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Sample records for crystal growth amorphous

  1. An investigation into the role of polymeric carriers on crystal growth within amorphous solid dispersion systems.

    Science.gov (United States)

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

    2015-04-06

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

  2. Induced growth of high quality ZnO thin films by crystallized amorphous ZnO

    Institute of Scientific and Technical Information of China (English)

    Wang Zhi-Jun; Song Li-Jun; Li Shou-Chun; Lu You-Ming; Tian Yun-Xia; Liu Jia-Yi; Wang Lian-Yuan

    2006-01-01

    This paper reports the induced growth of high quality ZnO thin film by crystallized amorphous ZnO. Firstly amorphous ZnO was prepared by solid-state pyrolytic reaction, then by taking crystallized amorphous ZnO as seeds (buffer layer), ZnO thin films have been grown in diethyene glycol solution of zinc acetate at 80℃. X-ray Diffraction curve indicates that the films were preferentially oriented [001] out-of-plane direction of the ZnO. Atomic force microscopy and scanning electron microscopy were used to evaluate the surface morphology of the ZnO thin film. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. The results indicate that high quality ZnO thin film was obtained.

  3. Inhibition of crystal nucleation and growth by water-soluble polymers and its impact on the supersaturation profiles of amorphous drugs.

    Science.gov (United States)

    Ozaki, Shunsuke; Kushida, Ikuo; Yamashita, Taro; Hasebe, Takashi; Shirai, Osamu; Kano, Kenji

    2013-07-01

    The impact of water-soluble polymers on drug supersaturation behavior was investigated to elucidate the role of water-soluble polymers in enhancing the supersaturation levels of amorphous pharmaceuticals. Hydroxypropyl methylcellulose (HPMC), polyvinylpyrrolidone (PVP), and Eudragit L-100 (Eudragit) were used as representative polymers, and griseofulvin and danazol were used as model drugs. Supersaturation profiles of amorphous drugs were measured in biorelevant dissolution tests. Crystal growth rate was measured from the decrease in dissolved drug concentration in the presence of seed crystals. Nucleation kinetics was evaluated by measuring the induction time for nucleation. All experiments were performed in the presence and absence of polymers. The degree of supersaturation of the amorphous model drugs increased with an increase in the inhibitory efficiency of polymers against crystal nucleation and growth (HPMC > PVP > Eudragit). In the presence of HPMC, the addition of seed crystals diminished the supersaturation ratio dramatically for griseofulvin and moderately for danazol. The results demonstrated that the polymers contributed to drug supersaturation by inhibiting both nucleation and growth. The effect of the polymers was drug dependent. The detailed characterization of polymers would allow selection of appropriate crystallization inhibitors and a planned quality control strategy for the development of supersaturable formulations. Copyright © 2013 Wiley Periodicals, Inc.

  4. Modelling of primary bcc-Fe crystal growth in a Fe{sub 85}B{sub 15} amorphous alloy

    Energy Technology Data Exchange (ETDEWEB)

    Palumbo, M. [Dip. Chimica I.F.M. and NIS, Universita di Torino, via Giuria 9, 10125 Turin (Italy); Baricco, M. [Dip. Chimica I.F.M. and NIS, Universita di Torino, via Giuria 9, 10125 Turin (Italy)]. E-mail: marcello.baricco@unito.it

    2005-05-15

    A kinetic modelling of primary crystallization in metallic glasses, based on the CALPHAD approach and the moving boundary model, has been applied to the Fe-B system. The DICTRA software has been used to perform numerical calculations. Kinetic and thermodynamic parameters (atomic mobilities and thermodynamic factors) are required and they have been obtained from the literature. Various simulations have been performed in order to evaluate the influence of different parameters choice. The soft impingement effect has been discussed. Furthermore, amorphous Fe{sub 85}B{sub 15} samples have been prepared and examined by differential scanning calorimetry. Calculated and experimental results, both on continuous heating and isothermal conditions, have been compared.

  5. Shock induced crystallization of amorphous Nickel powders

    Science.gov (United States)

    Cherukara, Mathew; Strachan, Alejandro

    2015-06-01

    Recent experimental work has shown the efficacy of amorphous Ni/crystalline Al composites as energetic materials, with flame velocities twice that of a comparable crystalline Ni/crystalline Al system. Of further interest is the recrystallization mechanisms in the pure amorphous Ni powders, both thermally induced and mechanically induced. We present large-scale molecular dynamics simulations of shock-induced recrystallization in loosely packed amorphous Nickel powders. We study the time dependent nucleation and growth processes by holding the shocked samples at the induced pressures and temperatures for extended periods following the passage of the shock (up to 6 ns). We find that the nanostructure of the recrystallized Ni and time scales of recrystallization are dependent on the piston velocity. At low piston velocities, nucleation events are rare, leading to long incubation times and a relatively coarse nanostructure. At higher piston velocities, local variations in temperature due to jetting phenomena and void collapse, give rise to multiple nucleation events on time scales comparable to the passage of the shock wave, leading to the formation of a fine-grained nanostructure. Interestingly, we observe that the nucleation and growth process occurs in two steps, with the first nuclei crystallizing into the BCC structure, before evolving over time into the expected FCC structure. U.S. Defense Threat Reduction Agency, HDTRA1-10-1-0119 (Program Manager Suhithi Peiris).

  6. Supersaturation, nucleation, and crystal growth during single- and biphasic dissolution of amorphous solid dispersions: polymer effects and implications for oral bioavailability enhancement of poorly water soluble drugs.

    Science.gov (United States)

    Sarode, Ashish L; Wang, Peng; Obara, Sakae; Worthen, David R

    2014-04-01

    The influence of polymers on the dissolution, supersaturation, crystallization, and partitioning of poorly water soluble compounds in biphasic media was evaluated. Amorphous solid dispersions (ASDs) containing felodipine (FLD) and itraconazole (ITZ) were prepared by hot melt mixing (HMM) using various polymers. The ASDs were analyzed using powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), and HPLC. Amorphous drug conversion was confirmed using DSC and PXRD, and drug stability by HPLC. Single- and biphasic dissolution studies of the ASDs with concurrent dynamic light scattering (DLS) and polarized light microscopic (PLM) analysis of precipitated drugs were performed. HPLC revealed no HMM-induced drug degradation. Maximum partitioning into the organic phase was dependent upon the degree of supersaturation. Although the highest supersaturation of FLD was attained using Eudragit® EPO and AQOAT® AS-LF with better nucleation and crystal growth inhibition using the latter, higher partitioning of the drug into the organic phase was achieved using Pharmacoat® 603 and Kollidon® VA-64 by maintaining supersaturation below critical nucleation. Critical supersaturation for ITZ was surpassed using all of the polymers, and partitioning was dependent upon nucleation and crystal growth inhibition in the order of Pharmacoat® 603>Eudragit® L-100-55>AQOAT® AS-LF. HMM drug-polymer systems that prevent drug nucleation by staying below critical supersaturation are more effective for partitioning than those that achieve the highest supersaturation.

  7. Quartz crystal growth

    Science.gov (United States)

    Baughman, Richard J.

    1992-01-01

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

  8. Femtosecond laser crystallization of amorphous Ge

    Science.gov (United States)

    Salihoglu, Omer; Kürüm, Ulaş; Yaglioglu, H. Gul; Elmali, Ayhan; Aydinli, Atilla

    2011-06-01

    Ultrafast crystallization of amorphous germanium (a-Ge) in ambient has been studied. Plasma enhanced chemical vapor deposition grown a-Ge was irradiated with single femtosecond laser pulses of various durations with a range of fluences from below melting to above ablation threshold. Extensive use of Raman scattering has been employed to determine post solidification features aided by scanning electron microscopy and atomic force microscopy measurements. Linewidth of the Ge optic phonon at 300 cm-1 as a function of laser fluence provides a signature for the crystallization of a-Ge. Various crystallization regimes including nanostructures in the form of nanospheres have been identified.

  9. Visualization of the crystallization of lactose from the amorphous state.

    Science.gov (United States)

    Price, Robert; Young, Paul M

    2004-01-01

    The physical stability and solid-state recrystallization of spray-dried 'amorphous' lactose particles were visualized using environmentally controlled atomic force microscopy (EC-AFM) and conventional optical microscopy. The morphology and crystalline state were investigated as a function of relative humidity (RH) and were correlated with bulk gravimetric vapor sorption measurements that were run in parallel. The metastable nature of amorphous spray-dried lactose particles was apparent at low RHs (lactose during moisture uptake at 58 and 75% RH suggested only a proportion of the collapsed particles undergoes nucleation and crystal growth. The irregular surface morphology of the recrystallized particles suggested a secondary nucleation and growth process. Primary nucleation of alpha-lactose monohydrate within the non-recrystallized particles required exposure to elevated RH (94% RH). In relation to bulk measurements of moisture-induced amorphous recrystallization of spray-dried lactose, the results suggest that recrystallization of amorphous lactose, above a critical RH, may be induced by the presence of very low levels of a seed material, which may dramatically reduce the activation energy barrier for nucleation and crystal growth. Copyright 2004 Wiley-Liss, Inc.

  10. Nickel-induced crystallization of amorphous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, J A; Arce, R D; Buitrago, R H [INTEC (CONICET-UNL), Gueemes 3450, S3000GLN Santa Fe (Argentina); Budini, N; Rinaldi, P, E-mail: jschmidt@intec.unl.edu.a [FIQ - UNL, Santiago del Estero 2829, S3000AOM Santa Fe (Argentina)

    2009-05-01

    The nickel-induced crystallization of hydrogenated amorphous silicon (a-Si:H) is used to obtain large grained polycrystalline silicon thin films on glass substrates. a-Si:H is deposited by plasma enhanced chemical vapour deposition at 200 deg. C, preparing intrinsic and slightly p-doped samples. Each sample was divided in several pieces, over which increasing Ni concentrations were sputtered. Two crystallization methods are compared, conventional furnace annealing (CFA) and rapid thermal annealing (RTA). The crystallization was followed by optical microscopy and scanning electron microscopy observations, X-ray diffraction, and reflectance measurements in the UV region. The large grain sizes obtained - larger than 100{mu}m for the samples crystallized by CFA - are very encouraging for the preparation of low-cost thin film polycrystalline silicon solar cells.

  11. On the crystallization of amorphous germanium films

    Science.gov (United States)

    Edelman, F.; Komem, Y.; Bendayan, M.; Beserman, R.

    1993-06-01

    The incubation time for crystallization of amorphous Ge (a-Ge) films, deposited by e-gun, was studied as a function of temperature between 150 and 500°C by means of both in situ transmission electron microscopy and Raman scattering spectroscopy. The temperature dependence of t0 follows an Arrhenius curve with an activation energy of 2.0 eV for free-sustained a-Ge films. In the case where the a-Ge films were on Si 3N 4 substrate, the activation energy of the incubation process was 1.3 eV.

  12. Crystallization inhibition of an amorphous sucrose system using raffinose

    Institute of Scientific and Technical Information of China (English)

    LEINEN K.M.; LABUZA T.P.

    2006-01-01

    The shelf life of pure amorphous sucrose systems, such as cotton candy, can be very short. Previous studies have shown that amorphous sucrose systems held above the glass transition temperature will collapse and crystallize. One study,however, showed that adding a small percent of another type of sugar, such as trehalose, to sucrose can extend the shelf life of the amorphous system by slowing crystallization. This study explores the hypothesis that raffinose increases the stability of an amorphous sucrose system. Cotton candy at 5 wt% raffinose and 95 wt% sucrose was made and stored at room temperature and three different relative humidities (%RH) 11%RH, 33%RH, and 43%RH. XRD patterns, and glass transition temperatures were obtained to determine the stability as a function of %RH. The data collected showed that raffinose slows sucrose crystallization in a low moisture amorphous state above the glass transition temperature and therefore improves the stability of amorphous sucrose systems.

  13. Formation of nanophases by crystallization of amorphous alloys

    Energy Technology Data Exchange (ETDEWEB)

    Baricco, M. [Turin Univ. (Italy). Dipt. di Chimica Inorganica; Tiberto, P. [Istituto Elettrotecnico Nazionale, Turin (Italy); Battezzati, L. [Turin Univ. (Italy). Dipt. di Chimica Inorganica

    1995-12-31

    A comparison is made of crystallization mechanisms in Fe-based amorphous alloys (Fe{sub 73.5}Cu{sub 1}Nb{sub 3}Si{sub 13.5}B{sub 9}, Fe{sub 90}Zr{sub 7}B{sub 3}), which lead to a nanocrystalline bcc phase with peculiar soft magnetic properties through primary crystallization. In all samples, the nucleation takes place uniformely throughout the material. The presence of atoms with low diffusivity (Zr, Nb) reduces the grain growth rate so that a small size of crystals is maintained. On the contrary, even extremely fast heating and short heat treatment do not produce nanocrystals in Fe{sub 40}Ni{sub 40}B{sub 20} although the crystallization mechanism is modified. However milling the ribbon leads to nanostructured crystalline phases. The formation of nanophases by crystallization is discussed considering the temperature dependence of nucleation frequency and growth rate. The effects of various thermodynamic and kinetic parameters are analyzed and the most favourable conditions for nanocrystallization are outlined. (orig.)

  14. Excimer laser crystallization of amorphous silicon on metallic substrate

    Science.gov (United States)

    Delachat, F.; Antoni, F.; Slaoui, A.; Cayron, C.; Ducros, C.; Lerat, J.-F.; Emeraud, T.; Negru, R.; Huet, K.; Reydet, P.-L.

    2013-06-01

    An attempt has been made to achieve the crystallization of silicon thin film on metallic foils by long pulse duration excimer laser processing. Amorphous silicon thin films (100 nm) were deposited by radiofrequency magnetron sputtering on a commercial metallic alloy (N42-FeNi made of 41 % of Ni) coated by a tantalum nitride (TaN) layer. The TaN coating acts as a barrier layer, preventing the diffusion of metallic impurities in the silicon thin film during the laser annealing. An energy density threshold of 0.3 J cm-2, necessary for surface melting and crystallization of the amorphous silicon, was predicted by a numerical simulation of laser-induced phase transitions and witnessed by Raman analysis. Beyond this fluence, the melt depth increases with the intensification of energy density. A complete crystallization of the layer is achieved for an energy density of 0.9 J cm-2. Scanning electron microscopy unveils the nanostructuring of the silicon after laser irradiation, while cross-sectional transmission electron microscopy reveals the crystallites' columnar growth.

  15. Thermodynamics, molecular mobility and crystallization kinetics of amorphous griseofulvin.

    Science.gov (United States)

    Zhou, Deliang; Zhang, Geoff G Z; Law, Devalina; Grant, David J W; Schmitt, Eric A

    2008-01-01

    Griseofulvin is a small rigid molecule that shows relatively high molecular mobility and small configurational entropy in the amorphous phase and tends to readily crystallize from both rubbery and glassy states. This work examines the crystallization kinetics and mechanism of amorphous griseofulvin and the quantitative correlation between the rate of crystallization and molecular mobility above and below Tg. Amorphous griseofulvin was prepared by rapidly quenching the melt in liquid N2. The thermodynamics and dynamics of amorphous phase were then characterized using a combination of thermal analysis techniques. After characterization of the amorphous phase, crystallization kinetics above Tg were monitored by isothermal differential scanning calorimetry (DSC). Transformation curves for crystallization fit a second-order John-Mehl-Avrami (JMA) model. Crystallization kinetics below Tg were monitored by powder X-ray diffraction and fit to the second-order JMA model. Activation energies for crystallization were markedly different above and below Tg suggesting a change in mechanism. In both cases molecular mobility appeared to be partially involved in the rate-limiting step for crystallization, but the extent of correlation between the rate of crystallization and molecular mobility was different above and below Tg. A lower extent of correlation below Tg was observed which does not appear to be explained by the molecular mobility alone and the diminishing activation energy for crystallization suggests a change in the mechanism of crystallization.

  16. Predicting Crystallization of Amorphous Drugs with Terahertz Spectroscopy.

    Science.gov (United States)

    Sibik, Juraj; Löbmann, Korbinian; Rades, Thomas; Zeitler, J Axel

    2015-08-03

    There is a controversy about the extent to which the primary and secondary dielectric relaxations influence the crystallization of amorphous organic compounds below the glass transition temperature. Recent studies also point to the importance of fast molecular dynamics on picosecond-to-nanosecond time scales with respect to the glass stability. In the present study we provide terahertz spectroscopy evidence on the crystallization of amorphous naproxen well below its glass transition temperature and confirm the direct role of Johari-Goldstein (JG) secondary relaxation as a facilitator of the crystallization. We determine the onset temperature Tβ above which the JG relaxation contributes to the fast molecular dynamics and analytically quantify the level of this contribution. We then show there is a strong correlation between the increase in the fast molecular dynamics and onset of crystallization in several chosen amorphous drugs. We believe that this technique has immediate applications to quantify the stability of amorphous drug materials.

  17. Investigation of crystallization and amorphization dynamics of phase-change thin films by subnanosecond laser pulses.

    Science.gov (United States)

    Kieu, Khanh; Narumi, Kenji; Mansuripur, Masud

    2006-10-20

    We report experimental results on amorphization and crystallization dynamics of reversible phase-change (PC) thin-film samples, GeSbTe and GeBiTe, for optical disk data storage. The investigation was conducted with subnanosecond laser pulses using a pump-and-probe configuration. Amorphization of the crystalline films could be achieved with a single subnanosecond laser pulse; the amorphization dynamics follow closely the temperature kinetics induced in the irradiated spot. As for crystallization of the samples initially in the amorphous state, a single subnanosecond pulse was found to be insufficient to fully crystallize the irradiated spot, but we could crystallize the PC film (in the area under the focused spot) by applying multiple short pulses. Our multipulse studies reveal that the GeSbTe crystallization is dominated by the growth of nuclei whose initial formation is slow but, once formed, their subsequent growth (under a sequence of subnanosecond pulses) happens quickly. In the case of GeBiTe samples, the crystalline nuclei appear to be present in the material initially, as they grow immediately upon illumination with laser pulses. Whereas our amorphous GeSbTe samples required approximately 200 pulses for full crystallization, for the GeBiTe samples approximately 15 pulses sufficed.

  18. Surface and bulk crystallization of amorphous solid water films: Confirmation of "top-down" crystallization

    Science.gov (United States)

    Yuan, Chunqing; Smith, R. Scott; Kay, Bruce D.

    2016-10-01

    The crystallization kinetics of nanoscale amorphous solid water (ASW) films are investigated using temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). TPD measurements are used to probe surface crystallization and RAIRS measurements are used to probe bulk crystallization. Isothermal TPD results show that surface crystallization is independent of the film thickness (from 100 to 1000 ML). Conversely, the RAIRS measurements show that the bulk crystallization time increases linearly with increasing film thickness. These results suggest that nucleation and crystallization begin at the ASW/vacuum interface and then the crystallization growth front propagates linearly into the bulk. This mechanism was confirmed by selective placement of an isotopic layer (5% D2O in H2O) at various positions in an ASW (H2O) film. In this case, the closer the isotopic layer was to the vacuum interface, the earlier the isotopic layer crystallized. These experiments provide direct evidence to confirm that ASW crystallization in vacuum proceeds by a "top-down" crystallization mechanism.

  19. Surface and bulk crystallization of amorphous solid water films: Confirmation of “top-down” crystallization

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Chunqing; Smith, R. Scott; Kay, Bruce D.

    2016-10-01

    The crystallization kinetics of nanoscale amorphous solid water (ASW) films are investigated using temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). TPD measurements are used to probe surface crystallization and RAIRS measurements are used to probe bulk crystallization. Isothermal TPD results show that surface crystallization is independent of the film thickness (from 100 to 1000 ML). Conversely, the RAIRS measurements show that the bulk crystallization time increases linearly with increasing film thickness. These results suggest that nucleation and crystallization begin at the ASW/vacuum interface and then the crystallization growth front propagates linearly into the bulk. This mechanism was confirmed by selective placement of an isotopic layer (5% D2O in H2O) at various positions in an ASW (H2O) film. In this case, the closer the isotopic layer was to the vacuum interface, the earlier the isotopic layer crystallized. These experiments provide direct evidence to confirm that ASW crystallization in vacuum proceeds by a “top-down” crystallization mechanism.

  20. Hydrogen-induced crystallization of an amorphous metal

    Energy Technology Data Exchange (ETDEWEB)

    Cha, Pil-Ryung [School of Advanced Materials Engineering, Kookmin University, Seoul 136-702 (Korea, Republic of)], E-mail: cprdream@kookmin.ac.kr; Kim, Yu Chan [Advanced Metals Research Center, Korean Institute of Science and Technology, Seoul 130-650 (Korea, Republic of); Kim, Ki-Bae [Advanced Metals Research Center, Korean Institute of Science and Technology, Seoul 130-650 (Korea, Republic of); Seok, Hyun-Kwang [Advanced Metals Research Center, Korean Institute of Science and Technology, Seoul 130-650 (Korea, Republic of); Fleury, Eric [Advanced Metals Research Center, Korean Institute of Science and Technology, Seoul 130-650 (Korea, Republic of); Han, Seung-Hee [Advanced Metals Research Center, Korean Institute of Science and Technology, Seoul 130-650 (Korea, Republic of)

    2007-04-15

    The influence of hydrogen on the structural stability of an amorphous nickel has been analyzed by molecular dynamics simulation. We find that the volume of the amorphous metal increases nonlinearly with the hydrogen concentration and that it crystallizes at a certain critical concentration. The crystallization is shown to be caused by hydrogen-induced transition from the amorphous to the supercooled liquid state, and the change of diffusion mechanism from atomic hopping to string-like collective motion is also observed at the transition.

  1. Growth of dopamine crystals

    Energy Technology Data Exchange (ETDEWEB)

    Patil, Vidya, E-mail: vidya.patil@ruparel.edu; Patki, Mugdha, E-mail: mugdha.patki@ruparel.edu [D. G. Ruparel College, Senapati Bapat Marg, Mahim, Mumbai – 400 016 (India)

    2016-05-06

    Many nonlinear optical (NLO) crystals have been identified as potential candidates in optical and electro-optical devices. Use of NLO organic crystals is expected in photonic applications. Hence organic nonlinear optical materials have been intensely investigated due to their potentially high nonlinearities, and rapid response in electro-optic effect compared to inorganic NLO materials. There are many methods to grow organic crystals such as vapor growth method, melt growth method and solution growth method. Out of these methods, solution growth method is useful in providing constraint free crystal. Single crystals of Dopamine have been grown by evaporating the solvents from aqueous solution. Crystals obtained were of the size of orders of mm. The crystal structure of dopamine was determined using XRD technique. Images of crystals were obtained using FEG SEM Quanta Series under high vacuum and low KV.

  2. Growth of dopamine crystals

    Science.gov (United States)

    Patil, Vidya; Patki, Mugdha

    2016-05-01

    Many nonlinear optical (NLO) crystals have been identified as potential candidates in optical and electro-optical devices. Use of NLO organic crystals is expected in photonic applications. Hence organic nonlinear optical materials have been intensely investigated due to their potentially high nonlinearities, and rapid response in electro-optic effect compared to inorganic NLO materials. There are many methods to grow organic crystals such as vapor growth method, melt growth method and solution growth method. Out of these methods, solution growth method is useful in providing constraint free crystal. Single crystals of Dopamine have been grown by evaporating the solvents from aqueous solution. Crystals obtained were of the size of orders of mm. The crystal structure of dopamine was determined using XRD technique. Images of crystals were obtained using FEG SEM Quanta Series under high vacuum and low KV.

  3. Depressurization amorphization of single-crystal boron carbide.

    Science.gov (United States)

    Yan, X Q; Tang, Z; Zhang, L; Guo, J J; Jin, C Q; Zhang, Y; Goto, T; McCauley, J W; Chen, M W

    2009-02-20

    We report depressurization amorphization of single-crystal boron carbide (B4C) investigated by in situ high-pressure Raman spectroscopy. It was found that localized amorphization of B4C takes place during unloading from high pressures, and nonhydrostatic stresses play a critical role in the high-pressure phase transition. First-principles molecular dynamics simulations reveal that the depressurization amorphization results from pressure-induced irreversible bending of C-B-C atomic chains cross-linking 12 atom icosahedra at the rhombohedral vertices.

  4. Crystallization kinetics of amorphous aluminum-tungsten thin films

    Energy Technology Data Exchange (ETDEWEB)

    Car, T.; Radic, N. [Rugjer Boskovic Inst., Zagreb (Croatia). Div. of Mater. Sci.; Ivkov, J. [Institute of Physics, Bijenicka 46, P.O.B. 304, HR-10000 Zagreb (Croatia); Babic, E.; Tonejc, A. [Faculty of Sciences, Physics Department, Bijenicka 32, P.O.B. 162, HR-10000 Zagreb (Croatia)

    1999-01-01

    Crystallization kinetics of the amorphous Al-W thin films under non-isothermal conditions was examined by continuous in situ electrical resistance measurements in vacuum. The estimated crystallization temperature of amorphous films in the composition series of the Al{sub 82}W{sub 18} to Al{sub 62}W{sub 38} compounds ranged from 800 K to 920 K. The activation energy for the crystallization and the Avrami exponent were determined. The results indicated that the crystallization mechanism in films with higher tungsten content was a diffusion-controlled process, whereas in films with the composition similar to the stoichiometric compound (Al{sub 4}W), the interface-controlled crystallization probably occurred. (orig.) With 4 figs., 1 tab., 26 refs.

  5. Nickel-disilicide-assisted excimer laser crystallization of amorphous silicon

    Institute of Scientific and Technical Information of China (English)

    Liao Yan-Ping; Shao Xi-Bin; Gao Feng-Li; Luo Wen-Sheng; Wu Yuan; Fu Guo-Zhu; Jing Hai; Ma Kai

    2006-01-01

    Polycrystalline silicon (poly-Si) thin film has been prepared by means of nickel-disilicide (NiSi2) assisted excimer laser crystallization (ELC). The process to prepare a sample includes two steps. One step consists of the formation of NiSi2 precipitates by heat-treating the dehydrogenated amorphous silicon (a-Si) coated with a thin layer of Ni. And the other step consists of the formation of poly-Si grains by means of ELC. According to the test results of scanning electron microscopy (SEM), another grain growth model named two-interface grain growth has been proposed to contrast with the conventional Ni-metal-induced lateral crystallization (Ni-MILC) model and the ELC model. That is, an additional grain growth interface other than that in conventional ELC is formed, which consists of NiSi2 precipitates and a-Si.The processes for grain growth according to various excimer laser energy densities delivered to the a-Si film have been discussed. It is discovered that grains with needle shape and most of a uniform orientation are formed which grow up with NiSi2 precipitates as seeds. The reason for the formation of such grains which are different from that of Ni-MILCwithout migration of Ni atoms is not clear. Our model and analysis point out a method to prepare grains with needle shape and mostly of a uniform orientation. If such grains are utilized to make thin-film transistor, its characteristics may be improved.

  6. Predicting Crystallization of Amorphous Drugs with Terahertz Spectroscopy

    DEFF Research Database (Denmark)

    Sibik, Juraj; Löbmann, Korbinian; Rades, Thomas;

    2015-01-01

    -to-nanosecond time scales with respect to the glass stability. In the present study we provide terahertz spectroscopy evidence on the crystallization of amorphous naproxen well below its glass transition temperature and confirm the direct role of Johari–Goldstein (JG) secondary relaxation as a facilitator......There is a controversy about the extent to which the primary and secondary dielectric relaxations influence the crystallization of amorphous organic compounds below the glass transition temperature. Recent studies also point to the importance of fast molecular dynamics on picosecond...... of the crystallization. We determine the onset temperature Tβ above which the JG relaxation contributes to the fast molecular dynamics and analytically quantify the level of this contribution. We then show there is a strong correlation between the increase in the fast molecular dynamics and onset of crystallization...

  7. Advanced Crystal Growth Technology

    Energy Technology Data Exchange (ETDEWEB)

    Land, T A; Hawley-Fedder, R A

    2005-03-01

    Although the fundamental mechanism of crystal growth has received and continues to receive deserved attention as a research activity, similar research efforts addressing the need for advanced materials and processing technology required to grow future high quality crystals has been sorely lacking. The purpose of this research effort is to develop advanced rapid growth processing technologies and materials suitable for providing the quality of products needed for advanced laser and photonics applications. In particular we are interested in developing a methodology for growing high quality KDP crystals based on an understanding of the fundamental mechanisms affecting growth. One problem in particular is the issue of control of impurities during the growth process. Many unwanted impurities are derived from the growth system containers and can adversely affect the optical quality and aspect ratio (shape) of the crystals. Previous studies have shown that even trace concentrations ({approx}10{sup -9} M) of impurities affect growth and even 'insignificant' species can have a large impact. It is also known that impurities affect the two growth faces of KDP very differently. Traces of trivalent metal impurities such as Fe{sup 3+}, Cr{sup 3+}, and Al{sup 3+} in solution are known to inhibit growth of the prismatic {l_brace}100{r_brace} faces of KDP while having little effect on the growth of the pyramidal {l_brace}101{r_brace} faces. This differentiation opens the possibility of intentionally adding select ions to control the aspect ratio of the crystal to obtain a more advantageous shape. This document summarizes our research efforts to improve KDP crystal growth. The first step was to control unwanted impurity addition from the growth vessel by developing an FEP liner to act as a barrier to the glass container. The other focus to develop an understanding of select impurities on growth rates in order to be able to use them to control the habit or shape of the

  8. Crystallization and X-ray diffraction of crystals formed in water-plasticized amorphous lactose.

    Science.gov (United States)

    Jouppila, K; Kansikas, J; Roos, Y H

    1998-01-01

    Effects of storage time and relative humidity on crystallization and crystal forms produced from amorphous lactose were investigated. Crystallization was observed from time-dependent loss of sorbed water and increasing intensities of peaks in X-ray diffraction patterns. The rate of crystallization increased with increasing storage relative humidity. Lactose crystallized mainly as alpha-lactose monohydrate and anhydrous crystals with alpha- and beta-lactose in a molar ratio of 5:3. The results suggested that the crystal form was defined by the early nucleation process. The crystallization data are important in modeling of crystallization phenomena and prediction of stability of lactose-containing food and pharmaceutical materials.

  9. Raman mapping for kinetic analysis of crystallization of amorphous drug based on distributional images.

    Science.gov (United States)

    Ueda, Hiroshi; Ida, Yasuo; Kadota, Kazunori; Tozuka, Yuichi

    2014-02-28

    The feasibility of Raman mapping for understanding the crystallization mechanism of an amorphous drug was investigated using described images. The crystallization tendency of amorphous indomethacin under dry condition at 30 °C was kinetically evaluated by means of Raman mapping and X-ray powder diffraction (XRPD) with change in the calculated crystallinities. Raman images directly revealed the occurrence of particle size-dependent non-uniform crystallization; slow crystallization of large particles, but fast crystallization of small particles. Kinetic analysis by fitting to the Kolmogorov-Johnson-Mehl-Avrami equation was performed for the crystallization profiles of both Raman mapping and XRPD data. For the Raman mapping data, the distribution of large particles was characterized and examined. The kinetic parameters calculated from the whole Raman image area agreed well with those of XRPD, suggesting accurate prediction of both techniques for the entire crystallization. Raman images revealed the change in the crystallization mechanism for the focused area; the large particles showed a reduced crystallization rate constant and an increase in the dimensional crystal growth exponent. Raman mapping is an attractive tool for quantitative and kinetic investigation of the crystallization mechanism with distributional images.

  10. Shaped Crystal Growth

    Science.gov (United States)

    Tatartchenko, Vitali A.

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

  11. Calcium Carbonate Storage in Amorphous Form and Its Template-Induced Crystallization

    Energy Technology Data Exchange (ETDEWEB)

    Han, T Y; Aizenberg, J

    2007-08-31

    Calcium carbonate crystallization in organisms often occurs through the transformation from the amorphous precursor. It is believed that the amorphous phase could be temporarily stabilized and stored, until its templated transition to the crystalline form is induced. Here we develop a bio-inspired crystallization strategy that is based on the above mechanism. Amorphous calcium carbonate (ACC) spherulitic particles are formed and stabilized on a self-assembled monolayer (SAM) of hydroxy-terminated alkanethiols on Au surface. The ACC is stored as a reservoir for ions and is induced to crystallize on command by introducing a secondary surface that is functionalized with carboxylic acid-terminated SAM. This secondary surface acts as a template for oriented and patterned nucleation. Various oriented crystalline arrays and micropatterned films are formed. We also show that the ACC phase can be doped with foreign ions (e.g. Mg) and organic molecules (e.g. dyes) and that these dopants later function as growth modifiers of calcite crystals and become incorporated into the crystals during the transformation process of ACC to calcite. We believe that our strategy opens the way of using a stabilized amorphous phase as a versatile reservoir system that can be converted in a highly controlled fashion to a crystalline form upon contacting the nucleating template.

  12. Crystal growth and crystallography

    Science.gov (United States)

    Chernov, A. A.

    1998-01-01

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

  13. Crystallization of amorphous Co-Nb-Zr sputtered films

    Energy Technology Data Exchange (ETDEWEB)

    Battezzati, L.; Baricco, M.; Attina, P.

    1986-08-01

    Thermal analysis results obtained with some sputtered Co-Nb-Zr alloys are presented. Microstructural determinations at some stages of the crystallization process were made with transmission electron microscopy and the results given. Crystallization occurs over a wider temperature range than for binary Co/sub 90/Zr/sub 10/ ribbons. Binary Co-Nb films crystallize in the range 750-800K, some 10 degrees below ternary films. The presence of zirconium enhances the stability of the amorphous phase. An explanation of the results is given.

  14. Enhanced crystallization of amorphous silicon thin films using embedded silicon nanocrystals

    Science.gov (United States)

    Anderson, Curtis Michael

    This thesis is concerned with the production of silicon thin films for photovoltaic applications. Much research has been carried out to find a stable, more efficient alternative to amorphous silicon, resulting in a number of various amorphous/crystalline mixed-phase film structures with properties superior to amorphous silicon. This thesis work details a completely new approach to mixed-phase film deposition, focusing on the fast crystallization of these films. The deposition of amorphous silicon films with embedded nanocrystals was carried out via a dual-plasma system. It is known that plasma conditions to produce high quality films are much different from those to produce particles. Hence the experimental system used here involved two separate plasmas to allow the optimum production of the crystalline nanoparticles and the amorphous film. Both plasmas use 13.56 MHz excitation voltage with diluted silane as the silicon precursor. The nanoparticle production reactor is a flow-through device that can be altered to control the size of the particles from around 5--30 nm average diameter. The film production reactor is a parallel-plate capacitively-coupled plasma system, into which the aerosol-suspended nanoparticles were injected. The nanocrystals could either be "co-deposited" simultaneously with the amorphous film, or be deposited separately in a layer-by-layer technique; both approaches are discussed in detail. Measurements of the film conductivity provide for the first time unambiguous evidence that the presence of nanocrystallites above 5 nm in the amorphous film have a direct impact on the electronic properties of co-deposited films. Further measurements of the film structure by transmission electron microscopy (TEM) and Raman spectroscopy demonstrate clearly the effect of embedded nanocrystals on the annealed crystallization process; the immediate growth of the crystal seeds has been observed. Additionally, a newly discovered mechanism of film crystallization

  15. Silicon heterojunction solar cell and crystallization of amorphous silicon

    Science.gov (United States)

    Lu, Meijun

    The rapid growth of photovoltaics in the past decade brings on the soaring price and demand for crystalline silicon. Hence it becomes necessary and also profitable to develop solar cells with over 20% efficiency, using thin (˜100mum) silicon wafers. In this respect, diffused junction cells are not the best choice, since the inescapable heating in the diffusion process not only makes it hard to handle thin wafers, but also reduces carriers' bulk lifetime and impairs the crystal quality of the substrate, which could lower cell efficiency. An alternative is the heterojunction cells, such as amorphous silicon/crystalline silicon heterojunction (SHJ) solar cell, where the emitter layer can be grown at low temperature (solar cell, including the importance of intrinsic buffer layer; the discussion on the often observed anomalous "S"-shaped J-V curve (low fill factor) by using band diagram analysis; the surface passivation quality of intrinsic buffer and its relationship to the performance of front-junction SHJ cells. Although the a-Si:H is found to help to achieve high efficiency in c-Si heterojuntion solar cells, it also absorbs short wavelength (cells. Considering this, heterojunction with both a-Si:H emitter and base contact on the back side in an interdigitated pattern, i.e. interdigitated back contact silicon heterojunction (IBC-SHJ) solar cell, is developed. This dissertation will show our progress in developing IBC-SHJ solar cells, including the structure design; device fabrication and characterization; two dimensional simulation by using simulator Sentaurus Device; some special features of IBC-SHJ solar cells; and performance of IBC-SHJ cells without and with back surface buffer layers. Another trend for solar cell industry is thin film solar cells, since they use less materials resulting in lower cost. Polycrystalline silicon (poly-Si) is one promising thin-film material. It has the potential advantages to not only retain the performance and stability of c

  16. Microstructural study of the crystallization of amorphous Fe–Sn–B ribbons

    Energy Technology Data Exchange (ETDEWEB)

    Maťko, Igor, E-mail: igor.matko@savba.sk [Institute of Physics, Slovak Academy of Sciences, Dúbravska cesta 9, 845 11 Bratislava (Slovakia); Illeková, Emília; Peter Švec Sr; Švec, Peter; Janičkovič, Dušan [Institute of Physics, Slovak Academy of Sciences, Dúbravska cesta 9, 845 11 Bratislava (Slovakia); Vodárek, Vlastimil [VŠB-Technical University of Ostrava, Department of Materials Engineering, 708 33 Ostrava-Poruba (Czech Republic)

    2014-12-05

    Highlights: • Amorphous Fe{sub 78}Sn{sub 5}B{sub 17} ribbons were prepared by planar flow casting. • Crystallization was studied by thermal analysis, XRD and TEM. • The crystallization begins by formation of specific nanocrystalline Fe(Sn) phase. • Role of Sn in formation of the nanocrystalline phase is discussed. • Next step of the crystallization corresponding to complex process is also analysed. - Abstract: Amorphous Fe{sub 78}Sn{sub 5}B{sub 17} ribbons were prepared by planar flow casting. The thermodynamic stability and the kinetics of observed phase transformations were monitored by thermal analysis. The structure and morphology of phases forming upon the thermally activated crystallization is studied by X-ray diffraction and transmission electron microscopy. The crystallization begins by nucleation-and-growth of specific nanocrystalline bcc-Fe(Sn) phase, its structure is explored more in details and the role of Sn in its formation is discussed. In the next step of the crystallization a transformation of remaining amorphous matrix to iron borides runs via rather complex process, which is inspected more in details as well.

  17. Microscopy and calorimetry as complementary techniques to analyze sugar crystallization from amorphous systems.

    Science.gov (United States)

    Mazzobre, María F; Aguilera, José M; Buera, María P

    2003-03-14

    A comparison of microscopic and macroscopic techniques to evaluate sugar crystallization kinetics is presented using amorphous lactose and lactose-trehalose mixtures. Polarized light video microscopy (PLV) and differential scanning calorimetry (DSC) were applied to measure crystallization kinetics, induction times and time for complete sugar crystallization at different storage temperatures (60-95 degrees C). DSC was also employed to measure the glass transition temperature (T(ag)) of the systems. PLV permitted direct observation, in real time, of growth of individual crystals and morphological aspects at a scale not detected by DSC. Taking the average of several microscopic observations, the results for temperature dependence of crystallization rate and time to complete lactose crystallization were similar to those obtained by DSC. Both PLV and DSC techniques showed that the presence of trehalose delayed lactose crystallization, without affecting the T(ag) value. For the analysis of sugar crystallization in amorphous systems, PLV and DSC proved to be complementary techniques. Validation of results obtained by PLV with results from DSC opens a new area of microstructural analysis of crystallizing systems.

  18. Large area crystallization of amorphous Si with overlapping high repetition rate laser pulses

    KAUST Repository

    Ryu, Sang-Gil

    2012-09-01

    This paper presents a pulsed laser crystallization technique, enabling large area crystallization of amorphous Si to produce grains having well-defined size and orientation. The method is developed by first determining the parameters influencing crystallization induced by single laser pulses of circular cross-sectional profile. In a second step, crystallization by overlapping round spots is examined. The experiments reveal three zones characterized by distinctly different crystallized morphologies following the laser irradiation. One of these zones corresponds to the regime of lateral crystal growth, wherein grains are driven towards the center of the spot by the radial temperature gradient. These findings are then applied to processing via line beam profiles that facilitate large area crystallization upon rapid translation of the specimen. Crystallization of extended areas hinges on the determination of the crystal growth length for a single spot. The pitch between successive pulses is then set on the basis of this information. It is shown that the pulse energy has only a weak effect on the crystal growth length. © 2012 Elsevier B.V.

  19. Effects of Polymeric Additives on the Crystallization and Release Behavior of Amorphous Ibuprofen

    Directory of Open Access Journals (Sweden)

    Su Yang Lee

    2013-01-01

    Full Text Available Some polymeric additives were studied to understand their effects on the amorphous phase of ibuprofen (IBU, used as a poorly water soluble pharmaceutical model compound. The amorphous IBU in bulk, as well as in nanopores (diameter ~24 nm of anodic aluminum oxide, was examined with the addition of poly(acrylic acid, poly(N-vinyl pyrrolidone, or poly(4-vinylphenol. Results of bulk crystallization showed that they were effective in limiting the crystal growth, while the nucleation of the crystalline phase in contact with water was nearly instantaneous in all cases. Poly(N-vinyl pyrrolidone, the most effective additive, was in specific interaction with IBU, as revealed by IR spectroscopy. The addition of the polymers was combined with the nanoscopic confinement to further stabilize the amorphous phase. Still, the IBU with addition of polymeric additives showed sustained release behavior. The current study suggested that the inhibition of the crystal nucleation was probably the most important factor to stabilize the amorphous phase and fully harness its high solubility.

  20. Insight into the crystallization of amorphous imine-linked polymer networks to 2D covalent organic frameworks.

    Science.gov (United States)

    Smith, Brian J; Overholts, Anna C; Hwang, Nicky; Dichtel, William R

    2016-03-04

    We explore the crystallization of a high surface area imine-linked two-dimensional covalent organic framework (2D COF). The growth process reveals rapid initial formation of an amorphous network that subsequently crystallizes into the layered 2D network. The metastable amorphous polymer may be isolated and resubjected to growth conditions to form the COF. These experiments provide the first mechanistic insight into the mechanism of imine-linked 2D COF formation, which is distinct from that of boronate-ester linked COFs.

  1. Crystallization behaviour of Al-Sm amorphous alloys

    Energy Technology Data Exchange (ETDEWEB)

    Battezzati, L. (Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universita di Torino, Via P. Giuria 9, 10125 Torino (Italy)); Baricco, M. (Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universita di Torino, Via P. Giuria 9, 10125 Torino (Italy)); Schumacher, P. (Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom)); Shih, W.C.; Greer, A.L.

    1994-05-01

    Various Al[sub 100-x]Sm[sub x] alloys (10[<=]qslantx[<=]qslant14) have been rapidly solidified by single-roller melt spinning with careful control of the atmosphere in the quenching device. The structural state and subsequent devitrification behaviour of the melt-spun ribbons are found to be particularly sensitive to the quenching conditions. Except for the thinnest ribbons, there are inhomogeneities both through the ribbon thickness and along the length. Both fully and partially amorphous ribbons have been obtained. The crystallization processes of the amorphous phases have been followed by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry (DSC). Al[sub 92]Sm[sub 8] shows primary crystallization of Al, followed by the formation of metastable phases; Al[sub 90]Sm[sub 10] transforms polymorphically to a metastable intermetallic; Al[sub 88]Sm[sub 12] and Al[sub 86]Sm[sub 14] display eutectic crystallization into Al and a metastable mixture of compounds. For Al[sub 90]Sm[sub 10], the DSC traces involve several overlapping peaks. This may be the result of transformations occurring in distinct parts of the ribbon with different mechanisms. A kinetic analysis of the crystallization processes has been performed by means of isothermal and non-isothermal DSC experiments. A discussion of the kinetic parameters derived from Kissinger and Avrami analyses is provided. ((orig.))

  2. The role of amorphous precursors in the crystallization of La and Nd carbonates.

    Science.gov (United States)

    Vallina, Beatriz; Rodriguez-Blanco, Juan Diego; Brown, Andrew P; Blanco, Jesus A; Benning, Liane G

    2015-07-28

    Crystalline La and Nd carbonates can be formed from poorly-ordered nanoparticulate precursors, termed amorphous lanthanum carbonate (ALC) and amorphous neodymium carbonate (ANC). When reacted in air or in aqueous solutions these precursors show highly variable lifetimes and crystallization pathways. We have characterized these precursors and the crystallization pathways and products with solid-state, spectroscopic and microscopic techniques to explain the differences in crystallization mechanisms between the La and Nd systems. ALC and ANC consist of highly hydrated, 10-20 nm spherical nanoparticles with a general formula of REE2(CO3)3·5H2O (REE = La, Nd). The stabilities differ by ∼2 orders of magnitude, with ANC being far more stable than ALC. This difference is due to the Nd(3+) ion having a far higher hydration energy compared to the La(3+) ion. This, together with temperature and reaction times, leads to clear differences not only in the kinetics and mechanisms of crystallization of the amorphous precursor La- and Nd-carbonate phases but also in the resulting crystallite sizes and morphologies of the end products. All crystalline La and Nd carbonates developed spherulitic morphologies when crystallization occurred from hydrous phases in solution at temperatures above 60 °C (La system) and 95 °C (Nd system). We suggest that spherulitic growth occurs due to a rapid breakdown of the amorphous precursors and a concurrent rapid increase in supersaturation levels in the aqueous solution. The kinetic data show that the crystallization pathway for both La and Nd carbonate systems is dependent on the reaction temperature and the ionic potential of the REE(3+) ion.

  3. Novel Transrotational Solid State Order Discovered by TEM in Crystallizing Amorphous Films

    Science.gov (United States)

    Kolosov, Vladimir

    Exotic thin crystals with unexpected transrotational microstructures have been discovered by transmission electron microscopy (TEM) for crystal growth in thin (10-100 nm) amorphous films of different chemical nature (oxides, chalcogenides, metals and alloys) prepared by various methods. Primarily we use our TEM bend contour technique. The unusual phenomenon can be traced in situ in TEM column: dislocation independent regular internal bending of crystal lattice planes in a growing crystal. Such transrotation (unit cell trans lation is complicated by small rotationrealized round an axis lying in the film plane) can result in strong regular lattice orientation gradients (up to 300 degrees per micrometer) of different geometries: cylindrical, ellipsoidal, toroidal, saddle, etc. Transrotation is increasing as the film gets thinner. Transrotational crystal resembles ideal single crystal enclosed in a curved space. Transrotational micro crystals have been eventually recognized by other authors in some vital thin film materials, i.e. PCMs for memory, silicides, SrTiO3. Atomic model and possible mechanisms of the phenomenon are discussed. New transrotational nanocrystalline model of amorphous state is also proposed Support of RF Ministry of Education and Science is acknowledged.

  4. Nucleation and crystallization kinetics of hydrated amorphous lactose above the glass transition temperature.

    Science.gov (United States)

    Schmitt, E A; Law, D; Zhang, G G

    1999-03-01

    The crystallization kinetics of amorphous lactose in the presence and absence of seed crystals were investigated at 57.5% relative humidity. Isothermal crystallization studies were conducted gravimetrically in an automated vacuum moisture balance at several temperatures between 18 and 32 degrees C. The crystallization rate constants were then determined from Johnson-Mehl-Avrami (JMA) treatment and isothermal activation energies were obtained from Arrhenius plots. Based on microscopic observations, a reaction order of 3 was used for JMA analysis. The nonisothermal activation energies were determined by differential scanning calorimetry using Kissinger's analysis. Isothermal activation energies for amorphous lactose with and without seed crystals were 89.5 (+/-5.6) kJ/mol and 186.5 (+/-17.6) kJ/mol, respectively. Nonisothermal activation energies with and without seed crystals were 71 (+/-7.5) kJ/mol and 80.9 (+/-8.9) kJ/mol, respectively. The similarity of the isothermal and nonisothermal activation energies for the sample with seeds suggested that crystallization was occurring by growth from a fixed number of preexisting nuclei. Markedly different isothermal and nonisothermal activation energies in the absence of seeds suggested a site-saturated nucleation mechanism, and therefore allowed calculation of an activation energy for nucleation of 317 kJ/mol.

  5. A method to evaluate the effect of contact with excipients on the surface crystallization of amorphous drugs.

    Science.gov (United States)

    Zhang, Si-Wei; Yu, Lian; Huang, Jun; Hussain, Munir A; Derdour, Lotfi; Qian, Feng; de Villiers, Melgardt M

    2014-12-01

    Amorphous drugs are used to improve the solubility, dissolution, and bioavailability of drugs. However, these metastable forms of drugs can transform into more stable, less soluble, crystalline counterparts. This study reports a method for evaluating the effect of commonly used excipients on the surface crystallization of amorphous drugs and its application to two model amorphous compounds, nifedipine and indomethacin. In this method, amorphous samples of the drugs were covered by excipients and stored in controlled environments. An inverted light microscope was used to measure in real time the rates of surface crystal nucleation and growth. For nifedipine, vacuum-dried microcrystalline cellulose and lactose monohydrate increased the nucleation rate of the β polymorph from two to five times when samples were stored in a desiccator, while D-mannitol and magnesium stearate increased the nucleation rate 50 times. At 50% relative humidity, the nucleation rates were further increased, suggesting that moisture played an important role in the crystallization caused by the excipients. The effect of excipients on the crystal growth rate was not significant, suggesting that contact with excipients influences the physical stability of amorphous nifedipine mainly through the effect on crystal nucleation. This effect seems to be drug specific because for two polymorphs of indomethacin, no significant change in the nucleation rate was observed under the excipients.

  6. Atomic structure and crystallization processes of amorphous (Co,Ni)–P metallic alloy

    Energy Technology Data Exchange (ETDEWEB)

    Modin, Evgeny B., E-mail: modin.eb@dvfu.ru [Far Eastern Federal University, Shukhanova 8, Vladivostok 690950 (Russian Federation); Pustovalov, Evgeny V.; Fedorets, Aleksander N.; Dubinets, Aleksander V.; Grudin, Boris N.; Plotnikov, Vladimir S. [Far Eastern Federal University, Shukhanova 8, Vladivostok 690950 (Russian Federation); Grabchikov, Sergey S. [Scientific and Practical Centre of Material Science, Belarus National Academy of Sciences, P. Brovki 19, Minsk 220072 (Belarus)

    2015-08-25

    Highlights: • The CoP–CoNiP amorphous alloys were studied by the Cs-corrected high resolution transmission electron microscopy. • In situ heating experiments showed that crystallization starts at 200–250 °C on the network frame and cell boundaries. • Crystal growth occurs at the free surface, then the remaining material in the volume is crystallized. • Adding nickel to the CoP alloy leads to higher thermal stability. • At the beginning of crystallization there are high diffusion coefficients, 1.2–2.4 ∗ 10{sup −18} m{sup 2}/s at 250 °C. - Abstract: This work concerns the in situ investigation of the atomic structure of (Co,Ni)–P alloys during relaxation and crystallization by high resolution transmission electron microscopy. The CoP–CoNiP alloys, in the initial state, have a hierarchical network-like disordered structure. Crystallization starts at 200–250 °C on the network frame and cell boundaries. In the early stages, crystal growth occurs at the free surface, then the remaining material in the volume is crystallized. The diffusion coefficient at the start of crystallization is 1.2–2.4 × 10{sup −18} m{sup 2}/s at 250 °C and we assume that the high diffusion speed is due to surface diffusion.

  7. Transformation of amorphous calcium carbonate to rod-like single crystal calcite via "copying" collagen template.

    Science.gov (United States)

    Xue, Zhonghui; Hu, Binbin; Dai, Shuxi; Du, Zuliang

    2015-10-01

    Collagen Langmuir films were prepared by spreading the solution of collagen over deionized water, CaCl2 solution and Ca(HCO3)2 solution. Resultant collagen Langmuir monolayers were then compressed to a lateral pressure of 10 mN/m and held there for different duration, allowing the crystallization of CaCO3. The effect of crystallization time on the phase composition and microstructure of CaCO3 was investigated. It was found that amorphous calcium carbonate (ACC) was obtained at a crystallization time of 6 h. The amorphous CaCO3 was transformed to rod-like single crystal calcite crystals at an extended crystallization time of 12 h and 24 h, via "copying" the symmetry and dimensionalities of collagen fibers. Resultant calcite crystallites were well oriented along the longitudinal axis of collagen fibers. The ordered surface structure of collagen fibers and electrostatic interactions played key roles in tuning the oriented nucleation and growth of the calcite crystallites. The mineralized collagen possessing both desired mechanical properties of collagen fiber and good biocompatibility of calcium carbonate may be assembled into an ideal biomaterial for bone implants.

  8. Modeling the Crystallization of Amorphous Silicon Thin Films Using a High Repetition Rate Scanning Laser

    Directory of Open Access Journals (Sweden)

    R. Černý

    2000-01-01

    Full Text Available An optimum design of experimental setup for the preparation of polycrystalline silicon (pc-Si films from amorphous layers applicable in the solar cell production is analyzed in the paper. In the computational simulations, the influence of basic characteristic parameters of the experimental procedure on the mechanisms of pc-Si lateral growth is studied. Among these parameters, the energy density of the applied laser and the thickness of the amorphous silicon (a-Si layer are identified as the most significant. As an optimum solution, the mechanism of pc-Si growth consisting in repeated melting of a part of already crystallized pc-Si layer by the scanning laser is proposed.

  9. Moisture-induced surface crystallization of spray-dried amorphous lactose particles studied by atomic force microscopy.

    Science.gov (United States)

    Mahlin, Denny; Berggren, Jonas; Alderborn, Göran; Engström, Sven

    2004-01-01

    The aim of this study was to show that atomic force microscopy (AFM) can be used to obtain mechanistic and kinetic information about the process of moisture-induced surface crystallization of single particles of amorphous lactose. Completely amorphous lactose particles were prepared by spray-drying a solution of alpha-lactose monohydrate, and moisture-induced crystallization was monitored for a bed of particles by microcalorimetry and for single particles by AFM. From the AFM images it was found that crystallization of the surface of single particles can be described in terms of a sequence of three events: an initial smoothening of the surface, formation of crystalline nanostructures dispersed in amorphous material, and growth of these structures to a complete crystalline surface. The surface roughness parameter rugosity was used to estimate the fraction crystalline surface, and the growth kinetics were found to obey the JMAK equation. The fraction crystalline surface at different times could also be estimated by determining the growth rate of individual crystals. It was concluded that AFM offers a unique means of visualizing the process of moisture-induced surface crystallization of amorphous particles and enables mechanistic and kinetic information about the process to be extracted. Copyright 2004 Wiley-Liss, Inc.

  10. Kinetics of the laser-induced solid phase crystallization of amorphous silicon-Time-resolved Raman spectroscopy and computer simulations

    Science.gov (United States)

    Očenášek, J.; Novák, P.; Prušáková, L.

    2017-01-01

    This study demonstrates that a laser-induced crystallization instrumented with Raman spectroscopy is, in general, an effective tool to study the thermally activated crystallization kinetics. It is shown, for the solid phase crystallization of an amorphous silicon thin film, that the integral intensity of Raman spectra corresponding to the crystalline phase grows linearly in the time-logarithmic scale. A mathematical model, which assumes random nucleation and crystal growth, was designed to simulate the crystallization process in the non-uniform temperature field induced by laser. The model is based on solving the Eikonal equation and the Arhenius temperature dependence of the crystal nucleation and the growth rate. These computer simulations successfully approximate the crystallization process kinetics and suggest that laser-induced crystallization is primarily thermally activated.

  11. The crystallization of Al-Sm amorphous alloys

    Energy Technology Data Exchange (ETDEWEB)

    Rizzi, P. [Turin Univ. (Italy). Dipt. di Chimica Inorganica; Baricco, M. [Turin Univ. (Italy). Dipt. di Chimica Inorganica; Battezzati, L. [Turin Univ. (Italy). Dipt. di Chimica Inorganica; Schumacher, P. [Cambridge Univ. (United Kingdom). Dept. of Metallurgy and Materials Science; Greer, A.L. [Cambridge Univ. (United Kingdom). Dept. of Metallurgy and Materials Science

    1995-12-31

    Amorphous alloys with composition Al{sub 100-x}Sm{sub x} (8 {<=} x {<=} 14) have been prepared by melt spinning in controlled atmosphere. The quenching conditions significantly influence the microstructure of as-quenched samples and their crystallization mechanisms. The crystallization was followed by means of DSC, XRD, TEM and SEM. Different mechanisms are observed as a function of composition. For low Sm content (Al{sub 92}Sm{sub 8}), a primary crystallization occurs at about 180 C, with the formation of Al nanocrystals with a grain size of about 15 nm. A polymorphic crystallization is found in Al{sub 90}Sm{sub 10}, with the formation of a metastable intermetallic phase at about 220 C. For higher Sm content (Al{sub 88}Sm{sub 12} and Al{sub 86}Sm{sub 14}), a eutectic crystallization at about 230 C gives a mixture of stable (Al and Al{sub 11}Sm{sub 3}) and metastable phases. (orig.)

  12. Effect of heating rate and kinetic model selection on activation energy of nonisothermal crystallization of amorphous felodipine.

    Science.gov (United States)

    Chattoraj, Sayantan; Bhugra, Chandan; Li, Zheng Jane; Sun, Changquan Calvin

    2014-12-01

    The nonisothermal crystallization kinetics of amorphous materials is routinely analyzed by statistically fitting the crystallization data to kinetic models. In this work, we systematically evaluate how the model-dependent crystallization kinetics is impacted by variations in the heating rate and the selection of the kinetic model, two key factors that can lead to significant differences in the crystallization activation energy (Ea ) of an amorphous material. Using amorphous felodipine, we show that the Ea decreases with increase in the heating rate, irrespective of the kinetic model evaluated in this work. The model that best describes the crystallization phenomenon cannot be identified readily through the statistical fitting approach because several kinetic models yield comparable R(2) . Here, we propose an alternate paired model-fitting model-free (PMFMF) approach for identifying the most suitable kinetic model, where Ea obtained from model-dependent kinetics is compared with those obtained from model-free kinetics. The most suitable kinetic model is identified as the one that yields Ea values comparable with the model-free kinetics. Through this PMFMF approach, nucleation and growth is identified as the main mechanism that controls the crystallization kinetics of felodipine. Using this PMFMF approach, we further demonstrate that crystallization mechanism from amorphous phase varies with heating rate. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

  13. Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Hellman, Frances

    1998-10-03

    OAK B204 Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films. The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and hTi-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials.

