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1

Fluid mechanics in crystal growth - The 1982 Freeman scholar lecture  

Microsoft Academic Search

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

Simon Ostrach

1983-01-01

2

Fluid mechanics in crystal growth - The 1982 Freeman scholar lecture  

NASA Technical Reports Server (NTRS)

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

Ostrach, S.

1983-01-01

3

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

4

Modification of crystal growth mechanism of yttrium oxalate in metastable solution  

Microsoft Academic Search

In the seeded crystallization of yttrium oxalate from a metastable supersaturated solution, the growth mechanism was observed to become modified by variations in agitation and additive concentration. From the desupersaturation curve, the crystal growth rate was estimated and described using a power law of supersaturation (RT=Kg?Cp). Without an additive in the metastable solution, the overall growth rate coefficient, Kg, increased

Min-Hyun Sung; Joon-Soo Kim; Woon-Soo Kim; Izumi Hirasawa; Woo-Sik Kim

2002-01-01

5

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

6

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

7

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

8

Non-equilibrium Solidification and Microsegregation Mechanism Based on Interface Evolution and Discrete Crystal Growth  

NASA Astrophysics Data System (ADS)

The interface layer and discrete crystal growth in solidification are traced by analyzing the microsegregation of aluminum alloy. Based on the interface evolution and discrete crystal growth, the non-equilibrium microsegregation mechanism is qualitatively proposed. The solute content of solid is decided by the solidification temperature of interface. And the solidification temperature of interface is further decided by the evolution of interface compositions and interface temperature. The fluctuation of interface compositions and actual interface temperature persists in the whole solidification process.

Ma, Xiaoping; Li, Dianzhong

2015-02-01

9

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

10

An instrument for in situ growth rate characterization of mechanically strained crystals  

NASA Astrophysics Data System (ADS)

The crystal growth and dissolution characteristics of a certain material can be considerably influenced by the strain present in a growing (dissolving) crystal. Strain can be induced in various ways. One of the most common and always present in industrial processes, where attrition processes are always accompanied by generation of mechanical strain in a newly formed small crystal fragments, is mechanical stressing, in situ, during preparation and handling. To gain deeper insights into some aspects of this phenomenon, a sophisticated equipment is needed for in situ controlled stressing of extremely brittle and fragile crystals. For this purpose, we have developed an apparatus which comprises a specially designed straining cell coupled with a laser Michelson interferometer for growth rate measurements. The straining cell is designed to accommodate crystals that undergo fracture below 200 microstrains. The stress imposed on a crystal is computer controlled with a precision of approximately 5%. Details of the instrument are given together with two examples of straining in situ brittle paracetamol and plastic sodium nitrate crystals. The measured changes in growth rate of a paracetamol crystal, in the quasi linear region 0-70 kPa are estimated to be (-9.4±0.1)×10-11 m/s/kPa.

Zikic, A. M.; Ristic, R. I.; Sherwood, J. N.

1998-07-01

11

Total immersion crystal growth  

NASA Technical Reports Server (NTRS)

Crystals of wide band gap materials are produced by positioning a holder receiving a seed crystal at the interface between a body of molten wide band gap material and an overlying layer of temperature-controlled, encapsulating liquid. The temperature of the layer decreases from the crystallization temperature of the crystal at the interface with the melt to a substantially lower temperature at which formation of crystal defects does not occur, suitably a temperature of 200 to 600 C. After initiation of crystal growth, the leading edge of the crystal is pulled through the layer until the leading edge of the crystal enters the ambient gas headspace which may also be temperature controlled. The length of the column of liquid encapsulant may exceed the length of the crystal such that the leading edge and trailing edge of the crystal are both simultaneously with the column of the crystal. The crystal can be pulled vertically by means of a pulling-rotation assembly or horizontally by means of a low-angle withdrawal mechanism.

Morrison, Andrew D. (inventor)

1987-01-01

12

On the genetic nature of isomorphism: Mechanism of component selection during crystal growth  

NASA Astrophysics Data System (ADS)

The concept of mixed-crystal formation, which has developed since the early 1980s, suggests the leading role of the metasomatic exchange between the crystal and solution. Compositions of solid and liquid phases shift to meet one another up to achieving thermodynamic equilibrium. This mechanism provides the regulation of the crystal composition during the process of isomorphism. The principles of the proposed assembly mechanism of selecting isomorphic components in the proportions dictated by a given combination of conditions (composition of the solution, supercooling or superheating, and temperature) are set forth as follows. The particle assemblages characterize a certain statistical distribution by the composition precipitate on the surface. Only those assemblages, which satisfy the aforementioned conditions, survive, whereas the other assemblages are dissolved, initiating the salting-out of the former assemblages. The validity of the proposed model is corroborated by the development of the assembly structure of autoepitaxial (K,Rb)HC8H4O4 nuclei on a KHC8H4O4 crystal observed with a Park CP atomic force microscope. The nuclei are widely scattered in composition, degree of faceting, and size, demonstrating their different stability and growth rate. Another example is the distribution of spontaneously precipitated mixed K(Br,Cl) crystals by isomorphic composition and size. The small and large fractions are enriched in KBr in comparison with medium-size fractions, while the volumetric proportions of the fractions reveal a bimodality with the complete absence of fractions 30-50 ?m. The traditionally discussed statistical selection of particular ions, which is probably second in importance; however, it may become crucial when the amount of one of the isomorphic components is rather small. While oversaturation is fairly high, crystallization without selection may be expected.

Glikin, A. E.

2007-12-01

13

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

14

Probing protein interaction chemistry through crystal growth: structure, mutation, and mechanism in subtilisin s88  

Microsoft Academic Search

Observations of systematic variation in the shapes of protein crystals have unique potential to report chemical effects on protein–protein interactions, because diffraction can be used to image the detailed structure that links an easily controlled “cause” (change in chemical conditions) with an easily observed “effect” (change in crystal shape). Crystal shape correlates directly with the relative growth rates of the

Qianwen Pan; D. T. Gallagher

2000-01-01

15

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

E-print Network

is that the adsorption of inhibitor leads to a reduction in interfacial tension or edge energy for the crystal surface or to a reduction in growth rate. The inhibition of crystal growth due to adsorption is impor- tant for both natural subcoolings.1,2 For the prevention of hydrate formation dur- ing the production of natural gas, the premium

Firoozabadi, Abbas

16

Mechanism of vapour growth and defect formation in large mercuric iodide crystals  

Microsoft Academic Search

The relationship between the kinetics of growth and the defect formation was investigated using a high resolution (± 15 ?m) video system for monitoring the growth rate and morphology of the crystals on one side and carrying an extensive characterisation of the crystals by various methods (3D mapping with ?-ray rocking curves, X-ray synchrotron transmission topography, atomic force microscopy) on

M. Piechotka

1995-01-01

17

AFM studies of the nucleation and growth mechanisms of macromolecular crystals  

NASA Astrophysics Data System (ADS)

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

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

1999-01-01

18

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

Microsoft Academic Search

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

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

2011-01-01

19

Mechanism of ionic strength dependence of crystal growth rates in a subtilisin variant  

Microsoft Academic Search

An orthorhombic crystal form of a subtilisin variant exhibits a systematic variation in growth rates of its three unique faces, resulting in pronounced morphology variations, depending on ionic strength. Several common salts cause a concentration-dependent change in the crystal habit from thin plates to isometric bars. Analysis of the four crystal contacts in the 1.8Å resolution X-ray structure leads to

D Travis Gallagher; Qianwen Pan; Gary L Gilliland

1998-01-01

20

Growth of ice discs from the vapor and the mechanism of habit change of ice crystals  

NASA Technical Reports Server (NTRS)

Ice crystals nucleated on a liquid nitrogen cooled glass fiber grow first as thin disks which subsequently transform to plates and columns as they thicken and extend to regions of higher supersaturation. Crystals are often found to be dislocation-free, which suggests that growth results from surface nucleation, the habit depending on preferential nucleation in an adsorbed multilayer on basal or prism face.

Keller, V. W.; Mcknight, C. V.; Hallett, J.

1980-01-01

21

Growth mechanism of long chain molecular crystals on KCl substrate due to annealing  

NASA Astrophysics Data System (ADS)

Long chain compound, calcium stearate ((CH 3(CH 2) 16COO) 2Ca), is deposited on an air-cleaved KCl (001) surface kept at 25°C in 1 x 10 -4 Pa with an average thickness of 1nm. After deposition, the films are annealed at different temperatures between 30 and 120°C for 5-120 min. As-deposited films consist of slender crystallites with a length of 0.5 ?m, in which molecules align along the <110> directions of KCl to grow epitaxially. Although the crystallites annealed at less than 50°C grow to be with a length of 1-5 ?m, they annealed above 80°C change to plate films. The growth mechanism of slender crystals and dynamics of molecular orientation change are thermodynamically discussed.

Yamanaka, Mikihiro; Mimura, Kohji; Yase, Kiyoshi; Sato, Kiyotaka; Inaoka, Kimio

1993-03-01

22

Liquid encapsulated crystal growth  

NASA Technical Reports Server (NTRS)

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

Morrison, Andrew D. (Inventor)

1989-01-01

23

Liquid encapsulated crystal growth  

NASA Technical Reports Server (NTRS)

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

Morrison, Andrew D. (inventor)

1987-01-01

24

Crystal growth and mechanical characterization of ZrMo2O8  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

25

Studies on growth, spectral and mechanical properties of new organic NLO crystal: Guanidinium 4-nitrobenzoate (GuNB)  

NASA Astrophysics Data System (ADS)

A new organic nonlinear optical single crystal guanidinium 4-nitrobenzoate (GuNB) was successfully grown by solution growth using the slow evaporation technique. Solubility and metastable zone width were determined for different solvents. The structure of the grown crystal has been determined by single crystal x-ray diffraction analysis. The presence of functional groups and coordination of para nitro benzoate ions in the GuNB crystal have been identified by FTIR and FT Raman spectroscopic studies. The optical transparency range has been studied through UV-vis-NIR spectroscopy. The second harmonic generation efficiency of the grown GuNB crystal has been obtained by the Kurtz-Perry powder technique. The laser induced surface damage threshold for the grown crystal has been measured using Nd: YAG laser. The mechanical behavior has also been studied by Vicker's microhardness test.

Arumanayagam, T.; Murugakoothan, P.

2013-01-01

26

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

NASA Astrophysics Data System (ADS)

Single crystals of triglycine sulphate (TGS) doped with n-bromo succinimide (NBS) were grown at ambient temperature by the slow evaporation technique. An aqueous solution containing 1-20 mol% of n-bromo succinimide as dopant was used for the growth of NBSTGS crystals. The incorporation of NBS in TGS crystals has been qualitatively confirmed by FTIR spectral data. The effect of the dopant on morphology and crystal properties was investigated. The cell parameters of the doped crystal were determined by the powder X-ray diffraction technique. The dielectric constant of NBS doped TGS crystal was calculated along the ferroelectric direction over the temperature range of 30-60 °C. The dielectric constant of NBSTGS crystals decrease with the increase in NBS concentration and considerable shift in the phase transition temperature ( TC) towards the higher temperature observed. Pyroelectric studies on doped TGS were carried out to determine the pyroelectric coefficient. The emergence of internal bias field due to doping was studied by collecting P- E hysteresis data. Temperature dependence of DC conductivity of the doped crystals was studied and gradual increase in the conductivity with the increase of dopant concentration was observed. The activation energy (? E) calculated was found to be lower in both the ferroelectric and the paraelectric phases for doped crystals compared to that of pure TGS. The micro-hardness studies were carried out at room temperature on thin plates cut perpendicular to the b-axis. Less doped TGS crystals show higher hardness values compared to pure TGS. Piezoelectric measurements were also carried out on 010 plates of doped TGS crystals at room temperature.

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

2011-09-01

27

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

28

Monitoring Crystal Growth From Solution  

NASA Technical Reports Server (NTRS)

Experimental system for monitoring growth of triglycine sulfate (TGS) crystals from solution is being studied. System consists of outer cell containing distilled water heated and stirred to maintain constant temperature to within plus or minus 0.1 degrees C, inner (growth) cell containing supersaturated solution of TGS, and seed crystal mounted in plastic-covered stainless-steel sting equiped with controlled cooling mechanism and temperature sensors.

Lal, R. B.

1982-01-01

29

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

NASA Astrophysics Data System (ADS)

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

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

2003-01-01

30

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

PubMed Central

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

2013-01-01

31

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

32

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

33

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

34

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

35

Crystal Growth Control  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

36

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

37

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. PMID:16230632

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

2005-01-01

38

Organic-inorganic interaction and the growth mechanism of hydroxyapatite crystals in gelatin matrices between 37 and 80 degrees C.  

PubMed

The crystal development of hydroxyapatite[HAp] phase in gelatin[GEL] matrices was investigated in the temperature range 37 to 80 degrees C by using X-ray diffraction, scanning electron microscopy(SEM), thermoanalytical measurement(DT/TGA), Fourier-Transformed Infra-Red(FT-IR) spectroscopy, and transmission electron microscopy(TEM) with electron diffraction(ED). It was found that during the coprecipitation of apatite phase in GEL matrices and the next aging process the crystallites were formed and developed through the two reaction mechanisms of organic-inorganic interaction between apatite phase and GEL molecules, and thermodynamic reaction for the crystal growing. The analytical evidences showed that there was a definite competition between these two mechanisms with the reaction temperature. Below 50 degrees C the crystal development of HAp was greatly suppressed by the existence of the GEL molecules, indicating the heterogeneous nucleation by the supposed number of carboxyl groups in GEL. Above 50 degrees C the effective organic components as a template for the heterogeneous nucleation of apatite crystallites were greatly degraded and so more amount of inorganic ions could be favorably accredited on the preexisting crystallites in virtue of the limited nucleation chance, finally resulting in the crystal growth. At higher temperature pretty big HAp crystals were developed with the depletion of the organics to be bound with crystallites in the slurry solution. Presumably it is believed that the poisoning of the functional groups in GEL molecules was vigorously occurred in the phosphoric acid environment above approximately 50 degrees C. PMID:16617418

Chang, Myung Chul; Douglas, William H; Tanaka, Junzo

2006-04-01

39

Growth rates of protein crystals  

PubMed Central

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

Schmit, Jeremy D.; Dill, Ken

2012-01-01

40

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

41

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

42

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

43

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

PubMed

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

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

2014-10-31

44

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.

45

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

46

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

47

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

48

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

49

Theoretical study of the prohibited mechanism for ethylene/vinyl acetate co-polymers to the wax crystal growth.  

PubMed

To understand the effect of pour point depressants (PPD) on the wax growth is important for designing PPD additives for use with different oils with high efficiency and good economics. In our current study, molecular mechanics, molecular dynamics, and quantum mechanics calculations were performed to investigate the prohibited mechanism of ethylene/vinyl acetate (EVA) additives on the paraffin deposition in oils. On the wax surface, a single C18 molecule and clusters were preferably deposited on the wax surface (010) in a parallel conformation, which resulted in the formation of large blocks of wax crystal. MD simulation indicated that the linear conformation of EVA was more favorable to be adsorbed onto the carbon backbone of the wax surface (010) with the polar fragments of vinyl acetate staying upside of the surface. Furthermore, four EVA molecules can efficiently optimize the inhibition effect for the deposition of the solute C18 molecules over 10x8 size wax surface (010). According to the simulation results, a simplified rational model was established to estimate the minimum dosage of EVA-type PPD for fuels with different paraffin contents. In a certain degree, this simplified model has provided an effective route to correlate microstructures and the properties of polymer-involving systems, which will shed light on the application of theoretical studies in industries. PMID:18072759

Zhang, Jinli; Zhang, Ming; Wan, Junjie; Li, Wei

2008-01-10

50

Protein crystal growth in low gravity  

NASA Technical Reports Server (NTRS)

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 shown to have normal solubility characteristics over the range of temperatures (5 to 25 C) and pH (5 to 7.5) studied. The solubility data combined with growth rate data gathered from the seeded growth of canavalin crystals indicated that the growth mechanism at high supersaturation ratios (>1.28) is screw dislocation like. A Schlieren apparatus was constructed and flow patterns were observed in Rochelle salt (sodium potassium tartrate), lysozyme, and canavalin. The critical parameters were identified as the change in density with concentration (dp/dc) and the change in index of refraction with concentration (dn/dc). Some of these values were measured for the materials listed.

Feigelson, Robert S.

1987-01-01

51

Growth, structural, thermal, dielectric, mechanical and optical characterization of 2, 3-Dimethoxy-10-oxostrychnidinium hydrogen oxalate dihydrate single crystal  

NASA Astrophysics Data System (ADS)

Single crystal of 2, 3-Dimethoxy-10-oxostrychnidinium hydrogen oxalate dihydrate has been grown by slow evaporation solution growth technique (SEST) using ethanol-water solution at room temperature. It crystallizes in the orthorhombic system with space group of P212121. The crystalline perfection of the grown single crystal has been examined by high resolution X-ray diffraction analysis (HRXRD). The optical absorption studies show that the crystal is transparent in the visible region with a lower cut-off wavelength of 342 nm and the optical energy band gap Eg is found to be 3.52 eV. The electrical properties have been assessed by dielectric measurement at different temperatures. Hardness values measured using Vickers hardness indenter show considerable anisotropy. Laser damage threshold study is also carried out for the grown crystal.

Krishnan, P.; Gayathri, K.; Jayasakthi, M.; Gunasekaran, S.; Anbalagan, G.

2013-11-01

52

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

53

What Variables Affect Crystal Growth?  

NSDL National Science Digital Library

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

54

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

55

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

56

Automated protein crystal growth facility  

NASA Technical Reports Server (NTRS)

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

Donald, Stacey

1994-01-01

57

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

58

Effects of impurities on crystal growth in fructose crystallization  

NASA Astrophysics Data System (ADS)

The influence of impurities on the crystallization of anhydrous fructose from aqueous solution was studied. The growth kinetics of fructose crystals in the fructose-water-glucose and fructose-water-difructose dianhydrides systems were investigated using photomicroscopic contact nucleation techniques. Glucose is the major impurity likely to be present in fructose syrup formed during corn wet milling, while several difructose dianhydrides are formed in situ under crystallization conditions and have been proposed as a cause in the decrease of overall yields. Both sets of impurities were found to cause inhibition of crystal growth, but the mechanisms responsible in each case are different. It was found that the presence of glucose increases the solubility of fructose in water and thus lowers the supersaturation of the solution. This is probably the main effect responsible for the decrease of crystal growth. Since the molecular structures of difructose dianhydrides are similar to that of fructose, they are probably "tailor-made" impurities. The decrease of crystal growth is probably caused by the incorporation of these impurities into or adsorption to the crystal surface which would accept fructose molecules in the orientation that existed in the difructose dianhydride.

Chu, Y. D.; Shiau, L. D.; Berglund, K. A.

1989-10-01

59

Dynamically controlled crystal growth system  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

60

Plenum type crystal growth process  

DOEpatents

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

Montgomery, Kenneth E. (Tracy, CA)

1992-01-01

61

Synthesis, growth, thermal, optical and mechanical properties of new organic NLO crystal: L-alanine DL-malic acid  

NASA Astrophysics Data System (ADS)

A new organic nonlinear optical crystal, L-alanine DL-malic acid (LADLMA), has been grown from aqueous solution by the slow cooling technique. L-alanine and DL-malic acid were used in the ratio 2:1 for synthesis. Crystals of size 24×13×8 mm 3 have been obtained in 26 days. Characterizations were carried out to study the structural, optical and mechanical properties of the grown crystals. Single crystal X-ray diffraction analysis shows that they belong to the orthorhombic system. To study the crystalline perfection of the grown crystals, high-resolution X-ray diffraction (HR-XRD) study was carried out. The vibrational frequencies of various functional groups have been derived from FTIR spectrum. Thermal behaviour of the crystal was investigated by TG-DTA analyses. Transmission spectrum has been recorded in the solution state and the cut-off frequency has been determined. Nonlinear optical property of the crystal has been confirmed using the Kurtz powder technique and a study of its second harmonic generation efficiency in comparison with KDP has been made. Knoop hardness test was carried out and its Young's modulus was calculated.

