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1

The influence of precipitant concentration on macromolecular crystal growth mechanisms  

NASA Astrophysics Data System (ADS)

Atomic force microscopy was applied to investigate the influence of protein and precipitant (sodium-potassium tartrate) concentration on thaumatin crystal growth mechanisms. At constant protein concentration, a decrease of salt concentration from 0.8 to 0.085 M caused a transition of the crystal growth mechanism from two-dimensional nucleation to dislocation growth. At different, fixed concentrations of salt, the protein concentration, which does not induce multiple crystal nucleation, was increased from 8 to 60 mg/ml with corresponding increases in the tangential velocity of growth steps from 5 to 17.5 nm/s. Results from these experiments suggest that a highly concentrated protein solution, as might be found in a protein rich phase, may not induce crystal nucleation, but can promote crystal growth if screw dislocations are present in the crystal.

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

2001-11-01

2

Determining the Molecular Growth Mechanisms of Tetragonal Lysozyme Crystals  

NASA Technical Reports Server (NTRS)

Studies of the growth of tetragonal lysozyme crystals employing atomic force microscopy (AFM) have shown the advantages of this technique in investigating the growth mechanisms of protein crystals [1]. The resolution of these studies was in the micron range, which revealed surface features such as the occurrence of dislocations and 2D nucleation islands, similar to those found in inorganic systems. They clearly showed that the crystals grew by these surface growth mechanisms. However, the studies also revealed some surprising features, such as bimolecular growth step heights and pronounced growth anisotropies on the (110) face, which could not be explained. In previous studies we employed Periodic Bond Chain (PBC) theory to tetragonal lysozyme crystal growth and found that the crystals were constructed by strongly bonded molecular chains forming helices about the 43 axes [2,3]. The helices were connected to each other with weaker bonds. The growth process was shown to proceed by the formation of these 43 helices, resulting in bimolecular growth steps on the (110) face. It was also shown to explain many other observations on tetragonal lysozyme crystal growth. Although PBC analysis is not a new technique [4], it has not been widely used as the mechanisms predicted from it could not be experimentally verified. In this study the growth process of these crystals was investigated, particularly for the (110) face, employing some newly developed high resolution AFM techniques. These techniques allowed individual lysozyme molecules on the crystal faces to be resolved and predictions from PBC analyses to be tested. The analyses had shown that of the two possible packing arrangements on (110) faces, only one would actually occur. Employing the first of the newly developed techniques, these faces were scanned by high resolution AFM. The resulting images were then compared with the theoretically constructed images for the two possible packing arrangements on the (110) face. The theoretical images were constructed by convolution of the crystal surface shape obtained from crystallographic data with the AFM tip shape. The comparison confirmed the prediction that the molecular packing arrangement of these faces corresponded to that for complete 43 helices. The second AFM technique that was developed was used to follow the growth process by measuring the dimensions of individual growth units on the (110) face. Linescans across a growth step, performed near the saturation limit of the crystals, allowed the growth unit dimensions to be measured. These measurements showed that growth on the (110) face proceeded by the formation of new 43 helices from the addition of at least tetramer units in the [110] direction. In the [001] direction growth proceeded by the addition of various aggregate units corresponding to the 4(sub 3) helices.

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

1998-01-01

3

Crystal growth mechanisms of the (0 1 0) face of ?-lactose monohydrate crystals  

NASA Astrophysics Data System (ADS)

The growth rates of the (0 1 0) face of ?-lactose monohydrate crystals were measured at 30, 40 and 50 °C in the relative supersaturation range 0.55-2.33 in aqueous solutions. The mechanisms of growth were investigated. Spiral growth was found to be the mechanism of growth up to a critical relative supersaturation ( s-1) crit=1.9 at 30 °C. Above the critical relative supersaturation, the crystal growth mechanisms were predicted to change. All growth models fit equally well to the growth rates. No two-dimensional nucleation was observed above critical supersaturation by AFM. On the other hand increased step height and roughness on the edges of steps were observed. It was concluded that the growth mechanism of the (0 1 0) face of ?-lactose monohydrate crystal is spiral growth. A parabolic relationship was obtained below critical supersaturation followed by a linear relationship with relative supersaturation.

Dincer, T. D.; Ogden, M. I.; Parkinson, G. M.

2009-04-01

4

Growth Mechanism of the (110) Face of Tetragonal Lysozyme Crystals  

NASA Technical Reports Server (NTRS)

The measured macroscopic growth rates of the (110) face of tetragonal lysozyme show an unexpectedly complex dependence on the supersaturation. In earlier studies it has been shown that an aggregate growth unit could account for experimental growth-rate trends. In particular molecular packing and interactions in the growth of the crystal were favored by completion of the helices along the 4, axes. In this study the molecular orientations of the possible growth units and the molecular growth mechanism were identified. This indicated that growth was a two-step process: aggregate growth units corresponding to the 4, helix are first formed in the bulk solution by stronger intermolecular bonds and then attached to the crystal face by weaker bonds. A more comprehensive analysis of the measured (110) growth rates was also undertaken. They were compared with the predicted growth rates from several dislocation and two-dimensional nucleation growth models, employing tetramer and Octamer growth units in polydisperse solutions and monomer units in monodisperse solutions. The calculations consistently showed that the measured growth rates followed the expected model relations with octamer growth units, in agreement with the predictions from the molecular level analyses.

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

1997-01-01

5

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

6

Molecular View of Protein Crystal Growth: Molecular Interactions, Surface Reconstruction and Growth Mechanism  

NASA Technical Reports Server (NTRS)

Studies of the growth and molecular packing of tetragonal lysozyme crystals suggest that there is an underlying molecular growth mechanism, in addition to the classical one involving screw dislocation/2D) nucleation growth. These crystals are constructed by strongly bonded molecular chains forming helices about the 43 axes. The helices are connected to each other by weaker bonds. Crystal growth proceeds by the formation of these 4(sub 3) helices, which would explain some unexpected observations by earlier investigators, such as bimolecular growth steps on the (110) face. Another consequence of these molecular considerations is that only one of two possible packing arrangements could occur on the crystal faces and that their growth unit was at least a tetramer corresponding to the 4(sub 3) helix. Two new high resolution atomic force microscopy (AFM) techniques were developed to directly confirm these predictions on tetragonal lysozyme crystals. Most earlier investigations of protein crystal growth with AFM were in the low resolution mode which is adequate to investigate the classical growth mechanisms, but cannot resolve molecular features and mechanisms. Employing the first of the newly developed techniques, high resolution AFM images of the (110) face were compared with the theoretically constructed images for the two possible packing arrangements on this face. The prediction that the molecular packing arrangement of these faces corresponded to that for complete 4(sub 3) helices was confirmed in this manner. This investigation also showed the occurrence of surface reconstruction on protein crystals. The molecules on the surface of the (110) face were found to pack closer along the 4(sub 3) axes than those in the interior. The second new AFM technique was used to follow the growth process by measuring the dimensions of individual growth units on the (110) face. Linescans across a growth step, performed near the saturation limit of the crystals, allowed the growth unit dimensions to be measured as they were being incorporated into the crystal. These measurements showed that growth on the (110) face proceeded by the formation of new 4(sub 3) helices from the addition of many growth units of at least tetramer size. This is the first time that a time-resolved AFM technique has been used to observe individual molecular events during crystal growth.

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

2000-01-01

7

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

8

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

9

Growth of (101) Faces of Tetragonal Lysozyme Crystals: Determination of the Growth Mechanism  

NASA Technical Reports Server (NTRS)

Measurements of the macroscopic growth rates of the (101) face of tetragonal lysozyme crystals indicate an unusual dependence on the supersaturation (Forsythe, Nadarajah & Pusey, 1998), similar to that observed for the (110) face. As done before for the (110) face, in this study the surface packing arrangement for the (101) face was constructed, based on earlier microscopic observations and theoretical analysis of the internal molecular packing. This allowed the minimum growth unit for this face to be identified as a tetramer corresponding to a single turn of helices centered about the 4(sub 3) axes, and the minimum growth step to be of unimolecular height. A macroscopic mathematical model for the growth of the (101) face was developed, based on the formation of aggregate growth units in solution and the addition of a unit to the crystal face by dislocation and two-dimensional nucleation mechanisms. The calculations showed that the best fits were obtained for tetramer or octamer growth units in this model, indicating that average size of the growth unit participating in the growth process was between these two sizes.

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

1998-01-01

10

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

11

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

12

Crystal growth, structural, optical, mechanical and thermal properties of a new nonlinear optical single crystal: L-Ornithine monohydrochloride  

NASA Astrophysics Data System (ADS)

Amino acid family crystals exhibit excellent nonlinear optical and electro optical properties. L-Ornithine monohydrochloride single crystal, belongs to the amino acid group, was grown by the slow evaporation solution growth technique at room temperature. The grown crystals were characterized by single crystal and powder X-ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, TGA, DTA and DSC analyses. UV-vis-NIR spectrum shows excellent transmission in the UV, visible and NIR region (300-1600 nm). The mechanical properties of grown crystals were studied using Vickers microhardness tester. Its second harmonic generation efficiency was tested using Nd:YAG laser and is 1.25 times that of KDP.

Balakrishnan, T.; Ramamurthi, K.

2009-03-01

13

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

14

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

15

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

16

Characterization of the growth mechanism of YIG crystal fibers using the laser heated pedestal growth method  

NASA Astrophysics Data System (ADS)

Yttrium iron garnet (YIG, Y 3Fe 5O 12) single-crystal fibers were grown by the laser heated pedestal growth (LHPG) method. Different compositions, with various Y 2O 3 and Fe 2O 3 ratios seeds were used. The microstructure and the compositional variation of the obtained crystals show that YIG single-crystal fibers could be directly grown at the stable freezing interface when the melt had a composition of 78-87 mol% Fe 2O 3. When the seed's Fe 2O 3 concentration was below 78 mol%, the yttrium orthoferrite (YFeO 3) would crystallize out until the composition of the melt increased along the liquidus curve until it needed a concentration of 78 mol% Fe 2O 3 or higher, whereupon YIG started to crystallize from the liquid. With the LHPG method, however, when Fe-rich ceramic rod used as a seed was employed to grow YIG crystal, the crystallographic orientation was indefinite. Therefore, YIG single-crystal fibers with the desired crystallographic orientation could only be obtained using a two-pass method. During the forward pass, YIG single crystal could be directly grown using a Fe-rich solvent, while during the backward pass, the crystallographic orientation of the grown crystal would be the same as that of the YIG seed.

Mao, Tze-Chern; Chen, Jyh-Chen; Hu, Chao-Chang

2005-08-01

17

Determination of the crystal growth mechanism of KCl in ethanol?water system  

NASA Astrophysics Data System (ADS)

The mechanism of crystal growth of KCl in ethanol-water system is studied by Nielsen's map-model, and the growth rate is estimated by the induction time (nucleation rate, growth rate) function in a salting-out crystallization system. In the experiments, the induction time and the particle size distribution of the final product were measured, and the solid-liquid interfacial tension was calculated from the induction period data. The map of rate control of crystal-growth for the KCl-ethanol-water salting out system was constructed by taking into consideration that the liquid-vapour interfacial tension varied with the variation of the ethanol concentration, and, as a consequence, the solid-liquid interfacial tension varied as well. As a result, diffusion controlled crystal growth was obtained as a rate-determining step for supersaturation ratios 0.01<0.45. For determining the crystal growth rate, the nucleation rate was estimated from the experimental average particle number and induction period, applying the assumption that all nuclei were born during the induction period. The results, obtained by using linear and non-linear regressions, have appeared to be in good agreement with the data published in the literature.

Liszi, I.; Hasznosné-Nezdei, M.; Lakatos, B. G.; Sapundzhiev, Ts. J.; Popov, R. G.

1999-03-01

18

Mechanisms of 1D crystal growth in reactive vapor transport: indium nitride nanowires.  

PubMed

Indium nitride (InN) nanowire synthesis using indium (In) vapor transport in a dissociated ammonia environment (reactive vapor transport) is studied in detail to understand the nucleation and growth mechanisms involved with the so-called "self-catalysis" schemes. The results show that the nucleation of InN crystal occurs first on the substrate. Later, In droplets are formed on top of the InN crystals because of selective wetting of In onto InN crystals. Further growth via liquid-phase epitaxy through In droplets leads the growth in one dimension (1D), resulting in the formation of InN nanowires. The details about the nucleation and growth aspects within these self-catalysis schemes are rationalized further by demonstrating the growth of heteroepitaxially oriented nanowire arrays on single-crystal substrates and "tree-like" morphologies on a variety of substrates. However, the direct nitridation of In droplets using dissociated ammonia results in the spontaneous nucleation and basal growth of nanowires directly from the In melt surface, which is quite different from the above-mentioned nucleation mechanism with the reactive vapor transport case. The InN nanowires exhibit a band gap of 0.8 eV, whereas the mixed phase of InN and In(2)O(3) nanowires exhibit a peak at approximately 1.9 eV in addition to that at 0.8 eV. PMID:16089500

Vaddiraju, Sreeram; Mohite, Aditya; Chin, Alan; Meyyappan, M; Sumanasekera, Gamini; Alphenaar, Bruce W; Sunkara, Mahendra K

2005-08-01

19

In situ imaging of silicalite-1 surface growth reveals the mechanism of crystallization.  

PubMed

The growth mechanism of silicalite-1 (MFI zeolite) is juxtaposed between classical models that postulate silica molecules as primary growth units and nonclassical pathways based on the aggregation of metastable silica nanoparticle precursors. Although experimental evidence gathered over the past two decades suggests that precursor attachment is the dominant pathway, direct validation of this hypothesis and the relative roles of molecular and precursor species has remained elusive. We present an in situ study of silicalite-1 crystallization at characteristic synthesis conditions. Using time-resolved atomic force microscopy images, we observed silica precursor attachment to crystal surfaces, followed by concomitant structural rearrangement and three-dimensional growth by accretion of silica molecules. We confirm that silicalite-1 growth occurs via the addition of both silica molecules and precursors, bridging classical and nonclassical mechanisms. PMID:24833388

Lupulescu, Alexandra I; Rimer, Jeffrey D

2014-05-16

20

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

21

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

22

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

23

Studies on surface micromorphology and growth mechanism of nonlinear optical crystal: L-arginine hydrochlorobromo monohydrate  

NASA Astrophysics Data System (ADS)

Chemical etching technique has been used for the first time to reveal dislocation structure of the L-arginine hydrochlorobromo monohydrate, C 6H 14N 4O 2HClBr.H 2O crystal on the polished {1 0 0}, {0 1 0} and {0 0 1} faces. Fast dissolving etchants could produce etch pits only on the 'F' faces but they have no effect on the 'S' face. Selective behaviour of the etchants for revealing inclined dislocations and cooperating spirals has been demonstrated. Presence of growth spirals on (1 0 0) face indicates that growth of this face is governed by screw dislocation mechanism.

Pal, Tanusri; Kar, Tanusree

2006-03-01

24

Stability of amorphous pharmaceutical solids: crystal growth mechanisms and effect of polymer additives.  

PubMed

We review recent progress toward understanding and enhancing the stability of amorphous pharmaceutical solids against crystallization. As organic liquids are cooled to become glasses, fast modes of crystal growth can emerge. One such growth mode, the glass-to-crystal or GC mode, occurs in the bulk, and another exists at the free surface, both leading to crystal growth much faster than predicted by theories that assume diffusion defines the kinetic barrier of crystallization. These phenomena have received different explanations, and we propose that GC growth is a solid-state transformation enabled by local mobility in glasses and that fast surface crystal growth is facilitated by surface molecular mobility. In the second part, we review recent findings concerning the effect of polymer additives on crystallization in organic glasses. Low-concentration polymer additives can strongly inhibit crystal growth in the bulk of organic glasses, while having weaker effect on surface crystal growth. Ultra-thin polymer coatings can inhibit surface crystallization. Recent work has shown the importance of molecular weight for crystallization inhibitors of organic glasses, besides "direct intermolecular interactions" such as hydrogen bonding. Relative to polyvinylpyrrolidone, the VP dimer is far less effective in inhibiting crystal growth in amorphous nifedipine. Further work is suggested for better understanding of crystallization of amorphous organic solids and the prediction of their stability. PMID:22434258

Sun, Ye; Zhu, Lei; Wu, Tian; Cai, Ting; Gunn, Erica M; Yu, Lian

2012-09-01

25

Growth mechanism of KAP crystals: surface morphology of the (010) face  

NASA Astrophysics Data System (ADS)

The surface morphology of the (010) face of KAP crystals growth from aqueous solution at low supersaturations (0.03 divided by 0.04) was investigated by the optical and electron microscopy using the gold decoration technique. The variety of growth patterns has been revealed: macroscopic hillocks, shallow hillocks, microscopic hillocks and numerous 2D nuclei. The macroscopic hillocks and smaller polygonal hillocks are formed by a group of cooperating dislocations or by a single dislocation. The density of observed shallow hillocks is higher than the dislocation density. The results reveal that, at low supersaturations, growth of the (010) face occurs by combined spiral and 2D nucleation mechanisms. The influence of low concentrations of organic additives on surface morphology of the (010) face has also been studied. The additives stimulate 2D nucleation and they increase the spread velocity of steps. The growth promoting effect of impurities is discussed in terms of the above data.

Kuznetsov, V. A.; Samotoin, N. D.; Okhrimenko, T. M.; Rak, Miroslawa

1999-04-01

26

Crystal growth under nonuniform conditions  

NASA Astrophysics Data System (ADS)

The tendency of crystals to maintain uniform growth despite spatial fluid mechanical variations is a characteristic feature of crystals, distinguishing them from ordinary mass transport processes. Due to this feature there exists a non-uniform supersaturation over the surface. A general crystal growth theory which allows for both uniform growth and supersaturation variation, predicts a minimum supersaturation below which uniform growth is not possible. A crystal growth experiment employing an impinging jet is suggested for the study of the effect upon growth quality of supersaturation variation. It is pointed out that it is possible in principle to determine the adsorption coefficient, a fundamental growth parameter, independently, without resorting to multiparameter fitting.

Kumar, C.; Estrin, J.

1981-02-01

27

Supra- and nanocrystallinity: specific properties related to crystal growth mechanisms and nanocrystallinity.  

PubMed

The natural arrangement of atoms or nanocrystals either in well-defined assemblies or in a disordered fashion induces changes in their physical properties. For example, diamond and graphite show marked differences in their physical properties though both are composed of carbon atoms. Natural colloidal crystals have existed on earth for billions of years. Very interestingly, these colloidal crystals are made of a fixed number of polyhedral magnetite particles uniform in size. Hence, opals formed of assemblies of silicate particles in the micrometer size range exhibit interesting intrinsic optical properties. A colorless opal is composed of disordered particles, but changes in size segregation within the self-ordered silica particles can lead to distinct color changes and patterning. In this Account, we rationalize two simultaneous supracrystal growth processes that occur under saturated conditions, which form both well-defined 3D superlattices at the air-liquid interface and precipitated 3D assemblies with well-defined shapes. The growth processes of these colloidal crystals, called super- or supracrystals, markedly change the mechanical properties of these assemblies and induce the crystallinity segregation of nanocrystals. Therefore, single domain nanocrystals are the primary basis in the formation of these supracrystals, while multiply twinned particles (MTPs) and polycrystals remain dispersed within the colloidal suspension. Nanoindentation measurements show a drop in the Young's moduli for interfacial supracrystals in comparison with the precipitated supracrystals. In addition, the value of the Young's modulus changes markedly with the supracrystal growth mechanism. Using scanning tunneling microscopy/spectroscopy, we successfully imaged very thick supracrystals (from 200 nm up to a few micrometers) with remarkable conductance homogeneity and showed electronic fingerprints of isolated nanocrystals. This discovery of nanocrystal fingerprints within supracrystals could lead to promising applications in nanotechnology. PMID:23003577

Pileni, M P

2012-11-20

28

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.

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

2012-01-01

29

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

NASA Astrophysics Data System (ADS)

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

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

2003-08-01

30

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

31

Determining the Molecular Growth Mechanisms of Protein Crystal faces by Atomic Force Microscopy  

NASA Technical Reports Server (NTRS)

A high resolution atomic force microscopy (AFM) study had shown that the molecular packing on the tetragonal lysozyme (110) face corresponded to only one of two possible packing arrangements, suggesting that growth layers on this face were of bimolecular height (Li et al., 1998). Theoretical analyses of the packing had also indicated that growth of this face should proceed by the addition of growth units of at least tetramer size corresponding to the 43 helices in the crystal. In this study an AFM linescan technique was devised to measure the dimensions of individual growth units on protein crystal faces. The growth process of tetragonal lysozyme crystals was slowed down by employing very low supersaturations. As a result images of individual growth events on the (110) face were observed, shown by jump discontinuities in the growth step in the linescan images. The growth unit dimension in the scanned direction was obtained by suitably averaging these images. A large number of scans in two directions on the (110) face were performed and the distribution of lysozyme aggregate sizes were obtained. A variety of growth units, all of which were 43 helical lysozyme aggregates, were shown to participate in the growth process with a 43 tetramer being the minimum observed size. This technique represents a new application for AFM allowing time resolved studies of molecular process to be carried out.

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

1998-01-01

32

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

33

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

34

Growth, thermal and mechanical properties of new nonlinear optical barium bis-paranitrophenolate paranitrophenol tetrahydrate single crystal  

SciTech Connect

Barium bis paranitrophenolate paranitrophenol tetrahydrate, a new semiorganic nonlinear optical single crystal has been grown by slow evaporation solution growth technique at room temperature of 30 deg. C. Crystal of dimensions of 29 mm x 11 mm x 5 mm was obtained in a period of 30 days. X-ray diffraction analysis reveal the newness of the crystal structure belonging to the orthorhombic class with lattice parameters a = 19.899(5) A, b = 28.019(8) A, c = 10.745(4) A and {alpha} = {beta} = {gamma} = 90{sup o}. The grown crystal is examined for its nonlinear optical nature with Kurtz powder technique after being sieved for particle sizes between 5 and 100 {mu}m and analyzed for its thermal and mechanical properties. The effective nonlinear optical coefficient being 16 times greater than that of KDP crystal, good thermal stability up to 120 deg. C with the Meyer's constant n < 2 helps fashion the crystal towards device geometry.

Varjula, A. Jonie; Ramanand, A. [Department of Physics, Loyola College, Chennai 600034 (India); Das, S. Jerome [Department of Physics, Loyola College, Chennai 600034 (India)], E-mail: sjeromedas2004@yahoo.com

2008-02-05

35

Surface characterization and growth mechanism of laminated Ti 3SiC 2 crystals fabricated by hot isostatic pressing  

NASA Astrophysics Data System (ADS)

Laminated Ti 3SiC 2 crystals were prepared by hot isostatic pressing from Ti, Si, C and Al powders with NaCl additive in argon at 1350 °C. The morphology and microstructure of Ti 3SiC 2 crystals were investigated by means of XRD, SEM, and TEM. The high symmetry and crystalline was revealed by high resolution transmission electronic microscope (HRTEM) and selected area electron diffraction (SAED). The growth mechanism of Ti 3SiC 2 crystals controlled by two-dimensional nucleation was put forward. The growth pattern of layered steps implies that the growth of the (0 0 2) face should undergo two steps, the intermittent two-dimensional nucleation and the continuous lateral spreading of layers on growth faces.

Wu, Qiong; Li, Changsheng; Tang, Hua

2010-09-01

36

Growth, Mechanical and Thermal Properties of Bi4Si3O12 Single Crystals  

NASA Astrophysics Data System (ADS)

Bi4Si3O12 (BSO) is an excellent scintillation crystal, and is becoming the desirable candidate for dual-readout calorimeters in high-energy physics. In this work, high quality BSO crystals are successfully grown by the modified Bridgman method. For the first time, its mechanical and thermal properties are investigated and compared with those of the famous scintillation crystal Bi4Ge3O12 (BGO). The Vickers hardness and fracture toughness of BSO crystal are higher than those of BGO crystal. Its specific heat, thermal diffusivity and thermal conductivity are measured to be 0.319 J·g-1K-1, 1.54 mm2·s-1 and 3.29 W·m-1K-1 at 298 K, respectively. The average thermal expansion coefficient is calculated to be 7.07 × 10-6K-1 from 300 to 1173 K. Compared with BGO crystal, BSO crystal possesses larger specific heat, thermal conductivity and smaller thermal expansion. These results indicate that BSO crystals possess better mechanical and thermal properties, which will benefit its practical applications.

Shen, Hui; Xu, Jia-Yue; Ping, Wei-Jie; He, Qing-Bo; Zhang, Yan; Jin, Min; Jiang, Guo-Jian

2012-07-01

37

Synthesis, growth, optical, mechanical, dielectric and thermal properties of 4-chloro-4'-chlorobenzylidene aniline single crystal.  

PubMed

The organic material 4-chloro-4'-chlorobenzylidene aniline (CCBA) was synthesized and confirmed by NMR and FTIR spectral analyses. CCBA crystal was grown from chloroform by slow evaporation at room temperature and the single crystal cell parameters were determined by single crystal X-ray diffraction method. The perfection of the grown crystal was analyzed by high resolution X-ray diffraction rocking curve analysis. Fluorescence spectrum indicated violet emission at 428 nm. The range of optical absorbance was ascertained by recording UV-vis-NIR spectrum. Load dependant microhardness measurements on this crystal revealed the mechanical behavior of the material. Stiffness constant, Meyer index and yield strength of CCBA crystal were calculated. Dielectric studies were carried out to estimate the dielectric parameters of the grown crystal in the frequency range from 100 Hz to 100 kHz. The thermal behavior of CCBA was investigated using differential scanning calorimetry (DSC) and no phase transition was identified in the temperature region 30-100°C. Further, the CCBA crystal was subjected to open aperture Z-scan studies in order to investigate the third order nonlinear optical (NLO) properties of CCBA crystal. PMID:21802980

Subashini, A; Bhagavannarayana, G; Ramamurthi, K

2011-11-01

38

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

NASA Astrophysics Data System (ADS)

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

Arumanayagam, T.; Ananth, S.; Murugakoothan, P.