  14. Solution growth of microcrystalline silicon on amorphous substrates

    Energy Technology Data Exchange (ETDEWEB)

    Heimburger, Robert

    2010-07-05

    This work deals with low-temperature solution growth of micro-crystalline silicon on glass. The task is motivated by the application in low-cost solar cells. As glass is an amorphous material, conventional epitaxy is not applicable. Therefore, growth is conducted in a two-step process. The first step aims at the spatial arrangement of silicon seed crystals on conductive coated glass substrates, which is realized by means of vapor-liquid-solid processing using indium as the solvent. Seed crystals are afterwards enlarged by applying a specially developed steady-state solution growth apparatus. This laboratory prototype mainly consists of a vertical stack of a silicon feeding source and the solvent (indium). The growth substrate can be dipped into the solution from the top. The system can be heated to a temperature below the softening point of the utilized glass substrate. A temperature gradient between feeding source and growth substrate promotes both, supersaturation and material transport by solvent convection. This setup offers advantages over conventional liquid phase epitaxy at low temperatures in terms of achievable layer thickness and required growth times. The need for convective solute transport to gain the desired thickness of at least 50 {mu}m is emphasized by equilibrium calculations in the binary system indium-silicon. Material transport and supersaturation conditions inside the utilized solution growth crucible are analyzed. It results that the solute can be transported from the lower feeding source to the growth substrate by applying an appropriate heating regime. These findings are interpreted by means of a hydrodynamic analysis of fluid flow and supporting FEM simulation. To ensure thermodynamic stability of all materials involved during steady-state solution growth, the ternary phase equilibrium between molybdenum, indium and silicon at 600 C was considered. Based on the obtained results, the use of molybdenum disilicide as conductive coating

  15. Kinetics of liquid-mediated crystallization of amorphous Ge from multi-frame dynamic transmission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Santala, M. K., E-mail: melissa.santala@oregonstate.edu; Campbell, G. H. [Materials Science Division, Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, California 94551 (United States); Raoux, S. [Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D-14109 Berlin (Germany)

    2015-12-21

    The kinetics of laser-induced, liquid-mediated crystallization of amorphous Ge thin films were studied using multi-frame dynamic transmission electron microscopy (DTEM), a nanosecond-scale photo-emission transmission electron microscopy technique. In these experiments, high temperature gradients are established in thin amorphous Ge films with a 12-ns laser pulse with a Gaussian spatial profile. The hottest region at the center of the laser spot crystallizes in ∼100 ns and becomes nano-crystalline. Over the next several hundred nanoseconds crystallization continues radially outward from the nano-crystalline region forming elongated grains, some many microns long. The growth rate during the formation of these radial grains is measured with time-resolved imaging experiments. Crystal growth rates exceed 10 m/s, which are consistent with crystallization mediated by a very thin, undercooled transient liquid layer, rather than a purely solid-state transformation mechanism. The kinetics of this growth mode have been studied in detail under steady-state conditions, but here we provide a detailed study of liquid-mediated growth in high temperature gradients. Unexpectedly, the propagation rate of the crystallization front was observed to remain constant during this growth mode even when passing through large local temperature gradients, in stark contrast to other similar studies that suggested the growth rate changed dramatically. The high throughput of multi-frame DTEM provides gives a more complete picture of the role of temperature and temperature gradient on laser crystallization than previous DTEM experiments.

  16. Crystallization of amorphous lactose at high humidity studied by terahertz time domain spectroscopy

    Science.gov (United States)

    McIntosh, Alexander I.; Yang, Bin; Goldup, Stephen M.; Watkinson, Michael; Donnan, Robert S.

    2013-02-01

    We report the first use of terahertz time-domain spectroscopy (THz-TDS) to study the hydration and crystallization of an amorphous molecular solid at high humidity. Lactose in its amorphous and monohydrate forms exhibits different terahertz spectra due to the lack of long range order in the amorphous material. This difference allowed the transformation of amorphous lactose to its monohydrate form at high humidity to be studied in real time. Spectral fitting of frequency-domain data allowed kinetic data to be obtained and the crystallization was found to obey Avrami kinetics. Bulk changes during the crystallization could also be observed in the time-domain.

  17. Growth habit of polar crystals

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Using coordination polyhedron rule, growth habit of polar crystals such as ZnO, ZnS and SiO2 is investigated. It shows that the growth rates in the positive and negative polar axis directions are different. The theoretical growth habit of ZnO crystal is hexagonal prism and the growth rates of its various faces are:V{0001}>V{0111}-->V{0110}->V{0111}->V{0001}-. The growth habit of ZnS crystal is tetrahedron and its growth rates of different crystal faces are: V{111}>V{001}>V{001} =V{100} =. The growth rate relationship between positive and negative polar axis directions of SiO2 crystal V[1120]-->V[1120]-.is These results are in agreement with the growth habits observed under hydrothermal conditions. The different growth rates between positive and negative polar axis directions cannot be explained by PBC theory.

  18. Low temperature amorphization and superconductivity in FeSe single crystals at high pressures

    Energy Technology Data Exchange (ETDEWEB)

    Stemshorn, Andrew K.; Tsoi, Georgiy; Vohra, Yogesh K.; Sinogeiken, Stanislav; Wu, Phillip M.; Huang, Yilin; Rao, Sistla M.; Wu, Maw-Kuen; Yeh, Kuo W.; Weir, Samuel T. (IP-Taiwan); (UAB); (Duke); (LLNL)

    2010-08-04

    In this study, we report low temperature x-ray diffraction studies combined with electrical resistance measurements on single crystals of iron-based layered superconductor FeSe to a temperature of 10 K and a pressure of 44 GPa. The low temperature high pressure x-ray diffraction studies were performed using a synchrotron source and superconductivity at high pressure was studied using designer diamond anvils. At ambient temperature, the FeSe sample shows a phase transformation from a PbO-type tetragonal phase to a NiAs-type hexagonal phase at 10 {+-} 2 GPa. On cooling, a structural distortion from a PbO-type tetragonal phase to an orthorhombic Cmma phase is observed below 100 K. At a low temperature of 10 K, compression of the orthorhombic Cmma phase results in a gradual transformation to an amorphous phase above 15 GPa. The transformation to the amorphous phase is completed by 40 GPa at 10 K. A loss of superconductivity is observed in the amorphous phase and a dramatic change in the temperature behavior of electrical resistance indicates formation of a semiconducting state at high pressures and low temperatures. The formation of the amorphous phase is attributed to a kinetic hindrance to the growth of a hexagonal NiAs phase under high pressures and low temperatures.

  19. Springer Handbook of Crystal Growth

    CERN Document Server

    Dhanaraj, Govindhan; Prasad, Vishwanath; Dudley, Michael

    2010-01-01

    Over the years, many successful attempts have been made to describe the art and science of crystal growth. Most modern advances in semiconductor and optical devices would not have been possible without the development of many elemental, binary, ternary, and other compound crystals of varying properties and large sizes. The objective of the Springer Handbook of Crystal Growth is to present state-of-the-art knowledge of both bulk and thin-film crystal growth. The goal is to make readers understand the basics of the commonly employed growth processes, materials produced, and defects generated. Almost 100 leading scientists, researchers, and engineers from 22 different countries from academia and industry have been selected to write chapters on the topics of their expertise. They have written 52 chapters on the fundamentals of bulk crystal growth from the melt, solution, and vapor, epitaxial growth, modeling of growth processes and defects, techniques of defect characterization as well as some contemporary specia...

  20. Crystallization and Transport Properties of Amorphous Cr-Si Thin Film Thermoelectrics

    Science.gov (United States)

    Novikov, S. V.; Burkov, A. T.; Schumann, J.

    2014-06-01

    We studied the thermoelectric properties, crystallization, and stability of amorphous and nanocrystalline states in Cr-Si composite films. Amorphous films, prepared by magnetron sputtering, were transformed into the nanocrystalline state by annealing with in situ thermopower and electrical resistivity measurements. We have found that the amorphous state is stable in these film composites to about 550 K. Prior to crystallization, the amorphous films undergo a structural relaxation, detected by peculiarities in the temperature dependences of the transport properties, but not visible in x-ray or electron diffraction. The magnitude and temperature dependences of electrical conductivity and thermopower indicate that electron transport in the amorphous films is through extended states. The amorphous films are crystallized at annealing temperatures above 550 K into a nanocrystalline composite with an average grain size of 10-20 nm.

  1. Pressure effects on Al89La6Ni5 amorphous alloy crystallization

    DEFF Research Database (Denmark)

    Zhuang, Yanxin; Jiang, Jianzhong; Zhou, T. J.

    2000-01-01

    The pressure effect on the crystallization of the Al89La6Ni5 amorphous alloy has been investigated by in situ high-pressure and high-temperature x-ray powder diffraction using synchrotron radiation. The amorphous alloy crystallizes in two steps in the pressure range studied (0-4 GPa). The first......(s). The applied pressure strongly affects the crystallization processes of the amorphous alloy. Both temperatures first decrease with pressure in the pressure range of 0-1 GPa and then increase with pressure up to 4 GPa. The results are discussed with reference to competing processes between the thermodynamic...

  2. Process induced disorder in crystalline materials: differentiating defective crystals from the amorphous form of griseofulvin.

    Science.gov (United States)

    Feng, Tao; Pinal, Rodolfo; Carvajal, M Teresa

    2008-08-01

    This research investigates milling induced disorder in crystalline griseofulvin. Griseofulvin was subjected to cryogenic milling for various lengths of time. For comparison, the amorphous form of griseofulvin was also prepared by the quench melt method. Different analytical techniques were used to study the differences between the cryomilled, amorphous and crystalline forms of the drug. Cryogenic milling of griseofulvin progressively reduces the crystallinity of the drug by inducing crystal defects, rather than amorphous materials. Raman analysis provides evidence of structural differences between the two. The differences between the defective crystals produced by milling and the amorphous form are significant enough as to be measurable in their bulk thermal properties. Defective crystals show significant decrease in the heat of fusion as a function of milling time but do not exhibit a glass transition nor recrystallization from the amorphous form. Crystal defects undergo recrystallization upon heating at temperatures well below the glass transition temperature (T(g)) in a process that is separate and completely independent from the crystallization of the amorphous griseofulvin, observed above T(g). Physical mixtures of defective crystals and amorphous drug demonstrate that the thermal events associated with each form persist in the mixtures, unaffected by the presence of the other form.

  3. Surrogate Seeds For Growth Of Crystals

    Science.gov (United States)

    Shlichta, Paul J.

    1989-01-01

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

  4. Calorimetric studies of non-isothermal crystallization in amorphous CuTi100– alloys

    Indian Academy of Sciences (India)

    N Mehta; K Singh; N S Saxena

    2011-12-01

    The present paper reports the composition dependence of pre-exponential factor and activation energy of non-isothermal crystallization in amorphous alloys of CuTi100– system using differential scanning calorimeter (DSC) technique. The applicability of Meyer–Neldel relation between the pre-exponential factor and activation energy of non-isothermal crystallization for amorphous alloys of Cu–Ti system was verified.

  5. Czochralski crystal growth: Modeling study

    Science.gov (United States)

    Dudukovic, M. P.; Ramachandran, P. A.; Srivastava, R. K.; Dorsey, D.

    1986-01-01

    The modeling study of Czochralski (Cz) crystal growth is reported. The approach was to relate in a quantitative manner, using models based on first priniciples, crystal quality to operating conditions and geometric variables. The finite element method is used for all calculations.

  6. The Growth of KLN Crystals

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    The growth temperature curve of the growth system for the potass ium li thium niobate (KLN) has been measured and the temperature decrease program has b een calculated. KLN crystals with a size up to 30mm × 15mm × 5 mm have be en grown by flux method. The primary factors of the cracking of KLN crystal hav e been discussed. A blue laser light output has been obtained by optical parame tric oscillator pumping.

  7. Protein Crystal Growth in Microgravity

    Institute of Scientific and Technical Information of China (English)

    毕汝昌; 桂璐璐; 师珂; 王耀萍; 陈世芝; 韩青; 胡永林; 沈福苓; 牛秀田; 华子谦; 卢光莹; 张健; 李松林; 龚为民; 牛立文; 黄其辰

    1994-01-01

    Protein crystal growth is quite important for the determination of protein structureswhich are essential to the understanding of life at molecular level as well as to the development of molecu-lar biotechnology.The microgravity environment of space is an ideal place to study the complicated pro-tein crystallization and to grow good-quality protein crystals.A number of crystal-growth experiments of10 different proteins were carried out in August,1992 on the Chinese re-entry satellite FSW-2 in spaceusing a tube crystallization equipment made in China.A total of 25 samples from 6 proteins producedcrystals,and the effects of microgravity on protein crystal growth were observed,especially for an acidicphospholipase A2 and henegg-white lysozyme which gave better crystals in space than earth-grown crys-tals in ground control experiments.The results have shown that the microgravity in space favors the im-provement of the size,perfection,morphology and internal order of the grown protein crytals.

  8. Capillarity creates single-crystal calcite nanowires from amorphous calcium carbonate.

    Science.gov (United States)

    Kim, Yi-Yeoun; Hetherington, Nicola B J; Noel, Elizabeth H; Kröger, Roland; Charnock, John M; Christenson, Hugo K; Meldrum, Fiona C

    2011-12-23

    Single-crystal calcite nanowires are formed by crystallization of morphologically equivalent amorphous calcium carbonate (ACC) particles within the pores of track etch membranes. The polyaspartic acid stabilized ACC is drawn into the membrane pores by capillary action, and the single-crystal nature of the nanowires is attributed to the limited contact of the intramembrane ACC particle with the bulk solution. The reaction environment then supports transformation to a single-crystal product.

  9. Formation and crystallization of bulk Pd82Si18 amorphous alloys

    Institute of Scientific and Technical Information of China (English)

    蒲建; 王敬丰; 肖建中; 崔昆

    2003-01-01

    Bulk amorphous Pd82Si18 alloy with the largest diameter of 8 mm was prepared by water quenching the molten alloy with flux medium in a quartz tube. The calculation result indicates that the bulk Pd82Si18 amorphous alloys have a low critical cooling rate (Rc) of 4.589 K/s or less. The experimental results show that purifying melt may improve glass forming ability(GFA) of undercooled melt, while liquid phase separation (LPS) of undercooled melt will decrease its GFA. There are some differences in crystallization experiments between bulk metallic glass and amorphous ribbons of Pd82Si18 alloys. These include the numbers of exothermic peak, glass transition temperature Tg, crystallization temperature Tx, region of undercooling liquid (ΔT=Tx-Tg) respectively. The links of cooling rates of melt and crystallization of Pd82Si18 amorphous alloys are explored.

  10. Crystal growth in salt efflorescence

    Science.gov (United States)

    Zehnder, Konrad; Arnold, Andreas

    1989-09-01

    Salt efflorescences strongly affect wall paintings and other monuments. The external factors governing the crystal habits and aggregate forms are studied phenomenologically in laboratory experiments. As salt contaminated materials dry, slats crystallize forming distinct sequences of crystal habits and aggregate forms on and underneath the surfaces. Four phases may be distinguished: (1) Large individual crystals with equilibrium forms grow immersed in a thick solution film; (2) granular crusts of small isometric crystals grow covered by a thin solution film; (3) fibrous crusts of columnar crystals grow from a coherent but thin solution film so that the crystals are in contact with solution only at their base; (4) whiskers grow from isolated spots of very thin solution films into the air. The main factor governing these morphologies is the humidity of the substrate. A porous material cracks while granular crystals (approaching their equilibrium forms) grow within the large pores. As the fissures widen, the habits pass into columnar crystals and then into whiskers. Because this succession corresponds to the crystallization sequence on the substrate surface it can be traced back to the same growth conditions.

  11. Step-by-Step Laser Crystallization of Amorphous Si:H/SiNx:H Multilayer for Active Layer in Microcavities

    Institute of Scientific and Technical Information of China (English)

    QIAN Bo; CHEN San; CEN Zhan-Hong; CHEN Kun-Ji; LIU Yan-Song; XU Jun; MA Zhong-Yuan; LI Wei; HUANG Xin-Fan

    2006-01-01

    @@ We report the crystallization and photoluminescence (PL) properties of amorphous Si:H/SiNx :H multilayer (ML)films treated by step-by-step laser annealing. The results of Raman measurements show that the nanocrystalline Si (nc-Si) grains are formed in the a-Si:H layers under the constrained growth mechanism. The blue shift of PL peak with grain size is observed and can be attributed to the quantum confinement effect. For comparison, we also report the crystallization and PL of a-Si:H/SiNx :H ML samples by normal one-step treatment. This method of step-by-step laser treatment will be a candidate to make nc-Si quantum dots in amorphous Si:H/SiNx :H ML as an active layer in microcavities.

  12. Investigation on Crystallization Kinetics of Zr-AI-Based Bulk Amorphous Alloys

    Institute of Scientific and Technical Information of China (English)

    王国明; 李维火; 方守狮; 华勤; 肖学山

    2005-01-01

    Zr65Al10Ni10Cu15, Zr52.5Al10Ni10Cu15Be12.5 and Zr52.5Al10Ni14.6 Cu17.9Ti5bulk amorphous alloys were prepared by copper mould casting. The crystallization kinetics was measured by differential scanning calorimeter(DSC) with different heating rates, and the activation energy was calculated using Kissinger equation. The relationship between thermal stability and rate constant of crystallization reaction is discussed on the view of crystallization kinetics, and the effect of small atom Beryllium on thermal stability of bulk amorphous alloys is also studied.

  13. Dehydration and crystallization of amorphous calcium carbonate in solution and in air.

    Science.gov (United States)

    Ihli, Johannes; Wong, Wai Ching; Noel, Elizabeth H; Kim, Yi-Yeoun; Kulak, Alexander N; Christenson, Hugo K; Duer, Melinda J; Meldrum, Fiona C

    2014-01-01

    The mechanisms by which amorphous intermediates transform into crystalline materials are poorly understood. Currently, attracting enormous interest is the crystallization of amorphous calcium carbonate, a key intermediary in synthetic, biological and environmental systems. Here we attempt to unify many contrasting and apparently contradictory studies by investigating this process in detail. We show that amorphous calcium carbonate can dehydrate before crystallizing, both in solution and in air, while thermal analyses and solid-state nuclear magnetic resonance measurements reveal that its water is present in distinct environments. Loss of the final water fraction--comprising less than 15% of the total--then triggers crystallization. The high activation energy of this step suggests that it occurs by partial dissolution/recrystallization, mediated by surface water, and the majority of the particle then crystallizes by a solid-state transformation. Such mechanisms are likely to be widespread in solid-state reactions and their characterization will facilitate greater control over these processes.

  14. Reversible crystal-to-amorphous-to-crystal phase transition and a large magnetocaloric effect in a spongelike metal organic framework material.

    Science.gov (United States)

    Tian, Chong-Bin; Chen, Rui-Ping; He, Chao; Li, Wei-Jin; Wei, Qi; Zhang, Xu-Dong; Du, Shao-Wu

    2014-02-21

    Reversible crystal-to-amorphous-to-crystal phase transition accompanied by changes in magnetic and NLO properties was first observed in a rigid non-porous spongelike MOF material. The crystal phase exhibits a high magnetocaloric effect, while the amorphous phase has potential application as a magnetic DMF sensor.

  15. Al-induced Lateral Crystallization of Amorphous Si Thin Films by Microwave Annealing

    Institute of Scientific and Technical Information of China (English)

    RAO Rui; XU Zhong-yang; ZENG Xiang-bing

    2002-01-01

    Al-induced lateral crystallization of amorphous silicon thin films by microwave annealing is investigated. The crystallized Si films are examined by optical microscopy , Raman spectroscopy, transmission electron microscopy and transmission electron diffraction micrography. After microwave annealing at 480 ℃ for 50 min,the amorphous Si is completely crystallized with large grains of main ( 111 ) orientation. The rate of lateral crystallization is 0.04μm/min. This process, labeled MILC-MA, not only lowers the temperature but also reduces the time of crystallization. The crystallization mechanism during microwave annealing and the electrical properties of polycrystalline Si thin films are analyzed. This MILC-MA process has potential applications in large area electronics.

  16. Growth of Solid Solution Crystals

    Science.gov (United States)

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

    1985-01-01

    The major objective of this program is to determine the conditions under which single crystals of solid solutions can be grown from the melt in a Bridgman configuration with a high degree of chemical homogeneity. The central aim is to assess the role of gravity in the growth process and to explore the possible advantages for growth in the absence of gravity. The alloy system being investigated is the solid solution semiconductor with x-values appropriate for infrared detector applications in Hg sub (1-x) Cd sub x Te the 8 to 14 micro m wavelength region. Both melt and Te-solvent growth are being considered. The study consists of an extensive ground-based experimental and theoretical research effort followed by flight experimentation where appropriate. Experimental facilities have been established for the purification, casting, and crystal growth of the alloy system. Facilities have been also established for the metallurgical, compositional, electric and optical characterization of the alloys. Crystals are being grown by the Bridgman-Stockbarger method and are analyzed by various experimental techniques to evaluate the effects of growth conditions on the longitudinal and radial compositional variations and defect densities in the crystals.

  17. Magnetocaloric effect in amorphous and partially crystallized Fe40Ni38Mo4B18 alloys

    Directory of Open Access Journals (Sweden)

    T. Thanveer

    2016-05-01

    Full Text Available A study of magnetocaloric effect in amorphous and partially crystallized Fe40Ni38Mo4B18 alloys is reported. Amorphous Fe40Ni38Mo4B18, near its magnetic ordering temperature (600K showed a magnetic entropy change ΔSM of 1.1 J/KgK and a relative cooling power of 36J/Kg in a field change of 10 kOe. Amorphous samples were partially crystallized by annealing at 700 K at different time intervals. Partially crystallized samples showed two distinct magnetic ordering temperature, one corresponding to the precipitated FeNi nanocrystals and the other one corresponding to the boron rich amorphous matrix. Magnetic ordering temperature of the residual amorphous matrix got shifted to the lower temperatures on increasing the annealing duration. Partially crystallised samples showed a magnetic entropy change of about 0.27J/kgK near the magnetic ordering temperature of the amorphous matrix (540K in a field change of 10 kOe. The decrease in ΔSM on partial crystallisation is attributed to the biphasic magnetic nature of the sample.

  18. Stabilisation of the amorphous state of a thin layer sandwiched between two crystals

    Energy Technology Data Exchange (ETDEWEB)

    Hyot, B.; Poupinet, L.; Desre, P.J

    2003-11-01

    It has been experimentally proven that thinning an amorphous layer, sandwiched between two crystals, up to the nanometer scale, leads to a higher crystallization temperature. The present work is an attempt to explain such behaviour on the basis of thermodynamical arguments. The approach assumes that a nanometric amorphous layer is submitted to the crystal field leading to a gradient of atomic density across the glassy layer. It is shown that the stabilisation of the glassy layer is expected when approaching a thickness of few nanometers. This study is closely related to the concerns of the phase change optical storage because such a technology involves both the use of very thin films and fast structural transitions between the two states (amorphous and crystalline) of the active material.

  19. Thermodynamic and Kinetic Study of Crystallization Reaction of Fe/Dy Multilayers Form Amorphous State

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    To give further insight into the behavior of Fe/Dy multilayers in the crystallization from as-deposited amorphous state, free energy diagram of Fe/Dy system was constructed based on Miedema semiempirical theory. It is shown that the crystallization of amorphous films is controlled by both thermodynamic and kinetic conditions. The calculated free energies of crystalline Fe and Dy are significantly lower than those in the amorphous states, which provide thermodynamic driving force for crystallization. During annealing, the kinetic phase evolution of the multilayers is controlled by free energy barrier of nucleation and critical-size of new phase nucleus. Thus it explains the experimental results that Fe crystallites formed first followed by Dy grains, whereas crystalline Fe-Dy intermetallic compounds were not observed during annealing at moderate temperatures.

  20. A resistivity study of crystallization of some FeNiB-based amorphous alloys

    Energy Technology Data Exchange (ETDEWEB)

    Riontino, G.; Baricco, M.; Marino, F.

    1986-07-01

    The amorphous-to-crystalline transformations has been studied extensively since the discovery of glassy alloys. Many physical and chemical properties vary drastically in the course of thermal treatments leading to crystallization, and this seems to be a limit to the applications of these materials. Nevertheless, the intermediate metastable crystallization products, in some cases, or the final crystalline phases show, in several cases, interesting properties. Among the very large number of amorphous systems up to now investigated, Metglas 2826 and 2826A (from Allied Chemical) have received particular attention, because of their magnetic and anticorrosive properties. In the present paper the authors discuss some results on amorphous alloys having compositions similar to the commercial ones and, in particular, they discuss the influence of phosphorus and chromium content on the electrical resistivity variations during thermal treatments up to crystallization.

  1. Evaluation of the Crystallization Tendency of Commercially Available Amorphous Tacrolimus Formulations Exposed to Different Stress Conditions.

    Science.gov (United States)

    Trasi, Niraj S; Purohit, Hitesh S; Taylor, Lynne S

    2017-07-07

    Tacrolimus, an immunosuppressant, is a poorly water soluble compound whereby the commercially available capsule formulations contain the drug in amorphous form. The goal of this study was to evaluate the robustness of the innovator product and five generic formulations to crystallization following storage at stress conditions. Products were purchased from a pharmacy and stored at 40°C/75% relative humidity (RH), open dish conditions. Crystallinity was determined using X-ray diffraction. The quantity of the ingredients in the formulations were determined using different approaches and the various factors that might cause instability in the formulations were studied. After 4 weeks of open dish storage at 40°C/75% RH, one of the generic formulations showed evidence of tacrolimus crystallization. Further investigations revealed batch-to-batch variations in crystallization tendency with the extent of crystallinity varying between 50 and 100% for different batches. Crystallization was also observed at lower storage temperatures (30°C) when the RH was maintained at 75%. It was found that crystallization could be induced in a model formulation by wet granulating an ethanolic solution of the drug with lactose and drying at 60-70°C followed by exposure to stress conditions. It seems probable that the generic that was susceptible to crystallization contains amorphous drug physically mixed with polymeric excipients, rather than as an amorphous solid dispersion. This study highlights the importance of considering the manufacturing process on the stability of the resultant amorphous product.

  2. Crystallization Growth of Single Crystal Cu by ContinuousCasting

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Crystallization growth of single-crystal Cu by continuous casting has been investigated using selfdesigned horizontal continuous casting equipment and XRD. Experimental results showed that the crystallization plane of (311), (220) and (111) were eliminated sequentially in evolutionary process. The final growth plane of crystal was (200), the direction of crystallization was [100],the growth direction of both sides of the rod inclined to axis, and the degree of deviation of direction [100] from the crystal axis was less than 10. In order to produce high quality single crystal, the solid-liquid interface morphology must be smooth, even be planar.

  3. Nucleation, evolution, and growth dynamics of amorphous silica nanosprings

    Science.gov (United States)

    Wojcik, Peter M.; Bakharev, Pavel V.; Corti, Giancarlo; McIlroy, D. N.

    2017-01-01

    The initial phases of amorphous silica nanospring formation via a vapor-liquid-solid mechanism are reported. The low temperature eutectic of Au-Si results in the formation of an asymmetrical shaped catalyst at the early stages of nanospring formation. As solid silica is formed below the Au-Si catalyst the system lowers its surface free energy and forms multiple amorphous silica nanowires beneath a common catalyst, as opposed to a single nanowire. The diameter of one of the nanowires forming the nanospring ranges between 10-20 nm. The difference in growth rates of the individual nanowires creates an asymmetry in the interfacial surface tension on the boundaries of the Au-Si catalyst/nanowires interface. Using Stokes’ theorem it is shown that there is a variable work of adhesion on the outer boundary of the Au-Si catalyst/nanowire interface of a nanospring, which is defined as an effective contact angle anisotropy. The anisotropic growth on the catalyst/nanowire boundary results in the nanowires coherently coiling into to a single, larger, helical structure with an overall diameter of 70-500 nm.

  4. Crystallization kinetics and molecular mobility of an amorphous active pharmaceutical ingredient: A case study with Biclotymol.

    Science.gov (United States)

    Schammé, Benjamin; Couvrat, Nicolas; Malpeli, Pascal; Delbreilh, Laurent; Dupray, Valérie; Dargent, Éric; Coquerel, Gérard

    2015-07-25

    The present case study focuses on the crystallization kinetics and molecular mobility of an amorphous mouth and throat drug namely Biclotymol, through differential scanning calorimetry (DSC), temperature resolved X-ray powder diffraction (TR-XRPD) and hot stage microscopy (HSM). Kinetics of crystallization above the glass transition through isothermal and non-isothermal cold crystallization were considered. Avrami model was used for isothermal crystallization process. Non-isothermal cold crystallization was investigated through Augis and Bennett model. Differences between crystallization processes have been ascribed to a site-saturated nucleation mechanism of the metastable form, confirmed by optical microscopy images. Regarding molecular mobility, a feature of molecular dynamics in glass-forming liquids as thermodynamic fragility index m was determined through calorimetric measurements. It turned out to be around m=100, describing Biclotymol as a fragile glass-former for Angell's classification. Relatively long-term stability of amorphous Biclotymol above Tg was analyzed indirectly by calorimetric monitoring to evaluate thermodynamic parameters and crystallization behavior of glassy Biclotymol. Within eight months of storage above Tg (T=Tg+2°C), amorphous Biclotymol does not show a strong inclination to crystallize and forms a relatively stable glass. This case study, involving a multidisciplinary approach, points out the importance of continuing looking for stability predictors.

  5. Cu clustering stage before the crystallization in Fe-Si-B-Nb-Cu amorphous alloys

    DEFF Research Database (Denmark)

    Ohnuma, M.; Hono, K.; Onodera, H.

    1999-01-01

    The Cu clustering stage before the crystallization of Fe-Si-B-Nb-Cu amorphous alloys have been studied by three dimensional atom probe (3DAP) small-angle neutron scattering (SANS) and high sensitive differential calorimetry (DSC). Cu clustering occurs prior to the onset of the primary crystalliza......The Cu clustering stage before the crystallization of Fe-Si-B-Nb-Cu amorphous alloys have been studied by three dimensional atom probe (3DAP) small-angle neutron scattering (SANS) and high sensitive differential calorimetry (DSC). Cu clustering occurs prior to the onset of the primary...

  6. Femtosecond Laser Crystallization of Boron-doped Amorphous Hydrogenated Silicon Films

    Directory of Open Access Journals (Sweden)

    P.D. Rybalko

    2016-10-01

    Full Text Available Crystallization of amorphous hydrogenated silicon films with femtosecond laser pulses is one of the promising ways to produce nanocrystalline silicon for photovoltaics. The structure of laser treated films is the most important factor determining materials' electric and photoelectric properties. In this work we investigated the effect of femtosecond laser irradiation of boron doped amorphous hydrogenated silicon films with different fluences on crystalline volume fraction and electrical properties of this material. A sharp increase of conductivity and essential decrease of activation energy of conductivity temperature dependences accompany the crystallization process. The results obtained are explained by increase of boron doping efficiency in crystalline phase of modified silicon film.

  7. A Century of Sapphire Crystal Growth

    Science.gov (United States)

    2004-05-17

    Crystal growth storage cabinet from Frémy’s lab.5,6 Flame Fusion and the Verneuil Process In 1885 rubies selling for $1000-2500...1891: Working with his student, M. Pacquier, Verneuil had developed most of what we now call Verneuil flame-fusion crystal growth . Verneuil ... Verneuil ) Crystal Growth Nassau, Gems Made by Man 11 • 1892: Verneuil eliminated crystal cracking by making contact area between ruby crystal

  8. Electrical conductivity and crystallization of amorphous bismuth ruthenate thin films deposited by spray pyrolysis.

    Science.gov (United States)

    Ryll, Thomas; Brunner, Andreas; Ellenbroek, Stefan; Bieberle-Hutter, Anja; Rupp, Jennifer L M; Gauckler, Ludwig J

    2010-11-14

    Amorphous oxide thin films with tailored functionality will be crucial for the next generation of micro-electro-mechanical-systems (MEMS). Due to potentially favorable electronic and catalytic properties, amorphous bismuth ruthenate thin films might be applied in this regard. We report on the deposition of amorphous bismuth ruthenate thin films by spray pyrolysis, their crystallization behavior and electrical conductivity. At room temperature the 200 nm thin amorphous films exhibit a high electrical conductivity of 7.7 × 10(4) S m(-1), which was found to be slightly thermally activated (E(a) = 4.1 × 10(-3) eV). It follows that a long-range order of the RuO(6) octahedra is no precondition for the electrical conductivity of Bi(3)Ru(3)O(11). Upon heating to the temperature range between 490 °C and 580 °C the initially amorphous films crystallize rapidly. Simultaneously, a transition from a dense and continuous film to isolated Bi(3)Ru(3)O(11) particles on the substrate takes place. Solid-state agglomeration is proposed as the mechanism responsible for disintegration. The area specific resistance of Bi(3)Ru(3)O(11) particles contacted by Pt paste on gadolinia doped ceria electrolyte pellets was found to be 7 Ω cm(2) at 607 °C in air. Amorphous bismuth ruthenate thin films are proposed for application in electrochemical devices operating at low temperatures, where a high electrical conductivity is required.

  9. Amorphous/crystal and polymer/filler interphases in biocomposites from poly(butylene succinate)

    Energy Technology Data Exchange (ETDEWEB)

    Signori, Francesca [Consiglio Nazionale delle Ricerche - Istituto per i Processi Chimico-Fisici (CNR-IPCF), Via G. Moruzzi 1, I-56124 Pisa (Italy); Pelagaggi, Martina [Universita di Pisa - Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, I-56126 Pisa (Italy); Bronco, Simona [Consiglio Nazionale delle Ricerche - Istituto per i Processi Chimico-Fisici (CNR-IPCF), Via G. Moruzzi 1, I-56124 Pisa (Italy); Righetti, Maria Cristina, E-mail: righetti@ipcf.cnr.it [Consiglio Nazionale delle Ricerche - Istituto per i Processi Chimico-Fisici (CNR-IPCF), Via G. Moruzzi 1, I-56124 Pisa (Italy)

    2012-09-10

    Highlights: Black-Right-Pointing-Pointer The existence of intermolecular interactions between poly(butylene succinate) and hemp fibres was proved from specific heat capacities data. Black-Right-Pointing-Pointer Different degrees of mobility of the poly(butylene succinate) amorphous segments were evidenced at the amorphous/crystal interphase. Black-Right-Pointing-Pointer Devitrification of the rigid amorphous fraction in poly(butylene succinate) was found to occur before and simultaneously with the fusion. - Abstract: Poly(butylene succinate)-hemp composites (PBS-hemp), with hemp content in the range 0-40 wt.%, were prepared in the melt and characterized. This paper focuses on the detailed analysis of the thermal behaviour of the PBS-hemp composites, investigated by differential scanning calorimetry (DSC), to enlighten the polymer/fibre interphase features. The occurrence of specific intermolecular interactions between PBS and hemp was assessed from specific heat capacity data. Different degrees of mobility of the PBS amorphous segments were found at the amorphous/crystal interphases. A broadening of the bulk glass transition was observed, and attributed to the presence of polymer segments slightly constrained. Moreover, a rigid amorphous fraction that devitrifies at temperatures higher than the bulk glass transition, partly before the melting region and partly simultaneously with the fusion, was observed and quantified, and attributed to the presence of major constraints probably occurring in geometrically restricted areas.

  10. Controllable crystallization and enhanced amorphous stability of Sb-Te films modified by Ag-doping

    Science.gov (United States)

    Zhong, Juechen; Luo, Yang; Gu, Ting; Wang, Zhenglai; Jiang, Kefeng; Wang, Guoxiang; Lu, Yegang

    2016-10-01

    Ag-doped Sb-Te films were deposited by magnetron co-sputtering and the structure, electrical, optical and thermal properties were analyzed. The results show that Ag-doping restrains crystal grain size, and changes a preferred orientation of the crystalline phase. The crystallization temperature is increased due to the Ag addition. Both amorphous resistance and crystalline resistance are enhanced and the resistance ratio reaches ˜104. Compared with Ge2Sb2Te5, Ag26.82(Sb3Te)73.18 film exhibits a better amorphous thermal stability, a higher crystallization temperature (˜166 °C), a wider optical band gap (0.515 eV), a larger crystallization activation energy (3.17 eV) as well as a better 10 years data retention at 92 °C.

  11. The role of pH and Mg on the stability and crystallization of amorphous calcium carbonate

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez-Blanco, J.D., E-mail: J.D.RodriguezBlanco@leeds.ac.uk [School of Earth and Environment, University of Leeds, Leeds LS2 9JT (United Kingdom); Shaw, S.; Bots, P.; Roncal-Herrero, T.; Benning, L.G. [School of Earth and Environment, University of Leeds, Leeds LS2 9JT (United Kingdom)

    2012-09-25

    Highlights: Black-Right-Pointing-Pointer We studied the effect of pH and Mg in the crystallization of amorphous CaCO{sub 3} (ACC). Black-Right-Pointing-Pointer The study combined synchrotron-based scattering with electron microscopy. Black-Right-Pointing-Pointer The pH-dependent C speciation and hydration strength of Mg{sup 2+} control ACC structure. Black-Right-Pointing-Pointer This ACC structure governs the ACC dissolution rate and crystallization pathway. - Abstract: The effects of pH and Mg on the crystallization of amorphous calcium carbonate (ACC) to vaterite and/or calcite were studied using a combination of in situ time resolved synchrotron-based techniques and electron microscopy. The experiments showed that Mg increased the stability of ACC and favoured the formation of calcite over vaterite. A neutral ({approx}7) starting pH during mixing promoted the transformation of ACC into calcite via a dissolution/reprecipitation mechanism. Conversely, when ACC formed in a solution that started with a high initial pH ({approx}11.5), the transformation to calcite occurred via metastable vaterite, which formed via a spherulitic growth mechanism. In a second stage this vaterite transformed to calcite via a surface-controlled dissolution and recrystallization mechanism. These crystallization pathways can be explained as a consequence of the pH-dependent composition, local structure, stability and dissolution rates of ACC.

  12. Zeolite crystal growth in space

    Science.gov (United States)

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

    1991-01-01

    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.

  13. Citrate effects on amorphous calcium carbonate (ACC) structure, stability, and crystallization

    DEFF Research Database (Denmark)

    Tobler, Dominique Jeanette; Rodriguez Blanco, Juan Diego; Dideriksen, Knud;

    2015-01-01

    Understanding the role of citrate in the crystallization kinetics of amorphous calcium carbonate (ACC) is essential to explain the formation mechanisms, stabilities, surface properties, and morphologies of CaCO3 biominerals. It also contributes to deeper insight into fluid-mineral inte...

  14. Relaxation and crystallization of amorphous carbamazepine studied by terahertz pulsed spectroscopy

    DEFF Research Database (Denmark)

    Zeitler, J Axel; Taday, Philip F; Pepper, Michael;

    2007-01-01

    At the example of carbamazepine the crystallization of a small organic molecule from its amorphous phase was studied using in situ variable temperature terahertz pulsed spectroscopy (TPS). Even though terahertz spectra of disordered materials in the glassy state exhibit no distinct spectral featu...

  15. Evidence of eutectic crystallization and transient nucleation in Al89La6Ni5 amorphous alloy

    DEFF Research Database (Denmark)

    Zhuang, Yanxin; Jiang, Jianzhong; Lin, Z. G.;

    2001-01-01

    The phase evolution with the temperature and time in the process of crystallization of Al89La6Ni5 amorphous alloy has been investigated by in situ high-temperature and high-pressure x-ray powder diffraction using synchrotron radiation. Two crystalline phases, fcc-Al and a metastable bcc-(AlNi)(11...

  16. Molecular relaxation behavior and isothermal crystallization above glass transition temperature of amorphous hesperetin.

    Science.gov (United States)

    Shete, Ganesh; Khomane, Kailas S; Bansal, Arvind Kumar

    2014-01-01

    The purpose of this paper was to investigate the relaxation behavior of amorphous hesperetin (HRN), using dielectric spectroscopy, and assessment of its crystallization kinetics above glass transition temperature (Tg ). Amorphous HRN exhibited both local (β-) and global (α-) relaxations. β-Relaxation was observed below Tg , whereas α-relaxation prominently emerged above Tg . β-Relaxation was found to be of Johari-Goldstein type and was correlated with α-process by coupling model. Secondly, isothermal crystallization experiments were performed at 363 K (Tg + 16.5 K), 373 K (Tg + 26.5 K), and 383 K (Tg + 36.5 K). The kinetics of crystallization, obtained from the normalized dielectric strength, was modeled using the Avrami model. Havriliak-Negami (HN) shape parameters, αHN and αHN .βHN , were analyzed during the course of crystallization to understand the dynamics of amorphous phase during the emergence of crystallites. HN shape parameters indicated that long range (α-like) were motions affected to a greater extent than short range (β-like) motions during isothermal crystallization studies at all temperature conditions. The variable behavior of α-like motions at different isothermal crystallization temperatures was attributed to evolving crystallites with time and increase in electrical conductivity with temperature.

  17. Growth model of lantern-like amorphous silicon oxide nanowires

    Science.gov (United States)

    Wu, Ping; Zou, Xingquan; Chi, Lingfei; Li, Qiang; Xiao, Tan

    2007-03-01

    Silicon oxide nanowire assemblies with lantern-like morphology were synthesized by thermal evaporation of the mixed powder of SnO2 and active carbon at 1000 °C and using the silicon wafer as substrate and source. The nano-lanterns were characterized by a scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), energy-dispersive spectroscope (EDS) and selective area electron diffraction (SAED). The results show that the nano-lantern has symmetrical morphology, with one end connecting with the silicon wafer and the other end being the tin ball. The diameter of the nano-lantern is about 1.5-3.0 µm. Arc silicon oxide nanowire assemblies between the two ends have diameters ranging from 70 to 150 nm. One single catalyst tin ball catalyzes more than one amorphous nanowires' growth. In addition, the growth mechanism of the nano-lantern is discussed and a growth model is proposed. The multi-nucleation sites round the Sn droplet's perimeter are responsible for the formation of many SiOx nanowires. The growing direction of the nanowires is not in the same direction of the movement of the catalyst tin ball, resulting in the bending of the nanowires and forming the lantern-like silicon oxide morphology. The controllable synthesis of the lantern-like silicon oxide nanostructure may have potential applications in the photoelectronic devices field.

  18. Growth model of lantern-like amorphous silicon oxide nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Wu Ping; Zou Xingquan; Chi Lingfei; Li Qiang; Xiao Tan [Department of Physics, Shantou University, Shantou 515063 (China)

    2007-03-28

    Silicon oxide nanowire assemblies with lantern-like morphology were synthesized by thermal evaporation of the mixed powder of SnO{sub 2} and active carbon at 1000 deg. C and using the silicon wafer as substrate and source. The nano-lanterns were characterized by a scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), energy-dispersive spectroscope (EDS) and selective area electron diffraction (SAED). The results show that the nano-lantern has symmetrical morphology, with one end connecting with the silicon wafer and the other end being the tin ball. The diameter of the nano-lantern is about 1.5-3.0 {mu}m. Arc silicon oxide nanowire assemblies between the two ends have diameters ranging from 70 to 150 nm. One single catalyst tin ball catalyzes more than one amorphous nanowires' growth. In addition, the growth mechanism of the nano-lantern is discussed and a growth model is proposed. The multi-nucleation sites round the Sn droplet's perimeter are responsible for the formation of many SiO{sub x} nanowires. The growing direction of the nanowires is not in the same direction of the movement of the catalyst tin ball, resulting in the bending of the nanowires and forming the lantern-like silicon oxide morphology. The controllable synthesis of the lantern-like silicon oxide nanostructure may have potential applications in the photoelectronic devices field.

  19. Ultrafast characterization of phase-change material crystallization properties in the melt-quenched amorphous phase.

    Science.gov (United States)

    Jeyasingh, Rakesh; Fong, Scott W; Lee, Jaeho; Li, Zijian; Chang, Kuo-Wei; Mantegazza, Davide; Asheghi, Mehdi; Goodson, Kenneth E; Wong, H-S Philip

    2014-06-11

    Phase change materials are widely considered for application in nonvolatile memories because of their ability to achieve phase transformation in the nanosecond time scale. However, the knowledge of fast crystallization dynamics in these materials is limited because of the lack of fast and accurate temperature control methods. In this work, we have developed an experimental methodology that enables ultrafast characterization of phase-change dynamics on a more technologically relevant melt-quenched amorphous phase using practical device structures. We have extracted the crystallization growth velocity (U) in a functional capped phase change memory (PCM) device over 8 orders of magnitude (10(-10) programmed PCM devices at very high heating rates (>10(8) K/s), which reveals the extreme fragility of Ge2Sb2Te5 in its supercooled liquid phase. Furthermore, these crystallization properties were studied as a function of device programming cycles, and the results show degradation in the cell retention properties due to elemental segregation. The above experiments are enabled by the use of an on-chip fast heater and thermometer called as microthermal stage (MTS) integrated with a vertical phase change memory (PCM) cell. The temperature at the PCM layer can be controlled up to 600 K using MTS and with a thermal time constant of 800 ns, leading to heating rates ∼10(8) K/s that are close to the typical device operating conditions during PCM programming. The MTS allows us to independently control the electrical and thermal aspects of phase transformation (inseparable in a conventional PCM cell) and extract the temperature dependence of key material properties in real PCM devices.

  20. In situ observation of shear-driven amorphization in silicon crystals

    Energy Technology Data Exchange (ETDEWEB)

    He, Yang; Zhong, Li; Fan, Feifei; Wang, Chongmin; Zhu, Ting; Mao, Scott X.

    2016-09-19

    Amorphous materials have attracted great interest in the scientific and technological fields. An amorphous solid usually forms under the externally driven conditions of melt-quenching, irradiation and severe mechanical deformation. However, its dynamic formation process remains elusive. Here we report the in situ atomic-scale observation of dynamic amorphization processes during mechanical straining of nanoscale silicon crystals by high resolution transmission electron microscopy (HRTEM). We observe the shear-driven amorphization (SDA) occurring in a dominant shear band. The SDA involves a sequence of processes starting with the shear-induced diamond-cubic to diamond-hexagonal phase transition that is followed by dislocation nucleation and accumulation in the newly formed phase, leading to the formation of amorphous silicon. The SDA formation through diamond-hexagonal phase is rationalized by its structural conformity with the order in the paracrystalline amorphous silicon, which maybe widely applied to diamond-cubic materials. Besides, the activation of SDA is orientation-dependent through the competition between full dislocation nucleation and partial gliding.

  1. Crystal growth of various ruthenates

    Energy Technology Data Exchange (ETDEWEB)

    Kunkemoeller, Stefan; Braden, Markus [II. Physikalisches Institut, Universitaet zu Koeln (Germany); Nugroho, Agung [Institut Teknologi Bandung (Indonesia)

    2013-07-01

    Ruthenates of the Ruddlesdon-Popper series exhibit a variety of interesting phenomena ranging from unconventional superconductivity to orbitally polarized Mott insulators. Unfortunately the crystal growth of most of these ruthenates is extremely difficult partially due to the high evaporation of ruthenium; this strongly limits the research on these fascinating materials. We have started to grow single crystals of layered and perovskite ruthenates by the travelling floating-zone method using a Canon SC1-MDH mirror furnace. For the layered Ca{sub 2-x}Sr{sub x}RuO{sub 4} series we focused first on the range of concentration where recent My-SR experiments reveal spin-density wave ordering to occur at relatively high temperature and with a sizeable ordered moment. Good quality crystals of Ca{sub 1.5}Sr{sub 0.5}RuO{sub 4} can be obtained, when an excess of 15 percent of ruthenium is added to the initial preparation of the rod and when a high growth speed up to 40mm/h is used. Even slight modifications of the growing conditions result in large amounts of (Sr/Ca)RuO{sub 3} and (Sr/Ca){sub 3}Ru{sub 2}O{sub 7} intergrowth phases. First attempts to grow perovskite and double-layered ruthenates are discussed as well.

  2. Annealing crystallization and catalytic activity of ultrafine NiB amorphous alloy

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Annealing crystallization of ultrafine NiB amorphous alloy prepared by the chemical reduction method was studied by DTA,XRD and XAFS techniques. The XRD and XAFS results have revealed that the crystallization process of ultrafine NiB amorphous alloy proceeds in two steps. First,ultrafine NiB amorphous alloy is crystallized to form metastable nanocrystalline Ni3B at an annealing temperature of 325℃. Second,the nanocrystalline Ni3B is further decom-posed into crystalline Ni at 380℃ or higher tempera ture,the local structure around Ni atoms in resultant product is similar to that in Ni foil. It was found that the catalytic ac-tivity of nanocrystalline Ni3B for benzene hydrogenation is much higher than that of ultrafine NiB amorphous alloy or crystalline Ni. The result indicates that the active sites of nanocrystalline Ni3B for benzene hydrogenation are com-posed of both Ni and B with proper geometry configuration.

  3. Correlation Between Superheated Liquid Fragility And Onset Temperature Of Crystallization For Al-Based Amorphous Alloys

    Directory of Open Access Journals (Sweden)

    Guo J.

    2015-06-01

    Full Text Available Amorphous alloys or metallic glasses have attracted significant interest in the materials science and engineering communities due to their unique physical, mechanical, and chemical properties. The viscous flow of amorphous alloys exhibiting high strain rate sensitivity and homogeneous deformation is considered to be an important characteristic in thermoplastic forming processes performed within the supercooled liquid region because it allows superplastic-like deformation behavior. Here, the correlation between the superheated liquid fragility, and the onset temperature of crystallization for Al-based alloys, is investigated. The activation energy for viscous flow of the liquid is also investigated. There is a negative correlation between the parameter of superheated liquid fragility and the onset temperature of crystallization in the same Al-based alloy system. The activation energy decreases as the onset temperature of crystallization increases. This indicates that the stability of a superheated liquid can affect the thermal stability of the amorphous alloy. It also means that a liquid with a large superheated liquid fragility, when rapidly solidified, forms an amorphous alloy with a low thermal stability.

  4. Hydrogen gas permeation through amorphous and partially crystallized Fe40Ni38Mo4B18

    Directory of Open Access Journals (Sweden)

    Rafaella Martins Ribeiro

    2012-10-01

    Full Text Available Samples of amorphous and partially crystallized Fe40Ni38Mo4B18 alloy were submitted to hydrogen gas permeation from 523 to 643 K. The hydrogen permeation curves exhibited a single sigmoidal shape, typical of tests where no hydride formation occurs. It was observed that the hydrogen diffusivity increases for the amorphous samples and partially crystallized alloy with the temperature increase. The hydrogen diffusion coefficient as a function of temperature was found to be D = 5.1 ± 0.5 × 10-12 exp (-11.0 ± 3.5/RT (m².s-1 for amorphous condition and D = 3.6 ± 0.5 × 10-11 exp (-19.8 ± 3.3/RT (m².s-1 for the partially crystallized condition. This suggests that the annihilation of defects in the amorphous structure and the crystalline phase precipitate contributes to the increase of the hydrogen diffusion.

  5. Kinetics of glass transition and crystallization in multicomponent bulk amorphous alloys

    Institute of Scientific and Technical Information of China (English)

    庄艳歆[1; 赵德乾[2; 张勇[3; 汪卫华[4; 潘明祥[5

    2000-01-01

    Differential scanning calorimeter (DSC) is used to investigate apparent activation energy of glass transition and crystallization of Zr-based bulk amorphous alloys by Kissinger equation under non-isothermal condition. It is shown that the glass transition behavior as well as crystallization reaction depends on the heating rate and has a characteristic of kinetic effects. After being isothermally annealed near glass transition temperature, the apparent activation energy of glass transition increases and the apparent activation energy of crystallization reaction decreases. However, the kinetic effects are independent of the pre-annealing.

  6. Introduction to crystal growth and characterization

    CERN Document Server

    Benz, Klaus-Werner

    2014-01-01

    This new textbook provides for the first time a comprehensive treatment of the basics of contemporary crystallography and crystal growth in a single volume. The reader will be familiarized with the concepts for the description of morphological and structural symmetry of crystals. The architecture of crystal structures of selected inorganic and molecular crystals is illustrated. The main crystallographic databases as data sources of crystal structures are described. Nucleation processes, their kinetics and main growth mechanism will be introduced in fundamentals of crystal growth. Some phase d

  7. Impact of polymers on the crystallization and phase transition kinetics of amorphous nifedipine during dissolution in aqueous media.

    Science.gov (United States)

    Raina, Shweta A; Alonzo, David E; Zhang, Geoff G Z; Gao, Yi; Taylor, Lynne S

    2014-10-06

    The commercial and clinical success of amorphous solid dispersions (ASD) in overcoming the low bioavailability of poorly soluble molecules has generated momentum among pharmaceutical scientists to advance the fundamental understanding of these complex systems. A major limitation of these formulations stems from the propensity of amorphous solids to crystallize upon exposure to aqueous media. This study was specifically focused on developing analytical techniques to evaluate the impact of polymers on the crystallization behavior during dissolution, which is critical in designing effective amorphous formulations. In the study, the crystallization and polymorphic conversions of a model compound, nifedipine, were explored in the absence and presence of polyvinylpyrrolidone (PVP), hydroxypropylmethyl cellulose (HPMC), and HPMC-acetate succinate (HPMC-AS). A combination of analytical approaches including Raman spectroscopy, polarized light microscopy, and chemometric techniques such as multivariate curve resolution (MCR) were used to evaluate the kinetics of crystallization and polymorphic transitions as well as to identify the primary route of crystallization, i.e., whether crystallization took place in the dissolving solid matrix or from the supersaturated solutions generated during dissolution. Pure amorphous nifedipine, when exposed to aqueous media, was found to crystallize rapidly from the amorphous matrix, even when polymers were present in the dissolution medium. Matrix crystallization was avoided when amorphous solid dispersions were prepared, however, crystallization from the solution phase was rapid. MCR was found to be an excellent data processing technique to deconvolute the complex phase transition behavior of nifedipine.

  8. CW laser induced crystallization of thin amorphous silicon films deposited by EBE and PECVD

    Energy Technology Data Exchange (ETDEWEB)

    Said-Bacar, Z., E-mail: zabardjade@yahoo.fr [InESS (UMR 7163 CNRS-UDS), 23 rue de Loess, 67037 Strasbourg Cedex 2 (France); Prathap, P. [InESS (UMR 7163 CNRS-UDS), 23 rue de Loess, 67037 Strasbourg Cedex 2 (France); Cayron, C. [CEA, LITEN, DEHT, Minatec, 17 rue des Martyrs, 38054 Cedex 9 (France); Mermet, F. [IREPA LASER, Pole API - Parc d' Innovation, 67400 Illkirch (France); Leroy, Y.; Antoni, F.; Slaoui, A.; Fogarassy, E. [InESS (UMR 7163 CNRS-UDS), 23 rue de Loess, 67037 Strasbourg Cedex 2 (France)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer The effect of hydrogen in CW laser crystallization of hydrogenated amorphous silicon thin films has been investigated. Black-Right-Pointing-Pointer Large hydrogen content results in decohesion of the films due to hydrogen effusion. Black-Right-Pointing-Pointer Very low hydrogen content or hydrogen free amorphous silicon film are suitable for crystallization induced by CW laser. Black-Right-Pointing-Pointer Grains of size between 20 and 100 {mu}m in width and about 200 {mu}m in long in scanning direction are obtained with these latter films. - Abstract: This work presents the Continuous Wave (CW) laser crystallization of thin amorphous silicon (a-Si) films deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) and by Electron Beam Evaporation (EBE) on low cost glass substrate. The films are characterized by Elastic Recoil Detection Analysis (ERDA) and by Fourier-Transform Infrared (FTIR) spectroscopy to evaluate the hydrogen content. Analysis shows that the PECVD films contain a high hydrogen concentration ({approx}10 at.%) while the EBE films are almost hydrogen-free. It is found that the hydrogen is in a bonding configuration with the a-Si network and in a free form, requiring a long thermal annealing for exodiffusion before the laser treatment to avoid explosive effusion. The CW laser crystallization process of the amorphous silicon films was operated in liquid phase regime. We show by Electron Backscatter Diffraction (EBSD) that polysilicon films with large grains can be obtained with EBE as well as for the PECVD amorphous silicon provided that for the latest the hydrogen content is lower than 2 at.%.

  9. Pressure-Reduction Technique for Crystal Growth

    Science.gov (United States)

    Shlichta, P. J.

    1981-01-01

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

  10. Crystallization of bulk samples of partially amorphous spray-dried lactose.

    Science.gov (United States)

    Darcy, P; Buckton, G

    1998-11-01

    The crystallization of partially amorphous spray-dried lactose was studied as a function of sample size. Crystallization occurred gradually over a period of 80 hr for a 95-g sample. The water content during crystallization was lower than that needed to cause crystallization if it had been distributed evenly throughout the bed, thus the absorbed water must have been unevenly distributed. The weight of the sample continued to change for days after crystallization was completed, because of the slow desorption of condensed water and the very slow formation of the hydrate form. Surprisingly, all samples with a weight between 42 and 95 g were found to take up the same mass (not percent) of water at the same time. This provides further evidence that the water was not evenly distributed throughout the sample. Water loss after this peak differed in the different weight samples, with the largest weights resulting in the lowest residual weight after 2 weeks. Only the sample of 22 g load had a different peak weight and a much lower weight loss after crystallization. This study provides detail of how partially amorphous bulk samples crystallize.

  11. Enhanced proton conductivity of niobium phosphates by interfacing crystal grains with an amorphous functional phase

    DEFF Research Database (Denmark)

    Huang, Yunjie; Yu, Lele; Li, Haiyan

    2016-01-01

    Niobium phosphate is an interesting proton conductor operational in the intermediate temperature range. In the present work two forms of phosphates were prepared: an amorphous one with high specific area and a crystalline one with low specific surface area. Both phosphates exhibited very low proton...... conductivities. An activation process was developed to convert the phosphates into crystal grains with a phosphorus rich amorphous phase along the grain boundaries. As a result, the obtained niobium phosphates showed considerably enhanced and stable proton conductivities. The activation effect was prominent when...... the high surface area amorphous phosphate was used as the precursor. At 250 °C thus obtained niobium phosphate showed a high and stable conductivity of 0.03 S cm−1 under dry atmosphere and of 0.06 S cm−1 at a water partial pressure of 0.12 atm....

  12. Epitaxial crystallization and nucleation during MeV-ion beam processing of amorphous GaAs surface layers

    Energy Technology Data Exchange (ETDEWEB)

    Bachmann, T. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Glaser, E. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Schulz, R. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Kaiser, U. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Safran, G. [Research Institute for Technical Physics, P.O. Box 76, H-1325 Budapest (Hungary)

    1996-06-01

    <100> -GaAs wafers were preamorphized in a thin surface layer using 50 keV {sup 14}N{sup +}-ions. Ion beam induced epitaxial crystallization (IBIEC) and interfacial amorphization (IBIIA) were studied as a function of the target temperature using MeV Ar{sup +}- or Kr{sup +}-ions. Backscattering experiments and electron microscopy show that the IBIEC process is stopped above a critical irradiation temperature due to enhanced ion beam induced nucleation and growth of crystallites. At a fixed dose an optimum irradiation temperature for IBIEC was found, at which the recrystallized layer thickness has a maximum and crystallite formation is negligible. This offers the possibility to crystallize much larger layer thicknesses than {approx}65 nm which stands for the maximum value reported up to now. (orig.).

