×3 mm(3)) have been grown using ethyl methyl ketone (EMK) as a solvent. The grown crystals have been subjected to various characterizations such as single crystal X-ray diffraction, powder XRD, Fourier Transform Infrared spectroscopy (FTIR), proton NMR, solid UV absorption, SHG studies. Single crystal X-ray diffraction reveals that the crystal system belongs to monoclinic with noncentrosymmetric space group P21. The UV-Vis absorption spectrum has been recorded and found that the cut off wavelength is 380 nm. Functional groups and the structure of the title compound have been confirmed by FTIR and (1)H NMR spectroscopic analyses respectively. Molecular mass of the CONS confirmed by the high resolution mass spectral analysis .The thermal behavior of the grown crystal has been studied by TG/DTA analysis and it shows the melting point is at 188.66 °C. Dislocations and growth pattern present in the grown crystal revealed by the etching study. The mechanical strength of the CONS crystal has been studied by Vicker's hardness measurement. The SHG efficiency of the grown crystal has been determined by Kurtz and Perry powder test which revealed that the CONS crystal (327 mV) has 15 times greater efficiency than that of KDP (21.7 mV). PMID:23624038

  8. Growth of oxide laser crystals

    NASA Astrophysics Data System (ADS)

    Kokta, Milan

    2007-09-01

    Optically pumped solid state lasers are frequently single crystals of inorganic oxides containing active elements. While, most of these crystals are simple inorganic oxides or binary mixtures of two oxides by adding active ions and activators, sometimes in significant quantities, these system become more complex. Resulting mixtures of four sometimes five oxides display more complicated properties than are those of simple oxides. Examples of such systems are CTH:YAG (Chromium, Thulium, Holmium Garnet), and CTE:YAG (Chromium, Thulium, Erbium Garnet). The need for very high optical quality crystal in laser applications made the manufacture (crystal growth and fabrication) one of the most demanding manufacturing processes. A description of the growth of research and development type crystals, as well as scaling the process to industrial level is described. The best understood and most practiced technique in commercial crystal growth is described along with its advantages and limitations. The effects of composition and properties of individual crystals on process variables, growth parameters, and thermal designs are described. The crystal quality enhancement and control by recognizing, understanding, and minimizing or elimination of crystal defects are described. Emphasis is given to material properties that play a role in the selection of growth parameters for individual host systems such as garnet-based or corundum-based laser crystals.

  9. Surrogate Seeds For Growth Of Crystals

    NASA Technical Reports Server (NTRS)

    Shlichta, Paul J.

    1989-01-01

    Larger crystals of higher quality grown. Alternative method for starting growth of crystal involves use of seed crystal of different material instead of same material as solution. Intended for growing single-crystal proteins for experiments but applicable in general to growth of crystals from solutions and to growth of semiconductor or other crystals from melts.

  10. Automated protein crystal growth facility

    NASA Technical Reports Server (NTRS)

    Donald, Stacey

    1994-01-01

    A customer for the protein crystal growth facility fills the specially designed chamber with the correct solutions, fills the syringes with their quenching solutions, and submits the data needed for the proper growth of their crystal. To make sure that the chambers and syringes are filled correctly, a NASA representative may assist the customer. The data needed is the approximate growth time, the growth temperature, and the desired crystal size, but this data can be changed anytime from the ground, if needed. The chambers are gathered and placed into numbered slots in special drawers. Then, data is entered into a computer for each of the chambers. Technicians map out when each chamber's growth should be activated so that all of the chambers have enough time to grow. All of this data is up-linked to the space station when the previous growth session is over. Anti-vibrational containers need to be constructed for the high forces encountered during the lift off and the landing of the space shuttle, and though our team has not designed these containers, we do not feel that there is any reason why a suitable one could not be made. When the shuttle reaches the space station, an astronaut removes a drawer of quenched chambers from the growth facility and inserts a drawer of new chambers. All twelve of the drawers can be replaced in this fashion. The optical disks can also be removed this way. The old drawers are stored for the trip back to earth. Once inside the growth facility, a chamber is removed by the robot and placed in one of 144 active sites at a time previously picked by a technician. Growth begins when the chamber is inserted into an active site. Then, the sensing system starts to determine the size of the protein crystal. All during the crystal's growth, the customer can view the crystal and read all of the crystal's data, such as growth rate and crystal size. When the sensing system determines that the crystal has reached the predetermined size, the robot is told to pick up a syringe filled with the correct quenchant solution and inject it into the chamber to stop the crystal growth. The chamber is then removed from the active site and placed into its original storage slot. Another chamber is then placed into the active site and the process is repeated in all of the active sites until all of the chambers have complted their growth. After ninety days (the scheduled time between shuttle visits), the crystal growth is completed, and the old drawers are replaced with new ones. Once the customer extracts the crystals, the chambers are retrieved for future customers.

  11. Growth, structural, spectral, mechanical, thermal and dielectric characterization of phosphoric acid admixtured L-alanine (PLA) single crystals.

    PubMed

    Rose, A S J Lucia; Selvarajan, P; Perumal, S

    2011-10-15

    Phosphoric acid admixtured L-alanine (PLA) single crystals were grown successfully by solution method with slow evaporation technique at room temperature. Crystals of size 18 mm×12 mm×8 mm have been obtained in 28 days. The grown crystals were colorless and transparent. The solubility of the grown samples has been found out at various temperatures. The lattice parameters of the grown crystals were determined by X-ray diffraction technique. The reflection planes of the sample were confirmed by the powder X-ray diffraction study and diffraction peaks were indexed. Fourier transform infrared (FTIR) studies were used to confirm the presence of various functional groups in the crystals. UV-visible transmittance spectrum was recorded to study the optical transparency of grown crystal. The nonlinear optical (NLO) property of the grown crystal was confirmed by Kurtz-Perry powder technique and a study of its second harmonic generation efficiency in comparison with potassium dihydrogen phosphate (KDP) has been made. The mechanical strength of the crystal was estimated by Vickers hardness test. The grown crystals were subjected to thermo gravimetric and differential thermal analysis (TG/DTA). The dielectric behavior of the sample was also studied. PMID:21775196

  12. Theory of Disc-Like Crystal Growth

    Microsoft Academic Search

    Jian-Jun Xu; Junichiro Shimizu

    2004-01-01

    The present paper is concerned with disc-like crystal growth from a pure undercooled melt. We assume that the growth of the top\\/bottom interface of the disc is very slow, dominated by the kinetic effect, while the growth of its side-interface is much faster, dominated by heat diffusion mechanism. We obtained the uniformly valid asymptotic solution for the basic state in

  13. Crystal Growth Inside an Octant

    E-print Network

    Jason Olejarz; P. L. Krapivsky

    2013-07-19

    We study crystal growth inside an infinite octant on a cubic lattice. The growth proceeds through the deposition of elementary cubes into inner corners. After re-scaling by the characteristic size, the interface becomes progressively more deterministic in the long-time limit. Utilizing known results for the crystal growth inside a two-dimensional corner, we propose a hyperbolic partial differential equation for the evolution of the limiting shape. This equation is interpreted as a Hamilton-Jacobi equation which helps in finding an analytical solution. Simulations of the growth process are in excellent agreement with analytical predictions. We then study the evolution of the sub-leading correction to the volume of the crystal, the asymptotic growth of the variance of the volume of the crystal, and the total number of inner and outer corners. We also show how to generalize the results to arbitrary spatial dimension.

  14. Studies on the growth, spectral, structural, electrical, optical and mechanical properties of Uronium 3-carboxy-4-hydroxybenzenesulfonate single crystal for third-order nonlinear optical applications.

    PubMed

    Silambarasan, A; Krishna Kumar, M; Thirunavukkarasu, A; Md Zahid, I; Mohan Kumar, R; Umarani, P R

    2015-05-01

    Organic Uronium 3-carboxy-4-hydroxybenzenesulfonate (UCHBS) nonlinear optical single crystal was grown by solution growth technique. The solubility and nucleation studies were performed for UCHBS at different temperatures 30, 35, 40, 45, 50 and 55°C. The crystal structure of UCHBS was elucidated from single crystal X-ray diffraction study. High resolution X-ray diffraction technique was employed to study the perfection and internal defects of UCHBS crystal. Infrared and Raman spectra were recorded to analyze the vibrational behavior of chemical bonds and its functional groups. The physico-chemical changes, stability and decomposition stages of the UCHBS compound were established by TG-DTA studies. The dielectric phenomenon of UCHBS crystal was studied at different temperatures with respect to frequency. Linear optical properties of transmittance, cut-off wavelength, band gap of UCHBS were found from UV-visible spectral studies. Third-order nonlinear optical susceptibility, nonlinear refractive index, nonlinear optical absorption coefficient values were measured by Z-scan technique. The mechanical properties of UCHBS crystal was studied by using Vicker's microhardness test. The growth features of UCHBS crystal were analyzed from etching studies. PMID:25699699

  15. Studies on the growth, spectral, structural, electrical, optical and mechanical properties of Uronium 3-carboxy-4-hydroxybenzenesulfonate single crystal for third-order nonlinear optical applications

    NASA Astrophysics Data System (ADS)

    Silambarasan, A.; Krishna Kumar, M.; Thirunavukkarasu, A.; Md Zahid, I.; Mohan Kumar, R.; Umarani, P. R.

    2015-05-01

    Organic Uronium 3-carboxy-4-hydroxybenzenesulfonate (UCHBS) nonlinear optical single crystal was grown by solution growth technique. The solubility and nucleation studies were performed for UCHBS at different temperatures 30, 35, 40, 45, 50 and 55 °C. The crystal structure of UCHBS was elucidated from single crystal X-ray diffraction study. High resolution X-ray diffraction technique was employed to study the perfection and internal defects of UCHBS crystal. Infrared and Raman spectra were recorded to analyze the vibrational behavior of chemical bonds and its functional groups. The physico-chemical changes, stability and decomposition stages of the UCHBS compound were established by TG-DTA studies. The dielectric phenomenon of UCHBS crystal was studied at different temperatures with respect to frequency. Linear optical properties of transmittance, cut-off wavelength, band gap of UCHBS were found from UV-visible spectral studies. Third-order nonlinear optical susceptibility, nonlinear refractive index, nonlinear optical absorption coefficient values were measured by Z-scan technique. The mechanical properties of UCHBS crystal was studied by using Vicker's microhardness test. The growth features of UCHBS crystal were analyzed from etching studies.

  16. Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    2003-01-01

    In order to rapidly and efficiently grow crystals, tools were needed to automatically identify and analyze the growing process of protein crystals. To meet this need, Diversified Scientific, Inc. (DSI), with the support of a Small Business Innovation Research (SBIR) contract from NASA s Marshall Space Flight Center, developed CrystalScore(trademark), the first automated image acquisition, analysis, and archiving system designed specifically for the macromolecular crystal growing community. It offers automated hardware control, image and data archiving, image processing, a searchable database, and surface plotting of experimental data. CrystalScore is currently being used by numerous pharmaceutical companies and academic and nonprofit research centers. DSI, located in Birmingham, Alabama, was awarded the patent Method for acquiring, storing, and analyzing crystal images on March 4, 2003. Another DSI product made possible by Marshall SBIR funding is VaporPro(trademark), a unique, comprehensive system that allows for the automated control of vapor diffusion for crystallization experiments.

  17. A study of crystal growth by solution technique

    NASA Technical Reports Server (NTRS)

    Lal, R. B.

    1981-01-01

    The mechanism of crystal growth by solution technique was studied. A low temperature solution crystal growth setup was developed. Crystals of triglycine sulfate (TGS) were grown using this arrangement. Some additional tasks were performed toward fabrication of experiments for future space flight.

  18. Two puzzling aspects of protein crystal growth

    NASA Technical Reports Server (NTRS)

    Grant, M. L.; Saville, D. A.

    1988-01-01

    A study is presented of several mechanisms which may reduce crystal growth rates and or terminate crystal growth. It is found that salt gradients which change the local chemical potential of the protein are insufficient to account for the slow crystal growth rates which have been reported. Contaminants which adsorb protein from solution may reduce the effective protein concentration, but the impurity's concentration and its affinity for protein are unknown. Association of protein molecules in bulk solution can reduce the monomer concentration significantly, but extant theory and experiment are not sensitive enough to determine the actual concentration of aggregates in solution. For systems of interest, shear-induced effects were found to be too weak to interfere with normal binding of incoming protein molecules. Although we found that most crystal growth occurs in a regime where both interfacial kinetics and diffusion influence crystal growth, the role of mass transfer rates on the terminal size of crystals is unknown, primarily because no data exist which cover the size range of interest (0.1 mm to 1 mm in length).

  19. A study of crystal growth by solution technique. [triglycine sulfate single crystals

    NASA Technical Reports Server (NTRS)

    Lal, R. B.

    1979-01-01

    The advantages and mechanisms of crystal growth from solution are discussed as well as the effects of impurity adsorption on the kinetics of crystal growth. Uncertainities regarding crystal growth in a low gravity environment are examined. Single crystals of triglycine sulfate were grown using a low temperature solution technique. Small components were assembled and fabricated for future space flights. A space processing experiment proposal accepted by NASA for the Spacelab-3 mission is included.

  20. Growth, spectroscopic investigation, optical, mechanical, chemical etching and nonlinear optical studies of semi-organic crystal: Bis (thiourea) zinc formate.

    PubMed

    Hanumantharao, Redrothu; Kalainathan, S

    2013-04-01

    Single crystals of Bis (thiourea) zinc formate (BTZF) were grown by slow evaporation method at room temperature. The grown crystal was confirmed by single crystal XRD, (1)H NMR and Mass spectroscopic techniques. Single crystal XRD technique revealed that material crystallized in monoclinic system with cell parameters a=8.693Å, b=7.151Å and c=9.311Å. The presence of hydrogen atoms in the grown sample was confirmed by proton NMR analysis. The mass spectral analysis was carried out to measure the accurate molecular mass of the compound. The recorded UV-Vis-NIR transmittance spectrum show excellent transmission in the range of 200-1100nm. Measuring transmittance of BTZF permitted the calculation of the extinction coefficient K, Reflectance R, as functions of photon energy. The etching study indicates the occurrence of different types of etch pit patterns on the growth surface. The Vickers (Hv) microhardness were carried out in the load range of 10-50g. Optical nonlinearities of BTZF have been investigated by Z-scan technique with He-Ne laser radiation of wavelength 638nm. PMID:23376259

  1. Biomolecular Modification of Inorganic Crystal Growth

    NASA Astrophysics Data System (ADS)

    De Yoreo, James J.

    2007-06-01

    The fascinating shapes and hierarchical designs of biomineralized structures are an inspiration to materials scientists because of the potential they suggest for biomolecular control over materials synthesis. Conversely, the failure to prevent or limit tissue mineralization in the vascular, skeletal, and urinary systems is a common source of disease. Understanding the mechanisms by which organisms direct or limit crystallization has long been a central challenge to the biomineralization community. One prevailing view is that mineral-associated macromolecules are responsible for either inhibiting crystallization or initiating and stabilizing non-equilibrium crystal polymorphs and morphologies through interactions between anionic moieties and cations in solution or at mineralizing surfaces. In particular, biomolecules that present carboxyl groups to the growing crystal have been implicated as primary modulators of growth. Here we review the results from a combination of in situ atomic force microscopy (AFM) and molecular modeling (MM) studies to investigate the effect of specific interactions between carboxylate-rich biomolecules and atomic steps on crystal surfaces during the growth of carbonates, oxalates and phosphates of calcium. Specifically, we how the growth kinetics and morphology depend on the concentration of additives that include citrate, simple amino acids, synthetic Asp-rich polypeptides, and naturally occurring Asp-rich proteins found in both functional and pathological mineral tissues. The results reveal a consistent picture of shape modification in which stereochemical matching of modifiers to specific atomic steps drives shape modification. Inhibition and other changes in growth kinetics are shown to be due to a range of mechanisms that depend on chemistry and molecular size. Some effects are well described by classic crystal growth theories, but others, such as step acceleration due to peptide charge and hydrophylicity, were previously unrealized. Finally, we show that the molecular scale observations are well correlated with macroscopic growth rate data.

  2. Crystal Growth of Water Ethanol Mixture

    NASA Astrophysics Data System (ADS)

    Ohkubo, Hidetoshi; Matsumoto, Nakamichi; Ochiai, Jun-Ichi; Nakajima, Masahiro

    Water ethanol mixture has a liquidus line (or crystallizing line) and a solidus line (or melting line) that are separated, and therefore it can have both liquid and solid phases existing together. As a result, with advances in low temperature technology in recent days, water ethanol mixture is attracting more and more attention as an environment friendly coolant or as a thermal storage material. In this study, we investigated the mechanism of mushy crystal formation and the state of am ushy layer formed on ac ooling surface, with the objective of utilizing water ethanol mixture as ac oolant or at hermal energy storage material. Two types of experiments were done in this work in order to study the mechanisms of crystal formation and growth. In one experiment, we studied the mechanism of crystal formation within a minute droplet of water ethanol mixture, and in the other, the mechanism of the crystal growth in the mushy layer formed in a liquid pool in contact with a cooling surface.

  3. Journal of Crystal Growth 130 (1993) 553--566 jo~*~ o~ CRYSTAL North-Holland GROWTH

    E-print Network

    Wadley, Haydn

    1993-01-01

    Journal of Crystal Growth 130 (1993) 553--566 jo~*~ o~ CRYSTAL North-Holland GROWTH Simulation of the eddy current sensing of gallium arsenide Czochralski crystal growth Haydn N.G. Wadley and Kumar P crystal is convex, single crystal growth occurs. Emerging monolithic microwave integrated cir- However

  4. Crystal growth in fused solvent systems

    NASA Technical Reports Server (NTRS)

    Ulrich, D. R.; Noone, M. J.; Spear, K. E.; White, W. B.; Henry, E. C.

    1973-01-01

    Research is reported on the growth of electronic ceramic single crystals from solution for the future growth of crystals in a microgravity environment. Work included growth from fused or glass solvents and aqueous solutions. Topics discussed include: crystal identification and selection; aqueous solution growth of triglycine sulphate (TGS); and characterization of TGS.

  5. Modeling Elasticity in Crystal Growth

    E-print Network

    K. R. Elder; Mark Katakowski; Mikko Haataja; Martin Grant

    2001-07-18

    A new model of crystal growth is presented that describes the phenomena on atomic length and diffusive time scales. The former incorporates elastic and plastic deformation in a natural manner, and the latter enables access to times scales much larger than conventional atomic methods. The model is shown to be consistent with the predictions of Read and Shockley for grain boundary energy, and Matthews and Blakeslee for misfit dislocations in epitaxial growth.

  6. Protein crystal growth; Proceedings of the First International Conference, Stanford University, CA, August 14-16, 1985

    NASA Technical Reports Server (NTRS)

    Feigelson, R. S. (editor)

    1986-01-01

    Papers are presented on mechanisms of nucleation and growth of protein crystals, the role of purification in the crystallization of proteins and nucleic acids, and the effect of chemical impurities in polyethylene glycol on macromolecular crystallization. Also considered are growth kinetics of tetragonal lysozyme crystals, thermodynamic and kinetic considerations for crystal growth of complex molecules from solution, protein single-crystal growth under microgravity, and growth of organic crystals in a microgravity environment. Papers are also presented on preliminary investigations of protein crystal growth using the Space Shuttle, convective diffusion in protein crystal growth, and the growth and characterization of membrane protein crystals.

  7. Journal of Crystal Growth 277 (2005) 578592 Nonlinear stability analysis of self-similar crystal growth

    E-print Network

    Lowengrub, John

    2005-01-01

    Journal of Crystal Growth 277 (2005) 578­592 Nonlinear stability analysis of self-similar crystal-similarly growing crystals was demonstrated recently in our previous work (J. Crystal Growth 267 (2004) 703). Here. Crystal Growth 266 (2004) 552). This enables us to accurately simulate the long-time, nonlinear dynamics

  8. Compact Apparatus For Growth Of Protein Crystals

    NASA Technical Reports Server (NTRS)

    Carter, Daniel C.; Miller, Teresa Y.

    1991-01-01

    Compact apparatus proposed specifically for growth of protein crystals in microgravity also used in terrestrial laboratories to initiate and terminate growth at prescribed times automatically. Has few moving parts. Also contains no syringes difficult to clean, load, and unload and introduces contaminant silicon grease into crystallization solution. After growth of crystals terminated, specimens retrieved and transported simply.

  9. Journal of Crystal Growth 266 (2004) 552567 Three-dimensional crystal growth--II: nonlinear simulation

    E-print Network

    Lowengrub, John

    2004-01-01

    Journal of Crystal Growth 266 (2004) 552­567 Three-dimensional crystal growth--II: nonlinear previous analysis (J Crystal Growth 240 (2002) 267) of the linear evolution of non-spherical growing to be carried out in a laboratory in which a desired shape of a crystal is achieved and maintained during growth

  10. Efg Crystal Growth Apparatus And Method

    SciTech Connect

    Mackintosh, Brian H. (Concord, MA); Ouellette, Marc (Nashua, NH)

    2003-05-13

    An improved mechanical arrangement controls the introduction of silicon particles into an EFG (Edge-defined Film-fed Growth) crucible/die unit for melt replenishment during a crystal growth run. A feeder unit injects silicon particles upwardly through a center hub of the crucible/die unit and the mechanical arrangement intercepts the injected particles and directs them so that they drop into the melt in a selected region of the crucible and at velocity which reduces splashing, whereby to reduce the likelihood of interruption of the growth process due to formation of a solid mass of silicon on the center hub and adjoining components. The invention also comprises use of a Faraday ring to alter the ratio of the electrical currents flowing through primary and secondary induction heating coils that heat the crucible die unit and the mechanical arrangement.

  11. Crystal growth and applications of mercuric iodide

    NASA Astrophysics Data System (ADS)

    Schieber, M.; Roth, M.; Schnepple, W. F.

    A brief summary is given of the crystal growth of mercuric iodide, a high-Z wide bandgap semiconductor suitable as a low noise, room temperature X-ray and gamma ray detector. The state of the art of the synthesis and purification of the starting material, mechanical properties and dislocation structure of HgI2, and recent success in the development of thick HgI2 spectrometers are summarized and reviewed.

  12. Growth of single crystal diamond

    NASA Astrophysics Data System (ADS)

    Regmi, Murari

    The subject of the research presented in this dissertation is the growth of single crystal diamond by microwave plasma chemical vapor deposition (CVD). Both heteroepitaxial and homoepitaxial growth methods have been examined, with emphasis on producing large diamond crystals of high structural and chemical perfection. By heteroepitaxy, epitaxial growth on a foreign substrate, diamond was grown on (001) Ir thin-film epitaxial buffer layers deposited on (001) strontium titanate (SrTiO3) by DC magnetron sputtering. To nucleate diamond on Ir, the Ir surface was bombarded with low energy ions extracted from the hydrocarbon plasma, a process known as DC biasing or bias-enhanced nucleation. Since this critical process is poorly understood, attention was paid to the spatial and temporal evolution of the Ir surface during the bias treatment. It was discovered that the biased Ir surface is etched on a surprisingly short time scale during which highly correlated nanopillars, 3-4 nm in height with mean separation 15 nm, emerge. The etching process is spatially non-uniform, propagating from substrate center to substrate edge in minutes. Diamond grew on Ir without an intervening phase. Lattice images revealed that interfacial strain from the 7% Ir-diamond lattice mismatch is largely relieved by misfit dislocations within 1 nm of the interface. It is suggested that the high nucleation density obtained with specific bias conditions is associated with the roughened Ir surface. To grow heteroepitaxial diamond as thick films, a two-step growth method was explored. This process involved the transfer of a thin heteroepitaxial diamond film, still attached to a substrate, to a second reactor where high growth rate conditions were possible. Characterization of films grown by this approach showed that the resulting diamond had much lower levels of internal strain, suggesting that the process could be used to grow diamond crystals of structural quality similar to natural diamond. In homoepitaxy, epitaxial growth on a substrate of the same material, diamond was deposited by CVD directly onto high-pressure, high-temperature Type Ib diamond substrates. Methods for removing substrate surface damage, as well as other imperfections, were devised by use of plasma etching. The characteristics and statistics of pits formed during etching were studied. Diamond growth methods were developed with the aim of minimizing the formation of various structural and chemical defects. To accomplish this, several growth parameters were varied, including substrate temperature, feed gas concentration, growth rate, substrate surface, microwave power, and reactor geometry. Regions of parameter space were found in which the diamond (001) surface remained smooth during growth, and complete suppression of instabilities that create hillocks or non-epitaxial crystallites was demonstrated. A great deal of information was obtained by interrupting growth, removing the crystal from the reactor for optical inspection, and then resuming the process with no apparent negative effects. Diamond crystals were grown on 3 x 3 mm2 substrates with thicknesses greater than 0.5 mm. The chemical purity of the crystals was such that it was impossible to observe signatures of substitutional nitrogen at the ppm level.

  13. Crystal growth and dendritic solidification

    Microsoft Academic Search

    James A. Sethian; John Strain

    1992-01-01

    The motion of complex solid\\/liquid boundaries in crystal growth is presently computed by a numerical model encompassing such physical effects as crystalline anisotropy, surface tension, molecular kinetics, and undercooling. The model recasts the equations of motion as a single, history-dependent boundary integral equation on the solid\\/liquid boundary, and moves the boundary by solving an equation formulated by Osher and Sethian

  14. Protein crystal growth in a microgravity environment

    NASA Technical Reports Server (NTRS)

    Bugg, Charles E.

    1988-01-01

    Protein crystal growth is a major experimental problem and is the bottleneck in widespread applications of protein crystallography. Research efforts now being pursued and sponsored by NASA are making fundamental contributions to the understanding of the science of protein crystal growth. Microgravity environments offer the possibility of performing new types of experiments that may produce a better understanding of protein crystal growth processes and may permit growth environments that are more favorable for obtaining high quality protein crystals. A series of protein crystal growth experiments using the space shuttle was initiated. The first phase of these experiments was focused on the development of micro-methods for protein crystal growth by vapor diffusion techniques, using a space version of the hanging drop method. The preliminary space experiments were used to evolve prototype hardware that will form the basis for a more advanced system that can be used to evaluate effects of gravity on protein crystal growth.

  15. Growth, structural, spectral, mechanical and dielectric characterization of RbCl-doped l-alanine hydrogen chloride monohydrate single crystals

    Microsoft Academic Search

    A. S. J. Lucia Rose; P. Selvarajan; S. Perumal

    2011-01-01

    Pure (undoped) and RbCl-doped LAHC single crystals were grown successfully by the solution method with the slow evaporation technique at room temperature. The grown crystals were colourless and transparent. The solubility of the grown samples were found out at various temperatures. The lattice parameters of the grown crystals were determined by the single crystal X-ray diffraction technique and the diffracting

  16. Journal of Crystal Growth 130 (1993) 495--506 ~ o~ CRYSTAL North-Holland GROWTH

    E-print Network

    Huppert, Herbert

    1993-01-01

    Journal of Crystal Growth 130 (1993) 495--506 ~ o~ CRYSTAL North-Holland GROWTH Solidification-eutectic aqueous solutions of NH4CI is rather sensitive to the microscopic details of the crystal growth. As reported in the cooling from below and resulting crystal- first by Copley et al. [1], after an initial

  17. Growth of Equally-Sized Insulin Crystals

    E-print Network

    Nanev, Christo N; Hodzhaoglu, Feyzim V

    2013-01-01

    Guidelines for growing insulin crystals of a uniform size are formulated and tested experimentally. A simple theoretical model based on the balance of matter predicts the time evolution of the crystal size and supersaturation. The time dependence of the size is checked experimentally. The experimental approach decouples crystal nucleation and growth processes according to the classical nucleation-growth-separation principle. Strict control over the nucleation process is exerted. Crystalline substance dispersity is predetermined during the nucleation stage of a batch crystallization process. To avert nutrition competition during the crystal growth stage, the number density of nucleated crystals is preset to be optimal.

  18. Pressure-Reduction Technique for Crystal Growth

    NASA Technical Reports Server (NTRS)

    Shlichta, P. J.

    1981-01-01

    Large crystals grown by varying pressure rather than temperature. In constant temerature pressure-reduction process crystal growth promoted as solubility decreases by factor of more than 10. Technique used to study crystal growth kinetics by "pressure wave"" analog of conventional "thermal wave" experiments. Technique has advantages of faster response and freedom from convective interference.

  19. Protein crystal growth in low gravity

    NASA Technical Reports Server (NTRS)

    Feigelson, Robert S.

    1991-01-01

    The objective of this research is to study the effect of low gravity on the growth of protein crystals and those parameters which will affect growth and crystal quality. The application of graphoepitaxy (artificial epitaxy) to proteins is detailed. The development of a method for the control of nucleation is discussed. The factor affecting the morphology of isocitrate lyase crystals is presented.

  20. Analytics of crystal growth in space

    NASA Technical Reports Server (NTRS)

    Wilcox, W. R.; Chang, C. E.; Shlichta, P. J.; Chen, P. S.; Kim, C. K.

    1974-01-01

    Two crystal growth processes considered for spacelab experiments were studied to anticipate and understand phenomena not ordinarily encountered on earth. Computer calculations were performed on transport processes in floating zone melting and on growth of a crystal from solution in a spacecraft environment. Experiments intended to simulate solution growth at micro accelerations were performed.

  1. Modelling the growth of feather crystals

    SciTech Connect

    Wood, H.J.; Hunt, J.D. [Univ. of Oxford (United Kingdom). Dept. of Materials] [Univ. of Oxford (United Kingdom). Dept. of Materials; Evans, P.V. [Alcan International Ltd., Banbury (United Kingdom). Banbury Labs.] [Alcan International Ltd., Banbury (United Kingdom). Banbury Labs.

    1997-02-01

    An existing numerical model of dendritic growth has been adapted to model the growth of twinned columnar dendrites (feather crystals) in a binary aluminium alloy, Examination of the effect of dendrite tip angle on growth has led to an hypothesis regarding the stability of a pointed tip morphology in these crystals.

  2. Measurable characteristics of lysozyme crystal growth

    NASA Technical Reports Server (NTRS)

    Gorti, Sridhar; Forsythe, Elizabeth L.; Pusey, Marc L.

    2005-01-01

    The behavior of protein crystal growth is estimated from measurements performed at both the microscopic and molecular levels. In the absence of solutal flow, it was determined that a model that balances the macromolecular flux toward the crystal surface with the flux of the crystal surface well characterizes crystal growth observed using microscopic methods. Namely, it was determined that the model provides accurate estimates for the crystal-growth velocities upon evaluation of crystal-growth measurements obtained in time. Growth velocities thus determined as a function of solution supersaturation were further interpreted using established deterministic models. From analyses of crystal-growth velocities, it was found that the mode of crystal growth varies with respect to increasing solution supersaturation, possibly owing to kinetic roughening. To verify further the hypothesis of kinetic roughening, crystal growth at the molecular level was examined using atomic force microscopy (AFM). From the AFM measurements, it was found that the magnitude of surface-height fluctuations, h(x), increases with increasing solution supersaturation. In contrast, the estimated characteristic length, xi, decreases rapidly upon increasing solution supersaturation. It was conjectured that the magnitude of both h(x) and xi could possibly determine the mode of crystal growth. Although the data precede any exact theory, the non-critical divergence of h(x) and xi with respect to increasing solution supersaturation was nevertheless preliminarily established. Moreover, approximate models to account for behavior of both h(x) and xi are also presented.

  3. Hanging drop crystal growth apparatus

    NASA Technical Reports Server (NTRS)

    Naumann, Robert J. (inventor); Witherow, William K. (inventor); Carter, Daniel C. (inventor); Bugg, Charles E. (inventor); Suddath, Fred L. (inventor)

    1990-01-01

    This invention relates generally to control systems for controlling crystal growth, and more particularly to such a system which uses a beam of light refracted by the fluid in which crystals are growing to detect concentration of solutes in the liquid. In a hanging drop apparatus, a laser beam is directed onto drop which refracts the laser light into primary and secondary bows, respectively, which in turn fall upon linear diode detector arrays. As concentration of solutes in drop increases due to solvent removal, these bows move farther apart on the arrays, with the relative separation being detected by arrays and used by a computer to adjust solvent vapor transport from the drop. A forward scattering detector is used to detect crystal nucleation in drop, and a humidity detector is used, in one embodiment, to detect relative humidity in the enclosure wherein drop is suspended. The novelty of this invention lies in utilizing angular variance of light refracted from drop to infer, by a computer algorithm, concentration of solutes therein. Additional novelty is believed to lie in using a forward scattering detector to detect nucleating crystallites in drop.

  4. Advanced protein crystal growth programmatic sensitivity study

    NASA Technical Reports Server (NTRS)

    1992-01-01

    The purpose of this study is to define the costs of various APCG (Advanced Protein Crystal Growth) program options and to determine the parameters which, if changed, impact the costs and goals of the programs and to what extent. This was accomplished by developing and evaluating several alternate programmatic scenarios for the microgravity Advanced Protein Crystal Growth program transitioning from the present shuttle activity to the man tended Space Station to the permanently manned Space Station. These scenarios include selected variations in such sensitivity parameters as development and operational costs, schedules, technology issues, and crystal growth methods. This final report provides information that will aid in planning the Advanced Protein Crystal Growth Program.

  5. Cluster Mechanism of Homogeneous Crystallization (Computer Study)

    NASA Astrophysics Data System (ADS)

    Belashchenko, D. K.

    2008-12-01

    A molecular dynamics (MD) study of homogeneous crystallization of liquid rubidium is conducted with an inter-particle pair potential. The equilibrium crystallization temperature of the models was 313 K. Models consisted of 500, 998, and 1968 particles in a basic cube. The main investigation method was as follows: to detect (along the MD run) the atoms with Voronoi polyhedrons (VP) of 0608 type (“0608-atoms,” as in a bcc crystal) and to detect the bound groups of 0608-atoms (“0608-clusters”) that could play the role of the seeds in crystallization. Full crystallization was observed only at temperatures lower than 185 K with the creation of a predominant bcc crystal. The crystallization mechanism of Rb models differs drastically from the mechanism adopted in classical nucleation theory. It consists of the growth of the total number of 0608-atoms on cooling and the formation of 0608-clusters, analogous to the case of coagulation of solute for a supersaturated two-component solution. At the first stage of the process the clusters have a very loose structure (something like medusa or octopus with many tentacles) and include inside atoms with other Voronoi polyhedron types. The dimensions of clusters quickly increase and approach those of the basic cube. 0608-atoms play the leading role in the crystallization process and activate the transition of the atoms involved in the 0608-coordination. The fast growth of the maximum cluster begins after it attains a critical size (about 150 0608-atoms). The fluctuations of cluster sizes are very important in the creation of a 0608-cluster of critical (threshold) size. These fluctuations are especially large in the interval from 180 K to 185 K.

  6. Crystallization seeds favour crystallization only during initial growth

    PubMed Central

    Allahyarov, E.; Sandomirski, K.; Egelhaaf, S.U.; Löwen, H.

    2015-01-01

    Crystallization represents the prime example of a disorder–order transition. In realistic situations, however, container walls and impurities are frequently present and hence crystallization is heterogeneously seeded. Rarely the seeds are perfectly compatible with the thermodynamically favoured crystal structure and thus induce elastic distortions, which impede further crystal growth. Here we use a colloidal model system, which not only allows us to quantitatively control the induced distortions but also to visualize and follow heterogeneous crystallization with single-particle resolution. We determine the sequence of intermediate structures by confocal microscopy and computer simulations, and develop a theoretical model that describes our findings. The crystallite first grows on the seed but then, on reaching a critical size, detaches from the seed. The detached and relaxed crystallite continues to grow, except close to the seed, which now prevents crystallization. Hence, crystallization seeds facilitate crystallization only during initial growth and then act as impurities. PMID:25975451

  7. Crystallization seeds favour crystallization only during initial growth.

    PubMed

    Allahyarov, E; Sandomirski, K; Egelhaaf, S U; Löwen, H

    2015-01-01

    Crystallization represents the prime example of a disorder-order transition. In realistic situations, however, container walls and impurities are frequently present and hence crystallization is heterogeneously seeded. Rarely the seeds are perfectly compatible with the thermodynamically favoured crystal structure and thus induce elastic distortions, which impede further crystal growth. Here we use a colloidal model system, which not only allows us to quantitatively control the induced distortions but also to visualize and follow heterogeneous crystallization with single-particle resolution. We determine the sequence of intermediate structures by confocal microscopy and computer simulations, and develop a theoretical model that describes our findings. The crystallite first grows on the seed but then, on reaching a critical size, detaches from the seed. The detached and relaxed crystallite continues to grow, except close to the seed, which now prevents crystallization. Hence, crystallization seeds facilitate crystallization only during initial growth and then act as impurities. PMID:25975451

  8. Nucleation and Convection Effects in Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Vekilow, Peter G.

    1998-01-01

    Our work under this grant has significantly contributed to the goals of the NASA supported protein crystallization program. We have achieved the main objectives of the proposed work, as outlined in the original proposal: (1) We have provided important insight into protein nucleation and crystal growth mechanisms to facilitate a rational approach to protein crystallization; (2) We have delineated the factors that currently limit the x-ray diffraction resolution of protein crystals, and their correlation to crystallization conditions; (3) We have developed novel technologies to study and monitor protein crystal nucleation and growth processes, in order to increase the reproducibility and yield of protein crystallization. We have published 17 papers in peer-reviewed scientific journals and books and made more than 15 invited and 9 contributed presentations of our results at international and national scientific meetings.

  9. Mechanics in Tumor Growth 1 Mechanics in Tumor Growth

    E-print Network

    Preziosi, Luigi

    Mechanics in Tumor Growth 1 1 Mechanics in Tumor Growth L. Graziano Polytechnic of Turin Department Torino, Italy Abstract. This chapter focuses on the mechanical aspects of tumor growth. After describing some of the main feature of tumor growth and in particular the phenomena involving stress

  10. Journal of Crystal Growth 129 (1993) 719--727 ~ CRYSTAL North-Holland GROWTH

    E-print Network

    Woodall, Jerry M.

    1993-01-01

    Journal of Crystal Growth 129 (1993) 719--727 ~ CRYSTAL North-Holland GROWTH Structural analysis-ray diffraction methods. Double crystal rocking curves from the as-deposited LT-GaAs show well defined interference fringes, indicating a high level of structural perfection. Triple crystal diffraction analysis

  11. Growth mechanism of NaClO 3 and NaBrO 3 crystals from aqueous solutions

    Microsoft Academic Search

    V. Surender; N. Arundhathi; K. Kishan Rao

    2006-01-01

    A study of growth rates of NaClO3 and NaBrO3 has been carried out using a small growth cell by in situ observation. Normal growth rates of (100) faces of NaClO3 and (111) faces of NaBrO3 along ?110? direction are measured under relatively high supersaturation ranging from 3–8%. In the initial stages of growth,\\u000a (100), (110) and (111) faces develop in

  12. Investigation of crystal growth from solutions

    NASA Technical Reports Server (NTRS)

    Miyagawa, I.

    1975-01-01

    Growth of organic compounds from solution, in particular Rochelle salt and triglycine sulphate, was investigated. Ground-based experiments showed that gravity-driven convection currents in the growth solution influenced defect production in crystals, degraded ferroelectric quality, and indicated that an experiment done in a zero-gravity environment would be beneficial. A crystal of Rochelle salt was grown on board Skylab-4. The quality of this crystal was compared to earth-grown crystals and its unusual features were studied. A typical defect produced in this convection-free environment was a long straight tube extending in the direction of the c crystal axis. These tubes were much longer and more regularly arranged than in similar earth-grown crystals. The crystal was actually several crystals with corresponding axes parallel to each other. Ferroelectric hysteresis experiments showed that some parts of the crystal had many defects, while other parts were of extremely good quality.

  13. Computer simulations of crystal growth defects

    NASA Astrophysics Data System (ADS)

    Heide, G.; Follner, H.; Jackson, R. A.; Wilde, P. J.

    In highly supersaturated solutions, potassium dichromate crystals exhibit a growth anomaly on (001): this face is rough and covered by many potassium dichromate platelets that are only a few ?m thick, even though the structure is centrosymmetric. The following study is based on the crystallite orientation and dichromate classification. The force field method showed that intergrowths of complete structural units (crystal nuclei) in the twin position are energetically favourable on (001) but not on the symmetrically equivalent (001) face. The energetically favourable intergrowth laws occur in nature as macroscopic twins. The necessary potential parameters were determined using a combination of empirical fitting, quantum mechanical ab initio calculations, and normal coordinate analysis of the vibration spectra. The empirical fitting was preformed using GULP program.

  14. Growth of polyhedral crystals from supersaturated vapor

    E-print Network

    Przemyslaw Gorka

    2007-03-26

    We examine the growth of crystals from vapor. We assume that the Wulff shape is a prism with a hexagonal base. The Gibbs-Thomson correction on the crystal surface is included in the model. Assuming that the-initial crystal has an admissible shape we show local in time existence of solutions.

  15. Intelligent decision support for protein crystal growth

    Microsoft Academic Search

    Igor Jurisica; Patrick Rogers; Janice I. Glasgow; Suzanne Fortier; Joseph R. Luft; Jennifer R. Wolfley; Melissa A. Bianca; George T. Detitta

    2001-01-01

    Current structural genomics projects are likely to produce hundreds of proteins a year for structural analysis. The primary goal of our research is to speed up the process of crystal growth for proteins in order to enable the determination of protein structure using single crystal X-ray diffraction. We describe Max, a working prototype that includes a high-throughput crystallization and evaluation

  16. Optical diagnostics of solution crystal growth

    NASA Technical Reports Server (NTRS)

    Kim, Yongkee; Reddy, B. R.; George, Tharayil G.; Lal, Ravindra B.

    1995-01-01

    Solution crystal growth monitoring of LAP/TGS crystals by various optical diagnostics systems, such as conventional and Mach-Zehnder (M-Z) interferometers, optical heterodyne technique, and ellipsometry, is under development. The study of the dynamics of the crystal growth process requires a detailed knowledge of crystal growth rate and the concentration gradient near growing crystals in aqueous solution. Crystal growth rate can be measured using conventional interferometry. Laser beam reflections from the crystal front as well as the back surface interfere with each other, and the fringe shift due to the growing crystal yields information about the growth rate. Our preliminary results indicate a growth rate of 6 A/sec for LAP crystals grown from solution. Single wavelength M-Z interferometry is in use to calculate the concentration gradient near the crystal. Preliminary investigation is in progress using an M-Z interferometer with 2 cm beam diameter to cover the front region of the growing crystal. In the optical heterodyne technique, phase difference between two rf signals (250 KHZ) is measured of which one is a reference signal, and the other growth signal, whose phase changes due to a change in path length as the material grows. From the phase difference the growth rate can also be calculated. Our preliminary results indicate a growth rate of 1.5 A/sec. the seed and solution temperatures were 26.46 C and 27.92 C respectively, and the solution was saturated at 29.0 C. an ellipsometer to measure the growth rate and interface layer is on order from JOBIN YVON, France. All these systems are arranged in such a manner that measurements can be made either sequentially or simultaneously. These techniques will be adapted for flight experiment.

  17. Thermosyphon Suspension For Growth Of Crystals

    NASA Technical Reports Server (NTRS)

    Nyce, Thomas A.

    1991-01-01

    Thermosyphon provides gentle convective flow of supersaturated solution that both suspends and contributes material to growing crystal. Apparatus includes heating section, cooling section, and expansion-and-growth chamber in closed flow loop. Intended for growth of protein crystals, so fragile they are easily damaged by high-shear flows produced by pumps.

  18. Growth of Sillenite-Structure Single Crystals

    Microsoft Academic Search

    V. M. Skorikov; Yu. F. Kargin; A. V. Egorysheva; V. V. Volkov; M. Gospodinov

    2005-01-01

    The main processes for preparing bulk single crystals and films of photorefractive and piezoelectric Bi12MxO20±? (M = Group II–VIII elements) sillenite compounds are considered. Experimental data are summarized on the crystal growth of\\u000a Bi12MxO20±? from the melt and under hydrothermal conditions, and the key morphological features of sillenites are analyzed. Various types\\u000a of macroscopic growth defects in sillenite-type crystals are

  19. Journal of Crystal Growth 267 (2004) 703713 Nonlinear theory of self-similar crystal growth and melting

    E-print Network

    Lowengrub, John

    2004-01-01

    Journal of Crystal Growth 267 (2004) 703­713 Nonlinear theory of self-similar crystal growth analysis (J. Crystal Growth, 240 (2002) 267) and dynamical numerical simulations (J. Crystal Growth 240 (2003) in press). Here, we develop a nonlinear theory of self- similar crystal growth and melting

  20. Diffusion, Viscosity and Crystal Growth in Microgravity

    NASA Technical Reports Server (NTRS)

    Myerson, Allan S.

    1996-01-01

    The diffusivity of TriGlycine Sulfate (TGS), Potassium Dihydrogen Phosphate (KDP), Ammonium Dihydrogen Phosphate (ADF) and other compounds of interest to microgravity crystal growth, in supersaturated solutions as a function of solution concentration, 'age' and 'history was studied experimentally. The factors that affect the growth of crystals from water solutions in microgravity have been examined. Three non-linear optical materials have been studied, potassium dihydrogen phosphate (KDP), ammonium dihydrogen phosphate (ADP) and triglycine sulfate (TGC). The diffusion coefficient and viscosity of supersaturated water solutions were measured. Also theoretical model of diffusivity and viscosity in a metastable state, model of crystal growth from solution including non-linear time dependent diffusivity and viscosity effect and computer simulation of the crystal growth process which allows simulation of the microgravity crystal growth were developed.

  1. Computational studies of dendritic crystal growth

    NASA Astrophysics Data System (ADS)

    Kim, Yung Tae

    In this dissertation, I will review my research on developing and validating novel ways to model dendritic crystal growth---the formation of snowflake-like patterns during the solidification of crystalline substances. After giving a brief introduction to the sharp-interface model and phase-field model, I will discuss the following topics: the universal dynamics of different phase-field models and the range of validity of the asymptotic analysis of Karma and Rappel; the creation of an improved level set method that is used to solve the sharp-interface model and compute time-dependent solidification microstructures; a review of two sidebranching mechanisms and suggestions on how to verify tip-oscillations by using different models of solidification; and an attempt to create an efficient cell dynamical system model to study universal features of dendritic growth.

  2. VGF growth of germanium single crystals without crucible contact

    NASA Astrophysics Data System (ADS)

    Langheinrich, D.; Pätzold, O.; Raabe, L.; Stelter, M.

    2010-08-01

    Experimental results on the vertical gradient freeze growth of germanium single crystals without crucible contact are presented. Two different approaches to establish a stable pressure difference necessary for avoiding the contact between crystal and crucible on solidification are described. Germanium crystals with a diameter of up to 3 in were grown almost without contact to the crucible wall. The effect of detachment is discussed with respect to the microscopical surface roughness and dislocation density of the grown crystals. In comparison to conventionally grown reference crystals the structural perfection of the detached-grown crystals is found to be much higher which can be attributed to the reduced thermal and thermo-mechanical stress in growth without wall contact.

  3. Transport and Growth Kinetics in Microgravity Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Otalora, F.; Garcia-Ruiz, J. M.; Carotenuto, L.; Castagnolo, D.; Novella, M. L.; Chernov, A. A.

    2002-01-01

    The dynamic coupling between mass transport and incorporation of growth units into the surface of a crystal growing from solution in microgravity is used to derive quantitative information on the crystal growth kinetics. To this end, new procedures for experiment preparation, interferometric data processing and model fitting have been developed. The use of experimental data from the bulk diffusive maw transport together with a model for steady state stagnant crystal growth allows the detailed quantitative understanding of the kinetics of both the concentration depletion zone around the crystal and the growth of the crystal interface. The protein crystal used in the experiment is shown to be growing in the mixed kinetic regime (0.2 x 10(exp -6) centimeters per second less than beta R/D less than 0.9 x 10(exp -6) centimeters per second).

  4. Hgi2 Sub 2 Crystal Growth for Nuclear Detectors

    NASA Technical Reports Server (NTRS)

    Schnepple, W. F.; Vandenberg, L.

    1985-01-01

    The objectives of this program are to obtain a benchmark quality sample grown at low-g conditions and to study vapor growth phenomena under space conditions. Ground-based crystals show a defect structure which impairs their performance as nuclear radiation detectors. These defects may be caused by the gravitational force acting on the crystal in its weakended state at the elevated growth temperature and by irregular convection patterns in the vapor during growth. Mechanical strength measurements have been performed (uniaxial compression tests) which show that the crystals exhibit slip parallel to the c-planes at stresses as low as 1/2 psi. Preliminary calculations using a simple linearized model indicate the oscillating instabilities in the convection part of the vapor transport system are unlikely, even at 1-g, provided that the utmost care is taken in the preparation of the crystal growth source material.

  5. Thermal crystallization mechanism of silk fibroin protein

    NASA Astrophysics Data System (ADS)

    Hu, Xiao

    In this thesis, the thermal crystallization mechanism of silk fibroin protein from Bombyx mori silkworm, was treated as a model for the general study of protein based materials, combining theories from both biophysics and polymer physics fields. A systematic and scientific path way to model the dynamic beta-sheet crystallization process of silk fibroin protein was presented in the following sequence: (1) The crystallinity, fractions of secondary structures, and phase compositions in silk fibroin proteins at any transition stage were determined. Two experimental methods, Fourier transform infrared spectroscopy (FTIR) with Fourier self-deconvolution, and specific reversing heat capacity, were used together for the first time for modeling the static structures and phases in the silk fibroin proteins. The protein secondary structure fractions during the crystallization were quantitatively determined. The possibility of existence of a "rigid amorphous phase" in silk protein was also discussed. (2) The function of bound water during the crystallization process of silk fibroin was studied using heat capacity, and used to build a silk-water dynamic crystallization model. The fundamental concepts and thermal properties of silk fibroin with/without bound water were discussed. Results show that intermolecular bound water molecules, acting as a plasticizer, will cause silk to display a water-induced glass transition around 80°C. During heating, water is lost, and the change of the microenvironment in the silk fibroin chains induces a mesophase prior to thermal crystallization. Real time FTIR during heating and isothermal holding above Tg show the tyrosine side chain changes only during the former process, while beta sheet crystallization occurs only during the latter process. Analogy is made between the crystallization of synthetic polymers according to the four-state scheme of Strobl, and the crystallization process of silk fibroin, which includes an intermediate precursor stage before crystallization. (3) The beta-sheet crystallization kinetics in silk fibroin protein were measured using X-ray, FTIR and heat flow, and the structure reveals the formation mechanism of the silk crystal network. Avrami kinetics theories, which were established for studies of synthetic polymer crystal growth, were for the first time extended to investigate protein self-assembly in multiblock silk fibroin samples. The Avrami exponent, n, was close to two for all methods, indicating formation of beta sheet crystals in silk proteins is different from the 3-D spherulitic crystal growth found in most synthetic homopolymers. A microphase separation pattern after chymotrypsin enzyme biodegradation was shown in the protein structures using scanning electron microscopy. A model was then used to explain the crystallization of silk fibroin protein by analogy to block copolymers. (4) The effects of metal ions during the crystallization of silk fibroin was investigated using thermal analysis. Advanced thermal analysis methods were used to analyze the thermal protein-metallic ion interactions in silk fibroin proteins. Results show that K+ and Ca2+ metallic salts play different roles in silk fibroin proteins, which either reduce (K+) or increase (Ca2+ ) the glass transition (Tg) of pure silk protein and affect the thermal stability of this structure.

