• P Ramasamy

      Articles written in Bulletin of Materials Science

    • Evidence of screw dislocations on (002) cleavages of lithium carbonate single crystals

      K S Raju M Palaniswamy P Ramasamy G S Laddha

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      Well-defined triangular etch pits are produced on etching (002) cleavages of lithium carbonate single crystals with 2% citric acid. On etching of cleavage face and matched face these pits nucleate at the intersection sites of dislocations with the cleavage face. On successive etching of a cleavage face, shallow irregular arrays of pits do not enlarge in size as compared to other isolated pits on the same face. These irregular arrays of pits have reasonable correspondence on an etched match face, suggesting they form at dislocation sites.

    • Heterogeneous nucleation and growth of polycrystalline silicon

      R Dhanasekaran P Ramasamy

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      The heterogeneous nucleation theory of silicon on SiO2 and Si3N4 substrates has been developed using classical theory. It is shown that the experimental observations can be explained on the basis of the bond energies of O-H, N-H and Si-H. A reaction model is proposed for the growth of silicon on silicon from silane, using hydrogen as a carrier gas in the temperature region 600–900°C. The growth rate of silicon is shown to be equal toPSiH4PH2 when the partial pressure of hydrogen is high, and is independent of the total pressure and the partial pressure of hydrogen in the lower region.

    • Electrodeposition kinetics of gallium arsenide

      S Moorthy Babu L Durai R Dhanasekaran P Ramasamy

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      A kinetic model has been developed for the electrodeposition of GaAs from solution containing reducible ions of both constituents and is based on the generalised Butler-Volmer equation. The effect of hydrogen ion concentration and activities of ions on the total current density is studied. Voltammograms corresponding to various values of hydrogen ion concentration and activities of ions are constructed by the computer simulation technique.

    • Superconductivity and morphological studies on Bi2Sr2CaCu2O8 single crystals grown from stoichiometric and nonstoichiometric melts

      R Jayavel P Murugakoothan C R Venkateswara Rao C Subramanian P Ramasamy B V Kumarasamy A V Narlikar

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      Single crystals of Bi2Sr2CaCu2O8 (2212) have been grown by self-flux technique using stoichiometric and non-stoichiometric melts of excess CuO and Bi2O3. Single-crystal and powder X-ray diffraction studies have been made on the grown crystals to confirm their single crystallinity and structure respectively. Resistivity and susceptibility measurements provide information on the superconducting nature of the crystals. The effects of fluxing agents and starting composition on surface morphology and superconducting properties have been discussed.

    • Investigation on the bulk growth of $\alpha$-LiIO$_3$ single crystals and the influence of pH on its structural, morphological and optical characteristics

      A SILAMBARASAN P RAJESH P RAMASAMY A K KARNAL RAJEEV BHATT INDRANIL BHAUMIK P K GUPTA

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      $\alpha$-LiIO$_3$ is an excellent optical material exhibiting strong nonlinear optical, piezoelectric and elasto-opticproperties. However, its practical applications are limited by the insufficient reproducibility of the mentioned propertiescaused by the strong influence of the growth conditions, and, in particular, pH of the solution from which $\alpha$-LiIO$_3$3 crystal is grown. Herein, we investigate to grow bulk size good quality crystals of $\alpha$-LiIO$_3$ based on the observed problems during its crystallization process. A systematic investigation was carried out to find the effect of pH on solubility, crystal growth, structural, surface and laser damage properties of $\alpha$-LiIO$_3$ single crystals. The structure and phase of LiIO$_3$ were confirmedby powder X-ray diffractometer analysis. The functional groups of the compound were identified using Fourier transforminfrared spectroscopy. Surface defects of the grown crystals were studied by etch patterns. The crystal grown at pH 10showed 10% optical transmission enhancement in comparison to the crystals grown at pH 2. The indirect optical bandgap ofthe crystal was reinvestigated using ultraviolet–Visible–near-infrared transmittance spectrum. The laser damage thresholdstudies of the crystals grown at pH 10 reveal the higher optical radiation stability against 532 nm laser. The second-ordernonlinear optical behaviour of $\alpha$-LiIO$_3$ crystals grown at different pH conditions have been investigated by using Kurtz andPerry powder technique with Nd:YAG laser pulses at the wavelength of 1064 nm.

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