Jaikumar, D.; Kalainathan, S.; Bhagavanarayana, G.

2009-12-01

62

Protein crystal growth in microgravity  

NASA Technical Reports Server (NTRS)

The overall scientific goals and rationale for growing protein crystals in microgravity are discussed. Data on the growth of human serum albumin crystals which were produced during the First International Microgravity Laboratory (IML-1) are presented. Potential scientific advantages of the utilization of Space Station Freedom are discussed.

Carter, Daniel

1992-01-01

63

A study of crystal growth by solution technique  

NASA Technical Reports Server (NTRS)

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

Lal, R. B.

1981-01-01

64

Ultraslow growth rates of giant gypsum crystals  

PubMed Central

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

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

2011-01-01

65

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

NASA Astrophysics Data System (ADS)

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

Hanumantharao, Redrothu; Kalainathan, S.

2013-04-01

66

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

67

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

68

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.

69

Dendritic growth of snow crystals  

Microsoft Academic Search

The hypothesis that allows the interpretation of dendritic growth of a snow crystal in terms of diffusion-limited aggregation\\u000a is criticized. The results of simulation of growth of quasi-two-dimensional crystals in two-and three-dimensional media based\\u000a on the classical two-parametric model of diffusion-limited aggregation are used as an argument in this criticism. It is established\\u000a that the model dimensionality considerably influences morphology

L. G. Gorbich; L. M. Martyushev

2005-01-01

70

Temperature Fluctuations During Crystal Growth  

NASA Technical Reports Server (NTRS)

Technique developed to deconvolve period and relative amplitude of fluctuations of heat flow inBridgman crystal growth. Temperature-measuring device with enough sensitivity and frequency response to make desired measurements inserted close as possible to substance monitored. Time-dependent temperature response recorded, and time domain response converted to frequency domain for further analysis. Fast fourier transform (FFT) of data on temperature oscillations shows particular behavior at some specific frequencies corresponding with striations, or defects observed on crystal. Useful procedure to help determine sources of some growth-induced crystalline defects. Other processes sensitive to small temperature fluctuations, such as diffusion, precipitation, and corrsion, benefit from technique.

Fripp, Archibald L., Jr.; Clark, Ivan O.; Debnam, William J., Jr.; Barber, Patrick G.; Crouch, Roger K.; Simchick, Richard T.

1988-01-01

71

Growth and characterization of zinc thiourea chloride (ZTC): a semiorganic nonlinear optical crystal  

Microsoft Academic Search

Growth of bulk zinc thiourea chloride single crystals from aqueous solution by solution growth technique is reported. It has been found that the solution pH influences the growth rate of the crystal along [001] and [010] directions. Single crystal X-ray diffraction analysis confirms the crystal structure. The grown crystals have been subjected to optical and mechanical property studies.

R. Rajasekaran; P. M. Ushasree; R. Jayavel; P. Ramasamy

2001-01-01

72

Crystal growth in fused solvent systems  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

73

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

74

Protein crystal growth in low gravity  

NASA Technical Reports Server (NTRS)

The solubility and growth of the protein canavalin, and the application of the schlieren technique to study fluid flow in protein crystal growth systems were investigated. These studies have resulted in the proposal of a model to describe protein crystal growth and the preliminary plans for a long-term space flight experiment. Canavalin, which may be crystallized from a basic solution by the addition of hydrogen (H+) ions, was shown to have normal solubility characteristics over the range of temperatures (5 to 25 C) and pH (5 to 7.5) studies. The solubility data combined with growth rate data gathered from the seeded growth of canavalin crystals indicated that the growth rate limiting step is a screw dislocation mechanism. A schlieren apparatus was constructed and flow patterns were observed in Rochelle salt (sodium potassium tartrate), lysozyme, and canavalin. The critical parameters were identified as the change in density with concentration (dp/dc) and the change in index of refraction with concentration (dn/dc). Some of these values were measured for the materials listed. The data for lyrozyme showed non-linearities in plots of optical properties and density vs. concentration. In conjunction with with W. A. Tiller, a model based on colloid stability theory was proposed to describe protein crystallization. The model was used to explain observations made by ourselves and others. The results of this research has lead to the development for a preliminary design for a long-term, low-g experiment. The proposed apparatus is univeral and capable of operation under microprocessor control.

Feigelson, Robert S.

1988-01-01

75

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

NASA Technical Reports Server (NTRS)

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

Feigelson, R. S. (editor)

1986-01-01

76

Crystal growth rates of tricaprin and trilaurin under high pressures  

NASA Astrophysics Data System (ADS)

The effect of hydrostatic pressure on a linear crystal growth rate of tricaprin and trilaurin was investigated by the use of a capillary method in the pressure range up to 200 MPa. The undercooling temperature, ? T, was varied from 0.65 to 16 K. In order to investigate crystal growth kinetics of triacylglycerols, the melting temperature, density and viscosity were also measured under high pressures. The crystal growth rates of tricaprin and trilaurin decrease with increasing values of pressure applied. It was found that the crystal growth rate, v, can be expressed by the form v= A? Tn with n which can take large value in a range of small ? T value, whereas n decreases with increasing ? T value. From the comparison with several theories for the crystal growth from melts, the present result suggests that the two triacylglycerols freeze by the dislocation mechanism in the small ? T range and by the continuous mechanism in the large ? T range.

Yokoyama, Chiaki; Tamura, Yuichi; Nishiyama, Yoshiyuki

1998-08-01

77

Nucleation and crystal growth in binary systems  

NASA Astrophysics Data System (ADS)

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

Alexandrov, D. V.

2014-03-01

78

Growth of Zinc Oxide Single Crystals by Vapor Phase Reaction  

Microsoft Academic Search

ZnO single crystals are grown by vapor phase reaction with ZnI2 source. When the growth region is maintained between 1150°C and 1200°C, crystals grow by oxidation, and between 970°C and 1020°C, by hydrolysis. Crystals are mainly needles 15 mm in length or plates 8 mm2 in area. Patterns suggesting their growth mechanisms are observed in their microphotographs. The present experiments

Masami Hirose

1971-01-01

79

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

Microsoft Academic Search

Phosphoric acid admixtured l-alanine (PLA) single crystals were grown successfully by solution method with slow evaporation technique at room temperature. Crystals of size 18mm×12mm×8mm 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

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

2011-01-01

80

Protein crystal growth in a microgravity environment  

NASA Technical Reports Server (NTRS)

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

Bugg, Charles E.

1988-01-01

81

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

82

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

83

Growth of ZnSe single crystals  

Microsoft Academic Search

The growth conditions of ZnSe single crystals were investigated by chemical vapor transport (CVT) and physical vapor transport (PVT) methods. The growth temperatures were about 850°C (CVT) and 1100°C (PVT). Single crystals of 18–20mm diameter, 30mm long and orange colored were grown. The homogeneity of crystals was measured. The etch pit density of good crystals is in the range of

C. S Fang; Q. T Gu; J. Q Wei; Q. W Pan; W Shi; J. Y Wang

2000-01-01

84

Hanging drop crystal growth apparatus  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

85

Cluster Mechanism of Homogeneous Crystallization (Computer Study)  

NASA Astrophysics Data System (ADS)

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

Belashchenko, D. K.

2008-12-01

86

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

87

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

88

Growth and Morphology of L-Alanine Crystals: Influence of Additive Adsorption  

Microsoft Academic Search

The effect of L-amino acids, as additives, on the crystal growth and morphology of L-alanine crystals has been studied. The crystal growth of L-alanine is described by the spiral growth mechanism. From examining the growth rate dependence on supersaturation at constant additive concentration, it is concluded that there is no change in the growth mechanism due to the presence of

David Lechuga-Ballesteros; Nair Rodriguez-Hornedo

1993-01-01

89

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

90

Mechanics of Cell Growth.  

PubMed

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

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

2012-06-01

91

Nucleation and Convection Effects in Protein Crystal Growth  

NASA Technical Reports Server (NTRS)

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

Vekilow, Peter G.

1998-01-01

92

Mechanically tunable photonic crystal lens  

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

93

Growth and characterization of zinc thiourea chloride (ZTC): a semiorganic nonlinear optical crystal  

NASA Astrophysics Data System (ADS)

Growth of bulk zinc thiourea chloride single crystals from aqueous solution by solution growth technique is reported. It has been found that the solution pH influences the growth rate of the crystal along [0 0 1] and [0 1 0] directions. Single crystal X-ray diffraction analysis confirms the crystal structure. The grown crystals have been subjected to optical and mechanical property studies.

Rajasekaran, R.; Ushasree, P. M.; Jayavel, R.; Ramasamy, P.

2001-07-01

94

Optical diagnostics of solution crystal growth  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

95

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

96

Crystal Growth and Spectroscopy of Diglycine  

NASA Technical Reports Server (NTRS)

Raman and infrared spectra have been obtained for alpha-diglycine (C4H8N2O3) single crystals. These dipeptide crystals are being grown as a models system for protein crystal growth studies. There have been previous Raman measurements on diglycine powder samples recorded, but there is no reference to measurements on oriented diglycine single crystals. Diglycine can grow in one of three forms, alpha, beta, or gamma.

Taylor, Taravia M.

1995-01-01

97

Growth, thermal, mechanical, structural and optical properties of organic NLO crystals of novel cis-2,6-bis(2-chlorophenyl)-3,3-dimethylpiperidin-4-one  

NASA Astrophysics Data System (ADS)

An organic NLO material viz., cis-2,6-bis(2-chlorophenyl)-3,3-dimethylpiperidin-4-one (2C3DMPO), has been synthesized and a slow evaporation technique was applied to produce a single crystal. X-ray diffraction study on the single crystal 2C3DMPO reveals a non-centro symmetric crystal, possessing a monoclinic space group P21 and prefers to adopt a chair conformation. The crystal has been characterised using UV, FT-IR and NMR spectral studies. Solubility study and mechanical study using micro hardness methods have also been carried out. Furthermore, the thermal stability of the crystal was established by TG/DTA. The second harmonic conversion efficiency of the crystal was determined using the Kurtz and Perry powder technique and the activity observed was 3.83 times greater than that of KDP.

Ponnuswamy, S.; Mohanraj, V.; Ilango, S. S.; Thenmozhi, M.; Ponnuswamy, M. N.

2015-02-01

98

Thermal crystallization mechanism of silk fibroin protein  

NASA Astrophysics Data System (ADS)

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

Hu, Xiao

99

Crystal growth kinetics of two-step growth process in liquid fluidized-bed crystallizers  

Microsoft Academic Search

The fluidized-bed crystallizers have long been used in the chemical industry and recently for water treatment as the so-called pellet reactors. This report summarizes the experimental results regarding hydrodynamics and crystal growth rates in laboratory-scale fluidized-bed crystallizers. The two-step crystal growth model rather than the over-all model is adopted to explain the observed kinetic behaviors. In using the two-step growth

Clifford Y. Tai

1999-01-01

100

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

101

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

102

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

103

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

104

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

105

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

106

Crystallization mechanism in melts of short n-alkane chains  

E-print Network

We study crystallization in a model system for eicosane (C20) by means of molecular dynamics simulation and we identify the microscopic mechanisms of homogeneous crystal nucleation and growth. For the nucleation process, we observe that chains first align and then straighten. Then the local density increases and finally the monomer units become ordered positionally. The subsequent crystal growth process is characterized by a sliding-in motion of the chains. Chains preferably attach to the crystalline cluster with one end and then move along the stems of already crystallized chains towards their final position. This process is cooperative, i.e. neighboring chains tend to get attached in clusters rather than independently

Anwar, Muhammad; Schilling, Tanja

2013-01-01

107

The Nucleation and Growth of Protein Crystals  

NASA Technical Reports Server (NTRS)

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

Pusey, Marc

2004-01-01

108

Visualization of RNA crystal growth by atomic force microscopy.  

PubMed Central

The crystallization of transfer RNA (tRNA) was investigated using atomic force microscopy (AFM) over the temperature range from 4 to 16 degrees C, and this produced the first in situ AFM images of developing nucleic acid crystals. The growth of the (110) face of hexagonal yeast tRNAPhe crystals was observed to occur at steps on vicinal hillocks generated by multiple screw dislocation sources in the temperature range of 13.5-16 degrees C. Two-dimensional nucleation begins to dominate at 13.5 degrees C, with the appearance of three-dimensional nuclei at 12 degrees C. The changes in growth mechanisms are correlated with variations in supersaturation which is higher in the low temperature range. Growth of tRNA crystals was characterized by a strong anisotropy in the tangential step movement and transformation of growth modes on single crystals were directly observed by AFM over the narrow temperature range utilized. Finally, lattice resolution images of the molecular structure of surface layers were recorded. The implications of the strong temperature dependence of tRNAPhe crystal growth are discussed in view of improving and better controlling crystallization of nucleic acids. PMID:9185567

Ng, J D; Kuznetsov, Y G; Malkin, A J; Keith, G; Giegé, R; McPherson, A

1997-01-01

109

Crystal growth of ribonuclease S under microgravity  

NASA Astrophysics Data System (ADS)

Expecting that protein crystal growth in space would show us a new aspect of its crystallization process and might result in the improvement of crystal quality, we performed a series of growth experiments for bovine pancreatic ribonuclease S crystals under microgravity. For this purpose, the COSIMA2 system launched in September 1989 was utilized. In one of the eight crystallization chamber setups in the COSIMA2 experiment, a large "Z-form" single crystal appeared and we found that (a) the space-grown single crystal exhibited a higher fraction of significant X-ray diffraction spots than ground-grown crystals of approximately the same size and (b) the corresponding Wilson plots also tended to show a slightly lower overall temperature factor for the space-grown crystals, although the quality of the plot was not sufficient for quantitative evaluation. Thus, mainly based on the above observation (a), it is most likely that the internal order of the ribonuclease S crystal was in fact improved through the crystallization under microgravity.

Asano, Koji; Fujita, Shozo; Senda, Toshiya; Mitsui, Yukio

1992-08-01

110

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

111

Illusory spirals and loops in crystal growth.  

PubMed

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

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

2013-10-22

112

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

113

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

114

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

115

Electrochemical Growth Of Crystals In Gels  

NASA Technical Reports Server (NTRS)

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

Barber, Patrick G.; Coleman, James

1988-01-01

116

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

117

Convection effects in protein crystal growth  

NASA Technical Reports Server (NTRS)

Protein crystals for X-ray diffraction study are usually grown resting on the bottom of a hanging drop of a saturated protein solution, with slow evaporation to the air in a small enclosed cell. The evaporation rate is controlled by hanging the drop above a reservoir of water, with its saturation vapor pressure decreased by a low concentration of a passive solute. The drop has a lower solute concentration, and its volume shrinks by evaporation until the molecular concentrations match. Protein crystals can also be grown from a seed crystal suspended or supported in the interior of a supersaturated solution. The main analysis of this report concerns this case because it is less complicated than hanging-drop growth. Convection effects have been suggested as the reason for the apparent cessation of growth at a certain rather small crystal size. It seeems that as the crystal grows, the number of dislocations increases to a point where further growth is hindered. Growth in the microgravity environment of an orbiting space vehicle has been proposed as a method for obtaining larger crystals. Experimental observations of convection effects during the growth of protein crystals have been reported.

Roberts, Glyn O.

1988-01-01

118

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

119

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

120

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. PMID:22332828

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

2012-01-01

121

Crystal growth under heat field rotation conditions  

NASA Astrophysics Data System (ADS)

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

Kokh, Alexandr E.; Kononova, Nadegda G.

2000-05-01

122

Solution growth of crystals in zero gravity  

NASA Technical Reports Server (NTRS)

A series of experiments will be performed in which triglycine sulfate (TGS) crystals will be grown by a low-temperature solution growth technique in the microgravity environment of the orbital Spacelab. Triglycine sulfate (TGS) crystals will be grown in the Fluid Experiment System (FES) facility on Spacelab 3 by slowly extracting heat at a controlled rate through a seed crystal of TGS suspended on an insulated sting in a saturated solution of TGS. The FES rack assembly designed for SL-3 is shown in Figure I-1, and a detailed view of the test cell layout is presented in Figure I-2. Variations in the liquid density, solution concentration and temperature around the growing crystal will be studied using a variety of techniques, such as schlieren, shadowgraph, and interferometric measurements. Growth in Earth gravity will also be studied by the same optical techniques, and in both cases the resulting crystalline features will be compared and correlated with the growth conditions.

Lai, R. B.

1982-01-01

123

Proposed Technique of Crystal-Ribbon Growth  

NASA Technical Reports Server (NTRS)

Technique for silicon crystal-ribbon growth from crucible, two inert wettable filaments dipped into silicon melt to guide growth of silicon sheet. Filaments clamped in place and tilted slightly away from each other and seed ribbon lowered into contact with melt to establish menisci between filaments.

Thornhill, J. W.

1984-01-01

124

(PCG) Protein Crystal Growth Isocitrate Lysase  

NASA Technical Reports Server (NTRS)

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

1989-01-01

125

(PCG) Protein Crystal Growth Isocitrate Lyase  

NASA Technical Reports Server (NTRS)

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

1989-01-01

126

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

127

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

128

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

129

Space-based crystal growth and thermocapillary flow  

NASA Technical Reports Server (NTRS)

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

Shen, Yong-Hong

1994-01-01

130

Relationship between surface structure, growth mechanism, and trace element incorporation in calcite  

Microsoft Academic Search

Crystal growth and coprecipitation experiments demonstrate the manner in which surface structure and, in turn, crystal structure influence growth mechanism and trace element incorporation in calcite. Dominant {1014} faces grow by the spiral mechanism, producing asymmetric polygonized growth hillocks comprised of two pairs of nonequivalent vicinal faces. Trace elements Mg, Mn, and Sr are differentially incorporated into structurally distinct growth

Jeanne Paquette; Richard J. Reeder

1995-01-01

131

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

132

Protein Crystal Growth Apparatus for Microgravity  

NASA Technical Reports Server (NTRS)

Apparatus for growing protein crystals under microgravity environment includes a plurality of protein growth assemblies stacked one above the other within a canister. Each of the protein growth assemblies includes a tray having a number of spaced apart growth chambers recessed below an upper surface. the growth chambers each having an upstanding pedestal and an annular reservoir about the pedestal for receiving a wick and precipitating agents. A well is recessed below the top of each pedestal to define a protein crystal growth receptacle. A flexible membrane is positioned on the upper surface of each tray and a sealing plate is positioned above each membrane, each sealing plate having a number of bumpers corresponding in number and alignment to the pedestals for forcing the membrane selectively against the upper end of the respective pedestal to seal the reservoir and the receptacle when the sealing plate is forced down.