  6. Crack propagation driven by crystal growth

    SciTech Connect

    A. Royne; Paul Meaking; A. Malthe-Sorenssen; B. Jamtveit; D. K. Dysthe

    2011-10-01

    Crystals that grow in confinement may exert a force on their surroundings and thereby drive crack propagation in rocks and other materials. We describe a model of crystal growth in an idealized crack geometry in which the crystal growth and crack propagation are coupled through the stress in the surrounding bulk solid. Subcritical crack propagation takes place during a transient period, which may be very long, during which the crack velocity is limited by the kinetics of crack propagation. When the crack is sufficiently large, the crack velocity becomes limited by the kinetics of crystal growth. The duration of the subcritical regime is determined by two non-dimensional parameters, which relate the kinetics of crack propagation and crystal growth to the supersaturation of the fluid and the elastic properties of the surrounding material.

  7. Protein-crystal growth experiment (planned)

    NASA Technical Reports Server (NTRS)

    Fujita, S.; Asano, K.; Hashitani, T.; Kitakohji, T.; Nemoto, H.; Kitamura, S.

    1988-01-01

    To evaluate the effectiveness of a microgravity environment on protein crystal growth, a system was developed using 5 cubic feet Get Away Special payload canister. In the experiment, protein (myoglobin) will be simultaneously crystallized from an aqueous solution in 16 crystallization units using three types of crystallization methods, i.e., batch, vapor diffusion, and free interface diffusion. Each unit has two compartments: one for the protein solution and the other for the ammonium sulfate solution. Compartments are separated by thick acrylic or thin stainless steel plates. Crystallization will be started by sliding out the plates, then will be periodically recorded up to 120 hours by a still camera. The temperature will be passively controlled by a phase transition thermal storage component and recorded in IC memory throughout the experiment. Microgravity environment can then be evaluated for protein crystal growth by comparing crystallization in space with that on Earth.

  8. Mechanisms for the Crystallization of ZBLAN

    NASA Technical Reports Server (NTRS)

    Ethridge, Edwin C.; Tucker, Dennis S.; Kaukler, William; Antar, Basil

    2003-01-01

    The objective of this ground based study is to test the hypothesis that shear thinning (the non-Newtonian response of viscosity to shear rate) is a viable mechanism to explain the observation of enhanced glass formation in numerous low-g experiments. In 1-g, fluid motion results from buoyancy forces and surface tension driven convection. This fluid flow will introduce shear in undercooled liquids in 1-g. In low-g it is known that fluid flows are greatly reduced so that the shear rate in fluids can be extremely low. It is believed that some fluids may have weak structure in the absence of flow. Very small shear rates could cause this structure to collapse in response to shear resulting in a lowering of the viscosity of the fluid. The hypothesis of this research is that: Shear thinning in undercooled liquids decreases the viscosity, increasing the rate of nucleation and crystallization of glass forming melts. Shear in the melt can be reduced in low-g, thus enhancing undercooling and glass formation. The viscosity of a model glass (lithium di-silicate, L2S) often used for crystallization studies has been measured at very low shear rates using a dynamic mechanical thermal analyzer. Our results are consistent with increasing viscosity with a lowering of shear rates. The viscosity of L2S may vary as much as an order of magnitude depending on the shear rate in the temperature region of maximum nucleation and crystal growth. Classical equations for nucleation and crystal growth rates, are inversely related to the viscosity and viscosity to the third power respectively. An order of magnitude variation in viscosity (with shear) at a given temperature would have dramatic effects on glass crystallization Crystallization studies with the heavy metal fluoride glass ZBLAN (ZrF2-BaF2-LaF3-AlF3-NaF) to examine the effect of shear on crystallization are being initiated. Samples are to be melted and quenched under quiescent conditions at different shear rates to determine the effect on crystallization. The results from this study are expected to advance the current scientific understanding of glass formation in low-g and glass crystallization under glass molding conditions and will improve the scientific understanding of technological processes such as fiber pulling, bulk amorphous alloys, and glass fabrication processes.

  9. Compatibility waves drive crystal growth on patterned substrates

    E-print Network

    Tim Neuhaus; Michael Schmiedeberg; Hartmut Löwen

    2013-07-08

    We explore the crystallization in a colloidal monolayer on a structured template starting from a few-particle nucleus. The competition between the substrate structure and that of the growing crystal induces a new crystal growth scenario. Unlike with the crystal growth in the bulk where a well-defined and connected crystal-fluid interface grows into the fluid, we identify a mechanism where a "compatibility wave" of the prescribed nucleus with the underlying substrate structure dictates the growth direction and efficiency. The growth process is strongly anisotropic and proceeds via transient island formation in front of an initial solid-fluid interface. We demonstrate the validity of this compatibility wave concept for a large class of substrate structures including a square-lattice and a quasicrystalline pattern. Dynamical density functional theory which provides a microscopic approach to the crystallization process is employed for colloidal hard spheres. Our predictions can be verified in experiments on confined colloids and also bear consequences for molecular crystal growth on structured substrates.

  10. Journal of Crystal Growth 240 (2002) 267276 Three-dimensional crystal growth--I: linear analysis and

    E-print Network

    Lowengrub, John

    2002-01-01

    Journal of Crystal Growth 240 (2002) 267­276 Three-dimensional crystal growth--I: linear analysis; in: H.S. Peiser (Ed.), Crystal Growth, Pergamon, Oxford, 1967, p. 703) of the quasi stability; A2. Growth from melt; A2. Single crystal growth *Corresponding author. Tel: +1-612-625-0753; fax

  11. (PCG) Protein Crystal Growth Porcine Elastase

    NASA Technical Reports Server (NTRS)

    1989-01-01

    (PCG) Protein Crystal Growth Porcine Elastase. This enzyme is associated with the degradation of lung tissue in people suffering from emphysema. It is useful in studying causes of this disease. Principal Investigator on STS-26 was Charles Bugg.

  12. The Growth of Large Single Crystals.

    ERIC Educational Resources Information Center

    Baer, Carl D.

    1990-01-01

    Presented is an experiment which demonstrates principles of experimental design, solubility, and crystal growth and structure. Materials, procedures and results are discussed. Suggestions for adapting this activity to the high school laboratory are provided. (CW)

  13. Illusory spirals and loops in crystal growth

    PubMed Central

    Shtukenberg, Alexander G.; Zhu, Zina; Bhandari, Misha; Song, Pengcheng; Kahr, Bart; Ward, Michael D.

    2013-01-01

    The theory of dislocation-controlled crystal growth identifies a continuous spiral step with an emergent lattice displacement on a crystal surface; a mechanistic corollary is that closely spaced, oppositely winding spirals merge to form concentric loops. In situ atomic force microscopy of step propagation on pathological l-cystine crystals did indeed show spirals and islands with step heights of one lattice displacement. We show by analysis of the rates of growth of smaller steps only one molecule high that the major morphological spirals and loops are actually consequences of the bunching of the smaller steps. The morphology of the bunched steps actually inverts the predictions of the theory: Spirals arise from pairs of dislocations, loops from single dislocations. Only through numerical simulation of the growth is it revealed how normal growth of anisotropic layers of molecules within the highly symmetrical crystals can conspire to create features in apparent violation of the classic theory. PMID:24101507

  14. Crystallization mechanisms of stoichiometric monomethylhydrazine—water mixtures

    Microsoft Academic Search

    N. Clavaguera; V Palumbo-Romand; M Ferriol; M. T Cohen-Adad

    1997-01-01

    Lights scattering measurements of crystallization under the isothermal regime of stoichiometric mixtures of CH3NHNH2·H2O, in the temperature range 180–200 K are modeled as nucleation-growth of the two crystalline forms, stable and metastable, that result as crystallization products. The modeling procedure is founded on the Johnson—Melh—Avrami—Komolgorov model with introduction of the competition between interface and diffusion growth limiting mechanisms. The nucleation

  15. Growth Of Oriented Crystals At Polymerized Membranes

    DOEpatents

    Charych, Deborah H. (Albany, CA), Berman, Amir (Ben-Shiva, IL)

    2000-01-25

    The present invention relates to methods and compositions for the growth and alignment of crystals at biopolymeric films. The methods and compositions of the present invention provide means to generate a variety of dense crystalline ceramic films, with totally aligned crystals, at low temperatures and pressures, suitable for use with polymer and plastic substrates.

  16. Electrochemical Growth Of Crystals In Gels

    NASA Technical Reports Server (NTRS)

    Barber, Patrick G.; Coleman, James

    1988-01-01

    Nucleation and growth rates readily controlled. Technique developed to grow crystals by controlling rate of transfer of one component into crystallization volume. Method involves electrochemically controlled generation of one of precipitation species, coupled with diffusion barrier. New procedure, developed in connection with formation of lead tin telluride by reaction in gels of metal ions with telluride ions.

  17. Organic Nanocrystals of the Resorcinarene Hexamer via Sonochemistry: Evidence of Reversed Crystal Growth Involving Hollow Morphologies

    PubMed Central

    Sander, John R. G.; Bu?ar, Dejan-Krešimir; Baltrusaitis, Jonas; MacGillivray, Leonard R.

    2012-01-01

    Nano- and micrometer scale crystals of a self-assembled hexamer have been synthesized via sonochemistry. The application of ultrasonic irradiation afforded hollow rhombic dodecahedron crystals of the C-methylcalix[4]resorcinarene hexamer. The formation of the hollow crystals is attributed to a reversed crystal growth mechanism heretofore only described in the synthesis of inorganic-based materials. PMID:22332828

  18. Gas-Phase Growth Kinetics And Morphology Of Lead And Germanium Telluride Crystals

    Microsoft Academic Search

    L. V. Yashina; V. I. Dernovskii; V. P. Zlomanov; V. I. Shtanov

    \\u000a The kinetics of crystal growth and their dependence on external factors provide information critical for understanding the\\u000a growth mechanism and for controlled production of crystals with a given composition and the required properties. Crystal growth\\u000a is investigated using both kinetic and morphologic principles. The former relates the growth rate to the experimental conditions\\u000a (temperature, source material composition, vapor composition and

  19. Crystal Growth by Physical Vapor Transport: Experiments and Simulation Dynamics

    NASA Technical Reports Server (NTRS)

    Ramachandran, N.; Worlikar, A.; Su, Ching-Hua; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    Crystal growth from the vapor phase has various advantages over melt growth. The main advantage is from a lower processing temperature, which makes the process more amenable in instances where the melting temperature of the crystal is high. Other benefits stem from the inherent purification mechanism in the process due to differences in the vapor pressures of the native elements and impurities, and the enhanced interfacial morphological stability during the growth process. Further, the implementation of PVT growth in closed ampoules affords experimental simplicity with minimal needs for complex process control, which makes it an ideal candidate for space investigations in systems where gravity tends to have undesirable effects on the growth process. Bulk growth of wide band gap II-VI semiconductors by PVT has been developed and refined over the past several years at NASA MSFC. A new modeling approach for PVT has also been recently formulated and its validation and testing is the main objective of this work.

  20. I. MATERIALS PREPARATION AND PROPERTIES. Section I. 1 : Crystal Growth.

    E-print Network

    Paris-Sud XI, Université de

    I. MATERIALS PREPARATION AND PROPERTIES. Section I. 1 : Crystal Growth. THE MELT-GROWTH of a preliminary LEC growth investigation. The charac- terization of the LEC crystals involves a survey of the main crystals. The growth of any large single crystal semiconductor with predetermined properties is an ultimate

  1. Protein crystal growth in low gravity

    NASA Technical Reports Server (NTRS)

    Feigelson, Robert S.

    1993-01-01

    This Final Technical Report for NASA Grant NAG8-774 covers the period from April 27, 1989 through December 31, 1992. It covers five main topics: fluid flow studies, the influence of growth conditions on the morphology of isocitrate lyase crystals, control of nucleation, the growth of lysozyme by the temperature gradient method and graphoepitaxy of protein crystals. The section on fluid flow discusses the limits of detectability in the Schlieren imaging of fluid flows around protein crystals. The isocitrate lyase study compares crystals grown terrestrially under a variety of conditions with those grown in space. The controlling factor governing the morphology of the crystals is the supersaturation. The lack of flow in the interface between the drop and the atmosphere in microgravity causes protein precipitation in the boundary layer and a lowering of the supersaturation in the drop. This lowered supersaturation leads to improved crystal morphology. Preliminary experiments with lysozyme indicated that localized temperature gradients could be used to nucleate crystals in a controlled manner. An apparatus (thermonucleator) was designed to study the controlled nucleation of protein crystals. This apparatus has been used to nucleate crystals of materials with both normal (ice-water, Rochelle salt and lysozyme) and retrograde (horse serum albumin and alpha chymotrypsinogen A) solubility. These studies have lead to the design of an new apparatus that small and more compatible with use in microgravity. Lysozyme crystals were grown by transporting nutrient from a source (lysozyme powder) to the crystal in a temperature gradient. The influence of path length and cross section on the growth rate was demonstrated. This technique can be combined with the thermonucleator to control both nucleation and growth. Graphoepitaxy utilizes a patterned substrate to orient growing crystals. In this study, silicon substrates with 10 micron grooves were used to grow crystals of catalase, lysozyme and canavalin. In all cases, the crystals grew oriented to the substrate. The supersaturation needed for nucleation and growth was lower on the patterned substrates. In some cases, isolated, large crystals were grown.

  2. (PCG) Protein Crystal Growth Isocitrate Lysase

    NASA Technical Reports Server (NTRS)

    1989-01-01

    (PCG) Protein Crystal Growth Isocitrate Lysase. Target enzyme for fungicides. A better understanding of this enzyme should lead to the discovery of more potent fungicides to treat serious crop diseases such as rice blast. It regulates the flow of metabolic intermediates required for cell growth. Principal Investigator on STS-26 was Charles Bugg.

  3. (PCG) Protein Crystal Growth Isocitrate Lyase

    NASA Technical Reports Server (NTRS)

    1989-01-01

    (PCG) Protein Crystal Growth Isocitrate Lyase. Target enzyme for fungicides. A better understanding of this enzyme should lead to the discovery of more potent fungicides to treat serious crop diseases such as rice blast. It regulates the flow of metabolic intermediates required for cell growth. Principal Investigator for STS-26 was Charles Bugg.

  4. Growth Modes and Energetics of 101 Face Lysozyme Crystal Growth

    NASA Technical Reports Server (NTRS)

    Gorti, Sridhar; Forsythe, Elizabeth L.; Pusey, L.

    2004-01-01

    From analyses of lysozyme 101 face growth rate data using a 2D nucleation model for layer-by-layer growth, we find the effective barrier for crystal growth to be gamma = 1.0 +/- 0.2 x 10(exp -13) erg/molecule. The magnitude of the effective barrier is 2.4 +/- 0.5 k(sub beta)T, at 22 C. We also find that beyond a critical solution supersaturation, sigma(sub c), crystal growth rates are more accurately described by a kinetic roughening hypothesis. Beyond sigma(sub c), crystals grow by the continuous addition of molecules anywhere on the crystal surface rather than layer-by-layer. The magnitude of the critical supersaturation (sigma(sub c), = 1.7 +/- 0.2) for a crossover from a layer-by-layer to continuous growth is found to be statistically independent of the solution conditions that vary with buffer pH, temperature or precipitant concentration. Using the experimentally determined values for gamma and sigma(sub c), we find the crystal growth unit to be comprised of 7 +/- 3 molecules. The energy barrier, E(sub c), for the continuous addition of the growth Units is 6.2 +/- 0.3 x 10(exp -13) erg/molecule or 15 +/1 1 k(sub beta)T at 22C.

  5. Growth and optical, thermal, mechanical and surface morphology studies of semiorganic nonlinear optical material: Dichlorobis (l-proline) zinc (II) crystal.

    PubMed

    Anbuselvi, D; Jayaraman, D; Arul Martin Mani, J; Joseph, V

    2014-06-01

    The organometallic nonlinear optical material Dichlorobis (l-proline) zinc (II) (DCBPZ) was crystallized using solution growth technique. XRD data reveal that the grown crystal belongs to orthorhombic system with space group P212121. The crystals were characterized using UV-vis-NIR, FTIR and NMR spectral studies, SEM-EDAX analysis and Atomic force microscopy (AFM), thermal and microhardness studies. Photoconductivity measurements were made to understand the response of the grown material to the visible light. The SHG efficiency of DCBPZ was also measured using Kurtz and Perry powder technique. It is observed that the NLO activity of DCBPZ is found to be twice that of KDP due to improved linear and nonlinear optical properties of the material. PMID:24637277

  6. Convective flow effects on protein crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz

    1995-01-01

    During the fifth semi-annual period under this grant we have pursued the following activities: (1) Characterization of the purity and further purification of lysozyme solutions, these efforts are summarized in Section 2; (2) Crystal growth morphology and kinetics studies with tetragonal lysozyme, our observation on the dependence of lysozyme growth kinetics on step sources and impurities has been summarized in a manuscript which was accepted for publication in the Journal of Crystal Growth; (3) Numerical modelling of the interaction between bulk transport and interface kinetics, for a detailed summary of this work see the manuscript which was accepted for publication in the Journal of Crystal Growth; and (4) Light scattering studies, this work has been summarized in a manuscript that has been submitted for publication to the Journal of Chemical Physics.

  7. Growth and characterization of diammonium copper disulphate hexahydrate single crystal

    SciTech Connect

    Siva Sankari, R. [Department of Physics, Agni College of Technology, Thalambur, Chennai 603103 (India); Perumal, Rajesh Narayana, E-mail: r.shankarisai@gmail.com [Department of Physics, SSN College of Engineering, Kalavakkam, Chennai 603110 (India)

    2014-03-01

    Graphical abstract: Diammonium copper disulphate hexahydrate (DACS) is one of the most promising inorganic dielectric crystals with exceptional mechanical properties. Good quality crystals of DACS were grown by using solution method in a period of 30 days. The grown crystals were subjected to single crystal X-ray diffraction analysis in order to establish their crystalline nature. Thermo gravimetric, differential thermal analysis, FTIR, and UV–vis–NIR analysis were performed for the crystal. Several solid state physical parameters have been determined for the grown crystals. The dielectric constant and the dielectric loss and AC conductivity of the grown crystal were studied as a function of frequency and temperature has been calculated and plotted. - Highlights: • Diammonium copper disulphate is grown for the first time and CCDC number obtained. • Thermal analysis is done to see the stability range of the crystals. • Band gap and UV cut off wavelength of the crystal are determined to be 2.4 eV and 472.86 nm, respectively. • Dielectric constant, dielectric loss and AC conductivity are plotted as a function of applied field. - Abstract: Diammonium copper disulphate hexahydrate is one of the most promising inorganic crystals with exceptional dielectric properties. A good quality crystal was harvested in a 30-day period using solution growth method. The grown crystal was subjected to various characterization techniques like single crystal X-ray diffraction analysis, thermo gravimetric, differential thermal analysis, FTIR, and UV–vis–NIR analysis. Unit cell dimensions of the grown crystal have been identified from XRD studies. Functional groups of the title compounds have been identified from FTIR studies. Thermal stability of the samples was checked by TG/DTA studies. Band gap of the crystal was calculated. The dielectric constant and dielectric loss were studied as a function of frequency of the applied field. AC conductivity was plotted as a function of temperature.

  8. Modeling the Growth Rates of Tetragonal Lysozyme Crystal Faces

    NASA Technical Reports Server (NTRS)

    Li, Meirong; Nadarajah, Arunan; Pusey, Marc L.

    1998-01-01

    The measured macroscopic growth rates of the (110) and (101) faces of tetragonal lysozyme show an unexpectedly complex dependence on the supersaturation. The growth rates decay asymptotically to zero when the supersaturation is lowered to zero and increase rapidly when the supersaturation is increased. When supersaturations are increased still further the growth rates attain a maximum before starting to decrease. However, growth of these crystals is known to proceed by the classical dislocation and 2D nucleation growth mechanisms. This anomaly can be explained if growth is assumed to occur not by monomer units but by lysozyme aggregates. Analysis of the molecular packing of these crystals revealed that they were constructed of strongly bonded 4(sub 3) helices, while weaker bonds were responsible for binding the helices to each other. It follows that during crystal growth the stronger bonds are formed before the weaker ones. Thus, the growth of these crystals could be viewed as a two step process: aggregate growth units corresponding to the 4(sub 3) helix are first formed in the bulk solution by stronger intermolecular bonds and then attached to the crystal face by weaker bonds on dislocation hillocks or 2D islands. This will lead to a distribution of aggregates in the solution with monomers and lower order aggregates being predominant at low supersaturations and higher order aggregates being predominant at high supersaturations. If the crystal grows mostly by higher order aggregates, such as tetramers and octamers, it would explain the anomalous dependence of the growth rates on the supersaturation. Besides the analysis of molecular packing, a comprehensive analysis of the measured (110) and (101) growth rates was also undertaken in this study. The distribution of aggregates in lysozyme nutrient solutions at various solution conditions were determined from reversible aggregation reactions at equilibrium. The supersaturation was defined for each aggregate species with respect to its concentration at saturation in order to apply growth rate models to this process. The measured growth rates were then compared with the predicted ones from several dislocation and 2D nucleation growth models, employing tetramer and octamer growth units in polydisperse solutions and monomer units in monodisperse solutions. For the (110) face, the calculations consistently showed that the measured growth rates followed the expected model relations with octamer growth units. For the (101) face, it is not possible to obtain a clear agreement between the predicted and measured growth rates for a single growth unit as done for the (110) face. However, the calculations do indicate that the average size of the growth unit is between a tetramer and an octamer. This suggests that tetramers, octamers and other intermediate size growth units all participate in the growth process for this face. These calculations show that it is possible to model the macroscopic protein crystal growth rates if the molecular level processes can be account for, particularly protein aggregation processes in the bulk solution. Our recent investigations of tetragonal lysozyme crystals employing high resolution atomic force microscopy scans have further confirmed the growth of these crystals by aggregate growth units corresponding to 4(sub 3) helices.

  9. Research support for cadmium telluride crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz

    1995-01-01

    The growth of single crystals of zinc selenide was carried out by both closed ampoule physical vapor transport and effusive ampoule physical vapor transport (EAPVT). The latter technique was shown to be a much more efficient method for the seeded growth of zinc selenide, resulting in higher transport rates. Furthermore, EAPVT work on CdTe has shown that growth onto (n 11) seeds is advantageous for obtaining reduced twinning and defect densities in II-VI sphalerite materials.

  10. Space-based crystal growth and thermocapillary flow

    NASA Technical Reports Server (NTRS)

    Shen, Yong-Hong

    1994-01-01

    The demand for larger crystals is increasing especially in applications associated with the electronic industry, where large and pure electronic crystals (notably silicon) are the essential material to make high-performance computer chips. Crystal growth under weightless conditions has been considered an ideal way to produce bigger and hopefully better crystals. One technique which may benefit from a microgravity environment is the float-zone crystal-growth process, a containerless method for producing high-quality electronic material. In this method, a rod of material to be refined is moved slowly through a heating device which melts a portion of it. Ideally, as the melt resolidifies it does so as a single crystal which is then used as substrate for building microelectronic devices. The possibility of contamination by contact with other material is reduced because of the 'float' configuration. However, since the weight of the material contained in the zone is supported by the surface-tension force, the size of the resulting crystal is limited in Earth-based productions; in fact, some materials have properties which prevent this process from being used to manufacture crystals of reasonable size. Consequently, there has been a great deal of interest in exploiting the microgravity environment of space to grow larger size crystals of electronic material using the float-zone method. In addition to allowing larger crystals to be grown, a microgravity environment would also significantly reduce the magnitude of convection induced by buoyancy forces during the melting state. This type of convection was once thought to be at least partially responsible for the presence of undesirable nonuniformities--called striations--in material properties observed in float-zone material. However, past experiments on crystal growth under weightless conditions found that even with the absence of gravity, the float-zone method sometimes still results striations. It is believed that another mechanism is playing a dominant role in the microgravity environment.

  11. Rapid growth of potassium dihydrogen phosphate crystals

    SciTech Connect

    Cooper, J.F.; Singleton, M.F.

    1985-01-24

    We report the development of a process for high rate (15 mm/d) growth of potassium dihydrogen phosphate single crystals. Correlations for mass transport by convective diffusion (to cones or disks under axially-impinging flow) are applied to published rate data on 3-mm KDP crystals to derive a semi-empirical kinetic equation for (101) growth rate measured in the z direction: g/sub z/ = k/sub g/ exp(-H/sub g//RT)(c/sub s/-c/sub sat/)/sup n/, where the coefficients found by linear regression are k/sub g/ = 3492 m/s, H/sub g/ = 41,399 J/mol and n = 2.277; and c/sub s/ and c/sub sat/ are, respectively, the surface- and saturation concentrations (kg-KDP/kg-water). Material properties, transport, and kinetic equations are then solved numerically to predict the dependence of growth rate on temperature, supersaturation, and the ratio of flow rate to a crystal dimension. The model is experimentally verified for 20 to 25 mm crystals grown at rates of 5 to 25 mm/d using a turbine to enhance solute flux to the pyramidal faces. We conclude that high growth rate of large crystals is possible and scales according to the ratio of characteristic velocity to crystal dimension. 22 references, 8 figures.

  12. Growth, spectral, thermal, dielectric, mechanical, linear and nonlinear optical, birefringence, laser damage threshold studies of semi-organic crystal: dibrucinium sulfate heptahydrate.

    PubMed

    Krishnan, P; Gayathri, K; Bhagavannarayana, G; Jayaramakrishnan, V; Gunasekaran, S; Anbalagan, G

    2013-08-01

    Dibrucinium sulfate heptahydrate (DBSH), a semi-organic nonlinear optical material, has been synthesized and single crystals were grown from water-ethanol solution at room temperature up to dimensions of 10×7×2 mm(3). The unit cell parameters were determined from single crystal and powder X-ray diffraction studies. The structural perfection of the grown crystal has been analyzed by high-resolution X-ray diffraction (HRXRD) study. FTIR and Raman studies were performed to identify the functional groups present in the title compound. The activation energy (E), entropy (?S), enthalpy (?H) and Gibbs free energy (?G), of the thermal decomposition reaction have been derived from thermo gravimetric (TGA) and differential thermal (DTA) analysis curves, using Coats-Redfern method. The variation of dielectric properties of the grown crystal with respect to frequency has been investigated at different temperatures. Microhardness measurements revealed the mechanical strength of grown crystal. The optical parameters, the optical band gap E(g) and width of localized states Eu were determined using the transmittance data in the spectral range 200-800 nm. The relative second harmonic efficiency of the compound is found to be 1.4 times greater than that of KDP. Birefringence and Laser damage threshold studies were carried out for the grown crystal. PMID:23666350

  13. Modeling Tetragonal Lysozyme Crystal Growth Rates

    NASA Technical Reports Server (NTRS)

    Gorti, Sridhar; Forsythe, Elizabeth L.; Pusey, Marc L.

    2003-01-01

    Tetragonal lysozyme 110 face crystal growth rates, measured over 5 orders of magnitude in range, can be described using a model where growth occurs by 2D nucleation on the crystal surface for solution supersaturations of c/c(sub eq) less than or equal to 7 +/- 2. Based upon the model, the step energy per unit length, beta was estimated to be approx. 5.3 +/- 0.4 x 10(exp -7) erg/mol-cm, which for a step height of 56 A corresponds to barrier of approx. 7 +/- 1 k(sub B)T at 300 K. For supersaturations of c/c(sub eq) > 8, the model emphasizing crystal growth by 2D nucleation not only could not predict, but also consistently overestimated, the highest observable crystal growth rates. Kinetic roughening is hypothesized to occur at a cross-over supersaturation of c/c(sub eq) > 8, where crystal growth is postulated to occur by a different process such as adsorption. Under this assumption, all growth rate data indicated that a kinetic roughening transition and subsequent crystal growth by adsorption for all solution conditions, varying in buffer pH, temperature and precipitant concentration, occurs for c/c(sub eq)(T, pH, NaCl) in the range between 5 and 10, with an energy barrier for adsorption estimated to be approx. 20 k(sub B)T at 300 K. Based upon these and other estimates, we determined the size of the critical surface nucleate, at the crossover supersaturation and higher concentrations, to range from 4 to 10 molecules.

  14. crystal: growth, crystal structure perfection, piezoelectric, and acoustic properties

    NASA Astrophysics Data System (ADS)

    Roshchupkin, Dmitry; Ortega, Luc; Plotitcyna, Olga; Irzhak, Dmitry; Emelin, Evgenii; Fahrtdinov, Rashid; Alenkov, Vladimir; Buzanov, Oleg

    2014-09-01

    A five-component crystal of lanthanum-gallium silicate group La3Ga5.3Ta0.5Al0.2O14 (LGTA) was grown by the Czochralski method. The LGTA crystal possesses unique thermal properties and substitution of Al for Ga in the unit cell leads to a substantial increase of electrical resistance at high temperatures. The unit cell parameters of LGTA were determined by powder diffraction. X-ray topography was used to study the crystal structure perfection: the growth banding normal to the growth axis were visualized. The independent piezoelectric constants d 11 and d 14 were measured by X-ray diffraction in the Bragg and Laue geometries. Excitation and propagation of surface acoustic waves were studied by the double-crystal X-ray diffraction at the BESSY II synchrotron radiation source. The analysis of the diffraction spectra of acoustically modulated crystals permitted the determination of the velocity of acoustic wave propagation and the power flow angles in different acoustic cuts of the LGTA crystal.

  15. Inclusion free cadmium zinc tellurium and cadmium tellurium crystals and associated growth method

    DOEpatents

    Bolotnikov, Aleskey E. (South Setauket, NY); James, Ralph B. (Ridge, NY)

    2010-07-20

    The present disclosure provides systems and methods for crystal growth of cadmium zinc tellurium (CZT) and cadmium tellurium (CdTe) crystals with an inverted growth reactor chamber. The inverted growth reactor chamber enables growth of single, large, high purity CZT and CdTe crystals that can be used, for example, in X-ray and gamma detection, substrates for infrared detectors, or the like. The inverted growth reactor chamber enables reductions in the presence of Te inclusions, which are recognized as an important limiting factor in using CZT or CdTe as radiation detectors. The inverted growth reactor chamber can be utilized with existing crystal growth techniques such as the Bridgman crystal growth mechanism and the like. In an exemplary embodiment, the inverted growth reactor chamber is a U-shaped ampoule.

  16. Book Reviews Crystal Growth Technology. Hans J. Scheel and

    E-print Network

    Regel, Liya L.

    Book Reviews Crystal Growth Technology. Hans J. Scheel and Tsuguo Fukuda Eds., John Wiley & Sons selected review papers from the First International School on Crystal Growth Technology held in 1998. Topics include some of the fundamentals of crystal growth, methods of character- ization, crystal

  17. Physica D 138 (2000) 282301 Spiral crystal growth

    E-print Network

    Smereka, Peter

    2000-01-01

    Physica D 138 (2000) 282­301 Spiral crystal growth Peter Smereka Department of Mathematics Communicated by H. Müller-Krumbhaar Abstract We numerically study the spiral mode of crystal growth using; Crystal growth; Interacting spirals 1. Introduction It is well documented that crystals grow in spiral

  18. An Apparatus for Growth of Small Crystals From Solutions.

    ERIC Educational Resources Information Center

    Mitrovic, Mico M.

    1995-01-01

    Describes an apparatus for crystal growth that was designed to study growth kinetics of small crystals from solutions and to obtain crystals of various substances. Describes the use of the apparatus in laboratory practical experiments in the field of crystal growth physics within the course "Solid State Physics". (JRH)

  19. CRYSTAL GROWTH IN RAT ENAMEL

    Microsoft Academic Search

    M. U. Nylen; E. D. EANES; K.-A. OMNELL

    1963-01-01

    Observations have been made, using electron microscopy and x-ray diffraction, on the changes in crystal size and shape which occur in developing rodent enamel during minerali- zation. Small enamel pieces isolated from ground sections of rat molars and incisors were either embedded in methacrylate and sectioned with a diamond knife for electron micros- copy, or they were mounted intact on

  20. Drop deployment system for crystal growth apparatus

    NASA Technical Reports Server (NTRS)

    Rhodes, Percy (inventor); Snyder, Robert S. (inventor); Pusey, Marc L. (inventor)

    1990-01-01

    A crystal growth apparatus is presented. It utilizes a vapor diffusion method for growing protein crystals, and particularly such an apparatus wherein a ball mixer is used to mix the fluids that form a drop within which crystals are grown. Particular novelty of this invention lies in utilizing a ball mixer to completely mix the precipitate and protein solutions prior to forming the drop. Additional novelty lies in details of construction of the vials, the fluid deployment system, and the fluid storage system of the preferred embodiment.

  1. Model for the mechanical stress due to the salt crystallization in porous materials

    Microsoft Academic Search

    R. M. Espinosa; L. Franke; G. Deckelmann

    2008-01-01

    This paper deals with the experimental investigation and the mathematical modelling of crystal growth in porous materials and resulting mechanical stress due to the crystallization pressure.Crystallization of potassium nitrate and of sodium sulphate was induced in two bricks by cooling down at constant rate. The measured temperatures describe indirectly the crystallization and the dissolution rates. Thus, the time-dependent amount of

  2. ELSEVIER Journal of Crystal Growth 164 (1996) 248-255 ,........ CRYSTAL

    E-print Network

    Florida, University of

    1996-01-01

    ELSEVIER Journal of Crystal Growth 164 (1996) 248-255 ,........ CRYSTAL GROWTH Initial growth. / Journal of Crystal Growth 164 (1996) 248-255 249 varies from 0.36-0.37% for x = 0 to 1 (aGa P = 5.4505 A Abstract The nucleation and growth of AI ~GaI_ ,.P grown by metalorganic molecular beam epitaxy

  3. Growth of Large Hematin Crystals in Biomimetic Solutions.

    PubMed

    Olafson, Katy N; Rimer, Jeffrey D; Vekilov, Peter G

    2014-05-01

    Hematin crystallization is an essential component of the physiology of malaria parasites. Several antimalarial drugs are believed to inhibit crystallization and expose the parasites to toxic soluble hematin. Hence, understanding the mechanisms of hematin crystal growth and inhibition is crucial for the design of new drugs. A major obstacle to microscopic, spectroscopic, and crystallographic studies of hematin crystallization has been the unavailability of large hematin crystals grown under conditions representative of the parasite anatomy. We have developed a biomimetic method to reproducibly grow large hematin crystals reaching 50 ?m in length. We imitate the digestive vacuole of Plasmodium falciparum and employ a two-phase solution of octanol and citric buffer. The nucleation of seeds is enhanced at the interface between the aqueous and organic phases, where an ordered layer of octanol molecules is known to serve as substrate for nucleation. The seeds are transferred to hematin-saturated octanol in contact with citric buffer. We show that the crystals grow in the octanol layer, while the buffer supplies hydrogen ions needed for bonds that link the hematin molecules in the crystal. The availability of large hematin crystals opens new avenues for studies of hematin detoxification of malaria parasites in host erythrocytes. PMID:24839403

  4. Surface Phenomena and Parameters of Crystal Growth: Simple Basics

    SciTech Connect

    Chernov, A. A. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore CA, 94551 (United States)

    2010-07-22

    Basic concepts of crystal growth and their practical use to semi-quantitatively estimate growth processes are explained: surface energy and free energy, driving force of crystallization, atomically rough vs smooth interface structure and the corresponding normal vs layer-by-layer growth modes, application of the activated complex concept to derive kinetic coefficient characterizing crystal growth rate at a given driving force. The Reader is supposed to be familiar with general physics and chemistry. No specific knowledge in crystal growth is required.

  5. Convective flow effects on protein crystal growth

    NASA Astrophysics Data System (ADS)

    Rosenberger, Franz; Monaco, Lisa A.

    A high-resolution microscopic interferometric setup for the monitoring of protein morphologies has been developed. Growth or dissolution of a crystal can be resolved with a long-term depth resolution of 200 A and a lateral resolution of 2 microns. This capability of simultaneously monitoring the interfacial displacement with high local depth resolution has yielded several novel results. We have found with lysozyme that (1) the normal growth rate is oscillatory, and (2) depending on the impurity content of the solution, the growth step density is either greater or lower at the periphery of a facet than in its center. The repartitioning of Na plus and Cl minus ions between lysozyme solutions and crystals was studied for a wide range of crystallization conditions. A nucleation-growth-repartitioning model was developed, to interpret the large body of data in unified way. The results strongly suggest that (1) the ion to lysozyne ratio in the crystal depends mostly on kinetic rather than crystallographic parameters, and (2) lysozyme crystals possess a salt-rich core with a diameter electron microscopy results appear to confirm this finding, which could have far-reaching consequences for x-ray diffraction studies. A computational model for diffusive-convective transport in protein crystallization has been applied to a realistic growth cell geometry, taking into account the findings of the above repartitioning studies and our kinetics data for the growth of lysozyme. The results show that even in the small cell employed, protein concentration nonuniformities and gravity-driven solutal convection can be significant. The calculated convection velocities are of the same order to magnitude as those found in earlier experiments. As expected, convective transport, i.e., at Og, lysozyme crystal growth remains kinetically limited. The salt distribution in the crystal is predicted to be non-uniform at both 1g and 0g, as a consequence of protein depletion in the solution. Static and dynamic light scattering studies in undersaturated and supersaturated solutions have been performed. Diffusivities in undersaturated solutions, were found to vary with lysozyme concentrations. Depending on the salt concentration, the diffusivities either increase or decrease. Interestingly, the corresponding static scattering intensities behave oppositely, Our current analysis indicates that these changes are inconsistent with aggregation in undersaturated solutions. However, the data are compatible with concentration-dependent changes of the interactions between protein and salt.

  6. Convective flow effects on protein crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Monaco, Lisa A.

    1994-01-01

    A high-resolution microscopic interferometric setup for the monitoring of protein morphologies has been developed. Growth or dissolution of a crystal can be resolved with a long-term depth resolution of 200 A and a lateral resolution of 2 microns. This capability of simultaneously monitoring the interfacial displacement with high local depth resolution has yielded several novel results. We have found with lysozyme that (1) the normal growth rate is oscillatory, and (2) depending on the impurity content of the solution, the growth step density is either greater or lower at the periphery of a facet than in its center. The repartitioning of Na plus and Cl minus ions between lysozyme solutions and crystals was studied for a wide range of crystallization conditions. A nucleation-growth-repartitioning model was developed, to interpret the large body of data in unified way. The results strongly suggest that (1) the ion to lysozyne ratio in the crystal depends mostly on kinetic rather than crystallographic parameters, and (2) lysozyme crystals possess a salt-rich core with a diameter electron microscopy results appear to confirm this finding, which could have far-reaching consequences for x-ray diffraction studies. A computational model for diffusive-convective transport in protein crystallization has been applied to a realistic growth cell geometry, taking into account the findings of the above repartitioning studies and our kinetics data for the growth of lysozyme. The results show that even in the small cell employed, protein concentration nonuniformities and gravity-driven solutal convection can be significant. The calculated convection velocities are of the same order to magnitude as those found in earlier experiments. As expected, convective transport, i.e., at Og, lysozyme crystal growth remains kinetically limited. The salt distribution in the crystal is predicted to be non-uniform at both 1g and 0g, as a consequence of protein depletion in the solution. Static and dynamic light scattering studies in undersaturated and supersaturated solutions have been performed. Diffusivities in undersaturated solutions, were found to vary with lysozyme concentrations. Depending on the salt concentration, the diffusivities either increase or decrease. Interestingly, the corresponding static scattering intensities behave oppositely, Our current analysis indicates that these changes are inconsistent with aggregation in undersaturated solutions. However, the data are compatible with concentration-dependent changes of the interactions between protein and salt.

  7. Optical monitoring of protein crystal growth

    NASA Technical Reports Server (NTRS)

    Choudry, A.

    1988-01-01

    The possibility of using various optical techniques for detecting the onset of nucleation in protein crystal growth was investigated. Direct microscopy, general metrologic techniques, light scattering, ultraviolet absorption, and interferometry are addressed along with techniques for determining pH value. The necessity for collecting basic data on the optical properties of the growth solution as a prerequisite to the evaluation of monitoring techniques is pointed out.

  8. Synthesis, growth, crystal structure, spectral, thermal, mechanical and optical studies of stilbazolium derivative single crystal: 2-[2-(4-Diethylamino-phenyl)-vinyl]-1-methyl-pyridinium naphthalene-2-sulfonate (DESNS).

    PubMed

    Senthil, K; Kalainathan, S; Ruban Kumar, A

    2014-04-24

    Single crystals of organic optical material, 2-[2-(4-Diethylamino-phenyl)-vinyl]-1-methyl-pyridinium naphthalene-2-sulfonate (DESNS) (15×10×9 mm(3)) were grown by a slow evaporation technique at room temperature using methanol-acetonitrile (1:1) mixed solvent. The molecular structure of the grown crystal was confirmed by single crystal X-ray diffraction studies, and it belongs to orthorhombic system with space group Pbca and the unit cell dimentions are a=11.5148(3) Å, b=15.4352(4) Å, c=27.2187(7) Å, Z=8. The crystallinity of the title crystals was confirmed from the powder XRD pattern. The presence of functional groups of the title crystal was confirmed from the FTIR spectral studies. The transparent range and cut off wavelength of the grown crystal was studied by the UV-Vis-NIR spectroscopic analysis. The mechanical properties and thermal behavior of the grown crystals were studied from Vickers microhardness test and TG/DTA. PMID:24509538

  9. The kinetics of nucleation and crystal growth and scaling laws for magmatic crystallization

    Microsoft Academic Search

    Genevieve Brandeis; Claude Jaupart

    1987-01-01

    Magmatic crystallization depends on the kinetics of nucleation and crystal growth. It occurs over a region of finite thickness called the crystallization interval, which moves into uncrystallized magma. We present a dimensional analysis which allows a simple understanding of the crystallization characteristics. We use scales for the rates of nucleation and crystal growth, denoted by Im and Ym respectively. The

  10. Journal of Crystal Growth 250 (2003) 499515 Induction time in crystallization of gas hydrates

    E-print Network

    Firoozabadi, Abbas

    2003-01-01

    Journal of Crystal Growth 250 (2003) 499­515 Induction time in crystallization of gas hydrates Dimo crystallite growth rate and the induction time in hydrate crystallization. These expressions are used Keywords: A1. Crystallization; A1. Growth rate; A1. Induction time; A1. Nucleation; B1. Gas Hydrates; B1

  11. ELSEVIER Journal of Crystal Growth 171 (1997) 442-446 j........ CRYSTAL

    E-print Network

    Huang, Jung-Chun

    1997-01-01

    ELSEVIER Journal of Crystal Growth 171 (1997) 442-446 j........ CRYSTAL G R O W T H Epitaxial polycrystalline structures were established on Si(111) substrates. The excellent crystal growth of the permalloy The crystal growth of permalloy films was carried out by vacuum product molecular beam epitaxy (MBE-930

  12. Growth of 4-(dimethylamino) benzaldehyde doped triglycine sulphate single crystals and its characterization

    Microsoft Academic Search

    Chitharanjan Rai; K. Sreenivas; S. M. Dharmaprakash

    2009-01-01

    Single crystals of triglycine sulphate (TGS) doped with 1mol% of 4-(dimethylamino) benzaldehyde (DB) have been grown from aqueous solution at ambient temperature by slow evaporation technique. The effect of dopant on the crystal growth and dielectric, pyroelectric and mechanical properties of TGS crystal have been investigated. X-ray powder diffraction pattern for pure and doped TGS was collected to determine the

  13. (PCG) Protein Crystal Growth Isocitrate Lysase

    NASA Technical Reports Server (NTRS)

    1993-01-01

    Comparison of Earth grown and Space grown Isocitrate Lysase crystals. Target enzyme for fungicides. A better understanding of this enzyme should lead to the discovery of more potent fungicides to treat serious crop diseases such as rice blast. It regulates the flow of metabolic intermediates required for cell growth. Principal Investigator was Charles Bugg.

  14. Crystal growth furnace safety system validation

    NASA Technical Reports Server (NTRS)

    Mackowski, D. W.; Hartfield, R.; Bhavnani, S. H.; Belcher, V. M.

    1994-01-01

    The findings are reported regarding the safe operation of the NASA crystal growth furnace (CGF) and potential methods for detecting containment failures of the furnace. The main conclusions are summarized by ampoule leak detection, cartridge leak detection, and detection of hazardous species in the experiment apparatus container (EAC).

  15. Mechanical Properties Of Large Sodium Iodide Crystals

    NASA Technical Reports Server (NTRS)

    Lee, Henry M.

    1988-01-01

    Report presents data on mechanical properties of large crystals of thallium-doped sodium iodide. Five specimens in shape of circular flat plates subjected to mechanical tests. Presents test results for each specimen as plots of differential pressure versus center displacement and differential pressure versus stress at center. Also tabulates raw data. Test program also developed procedure for screening candidate crystals for gamma-ray sensor. Procedure eliminates potentially weak crystals before installed and ensures material yielding kept to minimum.

  16. Crystal growth in a microgravity environment

    NASA Technical Reports Server (NTRS)

    Kroes, Roger L. (inventor); Reiss, Donald A. (inventor); Lehoczky, Sandor L. (inventor)

    1992-01-01

    Gravitational phenomena, including convection, sedimentation, and interactions of materials with their containers all affect the crystal growth process. If they are not taken into consideration they can have adverse effects on the quantity and quality of crystals produced. As a practical matter, convection, and sedimentation can be completely eliminated only under conditions of low gravity attained during orbital flight. There is, then, an advantage to effecting crystallization in space. In the absence of convection in a microgravity environment cooling proceeds by thermal diffusion from the walls to the center of the solution chamber. This renders control of nucleation difficult. Accordingly, there is a need for a new improved nucleation process in space. Crystals are nucleated by creating a small localized region of high relative supersaturation in a host solution at a lower degree of supersaturation.

  17. ICCG-10: Tenth International Conference on Crystal Growth. Poster presentation abstracts

    NASA Technical Reports Server (NTRS)

    1992-01-01

    Poster presentation abstracts from the tenth International Conference on Crystal Growth (ICCG) (Aug. 16-21, 1992) are provided. Topics discussed at the conference include crystal growth mechanisms, superconductors, semiconductors, laser materials, optical materials, and biomaterials. Organizing committees, ICCG advisory board and officers, and sponsors of the conference are also included.

  18. ICCG-10: Tenth International Conference on Crystal Growth. Oral presentation abstracts

    NASA Technical Reports Server (NTRS)

    1992-01-01

    Oral presentation abstracts from the tenth International Conference on Crystal Growth (ICCG) (Aug. 16-21, 1992) are provided. Topics discussed at the conference include superconductors, semiconductors, nucleation, crystal growth mechanisms, and laser materials. Organizing committees, ICCG advisory board and officers, and sponsors of the conference are also included.

  19. ELSEVIER Journal of Crystal Growth 179 (1997)297-308 j........ CRYSTAL

    E-print Network

    Walker, D. Greg

    1997-01-01

    ELSEVIER Journal of Crystal Growth 179 (1997)297-308 j........ CRYSTAL GROWTH Numerical reserved PII S0022-0248(97)00087-0 #12;298 D.I'E Mackowski et al. / Journal of Crystal Growth 179 (1997 a numerical investigation of the effects of thermal creep on the growth process in axisymmetric, binary

  20. Journal of Crystal Growth 271 (2004) 128133 Growth of strontium barium niobate

    E-print Network

    Osnabrück, Universität

    2004-01-01

    Journal of Crystal Growth 271 (2004) 128­133 Growth of strontium barium niobate: the liquidus. Czochralski method; A2. Growth from the melt; A2. Single crystal growth; B1. Niobates; B2. Ferroelectric;crystal growth at such a composition is greatly facilitated, practically all publications up to now deal

  1. Crystal growth and annealing for minimized residual stress

    DOEpatents

    Gianoulakis, Steven E. (Albuquerque, NM)

    2002-01-01

    A method and apparatus for producing crystals that minimizes birefringence even at large crystal sizes, and is suitable for production of CaF.sub.2 crystals. The method of the present invention comprises annealing a crystal by maintaining a minimal temperature gradient in the crystal while slowly reducing the bulk temperature of the crystal. An apparatus according to the present invention includes a thermal control system added to a crystal growth and annealing apparatus, wherein the thermal control system allows a temperature gradient during crystal growth but minimizes the temperature gradient during crystal annealing.

  2. Drop deployment system for crystal growth apparatus

    NASA Technical Reports Server (NTRS)

    Rhodes, Percy H. (Inventor); Snyder, Robert S. (Inventor); Pusey, Marc L. (Inventor)

    1992-01-01

    This invention relates to a crystal growth apparatus (10) generally used for growing protein crystals wherein a vapor diffusion method is used for growing the crystals. In this apparatus, a precipitating solution and a solution containing dissolved crystalline material are stored in separate vials (12, 14), each having a resilient diaphragm (28) across one end and an opening (24) with a puncturable septum (26) thereacross at an opposite end. The vials are placed in receptacles (30) having a manifold (41) with a manifold diaphragm (42) in contact with the vial diaphragm at one end of the receptacle and a hollow needle (36) for puncturing the septum at the other end of the manifold. The needles of each vial communicate with a ball mixer (40) that mixes the precipitate and protein solutions and directs the mixed solution to a drop support (64) disposed in a crystal growth chamber (16), the drop support being a tube with an inner bevelled surface (66) that provides more support for the drop (68) than the tubes of the prior art. A sealable storage region (70) intermediate the drop support and mixer provides storage of the drop (68) and the grown crystals.

