• Umananda M Bhatta

      Articles written in Bulletin of Materials Science

    • 𝑝-AgCoO2/𝑛-ZnO heterojunction diode grown by rf magnetron sputtering

      K A Vanaja Umananda M Bhatta R S Ajimsha S Jayalekshmi M K Jayaraj

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      𝑃-type transparent semiconducting AgCoO2 thin films were deposited by rf magnetron sputtering of sintered AgCoO2 target. The AgCoO2 films grown by rf sputtering were highly 𝑐-axis oriented showing only (001) reflections in the X-ray diffraction pattern unlike in the case of amorphous films grown by pulsed laser deposition (PLD). The bulk powder of AgCoO2 was synthesized by hydrothermal process. The optical bandgap was estimated as 4.15 eV and has a transmission of about 50% in the visible region. The temperature dependence of conductivity shows a semiconducting behaviour. The positive sign of Seebeck coefficient (+220 𝜇VK–1) indicates 𝑝-type conductivity. Transparent 𝑝–𝑛 heterojunction on glass substrate was fabricated by rf magnetron sputtering of 𝑝-AgCoO2 and 𝑛-type ZnO : Al thin films. The structure of the diode was glass/ITO/𝑛-ZnO/𝑝-AgCoO2. The junction between 𝑝-AgCoO2 and 𝑛-ZnO was found to be rectifying.

    • Thermal stability of gold-PS nanocomposites thin films

      Umananda M Bhatta Deepa Khushalani P V Satyam

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      Low-temperature transmission electron microscopy (TEM) studies were performed on polystyrene (PS, 𝑀w = 234 K) – Au nanoparticle composite thin films that were annealed up to 350°C under reduced pressure conditions. The composite thin films were prepared by wet chemical approach and the samples were then subsequently spin-coated on a carbon-coated copper grid for TEM measurements. TEM measurements were performed at liquid nitrogen temperatures to reduce the electron–beam-induced radiation damage. The results showed a marginal increase in Au nanoparticle diameter (2.3 nm–3.6 nm) and more importantly, an improved thermal stability of the polystyrene (PS) composite film much above its glass transition temperature

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