  13. Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of SnI{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Liu, H.; Tse, J. S., E-mail: john.tse@usask.ca [Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B2 (Canada); Hu, M. Y.; Bi, W.; Zhao, J.; Alp, E. E. [Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois 60439 (United States); Pasternak, M. [School of Physics and Astronomy, Tel Aviv University, Ramat Aviv (Israel); Taylor, R. D.; Lashley, J. C. [Los Alamos National Laboratory, PO Box 1663 Bikini Atoll Road, Los Alamos, New Mexico 87545 (United States)

    2015-10-28

    The pressure-induced amorphization and subsequent recrystallization of SnI{sub 4} have been investigated using first principles molecular dynamics calculations together with high-pressure {sup 119}Sn nuclear resonant inelastic x-ray scattering measurements. Above ∼8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ∼64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI{sub 4} under ambient conditions. Although high pressure structures of SnI{sub 4} were thought to be determined by random packing of equal-sized spheres, we detected electron charge transfer in each phase. This charge transfer results in a crystal structure packing determined by larger than expected iodine atoms.

  14. Crystallization in Fe- and Co-Based Amorphous Alloys Studied by In-Situ X-Ray Diffraction

    Science.gov (United States)

    Zhang, L. J.; Yu, P. F.; Cheng, H.; Zhang, M. D.; Liu, D. J.; Zhou, Z.; Jin, Q.; Liaw, P. K.; Li, G.; Liu, R. P.

    2016-12-01

    The amorphous alloys, Fe80Si20, Fe78Si9B13, and Fe4Co67Mo1.5Si16.5B11, were prepared by the spinning method in pure argon. The crystallization behaviors of the three amorphous alloys were researched by in-situ X-ray diffraction (XRD), and the crystallization activation energy was calculated, based on the results of differential scanning calorimetry. The crystallization mechanism of the Fe- and Co-based alloys was analyzed, based on the experimental data. The transformation kinetics was described in terms of Johnson-Mehl-Avrami kinetics, except that the Avrami exponent of the Fe78Si9B13 amorphous alloy annealed at 753 K (480 °C) was 4.12; the obtained values for the overall Avrami exponents of the other three amorphous alloys were below 1, as usually found for the Fe-Si amorphous alloys.

  15. Controlled growth of semiconductor crystals

    Science.gov (United States)

    Bourret-Courchesne, Edith D.

    1992-01-01

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

  16. Assessing the re-crystallization behaviour of amorphous lactose using the RH-perfusion cell.

    Science.gov (United States)

    Timmermann, Inga-Lis; Steckel, Hartwig; Trunk, Michael

    2006-08-01

    Many different reports have studied the crystallization behaviour of lactose, e.g., by exposing samples of amorphous lactose to different relative humidity at constant temperatures. However, only few reports are available investigating the formation of alpha-lactose monohydrate and beta-lactose during re-crystallization. Applying the static ampoule method in the microcalorimeter, the enthalpies of amorphous lactose were reported to be constantly 32 and 48 J/g, respectively, considering the mutarotation of lactose at 25 degrees C and 58% RH, 75% RH and 100% RH. In this study, an alternative microcalorimetric technique, the relative humidity-perfusion cell (RH-perfusion cell) was chosen. The RH-perfusion cell is able to deliver a constant and controlled flow of humidified air to the sample. Investigated compounds were purely amorphous lactose and different powder mixtures of lactose. They consisted of alpha-lactose monohydrate (Pharmatose 325M), beta-lactose (Pharmatose DCL21) or a combination (1:1) thereof as carriers, and different concentrations of amorphous lactose. The determination of the enthalpy of desorption of the just re-crystallization lactose by the RH-perfusion cell was used to discriminate whether the monohydrate or the anhydrous form of lactose was produced. Differences in the re-crystallization behaviour of lactose at 25 degrees C and 58-100% RH were found. At 60-80% RH purely amorphous lactose showed a high heat of desorption which can be attributed to a very high content of formed beta-lactose. Powder mixtures containing high contents of amorphous lactose (8% and 15%, respectively) blended with alpha-lactose monohydrate as a carrier resulted in similar results at the same RH ranges. The high amount of beta-lactose can be due to the equilibrium anomeric composition. Whereas powder mixtures containing beta-lactose as a carrier and amorphous lactose in a concentration of 1%, 8% and 15%, respectively, formed less beta-lactose than the mixtures

  17. Coordination polyhedron growth mechanism model and growth habit of crystals

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A new growth mechanism model, coordination polyhedron growth mechanism model, is introduced from the angle of the coordination of anion and cation to each other at the interface. It is pointed out that the force driving the growth unit to enter the crystal lattice is the electrostatic attraction force between ions, whose relative size can be approximately measured by the electrostatic bond strength (EBS) that reaches a nearest neighbor anion (or cation) in the parent phase from a cation (or anion) at the interface. The growth habits of NaCl, ZnS, CaF2 and CsI crystals are discussed, and a new growth habit rule is proposed as follows. When the growth rate of a crystal is determined by the step generation rate, the growth habit of this crystal is related to the coordination number of the ion with the smallest coordination rate at the interface of various crystal faces. The smaller the coordination number of the ion at the interface, the faster the growth rate of corresponding crystal face. When the growth of a crystal depends on the step movement rate, the growth habit of this crystal is related to the density of the ion with the smallest coordination rate at the interface of various crystal faces. The smaller the densities of the ion at the interface is, the faster the growth rate of corresponding crystal face will be.

  18. 2.5 D Transrotational Microcrystals and Nanostructures Revealed by TEM in Crystallizing Amorphous Films

    Science.gov (United States)

    Kolosov, Vladimir

    2015-03-01

    Unexpected transrotational microcrystals can be grown in thin 10-100 nm amorphous films. Crystals of different morphology (from nanowhiskers to spherulites, complex textures) and chemical nature (oxides, chalcogenides, metals and alloys) grown in thin films prepared by various methods are studied by transmission electron microscopy (TEM). We use primarily our TEM bend-contour method and SAED (HREM, AFM are also performed). The phenomenon resides in strong (up to 300 degrees/ μm) regular internal bending of crystal lattice planes in a growing crystal. It can be traced inside TEM in situ. Usual translation is complicated by slight regular rotation of the crystal unit cell (transrotation) most prominent at the mesoscale. Different geometries of transrotation of positive and negative curvature are revealed. Transrotational crystal resembles ideal single crystal enclosed in a curved space. It can be also considered similar to hypothetical endless 2.5 D analogy of MW nanotube/nano-onion halves. Transrotation is strongly increasing as the film gets thinner in the range 100-15 nm. Transrotations supplement dislocations and disclinations. New transrotational nanocrystalline model of amorphous state is proposed. Support of Ministry of Higher Education and Science is acknowledged.

  19. High hydrogen dilution and low substrate temperature cause columnar growth of hydrogenated amorphous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Bronsveld, Paula C.P.; Rath, Jatindra K.; Schropp, Ruud E.I. [Debye Institute for Nanomaterials Science, Nanophotonics - Physics of Devices, Utrecht University, P.O. Box 80000, 3508 TA Utrecht (Netherlands); Mates, Tomas; Fejfar, Antonin; Kocka, Jan [Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, 162 53 Praha 6 (Czech Republic)

    2010-03-15

    Columnar growth was observed in the amorphous part of mixed phase layers deposited at very low substrate temperatures. The width of the columns and the layer thickness at which they are first distinguishable in a cross-sectional transmission electron microscope (X-TEM) image, about 120 nm, is similar for the substrate temperature range of 40-100 C, but the columns are less well developed when either the substrate temperature is increased or the dilution ratio is lowered. This growth behaviour and the incubation layer are attributed to hydrogen-induced surface diffusion of growth precursors resulting in an amorphous-amorphous roughness transition. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  20. Induced crystallization of amorphous biosilica to cristobalite by silicatein.

    Science.gov (United States)

    Fuchs, Ido; Aluma, Yaniv; Ilan, Micha; Mastai, Yitzhak

    2014-02-27

    In nature it is known that silicatein (silica protein) controls the mineralization of a wide range of biosilicas. In this paper we present our results on the induced crystallization of biosilica to cristobalite, which is the thermodynamically most stable crystalline form of silica at a relatively low temperature and ambient pressure. The phase transformation of biosilica from marine sponges to cristobalite under thermal treatment was investigated by a variety of methods, e.g., X-ray diffraction, high-resolution electron microscopy-electron diffraction, and optical methods such as Fourier transform infrared (FTIR) spectroscopy. Our results show that biosilica from marine sponges exhibits a direct phase transformation to cristobalite structure at a relatively low temperature (850 °C). Furthermore, it is shown that porous silica templated with silicatein proteins extracted from sponges also exhibits a phase transformation to cristobalite structure at a relatively low temperature. The surprising discovery that silicatein filaments can induce direct crystallization of biosilica to cristobalite highlights the role of silicatein in governing the synthesis and the hierarchical structure control of biosilica minerals.

  1. A positron source using an axially oriented crystal associated to a granular amorphous converter

    CERN Document Server

    Xu, Cheng-Hai; Sievers, Peter; Artru, Xavier; Chevallier, Michel; Dadoun, Olivier; Pei, Guo-Xi; Strakhovenko, Vladimir M; Variola, Alessandro

    2012-01-01

    A non-conventional positron source using the intense l radiation from an axially oriented monocrystal which materializes into e(+)e(-') pairs in a granular amorphous converter is described. The enhancement of photon radiation by multi-GeV electrons crossing a tungsten crystal along its axis is reported. The resulting enhancement of pair production in an amorphous converter placed 2 meters downstream, is also reported. Sweeping off the charged particles from the crystal by a bending magnet upstream of the converter allows a significant reduction of the deposited energy density. Substituting a granular target made of small spheres for the usual compact one, makes the energy dissipation easier. The deposited energy and corresponding heating are analyzed and solutions for cooling are proposed. The configurations studied here for this kind of positron source allow its consideration for unpolarized positrons for the ILC.

  2. Crystallization of amorphous silicon by self-propagation of nanoengineered thermites

    Science.gov (United States)

    Hossain, Maruf; Subramanian, Senthil; Bhattacharya, Shantanu; Gao, Yuanfang; Apperson, Steve; Shende, Rajesh; Guha, Suchi; Arif, Mohammad; Bai, Mengjun; Gangopadhyay, Keshab; Gangopadhyay, Shubhra

    2007-03-01

    Crystallization of amorphous silicon (a-Si) thin film occurred by the self-propagation of copper oxide/aluminum thermite nanocomposites. Amorphous Si films were prepared on glass at a temperature of 250°C by plasma enhanced chemical vapor deposition. The platinum heater was patterned on the edge of the substrate and the CuO /Al nanoengineered thermite was spin coated on the substrate that connects the heater and the a-Si film. A voltage source was used to ignite the thermites followed by a piranha solution (4:1 of H2SO4:H2O2) etch for the removal of residual products of thermite reaction. Raman spectroscopy was used to confirm the crystallization of a-Si.

  3. A positron source using an axially oriented crystal associated to a granular amorphous converter

    Institute of Scientific and Technical Information of China (English)

    XU Cheng-Hai; Robert Chehab; Peter Sievers; Xavier Artru; Michel Chevallier; Olivier Dadoun; PEI Guo-Xi; Vladimir M. Strakhovenko; Alessandro Variola

    2012-01-01

    A non-conventional positron source using the intense γ radiation from an axially oriented monocrystal which materializes into e+e- pairs in a granular amorphous converter is described.The enhancement of photon radiation by multi-GeV electrons crossing a tungsten crystal along its 〈111〉 axis is reported.The resulting enhancement of pair production in an amorphous converter placed 2 meters downstream,is also reported.Sweeping off the charged particles from the crystal by a bending magnet upstream of the converter allows a significant reduction of the deposited energy density.Substituting a granular target made of small spheres for the usual compact one,makes the energy dissipation easier.The deposited energy and corresponding heating are analyzed and solutions for cooling are proposed.The configurations studied here for this kind of positron source allow its consideration for unpolarized positrons for the ILC.

  4. A TEM study on the crystallization of amorphous Fe 73Si 3B 24 alloys

    Science.gov (United States)

    Lijun, Wu; Lihua, Zhao; Wangyu, Hu; Lingling, Wang; Juemin, Xiao

    1994-02-01

    The crystallization of Fe 73Si 3B 24 amorphous alloys has been studied by transmission electron microscopy (TEM). A metastable phase P has been found and determined by a double tilting method in TEM. This phase belongs to a primitive tetragonal lattice with a = 0.62 nm and c = 1.43 nm. Its probable space group is P4nc or P4/mnc. In the Fe 2B phase, we found threefold twins which are rotated 120° around the [ overline1 1 0] axis. The crystallization process of this alloy is suggested to be Amorphous→Amorphous + α-Fe(Si) + Fe 3B + P → α-Fe(Si) + Fe 3B + Fe 2B → α-Fe(Si) + Fe 2B.

  5. Measurements of Protein Crystal Face Growth Rates

    Science.gov (United States)

    Gorti, S.

    2014-01-01

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

  6. Polar Growth Habit of KABO Crystal

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The polar growth habit of KABO crystal was discussed by the growth-units model of anionic coordination-polyhedra (ACP), and the relationship between stabilities of incorporation of those growth-units into various group faces and their corresponding morphologies was studied. It is put forward that the growth interface of crystal will be concave when negative plane is used as growth interface. Concave growth interface is very unfavorable for the quality of the crystal, because it is unsuitable for the transfer of the latent heat and impurities released during the deposition.

  7. Hydrogen related crystallization in intrinsic hydrogenated amorphous silicon films prepared by reactive radiofrequency magnetron sputtering at low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Senouci, D. [Laboratoire de Genie Physique, Universite Ibn-Khaldoun, 14000 Tiaret (Algeria); LPCMME, Departement de Physique, Universite d' Oran Es-senia, 3100, Oran (Algeria); Baghdad, R., E-mail: r_baghdad@mail.univ-tiaret.dz [Laboratoire de Genie Physique, Universite Ibn-Khaldoun, 14000 Tiaret (Algeria); Belfedal, A.; Chahed, L. [LPCMME, Departement de Physique, Universite d' Oran Es-senia, 3100, Oran (Algeria); Portier, X. [CIMAP, CEA, CNRS UMR 6252-ENSICAEN, UCBN, 6 Bvd Marechal Juin, 14050 Caen Cedex (France); Charvet, S. [LPMC, UFR des Sciences, Universite de Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens (France); Kim, K.H. [LPICM, Laboratoire de Physique des Interfaces et Couches Minces, CNRS UMR 7647, Ecole Polytechnique, 91128 Palaiseau (France); TOTAL S.A., Gas and Power, R and D Division, Courbevoie (France); Roca i Cabarrocas, P. [LPICM, Laboratoire de Physique des Interfaces et Couches Minces, CNRS UMR 7647, Ecole Polytechnique, 91128 Palaiseau (France); Zellama, K. [LPMC, UFR des Sciences, Universite de Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens (France)

    2012-11-01

    We present an investigation on the transition from amorphous to nanocrystalline silicon and associated hydrogen changes during the first steps of hydrogenated nanocrystalline silicon growth for films elaborated by reactive radiofrequency magnetron sputtering at a substrate temperature as low as room temperature and for deposition times varying from 3 to 60 min. Complementary experimental techniques have been used to characterize the films in their as-deposited state. They are completed by thermal hydrogen effusion experiments conducted in the temperature range, from room temperature to 800 Degree-Sign C. The results show that, during the initial stages of growth, the presence of a hydrogen-rich layer is necessary to initiate the crystallization process. - Highlights: Black-Right-Pointing-Pointer Nanocrystalline silicon growth at room temperature. Black-Right-Pointing-Pointer Transition from amorphous to nanocrystalline silicon. Black-Right-Pointing-Pointer Chemical reactions of H atoms with strained Si-Si bonds. Black-Right-Pointing-Pointer H selective etching and chemical transport caused the silicon nucleation.

  8. The model of solid phase crystallization of amorphous silicon under elastic stress

    OpenAIRE

    2000-01-01

    Solid phase crystallization of an amorphous silicon (a-Si) film stressed by a Si3N4 cap was studied by laser Raman spectroscopy. The a-Si films were deposited on Si3N4 (50 nm)/Si(100) substrate by rf sputtering. The stress in an a-Si film was controlled by thickness of a Si3N4 cap layer. The Si3N4 films were also deposited by rf sputtering. It was observed that the crystallization was affected by the stress in a-Si films introduced by the Si3N4 cap layer. The study suggests that the elastic s...

  9. The features of CNT growth on catalyst-content amorphous alloy layer by CVD-method

    Science.gov (United States)

    Dubkov, S.; Bulyarskii, S.; Pavlov, A.; Trifonov, A.; Kitsyuk, E.; Mierczynski, P.; Maniecki, T.; Ciesielski, R.; Gavrilov, S.; Gromov, D.

    2016-12-01

    This work is devoted to the CVD-synthesis of arrays of carbon nanotubes (CNTs) on Co-Zr-N-(O), Ni-Nb-N-(O), Co- Ta-N-(O) catalytic alloy films from gas mixture of C2H2+NH3+Ar at a substrate temperature of about 550°C.Heating of the amorphous alloy causes its crystallization and squeezing of the catalytic metal onto the surface. As a result, small catalyst particles are formed on the surface. The CNT growth takes place after wards on these particles. It should be noted that the growth of CNT arrays on these alloys is insensitive to the thickness of alloy film, which makes this approach technically attractive. In particular, the possibility of local CNT growth at the ends of the Co-Ta-N-(O) film and three-level CNT growth at the end of more complex structure SiO2/Ni-Nb-N-O/SiO2/Ni-Nb-N-O/SiO2/Ni-Nb-N-O/SiO2 is demonstrated.

  10. Collective relaxation dynamics and crystallization kinetics of the amorphous Biclotymol antiseptic.

    Science.gov (United States)

    Tripathi, Pragya; Romanini, Michela; Tamarit, Josep Lluis; Macovez, Roberto

    2015-11-10

    We employ dielectric spectroscopy to monitor the relaxation dynamics and crystallization kinetics of the Biclotymol antiseptic in its amorphous phase. The glass transition temperature of the material as determined by dielectric spectroscopy is Tg = 290 ± 1K. The primary (α) relaxation dynamics is observed to follow a Vogel-Fulcher-Tammann temperature dependence, with a kinetic fragility index m = 86 ± 13, which classifies Biclotymol as a relatively fragile glass former. A secondary relaxation is also observed, corresponding to an intramolecular dynamic process of the non-rigid Biclotymol molecule. The crystallization kinetics, measured at four different temperatures above the glass transition temperature, follows an Avrami behavior with exponent virtually equal to n = 2, indicating one-dimensional crystallization into needle-like crystallites, as experimentally observed, with a time-constant nucleation rate. The activation barrier for crystallization is found to be Ea = 115 ± 22 kJ mol(-1).

  11. Economic analysis of crystal growth in space

    Science.gov (United States)

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

    1972-01-01

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

  12. Crystal Shape Evolution in Detached Bridgman Growth

    Science.gov (United States)

    Volz, M. P.; Mazuruk, K.

    2013-01-01

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

  13. Crystallization kinetics of amorphous lactose, whey-permeate and whey powders.

    Science.gov (United States)

    Ibach, Alexander; Kind, Matthias

    2007-07-23

    Amorphous lactose, whey-permeate and whey powders have been converted to their crystalline forms by exposure to air at various temperatures and relative humidities. The total time required for sorption, induction and crystallization of these powders was observed by following the time-dependent mass change of the powders during treatment. These experiments have shown that higher temperatures and relative humidities lead to shorter crystallization times. Lactose crystallizes within 1 min at an air temperature of 100 degrees C and relative air humidity of 80%, whereas whey-permeate and whey powders requires up to 5 min at the same set of conditions. Thus, as previously described, the presence of proteins and salts in the whey-permeate and whey powders reduces the crystallization rate. The rate constants and activation energies have been determined over a range of temperatures and humidities to enable the calculation of crystallization times for the design of an industrial process that crystallizes whey and whey-permeate powders. Finally, the crystallization rates found in this work are sufficiently fast to be applicable in an industrial process that crystallizes whey and whey-permeate powders.

  14. Crystallization and X-ray diffraction of spray-dried and freeze-dried amorphous lactose.

    Science.gov (United States)

    Haque, Md Kamrul; Roos, Yrjö H

    2005-02-07

    Crystallization of spray-dried and freeze-dried amorphous lactose over different relative vapor pressures (RVP) and storage times was studied. Crystallization was observed from increasing peak intensities in X-ray diffraction patterns. Lactose was crystallized in the samples stored at RVP of 44.1% and above in both types of dehydrated powders. The rate of crystallization increased with increasing RVP and storage time. Similar crystallization behavior of both spray-dried and freeze-dried lactose was observed. Lactose crystallized as alpha-lactose monohydrate, anhydrous beta-lactose, and the anhydrous form of alpha- and beta-lactose in a molar ratio of 5:3 and 4:1 in both spray-dried and freeze-dried forms. Peak intensities of X-ray diffraction patterns for anhydrous beta-lactose were decreased, and for alpha-lactose monohydrate increased with increasing storage RVP and time. The crystallization data were successfully modeled using Avrami equation at RVP of 54.5% and above. The crystallization data obtained is helpful in understanding and predicting storage stability of lactose-containing food and pharmaceutical products.

  15. Crystal growth as an excitable medium.

    Science.gov (United States)

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

    2012-06-28

    Crystal growth has been widely studied for many years, and, since the pioneering work of Burton, Cabrera and Frank, spirals and target patterns on the crystal surface have been understood as forms of tangential crystal growth mediated by defects and by two-dimensional nucleation. Similar spirals and target patterns are ubiquitous in physical systems describable as excitable media. Here, we demonstrate that this is not merely a superficial resemblance, that the physics of crystal growth can be set within the framework of an excitable medium, and that appreciating this correspondence may prove useful to both fields. Apart from solid crystals, we discuss how our model applies to the biomaterial nacre, formed by layer growth of a biological liquid crystal.

  16. Aluminium-induced crystallization of amorphous silicon films deposited by DC magnetron sputtering on glasses

    Energy Technology Data Exchange (ETDEWEB)

    Kezzoula, F., E-mail: kezzoula@usa.com [UDTS 2Bd Frantz Fanon 7 merveilles Algiers (Algeria); Laboratory of Materials, Mineral and Composite (LMMC), Boumerdes University (Algeria); Hammouda, A. [UPR CNRS 3079 CEMHTI - 1D Avenue de la Recherche Scientifique, 45071 Orleans Cedex 2 (France); Equipe Couches Minces, Laboratoire de Physique des Materiaux, Faculte de Physique, USTHB, Algiers (Algeria); Universite d' Orleans, 45067 Orleans Cedex 2 (France); Kechouane, M. [Equipe Couches Minces, Laboratoire de Physique des Materiaux, Faculte de Physique, USTHB, Algiers (Algeria); Simon, P. [UPR CNRS 3079 CEMHTI - 1D Avenue de la Recherche Scientifique, 45071 Orleans Cedex 2 (France); Universite d' Orleans, 45067 Orleans Cedex 2 (France); Abaidia, S.E.H. [Laboratory of Materials, Mineral and Composite (LMMC), Boumerdes University (Algeria); Keffous, A. [UDTS 2Bd Frantz Fanon 7 merveilles Algiers (Algeria); Cherfi, R. [Equipe Couches Minces, Laboratoire de Physique des Materiaux, Faculte de Physique, USTHB, Algiers (Algeria); Menari, H.; Manseri, A. [UDTS 2Bd Frantz Fanon 7 merveilles Algiers (Algeria)

    2011-09-15

    Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) films were deposited by DC magnetron sputtering technique with argon and hydrogen plasma mixture on Al deposited by thermal evaporation on glass substrates. The a-Si/Al and a-Si:H/Al thin films were annealed at different temperatures ranging from 250 to 550 deg. C during 4 h in vacuum-sealed bulb. The effects of annealing temperature on optical, structural and morphological properties of as-grown as well as the vacuum-annealed a-Si/Al and a-Si:H/Al thin films are presented in this contribution. The averaged transmittance of a-Si:H/Al film increases upon increasing the annealing temperature. XRD measurements clearly evidence that crystallization is initiated at 450 deg. C. The number and intensity of diffraction peaks appearing in the diffraction patterns are more important in a-Si:H/Al than that in a-Si/Al layers. Results show that a-Si:H films deposited on Al/glass crystallize above 450 deg. C and present better crystallization than the a-Si layers. The presence of hydrogen induces an improvement of structural properties of poly-Si prepared by aluminium-induced crystallization (AIC).

  17. Crystallization kinetics of an amorphous Co77Si11.5B11.5 alloy

    Directory of Open Access Journals (Sweden)

    R. Nowosielski

    2006-04-01

    Full Text Available Purpose: This paper describes crystallization kinetics and changes magnetic properties involved by process of crystallization Co-Si-B amorphous alloy.Design/methodology/approach: The following experimental techniques were used: X-ray diffraction (XRD, electrical resistivity in situ measurements (four-point probe static and dynamic measurements of magnetic properties (magnetic balance, fluxmeter, Maxwell-Wien bridge.Findings: In this work has been performed influence of thermal annealing on crystallization kinetics and magnetic properties amorphous Co77Si11.5B11.5 alloy.Practical implications: The attractive properties of Co-Si-B alloy are of special interest for basic research on the materials as well as for their potential applications, like magnetic sensors. The Co soft magnetic material is used in noise filters, saturable reactors, miniature inductance elements for abating spike noise, mains transformers, choke coils, zero-phase current transformers, and magnetic heads etc., i.e., devices which are expected to exhibit high levels of permeability at high frequencies.Originality/value: It has been shown that thermal annealing at temperature close to the crystallization temperature leads to a significant increase of the initial magnetic permeability.

  18. Origin of “memory glass” effect in pressure-amorphized rare-earth molybdate single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Willinger, Elena, E-mail: kudrenko@fhi-berlin.mpg.de [Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka (Russian Federation); Fritz-Haber Institute of the Max Planck Society, 14195 Berlin (Germany); Sinitsyn, Vitaly; Khasanov, Salavat; Redkin, Boris; Shmurak, Semeon; Ponyatovsky, Eugeny [Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka (Russian Federation)

    2015-02-15

    The memory glass effect (MGE) describes the ability of some materials to recover the initial structure and crystallographic orientation after pressure-induced amorphization (PIA). In spite of numerous studies the nature and underlying mechanisms of this phenomenon are still not clear. Here we report investigations of MGE in β′-Eu{sub 2}(MoO{sub 4}){sub 3} single crystal samples subjected to high pressure amorphization. Using the XRD and TEM techniques we carried out detailed analysis of the structural state of high pressure treated single crystal samples as well as structural transformations due to subsequent annealing at atmospheric pressure. The structure of the sample has been found to be complex, mainly amorphous, however, the amorphous medium contains evenly distributed nanosize inclusions of a paracrystalline phase. The inclusions are highly correlated in orientation and act as “memory units” in the MGE. - Graphical abstract: Schematic representation of pressure-induced amorphization and “memory glass” effect in rare-earth molybdate single crystals. The XRD and TEM measurements have revealed the presence of the residual identically oriented paracrystalline nanodomains in the pressure-amorphized state. These domains preserve the information about initial structure and orientation of the sample. They act as memory units and crystalline seeds during transformation of the amorphous phase back to the starting single crystalline one. - Highlights: • Pressure-amorphized Eu{sub 2}(MoO4){sub 3} single crystals were studied ex-situ by XRD and TEM. • Tiny residual crystalline inclusions were found in amorphous matrix of sample. • The inclusions keep in memory the parent crystal structure and orientation. • The inclusions account for “memory glass” effect in rare-earth molibdates.

  19. Polymeric Amorphous Solid Dispersions: A Review of Amorphization, Crystallization, Stabilization, Solid-State Characterization, and Aqueous Solubilization of Biopharmaceutical Classification System Class II Drugs.

    Science.gov (United States)

    Baghel, Shrawan; Cathcart, Helen; O'Reilly, Niall J

    2016-09-01

    Poor water solubility of many drugs has emerged as one of the major challenges in the pharmaceutical world. Polymer-based amorphous solid dispersions have been considered as the major advancement in overcoming limited aqueous solubility and oral absorption issues. The principle drawback of this approach is that they can lack necessary stability and revert to the crystalline form on storage. Significant upfront development is, therefore, required to generate stable amorphous formulations. A thorough understanding of the processes occurring at a molecular level is imperative for the rational design of amorphous solid dispersion products. This review attempts to address the critical molecular and thermodynamic aspects governing the physicochemical properties of such systems. A brief introduction to Biopharmaceutical Classification System, solid dispersions, glass transition, and solubility advantage of amorphous drugs is provided. The objective of this review is to weigh the current understanding of solid dispersion chemistry and to critically review the theoretical, technical, and molecular aspects of solid dispersions (amorphization and crystallization) and potential advantage of polymers (stabilization and solubilization) as inert, hydrophilic, pharmaceutical carrier matrices. In addition, different preformulation tools for the rational selection of polymers, state-of-the-art techniques for preparation and characterization of polymeric amorphous solid dispersions, and drug supersaturation in gastric media are also discussed.

  20. Growth induced magnetic anisotropy in crystalline and amorphous thin films

    Energy Technology Data Exchange (ETDEWEB)

    Hellman, F.

    1998-07-20

    The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and Ni-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials. A brief summary of work done in each area is given.

  1. Transport and Growth Kinetics in Microgravity Protein Crystal Growth

    Science.gov (United States)

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

    2002-01-01

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

  2. Growth of single crystals of BaFe12O19 by solid state crystal growth

    Science.gov (United States)

    Fisher, John G.; Sun, Hengyang; Kook, Young-Geun; Kim, Joon-Seong; Le, Phan Gia

    2016-10-01

    Single crystals of BaFe12O19 are grown for the first time by solid state crystal growth. Seed crystals of BaFe12O19 are buried in BaFe12O19+1 wt% BaCO3 powder, which are then pressed into pellets containing the seed crystals. During sintering, single crystals of BaFe12O19 up to ∼130 μm thick in the c-axis direction grow on the seed crystals by consuming grains from the surrounding polycrystalline matrix. Scanning electron microscopy-energy dispersive spectroscopy analysis shows that the single crystal and the surrounding polycrystalline matrix have the same chemical composition. Micro-Raman scattering shows the single crystal to have the BaFe12O19 structure. The optimum growth temperature is found to be 1200 °C. The single crystal growth behavior is explained using the mixed control theory of grain growth.

  3. Temperature- and moisture-induced crystallization of amorphous lactose in composite particles with sodium alginate prepared by spray-drying.

    Science.gov (United States)

    Takeuchi, H; Yasuji, T; Yamamoto, H; Kawashima, Y

    2000-01-01

    The purpose of this study was to investigate the temperature- and moisture-induced crystallization of amorphous lactose in the composite particles prepared by spray-drying an aqueous solution of crystalline lactose and sodium alginate. The temperature-induced crystallization of amorphous lactose in the composite particles was suppressed by increasing the amount of sodium alginate in the particles. The stabilizing effect of sodium alginate on amorphous lactose in the composite particles was greater than that in physical mixtures having the same formulating ratios. The improved stability of amorphous lactose in the composite particles was attributed to an increase in the glass transition temperature (Tg) of the mixture. Moisture-induced crystallization of amorphous lactose was also retarded by increasing the amount of sodium alginate in composite particles. Although the Tg of the mixture was reduced by increasing the water content of the particles, the values were higher than that of 100% amorphous lactose when particles of the same water content were compared. The change in the Tg of the composite particles with increasing water content was interpreted as involving three components of the Gordon-Taylor equation. In the amorphous lactose-sodium alginate systems, the Tg values of the composite particles containing sodium alginate were higher than the theoretical line predicted by two components of the Gordon-Taylor equation. These results suggested that there was a specific interaction between the sodium alginate and lactose molecules. This specific interaction was suggested by the fact that only very little amorphous lactose was measured in the spray-dried composite particles stored under humid conditions using differential scanning calorimetry. This molecular interaction may also be partly responsible for the suppression of both the temperature- and moisture-induced crystallization of amorphous lactose in the composite particles.

  4. Promotion of protein crystal growth by actively switching crystal growth mode via femtosecond laser ablation

    Science.gov (United States)

    Tominaga, Yusuke; Maruyama, Mihoko; Yoshimura, Masashi; Koizumi, Haruhiko; Tachibana, Masaru; Sugiyama, Shigeru; Adachi, Hiroaki; Tsukamoto, Katsuo; Matsumura, Hiroyoshi; Takano, Kazufumi; Murakami, Satoshi; Inoue, Tsuyoshi; Yoshikawa, Hiroshi Y.; Mori, Yusuke

    2016-11-01

    Large single crystals with desirable shapes are essential for various scientific and industrial fields, such as X-ray/neutron crystallography and crystalline devices. However, in the case of proteins the production of such crystals is particularly challenging, despite the efforts devoted to optimization of the environmental, chemical and physical parameters. Here we report an innovative approach for promoting the growth of protein crystals by directly modifying the local crystal structure via femtosecond laser ablation. We demonstrate that protein crystals with surfaces that are locally etched (several micrometers in diameter) by femtosecond laser ablation show enhanced growth rates without losing crystal quality. Optical phase-sensitive microscopy and X-ray topography imaging techniques reveal that the local etching induces spiral growth, which is energetically advantageous compared with the spontaneous two-dimensional nucleation growth mode. These findings prove that femtosecond laser ablation can actively switch the crystal growth mode, offering flexible control over the size and shape of protein crystals.

  5. Effects of impurities on crystal growth in fructose crystallization

    Science.gov (United States)

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

    1989-10-01

    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.

  6. Growth of organic crystals via attachment and transformation of nanoscopic precursors

    Science.gov (United States)

    Jiang, Yuan; Kellermeier, Matthias; Gebaue, Denis; Lu, Zihao; Rosenberg, Rose; Moise, Adrian; Przybylski, Michael; Cölfen, Helmut

    2017-06-01

    A key requirement for the understanding of crystal growth is to detect how new layers form and grow at the nanoscale. Multistage crystallization pathways involving liquid-like, amorphous or metastable crystalline precursors have been predicted by theoretical work and have been observed experimentally. Nevertheless, there is no clear evidence that any of these precursors can also be relevant for the growth of crystals of organic compounds. Herein, we present a new growth mode for crystals of DL-glutamic acid monohydrate that proceeds through the attachment of preformed nanoscopic species from solution, their subsequent decrease in height at the surface and final transformation into crystalline 2D nuclei that eventually build new molecular layers by further monomer incorporation. This alternative mechanism provides a direct proof for the existence of multistage pathways in the crystallization of molecular compounds and the relevance of precursor units larger than the monomeric constituents in the actual stage of growth.

  7. Amorphous to crystal conversion as a mechanism governing the structure of luminescent YVO4:Eu nanoparticles.

    Science.gov (United States)

    Fleury, Blaise; Neouze, Marie-Alexandra; Guigner, Jean-Michel; Menguy, Nicolas; Spalla, Olivier; Gacoin, Thierry; Carriere, David

    2014-03-25

    The development of functional materials by taking advantage of the physical properties of nanoparticles needs an optimal control over their size and crystal quality. In this context, the synthesis of crystalline oxide nanoparticles in water at room temperature is a versatile and industrially appealing process but lacks control especially for "large" nanoparticles (>30 nm), which commonly consist of agglomerates of smaller crystalline primary grains. Improvement of these syntheses is hampered by the lack of knowledge on possible intermediate, noncrystalline stages, although their critical importance has already been outlined in crystallization processes. Here, we show that during the synthesis of luminescent Eu-doped YVO4 nanoparticles a transient amorphous network forms with a two-level structuration. These two prestructuration scales constrain topologically the nucleation of the nanometer-sized crystalline primary grains and their aggregation in nanoparticles, respectively. This template effect not only clarifies why the crystal size is found independent of the nucleation rate, in contradiction with the classical nucleation models, but also supports the possibility to control the final nanostructure with the amorphous phase.

  8. Kinetics of crystallization of a Fe-based multicomponent amorphous alloy

    Indian Academy of Sciences (India)

    Arun Pratap; T Lilly Shanker Rao; Kinnary Patel; Mukesh Chawda

    2009-10-01

    The Fe-based multicomponent amorphous alloys (also referred to as metallic glasses) are known to exhibit soft magnetic properties and, it makes them important for many technological applications. However, metallic glasses are in a thermodynamically metastable state and in case of high temperature operating conditions, the thermally activated crystallization would be detrimental to their magnetic properties. The study of crystallization kinetics of metallic glasses gives useful insight about its thermal stability. In the present work, crystallization study of Fe67Co18B14Si1 (2605CO) metallic glass has been carried out using differential scanning calorimetry (DSC) technique. Mössbauer study has also been undertaken to know the phases formed during the crystallization process. The alloy shows two-stage crystallization. The activation energy has been derived using the Kissinger method. It is found to be equal to 220 kJ/mol and 349 kJ/mol for the first and second crystallization peaks, respectively. The Mössbauer study indicates the formation of -(Fe, Co) and (Fe, Co)3B phases in the alloy.

  9. Crystallization study of amorphous sputtered NiTi bi-layer thin film

    Energy Technology Data Exchange (ETDEWEB)

    Mohri, Maryam, E-mail: mmohri@ut.ac.ir [School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe (Germany); Nili-Ahmadabadi, Mahmoud [School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Center of Excellence for High Performance Materials, University of Tehran, Tehran (Iran, Islamic Republic of); Chakravadhanula, Venkata Sai Kiran [Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe (Germany)

    2015-05-15

    The crystallization of Ni-rich/NiTiCu bi-layer thin film deposited by magnetron sputtering from two separate alloy targets was investigated. To achieve the shape memory effect, the NiTi thin films deposited at room temperature with amorphous structure were annealed at 773 K for 15, 30, and 60 min for crystallization. Characterization of the films was carried out by differential scanning calorimetry to indicate the crystallization temperature, grazing incidence X-ray diffraction to identify the phase structures, atomic force microscopy to evaluate surface morphology, scanning transmission electron microscopy to study the cross section of the thin films. The results show that the structure of the annealed thin films strongly depends on the temperature and time of the annealing. Crystalline grains nucleated first at the surface and then grew inward to form columnar grains. Furthermore, the crystallization behavior was markedly affected by composition variations. - Highlights: • A developed bi-layer Ni45TiCu5/Ni50.8Ti was deposited on Si substrate and crystallized. • During crystallization, The Ni{sub 45}TiCu{sub 5} layer is thermally less stable than the Ni-rich layer. • The activation energy is 302 and 464 kJ/mol for Cu-rich and Ni-rich layer in bi-layer, respectively.

  10. Amorphous solid dispersions and nano-crystal technologies for poorly water-soluble drug delivery.

    Science.gov (United States)

    Brough, Chris; Williams, R O

    2013-08-30

    Poor water-solubility is a common characteristic of drug candidates in pharmaceutical development pipelines today. Various processes have been developed to increase the solubility, dissolution rate and bioavailability of these active ingredients belonging to BCS II and IV classifications. Over the last decade, nano-crystal delivery forms and amorphous solid dispersions have become well established in commercially available products and industry literature. This article is a comparative analysis of these two methodologies primarily for orally delivered medicaments. The thermodynamic and kinetic theories relative to these technologies are presented along with marketed product evaluations and a survey of commercial relevant scientific literature.

  11. Nanoscale order and crystallization in nitrogen-alloyed amorphous GeTe

    Energy Technology Data Exchange (ETDEWEB)

    Darmawikarta, Kristof; Abelson, John R., E-mail: abelson@illinois.edu [Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 W. Green St., Urbana, Illinois 61801 (United States); Coordinated Science Laboratory, University of Illinois at Urbana-Champaign, 1308 W. Main St., Urbana, Illinois 61801 (United States); Raoux, Simone [IBM T. J. Watson Research Center, 1101 Kitchawan Road, Route 134, Yorktown Heights, New York 10598 (United States); Bishop, Stephen G. [Coordinated Science Laboratory, University of Illinois at Urbana-Champaign, 1308 W. Main St., Urbana, Illinois 61801 (United States); Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 1406 W. Green St., Urbana, Illinois 61801 (United States)

    2014-11-10

    The nanoscale order in amorphous GeTe thin films is measured using fluctuation transmission electron microscopy (FTEM). The order increases upon annealing at 145 °C, which indicates a coarsening of subcritical nuclei. This correlates with a reduction in the nucleation delay time in laser crystallization. A shift in the FTEM peak positions may indicate a transformation in local bonding. In samples alloyed with 12 at. % nitrogen, the order does not change upon annealing, the peak does not shift, and the nucleation time is longer. The FTEM data indicate that nitrogen suppresses the structural evolution necessary for the nucleation process and increases the thermal stability of the material.

  12. Growth, characterisation and electronic applications of amorphous hydrogenated carbon

    CERN Document Server

    Paul, S

    2000-01-01

    temperature on GaAs, has been studied and concluded to be satisfactory on the basis of good adherence and low leakage currents. Such a structure was motivated by the applicability in Metal Insulator Semiconductor Field Effect Transistors (MISFET). My thesis proposes solutions to a number of riddles associated with the material, hydrogenated amorphous carbon, (a-C:H). This material has lately generated interest in the electronic engineering community, owing to some remarkable properties. The characterisation of amorphous carbon films, grown by radio frequency plasma enhanced chemical vapour deposition has been reported. The coexistence of multiple phases in the same a-C:H film manifests itself in the inconsistent electrical behaviour of different parts of the film, thus rendering it difficult to predict the nature of films. For the first time, in this thesis, a reliable prediction of Schottky contact formation on a-C:H films is reported. A novel and simple development on a Scanning Electron Microscope, configu...

  13. Time-resolved synchrotron x-ray diffraction studies of the crystallization of amorphous Co(80-x)FexB₂₀

    Energy Technology Data Exchange (ETDEWEB)

    Simmons, L. M., E-mail: l.simmons@mmu.ac.uk [Division of Electrical and Electronic Engineering, School of Engineering, Manchester Metropolitan University, Manchester M1 5GD (United Kingdom); Greig, D. [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom); Lucas, C. A. [Oliver Lodge Laboratory, Department of Physics, University of Liverpool, Liverpool L69 7ZE (United Kingdom); Kilcoyne, S. H. [School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH (United Kingdom)

    2014-09-28

    This paper addresses the time-dependent crystallization process occurring in “bulk” amorphous Co(80-x)FexB₂₀ (x = 20, 40) metallic ribbons by means of synchrotron x-ray diffraction (SXRD) and transmission electron microscopy. Metallic ribbons, produced via melt-spinning technique, were annealed in-situ, with SXRD patterns collected every 60 s. SXRD reveals that Co₄₀Fe₄₀B₂₀ alloys crystallize from an amorphous structure to a primary bcc α-(Co,Fe) phase, whereas Co₆₀Fe₂₀B₂₀ initially crystallizes into the same bcc α-(Co,Fe) but exhibits cooperative growth of both stable and metastable boride phases later into the hold. Johnson-Mehl-Avrami-Kolmogorov statistics was used on post annealed samples to determine the mechanisms of growth and the activation energy (Ea) of the α-(Co,Fe) phase. Results indicate that the growth mechanisms are similar for both alloy compositions for all annealing temperatures, with the Avrami exponent of n = 1.51(1) and 2.02(6) for x = 20 and 40, respectively, suggesting one-dimensional growth, with a decreasing nucleation rate. Activation energy for α-(Co,Fe) was determined to be 2.7(1) eV and 2.4(3) eV in x = 20 and 40, respectively, suggesting that those alloys with a lower Co content have a stronger resistance to crystallization. Based on these results, fabrication of CoFeB magnetic tunnel junctions via depositing amorphous layers and subsequently annealing to induce lattice matching presents itself as a viable and efficient method, for increasing the giant magnetoresistance in magnetic tunnel junctions.

  14. Photographic appraisal of crystal lattice growth technique

    Directory of Open Access Journals (Sweden)

    Kapoor D

    2005-01-01

    Full Text Available Concept of creating mechanical retention for bonding through crystal growth has been successfully achieved in the present study. By using polyacrylic acid, sulphated with sulphuric acid as etchant, abundant crystal growth was demonstrated. Keeping in view the obvious benefits of crystal growth technique, the present SEM study was aimed to observe and compare the changes brought about by different etching agents (phosphoric acid, polyacrylic acid and polyacrylic acid sulphated and to evaluate their advantages and disadvantages in an attempt to reduce iatrogenic trauma caused due to surface enamel alteration. Control and experimental groups were made of 24 and 30 premolars, respectively, for scanning electron microscopic appraisal of normal unetched and etched enamel surface and fracture site and finished surface evaluation. When compared with conventional phosphoric acid and weaker polyacrylic acid, investigations indicated that crystal growth treatment on enamel surface caused minimal iatrogenic trauma and surface alteration were restored to the original untreated condition to a large extent.

  15. Illusory spirals and loops in crystal growth.

    Science.gov (United States)

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

    2013-10-22

    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.

  16. The Growth of Large Single Crystals.

    Science.gov (United States)

    Baer, Carl D.

    1990-01-01

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

  17. The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite.

    Science.gov (United States)

    Rodriguez-Blanco, Juan Diego; Shaw, Samuel; Benning, Liane G

    2011-01-01

    The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range of environmentally relevant temperatures (7.5-25 °C) using synchrotron-based in situ time-resolved Energy Dispersive X-ray Diffraction (ED-XRD) in conjunction with high-resolution electron microscopy, ex situ X-ray diffraction and infrared spectroscopy. The crystallization process occurs in two stages; firstly, the particles of ACC rapidly dehydrate and crystallize to form individual particles of vaterite; secondly, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate controlled by the surface area of calcite. The second stage of the reaction is approximately 10 times slower than the first. Activation energies of calcite nucleation and crystallization are 73±10 and 66±2 kJ mol(-1), respectively. A model to calculate the degree of calcite crystallization from ACC at environmentally relevant temperatures (7.5-40 °C) is also presented.

  18. Crystal growth and structural analysis of zirconium sulphoselenide single crystals

    Indian Academy of Sciences (India)

    K R Patel; R D Vaidya; M S Dave; S G Patel

    2008-08-01

    A series of zirconium sulphoselenide (ZrSSe3–, where = 0, 0.5, 1, 1.5, 2, 2.5, 3) single crystals have been grown by chemical vapour transport technique using iodine as a transporting agent. The optimum condition for the growth of these crystals is given. The stoichiometry of the grown crystals were confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and the structural characterization was accomplished by X-ray diffraction (XRD) studies. The crystals are found to possess monoclinic structure. The lattice parameters, volume, particle size and X-ray density have been carried out for these crystals. The effect of sulphur proportion on the lattice parameter, unit cell volume and X-ray density in the series of ZrSSe3– single crystals have been studied and found to decrease in all these parameters with rise in sulphur proportion. The grown crystals were examined under optical zoom microscope for their surface topography study. Hall effect measurements were carried out on grown crystals at room temperature. The negative value of Hall coefficient implies that these crystals are -type in nature. The conductivity is found to decrease with increase of sulphur content in the ZrSSe3– series. The electrical resistivity parallel to c-axis as well as perpendicular to -axis have been carried out in the temperature range 303–423 K. The results obtained are discussed in detail.

  19. Vapor Crystal Growth (VCG) experiment Cell

    Science.gov (United States)

    1992-01-01

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

  20. Technology of gallium nitride crystal growth

    CERN Document Server

    Ehrentraut, Dirk; Bockowski, Michal

    2010-01-01

    This book deals with the important technological aspects of the growth of GaN single crystals by HVPE, MOCVD, ammonothermal and flux methods for the purpose of free-standing GaN wafer production. Leading experts from industry and academia report in a very comprehensive way on the current state-of-the-art of the growth technologies and optical and structural properties of the GaN crystals are compared.

  1. On growth rate hysteresis and catastrophic crystal growth

    Science.gov (United States)

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

    2013-04-01

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

  2. Crystallization Kinetics of Amorphous In44Sb20Te36 Phase-Change Optical Recording Films on a Nanosecond Scale

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xue-Ru; WUTTIG Mattias

    2004-01-01

    @@ We propose a simple method to investigate the crystallization kinetics of amorphous In44Sb20 Te36 films on a nanosecond scale, based on local reflectivity measurements of the nanosecond laser-induced crystallization using a static tester. The pulse condition in terms of laser power and pulse width required for the onset of crystallization is established. Applying this pulse condition and Kissinger's analysis, an activation energy of 0. 57 eV is estimated for the crystallization. This value deviates substantially from the activation energy determined at lower sample temperatures where crystallization proceeds in a time scale of seconds rather than nanoseconds.

  3. Crystallization and thermal fatigue of ZrTiCuNiBe bulk amorphous alloys heated by laser pulses

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The crystallization and thermal fatigue behavior of Zr41Ti14Cu12.5Ni10Be22.5 bulk amorphous alloys heated by laser pulses was investigated. The results showed that crystallization occurred even below the crystallization temperature Tx in a low cycle time. Cracks appearred before or after crystallization of the heated area in the sample. The crystallization degree increased with the heating temperature and cycles. An increase in the fatigue cracks number was also observed. The plastic deformation in the heated area of the sample surface occurred, and became more pronounced with cycles and heating temperature.

  4. Historical aspects of crystal growth technology

    Science.gov (United States)

    Scheel, Hans J.

    2000-04-01

    The father of crystal fabrication technology is A. Verneuil with his flame-fusion growth method 1902. His principles of nucleation and growth control are adapted in most later growth methods from melt. The Czochralski method was essentially developed by Teal, Little and Dash. The multidisciplinary nature of crystal growth and epitaxy technology and the complex multiparameter processes, and also the scaling problem, have impeded the scientific development of this important area. Only recently it was possible to solve the striation problem and to understand the control of epitaxial growth modes for achieving structurally perfect layers of GaAs and high- Tc superconductors with atomically flat surfaces. The formation of crystal growth and epitaxy engineers and scientists as well as centers of excellence are necessary in order to develop crystal and epilayer fabrication technologies required for development of highest-efficiency white light-emitting diodes and photovoltaic solar cells for energy-saving lighting and as alternative source of energy. Also laser-fusion energy and other high technologies have to wait for progress in crystal growth technology.

  5. Pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} on amorphous dielectric layers towards monolithic 3D photonic integration

    Energy Technology Data Exchange (ETDEWEB)

    Li, Haofeng; Brouillet, Jeremy; Wang, Xiaoxin; Liu, Jifeng, E-mail: Jifeng.Liu@dartmouth.edu [Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755 (United States)

    2014-11-17

    We demonstrate pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} crystallized on amorphous layers at <450 °C towards 3D Si photonic integration. We developed two approaches to seed the lateral single crystal growth: (1) utilize the Gibbs-Thomson eutectic temperature depression at the tip of an amorphous GeSn nanotaper for selective nucleation; (2) laser-induced nucleation at one end of a GeSn strip. Either way, the crystallized Ge{sub 0.89}Sn{sub 0.11} is dominated by a single grain >18 μm long that forms optoelectronically benign twin boundaries with others grains. These pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} patterns are suitable for monolithic 3D integration of active photonic devices on Si.

  6. Crystal Growth Behaviors of Silicon during Melt Growth Processes

    Directory of Open Access Journals (Sweden)

    Kozo Fujiwara

    2012-01-01

    Full Text Available It is imperative to improve the crystal quality of Si multicrystal ingots grown by casting because they are widely used for solar cells in the present and will probably expand their use in the future. Fine control of macro- and microstructures, grain size, grain orientation, grain boundaries, dislocation/subgrain boundaries, and impurities, in a Si multicrystal ingot, is therefore necessary. Understanding crystal growth mechanisms in melt growth processes is thus crucial for developing a good technology for producing high-quality Si multicrystal ingots for solar cells. In this review, crystal growth mechanisms involving the morphological transformation of the crystal-melt interface, grain boundary formation, parallel-twin formation, and faceted dendrite growth are discussed on the basis of the experimental results of in situ observations.

  7. INTERFACIAL MASS TRANSPORT IN OXIDE CRYSTAL GROWTH

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    @@ A space high temperature in situobservation instrument (SHITISOI) is dedicated to visualize and record the whole growth process of oxide crystal in high temperature melts and solutions. Model experiments using transparent liquids such as KNbO3,Li2B4O7+KNbO3 were chosen to investigate effects of interracial mass transport in oxide crystal growth. For the scaling of the coupled velocity, heat and concentration fields in KNbO3 crystal growth, a rotating crystal growth process was performed and the widths of interfacial concentration, heat and momentum transition zones (The "boundary layers") are obtained, which are 7.5×10-a, 8.6×10-2 and 4.4×10-1 cm,respectively. Hence one can expect that interfacial concentration gradient will be confined to a narrow layer and in region of major concentration change at the in terface. In order to study a mechanism based on the interfacial mass transport resulting from hydrodynamics, the growth of KNbO3 grain in high temperature Li2B4O7 and KNbO3 solutin was studied. The result shows that the pivotal feature in the KNbO3 crystal growth is the initiated by KNbO3 solute surface tension gra dient which is caused by the slow diffusion of KNbO3 solutes. Direct comparison of the model predictions and experimental observed phenomena demonstrate the predictive capability of this model.

  8. Apatite Formation from Amorphous Calcium Phosphate and Mixed Amorphous Calcium Phosphate/Amorphous Calcium Carbonate.

    Science.gov (United States)

    Ibsen, Casper J S; Chernyshov, Dmitry; Birkedal, Henrik

    2016-08-22

    Crystallization from amorphous phases is an emerging pathway for making advanced materials. Biology has made use of amorphous precursor phases for eons and used them to produce structures with remarkable properties. Herein, we show how the design of the amorphous phase greatly influences the nanocrystals formed therefrom. We investigate the transformation of mixed amorphous calcium phosphate/amorphous calcium carbonate phases into bone-like nanocrystalline apatite using in situ synchrotron X-ray diffraction and IR spectroscopy. The speciation of phosphate was controlled by pH to favor HPO4 (2-) . In a carbonate free system, the reaction produces anisotropic apatite crystallites with large aspect ratios. The first formed crystallites are highly calcium deficient and hydrogen phosphate rich, consistent with thin octacalcium phosphate (OCP)-like needles. During growth, the crystallites become increasingly stoichiometric, which indicates that the crystallites grow through addition of near-stoichiometric apatite to the OCP-like initial crystals through a process that involves either crystallite fusion/aggregation or Ostwald ripening. The mixed amorphous phases were found to be more stable against phase transformations, hence, the crystallization was inhibited. The resulting crystallites were smaller and less anisotropic. This is rationalized by the idea that a local phosphate-depletion zone formed around the growing crystal until it was surrounded by amorphous calcium carbonate, which stopped the crystallization.

  9. Convective flow effects on protein crystal growth

    Science.gov (United States)

    Rosenberger, Franz

    1995-01-01

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

  10. On the effect of the amorphous silicon microstructure on the grain size of solid phase crystallized polycrystalline silicon

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Kashish; Branca, Annalisa; Illiberi, Andrea; Creatore, Mariadriana; Sanden, Mauritius C.M. van de [Department of Applied Physics, Eindhoven University of Technology (Netherlands); Tichelaar, Frans D. [Kavli Institute of Nanoscience, Delft University of Technology (Netherlands)

    2011-05-15

    In this paper the effect of the microstructure of remote plasma-deposited amorphous silicon films on the grain size development in polycrystalline silicon upon solid-phase crystallization is reported. The hydrogenated amorphous silicon films are deposited at different microstructure parameter values R* (which represents the distribution of SiH{sub x} bonds in amorphous silicon), at constant hydrogen content. Amorphous silicon films undergo a phase transformation during solid-phase crystallization and the process results in fully (poly-)crystallized films. An increase in amorphous film structural disorder (i.e., an increase in R*), leads to the development of larger grain sizes (in the range of 700-1100 nm). When the microstructure parameter is reduced, the grain size ranges between 100 and 450 nm. These results point to the microstructure parameter having a key role in controlling the grain size of the polycrystalline silicon films and thus the performance of polycrystalline silicon solar cells. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Method for solid state crystal growth

    Science.gov (United States)

    Nolas, George S.; Beekman, Matthew K.

    2013-04-09

    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.

  12. Annealed Crystallization and Catalytic activity of Ultrafine NiB Amorphous Alloy

    Institute of Scientific and Technical Information of China (English)

    WEIShiqing; HUTiandou; 等

    2001-01-01

    A Ultrafine amorphous NiB alloy was prepared via chemical reduction method;Its structures during the crystallizatioin precess was characterized by such techniques as Differential thermal analysis (DTA),X-ray absorption fine structure (XAFS) and X-ray diffraction(XRD),and correlated to the catalytic properties for benzene hydrogenation.It was found that the crystallization of amorphous NiB alloy was carried out in two steps,as indicated by two exothermic peaks centered at 598 and 652K respectively.During the first step.two metastable crystalline phases,i.e.,Ni3B and a noaocrstalline Ni phase(Ni-rich NiB alloy),were formed.Further annealing at higher temperature of 652 K may result in the decomposition of crystalline Ni3B and aggregation of nanocrystalline Ni,the benzene hydrogenation is optimized around the annealing temperature of 623K.It most probably results from the maximum amount of active site on nanocrystalline Ni formed by thermal treatment at appropriate annealing temperature.

  13. Crystallization Process of Heat-treated Amorphous Ni-P Alloy Coating

    Directory of Open Access Journals (Sweden)

    JIN Shi-wei

    2016-09-01

    Full Text Available Amorphous Ni-P alloy coatings were prepared on 45 carbon steel blocks using electrodeposition method. The thermal effect and quality change of Ni-P alloy coating under heating rate of 20℃/min were analyzed by differential scanning calorimetry (DSC and thermogravimetry (TG. Coatings were heat-treated at 300℃ and 400℃ for 0, 15, 30, 45, 60, 75min respectively, coating surface was characterized by scanning electron microscope (SEM, energy dispersive spectrometer (EDS, X-ray diffraction (XRD, microhardness tester. The result shows that the exothermic peak of Ni-P alloy coating appears at 284.8℃, coating quality and elemental composition are stable during the heat treatment. Crystallization process experiences a transformation of amorphous, metastable state NiP and Ni5P2, stable state Ni3P. The microhardness of coating can be improved remarkably after heat treatment, namely, the maximum value of heat-treated coating is 1036.56HV, which is nearly 2 times as hard as as-deposited coating. The corrosion resistance of heat-treated Ni-P alloy coating in NaCl solution is inferior to as-deposited coating, but they are both much better than 45 carbon steel substrate.

  14. Development of an intense positron source using a crystal--amorphous hybrid target for linear colliders

    CERN Document Server

    Uesugi, Y; Chehab, R; Dadoun, O; Furukawa, K; Kamitani, T; Kawada, S; Omori, T; Takahashi, T; Umemori, K; Urakawa, U; Satoh, M; Strakhovenko, V; Suwada, T; Variola, A

    2013-01-01

    In a conventional positron source driven by a few GeV electron beam, a high amount of heat is loaded into a positron converter target to generate intense positrons required by linear colliders, and which would eventually damage the converter target. A hybrid target, composed of a single crystal target as a radiator of intense gamma--rays, and an amorphous converter target placed downstream of the crystal, was proposed as a scheme which could overcome the problem.This paper describes the development of an intense positron source with the hybrid target. A series of experiments on positron generation with the hybrid target has been carried out with a 8--GeV electron beam at the KEKB linac. We observed that positron yield from the hybrid target increased when the incident electron beam was aligned to the crystal axis and exceeded the one from the conventional target with the converter target of the same thickness, when its thickness is less than about 2 radiation length. The measurements in the temperature rise o...

