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1

Fluid mechanics in crystal growth - The 1982 Freeman scholar lecture  

Microsoft Academic Search

An attempt is made to unify the current state of knowledge in crystal growth techniques and fluid mechanics. After identifying important fluid dynamic problems for such representative crystal growth processes as closed tube vapor transport, open reactor vapor deposition, and the Czochralski and floating zone melt growth techniques, research results obtained to date are presented. It is noted that the

Simon Ostrach

1983-01-01

2

Fluid mechanics in crystal growth - The 1982 Freeman scholar lecture  

NASA Technical Reports Server (NTRS)

An attempt is made to unify the current state of knowledge in crystal growth techniques and fluid mechanics. After identifying important fluid dynamic problems for such representative crystal growth processes as closed tube vapor transport, open reactor vapor deposition, and the Czochralski and floating zone melt growth techniques, research results obtained to date are presented. It is noted that the major effort to date has been directed to the description of the nature and extent of bulk transport under realistic conditions, where bulk flow determines the heat and solute transport which strongly influence the temperature and concentration fields in the vicinity of the growth interface. Proper treatment of near field, or interface, problems cannot be given until the far field, or global flow, involved in a given crystal growth technique has been adequately described.

Ostrach, S.

1983-01-01

3

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

USGS Publications Warehouse

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.

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

2000-01-01

4

Mechanism of habit change for atmospheric ice crystal growth  

NASA Astrophysics Data System (ADS)

The basic mechanism that controls the shape change of ice crystal with temperature and supersaturation, or so-called ice crystal habit change, was investigated. From the preliminary analysis of experimental data, it was found that surface kinetic processes on the crystal are responsible in controlling the habit change. Therefore, relevant surface factors and processes were identified first. One of the most important factors was the line tension, or the surface free energy on the side of the two-dimensional embryo. Based on the physical meaning of the line tension and the surface tension, their fundamental difference was clarified under ideal conditions. A method to represent the hexagonal ice crystal lattice under random hydrogen arrangement was developed. Applying this last method, the surface factors such as the line tension and the surface tension for the ideal ice crystal were computed by using the intermolecular potential of the water molecule. Roles of liquid-like layer, transitional liquid layer and interface roughening in the habit change was clarified. The ordinary Brunaeur-Emmett-Teller (BET) adsorption equation was modified to describe the ice crystal growth problem. Through these analyses, the origin of the habit change was traced to the unique characteristic of the hydrogen bond that expands during freezing of water. The same characteristic led to a minimum in the free energy of two-dimensional embryo formation on the crystal plane through the line tension, which was shown to be a function of chemical potential difference. The operation of the two-dimensional nucleation mechanism for ice crystal growth was thus confirmed. Semiquantitative simulation of the habit change process for ice crystals growing both in air and in vapor alone after considering various surface factors was carried out, and the results showed a reasonable agreement with experimental data.

Lu, Qiu-Jiang

5

Physical Mechanisms of Crystal Growth Modification by Biomolecules  

NASA Astrophysics Data System (ADS)

During the process of biomineralization, living organisms use macromolecules to direct the nucleation and growth of a variety of inorganic materials. Because biomineral structures exhibit complex topologies, hierarchical design, and unique materials properties, an understanding of the underlying mechanisms of biomolecular controls over mineral growth presents an opportunity to develop new strategies towards synthesis of novel materials for applications across a wide range of technologies. Herein 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 calcium carbonate and calcium oxalate crystal surfaces during the growth are reviewed. The results show how the stereochemical relationships between additive and atomic step leads to modifications of crystal shape. In some cases, the inhibitory effects of strong binders are well-explained by a model of growth inhibition based on the classic Cabrera-Vermilyea theory, but updated to take into account the particular nature of biomolecular adsorption dynamics. The consequences include a positive feedback between peptide adsorption and step inhibition that results in bistable growth with rapid switching from fast to near-zero growth rates for very small changes in supersaturation. The phenomenon of biomolecule-induced growth acceleration is also reviewed and shown to be common to both the oxalate and carbonate systems. The source of acceleration is related to the activation barrier for solute attachment to steps. Finally, experimental and theoretical results are presented that suggest most biomineral phases can not be described by conventional models in which kink formation due to thermal fluctuations at step edges is rapid enough to ensure the availability of kinks. Instead, growth is kink-limited. As a consequence, biomolecule-step interactions cannot be interpreted with traditional thermodynamic models based on minimization of the Gibbs free energy. Instead these interactions follow a different mechanism determined by the kinetics of attachment and detachment. The general nature of these findings support the plausibility of their application to industrial systems.

De Yoreo, James J.

2010-07-01

6

Crystal Growth and Fluid Mechanics Problems in Directional Solidification  

NASA Technical Reports Server (NTRS)

An investigation of a more complete theoretical understanding of convection effects in a vertical Bridgman apparatus is described. The aim is to develop a clear understanding of scalings of various features of dendritic crystal growth in the case that both the surface energy and undercooling are small.

Tanveer, S.; Baker, G. R.; Foster, M. R.

1996-01-01

7

Mechanisms of protein and virus crystal growth: An atomic force microscopy study of canavalin and STMV crystallization  

SciTech Connect

The evolution of surface morphology and step dynamics during growth of rhombohedral crystals of the protein canavalin and crystals of the cubic satellite tobacco mosaic virus (STMV) have been investigated for the first time 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 clusters 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 the 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.

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

1996-05-01

8

Crystal growth and fluid mechanics problems in directional solidification  

NASA Technical Reports Server (NTRS)

Broadly speaking, our efforts have been concentrated in two aspects of directional solidification: (A) a more complete theoretical understanding of convection effects in a Bridgman apparatus; and (B) a clear understanding of scalings of various features of dendritic crystal growth in the sensitive limit of small capillary effects. For studies that fall within class A, the principal objectives are as follows: (A1) Derive analytical formulas for segregation, interfacial shape and fluid velocities in mathematically amenable asymptotic limits. (A2) Numerically verify and extend asymptotic results to other ranges of parameter space with a view to a broader physical understanding of the general trends. With respect to studies that fall within class B, the principal objectives include answering the following questions about dendritic crystal growth: (B1) Are there unsteady dendrite solutions in 2-D to the completely nonlinear time evolving equations in the small surface tension limit with only a locally steady tip region with well defined tip radius and velocity? Is anisotropy in surface tension necessary for the existence of such solutions as it is for a true steady state needle crystal? How does the size of such a local region depend on capillary effects, anisotropy and undercooling? (B2) How do the different control parameters affect the nonlinear amplification of tip noise and dendritic side branch coarsening?

Tanveer, Saleh; Baker, Gregory R.; Foster, Michael R.

1994-01-01

9

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

USGS Publications Warehouse

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.

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

1998-01-01

10

Crystal growth mechanisms in miarolitic cavities in the Lake George ring complex and vicinity, Colorado  

USGS Publications Warehouse

The Crystal Peak area of the Pikes Peak batholith, near Lake George in central Colorado, is world-renowned for its crystals of amazonite (the blue-green variety of microcline) and smoky quartz. Such crystals, collected from individual miarolitic pegmatites, have a remakably small variation in crystal size within each pegmatite, and the shapes of plots of their crystal size distributions (CSDs) are invariably lognormal or close to lognormal in all cases. These observations are explained by a crystal growth mechanism that was governed initially by surface-controlled kinetics, during which crystals tended to grow larger in proportion to their size, thereby establishing lognormal CSDs. Surface-controlled growth was followed by longer periods of supply controlled growth, during which growth rate was predominantly size-independent, consequently preserving the lognormal shapes of the CSDs and the small size variation. The change from surface- to supply controlled growth kinetics may have resulted from an increasing demand for nutrients that exceeded diffusion limitations of the system. The proposed model for crystal growth in this locality appears to be common in the geologic record, and can be used with other information, such as isotopic data, to deduce physico-chemical conditions during crystal formation.

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

1999-01-01

11

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

PubMed

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

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

2014-01-24

12

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

NASA Astrophysics Data System (ADS)

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.

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

2014-01-01

13

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

14

New insights into the mechanism of CVD diamond growth: Single crystal diamond in MW PECVD reactors  

E-print Network

New insights into the mechanism of CVD diamond growth: Single crystal diamond in MW PECVD reactors Yu. A. Mankelevich a , P.W. May b, a Nuclear Physics Institute, Moscow State University, 119991 the gas-phase decomposition of a gas mixture containing a small quantity of a hydrocarbon in excess

Bristol, University of

15

An interfacial energy mechanism for the complete inhibition of crystal growth by inhibitor adsorption  

E-print Network

to the difference in interfacial tensions or edge energies for surfaces with and without an adsorbed inhibitor Leeden et al.25 We will take a different approach from the works in Ref. 24 and 25 to offerAn interfacial energy mechanism for the complete inhibition of crystal growth by inhibitor

Firoozabadi, Abbas

16

Crystal Growth Technology  

NASA Astrophysics Data System (ADS)

This volume deals with the technologies of crystal fabrication, of crystal machining, and of epilayer production and is the first book on industrial and scientific aspects of crystal and layer production. The major industrial crystals are treated: Si, GaAs, GaP, InP, CdTe, sapphire, oxide and halide scintillator crystals, crystals for optical, piezoelectric and microwave applications and more. Contains 29 contributions from leading crystal technologists covering the following topics:

    General aspects of crystal growth technology Silicon Compound semiconductors Oxides and halides Crystal machining Epitaxy and layer deposition Scientific and technological problems of production and machining of industrial crystals are discussed by top experts, most of them from the major growth industries and crystal growth centers. In addition, it will be useful for the users of crystals, for teachers and graduate students in materials sciences, in electronic and other functional materials, chemical and metallurgical engineering, micro-and optoelectronics including nanotechnology, mechanical engineering and precision-machining, microtechnology, and in solid-state sciences.

    Scheel, Hans J.; Fukuda, Tsuguo

    2004-06-01

17

Hydrothermal crystallization of barium titanate: Mechanisms of nucleation and growth  

NASA Astrophysics Data System (ADS)

Barium titanate is synthesized under hydrothermal conditions by the reaction of a variety of titania precursors with aqueous solutions of Ba(OH)sb2 at 80sp°C. Particles processed at relatively low concentrations of Ba(OH)sb2 are micro-sized and highly aggregated, but increasing concentrations cause the particle size to decrease, resulting in nanometer-sized and fairly monodispersed particles. The change in particle size and morphology at various Ba(OH)sb2 concentrations is controlled by the dissolution of titania and precipitation of BaTiOsb3. In order to explain the origin of "raspberry-like" BaTiOsb3 particles and the generation of hierarchically ordered BaTiOsb3 aggregate comprised of primary, crystalline particles, which exhibit an unusually high degree of crystallographic alignment, the role of colloidal stability and therefore controlled aggregation of precipitated primary particles is taken into account. Formation of SrTiOsb3 on BaTiOsb3 particles reveal that two different morphologies for the growing SrTiOsb3 exists and that the form taken by SrTiOsb3 depends on the degree of supersaturation. In concentrated solutions, homogeneous nucleation and aggregation growth occur. In dilute solutions, heterogeneous nucleation and continuous growth of SrTiOsb3 promote epitaxial growth. BaTiOsb3 particles prepared by the alkoxide (Ti(OCsb3Hsb7)sb4) -hydroxide (Ba(OH)sb2) route under hydrothermal conditions show that secondary processed such as aggregation and recrystallization are important to control the particle size and morphology. Particle clustering, and rearrangement of nanometer-sized BaTiOsb3 particles, and particulate uniformity can then be explained in terms of solution reactions and colloidal behavior.

Chun, Chang-Min

18

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

USGS Publications Warehouse

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).

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

2000-01-01

19

New AFM Techniques for Investigating Molecular Growth Mechanisms of Protein Crystals  

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

20

Growth Mechanism of Laser Annealing of Nickel-Induced Lateral Crystallized Silicon Films  

NASA Astrophysics Data System (ADS)

The growth mechanism of a hybrid process to crystallize amorphous silicon (a-Si) film was studied. In the process, a-Si was first converted to polycrystalline silicon (poly-Si) using Ni-metal-induced lateral crystallization (NILC), and then annealed with an excimer laser (ELA). Two regions based on different crystallization mechanisms were found on these NILC-ELA films: (A) a-Si melting region, and (B) a-Si/poly-Si melting region. In the a-Si melting region, the sizes and shapes of the needle Si grains were similar to those of NILC poly-Si. In the a-Si/poly-Si melting region, the shapes and sizes of poly-Si grains were quite different from those of NILC needlelike grains. Two crystallization regimes were found in the a-Si/poly-Si melting region: (1) geometrical coalescence regime and (2) complete melting regime. In the geometrical coalescence regime, the width of grains dramatically increased to 600 nm due to the geometrical coalescence of Si needle grains. However, in the complete melting regime, the NILC Si films melted completely. Small poly-Si grains were formed by homogeneous nucleation and growth.

Hu, Guo-Ren; Wu, YewChung Sermon; Chao, Chi-Wei; Shih, Hsieh-Chih

2006-01-01

21

Growth, Mechanical, Thermal and Spectral Properties of Cr3+?MgMoO4 Crystal  

PubMed Central

This paper reports the growth, mechanical, thermal and spectral properties of Cr3+?MgMoO4 crystals. The Cr3+?MgMoO4 crystals with dimensions up to 30 mm×18 mm×14 mm were obtained by TSSG method. The absorption cross-sections of 4A2?4T1 and 4A2?4T2 transitions are 12.94×10?20 cm2 at 493 nm and 7.89×10?20 cm2 at 705 nm for E//Ng, respectively. The Cr3+?MgMoO4 crystal shows broad band emission extending from 750 nm to 1300 nm with peak at about 705 nm. The emission cross-section with FWHM of 188 nm is 119.88×10?20 cm2 at 963 nm for E//Ng. The investigated results showed that the Cr3+?MgMoO4 crystal may be regarded as a potential tunable laser gain medium. PMID:22291935

Li, Lingyun; Huang, Yisheng; Zhang, Lizhen; Lin, Zhoubin; Wang, Guofu

2012-01-01

22

Mechanism for diamond nucleation and growth on single crystal copper surfaces implanted with carbon  

NASA Technical Reports Server (NTRS)

The nucleation and growth of diamond crystals on single-crystal copper surfaces implanted with carbon ions is studied. Microwave plasma-enhanced chemical-vapor deposition is used for diamond growth. The single-crystal copper substrates were implanted either at room or elevated temperature with carbon ions prior to diamond nucleation. This procedure leads to the formation of a graphite film on the copper surface which greatly enhances diamond crystallite nucleation. A simple lattice model is constructed for diamond growth on graphite as 111 line (diamond) parallel to 0001 line (graphite) and 110 line (diamond) parallel to 1 1 -2 0 (graphite).

Ong, T. P.; Xiong, Fulin; Chang, R. P. H.; White, C. W.

1992-01-01

23

Synthesis, growth, structural, optical, thermal, dielectric and mechanical studies of an organic guanidinium p-nitrophenolate crystal  

NASA Astrophysics Data System (ADS)

Guanidinium p-nitrophenolate (GUNP), a novel organic compound, was synthesized and crystals were grown from methanol solution by a slow evaporation solution growth technique. A single crystal X-ray diffraction study elucidated the crystal structure of GUNP belonging to the orthorhombic crystal system with space group Pnma. Thermal studies revealed that the GUNP crystal is thermally stable up to 192 °C. The lower cut-off wavelength of GUNP was found to be 505 nm by UV-vis-NIR spectral studies. The luminescence properties of the GUNP crystal were investigated. The three independent tensor coefficients ?11, ?22 and ?33 of the dielectric permittivity were calculated. The mechanical properties of the grown crystal were studied by Vickers' microhardness hardness technique.

Dhavamurthy, M.; Peramaiyan, G.; Mohan, R.

2014-08-01

24

Liquid encapsulated crystal growth  

NASA Technical Reports Server (NTRS)

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.

Morrison, Andrew D. (Inventor)

1989-01-01

25

Liquid encapsulated crystal growth  

NASA Technical Reports Server (NTRS)

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 and adjacent reservoir or by rotating the ampoule to rotate the crystal into the encapsulant layer.

Morrison, Andrew D. (inventor)

1987-01-01

26

Crystal growth, structural, thermal and mechanical behavior of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of L-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV-Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vicker's microhardness method.

Mahadevan, M.; Ramachandran, K.; Anandan, P.; Arivanandhan, M.; Bhagavannarayana, G.; Hayakawa, Y.

2014-12-01

27

Crystal growth, structural, thermal and mechanical behavior of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals.  

PubMed

Single crystals of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of l-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV-Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vicker's microhardness method. PMID:24967545

Mahadevan, M; Ramachandran, K; Anandan, P; Arivanandhan, M; Bhagavannarayana, G; Hayakawa, Y

2014-12-10

28

Growth, structural, optical, thermal and mechanical properties of ammonium pentaborate single crystal.  

PubMed

Nonlinear optical single crystals of ammonium pentaborate (APB) were grown by the slow cooling method from aqueous solution. Grown crystal was characterized by powder X-ray diffraction (PXRD) and FT-IR spectral analysis. Perfection of the grown crystal was evaluated by high-resolution X-ray diffractometry (HRXRD). The effect of nylon threading on the perfection of the grown bigger crystal was also studied by HRXRD. The range and percentage of optical transmission was ascertained by recording UV-vis-NIR spectrum. Thermal properties were investigated by TG-DTA and DSC analyses. Its mechanical hardness was estimated by Vickers microhardness tester. PMID:18329333

Balakrishnan, T; Bhagavannarayana, G; Ramamurthi, K

2008-11-15

29

Growth, structural, optical, thermal and mechanical properties of ammonium pentaborate single crystal  

NASA Astrophysics Data System (ADS)

Nonlinear optical single crystals of ammonium pentaborate (APB) were grown by the slow cooling method from aqueous solution. Grown crystal was characterized by powder X-ray diffraction (PXRD) and FT-IR spectral analysis. Perfection of the grown crystal was evaluated by high-resolution X-ray diffractometry (HRXRD). The effect of nylon threading on the perfection of the grown bigger crystal was also studied by HRXRD. The range and percentage of optical transmission was ascertained by recording UV-vis-NIR spectrum. Thermal properties were investigated by TG-DTA and DSC analyses. Its mechanical hardness was estimated by Vickers microhardness tester.

Balakrishnan, T.; Bhagavannarayana, G.; Ramamurthi, K.

2008-11-01

30

Crystal Growth and Design  

NSDL National Science Digital Library

An electronic version of this journal from the American Chemical Society is available for free through June 30, 2001. Crystal Growth and Design is "a new journal from the American Chemical Society, dedicated to publishing articles on the physical, chemical, and biological phenomena and processes related to crystal growth and design of new materials."

31

Crystal growth, structural, crystalline perfection, optical and mechanical properties of Nd3+ doped sulfamic acid (SA) single crystals  

NASA Astrophysics Data System (ADS)

Sulfamic acid (SA) single crystals, both pure and doped with 1, 2.5 and 5 mol% Nd, were grown successfully in an aqueous solution by the slow cooling method. Powder X-ray diffraction patterns were recorded to check the variation in the lattice parameters and phase of the crystals. The optical transparency was found to be higProd. Type: FTPhest (?80%) for the 1 mol% Nd3+ doped SA single crystal. The optical band gap was also calculated and found to be ?4.31, 4.20 and 3.67 eV. The influence of Nd3+ doping on the crystalline perfection was assessed by a high resolution X-ray diffractometer (HRXRD) and shows that the grown crystals could accommodate Nd3+ at the interstitial positions in the crystalline matrix of SA up to some critical concentration without any deterioration in the crystalline perfection. The etching studies were carried out and the etch pits densities were calculated. The mechanical property of grown single crystals was also studied.

Shkir, Mohd.; Riscob, B.; Ganesh, V.; Vijayan, N.; Gupta, Rahul; Plaza, J. L.; Dieguez, E.; Bhagavannarayana, G.

2013-10-01

32

Self-catalytic crystal growth, formation mechanism, and optical properties of indium tin oxide nanostructures  

PubMed Central

In-Sn-O nanostructures with rectangular cross-sectional rod-like, sword-like, and bowling pin-like morphologies were successfully synthesized through self-catalytic growth. Mixed metallic In and Sn powders were used as source materials, and no catalyst layer was pre-coated on the substrates. The distance between the substrate and the source materials affected the size of the Sn-rich alloy particles during crystal growth in a quartz tube. This caused In-Sn-O nanostructures with various morphologies to form. An X-ray photoelectron spectroscope and a transmittance electron microscope with an energy-dispersive X-ray spectrometer were used to investigate the elemental binding states and compositions of the as-synthesized nanostructures. The Sn doping and oxygen vacancies in the In2O3 crystals corresponded to the blue-green and yellow-orange emission bands of the nanostructures, respectively. PMID:23965167

2013-01-01

33

Measurements of Protein Crystal Face Growth Rates  

NASA Technical Reports Server (NTRS)

Protein crystal growth rates will be determined for several hyperthermophile proteins.; The growth rates will be assessed using available theoretical models, including kinetic roughening.; If/when kinetic roughening supersaturations are established, determinations of protein crystal quality over a range of supersaturations will also be assessed.; The results of our ground based effort may well address the existence of a correlation between fundamental growth mechanisms and protein crystal quality.

Gorti, S.

2014-01-01

34

Quartz crystal growth  

DOEpatents

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.

Baughman, Richard J. (Albuquerque, NM)

1992-01-01

35

Growth rates of protein crystals  

PubMed Central

Protein crystallization is important for structural biology. The rate at which a protein crystallizes is often the bottleneck in determining the protein’s structure. Here, we give a physical model for the growth rates of protein crystals. Most materials crystallize faster under stronger growth conditions, however, protein crystallization slows down under the strongest conditions. Proteins require a crystallization slot of ’just right’ conditions. Our model provides an explanation. Unlike simpler materials, proteins are orientationally asymmetrical. Under strong conditions, protein molecules attempt to crystallize too quickly, in wrong orientations, blocking surface sites for more productive crystal growth. The model explains the observation that increasing the net charge on a protein increases the crystal growth rate. The model predictions are in good agreement with experiments on the growth rates of tetragonal lysozyme crystals as a function of pH, salt concentration, temperature, and protein concentration. PMID:22339624

Schmit, Jeremy D.; Dill, Ken

2012-01-01

36

Protein crystal growth tray assembly  

NASA Technical Reports Server (NTRS)

A protein crystal growth tray assembly includes a tray that has a plurality of individual crystal growth chambers. Each chamber has a movable pedestal which carries a protein crystal growth compartment at an upper end. The several pedestals for each tray assembly are ganged together for concurrent movement so that the solutions in the various pedestal growth compartments can be separated from the solutions in the tray's growth chambers until the experiment is to be activated.

Carter, Daniel C. (inventor); Miller, Teresa Y. (inventor)

1992-01-01

37

Protein crystal growth in microgravity  

NASA Technical Reports Server (NTRS)

Major advances have been made in several of the experimental aspects of protein crystallography, leaving protein crystallization as one of the few remaining bottlenecks. As a result, it has become important that the science of protein crystal growth is better understood and that improved methods for protein crystallization are developed. Preliminary experiments with both small molecules and proteins indicate that microgravity may beneficially affect crystal growth. For this reason, a series of protein crystal growth experiments using the Space Shuttle was initiated. 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. Various optical techniques are being utilized to monitor the crystal growth process from the incipient or nucleation stage and throughout the growth phase. The eventual goal of these studies is to develop a system which utilizes optical monitoring for dynamic control of the crystallization process.

Rosenblum, William M.; Delucas, Lawrence J.; Wilson, William W.

1989-01-01

38

Synthesis, crystal growth, structural, optical, thermal and mechanical properties of novel organic NLO material: Ammonium malate  

Microsoft Academic Search

Ammonium malate (AM), an organic nonlinear optical material, has been synthesized and single crystals, with dimensions up to 38×35×27mm3, have been grown from aqueous solution. The crystal structure of AM has been determined, and it belongs to the non-centro symmetric space group Cc. The structural perfection of the grown crystals has been analysed by high-resolution X-ray diffraction (HRXRD) rocking curve

G. Anandha babu; G. Bhagavannarayana; P. Ramasamy

2008-01-01

39

Zeolite crystal growth in space  

NASA Technical Reports Server (NTRS)

The growth of large, uniform zeolite crystals in high yield in space can have a major impact on the chemical process industry. Large zeolite crystals will be used to improve basic understanding of adsorption and catalytic mechanisms, and to make zeolite membranes. To grow large zeolites in microgravity, it is necessary to control the nucleation event and fluid motion, and to enhance nutrient transfer. Data is presented that suggests nucleation can be controlled using chemical compounds (e.g., Triethanolamine, for zeolite A), while not adversely effecting growth rate. A three-zone furnace has been designed to perform multiple syntheses concurrently. The operating range of the furnace is 295 K to 473 K. Teflon-lined autoclaves (10 ml liquid volume) have been designed to minimize contamination, reduce wall nucleation, and control mixing of pre-gel solutions on orbit. Zeolite synthesis experiments will be performed on USML-1 in 1992.

Sacco, Albert, Jr.; Thompson, Robert W.; Dixon, Anthony G.

1991-01-01

40

Physical vapor transport crystal growth  

NASA Technical Reports Server (NTRS)

The goals of this research are two-fold: to study effective means of growing ZnSe crystals of good optical quality and to determine the advantages of growing such crystals in microgravity. As of this date the optimal conditions for crystal growth have not been determined. However, successful growth runs were made in two furnances and the results are given.

Yoel, Dave W.; Anderson, Elmer; Wu, Maw-Kuen; Cheng, H. Y.

1987-01-01

41

Crystal Shape Evolution in Detached Bridgman Growth  

NASA Technical Reports Server (NTRS)

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

Volz, M. P.; Mazuruk, K.

2013-01-01

42

Crystal Shape Evolution in Detached Bridgman Growth  

NASA Technical Reports Server (NTRS)

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.

Volz, M. P.; Mazuruk, K.

2013-01-01

43

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

44

Protein crystal growth in microgravity  

NASA Technical Reports Server (NTRS)

The crystals of most proteins or other biological macromolecules are poorly ordered and diffract to lower resolutions than those observed for most crystals of simple organic and inorganic compounds. Crystallization in the microgravity environment of space may improve crystal quality by eliminating convection effects near growing crystal surfaces. A series of 11 different protein crystal growth experiments was performed on U.S. Space Shuttle flight STS-26 in September 1988. The microgravity-grown crystals of gamma-interferon D1, porcine elastase, and isocitrate lyase are larger, display more uniform morphologies, and yield diffraction data to significantly higher resolutions than the best crystals of these proteins grown on earth.

Delucas, Lawrence J.; Smith, Craig D.; Smith, H. Wilson; Vijay-Kumar, Senadhi; Senadhi, Shobha E.; Ealick, Steven E.; Carter, Daniel C.; Snyder, Robert S.

1989-01-01

45

Protein Crystals and their Growth  

NASA Technical Reports Server (NTRS)

Recent results on binding between protein molecules in crystal lattice, crystal-solution surface energy, elastic properties and strength and spontaneous crystal cracking are reviewed and discussed in the first half of this paper (Sea 2-4). In the second par&, some basic approaches to solubility of proteins are followed by overview on crystal nucleation and growth (Sec 5). It is argued that variability of mixing in batch crystallization may be a source for scattering of crystal number ultimately appearing in the batch. Frequency at which new molecules join crystal lattice is measured by kinetic coefficient and related to the observable crystal growth rate. Numerical criteria to discriminate diffusion and kinetic limited growth are discussed on this basis in Sec 7. In Sec 8, creation of defects is discussed with the emphasis on the role of impurities and convection on macromolecular crystal I;erfection.

Chernov, A. A.

2004-01-01

46

Coating effects on crack growth in a single crystal nickel based alloy during thermo-mechanical fatigue  

SciTech Connect

Single crystal specimens of the nickel based alloy SRR99 with [001] orientation are subjected to TMF cycling between 300 C and 1,050 C, using a {minus}135{degree} lag between temperature and mechanical strain, and various R ratios. The in-situ observation of the test specimen by means of a computer vision system during TMF testing enables the initiation of microcracks to be detected when cracks have reached lengths of approximately 30 {micro}m at the surface. High densities of point initiated micro-cracks are generated during the early stages of the TMF life. Crack increment measurements reveal marked differences between the growth rates of individual micro-cracks. The presence of a nickel-aluminide coating consistently reduces the TMF life, due largely to higher growth rates of the main crack in the substrate. In order to estimate the influence of initial crack distribution and density on life, a two dimensional crack shielding model is incorporated in a computer program which is used to simulate the growth of interacting, parallel surface cracks. The effect of various parameters, including the density and the initial distribution of the microcracks, on the life spent to grow a crack to a pre-defined length, are discussed and the model predictions are compared with the experimental observations.

Bressers, J.; Timm, J. [Joint Research Centre, Petten (Netherlands). Inst. for Advanced Materials; Martinez-Esnaola, J.M.; Martin-Meizoso, A. [Centro de Estudios e Investigaciones Tecnicas de Guipuzcoa, San Sebastian (Spain)

1996-12-31

47

A unique growth mechanism of donut-shaped Mg–Al layered double hydroxides crystals revealed by AFM and STEM–EDX  

Microsoft Academic Search

Donut-like crystals of Mg–Al layered double hydroxides (LDH) are synthesized using a hydrothermal method with microwave heating. This morphology provides enlargement of the specific surface area of the {hk0} faces, needed for adsorption application. The growth mechanism for donut-shaped crystals is proposed on the basis of AFM and STEM–EDX images. The nucleation of Mg–Al LDH starts on the amorphous surface

W. N. Budhysutanto; F. J. Van Den Bruele; B. D. Rossenaar; D. Van Agterveld; W. J. P. van van Enckevort; H. J. M. Kramer

2011-01-01

48

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

PubMed

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

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

2014-04-01

49

Direct flow crystal growth system  

DOEpatents

A crystal is grown in a constantly filtered solution which is flowed directly into the growing face of a crystal. In a continuous flow system, solution at its saturation temperature is removed from a crystal growth tank, heated above its saturation temperature, filtered, cooled back to its saturation temperature, and returned to the tank.

Montgomery, Kenneth E. (Tracy, CA); Milanovich, Fred P. (Lafayette, CA)

1992-01-01

50

Cadmium oxide whisker crystals grown by the vapour-liquid-solid mechanism using various elements as growth initiators  

Microsoft Academic Search

CdO whisker crystals with micrometre thickness and length of up to 4.5 mm were grown by a simple technology described in previous publications of the authors. The whiskers grow on CdS crystal substrates, previously covered by a thin metal or silicon layer, on annealing in air at atmospheric pressure. The growth initiator used was Ag, Au, AI, Si, Mn, Ni,

N. Koparanova; Z. Zlatev; D. Genchev; G. Popovich

1994-01-01

51

High density protein crystal growth  

NASA Technical Reports Server (NTRS)

A protein crystal growth assembly including a crystal growth cell and further including a cell body having a top side and a bottom side and a first aperture defined therethrough, the cell body having opposing first and second sides and a second aperture defined therethrough. A cell barrel is disposed within the cell body, the cell barrel defining a cavity alignable with the first aperture of the cell body, the cell barrel being rotatable within the second aperture. A reservoir is coupled to the bottom side of the cell body and a cap having a top side is disposed on the top side of the cell body. The protein crystal growth assembly may be employed in methods including vapor diffusion crystallization, liquid to liquid crystallization, batch crystallization, and temperature induction batch mode crystallization.

Rouleau, Robyn (Inventor); Delucas, Lawrence (Inventor); Hedden, Douglas Keith (Inventor)

2004-01-01

52

Nucleation kinetics, growth, crystalline perfection, mechanical, thermal, optical and electrical characterization of brucinium 2-carboxy-6-nitrophthalate dihydrate single crystal  

NASA Astrophysics Data System (ADS)

Single crystals of brucinium 2-carboxy-6-nitrophthalate dihydrate (B2C6ND) have been grown by the slow evaporation solution technique at room temperature using water-ethanol (1:1) mixed solvent. The metastable zone width and induction period have been experimentally determined for the growth conditions. Nucleation kinetics and fundamental growth parameters such as surface free energy, critical radius and critical free energy change are also evaluated according to the experimental data. The crystal system and the lattice parameters have been confirmed by single crystal X-ray diffraction. The crystalline perfection of the grown B2C6ND crystals has been characterized by HRXRD method. Optical band gap and Urbach tail width of the sample have been studied employing UV-Vis absorption spectroscopy. The Vickers microhardness number (Hv), yield strength (?v) and stiffness constant (C11) of the grown crystal have been evaluated. The dielectric permittivity and dielectric loss of the grown B2C6ND crystal have been investigated as a function of frequency in the temperature range 313-353 K. The laser damage threshold value of B2C6ND crystal was estimated to be 2.8 GW/cm2 using a Nd:YAG laser.

Krishnan, P.; Gayathri, K.; Sivakumar, N.; Gunasekaran, S.; Anbalagan, G.

2014-06-01

53

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

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

Dinakaran, Paul M; Kalainathan, S

2013-07-01

54

Characterization and modeling of illite crystal particles and growth mechanisms in a zoned hydrothermal deposit, Lake City, Colorado  

USGS Publications Warehouse

Mean thickness measurements and crystal-thickness distributions (CTDs) of illite particles vary systematically with changes in hydrothermal alteration type, fracture density, and attendant mineralization in a large acid-sulfate/Mo-porphyry hydrothermal system at Red Mountain, near Lake City, Colorado. The hydrothermal illites characterize an extensive zone of quartz-sericite-pyrite alteration beneath two deeply rooted bodies of magmatic-related, quartz-alunite altered rock. Nineteen illites from a 3000 ft vertical drill hole were analyzed by XRD using the PVP-10 intercalation method and the computer program MudMaster (Bertaut-Warren-Averbach technique). Mean crystallite thicknesses, as determined from 001 reflections, range from 5-7 nanometers (nm) at depths from 0-1700 ft, then sharply increase to 10-16 nm at depths between 1800-2100 ft, and decrease again to 4-5 nm below this level. The interval of largest particle thickness correlates strongly with the zone of most intense quartz-sericite-pyrite alteration (QSP) and attendant high-density stockwork fracturing, and with the highest concentrations of Mo within the drill core. CTD shapes for the illite particles fall into two main categories: asymptotic and lognormal. The shapes of the CTDs are dependent on conditions of illite formation. The asymptotic CTDs correspond to a nucleation and growth mechanism, whereas surface-controlled growth was the dominant mechanism for the lognormal CTDs. Lognormal CTDs coincide with major through-going fractures or stockwork zones, whereas asymptotic CTDs are present in wallrock distal to these intense fracture zones. The increase in illite particle size and the associated zone of intense QSP alteration and stockwork veining was related by proximity to the dacitic magma(s), which supplied both reactants and heat to the hydrothermal system. However, no changes in illite polytype, which in other studies reflect temperature transitions, were observed within this interval.

Bove, D.J.; Eberl, D.D.; McCarty, D.K.; Meeker, G.P.