2012-11-01

39

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

SciTech Connect

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

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

2012-09-15

40

The influence of low frequency mechanical vibrations on the growth of single crystals  

NASA Technical Reports Server (NTRS)

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

Feigelson, R. S.; Elwell, D.

1985-01-01

41

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."

42

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

43

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.

2013-01-01

44

The role of hydration and complexing in the mechanism of impurity influence on crystal growth  

NASA Astrophysics Data System (ADS)

The influence of impurities of chlorides and nitrates of divalent Ca2+ and Ba2+ cations on the kinetic growth of potassium dihydrophosphate KH2PO4 crystals at a saturation temperature of 323 K and relative supersaturation of 0.03 has been investigated experimentally. It is established that the impurity acts differently, depending on the face index, the impurity concentration, cation hydration, and the stability of the complexes formed in the solution by impurity salt ions. A model is proposed to explain the different influence of impurity ions on the growth of crystal faces. This influence is determined by the different hydration of cations and enhanced association of cations and anions of impurity salts in the surface layer with a lower dielectric constant.

Efremova, E. P.; Okhrimenko, T. M.; Lyashchenko, A. K.

2012-05-01

45

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

PubMed

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

Liang, Yuan-Chang; Zhong, Hua

2013-01-01

46

Protein crystal growth  

NASA Technical Reports Server (NTRS)

Proteins account for 50% or more of the dry weight of most living systems and play a crucial role in virtually all biological processes. Since the specific functions of essentially all biological molecules are determined by their three-dimensional structures, it is obvious that a detailed understanding of the structural makeup of a protein is essential to any systematic research pertaining to it. At the present time, protein crystallography has no substitute, it is the only technique available for elucidating the atomic arrangements within complicated biological molecules. Most macromolecules are extremely difficult to crystallize, and many otherwise exciting and promising projects have terminated at the crystal growth stage. There is a pressing need to better understand protein crystal growth, and to develop new techniques that can be used to enhance the size and quality of protein crystals. There are several aspects of microgravity that might be exploited to enhance protein crystal growth. The major factor that might be expected to alter crystal growth processes in space is the elimination of density-driven convective flow. Another factor that can be readily controlled in the absence of gravity is the sedimentation of growing crystal in a gravitational field. Another potential advantage of microgravity for protein crystal growth is the option of doing containerless crystal growth. One can readily understand why the microgravity environment established by Earth-orbiting vehicles is perceived to offer unique opportunities for the protein crystallographer. The near term objectives of the Protein Crystal Growth in a Microgravity Environment (PCG/ME) project is to continue to improve the techniques, procedures, and hardware systems used to grow protein crystals in Earth orbit.

Bugg, Charles E.

1993-01-01

47

On the mechanism of impurity influence on growth kinetics and surface morphology of KDP crystals—II: experimental study of influence of bivalent and trivalent impurity ions on growth kinetics and surface morphology of KDP crystals  

NASA Astrophysics Data System (ADS)

The experimental results of the influence of bivalent (Ni 2+, Co 2+, Fe 2+, Mn 2+, Ba 2+, Ca 2+, Sr 2+) and trivalent (Fe 3+, Mn 3+, Y 3+, La 3+) impurity ions on growth rates and surface morphology of potassium dihydrogen phosphate (KDP) crystal faces are presented and discussed. The analysis of the obtained results is performed in conjunction with the theoretical results presented in our previous paper (Rak et al., J. Crystal Growth) concerning modelling of structure of defect centres formed in KDP crystals by these impurities. It is found that the effect of Me 3+ ions is caused mainly by their adsorption on crystal faces while, in case of Me 2+impurities, the ions incorporated into surface crystal layer and the lattice stresses generated by them play a leading role in the effect of bivalent impurities on growth kinetics and surface morphology (the structural mechanism of the impurity influence-SMII).

Eremina, T. A.; Kuznetsov, V. A.; Eremin, N. N.; Okhrimenko, T. M.; Furmanova, N. G.; Efremova, E. P.; Rak, Miros?awa

2005-01-01

48

Studies on growth defects and mechanical properties of nonlinear optical crystal: L-arginine hydrofluoride  

NASA Astrophysics Data System (ADS)

Chemical etching technique has been used for the first time to reveal dislocation structure of the cleavage plane of L-arginine hydrofluoride monohydrate (LAHF). Selective behaviour of the etchants for revealing macrosteps and cooperating spirals has been demonstrated. Presence of growth spirals on (1 0 0) face indicates that growth of this face is governed by screw dislocation mechanism. Microhardness measurement reveals that LAHF is harder than LAP.

Pal, Tanusri; Kar, Tanusree

2005-03-01

49

Crystal Growth Furnace (CGF)  

NASA Technical Reports Server (NTRS)

Crystal Growth Furnace (CGF) without the EAC internal support structure. Flown on USML-1 and USML-2. The Principal Investigators on these flights were: Larson, Lehoczky, Matthiesen, Wiedemeier. Processed 6 samples on USML-1 and 7 samples on USML-2.

1991-01-01

50

Rapid crystallization of faujasitic zeolites: mechanism and application to zeolite membrane growth on polymer supports.  

PubMed

Zeolites are microporous, crystalline aluminosilicates with the framework made up of T-O-T (T = Si, Al) bonds and enclosed cages and channels of molecular dimensions. Influencing and manipulating the nucleation and growth characteristics of zeolites can lead to novel frameworks and morphologies, as well as decreased crystallization time. In this study, we show that manipulating the supersaturation during synthesis of zeolite X/Y (FAU) via dehydration led to extensive nucleation. Controlled addition of water to this nucleated state promotes the transport of nutrients, with a 4-fold increase in the rate of crystal growth, as compared to conventional hydrothermal process. Structural signature of the nucleated state was obtained by electron microscopy, NMR, and Raman spectroscopy. This extensively intermediate nucleated state was isolated and used as the starting material for zeolite membrane synthesis on porous polymer supports, with membrane formation occurring within an hour. With this time frame for growth, it becomes practical to fabricate zeolite/polymer membranes using roll-to-roll technology, thus making possible new commercial applications. PMID:24758695

Severance, Michael; Wang, Bo; Ramasubramanian, Kartik; Zhao, Lin; Ho, W S Winston; Dutta, Prabir K

2014-06-17

51

Mechanisms for Species-Selective Oriented Crystal Growth at Organic Templates  

SciTech Connect

Langmuir monolayers floating on supersaturated aqueous subphases can act as templates for the growth of oriented inorganic films--a 'bioinspired' nucleation process. We have performed in situ grazing incidence x-ray diffraction studies of the selective nucleation of BaClF and BaF2 under fatty acid monolayers. The arrangement of the fatty acid headgroups, the monolayer charge, and ion-specific effects all play important roles in selecting the inorganic species. When the monolayer is in a neutral state, both BaClF and BaF2 nucleate at the interface and are well aligned, but when the monolayer headgroup is deprotonated, only oriented BaF2 grows at the interface. We also observe an enhanced alignment of BaF2 crystals during growth from highly supersaturated solutions, presumably due to reorganization of preformed crystals at the organic template. These results show that a delicate interplay between multiple factors governs the oriented growth of inorganic films at organic templates.

Kewalramani,S.; Kim, K.; Evmenenko, G.; Zschack, P.; Karapetrova, E.; Bai, J.; Dutta, P.

2007-01-01

52

Crystal growth and crystallography  

NASA Technical Reports Server (NTRS)

Selected topics that may be of interest for both crystal-structure and crystal-growth communities are overviewed. The growth of protein crystals, along with that of some other compounds, is one of the topics, and recent insights into related phenomena are considered as examples of applications of general principles. The relationship between crystal growth shape and structure is reviewed and an attempt to introduce semiquantitative characterization of binding for proteins is made. The concept of kinks for complex structures is briefly discussed. Even at sufficiently low supersaturations, the fluctuation of steps may not be sufficient to implement the Gibbs-Thomson law if the kink density is low enough. Subsurface ordering of liquids and growth of rough interfaces from melts is discussed. Crystals growing in microgravity from solution should be more perfect if they preferentially trap stress-inducing impurities, thus creating an impurity-depleted zone around themselves. Evidently, such a zone is developed only around the crystals growing in the absence of convection. Under terrestrial conditions, the self-purified depleted zone is destroyed by convection, the crystal traps more impurity and grows stressed. The stress relief causes mosaicity. In systems containing stress-inducing but poorly trapped impurities, the crystals grown in the absence of convection should be worse than those of their terrestrial counterparts.

Chernov, A. A.

1998-01-01

53

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

SciTech Connect

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

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

2011-11-15

54

The secrets of crystal growth  

SciTech Connect

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

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

1996-11-01

55

Protein crystal growth  

NASA Technical Reports Server (NTRS)

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

2001-01-01

56

Shaped Crystal Growth  

NASA Astrophysics Data System (ADS)

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

Tatartchenko, Vitali A.

57

Protein crystal growth in low gravity  

NASA Technical Reports Server (NTRS)

The mechanisms involved in protein crystallization and those parameters which influence the growth process and crystalline perfection were studied. The analysis of the flows around growing crystals is detailed. The preliminary study of the growth of isocitrate lyase and the crystal morphologies found are discussed. Preliminary results of controlled nucleation studies are presented.

Feigelson, Robert S.

1989-01-01

58

Infrared spectroscopic study of polytypic effects on the crystal-growth mechanism of n-hexatriacontane (n-C36H74)  

NASA Astrophysics Data System (ADS)

The solution-crystallization mechanism was investigated for two polytypes in the M011 modification of n-hexatriacontane (n-C36H74), single-layered structure Mon, and double-layered one Orth II. The crystal growth under controlled supersaturation was followed with a micro- Fourier-transform-infrared spectrometer equipped with an optical system for oblique transmission measurements. Supersaturation dependence of growth behavior was significantly different between Mon and Orth II. Although the Mon crystal continued growing at a supersaturation of 0.27, the overgrowth of Orth II on the (001) face of the Mon crystal was confirmed at supersaturations below 0.21. Such a polytypic transformation was not observed for the Orth II crystal at any supersaturation below 0.30. The growth rate of Mon showed a quadratic dependence on supersaturation, while that of Orth II was approximately linear, suggesting spiral growth and two-dimensional-nucleation mechanisms for Mon and Orth II, respectively.

Kubota, Hideki; Kaneko, Fumitoshi; Kawaguchi, Tatsuya; Kawasaki, Masatsugu

2005-10-01

59

Mechanisms of classical crystal growth theory explain quartz and silicate dissolution behavior  

PubMed Central

The central control of mineral weathering rates on biogeochemical systems has motivated studies of dissolution for more than 50 years. A complete physical picture that explains widely observed variations in dissolution behavior is lacking, and some data show apparent serious inconsistencies that cannot be explained by the largely empirical kinetic “laws.” Here, we show that mineral dissolution can, in fact, be understood through the same mechanistic theory of nucleation developed for mineral growth. In principle, this theory should describe dissolution but has never been tested. By generalizing nucleation rate equations to include dissolution, we arrive at a model that predicts how quartz dissolution processes change with undersaturation from step retreat, to defect-driven and homogeneous etch pit formation. This finding reveals that the “salt effect,” recognized almost 100 years ago, arises from a crossover in dominant nucleation mechanism to greatly increase step density. The theory also explains the dissolution kinetics of major weathering aluminosilicates, kaolinite and K-feldspar. In doing so, it provides a sensible origin of discrepancies reported for the dependence of kaolinite dissolution and growth rates on saturation state by invoking a temperature-activated transition in the nucleation process. Although dissolution by nucleation processes was previously unknown for oxides or silicates, our mechanism-based findings are consistent with recent observations of dissolution (i.e., demineralization) in biological minerals. Nucleation theory may be the missing link to unifying mineral growth and dissolution into a mechanistic and quantitative framework across the continuum of driving force.

Dove, Patricia M.; Han, Nizhou; De Yoreo, James J.

2005-01-01

60

Bridgman crystal growth  

NASA Technical Reports Server (NTRS)

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

Carlson, Frederick

1990-01-01

61

Fluid mechanics and mass transfer in melt crystal growth: Analysis of the floating zone and vertical Bridgman processes  

NASA Technical Reports Server (NTRS)

This research program focuses on analysis of the transport mechanisms in solidification processes, especially one of interest to the Microgravity Sciences and Applications Program of NASA. Research during the last year has focused on analysis of the dynamics of the floating zone process for growth of small-scale crystals, on studies of the effect of applied magnetic fields on convection and solute segregation in directional solidification, and on the dynamics of microscopic cell formation in two-dimensional solidification of binary alloys. Significant findings are given.

Brown, R. A.

1986-01-01

62

A comparative study on growth, structural, optical, thermal and mechanical properties of undoped and dye doped bis glycine cadmium chloride single crystals  

NASA Astrophysics Data System (ADS)

Dye inclusion crystals have attracted researchers in the context of crystal growth for applications in solid state lasers. Attempt to grow tris glycine cadmium chloride (TGCC) crystals yielded bis glycine cadmium chloride crystals. Single crystals of bis glycine cadmium chloride (BGCC) and organic dye, namely xylenol orange tetra sodium salt (XO) doped BGCC crystals, were grown from aqueous solutions by slow evaporation technique from the mixture of an aqueous solution of glycine and cadmium chloride in 3:1 molar ratio at a constant temperature of 35 °C. The grown crystals are up to the dimension of 20×20×5 mm 3. Characterization of the crystals was made using a single crystal X-ray diffractometer for obtaining the structure. The crystal is monoclinic with P2 1/ n space group. High-resolution X-ray diffraction (HRXRD) was used to evaluate crystalline perfection. Perfection of the undoped crystals is higher than those of the dye doped crystals. Thermal stability of the crystals is tested from differential scanning calorimetry. There is only one endothermic peak, indicating melting point. The optical transparency range of the crystals was identified from the UV-vis spectrum. Functional groups present in the crystals were studied by FT-IR spectral analysis. The mechanical strength of the crystals, measured by Vickers microhardness, and it has increased due to the presence of dye in the crystals.

Raju, B.; Saritha, A.; Bhagavannarayana, G.; Hussain, K. A.

2011-06-01

63

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

64

Purifying Silicon During Crystal Growth  

NASA Technical Reports Server (NTRS)

Direct current applied to molten silicon during crystallization causes impurities to migrate away from interface of growing crystal. Method improves purity of crystal without interfering with growth process or requiring additional operator attention.

Shlichta, P. J.

1984-01-01

65

Spiral Growth Patterns on Apatite Crystals  

Microsoft Academic Search

RECENTLY, observations of the growth spirals suggested by Frank's theory1 have been reported on crystals of beryl2, n-paraffin3, silicon carbide4, cadmium iodide5 and gold6; for mica7 experimental evidence has been put forward to support the hypothesis that here, too, the same mechanism is responsible for the growth of the crystals.

S. Amelinckx

1952-01-01

66

Growth rates of protein crystals.  

PubMed

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

2012-03-01

67

Laser-induced crystallization and crystal growth.  

PubMed

Recent streams of laser studies on crystallization and crystal growth are summarized and reviewed. Femtosecond multiphoton excitation of solutions leads to their ablation at the focal point, inducing local bubble formation, shockwave propagation, and convection flow. This phenomenon, called "laser micro tsunami" makes it possible to trigger crystallization of molecules and proteins from their supersaturated solutions. Femtosecond laser ablation of a urea crystal in solution triggers the additional growth of a single daughter crystal. Intense continuous wave (CW) near infrared laser irradiation at the air/solution interface of heavy-water amino acid solutions results in trapping of the clusters and evolves to crystallization. A single crystal is always prepared in a spatially and temporally controlled manner, and the crystal polymorph of glycine depends on laser power, polarization, and solution concentration. Upon irradiation at the glass/solution interface, a millimeter-sized droplet is formed, and a single crystal is formed by shifting the irradiation position to the surface. Directional and selective crystal growth is also possible with laser trapping. Finally, characteristics of laser-induced crystallization and crystal growth are summarized. PMID:21721131

Sugiyama, Teruki; Masuhara, Hiroshi

2011-11-01

68

Growth, structural, mechanical, spectral and dielectric characterization of NaCl-added Triglycine sulfate single crystals  

Microsoft Academic Search

Pure and sodium chloride (NaCl)-added Triglycine sulfate (TGS) crystals were grown from aqueous solutions by slow evaporation technique. The values of concentration of dopants in the mother solution were 0.2, 0.6 and 1mol%. The solubility of the grown samples have been found out at various temperatures. The determination of unit cell parameters was carried out by single crystal XRD method

N. Theresita Shanthi; P. Selvarajan; C. K. Mahadevan

2009-01-01

69

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

70

Synthesis, Growth, Structural, Spectroscopic, Optical, Thermal and Mechanical Studies of a Semi-Organic Nonlinear Optical Crystal:. L-Glutamic Acid Hydrochloride  

NASA Astrophysics Data System (ADS)

The semi-organic nonlinear optical single crystal of L-glutamic acid hydrochloride was grown by slow evaporation solution growth technique at room temperature. The cell parameters of the grown crystal were estimated by single crystal X-ray diffraction analysis. The presence of various functional groups was identified from Fourier transform infrared analysis. The transmission spectrum of this crystal show that the lower cut-off wavelength lies at 248 nm. Thermal analysis was performed to study the thermal stability of the grown crystal. The Kurtz powder second harmonic generation test shows that the crystal is a potential candidate for optical second harmonic generation. Mechanical properties of the grown crystal were determined and Vickers' hardness number was calculated.

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

71

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

72

Micropipe absorption mechanism of pore growth at foreign polytype boundaries in SiC crystals  

Microsoft Academic Search

Formation of pores at foreign polytype boundaries in bulk SiC crystals is studied by means of synchrotron radiation phase-sensitive radiography, optical and scanning electron microscopies, and color photoluminescence. It is demonstrated that pores are formed through coalescence of micropipes and extend along the polytype boundaries by means of micropipe absorption. A theoretical model is suggested, which describes the micropipe absorption

M. Yu. Gutkin; A. G. Sheinerman; M. A. Smirnov; T. S. Argunova; J. H. Je; S. S. Nagalyuk; E. N. Mokhov

2009-01-01

73

Crystal growth of artificial snow  

NASA Technical Reports Server (NTRS)

Snow crystals were grown onboard the space shuttle during STS-7 and STS-8 to facilitate the investigation of crystal growth under conditions of weightlessness. The experimental design and hardware are described. Space-grown snow crystals were polyhedrons looking like spheres, which were unlike snow crystals produced in experiments on Earth.

Kimura, S.; Oka, A.; Taki, M.; Kuwano, R.; Ono, H.; Nagura, R.; Narimatsu, Y.; Tanii, J.; Kamimiytat, Y.

1984-01-01

74

Crystallization kinetics and growth mechanism of Pb(Zr0.52·Ti0.48)O3 nanopowders  

NASA Astrophysics Data System (ADS)

In this study, Pb(Zr0.52·Ti0.48)O3 nanopowders were synthesized via sol-gel process. Particle morphology, crystalline phases and thermal behavior were characterized by scanning electron microscopy, X-ray diffraction and simultaneous thermal analyzer, respectively. The X-ray diffraction pattern showed perovskite phase clearly. The non-isothermal activation energy for the perovskite crystallization in Pb(Zr0.52·Ti0.48)O3 gel powders was 224.91 kJ mol-1. Both growth morphology parameter (n) and crystallization mechanism index (m) are close to 3.0, indicating that the bulk nucleation is dominant in the perovskite PZT formation. To determine dielectric properties, the calcined Pb(Zr0.52·Ti0.48)O3 nanopowders were pressed using uniaxial press. It was found that the Pb(Zr0.52·Ti0.48)O3 disks, by sintering at 1,200 °C for 2 and 10 h, and at 1 kHz frequency, had 966 and 1,490 of the dielectric constant, respectively.

Khajelakzay, Mohammad; Taheri-Nassaj, Ehsan

2014-04-01

75

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

76

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

77

Application of energy stability theory to problems in crystal growth  

NASA Technical Reports Server (NTRS)

The use of energy stability theory to study problems in crystal growth is outlined and justified in terms of convection mechanisms. An application to the float zone process of crystal growth is given as an illustration.

Neitzel, G. P.; Jankowski, D. F.

1990-01-01

78

Protein Crystal Growth in Microgravity  

NASA Astrophysics Data System (ADS)

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 ? -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.; Weber, Patricia C.; Salemme, F. Raymond; Ohlendorf, D. H.; Einspahr, H. M.; Clancy, L. L.; Navia, Manuel A.; McKeever, Brian M.; Nagabhushan, T. L.; Nelson, George; McPherson, A.; Koszelak, S.; Taylor, G.; Stammers, D.; Powell, K.; Darby, G.; Bugg, Charles E.

1989-11-01

79

Growth of single crystal diamond  

Microsoft Academic Search

The subject of the research presented in this dissertation is the growth of single crystal diamond by microwave plasma chemical vapor deposition (CVD). Both heteroepitaxial and homoepitaxial growth methods have been examined, with emphasis on producing large diamond crystals of high structural and chemical perfection. By heteroepitaxy, epitaxial growth on a foreign substrate, diamond was grown on (001) Ir thin-film

Murari Regmi

2007-01-01

80

Protein crystals and their growth  

NASA Technical Reports Server (NTRS)

Recent results on the associations between protein molecules in crystal lattices, crystal-solution surface energy, elastic properties, strength, and spontaneous crystal cracking are reviewed and discussed. In addition, some basic approaches to understanding the solubility of proteins are followed by an overview of crystal nucleation and growth. It is argued that variability of mixing in batch crystallization may be a source of the variation in the number of crystals ultimately appearing in the sample. The frequency at which new molecules join a crystal lattice is measured by the kinetic coefficient and is related to the observed crystal growth rate. Numerical criteria used to discriminate diffusion- and kinetic-limited growth are discussed on this basis. Finally, the creation of defects is discussed with an emphasis on the role of impurities and convection on macromolecular crystal perfection.

Chernov, Alexander A.

2003-01-01

81

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

82

Crack growth phenomena in micro-machined single crystal silicon and design implications for micro electro mechanical systems (MEMS)  

Microsoft Academic Search

The creation of micron-sized mechanisms using semiconductor processing technology is known collectively as MEMS, or Micro Electro Mechanical Systems. Many MEMS devices, such as accelerometers and switches, have mechanical structures fabricated from single crystal silicon, a brittle material. The reliability and longevity of these devices depends on minimizing the probability of fracture, and therefore requires a thorough understanding of crack

Alissa Mirella Fitzgerald

2000-01-01

83

Micropipe absorption mechanism of pore growth at foreign polytype boundaries in SiC crystals  

NASA Astrophysics Data System (ADS)

Formation of pores at foreign polytype boundaries in bulk SiC crystals is studied by means of synchrotron radiation phase-sensitive radiography, optical and scanning electron microscopies, and color photoluminescence. It is demonstrated that pores are formed through coalescence of micropipes and extend along the polytype boundaries by means of micropipe absorption. A theoretical model is suggested, which describes the micropipe absorption by an elliptic pore nucleated at the boundary of a foreign polytype inclusion. It is shown that depending on the inclusion distortion, the pore can either be a separate micropipe, or grow up to a certain length, or occupy the whole facet of the inclusion.

Gutkin, M. Yu.; Sheinerman, A. G.; Smirnov, M. A.; Argunova, T. S.; Je, J. H.; Nagalyuk, S. S.; Mokhov, E. N.

2009-12-01

84

Thermal Mechanical Fatigue Cracks Growth from Laser Drilled Holes in Single Crystal Material (Preprint).  

National Technical Information Service (NTIS)

The crack growth test results undergoing thermomechanical fatigue showed that the life of TMF specimens with notched laser drilled holes exhibit a debit by as much as 4 times that of smooth gage section specimens under the same loading conditions. Such a ...

A. Staroselsky D. C. Dudzinski M. Genest R. K. Kersey

2012-01-01

85

Crack growth phenomena in micro-machined single crystal silicon and design implications for micro electro mechanical systems (MEMS)  

NASA Astrophysics Data System (ADS)

The creation of micron-sized mechanisms using semiconductor processing technology is known collectively as MEMS, or Micro Electro Mechanical Systems. Many MEMS devices, such as accelerometers and switches, have mechanical structures fabricated from single crystal silicon, a brittle material. The reliability and longevity of these devices depends on minimizing the probability of fracture, and therefore requires a thorough understanding of crack growth phenomena in silicon. In this study, a special micro-machined fracture specimen, the compression-loaded double cantilever beam, was developed to study fracture phenomena in single crystal silicon on a size scale relevant to MEMS. The decreasing stress intensity geometry of this sample provided stable, controllable crack propagation in test sections as thin as 100 mum. Several common MEMS fabrication methods (plasma and chemical etch) were used to achieve a range of surface finishes. A 650 A thick titanium crack gage was used to directly measure crack extension as a function of time using the potential drop technique. High speed (100 MHz) data acquisition techniques were employed to capture fracture events on the sub-microsecond time scale. The stability of the sample design and the micron-scale resolution of the crack gage facilitated investigation into the existence of a stress corrosion effect in silicon. No evidence of sub-critical crack growth due to exposure to humid air was found in carefully controlled tests lasting up to 24 hours. Rapid crack propagation velocities (>1 km/s) during quasi-static loading were recorded using high speed data acquisition techniques. Unique evidence was found of reflected stress waves causing multiple, momentary arrests during rapid fracture events. These measurements, along with atomic force microscope scans of the fracture surfaces, offer new insight into the kinetics of the fracture process in silicon. Over 100 micro-machined samples were fractured in this research. Weibull analysis was employed to characterize, in a broadly applicable manner, the failure probability of samples as a function of surface preparation and applied stress intensity. A design study of an existing MEMS device is presented in order to demonstrate the utility of the data gathered during this research for predicting the failure of silicon MEMS devices.

