• M K Jayaraj

      Articles written in Bulletin of Materials Science

    • Transparent conducting zinc oxide thin film prepared by off-axis rf magnetron sputtering

      M K Jayaraj Aldrin Antony Manoj Ramachandran

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      Highly conducting and transparent ZnO : Al thin films were grown by off-axis rf magnetron sputtering on amorphous silica substrates without any post-deposition annealing. The electrical and optical properties of the films deposited at various substrate temperatures and target to substrate distances were investigated in detail. Optimized ZnO : Al films have conductivity of 2200 S cm–1 and average transmission in the visible range is higher than 85%. The conductivity and mobility show very little temperature dependence.

    • Effect of oxygen intercalation on properties of sputtered CuYO2 for potential use as 𝑝-type transparent conducting films

      R Manoj M Nisha K A Vanaja M K Jayaraj

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      Transparent films of copper yttrium oxide doped with 2% calcium have been prepared by rf magnetron sputtering. The films show a conductivity of 8 Scm-1 on intercalation of oxygen at high pressure, which reduced the transparency in the visible region. The Ca-doped CuYO2 films before oxygen intercalation show an average transmission of about 60% which reduces to about 45% upon oxygen intercalation. The temperature dependence of the conductivity indicates semiconductor behaviour with low activation energy of 0.59 eV at room temperature. The positive sign of Seebeck coefficient (+274 𝜇VK-1) confirms the 𝑝-type conductivity of the films. The optical bandgap of CuYO2 was found to be 3.15 eV.

    • 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.

    • Red luminescence from hydrothermally synthesized Eu-doped ZnO nanoparticles under visible excitation

      P M Aneesh M K Jayaraj

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      Eu-doped ZnO nanoparticles were synthesized by hydrothermal method. The Eu-dopant concentration has been varied by varying the amount of Eu-dopant concentration. These nanoparticles were structurally characterized by X-ray diffraction, transmission electron microscopy and selected area electron diffraction and it confirms the formation of nanoparticles having standard wurtzite structure. Photoluminescence studies show that these nanoparticles exhibit a sharp red luminescence due to the intra-4𝑓 transitions of Eu3+ ions at an excitation of 397 nm and 466 nm. Luminescence quenching is observed in the nanoparticles as the Eu-dopant concentration increases. Incorporation of Eu in the nanoparticles was confirmed by the energy dispersive X-ray studies.

    • Formation of hydroxyapatite coating on titanium at 200°C through pulsed laser deposition followed by hydrothermal treatment

      Manoj Komath P Rajesh C V Muraleedharan H K Varma R Reshmi M K Jayaraj

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      Pulsed laser deposition (PLD) has emerged as an acceptable technique to coat hydroxyapatite on titanium-based permanent implants for the use in orthopedics and dentistry. It requires substrate temperature higher than 400°C to form coatings of good adhesion and crystallinity. As this range of temperatures is likely to affect the bulk mechanical properties of the implant, lowering the substrate temperature during the coating process is crucial for the long-term performance of the implant. In the present study, hydroxyapatite target was ablated using a pulsed Nd:YAG laser (355 nm) onto commercially pure titanium substrates kept at 200°C. The coating thus obtained has been subjected to hydrothermal treatment at 200°C in an alkaline medium. The coatings were analysed using microscratch test, optical profilometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and infrared spectroscopy (FTIR). XRD, EDS and FTIR showed that the as-deposited coating contained amorphous calcium phosphate and the hydrothermal treatment converted it into crystalline hydroxyapatite. The micro-morphology was granular, with an average size of 1 micron. In the microscratch test, a remarkable increase in adhesion with the substrate was seen as a result of the treatment. The plasma plume during the deposition has been analysed using optical emission spectroscopy, which revealed atomic and ionic species of calcium, phosphorous and oxygen. The outcomes demonstrate the possibility of obtaining adherent and crystalline hydroxyapatite on titanium substrate at 200°C through pulsed laser deposition and subsequent hydrothermal treatment.

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