2002-01-01

55

Physicochemical principles of high-temperature crystallization and single crystal growth methods  

Microsoft Academic Search

The mechanisms of crystal growth are reviewed, with attention given to the physicochemical reactions taking place in the melt near the phase boundary; phenomena determining physical and chemical kinetics directly at the growth front; solid-phase processes occurring within the crystal. Methods for growing refractory single crystals are discussed with particular reference to the Verneuil method, zone melting, Czhochralskii growth, horizontal

Kh. S. Bagdasarov

1987-01-01

56

Automated protein crystal growth facility  

NASA Technical Reports Server (NTRS)

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.

Donald, Stacey

1994-01-01

57

Surrogate Seeds For Growth Of Crystals  

NASA Technical Reports Server (NTRS)

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.

Shlichta, Paul J.

1989-01-01

58

Structure, crystal growth, optical and mechanical studies of poly bis (thiourea) silver (I) nitrate single crystal: A new semi organic NLO material  

NASA Astrophysics Data System (ADS)

A new semi organic non linear optical polymeric crystal, bis (thiourea) silver (I) nitrate (TuAgN) with dimension 8 × 7 × 1.5 mm3 has been successfully grown from aqueous solution by slow evaporation solution technique. Single crystal X-ray diffraction study reveals that the crystal belongs to orthorhombic system with non centrosymmetric space group C2221. The crystalline perfection of the crystal was analyzed by high resolution X-ray diffraction (HRXRD) rocking curve measurements. Functional groups present in the crystal were analyzed qualitatively by infrared and Confocal Raman spectral analysis. Effects due to coordination of thiourea with metal ions were also discussed. Optical absorption study on TuAgN crystal shows the minimum absorption in the entire UV-Vis region and the lower cut off wavelength of TuAgN is found to be 318 nm. Thermal analysis shows that the material is thermally stable up to 180 °C. The mechanical strength and its parameters of the grown crystal were estimated by Vicker's microhardness test. The second harmonic generation (SHG) efficiency of the crystal was measured by Kurtz's powder technique infers that the crystal has nonlinear optical (NLO) efficiency 0.85 times that of KDP.

Sivakumar, N.; Kanagathara, N.; Varghese, B.; Bhagavannarayana, G.; Gunasekaran, S.; Anbalagan, G.

2014-01-01

59

Crystal growth inside an octant  

NASA Astrophysics Data System (ADS)

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 rescaling 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 subleading 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.

Olejarz, Jason; Krapivsky, P. L.

2013-08-01

60

Crystal growth inside an octant.  

PubMed

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 rescaling 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 subleading 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. PMID:24032777

Olejarz, Jason; Krapivsky, P L

2013-08-01

61

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

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

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

2015-05-01

62

Protein Crystal Growth  

NASA Technical Reports Server (NTRS)

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.

2003-01-01

63

Dynamically controlled crystal growth system  

NASA Technical Reports Server (NTRS)

Crystal growth can be initiated and controlled by dynamically controlled vapor diffusion or temperature change. In one aspect, the present invention uses a precisely controlled vapor diffusion approach to monitor and control protein crystal growth. The system utilizes a humidity sensor and various interfaces under computer control to effect virtually any evaporation rate from a number of different growth solutions simultaneously by means of an evaporative gas flow. A static laser light scattering sensor can be used to detect aggregation events and trigger a change in the evaporation rate for a growth solution. A control/follower configuration can be used to actively monitor one chamber and accurately control replicate chambers relative to the control chamber. In a second aspect, the invention exploits the varying solubility of proteins versus temperature to control the growth of protein crystals. This system contains miniature thermoelectric devices under microcomputer control that change temperature as needed to grow crystals of a given protein. Complex temperature ramps are possible using this approach. A static laser light scattering probe also can be used in this system as a non-invasive probe for detection of aggregation events. The automated dynamic control system provides systematic and predictable responses with regard to crystal size. These systems can be used for microgravity crystallization projects, for example in a space shuttle, and for crystallization work under terrestial conditions. The present invention is particularly useful for macromolecular crystallization, e.g. for proteins, polypeptides, nucleic acids, viruses and virus particles.

Bray, Terry L. (Inventor); Kim, Larry J. (Inventor); Harrington, Michael (Inventor); DeLucas, Lawrence J. (Inventor)

2002-01-01

64

Plenum type crystal growth process  

DOEpatents

Crystals are grown in a tank which is divided by a baffle into a crystal growth region above the baffle and a plenum region below the baffle. A turbine blade or stirring wheel is positioned in a turbine tube which extends through the baffle to generate a flow of solution from the crystal growing region to the plenum region. The solution is pressurized as it flows into the plenum region. The pressurized solution flows back to the crystal growing region through return flow tubes extending through the baffle. Growing crystals are positioned near the ends of the return flow tubes to receive a direct flow of solution.

Montgomery, Kenneth E. (Tracy, CA)

1992-01-01

65

Growth of codoped garnet crystals  

NASA Astrophysics Data System (ADS)

The formation of codoped (Cr, Nd) scandium, calcium, magnesium, zirconium, and aluminum substituted gadolinium gallium garnet (GGG) crystals is investigated. For the growth of the codoped GSGG a slope efficiency of about 7 percent was obtained and this value correlates well with the slope efficiency of Nd:YAG. The absorption band overlapping the 1.06 micron laser output and the temperature-induced striations that occur during GSGG crystal growth are analyzed. The relation between site selection in the garnets and the ionic radius is studied. The performance of Ca, Mg, and Zr substituted GGG crystals codoped with Cr and Nd is evaluated; a slope efficiency of 1 percent for up to 100 J input is obtained for the crystals. The effect of lattice defect structure on the growth of the crystals is examined.

Uhrin, R.; Belt, R. F.

66

Statistical mechanics of pinned elastic media with applications to flux lines and crystal growth problems  

NASA Astrophysics Data System (ADS)

Magnetic flux lines in high temperature superconductors show an extremely rich phenomenology, due to the anisotropy of these high-Tc materials and to the interplay between the elasticity of flux lines on one hand, and thermal and quenched disorder on the other. This thesis is a contribution to the study of this phenomenology, and consists of four main parts. In the first part, we use a replica Gaussian variational approach to study positional order of flux lines in a vortex lattice in samples of finite thickness L, and we find that the quasi-long range order found in previous studies is destroyed on asymptotic length scales for the center of mass positions of the flux lines. We then study the pinning of flux lattices in type II superconductors by a system of well separated, identical point pins, and argue that such a distribution of pinning centers can be modeled by a Gaussian random field with a suitably chosen covariance. The second part of this work is devoted to flux line liquids. In particular, we have constructed, within the framework of classical statistical mechanics, a mean field theory of dilute flux line liquids which goes beyond linear hydrodynamics. Within our approach, we find that interactions between vortices produce a massive term in the Hamiltonian of the internal modes of the flux lines which confines their transverse fluctuations. In the third part of this thesis, we study the nonequilibrium creep dynamics of a two-dimensional interface driven through a periodic potential, a problem which, in many ways, can be seen as a toy model for the more difficult problem of driven lattices, e.g. vortex lattices, through a periodic potential. Using dynamical renormalization group methods, we find that the nature of transport depends qualitatively on whether the temperature, T, is above or below the equilibrium roughening transition temperature T c. Above Tc, the velocity-force characteristics is Ohmic, with linear mobility exhibiting a jump discontinuity across the transition. Lastly, in the fourth and final part we study the effect of disorder on the spontaneous vortex (SV) lattice in ferromagnetic superconductors. We study the effects of thermal fluctuations, quenched disorder, and the nonlinear elasticity, all of which are strongly enhanced and lead to a SV solid which is characterized by elastic moduli that are wavevector-dependent out to arbitrary long length scales and exhibits non-Hookean elasticity. At weak external field H these imply a universal scaling of magnetic induction B(H) ˜ B(0) + cH alpha, with alpha ? 0.72. For weak disorder, we predict the SV solid is a topologically ordered vortex glass that is in the "columnar elastic glass" universality class. (Abstract shortened by UMI.)

Ettouhami, Abdel-Mouneim

67

A study of crystal growth by solution technique  

NASA Technical Reports Server (NTRS)

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.

Lal, R. B.

1981-01-01

68

Ultraslow growth rates of giant gypsum crystals.  

PubMed

Mineralogical processes taking place close to equilibrium, or with very slow kinetics, are difficult to quantify precisely. The determination of ultraslow dissolution/precipitation rates would reveal characteristic timing associated with these processes that are important at geological scale. We have designed an advanced high-resolution white-beam phase-shift interferometry microscope to measure growth rates of crystals at very low supersaturation values. To test this technique, we have selected the giant gypsum crystals of Naica ore mines in Chihuahua, Mexico, a challenging subject in mineral formation. They are thought to form by a self-feeding mechanism driven by solution-mediated anhydrite-gypsum phase transition, and therefore they must be the result of an extremely slow crystallization process close to equilibrium. To calculate the formation time of these crystals we have measured the growth rates of the {010} face of gypsum growing from current Naica waters at different temperatures. The slowest measurable growth rate was found at 55?°C, 1.4 ± 0.2 × 10(-5) nm/s, the slowest directly measured normal growth rate for any crystal growth process. At higher temperatures, growth rates increase exponentially because of decreasing gypsum solubility and higher kinetic coefficient. At 50?°C neither growth nor dissolution was observed indicating that growth of giant crystals of gypsum occurred at Naica between 58?°C (gypsum/anhydrite transition temperature) and the current temperature of Naica waters, confirming formation temperatures determined from fluid inclusion studies. Our results demonstrate the usefulness of applying advanced optical techniques in laboratory experiments to gain a better understanding of crystal growth processes occurring at a geological timescale. PMID:21911400

Van Driessche, A E S; García-Ruíz, J M; Tsukamoto, K; Patiño-Lopez, L D; Satoh, H

2011-09-20

69

Ultraslow growth rates of giant gypsum crystals  

PubMed Central

Mineralogical processes taking place close to equilibrium, or with very slow kinetics, are difficult to quantify precisely. The determination of ultraslow dissolution/precipitation rates would reveal characteristic timing associated with these processes that are important at geological scale. We have designed an advanced high-resolution white-beam phase-shift interferometry microscope to measure growth rates of crystals at very low supersaturation values. To test this technique, we have selected the giant gypsum crystals of Naica ore mines in Chihuahua, Mexico, a challenging subject in mineral formation. They are thought to form by a self-feeding mechanism driven by solution-mediated anhydrite-gypsum phase transition, and therefore they must be the result of an extremely slow crystallization process close to equilibrium. To calculate the formation time of these crystals we have measured the growth rates of the {010} face of gypsum growing from current Naica waters at different temperatures. The slowest measurable growth rate was found at 55?°C, 1.4 ± 0.2 × 10-5 nm/s, the slowest directly measured normal growth rate for any crystal growth process. At higher temperatures, growth rates increase exponentially because of decreasing gypsum solubility and higher kinetic coefficient. At 50?°C neither growth nor dissolution was observed indicating that growth of giant crystals of gypsum occurred at Naica between 58?°C (gypsum/anhydrite transition temperature) and the current temperature of Naica waters, confirming formation temperatures determined from fluid inclusion studies. Our results demonstrate the usefulness of applying advanced optical techniques in laboratory experiments to gain a better understanding of crystal growth processes occurring at a geological timescale. PMID:21911400

Van Driessche, A. E. S.; García-Ruíz, J. M.; Tsukamoto, K.; Patiño-Lopez, L. D.; Satoh, H.

2011-01-01

70

High-purity silicon crystal growth  

NASA Technical Reports Server (NTRS)

Crystal growth parameter effects on minority carrier lifetime and solar cell efficiencies were investigated using high purity techniques such as float zoning. Study objectives include the following: (1) optimize dopants and minority carrier lifetime in FZ material for high efficiency silicon solar cell applications; (2) improve the understanding of lifetime degradation mechanisms (point defects, impurities, thermal history, surface effects, etc.), and (3) crystallographic defect characterization of float zone and ribbon crystals via X-ray topography.

Ciszek, T.

1984-01-01

71

Vapor-phase synthesis, growth mechanism and thickness-independent elastic modulus of single-crystal tungsten nanobelts  

NASA Astrophysics Data System (ADS)

Single-crystal tungsten nanobelts with thicknesses from tens to hundreds of nanometers, widths of several micrometers and lengths of tens of micrometers were synthesized using chemical vapor deposition. Surface energy minimization was believed to have played a crucial role in the growth of the synthesized nanobelts enclosed by the low-energy {110} crystal planes of body-centered-cubic structure. The anisotropic growth of the crystallographically equivalent {110} crystal planes could be attributable to the asymmetric concentration distribution of the tungsten atom vapor around the nanobelts during the growth process. The elastic moduli of the synthesized tungsten nanobelts with thicknesses ranging from 65 to 306 nm were accurately measured using a newly developed thermal vibration method. The measured modulus values of the tungsten nanobelts were thickness-dependent. After eliminating the effect of surface oxidization using a core-shell model, the elastic modulus of tungsten nanobelts became constant, which is close to that of the bulk tungsten value of 410 GPa.

Wang, Shiliang; Chen, Guoliang; Huang, Han; Ma, Shujun; Xu, Hongyi; He, Yuehui; Zou, Jin

2013-12-01

72

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

PubMed

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

Hanumantharao, Redrothu; Kalainathan, S

2013-04-01

73

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

NASA Astrophysics Data System (ADS)

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, 1H NMR and Mass spectroscopic techniques. Single crystal XRD technique revealed that material crystallized in monoclinic system with cell parameters a = 8.693 Å, b = 7.151 Å and c = 9.311 Å. 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 200-1100 nm. 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 10-50 g. Optical nonlinearities of BTZF have been investigated by Z-scan technique with He-Ne laser radiation of wavelength 638 nm.

Hanumantharao, Redrothu; Kalainathan, S.

2013-04-01

74

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

NASA Technical Reports Server (NTRS)

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.

Lal, R. B.

1979-01-01

75

Optical diagnostics of solution crystal growth  

Microsoft Academic Search

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

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

1995-01-01

76

Crystal Growth - Fast and Slow  

NSDL National Science Digital Library

This lab is divided into two exercises that may be completed within a single three-hour session. The first exercise requires the mixture of aqueous solutions that will precipitate large euhedral crystals over the course of 1 to 2 weeks. These experiments are intended to mimic the slow growth of macroscopic minerals in thermal and chemical equilibrium. In the second exercise, students observe rapid growth of dendritic crystals in strongly undercooled solutions in order to visualize the disequilibrium growth processes that occur in the atmosphere, at chilled margins, and in highly supersaturated solutions.

77

Growth rate study of canavalin single crystals  

NASA Technical Reports Server (NTRS)

The dependence on supersaturation of the growth rate of single crystals of the protein canavalin is studied. In the supersaturation ranges studied, the rate-limiting step for growth is best described by a screw dislocation mechanism associated with interface attachment kinetics. Using a ln-ln plot, the growth-rate data is found to fit a predictive relationship of the form G = 0.012 x the supersaturation to the 6.66, which, together with the solubility curves, allows the growth rate to be estimated under a variety of conditions.

Demattei, R. C.; Feigelson, R. S.

1989-01-01

78

An analysis of growth experiments of gypsum crystals in suspension  

NASA Astrophysics Data System (ADS)

Experiments on the growth of gypsum crystals in suspension have been analysed by three methods. The most adequate description of the growth process has been obtained by applying a method, based on the relationship between the overall growth rate, the linear growth rates of the different crystals faces and the normalized volume of the crystals. The overall growth rate has been factorized into a concentration dependent function R and a function depending on the normalized volume of the crystals. Introduction of an expression for R, derived from the spiral growth model, has given a good fit with the experimental data. At constant concentration of the bulk solution the growth rate decreases with increasing normalized volume of the crystals. The results from the fitting procedure and the microscopic observations together indicate that the growth of gypsum occurs by a combined spiral growth and layer growth mechanism.

Van Rosmalen, G. M.; Daudey, P. J.; Marchée, W. G. J.

1981-04-01

79

Journal of Crystal Growth ] (  

E-print Network

by hydrothermal carbonation of calcium hydroxide G. Montes-Hernandeza,Ã, A. Ferna´ ndez-Marti´neza,b , L. Charleta 2008 Communicated by S. Veesler Abstract The hydrothermal carbonation of calcium hydroxide (Ca(OH)2 and surface area of the synthesized calcite crystals. The present study is focused on the estimation

80

Bridgman growth of large-aperture yttrium calcium oxyborate crystal  

SciTech Connect

Highlights: ? YCOB is a novel non-linear optical crystal possessing good thermal, mechanical and nonlinear optical properties. ? Large size crystal growth is key technology question for YCOB crystal. ? YCOB crystals 3 in. in diameter were grown with modified vertical Bridgman method. ? It is a more effective growth method to obtain large size and high quality YCOB crystal. -- Abstract: Large-aperture yttrium calcium oxyborate YCa{sub 4}O(BO{sub 3}){sub 3} (YCOB) crystals with 3 in. in diameter were grown with modified vertical Bridgman method, and the large crystal plate (63 mm × 68 mm × 20 mm) was harvested for high-average power frequency conversion system. The crack, facet growth and spiral growth can be effectively controlled in the as-grown crystal, and Bridgman method displays more effective in obtain large size and high quality YCOB crystal plate than Czochralski technique.

Wu, Anhua, E-mail: wuanhua@mail.sic.ac.cn [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China)] [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China); Jiang, Linwen; Qian, Guoxing; Zheng, Yanqing; Xu, Jun; Shi, Erwei [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China)] [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China)

2012-09-15

81

Biomolecular Modification of Inorganic Crystal Growth  

NASA Astrophysics Data System (ADS)

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.

De Yoreo, James J.

2007-06-01

82

Crystal growth in fused solvent systems  

NASA Technical Reports Server (NTRS)

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.

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

1973-01-01

83

Optical analysis of crystal growth  

NASA Technical Reports Server (NTRS)

Processing and data reduction of holographic images from Spacelab presents some interesting challenges in determining the effects of microgravity on crystal growth processes. Evaluation of several processing techniques, including the Computerized Holographic Image Processing System and the image processing software ITEX150, will provide fundamental information for holographic analysis of the space flight data.

Workman, Gary L.; Passeur, Andrea; Harper, Sabrina

1994-01-01

84

Observable Protein Crystal Growth Apparatus  

NASA Technical Reports Server (NTRS)

This diagram shows a cross sectrion of the fluid volume of an individual cell in the Observable Protein Crystal Growth Apparatus (OPCGA) to be operated aboard the International Space Station (ISS). The principal investigator is Dr. Alex McPherson of the University of California, Irvine. Each individual cell comprises two sample chambers with a rotating center section that isolates the two from each other until the start of the experiment and after it is completed. The cells are made from optical-quality quartz glass to allow photography and interferometric observations. Each cell has a small light-emitting diode and lens to back-light the solution. In protein crystal growth experiments, a precipitating agent such as a salt solution is used to absorb and hold water but repel the protein molecules. This increases the concentration of protein until the molecules nucleate to form crystals. This cell is one of 96 that make up the experiment module portion of the OPCGA.

2001-01-01

85

Laboratory studies of crystal growth in magma  

NASA Astrophysics Data System (ADS)

The proportions, compositions, and interrelationships among crystalline phases and glasses in volcanic rocks cryptically record pre-eruptive intensive conditions, the timing of changes in crystallization environment, and the devolatilization history of eruptive ascent. These parameters are recognized as important monitoring tools at active volcanoes and interpreting geologic events at prehistoric and remote eruptions, thus motivating our attempts to understand the information preserved in crystals through an experimental appoach. We are performing laboratory experiments in mafic, felsic, and intermediate composition magmas to study the mechanisms of crystal growth in thermochemical environments relevant to volcanic environments. We target features common to natural crystals in igneous rocks for our experimental studies of rapid crystal growth phenomena: (1) Surface curvature. Do curved interfaces and spongy cores represent evidence of dissolution (i.e., are they corrosion features), or do they record the transition from dendritic to polyhedral morphology? (2) Trapped melt inclusions. Do trapped liquids represent bulk (i.e., far-field) liquids, boundary layer liquids, or something intermediate, depending on individual species diffusivity? What sequence of crystal growth rates leads to preservation of sealed melt inclusions? (3) Subgrain boundaries. Natural phenocrysts commonly exhibit tabular subgrain regions distinguished by small angle lattice misorientations or "dislocation lamellae" and undulatory extinction. Might these crystal defects be produced as dendrites undergo ripening? (4) Clusters. Contacting clusters of polymineralic crystals are the building blocks of cumulates, and are ubiquitous features of mafic volcanic rocks. Are plagioclase and clinopyroxene aligned crystallographically, suggesting an epitaxial (surface energy) relationship? (5) Log-normal size distribution. What synthetic cooling histories produce "natural" distributions of crystal sizes, and are phenocrystic textures uniquely attributed to staged cooling? In addition, we seek to explore the limitations of the experimental approach. Which aspects of natural crystallization sequences are adequately reproduced in experimental charges, and which are compromised by the obligatory reduced temporal and spatial scales of crystal growth experiments? What are the implications of synthetic starting materials and thermal pre-treatments for nucleation, growth, heterophase equilibria, and textural maturation?

Hammer, J. E.; Welsch, B. T.; First, E.; Shea, T.

2012-12-01

86

Efg Crystal Growth Apparatus And Method  

DOEpatents

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.

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

2003-05-13

87

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

NASA Technical Reports Server (NTRS)

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.

Feigelson, R. S. (editor)

1986-01-01

88

Computational analyses of crystal growth  

NASA Technical Reports Server (NTRS)

Two important aspects of Hg/Cd/Te crystal growth processes are discussed. First, the thermal field and second, the fluid movement in the melt zone. The thermal analysis includes numerical calculation of axisymmetric heat conduction within the sample. It also includes a three-dimensional radiation model to calculate the radiative heat exchange between the furnace and the crystal as determined by the complex geometry of the furnace and the adiabatic shield. The thermal analysis also includes a crystal conductivity which is dependent on temperature and composition. To tackle the fluid flow aspect of the problem, an attempt was made to use a newly developed incompressible flow code based on the slight compressibility, and hence the finite sound speed, of all real fluids.

Dakhoul, Youssef M.

1987-01-01

89

Nucleation and crystal growth in binary systems  

NASA Astrophysics Data System (ADS)

A time-dependent nucleation of spherical crystals accompanied by their growth in metastable binary melts at the intermediate stage of phase transitions is analyzed. Two integro-differential models of governing equations are solved analytically for size- and supercooling-dependent growth rates and different expressions for the nucleation frequency. Two important cases of the Weber-Volmer-Frenkel-Zel’dovich and Meirs nucleation kinetic mechanisms are considered. The first model of crystal growth without fluctuating rates is completely solved by means of the saddle-point method. The exact analytical solution of the second model, taking into account the presence of fluctuations in particle growth rates, is found in a parametric form. The present theory describing binary systems generalizes the theories describing single-component systems recently developed in the absence (Alexandrov and Malygin 2013 J. Phys. A: Math. Theor. 46 455101) and in the presence (Alexandrov and Malygin 2014 Modelling Simul. Mater. Sci. Eng. 22 015003) of fluctuations in crystal growth rates.

Alexandrov, D. V.

2014-03-01

90

The role of the solvent in crystal growth from solution  

NASA Astrophysics Data System (ADS)

This review explores the mechanisms by which solvents influence crystal growth with particular reference to molecular crystals. Examples discussed range from small organic molecules such as hexamethylene tetramine and succinic acid to much larger molecules such as triglycerides and paraffins. In particular the concepts of surface adsorption and surface roughening in the presence of solvents are addressed and their influence on morphology examined. The applicability of these concepts to the growth of protein crystals is considered.

Davey, R. J.

1986-08-01

91

Method of Promoting Single Crystal Growth During Melt Growth of Semiconductors  

NASA Technical Reports Server (NTRS)

The method of the invention promotes single crystal growth during fabrication of melt growth semiconductors. A growth ampoule and its tip have a semiconductor source material placed therein. The growth ampoule is placed in a first thermal environment that raises the temperature of the semiconductor source material to its liquidus temperature. The growth ampoule is then transitioned to a second thermal environment that causes the semiconductor source material in the growth ampoule's tip to attain a temperature that is below the semiconductor source material's solidus temperature. The growth ampoule so-transitioned is then mechanically perturbed to induce single crystal growth at the growth ampoule's tip.

Su, Ching-Hua (Inventor)

2013-01-01

92

Crystal growth and annealing method and apparatus  

SciTech Connect

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. An embodiment of the present invention comprises a secondary heater incorporated into a conventional crystal growth and annealing apparatus. The secondary heater supplies heat to minimize the temperature gradients in the crystal during the annealing process. The secondary heater can mount near the bottom of the crucible to effectively maintain appropriate temperature gradients.

Gianoulakis, Steven E. (Albuquerque, NM); Sparrow, Robert (North Brookfield, MA)

2001-01-01

93

Protein crystal growth in a microgravity environment  

NASA Technical Reports Server (NTRS)

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.

Bugg, Charles E.

1988-01-01

94

Protein crystal growth in low gravity  

NASA Technical Reports Server (NTRS)

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.

Feigelson, Robert S.

1991-01-01

95

Growth of cholesterol crystals in silica gel  

Microsoft Academic Search

depends on its physical and chemical properties. The growth of crystals of cholesterol in aqueous and other solutions have been reported in the literature [1-3]. The growth of cholesterol monohydrate crystals in supersaturated model bile solution has been studied by Toor et al. [4], but no attempt seems to have been made so far to grow cholesterol crystals by a

S. Narayana Kalkura; S. Devanarayanan

1986-01-01

96

Crystal growth and application of large size YCOB crystal for high power laser  

NASA Astrophysics Data System (ADS)

Yttrium calcium oxyborate YCa4O(BO3)3 (YCOB) is a novel non-linear optical crystal possessing good thermal, mechanical and nonlinear optical properties. It is regards the important candidate frequency conversion material for the high-average power laser system. In this work, we described our effort to achieve the successful growth of large size YCOB single crystals, and the crystal quality of large size YCOB crystal grown by the Bridgman method. The OPCPA application of YCOB element was also introduced simply. The results confirmed that Bridgman technology can be used for the growth of large size YCOB crystal as an alternative to Czochralski method.

Wu, Anhua; Xu, Jun; Zheng, Yanqing; Liang, Xiaoyan

2014-10-01

97

Protein single crystal growth under microgravity  

NASA Astrophysics Data System (ADS)

Crystal growth conditions for proteins under microgravity were investigated with two model compounds (?-galactosidase and lysozyme). The single crystals obtained have been found to be significantly larger than those prepared in the same environment on earth.

Littke, Walter; John, Christina

1986-08-01

98

Analytics of crystal growth in space  

NASA Technical Reports Server (NTRS)

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.

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

1974-01-01

99

Instability of the single-crystal growth of large-diameter silicon crystals with dislocations  

Microsoft Academic Search

Metallographic, SEM, and X-ray investigations were carried out to elucidate the character and sequence of changes in the growth mechanism and structure of large-diameter (80-150 mm) Czochralski-grown silicon crystals of 111 and 100 line orientations after the termination of growth without dislocations. The single-crystal growth was found to be unstable and to be disrupted by the formation of twins or

N. I. Bletskan; A. N. Buzynin; N. A. Butylkina; Iu. S. Dementev; Iu. M. Litvinov; A. E. Lukianov; V. N. Stepchenkov

1984-01-01

100

Controlled growth of semiconductor crystals  

DOEpatents

A method for growth of III-V, II-VI and related semiconductor single crystals that suppresses random nucleation and sticking of the semiconductor melt at the crucible walls. Small pieces of an oxide of boron B.sub.x O.sub.y are dispersed throughout the comminuted solid semiconductor charge in the crucible, with the oxide of boron preferably having water content of at least 600 ppm. The crucible temperature is first raised to a temperature greater than the melt temperature T.sub.m1 of the oxide of boron (T.sub.m1 =723.degree. K. for boron oxide B.sub.2 O.sub.3), and the oxide of boron is allowed to melt and form a reasonably uniform liquid layer between the crucible walls and bottom surfaces and the still-solid semiconductor charge. The temperature is then raised to approximately the melt temperature T.sub.m2 of the semiconductor charge material, and crystal growth proceeds by a liquid encapsulated, vertical gradient freeze process. About half of the crystals grown have a dislocation density of less than 1000/cm.sup.2. If the oxide of boron has water content less than 600 ppm, the crucible material should include boron nitride, a layer of the inner surface of the crucible should be oxidized before the oxide of boron in the crucible charge is melted, and the sum of thicknesses of the solid boron oxide layer and liquid boron oxide layer should be at least 50 .mu.m.

Bourret-Courchesne, Edith D. (Richmond, CA)

1992-01-01

101

Controlled growth of semiconductor crystals  

DOEpatents

A method is disclosed for growth of III-V, II-VI and related semiconductor single crystals that suppresses random nucleation and sticking of the semiconductor melt at the crucible walls. Small pieces of an oxide of boron B[sub x]O[sub y] are dispersed throughout the comminuted solid semiconductor charge in the crucible, with the oxide of boron preferably having water content of at least 600 ppm. The crucible temperature is first raised to a temperature greater than the melt temperature T[sub m1] of the oxide of boron (T[sub m1]=723 K for boron oxide B[sub 2]O[sub 3]), and the oxide of boron is allowed to melt and form a reasonably uniform liquid layer between the crucible walls and bottom surfaces and the still-solid semiconductor charge. The temperature is then raised to approximately the melt temperature T[sub m2] of the semiconductor charge material, and crystal growth proceeds by a liquid encapsulated, vertical gradient freeze process. About half of the crystals grown have a dislocation density of less than 1000/cm[sup 2]. If the oxide of boron has water content less than 600 ppm, the crucible material should include boron nitride, a layer of the inner surface of the crucible should be oxidized before the oxide of boron in the crucible charge is melted, and the sum of thicknesses of the solid boron oxide layer and liquid boron oxide layer should be at least 50 [mu]m. 7 figs.

Bourret-Courchesne, E.D.

1992-07-21

102

Effect of L-tyrosine on the solubility, growth, structural, optical, SHG, dielectric and mechanical properties of KDP single crystals  

NASA Astrophysics Data System (ADS)

The effect of L-tyrosine doping on various properties of potassium dihydrogen phosphate single crystals grown by slow cooling along with seed rotation method has been investigated. The crystalline nature of the grown crystals has been analyzed by powder X-ray diffraction analysis. The presence of various functional groups is identified by Fourier transform spectroscopy. Optical transparency of the grown crystals has been analyzed by UV-Vis-NIR spectral analysis. 90% of transmittance was observed for L-tyrosine added potassium dihydrogen phosphate crystal. Thermal stability and micro hardness measurement was examined by TG-DTA and Vickers microhardness study. Second harmonic study was carried out using Kurtz and Perry method. Dielectric and laser damage threshold studies were carried out.

Boopathi, K.; Ramasamy, P.

2014-11-01

103

Advanced protein crystal growth programmatic sensitivity study  

NASA Technical Reports Server (NTRS)

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.

1992-01-01

104

Mechanics in Tumor Growth 1 Mechanics in Tumor Growth  

E-print Network

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

Preziosi, Luigi

105

Nucleation and Convection Effects in Protein Crystal Growth  

NASA Technical Reports Server (NTRS)

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.

Vekilow, Peter G.

1998-01-01

106

Mechanically tunable photonic crystal lens  

NASA Astrophysics Data System (ADS)

We designed, fabricated and characterized MEMS-enabled mechanically-tunable photonic crystal lens comprised of 2D photonic crystal and symmetrical electro-thermal actuators. The 2D photonic crystal was made of a honeycomb-lattice of 340 nm thick, 260 nm diameter high-index silicon rods embedded in low-index 10 ?m thick SU-8 cladding. Silicon input waveguide and deflection block were also fabricated for light in-coupling and monitoring of focused spot size, respectively. When actuated, the electro-thermal actuators induced mechanical strain which changed the lattice constant of the photonic crystal and consequently modified the photonic band structure. This in turn modified the focal-length of the photonic crystal lens. The fabricated device was characterized using a tunable laser (1400~1602 nm) and an infrared camera during actuation. At the wavelength of 1450 nm, the lateral light spot size observed at the deflection block gradually decreased 40%, as applied current increased from 0 to 0.7 A, indicating changes in focal length in response to the mechanical stretching.

Cui, Y.; Tamma, V. A.; Lee, J.-B.; Park, W.

2010-08-01

107

Investigation of crystal growth from solutions  

NASA Technical Reports Server (NTRS)

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.

Miyagawa, I.

1975-01-01

108

Innovation in crystal growth: A personal perspective  

NASA Astrophysics Data System (ADS)

The evolution of crystal growth has been crucially dependent on revolutionary innovations and initiatives involving ideas, technology and communication. A personal perspective is presented on some of these aspects in connection with the early history of semiconductors that have helped evolve our knowledge and advance the science and technology of crystal growth. The presentation considers examples from work on germanium, silicon, indium antimonide, gallium arsenide, indium phosphide, gallium phosphide and mercury cadmium telluride. In connection with metal organic vapour phase epitaxy (MOVPE), the influence of adduct purification for alkyls is noted together with the growth of Hg xCd 1-xTe. The role of crystal growth organisations together with initiatives in the publication of the Journal of Crystal Growth (JCG) and the pivotal role of the International Organisation of Crystal Growth (IOCG) are also highlighted in the quest for scientific excellence.

Mullin, J. B.

2008-04-01

109

The effect of gravitation on crystal growth  

NASA Astrophysics Data System (ADS)

A method of solving Stefan problems, which pays equal attention to transport and surface phenomena, is formulated in the paper. This method is applied to a system with a planar interface. It is proved that gravitation may affect the rate of crystallization implicity, by acting on the convective velocity, on the values of the parameters of state, and on material constants. Formulae which describe the explicit effect of the acceleration of gravitation on the rate of growth, are derived for a flat (diffuse) boundary. These relations indicate the existence of a critical value of g at which the mechanism of crystallization changes. The significance of the jitter-effect and the effect of constitutive assumptions on convection are discussed.

Š?astna, J.; Vodák, F.

1981-05-01

110

Growth, structural, optical and mechanical studies on acid mixed glycine metal salt (GABN) crystal as potential NLO material  

NASA Astrophysics Data System (ADS)

Transparent crystals of ?-glycine with ammonium nitrate and barium nitrate (GABN) have been grown from aqueous solution by slow evaporation technique at room temperature. Crystals of size 11 × 7 × 4 mm 3 have been obtained in about 3-4 weeks time. The solubility of GABN has been determined in water. The grown crystal belongs to orthorhombic system with cell parameters a = 7.317 A.U, b = 12.154 A.U and c = 5.468 A.U with a unit cell volume 486.35 (A.U) 3. The presence of chemical components/groups has been identified by CHN, EDAX and NMR analysis. Comparative IR and Raman studies indicate a molecule with a lack of centre of symmetry. A wide transparency window useful for optoelectronic applications is indicated by the UV Studies. Using a Nd-YAG laser (1064 nm), the optical second harmonic generation (SHG) conversion efficiency of GABN is found to be 1.406 times of that of standard KDP. On exposure to light the GABN crystals are found to exhibit negative photoconductivity. I-V characteristics, SEM studies, dielectrics studies, and Vickers micro hardness measurement have been carried out.