Fitzgerald, Alissa Mirella

86

Protein crystal growth in space  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

87

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

88

MCT crystal growth  

NASA Technical Reports Server (NTRS)

Convection and segregation in directional solidification and crystal growth by the Bridgman-Stockbarger technique are traditionally treated by assuming axisymmetric thermal condition on the ampoule wall. It is, however, difficult to achieve such a condition in an experimental setup. Any deviation from an axisymmetric temperature field on the wall of a vertical ampoule represents a horizontal temperature gradient. The horizontal density gradient that results from thermal expansion in the melt under this condition must lead on earth to some buoyance-driven convection, no matter what the axial (vertical) temperature distribution that is imposed on the melt. The magnitude of such convective flows for conditions representative of the MSFC mercury-cadmium-telluride (MCT) Bridgman setup is studied.

Baird, James K.

1988-01-01

89

MCT crystal growth  

NASA Astrophysics Data System (ADS)

Convection and segregation in directional solidification and crystal growth by the Bridgman-Stockbarger technique are traditionally treated by assuming axisymmetric thermal condition on the ampoule wall. It is, however, difficult to achieve such a condition in an experimental setup. Any deviation from an axisymmetric temperature field on the wall of a vertical ampoule represents a horizontal temperature gradient. The horizontal density gradient that results from thermal expansion in the melt under this condition must lead on earth to some buoyance-driven convection, no matter what the axial (vertical) temperature distribution that is imposed on the melt. The magnitude of such convective flows for conditions representative of the MSFC mercury-cadmium-telluride (MCT) Bridgman setup is studied.

Baird, James K.

1988-02-01

90

Crystal growth apparatus  

NASA Astrophysics Data System (ADS)

This invention relates generally to crystal growth devices, and more particularly to a device in which protein crystals are grown in a hanging drop. The drop is suspended from a surface positioned in the interior of an enclosure which is sealably coupled via a valve to a vessel containing solvent used in the drop. A second opening in the enclosure is coupled via a valve to a vessel containing a selected desiccant material. The valve may be fully or partially opened to add a selected quantity of solvent in a vapor phase to the drop, and the valve may be fully or partially opened to cause a selected quantity of solvent to evaporate from the drop. The process is monitored by a camera, and in conjunction with a graduated pattern superimposed over the drop, relative volumes of the drop are determined. Alternately, the process may be automated by using a computer coupled to servo motors, which in turn are coupled to and operate a cap and valves, respectively. The computer is responsive to a detection device which detects changes of light passing through the drop from the light source.

Herrmann, Frederick T.; Herren, Blair J.

1990-04-01

91

Infrared spectroscopic study of polytypic effects on the crystal-growth mechanism of n-hexatriacontane (n-C36H74).  

PubMed

The solution-crystallization mechanism was investigated for two polytypes in the M011 modification of n-hexatriacontane (n-C36H74), single-layered structure Mon, and double-layered one Orth II. The crystal growth under controlled supersaturation was followed with a micro- Fourier-transform-infrared spectrometer equipped with an optical system for oblique transmission measurements. Supersaturation dependence of growth behavior was significantly different between Mon and Orth II. Although the Mon crystal continued growing at a supersaturation of 0.27, the overgrowth of Orth II on the (001) face of the Mon crystal was confirmed at supersaturations below 0.21. Such a polytypic transformation was not observed for the Orth II crystal at any supersaturation below 0.30. The growth rate of Mon showed a quadratic dependence on supersaturation, while that of Orth II was approximately linear, suggesting spiral growth and two-dimensional-nucleation mechanisms for Mon and Orth II, respectively. PMID:16223308

Kubota, Hideki; Kaneko, Fumitoshi; Kawaguchi, Tatsuya; Kawasaki, Masatsugu

2005-10-01

92

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

PubMed

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

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

2011-10-15

93

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

94

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

95

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) [Tracy, CA; Milanovich, Fred P. (Lafayette, CA) [Lafayette, CA

1992-01-01

96

Phase-field-crystal simulation of nonequilibrium crystal growth  

NASA Astrophysics Data System (ADS)

By using the phase field crystal model, we simulate the morphological transition of the crystal growth of equilibrium crystal shape, dendrite, and spherical crystal shape. The relationship among growth morphology, velocity, and density distribution is investigated. The competition between interface energy anisotropy and interface kinetic anisotropy gives rise to the pattern selection of dendritic growth in the diffusion controlled regime under low-crystal-growth velocities. The trapping effect in density diffusion suppresses morphological instabilities under high-crystal-growth velocities, resulting in isotropic growth of spherical crystal. Finally, a morphological phase diagram of crystal growth is constructed as function of the phase field crystal model parameters.

Tang, Sai; Yu, Yan-Mei; Wang, Jincheng; Li, Junjie; Wang, Zhijun; Guo, Yaolin; Zhou, Yaohe

2014-01-01

97

Bioengineering single crystal growth.  

PubMed

Biomineralization is a "bottom-up" synthesis process that results in the formation of inorganic/organic nanocomposites with unrivaled control over structure, superior mechanical properties, adaptive response, and the capability of self-repair. While de novo design of such highly optimized materials may still be out of reach, engineering of the biosynthetic machinery may offer an alternative route to design advanced materials. Herein, we present an approach using micro-contact-printed lectins for patterning sea urchin embryo primary mesenchyme cells (PMCs) in vitro. We demonstrate not only that PMCs cultured on these substrates show attachment to wheat germ agglutinin and concanavalin A patterns but, more importantly, that the deposition and elongation of calcite spicules occurs cooperatively by multiple cells and in alignment with the printed pattern. This allows us to control the placement and orientation of smooth, cylindrical calcite single crystals where the crystallographic c-direction is parallel to the cylinder axis and the underlying line pattern. PMID:21265521

Wu, Ching-Hsuan; Park, Alexander; Joester, Derk

2011-02-16

98

Protein crystal growth in space  

NASA Technical Reports Server (NTRS)

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

Delucas, Lawrence J.; Bugg, Charles E.

1991-01-01

99

Crystal Growth by Evaporation  

NSDL National Science Digital Library

This activity introduces students to the idea that crystals 'grow' (crystallize or precipitate) and that minerals or rocks also form this way, providing a very general idea of the nature of magma (molten material that eventually crystallizes into igneous rocks). Using solutions mixed by the teacher, they will observe and sketch the formation of crystals of potassium dichromate and copper II acetate by placing drops of the solutions on microscope slides and drying them on a hot plate. Discussion questions are provided.

100

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

101

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

102

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) [Tracy, CA

1992-01-01

103

Crystal Growth Using MEPHISTO  

NASA Technical Reports Server (NTRS)

The shuttle flight experiment "In Situ Monitoring of Crystal Growth Using MEPHISTO" was accomplished during STS-87 as part of the fourth flight of the United States Microgravity Payload (USMP-4), which was flown from November 19 to December 5, 1997. The data returned from that flight are just now beginning to yield quantitative results. This project is an international collaboration: the furnace system known as MEPHISTO was built in France by CNES (French National Space Agency) and CEA (French Atomic Energy Commission); the principal investigator, Prof. Reza Abbaschian, is from the University of Florida at Gainesville; and numerical and analytical modeling support includes collaborators from the University of New South Wales, Australia, the University of Wisconsin at Milwaukee, the National Institute of Standards and Technology, and the NASA Lewis Research Center. MEPHISTO is a French acronym that translates into English as Materials for the Study of Interesting Phenomena of Solidification on Earth and in Orbit. Since this was the fourth flight of the MEPHISTO furnace, the experiment is referred to as MEPHISTO-4. MEPHISTO-4 was a directional solidification experiment that studied the liquid-to-solid transformation of bismuth alloyed with tin. Directional solidification is a freezing technique common to the processing of the electronic materials used in integrated circuits and detectors, such as silicon and germanium. When liquids are frozen on Earth, they must be cooled. The cooling causes stirring because of density variations in the liquid. This stirring, known as natural convection, influences the quality of the resulting solid. During freezing, regions of high and low concentrations of tin are created. This introduces another important phenomenon: diffusion, or the movement by molecular action of matter from regions of high concentration to regions of lower concentration. In MEPHISTO-4, it is tin that diffuses from the high-concentration region in front of the solid-liquid interface to more distant low-concentration regions.

deGroh, Henry C., III

1999-01-01

104

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

105

The crystallization of potassium nitrate. II. Growth rate dispersion  

Microsoft Academic Search

The effect of growth rate dispersion (GRD) had to be examined. Therefore, the face-specific growth rate of KNO3 {1 1 1} faces was determined, carrying out single crystal growth experiments with crystals treated in different ways (untreated, hurt, annealed, mechanically strained). For a supersaturation ? > 0.001, the growth can be described by the random fluctuation (RF) model. An even

A. Herden; R. Lacmann

1997-01-01

106

Twisted mannitol crystals establish homologous growth mechanisms for high-polymer and small-molecule ring-banded spherulites.  

PubMed

D-Mannitol belongs to a large and growing family of crystals with helical morphologies (Yu, L. J. Am. Chem. Soc.2003, 125, 6380). Two polymorphs of D-mannitol, ? and ?, when grown in the presence of additives such as poly(vinylpyrrolidone) (PVP) or D-sorbitol, form ring-banded spherulites composed of handed helical fibrils, where the helix axes correspond to the radial growth directions. The two polymorphs form helices with opposite senses in the presence of PVP but the same sense in the presence of D-sorbitol. The characteristic dimensions of the fibrils, including thickness, aspect ratio, and pitch, were determined by scanning probe and electron microscopies. These values must form the basis of any theory that presupposes what forces give rise to crystal twisting, a problem that has been broached but unsettled in the literature of polymer crystallization. The interdependence of the rhythmic variations of both linear and circular birefringence, as determined by Mueller matrix microscopy, informs the cooperative organization of mannitol fibers. The microstructure of mannitol ring-banded spherulites compares favorably to that of high polymers and is evaluated within the context of current theories of crystal twisting. PMID:22413815

Shtukenberg, Alexander G; Cui, Xiaoyan; Freudenthal, John; Gunn, Erica; Camp, Eric; Kahr, Bart

2012-04-11

107

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.

Van Driessche, A. E. S.; Garcia-Ruiz, J. M.; Tsukamoto, K.; Patino-Lopez, L. D.; Satoh, H.

2011-01-01

108

Two puzzling aspects of protein crystal growth  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

109

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.

110

CVD-diamond single-crystal growth  

NASA Astrophysics Data System (ADS)

The synthesis of diamond volume crystals is of particular interest due to the material's outstanding physical and mechanical properties. Various techniques are pursued by numerous research groups. In hot-filament CVD (HF-CVD) we found a new process parameter window where the growth of single diamond volume crystals can be stabilized. These parameters are far beyond growth conditions for HF-CVD diamond coating processes. Extremely low methane content in the feed gas along with high substrate temperatures allows single diamond nuclei of a certain minimum size to grow stable. Crystals up to 100 ?m in diameter were successfully synthesized on ultrasonic pretreated substrates. They were characterized by SEM and Raman spectroscopy. A model for the observed exclusive growth of sufficiently large nuclei is presented. Based on well accepted diamond growth models, an advanced growth theory for the different morphologies and diamond qualities at the {1 0 0} and {1 1 1} faces of the crystals is postulated. The results give bases on which growing processes can be optimized and upscaled in order to evaluate the applicability of the method for single-crystal diamond growth.

Schwarz, S.; Rottmair, C.; Hirmke, J.; Rosiwal, S.; Singer, R. F.

2004-11-01

111

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

112

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

113

Kinetics of crystal growth in a terrestrial magma ocean  

NASA Astrophysics Data System (ADS)

One of the central problems in the differentiation of a terrestrial magma ocean is the problem of crystal sizes. Crystal sizes in a convective magma ocean are controlled by kinetics of nucleation and crystal growth. In contrast with crystallization in other relatively well studied systems, nucleation and crystallization in downward moving magma occur as a result of adiabatic compression, also known as adiabatic 'cooling'. The problem of crystal sizes is solved analytically for an arbitrary crystal growth law. The following assumptions are made: convection is not influenced by the kinetics of nucleation and crystal growth, interface kinetics is the rate controlling mechanism of crystal growth, and the adiabatic cooling is sufficiently slow for the asymptotic solution to be valid.

Solomatov, Viatcheslav S.; Stevenson, David J.

1993-03-01

114

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

115

(PCG) Protein Crystal Growth Canavalin  

NASA Technical Reports Server (NTRS)

(PCG) Protein Crystal Growth Canavalin. The major storage protein of leguminous plants and a major source of dietary protein for humans and domestic animals. It is studied in efforts to enhance nutritional value of proteins through protein engineerings. It is isolated from Jack Bean because of it's potential as a nutritional substance. Principal Investigator on STS-26 was Alex McPherson.

1989-01-01

116

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

117

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: High-Rate Growth and Nitrogen Distribution in Homoepitaxial Chemical Vapour Deposited Single-crystal Diamond  

NASA Astrophysics Data System (ADS)

High rate (> 50 ?m/h) growth of homoepitaxial single-crystal diamond (SCD) is carried out by microwave plasma chemical vapour deposition (MPCVD) with added nitrogen in the reactant gases of methane and hydrogen, using a polycrystalline-CVD-diamond-film-made seed holder. Photoluminescence results indicate that the nitrogen concentration is spatially inhomogeneous in a large scale, either on the top surface or in the bulk of those as-grown SCDs. The presence of N-distribution is attributed to the facts: (i) a difference in N-incorporation efficiency and (ii) N-diffusion, resulting from the local growth temperatures changed during the high-rate deposition process. In addition, the formed nitrogen-vacancy centres play a crucial role in N-diffusion through the growing crystal. Based on the N-distribution observed in the as-grown crystals, we propose a simple method to distinguish natural diamonds and man-made CVD SCDs. Finally, the disappearance of void defect on the top surface of SCDs is discussed to be related to a filling-in mechanism.

Li, Hong-Dong; Zou, Guang-Tian; Wang, Qi-Liang; Cheng, Shao-Heng; Li, Bo; Lü, Jian-Nan; Lü, Xian-Yi; Jin, Zeng-Sun

2008-05-01

118

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

119

Growth and dielectric, mechanical, thermal and etching studies of an organic nonlinear optical L-arginine trifluoroacetate (LATF) single crystal  

SciTech Connect

L-arginine trifluoroacetate, an organic nonlinear optical material, has been synthesized from aqueous solution. Bulk single crystal of dimension 57 mm x 5 mm x 3 mm has been grown by temperature lowering technique. Powder X-ray diffraction studies confirmed the monoclinic structure of the grown L-arginine trifluoroacetate crystal. Linear optical property of the grown crystal has been studied by UV-vis spectrum. Dielectric response of the L-arginine trifluoroacetate crystal was analysed for different frequencies and temperatures in detail. Microhardness study on the sample reveals that the crystal possesses relatively higher hardness compared to many organic crystals. Thermal analyses confirmed that the L-arginine trifluoroacetate material is thermally stable upto 212 deg. C. The etching studies have been performed to assess the perfection of the L-arginine trifluoroacetate crystal. Kurtz powder second harmonic generation test confirms the nonlinear optical properties of the as-grown L-arginine trifluoroacetate crystal.

Arjunan, S. [Department of Physics, Panimalar Engineering College, Chennai 602103 (India); Department of Physics, Presidency College, Chennai 600005 (India); Mohan Kumar, R. [Crystal Growth Centre, Anna University, Chennai 600025 (India); Mohan, R. [Department of Physics, Presidency College, Chennai 600005 (India); Jayavel, R. [Crystal Growth Centre, Anna University, Chennai 600025 (India)], E-mail: arjunan_hce@yahoo.co.in

2008-08-04

120

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

Microsoft Academic Search

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

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

2011-01-01

121

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

122

Compact Apparatus For Growth Of Protein Crystals  

NASA Technical Reports Server (NTRS)

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

Carter, Daniel C.; Miller, Teresa Y.

1991-01-01

123

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

124

Fluorapatite crystal growth from modified seawater solutions  

SciTech Connect

Seeded precipitation experiments were conducted in a pH/fluoride-stat system to study the crystal growth of fluorapatite (FAP) in carbonate-free NaCl-CaCl{sub 2}-NaF-Na{sub 2}HPO{sub 4} solutions, at seawater calcium concentration, chlorinity, and pH. With increasing supersaturation, the dependence of the growth rate on the relative supersaturation changes from parabolic to exponential. This is interpreted as reflecting a transition in the crystal growth mechanism from growth at dislocation-induced surface steps to surface nucleation-controlled growth. The analysis of the kinetic data leads to a mineral-aqueous solution interfacial tension for FAP of 289 mJ/M{sup 2}. The Arrhenius activation energy of the growth reaction in the temperature range 12 to 35C is 47 kJ/mol. The effect of pH on FAP growth was tested for pH values from 7 to 8.5. In this range, growth of FAP is catalyzed by hydrogen ions. The apparent growth rate constant is proportional to (a{sub H{sup +}}){sup m} where m, the rate order with respect to H{sup +}, is a non-integral number which depends on pH. At identical degrees of supersaturation, the growth rate of FAP at pH = 7 is nearly twice that at pH = 8. When corrected for bottom water temperatures, pore water pH, and the retardation of Mg{sup 2+}, the experimental growth rates predict that during burial in modern phosphatic sediments, apatite particles grow to sizes on the order of 0.1-10{mu}m. The relatively slow growth kinetics of FAP are consistent with the observed small particle sizes of marine sedimentary apatite.

Van Cappellen, P.; Berner, R.A. (Yale Univ., New Haven, CT (United States))

1991-05-01

125

Protein crystal growth—Microgravity aspects  

NASA Astrophysics Data System (ADS)

Protein crystals, grown under reduced gravity conditions, are either superior or inferior in their structural perfection than their Earth-grown counterparts. A reduction of the crystals' quality due to low-gravity effects on the growth processes cannot be understood from existing models. In this paper we put forth a rationale which predicts either advantages or disadvantages of microgravity growth. This rationale is based on the changes in the effective solute and impurity supply rates in microgravity and their effects on the intrinsic growth rate fluctuations that arise from the coupling of bulk transport to nonlinear interfacial kinetics and cause severe inhomogeneities. Depending on the specific diffusivity and kinetic coefficient of a protein and the impurities in the solution, either transport enhancement through forced flow or transport suppression under reduced gravity can result in a reduction of the kinetic fluctuations and, thus, growth with higher structural perfection. Investigating this mechanism of microgravity effects, we first demonstrate a one-to-one correspondence between these fluctuations, that are due to the bunching of growth steps, and the formation of defects in the crystals. We have confirmed the forced flow aspects of this rationale in ground-based experiments with lysozyme utilizing flowing solutions with varying, well characterized impurity contents.

Vekilov, Peter G.

1999-01-01

126

Proceedings of the Soviet Conference on Crystal Growth (3RD).  

National Technical Information Service (NTIS)

The USSR symposium on crystal growth covered basic theories and methods for crystal growth, testing and determination. Discussions were made on crystal growth theories, the water-heating crystal growing method, the flame melting crystal growing method, th...

Chang Shou-ch'ing

1968-01-01

127

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

NASA Astrophysics Data System (ADS)

Pure (undoped) and RbCl-doped LAHC single crystals were grown successfully by the solution method with the slow evaporation technique at room temperature. The grown crystals were colourless and transparent. The solubility of the grown samples were found out at various temperatures. The lattice parameters of the grown crystals were determined by the single crystal X-ray diffraction technique and the diffracting planes were indentified by recording the powder X-ray diffraction pattern. UV-visible transmittance studies were carried out for the grown samples. Chemical analysis and atomic absorption studies indicate the presence of rubidium in the doped LAHC crystals. Nonlinear optical studies reveal that the SHG efficiency increases when the LAHC crystal is doped with rubidium chloride (RbCl). From microhardness studies, it is observed that the RbCl-doped LAHC crystal is harder than the pure sample. It is observed that the dielectric properties of the LAHC crystal are altered when it is doped with rubidium chloride.

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

2011-02-01

128

Arcade Games for Teaching Crystal Growth  

NASA Astrophysics Data System (ADS)

The growth behavior of crystals depends on the relative rates of two consecutive steps in the process. One is the flow of growth units toward the crystal face. The other is the ability of the crystal structure to allocate the landing growth units on the right crystal position, minimizing reticular energy. Using the analogy of building a tessellate wall by a wall-maker and playing the arcade game called Tetris, students can grasp this fundamental idea of the crystal growth theory. For instance, the reluctance of large biological macromolecules such as proteins to crystallize, and the increasing interest in crystal growth techniques where mass transport is controlled by diffusion, are immediately understood. Using these analogies, the teacher can introduce other crystal properties such as polymorphism and mosaicity and discuss how they are related to growth conditions.

García-Ruiz, J. M.

1999-04-01

129

Crystal growth and annealing method and apparatus  

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. 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

130

Fluorapatite crystal growth from modified seawater solutions  

NASA Astrophysics Data System (ADS)

Seeded precipitation experiments were conducted in a pH/fluoride-stat system to study the crystal growth of fluorapatite ( FAP ) in carbonate-free NaCl-CaCl 2-NaF-Na 2HPO 4 solutions, at seawater calcium concentration, chlorinity, and pH. With increasing supersaturation, the dependence of the growth rate on the relative supersaturation changes from parabolic to exponential. This is interpreted as reflecting a transition in the crystal growth mechanism from growth at dislocation-induced surface steps to surface nucleation-controlled growth. The analysis of the kinetic data leads to a mineral-aqueous solution interfacial tension for FAP of 289 mJ/m 2. The Arrhenius activation energy of the growth reaction in the temperature range 12 to 35°C is 47 kJ/mol. The inhibition of FAP growth by Mg 2+ ions was investigated over a range of total dissolved Mg of 0 to 60 mM. At dissolved magnesium concentrations typical of marine pore waters (40-60 mM), the rate of FAP growth is 15 to 20 times slower than in the absence of Mg 2+, for the same degree of supersaturation, at 25 °C and pH = 8. The inhibitory effect can be explained by the blocking of growth sites at the surface of FAP crystals by adsorbed Mg 2+ ions. A simple Langmuir adsorption model for the retardation effect of Mg 2+ is supported by the results. The effect of pH on FAP growth was tested for pH values from 7 to 8.5. In this range, growth of FAP is catalyzed by hydrogen ions. The apparent growth rate constant is proportional to ( aH+) m where m, the rate order with respect to H +, is a non-integral number which depends on pH. At identical degrees of supersaturation, the growth rate of FAP at pH = 7 is nearly twice that at pH = 8. When corrected for bottom water temperatures, pore water pH, and the retardation of Mg 2+, the experimental growth rates predict that during burial in modern phosphatic sediments, apatite particles grow to sizes on the order of 0.1-10 ?rn. The relatively slow growth kinetics of FAP are consistent with the observed small particle sizes of marine sedimentary apatite.

Van Cappellen, Philippe; Berner, Robert A.

131

Crystal growth and high-temperature properties of intermetallic compound nickel aluminide  

Microsoft Academic Search

Investigations have been performed to the studying single crystal growth mechanism of intermetallic compound Ni3Al and to understand its mechanical behavior in single crystal and polycrystalline form at elevated temperatures under an oxidizing environment. Two crystal growth techniques, electron beam zone melting and Bridgman method, are combined together to grow single crystals in this work. The effects of the concentration

Zhigang Xiao

1999-01-01

132

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

133

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

134

Heat and mass transfer during crystal growth  

Microsoft Academic Search

Quality of semiconductor and oxide crystals which are grown from the melts plays an important role for electronic and\\/or optical devices. The crystal quality is significantly affected by the heat and mass transfer in the melts during crystal growth in a growth furnace such as Czochralski or horizontal Bridgman methods. This paper reviews the present understanding of phenomena of the

Koichi Kakimoto; Hiroyuki Ozoe

1998-01-01

135

Calcium oxalate crystal growth in human urinary stones  

SciTech Connect

Calcium oxalate stones are very common and increasing. Crystal growth is no less important than the crystal nucleation in the pathogenesis of stone formation. The crystal growth was studied in human calcium oxalate stones by a combined electron microscopy and x-ray diffraction. The main mode of weddellite growth was interpenetration twinning of tetrahedral bipyramids. Bipyramids may form as initial crystal seeds, develop from anhedral crystals (crystals which lack flat symmetric faces) of spherular or mulberry shape, develop on the surface of preformed bipyramids by spiral dislocation mechanisms, or develop on whewellite crystal by heterogeneous nucleation and epitaxy. Heterogeneous nucleations of whewellite on weddellite, and calcium apatite on whewellite were also observed. Whewellite grew mainly by parallel twinning. Interpenetration twinning was exceptional. Transformation of anhedral to euhedral (completely bounded by flat faces that are set ar fixed angles to one another) whewellite occurred by parallel fissurations followed by brick wall like stacking of the crystals, while euhedral transformation of weddellite occurred by protrusion of bipyramids frm anhedral crystal surface. Occasionally, an evidence of crystal dissolution was noted. Although an aggregation of crystals is believed to play a pivotal role in stone nidus formation, growth in size of the formed crystals, and twinning and epitactic crystal intergrowth apparently play a significant role in the obstructive urinary stone formation.

Kim, K.M.; Johnson, F.B.

1981-01-01

136

Physical phenomena related to crystal growth in the space environment  

NASA Technical Reports Server (NTRS)

The mechanism of crystal growth which may be affected by the space environment was studied. Conclusions as to the relative technical and scientific advantages of crystal growth in space over earth bound growth, without regard to economic advantage, were deduced. It was concluded that the crucibleless technique will most directly demonstrate the unique effects of the greatly reduced gravity in the space environment. Several experiments, including crucibleless crystal growth using solar energy and determination of diffusion coefficients of common dopants in liquid silicon were recommended.

Chu, T. L.

1973-01-01

137

Student Augmentation for Crystal Growth Research.  

National Technical Information Service (NTIS)

Three graduate students and one undergraduate student were supported to pursue research in the area of crystal growth and complement the research activities of AFOSR/DARPA MURI project on integrated intelligent modeling, design and control of crystal grow...

V. Prasad

1999-01-01

138

Protein Crystal Growth in Low Gravity. Annual Report January1 - December 31, 1986.  

National Technical Information Service (NTIS)

The solubility and growth mechanism of canavalin were studied, and the applicability of the Schlieren technique to protein crystal growth was investigated. Canavalin which may be crystallized from a basic solution by the addition of hydrogen (H+) ions was...

