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M.z. Saghir - One of the best experts on this subject based on the ideXlab platform.

  • Characterization of CdGeAs2 grown by the Float Zone technique under microgravity
    Journal of Crystal Growth, 1999
    Co-Authors: D. Labrie, A. Ginovker, B. E. Paton, A. E. George, A.m. Simpson, M.z. Saghir
    Abstract:

    Abstract One polycrystalline and one single-crystal CdGeAs2 feed rods with 9 mm diameter were processed by the Float-Zone technique under microgravity on SPACEHAB-SH04 during the STS-77 Space Shuttle Endeavour mission. An eutectic salt of LiCl and KCl was used as an encapsulant to suppress Cd and As evaporation from the melt. Post-flight chemical, structural, electronic, and optical characterization of the two samples is presented. Single-crystal growth was achieved using a seed crystal.

  • Float-Zone crystal growth of CdGeAs2 in microgravity: numerical simulation and experiment
    Journal of Crystal Growth, 1999
    Co-Authors: M.z. Saghir, D. Labrie, A. Ginovker, B. E. Paton, A. E. George, K. Olson, A.m. Simpson
    Abstract:

    Abstract Two CdGeAs 2 samples have been successfully grown under microgravity on SPACEHAB-SH04 during the STS-77 Space Shuttle Endeavour mission. One polycrystalline and one single crystal CdGeAs 2 feed rods with 9 mm diameter were processed by the Float-Zone method. An eutectic salt of LiCl and KCl was used as an encapsulant to suppress Cd and As evaporation from the melt. Numerical modeling of the Float Zone shows that salt encapsulation plays an important role in reducing Marangoni convection. The interface between the salt and CdGeAs 2 was shown not to deform in the Float Zone due to the weak capillary pressure.

  • Three-dimensional modeling of Bi12GeO20 using the Float Zone technique
    Journal of Crystal Growth, 1998
    Co-Authors: M.z. Saghir, M.r Islam, N. Maffei, D.h.h. Quon
    Abstract:

    Float Zone crystal growth of Bi12GeO20 under terrestrial and microgravity conditions has been modeled by numerical simulation using the finite element technique. A three-dimensional asymmetrically heated molten rod model is developed to obtain a quantitative estimate of the Rayleigh and Marangoni convection. The free surface deformation resulting from the combined effect of viscous, gravitational and capillary forces as a function of the temperature difference is reported. The temperature distribution and the flow behavior in the Float Zone were examined for various asymmetrical heating conditions. The results showed that nonuniform heating in the axial direction is a critical parameter for the growth of Bi12GeO20 by the Float Zone technique.

  • Float-Zone crystal growth of Bi12GeO20 in a microgravity environment
    Journal of Crystal Growth, 1997
    Co-Authors: N. Maffei, D.h.h. Quon, J. Aota, A.k. Kuriakose, M.z. Saghir
    Abstract:

    Abstract Bismuth germanate (Bi 12 GeO 20 ) is a photorefractive material with tremendous potential in optoelectronic devices. The Float-Zone technique (FZ) was used to produce crystals of this material in space. To the best of the authors' knowledge this is the first time an oxide material has been Float-Zoned in microgravity. The application of this containerless technique in the absence of gravitational forces should result in the production of large uniform crystals possessing superior optical properties.

  • Numerical study on transient convection in Float Zone induced by g-jitters
    Journal of Crystal Growth, 1994
    Co-Authors: H.l. Chen, M.z. Saghir, D.h.h. Quon, S. Chehab
    Abstract:

    Abstract The transient convection in the Float Zone caused by axial g-jitters is studied. A numerical code based on the finite difference method is developed to solve time-dependent buoyancy and surface tension driven convections in the Float Zone with non-deformable surface. First, the effects of g-jitters on the Float Zone crystal growth of bismuth silicate (BSO) in microgravity environment are investigated. The ranges of frequency and amplitude which may cause a vigorous transient convection in the BSO Float Zone are predicted. Second, the numerical analysis is extended to a parametric study to investigate more general characteristics of transient convection induced by the g-jitter. The examined problem is defined and is characterized with a set of parameters of the Marangoni number, Prandtl number, amplitude and frequency of the g-jitter. The responses of both temperature and velocity to the g-jitters are examined for various combinations of these parameters.

W. Schröder - One of the best experts on this subject based on the ideXlab platform.

Jürgen Wollweber - One of the best experts on this subject based on the ideXlab platform.