  3. Lead isotope variation with growth zoning in a galena crystal

    USGS Publications Warehouse

    Cannon, R.S., Jr.; Pierce, A.P.; Delevaux, M.H.

    1963-01-01

    A large crystal of lead sulfide from Picher, Oklahoma, has significant differences in isotopic composition of lead in successive growth zones. Lead isotope ratios in the parent ore-fluid evidently changed with time during crystal growth. The growth history of this crystal, interpreted quantitatively, points to a tentative hypothesis of genesis of Mississippi Valley deposits of lead and zinc.

  4. Microrobotic Streak Seeding For Protein Crystal Growth CUCS04104

    E-print Network

    Microrobotic Streak Seeding For Protein Crystal Growth CUCS­041­04 Atanas Georgiev 1 Peter Allen 1 that consists of picking individual protein crystal from growth solution the purpose X­ray data collection) transferred protein solution that optimized their growth. building high­throughput protein crystal production

  5. Cloud structure and crystal growth in nimbostratus clouds. Mengistu Wolde*

    E-print Network

    Vali, Gabor

    1 Cloud structure and crystal growth in nimbostratus clouds. Mengistu Wolde* , Gabor Vali-mail: mengistu.wolde@nrc.ca. #12;2 Abstract Cloud structure and crystal growth in two nimbostratus were examined made available by large scale lifting was taken up by depositional growth of the ice crystals

  6. Optimal solutions for a free boundary problem for crystal growth

    E-print Network

    Seidman, Thomas I.

    Optimal solutions for a free boundary problem for crystal growth Pekka Neittaanm¨ aki Thomas I. Seidman Abstract. We consider a free boundary problem modeling the growth/dissolution of a crystal boundary problem corresponding to a model of growth (dissolution) of a radially symmetric crystal grain

  7. Coarsening Scenarios in Unstable Crystal Growth

    NASA Astrophysics Data System (ADS)

    Biagi, Sofia; Misbah, Chaouqi; Politi, Paolo

    2012-08-01

    Crystal surfaces may undergo thermodynamical as well as kinetic, out-of-equilibrium instabilities. We consider the case of mound and pyramid formation, a common phenomenon in crystal growth and a long-standing problem in the field of pattern formation and coarsening dynamics. We are finally able to attack the problem analytically and get rigorous results. Three dynamical scenarios are possible: perpetual coarsening, interrupted coarsening, and no coarsening. In the perpetual coarsening scenario, mound size increases in time as L˜tn, where the coarsening exponent is n=1/3 when faceting occurs, otherwise n=1/4.

  8. Unsteady-state transfer of impurities during crystal growth of sucrose in sugarcane solutions

    NASA Astrophysics Data System (ADS)

    Martins, P. M.; Ferreira, A.; Polanco, S.; Rocha, F.; Damas, A. M.; Rein, P.

    2009-07-01

    In this work, we present growth rate data of sucrose crystals in the presence of impurities that can be used by both sugar technologists and crystal growth scientists. Growth rate curves measured in a pilot-scale evaporative crystallizer suggest a period of slow growth that follows the seeding of crystals into supersaturated technical solutions. The observed trend was enhanced by adding typical sugarcane impurities such as starch, fructose or dextran to the industrial syrups. Maximum growth rates of sucrose resulted at intermediate rather than high supersaturation levels in the presence of the additives. The effects of the additives on the sucrose solubility and sucrose mass transfer in solution were taken into account to explain the observed crystal growth kinetics. A novel mechanism was identified of unsteady-state adsorption of impurities at the crystal surface and their gradual replacement by the crystallizing solute towards the equilibrium occupation of the active sites for growth. Specifically designed crystallization experiments at controlled supersaturation confirmed this mechanism by showing increasing crystal growth rates with time until reaching a steady-state value for a given supersaturation level and impurity content.

  9. Convective flow effects on protein crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Monaco, Lisa A.

    1993-01-01

    The experimental setup for the in-situ high resolution optical monitoring of protein crystal growth/dissolution morphologies was substantially improved. By augmenting the observation system with a temperature-controlled enclosure, laser illumination for the interferometric microscope, and software for pixel by pixel light intensity recording, a height resolution of about two unit cells for lysozyme can now be obtained. The repartitioning of Na(+) and Cl(-) ions between lysozyme solutions and crystals was studied. Quite unexpectedly, it was found that the longer crystals were in contact with their solution, the lower was their ion content. The development of a model for diffusive-convective transport and resulting distribution of the growth rate on facets was completed. Results obtained for a realistic growth cell geometry show interesting differences between 'growth runs' at 1g and 0g. The kinematic viscosity of lysozyme solutions of various supersaturations and salt concentrations was monitored over time. In contrast to the preliminary finding of other authors, no changes in viscosity were found over four days. The experimental setup for light scattering investigations of aggregation and nucleation in protein solutions was completed, and a computer program for the evaluation of multi-angle light scattering data was acquired.

  10. Journal of Crystal Growth 304 (2007) 114117 Single crystal growth of YbRh2Si2 using Zn flux

    E-print Network

    Broholm, Collin Leslie

    2007-01-01

    Journal of Crystal Growth 304 (2007) 114­117 Single crystal growth of YbRh2Si2 using Zn flux-temperature solution technique, using Zn flux and followed by a decanting process. As opposed from the crystals growth: A1. Growth from high-temperature solutions; A1. Single crystal; B2. YbRh2Si2 1. Introduction YbRh2Si

  11. Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Brebrick, Robert F.; Volz, Martin P.; Burger, Arnold; Dudley, Michael; Matyi, Richard J.; Ramachandran, Narayanan; Sha, Yi-Gao; Volz, Martin P.; Shih, Hung-Dah

    2001-01-01

    Crystal growth by vapor transport has several distinct advantages over melt growth techniques. Among various potential benefits from material processing in reduced gravity the followings two are considered to be related to crystal growth by vapor transport: (1) elimination of the crystal weight and its influence on the defect formation and (2) reduction of natural buoyancy-driven convective flows arising from thermally and/ or solutally induced density gradient in fluids. The previous results on vapor crystal growth of semiconductors showed the improvements in surface morphology, crystalline quality, electrical properties and dopant distribution of the crystals grown in reduced gravity as compared to the crystals grown on Earth. But the mechanisms, which are responsible for the improvements and cause the gravitational effects on the complicated and coupled processes of vapor mass transport and growth kinetics, are not well understood.

  12. A unified description of attachment-based crystal growth.

    PubMed

    Zhang, Hengzhong; De Yoreo, James J; Banfield, Jillian F

    2014-07-22

    Crystal growth is one of the most fundamental processes in nature. Understanding of crystal growth mechanisms has changed dramatically over the past two decades. One significant advance has been the recognition that growth does not only occur atom by atom, but often proceeds via attachment and fusion of either amorphous or crystalline particles. Results from recent experiments and calculations can be integrated to develop a simple, unified conceptual description of attachment-based crystal growth. This enables us to address three important questions: What are the driving forces for attachment-based growth? For crystalline particles, what enables the particles to achieve crystallographic coalignment? What determines the surface on which attachment occurs? We conclude that the extent of internal nanoparticle order controls the degree of periodicity and anisotropy in the surrounding electrostatic field. For crystalline particles, the orienting force stemming from the electrostatic field can promote oriented attachment events, although solvent-surface interactions modulate this control. In cases where perfect crystallographic alignment is not achieved, misorientation gives rise to structural defects that can fundamentally modify nanomaterial properties. PMID:25000275

  13. High-purity silicon crystal growth investigations

    NASA Technical Reports Server (NTRS)

    Ciszek, T. F.; Hurd, J. L.; Schuyler, T.

    1985-01-01

    The study of silicon sheet material requirements for high efficiency solar cells is reported. Research continued on obtaining long lifetime single crystal float zone silicon and on understanding and reducing the mechanisms that limit the achievement of long lifetimes. The mechanisms studied are impurities, thermal history, point defects, and surface effect. The lifetime related crystallographic defects are characterized by X-ray topography and electron beam induced current.

  14. (PCG) Protein Crystal Growth Gamma-Interferon

    NASA Technical Reports Server (NTRS)

    1989-01-01

    (PCG) Protein Crystal Growth Gamma-Interferon. Stimulates the body's immune system and is used clinically in the treatment of cancer. Potential as an anti-tumor agent against solid tumors as well as leukemia's and lymphomas. It has additional utility as an anti-ineffective agent, including antiviral, anti-bacterial, and anti-parasitic activities. Principal Investigator on STS-26 was Charles Bugg.

  15. Thermal crystallization mechanism of silk fibroin protein

    Microsoft Academic Search

    Xiao Hu

    2009-01-01

    In this thesis, the thermal crystallization mechanism of silk fibroin protein from Bombyx mori silkworm, was treated as a model for the general study of protein based materials, combining theories from both biophysics and polymer physics fields. A systematic and scientific path way to model the dynamic beta-sheet crystallization process of silk fibroin protein was presented in the following sequence:

  16. Polarimetric radar observations of the growth of highly-aligned ice crystals in the presence of supercooled water

    E-print Network

    Hogan, Robin

    Polarimetric radar observations of the growth of highly-aligned ice crystals in the presence aligned, which suggeststhat the normal growth mechanism (for the larger crystals at least) is aggrega to the radar signal themselves, the indication is that ice crystals in a highly supersaturated envir- onment

  17. Numerical Simulations for spiral crystal growth with impurity, interlaced spiral

    E-print Network

    Ishii, Hitoshi

    Numerical Simulations for spiral crystal growth with impurity, interlaced spiral and variable, then the crystal may need extremely high driving force around screw dislocation. #12;Hollow core type growth r ·Variable driving force by distance from a screw dislocation ·Wisker like growth ·Hollow core like growth

  18. The growth and dissolution of ammonium perchlorate crystals in a fluidized bed crystallizer

    Microsoft Academic Search

    S. Ü. Tanrikulu; I. Ero?lu; A. N. Bulutcu; S. Özkar

    1998-01-01

    The growth and the dissolution of ammonium perchlorate crystals were studied in pure and in sodium chloride containing aqueous solutions, in a fluidized bed crystallizer. The presence of sodium chloride in the solution reduced the growth and the dissolution rates of ammonium perchlorate crystals. The growth rates were interpreted in terms of supersaturation levels. The orders and rate constants were

  19. Physical aspects of protein crystal growth investigated with the Advanced Protein Crystallization Facility in reduced-gravity environments.

    PubMed

    Vergara, Alessandro; Lorber, Bernard; Zagari, Adriana; Giegé, Richard

    2003-01-01

    The physicochemical aspects of protein crystallization in reduced-gravity environments ( micro g) have been investigated with the Advanced Protein Crystallization Facility during six space missions. This review summarizes the results, dealing with the mechanisms of nucleation and crystal growth and with the quality of the crystals that were obtained under reduced gravity as well as under normal gravity on earth. Statistical analyses of the experimental data strongly support the fact that micro g has a positive effect on crystallization and on crystal quality. A comparison of experiments and theories of protein crystallization in reduced-gravity environments is presented. Recommendations for improving the performance of protein crystallization experiments in micro g and on earth are discussed. PMID:12499533

  20. Mechanisms of Stranski Krastanov Growth

    NASA Astrophysics Data System (ADS)

    Baskaran, Arvind; Smereka, Peter

    2011-03-01

    During the Heteroepitaxial growth of strained semiconductor films (like Ge on Si) the self assembly of quantum dots is observed. This is often reported in experiments to take place though the Stranski Krastanov (SK) growth mode, where the film grows in a layer by layer fashion up to a certain critical thickness after which islands (dots) form. In this talk we present a study of the SK growth mode using a solid on solid Kinetic Monte Carlo model. The importance of the use of such an discrete stochastic model and its merits over the continuum approach will be outlined. Entropy is found to play a very crucial role in the SK growth mode. The mechanism of the SK growth is understood in the context of a delicate balance of the energy and entropy. This is joint work with Peter Smereka.

  1. The effect of protein impurities on lysozyme crystal growth.

    PubMed

    Judge, R A; Forsythe, E L; Pusey, M L

    1998-09-20

    While bulk crystallization from impure solutions is used industrially as a purification step for a wide variety of materials, it is a technique that has rarely been used for proteins. Proteins have a reputation for being difficult to crystallize and high purity of the initial crystallization solution is considered paramount for success in the crystallization. Although little is written on the purifying capability of protein crystallization or of the effect of impurities on the various aspects of the crystallization process, recent published reports show that crystallization shows promise and feasibility as a purification technique for proteins. To further examine the issue of purity in macromolecule crystallization, this study investigates the effect of the protein impurities, avidin, ovalbumin, and conalbumin at concentrations up to 50%, on the solubility, crystal face growth rates, and crystal purity of the protein lysozyme. Solubility was measured in batch experiments while a computer controlled video microscope system was used to measure the ¿110¿ and ¿101¿ lysozyme crystal face growth rates. While little effect was observed on solubility and high crystal purity was obtained (>99.99%), the effect of the impurities on the face growth rates varied from no effect to a significant face specific effect leading to growth cessation, a phenomenon that is frequently observed in protein crystal growth. The results shed interesting light on the effect of protein impurities on protein crystal growth and strengthen the feasibility of using crystallization as a unit operation for protein purification. PMID:10099398

  2. On the origin of size-dependent and size-independent crystal growth: Influence of advection and diffusion

    USGS Publications Warehouse

    Kile, D.E.; Eberl, D.D.

    2003-01-01

    Crystal growth experiments were conducted using potassium alum and calcite crystals in aqueous solution under both non-stirred and stirred conditions to elucidate the mechanism for size-dependent (proportionate) and size-independent (constant) crystal growth. Growth by these two laws can be distinguished from each other because the relative size difference among crystals is maintained during proportionate growth, leading to a constant crystal size variance (??2) for a crystal size distribution (CSD) as the mean size increases. The absolute size difference among crystals is maintained during constant growth, resulting in a decrease in size variance. Results of these experiments show that for centimeter-sized alum crystals, proportionate growth occurs in stirred systems, whereas constant growth occurs in non-stirred systems. Accordingly, the mechanism for proportionate growth is hypothesized to be related to the supply of reactants to the crystal surface by advection, whereas constant growth is related to supply by diffusion. Paradoxically, micrometer-sized calcite crystals showed proportionate growth both in stirred and in non-stirred systems. Such growth presumably results from the effects of convection and Brownian motion, which promote an advective environment and hence proportionate growth for minute crystals in non-stirred systems, thereby indicating the importance of solution velocity relative to crystal size. Calcite crystals grown in gels, where fluid motion was minimized, showed evidence for constant, diffusion-controlled growth. Additional investigations of CSDs of naturally occurring crystals indicate that proportionate growth is by far the most common growth law, thereby suggesting that advection, rather than diffusion, is the dominant process for supplying reactants to crystal surfaces.

  3. Global Weak Solutions of a Polymer Crystal Growth Model Department of Mathematics, Iowa State University

    E-print Network

    Burger, Martin

    mechanisms involved in the solidification from a melt, namely the nucleation and growth of crystals the thermal melting point Tm and the glass transition temperature Tg. The mathematical modeling of all the mechanisms including nucleation, growth, and deposition is very complicated. It may be appropriate

  4. Computer-controlled growth of organic crystals from solutions

    Microsoft Academic Search

    Bernard Marciniak; Michal Strozik; Jan Konopacki; Jerzy Dabrowski

    1997-01-01

    A new type apparatus for growth of organic single crystals from solutions by lowering temperature is described. Microcomputer system 'Crystal 01' our design was used to control the rate of temperature lowering and agitation of the crystal and growth solution. At the range of temperature 313 - 298 K practically linear cooling T equals minus 0.0008 t plus 313.02, R2

  5. Convective flow effects on protein crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Monaco, Lisa A.

    1995-01-01

    During the fourth semi-annual period under this grant we have pursued the following activities: (1) crystal growth morphology and kinetics studies with tetragonal lysozyme. These clearly revealed the influence of higher molecular weight protein impurities on interface shape; (2) characterization of the purity and further purification of lysozyme solutions. These efforts have, for the first time, resulted in lysozyme free of higher molecular weight components; (3) continuation of the salt repartitioning studies with Seikagaku lysozyme, which has a lower protein impurity content that Sigma stock. These efforts confirmed our earlier findings of higher salt contents in smaller crystals. However, less salt is in corporated into the crystals grown from Seikagaku stock. This strongly suggests a dependence of salt repartitioning on the concentration of protein impurities in lysozyme. To test this hypothesis, repartitioning studies with the high purity lysozyme prepared in-house will be begun shortly; (4) numerical modelling of the interaction between bulk transport and interface kinetics. These simulations have produced interface shapes which are in good agreement with out experimental observations; and (5) light scattering studies on under- and supersaturated lysozyme solutions. A consistent interpretation of the static and dynamic data leaves little doubt that pre-nucleation clusters, claimed to exist even in undersaturated solutions, are not present. The article: 'Growth morphology response to nutrient and impurity nonuniformities' is attached.

  6. MOF crystal growth: UV resonance Raman investigation of metal-ligand binding in solution and accelerated crystal growth methods.

    PubMed

    Petersen, Thomas D; Balakrishnan, Gurusamy; Weeks, Colin L

    2015-07-01

    Determining the mechanism of metal-organic framework (MOF) crystal growth is important for the development of more efficient and reliable synthetic methods. Resonance Raman spectroscopy has been used for the first time to detect interactions in solution between metal ions and bridging ligands as MOFs form. UV excitation (229 nm) produced strong resonance enhancement of 4,4'-bipyridine (bpy) vibrational bands and showed that soluble Co(2+)-bpy species formed in solution prior to the growth of MOF crystals from bpy and Co(NO3)2. The results of the Raman experiments informed the development of faster methods for synthesizing [Co2(bpy)3(NO3)4]n 2D bilayer and [Co(bpy)(NO3)2(H2O)2]n 1D chain MOFs. PMID:26100962

  7. Growth of equiaxed dendritic crystals settling in an undercooled melt

    E-print Network

    Beckermann, Christoph

    176 Growth of equiaxed dendritic crystals settling in an undercooled melt A. Badillo and C Abstract Experiments were conducted to measure the dendrite tip growth velocities of equiaxed dendritic direction relative to the crystal. The average of the measured tip growth velocities of all six dendrite

  8. New Aspects of Crystal Growth of Solid 4He Studied by Acoustic Wave

    NASA Astrophysics Data System (ADS)

    Okuda, Yuichi; Nomura, Ryuji

    2008-11-01

    The new aspects of crystal growth in solid 4He at low temperatures are revealed by manipulating the crystal with a radiation pressure of acoustic waves. The acoustic radiation pressure is generally a tiny nonlinear effect, but it has given unexpected effect on the surface of 4He owing to the markedly high growth rate of the crystal. Radiation pressure induces crystallization or melting. Owing to the strong temperature dependences of the growth rate of an atomically rough surface, which increases divergingly towards T=0, and the numerical value of the ratio of the sound velocities in both phases, the crystal melts at high temperatures when the sound wave is applied from the solid side, while it grows at low temperatures under the same conditions. We found a new type of growth mechanism of a c-facet driven by a strong radiation pressure. The growth rate of a c-facet was found to be much higher than the conventional screw-dislocation-mediated mechanism. Theoretical analysis that treated elementary steps as quantum mechanical quasi-particles reproduced the observed important feasures. The superflow around steps was taken into account as the kinetic energy of the steps. Finally, it was demonstrated that the use of radiation pressure enables the creation of negative crystals or superfluid bubbles in the crystal. Various interesting motions and shapes of the negative crystal were observed and interpreted using a simple model.

  9. Helical growth of aluminum nitride: new insights into its growth habit from nanostructures to single crystals.

    PubMed

    Zhang, Xing-Hong; Shao, Rui-Wen; Jin, Lei; Wang, Jian-Yu; Zheng, Kun; Zhao, Chao-Liang; Han, Jie-Cai; Chen, Bin; Sekiguchi, Takashi; Zhang, Zhi; Zou, Jin; Song, Bo

    2015-01-01

    By understanding the growth mechanism of nanomaterials, the morphological features of nanostructures can be rationally controlled, thereby achieving the desired physical properties for specific applications. Herein, the growth habits of aluminum nitride (AlN) nanostructures and single crystals synthesized by an ultrahigh-temperature, catalyst-free, physical vapor transport process were investigated by transmission electron microscopy. The detailed structural characterizations strongly suggested that the growth of AlN nanostructures including AlN nanowires and nanohelixes follow a sequential and periodic rotation in the growth direction, which is independent of the size and shape of the material. Based on these experimental observations, an helical growth mechanism that may originate from the coeffect of the polar-surface and dislocation-driven growth is proposed, which offers a new insight into the related growth kinetics of low-dimensional AlN structures and will enable the rational design and synthesis of novel AlN nanostructures. Further, with the increase of temperature, the growth process of AlN grains followed the helical growth model. PMID:25976071

  10. Residual Gases in Crystal Growth Systems

    NASA Technical Reports Server (NTRS)

    Palosz, W.

    2003-01-01

    Residual gases present in closed ampoules may affect different crystal growth processes. That seems to be particularly true under microgravity conditions where, due to weightlessness of the melt, the gases may lead to detached solidification and/or formation of voids and bubbles, as observed in the past. For that reason a good understanding and control of formation of residual gases is important for an optimum design and meaningful interpretation of crystal growth experiments. Our extensive experimental and theoretical studies of the subject, summarized in this paper, include degassing of silica glass and generation of gases from different source materials. Different materials processing conditions, like outgassing under vacuum, annealing in hydrogen, resublimation, different material preparation procedures, multiple annealings, different processing times, and others were applied and their effect on the amount and composition of gas were analyzed. The experimental results were interpreted based on theoretical calculations on diffusion in silica glass and source materials and thermochemistry of the system. Procedures for a reduction of the amount of gas are also discussed.

  11. An integrated process model for the growth of oxide crystals by the Czochralski method

    NASA Astrophysics Data System (ADS)

    Derby, J. J.; Atherton, L. J.; Gresho, P. M.

    1989-10-01

    A comprehensive model for the Czochralski growth of oxide crystals is developed which integrates analyses of global heat transfer, transport phenomena in the crystal and melt, and the interfaces of the growth system. In the crystal and the melt, steady-state axisymmetric solutions for heat transfer and fluid mechanics are computed along with a self-consistent description of the free boundaries of the melt/crystal interface, the melt meniscus, and the crystal diameter. Results are presented for the growth of a large-dimension oxide crystal with realistic thermophysical properties similar to those of gadolinium gallium garnet. Comparisons between the results of this model and those of Sackinger et al. (1988) demonstrate the importance of realistic heat transfer boundary conditions. Calculations also show the effects of pedestal heat transfer on the flow in the melt.

  12. A novel growth process of calcium carbonate crystals in silk fibroin hydrogel system.

    PubMed

    Ma, Yufei; Feng, Qingling; Bourrat, Xavier

    2013-05-01

    We report an interesting finding of calcium carbonate (CaCO3) crystal growth in the silk fibroin (SF) hydrogel with different concentrations by a simple ion diffusion method. The experimental results indicate that the CaCO3 crystals obtained from silk fibroin gels with low and high concentrations are all calcites with unusual morphologies. Time-dependent growth study was carried out to investigate the crystallization process. It is believed that silk fibroin hydrogel plays an important role in the process of crystallization. The possible formation mechanism of CaCO3 crystals is proposed. This study provides a better explanation of the influence of silk fibroin concentration and its structure on CaCO3 crystals growth. PMID:23498277

  13. Effects of crystal rotation rate on the melt crystal interface of a CZ-Si crystal growth in a transverse magnetic field

    NASA Astrophysics Data System (ADS)

    Liu, Lijun; Kakimoto, Koichi

    2008-01-01

    A series of computations were carried out to study the effect of crystal rotation rate on the melt-crystal interface shape and temperature gradient at the interface during CZ-Si crystal growth in a transverse magnetic field (TMCZ). A three-dimensional (3D) global model was used in this study. It was found that the interface deflection changes from non-uniformity in the azimuthal direction to an axisymmetric distribution with increasing crystal rotation rate. The mechanism of this effect is mainly attributed to the spatial fluctuations of local growth rate, which is derived as a function of crystal rotation rate and non-uniformity of interface deflection in the azimuthal direction. It contributes to the formation of the shape of the melt-crystal interface through the heat release of solidification at the melt-crystal interface. Even though the melt-crystal interface shape is nearly axisymmetric at a high crystal rotation rate, local growth rate fluctuations are still noticeable and play an important role in the characteristics of heat transfer and impurity segregation at the melt-crystal interface.

  14. Journal of Crystal Growth 241 (2002) 220230 Driving force for crystallization of gas hydrates

    E-print Network

    Firoozabadi, Abbas

    2002-01-01

    Journal of Crystal Growth 241 (2002) 220­230 Driving force for crystallization of gas hydrates Dimo by R. Kern Abstract A general expression is derived for the supersaturation for crystallization of one and in the hydrate crystal. Expressions for the supersaturation are obtained for solutions supersaturated

  15. Anion-switchable supramolecular gels for controlling pharmaceutical crystal growth

    NASA Astrophysics Data System (ADS)

    Foster, Jonathan A.; Piepenbrock, Marc-Oliver M.; Lloyd, Gareth O.; Clarke, Nigel; Howard, Judith A. K.; Steed, Jonathan W.

    2010-12-01

    We describe the use of low-molecular-weight supramolecular gels as media for the growth of molecular crystals. Growth of a range of crystals of organic compounds, including pharmaceuticals, was achieved in bis(urea) gels. Low-molecular-weight supramolecular gelators allow access to an unlimited range of solvent systems, in contrast to conventional aqueous gels such as gelatin and agarose. A detailed study of carbamazepine crystal growth in four different bis(urea) gelators, including a metallogelator, is reported. The crystallization of a range of other drug substances, namely sparfloxacin, piroxicam, theophylline, caffeine, ibuprofen, acetaminophen (paracetamol), sulindac and indomethacin, was also achieved in supramolecular gel media without co-crystal formation. In many cases, crystals can be conveniently recovered from the gels by using supramolecular anion-triggered gel dissolution; however, crystals of substances that themselves bind to anions are dissolved by them. Overall, supramolecular gel-phase crystallization offers an extremely versatile new tool in pharmaceutical polymorph screening.

  16. Pharmacologic mechanisms of crystal meth

    PubMed Central

    Kish, Stephen J.

    2008-01-01

    Crystal meth is a form of the stimulant drug methamphetamine that, when smoked, can rapidly achieve high concentrations in the brain. Methamphetamine causes the release of the neurotransmitters dopamine, norepinephrine and serotonin and activates the cardiovascular and central nervous systems. The levels of dopamine are low in the brain of some drug users, but whether this represents neuronal loss is uncertain. The areas of the brain involved in methamphetamine addiction are unknown but probably include the dopamine-rich striatum and regions that interact with the striatum. There is no medication approved for the treatment of relapses of methamphetamine addiction; however, potential therapeutic agents targeted to dopamine and nondopamine (e.g., opioid) systems are in clinical testing. PMID:18559805

  17. Journal of Crystal Growth 127 (1993) 499--502 ~ 0~ CRYSTAL North-Holland GROWT H

    E-print Network

    Woodall, Jerry M.

    1993-01-01

    Journal of Crystal Growth 127 (1993) 499--502 ~ 0~ CRYSTAL North-Holland GROWT H Two be incorporated in GaAs and AIGaAs epilayers. By switching the growth mode at these low substrate temperatures. This was followed barriers. A film structure with As clusters in the by the growth of quantum well structures

  18. Growth rate changes of sodium chlorate crystals independent of growth conditions

    NASA Astrophysics Data System (ADS)

    Mitrovi?, M. M.; Žeki?, A. A.; Baroš, Z. Z.

    2008-10-01

    Results of investigations of the growth rate changes inherent to the crystal are presented. It is shown that, in initial growth stage, there exist crystal growth rate changes independent of experimental conditions, with tendency to level during the time. Time evolution of sodium chlorate crystals growth rate dispersion is also presented. The results obtained show that these changes must be included in the interpretations of the growth rate changes affected by various parameters (supersaturation, temperature, fields, stress, impurities, etc.), which have not previously been taken into account. These results may improve the current crystal growth theories.

  19. Effect of L-Valine on the growth and characterization of Sodium Acid Phthalate (SAP) single crystals

    NASA Astrophysics Data System (ADS)

    Nirmala, L. Ruby; Prakash, J. Thomas Joseph

    2013-06-01

    Undoped and amino acid doped good quality single crystals of Sodium Acid Phthalate crystals (SAP) were grown by slow evaporation solution growth technique which are semiorganic in nature. The effect of amino acid (L-Valine) dopant on the growth and the properties of SAP single crystal was investigated. The single crystal X-ray diffraction studies and FT-IR studies were carried out to identify the crystal structure and the presence of functional groups in undoped and L-Valine doped SAP crystals. The transparent nature of the grown crystal was observed using UV-Visible spectrum. The thermal decomposition of the doped SAP crystals was investigated by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The enhancement in the NLO property of the undoped and L-Valine doped SAP crystals using KDP crystal as a reference was studied using SHG measurements. Vickers micro hardness measurements are used for the study of mechanical strength of the grown crystals.

  20. The role of {1 0 0} side faces for lateral growth of tabular silver bromide crystals

    NASA Astrophysics Data System (ADS)

    Bögels, G.; Meekes, H.; Bennema, P.; Bollen, D.

    1998-07-01

    In this study the growth of {1 1 1} tabular silver bromide crystals will be examined in situ under different conditions to determine a general growth mechanism. We established the side-face structure and aspect ratio of the tabular crystals for different concentrations of silver bromide dissolved in DMSO during the growth. The morphology of non-twinned crystals was studied to examine the relative growth rate of the {1 0 0} faces as compared to the {1 1 1} faces. It will be shown that there is a strong dependency between the relative growth rate of the {1 0 0} faces and the aspect ratio and side-face structures of the {1 1 1} tabular crystals. Relative fast growth of the {1 0 0} faces in comparison to the {1 1 1} faces leads to high aspect ratios and side-face structures with acute edges built up by {1 1 1} side faces. Relative slower growth leads to lower aspect ratios and ridge side-face structures built up by stable {1 1 1} and {1 0 0} faces. The lateral growth for all conditions can be explained by the substep mechanism proposed in an earlier study. This mechanism explains the increase of growth rate of a {1 1 1} side face that is linked via a twin plane to a faster growing {1 0 0} side face. From this mechanism and the observations it will be shown that the faces between the twin planes for double-twinned tabular crystals can be determined. The results presented here are not only valid for tabular crystals grown in the DMSO system but also for tabular crystals grown from the vapour phase and in the industrial precipitation method.

  1. Protein Crystal Growth With the Aid of Microfluidics

    NASA Technical Reports Server (NTRS)

    vanderWoerd, Mark

    2003-01-01

    Protein crystallography is one of three well-known methods to obtain the structure of proteins. A major rate limiting step in protein crystallography is protein crystal nucleation and growth, which is still largely a process conducted by trial-and-error methods. Many attempts have been made to improve protein crystal growth by performing growth in microgravity. Although the use of microgravity appears to improve crystal quality in some attempts, this method has been inefficient because several reasons: we lack a fundamental understanding of macromolecular crystal growth in general and of the influence of microgravity in particular, we have to start with crystal growth conditions in microgravity based on conditions on the ground and finally the hardware does not allow for experimental iteration without reloading samples on the ground. To partially accommodate the disadvantages of the current hardware, we have used microfluidic technology (Lab-on-a-Chip devices) to design the concept of a more efficient crystallization device, suitable for use on the International Space Station and in high-throughput applications on the ground. The concept and properties of microfluidics, the application design process, and the advances in protein crystal growth hardware will be discussed in this presentation. Some examples of proteins crystallized in the new hardware will be discussed, including the differences between conventional crystallization versus crystallization in microfluidics.

  2. Numerical analysis of sapphire crystal growth by the Kyropoulos technique

    NASA Astrophysics Data System (ADS)

    Demina, S. E.; Bystrova, E. N.; Lukanina, M. A.; Mamedov, V. M.; Yuferev, V. S.; Eskov, E. V.; Nikolenko, M. V.; Postolov, V. S.; Kalaev, V. V.

    2007-09-01

    A numerical model has been suggested to analyze processes occurring during sapphire crystal growth by the Kyropoulos technique. The model accounts for the radiative heat exchange in the crystal and melt convection together with the crystallization front formation. The theoretical predictions agree well with available experimental data.

  3. Continuum models of crystal growth from atomic beams with and without desorption

    Microsoft Academic Search

    J. Villain

    1991-01-01

    Continuum equations appropriate to describe crystal growth from atom beams are derived in various cases. When desorption is important, the growth is described on very long lengthscales by the Kardar-Parisi-Zhang equation, but should be corrected for shorter lengthscales where surface diffusion is the dominant mechanism. In the absence of desorption, an important effect at sufficiently low temperature comes from the

  4. Growth and Characterization of Chalcogenide Crystals by Vapour Method

    NASA Astrophysics Data System (ADS)

    Reshmi, P. M.; Kunjomana, A. G.; Chandrasekharan, K. A.

    2011-07-01

    A horizontal linear gradient two zone furnace was designed and employed to grow single crystals of indium telluride by Physical Vapour Deposition (PVD) method. It was calibrated for various trials including, series and parallel combinations of coils, and set temperatures. Systematic growth runs for chalcogenide crystals were performed by varying the source and growth temperatures. Crystals of different sizes and morphologies were obtained. The morphology and chemical analysis of the grown crystals were investigated by Scanning Electron Microscope (SEM) and Energy Dispersive Analysis using X-rays (EDAX). The hardness of the crystals was estimated using a Vickers microhardness tester.

  5. Space manufacturing in an automated crystal growth facility

    NASA Technical Reports Server (NTRS)

    Quinn, Alberta W.; Herrmann, Melody C.; Nelson, Pamela J.

    1989-01-01

    An account is given of a Space Station Freedom-based robotic laboratory system for crystal growth experiments; the robot must interface with both the experimental apparatus and such human input as may be required for control and display. The goal of the system is the simultaneous growth of several hundred protein crystals in microgravity. The robot possesses six degrees-of-freedom, allowing it to efficiently manipulate the cultured crystals as well as their respective growth cells; the crystals produced are expected to be of sufficiently high quality for complete structural determination on the basis of XRD.

  6. Ground Based Program for the Physical Analysis of Macromolecular Crystal Growth

    NASA Technical Reports Server (NTRS)

    Malkin, Alexander J.

    1998-01-01

    During the past year we have focused on application of in situ Atomic Force Microscopy (AFM) for studies of the growth mechanisms and kinetics of crystallization for different macromolecular systems. Mechanisms of macrostep formation and their decay, which are important in understanding of defect formation, were studied on the surfaces of thaumatin, catalase, canavalin and lysozyme crystals. Experiments revealed that step bunching on crystalline surfaces occurred either due to two- or three-dimensional nucleation on the terraces of vicinal slopes or as a result of uneven step generation by complex dislocation sources. No step bunching arising from interaction of individual steps in the course of the experiment was observed. The molecular structure of the growth steps for thaumatin and lipase crystals were deduced. It was further shown that growth step advance occurs by incorporation of single protein molecules. In singular directions growth steps move by one-dimensional nucleation on step edges followed by lateral growth. One-dimensional nuclei have different sizes, less then a single unit cell, varying for different directions of step movement. There is no roughness due to thermal fluctuations, and each protein molecule which incorporated into the step remained. Growth kinetics for catalase crystals was investigated over wide supersaturation ranges. Strong directional kinetic anisotropy in the tangential step growth rates in different directions was seen. The influence of impurities on growth kinetics and cessation of macromolecular crystals was studied. Thus, for catalase, in addition to pronounced impurity effects on the kinetics of crystallization, we were also able to directly observe adsorption of some impurities. At low supersaturation we repeatedly observed filaments which formed from impurity molecules sedimenting on the surfaces. Similar filaments were observed on the surfaces of thaumatin, canavalin and STMV crystals as well, but the frequency was low compared with catalase crystallization. Cessation of growth of xylanase and lysozyme crystals was also observed and appeared to be a consequence of the formation of dense impurity adsorption layers. Attachment: "An in situ AFM investigation of catalase crystallization", "Atomic force microscopy studies of living cells: visualization of motility, division, aggregation, transformation, and apoptosis", AFM studies on mechanisms of nucleation and growth of macromolecular crystals", and "In situ atomic force microscopy studies of surface morphology, growth kinetics, defect structure and dissolution in macromolecular crystallization".

  7. Oscillatory zoning: a pathological case of crystal growth

    Microsoft Academic Search

    Claude J. Allègre; Ariel Provost; Claude Jaupart

    1981-01-01

    A new theory of oscillatory zoning in naturally grown plagioclase crystals is presented. This describes explicitly the coupling between the interface kinetics and the diffusion of chemical species in the melt. The crystal growth rate R responds with a finite delay time to concentration changes at the interface. Thus the growth rate cannot be simply some function of the supersaturation.

  8. Synthesis, crystal growth, solubility, structural, optical, dielectric and microhardness studies of Benzotriazole-4-hydroxybenzoic acid single crystals

    NASA Astrophysics Data System (ADS)

    Silambarasan, A.; Krishna Kumar, M.; Thirunavukkarasu, A.; Mohan Kumar, R.; Umarani, P. R.

    2015-06-01

    Organic Benzotriazole-4-hydroxybenzoic acid (BHBA), a novel second-order nonlinear optical single crystal was grown by solution growth method. The solubility and nucleation studies were performed for BHBA crystal at different temperatures 30, 35, 40 45 and 50 °C. Single crystal X-ray diffraction study reveals that the BHBA belongs to Pna21 space group of orthorhombic crystal system. The crystal perfection of BHBA was examined from powder and high resolution X-ray diffraction analysis. UV-visible and photoluminescence spectra were recorded to study its transmittance and excitation, emission behaviors respectively. Kurtz powder second harmonic generation test reveals that, the frequency conversion efficiency of BHBA is 3.7 times higher than that of potassium dihydrogen phosphate (KDP) crystal. The dielectric constant and dielectric loss values were estimated for BHBA crystal at various temperatures and frequencies. The mechanical property of BHBA crystal was studied on (110), (010) and (012) planes by using Vicker's microhardness test. The chemical etching study was performed on (012) facet of BHBA crystal to analyze its growth feature.

  9. Kinetic mechanism of chain folding in polymer crystallization.

    PubMed

    Stepanow, S

    2014-09-01

    I develop a kinetic mechanism to explain chain folding in polymer crystallization which is based on the competition between the formation of stems, which is due to frequent occupations of trans states along the chains in the supercooled polymer melt, and the random coil structure of the polymer chains. Setting equal the average formation time of stems of length d(l) with the Rouse time of a piece of polymer of the same arc length d(l) yields a lower bound for the thickness of stems and bundles. The estimated lamellar thickness is inversely proportional to the supercooling. The present approach emphasizes the importance of repulsive interactions in polymer crystallization, which are expected to be responsible for the logarithmic lamellar thickening and the increase of lamellar thickness with pressure. An expression for the growth rate for formation and deposition of stems is derived by considering the growth as a dynamic multistage process. PMID:25314466

  10. Effect of impurities on crystal growth rate of ammonium pentaborate

    NASA Astrophysics Data System (ADS)

    ?ahin, Ö.; Özdemir, M.; Genli, N.

    2004-01-01

    The effect of sodium chloride, borax and boric acid of different concentrations on the growth rate of ammonium pentaborate octahydrate crystals (APBO) was measured and was found to depend on supersaturation in a fluidized bed crystallizer. The presence of impurities in APBO solution increases the growth rate compared with growth from pure solution. It was found that the presence of sodium chloride, borax and boric acid decreases the reaction rate constant kr, while it increases the mass-transfer coefficient, K, of APBO crystals. In pure aqueous solution, the crystal growth rate of APBO is mainly controlled by diffusion. However, both diffusion and integration steps affect the growth rate of APBO crystals in the presence of sodium chloride, borax and boric acid. The mass-transfer coefficient, K, reaction rate constant, kr and reaction order, r were calculated from general mass-transfer equation by using genetic algorithm method making no assumption.

  11. Kinetic Roughening Transition and Energetics of Tetragonal Lysozyme Crystal Growth

    NASA Technical Reports Server (NTRS)

    Gorti, Sridhar; Forsythe, Elizabeth L.; Pusey, Marc L.

    2004-01-01

    Interpretation of lysozyme crystal growth rates using well-established physical theories enabled the discovery of a phenomenon possibly indicative of kinetic roughening. For example, lysozyme crystals grown above a critical supersaturation sigma, (where supersaturation sigma = ln c/c(sub eq), c = the protein concentration and c(sub eq) = the solubility concentration) exhibit microscopically rough surfaces due to the continuous addition of growth units anywhere on the surface of a crystal. The rate of crystal growth, V(sub c), for the continuous growth process is determined by the continuous flux of macromolecules onto a unit area of the crystal surface, a, from a distance, xi, per unit time due to diffusion, and a probability of attachment onto the crystal surface, expressed. Based upon models applied, the energetics of lysozyme crystal growth was determined. The magnitudes of the energy barriers of crystal growth for both the (110) and (101) faces of tetragonal lysozyme crystals are compared. Finally, evidence supportive of the kinetic roughening hypothesis is presented.

  12. Industrial challenges for numerical simulation of crystal growth

    NASA Astrophysics Data System (ADS)

    Bogdanov, M.; Ofengeim, D.; Zhmakin, A.

    2004-03-01

    Numerical simulation of industrial crystal growth is difficult due to its multidisciplinary nature and the complex geometry of the real-life growth equipment. An attempt is made to itemize physical phenomena dominant in the different methods for growth of bulk crystals from the melt and the vapor phase as well as to review corresponding numerical approaches. Academic research and industrial applications are compared. Development of a computational engine and a graphic user interface of the industry-oriented codes is discussed. A simulator for the entire growth process of bulk crystals by sublimation method is described.

  13. Laser Schlieren Crystal-Growth Imager

    NASA Technical Reports Server (NTRS)

    Owen, R. B.; Johnston, M. H.

    1986-01-01

    Crystal observed as it grows from melt with aid of laser schlieren imaging. Observation method allows entire perimeter of growing crystal to be inspected. Isolated crystal facets examined, convection flows and temperature and concentration gradients revealed. Method does not require contact with, or proximity to, crystal.

  14. High temperature solution growth of perovskite Pb 2CoWO 6 single crystals

    NASA Astrophysics Data System (ADS)

    Sun, B. N.; Boutellier, R.; Sciau, Ph.; Burkhardt, E.; Rodriguez, V.; Schmid, H.

    1991-05-01

    Single crystals of the perovskite Pb 2CoWO 6 (PCW) of sufficient size and homogeneity for optical and X-ray characterizations have been grown in sealed Pt crucibles by a slow cooling method of high temperature solution growth using PbO as flux. The best growth conditions were found to be: (1) 1130 to 830°C as growth temperatures, (2) (1 - x)PCW + xPbO with x (in wt%) varying from 0.35 to 0.43 as starting compositions and (3) 0.3 to 0.4°C/h as cooling rates. The common problem of separating the grown crystals from the residual flux has been solved by a flux separation technique using a porous ceramic piece which sucked the liquid at the end of the growth process inside the sealed Pt crucible. The growth morphology of PCW was found to be related to the cooling rate of the growth solution. Quasi-cubic {100} crystals with small {111} faces were grown at a small cooling rate, whereas cubo-octahedral {111}+{100}; crystals at a higher cooling rate. The PbO concentration in the starting composition was shown to have no significant effect on the growth morphology of PCW. Growth mechanisms are discussed according to the results of some surface micromorphological observations. Growth spirals and growth layers were observed on the (100) surface, giving evidence of a layer growth mechanism. A higher cooling rate induced growth instability and brought on formation of hopper crystals which are difficult to be cut and polished into thin plates necessary for subsequent characterizations. Some results of a polarized light microscopy study of domains in transmitted light and of X-ray diffraction characterizations are summarized, showing the high quality of the grown crystals.

  15. Kinetic Roughening and Energetics of Tetragonal Lysozyme Crystal Growth

    NASA Technical Reports Server (NTRS)

    Gorti, Sridhar; Forsythe, Elizabeth L.; Pusey, Marc L.

    2003-01-01

    Lysozyme crystal growth rates over 5 orders of magnitude in range can be described using a layer-by-layer model where growth occurs by 2D nucleation on the crystal surface. Based upon the 2D nucleation model of layer growth, the effective barrier for growth was determined to be gamma = 1.3 plus or minus 0.3 x 10(exp -13) erg/molecule, corresponding to a barrier of 3.2 plus or minus 0.7 k(sub B)T, at 22 C. For solution supersaturation, In c/c(sub eq) greater than or equal to 1.9 plus or minus 0.2, the nucleation model would not predict or consistently estimate the highest observable crystal growth rates. As such, a kinetic roughening hypothesis where crystal growth occurs by a continuous mode was implemented for all growth rate data obtained above In c(sub r)/c(sub eq) greater than or equal to 2. That is, independent of the solution conditions that vary with either buffer pH, temperature or precipitant concentration, crystal growth occurs by the continuous addition of molecules anywhere on the crystal surface, above a roughening solution supersaturation. The energy barrier, E(sub c), for the continuous growth process is determined as 6.1 plus or minus 0.4 x 10(exp -13) erg/molecule or 15 plus or minus 1 k(sub B)T at 22 C.

  16. Universality classes for unstable crystal growth

    NASA Astrophysics Data System (ADS)

    Biagi, Sofia; Misbah, Chaouqi; Politi, Paolo

    2014-06-01

    Universality has been a key concept for the classification of equilibrium critical phenomena, allowing associations among different physical processes and models. When dealing with nonequilibrium problems, however, the distinction in universality classes is not as clear and few are the examples, such as phase separation and kinetic roughening, for which universality has allowed to classify results in a general spirit. Here we focus on an out-of-equilibrium case, unstable crystal growth, lying in between phase ordering and pattern formation. We consider a well-established 2+1-dimensional family of continuum nonlinear equations for the local height h(x,t) of a crystal surface having the general form ?th(x,t)=-?.[j(?h)+?(?2h)]: j (?h) is an arbitrary function, which is linear for small ?h, and whose structure expresses instabilities which lead to the formation of pyramidlike structures of planar size L and height H. Our task is the choice and calculation of the quantities that can operate as critical exponents, together with the discussion of what is relevant or not to the definition of our universality class. These aims are achieved by means of a perturbative, multiscale analysis of our model, leading to phase diffusion equations whose diffusion coefficients encapsulate all relevant information on dynamics. We identify two critical exponents: (i) the coarsening exponent, n, controlling the increase in time of the typical size of the pattern, L ˜tn; (ii) the exponent ?, controlling the increase in time of the typical slope of the pattern, M ˜t?, where M ?H/L. Our study reveals that there are only two different universality classes, according to the presence (n =1/3, ? =0) or the absence (n =1/4, ? >0) of faceting. The symmetry of the pattern, as well as the symmetry of the surface mass current j (?h) and its precise functional form, is irrelevant. Our analysis seems to support the idea that also space dimensionality is irrelevant.

  17. A Kinetic Model To Simulate Protein Crystal Growth in an Evaporation-Based Crystallization Platform

    E-print Network

    Kenis, Paul J. A.

    is started with an initial protein concentration that is closer to the solubility boundary. Here we develop that kinetic constants for nucleation and crystal growth for different proteins can be extracted by applying, as a result, each experiment yields information on crystal solubility, as well as on crystal nucleation

  18. Protein crystal growth in space, past and future

    NASA Astrophysics Data System (ADS)

    DeLucas, Lawrence J.; Moore, Karen M.; Long, Marianna M.; Rouleau, Robyn; Bray, Terry; Crysel, William; Weise, Lance

    2002-04-01

    The Center for Biophysical Sciences and Engineering (CBSE) at the University of Alabama at Birmingham has performed protein crystal growth experiments on more than 39 US space shuttle missions. Results from these experiments have clearly demonstrated that the microgravity environment is beneficial in that a number of proteins crystallized were larger and of higher quality than their Earth-grown counterparts. Improvement in crystal quality is judged by analysis of ultimate diffraction resolution, individual peak mosaicity, and electron density maps. There are now a number of protein crystals that exhibited resolution improvements of 0.5-1.5 Å. Mosaicity studies revealed dramatic decreases in peak widths for the microgravity-grown crystals. These microgravity results plus data from a variety of other investigators have stimulated various space agencies to support fundamental studies in macromolecular crystal growth processes. The CBSE has devoted substantial effort toward the development of dynamically controlled crystal growth systems which allow scientists to optimize crystallization parameters on Earth or in space. These systems enable monitoring and control of the approach to nucleation and post-nucleation growth phases, thereby dramatically improving the crystal size and X-ray diffraction characteristics. The CBSE is currently designing a complete crystallographic laboratory for the International Space Station including: a crystal growth rack, which will support a variety of crystallization hardware systems; an X-ray diffraction rack for crystal characterization or a complete X-ray data set collection; and robotically controlled crystal harvesting/cryopreservation systems that can be operated with minimal crew time via telerobotic and/or robotic procedures. Key elements of the X-ray system include unique X-ray focusing technology combined with a lightweight, low-power source. The X-ray detection system is based on commercial CCD-based technology. This paper will describe the X-ray facility envisioned for the International Space Station.

  19. Growth and characterization studies on glycine barium dichloride single crystals for NLO applications

    NASA Astrophysics Data System (ADS)

    Prakash, J. Thomas Joseph; Vijayan, N.; Kumararaman, S.

    2008-12-01

    The novel nonlinear optical single crystal of glycine barium chloride has been successfully synthesized by taking the appropriate amount of glycine and barium dichloride and single crystals have been grown by slow evaporation solution growth technique at room temperature. The grown single crystals have been analyzed with XRD, FT-IR, TG/DTA measurements. Its mechanical behavior has been assessed by Vickers Microhardness measurements. Its nonlinear optical property has been tested by Kurtz powder technique. Its optical behavior was examined by UV-vis, and found that the crystal is transparent in the region between 250 and 1200 nm.

