• R V Nandedkar

      Articles written in Bulletin of Materials Science

    • Development of a total reflection X-ray fluorescence spectrometer for ultra-trace element analysis

      M K Tiwari B Gowrishankar V K Raghuvanshi R V Nandedkar K J S Sawhney

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      A simple and fairly inexpensive total reflection X-ray fluorescence (TXRF) spectrometer has been designed, constructed and realized. The spectrometer is capable of ultra-trace multielement analysis as well as performs surface characterization of thin films. The TXRF setup comprises of an X-ray generator, a slitcollimator arrangement, a monochromator/cutoff-stage, a sample reflector stage and an X-ray detection system. The glancing angle of incidence on the two reflectors is implemented using a sine-bar mechanism that enables precise angle adjustments. An energy dispersive detector and a GM counter are employed for measuring respectively the fluorescence intensities and the direct X-ray beam intensity. A Cu-target X-ray generator with its line focus window is used as an excitation source. The spectrometer is quite portable with its compact design and use of a peltier cooled solid state detector for energy dispersive detection. Alignment and characterization of the TXRF system has been performed and the minimum detection limits for various elements have been determined to be in the range of 100 pg to 5 ng even at low X-ray generator powers of 30 kV, 5 mA. The capability of the TXRF system developed for thin film characterization is also demonstrated.

    • X-ray reflectivity investigation of interlayer at interfaces of multilayer structures: application to Mo/Si multilayers

      M Nayak G S Lodha R V Nandedkar

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      We report the effect of interlayer on multilayer X-ray reflectivity (XRR) profile using simulations at 8.047 keV (CuK𝛼) energy. We distinguished the effect of interfacial roughness and in-depth interlayer on reflectivity profile. The interfacial roughness reduces the intensity of individual peak while the in-depth interlayer redistributed the reflectivity profile. We are able to discern the asymmetry in interlayer thickness at two interfaces if the interfacial roughness is small compared to in-depth interlayer thickness. The limitation is that, the sensitivity decreases with increasing interfacial roughness. This interlayer model is applied for electron beam evaporated Mo/Si multilayers. The Mo–on–Si interlayer thickness is 10 ± 0.5 Å and Si–on–Mo interlayer thickness is 8 ± 0.5 Å. The nature of interfacial compound is identified using X-ray photoelectron spectroscopy (XPS). The mechanism of interlayer asymmetry is explained on the basis of different heats of sublimation of Mo and Si.

    • Effect of isochronal annealing on phase transformation studies of iron oxide nanoparticles

      Anjali J Deotale R V Nandedkar A K Sinha Anuj Upadhyay Puspen Mondal A K Srivastava S K Deb

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      The effect of isochronal annealing on the phase transformation in iron oxide nanoparticles is reported in this work. Iron oxide nanoparticles were successfully synthesized using an ash supported technique followed by annealing for 2 h at various temperatures between 300 and 700° C. It was observed using X-ray diffraction (XRD) and transmission electron microscopy (TEM) that as-grown samples have mixed phases of crystalline haematite (α-Fe2O3) and a minor phase of either maghemite (𝛾-Fe2O3) or magnetite (Fe3O4). On annealing, the minor phase transforms gradually to haematite. The phase transformation is complete at annealing temperature of 442° C as confirmed by differential scanning calorimetric (DSC) analysis. The unresolved phases in XRD were further analysed and confirmed to be maghemite from the X-ray absorption near edge structure (XANES) studies. The magnetic measurements showed that at room temperature nano-𝛼-Fe2O3 is weak ferromagnetic, and its magnetization is larger than the bulk value. The mixed phase sample shows higher value of magnetization because of the presence of ferromagnetic 𝛾-Fe2O3 phase.

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