R. S. Feigelson

1987-01-01

139

Measurable characteristics of lysozyme crystal growth  

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

140

Protein crystal growth in low gravity  

NASA Technical Reports Server (NTRS)

The effect of low gravity on the growth of protein crystals and those parameters which will affect growth and crystal quality was studied. The proper design of the flight hardware and experimental protocols are highly dependent on understanding the factors which influence the nucleation and growth of crystals of biological macromolecules. Thus, those factors are investigated and the body of knowledge which has been built up for small molecule crystallization. These data also provide a basis of comparison for the results obtained from low-g experiments. The flows around growing crystals are detailed. The preliminary study of the growth of isocitrate lyase, the crystal morphologies found and the preliminary x ray results are discussed. The design of two apparatus for protein crystal growth by temperature control are presented along with preliminary results.

Feigelson, Robert S.

1990-01-01

141

(PCG) Protein Crystal Growth Horse Serum Albumin  

NASA Technical Reports Server (NTRS)

Horse Serum Albumin crystals grown during the USML-1 (STS-50) mission's Protein Crystal Growth Glovebox Experiment. These crystals were grown using a vapor diffusion technique at 22 degrees C. The crystals were allowed to grow for nine days while in orbit. Crystals of 1.0 mm in length were produced. The most abundant blood serum protein, regulates blood pressure and transports ions, metabolites, and therapeutic drugs. Principal Investigator was Edward Meehan.

1995-01-01

142

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

143

Optical Diagnostics of Solution Crystal Growth  

NASA Technical Reports Server (NTRS)

Non-contact optical techniques such as, optical heterodyne, ellipsometry and interferometry, for real time in-situ monitoring of solution crystal growth are demonstrated. Optical heterodyne technique has the capability of measuring the growth rate as small as 1A/sec. In a typical Michelson interferometer set up, the crystal is illuminated by a Zeeman laser with frequency omega(sub 1) and the reference beam with frequency omega(sub 2). As the crystal grows, the phase of the rf signal changes with respect to the reference beam and this phase change is related to the crystal growth rate. This technique is demonstrated with two examples: (1) by measuring the copper tip expansion/shrinkage rate and (2) by measuring the crystal growth rate of L-Arginine Phosphate (LAP). The first test shows that the expansion/shrinkage rate of copper tip was fast in the beginning, and gets slower as the expansion begins to stabilize with time. In crystal growth, the phase change due the crystal growth is measured using a phase meter and a strip chart recorder. Our experimental results indicate a varied growth rate from 69.4 to 92.6A per sec. The ellipsometer is used to study the crystal growth interface. From these measurements and a theoretical modeling of the interface, the various optical parameters can be deduced. Interferometry can also be used to measure the growth rate and concentration gradient in the vicinity of the crystal.

Kim, Yongkee; Reddy, B. R.; George, T. G.; Lal, R. B.

1996-01-01

144

Segregation reduction in Bridgman crystal growth  

NASA Astrophysics Data System (ADS)

Dopant segregation in crystal growth results in nonuniform dopant distributions and hence nonuniform physical properties in the resultant crystals. Three different methods in vertical Bridgman crystal and one method in horizontal Bridgman crystal growth were developed to reduce dopant segregation in Bridgman crystal growth. A replenishing melt of a proper composition was supplied at a proper rate with suppression of dopant back diffusion. This allowed the composition of the growth melt and hence the composition of the growing crystal to remain constant. Crystal of uniform compositions were grown, including LiNOsb3-doped NaNOsb3, KNOsb3-doped NaNOsb3, Cd-doped InSb and Cdsb1-xZnsbxTe.

Tao, Ying

145

Determination of relative growth rates of natural quartz crystals  

PubMed

Although the theory describing crystal growth in the geological environment is well established, there are few quantitative studies that delimit the absolute time involved in the growth of natural crystals. The actual mechanisms responsible for the variation in size and shape of individual crystal faces are, in fact, not well understood. Here we describe a micro-infrared spectroscopic study of a single, gem-quality quartz crystal that allows us to measure the size, shape and relative growth rate of each of the crystal faces that are active throughout its growth history. We demonstrate that the abundances of hydrogen-bearing impurities can serve as 'speedometers' to monitor the growth rate of advancing crystal faces. Our technique can be applied to crystals from a variety of geological environments to determine their growth histories. Within the electronics industry, the technique might facilitate the production of defect-free synthetic crystals required for high-quality resonators and, ultimately, might allow determination of the absolute time involved in geological processes such as the crystallization of magmas, fluid flow in metamorphism and the sealing of open cracks in earthquake rupture zones. PMID:10786791

Ihinger; Zink

2000-04-20

146

MCT crystal growth. Final report  

SciTech Connect

Convection and segregation in directional solidification and crystal growth by the Bridgman-Stockbarger technique are traditionally treated by assuming axisymmetric thermal condition on the ampoule wall. It is, however, difficult to achieve such a condition in an experimental setup. Any deviation from an axisymmetric temperature field on the wall of a vertical ampoule represents a horizontal temperature gradient. The horizontal density gradient that results from thermal expansion in the melt under this condition must lead on earth to some buoyance-driven convection, no matter what the axial (vertical) temperature distribution that is imposed on the melt. The magnitude of such convective flows for conditions representative of the MSFC mercury-cadmium-telluride (MCT) Bridgman setup is studied.

Baird, J.K.

1988-02-01

147

Growth of Solid Solution Single Crystals.  

National Technical Information Service (NTIS)

The bulk growth of HgCdTe crystals by modified Bridgman techniques and by quenching anneal recrystallization yields deficient material. The primary complication for growth arises from a pronounced tendency for constitutional supercooling caused by the cha...

A. F. Witt

1981-01-01

148

Investigation of Crystal Growth from Solutions.  

National Technical Information Service (NTIS)

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, degr...

I. Miyagawa

1975-01-01

149

Applications of Atomic Force Microscopy in Macromolecular Crystal Growth  

NASA Astrophysics Data System (ADS)

A series of protein and virus crystals was investigated, in situ, using atomic force microscopy. Most of the crystals grew principally on steps generated by two dimensional nucleation on surfaces, though some, such as canavalin, grew by development of spiral dislocations. Apoferritin grew by a rarely encountered mechanism, normal growth, usually associated only with melt or vapor phase crystallization. Cubic crystals of satellite tobacco mosaic virus (STMV) grew, at moderate to high levels of supersaturation, by the direct addition of three- dimensional nuclei followed by their rapid normal growth and lateral expansion, a mechanism not previously described to promote controlled and reproducible crystal growth from solutions. Biological macromolecules apparently utilize a more diverse range of growth mechanisms in their crystallization than any previously studied material. High resolution AFM analyses have allowed us to record the first, real time, in situ atomic force microscope images, on the nanometer scale, of the incorporation of molecules into the growth steps of crystals grown from solution. The molecular structure of the growth step edge and surface layer on the (101) faces of tetragonal thaumatin crystals were resolved. It was shown that, although the growth step height corresponds to the unit cell containing eight thaumatin molecules, its advancement occurs by the addition of individual protein molecules rather than molecular clusters. Models for the packing of molecules on the surface layer, and of the structure of the step edge were developed which agree well with experimental data. Again, using high resolution, in situ atomic force microscopy, the initial stages of the formation and development of two- and three-dimensional nuclei on the surface of protein crystals were recorded. From these we conclude that non crystalline aggregates, with short range order, present both on the crystal-solution interface, and in the volume of the solution, give rise to two- and three-dimensional crystalline nuclei respectively. The transition to a crystalline phase is guided by the underlying crystalline lattice.

McPherson, Alexander

1997-03-01

150

Anisotropy of crystal growth mechanisms, dielectricity, and magnetism of multiferroic Bi2FeMnO6 thin films  

NASA Astrophysics Data System (ADS)

Epitaxial Bi2FeMnO6 (BFMO) thin films deposited on various Nb:SrTiO3 substrates show that the lattice parameters are very sensitive to epitaxial strains. Compressive and tensile strains are induced to the in-plane lattice constants of the (100) and (111) oriented films, respectively, while that of the (110) oriented thin film stay unstrained. The thin films also exhibit a strongly anisotropic growth habit depending on the substrate. Spiral growth, such as in the (100) BFMO film, is unique in samples prepared by pulsed laser deposition. Extrinsic dielectric constants at low frequencies are attributed to oxygen vacancies via the Maxwell-Wagner effect. All the samples show saturated hysteresis loops with very small coercive fields at 200 K, indicating the presence of weak ferromagnetism.

Liu, P.; Cheng, Z. X.; Du, Y.; Feng, L. Y.; Fang, H.; Wang, X. L.; Dou, S. X.

2013-05-01

151

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

152

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

153

Growth and Properties of Hydorxyapatite Single Crystals.  

National Technical Information Service (NTIS)

Four methods were attempted for the growth of large single crystals of hydroxyapatite: hydrothermal synthesis, growth in gels under hydrothermal conditions, growth in aqueous solution at 100C, and growth under conditions where the pH is controlled by the ...

J. F. Kirn H. Leidheiser

1967-01-01

154

Innovation in crystal growth: A personal perspective  

Microsoft Academic Search

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,

J. B. Mullin

2008-01-01

155

Thermosyphon Suspension For Growth Of Crystals  

NASA Technical Reports Server (NTRS)

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

Nyce, Thomas A.

1991-01-01

156

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

157

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

158

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

159

Continuing adventures in lysozyme crystal growth. [in earth laboratory experiments  

NASA Technical Reports Server (NTRS)

Results obtained on the crystal nucleation and growth of lysozyme are presented. Special attention is given to the anion-protein binding, the nucleation kinetics, the mechanisms of aggregation, and the conditions that promote or inhibit lysozyme (110)-face growth rate. The emerging theory that is currently being used for data interpretation and for designing new experimental approaches is outlined.

Pusey, Marc L.

1992-01-01

160

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

161

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

162

Seeded Single Crystal Silicon Carbide Growth and Resulting Crystals.  

National Technical Information Service (NTIS)

A method is disclosed for producing a high quality bulk single crystal of silicon carbide in a seeded growth system and in the absence of a solid silicon carbide source, by reducing the separation between a silicon carbide seed crystal and a seed holder u...

D. P. Malta H. M. Hobgood J. R. Jenny M. Brady S. G. Mueller

2005-01-01

163

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

164

Nucleation and growth kinetics of struvite crystallization.  

PubMed

Struvite crystallization technology is being widely applied in full-scale due to a surge in nutrient demand and phosphate price increases. Past investigations on struvite crystallization focused on process efficiency and thermodynamics, and less on kinetics, while mainly using fluidized bed type crystallizer. In this work, nucleation and growth kinetic data were measured using stirred vessel. The primary and secondary nucleation was measured in synthetic wastewater, and crystal growth in digested supernatant. The measured kinetic data was correlated with solution supersaturation. The dependence of growth rate on relative supersaturation in the digested was higher compared to synthetic wastewater. The crystal polymorph in synthetic wastewater and real wastewater was comparable. Products from the growth studies showed narrow size distribution and favorable separation characteristics. The secondary nucleation rate showed second order dependence on relative supersaturation. The nucleation induction time decreased with an increase in supersaturation ratio with a clear distinction between homogenous and heterogeneous primary nucleation. PMID:23541308

Mehta, Chirag M; Batstone, Damien J

2013-05-15

165

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

166

The crystal growth of barium flouride in aqueous solution  

NASA Astrophysics Data System (ADS)

The kinetics of growth of barium flouride seed crystals were investigated in aqueous solution at 25°C using a constant composition method, in which the supersaturation and ionic strength were maintained constant by the addition of titrants consisting of barium nitrate and potassium flouride solutions. The rates of reaction, studied over a range of supersaturation (? ? 0.4 to 1.0), were interpreted in terms of crystal growth models. A spiral growth mechanism best describes the data, and scanning electron microscopy indicates a three-dimensional growth. In the presence of inorganic additives such as phosphate, however, induction periods precede a morphological two-dimensional crystallization. Coulter Counter results show little crystal agglomeration.

Barone, J. P.; Svrjcek, D.; Nancollas, G. H.

1983-06-01

167

Synchrotron X-ray imaging for crystal growth studies  

NASA Astrophysics Data System (ADS)

The features associated with modern synchrotron radiation machines (intense and coherent beams) result in a substantial extension of X-ray imaging capabilities in terms of spatial and temporal resolution, phase contrast and 3D images. This allows crystal growth-related information to be obtained which is not available otherwise. After briefly describing the main synchrotron radiation based imaging techniques of interest, we give original examples illustrating the new capabilities for crystal growth: characterisation of crystals grown for applications, such as ice tri-crystals produced for mechanical deformation studies; SiC; crystalline silicon for solar photovoltaic cells; in situ and in real time studies of quasicrystal growth (AlPdMn); and ultrafast tomography for the study of the growth of dendrites in metallic alloys.

Baruchel, José; Di Michiel, Marco; Lafford, Tamzin; Lhuissier, Pierre; Meyssonnier, Jacques; Nguyen-Thi, Henri; Philip, Armelle; Pernot, Petra; Salvo, Luc; Scheel, Mario

2013-02-01

168

Melt-Growth Dynamics in CdTe Crystals  

NASA Astrophysics Data System (ADS)

We use a new, quantum-mechanics-based bond-order potential (BOP) to reveal melt growth dynamics and fine scale defect formation mechanisms in CdTe crystals. Previous molecular dynamics simulations of semiconductors have shown qualitatively incorrect behavior due to the lack of an interatomic potential capable of predicting both crystalline growth and property trends of many transitional structures encountered during the melt?crystal transformation. Here, we demonstrate successful molecular dynamics simulations of melt growth in CdTe using a BOP that significantly improves over other potentials on property trends of different phases. Our simulations result in a detailed understanding of defect formation during the melt growth process. Equally important, we show that the new BOP enables defect formation mechanisms to be studied at a scale level comparable to empirical molecular dynamics simulation methods with a fidelity level approaching quantum-mechanical methods.

Zhou, X. W.; Ward, D. K.; Wong, B. M.; Doty, F. P.

2012-06-01

169

Growth and Characterization of Silicon Carbide Crystals  

NASA Astrophysics Data System (ADS)

Silicon carbide is a semiconductor that is highly suitable for various high-temperature and high-power electronic technologies due to its large energy bandgap, thermal conductivity, and breakdown voltage, among other outstanding properties. Large-area high-quality single-crystal wafers are the chief requirement to realize the potential of silicon carbide for these applications. Over the past 20 years, considerable advances have been made in silicon carbide single-crystal growth technology through understanding of growth mechanisms and defect nucleation. Wafer sizes have been greatly improved from wafer diameters of a few millimeters to 100 mm, with overall dislocation densities steadily reducing over the years. Device-killing micropipe defects have almost been eliminated, and the reduction in defect densities has facilitated enhanced understanding of various defect configurations in bulk and homoepitaxial layers. Silicon carbide electronics is expected to continue to grow and steadily replace silicon, particularly for applications under extreme conditions, as higher-quality, lower-priced large wafers become readily available.

Dhanaraj, Govindhan; Raghothamachar, Balaji; Dudley, Michael

170

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

171

On growth rate hysteresis and catastrophic crystal growth  

NASA Astrophysics Data System (ADS)

Different crystal growth rates as supersaturation is increasing or decreasing in impure media is a phenomenon called growth rate hysteresis (GRH) that has been observed in varied systems and applications, such as protein crystallization or during biomineralization. We have recently shown that the transient adsorption of impurities onto newly formed active sites for growth (or kinks) is sensitive to the direction and rate of supersaturation variation, thus providing a possible explanation for GRH [6]. In the present contribution, we expand on this concept by deriving the analytical expressions for transient crystal growth based on the energetics of growth hillock formation and kink occupation by impurities. Two types of GRH results are described according to the variation of kink density with supersaturation: for nearly constant density, decreasing or increasing supersaturation induce, respectively, growth promoting or inhibiting effects relative to equilibrium conditions. This is the type of GRH measured by us during the crystallization of egg-white lysozyme. For variable kink density, slight changes in the supersaturation level may induce abrupt variations in the crystal growth rate. Different literature examples of this so-called 'catastrophic' crystal growth are discussed in terms of their fundamental consequences.

Ferreira, Cecília; Rocha, Fernando A.; Damas, Ana M.; Martins, Pedro M.

2013-04-01

172

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

173

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.

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

2013-01-01

174

Research support for cadmium telluride crystal growth  

NASA Technical Reports Server (NTRS)

Work performed during the period 11 Feb. 1992 to 10 Aug. 1993 on research support for cadmium telluride crystal growth is reported. Work on chemical impurity characterization and mass spectroscopy is described.

Rosenberger, Franz; Banish, Michael

1993-01-01

175

Research Support for Cadmium Telluride Crystal Growth.  

National Technical Information Service (NTIS)

Work performed during the period 11 Feb. 1992 to 10 Aug. 1993 on research support for cadmium telluride crystal growth is reported. Work on chemical impurity characterization and mass spectroscopy is described.

F. Rosenberger M. Banish

1993-01-01

176

The Growth of Large Single Crystals.  

ERIC Educational Resources Information Center

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

Baer, Carl D.

1990-01-01

177

Investigation of Growth of Electromagnetic Single Crystals.  

National Technical Information Service (NTIS)

Research was carried out on the growth of single crystals of plain and doped sapphire, ruby, spinel, yttrium oxide, magnesium titanate, yttrium iron garnet, beryl, cerium molybdate, lanthanum molybdate, sodium ferrite, and high melting fluorides. The meth...

C. M. Cobb J. A. Adamski E. B. Wallis

1964-01-01

178

Growth and Properties of Lanthanum Oxysulfide Crystals  

Microsoft Academic Search

To better determine the optical properties of the rare-earth oxysulfide phosphors and to lay the foundation for their application in single-crystal form as scintillators and lasers we have grown, for the first time, single crystals of these materials. A description of present growth techniques will be presented. Materials problems and our progress toward their solutions will be discussed. Single-crystal properties,

L. E. Sobon; K. A. Wickersheim; R. A. Buchanan; R. V. Alves

1971-01-01

179

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

PubMed

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

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

2014-06-01

180

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

181

Protein crystal growth (5-IML-1)  

NASA Technical Reports Server (NTRS)

Proteins (enzymes, hormones, immunoglobulins) account for 50 pct. or more of the dry weight of most living systems. A detailed understanding of the structural makeup of a protein is essential to any systematic research pertaining to it. Most macromolecules are extremely difficult to crystallize, and many otherwise exciting projects have terminated at the crystal growth stage. In principle, there are several aspects of microgravity that might be exploited to enhance protein crystal growth. The major factor is the elimination of density driven convective flow. Other factors that can be controlled in the absence of gravity is the sedimentation of growing crystals in a gravitational field, and the potential advantage of doing containerless crystal growth. As a result of these theories and facts, one can readily understand why the microgravity environment of an Earth orbiting vehicle seems to offer unique opportunities for the protein crystallographer. This perception has led to the establishment of the Protein Crystal Growth in a Microgravity Environment (PCG/ME) project. The results of experiments already performed during STS missions have in many cases resulted in large protein crystals which are structurally correct. Thus, the near term objective of the PCG/ME project is to continue to improve the techniques, procedures, and hardware systems used to grow protein crystals in Earth orbit.

Bugg, Charles E.

1992-01-01

182

Microscopic model of protein crystal growth  

Microsoft Academic Search

A microscopic, reversible model to study protein crystal nucleation and growth is presented. The probability of monomer attachment to the growing crystal was assumed to be proportional to the protein volume fraction and the orientational factor representing the anisotropy of protein molecules. The rate of detachment depended on the free energy of association of the given monomer in the lattice,

Andrzej M. Kierzek; Piotr Pokarowski; Piotr Zielenkiewicz

2000-01-01

183

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

184

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

185

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

186

Growth kinetics and morphology of polymer crystals  

NASA Astrophysics Data System (ADS)

Originating from the nature of chain folding, polymer single crystals are quite unique in the growth kinetics and morphology. The developments of the understanding in the past 50 years are discussed and the unsolved important issues will be suggested. Polymer single crystals are thin lamellae with the thickness in the order of 10nm determined by the period of chain folding, which keeps a constant value for the isothermal crystallization. The growth of polymer single crystals is modeled by the kinetics of creation and annihilation of growth steps on a rectangular substrate with the pre-determined thickness. The growth face is therefore regarded as a one-dimensional substrate and the kinks and anti-kinks on the substrate correspond to the growth steps propagating in the opposite directions. The kinetic equations of those kinks proposed by Seto and Frank well describe the transition of growth regime as a crossover from single nucleation to multi-nucleation on the basis of the standard model of chain-folded polymer crystallization with surface nucleation proposed by Lauritzen and Hoffman. However, the analysis of the growth kinetics and morphology of single crystals having curved growth front suggests an unusual behavior of the step propagation velocity. The anomaly can be accounted for by a self-poisoning of the growth step interrupted by polymer chains with folding shorter than required. An entropic barrier of pinning proposed by Sadler and Gilmer is a possible candidate of the self-poisoning and is in accordance with recent computer simulation results suggesting the kinetics on a rugged free energy landscape having a resemblance to protein folding. Therefore, the quantitative evaluation of the kinetic barriers of surface nucleation and pinning has been an important issue. In addition, examination of the kinetics of melting will have valuable information because melting of a crystal must be free from nucleation but can still be limited by the entropic barrier.

Toda, Akihiko

2007-03-01

187

Protein crystal growth in low gravity  

NASA Technical Reports Server (NTRS)

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

Feigelson, Robert S.

1993-01-01

188

Electrochemical crystal growth of perovskite ruthenates  

Microsoft Academic Search

Single crystals of CaRu1?xMnxO3 and SrRuO3 were grown using an electrochemical technique with calcium or strontium chloride as a solvent, and the crystallographic properties of grown crystals were characterized by single-crystal X-ray diffraction and powder X-ray diffraction. CaRu1?xMnxO3 and SrRuO3 crystals with natural surfaces were obtained on the cathode, reflecting the characteristic of the growth in a liquid phase. In

H. Samata; Y. Saeki; S. Mizusaki; Y. Nagata; T. C. Ozawa; A. Sato

2009-01-01

189

Optical and Mechanical Characteristics of PETN Single Crystal  

NASA Astrophysics Data System (ADS)

Pentaerythritol tetranitrate (PETN) is an extensively used crystalline high explosive. A good understanding of the laser- induced chemical decomposition and growth to detonation of PETN is important. This work on PETN single crystals focused primarily on its mechanical and optical properties under laser pulse interaction. Laser pulse (E<2 J, ?= 150 ps, &=tilde; 1.06 ?m) was focused on the single crystal surface to focal point size 80 .. 800 ?m. The goal of this work was to study the early stages of laser-induced explosion decomposition. Crystal response to the laser radiation was determined by the luminescence and conductivity of crystals. Explosion decomposition of PETN single crystals failed to occur within the studied range of initiation energies. Experiments measured the threshold of the optical breakdown for PETN and determined energies when its mechanical destruction begins. Analysis of experiments allowed a new scheme to be proposed for experiments when the laser radiation energy is injected inside the crystal.

Gromov, V. T.

2005-07-01

190

Growth rate dispersion of small ammonium alum crystals  

NASA Astrophysics Data System (ADS)

The growth rates of small (below 60 ?m) and large (about 1 mm) crystals of ammonium alum was measured during batch crystallization from aqueous solutions. The growth rate distribution of small crystals is close to normal. With increasing supersaturation the growth rate of the large crystals increases more rapidly than that of small crystals.

Teodossiev, N.

1987-01-01

191

Crystal Growth by Physical Vapor Transport: Experiments and Simulation Dynamics  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

192

Possibilities and Limitations of Multioxides Crystals Growth.  

National Technical Information Service (NTIS)

The main methods of crystal growth from the melt the Czochralski and floating zone will be discussed and compared. Advantages, disadvantages and limitations of both methods as well as ways of solving some of the problems existing during growth of differen...

J. Fink-Finowicki M. Berkowski R. Aleksiyko

2001-01-01

193

Synthesis, growth, structural, spectral, linear and nonlinear optical and mechanical studies of a novel organic NLO single crystal 4-Bromo 4-Nitrostilbene (BONS) for nonlinear optical applications  

NASA Astrophysics Data System (ADS)

Single crystal of 4-Bromo 4-Nitrostilbene (BONS), a new organic nonlinear optical material was synthesized and crystals were grown with dimensions up to 8 × 6 × 3 mm3 from ethyl methyl ketone (EMK) solvent by slow evaporation method. Single crystal X-ray diffractometer was used to measure the unit cell parameters and confirmed the BONS structure as orthorhombic with the space group P212121. The sample has been subjected to powder X-ray diffraction to identify the crystalline nature and the prominent peaks were indexed. The functional groups were identified from Fourier transform infrared (FTIR) spectral analysis. Proton NMR analysis confirms the protonation in the structure of the title compound. Optical behaviour of BONS has been observed by UV-Vis absorption spectral analysis which shows the low cut off wavelength lies at 405 nm and found that the energy band gap of the crystal is 2.90 eV. Thermal stability of the material has been confirmed by TG/DTA analyses. The BONS compound formation analyzed by mass spectroscopic analysis. The mechanical strength of the crystal was found using Vickers microhardness measurement. The laser damage threshold (LDT) for the grown crystal was measured by using Nd:YAG laser. Photoluminescence spectrum indicated green light emission at 515.44 nm. The Kurtz powder second harmonic generation test shows that the BONS crystal (1.5 V) is a very potential NLO candidate for optical generation and it has SHG efficiency 69 times greater than that of KDP (21.7 mV).

Dinakaran, Paul M.; Kalainathan, S.

2013-03-01

194

Organic nanocrystals of the resorcinarene hexamer via sonochemistry: evidence of reversed crystal growth involving hollow morphologies.  

PubMed

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

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

2012-04-25

195

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

PubMed Central

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

Sander, John R. G.; Bucar, Dejan-Kresimir; Baltrusaitis, Jonas; MacGillivray, Leonard R.

