B.K. Panigrahi

Electrical transport studies of Ag nanoclusters embedded in glass matrix

Abstract Silver nanoclusters embedded in glass matrices have been obtained by the combined use of ion exchange and subsequent ion implantation. XRD and UV-visible spectro-photometric analysis have confirmed the formation of Ag nano-clusters in the ion-irradiated samples. Temperature-dependent resistivity measurements of the irradiated samples have been found to follow ρ ( T )∝exp√( T 0 / T ) in the temperature range of 80–280xa0K. The observed behaviour of ρ ( T ) is consistent with charge transport due to hopping between isolated, conducting islands. The separation distance between the conducting islands has been found to be a function of fluence.

Correlation between microstructure and optical properties of ZnO nanoparticles synthesized by ball milling

Zinc oxide (ZnO) nanoparticles (NPs) in the size range ∼7–35u2002nm are synthesized by ball-milling technique, and microstructural and optical properties of the NPs are studied using varieties of techniques. Results from ball-milled NPs are compared with those of the commercially available ZnO nanopowder. X-ray diffraction pattern of the milled NPs indicates lattice strain in the NPs. High-resolution transmission electron microscopy analysis reveal severe lattice distortion and reduction in lattice spacing in some of the NPs. Optical absorption spectra of milled NPs show enhanced absorption peaked at 368 nm, which is blueshifted with reference to starting ZnO powder. Room-temperature photoluminescence spectra show five peaks consisting of ultraviolet and visible bands, and relative intensity of these peaks drastically changes with increasing milling time. Raman spectra of milled powders show redshift and broadening of the Raman modes of ZnO, and a new Raman mode evolve in the milled NPs. A correlation between...

Crystalline to amorphous transition and band structure evolution in ion-damaged silicon studied by spectroscopic ellipsometry

Crystalline to amorphous transition and subsequent microstructural evolution in silicon induced by Ar+-ion implantation over a wide range of ion fluences (6×1013–1×1017 cm−2) have been investigated by spectroscopic ellipsometry. In the evaluation of the optical and microstructural properties of the damaged layer, the contribution of the surface overlayer to the measured dielectric spectra was separated by fitting a multilayer model with an effective medium approximation. The best fit to the dielectric spectra for disordered silicon could be obtained by taking our highest-fluence implanted (fluence=1×1017 ions/cm2) amorphous silicon (a-Si) data as reference data instead of a-Si data available in the handbook. The derivative spectra as a function of fluence show a distinct and sharp transition from the crystalline to amorphous phase. The threshold fluence for this transition is derived from fitting. Evaluation of standard sum rules and optical moments for imaginary part of the pseudodielectric function reve...

Silicide phase formation in Ni/Si system: Depth-resolved positron annihilation and Rutherford backscattering study

Silicidation in Ni∕Si thin-film junction has been investigated using depth-resolved positron annihilation spectroscopy (PAS) and Rutherford backscattering spectrometry (RBS). Identification of various silicide phases from an analysis of the positron annihilation parameters is consistent with the RBS results. Absence of vacancy defects in the silicide region is clearly brought out by PAS.

On the role of oxygen in the catalysis of C54 titanium disilicide by Ti5Si3 phase

The influence of the native SiO2 in the phase formation sequence of Ti∕Si system has been studied. Furnace annealing of Ti∕Si couples has been investigated by secondary-ion-mass spectrometry, Rutherford backscattering, and glancing incidence x-ray diffraction. The influence of dilute concentration of oxygen at the interface in altering reaction kinetics was studied. These studies reveal that the highly metallic Ti5Si3 phase forms during the intermediate stages of heat treatment. This phase is found to catalyze the direct formation of the low-resistive C54 TiSi2 phase, completely bypassing its polymorphic C49 counterpart. X-ray-diffraction line profile analysis of Bragg peaks indicates that the formation of the C54 phase is accompanied by a reduction in the microstrain. Subsequent annealing results in the complete transformation to TiSi2 with an increase in the average grain size.

Low field magnetoconductance studies in aggregated Al nano-clusters

Abstract Nano-aggregates of Al have been formed by 70 keV He+ irradiation on spin cast films of aluminum acetyl acetonate. Three fold increase in conductivity was observed for a fluence range of 1×1016–5×1017 ions/cm2. Electrical transport of the charge carriers was observed to follow Mott’s variable range hopping (VRH) mechanism in 3D nano-aggregates of Al in the temperature regime of 110–300 K. Low field (≤1 T) magnetoresistance (MR) studies in these samples showed change in sign of MR from positive for a sample with low zero field resistance [R(H=0)] to negative for samples with high R(H=0) owing to quantum interference phenomena of hopping paths.