Khandpekar, Mahendra M.; Dongare, Shailesh S.; Patil, Shirish B.; Pati, Shankar P.

2012-03-01

111

Salt-induced aggregation of lysozyme: Implications for crystal growth  

NASA Technical Reports Server (NTRS)

Crystallization of proteins is a prerequisite for structural analysis by x-ray crystallography. While improvements in protein crystals have been obtained in microgravity onboard the U.S. Space Shuttle, attempts to improve the crystal growth process both on the ground and in space have been limited by our lack of understanding of the mechanisms involved. Almost all proteins are crystallized with the aid of a precipitating agent. Many of the common precipitating agents are inorganic salts. An understanding of the role of salts on the aggregation of protein monomers is the key to the elucidation of the mechanisms involved in protein crystallization. In order for crystallization to occur individual molecules must self-associate into aggregates. Detection and characterization of aggregates in supersaturated protein solutions is the first step in understanding salt-induced crystallization.

Wilson, Lori J.

1994-01-01

112

Economic analysis of crystal growth in space  

NASA Technical Reports Server (NTRS)

Many advanced electronic technologies and devices for the 1980's are based on sophisticated compound single crystals, i.e. ceramic oxides and compound semiconductors. Space processing of these electronic crystals with maximum perfection, purity, and size is suggested. No ecomonic or technical justification was found for the growth of silicon single crystals for solid state electronic devices in space.

Ulrich, D. R.; Chung, A. M.; Yan, C. S.; Mccreight, L. R.

1972-01-01

113

Mechanics of Cell Growth.  

PubMed

Cell growth describes an essential feature of biological tissues. This growth process may be modeled by using a set of relatively simple governing equations based on the axioms of mass and momentum balance, and using a continuum framework that describes cells and tissues as mixtures of a solid matrix, a solvent and multiple solutes. In this model the mechanics of cell growth is driven by osmotic effects, regulated by the cells' active uptake of solutes and passive uptake of solvent. By accounting for the anisotropy of the cells' cytoskeletal structures or extracellular matrix, as well as external constraints, a wide variety of growing shapes may be produced as illustrated in various examples. PMID:22904576

Ateshian, Gerard A; Morrison, Barclay; Holmes, Jeffrey W; Hung, Clark T

2012-06-01

114

Crystal structures and growth mechanism for ultrathin films of ionic compound materials: FeO(111) on Pt(111)  

Microsoft Academic Search

The growth and atomic structures of epitaxial iron-oxide films on Pt(111) were studied with scanning tunneling microscopy and high-resolution low-energy electron diffraction. During the initial layer-by-layer growth of FeO(111) four different structures are formed as the coverage increases to 2.5 monolayers, then a three-dimensional growth of Fe3O4(111) islands begins. The structural transformations demonstrate that the relaxations within the FeO(111) films

W. Ranke; M. Ritter; W. Weiss

1999-01-01

115

Analysis of Monomer Aggregation and Crystal Growth Rates of Lysozyme  

NASA Technical Reports Server (NTRS)

This project was originally conceived to analyze the extensive data of tetragonal lysozyme crystal growth rates collected at NASA/MSFC by Dr. Marc L. Pusey's research group. At that time the lack of analysis of the growth rates was hindering progress in understanding the growth mechanism of tetragonal lysozyme and other protein crystals. After the project was initiated our initial analysis revealed unexpected complexities in the growth rate behavior. This resulted in an expansion in the scope of the project to include a comprehensive investigation of the growth mechanisms of tetragonal lysozyme crystals. A discussion of this research is included as well a list of presentations and publications resulting from the research. This project contributed significantly toward the education of several students and fostered extensive collaborations between investigators.

Nadarajah, Arunan

1996-01-01

116

Diffusion, Viscosity and Crystal Growth in Microgravity  

NASA Technical Reports Server (NTRS)

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.

Myerson, Allan S.

1996-01-01

117

Thermal crystallization mechanism of silk fibroin protein  

NASA Astrophysics Data System (ADS)

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.

Hu, Xiao

118

Transport and Growth Kinetics in Microgravity Protein Crystal Growth  

NASA Technical Reports Server (NTRS)

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).

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

2002-01-01

119

Growth and characterization of ammonium acid phthalate single crystals  

NASA Astrophysics Data System (ADS)

Ammonium acid phthalate (AAP) has been synthesized and single crystals were grown by slow evaporation solution growth technique. The unit cell parameters were confirmed by single crystal X-ray diffraction analysis and it belongs to orthorhombic system with the space group of Pcab. The high resolution X-ray diffraction studies revealed the crystalline perfection of the grown crystal. The various functional groups of AAP were identified by FT-IR and Raman spectral analyses. Thermal stability of the grown crystals was studied by TGA/DTA. The optical properties of the grown crystals were analyzed by UV-Vis-NIR and photoluminescence spectral studies. The mechanical property of the grown crystal was studied by Vickers microhardness measurement. The growth features of AAP were analyzed by chemical etching.

Arunkumar, A.; Ramasamy, P.

2013-04-01

120

Hgi2 Sub 2 Crystal Growth for Nuclear Detectors  

NASA Technical Reports Server (NTRS)

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.

Schnepple, W. F.; Vandenberg, L.

1985-01-01

121

Protein-crystal growth experiment (planned)  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

122

Macromolecular crystal growth in microgravity  

NASA Astrophysics Data System (ADS)

Two T=1 and one T=3 plant viruses, along with a protein were crystallized in microgravity during the International Microgravity Laboratory-2 (IML-2) mission in July of 1994 (Koszelak, et al. 1995). The method employed was liquid-liquid diffusion in the European Space Agency's Advanced Protein Crystallization Facility (APCF). Distinctive alterations in the habits of Turnip Yellow Mosaic Virus (TYMV) crystals and hexagonal canavalin crystals were observed. Crystals of cubic Satellite Tobacco Mosaic Virus (STMV) more than thirty times the volume of crystals grown in the laboratory were produced in microgravity. X-ray diffraction analysis demonstrated that both crystal forms of canavalin and the cubic STMV crystals diffracted to significantly higher resolution and had superior diffraction properties as judged by relative Wilson plots.

McPherson, Alexander

1996-03-01

123

Mechanisms for the Crystallization of ZBLAN  

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

124

The Nucleation and Growth of Protein Crystals  

NASA Technical Reports Server (NTRS)

Obtaining crystals of suitable size and high quality continues to be a major bottleneck in macromolecular crystallography. Currently, structural genomics efforts are achieving on average about a 10% success rate in going from purified protein to a deposited crystal structure. Growth of crystals in microgravity was proposed as a means of overcoming size and quality problems, which subsequently led to a major NASA effort in microgravity crystal growth, with the agency also funding research into understanding the process. Studies of the macromolecule crystal nucleation and growth process were carried out in a number of labs in an effort to understand what affected the resultant crystal quality on Earth, and how microgravity improved the process. Based upon experimental evidence, as well as simple starting assumptions, we have proposed that crystal nucleation occurs by a series of discrete self assembly steps, which 'set' the underlying crystal symmetry. This talk will review the model developed, and its origins, in our laboratory for how crystals nucleate and grow, and will then present, along with preliminary data, how we propose to use this model to improve the success rate for obtaining crystals from a given protein.

Pusey, Marc

2004-01-01

125

Electromagnetic Phenomena in Crystal Growth  

Microsoft Academic Search

Integrated circuits and optical devices are produced on wafers sliced from single crystals that are grown from a body of liquid\\u000a semiconductor or melt. The crystal must have few defects, such as dislocations, and must have uniform distributions of dopants,\\u000a which are added to the melt to give the crystal the desired electrical or optical properties. Since molten semiconductors\\u000a have

John S. Walker

126

Silicon carbide - Progress in crystal growth  

NASA Technical Reports Server (NTRS)

Recent progress in the development of two processes for producing large-area high-quality single crystals of SiC is described: (1) a modified Lely process for the growth of the alpha polytypes (e.g., 6H SiC) initially developed by Tairov and Tsvetkov (1978, 1981) and Ziegler et al. (1983), and (2) a process for the epitaxial growth of the beta polytype on single-crystal silicon or other substrates. Growth of large-area cubic SiC on Si is described together with growth of defect-free beta-SiC films on alpha-6H SiC crystals and TiC lattice. Semiconducting qualities of silicon carbide crystals grown by various techniques are discussed.

Powell, J. Anthony

1987-01-01

127

Illusory spirals and loops in crystal growth  

PubMed Central

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

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

2013-01-01

128

(PCG) Protein Crystal Growth Porcine Elastase  

NASA Technical Reports Server (NTRS)

(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.

1989-01-01

129

Growth Of Oriented Crystals At Polymerized Membranes  

DOEpatents

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.

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

2000-01-25

130

Crystallization of authentic recombinant human growth hormone  

SciTech Connect

Large single crystals of natural-sequence recombinant human growth hormone (rhGH) have been grown from a medium containing polyethylene glycol and a non-ionic detergent, ..beta..-octyl glucoside. The identity of the crystals was confirmed by gel electrophoresis and anion exchange chromatography.

Jones, N.D.; DeHoniesto, J.; Tackitt, P.M.; Becker, G.W.

1987-05-01

131

Vapor Crystal Growth (VCG) experiment Cell  

NASA Technical Reports Server (NTRS)

The image shows a test cell of Crystal Growth experiment inside the Vapor Crystal Growth System (VCGS) furnace aboard the STS-42, International Microgravity Laboratory-1 (IML-1), mission. The goal of IML-1, a pressurized marned Spacelab module, was to explore in depth the complex effects of weightlessness of living organisms and materials processing. More than 200 scientists from 16 countires participated in the investigations.

1992-01-01

132

Stability limits for the horizontal ribbon growth of silicon crystals  

NASA Astrophysics Data System (ADS)

A rigorous, thermal-capillary model, developed to couple heat transfer, melt convection and capillary physics, is employed to assess stability limits of the HRG system for growing silicon ribbons. Extending the prior understanding of this process put forth by Daggolu et al. [Thermal-capillary analysis of the horizontal ribbon growth of silicon crystals, Journal of Crystal Growth 355 (2012) 129-139], model results presented here identify additional failure mechanisms, including the bridging of crystal onto crucible, the spilling of melt from the crucible, and the undercooling of melt at the ribbon tip, that are consistent with prior experimental observations. Changes in pull rate, pull angle, melt height, and other parameters are shown to give rise to limits, indicating that only narrow operating windows exist in multi-dimensional parameter space for stable growth conditions that circumvent these failure mechanisms.

Daggolu, Parthiv; Yeckel, Andrew; Bleil, Carl E.; Derby, Jeffrey J.

2013-01-01

133

Studies on the growth, structural, thermal, mechanical and optical properties of the semiorganic nonlinear optical crystal L-glutamic acid hydrobromide  

NASA Astrophysics Data System (ADS)

Single crystals of optically significant L-glutamic acid hydrobromide were grown from aqueous solutions and their various properties were characterized. The title compound was synthesized with stoichiometric ratio 1:1, purified by recrystallization, confirmed by powder X-ray diffraction and its solubility in double distilled water in the temperature range 30-80 °C was determined by the gravimetric method. Large dimensional (45×26×14 mm3) optically transparent single crystal of the compound was grown by a controlled slow cooling method combined with the reversible seed rotation technique. The morphological importance of the grown crystal was studied in accordance with equilibrium morphology. Samples of the grown crystal were subjected to single crystal X-ray diffraction study for structural analysis, Fourier transform infrared spectroscopy for functional group analysis, TG-DTA/DSC for thermal analysis, Vickers microhardness study for mechanical strength, UV-vis-NIR spectral analysis for optical transparency and the Kurtz powder method for SHG efficiency of the grown crystal. Results indicate that the grown crystal has significant improvement in its thermal, optical and SHG properties when compared to pure L-glutamic acid polymorphs.

Dhanasekaran, P.; Srinivasan, K.

2013-07-01

134

Crystal growth under heat field rotation conditions  

NASA Astrophysics Data System (ADS)

Rotation of the heat field which is applied to the outer walls of a crystallizer or growth crucible, provides a contact-free induction of forced convection (i.e. flow azimuthal component) in a medium of crystallization. Thus, the stirring of a melt or solution is gained without the direct effect of a rotating crystal, or crucible, or various mixers. This allows to simplify crystallization and to escape vibration and other excitations. The circular movement of a heat field by the perimeter of a growing crystal, which proceeds at a certain amplitude and frequency, provides the formation of a structurally perfect single crystal. An original heating furnace provides the rotation of the heat field. Thermal control of this furnace allows maintainance of a necessary temperature in a growth zone with high precision; it is possible to set the amplitude and frequency of thermal oscillation in a wide range of values. This technique was tested for the growth of nonlinear-optical CLBO crystals from a high-temperature melt-solution and KDP crystals from a water solution.

Kokh, Alexandr E.; Kononova, Nadegda G.

2000-05-01

135

Thermal modelling of bridgman crystal growth  

NASA Astrophysics Data System (ADS)

Electrical analogues have been used to model the thermal behaviour of a Bridgman crystal growing system. Computer analysis of the analogues yields detailed information on temperatures and heat flows in a complete system, i.e. furnace, water-jacket, ampoule and crystal. For the particular system modelled it is found that isotherm shapes within the crystal during the critical early stages of growth are strongly affected by the way heat is lost from the bottom of the ampoule. By changing the shape of the ampoule bottom or by changing the conductivity of the stem supporting the ampoule the isotherm shapes can be readily altered. The model also shows that the crystal growth rate is 15% slower than the ampoule lowering speed early in the growth cycle.

Jones, C. L.; Capper, P.; Gosney, J. J.

1982-02-01

136

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

137

Growth Modes and Energetics of 101 Face Lysozyme Crystal Growth  

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

138

Growth and defects of explosives crystals  

SciTech Connect

Large single crystals of PETN, RDX, and TNT can be grown easily from evaporating ethyl acetate solutions. The crystals all share a similar type of defect that may not be commonly recognized. The defect generates conical faces ideally mosaic crystals, and may account for the polymorphs'' of TNT and detonator grades of PETN. TATB crystals manufactured by the amination of trichlorotrinitrobenzene in dry toluene entrain two forms of ammonium chloride. One of these forms causes worm holes'' in the TATB crystals that may be the reason for its unusually low failure diameters. Strained HMX crystals form mechanical twins that can spontaneously revert back to the untwinned form when the straining force is removed. Large strains or temperatures above 100[degrees]C lock in the mechanical twins.

Cady, H.H.

1992-01-01

139

Growth and defects of explosives crystals  

NASA Astrophysics Data System (ADS)

Large single crystals of PETN, RDX, and TNT can be grown easily from evaporating ethyl acetate solutions. The crystals all share a similar type of defect that may not be commonly recognized. The defect generates conical faces, ideally mosaic crystals, and may account for the 'polymorphs' of TNT and detonator grades of PETN. TATB crystals manufactured by the amination of trichlorotrinitrobenzene in dry toluene entrain two forms of ammonium chloride. One of these forms causes 'worm holes' in the TATB crystals that may be the reason for its unusually low failure diameters. Strained HMX crystals form mechanical twins that can spontaneously revert back to the untwinned form when the straining force is removed. Large strains or temperatures above 100 C lock in the mechanical twins.

Cady, H. H.

140

Growth and defects of explosives crystals  

SciTech Connect

Large single crystals of PETN, RDX, and TNT can be grown easily from evaporating ethyl acetate solutions. The crystals all share a similar type of defect that may not be commonly recognized. The defect generates conical faces ideally mosaic crystals, and may account for the ``polymorphs`` of TNT and detonator grades of PETN. TATB crystals manufactured by the amination of trichlorotrinitrobenzene in dry toluene entrain two forms of ammonium chloride. One of these forms causes ``worm holes`` in the TATB crystals that may be the reason for its unusually low failure diameters. Strained HMX crystals form mechanical twins that can spontaneously revert back to the untwinned form when the straining force is removed. Large strains or temperatures above 100{degrees}C lock in the mechanical twins.

Cady, H.H.

1992-12-01

141

Convective flow effects on protein crystal growth  

NASA Technical Reports Server (NTRS)

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.

Rosenberger, Franz

1995-01-01

142

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

PubMed

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

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

2013-08-01

143

Research support for cadmium telluride crystal growth  

NASA Technical Reports Server (NTRS)

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.

Rosenberger, Franz

1995-01-01

144

Macromolecular Crystal Growth by Means of Microfluidics  

NASA Technical Reports Server (NTRS)

We have performed a feasibility study in which we show that chip-based, microfluidic (LabChip(TM)) technology is suitable for protein crystal growth. This technology allows for accurate and reliable dispensing and mixing of very small volumes while minimizing bubble formation in the crystallization mixture. The amount of (protein) solution remaining after completion of an experiment is minimal, which makes this technique efficient and attractive for use with proteins, which are difficult or expensive to obtain. The nature of LabChip(TM) technology renders it highly amenable to automation. Protein crystals obtained in our initial feasibility studies were of excellent quality as determined by X-ray diffraction. Subsequent to the feasibility study, we designed and produced the first LabChip(TM) device specifically for protein crystallization in batch mode. It can reliably dispense and mix from a range of solution constituents into two independent growth wells. We are currently testing this design to prove its efficacy for protein crystallization optimization experiments. In the near future we will expand our design to incorporate up to 10 growth wells per LabChip(TM) device. Upon completion, additional crystallization techniques such as vapor diffusion and liquid-liquid diffusion will be accommodated. Macromolecular crystallization using microfluidic technology is envisioned as a fully automated system, which will use the 'tele-science' concept of remote operation and will be developed into a research facility for the International Space Station as well as on the ground.

vanderWoerd, Mark; Ferree, Darren; Spearing, Scott; Monaco, Lisa; Molho, Josh; Spaid, Michael; Brasseur, Mike; Curreri, Peter A. (Technical Monitor)

2002-01-01

145

Single crystal growth of actinide compounds  

Microsoft Academic Search

During recent years, the importance of solid state actinide research has been increasingly recognized. Further progress in actinide solid state physics depends on the availability of pure and perfect single crystals. Actinide compounds have large magnetic anisotropy with anisotropy fields of 8 × 107 A.m-1 or higher. Investigation of the mechanism responsible for such unique behaviour requires large single crystals

J. C. Spirlet; W. Müller; J. van Audenhove

1985-01-01

146

Control of hydroxyapatite crystal growth by gallic acid.  

PubMed

The purpose of this study is to detect the effect of gallic acid (GA) on hydroxyapatie crystal growth and find the mechanism of the regulation. We evaluated the morphology of HAP crystals grown under various amounts of GA (0, 0.05, 1, and 4 gL(-1)). Subsequently, the chemical composition, crystal size and the morphology were investigated via the energy-dispersive X-ray spectrometer, attenuated total fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction analysis, transmission electron microscope and scanning electron microscopy. In all groups, the Ca/P ratio was closed to 1.67. In the absence of GA, crystals did not arrange, while in the presence of GA, crystals tended to form spherules. The size of the crystals decreased with the concentration of GA increased. These results indicated the role of GA on the growth and morphology of hydroxyapatite crystals, which might be the key mechanism for gallic acid regulating the mineralization. PMID:25748466

Tang, Bei; Yuan, He; Cheng, Lei; Zhou, Xuedong; Huang, Xuelian; Li, Jiyao

2015-02-01

147

Growth and characterization of large CLBO crystals  

NASA Astrophysics Data System (ADS)

A high optical quality Cesium lithium borate (CLBO) crystal with dimensions of 146×132×118 mm was grown by the Kyropoulos method. The 4th harmonic generation of a frequency doubled Nd:YAG laser, from 532 to 266 nm, was carried out with a CLBO crystal doubler, and an average output power of 28.4 W was achieved at 266 nm. Polished surfaces were etched to reveal the cracking mechanism of CLBO crystals. Through observation and comparison of the surface etching patterns, it is proved that CLBO crystals crack under chemical attack by water molecules penetrating from the (1 0 0) and (0 1 0) crystallographic planes.

Yuan, Xin; Shen, Guangqiu; Wang, Xiaoqing; Shen, Dezhong; Wang, Guiling; Xu, Zuyan

2006-07-01

148

Method for solid state crystal growth  

DOEpatents

A novel method for high quality crystal growth of intermetallic clathrates is presented. The synthesis of high quality pure phase crystals has been complicated by the simultaneous formation of both clathrate type-I and clathrate type-II structures. It was found that selective, phase pure, single-crystal growth of type-I and type-II clathrates can be achieved by maintaining sufficient partial pressure of a chemical constituent during slow, controlled deprivation of the chemical constituent from the primary reactant. The chemical constituent is slowly removed from the primary reactant by the reaction of the chemical constituent vapor with a secondary reactant, spatially separated from the primary reactant, in a closed volume under uniaxial pressure and heat to form the single phase pure crystals.

Nolas, George S.; Beekman, Matthew K.

2013-04-09

149

High quality factor single-crystal diamond mechanical resonators  

NASA Astrophysics Data System (ADS)

Single-crystal diamond is a promising material for microelectromechanical systems (MEMs) because of its low mechanical loss, compatibility with extreme environments, and built-in interface to high-quality spin centers. But its use has been limited by challenges in processing and growth. We demonstrate a wafer bonding-based technique to form diamond on insulator, from which we make single-crystal diamond micromechanical resonators with mechanical quality factors as high as 338 000 at room temperature. Variable temperature measurements down to 10 K reveal a nonmonotonic dependence of quality factor on temperature. These resonators enable integration of single-crystal diamond into MEMs technology for classical and quantum applications.

Ovartchaiyapong, P.; Pascal, L. M. A.; Myers, B. A.; Lauria, P.; Bleszynski Jayich, A. C.

2012-10-01

150

Convective flow effects on protein crystal growth  

NASA Technical Reports Server (NTRS)

The long-term stability of the interferometric setup for the monitoring of protein morphologies has been improved. Growth or dissolution of a crystal on a 100 A scale can now be clearly distinguished from dimensional changes occurring within the optical path of the interferometer. This capability of simultaneously monitoring the local interfacial displacement at several widely-spaced positions on the crystal surface with high local depth resolution, has already yielded novel results. We found with lysozyme that (1) the normal growth rate is oscillatory, and (2) the mean growth step density is greater at the periphery of a facet than in its center. The repartitioning of Na(+) and Cl(-) 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 a unified way. The results strongly suggests that (1) the ion to lysozyme ratio in the crystal depends mostly on kinetic rather than crystallographic parameters, and (2) lysozyme crystals possess a salt-rich core with a diameter on the order of 10 microns. The computational model for diffusive-convective transport in protein crystallization (see the First Report) has been applied to a realistic growth cell geometry, taking into account the findings of the above repartitioning studies. These results show that some elements of a moving boundary problem must be incorporated into the model in order to obtain a more realistic description. Our experimental setup for light scattering investigations of aggregation and nucleation in protein solutions has been extensively tested. Scattering intensity measurements with a true Rayleigh scatterer produced systematically increased forward scattering, indicating problems with glare. These have been resolved. Preliminary measurements with supersaturated lysozyme solutions revealed that the scatterers grow with time. Work has begun on a computer program for the unified evaluation of simultaneously obtained, multi-angle static and dynamic light scattering data.

Rosenberger, Franz; Monaco, Lisa A.

1994-01-01

151

Unidirectional seeded single crystal growth from solution of benzophenone  

Microsoft Academic Search

A novel crystal growth method has been established for the growth of single crystal with selective orientation at room temperature. Using volatile solvent, the saturated solution containing the material to be crystallized was taken in an ampoule and allowed to crystallize by slow solvent evaporation assisted with a ring heater. The orientation of the growing crystal was imposed by means

K. Sankaranarayanan; P. Ramasamy

2005-01-01

152

Single crystal growth of SiC and electronic devices  

Microsoft Academic Search

Single crystal growth of silicon carbide (Sic) and application to electronic devices are reviewed. In the crystal growth, bulk and homoepitaxial growth are picked up, and crystal quality and electrical properties are described. For electronic devices, various device processes are argued. Power devices based on Sic are stressed in this review.Bulk single crystals of SiC can be grown by a

Akira Itoh; Hiroyuki Matsunami

1997-01-01

153

Crystal growth of ZnO  

NASA Astrophysics Data System (ADS)

Centimeter-sized crystals of zinc oxide have been grown by the top-seeded solution growth method and traveling-solvent floating-zone method using a mixed solvent of V 2O 5+B 2O 3 and MoO 3+V 2O 5. The crystals were brown, pale yellow and white semi-transparent in color depending on the solvent used. The characterization of the crystals by scanning electron microscopy X-ray energy-dispersion spectroscopy is reported.

Oka, Kunihiko; Shibata, Hajime; Kashiwaya, Satoshi

2002-04-01

154

Phase-Field Simulations of Crystal Growth  

SciTech Connect

This course gives an elementary introduction to the phase-field method and to its applications for the modeling of crystal growth. Two different interpretations of the phase-field variable are given and discussed. It can be seen as a physical order parameter that characterizes a phase transition, or as a smoothed indicator function that tracks domain boundaries. Elementary phase-field models for solidification and epitaxial growth are presented and are applied to the dendritic growth of a pure substance and the step-flow growth on a vicinal surface.

Plapp, Mathis [Physique de la Matiere Condensee, Ecole Polytechnique, CNRS, 91128 Palaiseau (France)

2010-07-22

155

In situ observation of mono-molecular growth steps on aqueous solution grown crystals and the transport of molecules to the crystals  

NASA Technical Reports Server (NTRS)

Direct in situ observation of mono-molecular growth steps on a crystal growing in an aqueous solution became possible. The combination of this method with high resolution Schlieren methods or interferometry, permits the growth mechanism of crystals to be investigated directly. Since the observation of growth steps on crystals is the most direct and sensitive way for investigating a crystal growth mechanism, it would contribute to revealing fundamental differences between the growth in space and on Earth. The method was recently extended to in situ observation of the growth processes at high temperatures (1800K).

Tsukamoto, Katsuo

1987-01-01

156

Growth of Large Hematin Crystals in Biomimetic Solutions.  

PubMed

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

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

2014-05-01

157

Convective flow effects on protein crystal growth  

NASA Technical Reports Server (NTRS)

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.

Rosenberger, Franz; Monaco, Lisa A.

1994-01-01

158

Electrical and mechanical properties of vapour grown gallium monotelluride crystals  

NASA Astrophysics Data System (ADS)

The physical vapour deposition (PVD) of gallium monotelluride (GaTe) in different crystalline habits was established in the growth ampoule, strongly depending on the temperature gradient. Proper control on the temperatures of source and growth zones in an indigenously fabricated dual zone furnace could yield the crystals in the form of whiskers and spherulites. Optical and electron microscopic images were examined to predict the growth mechanism of morphologies. The structural parameters of the grown spherulites were determined by X-ray powder diffraction (XRD). The stoichiometric composition of these crystals was confirmed using energy dispersive analysis by X-rays (EDAX). The type and nature of electrical conductivity were identified by the conventional hot probe and two probe methods, respectively. The mechanical parameters, such as Vickers microhardness, work hardening index, and yield strength, were deduced from microindentation measurements. The results show that the vapour grown p-GaTe crystals exhibit novel physical properties, which make them suitable for device applications.

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

2013-10-01

159

Crystal growth furnace safety system validation  

NASA Technical Reports Server (NTRS)

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).

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

1994-01-01

160

Method for crystal growth control  

DOEpatents

The growth of a crystalline body of a selected material is controlled so that the body has a selected cross-sectional shape. The apparatus is of the type which includes the structure normally employed in known capillary die devices as well as means for observing at least the portion of the surfaces of the growing crystalline body and the meniscus (of melt material from which the body is being pulled) including the solid/liquid/vapor junction in a direction substantially perpendicular to the meniscus surface formed at the junction when the growth of the crystalline body is under steady state conditions. The cross-sectional size of the growing crystalline body can be controlled by determining which points exhibit a sharp change in the amount of reflected radiation of a preselected wavelength and controlling the speed at which the body is being pulled or the temperature of the growth pool of melt so as to maintain those points exhibiting a sharp change at a preselected spatial position relative to a predetermined reference position. The improvement comprises reference object means positioned near the solid/liquid/vapor junction and capable of being observed by the means for observing so as to define said reference position so that the problems associated with convection current jitter are overcome.

Yates, Douglas A. (Burlington, MA); Hatch, Arthur E. (Waltham, MA); Goldsmith, Jeff M. (Medford, MA)

1981-01-01

161

On the elementary processes of protein crystallization: Bond selection mechanism  

NASA Astrophysics Data System (ADS)

The paper explores the application of bond selection mechanism (BSM) in protein crystal growth; previously, BSM was employed to explain the slow rate of protein crystal nucleation, equilibrium crystal shape and energy barrier in nucleus formation (C.N. Nanev, Prog. Cryst. Growth Charact. Mater. 59 (2013) 133-169). Now, the elementary growth processes are considered from BSM perspective and the crystal growth shape is tackled, the latter resulting from a strong directional kinetic anisotropy in step advancement rates in different crystallographic directions. The most significant surface patterns of growing protein crystals, such as two-dimensional nuclei and growth spiral shapes observed by atomic force microscopy (AFM), are also considered. The activation barrier associated with entering of a protein molecule into the kink site is evaluated and the start of the kinetic roughening is established. Crystal lattice bond energies are estimated (being well above the thermal energy, kBT) from the supersaturation dependence of 2D- into 1D-nuclei transformation.

Nanev, Christo N.

2014-09-01

162

Growth of large SbSI crystals  

NASA Astrophysics Data System (ADS)

In this paper a novel method of SbSI single crystals fabrication is presented. In this method a sonochemically prepared SbSI gel is used as an intermediate product in a vapour growth process. The main advantages of the presented technique are as follows. First, the SbSI gel source material has lower temperature of sublimation and allows to avoid explosions during SbSI synthesis (the sonochemical synthesis is free of any explosion hazard). Second, but not least, the grown SbSI single crystals have smaller ratio of longitudinal and lateral dimensions. The cross sections of the presented crystals are relatively large (they are up to 9 mm2). The crystals have been characterized by X-ray diffraction, angle-resolved optical spectroscopy, and diffusive reflectivity.

Szperlich, Piotr; Toro?, Bart?omiej; Nowak, Marian; Jesionek, Marcin; K?pi?ska, Miros?awa; Bogdanowicz, W?odzimierz

2014-12-01

163

Crystal growth in a microgravity environment  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

164

Nucleation and growth control in protein crystallization  

NASA Technical Reports Server (NTRS)

The five topics summarized in this final report are as follows: (1) a technique for the expedient, semi-automated determination of protein solubilities as a function of temperature and application of this technique to proteins other than lysozyme; (2) a small solution cell with adjustable temperature gradients for the growth of proteins at a predetermined location through temperature programming; (3) a microscopy system with image storage and processing capability for high resolution optical studies of temperature controlled protein growth and etching kinetics; (4) growth experiments with lysozyme in thermosyphon flow ; and (5) a mathematical model for the evolution of evaporation/diffusion induced concentration gradients in the hanging drop protein crystallization technique.

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

1990-01-01

165

Irradiation growth of zirconium single crystals  

NASA Astrophysics Data System (ADS)

Irradiation growth of zirconium single crystals has been studied during neutron irradiation at 353 K and 553 K at fluences up to 2× 10 25 n/m 2. The results may be summarized as follows: (a) there was an expansion parallel to the a-axis and a c-axis contraction; (b) the growth strains were small (~10 -4), (c) growth saturated at fluences less than ~5× 10 24 n/m 2, (d) the growth behaviour was only weakly dependent on temperature for the range studied, (e) there was a calculated volume increase of the same order as the growth strain, and (f) single crystals prepared from stock of iodide and zone-refined purity showed similar growth behaviour at 553 K. The a-axis expansion is attributed to the annihilation of an excess of interstitials at < a>-type dislocations and interstitial loops. The c-axis contraction may be caused by: (1) elastic relaxation around vacancies or small vacancy clusters, (2) non-linear elastic effects at the dislocation cores of small < a>-type loops, or (3) sub-microscopic vacancy loops with < c>-component Burgers vectors. Comparison with data from polycrystalline zirconium confirms that grain boundaries can play an important role in the irradiation growth of zirconium.

Carpenter, G. J. C.; Murgatroyd, R. A.; Rogerson, A.; Watters, J. F.

1981-10-01

166

Apparatus for monitoring crystal growth  

DOEpatents

A system and method are disclosed for monitoring the growth of a crystalline body from a liquid meniscus in a furnace. The system provides an improved human/machine interface so as to reduce operator stress, strain and fatigue while improving the conditions for observation and control of the growing process. The system comprises suitable optics for forming an image of the meniscus and body wherein the image is anamorphic so that the entire meniscus can be viewed with good resolution in both the width and height dimensions. The system also comprises a video display for displaying the anamorphic image. The video display includes means for enhancing the contrast between any two contrasting points in the image. The video display also comprises a signal averager for averaging the intensity of at least one preselected portions of the image. The value of the average intensity, can in turn be utilized to control the growth of the body. The system and method are also capable of observing and monitoring multiple processes.

Sachs, Emanual M. (Watertown, MA)

1981-01-01

167

Method of monitoring crystal growth  

DOEpatents

A system and method are disclosed for monitoring the growth of a crystalline body from a liquid meniscus in a furnace. The system provides an improved human/machine interface so as to reduce operator stress, strain and fatigue while improving the conditions for observation and control of the growing process. The system comprises suitable optics for forming an image of the meniscus and body wherein the image is anamorphic so that the entire meniscus can be viewed with good resolution in both the width and height dimensions. The system also comprises a video display for displaying the anamorphic image. The video display includes means for enhancing the contrast between any two contrasting points in the image. The video display also comprises a signal averager for averaging the intensity of at least one preselected portions of the image. The value of the average intensity, can in turn be utilized to control the growth of the body. The system and method are also capable of observing and monitoring multiple processes.

Sachs, Emanual M. (Watertown, MA)

1982-01-01

168

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

NASA Technical Reports Server (NTRS)

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.

1992-01-01

169

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

NASA Technical Reports Server (NTRS)

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.

1992-01-01

170

High-purity silicon crystal growth investigations  

NASA Technical Reports Server (NTRS)

Information is given on evaporation and segregation contributions to impurity profiles of floating zone crystals (FZ); high-purity silicon float zoning (FZ); minority-carrier lifetime measurement of heavily doped silicon crystals; the effect of some crystal growth parameters on minority-carrier lifetime; and defect investigations by X-ray topography in graphical and tabular form. It was concluded that evaporation contributes substantially to impurity reduction when FZ or cold-crucible growth is conducted in a vacuum; boron and gallium may be more favorable dopants than indium or aluminum for obtaining high minority-carrier lifetimes; minority-carrier lifetimes greater than 100 microseconds are feasible at a 2 times 10 to the 17th power cm-3 doping level; minority-carrier lifetime decreases with increasing crystal cooling rate and also with the presence of dislocations; the method used to clean silicon feed rods affects lifetime; and microdefect densities in dislocation-free FZ crystals appear to be lower with Ga doping than with B doping.

Ciszek, T. F.; Schuyler, T.; Hurd, J. L.; Fearheiley, M.; Evans, C.; Elder, R.