  15. Supersaturation and crystallization: non-equilibrium dynamics of amorphous solid dispersions for oral drug delivery.

    Science.gov (United States)

    Kawakami, Kohsaku

    2017-06-01

    Amorphous solid dispersions (ASDs) are one of the key formulation technologies that aid the development of poorly soluble candidates. However, their dynamic behaviors, including dissolution and crystallization processes, are still full of mystery. Further understanding of these processes should enhance their wider use. Areas covered: The first part of this review describes the current understanding of the dissolution of ASDs, where phase separation behavior is frequently involved and attempts to develop appropriate dissolution tests to achieve an in vitro-in vivo correlation are examined. The second part of this review discusses crystallization of the drug molecule with the eventual aim of establishing an accelerated testing protocol for predicting its physical stability. Expert opinion: The phase separation behavior from the supersaturated state during the dissolution test must be understood, and its relevance to the oral absorption behavior needs to be clarified. Research efforts should focus on the differences between the phase behavior in in vitro and in vivo situations. Initiation time of the crystallization was shown to be predicted only from storage and glass transition temperatures. This finding should encourage the establishment of testing protocol of the physical stability of ASDs.

  16. Stability and plasticizing and crystallization effects of vitamins in amorphous sugar systems.

    Science.gov (United States)

    Zhou, Yankun; Roos, Yrjö H

    2012-02-01

    Increased molecular mobility and structural changes resulting from water plasticization of glassy solids may lead to loss of the entrapped compounds from encapsulant systems. In the present study, the stability of water-soluble vitamins, vitamin B(1) (vB(1), thiamin hydrochloride) and vitamin C (vC, ascorbic acid), in freeze-dried lactose and trehalose at various water activities was studied. Water sorption of lactose-vB(1), lactose-vC, trehalose-vB(1), and trehalose-vC systems was determined gravimetrically. Glass transition and crystallization of anhydrous and plasticized sugar-vitamin systems were determined using thermal analysis. Critical water activity was calculated using water sorption and glass transition data. The retention of the vitamins was measured spectrophotometrically. The results showed that the amorphous structure protected the entrapped vitamins at low a(w). Crystallization of lactose accelerated vitamin degradation, whereas trehalose retained much higher amounts of the vitamins. Glass transition and critical water activity of solids and crystallization of component sugars should be considered in the stabilization of sensitive components.

  17. Laboratory studies of crystal growth in magma

    Science.gov (United States)

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

    2012-12-01

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

  18. Effect of high pressure on microstructure of crystallizing amorphous Nd9Fe85B6 alloy

    Institute of Scientific and Technical Information of China (English)

    WU Wei; LI Hui; XIE Yanwu; ZHANG Xiangyi

    2008-01-01

    The effect of high pressure on the microstructure of annealed amorphous NdgFegsB6 alloy was studied. It was found that applica- tion of high pressure made the microstructure of the crystallized alloy much more homogeneous. The average grain size of the Nd2Fe14B phase decreased with the increase of pressure, whereas, the size of the α-Fe first increased when a pressure of 1 Gpa was applied and then decreased with further increase of pressure. Pressure-induced (410) texture of the Nd2Fe14B phase was also observed. The present study sug-gested an effective route for controlling the microstructure in a nanoscale solid.

  19. Synthesis of bulk nanostructured aluminum containing in situ crystallized amorphous particles

    Science.gov (United States)

    Zhang, Zhihui

    5083 Al containing in situ crystallized Al85Ni10La 5 amorphous particles (10% and 20% in volume fraction) was synthesized through a powder metallurgy route consisting of cold isostatic pressing, degassing and hot extrusion. The nanostructured 5083 Al powders (grain size ˜28 nm) were produced through mechanical milling in liquid nitrogen. The Al 85Ni10La5 powders were produced via gas atomization using helium gas and the fraction in the size range of compressive fracture strength of the as-extruded 10% and 20% Al85Ni10La5 composites were determined to be 1025 MPa and 837 MPa, respectively. The influence of secondary processing, i.e., swaging, following extrusion on the mechanical behavior was also studied. The coarse grain formation in cryomilled 5083 Al during the thermomechanical process was discussed and it was evident that grain rotation and coalescence played an important role in the overall mechanism.

  20. Fe-Zr-Nd-Y-B permanent magnet derived from crystallization of bulk amorphous alloy

    Science.gov (United States)

    Tan, Xiaohua; Xu, Hui; Bai, Qin; Dong, Yuanda

    2007-12-01

    The microstructure and magnetic properties of Nd2Fe14B/(Fe3B,α-Fe) nanocomposite magnet derived form crystallization of bulk amorphous Fe68Zr2Y4B21Nd5 alloy, which was prepared by copper mold casting, have been investigated. The obtaining maximum values of Ms, Mr, Hci, and (BH)max annealed at 963K for Fe68Zr2Nd5Y4B21 alloy are 86Am2/kg, 49Am2/kg, 380kA/m, and 43kJ/m3, respectively. δM plot, high resolution transmission electron microscopy observation, and three-dimensional atom probe technique clarified that the hard magnetic behavior is due to the exchange coupling between soft and hard magnetic nanophases.

  1. The growth of Nd: YAG single crystals

    Directory of Open Access Journals (Sweden)

    ANDREJA VALCIC

    2002-04-01

    Full Text Available Y3Al5O12 doped with 0.8 % wt. Nd (Nd:YAG single crystals were grown by the Czochralski technique under an argon atmosphere. The conditions for growing the Nd: YAG single crystals were calculated by using a combination of Reynolds and Grashof numbers. The critical crystal diameter and the critical rate of rotation were calculated from the hydrodynamics of the melt. The crystal diameter Dc = 1.5 cm remained constant during the crystal growth, while the critical rate of rotation changed from wc = 38 rpm after necking to wc = 13 rpm at the end of the crystal. The value of the rate of crystal growth was experimentally found to be 0.8–1.0 mm/h. According to our previous experiments, it was confirmed that 20 min exposure to conc. H3PO4 at 603 K was suitable for chemical polishing. Also, one-hour exposure to conc. H3PO4 at 493 K was found to be suitable for etching. The lattice parameter a = 1.201 (1 nm was determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

  2. On the effect of the underlying ZnO:Al layer on the crystallization kinetics of hydrogenated amorphous silicon

    NARCIS (Netherlands)

    Sharma, K.; Ponomarev, M. V.; M. C. M. van de Sanden,; Creatore, M.

    2013-01-01

    In this contribution, we analyze the thickness effect of the underlying aluminum doped-zinc oxide (ZnO:Al) layers on the structural properties and crystallization kinetics of hydrogenated amorphous silicon (a-Si:H) thin films. It is shown that the disorder in as-deposited a-Si:H films, as probed by

  3. Biomolecular Modification of Inorganic Crystal Growth

    Energy Technology Data Exchange (ETDEWEB)

    De Yoreo, J J

    2007-04-27

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

  4. Dynamics of interstitial atoms and vacancies during the crystallization of amorphous Si and Ge films by flash lamp annealing

    Science.gov (United States)

    Matsuo, Naoto; Yoshioka, Naoki; Heya, Akira

    2017-08-01

    We examined the dynamics of interstitial atoms and vacancies in amorphous Si (a-Si) and a-Ge films crystallized by flash lamp annealing in consideration of the self-diffusion coefficients of Si and Ge. We found that the interstitial atoms play an important role in the liquid-phase crystallization (LPC) of a-Si films, whereas the vacancies are more important for the solid-phase crystallization (SPC) of a-Si films along with the LPC and SPC of a-Ge films. For Si, the crystal defect density of the film crystallized by LPC was higher than that of the film crystallized by SPC; the opposite result was achieved for Ge. This phenomenon is considered to be attributed to the existence of interstitial atoms introduced in Si. The thermodynamic calculated results related to the relationship between the point defect and SPC or LPC supported the crystallization mechanism.

  5. Impact of surfactants on the crystallization of aqueous suspensions of celecoxib amorphous solid dispersion spray dried particles.

    Science.gov (United States)

    Chen, Jie; Ormes, James D; Higgins, John D; Taylor, Lynne S

    2015-02-02

    Amorphous solid dispersions are frequently prepared by spray drying. It is important that the resultant spray dried particles do not crystallize during formulation, storage, and upon administration. The goal of the current study was to evaluate the impact of surfactants on the crystallization of celecoxib amorphous solid dispersions (ASD), suspended in aqueous media. Solid dispersions of celecoxib with hydroxypropylmethylcellulose acetate succinate were manufactured by spray drying, and aqueous suspensions were prepared by adding the particles to acidified media containing various surfactants. Nucleation induction times were evaluated for celecoxib in the presence and absence of surfactants. The impact of the surfactants on drug and polymer leaching from the solid dispersion particles was also evaluated. Sodium dodecyl sulfate and Polysorbate 80 were found to promote crystallization from the ASD suspensions, while other surfactants including sodium taurocholate and Triton X100 were found to inhibit crystallization. The promotion or inhibition of crystallization was found to be related to the impact of the surfactant on the nucleation behavior of celecoxib, as well as the tendency to promote leaching of the drug from the ASD particle into the suspending medium. It was concluded that surfactant choice is critical to avoid failure of amorphous solid dispersions through crystallization of the drug.

  6. Studies of laser crystal growth. 1. Production of crystal growth furnaces and operating results

    Energy Technology Data Exchange (ETDEWEB)

    Sugiyama, Akira; Sasuga, Tsuneo; Arisawa, Takashi; Takuma, Hiroshi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Anzai, Yutaka; Katsurayama, Masamichi; Yamazaki, Takafumi; Yamagishi, Kiyoshi

    1997-10-01

    Table top short pulse Peta-watt laser system is the most promising light source to drive studying high energy field physics in advance photon research. To achieve high efficiency laser oscillation in stable condition, it is required to pull out the best performance from laser crystals as the gain medium. Therefore, we have conducted cooperative investigation with Mitsui Mining and Smelting Co., LTD. to create large ideal laser crystals by improved growth methods which solve several problems in usual growth techniques. This report describes specifications, results of operation, and improvements in two different types of growth furnaces which make homogeneous doped concentration along growth direction of Nd:YAG laser crystal and large fluoride laser crystals with a wide band gap, respectively. It also describes the first four results of crystals such as YAG, Nd:YAG, YLF, and LBO grown by these furnaces. (author)

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

    Science.gov (United States)

    Mitrovic, Mico M.

    1995-01-01

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

  8. Amorphous nanoshell formed through random growth and related plasmonic behaviors

    Science.gov (United States)

    Wang, Yuwei; Shen, Hongming; He, Yingbo; Cheng, Yuqing; Perriat, Pascal; Martini, Matteo; Tillement, Olivier; Gong, Qihuang; Lu, Guowei

    2014-08-01

    The optical properties of gold nanoshell formed through random growth process were numerically investigated by employing finite-difference time-domain method. The growth process can be divided approximately into four stages according to the optical spectra and 3D morphology. The incomplete nanoshell with surface coverage ratio (R) around 70% was found to form surface ‘hot spots' with high field enhancement, which are useful for surface enhanced Raman scattering. Additionally, high Purcell factor and quantum efficiency at the core center for the nanoshells with R ∼ 90% are suitable for encapsulated fluorescent probe that can exploit the high surface plasmonic enhancement effect.

  9. The growth of sapphire single crystals

    Directory of Open Access Journals (Sweden)

    STEVAN DJURIC

    2001-06-01

    Full Text Available Sapphire (Al2O3 single crystals were grown by the Czochralski technique both in air and argon atmospheres. The conditions for growing sapphire single crystals were calculated by using a combination of Reynolds and Grashof numbers. Acritical crystal diameter dc = 20 mm and the critical rate of rotation wc = 20 rpm were calculated from the hydrodynamics of the melt. The value of the rate of crystal growth was experimentally found to be 3.5 mm/h. According to our previous experiments, it was confirmed that three hours exposures to conc. H3PO4 at 593 K was suitable for chemical polishing. Also, three hours exposure to conc.H3PO4 at 523 K was found to be a suitable etching solution. The lattice parameters a = 0.47573 nm and c = 1.29893 nm were determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

  10. Influence of pulsing current on the glass transition and crystallizing kinetics of a Zr base bulk amorphous alloy

    Institute of Scientific and Technical Information of China (English)

    WU Wenfei; YAO Kefu; ZHAO Zhankui

    2004-01-01

    Based on the thermal analysis, the influence of pulsing current on the glass transition and crystallizing kinetics of Zr41.3Ti14.2Cu12.8Ni10.3Be21.4 bulk amorphous alloy has been studied. The obtained results show that after the Zr41.3Ti14.2Cu12.8Ni10.3Be21.4 bulk amorphous alloy was pretreated by high-density pulsing current at low temperature, its glass transition temperature Tg, the initial crystallizing temperature Tx and the corresponding exothermic peak of crystallization Tpi were reduced. But the temperature range of supercooled liquid ΔT=Tx-Tg is almost the same. The calculated results with Kissinger equation show that the activation energy of glass transition of the alloy pretreated is reduced significantly, while the activation energy of crystallization is basically unchanged. The influence of pulsing current on the glass transition and crystallization of the Zr41.3Ti14.2Cu12.8Ni10.3Be21.4 bulk amorphous alloy is believed to be related with the structure relaxation of the glass caused by the current.

  11. Growth of single-crystal gallium nitride

    Science.gov (United States)

    Clough, R.; Richman, D.; Tietjen, J.

    1970-01-01

    Use of ultrahigh purity ammonia prevents oxygen contamination of GaN during growth, making it possible to grow the GaN at temperatures as high as 825 degrees C, at which point single crystal wafers are deposited on /0001/-oriented sapphire surfaces.

  12. Shear-mediated crystallization from amorphous calcium phosphate to bone apatite.

    Science.gov (United States)

    Niu, Xufeng; Wang, Liyang; Tian, Feng; Wang, Lizhen; Li, Ping; Feng, Qingling; Fan, Yubo

    2016-02-01

    The contribution of fluid shear stress (FSS) on the conversion of amorphous calcium phosphate (ACP) to bone apatite is investigated. The ACP precursors are prepared by using a wet-chemistry method and further exposed to the constant FSS environment with values of 0.5, 1.0, 1.5, and 2.0Pa. At the designated time points, the apatites are characterized by transmission electron microscopy, X-ray diffraction, and inductively coupled plasma-mass spectroscopy. The results show that, the low FSS (≤1.0Pa) has positive effects on the transition of ACP, characterized by the accelerated crystallization velocity and the well-organized calcium-deficient hydroxyapatite (CDHA) structure, whereas the high FSS (>1.0Pa) has negative effects on this conversion process, characterized by the poor CDHA crystal morphologies and the destroyed structures. The bioactivity evaluations further reveal that, compared with the FSS-free group, the CDHA prepared under 1.0Pa FSS for 9h presents the more biocompatible features with pre-osteoblast cells. These results are helpful for understanding the mechanism of apatite deposition in natural bone tissue.

  13. The release of trapped gases from amorphous solid water films. I. "Top-down" crystallization-induced crack propagation probed using the molecular volcano.

    Science.gov (United States)

    May, R Alan; Smith, R Scott; Kay, Bruce D

    2013-03-14

    In this (Paper I) and the companion paper (Paper II; R. May, R. Smith, and B. Kay, J. Chem. Phys. 138, 104502 (2013)), we investigate the mechanisms for the release of trapped gases from underneath amorphous solid water (ASW) films. In prior work, we reported the episodic release of trapped gases in concert with the crystallization of ASW, a phenomenon that we termed the "molecular volcano." The observed abrupt desorption is due to the formation of cracks that span the film to form a connected pathway for release. In this paper, we utilize the "molecular volcano" desorption peak to characterize the formation of crystallization-induced cracks. We find that the crack length distribution is independent of the trapped gas (Ar, Kr, Xe, CH4, N2, O2, or CO). Selective placement of the inert gas layer is used to show that cracks form near the top of the film and propagate downward into the film. Isothermal experiments reveal that, after some induction time, cracks propagate linearly in time with an Arrhenius dependent velocity corresponding to an activation energy of 54 kJ∕mol. This value is consistent with the crystallization growth rates reported by others and establishes a direct connection between crystallization growth rate and the crack propagation rate. A two-step model in which nucleation and crystallization occurs in an induction zone near the top of the film followed by the propagation of a crystallization∕crack front into the film is in good agreement with the temperature programmed desorption results.

  14. Synthesis of Poly-Silicon Thin Films on Glass Substrate Using Laser Initiated Metal Induced Crystallization of Amorphous Silicon for Space Power Application

    Science.gov (United States)

    Abu-Safe, Husam H.; Naseem, Hameed A.; Brown, William D.

    2007-01-01

    Poly-silicon thin films on glass substrates are synthesized using laser initiated metal induced crystallization of hydrogenated amorphous silicon films. These films can be used to fabricate solar cells on low cost glass and flexible substrates. The process starts by depositing 200 nm amorphous silicon films on the glass substrates. Following this, 200 nm of sputtered aluminum films were deposited on top of the silicon layers. The samples are irradiated with an argon ion cw laser beam for annealing. Laser power densities ranging from 4 to 9 W/cm2 were used in the annealing process. Each area on the sample is irradiated for a different exposure time. Optical microscopy was used to examine any cracks in the films and loss of adhesion to the substrates. X-Ray diffraction patterns from the initial results indicated the crystallization in the films. Scanning electron microscopy shows dendritic growth. The composition analysis of the crystallized films was conducted using Energy Dispersive x-ray Spectroscopy. The results of poly-silicon films synthesis on space qualified flexible substrates such as Kapton are also presented.

  15. Fast crystallization of amorphous Gd{sub 2}Zr{sub 2}O{sub 7} induced by thermally activated electron-beam irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Zhangyi; Qi, Jianqi, E-mail: qijianqi@scu.edu.cn; Zhou, Li; Feng, Zhao; Yu, Xiaohe [College of Physical Science and Technology, Sichuan University, Chengdu 610064 (China); Key Laboratory of Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Gong, Yichao [College of Materials Science and Engineering, Sichuan University, Chengdu 610064 (China); Yang, Mao; Wei, Nian [College of Physical Science and Technology, Sichuan University, Chengdu 610064 (China); Key Laboratory of High Energy Density Physics of Ministry of Education, Sichuan University, Chengdu 610064 (China); Shi, Qiwu [College of Physical Science and Technology, Sichuan University, Chengdu 610064 (China); College of Materials Science and Engineering, Sichuan University, Chengdu 610064 (China); Lu, Tiecheng, E-mail: lutiecheng@scu.edu.cn [College of Physical Science and Technology, Sichuan University, Chengdu 610064 (China); Key Laboratory of Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Key Laboratory of High Energy Density Physics of Ministry of Education, Sichuan University, Chengdu 610064 (China)

    2015-12-07

    We investigate the ionization and displacement effects of an electron-beam (e-beam) on amorphous Gd{sub 2}Zr{sub 2}O{sub 7} synthesized by the co-precipitation and calcination methods. The as-received amorphous specimens were irradiated under electron beams at different energies (80 keV, 120 keV, and 2 MeV) and then characterized by X-ray diffraction and transmission electron microscopy. A metastable fluorite phase was observed in nanocrystalline Gd{sub 2}Zr{sub 2}O{sub 7} and is proposed to arise from the relatively lower surface and interface energy compared with the pyrochlore phase. Fast crystallization could be induced by 120 keV e-beam irradiation (beam current = 0.47 mA/cm{sup 2}). The crystallization occurred on the nanoscale upon ionization irradiation at 400 °C after a dose of less than 10{sup 17} electrons/cm{sup 2}. Under e-beam irradiation, the activation energy for the grain growth process was approximately 10 kJ/mol, but the activation energy was 135 kJ/mol by calcination in a furnace. The thermally activated ionization process was considered the fast crystallization mechanism.

  16. Porosity effects on crystallization kinetics of amorphous solid water: Implications for cold icy objects in the outer solar system

    Science.gov (United States)

    Mitchell, Emily H.; Raut, Ujjwal; Teolis, Benjamin D.; Baragiola, Raúl A.

    2017-03-01

    We have investigated the effects of porosity on the crystallization kinetics of amorphous solid water (ASW). Porosity in ASW films, condensed from the vapor phase at varying incidences at 10 K, was characterized using ultraviolet-visible interferometry and quartz crystal microgravimetry. The films were heated to crystallization temperatures between 130 and 141 K, resulting in partial pore compaction. The isothermal phase transformation was characterized using transmission infrared spectroscopy to monitor the time evolution of the 3.1-μm Osbnd H stretch absorption band. We find that ASW crystallization unfolds in two distinct stages. The first stage, responsible for ∼10% transformation, is initiated from nucleation at the external surface. The dominant second stage begins with nucleation at the internal pore surfaces and completes the transformation of the film at a faster rate compared to the first stage. A key finding is that porosity has major influence on crystallization kinetics; a film with five-times-higher porosity was observed to crystallize ∼15 times faster, compared to the less porous counterpart. We extrapolate our results to predict crystallization times for amorphous ices condensed on Europa's surface from plume sources, as recently observed by the Hubble Space Telescope.

  17. Ordered Growth of Topological Insulator Bi2Se3 Thin Films on Dielectric Amorphous SiO2 by MBE

    OpenAIRE

    2013-01-01

    Topological insulators (TIs) are exotic materials which have topologically protected states on the surface due to the strong spin-orbit coupling. However, a lack of ordered growth of TI thin films on amorphous dielectrics and/or insulators presents a challenge for applications of TI-junctions. We report the growth of topological insulator Bi2Se3 thin films on amorphous SiO2 by molecular beam epitaxy (MBE). To achieve the ordered growth of Bi2Se3 on amorphous surface, the formation of other ph...

  18. Optimizing amorphous indium zinc oxide film growth for low residual stress and high electrical conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Mukesh [Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO 80401 (United States); Sigdel, A.K. [Department of Physics and Astronomy, University of Denver, Denver, CO 80208 (United States); National Center for Photovoltaics, National Renewal Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401 (United States); Gennett, T.; Berry, J.J.; Perkins, J.D.; Ginley, D.S. [National Center for Photovoltaics, National Renewal Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401 (United States); Packard, C.E., E-mail: cpackard@mines.edu [Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO 80401 (United States); National Center for Photovoltaics, National Renewal Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401 (United States)

    2013-10-15

    With recent advances in flexible electronics, there is a growing need for transparent conductors with optimum conductivity tailored to the application and nearly zero residual stress to ensure mechanical reliability. Within amorphous transparent conducting oxide (TCO) systems, a variety of sputter growth parameters have been shown to separately impact film stress and optoelectronic properties due to the complex nature of the deposition process. We apply a statistical design of experiments (DOE) approach to identify growth parameter–material property relationships in amorphous indium zinc oxide (a-IZO) thin films and observed large, compressive residual stresses in films grown under conditions typically used for the deposition of highly conductive samples. Power, growth pressure, oxygen partial pressure, and RF power ratio (RF/(RF + DC)) were varied according to a full-factorial test matrix and each film was characterized. The resulting regression model and analysis of variance (ANOVA) revealed significant contributions to the residual stress from individual growth parameters as well as interactions of different growth parameters, but no conditions were found within the initial growth space that simultaneously produced low residual stress and high electrical conductivity. Extrapolation of the model results to lower oxygen partial pressures, combined with prior knowledge of conductivity–growth parameter relationships in the IZO system, allowed the selection of two promising growth conditions that were both empirically verified to achieve nearly zero residual stress and electrical conductivities >1480 S/cm. This work shows that a-IZO can be simultaneously optimized for high conductivity and low residual stress.

  19. Flux growth of BPO 4 crystals

    Science.gov (United States)

    Li, Zhihua; Wu, Yicheng; Fu, Peizhen; Pan, Shilie; Chen, Chuangtian

    2004-10-01

    Single crystals of BPO4 with sizes up to 15×10×12 mm3 were grown by top-seeded solution growth method using Li2O-Li4P2O7 as fluxes. The components volatilized from the melt were characterized by the method of X-ray powder diffraction. The defects of grown crystals have also been investigated. The measured ultraviolet cutoff edge of BPO4 was about 130 nm. Its density was 2.82 g/cm3 determined using drainage method.

  20. Strong enhancement of spontaneous emission in amorphous-silicon-nitride photonic crystal based coupled-microcavity structures

    Energy Technology Data Exchange (ETDEWEB)

    Bayindir, M.; Tanriseven, S.; Aydinli, A.; Ozbay, E. [Bilkent Univ., Ankara (Turkey). Dept. of Physics

    2001-07-01

    We investigated photoluminescence (PL) from one-dimensional photonic band gap structures. The photonic crystals, a Fabry-Perot (FP) resonator and a coupled-microcavity (CMC) structure, were fabricated by using alternating hydrogenated amorphous-silicon-nitride and hydrogenated amorphous-silicon-oxide layers. It was observed that these structures strongly modify the PL spectra from optically active amorphous-silicon-nitride thin films. Narrow-band and wide-band PL spectra were achieved in the FP microcavity and the CMC structure, respectively. The angle dependence of PL peak of the FP resonator was also investigated. We also observed that the spontaneous emission increased drastically at the coupled-cavity band edge of the CMC structure due to extremely low group velocity and long photon lifetime. The measurements agree well with the transfer-matrix method results and the prediction of the tight-binding approximation. (orig.)

  1. Strong enhancement of spontaneous emission in amorphous-silicon-nitride photonic crystal based coupled-microcavity structures

    Science.gov (United States)

    Bayindir, M.; Tanriseven, S.; Aydinli, A.; Ozbay, E.

    We investigated photoluminescence (PL) from one-dimensional photonic band gap structures. The photonic crystals, a Fabry-Perot (FP) resonator and a coupled-microcavity (CMC) structure, were fabricated by using alternating hydrogenated amorphous-silicon-nitride and hydrogenated amorphous-silicon-oxide layers. It was observed that these structures strongly modify the PL spectra from optically active amorphous-silicon-nitride thin films. Narrow-band and wide-band PL spectra were achieved in the FP microcavity and the CMC structure, respectively. The angle dependence of PL peak of the FP resonator was also investigated. We also observed that the spontaneous emission increased drastically at the coupled-cavity band edge of the CMC structure due to extremely low group velocity and long photon lifetime. The measurements agree well with the transfer-matrix method results and the prediction of the tight-binding approximation.

  2. Crystallization and Growth of Colloidal Nanocrystals

    CERN Document Server

    Leite, Edson Roberto

    2012-01-01

    Since the size, shape, and microstructure of nanocrystalline materials strongly impact physical and chemical properties, the development of new synthetic routes to  nanocrystals with controlled composition and morphology is a key objective of the nanomaterials community. This objective is dependent on control of the nucleation and growth mechanisms that occur during the synthetic process, which in turn requires a fundamental understanding of both classical nucleation and growth and non-classical growth processes in nanostructured materials.  Recently, a novel growth process called Oriented Attachment (OA) was identified which appears to be a fundamental mechanism during the development of nanoscale  materials. OA is a special case of aggregation that provides an important route by which nanocrystals grow, defects are formed, and unique—often symmetry-defying—crystal morphologies can be produced. This growth mechanism involves reversible self-assembly of primary nanocrystals followed by reorientati...

  3. Al-Induced Crystallization Growth of Si Films by Inductively Coupled Plasma Chemical Vapour Deposition

    Institute of Scientific and Technical Information of China (English)

    LI Jun-Shuai; WANG Jin-Xiao; YIN Min; GAO Ping-Qi; HE De-Yan

    2006-01-01

    Polycrystalline Si (poly-Si) films are in situ grown on Al-coated glass substrates by inductively coupled plasma chemical vapour deposition at a temperature as low as 350 C. Compared to the traditional annealing crystallization of amorphous Si/Al-layer structures, no layer exchange is observed and the resultant poly-Si film is much thicker than Al layer. By analysing the depth profiles of the elemental composition, no remains of Al atoms are detected in Si layer within the limit (< 0.01 at. %) of the used evaluations. It is indicated that the poly-Si material obtained by Al-induced crystallization growth has more potential applications than that prepared by annealing the amorphous Si/Al-layer structures.

  4. Amorphous inclusions during Ge and GeSn epitaxial growth via chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Gencarelli, F., E-mail: federica.gencarelli@imec.be [imec, Kapeldreef 75, 3001 Leuven (Belgium); Dept. of Metallurgy and Materials Engineering, KU Leuven, B-3001 Leuven (Belgium); Shimura, Y. [imec, Kapeldreef 75, 3001 Leuven (Belgium); Nuclear and Radiation Physics Section, KU Leuven, B-3001 Leuven (Belgium); Kumar, A. [imec, Kapeldreef 75, 3001 Leuven (Belgium); Nuclear and Radiation Physics Section, KU Leuven, B-3001 Leuven (Belgium); Vincent, B.; Moussa, A.; Vanhaeren, D.; Richard, O.; Bender, H. [imec, Kapeldreef 75, 3001 Leuven (Belgium); Vandervorst, W. [imec, Kapeldreef 75, 3001 Leuven (Belgium); Nuclear and Radiation Physics Section, KU Leuven, B-3001 Leuven (Belgium); Caymax, M.; Loo, R. [imec, Kapeldreef 75, 3001 Leuven (Belgium); Heyns, M. [imec, Kapeldreef 75, 3001 Leuven (Belgium); Dept. of Metallurgy and Materials Engineering, KU Leuven, B-3001 Leuven (Belgium)

    2015-09-01

    In this work, we discuss the characteristics of particular island-type features with an amorphous core that are developed during the low temperature epitaxial growth of Ge and GeSn layers by means of chemical vapor deposition with Ge{sub 2}H{sub 6}. Although further investigations are needed to unambiguously identify the origin of these features, we suggest that they are originated by the formation of clusters of H and/or contaminants atoms during growth. These would initially cause the formation of pits with crystalline rough facets over them, resulting in ring-shaped islands. Then, when an excess surface energy is overcome, an amorphous phase would nucleate inside the pits and fill them. Reducing the pressure and/or increasing the growth temperature can be effective ways to prevent the formation of these features, likely due to a reduction of the surface passivation from H and/or contaminant atoms. - Highlights: • Island features with amorphous cores develop during low T Ge(Sn) CVD with Ge{sub 2}H{sub 6.} • These features are thoroughly characterized in order to understand their origin. • A model is proposed to describe the possible evolution of these features. • Lower pressures and/or higher temperatures avoid the formation of these features.

  5. The influence of PVP incorporation on moisture-induced surface crystallization of amorphous spray-dried lactose particles.

    Science.gov (United States)

    Mahlin, Denny; Berggren, Jonas; Gelius, Ulrik; Engström, Sven; Alderborn, Göran

    2006-09-14

    We have recently shown that atomic force microscopy (AFM) may be an appropriate method for characterisation of the re-crystallization of amorphous particles. In this study, spray-dried composite particles consisting of lactose and polyvinyl pyrrolidon (PVP) were characterised by AFM and electron spectroscopy for chemical analysis (ESCA), and their response on increasing the relative humidity (RH) was investigated. The PVP content in the particles used was 0, 5 or 25 wt.% of either PVP K17 or PVP K90. All composite particles were found to be enriched with PVP at the surface. The incorporation of PVP in the particles influenced the way the particles responded to an increase in RH. The specific RH interval in which the surface of the particles smoothened and the RH where crystallization could be detected, increased with an increase in the amount and molecular weight of the PVP in the particles. The crystallization kinetics of single particles was analysed with AFM and by utilising the JMAK equation. The rate constant for this transformation increased in an exponential manner with increasing RH. Furthermore, above the RH needed for the crystallization to occur, the exponential increase in the crystallization rate was larger for particles with higher polymer content which indicates that the stabilising effect decreases as the water content in the particles becomes higher. In this study we report a method for determination of crystallization kinetics on single composite particles, which is valuable when evaluating the effect of stabilisers in amorphous powders.

  6. Bridgman growth of bismuth tellurite crystals

    Indian Academy of Sciences (India)

    Anhua Wu; Jiayue Xu; Guoxing Qian; Baoliang Lu; Zengwei Ge; Linyao Tang; Xianjun Wu

    2005-10-01

    The photorefractive crystal, Bi2TeO5, was grown by the modified Bridgman method for the first time. High purity Bi2O3 and TeO2 were used as starting materials and were mixed thoroughly with molar ratio of Bi2O3/TeO2 = 1 : 1. Platinum crucible was fabricated with a seed well of 10 mm in diameter and several folds were pressed so that the spontaneous nuclei could be eliminated through competition. The crucible was sealed during the growth so that the evaporation of TeO2 was controlled effectively. By optimizing growth parameters, transparent and crack-free Bi2TeO5 crystal up to 25 mm in diameter and 40 mm in length was grown successfully.

  7. Effect of crystallization on corrosion behavior of Fe40Ni38B18Mo4 amorphous alloy in 3.5% sodium chloride solution

    DEFF Research Database (Denmark)

    Wu, Y.F.; Chiang, Wen-Chi; Wu, J.K.

    2008-01-01

    After the crystallization of F40Ni38B18Mo4 amorphous alloy by vacuum annealing, the corrosion resistance of its crystalline state shows inferior to its amorphous state due to the local cell action between Ni phase and (Fe, Ni, Mo)(23)B-6 phase in matrix....

  8. Engineering crystal growth of calcium hydrogenphosphate dihydrate

    Energy Technology Data Exchange (ETDEWEB)

    Sikiric, M.; Babic-Ivancic, V. [Institut Rudjer Boskovic, Zagreb (Croatia); Milat, O. [Zagreb Univ. (Croatia). Inst. za Fiziku; Sarig, S.; Fueredi-Milhofer, H. [Hebrew Univ., Jerusalem (Israel). Inst. of Applied Chemistry

    2001-07-01

    The factors underlying calcium hydrogenphosphate dihydrate (CaHPO{sub 4}.2H{sub 2}O, DCPD) interactions with several structurally different additives: glutamic and aspartic acid, sodium citrate, hexaammonium tetrapolyphosphate, calcium phytate and polyaspartic acid were studied. DCPD crystals were prepared under controlled conditions by fast mixing of the anionic and cationic reactant solutions and subsequent growth without further stirring in the course of 24 hours at 37 C. The initial conditions were c(CaCl{sub 2}) = c(Na{sub 2}HPO{sub 4}) = 0.021 mol dm{sup -3}, c(NaCl) = 0.3 mol dm{sup -3}, pH{sub i} 5.5. The respective additive was added to the anionic component prior to pH adjustment. Crystals were characterized by X-ray diffraction, while their morphology was observed by optical and scanning electron microscopy (SEM). The Miller indices of the crystal faces were determined from SEM micrographs, after the orientation of the most prominent face was ascertained by the Weissenberg method. Mechanism of additive-DCPD crystals interaction depends on size and structure of additive molecule, structural fit between organic molecule and the ionic structure of particular crystal face. Small molecules (ions) specifically adsorb on lateral faces by electrostatic interactions, while macromolecules and molecules with hindered structure specifically adsorb on dominant (010) face, for which certain degree of structural fit is necessary. (orig.)

  9. Growth of piezoelectric crystals by Czochralski method

    OpenAIRE

    Cochet-Muchy, D.

    1994-01-01

    The Czochralski method is one of the most widely used industrial technique to grow single-crystals, since it applies to a very large range of compounds, such as semiconductors, oxides, fluorides, etc... Many exhibit piezoelectric properties and some of them find applications in Surface-Acoustic-Waves or Bulk-Acoustic-Waves devices. That explains the large amount of work made on the development of the corresponding growth processes and the high levels of production achieved in the world today....

  10. Sealed silica pressure ampoules for crystal growth

    Science.gov (United States)

    Holland, L. R.

    1984-01-01

    The properties of vitreous silica and the mechanics of thick walled pressure vessels are reviewed with regard to the construction of sealed silica crucibles such as are used in the growth of mercury-cadmium telluride crystals. Data from destructive rupture tests are reported, failure modes discussed, and recommendations for design given. Ordinary commercial clear vitreous silica from flame fused quartz can withstand a surface stress of 20 MPa or more in this application.

  11. Studying Crystal Growth With the Peltier Effect

    Science.gov (United States)

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

    1986-01-01

    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.

  12. Silicon nanocrystals on amorphous silicon carbide alloy thin films: Control of film properties and nanocrystals growth

    Energy Technology Data Exchange (ETDEWEB)

    Barbe, Jeremy, E-mail: jeremy.barbe@hotmail.com [CEA, Liten, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France); Universite de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d' Energie), 118 route de Narbonne, 31062 Toulouse (France); Xie, Ling; Leifer, Klaus [Department of Engineering Sciences, Uppsala University, Box 534, S-751 21 Uppsala (Sweden); Faucherand, Pascal; Morin, Christine; Rapisarda, Dario; De Vito, Eric [CEA, Liten, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France); Makasheva, Kremena; Despax, Bernard [Universite de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d' Energie), 118 route de Narbonne, 31062 Toulouse (France); CNRS, LAPLACE, F-31062 Toulouse (France); Perraud, Simon [CEA, Liten, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France)

    2012-11-01

    The present study demonstrates the growth of silicon nanocrystals on amorphous silicon carbide alloy thin films. Amorphous silicon carbide films [a-Si{sub 1-x}C{sub x}:H (with x < 0.3)] were obtained by plasma enhanced chemical vapor deposition from a mixture of silane and methane diluted in hydrogen. The effect of varying the precursor gas-flow ratio on the film properties was investigated. In particular, a wide optical band gap (2.3 eV) was reached by using a high methane-to-silane flow ratio during the deposition of the a-Si{sub 1-x}C{sub x}:H layer. The effect of short-time annealing at 700 Degree-Sign C on the composition and properties of the layer was studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It was observed that the silicon-to-carbon ratio in the layer remains unchanged after short-time annealing, but the reorganization of the film due to a large dehydrogenation leads to a higher density of SiC bonds. Moreover, the film remains amorphous after the performed short-time annealing. In a second part, it was shown that a high density (1 Multiplication-Sign 10{sup 12} cm{sup -2}) of silicon nanocrystals can be grown by low pressure chemical vapor deposition on a-Si{sub 0.8}C{sub 0.2} surfaces at 700 Degree-Sign C, from silane diluted in hydrogen. The influence of growth time and silane partial pressure on nanocrystals size and density was studied. It was also found that amorphous silicon carbide surfaces enhance silicon nanocrystal nucleation with respect to SiO{sub 2}, due to the differences in surface chemical properties. - Highlights: Black-Right-Pointing-Pointer Silicon nanocrystals (Si-NC) growth on amorphous silicon carbide alloy thin films Black-Right-Pointing-Pointer Plasma deposited amorphous silicon carbide films with well-controlled properties Black-Right-Pointing-Pointer Study on the thermal effect of 700 Degree-Sign C short-time annealing on the layer properties Black-Right-Pointing-Pointer Low pressure

  13. Orientational order controls crystalline and amorphous thermal transport in superatomic crystals

    Science.gov (United States)

    Ong, Wee-Liat; O'Brien, Evan S.; Dougherty, Patrick S. M.; Paley, Daniel W.; Fred Higgs, C., III; McGaughey, Alan J. H.; Malen, Jonathan A.; Roy, Xavier

    2017-01-01

    In the search for rationally assembled functional materials, superatomic crystals (SACs) have recently emerged as a unique class of compounds that combine programmable nanoscale building blocks and atomic precision. As such, they bridge traditional semiconductors, molecular solids, and nanocrystal arrays by combining their most attractive features. Here, we report the first study of thermal transport in SACs, a critical step towards their deployment as electronic, thermoelectric, and phononic materials. Using frequency domain thermoreflectance (FDTR), we measure thermal conductivity in two series of SACs: the unary compounds Co6E8(PEt3)6 (E = S, Se, Te) and the binary compounds [Co6E8(PEt3)6][C60]2. We find that phonons that emerge from the periodicity of the superstructures contribute to thermal transport. We also demonstrate a transformation from amorphous to crystalline thermal transport behaviour through manipulation of the vibrational landscape and orientational order of the superatoms. The structural control of orientational order enabled by the atomic precision of SACs expands the conceptual design space for thermal science.

  14. Direct investigations on strain-induced cold crystallization behavior and structure evolutions in amorphous poly(lactic acid) with SAXS and WAXS measurements

    DEFF Research Database (Denmark)

    Zhou, Chengbo; Li, Hongfei; Zhang, Wenyang

    2016-01-01

    Strain-induced cold crystallization behavior and structure evolution of amorphous poly(lactic acid) (PLA) stretched within 70-90 degrees C were investigated via in situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) measurements as well as differential...... first then forms crystal with strain increasing. The stacked structure consisting of less perfect crystalline phase, mesocrystal and oriented amorphous phase emerges at the final stage of stretching. Drawing at 80 degrees C, only the crystal can be induced at lower strain with higher crystallization...... in strain-induced crystallization behavior of amorphous PLA within 70-90 degrees C can be attributed to the competition between chain orientation caused by stretching and chain relaxation. It was proposed that the strain-induced mesocrystal/crystal and the lamellae are formed from the mesophase originally...

  15. Laser-induced ferroelectric domain engineering in LiNbO3 crystals using an amorphous silicon overlayer

    Science.gov (United States)

    Zisis, G.; Martinez-Jimenez, G.; Franz, Y.; Healy, N.; Masaud, T. M.; Chong, H. M. H.; Soergel, E.; Peacock, A. C.; Mailis, S.

    2017-08-01

    We report laser-induced poling inhibition and direct poling in lithium niobate crystals (LiNbO3), covered with an amorphous silicon (a-Si) light-absorbing layer, using a visible (488 nm) continuous wave laser source. Our results show that the use of the a-Si overlayer produces deeper poling inhibited domains with minimum surface damage, as compared to previously reported UV laser writing experiments on uncoated crystals, thus increasing the applicability of this method in the production of ferroelectric domain engineered structures for nonlinear optical applications. The characteristics of the poling inhibited domains were investigated using differential etching and piezoresponse force microscopy.

  16. Indium (In)- and tin (Sn)-based metal induced crystallization (MIC) on amorphous germanium (α-Ge)

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Dong-Ho; Park, Jin-Hong, E-mail: jhpark9@skku.edu

    2014-12-15

    Highlights: • In- and Sn-based MIC phenomenon on amorphous (α)-Ge is newly reported. • The In- and Sn-MIC phenomenon respectively started at 250 °C and 400 °C. • The Sn-MIC process presents higher sheet resistance and bigger crystal grains. - Abstract: In this paper, metal-induced crystallization (MIC) phenomenon on α-Ge by indium (In) and tin (Sn) are thoroughly investigated. In- and Sn-MIC process respectively started at 250 °C and 400 °C. Compared to the previously reported MIC samples including In-MIC, Sn-MIC process presented higher sheet resistance (similar to that of SPC) and bigger crystal grains above 50 nm (slightly smaller than that of SPC). According to SIMS analysis, Sn atoms diffused more slowly into Ge than In at 400 °C, providing lower density of heterogeneous nuclei induced by metals and consequently larger crystal grains.

  17. Crystallization of the Al-Ni-Sm amorphous alloys; Cristalizacao de ligas amorfas no sistema Al-Ni-Sm

    Energy Technology Data Exchange (ETDEWEB)

    Danez, G.P., E-mail: gabidanez@hotmail.co [Universidade Federal de Sao Carlos (PPG-CEMUFSCar), SP (Brazil). Programa de Pos-Graduacao em Ciencia e Engenharia de Materiais; Aliaga, L.C.R.; Kiminami, C.S.; Bolfarini, C.; Botta, W.J. [Universidade Federal de Sao Carlos (DEMa/UFSCar), SP (Brazil). Dept. de Engenharia de Materiais

    2010-07-01

    Aluminum based amorphous alloys have received special attention due to unique properties such as high mechanical strength, corrosion, ductility and toughness as well as wear resistance. On the other hand, these properties can be improved by controlled crystallization of Al matrix with grain size ranged between 5 to 50 nanometers. The goal of this work was to study the thermal crystallization behavior of Al-Ni-Sm alloys. Compositions with the same topological instability ({lambda} = 0.1) were selected. Alloys were prepared in arc-melting furnace and ribbons were processed by melt-spinning technique. Samples ribbons were submitted to heating in order to induce crystallization, and its structure analyzed by x-ray diffraction. The difference in crystallization behavior is discussed in function of the topological instability due to the variation of the proportion of the transition metal to the rare-earth. (author)

  18. Growth units model of anion coordination-polyhedra and its application to crystal growth

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xuehua; LUO Haosu; ZHONG Weizhuo

    2004-01-01

    Growth units model of anion coordination-polyhedra ACP model emphasizes the influence of intrinsic structure of crstal upon the crystal growth and the importance of the external conditions on which crystals grow. The ACP model is used to analyze some problems in crystal growth, such as the formation of dendrite in the crystal structure,growth habit of polar crystal, and formation of allomerism and polymorphism.

  19. Growth of the (001 face of borax crystals

    Directory of Open Access Journals (Sweden)

    Suharso Suharso

    2010-06-01

    Full Text Available he growth rates of borax crystals from aqueous solutions in the (001 direction at various relative supersaturations were measured using in situ cell optical microscopy method. The result shows that the growth mechanism of the (001 face of borax crystal at temperature of 20 °C is spiral growth mechanism.   Keywords: Growth mechanism, borax.

  20. Growth of the (001) face of borax crystals

    OpenAIRE

    Suharso, Suharso

    2010-01-01

    he growth rates of borax crystals from aqueous solutions in the (001) direction at various relative supersaturations were measured using in situ cell optical microscopy method. The result shows that the growth mechanism of the (001) face of borax crystal at temperature of 20 °C is spiral growth mechanism.   Keywords: Growth mechanism, borax.

  1. Crystallization of Fe78Si9B13 Bulk Crystaline/Amorphous (c/a) Composite

    Institute of Scientific and Technical Information of China (English)

    JIN Shifeng; WANG Weimin; NIU Yuchao; ZHANG Jiteng; LI Guihua; BIAN Xiufang

    2008-01-01

    A metallic crystalline/amorphous (c/a) bulk composite was prepared by the slow cooling method after remelting the amorphous Fe78Si9B13 ribbon. By X-ray diffraction (XRD),differential scanning calorimetry (DSC) and scanning electron microscope (SEM), the composite consists of the primary dendrite a-Fe (without Si) as well as the amorphous matrix. After being anneal at 800 K, the uniform spheroid particles are formed in the c/a composite, which does not form in the amorphous ribbon under the various annealing process. Energy dispersive analysis of X-rays (EDAX), SEM and XRD were applied to give more detailed information. The formation and evolution of the particle may stimulate the possible application of the Fe-matrix amorphous alloy.

  2. The impact of space research on semiconductor crystal growth technology

    Science.gov (United States)

    Witt, A. F.

    1983-01-01

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

  3. In-situ detection of growth striations by crystallization electromotive force measurement during Czochralski crystal growth

    Science.gov (United States)

    Zhu, Yunzhong; Ma, Decai; Long, Siwei; Tang, Feng; Lin, Shaopeng; Wang, Biao

    2017-10-01

    Growth striations, as macrodefects of crystalline materials, are mainly caused by convection and temperature fluctuations in growth interface. For decades, striations have been widely regarded as an inherent problem. Even in the well-developed Czochralski method, the striation formation process is difficult to inspect in situ. In view of this long-standing issue, after systematically studying the temperature, weight, and output power during crystal growth and numerically modeling the growth process, we found that the regularity of the growth interface electromotive force (GEMF) is related to the distribution of striations. Furthermore, the GEMF quantifies interface fluctuations (711.2 s, 16.6 μm) and thermal hysteresis (107 s), presenting finer details than those provided by a thermocouple and a load cell. In this paper, GEMF is found to be an outstanding choice for monitoring the crystal growth status in real time. As an additional feedback, a new automatic control method could be developed for reducing growth striations and promoting crystal quality.

  4. Correlation of inhibitory effects of polymers on indomethacin precipitation in solution and amorphous solid crystallization based on molecular interaction.

    Science.gov (United States)

    Chauhan, Harsh; Kuldipkumar, Anuj; Barder, Timothy; Medek, Ales; Gu, Chong-Hui; Atef, Eman

    2014-02-01

    To correlate the polymer's degree of precipitation inhibition of indomethacin in solution to the amorphous stabilization in solid state. Precipitation of indomethacin (IMC) in presence of polymers was continuously monitored by a UV spectrophotometer. Precipitates were characterized by PXRD, IR and SEM. Solid dispersions with different polymer to drug ratios were prepared using solvent evaporation. Crystallization of the solid dispersion was monitored using PXRD. Modulated differential scanning calorimetry (MDSC), IR, Raman and solid state NMR were used to explore the possible interactions between IMC and polymers. PVP K90, HPMC and Eudragit E100 showed precipitation inhibitory effects in solution whereas Eudragit L100, Eudragit S100 and PEG 8000 showed no effect on IMC precipitation. The rank order of precipitation inhibitory effect on IMC was found to be PVP K90 > Eudragit E100 > HPMC. In the solid state, polymers showing precipitation inhibitory effect also exhibited amorphous stabilization of IMC with the same rank order of effectiveness. IR, Raman and solid state NMR studies showed that rank order of crystallization inhibition correlates with strength of molecular interaction between IMC and polymers. Correlation is observed in the polymers ability to inhibit precipitation in solution and amorphous stabilization in the solid state for IMC and can be explained by the strength of drug polymer interactions.

  5. Study on the Crystallization of Amorphous Cr-Si-Ni Thin Films Using in situ X-ray Diffraction

    Institute of Scientific and Technical Information of China (English)

    Xianping DONG; Jiansheng WU

    2001-01-01

    Crystallization behavior of amorphous Cr-Si-Ni thin films was investigated by means of high temperature in situ X-ray diffraction measurements. The diffraction spectra were recorded isothermally at temperature between 250 and 750℃. The in situ testing of crystallization enables the direct observation of structure evolution which is dependent on heat treatment.Based on the testing results, the grain sizes of the crystalline phases were compared and phase transition tendency was understood. In the mean time, electrical properties of the films as functions of annealing temperature and time have been studied. The increase of volume fraction of CrSi2 crystallinc phases in the Cr-Si-Ni films leads to the decrease in conductivity of the films.The annealing behavior of temperature coefficient of resistance (TCR) is a result of competition between a negative contribution caused by the weak localization effects in amorphous region and a positive contribution caused by CrSi2 grains. Thus the proper mixture of amorphous and crystalline constituents could result in a final zero TCR.

  6. Ordered growth of topological insulator Bi2Se3 thin films on dielectric amorphous SiO2 by MBE.

    Science.gov (United States)

    Jerng, Sahng-Kyoon; Joo, Kisu; Kim, Youngwook; Yoon, Sang-Moon; Lee, Jae Hong; Kim, Miyoung; Kim, Jun Sung; Yoon, Euijoon; Chun, Seung-Hyun; Kim, Yong Seung

    2013-11-07

    Topological insulators (TIs) are exotic materials which have topologically protected states on the surface due to strong spin-orbit coupling. However, a lack of ordered growth of TI thin films on amorphous dielectrics and/or insulators presents a challenge for applications of TI-junctions. We report the growth of topological insulator Bi2Se3 thin films on amorphous SiO2 by molecular beam epitaxy (MBE). To achieve the ordered growth of Bi2Se3 on an amorphous surface, the formation of other phases at the interface is suppressed by Se passivation. Structural characterizations reveal that Bi2Se3 films are grown along the [001] direction with a good periodicity by the van der Waals epitaxy mechanism. A weak anti-localization effect of Bi2Se3 films grown on amorphous SiO2 shows a modulated electrical property by the gating response. Our approach for ordered growth of Bi2Se3 on an amorphous dielectric surface presents considerable advantages for TI-junctions with amorphous insulator or dielectric thin films.

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

    Science.gov (United States)

    Bagdasarov, Kh. S.

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

  8. Spatially-Resolved Crystallization of Amorphous Silicon Films on the Glass Substrate by Multi-beam Laser Interference

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Laser interference induced crystallization of amorphous silicon (a-Si) on the glass substrate was performed using a Q-switched Nd:YAG (yttrium aluminum garnet) laser. White light interferometer (WLI) and atomic force microscope (AFM) were used to characterize the morphology of the structured films, while X-ray diffraction (XRD), combined with the AFM, was used to analyse the crystalline structure of the film. The experimental results show that the laser energy density above a certain threshold, in the range of 400-500 mJ/cm2,triggers the patterned crystallizations which take the form similar to the laser intensity distribution. For the patterned crystallization under multipulse exposure, a definite polycrystalline structure with individual phases was observed by XRD. The difference in feature form, e.g., deepened craters or heightened lines, is related to the laser energy density relative to the threshold of evaporation of the material.

  9. Advances in the understanding of crystal growth mechanisms

    CERN Document Server

    Nishinaga, T; Harada, J; Sasaki, A; Takei, H

    1997-01-01

    This book contains the results of a research project entitled Crystal Growth Mechanisms on an Atomic Scale, which was carried out for 3 years by some 72 reseachers. Until recently in Japan, only the technological aspects of crystal growth have been emphasized and attention was paid only to its importance in industry. However the scientific aspects also need to be considered so that the technology of crystal growth can be developed even further. This project therefore aimed at understanding crystal growth and the emphasis was on finding growth mechanisms on an atomic scale.

  10. Crystallization and Corrosion Resistance in Different Aqueous Solutions of Zr50.7Ni28Cu9Al12.3 Amorphous Alloy and Its Crystallization Counterparts

    Science.gov (United States)

    Ge, Wenjuan; Li, Boyu; Axinte, Eugen; Zhang, Zitang; Shang, Caiyun; Wang, Yan

    2017-02-01

    The Zr50.7Ni28Cu9Al12.3 amorphous alloy and its crystallization counterparts have been prepared using a melt spinning technique and proper annealing treatment. The as-annealed products at 768 K are amorphous composites consisting of a main amorphous phase and a few ZrO2 nanocrystals. The corrosion behaviors have been investigated in 0.5-M NaCl, 1-M HCl, and 0.5-M H2SO4 solutions. The results show that amorphous composites present the enhanced corrosion resistance in Cl- containing solutions due to the formation of compact passive films, which are promoted by an appropriate quantity of ZrO2 nanocrystals. Nevertheless, the relaxed samples possess good corrosion resistance in H2SO4 solution, which is attributed to the existence of Zr(Al, Ni)-rich protective film induced by the depletion of Cu. In addition, corrosion resistance of the tested alloys is relatively superior in H2SO4 solution, especially for pitting corrosion resistance, and inferior in HCl solution.

  11. Single crystal growth and anisotropic crystal-fluid interface tension in soft colloidal systems

    NARCIS (Netherlands)

    Nguyen, V.D.; Hu, Z.; Schall, P.

    2011-01-01

    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

  12. Crystallization kinetics of Fe-B based amorphous alloys studied in-situ using X-rays diffraction and differential scanning calorimetry

    Directory of Open Access Journals (Sweden)

    Santos D.R. dos

    2001-01-01

    Full Text Available The crystallization processes for the amorphous metallic alloys Fe74B17Si2Ni4Mo3 and Fe86B6Zr7Cu1 (at. % were investigated using X-rays diffraction measurements performed in-situ during Joule-heating, with simultaneous monitoring of the electrical resistance. We determined the main structural transitions and crystalline phases formed during heating, and correlated these results to the observed resistance variations. As the annealing current is increased, the resistance shows an initial decrease due to stress relaxation, followed by a drop to a minimum value due to massive nucleation and growth of alpha-Fe nanocrystals. Further annealing causes the formation of small fractions of Fe-B, B2Zr or ZrO2, while the resistance increases due to temperature enhancement. In situ XRD measurements allowed the identification of metastable phases, as the gamma-Fe phase which occurs at high temperatures. The exothermal peaks observed in the differential scanning calorimetry (DSC for each alloy corroborate the results. We also have performed DSC measurements with several heating rates, which allowed the determination of the Avrami exponent and crystallization activation energy for each alloy. The obtained activation energies (362 and 301 kJ/mol for Fe-B-Zr-Cu; 323 kJ/mol for Fe-B-Si-Ni-Mo are comparable to reported values for amorphous iron alloys, while the Avrami exponent values (n = 1.0 or n = 1.2 are consistent with diffusion controlled crystallization processes with nucleation rates close to zero.

  13. A comparative study of the structure and crystallization of bulk metallic amorphous rod Pr60Ni30Al10 and melt-spun metallic amorphous ribbon Al87Ni10Pr3

    Institute of Scientific and Technical Information of China (English)

    Meng Qing-Ge; Li Jian-Guo; Zhou Jian-Kun

    2006-01-01

    Pr-based bulk metallic amorphous (BM1 rods (Pr60Ni30Al10) and Al-based amorphous ribbons (Al87Ni10Pr3)have been prepared by using copper mould casting and single roller melt-spun techniques, respectively. Thermal parameters deduced from differential scanning calorimeter (DS3 indicate that the glass-forming ability (GF1 of Pr60Nia0Al10 BMA rod is far higher than that of Al87Ni10Pr3 ribbon. A comparative study about the differences in structure between the two kinds of glass-forming alloys, superheated viscosity and crystallization are also made. Compared with the amorphous alloy Al87Ni10Pr3, the BMA alloy Pr60Ni30Al10 shows high thermal stability and large viscosity, small diffusivity at the same superheated temperatures. The results of x-Ray diffraction (XRD) and transmission electron microscope (TEM) show the pronounced difference in structure between the two amorphous alloys.Together with crystallization results, the main structure compositions of the amorphous samples are confirmed. It seems that the higher the GFA, the more topological type clusters in the Pr-Ni-Al amorphous alloys, the GFAs of the present glass-forming alloys are closely related to their structures.

  14. CRYSTAL GROWTH OF RARE EARTH COMPOUNDS IN CLOSED SYSTEM

    OpenAIRE

    1991-01-01

    Remarkable improvements have been made on the crystal growth of rare earth pnictides and chalchogenides by the development of new growth technique and the construction of several new equipments for the crystal growth such as electron beam welding system of tungsten crucible provided with large glove box and vacuum HF furnace. This system has really worked on obtaining excellent quality of single crystals and made easier to explore unknown materials of rare earth compounds. Interesting and att...

  15. Growth of Hydroxyapatite Crystal in the Presence of Origanic Film

    Institute of Scientific and Technical Information of China (English)

    Yong LIU; Suping HUANG; Xiaohong DAN; Kechao ZHOU

    2004-01-01

    The growth of hydroxyapatite (Hap) crystal in the presence of hexadecylamine was investigated. Due to its high polarity and high charge density, the organic film could increase the ion supersaturation on its surface. Therefore the growth of pure Hap crystals was accelerated. Moreover, the positive headgroups of the organic film could act as recognized nucleation sites and orient the growth of Hap crystals along thedirection.