U. Thiemann - One of the best experts on this subject based on the ideXlab platform.

  • Growth and shrinkage of surface stacking faults in Float-Zone and Czochralski silicon
    Journal of Applied Physics, 1994
    Co-Authors: M. Dammann, H. Baltes, N. Strecker, U. Thiemann
    Abstract:

    A model for the growth and shrinkage of stacking faults in silicon is presented. It accounts for interstitial traps and a nonuniform concentration of intrinsic point defects. The complete system of balance equations of intrinsic point defects is solved numerically to simulate the kinetics of stacking faults during oxidation under the assumption that Float‐Zone silicon contains less interstitial traps than Czochralski silicon. Investigation of the influence of different interstitial trap concentrations on the growth and shrinkage of surface stacking faults shows that the kinetics of surface stacking faults is not strongly affected by the presence of interstitial traps. Surface stacking faults are expected to grow in Float‐Zone and Czochralski silicon in a similar way.

D.h.h. Quon - One of the best experts on this subject based on the ideXlab platform.

  • Three-dimensional modeling of Bi12GeO20 using the Float Zone technique
    Journal of Crystal Growth, 1998
    Co-Authors: M.z. Saghir, M.r Islam, N. Maffei, D.h.h. Quon
    Abstract:

    Float Zone crystal growth of Bi12GeO20 under terrestrial and microgravity conditions has been modeled by numerical simulation using the finite element technique. A three-dimensional asymmetrically heated molten rod model is developed to obtain a quantitative estimate of the Rayleigh and Marangoni convection. The free surface deformation resulting from the combined effect of viscous, gravitational and capillary forces as a function of the temperature difference is reported. The temperature distribution and the flow behavior in the Float Zone were examined for various asymmetrical heating conditions. The results showed that nonuniform heating in the axial direction is a critical parameter for the growth of Bi12GeO20 by the Float Zone technique.

  • Float-Zone crystal growth of Bi12GeO20 in a microgravity environment
    Journal of Crystal Growth, 1997
    Co-Authors: N. Maffei, D.h.h. Quon, J. Aota, A.k. Kuriakose, M.z. Saghir
    Abstract:

    Abstract Bismuth germanate (Bi 12 GeO 20 ) is a photorefractive material with tremendous potential in optoelectronic devices. The Float-Zone technique (FZ) was used to produce crystals of this material in space. To the best of the authors' knowledge this is the first time an oxide material has been Float-Zoned in microgravity. The application of this containerless technique in the absence of gravitational forces should result in the production of large uniform crystals possessing superior optical properties.

  • Numerical study on transient convection in Float Zone induced by g-jitters
    Journal of Crystal Growth, 1994
    Co-Authors: H.l. Chen, M.z. Saghir, D.h.h. Quon, S. Chehab
    Abstract:

    Abstract The transient convection in the Float Zone caused by axial g-jitters is studied. A numerical code based on the finite difference method is developed to solve time-dependent buoyancy and surface tension driven convections in the Float Zone with non-deformable surface. First, the effects of g-jitters on the Float Zone crystal growth of bismuth silicate (BSO) in microgravity environment are investigated. The ranges of frequency and amplitude which may cause a vigorous transient convection in the BSO Float Zone are predicted. Second, the numerical analysis is extended to a parametric study to investigate more general characteristics of transient convection induced by the g-jitter. The examined problem is defined and is characterized with a set of parameters of the Marangoni number, Prandtl number, amplitude and frequency of the g-jitter. The responses of both temperature and velocity to the g-jitters are examined for various combinations of these parameters.

  • Float-Zone crystal growth of bismuth germanate and numerical simulation
    Journal of Crystal Growth, 1993
    Co-Authors: D.h.h. Quon, M.z. Saghir, S. Chehab, J. Aota, A.k. Kuriakose, S. S. B. Wang, H.l. Chen
    Abstract:

    Abstract Bismuth germanium Oxide BGO (Bi12GeO20) single crystals are known to have great potential for technological applications in solid-state devices. Our work involves crystal growth of this material from the melt using a Float-Zone (FZ) technique in both terrestrial and microgravity environments. The ground-based (normal gravity) experiments are presently being carried out, and the ensuing results will be used to optimize the microgravity experiments which will be executed aboard the SPACEHAB Shuttle mission scheduled for April 1994. The crystal growth technique that is being developed requires BGO feed rods of high quality. The methods developed to produce these, and the important Float Zone parameters such as temperature, translation rate and uniformity of radial heat distribution of the furnace for the crystal growth are discussed. An analysis of the effect of shape and convection patterns on the materials, using numerical simulation to compare the theoretical predictions with the experimental results is also presented.