1986-01-01

171

Crystal growth and annealing for minimized residual stress  

DOEpatents

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.

Gianoulakis, Steven E. (Albuquerque, NM)

2002-01-01

172

Growth of single crystals by vapor transport  

NASA Technical Reports Server (NTRS)

The primary objectives of the program were to establish basic vapor transport and crystal growth properties and to determine thermodynamic, kinetic and structural parameters relevant to chemical vapor transport systems for different classes of materials. An important aspect of these studies was the observation of the effects of gravity-caused convection on the mass transport rate and crystal morphology. These objectives were accomplished through extensive vapor transport, thermochemical and structural studies on selected Mn-chalcogenides, II-VI and IV-VI compounds.

Wiedemeier, H.

1978-01-01

173

FNAS/advanced protein crystal growth  

NASA Technical Reports Server (NTRS)

A scintillation method is presented for determination of the temperature dependence of the solubility, S(T), of proteins in 50-100 micro-l volumes of solution. S(T) data for lysozyme and horse serum albumin were obtained for various combinations of pH and precipitant concentrations. The resulting kinetics and equilibrium information was used for dynamic control, that is the separation of nucleation and growth stages in protein crystallization. Individual lysozyme and horse serum albumin crystals were grown in 15-20 micro-l solution volumes contained in x-ray capillaries.

Rosenberger, Franz

1992-01-01

174

Crystal Splitting in the Growth of Bi2S3  

SciTech Connect

Novel Bi{sub 2}S{sub 3} nanostructures with a sheaf-like morphology are obtained via reaction of bismuth acetate-oleic acid complex with elemental sulfur in 1-octadecence. We propose these structures form by the splitting crystal growth mechanism, which is known to account for the morphology some mineral crystals assume in nature. By controlling the synthetic parameters, different forms of splitting, analogous to observed in minerals, are obtained in our case of Bi{sub 2}S{sub 3}. These new and complex Bi{sub 2}S{sub 3} nanostructures are characterized by TEM, SEM, XRD and ED.

Tang, Jing; Alivisatos, A. Paul

2006-06-15

175

Bulk Crystal Growth - Methods and Materials  

NASA Astrophysics Data System (ADS)

This chapter covers the field of bulk single crystals of materials used in electronics and optoelectronics. These crystals are used in both active and passive modes (to produce devices directly in/on bulk-grown slices of material, or as substrates in epitaxial growth, respectively). Single-crystal material usually provides superior properties to polycrystalline or amorphous equivalents. The various bulk growth techniques are outlined, together with specific critical features, and examples are given of the types of materials (and their current typical sizes) grown by these techniques. Materials covered range from Group IV (Si, Ge, SiGe, diamond, SiC), Group III-V (such as GaAs, InP, nitrides) Group II-IV (including CdTe, ZnSe, MCT) through to a wide range of oxide/halide/phosphate/borate materials. This chapter is to be treated as a snapshot only; the interested reader is referred to the remainder of the chapters in this Handbook for more specific growth and characterization details on the various materials outlined in this chapter. This chapter also does not cover the more fundamental aspects of the growth of the particular materials covered; for these, the reader is again referred to relevant chapters within the Handbook, or to other sources of information in the general literature.

Capper, Peter

176

Protein crystal growth in low gravity  

NASA Technical Reports Server (NTRS)

This research involved (1) using the Atomic Force Microscope (AFM) in a study on the growth of lysozyme crystals and (2) refinement of the design of the Thermonucleator which controls the supersaturation required for the nucleation and growth of protein crystals separately. AFM studies of the (110) tetragonal face confirmed that lysozyme crystals grow by step propagation. There appears to be very little step pile up in the growth regimes which we studied. The step height was measured at = 54A which was equal to the (110) interpane spacing. The AFM images showed areas of step retardation and the formation of pits. These defects ranged in size from 0.1 to 0.4 mu. The source of these defects was not determined. The redesign of the Thermonucleator produced an instrument based on thermoelectric technology which is both easier to use and more amenable to use in a mu g environment. The use of thermoelectric technology resulted in a considerable size reduction which will allow for the design of a multi-unit growth apparatus. The performance of the new apparatus was demonstrated to be the same as the original design.

Feigelson, Robert S.

1994-01-01

177

Convective flow effects on protein crystal growth  

NASA Technical Reports Server (NTRS)

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.

Rosenberger, Franz; Monaco, Lisa A.

1993-01-01

178

Crystal growth and furnace analysis  

NASA Technical Reports Server (NTRS)

A thermal analysis of Hg/Cd/Te solidification in a Bridgman cell is made using Continuum's VAST code. The energy equation is solved in an axisymmetric, quasi-steady domain for both the molten and solid alloy regions. Alloy composition is calculated by a simplified one-dimensional model to estimate its effect on melt thermal conductivity and, consequently, on the temperature field within the cell. Solidification is assumed to occur at a fixed temperature of 979 K. Simplified boundary conditions are included to model both the radiant and conductive heat exchange between the furnace walls and the alloy. Calculations are performed to show how the steady-state isotherms are affected by: the hot and cold furnace temperatures, boundary condition parameters, and the growth rate which affects the calculated alloy's composition. The Advanced Automatic Directional Solidification Furnace (AADSF), developed by NASA, is also thermally analyzed using the CINDA code. The objective is to determine the performance and the overall power requirements for different furnace designs.

Dakhoul, Youssef M.

1986-01-01

179

Lead isotope variation with growth zoning in a galena crystal  

USGS Publications Warehouse

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.

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

1963-01-01

180

Bulk crystal growth and characterization of non-linear optical bisthiourea zinc chloride single crystal by unidirectional growth method  

Microsoft Academic Search

The unidirectional crystal growth method has been employed for the bulk growth of semi-organic non-linear optical bisthiourea zinc chloride single crystal along a-axis with high solute-crystal conversion efficiency. Single crystal X-ray diffraction studies confirm the orthorhombic structure. Optical studies reveal very high transmission of the crystal along the growth axis. Dielectric study shows that the dielectric constant decreases with increase

R. Uthrakumar; C. Vesta; C. Justin Raj; S. Krishnan; S. Jerome Das

2010-01-01

181

Growth of solid solution single crystals  

NASA Technical Reports Server (NTRS)

Based on the thermophysical properties of Hg sub 1-x Cd sub x Te alloys, the reasons are discussed for the failure of conventional Bridgman-Stockbarger growth methods to produce high quality homogeneous crystals in the presence of Earth's gravity. The deleterious effects are considered which arise from the dependence of the thermophysical properties on temperature and composition and from the large amount of heat carried by the fused silica ampules. An improved growth method, developed to optimize heat flow conditions, is described and experimental results are presented. The problems associated with growth in a gravitational environment are discussed. The anticipated advantages of growth in microgravity are given and the implications of the requirements for spaceflight experiments are summarized.

Lehoczky, S. L.; Szofran, F. R.

1987-01-01

182

Growth of solid solution single crystals  

NASA Technical Reports Server (NTRS)

Based on the thermophysical properties of Hg sub 1-x Cd sub x Te alloys, the reasons are discussed for the failure of conventional Bridgman-Stockbarger growth methods to produce high quality homogeneous crystals in the prescence of Earth's gravity. The deleterious effects are considered which arise from the dependence of the thermophysical properties on temperature and composition and from the large amount of heat carried by the fused silica ampules. An improved growth method, developed to optimize heat flow conditions, is described and experimental results are presented. The problems associated with growth in a gravitational environment are discussed. The anticipated advantages of growth in microgravity are given and the implications of the requirements for spaceflight experiments are summarized.

Lehoczky, S. L.; Szofran, F. R.

1988-01-01

183

Flux growth of ZnS single crystals and their characterization  

NASA Astrophysics Data System (ADS)

Cubic zinc sulfide crystals were grown by a flux method using PbCl 2 as a flux. The crystals were grown in the shape of platy or bulky crystals. The surface microtopographs of the crystals were observed by a differential interference microscope. One surface (top surface) of the platy crystals showed layer growth pattern that suggested the spiral growth mechanism, whereas another surface (back surface) showed the dendritic pattern. The luminescence property of the crystals was studied by means of cathode luminescence spectroscopy. Three peaks of spectra were observed at the wavelength of about 560, 470 and 336 nm depending on the purity, growth shapes, and top or back faces of platy crystals. The intensity of these spectra was varied depending on the growth conditions.

Ooshita, Katsuhiko; Inoue, Tetsuo; Sekiguchi, Takashi; Yanagiya, Shin-ichiro; Mori, Atsushi

2004-06-01

184

Subtilisin surface properties and crystal growth kinetics  

NASA Astrophysics Data System (ADS)

Our previous study showed that the solubility and crystal growth rate of the protein subtilisin changed with the substitution of small numbers of surface amino acid residues. Structural and energetic comparisons of crystal structures of two subtilisin mutants were conducted to explore the reason for changes in the growth rate of subtilisin crystals. Unique lattice contact patches were determined for the two mutants. The loss of solvent accessible surface area (ASA), the average hydrophobicity and the number of hydrogen bonds and salt bridges were calculated to quantify surface properties of the contact patches. The structural comparison showed that the three amino acid mutations (Purafect ®?Properase ®) are all in contact patches and provide extra atomic contacts. For Properase ® subtilisin, the number of contacting residues and the loss of ASA increased. Binding energetic calculations, based on the detailed protein structures, were performed to determine non-electrostatic interaction contributions for the required crystallographic orientation and the number of energetically favored, false-binding orientations. The agreement and disparity between molecular structure and macroscopic crystallization behavior are discussed.

Pan, Xiaojing; Bott, Rick; Glatz, Charles E.

2003-07-01

185

(PCG) Protein Crystal Growth Gamma-Interferon  

NASA Technical Reports Server (NTRS)

(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.

1989-01-01

186

Large-aperture YCOB crystal growth for frequency conversion in the high average power laser system  

Microsoft Academic Search

Yttrium calcium oxyborate YCa4O(BO3)3 (YCOB) is a novel non-linear optical crystal possessing good thermal, mechanical and non-linear optical properties. Large-aperture YCOB crystals with 75mm diameter were grown for high-average power frequency conversion on the mercury laser system. The growth morphology (included facet and spiral growth), cracking and inclusions in the as-grown crystal boule were discussed as the critical problem for

Yiting Fei; Bruce H. T. Chai; C. A. Ebbers; Z. M. Liao; K. I. Schaffers; P. Thelin

2006-01-01

187

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

NASA Technical Reports Server (NTRS)

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.

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

188

Modeling of Continuum Transport and Meso-Scale Kinetics during Solution Crystal Growth  

NASA Astrophysics Data System (ADS)

Solution crystal growth is widely applied in many industries and fundamental research, and it is employed to crystallize materials ranging from inorganic molecules, small organic molecules, to large organic molecules. However, despite the broad application, fundamental factors regarding this crystal growth process are not well understood. In this thesis, numerical models are developed to study the influences of macro-scale mass transfer limitations and meso-scale growth kinetics on solution crystal growth. A parallel, finite element model is implemented to compute three-dimensional fluid flow and mass transfer during crystal growth and is especially applied to the growth systems in Atomic Force Microscopy fluid cells. This work assesses the parametric sensitivity of growth conditions to factors such as the strength of flow, the frequency of scanning motion, the size of the crystal, and the kinetics of the growing surface. Accounting for such effects will be very important to understand solution crystal growth and to interpret AFM measurements of growth dynamics. Additionally, a simplified two-dimensional numerical model focused on the region near the growing crystal surface and the AFM cantilever was developed based on the calculated results of the three-dimensional model. With this two-dimensional model, we provide basic understanding of the fluid flow and mass transfer where the AFM measurements were made, and simplified the revision of AFM measurements interpretation. A fundamental theoretical model based on the phase-field approach is developed to simulate nano-scale island growth and spiral step growth on crystal surfaces in a supersaturated liquid and is validated by comparison to zinc oxide nanowires synthesis experiments. Results obtained by this work help to explain how experimental factors affect the crystal growth and crystal microstructures and the correlation between island growth and spiral growth mechanisms.

Wang, Wei

189

Growth and adhesion properties of monosodium urate monohydrate (MSU) crystals  

NASA Astrophysics Data System (ADS)

The presence of monosodium urate monohydrate (MSU) crystals in the synovial fluid has long been associated with the joint disease gout. To elucidate the molecular level growth mechanism and adhesive properties of MSU crystals, atomic force microscopy (AFM), scanning electron microscopy, and dynamic light scattering (DLS) techniques were employed in the characterization of the (010) and (1-10) faces of MSU, as well as physiologically relevant solutions supersaturated with urate. Topographical AFM imaging of both MSU (010) and (1-10) revealed the presence of crystalline layers of urate arranged into v-shaped features of varying height. Growth rates were measured for both monolayers (elementary steps) and multiple layers (macrosteps) on both crystal faces under a wide range of urate supersaturation in physiologically relevant solutions. Step velocities for monolayers and multiple layers displayed a second order polynomial dependence on urate supersaturation on MSU (010) and (1-10), with step velocities on (1-10) generally half of those measured on MSU (010) in corresponding growth conditions. Perpendicular step velocities on MSU (010) were obtained and also showed a second order polynomial dependence of step velocity with respect to urate supersaturation, which implies a 2D-island nucleation growth mechanism for MSU (010). Extensive topographical imaging of MSU (010) showed island adsorption from urate growth solutions under all urate solution concentrations investigated, lending further support for the determined growth mechanism. Island sizes derived from DLS experiments on growth solutions were in agreement with those measured on MSU (010) topographical images. Chemical force microscopy (CFM) was utilized to characterize the adhesive properties of MSU (010) and (1-10). AFM probes functionalized with amino acid derivatives and bio-macromolecules found in the synovial fluid were brought into contact with both crystal faces and adhesion forces were tabulated into histograms for comparison. AFM probes functionalized with -COO-, -CH3, and -OH functionalities displayed similar adhesion force with both crystal surfaces of MSU, while adhesion force on (1-10) was three times greater than (010) for -NH2+ probes. For AFM probes functionalized with bovine serum albumin, adhesion force was three times greater on MSU (1-10) than (010), most likely due to the more ionic nature of (1-10).

Perrin, Clare M.

190

The Effect of Protein Impurities on Lysozyme Crystal Growth  

NASA Technical Reports Server (NTRS)

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. In order 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 f {101} 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.

Judge, Russell A.; Forsythe, Elizabeth L.; Pusey, Marc L.

1998-01-01

191

Mechanics and growth of tissues  

NASA Astrophysics Data System (ADS)

During development or during tumor growth, cells organize collectively by cell division and apoptosis in a tissue. The aim of our work is to build up theoretical tools based on non-equilibrium statistical mechanics and continuum mechanics to describe the mechanical properties of tissues and to apply them to various biologically relevant situations. We first show that because of the coupling between cell division and the local stress, a tissue can be considered as a visco-elastic liquid at time scales larger than the cell division time. We then show recent model experiments on cell aggregates showing the effect of mechanical stress on tissue growth. Finally, we use the hydrodynamic description to discuss the steady state structure of villis which are the protrusions of the surface of the intestine. We describe the formation of villis as a buckling instability of a polar cell monolayer. Similar instabilities occur as well for tube-like cellular structures such as arteries.

Joanny, Jean-Francois

2013-03-01

192

Practical aspects of silicon float zone crystal growth  

NASA Technical Reports Server (NTRS)

The float zone (FZ) growth method for silicon crystallization has advantages and disadvantages when compared to the other principal growth method, the Czochralski (CZ) technique. CZ growth is attractive for the following reasons: large diameters, high single crystal yields, low thermal gradients, low operator skill requirements, efficient power utilization, and low feed material costs. Some areas where FZ growth is advantageous include high purity, axial resistivity uniformity (on a macroscale), visibility of the growth region, low consumable material costs, and high growth rates.

Ciszek, T. T.

1980-01-01

193

Convective flow effects on protein crystal growth  

NASA Technical Reports Server (NTRS)

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.

Rosenberger, Franz; Monaco, Lisa A.

1995-01-01

194

Large Single Crystal growth of Bi2212 superconducting oxide  

Microsoft Academic Search

A floating zone method was used to study the effects of the growth velocity and starting composition of the feed rod on the crystal growth behaviour of Bi-2212 superconducting materials. It shows that a necessary condition for large single crystal growth is that the solid-liquid interface of a rod maintains a planar interface during crystal growth. The planar solid-liquid interface

Genda Gu; Gangyong Xu; John Tranquada

2006-01-01

195

Dislocation density control in high-purity germanium crystal growth  

NASA Astrophysics Data System (ADS)

High-purity germanium (HP-Ge) crystals were grown in hydrogen atmosphere by Czochralski method. The control of dislocation density in high-purity germanium crystal growth was studied. It could be shown that by control of the temperature gradient during crystal growth the dislocation density distribution in the crystal can be controlled to a degree which allows for the growth of crystal fulfilling detector requirements. Crystals with diameters of 3.5 and 9 cm were grown according to the relationship between axial temperature gradient and dislocation density to be able to meet the requirements of detector fabrication by having dislocation density in the range 2000-7000 cm-2.

Wang, Guojian; Guan, Yutong; Mei, Hao; Mei, Dongming; Yang, Gang; Govani, Jayesh; Khizar, Muhammad

2014-05-01

196

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

USGS Publications Warehouse

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.

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

2003-01-01

197

Studies on Growth and Characterization of bis Thiourea Lead Chloride:. a Novel Nonlinear Optical Crystal  

NASA Astrophysics Data System (ADS)

Single crystals of the metal-organic nonlinear optical material bis thiourea lead chloride were grown from solution growth technique for the first time. The grown crystals were characterized by single crystal X-ray diffraction analysis to confirm the crystal structure. The presence of various functional groups and the coordination of metal ions to thiourea were confirmed by Fourier transform infrared analysis. UV-Vis. spectrum was recorded to study the optical transparency of the grown crystals. The second order nonlinear optical property of the grown crystal was examined by Kurtz powder technique and mechanical behavior was studied by Vickers micro hardness test.

Kirubavathi, K.; Selvaraju, K.; Kumararaman, S.

198

Solid State Pathways to Complex Shape Evolution and Tunable Porosity during Metallic Crystal Growth  

PubMed Central

Growing complex metallic crystals, supported high index facet nanocrystal composites and tunable porosity metals, and exploiting factors that influence shape and morphology is crucial in many exciting developments in chemistry, catalysis, biotechnology and nanoscience. Assembly, organization and ordered crystallization of nanostructures into complex shapes requires understanding of the building blocks and their association, and this relationship can define the many physical properties of crystals and their assemblies. Understanding crystal evolution pathways is required for controlled deposition onto surfaces. Here, complex metallic crystals on the nano- and microscale, carbon supported nanoparticles, and spinodal porous noble metals with defined inter-feature distances in 3D, are accomplished in the solid-state for Au, Ag, Pd, and Re. Bottom-up growth and positioning is possible through competitive coarsening of mobile nanoparticles and their site-specific crystallization in a nucleation-dewetted matrix. Shape evolution, density and growth mechanism of complex metallic crystals and porous metals can be imaged during growth. PMID:24026532

Valenzuela, Carlos Díaz; Carriedo, Gabino A.; Valenzuela, María L.; Zúñiga, Luis; O'Dwyer, Colm

2013-01-01

199

Czochralski single crystal growth, modeling, and characterization of ilmenite  

Microsoft Academic Search

Ilmenite is a wide band gap material, and could be used for electronic applications. Since ilmenite is stoichiometric at its melting point, the single crystals are grown using Czochralski crystal growth method. Earlier research in ilmenite uses ceramic material, and smaller size single crystals. In this research large size single crystals of ilmenite are grown. To grow large size single

Jayakumar Muthusami

1998-01-01

200

Features of beryllium aluminate crystal growth by the method of horizontally oriented crystallization  

NASA Astrophysics Data System (ADS)

The method of horizontally oriented (one-dimensional) crystallization (HOC) was applied for growth of chrome-doped beryllium aluminate (alexandrite) single crystals. The stratified hydrodynamic structure of melt in the boat-like crystallization container that predetermines major features of crystal growth was revealed by model experiment. Patterns of (1 2 0), (1 3 0), and (1 0 0) growth sectors of crystal volume and zones of preferred entrapment of gas-melt inclusions as well as efficient distribution coefficient of chrome on crystallization (inversion included) and distribution behavior of dopant along the grown crystals are illustrated and discussed. Occurrence of metal microinclusions of crystallization container material (Mo) in grown alexandrite crystals is analyzed. It is shown that alexandrite crystals grown by the HOC method have some advantages compared to the crystals grown by the Czochralski method.

Gurov, V. V.; Tsvetkov, E. G.; Kirdyashkin, A. G.

2003-09-01

201

Crystal growth formation in melt extrudates.  

PubMed

The purpose of the study was to investigate the physical state of hot-melt extruded guaifenesin tablets containing either Acryl-EZE or Eudragit L100-55 and to study the physicochemical factors influencing crystal growth of guaifenesin on the surface of the extrudates. The powder mixtures containing Acryl-EZE were extruded on a single-screw Randcastle Microtruder at 20rpm and at temperatures of 90, 95, 110 degrees C (zones 1, 2, 3, respectively) and 115 degrees C (die), before being manually cut into tablets (250+/-5mg). Extrudates containing Eudragit L100-55, TEC and guaifenesin were extruded at temperatures ranging from 60 to 115 degrees C. Modulated differential calorimetry (DSC) was used to demonstrate the plasticizing effect of guaifenesin on Eudragit L100-55. Powder X-ray diffraction (PXRD) showed that while the drug powder is crystalline, extrudates containing up to 25% drug exhibited an amorphous diffraction profile. Extrudates containing higher drug concentrations showed an amorphous profile with some crystalline peaks corresponding to guaifenesin, indicating that the limit of solubility of drug in the matrix had been exceeded. Scanning electron microscopy was used to demonstrate that drug crystallization was a surface phenomenon and dependent on the drug concentration. In vitro dissolution testing showed no effect of surface crystallization of guaifenesin on drug release rates of extruded matrix tablets. The influence of hydrophilic polymeric additives including PVP K25, polycarbophil, PEG 3,350, poloxamer 188 or poly(ethylene oxide) as crystal growth inhibitors was investigated at a level of 10% based on the drug content. The extent of crystal growth was reduced for all additives. Complete drug release in pH 6.8 phosphate buffer was prolonged from 4h in extrudates containing Acryl-EZE and guaifenesin to 8h in extrudates containing Eudragit L100-55, TEC and guaifenesin. Drug release in extrudates containing Eudragit L100-55 and guaifenesin was not affected by the presence of hydrophilic additives present at 10% based on the drug content. In vitro drug release studies showed no significant change during storage for up to 6 months at 25 degrees C/60% relative humidity and 40 degrees C/75% relative humidity. PMID:17524578

Bruce, Caroline; Fegely, Kurt A; Rajabi-Siahboomi, Ali R; McGinity, James W

2007-08-16

202

Growth dynamics for DNA-guided nanoparticle crystallization.  

PubMed

Spherical nucleic acid (SNA) nanostructures assemble into a large variety of well-defined crystalline superlattices via DNA-directed hybridization. Crystallities of SNA with various shapes emerge during the assembly process, which coalesce during coarsening, leading to polycrystalline materials. Here, we investigate the growth dynamics of SNAs into body-centered cubic superlattices and the coalescence of SNA aggregates using a colloidal model formulated from the competition of electrostatic core repulsions and localized DNA hybridization attractions. We find that the growth law of isolated SNA crystallities is well-described by the power law t(1/2), in agreement with experimental observations. At later times, coalescence slows the growth dynamics considerably and is dependent on the orientational mismatch (misorientation angle) of the coalescing crystallites. Molecular dynamics simulations show that the misorientation angle decreases continually during the coalescence, which is a signature of the grain rotation induced coalescence mechanism. This mechanism is followed by the coarsening of a "neck" that develops at the boundary between the coalescing crystallites. Remarkably, we find faster coalescence dynamics for larger SNAs compared to smaller SNAs due to their enhanced surface diffusion, which more effectively reduces curvature at the boundary of two superlattices. These findings provide fundamental insight into the relationship between nanoparticle surface chemistry and its crystallite growth and coalescence. PMID:24274629

Dhakal, Subas; Kohlstedt, Kevin L; Schatz, George C; Mirkin, Chad A; Olvera de la Cruz, Monica

2013-12-23

203

A general mechanism of polycrystalline growth.  

PubMed

Most research into microstructure formation during solidification has focused on single-crystal growth ranging from faceted crystals to symmetric dendrites. However, these growth forms can be perturbed by heterogeneities, yielding a rich variety of polycrystalline growth patterns. Phase-field simulations show that the presence of particulates (for example, dirt) or a small rotational-translational mobility ratio (characteristic of high supercooling) in crystallizing fluids give rise to similar growth patterns, implying a duality in the growth process in these structurally heterogeneous fluids. Similar crystallization patterns are also found in thin polymer films with particulate additives and pure films with high supercooling. This duality between the static and dynamic heterogeneity explains the ubiquity of polycrystalline growth patterns in polymeric and other complex fluids. PMID:15300243

Gránásy, László; Pusztai, Tamás; Börzsönyi, Tamás; Warren, James A; Douglas, Jack F

2004-09-01

204

Optimization of heating conditions during Cz BGO crystal growth  

NASA Astrophysics Data System (ADS)

We have studied the effect of geometrical and physical parameters of additional lower heater on thermal conditions during BGO growth by the Czochralski technique, in particular, on keeping flat melt/crystal interface during the whole growth process. Numerical simulation by CGSim software was used as an efficient tool for the analysis. After revealing optimal growth conditions and hot zone design by modeling, we have modified experimental growth setup and successfully improved crystal growth process in close agreement to modeling predictions.

Kolesnikov, A. V.; Galenin, E. P.; Sidletskiy, O. Ts.; Kalaev, V. V.

2014-12-01

205

Electrochemical Sc 2O 3 single crystal growth  

Microsoft Academic Search

Scandium oxide single crystals were successfully grown electrochemically by applying the Sc3+ ion-conducting Sc2(MoO4)3 solid electrolyte at 1223K. The single crystal growth can be regulated by the electrolysis condition, and the crystal size can be intentionally controlled by adjusting the electrolysis period. Although the single crystal growth of such refractory oxides as Sc2O3 is considerably difficult by the conventional thermal

Toshiyuki Masui; Young Woon Kim; Nobuhito Imanaka; Gin-ya Adachi

2004-01-01

206

Crystal growth of calcium sulphate dihydrate at low supersaturation  

NASA Astrophysics Data System (ADS)

The growth rate of calcium sulphate dihydrate crystals, gypsum, in aqueous suspension has been shown to be screw dislocation controlled in the supersaturation range 1.03< {C}/{C s}<1.15 . Constant composition experiments show that the overall rate of growth decreases with increasing mass of the crystals. A combination of normal spiral growth, growth of cooperating spirals with non-parallel Burgers vectors, and growth of grain boundary spirals, together with partial outgrowth of concave parts of the crystals, can explain the rate of growth found for different preparations of gypsum crytals.

Christoffersen, M. R.; Christoffersen, J.; Weijnen, M. P. C.; Van Rosmalen, G. M.

1982-08-01

207

Morphological stability and kinetics in crystal growth from vapors  

NASA Technical Reports Server (NTRS)

The following topics are discussed: (1) microscopy image storage and processing system; (2) growth kinetics and morphology study with carbon tetrabromide; (3) photothermal deflection vapor growth setup; (4) bridgman growth of iodine single crystals; (5) vapor concentration distribution measurement during growth; and (6) Monte Carlo modeling of anisotropic growth kinetics and morphology. A collection of presentations and publications of these results are presented.

Rosenberger, Franz

1990-01-01

208

Growth of urea crystals by physical vapor transport  

NASA Technical Reports Server (NTRS)

This work demonstrates that high optical quality crystals of urea can be grown by the physical vapor transport method. The unique features of this method are compared with growth from methanol/water solutions. High growth rates, exceeding 2.5 mm/day, were achieved, and cm-size optical quality single crystals were obtained. Details of the growth technique and the physical properties of the crystals are presented.

Feigelson, R. S.; Route, R. K.; Kao, T.-M.

1985-01-01

209

Indium antimonide crystal growth experiment M562. [Skylab weightless conditions  

NASA Technical Reports Server (NTRS)

It was established that ideal diffusion controlled steady state conditions, never accomplished on earth, were achieved during the growth of Te-doped InSb crystals in Skylab. Surface tension effects led to nonwetting conditions under which free surface solidification took place in confined geometry. It was further found that, under forced contact conditions, surface tension effects led to the formation of surface ridges (not previously observed on earth) which isolated the growth system from its container. In addition, it was possible, for the first time, to identify unambiguously: the origin of segregation discontinuities associated with facet growth, the mode of nucleation and propagation of rotational twin boundaries, and the specific effect of mechanical-shock perturbations on segregation. The results obtained prove the advantageous conditions provided by outer space. Thus, fundamental data on solidification thought to be unattainable because of gravity-induced interference on earth are now within reach.

Gatos, H. C.; Witt, A. F.

1974-01-01

210

Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride  

NASA Astrophysics Data System (ADS)

Good quality single crystals of pure and metal ion (Ni 2+) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline perfection and the EDAX spectrum confirms the presence of dopant in the lattice of the parent crystal. The DRS UV-visible spectral study reveals improved transparency for the doped crystal, ascertaining the inclusion of metal ion in the lattice. The optical band gap of the pure and doped crystals was calculated to be 4.8 and 5.2 eV respectively from the UV transmission spectrum. The vickers hardness test brings forth higher hardness value for Ni 2+doped BTZC as compared to pure BTZC crystal. The dielectric measurement exhibits very low dielectric constant and dielectric loss at higher frequencies for both the pure and Ni 2+doped BTZC. The existence of second harmonic generation signals in the crystal also has been confirmed by performing the Kurtz powder test.

Parasuraman, K.; Sakthi Murugesan, K.; Uthrakumar, R.; Jerome Das, S.; Milton Boaz, B.

2011-10-01

211

Common twinning characteristics of silicon and III-V compound crystals during growth from the melt  

Microsoft Academic Search

A comparative study is made of the newly discovered and known twinning characteristics of silicon and III-V compound crystals grown from the melt by the Czochralski, Stepanov, and crucibleless zone melting techniques. The structural characteristics of twinned crystals are examined. The possible mechanisms of growth-related twinning are analyzed in the light of the available experimental data.

A. N. Buzynin; V. A. Antonov; V. V. Osiko; V. M. Tatarintsev

1988-01-01

212

Volume Diffusion Growth Kinetics and Step Geometry in Crystal Growth  

NASA Technical Reports Server (NTRS)

The role of step geometry in two-dimensional stationary volume diff4sion process used in crystal growth kinetics models is investigated. Three different interface shapes: a) a planar interface, b) an equidistant hemispherical bumps train tAx interface, and c) a train of right angled steps, are used in this comparative study. The ratio of the super-saturation to the diffusive flux at the step position is used as a control parameter. The value of this parameter can vary as much as 50% for different geometries. An approximate analytical formula is derived for the right angled steps geometry. In addition to the kinetic models, this formula can be utilized in macrostep growth models. Finally, numerical modeling of the diffusive and convective transport for equidistant steps is conducted. In particular, the role of fluid flow resulting from the advancement of steps and its contribution to the transport of species to the steps is investigated.

Mazuruk, Konstantin; Ramachandran, Narayanan

1998-01-01

213

Vertical unseeded vapor growth of large CdTe crystals  

NASA Astrophysics Data System (ADS)

Single crystals of CdTe were grown by the vertical, unseeded vapor growth technique. The faceted, high quality crystals showed higher purity than the ˜6N source materials. The growth rate was found to be strongly dependent on the excess Te present in the growth charge. A maximum growth rate of about 2 g/day was observed at about 0.001-0.02 mol% excess Te at charge preparation. X-ray analysis and metallography of the crystals and mechano-chemical polished slices revealed high quality monocrystallinity. The crystals showed high resistivity (? 10 8 ? cm) and did have nuclear radiation detection properties.

Yellin, N.; Eger, D.; Shachna, A.

1982-12-01

214

Anion-switchable supramolecular gels for controlling pharmaceutical crystal growth  

NASA Astrophysics Data System (ADS)

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.

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

2010-12-01

215

In situ monitoring of crystal growth and dissolution of oriented layered double-hydroxide crystals immobilized on silicon  

NASA Astrophysics Data System (ADS)

Layered double-hydroxide (LDH) minerals have recently attracted attention through their potential industrial application as fillers in mineral-polymer nanocomposite materials and, separately, as solid base catalysts to promote a range of reactions in an environmentally sound way. Little research has been undertaken on the crystal growth mechanism of LDHs using in situ methods. Recently, advances have been made in the controlled deposition and immobilisation of nanometre-sized LDH crystals onto a silicon substrate with preferred orientation. In this work we present initial studies using atomic force microscopy to image in real time immobilised LDH crystals during stages of hydration, growth and dissolution. The various stages were recorded by adjusting the reactant concentrations of the surrounding aqueous solution, allowing crystal dynamics to be visualised. Under certain conditions preferred stability of certain-sized LDH crystals relative to others was observed, indicating the operation of an Ostwald ripening process in samples containing a heterogeneous distribution of crystallite sizes.

Greenwell, H. C.; Bindley, L. A.; Unwin, P. R.; Holliman, P. J.; Jones, W.; Coveney, P. V.; Barnes, S. L.

2006-08-01

216

Comment on "Evaluation of X-ray diffraction methods for determining the crystal growth mechanisms of clay minerals in mudstones, shales and slates," by L. N. Warr and D. R. Peacor  

USGS Publications Warehouse

A recent paper by Warr and Peacor (2002) suggested that our use of the Bertaut-Warren-Averbach technique (MudMaster computer program) for studying changes in crystallite thickness distributions (CTDs) of clay minerals during diagenesis and very low-grade metamorphism is not reliable because it is dependent on many variables which can not be fully controlled. Furthermore, the authors implied that the measured shapes of CTDs cannot be used with confidence to deduce crystal growth mechanisms and histories for clays, based on our CTD simulation approach (using the Galoper computer program). We disagree with both points, and show that the techniques are powerful, reliable and useful for studying clay mineral alteration in rocks. ?? 2003 Schweiz. Mineral. Petrogr. Ges.

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

2003-01-01

217

Growth and characterization of metal-organic crystal: Tetra thiourea cobalt chloride (TTCoC)  

NASA Astrophysics Data System (ADS)

Single crystals of tetra thiourea cobalt chloride (TTCoC) having dimension of 25 mm×24 mm×7 mm were grown by slow evaporation solution growth technique. The structural perfection of the grown crystals was analyzed by high-resolution X-ray diffraction (HRXRD). The mechanical property of the grown crystals has been analyzed by Vicker's microhardness method. The dielectric constant measurements were carried out and the nature of variation of dielectric constant ?r and dielectric loss D were studied and reported.

Murugan, G. Senthil; Ramasamy, P.