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

    Science.gov (United States)

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

    2010-12-01

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

  17. Effects of heating time on the growth and behavior of amorphous carbon nanostructures from ferrocene

    Science.gov (United States)

    Rafiqul Islam, Md; Rashid, A. K. M. B.; Ferdous, Md; Shafiul Azam, Md

    2017-05-01

    Heating time is one of the crucial factors in various methods employed for the synthesis of carbon nanostructures (CNSs) from ferrocene. However, the effects of heating time on the growth and morphology of the nanostructured materials has not been well explored yet, particularly for amorphous carbon. Herein, we investigate how the variation of heating time impacts the growth of CNSs by carrying out the reaction between ferrocene and ammonium chloride in a solvent free condition at 250 °C. Several different forms of carbon nanostructures yielded from this reaction at 25 min (CNS-25), 30 min (CNS-30), 35 min (CNS-35) and 40 min (CNS-40) were analyzed by means of field emission scanning electron microscopy (FESEM) coupled with energy-dispersive x-ray (EDX), Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy. The final product CNS-40 was washed several times with concentrated hydrochloric acid solution to remove the impurities and then characterized by the means of similar techniques. FTIR spectra of all the nanostructures confirmed the presence of several functional groups such as C  =  C, C-O and -OH etc, which are common in carbonaceous nanostructures. However, the FESEM images obtained are significantly different and suggest a gradual growth of the carbon nanostructures ending up with long carbon nanotubes after 40 min. No absorption peak in the visible region of the UV-Vis spectra of the final product confirms the amorphous nature, which is also supported by XRD of the synthesized nanotube. Moreover, a noteworthy redshift in the UV-Vis peaks reflecting a huge increase in length and diameter of the nanostructures indicates the maximum longitudinal growth of the carbon nanotubes occurs during 35 min to 40 min.

  18. Effect of rare-earth elements on nanophase evolution, crystallization behaviour and mechanical properties in Al–Ni–R (R = La/Mischmetal) amorphous alloys

    Indian Academy of Sciences (India)

    K L Sahoo; Amitava Mitra; Sukomal Ghosh

    2005-10-01

    The crystallization behaviour and evolution of nanoparticles in amorphous Al–Ni–Mischmetal (Mm) and Al–Ni–La alloys during heat treatment have been studied. Rapidly solidified ribbons were obtained by induction melting and ejecting the melt onto a rotating Cu wheel in an Ar atmosphere. The crystallization behaviour of the melt-spun ribbons was investigated using differential scanning calorimetry and X-ray diffractometry (XRD). XRD studies confirmed that all the ribbons were fully amorphous. Al–Ni–Mm systems showed a three-stage crystallization process whereas Al–Ni–La system, in general, showed a two-stage crystallization process on annealing. Crystallization kinetics was analysed by Kissinger and Johnson–Mehl–Avrami approaches. In Al–Ni–La alloys, the crystallization pathways depend on the La concentration. Microhardness of all the ribbons was examined at different temperatures and correlated with the corresponding evolution of phases.

  19. Crystal growth in zinc borosilicate glasses

    Science.gov (United States)

    Kullberg, Ana T. G.; Lopes, Andreia A. S.; Veiga, João P. B.; Monteiro, Regina C. C.

    2017-01-01

    Glass samples with a molar composition (64+x)ZnO-(16-x)B2O3-20SiO2, where x=0 or 1, were successfully synthesized using a melt-quenching technique. Based on differential thermal analysis data, the produced glass samples were submitted to controlled heat-treatments at selected temperatures (610, 615 and 620 °C) during various times ranging from 8 to 30 h. The crystallization of willemite (Zn2SiO4) within the glass matrix was confirmed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Under specific heat-treatment conditions, transparent nanocomposite glass-ceramics were obtained, as confirmed by UV-vis spectroscopy. The influence of temperature, holding time and glass composition on crystal growth was investigated. The mean crystallite size was determined by image analysis on SEM micrographs. The results indicated an increase on the crystallite size and density with time and temperature. The change of crystallite size with time for the heat-treatments at 615 and 620 °C depended on the glass composition. Under fixed heat-treatment conditions, the crystallite density was comparatively higher for the glass composition with higher ZnO content.

  20. Crystallization from amorphous structure to hexagonal quantum dots induced by an electron beam on CdTe thin films

    Science.gov (United States)

    Becerril, M.; Zelaya-Angel, O.; Medina-Torres, A. C.; Aguilar-Hernández, J. R.; Ramírez-Bon, R.; Espinoza-Beltran, F. J.

    2009-02-01

    Amorphous cadmium-telluride films were prepared by rf sputtering on Corning 7059 glass substrates at room temperature. The deposition time was 10 and 12 h with a thickness of 400 and 480 (±40 nm), respectively. As-prepared films were amorphous according to X-ray diffraction (XRD) patterns, but a win-fit-software analysis of the main XRD broad band suggests a wurtzite structure at short range. Transmission electron microscopy (TEM) at 200 keV produces crystallization of the amorphous CdTe. The TEM-electron beam induces the formation of CdTe quantum dots with the wurtzite hexagonal structure (the metastable structure of CdTe) and with ˜6 nm of average grain size. As effect of a probable distortion of the CdTe crystalline lattice, the unit cell volume (UCV) shrinks to about 30% with respect to the bulk-UCV of CdTe. Besides, the energy band gap increases as expected, according to literature data on quantum confinement.

  1. Rapid amorphization of molecular crystals by absorption of solvent molecules in the presence of hydrophilic matrices

    Energy Technology Data Exchange (ETDEWEB)

    Nakayama, S., E-mail: nakayama@nara-m.co.j [Technofarm Axesz Co., Ltd., 3-45-4 Kamiishihara, Chofu, Tokyo 182-0035 (Japan); Nara Machinery Co., Ltd., 2-5-7 Jounan-jima, Tokyo 143-0002 (Japan); Watanabe, T. [Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama 223-8522 (Japan); Senna, M. [Technofarm Axesz Co., Ltd., 3-45-4 Kamiishihara, Chofu, Tokyo 182-0035 (Japan); Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama 223-8522 (Japan)

    2009-08-26

    Two organic molecular crystalline species, ibuprophen (IB) and indomethacine (IM) were subjected to methanol absorption in the presence of hydrophilic organic matrix, hydroxypropyl methylcellulose (HPMC). While spraying of 8-10% methanol or water on the drug-matrix mixture decreased the subsequent milling time for amorphization, absorption of methanol in a closed container caused spontaneous amorphization of IB was observed to give a nanocomposites with macroscopic agglomerates up to 250 mum after methanol absorption for overnight. Gentle mechanical homogenization under saturated methanol vapor with a newly developed apparatus, a tandem rotation mill (TRM), brought about homogeneous grains of IB-HPMC nanocomposites with the average particle size, 30 mum. We observed amorphous particles of IB in 60 nm regime dispersed in HPMC matrix under a transmission electron microscope (TEM). In the case of IM, mechanical homogenization with TRM was indispensable to obtain similar nanocomposites with HPMC.

  2. Bonding Energy and Growth Habit of Lithium Niobate Single Crystals

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    On the basis of crystallographic structure of lithium niobate (LN), the bonding energy was quantitatively calculated by the bond valence sum model, which was employed to investigate the crystal growth. A possible relationship between the crystal growth habit and chemical bonding energy of LN crystals are found. It is found that the higher the bond energy, the slower the growth rate, and the more important the plane. The analytical results indicate that (012) plane is the most influential face for the LN crystal growth, which consists well with the standard card (JCPDS Card: 20-0631) and our previous experimental observation. The current work shows that the chemical bond analysis of LN crystals allows us to predict its growth habit and thus to obtain the expected morphology during the spontaneous growth.

  3. Crystal growth in fluid flow: Nonlinear response effects

    Science.gov (United States)

    Peng, H. L.; Herlach, D. M.; Voigtmann, Th.

    2017-08-01

    We investigate crystal-growth kinetics in the presence of strong shear flow in the liquid, using molecular-dynamics simulations of a binary-alloy model. Close to the equilibrium melting point, shear flow always suppresses the growth of the crystal-liquid interface. For lower temperatures, we find that the growth velocity of the crystal depends nonmonotonically on the shear rate. Slow enough flow enhances the crystal growth, due to an increased particle mobility in the liquid. Stronger flow causes a growth regime that is nearly temperature-independent, in striking contrast to what one expects from the thermodynamic and equilibrium kinetic properties of the system, which both depend strongly on temperature. We rationalize these effects of flow on crystal growth as resulting from the nonlinear response of the fluid to strong shearing forces.

  4. Nucleation and crystal growth in laser patterned lines in glasses

    Directory of Open Access Journals (Sweden)

    Takayuki Komatsu

    2016-07-01

    Full Text Available Laser-induced crystallization is a new method for the design and control of the crystallization of glasses and opens a new door in the study of nucleation and crystal growth in glasses. Nonlinear optical Sm-doped -BaB2O4 (-BBO crystal lines were patterned by continuous wave Yb:YVO4 fiber laser (wavelength 1080 nm in 8Sm2O3-42BaO-50B2O3 glass as an example, and nucleation and crystal growth behaviors in the laser-patterned bending and crossing lines were examined. It was confirmed that the growth of c-axis oriented -BBO crystals follows along the laser scanning direction even if laser scanning direction changes. The model of self-organized homo-epitaxial crystal growth was demonstrated for the orientation of -BBO crystals at the crossing point of two lines, in which the first crystal line at the crossing point acts as nucleation site for the second crystal line. This study proposes a new crystal growth technology.

  5. Reinvestigation of growth of 'L-valine zinc sulphate' crystal.

    Science.gov (United States)

    Srinivasan, Bikshandarkoil R; Jyai, Rita N

    2014-01-01

    A reinvestigation of the growth of l-valine zinc sulphate crystal is reported. The slow evaporation of an aqueous solution containing l-valine and zinc sulphate heptahydrate results in the fractional crystallization of l-valine and not the organic inorganic hybrid nonlinear optical l-valine zinc sulphate crystal, as reported by Puhal Raj and Ramachandra Raja (2012).

  6. Stability of melt crystal growth under microgravity conditions

    Science.gov (United States)

    Tatarchenko, V. A.

    The conception of dynamic stability of melt crystal growth has been developed. The method based on the Lyapunov stability theory has been used to the study stability of crystallization by capillary shaping techniques including Czokhralsky, Stepanov, Kiropoulos, Verneuil and floating zone methods. Preliminary results of the stability analysis of crystallization by floating zone technique under microgravity conditions are presented here.

  7. Solvent-mediated amorphous-to-crystalline transformation of nitrendipine in amorphous particle suspensions containing polymers

    DEFF Research Database (Denmark)

    Xia, Dengning; Wu, Jian-Xiong; Cui, Fude;

    2012-01-01

    quantitatively determined using image analysis based on polarized light microscopy. The findings from the image analysis revealed that the transformation process occurred through the dissolution of amorphous drug precipitate followed by the nucleation and growth of the crystalline phase with the amorphous....... However, a further increase in drug concentration to 100mg/ml decelerated the growth of nitrendipine crystals. Combining image analysis of polarized light micrographs together with Raman spectroscopy and XRPD provided an in-depth insight into solid state transformations in amorphous nitrendipine...

  8. Simulation of Single Crystal Growth: Heat and Mass Transfer

    CERN Document Server

    Zhmakin, A I

    2015-01-01

    The heat transfer (conductive, convective, radiative) and the related problems (the unknown phase boundary fluid/crystal, the assessment of the quality of the grown crystals) encountered in the melt and vapour growth of single crystal as well as the corresponding macroscopic models are reviewed. The importance of the adequate description of the optical crystal properties (semitransparency, absorption, scattering, refraction, diffuse and specular reflecting surfaces) and their effect on the heat transfer is stressed. The problems of the code verification and validation are discussed; differences between the crystal growth simulation codes intended for the research and for the industrial applications are indicated.

  9. On the growth of calcium tartrate tetrahydrate single crystals

    Indian Academy of Sciences (India)

    X Sahaya Shajan; C Mahadevan

    2004-08-01

    Calcium tartrate single crystals were grown using silica gel as the growth medium. Calcium formate mixed with formic acid was taken as the supernatant solution. It was observed that the nucleation density was reduced and the size of the crystals was improved to a large extent compared to the conventional way of growing calcium tartrate crystals with calcium chloride. The role played by formate–formic acid on the growth of crystals is discussed. The grown crystals were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction analysis (XRD), microhardness measurement, Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and differential thermal analysis (DTA). The results obtained are compared with the previous work.

  10. Nucleation and crystal growth in laser patterned lines in glasses

    OpenAIRE

    Takayuki Komatsu; Tsuyoshi Honma

    2016-01-01

    Laser-induced crystallization is a new method for the design and control of the crystallization of glasses and opens a new door in the study of nucleation and crystal growth in glasses. Nonlinear optical Sm-doped -BaB2O4 (-BBO) crystal lines were patterned by continuous wave Yb:YVO4 fiber laser (wavelength 1080 nm) in 8Sm2O3-42BaO-50B2O3 glass as an example, and nucleation and crystal growth behaviors in the laser-patterned bending and crossing lines were examined. It was confirmed that the...

  11. Effect of Ion Bombardment on the Growth and Properties of Hydrogenated Amorphous Silicon-Germanium Alloys

    Science.gov (United States)

    Perrin, Jérôme; Takeda, Yoshihiko; Hirano, Naoto; Matsuura, Hideharu; Matsuda, Akihisa

    1989-01-01

    We report a systematic investigation of the effect of ion bombardment during the growth of amorphous silicon-germanium alloy films from silane and germane rf-glow discharge. Independent control of the plasma and the ion flux and energy is obtained by using a triode configuration. The ion contribution to the total deposition rate can reach 20% on negatively biased substrates. Although the Si and Ge composition of the film does not depend on the ion flux and energy, the optical, structural and electronic properties are drastically modified at low deposition temperatures when the maximum ion energy increases up to 50 eV, and remain constant above 50 eV. For a Ge atomic concentration of 37% and a temperature of 135°C, the optical gap decreases from 1.67 to 1.45 eV. This is correlated with a modification of hydrogen bonding configurations. Silicon dihydride sites disappear and preferential attachment of hydrogen to silicon is reduced in favour of germanium. Moreover the photoconductivity increases which shows that ion bombardment is a key parameter to optimize the quality of low band gap amorphous silicon-germanium alloys.

  12. On the elastic contribution to crystal growth in complex environments

    Science.gov (United States)

    Gadomski, A.; Siódmiak, J.

    2005-03-01

    Based on a number of experimental studies, we propose to consider how elastic interactions between a crystal and its surroundings change crystal growing conditions. To aim to do this, we analyze the influence of some nonequilibrium modification of the Gibbs-Thomson thermodynamic condition, prescribed at the crystal boundary, on some properties of a kinetic model of protein crystal growth in a mass-convection regime. Next, to draw the physical picture more realistically, we study the influence of a certain stochastic perturbation on the crystal growth rate. To fulfill the task we apply the description of crystal growth in terms of nonequilibrium thermodynamics at a mesoscopic level. The proposed model offers a quite comprehensive picture of the formation of modern organic crystalline materials such as non-Kossel crystals.

  13. Space manufacturing in an automated crystal growth facility

    Science.gov (United States)

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

    1989-01-01

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

  14. Preparation for microgravity science investigation of compound semiconductor crystal growth

    Science.gov (United States)

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

    1985-01-01

    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.

  15. Issues in the growth of bulk crystals of infrared materials

    Science.gov (United States)

    Bachmann, K. J.; Golowsky, H.

    1987-01-01

    Attention is given to the relevant criteria governing materials choice in the growth of IR optoelectronic bulk single crystals of III-V and II-VI alloy and I-III-VI2 compound types. The most important considerations concern the control of crystal purity, microstructural perfection, stoichiometry, and uniformity during crystal growth, as well as the control of surface properties in wafer fabrication. Specific examples are given to illustrate the problems encountered and their preferred solutions.

  16. Computing the crystal growth rate by the interface pinning method

    DEFF Research Database (Denmark)

    Pedersen, Ulf Rørbæk; Hummel, Felix; Dellago, Christoph

    2015-01-01

    -phase configurations are stabilized by adding a spring-like bias field coupling to an order-parameter that discriminates between the two phases. Crystal growth is a Smoluchowski process and the crystal growth rate can, therefore, be computed from the terminal exponential relaxation of the order parameter. The approach...... from first principles. A generalized version of the method may be used for computing the rates of crystal nucleation or other rare events....

  17. Hard sphere crystal nucleation and growth near large spherical impurities

    Science.gov (United States)

    de Villeneuve, V. W. A.; Verboekend, D.; Dullens, R. P. A.; Aarts, D. G. A. L.; Kegel, W. K.; Lekkerkerker, H. N. W.

    2005-11-01

    We report how large spherical impurities affect the nucleation and growth of hard sphere colloidal crystals. Both the impurities and the colloids are fluorescently labelled polymethylmetacrylate particles and are dispersed in an optically and density matching solvent mixture. Crystal growth, initiated either at the impurity surface, or at the sample bottom, was studied by imaging sequences of two-dimensional xy-slices in the plane of the impurity's centre of mass with a laser scanning confocal microscope. At least two factors determine whether a large impurity can function as a seed for heterogeneous nucleation: timescales and impurity curvature. The curvature needs to be sufficiently low for crystal nuclei to form on the impurity surface. If bulk crystal growth has already approached the impurity, bulk growth is dominant over growth of crystallites on the impurity surface. Such surface crystallites eventually reorient to adapt to the overall bulk crystal symmetry.

  18. Needs and Opportunities in Crystal Growth.

    Science.gov (United States)

    Mroczkowski, Stanley

    1980-01-01

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

  19. Applicability of Johnson-Mehl-Avrami model to crystallization kinetics of Zr60Al15Ni25 bulk amorphous alloy

    Institute of Scientific and Technical Information of China (English)

    YAN Zhi-jie; DANG Shu-e; WANG Xiang-hui; LIAN Pei-xia

    2008-01-01

    The applicability of Johnson-Mehl-Avrami(JMA) model to the crystallization kinetics of Zr60Al15Ni25 bulk amorphous alloy is investigated by differential scanning calorimetry(DSC) under isochronal and isothermal conditions. A criterion xm, at which a defined function z(x) exhibits the maximum value, is introduced to check the validity of JMA model to the kinetics analysis. The value of xm has a constant of 0.632 for JMA model. It is found that the values of xm at different isothermal annealing temperatures (743, 748, 753 and 758 K) are almost near 0.632, which indicates that the isothermal crystallization kinetics can be modeled by JMA equation. However, the values of xm at different heating rates (10, 20, 30 and 40 K/min) are about 0.52, implying that JMA model is not valid to the isochronal crystallization kinetics. The reason why the JMA model is not valid to the isochronal crystallization kinetics is discussed.

  20. Inhibition mechanism of aspartic acid on crystal growth of hydroxyapatite

    Institute of Scientific and Technical Information of China (English)

    HUANG Su-ping; ZHOU Ke-chao; LI Zhi-you

    2007-01-01

    The effects of aspartic acid on the crystal growth, morphology of hydroxyapatite(HAP) crystal were investigated, and the inhibition mechanism of aspartic acid on the crystal growth of hydroxyapatite was studied. The results show that the crystal growth rate of HAP decreases with the increase of the aspartic acid concentration, and the HAP crystal is thinner significantly compared with that without amino acid, which is mainly due to the (10(-)10) surface of HAP crystal being inhibited by the aspartic acids. The calculation analysis indicates that the crystal growth mechanism of HAP, following surface diffusion controlled mechanism, is not changed due to the presence of aspartic acid. AFM result shows that the front of terrace on vicinal growth hillocks is pinned, which suggests that the aspartic acid is adsorbed onto the (10(-)10) surface of HAP and interacts with the Ca2+ ions of HAP surface, so as to block the growth active sites and result in retarding of the growth of HAP crystal.

  1. Single Crystal Growth of Zirconia Utilizing a Skull Melting Technique,

    Science.gov (United States)

    1979-08-01

    help eliminate many crystal growth problems. The flame-fusion apparatus was invented by A. Verneuil 3 over 75 years ago and has been used for growth of...AOAO2 23 OMEAIRDEVLOPENT CNT RI RIFISS AFB NY F /S .7/ NGLE CRYSTAL GROWTH OF Z RONA UT IXZIN A SKULL MELTING TE-SCUl AUG 79 A C MARSHALL, J A ADAMSK...Crucible-less synthesis 50. ABSTRACT (Ceefiw.. - eooe edi. ,.e.eimwd identiby Slek ~b.,) Investigation into the growth of single crystal materials are

  2. Characterization of the Bridgman crystal growth process by radiographic imaging

    Science.gov (United States)

    Fripp, Archibald L.; Debnam, W. J.; Woodell, G. W.; Berry, R. F.; Simchick, R. T.; Sorokach, S. K.; Barber, P. G.

    1991-01-01

    Elemental (Ge) and alloy (PbSnTe) crystal growth that is monitored via radiography to reveal both the interface position and the shape in real time is discussed for both seeded and unseeded growth. It is concluded that the interface position and the actual growth rate of a Bridgman grown crystal is dependent on the growth conditions. The actual growth rate which is a strong function of the degree of supercooling exceeded the pull rate by a factor of greater than two. The interface shape changed from concave to flat to convex during the growth.

  3. Characterization of the Bridgman crystal growth process by radiographic imaging

    Science.gov (United States)

    Fripp, Archibald L.; Debnam, W. J.; Woodell, G. W.; Berry, R. F.; Simchick, R. T.; Sorokach, S. K.; Barber, P. G.

    1991-01-01

    Elemental (Ge) and alloy (PbSnTe) crystal growth that is monitored via radiography to reveal both the interface position and the shape in real time is discussed for both seeded and unseeded growth. It is concluded that the interface position and the actual growth rate of a Bridgman grown crystal is dependent on the growth conditions. The actual growth rate which is a strong function of the degree of supercooling exceeded the pull rate by a factor of greater than two. The interface shape changed from concave to flat to convex during the growth.

  4. Effect of irradiation temperature on crystallization of {alpha}-Fe induced by He irradiations in Fe{sub 80}B{sub 20} amorphous alloy

    Energy Technology Data Exchange (ETDEWEB)

    San-noo, Toshimasa; Toriyama, Tamotsu; Wakabayashi, Hidehiko; Iijima, Hiroshi [Musashi Inst. of Tech., Tokyo (Japan); Hayashi, Nobuyuki; Sakamoto, Isao

    1997-03-01

    Since amorphous alloys are generally highly resistant to irradiation and their critical radiation dose is an order of magnitude higher for Fe-B amorphous alloy than Mo-methods, these alloys are expected to become applicable as for fusion reactor materials. The authors investigated {alpha}-Fe crystallization in an amorphous alloy, Fe{sub 80}B{sub 20} using internal conversion electron Moessbauer spectroscopy. The amount of {alpha}-Fe component was found to increase by raising the He-irradiation dose. The target part was modified to enable He ion radiation at a lower temperature (below 400 K) by cooling with Peltier element. Fe{sub 80}B{sub 20} amorphous alloy was cooled to keep the temperature at 300 K and exposed to 40 keV He ion at 1-3 x 10{sup 8} ions/cm{sup 2}. The amount of {alpha}-Fe crystal in each sample was determined. The crystal formation was not observed for He ion radiation below 2 x 10{sup 18} ions/cm{sup 2}, but that at 3 x 10{sup 8} ions/ cm{sup 2} produced a new phase ({delta} +0.40 mm/sec, {Delta} = 0.89 mm/sec). The decrease in the radiation temperature from 430 to 300 K resulted to extremely repress the production of {alpha}-Fe crystal, suggesting that the crystallization induced by He-radiation cascade is highly depending on the radiation temperature. (M.N.)

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

    Institute of Scientific and Technical Information of China (English)

    DUAN Li; KANG Qi

    2009-01-01

    Real-time phase shift Mach-Zehnder interference technique,imaging technique,and computer image processing technique were combined to perform a real-time diagnosis of NaCIO3 crystal,which described both the dissolution process end the crystallization process of the NaCIO3 crystal in real-time condition.The dissolution fringes and the growth fringes in the process were obtained.Moreover,a distribution of concentration field in this process was obtained by inversion calculation.Finally,the buoyancy convection phenomenon caused by gravity in the crystal growth process was analyzed.The results showed that this convection phenomenon directly influences the growth rate of each crystal face in the crystal.

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

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Real-time phase shift Mach-Zehnder interference technique, imaging technique, and computer image processing technique were combined to perform a real-time diagnosis of NaClO3 crystal, which de- scribed both the dissolution process and the crystallization process of the NaClO3 crystal in real-time condition. The dissolution fringes and the growth fringes in the process were obtained. Moreover, a distribution of concentration field in this process was obtained by inversion calculation. Finally, the buoyancy convection phenomenon caused by gravity in the crystal growth process was analyzed. The results showed that this convection phenomenon directly influences the growth rate of each crystal face in the crystal.

  7. Calcite crystal growth rate inhibition by polycarboxylic acids

    Science.gov (United States)

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

    2001-01-01

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

  8. Growth and Characterization on PMN-PT-Based Single Crystals

    Directory of Open Access Journals (Sweden)

    Jian Tian

    2014-07-01

    Full Text Available Lead magnesium niobate—lead titanate (PMN-PT single crystals have been successfully commercialized in medical ultrasound imaging. The superior properties of PMN-PT crystals over the legacy piezoelectric ceramics lead zirconate titanate (PZT enabled ultrasound transducers with enhanced imaging (broad bandwidth and improved sensitivity. To obtain high quality and relatively low cost single crystals for commercial production, PMN-PT single crystals were grown with modified Bridgman method, by which crystals were grown directly from stoichiometric melt without flux. For ultrasound imaging application, [001] crystal growth is essential to provide uniform composition and property within a crystal plate, which is critical for transducer performance. In addition, improvement in crystal growth technique is under development with the goals of improving the composition homogeneity along crystal growth direction and reducing unit cost of crystals. In recent years, PIN-PMN-PT single crystals have been developed with higher de-poling temperature and coercive field to provide improved thermal and electrical stability for transducer application.

  9. Compression-induced crystallization of amorphous indomethacin in tablets: characterization of spatial heterogeneity by two-dimensional X-ray diffractometry.

    Science.gov (United States)

    Thakral, Naveen K; Mohapatra, Sarat; Stephenson, Gregory A; Suryanarayanan, Raj

    2015-01-05

    Tablets of amorphous indomethacin were compressed at 10, 25, 50, or 100 MPa using either an unlubricated or a lubricated die and stored individually at 35 °C in sealed Mylar pouches. At selected time points, tablets were analyzed by two-dimensional X-ray diffractometry (2D-XRD), which enabled us to profile the extent of drug crystallization in tablets, in both the radial and axial directions. To evaluate the role of lubricant, magnesium stearate was used as "internal" and/or "external" lubricant. Indomethacin crystallization propensity increased as a function of compression pressure, with 100 MPa pressure causing crystallization immediately after compression (detected using synchrotron radiation). However, the drug crystallization was not uniform throughout the tablets. In unlubricated systems, pronounced crystallization at the radial surface could be attributed to die wall friction. The tablet core remained substantially amorphous, irrespective of the compression pressure. Lubrication of the die wall with magnesium stearate, as external lubricant, dramatically decreased drug crystallization at the radial surface. The spatial heterogeneity in drug crystallization, as a function of formulation composition and compression pressure, was systematically investigated. When formulating amorphous systems as tablets, the potential for compression induced crystallization warrants careful consideration. Very low levels of crystallization on the tablet surface, while profoundly affecting product performance (decrease in dissolution rate), may not be readily detected by conventional analytical techniques. Early detection of crystallization could be pivotal in the successful design of a dosage form where, in order to obtain the desired bioavailability, the drug may be in a high energy state. Specialized X-ray diffractometric techniques (2D; use of high intensity synchrotron radiation) enabled detection of very low levels of drug crystallization and revealed the heterogeneity in

  10. Isothermal and non-isothermal crystallization in amorphous sucrose and lactose at low moisture contents.

    Science.gov (United States)

    Kedward, C J; MacNaughtan, W; Mitchell, J R

    2000-11-03

    Differential scanning calorimetry has been used in isothermal and non-isothermal modes to provide information on the crystallization of sucrose and lactose at low water contents. Using approaches previously applied to polymer crystallization an attempt has been made to combine the isothermal and non-isothermal data into a single curve. This is achieved by the use of appropriate shift factors in the time and temperature domains. This was successful for sucrose but not for lactose. It was suggested that this was because lactose crystallizes into multiple forms whereas sucrose crystallizes in a single form.

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

    Science.gov (United States)

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

    2000-01-01

    Calcite crystal growth experiments were undertaken to test a recently proposed model that relates crystal growth mechanisms to the shapes of crystal size distributions (CSDs). According to this approach, CSDs for minerals have three basic shapes: (1) asymptotic, which is related to a crystal growth mechanism having constant-rate nucleation accompanied by surface-controlled growth; (2) lognormal, which results from decaying-rate nucleation accompanied by surface-controlled growth; and (3) a theoretical, universal, steady-state curve attributed to Ostwald ripening. In addition, there is a fourth crystal growth mechanism that does not have a specific CSD shape, but which preserves the relative shapes of previously formed CSDs. This mechanism is attributed to supply-controlled growth. All three shapes were produced experimentally in the calcite growth experiments by modifying nucleation conditions and solution concentrations. The asymptotic CSD formed when additional reactants were added stepwise to the surface of solutions that were supersaturated with respect to calcite (initial Ω = 20, where Ω = 1 represents saturation), thereby leading to the continuous nucleation and growth of calcite crystals. Lognormal CSDs resulted when reactants were added continuously below the solution surface, via a submerged tube, to similarly supersaturated solutions (initial Ω = 22 to 41), thereby leading to a single nucleation event followed by surface-controlled growth. The Ostwald CSD resulted when concentrated reactants were rapidly mixed, leading initially to high levels of supersaturation (Ω >100), and to the formation and subsequent dissolution of very small nuclei, thereby yielding CSDs having small crystal size variances. The three CSD shapes likely were produced early in the crystallization process, in the nanometer crystal size range, and preserved during subsequent growth. Preservation of the relative shapes of the CSDs indicates that a supply-controlled growth mechanism

  12. Crystal growth mechanisms of the (0 1 0) face of α-lactose monohydrate crystals

    Science.gov (United States)

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

    2009-04-01

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

  13. Chemical Bond Calculations of Crystal Growth of KDP and ADP

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A novel method was proposed to calculate the crystal morphology (or growth habit) on the basis of chemical bond analysis. All constituent chemical bonds were distinguished as relevant and independent bonds according to their variations during the crystallization process. By employing the current method, the influence of specific growth conditions on the crystal morphology can be considered in the structure analysis process. The ideal morphologies of both KDP (KH2PO4) and ADP (NH4H2PO4) crystals were calculated and compared with our obtained crystallites at room temperature, which validates the present calculation method very well.

  14. Use of successive ionic layer adsorption and reaction (SILAR) method for amorphous titanium dioxide thin films growth

    Science.gov (United States)

    Kale, S. S.; Mane, R. S.; Chung, Hoeil; Yoon, Moon-Young; Lokhande, C. D.; Han, Sung-Hwan

    2006-11-01

    Use of successive ionic layer adsorption and reaction (SILAR) method was preferred for the growth of amorphous titanium dioxide (TiO 2) thin films at ambient temperature. Further, these films were annealed at 673 K for 2 h in air for structural improvement and characterized for structural, surface morphological, optical and electrical properties. An amorphous structure of TiO 2 was retained even after annealing as confirmed from XRD studies. The spherical grains of relatively large size were compressed after annealing. A red shift in band gap energy and decrease in electrical resistivity were observed due to annealing treatment.

  15. Shear-band propagation in fully amorphous and partially crystallized Mg-based alloys studied by nanoindentation and transmission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Castellero, A. [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom) and Laboratory of Metal Physics and Technology, Department of Materials, ETH Zuerich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich (Switzerland)]. E-mail: alberto.castellero@unito.it; Lloyd, S.J. [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom); Madge, S.V. [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom); International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), PO Balapur, Hyderabad 500 005 (India); Kovacs, Zs. [Department of General Physics, Eoetvoes Lorand University, Pazmany P. setany 1/a, 1117 Budapest (Hungary); Loeffler, J.F. [Laboratory of Metal Physics and Technology, Department of Materials, ETH Zuerich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich (Switzerland); Baricco, M. [Dipartimento di Chimica I.F.M. and N.I.S., Universita degli Studi di Torino, Via P. Giuria 9, I-10125 Turin (Italy); Greer, A.L. [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom)

    2007-05-31

    Fully amorphous and partially crystallized Mg{sub 66}Ni{sub 20}Nd{sub 14} and partially crystallized Mg{sub 60}Cu{sub 30}Y{sub 10} alloys were indented and, subsequently, thinned along the cross-section of the indent by means of a focused ion beam (FIB) for transmission electron microscopy (TEM) observation. Depending on the crystallized fraction and the crystal size, the volume deformed under the indenter tip shows different features that can be associated with the different ability of the shear bands to propagate in the two partially devitrified metallic glasses.

  16. Universality classes for unstable crystal growth.

    Science.gov (United States)

    Biagi, Sofia; Misbah, Chaouqi; Politi, Paolo

    2014-06-01

    Universality has been a key concept for the classification of equilibrium critical phenomena, allowing associations among different physical processes and models. When dealing with nonequilibrium problems, however, the distinction in universality classes is not as clear and few are the examples, such as phase separation and kinetic roughening, for which universality has allowed to classify results in a general spirit. Here we focus on an out-of-equilibrium case, unstable crystal growth, lying in between phase ordering and pattern formation. We consider a well-established 2+1-dimensional family of continuum nonlinear equations for the local height h(x,t) of a crystal surface having the general form ∂_{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 β, controlling the increase in time of the typical slope of the pattern, M∼t^{β}, where M≈H/L. Our study reveals that there are only two different universality classes, according to the presence (n=1/3, β=0) or the absence (n=1/4, β>0) of faceting. The symmetry of the pattern, as well as the symmetry of the surface mass current j(∇h) and its precise functional form, is irrelevant. Our analysis seems to support the idea that also space dimensionality is irrelevant.

  17. Growth and defects of explosives crystals

    Science.gov (United States)

    Cady, H. H.

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

  18. Gap states in the electronic structure of SnO2 single crystals and amorphous SnOx thin films

    Science.gov (United States)

    Haeberle, J.; Machulik, S.; Janowitz, C.; Manzke, R.; Gaspar, D.; Barquinha, P.; Schmeißer, D.

    2016-09-01

    The electronic structure of a SnO2 single crystal is determined by employing resonant photoelectron spectroscopy. We determine the core level, valence band, and X-ray absorption (XAS) data and compare these with those of amorphous SnOx thin films. We find similar properties concerning the data of the core levels, the valence band features, and the absorption data at the O1s edge. We find strong signals arising from intrinsic in-gap states and discuss their origin in terms of polaronic and charge-transfer defects. We deduce from the XAS data recorded at the Sn3d edge that the Sn4d10 ground state has contributions of 4d9 and 4d8 states due to configuration interaction. We identify localized electronic states depending on the strength of the 4d-5s5p interaction and of the O2p-to-Sn4d charge-transfer processes, both appear separated from the extended band-like states of the conduction band. For the amorphous SnOx thin films, significant differences are found only in the absorption data at the Sn3d-edge due to a stronger localization of the in-gap states.

  19. Nano-Crystallization of High-Entropy Amorphous NbTiAlSiWxNy Films Prepared by Magnetron Sputtering

    Directory of Open Access Journals (Sweden)

    Wenjie Sheng

    2016-06-01

    Full Text Available High-entropy amorphous NbTiAlSiWxNy films (x = 0 or 1, i.e., NbTiAlSiNy and NbTiAlSiWNy were prepared by magnetron sputtering method in the atmosphere of a mixture of N2 + Ar (N2 + Ar = 24 standard cubic centimeter per minute (sccm, where N2 = 0, 4, and 8 sccm. All the as-deposited films present amorphous structures, which remain stable at 700 °C for over 24 h. After heat treatment at 1000 °C the films began to crystalize, and while the NbTiAlSiNy films (N2 = 4, 8 sccm exhibit a face-centered cubic (FCC structure, the NbTiAlSiW metallic films show a body-centered cubic (BCC structure and then transit into a FCC structure composed of nanoscaled particles with increasing nitrogen flow rate. The hardness and modulus of the as-deposited NbTiAlSiNy films reach maximum values of 20.5 GPa and 206.8 GPa, respectively. For the as-deposited NbTiAlSiWNy films, both modulus and hardness increased to maximum values of 13.6 GPa and 154.4 GPa, respectively, and then decrease as the N2 flow rate is increased. Both films could be potential candidates for protective coatings at high temperature.

  20. Phase Relationship in Phenol-Insulin Crystal Growth System

    Institute of Scientific and Technical Information of China (English)

    梁栋材; 宋浪舟; 万柱礼; 常文瑞

    1994-01-01

    Based on the crystal growth system of rhombohedral 2Zn-insulin,the phase transition ofinsulin crystals has been investigated with the phenol concentration as an independent component.The dia-gram of the phase relationship in this crystal growth system was established,and two points of phase transi-tion were found.The transition point Ⅰ indicates the phase transition between rhombohedral 2Zn-insulin crys-tal and rhombohedral 4Zn-insulin crystal,and these two phases coexist within a narrow region of phenol con-centration (0.028%-0.029% (g/ml)).Point Ⅱ at 0.76%-0.77% (g/ml) of phenol concentration showsthe phase transition between rhombohcdral crystal and monoclinic crystals,and a new phase of monocliniccrystal (B-form monoclinic insulin crystal) has been observed.This paper reports the diagram of phase rela-tionship obtained from our experiments,and analyses and discusses the dependence of phase transition of in-sulin crystals on phenol concentration in crystal growth system.

  1. Progress in modeling of fluid flows in crystal growth processes

    Institute of Scientific and Technical Information of China (English)

    Qisheng Chen; Yanni Jiang; Junyi Yan; Ming Qin

    2008-01-01

    Modeling of fluid flows in crystal growth processes has become an important research area in theoretical and applied mechanics.Most crystal growth processes involve fluid flows,such as flows in the melt,solution or vapor.Theoretical modeling has played an important role in developing technologies used for growing semiconductor crystals for high performance electronic and optoelectronic devices.The application of devices requires large diameter crystals with a high degree of crystallographic perfection,low defect density and uniform dopant distribution.In this article,the flow models developed in modeling of the crystal growth processes such as Czochralski,ammono-thermal and physical vapor transport methods are reviewed.In the Czochralski growth modeling,the flow models for thermocapillary flow,turbulent flow and MHD flow have been developed.In the ammonothermal growth modeling,the buoyancy and porous media flow models have been developed based on a single-domain and continuum approach for the composite fluid-porous layer systems.In the physical vapor transport growth modeling,the Stefan flow model has been proposed based on the flow-kinetics theory for the vapor growth.In addition,perspectives for future studies on crystal growth modeling are proposed.

  2. Method of Promoting Single Crystal Growth During Melt Growth of Semiconductors

    Science.gov (United States)

    Su, Ching-Hua (Inventor)

    2013-01-01

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

  3. Growth of Solid Solution Single Crystals

    Science.gov (United States)

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

    2001-01-01

    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.

  4. Crystal growth methods dedicated to low solubility actinide oxalates

    Energy Technology Data Exchange (ETDEWEB)

    Tamain, C., E-mail: christelle.tamain@cea.fr [CEA, Nuclear Energy Division, Marcoule, RadioChemistry & Processes Department, F-30207 Bagnols sur Cèze (France); Arab-Chapelet, B. [CEA, Nuclear Energy Division, Marcoule, RadioChemistry & Processes Department, F-30207 Bagnols sur Cèze (France); Rivenet, M. [University Lille Nord de France, Unité de Catalyse et de Chimie du Solide, UCCS UMR CNRS 8181, ENSCL-USTL, B.P. 90108, F-59652 Villeneuve d’Ascq Cedex (France); Grandjean, S. [CEA, Nuclear Energy Division, Marcoule, RadioChemistry & Processes Department, F-30207 Bagnols sur Cèze (France); Abraham, F. [University Lille Nord de France, Unité de Catalyse et de Chimie du Solide, UCCS UMR CNRS 8181, ENSCL-USTL, B.P. 90108, F-59652 Villeneuve d’Ascq Cedex (France)

    2016-04-15

    Two novel crystal growth syntheses dedicated to low solubility actinide-oxalate systems and adapted to glove box handling are described. These methods based on the use of precursors of either actinide metal or oxalic acid have been optimized on lanthanide systems (analogue of actinides(III)) and then assessed on real actinide systems. They allow the synthesis of several actinide oxalate single crystals, Am{sub 2}(C{sub 2}O{sub 4}){sub 3}(H{sub 2}O){sub 3}·xH{sub 2}O, Th(C{sub 2}O{sub 4}){sub 2}·6H{sub 2}O, M{sub 2+x}[Pu{sup IV}{sub 2−x}Pu{sup III}{sub x}(C{sub 2}O{sub 4}){sub 5}]·nH{sub 2}O and M{sub 1−x}[Pu{sup III}{sub 1−x}Pu{sup IV}{sub x}(C{sub 2}O{sub 4}){sub 2}·H{sub 2}O]·nH{sub 2}O. It is the first time that these well-known compounds are formed by crystal growth methods, thus enabling direct structural studies on transuranic element systems and acquisition of basic data beyond deductions from isomorphic (or not) lanthanide compounds. Characterizations by X-ray diffraction, UV–visible solid spectroscopy, demonstrate the potentialities of these two crystal growth methods to obtain oxalate compounds. - Graphical abstract: Two new single crystal growth methods dedicated to actinide oxalate compounds. - Highlights: • Use of diester as oxalate precursor for crystal growth of actinide oxalates. • Use of actinide oxide as precursor for crystal growth of actinide oxalates. • Crystal growth of Pu(III) and Am(III) oxalates. • Crystal growth of mixed Pu(III)/Pu(IV) oxalates.

  5. Evaluate the ability of PVP to inhibit crystallization of amorphous solid dispersions by density functional theory and experimental verify.

    Science.gov (United States)

    Wang, Bing; Wang, Dandan; Zhao, Shan; Huang, Xiaobin; Zhang, Jianbin; Lv, Yan; Liu, Xiaocen; Lv, Guojun; Ma, Xiaojun

    2017-01-01

    In this study, we used density functional theory (DFT) to predict polymer-drug interactions, and then evaluated the ability of poly (vinyl pyrrolidone) (PVP) to inhibit crystallization of amorphous solid dispersions by experimental-verification. Solid dispersions of PVP/resveratrol (Res) and PVP/griseofulvin (Gri) were adopted for evaluating the ability of PVP to inhibit crystallization. The density functional theory (DFT) with the B3LYP was used to calculate polymer-drug and drug-drug interactions. Fourier transform infrared spectroscopy (FTIR) was used to confirm hydrogen bonding interactions. Polymer-drug miscibility and drug crystallinity were characterized by the modulated differential scanning calorimetry (MDSC) and X-ray powder diffraction (XRD). The release profiles were studied to investigate the dissolution advantage. DFT results indicated that EPVP-Res>ERes-Res (E: represents hydrogen bonding energy). A strong interaction was formed between PVP and Res. In addition, Fourier transform infrared spectroscopy (FTIR) analysis showed hydrogen bonding formed between PVP and Res, but not between PVP and Gri. MDSC and XRD results suggested that 70-90wt% PVP/Res and PVP/Gri solid dispersions formed amorphous solid dispersions (ASDs). Under the accelerated testing condition, PVP/Res dispersions with higher miscibility quantified as 90/10wt% were more stable than PVP/Gri dispersions. The cumulative dissolution rate of 90wt% PVP/Res dispersions still kept high after 90days storage due to the strong interaction. However, the cumulative dissolution rate of PVP/Gri solid dispersions significantly dropped because of the recrystallization of Gri. Copyright © 2016 Elsevier B.V. All rights reserved.

  6. Growth and characterization of DAST crystal with large-thickness

    Science.gov (United States)

    Cao, Lifeng; Teng, Bing; Zhong, Degao; Hao, Lun; Sun, Qing

    2016-10-01

    Highly nonlinear optical 4-N, N-dimethylamino-4-N-methyl stilbazolium tosylate (DAST) crystals with large surface and thickness was grown by the slope nucleation technology with slow-cooling in a high concentration solution. The structure and composition of the crystal were confirmed by X-ray diffraction (XRD). The surface morphology of the crystal was characterized by optical microscope. Growth layers were observed on the (001) surface and several isolated "island layers" were also found. The mechanism of crystal growth was analyzed. Etching behavior of the (001) and (00 1 bar) faces of the crystal was studied with methanol, respectively. Optical properties of the crystal were also characterized by UV-vis-NIR spectrometer. The dielectric constants and the dielectric loss were tested by impedance analyzer.

  7. Development of novel growth methods for halide single crystals

    Science.gov (United States)

    Yokota, Yuui; Kurosawa, Shunsuke; Shoji, Yasuhiro; Ohashi, Yuji; Kamada, Kei; Yoshikawa, Akira

    2017-03-01

    We developed novel growth methods for halide scintillator single crystals with hygroscopic nature, Halide micro-pulling-down [H-μ-PD] method and Halide Vertical Bridgman [H-VB] method. The H-μ-PD method with a removable chamber system can grow a single crystal of halide scintillator material with hygroscopicity at faster growth rate than the conventional methods. On the other hand, the H-VB method can grow a large bulk single crystal of halide scintillator without a quartz ampule. CeCl3, LaBr3, Ce:LaBr3 and Eu:SrI2 fiber single crystals could be grown by the H-μ-PD method and Eu:SrI2 bulk single crystals of 1 and 1.5 inch in diameter could be grown by the H-VB method. The grown fiber and bulk single crystals showed comparable scintillation properties to the previous reports using the conventional methods.

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

    Science.gov (United States)

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

    2015-04-01

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

  9. Nucleation and structural growth of cluster crystals

    CERN Document Server

    Leitold, Christian

    2016-01-01

    We study the nucleation of crystalline cluster phases in the generalized exponential model with exponent n=4. Due to the finite value of this pair potential for zero separation, at high densities the system forms cluster crystals with multiply occupied lattice sites. Here, we investigate the microscopic mechanisms that lead to the formation of cluster crystals from a supercooled liquid in the low-temperature region of the phase diagram. Using molecular dynamics and umbrella sampling, we calculate the free energy as a function of the size of the largest crystalline nucleus in the system, and compare our results with predictions from classical nucleation theory. Employing bond-order parameters based on a Voronoi tessellation to distinguish different crystal structures, we analyze the average composition of crystalline nuclei. We find that even for conditions where a multiply-occupied fcc crystal is the thermodynamically stable phase, the nucleation into bcc cluster crystals is strongly preferred. Furthermore, w...

  10. Nonlinear Optical BBO Crystals: Growth, Properties and Applications

    Institute of Scientific and Technical Information of China (English)

    唐鼎元

    2000-01-01

    Low temperature phase barium metaborate β-BaB2O4 (BBO) is an important nonlinear optical material. Up to now, the BBO single crystals with large size and good optical quality were grown from Na2O or NaF fluxed solvents by the top-seeded solution growth (TSSG) technique with or without pulling. In order to improve the growth rate and quality of BBO crystals, several new techniques such as continuous feeding, forced stirring and cooling growing crystals etc. have been suggested. Applications of BBO as an excellent nonlinear optical crystal include mainly frequency conversion of various laser radiation, high average power frequency conversion, frequency doubling of ultrashort pulses and broadly tunable optical parametric oscillators (OPO).This paper is a brief review on the growth, properties and applications of BBO crystals.

  11. Modelling of Heat Transfer in Single Crystal Growth

    CERN Document Server

    Zhmakin, Alexander I

    2014-01-01

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

  12. In-situ X-ray diffraction studies of time and thickness dependence of crystallization of amorphous TiO{sub 2} thin films and stress evolution

    Energy Technology Data Exchange (ETDEWEB)

    Kuzel, R., E-mail: kuzel@karlov.mff.cuni.c [Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University in Prague, 121 16 Praha 2 (Czech Republic); Nichtova, L.; Matej, Z. [Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University in Prague, 121 16 Praha 2 (Czech Republic); Musil, J. [Department of Physics, Faculty of Applied Sciences, University of West Bohemia in Pilsen, Pilsen (Czech Republic)

    2010-12-30

    Remarkable properties of titanium dioxide films such as hydrophilicity or photocatalytic activity depend largely on their phase composition, microstructure and in particular on the crystallinity. By in-situ X-ray diffraction studies of isochronal and isothermal annealing of amorphous films with different thickness at different temperatures it was found that the crystallization process can be quite well described by the Johnson-Mehl-Avrami-Kolmogorov formula modified by the introduction of crystallization onset. This and other parameters of the formula strongly depend on the film thickness. For thickness below about 500 nm the crystallization is very slow. Simultaneously, the appearance and increase of tensile stresses with the annealing time were observed and these stresses were confirmed by detailed studies by both total pattern fitting and sin{sup 2{psi}} method on post-annealed samples. The stresses rapidly increase with decreasing thickness of the films. It seems that there is a strong correlation between the stresses and crystallization onset and/or crystallization rate. Tensile stresses that are generated during crystallization further inhibit crystallization and cause significant thickness dependence of the crystallization. The temperature and time dependence of microstructure of crystallized amorphous films differ significantly from those obtained for as-deposited nanocrystalline films or nanocrystalline powders. During annealing, quite large crystallites are formed quickly with the preferred orientation (001) that is suppressed with the proceeding time.

  13. Crystallization kinetics of amorphous Te(Bi2Se3)1– glasses

    Indian Academy of Sciences (India)

    Manish Saxena

    2004-12-01

    The activation energy plays a dominant role in deciding the utility of the material for the specific purpose—here storage. The dependence of the peak temperature of crystallization (p) on the composition and heating rate () has been studied here. From the heating rate dependence, p, the activation energy for crystallization (c) has been evaluated. The activation energy, c, calculated using three different approaches is found to decrease with the increase in Bi content. This analysis helps in finding the suitability of an alloy to be used in phase transition optical memories/switches. The results have been analysed using Kissinger’s equation for non-isothermal crystallization of materials.

  14. Zeolite Crystal Growth (ZCG) Flight on USML-2

    Science.gov (United States)

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

    1997-01-01

    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.

  15. A Multiscale simulation method for ice crystallization and frost growth

    Science.gov (United States)

    Yazdani, Miad

    2015-11-01

    Formation of ice crystals and frost is associated with physical mechanisms at immensely separated scales. The primary focus of this work is on crystallization and frost growth on a cold plate exposed to the humid air. The nucleation is addressed through Gibbs energy barrier method based on the interfacial energy of crystal and condensate as well as the ambient and surface conditions. The supercooled crystallization of ice crystals is simulated through a phase-field based method where the variation of degree of surface tension anisotropy and its mode in the fluid medium is represented statistically. In addition, the mesoscale width of the interface is quantified asymptotically which serves as a length-scale criterion into a so-called ``Adaptive'' AMR (AAMR) algorithm to tie the grid resolution at the interface to local physical properties. Moreover, due to the exposure of crystal to humid air, a secondary non-equilibrium growth process contributes to the formation of frost at the tip of the crystal. A Monte-Carlo implementation of Diffusion Limited Aggregation method addresses the formation of frost during the crystallization. Finally, a virtual boundary based Immersed Boundary Method (IBM) is adapted to address the interaction of ice crystal with convective air during its growth.

  16. Imaging and interferometric analysis of protein crystal growth

    Science.gov (United States)

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

    2008-04-01

    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.

  17. Growth features of ammonium hydrogen -tartrate single crystals

    Indian Academy of Sciences (India)

    G Sajeevkumar; R Raveendran; B S Remadevi; Alexander Varghese Vaidyan

    2004-08-01

    Ammonium hydrogen -tartrate (-AHT) single crystals were grown in silica gel. The growth features of these crystals with variation of parameters like specific gravity of the gel, gel pH, acid concentrations, concentration of the feed solution and gel age were studied in detail.

  18. Cross-twinning model of fcc crystal growth

    NARCIS (Netherlands)

    Waal, van de Benjamin W.

    1996-01-01

    The theory developed in 1960 by Wagner, Hamilton and Seidensticker (WHS-theory) to explain observed crystal growth phenomena in Ge is critically reviewed and shown to be capable of explaining preservation of ABC stacking order in two dimensions in fcc crystals of effectively spherical closed shell m

  19. An automatic system for crystal growth studies at constant supersaturation

    Science.gov (United States)

    March, J. G.; Costa-Bauzá, A.; Grases, F.; Söhnel, O.

    1992-01-01

    An automatic system for growing crystals from seeded supersaturated solutions at constant supersaturation is described. Control of burettes and data acquisition are controlled by computer. The system was tested with a study of the calcium oxalate kinetics of crystal growth. PMID:18924950

  20. Modeling and simulation of Si crystal growth from melt

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Lijun; Liu, Xin; Li, Zaoyang [National Engineering Research Center for Fluid Machinery and Compressors, School of Energy and Power Engineering, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Miyazawa, Hiroaki; Nakano, Satoshi; Kakimoto, Koichi [Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580 (Japan)

    2009-07-01

    A numerical simulator was developed with a global model of heat transfer for any crystal growth taking place at high temperature. Convective, conductive and radiative heat transfers in the furnace are solved together in a conjugated way by a finite volume method. A three-dimensional (3D) global model was especially developed for simulation of heat transfer in any crystal growth with 3D features. The model enables 3D global simulation be conducted with moderate requirement of computer resources. The application of this numerical simulator to a CZ growth and a directional solidification process for Si crystals, the two major production methods for crystalline Si for solar cells, was introduced. Some typical results were presented, showing the importance and effectiveness of numerical simulation in analyzing and improving these kinds of Si crystal growth processes from melt. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. The crystal growth of barium flouride in aqueous solution

    Science.gov (United States)

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

    1983-06-01

    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 (σ ≈ 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.

  2. Manufacture of Bulk Amorphous Crystal and Micro-Crystal for Pr60Cu(20-x)Ni10Al10Fex and Characteristics of Its Magnetic Apparatus

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Bulk amorphous crystal and microcrystal for Pr60Cu(20-x)Ni10Al10Fex (x=0, 8, 15, 20) with the diameter of Φ 2~6 mm were manufactured by electric arc smelting, high frequency heating and copper mold upper suction casting, and its structure was analyzed by X-ray diffract meter. It showed soft magnetic characteristic gradually when Fe content in it was up to 8%. The material was applied to magnetic-electric sensor as key component, output signal of which was measured with the change of Fe content. It shows that the signal changes from weak to strong with the increase of Fe content and presents the largest peak value when Fe is replaced by Cu completely.

  3. Crystal size growth in the liquid phase methanol synthesis catalyst

    Energy Technology Data Exchange (ETDEWEB)

    Sawant, A.; Lee, S.; Foos, A.

    1988-01-01

    The phenomenon of crystal growth in the methanol synthesis catalyst has been studied. Crystallite size distributions in the CuO/ZnO/Al/sub 2/O/sub 3/ methanol synthesis catalyst have been determined. The effects of temperature, reaction environment and time under reaction conditions have been studied. It is observed that water in the reaction mixture promotes crystal growth. 26 refs., 10 figs., 1 tab.

  4. Kinetics of the growth of filamentary KH2PO4 crystals on a seed crystal

    Science.gov (United States)

    Titaeva, E. K.; Kuritsyn, M. S.; Noskova, A. N.; Portnov, V. N.

    2017-08-01

    At oversaturations exceeding the inert range end for face {101} due to the presence of admixture Al(NO3)3 · 9H2O, a new phase is observed during the growth of this face in the form of filamentary crystals. Some experimental dependences of the growth rate of filamentary potassium dihydrophosphate (KH2PO4) crystals on the oversaturation have been obtained at different admixture concentrations. The growth of filamentary crystals occurs by the mechanism of two-dimensional nucleation. Their formation is governed by the effect of [AlHPO4]+ complexes in the form of Cabrera and Vermilyea stoppers.

  5. Theory of the intermediate stage of crystal growth with applications to insulin crystallization

    Science.gov (United States)

    Barlow, D. A.

    2017-07-01

    A theory for the intermediate stage of crystal growth, where two defining equations one for population continuity and another for mass-balance, is used to study the kinetics of the supersaturation decay, the homogeneous nucleation rate, the linear growth rate and the final distribution of crystal sizes for the crystallization of bovine and porcine insulin from solution. The cited experimental reports suggest that the crystal linear growth rate is directly proportional to the square of the insulin concentration in solution for bovine insulin and to the cube of concentration for porcine. In a previous work, it was shown that the above mentioned system could be solved for the case where the growth rate is directly proportional to the normalized supersaturation. Here a more general solution is presented valid for cases where the growth rate is directly proportional to the normalized supersaturation raised to the power of any positive integer. The resulting expressions for the time dependent normalized supersaturation and crystal size distribution are compared with experimental reports for insulin crystallization. An approximation for the maximum crystal size at the end of the intermediate stage is derived. The results suggest that the largest crystal size in the distribution at the end of the intermediate stage is maximized when nucleation is restricted to be only homogeneous. Further, the largest size in the final distribution depends only weakly upon the initial supersaturation.

  6. Growth and characterization of lead bromide crystals

    Science.gov (United States)

    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

    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.

  7. Assessment of degree of disorder (amorphicity) of lyophilized formulations of growth hormone using isothermal microcalorimetry.

    Science.gov (United States)

    Mosharraf, Mitra

    2004-05-01

    When determining the degree of disorder of a lyophilized cake of a protein, it is important to use an appropriate analytical technique. Differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD) are the most commonly used thermoanalytical techniques for characterizing freeze-dried protein formulations. Unfortunately, these methods are unable to detect solid-state disorder at levels IMC) in the assessment of degree of solid-state disorder (amorphicity) of lyophilized formulations of proteins. For this purpose, two formulations of growth hormone were prepared by lyophilization. These formulations consisted of the same amounts of protein, mannitol, glycine, and phosphate buffer, but differed in the freeze-drying procedure. After lyophilization, the recrystallization of the samples was studied using IMC at 25 degrees C under different relative humidities (58-75%). The effect of available surface area was studied by determining the heat of recrystallization (Q) of the samples before and after disintegration of the cakes. The results showed that, in contrast to DSC, IMC allowed detection of the recrystallization event in the formulations. Although both formulations were completely disordered and indistinguishable according to XRPD method, IMC revealed that formulation B had a different solid-sate structure than formulation A. This difference was the result of differences in the freeze-drying parameters, demonstrating the importance of choosing appropriate analytical methodology.

  8. On the relationship between crystalline structure and amorphous phase dynamics during isothermal crystallization of bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymers.

    Science.gov (United States)

    Sics, I; Ezquerra, T A; Nogales, A; Baltá-Calleja, F J; Kalniņs, M; Tupureina, V

    2001-01-01

    The isothermal crystallization process of a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer, P(HB-co-HV) with a HB/HV ratio 78/22 was investigated by simultaneous small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and dielectric spectroscopy (DS). By use of this experimental setup (SWD), we have obtained simultaneous information about changes occurring in both the crystalline and the amorphous phases during crystallization. By using the Havriliak-Negami formalism to analyze the dielectric relaxation data, a strong dependence of the relaxation curve shape with the development of the crystalline phase was found. However, in this particular copolymer, the developing crystalline domains do not affect significantly the average segmental mobility in the amorphous phase. This effect is discussed in the light of the enrichment of amorphous phase by HV comonomer units during primary crystallization, hindering the secondary crystallization processes. Results support the hypothesis that the decrease of the physical-aging-like behavior, observed in P(HB-co-HV) copolymers as the amount of HV increases, can be attributed to the progressive inhibition of secondary crystallization mechanisms.