Carter, Daniel C. (Inventor); Dowling, Timothy E. (Inventor)

1997-01-01

133

Growth and characterization of large CLBO crystals  

NASA Astrophysics Data System (ADS)

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

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

2006-07-01

134

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

135

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

136

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

137

Interaction between Convection and Heat Transfer in Crystal Growth  

NASA Technical Reports Server (NTRS)

Crystals are integral components in some of our most sophisticated and rapidly developing industries. Single crystals are solids with the most uniform structures that can be obtained on an atomic scale. Because of their structural uniformity, crystals can transmit acoustic and electromagnetic waves and charged particles with essentially no scattering or interferences. This transparency, which can be selectively modified by controlled additions of impurities known as dopants, is the foundation of modern electronic industry. It has brought about widespread application of crystals in transistors, lasers, microwave devices, infrared detectors, magnetic memory devices, and many other magnets and electro-optic components. The performance of a crystal depends strongly on its compositional homogeneity. For instance, in modern microcircuitry, compositional variations of a few percent (down to a submicron length scale) can seriously jeopardize predicted yields. Since crystals are grown by carefully controlled phase transformations, the compositional adjustment in the solid is often made during growth from the nutrient. Hence, a detailed understanding of mass transfer in the nutrient is essential. Moreover, since mass transfer is often the slowest process during growth, it is usually the rate limiting mechanism. Crystal growth processes are usually classified according to the nature of the parent phase. Nevertheless, whether the growth occurs by solidification from a melt (melt growth), nucleation from a solution (solution growth), condensation from a vapor (physical vapor transport) or chemical reaction of gases (chemical vapor deposition), the parent phase is a fluid. As is with most non-equilibrium processes involving fluids, liquid or vapor, fluid motion plays an important role, affecting both the concentration and temperature gradients at the soli-liquid interface.

1998-01-01

138

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

139

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

Microsoft Academic Search

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

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

2008-01-01

140

Growth of Large Hematin Crystals in Biomimetic Solutions.  

PubMed

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

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

2014-05-01

141

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

142

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

143

Fractal aggregation and dendritic crystal growth  

Microsoft Academic Search

A lattice gas model is used to study random crystal growth in a finite density gas. The model interpolates between the diffusion-limited aggregation (DLA) and the Eden models. In the DLA model, the open fractal structure usually seen in simulated dendrite experiments comes from the fact that the Laplacian field, which is an approximation of the diffusion field, does not

Makio Uwaha; Yukito Saito

1990-01-01

144

Spacelab 3 vapor crystal growth experiment  

NASA Technical Reports Server (NTRS)

The Space Shuttle Challenger, with Spacelab 3 as its payload, was launched into orbit April 29, 1985. The mission, number 51-B, emphasized materials processing in space, although a wide variety of experiments in other disciplines were also carried onboard. One of the materials processing experiments on this flight is described, specifically the growth of single crystals of mercuric iodide by physical vapor transport.

Schnepple, W.; Vandenberg, L.; Skinner, N.; Ortale, C.

1987-01-01

145

(PCG) Protein Crystal Growth Isocitrate Lysase  

NASA Technical Reports Server (NTRS)

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

1993-01-01

146

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

147

Crystal nucleation and growth from supercooled melts  

Microsoft Academic Search

We review our recent work on the crystal nucleation and growth from supercooled model liquids. In particular, we discuss the issue of the selection of a specific crystalline or polymorph during the crystallisation process. We show on a variety of systems how, by modifying the thermodynamic conditions of crystallisation, we achieve the control of polymorphism in model systems. More specifically,

J. Delhommelle

2011-01-01

148

Method for crystal growth control  

DOEpatents

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

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

1981-01-01

149

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

150

Crystal growth in a microgravity environment  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

151

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

152

Carbon nanotube seeded silicon crystal growth  

NASA Astrophysics Data System (ADS)

Crystal growth of liquid silicon on the heterogeneous surfaces of carbon nanotubes (CNTs) is simulated. Silicon atoms are concentrated to form perfect coaxial cylindrical configurations around CNT cores. The heredity effect makes silicon imprint cylindrical shapes of CNTs during the solidification. The CNTs have a great influence on the stacking sequence of silicon atoms. Growth competition between CNT cores is clearly observed, which results in defects at the shared interface. The internal potential field around CNTs is responsible for growth competition and the heredity effect.

Li, Y. F.; Li, H.; Sun, F. W.; Zhang, X. Q.; Liew, K. M.

2011-07-01

153

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

154

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

Microsoft Academic Search

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

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

2009-01-01

155

Apparatus for monitoring crystal growth  

DOEpatents

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

Sachs, Emanual M. (Watertown, MA)

1981-01-01

156

Method of monitoring crystal growth  

DOEpatents

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

Sachs, Emanual M. (Watertown, MA)

1982-01-01

157

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

NASA Technical Reports Server (NTRS)

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

1992-01-01

158

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

159

On the growth of microscopic hurt and unhurt crystals  

NASA Astrophysics Data System (ADS)

The effect of secondary nucleation depends strongly on the growth behaviour of the nuclei. Therefore the growth rate of small (<12 ?m) damaged crystals was compared with that of regular shaped crystals: Damaged NaCl crystals do not grow, K 2SO 4 crystals grow slower and potash-alum crystals grow faster than the corresponding unhurt crystals. As more detailed experiments are still to be done, this paper makes no attempt to explain the above mentioned phenomena.

Offermann, H.; Ulrich, J.

1983-09-01

160

The Averaged Face Growth Rates of lysozyme Crystals: The Effect of Temperature  

NASA Technical Reports Server (NTRS)

Measurements of the averaged or macroscopic face growth rates of lysozyme crystals are reported here for the (110) face of tetragonal lysozyme, at three sets of pH and salt concentrations, with temperatures over a 4-22 C range for several protein concentrations. The growth rate trends with supersaturation were similar to previous microscopic growth rate measurements. However, it was found that at high super-saturations the growth rates attain a maximum and then start decreasing. No 'dead zone' was observed but the growth rates were found to approach zero asymptotically at very low super-saturations. The growth rate data also displayed a dependence on pH and salt concentration which could not be characterized solely by the super-saturation. A complete mechanism for lysozyme crystal growth, involving the formation of an aggregate growth unit, mass transport of the growth unit to the crystal interface and faceted crystal growth by growth unit addition, is suggested. Such a mechanism may provide a more consistent explanation for the observed growth rate trends than those suggested by other investigators. The nutrient solution interactions leading to the formation of the aggregate growth unit may, thus, be as important as those occurring at the crystal interface and may account for the differences between small molecule and protein crystal growth.

Nadarajah, Arunan; Forsythe, Elizabeth L.; Pusey, Marc L.

1995-01-01

161

The Biological Macromolecule Crystallization Database and NASA Protein Crystal Growth Archive  

Microsoft Academic Search

database entries include data abstracted from published crystallographic reports. Each entry consists of information describ- ing the biological macromolecule,crystal- lized and crystal data and the crystallization conditions for each crystal form. The BMCD serves as the NASA Protein Crystal Growth Archive in that it contains protocols and results of crystallization experiments undertaken in microgravity (space). These database entries report the

Gary L. Gilliland; Michael Tung; Jane Ladner

1996-01-01

162

Growth of single crystals by vapor transport  

NASA Technical Reports Server (NTRS)

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

Wiedemeier, H.

1978-01-01

163

Crystal Splitting in the Growth of Bi2S3  

SciTech Connect

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

Tang, Jing; Alivisatos, A. Paul

2006-06-15

164

Protein crystal growth in low gravity  

NASA Technical Reports Server (NTRS)

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

Feigelson, Robert S.

1994-01-01

165

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

166

Bulk Crystal Growth - Methods and Materials  

NASA Astrophysics Data System (ADS)

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

Capper, Peter

167

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

168

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. PMID:17296943

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

2007-01-01

169

Controlled Crystal Growth and Solid-Liquid Interface in temperature-sensitive colloidal systems  

NASA Astrophysics Data System (ADS)

We use temperature-sensitive colloidal NIPA systems to study crystal growth at the ``atomic scale''. By applying a temperature gradient we are able to control the growth of large colloidal single crystals. We visualize the nucleation of these crystals and solidification at the crystal-liquid interface in three dimensions by using confocal microscopy. Trajectories of particles on both the crystal and liquid side of an advancing interface are determined. These elucidate the mechanism of particle assembly at the interface of a growing crystal. At later stages of crystal growth, the interface becomes stationary, and we use the fluctuations of the stationary interface to determine the interface stiffness. Our data suggests a strong anisotropy of the interface tension. These microscopic observations provide unique insight into the mechanism of solidification.

Nguyen, Duc; Hu, Zhibing; Schall, Peter

2009-03-01

170

Colloidal crystal growth by evaporation-induced convective steering  

NASA Astrophysics Data System (ADS)

We simulate evaporation-driven self-assembly of colloidal crystals using an equivalent network model. Relationships between a regular hexagonally close-packed array of hard, monodisperse spheres, the associated pore space, and selectivity mechanisms for face-centered cubic microstructure propagation are described. Accounting for contact line rearrangement and evaporation at a series of exposed menisci, the equivalent network model describes creeping flow of solvent into and through a rigid colloidal crystal. Observations concerning colloidal crystal growth are based on the convective steering hypothesis, which posits that solvent flow into and through the pore space of the crystal may play a major role in colloidal self-assembly. Aspects of the convective steering and deposition of high-Peclet-number rigid spherical particles at a crystal boundary are inferred from spatially resolved solvent flow into the crystal. Gradients in local flow through boundary channels were predicted due to the channels' spatial distribution relative to a pinned free surface contact line. When the free surface contact line is pinned near the leading crystal edge, the network simulations suggest that rows of particles preferentially nucleate furthest from the substrate. These lattice sites propagate the existing microstructure and lead to a declining shelf formation.

Brewer, Damien D.; Kumar, Satish; Tsapatsis, Michael

2009-11-01

171

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

172

Studying Crystal Growth With the Peltier Effect  

NASA Technical Reports Server (NTRS)

Peltier interface demarcation (PID) shown useful as aid in studying heat and mass transfer during growth of crystals from molten material. In PID, two dissimilar "metals" solid and liquid phases of same material. Current pulse passed through unidirectionally solidifying sample to create rapid Peltier thermal disturbance at liquid/solid interface. Disturbance, measured by thermocouple stationed along path of solidification at or near interface, provides information about position and shape of interface.

Larsen, David J., Jr.; Dressler, B.; Silberstein, R. P.; Poit, W. J.

1986-01-01

173

(PCG) Protein Crystal Growth Gamma-Interferon  

NASA Technical Reports Server (NTRS)

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

1989-01-01

174

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

NASA Astrophysics Data System (ADS)

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

Wang, Wei

175

Mechanics and growth of tissues  

NASA Astrophysics Data System (ADS)

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

Joanny, Jean-Francois

2013-03-01

176

Accelerated protein crystal growth by protein thin film template  

NASA Astrophysics Data System (ADS)

A new method based on Langmuir-Blodgett (LB) technology is presented for the template stimulation of protein crystal growth. The new approach allows the acceleration of the hen egg white lysozyme (HEWL) crystal growth rate in comparison with such a classical vapour diffusion method as hanging drop. Protein thin films were coated on the cover slide of the common crystallization plates. Lysozyme crystal growth was observed on the LB thin films of HEWL.

Pechkova, Eugenia; Nicolini, Claudio

2001-11-01

177

Mechanical Characterization of Partially Crystallized Sphere Packings  

NASA Astrophysics Data System (ADS)

We study grain-scale mechanical and geometrical features of partially crystallized packings of frictional spheres, produced experimentally by a vibrational protocol. By combining x-ray computed tomography, 3D image analysis, and discrete element method simulations, we have access to the 3D structure of internal forces. We investigate how the network of mechanical contacts and intergranular forces change when the packing structure evolves from amorphous to near perfect crystalline arrangements. We compare the behavior of the geometrical neighbors (quasicontracts) of a grain to the evolution of the mechanical contacts. The mechanical coordination number Zm is a key parameter characterizing the crystallization onset. The high fluctuation level of Zm and of the force distribution in highly crystallized packings reveals that a geometrically ordered structure still possesses a highly random mechanical backbone similar to that of amorphous packings.

Hanifpour, M.; Francois, N.; Vaez Allaei, S. M.; Senden, T.; Saadatfar, M.

2014-10-01

178

The Biological Macromolecule Crystallization Database and NASA Protein Crystal Growth Archive.  

PubMed

The NIST/NASA/CARB Biological Macromolecule Crystallization Database (BMCD), NIST Standard Reference Database 21, contains crystal data and crystallization conditions for biological macromolecules. The database entries include data abstracted from published crystallographic reports. Each entry consists of information describing the biological macromolecule crystallized and crystal data and the crystallization conditions for each crystal form. The BMCD serves as the NASA Protein Crystal Growth Archive in that it contains protocols and results of crystallization experiments undertaken in microgravity (space). These database entries report the results, whether successful or not, from NASA-sponsored protein crystal growth experiments in microgravity and from microgravity crystallization studies sponsored by other international organizations. The BMCD was designed as a tool to assist x-ray crystallographers in the development of protocols to crystallize biological macromolecules, those that have previously been crystallized, and those that have not been crystallized. PMID:11542472

Gilliland, G L; Tung, M; Ladner, J

1996-01-01

179

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

180

Crystal growth within a phase change memory cell  

NASA Astrophysics Data System (ADS)

In spite of the prominent role played by phase change materials in information technology, a detailed understanding of the central property of such materials, namely the phase change mechanism, is still lacking mostly because of difficulties associated with experimental measurements. Here, we measure the crystal growth velocity of a phase change material at both the nanometre length and the nanosecond timescale using phase-change memory cells. The material is studied in the technologically relevant melt-quenched phase and directly in the environment in which the phase change material is going to be used in the application. We present a consistent description of the temperature dependence of the crystal growth velocity in the glass and the super-cooled liquid up to the melting temperature.

Sebastian, Abu; Le Gallo, Manuel; Krebs, Daniel

2014-07-01

181

Crystal growth within a phase change memory cell.  

PubMed

In spite of the prominent role played by phase change materials in information technology, a detailed understanding of the central property of such materials, namely the phase change mechanism, is still lacking mostly because of difficulties associated with experimental measurements. Here, we measure the crystal growth velocity of a phase change material at both the nanometre length and the nanosecond timescale using phase-change memory cells. The material is studied in the technologically relevant melt-quenched phase and directly in the environment in which the phase change material is going to be used in the application. We present a consistent description of the temperature dependence of the crystal growth velocity in the glass and the super-cooled liquid up to the melting temperature. PMID:25000349

Sebastian, Abu; Le Gallo, Manuel; Krebs, Daniel

2014-01-01

182

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

183

Diameter Control of HP-Ge Crystal Growth  

NASA Astrophysics Data System (ADS)

Large single crystals of germanium are being grown using the Czochralski technique, in which a precisely cut seed crystal is dipped into the molten germanium and then withdrawn slowly, while maintaining the temperature of the melt just above the freezing point. Typically the seed is rotated while the crystal is being formed. The resulting crystal is typically oriented with a (100) crystal axis parallel to the growth direction. The crystal growth process is conducted in a hydrogen (H2) atmosphere, with the H2 flowing inside a quartz envelope. High purity germanium (HP-Ge) crystals with diameter 3 ˜ 9 cm are grown on weekly basis at university of South Dakota. As Czochralski growth is a dynamic process, the thermal geometry in the furnace undergoes a considerable change during the crystal growth process. A load cell was introduced to control the crystal growth process. Growing crystals with automation system is studied. In order to grow crystal automatically, the relationship between input power and crystal weight or crystal diameter is investigated. We show that HP-Ge crystal growth could be controlled automatically using software with feedback system.

Mei, Hao

2013-03-01

184

Growth and properties of triglycine sulfate (TGS) crystals: Review  

Microsoft Academic Search

The present status of data on growth and properties of pure and doped single crystals of triglycine sulfate (TGS) is reviewed. The results of growth and characteristics of TGS crystals grown in the low-gravity environment of the space shuttle for infrared detector applications are presented. Applications of crystals in various devices are also described.

R. B. Lal; A. K. Batra

1993-01-01

185

Crystal growth kinetics of the two-step model  

NASA Astrophysics Data System (ADS)

The single crystal technique was used to measure the growth rate of the potassium alum (111) face and the magnesium sulfate (110) face. The two-step model was found appropriate to describe the growth kinetics with the surface integration order of two for potassium alum crystal and of one for magnesium sulfate crystal. The individual rate constants, Kd and Kr, were determined accordingly.

Tai, Clifford Y.; Lin, Chiu-Hsiung

1987-03-01

186

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

187

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

PubMed Central

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

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

2013-01-01

188

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

189

The influence of internal crystal perfection on growth rate dispersion in a continuous suspension crystallizer  

NASA Astrophysics Data System (ADS)

The objective of the work presented here is to demonstrate the influence of induced lattice strain on growth behaviour of potassium alum crystals in a continuously operated mixed suspension mixed product removal (MSMPR) crystallizer. Therefore crystal size distributions in the crystallizer and individual growth velocities, especially of small particles (initial size 20-60 ?m) in a flow-through cell, were simultaneously determined. Moreover Laue diffraction patterns of crystals withdrawn from the MSMPR crystallizer were carried out indicating lattice deformation and strain. Most crystals exhibit constant crystal growth (CCG) behaviour with significant growth rate dispersion. The mean growth rate of small particles in the sub-sieve size range is considerably smaller than the mean rate of product sized crystals at constant supersaturation. Small potash alum crystals show a clear tendency of increased lattice strain with increasing supersaturation which can be explained by the refaceting process of attrition nuclei in the crystallizer. The average amount of induced strain in crystals having the same growth history is obviously related to crystal size. Only slightly strained particles with sufficiently high growth rates will reach the product size range in the MSMPR crystallizer.

Zacher, U.; Mersmann, A.

1995-01-01

190

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

Microsoft Academic Search

Good quality single crystals of pure and metal ion (Ni 2+ ) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals

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

2011-01-01

191

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

Microsoft Academic Search

Good quality single crystals of pure and metal ion (Ni2+) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline

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

2011-01-01

192

Optimization of heating conditions during Cz BGO crystal growth  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

193

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

194

Morphological stability and kinetics in crystal growth from vapors  

NASA Technical Reports Server (NTRS)

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

Rosenberger, Franz

1990-01-01

195

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

196

Epitaxial few-layer graphene: towards single crystal growth  

NASA Astrophysics Data System (ADS)

We review our research towards single-crystal growth of epitaxial few-layer graphene (FLG) on SiC substrates. We have established a method for evaluating the number of graphene layers microscopically using low-energy electron microscopy. Scanning probe microscopy in air is also useful for estimating the number-of-layers distribution in epitaxial FLG. The number-of-layers dependence of the work function and C1s binding energy is determined using photoelectron emission microscopy. We investigate the growth processes of epitaxial FLG on the basis of the microscopic observations of surface morphology and graphene distribution. To gain insights into the growth mechanism, we calculate the SiC surface structures with various C coverages using a first-principles scheme. Uniform bilayer graphene a few micrometres in size is obtained by annealing in UHV.

Hibino, H.; Kageshima, H.; Nagase, M.

2010-09-01

197

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

198

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

199

Vapor Crystal Growth International Microgravity Laboratory (IML-1)  

NASA Technical Reports Server (NTRS)

Vapor Crystal Growth System developed in IML-1, Mercuric Iodide Crystal grown in microgravity FES/VCGS (Fluids Experiment System/Vapor Crystal Growth Facility). During the mission, mercury iodide source material was heated, vaporized, and transported to a seed crystal where the vapor condensed. Mercury iodide crystals have practical uses as sensitive X-ray and gamma-ray detectors. In addition to their excellent optical properties, these crystals can operate at room temperature, which makes them useful for portable detector devices for nuclear power plant monitoring, natural resource prospecting, biomedical applications, and astronomical observing.