2009-01-01

218

Acquisition of Single Crystal Growth and Characterization Equipment  

SciTech Connect

Final Report for DOE Grant No. DE-FG02-04ER46178 'Acquisition of Single Crystal Growth and Characterization Equipment'. There is growing concern in the condensed matter community that the need for quality crystal growth and materials preparation laboratories is not being met in the United States. It has been suggested that there are too many researchers performing measurements on too few materials. As a result, many user facilities are not being used optimally. The number of proficient crystal growers is too small. In addition, insufficient attention is being paid to the enterprise of finding new and interesting materials, which is the driving force behind much of condensed matter research and, ultimately, technology. While a detailed assessment of this situation is clearly needed, enough evidence of a problem already exists to compel a general consensus that the situation must be addressed promptly. This final report describes the work carried out during the last four years in our group, in which a state-of-the-art single crystal growth and characterization facility was established for the study of novel oxides and intermetallic compounds of rare earth, actinide and transition metal elements. Research emphasis is on the physics of superconducting (SC), magnetic, heavy fermion (HF), non-Fermi liquid (NFL) and other types of strongly correlated electron phenomena in bulk single crystals. Properties of these materials are being studied as a function of concentration of chemical constituents, temperature, pressure, and magnetic field, which provide information about the electronic, lattice, and magnetic excitations at the root of various strongly correlated electron phenomena. Most importantly, the facility makes possible the investigation of material properties that can only be achieved in high quality bulk single crystals, including magnetic and transport phenomena, studies of the effects of disorder, properties in the clean limit, and spectroscopic and scattering studies through efforts with numerous collaborators. These endeavors will assist the effort to explain various outstanding theoretical problems, such as order parameter symmetries and electron-pairing mechanisms in unconventional superconductors, the relationship between superconductivity and magnetic order in certain correlated electron systems, the role of disorder in non-Fermi liquid behavior and unconventional superconductivity, and the nature of interactions between localized and itinerant electrons in these materials. Understanding the mechanisms behind strongly correlated electron behavior has important technological implications.

Maple, M. Brian; Zocco, Diego A.

2008-12-09

219

In vitro crystallization, characterization and growth-inhibition study of urinary type struvite crystals  

NASA Astrophysics Data System (ADS)

The formation of urinary stones, known as nephrolithiasis or urolithiasis, is a serious, debilitating problem throughout the world. Struvite—NH4MgPO4·6H2O, ammonium magnesium phosphate hexahydrate, is one of the components of urinary stones (calculi). Struvite crystals with different morphologies were grown by in vitro single diffusion gel growth technique with different growth parameters. The crystals were characterized by powder XRD, FT-IR, thermal analysis and dielectric study. The powder XRD results of struvite confirmed the orthorhombic crystal structure. The FT-IR spectrum proved the presence of water of hydration, metal-oxygen bond, N-H bond and P-O bond. For thermal analysis TGA, DTA and DSC were carried out simultaneously. The kinetic and thermodynamic parameters of dehydration/decomposition process were calculated. Vickers micro-hardness and related mechanical parameters were also calculated. The in vitro growth inhibition studies of struvite by the juice of Citrus medica Linn as well as the herbal extracts of Commiphora wightii, Boerhaavia diffusa Linn and Rotula aquatica Lour were carried out and found potent inhibitors of struvite.

Chauhan, Chetan K.; Joshi, Mihir J.

2013-01-01

220

Growth mechanisms for doped clusters  

NASA Astrophysics Data System (ADS)

Structural growth mechanisms for metal doped nanoclusters are investigated in combined experimental and theoretical studies. In particular, silicon, copper and gold clusters incorporating a transition metal dopant atom are investigated: SinX (X=Cu, V), CunSc+ and AunY+ with n < 20. The doped clusters are produced with a dual-target dual-laser vaporization source. Structural information about the doped nanoclusters is provided by infrared multi-photon dissociation spectroscopy. Their size and composition dependent stability is studied with photofragmentation and mass spectrometry. A detailed understanding of the role of the dopant atom in the structural growth and in the electronic structure of the clusters is obtained by comparison with quantum chemical computations using density functional theory.

Janssens, Ewald; Lievens, Peter

2011-06-01

221

Polyhydroxycarboxylic acids as inhibitors of calcium oxalate crystal growth; Relation between inhibitory capacity and chemical structure  

NASA Astrophysics Data System (ADS)

The kinetics of crystal growth of calcium oxalate monohydrate seed crystals were investigated potentiometrically in the presence of several polyhydroxycarboxylic acids; etylenediaminetetraacetic acid, citric acid, isocitric acid, malic acid and succinic acid, and it was found that they inhibited crystal growth, except in the case of isocitric acid manifested no-effects. An apparent rate order of 2 in the presence of all the inhibitors, suggested a spiral growth mechanism. Application to a kinetic Langmuir-type model suggested that adsorption of the polyhydroxycarboxylic acids, at the active growth sites, is the cause of the reduction in the crystal growth rates. The inhibitory action of the different substances assayed was comparatively evaluated. Relations between chemical structure and inhibitory capacity were established.

Grases, F.; Millan, A.; Garcia-Raso, A.

1988-07-01

222

Protein Crystal Growth With the Aid of Microfluidics  

NASA Technical Reports Server (NTRS)

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.

vanderWoerd, Mark

2003-01-01

223

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

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

224

Growth of strontium tartrate tetrahydrate single crystals in silica gels  

Microsoft Academic Search

Growth of single crystals of strontium tartrate tetrahydrate by controlled diffusion in silica gels has been narrated. In the field of material science, there is always a keen and competitive race to grow perfect single crystals with sufficient purity and perfection. Successful attempts to larger as well as more perfect crystals of SrTr are described in this paper and thus

A. R. Patel; S. K. Arora

1976-01-01

225

A chain mechanism for flagellum growth  

NASA Astrophysics Data System (ADS)

Bacteria swim by means of long flagella extending from the cell surface. These are assembled from thousands of protein subunits translocated across the cell membrane by an export machinery at the base of each flagellum. Unfolded subunits then transit through a narrow channel at the core of the growing flagellum to the tip, where they crystallize into the nascent structure. As the flagellum lengthens outside the cell, the rate of flagellum growth does not change. The mystery is how subunit transit is maintained at a constant rate without a discernible energy source in the channel of the external flagellum. We present evidence for a simple physical mechanism for flagellum growth that harnesses the entropic force of the unfolded subunits themselves. We show that a subunit docked at the export machinery can be captured by a free subunit through head-to-tail linkage of juxtaposed amino (N)- and carboxy (C)-terminal helices. We propose that sequential rounds of linkage would generate a multisubunit chain that pulls successive subunits into and through the channel to the flagellum tip, and by isolating filaments growing on bacterial cells we reveal the predicted chain of head-to-tail linked subunits in the transit channel of flagella. Thermodynamic analysis confirms that links in the subunit chain can withstand the pulling force generated by rounds of subunit crystallization at the flagellum tip, and polymer theory predicts that as the N terminus of each unfolded subunit crystallizes, the entropic force at the subunit C terminus would increase, rapidly overcoming the threshold required to pull the next subunit from the export machinery. This pulling force would adjust automatically over the increasing length of the growing flagellum, maintaining a constant rate of subunit delivery to the tip.

Evans, Lewis D. B.; Poulter, Simon; Terentjev, Eugene M.; Hughes, Colin; Fraser, Gillian M.

2013-12-01

226

Kinetic mechanism of chain folding in polymer crystallization  

NASA Astrophysics Data System (ADS)

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 dl with the Rouse time of a piece of polymer of the same arc length dl 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.

Stepanow, S.

2014-09-01

227

Kinetic mechanism of chain folding in polymer crystallization  

E-print Network

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 is derived by considering the growth as a dynamic multistage process.

S. Stepanow

2014-09-22

228

Preliminary investigations of protein crystal growth using the Space Shuttle  

NASA Technical Reports Server (NTRS)

Four preliminary Shuttle experiments are described which have been used to develop prototype hardware for a more advanced system that will evaluate effects of gravity on protein crystal growth. The first phase of these experiments has centered on the development of micromethods for protein crystal growth by vapor-diffusion techniques (using a space version of the hanging-drop method) and on dialysis using microdialysis cells. Results suggest that the elimination of density-driven sedimentation can effect crystal morphology. In the dialysis experiment, space-grown crystals of concanavalin B were three times longer and 1/3 the thickness of earth-grown crystals.

Delucas, L. J.; Suddath, F. L.; Snyder, R.; Naumann, R.; Broom, M. B.; Pusey, M.; Yost, V.; Herren, B .; Carter, D.

1986-01-01

229

Phase transition mechanisms in lanthanide elemental crystals  

NASA Astrophysics Data System (ADS)

A unifying theoretical description is given of the phase transition mechanisms occurring in lanthanide elemental crystals. The hcp-9R-dhcp-fcc sequence of reconstructive phase transitions is interpreted in terms of crossover between displacive and reordering mechanisms. The distorted fcc, monoclinic, ?-U-type and bct high-pressure phases can be depicted by purely displacive mechanisms, the low symmetry of these phases resulting from the non-spherical shape of the electronic shells induced by the delocalization of the f-electrons.

Dmitriev, V. P.; Kuznetsov, A. Yu.; Machon, D.; Weber, H.-P.; Tolédano, P.

2003-03-01

230

Taylor vortices formed in the melt during paratellurite crystal growth  

NASA Astrophysics Data System (ADS)

The hydrodynamics of tellurium dioxide melt during Czochralski growth of paratellurite crystals with a diameter up to 80 mm was experimentally investigated. The images of the melt surface during crystal growth are obtained. It is shown that a stable system of Taylor vortices in the form of two convection cells is formed at definite Reynolds numbers.

Kolesnikov, A. I.; Grechishkin, R. M.; Tret'yakov, S. A.; Gritsunova, O. V.; Vorontsova, E. Yu.

2008-12-01

231

Growth and characterization of a new organic single crystal: 1-(4-Nitrophenyl) pyrrolidine (4NPY).  

PubMed

A new 1-(4-Nitrophenyl) pyrrolidine single crystal has grown by slow evaporation solution growth technique. The grown crystal have characterized by single crystal X-ray analysis, and it shows that 1-(4-Nitrophenyl) pyrrolidine crystallizes in the orthorhombic space group Pbca, with cell parameters a=10.3270 (5)Å, b=9.9458 (6)Å, c=18.6934 (12)Å, and Z=8. Powder XRD pattern confirmed that grown crystal posses highly crystalline nature. The functional groups have identified by using FTIR spectral analysis. The absorbance and the luminescence spectra of the title compound have analyzed using UV-Visible and PL spectra. The thermo analytical properties of the crystal have studied using TG/DTA spectrum. The mechanical property of the grown crystal has determined using Vickers micro hardness measurement. The grown features of the crystal have analyzed using etching technique. PMID:25523042

Nirosha, M; Kalainathan, S; Aravindan, P G

2015-03-01

232

Influence of convection on the growth of crystals from solution  

NASA Technical Reports Server (NTRS)

This is a review of the influence of convection on the growth of crystals from solution. The growth rate is increased by convection up to the point where interface kinetics becomes rate controlling. Compositional inhomogeneity and morphological instability (inclusion formation) are probably worse for gentle convection than for either no convection or for vigorous stirring. Stirring, particularly of crystal suspensions, can cause an orders of magnitude increase in the rate of formation of new crystals. This is called 'secondary nucleation'.

Wilcox, William R.

1983-01-01

233

Vertical unseeded vapor growth of large ?-GeTe crystals  

NASA Astrophysics Data System (ADS)

Well faceted, large, single crystals of ?-GeTe were grown by the vertical, unseeded vapor growth technique. The growth rate was 2 mm/day. X-rays analysis and metallography of the crystal as well as mechano-chemical polished slices revealed good monocrystallinity and homogeneity. Ge crystallites separated out of the GeTe crystallizing material due to the noncongruent vaporization of GeTe.

Yellin, N.; Gafni, G.

1981-05-01

234

Crystal growth in fused solvent systems. [in space environment  

NASA Technical Reports Server (NTRS)

The successful nucleation of bismuth germanate, B12GeO20 on a high quality seed and the growth of regions of single crystals of the same orientation of the seed are reported. Lead germanate, Pb5Ge3O11 was also identified as a ferroelectric crystal with large electrooptic and nonlinear optic constants. Solvent criteria, solvent/development, and crystal growth are discussed, and recommendations for future studies are included.

Ulrich, D. R.; Noval, B. A.; White, W. B.; Spear, K. E.; Henry, E. C.

1974-01-01

235

Magnetic field controlled FZ single crystal growth of intermetallic compounds  

Microsoft Academic Search

Intermetallic rare-earth-transition-metal compounds with their coexistence of magnetic ordering and superconductivity are still of great scientific interest. The crystal growth of bulk single crystals is very often unsuccessful due to an unfavorable solid–liquid interface geometry enclosing concave fringes. The aim of the work is the contactless control of heat and material transport during floating-zone single crystal growth of intermetallic compounds.

R. Hermann; G. Behr; G. Gerbeth; J. Priede; H.-J. Uhlemann; F. Fischer; L. Schultz

2005-01-01

236

Growth of Triglycine Sulfate (TGS) crystals aboard Spacelab-3  

NASA Technical Reports Server (NTRS)

An experiment to study the growth of single crystals of triglycine sulfate (NH2CH2COOH)3 H2SO4 (TGS) was successfully carried out on the Spacelab-3 mission during April 29 to May 6, 1985. Two crystals of TGS were grown during the flight, using a specially developed cooled sting technique of solution crystal growth. For the first time in any flight experiment the growth was monitored on-board as well as on ground by video-schlieren technique. Hundreds of holograms were taken for the solution/crystal interaction during the growth process. Preliminary results indicate that the optical system worked very well and the quality of reconstructed holograms is satisfactory. The cooled sting technique was successfully demonstrated. Holographic interferograms indicate convection free, diffusion limited growth. Some of the preliminary results of crystal quality are also presented.

Lal, R. B.; Aggarwal, M. D.; Batra, A. K.; Kroes, R. L.; Wilcox, William R.; Trolinger, James R.; Cirino, Philip

1987-01-01

237

Laser Schlieren Crystal-Growth Imager  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

238

Synthesis mechanisms of poly(oxybenzoate) liquid crystal polymers  

Microsoft Academic Search

Evidence is presented for the growth of bilayered lamellae during the polymerization ofp-acetoxybenzoic acid to form uniform thickness poly(p-oxybenzoate) lamellar crystals. Fracturing one preparation of these crystals lead to the formation of fibers connecting the fracture faces, reminiscent of those formed during fracture of folded chain flexible polymer single crystals. The results raise questions concerning previously proposed polymerization — crystal

J. Liu; P. H. Gell

1992-01-01

239

Continuum Mechanics of Line Defects in Liquid Crystals and Liquid Crystal Elastomers A. Acharya and K. Dayal Continuum Mechanics of Line Defects in Liquid Crystals  

E-print Network

04]. When the liquid crystal molecules are linked to polymer molecule backbones, director elasticityContinuum Mechanics of Line Defects in Liquid Crystals and Liquid Crystal Elastomers A. Acharya and K. Dayal Continuum Mechanics of Line Defects in Liquid Crystals and Liquid Crystal Elastomers Amit

Acharya, Amit

240

Vapor Growth and Characterization of Cr-Doped ZnSe Crystals  

NASA Technical Reports Server (NTRS)

Cr-doped ZnSe single crystals were grown by a self-seeded physical vapor transport technique in both vertical (stabilized) and horizontal configurations. The source materials were mixtures of ZnSe and CrSe. Growth temperatures were in the range of 1140-1150 C and the furnace translation rates were 1.9-2.2 mm/day. The surface morphology of the as-grown crystals was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Different features of the as-grown surface of the vertically and horizontally grown crystals suggest that different growth mechanisms were involved in the two growth configurations. The [Cr] doping levels were determined to be in the range of 1.8-8.3 x 10 (exp 19) cm (exp -3) from optical absorption measurements. The crystalline quality of the grown crystals were examined by high-resolution triple-crystal X-ray diffraction (HRTXD) analysis.

Su, Ching-Hua; Feth, Shari; Volz, M. P.; Matyi, R.; George, M. A.; Chattopadhyay, K.; Burger, A.; Lehoczky, S. L.

1999-01-01

241

Calcite crystal growth rate inhibition by polycarboxylic acids  

USGS Publications Warehouse

Calcite crystal growth rates measured in the presence of several polycarboxyclic acids show that tetrahydrofurantetracarboxylic acid (THFTCA) and cyclopentanetetracarboxylic acid (CPTCA) are effective growth rate inhibitors at low solution concentrations (0.01 to 1 mg/L). In contrast, linear polycarbocylic acids (citric acid and tricarballylic acid) had no inhibiting effect on calcite growth rates at concentrations up to 10 mg/L. Calcite crystal growth rate inhibition by cyclic polycarboxyclic acids appears to involve blockage of crystal growth sites on the mineral surface by several carboxylate groups. Growth morphology varied for growth in the absence and in the presence of both THFTCA and CPTCA. More effective growth rate reduction by CPTCA relative to THFTCA suggests that inhibitor carboxylate stereochemical orientation controls calcite surface interaction with carboxylate inhibitors. ?? 20O1 Academic Press.

Reddy, M.M.; Hoch, A.R.

2001-01-01

242

Universality classes for unstable crystal growth  

NASA Astrophysics Data System (ADS)

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.

Biagi, Sofia; Misbah, Chaouqi; Politi, Paolo

2014-06-01

243

Industrial Challenges for Numerical Simulation of Crystal Growth  

Microsoft Academic Search

Numerical simulation of industrial crystal growth is dificult due to its multidisciplinary nature and complex geometry of\\u000a real-life growth equipment. An attempt is made to itemize physical phenomena dominant in different methods for growth of bulk\\u000a crystals from melt and from vapour phase and to review corresponding numerical approaches. Academic research and industrial\\u000a applications are compared. Development of computational engine

Dmitry K. Ofengeim; Alexander I. Zhmakin

2003-01-01

244

Protein and virus crystal growth on international microgravity laboratory-2.  

PubMed Central

Two T = 1 and one T = 3 plant viruses, along with a protein, were crystallized in microgravity during the International Microgravity Laboratory-2 (IML-2) mission in July of 1994. The method used was liquid-liquid diffusion in the European Space Agency's Advanced Protein Crystallization Facility (APCF). Distinctive alterations in the habits of Turnip Yellow Mosaic Virus (TYMV) crystals and hexagonal canavalin crystals were observed. Crystals of cubic Satellite Tobacco Mosaic Virus (STMV) more than 30 times the volume of crystals grown in the laboratory were produced in microgravity. X-ray diffraction analysis demonstrated that both crystal forms of canavalin and the cubic STMV crystals diffracted to significantly higher resolution and had superior diffraction properties as judged by relative Wilson plots. It is postulated that the establishment of quasi-stable depletion zones around crystals growing in microgravity are responsible for self-regulated and more ordered growth. Images FIGURE 1 FIGURE 2 FIGURE 6 PMID:7669890

Koszelak, S; Day, J; Leja, C; Cudney, R; McPherson, A

1995-01-01

245

Large-aperture YCOB crystal growth for frequency conversion in the high average power laser system  

NASA Astrophysics Data System (ADS)

Yttrium calcium oxyborate YCa4O(BO3)3 (YCOB) is a novel non-linear optical crystal possessing good thermal, mechanical and non-linear optical properties. Large-aperture YCOB crystals with 75 mm diameter were grown for high-average power frequency conversion on the mercury laser system. The growth morphology (included facet and spiral growth), cracking and inclusions in the as-grown crystal boule were discussed as the critical problem for large-aperture YCOB crystal growth. This can be minimized through modification of the growth program, including pulling rate, separation procedure, and cooling program. High-average power frequency conversion of the mercury laser using YCOB has been demonstrated, and experimental validation of YCOB material yields 50% conversion at 10 Hz has been achieved.

Fei, Yiting; Chai, Bruce H. T.; Ebbers, C. A.; Liao, Z. M.; Schaffers, K. I.; Thelin, P.

2006-04-01

246

Mutagenesis of the crystal contact of acidic fibroblast growth factor  

PubMed Central

An attempt has been made to improve a crystal contact of human acidic fibroblast growth factor (haFGF; 140 amino acids) to control the crystal growth, because haFGF crystallizes only as a thin-plate form, yielding crystals suitable for X-ray but not neutron diffraction. X-ray crystal analysis of haFGF showed that the Glu81 side chain, located at a crystal contact between haFGF molecules, is in close proximity with an identical residue related by crystallographic symmetry, suggesting that charge repulsion may disrupt suitable crystal-packing interactions. To investigate whether the Glu residue affects the crystal-packing interactions, haFGF mutants in which Glu81 was replaced by Ala, Val, Leu, Ser and Thr were constructed. Although crystals of the Ala and Leu mutants were grown as a thin-plate form by the same precipitant (formate) as the wild type, crystals of the Ser and Thr mutants were grown with increased thickness, yielding a larger overall crystal volume. X-ray structural analysis of the Ser mutant determined at 1.35?Å resolution revealed that the hydroxy groups of Ser are linked by hydrogen bonds mediated by the formate used as a precipitant. This approach to engineering crystal contacts may contribute to the development of large protein crystals for neutron crystallography. PMID:18421160

Honjo, Eijiro; Tamada, Taro; Adachi, Motoyasu; Kuroki, Ryota; Meher, Akshaya; Blaber, Michael

2008-01-01

247

Growth of (Na, K, Li)(Nb, Ta)O 3 single crystals by solid state crystal growth  

Microsoft Academic Search

A single crystal of (Na, K, Li)(Nb, Ta)O3 has been grown for the first time by the solid state crystal growth process. A seed crystal of ?001?-oriented KTaO3 was embedded in a matrix of (Na, K, Li)(Nb, Ta)O3 powder, which was then densified by hot-pressing. During annealing of the hot-pressed sample, a single crystal of (Na, K, Li)(Nb, Ta)O3 of

John G. Fisher; Andreja Ben?an; Janez Bernard; Janez Holc; Marija Kosec; Sophie Vernay; Daniel Rytz

2007-01-01

248

Growth of Solid Solution Single Crystals  

NASA Technical Reports Server (NTRS)

The solidification of a solid solution semiconductor, having a wide separation between liquidus and serious has been extensively studied in ground based, high magnetic field and Spacelab experiments. Two alloys of mercury cadmium telluride have been studied; mercury cadmium telluride with 80.0 mole percent of HgTe and 84.8 mole percent respectively. These alloys are extremely difficult to grow by directional solidification on earth due to high solutal and thermal density differences that give rise to fluid flow and consequent loss of interface shape and composition. Diffusion controlled growth is therefore impossible to achieve in conventional directional solidification. The ground based experiments consisted of growing crystals in several different configurations of heat pipe furnaces, NASA's Advanced Automated Directional Solidification Furnace (AADSF), and a similar furnace incorporated in a superconducting magnet capable of operating at up to 5T. The first microgravity experiment took place during the flight of STS-62 in March 1994, with the AADSF installed on the second United States Microgravity Payload (USMP-2). The alloy was solidified at 3/4 inch per day over a 9 day period, and for the first time a detailed evaluation was performed of residual acceleration effects. The second flight experiment took place in the fourth United States Microgravity Payload Mission (USMP-4) in November 1997. Due to contamination of the furnace system by a previously processed sample, the sample was not received until May 1998, and the preliminary analysis shows that the conditions prevailing during the experiment were quite different from the requirements requested prior to the mission. Early results are indicating that the sample may not accomplish the desired objectives. As with the USMP-2 mission, the results of the ground based experiments were compared with the crystal grown in orbit under microgravity conditions. On the earth, it has been demonstrated that the application of the magnetic field leads to a significant reduction in fluid flow, with improved homogeneity of composition. The field strength required to suppress flow increases with diameter of the material. The 8 mm diameter sample used here was less than the upper diameter limit for a ST magnet. The configuration for USMP-4 was changed so that the material was seeded and other processing techniques were also modified. It was decided to examine the effects of a strong magnetic field under the modified configuration and parameters. A further change from USMP-2 was that a different composition of material was grown, namely with 0.152 mole fraction of cadmium telluride rather than the 0.200 of the USMP-2 experiment. The objective was to grow highly homogeneous, low defect density material of a composition at which the conduction band and the valence band of the material impinge against each other. As indicated, the furnace was contaminated during the mission. As a result of solid debris remaining in the furnace bore, the cartridge in this experiment, denoted as SL1-417, was significantly bent during the insertion phase. During translation the cartridge scraped against the plate which isolates the hot and cold zones of the furnace. Thermocouples indicated that a thermal assymetry resulted. The scraping in the slow translation or crystal growth part of the processing was not smooth and it is probable that the jitter was sufficient to give rise to convection in the melt. Early measurements of composition from the surface of the sample have shown that the composition varies in an oscillatory manner.

Lehoczky, Sandor L.; Szofran, F. R.; Gillies, Donald C.; Watring, D. A.

1999-01-01

249

Michelson interferometric studies of protein and virus crystal growth  

NASA Astrophysics Data System (ADS)

In situ laser Michelson interferometry was utilized to investigate the growth kinetics and surface morphology in canavalin, thaumatin, and turnip yellow mosaic virus (TYMV) crystallization. Interferometric patterns and kinetic measurements from growing macromolecular crystals as small as 20 ?m were obtained. This study shows that for the crystallization of canavalin, dislocations are the sources of growth steps on the surfaces of growing crystals. Supersaturation dependencies of the normal growth rates, tangential growth step velocities, and the slopes of the dislocation hillocks were determined. The kinetic coefficient ? was estimated for canavalin grown from two different precipitant systems to be 3.2 × 10 -4 and 5.3 × 10 -4 cm s -1, respectively. The change in activities of dislocation sources under different growth conditions was analyzed.

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

1996-09-01

250

Crystal growth of high quality nonlinear optical crystals of L-arginine trifluoroacetate  

NASA Astrophysics Data System (ADS)

Grow of good optical quality single crystals of L-arginine trifluoroacetate (LATF), a new semiorganic nonlinear optical (NLO) material is reported. Bulk crystals have been successfully grown from solution by the temperature lowering method. Growth rate and effects of seed orientation on morphologies of LATF crystals were studied. The crystals were characterized by density measurement, optical absorption spectrum, differential scanning calorimetry (DSC) and microhardness studies.

Liu, Xiaojing; Wang, Zeyan; Zhang, Guanghui; Wang, Xinqiang; Duan, Aidong; Sun, Zhihua; Zhu, Luyi; Xu, Dong

2007-10-01

251

Single crystal growth and characterization of the nonlinear optical crystal l-arginine hydrofluoride  

Microsoft Academic Search

In this communication, single crystal growth of the nonlinear optical crystal l-arginine hydrofluoride C6H14N4O2. HF (here after abbreviated as LAHF) of dimensions up to 20×15×3mm3 is reported. Crystals have been grown by the temperature lowering method and also by slow evaporation method at constant temperature 30°C from its aqueous solution with pH at 2.2. As-grown single crystals were then characterized

Tanusri Pal; Tanusree Kar

2002-01-01

252

Passive particle dosimetry. [silver halide crystal growth  

NASA Technical Reports Server (NTRS)

Present methods of dosimetry are reviewed with emphasis on the processes using silver chloride crystals for ionizing particle dosimetry. Differences between the ability of various crystals to record ionizing particle paths are directly related to impurities in the range of a few ppm (parts per million). To understand the roles of these impurities in the process, a method for consistent production of high purity silver chloride, and silver bromide was developed which yields silver halides with detectable impurity content less than 1 ppm. This high purity silver chloride was used in growing crystals with controlled doping. Crystals were grown by both the Czochalski method and the Bridgman method, and the Bridgman grown crystals were used for the experiments discussed. The distribution coefficients of ten divalent cations were determined for the Bridgman crystals. The best dosimeters were made with silver chloride crystals containing 5 to 10 ppm of lead; other impurities tested did not produce proper dosimeters.

Childs, C. B.

1977-01-01

253

Growth of zeolite crystals in the microgravity environment of space  

NASA Technical Reports Server (NTRS)

Zeolites are hydrated, crystalline aluminosilicates with alkali and alkaling earth metals substituted into cation vacancies. Typically zeolite crystals are 3 to 8 microns. Larger cyrstals are desirable. Large zeolite crystals were produced (100 to 200 microns); however, they have taken restrictively long times to grow. It was proposed if the rate of nucleation or in some other way the number of nuclei can be lowered, fewer, larger crystals will be formed. The microgravity environment of space may provide an ideal condition to achieve rapid growth of large zeolite crystals. The objective of the project is to establish if large zeolite crystals can be formed rapidly in space.

Sacco, A., Jr.; Sand, L. B.; Collette, D.; Dieselman, K.; Crowley, J.; Feitelberg, A.

1986-01-01

254

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

NASA Technical Reports Server (NTRS)

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).

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

2000-01-01

255

Float-Zone silicon crystal growth at reduced RF frequencies  

NASA Astrophysics Data System (ADS)

The growth of Float-Zone silicon crystals of larger crystal diameter requires increasing power, e.g. increasing voltage at the inductor, which is limited by the breakdown voltage. Reduced working frequencies could help to solve this problem. However, the smooth melting of the feed rod is at risk for this case. The aim of this work is to investigate how a stable FZ-growth at reduced RF frequencies can be achieved and how the crystal parameters are influenced. Dislocation-free crystals of 4 inch diameter were grown at RF frequencies of 2.0 and 1.7 MHz. It was confirmed that lower frequencies reduce the risk of arcing and silicon "nose" formation can be suppressed. Therefore, reduced RF frequencies can help to enable the growth of silicon FZ-crystals with bigger diameters.

Rost, H.-J.; Menzel, R.; Luedge, A.; Riemann, H.

2012-12-01

256

Modelling of Heat Transfer in Single Crystal Growth  

E-print Network

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...

Zhmakin, Alexander I

2014-01-01

257

Initial development of a high-pressure crystal growth facility: Center director's discretionary fund  

NASA Technical Reports Server (NTRS)

A low-cost, flexible, high-pressure (600 psi) system for crystal growth and related thermophysical properties measurements was designed, assembled, and tested. The furnace system includes a magnetically coupled translation mechanism that eliminates the need for a high-pressure mechanical feedthru. The system is currently being used for continuing crystal growth experiments and thermophysical properties measurements on several material systems including Hg(1-x)Cd(x)Te, Hg(1-x)Zn(x)Te, and Hg(1-x)Zn(x)Se.

Szofran, F. R.; Lehoczky, S. L.; Cobb, S. D.; Gillies, D. C.

1993-01-01

258

Large-volume protein crystal growth for neutron macromolecular crystallography.  

PubMed

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

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

2015-04-01

259

Crystal growth of lead carbonates: Influence of the medium and relationship between structure and habit  

NASA Astrophysics Data System (ADS)

The crystal-growth features of cerussite and hydrocerussite formed by two different chemical reactions are studied. With respect to the former, acid-vapour oxidation and latter carbonation of metallic lead produced a nanocrystalline precipitate for the lead carbonates. In the latter, cerussite and hydrocerusite are precipitated after mixing two mother solutions in liquid and solid porous media, forming diverse polyhedral morphologies. Crystal growth in gel medium gives rise to pseudo-cubic morphologies by the aggregation of one-micron-sized particles of cerussite. Skeletal morphologies composed of cyclically twinned crystals of cerussite also occur in gel-growth experiments. These morphologies were determined by kinetic factors, in particular by high supersaturation conditions that led to high growth rates. Kinetics also favoured the predominance of weak over strong interactions during crystal growth. The habit observed for cerussite crystals has been explained based on crystal-structure considerations and quantum-mechanical calculations. In particular, the crystal growth along the a direction in cyclically twinned crystals is explained by the binding forces between the CO32- molecular group and Pb2+, defining an uninterrupted chain of strong bonds along that direction. However, the preferred growth along the c direction observed for the cerussite crystal formed in gel media is here attributed to an intermolecular interaction through C-C bonds. The occurrence of a chemical bonding between the C atoms of the CO32- molecular groups aligned along the c direction is clearly shown by the theoretical analysis of the electron density with the quantum theory of atoms in molecules (QTAIM).

Sánchez-Navas, Antonio; López-Cruz, Olimpia; Velilla, Nicolás; Vidal, Isaac

2013-08-01

260

Protein Single Crystal Growth under Microgravity  

NASA Astrophysics Data System (ADS)

The preparation of suitably large protein single crystals is essentially the rate-determining step of protein x-ray structure determinations. Attempts to produce single crystals with two model compounds--? -galactosidase and lysozyme--under conditions of microgravity were successful. Crystals formed by salting out from solutions kept free of convection were 27 and 1000 times larger in volume, respectively, than those produced in the same apparatus but exposed to terrestrial gravitation.

Littke, Walter; John, Christina

1984-07-01

261

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

NASA Astrophysics Data System (ADS)

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.

Su, Ching-Hua

2015-01-01

262

Chamber Design For Slow Nucleation Protein Crystal Growth  

NASA Technical Reports Server (NTRS)

Multiple-chamber dialysis apparatus grows protein crystals on Earth or in microgravity with minimum of intervention by technician. Use of multiple chambers provides gradation of nucleation and growth rates.

Pusey, Marc Lee

1995-01-01

263

Modeling of Macroscopic/Microscopic Transport and Growth Phenomena in Zeolite Crystal Solutions Under Microgravity Conditions  

NASA Technical Reports Server (NTRS)

Crystals grown from liquid solutions have important industrial applications. Zeolites, for instance, a class of crystalline aluminosilicate materials, form the backbone of the chemical process industry worldwide, as they are used as adsorbents and catalysts. Many of the phenomena associated with crystal growth processes are not well understood due to complex microscopic and macroscopic interactions. Microgravity could help elucidate these phenomena and allow the control of defect locations, concentration, as well as size of crystals. Microgravity in an orbiting spacecraft could help isolate the possible effects of natural convection (which affects defect formation) and minimize sedimentation. In addition, crystals will stay essentially suspended in the nutrient pool under a diffusion-limited growth condition. This is expected to promote larger crystals by allowing a longer residence time in a high-concentration nutrient field. Among other factors, the crystal size distribution depends on the nucleation rate and crystallization. These two are also related to the "gel" polymerization/depolymerization rate. Macroscopic bulk mass and flow transport and especially gravity, force the crystals down to the bottom of the reactor, thus forming a sedimentation layer. In this layer, the growth rate of the crystals slows down as crystals compete for a limited amount of nutrients. The macroscopic transport phenomena under certain conditions can, however, enhance the nutrient supply and therefore, accelerate crystal growth. Several zeolite experiments have been performed in space with mixed results. The results from our laboratory have indicated an enhancement in size of 30 to 70 percent compared to the best ground based controls, and a reduction of lattice defects in many of the space grown crystals. Such experiments are difficult to interpret, and cannot be easily used to derive empirical or other laws since many physical parameters are simultaneously involved in the process. At the same time, however, there is increased urgency to develop such an understanding in order to more accurately quantify the process. In order to better understand the results obtained from our prior space experiments, and design future experiments, a detailed fluid dynamic model simulating the crystal growth mechanism is required. This will not only add to the fundamental knowledge on the crystallization of zeolites, but also be useful in predicting the limits of size and growth of these important industrial materials. Our objective is to develop macro/microscopic theoretical and computational models to study the effect of transport phenomena in the growth of crystals grown in solutions. Our effort has concentrated so far in the development of separate macroscopic and microscopic models. The major highlights of our accomplishments are described.