  9. Growth and characterization of strontium tartrate pentahydrate crystals

    Energy Technology Data Exchange (ETDEWEB)

    Firdous, A.; Ahmad, M.M. [Department of Physics, National Institute of Technology, Kashmir (India); Quasim, I.; Kotru, P.N. [Crystal Growth and Materials Research Laboratory, Department of Physics and Electronics, University of Jammu (India)

    2008-10-15

    Silica gel impregnated with L-tartaric acid and using strontium nitrate as the second reactant leads to the growth of well faceted strontium tartrate pentahydrate single crystals.The morphological developmen and internal cell dimensions are observed to be different from the ones reported in the literature for strontium tartrate trihydrate crystals. The crystals are characterized using XRD, CH analysis, SEM, FTIR spectroscopy and thermoanalytical techniques. The crystals are observed to be thermally stable upto about 105 C but thereafter start decomposing and ejecting water of hydration at various stages, finally reducing to strontium oxide. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Growth morphology and structural characteristic of C70single crystals

    Institute of Scientific and Technical Information of China (English)

    周维亚; 解思深; 吴源; 常保和; 王刚; 钱露茜

    1999-01-01

    Large size C70 single crystals with the dimension of more than 5 mm are grown from the vapor phase by controlling nucleation. X-ray diffraction and electron diffraction confirm that in the C70 single crystal a phase of the hexagonal close-packed (hcp) structure coexists with a minor face-center-cubic (fcc) phase at room temperature. The morphologies and their formation mechanism of the C70 single crystals are investigated by means of scanning electron microscopy and optical microscopy. The influence of growth conditions on the morphologies of C70 single crystals is discussed.

  11. Growth and characterization of CdS crystals

    Science.gov (United States)

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

    1990-01-01

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

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

    Science.gov (United States)

    Lundquist, C. A.

    1974-01-01

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

  13. Fluid mechanics in crystal growth - The 1982 Freeman scholar lecture

    Science.gov (United States)

    Ostrach, S.

    1983-01-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-03-01

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

  15. Atomic simulation of amorphization and crystallization of Ag50 Au50 alloy during rapid solidification

    Institute of Scientific and Technical Information of China (English)

    王丽; 杨华; 张均艳; 边秀房; 衣粟

    2002-01-01

    By means of constant temperature and constant pressure molecular dynamic simulation technique, a series of simulations of the glass transition and crystallization processes of Ag50Au50 were performed. The atoms interact via EAM potential function. Pair correlation functions of liquid Ag50Au50 during different cooling rates and temperatures were simulated to reveal the structural features of liquid, super-cooled liquid, glass state and crystal. The thermodynamics and kinetics of structure transition of Ag50Au50 during cooling processes were performed.

  16. Protein crystal growth and the International Space Station

    Science.gov (United States)

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

    1999-01-01

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

  17. Mathematical model to analyze the dissolution behavior of metastable crystals or amorphous drug accompanied with a solid-liquid interface reaction.

    Science.gov (United States)

    Hirai, Daiki; Iwao, Yasunori; Kimura, Shin-Ichiro; Noguchi, Shuji; Itai, Shigeru

    2017-02-21

    Metastable crystals and the amorphous state of poorly water-soluble drugs in solid dispersions (SDs), are subject to a solid-liquid interface reaction upon exposure to a solvent. The dissolution behavior during the solid-liquid interface reaction often shows that the concentration of drugs is supersaturated, with a high initial drug concentration compared with the solubility of stable crystals but finally approaching the latter solubility with time. However, a method for measuring the precipitation rate of stable crystals and/or the potential solubility of metastable crystals or amorphous drugs has not been established. In this study, a novel mathematical model that can represent the dissolution behavior of the solid-liquid interface reaction for metastable crystals or amorphous drug was developed and its validity was evaluated. The theory for this model was based on the Noyes-Whitney equation and assumes that the precipitation of stable crystals at the solid-liquid interface occurs through a first-order reaction. Moreover, two models were developed, one assuming that the surface area of the drug remains constant because of the presence of excess drug in the bulk and the other that the surface area changes in time-dependency because of agglomeration of the drug. SDs of Ibuprofen (IB)/polyvinylpyrrolidone (PVP) were prepared and their dissolution behaviors under non-sink conditions were fitted by the models to evaluate improvements in solubility. The model assuming time-dependent surface area showed good agreement with experimental values. Furthermore, by applying the model to the dissolution profile, parameters such as the precipitation rate and the potential solubility of the amorphous drug were successfully calculated. In addition, it was shown that the improvement in solubility with supersaturation was able to be evaluated quantitatively using this model. Therefore, this mathematical model would be a useful tool to quantitatively determine the supersaturation

  18. Slanted stacking faults and persistent face centered cubic crystal growth in sedimentary colloidal hard sphere crystals

    NARCIS (Netherlands)

    Hilhorst, J.; Wolters, J. R.; Petukhov, A.V.

    2010-01-01

    Hard sphere crystal growth is a delicate interplay between kinetics and thermodynamics, where the former is commonly thought to favour a random hexagonal close packed structure and the latter leads to a face centered cubic crystal. In this article, we discuss the influence of slanted stacking faults

  19. Crystal growth of CVD diamond and some of its peculiarities

    CERN Document Server

    Piekarczyk, W

    1999-01-01

    Experiments demonstrate that CVD diamond can form in gas environments that are carbon undersaturated with respect to diamond. This fact is, among others, the most serious violation of principles of chemical thermodynamics. In this $9 paper it is shown that none of the principles is broken when CVD diamond formation is considered not a physical process consisting in growth of crystals but a chemical process consisting in accretion of macro-molecules of polycyclic $9 saturated hydrocarbons belonging to the family of organic compounds the smallest representatives of which are adamantane, diamantane, triamantane and so forth. Since the polymantane macro-molecules are in every respect identical with $9 diamond single crystals with hydrogen-terminated surfaces, the accretion of polymantane macro- molecules is a process completely equivalent to the growth of diamond crystals. However, the accretion of macro-molecules must be $9 described in a way different from that used to describe the growth of crystals because so...

  20. Chemical Bond Analysis of Single Crystal Growth of Magnesium Oxide

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Starting from the crystallographic structure of magnesium oxide (MgO), both the chemical bond model of solids and Pauling's third rule (polyhedral sharing rule) were employed to quantitatively analyze the chemical bonding structure of constituent atoms and single crystal growth. Our analytical results show that MgO single crystals prefer to grow along the direction and the growth rate of the {100} plane is the slowest one. Therefore, the results show that the {100} plane of MgO crystals can be the ultimate morphology face, which is in a good agreement with our previous experimental results. The study indicate that the structure analysis is an effective tool to control the single-crystal growth.

  1. Selectivity of Crystal Growth Direction in Layered Double Hydroxides

    Institute of Scientific and Technical Information of China (English)

    赵芸; 梁吉; 李峰; 段雪

    2004-01-01

    Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-Al layered double hydroxides (LDHs) were synthesized using a coprecipitation method. The influences of aging temperature, aging time, and Mg/Al molar ratio on the crystal structure, the LDHs particle size, and the selectivity of crystal growth in different directions were investigated. The results show that the size of the crystallites in the a direction is larger than that in the c direction for all experimental conditions, indicating faster crystal growth in the a direction than in the c direction. The crystallite sizes in the a and c directions both increase with decreasing Mg/Al molar ratio but with less difference between the sizes in the two directions. Therefore, the crystal growth rate in the c direction increases more than that in the a direction as the Mg/Al molar ratio decreases. The influence of the aging time, aging temperature, and Mg/Al molar ratio on the selectivity of the crystal growth direction can be used to prepare LDHs with selected sizes in the a and c directions.

  2. Crystal Growth and Characterization of Bil3

    Science.gov (United States)

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

    1997-01-01

    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.

  3. The growth of ruby single crystals

    Directory of Open Access Journals (Sweden)

    ALEKSANDAR GOLUBOVIC

    2005-02-01

    Full Text Available Ruby (Cr:Al2O3 single crystals were grown by the Czochralski technique in an argon atmosphere. The critical crystal diameter dc = 1.0 cm and the critical rate of rotation wc = 20 rpm were calculated by equations of the hydrodynamics of the melt. The rate of crystal growthwas experimentally obtained to be 2.7 mm/h. For chemical polishing, conc. H3PO4 at 593 K for an exposure of 3 hours was determined. Conc. H3PO4 at 523 K for an exposure of 3 h was found to be a suitable etching solution. The lattice parameters a = 0.47627(6 nm and c = 1.301(1 nm were determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

  4. Growth and characterization of doped LiF crystals

    Energy Technology Data Exchange (ETDEWEB)

    Khan, S.; Kim, H. J. [Kyungpook National University, Daegu (Korea, Republic of); Rooh, G. [Abdul Wali Khan University, Mardan (Pakistan); Kim, S. H. [Cheongju University, Cheongju (Korea, Republic of)

    2014-12-15

    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.

  5. Strong Metal-Support Interaction: Growth of Individual Carbon Nanofibers from Amorphous Carbon Interacting with an Electron Beam

    DEFF Research Database (Denmark)

    Zhang, Wei; Kuhn, Luise Theil

    2013-01-01

    The article discusses the growth behavior of carbon nanofibers (CNFs). It mentions that CNFs can be synthesized using methods such as arc-discharge, laser ablation and chemical vapor deposition. It further states that CNFs can be grown from a physical mixing of amorphous carbon and CGO/Ni nanopar....../Ni nanoparticles, devoid of any gaseous carbon source and external heating and stimulated by an electron beam in a 300 kilo volt transmission electron microscope....

  6. Growth of Tungsten Bronze Family Crystals

    Science.gov (United States)

    1989-03-01

    retracti e index nuclear activation of undoped and cerium-doped SBN. Since undoped SBN is photorefractie while containing only trace These equations %ere...Boules as large as 2 to 2.5 cm in diameter are now routinely grown. AXIS APERTURlE OMAA RETICON ABERRATOR r. POLARIZATIONI , ~ SSN ETALI Rt EAM ’SPLITTER...1tMl-R 1A, (REFERENCE OMIA WITH CRYSTAL SBN Cxi SEIN CeRETICON PHOTODIODE RETICON PHOTODIODE I POLARIZED EXTRAORDINARY OMAA (REFERENCE C2= CRYSTAL 9O I

  7. Amorphous iron (II) carbonate

    DEFF Research Database (Denmark)

    Sel, Ozlem; Radha, A.V.; Dideriksen, Knud;

    2012-01-01

    exothermic than that of amorphous calcium carbonate (ACC). This suggests that enthalpy of crystallization in carbonate systems is ionic-size controlled, which may have significant implications in a wide variety of conditions, including geological sequestration of anthropogenic carbon dioxide.......Abstract The synthesis, characterization and crystallization energetics of amorphous iron (II) carbonate (AFC) are reported. AFC may form as a precursor for siderite (FeCO3). The enthalpy of crystallization (DHcrys) of AFC is similar to that of amorphous magnesium carbonate (AMC) and more...

  8. Effects of impurities on growth habit of KDP crystal

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The effects of metaphosphate, boric acid and quaternary ammonium cations with different concentration on the growth habit of KDP crystal are reported. The results are analyzed and discussed, which show that the effects of different impurities on the growth habit of KDP are not the same. It is due to the different adsorption mechanism of the impurities.

  9. Large Polycrystalline Silicon Grains Prepared by Excimer Laser Crystallization of Sputtered Amorphous Silicon Film with Process Temperature at 100 °C

    Science.gov (United States)

    He, Ming; Ishihara, Ryoichi; Neihof, Ellen J. J.; van Andel, Yvonne; Schellevis, Hugo; Metselaar, Wim; Beenakker, Kees

    2007-03-01

    Large polycrystalline silicon (poly-Si) grains with a diameter of 1.8 μm are successfully prepared by excimer laser crystallization (ELC) of a sputtered amorphous silicon (α-Si) film at a maximum process temperature of 100 °C. By pulsed DC magnetron sputtering, α-Si is deposited on a non-structured oxidized wafer. It is found that the α-Si film deposited with a bias is easily ablated during ELC, even at an energy density below the super lateral growth (SLG) region. However, the α-Si film deposited without a bias can endure an energy density well beyond the SLG region without ablation. This zero-bias sputtered α-Si film with a high compressive stress has a low Ar content and a high density, which is beneficial for the suppression of ablation. Large grains with a petal-like shape can be obtained in a wide energy density window, which can be a result from some fine crystallites in the α-Si matrix. These large grains with a low process temperature are promising for the direct formation of system circuits as well as a high-quality display on a plastic foil.

  10. Wet chemical synthesis and magnetic properties of single crystal Co nanochains with surface amorphous passivation Co layers

    Directory of Open Access Journals (Sweden)

    Zhou Shao-Min

    2011-01-01

    Full Text Available Abstract In this study, for the first time, high-yield chain-like one-dimensional (1D Co nanostructures without any impurity have been produced by means of a solution dispersion approach under permanent-magnet. Size, morphology, component, and structure of the as-made samples have been confirmed by several techniques, and nanochains (NCs with diameter of approximately 60 nm consisting of single-crystalline Co and amorphous Co-capped layer (about 3 nm have been materialized. The as-synthesized Co samples do not include any other adulterants. The high-quality NC growth mechanism is proposed to be driven by magnetostatic interaction because NC can be reorganized under a weak magnetic field. Room-temperature-enhanced coercivity of NCs was observed, which is considered to have potential applications in spin filtering, high density magnetic recording, and nanosensors. PACS: 61.46.Df; 75.50; 81.07.Vb; 81.07.

  11. A New Physical Metallurgy Phenomenon-the Shock Wave Nanocrystallization of Amorphous Alloys

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Some results of amorphous alloy nanocrystallization by shock wave are presented. Compared with the well knownannealing crystallization, these results seem novel and are very difficult to be explained by the diffusion theory, such asnucleation and growth mechanism in the solid state phase transitions. The shock wave crystallization of amorphousalloy is a new metallurgical phenomenon with possibilities for improving the crystallization theory in physics.

  12. Molecular modifiers reveal a mechanism of pathological crystal growth inhibition

    Science.gov (United States)

    Chung, Jihae; Granja, Ignacio; Taylor, Michael G.; Mpourmpakis, Giannis; Asplin, John R.; Rimer, Jeffrey D.

    2016-08-01

    Crystalline materials are crucial to the function of living organisms, in the shells of molluscs, the matrix of bone, the teeth of sea urchins, and the exoskeletons of coccoliths. However, pathological biomineralization can be an undesirable crystallization process associated with human diseases. The crystal growth of biogenic, natural and synthetic materials may be regulated by the action of modifiers, most commonly inhibitors, which range from small ions and molecules to large macromolecules. Inhibitors adsorb on crystal surfaces and impede the addition of solute, thereby reducing the rate of growth. Complex inhibitor-crystal interactions in biomineralization are often not well elucidated. Here we show that two molecular inhibitors of calcium oxalate monohydrate crystallization—citrate and hydroxycitrate—exhibit a mechanism that differs from classical theory in that inhibitor adsorption on crystal surfaces induces dissolution of the crystal under specific conditions rather than a reduced rate of crystal growth. This phenomenon occurs even in supersaturated solutions where inhibitor concentration is three orders of magnitude less than that of the solute. The results of bulk crystallization, in situ atomic force microscopy, and density functional theory studies are qualitatively consistent with a hypothesis that inhibitor-crystal interactions impart localized strain to the crystal lattice and that oxalate and calcium ions are released into solution to alleviate this strain. Calcium oxalate monohydrate is the principal component of human kidney stones and citrate is an often-used therapy, but hydroxycitrate is not. For hydroxycitrate to function as a kidney stone treatment, it must be excreted in urine. We report that hydroxycitrate ingested by non-stone-forming humans at an often-recommended dose leads to substantial urinary excretion. In vitro assays using human urine reveal that the molecular modifier hydroxycitrate is as effective an inhibitor of nucleation

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

    Directory of Open Access Journals (Sweden)

    Carl W Carruthers

    Full Text Available 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-γ 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-γ 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.

  14. Crystal Growth Models of Dexamethasone Sodium Phosphate in a MSMPR Reactive Crystallizer

    Institute of Scientific and Technical Information of China (English)

    郝红勋; 王静康; 王永莉; 侯宝红

    2005-01-01

    The reactive crystallization process of dexamethasone sodium phosphate was investigated in a continuous mixed-suspension, mixed-product-removal(MSMPR) crystallizer. Analyzing experimental data, it was found that the growth of product crystal was size-dependent. The Bransom, CR, ASL, M J2 and M J3 size-dependent growth models were discussed in details. Using experimental steady state population density data of dexamethasone sodium phosphate, parameters of five size-dependent growth models were determined by the method of non-linear least-squares. By comparison of experimental population density and linear growth rate data with those obtained from the five size-dependent growth models, it was found that the MJ3 model predicts the growth more accurately than do the other four models. Based on the theory of population balance, the crystal nucleation and growth rate equations of dexamethasone sodium phosphate were determined by non-linear regression method. The effects of different operation parameters such as supersaturation, magma density and temperature on the quality of product crystal were also discussed, and the optimal operation conditions were derived.

  15. Synthesis, crystal growth and mechanical properties of Bismuth Silicon Oxide (BSO) single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Riscob, B. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Institute for Plasma Research, Bhat, Gandhinagar 382428, Gujarat (India); Shkir, Mohd. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Ganesh, V. [Department of Physics, Kakatiya University, Warangal 506 009 (India); Vijayan, N.; Maurya, K.K. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Kishan Rao, K. [Department of Physics, Kakatiya University, Warangal 506 009 (India); Bhagavannarayana, G., E-mail: bhagavan@mail.nplindia.ernet.in [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India)

    2014-03-05

    Highlights: • Synthesis of Bismuth Silicon Oxide (BSO). • Single crystal growth of BSO by Czochralski (Cz) method. • Complete mechanical analysis by device fabrication point of view. • Theoretical and experimental calculations of mechanical properties. -- Abstract: Bismuth Silicon Oxide (BSO) is an efficient material for piezo-electric and electro-optic applications. In this article, growth of BSO single crystal by high temperature Czochralski melt growth technique and its detailed mechanical characterization by Vickers microhardness, fracture toughness, crack propagation, brittleness index and yield strength have been reported. The raw material was synthesized by solid state reaction using the stoichiometric ratio of high purity bismuth tri-oxide and silicon di-oxide. The synthesized material was charged in the platinum crucible and then melted. The required rotation and pulling rate was optimized for BSO single crystal growth and good quality single crystal has been harvested after a time span of 5 days. Powder X-ray diffraction analysis confirms the parent crystallization phase of BSO. The experimentally studied mechanical behavior of the crystal is explained using various theoretical models. The anisotropic nature of the crystals is studied using Knoop indentation technique.

  16. Growth of aluminum nitride bulk crystals by sublimation

    Science.gov (United States)

    Liu, Bei

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

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

    Science.gov (United States)

    Su, Ching-Hua

    2014-01-01

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

  18. Crystal growth and physical properties of Ferro-pnictides

    Energy Technology Data Exchange (ETDEWEB)

    Aswartham, Saicharan

    2012-11-08

    The thesis work presented here emphasizes important aspects of crystal growth and the influence of chemical substitution in Fe-As superconductors. High temperature solution growth technique is one of most powerful and widely used technique to grow single crystals of various materials. The biggest advantage of high temperature solution growth technique is the, possibility of growing single crystals from both congruently and incongruently melting materials. Solution growth technique has the potential to control high vapour pressures, given the fact that, in Fe-based superconductors elements with high vapour pressure like As, K, Li and Na have to be handled during the crystal growth procedure. In this scenario high temperature solution growth is the best suitable growth technique to synthesize sizable homogeneous single crystals. Using self-flux high temperature solution growth technique, large centimeter-sized high quality single crystals of BaFe{sub 2}As{sub 2} were grown. This pristine compound BaFe{sub 2}As{sub 2} undergoes structural and magnetic transition at T{sub S/N} = 137 K. By suppressing this magnetic transition and stabilizing tetragonal phase with chemical substitution, like Co-doping and Na-doping, bulk superconductivity is achieved. Superconducting transitions of as high as T{sub c} = 34 K with Na substitution and T{sub c} = 25 K with Co-doping were obtained. A combined electronic phase diagram has been achieved for both electron doping with Co and hole doping with Na in BaFe{sub 2}As{sub 2}. Single crystals of LiFe{sub 1-x}Co{sub x}As with x = 0, 0.025, 0.05 and 0.075 were grown by a self-flux high temperature solution growth technique. The charge doping in LiFeAs is achieved with the Co-doping in Fe atoms. The superconducting properties investigated by means of temperature dependent magnetization and resistivity revealed that superconductivity is shifted to lower temperatures and with higher amount of charge carriers superconductivity is killed

  19. Aluminum nitride bulk crystal growth in a resistively heated reactor

    Science.gov (United States)

    Dalmau, Rafael Federico

    A resistively heated reactor capable of temperatures in excess of 2300°C was used to grow aluminum nitride (AlN) bulk single crystals from an AlN powder source by physical vapor transport (PVT) in nitrogen atmosphere. AlN crystals were grown at elevated temperatures by two different methods. Self-seeded crystals were obtained by spontaneous nucleation on the crucible walls, while seeded growth was performed on singular and vicinal (0001) surfaces of silicon carbide (SiC) seeds. During self-seeded growth experiments a variety of crucible materials, such as boron nitride, tungsten, tantalum, rhenium, tantalum nitride, and tantalum carbide, were evaluated. These studies showed that the morphology of crystals grown by spontaneous nucleation strongly depends on the growth temperature and contamination in the reactor. Crucible selection had a profound effect on contamination in the crystal growth environment, influencing nucleation, coalescence, and crystal morphology. In terms of high-temperature stability and compatibility with the growth process, the best results for AlN crystal growth were obtained in crucibles made of sintered tantalum carbide or tantalum nitride. In addition, contamination from the commercially purchased AlN powder source was reduced by presintering the powder prior to growth, which resulted in a drastic reduction of nearly all impurities. Spontaneously grown single crystals up to 15 mm in size were characterized by x-ray diffraction, x-ray topography, glow discharge mass spectrometry, and secondary ion mass spectrometry. Average dislocation densities were on the order of 103 cm -3, with extended areas virtually free of dislocations. High resolution rocking curves routinely showed peak widths as narrow as 7 arcsec, indicating a high degree of crystalline perfection. Low-temperature partially polarized optical reflectance measurements were used to calculate the crystal-field splitting parameter of AlN, Deltacr = -230 meV, and a low-temperature (1

  20. Crystal growth and magnetic property of YFeO3 crystal

    Indian Academy of Sciences (India)

    Anhua Wu; Hui Shen; Jun Xu; Zhanliang Wang; Linwen Jiang; Liqing Luo; Shujuan Yuan; Shixun Cao; Huaijin Zhang

    2012-04-01

    YFeO3 and other rare earth substituted crystals with distorted orthorhombic pervoskite-like structure (space group, ) have attracted much attention due to their remarkable magnetic properties of primary significance for technological applications. In the present work, the floating zone growth of YFeO3 crystals has been systematically investigated and high quality YFeO3 crystal was obtained by optimized process. The magnetic properties of YFeO3 crystal were investigated, and it indicated the high magneto-optical property in YFeO3 crystals with specific orientation due to its anisotropy. YFeO3 crystals display superior performance in the application magneto-optical current sensors and fast latching optical switches.

  1. Control of nucleation and growth in protein crystal growth

    Science.gov (United States)

    Rosenberger, Franz; Meehan, Edward J.

    1988-01-01

    The potential advantages of nucleation and growth control through temperature, rather than the addition of precipitants or removal of solvent, are discussed. A simple light scattering arrangement for the characterization of nucleation and growth conditions in solutions is described. The temperature dependence of the solubility of low ionic strength lysozyme solutions is applied in preliminary nucleation and growth experiments.

  2. Direct synthesis of multilayer graphene on an insulator by Ni-induced layer exchange growth of amorphous carbon

    Science.gov (United States)

    Murata, H.; Toko, K.; Saitoh, N.; Yoshizawa, N.; Suemasu, T.

    2017-01-01

    Multilayer graphene (MLG) growth on arbitrary substrates is desired for incorporating carbon wiring and heat spreaders into electronic devices. We investigated the metal-induced layer exchange growth of a sputtered amorphous C layer using Ni as a catalyst. A MLG layer uniformly formed on a SiO2 substrate at 600 °C by layer exchange between the C and Ni layers. Raman spectroscopy and electron microscopy showed that the resulting MLG layer was highly oriented and contained relatively few defects. The present investigation will pave the way for advanced electronic devices integrated with carbon materials.

  3. Hydrothermal crystal growth of oxides for optical applications

    Science.gov (United States)

    McMillen, Colin David

    2007-12-01

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

  4. Pathways to self-organization: crystallization via nucleation and growth

    CERN Document Server

    Jungblut, Swetlana

    2016-01-01

    Crystallization, a prototypical self-organization process during which a disordered state spontaneously transforms into a crystal characterized by a regular arrangement of its building blocks, usually proceeds by nucleation and growth. In the initial stages of the transformation, a localized nucleus of the new phase forms in the old one due to a random fluctuation. Most of these nuclei disappear after a short time, but rarely a crystalline embryo may reach a critical size after which further growth becomes thermodynamically favorable and the entire system is converted into the new phase. In these lecture notes, we will discuss several theoretical concepts and computational methods to study crystallization. More specifically, we will address the rare event problem arising in the simulation of nucleation processes and explain how to calculate nucleation rates accurately. Particular attention is directed towards discussing statistical tools to analyze crystallization trajectories and identify the transition mech...

  5. Growth and Characterization of Agar Gel Grown Brushite Crystals

    Directory of Open Access Journals (Sweden)

    V. B. Suryawanshi

    2014-01-01

    Full Text Available Brushite [CaHPO4·2H2O] or calcium hydrogen phosphate dihydrate (CHPD also known as urinary crystal is a stable form of calcium phosphate. The brushite crystals were grown by single and double diffusion techniques in agar-agar gel at room temperature. Effects of different growth parameters were discussed in single diffusion and double diffusion techniques. Good quality star, needle, platy, rectangular, and prismatic shaped crystals in single diffusion and nuclei with dendritic growth were obtained in double diffusion. These grown nuclei were characterized by scanning electron microscopy (SEM, Fourier transform infrared (FTIR spectroscopy, X-ray diffraction (XRD, and thermogravimetric analysis (TGA. SEM has shown the different morphologies of crystals; FTIR has confirmed the presence of functional groups; crystalline nature was supported by XRD, whereas the TGA indicates total 24.68% loss in weight and formation of stable calcium pyrophosphate (Ca2P2O7 at 500°C.

  6. Fabrication of Ti-based composites based on bulk amorphous alloys by spark plasma sintering and crystallization of amorphous phase%放电等离子烧结-非晶晶化法合成钛基块状非晶复合材料

    Institute of Scientific and Technical Information of China (English)

    李元元; 杨超; 李小强; 陈友

    2011-01-01

    In order to circumvent low plasticity of bulk amorphous alloys (BAAs), a material forming method by coupling spark plasma sintering with crystallization of amorphous phase, fabricating composites based on BAAs (CBBAAs) with excellent mechanical property was reviewed systematically. By appropriate annealing of sintered BAAs prepared from spark plasma sintering in the supercooled liquid region of a mechanically alloyed amorphous powder, crystallized ductile β-Ti phase with controllable grain size, phase morphology and distribution can precipitate from the amorphous phase, and therefore, CBBAAs with a matrix of amorphous phase or crystallized β-Ti phase were obtained. The effect of different additions or substitute elements on the particle size, thermal property and microstructure of TiNbCuNiAl amorphous powder, and the influence of different sintering parameters on the microstructure and mechanical property of fabricated CBBAAs were investigated. The theoretical bases of fabricating crystallized phase-containing CBBAAs, and nucleation and growth mechanism of crystalline phase during the crystallization process were elucidated. The facture mechanism of fabricated CBBAAs under stress was explained based on a proposed "Developed hard-soft model". The results provide a promising method for fabricating large-sized crystallized phase-containing bulk composites with excellent mechanical property by powder metallurgy.%鉴于块状非晶合金(BAAs)的低塑性特征,回顾了利用放电等离子烧结-非晶晶化法制备高性能块状材料的成形技术,即先机械合金化制备钛基多组元非晶合金粉末,然后利用放电等离子烧结在粉末的过冷液相区固结非晶粉末,再利用非晶晶化法使烧结的非晶块体在随后的烧结和热处理过程中晶化析出-Ti延性相,控制延性相的形貌、尺度和分布,合成以非晶相或β-Ti晶化相为基体的钛基块状非晶复合材料(CBBAAs),研究不同添加或替换组元对TiNb

  7. Growth, crystalline perfection and characterization of benzophenone oxime crystal

    Science.gov (United States)

    Rajasekar, M.; Muthu, K.; Meenatchi, V.; Bhagavannarayana, G.; Mahadevan, C. K.; Meenakshisundaram, SP.

    Single crystals of benzophenone oxime (BPO) have been grown by slow evaporation solution growth technique from ethanol at room temperature. The single crystal X-ray diffraction study reveals that the crystal belongs to monoclinic system and cell parameters are, a = 9.459 Å, b = 8.383 Å, c = 26.690 Å, v = 2115 Å3 and β = 92.807°. The structure and the crystallinity of the materials were further confirmed by powder X-ray diffraction analysis. The various functional groups present in the molecule are confirmed by FT-IR analysis. The TG/DSC studies reveal the purity of the material and the crystals are transparent in the entire visible region having a lower optical cut-off at ˜300 nm. The crystalline perfection was evaluated by high-resolution X-ray diffraction (HRXRD). The crystal is further characterized by Kurtz powder technique, dielectric studies and microhardness analysis.

  8. Controlled Growth of Rubrene Nanowires by Eutectic Melt Crystallization

    Science.gov (United States)

    Chung, Jeyon; Hyon, Jinho; Park, Kyung-Sun; Cho, Boram; Baek, Jangmi; Kim, Jueun; Lee, Sang Uck; Sung, Myung Mo; Kang, Youngjong

    2016-03-01

    Organic semiconductors including rubrene, Alq3, copper phthalocyanine and pentacene are crystallized by the eutectic melt crystallization. Those organic semiconductors form good eutectic systems with the various volatile crystallizable additives such as benzoic acid, salicylic acid, naphthalene and 1,3,5-trichlorobenzene. Due to the formation of the eutectic system, organic semiconductors having originally high melting point (Tm > 300 °C) are melted and crystallized at low temperature (Te = 40.8–133 °C). The volatile crystallizable additives are easily removed by sublimation. For a model system using rubrene, single crystalline rubrene nanowires are prepared by the eutectic melt crystallization and the eutectic-melt-assisted nanoimpinting (EMAN) technique. It is demonstrated that crystal structure and the growth direction of rubrene can be controlled by using different volatile crystallizable additives. The field effect mobility of rubrene nanowires prepared using several different crystallizable additives are measured and compared.

  9. Vapor Growth of Mercuric Iodide Tetragonal Prismatic Crystals

    Science.gov (United States)

    2013-03-01

    These steps were followed by immersion in 1% potassium iodide (KI) solution. The apparatus were then cleaned and rinsed thoroughly with deionized (DI...Pergamon Press, 1973. [34] N. Lyakh, “Composition and kinetic characteristics of vapour phase during mercuric iodide growing,” Crystal Res. Technol...DTRA-TR-13-6 Vapor Growth of Mercuric Iodide Tetragonal Prismatic Crystals Approved for public release, distribution is unlimited. March 2013

  10. Defect reduction in seeded aluminum nitride crystal growth

    Science.gov (United States)

    Bondokov, Robert T.; Morgan, Kenneth E.; Schowalter, Leo J.; Slack, Glen A.

    2017-06-06

    Bulk single crystal of aluminum nitride (AlN) having an areal planar defect density .ltoreq.100 cm.sup.-2. Methods for growing single crystal aluminum nitride include melting an aluminum foil to uniformly wet a foundation with a layer of aluminum, the foundation forming a portion of an AlN seed holder, for an AlN seed to be used for the AlN growth. The holder may consist essentially of a substantially impervious backing plate.

  11. Defect reduction in seeded aluminum nitride crystal growth

    Energy Technology Data Exchange (ETDEWEB)

    Bondokov, Robert T.; Morgan, Kenneth E.; Schowalter, Leo J.; Stack, Glen A.

    2017-04-18

    Bulk single crystal of aluminum nitride (AlN) having an areal planar defect density.ltoreq.100 cm.sup.-2. Methods for growing single crystal aluminum nitride include melting an aluminum foil to uniformly wet a foundation with a layer of aluminum, the foundation forming a portion of an AlN seed holder, for an AlN seed to be used for the AlN growth. The holder may consist essentially of a substantially impervious backing plate.

  12. Growth of lead molybdate crystals by vertical Bridgman method

    Indian Academy of Sciences (India)

    Hongbing Chen; Congxin Ge; Rongsheng Li; Jinhao Wang; Changgen Wu; Xianling Zeng

    2005-10-01

    The growth of PbMoO4 crystals by the modified Bridgman method has been reported in this paper. The feed material with strict stoichiometric composition is desirable for the Bridgman growth of the crystals. The continuous composition change of the melts during growth can be avoided because the volatilization of melts is limited by sealed platinum crucibles. By means of the optimum growth parameters such as the growth rate of < 1.2 mm/h and the temperature gradient of 20 ∼ 40°C/cm across the solid–liquid interface under the furnace temperature of 1140 ∼ 1200°C, large size crystals with high optical uniformity were grown successfully. The distribution of Pb and Mo concentration along the growth axis was measured by X-ray fluorescence analysis. The single crystallinity of the grown sample was evaluated by the double-crystal X-ray rocking curve. The transmission spectra were measured in the range of 300–800 nm at room temperature.

  13. Zeolite crystal growth in space - What has been learned

    Science.gov (United States)

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

    1993-01-01

    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.

  14. Growth and Physical Structure of Amorphous Boron Carbide Deposited by Magnetron Sputtering on a Silicon Substrate with a Titanium Interlayer

    Directory of Open Access Journals (Sweden)

    Roberto Caniello

    2013-01-01

    Full Text Available Multilayer amorphous boron carbide coatings were produced by radiofrequency magnetron sputtering on silicon substrates. To improve the adhesion, titanium interlayers with different thickness were interposed between the substrate and the coating. Above three hundreds nanometer, the enhanced roughness of the titanium led to the growth of an amorphous boron carbide with a dense and continuing columnar structure, and no delamination effect was observed. Correspondingly, the adhesion of the coating became three time stronger than in the case of a bare silicon substrate. Physical structure and microstructural proprieties of the coatings were investigated by means of a scan electron microscopy, atomic force microscopy and X-ray diffraction. The adhesion of the films was measured by a scratch tester.

  15. Stability limits for the horizontal ribbon growth of silicon crystals

    Science.gov (United States)

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

    2013-01-01

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

  16. Directed Growth of Orthorhombic Crystals in a Micropillar Array.

    Science.gov (United States)

    Holzner, Gregor; Binder, Claudia; Kriel, Frederik H; Priest, Craig

    2017-02-14

    We report directed growth of orthorhombic crystals of potassium permanganate in spatial confinement of a micropillar array. The solution is introduced by spontaneous wicking to give a well-defined film (thickness 10-15 μm; volume ∼600 nL) and is connected to a reservoir (several microliters) that continuously "feeds" the evaporating film. When the film is supersaturated, crystals nucleate and preferentially grow in specific directions guided by one of several possible linear paths through the pillar lattice. Crystals that do not initially conform are stopped at an obstructing pillar, branch into another permitted direction, or spontaneously rotate to align with a path and continue to grow. Microspectroscopy is able to track the concentration of solute in a small region of interest (70 × 100 μm(2)) near to growing crystals, revealing that the solute concentration initially increases linearly beyond the solubility limit. Crystal growth near the region of interest resulted in a sharp decrease in the local solute concentration (which rapidly returns the concentration to the solubility limit), consistent with estimated diffusion time scales (crystal orientation in nanoliter samples will provide new insight into microscale dynamics of microscale crystallization.

  17. Crystal growth of aragonite in the presence of phosphate

    Science.gov (United States)

    Tadier, Solène; Rokidi, Stamatia; Rey, Christian; Combes, Christèle; Koutsoukos, Petros G.

    2017-01-01

    The crystal growth of aragonite was investigated at pH 7.8, 37 °C and constant solution supersaturation from aragonite-seeded supersaturated solutions. The effect of the presence of orthophosphate ions in the supersaturated solution on the kinetics of crystallization of aragonite was investigated over the range of orthophosphate concentrations of 0.25 μM-1 mM. In the presence of orthophosphate in the range of 0.25 μM-8 μM, the crystal growth rate of aragonite decreased with increasing phosphate concentration. At orthophosphate concentration levels exceeding 2 μM, induction times were measured and were found to increase with orthophosphate concentration. At orthophosphate concentration levels >8 μM, the crystal growth of aragonite was inhibited, suggesting the blockage of the active growth sites by the adsorption of orthophosphate ions. Adsorption was confirmed by the investigation of orthophosphate uptake on aragonite, which was: i) found to depend on the equilibrium concentration of orthophosphate in aqueous solutions saturated with respect to aragonite; ii) not influenced by the ionic strength of the electrolyte up to 0.15 M NaCl, showing that electrostatic interactions between orthophosphate and CaCO3 did not play a significant role in this concentration range. Adsorption data of orthophosphate on the aragonite crystals gave satisfactory fit to the Langmuir adsorption model and was confirmed by XPS analysis.

  18. Modelling of transport phenomena and defects in crystal growth processes

    Indian Academy of Sciences (India)

    S Pendurti; H Zhang; V Prasad

    2001-02-01

    A brief review of single crystal growth techniques and the associated problems is presented. Emphasis is placed on models for various transport and defect phenomena involoved in the growth process with the ultimate aim of integrating them into a comprehensive numerical model. The sources of dislocation nucleation in the growing crystal are discussed, and the propagation and multiplication of these under the action of thermal stresses is discussed. A brief description of a high-level numerical technique based on multiple adaptive grid generation and finite volume discretization is presented, followed by the result of a representative numerical simulation.

  19. Solid state characterization of azelnidipine-oxalic acid co-crystal and co-amorphous complexes: The effect of different azelnidipine polymorphs.

    Science.gov (United States)

    Pan, Yahui; Pang, Wenzhe; Lv, Jie; Wang, Jing; Yang, Caiqin; Guo, Wei

    2017-02-04

    In present study, based on the two polymorphs (α and β form) of azelnidipine (AZE), 12 complexes of AZE and oxalic acid (OXA) were prepared by solvent-assisted grinding (SG) and neat powder grinding (NG) methods at the AZE/OXA molar ratios of 2:1, 1:1, and 1:2. The effect of the different polymorphs of AZE on the micro-structure of the complexes were investigated by powder X-ray diffraction (PXRD), tempreture modulated differential scanning calorimetry and thermogravimetric analysis, cryo-field emission scanning electron microscope system, fourier transform infrared (FTIR), and solid-state nuclear magnetic resonance spectroscopy. β-AZE-OXA co-crystal was produced at β-AZE/OXA molar ratio of 2:1 when SG method was used; while α-AZE was used to produce α-AZE-OXA co-crystal at same condition. However, the other 10 combinations were in co-amorphous forms, including the NG samples with α (or β)-AZE/OXA molar ratios of 2:1, 1:1 (SG and NG), and 1:2 (SG and NG). Although the XRD pattern and IR spectra of the two co-crystals showed no difference, the melting enthalpy and specific heat cp of the β-AZE-OXA co-crystal was higher than that of the α-AZE-OXA co-crystal, indicating that the numbers of solvent molecules which entered the two co-crystal lattices were different. Interestingly, obvious difference occurred in the IR spectra between the α-AZE-OXA and β-AZE-OXA co-amorphous systems. 1745cm(-1) wave-numbers, which were assigned to the free CO groups, appeared in the α-AZE-OXA co-amorphous systems even when just a small amount of OXA was introduced, thereby indicating the presence of different intermolecular forces in the two series of co-amorphous forms. The solubility in different media and the dissolution rate in 0.1molL(-1) HCl of the 12 complexes were determined. The dramatically improved dissolution rates of the α- and β-AZE-OXA 1:2 (NG) combinations in vitro showed potential in improving the physicochemical properties of AZE by co-amorphous complex

  20. Crystal-growth Underground Breeding Extra-sensitive Detectors

    Science.gov (United States)

    Mei, Dongming

    2012-02-01

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

  1. The dynamic nature of crystal growth in pores

    Science.gov (United States)

    Godinho, Jose R. A.; Gerke, Kirill M.; Stack, Andrew G.; Lee, Peter D.

    2016-09-01

    The kinetics of crystal growth in porous media controls a variety of natural processes such as ore genesis and crystallization induced fracturing that can trigger earthquakes and weathering, as well as, sequestration of CO2 and toxic metals into geological formations. Progress on understanding those processes has been limited by experimental difficulties of dynamically studying the reactive surface area and permeability during pore occlusion. Here, we show that these variables cause a time-dependency of barite growth rates in microporous silica. The rate is approximately constant and similar to that observed on free surfaces if fast flow velocities predominate and if the time-dependent reactive surface area is accounted for. As the narrower flow paths clog, local flow velocities decrease, which causes the progressive slowing of growth rates. We conclude that mineral growth in a microporous media can be estimated based on free surface studies when a) the growth rate is normalized to the time-dependent surface area of the growing crystals, and b) the local flow velocities are above the limit at which growth is transport-limited. Accounting for the dynamic relation between microstructure, flow velocity and growth rate is shown to be crucial towards understanding and predicting precipitation in porous rocks.

  2. Effect of Co2+ doping on solubility, crystal growth and properties of ADP crystals

    Science.gov (United States)

    Ganesh, V.; Shkir, Mohd.; AlFaify, S.; Yahia, I. S.

    2016-09-01

    Bulk size crystal growth of ADP with different concentrations doping of cobalt (Co2+) has been done by low cost slow evaporation technique at ambient conditions. The solubility measurement was carried out on pure and doped crystals and found that the solubility is decreasing with doping concentrations. The presence of Co2+ ion in crystalline matrix of ADP has been confirmed by structural, vibrational and elemental analyses. Scanning electron microscopic study reveals that the doping has strong effect on the quality of the crystals. The optical absorbance and transmission confirms the enhancement of quality of ADP crystals due to Co2+ doping and so the optical band gap. Further the dislocation, photoluminescence, dielectric and mechanical studies confirms that the properties of grown crystals with Co2+ doping has been enriched and propose it as a better candidate for optoelectronic applications.

  3. Controlling protein crystal growth rate by means of temperature

    Energy Technology Data Exchange (ETDEWEB)

    SantamarIa-Holek, I; Gadomski, A [Institute of Mathematics and Physics, University of Technology and Life Sciences, PL-85796 Bydgoszcz (Poland); RubI, J M, E-mail: isholek.fc@gmail.com, E-mail: agad@utp.edu.pl, E-mail: mrubi@ub.edu [Departament de Fisica Fonamental, University of Barcelona, Av. Diagonal 647, E-08028 Barcelona (Spain)

    2011-06-15

    We have proposed a model to analyze the growth kinetics of lysozyme crystals/aggregates under non-isothermal conditions. The model was formulated through an analysis of the entropy production of the growth process which was obtained by taking into account the explicit dependence of the free energy on the temperature. We found that the growth process is coupled with temperature variations, resulting in a novel Soret-type effect. We identified the surface entropy of the crystal/aggregate as a decisive ingredient controlling the behavior of the average growth rate as a function of temperature. The behavior of the Gibbs free energy as a function of temperature is also analyzed. The agreement between theory and experiments is very good in the range of temperatures considered.

  4. Controlling protein crystal growth rate by means of temperature.

    Science.gov (United States)

    Sanamaría-Holek, I; Gadomski, A; Rubí, J M

    2011-06-15

    We have proposed a model to analyze the growth kinetics of lysozyme crystals/aggregates under non-isothermal conditions. The model was formulated through an analysis of the entropy production of the growth process which was obtained by taking into account the explicit dependence of the free energy on the temperature. We found that the growth process is coupled with temperature variations, resulting in a novel Soret-type effect. We identified the surface entropy of the crystal/aggregate as a decisive ingredient controlling the behavior of the average growth rate as a function of temperature. The behavior of the Gibbs free energy as a function of temperature is also analyzed. The agreement between theory and experiments is very good in the range of temperatures considered.

  5. Amorphous and crystalline aerosol particles interacting with water vapor – Part 1: Microstructure, phase transitions, hygroscopic growth and kinetic limitations

    Directory of Open Access Journals (Sweden)

    T. Koop

    2009-03-01

    Full Text Available Interactions with water are crucial for the properties, transformation and climate effects of atmospheric aerosols. Here we outline characteristic features and differences in the interaction of amorphous and crystalline aerosol particles with water vapor. Using a hygroscopicity tandem differential mobility analyzer (H-TDMA, we performed hydration, dehydration and cyclic hydration&dehydration experiments with aerosol particles composed of levoglucosan, oxalic acid and ammonium sulfate (diameters ~100–200 nm, relative uncertainties <0.4%, relative humidities <5% to 95% at 298 K. The measurements and accompanying Köhler model calculations provide new insights into particle microstructure, surface adsorption, bulk absorption, phase transitions and hygroscopic growth. The results of these and related investigations lead to the following main conclusions: 1. Many organic substances (including carboxylic acids, carbohydrates and proteins tend to form amorphous rather than crystalline phases upon drying of aqueous solution droplets. Depending on viscosity and microstructure, the amorphous phases can be classified as glasses, rubbers, gels or viscous liquids. 2. Amorphous organic substances tend to absorb water vapor and undergo gradual deliquescence and hygroscopic growth at much lower relative humidity than their crystalline counterparts. 3. In the course of hydration and dehydration, certain organic substances can form rubber- or gel-like structures (supra-molecular networks and undergo stepwise transitions between swollen and collapsed network structures. 4. Organic gels or (semi-solid amorphous shells (glassy, rubbery, ultra-viscous with low molecular diffusivity can kinetically limit the uptake and release of water by submicron aerosol particles on (multi-second time scales, which may influence the hygroscopic growth and activation of aerosol particles as cloud condensation nuclei (CCN and ice nuclei (IN. 5. The shape and porosity of amorphous

  6. Accumulated distribution of material gain at dislocation crystal growth

    Science.gov (United States)

    Rakin, V. I.

    2016-05-01

    A model for slowing down the tangential growth rate of an elementary step at dislocation crystal growth is proposed based on the exponential law of impurity particle distribution over adsorption energy. It is established that the statistical distribution of material gain on structurally equivalent faces obeys the Erlang law. The Erlang distribution is proposed to be used to calculate the occurrence rates of morphological combinatorial types of polyhedra, presenting real simple crystallographic forms.

  7. Growth and high pressure studies of zirconium sulphoselenide single crystals

    Indian Academy of Sciences (India)

    K R Patel; R D Vaidya; M S Dave; S G Patel

    2009-11-01

    Transition metal trichalcogenides are well suited for extreme pressure lubrication. These materials being semiconducting and of layered structure may undergo structural and electronic transition under pressure. In this paper authors reported the details about synthesis and characterization of zirconium sulphoselenide single crystals. The chemical vapour transport technique was used for the growth of zirconium sulphoselenide single crystals. The energy dispersive analysis by X-ray (EDAX) gave the confirmation about the stoichiometry of the as-grown crystals and other structural characterizations were accomplished by X-ray diffraction (XRD) study. The variation of electrical resistance was monitored in a Bridgman opposed anvil set-up up to 8 GPa pressure to identify the occurrence of any structural transition. These crystals do not possess any structural transitions upto the pressure limit examined.

  8. Crystal nucleation and near-epitaxial growth in nacre

    CERN Document Server

    Olson, Ian C; Tamura, Nobumichi; Kunz, Martin; Gilbert, Pupa U P A

    2013-01-01

    Nacre, the iridescent inner lining of many mollusk shells, interests materials scientists because of its unique brick-and-mortar periodic structure at the sub-micron scale and its remarkable resistance to fracture. However, it remains unclear how nacre forms. Here we present 20-nm, 2{\\deg}-resolution Polarization-dependent Imaging Contrast (PIC) images of shells from 15 species, mapping nacre tablets and their orientation patterns, showing where crystals nucleate and how they grow in nacre. In all shells we found stacks of co-oriented aragonite (CaCO3) tablets arranged into vertical columns or staggered diagonally. Only near the nacre-prismatic boundary are disordered crystals nucleated, as spherulitic aragonite. Overgrowing nacre tablet crystals are most frequently co-oriented with the underlying spherulitic aragonite or with another tablet, connected by mineral bridges. Therefore aragonite crystal growth in nacre is epitaxial or near-epitaxial, with abrupt or gradual changes in orientation, with c-axes with...

  9. Second harmonic generation and crystal growth of new chalcone derivatives

    Science.gov (United States)

    Patil, P. S.; Dharmaprakash, S. M.; Ramakrishna, K.; Fun, Hoong-Kun; Sai Santosh Kumar, R.; Narayana Rao, D.

    2007-05-01

    We report on the synthesis, crystal structure and optical characterization of chalcone derivatives developed for second-order nonlinear optics. The investigation of a series of five chalcone derivatives with the second harmonic generation powder test according to Kurtz and Perry revealed that these chalcones show efficient second-order nonlinear activity. Among them, high-quality single crystals of 3-Br-4'-methoxychalcone (3BMC) were grown by solvent evaporation solution growth technique. Grown crystals were characterized by X-ray powder diffraction (XRD), laser damage threshold, UV-vis-NIR and refractive index measurement studies. Infrared spectroscopy, thermogravimetric analysis and differential thermal analysis measurements were performed to study the molecular vibration and thermal behavior of 3BMC crystal. Thermal analysis does not show any structural phase transition.

  10. Maintenance of supersaturation II: indomethacin crystal growth kinetics versus degree of supersaturation.

    Science.gov (United States)

    Patel, Dhaval D; Anderson, Bradley D

    2013-05-01

    This study compares the kinetics of crystal growth of indomethacin from supersaturated suspensions at varying degrees of supersaturation (2 ≤ S ≥ 9) in the presence of seed crystals of the γ-form of indomethacin, the lowest energy polymorph. At high S (6 ≤ S ≥ 9), the crystal growth was first order with rate coefficients (kG ) that were nearly constant and consistent with the value predicted for bulk-diffusion control. At lower S (supersaturation suggesting that a higher energy surface layer was deposited on the γ-form seed crystals during crystal growth. When growth experiments were repeated at low S in the presence of indomethacin seed crystals isolated from a previous crystal growth experiment (i.e., seed crystals having higher energy surface), kG matched the higher values observed for bulk diffusion-controlled crystal growth. Crystal growth experiments were also conducted at S supersaturation during oral absorption. Copyright © 2013 Wiley Periodicals, Inc.

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

    Science.gov (United States)

    Han, Samuel S.

    1990-01-01

    A numerical analysis of transient combined heat and mass transfer across a rectangular cavity is performed. The physical parameters are selected to represent a range of possible crystal growth in solutions. Good agreements with measurement data are observed. It is found that the thermal and solute fields become highly oscillatory when the thermal and solute Grashof numbers are large.

  12. Solidification and crystal growth of solid solution semiconducting alloys

    Energy Technology Data Exchange (ETDEWEB)

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

    1984-10-01

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

  13. Phase field simulations of ice crystal growth in sugar solutions

    NARCIS (Netherlands)

    Sman, Van Der R.G.M.

    2016-01-01

    We present the first model ever, that describes explicitly ice crystal growth in a sugar solution during freezing. This 2-D model uses the phase field method, supplemented with realistic, and predictive theories on the thermodynamics and (diffusion) kinetics of this food system. We have to make u

  14. Solidification and crystal growth of solid solution semiconducting alloys

    Science.gov (United States)

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

    1984-01-01

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

  15. Fe71Nb6B23非晶薄带的非等温晶化动力学研究%Non-isothermal Crystallization Kinetics of Fe71Nb6B23 Amorphous Ribbons

    Institute of Scientific and Technical Information of China (English)

    朱满; 李俊杰; 坚增运; 常芳娥

    2012-01-01

    The Fe71Nb6B23 amorphous ribbons were prepared using melt spinning method. Differential scanning calorimeter was applied to investigate non-isothermal crystallization kinetics of the amorphous ribbons at different heating rates from 10 to 40 K/min. As the heating rate is increased, the values of Tg, Tx, and Tp are shifted toward a higher temperature region, suggesting that the amorphous ribbons have obvious crystallization kinetics. The effective activation energies including Eg, Ex and Ep were calculated with Kissinger and Ozawa equations by means of DSC traces at different step-up temperature rates. Thermodynamical mechanism of the amorphous ribbons was explained. The results reveal that the nucleation is quite more difficult than growth of the grains because Ex is larger than Ep. And the crystallization kinetics is more obvious than that of glass transition.%采用单辊急冷法制备了Fe71Nb6B23非晶薄带,并用差示扫描热分析法(DSC)研究了该非晶合金的变温晶化动力学.从DSC曲线可知,玻璃化转变温度Tg、晶化起始温度Tx和晶化峰值温度Tp均随着升温速率的增加向高温方向移动,这些特征温度均具有明显的动力学效应.分别利用Kissinger方程和Ozawa方程计算了该Fe基非晶薄带的玻璃化转变激活能Eg、晶化激活能Ex和激活能Ep,并解释了此非晶合金具有高的热稳定性的热力学机制.结果表明:两种方程计算得出的Ex均大于Ep,表明该合金的形核过程比晶粒长大更为困难;晶化的动力学效应较玻璃化转变更为明显.

  16. Porosity effects on crystallization kinetics of Amorphous Solid Water: Implications for cold icy objects in the Outer Solar System

    Science.gov (United States)

    Mitchell, Emily H.; Raut, Ujjwal; Baragiola, Raul A.

    2015-11-01

    Crystalline ice has been identified on the cold surfaces of most icy satellites and TNOs [1]. This is surprising since accretion of water vapor at temperatures (T isothermal transition from amorphous to fully crystalline phase was characterized by analyzing the time-dependent evolution of the OH-stretch absorption band using transmission infrared spectroscopy. Our initial results show that τc decreases with increasing porosity; for instance, a film deposited at 45° was observed to crystallize ~6 times faster than a film deposited at 0°. The preliminary estimate of the porosity of the 45° film is ~50% higher than that of the film deposited at normal incidence. Our findings can explain the reported variation in temperature-dependent τc [2] and contribute to the understanding of crystalline ice on cold bodies in the Outer Solar System.1. Mastrapa, R.M.E. et al. In: Gudipati, M.S. & Castillo-Rogez, J., Eds, The Science of Solar System Ices, Springer, New York, 2013.2. Baragiola, R.A. In: Devlin & Buch, Eds, Water in Confining Geometries, Springer-Verlag, 2003.3. Jewitt, D.C. & Luu, J., Nature 432, 731, 2004.4. Porter, S.B. et al. Icarus 208, 492, 2010.5. Stevenson, K.P., et al. Science 283, 1505, 1999.6. Francis, R.J. & O’Hare, D., J. Chem. Soc., Dalton Trans., 3133, 1998.7. Kirsch, B.L. et al., J. Phys. Chem. B., 108, 12698, 2004.

  17. Crystal Growth of Solid Solution HgCdTe Alloys

    Science.gov (United States)

    Lehoczky, Sandor L.

    1997-01-01

    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.

  18. Growth of lead-tin telluride crystals under high gravity

    Science.gov (United States)

    Regel, L. L.; Turchaninov, A. M.; Shumaev, O. V.; Bandeira, I. N.; An, C. Y.; Rappl, P. H. O.

    1992-04-01

    The influence of high gravity environment on several growth habits of lead-tin telluride crystals began to be investigated. Preliminary experiments with Pb 0.8Sn 0.2te grown by the Bridgman technique had been made at the centrifuge facilities of the Y.A. Gagarin Cosmonauts Center in the USSR, using accelerations of 5 g, 5.2 g and 8 g. The Sn distribution for these crystals was compared with that obtained for growth at normal gravity and the results show the existence of significant compositional inhomogeneities along the axial direction. Convection currents at high gravity seem to help multiple nucleation and subsequent random orientation of growth. Analyses of carrier concentrations as well as morphological characteristics were also made.

  19. Using Microfluidics to Decouple Nucleation and Growth of Protein Crystals.

    Science.gov (United States)

    Shim, Jung-Uk; Cristobal, Galder; Link, Darren R; Thorsen, Todd; Fraden, Seth

    2007-01-01

    A high throughput, low volume microfluidic device has been designed to decouple the physical processes of protein crystal nucleation and growth. This device, called the Phase Chip, is constructed out of poly(dimethylsiloxane) (PDMS) elastomer. One of the Phase Chip's innovations is to exploit surface tension forces to guide each drop to a storage chamber. We demonstrate that nanoliter water-in-oil drops of protein solutions can be rapidly stored in individual wells thereby allowing the screening of 1000 conditions while consuming a total of only 10 mug protein on a 20 cm(2) chip. Another significant advance over current microfluidic devices is that each well is in contact with a reservoir via a dialysis membrane through which only water and other low molecular weight organic solvents can pass, but not salt, polymer, or protein. This enables the concentration of all solutes in a solution to be reversibly, rapidly, and precisely varied in contrast to current methods, such as the free interface diffusion or sitting drop methods, which are irreversible. The Phase Chip operates by first optimizing conditions for nucleation by using dialysis to supersaturate the protein solution, which leads to nucleation of many small crystals. Next, conditions are optimized for crystal growth by using dialysis to reduce the protein and precipitant concentrations, which leads small crystals to dissolve while simultaneously causing only the largest ones to grow, ultimately resulting in the transformation of many small, unusable crystals into a few large ones.

  20. Microstructure and crystal growth direction of Al-Mg alloy

    Directory of Open Access Journals (Sweden)

    Ti-jun Chen

    2015-03-01

    Full Text Available The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basically same for the alloys prepared by these two methods. The primary grains change from cellular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cellular or columnar grain region and the primary trunk spacing decrease. All of these changes are mainly attributed to the constitutional supercooling resulting from Mg element. Comparatively, the cellular or columnar crystals of the directionally solidified alloys are straighter and more parallel than those of the permanent mould casting alloys. These have straight or wavy grain boundaries, one of the most important microstructure characteristics of feathery grains. However, the transverse microstructure and growth direction reveal that they do not belong to feathery grains. The Mg seemingly can affect the crystal growth direction, but does not result in the formation of feathery grains under the conditions employed in the study.

  1. Vapor Growth of Alloy-Type Semiconductor Crystals

    Science.gov (United States)

    Wiedemeier, H.

    1985-01-01

    The present effort is part of a continuing research program directed towards the investigation of basic vapor transport phenomena and of crystal growth properties of electronic materials. The primary purpose of ground-based studies is the development and definition of optimum experimental parameters for flight experiments. The ground-based effort includes the investigation of gravity-driven convection effects on mass transport rates and on crystal morphology for different orientations of the density gradient with respect to the gravity vector, and as a function of pressure and of temperature. In addition to the experimental tasks, theoretical efforts involve the quantitative thermodynamic analysis of the systems under investigation, the computation of fluid dynamic parameters, and the consideration of other possible effects on fluid flow under vertical, stabilizing and microgravity conditions. The specific experiments to be performed in a microgravity environment include the investigation of vapor transport and crystal growth phenomena of the GeSe-Xenon system and of the mass flux and growth of bulk and layer-type crystals of Hg sub (1-x) Cd sub x Te using HgI as a transport agent.