1992-01-01

200

Melting Mechanisms of 3D Colloidal Crystals  

NASA Astrophysics Data System (ADS)

We study the melting mechanisms of 3D colloidal crystals using aqueous suspensions of thermally responsive NIPA microgel colloidal particles. Below 32 ^oC, the particle radius decreases approximately linearly with increasing temperature. We use this effect to tune the volume fraction of nearly hard-sphere aqueous NIPA colloidal suspensions from 0.74 to 0.54. Using video tracking microscopy, we measured the Lindemann parameter of particles within the crystal as a function of temperature. Interestingly, we find that melting of the 3D colloidal crystals starts at grain boundaries and free surfaces, rather than isolated vacancies or dislocations. Very near the melting temperature, the Lindemann parameter for particles near the grain boundaries and free surfaces was ˜0.16; the parameter decreased approximately exponentially with distance into the bulk crystal. These works has been partially supported by NSF through MRSEC DMR-0203378 and DMR-079909 and by NASA grant NAG8- 2172.

Alsayed, A. M.

2005-03-01

201

Influence of pH on the growth and characteristics of nonlinear optical zinc thiourea chloride (ZTC) single crystals  

Microsoft Academic Search

Growth of bulk zinc thiourea chloride (ZTC) single crystals from aqueous solution by low temperature solution growth technique has been reported. In this report we bring out the influence of pH on the structural, optical, electrical and mechanical properties of the grown crystals. At pH 5.3, the crystals are elongated along a-axis. Bulk crystals have been grown from the optimized

R. Rajasekaran; R. Mohan Kumar; R Jayavel; P Ramasamy

2003-01-01

202

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

203

Anion-switchable supramolecular gels for controlling pharmaceutical crystal growth  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

204

In situ observation and simulation of growth process of faceted RE123 crystals  

NASA Astrophysics Data System (ADS)

To clarify the growth mechanism of faceted REBa 2Cu 3O 7-? (RE123, RE = Sm, Y) crystals, the growth process of the crystals was observed in situ by using a high temperature microscope. The growth rate of each faceted interface of a crystal growing from the liquid + 211 phases under an undercooling was obtained from the relationship between the position of each interface and growth time. It was observed that some of the faceted interfaces of a growing crystal stopped growing after a period of time, while other interfaces continued to grow with a growth rate approximated by a function of the undercooling. The above stoppage of the growth was observed in situ for the first time, and this fact could give powerful support to the mechanism for a similar phenomenon in REBCO films which were fabricated by the trifluoroacetates metal organic deposition method: growing microstructures of RE123 crystals in the film were revealed by transmission electron microscopy (TEM) for quenched specimens. Some very thin a-axis grains were formed by a change in c-axis growth rate. Furthermore, we showed the above growth and stop phenomena of faceted interfaces of REBCO crystal grains using numerical simulations.

Mori, N.; Maebatake, T.; Teranishi, R.; Yamada, K.; Mukaida, M.; Miura, M.; Yoshizumi, M.; Izumi, T.

2010-11-01

205

X-ray initiation of nonthermal growth of single crystal pyramids in amorphous barium titanate  

NASA Astrophysics Data System (ADS)

Nonthermal crystallization of amorphous barium titanate (BTO) was initiated by a monochromatic x-ray microbeam from a synchrotron radiation source. Following x-ray exposure, micron-sized BTO single crystals with a true square pyramid shape appeared on the surface of an amorphous BTO substrate-free film. The location and size of the areas in which crystal growth appeared fit well the x-ray microbeam path and size, respectively. A plausible mechanism of x-ray induced initiation of nonthermal crystallization in BTO is proposed. The observed phenomenon holds promise for materials engineering at nanoscale and crystallization of amorphous materials in situations where heating must be avoided.

Feldman, Y.; Lyahovitskaya, V.; Leitus, G.; Lubomirsky, I.; Wachtel, E.; Bushuev, V. A.; Vaughan, G.; Barkay, Z.; Rosenberg, Yu.

2009-08-01

206

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

207

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

208

Luminescence labeling and dynamics of growth active crystal surface structures  

NASA Astrophysics Data System (ADS)

One aspect of the multifaceted proposal by A. G. Cairns-Smith (CS), that imperfect crystals have the capacity to act as primitive genes by transferring the disposition of their imperfections from one crystal to another, is investigated. An experiment was designed in a model crystalline system unrelated to the composition of the pre-biotic earth but suited to a well-defined test. Plates of potassium hydrogen phthalate were studied in order to ascertain whether, according to CS, parallel screw dislocations could serve as an information store with cores akin to punches in an old computer card. Evidence of screw dislocations was obtained from their associated growth hillocks through differential interference contrast microscopy, atomic force microscopy, and luminescence labeling of hillocks in conjunction with confocal laser scanning microscopy. Inheritance was evaluated by the corresponding patterns of luminescence developed in 'daughter' crystals grown from seed in the presence of fluorophores. The dispositions and evolution of growth active hillock patterns were quantified by fractal correlation analysis and statistical analysis. Along the way, we came to realize that transferring information encoded in the disposition of screw dislocations is complicated by several factors that lead to 'mutations' in the information stored in the pattern of defects. These observations forced us to confront the fundamental mechanisms that give rise to screw dislocations. It became clear that inter-hillock correlations play a significant role in the appearance of new dislocations through growth, and cause the overall pattern of hillocks to be non-random. Tendencies for clustering and correlations along various crystallographic directions were observed. Investigations into the dye-crystal surface chemistries and interactions with hillock steps also ensued through a combination of experimental techniques and force-field calculations. It was established that certain dye molecules not only recognize some propagating steps as opposed to others, but preferentially choose between kinks propagating in opposing directions on the same step. Beyond providing the first experimental test of the CS proposal, this work is aimed at understanding the nucleation, evolution, and impurity interactions of growth-induced screw dislocations, a necessary ingredient for the growth of crystals at low supersaturation.

Bullard, Theresa Vivian

209

Protein Crystal Growth With the Aid of Microfluidics  

NASA Technical Reports Server (NTRS)

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

vanderWoerd, Mark

2003-01-01

210

Kinetic mechanism of chain folding in polymer crystallization  

NASA Astrophysics Data System (ADS)

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

Stepanow, S.

2014-09-01

211

Investigation on Growth and Surface Analysis of DAST Single Crystals  

SciTech Connect

We have explored the growth of bulk size N, N-dimethylamino-N'-methylstilbazolium p-toluenesulphonate (DAST) using slope nucleation method. The grown crystal was characterized by single crystal X-ray diffraction (XRD), and CHN analyses. The surface morphology of the crystal was analyzed using Scanning electron microscopy (SEM).

Thomas, Tina; Vijay, R. Jerald; Gunaseelan, R.; Sagayaraj, P. [Department of Physics, Loyola College, Chennai - 600 034 (India)

2011-07-15

212

Microrobotic Streak Seeding For Protein Crystal Growth CUCS04104  

E-print Network

Microrobotic Streak Seeding For Protein Crystal Growth CUCS­041­04 Atanas Georgiev 1 Peter Allen 1 crystallographers streak seeding it is used entice certain protein crystals grow. Our system features a of custom this paper known crystallographers streak seeding a technique where small nuclei (or micro­crystals

213

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

214

Step flow and polytype transformation in growth of 4H-SiC crystals  

NASA Astrophysics Data System (ADS)

4H-SiC crystals containing polytype defects are investigated by optical microscopy, atomic force microscopy, and Raman scattering, aiming at understanding the mechanism of polytype transformation during growth processes. It is observed that the crystal surfaces around the facet are uneven and contain many macroscopic triangular domains, consisting of wide triangular terraces and giant macrosteps. Nucleation and growth on the wide terraces are demonstrated to be responsible for the polytype transformation. A possible polytype transformation mechanism is put forward, which can explain the stabilizing effect of nitrogen on 4H-SiC growth.

Liu, Chunjun; Chen, Xiaolong; Peng, Tonghua; Wang, Bo; Wang, Wenjun; Wang, Gang

2014-05-01

215

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

216

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

217

Space manufacturing in an automated crystal growth facility  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

218

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

E-print Network

1 Cloud structure and crystal growth in nimbostratus clouds. Mengistu Wolde* , Gabor Vali-mail: mengistu.wolde@nrc.ca. #12;2 Abstract Cloud structure and crystal growth in two nimbostratus were examined using in situ and airborne radar observations. In both cases, structure throughout the cloud depth

Vali, Gabor

219

Molecular dynamics simulations of gold-catalyzed growth of silicon bulk crystals and nanowires  

E-print Network

ARTICLES Molecular dynamics simulations of gold-catalyzed growth of silicon bulk crystals with Au­Si liquids is studied by molecular dynamics simulations using an empirical potential fitted of the NW nucleation and growth mechanisms at the atomistic level. Atomistic simulations, such as molecular

Cai, Wei

220

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

221

High-pressure growth of NaMn 7O 12 crystals  

NASA Astrophysics Data System (ADS)

With the aim of producing large crystals of metastable NaMn 7O 12 manganite, suitable for physical measurements (i.e.: RXS, Raman, EPR, STS, single-crystal neutron diffraction), we carried out a systematic investigation of the parameters controlling the growth of crystals, including the thermodynamic variables ( T, P, and reagent composition) and the kinetic factors, such as reaction time and heating/cooling rate. By varying each parameter while maintaining constant the other ones, we found the thermodynamic conditions under which an optimum equilibrium is reached between the competing nucleation and growth rates. They were found to range between 400 and 700 °C ( T) and between 20 and 60 Kbars ( P), respectively. Under these conditions, we further optimized the growth process, by establishing the most appropriate growth duration (several hours), reagent type (pre-reacted precursor) and composition (presence of 0.4 mole% water and of 5% Na excess with respect to the stoichiometric composition). Typical crystals having several hundreds ?m in linear sizes were reproducibly obtained, while the largest sample was about 800 ?m. A description of the crystal growth mechanism, based on the experimental results, is also presented and discussed. It assumes that two different mechanisms control the crystal growth, depending on whether the crystallization is taking place outside the stability field, i.e. in presence of native reagents, or inside it, i.e. in a polycrystalline NaMn 7O 12 phase matrix. In the first case, large crystal growth occurs thanks to the low nucleation and high diffusion rates, while in the second one the crystallization is due to the solid-state mechanism based on the free energy reduction caused by grain boundary migration.

Gilioli, Edi; Calestani, Gianluca; Licci, Francesca; Paorici, Carlo; Gauzzi, Andrea; Bolzoni, Fulvio; Prodi, Andrea

2006-12-01

222

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

PubMed

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

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

2015-03-01

223

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

224

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

225

Growth, characterization and application of KTN family nonlinear optical crystals  

Microsoft Academic Search

We have recently grown KLTN:(Cu, Ni, Ni\\/Ti) and strontium barium titanate (SBT) crystals and characterized their nonlinear-optical properties. The growth of these high quality crystals is a result of recent improvements in the crystal growth system; namely, improved flux uniformity and higher operating temperature. These and other materials have been characterized for application to holographic data storage and quasi-phase matched

Amnon Yariv; Anthony Kewitsch; Rudy Hofmeister

1994-01-01

226

Research on TGS single crystal growth with modulated structure  

NASA Astrophysics Data System (ADS)

The experimental results of TGS crystal growth with modulated structure (periodic laminar of ferroelectric domains) is briefly discussed in this paper. The method used here is to add some DL-alanine additive in the solution of TGS and to apply the electric field during crystal growth, the direction of which is periodically varied. By using this method, TGS single crystals containing a nearly regular and flat periodic laminar structure of ferroelectric domains have been fabricated.

Wang, Wenshan; Qi, Ming

1986-12-01

227

Lattice Boltzmann model for crystal growth from supersaturated solution  

Microsoft Academic Search

We develop a new, lattice effects-free lattice Boltzmann model for simulating crystal growth from supersaturated solution. Simulations of crystal growth from a single or multiple nuclei in a domain initially filled with supersaturated solution are presented, such as in the case of gas hydrate formation. We find that as the process changes from diffusion-controlled to surface reaction-controlled, the crystal transforms

Qinjun Kang; Dongxiao Zhang; Peter C. Lichtner; Ioannis N. Tsimpanogiannis

2004-01-01

228

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

229

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

230

Universality classes for unstable crystal growth.  

PubMed

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 ?_{t}h(x,t)=-?·[j(?h)+?(?^{2}h)]: 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?t^{n}; (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. PMID:25019732

Biagi, Sofia; Misbah, Chaouqi; Politi, Paolo

2014-06-01

231

The significance of intergranular diffusion to the mechanisms and kinetics of porphyroblast crystallization  

Microsoft Academic Search

The spatial disposition, compositional zoning profiles, and size distributions of garnet crystals in 11 specimens of pelitic schist from the Picuris Range of New Mexico (USA) demonstrate that the kinetics of intergranular diffusion controlled the nucleation and growth mechanisms of porphyroblasts in these rocks. An ordered disposition of garnet centers and a significant correlation between crystal radius and near-neighbor distances

William D. Carlson

1989-01-01

232

Growth Defect Studies in SiC Single Crystals  

Microsoft Academic Search

Growth defects in vapor grown 6H-SiC single crystals have been studied using a combination of techniques, including: synchrotron white beam x-ray topography (SWBXT), conventional optical microscopy, fluorescence microscopy, and epi-fluorescence laser scanning confocal microscopy (LSCM). These studies of crystal sections cut both parallel and perpendicular to the [0001] growth axis focused on growth dislocations of screw character running approximately parallel

Michael Dudley; William M. Vetter

1996-01-01

233

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

PubMed Central

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

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

1995-01-01

234

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

SciTech Connect

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 P2{sub 1}. 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 d{sub 33} 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, E-mail: nanosen@gmail.com; Ramasamy, P., E-mail: nanosen@gmail.com [Centre for Crystal Growth, SSN College of Engineering, Kalavakkam, Tamilnadu - 603110 (India)

2014-04-24

235

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

236

Growth of large KDP crystals for laser fusion experiments  

NASA Astrophysics Data System (ADS)

The growth of huge KDP crystals which have a 40 cm × 40 cm cross section for a frequency converter for high power laser system for nuclear fusion experiments is described. The main factor limiting the growth rate is spontaneous nucleation. We could successfully grow a crystal by a three-vessel method (TVM) at the rate of 2.9 mm/day over half a year without nucleation by setting the temperature of the crystallizer lower than room temperature. The TVM proved to be superior to a conventional temperature reduction method. The bulk laser damage threshold was improved two to three times that of conventionally grown crystals by reducing organic impurities in the growth solution. These techniques are very important for the growth of large KDP crystals of good quality for high power lasers.

Sasaki, Takatomo; Yokotani, Atsushi

1990-01-01

237

Numerical computations of faceted pattern formation in snow crystal growth.  

PubMed

Faceted growth of snow crystals leads to a rich diversity of forms with remarkable sixfold symmetry. Snow crystal structures result from diffusion-limited crystal growth in the presence of anisotropic surface energy and anisotropic attachment kinetics. It is by now well understood that the morphological stability of ice crystals strongly depends on supersaturation, crystal size, and temperature. Until very recently it was very difficult to perform numerical simulations of this highly anisotropic crystal growth. In particular, obtaining facet growth in combination with dendritic branching is a challenging task. We present numerical simulations of snow crystal growth in two and three spacial dimensions using a computational method recently introduced by the present authors. We present both qualitative and quantitative computations. In particular, a linear relationship between tip velocity and supersaturation is observed. In our computations, surface energy effects, although small, have a pronounced effect on crystal growth. We compute solid plates, solid prisms, hollow columns, needles, dendrites, capped columns, and scrolls on plates. Although all these forms appear in nature, it is a significant challenge to reproduce them with the help of numerical simulations for a continuum model. PMID:23005427

Barrett, John W; Garcke, Harald; Nürnberg, Robert

2012-07-01

238

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

239

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

240

Layer-by-Layer Growth of Binary Colloidal Crystals  

NASA Astrophysics Data System (ADS)

We report the growth of binary colloidal crystals with control over the crystal orientation through a simple layer-by-layer process. Well-ordered single binary colloidal crystals with a stoichiometry of large (L) and small (S) particles of LS2 and LS were generated. In addition, we observed the formation of an LS3 superstructure. The structures formed as a result of the templating effect of the first layer and the forces exerted by the surface tension of the drying liquid. By using spheres of different composition, one component can be selectively removed, as is demonstrated in the growth of a hexagonal non-close-packed colloidal crystal.

Velikov, Krassimir P.; Christova, Christina G.; Dullens, Roel P. A.; van Blaaderen, Alfons

2002-04-01

241

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

242

The Growth of p-Type AIII BIII C2V I Single Crystals  

NASA Astrophysics Data System (ADS)

AIIIBIIIC2VI single crystals were grown by the modified Bridgman-Stockbarger method, a procedure similar to direct freezing in our crystal growth laboratory. AIIIBIIIC2VI compounds are collected into two groups (III. group: TI, Ga, In and VI. group: Se, S, Te): 1. TlGaSe2, TlGaS2 and TlInS2 have layer structure. 2. TlInSe2, TlInTe2 and TlGaTe2 have chained structure. The main reasons such crystals grown with this method is similar to the direct freezing method because 1) quality of crystals is the same as crystals grown by other methods, and 2) growth time of crystals is shorter by about 5-10 days. None of the grown crystals had cracks and voids on the surface. Freshly cleaved crystals had a mirror-like surface and there was no need for mechanical or chemical polishing. The X-ray Laue back reflection method was used to test the crystallinity of the prepared samples. It was found that the crystals was p-type by hot probe technique. The ingots produced were single crystals and the useful region of single crystal was approximately 90% of the bulk.

Gürbulak, Bekýr; Coþkun, Cevdet; Doðan, Seydý; Ateþ, Aytunç; Yoðurtçu, Yahya Kemal

2000-01-01

243

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

244

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

245

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

246

Predicting crystal structure by merging data mining with quantum mechanics  

E-print Network

ARTICLES Predicting crystal structure by merging data mining with quantum mechanics CHRISTOPHER C crystal structures will form in an alloy system. Crystal structure can only be predicted effectively the stable crystal structure of materials. C rystal structure occupies a central and often critical role

Ceder, Gerbrand

247

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

NASA Astrophysics Data System (ADS)

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

Su, Ching-Hua

2015-01-01

248

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

249

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

250

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

251

Heat-Exchanger Method of Crystal Growth  

NASA Technical Reports Server (NTRS)

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

Khattak, C. P.; Schmid, F.

1982-01-01

252

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

253

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

254

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

PubMed

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

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

2013-01-22

255

Growth of large single crystals of the orthorhombic paracetamol  

NASA Astrophysics Data System (ADS)

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

Mikhailenko, M. A.

2004-05-01

256

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 VDX TM 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.

2008-04-01

257

Crystal growth of SiC for electronic applications  

NASA Technical Reports Server (NTRS)

The development of SiC as a high temperature semiconductor material is discussed, focusing on the epitaxial growth of single crystal SiC films on inexpensive single crystal silicon wafers. Progress in the improvement of film morphology and the elimination of antiphase disorder is examined. Potential candidate materials for high temperature semiconductor devices are compared and SiC films are evaluated.

Matus, Lawrence G.; Powell, J. Anthony

1989-01-01

258

Growth and characterization of rare earths doped triglycine sulfate crystals  

Microsoft Academic Search

Ferroelectric triglycine sulfate (TGS) single crystals have been grown by a temperature-lowering technique from the aqueous solution by doping with samarium sulfate, ytterbium sulfate and terbium sulfate in the ferroelectric phase. The effects of these different dopants on the morphology, growth and various properties such as dielectric, pyroelectric and piezoelectric of doped TGS crystals have been investigated. The decrease in

A. K. Batra; Padmaja Guggilla; Dewanna Cunningham; M. D. Aggarwal; R. B. Lal

2006-01-01

259

Crystal growth and perfection of large octahedral synthetic diamonds  

NASA Astrophysics Data System (ADS)

Octahedral diamond crystals grown by the temperature gradient method at 1550 °C using a BARS apparatus have been studied. Dislocations and planar defects in diamond crystals have been found and characterized by selective etching and X-ray diffraction topography. It is found that the diamond crystals contained not more than four bunches of extended defects. Large planar defects and narrow bunches of straight <1 1 1> dislocations extend from the seed crystal. <1 1 1> dislocations initiate stacking faults and partial dislocations in the <1 1 2> direction. These defects also give rise to <2 2 1> dislocations. Partial dislocations are dominant. Screw and then edge and mixed dislocations appear as the densities of linear and planar defects increase in the bunch. Combined cathodo- and photoluminescence topographic, X-ray topographic and selective etching studies of {1 1 1} faces showed, that single <1 1 1> dislocations are the sources of large low-elevation hillocks, which appeared during crystal growth. It is concluded that diamond crystal growth at the specified average rates of 39-45 ?m/h is a phenomenon involving the simultaneous participation of dislocations and two-dimensional nucleation as sources of growth steps. The studies have shown that dislocation-free regions in the octahedral diamond crystals weighing 3 carats occupy about 58 mm 3, and some crystals have completely dislocation-free {1 1 1} growth sectors.