2012-01-01

196

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

197

Bridgman growth of paratellurite single crystals  

Microsoft Academic Search

The growth of paratellurite single crystals by the vertical-gradient freezing technique is reported for the first time. Boules of 120mm long and 25mm in diameter were obtained under a temperature gradient of 10°Ccm?1 and translation rates lower than 0.6mmh?1. The spatial distribution of defects along the growth axis reveals a continuous evolution of the free convective fluid-flow regime as growth

P. Veber; J. Mangin; P. Strimer; P. Delarue; C. Josse; L. Saviot

2004-01-01

198

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

199

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

200

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

201

Mechanical Properties Of Large Sodium Iodide Crystals  

NASA Technical Reports Server (NTRS)

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

Lee, Henry M.

1988-01-01

202

Studies on tetragonal lysozyme crystal growth rates.  

PubMed

A computer-controlled apparatus able to simultaneously follow the face growth rate of up to 40 crystals was developed. This apparatus was used to investigate the effects of solution pH on the (110) and (101) face growth rates of tetragonal lysozyme. Growth rates were measured at pH 4.0, 4.4, 4.8 and 5.2, in 0.1 M sodium acetate buffer with 5% NaCl, 295 K. Initial crystal sizes ranged from 10 to 40 microm. Plots of log supersaturation ratio (either C/C(sat) or C/C(sat) - 1) versus log(growth rate) are not linear, typically having a slope of approximately 8 at the lowest growth rates determined (10(-6) microm s(-1)), which falls off to a slope of approximately 2 at the highest growth rates (10(-2) microm s(-1)) measured. Ratios of C/C(sat) ranged from 4 to >20. The data show that lower solubility solutions require higher supersaturation ratios for equivalent growth rates. Data for the growth rate of the (101) face at pH 4.0 were widely scattered, especially at lower supersaturation ratios. Time-lapse video of crystals at low supersaturations shows that initially only the (110) faces grow, leaving 'notches' at the (110)-(110) corners. These corners then fill in and macro-steps appear on the (101) faces which rapidly move inward in the form of an octagon, restoring the crystal to a 'normal' appearance. This phenomenon has been observed for tetragonal crystals grown in either still or flowing solutions. Flowing solutions at lower supersaturations also gave cases where the corners did not fill in, with the (110) faces continuing to grow out until growth ceased. PMID:15299425

Forsythe, E; Ewing, F; Pusey, M

1994-07-01

203

Modeling and simulation of faceted thin film crystal growth  

NASA Astrophysics Data System (ADS)

The control of crystal shape is one of the keys to the fine tuning of mechanical, electrical, and optical properties of many thin film materials. Realistic three-dimensional crystal growth morphology prediction is hindered by the difficulties in obtaining the full set of strong anisotropic physical-chemical quantities and the complexities of many competing growth mechanisms. To bypass these difficulties, we focus on the intrinsic factors controlling crystal growth morphologies. First, we identify the symmetry group of crystal growth shape and the interface stiffness tensor. As a byproduct, we propose an efficient thermal fluctuation simulation method to determine the interface stiffness tensor. Then, we identify the essential differences between equilibrium and nonequilibrium crystal growth. Next, we demonstrate that, beyond a critical length scale, the kinetic growth morphology is controlled by shape-independent growth velocities. This leads to our focus on the v-plot (i.e., polar plot of velocity versus surface orientations) model. Meanwhile, based on graph theory and growth processes classification, we develop a systematic approach to determine the full set of dimensionless numbers representing the competitions between growth processes. Then, a systematic approach is proposed to determine the v-plot. Next, a level set method tailored for selective area growth (SAG) is developed. The application of the v-plot and level set simulation methods to GaN grown by SAG is able to capture all of the major features of growth morphologies observed in a diverse set of experiments. Furthermore, the simulations correctly predict the stability of fast growing surfaces against perturbations and unveil the intrinsic imperfect nature of crystal merging. Based on the simulation result, a simple residual mismatch strain model is proposed to deduce that smaller aspect ratio (window width to island height) is preferred to produce lower angle grain boundaries on merging and higher quality crystals. Finally, the effects of non-surface energies on equilibrium crystal shape are studied. The major conclusion is that although the non-surface energies modify the Wulff shape, they only distort the Wulff shape and do not create or remove orientations. This conclusion greatly reduces the efforts to solve the variational problem associated with energy minimization.

Du, Danxu

204

Modeling Tetragonal Lysozyme Crystal Growth Rates  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

205

Modeling the Growth Rates of Tetragonal Lysozyme Crystal Faces  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

206

Protein Crystal Growth Dynamics and Impurity Incorporation  

NASA Technical Reports Server (NTRS)

The general concepts and theories of crystal growth are proven to work for biomolecular crystallization. This allowed us to extract basic parameters controlling growth kinetics - free surface energy, alpha, and kinetic coefficient, beta, for steps. Surface energy per molecular site in thermal units, alpha(omega)(sup 2/3)/kT approx. = 1, is close to the one for inorganic crystals in solution (omega is the specific molecular volume, T is the temperature). Entropic restrictions on incorporation of biomolecules into the lattice reduce the incorporation rate, beta, by a factor of 10(exp 2) - 10(exp 3) relative to inorganic crystals. A dehydration barrier of approx. 18kcal/mol may explain approx. 10(exp -6) times difference between frequencies of adding a molecule to the lattice and Brownian attempts to do so. The latter was obtained from AFM measurements of step and kink growth rates on orthorhombic lysozyme. Protein and many inorganic crystals typically do not belong to the Kossel type, thus requiring a theory to account for inequivalent molecular positions within its unit cell. Orthorhombic lysozyme will serve as an example of how to develop such a theory. Factors deteriorating crystal quality - stress and strain, mosaicity, molecular disorder - will be reviewed with emphasis on impurities. Dimers in ferritin and lysozyme and acetylated lysozyme, are microheterogeneous i.e. nearly isomorphic impurities that are shown to be preferentially trapped by tetragonal lysozyme and ferritin crystals, respectively. The distribution coefficient, K defined as a ratio of the (impurity/protein) ratios in crystal and in solution is a measure of trapping. For acetylated lysoyzme, K = 2.15 or, 3.42 for differently acetylated forms, is independent of both the impurity and the crystallizing protein concentration. The reason is that impurity flux to the surface is constant while the growth rate rises with supersaturation. About 3 times lower dimer concentration in space grown ferritin and lysozyme crystals might be examples explaining higher quality of the space grown protein crystal. Depletion of solution with respect to isomorphic impurities around a growing crystal may be K times deeper than with respect to the crystallizing protein.

Chernov, Alex A.; Thomas, Bill

2000-01-01

207

Crack growth in single-crystal silicon  

NASA Technical Reports Server (NTRS)

Crack growth in single-crystal silicon at room temperature in air was evaluated by double torsion (DT) load-relaxation method and monitored by acoustic emission (AE) technique. Both DT and AE methods indicated lack of subcritical crack growth in silicon. At the critical stress intensity factor, the crack front was found to be jumping several times in a 'mirror' region and then followed by fast crack growth in a 'hackle' region. Hackle marks were found to be associated with plastic deformation at the tip of the fast moving crack. No dislocation etch pits were found in the 'mirror' region, in which crack growth may result from interatomic bonds broken at the crack tip under stress without any plastic deformation. Acoustic emission appears to be spontaneously generated from both interatomic bonds broken and dislocation generation at the moving crack tip during the crack growth in single-crystal silicon.

Chen, C. P.; Leipold, M. H.

1986-01-01

208

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

209

Kinetic Monte Carlo simulations of the growth of polymer crystals  

NASA Astrophysics Data System (ADS)

Based upon kinetic Monte Carlo simulations of crystallization in a simple polymer model we present a new picture of the mechanism by which the thickness of lamellar polymer crystals is constrained to a value close to the minimum thermodynamically stable thickness, lmin. The free energetic costs of the polymer extending beyond the edges of the previous crystalline layer and of a stem being shorter than lmin provide upper and lower constraints on the length of stems in a new layer. Their combined effect is to cause the crystal thickness to converge dynamically to a value close to lmin where growth with constant thickness then occurs. This description contrasts with those given by the two dominant theoretical approaches. However, at small supercoolings the rounding of the crystal profile does inhibit growth as suggested in Sadler and Gilmer's entropic barrier model.

Doye, Jonathan P. K.; Frenkel, Daan

1999-02-01

210

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

211

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

212

A mechanistic model for calcite crystal growth using surface speciation  

NASA Astrophysics Data System (ADS)

A new mechanistic model for the crystal growth kinetics of calcite is presented, accounting for the presence of various surface complexes. Calcite crystal growth rates were determined with the constant composition method at ? c (calcite supersaturation) values of 1.5-9.8. In general the rate increases with ? c, but variations in CO 2 partial pressures and the (CO 32-)/(Ca 2+) ratio also have a major effect on the crystal growth rate. These effects are eliminated by assuming that calcite crystal growth proceeds through three reversible reactions, in which CaCO 30(aq) and Ca 2+(aq) are incorporated at specific surface complexes. The model derived rates closely follow the experimental rates over the entire experimental range ( r = 0.996, n = 23). The obtained rate constants indicate that CaCO 30(aq) is ?20 times more reactive than Ca 2+(aq) at the calcite-water interface. This agrees with the fact that dehydration of metal ions precedes crystal growth and, in analogy with other metal-ligand complexes, the CO 32- ligand will increase the rate of water exchange of Ca. This model is a modified version of a rhodochrosite crystal growth model (Sternbeck, 1997) which allows for the comparison of reaction mechanisms and rate constants. The rate constants for incorporation of CaCO 30(aq) at the mineral surface are 55 to 270 times higher than for MnCO 30(aq). This difference can not likely be explained by the water exchange rates, but may be due to the fact that ligand exchange mechanisms for Ca and Mn differ.

Nilsson, Ö.; Sternbeck, J.

1999-01-01

213

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

214

An Apparatus for Growth of Small Crystals From Solutions.  

ERIC Educational Resources Information Center

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

Mitrovic, Mico M.

1995-01-01

215

Calcium oxalate crystal growth in human urinary stones  

Microsoft Academic Search

Calcium oxalate stones are very common and increasing. Crystal growth is no less important than the crystal nucleation in the pathogenesis of stone formation. The crystal growth was studied in human calcium oxalate stones by a combined electron microscopy and x-ray diffraction. The main mode of weddellite growth was interpenetration twinning of tetrahedral bipyramids. Bipyramids may form as initial crystal

K. M. Kim; F. B. Johnson

1981-01-01

216

Liquid crystal growth at interfaces  

NASA Astrophysics Data System (ADS)

Liquid crystals exhibit a wealth of surface phenomena at interfaces. This work has concentrated on the studies of liquid crystal wetting behaviors under the Anopore confined geometry by using the high-resolution ac calorimeters as well as DNMR. Smectic layering at a solid surface were studied for mixtures 5CB + 12CB confined to the aliphatic acid treated Anopore. A thermodynamic signature was found to be associated with the surface-induced Smectic wetting for Anopore pore surfaces. The signature consists of series of small specific heat peaks, which can be associated to discrete Smectic wetting of the solid surface. With increasing 5CB concentration, the small smectic layering peaks broaden and decrease in size. The fact that the smectic wetting still exists at a 25% 5CB concentration means that the surface smectic order is formed deep in isotropic phase. The temperature positions of small peaks downshift linearly with increasing 5CB concentration. This indicates that the surface layer retains most of its characteristics until the translational smectic order is destroyed by the nematic orientational order. While the specific heat results of bulk m¯.O.8¯ show no abnormal behavior, the specific heat results for several members of n¯.O.m¯ confined to Anopore membranes showed a thermodynamic signature related to the nematic prewetting of the pore surfaces. The distinct signature consists of a bump appearing at a temperature 0.1--1.2 K above TNI. From this we estimate that there is a 5 nm thick surface layer in the isotropic phase wetting the solid wall of the 0.2 mum diameter pores. DNMR measurements determine that the molecular alignment in Anopore is perpendicular to the pore axis. The temperature difference of the prewetting peak from the TNI increases linearly with increasing m. This may be related to an increasing anchoring energy of m¯.O.8¯ with increasing chain length. The studies of m¯.O.8¯ in surfactant treated Anopore indicate that the prewetting only occurs for intermediate liquid crystal-surface interaction. Studies of 10. O.8¯ and 11.O.8¯ confined to different pore size Anopore also show that finite size effects may also play a role.

Liu, Xuewu

217

Crack Growth in Single-Crystal Silicon  

NASA Technical Reports Server (NTRS)

Report describes experiments on crack growth in single-crystal silicon at room temperature in air. Crack growth in (111) cleavage plane of wafers, 50 by 100 by 0.76 mm in dimension, cut from Czochralski singlecrystal silicon studied by double-torsion load-relaxation method and by acoustic-emission measurements. Scanning electron microscopy and X-ray topography also employed. Results aid in design and fabrication of silicon photovoltaic and microelectronic devices.

Chen, C. P.; Leipold, M. H.

1986-01-01

218

Optical monitoring of protein crystal growth  

NASA Technical Reports Server (NTRS)

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

Choudry, A.

1988-01-01

219

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) [Burlington, MA; Hatch, Arthur E. (Waltham, MA) [Waltham, MA; Goldsmith, Jeff M. (Medford, MA) [Medford, MA

1981-01-01

220

Optical and Mechanical Characteristics of PETN Single Crystal  

Microsoft Academic Search

Pentaerythritol tetranitrate (PETN) is an extensively used crystalline high explosive. A good understanding of the laser- induced chemical decomposition and growth to detonation of PETN is important. This work on PETN single crystals focused primarily on its mechanical and optical properties under laser pulse interaction. Laser pulse (E<2 J, tau= 150 ps, &=tilde; 1.06 mum) was focused on the single

V. T. Gromov

2005-01-01

221

Structural, spectral and mechanical studies of bimetallic crystal: cadmium manganese thiocyanate single crystals  

NASA Astrophysics Data System (ADS)

A nonlinear optical bimetallic thiocyanate complex crystal, cadmium manganese thiocyanate (CMTC) has been successfully synthesized. The growth of single crystals of cadmium manganese thiocyanate has been accomplished from aqueous solution using slow evaporation method. The presence of manganese and cadmium in the synthesized material was confirmed through energy dispersive spectrum (EDS) analysis. Structural analysis was carried out using powder X-ray diffractometer (PXRD) and crystalline perfection of the grown crystals was ascertained by high-resolution X-ray diffraction (HRXRD) analysis. Fourier transform infrared (FTIR) spectrum was taken to confirm the functional groups. The transmittance spectrum of the crystal in the UV-visible region has been recorded and the cutoff wavelength has been determined. The dielectric measurements for the crystals were performed for various frequencies and temperatures. The mechanical properties were evaluated by Vickers microhardness testing, which reveals hardness and stiffness constant of the crystals.

Manikandan, M.; Vijaya Prasath, G.; Bhagavannarayan, G.; Vijayan, N.; Mahalingam, T.; Ravi, G.

2012-09-01

222

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

DOEpatents

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

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

2010-07-20

223

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

224

Growth of organic crystals by Ostwald ripening  

NASA Technical Reports Server (NTRS)

The objective of this investigation is to evaluate the growth of various organic crystals by chemical precipitation and Ostwald ripening. Six precipitation reactors were flown on STS-51A. Five of the reactors contained proprietary materials. The sixth contained urea dissolved in ethanol with toluene as the precipitating agent. The size distribution will be analyzed and compared with a similar model being developed.

Egbert, W.; Podsiadly, C.; Naumann, R.

1985-01-01

225

A clarified gel for crystal growth  

NASA Technical Reports Server (NTRS)

A procedure for preparing clarified sodium silicate gels suitable for crystal growth is described. In the method described here, the silicate stock is clarified by pretreating it with cation exchange resins before preparing the gels. Also, a modified recipe is proposed for preparing gels to achieve improved transparency.

Barber, P. G.; Simpson, N. R.

1985-01-01

226

Growth of Solid Solution Single Crystals  

NASA Technical Reports Server (NTRS)

The objective of the study is to establish the effects of processing semiconducting, solid solution, single crystals in a microgravity environment on the metallurgical, compositional, electrical, and optical characteristics of the crystals. The alloy system being investigated is the solid solution semiconductor Hg(1-x)Cd(x)Te, with x-values appropriate for infrared detector applications in the 8 to 14 mm wavelength region. Both melt and Te-solvent growth are being performed. The study consists of an extensive ground-based experimental and theoretical research effort followed by flight experimentation where appropriate. The ground-based portion of the investigation also includes the evaluation of the relative effectiveness of stabilizing techniques, such as applied magnetic fields, for suppressing convective flow during the melt growth of the crystals.

Lehoczky, Sandor L.; Szofran, Frank R.; Gillies, Donald C.; Watring, Dale A.

1999-01-01

227

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

228

Surface Phenomena and Parameters of Crystal Growth: Simple Basics  

SciTech Connect

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

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

2010-07-22

229

Radiative heat exchange in Czochralski crystal growth  

NASA Astrophysics Data System (ADS)

The effect of diffuse-gray radiation on the parametric sensitivity and stability of the Czochralski crystal growth was analyzed using a thermal-capillary model (TCM) which governs heat transfer in the system, the shapes of the melt/crystal and melt/gas interfaces, and the shape of the growing crystal. The entire model was solved by a finite-element analysis for simultaneous calculation of the temperature field and interface shapes either by Newton's method for the quasi-steady-state model or by implicit time integration for transient simulations. Proportional and integral feedback control strategies were demonstrated for the control of the crystal radius by incorporating a servo-control equation for the heater temperature into the dynamic simulation based on the TCM.

Atherton, L. J.; Derby, J. J.; Brown, R. A.

1987-07-01

230

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

231

Electrochemical crystal growth of perovskite ruthenates  

NASA Astrophysics Data System (ADS)

Single crystals of CaRu 1-xMn xO 3 and SrRuO 3 were grown using an electrochemical technique with calcium or strontium chloride as a solvent, and the crystallographic properties of grown crystals were characterized by single-crystal X-ray diffraction and powder X-ray diffraction. CaRu 1-xMn xO 3 and SrRuO 3 crystals with natural surfaces were obtained on the cathode, reflecting the characteristic of the growth in a liquid phase. In spite of the low synthesis temperature of 780 °C, the size of CaRuO 3 crystals was relatively large (˜2.5 mm in length). The Mn content of grown crystals was in proportion to the molar ratio of Mn 2O 3/RuO 2 at the synthesis, and CaRu 1-xMn xO 3 crystals with different compositions could be obtained by only changing the ratio of the raw materials.

Samata, H.; Saeki, Y.; Mizusaki, S.; Nagata, Y.; Ozawa, T. C.; Sato, A.

2009-01-01

232

Pharmacologic mechanisms of crystal meth  

Microsoft Academic Search

Crystal meth is a form of the stimulant drug methamphet- amine that, when smoked, can rapidly achieve high concen- trations in the brain. Methamphetamine causes the release of the neurotransmitters dopamine, norepinephrine and serotonin and activates the cardiovascular and central ner- vous systems. The levels of dopamine are low in the brain of some drug users, but whether this represents

Stephen J. Kish

2008-01-01

233

Crystal growth and polishing method of lithium aluminum oxide crystal  

NASA Astrophysics Data System (ADS)

LiAlO 2 is an interesting substrate for growing GaN semiconductor material since the lattice mismatch between LiAlO 2 and GaN is as small as 1.7%. LiAlO 2 substrate are easily fabricated due to its low hardness, and chemical etchability. A unique feature of GaN grown on a (1 0 0) LiAlO 2 substrate is that it grows along the M-plane ( 1 0 1? 0), which is non-polar. In this orientation, the spontaneous polarization can be eliminated. This paper describes the growth of (1 0 0) LiAlO 2 single crystals using the Czochralski method. Two crystal boules are presented and compared. The crystal's structure was identified as the ? phase by X-ray diffraction scan. A method for polishing a crystal to obtain a smooth scratch-free LiAlO 2 single crystal substrate surface with a room mean square roughness below 1.0 nm is proposed. The surface morphology of the polished LiAlO 2 surface was evaluated by atomic force microscope.

Chou, Mitch M. C.; Huang, Sin Jie; Hsu, Chuck W. C.

2007-05-01

234

Mechanisms, kinetics, impurities and defects: consequences in macromolecular crystallization.  

PubMed

The nucleation and growth of protein, nucleic acid and virus crystals from solution are functions of underlying kinetic and thermodynamic parameters that govern the process, and these are all supersaturation-dependent. While the mechanisms of macromolecular crystal growth are essentially the same as for conventional crystals, the underlying parameters are vastly different, in some cases orders of magnitude lower, and this produces very different crystallization processes. Numerous physical features of macromolecular crystals are of serious interest to X-ray diffractionists; the resolution limit and mosaicity, for example, reflect the degree of molecular and lattice order. The defect structure of crystals has an impact on their response to flash-cooling, and terminal crystal size is dependent on impurity absorption and incorporation. The variety and extent of these issues are further unique to crystals of biological macromolecules. All of these features are amenable to study using atomic force microscopy, which provides direct images at the nanoscale level. Some of those images are presented here. PMID:24699728

McPherson, Alexander; Kuznetsov, Yurii G

2014-04-01

235

Laser crystallization and localized growth of nanomaterials for solar applications  

NASA Astrophysics Data System (ADS)

Laser-assisted localized growth of semiconducting nanostructures is reported. As is the case of conventional crystal growth, localized laser enables three kinds of crystal growth: (1) melt growth (recrystallization) of amorphous silicon nanopillars by pulsed laser; (2) vapor growth (chemical vapor deposition) of germanium nanowires; (3) solution growth (hydrothermal growth) of zinc oxide nanowires. The results not only demonstrate programmable and digital fabrication of laser-assisted crystal growth, but also reveal unusual growth chacracteristics (grain morphologies, growth kinetics). Related to solar applications, it is suggested that these structures can act as epitaxial seeds for growth of coarse grains and as multi-spectral centers for enhanced and engineered light absorption.

In, Jungbin; Ryu, Sang-Gil; Lee, Daeho; Ahn, Sanghoon; Zheng, Andy Cheng; Hwang, David Jae-Seok; Grigoropoulos, Costas P.

2013-09-01

236

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

237

Coarsening Scenarios in Unstable Crystal Growth  

NASA Astrophysics Data System (ADS)

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

Biagi, Sofia; Misbah, Chaouqi; Politi, Paolo

2012-08-01

238

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

239

Method of controlling defect orientation in silicon crystal ribbon growth  

NASA Technical Reports Server (NTRS)

The orientation of twinning and other effects in silicon crystal ribbon growth is controlled by use of a starting seed crystal having a specific (110) crystallographic plane and (112) crystallographic growth direction.

Leipold, M. H. (inventor)

1978-01-01

240

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

241

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

242

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

243

Enhancing the Mechanical Properties of Single-Crystal CVD Diamond  

SciTech Connect

Approaches for enhancing the strength and toughness of single-crystal diamond produced by chemical vapor deposition (CVD) at high growth rates are described. CVD processes used to grow single-crystal diamond in high density plasmas were modified to incorporate boron and nitrogen. Semi-quantitative studies of mechanical properties were carried out using Vickers indentation techniques. The introduction of boron in single-crystal CVD diamond can significantly enhance the fracture toughness of this material without sacrificing its high hardness ({approx}78 GPa). Growth conditions were varied to investigate its effect on boron incorporation and optical properties by means of photoluminescence, infrared, and ultraviolet-visible absorption spectroscopy. Boron can be readily incorporated into single-crystal diamond by the methods used, but with nitrogen addition, the incorporation of boron was hindered. The spectroscopic measurements indicate that nitrogen and boron coexist in the diamond structure, which helps explain the origin of the enhanced fracture toughness of this material. Further, low pressure/high temperature annealing can enhance the intrinsic hardness of single-crystal CVD diamond by a factor of two without appreciable loss in fracture toughness. This doping and post-growth treatment of diamond may lead to new technological applications that require enhanced mechanical properties of diamond.

Liang, Q.; Yan, C; Meng, Y; Lai, J; Krasnicki, S; Mao, H; Hemley, R

2009-01-01

244

KDP crystal growth from solution studied with Diffrasor technique  

Microsoft Academic Search

The growth of KDP crystals from solution is studied in coherent light with an optical apparatus called Diffrasor. It is aimed to study interface phenomena during crystal growth from fluid phases, mostly from solution. It provides data about concentration gradients inside the fluid by measuring the deflection occurring in a laser beam which crosses the solution during crystal growth. It

E. Piano; Gian A. dall'Aglio; Alberto Diaspro

1999-01-01

245

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

246

(PCG) Protein Crystal Growth Human Serum Albumin  

NASA Technical Reports Server (NTRS)

(PCG) Protein Crystal Growth Human Serum Albumin. Contributes to many transport and regulatory processes and has multifunctional binding properties which range from various metals, to fatty acids, hormones, and a wide spectrum of therapeutic drugs. The most abundant protein of the circulatory system. It binds and transports an incredible variety of biological and pharmaceutical ligands throughout the blood stream. Principal Investigator on STS-26 was Larry DeLucas.

1989-01-01

247

A Comparative Study of Defects and Growth in Organic Crystal Family of Hydrogen Phthalates  

NASA Astrophysics Data System (ADS)

The organic crystals of potassium hydrogen phthalate (KAP) (or rubidium hydrogen phthalate(RAP)) and thallium hydrogen phthalate(TAP) crystallize out in the same space group of P21ab. The growth morphological change between them has been studied via defective observation and growth theoretical calculation, which indicates that the crystals of KAP and RAP grow through the 2D mechanism and the growth mechanism of (001) faces in TAP changes to defect mechanism. The theoretical results are in good agreement with the experimental ones.

