• Ramesh Chandra

      Articles written in Bulletin of Materials Science

    • Study of galvanomagnetic effects in Bi-Sr-Ca-Cu-O films

      Ramesh Chandra Neeraj Khare A K Gupta D K Walia Sangeeta Chaudhry V N Ojha V S Tomar

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      Galvanomagnetic effect has been studied at 77 K on Bi-Sr-Ca-Cu-O films as a function of d.c. bias current. These films were prepared by spray pyrolysis and screen-printing techniques, withTc (R=0) 80 K and 100 K respectively. Magnetic field dependence ofIc of sprayed-film showed very small hysteresis whereas screen-printed film showed greater hysteresis. Application of small magnetic field on these films destroyed the zero-resistance state and a finite resistance was developed. The slope of the resistance vs magnetic field curveΔR/ΔH depended on the current flowing through the sample. To increaseΔR/ΔH, meander-shape pattern was prepared on the sprayed film. In generalΔR/ΔH increased by a factor of 103 after sample patterning. The possibility of using these films as a sensitive magnetic field sensor is discussed.

    • Synthesis and characterization of electroless Ni–P coated graphite particles

      M Ananth Kumar Ramesh Chandra Agarwala Vijaya Agarwala

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      Electroless alkaline bath is used to coat Ni–P graphite particles of average size, 150 𝜇m. Amorphous nickel and graphite phases are observed in X-ray diffraction of the coated particles. The crystallite size from diffraction peaks is found to be 9.56 nm. The microstructural studies are carried out with field emission scanning electron microscope (SEM) on the uncoated and coated graphite particles. Uncoated particles showed irregular and fractured surfaces while the surface of coated particles revealed the presence of Ni–P globules. Sizes of Ni–P globules are observed to be in the range 175–250 nm. The presence of Ni and P are confirmed by the energy dispersive spectrometer results. The effect of coating bath composition is studied and an increasing trend in deposition is observed up to 50 gl–1 of stabilizer as well as up to 20 gl–1 of the reducing agent, however, the trend reverses afterwards. The phenomena of nucleation and growth of the Ni–P layer over the graphite surface have been demonstrated through SEM studies and a model has been proposed to demonstrate the growth mechanism of Ni–P globules.

    • Microstructural characteristics and mechanical properties of magnetron sputtered nanocrystalline TiN films on glass substrate

      Vipin Chawla R Jayaganthan Ramesh Chandra

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      Nanocrystalline TiN thin films were deposited on glass substrate by d.c. magnetron sputtering. The microstructural characteristics of the thin films were characterized by XRD, FE-SEM and AFM. XRD analysis of the thin films, with increasing thickness, showed the (200) preferred orientation up to 1.26 𝜇m thickness and then it transformed into (220) and (200) peaks with further increase in thickness up to 2.83 𝜇m. The variation in preferred orientation was due to the competition between surface energy and strain energy during film growth. The deposited films were found to be very dense nanocrystalline film with less porosity as evident from their FE-SEM and AFM images. The surface roughness of the TiN films has increased slightly with the film thickness as observed from its AFM images. The mechanical properties of TiN films such as hardness and modulus of elasticity (𝐸) were investigated by nanoindentation technique. The hardness of TiN thin film was found to be thickness dependent. The highest hardness value (24 GPa) was observed for the TiN thin films with less positive micro strain.

    • Effect of power variation on wettability and optical properties of co-sputtered titanium and zirconium oxynitride films

      Sushant K Rawal Amit Kumar Chawla R Jayaganthan Ramesh Chandra

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      The present paper deals with deposition of titanium and zirconium oxynitride films prepared from cosputtering titanium and zirconium targets by reactive RF magnetron sputtering. The effect of power variation on various properties of the deposited films is analysed. The film gets transformed from amorphous to well crystalline oxynitride films with gradual increase of target powers as observed from XRD graphs. The films exhibit hydrophilic and hydrophobic behaviours depending upon the presence of various phases. Surface energy decreases as the film properties change from hydrophilic to hydrophobic due to greater contact angle values. The optical properties were measured by UV–Vis–NIR spectrophotometer, transmission spectra and bandgap values show variation with respect to change in elemental composition as determined from EDS analysis.

    • Effect of annealing temperature and CdCl$_2$ treatment on the photo-conversion efficiency of CdTe/Zn$_{0.1}$Cd$_{0.9}$S thin film solar cells


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      We report the effects of annealing in conjunction with CdCl$_2$ treatment on the photovoltaic properties of CdTe/Zn$_{0.1}$Cd$_{0.9}$S thin film solar cells. CdTe layer is subjected to dry CdCl$_2$ treatment by thermal evaporation method and subsequently, heat treated in air using a tube furnace from 400 to 500$^{\circ}$C. AFM and XRD results show improved grain size and crystallographic properties of the CdTe film with dry CdCl$_2$ treatment. This recrystallization and grain growth of the CdTe layer upon CdCl$_2$ treatment translates into improved photo-conversion efficiencies of CdTe/Zn$_{0.1}$Cd$_{0.9}$S cell. The results of dry CdCl$_2$ treatment were compared with conventional wet CdCl$_2$ treatment. Photo-conversion efficiency of 5.2% is achieved for dry CdCl$_2$-treated cells in comparison with 2.4% of wet-treated cell at heat treatment temperature of 425$^{\circ}$C.

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