Khokhryakov, Alexander F.; Palyanov, Yuri N.; Kupriyanov, Igor N.; Borzdov, Yuri M.; Sokol, Alexander G.; Härtwig, Jürgen; Masiello, Fabio

2011-02-01

260

Novel protein crystal growth technology: Proof of concept  

Microsoft Academic Search

A technology for crystal growth, which overcomes certain shortcomings of other techniques, is developed and its applicability to proteins is examined. There were several unknowns to be determined: the design of the apparatus for suspension of crystals of varying (growing) diameter, control of the temperature and supersaturation, the methods for seeding and\\/or controlling nucleation, the effect on protein solutions of

Thomas A. Nyce; Franz Rosenberger

1989-01-01

261

The growth technology for 300 mm single crystal silicon  

Microsoft Academic Search

The fabrication technique for 300 mm silicon single crystals and wafers is the central topic of silicon material research recently. The study on the growth technique of 300 mm silicon ingots has been developed in our institute since 1997. The research mainly focuses on the following aspects: (1) process conditions for fabrication of the dislocation-free silicon single crystal; (2) oxygen

H Tu; Q Zhou; G Zhang; J Wang; Q Chang; F Qin; F Fang; Z Wu; G Wan

2001-01-01

262

Transport modes during crystal growth in a centrifuge  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

263

Definition study for temperature control in advanced protein crystal growth  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

264

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

265

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. PMID:24297886

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

2013-01-01

266

NELSEVIER Journal of Crystal Growth 181 (1997)351 362 J........ CRYSTAL  

E-print Network

microscopy (AFM) to study the (0 0 0 1) growth surface of a 6H-SiC single crystal at the points where microscopy study of super-dislocation/micropipe complexes on the 6H-SiC(0 0 0 1) growth surface Jennifer.72; 61.72.F Keywor&." Atomic force microscopy; SiC; Spiral growth; Screw dislocations; Micropipes 1

Rohrer, Gregory S.

267

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

268

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

269

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

270

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

271

Imaging System For Measuring Macromolecule Crystal Growth Rates in Microgravity  

NASA Technical Reports Server (NTRS)

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

Corder, Eric L.; Briscoe, Jeri

2004-01-01

272

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.

273

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

PubMed

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

Ruby Nirmala, L; Thomas Joseph Prakash, J

2013-02-01

274

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

275

Growth of zinc selenide crystals doped with magnesium  

SciTech Connect

The present work examines the growth conditions and several properties of zinc selenide crystals doped with magnesium selenide. Doped crystals of Zn /SUB 1-x/ Mg /SUB x/ Se solid solutions in the composition range O is less than or equal to x which is less than or equal to 0.21 were grown. The structural and optical properties of the crystals were studied. Crystals of the cubic phase can be grown up to x is less than 0.18 without residual stresses.

Kulakov, M.P.; Fadeev, A.V.

1986-08-01

276

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

277

Mechanics in Tumor Growth 1 Mechanics in Tumor Growth  

E-print Network

the extracellular matrix. As will be described in the following this process is affected by the stress applied some of the main feature of tumor growth and in particular the phenomena involving stress description, one can say that the cells forming a compact tumor, like other cells in the body, live

Preziosi, Luigi

278

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

279

Ammonothermal growth of GaN crystals in alkaline solutions  

NASA Astrophysics Data System (ADS)

A method for the growth of GaN bulk crystals under ammonothermal conditions is described. Gallium nitride is shown to have a retrograde solubility in ammonobasic solutions. Using polycrystalline GaN as nutrient and hydride vapor phase epitaxy GaN templates as seeds, the crystals were grown in the hot zone. The ammonothermal growth experiments were carried out in ammonobasic solutions in high nickel content autoclaves for up to 3 weeks. Growth rates up to 50 ?m/day were achieved and single crystals of GaN up to 10×10×1 mm 3 were obtained. The ammonothermal crystals are of high quality, as characterized by optical microscopy, scanning electron microscopy, high-resolution X-ray diffraction and photoluminescence measurements.

Wang, Buguo; Callahan, M. J.; Rakes, K. D.; Bouthillette, L. O.; Wang, S.-Q.; Bliss, D. F.; Kolis, J. W.

2006-01-01

280

Liquid nitrogen dewar for protein crystal growth  

NASA Technical Reports Server (NTRS)

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

2001-01-01

281

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

282

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

283

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

284

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

285

Three-dimensional simulation of floating-zone crystal growth of oxide crystals  

NASA Astrophysics Data System (ADS)

The floating-zone (FZ) method is a popular technique for the growth of high-temperature oxide crystals. However, the growth usually requires skillful control of the zone stability, which is strongly coupled with heat flow, interfaces, and the grown crystal morphology. In this report, we present a three-dimensional self-consistent simulation of floating-zone oxide growth in a mirror furnace by taking these factors into account simultaneously. This model is based on an efficient finite volume method with multigrid acceleration and interface tracking. The steady growth of a YAG crystal in a double-ellipsoid mirror furnace is taken as an example to illustrate the intricate coupling of convection, interfaces, meniscus, and the grown crystal shape.

Lan, C. W.

2003-01-01

286

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

NASA Astrophysics Data System (ADS)

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

Derby, J. J.; Xiao, Q.

1991-09-01

287

The crystallization and growth of AlB2 single crystal flakes in aluminum  

Microsoft Academic Search

An {ital in situ} high temperature heat treatment was used to investigate the crystallization and growth behavior of AlB flakes in aluminum. Aluminum samples containing 1.8% boron were heated above the liquidus and then rapidly cooled through the Al{sub (L)}+AlB region to avoid the formation of AlB crystals. Subsequently, a homogeneous distribution of high aspect ratio AlB flakes crystallized upon

C. Deppisch; G. Liu; A. Hall; Y. Xu; A. Zangvil; J. K. Shang; J. Economy

1998-01-01

288

Shallow Melt Apparatus for Semicontinuous Czochralski Crystal Growth  

DOEpatents

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

Wang, T.; Ciszek, T. F.

2006-01-10

289

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

NASA Technical Reports Server (NTRS)

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

Zefiro, L.

1980-01-01

290

Growth of crystals for synchrotron radiation Mössbauer investigation  

NASA Astrophysics Data System (ADS)

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

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

1991-10-01

291

Growth and characterization of doped LiF crystals  

NASA Astrophysics Data System (ADS)

Transparent and crack-free crystals of LiF: x ( x = Ca, Pb, Na, Tl) were successfully grown by using the Czochralski method. Growth parameters such as the pulling and the rotation rates were optimized. The grown crystals were characterized and compared by using X-ray luminescence. Tl- and Na-doped crystals showed better luminescence intensity than crystals with other dopants. Thermoluminescence (TL) glow curves were obtained to study the crystal defects in the grown samples. Activation energies were calculated from the TL glow curves. The temperature dependence of the light yield in the temperature range from 10 to 300 K under alpha particle excitation was also investigated. The light yield was found to be larger at low temperatures. Na- and Tl-doped crystals showed 35% and 20% increases in the light yield, respectively, at low temperatures as compared to room temperature.

Khan, Sajid; Kim, H. J.; Rooh, Gul; Kim, Sunghwan

2014-12-01

292

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

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

293

Studies of light emission and epitaxial growth on crystal surfaces  

NASA Astrophysics Data System (ADS)

The integration of novel structures and devices into semiconductor electronics requires a detailed understanding of the physical phenomena exhibited by impurities at crystal surfaces. Using this understanding, the optical properties and structure of deposited atoms can be selected. This thesis describes studies of light emission from a fraction of a monolayer of Er atoms on a silicon surface and of the low-temperature growth and doping of crystalline Si thin films mediated by Pb. Erbium atoms at an As-terminated Si (111) surface can be made to emit light at the 1.55 gin wavelength associated with an internal transition in the Er3+ ion. The As-terminated surface suppresses competing non- radiative surface recombination mechanisms. Following the deposition of Er, its characteristic light emission is observed only after oxygen reacts with the surface. The intensity of the light emitted by Er increases significantly upon cooling. No light emission was observed from Er atoms deposited on 7 x 7 or H-terminated surfaces. A monolayer of Pb mediates high-quality homoepitaxial growth on Si (111) surfaces at temperatures where growth with other overlayer elements or on bare surfaces leads to amorphous or highly defective crystalline films. Nearly defect-free epitaxy proceeds at temperatures as low as 310°C for film thicknesses up to 1000 Å with no sign that this is an upper limit. When Pb and Si are deposited on an As-terminated Si (111) substrate, the Pb floats on the surface of the growing Si film and the As layer remains buried at the substrate-film interface. Because the Pb overlayer mediates growth without doping the film, the electrical properties are determined by the As atoms. With a donor density in excess of 1 × 1021 cm -3 in a layer less than 50 Å in thickness, the heavily doped interface region represents the highest concentration of electrically active As achieved by any delta-doping method.

Evans, Paul Gregory

2000-11-01

294

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

PubMed Central

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

Day, J.; McPherson, A.

1992-01-01

295

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

PubMed

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

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

2014-10-01

296

Growth and microtopographic study of CuAlS2 single crystals  

NASA Astrophysics Data System (ADS)

CuAlS2 single crystals were grown by chemical vapour transport (CVT) technique in a close-spaced geometry. The elemental composition of the as-grown CuAlS2 single crystals was determined by energy dispersive analysis of X-ray (EDAX). The crystal structure and lattice parameters were determined by X-ray diffraction (XRD). The optical band gap was determined from absorbance spectrum. Defects, growth mechanism, etc. were studied from the microstructure analysis. The obtained results are discussed in details.

Chaki, Sunil H.; Deshpande, M. P.; Mahato, Kanchan S.

2013-06-01

297

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

NASA Astrophysics Data System (ADS)

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

Mann, Matthew; Jackson, Summer; Kolis, Joseph

2010-11-01

298

Novel protein crystal growth technology: Proof of concept  

NASA Technical Reports Server (NTRS)

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

Nyce, Thomas A.; Rosenberger, Franz

1989-01-01

299

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

300

Synthesis, crystal growth and spectroscopic investigation of novel metal organic crystal: ?-alanine cadmium bromide monohydrate (?-ACBM).  

PubMed

?-Alanine cadmium bromide monohydrate (?-ACBM), a new metal organic crystal has been grown from aqueous solution by slow evaporation technique. The grown crystals have been subjected to single crystal X-ray diffraction analysis to determine the crystal structure. The ?-ACBM crystallized in monoclinic system with space group P2(1)/c. The presence of protons and carbons in the ?-alanine cadmium bromide monohydrate was confirmed by (1)H and (13)C nuclear magnetic resonance spectral analysis. The mode of vibration of different molecular groups present in ?-ACBM was identified by FT-IR spectral analysis. Transparency of crystals in UV-Vis-NIR region has also been studied. The thermal characteristics of as-grown crystals were analyzed using thermo gravimetric and differential thermal analyses. The magnetic property of the grown crystal was investigated using Vibrating Sample Magnetometer (VSM) at ambient temperature. The mechanical stability of ?-ACBM was evaluated by Vickers microhardness measurement. PMID:24691377

Renugadevi, R; Kesavasamy, R

2014-07-15

301

A generalized electrochemical aggregative growth mechanism.  

PubMed

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

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

2013-08-01

302

Vapor crystal growth technology development: Application to cadmium telluride  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

303

Ground Based Program for the Physical Analysis of Macromolecular Crystal Growth  

NASA Technical Reports Server (NTRS)

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

Malkin, Alexander J.

1999-01-01

304

Journal of Crystal Growth 304 (2007) 399401 Growth of high quality, epitaxial InSb nanowires  

E-print Network

Journal of Crystal Growth 304 (2007) 399­401 Growth of high quality, epitaxial InSb nanowires Hyun March 2007 Communicated by R.M. Biefeld Available online 1 April 2007 Abstract The growth of InSb nanowires on an InSb(1 1 1) substrate in a closed system is described. A high density InSb nanowires

Wang, Zhong L.

305

A Microfluidic, High Throughput Protein Crystal Growth Method for Microgravity  

PubMed Central

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

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

2013-01-01

306

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

PubMed

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

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

2013-01-01

307

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

NASA Technical Reports Server (NTRS)

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

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

1971-01-01

308

Hydrothermal crystal growth of oxides for optical applications  

NASA Astrophysics Data System (ADS)

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

McMillen, Colin David

2007-12-01

309

High-thermal-gradient Superalloy Crystal Growth  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

310

Data acquisition from a crystal growth furnace  

NASA Technical Reports Server (NTRS)

Digital acquisition from a furnace for growing the lead tin telluride crystal based on Asyst software is described. It is shown that the use of Asyst for the acquisition of experimental data makes it possible to handle large amounts of data and to drastically reduce the time required for displaying the data from several hours to less than 5 minutes.

Woodell, Glenn A.

1988-01-01

311

INTERNATIONAL Macromolecular crystal growth and optimisation methods  

E-print Network

. Athens Membrane proteins: the paradigm of nicotinic acetylcholine receptors in muscle and nerve Dr of the E.U. "TOPCRYST" project for Imperial College The joys and challenges of crystallising proteins, Ireland Crystallizing Membrane Proteins for Structure-Function Studies Using Lipidic Systems Professor

312

Growth mechanism of hydrogen clusters  

SciTech Connect

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

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

1997-07-01

313

Wafer-scale growth of single-crystal monolayer graphene on reusable hydrogen-terminated germanium.  

PubMed

The uniform growth of single-crystal graphene over wafer-scale areas remains a challenge in the commercial-level manufacturability of various electronic, photonic, mechanical, and other devices based on graphene. Here, we describe wafer-scale growth of wrinkle-free single-crystal monolayer graphene on silicon wafer using a hydrogen-terminated germanium buffer layer. The anisotropic twofold symmetry of the germanium (110) surface allowed unidirectional alignment of multiple seeds, which were merged to uniform single-crystal graphene with predefined orientation. Furthermore, the weak interaction between graphene and underlying hydrogen-terminated germanium surface enabled the facile etch-free dry transfer of graphene and the recycling of the germanium substrate for continual graphene growth. PMID:24700471

Lee, Jae-Hyun; Lee, Eun Kyung; Joo, Won-Jae; Jang, Yamujin; Kim, Byung-Sung; Lim, Jae Young; Choi, Soon-Hyung; Ahn, Sung Joon; Ahn, Joung Real; Park, Min-Ho; Yang, Cheol-Woong; Choi, Byoung Lyong; Hwang, Sung-Woo; Whang, Dongmok

2014-04-18

314

Single crystal growth and anisotropic crystal-fluid interfacial free energy in soft colloidal systems.  

PubMed

We measure the anisotropy of the crystal-fluid interfacial free energy in soft colloidal systems. A temperature gradient is used to direct crystal nucleation and control the growth of large single crystals in order to achieve well-equilibrated crystal-fluid interfaces. Confocal microscopy is used to follow both the growth process and the equilibrium crystal-fluid interface at the particle scale: heterogeneous crystal nucleation, the advancing interface, and the stationary equilibrium interface. We use the measured growth velocity to determine the chemical potential difference between crystal and fluid phases. Well-equilibrated, large crystal-fluid interfaces are then used to determine the interfacial free energy and its anisotropy directly from thermally excited interface fluctuations. We find that while the measured average interfacial free energy is in good agreement with values found in simulations, the anisotropy is significantly larger than simulation values. Finally, we investigate the effect of impurities on the advancing interface. We determine the critical force needed to overcome impurity particles from the local interface curvature. PMID:21867183

Nguyen, Van Duc; Hu, Zhibing; Schall, Peter

2011-07-01

315

Reinvestigation of growth of thiourea urea zinc sulfate crystal  

NASA Astrophysics Data System (ADS)

Reinvestigation of the growth of thiourea urea zinc sulfate crystal is reported. Aqueous reaction of thiourea, urea and zinc sulfate in 1:1:1 mol ratio results in the formation of the well known [Zn(tu)3(SO4)] (1) (tu = thiourea) crystal and not the 'so called' novel semiorganic nonlinear optical thiourea urea zinc sulfate (2) crystal, as claimed by Redrothu Hanumantha Rao, S. Kalainathan, Spectroscopic investigation, nucleation, growth, optical, thermal and second harmonic studies of novel semi-organic nonlinear optical crystal - Thiourea urea zinc sulfate, Spectrochim. Acta A97 (2012) 456-463. In this work, we demonstrate the usefulness of elemental analytical data, infrared and NMR spectra and X-ray powder pattern, for accurate product characterization.

Srinivasan, Bikshandarkoil R.; Naik, Teja A.; Tylczy?ski, Zbigniew; Priolkar, K. R.

2014-01-01

316

Jurgen Geiser Simulation in crystal growth for SiC  

E-print Network

to the model and the technical apparatus SiC growth by physical vapor transport (PVT) SiC-seed-crystal , Gas), Si, SiC2, Si2C, . . . is created · an SiC single crystal grows on a cooled seed Center for Applied A S ¡ ¢ ¡ £ ¤¥ £ ¦ ¤ ¤§¨ ¤¥ ¢¥© ¥¡ £ ¢ ¡ ¨ ¦ ¤ ¢ ¤ ¦ ¨ ¥ ¦ ¤¥ ¢ ¤ ¢ ¨ ! £ ¤ © ¨ " ¤#¡ £ $ © ¨ % ¡ £ ¢ ¨ ¡ & ' & J¨urgen Geiser Simulation in crystal growth for SiC single crystal : Numerical Methods

Geiser, Juergen

317

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

NASA Astrophysics Data System (ADS)

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

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

2000-01-01

318

The effect of nitric acid (HNO3) on growth, spectral, thermal and dielectric properties of triglycine sulphate (TGS) crystal.  