  20. Growth and characterization studies on glycine barium dichloride single crystals for NLO applications.

    PubMed

    Prakash, J Thomas Joseph; Vijayan, N; Kumararaman, S

    2008-12-15

    The novel nonlinear optical single crystal of glycine barium chloride has been successfully synthesized by taking the appropriate amount of glycine and barium dichloride and single crystals have been grown by slow evaporation solution growth technique at room temperature. The grown single crystals have been analyzed with XRD, FT-IR, TG/DTA measurements. Its mechanical behavior has been assessed by Vickers Microhardness measurements. Its nonlinear optical property has been tested by Kurtz powder technique. Its optical behavior was examined by UV-vis, and found that the crystal is transparent in the region between 250 and 1200 nm. PMID:18440858

  1. The effect of a nucleating agent on lamellar growth in melt-crystallizing polyethylene oxide

    E-print Network

    F. Aliotta; G. Di Marco; R. Ober; M. Pieruccini

    2002-12-13

    The effects of a (non co-crystallizing) nucleating agent on secondary nucleation rate and final lamellar thickness in isothermally melt-crystallizing polyethylene oxide are considered. SAXS reveals that lamellae formed in nucleated samples are thinner than in the pure samples crystallized at the same undercoolings. These results are in quantitative agreement with growth rate data obtained by calorimetry, and are interpreted as the effect of a local decrease of the basal surface tension, determined mainly by the nucleant molecules diffused out of the regions being about to crystallize. Quantitative agreement with a simple lattice model allows for some interpretation of the mechanism.

  2. Large-size germanium crystal growth for rare event physics

    NASA Astrophysics Data System (ADS)

    Mei, Dongming; Wang, Guojian; Mei, Hao; Guan, Yutong; Yang, Gang; Govani, Jayesh; Cubed Collaboration

    2014-09-01

    Cosmogenic production in germanium crystals grown on the surface can limit the sensitivity for the next generation deep underground experiments in searching for rare event physics beyond the Standard Model. One of the best solutions to eliminate unwanted cosmogenics is to produce the germanium crystals and detectors in an underground environment. The goal of this project is to create state-of-the-art detectors to advance neutrinoless double-beta decay and dark matter exploration research and technology while simultaneously paving the way for infrastructure to support an underground laboratory for zone refining, crystal growth, and detector fabrication. The greatest challenge in the growth of germanium crystals is a lack of precise control of individual crystal properties such as the impurity distribution, the dislocation density, and the crystalline structure. With knowledge gained from the pioneers in the field of crystal growth, the researchers have developed a novel technique to grow detector-grade crystals. In this paper, we will report detector-grade large-size germanium crystal growth at the University of South Dakota. Cosmogenic production in germanium crystals grown on the surface can limit the sensitivity for the next generation deep underground experiments in searching for rare event physics beyond the Standard Model. One of the best solutions to eliminate unwanted cosmogenics is to produce the germanium crystals and detectors in an underground environment. The goal of this project is to create state-of-the-art detectors to advance neutrinoless double-beta decay and dark matter exploration research and technology while simultaneously paving the way for infrastructure to support an underground laboratory for zone refining, crystal growth, and detector fabrication. The greatest challenge in the growth of germanium crystals is a lack of precise control of individual crystal properties such as the impurity distribution, the dislocation density, and the crystalline structure. With knowledge gained from the pioneers in the field of crystal growth, the researchers have developed a novel technique to grow detector-grade crystals. In this paper, we will report detector-grade large-size germanium crystal growth at the University of South Dakota. DE-FG02-10ER46709 and the state of South Dakota.

  3. Needs and Opportunities in Crystal Growth.

    ERIC Educational Resources Information Center

    Mroczkowski, Stanley

    1980-01-01

    Presents a survey of the scientific basis for single crystals production, discussing some of the theoretical and experimental advances in the area. Future prospects for semiconductors, magnetic lasers, nonlinear optics, piezoelectrics, and other crystals are surveyed. (Author/CS)

  4. Book ReViews Crystal Growth Technology: From Fundamentals and

    E-print Network

    Regel, Liya L.

    on melt growth of large crystals of commercial importance, with little coverage of solution growth and virtually nothing on thin film deposition. The articles begin with thermodynamics, continue with modeling growth from the melt. Liya L. Regel and William R. Wilcox Clarkson UniVersity CG800822X 10.1021/cg800822x

  5. Acicular crystal-assembled TiO 2 thin films and their deposition mechanism

    Microsoft Academic Search

    Yoshitake Masuda; Kazumi Kato

    2009-01-01

    Acicular crystal-assembled TiO2 thin films were prepared on fluorine-doped tin oxide (FTO) substrates in aqueous solutions. They consisted of anatase crystals grown along the c-axis, which caused high c-axis orientation in X-ray diffraction patterns and electron diffraction patterns. Morphologies of TiO2 crystals were controlled by growth conditions to fabricate several types of TiO2 thin films. Furthermore, deposition mechanism of acicular

  6. Nucleation and Growth of Discotic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Cheng, Zhengdong; Wang, Xuezhen; Zhang, Lecheng; Shinde, Abhijeet; Liquid Crystals of Nanoplates in Microgravity Team

    2015-03-01

    We investigate the nucleation and growth of liquid crystals of plate-shaped charged zirconium phosphate (ZrP) monolayers with various sizes, temperature and salt concentrations. The smaller the platelets size, or the higher the temperature, or the higher the salt concentration (from 0 to 0.6M), the faster the Isotropic-Nematic (I-N) separation took place. We established the I-N transition phase diagram of charged platelets in the temperature verse volume fraction plane, and discovered that N phase can be melted by increasing temperature, and coexistent samples are more sensitive to polydispersity at higher temperature and higher concentrations. We also found that salt concentration in the ZrP suspensions contributed to the formation of an apparently twisted phase. This work is supported by NSF (DMR-1006870) and NASA (NASA-NNX13AQ60G). X.Z. Wang acknowledges support from the Mary Kay O'Connor Process Safety Center (MKOPSC) at Texas A&M University.

  7. Method For Growth of Crystal Surfaces and Growth of Heteroepitaxial Single Crystal Films Thereon

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony (Inventor); Larkin, David J. (Inventor); Neudeck, Philip G. (Inventor); Matus, Lawrence G. (Inventor)

    2000-01-01

    A method of growing atomically-flat surfaces and high quality low-defect crystal films of semiconductor materials and fabricating improved devices thereon is discussed. The method is also suitable for growing films heteroepitaxially on substrates that are different than the film. The method is particularly suited for growth of elemental semiconductors (such as Si), compounds of Groups III and V elements of the Periodic Table (such as GaN), and compounds and alloys of Group IV elements of the Periodic Table (such as SiC).

  8. A method of promoting single crystal yield during melt growth of semiconductors by directional solidification

    NASA Astrophysics Data System (ADS)

    Su, Ching-Hua

    2015-01-01

    For certain semiconductors with important applications, the existing unseeded bulk directional solidification crystal growth technique from the melt usually results in poor quality multi-crystalline ingots which causes the low yield of the commercial growth process. The multi-grained crystal growth is mainly caused by the large supercool of the melt, which not only results in a large section of ingot solidifying uncontrollably under spontaneous nucleation but also prohibits the ideal growth condition that small single crystal nuclei form at the very tip of the ampoule and grow into large single grains. To promote nucleation under the condition of small supercooling, a method was employed to induce nucleation by mechanical perturbation at a critical time during growth. The technique was applied to the bulk crystal growth process of Cd1-xZnxTe ingots. The comparison between the crystalline quality of the crystals grown with and without the mechanically induced nucleation shows that the yield of single crystalline can been vastly improved with the application of the technique.

  9. Viscous Fingering and Dendritic Growth of Surface Crystallized Sr2TiSi2O8 Fresnoite

    PubMed Central

    Wisniewski, Wolfgang; Patschger, Marek; Rüssel, Christian

    2013-01-01

    During the quenching of a melt with the composition 2SrO·TiO2·2.75SiO2, cubic SrTiO3- and tetragonal Sr2TiSi2O8-crystals are formed at the surface. Subsequent crystal growth leads to dendritic fresnoite structures which become increasingly finer until the mechanism changes to viscous fingering during further cooling. In the final stages of this initial growth step, the crystal orientations of these dendrites systematically change. Due to a complete absence of bulk nucleation in this system, crystal growth is resumed upon reheating to 970°C and fractal growth with the c-axis tilted by about 45° from the main growth direction is observed. The results are interpreted to confirm the link between viscous fingering and dendritic growth in the case of a true crystallization process. PMID:24356207

  10. Spiral and target patterns in bivalve nacre manifest a natural excitable medium from layer growth of a biological liquid crystal.

    PubMed

    Cartwright, Julyan H E; Checa, Antonio G; Escribano, Bruno; Sainz-Díaz, C Ignacio

    2009-06-30

    Nacre is an exquisitely structured biocomposite of the calcium carbonate mineral aragonite with small amounts of proteins and the polysaccharide chitin. For many years, it has been the subject of research, not just because of its beauty, but also to discover how nature can produce such a superior product with excellent mechanical properties from such relatively weak raw materials. Four decades ago, Wada [Wada K (1966) Spiral growth of nacre. Nature 211:1427] proposed that the spiral patterns in nacre could be explained by using the theory Frank [Frank F (1949) The influence of dislocations on crystal growth. Discuss Faraday Soc 5:48-54] had put forward of the growth of crystals by means of screw dislocations. Frank's mechanism of crystal growth has been amply confirmed by experimental observations of screw dislocations in crystals, but it is a growth mechanism for a single crystal, with growth fronts of molecules. However, the growth fronts composed of many tablets of crystalline aragonite visible in micrographs of nacre are not a molecular-scale but a mesoscale phenomenon, so it has not been evident how the Frank mechanism might be of relevance. Here, we demonstrate that nacre growth is organized around a liquid-crystal core of chitin crystallites, a skeleton that the other components of nacre subsequently flesh out in a process of hierarchical self-assembly. We establish that spiral and target patterns can arise in a liquid crystal formed layer by layer through the Burton-Cabrera-Frank [Burton W, Cabrera N, Frank F (1951) The growth of crystals and the equilibrium structure of their surfaces. Philos Trans R Soc London Ser A 243:299-358] dynamics, and furthermore that this layer growth mechanism is an instance of an important class of physical systems termed excitable media. Artificial liquid crystals grown in this way may have many technological applications. PMID:19528636

  11. The effects of polydispersity and metastability on crystal growth kinetics

    E-print Network

    John J. Williamson; R. Mike L. Evans

    2013-02-25

    We investigate the effect of metastable gas-liquid (G-L) separation on crystal growth in a system of either monodisperse or slightly size-polydisperse square well particles, using a simulation setup that allows us to focus on the growth of a single crystal. Our system parameters are such that, inside the metastable G-L binodal, a macroscopic layer of the gas phase "coats" the crystal as it grows, consistent with experiment and theoretical free energy considerations. Crucially, the effect of this metastable G-L separation on the crystal growth rate depends qualitatively on whether the system is polydisperse. We measure reduced polydispersity and qualitatively different local size ordering in the crystal relative to the fluid, proposing that the required fractionation is dynamically facilitated by the gas layer. Our results show that polydispersity and metastability, both ubiquitous in soft matter, must be considered in tandem if their dynamical effects are to be understood.

  12. Modelling of Heat Transfer in Single Crystal Growth

    E-print Network

    Zhmakin, Alexander I

    2014-01-01

    An attempt is made to review the heat transfer and the related problems encountered in the simulation of single crystal growth. The peculiarities of conductive, convective and radiative heat transfer in the different melt, solution, and vapour growth methods are discussed. The importance of the adequate description of the optical crystal properties (semitransparency, specular reflecting surfaces) and their effect on the heat transfer is stresses. Treatment of the unknown phase boundary fluid/crystal as well as problems related to the assessment of the quality of the grown crystals (composition, thermal stresses, point defects, disclocations etc.) and their coupling to the heat transfer/fluid flow problems is considered. Differences between the crystal growth simulation codes intended for the research and for the industrial applications are indicated. The problems of the code verification and validation are discussed; a brief review of the experimental techniques for the study of heat transfer and flow structu...

  13. Microfluidic experiments reveal that antifreeze proteins bound to ice crystals suffice to prevent their growth

    PubMed Central

    Celik, Yeliz; Drori, Ran; Pertaya-Braun, Natalya; Altan, Aysun; Barton, Tyler; Bar-Dolev, Maya; Groisman, Alex; Davies, Peter L.; Braslavsky, Ido

    2013-01-01

    Antifreeze proteins (AFPs) are a subset of ice-binding proteins that control ice crystal growth. They have potential for the cryopreservation of cells, tissues, and organs, as well as for production and storage of food and protection of crops from frost. However, the detailed mechanism of action of AFPs is still unclear. Specifically, there is controversy regarding reversibility of binding of AFPs to crystal surfaces. The experimentally observed dependence of activity of AFPs on their concentration in solution appears to indicate that the binding is reversible. Here, by a series of experiments in temperature-controlled microfluidic devices, where the medium surrounding ice crystals can be exchanged, we show that the binding of hyperactive Tenebrio molitor AFP to ice crystals is practically irreversible and that surface-bound AFPs are sufficient to inhibit ice crystal growth even in solutions depleted of AFPs. These findings rule out theories of AFP activity relying on the presence of unbound protein molecules. PMID:23300286

  14. Large-volume protein crystal growth for neutron macromolecular crystallography.

    PubMed

    Ng, Joseph D; Baird, James K; Coates, Leighton; Garcia-Ruiz, Juan M; Hodge, Teresa A; Huang, Sijay

    2015-04-01

    Neutron macromolecular crystallography (NMC) is the prevailing method for the accurate determination of the positions of H atoms in macromolecules. As neutron sources are becoming more available to general users, finding means to optimize the growth of protein crystals to sizes suitable for NMC is extremely important. Historically, much has been learned about growing crystals for X-ray diffraction. However, owing to new-generation synchrotron X-ray facilities and sensitive detectors, protein crystal sizes as small as in the nano-range have become adequate for structure determination, lessening the necessity to grow large crystals. Here, some of the approaches, techniques and considerations for the growth of crystals to significant dimensions that are now relevant to NMC are revisited. These include experimental strategies utilizing solubility diagrams, ripening effects, classical crystallization techniques, microgravity and theoretical considerations. PMID:25849493

  15. Growth direction of columnar crystals solidified in flowing melt

    Microsoft Academic Search

    K. Murakami; H. Aihara; T. Okamuto

    1984-01-01

    Aluminum-copper alloys containing 0.5-8.8 wt Cu were unidirectionally solidified. Columnar crystals were grown in flowing melts at flow rates ranging from 4 to 90 cm\\/s, and the deflection angle of the crystal growth direction in the upstream direction was measured as functions of flow rate and copper content. The columnar crystals originated from nuclei or solid particles with the most

  16. Instability of needle crystals in anisotropic dendritic growth

    Microsoft Academic Search

    Fong Liu; Nigel Goldenfeld

    1990-01-01

    The linear stability of steady-state needle crystals in dendritic growth is studied in the presence of anisotropies in both surface tension and interfacial kinetics. The needle crystals are linearly unstable for certain ranges of values of the surface tension and kinetic coefficients. This instability results in complex tip-splitting and sidebranching events that lead to morphological transitions.

  17. Growth of large single crystals of the orthorhombic paracetamol

    NASA Astrophysics Data System (ADS)

    Mikhailenko, M. A.

    2004-05-01

    A new procedure for the growth of large (cm-range) single crystals of the metastable orthorhombic (s.g. Pcab) polymorph of paracetamol is described. The crystals were grown by very slow cooling of hot water solutions under the conditions, when the multiple nucleation was prevented. The samples were characterized by DSC and X-ray diffraction.

  18. Edge-controlled growth and kinetics of single-crystal graphene domains by chemical vapor deposition

    PubMed Central

    Ma, Teng; Ren, Wencai; Zhang, Xiuyun; Liu, Zhibo; Gao, Yang; Yin, Li-Chang; Ma, Xiu-Liang; Ding, Feng; Cheng, Hui-Ming

    2013-01-01

    The controlled growth of large-area, high-quality, single-crystal graphene is highly desired for applications in electronics and optoelectronics; however, the production of this material remains challenging because the atomistic mechanism that governs graphene growth is not well understood. The edges of graphene, which are the sites at which carbon accumulates in the two-dimensional honeycomb lattice, influence many properties, including the electronic properties and chemical reactivity of graphene, and they are expected to significantly influence its growth. We demonstrate the growth of single-crystal graphene domains with controlled edges that range from zigzag to armchair orientations via growth–etching–regrowth in a chemical vapor deposition process. We have observed that both the growth and the etching rates of a single-crystal graphene domain increase linearly with the slanted angle of its edges from 0° to ?19° and that the rates for an armchair edge are faster than those for a zigzag edge. Such edge-structure–dependent growth/etching kinetics of graphene can be well explained at the atomic level based on the concentrations of the kinks on various edges and allow the evolution and control of the edge and morphology in single-crystal graphene following the classical kinetic Wulff construction theory. Using these findings, we propose several strategies for the fabrication of wafer-sized, high-quality, single-crystal graphene. PMID:24297886

  19. Anion-switchable supramolecular gels for controlling pharmaceutical crystal growth

    Microsoft Academic Search

    Jonathan A. Foster; Marc-Oliver M. Piepenbrock; Gareth O. Lloyd; Nigel Clarke; Judith A. K. Howard; Jonathan W. Steed

    2010-01-01

    We describe the use of low-molecular-weight supramolecular gels as media for the growth of molecular crystals. Growth of a range of crystals of organic compounds, including pharmaceuticals, was achieved in bis(urea) gels. Low-molecular-weight supramolecular gelators allow access to an unlimited range of solvent systems, in contrast to conventional aqueous gels such as gelatin and agarose. A detailed study of carbamazepine

  20. Definition study for temperature control in advanced protein crystal growth

    NASA Technical Reports Server (NTRS)

    Nyce, Thomas A.; Rosenberger, Franz; Sowers, Jennifer W.; Monaco, Lisa A.

    1990-01-01

    Some of the technical requirements for an expedient application of temperature control to advanced protein crystal growth activities are defined. Lysozome was used to study the effects of temperature ramping and temperature gradients for nucleation/dissolution and consecutive growth of sizable crystals and, to determine a prototype temperature program. The solubility study was conducted using equine serum albumin (ESA) which is an extremely stable, clinically important protein due to its capability to bind and transport many different small ions and molecules.

  1. Transport modes during crystal growth in a centrifuge

    NASA Technical Reports Server (NTRS)

    Arnold, William A.; Wilcox, William R.; Carlson, Frederick; Chait, Arnon; Regel', Liia L.

    1992-01-01

    Flow modes arising under average acceleration in centrifugal crystal growth, the gradient of acceleration, and the Coriolis force are investigated using a fully nonlinear three-dimensional numerical model for a centrifugal crystal growth experiment. The analysis focuses on an examination of the quasi-steady state flow modes. The importance of the gradient acceleration is determined by the value of a new nondimensional number, Ad.

  2. Heat-Exchanger Method of Crystal Growth

    NASA Technical Reports Server (NTRS)

    Khattak, C. P.; Schmid, F.

    1982-01-01

    Large crystals of silicon are grown from melt, in either vacuum or pressurized atmosphere, without moving crucible, furnace, or anything else. Seed crystal is mounted on helium-cooled heat exchanger, which prevents seed from melting when furnace melts rest of silicon material in crucible; heat exchanger draws off heat from melt so that a solid ingot grows outward from seed in a regular crystal structure. Bottom of crucible is insulated so that heat exchanger cools only seed.

  3. Mathematical Existence of Crystal Growth with GibbsThomson Curvature E#ects 1

    E-print Network

    Wang, Lihe

    Mathematical Existence of Crystal Growth with Gibbs­Thomson Curvature E#ects 1 by Fred Almgren 2 one type of growth of a crystal as it freezes from a cold melt. The crystal freezes (melts) as rapidly. CHAPTER 2. Ingredients of our model of crystal growth. 2.1 The ambient space. 2.2 Crystals. 2.3 Heat

  4. A novel method for measurement of crystal growth rate

    NASA Astrophysics Data System (ADS)

    Kim, Do Yeon; Yang, Dae Ryook

    2013-06-01

    A new method for measurement of crystal growth rate is proposed, in an attempt to make the measuring of growth rate more convenient than the existing methods. In this newly proposed method, the point of nucleation under a constant cooling rate condition was measured as changing the amount of seeds. The growth kinetics parameters were then estimated using the experimental data to match the points of nucleation. Experiments were performed with potash alum in the water system and growth kinetic parameters were estimated. Compared with existing results, the proposed method showed tolerable discrepancy in the growth kinetic parameters. The proposed method can be an alternative technique for measurement of growth rate.

  5. A kinetic model to simulate protein crystal growth in an evaporation-based crystallization platform

    SciTech Connect

    Talreja, S.; Kenis, P; Zukoski, C

    2007-01-01

    The quality, size, and number of protein crystals grown under conditions of continuous solvent extraction are dependent on the rate of solvent extraction and the initial protein and salt concentration. An increase in the rate of solvent extraction leads to a larger number of crystals. The number of crystals decreases, however, when the experiment is started with an initial protein concentration that is closer to the solubility boundary. Here we develop a kinetic model capable of predicting changes in the number and size of protein crystals as a function of time under continuous evaporation. Moreover, this model successfully predicts the initial condition of drops that will result in gel formation. We test this model with experimental crystal growth data of hen egg white lysozyme for which crystal nucleation and growth rate parameters are known from other studies. The predicted and observed rates of crystal growth are in excellent agreement, which suggests that kinetic constants for nucleation and crystal growth for different proteins can be extracted by applying a kinetic model in combination with observations from a few evaporation-based crystallization experiments.

  6. Conduction mechanism of single-crystal alumina

    NASA Technical Reports Server (NTRS)

    Will, Fritz G.; Delorenzi, Horst G.; Janora, Kevin H.

    1992-01-01

    The fully guarded three-terminal technique was used to perform conductivity measurements on single-crystal alumina at temperatures of 400-1300 C. The conductivity was also determined as a function of time at various temperatures and applied fields. Further, the fractions of the current carried by Al and O ions (ionic transference numbers) were determined from long-term transference experiments in the temperature range 1100-1300 C. A mathematical model of the conduction mechanism is proposed, and model predictions are compared with experimental results.

  7. Crystal growth and magnetic properties of GdFeO3 crystals by floating zone method

    NASA Astrophysics Data System (ADS)

    Wu, Anhua; Wang, Zhanliang; Wang, Bo; Ban, Xiaolei; Jiang, Linwen; Xu, Jun; Yuan, Shujuan; Cao, Shixun

    2014-05-01

    GdFeO3 and other rare earth substituted crystals with distorted orthorhombic pervoskite-like structure (space group Pbnm) have attracted much attention due to their remarkable magnetic properties of primary significance for technological applications. In the present work, the floating zone growth of GdFeO3 crystals has been systematically investigated and high quality GdFeO3 crystal was obtained by optimized process. The intrinsic magnetic properties of GdFeO3 crystal were investigated. GdFeO3 crystal displayed paramagnetic characteristic at low temperature, as temperature increased, a transition from paramagnetism to antiferromagnetism was observed.

  8. Vapor crystal growth studies of single crystals of mercuric iodide (3-IML-1)

    NASA Technical Reports Server (NTRS)

    Vandenberg, Lodewijk

    1992-01-01

    A single crystal of mercuric iodide (HgI2) will be grown during the International Microgravity Lab. (IML-1) mission. The crystal growth process takes place by sublimation of HgI2 from an aggregate of purified material, transport of the molecules in the vapor from the source to the crystal, and condensation on the crystal surface. The objectives of the experiment are as follow: to grow a high quality crystal of HgI2 of sufficient size so that its properties can be extensively analyzed; and to study the vapor transport process, specifically the rate of diffusion transport at greatly reduced gravity where convection is minimized.

  9. Radiochemical study of the kinetics of crystal growth in gels

    Microsoft Academic Search

    Alexandru Cecal; Mircea Palamaru; Anca Juverdeanu; Marcel Giosan

    1996-01-01

    A kinetic study was performed on nucleation and growth of crystals containing radioactive ions in gelatin and agar gels. The investigated crystals were: 60CoHPO4, 60CoS, 60Co(OH)2, 60Co(SCN)2, 204Tl(OH)3, and 204Tl[(C2H5)2NCS2]3. The study shows that the crystal growth rate depends on the cation size and charge, the nature of anion as well as on the colloidal medium. The crystallisation process in

  10. Nucleation and growth of inorganic crystals at the organic-inorganic interface

    NASA Astrophysics Data System (ADS)

    Dennis, Shelli R.

    1998-12-01

    Surface-directed nucleation and oriented crystal growth have been addressed using Langmuir monolayers in contact with supersaturated mineralizing solutions. This model system has been designed to control the chemical composition, orientation, and spacing of the functional groups exposed to the mineralizing solution and to control the ionic composition, supersaturation and pH of the solution. Light scattering microscopy (LSM) has been introduced as a novel technique to investigate early nucleation events in situ. Zwitterionic dipalmitoylphosphatidylcholine (DPPC) and negatively charged dimyristoylphosphatidylserine (DMPS) monolayers have been compared to study the role of surface chemistry on calcium oxalate crystal nucleation. A quantitative analysis of the number and apparent area of light scattering centers is presented for DPPC and DMPS monolayers. Although induction times could not be determined with LSM because of low nucleation densities, crystal growth could be directly monitored with LSM beneath DMPS monolayers. Phospholipid monolayers in the phase coexistence region have been used to investigate the role of lattice matching on calcium oxalate crystal nucleation and growth. LSM has been combined with fluorescence microscopy to determine the location of crystals relative to the liquid-condensed (LC) and liquid-expanded (LE) phases. Light scattering centers are found at the LC domain edges for DPPC and DMPS monolayers, and the LC domains aggregate during calcium oxalate crystal growth. Boehmite crystals injected beneath DMPS monolayers migrate from the LE phase to the LC domain edges where they become trapped. The phase, morphology, and orientation of mature calcium oxalate crystals grown beneath phospholipid monolayers have been investigated to obtain a better understanding of the molecular mechanisms controlling crystal nucleation and oriented growth. Mature calcium oxalate crystals grown beneath zwitterionic DPPC monolayers and negatively charged DMPS monolayers are oriented with respect to the monolayers but exhibit different crystal morphologies. Raman spectroscopy strongly suggests that crystals grown beneath either monolayer are calcium oxalate monohydrate (COM) crystals. Dimyristoyl-phosphatidylethanolamine, dimyristoylphosphatidic acid, eicosanoic acid, and eicosanol monolayers have also been studied to help elucidate the molecular mechanisms controlling the COM crystal orientation and morphology. The potential roles of lattice matching, hydrogen bonding, stereochemistry and electrostatics are discussed in detail.

  11. New simulation model of multicomponent crystal growth and inhibition.

    PubMed

    Wathen, Brent; Kuiper, Michael; Walker, Virginia; Jia, Zongchao

    2004-04-01

    We review a novel computational model for the study of crystal structures both on their own and in conjunction with inhibitor molecules. The model advances existing Monte Carlo (MC) simulation techniques by extending them from modeling 3D crystal surface patches to modeling entire 3D crystals, and by including the use of "complex" multicomponent molecules within the simulations. These advances makes it possible to incorporate the 3D shape and non-uniform surface properties of inhibitors into simulations, and to study what effect these inhibitor properties have on the growth of whole crystals containing up to tens of millions of molecules. The application of this extended MC model to the study of antifreeze proteins (AFPs) and their effects on ice formation is reported, including the success of the technique in achieving AFP-induced ice-growth inhibition with concurrent changes to ice morphology that mimic experimental results. Simulations of ice-growth inhibition suggest that the degree of inhibition afforded by an AFP is a function of its ice-binding position relative to the underlying anisotropic growth pattern of ice. This extended MC technique is applicable to other crystal and crystal-inhibitor systems, including more complex crystal systems such as clathrates. PMID:15054746

  12. Some effects of crystal rotation on large-scale Czochralski oxide growth: analysis via a hydrodynamic thermal-capillary model

    NASA Astrophysics Data System (ADS)

    Derby, J. J.; Xiao, Q.

    1991-09-01

    A hydrodynamic thermal-capillary model (HTCM) for heat transfer in Czochralski crystal growth systems is used to calculate steady-state, axisymmetric solutions for heat transfer and fluid mechanics while incorporating a self-consistent description of the free boundaries of the melt/crystal interface, the melt meniscus, and the crystal diameter. The model employs a Galerkin finite-element method to discretize the model equations, and solutions are obtained using a Newton-Raphson iterative scheme. Sample results are presented for the growth of a large-dimension oxide crystal with thermophysical properties similar to those of gadolinium gallium garnet (GGG). Calculations with the HTCM show the effects of crystal rotation on heat transfer, flow in the melt, and melt/crystal interface shape. Severe deflections of the melt/crystal interface are calculated for moderate rotation rates, and limit points in the steady-state solutions are found with respect to crystal rotation.

  13. Protein crystal growth and the International Space Station

    NASA Technical Reports Server (NTRS)

    DeLucas, L. J.; Moore, K. M.; Long, M. M.

    1999-01-01

    Protein structural information plays a key role in understanding biological structure-function relationships and in the development of new pharmaceuticals for both chronic and infectious diseases. The Center for Macromolecular Crystallography (CMC) has devoted considerable effort studying the fundamental processes involved in macromolecular crystal growth both in a 1-g and microgravity environment. Results from experiments performed on more than 35 U.S. space shuttle flights have clearly indicated that microgravity can provide a beneficial environment for macromolecular crystal growth. This research has led to the development of a new generation of pharmaceuticals that are currently in preclinical or clinical trials for diseases such as cutaneous T-cell lymphoma, psoriasis, rheumatoid arthritis, AIDS, influenza, stroke and other cardiovascular complications. The International Space Station (ISS) provides an opportunity to have complete crystallographic capability on orbit, which was previously not possible with the space shuttle orbiter. As envisioned, the x-ray Crystallography Facility (XCF) will be a complete facility for growing protein crystals; selecting, harvesting, and mounting sample crystals for x-ray diffraction; cryo-freezing mounted crystals if necessary; performing x-ray diffraction studies; and downlinking the data for use by crystallographers on the ground. Other advantages of such a facility include crystal characterization so that iterations in the crystal growth conditions can be made, thereby optimizing the final crystals produced in a three month interval on the ISS.

  14. Vapor growth of mercuric iodide tetragonal prismatic crystals

    NASA Astrophysics Data System (ADS)

    Ariesanti, Elsa

    The effect of polyethylene addition on the growth of mercuric iodide (HgI2) tetragonal prismatic crystals is examined. Three types of polyethylene powder are utilized: low molecular weight (Mw ˜ 4 x 103), ultra high molecular weight (Mw ˜ 3-6 x 1066), and spectrophotometric grade polyethylenes. Among these types of polyethylene, the low molecular weight polyethylene produces the most significant change in HgI2 morphology, with {110} being the most prominent crystal faces. Thermal desorption - gas chromatography/ mass spectroscopy (TD-GC/MS) studies show that thermal desorption of the low molecular weight polyethylene at 100°C and 150°C produce isomers of alkynes, odd nalkanes, and methyl (even-n) alkyl ketones. HgI2 growth runs with n-alkanes, with either neicosane, n-tetracosane, or n-hexatriacontane, cannot replicate the crystal shapes produced during growth with the low molecular weight polyethylene, whereas HgI2 growth runs with ketones, with either 3-hexadecanone or 14-heptacosanone, produce HgI2 tetragonal prismatic crystals, similar to the crystals grown with the low molecular weight polyethylene. C-O double bond contained in any ketone is a polar bond and this polar bond may be attracted to the mercury atoms on the top-most layer of the {110} faces through dipoledipole interaction. As a result, the growth of the {110} faces is impeded, with the crystals elongated in the [001] direction and bounded by the {001} faces along with large, prismatic {110} faces.

  15. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1983-01-01

    GaAs device technology has recently reached a new phase of rapid advancement, made possible by the improvement of the quality of GaAs bulk crystals. At the same time, the transition to the next generation of GaAs integrated circuits and optoelectronic systems for commercial and government applications hinges on new quantum steps in three interrelated areas: crystal growth, device processing and device-related properties and phenomena. Special emphasis is placed on the establishment of quantitative relationships among crystal growth parameters-material properties-electronic properties and device applications. The overall program combines studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and investigation of electronic properties and phenomena controlling device applications and device performance.

  16. Nano-structured intermetallic compound TiAl obtained by crystallization of mechanically alloyed amorphous TiAl, and its subsequent grain growth

    Microsoft Academic Search

    M. Kambara; K. Uenishi; K. F. Kobayashi

    2000-01-01

    The amorphization process during mechanical alloying (MA) was investigated for the Al-50at%Ti and Al-50at%Ti-10vol%TiB2 powder mixtures. Pure metallic powders of Al and Ti were finely mixed and transformed to the amorphous phase after being milled for about 2880 ks. In the case of Al-50at%Ti-10vol%TiB2 powder, the amorphous alloys with a fine dispersion of TiB2 particles could be obtained for a

  17. High speed crystal growth and solidification using laser heating

    Microsoft Academic Search

    J. M. Poate

    1986-01-01

    High speed melting and freezing phenomena are reviewed with emphasis on silicon crystal growth. Laser heating has been particularly advantageous for the exploration of such velocity regimes. New transient probe techniques have been developed to investigate interface motion. The solid-phase epitaxial growth of amorphous Si overlayers is first discussed. Silicon liquid-phase epitaxy and enhanced dopant segregation effects up to velocities

  18. (PCG) Protein Crystal Growth HIV Reverse Transcriptase

    NASA Technical Reports Server (NTRS)

    1992-01-01

    HIV Reverse Transcriptase crystals grown during the USML-1 (STS-50) mission using Commercial Refrigerator/Incubator Module (CR/IM) at 4 degrees C and the Vapor Diffusion Apparatus (VDA). Reverse transcriptase is an enzyme responsible for copying the nucleic acid genome of the AIDS virus from RNA to DNA. Studies indicated that the space-grown crystals were larger and better ordered (beyond 4 angstroms) than were comparable Earth-grown crystals. Principal Investigators were Charles Bugg and Larry DeLucas.

  19. Growth and properties of PMN-PT single crystals

    NASA Astrophysics Data System (ADS)

    Jiang, X.; Tang, F.; Wang, J. T.; Chen, T.-P.

    2001-11-01

    Piezoelectric single crystals of Pb(Mg 1/3Nb 2/3)O 3-PbTiO 3 (PMN-PT) show superior properties to piezoelectric ceramics and piezoelectric films in device applications. However, the applications of PMN-PT single crystals are limited by the lack of a simple and reproducible fabrication technique. By studying the effect of fabrication condition on the growth of PMN-PT single crystals in the flux method, we successfully obtained PMN-PT single crystals. The size of the obtained crystals varied from 1 to 4 mm, mostly showing regular cubic shape. X-ray diffraction technique identified the crystal phase was PMN-PT. Electron diffraction spectroscope analysis indicated that the composition of the single crystals was closed to the designed solid solution. The (0 0 1) single crystals showed a dielectric constant peak of 15,200 at 42°C. The crystals had a remnant polarization 16 ?c/cm 2, a spontaneous polarization 22.1 ?c/cm 2, and a coercive field 2.55 kV/cm. Our measurement indicated the temperature dependence and frequency dependence of the dielectric constant and dielectric loss of PMN-PT single crystals. The results will be a great help for the applications of PMN-PT single crystals.

  20. Progress in the crystal growth of Ce:LiSAF

    NASA Astrophysics Data System (ADS)

    Castillo, Vida K.; Quarles, Gregory J.

    1995-04-01

    The search for an efficient solid state laser with tunable emission in the ultraviolet wavelength region has resulted in the growth and development of cerium doped colquiriite crystals, such as LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF). Results from preliminary research at Lawrence Livermore National Laboratory indicate that Ce:LiSAF is the preferred material of the colquiriite hosts, since it shows higher gains than Ce:LiCAF. Although the growth of chromium doped LiSAF has been developed to produce long boules of near-scatter-free material, the doping of LiSAF with cerium introduces different variables into the growth of high optical quality crystals. The main crystal growth issue for Ce:LiSAF is the charge compensation mandated by the substitution of the trivalent cerium ion for divalent strontium, which is located in the only site large enough to support the cerium ion. Initial growth runs produced opaque, heavily cracked crystals with less than 10 mm of cleaner, single crystal material. The addition of charge compensating ions into the starting charge and their effect in attaining higher doped and less-stressed material is discussed. The selection of growth parameters needed to produce higher-doped, near-scatter-free Ce:LiSAF will also be described.

  1. Crystal growth of calcium apatites from dilute solutions

    NASA Astrophysics Data System (ADS)

    Moreno, E. C.; Varughese, K.

    1981-05-01

    The dependence of the kinetics of crystal growth of hydroxyapatite, HA, on concentration of seeds and degree of solution supersaturation is examined. Empirical relations are obtained between the initial rates of precipitation and the two aforementioned variables. The results clearly indicate that the precipitating phase, under the selected experimental conditions, is HA. The driving force for precipitation is the supersaturation with respect to this calcium phosphate. The data obtained from kinetic studies are consistent with the BCF theory of crystal growth which relates the mean linear rate of growth to the degree of supersaturation. This observation is also valid for systems in which the precipitating phases are fluoridated hydroxyapatites, Ca 5F x?(OH) 1- x(PO 4) 3, FHA. In this case, supersaturation is calculated with respect to the specific FHA precipitated. The degree of fluoridation, x, appears to be determined by the activity of hydrofluoric acid in solution which remains fairly constant during precipitation but varies for each initial fluoride concentration used. Studies are reported on the kinetics of crystal growth of HA in the presence of biological inhibitors. Two proline-rich proteins and a peptide, statherin, of salivary origin are powerful inhibitors of HA crystal growth. It appears that their mode of action is related to their adsorption onto the surface of apatite seeds. The results suggest that the adsorption sites are the same as the sites where crystal growth takes place.

  2. A Model for Tetragonal Lysozyme Crystal Nucleation and Growth

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Macromolecular crystallization is a complex process, involving a system that typically has 5 or more components (macromolecule, water, buffer + counter ion, and precipitant). Whereas small molecules have only a few contacts in the crystal lattice, macromolecules generally have 10's or even 100's of contacts between molecules. These can range from hydrogen bonds (direct or water-mediated), through van der Waals, hydrophobic, salt bridges, and ion-mediated contacts. The latter interactions are stronger and require some specificity in the molecular alignment, while the others are weaker, more prevalent, and more promiscuous, i.e., can be readily broken and reformed between other sites. Formation of a consistent, ordered, 3D structure may be difficult or impossible in the absence of any or presence of too many strong interactions. Further complicating the process is the inherent structural asymmetry of monomeric (single chain) macromolecules. The process of crystal nucleation and growth involves the ordered assembly of growth units into a defined 3D lattice. We suggest that for many macromolecules, particularly those that are monomeric, this involves a preliminary solution-phase assembly process into a growth unit having some symmetry prior to addition to the lattice, recapitulating the initial stages of the nucleation process. If this model is correct then fluids and crystal growth models assuming a strictly monodisperse nutrient solution need to be revised. This model has been developed from experimental evidence based upon face growth rate, AFM, and fluorescence energy transfer data for the nucleation and growth of tetragonal lysozyme crystals.

  3. Kinetics of non-isothermal crystallization process and activation energy for crystal growth in amorphous materials

    Microsoft Academic Search

    Kazumasa Matusita; Takayuki Komatsu; Ryosuke Yokota

    1984-01-01

    An equation expressing the volume fraction,x, of crystals precipitating in a glass heated at a constant rate, a, was derived. When crystal particles grow m-dimensionally,x is expressed as In [- ln(1 -x)] = -n (na - 1.052mE\\/RT + Constant whereE is the activation energy for crystal growth andn is a numerical factor depending on the nucleation process. When the nuclei

  4. Transient natural convection heat and mass transfer in crystal growth

    NASA Technical Reports Server (NTRS)

    Han, Samuel S.

    1988-01-01

    A numerical analysis of transient combined heat and mass transfer across a rectangular cavity is performed by a numerical method based on the SIMPLE algorithm. The physical parameters are selected to represent a range of possible crystal growth in solutions. Numerical results are compared with available experimental data to confirm the accuracy of the results. Good qualitative agreements are obtained for the average mass transfer rate across the cavity. Also, qualitative agreements are observed for the global development of thermal and solute fields. It is found that the thermal and solute fields become highly oscillatory when the thermal and solute Grashof numbers are large. Oscillations are probably caused by a number of different instability mechanisms. By reducing the gravity some of these instabilities were made to disappear at the lower Grashof numbers. Transient temperature and solute distribution near the crystal growing surface are highly non-uniform at the higher Grashof numbers. These non-uniformities are less severe in the reduced gravity environments but still exist. The effects of convection on the rate of average mass transfer are more than one order of magnitude higher than those of conduction in the range of Grashof numbers studied. Dependency of mass transfer rate on the Grashof number indicates that the convection effects many not be negligible even in the microgravity environments for the range of parameters investigated.

  5. High Thermal Conducting Boron Arsenide: Crystal Growth and Characterization

    NASA Astrophysics Data System (ADS)

    Lv, Bing; Lan, Yucheng; Wang, Xiqu; Zhang, Qian; Hu, Yongjie; Jacobson, Allan J.; Broido, David; Chen, Gang; Ren, Zhifeng; Chu, Ching-Wu

    2015-03-01

    Intrigued by recent calculations [Phys. Rev. Lett. 111, 025901(2013)] which predict a remarkably high thermal conductivity of ~ 2,000 Wm-1K-1 , comparable to that of diamond, in cubic boron arsenide (BAs) crystals, we have succeeded in synthesizing single crystals of BAs with a zinc blende structure and lattice parameters of a = 4.7830(7) Å characterized by X-ray single crystal diffraction and transmission electron microscopy (TEM). A relatively high thermal conductivity is obtained but still smaller than the predicted value. We attribute the difference of thermal conductivity value to the defect scattering associated with crystal twinning and As vacancies, verified both from experimental evidence and theoretical calculations. The predicted super-thermal-conductivity may be achieved in BAs single crystals with further improvement of crystal growth by removing the defects. Lawrence Berkeley National Laboratory, Berkeley California 94720.

  6. Growth of crystals for synchrotron radiation Mössbauer investigation

    NASA Astrophysics Data System (ADS)

    Kotrbova, M.; Hejduk, J.; Malnev, V. V.; Seleznev, V. N.; Yagupov, S. V.; Andronova, N. V.; Chechin, A. I.; Mikhailov, A. Yu.

    1991-10-01

    Iron borate crystals (FeBO 3) were flux grown at the Physical Institute (Prague) and at Simferopol State University. During the crystal growth procedure the temperature regime was held constant to 0.1°C accuracy. Crystals were investigated with the help of a double crystal X-ray diffractometer DRON-2 (SiO 2(30 overline33)?FeBO 3(444), MoK ? 1 radiation). The rocking curve measurements were carried out in a constant magnetic field of 1kG. Most of the crystal surface has a rocking curve 10?-15? wide. Some parts of some crystals with the area 1 × 1 mm 2 have rocking curves of 3?-4? width and can be considered ideal.

  7. The effect of growth rate, diameter and impurity concentration on structure in Czochralski silicon crystal growth

    NASA Technical Reports Server (NTRS)

    Digges, T. G., Jr.; Shima, R.

    1980-01-01

    It is demonstrated that maximum growth rates of up to 80% of the theoretical limit can be attained in Czochralski-grown silicon crystals while maintaining single crystal structure. Attaining the other 20% increase is dependent on design changes in the grower, to reduce the temperature gradient in the liquid while increasing the gradient in the solid. The conclusions of Hopkins et al. (1977) on the effect of diameter on the breakdown of structure at fast growth rates are substantiated. Copper was utilized as the test impurity. At large diameters (greater than 7.5 cm), concentrations of greater than 1 ppm copper were attained in the solid (45,000 ppm in the liquid) without breakdown at maximum growth speeds. For smaller diameter crystals, the sensitivity of impurities is much more apparent. For solar cell applications, impurities will limit cell performance before they cause crystal breakdown for fast growth rates of large diameter crystals.

  8. Determination of the activation energy for crystal growth by differential thermal analysis

    Microsoft Academic Search

    K. Matusita; S. Sakka; Y. Matsui

    1975-01-01

    A method for determining the activation energy for crystal growth was calculated on the basis of the heat balance in the differential thermal analysis (DTA) measurements and the mechanism of nucleation and growth. The theoretical analysis showed that the term ln[Cpd(dT)\\/dt+KdT] should be a linear function of l\\/T, whereCp is the heat capacity of sample and sample holder,K is the

  9. Controlled growth of single-crystal twelve-pointed graphene grains on a liquid Cu surface.

    PubMed

    Geng, Dechao; Meng, Lan; Chen, Bingyan; Gao, Enlai; Yan, Wei; Yan, Hui; Luo, Birong; Xu, Jie; Wang, Huaping; Mao, Zupan; Xu, Zhiping; He, Lin; Zhang, Zhiyong; Peng, Lianmao; Yu, Gui

    2014-10-01

    The controlled fabrication of single-crystal twelve-pointed graphene grains is demonstrated for the first time by ambient pressure chemical vapor deposition on a liquid Cu surface. An edge-diffusion limited mechanism is proposed. The highly controllable growth of twelve-pointed graphene grains presents an intriguing case for the fundamental study of graphene growth and should exhibit wide applications in graphene-based electronics. PMID:25043403

  10. Model of nucleation and growth of crystals in cooling magmas

    Microsoft Academic Search

    Atsushi Toramaru

    1991-01-01

    The nucleation and growth of liquidus phases in cooling magmas at constant rates are modeled taking into account homogeneous\\u000a nucleation, diffusion-limited growth, and depletion of crystallizing component from melt, and the temperature-dependent diffusivity.\\u000a The formulation of governing equations shows that four dimensionless parameters, whose physical meanings are the nucleation\\u000a difficulty, the fusion enthalpy, the ratio of the growth rate to

  11. Hydrothermal crystal growth of the potassium niobate and potassium tantalate family of crystals

    SciTech Connect

    Mann, Matthew [Department of Chemistry, Clemson University, Clemson, SC 29634 (United States); Center for Optical Materials Science and Engineering Technologies (COMSET), 91 Technology Drive, Anderson, SC 29625 (United States); Jackson, Summer [Department of Chemistry, Clemson University, Clemson, SC 29634 (United States); Kolis, Joseph, E-mail: kjoseph@clemson.ed [Department of Chemistry, Clemson University, Clemson, SC 29634 (United States); Center for Optical Materials Science and Engineering Technologies (COMSET), 91 Technology Drive, Anderson, SC 29625 (United States)

    2010-11-15

    Single crystals of KNbO{sub 3} (KN), KTaO{sub 3} (KT), and KTa{sub 1-x}Nb{sub x}O{sub 3} (x=0.44, KTN) have been prepared by hydrothermal synthesis in highly concentrated KOH mineralizer solutions. The traditional problems of inhomogeneity, non-stoichiometry, crystal striations and crystal cracking resulting from phase transitions associated with this family compounds are minimized by the hydrothermal crystal growth technique. Crystals of good optical quality with only minor amounts of metal ion reduction can be grown this way. Reactions were also designed to provide homogeneous distribution of tantalum and niobium metal centers throughout the KTN crystal lattice to maximize its electro-optic properties. Synthesis was performed at relatively low (500-660 {sup o}C) temperatures in comparison to the flux and Czochralski techniques. This work represents the largest crystals of this family of compounds grown by hydrothermal methods to date. -- Graphical Abstract:

  12. Nucleation and growth of polytypic-layered crystals from the network liquid zinc chloride

    NASA Astrophysics Data System (ADS)

    Wilson, Mark

    2003-06-01

    The liquid to solid crystallization for zinc (II) chloride is studied by molecular dynamics computer simulation. The transition is unusual in that it involves a change from a three-dimensional network liquid structure to a pseudo-two-dimensional layered crystal. The crystallization events are observed from four distinct liquid starting configurations and are identified by reference to the time evolution of the system energetics and Bragg peaks associated with the cation layering. Order parameters and molecular graphics are applied to understand the transitions at an atomistic length scale. Mechanisms are presented for the initial layer growth, the coherent joining of the layered crystallites, and the destruction of high-energy grain boundaries. The growth kinetics are analyzed by defining times for catastrophic and critical nucleation. The final crystal structures are shown to have essentially random anion close-packed stacking sequences consistent with the large number of experimentally observed polytypic structures. The formation of grain boundary stacking faults is also observed.

  13. Novel protein crystal growth technology: Proof of concept

    NASA Technical Reports Server (NTRS)

    Nyce, Thomas A.; Rosenberger, Franz

    1989-01-01

    A technology for crystal growth, which overcomes certain shortcomings of other techniques, is developed and its applicability to proteins is examined. There were several unknowns to be determined: the design of the apparatus for suspension of crystals of varying (growing) diameter, control of the temperature and supersaturation, the methods for seeding and/or controlling nucleation, the effect on protein solutions of the temperature oscillations arising from the circulation, and the effect of the fluid shear on the suspended crystals. Extensive effort was put forth to grow lysozyme crystals. Under conditions favorable to the growth of tetragonal lysozyme, spontaneous nucleation could be produced but the number of nuclei could not be controlled. Seed transfer techniques were developed and implemented. When conditions for the orthorhombic form were tried, a single crystal 1.5 x 0.5 x 0.2 mm was grown (after in situ nucleation) and successfully extracted. A mathematical model was developed to predict the flow velocity as a function of the geometry and the operating temperatures. The model can also be used to scaleup the apparatus for growing larger crystals of other materials such as water soluble non-linear optical materials. This crystal suspension technology also shows promise for high quality solution growth of optical materials such as TGS and KDP.

  14. Investigation of YBa2Cu4O8 single crystal growth by KOH flux

    NASA Astrophysics Data System (ADS)

    Sun, G. L.; Song, Y. T.; Lin, C. T.

    2008-12-01

    The growth of YBa2Cu4O8 single crystals was performed using KOH flux under ambient pressure. By testing five sorts of crucible material, ZrO2 and Al2O3 are found to be suitable for the growth. A stepwise-cooling method was applied to increase the size of the crystals. The as-grown crystals could be separated from the residual flux by methanol solvent. The crystals showed a plate-like morphology with dimensions 1.2 × 0.5 × 0.3 mm3. Study of the structure in the (001) plane indicated that the formation of the crystal occurred by a two-dimensional nucleation or spiral growth mechanism, depending on the supersaturation of the solution. Defects in the crystals were revealed by etching, which exhibited an interesting feature of etch pits with an orthorhombic structure consisting of {001}, {100} and {010} faces. The superconducting property of the crystals shows very sharp transition at a Tc of 82.9 K.

