Nilesh Kulkarni

Facile synthesis of ultra-small monodisperse ceria nanocrystals at room temperature and their catalytic activity under visible light

An optimized facile method has been developed to synthesize ultra-small monodisperse ceria nanocrystals (3 to 4 nm) strictly at RT. The presence of well resolved broad peaks ([111], [200], [220] and [311]) for as-synthesized samples reveal the formation of the cubic phase of ceria. The detailed characterization by TEM exhibited the formation of monodisperse and crystalline ceria nanocrystals. These as-synthesized nanocrystals have shown autocatalytic behaviour and photocatalytic activity under visible sunlight, hence appears to be potential candidates for biomedical (antioxidant), solar cell applications.

Formation of Au0.6Ge0.4 alloy induced by Au-ion irradiation of Au/Ge bilayer

We report on the formation of a-axis oriented Au0.6Ge0.4 alloy on a Si(100) substrate on 120 MeV Au-ion irradiation of a Au/Ge bilayer and subsequent vacuum annealing at 360 °C. Irradiation-induced changes occurring across the Au/Ge interface were studied using Rutherford backscattering spectrometry. Phase identification was done by x-ray diffraction and the surface morphology of the samples was studied by scanning electron microscopy. Formation of oriented Au0.6Ge0.4 alloy was confirmed by transmission electron microscopy and discussed on the basis of swift heavy ion induced effects followed by thermal annealing.

Enhanced magnetization in cubic ferrimagnetic CuFe2O4 nanoparticles synthesized from a citrate precursor: the role of Fe2+

We report a simple liquid dehydration route involving citrate precursors to synthesize single-phase ferrimagnetic copper ferrite (CuFe2O4) nanoparticles with a cubic crystal structure. Superparamagnetism was exhibited by 5 nm CuFe2O4 particles while ferrimagnetism prevailed at 11 nm and above. The cubic CuFe2O4 samples grown under specific conditions show a systematic enhancement in the saturation magnetization. Both quantitative chemical analysis and the unit cell volume data indicate that samples with larger magnetization contain a higher fraction of Fe2+ ions in place of Fe3+. We provide a plausible model for the cation distribution among the available tetrahedral and octahedral sites that quantitatively explains the observed enhancement in the saturation magnetization. This appears to be the first attempt to increase the magnetization by controlling the Fe2+ concentration.

Array of Cu2O nano-columns fabricated by oblique angle sputter deposition and their application in photo-assisted proton reduction

Nano-columnar arrays of Cu2O were grown by the oblique angle sputter deposition technique based on the self-shadowing principle. The as-grown nano-columnar samples are oriented along {111} direction, and they are highly transmitting in the visible range with a low reflectance. In this work, we show the photo-electrochemical activity of nano-columnar array of Cu2O, which shows a higher (∼25%) photocurrent density and a two-fold enhancement in the incident-to-photon conversion efficiency as compared to continuous thin film of Cu2O in photo-assisted proton reduction type reaction. The improvement in electrochemical activity of nano-columnar Cu2O photocathode can be attributed to the change in morphology, crystal structure, as well as electrical property, which shows a higher degree of band bending, increased donor carrier (e−) density and lower width of space charge region as revealed by capacitance measurements and Mott-Schottky analysis.

Laser plasma interaction in copper nano-particle targets

AbstractIn this paper, we present the results of studies on ion emission characteristics of a laser plasma produced from a copper nano-particle layer of 1–3 mm thickness coated over polished surface of a solid copper target. Laser intensityof 10 13 –10 14 W/cm 2 was produced on the targets by a 2 J Nd:glass laser having a variable pulse duration of 300–800 ps. Nano-particle size wasin the range of 15–25 nm. Ion emission from the nano-particle plasma was compared with plasma generated from apolished copper target. Ion emission from the nano-structured target was observed to depend on the polarization of theincident laser beam. This effect was stronger for a shorter laser pulse. X-ray emission was measured in the soft andhard X-ray region (0.7 to 8 keV) using various X-ray filters. A nano-particle coated target is found to yield a largerflux as well as velocity of ions as compared to polished target when the laser polarization is parallel to the planecontaining target normal and detector axis. However, no X-ray enhancement has been observed in the wavelengthrange 1.5 to 20 A˚ .Keywords: Ion emission; Laser-plasma interaction; Laser-plasma; Nano-particles

Non-monotonic size dependence of the elastic modulus of nanocrystalline ZnO embedded in a nanocrystalline silver matrix

We present the first high pressure Raman study of nanocrystalline ZnO with different average crystallite sizes. The problem of low Raman signals from nanometer-sized particles was overcome by forming a nanocomposite of Ag and ZnO nanoparticles. The presence of the nanodispersed Ag particles leads to a substantial surface enhancement of the Raman signal from ZnO. We find that the elastic modulus of nanocrystalline ZnO shows a non-monotonic dependence on the crystallite size and suggest that the non-monotonicity arises from an interplay between the elastic properties of the individual grains and the intergranular region.

PHYSICO-CHEMICAL, STRUCTURAL AND ELECTRICAL STUDIES OF Cu–Zn FERRITES SYNTHESIZED BY NOVEL CHEMICAL ROUTE

The physico-chemical, structural and electrical properties of zinc substituted copper ferrites having the general formula Cu1-xZnxFe2O4(x=0.0 to x=0.8) have been studied as a function of zinc ion concentration. The sample was prepared by co-precipitation method from corresponding metal sulphates. X-ray diffraction patterns were used to confirm the structure of synthesized samples. The calculated and theoretical values of average lattice constant, tetrahedral bond, tetrahedral edge and unshared octahedral edge were found to increase, while the shared octahedral edge and octahedral bond decrease as the Zn ion concentration increases. The dielectric constant (e′) and dielectric loss tangent (tan δ) were measured at a constant frequency 1 kHz as a function of temperature. The dielectric constant and loss tangent were found to increase with rise in temperature. The conduction mechanism in these ferrites is discussed on the basis of electron exchange between Fe2+ and Fe3+ ions. The temperature dependent dc resistivity was carried out in the temperature range 300 to 800 K. The plots of log ρ versus 103/T are linear showing two regions, corresponding to ferrimagnetic and paramagnetic regions.