Naresh Mishra

The effect of simultaneous substitution of Ga3+ and Zn2+ in YBa2 Cu3O7−y has been studied with respect to its superconducting transition temperature and structural parameters. The result indicates the preferential substitution of Zn and Ga at plane and chain sites of Cu respectively as well as the creation of local magnetic moments at the respective sites due to slowing down of spin and charge fluctuations. The mutual coupling of the moments at the chain- and plane-sites gives rise to enhanced depression of Tc.

In the present study, we probe into the phase transition from anatase to rutile in nanocrystalline thin films under thermal annealing and swift heavy ion (SHI) irradiation. TiO2 thin films were prepared through chemical route using sol-gel and spin coating techniques on silicon (100) substrates. The structural studies of the annealed films were characterized by GAXRD and Raman spectroscopy. Though

ABSTRACT Two sets of gold thin films of thickness of ~ 20 and ~ 50 nms, grown by thermal evaporation method on (100) silicon wafers were irradiated by 197 MeV Au ions. Grazing incidence X-Ray diffraction (GIXRD) study revealed lattice expansion on decreasing the film thickness. 197 MeV Au ion irradiation did not affect either the cubic crystal structure of gold or its lattice parameter. Atomic force microscopy (AFM) study indicated that the evolution of the surface morphology with ion fluence crucially depended on the film thickness, the thinner film being more sensitive than the thicker one. Irradiation led to nanoparticles formation on the surface of the films. This observation is in contrast to the generally perceived damaging role of swift heavy ion (SHI) irradiation. Power spectral density analysis of the roughness along both the lateral and vertical directions demonstrated dominance of surface diffusion over volume diffusion induced by SHI irradiation. A comparison of the sputtering yield obtained from Rutherford back scattering (RBS) spectra of the irradiated films and transmission electron microscopy (TEM) of the particles sputtered from the films and collected by a catcher grid during irradiation indicated that more than the surface and volume diffusion processes, it is the irradiation induced sputtering that controls the overall surface morphology of the films. The surface roughness increase with ion fluence and the irradiation induced sputtering yield was found to be larger in thinner films. Film thickness dependence of the evolution of surface morphology and sputtering yield with 197 MeV Au ion irradiation clearly indicates the dominance of the electronic energy loss over the nuclear energy loss of the projectiles ions in the target medium and opens up the ways for examining the applicability of different models of ion-matter interaction in systems with reduced dimensions.

ABSTRACT In this study, rutile titanium dioxide thin films deposited on Si (100) substrates by DC magnetron sputtering are irradiated by 79 MeV Br ions. Though each Br ion is expected to amorphize the medium along its path, the film remains crystalline even at the highest fluence of irradiation. The evolution of surface of the films with Br ion fluence is studied using atomicforce microscopy. The films were found to smoothen under dense electronic excitation of Br ions. The irregular shape grain of the pristine films convert to circular shape at a fluence of 1 Multiplication-Sign 10{sup 13} Br ions cm{sup -2}. Power spectral density (PSD) analysis of the AFM images indicates that irradiation induced smoothing of the surfaces is governed by the surface diffusion process.

Evolution of c-axis oriented YBa2Cu3O7-y (YBCO) thin films under 200 MeV Ag ion irradiation at 79 K is studied by in-situ temperature dependent resistivity and in-situ low temperature x-ray diffraction. The electronic energy loss (25.18 keV nm-1) of these ions is shown to induce secondary electrons, which create oxygen disorder selectively in the CuO basal planes of fully oxygenated YBCO

... One of the authors, CR, acknowledges UGC-DAE-CSR, India, for supporting a project Ref noCSR-I/CSR Indore/PROJ/ SANC/14/2007/10/223/423. The UGC-DAE Consortium for Scientific Research (CSR), Indore, is acknowledged for characterization support. 5 Page 7. J. Phys. ...

Temperature-dependent electrical resistivity of a set of YBa2Cu3O7/Ag composite thick films prepared by a reaction diffusion technique was analyzed to determine activation energy. Both measurement current and magnetic field were varied to study rho vs T characteristics. The applied magnetic field and the measurement current tilt the potential profile that reduces the potential barrier and enhances the vortex motion in

Modification of the surface morphologies of titanium oxide nanoparticle thin films under swift heavy ion (SHI) irradiation was investigated using glancing angle X-ray diffractometry and atomic force microscopy. Irradiation at low ion fluences leads to grain fragmentation and a narrowing of the grain size distribution, whereas grain growth with increased average grain size and grain size distribution occur at high

ABSTRACT In the present study, we report the modification of pulsed laser deposited c-axis oriented thin films of YBa2Cu3O7−y (YBCO) in a cylindrical region around the path of swift heavy ions (SHIs). Our in situ temperature-dependent resistivity measurement and in situ low-temperature X-ray diffraction (XRD) study on YBCO irradiated at liquid nitrogen temperature with 200 MeV Ag ions shows that the SHI-induced secondary electrons selectively create point defects at CuO basal chains of YBCO. Beyond a critical fluence (1012 ions/cm2), the radially strained region around the amorphous latent tracks estimated from full width at half-maximum of (00l) XRD peaks tends to overlap, and a two-step superconducting transition evolves instead of a single transition in the in situ resistivity measurement.

NQR measurements on YBa 2(Cu 1-xGa x) 3O 7-δ( δ ⋍ 0.05) at 4.2K are reported. Resonance lines become broader with the introduction of Ga-ions suggesting a distribution of the electric field gradient (EFG) at the Cu-sites. EFG at both the sites is affected though Ga-ions occupy only the chain sites. Spin-lattice relaxation time reduces sharply with the increase of x which suggests strongly that certain copper atoms acquire magnetic moment as a consequence of introducing non magnetic gallium atoms.