  15. Transient from crystallization to fractal growth observed in both boar bile and SnI2 vapour

    NASA Astrophysics Data System (ADS)

    Zhang, Jizhong; Shen, Yuhua; Xie, Anjian

    2003-04-01

    A visual transient of the growth mechanism from crystallization to fractal growth was observed clearly in a drop of boar bile. The growing crystals were replaced by treelike fractal structures during solidification of the sample. It is fascinating to compare the transient with the result observed in SnI2 vapour. They were completely identical, and revealed that under certain conditions a linear growth could be transferred spontaneously into nonlinear growth. It may be possible to consider the transient as a 'bridge' between linear and nonlinear growth, and to develop a quantitative expression of transient dynamics.

  16. Micromechanisms of fatigue crack growth in a single crystal Inconel 718 nickel-based superalloy

    SciTech Connect

    Mercer, C.; Soboyejo, A.B.O.; Soboyejo, W.O. (Ohio State Univ., Columbus, OH (United States))

    1999-07-09

    The fatigue crack growth behavior of an experimental, single crystal alloy, of equivalent nominal chemical composition to Inconel 718 is presented. Fracture modes under cyclic loading were determined by scanning electron microscopy. The results of the fractographic analyses are presented on a fracture mechanism map that shows the dependence of the fatigue fracture mechanisms on the maximum stress intensity factor, K[sub max], and the stress intensity factor range, [Delta]K. Crack-tip deformation mechanisms associated with fatigue crack growth were studied using transmission electron microscopy. The relative effects of [Delta]K and K[sub max] on the fatigue crack growth behavior of this material are discussed within the context of a two-parameter crack growth law. The influence of grain boundaries on the fatigue crack growth resistance of materials such as Inconel 718 is also discussed in light of the results of this investigation.

  17. Crystal Growth of Ternary Compound Semiconductors in Low Gravity Environment

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua

    2014-01-01

    A low gravity material experiment will be performed in the Material Science Research Rack (MSRR) on International Space Station (ISS). There are two sections of the flight experiment: (I) crystal growth of ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, by physical vapor transport (PVT) and (II) melt growth of CdZnTe by directional solidification. The main objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the grown crystals as results of buoyancy-driven convection and growth interface fluctuations caused by irregular fluid-flows on Earth. The investigation consists of extensive ground-based experimental and theoretical research efforts and concurrent flight experimentation. This talk will focus on the ground-based studies on the PVT crystal growth of ZnSe and related ternary compounds. The objectives of the ground-based studies are (1) obtain the experimental data and conduct the analyses required to define the optimum growth parameters for the flight experiments, (2) perfect various characterization techniques to establish the standard procedure for material characterization, (3) quantitatively establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low-gravity environment and (4) develop theoretical and analytical methods required for such evaluations. ZnSe and related ternary compounds have been grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals have been characterized extensively by various techniques to correlate the grown crystal properties with the growth conditions.

  18. A Microfluidic, High Throughput Protein Crystal Growth Method for Microgravity

    PubMed Central

    Carruthers Jr, Carl W.; Gerdts, Cory; Johnson, Michael D.; Webb, Paul

    2013-01-01

    The attenuation of sedimentation and convection in microgravity can sometimes decrease irregularities formed during macromolecular crystal growth. Current terrestrial protein crystal growth (PCG) capabilities are very different than those used during the Shuttle era and that are currently on the International Space Station (ISS). The focus of this experiment was to demonstrate the use of a commercial off-the-shelf, high throughput, PCG method in microgravity. Using Protein BioSolutions’ microfluidic Plug Maker™/CrystalCard™ system, we tested the ability to grow crystals of the regulator of glucose metabolism and adipogenesis: peroxisome proliferator-activated receptor gamma (apo-hPPAR-? LBD), as well as several PCG standards. Overall, we sent 25 CrystalCards™ to the ISS, containing ~10,000 individual microgravity PCG experiments in a 3U NanoRacks NanoLab (1U = 103 cm.). After 70 days on the ISS, our samples were returned with 16 of 25 (64%) microgravity cards having crystals, compared to 12 of 25 (48%) of the ground controls. Encouragingly, there were more apo-hPPAR-? LBD crystals in the microgravity PCG cards than the 1g controls. These positive results hope to introduce the use of the PCG standard of low sample volume and large experimental density to the microgravity environment and provide new opportunities for macromolecular samples that may crystallize poorly in standard laboratories. PMID:24278480

  19. A microfluidic, high throughput protein crystal growth method for microgravity.

    PubMed

    Carruthers, Carl W; Gerdts, Cory; Johnson, Michael D; Webb, Paul

    2013-01-01

    The attenuation of sedimentation and convection in microgravity can sometimes decrease irregularities formed during macromolecular crystal growth. Current terrestrial protein crystal growth (PCG) capabilities are very different than those used during the Shuttle era and that are currently on the International Space Station (ISS). The focus of this experiment was to demonstrate the use of a commercial off-the-shelf, high throughput, PCG method in microgravity. Using Protein BioSolutions' microfluidic Plug Maker™/CrystalCard™ system, we tested the ability to grow crystals of the regulator of glucose metabolism and adipogenesis: peroxisome proliferator-activated receptor gamma (apo-hPPAR-? LBD), as well as several PCG standards. Overall, we sent 25 CrystalCards™ to the ISS, containing ~10,000 individual microgravity PCG experiments in a 3U NanoRacks NanoLab (1U = 10(3) cm.). After 70 days on the ISS, our samples were returned with 16 of 25 (64%) microgravity cards having crystals, compared to 12 of 25 (48%) of the ground controls. Encouragingly, there were more apo-hPPAR-? LBD crystals in the microgravity PCG cards than the 1g controls. These positive results hope to introduce the use of the PCG standard of low sample volume and large experimental density to the microgravity environment and provide new opportunities for macromolecular samples that may crystallize poorly in standard laboratories. PMID:24278480

  20. Structural non-uniformities in mercuric iodide crystals grown by two different vapour growth techniques

    NASA Astrophysics Data System (ADS)

    Rossberg, A.; Piechotka, M.; Wetzel, G.; Gastaldi, J.; Magerl, A.; Kaldis, E.

    1996-09-01

    The origin of extended structural defects and their distribution in vapour grown mercuric iodide crystals has been investigated. Starting from a highly purified and nearly stoichiometric source material, crystals were grown in different laboratories using different implementations of the vapour growth technique. The as-grown crystals were then investigated by means of ?-ray rocking curves (3D mapping) and synchrotron X-ray transmission topography. It has been found that not only the amount and distribution of mosaicity (tilt, twist), but also striations and grain boundaries depend primarily on the performance of the temperature control loops and on the 3D temperature fields during the growth in a particular apparatus. High radial or axial temperature gradients lead to the enhanced formation of grain boundaries and striations. Different growth mechanisms could be deduced from the different striation patterns observed.

  1. Polymer crystallization in a temperature gradient field with controlled crystal growth rate

    NASA Technical Reports Server (NTRS)

    Hansen, D.; Taskar, A. N.; Casale, O.

    1971-01-01

    A method is described for studying the influence of a temperature gradient on the crystallization of quiescent polymer melts. The apparatus used consists of two brass plates with embedded electrical resistance heaters and cooling coils. The crystallizations experiments were conducted by placing polymer specimens between the paltes, and manually adjusting heaters and cooling fluids for temperature control. Linear polyethylene, isotactic polyprophylene, and a high density polyethylene were used. It is concluded that the role of a temperature gradient in producing oriented crystallization is in producing conditions which lead the spherulitic growth pattern to proceed primarily in one direction. Steep gradients diminish the penetration of supercooling and favors oriented growth.

  2. A low temperature furnace for solution crystal growth on the International Space Station

    NASA Astrophysics Data System (ADS)

    Baç, Nurcan; Harpster, Joseph; Maston, Robert A.; Sacco, Albert

    2000-01-01

    The Zeolite Crystal Growth Furnace Unit (ZCG-FU) is the first module in an integrated payload designed for low temperature crystal growth in solutions on the International Space Station (ISS). This payload is scheduled to fly on the ISS flight 7A.1 in an EXPRESS rack. Its name originated from early shuttle flight experiments limited to the growth of zeolite crystals but has since grown to include other materials of significant commercial interest using the solution method of crystal growth. Zeolites, ferroelectrics, piezeoelectrics and silver halides are some of the materials considered. The ZCG-FU experiment consists of a furnace unit and its electronic control system, and mechanically complex, crystal growth autoclaves suitable for use with a particular furnace and solution. The ZCG facility is being designed to grow into four independent furnaces controlled by IZECS (Improved Zeolite Electronic Control System). IZECS provides monitoring of critical parameters, data logging, safety monitoring, air-to-ground control and operator interfacing. It is suitable for controlling the four furnaces either individually or all at one time. It also contains the power management solid-state drivers and switches for the ZCG-FU furnace. The furnace contains 19 tubes operating at three different temperature zones. .

  3. Hydrothermal crystal growth of oxides for optical applications

    NASA Astrophysics Data System (ADS)

    McMillen, Colin David

    2007-12-01

    The manipulation of light has proven to be an integral part of today's technology-based society. In particular, there is great interest in obtaining coherent radiation in all regions of the optical spectrum to advance technology in military, medical, industrial, scientific and consumer fields. Exploring new crystal growth techniques as well as the growth of new optical materials is critical in the advancement of solid state optics. Surprisingly, the academic world devotes little attention to the growth of large crystals. This shortcoming has left gaps in the optical spectrum inaccessible by solid state devices. This dissertation explores the hydrothermal crystal growth of materials that could fill two such gaps. The first gap exists in the deep-UV region, particularly below 200 nm. Some materials such as LiB3O5 and beta-BaB2O4 can generate coherent light at wavelengths as low as 205 nm. The growth of these materials was explored to investigate the feasibility of the hydrothermal method as a new technique for growing these crystals. Particular attention was paid to the descriptive chemistry surrounding these systems, and several novel structures were elucidated. The study was also extended to the growth of materials that could be used for the generation of coherent light as low as 155 nm. Novel synthetic schemes for Sr2Be2B2O7 and KBe2BO 3F2 were developed and the growth of large crystals was explored. An extensive study of the structures, properties and crystal growth of related compounds, RbBe2BO3F2 and CsBe2BO 3F2, was also undertaken. Optimization of a number of parameters within this family of compounds led to the hydrothermal growth of large, high quality single crystal at rates suitable for large-scale growth. The second gap in technology is in the area of high average power solid state lasers emitting in the 1 mum and eye-safe (>1.5 mum) regions. A hydrothermal technique was developed to grow high quality crystals of Sc 2O3 and Sc2O3 doped with suitable lanthanide activator ions. Preliminary spectroscopic studies were performed and large crystals were again grown at rates suitable for commercial production. The synthesis of ultra-high purity Ln2O3 (Ln = Sc, Y, La-Lu) nanoparticles was also explored to advance the development of ceramic-based solid state lasers. Crystal growth is a complex task involving a great number of intricacies that must be understood and balanced. This dissertation has advanced the art and science of growing crystals, and documented the development of large, high quality crystals of advanced optical materials The materials and hydrothermal crystal growth techniques developed over the course of this work represent important progress toward controlling the optical spectrum.

  4. Effect of power arrangement on the crystal shape during the Kyropoulos sapphire crystal growth process

    NASA Astrophysics Data System (ADS)

    Chen, Chun-Hung; Chen, Jyh-Chen; Lu, Chung-Wei; Liu, Che-Ming

    2012-08-01

    The Kyropoulos (KY) method is commonly used to grow large sized sapphire single crystals. The shape of the sapphire crystal thus grown is determined by the heater arrangement and the power reduction history in the Kyropoulos furnace. In order to grow high-quality sapphire single crystal, the heater arrangement should allow different power inputs in different sections in order to control the thermal field in the melt during the growth process. In this study, a numerical computation is performed to investigate the effects of the heater arrangement on the thermal and flow transport, the shape of the crystal-melt interface, and the power requirements during the Kyropoulos sapphire crystal growth process in a resistance heated furnace. Four different power ratio arrangements in a three-zone heater are considered. The results show that for the power arrangements considered herein, the temperature gradients along the crystallization front do not exceed 0.05 K/mm, and that, after the growth of the crown, the crystal maintains an almost constant diameter. The remelting phenomenon may occur during growth when the input power of the upper side of the heater is higher than that of the lower side of the heater.

  5. Faceting and branching in 2D crystal growth.

    PubMed

    Tegze, György; Tóth, Gyula I; Gránásy, László

    2011-05-13

    Using atomic scale time-dependent density functional calculations we confirm that both diffusion-controlled and diffusionless crystallization modes exist in simple 2D systems. We provide theoretical evidence that a faceted to nonfaceted transition is coupled to these crystallization modes, and faceting is governed by the local supersaturation at the fluid-crystalline interface. We also show that competing modes of crystallization have a major influence on mesopattern formation. Irregularly branched and porous structures are emerging at the crossover of the crystallization modes. The proposed branching mechanism differs essentially from dendritic fingering driven by diffusive instability. PMID:21668173

  6. Growth and characterization of Cadmium Thiosemicarbazide Bromide crystals for antibacterial and nonlinear optical applications

    NASA Astrophysics Data System (ADS)

    Thomas Joseph Prakash, J.; Martin Sam Gnanaraj, J.

    2015-01-01

    Semiorganic nonlinear optical crystals of Cadmium Thiosemicarbazide Bromide was grown by slow evaporation solution growth technique. The unit cell parameters were estimated by subjecting the crystals to single crystal X-ray diffraction. The grown crystals were subjected to Powder X-ray diffraction for analyzing the crystalline nature of the sample. FTIR studies reveal the functional groups and the optical characters were analyzed by UV-Vis spectral studies. Mechanical stability of the sample was assessed by Vicker's micro hardness test. The presence of surface dislocations was identified by chemical etching technique. Antibacterial study was carried out against ACDP declared harmful pathogens. SHG efficiency of CTSB crystal was tested using Nd: YAG laser and it was found to be ?1.8 times that of potassium dihydrogen phosphate.

  7. Growth of High Quality A N Single Crystals and Their Optical Properties

    E-print Network

    Nabben, Reinhard

    Growth of High Quality A N Single Crystals and Their Optical Properties M. strassburgl, J a two-step growth process in a TaN crucible. Crystal defects and the effect of incorporated impurities,2,3]. Hence, the growth and crystal quality opiimhtion of buk AiN crystals is of primary importance

  8. Effects of substrate crystallographic orientations on crystal growth and microstructure development in laser

    E-print Network

    DuPont, John N.

    Effects of substrate crystallographic orientations on crystal growth and microstructure development in laser surface-melted superalloy single crystals. Mathematical modeling of single-crystal growth that the substrate orientation has a predominant effect on crystal growth pattern, and simultaneously influences

  9. Crystallisation in flow Part II: Modelling crystal growth kinetics controlled by boundary layer thickness

    E-print Network

    Paris-Sud XI, Université de

    1 Crystallisation in flow Part II: Modelling crystal growth kinetics controlled by boundary layer already done in the case of a flow parallel to the crystal face. This crystal growth model is applied, based on crystal growth processes. The idea that mineral shapes and textures are related

  10. Modelling of 3D Melt Flow in Czochralski Crystal Growth Petr Knobloch 1 and Lutz Tobiska

    E-print Network

    Knobloch, Petr

    Modelling of 3D Melt Flow in Czochralski Crystal Growth Petr Knobloch 1 and Lutz Tobiska Otto to the crystal growth velocity and maintain the melt free surface in a constant position. The crystal growth]) is the mostly used technique for producing semiconductor single crystals, the most important of which

  11. Crystal Growth Simulations: a new Mathematical Model based on the Minkowski

    E-print Network

    Villa, Elena

    Crystal Growth Simulations: a new Mathematical Model based on the Minkowski Sum of Sets Alessandra. Realistic crystal growth simulators can give information on what would be the surface structure of a crystal the mother phase, that we assume to be gaseous, to the crystal (solid) phase. Specifically, Growth Units

  12. Self-Organized Growth of Complex Nanotube Patterns on Crystal Surfaces

    E-print Network

    Joselevich, Ernesto

    Self-Organized Growth of Complex Nanotube Patterns on Crystal Surfaces Ernesto Joselevich-organized growth directed by well-defined crystal surfaces, or "nanotube epitaxy". We identify three different to "nanotube epitaxy" Epitaxy generally refers to the "growth of a crystal of one material on the crystal base

  13. High-thermal-gradient Superalloy Crystal Growth

    NASA Technical Reports Server (NTRS)

    Pearson, D. D.; Anton, D. L.; Giamei, A. F.

    1985-01-01

    Single, (001)-oriented crystals of PWA 1480 were processed in alumina/silica shell molds in a laboratory high gradient furnace. The furnace employs a graphite resistance heated element, a radiation baffle, and a water cooled radiation trap below the baffle. All crystals were grown in vacuum (10 torr) and all heat transfer was radiative. The element is constructed with a variable cross section that is tapered just above the baffle to maximize heat input and therefore thermal gradient. A maximum alloy temperature of 1600 C was used. A thermal gradient of 130 deg C/cm was recorded at 1370 C just above the solidus of the PWA 1480 alloys. Crystal bars with 14.4 and 17.5 mm diameters were grown in alumina/silica shell molds. Each crystal was started from a 1.6 mm pencil seed at a rate of 76 mm/hr and slowly accelerated to a rate of 200 mm/hr under computer control. Volume percent porosity and average pore size were measured as functions of distance in representative bars. Low cycle fatigue behavior and stress rupture properties were determined.

  14. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1980-01-01

    The apparatus and techniques used in effort to determine the relationships between crystal growth and electronic properties are described with emphasis on electroepitaxy and melt-grown gallium aresenide crystal. Applications of deep level transient spectroscopy, derivative photocapitance spectroscopy, and SEM-cathodoluminescene in characterizing wide bandgap semiconductors; determining photoionization in MOS, Schottky barriers, and p-n junctions; and for identifying inhomogeneities are examined, as well as the compensation of indium phosphide.

  15. Synthesis, crystal growth and characterization of nonlinear optical organic crystal: p-Toluidinium p-toluenesulphonate

    SciTech Connect

    Vijayakumar, P. [Centre for Crystal Growth, SSN College of Engineering, SSN Nagar, Tamilnadu 603110 (India)] [Centre for Crystal Growth, SSN College of Engineering, SSN Nagar, Tamilnadu 603110 (India); Anandha Babu, G., E-mail: anandcgc@gmail.com [Centre for Crystal Growth, SSN College of Engineering, SSN Nagar, Tamilnadu 603110 (India); Ramasamy, P. [Centre for Crystal Growth, SSN College of Engineering, SSN Nagar, Tamilnadu 603110 (India)] [Centre for Crystal Growth, SSN College of Engineering, SSN Nagar, Tamilnadu 603110 (India)

    2012-04-15

    Graphical abstract: p-Toluidinium p-toluenesulphonate (p-TTS) an organic nonlinear optical crystal has been grown from the aqueous solution by slow evaporation solution growth technique. Single crystal X-ray diffraction analysis reveals that p-TTS crystallizes in monoclinic crystal system. p-TTS single crystal belongs to negative birefringence crystal. Second harmonic conversion efficiency of p-TTS has been found to be 1.3 times higher than that of KDP. Multiple shot surface laser damage threshold is determined to be 0.30 GW/cm{sup 2} at 1064 nm laser radiation. Highlights: Black-Right-Pointing-Pointer It deals with the synthesis, growth and characterization of p-TTS an organic NLO crystal. Black-Right-Pointing-Pointer Wide optical transparency window between 280 nm and 1100 nm. Black-Right-Pointing-Pointer Negative birefringence crystal and dispersion of birefringence is negligibly small. Black-Right-Pointing-Pointer Thermal study reveals that the grown crystal is stable up to 210 Degree-Sign C. Black-Right-Pointing-Pointer Multiple shot surface laser damage threshold is 0.30 GW/cm{sup 2} at 1064 nm laser radiation. -- Abstract: p-Toluidinium p-toluenesulphonate (p-TTS) an organic nonlinear optical crystal has been grown from the aqueous solution by slow evaporation solution growth technique. Single crystal X-ray diffraction analysis reveals that p-TTS crystallizes in monoclinic crystal system. The structural perfection of the grown p-TTS single crystal has been analyzed by high-resolution X-ray diffraction rocking curve measurements. Fourier transform infrared spectral studies have been performed to identify the functional groups. The optical transmittance window and the lower cutoff wavelength of the grown crystals have been identified by UV-vis-IR studies. Birefringence of p-TTS crystal has been studied using channel spectrum measurement. The laser damage threshold value was measured using Nd:YAG laser. The second harmonic conversion efficiency of p-TTS has been determined using Kurtz powder technique. Thermo gravimetric and differential thermal analyses were used to study its thermal properties. Dielectric constant, dielectric loss and AC conductivity of the grown p-TTS single crystal has been studied.

  16. Nucleation and Convection Effects in Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz

    1997-01-01

    Work during the second year under this grant (NAG8-1161) resulted in several major achievements. We have characterized protein impurities as well as microheterogeneities in the proteins hen egg white lysozyme and horse spleen apoferritin, and demonstrated the effects of these impurities on nucleation and crystallization. In particular, the purification of apoferritin resulted in crystals with an X-ray diffraction resolution of better than 1.8 A, i.e. a 1 A improvement over earlier work on the cubic form. Furthermore, we have shown, in association with studies of liquid-liquid phase separation, that depending on the growth conditions, lysozyme can produce all growth morphologies that have been observed with other proteins. Finally, in connection with our experimental and simulation work on growth step bunching, we have developed a system-dependent criterion for advantages and disadvantages of crystallization from solution under reduced gravity. In the following, these efforts are described in some detail.

  17. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, Harry C.; Lagowski, Jacek

    1989-01-01

    The program on Crystal Growth of Device Quality GaAs in Space was initiated in 1977. The initial stage covering 1977 to 1984 was devoted strictly to ground-based research. By 1985 the program had evolved into its next logical stage aimed at space growth experiments; however, since the Challenger disaster, the program has been maintained as a ground-based program awaiting activation of experimentation in space. The overall prgram has produced some 80 original scientific publications on GaAs crystal growth, crystal characterization, and new approaches to space processing. Publication completed in the last three years are listed. Their key results are outlined and discussed in the twelve publications included as part of the report.

  18. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1985-01-01

    The present program has been aimed at solving the fundamental and technological problems associated with Crystal Growth of Device Quality in Space. The initial stage of the program was devoted strictly to ground-based research. The unsolved problems associated with the growth of bulk GaAs in the presence of gravitational forces were explored. Reliable chemical, structural and electronic characterization methods were developed which would permit the direct relation of the salient materials parameters (particularly those affected by zero gravity conditions) to the electronic characteristics of single crystal GaAs, in turn to device performance. These relationships are essential for the development of optimum approaches and techniques. It was concluded that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail.

  19. A generalized electrochemical aggregative growth mechanism.

    PubMed

    Ustarroz, Jon; Hammons, Joshua A; Altantzis, Thomas; Hubin, Annick; Bals, Sara; Terryn, Herman

    2013-08-01

    The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberration-corrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the Volmer-Weber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks. PMID:23809002

  20. Anisotropy in the crystal growth of hexagonal ice, Ih

    NASA Astrophysics Data System (ADS)

    Rozmanov, Dmitri; Kusalik, Peter G.

    2012-09-01

    Growth of ice crystals has attracted attention because ice and water are ubiquitous in the environment and play critical roles in natural processes. Hexagonal ice, Ih, is the most common form of ice among 15 known crystalline phases of ice. In this work we report the results of an extensive and systematic molecular dynamics study of the temperature dependence of the crystal growth on the three primary crystal faces of hexagonal ice, the basal {0001} face, the prism lbrace 10bar{1}0rbrace face, and the secondary prism lbrace 11bar{2}0rbrace face, utilizing the TIP4P-2005 water model. New insights into the nature of its anisotropic growth are uncovered. It is demonstrated that the ice growth is indeed anisotropic; the growth and melting of the basal face are the slowest of the three faces, its maximum growth rates being 31% and 43% slower, respectively, than those of the prism and the secondary prism faces. It is also shown that application of periodic boundary conditions can lead to varying size effect for different orientations of an ice crystal caused by the anisotropic physical properties of the crystal, and results in measurably different thermodynamic melting temperatures in three systems of similar, yet moderate, size. Evidence obtained here provides the grounds on which to clarify the current understanding of ice growth on the secondary prism face of ice. We also revisit the effect of the integration time step on the crystal growth of ice in a more thorough and systematic way. Careful evaluation demonstrates that increasing the integration time step size measurably affects the free energy of the bulk phases and shifts the temperature dependence of the growth rate curve to lower temperatures by approximately 1 K when the step is changed from 1 fs to 2 fs, and by 3 K when 3 fs steps are used. A thorough investigation of the numerical aspects of the simulations exposes important consequences of the simulation parameter choices upon the delicate dynamic balance that is involved in ice crystal growth.

  1. TlBr crystal growth, purification and characterisation

    NASA Astrophysics Data System (ADS)

    Kozlov, V.; Leskelä, M.; Prohaska, T.; Schultheis, G.; Stingeder, G.; Sipilä, H.

    2004-09-01

    TlBr single crystals are promising materials as room temperature X- and gamma ray detectors. However, the TlBr detector performance is generally limited by the quality of the initial crystal material. In this work, the chemical aspects of synthesis, purification, and crystal growth are emphasised. The aim of this paper was to develop characterisation methods for TlBr and study the effect of different impurities on the properties of TlBr. Samples of different types were selected for the investigations, viz. melt grown crystals and material precipitated from water solution. One important topic in the research was to study the purification of TlBr crystals by annealing in pure water. In this paper, the materials were characterised by X-ray diffraction, FTIR spectroscopy, I-V measurements and trace element analysis.

  2. Crystal growth of organics for nonlinear optical applications

    NASA Technical Reports Server (NTRS)

    Singh, N. B.; Mazelsky, R.

    1993-01-01

    The crystal growth and characterization of organic and inorganic nonlinear optical materials were extensively studied. For example, inorganic crystals such as thallium arsenic selenide were studied in our laboratory for several years and crystals in sizes over 2.5 cm in diameter are available. Organic crystals are suitable for the ultraviolet and near infrared region, but are relatively less developed than their inorganic counterparts. Very high values of the second harmonic conversion efficiency and the electro-optic coefficient were reported for organic compounds. Single crystals of a binary organic alloy based on m.NA and CNA were grown and higher second harmonic conversion efficiency than the values reported for m.NA were observed.

  3. Crystal growth and scintillation properties of LSO and LYSO crystals

    NASA Astrophysics Data System (ADS)

    Mao, Rihua; Wu, Chen; Dai, Ling'En; Lu, Sheng

    2013-04-01

    Lutetium oxyorthosilicate (LSO) and lutetium-yttrium oxyorthosilicate (LYSO) single crystals were grown by Czochralski method and samples with dimension of 17 mm in cubic were made. The optical and scintillation properties for these samples were performed. It was found that optical transmittance observed for both LSO and LYSO matches well with the theoretical limits. The light output (L.O.) measured by a PMT with bialkali cathode was found to be 4100 p.e./MeV with an energy resolution of 10.2% and a decay time of 42 ns. Light output non-proportionality was found in energy scale below 356 keV. The ?-ray induced afterglow in LYSO found much less than that of the LSO sample.

  4. Commercial Protein Crystal Growth: Protein Crystallization Facility (CPCG-H)

    NASA Astrophysics Data System (ADS)

    DeLucas, Lawrence J.

    2002-12-01

    Within the human body, there are thousands of different proteins that serve a variety of different functions, such as making it possible for red blood cells to carry oxygen in our bodies. Yet proteins can also be involved in diseases. Each protein has a particular chemical structure, which means it has a unique shape. It is this three-dimensional shape that allows each protein to do its job by interacting with chemicals or binding with other proteins. If researchers can determine the shape, or shapes, of a protein, they can learn how it works. This information can then be used by the pharmaceutical industry to develop new drugs or improve the way medications work. The NASA Commercial Space Center sponsoring this experiment - the Center for Biophysical Sciences and Engineering at the University of Alabama at Birmingham - has more than 60 industry and academic partners who grow protein crystals and use the information in drug design projects.

  5. Study on buoyancy convection phenomenon in the crystal growth process

    Microsoft Academic Search

    Li Duan; Qi Kang

    2009-01-01

    Real-time phase shift Mach-Zehnder interference technique, imaging technique, and computer image processing technique were\\u000a combined to perform a real-time diagnosis of NaClO3 crystal, which described both the dissolution process and the crystallization process of the NaClO3 crystal in real-time condition. The dissolution fringes and the growth fringes in the process were obtained. Moreover, a\\u000a distribution of concentration field in this

  6. Modelling the growth of triglycine sulphate crystals in Spacelab 3

    NASA Technical Reports Server (NTRS)

    Yoo, Hak-Do; Wilcox, William R.; Lal, Ravindra; Trolinger, James D.

    1988-01-01

    Two triglycine sulphate crystals were grown from an aqueous solution on the Spacelab 3 mission. Using a diffusion coefficient of 0.00002 sq cm/sec, a computer simulation gave reasonable agreement between experimental and theoretical crystal sizes and interferometric lines in the solution near the growing crystal. This diffusion coefficient is larger than most measured values, possibly due to fluctuating accelerations on the order of 0.001 g. The average acceleration was estimated to be less than 10 to the -6th g. At this level buoyancy-driven convection is predicted to add approximately 20 percent to the steady-state growth rate.

  7. Decomposition of crystal-growth equations in multicomponent melts

    NASA Astrophysics Data System (ADS)

    Dudorov, M. V.

    2014-06-01

    Using a variational approach, the macroscopic laws of the growth of a new-phase, multicomponent particle are compared to the physicochemical laws of processes in the “new phase - initial melt” system. A suitable equation-based method has been developed to calculate the growth of a new-phase particle under the conditions of diffusion growth and non-equilibrium solute trapping by the quickly growing front of a new phase. The laws of crystal growth have been studied while annealing the amorphous alloy FINEMET® Fe73.5Cu1Nb3Si13.5B9.

  8. Crystal growth of lanthanum calcium borate (LCB) single crystals from melt and its characterization

    NASA Astrophysics Data System (ADS)

    Senthi lkumar, M.; Kalidasan, M.; Sugan; Dhanasekaran, R.

    2013-01-01

    Non-linear optical lanthanum calcium borate (LCB) single crystals were grown by the melt growth method using the Czohralski technique. The polycrystalline LCB compound is synthesized using the solid state reaction method. The grown crystals were characterized by XRD, EDAX, DTA, HRXRD, specific heat, dielectric and NLO studies. The powder XRD pattern revealed the formation of LCB compound and the lattice parameters of the grown crystals were identified through single crystal XRD studies. The melting point of the LCB compound is analyzed by the DTA measurements. Good crystalline nature of the grown crystal is observed from HRXRD analysis. Specific heat measurements in the temperature range 50-550 °C are carried out for the as grown crystal samples. The results obtained by the dielectric and NLO studies are also presented.

  9. Numerical Modeling of Physical Vapor Transport in Contactless Crystal Growth Geometry

    NASA Technical Reports Server (NTRS)

    Palosz, W.; Lowry, S.; Krishnam, A.; Przekwas, A.; Grasza, K.

    1998-01-01

    Growth from the vapor under conditions of limited contact with the walls of the growth ampoule is beneficial for the quality of the growing crystal due to reduced stress and contamination which may be caused by interactions with the growth container. The technique may be of a particular interest for studies on crystal growth under microgravity conditions: elimination of some factors affecting the crystal quality may make interpretation of space-conducted processes more conclusive and meaningful. For that reason, and as a part of our continuing studies on 'contactless' growth technique, we have developed a computational model of crystal growth process in such system. The theoretical model was built, and simulations were performed using the commercial computational fluid dynamics code, (CFD) ACE. The code uses an implicit finite volume formulation with a gray discrete ordinate method radiation model which accounts for the diffuse absorption and reflection of radiation throughout the furnace. The three-dimensional model computes the heat transfer through the crystal, quartz, and gas both inside and outside the ampoule, and mass transport from the source to the crystal and the sink. The heat transport mechanisms by conduction, natural convection, and radiation, and mass transport by diffusion and convection are modeled simultaneously and include the heat of the phase transition at the solid-vapor interfaces. As the thermal boundary condition, temperature profile along the walls of the furnace is used. For different thermal profiles and furnace and ampoule dimensions, the crystal growth rate and development of the crystal-vapor and source-vapor interfaces (change of the interface shape and location with time) are obtained. Super/under-saturation in the ampoule is determined and critical factors determining the 'contactless' growth conditions are identified and discussed. The relative importance of the ampoule dimensions and geometry, the furnace dimensions and its temperature, and the properties of the grown material are analyzed. The results of the simulations are compared with related experimental results on growth of CdTe, CdZnTe, ZnTe, PbTe, and PbSnTe crystals by this technique.

  10. A framework for optimization of crystal growth processes applied to VGF growth of fluorides

    NASA Astrophysics Data System (ADS)

    Backofen, Rainer; Voigt, Axel; Wulff-Molder, Dirk

    2005-02-01

    We develop a flexible framework for optimization of crystal growth processes. This framework is based on an accurate and robust process model and combines two optimization loops. Adapting of model parameters and optimizing of process parameters.

  11. Generation and Propagation of Defects During Crystal Growth

    Microsoft Academic Search

    Helmut Klapper

    2010-01-01

    \\u000a \\u000a This \\u000a \\u000a \\u000a \\u000a \\u000a \\u000a chapter presents a review of the typical growth defects of crystals fully grown on (planar) habit faces, i.e., of crystals\\u000a grown in all kinds of solutions, in supercooled melt (mainly low-melting organics) and in the vapor phase. To a smaller extent\\u000a growth on rounded faces from the melt is also considered when this seems appropriate to bring out analogies or discuss

  12. Computer-controlled float zone crystal growth

    NASA Technical Reports Server (NTRS)

    Chan, Y. T.; Mailloux, P. A.

    1993-01-01

    A PC-based computer control system to automate a high-temperature float zone growth of titanium carbide is reported. The control strategy of the computer control system relies on the relations derived from a combination of empirical relations and results from detailed mathematical analysis of the physical transports of the entire float zone assembly. A system control computer program was written to establish real-time determination of the size of the molten zone from a thermal image, control parameters from established relationships, and collected processed data to achieve control objectives. We found that the developed computer control allows the growth process to be operated nearer the stability limit. Any slight variations in growth conditions can be corrected in time to avoid any instability growth, which otherwise cannot be adjusted via manual control.

  13. Interface stability and defect formation during crystal growth

    SciTech Connect

    Fabietti, L.M.R.

    1991-01-08

    Unidirectional solidification experiments have been carried out in organic crystals with the aim of improving our knowledge on the effects of constraints on the interface morphology and to increase our understanding of the growth of anisotropic materials. The experimental information shows that lateral constraints such as a sharp change in the cross-sectional area in the solid liquid interface path, can produce important changes in the microstructure if the interface morphology is planar, cellular or dendritic. The study of anisotropic materials cover several topics. It is first shown that slight anisotropy does not influence the dendrite tip selection criterion. This conclusion is obtained from the analysis of the relationship between tip radius and velocity for dendrites growing under the steady state condition for two different materials, CBr{sub 4} and C{sub 2}Cl{sub 6}, which have different surface energy anisotropy values. The values of the dendrite operating parameters {sigma}* are compared with the predictions of the solvability theory and the morphological stability theory. The experiments show better agreement with the latter theory. Critical experiments have been designed and carried out to find the response functions which determine the composition and temperature of the interface as a function of velocity in faceted materials. The experiments, carried out in Napthalene-Camphor system, indicate a strong temperature dependence of the planar interface growth which can be correlated with the step growth mechanism. Experiments on the interface instability show an important dependence on the crystallographic orientation. Unidirectional solidification experiments in zone refined Napthalene confined in very thin cells (gap size {le} 50 {mu}m) have proven to be a good method to study the defect production at the solid liquid interface. 118 refs., 90 figs., 5 tabs.

  14. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Lagowski, J.

    1981-01-01

    Experimental and theoretical efforts in the development of crystal growth approaches, effective techniques for electronic characterization on a macro and microscale, and in the discovery of phenomena and processes relevant to GaAs device applications are reported. The growth of electron trap-free bulk GaAS with extremely low density of dislocations is described. In electroepitaxy, growth configuration which eliminates the substrate back-contact was developed. This configuration can be extended to the simultaneous growth on many substrates with a thin solution layer sandwiched between any two of them. The significant reduction of Joule heating effects in the configuration made it possible to realize the in situ measurement of the layer thickness and the growth velocity. Utilizing the advantages of electroepitaxy in achieving abrupt acceleration (or deceleration) of the growth it was shown that recombination centers are formed as a result of growth acceleration.

  15. Single crystal growth by gel technique and characterization of lithium hydrogen tartrate

    NASA Astrophysics Data System (ADS)

    Ahmad, Nazir; Ahmad, M. M.; Kotru, P. N.

    2015-02-01

    Single crystal growth of lithium hydrogen tartrate by gel encapsulation technique is reported. Dependence of crystal count on gel density, gel pH, reactant concentration and temperature are studied and the optimum conditions for these crystals are worked out. The stoichiometric composition of the grown crystals is determined using EDAX/AES and CH analysis. The grown crystals are characterized by X-ray diffraction, FTIR and Uv-Visible spectroscopy. It is established that crystal falls under orthorhombic system and space group P222 with the cell parameters as: a=10.971 Å, b=13.125 Å and c=5.101 Å; ?=90.5o, ?=?=90°. The morphology of the crystals as revealed by SEM is illustrated. Crystallite size, micro strain, dislocation density and distortion parameters are calculated from the powder XRD results of the crystal. UV-vis spectroscopy shows indirect allowed transition with an optical band gap of~4.83 eV. The crystals are also shown to have high transmittance in the entire visible region. Dependence of dielectric constant, dielectric loss and conductivity on frequency of the applied ac field is analyzed. The frequency-dependent real part of the complex ac conductivity is found to follow the universal dielectric response: ?ac (?)~?s. The trend in the variation of frequency exponent with frequency corroborates the fact that correlated barrier hopping is the dominant charge-transport mechanism in the present system.

  16. Growth mechanism of hydrogen clusters

    SciTech Connect

    Nickel, N.H.; Anderson, G.B.; Johnson, N.M.; Walker, J.

    1997-07-01

    It is demonstrated that the exposure of polycrystalline silicon (poly-Si) to monatomic hydrogen results in the formation of H clusters. These H stabilized platelets appear in the near-surface region (100 nm) and are predominantly oriented along {l_brace}111{r_brace} crystallographic planes. Platelet concentrations of {approx}5 x 10{sup 15}, 1.5 x 10{sup 16} -cm{sup {minus}3}, and 2.4 x 10{sup 17} cm{sup {minus}3} were observed in nominally undoped poly-Si, phosphorous doped poly-Si (P = 10{sup 17} cm{sup {minus}3}), and phosphorous doped single crystal silicon (P > 3 x 10{sup 18} cm{sup {minus}3}), respectively. Results obtained on doped c-Si demonstrate that platelet generation occurs only at Fermi-level positions of E{sub C} - E{sub F} < 0.4 eV.

  17. 2D modeling of the regeneration surface growth on crystals

    NASA Astrophysics Data System (ADS)

    Thomas, V. G.; Gavryushkin, P. N.; Fursenko, D. A.

    2012-11-01

    A physical model is proposed to describe the growth of regeneration surfaces (flat crystal surfaces that are not parallel to any possible faces). According to this model, the change in the growth rate of a regeneration surface during its evolution and the decrease in the number of subindividuals forming the growth front can be explained by the implementation of two types of geometric selection: within each subindividual (the absorption of rapidly growing faces by slowly growing ones) and between subindividuals (when subindividuals absorb each other). A numerical modeling of the growth of the regeneration surface (30.30.19) of potassium alum crystals showed quantitative agreement between the model proposed and the experimental data.

  18. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1986-01-01

    It was established that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail. It was further established that in compound semiconductors with a volatile constituent, control of stoichiometry is far more critical than any other crystal growth parameter. It was also shown that, due to suppression of nonstoichiometric fluctuations, the advantages of space for growth of semiconductor compounds extend far beyond those observed in elemental semiconductors. A novel configuration was discovered for partial confinement of GaAs melt in space which overcomes the two major problems associated with growth of semiconductors in total confinement. They are volume expansion during solidification and control of pressure of the volatile constituent. These problems are discussed in detail.

  19. Predicting crystal structure by merging data mining with quantum mechanics

    Microsoft Academic Search

    Christopher C. Fischer; Kevin J. Tibbetts; Dane Morgan; Gerbrand Ceder

    2006-01-01

    Modern methods of quantum mechanics have proved to be effective tools to understand and even predict materials properties. An essential element of the materials design process, relevant to both new materials and the optimization of existing ones, is knowing which crystal structures will form in an alloy system. Crystal structure can only be predicted effectively with quantum mechanics if an

  20. Crystal growth of bullet-shaped magnetite in magnetotactic bacteria of the Nitrospirae phylum.

    PubMed

    Li, Jinhua; Menguy, Nicolas; Gatel, Christophe; Boureau, Victor; Snoeck, Etienne; Patriarche, Gilles; Leroy, Eric; Pan, Yongxin

    2015-02-01

    Magnetotactic bacteria (MTB) are known to produce single-domain magnetite or greigite crystals within intracellular membrane organelles and to navigate along the Earth's magnetic field lines. MTB have been suggested as being one of the most ancient biomineralizing metabolisms on the Earth and they represent a fundamental model of intracellular biomineralization. Moreover, the determination of their specific crystallographic signature (e.g. structure and morphology) is essential for palaeoenvironmental and ancient-life studies. Yet, the mechanisms of MTB biomineralization remain poorly understood, although this process has been extensively studied in several cultured MTB strains in the Proteobacteria phylum. Here, we show a comprehensive transmission electron microscopy (TEM) study of magnetic and structural properties down to atomic scales on bullet-shaped magnetites produced by the uncultured strain MYR-1 belonging to the Nitrospirae phylum, a deeply branching phylogenetic MTB group. We observed a multiple-step crystal growth of MYR-1 magnetite: initial isotropic growth forming cubo-octahedral particles (less than approx. 40 nm), subsequent anisotropic growth and a systematic final elongation along [001] direction. During the crystal growth, one major {111} face is well developed and preserved at the larger basal end of the crystal. The basal {111} face appears to be terminated by a tetrahedral-octahedral-mixed iron surface, suggesting dimensional advantages for binding protein(s), which may template the crystallization of magnetite. This study offers new insights for understanding magnetite biomineralization within the Nitrospirae phylum. PMID:25566884

  1. Growth of large detector crystals. CRADA final report

    SciTech Connect

    Boatner, L.A. [Oak Ridge National Lab., TN (United States); Samuelson, S. [Deltronic Crystal Industries, Dover, NJ (United States)

    1997-06-18

    In the course of a collaborative research effort between L.A. Boatner of Oak Ridge National Laboratory and Prof. Alex Lempicki of the Department of Chemistry of Boston University, a new highly efficient and very fast scintillator for the detection of gamma-rays was discovered. This new scintillator consists of a single crystal of lutetium orthophosphate (LuPO{sub 4}) to which a small percentage of trivalent cerium is added as an activator ion. The new lutetium orthophosphate-cerium scintillator was found to be superior in performance to bismuth germanium oxide--a material that is currently widely used as a gamma-ray detector in a variety of medical, scientific, and technical applications. Single crystals of LuPO{sub 4} and related rare-earth orthophosphates had been grown for a number of years in the ORNL Solid State Division prior to the discovery of the efficient gamma-ray-scintillation response of LuPO{sub 4}:Ce. The high-temperature-solvent (flux-growth) method used for the growth of these crystals was capable of producing crystals in sizes that were adequate for research purposes but that were inadequate for commercial-scale production and widespread application. The CRADA between ORNL and Deltronic Crystal Industries of Dover, NJ was undertaken for the purpose of investigating alternate approaches, such as top-seeded-solution growth, to the growth of LuPO{sub 4}:Ce scintillator crystals in sizes significantly larger than those obtainable through the application of standard flux-growth methods and, therefore, suitable for commercial sales and applications.

  2. Crystal-growth Underground Breeding Extra-sensitive Detectors

    NASA Astrophysics Data System (ADS)

    Mei, Dongming

    2012-02-01

    CUBED (Center for Ultra-Low Background Experiments at DUSEL) collaborators from USD, SDSMT, SDSU, Sanford Lab, and Lawrence Berkeley National Laboratory are working on the development of techniques to manufacture crystals with unprecedented purity levels in an underground environment that may be used by experiments proposed for DUSEL. The collaboration continues to make significant progress toward its goal of producing high purity germanium crystals. High quality crystals are being pulled on a weekly basis at the temporary surface growth facility located on the USD campus. The characterization of the grown crystals demonstrates that the impurity levels are nearly in the range of the needed impurity level for detector-grade crystals. Currently, the crystals are being grown in high-purity hydrogen atmosphere. With an increase in purity due to the zone refining, the group expects to grow high-purity crystals by the end of 2011. The one third of the grown crystals will be manufactured to be detectors; the remaining will be fabricated in to wafers that have large applications in electro and optical devices as well as solar panels. This would allow the research to be connected to market and create more than 30 jobs and multi millions revenues in a few years.

  3. Characterization and In-Situ Monitoring of ZnSe Crystal Growth by Seeded PVT for Microgravity Applications

    NASA Technical Reports Server (NTRS)

    Feth, Shari T.

    2001-01-01

    Crystal growth from the vapor phase continues to play a significant role in the production of II-VI semiconductor compounds (ZnO, ZnTe, CdTe, etc.) and SiC. As compared to melt growth methods (where available) the advantages are: (1) lower growth temperature(s); (2) reduction in defect concentration; (3) additional purification; and (4) enhanced crystal perfection. A powerful tool in determining the mechanism of PVT is microgravity. Under normal gravity conditions the transport mechanism is a superposition of diffusive and convective fluxes. Microgravity offers the possibility of studying the transport properties without the influence of convective effects. Research on the crystal growth of ZnSe by PVT (P.I.: Su of NASA/MSFC) will help to clarify the effects of convection on crystal growth. A crystal growth furnace with in-situ and real time optical monitoring capabilities was constructed and used to monitor the vapor composition and growing crystal surface morphology during the PVT growth of ZnSe. Using photoluminescence and SIMS, ex-situ, the incorporation of point defects (Zn vacancy) and impurities was found to be correlated to the gravity vector due to the influence of the convective flow. A summary of the results to date will be presented.

  4. Modeling Conformal Growth in Photonic Crystals and Comparing to Experiment

    Microsoft Academic Search

    Andrew Brzezinski; Ying-Chieh Chen; Pierre Wiltzius; Paul Braun

    2008-01-01

    Conformal growth, e.g. atomic layer deposition (ALD), of materials such as silicon and TiO2 on three dimensional (3D) templates is important for making photonic crystals. However, reliable calculations of optical properties as a function of the conformal growth, such as the optical band structure, are hampered by difficultly in accurately assessing a deposited material's spatial distribution. A widely used approximation

  5. Kinetics of Crystal Growth From Silicate Melts: Anorthite and Diopside

    Microsoft Academic Search

    R. James Kirkpatrick; Gilpin R. Robinson; James Fred Hays

    1976-01-01

    Rates of linear crystal growth have been measured for diopside and anorthite growing from their own melts by using a microscope heating stage. Rates were obtained for undercoolings of as little as 13øC. The rates are higher for diopside than for anorthite. Maximum growth rates observed are 1.5 X 10 -' cm\\/s (AT = 194øC) for anorthite and 2.2 X

  6. Fabrication of whispering gallery mode cavity using crystal growth

    E-print Network

    Kudo, Hiroshi; Kato, Takumi; Yokoo, Atsushi; Tanabe, Takasumi

    2013-01-01

    We developed a new method for fabricating crystalline whispering gallery mode cavities based on laser-heated pedestal growth. We fabricated sapphire cavities and obtained a Q factor of 16000 with a cavity whose diameter was about 240 um. We showed numerically that the cross-sectional shape of the cavity is sensitive to the cavity Q, and we controlled it successfully by changing the growth condition in the molten zone, without significantly degrading the crystal structure.

  7. Chiral Symmetry Breaking in Crystal Growth: Is Hydrodynamic Convection Relevant?

    NASA Technical Reports Server (NTRS)

    Martin, B.; Tharrington, A.; Wu, Xiao-Lun

    1996-01-01

    The effects of mechanical stirring on nucleation and chiral symmetry breaking have been investigated for a simple inorganic molecule, sodium chlorate (NaClO3). In contrast to earlier findings, our experiment suggests that the symmetry breaking may have little to do with hydrodynamic convection. Rather the effect can be reasonably accounted for by mechanical damage to incipient crystals. The catastrophic events, creating numerous small 'secondary' crystals, produce statistical domination of one chiral species over the other. Our conclusion is supported by a number of observations using different mixing mechanisms.

  8. Growth twinning in magnesium oxide smoke crystals

    Microsoft Academic Search

    R. R. Cowley; R. L. Segall; R. St. C. Smart; C. Smart; P. S. Turner

    1979-01-01

    Growth twins in magnesium oxide are shown to occur when magnesium is burnt in air in the presence of water vapour. The twins are coherent and the external morphology shows mirror symmetry across the {111} composition plane. The significance of the existence and form of these twins in such a highly ionic material is considered in terms of the structure

  9. Selective anisotropic growth of zeolite crystals

    E-print Network

    Desai, Tasha April

    2013-02-22

    . To achieve this end we are attempting to grow zeolite particles in the confined water spaces formed in water/surfactant systems, using these "nanoreactors" to modulate zeolite growth. Our work to date has focused on the synthesis of two-dimensional (5x100x...

  10. Visual Simulation of Ice Crystal Growth

    Microsoft Academic Search

    Theodore Kim; Ming C. Lin

    2003-01-01

    The beautiful, branching structure of ice is one of the most striking visual phenomena of the winter landscape. Yet there is little study about modeling this effect in computer graphics. In this paper, we present a novel approach for visual simulation of ice growth. We use a numerical simulation technique from computational physics, the \\

  11. Growth and properties of benzil doped benzimidazole (BMZ) single crystals

    SciTech Connect

    Babu, R. Ramesh, E-mail: rampap2k@yahoo.co.in [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India); Sukumar, M. [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India)] [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Vasudevan, V. [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India) [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India); Shakir, Mohd. [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India)] [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India); Ramamurthi, K. [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India)] [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Bhagavannarayana, G. [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India)] [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India)

    2010-09-15

    In the present work, we have made an attempt to study the effect of benzil doping on the properties of benzimidazole single crystals. For this purpose we have grown pure and benzil doped benzimidazole single crystals by vertical Bridgman technique. The grown crystals were characterized by various characterization techniques. The presence of dopants confirmed by powder X-ray diffraction (XRD). Crystalline perfection of the grown crystals has been analysed by high-resolution X-ray diffraction (HRXRD). The transmittance, electrical property and mechanical strength have been analysed using UV-vis-NIR spectroscopic, dielectric and Vicker's hardness studies. The relative second harmonic generation efficiency of pure and doped benzimidazole crystals measured using Kurtz powder test.

