• H L Bhat

      Articles written in Bulletin of Materials Science

    • Crystal growth from solutions under microgravity environment

      H L Bhat

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      The growth of large and perfect single crystals are now of considerable interest because of their increasing scientific and industrial importance. Any imperfection in the crystal causes malfunctioning, rapid aging, low reliability and low yield in manufacture. Due to the availability of earth orbiting spaceships, there is a possibility of growing these crystals with high purity. In this review paper, the author discusses mainly the growth of crystals under microgravity conditions (in spaceships) and their basic principles and also their relative merits.

    • Defect characterization of KTP single crystals

      G Dhanaraj T Shripathi H L Bhat

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      Potassium titanyl phosphate (KTP) is a relatively new nonlinear optical material with excellent combination of physical properties. This paper presents the combined etching and X-ray topographic studies carried out on KTP crystals with a view to characterizing their defects. KTP crystals employed in this investigation were grown from flux. Optical microscopic study of habit faces revealed growth layers and growth hillocks on (100) and (011) faces respectively. Etching of (011) habit faces proved that growth hillocks corresponded to the emergence point of dislocation out crops on these faces. The suitability of the new etchant to reveal dislocation was confirmed by etching the matched pairs obtained by cleaving. The defects present in the crystal were also studied by X-ray topography. The defect configuration in these crystals is characteristic of crystals grown from solution. The dislocations arc predominantly linear with their origin either at the nucleation centre or inclusions. In general, grown crystals were found to have low dislocation density and often large volumes of crystals free from dislocation could be obtained.

    • Influence of deviation from stoichiometry on the photoluminescence in CdTe doped with indium

      Suma Gurumurthy K S R K Rao A K Sreedhar H L Bhat B Sundersheshu R K Bagai Vikram Kumar

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      Low temperature photoluminescence of vacuum and cadmium annealed CdTe:In is reported here. A new peak at ∼ 1·14 eV related to transitions from the conduction band to an acceptor involving a tellurium vacancy has been observed.

    • Physical characterization of the organic nonlinear optical crystal — 3-methoxy 4-hydroxy benzaldehyde

      V Venkataramanan Sanjay Uchil H L Bhat

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      We highlight our recent experimental work on an efficient molecular nonlinear optical crystal, 3-methoxy 4-hydroxy benzaldehyde (MHBA). Optical quality single crystals of MHBA were grown from mixtures of solvents and from melt. The overall absorption and transparency window were improved by growing them in a mixture of chloroform and acetone. The grown crystals were characterized for their optical transmission, mechanical hardness and laser damage. We have observed a strong correlation between mechanical properties and laser induced damage.

    • Growth and characterization of some novel crystals for nonlinear optical applications

      H L Bhat

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      The advent of high intensity lasers coupled with the recent advances in crystal technology has led to rapid progress in the field of nonlinear optics. This article traces the history of materials development that has taken place over the past forty odd years and dwells on the current status in this important area. The materials aspect is discussed under three classes viz. inorganic, organic and semiorganic crystals. In the end, some of the crystal growth work that has been carried out in author’s laboratory is presented.

    • Liquid phase epitaxial growth of pure and doped GaSb layers: morphological evolution and native defects

      P S Dutta H L Bhat Vikram Kumar

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      Undoped and Te-doped gallium antimonide (GaSb) layers have been grown on GaSb bulk substrates by the liquid phase epitaxial technique from Ga-rich and Sb-rich melts. The nucleation morphology of the grown layers has been studied as a function of growth temperature and substrate orientation. MOS structures have been fabricated on the epilayers to evaluate the native defect content in the grown layers from theC-V characteristics. Layers grown from antimony rich melts always exhibitp-type conductivity. In contrast, a type conversion fromp- ton- was observed in layers grown from gallium rich melts below 400 C. The electron mobility of undopedn-type layers grown from Ga-rich melts and tellurium doped layers grown from Sb- and Ga-rich solutions has been evaluated.

    • Pulsed laser deposition of indium antimonide

      R Venkataraghavan K M Satyalakshmi K S R K Rao A K Sreedhar M S Hegde H L Bhat

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      Single crystalline oriented films of indium antimonide have been grown on cadmium telluride substrates by the pulsed laser deposition technique. The films were (111) oriented which is the substrate orientation. The composition of the grown films were found to deviate from that of the target owing to loss of antimony during evaporation. This deviation from stoichiometry led to film-substrate reaction, resulting in mixed interface. The antimony deficiency in the films were controlled by correcting the stoichiometry, which led to avoiding mixed interfaces. The stoichiometric films showed good surface morphology and well defined sharp interfaces. The IR transmission spectrum showed sharp band to band absorption and effective detection in the MWIR.

    • Design and fabrication of liquid phase epitaxy system

      R Venkataraghavan N K Udayashankar Blasius Victor Rodrigues K S R K Rao H L Bhat

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      The design and fabrication of a simple and versatile liquid phase epitaxial (LPE) system has been described. The present LPE system makes use of the horizontal multi-bin boat and slider arrangement which enables the growth of even multilayered structures. The growth chamber is heated by a single-zone resistive furnace precisely controlled through a Eurotherm 902P temperature programmer and controller. The vacuum manifolds and accessories are set up in such a way as to ensure high vacuum needed for growth experiments. The provision is also made to admit high purity gases like hydrogen or nitrogen into the growth chamber. The design has been kept simple without sacrificing the versatility and adaptability for novel growth experiments. The typical films grown by this LPE system are also presented.

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