  2. Twin-mediated crystal growth: an enigma resolved

    Science.gov (United States)

    Shahani, Ashwin J.; Gulsoy, E. Begum; Poulsen, Stefan O.; Xiao, Xianghui; Voorhees, Peter W.

    2016-06-01

    During crystal growth, faceted interfaces may be perturbed by defects, leading to a rich variety of polycrystalline growth forms. One such defect is the coherent Σ3 {111} twin boundary, which is widely known to catalyze crystal growth. These defects have a profound effect on the properties of many materials: for example, electron-hole recombination rates strongly depend on the character of the twin boundaries in polycrystalline Si photovoltaic cells. However, the morphology of the twinned interface during growth has long been a mystery due to the lack of four-dimensional (i.e., space and time resolved) experiments. Many controversial mechanisms have been proposed for this process, most of which lack experimental verification. Here, we probe the real-time interfacial dynamics of polycrystalline Si particles growing from an Al-Si-Cu liquid via synchrotron-based X-ray tomography. Our novel analysis of the time evolution of the interfacial normals allows us to quantify unambiguously the habit plane and grain boundary orientations during growth. This, when combined with direct measurements of the interfacial morphology provide the first confirmation of twin-mediated growth, proposed over 50 years ago. Using the insights provided by these experiments, we have developed a unified picture of the phenomena responsible for the dynamics of faceted Si growth.

  3. The influence of polyaspartate additive on the growth and morphology of calcium carbonate crystals

    Science.gov (United States)

    Gower, Laurie Anne

    The addition of low levels of polyaspartate to a supersaturated calcium carbonate (CaCOsb3) solution leads to unusual morphologies in the inorganic phase. Spherulitic vaterite aggregates with helical protrusions, and distorted calcite crystals that contain spiral pits, have been produced. The helical particles are coated with an inorganic membrane that appears to be responsible for the helical twist. The polymer also causes deposition of thin CaCOsb3 tablets and films on the glass substrate. Two distinct types of films are deposited; the first is a mosaic of calcite crystals, and the second is spherulitic vaterite. In situ observations of the crystallization reaction have determined that the thin-film morphology is a result of the phase separation of a hydrated CaCOsb3/polymer liquid-precursor, whereby accumulation of isotropic droplets creates a coating on the substrate, and subsequent dehydration and crystallization yields birefringent CaCOsb3 films. During the amorphous to crystalline transition, incremental growth steps lead to "transition bars" and sectored calcite tablets. This in vitro system was originally modeled after certain aspects of CaCOsb3 biomineralization, in which the soluble proteins extracted from biominerals tend to have high levels of aspartic acid residues. Based on the similarities between features exhibited by the products of this system and those in biominerals, an argument has been presented to suggest that this polymer-induced liquid-precursor (PILP) process is involved in the morphogenesis of CaCOsb3 biominerals. These features include the following: thin CaCOsb3 tablets that grow laterally; tablets that express unstable crystallographic faces; non-faceted single crystals with curved surfaces; spatially-delineated single crystals; sectored calcite tablets; hollow-shell spheres; calcium carbonate cements; and magnesium-bearing calcites. This work has demonstrated that a means of morphological control can be accomplished through non

  4. Amorphous calcium carbonate particles form coral skeletons

    Science.gov (United States)

    Mass, Tali; Giuffre, Anthony J.; Sun, Chang-Yu; Stifler, Cayla A.; Frazier, Matthew J.; Neder, Maayan; Tamura, Nobumichi; Stan, Camelia V.; Marcus, Matthew A.; Gilbert, Pupa U. P. A.

    2017-09-01

    Do corals form their skeletons by precipitation from solution or by attachment of amorphous precursor particles as observed in other minerals and biominerals? The classical model assumes precipitation in contrast with observed “vital effects,” that is, deviations from elemental and isotopic compositions at thermodynamic equilibrium. Here, we show direct spectromicroscopy evidence in Stylophora pistillata corals that two amorphous precursors exist, one hydrated and one anhydrous amorphous calcium carbonate (ACC); that these are formed in the tissue as 400-nm particles; and that they attach to the surface of coral skeletons, remain amorphous for hours, and finally, crystallize into aragonite (CaCO3). We show in both coral and synthetic aragonite spherulites that crystal growth by attachment of ACC particles is more than 100 times faster than ion-by-ion growth from solution. Fast growth provides a distinct physiological advantage to corals in the rigors of the reef, a crowded and fiercely competitive ecosystem. Corals are affected by warming-induced bleaching and postmortem dissolution, but the finding here that ACC particles are formed inside tissue may make coral skeleton formation less susceptible to ocean acidification than previously assumed. If this is how other corals form their skeletons, perhaps this is how a few corals survived past CO2 increases, such as the Paleocene–Eocene Thermal Maximum that occurred 56 Mya.

  5. Study of Growth Mechanism of Lysozyme Crystal by Batch Crystallization Method

    Institute of Scientific and Technical Information of China (English)

    Hai Liang CUI; Yong YU; Wan Chun CHEN; Qi KANG

    2006-01-01

    The lysozyme crystals were made by batch crystallization method and the distribution of aggregate in solution were measured by dynamic light scattering. The results showed that the dimension of aggregate increased with the increase of the concentration of lysozyme and NaC1,lysozyme molecules aggregated gradually in solution and finally arrived at balance each other.The higher the concentrations of lysozyme and NaC1 were, the faster the growth rate of (110) face was. The growth rates of lysozyme crystal were obtained by a Zeiss microscope, and the effective surface energy (α) of growing steps were calculated about 4.01×l0-8 J.cm-2 according to the model of multiple two-dimensional nucleation mechanism.

  6. Crystal Splitting in the Growth of Bi2S3

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Jing; Alivisatos, A. Paul

    2006-06-15

    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.

  7. III-V semiconductor solid solution single crystal growth

    Science.gov (United States)

    Gertner, E. R.

    1982-01-01

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

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

    Science.gov (United States)

    Conlon, William M. (Inventor)

    1996-01-01

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

  9. Dependence of calcite growth rate and Sr partitioning on solution stoichiometry: Non-Kossel crystal growth

    NARCIS (Netherlands)

    Nehrke, G.; Reichart, G.-J.; Van Cappellen, P.; Meile, C.; Bijma, J.

    2007-01-01

    Seeded calcite growth experiments were conducted at fixed pH (10.2) and two degrees of supersaturation (Ω = 5, 16), while varying the Ca2+ to CO3 2- solution ratio over several orders of magnitude. The calcite growth rate and the incorporation of Sr in the growing crystals strongly depended on

  10. In situ atomic force microscopy of layer-by-layer crystal growth and key growth concepts

    Science.gov (United States)

    Rashkovich, L. N.; de Yoreo, J. J.; Orme, C. A.; Chernov, A. A.

    2006-12-01

    Contradictions that have been found recently between the representations of classical theory and experiments on crystal growth from solutions are considered. Experimental data show that the density of kinks is low in many cases as a result of the low rate of their fluctuation generation, the Gibbs-Thomson law is not always applicable in these cases, and there is inconsistency with the Cabrera-Vermilyea model. The theory of growth of non-Kossel crystals, which is to be developed, is illustrated by the analysis of the experimental dependence of the growth rate on the solution stoichiometry.

  11. Relationship between the crystallization rates of amorphous nifedipine, phenobarbital, and flopropione, and their molecular mobility as measured by their enthalpy relaxation and (1)H NMR relaxation times.

    Science.gov (United States)

    Aso, Y; Yoshioka, S; Kojima, S

    2000-03-01

    Isothermal crystallization of amorphous nifedipine, phenobarbital, and flopropione was studied at temperatures above and below their glass transition temperatures (T(g)). A sharp decrease in the crystallization rate with decreasing temperature was observed for phenobarbital and flopropione, such that no crystallization was observed at temperatures 20-30 degrees C lower than their T(g) within ordinary experimental time periods. In contrast, the crystallization rate of nifedipine decreased moderately with decreasing temperature, and considerable crystallization was observed at 40 degrees C below its T(g) within 4 months. The molecular mobility of these amorphous drugs was assessed by enthalpy relaxation and (1)H-NMR relaxation measurements. The enthalpy relaxation time of nifedipine was smaller than that of phenobarbital or flopropinone at the same T - T(g) values, suggesting higher molecular mobility of nifedipine. The spin-lattice relaxation time in the rotating frame (T(1rho)) decreased markedly at temperature above T(g). The slope of the Arrhenius type plot of the T(1rho) for nifedipine protons changed at about 10 degrees C below the T(g), whereas the slope for phenobarbital protons became discontinuous at about 10 degrees C above the T(g). Even at temperatures below its T(g), the spin-spin relaxation process of nifedipine could be described by the sum of its Gaussian relaxation, which is characteristic of solid protons, and its Lorentzian relaxation, which is characteristic of protons with higher mobility. In contrast, no Lorentzian relaxation was observed for phenobarbital or flopropione at temperatures below their T(g). These results also suggest that nifedipine has higher molecular mobility than phenobarbital and flopropione at temperatures below T(g). The faster crystallization of nifedipine than that of phenobarbital or flopropione observed at temperatures below its T(g) may be partly ascribed to its higher molecular mobility at these temperatures.

  12. Influence of the rare earth concentration on the crystallization process of Fe-Dy-B amorphous alloys. Study of Fe74Dy6B20 and Fe70Dy10B20 alloys

    Science.gov (United States)

    Ravach, G.; Machizaud, F.; Teillet, J.; LeBreton, J. M.; Fnidiki, A.

    2000-04-01

    The crystallization behaviour of Fe74 Dy6 B20 and Fe70 Dy10 B20 amorphous alloys was carefully investigated by differential scanning calorimetry, Mössbauer spectrometry and x-ray diffraction up to 800 °C. Calorimetric studies were performed in limited temperature ranges that were progressively extended. For Fe74 Dy6 B20 , after partial crystallization into the tetragonal Fe3 B compound, the remaining amorphous part segregates into two amorphous `phases', respectively enriched and impoverished in dysprosium. Tetragonal Fe3 B further transforms into orthorhombic Fe3 B. Metastable Dy3 Fe62 B14 compound then forms from the Dy-impoverished amorphous fraction, and subsequent crystallization of the Dy1 + icons/Journals/Common/varepsilon" ALT="varepsilon" ALIGN="MIDDLE"/> Fe4 B4 phase occurs in the Dy-enriched fraction. Finally, Dy3 Fe62 B14 decomposes into bcc iron, Dy1 + icons/Journals/Common/varepsilon" ALT="varepsilon" ALIGN="MIDDLE"/> Fe4 B4 and iron borides. The nature of the first crystallization product suggests the existence of local environments of t-Fe3 B type for this Dy concentration. The crystallization process of Fe70 Dy10 B20 strongly differs from that of Fe74 Dy6 B20 . Segregation phenomena occur in the amorphous state prior to any crystallization. If the nature of the first crystallization product is assumed to be correlated with short-range order in the amorphous state, our results suggest that the local environments differ from those of Fe74 Dy6 B20 , as they probably involve dysprosium atoms. This behaviour would agree with a previous Mössbauer study performed on the as-quenched amorphous alloys, providing evidence for a structural modification of the iron environments in the rare earth concentration range 8-9 at.%.

  13. Crystal growth in a three-phase system: diffusion and liquid-liquid phase separation in lysozyme crystal growth.

    Science.gov (United States)

    Heijna, M C R; van Enckevort, W J P; Vlieg, E

    2007-07-01

    In the phase diagram of the protein hen egg-white lysozyme, a region is present in which the lysozyme solution demixes and forms two liquid phases. In situ observations by optical microscopy show that the dense liquid droplets dissolve when crystals grow in this system. During this process the demixed liquid region retracts from the crystal surface. The spatial distribution of the dense phase droplets present special boundary conditions for Fick's second law for diffusion. In combination with the cylindrical symmetry provided by the kinetically roughened crystals, this system allows for a full numerical analysis. Using experimental data for setting the boundary conditions, a quasi-steady-state solution for the time-dependent concentration profile was shown to be valid. Comparison of kinetically rough growth in a phase separated system and in a nonseparated system shows that the growth kinetics for a three-phase system differs from a two-phase system, in that crystals grow more slowly but the duration of growth is prolonged.

  14. Nanoparticle-mediated nonclassical crystal growth of sodium fluorosilicate nanowires and nanoplates

    Directory of Open Access Journals (Sweden)

    Hongxia Li

    2011-12-01

    Full Text Available We observed nonclassical crystal growth of the sodium fluorosilicate nanowires, nanoplates, and hierarchical structures through self-assembly and aggregation of primary intermediate nanoparticles. Unlike traditional ion-by-ion crystallization, the primary nanoparticles formed first and their subsequent self-assembly, fusion, and crystallization generated various final crystals. These findings offer direct evidences for the aggregation-based crystallization mechanism.

  15. Microgravity protein crystal growth; results and hardware development

    Science.gov (United States)

    DeLucas, Lawrence J.; Smith, Graig D.; Carter, Daniel C.; Snyder, Robert S.; McPherson, A.; Koszelak, S.; Bugg, Charles E.

    1991-02-01

    Protein crystal growth experiments have been performed on a series of US shuttle missions. Crystallographic studies of proteins and nucleic acids have played key roles in establishing the structural foundations of molecular biology and biochemistry and for revealing structure/function relationships that are of major importance in understanding how macromolecules operate in biological systems. A number of major advances in the technology involved in determining protein structures have shortened the time span involved in structure determination. The major bottleneck in the widespread application of protein crystallography is the ability to produce high quality crystals that are suitable for a complete structural analysis. Evidence from several investigations indicates that crystals of superior quality can be obtained in a microgravity environment. This paper summarizes results obtained from a series of US shuttle missions and describes new hardware currently being developed for future shuttle missions.

  16. Physical modelling of Czochralski crystal growth in horizontal magnetic field

    Science.gov (United States)

    Grants, Ilmārs; Pal, Josef; Gerbeth, Gunter

    2017-07-01

    This study addresses experimentally the heat transfer, the temperature azimuthal non-uniformity and the onset of oscillations in a low temperature physical model of a medium-sized Czochralski crystal growth process with a strong horizontal magnetic field (HMF). It is observed that under certain conditions the integral heat flux may decrease with increasing magnetic field strength at the same time as the flow velocity increases. The azimuthal non-uniformity of the temperature field in the melt near the crystal model rim is only little influenced by its rotation rate outside of a narrow range where the centrifugal force balances the buoyant one. The flow oscillation onset has been observed for two values of the HMF strength. Conditions of this onset are little influenced by the crystal rotation. The critical temperature difference of the oscillation onset considerably exceeds that of the Rayleigh-Bénard (RB) cell in a strong HMF.

  17. Chemical and Biological Sensing using Diatom Photonic Crystal Biosilica with In-Situ Growth Plasmonic Nanoparticles.

    Science.gov (United States)

    Kong, Xianming; Squire, Kenny; Li, Erwen; LeDuff, Paul; Rorrer, Gregory; Tang, Suning; Chen, Bin; McKay, Christopher; Navarro-Gonzalez, Rafael; Wang, Alan

    2016-12-07

    In this paper, we described a new type of bioenabled nano-plasmonic sensors based on diatom photonic crystal biosilica with in-situ growth silver nanoparticles and demonstrated label-free chemical and biological sensing based on surface-enhanced Raman scattering (SERs) from complex samples. Diatoms are photosynthetic marine micro-organisms that create their own skeletal shells of hydrated amorphous silica, called frustules, which possess photonic crystal-like hierarchical micro- & nano-scale periodic pores. Our research shows that such hybrid plasmonic-biosilica nanostructures formed by cost-effective and eco-friendly bottom-up processes can achieve ultra-high limit of detection for medical applications, food sensing, water/air quality monitoring and geological/space research. The enhanced sensitivity comes from the optical coupling of the guided-mode resonance of the diatom frustules and the localized surface plasmons of the silver nanoparticles. Additionally, the nanoporous, ultra-hydrophilic diatom biosilica with large surface-to-volume ratio can concentrate more analyte molecules to the surface of the SERS substrates, which can help to detect biomolecules that cannot be easily adsorbed by metallic nanoparticles.

  18. Atomic simulation on evolution of nano-crystallizaion in amorphous metals

    Institute of Scientific and Technical Information of China (English)

    WANG Yu; WANG Xiu-xi; WANG Hai-long

    2006-01-01

    The deformation-induced nano-crystallization behavior of amorphous pure Ni was investigated by using a molecular dynamics simulation. The microevolution mechanism of the nano-crystallization,the crystallization process in the multicomponent amorphous Ni-Pd alloys and the temperature effect on the nano-crystallization behavior in amorphous metals were studied. The results show that the small nano-crystalline grain will nucleate and grow during the compression deformation. The deformation induces the growth of the ordered clusters in the amorphous metals and the nano-crystalline grain grows under the shearing combination and shearing deposition. The nano-crystalline grain will nucleate in a lower strain under a higher temperature. The combining severe plastic deformation with thermal annealing treatments presents a new opportunity for developing bulk nano-crystalline materials with controlled microstructures.

  19. The nacre protein perlucin nucleates growth of calcium carbonate crystals.

    Science.gov (United States)

    Blank, S; Arnoldi, M; Khoshnavaz, S; Treccani, L; Kuntz, M; Mann, K; Grathwohl, G; Fritz, M

    2003-12-01

    Atomic force microscopy (AFM) in aqueous solution was used to investigate native nacre of the marine snail Haliotis laevigata on the microscopic scale and the interaction of purified nacre proteins with calcium carbonate crystals on the nanoscopic scale. These investigations were controlled by scanning electron microscopy (SEM), light microscopy (LM) and biochemical methods. For investigations with AFM and SEM, nacre was cleaved parallel to the aragonite tablets in this biogenic polymer/mineral composite. Multilamellar organic sheets consisting of a core of chitin with layers of proteins attached on both sides lay between the aragonite layers consisting of confluent aragonite tablets. Cleavage appeared to occur between the aragonite tablet layer and the protein layer. AFM images revealed a honeycomb-like structure to the organic material with a diameter of the 'honeycombs' equalling that of the aragonite tablets. The walls of the structures consisted of filaments, which were suggested to be collagen. The flat regions of the honeycomb-like structures exhibited a hole with a diameter of more than 100 nm. When incubated in saturated calcium carbonate solution, aragonite needles with perfect vertical orientation grew on the proteinacous surface. After treatment with proteinase K, no growth of orientated aragonite needles was detected. Direct AFM measurements on dissolving and growing calcite crystals revealed a surface structure with straight steps the number of which decreased with crystal growth. When the purified nacre protein perlucin was added to the growth solution (a super-saturated calcium carbonate solution) new layers were nucleated and the number of steps increased. Anion exchange chromatography of the water-soluble proteins revealed a mixture of about 10 different proteins. When this mixture was dialysed against saturated calcium carbonate solution and sodium chloride, calcium carbonate crystals precipitated together with perlucin leaving the other proteins

  20. Analysis of the carbon source for diamond crystal growth

    Institute of Scientific and Technical Information of China (English)

    LI Li; XU Bin; LI MuSen

    2008-01-01

    The lattice constants of diamond and graphite at high pressure and high temperature (HPHT) were calculated on the basis of linear expansion coefficient and elastic constant. According to the empirical electron theory of solids and molecules (EET), the valence electron structures (VESs) of diamond, graphite crystal and their common planes were calculated. The relationship between diamond and graphite structure was analyzed based on the boundary condition of the improved Thomas-Fermi-Dirac theory by Cheng (TFDC). It was found that the electron densities of common planes in graphite were not continuous with those of planes in diamond at the first order of approximation. The results show that during the course of diamond single crystal growth at HPHT with metal catalyst, the carbon sources forming diamond structure do not come from the graphite structure directly. The diamond growth mechanism was discussed from the viewpoint of valence electron structure.

  1. Growth morphology of zinc tris(thiourea) sulphate crystals

    Indian Academy of Sciences (India)

    Sunil Verma; M K Singh; V K Wadhawan; C H Suresh

    2000-06-01

    The growth morphology of crystals of zinc tris(thiourea) sulphate (ZTS) is investigated experimentally, and computed using the Hartman–Perdok approach. Attachment energies of the observed habit faces are calculated for determining their relative morphological importance. A computer code is developed for carrying out these calculations. A special procedure is adopted for computing the cohesive energy of a slice of the structure parallel to any rational crystallographic plane. For estimating the cohesive energies, formal charges on the experimentally determined atomic positions in the molecules of ZTS are calculated by ab initio molecular-orbital computations, with wave functions obtained by the Hartree–Fock procedure. Fairly good agreement with the observed crystal morphology is obtained for a model of growth mechanism in which ZTS is assumed to exist in solution as zinc tris(thiourea) ions and sulphate ions.

  2. A new approach to the CZ crystal growth weighing control

    Science.gov (United States)

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

    2014-03-01

    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.

  3. Mathematical modeling and numerical simulation of Czochralski Crystal Growth

    Energy Technology Data Exchange (ETDEWEB)

    Jaervinen, J.; Nieminen, R. [Center for Scientific Computing, Espoo (Finland)

    1996-12-31

    A detailed mathematical model and numerical simulation tools based on the SUPG Finite Element Method for the Czochralski crystal growth has been developed. In this presentation the mathematical modeling and numerical simulation of the melt flow and the temperature distribution in a rotationally symmetric crystal growth environment is investigated. The temperature distribution and the position of the free boundary between the solid and liquid phases are solved by using the Enthalpy method. Heat inside of the Czochralski furnace is transferred by radiation, conduction and convection. The melt flow is governed by the incompressible Navier-Stokes equations coupled with the enthalpy equation. The melt flow is numerically demonstrated and the temperature distribution in the whole Czochralski furnace. (author)

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

    Science.gov (United States)

    Overfelt, Tony; Wells, Mark; Blake, John

    1993-02-01

    Investigators worldwide are preparing experiments to test the influence of low gravity found in space on the growth of many crystalline materials. However, power limitations prevent existing space crystal growth furnaces from being able to process samples any larger than about 2 cm, and in addition, the background microgravity levels found on the Space Shuttle are not low enough to significantly benefit samples much larger than 2 cm. This paper describes a novel concept of a free-flying platform utilizing well-established solar furnace technology to enable materials processing in space experiments on large-diameter crystals. The conceptual design of this Solar Furnace Satellite is described along with its operational scenario and the anticipated g levels.

  5. Growth morphologies and optical properties of LTA single crystal.

    Science.gov (United States)

    Liu, Xiaojing; Ren, Miaojuan; Chen, Gang; Wang, Peiji

    2013-12-01

    Atomic force microscopy (AFM) has been used to study the growth morphologies of l-threonine acetate (abbreviated as LTA) crystal. Spiral growth hillocks and typical step patterns are described and discussed. Nuclei with various shapes often distribute at the larger step terraces. Eventually, in order to investigate microscopic second order nonlinear optical properties of LTA crystals, the molecular dipole moment (μ), polarizability (α), and first hyperpolarizability (β) were computed using a series of basis sets including polarized and diffuse functions at the framework of Hartree-Fock and density functional theory methods. The study is helpful to the further development of l-threonine analogs with improved nonlinear optical properties. Copyright © 2013 Elsevier B.V. All rights reserved.

  6. Synthesis, crystal structure, crystal growth and physical properties of N,N-diethyl anilinium picrate

    Science.gov (United States)

    Subramaniyan @ Raja, R.; Anandha Babu, G.; Ramasamy, P.

    2011-11-01

    Crystalline substance of N,N-diethyl anilinium picrate (NNDEAP) has been synthesized and single crystals of NNDEAP were successfully grown for the first time by the slow evaporation solution growth technique at room temperature with dimensions 14×10×10 mm3. The formation of the new crystal has been confirmed by single crystal X-ray diffraction studies. The structural perfection of the grown crystal was analyzed by high resolution X-ray diffraction (HRXRD) measurements. The functional groups of NNDEAP have been identified by Fourier transform infrared spectral studies. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) have also been carried out and the thermal behavior of NNDEAP has been studied. The UV-vis-NIR studies have been carried out to identify the optical transmittance and the cut off wavelength of NNDEAP is identified. The dielectric loss and the dielectric constant as a function of frequency and temperature were measured for the grown crystal and the nature of variation of dielectric constant εr and dielectric losses (tan δ) were studied. Vicker's hardness test has been carried out on NNDEAP to measure the load dependent hardness. The laser induced surface damage threshold for the grown crystal was measured using Nd:YAG laser.

  7. Crystal growth and reflectivity studies of Zn1–MnTe crystals

    Indian Academy of Sciences (India)

    K Veera Brahmam; D Raja Reddy; B K Reddy

    2005-08-01

    Single crystals of Zn1–MnTe were prepared by vertical Bridgman crystal growth method for different concentrations of Mn. Chemical analysis and reflectivity studies were carried out for compositional and band structure properties. Microscopic variation in composition between starting and end compounds was observed from EDAX analysis. Linear dependence of fundamental absorption edge (0) as a function of Mn concentration () was expressed in terms of a straight line fit and a shift in 0 towards higher energy was observed in reflectivity spectra of Zn1–MnTe.

  8. Screening and Crystallization Plates for Manual and High-throughput Protein Crystal Growth

    Science.gov (United States)

    Thorne, Robert E. (Inventor); Berejnov, Viatcheslav (Inventor); Kalinin, Yevgeniy (Inventor)

    2010-01-01

    In one embodiment, a crystallization and screening plate comprises a plurality of cells open at a top and a bottom, a frame that defines the cells in the plate, and at least two films. The first film seals a top of the plate and the second film seals a bottom of the plate. At least one of the films is patterned to strongly pin the contact lines of drops dispensed onto it, fixing their position and shape. The present invention also includes methods and other devices for manual and high-throughput protein crystal growth.

  9. Growth induced magnetic anisotropy in amorphous thin films. Annual progress report year 1, November 4, 1994--October 31, 1995

    Energy Technology Data Exchange (ETDEWEB)

    Hellman, F. [Univ. of California, San Diego, La Jolla, CA (United States). Dept. of Physics

    1995-07-01

    The work in the past year has primarily involved three areas of magnetic thin films: amorphous rare earth-transition metal alloys, epitaxial COPt3 thin films, and exchange coupled antiferromagnetic insulators. In the amorphous alloys, the authors have focused on understanding the cause and the effect of the growth-surface-induced perpendicular magnetic anisotropy. Using the results of previous work, they are able to control this anisotropy quite precisely. This anisotropy is predicted to have dramatic and as-yet unobserved effects on the underlying nature of the magnetism. The work on the epitaxial Co-Pt alloys was originally undertaken as a comparison study to the amorphous alloys. The authors have discovered that these alloys exhibit a remarkable new phenomena; a surface-induced miscibility gap in a material which is believed to be completely miscible in the bulk. This miscibility gap is 100% correlated with the perpendicular anisotropy, although the connection is not yet clear, and is presumably linked to a magnetic energy of mixing which tends to drive a material towards clustering. The problem of exchange coupling in multilayers impacts many of the current research areas in magnetism. NiO/CoO multilayers can be prepared with coherent interfaces. The specific heat shows unambiguously the ordering of the spins in the layers. The results show clearly the transition from a single transition temperature to two distinct transitions with increasing thickness of the individual layers. From this data, the authors are able to determine the interface magnetic exchange coupling constant and the effect on the transition temperature of finite layer thickness.

  10. Crystallization of undercooled liquid fenofibrate.

    Science.gov (United States)

    Amstad, Esther; Spaepen, Frans; Weitz, David A

    2015-11-28

    Formulation of hydrophobic drugs as amorphous materials is highly advantageous as this increases their solubility in water and therefore their bioavailability. However, many drugs have a high propensity to crystallize during production and storage, limiting the usefulness of amorphous drugs. We study the crystallization of undercooled liquid fenofibrate, a model hydrophobic drug. Nucleation is the rate-limiting step; once seeded with a fenofibrate crystal, the crystal rapidly grows by consuming the undercooled liquid fenofibrate. Crystal growth is limited by the incorporation of molecules into its surface. As nucleation and growth both entail incorporation of molecules into the surface, this process likely also limits the formation of nuclei and thus the crystallization of undercooled liquid fenofibrate, contributing to the good stability of undercooled liquid fenofibrate against crystallization.

  11. Growth of crystalline semiconductor materials on crystal surfaces

    CERN Document Server

    Aleksandrov, L

    2013-01-01

    Written for physicists, chemists, and engineers specialising in crystal and film growth, semiconductor electronics, and various applications of thin films, this book reviews promising scientific and engineering trends in thin films and thin-films materials science. The first part discusses the physical characteristics of the processes occurring during the deposition and growth of films, the principal methods of obtaining semiconductor films and of reparing substrate surfaces on which crystalline films are grown, and the main applications of films. The second part contains data on epitaxial i

  12. Special phase transformation and crystal growth pathways observed in nanoparticles†

    Directory of Open Access Journals (Sweden)

    Finnegan Michael P

    2003-11-01

    Full Text Available 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.

  13. Non-linear optical titanyl arsenates: Crystal growth and properties

    Science.gov (United States)

    Nordborg, Jenni Eva Louise

    Crystals are appreciated not only for their appearance, but also for their unique physical properties which are utilized by the photonic industry in appliances that we come across every day. An important part of enabling the technical use of optical devices is the manufacture of crystals. This dissertation deals with a specific group of materials called the potassium titanyl phosphate (KIP) family, known for their non-linear optical and ferroelectric properties. The isomorphs vary in their linear optical and dielectric properties, which can be tuned to optimize device performance by forming solid solutions of the different materials. Titanyl arsenates have a wide range of near-infrared transmission which makes them useful for tunable infrared lasers. The isomorphs examined in the present work were primarily RbTiOASO4 (RTA) and CsTiOAsO4 (CTA) together with the mixtures RbxCs 1-xTiOAsO4 (RCTA). Large-scale crystals were grown by top seeding solution growth utilizing a three-zone furnace with excellent temperature control. Sufficiently slow cooling and constant upward lifting produced crystals with large volumes useable for technical applications. Optical quality RTA crystals up to 10 x 12 x 20 mm were grown. The greater difficulty in obtaining good crystals of CTA led to the use of mixed RCTA materials. The mixing of rubidium and cesium in RCTA is more favorable to crystal growth than the single components in pure RTA and CTA. Mixed crystals are rubidium-enriched and contain only 20-30% of the cesium concentration in the flux. The cesium atoms show a preference for the larger cation site. The network structure is very little affected by the cation substitution; consequently, the non-linear optical properties of the Rb-rich isomorphic mixtures of RTA and CTA can be expected to remain intact. Crystallographic methods utilizing conventional X-ray tubes, synchrotron radiation and neutron diffraction have been employed to investigate the properties of the atomic

  14. Luminescence labeling and dynamics of growth active crystal surface structures

    Science.gov (United States)

    Bullard, Theresa Vivian

    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

  15. Oriented growth and assembly of zeolite crystals on substrates

    Institute of Scientific and Technical Information of China (English)

    ZHOU Ming; ZHANG BaoQuan; LIU XiuFeng

    2008-01-01

    The aligned array and thin film of zeolites and molecular sieves possess a variety of potential applica-tions in membrane separation and catalysis, chemical sensors, and microelectronic devices. There are two main synthesis methods for manufacturing the aligned arrays and thin films of zeolites and mo-lecular sieves, i.e. in situ hydrothermal reaction and self-assembly of crystal grains on substrates. Both of them have attracted much attention in the scientific community worldwide. A series of significant progress has been made in recent years. By the in situ hydrothermal synthesis, the oriented nucleation and growth of zeolite and molecular sieve crystals can be achieved by modifying the surface properties of substrates or by changing the composition of synthesis solutions, leading to the formation of uni-formly oriented multicrystal-aligned arrays or thin films. On the other hand, the crystal grains of zeo-lites and molecular sieves can be assembled onto the substrate surface in required orientation using different bondages, for instance, the microstructure in the array or thin film can be controlled. This review is going to summarize and comment the significant results and progress reported recently in manufacturing highly covered and uniformly aligned arrays or thin films of zeolites and molecular sieves. It involves (1) in situ growth of highly aligned zeolite arrays and thin films via embedding func-tional groups on the substrate surface, modifying the surface microstructure of substrates, as well as varying the composition of synthesis solutions; (2) assembly of zeolite and molecular sieve crystals on various substrates to form aligned arrays and thin films with full coverage by covalent, ionic, and in-termolecular coupling interactions between crystals and substrates; (3) coupling surface assembly with microcontact printing or photoetching technique to produce patterned zeolite arrays and thin films. Finally, the functionality and applications of zeolite

  16. Trehalose amorphization and recrystallization.

    Science.gov (United States)

    Sussich, Fabiana; Cesàro, Attilio

    2008-10-13

    The stability of the amorphous trehalose prepared by using several procedures is presented and discussed. Amorphization is shown to occur by melting (T(m)=215 degrees C) or milling (room temperature) the crystalline anhydrous form TRE-beta. Fast dehydration of the di-hydrate crystalline polymorph, TRE-h, also produces an amorphous phase. Other dehydration procedures of TRE-h, such as microwave treatment, supercritical extraction or gentle heating at low scan rates, give variable fractions of the polymorph TRE-alpha, that undergo amorphization upon melting (at lower temperature, T(m)=130 degrees C). Additional procedures for amorphization, such as freeze-drying, spray-drying or evaporation of trehalose solutions, are discussed. All these procedures are classified depending on the capability of the undercooled liquid phase to undergo cold crystallization upon heating the glassy state at temperatures above the glass transition temperature (T(g)=120 degrees C). The recrystallizable amorphous phase is invariably obtained by the melt of the polymorph TRE-alpha, while other procedures always give an amorphous phase that is unable to crystallize above T(g). The existence of two different categories is analyzed in terms of the transformation paths and the hypothesis that the systems may exhibit different molecular mobilities.

  17. Temperature-induced crystallization and compactibility of spray dried composite particles composed of amorphous lactose and various types of water-soluble polymer.

    Science.gov (United States)

    Takeuchi, H; Yasuji, T; Yamamoto, H; Kawashima, Y

    2000-04-01

    The purpose of this study was to investigate the temperature-induced crystallization and the compactibility of the composite particles containing amorphous lactose and various types of polymers. The composite particles were prepared by spray-drying an aqueous solution of lactose and various types of gel forming water-soluble polymers at various formulating ratios. The stabilizing effect of hydroxypropylcellulose (HPC) and polyvinyl pyrrolidone (PVP) on amorphous lactose in the composite particles was smaller than that of sodium alginate in comparing at the same formulating ratios. The difference in the stability of amorphous lactose in the composite particles was attributed to the difference in the glass transition temperature (Tg) of the composite particles caused by the polymers formulated. The tensile strength of compacted spray-dried composite particles containing the polymers was higher than commercial lactose for direct tabletting (DCL21). The tensile strength of the composite particles was increased with an increase in water content in the particles. The difference in compactibility of the composite particles containing the different amount of polymer and water could be explained by the difference in Tg of the particles.

  18. Growth and properties of Lithium Salicylate single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Zaitseva, N; Newby, J; Hull, G; Saw, C; Carman, L; Cherepy, N; Payne, S

    2009-02-13

    An attractive feature of {sup 6}Li containing fluorescence materials that determines their potential application in radiation detection is the capture reaction with slow ({approx}< 100 keV) neutrons: {sup 6}Li + n = {sup 4}He + {sup 3}H + 4.8MeV. The use of {sup 6}Li-salicylate (LiSal, LiC{sub 6}H{sub 5}O{sub 3}) for thermal neutron detection was previously studied in liquid and polycrystalline scintillators. The studies showed that both liquid and polycrystalline LiSal scintillators could be utilized in pulse shape discrimination (PSD) techniques that enable separation of neutrons from the background gamma radiation. However, it was found that the efficiency of neutron detection using LiSal in liquid solutions was severely limited by its low solubility in commonly used organic solvents like, for example, toluene or xylene. Better results were obtained with neutron detectors containing the compound in its crystalline form, such as pressed pellets, or microscopic-scale (7-14 micron) crystals dispersed in various media. The expectation drown from these studies was that further improvement of pulse height, PSD, and efficiency characteristics could be reached with larger and more transparent LiSal crystals, growth of which has not been reported so far. In this paper, we present the first results on growth and characterization of relatively large, a cm-scale size, single crystals of LiSal with good optical quality. The crystals were grown both from aqueous and anhydrous (methanol) media, mainly for neutron detection studies. However, the results on growth and structural characterization may be interesting for other fields where LiSal, together with other alkali metal salicylates, is used for biological, medical, and chemical (as catalyst) applications.

  19. Researches on the Growth Habit and Optical Properties of Fe3+ Ion Doped KDP Crystal

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    During the process of KDP crystal growth, metal ions strongly affect the growth habit and optical properties of KDP single crystal. In this paper, KDP crystals were grown from an aqueous solution doped with different concentration of Fe3+ dopant by traditional temperaturereduction method and "point-seed" rapid growth method. Furthermore, we examined the light scatter and measured the transmission of these KDP crystals. It is found that the dopant of Fe3+ ion can improve the stability of the KDP growth solution when its concentration is less than 30 ppm.The effects of Fe3+ ion on the growth habit and optical properties of KDP crystal are also obvious.

  20. Growth, spectral and crystallization perfection studies of semi organic non linear optical crystal - L-alanine lithium chloride

    Science.gov (United States)

    Redrothu, Hanumantharao; Kalainathan, S.; Bhagavannarayana, G.

    2012-06-01

    Single crystals of L-alanine lithium chloride single crystals were successfully grown using slow evaporation solution growth technique at constant temperature (303K). The formation of the new crystal has been confirmed by single-crystal X-ray diffraction, FT-IR studies. The crystalline perfection was analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. The powder second harmonic generation (SHG) has been confirmed by Nd: YAG laser. The results have been discussed in detail.

  1. Comparison of optical transients during the picosecond laser pulse-induced crystallization of GeSbTe and AgInSbTe phase-change thin films: Nucleation-driven versus growth-driven processes

    Science.gov (United States)

    Liang, Guangfei; Li, Simian; Huang, Huan; Wang, Yang; Lai, Tianshu; Wu, Yiqun

    2013-09-01

    Direct comparison of the real-time in-situ crystallization behavior of as-deposited amorphous Ge2Sb2Te5 (GeSbTe) and Ag8In14Sb55Te23 (AgInSbTe) phase-change thin films driven by picosecond laser pulses was performed by a time-resolved optical pump-probe technique with nanosecond resolution. Different optical transients showed various crystallization processes because of the dissimilar nucleation- and growth-dominated mechanisms of the two materials. The effects of laser pulse fluence, thermal conductive structure, and successive pulse irradiation on their crystallization dynamics were also discussed. A schematic was then established to describe the different crystallization processes beginning from the as-deposited amorphous state. The results may provide further insight into the phase-change mechanism under extra-non-equilibrium conditions and aid the development of ultrafast phase-change memory materials.

  2. Solid phase epitaxy amorphous silicon re-growth: some insight from empirical molecular dynamics simulation

    CERN Document Server

    Krzeminski, Christophe; 10.1140/epjb/e2011-10958-7

    2011-01-01

    The modelling of interface migration and the associated diffusion mechanisms at the nanoscale level is a challenging issue. For many technological applications ranging from nanoelectronic devices to solar cells, more knowledge of the mechanisms governing the migration of the silicon amorphous/crystalline interface and dopant diffusion during solid phase epitaxy is needed. In this work, silicon recrystallisation in the framework of solid phase epitaxy and the influence on orientation effects have been investigated at the atomic level using empirical molecular dynamics simulations. The morphology and the migration process of the interface has been observed to be highly dependent on the original inter-facial atomic structure. The [100] interface migration is a quasi-planar ideal process whereas the cases [110] and [111] are much more complex with a more diffuse interface. For [110], the interface migration corresponds to the formation and dissolution of nanofacets whereas for [111] a defective based bilayer reor...

  3. Crystal growth of LiIn1-xGaxSe2 crystals

    Science.gov (United States)

    Wiggins, Brenden; Bell, Joseph; Woodward, Jonathan; Goodwin, Brandon; Stassun, Keivan; Burger, Arnold; Stowe, Ashley

    2017-06-01

    Lithium containing chalcogenide single crystals have become very promising materials for photonics and radiation detection. Detection applications include nuclear nonproliferation, neutron science, and stellar investigations for the search of life. Synthesis and single crystal growth methods for lithium containing chalcogenide, specifically LiIn1-xGaxSe2, single crystals are discussed. This study elucidates the possibility of improving neutron detection by reducing the indium capture contribution; with the incorporation of the lithium-6 isotope, gallium substitution may overcome the neutron detection efficiency limitation of 6LiInSe2 due to appreciable neutron capture by the indium-115 isotope. As a figure of merit, the ternary parent compounds 6LiInSe2 and 6LiGaSe2 were included in this study. Quality crystals can be obtained utilizing the vertical Bridgman method to produce quaternary compounds with tunable optical properties. Quaternary crystals of varying quality depending on the gallium concentration, approximately 5×5×2 mm3 or larger in volume, were harvested, analyzed and revealed tunable absorption characteristics between 2.8-3.4 eV.

  4. Acquisition of Single Crystal Growth and Characterization Equipment

    Energy Technology Data Exchange (ETDEWEB)

    Maple, M. Brian; Zocco, Diego A.

    2008-12-09

    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

  5. Optimal Control of Oxygen Concentration in a Magnetic Czochralski Crystal Growth by Response Surface Methodology

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Concepts and techniques of response surface methodology have been widely applied in many branches of engineering, especially in the chemical and manufacturing areas. This paper presents an application of the methodology in a magnetic crystal Czochralski growth system for single crystal silicon to optimize the oxygen concentration at the crystal growth interface in a cusp magnetic field. The simulation demonstrates that the response surface methodology is a feasible algorithm for the optimization of the Czochralski crystal growth process.

  6. An efficient light trapping scheme based on textured conductive photonic crystal back reflector for performance improvement of amorphous silicon solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Peizhuan; Hou, Guofu, E-mail: gfhou@nankai.edu.cn; Huang, Qian; Zhao, Jing; Zhang, Jianjun, E-mail: jjzhang@nankai.edu.cn; Ni, Jian; Zhang, Xiaodan; Zhao, Ying [Tianjin Key Laboratory of Photoelectronic Thin-Film Devices and Technique, Institute of Photoelectronics, Nankai University, Tianjin 300071 (China); Fan, QiHua [Department of Electrical Engineering and Computer Science, South Dakota State University, Brookings, South Dakota 57007 (United States)

    2014-08-18

    An efficient light trapping scheme named as textured conductive photonic crystal (TCPC) has been proposed and then applied as a back-reflector (BR) in n-i-p hydrogenated amorphous silicon (a-Si:H) solar cell. This TCPC BR combined a flat one-dimensional photonic crystal and a randomly textured surface of chemically etched ZnO:Al. Total efficiency enhancement was obtained thanks to the sufficient conductivity, high reflectivity and strong light scattering of the TCPC BR. Unwanted intrinsic losses of surface plasmon modes are avoided. An initial efficiency of 9.66% for a-Si:H solar cell was obtained with short-circuit current density of 14.74 mA/cm{sup 2}, fill factor of 70.3%, and open-circuit voltage of 0.932 V.

  7. 70 °C synthesis of high-Sn content (25%) GeSn on insulator by Sn-induced crystallization of amorphous Ge

    Energy Technology Data Exchange (ETDEWEB)

    Toko, K., E-mail: toko@bk.tsukuba.ac.jp; Oya, N.; Suemasu, T. [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Saitoh, N.; Yoshizawa, N. [Electron Microscope Facility, TIA, AIST, 16-1 Onogawa, Tsukuba 305-8569 (Japan)

    2015-02-23

    Polycrystalline GeSn thin films are fabricated on insulating substrates at low temperatures by using Sn-induced crystallization of amorphous Ge (a-Ge). The Sn layer stacked on the a-Ge layer (100-nm thickness each) had two roles: lowering the crystallization temperature of a-Ge and composing GeSn. Slow annealing at an extremely low temperature of 70 °C allowed for a large-grained (350 nm) GeSn layer with a lattice constant of 0.590 nm, corresponding to a Sn composition exceeding 25%. The present investigation paves the way for advanced electronic optical devices integrated on a flexible plastic substrate as well as on a Si platform.

  8. Material-dependent amorphization and epitaxial crystallization in ion-implanted AlAs/GaAs layer structures

    Energy Technology Data Exchange (ETDEWEB)

    Cullis, A.G.; Chew, N.G.; Whitehouse, C.R. (Royal Signals and Radar Establishment, St. Andrews Road, Malvern, Worcestershire WR14 3PS, United Kingdom (GB)); Jacobson, D.C.; Poate, J.M.; Pearton, S.J. (AT T Bell Laboratories, 600 Mountain Avenue, Murray Hill, New Jersey 07974)

    1989-09-18

    When AlAs/GaAs layer samples are subjected to Ar{sup +} ion bombardment at liquid-nitrogen temperature, it is shown that very different damage structures are produced in the two materials. While the GaAs is relatively easily amorphized, the AlAs is quite resistant to damage accumulation and remains crystalline for the ion doses employed in these investigations. Epitaxial regrowth of buried amorphous GaAs layers of thicknesses up to 150 nm can be induced by rapid thermal annealing. It is demonstrated that differences in the initial damage state have a strong influence upon the nature of lattice defects produced by annealing.

  9. Growth and Characterization of Lead-free Piezoelectric Single Crystals

    Directory of Open Access Journals (Sweden)

    Philippe Veber

    2015-11-01

    Full Text Available Lead-free piezoelectric materials attract more and more attention owing to the environmental toxicity of lead-containing materials. In this work, we review our first attempts of single crystal grown by the top-seeded solution growth method of BaTiO3 substituted with zirconium and calcium (BCTZ and (K0.5Na0.5NbO3 substituted with lithium, tantalum, and antimony (KNLSTN. The growth methodology is optimized in order to reach the best compositions where enhanced properties are expected. Chemical analysis and electrical characterizations are presented for both kinds of crystals. The compositionally-dependent electrical performance is investigated for a better understanding of the relationship between the composition and electrical properties. A cross-over from relaxor to ferroelectric state in BCTZ solid solution is evidenced similar to the one reported in ceramics. In KNLSTN single crystals, we observed a substantial evolution of the orthorhombic-to-tetragonal phase transition under minute composition changes.

  10. Diagenetic Crystal Growth in the Murray Formation, Gale Crater, Mars

    Science.gov (United States)

    Kah, L. C.; Kronyak, R. E.; Ming, D. W.; Grotzinger, J. P.; Schieber, J.; Sumner, D. Y.; Edgett, K. S.

    2015-01-01

    The Pahrump region (Gale Crater, Mars) marks a critical transition between sedimentary environments dominated by alluvial-to-fluvial materials associated with the Gale crater rim, and depositional environments fundamentally linked to the crater's central mound, Mount Sharp. At Pahrump, the Murray formation consists of an approximately 14-meter thick succession dominated by massive to finely laminated mudstone with occasional interbeds of cross-bedded sandstone, and is best interpreted as a dominantly lacustrine environment containing tongues of prograding fluvial material. Murray formation mudstones contain abundant evidence for early diagenetic mineral precipitation and its subsequent removal by later diagenetic processes. Lenticular mineral growth is particularly common within lacustrine mudstone deposits at the Pahrump locality. High-resolution MAHLI images taken by the Curiosity rover permit detailed morphological and spatial analysis of these features. Millimeter-scale lenticular features occur in massive to well-laminated mudstone lithologies and are interpreted as pseudomorphs after calcium sulfate. The distribution and orientation of lenticular features suggests deposition at or near the sediment-water (or sediment-air) interface. Retention of chemical signals similar to host rock suggests that original precipitation was likely poikilotopic, incorporating substantial amounts of the primary matrix. Although poikilotopic crystal growth is common in burial environments, it also occurs during early diagenetic crystal growth within unlithified sediment where high rates of crystal growth are common. Loss of original calcium sulfate mineralogy suggests dissolution by mildly acidic, later-diagenetic fluids. As with lenticular voids observed at Meridiani by the Opportunity Rover, these features indicate that calcium sulfate deposition may have been widespread on early Mars; dissolution of depositional and early diagenetic minerals is a likely source for both calcium

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

    Science.gov (United States)

    Chauhan, Chetan K.; Joshi, Mihir J.

    2013-01-01

    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.

  12. On the structural-optical properties of Al-containing amorphous Si thin films and the metal-induced crystallization phenomenon

    Energy Technology Data Exchange (ETDEWEB)

    Zanatta, A. R. [Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, SP 13566-590 (Brazil); Kordesch, M. E. [Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701 (United States)

    2014-08-21

    Amorphous (a-)Si-based materials always attracted attention of the scientific community, especially after their use in commercial devices like solar cells and thin film transistors in the 1980s. In addition to their technological importance, the study of a-Si-based materials also present some interesting theoretical-practical challenges. Their crystallization as induced by metal species is one example, which is expected to influence the development of electronic-photovoltaic devices. In fact, the amorphous-to-crystalline transformation of the a-SiAl system has been successfully applied to produce solar cells suggesting that further improvements can be achieved. Stimulated by these facts, this work presents a comprehensive study of the a-SiAl system. The samples, with Al contents in the ∼0−15 at. % range, were made in the form of thin films and were characterized by different spectroscopic techniques. The experimental results indicated that: (a) increasing amounts of Al changed both the atomic structure and the optical properties of the samples; (b) thermal annealing induced the crystallization of the samples at temperatures that depend on the Al concentration; and (c) the crystallization process was also influenced by the annealing duration and the structural disorder of the samples. All of these aspects were addressed in view of the existing models of the a-Si crystallization, which were also discussed to some extent. Finally, the ensemble of experimental results suggest an alternative method to produce cost-effective crystalline Si films with tunable structural-optical properties.

  13. Some Aspects of PVT Low Supersaturation Nucleation and Contactless Crystal Growth

    Science.gov (United States)

    Grasza, K.; Palosz, W.

    1996-01-01

    The basic principles of the contactless growth of crystals from the vapor in combination with the process of low-supersaturation nucleation are discussed. The mathematical formulation of the morphological stability criterion in vapor growth systems is given and its implications for contactless growth technique are analyzed. A diagram for selection of proper temperature conditions for growth of CdTe crystals is presented.

  14. Single Crystals of Organolead Halide Perovskites: Growth, Characterization, and Applications

    KAUST Repository

    Peng, Wei

    2017-04-01

    crystals will be discussed in Chapter 3 and 4. Despite their outstanding charge transport characteristics, organolead halide perovskite single crystals grown by hitherto reported crystallization methods are not suitable for most optoelectronic devices due to their small aspect ratios and free standing growth. As the other major part of work of this dissertation, explorative work on growing organolead halide perovskite monocrystalline films and further their application in solar cells will be discussed in Chapter 5.

  15. Solvent-shift strategy to identify suitable polymers to inhibit humidity-induced solid-state crystallization of lacidipine amorphous solid dispersions.

    Science.gov (United States)

    Sun, Mengchi; Wu, Chunnuan; Fu, Qiang; Di, Donghua; Kuang, Xiao; Wang, Chao; He, Zhonggui; Wang, Jian; Sun, Jin

    2016-04-30

    The solvent-shift strategy was used to identify appropriate polymers that inhibit humidity-induced solid-state crystallization of amorphous solid dispersions (ASDs). Lacidipine with the polymers, PVP-K30, HPMC-E5 or Soluplus, were combined to form amorphous solid dispersions prepared by solvent evaporation. The formulations were characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and Fourier-transform infrared spectroscopy (FT-IR) and were subjected to in vitro dissolution testing. The moisture had a significant impact on the amount dissolved for the solid dispersions. Molecular docking studies established that hydrogen bonding was critical for the stabilization of the solid dispersions. The rank order of the binding energy of the drug-polymer association was Soluplus (-6.21 kcal/mol)>HPMC-E5 (-3.21 kcal/mol)>PVP-K30 (-2.31 kcal/mol). PVP-K30 had the highest water uptake among the polymers, as did ASD system of lacidipine-PVP-K30 ASDs. In the Soluplus ASDs, with its strong drug-polymer interactions and low water uptake, moisture-induced solid-state crystallization was not observed.

  16. Validation, verification, and benchmarking of crystal growth simulations

    Science.gov (United States)

    Dadzis, K.; Bönisch, P.; Sylla, L.; Richter, T.

    2017-09-01

    The variety of physical phenomena in crystal growth processes requires diverse software tools for the numerical simulations. Both, dedicated 2D or 3D ready-to-use software for coupled simulations of a crystallization furnace and general-purpose 3D simulation packages have been used in the literature. This work proposes a general strategy for model development: validation of the physical model using model experiments; verification of the numerical model using analytical or high-accuracy solutions; testing of the computational efficiency using complex benchmark cases. The application of these steps is demonstrated for various models in directional solidification of silicon showing the capabilities of various open source or commercial software packages.

  17. Modelling of Verneuil process for the sapphire crystal growth

    Science.gov (United States)

    Barvinschi, Floricica; Santailler, Jean-Louis; Duffar, Thierry; Le Gal, Hervé

    1999-03-01

    The finite element software FIDAP was used to simulate the Verneuil crystal growth process. The turbulent combustion between hydrogen and oxygen, giving water, the hydrodynamics of the gas phase, the inlet and outlet chemical species flow resulting from the combustion and the heat transfer in the furnace (including internal wall-to-wall radiation) are taken into account. A problem with 10 degrees of freedom per node is generated, solved and the results of the axisymmetric model have shown that the coupling of all these phenomena can be achieved in one numerical model. The effects of transparency of the crystal is discussed. A qualitative agreement between some experimental observations and the model is found, so that modelling may be a good tool for studying the Verneuil process. Nevertheless, some improvements of the model in conjunction with other experimental validations appear necessary.

  18. Model of apparent crystal growth rate and kinetics of seeded precipitation from sodium aluminate solution

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-bin; LIU Zhi-jian; XU Xiao-hui; ZHOU Qiu-sheng; PENG Zhi-hong; LIU Gui-hua

    2005-01-01

    Based on the population balance equation in a batch crystallizer characteristic of seeded precipitation, a model to calculate the rate of apparent crystal growth of aluminum hydroxide from the size distribution was deve-loped. The simulation results indicate that the rate of apparent crystal growth during seeded precipitation exhibits a manifest dependence on the crystal size. In general, there is an obvious increase in the apparent crystal growth rate with the augment in crystal size. The apparent activation energy increases with the increase of characteristic crystal size, which indicates that the growth of small crystals is controlled by surface chemical reaction; it is gradually controlled by both the surface reaction and diffusion with the augment in crystal size.

  19. Inhibition of surface crystallisation of amorphous indomethacin particles in physical drug-polymer mixtures

    DEFF Research Database (Denmark)

    Priemel, Petra A; Laitinen, Riikka; Barthold, Sarah

    2013-01-01

    Surface coverage may affect the crystallisation behaviour of amorphous materials. This study investigates crystallisation inhibition in powder mixtures of amorphous drug and pharmaceutical excipients. Pure amorphous indomethacin (IMC) powder and physical mixtures thereof with Eudragit(®) E...... stability than pure IMC whereas IMC Soluplus(®) mixtures did not. Water uptake was higher for mixtures containing Soluplus(®) than for amorphous IMC or IMC Eudragit(®) mixtures. However, the Tg of amorphous IMC was unaffected by the presence (and nature) of polymer. SEM revealed that Eudragit(®) particles...... through reduced IMC surface molecular mobility. Polymer particles may also mechanically hinder crystal growth outwards from the surface. This work highlights the importance of microparticulate surface coverage of amorphous drug particles on their stability....

  20. In situ investigation of growth rates and growth rate dispersion of α-lactose monohydrate crystals

    Science.gov (United States)

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

    2009-02-01

    The growth rates and growth rate dispersion (GRD) of four different faces of α-lactose monohydrate crystal were measured at 30, 40 and 50 °C in the relative supersaturation range 0.55-2.33 in aqueous solutions. The overall growth rate of the crystal is around 50-60% of the (0 1 0) face of the crystal. The power law was applied to the growth rates of the four faces and the activation energies were calculated to be between 9.5 and 13.7 kcal/mol. This indicates a diffusion-controlled growth, but the exponents calculated are between 2.5 and 3.1 which are higher than unity. Introduction of critical supersaturation decreased the exponents to between 1.8 and 2.4. The variance of GRD for the (0 1 0) face is twice the variance of the GRD of the (1 1 0) and (1 0 0) faces and 10 times higher than the (1 1¯ 1¯) face at the same supersaturations and temperatures. The GRD of the four faces were similar when expressed as a function of growth rate. However, the (0 1 1) face displayed lower GRD than the other faces at the same temperatures and supersaturations.

  1. Potential productivity benefits of float-zone versus Czochralski crystal growth

    Science.gov (United States)

    Abe, T.

    1985-01-01

    Efficient mass production of single-crystal silicon is necessary for the efficient silicon solar arrays needed in the coming decade. However, it is anticipated that there will be difficulty growing such volumes of crystals using conventional Czochralski (Cz) methods. While the productivity of single crystals might increase with a crystal diameter increase, there are two obstacles to the mass production of large diameter Czochralski crystals, the long production cycle due to slow growth rate and the high heat requirements of the furnaces. Also counterproductive would be the large resistivity gradient along the growth direction of the crystals due to impurity concentration. Comparison between Float zone (FZ) and Cz crystal growth on the basis of a crystal 150 mm in diameter is on an order of two to four times in favor of the FZ method. This advantage results from high growth rates and steady-state growth while maintaining a dislocation-free condition and impurity segregation.

  2. Recovery of surfaces from impurity poisoning during crystal growth

    Science.gov (United States)

    Land, Terry A.; Martin, Tracie L.; Potapenko, Sergey; Palmore, G. Tayhas; de Yoreo, James J.

    1999-06-01

    Growth and dissolution of crystal surfaces are central to processes as diverse as pharmaceutical manufacturing,, corrosion, single-crystal production and mineralization in geochemical and biological environments,. Impurities are either unavoidable features of these processes or intentionally introduced to modify the products. Those that act as inhibiting agents induce a so-called `dead zone', a regime of low supersaturation where growth ceases. Models based on the classic theory of Cabrera and Vermilyea explain behaviour near the dead zone in terms of the pinning of elementary step motion by impurities,. Despite general acceptance of this theory, a number of commonly investigated systems exhibit behaviour not predicted by such models. Moreover, no clear microscopic picture of impurity-step interactions currently exists. Here we use atomic force microscopy to investigate the potassium dihydrogen phosphate {100} surface as it emerges from the dead zone. We show that traditional models are not able to account for the behaviour of this system because they consider only elementary steps, whereas it is the propagation of macrosteps (bunches of monolayer steps) that leads to resurrection of growthout of the dead zone. We present a simple physical model of this process that includes macrosteps and relates characteristics of growth near the dead zone to the timescale for impurity adsorption.

  3. Kinetics of faceting of crystals in growth, etching, and equilibrium

    Science.gov (United States)

    Vlachos, D. G.; Schmidt, L. D.; Aris, R.