  12. Growth and characterization of biadmixtured TGS single crystals

    NASA Astrophysics Data System (ADS)

    Bharthasarathi, T.; Siva Shankar, V.; Jayavel, R.; Murugakoothan, P.

    2009-02-01

    Single crystals of triglycine sulfate (TGS) with L-glutamine and L-methionine were grown in aqueous solutions by a slow cooling method. The grown crystals were subjected to single crystal and powder X-ray diffraction studies to identify the morphology and the structure. FTIR and UV-visible spectra reveal the functional group identification and optical property of the grown crystals. The dielectric studies were carried out to identify the phase transition temperature and to find the dielectric constant. Microhardness studies have been carried out to assess the mechanical property. P- E hysteresis studies were carried out to find the values of spontaneous polarization and coercive field for doped TGS crystals.

  13. Electrochemical Growth of Single-Crystal Metal Nanowires via a

    E-print Network

    physical properties and potential applications as interconnects in future generations of nanometer the electro- chemical growth of copper single-crystal wires in polycar- bonate and anodic alumina membranes. The diameters of these wires range from micrometers down to nanometers (70 nm). Similarly, Pb, Bi, and Ag single

  14. Generic features of late-stage crystal growth

    Microsoft Academic Search

    Fong Liu; Nigel Goldenfeld

    1990-01-01

    A cell dynamical system model, which realistically incorporates diffusion, is developed to study various aspects of late-stage crystal growth. The algorithm is computationally efficient, allowing the development of complex spatial structures to be studied, and is motivated by renormalization group considerations. We establish the existence of an asymptotic dense branching morphology and relate it to diffusion-limited aggregation. Our findings indicate

  15. Nucleation, crystal growth and the thermal regime of cooling magmas

    Microsoft Academic Search

    Geneviéve Brandeis; Claude Jaupart; Claude J. Allégre

    1984-01-01

    Crystallization at the margin of a quiet cooling magma has been studied numerically, taking into account the kinetics of crystalligation. The variables are the latent heat value, the growth and nucleation functions, the initial magma temperature, and the thermal contrast between magma and country rock. We have investigated a wide range of values for these parameters corresponding to natural conditions.

  16. Crystal growth, magnetism, transport and superconductivity of two dimensional sodium cobalt oxide single crystals

    Microsoft Academic Search

    Dapeng Chen

    2008-01-01

    The objective of this work was to study the single crystal growth of NaxCoO2 by the optical floating zone technique and the intrinsic properties of the high quality single crystal samples thus produced. The properties of the superconductors derived from it will also be reported. This thesis, after a literature review on the NaxCoO2 family and the superconductors derived from

  17. Iminodiacetic acid doped ferroelectric triglycine sulphate crystal: Crystal growth and characterization

    Microsoft Academic Search

    Chitharanjan Rai; B. Narayana Moolya; S. M. Dharmaprakash

    2011-01-01

    Single crystals of iminodiacetic acid (HN(CH2COOH)2) doped triglycine sulphate (IDATGS) crystals have been grown from aqueous solution containing 1–10mol% of iminodiacetic acid at constant temperature by slow evaporation technique. The effects of different amounts of doping entities on the growth habit have been investigated. X-ray powder diffraction pattern for pure and doped TGS was collected to determine the lattice parameters.

  18. Progress in the crystal growth of Ce : colquiriites

    NASA Astrophysics Data System (ADS)

    Castillo, Vida K.; Quarles, Gregory J.

    1997-04-01

    The search for an efficient solid-state laser with tunable emission in the ultraviolet wavelength region has resulted in the growth and development of cerium-doped colquiriite crystals, such as LiCaAlF 6 (LiCAF) and LiSrAlF 6 (LiSAF). Unfortunately, the doping of LiSAF and LiCAF with Ce 3+ introduces different variables into the growth of high optical quality crystals, due to the charge imbalance induced when this trivalent ion substitutes for the divalent site. Charge compensation with Na + tends to produce a more uniformly doped crystal with improved laser properties. Although preliminary research indicated that Ce : LiSAF may be the preferred material of the colquiriite hosts, Ce : LiCAF has also proved to be quite promising.

  19. Crystal structure and functional mechanism of a human antimicrobial membrane channel

    E-print Network

    de Groot, Bert

    Crystal structure and functional mechanism of a human antimicrobial membrane channel Chen Songa resistance. Although more than 1,700 host-defense peptides have been identified, the structural the antibiotic mecha- nism of this major human antimicrobial, found to suppress Staphy- lococcus aureus growth

  20. Growth and characterization of ? and ?-glycine single crystals

    NASA Astrophysics Data System (ADS)

    Srinivasan, T. P.; Indirajith, R.; Gopalakrishnan, R.

    2011-03-01

    Single crystals of ?- and ?-glycine were grown by the slow evaporation solution growth method using deionised water as solvent. The ?-glycine was transformed to ?-glycine by addition of KNO3 as additive and both the forms of glycine single crystals were grown and the characteristic properties were studied and compared. From the single crystal XRD analysis the grown ?- and ?-glycine crystals are confirmed. The presence of the functional groups of ?- and ?-glycine was analyzed from the recorded FT-IR spectrum. The optical transmission was ascertained from UV-vis-NIR spectrum. The lower cut-off wavelengths of ?- and ?-glycine are 292 and 272 nm, respectively. The second harmonic generation relative efficiency was measured by the Kurtz and Perry powder technique. Group theoretical analysis predicts 120 vibrational optical modes in ?-glycine and 90 vibrational optical modes in ?-glycine. The TGA, DTA and dielectric studies were carried out to explore information about thermal and dielectric behavior, respectively, for ?- and ?-glycine.

  1. Journal of Crystal Growth 307 (2007) 302308 Equilibrium analysis of zirconium carbide CVD growth

    E-print Network

    Anderson, Timothy J.

    2007-01-01

    Journal of Crystal Growth 307 (2007) 302­308 Equilibrium analysis of zirconium carbide CVD growth analysis; A3. Metalorganic chemical vapor deposition; A3. Zirconium carbide 1. Introduction Zirconium, is not straightforward particularly by chemical vapor deposition (CVD). Although atmospheric halide CVD using zirconium

  2. Crystal growth rates and optical resolution of DL-methionine hydrochloride by preferential crystallization from aqueous solution

    NASA Astrophysics Data System (ADS)

    Srimahaprom, Watcharakarn; Flood, Adrian E.

    2013-01-01

    Optical resolution of DL-methionine hydrochloride (DL-met·HCl) by preferential crystallization was studied for the purification of L-met·HCl (the desired enantiomer) from supersaturated solutions of DL-met·HCl. The nucleation thresholds (NT) of DL-met·HCl affect the maximum resolution time suitable for preferential crystallization and also the percentage purity of the product crystals. Crystal growth rates of L-met·HCl single crystals both in supersaturated solutions of DL-met·HCl and in supersaturated solutions of pure L-met·HCl were measured in order to model the preferential crystallization more effectively. Results showed that the growth rate depends strongly on the relative supersaturation (especially from pure L-met·HCl solutions), that there is a wide crystal growth rate distribution in growth from both types of solution, and that the growth is faster from pure L-met·HCl solutions, as expected. A batch crystallizer seeded with L-met·HCl crystals was used to study the preferential crystallization, and to study the behavior of purity decrease of the product crystals during the crystallization process. The purity of the L-met·HCl product decreased to the equilibrium value over time, with almost no plateau at 100% purity (as is hoped for in preferential crystallizations). This is explainable by the very short induction times for nucleation in these solutions, and also that the L-met·HCl seed crystals may act as a template for the nucleation of the counter-enantiomer.

  3. Crystal Growth and Characterization of Lead Iodide

    NASA Astrophysics Data System (ADS)

    Chen, Ying-Fang; Chen, Kuo-Tong; Chen, Henry; Chattopadhyay, Kaushik; Burger, Arnold

    1997-11-01

    Zone-refining method has been employed to purify lead iodide source material and chemical analysis indicates that most of the impurities accumulate in the last-to-freeze region due to the zone- refining process. A single crystal was grown by Bridgman method using materials from the middle region which in theory should be the purest. Low temperature photoluminescence (PL) and current- voltage measurement were employed to verify the distribution of impurity and a correlation with resistivity data was established. The results shows that the middle section of the ingot has indeed the highest purity and resistivity with no observable deviation from stoichiometry.(The authors at Fisk would like to acknowledge support provided by NASA under Grant No. NCC8-133.)

  4. Growth and characterization of 4-methyl benzene sulfonamide single crystals

    NASA Astrophysics Data System (ADS)

    Thirumalaiselvam, B.; Kanagadurai, R.; Jayaraman, D.; Natarajan, V.

    2014-11-01

    Single crystals of 4-methyl benzene sulfonamide (4MBS) were successfully grown from aqueous solution by low temperature solution growth technique. The grown crystal was characterized by single crystal XRD and powder XRD methods to obtain the lattice parameters and the diffraction planes of the crystal. UV-vis-NIR absorption spectrum was used to measure the range of optical transmittance and optical band gap energy. The optical transmission range was measured as 250-1200 nm. FTIR spectral studies were carried out to identify the presence of functional groups in the grown crystal. The thermal behavior of the crystal was investigated from thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC) study. The absence of SHG was noticed by Kurtz and Perry powder technique. The third order NLO behavior of the material was confirmed by measuring the nonlinear optical properties using Z-scan technique and it was found that the crystal is capable of exhibiting saturation absorption and self-defocusing performance.

  5. On the origin of surface imposed anisotropic growth of salicylic and acetylsalicylic acids crystals during droplet evaporation.

    PubMed

    Przyby?ek, Maciej; Cysewski, Piotr; Pawelec, Maciej; Zió?kowska, Dorota; Kobierski, Miros?aw

    2015-03-01

    In this paper droplet evaporative crystallization of salicylic acid (SA) and acetylsalicylic acid (ASA) crystals on different surfaces, such as glass, polyvinyl alcohol (PVA), and paraffin was studied. The obtained crystals were analyzed using powder X-ray diffraction (PXRD) technique. In order to better understand the effect of the surface on evaporative crystallization, crystals deposited on glass were scraped off. Moreover, evaporative crystallization of a large volume of solution was performed. As we found, paraffin which is non-polar surface promotes formation of crystals morphologically similar to those obtained via bulk evaporative crystallization. On the other hand, when crystallization is carried out on the polar surfaces (glass and PVA), there is a significant orientation effect. This phenomenon is manifested by the reduction of the number of peaks in PXRD spectrum recorded for deposited on the surface crystals. Noteworthy, reduction of PXRD signals is not observed for powder samples obtained after scraping crystals off the glass. In order to explain the mechanism of carboxylic crystals growth on the polar surfaces, quantum-chemical computations were performed. It has been found that crystal faces of the strongest orientation effect can be characterized by the highest surface densities of intermolecular interactions energy (IIE). In case of SA and ASA crystals formed on the polar surfaces the most dominant faces are characterized by the highest adhesive and cohesive properties. This suggests that the selection rules of the orientation effect comes directly from surface IIE densities. PMID:25690367

  6. Kinetics of Nucleation and Crystal Growth in Glass Forming Melts in Microgravity

    NASA Technical Reports Server (NTRS)

    Day, Delbert E.; Ray, Chandra S.

    1999-01-01

    The following list summarizes the most important results that have been consistently reported for glass forming melts in microgravity: (1) Glass formation is enhanced for melts prepared in space; (2) Glasses prepared in microgravity are more chemically homogeneous and contain fewer and smaller chemically heterogeneous regions than identical glasses prepared on earth; (3) Heterogeneities that are deliberately introduced such as Pt particles are more uniformly distributed in a glass melted in space than in a glass melted on earth; (4) Glasses prepared in microgravity are more resistant to crystallization and have a higher mechanical strength and threshold energy for radiation damage; and (5) Glasses crystallized in space have a different microstructure, finer grains more uniformly distributed, than equivalent samples crystallized on earth. The preceding results are not only scientifically interesting, but they have considerable practical implications. These results suggest that the microgravity environment is advantageous for developing new and improved glasses and glass-ceramics that are difficult to prepare on earth. However, there is no suitable explanation at this time for why a glass melted in microgravity will be more chemically homogeneous and more resistant to crystallization than a glass melted on earth. A fundamental investigation of melt homogenization, nucleation, and crystal growth processes in glass forming melts in microgravity is important to understanding these consistently observed, but yet unexplained results. This is the objective of the present research. A lithium disilicate (Li2O.2SiO2) glass will be used for this investigation, since it is a well studied system, and the relevant thermodynamic and kinetic parameters for nucleation and crystal growth at 1-g are available. The results from this research are expected to improve our present understanding of the fundamental mechanism of nucleation and crystal growth in melts and liquids, and to lead improvements in glass processing technology on earth, with the potential for creating new high performance glasses and glass-ceramics.

  7. Growth, structure, and properties of KTiOPO{sub 4} crystals doped with iron

    SciTech Connect

    Voronkova, V. I., E-mail: voronk@polly.phys.msu.ru; Leont'eva, I. N. [Moscow State University, Faculty of Physics (Russian Federation); Sorokina, N. I. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Ovsetsina, T. I. [Nizhni Novgorod State University (Russian Federation); Verin, I. A. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

    2006-12-15

    A series of iron-doped KTiOPO{sub 4} (KTP: Fe) single crystals in which iron substitutes for 0.1-0.3% titanium was grown. The structure of the KTP: Fe crystals was determined, and their dielectric and conducting properties were studied. An X-ray diffraction analysis failed to reveal such a small amount of Fe{sup +3} ions in titanium octahedral positions of the structure. It was found that an increase in the iron concentration results in a lowering of the symmetry of Ti(1)O{sub 6} and Ti(2)O{sub 6} octahedra. The splitting of the dielectric anomaly due to the ferroelectric phase transition was explained by the mechanism of incorporation of an impurity into different growth pyramids of the crystals. It was established that the aging of the KTP: Fe crystals leads to changes in the permittivity and electrical conductivity during long storage.

  8. Astronauts Lodewijk van den Berg observes growth of crystals in VCGS

    NASA Technical Reports Server (NTRS)

    1985-01-01

    Lodewijk van den Berg, STS 51-B payload specialist, observes the growth of mercuric iodide crystal in the vapor crystal growth system (VCGS) on the Spacelab 3 science module aboard the orbiter Challenger.

  9. Follow up on the crystal growth experiments of the LDEF

    NASA Technical Reports Server (NTRS)

    Nielsen, K. F.; Lind, M. D.

    1992-01-01

    The 4 solution growth experiments on the LDEF were presented thoroughly elsewhere. The CaCO3-experiment, and to a certain extent also the TTF-TCNQ-experiments yielded useful results. In Jan. 1992, the next series of solution growth experiments were sent to ESA for shipment to KSC. As on the LDEF, the SGF (solution growth facility) of the EURECA-1 contains 4 large experiments. From the beginning, the planning and developments were introduced. Still, the basic concept was maintained, and the CaCO3-experiment, that showed the best results on the LDEF, will now be repeated with improved technology and in larger scale on the EURECA-1. The contents of the 4 SGF experiments are as follows: (1) growth of calcium-carbonate crystals; (2) formation and transformation of tri-calcium-phosphate; (3) growth of zeolite crystals; and (4) soret coefficient measurements (diffusion). The scientific background for the choice of experiments and the major improvements of the SGF are reviewed. Furthermore, some ideas on basic microgravity solution growth experimentation from ESA's newly established EWG (Expert Working Group) on solution growth are reported.

  10. Electrochemical Liquid-Liquid-Solid (ec-LLS) Crystal Growth: A Low-Temperature Strategy for Covalent Semiconductor Crystal Growth.

    PubMed

    Fahrenkrug, Eli; Maldonado, Stephen

    2015-07-21

    This Account describes a new electrochemical synthetic strategy for direct growth of crystalline covalent group IV and III-V semiconductor materials at or near ambient temperature conditions. This strategy, which we call "electrochemical liquid-liquid-solid" (ec-LLS) crystal growth, marries the semiconductor solvation properties of liquid metal melts with the utility and simplicity of conventional electrodeposition. A low-temperature liquid metal (i.e., Hg, Ga, or alloy thereof) acts simultaneously as the source of electrons for the heterogeneous reduction of oxidized semiconductor precursors dissolved in an electrolyte as well as the solvent for dissolution of the zero-valent semiconductor. Supersaturation of the semiconductor in the liquid metal triggers eventual crystal nucleation and growth. In this way, the liquid electrolyte-liquid metal-solid crystal phase boundary strongly influences crystal growth. As a synthetic strategy, ec-LLS has several intrinsic features that are attractive for preparing covalent semiconductor crystals. First, ec-LLS does not require high temperatures, toxic precursors, or high-energy-density semiconductor reagents. This largely simplifies equipment complexity and expense. In practice, ec-LLS can be performed with only a beaker filled with electrolyte and an electrical circuit capable of supplying a defined current (e.g., a battery in series with a resistor). By this same token, ec-LLS is compatible with thermally and chemically sensitive substrates (e.g., plastics) that cannot be used as deposition substrates in conventional syntheses of covalent semiconductors. Second, ec-LLS affords control over a host of crystal shapes and sizes through simple changes in common experimental parameters. As described in detail herein, large and small semiconductor crystals can be grown both homogeneously within a liquid metal electrode and heterogeneously at the interface of a liquid metal electrode and a seed substrate, depending on the particular details chosen for ec-LLS. Third, the rate of introduction of zero-valent materials into the liquid metal is precisely gated with a high degree of resolution by the applied potential/current. The intent of this Account is to summarize the key elements of ec-LLS identified to date, first contextualizing this method with respect to other semiconductor crystal growth methods and then highlighting some unique capabilities of ec-LLS. Specifically, we detail ec-LLS as a platform to prepare Ge and Si crystals from bulk- (?1 cm(3)), micro- (?10(-10) cm(3)), and nano-sized (?10(-16) cm(3)) liquid metal electrodes in common solvents at low temperature. In addition, we describe our successes in the preparation of more compositionally complex binary covalent III-V semiconductors. PMID:26132141

  11. Crystal growth in porous materials—I: The crystallization pressure of large crystals

    Microsoft Academic Search

    Michael Steiger

    2005-01-01

    A critical review of the existing literature on the pressure exerted by growing crystals in porous materials reveals that a number of different equations are in use. A derivation of an equation for the crystallization pressure based on the chemical potentials of the loaded and the unloaded faces of a growing crystal is provided. The equation obtained is compared to

  12. Detached and Floating-Zone Growth of Semiconductor Crystals on the ISS

    NASA Technical Reports Server (NTRS)

    Dold, P.; Kaiser, N.; Benz, K. W.; Croell, A.; Szofran, F. R.; Cobb, S.; Volz, M.; Schweizer, M.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    Understanding the mechanism of detached Bridgman growth and establishing the growth of large scale germanium-silicon crystals by the float-zone technique are the key points of the project "RDGS - Reduction of Defects in Germanium-Silicon". The contact angle of the melt and the growth angle of the crystal are essential parameters which allow a controlled use of detached growth. The contact angle was determined for a variety of different substrates and melt compositions; pBN showed the highest value for pure germanium as well as for germanium-rich GeSi melts. The growth angle of Ge(sub 0.95) Si(sub 0.05) was measured to be 8.5-10.5 degrees which concurs with the values of pure germanium and silicon, respectively. The temperature dependence and the concentration dependence of the surface tension were determined for concentrations up to 10at% silicon (partial derivative (gamma)/partial derivative T=-0.08 (raised dot) 10(exp -3)N/m (raised dot) K, partial derivative (gamma)/partial derivative (C)=2.2 (raised dot) 10(exp -3)N/m (raised dot) at%). Using these values, the critical Marangoni number indicating the transition to time-dependent thermocapillary flow will be exceeded for the growth of large scale float-zone crystals onboard the ISS. Therefore, suitable tools for flow control are required.

  13. Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar

    2002-01-01

    Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 4(sub 3) helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.

  14. Microrobotic Streak Seeding For Protein Crystal Growth CUCS-041-04

    E-print Network

    Microrobotic Streak Seeding For Protein Crystal Growth CUCS-041-04 Atanas Georgiev1 , Peter K the task known as crystal mounting that consists of picking an individual protein crystal from its growth Abstract We present a microrobotic system for protein crystal micromanipulation tasks. The focus

  15. Crystals

    NSDL National Science Digital Library

    Lawrence Hall of Science

    2009-01-01

    In this earth science/math/art activity, learners use simple ingredients to grow crystals and examine the repeating geometric shapes and patterns. Learners compare the growth of crystals from four types of crystal-starters (table salt, Borax, sand, and Epsom salt) to see which starter grows the most crystals in 14 days. Learners report their results online and find out what other learners discovered. Afterward, learners can use the crystals they grew to create works of art.

  16. The growth of ZnO crystals from the melt

    E-print Network

    Klimm, D; Schulz, D; Fornari, R

    2008-01-01

    The peculiar properties of zinc oxide (ZnO) make this material interesting for very different applications like light emitting diodes, lasers, and piezoelectric transducers. Most of these applications are based on epitaxial ZnO layers grown on suitable substrates, preferably bulk ZnO. Unfortunately the thermochemical properties of ZnO make the growth of single crystals difficult: the triple point 1975 deg C., 1.06 bar and the high oxygen fugacity at the melting point p_O2 = 0.35 bar lead to the prevailing opinion that ZnO crystals for technical applications can only be grown either by a hydrothermal method or from "cold crucibles" of solid ZnO. Both methods are known to have significant drawbacks. Our thermodynamic calculations and crystal growth experiments show, that in contrast to widely accepted assumptions, ZnO can be molten in metallic crucibles, if an atmosphere with "self adjusting" p_O2 is used. This new result is believed to offer new perspectives for ZnO crystal growth by established standard techn...

  17. Crystal growth and characterization of rare-earth-doped gallates of alkaline earth and lanthanum

    NASA Astrophysics Data System (ADS)

    Ryba-Romanowski, Witold; Golab, Stanislaw; Berkowski, Marek

    1991-08-01

    We present the results of investigation of crystal growth optical and mechanical properties of optically uniaxial and piezoelectric crystals Owing to several advantages the crystals are well suited for practical application as laser active materials or high temperature piezoelectric sensors. I . I NT R 0 D U C T I 0 N During past few years a considerable progress has been made in the growing technique of single crystals of compounds with a general chemical formula ABC3O7 where A:Ba B:La Sm and C : Al Several compounds belonging to that large family were first obtained in the polycrystalline form y sintering the stoichiometric mixture of oxides at high temperature. 1 Preliminary x-ray investigation indicated that the crystals were of tetragonal symmetry space group P421m - D32d. Since all these compounds have identical structure and nearly the same unit cell parameters can expect that they will form solid solutions with a nonlimited or limited mutual solubility. In this paper we summarize the available information concernig the crystal growth and properties of two representatives of these compounds.

  18. Temperature and Enhanced Adduct Mobility on the Growth of MMTWNMP Single Crystals

    NASA Astrophysics Data System (ADS)

    Srinivasan, R.; Raghavan, C. M.; Saravanan, L.; Jayavel, R.; Baskar, K.

    2011-07-01

    A novel organometallic nonlinear optical crystal material; diaquatetrakis (thiocyanato) manganese (II) mercury (II)-N-methyl-2-pyrrolidone, MnHg(SCN)4(H2O)2.2(C3H6CONCH3), (abbreviated as MMTWNMP) of very good transparency was grown by low temperature solution growth method. The improvement on the quality of the single crystal was analyzed and explained based on the temperature effect and the mobility of adduct N-Methyl Pyrrolidone molecules. A mechanism for the basic mass transport is proposed and reasoned.

  19. ELSEVIER Journal of Crystal Growth 139 (1994) 134--146 Segregation and flow during the solidification of alloys

    E-print Network

    Huppert, Herbert

    1994-01-01

    M CRYSTAL GROWTH ELSEVIER Journal of Crystal Growth 139 (1994) 134--146 Segregation and flow during in which solid crystals are bathed in ity solution for growth of a planar crystal front in liquid by the detailed [11and was extended by Ruhinstein [2] to simple study of the growth of individual crystals

  20. Thermal-mechanical modeling of single crystal AlN and GaN

    NASA Astrophysics Data System (ADS)

    Karvanirabori, Payman

    In this work, thermal-mechanical models are being developed, based on underlying micromechanical behavior of III-nitride single crystals at growth temperatures, for use in process design. A crystal plasticity model that is capable of capturing the underlying mechanisms of dislocation motion, multiplication, and interactions in wurtzite structure (hexagonal) crystals is defined to accurately model the elastic-plastic behavior of GaN and AlN crystals at elevated temperatures. The model for AlN is extended from relations developed for GaN based on available experimental data. Algorithms for integrating the constitutive model and computing the consistent tangent modulus are formulated, and the material model is implemented into a crystal plasticity finite element framework. Finite element models of crystal growth for different processing conditions are simulated. The simulation predicts cracking and dislocation defect density in order to improve the yield and reduce the manufacturing cost of high quality III-nitride semiconductors. Furthermore, the resulting simulation capability can be used in conjunction with relevant experiments to backout key thermal-mechanical material properties at high temperatures.

  1. ?-amylase crystal growth investigated by in situ atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Astier, J. P.; Bokern, D.; Lapena, L.; Veesler, S.

    2001-06-01

    The growth behavior of porcine pancreatic ?-amylase at defined supersaturation has been investigated by means of temperature controlled in situ atomic force microscopy (AFM). The step velocities measured by AFM were in overall agreement with the normal growth rates of an individual face measured by optical microscopy. In addition, highly local growth dynamics could be visualized. Imaging in tapping mode revealed crystalline amylase aggregates attached to the basal face and their subsequent incorporation into growing terraces producing a macrodefect. At high supersaturation ( ?=1.6) 2-D nucleation was found to be the dominating growth mechanism, whereas at lower supersaturation ( ?=1.3) the growth process appears to be defect controlled (spiral growth). The analysis of step heights on 2-D nucleation islands (monomolecular protein layers) and growth steps (two molecules in height) in combination with results from light scattering experiments suggest that a single protein molecule is the basic growth unit.

  2. Observations of an Impurity-driven Hysteresis Behavior in Ice Crystal Growth at Low Pressure

    E-print Network

    Libbrecht, Kenneth G.

    Observations of an Impurity-driven Hysteresis Behavior in Ice Crystal Growth at Low Pressure Abstract. We describe observations of a novel hysteresis behavior in the growth of ice crystals under near the growth velocity vn normal to the surface of a crystal facet in terms of the Hertz-Knudsen formula vn

  3. Crystal nucleation and cluster-growth kinetics in a model glass under shear

    E-print Network

    Paris-Sud XI, Université de

    Crystal nucleation and cluster-growth kinetics in a model glass under shear Anatolii V. Mokshin1, 2010) Crystal nucleation and growth processes induced by an externally applied shear strain in a model The study of phase transformation between liquid and crystal through a nucleation and subsequent growth

  4. 12 Journal of Crystal Growth 79 (1986) 12--18 North-Holland, Amsterdam

    E-print Network

    Huppert, Herbert

    1986-01-01

    12 Journal of Crystal Growth 79 (1986) 12--18 North-Holland, Amsterdam MULTICOMPONENT, the components might be heat and corn- results to areas of crystal growth, geology and position or two different that influence sity is everywhere increasing with depth. This is both the rate of crystal growth and the develop

  5. A MATHEMATICAL MODEL FOR CRYSTAL GROWTH BY AGGREGATION OF PRECURSOR METASTABLE NANOPARTICLES

    E-print Network

    A MATHEMATICAL MODEL FOR CRYSTAL GROWTH BY AGGREGATION OF PRECURSOR METASTABLE NANOPARTICLES;Submitted to Journal of Physical Chemistry B A Mathematical Model for Crystal Growth by Aggregation;Abstract A mathematical model is developed to describe aggregative crystal growth, including oriented

  6. Journal of Crystal Growth 232 (2001) 273284 Precision measurement of ternary diffusion coefficients and

    E-print Network

    Annunziata, Onofrio

    2001-01-01

    Journal of Crystal Growth 232 (2001) 273­284 Precision measurement of ternary diffusion coefficients and implications for protein crystal growth: lysozyme chloride in aqueous ammonium chloride at 258 the driving force for nucleation and crystal growth of lysozyme chloride. # 2001 Elsevier Science B.V. All

  7. A Local Cellular Model for Snow Crystal Growth (preprint) Clifford A. Reiter

    E-print Network

    Reiter, Clifford A.

    1 A Local Cellular Model for Snow Crystal Growth (preprint) Clifford A. Reiter Department to investigate the impact of varying conditions of growth. Introduction Snow crystals exhibit remarkable crystals. Our goal is to create a simple local model for snowflake growth that exhibits the variety of 2

  8. A Numerical Study of Anisotropic Crystal Growth with Bunching under Very Singular

    E-print Network

    Soatto, Stefano

    A Numerical Study of Anisotropic Crystal Growth with Bunching under Very Singular Vertical bunching effect in crystal growth under curvature and a singular vertical diffusive regularization. Our assump- tion is that the mobility of the growth depends on the height of the given crystal

  9. A THERMAL ELASTIC MODEL FOR DIRECTIONAL CRYSTAL GROWTH WITH WEAK ANISOTROPY

    E-print Network

    Huang, Huaxiong

    A THERMAL ELASTIC MODEL FOR DIRECTIONAL CRYSTAL GROWTH WITH WEAK ANISOTROPY JINBIAO WU, C. SEAN and material anisotropy are considered and our solution can be applied to crystals grown by various growth. Key words. Crystal growth, asymptotic expansion, anisotropy, facet formation, thermal stress

  10. IGR Report on GR/M47249 Crystal Growth of Novel Oxides with a Light Furnace

    E-print Network

    Boothroyd, Andrew

    1 IGR Report on GR/M47249 Crystal Growth of Novel Oxides with a Light Furnace AT Boothroyd, SJ clear that a crystal- growth facility was needed to provide a reliable and plentiful supply of new the world in crystal growth of new materials The present grant provided funding to install and operate

  11. Bulk PPKTP by crystal growth from high temperature solution , B. Mnaert a

    E-print Network

    Paris-Sud XI, Université de

    Bulk PPKTP by crystal growth from high temperature solution A. Peña a , B. Ménaert a , B. Boulanger-poled LiNbO3 (PPLN) crystal, another ferroelectric medium widely used for QPM [10]. In situ growth generation (OPG) [12]. Here we propose a crystal growth process starting from a thin seed of PPKTP obtained

  12. 1529-6466/03/0054-0003$05.00 Principles of Crystal Nucleation and Growth

    E-print Network

    Dove, Patricia M.

    1529-6466/03/0054-0003$05.00 Principles of Crystal Nucleation and Growth James J. De Yoreo tool for students of biomineralization. However, crystal growth is a science of great breadth and depth reviews that specifically address the crystal growth field of study as it relates to biomineral formation

  13. Precision Measurements of Ice Crystal Growth Rates Kenneth G. Libbrecht1

    E-print Network

    Libbrecht, Kenneth G.

    Precision Measurements of Ice Crystal Growth Rates Kenneth G. Libbrecht1 Department of Physics precise measurements of the growth rates of the principal facets of ice crystals. Particular attention Introduction The growth of snow crystals from water vapor in air is governed by a number of factors, with vapor

  14. Journal of Crystal Growth 280 (2005) 587593 Optimization of the mineral content in polymeric gels

    E-print Network

    Azad, Abdul-Majeed

    2005-01-01

    Journal of Crystal Growth 280 (2005) 587­593 Optimization of the mineral content in polymeric gels that the optimal growth of hydroxyapatite crystals will take place at the stoichiometric Ca/P molar ratio of 1 other than the formation and growth of hydroxyapatite crystals. Therefore, the optimal level

  15. The in uence of the crystal lattice on coarsening in unstable epitaxial growth

    E-print Network

    Biehl, Michael

    The in uence of the crystal lattice on coarsening in unstable epitaxial growth M. Ahr 1#3; , M of epitaxial growth in the presence of a large Schwoebel barrier on di#11;erent crystal surfaces: simple cubic theoretical under- standing of the late phases of epitaxial crystal growth is still lacking

  16. A Critical Look at Ice Crystal Growth Data KENNETH G. LIBBRECHT1

    E-print Network

    Libbrecht, Kenneth G.

    , as is the structure of ice Ih, the normal form of ice. And yet, the growth of ice crystals from the vapor exhibitsA Critical Look at Ice Crystal Growth Data KENNETH G. LIBBRECHT1 Norman Bridge Laboratory. I review published data relating to the growth of ice crystals from water vapor under various

  17. III-V semiconductor solid solution single crystal growth

    NASA Technical Reports Server (NTRS)

    Gertner, E. R.

    1982-01-01

    The feasibility and desirability of space growth of bulk IR semiconductor crystals for use as substrates for epitaxial IR detector material were researched. A III-V ternary compound (GaInSb) and a II-VI binary compound were considered. Vapor epitaxy and quaternary epitaxy techniques were found to be sufficient to permit the use of ground based binary III-V crystals for all major device applications. Float zoning of CdTe was found to be a potentially successful approach to obtaining high quality substrate material, but further experiments were required.

  18. The growth of InP crystals from the melt

    Microsoft Academic Search

    K. J. Bachmann; E. Buehler

    1974-01-01

    The growth of InP crystals from the melt is discussed on the basis of new data on the pTx relations for the In\\/P system in\\u000a the vicinity of stoichiometric InP. The preparation of nominally undoped n-type material by the gradient-freeze technique\\u000a with visual control of the seeding process is described. Zn- and Cd-doped p-type crystals were prepared in a modified

  19. Breadboard activities for advanced protein crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Banish, Michael

    1993-01-01

    The proposed work entails the design, assembly, testing, and delivery of a turn-key system for the semi-automated determination of protein solubilities as a function of temperature. The system will utilize optical scintillation as a means of detecting and monitoring nucleation and crystallite growth during temperature lowering (or raising, with retrograde solubility systems). The deliverables of this contract are: (1) turn-key scintillation system for the semi-automatic determination of protein solubilities as a function of temperature, (2) instructions and software package for the operation of the scintillation system, and (3) one semi-annual and one final report including the test results obtained for ovostatin with the above scintillation system.

  20. Crystal growth, morphology, thermal and spectral studies of an organosulfur nonlinear optical bis(guanidinium) 5-sulfosalicylate (BG5SS) single crystals

    NASA Astrophysics Data System (ADS)

    Dhavamurthy, M.; Peramaiyan, G.; Babu, K. Syed Suresh; Mohan, R.

    2015-04-01

    Organosulfur nonlinear optical single crystals of orthorhombic bis(guanidinium) 5-sulfosalicylate (2CH6N3 +·C7H4O6S2-·H2O) with dimension 14 mm × 4 mm × 5 mm have been grown from methanol and water solvents in 1:1 ratio by the slow evaporation growth technique. The crystal structure and morphology of the crystals have been studied by single-crystal X-ray diffraction. FTIR spectroscopic studies were carried out to identify the functional groups and vibrational modes present in the grown crystals. The UV-Vis spectrum was studied to analyze the linear optical properties of the grown crystals. The thermal gravimetric analysis was conducted on the grown crystals, and the result revealed that the grown crystal is thermally stable up to 65 °C. The dielectric tensor components ? 11, ? 22 and ? 33 of BG5SS crystal were evaluated as a function of frequency at 40 °C. The surface laser damage threshold for the grown crystal was measured using Nd:YAG laser. Further, Vickers micro-hardness study was carried out to analyze the mechanical strength of the grown crystals for various loads.

  1. Bulk crystal growth of scintillator materials for gamma ray detectors

    NASA Astrophysics Data System (ADS)

    Aggarwal, Mohan

    2008-10-01

    Within the past few years, it has been demonstrated that several new rare earth halide scintillation detector crystals such as cerium doped lanthanum bromide (LaBr3:Ce) have high output and improved energy deposit to light linearity and thus they can substantially enhance the performance of the next generation of gamma ray detectors. These detectors have a variety of applications in NASA hard x-ray and gamma ray missions, high energy physics, home land security and medical imaging applications. This cerium doped lanthanum bromide crystal has ˜1100% the light output of BGO, resulting in better energy resolution than conventional scintillators. This is equivalent to 60000 photons per MeV of deposited energy. This new series of scintillator materials promise to usher a breakthrough in the field, if sufficiently large and clear crystals of this material can be grown. These halides however are highly hygroscopic and hence pose some difficulty in growing crystals. Efforts are being made to grow this and other materials in this family of crystals and successful results have been achieved. An overview of the challenges encountered during the synthesis and melt crystal growth of these rare earth halide scintillators shall be presented.

  2. Statistical Analysis of Crystallization Database Links Protein Physico-Chemical Features with Crystallization Mechanisms

    PubMed Central

    Fusco, Diana; Barnum, Timothy J.; Bruno, Andrew E.; Luft, Joseph R.; Snell, Edward H.; Mukherjee, Sayan; Charbonneau, Patrick

    2014-01-01

    X-ray crystallography is the predominant method for obtaining atomic-scale information about biological macromolecules. Despite the success of the technique, obtaining well diffracting crystals still critically limits going from protein to structure. In practice, the crystallization process proceeds through knowledge-informed empiricism. Better physico-chemical understanding remains elusive because of the large number of variables involved, hence little guidance is available to systematically identify solution conditions that promote crystallization. To help determine relationships between macromolecular properties and their crystallization propensity, we have trained statistical models on samples for 182 proteins supplied by the Northeast Structural Genomics consortium. Gaussian processes, which capture trends beyond the reach of linear statistical models, distinguish between two main physico-chemical mechanisms driving crystallization. One is characterized by low levels of side chain entropy and has been extensively reported in the literature. The other identifies specific electrostatic interactions not previously described in the crystallization context. Because evidence for two distinct mechanisms can be gleaned both from crystal contacts and from solution conditions leading to successful crystallization, the model offers future avenues for optimizing crystallization screens based on partial structural information. The availability of crystallization data coupled with structural outcomes analyzed through state-of-the-art statistical models may thus guide macromolecular crystallization toward a more rational basis. PMID:24988076

  3. K-feldspar phenocrysts in microgranular magmatic enclaves: A cathodoluminescence and geochemical study of crystal growth as a marker of magma mingling dynamics

    NASA Astrophysics Data System (ADS)

    S?aby, Ewa; Götze, Jens; Wörner, Gerhard; Simon, Klaus; Wrzalik, Roman; ?migielski, Micha?

    2008-09-01

    The crystallization history of zoned K-feldspar phenocrysts in microgranular magmatic enclaves in the Karkonosze granite (SW Poland) reveals that the crystals grew in stirred coeval magmas of contrasting compositions. The growth mechanism and crystal compositions are investigated using cathodoluminescence and profiling by Electron Microprobe and Laser Ablation ICP-MS. These methods provide insight into the crystallization process and the varying compositions of the host melt. The phenocrysts show two types of growth patterns — with or without resorption interfaces. The trace-element distribution, heterogeneous across different zones and within single phenocryst zones, reflects a dynamic process of crystal growth from compositionally heterogeneous magma. Hybridization is also reflected in the density of structural Al-O --Al defects — features that relate to coupled Ba-Al incorporation into the crystal structure. Differences in structural-defect densities and crystal composition trace the degree of hybridization in the granitic magma during the growth of the K-feldspar phenocrysts.

  4. Control of crystal growth in water purification by directional freeze crystallization

    NASA Technical Reports Server (NTRS)

    Conlon, William M. (Inventor)

    1996-01-01

    A Directional Freeze Crystallization system employs an indirect contact heat exchanger to freeze a fraction of liquid to be purified. The unfrozen fraction is drained away and the purified frozen fraction is melted. The heat exchanger must be designed in accordance with a Growth Habit Index to achieve efficient separation of contaminants. If gases are dissolved in the liquid, the system must be pressurized.

  5. Guidance mechanisms in hollow-core photonic crystal fiber

    Microsoft Academic Search

    F. Benabid; P. J. Roberts

    2008-01-01

    We review recent progress on the understanding of optical guidance mechanisms in hollow-core photonic crystal fibers. Two classes of hollow-core photonic crystal fiber are identified, one guides via a photonic bandgap and the other guides by virtue of an inhibited coupling between core and cladding mode constituents. For the former fiber type, we explore how the bandgap is formed using

  6. Growth of CuCl single crystals by the top seeded solution growth method

    NASA Astrophysics Data System (ADS)

    Inoue, Tetsuo; Kuriyama, Masao; Komatsu, Hiroshi

    1991-06-01

    CuCl crystals were grown from a solution containing KCl as a flux using the top seeded solution growth method. The essential driving force for growth in this study was mass transport via the temperature gradient and the melt temperatures were kept constant during growth. This is an important distinction from the more common type of top seeded solution growth, where decreasing temperature drives the growth. The effects of the seed orientation ([100], [111] and [110]), KCl concentration (3.0-24.9 mol%) and growth rate (0.25-5.22 mm/h) upon the crystal quality were studied. The most favorable conditions were 3.0 mol% KCl and R ? 0.6 mm/h. Transparent crystals with large grain size (5-10 mm in diameter) were obtained under these conditions. The distribution of KCl inclusions and the internal strains in the crystals were also examined, using the dark-field illumination and the photo-elastic method, respectively.

  7. Susceptor for EFG crystal growth apparatus

    DOEpatents

    Menna, Andrew A. (Belmont, MA)

    1996-09-03

    An improved susceptor for a crucible/die assembly for growing tubular crystalline structures by the EFG process is provided. The crucible/die assembly comprises a die having a substantially polygonally-shaped top end surface for supporting a film of silicon feed material that is replenished from a melt in the crucible through capillary action. A hollow crystalline body is grown from the film of silicon material on the top end surface of the die. The heat susceptor is made of graphite or similar material, and has a peripheral configuration similar to that of the die. Further, the upper surface of the heat susceptor has a central land and a plurality of circumferentially-spaced upwardly extending projections. The central land thermally contacts a central portion of the lower surface of the crucible/die, and the projections thermally contact the lower surface of the crucible/die at its corners, whereby a temperature distribution is provided that permits growth of hollow bodies having more nearly constant thickness walls.

  8. Growth and characterization of new semi-organic L-proline strontium chloride monohydrate single crystals

    NASA Astrophysics Data System (ADS)

    Gupta, Manoj K.; Sinha, Nidhi; Kumar, Binay

    2011-01-01

    The present communication deals with the synthesis, single crystal growth and characterization of a new nonlinear optical material L-proline strontium chloride monohydrate ( L-PSCM). Single crystals have been grown using the slow solvent evaporation technique. Single crystal XRD analysis confirmed that the crystal belongs to the orthorhombic structure with lattice parameter a=6.6966(3) Å, b=12.4530(5) Å, c=15.2432(5) Å and space group P2 12 12 1. Presence of various functional groups in L-PSCM and protonation of the ions were confirmed by Fourier transform infrared spectroscopy (FT-IR) analysis. The melting point of the single crystal was found to be 126 °C using DSC. Ultraviolet-visible spectral analyses showed that the crystal has low UV cut-off at 226 nm combined with very good transparency of 90% in a wide range. The optical band gap was estimated to be 5.82 eV. Capacitance and dielectric-loss measurements were carried out at different temperatures in the frequency range 1 kHz-2 MHz. The dielectric constant and loss factor were found to be 21 and 0.03 at 1 kHz at room temperature, respectively. Microhardness mechanical studies show that hardness number ( Hv) increases with load for L-PSCM single crystals the by Vickers microhardness method. Second harmonic generation (SHG) efficiency was found to be 0.078 times the value of KDP.

  9. Predicting crystal structure by merging data mining with quantum mechanics

    E-print Network

    Ceder, Gerbrand

    ARTICLES Predicting crystal structure by merging data mining with quantum mechanics CHRISTOPHER C@mit.edu Published online: 9 July 2006; doi:10.1038/nmat1691 Modern methods of quantum mechanics have proved with quantum mechanics if an algorithm to direct the search through the large space of possible structures

  10. Design of ceramic springs for use in semiconductor crystal growth in microgravity

    NASA Astrophysics Data System (ADS)

    Kaforey, M. L.; Deeb, C. W.; Matthiesen, D. H.

    2000-04-01

    Segregation studies can be done in microgravity to reduce buoyancy-driven convection and investigate diffusion-controlled growth during the growth of semiconductor crystals. During these experiments, it is necessary to prevent free surface formation in order to avoid surface tension driven convection (Marangoni convection). Semiconductor materials such as gallium arsenide and germanium shrink upon melting, so a spring is necessary to reduce the volume of the growth chamber and prevent the formation of a free surface when the sample melts. A spring used in this application must be able to withstand both the high temperature and the processing atmosphere. During the growth of gallium arsenide crystals during the GTE Labs/USAF/NASA GaAs GAS Program and during the CWRU GaAs programs aboard the First and Second United States Microgravity Laboratories, springs made of pyrolytic boron nitride (PBN) leaves were used. The mechanical properties of these PBN springs have been investigated and springs having spring constants ranging from 0.25 to 25 N/mm were measured. With this improved understanding comes the ability to design springs for more general applications, and guidelines are given for optimizing the design of PBN springs for crystal growth applications.

  11. Design of Ceramic Springs for Use in Semiconductor Crystal Growth in Microgravity

    NASA Technical Reports Server (NTRS)

    Kaforey, M. F.; Deeb, C. W.; Matthiesen, D. H.

    1999-01-01

    Segregation studies can be done in microgravity to reduce buoyancy driven convection and investigate diffusion-controlled growth during the growth of semiconductor crystals. During these experiments, it is necessary to prevent free surface formation in order to avoid surface tension driven convection (Marangoni convection). Semiconductor materials such as gallium arsenide and germanium shrink upon melting, so a spring is necessary to reduce the volume of the growth chamber and prevent the formation of a free surface when the sample melts. A spring used in this application must be able to withstand both the high temperature and the processing atmosphere. During the growth of gallium arsenide crystals during the GTE Labs/USAF/NASA GaAs GAS Program and during the CWRU GaAs programs aboard the First and Second United States microgravity Laboratories, springs made of pyrolytic boron nitride (PBN) leaves were used. The mechanical properties of these PBN springs have been investigated and springs having spring constants ranging from 0.25 N/mm to 25 N/mm were measured. With this improved understanding comes the ability to design springs for more general applications, and guidelines are given for optimizing the design of PBN springs for crystal growth applications.

  12. Modelling the growth of triglycine sulphate crystals in Spacelab 3

    NASA Technical Reports Server (NTRS)

    Yoo, Hak-Do; Wilcox, William R.; Lal, Ravindra; Trolinger, James D.

    1988-01-01

    Two triglycine sulphate crystals were grown from an aqueous solution in Spacelab 3 aboard a Space Shuttle. Using a diffusion coefficient of 0.00002 sq cm/s, a computerized simulation gave reasonable agreement between experimental and theoretical crystal sizes and interferometric lines in the solution near the growing crystal. This diffusion coefficient is larger than most measured values, possibly due to fluctuating accelerations on the order of .001 g (Earth's gravity). The average acceleration was estimated to be less than .000001 g. At this level, buoyancy driven convection is predicted to add approx. 20 percent to the steady state growth rate. Only very slight distortion of the interferometric lines was observed at the end of a 33 hr run. It is suggested that the time to reach steady state convective transport may be inversely proportional to g at low g, so that the full effect of convection was not realized in these experiments.

  13. Growth and evaluation of some urea derivative crystals

    Microsoft Academic Search

    M Ardoino; L Zeng; C Razzetti; M Zha; L Zanotti; M Curti

    2000-01-01

    Looking for compounds with optical properties comparable or better than those of urea we have performed crystallization tests on phenylurea, 1,1-dimethylurea and 1,3-dimethylurea. Appreciable results have been obtained for 1,3-dimethylurea grown by the normal freezing method. The ingots display good keeping and mechanical properties. Phase matching has been achieved with an encouraging doubling efficiency.

  14. Solar furnace satellite for large diameter crystal growth in space

    NASA Technical Reports Server (NTRS)

    Overfelt, Tony; Wells, Mark; Blake, John

    1993-01-01

    Investigators worldwide are preparing experiments to test the influence of low gravity found in space on the growth of many crystalline materials. However, power limitations prevent existing space crystal growth furnaces from being able to process samples any larger than about 2 cm, and in addition, the background microgravity levels found on the Space Shuttle are not low enough to significantly benefit samples much larger than 2 cm. This paper describes a novel concept of a free-flying platform utilizing well-established solar furnace technology to enable materials processing in space experiments on large-diameter crystals. The conceptual design of this Solar Furnace Satellite is described along with its operational scenario and the anticipated g levels.

  15. Contactless heater floating zone refining and crystal growth

    NASA Technical Reports Server (NTRS)

    Kou, Sindo (Inventor); Lan, Chung-Wen (Inventor)

    1993-01-01

    Floating zone refining or crystal growth is carried out by providing rapid relative rotation of a feed rod and finish rod while providing heat to the junction between the two rods so that significant forced convection occurs in the melt zone between the two rods. The forced convection distributes heat in the melt zone to allow the rods to be melted through with a much shorter melt zone length than possible utilizing conventional floating zone processes. One of the rods can be rotated with respect to the other, or both rods can be counter-rotated, with typical relative rotational speeds of the rods ranging from 200 revolutions per minute (RPM) to 400 RPM or greater. Zone refining or crystal growth is carried out by traversing the melt zone through the feed rod.

  16. Crystallization in supercooled liquid Cu: Homogeneous nucleation and growth

    NASA Astrophysics Data System (ADS)

    E, J. C.; Wang, L.; Cai, Y.; Wu, H. A.; Luo, S. N.

