• Rajkumar

      Articles written in Bulletin of Materials Science

    • Semiconductor applications of plasma immersion ion implantation technology

      Mukesh Kumar Rajkumar Dinesh Kumar P J George

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      Many semiconductor integrated circuit manufacturing processes require high dose of implantation at very low energies. Conventional beam line ion implantation system suffers from low beam current at low energies, therefore, cannot be used economically for high dose applications. Plasma immersion ion implantation (PIII) is emerging as a potential technique for such implantations. This method offers high dose rate irrespective of implantation energy. In the present study nitrogen ions were implanted using PIII in order to modify the properties of silicon and some refractory metal films. Oxidation behaviour of silicon was observed for different implantation doses. Diffusion barrier properties of refractory barrier metals were studied for copper metallization.

    • Microrheology of concentrated DNA solutions using optical tweezers

      Arun S Rajkumar B M Jaffar Ali

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      Semiflexible biopolymers play a vital role in shaping cellular structure and rigidity. In this work, we report the determination of microrheological properties of concentrated, double-stranded calf thymus DNA (CT-DNA) solutions using passive, laser-scattering based particle-tracking methodology. From power spectral analysis, we obtain dynamic shear moduli of the polymer solutions stretching over three decades of frequency (100–103 Hz) and over concentration ranges spanning from very dilute to concentrated regime. We also study the effects of altered ionic strength and denaturation on the shear modulus. Our results indicate that (CT-DNA) exhibits predominantly elastic behaviour in the concentration range we probed. From the measurements of the plateau shear modulus, 𝐺p, we conclude that DNA generally behaves like a semiflexible polymer in a good solvent even at low ionic strength. We have thus demonstrated application of passive microrheological method using optical tweezers to DNA solutions. Further extensions of the technique and its applications are discussed.

    • Growth, optical, thermal and mechanical characterization of an organic crystal: Brucinium 5-sulfosalicylate trihydrate

      K Gayathri P Krishnan P R Rajkumar G Anbalagan

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      Single crystals of Brucinium 5-sulfosalicylate trihydrate (B5ST) were grown from ethanol–water (1:1) mixed solvent by the slow solvent evaporation method. X-ray powder diffraction analysis reveals that the crystal belongs to orthorhombic system with space group 𝑃212121. The various reflections were indexed and the lattice parameters were calculated. Photoluminescence (PL) shows peaks corresponding to protonation of the amino group. The optical absorption spectrum shows that the crystal has 90% transmittance in the visible region with a lower cut-off wavelength of 312 nm. Thermal analysis performed on the grown crystal indicates the thermal stability of the crystal and various thermodynamical parameters were calculated from the thermogravimetry (TG) data. The mechanical properties like Vickers microhardness number (𝐻v), stiffness constant (𝐶11) and yield strength (𝜎v) of the crystal were estimated by Vickers hardness test.

    • Synthesis and characterization of hydroxyapatite/alumina ceramic nanocomposites for biomedical applications


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      In the present work, nanocrystalline hydroxyapatite/alumina (HAp−Al$_2$O$_3$) composite was prepared under specially designed stir-type hydrothermal reactor. The composite was prepared at two different temperatures under autogenous pressure and analysed for crystallinity, size, shape, composition and thermomechanical stability. The electron microscopy study shows the formation of HAp−Al$_2$O$_3$ composite nanorods with uniform distribution. The thermogravimetry analysis reveals better thermomechanical property with minimal weight loss at increased temperature. The effect ofdifferent concentrations of HAp−Al$_2$O$_3$ composite powders against MG63 human osteosarcoma cell lines shows excellent compatibility (80%) at high concentration of 200 $\mu$g ml$^{−1}$. These studies facilitate the formation of biocompatible HAp−Al$_2$O$_3$ composite nanorods for biomedical applications.

© 2017 Indian Academy of Sciences, Bengaluru.