    1993-03-01

    The faceting of crystals in equilibrium with the gas phase and also during crystal growth and etching conditions is studied using the Monte Carlo method. The dynamics of the transformation of unstable crystallographic orientations into hill and valley structures and the spatial patterns that develop are examined as functions of surface temperature, crystallographic orientation, and strength of interatomic potential for two transport processes: adsorption-desorption and surface diffusion. The results are compared with the continuum theory for facet formation. Thermodynamically unstable orientations break into hill and valley structures, and faceting exhibits three time regimes: disordering, facet nucleation, and coarsening of small facets to large facets. Faceting is accelerated as temperature increases, but thermal roughening can occur at high temperatures. Surface diffusion is the dominant mechanism at short times and small facets but adsorption-desorption becomes important at long times and large facets. Growth and etching promote faceting for conditions close to equilibrium but induce kinetic roughening for conditions far from equilibrium. Simultaneous irreversible growth and etching conditions with fast surface diffusion result in enhanced faceting.

  4. Modeling of crystal morphology : growth simulation on facets in arbitrary orientations

    NARCIS (Netherlands)

    Boerrigter, Stephan Xander Mattheus

    2003-01-01

    Many aspects of crystal morphology modeling are studied in this thesis. Most important of all, is the dependence of crystal growth on supersaturation--the driving force for crystallization--which not only influences the crystal morphology, but also polymorphism and nucleation. It is shown that an

  5. A study about some phosphate derivatives as inhibitors of calcium oxalate crystal growth

    Science.gov (United States)

    Grases, F.; March, P.

    1989-08-01

    The kinetic of crystal growth of calcium oxalate monohydrate seed crystals were investigated potentiometrically in the presence of several phosphate derivatives, D-fructose-1,6-diphosphate, pyrophosphate, methylene diphosphonate and phytate, and it was found that in some cases they strongly inhibited crystal growth. The inhibitory action of the different substances assayed was comparatively evaluated.

  6. Growth Defects in Langasite Crystals Observed with White Beam Synchrotron Radiation Topography

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Langasite single crystal was grown by the Czochralski method and its perfection was assessed by white beam synchrotron radiation topography. It is found that the growth core and the growth striations are the primary growth defects and they show strong X-ray kinematical contrast in the topographs. Another typical defect in LGS crystal is dislocation. The formation mechanisms of these growth defects in LGS crystals were discussed.

  7. Viscosity solutions for a polymer crystal growth model

    CERN Document Server

    Cardaliaguet, Pierre; Monteillet, Aurélien

    2010-01-01

    We prove existence of a solution for a polymer crystal growth model describing the movement of a front $(\\Gamma(t))$ evolving with a nonlocal velocity. In this model the nonlocal velocity is linked to the solution of a heat equation with source $\\delta_\\Gamma$. The proof relies on new regularity results for the eikonal equation, in which the velocity is positive but merely measurable in time and with H\\"{o}lder bounds in space. From this result, we deduce \\textit{a priori} regularity for the front. On the other hand, under this regularity assumption, we prove bounds and regularity estimates for the solution of the heat equation.

  8. Growth of bulk gadolinium pyrosilicate single crystals for scintillators

    Science.gov (United States)

    Gerasymov, I.; Sidletskiy, O.; Neicheva, S.; Grinyov, B.; Baumer, V.; Galenin, E.; Katrunov, K.; Tkachenko, S.; Voloshina, O.; Zhukov, A.

    2011-03-01

    Ce, Pr, and La-doped gadolinium pyrosilicate Gd2Si2O7 (GPS) single crystals were grown by the Czochralski and Top Seeded Solution Growth (TSSG) techniques for the first time. Formation conditions of different pyrosilicate phases were determined. X-ray luminescence integral intensity of Ce-doped GPS is about one order of magnitude higher in comparison with gadolinium oxyorthosilicate Gd2SiO5:Ce (GSO:Ce). All samples demonstrate temperature stability of luminescence yield up to 400 K.

  9. Direction-specific interactions control crystal growth by oriented attachment

    DEFF Research Database (Denmark)

    Li, Dongsheng; Nielsen, Michael H; Lee, Jonathan R.I.

    2012-01-01

    initiated at the contact point. Interface elimination proceeds at a rate consistent with the curvature dependence of the Gibbs free energy. Measured translational and rotational accelerations show that strong, highly direction-specific interactions drive crystal growth via oriented attachment....... using a fluid cell to directly observe oriented attachment of iron oxyhydroxide nanoparticles. The particles undergo continuous rotation and interaction until they find a perfect lattice match. A sudden jump to contact then occurs over less than 1 nanometer, followed by lateral atom-by-atom addition...

  10. Fluid flow and solute segregation in EFG crystal growth process

    Science.gov (United States)

    Bunoiu, O.; Nicoara, I.; Santailler, J. L.; Duffar, T.

    2005-02-01

    The influence of the die geometry and various growth conditions on the fluid flow and on the solute distribution in EFG method has been studied using numerical simulation. The commercial FIDAP software has been used in order to solve the momentum and mass transfer equations in the capillary channel and in the melt meniscus. Two types of shaper design are studied and the results are in good agreement with the void distribution observed in rod-shaped sapphire crystals grown by the EFG method in the various configurations.

  11. Velocity selection in the symmetric model of dendritic crystal growth

    Science.gov (United States)

    Barbieri, Angelo; Hong, Daniel C.; Langer, J. S.

    1987-01-01

    An analytic solution of the problem of velocity selection in a fully nonlocal model of dendritic crystal growth is presented. The analysis uses a WKB technique to derive and evaluate a solvability condition for the existence of steady-state needle-like solidification fronts in the limit of small under-cooling Delta. For the two-dimensional symmetric model with a capillary anisotropy of strength alpha, it is found that the velocity is proportional to (Delta to the 4th) times (alpha exp 7/4). The application of the method in three dimensions is also described.

  12. Kinetic Processes Crystal Growth, Diffusion, and Phase Transformations in Materials

    CERN Document Server

    Jackson, Kenneth A

    2004-01-01

    The formation of solids is governed by kinetic processes, which are closely related to the macroscopic behaviour of the resulting materials. With the main focus on ease of understanding, the author begins with the basic processes at the atomic level to illustrate their connections to material properties. Diffusion processes during crystal growth and phase transformations are examined in detail. Since the underlying mathematics are very complex, approximation methods typically used in practice are the prime choice of approach. Apart from metals and alloys, the book places special emphasis on th

  13. Viscosity solutions for a polymer crystal growth model

    OpenAIRE

    Cardaliaguet, Pierre; Ley, Olivier; Monteillet, Aurélien

    2011-01-01

    International audience; We prove existence of a solution for a polymer crystal growth model describing the movement of a front $(\\Gamma(t))$ evolving with a nonlocal velocity. In this model the nonlocal velocity is linked to the solution of a heat equation with source $\\delta_\\Gamma$. The proof relies on new regularity results for the eikonal equation, in which the velocity is positive but merely measurable in time and with H\\"{o}lder bounds in space. From this result, we deduce \\textit{a pri...

  14. Biaxial CdTe/CaF{sub 2} films growth on amorphous surface

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, W., E-mail: yuanw@rpi.ed [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Tang, F.; Li, H.-F.; Parker, T. [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); LiCausi, N. [Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Lu, T.-M. [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Bhat, I. [Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Wang, G.-C. [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Lee, S. [US Army Armament Research, Development and Engineering Center, Benet Labs, Watervliet, NY 12189 (United States)

    2009-10-30

    A continuous and highly biaxially textured CdTe film was grown by metal organic chemical vapor deposition on an amorphous substrate using biaxial CaF{sub 2} nanorods as a buffer layer. The interface between the CdTe film and CaF{sub 2} nanorods and the morphology of the CdTe film were studied by transmission electron microscopy (TEM) and scanning electron microscopy. Both the TEM and X-ray pole figure analysis clearly reveal that the crystalline orientation of the continuous CdTe film followed the {l_brace}111{r_brace}<121> biaxial texture of the CaF{sub 2} nanorods. A high density of twin faults was observed in the CdTe film. Furthermore, the near surface texture of the CdTe thin film was investigated by reflection high-energy electron diffraction (RHEED) and RHEED surface pole figure analysis. Twinning was also observed from the RHEED surface pole figure analysis.

  15. Room Temperature Growth of Hydrogenated Amorphous Silicon Films by Dielectric Barrier Discharge Enhanced CVD

    Institute of Scientific and Technical Information of China (English)

    GUO Yu; ZHANG Xiwen; HAN Gaorong

    2007-01-01

    Hydrogenated amorphous silicon (a-Si:H) films were deposited on Si (100) and glass substrates by dielectric barrier discharge enhanced chemical vapour deposition (DBD-CVD)in (SiH4+H2) atmosphere at room temperature.Results of the thickness measurement,SEM (scanning electron microscope),Raman,and FTIR (Fourier transform infrared spectroscopy) show that with the increase in the applied peak voltage,the deposition rate and network order of the films increase,and the hydrogen bonding configurations mainly in di-hydrogen (Si-H2) and poly hydrogen (SiH2)n are introduced into the films.The UV-visible transmission spectra show that with the decrease in Sill4/ (SiH4+H2) the thin films'band gap shifts from 1.92 eV to 2.17 eV.These experimental results are in agreement with the theoretic analysis of the DBD discharge.The deposition of a-Si:H films by the DBD-CVD method as reported here for the first time is attractive because it allows fast deposition of a-Si:H films on large-area low-melting-point substrates and requires only a low cost of production without additional heating or pumping equipment.

  16. Crystallization kinetics and phase transformation in amorphous Fe74Co10B16 and Fe67Co18B14Si1 alloys

    Directory of Open Access Journals (Sweden)

    B. Bhanu Prasad

    2015-06-01

    Full Text Available Crystallization kinetics and phase transformation studies have been carried out on amorphous Fe74Co10B16 (S1 and Fe67Co18B14Si1 (S2 alloys using Mossbauer Spectroscopy (MS, Electrical Resistivity (ER, Differential Scanning Calorimetry(DSC, X-ray Diffraction(XRD and Transmission Electron Microscopy(TEM to determine the thermal stability. Results show that the transformation to an equilibrium crystalline state occurs through a two step process. Crystallization process is associated with precipitation of two or more phases which are magnetic in nature. From DSC curves, the activation energy of sample S2 has been calculated using Kissinger, Matusita-Sakka and Augis-Bennet methods and the average value is found to be 211 kJ/mol. The detected phases upon crystallization in the samples are α–(Fe-Co and (Fe-Co2B. Exact compositions of these phases in the completely crystallized sample are found to be α–(Fe0.7Co0.3 and (Fe0.3Co0.72B.

  17. In Situ Laser Crystallization of Amorphous Silicon for TFT Applications: Controlled Ultrafast Studies in the Dynamic TEM

    Energy Technology Data Exchange (ETDEWEB)

    Taheri, M; Teslich, N; Lu, J P; Morgan, D; Browning, N

    2008-02-08

    An in situ method for studying the role of laser energy on the microstructural evolution of polycrystalline Si is presented. By monitoring both laser energy and microstructural evolution simultaneously in the dynamic transmission electron microscope, information on grain size and defect concentration can be correlated directly with processing conditions. This proof of principle study provides fundamental scientific information on the crystallization process that has technological importance for the development of thin film transistors. In conclusion, we successfully developed a method for studying UV laser processing of Si films in situ on nanosecond time scales, with ultimate implications for TFT application improvements. In addition to grain size distribution as a function of laser energy density, we found that grain size scaled with laser energy in general. We showed that nanosecond time resolution allowed us to see the nucleation and growth front during processing, which will help further the understanding of microstructural evolution of poly-Si films for electronic applications. Future studies, coupled with high resolution TEM, will be performed to study grain boundary migration, intergranular defects, and grain size distribution with respect to laser energy and adsorption depth.

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

    Science.gov (United States)

    Bolotnikov, Aleskey E.; James, Ralph B.

    2010-07-20

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

  19. Growth and evaluation of lanthanoids orthoniobates single crystals processed by a miniature pedestal growth technique

    Energy Technology Data Exchange (ETDEWEB)

    Octaviano, E.S. [Universidade Camilo Castelo Branco, Descalvado, SP (Brazil); Reyes Ardila, D. [Departmento de Fisica, Universidad de Santiago de Chile (Chile); Andrade, L.H.C.; Siu Li, M.; Andreeta, J.P. [Instituto de Fisica de Sao Carlos, Departamento de Fisica e Ciencia dos Materiais, Universidade de Sao Paulo, Sao Carlos, SP (Brazil)

    2004-10-01

    Optimized conditions for the growth of lanthanoids orthoniobates (LnNbO{sub 4}, Ln=lanthanide elements) single crystal minirods by a floating zone technique were investigated. Adequate atmospheres and pulling to feeding speed ratios to grow these materials were determined. Emphasis is given to the study of LaNbO{sub 4} because of their more favorable growth conditions and crystalline quality. This material can be efficiently doped with rare earth elements such as erbium. It grows with high crystallinity and its preferential growth direction is [110]. A preliminary evaluation of optical properties of Er{sup 3+}-doped LaNbO{sub 4} single crystal under the Judd-Ofelt formalism indicates spectral parameters {omega}{sub t} close and even larger than for Er{sup 3+} ions in YVO{sub 4}. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Refining stability and dissolution rate of amorphous drug formulations

    DEFF Research Database (Denmark)

    Grohganz, Holger; Priemel, Petra A; Löbmann, Korbinian;

    2014-01-01

    amorphous counterpart is often seen as a potential solution to increase the solubility. However, amorphous systems are physically unstable. Therefore, pharmaceutical formulations scientists need to find ways to stabilise amorphous forms. Areas covered: The use of polymer-based solid dispersions is the most......Introduction: Poor aqueous solubility of active pharmaceutical ingredients (APIs) is one of the main challenges in the development of new small molecular drugs. Additionally, the proportion of poorly soluble drugs among new chemical entities is increasing. The transfer of a crystalline drug to its...... established technique for the stabilisation of amorphous forms, and this review will initially focus on new developments in this field. Additionally, newly discovered formulation approaches will be investigated, including approaches based on the physical restriction of crystallisation and crystal growth...

  1. Numerical computation of sapphire crystal growth using heat exchanger method

    Science.gov (United States)

    Lu, Chung-Wei; Chen, Jyh-Chen

    2001-05-01

    The finite element software FIDAP is employed to study the temperature and velocity distribution and the interface shape during a large sapphire crystal growth process using a heat exchanger method (HEM). In the present study, the energy input to the crucible by the radiation and convection inside the furnace and the energy output through the heat exchanger is modeled by the convection boundary conditions. The effects of the various growth parameters are studied. It is found that the contact angle is obtuse before the solid-melt interface touches the sidewall of the crucible. Therefore, hot spots always appear in this process. The maximum convexity decreases significantly when the cooling-zone radius (RC) increases. The maximum convexity also decreases significantly as the combined convection coefficient inside the furnace (hI) decreases.

  2. On the origin of radiation growth of hcp crystals

    Energy Technology Data Exchange (ETDEWEB)

    Golubov, Stanislav I [ORNL; Barashev, Aleksandr [University of Liverpool; Stoller, Roger E [ORNL

    2012-03-01

    The aim of the present work is to study theoretically the radiation growth (RG) of hcp-type materials with a particular focus on the effect of one-dimensionally (1-D) migrating clusters of self-interstitial atoms (SIAs), which are steadily produced in displacement cascades under neutron or heavy-ion irradiation. A reaction-diffusion model is developed for the description of RG in single hcp-type metallic crystals. The model reproduces all RG stages observed in neutron-irradiated annealed samples of pure Zr and Zr alloys, such as high strain rate at low, strain saturation at intermediate and breakaway growth at relatively high irradiation doses. In addition, it accounts for the striking observations of negative strains in prismatic directions and coexistence of vacancy- and SIA-type prismatic loops. The role of cold work in RG behavior and alignment of the vacancy-type loops along basal planes are revealed and the maximum strain rate is estimated.

  3. Semiconductor Crystal Growth in Static and Rotating Magnetic fields

    Science.gov (United States)

    Volz, Martin

    2004-01-01

    Magnetic fields have been applied during the growth of bulk semiconductor crystals to control the convective flow behavior of the melt. A static magnetic field established Lorentz forces which tend to reduce the convective intensity in the melt. At sufficiently high magnetic field strengths, a boundary layer is established ahead of the solid-liquid interface where mass transport is dominated by diffusion. This can have a significant effect on segregation behavior and can eliminate striations in grown crystals resulting from convective instabilities. Experiments on dilute (Ge:Ga) and solid solution (Ge-Si) semiconductor systems show a transition from a completely mixed convective state to a diffusion-controlled state between 0 and 5 Tesla. In HgCdTe, radial segregation approached the diffusion limited regime and the curvature of the solid-liquid interface was reduced by a factor of 3 during growth in magnetic fields in excess of 0.5 Tesla. Convection can also be controlled during growth at reduced gravitational levels. However, the direction of the residual steady-state acceleration vector can compromise this effect if it cannot be controlled. A magnetic field in reduced gravity can suppress disturbances caused by residual transverse accelerations and by random non-steady accelerations. Indeed, a joint program between NASA and the NHMFL resulted in the construction of a prototype spaceflight magnet for crystal growth applications. An alternative to the suppression of convection by static magnetic fields and reduced gravity is the imposition of controlled steady flow generated by rotating magnetic fields (RMF)'s. The potential benefits of an RMF include homogenization of the melt temperature and concentration distribution, and control of the solid-liquid interface shape. Adjusting the strength and frequency of the applied magnetic field allows tailoring of the resultant flow field. A limitation of RMF's is that they introduce deleterious instabilities above a

  4. The influence of crystal morphology on the kinetics of growth of calcium oxalate monohydrate

    Science.gov (United States)

    Millan, A.; Sohnel, O.; Grases, F.

    1997-08-01

    The growth of several calcium oxalate monohydrate seeds in the presence and absence of additives (phytate, EDTA and citrate) has been followed by potentiometry measurements. Growth rates have been calculated from precipitate curves by a cubic spline method and represented in logarithmic plots versus supersaturation. Crystal growth kinetics were found to be dependent on crystal morphology, crystal perfection and degree of aggregation. Some seeds were dissolving in supersaturated solutions. Other seeds showed an initial growth phase of high-order kinetics. The effect of the additives was also different on each seed. Three alternative mechanisms for calcium oxalate crystal growth are proposed.

  5. A preliminary review of organic materials single crystal growth by the Czochralski technique

    Science.gov (United States)

    Penn, B. G.; Shields, A. W.; Frazier, D. O.

    1988-01-01

    The growth of single crystals of organic compounds by the Czochralski method is reviewed. From the literature it is found that single crystals of benzil, a nonlinear optical material with a d sub 11 value of 11.2 + or - 1.5 x d sub 11 value of alpha quartz, has fewer dislocations than generally contained in Bridgman crystals. More perfect crystals were grown by repeated Czochralski growth. This consists of etching away the defect-containing portion of a Czochralski grown crystal and using it as a seed for further growth. Other compounds used to grow single crystals are benzophenone, 12-tricosanone (laurone), and salol. The physical properties, growth apparatus, and processing conditions presented in the literature are discussed. Moreover, some of the possible advantages of growing single crystals of organic compounds in microgravity to obtain more perfect crystals than on Earth are reviewed.

  6. Solution Growth and Characterization of Single Crystals on Earth and in Microgravity

    Science.gov (United States)

    Aggarwal, M. D.; Currie, J. R.; Penn, B. G.; Batra, A. K.; Lal, R. B.

    2007-01-01

    Crystal growth has been of interest to physicists and engineers for a long time because of their unique properties. Single crystals are utilized in such diverse applications as pharmaceuticals, computers, infrared detectors, frequency measurements, piezoelectric devices, a variety of high-technology devices, and sensors. Solution crystal growth is one of the important techniques to grow a variety of crystals when the material decomposes at the melting point and a suitable solvent is available to make a saturated solution at a desired temperature. In this Technical Memorandum (TM) an attempt is made to give the fundamentals of growing crystals from solution including improved designs of various crystallizers. Since the same solution crystal growth technique could not be used in microgravity, the authors proposed a new cooled-sting technique to grow crystals in space. The authors experience from conducting two Space Shuttle solution crystal growth experiments are also detailed in this TM and the complexity of solution growth experiments to grow crystals in space are also discussed. These happen to be some of the early experiments performed in space, and various lessons learned are described. A brief discussion of protein crystal growth that shares basic principles of the solution growth technique is given, along with some flight hardware information for growth in microgravity.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-05-01

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

  8. Role of atomic-level defects and electronic energy loss on amorphization in LiNbO3 single crystals

    Science.gov (United States)

    Sellami, N.; Crespillo, M. L.; Xue, H.; Zhang, Y.; Weber, W. J.

    2017-08-01

    Understanding complex non-equilibrium defect processes, where multiple irradiation mechanisms may take place simultaneously, is a long standing subject in material science. The separate and combined effects of elastic and inelastic energy loss are a very complicated and challenging topic. In this work, LiNbO3 has been irradiated with 0.9 MeV Si+ and 8 MeV O3+, which are representative of regimes where nuclear (S n) and electronic (S e) energy loss are dominant, respectively. The evolution of damage has been investigated by Rutherford backscattering spectrometry (RBS) in channeling configuration. Pristine samples were irradiated with 0.9 MeV Si+ ions to create different pre-existing damage states. Below the threshold (S e,th  =  5-6 keV nm-1) for amorphous track formation in this material, irradiation of the pristine samples with a highly ionizing beam of 8 MeV O3+ ions, with nearly constant S e of about 3 keV nm-1, induces a crystalline to amorphous phase transition at high ion fluences. In the pre-damaged samples, the electronic energy loss from the 8 MeV O3+ ions interacts synergistically with the pre-existing damage, resulting in a rapid, non-linear increase in damage production. There is a significant reduction in the incubation fluence for rapid amorphization with the increasing amount of pre-existing damage. These results highlight the important role of atomic-level defects on increasing the sensitivity of some oxides to amorphization induced by electronic energy loss. Controlling the nature and amount of pre-damage may provide a new approach to tuning optical properties for photonic device applications.

  9. SiGe crystal growth aboard the international space station

    Science.gov (United States)

    Kinoshita, K.; Arai, Y.; Tsukada, T.; Inatomi, Y.; Miyata, H.; Tanaka, R.

    2015-05-01

    A silicon germanium mixed crystal Si1-xGex (x~0.5) 10 mm in diameter and 9.2 mm in length was grown by the traveling liquidus-zone (TLZ) method in microgravity by suppressing convection in a melt. Ge concentration of 49.8±2.5 at% has been established for the whole of the grown crystal. Compared with the former space experiment, concentration variation in the axial direction increased from ±1.5 at% to ±2.5 at% although average Ge concentration reached to nearly 50 at%. Excellent radial Ge compositional uniformity 52±0.5 at% was established in the region of 7-9 mm growth length, where axial compositional uniformity was also excellent. The single crystalline region is about 5 mm in length. The interface shape change from convex to concave is implied from both experimental results and numerical analysis. The possible cause of increase in concentration variation and interface shape change and its relation to the two-dimensional growth model are discussed.

  10. Growth of BPO4 single crystals from Li2Mo3O10 flux

    Science.gov (United States)

    Xu, Guogang; Li, Jing; Han, Shujuan; Guo, Yongjie; Wang, Jiyang

    2010-12-01

    Transparent single crystal of BPO4 with a typical sizes of 5 × 7 × 9 mm3 have been grown by the top-seeded solution growth (TSSG) slow-cooling method using Li2Mo3O10 as the flux. X-ray powder diffraction result shows that the as-grown crystal was well crystallized and indexed in a tetragonal system. The processing parameters and the effects of the flux on the crystal growth were investigated.

  11. Structures and growth mechanisms of poly-(3-hydroxybutyrate) (PHB) crystallized from solution and thin melt film

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The spherulitic structures and morphologies of poly-(3-hydroxybutyrate) (PHB) crystallized from a so- lution and a thin melt film were investigated in this study. The formation mechanisms of banded spherulites under different crystallization conditions are proposed. It was found that the formation of banded spherulites was caused by the rhythmic crystal growth of the spherulites and lamellar twisting growth for the polymer crystallization from a thin melt film and a solution, respectively.

  12. Study on Characteristics of Crystal Growth of NdFeB Cast Alloys

    Institute of Scientific and Technical Information of China (English)

    李波; 郭炳麟; 王东玲; 刘涛; 喻晓军

    2004-01-01

    The characteristic of crystal growth of NdFeB cast alloys was studied.It is found that the crystal growth orientation of conventional ingots is along or .As the cooling rate increases,the crystallization orientation changes from a axis to c axis,along which the grain is easy to be magnetized.Meanwhile,by analyzing the change of crystallization orientation,the influence on the property of magnets was discussed.

  13. A peek into the history of sapphire crystal growth

    Science.gov (United States)

    Harris, Daniel C.

    2003-09-01

    After the chemical compositions of sapphire and ruby were unraveled in the middle of the 19th century, chemists set out to grow artificial crystals of these valuable gemstones. In 1885 a dealer in Geneva began to sell ruby that is now believed to have been created by flame fusion. Gemnologists rapidly concluded that the stones were artificial, but the Geneva ruby stimulated A. V. L. Verneuil in Paris to develop a flame fusion process to produce higher quality ruby and sapphire. By 1900 there was brisk demand for ruby manufactured by Verneuil's method, even though Verneuil did not publicly announce his work until 1902 and did not publish details until 1904. The Verneuil process was used with little alteration for the next 50 years. From 1932-1953, S. K. Popov in the Soviet Union established a capability for manufacturing high quality sapphire by the Verneuil process. In the U.S., under government contract, Linde Air Products Co. implemented the Verneuil process for ruby and sapphire when European sources were cut off during World War II. These materials were essential to the war effort for jewel bearings in precision instruments. In the 1960s and 1970s, the Czochralski process was implemented by Linde and its successor, Union Carbide, to make higher crystal quality material for ruby lasers. Stimulated by a government contract for structural fibers in 1966, H. LaBelle invented edge-defined film-fed growth (EFG). The Saphikon company, which is currently owned by Saint-Gobain, evolved from this effort. Independently and simultaneously, Stepanov developed edge-defined film-fed growth in the Soviet Union. In 1967 F. Schmid and D. Viechnicki at the Army Materials Research Lab grew sapphire by the heat exchanger method (HEM). Schmid went on to establish Crystal Systems, Inc. around this technology. Rotem Industries, founded in Israel in 1969, perfected the growth of sapphire hemispheres and near-net-shape domes by gradient solidification. In the U.S., growth of near

  14. Effect of gallbladder hypomotility on cholesterol crystallization and growth in CCK-deficient mice.

    Science.gov (United States)

    Wang, Helen H; Portincasa, Piero; Liu, Min; Tso, Patrick; Samuelson, Linda C; Wang, David Q-H

    2010-02-01

    We investigated the effect of gallbladder hypomotility on cholesterol crystallization and growth during the early stage of gallstone formation in CCK knockout mice. Contrary to wild-type mice, fasting gallbladder volumes were enlarged and the response of gallbladder emptying to a high-fat meal was impaired in knockout mice on chow or the lithogenic diet. In the lithogenic state, large amounts of mucin gel and liquid crystals as well as arc-like and tubular crystals formed first, followed by rapid formation of classic parallelogram-shaped cholesterol monohydrate crystals in knockout mice. Furthermore, three patterns of crystal growth habits were observed: proportional enlargement, spiral dislocation growth, and twin crystal growth, all enlarging solid cholesterol crystals. At day 15 on the lithogenic diet, 75% of knockout mice formed gallstones. However, wild-type mice formed very little mucin gel, liquid, and solid crystals, and gallstones were not observed. We conclude that lack of CCK induces gallbladder hypomotility that prolongs the residence time of excess cholesterol in the gallbladder, leading to rapid crystallization and precipitation of solid cholesterol crystals. Moreover, during the early stage of gallstone formation, there are two pathways of liquid and polymorph anhydrous crystals evolving to monohydrate crystals and three modes for cholesterol crystal growth.

  15. Growth of Bi-2212 single crystals by a horizontal Bridgman method using different oxygen pressure

    Energy Technology Data Exchange (ETDEWEB)

    Fujiwara, M.; Makino, T.; Nakabayashi, T. [Department of Electrical and Electronic Engineering, Tottori University, Koyama-Minami, Tottori 680-8552 (Japan); Tanaka, H. [Yonago National College of Technology, 4448 Hikona Yonago, Tottori 683-8502 (Japan); Kinoshita, K., E-mail: kinoshita@ele.tottori-u.ac.j [Department of Electrical and Electronic Engineering, Tottori University, Koyama-Minami, Tottori 680-8552 (Japan); Kishida, S. [Department of Electrical and Electronic Engineering, Tottori University, Koyama-Minami, Tottori 680-8552 (Japan)

    2009-10-15

    We compared the crystallinity of the Bi-2212 single crystals grown by the horizontal Bridgman (HB) method with those grown by the vertical Bridgman (VB) method in terms of resistivity, rho. It was clarified that crystals far inside the ingot grown by HB method showed the equivalent crystallinity to crystals grown by VB method, whereas crystals near the surface of the ingot grown by HB method showed the similar crystallinity to crystals grown by TSFZ method, which is sensitive to the growth atmosphere.

  16. Effect of Crystal Growth Direction on Domain Structure of Mn-Doped (Na,K)NbO3 Crystal

    Science.gov (United States)

    Tsuchida, Kohei; Kakimoto, Ken-ichi; Kagomiya, Isao

    2013-09-01

    Single crystals of (Na0.55K0.45)(Nb0.995Mn0.005)O3 have been grown by a floating zone method in N2 and decompression atmosphere to avoid alkaline metal volatilization on the SrTiO3 material base. The variation of their ferroelectric domain structure and the chemical composition of the grown crystal in the growth direction were evaluated. In the crystal grown in N2 atmosphere, the Na and K are not distributed homogeneously. In addition, the phase transition temperature TC and TO-T showed different values between the grown crystal and raw material. By using laser scanning confocal microscope, the domain structures of the grown crystal revealed random patterns in the initial growth stage and lamellar patterns in the progressing crystal growth. In decompression atmosphere, the TC and TO-T values of the grown crystal were similar to those of the raw material and the domain structures showed a constant domain size. The electrical property of the crystal became stable and the domain structure was easily switched against applied electrical field because the oriented lamellar domain was created during cooling of the crystal.

  17. EFFECT OF SODIUM DODECYLBENZENESULFONIC ACID (SDBS ON THE GROWTH RATE AND MORPHOLOGY OF BORAX CRYSTAL

    Directory of Open Access Journals (Sweden)

    Suharso Suharso

    2010-06-01

    Full Text Available An investigation of the effect of sodium dodecylbenzenesulfonic acid (SDBS on both growth rate and morphology of borax crystal has been carried out.  This experiment was carried out at temperature of 25 °C and relative supersaturation of 0.21 and 0.74 under in situ cell optical microscopy method.  The result shows that SDBS inhibits the growth rate and changes the morphology of borax crystal.   Keywords: Borax; growth rate; crystallization, SDBS

  18. EFFECT OF SODIUM DODECYLBENZENESULFONIC ACID (SDBS) ON THE GROWTH RATE AND MORPHOLOGY OF BORAX CRYSTAL

    OpenAIRE

    Suharso, Suharso

    2010-01-01

    An investigation of the effect of sodium dodecylbenzenesulfonic acid (SDBS) on both growth rate and morphology of borax crystal has been carried out.  This experiment was carried out at temperature of 25 °C and relative supersaturation of 0.21 and 0.74 under in situ cell optical microscopy method.  The result shows that SDBS inhibits the growth rate and changes the morphology of borax crystal.   Keywords: Borax; growth rate; crystallization, SDBS

  19. Crystal growth, structural and thermal studies of amino acids admixtured L-arginine phosphate monohydrate single crystals

    Science.gov (United States)

    Anandan, P.; Saravanan, T.; Parthipan, G.; Kumar, R. Mohan; Bhagavannarayana, G.; Ravi, G.; Jayavel, R.

    2011-05-01

    To study the improved characteristics of L-arginine phosphate monohydrate (LAP) crystals, amino acids mixed LAP crystals have been grown by slow cooling method. Amino acids like glycine, L-alanine, and L-valine have been selected for doping. Optical quality bulk crystals have been harvested after a typical growth period of about twenty days. The effect of amino acids in the crystal lattice and molecular vibrational frequencies of various functional groups in the crystals have been studied using X-ray powder diffraction and Fourier Transform infrared (FTIR) analyses respectively. Thermal behavior of the amino acids mixed LAP crystals have been studied from the TG and DTG analyses. High-resolution X-ray diffraction studies have been carried out to find the crystalline nature. Optical transmission studies have been carried out by UV-vis spectrophotometer. The cut off wavelength is below 240 nm for the grown crystals.

  20. Mechanical properties and structure of zirconia-mullite ceramics prepared by in-situ controlled crystallization of Si-Al-Zr-O amorphous bulk

    Institute of Scientific and Technical Information of China (English)

    LIANG Shu-quan; ZHONG Jie; TAN Xiao-ping; TANG Yan

    2008-01-01

    Zirconia-mullite nano-composite ceramics were fabricated by in-situ controlled crystallization of Si-Al-Zr-O amorphous bulk, which were first treated at 900-1 000 ℃ for nucleation, then treated at higher temperature for crystallization to obtain ultra-fine zirconia-mullite composite ceramics. The effects of treating temperature and ZrO2 addition on mechanical properties and microstructure were analyzed. A unique structure in which there are a lot of near equiaxed t-ZrO2 grains and fine yield-cracks has been developed in the samples with 15% zirconia addition treated at 1 150 ℃. This specific microstructure is much more effective in toughening ceramics matrix and results in the best mechanical properties. The flexural strength and fracture toughness are 520 MPa and 5.13 MPa·m1/2, respectively. Either higher zirconia addition or higher crystallization temperature will produce large size rod-like ZrO2 and mullite grains, which are of negative effect on mechanical properties of this new composite ceramics.

  1. Growth morphology of nanoscale sputter-deposited Au films on amorphous soft polymeric substrates

    Energy Technology Data Exchange (ETDEWEB)

    Ruffino, F.; Grimaldi, M.G. [Universita di Catania, Dipartimento di Fisica e Astronomia, Catania (Italy); MATIS CNR-IMM, Catania (Italy); Torrisi, V.; Marletta, G. [University of Catania and CSGI, Laboratory for Molecular Surface and Nanotechnology (LAMSUN), Department of Chemical Sciences, Catania (Italy)

    2011-06-15

    The growth of a room-temperature sputter-deposited thin Au film on two soft polymeric substrates, polystyrene (PS) and poly(methyl methacrylate) (PMMA), from nucleation to formation of a continuous film is investigated by means of atomic force microscopy. In particular, we studied the surface morphology evolution of the film as a function of the deposition time observing an initial Au three-dimensional island-type growth. Then the Au film morphology evolves, with increasing deposition time, from hemispherical islands to partially coalesced worm-like island structures, to percolation, and finally to a continuous and rough film. The overall Au morphology evolution is discussed in the framework of the interrupted coalescence model, allowing us to evaluate the island critical radius for the partial coalescence R{sub c}=8.7{+-}0.9 nm for Au on PS and R{sub c}=7.6{+-}0.8 nm for Au on PMMA. Furthermore, the application of the kinetic freezing model allows us to evaluate the room-temperature surface diffusion coefficient D{sub s}{approx}1.8 x 10{sup -18} m{sup 2}/s for Au on PS and D{sub s}{approx}1.1 x 10{sup -18} m{sup 2}/s for Au on PMMA. The application of the Vincent model allows us, also, to evaluate the critical coverage (at which the percolation occurs) P{sub c}=61% for Au on PS and P{sub c}=56% for Au on PMMA. Finally, the dynamic scaling theory of a growing interface was applied to characterize the kinetic roughening of the Au film on both PMMA and PS. Such analyses allow us to evaluate the dynamic scaling, growth, and roughness exponents z=3.8{+-}0.4, {beta}=0.28{+-}0.03, {alpha}=1.06{+-}0.05 for the growth of Au on PS and z=4.3{+-}0.3, {beta}=0.23{+-}0.03, {alpha}=1.03{+-}0.05 for the growth of Au on PMMA, in agreement with a non-equilibrium but conservative and linear growth process in which the surface diffusion phenomenon plays a key role. (orig.)

  2. Ballistic aggregation on two-dimensional arrays of seeds with oblique incident flux: Growth model for amorphous Si on Si

    Science.gov (United States)

    Ye, D.-X.; Lu, T.-M.

    2007-12-01

    Amorphous silicon (Si) structures on two-dimensional arrays of seeds on a Si substrate were experimentally prepared at near room temperature using a physical vapor deposition system with an 85° oblique incident flux. In the stationary deposition case where the substrate is fixed at a position, the Si on the seeds form a ballistic inclined fanlike structure with an initial cone shape and the fan size R grows with time in a power law form tp , where ptilde 1 . We show that with a swing rotation where the substrate is rotated back-and-forth azimuthally, the fan size grows slower (pshadowing, surface diffusion, and substrate rotation in a three-dimensional Monte Carlo simulator. The evolution of the fanlike structures at different deposition times was simulated for both stationary deposition and swing rotation. The growth of the fan size R with time t in simulations was quantitatively analyzed and the exponents ptilde 1.0 and ptilde 0.46 were extracted for the stationary deposition and the swing rotation, respectively. For stationary deposition, the exponent 1 does not change significantly with the strength of surface diffusion. However, the fan-out angle decreases with the increased strength of surface diffusion. For swing rotation, the reduced exponent 0.46 at the initial stages of growth is primarily due to the self-shadowing of the fan itself under rotation. At the later stages of growth, the saturation of the fan size produces uniform rods and is due to the global shadowing from the adjacent fan structures. The morphology and the exponent obtained from our simulations are consistent with our experimental observations.

  3. Confined Crystal Growth in Space. Deterministic vs Stochastic Vibroconvective Effects

    Science.gov (United States)

    Ruiz, Xavier; Bitlloch, Pau; Ramirez-Piscina, Laureano; Casademunt, Jaume

    The analysis of the correlations between characteristics of the acceleration environment and the quality of the crystalline materials grown in microgravity remains an open and interesting question. Acceleration disturbances in space environments usually give rise to effective gravity pulses, gravity pulse trains of finite duration, quasi-steady accelerations or g-jitters. To quantify these disturbances, deterministic translational plane polarized signals have largely been used in the literature [1]. In the present work, we take an alternative approach which models g-jitters in terms of a stochastic process in the form of the so-called narrow-band noise, which is designed to capture the main statistical properties of realistic g-jitters. In particular we compare their effects so single-frequency disturbances. The crystalline quality has been characterized, following previous analyses, in terms of two parameters, the longitudinal and the radial segregation coefficients. The first one averages transversally the dopant distribution, providing continuous longitudinal information of the degree of segregation along the growth process. The radial segregation characterizes the degree of lateral non-uniformity of the dopant in the solid-liquid interface at each instant of growth. In order to complete the description, and because the heat flux fluctuations at the interface have a direct impact on the crystal growth quality -growth striations -the time dependence of a Nusselt number associated to the growing interface has also been monitored. For realistic g-jitters acting orthogonally to the thermal gradient, the longitudinal segregation remains practically unperturbed in all simulated cases. Also, the Nusselt number is not significantly affected by the noise. On the other hand, radial segregation, despite its low magnitude, exhibits a peculiar low-frequency response in all realizations. [1] X. Ruiz, "Modelling of the influence of residual gravity on the segregation in

  4. High Growth Rate Deposition of Hydrogenated Amorphous Silicon-Germanium Films and Devices Using ECR-PECVD

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yong [Iowa State Univ., Ames, IA (United States)

    2002-01-01

    Hydrogenated amorphous silicon germanium films (a-SiGe:H) and devices have been extensively studied because of the tunable band gap for matching the solar spectrum and mature the fabrication techniques. a-SiGe:H thin film solar cells have great potential for commercial manufacture because of very low cost and adaptability to large-scale manufacturing. Although it has been demonstrated that a-SiGe:H thin films and devices with good quality can be produced successfully, some issues regarding growth chemistry have remained yet unexplored, such as the hydrogen and inert-gas dilution, bombardment effect, and chemical annealing, to name a few. The alloying of the SiGe introduces above an order-of-magnitude higher defect density, which degrades the performance of the a-SiGe:H thin film solar cells. This degradation becomes worse when high growth-rate deposition is required. Preferential attachment of hydrogen to silicon, clustering of Ge and Si, and columnar structure and buried dihydride radicals make the film intolerably bad. The work presented here uses the Electron-Cyclotron-Resonance Plasma-Enhanced Chemical Vapor Deposition (ECR-PECVD) technique to fabricate a-SiGe:H films and devices with high growth rates. Helium gas, together with a small amount of H2, was used as the plasma species. Thickness, optical band gap, conductivity, Urbach energy, mobility-lifetime product, I-V curve, and quantum efficiency were characterized during the process of pursuing good materials. The microstructure of the a-(Si,Ge):H material was probed by Fourier-Transform Infrared spectroscopy. They found that the advantages of using helium as the main plasma species are: (1) high growth rate--the energetic helium ions break the reactive gas more efficiently than hydrogen ions; (2) homogeneous growth--heavy helium ions impinging on the surface promote the surface mobility of the reactive radicals, so that heteroepitaxy growth as clustering of Ge and Si, columnar structure are

  5. Cohesion of Amorphous Silica Spheres: Toward a Better Understanding of the Coagulation Growth of Silicate Dust Aggregates

    CERN Document Server

    Kimura, Hiroshi; Senshu, Hiroki; Kobayashi, Hiroshi

    2016-01-01

    Adhesion forces between submicrometer-sized silicate grains play a crucial role in the formation of silicate dust agglomerates, rocky planetesimals, and terrestrial planets. The surface energy of silicate dust particles is the key to their adhesion and rolling forces in a theoretical model based on the contact mechanics. Here we revisit the cohesion of amorphous silica spheres by compiling available data on the surface energy for hydrophilic amorphous silica in various circumstances. It turned out that the surface energy for hydrophilic amorphous silica in a vacuum is a factor of 10 higher than previously assumed. Therefore, the previous theoretical models underestimated the critical velocity for the sticking of amorphous silica spheres, as well as the rolling friction forces between them. With the most plausible value of the surface energy for amorphous silica spheres, theoretical models based on the contact mechanics are in harmony with laboratory experiments. Consequently, we conclude that silicate grains ...

  6. Investigation of the crystallization process of amorphous silicon thin films%非晶硅薄膜晶化过程的研究

    Institute of Scientific and Technical Information of China (English)

    黄木香; 杨琳; 刘玉琪; 王江涌

    2012-01-01

    Polycrystalline silicon thin film is a high quality material for micro - electronic components, thin film transistors and large flat-panel LCD displays because of its high electrical mobility and stable photoelectric properties. Moreover, it has been regarded as a candidate material for making high efficiency, lower energy consumption and optimized thin film solar cells. Therefore, how to fabricate polycrystalline silicon thin film is a very meaningful research topic. Solid phase crystallization is a usual method to fabricate polycrystalline silicon thin film, by high temperature annealing to transfer amorphous film to polycrystalline phase, In this paper, the solid phase crystallization process of amorphous silicon thin films fabricated by different techniques are studied systematically by XRD and Raman spectroscopy.%多晶硅薄膜具有较高的电迁移率和稳定的光电性能,是制备微电子器件、薄膜晶体管、大面积平板液晶显示的优质材料.多晶硅薄膜被公认为是制备高效、低耗、最理想的薄膜太阳能电池的材料.因此,如何制备多晶硅薄膜是一个非常有意义的研究课题.固相法是制备多晶硅薄膜的一种常用方法,它是在高温退火的条件下,使非晶硅薄膜通过固相相变而成为多晶硅薄膜.本文采用固相法,利用X-ray衍射及拉曼光谱,对用不同方法制备的非晶硅薄膜的晶化过程进行了系统地研究.

  7. The Durability of Various Crucible Materials for Aluminum Nitride Crystal growth by Sublimation

    Energy Technology Data Exchange (ETDEWEB)

    Liu,B.; Edgar, J.; Gu, Z.; Zhuang, D.; Raghothamachar, B.; Dudley, M.; Sarua, A.; Kuball, M.; Meyer, H.

    2004-01-01

    Producing high purity aluminum nitride crystals by the sublimation-recondensation technique is difficult due to the inherently reactive crystal growth environment, normally at temperature in excess of 2100 C. The durability of the furnace fixture materials (crucibles, retorts, etc.) at such a high temperature remains a critical problem. In the present study, the suitability of several refractory materials for AlN crystal growth is investigated, including tantalum carbide, niobium carbide, tungsten, graphite, and hot-pressed boron nitride. The thermal and chemical properties and performance of these materials in inert gas, as well as under AlN crystal growth conditions are discussed. TaC and NbC are the most stable crucible materials with very low elemental vapor pressures in the crystal growth system. Compared with refractory material coated graphite crucibles, HPBN crucible is better for AlN self-seeded growth, as crystals tend to nucleate in thin colorless platelets with low dislocation density.

  8. The growth of Nd:CaWO4 single crystals

    Directory of Open Access Journals (Sweden)

    ALEKSANDAR GOLUBOVIC

    2003-12-01

    Full Text Available CaWO4 doped with 0.8 % at. Nd (Nd:CaWO4 single crystals were grown from the melt in air by the Czochralski technique. The critical diameter dc = 1.0 cm and the critical rate of rotation wc = 30 rpm were calculated from hydrodynamic equations for buoyancy-driven and forced convection. The rate of crystal growth was experimentally obtained to be 6.7 mm/h. For chemical polishing, a solution of 1 part saturated chromic acid (CrO3 in water and 3 parts conc. H3PO4 (85 % at 433 K with an exposure time of 2 h was found to be adequate. A mixture of 1 part concentrated HF and 2 parts chromic acid at room temperature after exposure for 30 min was found to be a suitable etching solution. The lattice parameters a = 0.52404 (6 nm, c = 1.1362 (6 nm and V0 = 0.312 (2 nm3 were determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

  9. Preparation of anhydrous lanthanum bromide for scintillation crystal growth

    Institute of Scientific and Technical Information of China (English)

    ZHANG Tong; LI Hongwei; ZHAO Chunlei; YU Jinqiu; HU Yunsheng; CUI Lei; HE Huaqiang

    2012-01-01

    This paper reported an efficient and economical method for preparation of anhydrous LaBr3 for scintillation crystal growth.High purity anhydrous LaBr3 powders in large quantities were successfully obtained by stepped dehydration of LaBr3·7H2O using NH4Br as additive.Experiments revealed that adding proper amount of NH4Br could effectively restrain the hydrolysis of LaBr3 during dehydration and thus decreased the yield of deleterious impurity of LaOBr.Optimum preparation conditions,including the amount of NH4Br in use,the dehydration temperature and atmosphere,were investigated by DTA/TG and water/oxygen analysis.The Raman characterization of the as-prepared anhydrous LaBr3 was also presented.

  10. Growth of single-crystal YAG fiber optics.

    Science.gov (United States)

    Nie, Craig D; Bera, Subhabrata; Harrington, James A

    2016-07-11

    Single-crystal YAG (Y3Al5O12) fibers have been grown by the laser heated pedestal growth technique with losses as low as 0.3 dB/m at 1.06 μm. These YAG fibers are as long as about 60 cm with diameters around 330 μm. The early fibers were grown from unoriented YAG seed fibers and these fibers exhibited facet steps or ridges on the surface of the fiber. However, recently we have grown fibers using an oriented seed to grow step-free fibers. Scattering losses made on the fibers indicate that the scattering losses are equal to about 30% of the total loss.

  11. High Speed Crystal Growth by Q-switched Laser Melting

    Science.gov (United States)

    Cullis, A. G.

    1984-01-01

    The modification of the structural and electrical properties of semiconductors short radiation pulses obtained from Q-switched lasers is described. These modifications are accomplished by high heating and cooling rates. This processing revealed novel crystal growth and high speed resolidification phenomena. The behavior of semiconductor Si is analyzed. The annealing process typically employs short pulses of radiation in or near the visible region of the spectrum. The Q-switched ruby and Nd-YAG lasers are commonly used and these are sometimes mode locked to reduce the pulse length still further. Material to be annealed can be processed with a single large area radiation spot. Alternatively, a small radiation spot size can be used and a large sample area is covered by overlapping irradiated regions.

  12. New Methods of Simulation of Mn(II) EPR Spectra: Single Crystals, Polycrystalline and Amorphous (Biological) Materials

    Science.gov (United States)

    Misra, Sushil K.

    Biological systems exhibit properties of amorphous materials. The Mn(II) ion in amorphous materials is characterized by distributions of spin-Hamiltonian parameters around mean values. It has a certain advantage over other ions, being one of the most abundant elements on the earth. The extent to which living organisms utilize manganese varies from one organism to the other. There is a fairly high concentration of the Mn(II) ion in green plants, which use it in the O2 evolution reaction of photosynthesis (Sauer, 1980). Structure-reactivity relationships in Mn(II)-O2 complexes are given in a review article by Coleman and Taylor (1980). Manganese is a trace requirement in animal nutrition; highly elevated levels of manganese in the diet can be toxic, probably because of an interference with iron homeostasis (Underwood, 1971). On the other hand, animals raised with a dietary deficiency of manganese exhibit severe abnormalities in connective tissue; these problems have been attributed to the obligatory role of Mn(II) in mucopolysaccharide metabolism (Leach, 1971). Mn(II) has been detected unequivocally in living organisms.

  13. In-Situ Crystallization of a Lithium Disilicate Glass--Effect of Pressure on Crystal Growth Rate

    Science.gov (United States)

    Fuss, T.; Ray, C. S.; Lesher, C. E.; Day, D. E.

    2006-01-01

    Crystallization of a Li2O.2SiO2 (LS2) glass subjected to a uniform hydrostatic pressure of 4.5 GPa and 6 GPa was investigated up to a temperature of 750 C. The density of the compressed glass is about 2% greater at 4.5 GPa than at 1 atm and, depending upon the processing temperature, up to 10% greater at 6 GPa. Crystal growth rates investigated as a function of temperature and pressure show that lithium disilicate crystal growth is an order of magnitude slower at 4.5 GPa than 1 atm resulting in a shift of +45 C (plus or minus 10 C) in the growth rate curve at high pressure compared to 1 atm condition. At 6 GPa lithium disilicate crystallization is suppressed entirely, while a new high pressure lithium metasilicate crystallizes at temperatures 95 C (plus or minus 10 C) higher than those reported for lithium disilicate crystallization at 1 atm. The decrease in crystal growth rate with increasing pressure for lithium disilicate glass up to 750 C is related to an increase in viscosity with pressure associated with fundamental changes in glass structure accommodating densification.

  14. Features of exoelectron emission in amorphous metallic alloys

    CERN Document Server

    Veksler, A S; Morozov, I L; Semenov, A L

    2001-01-01

    The peculiarities of the photothermostimulated exoelectron emission in amorphous metallic alloys of the Fe sub 6 sub 4 Co sub 2 sub 1 B sub 1 sub 5 composition are studied. It is established that the temperature dependences of the exoelectron emission spectrum adequately reflect the two-stage character of the amorphous alloy transition into the crystalline state. The exoelectron emission spectrum is sensitive to the variations in the modes of the studied sample thermal treatment. The thermal treatment of the amorphous metallic alloy leads to growth in the intensity of the exoelectrons yield. The highest growth in the intensify of the exoelectron emission was observed in the alloys at the initial stage of their crystallization

  15. Plasma deposition of amorphous silicon-based materials

    CERN Document Server

    Bruno, Giovanni; Madan, Arun

    1995-01-01

    Semiconductors made from amorphous silicon have recently become important for their commercial applications in optical and electronic devices including FAX machines, solar cells, and liquid crystal displays. Plasma Deposition of Amorphous Silicon-Based Materials is a timely, comprehensive reference book written by leading authorities in the field. This volume links the fundamental growth kinetics involving complex plasma chemistry with the resulting semiconductor film properties and the subsequent effect on the performance of the electronic devices produced. Key Features * Focuses on the plasma chemistry of amorphous silicon-based materials * Links fundamental growth kinetics with the resulting semiconductor film properties and performance of electronic devices produced * Features an international group of contributors * Provides the first comprehensive coverage of the subject, from deposition technology to materials characterization to applications and implementation in state-of-the-art devices.

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

    Science.gov (United States)

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

    2015-06-01

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

  17. Crystal growth iron based pnictide compounds; Kristallzuechtung eisenbasierter Pniktidverbindungen

    Energy Technology Data Exchange (ETDEWEB)

    Nacke, Claudia

    2012-11-15

    The present work is concerned with selected crystal growth method for producing iron-based superconductors. The first part of this work introduces significant results of the crystal growth of BaFe{sub 2}As{sub 2} and the cobalt-substituted compound Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} with x{sub Nom} = 0.025, 0.05, 0.07, 0.10 and 0.20. For this purpose a test procedure for the vertical Bridgman method was developed. The second part of this work contains substantial results for growing a crystal of LiFeAs and the nickel-substituted compound Li{sub 1-δ}Fe{sub 1-x}Ni{sub x}As with x{sub Nom} = 0.015, 0.025, 0.05, 0.06, 0.075 and 0.10. For this purpose a test procedure for the melt flow process has been developed successfully. [German] Die vorliegende Arbeit befasst sich mit ausgewaehlten Kristallzuechtungsverfahren zur Herstellung eisenbasierter Supraleiter. Der erste Teil dieser Arbeit fuehrt wesentliche Ergebnisse der Kristallzuechtung von BaFe{sub 2}As{sub 2} sowie der Cobalt-substituierten Verbindung Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} mit x{sub Nom} =0.025, 0.05, 0.07, 0.10 und 0.20 auf. Hierzu wurde eine Versuchsdurchfuehrung fuer das vertikale Bridgman-Verfahren konzipiert, mit welcher erfolgreich Kristalle dieser Zusammensetzungen gezuechtet wurden. Der zweite Teil dieser Arbeit enthaelt wesentliche Ergebnisse zur Kristallzuechtung von LiFeAs sowie der Nickel-substituierten Verbindung Li{sub 1-δ}Fe{sub 1-x}Ni{sub x}As mit x{sub Nom} = 0.015, 0.025, 0.05, 0.06, 0.075 und 0.10. Hierfuer wurde erfolgreich eine Versuchsdurchfuehrung fuer das Schmelzfluss-Verfahren entwickelt.

  18. Crystal growth and scintillation properties of undoped and Ce3+-doped GdI3 crystals

    Science.gov (United States)

    Ye, Le; Li, Huanying; Wang, Chao; Shi, Jian; Chen, Xiaofeng; Wang, Zhongqing; Huang, Yuefeng; Xu, Jiayue; Ren, Guohao

    2017-02-01

    The growth and scintillation properties of undoped and Ce3+-doped GdI3 crystals were reported in this paper. These GdI3:χ%Ce (χ = 0, 1, 2) crystals were grown by the vertical Bridgman growth technique in evacuated quartz crucibles. X-ray excited optical luminescence spectra of GdI3:Ce exhibit a broad emission band (450 nm-650 nm) peaking at 520 nm corresponding to 5d1→4f1 transition of Ce3+ while the undoped GdI3 crystal consists of a broad band (400 nm-600 nm) and several sharp lines peaking at 462 nm, 482 nm, 492 nm, 549 nm, 579 nm owing to the impurities ions and defects. The excitation spectra of Ce3+ doped GdI3 consist of two broad bands between 300 nm and 500 nm corresponding to 4f1→5d1 absorption of Ce3+. The other absorption peaking at 262 nm in the spectrum of GdI3:2%Ce is assigned to band-to-band exciton transition. The excitation spectrum of undoped GdI3 contains a flat absorption band from 330 to 370 nm and a broad band between 390 and 450 nm peaking at 414 nm corresponding to the absorption of the unintentionally doped Ce3+, Dy3+, Ho3+ impurities and other defects. The emission spectrum of undoped GdI3 under 332 nm excitation has the identical line peaks with the spectrum measured under X-ray excitation. The emission spectra of GdI3:2%Ce and GdI3:1%Ce show a broad band in the range of 450-750 nm with the maximum at 550 nm corresponding to 5d1→4f1 transitions of Ce3+ ion. The GdI3, GdI3:1%Ce and GdI3:2%Ce show fast principle decay time constant 73 ns, 69 ns and 58 ns respectively, besides, the undoped also shows a slow decay constant 325 ns which doesn't appear in Ce3+-doped GdI3 crystal. The energy resolutions of GdI3:χ%Ce (χ = 1, 2) measured at 662 KeV are about 3%-5% and the undoped GdI3 is 13.3%.

  19. On geological interpretations of crystal size distributions: Constant vs. proportionate growth

    Science.gov (United States)

    Eberl, D.D.; Kile, D.E.; Drits, V.A.

    2002-01-01

    Geological interpretations of crystal size distributions (CSDs) depend on understanding the crystal growth laws that generated the distributions. Most descriptions of crystal growth, including a population-balance modeling equation that is widely used in petrology, assume that crystal growth rates at any particular time are identical for all crystals, and, therefore, independent of crystal size. This type of growth under constant conditions can be modeled by adding a constant length to the diameter of each crystal for each time step. This growth equation is unlikely to be correct for most mineral systems because it neither generates nor maintains the shapes of lognormal CSDs, which are among the most common types of CSDs observed in rocks. In an alternative approach, size-dependent (proportionate) growth is modeled approximately by multiplying the size of each crystal by a factor, an operation that maintains CSD shape and variance, and which is in accord with calcite growth experiments. The latter growth law can be obtained during supply controlled growth using a modified version of the Law of Proportionate Effect (LPE), an equation that simulates the reaction path followed by a CSD shape as mean size increases.

  20. Predicting crystal growth via a unified kinetic three-dimensional partition model.

    Science.gov (United States)

    Anderson, Michael W; Gebbie-Rayet, James T; Hill, Adam R; Farida, Nani; Attfield, Martin P; Cubillas, Pablo; Blatov, Vladislav A; Proserpio, Davide M; Akporiaye, Duncan; Arstad, Bjørnar; Gale, Julian D

    2017-04-03

    Understanding and predicting crystal growth is fundamental to the control of functionality in modern materials. Despite investigations for more than one hundred years, it is only recently that the molecular intricacies of these processes have been revealed by scanning probe microscopy. To organize and understand this large amount of new information, new rules for crystal growth need to be developed and tested. However, because of the complexity and variety of different crystal systems, attempts to understand crystal growth in detail have so far relied on developing models that are usually applicable to only one system. Such models cannot be used to achieve the wide scope of understanding that is required to create a unified model across crystal types and crystal structures. Here we describe a general approach to understanding and, in theory, predicting the growth of a wide range of crystal types, including the incorporation of defect structures, by simultaneous molecular-scale simulation of crystal habit and surface topology using a unified kinetic three-dimensional partition model. This entails dividing the structure into 'natural tiles' or Voronoi polyhedra that are metastable and, consequently, temporally persistent. As such, these units are then suitable for re-construction of the crystal via a Monte Carlo algorithm. We demonstrate our approach by predicting the crystal growth of a diverse set of crystal types, including zeolites, metal-organic frameworks, calcite, urea and l-cystine.