Gatsonis, Nikos A.; Alexandrou, Andreas; Shi, Hui; Ongewe, Bernard; Sacco, Albert, Jr.

1999-01-01

264

On the growth of calcium tartrate tetrahydrate single crystals  

Microsoft Academic Search

Calcium tartrate single crystals were grown using silica gel as the growth medium. Calcium formate mixed with formic acid\\u000a was taken as the supernatant solution. It was observed that the nucleation density was reduced and the size of the crystals\\u000a was improved to a large extent compared to the conventional way of growing calcium tartrate crystals with calcium chloride.\\u000a The

X. Sahaya Shajan; C. Mahadevan

2004-01-01

265

Growth of 450 mm diameter semiconductor grade silicon crystals  

Microsoft Academic Search

Research and development of the next generation 450mm semiconductor grade silicon crystal and related technology have been carried out in MEMC following the company’s philosophy to stay one generation ahead on research and development. The first 450mm dislocation free crystal was grown in early 2009 and the first 450mm semiconductor wafer was produced shortly after. General challenges in crystal growth

Zheng Lu; Steven Kimbel

2011-01-01

266

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

PubMed

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

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

2013-01-22

267

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

PubMed Central

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

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

2013-01-01

268

Viscous Fingering and Dendritic Growth of Surface Crystallized Sr2TiSi2O8 Fresnoite  

PubMed Central

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

Wisniewski, Wolfgang; Patschger, Marek; Rüssel, Christian

2013-01-01

269

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

PubMed Central

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

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

2009-01-01

270

Numerical simulation of single crystal growth by submerged heater method  

Microsoft Academic Search

A novel method of crystal growth which utilizes an axial submerged heater is proposed and numerically simulated. Single crystals should be grown by directional solidification in vertical bottom seeded crucibles. Submerged in the melt, the heater supplies the heat axially downward, enclosing and stratifying a small active portion of the melt.

Aleksandar G. Ostrogorsky

1990-01-01

271

Use of an inhomogenous magnetic field for silicon crystal growth  

Microsoft Academic Search

The flow of liquid silicon and oxygen transfer during crystal growth under three different types of cusp-shaped magnetic field were clarified using numerical simulation, flow visualization, and infrared measurement of oxygen concentration in grown crystals. Velocity vectors obtained from numerical simulation are almost parallel to cusp-shaped magnetic fields since flow parallel to a magnetic field does not produce a Lorentz

K. Kakimoto; M. Eguchi; H. Ozoe

1997-01-01

272

Influences of high magnetic field on glycine crystal growth  

Microsoft Academic Search

The effects of horizontal high magnetic field (8T) on both the orientation of the ?-form glycine crystal and the growth rate were studied. The ?-form glycine crystal is oriented in the high magnetic field in such a way that its crystallographic c-axis is at about 45° with the direction of magnetic field. This orientation is explained by the magnetic susceptibility

Manabu Sueda; Akio Katsuki; Yoshihisa Fujiwara; Yoshifumi Tanimoto

2006-01-01

273

Growth kinetics of constant-composition binary crystals from solutions  

NASA Astrophysics Data System (ADS)

Expression have been derived for the kinetics of dislocation growth of two-component crystals. They relate the growth rate V to the supersaturation and the concentration ratio of the components in the solution (?). It has been shown that at constant supersaturation, the function V(?) has a maximum whose position depends on the supersaturation and the thickness of the diffusion layer. The equations obtained permit experimental data on the crystallization kinetics of gypsum, LaB 6 and other compounds to be explained.

Moshkin, S. V.; Nardov, A. V.

1981-04-01

274

Definition study for temperature control in advanced protein crystal growth  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

275

Transport modes during crystal growth in a centrifuge  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

276

Growth of high temperature superconducting single crystals  

Microsoft Academic Search

YBa2-xSrxCu3O7-y and YBa2Cu3O7 high-Tc superconducting single crystal up to 2.5×2×1 mm having orthorhombic lattices and transition temperatures of 84 and 94 K, respectively, have been grown. Conductivity anisotropy has been confirmed. The grown single crystals exhibit superconducting properties even without additional thermal treatment.

A. P. Voronov; V. M. Dmitriev; M. B. Kosmyna; S. F. Prokopovich; V. P. Seminozhenko

1988-01-01

277

Ames Lab 101: Single Crystal Growth  

SciTech Connect

Ames Laboratory scientist Deborah Schlagel talks about the Lab's research in growing single crystals of various metals and alloys. The single crystal samples are vital to researchers' understanding of the characteristics of a materials and what gives these materials their particular properties.

Schlagel, Deborah

2013-09-27

278

Ames Lab 101: Single Crystal Growth  

ScienceCinema

Ames Laboratory scientist Deborah Schlagel talks about the Lab's research in growing single crystals of various metals and alloys. The single crystal samples are vital to researchers' understanding of the characteristics of a materials and what gives these materials their particular properties.

Schlagel, Deborah

2014-06-04

279

Growth morphology of primary silicon in cast Al Si alloys and the mechanism of concentric growth  

NASA Astrophysics Data System (ADS)

Faceted growth of primary silicon crystals in cast hypereutectic aluminium-silicon alloys is studied by measurement of spacings between successive growth traces observed in microsections. A general equation, derived to specify conditions for stable growth of silicon crystal, is supported by spacing measurements. Some examples of departures from stable silicon growth are studied. Three stages in the development of faceted crystal growth are recognized, changing from spheroidal to faceted to unstable with increasing crystal diameter.

Wang, Ru-yao; Lu, Wei-hua; Hogan, L. M.

1999-11-01

280

Follow up on the crystal growth experiments of the LDEF  

NASA Technical Reports Server (NTRS)

The results of the 4 solution growth experiments on the LDEF have been published elsewhere. Both the crystals of CaCO3, which were large and well shaped, and the much smaller TTF-TCNQ crystals showed unusual morphological behavior. The follow up on these experiments was begun in 1981, when ESA initiated a 'Concept Definition Study' on a large, 150 kg, Solution Growth Facility (SGF) to be included in the payload of EURECA-1, the European Retrievable Carrier. This carrier was a continuation of the European Spacelab and at that time planned for launch in 1987. The long delay of the LDEF retrieval and of subsequent missions brought about reflections both on the concept of crystal growth in space and on the choice of crystallization materials that had been made for the LDEF. Already before the LDEF retrieval, research on TTF-TCNQ had been stopped, and a planned growth experiment with TTF-TCNQ on the SGF/EURECA had been cancelled. The target of the SGF investigation is now more fundamental in nature. None of the crystals to be grown here are, like TTF-TCNQ, in particular demand by science or industry, and the crystals only serve the purpose of model crystals. The real purpose of the investigation is to study the growth behavior. One of the experiments, the Soret Coefficient Measurement experiment is not growing crystals at all, but has it as its sole purpose to obtain accurate information on thermal diffusion, a process of importance in crystal growth from solution.

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

1993-01-01

281

Crystal grain growth at the ? -uranium phase transformation in praseodymium  

NASA Astrophysics Data System (ADS)

Structural phase transformations under pressure are examined in praseodymium metal for the range 0-40GPa at ambient temperature. Pressure was generated with a diamond-anvil cell, and data were collected using high-resolution synchrotron x-ray diffraction and the image plate technique. The structural sequence double hexagonal close packed (dhcp)?face centered cubic (fcc)?distorted-fcc (d-fcc)? ? -uranium (?-U) is observed with increasing pressure. Rietveld refinement of all crystallographic phases provided confirmation of the hR24 structure for the d-fcc phase while the previously reported monoclinic phase between the d-fcc and the ?-U phase was not confirmed. We observe dramatic crystal grain growth during the volume collapse concurrent with the symmetry-lowering transition to the ?-U structure. No preferred orientation axis is observed, and the formation process for these large grains is expected to be via a nucleation and growth mechanism. An analogous effect in rare earth metal cerium suggests that the grain growth during transformation to the ?-U structure is a common occurrence in f -electron metals at high pressures.

Cunningham, Nicholas C.; Velisavljevic, Nenad; Vohra, Yogesh K.

2005-01-01

282

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

NASA Technical Reports Server (NTRS)

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.

Vandenberg, Lodewijk

1992-01-01

283

Anomalous Crystal Growth In Supercooled OTP On Temperature Cycling  

NASA Astrophysics Data System (ADS)

It has been previously observed [1] that when the fragile glass former o-terphenyl (OTP) is supercooled to -23 ^oC, well below its normal freezing temperature but above its glass transition temperature, an anomalous growth mode appears indicated by a sudden increase in the crystal growth velocity. We report observations of this anomalous crystal growth when the temperature is raised briefly above the apparent transition temperature and then cooled back down. We find that when the temperature is raised to -20.5 ^oC or less the original anomalous growth continues to grow, apparently uninterrupted. When the temperature is raised above -19 ^oC the original anomalous growth does not continue to grow, although new anomalous growth nucleates. One interpretation of these results is that the transition temperature for the anomalous growth is around -20 ^oC. [4pt] [1] M. Hatase, M. Hanaya, and M. Oguni, J. Non-Cryst. Solids 333, 129 (2004)

Hall, Stephen C.; Lindsay, Sean

2010-03-01

284

Quantitative analysis of crystal growth. Tryptophanyl-tRNA synthetase crystal polymorphism and its relationship to catalysis.  

PubMed

We show that quantitative analysis of replicated, full-factorial crystal growth experiments and, by implication, similar studies of a wide variety of other phenomena, can be a powerful tool for analyzing macromolecular systems with complex, interacting dependencies on functionally significant factors. Bacillus stearothermophilus tryptophanyl-tRNA synthetase crystallizes in three different crystal forms depending on the ligands present under otherwise identical conditions. Comparison of crystallographic space groups for complexes with different ligands reveals that the three forms entail at least two very different families of packing arrangements that are correlated with specific changes in the enzyme ligation state. One is associated with the ligand-free enzyme, substrate ligands, and the binding of the activated amino acid; the other results from the presence of high ATP concentrations and/or the synthesis of the unusual acyl-transfer product, tryptophanyl-2'(3') ATP. Together with previous physico-chemical studies of aminoacyl-tRNA synthetases, these observations suggest that the two families are related, respectively, to the biochemical processes of amino acid activation and acyl transfer. Further evidence that the crystal polymorphism results from an underlying protein conformational polymorphism has now been obtained by quantitative analysis of how crystal growth depends on pH and the substrates tryptophan and ATP. The analysis consists first in showing that crystallization conditions for the unliganded protein are very favorable, suggesting that variation in crystal growth induced by pH and substrates under otherwise identical conditions is due to their effects on the protein conformation and not on incidental perturbations of crystal growth, per se. Next, crystal growth experiments are shown to be reproducible enough to support statistical analysis of quantitative scores assigned to the results. Finally, the observed variation in scores can be attributed at high confidence levels chiefly to three effects: that of pH alone, the synergistic effects of pH plus tryptophan, and of tryptophan plus ATP. These statistical inferences are consistent with other biochemical data, and support the conclusions based on crystal packing that representative stages of the enzyme mechanism have been trapped in the different crystal forms. The pH-tryptophan interaction implies that there is a pH-dependent conformational change favoring high affinity substrate binding at high pH. The pH-ATP interaction implies that a subsequent conformational change, not previously considered, occurs between tryptophan activation and acyl transfer. PMID:8176729

Carter, C W; Doublié, S; Coleman, D E

1994-05-01

285

Imaging System For Measuring Macromolecule Crystal Growth Rates in Microgravity  

NASA Technical Reports Server (NTRS)

In order to determine how macromolecule crystal quality improvement in microgravity is related to crystal growth characteristics, a team of scientists and engineers at NASA's Marshal Space Flight Center (MSFC) developed flight hardware capable of measuring the crystal growth rates of a population of crystals growing under the same conditions. As crystal growth rate is defined as the change or delta in a defined dimension or length (L) of crystal over time, the hardware was named Delta-L. Delta-L consists of three sub assemblies: a fluid unit including a temperature-controlled growth cell, an imaging unit, and a control unit (consisting of a Data Acquisition and Control Unit (DACU), and a thermal control unit). Delta-L will be used in connection with the Glovebox Integrated Microgravity Isolation Technology (g-LIMIT) inside the Microgravity Science Glovebox (MSG), onboard the International Space Station. This paper will describe the Delta-L imaging system. The Delta-L imaging system was designed to locate, resolve, and capture images of up to 10 individual crystals ranging in size from 10 to 500 microns with a point-to-point accuracy of +/- 2.0 microns within a quartz growth cell observation area of 20 mm x 10 mm x 1 mm. The optical imaging system is comprised of a video microscope camera mounted on computer controlled translation stages. The 3-axis translation stages and control units provide crewmembers the ability to search throughout the growth cell observation area for crystals forming in size of approximately 10 microns. Once the crewmember has selected ten crystals of interest, the growth of these crystals is tracked until the size reaches approximately 500 microns. In order to resolve these crystals an optical system with a magnification of 10X was designed. A black and white NTSC camera was utilized with a 20X microscope objective and a 0.5X custom designed relay lens with an inline light to meet the magnification requirement. The design allows a 500 pm crystal to be viewed in the vertical dimension on a standard NTSC monitor (4:3 aspect ratio). Images of the 10 crystals are collected periodically and stored in sets by the DACU.

Corder, Eric L.; Briscoe, Jeri

2004-01-01

286

Growth and characterization of pure and KCl doped zinc thiourea chloride (ZTC) single crystals  

NASA Astrophysics Data System (ADS)

Potassium Chloride (KCl) as an additive is added into zinc thiourea chloride solution in a small amount (1 M%) by the method of slow evaporation solution growth technique at room temperature to get a new crystal. Due to the doping of the impurities on the crystals, remarkable changes in the physical properties were obtained. The grown crystals have been subjected to different instrumentation methods. The incorporation of the amount of potassium and zinc in the crystal lattices has been determined by AAS method. The lattice dimensions have been identified from single crystal X-ray diffraction measurements. The presence of functional group for the grown crystals has been identified by FTIR analysis. The optical, thermal and mechanical behaviors have been assessed by UV-Vis, TG/DTA and Vickers hardness methods respectively. The presence of dislocations of atoms has been identified by etching studies.

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

2013-02-01

287

Growth and characterization of pure and KCl doped zinc thiourea chloride (ZTC) single crystals.  

PubMed

Potassium Chloride (KCl) as an additive is added into zinc thiourea chloride solution in a small amount (1M%) by the method of slow evaporation solution growth technique at room temperature to get a new crystal. Due to the doping of the impurities on the crystals, remarkable changes in the physical properties were obtained. The grown crystals have been subjected to different instrumentation methods. The incorporation of the amount of potassium and zinc in the crystal lattices has been determined by AAS method. The lattice dimensions have been identified from single crystal X-ray diffraction measurements. The presence of functional group for the grown crystals has been identified by FTIR analysis. The optical, thermal and mechanical behaviors have been assessed by UV-Vis, TG/DTA and Vickers hardness methods respectively. The presence of dislocations of atoms has been identified by etching studies. PMID:23220671

Ruby Nirmala, L; Thomas Joseph Prakash, J

2013-02-01

288

Direct growth of self-crystallized graphene and graphite nanoballs with Ni vapor-assisted growth: From controllable growth to material characterization  

NASA Astrophysics Data System (ADS)

A directly self-crystallized graphene layer with transfer-free process on arbitrary insulator by Ni vapor-assisted growth at growth temperatures between 950 to 1100°C via conventional chemical vapor deposition (CVD) system was developed and demonstrated. Domain sizes of graphene were confirmed by Raman spectra from ~12 nm at growth temperature of 1000°C to ~32 nm at growth temperature of 1100°C, respectively. Furthermore, the thickness of the graphene is controllable, depending on deposition time and growth temperature. By increasing growth pressure, the growth of graphite nano-balls was preferred rather than graphene growth. The detailed formation mechanisms of graphene and graphite nanoballs were proposed and investigated in detail. Optical and electrical properties of graphene layer were measured. The direct growth of the carbon-based materials with free of the transfer process provides a promising application at nanoelectronics.

Yen, Wen-Chun; Chen, Yu-Ze; Yeh, Chao-Hui; He-Hau, Jr.; Chiu, Po-Wen; Chueh, Yu-Lun

2014-05-01

289

Direct growth of self-crystallized graphene and graphite nanoballs with Ni vapor-assisted growth: From controllable growth to material characterization  

PubMed Central

A directly self-crystallized graphene layer with transfer-free process on arbitrary insulator by Ni vapor-assisted growth at growth temperatures between 950 to 1100°C via conventional chemical vapor deposition (CVD) system was developed and demonstrated. Domain sizes of graphene were confirmed by Raman spectra from ~12?nm at growth temperature of 1000°C to ~32?nm at growth temperature of 1100°C, respectively. Furthermore, the thickness of the graphene is controllable, depending on deposition time and growth temperature. By increasing growth pressure, the growth of graphite nano-balls was preferred rather than graphene growth. The detailed formation mechanisms of graphene and graphite nanoballs were proposed and investigated in detail. Optical and electrical properties of graphene layer were measured. The direct growth of the carbon-based materials with free of the transfer process provides a promising application at nanoelectronics. PMID:24810224

Yen, Wen-Chun; Chen, Yu-Ze; Yeh, Chao-Hui; He, Jr-Hau; Chiu, Po-Wen; Chueh, Yu-Lun

2014-01-01

290

Skylab experiments on semiconductors and alkali halides. [single crystal growth  

NASA Technical Reports Server (NTRS)

The space processing experiments performed during the Skylab missions included one on single crystal growth of germanium selenide and telluride, one on pure and doped germanium crystals, two on pure and doped indium antimonide, one on gallium-indium-antimony systems, and one on a sodium chloride-sodium fluoride eutectic. In each experiment, three ampoules of sample were processed in the multipurpose electric furnace within the Skylab Materials Processing Facility. All were successful in varying degrees and gave important information about crystal growth removed from the effects of earth surface gravity.

Lundquist, C. A.

1974-01-01

291

Crocodile: An automated apparatus for organic crystal growth from solution  

NASA Astrophysics Data System (ADS)

CROCODILE ( CROissance de Cristaux Organiques par DIffusion Liquide dans l' Espace) is a space instrument dedicated to crystal growth from solution. The selected material N (4 nitrophenyl) (L) prolinol (NPP) is the result of studies on organic crystal in the frame of an extended program initiated by CNES for many years. The apparatus was flown aboard PHOTON, an automatic satellite, in April 1990, for a flight duration of more than 15 days. This paper describes the instrument design, with emphasis on specific and original technology well adapted to crystal growth from solution, and extendable to any space experiment on fluids. Preliminary details of the flight campaign will also be discussed.

Gonzalez, F.; Cunisse, M.; Perigaud, A.

292

(PCG) Protein Crystal Growth HIV Reverse Transcriptase  

NASA Technical Reports Server (NTRS)

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.

1992-01-01

293

Protein crystal growth and the International Space Station  

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

294

Crystal Growth and Properties of Nonlinear Optical Materials  

NASA Astrophysics Data System (ADS)

Nonlinear optical (NLO) crystals are a critical, enabling technology in the development of solid state laser sources, allowing the output from the most mature laser source operating a few discrete wavelengths to be shifted almost anywhere in the electromagnetic spectrum spanning from the ultraviolet to the far-infrared. For efficient frequency conversion, a nonlinear crystal must simultaneously satisfy a long list of material requirements, some of which are intrinsic, while others are extrinsic and must be controlled through careful processing. A wide range of materials and growth techniques are required to in order to produce crystals which operate in the various wavelength regimes of interest. The basic principles of NLO frequency conversion are introduced and used to derive the material property requirements. The crystal growth, properties, and performance of state-of-the-art nonlinear optical crystals are surveyed, and future directions in the development of new and improved NLO materials are identified.

Schunemann, Peter G.

2007-06-01

295

Crystal growth of device quality GaAs in space  

NASA Technical Reports Server (NTRS)

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.

Gatos, H. C.; Lagowski, J.

1983-01-01

296

Liquid nitrogen dewar for protein crystal growth  

NASA Technical Reports Server (NTRS)

Gaseous Nitrogen Dewar apparatus developed by Dr. Alex McPherson of the University of California, Irvine for use aboard Mir and the International Space Station allows large quantities of protein samples to be crystallized in orbit. The specimens are contained either in plastic tubing (heat-sealed at each end). Biological samples are prepared with a precipitating agent in either a batch or liquid-liquid diffusion configuration. The samples are then flash-frozen in liquid nitrogen before crystallization can start. On orbit, the Dewar is placed in a quiet area of the station and the nitrogen slowly boils off (it is taken up by the environmental control system), allowing the proteins to thaw to begin crystallization. The Dewar is returned to Earth after one to four months on orbit, depending on Shuttle flight opportunities. The tubes then are analyzed for crystal presence and quality

2001-01-01

297

Growth and characterization of lead bromide crystals  

NASA Technical Reports Server (NTRS)

Lead(II) bromide was purified by a combination of directional freezing and zone-refining methods. Differential thermal analysis of the lead bromide showed that a destructive phase transformation occurs below the melting temperature. This transformation causes extensive cracking, making it very difficult to grow a large single crystal. Energy of phase transformation for pure lead bromide was determined to be 24.67 cal/g. To circumvent this limitation, crystals were doped by silver bromide which decreased the energy of phase transformation. The addition of silver helped in achieving the size, but enhanced the inhomogeneity in the crystal. The acoustic attenuation constant was almost identical for the pure and doped (below 3000 ppm) crystals.

Singh, N. B.; Gottlieb, M.; Henningsen, T.; Hopkins, R. H.; Mazelsky, R.; Glicksman, M. E.; Coriell, S. R.; Santoro, G. J.; Duval, W. M. B.

1992-01-01

298

Center for the development of commercial crystal growth in space  

NASA Technical Reports Server (NTRS)

The second year of operation of the Center for Commercial Crystal Growth in Space is described. This center is a consortium of businesses, universities and national laboratories. The primary goal of the Center's research is the development of commercial crystal growth in space. A secondary goal is to develop scientific understanding and technology which will improve commercial crystal growth on earth. In order to achieve these goals the Center's research is organized into teams by growth technique; melt growth, solution growth, and vapor growth. The melt growth team is working on solidification and characterization of bulk crystals of gallium arsenide and cadmium telluride. They used high resolution X-ray topography performed at the National Synchrotron Light Source at Brookhaven National Laboratory. Streak-like features were found in the diffraction images of semi-insulating undoped LEC GaAs. These were shown to be (110) antiphase boundaries, which have not been reported before but appear to be pervasive and responsible for features seen via less-sensitive characterization methods. The results on CdTe were not as definitive, but indicate that antiphase boundaries may also be responsible for the double peaks often seen in X-ray rocking curves of this material. A liquid encapsulated melt zone system for GaAs has been assembled and techniques for casting feed rods developed. It was found that scratching the inside of the quartz ampoules with silicon carbide abrasive minimized sticking of the GaAs to the quartz. Twelve floating zone experiments were done.

Wilcox, William R.

1989-01-01

299

The growth habits and surface structure of ice crystals  

Microsoft Academic Search

Evidence to show that the layer growth of ice crystals occurs mainly by the surface diffusion of molecules to the growing steps is presented. Measurements of the rate-of-change of separation of adjacent growth steps allow the mean migration distance xs of molecules on the basal face to be deduced; this parameter shows a remarkable variation with temperature over the range

B. J. Mason; G. W. Bryant; A. P. Van den Heuvel

1963-01-01

300

Czochralski growth of gallium indium antimonide alloy crystals  

SciTech Connect

Attempts were made to grow alloy crystals of Ga{sub 1{minus}x}In{sub x}Sb by the conventional Czochralski process. A transparent furnace was used, with hydrogen purging through the chamber during crystal growth. Single crystal seeds up to about 2 to 5 mole% InSb were grown from seeds of 1 to 2 mole% InSb, which were grown from essentially pure GaSb seeds of the [111] direction. Single crystals were grown with InSb rising from about 2 to 6 mole% at the seed ends to about 14 to 23 mole% InSb at the finish ends. A floating-crucible technique that had been effective in reducing segregation in doped crystals, was used to reduce segregation in Czochralski growth of alloy crystals of Ga{sub 1{minus}x}In{sub x}Sb. Crystals close to the targeted composition of 1 mole% InSb were grown. However, difficulties were encountered in reaching higher targeted InSb concentrations. Crystals about 2 mole% were grown when 4 mole% was targeted. It was observed that mixing occurred between the melts rendering the compositions of the melts; and, hence, the resultant crystal unpredictable. The higher density of the growth melt than that of the replenishing melt could have triggered thermosolutal convection to cause such mixing. It was also observed that the floating crucible stuck to the outer crucible when the liquidus temperature of the replenishing melt was significantly higher than that of the growth melt. The homogeneous Ga{sub 1{minus}x}In{sub x}Sb single crystals were grown successfully by a pressure-differential technique. By separating a quartz tube into an upper chamber for crystal growth and a lower chamber for replenishing. The melts were connected by a capillary tube to suppress mixing between them. A constant pressure differential was maintained between the chambers to keep the growth melt up in the growth chamber. The method was first tested with a low temperature alloy Bi{sub 1{minus}x}Sb{sub x}. Single crystals of Ga{sub 1{minus}x}In{sub x}Sb were grown with uniform compositions up to nearly 5 mole% InSb.

Tsaur, S.C.

1998-02-01

301

Crystal growth and characterization of monometallic NLO single crystals of Cd(IO 3) 2  

Microsoft Academic Search

This work aims to study the growth and physicochemical properties of second-order nonlinear optical active inorganic crystal of cadmium iodate (CDI). Efforts have been made to grow an improved size single crystal of CDI by the slow-cooling technique. The XRD data of CDI are determined by single-crystal XRD analysis. CDI is further characterized by UV–vis–NIR spectroscopy, TGA, dielectric, ac conductivity,

S. M. Ravi Kumar; N. Melikechi; S. Selvakumar; P. Sagayaraj

2009-01-01

302

Transient natural convection heat and mass transfer in crystal growth  

NASA Technical Reports Server (NTRS)

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.

Han, Samuel S.

1988-01-01

303

Shallow Melt Apparatus for Semicontinuous Czochralski Crystal Growth  

DOEpatents

In a single crystal pulling apparatus for providing a Czochralski crystal growth process, the improvement of a shallow melt crucible (20) to eliminate the necessity supplying a large quantity of feed stock materials that had to be preloaded in a deep crucible to grow a large ingot, comprising a gas tight container a crucible with a deepened periphery (25) to prevent snapping of a shallow melt and reduce turbulent melt convection; source supply means for adding source material to the semiconductor melt; a double barrier (23) to minimize heat transfer between the deepened periphery (25) and the shallow melt in the growth compartment; offset holes (24) in the double barrier (23) to increase melt travel length between the deepened periphery (25) and the shallow growth compartment; and the interface heater/heat sink (22) to control the interface shape and crystal growth rate.

Wang, T.; Ciszek, T. F.

2006-01-10

304

Shallow melt apparatus for semicontinuous czochralski crystal growth  

DOEpatents

In a single crystal pulling apparatus for providing a Czochralski crystal growth process, the improvement of a shallow melt crucible (20) to eliminate the necessity supplying a large quantity of feed stock materials that had to be preloaded in a deep crucible to grow a large ingot, comprising a gas tight container a crucible with a deepened periphery (25) to prevent snapping of a shallow melt and reduce turbulent melt convection; source supply means for adding source material to the semiconductor melt; a double barrier (23) to minimize heat transfer between the deepened periphery (25) and the shallow melt in the growth compartment; offset holes (24) in the double barrier (23) to increase melt travel length between the deepened periphery (25) and the shallow growth compartment; and the interface heater/heat sink (22) to control the interface shape and crystal growth rate.

Wang, Tihu; Ciszek, Theodore F.

2006-01-10

305

Ice Crystal Growth Rates Under Upper Troposphere Conditions  

NASA Technical Reports Server (NTRS)

Atmospheric conditions for growth of ice crystals (temperature and ice supersaturation) are often not well constrained and it is necessary to simulate such conditions in the laboratory to investigate such growth under well controlled conditions over many hours. The growth of ice crystals from the vapour in both prism and basal planes was observed at temperatures of -60 C and -70 C under ice supersaturation up to 100% (200% relative humidity) at pressures derived from the standard atmosphere in a static diffusion chamber. Crystals grew outward from a vertical glass filament, thickening in the basal plane by addition of macroscopic layers greater than 2 m, leading to growth in the prism plane by passing of successive layers conveniently viewed by time lapse video.

Peterson, Harold S.; Bailey, Matthew; Hallett, John

2010-01-01

306

Electromagnetic induction heating for single crystal graphene growth: morphology control by rapid heating and quenching.  

PubMed

The direct observation of single crystal graphene growth and its shape evolution is of fundamental importance to the understanding of graphene growth physicochemical mechanisms and the achievement of wafer-scale single crystalline graphene. Here we demonstrate the controlled formation of single crystal graphene with varying shapes, and directly observe the shape evolution of single crystal graphene by developing a localized-heating and rapid-quenching chemical vapor deposition (CVD) system based on electromagnetic induction heating. Importantly, rational control of circular, hexagonal, and dendritic single crystalline graphene domains can be readily obtained for the first time by changing the growth condition. Systematic studies suggest that the graphene nucleation only occurs during the initial stage, while the domain density is independent of the growth temperatures due to the surface-limiting effect. In addition, the direct observation of graphene domain shape evolution is employed for the identification of competing growth mechanisms including diffusion-limited, attachment-limited, and detachment-limited processes. Our study not only provides a novel method for morphology-controlled graphene synthesis, but also offers fundamental insights into the kinetics of single crystal graphene growth. PMID:25762066

Wu, Chaoxing; Li, Fushan; Chen, Wei; Veeramalai, Chandrasekar Perumal; Ooi, Poh Choon; Guo, Tailiang

2015-01-01

307

Electromagnetic induction heating for single crystal graphene growth: morphology control by rapid heating and quenching  

NASA Astrophysics Data System (ADS)

The direct observation of single crystal graphene growth and its shape evolution is of fundamental importance to the understanding of graphene growth physicochemical mechanisms and the achievement of wafer-scale single crystalline graphene. Here we demonstrate the controlled formation of single crystal graphene with varying shapes, and directly observe the shape evolution of single crystal graphene by developing a localized-heating and rapid-quenching chemical vapor deposition (CVD) system based on electromagnetic induction heating. Importantly, rational control of circular, hexagonal, and dendritic single crystalline graphene domains can be readily obtained for the first time by changing the growth condition. Systematic studies suggest that the graphene nucleation only occurs during the initial stage, while the domain density is independent of the growth temperatures due to the surface-limiting effect. In addition, the direct observation of graphene domain shape evolution is employed for the identification of competing growth mechanisms including diffusion-limited, attachment-limited, and detachment-limited processes. Our study not only provides a novel method for morphology-controlled graphene synthesis, but also offers fundamental insights into the kinetics of single crystal graphene growth.

Wu, Chaoxing; Li, Fushan; Chen, Wei; Veeramalai, Chandrasekar Perumal; Ooi, Poh Choon; Guo, Tailiang

2015-03-01

308

Experimental techniques for determination of the role of diffusion and convection in crystal growth from solution  

NASA Technical Reports Server (NTRS)

Various studies of the concentration of the solution around a growing crystal using interferometric techniques are reviewed. A holographic interferometric technique used in laboratory experiments shows that a simple description of the solution based on the assumption of a purely diffusive mechanism appears inadequate since the convection, effective even in reduced columns, always affects the growth.

Zefiro, L.

1980-01-01

309

Advantages of ice crystal growth experiments in a low gravity environment  

NASA Technical Reports Server (NTRS)

The effects of convective fluid motions and mechanical supports on ice crystal growth in experiments conducted on earth can be inferred from studies conducted in their absence in a low-gravity environment. Current experimental results indicate the effects may be significant.

Anderson, B. J.; Keller, V. W.; Hallett, J.

1979-01-01

310

Four lectures on the physics of crystal growth  

NASA Astrophysics Data System (ADS)

Several aspects of the theory of epitaxial crystal growth from atomic or molecular beams are developed from the perspective of statistical physics. Lectures are devoted to the rate equation theory of two-dimensional nucleation and its limitations; the growth of multilayer wedding cakes in the presence of strong step edge barriers; the continuum theory of mound coarsening; and growth-induced step meandering on vicinal surfaces.

Krug, Joachim

2002-10-01

311

Macromolecular crystal growth experiments on International Microgravity Laboratory--1.  

PubMed Central

Macromolecular crystal growth experiments, using satellite tobacco mosaic virus (STMV) and canavalin from jack beans as samples, were conducted on a US Space Shuttle mission designated International Microgravity Laboratory--1 (IML-1), flown January 22-29, 1992. Parallel experiments using identical samples were carried out in both a vapor diffusion-based device (PCG) and a liquid-liquid diffusion-based instrument (CRYOSTAT). The experiments in each device were run at 20-22 degrees C and at colder temperatures. Crystals were grown in virtually every trial, but the characteristics of the crystals were highly dependent on the crystallization technique employed and the temperature experience of the sample. In general, very good results, based on visual inspection of the crystals, were obtained in both PCG and CRYOSTAT. Unusually impressive results were, however, achieved for STMV in the CRYOSTAT instrument. STMV crystals grown in microgravity by liquid-liquid diffusion were more than 10-fold greater in total volume than any STMV crystals previously grown in the laboratory. X-ray diffraction data collected from eight STMV crystals grown in CRYOSTAT demonstrated a substantial improvement in diffraction quality over the entire resolution range when compared to data from crystals grown on Earth. In addition, the extent of the diffraction pattern for the STMV crystals grown in space extended to 1.8 A resolution, whereas the best crystals that were ever grown under conditions of Earth's gravity produced data limited to 2.3 A resolution. Other observations indicate that the growth of macromolecular crystals is indeed influenced by the presence or absence of gravity. These observations further suggest, consistent with earlier results, that the elimination of gravity provides a more favorable environment for such processes. PMID:1303744

Day, J.; McPherson, A.

1992-01-01

312

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

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

313

Novel protein crystal growth technology: Proof of concept  

NASA Technical Reports Server (NTRS)

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.

Nyce, Thomas A.; Rosenberger, Franz

1989-01-01

314

Crystal Growth and Characterization of Bil3  

NASA Technical Reports Server (NTRS)

Bismuth tri-iodide (BiI3) have been grown by physical vapor transport (PVT), and by the Bridgman (melt) method. These crystals along with pure and stoichiometric BiI3 powder have been investigated by differential scanning calorimetry (DSC). The DSC results show that pure BiI3 powder has no phase transition and melts around 408 C. While we found no evidence for the high temperature dissociation of BiI3, the DSC measurements show that crystals grown from melt method contain a significantly large amount of Bi-rich phases than crystals grown from PVT method, as indicated by phase transition detected at 270, 285, 298 and 336 C.