    2015-02-01

    Homogeneous nucleation and growth during crystallization of supercooled liquid Cu are investigated with molecular dynamics simulations, and the microstructure is characterized with one- and two-dimensional x-ray diffraction. The resulting solids are single-crystal or nanocrystalline, containing various defects such as stacking faults, twins, fivefold twins, and grain boundaries; the microstructure is subject to thermal fluctuations and extent of supercooling. Fivefold twins form via sequential twinning from the solid-liquid interfaces. Critical nucleus size and nucleation rate at 31% supercooling are obtained from statistical runs with the mean first-passage time and survival probability methods, and are about 14 atoms and 1032 m-3s-1, respectively. The bulk growth dynamics are analyzed with the Johnson-Mehl-Avrami law and manifest three stages; the Avrami exponent varies in the range of 1-19, which also depends on thermal fluctuations and supercooling.

  17. Numerical Study of Crystal Size Distribution in Polynuclear Growth

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Hidetsugu; Ohishi, Takuma

    2015-06-01

    The crystal size distribution in polynuclear growth is numerically studied using a coupled map lattice model. The width of the size distribution depends on c/D, where c is the growth rate at interface sites and D is the diffusion constant. When c/D is sufficiently small, the width W increases linearly with c/D and saturates at large c/D. Monodisperse square and cubic crystals are obtained respectively on square and cubic lattices when c/D is sufficiently small for a small kinetic parameter b. The linear dependence of W on c/D in a parameter range of small c/D is explained by the eigenfunction for the first eigenvalue in a two-dimensional model and a mean-field model. For the mean-field model, the slope of the linear dependence is evaluated theoretically.

  18. Mechanical testing of large thallium doped sodium iodide single crystals

    NASA Technical Reports Server (NTRS)

    Lee, H. M.

    1985-01-01

    The findings of mechanical tests performed on five thallium-doped sodium iodide NaI(Tl) crystals are presented. These crystals are all in the shape of circular flat plates, 20.0 in. in diameter an d0.5 in. thick. The test setup, testing procedure, and the test data are presented. Large crystals exhibit a high degree of material plasticity, as well as a much higher strength than previously anticipated, on the order of 500 psi. Also revealed from the testing is the fact that crystal with a large number of grain boundaries developed less plasticity, and therefore less permanent deformation, than those with fewer grain boundaries.

  19. Mems-based mechanically tunable flexible photonic crystal

    Microsoft Academic Search

    Y. H. Cui; Q. Wu; J. Jeon; M. J. Kim; J.-B. Lee

    2009-01-01

    We report design, fabrication and characterization of a MEMS-based tunable flexible photonic crystal, which is comprised of a periodic array of 290 nm diameter high-index (3.46) silicon rod embedded in a low-index (1.56) SU-8. A couple of chevron electro-thermal actuators are attached to the flexible photonic crystal and tunability is achieved by mechanical force generated by the actuators. The mechanical

  20. Effects of crystal quality and preferred orientation on the irreversible growth of compact TATB cylindrical explosives

    NASA Astrophysics Data System (ADS)

    Zhang, Haobin; Xu, Jingjiang; Liu, Yu; Huang, Hui; Sun, Jie

    2013-09-01

    Three kinds of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) cylinders compacted with TATB raw materials, recrystallized near-spherical and platy TATB crystals are compared to investigate the effects of crystal quality and preferred orientation on their irreversible growth. The results show that the higher the crystal quality, the lower the irreversible volume growth. The compacted cylinders of raw material TATB, with the poorest crystal quality, possess more irreversible growth than those with recrystallized high quality TATB crystals. Irreversible growth of TATB cylinders are also affected by crystal preferred orientation. With the same crystal quality, crystal preferred orientation leads to anisotropic irreversible dimension growth, but has no effect on the volume expansion of TATB cylinders. By changing the crystal quality and preferred orientation, the deformation problem of TATB-based PBX explosives may be restricted.

  1. Diffuse interface model of diffusion-limited crystal growth

    Microsoft Academic Search

    Joseph B. Collins; Herbert Levine

    1985-01-01

    A general approach to diffusion-limited crystal growth is proposed. It consists of a modified (nonequilibrium) Cahn-Hilliard representation of the interface coupled to a diffusion equation. Arguments are given as to its superiority over previous models. These are illlustrated in a one-dimensional solution which shows how the system selects a unique interface velocity. The selection can be interpreted as the requirement

  2. Computer Simulation of Growth Process of Binary Quasi Crystal

    Microsoft Academic Search

    Yasushi Sasajima; Katsumi Adachi; Hideki Tanaka; Minoru Ichimura; Masanori Itaba; Satoru Ozawa

    1994-01-01

    We performed Monte Carlo simulation of the aggregation process of a two-component Lennard-Jones system on the two-dimensional (2D) Penrose lattice for the purpose of studying the details of the creation and growth process of quasi crystals. We adopted the potential parameter values proposed by Widom et al. [Phys. Rev. Lett. 58 (1987) 706]. The present simulation clarified that the stability

  3. Crystal grain growth during room temperature high pressure Martensitic alpha to omega transformation in zirconium

    SciTech Connect

    Velisavljevic, Nenad [Los Alamos National Laboratory; Chesnut, Gary N [Los Alamos National Laboratory; Stevens, Lewis L [Los Alamos National Laboratory; Dattelbaum, Dana M [Los Alamos National Laboratory

    2008-01-01

    Systematic increase in transition pressure with increase in interstitial impurities is observed for the martensitic {alpha} {yields} {omega} structural phase transition in Zr. Significant room temperature crystal grain growth is also observed for the two highest purity samples at this transition, while in the case of the lowest purity sample interstitial impurities obstruct grain growth even as the sample is heated to 1279 K. Our results show the importance of impurities in controlling structural phase stability and other mechanical properties associated with the {alpha} {yields} {omega} structural phase transition.

  4. Acidic peptide and polyribonucleotide crystal growth inhibitors in human urine.

    PubMed

    Ito, H; Coe, F L

    1977-11-01

    Urine contains nondialyzable inhibitors of calcium oxalate crystal growth. We have pursued the hypothesis that these inhibitors may, in part, be acidic peptides and polyribonucleotide fragments. Homopolyribonucleotides and RNA inhibit calcium oxalate crystal growth at 5 x 10(-6) M of constituent ribonucleotide, whereas the monomer nucleotides are inactive at 10(-4) M. Poly-L-aspartic or glutamic acid are also inhibitory at 5 X 10(-6) M of amino acid, whereas the monomeric amino acids are inert. Gastric pepsin, a naturally occurring acidic peptide, is inhibitory. Incubation with nonspecific protease reduced the inhibitory effectiveness of normal human urine consistently and significantly, a fact compatible with an important contribution of peptides. A variable additional reduction was produced by subsequent treatment with ribonuclease, suggesting only a small role for polyribonucleotide. Sequential ion exchange and gel filtration chromatography and preparative disc gel electrophoresis yielded inhibitory material enriched with peptides that were strongly acidic and high in proline. Peptides and ribonucleotides seem to contribute to urinary nondialyzable crystal growth inhibitory activity. PMID:920814

  5. Effect of Lead Chloride on the Growth and Surface Properties of Potassium Chloride Crystals from Aqueous Solutions

    NASA Astrophysics Data System (ADS)

    Podder, Jiban; Evitts, Richard William; Besant, Robert William

    2014-05-01

    Pure potassium chloride (KCl) and lead chloride (PbCl2)-doped KCl crystals were grown from saturated aqueous solutions by a solvent evaporation process. The effects of Pb2+ on the surface morphology, structural and mechanical properties of KCl crystal were investigated. The surface morphology of the cubic structured crystals was studied by scanning electron microscopy (SEM), X-ray diffraction and the elemental mappings at the microstructural level were determined by energy dispersive X-ray (EDX) spectroscopy. The mass growth rate was found to decrease when the Pb2+ ions were present and the volume growth flux was also found to decrease with time and initial concentration of impurity. A Vickers micro-hardness study shows that Pb-doped KCl crystals are harder than pure KCl crystals.

  6. Some Aspects of PVT Low Supersaturation Nucleation and Contactless Crystal Growth

    NASA Technical Reports Server (NTRS)

    Grasza, K.; Palosz, W.

    1996-01-01

    The basic principles of the contactless growth of crystals from the vapor in combination with the process of low-supersaturation nucleation are discussed. The mathematical formulation of the morphological stability criterion in vapor growth systems is given and its implications for contactless growth technique are analyzed. A diagram for selection of proper temperature conditions for growth of CdTe crystals is presented.

  7. Investigation on the influence of foreign metal ions in crystal growth and characterization of L-Alaninium Maleate (LAM) single crystals.

    PubMed

    Ruby Nirmala, L; Thomas Joseph Prakash, J

    2013-11-01

    A Nonlinear Optical, good quality, single crystals of doped and undoped l-Alaninium Maleate (LAM) were grown by slow evaporation solution growth technique at room temperature. The lattice parameters were analyzed by single crystal X-ray diffraction technique. The identification of Cadmium ion in the doped crystals was done using the EDAX spectrum. The presence of functional group of the dopant with LAM molecule was studied using FTIR spectra. The results of UV-Vis study is used to compare the transparencies of the doped and undoped LAM crystals. The optical band gap energy of the grown crystal was also calculated. The relative second harmonic generation (SHG) efficiency measurement with KDP reference is used to find the incorporation of metal to l-Alaninium Maleate crystals and the parent material. Also the thermal stability of the grown crystals was studied by TGA/DTA spectrum. The mechanical stability of the grown crystals was confirmed through Vickers micro hardness study. By parallel plate capacitor technique, the dielectric response was studied over a wide range of frequencies at different temperatures. The various studies showed the incorporation of the impurity Cd(2+) into LAM crystals and the investigations indicated that the impurity played an important role in the changes of the spectral and structural properties of LAM crystals. PMID:23892119

  8. A simple apparatus for controlling nucleation and size in protein crystal growth

    NASA Technical Reports Server (NTRS)

    Gernert, Kim M.; Smith, Robert; Carter, Daniel C.

    1988-01-01

    A simple device is described for controlling vapor equilibrium in macromolecular crystallization as applied to the protein crystal growth technique commonly referred to as the 'hanging drop' method. Crystal growth experiments with hen egg white lysozyme have demonstrated control of the nucleation rate. Nucleation rate and final crystal size have been found to be highly dependent upon the rate at which critical supersaturation is approached. Slower approaches show a marked decrease in the nucleation rate and an increase in crystal size.

  9. High purity germanium crystal growth at the University of South Dakota

    NASA Astrophysics Data System (ADS)

    Wang, Guojian; Mei, Hao; Mei, Dongming; Guan, Yutong; Yang, Gang

    2015-05-01

    High-purity germanium crystal growth is challenging work, requiring the control of individual crystal properties such as the impurity distribution, the dislocation density, and the crystalline structure. Currently, we grow high-purity germanium crystals by the Czochralski method in our laboratory in order to understand the details of the growing process, especially for large diameter crystals. In this paper, we report the progress of detector-grade germanium crystal growth at the University of South Dakota.

  10. Growth rates of ibuprofen crystals grown from ethanol and aqueous ethanol

    Microsoft Academic Search

    A. Rashid; E. T. White; T. Howes; J. D. Litster; I. Marziano

    To quantify the crystallization of racemic ibuprofen [2-(4-isobutyl-phenyl)-propionic acid] from aqueous ethanol it is necessary to know the growth rate kinetics. Growth rates were measured by adding SPG (size proportional growth) seed crystals to an isothermal non-nucleating batch crystallization and sampling during the batch. The supersaturation was measured by refractive index and the crystal size by laser light scattering (Malvern).

  11. The growth of benzophenone crystals by Sankaranarayanan-Ramasamy (SR) method and slow evaporation solution technique (SEST): A comparative investigation

    SciTech Connect

    Senthil Pandian, M.; Boopathi, K. [Centre for Crystal Growth, SSN College of Engineering, Kalavakkam 603 110, Tamilnadu (India)] [Centre for Crystal Growth, SSN College of Engineering, Kalavakkam 603 110, Tamilnadu (India); Ramasamy, P., E-mail: ramasamyp@ssn.edu.in [Centre for Crystal Growth, SSN College of Engineering, Kalavakkam 603 110, Tamilnadu (India); Bhagavannarayana, G. [Materials Characterization Division, National Physical Laboratory, New Delhi 110 012 (India)] [Materials Characterization Division, National Physical Laboratory, New Delhi 110 012 (India)

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer Benzophenone single crystal was grown by Sankaranarayanan-Ramasamy method which has the sizes of 1060 mm length and 55 mm diameter for the first time. Black-Right-Pointing-Pointer The conventional and SR-grown benzophenone crystals were characterized and compared using HRXRD, etching, laser damage threshold, microhardness, UV-transmittance, birefringence and dielectric analysis. Black-Right-Pointing-Pointer The SR-grown benzophenone crystal has higher LDT, microhardness, transparency, dielectric permittivity, birefringence and lower FWHM, EPD, dielectric loss than the crystal grown by conventional method. Black-Right-Pointing-Pointer The probable reason for higher crystalline perfection in SR-grown crystal was discussed. -- Abstract: Longest unidirectional Left-Pointing-Angle-Bracket 1 0 0 Right-Pointing-Angle-Bracket benzophenone (BP) crystal having dimension of 1060 mm length and 55 mm diameter was grown by Sankaranarayanan-Ramasamy method. The growth rate was measured by monitoring the elevation of the crystal-solution interface at different temperatures. The high resolution X-ray diffraction and etching measurements indicate that the unidirectional grown benzophenone crystal has good crystalline perfection and less density of defects. The optical damage threshold of SEST and SR grown BP crystals has been investigated and found that the SR grown benzophenone crystal has higher laser damage threshold value than the conventional method grown crystal. Microhardness measurement shows that crystals grown by SR method have a higher mechanical stability than the crystals grown by SEST method. Dielectric permittivity and birefringence are high in SR grown crystal compared to SEST grown BP crystal. The UV-vis-NIR results show that SR method grown crystal exhibits 7% higher transmittance as against crystals grown by conventional method.

  12. Investigating the role of oriented nucleus in polymer shish-kebab crystal growth via phase-field method.

    PubMed

    Wang, Xiaodong; Ouyang, Jie; Su, Jin; Zhou, Wen

    2014-03-21

    The phase-field method has been developed to simulate the shish-kebab crystal growth in polymer crystallization by introducing the oriented nucleus. With the help of this developed phase-field model, the role of oriented nucleus in polymer shish-kebab crystal growth has been investigated. It appears that the growth mechanisms of shish-kebab crystal on a preformed oriented nucleus may be attributed to epitaxial growth and lattice match. First the oriented nucleus (early shish) further grows into stable shish entity through epitaxial growth, and then lattice match supplies the sites for kebabs and epitaxial lateral growth from these sites forms the kebabs. It also has been verified that kebabs can be grown on oriented nucleus in the total absence of any flow. Therefore, with regard to flow induced shish-kebab crystal, the oriented nucleus plays a major role in the growth of shish-kebab morphology and the flow mainly helps to generate the oriented nucleus. Besides, when the nucleus possesses a rod-like profile, the kebabs are generally parallel and equidistantly distributed, and the well-defined interval between adjacent kebabs is strongly influenced by the orientation angle of the rod-like nucleus. On the other hand, when the nucleus is slightly curved and presents a thread-like profile, the distribution of kebabs on the shish is no longer equidistant and the influence of orientation angle on the kebab density becomes weak. PMID:24655167

  13. Growth rates anisotropy of synthetic quartz crystals grown on Z-cut hexagonal seeds and computer simulations of growth process

    Microsoft Academic Search

    H. Iwasaki; F. Iwasaki; V. S. Balitsky; L. V. Balitskaya; I. B. Makhina

    1998-01-01

    In quartz crystals grown on Z-cut hexagonal seeds in Na2CO3 solution, relations between specific sizes on as-grown crystal and growth rates normal to principal faces, R,r,m,Z, were formulated by two procedures; geometrical scheme on crystal form and crystal growth scheme by computer experiments. Growth rates, gr(R), gr(r), gr(m), gr(Z), were evaluated respectively to be 0.017, 0.046, 0.0016, 0.25(mm\\/d). The growth

  14. Bacterial growth and form under mechanical compression

    PubMed Central

    Si, Fangwei; Li, Bo; Margolin, William; Sun, Sean X.

    2015-01-01

    A combination of physical and chemical processes is involved in determining the bacterial cell shape. In standard medium, Escherichia coli cells are rod-shaped, and maintain a constant diameter during exponential growth. Here, we demonstrate that by applying compressive forces to growing E. coli, cells no longer retain their rod-like shapes but grow and divide with a flat pancake-like geometry. The deformation is reversible: deformed cells can recover back to rod-like shapes in several generations after compressive forces are removed. During compression, the cell elongation rate, proliferation rate, DNA replication rate, and protein synthesis are not significantly altered from those of the normal rod-shaped cells. Quantifying the rate of cell wall growth under compression reveals that the cell wall growth rate depends on the local cell curvature. MreB not only influences the rate of cell wall growth, but also influences how the growth rate scales with cell geometry. The result is consistent with predictions of a mechanochemical model, and suggests an active mechanical role for MreB during cell wall growth. The developed compressive device is also useful for studying a variety of cells in unique geometries. PMID:26086542

  15. Utilizing Controlled Vibrations in a Microgravity Environment to Understand and Promote Microstructural Homogeneity During Floating-Zone Crystal Growth

    NASA Technical Reports Server (NTRS)

    Grugel, Richard N.

    1999-01-01

    It has been demonstrated in floating-zone configurations utilizing silicone oil and nitrate salts that mechanically induced vibration effectively minimizes detrimental, gravity independent, thermocapillary flow. The processing parameters leading to crystal improvement and aspects of the on-going modeling effort are discussed. Plans for applying the crystal growth technique to commercially relevant materials, e.g., silicon, as well as the value of processing in a microgravity environment are presented.

  16. Crucible materials for growth of aluminum nitride crystals

    NASA Astrophysics Data System (ADS)

    Schlesser, R.; Dalmau, R.; Zhuang, D.; Collazo, R.; Sitar, Z.

    2005-07-01

    The growth of aluminum nitride (AlN) bulk crystals by sublimation of an AlN source requires elevated temperatures, typically in a range of 1800-2300 °C. These temperature requirements, combined with the chemically aggressive nature of the Al vapor, severely limit the choice of reactor hot-zone materials, and most notably, the selection of reaction crucibles. Aside from refractory elements, potentially promising compound materials include refractory nitrides, carbides, and borides. In this work, TaC crucibles were fabricated using a binderless sintering process and were tested in AlN bulk growth experiments. Elemental analysis of crystals grown in these crucibles revealed extremely low Ta contamination, below the analytical detection limit of 1 ppm by weight and C contamination levels as low as 50 ppm by weight; C contamination likely originated from sources unrelated to the crucible material. Crucibles were re-used in several consecutive growth runs; average crucible lifetimes exceeded 200 h at growth temperatures exceeding 2200 °C.

  17. Development of SiC Large Tapered Crystal Growth

    NASA Technical Reports Server (NTRS)

    Neudeck, Phil

    2011-01-01

    Research Focus Area: Power Electronics, Temperature Tolerant Devices. Demonstrate initial feasibility of totally new "Large Tapered Crystal" (LTC) process for growing vastly improved large-diameter wide-band gap wafers. Addresses Targets: The goal of this research is to experimentally investigate and demonstrate feasibility of the key unproven LTC growth processes in SiC. Laser-assisted growth of long SiC fiber seeds. Radial epitaxial growth enlargement of seeds into large SiC boules. Uniqueness and Impacts open a new technology path to large-diameter SiC and GaN wafers with 1000-fold defect density improvement at 2-4 fold lower cost. Leapfrog improvement in wide band gap power device capability and cost.

  18. Development of SiC Large Tapered Crystal Growth

    NASA Technical Reports Server (NTRS)

    Neudeck, Phil

    2011-01-01

    Objective center dot Demonstrate initial feasibility of totally new "Large Tapered Crystal" (LTC) process for growing vastly improved large-diameter wide-band gap wafers. Research Focus Area: Power Electronics è? Temperature Tolerant Devices 3 Addresses Targets center dot The goal of this research is to experimentally investigate and demonstrate feasibility of the key unproven LTC growth processes in SiC. center dot Laser-assisted growth of long SiC fiber seeds. center dot Radial epitaxial growth enlargement of seeds into large SiC boules. Uniqueness and Impacts center dot Open a new technology path to large-diameter SiC and GaN wafers with 1000-fold defect density improvement at 2-4 fold lower cost. center dot Leapfrog improvement in wide band gap power device capability and cost.

  19. Nucleation and Crystal Growth of Organic-Inorganic Lead Halide Perovskites under Different Relative Humidity.

    PubMed

    Gao, Hao; Bao, Chunxiong; Li, Faming; Yu, Tao; Yang, Jie; Zhu, Weidong; Zhou, Xiaoxin; Fu, Gao; Zou, Zhigang

    2015-05-01

    Organic-inorganic lead halide perovskite compounds are very promising materials for high-efficiency perovskite solar cells. But how to fabricate high-quality perovksite films under controlled humidity conditions is still an important issue due to their sensitivity to moisture. In this study, we investigated the influence of ambient humidity on crystallization and surface morphology of one-step spin-coated perovskite films, as well as the performance of solar cells based on these perovskite films. On the basis of experimental analyses and thin film growth theory, we conclude that the influence of ambient humidity on nucleation at spin-coating stage is quite different from that on crystal growth at annealing stage. At the spin-coating stage, high nucleation density induced by high supersaturation prefers to appear under anhydrous circumstances, resulting in layer growth and high coverage of perovskite films. But at the annealing stage, the modest supersaturation benefits formation of perovskite films with good crystallinity. The films spin-coated under low relative humidity (RH) followed by annealing under high RH show an increase of crystallinity and improved performance of devices. Therefore, a mechanism of fast nucleation followed by modest crystal growth (high supersaturation at spin-coating stage and modest supersaturation at annealing stage) is suggested in the formation of high-quality perovskite films. PMID:25871284

  20. Dynamic Light Scattering Study of Inhibition of Nucleation and Growth of Hydroxyapatite Crystals by Osteopontin

    PubMed Central

    de Bruyn, John R.; Goiko, Maria; Mozaffari, Maryam; Bator, Daniel; Dauphinee, Ron L.; Liao, Yinyin; Flemming, Roberta L.; Bramble, Michael S.; Hunter, Graeme K.; Goldberg, Harvey A.

    2013-01-01

    We study the effect of isoforms of osteopontin (OPN) on the nucleation and growth of crystals from a supersaturated solution of calcium and phosphate ions. Dynamic light scattering is used to monitor the size of the precipitating particles and to provide information about their concentration. At the ion concentrations studied, immediate precipitation was observed in control experiments with no osteopontin in the solution, and the size of the precipitating particles increased steadily with time. The precipitate was identified as hydroxyapatite by X-ray diffraction. Addition of native osteopontin (nOPN) extracted from rat bone caused a delay in the onset of precipitation and reduced the number of particles that formed, but the few particles that did form grew to a larger size than in the absence of the protein. Recombinant osteopontin (rOPN), which lacks phosphorylation, caused no delay in initial calcium phosphate precipitation but severely slowed crystal growth, suggesting that rOPN inhibits growth but not nucleation. rOPN treated with protein kinase CK2 to phosphorylate the molecule (p-rOPN) produced an effect similar to that of nOPN, but at higher protein concentrations and to a lesser extent. These results suggest that phosphorylations are critical to OPN’s ability to inhibit nucleation, whereas the growth of the hydroxyapatite crystals is effectively controlled by the highly acidic OPN polypeptide. This work also demonstrates that dynamic light scattering can be a powerful tool for delineating the mechanism of protein modulation of mineral formation. PMID:23457612

  1. A simple method for systematically controlling ZnO crystal size and growth orientation

    SciTech Connect

    Zhang Rong [Department of Paper and Chemical Engineering, Miami University, Oxford, OH 45056 (United States); Kerr, Lei L. [Department of Paper and Chemical Engineering, Miami University, Oxford, OH 45056 (United States)], E-mail: kerrll@muohio.edu

    2007-03-15

    We present a simple, easy and reproducible method to systematically control the dimension and shape evolution of zinc oxide (ZnO) as thin film on glass substrate by chemical bath deposition (CBD). The only varying factor to control crystal transformation is the molar ratio of Cd{sup 2+}/Zn{sup 2+}, R{sub m}, in the initial chemical solution. With the increase of R{sub m}, ZnO crystals transformed from long-and-slim hexagonal rods to fat-and-short hexagonal pyramids, and then to twinning hexagonal dots as observed by scanning electron microscopy (SEM). Film crystallinity was characterized by X-ray diffraction (XRD). Chemical component analysis by energy dispersive spectroscopy (EDS) showed that most cadmium was present in the residual solution instead of the developed film and the precipitate at the bottom of beaker. The mechanism of the cadmium effect, with different initial concentrations, on ZnO crystal transformation was tentatively addressed. We believe that cadmium influences the chelate ligands adsorption onto (0001-bar) plane of ZnO crystals, alters the crystal growth orientation, and thus directs the transformation of the size and shape of ZnO crystals.

  2. The mechanism of grain growth in ceramics

    NASA Technical Reports Server (NTRS)

    Kapadia, C. M.; Leipold, M. H.

    1972-01-01

    The theory of grain boundary migration as a thermally activated process is reviewed, the basic mechanisms in ceramics being the same as in metals. However, porosity and non-stochiometry in ceramic materials give an added dimension to the theory and make quantitative treatment of real systems rather complex. Grain growth is a result of several simultaneous (and sometimes interacting) processes; these are most easily discussed separately, but the overall rate depends on their interaction. Sufficient insight into the nature of rate controlling diffusion mechanisms is necessary before a qualitative understanding of boundary mobility can be developed.

  3. Influence of vacuum degree on growth of Bi2Te3 single crystal

    NASA Astrophysics Data System (ADS)

    Tang, Yan-Kun; Zhao, Wen-Juan; Zhu, Hua-Qiang; Huang, Yong-Chao; Cao, Wei-Wei; Yang, Qian; Yao, Xiao-Yan; Zhai, Ya; Dong, Shuai

    2015-07-01

    Bi2Te3 single crystals were prepared by the solid-state reaction method. The effect of the vacuum on the growth of Bi2Te3 single crystals was studied with varying the oxygen content by controlling the air pressure in the silica tube. High quality Bi2Te3 single crystals have been obtained and there is no influence on the growth by an extremely small amount of oxygen in a high vacuum at 1.0 × 10?3 Pa. As the air pressure is increased at 1.0 × 10?2 Pa, oxygen only mainly impacts on the growth of the surface for the prepared samples. Micron-sized rod-like structure and flower-like clusters are observed on the surface. For the samples prepared at 1.0 × 10?1 Pa, x-ray diffraction data show that the yellow part on the surface is Bi2TeO5, while the Bi2Te3 single crystal is still the major phase as the inside part. More interestingly, various crystal morphologies are observed by scanning electron microscope for Bi2Te3 near the boundary between Bi2Te3 and Bi2TeO5. Possible growth mechanisms for Bi2Te3 with different morphologies are discussed in detail. Project supported by the National Natural Science Foundation of China (Grant Nos. 10904013 and 11274060), the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BK2009260 and BK20141329), and the Scientific Research Staring Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of China.

  4. Phase-field simulations of dendritic crystal growth in a forced flow C. Beckermann,1,

    E-print Network

    Beckermann, Christoph

    by crystal- line anisotropy in the tip selection, and this theory has been confirmed by phase-fieldPhase-field simulations of dendritic crystal growth in a forced flow X. Tong,1 C. Beckermann,1, * A; published 15 May 2001 Convective effects on free dendritic crystal growth into a supercooled melt in two

  5. Journal of Crystal Growth 198/199 (1999) 1256--1261 Hyperbolic flow by mean curvature

    E-print Network

    Rotstein, Horacio G.

    1999-01-01

    Journal of Crystal Growth 198/199 (1999) 1256--1261 Hyperbolic flow by mean curvature Horacio G has been obtained and successfully used to model crystal growth, shrinkage processes and other types transitions; Flow by mean curvature; Crystalline curvature; Memory effects 1. Introduction Helium crystals may

  6. A new formulation for dendritic crystal growth in two E.A. Coutsias* and H. Segur

    E-print Network

    Coutsias, Evangelos

    A new formulation for dendritic crystal growth in two dimensions E.A. Coutsias* and H. Segur #3; U The objective of this paper is to study the growth of dendritic crystals in two spatial dimensions plus time other advantages, this formulation permits a larger class of behaviours far from the tip of the crystal

  7. Growth and Characterization of Yttrium Calcium Oxy Borate (YCOB) Single Crystals for Nonlinear Optical Applications

    Microsoft Academic Search

    R. Arun Kumar; M. Senthilkumar; R. Dhanasekaran

    2008-01-01

    The growth of yttrium calcium oxy borate (YCOB) single crystals by the flux technique is reported. Polycrystalline YCOB sample was synthesized and confirmed. Differential thermal analysis was carried out with lithium carbonate flux. The growth of YCOB crystals by flux technique was attempted and several crystals with dimensions of 3×3×5 mm were obtained. Powder XRD analysis confirms the formation of YCOB

  8. Modeling of facet formation in SiC bulk crystal growth

    Microsoft Academic Search

    I. D. Matukov; D. S. Kalinin; M. V. Bogdanov; S. Yu. Karpov; D. Kh. Ofengeim; M. S. Ramm; J. S. Barash; E. N. Mokhov; A. D. Roenkov; Yu. A. Vodakov; M. G. Ramm; H. Helava; Yu. N. Makarov

    2004-01-01

    Control of the crystallization front profile is of great importance for various aspects of bulk SiC crystal growth by physical vapor transport. The structural defect density, doping uniformity, and polytype stability are largely dependent on the profile evolution. In this paper, we consider the binary crystal growth from the multicomponent vapor and suggest a model of facet formation. The model

  9. Robust self-replication of combinatorial information via crystal growth and scission

    PubMed Central

    Schulman, Rebecca; Yurke, Bernard; Winfree, Erik

    2012-01-01

    Understanding how a simple chemical system can accurately replicate combinatorial information, such as a sequence, is an important question for both the study of life in the universe and for the development of evolutionary molecular design techniques. During biological sequence replication, a nucleic acid polymer serves as a template for the enzyme-catalyzed assembly of a complementary sequence. Enzymes then separate the template and complement before the next round of replication. Attempts to understand how replication could occur more simply, such as without enzymes, have largely focused on developing minimal versions of this replication process. Here we describe how a different mechanism, crystal growth and scission, can accurately replicate chemical sequences without enzymes. Crystal growth propagates a sequence of bits while mechanically-induced scission creates new growth fronts. Together, these processes exponentially increase the number of crystal sequences. In the system we describe, sequences are arrangements of DNA tile monomers within ribbon-shaped crystals. 99.98% of bits are copied correctly and 78% of 4-bit sequences are correct after two generations; roughly 40 sequence copies are made per growth front per generation. In principle, this process is accurate enough for 1,000-fold replication of 4-bit sequences with 50% yield, replication of longer sequences, and Darwinian evolution. We thus demonstrate that neither enzymes nor covalent bond formation are required for robust chemical sequence replication. The form of the replicated information is also compatible with the replication and evolution of a wide class of materials with precise nanoscale geometry such as plasmonic nanostructures or heterogeneous protein assemblies. PMID:22493232

  10. Ice crystal growth in a dynamic thermal diffusion chamber

    NASA Technical Reports Server (NTRS)

    Keller, V. W.

    1980-01-01

    Ice crystals were grown in a supersaturated environment produced by a dynamic thermal diffusion chamber, which employed two horizontal plates separated by a distance of 2.5 cm. Air was circulated between and along the 1.2 m length of the plates past ice crystals which nucleated and grew from a fiber suspended vertically between the two plates. A zoom stereo microscope with a magnification which ranged from 3X to 80X and both 35 mm still photographs and 16 mm time lapse cine films taken through the microscope were used to study the variation of the shape and linear growth rate of ice crystals as a function of the ambient temperature, the ambient supersaturation, and the forced ventilation velocity. The ambient growth conditions were varied over the range of temperature 0 to -40 C, over the range of supersaturation 4% to 50% with respect to ice, and over the range of forced ventilation velocities 0 cm/s to 20 cm/s.

  11. Synthesis, linear optical, non-linear optical, thermal and mechanical characterizations of dye-doped semi-organic NLO crystals

    NASA Astrophysics Data System (ADS)

    Sesha Bamini, N.; Vidyalakshmy, Y.; Choedak, Tenzin; Kejalakshmy, N.; Muthukrishnan, P.; Ancy, C. J.

    2015-06-01

    Organic laser dyes Coumarin 485, Coumarin 540 and Rhodamine 590 Chloride were used to dope potassium acid phthalate crystals (KAP). Dye-doped KAP crystals with different dye concentrations such as 0.01 mM, 0.03 mM, 0.05 mM, 0.07 mM and 0.09 mM (in the KAP growth solution) were grown. The linear optical, non-linear optical, mechanical and thermal characterizations of dye-doped KAP crystals were studied and compared to understand the effect of dye and dye concentration on the KAP crystal. Absorption and emission studies of KAP and dye-doped KAP single crystals indicated the inclusion of the dye into the KAP crystal lattice. The effect of dye and its concentration on the SHG efficiency of the KAP crystal was studied using the Kurtz and Perry powder technique. It was observed that the absorption maximum wavelength and concentration of the dye used for doping the KAP single crystal decided the SHG efficiency of the dye-doped KAP single crystals. The mechanical hardness of the dye-doped and undoped (pure) KAP single crystals were studied using the Vickner’s microhardness test. It was observed that doping the KAP crystals with the laser dyes changed them from softer material to harder material. Etching studies showed an improvement in the optical quality of the KAP crystal after doping with laser dyes.

  12. A discussion of mechanisms proposed to explain habit changes of vapor-grown ice crystals

    NASA Astrophysics Data System (ADS)

    Levi, Laura; Nasello, Olga B.

    In the present work, surface kinetics processes that can contribute to the growth behavior of ice crystals from the vapor phase are revised and proposed interpretations of crystal habit changes are discussed. Following the main initial papers on this subject by Hallet, Mason et al. and Kobayashi, relationships are considered between linear growth rate and step velocity. More recent results obtained by Sei and Gonda (SG2) for molecular steps naturally formed on basal and prism surfaces are shown to confirm Hallet's interpretation of previous curves obtained for the velocity of giant steps that were artificially formed on basal surfaces only. The different behavior of the condensation coefficient ?( T) characterizing growth in pure water vapor, observed by Lamb and Scott for surfaces intersecting a substrate and by Sei and Gonda for free surfaces, is discussed by considering that ? is the product of the adsorption and accommodation coefficients ? and ?, respectively. It is noted that, as in previous works, ?=1 was assumed, the variations of ? discussed to interpret crystal habit changes were made to coincide with variations of ?. However, Sei and Gonda's results show that in the temperature range where crystal habit changes are observed, values of ?( T)?1 are found. As these depend on surface orientation, they should play an important role in the phenomenon. The dependence of crystal habits on two-dimensional nucleation is also discussed on the basis of measurements carried out by Nelson and Knight of the critical supersaturation ?cr on the basal and prism surfaces. A possible relationship between the curves for ?cr( T) and those of ?( T) derived from Sei and Gonda's results is suggested. The mechanisms determining the large anisotropy exhibited by crystals grown in atmospheric conditions are discussed by taking into account that the growth rate curves R( T) on the basal and prism surfaces show a correlation between maximum and minimum values, which are not observed for crystals grown in pure vapor.

  13. Mechanical phase matching of birefringent non-linear crystals.

    PubMed

    Deyra, Loïc; Balembois, François; Guilbaud, André; Villeval, Philippe; Georges, Patrick

    2014-09-22

    Second-order nonlinear processes such as second harmonic generation or parametric amplification have found numerous applications in the scientific and industrial world, from micromachining to petawatt laser facilities. These nonlinear interactions are mostly carried out in birefringent crystals because of their low cost and the possibility to operate at high powers Phase-matching configurations in birefringent crystals are determined by their refractive indexes. Here, we show that an important mechanical stress can be used to significantly change the phase-matching properties of a birefringent crystal. As an example, we demonstrate the shift of second harmonic non-critical phase matching wavelength of LiB3O5 (LBO) crystal at room temperature from 1200 nm to 1120 nm by applying compressive forces up to 100 MPa. We believe that this mechanical phase matching can be used as an additional degree of freedom to optimize nonlinear optical frequency mixing geometries. PMID:25321800

  14. Struvite crystal growth inhibition by trisodium citrate and the formation of chemical complexes in growth solution

    NASA Astrophysics Data System (ADS)

    Prywer, Jolanta; Mielniczek-Brzóska, Ewa; Olszynski, Marcin

    2015-05-01

    Effect of trisodium citrate on the crystallization of struvite was studied. To evaluate such an effect an experiment of struvite growth from artificial urine was performed. The investigations are related to infectious urinary stones formation. The crystallization process was induced by the addition of aqueous ammonia solution to mimic the bacterial activity. The spectrophotometric results demonstrate that trisodium citrate increases induction time with respect to struvite formation and decreases the growth efficiency of struvite. The inhibitory effect of trisodium citrate on the nucleation and growth of struvite is explained in base of chemical speciation analysis. Such an analysis demonstrates that the inhibitory effect is related with the fact that trisodium citrate binds NH4 + and Mg2+ ions in the range of pH from 7 to 9.5 characteristic for struvite precipitation. The most important is the MgCit- complex whose concentration strongly depends on an increase in pH rather than on an increase in citrate concentrations.

  15. Atomic force microscopy of insulin single crystals: direct visualization of molecules and crystal growth.

    PubMed Central

    Yip, C M; Ward, M D

    1996-01-01

    Atomic force microscopy performed on single crystals of three different polymorphs of bovine insulin revealed molecularly smooth (001) layers separated by steps whose heights reflect the dimensions of a single insulin hexamer. Whereas contact mode imaging caused etching that prevented molecular-scale resolution, tapping mode imaging in solution provided molecular-scale contrast that enabled determination of lattice parameters and polymorph identification while simultaneously enabling real-time examination of growth modes and assessment of crystal quality. Crystallization proceeds layer by layer, a process in which the protein molecules assemble homoepitaxially with nearly perfect orientational and translational commensurism. Tapping mode imaging also revealed insulin aggregates attached to the (001) faces, their incorporation into growing terraces, and their role in defect formation. These observations demonstrate that tapping mode imaging is ideal for real-time in situ investigation of the crystallization of soft protein crystals of relatively small proteins such as insulin, which cannot withstand the lateral shear forces exerted by the scanning probe in conventional imaging modes. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 PMID:8842243

  16. Solution Growth and Characterization of Single Crystals on Earth and in Microgravity

    NASA Technical Reports Server (NTRS)

    Aggarwal, M. D.; Currie, J. R.; Penn, B. G.; Batra, A. K.; Lal, R. B.

    2007-01-01

    Crystal growth has been of interest to physicists and engineers for a long time because of their unique properties. Single crystals are utilized in such diverse applications as pharmaceuticals, computers, infrared detectors, frequency measurements, piezoelectric devices, a variety of high-technology devices, and sensors. Solution crystal growth is one of the important techniques to grow a variety of crystals when the material decomposes at the melting point and a suitable solvent is available to make a saturated solution at a desired temperature. In this Technical Memorandum (TM) an attempt is made to give the fundamentals of growing crystals from solution including improved designs of various crystallizers. Since the same solution crystal growth technique could not be used in microgravity, the authors proposed a new cooled-sting technique to grow crystals in space. The authors experience from conducting two Space Shuttle solution crystal growth experiments are also detailed in this TM and the complexity of solution growth experiments to grow crystals in space are also discussed. These happen to be some of the early experiments performed in space, and various lessons learned are described. A brief discussion of protein crystal growth that shares basic principles of the solution growth technique is given, along with some flight hardware information for growth in microgravity.

  17. Growth and Characteristics of Bulk Single Crystals Grown from Solution on Earth and in Microgravity

    NASA Technical Reports Server (NTRS)

    Aggarwal, M. D.; Batra, A. K.; Lal, R. B.; Penn, Benjamin G.; Frazier, Donald O.

    2011-01-01

    The growth of crystals has been of interest to physicists and engineers for a long time because of their unique properties. Single crystals are utilized in such diverse applications as pharmaceuticals, computers, infrared detectors, frequency measurements, piezoelectric devices, a variety of high technology devices and sensors. Solution crystal growth is one of the important techniques to grow a variety of crystals when the material decomposes at the melting point and a suitable solvent is available to make a saturated solution at a desired temperature. In this chapter an attempt is made to give some fundamentals of growing crystals from solution including improved designs of various crystallizers. Since the same solution crystal growth technique could not be used in microgravity, authors had proposed a new cooled sting technique to grow crystals in space. Authors? experiences of conducting two space shuttle experiments relating to solution crystal growth are also detailed in this work. The complexity of these solution growth experiments to grow crystals in space are discussed. These happen to be some of the early experiments performed in space, and various lessons learned are described. A brief discussion of protein crystal growth that also shares basic principles of solution growth technique is given along with some flight hardware information for its growth in microgravity.

  18. Novel ZnS nanostructures: Synthesis, growth mechanism, and applications

    NASA Astrophysics Data System (ADS)

    Moore, Daniel F.

    Motivated by a desire to understand the basic concepts of one-dimensional nanostructure growth, the research described in this thesis aims at understanding the basic mechanisms controlling the synthesis and formation of a specific group of II-VI semiconducting nanostructures. In particular, this thesis examines one-dimensional nanostructures (such as nanobelts and nanowires) and different morphologies of ZnS that result from the interesting properties that the materials have at the nanoscale. In order to understand how to tune these properties in the nanostructure, it is necessary to have an understanding of the growth mechanism that dictates the morphology, structure, and rate of growth of the nanomaterial. It is necessary to understand what impact changes to the macroscopic setup in the experiment have on the nanoscopic scale of the nanomaterials. Having a larger understanding and exerting more precise control over the growth of nanomaterials will allow a higher level of selectivity, more control over dimensionality and the type of morphology, easier manipulation, and the simpler incorporation of these structures into a nanotechnological device. The main focus of the research was on CdSe and ZnS, with the bulk of the research being conducted on ZnS nanostructures. These materials were chosen for their potential for extensive research, their possible applications in optoelectronics, their potential to form the wurtzite crystal structure, and the potential generalization of results to other nanomaterials. The framework for the research is given first. Then a description of the experimental setup and a model for the growth of nanostructures is discussed. A brief overview of the synthesis of CdSe nanostructures is given and then a detailed analysis of the synthesis of specific ZnS one-dimensional morphologies is presented.

  19. Effect of lead(II) impurity on the growth of sodium chloride crystals

    Microsoft Academic Search

    N. Kubota; H. Otosaka; N. Doki; M. Yokota; A. Sato

    2000-01-01

    The growth kinetics of the (100) face of sodium chloride crystals were measured in aqueous solution in the presence of a trace of lead(II) as a function of supersaturation and impurity concentration. The growth kinetic data are analyzed successfully using the kinetic model proposed by Kubota and Mullin [J. Crystal Growth 152 (1995) 203]. The value of the Langmuir constant

  20. Aerodynamic Stability and the Growth of Triangular Snow Crystals K. G. Libbrecht and H. M. Arnold

    E-print Network

    Libbrecht, Kenneth G.

    Aerodynamic Stability and the Growth of Triangular Snow Crystals K. G. Libbrecht and H. M. Arnold growth perturbations of the more-typical hexagonal forms. We then describe an aerodynamic model leads to air flow around the crystal that promotes the growth of alternating facets. Aerodynamic effects

  1. Crystal Growth and the Role of the Organic Network in Eggshell Biomineralization

    Microsoft Academic Search

    Heather Silyn-Roberts; R. M. Sharp

    1986-01-01

    A model based on geometrical crystal growth considerations is proposed for the deposition of the crocodilian, testudinian and avian eggshells. In each shell column, crystal deposition is initiated at a single location, from which growth fans out at all angles to the shell normal. In both calcitic and aragonitic shells, growth is in the [001] direction, resulting in an increase

  2. A physicist's view of biotechnology. [small molecule crystal growth in space

    NASA Technical Reports Server (NTRS)

    Kroes, Roger L.

    1987-01-01

    Theories and techniques for small molecule crystal growth are reviewed, with emphasis on space processing possibilities, particularly for protein crystal growth. The general principles of nucleation, growth, and mass and heat transport are first discussed. Optical systems using schlieren, shadowgraph, and holographic techniques are considered, and are illustrated with the example of the NASA developed Fluids Experiment System flow aboard Spacelab 3.

  3. Development of SiC Large Tapered Crystal Growth

    NASA Technical Reports Server (NTRS)

    Neudeck, Phil

    2010-01-01

    Majority of very large potential benefits of wide band gap semiconductor power electronics have NOT been realized due in large part to high cost and high defect density of commercial wafers. Despite 20 years of development, present SiC wafer growth approach is yet to deliver majority of SiC's inherent performance and cost benefits to power systems. Commercial SiC power devices are significantly de-rated in order to function reliably due to the adverse effects of SiC crystal dislocation defects (thousands per sq cm) in the SiC wafer.

  4. Viscosity solutions for a polymer crystal growth model

    E-print Network

    Cardaliaguet, Pierre; Monteillet, Aurélien

    2010-01-01

    We prove existence of a solution for a polymer crystal growth model describing the movement of a front $(\\Gamma(t))$ evolving with a nonlocal velocity. In this model the nonlocal velocity is linked to the solution of a heat equation with source $\\delta_\\Gamma$. The proof relies on new regularity results for the eikonal equation, in which the velocity is positive but merely measurable in time and with H\\"{o}lder bounds in space. From this result, we deduce \\textit{a priori} regularity for the front. On the other hand, under this regularity assumption, we prove bounds and regularity estimates for the solution of the heat equation.

  5. VISCOSITY SOLUTIONS FOR A POLYMER CRYSTAL GROWTH MODEL

    E-print Network

    Paris-Sud XI, Université de

    The paper is devoted to the analysis of following system of equations: i) ut(x, t) = ¯g(v(x, t))|Du(x, t)| in RN � (0, +) ii) vt(x, t) - v(x, t) + ¯g(v(x, t))HN-1{u(·, t) = 0} = 0 in RN � (0, +) iii) v(x, 0) = v of this system modelizes the growth of the surface (t) of a polymer crystal in a nonhomogeneous temperature field

  6. Optical floating zone crystal growth and magnetic properties of MgCr2O4

    NASA Astrophysics Data System (ADS)

    Koohpayeh, S. M.; Wen, J.-J.; Mourigal, M.; Dutton, S. E.; Cava, R. J.; Broholm, C. L.; McQueen, T. M.

    2013-12-01

    Large, high-quality single crystals of the magnesium chromate spinel, MgCr2O4, have been grown by the optical floating zone technique. The impact of experimental parameters including the feed rod density, growth atmosphere, temperature gradient, and the growth rate on eventual crystal quality have been studied. The best single crystals were obtained by growing in purified argon, at high growth rates of 8-24 mm/h and using a slow cooling procedure. The crystals were characterized using Laue and powder X-ray diffraction, energy dispersive X-ray analysis, and magnetization measurements. Lattice parameter measurements taken from the crystals prepared at various growth conditions combined with the magnetic data show that off-stoichiometric crystals have larger lattice constants and a higher magnetic susceptibility at TN. Our results demonstrate the importance of correlating growth conditions with structural and physical properties to produce high quality single crystals that have physical properties commensurate with stoichiometric powder samples.

  7. Alloy Phase Diagrams for III-P Semiconductor Crystal Growth

    NASA Astrophysics Data System (ADS)

    Gennett, Adam

    Bulk crystals of III-V ternary and quaternary semiconductors with tunable band gaps and lattice constants are attractive for numerous electronic and optoelectronic applications. In particular, the ternary GaxIn 1-xP has a band gap range of 1.351 - 2.261 eV, which corresponds to wavelengths in the near infrared to green range of the electromagnetic spectrum, and lattice constant ranging of 5.4512 - 5.8688 A. This makes it attractive for applications such as a high energy junction in multi-junction photovoltaics, terahetrtz emission, and as a substrate for yellow, amber, orange, and red AlGaInP LEDs. However, bulk growth of GaxIn1-xP ternary III-V semiconductor crystals using elemental Ga-In-P melts or pseudo-binary GaP-InP melts is significantly challenging due to the high vapor pressure of phosphorus at the typical growth temperatures, the large variation in the lattice constant of the constituent binaries, and the slow growth rates necessary in order to avoid the formation of cracks, dislocations, and multiphase inhomogeneities. Lowering the growth temperature is desirable such that the vapor pressure of phosphorus can be more easily managed. Low growth temperatures can be achieved by using gallium or indium rich solutions, as is currently used for liquid phase epitaxy. However, this approach is less attractive for growing bulk crystals due to numerous experimental difficulties such as high segregation of gallium in indium as well as sticking of the growth solution to the crucible wall and to the grown crystal, making crystal extraction without causing damage challenging. The objective of this research is to establish the conditions required for the growth of uniform composition bulk crystals of GaxIn 1-xP at any desired composition from a stoichiometric GaxIn 1-xPySb1-y quaternary melt, as well as conditions for compositional grading from a binary III-V material seed. Due to large number of conditions of melt composition and temperature that are possible, trial and error experimentation to determine said condition would be time consuming and costly. To reduce the amount of experimentation that must be done equilibrium phase diagram are constructed using the CALPHAD method. Calculations are performed using Gibbs free energy minimization software commercially available from Thermo-Calc Software, Inc., and databases containing thermochemical data on binary III-V material systems. Diagrams were calculated for temperatures between 530 °C and 1475 °C, thus providing coverage of the entire temperature range where both a segregated liquid and solid phase exist and liquid phase solution growth is possible. Data from these phase diagrams were used to establish conditions of temperature and melt composition for growth of any solid composition of GaxIn1-xP, as well as theoretical Scheil solidification profiles for various starting charge compositions. Additionally, equilibrium phase data was used to create models for rates at which the depleted phosphide components (GaP and InP) must be replenished in the melt solution in order to grow bulk crystals of uniform axial compositions. It was also determined from the Scheil solidification curves that it is theoretically possible for self-grading of the solid composition to occur followed by growth of a solid with uniform axial composition simply by cooling a system with sufficiently high atom fractions of phosphorus and sufficiently low atom fractions of gallium. Experiments were carried out to test conditions for growth given by the phase diagrams, as well as validate the Scheil solidification profiles and the possibility of compositional grading to high-GaP compositions through feed of GaP. Growth of different GaxIn1-xP compositions from this melt and compositional grading toward high-GaP compositions was demonstrated to feasible. In addition, the extent of the solubility of GaP and InP as well as their low diffusion rates in InSb was demonstrated. Finally, high sensitivity of the solid composition to small changes in the melt composition was demonstrated for conditions where the at

  8. Model-based control of thermal stresses during LEC growth of GaAs II. Crystal growth experiments

    NASA Astrophysics Data System (ADS)

    Kelly, Kevin W.; Motakef, Shahryar; Koai, Keith

    1991-08-01

    A heat flux control system (HFCS) developed to provide for active control of the thermal environment of LEC growth process, and a numerical model capable of accurate prediction of the thermal field in the growth system are used to control stresses during growth and cool-down of GaAs crystals. Three crystal growth experiments using this combination of hardware and modeling capability are reported. Results indicate that by maintaining thermal stresses in the crystal at below the critical resolved shear stress (CRSS) of the matrix, low dislocation density (EPD approximately 3000 cm -2) material can be obtained. The EPD in crystals experiencing stresses larger than this value are one-order-of-magnitude higher. Issues related to crystal-melt separation and diameter control, as well as various approaches to integration of the model with the growth process, are discussed.

