arXiv subjects

V. M. Naik

Publications and source records attributed to V. M. Naik.

4 recordsLinked to original sources

arXiv2013

Influence of excitation frequency on Raman modes of In1-xGaxN thin films

Low energy optical modes of MBE-grown In1-xGaxN thin films with different values of x are investigated using Raman spectroscopy. We also studied the influence of Raman excitation frequency using red and green lasers on scattering intensity of various Raman modes. For those In1-xGaxN alloys whose bandgap energy is close to the red laser, a huge enhancement in the intensities of A1(LO) mode and its 2A1(LO) replica is observed when excited with red laser as compared to the green laser excitation. We found that the energies of longitudinal optical modes (A1 (LO) and 2A1 (LO)) vary nonlinearly unlike the E2 mode with increasing Ga atomic fraction. A Raman mode ~ 540 cm-1 was observed in all In1-xGaxN films with low energy red laser excitation but was absent with green laser excitation. We attribute this mode to A1(TO) mode of the underneath GaN buffer layer.

cond-mat.mtrl-sci↗

arXiv2008

Ferromagnetism and spin polarized charge carriers in In$_{2}$O$_{3}$ thin films

We present evidence for spin polarized charge carriers in In$_2$O$_3$ films. Both In$_2$O$_3$ and Cr doped In$_2$O$_3$ films exhibit room temperature ferromagnetism after vacuum annealing, with a saturation moment of approximately 0.5 emu/cm$^3$. We used Point Contact Andreev Reflection measurements to directly determine the spin polarization, which was found to be approximately 50$\pm$5% for both compositions. These results are consistent with suggestions that the ferromagnetism observed in certain oxide semiconductors may be carrier mediated.

cond-mat.mtrl-sci↗

arXiv2004

Ferromagnetism at 300 K in spin-coated anatasea and rutile Ti0.95Fe0.05O2 films

Thin films of Ti1-xFexO2 (x=0 and 0.05) have been prepared on sapphire substrates by spin-on technique starting from metal organic precursors. When heat treated in air at 550 and 700 degrees C respectively, these films present pure anatase and rutile structures as shown both by X-ray diffraction and Raman spectroscopy. Optical absorption indicate a high degree of transparency in the visible region. Such films show a very small magnetic moment at 300 K. However, when the anatase and the rutile films are annealed in a vacuum of 1x10-5 Torr at 500 degrees C and 600 degrees C respectively, the magnetic moment, at 300 K, is strongly enhanced reaching 0.46 $μ$B/Fe for the anatase sample and 0.48 $μ$B/Fe for the rutile one. The ferromagnetic Curie temperature of these samples is above 350 K.

cond-mat.mtrl-sci↗

arXiv1999

Structure and Rheology of the Defect-gel States of Pure and Particle-dispersed Lyotropic Lamellar Phases

We present important new results from light-microscopy and rheometry on a moderately concentrated lyotropic smectic, with and without particulate additives. Shear-treatment aligns the phase rapidly, except for a striking network of oily-streak defects, which anneals out much more slowly. If spherical particles several microns in diameter are dispersed in the lamellar medium, part of the defect network persists under shear-treatment, its nodes anchored on the particles. The sample as prepared has substantial storage and loss moduli, both of which decrease steadily under shear-treatment. Adding particles enhances the moduli and retards their decay under shear. The data for the frequency-dependent storage modulus after various durations of shear-treatment can be scaled to collapse onto a single curve. The elasticity and dissipation in these samples thus arises mainly from the defect network, not directly from the smectic elasticity and hydrodynamics.

cond-mat.soft↗