Guan, Tie-tang; Zhao, Qing-lan; Li, Yuan-zhong; Huang, Yi-sen

1998-01-01

248

Dynamic pressure-induced dendritic and shock crystal growth of ice VI  

PubMed Central

Crystal growth mechanisms are crucial to understanding the complexity of crystal morphologies in nature and advanced technological materials, such as the faceting and dendrites found in snowflakes and the microstructure and associated strength properties of structural and icy planetary materials. In this article, we present observations of pressure-induced ice VI crystal growth, which have been predicted theoretically, but had never been observed experimentally to our knowledge. Under modulated pressure conditions in a dynamic-diamond anvil cell, rough single ice VI crystal initially grows into well defined octahedral crystal facets. However, as the compression rate increases, the crystal surface dramatically changes from rough to facet, and from convex to concave because of a surface instability, and thereby the growth rate suddenly increases by an order of magnitude. Depending on the compression rate, this discontinuous jump in crystal growth rate or “shock crystal growth” eventually produces 2D carpet-type fractal morphology, and moreover dendrites form under sinusoidal compression, whose crystal morphologies are remarkably similar to those predicted in theoretical simulations under a temperature gradient field. The observed strong dependence of the growth mechanism on compression rate, therefore, suggests a different approach to developing a comprehensive understanding of crystal growth dynamics.

Lee, Geun Woo; Evans, William J.; Yoo, Choong-Shik

2007-01-01

249

A unified description of attachment-based crystal growth.  

PubMed

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

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

2014-07-22

250

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

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

251

A visualization and computational study of horizontal Bridgman crystal growth  

Microsoft Academic Search

A transparent three-zone horizontal Bridgman furnace was used for the crystal growth of sodium nitrate. During crystal growth, the heating profiles and the growth front shape as well as flow patterns were recorded. To further understand the heat flow, a three-dimensional computer model based on an efficient multigrid finite volume method was also used to simulate the growth. Key process

C. W Lan; M. C Su; M. C Liang

2000-01-01

252

Crystal mechanics of some alkali halides  

NASA Astrophysics Data System (ADS)

A three-body-force shell model (TSM) has been employed for a comprehensive and unified calculation of the crystal mechanics of some alkali halides. This includes the description of phonon dispersion, two-phonon Raman and infrared spectra, specific heats, cohesive energy, relative stability, phase-transition pressure and volume, dielectric constants, quasi- harmonic elastic and photoelastic properties of lithium fluoride, potassiumchloride and rubidium chloride. These predictions are reasonably good and have led to the conclusion that TSM is an appropriate model for lattice mechanical descriptions of ionic crystals.

Nirwal, V. V. S.; Singh, R. K.

1981-02-01

253

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

254

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

255

Synthesis, growth, structural, optical, spectral, thermal and mechanical studies of 4-methoxy 4-nitrostilbene (MONS): A new organic nonlinear optical single crystal  

NASA Astrophysics Data System (ADS)

4-Methoxy 4-nitrostilbene (MONS), a new organic nonlinear optical material has been synthesized. Based on the solubility data good quality single crystal with dimensions up to 38 × 11 × 3 mm3 has been grown by slow evaporation method using ethyl methyl ketone (MEK) as a solvent. Powder XRD confirms the crystalline property and also the diffraction planes have been indexed. The lattice parameters for the grown MONS crystals were determined by using single crystal X-ray diffraction analysis and it reveals that the crystal lattice system is triclinic. The crystalline perfection of the grown crystals has been analysed by high resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectrum for powdered MONS sample confirms the functional groups present in the grown crystal. The UV-vis absorption spectrum has been recorded in the range of 190-1100 nm and the cut off wavelength 499 nm has been determined. The optical constants of MONS have been determined through UV-vis-NIR spectroscopy. The MONS crystals were further subjected to other characterizations. i.e., 1H NMR, TG/DTA, photoluminescence and microhardness test. The Kurtz and Perry powder technique confirms the NLO property of the grown crystal and the SHG efficiency of MONS was found to be 1.55× greater than that of KDP crystal.

Dinakaran, Paul M.; Bhagavannarayana, G.; Kalainathan, S.

2012-11-01

256

Crystal Growth and Physical Characterizations of GaPO4.  

National Technical Information Service (NTIS)

An investigation concerning GaPO4 crystal growth in sulphuric and phosphoric acid media through the slow heating and vertical reverse temperature gradient methods is reported. Systematic study of growth parameters shows a Vx growth rate always much greate...

E. Philippot A. Ibanez A. Goiffon B. Capelle A. Zarka

1992-01-01

257

Crystal splitting in the growth of ?-FeO(OH)  

NASA Astrophysics Data System (ADS)

?-FeO(OH) (akaganeite-Q) nanostructures with a sheaflike morphology are obtained via the hydrolysis of FeCl 3 solutions at different temperatures. The individual filaments have an average diameter of ˜60 nm, and the sheaves are ˜3.2 ?m in length at 80 °C for 10 h. These structures may be formed by the splitting crystal growth mechanism, which is known to explain the morphology some mineral crystals present in nature. By control of the synthetic parameters, different morphologies are obtained, complex sheaf structures have also been found which have been observed to occur by crystal splitting in minerals. These new ?-FeO(OH) structures are characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Hu, Yinghua; Chen, Kezheng

2007-10-01

258

Polymorphism, growth and characterization of a new organic nonlinear optical crystal: 4-dimethylaminobenzaldehyde-4-nitrophenylhydrazone (DANPH)  

NASA Astrophysics Data System (ADS)

A new organic nonlinear optical crystal, 4-dimethylaminobenzaldehyde-4-nitrophenylhydrazone (DANPH), has been prepared and investigated with regard to polymorphism, growth, and characterization of the structural and physical properties. Recrystallization of DANPH in various solvents under different conditions showed the existence of three crystalline phases, a co-crystal (form I) of DANPH with benzene in a ratio 4 to 1 in space group P2 12 12, red greenish prisms (form II) in space group Cc, and red orange plates (form III) in space group {P2 1}/{c}. The growth of crystals with interesting linear and nonlinear optical properties (form II) was investigated by using different growth techniques: solution growth, gel growth and physical vapor transport growth. With these methods bulk crystals, very thin plates, and films were grown, respectively. By the analysis of crystal structures and phase stabilities of the forms II and III, the mechanism of polymorphism was investigated.

Pan, F.; Bosshard, Ch.; Wong, M. S.; Serbutoviez, C.; Follonier, S.; Günter, P.; Schenk, K.

1996-08-01

259

Alloy Semiconductor Crystal Growth Under Microgravity  

SciTech Connect

Microgravity studies on the dissolution and crystallization of In{sub x}Ga{sub 1-x}Sb have been done using a sandwich combination of InSb and GaSb as the starting material using the Chinese recoverable satellite. The same type of experiment was performed under 1G gravity condition for comparison. From these experiments and the numerical simulation, it is found that the shape of the solid/liquid interface and composition profile in the solution was found to be significantly affected by gravity. GaSb seed was dissolved faster than GaSb feed even though the GaSb feed temperature was higher than that of GaSb seed temperature. These results clearly indicate that solute transport due to gravity affects dissolution and growth processes of alloy semiconductor bulk crystals.

Hayakawa, Yasuhiro; Arivanandhan, Mukannan; Rajesh, Govindasamy; Tanaka, Akira [Research Institute of Electronics, Shizuoka University, Johoku 3-5-1, Naka-Ku, Hamamatsu, Shizuoka 432-8011 (Japan); Ozawa, Tetsuo [Shizuoka Institute of Science and Technology, 2200-2 Toyozawa, Fukuroi, Shizuoka 437-8555 (Japan); Okano, Yasunori [Graduate School of Engineering Science, Osaka University, 1-3 Machiganeyama, Osaka 560-8531 (Japan); Sankaranarayanan, Krishnasamy [Alagappa University, Karaikudi, Tamilnadu (India); Inatomi, Yuko [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan)

2010-12-01

260

Growth and characterization of sapphire ribbon crystals  

NASA Astrophysics Data System (ADS)

The potential for improving the crystal quality of sapphire prepared by the edge-defined, film-fed growth technique was investigate. Crystal imperfections were observed by optical microscopy and X-ray topography. Saphire ribbons were grown in single or multiple forms in an induction furnace with graphite susceptors and molybdenum reflectors. Voids, grain boundaries and dislocations appeared in the sapphire ribons in relation to the growth conditions. Voids were formed by increasing the growth rate above about 0.7 mm/min. Grain boundaries were formed by imperfect epitaxy between the seed and the melt, or by polygonization of grown-in dislocations. Stress-induced and grown-in dislocations were separately observed in the ribbons free from voids and grain boundaries. The stress-induced dislocations were mostly suppressed by cooling the ribbons at rates below 150°C/h. Grown-in dislocations were completely eliminated by realizing a convex interface by necking down or by using an inclined top die. Dislocation free sapphire ribbons were realized

Wada, Kazumi; Hoshikawa, Keigo

1980-09-01

261

The impact of space research on semiconductor crystal growth technology  

NASA Technical Reports Server (NTRS)

Crystal growth experiments in reduced gravity environment and related ground-based research have contributed significantly to the establishment of a scientific basis for semiconductor growth from the melt. NASA-sponsored research has been instrumental in the introduction of heat pipes for heat and mass transfer control in crystal growth and in the development of magnetic field induced melt stabilization, approaches primarily responsible for recent advances in crystal growth technology.

Witt, A. F.

1983-01-01

262

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

263

Bio-inspired Crystal Growth by Synthetic Templates  

Microsoft Academic Search

Recent advances in bio-inspired strategies for the controlled growth of inorganic crystals using synthetic\\u000a templates will be overviewed. There are a huge number of additives with different functionalities\\u000a which can influence crystal growth; however, we only focus on the controlled growth and mineralization of\\u000a inorganic minerals using synthetic templates as crystal growth modifiers, including biopolymers and synthetic\\u000a polymers. New trends in

Shu-Hong Yu

264

Physical vapor transport crystal growth of ZnO  

NASA Astrophysics Data System (ADS)

Zinc oxide (ZnO) has a wide band gap, high stability and a high thermal operating range that makes it a suitable material as a semiconductor for fabricating light emitting diodes (LEDs) and laser diodes, photodiodes, power diodes and other semiconductor devices. Recently, a new crystal growth for producing ZnO crystal boules was developed, which was physical vapor transport (PVT), at temperatures exceeding 1500 °C under a certain system pressure. ZnO crystal wafers in sizes up to 50 mm in diameter were produced. The conditions of ZnO crystal growth, growth rate and the quality of ZnO crystal were analyzed. Results from crystal growth and material characterization are presented and discussed. Our research results suggest that the novel crystal growth technique is a viable production technique for producing ZnO crystals and substrates for semiconductor device applications.

Yang, Liu; Jianping, Ma; Fuli, Liu; Yuan, Zang; Yantao, Liu

2014-03-01

265

Roughness effect on the overall growth rate of sucrose crystals  

NASA Astrophysics Data System (ADS)

The roughness effect on crystal growth rate was investigated at 35C in a fluidized bed crystallizer and in a batch crystallizer. The crystallization of sucrose in pure aqueous solutions was the study subject. The results show that the sucrose crystals exhibit time-dependent growth rate. The overall growth rate decreased continually with time until a constant value was reached, that corresponds to a decrease of 40% considering the experiments of 13 and 63 min duration in the fluidized bed crystallizer. The decrease of the growth rates with the contact time between crystals and supersaturated solution was interpreted in terms of the increase of surfaces' roughness. According to SEM micrographs, the surface roughness increases significantly with residence time and supersaturation. The roughness appears to be the result of faulty integration of growth clusters in the crystal surface. The batch experiments show that the surface roughness acts like a strong impurity. The results were interpreted according to the Kubota-Mullin model.

Ferreira, A.; Faria, N.; Rocha, F.

2008-01-01

266

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

267

Fluid Physics and Macromolecular Crystal Growth in Microgravity  

NASA Technical Reports Server (NTRS)

The molecular structure of biological macromolecules is important in understanding how these molecules work and has direct application to rational drug design for new medicines and for the improvement and development of industrial enzymes. In order to obtain the molecular structure, large, well formed, single macromolecule crystals are required. The growth of macromolecule crystals is a difficult task and is often hampered on the ground by fluid flows that result from the interaction of gravity with the crystal growth process. One such effect is the bulk movement of the crystal through the fluid due to sedimentation. A second is buoyancy driven convection close to the crystal surface. On the ground the crystallization process itself induces both of these flows. Buoyancy driven convection results from density differences between the bulk solution and fluid close to the crystal surface which has been depleted of macromolecules due to crystal growth. Schlieren photograph of a growing lysozyme crystal illustrating a 'growth plume' resulting from buoyancy driven convection. Both sedimentation and buoyancy driven convection have a negative effect on crystal growth and microgravity is seen as a way to both greatly reduce sedimentation and provide greater stability for 'depletion zones' around growing crystals. Some current crystal growth hardware however such as those based on a vapor diffusion techniques, may also be introducing unwanted Marangoni convection which becomes more pronounced in microgravity. Negative effects of g-jitter on crystal growth have also been observed. To study the magnitude of fluid flows around growing crystals we have attached a number of different fluorescent probes to lysozyme molecules. At low concentrations, less than 40% of the total protein, the probes do not appear to effect the crystal growth process. By using these probes we expect to determine not only the effect of induced flows due to crystal growth hardware design but also hope to optimize crystallization hardware so that destructive flows are minimized both on the ground and in microgravity.

Pusey, M.; Snell, E.; Judge, R.; Chayen, N.; Boggon, T.

2000-01-01

268

Growth morphology of {1 0 1} surfaces of L-arginine trifluoroacetate crystals investigated by AFM  

NASA Astrophysics Data System (ADS)

Surface morphology of {1 0 1} surfaces of L-arginine trifluoroacetate (LATF) crystals have been investigated by atomic force microscopy (AFM). The dominant growth mechanism of the LATF crystals is the formation and expansion of dislocation spirals. Rectangular dislocation growth hillocks oriented with their longer sides in the [0 1 0] direction, which indicates the fast growth along this direction. Apart from that, typical step morphologies are presented and discussed on the basis of the observations.

Liu, X. J.; Wang, Z. Y.; Yu, G. W.; Sun, Z. H.; Zhang, G. H.; Wang, X. Q.; Zhu, L. Y.; Yu, G.; Xu, D.

2007-04-01

269

Materials of construction for silicon crystal growth  

NASA Technical Reports Server (NTRS)

The performance of materials for construction and in contact with molten silicon for crystal growth is presented. The basis for selection considers physical compatibility, such as thermal expansion and strength, as well as chemical compatibility as indicated by contamination of the silicon. A number of new high technology materials are included as well as data on those previously used. Emphasis is placed on the sources and processing of such materials in that results are frequently dependent on the way a material is prepared as well as its intrinsic constituents.

Leipold, M. H.; Odonnell, T. P.; Hagan, M. A.

1980-01-01

270

Growth and Electrical Properties of Zinc-Cadmium Sulfide Graded-Band-GAP Crystals.  

National Technical Information Service (NTIS)

Large quasi-single crystals of Zn(sub x)Cd(sub 1-x)S with increasing x along the growth direction, have been successfully grown by vapor-growth techniques. Typical dimensions are 15 X 3 X 4 mm. The growth mechanism is studied, and, as a result, it is beli...

Indradev L. J. Van Ruyven F. Williams

1968-01-01

271

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

272

Growth of potassium sodium niobate single crystals by solid state crystal growth  

Microsoft Academic Search

Single crystals of (K0.5Na0.5)NbO3 have been grown for the first time by the solid state crystal growth process. A KTaO3 seed crystal was embedded in a matrix of (KxNa1?x)NbO3 powder with a nominal composition of (K0.5Na0.5)NbO3. K4CuNb8O23 was used as a liquid-phase sintering aid. During sintering a single crystal of (K0.5Na0.5)NbO3 grew on the KTaO3 seed. Scanning electron microscopy energy

John G. Fisher; Andreja Bencan; Janez Holc; Marija Kosec; Sophie Vernay; Daniel Rytz

2007-01-01

273

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

274

Special phase transformation and crystal growth pathways observed in nanoparticles+  

PubMed Central

Phase transformation and crystal growth in nanoparticles may happen via mechanisms distinct from those in bulk materials. We combine experimental studies of as-synthesized and hydrothermally coarsened titania (TiO2) and zinc sulfide (ZnS) with thermodynamic analysis, kinetic modeling and molecular dynamics (MD) simulations. The samples were characterized by transmission electron microscopy, X-ray diffraction, synchrotron X-ray absorption and scattering, and UV-vis spectroscopy. At low temperatures, phase transformation in titania nanoparticles occurs predominantly via interface nucleation at particle–particle contacts. Coarsening and crystal growth of titania nanoparticles can be described using the Smoluchowski equation. Oriented attachment-based crystal growth was common in both hydrothermal solutions and under dry conditions. MD simulations predict large structural perturbations within very fine particles, and are consistent with experimental results showing that ligand binding and change in aggregation state can cause phase transformation without particle coarsening. Such phenomena affect surface reactivity, thus may have important roles in geochemical cycling.

Gilbert, Benjamin; Zhang, Hengzhong; Huang, Feng; Finnegan, Michael P; Waychunas, Glenn A; Banfield, Jillian F

2003-01-01

275

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

276

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

277

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

278

Growth of Oxalic Acid Single Crystals from Solution: Solvent Effects on Crystal Habit  

Microsoft Academic Search

Single crystals of oxalic acid dihydrate are difficult to grow from pure water solution, but good single crystals of the material may be obtained by growth from mixtures of acetone and water. The solvent markedly affects the crystal habit. Crystals grown in mixtures of acetone and water develop the prismatic habit, while those grown in water alone develop the tabular

John L. Torgesen; John Strassburger

1964-01-01

279

Crystal growth of YBCO coated conductors by TFA MOD method  

NASA Astrophysics Data System (ADS)

The crystal growth mechanism of TFA (trifluoroacetates)-MOD (metal organic deposition) derived YBa 2Cu 3O y has been investigated to understand the process for higher production rates of the conversion process. YBCO films were prepared by TFA-MOD on CeO 2/Gd 2Zr 2O 7/Hastelloy C276 substrates. The growth rates of YBCO derived from Y:Ba:Cu = 1:2:3 and 1:1.5:3 starting solutions were investigated by XRD and TEM analyses. YBCO growth proceeds in two steps of the epitaxial one from the substrate and solid state reaction. The overall growth rate estimated from the residual amounts of BaF 2 with time measured by XRD is proportional to a square root of P(H 2O). The trend was independent of the composition of starting solutions, however, the growth rate obtained from the 1:1.5:3 starting solutions was high as twice as that of 1:2:3, which could not be explained by the composition of BaF 2 included in the precursor films. On the other hand, the growth rate measured from the thickness of the YBCO quenched film at the same process time showed no difference between the samples of 1:2:3 and 1:1.5:3. The epitaxial growth rate of 1:1.5:3 was also the same as the overall growth rate of that, which means there was no solid state reaction to form YBCO after the epitaxial growth. The YBCO growth mechanism was found to be as follows; YBCO crystals nucleate at the surface of the substrate and epitaxially grow into the precursor by layer-by-layer by a manner with trapping unreacted particles. The amounts of YBCO and the unreacted particles trapped in the YBCO film are independent of the composition of the starting solution in this step. Unreacted particles react with each other to form YBCO and pores by solid state reaction as long as there is BaF 2 left in the film. The Ba-poor starting solution gives little BaF 2 left in the film and so the solid state reaction is completed within a short time, resulting in the fast overall growth rate.

Yoshizumi, M.; Nakanishi, T.; Matsuda, J.; Nakaoka, K.; Sutoh, Y.; Izumi, T.; Shiohara, Y.

2008-09-01

280

Growth rate dispersion of single potassium alum crystals  

NASA Astrophysics Data System (ADS)

The dispersion of growth rates is a lively discussed matter. However, still no acceptable explanation exists for the reason of the phenomenon describing that crystals of the same size growing under the same constant environmental conditions (as supersaturation, temperature and hydrodynamics) might grow with different rates. The individual face-specific growth rates of potassium aluminium alum crystals (diameter 1-3 mm) have been directly determined at different supersaturations ( ? = 0.5-5%). It was found that the order of growth rates of the appearing faces of unhurt and hurt crystals is {111} < {100{ < {110{. Further experiments have shown that face-specific growth rates of unhurt crystals (out of evaporation crystallization) are lower than those of hurt crystals (out of batch crystallization experiments).

Lacmann, Rolf; Tanneberger, Ulrike

1995-01-01

281

Growth aspects of semi-organic nonlinear optical ?-arginine tetrafluoroborate single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of L-arginine tetrafluoroborate ( L-AFB), a semi-organic NLO material, have been grown from aqueous solution. Since L-AFB is known to form highly viscous solution in water, growth by slow cooling has been difficult for optical quality crystals. In this study, highly transparent L-AFB crystals have been successfully grown by slow evaporation by keeping the saturated solution under special condition. The grown crystals were subjected to structural, optical and mechanical property studies. XRD studies reveal that L-AFB crystals possess orthorhombic structure. Fourier transform infrared absorption studies confirm the chemical constituents and presence of functional groups in the grown crystals. L-AFB crystals possess a higher hardness values compared to other semi-organic crystals. The linear and nonlinear optical properties of the grown crystals have also been studied.

Babu, D. Rajan; Jayaraman, D.; Kumar, R. Mohan; Ravi, G.; Jayavel, R.

2003-03-01

282

Protein Crystal Growth Activities on STS-42  

NASA Technical Reports Server (NTRS)

The Protein Crystal Growth (PCG) middeck payload is currently manifested to fly on STS-42 in January 1992. This payload is a joint effort between NASA s Office of Commercial Programs (OCP) and Office of Space Science and Applications (OSSA). The PCG experiments are managed by the Center for Macromolecular Crystallography (CMC), a NASA Center for the Commercial Development of Space (CCDS) based at the University of Alabama at Birmingham (UAB). This is the eighth flight of a payload in the PCG program that is jointly sponsored by the OCP and the OSSA. The flight hardware for STS-42 includes six Vapor Diffusion Apparatus (VDA) trays stored in two Refrigerator/Incubator Modules (R/TM s). The VDA trays will simultaneously conduct 120 experiments involving 15 different protein compounds, four of which are sponsored by the OCP, the UAB CCDS, and four co-investigators.

1992-01-01

283

Specific mass increment and nonequilibrium crystal growth  

NASA Astrophysics Data System (ADS)

Unsteady nonequilibrium crystallization of ammonium chloride from an aqueous solution resulting in the formation of irregular, so-called seaweed, structures is experimentally investigated. It is shown that specific increment of mass for the coexisting structures (or parts thereof) is the same and changes with time (t) according to the power law a/t-b, where the factor a=1.87±0.09 and the factor b is determined by the system relaxation time. The normalization of the power law to the total time of structure growth allows obtaining a universal law that describes the specific mass increment with time for both seaweed and dendrite structures (including the non-coexisting ones).

Martyushev, Leonid M.; Terentiev, Pavel S.

2013-09-01

284

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

PubMed

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

Ma, Yufei; Feng, Qingling; Bourrat, Xavier

2013-05-01

285

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

286

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

287

Crystal Growth Rate Dispersion: A Predictor of Crystal Quality in Microgravity?  

NASA Technical Reports Server (NTRS)

In theory macromolecular crystals grow through a process involving at least two transport phenomena of solute to the crystal surface: diffusion and convection. In absence of standard gravitational forces, the ratio of these two phenomena can change and explain why crystal growth in microgravity is different from that on Earth. Experimental evidence clearly shows, however, that crystal growth of various systems is not equally sensitive to reduction in gravitational forces, leading to quality improvement in microgravity for some crystals but not for others. We hypothesize that the differences in final crystal quality are related to crystal growth rate dispersion. If growth rate dispersion exists on Earth, decreases in microgravity, and coincides with crystal quality improvements then this dispersion is a predictor for crystal quality improvement. In order to test this hypothesis, we will measure growth rate dispersion both in microgravity and on Earth and will correlate the data with previously established data on crystal quality differences for the two environments. We present here the first crystal growth rate measurement data for three proteins (lysozyme, xylose isomerase and human recombinant insulin), collected on Earth, using hardware identical to the hardware to be used in microgravity and show how these data correlate with crystal quality improvements established in microgravity.

Kephart, Richard D.; Judge, Russell A.; Snell, Edward H.; vanderWoerd, Mark J.

2003-01-01

288

Magnetic Control in Crystal Growth from a Melt  

NASA Astrophysics Data System (ADS)

Control of bulk melt crystal growth techniques is desirable for producing semiconductors with the highest purity and ternary alloys with tunable electrical properties. Because these molten materials are electrically conducting, external magnetic fields are often employed to regulate the flow in the melt. However, complicated by the coupled flow, thermal, electromagnetic and chemical physics, such magnetic control is typically empirical or even an educated guess. Two magnetic flow control mechanisms: flow damping by steady magnetic fields, and flow stirring by alternating magnetic fields, are investigated numerically. Magnetic damping during optically-heated float-zone crystal growth is modeled using a spectral collocation method. The Marangoni convection at the free melt-gas interface is suppressed when exposed to a steady axial magnetic field, measured by the Hartmann number Ha. As a result, detrimental flow instabilities are suppressed, and an almost quiescent region forms in the interior, ideal for single crystal growth. Using normal mode linear stability analyses, dominant flow instabilities are determined in a range applicable to experiments (up to Ha = 300 for Pr = 0.02, and up to Ha = 500 for Pr = 0.001). The hydrodynamic nature of the instability for small Prandtl number Pr liquid bridges is confirmed by energy analyses. Magnetic stirring is modeled for melt crystal growth in an ampule exposed to a transverse rotating magnetic field. Decoupled from the flow field at small magnetic Reynolds number, the electromagnetic field is first solved via finite element analysis. The flow field is then solved using the spectral element method. At low to moderate AC frequencies (up to a few kHz), the electromagnetic body force is dominant in the azimuthal direction, which stirs a steady axisymmetric flow primarily in the azimuthal direction. A weaker secondary flow develops in the meridional plane. However, at high AC frequencies (on the order of 10 kHz and higher), only the flow within a skin depth is directly stirred due to the magnetic shielding effect. By regulating the flow in the melt, magnetic control can improve grown-crystal properties in new materials, and achieve economically viable growth rates for production of novel crystalline semiconductors.