PubMed

The effect of nitric acid (HNO(3)) addition on the growth of triglycine sulphate (TGS) crystal has been studied from the aqueous solution for various concentrations of nitric acid. Significant changes in the crystal size and morphology have been observed in all the grown samples. Single crystal and powder X-ray diffraction analyses confirm the structure and cell parameter values of pure and HNO(3) doped TGS crystals. FT-Raman and FTIR spectra confirm the characteristics absorption bands of pure and HNO(3) doped TGS crystals. The composition of TGS crystals have been confirmed by CHNS analysis. Physical properties such as thermal, dielectric and mechanical studies have been performed for the pure and HNO(3) doped TGS crystals. The dielectric constants of the crystals have been studied as a function of frequency. The results suggest that the HNO(3) is doped into TGS crystal and that the doping increases its dielectric constant. PMID:20004141

Parimaladevi, R; Sekar, C; Krishnakumar, V

2010-02-01

319

Kinetics of gypsum crystal growth on a reverse osmosis membrane  

Microsoft Academic Search

The development of calcium sulfate dihydrate (gypsum) mineral scale in reverse osmosis (RO) membrane desalting was investigated by direct real-time observation of crystal growth. Gypsum scaling studies were conducted in a specially modified plate-and-frame reverse osmosis cell fitted with an optical window, with dark-field membrane lighting arrangement within the membrane cell to enhance crystal boundaries and allow recording of digital

Michal Uchymiak; Eric Lyster; Julius Glater; Yoram Cohen

2008-01-01

320

Nucleation and Convection Effects in Protein Crystal Growth  

NASA Technical Reports Server (NTRS)

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

Rosenberger, Franz

1997-01-01

321

Crystal growth of device quality GaAs in space  

NASA Technical Reports Server (NTRS)

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

Gatos, Harry C.; Lagowski, Jacek

1989-01-01

322

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

323

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

PubMed

Semiorganic nonlinear optical crystals of Cadmium Thiosemicarbazide Bromide was grown by slow evaporation solution growth technique. The unit cell parameters were estimated by subjecting the crystals to single crystal X-ray diffraction. The grown crystals were subjected to Powder X-ray diffraction for analyzing the crystalline nature of the sample. FTIR studies reveal the functional groups and the optical characters were analyzed by UV-Vis spectral studies. Mechanical stability of the sample was assessed by Vicker's micro hardness test. The presence of surface dislocations was identified by chemical etching technique. Antibacterial study was carried out against ACDP declared harmful pathogens. SHG efficiency of CTSB crystal was tested using Nd: YAG laser and it was found to be ?1.8 times that of potassium dihydrogen phosphate. PMID:25048404

Thomas Joseph Prakash, J; Martin Sam Gnanaraj, J

2015-01-25

324

Fundamental Studies of Crystal Growth of Microporous Materials  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

325

Emittance concept and growth mechanisms  

SciTech Connect

The authors present an introduction to the subjects of emittance and space-charge effects in charged-particle beams. This is followed by a discussion of three important topics that are at the frontier of this field. The first is a simple model, describing space-charge-induced emittance growth, which yields scaling formulas and some physical explanations for some of the surprising results. The second is a discussion of beam halo, an introduction to the particle-core model, and a brief summary of its results. The third topic is an introduction to the hypothesis of equipartitioning for collisionless particle beams.

Wangler, T.P. [Los Alamos National Lab., NM (United States). Accelerator Operations and Technology Div.

1996-05-01

326

Synthesis, growth and characterization of cadmium manganese thiocyanate (CMTC) crystal.  

PubMed

Single crystals of cadmium manganese thiocyanate, CdMn(SCN)4 (CMTC) have been successfully synthesized and grown by slow evaporation solution growth technique using water as solvent at room temperature. The crystal was characterized by different techniques for finding its suitability for device fabrications. From the single crystal XRD the crystal system was identified as tetragonal. The functional groups were identified from FTIR analysis. The optical studies have been carried out and found that the tendency of transmission observed from the specimen with respect to the wavelength of light is practically more suitable for the present trends in communication engineering. From the thermal analysis the decomposing temperature of the grown crystal is more significant when compared with the studies performed earlier. PMID:21640636

Paramasivam, P; Raja, C Ramachandra

2011-09-01

327

Crystal growth of organics for nonlinear optical applications  

NASA Technical Reports Server (NTRS)

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

Singh, N. B.; Mazelsky, R.

1993-01-01

328

Crystal growth furnace with trap doors  

NASA Technical Reports Server (NTRS)

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

Sachs, Emanual M. (Inventor); Mackintosh, Brian H. (Inventor)

1982-01-01

329

Zeolite crystal growth in space - What has been learned  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

330

Adaptive temperature profile control of a multizone crystal growth furnace  

NASA Technical Reports Server (NTRS)

An intelligent measurement system is described which is used to assess the shape of a crystal while it is growing inside a multizone transparent furnace. A color video imaging system observes the crystal in real time, and determines the position and the shape of the interface. This information is used to evaluate the crystal growth rate, and to analyze the effects of translational velocity and temperature profiles on the shape of the interface. Creation of this knowledge base is the first step to incorporate image processing into furnace control.

Batur, C.; Sharpless, R. B.; Duval, W. M. B.; Rosenthal, B. N.

1991-01-01

331

Modelling the growth of triglycine sulphate crystals in Spacelab 3  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

332

Catalyzed growth of doped TGS single crystals for infrared applications  

NASA Astrophysics Data System (ADS)

Single crystals of triglycine sulphate (TGS) doped with Pr3+ Sm3+, Pd2+, Co2+, Pt4+ and PO43- with L-alanin were grown from aqueous solutions by means of the slow cooling method. Surface morphology, domain structure and P-E hysteresis loops have been investigated. The model of catalyzed growth of {001}and{101}crystal pyramids on the basis of metal-glycine complexes has been suggested. We have found on the basis of experimental results that TGS single crystals doped with Pt4+ and L-alanin are excellent materials for construction of infrared detectors.

Novotny, Jan; Zelinka, J.; Podvalova, Z.

2002-03-01

333

Interface stability and defect formation during crystal growth  

SciTech Connect

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

Fabietti, L.M.R.

1991-01-08

334

Mechanisms Limiting Body Growth in Mammals  

PubMed Central

Recent studies have begun to provide insight into a long-standing mystery in biology—why body growth in animals is rapid in early life but then progressively slows, thus imposing a limit on adult body size. This growth deceleration in mammals is caused by potent suppression of cell proliferation in multiple tissues and is driven primarily by local, rather than systemic, mechanisms. Recent evidence suggests that this progressive decline in proliferation results from a genetic program that occurs in multiple organs and involves the down-regulation of a large set of growth-promoting genes. This program does not appear to be driven simply by time, but rather depends on growth itself, suggesting that the limit on adult body size is imposed by a negative feedback loop. Different organs appear to use different types of information to precisely target their adult size. For example, skeletal and cardiac muscle growth are negatively regulated by myostatin, the concentration of which depends on muscle mass itself. Liver growth appears to be modulated by bile acid flux, a parameter that reflects organ function. In pancreas, organ size appears to be limited by the initial number of progenitor cells, suggesting a mechanism based on cell-cycle counting. Further elucidation of the fundamental mechanisms suppressing juvenile growth is likely to yield important insights into the pathophysiology of childhood growth disorders and of the unrestrained growth of cancer. In addition, improved understanding of these growth-suppressing mechanisms may someday allow their therapeutic suspension in adult tissues to facilitate tissue regeneration. PMID:21441345

Lui, Julian C.

2011-01-01

335

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

336

Crystal growth of device quality GaAs in space  

NASA Technical Reports Server (NTRS)

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

Lagowski, J.

1981-01-01

337

Mechanics of instability-related delamination growth  

NASA Technical Reports Server (NTRS)

Local buckling of a delaminated group of plies can lead to higher interlaminar stresses and delamination growth. The mechanics of instability-related delamination growth (IRDG) had been described previously for the through-width delamination. This paper describes the mechanics of IRDG for the embedded delamination subjected to either uniaxial or axisymmetric loads. The mechanics of IRDG are used to explain the dramatic differences in strain-energy release rates observed for the through-width, the axisymmetrically loaded embedded delamination, and the uniaxially loaded embedded delamination.

Whitcomb, John D.

1990-01-01

338

Mechanics of instability-related delimination growth  

NASA Technical Reports Server (NTRS)

Local buckling of a delaminated group of plies can lead to higher interlaminar stresses and delamination growth. The mechanics of instability-related delamination growth (IRDG) had been described previously for the through-width delamination. This paper describes the mechanics of IRDG for the embedded delamination subjected to either uniaxial or axisymmetric loads. The mechanics of IRDG are used to explain the dramatic differences in strain-energy release rates observed for the through-width, the axisymmetrically loaded embedded delamination, and the uniaxially loaded embedded delamination.

Whitcomb, John D.

1988-01-01

339

Enhanced growth rate for ammonothermal gallium nitride crystal growth using ammonium iodide mineralizer  

NASA Astrophysics Data System (ADS)

High-temperature gallium nitride (GaN) crystal growth using the acidic ammonothermal method with ammonium iodide (NH4I) as a mineralizer was investigated. The growth rate reached 105 ?m/day, which was much higher than that previously achieved using acidic ammonothermal methods, and exceeded 100 ?m/day, which is the minimum growth rate required for industrial applications. When NH4I was used as a mineralizer, high-speed crystal growth was achieved at a relatively low pressure compared to the case of using an ammonium chloride (NH4Cl) as a mineralizer.

Tomida, D.; Kagamitani, Y.; Bao, Q.; Hazu, K.; Sawayama, H.; Chichibu, S. F.; Yokoyama, C.; Fukuda, T.; Ishiguro, T.

2012-08-01

340

Investigation on growth and macro-defects of a UV nonlinear optical crystal: ZnCd(SCN) 4  

NASA Astrophysics Data System (ADS)

Large single crystals of the coordination complex nonlinear optical material zinc cadmium thiocyanate, ZnCd(SCN) 4 (abbreviated as ZCTC), were grown from aqueous solutions by the solvent evaporation method. The morphology of the crystals was indexed. The grown crystals were characterized by the powder X-ray diffraction analysis allowing to identify the diffraction planes. Six kinds of macro-defects were found in ZCTC large crystals. These defects include cracks, inclusions, negative crystals, growth striations, sector boundaries and straight pipes. The morphologies and distribution regularities of these defects were observed and analyzed using optical microscopy. Their formation mechanisms and the methods of eliminating these defects are discussed.

Wang, X. Q.; Zhang, J. G.; Xu, D.; Lü, M. K.; Yuan, D. R.; Xu, S. X.; Huang, J.; Zhang, G. H.; Guo, S. Y.; Wang, S. L.; Duan, X. L.; Ren, Q.; Lü, G. T.

2002-02-01

341

Thermal Optimization of Growth and Quality in Protein Crystals  

NASA Technical Reports Server (NTRS)

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

Wiencek, John M.

1996-01-01

342

2D modeling of the regeneration surface growth on crystals  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

343

Structural investigation of the seeding process for physical vapor transport growth of 4H-SiC single crystals  

NASA Astrophysics Data System (ADS)

Structural investigation of the seeding process for the physical vapor transport (PVT) growth of 4H-SiC single crystals was conducted by high-resolution x-ray diffraction (HRXRD) and synchrotron x-ray topography. Characteristic lattice plane bending behavior was observed in the near-seed regions of the grown crystals. The bending of the (112¯0) lattice plane was localized near the seed/grown crystal interface, and the (0001) basal plane bent convexly in the growth direction near the interface, indicative of the insertion of extra-half planes pointing toward the growth direction during the seeding process for PVT growth. This study discusses a possible mechanism for the observed lattice plane bending and sheds light on defect formation processes during the PVT growth of 4H-SiC single crystals.

Ohtani, Noboru; Ohshige, Chikashi; Katsuno, Masakazu; Fujimoto, Tatsuo; Sato, Shinya; Tsuge, Hiroshi; Ohashi, Wataru; Yano, Takayuki; Matsuhata, Hirofumi; Kitabatake, Makoto

2014-01-01

344

Hanging drop crystal growth apparatus and method  

NASA Technical Reports Server (NTRS)

An apparatus (10) is constructed having a cylindrical enclosure (16) within which a disc-shaped wicking element (18) is positioned. A well or recess (22) is cut into an upper side (24) of this wicking element, and a glass cover plate or slip (28) having a protein drop disposed thereon is sealably positioned on the wicking element (18), with drop (12) being positioned over well or recess (22). A flow of control fluid is generated by a programmable gradient former (16), with this control fluid having a vapor pressure that is selectively variable. This flow of control fluid is coupled to the wicking element (18) where control fluid vapor diffusing from walls (26) of the recess (22) is exposed to the drop (12), forming a vapor pressure gradient between the drop (12) and the control fluid vapor. Initially, this gradient is adjusted to draw solvent from the drop (12) at a relatively high rate, and as the critical supersaturation point is approached (the point at which crystal nucleation occurs), the gradient is reduced to more slowly draw solvent from the drop (12). This allows discrete protein molecules more time to orient themselves into an ordered crystalline lattice, producing protein crystals which, when processed by X-ray crystallography, possess a high degree of resolution.

Carter, Daniel C. (Inventor); Smith, Robbie E. (Inventor)

1989-01-01

345

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

PubMed

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

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

2015-02-01

346

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

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

347

Growth and characterization of terbium fumarate heptahydrate single crystals  

NASA Astrophysics Data System (ADS)

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

Want, B.; Shah, M. D.

2014-03-01

348

Simulations of nucleation and early growth stages of protein crystals.  

PubMed Central

Analysis of known protein crystal structures reveals that interaction energies between monomer pairs alone are not sufficient to overcome entropy loss related to fixing monomers in the crystal lattice. Interactions with several neighbors in the crystal are required for stabilization of monomers in the lattice. A microscopic model of nucleation and early growth stages of protein crystals, based on the above observations, is presented. Anisotropy of protein molecules is taken into account by assigning free energies of association (proportional to the buried surface area) to individual monomer-monomer contacts in the lattice. Lattice simulations of the tetragonal lysozyme crystal based on the model correctly reproduce structural features of the movement of dislocation on the (110) crystal face. The dislocation shifts with the speed equal to the one determined experimentally if the geometric probability of correct orientation is set to 10(-5), in agreement with previously published estimates. At this value of orientational probability, the first nuclei, the critical size of which for lysozyme is four monomers, appear in 1 ml of supersaturated solution on a time scale of microseconds. Formation of the ordered phase proceeds through the growth of nuclei (rather then their association) and requires nucleations on the surface at certain stages. Images FIGURE 2 PMID:9251778

Kierzek, A M; Wolf, W M; Zielenkiewicz, P

1997-01-01

349

The Growth of Protein Crystals Using McDUCK  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

350

Modeling snow crystal growth III: three-dimensional snowfakes  

E-print Network

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

Janko Gravner; David Griffeath

2007-11-26

351

Crewmember working on the spacelab Zeolite Crystal Growth experiment.  

NASA Technical Reports Server (NTRS)

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

1992-01-01

352

Crewmember working on the mid deck Zeolite Crystal Growth experiment.  

NASA Technical Reports Server (NTRS)

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

1992-01-01

353

Growth of high purity large synthetic diamond crystals  

Microsoft Academic Search

This paper reviews achievements at the Diamond Research Laboratory where, in the past, large, nitrogen-containing type Ib crystals of up to 25ct in weight have been synthesised by the temperature gradient method. Further work has focused on reducing the nitrogen point defect incorporation in synthetic diamond by introducing nitrogen getters into the synthesis cell used for this growth process. This

R. C. Burns; J. O. Hansen; R. A. Spits; M. Sibanda; C. M. Welbourn; D. L. Welch

1999-01-01

354

Solid state growth mechanisms for carbon nanotubes  

Microsoft Academic Search

The mechanisms by which carbon nanotubes nucleate and grow remain poorly understood. This paper reviews the models which have been proposed to explain nanotube growth in the arc-evaporation and laser-vaporisation processes. Many of the early models assumed that growth is a gas phase phenomenon but there is growing experimental evidence that the formation of both multiwalled and single-walled tubes involves

Peter J. F. Harris; J. J. Thomson

2007-01-01

355

Time-dependent simulation of Czochralski silicon crystal growth  

NASA Astrophysics Data System (ADS)

We have developed a detailed mathematical model and numerical simulation tools based on the streamline upwind/Petrov-Galerkin (SUPG) finite element formulation for the Czochralski silicon crystal growth. In this paper we consider the mathematical modeling and numerical simulation of the time-dependent melt flow and temperature field in a rotationally symmetric crystal growth environment. Heat inside the Czochralski furnace is transferred by conduction, convection and radiation, Radiating surfaces are assumed to be opaque, diffuse and gray. Hence the radiative heat exchange can be modeled with a non-local boundary condition on the radiating part of the surface. The position of the crystal-melt interface is solved by the enthalpy method. The melt flow is assumed to be laminar and governed by the cylindrically symmetric and incompressible Navier-Stokes equations coupled with the calculation of temperature.

Järvinen, Jari; Nieminen, Risto; Tiihonen, Timo

1997-10-01

356

A novel crystal growth technique from the melt: Levitation-Assisted Self-Seeding Crystal Growth Method  

NASA Astrophysics Data System (ADS)

A novel melt crystal growth technique was developed and applied for growing bulk In2O3 single crystals. In this new method the In2O3 starting material inside an inductively heated metal crucible is subjected to a controlled decomposition in such a way that a certain amount of free metallic indium forms. As a result, the electromagnetic field from an RF coil couples also to the In2O3 starting material, in addition to the metal crucible, which facilitates the melting. Liquid In2O3 has good electrical conductivity so that eddy currents are induced in the melt close to the crucible wall. This in turn induces a counter magnetic field that ultimately leads to levitation of a portion of the molten In2O3. The amount of the levitated material depends on the mutual RF coil-crucible position, their configurations as well as other components of a growth furnace. A consequence of the partial levitation of In2O3 melt is the formation of a liquid neck between the levitated and the quiescent melt portions. This neck is crucial as it acts as a seed during the crystallization process. The neck can be further shaped by controlled overheating or soaking. By cooling down, two single crystals are formed on the opposite sides of the seed. We named this new crystal growth technique “Levitation-Assisted Self-Seeding Crystal Growth Method”. It is in principle applicable to any oxides whose melts are electrically conductive. Thanks to this method we have successfully grown truly bulk In2O3 single crystals from the melt for the first time worldwide.

Galazka, Zbigniew; Uecker, Reinhard; Fornari, Roberto

2014-02-01

357

Precise tailoring of the crystal size distribution by controlled growth and continuous seeding from impinging jet crystallizers  

E-print Network

Precise tailoring of the crystal size distribution by controlled growth and continuous seeding from by combining controlled seeding by impinging jet crystallization with a batch crystallizer operating by any process equipment that can continuously provide crystal seeds, typically through the application

Braatz, Richard D.

358

Containerless protein crystallization in floating drops: application to crystal growth monitoring under reduced nucleation conditions  

NASA Astrophysics Data System (ADS)

A micromethod was developed for the batch crystallization of proteins under conditions were the solution has no contact with the container walls. Drops of crystallization solutions (5 to 100 ?l) are placed at the interface between two layers of inert and non-miscible silicone fluids contained in square glass or plastic cuvettes. The densities of the fluids are either lower or higher than those of the major precipitating agents of macromolecules, including aqueous solutions containing salts, polyethylene glycols or alcohols. Several proteins and a spherical plant virus were crystallized in the temperature range 4°C-20°C using this set-up. A thermostated device was built for the dynamic control of the temperature of crystallization drops and the monitoring of crystal growth by video-microscopy. In all cases, the habit of the crystals grown in floating drops are identical to those of controls grown in sealed glass tubes without silicone fluid. The comparison of the number of crystals in drops kept under one layer of fluid and in floating drops of the same volume indicates that heterogeneous nucleation is minimized when protein crystallization is performed in floating drops. The advantages and limitations of this novel containerless crystallization method are discussed.

Lorber, Bernard; Giegé, Richard

1996-10-01

359

Identification and control of a multizone crystal growth furnace  

NASA Technical Reports Server (NTRS)

This paper presents an intelligent adaptive control system for the control of a solid-liquid interface of a crystal while it is growing via directional solidification inside a multizone transparent furnace. The task of the process controller is to establish a user-specified axial temperature profile and to maintain a desirable interface shape. Both single-input-single-output and multi-input-multi-output adaptive pole placement algorithms have been used to control the temperature. Also described is an intelligent measurement system to assess the shape of the crystal while it is growing. A color video imaging system observes the crystal in real time and determines the position and the shape of the interface. This information is used to evaluate the crystal growth rate, and to analyze the effects of translational velocity and temperature profiles on the shape of the interface. Creation of this knowledge base is the first step to incorporate image processing into furnace control.

