Growth Of Large-size Crystals Research Articles

Investigations on the nucleation kinetics of methyl-para-hydroxy benzoate single crystals

The solubility, metastable zone width and induction period have been determined for the solution grown methyl-para-hydroxy benzoate (MHB) single crystals. Nucleation parameters such as Gibbs free energy, radius of critical nucleus, critical free energy barrier and number of molecules in the critical nucleus and nucleation rate have also been investigated. Interfacial energy has been estimated using the experimentally determined induction period values. It is observed that the nucleation rate increases with the increase of supersaturation. The evaluated interfacial tension values are found to be comparable with the theoretical values. The growth parameters of MHB were optimized for the growth of large size crystals.

Growth of plate-type β-FeSi 2 single crystals by optimization of composition ratio of source materials

The importance of the β-FeSi 2 bulk single crystals has increased not only to investigate the intrinsic properties of β-FeSi 2 but also to use it as substrate of β-FeSi 2 thin films for optical devices. Though single crystals of β-FeSi 2 are grown by chemical vapor transport (CVT) method, most of those crystals are needle-like and widths of those flat surfaces are 0.5 mm or less. In order to understand the mechanism of the growth process of β-FeSi 2 by the CVT method and to obtain the conditions for large size crystal growth, we have carried out in-situ observations of the crystal growth by using a transparent electric furnace. Based on the experimental data, we have proposed the most likely reaction process, FeI 2(g) + 2SiI 4(g)→FeSi 2(s) + 5I 2(g), and we found that the crystal growth progresses under the environment where the FeI 2 gas is insufficient compared with a suitable ratio of FeI 2/SiI 4. Then, to raise the partial pressure of FeI 2 gas, the composition ratio of Fe to Si for the source material was increased and we have obtained the plate-type β-FeSi 2 crystals that exceeded a few square millimeters in size.

Growth of large-size crystal of PbWO 4 by vertical Bridgman method with multi-crucibles

In this paper, we report the crystal growth of large-size lead tungstate (PbWO 4) crystals by modified vertical Bridgman method with multi-crucibles. The growth conditions were also studied and optimal growth parameters were obtained. The uniformity of grown PbWO 4 and the impurities in grown PbWO 4 were analyzed by glow discharge mass spectroscopy method. The measurements of lattice parameters and phase analysis were carried out by X-ray diffraction. The scintillation properties of grown PbWO 4 crystals were investigated.

Development of BSO (Bi4Si3O12) crystal for radiation detector

Colorless and crack-free single crystals of bismuth silicate (Bi4Si3O12, BSO) scintillators have been grown by the vertical Bridgman method. Some segregation phases have been found to form on the surface and at the top of the crystals grown from both stoichiometric and off-stoichiometric melt compositions. The excitation and emission spectra are similar to BGO. The light output is 20% of BGO, giving energy resolution of 32% for 662 keV γ-rays (137Cs). The decay constants are 2.4 ns (for 6% of intensity), 26 ns (12%) and 99 ns (82%). The radiation hardness against 60Co γ-rays was found about 105–106 rad at the emission peak of 480 nm for undoped and it was almost negligible up to 107 rad for 0.2 at.% Ce doped crystals. We have also achieved a considerable improvement in the growth of large size crystals, offering the possible application in γ-ray detectors at high energies. Clear blocks with transverse/longitudinal dimensions as large as 25 mm/200 mm were produced with good reproducibility. The pulse height uniformity along the longitudinal axis is within ±2%. The scintillation characteristics are similar to those of small crystals.

Effect of temperature and deuterium concentration on the growth of deuterated potassium dihydrogen phosphate (DKDP) single crystals

The growth condition of tetragonal phase deuterated potassium dihydrogen phosphate (DKDP) with higher deuterium concentration is optimized for the growth of large size crystals. The variation of lattice parameter values of the crystal in comparison with potassium dihydrogen phosphate (KDP) crystal is found. Etching studies have been done for both monoclinic and tetragonal phases of the DKDP crystals. The percentage and range of transmission of KDP and DKDP crystals were found from uv – visible spectroscopy.

The influence of electrolyte media on the deposition-dissolution behaviour of lead dioxide on glassy carbon electrode

A comparative study of electrodeposition of PbO 2 from 1.0 M HClO 4, 1.0 HNO 3, 1.0 M acetic acid-1.0 M sodium acetate and 3.0 M KOH solutions containing 0.1 M Pb 2+ salts, on glassy carbon electrodes was carried out using cyclic voltammetric and chronoamperometric measurements. The oxidative formation of PbO 2 is found to follow 3-D nucleative growth with the same order of nucleation over voltage in these media involving pH variations between 0 and 14.5. Multisweep cyclic voltammetric studies indicate that the medium influence comes primarly through he chemical dissolution process following PbO 2 nuclei formation. In alkaline media, smaller nuclei undergo continuous chemical dissolution, leading to the growth of large-sized crystals. In acidic media, since chemical dissolution is less likely, a phase of different crystal sizes with a more compact structure evolves.

Germanium radiation detector manufacturing: Process and advances

The germanium radiation detector manufacturing process from material refining and crystal growing to detector machining and fabrication is outlined. Several new advances in detector mounting and cooling are also described. Trends in detector and crystal development are discussed, and current achievements in the growth of large size crystals are presented.

Some Aspects of Large-Size Crystal Growth of Semiconductors

Some Aspects of Large-Size Crystal Growth of Semiconductors

Méthode de synthése et de croissanceápartir de solution, de monocristaux homogénes de semiconducteurs

In order to grow homogeneous single crystals of semiconducting compounds, we have devised a new method of growth from solution, which ensures constant and selective thermodynamic conditions at the liquid-solid interface, and allows the growth of large-size crystals. The concentration of the solute in the solvent, and the crystallization temperature, are kept at constant values. This is obtained by continuously feeding the solvent with the solute, at a well defined rate, which exactly compensates the progressive exhaustion of the melt due to crystallization. Thus a stationary regime is established for the transport of the solute from a source, through the melt, to the crystal. Simultaneously a steep temperature gradient in the temperature range corresponding to the saturation of the melt ensures an oriented growth. This method has been studied in the case of compounds containing a volatile component, the non-volatile component being generally used as the solvent. The rate of dissolution of the solute in the solvent is controlled by the vapour pressure of the volatile component and the temperature of the melt at the liquid-vapour interface. The rate of transport of the solute in the melt depends on its diffusion coefficient and on the temperatures at the interfaces liquid-vapour and liquid-crystal. The speed of growth of the crystal, necessary to establish the stationary regime, may be calculated as a function of these parameters.