Huang, Yue

289

Holographic phase-contrast microphotography for crystal growth research  

Microsoft Academic Search

This paper discusses the principle of using holographic phase-contrast microphotography in crystal growth research and the conditions for improving the resolution and the quality of the reconstructed image. The regularities in variation of the crystal surface morphology and the concentration fields in different states for the crystals growing from aqueous solutions are observed. The saturation and supersaturation of the solutions

Xiling Yu; Aijian Wei

1987-01-01

290

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

291

Growth process of carbyne crystals by synchrotron irradiation  

Microsoft Academic Search

Growth of small carbyne crystals in a thin amorphous carbon film has been observed by high-resolution transmission electron microscopy (HRTEM). The as-deposited film was composed of diamond and graphite crystallites of size 1 nm. Circular ?-phase carbyne crystals predominantly grew to 20 nm in size and transformed into (?+?)-phase crystals with an elongated shape of 100 nm in length. The

Yuki Kimura; Chihiro Kaito; Katsumi Hanamoto; Muneo Sasaki; Seiji Kimura; Toshitaka Nakada; Yoshio Saito; Yasuyuki Nakayama

2002-01-01

292

Crystal nucleation and near-epitaxial growth in nacre.  

PubMed

Nacre is the iridescent inner lining of many mollusk shells, with a unique lamellar structure at the sub-micron scale, and remarkable resistance to fracture. Despite extensive studies, nacre formation mechanisms remain incompletely understood. Here we present 20-nm, 2°-resolution polarization-dependent imaging contrast (PIC) images of shells from 15 mollusk species, mapping nacre tablets and their orientation patterns. These data show where new crystal orientations appear and how similar orientations propagate as nacre grows. In all shells we found stacks of co-oriented aragonite (CaCO?) tablets arranged into vertical columns or staggered diagonally. Near the nacre-prismatic (NP) boundary highly disordered spherulitic aragonite is nucleated. Overgrowing nacre tablet crystals are most frequently co-oriented with the underlying aragonite spherulites, or with another tablet. Away from the NP-boundary all tablets are nearly co-oriented in all species, with crystal lattice tilting, abrupt or gradual, always observed and always small (plus or minus 10°). Therefore aragonite crystal growth in nacre is near-epitaxial. Based on these data, we propose that there is one mineral bridge per tablet, and that "bridge tilting" may occur without fracturing the bridge, hence providing the seed from which the next tablet grows near-epitaxially. PMID:24121160

Olson, Ian C; Blonsky, Adam Z; Tamura, Nobumichi; Kunz, Martin; Pokroy, Boaz; Romao, Carl P; White, Mary Anne; Gilbert, Pupa U P A

2013-12-01

293

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

294

Growth of GaInAs bulk mixed crystals as a substrate with a tailored lattice parameter  

NASA Astrophysics Data System (ADS)

The possibility of growing bulk mixed crystals for different demands is discussed. Three different melt growth methods are compared under consideration of the phase diagram and the dominant transport mechanism in the fluid phase with respect to their ability to grow homogeneous mixed crystals. Growth results are presented for the growth of Ga xIn 1- xAs ( x?0.93) mixed crystals by the horizontal Bridgman method and the zone levelling technique.

Sell, H.-J.

1991-01-01

295

A low cost puller for crystal growth in fluorinating atmospheres  

NASA Astrophysics Data System (ADS)

A resistance heated Czochralski puller, for the growth of high quality rare earth fluoride single crystals in fluorinating atmospheres, has been designed and built. It has been constructed almost entirely from Monel. Technical details are given to aid others interested in growing fluoride materials to design and construct their own crystal growth unit.

Selgert, P.; Whippey, N. R.; Assmus, W.

1984-11-01

296

Preparation Techniques for Growth of Single Crystals of Nonmetallic Materials.  

National Technical Information Service (NTIS)

The report describes two techniques for growth of highpurity single crystals of nonmetallic materials using r-f induction-heating equipment in a frequency range of 5 to 100 Mc. One technique used for single-crystal growth was the Verneuil method using an ...

E. M. Clausen J. W. Rutter

1964-01-01

297

CRYSTAL SIZE GROWTH IN THE LIQUID PHASE METHANOL SYNTHESIS CATALYST  

Microsoft Academic Search

The phenomenon of crystal growth in the methanol synthesis catalyst has been studied. Crystallite size distributions in the cuo\\/ZnO\\/Al2O3 methanol synthesis catalyst have been determined. The effects of temperature, reaction environment and time under reaction conditions have been studied. It is observed that water in the reaction mixture promotes crystal growth.

Ashok Sawant; Sunggyu Lee; Annabelle Foos

1988-01-01

298

Holographic instrumentation for monitoring crystal growth in space  

NASA Technical Reports Server (NTRS)

Measurement requirements and candidates for measuring crystal growth in space are described, emphasizing holographic instrumentation. Existing instrumentation planned for the IML-1 Spaceflight is described along with advanced concepts for future application which incorporate diode lasers, fiber optics, and holographic optical elements. Particle image displacement velocimetry in crystal growth chambers is described.

Trolinger, James D.; Lal, Ravindra B.; Batra, Ashok K.

1990-01-01

299

Preparation for microgravity science investigation of compound semiconductor crystal growth  

NASA Technical Reports Server (NTRS)

Preparatory work on Bridgman directional solidification (BDS) of PbSnTe crystals prior to microgravity crystal growth experiments on Shuttle flights are reported. Gravitational effects become important in crystal growth when density gradients are present. The situation is critical in BDS of PbSnTe because of the necessity of obtaining homogeneous compositional distributions, which can be disturbed when convective processes occur. Numerical models have been defined which quantify the effects of convection in the crystal growth solution. The models were verified by earth-based crystal-growth tests in a two-zone furnace using equal concentrations of each of the elements. Data are provided to demonstrate the differences in composition among crystals grown at different orientations to the gravitational field vector.

Fripp, A. L.; Debnam, W. J.; Clark, I. O.; Crouch, R. K.; Carlson, F. M.

1985-01-01

300

Computer-controlled growth of organic crystals from solutions  

NASA Astrophysics Data System (ADS)

A new type apparatus for growth of organic single crystals from solutions by lowering temperature is described. Microcomputer system 'Crystal 01' our design was used to control the rate of temperature lowering and agitation of the crystal and growth solution. At the range of temperature 313 - 298 K practically linear cooling T equals minus 0.0008 t plus 313.02, R2 equals 0.9998 with the rate 0.05 K/h was achieved.

Marciniak, Bernard; Strozik, Michal; Konopacki, Jan; Dabrowski, Jerzy

1997-07-01

301

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

302

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

303

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

304

Classical growth of hard-sphere colloidal crystals  

NASA Astrophysics Data System (ADS)

The classical theory of nucleation and growth of crystals is examined for concentrated suspensions of hard-sphere colloidal particles. The work of Russel is modified, extended, and evaluated, explicitly. Specifically, the Wilson-Frenkel growth law is modified to include the Gibbs-Thomson effect and is evaluated numerically. The results demonstrate that there is a critical nucleus radius below which crystal nuclei will not grow. A kinetic coefficient determines the maximum growth velocity possible. For large values of this coefficient, quenches to densities above the melting density show interface limited growth with the crystal radius increasing linearly with time. For quenches into the coexistence region the growth is diffusion limited, with the crystal radius increasing as the square root of elapsed time. Smaller values of the kinetic coefficient produce long lived transients which evidence quasi-power-law growth behavior with exponents between one half and unity. The smaller kinetic coefficients also lead to larger crystal compression. Crystal compression and nonclassical exponents have been observed in recent experiments. The theory is compared to data from small angle scattering studies of nucleation and growth in suspensions of hard colloidal spheres. The experimental nucleation rate is much larger than the theoretically predicted value as the freezing point is approached but shows better agreement near the melting point. The crystal growth with time is described reasonably well by the theory and suggests that the experiments are observing long lived transient rather than asymptotic growth behavior. (c) 1995 The American Physical Society

Ackerson, Bruce J.; Schätzel, Klaus

1995-12-01

305

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

306

Controlled Growth of Organic Semiconductor Films Using Liquid Crystal Solvents  

NASA Astrophysics Data System (ADS)

Interest in using organic semiconductors in applications such as large area displays, photovoltaic devices, and RFID tags stems in part from their prospects for enabling significantly reduced manufacturing costs compared to traditional inorganic semiconductors. However many of the best performing prototype devices produced so far have involved expensive or time-consuming fabrication methods, such as the use of single crystals or thin films deposited under high vacuum conditions. We present a new approach for growing low molecular weight organic crystalline films at ambient conditions based on a vapor-liquid-solid growth mechanism using thermotropic nematic liquid crystal (LC) solvents. Tetracene is deposited via atmospheric-pressure sublimation onto substrates coated by a LC layer oriented using rubbed polyimide, producing films that are highly crystalline, with large grain sizes, and possessing macroscopic uniaxial orientation. This poster will describe the growth mechanism, discuss the effects of processing conditions such as LC layer thickness, substrate temperature and flux rate, and compare the results to a model of diffusion limited aggregation accounting for the finite thickness of the solvent layer.

Bufkin, Kevin; Ohlson, Brooks; Hillman, Ben; Johnson, Brad; Patrick, David

2008-03-01

307

Controlled Growth of Organic Semiconductor Films Using Liquid Crystal Solvents  

NASA Astrophysics Data System (ADS)

Interest in using organic semiconductors in applications such as large area displays, photovoltaic devices, and RFID tags stems in part from their prospects for enabling significantly reduced manufacturing costs compared to traditional inorganic semiconductors. However many of the best performing prototype devices produced so far have involved expensive or time-consuming fabrication methods, such as the use of single crystals or thin films deposited under high vacuum conditions. We present a new approach for growing low molecular weight organic crystalline films at ambient conditions based on a vapor-liquid-solid growth mechanism using thermotropic nematic liquid crystal (LC) solvents. Tetracene is deposited via atmospheric-pressure sublimation onto substrates coated by a LC layer oriented using rubbed polyimide, producing films that are highly crystalline, with large grain sizes, and possessing macroscopic uniaxial orientation. This poster will describe the growth mechanism, discuss the effects of processing conditions such as LC layer thickness, substrate temperature and flux rate, and compare the results to a model of deposition-diffusion aggregation accounting for the finite thickness of the solvent layer.

Bufkin, Kevin; Ohlson, Brooks; Hillman, Ben; Johnson, Brad; Patrick, David

2008-05-01

308

Investigation on crystalline perfection, mechanical, piezoelectric and ferroelectric properties of L-tartaric acid single crystal  

NASA Astrophysics Data System (ADS)

Polar organic nonlinear optical material, L-tartaric acid single crystals have been grown from slow evaporation solution growth technique. Single crystal X-ray diffraction study indicates that the grown crystal crystallized in monoclinic system with space group P21. Crystalline perfection of the crystal has been evaluated by high resolution X-ray diffraction technique and it reveals that the crystal quality is good and free from structural grain boundaries. Mechanical stability of the crystal has been analyzed by Vickers microhardness measurement and it exhibits reverse indentation size effect. Piezoelectric d33 co-efficient for the crystal has been examined and its value is 47 pC/N. The ferroelectric behaviour of the crystal was analyzed by polarization-electric field hysteresis loop measurement.

Murugan, G. Senthil; Ramasamy, P.

2014-04-01

309

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

310

Kinetic Roughening Transition and Energetics of Tetragonal Lysozyme Crystal Growth  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

311

Determination of struvite crystallization mechanisms in urine using turbidity measurement.  

PubMed

Sanitation improvement in developing countries could be achieved through wastewater treatment processes. Nowadays alternative concepts such as urine separate collection are being developed. These processes would be an efficient way to reduce pollution of wastewater while recovering nutrients, especially phosphorus, which are lost in current wastewater treatment methods. The precipitation of struvite (MgNH(4)PO(4)?6H(2)O) from urine is an efficient process yielding more than 98% phosphorus recovery with very high reaction rates. The work presented here aims to determine the kinetics and mechanisms of struvite precipitation in order to supply data for the design of efficient urine treatment processes. A methodology coupling the resolution of the population balance equation to turbidity measurement was developed, and batch experiments with synthetic and real urine were performed. The main mechanisms of struvite crystallization were identified as crystal growth and nucleation. A satisfactory approximation of the volumetric crystal size distribution was obtained. The study has shown the low influence on the crystallization process of natural organic matter contained in real urine. It has also highlighted the impact of operational parameters. Mixing conditions can create segregation and attrition which influence the nucleation rate, resulting in a change in crystals number, size, and thus final crystal size distribution (CSD). Moreover urine storage conditions can impact urea hydrolysis and lead to spontaneous struvite precipitation in the stock solution also influencing the final CSD. A few limits of the applied methodology and of the proposed modelling, due to these phenomena and to the turbidity measurement, are also discussed. PMID:22975737

Triger, Aurélien; Pic, Jean-Stéphane; Cabassud, Corinne

2012-11-15

312

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

Microsoft Academic Search

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

J. Villain

1991-01-01

313

Conduction mechanism of single-crystal alumina  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

314

Ground Based Program for the Physical Analysis of Macromolecular Crystal Growth  

NASA Technical Reports Server (NTRS)

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

Malkin, Alexander J.

1998-01-01

315

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

316

Needs and Opportunities in Crystal Growth.  

ERIC Educational Resources Information Center

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

Mroczkowski, Stanley

1980-01-01

317

Growth of Dislocation-Free Gallium Crystals.  

National Technical Information Service (NTIS)

Single crystals of gallium were grown with large portions free of dislocations detectable by anomalous transmission of x-rays. The crystals are grown by an unconstrained solidification technique. The very small supersaturation of vacancies in gallium at r...

S. H. McFarlane C. Elbaum

1965-01-01

318

Calcite Crystal Growth Rate Inhibition by Polycarboxylic Acids  

Microsoft Academic Search

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

Michael M. Reddy; Anthony R. Hoch

2001-01-01

319

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

NASA Astrophysics Data System (ADS)

Acicular crystal-assembled TiO 2 thin films were prepared on fluorine-doped tin oxide (FTO) substrates in aqueous solutions. They consisted of anatase crystals grown along the c-axis, which caused high c-axis orientation in X-ray diffraction patterns and electron diffraction patterns. Morphologies of TiO 2 crystals were controlled by growth conditions to fabricate several types of TiO 2 thin films. Furthermore, deposition mechanism of acicular crystals was investigated by comparison of crystal morphologies deposited for different immersion periods using solution aging method.

Masuda, Yoshitake; Kato, Kazumi

2009-01-01

320

Growth of benzophenone single crystals from solution: A novel approach with 100% solute - crystal conversion efficiency  

Microsoft Academic Search

An unidirectional 60mm diameter benzophenone single crystal was successfully grown by utilizing a novel crystal growth method at room temperature. <110> oriented single crystal ingots were grown out of xylene as solvent and by fixing a seed at the bottom of the ampoule. The obtained benzophenone ingots with the sizes of 10mm, 25mm and 60mm diameter evident that ease in

K. Sankaranarayanan; P. Ramasamy

2006-01-01

321

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.

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

2008-01-01

322

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

323

Sizes and spatial relationships of crystals in granitic plutons: Exploring the crystallization gaps, heterogeneous nucleation, and mechanical clustering of crystals  

NASA Astrophysics Data System (ADS)

Quantitative measurements on magmatic textures provide an important insight into nucleation and growth rates as well as mechanical effects such as crystal settling and melt extraction in magma reservoirs. Crystal size distribution (CSD) measurements and spatial analysis are routinely applied to dilute volcanic suspensions but comparable data on holocrystalline multiphase plutonic rocks are uncommon. We present quantitative description of CSDs and spatial relationships for all rock-forming minerals from an intrusive suite of the Fichtelgebirge/Smr?iny granite batholith in central Europe. This composite body represents two spatially unrelated chambers, consisting of peraluminous biotite, two-mica, and tourmaline-muscovite granites, crystallized as texturally diverse batches covering equigranular, serial porphyritic, and hiatal porphyritic fine- to coarse-grained types. All granite samples exhibit straight to concave-up CSDs in the natural log of population density vs. crystal size projection. Straight CSDs were only found in fine-grained biotite-rich granites representing early crystallizing roof facies of the batholith. For all other samples, the slope decreases from -65 to nearly 0 mm-1 as grain size increases. The curvature can result from superposition of two quasilinear segments. It cannot be produced by two separate crystallization events because the population of larger grains is about 10 times more abundant by volume than the fine one. Instead, we propose that the concave-up CSDs developed in situ, with enhanced nucleation and/or reduced growth rates during the final stage of solidification. Spatial analysis and measurements of contact relationships reveal significant clustering of crystals except near the roof of the batholith. The clustering index decreases to 0.6 for the smallest crystals (random = 1), Ripley's Ľ-function reaches 0.8 mm, and the clusters are mineral sensitive: pairs of like phases appear to be more clustered than the unlike pairs. The observed parameters were reproduced by a three-dimensional numerical model with time-dependent nucleation and growth rates, and with variable degree of clustering induced by changing the ratio of homogeneous vs. heterogeneous nucleation rate, between

Špillar, V.; Dolejš, D.

2012-04-01

324

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

325

Design of a solution crystal growth crystallizer with a versatile electronic reciprocal motion control for a crystals holder  

Microsoft Academic Search

A description of a modified crystallizer for growing large crystals from solutions along with the design of a versatile electronic reciprocating control system to change and reciprocate the motor speed containing the seed holding rod for solution growth crystallizer is presented. In this system, rotation rate and number of revolutions in the clockwise and counter clockwise direction can be adjusted

A. K. Batra; C. R. Carmichael-Owens; M. Simmons; M. D. Aggarwal; R. B. Lal

2005-01-01

326

Simple micromechanical model of protein crystals for their mechanical characterizations  

NASA Astrophysics Data System (ADS)

Proteins have been known to perform the excellent mechanical functions and exhibit the remarkable mechanical properties such as high fracture toughness in spider silk protein [1]. This indicates that the mechanical characterization of protein molecules and/or crystals is very essential to understand such remarkable mechanical function of protein molecules. In this study, for gaining insight into mechanical behavior of protein crystals, we developed the micromechanical model by using the empirical potential field prescribed to alpha carbon atoms of a protein crystal in a unit cell. We consider the simple protein crystals for their mechanical behavior under tensile loading to be compared with full atomic models

Yoon, G.; Eom, K.; Na, S.

2010-06-01

327

Protein crystal growth in space, past and future  

NASA Astrophysics Data System (ADS)

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

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

2002-04-01

328

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

329

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

330

Development and Fabrication of Mechanically Compensated Crystal Units.  

National Technical Information Service (NTIS)

Research conducted on temperature compensation techniques for quartz frequency control crystals is reported. Mechanically actuated variable reactive elements are under study for use with such crystals to offset frequency shifts normally encountered as a r...

E. A. Roberts

1966-01-01

331

Crystal growth and characterization of La 3Ga 5SiO 14 single crystals  

Microsoft Academic Search

An almost colorless La3Ga5SiO14 (LGS) single crystal with 26 mm in diameter and 25 mm in length was grown by the Czochralski technique. The coloration of the crystal depends on the growth atmosphere. The cutoff wavelength of the colorless LGS crystal is shorter than an annealed crystal and the piezoelectric properties of the former are nearly equal to those of

Zengmei Wang; Duorong Yuan; Lihu Pan; Peilin Zhang; Xiufeng Cheng; Minglei Zhao; Zhengfa Li; Xiulan Duan; Zhenxiang Chen; Shiyi Guo; Dong Xu; Mengkai Lv

2003-01-01

332

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

333

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

334

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

335

The dispersion of growth rate as a result of different crystal perfection  

NASA Astrophysics Data System (ADS)

The aim of the cooperative work of the above mentioned institutes was to find out the reason for growth rate dispersion (GRD). Measurements of growth rate (overall or face-specific), microhardness (HV), etch pit density (EPD) and crystal perfection (X-ray topography and Laue X-ray method) were carried out using KAl(SO 4) 2 · 12H 2O (PA) and KNO 3 (PN) crystals. The investigated crystals were grown under different conditions and treated in different ways. It is possible to influence the growth rate by well-directed alternations of supersaturation (? 1, ? 2, ? 1), strain, mechanical stress, annealing and surface roughening. Depending on observation time, the constant crystal growth model (CCG model) (a few hours) as well as the random fluctuation model (RF model; a few days up to a month) describe the growth behaviour of PA. The growth of PN can only be described by the RF model. At constant supersaturation, the average growth rate of small particles in the subsieve size range (up to 60 ?m) is considerably smaller than the average rate of larger crystals of the product size range (500 ?m) in an MSMPR (mixed suspension mixed product removal) crystallizer.

Tanneberger, U.; Lacmann, R.; Herden, A.; Klapper, H.; Schmiemann, D.; Becker, R. A.; Mersmann, A.; Zacher, U.

1996-09-01

336

Activation energy of crystal growth in PbTiO 3 glass using differential thermal analysis  

Microsoft Academic Search

The crystallization mechanism in the PbO–TiO2–B2O3–BaO lead titanate glass system was investigated to determine the activation energy (E) of crystallization using differential thermal analysis (DTA). Two main exothermic peaks were observed in the DTA measurements, which were attributed to the formation of PbTiO3 and barium–titanium–borate (BTB) phases. Bulk crystallization dominated in PbTiO3 crystal growth, whereas the BTB phase showed one-dimensional

Seon W Lee; K. B Shim; K. H Auh; P Knott

1999-01-01

337

Second harmonic chalcone crystal: Synthesis, growth and characterization  

NASA Astrophysics Data System (ADS)

The novel nonlinear optical chalcone derivative (2 E)-3-[4-(methylsulfanyl)phenyl]-1-(3-bromophenyl)prop-2-en-1-one (3Br4MSP) crystals have been grown by slow evaporation technique at ambient temperature. The crystal was subjected to different types of characterization method in order to study its possible application in nonlinear optics. The structure determination of the grown crystal was done by single crystal X-ray diffraction study. The morphology of the crystal is studied. The crystal was subjected to thermal analysis to find its thermal stability. The grown crystals were characterized for their optical transmission and mechanical hardness. The second harmonic generation (SHG) efficiency of the crystal is obtained by classical powdered technique. The laser damage threshold for 3Br4MSP crystal was determined using Q-switched Nd:YAG laser.

D'silva, E. D.; Narayan Rao, D.; Philip, Reji; Butcher, Ray J.; Rajnikant; Dharmaprakash, S. M.

2011-05-01

338

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 solidus has been extensively studied in ground based, high magnetic field and Spacelab experiments. Two alloys of mercury cadmium telluride have been studied; with 80.0 mole percent of HgTe and 84.8 mole percent of HgTe respectively, the remainder being cadmium telluride. Such 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 correlating composition variations to measured residual acceleration. 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, analysis shows that the conditions prevailing during the experiment were quite different from the requirements requested prior to the mission. The results indicate that the sample did accomplish the desired objectives.

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

2001-01-01

339

Fluid Physics and Macromolecular Crystal Growth in Microgravity  

NASA Technical Reports Server (NTRS)

The molecular structure of biological macromolecules is important in understanding how these molecules work and has direct application to rational drug design for new medicines and for the improvement and development of industrial enzymes. In order to obtain the molecular structure, large, well formed, single macromolecule crystals are required. The growth of macromolecule crystals is a difficult task and is often hampered on the ground by fluid flows that result from the interaction of gravity with the crystal growth process. One such effect is the bulk movement of the crystal through the fluid due to sedimentation. A second is buoyancy driven convection close to the crystal surface. On the ground the crystallization process itself induces both of these flows.

Pusey, M.; Snell, E.; Judge, R.; Chayen, N.; Boggon, T.; Helliwell, J.; Rose, M. Franklin (Technical Monitor)

2000-01-01

340

Investigation of Crystal Growth from Solutions.  

National Technical Information Service (NTIS)

The quality was investigated of a crystal of Rochelle salt grown from a solution placed in the zero-gravity environment of Skylab 4. The crystal has the following unique features: (1) the typical cavity is a long tube extending along the c-axis, the avera...

I. Miyagawa

1974-01-01

341

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

342

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

343

Sodium sulfate heptahydrate I: The growth of single crystals  

NASA Astrophysics Data System (ADS)

Sodium sulfate is one of the most damaging salts for porous building materials. In our quest to increase the durability of civil structures and cultural heritage we need to understand its crystallization behavior. In this paper we investigate the cooling-induced growth of the metastable heptahydrate crystal phase by combining nuclear magnetic resonance, for non-destructive measurement of the concentration, with time-lapse microscopy, to visualize the crystal growth. The growth rate is found to be controlled by interface attachment kinetics. The kinetic growth parameter Gk ranges from 0.001 to 0.007 mm/s for single crystals in a temperature range of 4.8-13 °C.

Derluyn, Hannelore; Saidov, Tamerlan A.; Espinosa-Marzal, Rosa M.; Pel, Leo; Scherer, George W.

2011-08-01

344

Single Crystal Growth of Potassium Lithium Niobate for SAW Applications.  

National Technical Information Service (NTIS)

We have successfully demonstrated the growth of good quality, crack-free medium size KLN single crystals using the Czochralski method, with dielectric and piezoelectric properties comparable or superior to the best known bronze composition SBN. However, w...

R. R. Neurgaonkar

1983-01-01

345

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

346

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

347

Aluminum nitride bulk crystal growth in a resistively heated reactor  

Microsoft Academic Search

A resistively heated reactor capable of temperatures in excess of 2300°C was used to grow aluminum nitride (AlN) bulk single crystals from an AlN powder source by physical vapor transport (PVT) in nitrogen atmosphere. AlN crystals were grown at elevated temperatures by two different methods. Self-seeded crystals were obtained by spontaneous nucleation on the crucible walls, while seeded growth was

Rafael Federico Dalmau

2005-01-01

348

Improved Transparent Furnace For Crystal-Growth Experiments  

NASA Technical Reports Server (NTRS)

Novel design and fabrication process for transparent crystal-growing furnace developed. Design consists of one or more heater zones in which heating wire coiled around insides of quartz tubes. Ampoule of material supported inside furnace by guide wire. Crystal then grown by directional freezing of material in ampoule. Distinct feature of use of quartz is capability of direct visual observation of crystal-growth process during experiment. Study of transparent electronic materials conducted in new furnaces.