Batur, C.; Sharpless, R. B.; Duval, W. M. B.; Rosenthal, B. N.; Singh, N. B.

1992-01-01

360

Growth and characterization of rare earths doped triglycine sulfate crystals  

NASA Astrophysics Data System (ADS)

Ferroelectric triglycine sulfate (TGS) single crystals have been grown by a temperature-lowering technique from the aqueous solution by doping with samarium sulfate, ytterbium sulfate and terbium sulfate in the ferroelectric phase. The effects of these different dopants on the morphology, growth and various properties such as dielectric, pyroelectric and piezoelectric of doped TGS crystals have been investigated. The decrease in values of dielectric constant and pyroelectric coefficient is observed while the dielectric loss has increased. Using these parameters, figure-of-merits for their use in infrared sensors have also been reported and compared with pure TGS crystal. The Vickers's hardness of doped TGS crystals along (0 1 0) crystallographic face has increased.

Batra, A. K.; Guggilla, Padmaja; Cunningham, Dewanna; Aggarwal, M. D.; Lal, R. B.

2006-01-01

361

Czochralski growth of heavily tin-doped Si crystals  

NASA Astrophysics Data System (ADS)

Heavily tin (Sn)-doped Si crystals in a concentration up to 4×1019 cm-3 were grown by the Czochralski method. Variation of Sn concentration in the crystals was well expressed by the Pfann equation using a segregation coefficient of k=0.016. From the occurrence of growth interface instability and the appearance of Sn precipitates in the grown crystals, the solubility limit of Sn was considered to be around 5×1019 cm-3. Interstitially dissolved oxygen Oi was presented at a concentration of 8-9×1017 cm-3 in the grown Sn-doped crystals. The FT-IR absorption peak relating to a Si-Oi-Si quasi-molecule at 1106 cm-1 showed preferential occupation of Oi at the bond-centered position of Si-Si. The Oi peak shifted to the lower wave number side with increasing Sn concentration in Si, implying expansion of the Si-Si bond.

Yonenaga, I.; Taishi, T.; Inoue, K.; Gotoh, R.; Kutsukake, K.; Tokumoto, Y.; Ohno, Y.

2014-06-01

362

Mechanical forces of fission yeast growth.  

PubMed

Mechanical properties contribute to the control of cell size, morphogenesis, development, and lifestyle of fungal cells. Tip growth can be understood by a viscoplastic model, in which growth is derived by high internal turgor pressure and cell-wall elasticity. To understand how these properties regulate growth in the rod-shaped fission yeast Schizosaccaromyces pombe, we devised femtoliter cylindrical polydimethylsiloxane (PDMS) microchambers with varying elasticity as force sensors for single cells. By buckling cells in these chambers, we determine the elastic surface modulus of the cell wall to be 20.2 +/- 6.1 N.m(-1). By analyzing the growth of the cells as they push against the walls of the chamber, we derive force-velocity relationships and values for internal effective turgor pressure of 0.85 +/- 0.15 MPa and a growth-stalling force of 11 +/- 3 muN. The behavior of cells buckling under the force of their own growth provides an independent test of this model and parameters. Force generation is dependent on turgor pressure and a glycerol synthesis gene, gpd1(+) (glycerol-3-phosphate dehydrogenase), and is independent of actin cables. This study develops a quantitative framework for tip cell growth and characterizes mechanisms of force generation that contribute to fungal invasion into host tissues. PMID:19500986

Minc, Nicolas; Boudaoud, Arezki; Chang, Fred

2009-07-14

363

The mechanical properties of single crystal {alpha}-Si{sub 3}N{sub 4}  

SciTech Connect

The ambient and high temperature mechanical properties of single crystal {alpha}{minus}Si{sub 3}N{sub 4} synthesized by chemical vapor deposition are reported. Crack patterns in the as-grown crystals and around Vicker`s indentations reveal that significant residual stresses develop during growth. Indentation studies indicate that the cleavage is essentially isotropic in {alpha}{minus}Si{sub 3}N{sub 4} at 25 C as well as at 1400 C. Transmission electron microscopy on crystals deformed at high temperatures, confirmed previous observation that high-temperature slip occurs primarily on (1011)[1120] system.

Reimanis, I.E.; Suematsu, H.; Petrovic, J.J.; Mitchell, T.E.

1993-11-01

364

Crystal Growth of Solid Solution HgCdTe Alloys  

NASA Technical Reports Server (NTRS)

The growth of homogenous crystals of HgCdTe alloys is complicated by the large separation between their liquidus and solidus temperatures. Hg(1-x)Cd(x)Te is representative of several alloys which have electrical and optical properties that can be compositionally tuned for a number of applications. Limitations imposed by gravity during growth and results from growth under reduced conditions are described. The importance of residual accelerations was demonstrated by dramatic differences in compositional distribution observed for different attitudes of the space shuttle that resulted in different steady acceleration components.

Lehoczky, Sandor L.

1997-01-01

365

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

E-print Network

Journal of Crystal Growth 271 (2004) 128­133 Growth of strontium barium niobate: the liquidus. Roth Available online 11 September 2004 Abstract The liquidus­solidus phase diagram of strontium barium, and dielectric properties, strontium barium niobate, SrxBa1�xNb2O6--hen- ceforth denoted as SBN, is one

Osnabrück, Universität

366

Journal of Crystal Growth 274 (2005) 1420 Growth and characterization of single-crystalline gallium  

E-print Network

Journal of Crystal Growth 274 (2005) 14­20 Growth and characterization of single commercial and research GaN produc- tion relies upon sapphire or occasionally SiC. Unfortunately, the large; accepted 22 September 2004 Communicated by C.R. Abernathy Abstract Self-separating single

Anderson, Timothy J.

367

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

NASA Technical Reports Server (NTRS)

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

Lal, Ravindra

1994-01-01

368

The effect of nucleation and crystal growth on isotope fractionation  

NASA Astrophysics Data System (ADS)

A set of "free-drift" experiments is conducted to precipitate aragonites from seawater at controlled temperature (25-55oC) and CO2 degassing rate in the lab. These experiments help to calibrate a coupled degassing-nucleation-crystal growth model, which not only can reproduce measured pH and alkalinity over the course of the experiments, but also predict crystal size within a factor of two of the measured values, the activation energy of the precipitation reaction constant to be 24.3±1.3 kJ/mol, the surface energy of aragonite crystals that is consistent with estimation by atomistic simulation and crystal morphology. Forward simulation of our precipitation experiments using calibrated parameters reveal the supersaturation of seawater arrives at a critical value (~13-50 in our experiment) before nucleation initiates and when the concentration of the total dissolved inorganic carbon (DIC) reduces to that of Ca. This result cannot be explained by classical nucleation theory (CNT), but is consistent with recently proposed "two-step" nucleation model, implying solution chemistry determines when the nucleation starts but the surface properties of crystal (surface energy and crystal morphology) determine the size of the crystal. It also requires not only carbonate ions but all other DIC species within a sphere of a-few-micron radius actively participate into the nucleation process. This model is then used as a framework to understand oxygen and Mg isotope fractionation between carbonates and fluid. Our results suggest nucleation and crystal growth will affect isotope fractionation at different levels depending on experimental conditions. A quantitative analysis using our model can help reconcile the isotope fractionation factors determined by various experimental approaches.

Wang, Z.; Gaetani, G. A.; Liu, C.; Hu, P.; Cohen, A. L.

2011-12-01

369

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

370

Epitaxial growth of single crystal films  

NASA Technical Reports Server (NTRS)

An experiment in gallium arsenide liquid phase epitaxy (LPE) on a flight of the SPAR 6 is described. A general purpose LPE processor suitable for either SPAR or Space Transportation System flights was designed and built. The process was started before the launch, and only the final step, in which the epitaxial film is grown, was performed during the flight. The experiment achieved its objectives; epitaxial films of reasonably good quality and very nearly the thickness predicted for convection free diffusion limited growth were produced. The films were examined by conventional analytical techniques and compared with films grown in normal gravity.

Lind, M. D.; Kroes, R. L.; Immorlica, A. A., Jr.

1981-01-01

371

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

372

Growth and characteristics of tgs crystals grown aboard first international microgravity laboratory (IML1)  

Microsoft Academic Search

The growth and detector characteristics of TGS crystals grown in a low gravity environment of space are presented. High resolution monochromatic synchrotron X-ray diffraction imaging of the space grown crystal indicates an extraordinary crystal quality.

R. B. Lal; A. K. Batra; J. D. Trolinger; W. R. Wilcox; B. Steiner

1994-01-01

373

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

NASA Astrophysics Data System (ADS)

Single crystals of triglycine sulphate (TGS) doped with 1 mol% of 4-(dimethylamino) benzaldehyde (DB) have been grown from aqueous solution at ambient temperature by slow evaporation technique. The effect of dopant on the crystal growth and dielectric, pyroelectric and mechanical properties of TGS crystal have been investigated. X-ray powder diffraction pattern for pure and doped TGS was collected to determine the lattice parameters. FTIR spectra were employed to confirm the presence of 4-(dimethylamino) benzaldehyde in TGS crystal, qualitatively. The dielectric permittivity has been studied as a function of temperature by cooling the sample at a rate of 1 °C/min. An increase in the Curie temperature Tc=51 °C (for pure TGS, Tc=48.5 °C) and decrease in maximum permittivity has been observed for doped TGS when compared to pure TGS crystal. Pyroelectric studies on doped TGS were carried out to determine pyroelectric coefficient. The Vickers's hardness of the doped TGS crystals along (0 1 0) face is higher than that of pure TGS crystal for the same face. Domain patterns on b-cut plates were observed using scanning electron microscope. The low dielectric constant, higher pyroelectric coefficient and higher value of hardness suggest that doped TGS crystals could be a potential material for IR detectors.

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

2009-11-01

374

Growth of Semiconductor Single Crystals from Vapor Phase  

NASA Astrophysics Data System (ADS)

Growth of single crystals from the vapor phase is considered to be an important method to obtain stoichiometric crystalline materials from inexpensive and readily available raw materials. Elements or compounds which are relatively volatile can be grown from vapor phase. Most II-VI, I-III-VI2, and III-N compounds are high-melting-point materials which may be grown as single crystals by careful use of vapor phase. The chemical vapor transport (CVT) method has been widely used as an advantageous method to grow single crystals of different compounds at temperatures lower than their melting points. This method is quite useful for the growth of II-VI and I-III-VI2 compounds, which generally have high melting point and large dissociation pressure at the melting point. In addition, they undergo solid-state phase transition during cooling or heating processes, which makes the growth of these compounds by some other methods, such as from the melt, difficult. In addition, the low growth temperature involved reduces defects produced by thermal strain, pollution from the crucible, and the cost of the growth equipment. II-VI compound semiconductors cover a very broad range of electronic and optical properties due to the large range of their energy gaps. These materials in the form of bulk single crystals or thin films are used in light emitters, detectors, linear and nonlinear optical devices, semiconductor electronics, and other devices. The development of growth technology for II-VI compound semiconductors from the vapor phase with the necessary theoretical background is important. I-III-VI2 chalcopyrite compounds are of technological interest since they show promise for application in areas of visible and infrared light-emitting diodes, infrared detectors, optical parametric oscillators, upconverters, far-infrared generation, and solar energy conversion.

Dhanasekaran, Ramasamy

375

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

NASA Technical Reports Server (NTRS)

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

Day, Delbert E.; Ray, Chandra S.

1999-01-01

376

Biological Macromolecule Crystallization Database, Version 3.0: new features, data and the NASA archive for protein crystal growth data.  

PubMed

Version 3.0 of the NIST/NASA/CARB Biological Macromolecule Crystallization Database (BMCD) includes crystal and crystallization data on all forms of biological macromolecules which have produced crystals suitable for X-ray diffraction studies. The data include summary information on each of the macromolecules, crystal data, crystallization conditions and comments about the crystallization procedure if it varies from the traditional methods employed for crystal growth. The database-management software maintains continuity with previous versions providing similar search procedures and displays. Version 3.0 of the BMCD includes protocols and results of crystallization experiments undertaken in space. These new data are comprised of both the NASA Protein Crystal Growth Archive, which includes information on all NASA-sponsored protein crystal growth experiments, and data describing other internationally sponsored microgravity macromolecule crystallization studies. The entries for the space growth crystallization experiments contain the crystallization protocols, apparatus descriptions, flight summary data, indication of success or failure of the experiments, references, etc. Other new features of the BMCD include the addition of crystallization procedures for small peptides and cross references to other structural biology databases. PMID:15299394

Gilliland, G L; Tung, M; Blakeslee, D M; Ladner, J E

1994-07-01

377

Large volume single crystal growth of cadmium zinc telluride with minimal secondary phases for room temperature radiation detector application  

NASA Astrophysics Data System (ADS)

Two major aspects of Cadmium Zinc Telluride (CdZnTe) crystal growth for room temperature radiation detection application namely tellurium rich second phase defects and single crystal yield have been addressed. Various approaches were considered towards the minimization of these defects both during growth and post growth thermal treatment in cadmium environment. Since the issue of retrograde solubility in CdZnTe pseudo binary alloy system causes tellurium precipitation, different cooling mechanisms were also devised to achieve minimal secondary phases. Some important and encouraging results were obtained relative to the size and distribution of secondary phases upon growing the crystal with different growth rate and different cooling rate of the crystal after growth. Thermomigration of tellurium were also observed while post processing samples in a temperature gradient, in (Cd,Zn) atmosphere. Results indicated orders of magnitude reduction on secondary phases at the expense of sample resistivity. Apart from the issue of secondary phases, CdZnTe also suffers from low single crystal yield. Since grain boundaries and twins are known to hinder the transport properties of charge carriers, it is necessary to have large single crystal volumes with good uniformity for better charge collection efficiency. In our crystal growth facility, single crystal volumes up to 25x25x20 mm3 have been grown using unseeded vertical Bridgman technique. However reproducibility has been a major issue as far as single crystal yield is concerned. In order to consistently produce large volume detector grade material, seeding was attempted in vertical Bridgman set up in which crystals are grown on top of another appropriately oriented seed crystal. Certain important requirements for successful seeded growth are partial melting of the seed from top, proper melt mixing before starting growth and maintaining a convex interface shape to promote outward grain growth. To achieve these conditions, extreme care was taken in designing our experimental set up. Seed crystals with various orientations have been used in different growths. Preliminary results on these growths indicate success in achieving partial seed melting and proper control on the thermal environment. The grown crystals exhibited large number of twins suggesting that the use of seed crystal with proper orientation is critical.

Swain, Santosh Kumar

378

Growth and nonlinear optical studies of N-acetyl-L-cysteine crystal  

NASA Astrophysics Data System (ADS)

Crystals of N-acetyl-L-cysteine have been grown by slow evaporation solution growth technique using water as solvent. Cell parameters of the crystals were confirmed by powder X-ray diffraction. Functional groups were identified and their vibrational activity was studied by investigating the FTIR spectrum. Decomposition nature of the grown material was studied in thermal analysis. Transparent nature of the crystal in UV-VIS-NIR region was examined by optical absorption spectrum. Frequency conversion process was tested and the title crystal has two times larger relative second harmonic conversion efficiency compared to the standard KDP. Static and dynamic values of first-order hyperpolarizability were calculated and also the electronic excitation mechanism was analyzed.

Prasad, L. Guru; Krishnakumar, V.; Nagalakshmi, R.

2012-01-01

379

Astronauts Don Lind observes growth of crystals in VCGS aboard orbiter  

NASA Technical Reports Server (NTRS)

Astronauts Don L. Lind, 51-B Spacelab 3 mission specialist, observes the growth of mercuric iodide crystal in the vapor crystal growth system (VCGS) on the Spacelab 3 science module aboard the orbiter Challenger.

1985-01-01

380

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

PubMed

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

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

2015-03-01

381

Liquid crystalline growth within a phase-field crystal model  

E-print Network

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

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

2015-01-09

382

Growth Mechanism of Indium Tin Oxide Whiskers Prepared by Sputtering  

NASA Astrophysics Data System (ADS)

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

Takaki, Satoru; Aoshima, Yuki; Satoh, Ryohei

2007-06-01

383

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

NASA Astrophysics Data System (ADS)

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

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

2001-06-01

384

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

NASA Astrophysics Data System (ADS)

Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 43 helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.

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

2002-11-01

385

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

386

Device and Method for Screening Crystallization Conditions in Solution Crystal Growth  

NASA Technical Reports Server (NTRS)

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

Carter, Daniel C. (Inventor)

1997-01-01

387

Device and method for screening crystallization conditions in solution crystal growth  

NASA Technical Reports Server (NTRS)

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

Carter, Daniel C. (inventor)

1995-01-01

388

Verification of the constant crystal growth model for attrition particles and its relevance to the modeling of crystallizers  

NASA Astrophysics Data System (ADS)

Potash alum-water system growth experiments have been carried out in a stagnant cell as reported by Garside and Larson for attrition particles with sizes L0 between 5 and 50 µm. Crystals with sizes Lo larger than 400 µm were investigated in a flow-through cell. In the stagnant growth cell large fluctuations of growth rate in the beginning have been observed. After about 5 to 10 min the growth rate of each crystal becomes constant. A constant linear growth rate of every fixed crystal has been measured in the flow-through cell. The growth rate dispersion according to the CCG model has been verified.

Wang, S.; Mersmann, A.; Kind, M.

1990-01-01

389

Crystals  

NSDL National Science Digital Library

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

Science, Lawrence H.

2009-01-01

390

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

PubMed Central

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

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

2014-01-01

391

Isothermal batch crystallization of alpha-lactose: A kinetic model combining mutarotation, nucleation and growth steps  

Microsoft Academic Search

A kinetic model combining first-order differential equations of the three consecutive steps of lactose crystallization, i.e., mutarotation, nucleation and crystal growth rate, was developed. Numerical solutions successfully fitted the variations of crystal mass growth rate as a function of lactose concentration during unseeded isothermal batch crystallization, at different initial lactose concentrations and temperatures. The model allowed the induction phase and

A. Mimouni; P. Schuck; S. Bouhallab

2009-01-01

392

Solution growth of Triglycine Sulfate (TGS) crystals on the International Microgravity Laboratory (IML1)  

Microsoft Academic Search

An experiment was planned for the International Microgravity Laboratory (IML-1) to be launched around Feb. 1991. Crystals of triglycine sulfate (TGS) will be grown by low temperature solution crystal growth technique using a multiuser facility called Fluid Experiment System (FES). A special cooled sting technique of solution crystal growth will be used where heat is extracted from the seed crystal

Ravi B. Lal; Ashok K. Batra; Li Yang; W. R. Wilcox; J. D. Trolinger

1989-01-01

393

FAST AND ACCURATE NUMERICAL APPROACHES FOR STEFAN PROBLEMS AND CRYSTAL GROWTH  

E-print Network

at a seed crystal crystal at the center. The situation is intrinsically unstable. The moving front \\GammaFAST AND ACCURATE NUMERICAL APPROACHES FOR STEFAN PROBLEMS AND CRYSTAL GROWTH ZHILIN LI \\Lambda, particularly for the Stefan problems and the problem of unstable crystal growth. We will focus on the issues

394

Growth Mechanism of a Unique Hierarchical Vaterite Structure  

NASA Astrophysics Data System (ADS)

Calcium carbonate is one of the most significant minerals in nature as well as in biogenic sources. Calcium carbonate occurs naturally in three crystalline polymorphs, i.e., calcite, aragonite, and vaterite. Although it has been attracted much research attention to understanding of the formation mechanisms of the material, the properties of the vaterite polymorph is not well known. Here we report synthesis and formation mechanism of a unique hierarchical structure of vaterite. The material is grown by a controlled diffusion method. The structure possesses a core and an outer part. The core is convex lens-like and is formed by vaterite nanocrystals that have small misorientations. The outer part is separated into six garlic clove-like segments. Each segment possesses piles of plate-like vaterite crystals, and the orientations of the plates continuously change from pile to pile. Based on real-time experimental results and the structural analysis, a growth mechanism is presented.