  9. Growth of terbium gallium garnet (TGG) magneto-optic crystals by edge-defined film-fed growth method

    NASA Astrophysics Data System (ADS)

    Zhuang, Naifeng; Song, Caigen; Guo, Liwei; Wang, Rongfeng; Hu, Xiaolin; Zhao, Bin; Lin, Shukun; Chen, Jianzhong

    2013-10-01

    Although terbium gallium garnet (TGG) single crystals suitable for practical applications have been grown by the Czochralski technique due to its congruent melting nature, the interface shape readily deteriorates to spiral growth when grown with a flat interface or facet formation when grown with a convex interface. The Edge-defined Film-fed Growth (EFG) method was used to grow TGG crystals for the first time. The influence of the raw material sintering temperature, growth atmosphere, growth rate and other growth conditions on the crystal quality were investigated. The Verdet constant of as-grown crystal was measured as 39 rad/T.m at 1064 nm by the extinction method, which was close to the literature value. The source of color centers in the crystals is also discussed.

  10. Numerical modeling of crystal growth on a centrifuge for unstable natural convection configurations

    NASA Technical Reports Server (NTRS)

    Ramachandran, N.; Downey, J. P.; Curreri, P. A.; Jones, J. C.

    1993-01-01

    The fluid mechanics associated with crystal growth processes on centrifuges is modeled using 2D and 3D models. Two-dimensional calculations show that flow bifurcations exist in such crystal growth configurations where the ampoule is oriented in the same direction as the resultant gravity vector and a temperature gradient is imposed on the melt. A scaling analysis is formulated to predict the flow transition point from the natural convection dominated regime to the Coriolis force dominated regime. Results of 3D calculations are presented for two thermal configurations of the crystal growth cell: top heated and bottom heated with respect to the centrifugal acceleration. In the top heated configuration, a substantial reduction in the convection intensity within the melt can be attained by centrifuge operations, and close to steady diffusion-limited thermal conditions can be achieved over a narrow range of the imposed microgravity level. In the bottom heated configuration the Coriolis force has a stabilizing effect on fluid motion by delaying the onset of unsteady convection.

  11. Semiconductor Crystal Growth in Static and Rotating Magnetic fields

    NASA Technical Reports Server (NTRS)

    Volz, Martin

    2004-01-01

    Magnetic fields have been applied during the growth of bulk semiconductor crystals to control the convective flow behavior of the melt. A static magnetic field established Lorentz forces which tend to reduce the convective intensity in the melt. At sufficiently high magnetic field strengths, a boundary layer is established ahead of the solid-liquid interface where mass transport is dominated by diffusion. This can have a significant effect on segregation behavior and can eliminate striations in grown crystals resulting from convective instabilities. Experiments on dilute (Ge:Ga) and solid solution (Ge-Si) semiconductor systems show a transition from a completely mixed convective state to a diffusion-controlled state between 0 and 5 Tesla. In HgCdTe, radial segregation approached the diffusion limited regime and the curvature of the solid-liquid interface was reduced by a factor of 3 during growth in magnetic fields in excess of 0.5 Tesla. Convection can also be controlled during growth at reduced gravitational levels. However, the direction of the residual steady-state acceleration vector can compromise this effect if it cannot be controlled. A magnetic field in reduced gravity can suppress disturbances caused by residual transverse accelerations and by random non-steady accelerations. Indeed, a joint program between NASA and the NHMFL resulted in the construction of a prototype spaceflight magnet for crystal growth applications. An alternative to the suppression of convection by static magnetic fields and reduced gravity is the imposition of controlled steady flow generated by rotating magnetic fields (RMF)'s. The potential benefits of an RMF include homogenization of the melt temperature and concentration distribution, and control of the solid-liquid interface shape. Adjusting the strength and frequency of the applied magnetic field allows tailoring of the resultant flow field. A limitation of RMF's is that they introduce deleterious instabilities above a critical magnetic field value. Growth conditions in which static magnetic fields rotational magnetic fields, and reduced gravitational levels can have a beneficial role will be described.

  12. Effect of crucible shape on heat transport and melt-crystal interface during the Kyropoulos sapphire crystal growth

    NASA Astrophysics Data System (ADS)

    Chen, C.; Chen, H. J.; Yan, W. B.; Min, C. H.; Yu, H. Q.; Wang, Y. M.; Cheng, P.; Liu, C. C.

    2014-02-01

    In this work, a special crucible shape with a round shape for the outer wall and an inverted conical shape for the inner wall is presented to investigate the thermal and flow transport, as well as the shape of the crystal-melt interface during the Kyropoulos sapphire crystal growth, by using the numerical simulation method. The results show that the growth system with proposed crucible shape can result in more suitable thermal and flow fields, a lower convexity at shouldering and equal-diameter growth stage and a higher convexity at the following stage. Thus, the results are benefit for the quality of the sapphire crystal.

  13. Growth, spectral, dielectric and antimicrobial studies on 4-piperidinium carboxylamide picrate crystals

    NASA Astrophysics Data System (ADS)

    Dhanabal, T.; Tharanitharan, V.; Amirthaganesan, G.; Dhandapani, M.

    2014-07-01

    Single crystal of 4-piperidinium carboxylamide picrate was grown by slow evaporation solution growth technique at ambient temperature. The average dimensions of grown crystal were 0.7 × 0.3 × 0.2 cm3. The solubility of the compound was analyzed using methanol and acetone. Optical property of the compound was ascertained by UV-visible absorption spectral study. The sharp and well defined Bragg peaks observed in the powder X-ray diffraction pattern confirm its crystallinity. The different kinds of protons and carbons in the compound were confirmed by 1H and 13C NMR spectral analyses. The presence of various functional groups in the compound was assigned through polarized Raman spectral study. The mechanical property of the crystal was measured by Vicker's microhardness test and the compound was found to be soft material. The dielectric constant and dielectric loss of the crystal decrease with increase in frequency. The antibacterial and antifungal activities of the crystal were studied by disc diffusion method and found that the compound shows good inhibition efficiency against various bacteria and fungi species.

  14. Growth, spectral, dielectric and antimicrobial studies on 4-piperidinium carboxylamide picrate crystals.

    PubMed

    Dhanabal, T; Tharanitharan, V; Amirthaganesan, G; Dhandapani, M

    2014-07-15

    Single crystal of 4-piperidinium carboxylamide picrate was grown by slow evaporation solution growth technique at ambient temperature. The average dimensions of grown crystal were 0.7×0.3×0.2 cm(3). The solubility of the compound was analyzed using methanol and acetone. Optical property of the compound was ascertained by UV-visible absorption spectral study. The sharp and well defined Bragg peaks observed in the powder X-ray diffraction pattern confirm its crystallinity. The different kinds of protons and carbons in the compound were confirmed by (1)H and (13)C NMR spectral analyses. The presence of various functional groups in the compound was assigned through polarized Raman spectral study. The mechanical property of the crystal was measured by Vicker's microhardness test and the compound was found to be soft material. The dielectric constant and dielectric loss of the crystal decrease with increase in frequency. The antibacterial and antifungal activities of the crystal were studied by disc diffusion method and found that the compound shows good inhibition efficiency against various bacteria and fungi species. PMID:24699288

  15. Quantitative analysis of molecular-level DNA crystal growth on a 2D surface

    PubMed Central

    Lee, Junwye; Hamada, Shogo; Hwang, Si Un; Amin, Rashid; Son, Junyoung; Dugasani, Sreekantha Reddy; Murata, Satoshi; Park, Sung Ha

    2013-01-01

    Crystallization is an essential process for understanding a molecule's aggregation behavior. It provides basic information on crystals, including their nucleation and growth processes. Deoxyribonucleic acid (DNA) has become an interesting building material because of its remarkable properties for constructing various shapes of submicron-scale DNA crystals by self-assembly. The recently developed substrate-assisted growth (SAG) method produces fully covered DNA crystals on various substrates using electrostatic interactions and provides an opportunity to observe the overall crystallization process. In this study, we investigated quantitative analysis of molecular-level DNA crystallization using the SAG method. Coverage and crystal size distribution were studied by controlling the external parameters such as monomer concentration, annealing temperature, and annealing time. Rearrangement during crystallization was also discussed. We expect that our study will provide overall picture of the fabrication process of DNA crystals on the charged substrate and promote practical applications of DNA crystals in science and technology. PMID:23817625

  16. The effect of aspect ratio and fluid flow on crystal growth

    NASA Technical Reports Server (NTRS)

    Barber, Patrick G.

    1986-01-01

    Supersaturated solutions were conditioned at different aspect ratios before crystal growth. The conditioned solutions were poured out into a dish to initiate crystal nucleation and growth. The rate of growth was measured microscopically and found to depend upon the aspect ratio. Secondly, the number and size of crystals formed was found to depend upon the aspect ratio. The data support the above conclusion, but do not prove it.

  17. Floating Zone Growth and Scintillation Characteristics of Cerium-Doped Gadolinium Pyrosilicate Single Crystals

    Microsoft Academic Search

    S. Kawamura; J. H. Kaneko; M. Higuchi; T. Yamaguchi; J. Haruna; Y. Yagi; K. Susa; F. Fujita; A. Homma; S. Nishiyama; K. Kurashige; H. Ishibashi; M. Furusaka

    2007-01-01

    Growth of cerium-doped gadolinium pyrosilicate single crystals, which show 2.5 times greater light output for gamma-rays and five times greater light output for alpha-particles than GSO single crystals, is accomplished using the floating zone growth method (FZ method). Although growth of (GPS) single crystal is considered to be difficult because it melts incongruently according to the phase diagram of system,

  18. Experimental and theoretical analysis of sublimation growth of AlN bulk crystals

    Microsoft Academic Search

    Yu. N. Makarov; O. V. Avdeev; I. S. Barash; D. S. Bazarevskiy; T. Yu. Chemekova; E. N. Mokhov; S. S. Nagalyuk; A. D. Roenkov; A. S. Segal; Yu. A. Vodakov; M. G. Ramm; S. Davis; G. Huminic; H. Helava

    2008-01-01

    The current status of sublimation growth of aluminum nitride (AlN) bulk crystals is discussed. Growth of AlN single-crystal layers on silicon carbide (SiC) seeds in pre-carbonized tantalum crucibles in graphite equipment and of AlN bulk crystals on the AlN layers in tungsten crucibles and equipment is considered. All stages of the technology, including pre-growth processing (preparation of durable crucibles, high-purity

  19. Flux growth and characterizations of NdPO 4 single crystals

    Microsoft Academic Search

    Yongzheng Wang; Jing Li; Jiyang Wang; Shujuan Han; Yongjie Guo

    2010-01-01

    Neodymium phosphate single crystals, NdPO4, have been grown by a flux growth method using Li2CO3-2MoO3 as a flux. The as-grown crystals were characterized by X-ray powder diffraction(XRPD), differential thermal analysis (DTA) and thermogravimetric analysis (TG) techniques. The results show that the as-grown crystals were well crystallized. The crystal was stable over the temperature range from 26 to 1200°C in N2.

  20. Flux growth and spectral properties of Yb:YAB single crystal with high Yb 3+ concentration

    Microsoft Academic Search

    Jinsheng Liao; Yanfu Lin; Yujin Chen; Zundu Luo; Yidong Huang

    2004-01-01

    Ytterbium-doped yttrium aluminium borate (Yb:YAB) crystals with high Yb3+ concentration have been obtained by the top-seeded solution growth techniques. The polarized absorption spectra, fluorescence spectra and lifetime of 65.5at% Yb3+-doped YAB crystal were measured at room temperature. The spectroscopic parameters of the crystal were compared with those of low Yb3+-doped YAB crystal. The results demonstrated that the Yb:YAB crystals with

  1. Growth, morphology, spectral and thermal studies of gel grown diclofenac acid crystals

    NASA Astrophysics Data System (ADS)

    Ramachandran, E.; Ramukutty, S.

    2014-03-01

    The crystal growth of diclofenac acid in silica gel is the first to be reported in literature. The growth parameters were varied to optimize the suitable growth condition. Single crystal X-ray diffraction method was used for the conformation of the crystal structure. Morphology studies showed that the growth is prominent along the b-axis and the prominent face is {002}. Fourier transform infrared spectral study was performed to identify the functional groups present in the crystal. Thermal stability and decomposition of the material were analyzed using thermo calorimetry in the temperature range 30-500 °C.

  2. Deformation mechanisms in tungsten single crystals in ballistic impact experiments

    NASA Astrophysics Data System (ADS)

    Bruchey, W. J., Jr.; Herring, R. N.; Kingman, P. W.; Horwath, E. J.

    1993-05-01

    The performance of tungsten single crystals in ballistic impact varies strongly as a function of crystallographic orientation. The deformation structure of recovered single crystal rods fired in ballistic environments has been characterized by optical microscopy, SEM and TEM, and x-ray diffraction. The observed microstructures are varied and provide substantial insights into the factors governing the penetration and flow behavior under ballistic conditions. Crystallographic orientation influences the potential for developing shear which enhances material flow, and this enhancement ultimately maximizes the energy available for target penetration. Microstructural analysis elucidates the various mechanisms occuring during the flow process for single crystals of high-symmetry orientations, and suggests possible analogies between the penetration behavior of the tungsten single crystals and other materials.

  3. A peek into the history of sapphire crystal growth

    NASA Astrophysics Data System (ADS)

    Harris, Daniel C.

    2003-09-01

    After the chemical compositions of sapphire and ruby were unraveled in the middle of the 19th century, chemists set out to grow artificial crystals of these valuable gemstones. In 1885 a dealer in Geneva began to sell ruby that is now believed to have been created by flame fusion. Gemnologists rapidly concluded that the stones were artificial, but the Geneva ruby stimulated A. V. L. Verneuil in Paris to develop a flame fusion process to produce higher quality ruby and sapphire. By 1900 there was brisk demand for ruby manufactured by Verneuil's method, even though Verneuil did not publicly announce his work until 1902 and did not publish details until 1904. The Verneuil process was used with little alteration for the next 50 years. From 1932-1953, S. K. Popov in the Soviet Union established a capability for manufacturing high quality sapphire by the Verneuil process. In the U.S., under government contract, Linde Air Products Co. implemented the Verneuil process for ruby and sapphire when European sources were cut off during World War II. These materials were essential to the war effort for jewel bearings in precision instruments. In the 1960s and 1970s, the Czochralski process was implemented by Linde and its successor, Union Carbide, to make higher crystal quality material for ruby lasers. Stimulated by a government contract for structural fibers in 1966, H. LaBelle invented edge-defined film-fed growth (EFG). The Saphikon company, which is currently owned by Saint-Gobain, evolved from this effort. Independently and simultaneously, Stepanov developed edge-defined film-fed growth in the Soviet Union. In 1967 F. Schmid and D. Viechnicki at the Army Materials Research Lab grew sapphire by the heat exchanger method (HEM). Schmid went on to establish Crystal Systems, Inc. around this technology. Rotem Industries, founded in Israel in 1969, perfected the growth of sapphire hemispheres and near-net-shape domes by gradient solidification. In the U.S., growth of near-net-shape sapphire domes was demonstrated by both the EFG and HEM methods in the 1980s under government contract, but neither method entered commercial production. Today, domes in the U.S. are made by "scooping" sapphire boules with diamond-impregnated cutting tools. Commercial markets for sapphire, especially in the semiconductor industry, are healthy and growing at the dawn of the 21st century.

  4. ELSEVIER Journal of Crystal Growth 143 (1994) 317--333 The influence of oscillatory and steady shears on interfacial

    E-print Network

    Schulze, Tim

    1994-01-01

    ~N~H CRYSTAL GROWTH ELSEVIER Journal of Crystal Growth 143 (1994) 317--333 The influence reserved SSDI 0022-0248(94)00418-L #12;315 T.P. Schuize, S.H. Divis/Journal of Crystal Growth 143 (1994) 3 by a simple harmonic, lateral oscillation of the crystal, resulting in solidification into a compressed Stokes

  5. Structure, Growth Process, and Growth Mechanism of Perovskite in High-Titanium-Bearing Blast Furnace Slag

    NASA Astrophysics Data System (ADS)

    Liu, Lu; Hu, Meilong; Xu, Yuzhou; Bai, Chenguang; Gan, Yunhua

    2015-05-01

    The isothermal crystallization of perovskite in TiO2-CaO-SiO2-Al2O3-MgO high-titanium-bearing blast furnace slag was observed in situ at 1698 K (1425 °C) using a confocal scanning laser microscope. The dendrite structure of perovskite (CaTiO3) thus obtained showed vividly the primary dendrite trunks and secondary dendrite arms. Furthermore, the dendritic growth of perovskite in liquid slag was clearly observed on line. The results showed that the dendrite arrays in which the primary dendrite trunks observed on slag surface were parallel with each other grew toward the same direction. The secondary dendrite arms grew in the perpendicular direction with the primary trucks and stopped growing when they encounter. The perovskite dendrites showed a linear growth at two stages. The dendrites grew faster at early stage at about 5 to 7 ?m/s and grew with a lower growth rate at about 1 to 2 ?m/s in later stage. Finally, the growth mechanism of perovskite in melt was analyzed with the solidification theory. Based on the theoretical calculation of equilibrium phases in slag, the initial slag could be considered as a binary component system. One component was perovskite and the other component was the sum of all the other species that did not attend the crystallization of perovskite (included SiO2, Al2O3, and MgO, as well as CaO and TiO2 that were not involved in the solid formation). The formation of perovskite required the diffusion of CaO and TiO2 to the solid/liquid interface and the rejection of the other species from the interface. The solid/liquid equilibrium schematic diagram was made based on the calculation.

  6. Effect of fluoride on crystal growth of calcium apatites in the presence of a salivary inhibitor.

    PubMed

    Margolis, H C; Varughese, K; Moreno, E C

    1982-01-01

    The effect of fluoride on the kinetics of crystal growth of calcium apatites was studied using seed crystals of hydroxyapatite coated with PRP-3, a proline-rich phosphoprotein salivary inhibitor of crystal growth. Initial precipitation rates in the presence of PRP-3, under conditions of partial inhibition, were enhanced by fluoride, effectively counteracting the inhibitory activity of the macromolecule. This rate enhancement is related to an increase in the precipitation driving force, i.e., the degree of supersaturation with respect to the precipitating phase; in this case a fluoridated hydroxyapatite. The growth of this phase takes place at the uncovered crystal growth sites which have been previously shown to be the same sites as the adsorption sites for the protein inhibitors. Explanations based on fluoride activation of secondary crystal growth sites and on the displacement of adsorbed inhibitor by fluoride are not substantiated by the present results. It has been demonstrated that under conditions of maximum coverage of available crystal growth sites by PRP-3, resulting in no apparent crystal growth, measurable crystal growth is observed upon the addition of fluoride (1 ppm). This phenomenon is best explained by the fact that at maximum PRP-3 coverage, a small number (16%) of crystal growth sites remain uncovered, which support an unmeasurable rate of crystal growth. Upon the addition of fluoride, this rate is significantly enhanced. It is suggested that the fraction of uncovered growth sites is related to steric interactions of the PRP-3 molecule in the adsorbed state. Overall, the results presented suggest that fluoride can accelerate crystal growth in an environment such as the enamel surface where the acquired pellicle is formed. PMID:6293672

  7. Influence of Filler on the Mechanical Properties and Kinetic Crystallization Behavior of Polylactic Acid (PLA)

    NASA Astrophysics Data System (ADS)

    Mitsuta, Ryo; Inoue, Ryohei; Hara, Ryosuke; Sato, Sadao

    The kinetic crystallization behavior of PLA (polylactic acid) and PLA/MMT nanocomposites containing 3 wt% montmorillonite (MMT) was examined in order to develop a new technique for obtaining the relative crystallization degree of a material from the spherulite occupation area based on images obtained using a charge-coupled device (CCD) camera. In addition, the relative crystallization degree is discussed in terms of the Ozawa theory. The effect of MMT filler on the mechanical properties of PLA/MMT nanocomposites, the number of spherulites generated in the nanocomposites, and the linear growth rate of these spherulites were also examined experimentally. The relative crystallization curves obtained by CCD and by DSC measurement were found to be approximately the same. Moreover, it was found that the Ozawa theory could be applied not only to PLA but also to PLA/MMT nanocomposites. In these nanocomposites, the number of spherulites decreased and the linear growth rate slightly increased ; moreover, the rate of crystallization also increased. The tensile and flexural modulus of the PLA/MMT nanocomposites containing 3 wt% MMT were 5.2-14.3% greater than those of PLA, and annealing resulted in a further increase of about 4.0-20.7%. However, the Izod impact value decreased due to the increase in rigidity caused by annealing and the addition of filler.

  8. Crystallization Kinetics and Phase Transformation Mechanisms in Cu56Zr44 Glassy Alloy

    NASA Astrophysics Data System (ADS)

    Kalay, Ilkay; Kramer, Matthew J.; Napolitano, Ralph E.

    2015-04-01

    The kinetics and phase selection mechanisms involved in the crystallization of an amorphous Cu-Zr alloy of eutectic composition (Cu56Zr44) were investigated using in situ high-energy X-ray diffraction (HEXRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) under isothermal and constant heating rate conditions. In situ HEXRD results for 10 K/min (10 °C/min) heating indicate that the amorphous alloy devitrifies into CuZr2 and mainly Cu10Zr7 at the crystallization temperature of 725 K (452 °C). The sequence continues with the precipitation of CuZr (B2) at 1004 K (731 °C), where these three phases coexist until the decomposition of CuZr2 is observed at 1030 K (757 °C). The two equilibrium phases Cu10Zr7 and CuZr (B2) remain present on further heating until melting at the eutectic temperature for the Cu56Zr44 alloy. TEM investigation of the isothermal [705 K (432 °C)] crystallization sequence reveals primary nucleation and growth of the Cu10Zr7 phase, where growth of the Cu10Zr7 crystals is initially planar with a transition to a cellular morphology, associated with partitioning of Zr at the growth front. Related cellular structures and composition profiles are quantified.

  9. Colouring mechanism of dyed KDP crystal by quantum chemistry

    Microsoft Academic Search

    Yusuke Asakuma; Motosuke Nishimura; Qin Li; H. Ming Ang; Moses Tade; Kouji Maeda; Keisuke Fukui

    2007-01-01

    Dye adsorption mechanism, in particular, colouring mechanism of KDP (KH2PO4) crystal was investigated by quantum chemistry in this study. Phenomena, such as different preferentially coloured faces of KDP when co-crystallised with different dyes, are explained by the minimum and maximum values of electrostatic potential (ESP). Furthermore, it is found that the ESP distribution of a dye molecule may not necessarily

  10. Mechanisms for the Crystallization of Zblan

    NASA Technical Reports Server (NTRS)

    Ethridge, Edwin C.; Tucker, Dennis S.

    2001-01-01

    The heavy metal fluoride glasses represent a class of reasonably good glass forming compositions with very unique infrared optical properties that have been of interest to researchers for 20 years. The most extensively studied glass with the most potential for practical applications is ZBLAN which contains the fluorides of zirconium, barium, lanthanum, aluminum, and sodium. It has a broad transmission range (0.3-6 um), low index of refraction (about 1.43), low dispersion, low Raleigh scattering, ultra-low thermal 2 dispersion, and potential ultra-low signal attenuation. Potential applications include fiber amplifiers, fiber optic gyroscopes, delivery systems for laser cutting, drilling and surgery, radiation resistant data links, nonlinear optical systems, and ultra-low-loss repeater-less transcontinental and transoceanic optical fiber. Potential markets for these materials are in the tens of billions of dollars per year. Optical fiber from this system possess excellent transmission characteristics in the IR, but the glass is somewhat susceptible to nucleation and crystallization. The theoretical intrinsic loss coefficient for ZBLAN at 2 microns is 0.00 1 dB/Km. Extrinsic losses, however, cause significant attenuation. The lowest loss coefficient measured is 0.7 dB/Km. This compares with the loss coefficient for fiber optic grade fused silica glass of 0.2 dB/Km. The extrinsic losses in ZBLAN have been attributed to 1) impurities which might be lowered by containerless processing and 2) to scattering from micro-crystallites that form during glass preform production or during fiber drawing.

  11. Effect of Crystal Growth Direction on Domain Structure of Mn-Doped (Na,K)NbO3 Crystal

    NASA Astrophysics Data System (ADS)

    Tsuchida, Kohei; Kakimoto, Ken-ichi; Kagomiya, Isao

    2013-09-01

    Single crystals of (Na0.55K0.45)(Nb0.995Mn0.005)O3 have been grown by a floating zone method in N2 and decompression atmosphere to avoid alkaline metal volatilization on the SrTiO3 material base. The variation of their ferroelectric domain structure and the chemical composition of the grown crystal in the growth direction were evaluated. In the crystal grown in N2 atmosphere, the Na and K are not distributed homogeneously. In addition, the phase transition temperature TC and TO-T showed different values between the grown crystal and raw material. By using laser scanning confocal microscope, the domain structures of the grown crystal revealed random patterns in the initial growth stage and lamellar patterns in the progressing crystal growth. In decompression atmosphere, the TC and TO-T values of the grown crystal were similar to those of the raw material and the domain structures showed a constant domain size. The electrical property of the crystal became stable and the domain structure was easily switched against applied electrical field because the oriented lamellar domain was created during cooling of the crystal.

  12. Cationic coordination compound Cs2Hg3I8 for IR NLO material: Synthesis, crystal growth and characterizations

    NASA Astrophysics Data System (ADS)

    Sathiskumar, S.; Kathiravan, P.; Balakrishnan, T.

    2015-06-01

    Single crystals Cs2Hg3I8 of dimensions 5 × 3 × 4 mm3 were grown by solution growth method at room temperature and structurally characterized by single crystal X - ray diffraction. Cs2Hg3I8 compound crystallizes in a noncentrosymmetric space group Cm with the crystal data of a = 7.4415 Å, b = 21.6629 Å, c = 7.6726 Å, ?, ? = 90°, ? = 108.05° and Z = 2. The grown crystals were characterized by powder X - ray diffraction analysis and the various diffraction planes are indexed. The presence of functional groups was identified qualitatively by Fourier transform infrared and FT - Raman spectral analyses. Ultraviolet - visible spectral analyses shows that the crystal has low UV cut off at 388 nm combined with very good transparency of 98 % in a wide range. The optical band gap was estimated to be 3 eV. Mechanical hardness of the grown crystal Cs2Hg3I8 was determined. The dielectric response of the crystal with varying frequencies was studied. Differential scanning calorimetry (DSC) analysis shows that the grown crystal has very good thermal stability up to 97.5°C.

  13. Growth and optical properties of gray-track-resistant KTiOPO4 single crystals

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Wang, Hongyan; Ma, Changqin; Jia, Yanwei; Li, Jing; Wang, Jiyang; Boughton, Robert; Jiang, Huaidong

    2015-02-01

    We succeeded in growing gray-track-resistant KTP single crystals in a KTP-K6P4O13(K6)-PbO system using TSSG (top-seeded solution growth) and have explored the mechanism of gray track formation using combined characterization technologies. The optical and laser properties of the crystals were estimated. To obtain a better understanding of the gray track effect, in situ X-ray absorption near-edge structure (XANES) measurements using the total electron yield (TEY) method in the region of gray track formation was performed. Electron paramagnetic resonance (EPR) was used to further confirm the existence of Ti3+. The results indicate that the formation of the gray track is related to Ti3+ centers.

  14. Crystal growth, structural and thermal studies of amino acids admixtured L-arginine phosphate monohydrate single crystals

    NASA Astrophysics Data System (ADS)

    Anandan, P.; Saravanan, T.; Parthipan, G.; Kumar, R. Mohan; Bhagavannarayana, G.; Ravi, G.; Jayavel, R.

    2011-05-01

    To study the improved characteristics of L-arginine phosphate monohydrate (LAP) crystals, amino acids mixed LAP crystals have been grown by slow cooling method. Amino acids like glycine, L-alanine, and L-valine have been selected for doping. Optical quality bulk crystals have been harvested after a typical growth period of about twenty days. The effect of amino acids in the crystal lattice and molecular vibrational frequencies of various functional groups in the crystals have been studied using X-ray powder diffraction and Fourier Transform infrared (FTIR) analyses respectively. Thermal behavior of the amino acids mixed LAP crystals have been studied from the TG and DTG analyses. High-resolution X-ray diffraction studies have been carried out to find the crystalline nature. Optical transmission studies have been carried out by UV-vis spectrophotometer. The cut off wavelength is below 240 nm for the grown crystals.

  15. A discrete mechanics approach to dislocation dynamics in BCC crystals

    NASA Astrophysics Data System (ADS)

    Ramasubramaniam, A.; Ariza, M. P.; Ortiz, M.

    2007-03-01

    A discrete mechanics approach to modeling the dynamics of dislocations in BCC single crystals is presented. Ideas are borrowed from discrete differential calculus and algebraic topology and suitably adapted to crystal lattices. In particular, the extension of a crystal lattice to a CW complex allows for convenient manipulation of forms and fields defined over the crystal. Dislocations are treated within the theory as energy-minimizing structures that lead to locally lattice-invariant but globally incompatible eigendeformations. The discrete nature of the theory eliminates the need for regularization of the core singularity and inherently allows for dislocation reactions and complicated topological transitions. The quantization of slip to integer multiples of the Burgers' vector leads to a large integer optimization problem. A novel approach to solving this NP-hard problem based on considerations of metastability is proposed. A numerical example that applies the method to study the emanation of dislocation loops from a point source of dilatation in a large BCC crystal is presented. The structure and energetics of BCC screw dislocation cores, as obtained via the present formulation, are also considered and shown to be in good agreement with available atomistic studies. The method thus provides a realistic avenue for mesoscale simulations of dislocation based crystal plasticity with fully atomistic resolution.

  16. Journal of Crystal Growth 272 (2004) 400406 Nucleation and growth of InN thin films using conventional

    E-print Network

    Zettl, Alex

    2004-01-01

    Journal of Crystal Growth 272 (2004) 400­406 Nucleation and growth of InN thin films using and pulsed metalorganic vapor-phase epitaxy. The nucleation and evolution of thin film growthN (0oxo1) are very promising for visible and near IR optoelec- tronics and high-efficiency solar cells

  17. Unidirectional growth of <0 0 1> triglycine zinc chloride crystal by Sankaranarayanan-Ramasamy (SR) method and its characterization

    NASA Astrophysics Data System (ADS)

    Aravinth, K.; Senthil Pandian, M.; Ramasamy, P.

    2015-03-01

    Bulk nonlinear optical single crystal of triglycine zinc chloride (TGZC) of size 15 mm diameter and 50 mm length was successfully grown from solution by unidirectional growth method of Sankaranarayanan-Ramasamy (SR). The growth conditions were optimized and a maximum growth rate of 1.5 mm per day was realized. The crystal system and lattice parameters were confirmed by powder X-ray diffraction studies. The structural perfection of the SR method grown crystal has been analyzed by high resolution X-ray diffraction measurement. The UV-Vis-NIR studies show that the cutoff wavelength is around 240 nm. The dielectric measurements were carried out to determine the dielectric behavior for the crystal. The observations are made in the frequency range 1 kHz-2 MHz at the temperature range of 43-150 °C. The fluorescence spectra of grown TGZC single crystals exhibit emission peak at 485 nm. The microhardness measurements were used to analyze the mechanical strength of the grown TGZC crystal. The SHG efficiency of TGZC was confirmed by Kurtz-Perry powder method.

  18. Mathematics and Mechanics of Solids (to appear) Stressmodulated growth

    E-print Network

    Ambrosi, Davide

    with growth. Many studies show a strong interaction between the stress state of the body and finite growth. Yamamoto et al. [25] studied the effects of static stress on the mechanical properties of cultured collagenMathematics and Mechanics of Solids (to appear) Stress­modulated growth D. Ambrosi1 , F. Guana2 1

  19. Kinematics of crystal growth in syntectonic fibrous veins

    Microsoft Academic Search

    J. L. Urai; P. F. Williams; H VANROERMUND

    1991-01-01

    Abstract--Detaded observations of a set of fibrous antitaxial calcite veins in a slate reveal that some,of the calcite fibres do not connect material markers,on both sides of the vein and can therefore not have tracked the full opening trajectory dunng,vein growth. Thts calls for a better understanding,of the mechanisms,of fibre formation and reliable criteria to test the tracking hypothesis. Based

  20. Crystal Growth of Hen Egg-White Lysozyme (HEWL) under Various Gravity Conditions

    NASA Astrophysics Data System (ADS)

    Pan, Weichun; Xu, Jin; Tsukamoto, Katsuo; Koizumi, Masako; Yamazaki, Tomoya; Zhou, Ru; Li, Ang; Fu, Yuying

    2013-08-01

    Motivated by the enhancement of protein quality under microgravity condition, the behaviors of crystal growth under various gravity conditions have been monitored via Foton Satellite and parabolic flight. We found that the normal growth rate and the step velocity would be enhanced only at high protein concentration. Although the difference of diffusion between monomer lysozyme molecule and main impurity species in HWEL dimer may be able to explain this enhancement in long period at high protein concentration, it is not valid at low lysozyme concentration and it can't explain the results obtained by parabolic flight, in which microgravity condition maintained only about 20 s. In order to compromise this contradiction, cluster, universal existing in protein solution, has been picked up. The dynamic light scattering technique figured out dimer is served as the seed for cluster formation. Due to its large size, cluster keeps still under microgravity. Via this mechanism, the purification of lysozyme above crystal surface has been achieved. We also found the two supergravity (˜1.5 g) periods immediately before and after microgravity period have different effects on the step velocity. The pre-MG period depresses the step velocity while the post-MG enhances it. This odd phenomenon ascribes to two factors: (1) the flow rate modification and (2) the purity of protein solution immediate above crystal surface.

  1. Development of optical systems. [holographic technique for monitoring crystal growth

    NASA Technical Reports Server (NTRS)

    Vikram, Chandra S.

    1995-01-01

    Several key aspects of multi-color holography and laser speckle technique to study holographic reconstructions are considered in the report. Holographic fringe contrast in two-color holography in the presence of a fluid cell in the object beam is discussed in detail. A specific example of triglycine sulfate crystal growth is also considered. A breadboard design using fiber optics and diode lasers for three-color holography for fluid experiments is presented. A possible role of multi-color holography in various new applications is summarized. Finally, the use of a a laser speckle technique is demonstrated for the study of holographic reconstructions. The demonstration is performed using a Spacelab 3 hologram.

  2. Crystal Growth and Other Materials Physical Researches in Space Environment

    NASA Astrophysics Data System (ADS)

    Pan, Mingxiang

    Material science researches in space environment are based on reducing the effects of buoyancy driven transport, the effects of atomic oxygen, radiation, extremes of heat and cold and the ultrahigh vacuum, so as to unveil the underlying fundamental phenomena, lead maybe to new potential materials or new industrial processes and develop space techniques. Currently, research program on materials sciences in Chinese Manned Space Engineering (CMSE) is going on. More than ten projects related to crystal growth and materials processes are selected as candidates to be executed in Shenzhou spacecraft, Tiangong Space Laboratory and Chinese Space Station. In this talk, we will present some examples of the projects, which are being prepared and executed in the near future flight tasks. They are both basic and applied research, from discovery to technology.

  3. High Speed Crystal Growth by Q-switched Laser Melting

    NASA Technical Reports Server (NTRS)

    Cullis, A. G.

    1984-01-01

    The modification of the structural and electrical properties of semiconductors short radiation pulses obtained from Q-switched lasers is described. These modifications are accomplished by high heating and cooling rates. This processing revealed novel crystal growth and high speed resolidification phenomena. The behavior of semiconductor Si is analyzed. The annealing process typically employs short pulses of radiation in or near the visible region of the spectrum. The Q-switched ruby and Nd-YAG lasers are commonly used and these are sometimes mode locked to reduce the pulse length still further. Material to be annealed can be processed with a single large area radiation spot. Alternatively, a small radiation spot size can be used and a large sample area is covered by overlapping irradiated regions.

  4. A scanning electron microscopic study of the growth of hydroxyapatite crystals

    Microsoft Academic Search

    J. L. Meyer; J. D. Eick; G. H. Nancollas; L. N. Johnson

    1972-01-01

    The crystal growth of hydroxyapatite at 25° and at a constant pH of 7.4 has been studied with the aid of a scanning electron microscope. The reproducible technique of seeded growth from stable supersaturated solutions was used effectively to produce samples of the mineral at various distinct stages of growth. Phase changes were observed as the growth proceeded and these

  5. Growth mechanisms and dune orientation on Titan

    NASA Astrophysics Data System (ADS)

    Lucas, Antoine; Rodriguez, Sebastien; Narteau, Clement; Cahrnay, Benjamin; Courrech du Pont, Sylvain; Tokano, Tetsuya; Garcia, Amandine; Thiriet, Melanie; Hayes, Alexander; Lorenz, Ralph; Aharonson, Oded

    2015-04-01

    Dune fields on Titan cover more than 17 % of the moon's surface, constituting the largest known surface reservoir of organics. Their confinement to the equatorial belt, shape, and eastward direction of propagation offer crucial information regarding both the wind regime and sediment supply. Herein, we present a comprehensive analysis of Titan's dune orientations using automated detection techniques on non-local denoised radar images. By coupling a new dune growth mechanism with actual wind fields generated by climate modelling, we find that Titan's dunes grow by elongation on a non-mobile substratum. To be fully consistent with both the local crestline orientations and the eastward propagation of Titan's dunes, the sediment should be predominantly transported by strong eastward winds, most likely generated by equinoctial storms or occasional fast westerly gusts. Additionally, convergence of the meridional transport predicted in models can explain why Titan's dunes are confined within plus or minus 30 deg. latitudes, where sediment fluxes converge.

  6. Growth mechanisms and dune orientation on Titan

    NASA Astrophysics Data System (ADS)

    Lucas, Antoine; Rodriguez, Sébastien; Narteau, Clément; Charnay, Benjamin; Pont, Sylvain Courrech; Tokano, Tetsuya; Garcia, Amandine; Thiriet, Mélanie; Hayes, Alexander G.; Lorenz, Ralph D.; Aharonson, Oded

    2014-09-01

    Dune fields on Titan cover more than 17% of the moon's surface, constituting the largest known surface reservoir of organics. Their confinement to the equatorial belt, shape, and eastward direction of propagation offer crucial information regarding both the wind regime and sediment supply. Herein, we present a comprehensive analysis of Titan's dune orientations using automated detection techniques on nonlocal denoised radar images. By coupling a new dune growth mechanism with wind fields generated by climate modeling, we find that Titan's dunes grow by sediment transport on a nonmobile substratum. To be fully consistent with both the local crestline orientations and the eastward propagation of Titan's dunes, the sediment should be predominantly transported by strong eastward winds, most likely generated by equinoctial storms or occasional fast westerly gusts. Additionally, convergence of the meridional transport predicted in models can explain why Titan's dunes are confined within ±30° latitudes, where sediment fluxes converge.

  7. Biophysical mechanism of differential growth during gravitropism

    NASA Technical Reports Server (NTRS)

    Cosgrove, D.

    1984-01-01

    A research project is described the goal of which is to determine the mechanism of gravitropic curvature in plant stems at the biophysical and the cellular level. The reorientation of plant organs under the influence of gravity is due to differential growth of the upper and lower sides of the organ. The rate of plant cell enlargement is governed by four biophysical parameters: (1) the extensibility of the cell wall; (2) the minimum stress in the cell wall required for wall expansion (the "yield threshold'); (3) the osmotic pressure difference between the cell contents and the water source; and (4) the hydraulic conductivity of the pathway for water uptake. Gravitropic response must involve differential alteration of one or more of these four parameters on the two sides of the growing organ. Each of these factors will be examined to assess the role it plays in gravitropism.

  8. A Novel Growth Process of Calcium Carbonate Crystals in Silk Fibroin Hydrogel System

    E-print Network

    Paris-Sud XI, Université de

    to silk-fibroin-like protein in nacre in amino acid sequence and secondary structure [14] compared1 A Novel Growth Process of Calcium Carbonate Crystals in Silk Fibroin Hydrogel System Yufei Ma carbonate (CaCO3) crystal growth in the silk fibroin (SF) hydrogel with different concentrations by a simple

  9. Modeling of ice crystal growth in laminar falling films for the production of pumpable ice slurries

    Microsoft Academic Search

    Kamal A. R. Ismail; Musa M. Radwan

    2003-01-01

    A generalized model has been developed to approximate the rate of ice crystal growth in a laminar developing falling film. In this model, the conservation equations of mass, momentum, energy and the transport equation governing ice crystal growth were solved numerically using finite differences based on the control volume method. The thermophysical properties of the mixture, such as density, specific

  10. The crystal structure and growth direction of nanowire arraysCu fabricated on a copper surface

    E-print Network

    Wang, Zhong L.

    The crystal structure and growth direction of nanowire arraysCu 2 S fabricated on a copper surface We examine the crystal structure and growth direction of nanowire arrays grown from copper surfaces10 On this line, we have recently discovered that by exposing a surfactant-treated copper surface

  11. Expression of osteopontin, a urinary inhibitor of stone mineral crystal growth, in rat kidney

    Microsoft Academic Search

    Jack G Kleinman; Ann Beshensky; Elaine M Worcester; Dennis Brown

    1995-01-01

    Expression of osteopontin, a urinary inhibitor of stone mineral crystal growth, in rat kidney. Cultured mouse kidney cortical cells secrete osteopontin, a bone matrix protein that is also found in urine. Osteopontin is associated with cell proliferation\\/tumerogenesis and also inhibits kidney stone mineral crystal growth [1]. Using antibodies raised against osteopontin isolated from the culture medium, we localized osteopontin in

  12. Growth and electrochromic properties of single-crystal V2O5 nanorod arrays

    E-print Network

    Cao, Guozhong

    Growth and electrochromic properties of single-crystal V2O5 nanorod arrays Katsunori Takahashi reports a study on the template-based growth and electrochromic properties of single-crystal vanadium demonstrated significantly enhanced electrochromic properties; both the larger change of transmittance

  13. Magnetic field effects on float-zone Si crystal growth. III. Strong axial fields

    NASA Astrophysics Data System (ADS)

    Robertson, Glenn D.; O'Connor, Dennis

    1986-07-01

    Axial magnetic fields ranging in strength up to 5000 G have been applied during the float-zone growth of dislocation-free Ga-doped <100> silicon crystals. All crystals were grown at a pull rate of 4 mm/min with rotation rates from 12 to 0 rpm. Evaluation by spreading resistance showed a marked reduction in the dopant concentration fluctuations for certain growth conditions in axial fields greater than 3000 G. However, in the strong fields the growth axis of the crystals wandered randomly and made such crystals very difficult to grow, especially as the rotation rate was reduced. A crystal growth without rotation in a 5000 G field gave the most uniform doping but only in a central "core" region extending over about one third of the crystal diameter.

  14. Method for the growth of large low-defect single crystals

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony (Inventor); Neudeck, Philip G. (Inventor); Trunek, Andrew J. (Inventor); Spry, David J. (Inventor)

    2008-01-01

    A method and the benefits resulting from the product thereof are disclosed for the growth of large, low-defect single-crystals of tetrahedrally-bonded crystal materials. The process utilizes a uniquely designed crystal shape whereby the direction of rapid growth is parallel to a preferred crystal direction. By establishing several regions of growth, a large single crystal that is largely defect-free can be grown at high growth rates. This process is particularly suitable for producing products for wide-bandgap semiconductors, such as SiC, GaN, AlN, and diamond. Large low-defect single crystals of these semiconductors enable greatly enhanced performance and reliability for applications involving high power, high voltage, and/or high temperature operating conditions.

  15. Interface Shape and Growth Rate Analysis of Se/GaAs Bulk Crystals Grown in the NASA Crystal Growth Furnace (CGF)

    NASA Technical Reports Server (NTRS)

    Bly, J. M.; Kaforey, M. L.; Matthiesen, D. H.; Chait, A.

    1997-01-01

    Selenium-doped gallium arsenide, Se/GaAs, bulk crystals have been grown on earth using NASA's crystal growth furnace (CGF) in preparation for microgravity experimentation on the USML-2 spacelab mission. Peltier cooling pulses of 50 ms duration, 2040 A magnitude, and 0.0033 Hz frequency were used to successfully demark the melt-solid interface at known times during the crystal growth process. Post-growth characterization included interface shape measurement, growth rate calculation, and growth rate transient determinations. It was found that the interface shapes were always slightly concave into the solid. The curvature of the seeding interfaces was typically 1.5 mm for the 15 mm diameter samples. This was in agreement with the predicted interface shapes and positions relative to the furnace determined using a numerical model of the sample/ampoule/cartridge assembly (SACA).

  16. Nucleation and growth of aragonite crystals at the growth front of nacres in pearl oyster, Pinctada fucata.

    PubMed

    Saruwatari, Kazuko; Matsui, Tomoyuki; Mukai, Hiroki; Nagasawa, Hiromichi; Kogure, Toshihiro

    2009-06-01

    The growth front of nacreous layer, which lies just above the outer prismatic layer, is one of the crucial areas to comprehend the formation of nacreous aragonite. The crystallographic properties of aragonite crystals at the growth front in pearl oyster, Pinctada fucata, were investigated using scanning electron microscopy with electron back-scattered diffraction, and transmission electron microscopy with focused ion beam sample preparation technique. Nano-sized aragonite crystals nucleate with random crystallographic orientation inside the dimples on the surface of the organic matrix that covers the outer prismatic columns. The dimples are filled with horn-like aragonite crystals, which enlarge from the bottom to the upper surface to form hemispheric domes. The domes grow concentrically and coalesce together to become the initial nacreous layer. The c-axes of aragonite at the top surface of the domes are preferentially oriented perpendicular to the surface. The horn-like aragonite and its crystallographic orientation are probably attained by geometrical selection with the fastest growth rate of aragonite along the c-axis, until organic sheets are continuously formed and interrupt the crystal growth of aragonite. The further crystal growth along the shell thickness is attained via mineral bridges through discontinuity or holes in the organic sheets. These results indicate that the crystal growth of aragonite at the growth front results from not only biotic process but also inorganic ones such as geometrical selection and mineral bridges. PMID:19328543

  17. The dispersion of growth rate as a result of different crystal perfection

    Microsoft Academic Search

    U. Tanneberger; R. Lacmann; A. Herden; H. Klapper; D. Schmiemann; R. A. Becker; A. Mersmann; U. Zacher

    1996-01-01

    The aim of the cooperative work of the above mentioned institutes was to find out the reason for growth rate dispersion (GRD). Measurements of growth rate (overall or face-specific), microhardness (HV), etch pit density (EPD) and crystal perfection (X-ray topography and Laue X-ray method) were carried out using KAl(SO4)2 · 12H2O (PA) and KNO3 (PN) crystals. The investigated crystals were

  18. Incorporation of boron and vanadium during PVT growth of 6H-SiC crystals

    Microsoft Academic Search

    M. Bickermann; B. M. Epelbaum; D. Hofmann; T. L. Straubinger; R. Weingärtner; A. Winnacker

    2001-01-01

    To obtain semi-insulating SiC by vanadium and boron co-doping during PVT growth, a detailed understanding of the dopant (B,V) incorporation is required. Crystal growth of 1.4?? 6H-SiC on either Si or C face, doped with boron or vanadium, respectively, was performed. For reference purposes, also nominally undoped SiC crystals were grown. It is shown that in nominally undoped crystals nitrogen

  19. CCMR: Growth of Olivine Single Crystals for Point Defect and Transport Investigations

    NSDL National Science Digital Library

    Maier, Mitchell

    2010-08-15

    Using the float-zone technique and an image furnace, single crystals of the olivine compound Mn2SiO4 were grown to be used for defect-related properties analysis. The crystals grown so far are not of high enough quality to perform this analysis on; however, the crystals are well suited for producing oriented seed crystals for later high quality crystal growth. The crystals were grown with the aid of a ceramic afterheater. This type of afterheater proved effective at growing crack-free single crystals, and the use of an afterheater is planned to be implemented for all further growth of high-quality single crystals of Mn2SiO4.

  20. Indium telluride nanotubes: Solvothermal synthesis, growth mechanism, and properties

    NASA Astrophysics Data System (ADS)

    Zhou, Liyan; Yan, Shancheng; Lu, Tao; Shi, Yi; Wang, Jianyu; Yang, Fan

    2014-03-01

    A convenient solvothermal approach was applied for the first time to synthesize In2Te3 nanotubes. The morphology of the resultant nanotubes was studied by scanning electron microscopy and transmission electron microscopy. Nanotubes with a relatively uniform diameter of around 500 nm, tube wall thickness of 50-100 nm, and average length of tens of microns were obtained. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy were used to study the crystal structures, composition, and optical properties of the products. To understand the growth mechanism of the In2Te3 nanotubes, we studied the influences of temperature, reaction time, and polyvinylpyrrolidone (PVP) and ethylene diamine (EDA) dosages on the final products. Based on the experimental results, a possible growth mechanism of In2Te3 nanotubes was proposed. In this mechanism, TeO3-2 is first reduced to allow nucleation. Circumferential edges of these nucleated molecules attract further deposition, and nanotubes finally grow rapidly along the c-axis and relatively slowly along the circumferential direction. The surface area of the products was determined by BET and found to be 137.85 m2 g-1. This large surface area indicates that the nanotubes may be suitable for gas sensing and hydrogen storage applications. The nanotubes also showed broad light detection ranging from 300 nm to 1100 nm, which covers the UV-visible-NIR regions. Such excellent optical properties indicate that In2Te3 nanotubes may enable significant advancements in new photodetection and photosensing applications.