Rosenthal, Bruce N.; White, Steve; Kalinowski, Joseph M.

1989-01-01

349

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

350

Zone refining and single crystal growth of cuprous oxide  

Microsoft Academic Search

A method of purification and single crystal growth of cuprous oxide by an R. F. induction heating float zone technique was developed. Ingots of 5\\/1 inches diameter and 6 inches long, with three to six columnar crystals extending the entire length of the rod, were prepared. After etching, these rods can be viewed as red by transmitted visible light. The

ANAND SWAROOP KAKAR

1978-01-01

351

Growth and Structure of Single-Crystal Films.  

National Technical Information Service (NTIS)

This research project was concerned with basic research on the growth and structure of single-crystal films of metals obtained by evaporation in ultra-high vaccum onto two types of substrates: mica and metal single-crystal films. The films were prepared i...

E. Grunbaum

1968-01-01

352

Imaging and interferometric analysis of protein crystal growth  

NASA Astrophysics Data System (ADS)

Protein crystals are grown under controlled temperature, concentration and vapor pressure conditions, usually by vapor diffusion, liquid-liquid diffusion and dialysis techniques. The present study examines the effects of protein concentration, drop size and reservoir height on the crystal growth of Hen Egg White Lysozyme (HEWL). Crystals are grown by the hanging drop vapor diffusion method using Modular VDXTM Plates. Due to the vapor pressure difference created between the protein drop and the reservoir, evaporation takes place till equilibrium is attained. Crystal formation takes place after a certain level of supersaturation is attained when the protein precipitates out in crystalline form. The observations revealed that the growth is faster for higher lysozyme concentration, smaller drop sizes and larger reservoir heights. The morphology of the crystals is viewed during the growth process using stereomicroscope. The number of crystals formed is the maximum for higher concentrations, drop sizes and reservoir heights. When the number of crystals formed is less, the size of the crystals is comparatively larger. The effect of evaporation of water vapor from the protein drop into the reservoir is studied using Mach-Zehnder interferometry. The recorded interferograms and shadowgraph images indicate the diffusion of condensed water into the reservoir. The radius of the drop is determined using the shadowgraph images of the growth process. The radius decreases with evaporation and the rate of decrease of radius is highest for higher protein concentrations, smaller drop sizes and larger reservoir heights.

Raghunandan, Ranjini; Gupta, Anamika Sethia; Muralidhar, K.

2008-05-01

353

Crystal growth and roughening of solid D{sub 2}  

SciTech Connect

Near the triple point, growth shapes of vapor deposited hexagonal close packed D{sub 2} crystals reveal two crystal orientations contain facets which persist up to the melt. This observation is in contrast with previous experiments on rare gas solids and H{sub 2} where the highest T{sub r} measured is 0.8 T{sub tp}.

Kozioziemski, B.J.; Collins, G.W.; Bernat, T.P.

1997-03-26

354

Acquisition of Single Crystal Growth and Characterization Equipment  

Microsoft Academic Search

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

M. Brian Maple; Diego A. Zocco

2008-01-01

355

Crystal growth from the vapor in low gravity environments  

SciTech Connect

Effects of earth's gravity on fluids and gases are discussed. Crystal growth in microgravity has been studied since the first Skylab mission. Crystal growth from the vapor has been accomplished in space using the chemical vapor transport method, and the principles behind this method and the results obtained in space are discussed, particularly in the germanium chalcogenide systems. Chemical vapor deposition in space offer promising applications. (DLC)

Santandrea, R.P.

1985-01-01

356

Zeolite Crystal Growth (ZCG) Flight on USML-2  

NASA Technical Reports Server (NTRS)

The extensive use of zeolites and their impact on the world's economy has resulted in many efforts to characterize their structure, and improve the knowledge base for nucleation and growth of these crystals. The zeolite crystal growth (ZCG) experiment on USML-2 aimed to enhance the understanding of nucleation and growth of zeolite crystals, while attempting to provide a means of controlling the defect concentration in microgravity. Zeolites A, X, Beta, and Silicalite were grown during the 16 day - USML-2 mission. The solutions where the nucleation event was controlled yielded larger and more uniform crystals of better morphology and purity than their terrestrial/control counterparts. The external surfaces of zeolite A, X, and Silicalite crystals grown in microgravity were smoother (lower surface roughness) than their terrestrial controls. Catalytic studies with zeolite Beta indicate that crystals grown in space exhibit a lower number of Lewis acid sites located in micropores. This suggests fewer structural defects for crystals grown in microgravity. Transmission electron micrographs (TEM) of zeolite Beta crystals also show that crystals grown in microgravity were free of line defects while terrestrial/controls had substantial defects.

Sacco, Albert, Jr.; Bac, Nurcan; Warzywoda, Juliusz; Guray, Ipek; Marceau, Michelle; Sacco, Teran L.; Whalen, Leah M.

1997-01-01

357

Estimated effects of silicone glue on protein crystal growth  

NASA Astrophysics Data System (ADS)

Silicone glue (modified silicone polymer) is widely used for both experiments involving inorganic crystal growth and those involving organic materials like proteins. This material is very useful for building a hand-made experiment setup or for fixing protein crystals to specific locations. Though silicone glue is regarded as harmful to proteins, no systematic verification was performed to investigate its impurity effects on protein crystal growth. We focused on and estimated the impurity effects of silicone glue on protein crystal growth. Hen egg white lysozyme (HEWL) was used as a model protein. Surface morphology and step velocity of tetragonal lysozyme crystals in the presence and absence of silicone glue were investigated by laser confocal interference contrast microscopy (LCM-DIM). The surface morphology of a tetragonal lysozyme crystal in the presence of silicone glue corresponded to that grown in a lysozyme solution without silicone glue. The dependency of step velocities on supersaturation in the presence of silicone glue also exhibited the same tendency as that of a glue-free system. These two phenomena indicate that the silicone glue did not act as an impurity on lysozyme crystals. Therefore, we conclude that silicone glue is an effective material for various unique experiments involving protein crystals or for applying new methods to create large, high-quality protein crystals.

Maruyama, Mihoko; Shimizu, Noriko; Sugiyama, Shigeru; Takahashi, Yoshinori; Adachi, Hiroaki; Takano, Kazufumi; Murakami, Satoshi; Inoue, Tsuyoshi; Matsumura, Hiroyoshi; Mori, Yusuke

2010-09-01

358

Ice crystal growth in water vapor at high saturation  

NASA Technical Reports Server (NTRS)

A simple technique is presented for estimating the energy of formation of monolayer icelike clusters at ice-vapor interfaces. Under the assumptions that the ice surfaces are smooth and sparsely covered with monomers, dimers, etc., in near equilibrium with the vapor, and that the bond energies and configurational entropy dominate the energy of formation, it is found that the basal surfaces prefer triangular embryos with an orientation which reverses from layer to layer, whereas the most stable clusters on the prism surfaces are rectangular in configuration. The preferred prism clusters are determined to have a significantly lower critical energy of formation than the basal clusters due to differences in both corner free energy and configurational entropy. This phenomenon provides a mechanism for strongly anisotropic crystal growth at high saturations.

Bartley, D. L.

1976-01-01

359

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.

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

2013-01-01

360

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

361

Development of a thermal stress analysis system for anisotropic single crystal growth  

Microsoft Academic Search

We developed a thermal stress analysis system for anisotropic single crystal growth. The analysis system takes account of crystal anisotropy in elastic constants and thermal expansion coefficients and can deal with the thermal stress analyses of five kinds of single crystals, that is, cubic crystal, trigonal crystal, monoclinic crystal, tetragonal crystal and orthorhombic crystal. After calculating thermal stress, we can

N. Miyazaki

2002-01-01

362

Catalytic effect of the impurities on growth of KAP and KDP crystals  

NASA Astrophysics Data System (ADS)

New experimental results concerning the influence of impurities on growth kinetics of KAP and KDP crystals are presented. The above crystals were chosen for these studies because apart from being useful technologically, they are very different one from another in structure and chemical nature. The organic impurities which were used in our experiments differ by chemical class causing different mechanisms of their influence on crystallization. In almost all experiments, however, the increase in crystal growth rate was observed for very low additives concentration, while an analogous decrease was observed for greater impurity concentrations. We call such an effect of increase in the growth rate: catalytic effect, and it was observed for 'tailor-made' additives too. The results are interpreted theoretically in terms of reduction in the edge free energy caused by additive adsorption at the step edge.

Kuznetsov, V. A.; Okhrimenko, T. M.; Rak, Miroslawa

1997-07-01

363

Growth kinematics of the regeneration surfaces of crystals  

NASA Astrophysics Data System (ADS)

A formula for the propagation velocity of the regeneration surface front is derived under the assumption of equal growth rates of the polyhedral crystal faces and the corresponding faces forming subindividuals of the regeneration surface. It is shown that both sharp minima (increase of the face) and sharp maxima (decrease of the face) can correspond to faces in the growth rate diagram. An experimental diagram of the growth rates of the [110] zone of potash alum crystals is constructed which confirms the analytical conclusions. It is established that the regeneration surface growth rate decreases with time. This effect is caused by the disappearance of rapidly growing faces from subindividual faceting. The faceting of a regenerating crystal changes in the direction of successive disappearance of sharp maxima in the growth rate diagram.

Gavryushkin, P. N.; Thomas, V. G.

2009-03-01

364

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

365

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

366

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

367

Viscous fingering and dendritic growth of surface crystallized Sr2TiSi2O8 fresnoite.  

PubMed

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

368

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.

Wisniewski, Wolfgang; Patschger, Marek; Russel, Christian

2013-01-01

369

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

370

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.

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

2009-01-01

371

Growth rate enhancement of potash alum crystals by microcrystals  

NASA Astrophysics Data System (ADS)

During the steady growth of a single crystal of potash alum fixed in a clear supersaturated solution, secondary nucleation was intentionally induced by adding ground potash alum crystals and the resulting changes in the growth rate and the solution concentration were measured. The growth rates after the nucleation were found to abruptly increase by a factor of up to 3, and to gradually return to the steady growth rates or to some constant values. At the same time, the solution concentration started to decrease at the moment of the nucleation. As a measure of the growth rate increase the enhancement coefficient, ? 0, was introduced which was defined as the ratio of the growth rates in the presence to the absence of microcrystals at the same supersaturation. The values of ? 0 were found to be almost independent of the growth rate in the absence of microcrystals, i.e. the solution supersaturation.

Matsuoka, Masakuni; Kamada, Toyohiro; Takiyama, Hiroshi

1996-01-01

372

Computational Models for Crystal Growth of Radiation Detector Materials: Growth of CZT by the EDG Method  

SciTech Connect

Crystals are the central materials element of most gamma radiation detection systems, yet there remains surprisingly little fundamental understanding about how these crystals grow, how growth conditions affect crystal properties, and, ultimately, how detector performance is affected. Without this understanding, the prospect for significant materials improvement, i.e., growing larger crystals with superior quality and at a lower cost, remains a difficult and expensive exercise involving exhaustive trial-and-error experimentation in the laboratory. Thus, the overall goal of this research is to develop and apply computational modeling to better understand the processes used to grow bulk crystals employed in radiation detectors. Specifically, the work discussed here aims at understanding the growth of cadmium zinc telluride (CZT), a material of long interest to the detector community. We consider the growth of CZT via gradient freeze processes in electrodynamic multi-zone furnaces and show how crucible mounting and design are predicted to affect conditions for crystal growth. (authors)

Derby, Jeffrey J.; Gasperino, David [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455-0132 (United States)

2008-07-01

373

A novel method for measurement of crystal growth rate  

NASA Astrophysics Data System (ADS)

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

Kim, Do Yeon; Yang, Dae Ryook

2013-06-01

374

Protein crystal growth in low gravity  

NASA Technical Reports Server (NTRS)

A study is presented of the crystallization of isocitrate lyase (ICL) and the influence of the lack of thermal solutal convection in microgravity on the morphology of ICL crystals is discussed. The latest results of studies with thermonucleation are presented. These include the nucleation of a protein with retrograde solubility and an unknown solubility curve. A new design for a more microgravity compatible thermonuclear is presented.

Feigelson, Robert S.

1992-01-01

375

Dendritic Growth of Hard-Sphere Crystals. Experiment 34  

NASA Technical Reports Server (NTRS)

Recent observations of the disorder-order transition for colloidal hard spheres under microgravity revealed dendritic crystallites roughly 1-2 mm in size for samples in the coexistence region of the phase diagram. Order-of-magnitude estimates rationalize the absence of large or dendritic crystals under normal gravity and their stability to annealing in microgravity. A linear stability analysis of the Ackerson and Schaetzel model for crystallization of hard spheres establishes the domain of instability for diffusion-limited growth at small supersaturations. The relationship between hard-sphere and molecular crystal growth is established and exploited to relate the predicted linear instability to the well-developed dendrites observed.

Russel, W. B.; Chaikin, P. M.; Zhu, Ji-Xiang; Meyer, W. V.; Rogers, R.

1998-01-01

376

Growth and characterization of CdS crystals  

NASA Technical Reports Server (NTRS)

A growth method for the physical vapor transport of compound semiconductors in closed ampoules is described. With the unique techniques applied in the heat treatment of the starting materials and the temperature profiles provided by the three-zone translational furnace, large crystals of CdS have been grown successfully by the method at lower temperatures than previously used. Both unseeded and seeded growth have been investigated. The CdS crystals were examined using optical and scanning electron microscopies (SEM) to study the microstructure and the dislocation etch-pits. The crystals were further characterized by infrared (IR) and ultraviolet (UV) transmission measurements.

Su, Ching-Hua; Lehoczky, S. L.; Szofran, F. R.

1990-01-01

377

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

378

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.

379

CROCODILE: an automated apparatus for organic crystal growth from solution.  

PubMed

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 extendible to any space experiment on fluids. Preliminary details of the flight campaign will also be discussed. PMID:11541155

Gonzalez, F; Cunisse, M; Perigaud, A

1991-12-01

380

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

PubMed Central

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

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

2013-01-01

381

Growth of eutectic silicon from primary silicon crystals in aluminium-silicon alloys  

SciTech Connect

Technological interest in aluminium-silicon alloys derives, fundamentally, from their excellent moulding properties provided by the presence of silicon. In addition, they possess high thermal and electrical conductivities and good corrosion resistance. The possibility of modification of their cast structure by adding small quantities of alkaline and alkaline-earth elements makes their mechanical characteristics very competitive. Metallographic observations of the structures of primary and eutectic silicon crystals, and their possible synergistic influence, provide useful data on the critical stages of formation and growth of eutectic silicon phase. The nucleation and growth of eutectic silicon, removed from the cooperative precipitation zone, induce refinement in crystal size and, therefore, an improvement of the mechanical properties of the moulded structure. The aim of this investigation was to observe the influence of primary silicon crystals on the nucleation and growth of eutectic silicon.

Criado, A.J.; Martinez, J.A.; Calabres, R. [Complutense Univ. of Madrid (Spain). Dept. of Materials Science and Metallurgical Engineering] [Complutense Univ. of Madrid (Spain). Dept. of Materials Science and Metallurgical Engineering

1997-01-01

382

Growth of Sb-Bi gradient single crystals  

SciTech Connect

The growth conditions and structural quality of Sb-Bi gradient single crystals with Bi content from 2 to 18 at %, grown by the Czochralski method with solid phase feed, are investigated. Bi distribution in the crystals along their pulling direction are studied by electron probe microanalysis and the change in the interplanar spacing is analyzed by double-crystal X-ray diffraction. It is established that the pulling rate and feed mass affect the Bi distribution in Sb-Bi single crystals.

Kozhemyakin, G. N., E-mail: genakozhemyakin@mail.ru; Lutskiy, D. V. [Dal Eastern Ukraine National University (Ukraine); Rom, M. A.; Mateychenko, P. V. [National Academy of Sciences of Ukraine, Institute for Single Crystals (Ukraine)

2008-12-15

383

Anion-switchable supramolecular gels for controlling pharmaceutical crystal growth.  

PubMed

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. PMID:21107367

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

2010-12-01

384

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

385

Morphological stability and fluid dynamics of vapor crystal growth  

NASA Technical Reports Server (NTRS)

A fundamental understanding of the conditions under which crystals can retain morphological stability, i.e., shape stability of the advancing interface, during growth from vapors was studied. Morphological stability (MS) is a necessary condition for the growth of homogeneous single crystals required for numerous device applications. For crystallization from melts, the MS concepts are well developed and are essentially based on heat and mass transfer conditions about the advancing interface. For crystallization from vapors, the MS requirements are more complex and not well understood. The added complexity arises from the fact that anisotropies in interfacial kinetics are typically stronger in crystallization from vapors than from melts. These pronounced anisotropies root in the distinctly lower atomic roughness of most vapor-solid interfaces.

Rosenberger, F.

1985-01-01

386

Vapor growth of mercuric iodide tetragonal prismatic crystals  

NASA Astrophysics Data System (ADS)

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

Ariesanti, Elsa

387

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

388

Single crystal growth of potassium lithium niobate for SAW applications  

NASA Astrophysics Data System (ADS)

The growth of good quality, crack free medium size KLN single crystals using the Czochralski method, with dielectric and piezoelectric properties comparable or superior to the best known bronze composition SBN was demontrated. However, large ( 1 cm diameter) KLN crystals suitable for SAE Surface Acoustic Waves characterization without considerable cracking were not grown. Therefore, in pursuit of alternative bronze compositions with the potential for large crystal growth, work was initiated or, the growth and characterization of PBN and the stuffed bronze BSKNN. Initial characterization work shows both of these materials to be very promising for future SAW device development, and good quality single crystals of BSKNN with 1 cm square cross-section already were successfully grown. The physical properties of PBN and BSKNN also make them of interest for other piezoelectric, electro-optic, and nonlinear optic applications in addition to SAW devices.

Neurgaonkar, R. R.

1982-10-01

389

Growth and Characterization of New Nonlinear Optical Single Crystals of 3-AMINOPHENOL Orthophosphoric Acid (3-AMPHPH)  

NASA Astrophysics Data System (ADS)

The semi-organic 3-aminophenol-orthophosphoric acid (denoted as 3-amphph) single crystals were grown by slow evaporation solution technique with water as solvent. The resulted crystal has well-defined surface morphology and is transparent and colorless with a size of 29 × 17 × 4 mm3. The powder X-ray diffraction (XRD), NMR spectroscopic technique, UV-vis-NIR, TG/DTA and dielectric analysis are used to characterize the crystals. XRD analysis revealed that the crystal lattice of 3-amphph is orthorhombic having cell parameters a = 4.481(2) Å, b = 9.782(4) Å, c = 18.326(4) Å with non-centrosymmetric space group P212121. Nonlinear optical studies indicated that the second harmonic generation (SHG) efficiency is 2.22 times that of the standard potassium dihydrogen phosphate (KDP) crystals. Growth mechanism and surface textures of the as-grown single crystals were analyzed by chemical etching analysis.

Raj, K. Russel; Murugakoothan, P.

390

A Critical Look at Ice Crystal Growth Data  

Microsoft Academic Search

I review published data relating to the growth of ice crystals from water vapor under various conditions, and I critically examine the different measurements to determine what useful information can be extracted from each. I show that most, and possibly all, of the existing growth data have been seriously distorted by systematic errors of one form or another, to varying

Kenneth G. Libbrecht

2004-01-01

391

Crystal Growth of Device Quality GaAs in Space.  

National Technical Information Service (NTIS)

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 e...

H. C. Gatos J. Lagowski

1989-01-01

392

Hydrothermal crystal growth of oxides for optical applications  

Microsoft Academic Search

The manipulation of light has proven to be an integral part of today's technology-based society. In particular, there is great interest in obtaining coherent radiation in all regions of the optical spectrum to advance technology in military, medical, industrial, scientific and consumer fields. Exploring new crystal growth techniques as well as the growth of new optical materials is critical in

Colin David McMillen

2007-01-01

393

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

394

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

395

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

PubMed

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

396

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

397

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.

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

2014-01-01

398

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

Microsoft Academic Search

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

Kazumasa Matusita; Takayuki Komatsu; Ryosuke Yokota

1984-01-01

399

Impact of surfactants on the crystal growth of amorphous celecoxib.  

PubMed

The purpose of this study was to investigate the impact of surfactants on the rate of crystal growth of amorphous celecoxib, both in the presence and absence of a polymer. Celecoxib is a poorly water-soluble non-steroidal anti-inflammatory drug. Such compounds may be formulated as amorphous solid dispersions to improve bioavailability, and solid dispersions can contain both a surfactant and a polymer. While the impact of polymers on crystal growth rates has been studied, the effect of surfactants is largely unexplored. Herein, the effect of sodium lauryl sulfate (SLS), sucrose palmitate and d-? tocopherol polyethylenglycol 1000 succinate (TPGS) at a 10% (w/w) concentration on the crystal growth rate of celecoxib was investigated. Linear crystal growth rates as a function of temperature (70-120 °C) were measured using optical microscopy. The mixtures were characterized using differential scanning calorimetry (DSC), infrared spectroscopy, and X-ray diffraction. The results indicate that the surfactants increase the crystal growth rate of amorphous celecoxib. However, addition of polyvinyl pyrrolidone (PVP) helped to mitigate the increase in growth rates, although the ternary systems were highly complex. Thus it is clear that the impact of a surfactant on the physical stability of an amorphous solid dispersion should be considered during formulation. PMID:24333451

Mosquera-Giraldo, Laura I; Trasi, Niraj S; Taylor, Lynne S

2014-01-30

400

A Model for Tetragonal Lysozyme Crystal Nucleation and Growth  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

401

Modeling of crystal growth and nucleation rates for pentaerythritol batch crystallization  

Microsoft Academic Search

The kinetics of crystallization – nucleation and crystal growth – was determined for a seeded batch cooling process. Several experiments were done utilizing always the same condition: initial concentration, seed mass and size distribution, and cooling rate. From one experiment to other the agitation speed was varied. As the utilized reactor is able to measure torque of the impeller, the

A. Bernardo; M. Giulietti

2010-01-01

402

THERMAL STRESS ANALYSIS OF TETRAGONAL SINGLE CRYSTAL DURING GROWTH PROCESS : PMO SINGLE CRYSTAL  

Microsoft Academic Search

A three-dimensional finite element computer code was developed to deal with thermal stress analyses of tetragonal single crystals during the growth. They have the crystal anisotropy, so three-dimensional analysis is required for calculation of the thermal stress, even though they have axisymmetrical shapes. A tensor transformation technique was used to obtain the components of elastic constant matrix and thermal strain

N. Miyazaki; Y. Matsuura; D. Imahase

403

Growth promoting effect of organic impurities on growth kinetics of KAP and KDP crystals  

NASA Astrophysics Data System (ADS)

The experimental results of the influence of a variety of organic impurities differing in their chemical behavior on the growth rates of different faces of KAP and KDP crystals are presented. It was observed that, with increasing additive concentration in practically all experiments, an impurity leads first to an increase and then a decrease in the growth rate, passing through a maximum. These features of the influence of an additive on crystal growth kinetics depend on the chemical nature of both the impurity and the crystal face. The initial growth promoting effect of additives is discussed in terms of the chemical nature of the materials used in the experiments and changes in the thermodynamic and kinetic parameters involved in the crystal growth models. The analysis suggests that the growth promoting effect is not connected with a decrease in the edge free energy in a simple manner.

Kuznetsov, V. A.; Okhrimenko, T. M.; Rak, Miros?awa

1998-09-01

404

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

405

Growth and luminescence of CsBr:Cu crystals  

SciTech Connect

Special features of the incorporation of a copper impurity into CsBr crystals are studied for different types of impurities (metallic copper, CuO, and CuBr{sub 2}) and crystal-growth techniques (the Bridgman method or the method of isothermal evaporation from solution). The optical characteristics of these crystals (absorption, photoluminescence, and photostimulated-luminescence spectra) are investigated. The copper impurity is shown to enter CsBr:Cu{sub met} crystals in the monovalent state Cu{sup +} and CsBr:CuO and CsBr:CuBr{sub 2} crystals in the divalent state Cu{sup 2+}. It is found that the CsBr crystals doped with Cu{sup +} and Cu{sup 2+} ions exhibit intense photostimulated luminescence and can be used as storage phosphors for visualization of X-ray images.

Zorenko, Yu., E-mail: Zorenko@rd.wups.lviv.ua; Turchak, R.; Voznyak, T.; Savchin, V. [Lviv National University (Ukraine); Batenchuk, M.; Winnacker, A. [University of Erlangen-Nuernberg, Institute of Materials Science VI (Germany)

2006-03-15

406

Dislocation Elimination in Czochralski Silicon Crystal Growth Revealed by White X-ray Topography Combined with Topo-tomographic Technique  

SciTech Connect

We have examined the neck of a large-diameter [001]-oriented Czochralski silicon crystal by synchrotron white X-ray topography combined with a topo-tomographic technique in order to explain the mechanism of dislocation elimination due to Dash necking in industrial-scale crystal growth. In the portion where the grown crystal was transformed from a dislocated region to a dislocation-free region, dislocation half loops were first generated at the dislocation tangles. These loops then expanded on the {l_brace}111{r_brace} glide planes and then terminated inside the crystal. In some cases, they reached the side of the crystal. A new mechanism for the elimination of dislocations is proposed based on the fact that dislocations in the neck are not accompanied by the solid-melt interface during the crystal growth, and they proceed in the crystal after the movement of the interface.

Kawado, Seiji [Rigaku Corporation, 3-9-12 Matsubara-cho, Akishima-shi, Tokyo 196-8666 (Japan); Iida, Satoshi [Faculty of Science, Toyama University, 3190 Gofuku, Toyama 930-8555 (Japan); Kajiwara, Kentaro [Japan Synchrotron Radiation Research Institute, SPring-8, 1-1-1 Kouto, Sayou, Hyogo 679-5198 (Japan); Suzuki, Yoshifumi; Chikaura, Yoshinori [Graduate School of Engineering, Kyushu Institute of Technology, Tobata-ku, Kitakyushu 804-8550 (Japan)

2007-01-19

407