Hayes, Julia; Chen, Kuo-Tong; Burger, Arnold

1997-01-01

315

Environmental Scanning Electron Microscopy of Ice Crystal Nucleation and Growth  

NASA Astrophysics Data System (ADS)

Ice crystal nucleation and growth are dual processes that can be studied uniquely through Environmental Scanning Electron Microscopy (ESEM). By utilizing differential pumping systems and a Peltier element to vary the vapor pressure and to achieve temperatures below the freezing point, respectively, it is possible to obtain supersaturated conditions relative to ice in the sample chamber of an Environmental Scanning Electron Microscope. Ice crystals were nucleated on a variety of atmospherically relevant substrates and grown in a pure water vapor environment in the chamber of a FEI-Quanta 200 ESEM. To initiate ice crystal nucleation, the Peltier element was set at a temperature between -10°C and -25°C, while the chamber water vapor pressure was adjusted to just below the frost point. Ice crystal nucleation and growth was then controlled by careful adjustments of chamber pressure and temperature, where high-magnification images of hexagonal ice crystals were acquired at nanoscale resolution. These images display prominent mesoscopic surface topography including linear strands, crevasses, islands, and steps. The surface features are seen to be ubiquitously present at all observed temperatures, at many supersaturated and subsaturated conditions, and on all crystal facets. Additionally, a pre-growth "shadow" resembling a dark spot sometimes appeared on areas of the sample stage immediately preceding ice crystal nucleation and growth. The observations represent the most highly magnified images of ice surfaces yet reported and significantly expand the range of ambient conditions where the features are conspicuous. New knowledge of the presence and characteristics of these features could transform the fundamental understanding of ice crystal growth kinetics and its physical parameterization in the context of atmospheric and cryospheric science. To the extent these observations are applicable to atmospheric ice, the results suggest that the radiative representation of ice and mixed-phase cloud properties in climate models could be markedly affected.

Amaral, M.; Miller, A. L.; Magee, N. B.

2012-12-01

316

Growth of aluminum nitride bulk crystals by sublimation  

NASA Astrophysics Data System (ADS)

The commercial potential of III-nitride semiconductors is already being realized by the appearance of high efficiency, high reliability, blue and green LEDS around the world. However, the lack of a native nitride substrate has hindered the full-realization of more demanding III-nitride devices. To date, single aluminum nitride (AlN) crystals are not commercially available. New process investigation is required to scale up the crystal size. New crucibles stable up to very high temperatures (˜2500°C) are needed which do not incorporate impurities into the growing crystals. In this thesis, the recent progresses in bulk AlN crystal growth by sublimation-recondensation were reviewed first. The important physical, optical and electrical properties as well as chemical and thermal stabilities of AlN were discussed. The development of different types of growth procedures including self-seeding, substrate employed and a new "sandwich" technique were covered in detail. Next, the surface morphology and composition at the initial stages of AlN grown on 6H-SiC (0001) were investigated. Discontinuous AlN coverage occurred after 15 minutes of growth. The initial discontinuous nucleation of AlN and different lateral growth of nuclei indicated discontinuous AIN direct growth on on-axis 6H-SiC substrates. At the temperature in excess of 2100°C, the durability of the furnace fixture materials (crucibles, retorts, etc.) remains a critical problem. The thermal and chemical properties and performance of several refractory materials, including tantalum carbide, niobium carbide, tungsten, graphite, and hot-pressed boron nitride (HPBN), in inert gas, as well as under AIN crystal growth conditions were discussed. TaC and NbC are the most stable crucible materials in the crystal growth system. HPBN crucible is more suitable for AlN self-seeding growth, as crystals tend to nucleate in thin colorless platelets with low dislocation density. Finally, clear and colorless thin platelet AlN single crystals up to 60 mm2 were prepared at 2100°C, 800 torr in HPBN crucibles by free-nucleation. About 1 mm thick AlN/SiC alloy crystals were grown on off-axis 6H-SiC substrate in a TaC crucible by seeded growth.

Liu, Bei

317

Epitaxial growth of germanium thin films on crystal silicon substrates by solid phase crystallization  

NASA Astrophysics Data System (ADS)

We have investigated the solid phase crystallization (SPC) of amorphous germanium (a-Ge) precursors on single crystalline silicon (c-Si) substrates as seed layers and successfully obtained the epitaxial growth of Ge. The n-type (100) Si substrate is most suitable for preferential growth following the substrate orientation, because the velocity of preferential growth is higher than those on the other substrates and preferential growth is completed before random nucleation. The impurity contamination in the a-Ge precursors probably enhances random nucleation. The epitaxial growth is disturbed by the impurity contamination at a relatively high SPC temperature in the intrinsic and p-type Si substrates with the (100) orientation and the n-type and intrinsic Si substrates with the (111) orientation, because the lower velocity of preferential growth allows random crystallization. Almost no epitaxial growth is observed on the p-type (111) Si substrates even when low-impurity a-Ge precursors are used.

Isomura, Masao; Kanai, Mikuri

2015-04-01

318

Crystal Growth of Ternary Compound Semiconductors in Low Gravity Environment  

NASA Technical Reports Server (NTRS)

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.

Su, Ching-Hua

2014-01-01

319

Growth of 4-in diameter near-stoichiometric lithium tantalate single crystals  

NASA Astrophysics Data System (ADS)

We present the aspects on the growth of 4-in diameter near-stoichiometric lithium tantalate (SLT) crystals, from lithium-enriched melt, employing double crucible Czochralski (DCCZ) technique. The difficulties encountered during growth such as crack and mechanical twin formation are discussed in detail and the same overcame by adopting suitable experimental parameters. The wafers sliced from the crystals are found to be compositionally homogeneous and free from sub-grains. The variation in the refractive indices across the wafer is of the order of 10 -5. We could not observe any marked difference either in the absorption edge or poling field for domain inversion at different locations in the wafer.

Kumaragurubaran, S.; Takekawa, S.; Nakamura, M.; Kitamura, K.

2005-11-01

320

A Microfluidic, High Throughput Protein Crystal Growth Method for Microgravity  

PubMed Central

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

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

2013-01-01

321

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

PubMed

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

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

2013-01-01

322

Ground Based Program for the Physical Analysis of Macromolecular Crystal Growth  

NASA Technical Reports Server (NTRS)

In a reported period in situ atomic force microscopy was utilized in our laboratory to study mechanisms of growth and kinetics of crystallization of ten protein and virus crystals. These included canavalin, thaumatin, apoferritin, lipase, catalase, t-RNA, lysozyme, xylanase, turnip yellow mosaic virus (TYMV) and satellite tobacco mosaic virus (STMV). We have also designed and constructed in our laboratory both in situ conventional two-beam Michelson and phase shift Mach-Zenhder interferometers. Computer software for the processing of the interferometric images was developed as well. Interferometric techniques were applied for studies of growth kinetics and transport phenomena in crystallization of several macromolecular crystals. As a result of this work we have published 21 papers and have given many presentations at international and national meetings. A list of these publications and conference presentations is attached.

Malkin, Alexander J.

1999-01-01

323

Vapor crystal growth technology development: Application to cadmium telluride  

NASA Technical Reports Server (NTRS)

Growth of bulk crystals by physical vapor transport was developed and applied to cadmium telluride. The technology makes use of effusive ampoules, in which part of the vapor contents escapes to a vacuum shroud through defined leaks during the growth process. This approach has the advantage over traditional sealed ampoule techniques that impurity vapors and excess vapor constituents are continuously removed from the vicinity of the growing crystal. Thus, growth rates are obtained routinely at magnitudes that are rather difficult to achieve in closed ampoules. Other advantages of this effusive ampoule physical vapor transport (EAPVT) technique include the predetermination of transport rates based on simple fluid dynamics and engineering considerations, and the growth of the crystal from close to congruent vapors, which largely alleviates the compositional nonuniformities resulting from buoyancy driven convective transport. After concisely reviewing earlier work on improving transport rates, nucleation control, and minimization of crystal wall interactions in vapor crystal growth, a detail account is given of the largely computer controlled EAPVT experimentation.

Rosenberger, Franz; Banish, Michael; Duval, Walter M. B.

1991-01-01

324

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

NASA Technical Reports Server (NTRS)

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.

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

1971-01-01

325

Fluid Physics and Macromolecular Crystal Growth in Microgravity  

NASA Technical Reports Server (NTRS)

The first protein crystallization experiment in microgravity was launched in April, 1981 and used Germany's Technologische Experimente unter Schwerelosigkeit (TEXUS 3) sounding rocket. The protein P-galactosidase (molecular weight 465Kda) was chosen as the sample with a liquid-liquid diffusion growth method. A sliding device brought the protein, buffer and salt solution into contact when microgravity was reached. The sounding rocket gave six minutes of microgravity time with a cine camera and schlieren optics used to monitor the experiment, a single growth cell. In microgravity a strictly laminar diffusion process was observed in contrast to the turbulent convection seen on the ground. Several single crystals, approx 100micron in length, were formed in the flight which were of inferior but of comparable visual quality to those grown on the ground over several days. A second experiment using the same protocol but with solutions cooled to -8C (kept liquid with glycerol antifreeze) again showed laminar diffusion. The science of macromolecular structural crystallography involves crystallization of the macromolecule followed by use of the crystal for X-ray diffraction experiments to determine the three dimensional structure of the macromolecule. Neutron protein crystallography is employed for elucidation of H/D exchange and for improved definition of the bound solvent (D20). The structural information enables an understanding of how the molecule functions with important potential for rational drug design, improved efficiency of industrial enzymes and agricultural chemical development. The removal of turbulent convection and sedimentation in microgravity, and the assumption that higher quality crystals will be produced, has given rise to the growing number of crystallization experiments now flown. Many experiments can be flown in a small volume with simple, largely automated, equipment - an ideal combination for a microgravity experiment. The term "protein crystal growth" is often historically used to describe these microgravity experiments. This is somewhat inaccurate as the field involves the study of many varied biological molecules including viruses, proteins, DNA, RNA and complexes of those structures. For this reason we use the term macromolecular crystal growth. In this chapter we review a series of diagnostic microgravity crystal growth experiments carried out principally using the European Space Agency (ESA) Advanced Protein Crystallization Facility (APCF). We also review related research, both experimental and theoretical, on the aspects of microgravity fluid physics that affect microgravity protein crystal growth. Our experiments have revealed some surprises that were not initially expected. We discuss them here in the context of practical lessons learnt and how to maximize the limited microgravity opportunities available.

Helliwell, John R.; Snell, Edward H.; Chayen, Naomi E.; Judge, Russell A.; Boggon, Titus J.; Pusey, M. L.; Rose, M. Franklin (Technical Monitor)

2000-01-01

326

High-thermal-gradient Superalloy Crystal Growth  

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

327

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

NASA Astrophysics Data System (ADS)

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.

DeLucas, Lawrence J.

2002-12-01

328

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

NASA Astrophysics Data System (ADS)

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. .

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

2000-01-01

329

Investigation of nucleation and crystal growth kinetics of nickel manganese oxalates  

NASA Astrophysics Data System (ADS)

The nucleation and the crystal growth rates of mixed nickel manganese oxalates have been determined from the changes of the ionic concentration of the solution and the crystal size distribution during the precipitation process within a supersaturation range 0-0.1 M. Thermodynamic solubility calculations have been used to identify the different species contributing the precipitation reaction and for estimation of the thermodynamic constant. Experimental data show that the nucleation rate of mixed nickel manganese oxalate in this supersaturation range is consistent with a primary heterogeneous mechanism and was found to obey to an exponential law. The crystal growth rates indicate a surface-integration-controlled mechanism with a first-order law with respect to the supersaturation.

Aoun-Habbache, Montaha; Guillemet-Fritsch, Sophie; Lemaître, Jacques; Jones, Alan

2005-06-01

330

Crystal growth of device quality GaAs in space  

NASA Technical Reports Server (NTRS)

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.

Gatos, H. C.; Lagowski, J.

1980-01-01

331

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

332

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

PubMed

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. PMID:25048404

Thomas Joseph Prakash, J; Martin Sam Gnanaraj, J

2015-01-25

333

Crystal growth of device quality GaAs in space  

NASA Technical Reports Server (NTRS)

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.

Gatos, H. C.; Lagowski, J.

1985-01-01

334

Crystal growth of device quality GaAs in space  

NASA Technical Reports Server (NTRS)

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.

Gatos, Harry C.; Lagowski, Jacek

1989-01-01

335

Crystal growth of device quality GaAs in space  

NASA Astrophysics Data System (ADS)

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.

Gatos, Harry C.; Lagowski, Jacek

1989-02-01

336

Nucleation and Convection Effects in Protein Crystal Growth  

NASA Technical Reports Server (NTRS)

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.

Rosenberger, Franz

1997-01-01

337

A generalized electrochemical aggregative growth mechanism.  

PubMed

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

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

2013-08-01

338

Fundamental Studies of Crystal Growth of Microporous Materials  

NASA Technical Reports Server (NTRS)

Microporous materials are framework structures with well-defined porosity, often of molecular dimensions. Zeolites contain aluminum and silicon atoms in their framework and are the most extensively studied amongst all microporous materials. Framework structures with P, Ga, Fe, Co, Zn, B, Ti and a host of other elements have also been made. Typical synthesis of microporous materials involve mixing the framework elements (or compounds, thereof) in a basic solution, followed by aging in some cases and then heating at elevated temperatures. This process is termed hydrothermal synthesis, and involves complex chemical and physical changes. Because of a limited understanding of this process, most synthesis advancements happen by a trial and error approach. There is considerable interest in understanding the synthesis process at a molecular level with the expectation that eventually new framework structures will be built by design. The basic issues in the microporous materials crystallization process include: (1) Nature of the molecular units responsible for the crystal nuclei formation; (2) Nature of the nuclei and nucleation process; (3) Growth process of the nuclei into crystal; (4) Morphological control and size of the resulting crystal; (5) Surface structure of the resulting crystals; (6) Transformation of frameworks into other frameworks or condensed structures. The NASA-funded research described in this report focuses to varying degrees on all of the above issues and has been described in several publications. Following is the presentation of the highlights of our current research program. The report is divided into five sections: (1) Fundamental aspects of the crystal growth process; (2) Morphological and Surface properties of crystals; (3) Crystal dissolution and transformations; (4) Modeling of Crystal Growth; (5) Relevant Microgravity Experiments.

Dutta, P.; George, M.; Ramachandran, N.; Schoeman, B.; Curreri, Peter A. (Technical Monitor)

2002-01-01

339

Effects of ionic inflow and organic matrix on crystal growth of octacalcium phosphate; relevant to tooth enamel formation  

NASA Astrophysics Data System (ADS)

The mechanism of the lengthwise and oriented growth of enamel apatite crystals was studied on the basis of a hypothesis that (1) enamel crystals grow initially as octacalcium phosphate (OCP) as a precursor of apatite and (2) a one-directional Ca 2+ ion supply from the ameloblasts promotes the lengthwise and oriented growth of the crystals. To test this, OCP crystals were grown in a model system of enamel formation, where a cation selective membrane was used to control the Ca 2+ ion diffusion, at 37°C and at pH 6.3-7.4. The lengthwise and oriented growth of OCP was enhanced by the Ca influx from the membrane. H + ion enhanced while F -, Mg 2+ and CO 32- ions decreased the growth in the c-axis direction. F - induced an epitaxial overgrowth of apatite on the (1 0 0) of OCP, embedding an OCP lamella in the center of a crystal. When 5% polyacrylamide gel was attached to the membrane, OCP grew in long plate-like or ribbon-like crystals at pHs between 6.5 and 7.4. The length of these crystals was greater than that of those grown on the membrane without gel. The crystal size decreased with an increase in gel concentration from 5 to 20%. When a thin slice of tendon was used in place of the membrane, long OCP crystals grew along the collagen fibrils; these crystals were oriented with their axis of elongation perpendicular to the direction of ionic inflow. The size of crystals grown inside the collagenous matrix was much smaller than the size of crystals formed outside of the matrix and on the membrane. Thus, crystal growth was regulated by ionic diffusion and the matrix. When there were no constituents which regulated the growth direction, OCP crystals tended to grow along the direction of ionic inflow.

Iijima, Mayumi; Moriwaki, Yutaka

1999-03-01

340

Dispersity and growth kinetics of K2SO4 crystals in drops of an evaporating solution  

NASA Astrophysics Data System (ADS)

Growth of K2SO4 crystals is studied in solution drops that have different initial heights and evaporate in different times. The dependences of the crystal size on the crystal growth time are obtained. The following three crystal growth modes are detected: rapid crystal growth in a supersaturated solution, a stop in the growth as a result of complete removal of supersaturation, and slow growth at a quasi-equilibrium solution concentration. The dispersities of the crystals that are retained at the bottom of the drop after complete evaporation of the solvent are calculated. A linear relation between the crystal dispersity and the reciprocal crystal growth time is revealed. The dispersity of K2SO4 crystals and the dispersity of the solid-solution dendrites in aluminum alloys are found to exhibit the same character of their dependences on the reciprocal crystal growth time.

Fedorov, V. Yu.

2009-05-01

341

Crystal growth of organics for nonlinear optical applications  

NASA Technical Reports Server (NTRS)

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.

Singh, N. B.; Mazelsky, R.

1993-01-01

342

Modelling the growth of triglycine sulphate crystals in Spacelab 3  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

343

Zeolite crystal growth in space - What has been learned  

NASA Technical Reports Server (NTRS)

Three zeolite crystal growth experiments developed at WPI have been performed in space in last twelve months. One experiment, GAS-1, illustrated that to grow large, crystallographically uniform crystals in space, the precursor solutions should be mixed in microgravity. Another experiment evaluated the optimum mixing protocol for solutions that chemically interact ('gel') on contact. These results were utilized in setting the protocol for mixing nineteen zeolite solutions that were then processed and yielded zeolites A, X and mordenite. All solutions in which the nucleation event was influenced produced larger, more 'uniform' crystals than did identical solutions processed on earth.

Sacco, A., Jr.; Thompson, R. W.; Dixon, A. G.

1993-01-01

344

Colloidal crystal growth at externally imposed nucleation clusters  

E-print Network

We study the conditions under which and how an imposed cluster of fixed colloidal particles at prescribed positions triggers crystal nucleation from a metastable colloidal fluid. Dynamical density functional theory of freezing and Brownian dynamics simulations are applied to a two-dimensional colloidal system with dipolar interactions. The externally imposed nucleation clusters involve colloidal particles either on a rhombic lattice or along two linear arrays separated by a gap. Crystal growth occurs after the peaks of the nucleation cluster have first relaxed to a cutout of the stable bulk crystal.

Sven van Teeffelen; Christos N. Likos; Hartmut Löwen

2008-02-15

345

The influence of pH on the habit and the rate of alpha-LiIO3 crystal growth  

NASA Astrophysics Data System (ADS)

The influence of the pH on both the habit and the growth rate of alpha-LiIO3 crystals grown from solution by a constant temperature evaporation method has been studied under static and rotary conditions. The results indicated that the morphology of the alpha-LiIO3 crystals grown had hexagonal prismatic faces and hexagonal double pyramidal faces and that the crystal growth rates along the z-direction were faster than the rates in the opposite direction if the pH was more than critical. If, however, the pH was less than critical, then the crystal habit was bounded by the prismatic and pyramidal faces, and crystal growth rates in the z-direction were slower than in the opposite direction. The mechanism to explain the reversal of the growth rate at critical pH was proposed on the basis of the electrical double layer theory and the molecular adsorption theory.

Chen, W. C.; Ma, W. Y.; Liu, D. D.; Xie, A. Y.

1987-08-01

346

Crystal growth furnace with trap doors  

DOEpatents

An improved furnace is provided for growing crystalline bodies from a melt. The improved furnace is characterized by a door assembly which is remotely controlled and is arranged so as to selectively shut off or permit communication between an access port in the furnace enclosure and a hot zone within that enclosure. The invention is especially adapted to facilitate use of crystal growing cartridges of the type disclosed in U.S. Pat. No. 4,118,197.

Sachs, Emanual M. (Watertown, MA); Mackintosh, Brian H. (Lexington, MA)

1982-06-15

347

Single crystal growth of organic photoconductors: phthalocyanine  

Microsoft Academic Search

An effective method of growing single crystals of organic photoconductors such as phthalocyanine in the presence of doping\\u000a impurity such as iodine by vacuum sublimation is discussed in this paper. This method is very useful especially when an organic\\u000a material does not have a melting point but decomposes above a particular temperature. So far, doping has been done by exposing

Francis P Xavier; George J Goldsmith

1996-01-01

348

Crucibleless crystal growth and Radioluminescence study of calcium tungstate single crystal fiber  

NASA Astrophysics Data System (ADS)

In this article, single phase and high optical quality scheelite calcium tungstate single crystal fibers were grown by using the crucibleless laser heated pedestal growth technique. The as-synthesized calcium tungstate powders used for shaping seed and feed rods were investigated by X-ray diffraction technique. As-grown crystals were studied by Raman spectroscopy and Radioluminescence measurements. The results indicate that in both two cases, calcined powder and single crystal fiber, only the expected scheelite CaWO4 phase was observed. It was verified large homogeneity in the crystal composition, without the presence of secondary phases. The Radioluminescence spectra of the as-grown single crystal fibers are in agreement with that present in Literature for bulk single crystals, presented a single emission band centered at 420 nm when irradiated with ?-rays.

Silva, M. S.; Jesus, L. M.; Barbosa, L. B.; Ardila, D. R.; Andreeta, J. P.; Silva, R. S.

2014-11-01

349

Growth mechanism of hydrogen clusters  

SciTech Connect

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.

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

1997-07-01

350

Crystal growth of device quality GaAs in space  

NASA Technical Reports Server (NTRS)

The crystal growth, device processing and device related properties and phenomena of GaAs are investigated. Our GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor materials (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; (3) investigation of electronic properties and phenomena controlling device applications and device performance. The ground based program is developed which would insure successful experimentation with and eventually processing of GaAs in a near zero gravity environment.

Gatos, H. C.; Lagowski, J.

1984-01-01

351

Interface stability and defect formation during crystal growth  

SciTech Connect

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.

Fabietti, L.M.R.

1991-01-08

352

Crystal growth of device quality GaAs in space  

NASA Technical Reports Server (NTRS)

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.

Lagowski, J.

1981-01-01

353

Thermal Optimization of Growth and Quality in Protein Crystals  

NASA Technical Reports Server (NTRS)

Experimental evidence suggests that larger and higher quality crystals can be attained in the microgravity of space; however, the effect of growth rate on protein crystal quality is not well documented. This research is the first step towards providing strategies to grow crystals under constant rates of growth. Controlling growth rates at a constant value allows for direct one-to-one comparison of results obtained in microgravity and on earth. The overall goal of the project was to control supersaturation at a constant value during protein crystal growth by varying temperature in a predetermined manner. Applying appropriate theory requires knowledge of specific physicochemical properties of the protein solution including the effect of supersaturation on growth rates and the effect of temperature on protein solubility. Such measurements typically require gram quantities of protein and many months of data acquisition. A second goal of the project applied microcalorimetry for the rapid determination of these physicochemical properties using a minimum amount of protein. These two goals were successfully implemented on hen egg-white lysozyme. Results of these studies are described in the attached reprints.

Wiencek, John M.

1996-01-01

354

Numerical Modeling of Physical Vapor Transport in Contactless Crystal Growth Geometry  

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

355

Deformation behavior during thermo-mechanical fatigue of a nickel-based single crystal superalloy  

Microsoft Academic Search

The deformation and damage mechanisms of a single crystal nickel-based superalloy CMSX-4 have been investigated under out-of-phase thermo-mechanical fatigue (OP TMF) condition. The failure mechanism was oxide-layered surface initiated crack followed by its planar growth along ? channel. However, the deformation was highly localized to area near crack tip, where multiple groups of parallel twin plates on {111} planes formed

H. U. Hong; B. G. Choi; I. S. Kim; Y. S. Yoo; C. Y. Jo

2011-01-01

356

Growth of bulk GaN single crystals by the pressure-controlled solution growth method  

Microsoft Academic Search

Crystal growth of GaN by the pressure-controlled solution growth (PC-SG) method has been carried out using a high-pressure furnace. We have investigated the effect of the supersaturation of nitrogen atoms (the rate of increase of nitrogen pressure) in order to grow large GaN single crystals. It was found that the rate of increase of nitrogen pressure affected the size of

T. Inoue; Y Seki; O Oda; S Kurai; Y Yamada; T Taguchi

2001-01-01

357

Crystal growth of device quality GaAs in space  

NASA Technical Reports Server (NTRS)

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.

Gatos, H. C.; Lagowski, J.

1986-01-01

358

Growth of large zeolite crystals in space  

NASA Technical Reports Server (NTRS)

Synthesis studies performed using close analogs of triethanolamine (TEA) have shown that all three hydroxyl groups and the amine group in this molecule are necessary to provide nucleation suppression. Studies using C-13 nuclear magnetic resonance (NMR) revealed that the hydroxyl ions and the amine group are involved in the formation of an aluminum complex. It was also shown that silicate species fo not interact this way with TEA in an alkaline solution. These results suggest that successful aluminum complexation leads to nucleation in zeolite-A crystallization.

Sacco, A., Jr.; Dixon, A.; Thompson, R.; Scott, G.; Ditr, J.

1988-01-01

359

Analytics of crystal growth in space  

NASA Technical Reports Server (NTRS)

The variation of radial impurity distribution induced by surface tension driven flow increases as the zone length decreases in silicon crystals grown by floating zone melting. In combined buoyancy driven and surface tension driven convection at the gravity of earth, the buoyancy contribution becomes relatively smaller as the zone diameter decreases and eventually convection is dominated by the surface tension driven flow (in the case of silicon, for zones of less than about 0.8 cm in diameter). Preliminary calculations for sapphire suggest the presence of an oscillatory surface tension driven convection as a result of an unstable melt surface temperature that results when the zone is heated by a radiation heater.

Chang, C. E.; Lefever, R. A.; Wilcox, W. R.

1975-01-01

360

Crystal growth of device quality GaAs in space  

Microsoft Academic Search

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

Harry C. Gatos; Jacek Lagowski

1989-01-01

361

Selective anisotropic growth of zeolite crystals  

E-print Network

. 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...

Desai, Tasha April

2013-02-22

362

Erythritol: crystal growth from the melt.  

PubMed

The structural changes occurring on erythritol as it is cooled from the melt to low temperature, and then heated up to the melting point have been investigated by differential scanning calorimetry (DSC), polarized light thermal microscopy (PLTM), X-ray powder diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR). By DSC, it was possible to set up the conditions to obtain an amorphous solid, a crystalline solid, or a mixture of both materials in different proportions. Two crystalline forms have been identified: a stable and a metastable one with melting points of 117 and 104 degrees C, respectively. The fusion curve decomposition of the stable form revealed the existence of three conformational structures. The main paths of the crystallization from the melt were followed by PLTM. The texture and colour changes allowed the characterization of the different phases and transitions in which they are involved on cooling as well as on heating processes. The type of crystallization front and its velocity were also followed by microscopic observation. These observations, together with the data provided by PXRD, allowed elucidating the transition of the metastable form into the stable one. The structural changes occurring upon the cooling and subsequent heating processes, namely those arising from intermolecular hydrogen bonds, were also accompanied by infrared spectroscopy. Particular attention was given to the spectral changes occurring in the OH stretching region. PMID:20045045

Lopes Jesus, A J; Nunes, Sandra C C; Ramos Silva, M; Matos Beja, A; Redinha, J S

2010-03-30

363

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

PubMed

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

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

2015-02-01

364

Optimization of the Crystal Surface Temperature Distribution in the Single-Crystal Growth Process by the Czochralski Method  

Microsoft Academic Search

The optimization of the crystal surface temperature distribution is performed for single-crystal growth in the Czochralski process. In the optimization problem, we seek an optimal solution in the sense that the index of crystalline defects is minimized while the single-crystal growth rate is maximized. In the objective function, the von Mises stress is considered a driving force that induces crystalline

Ja Hoon Jeong

2002-01-01

365

Growth and characterization of terbium fumarate heptahydrate single crystals  

NASA Astrophysics Data System (ADS)

The growth of terbium fumarate heptahydrate single crystals was achieved by single gel diffusion technique using silica gel as a medium of growth. The effect of various growth parameters on the nucleation rate of these crystals was studied. The crystals were characterized by different physico-chemical techniques of characterization. Powder X-ray diffraction pattern showed that terbium fumarate is a crystalline compound. Fourier transform infrared spectroscopy was performed for the identification of water and other functional groups present in the compound. UV-vis and photoluminescence spectrophotometric experiments were carried out to study the optical properties of the grown crystals. Elemental analysis suggested the chemical formula of the crystals to be Tb2(C4H2O4)3·7H2O. The presence of seven molecules of water was also supported by the thermogravimetric analysis. The hydrated compound was found to be thermally stable upto a temperature of about 110 °C and its anhydrous form up to the temperature of 410 °C. The thermal decomposition of the compound in the nitrogen atmosphere leads to the formation of terbium oxide as the final product. An attempt was made to relate the experimental results with the classical nucleation theory.

Want, B.; Shah, M. D.

2014-03-01

366

Crystal Growth of Laser Host Fluorides and Oxides  

NASA Astrophysics Data System (ADS)

Following the discovery of the first laser action based on ruby, hundreds of additional doped crystals have been shown to lase. Among those, many crystals, such as Ti:Al2O3, Nd:Y3Al5O12, Nd:YVO4, Yb:Y3Al5O12, Yb:Ca5(PO4)3F, and Cr:LiCAF have come to practical application, and are being widely used in scientific research, manufacturing and communication industries, military applications, and other fields of modern engineering. These crystals are mainly oxides and fluorides, which are grown from melt. This chapter reviews the major results obtained during recent years in the growth of various crystalline oxides and fluorides for laser operation, with emphasis on crystals doped with the additional ions Ti3+, Nd3+, and Yb3+. On the other hand, special attention is paid to discuss the elimination of growth defects in these crystals. Limited by the length of this chapter, for each crystal, only outstanding defects are considered herein.

Li, Hongjun; Xu, Jun

367

The Growth of Protein Crystals Using McDUCK  

NASA Technical Reports Server (NTRS)

Most of the current microgravity crystal growth hardware is optimized to produce crystals within the limited time available on orbit. This often results in the actual nucleation and growth process being rushed or the system not coming to equilibrium within the limited time available. Longer duration hardware exists, but one cannot readily pick out crystals grown early versus those which nucleated and grew more slowly. We have devised a long duration apparatus, the Multi-chamber Dialysis Unit for Crystallization Kinetics, or McDUCK. This apparatus-is a series of protein chambers, stacked upon a precipitant reservoir chamber. All chambers are separated by a dialysis membrane, which serves to pass small molecules while retaining the protein. The volume of the Precipitant chamber is equal to the sum of the volumes of the protein chamber. In operation, the appropriate chambers are filled with precipitant solution or protein solution, and the McDUCK is placed standing upright, with the precipitant chamber on the bottom. The precipitant diffuses upwards over time, with the time to reach equilibration a function of the diffusivity of the precipitant and the overall length of the diffusion pathway. Typical equilibration times are approximately 2-4 months, and one can readily separate rapid from slow nucleation and growth crystals. An advantage on Earth is that the vertical precipitant concentration gradient dominates that of the solute, thus dampening out solute density gradient driven convective flows. However, large Earth-grown crystals have so far tended to be more two dimensional. Preliminary X-ray diffraction analysis of lysozyme crystals grown in McDUCK have indicated that the best, and largest, come from the middle chambers, suggesting that there is an optimal growth rate. Further, the improvements in diffraction resolution have been better signal to noise ratios in the low resolution data, not an increase in resolution overall. Due to the persistently large crystals grown we are currently proposing McDUCK for the growth of macromolecule crystals for use in neutron diffraction studies.

Ewing, Felicia; Wilson, Lori; Nadarajah, Arunan; Pusey, Marc

1998-01-01

368

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

Microsoft Academic Search

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

Dapeng Chen

2008-01-01

369

Thermal-mechanical fatigue crack growth in aircraft engine materials  

NASA Astrophysics Data System (ADS)

This thesis summarizes the major technical achievements obtained as a part of a collaborative research and development project between Ecole Polytechnique and Pratt & Whitney Canada. These achievements include: (1) a thermal-mechanical fatigue (TMF) testing rig which is capable of studying the fatigue behaviors of gas turbine materials under simultaneous changes of temperatures and strains or stress; (2) an advanced alternative current potential drop (ACPD) measurement system which is capable of performing on-line monitoring of fatigue crack initiation and growth in specimen testing under isothermal and TMF conditions; (3) fatigue crack initiation and short crack growth data for the titanium specimens designed with notch features associated with bolt holes of compressor discs; (4) thermal-mechanical fatigue crack growth data for two titanium alloys being used in PWC engine components, which explained the material fatigue behavior encountered in full-scale component testing; (5) a complete fractographic analysis for the tested specimens which enhanced the understanding of the fatigue crack growth mechanisms and helped to establish an analytical crack growth model; and (6) application of the ACPD fatigue crack monitoring technique to single tooth firtree specimen (STFT) LCF testing of PWA 1480 single crystal alloy. Finally, a comprehensive discussion concerning the results pertaining to this research project is presented.

Dai, Yi

1993-08-01

370

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

NASA Technical Reports Server (NTRS)

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.

Feth, Shari T.

2001-01-01

371

Crystal growth and characterization of new laser materials  

NASA Astrophysics Data System (ADS)

Two new laser materials are described. The first one belongs to the magnetoplumbite structural type and the second one belongs to the gehlenite type. Crystal growth, optical properties and laser efficiency are determined. These materials exhibit two main advantages: broad tunability ranges and ability to be diode-pumped.

Collongues, R.; Lejus, A. M.; Théry, J.; Vivien, D.

1993-03-01

372

Solidification and crystal growth of solid solution semiconducting alloys  

NASA Technical Reports Server (NTRS)

Problems associated with the solidification and crytal growth of solid-solution semiconducting alloy crystals in a terrestrial environment are described. A detailed description is given of the results for the growth of mercury cadmium telluride (HgCdTe) alloy crystals by directional solidification, because of their considerable technological importance. A series of HgCdTe alloy crystals are grown from pseudobinary melts by a vertical Bridgman method using a wide range of growth rates and thermal conditions. Precision measurements are performed to establish compositional profiles for the crystals. The compositional variations are related to compositional variations in the melts that can result from two-dimensional diffusion or density gradient driven flow effects ahead of the growth interface. These effects are discussed in terms of the alloy phase equilibrium properties, the recent high temperature thermophysical data for the alloys and the highly unusual heat transfer characteristics of the alloy/ampule/furnace system that may readily lead to double diffusive convective flows in a gravitational environment.

Lehoczky, S. L.; Szofran, F. R.

1984-01-01

373

Modeling snow crystal growth III: three-dimensional snowfakes  

E-print Network

We introduce a three-dimensional, computationally feasible, mesoscopic model for snow crystal growth, based on diffusion of vapor, anisotropic attachment, and a semi-liquid boundary layer. Several case studies are presented that faithfully emulate a wide variety of physical snowflakes.

Janko Gravner; David Griffeath

2007-11-26

374

Crewmember working on the spacelab Zeolite Crystal Growth experiment.  

