• Harsh

      Articles written in Bulletin of Materials Science

    • Raman study on single-walled carbon nanotubes with different laser excitation energies

      S S Islam Khurshed Ahmad Shah H S Mavi A K Shaukla S Rath Harsh

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      The industrial use of carbon nanotubes is increasing day by day; therefore, it is very important to identify the nature of carbon nanotubes in a bundle. In this study, we have used the Raman spectroscopic analysis on vertically aligned single-walled carbon nanotubes (SWCNTs) grown by the chemical vapour deposition (CVD) technique. The grown sample is excited with two laser excitation wavelengths, 633 nm from He–Ne laser and 514.5 nm from Ar+ laser. Raman spectrum in the backscattering geometry provides the characteristic spectra of SWCNTs with its radial breathing mode (RBM), defect-induced disorder mode (D band), and highenergy modes (G and M bands). The Raman signal positions of the spectra in RBM, G and M bands confirm the grown sample to be of semiconducting type in nature.

    • Wavelength dependent laser-induced etching of Cr–O doped GaAs: Morphology studies by SEM and AFM

      B Joshi S S Islam H S Mavi Vinita Kumari T Islam A K Shukla Harsh

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      The laser induced etching of semi-insulating GaAs $\langle$100$\rangle$ is carried out to create porous structure under super- and sub-bandgap photon illumination (ℎν). The etching mechanism is different for these separate illuminations where defect states play the key role in making distinction between these two processes. Separate models are proposed for both the cases to explain the etching efficiency. It is observed that under sub-bandgap photon illumination the etching process starts vigorously through the mediation of intermediate defect states. The defect states initiate the pits formation and subsequently pore propagation occurs due to asymmetric electric field in the pore. Formation of GaAs nanostructures is observed using scanning electron (SEM) and atomic force microscopy (AFM).

    • A comparative study on phase co-existence of La$_{1/4}$Pr$_{3/8}$Ca$_3$/8MnO$_3$ in a polycrystalline bulk and thin film

      HARSH BHATT YOGESH KUMAR C L PRAJAPAT M K THOTA SURENDRA SINGH

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      We present a comparative study on phase co-existence in La$_{1/4}$Pr$_{3/8}$Ca$_{3/8}$MnO$_3$ (LPCMO) in a polycrystalline bulk and thin film form. The X-ray diffraction results confirm the formation of single-phase polycrystalline bulk and c-axisoriented strained epitaxial thin films on a LaAlO$_3$ substrate. Scanning electron microscopy images show a homogeneous microstructure growth for both the bulk as well as thin film samples. The temperature dependent magnetization curves for bulk and thin film show remarkably different features indicating the presence of very different phase separation scenarios.A two-step rise and a large thermal hysteresis are observed between zero-field cooled and field-cooled magnetization plots in the bulk sample. However, the magnetization of the film shows a very small hysteresis and a negligible signature of the CO-AFM state for the same composition. The field dependent magnetization plots indicate that in a bulk form LPCMO is a soft magnet and shows a metamagnetic behaviour while in a thin film form it acts as a hard magnet and the metamagnetic behaviour is completely lost.

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