Ma, Guobin; Xu, Yifei; Wang, Mu

2013-03-01

395

Optical spectroscopy, crystalline perfection, etching and mechanical studies on P-nitroaniline (PNA) single crystals  

NASA Astrophysics Data System (ADS)

In this work we have presented the bulk growth of P-nitroaniline (PNA) single crystals by slow evaporation solution technique using methanol as a solvent at 300 K. Crystal system and lattice parameters were confirmed by powder X-ray diffraction analysis. Optical absorption and reflectance spectrums were recorded in the wavelength range of 150-3000 nm. Various optical parameters such as transmission (=>57%), optical band gap (=˜2.43 eV) were calculated. High-resolution X-ray diffraction study reveals that the grown crystal is having good crystalline perfection as the FWHM was found to be 39 arc s. Etching study was carried on PNA crystal with different etchants and suggests that the grown crystals are of better quality with less dislocation density (=3 × 103). The various mechanical parameters such as hardness, Mayer index, fracture toughness, brittle index were also calculated.

Shkir, Mohd.; Riscob, B.; Hasmuddin, Mohd.; Singh, Preeti; Ganesh, V.; Wahab, M. A.; Dieguez, Ernesto; Bhagavannarayana, G.

2014-01-01

396

Growth and morphology of W 18O 49 crystals produced by microwave decomposition of ammonium paratungstate  

NASA Astrophysics Data System (ADS)

By microwave irradiation of ammonium paratungstate (APT, (NH 4) 10H 2W 12O 42 × 4H 2O), needle crystals of W 18O 49 with a wide variety of size and morphology were formed. Their sizes and morphologies varied depending on various facets of individual APT pseudomorphous particles on which whiskers were grown, and among neighbouring decomposed APT pseudomorphous particles. Based on scanning electron and transmission electron-microscopic observations, it has been concluded that individual whiskers were monocrystalline and grew by a root growth mechanism from a nucleus formed in the amorphous layer, and that a rapid leader-like whisker growth in length was followed by a subsequent slower growth in thickness. Any evidence supporting a screw dislocation mechanism or tip growth by vapour-liquid-solid have not been detected.

Pfeifer, J.; Badaljan, E.; Tekula-Buxbaum, P.; K´cs, T.; Geszti, O.; T´th, A. L.; Lunk, H.-J.

1996-12-01

397

Protein Crystal Growth (PCG) experiment aboard mission STS-66  

NASA Technical Reports Server (NTRS)

On the Space Shuttle Orbiter Atlantis' middeck, Astronaut Joseph R. Tarner, mission specialist, works at an area amidst several lockers which support the Protein Crystal Growth (PCG) experiment during the STS-66 mission. This particular section is called the Crystal Observation System, housed in the Thermal Enclosure System (COS/TES). Together with the Vapor Diffusion Apparatus (VDA), housed in Single Locker Thermal Enclosure (SLTES), the COS/TES represents the continuing research into the structure of proteins and other macromolecules such as viruses.

2000-01-01

398

III-V semiconductor solid solution single crystal growth  

NASA Technical Reports Server (NTRS)

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

Gertner, E. R.

1982-01-01

399

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

400

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

SciTech Connect

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

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

2011-12-31

401

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

SciTech Connect

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

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

2011-01-30

402

Ultrasonic reactivation of phosphonate poisoned calcite during crystal growth.  

PubMed

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

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

2011-09-01

403

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

NASA Astrophysics Data System (ADS)

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

Zou, Yunfeng

404

Semiconducting icosahedral boron arsenide crystal growth for neutron detection  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

405

Mechanisms in the solution growth of free-standing two-dimensional inorganic nanomaterials.  

PubMed

Free-standing two-dimensional (2D) nanomaterials have attracted extensive and growing research interest owing to their exotic physical and mechanical properties, which have enabled their applications in electronics, optoelectronics, electrochemical and biomedical devices. Current synthesis strategies rely largely on top-down approaches such as etching and exfoliation. Among bottom-up approaches in literature, there lacks a systematic understanding of the mechanisms of 2D crystal growth, unlike one-dimensional nanomaterials whose growth mechanisms have been well documented. To date, the growth design of free-standing 2D nanomaterials has remained a case-by-case practice. This review focuses on the bottom-up solution synthesis of free-standing 2D nanomaterials and summarizes the general mechanisms and empirical methodologies that can lead to 2D crystal growth. A brief outlook on the development of synthesis and application of solution-grown 2D nanomaterials is also presented. PMID:24816866

Wang, Fei; Wang, Xudong

2014-06-21

406

Mechanisms in the solution growth of free-standing two-dimensional inorganic nanomaterials  

NASA Astrophysics Data System (ADS)

Free-standing two-dimensional (2D) nanomaterials have attracted extensive and growing research interest owing to their exotic physical and mechanical properties, which have enabled their applications in electronics, optoelectronics, electrochemical and biomedical devices. Current synthesis strategies rely largely on top-down approaches such as etching and exfoliation. Among bottom-up approaches in literature, there lacks a systematic understanding of the mechanisms of 2D crystal growth, unlike one-dimensional nanomaterials whose growth mechanisms have been well documented. To date, the growth design of free-standing 2D nanomaterials has remained a case-by-case practice. This review focuses on the bottom-up solution synthesis of free-standing 2D nanomaterials and summarizes the general mechanisms and empirical methodologies that can lead to 2D crystal growth. A brief outlook on the development of synthesis and application of solution-grown 2D nanomaterials is also presented.

Wang, Fei; Wang, Xudong

2014-05-01

407

Control of crystal growth in water purification by directional freeze crystallization  

NASA Technical Reports Server (NTRS)

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

Conlon, William M. (Inventor)

1996-01-01

408

Crystal settling and crystal growth caused by Ostwald Ripening in a terrestrial magma ocean under rotation  

NASA Astrophysics Data System (ADS)

About 4.5 billion years ago the earth was covered by a heavily convecting and rotating global magma ocean which was caused by an impact of a mars-sized impactor in a later stage of the earth's accretion. After the separation of metal and silicate (see A. Möller, U. Hansen (2013)) and the formation of the earth's core it began to crystallize. Small silicate crystals emerge and grow by Ostwald Ripening when the fluid is supersaturated. This process results in shrinking of small crystals and growing of large crystals on behalf of the smaller ones. This leads to an altering of the crystal settling time. One question which is still under great debate is whether fractional or equilibrium crystallization occurred in the magma ocean. Fractional crystallization means that different mineral fractions settle one after the other which would lead to a strongly differentiated mantle after solidification of the magma ocean. In contrast to that equilibrium crystallization would result in a well mixed mantle. Whether fractional or equilibrium crystallization occurred is for example important for the starting model of plate tectonics or the understanding of the mantle development until today. To study the change of crystal radius in a convecting and rotating magma ocean we employed a 3D numerical model. Due to the low viscosity and strong rotation the influence of rotation on the early magma Ocean cannot be neglected. In the model the crystals are able to influence each other and the fluid flow. They are able to grow, shrink, vanish and form and gravitational, Coriolis and drag forces due to the fluid act on them. In our present work we study the crystal settling depending on different rotation rates and rotation axes with two configurations. For the polar setting the rotation axis is parallel, at the equator it is perpendicular to gravity. Low rotation at the pole leads to a large fraction of suspended crystals. With increasing rotation the crystals settle and form a thick layer at the bottom of the magma ocean. At the equator we find three regimes (see A. Möller, U. Hansen (2013)) depending on the rotation strength. At low rotation a high fraction of silicate crystals settle at the bottom. At higher rotation the crystals form a thick layer in the bottom 1/3 of box. At high rotation all crystals are suspended and we observe a ribbon structure in the middle of the box. With a second model we investigate growing and shrinking of crystals by Ostwald Ripening and include formation and melting. In general we observe the same behaviour and regimes as described above, however due to Ostwald Ripening the evolution of crystal radius with time depends on the strength of rotation and on the orientation of the rotation axis. Very first results show that at the pole the growth of the silicate crystals is limited. The resulting small radius leads to a slow crystal settling. At the equator the crystals are able to grow larger than at the pole and therefore settle faster. This could lead to an asymmetrical crystallization of the magma ocean. In an extreme case due to the different settling times this could lead to a well mixed mantle at the pole whereas at the equator the mantle could be strongly differentiated after the solidification of the magma ocean.

Maas, C.; Moeller, A.; Hansen, U.

2013-12-01

409

Self-oscillatory ice crystal growth in antifreeze protein (AFP) and glycoprotein (AFGP) solutions  

NASA Astrophysics Data System (ADS)

AFPs and AFGPs allow many organisms including fish, plants and insects to survive sub-freezing environments. They occur in a wide range of compositions and structure, but to some extent they all accomplish the same functions: they suppress the freezing temperature, inhibit recrystallization, and modify ice crystal growth. A complete description of the AFGP/AFP surface mechanism as well as other ice surface phenomenon has eluded scientists primarily due to a lack of direct surface studies. We study ice crystal growth in AFGP and AFP solutions with phase contrast microscopy during free solution growth under various conditions including microgravity. Free-solution growth experiments show an anisotropic self-oscillatory growth mode of the steps and interface near the freezing temperature and enhancement of the growth rates in the c-axis. These results contradict the previous ?tight-binding? mechanism thought to be responsible for antifreeze function. To study the effects of temperature driven convective flows on the interface kinetics, microgravity experiments were performed in a jet airplane during a parabolic flight path. Step propagation on the basal plane slows down considerably when entering the microgravity condition and reaches a critical condition just below 0.2g.

Zepeda, Salvador; Nakaya, Hiroyuki; Uda, Yukihiro; Yokoyama, Etsuro; Furukawa, Yoshinori

2006-03-01

410

Simulation of heat transfer and convection during sapphire crystal growth in a modified heat exchanger method  

NASA Astrophysics Data System (ADS)

Quasi-steady-state (QSS) and transient models, developed using the CrysMAS code, are employed to study the effects of transport mechanisms and cold finger design on the temperature distribution, melt flow field, and melt-crystal interface shape during the crystal growth of sapphire by a small-scale, modified heat exchanger method (HEM). QSS computations show the importance and effects of various heat transfer mechanisms in the crystal and melt, including conduction, internal radiation, and melt convection driven by buoyant and Marangoni forces. The design of the cold finger is demonstrated to have significant effects on growth states. Notably, transient computations on an idealized heat transfer model, supplemented with QSS calculations of a model with rigorous heat transfer representation, show that non-uniform growth conditions arise under uniform cooling of the system via a linear decrease in furnace set points. We suggest that more uniform HEM growth conditions may be achieved by using non-linear cool-down strategies.

Zhang, Nan; Park, Hyun Gyoon; Derby, Jeffrey J.

2013-03-01

411

Growth and characterization of single crystal refractory oxide fibers  

NASA Astrophysics Data System (ADS)

Single-crystal Nd:YAG, sapphire, and LiNbO3 fibers 30-500 microns in diameter have been produced using the pedestal growth method. It is shown that stable growth is possible with typical diameter reduction ratios of 2-4:1; the laser power necessary to produce a stable melt zone varies from over 20 watts for a 1-mm rod of sapphire to several hundred milliwatts for 100-micron fibers of LiNbO3. The major problem with the current growth system is insufficient control over fiber diameter fluctuations. Fibers produced to date have diameters varying by up to 5 percent. A second-generation growth system is described which is expected to produce fibers with precisely controlled diameters.

Fejer, M.; Byer, R. L.; Feigelson, R.; Kway, W.

1982-12-01

412

Liquid drop stability for protein crystal growth in microgravity  

NASA Technical Reports Server (NTRS)

It is possible to grow protein crystals for biomedical research in microgravity by deploying a protein-rich solution from a syringe, forming a drop in which crystallization can occur with the proper degree of supersaturation. Drop stability is critical to the success of this research, due to the large drop sizes which can be achieved in space. In order to determine the type of syringe tips most suitable to support these large drops, tests were performed during brief periods of weightlessness onboard the NASA KC-135 low-gravity simulation aircraft. The drops were analyzed using three simple models in which the samples were approximated by modified pendulum and spring systems. It was concluded that the higher frequency systems were the most stable, indicating that of the syringes utilized, a disk-shaped configuration provided the most stable environment of low-gravity protein crystal growth.

Owen, Robert B.; Broom, Beth H.; Snyder, Robert S.; Daniel, Ron

1987-01-01

413

Modelling the growth of triglycine sulphate crystals in Spacelab 3  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

414

Metastable Solution Thermodynamic Properties and Crystal Growth Kinetics  

NASA Technical Reports Server (NTRS)

The crystal growth rates of NH4H2PO4, KH2PO4, (NH4)2SO4, KAl(SO4)2 central dot 12H2O, NaCl, and glycine and the nucleation rates of KBr, KCl, NaBr central dot 2H2O, (NH4)2Cl, and (NH4)2SO4 were expressed in terms of the fundamental driving force of crystallization calculated from the activity of supersaturated solutions. The kinetic parameters were compared with those from the commonly used kinetic expression based on the concentration difference. From the viewpoint of thermodynamics, rate expressions based on the chemical potential difference provide accurate kinetic representation over a broad range of supersaturation. The rates estimated using the expression based on the concentration difference coincide with the true rates of crystallization only in the concentration range of low supersaturation and deviate from the true kinetics as the supersaturation increases.

Kim, Soojin; Myerson, Allan S.

1996-01-01

415

Modeling and control of the Czochralski crystal growth process  

NASA Astrophysics Data System (ADS)

The Czochralski process is a method of pulling crystal from the melt that is widely used by the semiconductor industry. The current breadth of this industry makes the method indespensible. The International Technology Roadmap for Semiconductors forecasts the use of 35 nm technology on 64 Gbit DRAM and 10 GHz processor speeds by the end of this decade. This implies the need for higher quality crystals, and therefore improved growth systems. Furthermore, industry has noted a problem with rapid pull rate variation contributing to structural defects in the grown crystals. It was proposed by industry to investigate elimination of the pull rate as a control input. The current state of the system as well as the predicted path of the industry served to motivate development of a new control scheme. The first objective of this work was to develop or enhance a first-principles based model of the process. This model must be kept at a manageable order to accommodate online simulation while still capturing the dominant process physics. The model must also be formulated as a time differential equation in order to apply the desired control theories. The second objective of this work was to answer industry's question regarding elimination of pull rate as a manipulated input. The final objective of this work was to use the model to design a new control algorithm. The control development includes consideration of the time delay between heater and the crystal. The work is based on silicon growth, but the developments are kept as generic as possible for future application to other materials. Data from industry crystal growths as well as experimental results reported in literature will be used to gauge the effectiveness of the new designs.

Martinez, Denise Marie

416

Crystallization in supercooled liquid Cu: Homogeneous nucleation and growth.  

PubMed

Homogeneous nucleation and growth during crystallization of supercooled liquid Cu are investigated with molecular dynamics simulations, and the microstructure is characterized with one- and two-dimensional x-ray diffraction. The resulting solids are single-crystal or nanocrystalline, containing various defects such as stacking faults, twins, fivefold twins, and grain boundaries; the microstructure is subject to thermal fluctuations and extent of supercooling. Fivefold twins form via sequential twinning from the solid-liquid interfaces. Critical nucleus size and nucleation rate at 31% supercooling are obtained from statistical runs with the mean first-passage time and survival probability methods, and are about 14 atoms and 10(32) m(-3)s(-1), respectively. The bulk growth dynamics are analyzed with the Johnson-Mehl-Avrami law and manifest three stages; the Avrami exponent varies in the range of 1-19, which also depends on thermal fluctuations and supercooling. PMID:25681932

E, J C; Wang, L; Cai, Y; Wu, H A; Luo, S N

2015-02-14

417

Contactless heater floating zone refining and crystal growth  

NASA Technical Reports Server (NTRS)

Floating zone refining or crystal growth is carried out by providing rapid relative rotation of a feed rod and finish rod while providing heat to the junction between the two rods so that significant forced convection occurs in the melt zone between the two rods. The forced convection distributes heat in the melt zone to allow the rods to be melted through with a much shorter melt zone length than possible utilizing conventional floating zone processes. One of the rods can be rotated with respect to the other, or both rods can be counter-rotated, with typical relative rotational speeds of the rods ranging from 200 revolutions per minute (RPM) to 400 RPM or greater. Zone refining or crystal growth is carried out by traversing the melt zone through the feed rod.

Kou, Sindo (Inventor); Lan, Chung-Wen (Inventor)

1993-01-01

418

A new approach to the CZ crystal growth weighing control  

NASA Astrophysics Data System (ADS)

The aim of a new approach was to improve the robustness of the weighing control of CZ growth especially for semiconductors, for which the “anomalous“ behavior of the apparent weight provokes instability of the servo-loop. In the described method, the periodic reciprocating measuring motion of small amplitude is superposed on the uniform pull-rod movement. The cross-sectional area is determined from the weight sensor responses that are modulated mainly by the forces of hydrostatic pressure. By the example of germanium crystal growth, it is shown that in the control system, based on such a way of the diameter measuring, a simple PI control law provides a good close loop system's stability and dynamics for the materials with the “anomalous” behavior of a weighing signal. The effect of a meniscus on the modulation measuring of a crystal diameter is also discussed.

Kasimkin, P. V.; Moskovskih, V. A.; Vasiliev, Y. V.; Shlegel, V. N.; Yuferev, V. S.; Vasiliev, M. G.; Zhdankov, V. N.

2014-03-01

419

Investigation of Vibrational Control of the Bridgman Crystal Growth Technique  

NASA Technical Reports Server (NTRS)

The character of natural buoyant convection in rigidly contained inhomogeneous fluids can be drastically altered by vibrating the container. Vibrations are expected to play a crucial influence on heat and mass transfer onboard the International Space Station (ISS). It is becoming evident that substantial vibrations will exist on the ISS in the wide frequency spectrum. In general, vibrational flows are very complex and governed by many parameters. In many terrestrial crystal growth situations, convective transport of heat and constituent components is dominated by buoyancy driven convection arising from compositional and thermal gradients. Thus, it may be concluded that vibro-convective flow can potentially be used to influence and even control transport in some crystal growth situations.

Fedoseyev, Alexandre I.; Alexander, J. I. D.; Feigelson, R. S.; Zharikov, E. V.; Ostrogorsky, A. G.; Marin, C.; Volz, M. P.; Kansa, E. J.; Friedman, M. J.

2001-01-01

420

Growth mechanisms of silver nanoparticles: a molecular dynamics study  

NASA Astrophysics Data System (ADS)

The shape control of metal nanoparticles allows one to finely tune their properties with great versatility. A self-seeding coreduction method has recently been developed for the synthesis of silver nanodiscs, triangular nanoplates and nanospheres. The addition of surfactants was found to be one of the most important factors in determining the final particle shape. In this paper, molecular dynamics simulations are performed to understand the growth mechanisms of silver nanoparticles for different surfactants (i.e. bis(2-ethylhexyl) sulfosuccinate, 1-dodecanethiol and cetyltrimethyl ammonium). The interaction energies between the surfactants and the silver crystal plane (i.e. (100), (110), (111)) are calculated. The molecular structural property of surfactants at the silver surface is also examined. It is demonstrated that the calculated interaction energies explain well the growth behaviour observed in the silver nanoparticle systems. Molecular dynamics simulation could provide a theoretical guideline for the choice of surfactants and hence the synthesis of various metal nanoparticles with controlled shape.

Zeng, Qinghua; Jiang, Xuchuan; Yu, Aibing; Lu, Gaoqing Max

2007-01-01