NASA Technical Reports Server (NTRS)

View showing Payload Specialists Bonnie Dunbar and Larry DeLucas in the aft section of the U. S. Microgravity Laboratory-1. Dunbar is preparing to load a sample in the Crystal Growth Furnace (CGF) Integrated Furnace Experiment Assembly (IFEA) in rack 9 of the Microgravity Laboratory. DeLucas is checking out the multi-purpose Glovebox Facility.

1992-01-01

375

Crewmember working on the mid deck Zeolite Crystal Growth experiment.  

NASA Technical Reports Server (NTRS)

View showing Payload Specialist Bonnie Dunbar, in the mid deck, conducting the Zeolite Crystal Growth (ZCG) Experiment in the mid deck stowage locker work area. View shows assembly of zeolite sample in the metal autoclave cylinders prior to insertion into the furnace.

1992-01-01

376

Growth Rates of Zinc Crystals from the Vapor Phase  

Microsoft Academic Search

The rate of growth of zinc crystals from the vapor phase has been studied as a function of the vapor supersaturation ? at a temperature of 390°C. The ? values ranged between 0.009 and 0.09. The rate R was found to vary approximately linearly with ?, permitting estimates to be made of the two parameters ?1 and ?C0, appearing in

Robert L. Parker; Lawrence M. Kushner

1961-01-01

377

Numerical computation of sapphire crystal growth using heat exchanger method  

Microsoft Academic Search

The finite element software FIDAP is employed to study the temperature and velocity distribution and the interface shape during a large sapphire crystal growth process using a heat exchanger method (HEM). In the present study, the energy input to the crucible by the radiation and convection inside the furnace and the energy output through the heat exchanger is modeled by

Chung-Wei Lu; Jyh-Chen Chen

2001-01-01

378

Two-wall fused-silica ampoules for crystal growth  

NASA Astrophysics Data System (ADS)

A fused-silica ampoule has been developed for use in ground and space based crystal growth. The ampoule provides two levels of material containment. It also mitigates undesirable thermal gradients. The ampoule has demonstrated it can sustain Space Transportation System launch and landing loads.

Yoel, David W.; Thomas, Terrance L.; Garman, David M.

1988-10-01

379

Computing the crystal growth rate by the interface pinning method  

NASA Astrophysics Data System (ADS)

An essential parameter for crystal growth is the kinetic coefficient given by the proportionality between supercooling and average growth velocity. Here, we show that this coefficient can be computed in a single equilibrium simulation using the interface pinning method where two-phase configurations are stabilized by adding a spring-like bias field coupling to an order-parameter that discriminates between the two phases. Crystal growth is a Smoluchowski process and the crystal growth rate can, therefore, be computed from the terminal exponential relaxation of the order parameter. The approach is investigated in detail for the Lennard-Jones model. We find that the kinetic coefficient scales as the inverse square-root of temperature along the high temperature part of the melting line. The practical usability of the method is demonstrated by computing the kinetic coefficient of the elements Na and Si from first principles. A generalized version of the method may be used for computing the rates of crystal nucleation or other rare events.

Pedersen, Ulf R.; Hummel, Felix; Dellago, Christoph

2015-01-01

380

Modeling snow crystal growth III: three-dimensional snowfakes  

Microsoft Academic Search

We introduce a three-dimensional, computationally feasible, mesoscopic model for snow crystal growth, based on diffusion of vapor, anisotropic attachment, and a semi-liquid boundary layer. Several case studies are presented that faithfully emulate a wide variety of physical snowflakes.

Janko Gravner; David Griffeath

2007-01-01

381

Factors affecting isotherm shape during Bridgman crystal growth  

NASA Astrophysics Data System (ADS)

Isotherm shape is an important factor controlling the quality of Bridgman grown crystals. A convex (relative to the solid) isotherm will often lead to the best crystallinity but if segregation is important a flat isotherm is desirable. A thermal model is used to establish the effects of temperature dependent conductivity, ampoule transparency and furnace temperature profile on heat flows and temperature distributions in the growing crystal. The shape of the first-to-freeze isotherm is found to depend on the furnace profile and the way heat is lost from the base of the melt. A convex isotherm requires a shallow profile and high end losses. As growth progresses end losses are less important and the growth isotherm shape is determined by the crystal-melt conductivity and the furnace profile.

Jones, C. L.; Capper, P.; Gosney, J. J.; Kenworthy, I.

1984-11-01

382

Protein crystal growth in microgravity: Temperature induced large scale crystallization of insulin  

NASA Technical Reports Server (NTRS)

One of the major stumbling blocks that prevents rapid structure determination using x-ray crystallography is macro-molecular crystal growth. There are many examples where crystallization takes longer than structure determination. In some cases, it is impossible to grow useful crystals on earth. Recent experiments conducted in conjuction with NASA on various Space Shuttle missions have demonstrated that protein crystals often grow larger and display better internal molecular order than their earth-grown counterparts. This paper reports results from three Shuttle flights using the Protein Crystallization Facility (PCF). The PCF hardware produced large, high-quality insulin crystals by using a temperature change as the sole means to affect protein solubility and thus, crystallization. The facility consists of cylinders/containers with volumes of 500, 200, 100, and 50 ml. Data from the three Shuttle flights demonstrated that larger, higher resolution crystals (as evidenced by x-ray diffraction data) were obtained from the microgravity experiments when compared to earth-grown crystals.

Long, Marianna M.; Delucas, Larry J.; Smith, C.; Carson, M.; Moore, K.; Harrington, Michael D.; Pillion, D. J.; Bishop, S. P.; Rosenblum, W. M.; Naumann, R. J.

1994-01-01

383

Epitaxial Crystal Growth: Methods and Materials  

NASA Astrophysics Data System (ADS)

The epitaxial growth of thin films of material for a wide range of applications in electronics and optoelectronics is a critical activity in many industries. The original growth technique used, in most instances, was liquid-phase epitaxy (LPE), as this was the simplest and often the cheapest route to producing device-quality layers. These days, while some production processes are still based on LPE, most research into and (increasingly) much of the production of electronic and optoelectronic devices now centers on metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). These techniques are more versatile than LPE (although the equipment is more expensive), and they can readily produce multilayer structures with atomic-layer control, which has become more and more important in the type of nanoscale engineering used to produce device structures in as-grown multilayers. This chapter covers these three basic techniques, including some of their more common variants, and outlines the relative advantages and disadvantages of each. Some examples of growth in various important systems are also outlined for each of the three techniques.

Capper, Peter; Irvine, Stuart; Joyce, Tim

384

An Investigation into the Role of Polymeric Carriers on Crystal Growth within Amorphous Solid Dispersion Systems.  

PubMed

Using phase diagrams derived from Flory-Huggins theory, we defined the thermodynamic state of amorphous felodipine within three different polymeric carriers. Variation in the solubility and miscibility of felodipine within different polymeric materials (using F-H theory) has been identified and used to select the most suitable polymeric carriers for the production of amorphous drug-polymer solid dispersions. With this information, amorphous felodipine solid dispersions were manufactured using three different polymeric materials (HPMCAS-HF, Soluplus, and PVPK15) at predefined drug loadings, and the crystal growth rates of felodipine from these solid dispersions were investigated. Crystallization of amorphous felodipine was studied using Raman spectral imaging and polarized light microscopy. Using this data, we examined the correlation among several characteristics of solid dispersions to the crystal growth rate of felodipine. An exponential relationship was found to exist between drug loading and crystal growth rate. Moreover, crystal growth within all selected amorphous drug-polymer solid dispersion systems were viscosity dependent (?(-?)). The exponent, ?, was estimated to be 1.36 at a temperature of 80 °C. Values of ? exceeding 1 may indicate strong viscosity dependent crystal growth in the amorphous drug-polymer solid dispersion systems. We argue that the elevated exponent value (? > 1) is a result of drug-polymer mixing which leads to a less fragile amorphous drug-polymer solid dispersion system. All systems investigated displayed an upper critical solution temperature, and the solid-liquid boundary was always higher than the spinodal decomposition curve. Furthermore, for PVP-FD amorphous dispersions at drug loadings exceeding 0.6 volume ratio, the mechanism of phase separation within the metastable zone was found to be driven by nucleation and growth rather than liquid-liquid separation. PMID:25692314

Tian, Yiwei; Jones, David S; Andrews, Gavin P

2015-04-01

385

In Situ ?GISAXS: II. Thaumatin Crystal Growth Kinetic  

PubMed Central

The formation of thaumatin crystals by Langmuir-Blodgett (LB) film nanotemplates was studied by the hanging-drop technique in a flow-through cell by synchrotron radiation micrograzing-incidence small-angle x-ray scattering. The kinetics of crystallization was measured directly on the interface of the LB film crystallization nanotemplate. The evolution of the micrograzing-incidence small-angle x-ray scattering patterns suggests that the increase in intensity in the Yoneda region is due to protein incorporation into the LB film. The intensity variation suggests several steps, which were modeled by system dynamics based on first-order differential equations. The kinetic data can be described by two processes that take place on the LB film, a first, fast, process, attributed to the crystal growth and its detachment from the LB film, and a second, slower process, attributed to an unordered association and conversion of protein on the LB film. PMID:20713011

Gebhardt, Ronald; Pechkova, Eugenia; Riekel, Christian; Nicolini, Claudio

2010-01-01

386

Hot zone design for controlled growth to mitigate cracking in laser crystal growth  

NASA Astrophysics Data System (ADS)

Cracking is a major problem during large diameter crystal growth. The objective of this work is to design an effective hot zone for a controlled growth of Yb:S-FAP [Yb3+:Sr5(PO4)3F] laser crystal by the Czochralski technology and effective cooling that can reduce stress. Theoretical and numerical analyses are performed to study the causes of cracking, mitigate the major cracking, as well as reduce cooling time. In the current system, three locations in the crystal are prone to crack, such as the top shoulder of the crystal, the middle portion above the crucible edge, and the bottom tail portion. Based on numerical simulations, we propose a new hot zone design and cooling procedure to grow and cool large diameter crystal without cracking.

Zhang, Hui; Zheng, Lili; Fang, Haisheng

2011-03-01

387

Direct observation of crystal growth from solution using optical investigation of a growing crystal face  

NASA Technical Reports Server (NTRS)

The first technical report for the period 1 Jan. 1993 till 31 Dec. 1993 for the research entitled, 'Direct observation of crystal growth from solution using Optical Investigation of a growing crystal Face' is presented. The work on the project did not start till 1 June 1993 due to the non-availability of the required personnel. The progress of the work during the period 1 June 1993 till the end of 1993 is described. Significant progress was made for testing various optical diagnostic techniques for monitoring crystal solution. Some of the techniques that are being tested are: heterodyne detection technique, in which changes in phase are measured as a interferometric function of time/crystal growth; a conventional technique, in which a fringe brightness is measured as a function of crystal growth/time; and a Mach-Zehnder interferometric technique in which a fringe brightness is measured as a function of time to obtain information on concentration changes. During the second year it will be decided to incorporate the best interferometric technique along with the ellipsometric technique, to obtain real time in-situ growth rate measurements. A laboratory mock-up of the first two techniques were made and tested.

Lal, Ravindra

1994-01-01

388

Crystal growth and terahertz wave generation of organic NLO crystals: OH1  

NASA Astrophysics Data System (ADS)

The organic nonlinear optical (NLO) crystal OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene) malononitrile) was grown by the seeded solution growth method with size up to 11×11×10 mm3. The cooling rate would affect the crystal formation and lead to the different shapes of OH1 crystals. The hydrogen-bond interactions between the OH1 molecules played a prominent influence on the molecular alignment and the direction of crystal growth. Furthermore, the OH1 crystals grown from the seeds on different orientations would form different morphologies. X-ray rocking curve showed good quality of the grown crystals. Continuous stiffness measurement showed that the hardness of the OH1 (100) and (111) plane was about 0.67 GPa and 0.51 GPa, while the Young's modulus was about 9.68 GPa and 11.91 GPa, respectively. The transmission spectra in the range of 0.5-20 ?m was measured and there was a transmission window appearing in the mid-infrared waveband of 4-6 ?m. With the OH1 crystal obtained, continuous THz wave radiation ranging from 0.25 to 3.0 THz was generated by an optical rectification method, which was two times as large as that generated from ZnTe in the low frequency band.

Li, Yin; Wu, Zhongan; Zhang, Xinyuan; Wang, Li; Zhang, Jianxiu; Wu, Yicheng

2014-09-01

389

Growth and characterization of 4-methyl benzene sulfonamide single crystals  

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

390

Transport phenomena of growth-in-gel zeolite crystallization in microgravity  

NASA Technical Reports Server (NTRS)

Secondary nucleation (SN) due to crystal sedimentation has been believed to be one of the major effects that causes smaller sizes of final zeolite crystals. The present investigation indicates that, in a reactor, this gravity-induced SN occurs only within a white opaque column termed the gel portion. Under normal gravity this portion shrinks to the bottom of the hydrothermal reactor, leaving a clear portion of solution at the top, due to depletion of the flocculated gel particles. Solution phase nucleation and crystallization is assumed and a correlation for the shrinkage is therefore derived, which shows good agreement with experimental observations. A non-dimensional parameter is suggested as a criterion for the occurrence of SN. Based on the parameter whether or not microgravity is beneficial to zeolite growth is discussed. Also, the growth mechanism and the transport phenomena in the absence of gravity are discussed.

Zhang, H.; Ostrach, S.; Kamotani, Y.

1993-01-01

391

Fractal growth of liquid crystals as a hysteresis phenomenon  

NASA Astrophysics Data System (ADS)

Fractal percolation growth of liquid crystal phases within a supercooled isotropic liquid medium has been observed in recent years. Notable examples include the B2 phase of `banana' mesogens [1] and the smectic C phase of a calamitic hydrogen-bonding liquid crystal [2]. Here we present a dynamical model that describes such fractal growth as well as the spherical growth conventionally observed for nematics and cholesterics. The essential idea is that the supercooled medium does not fully respond to the temperature quench immediately (hysteresis). Its fraction of space available for the phase transition only relaxes from 0 to 1 at some finite rate. Depending on the coupling between the relaxation and growth rates, the liquid crystal phase either grows as a percolation cluster of fractal dimension D 1.89 or approaches a spherical shape of Euclidean dimension D -> 2. The crossover behaviour from relatively slow to fast relaxation is thoroughly investigated. Possible causes of the hysteresis for fractal growth will be discussed. [1] I. Dierking, Liq. Cryst. Today 12(1), (2003), 1 [2] I. Dierking, Chan H. K., Culfaz F., McQuire S., Phys. Rev. E 70, (2004), 051701

Chan, Ho-Kei; Dierking, Ingo

2006-03-01

392

Follow up on the crystal growth experiments of the LDEF  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

393

Crystals  

NSDL National Science Digital Library

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.

Lawrence Hall of Science

2009-01-01

394

Multiscale Modeling of Crystal Growth and Microstructural Evolution of CdZnTe  

NASA Astrophysics Data System (ADS)

Crystal growth models and modeling tools for CdTe and CZT along with experimental melt-growth data will be presented and discussed. The emphasis will be on creating a multiscale-modeling framework that can be applied to solve portions of the crystal quality and reproducibility problem of CZT crystals grown for high-resolution radiation detectors. The growth models and methods include ab initio models of CdTe, ab initio molecular dynamics (MD) models CdTe, MD of solidification of CdTe, equilibrium growth defects in CdTe, and development of coarser-scale microstructural evolution models using phase field methods. These model and theory results will be discussed in terms of designing a multiscale approach to two relevant problems in CZT crystal growth, namely solid-liquid interface (SLI) stability and concurrent defect generation in the hot but cooling CZT solid. This dovetails with recent experimental research focused on the growth of CdTe from Te-rich melts with an emphasis on SLI instability. Experimental data on SLI instabilities will be featured as well as results of transmitted IR data on Te-particle distributions in as-grown CZT. A new mechanism of Te-particle genesis and spatial arrangement in CdTe and CZT is discussed in terms of a Rayleigh instability mechanism coupled with crystallographic SLI instabilities during growth. However, there are gaps in our capabilities at every length and time scale, plus gaps in building coarse-grained models from fine-scale models, in statistical representations of complex equilibria, and in understanding the complexities of solidification in ternary alloy systems where coupled thermal, concentration, stress, liquid flow, and SLI morphological fields exist. The talk concludes with an assessment of methods and approaches to address desired models and simulations of CZT solidification from the melt.

Henager, Charles, Jr.

2013-03-01

395

Crystal Growth, Thermal, Optical and Microhardness Studies of Tris (thiourea) Magnesium Sulphate:. a Semiorganic Nlo Material  

NASA Astrophysics Data System (ADS)

Single crystals of tris (Thiourea) magnesium sulphate (MTS) were grown from aqueous solution by low temperature solution growth technique. The grown crystals have been characterized by X-ray diffraction to confirm the formation of the crystalline phases. The presence of functional groups was identified by Fourier transform infrared spectroscopy. The optical transmission spectrum showed that a lower cut-off wavelength of MTS crystal is below 300 nm and it has a wide transparency window, which is suitable for second harmonic generation of laser in the blue region. The thermal stabilities were studied by differential thermal analysis (DTA) and thermo gravimetric analysis (TGA). Nonlinear optical characteristics of MTS were studied using Q-switched Nd:YAG laser (?=1064 nm). The micro-hardness studies reveal the mechanical properties of the grown crystals.

Pasupathi, G.; Philominathan, P.

396

Growth and characterization of piezoelectric Sr3Ga2Ge4O14 crystals.  

PubMed

Langasite (La3Ga5SiO14, LGS) and its isomorphs, have attracted much attention for their potential for surface acoustic wave (SAW) and bulk acoustic wave (BAW) applications. Among these homologous compounds, Sr3Ga2Ge4O14 (SGG) attracted our attention due to its superior piezoelectric properties and lower growth temperature. In this work, SGG single crystal has been grown successfully by the vertical Bridgman method with crucible-sealing technique. SGG wafers of 2 in. have been fabricated. The basic physical properties of SGG crystals were measured. The results demonstrate that piezoelectric and mechanical properties of SGG crystals are better than that of LGS crystal and it is expected to be a potential substrate material for SAW and BAW applications. PMID:16781749

Wu, Anhua; Xu, Jiayue; Zhou, Juan; Lu, Baoliang; Wu, Xianjun; Li, Xinhua; Qian, Guoxing

2006-12-22

397

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

PubMed

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

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

2015-03-01

398

Crystal growth, X-ray diffraction and nonlinear optical properties of Nb : KTiOPO 4 crystal  

Microsoft Academic Search

The crystal growth experiment of Nb:KTP crystal has been reported. The effect of Nb concentration and seed crystal on the Nb:KTP crystal growth has also been studied. The type II phase-matched (PM) second harmonic generation (SHG) cut-off wavelength and optimal SHG PM angle of Nd:YAG 1.0642?m laser and Nd:YAlO31.0795?m laser have been measured. It shows that Nb concentration has a

D. Y Zhang; H. Y Shen; W Liu; W. Z Chen; G. F Zhang; R. R Zeng; C. H Huang; W. X Lin; J. K Liang

2000-01-01

399

Experiment MA-028 crystal growth. [low gravity manufacturing of single crystals from Apollo/Soyuz Test Project  

NASA Technical Reports Server (NTRS)

A crystal growth experiment is reported on orbital space flights. The experiment was performed during the Apollo-Soyuz Test Project. The Crystal Growth Experiment assessed a novel process for growing single crystals of insoluble substances by allowing two or more reactant solutions to diffuse toward each other through a region of pure solvent in zero gravity. The experiment was entirely successful and yielded crystals of about the expected size, quality, and number.

Lind, D. M.

1976-01-01

400

Observation of Growth Pulsations in Polymer Dendritic Crystallization in PEO/PMMA Blend Films  

NSDL National Science Digital Library

We investigate the existence of growth pulsations in dendritic growth using polymer blend films where the crystallization morphology can be studied at high undercooling and over long timescales due to the relatively slow rate of crystallization.

Douglas, Jack

2002-01-01

401

Device and method for screening crystallization conditions in solution crystal growth  

NASA Technical Reports Server (NTRS)

A device and method for detecting optimum protein crystallization conditions and for growing protein crystals in either 1g or microgravity environments comprising a housing, defining at least one pair of chambers for containing crystallization solutions is presented. The housing further defines an orifice therein for providing fluid communication between the chambers. The orifice is adapted to receive a tube which contains a gelling substance for limiting the rate of diffusive mixing of the crystallization solutions. The solutions are diffusively mixed over a period of time defined by the quantity of gelling substance sufficient to achieve equilibration and to substantially reduce density driven convection disturbances therein. The device further includes endcaps to seal the first and second chambers. One of the endcaps includes a dialysis chamber which contains protein solution in which protein crystals are grown. Once the endcaps are in place, the protein solution is exposed to the crystallization solutions wherein the solubility of the protein solution is reduced at a rate responsive to the rate of diffusive mixing of the crystallization solutions. This allows for a controlled approach to supersaturation and allows for screening of crystal growth conditions at preselected intervals.

Carter, Daniel C. (inventor)

1995-01-01

402

Device and Method for Screening Crystallization Conditions in Solution Crystal Growth  

NASA Technical Reports Server (NTRS)

A device and method for detecting optimum protein crystallization conditions and for growing protein crystals in either 1 g or microgravity environments comprising a housing defining at least one pair of chambers for containing crystallization solutions. The housing further defines an orifice therein for providing fluid communication between the chambers. The orifice is adapted to receive a tube which contains a gelling substance for limiting the rate of diffusive mixing of the crystallization solutions. The solutions are diffusively mixed over a period of time defined by the quantity of gelling substance sufficient to achieve equilibration and to substantially reduce density driven convection disturbances therein. The device further includes endcaps to seal the first and second chambers. One of the endcaps includes a dialysis chamber which contains protein solution in which protein crystals are grown. Once the endcaps are in place. the protein solution is exposed to the crystallization solutions wherein the solubility of the protein solution is reduced at a rate responsive to the rate of diffusive mixing of the crystallization solutions. This allows for a controlled approach to supersaturation and allows for screening of crystal growth conditions at preselected intervals.

Carter, Daniel C. (Inventor)

1997-01-01

403

Vapour growth and characterization of beta indium sesquitelluride crystals  

NASA Astrophysics Data System (ADS)

Physical Vapour Deposition (PVD) provides stoichiometric crystals of different morphology, depending upon the materials, geometry of ampoules, temperature profiles, growth parameters and kinetics of crystallization. The crystal forms such as needles, platelets and spherulites of beta indium sesquitelluride (?-In2Te3) were produced by controlling the temperature of source and growth zones. The X-Ray Diffraction (XRD) and chemical analysis of the spherulitic crystals confirmed zinc blende structure with beta phase. Their resistivity (135.16 ? cm) at room temperature (300 K) was determined by van der Pauw method. The temperature dependence of DC conductivity was investigated using the conventional two-probe technique. The variation of dielectric constant (?1) and dielectric loss (tan ?) with temperature has been studied for different frequencies (1 kHz-1 MHz). The AC conductivity, ?ac(?) was found to vary with angular frequency as ?s, where s is the frequency exponent. The values of s lie very close to unity and show a slight decrease with increase in temperature, which indicate a Correlated Barrier Hopping (CBH) between centres forming Intimate Valence Alternation Pairs (IVAP). The activation energy for conduction ranges from 0.187 eV to 0.095 eV. The microhardness of ?-In2Te3 spherulites is found to be 353.5 kg/mm2, which is higher than that of other semiconducting chalcogenides. The results thus obtained on crystals grown from vapour phase open up ample possibilities for radiation detector applications.

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

2014-05-01

404

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

PubMed Central

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

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

2014-01-01

405

Liquid crystalline growth within a phase-field crystal model  

E-print Network

By using a phase-field crystal (PFC) model, the liquid-crystal growth of the plastic triangular phase is simulated with emphasis on crystal shape and topological defect formation. The equilibrium shape of a plastic triangular crystal (PTC) grown from a isotropic phase is compared with that grown from a columnar/smectic A (CSA) phase. While the shape of a PTC nucleus in the isotropic phase is almost identical to that of a classical PFC model, the shape of a PTC nucleus in CSA is affected by the orientation of stripes in the CSA phase, and irregular hexagonal, elliptical, octagonal, and rectangular shapes are obtained. Concerning the dynamics of the growth process we analyse the topological structure of the nematic-order, which starts from nucleation of $+\\frac{1}{2}$ and $-\\frac{1}{2}$ disclination pairs at the PTC growth front and evolves into hexagonal cells consisting of $+1$ vortices surrounded by six satellite $-\\frac{1}{2}$ disclinations. It is found that the orientational and the positional order do not evolve simultaneously, the orientational order evolves behind the positional order, leading to a large transition zone, which can span over several lattice spacings.

Sai Tang; Simon Praetorius; Rainer Backofen; Axel Voigt; Yan-Mei Yu; Jincheng Wang

2015-01-09

406

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

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

407

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

NASA Technical Reports Server (NTRS)

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.

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

408

III-V semiconductor solid solution single crystal growth  

NASA Technical Reports Server (NTRS)

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.

Gertner, E. R.

1982-01-01

409

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

NASA Astrophysics Data System (ADS)

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.

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

2011-07-01

410

Ultrasonic reactivation of phosphonate poisoned calcite during crystal growth.  

PubMed

The effect of ultrasonic irradiation (42,150 Hz, 17 W dm(-3)/7.1 W cm(-2)) on the growth of calcite in the presence of the inhibitor nitrilotris(methylene phosphonic acid) (NTMP) was investigated at constant composition conditions. In seeded growth experiments, it was found that the inhibiting effect of NTMP on crystal growth could be seriously mitigated under influence of ultrasonic irradiation. An approximately twofold increase in volumetric growth rate was achieved during ultrasonic irradiation, and recovery of the growth rate following inhibition was strongly enhanced compared to growth experiments without ultrasonic irradiation. The results could be explained in part by the physical effect of ultrasound that causes breakage and attrition of poisoned crystals, which resulted in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that there is also a chemical effect of ultrasound that plays an important role. Several breakdown products were identified, which showed that ultrasound caused the progressive loss of phosphonate groups from NTMP, probably by means of physicochemically generated free radicals and/or pyrolysis in the hot bubble-bulk interface. PMID:21463963

Boels, L; Wagterveld, R M; Witkamp, G J

2011-09-01

411

Time-dependent Protein-directed Growth of Gold Nanoparticles within a Single Crystal of Lysozyme  

SciTech Connect

Gold nanoparticles are useful in biomedical applications due to their distinct optical properties and high chemical stability. Reports of the biogenic formation of gold colloids from gold complexes has also led to an increased level of interest in the biomineralization of gold. However, the mechanism responsible for biomolecule-directed gold nanoparticle formation remains unclear due to the lack of structural information about biological systems and the fast kinetics of biomimetic chemical systems in solution. Here we show that intact single crystals of lysozyme can be used to study the time-dependent, protein-directed growth of gold nanoparticles. The protein crystals slow down the growth of the gold nanoparticles, allowing detailed kinetic studies to be carried out, and permit a three-dimensional structural characterization that would be difficult to achieve in solution. Furthermore, we show that additional chemical species can be used to fine-tune the growth rate of the gold nanoparticles.

H Wei; Z Wang; J Zhang; S House; Y Gao; L Yang; H Robinson; L Tan; H Xing; C Hou

2011-12-31

412

Time-dependent, protein-directed growth of gold nanoparticles within a single crystal of lysozyme  

SciTech Connect

Gold nanoparticles are useful in biomedical applications due to their distinct optical properties and high chemical stability. Reports of the biogenic formation of gold colloids from gold complexes has also led to an increased level of interest in the biomineralization of gold. However, the mechanism responsible for biomolecule-directed gold nanoparticle formation remains unclear due to the lack of structural information about biological systems and the fast kinetics of biomimetic chemical systems in solution. Here we show that intact single crystals of lysozyme can be used to study the time-dependent, protein-directed growth of gold nanoparticles. The protein crystals slow down the growth of the gold nanoparticles, allowing detailed kinetic studies to be carried out, and permit a three-dimensional structural characterization that would be difficult to achieve in solution. Furthermore, we show that additional chemical species can be used to fine-tune the growth rate of the gold nanoparticles.

Wei, H.; Robinson, H.; Wang, Z.; Zhang, J.; House, S.; Gao, Y.-G.; Yang, L.; Tan, L. H.; Xing, H.; Hou, C.; Robertson, I. M.; Zuo, J.-M.; Lu, Y.

2011-01-30

413

Semiconducting icosahedral boron arsenide crystal growth for neutron detection  

NASA Astrophysics Data System (ADS)

Semiconducting icosahedral boron arsenide, B12As2, is an excellent candidate for neutron detectors, thermoelectric converters, and radioisotope batteries, for which high quality single crystals are required. Thus, the present study was undertaken to grow B12As2 crystals by precipitation from metal solutions (nickel) saturated with elemental boron (or B12As2 powder) and arsenic in a sealed quartz ampoule. B12As2 crystals of 10-15 mm were produced when a homogeneous mixture of the three elements was held at 1150 °C for 48-72 h and slowly cooled (3.5 °C/h). The crystals varied in color and transparency from black and opaque to clear and transparent. X-ray topography (XRT), and elemental analysis by energy dispersive X-ray spectroscopy (EDS) confirmed that the crystals had the expected rhombohedral structure and chemical stoichiometry. The concentrations of residual impurities (nickel, carbon, etc.) were low, as measured by Raman spectroscopy and secondary ion mass spectrometry (SIMS). Additionally, low etch-pit densities (4.4×107 cm-2) were observed after etching in molten KOH at 500 °C. Thus, the flux growth method is viable for growing large, high-quality B12As2 crystals.

Whiteley, C. E.; Zhang, Y.; Gong, Y.; Bakalova, S.; Mayo, A.; Edgar, J. H.; Kuball, M.

2011-03-01

414

Predicting crystal structure by merging data mining with quantum mechanics  

E-print Network

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

Ceder, Gerbrand

415

Aqueous extract of Costus arabicus inhibits calcium oxalate crystal growth and adhesion to renal epithelial cells.  

PubMed

Costus arabicus L. (C. arabicus) is a plant used in Brazilian folk medicine to treat urolithiasis; however, its mechanism of action is unclear. The interaction between calcium oxalate (CaOx) crystals and the renal epithelium is important in calculogenesis, and compounds that modulate this process represent candidate therapeutic agents for stone prevention. Therefore, we assessed the inhibitory activity of C. arabicus on CaOx crystallization and the interaction of CaOx crystals with the renal epithelium. A seeded CaOx monohydrate (COM) crystallization system was used to study the effect of C. arabicus on crystal growth. Madin Darby canine kidney (MDCK) cells were used to study [(14)C] COM crystal adhesion in the presence and absence of an aqueous extract of C. arabicus. Cytotoxicity was assessed using a tetrazolium (MTS) cell proliferation assay. Aqueous extracts of C. arabicus decreased crystal growth in a concentration-dependent fashion. Precoating crystals with C. arabicus extract prevented their adhesion to MDCK cells, while pretreating cells did not show any effect. The extract was non-cytotoxic in concentrations of at least 1 mg/ml, which is likely above concentrations achievable in the urine following oral ingestion and excretion. No inhibitory activity was found in hexane, methyl chloride, n-butanol and ethyl acetate fractions of an ethanol extract of the herb. An aqueous extract of C. arabicus may disrupt calculogenesis by interacting with CaOx crystal surfaces. Activity was present in the aqueous extract; therefore, this agent may be bioavailable when administered orally. Fractionation results suggest that the active agent might be a polar polysaccharide. Further identification and characterization along these lines may be warranted. PMID:25652357

de Cógáin, Mitra R; Linnes, Michael P; Lee, Hyo Jung; Krambeck, Amy E; de Mendonça Uchôa, Julio Cezar; Kim, Sung-Hoon; Lieske, John C

2015-04-01

416

Applications of Mechanical Vapor Recompression to Evaporation and Crystallization  

E-print Network

Over the past 10-15 years, mechanical vapor recompression (MVR) has become the preferred system in many industrial evaporation and crystallization applications, because of its economy and simplicity of operation. In most instances, the need...

Outland, J. S.

417

Coupled convection, segregation, and thermal stress modeling of low and high pressure Czochralski crystal growth  

NASA Astrophysics Data System (ADS)

Czochralski (Cz) method is a dominant single crystal growth technology for microelectronics applications. The demand for large diameter, low defect density, and uniform single crystals has motivated extensive research on Cz Si growth as well as high pressure liquid-encapsulated Czochralski (HPLEC) growth of III-V compound crystals, e.g., GaAs and InP. The transport phenomena of Cz growth is quite complex, particularly under the industrial growth conditions. The relationship between the process parameters and material properties is further complicated by convective flows of the gas if a high pressure condition is to be maintained for the growth. Two important factors that greatly influence the quality of the crystals, are: (a) impurity and dopant distributions and (b) thermal stresses in the crystal. A comprehensive model which incorporates all of the major physical mechanisms of HPLEC growth, has been developed. For numerical simulation, a novel scheme of combined finite volume (FVM) and finite element (FEM) methods has been devised for thermal-mechanical calculations, that uses multizone adaptive grid generation (MAGG) technique for both FVM and FEM modules. By combining the FVM for thermal transport modeling and FEM for solid stress calculations, valuable experiences in both fields have been employed, and a reliable and robust predictive tool for a large class of problems has been developed. This requires minimum effort and cost in both software development and computing environment and shows a great promise. It makes the investigation of coupled thermal convection and stress phenomena much easier to perform. A two time-scale, mass conserving scheme has also been developed to perform macro-segregation calculations. Both Cz and HPLEC (high pressure liquid-encapsulant Czochralski) processes have been investigated. It is found that both melt and gas convective flows have significant influence on stress distribution in the crystal. It is shown that pure conduction-based models can not make accurate predictions of stresses in as-grown crystals. Use of a heat transfer coefficient to account for gas convection as many investigators have done in the past, is therefore not sufficient. Both melt and gas convection must be accounted in all future models if more accurate flow, temperature and stress calculations are desired. The predicted stress distributions agree qualitatively with experimental results. For macro-segregation analysis, it is found that the dopant distribution is controlled by the melt flow pattern.

Zou, Yunfeng

418

Growth Mechanism of Indium Tin Oxide Whiskers Prepared by Sputtering  

NASA Astrophysics Data System (ADS)

Whisker structures of indium tin oxide were prepared on a glass substrate by conventional sputtering using an indium-tin alloy target. Whisker structures grew well at higher temperatures than the crystallization temperature of In2O3 and the melting temperature of the In-Sn alloy, and also under the sputtering conditions of comparatively scarce oxygen and a high sputtering rate. These sputtering conditions correspond to the transition mode of reactive sputtering. The whisker structures were categorized into a structure consisting of many needles and a structure consisting of many trunks with side branches. Each whisker was a bcc single crystal growing along the <222> direction and had a spherical droplet-like structure on the tip. Consequently, it was revealed that In-Sn droplets acted as important cores of whisker growth. The indium tin oxide (ITO) whiskers were grown by a self-catalytic vapor-liquid-solid mechanism promoted by the supersaturation of indium vapor.

Takaki, Satoru; Aoshima, Yuki; Satoh, Ryohei

2007-06-01

419

Control of crystal growth in water purification by directional freeze crystallization  

NASA Technical Reports Server (NTRS)

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.

Conlon,