• Chandrabhas Narayana

      Articles written in Bulletin of Materials Science

    • Effect of substrate roughness on growth of diamond by hot filament CVD

      Awadesh K Mallik S R Binu L N Satapathy Chandrabhas Narayana Md Motin Seikh S A Shivashankar S K Biswas

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      Polycrystalline diamond coatings are grown on Si (100) substrate by hot filament CVD technique. We investigate here the effect of substrate roughening on the substrate temperature and methane concentration required to maintain high quality, high growth rate and faceted morphology of the diamond coatings. It has been shown that as we increase the substrate roughness from 0.05 𝜇m to 0.91 𝜇m (centre line average or CLA) there is enhancement in deposited film quality (Raman peak intensity ratio of 𝑠𝑝3 to non-𝑠𝑝3 content increases from 1.65 to 7.13) and the substrate temperature can be brought down to 640°C without any additional substrate heating. The coatings grown at adverse conditions for 𝑠𝑝3 deposition has cauliflower morphology with nanocrystalline grains and coatings grown under favourable 𝑠𝑝3 condition gives clear faceted grains.

    • Metal-coated magnetic nanoparticles for surface enhanced Raman scattering studies

      G V Pavan Kumar N Rangarajan B Sonia P Deepika Nashiour Rohman Chandrabhas Narayana

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      We report the optimization and usage of surfactantless, water dispersible Ag and Au-coated 𝛾 –Fe2O3 nanoparticles for applications in surface-enhanced Raman scattering (SERS). These nanoparticles, with plasmonic as well as super paramagnetic properties exhibit Raman enhancement factors of the order of 106 (105) for Ag (Au) coating, which are on par with the conventional Ag and Au nanoparticles. Raman markers like 2-naphthalenethiol, rhodamine-B and rhodamine-6G have been adsorbed to these nanoparticles and tested for nonresonant SERS at low concentrations. Further, to confirm the robustness of Ag-coated nanoparticles, we have performed temperaturedependent SERS in the temperature range of 77–473 K. The adsorbed molecules exhibit stable SERS spectra except at temperatures >323 K, where the thermal desorption of test molecule (naphthalenethiol) were evident. The magnetic properties of these nanoparticles combined with SERS provide a wide range of applications.

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