• S T Lakshmikumar

      Articles written in Bulletin of Materials Science

    • Development of a roller quenching apparatus for the production of amorphous phases

      S T Lakshmikumar R M Mallya E S R Gopal

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      The details of an apparatus designed to produce amorphous phases by rapid quenching from the melt are described. A drop of molten material is squeezed between two copper rollers rotating against each other at 5000 RPM and a thin foil of the material is produced. The system produces cooling rates of the order of 105 K/sec. Details of the development and construction are mentioned.

    • A note on the composition dependence of elastic properties of Se-P glasses

      V C Padaki S T Lakshmikumar A M Jayannavar E S R Gopal

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      Longitudinal and shear wave ultrasonic velocities are reported in Se-P glasses over the composition range 0–50 at % P. The glass transition temperaturesTg show maxima at 30 and 50 at % of P, in consonance with earlier data. The bulk modulus shows minima at these compositions, contrary to the expectation of maxima. These are discussed in relation to the formation of compounds at specific compositions and the nature of the covalent bonding in the glasses.

    • High resolutionV-I characteristics measurements on highTc superconductors

      Kapil M S Bajaj Biswanath Sarkar S T Lakshmikumar Ravi Mehrotra

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      V-I characteristics of sintered superconducting pellets of YBa2Cu3O7−δ was measured with a resolution one order of magnitude better than the usual dc techniques employing nanovoltmeters. For this purpose software-based lock-in-amplifier technique was developed and used. A square-wave excitation current was used. The voltage signal was digitized into a time series and Fourier-analysed on a computer in this technique. Our results show a very small frequency-dependent resistance in some samples which are nominally superconducting. These results help in checking the material quality and defining the critical current densities better.

    • Influence of ion-induced interfacial chemical reactivity on contact resistance

      S T Lakshmikumar

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      Contact resistance measurements of chromium contacts deposited by partially ionized beam deposition on transparent conducting indium tin oxide (ITO) were performed. These provide a direct experimental evidence of the influence of interfacial chemical interaction on the contact resistance. The interfacial reactivity is controlled by modifying the energy and flux of ionized chromium atoms deposited on ITO employing a specially designed partially ionized deposition system with very high ionization efficiency. The true contact resistivityρc is obtained by iteratively correcting the experimentally measured values for the finite sheet resistance of the ITO layer.ρc decreases linearly with the energy of the ionized chromium. Auger sputter profiling shows no structural modifications at the interface due to a change in the energy of the chromium atoms, confirming that the observed change in the contact resistivity is directly related to interfacial chemical bonding of the atoms with the oxygen atoms in the ITO leading to a local increase of carrier concentration and lower interfacial resistance.

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