Shankar Patil

Synthesis and magnetostructural studies of amine functionalized superparamagnetic iron oxide nanoparticles

Superparamagnetic iron oxide nanoparticles are synthesized through co precipitation method by using the new generation base diisopropylamine (DIPA) which electrostatically complexes with iron ions, reduces them and subsequently caps the nanoparticle. Coating of DIPA on the surface of the nanoparticles was confirmed through FTIR and TG-DTA. We investigate the effect of reaction time as well concentration of DIPA on the particle size and magnetic properties of Fe3O4 nanoparticles. Effect of concentration of DIPA on particle size reveals that the nanocrystallite size of Fe3O4 nanoparticles increases to its maximum (the increase is nominally 5.2 nm to 8.5 nm) and then reduces (3.2 nm). Particle size and magnetic properties of the synthesized nanoparticles are also influenced by reaction time; in general as the reaction time increases the particle size increases. The lattice parameter of iron oxide nanoparticles varies from ∼8.32 to ∼8.39 A with reaction time. From magnetic measurements, superparamagnetism of the Fe3O4 nanoparticles was confirmed. The results clearly suggest that the magneto-structural properties of Fe3O4 (or any ferrite) can be easily tuned by using DIPA.

Nanoscale modulation of electronic states across unit cell steps on the surface of an epitaxial colossal magnetoresistance manganite film

The nature of electronic states near the edge of unit cell steps on the surface of epitaxial La0.7Sr0.3MnO3 (LSMO) thin films grown by real-time reflection high energy electron diffraction monitored pulsed laser deposition is examined by scanning tunneling microscopy and scanning tunneling spectroscopy techniques. It is observed that the electronic states are strongly modulated near the step edge with considerably high gap at the edge and low gap on the terrace. This modulation weakens at low temperature. The temperature evolution of the density of states and the nature of gap in deep metallic state of LSMO are also discussed.

Nano-Heteroarchitectures of Two-Dimensional MoS2@ One-Dimensional Brookite TiO2 Nanorods: Prominent Electron Emitters for Displays

We report comparative field electron emission (FE) studies on a large-area array of two-dimensional MoS2-coated @ one-dimensional (1D) brookite (β) TiO2 nanorods synthesized on Si substrate utilizing hot-filament metal vapor deposition technique and pulsed laser deposition method, independently. The 10 nm wide and 760 nm long 1D β-TiO2 nanorods were coated with MoS2 layers of thickness ∼4 (±2), 20 (±3), and 40 (±3) nm. The turn-on field (Eon) of 2.5 V/μm required to a draw current density of 10 μA/cm2 observed for MoS2-coated 1D β-TiO2 nanorods emitters is significantly lower than that of doped/undoped 1D TiO2 nanostructures, pristine MoS2 sheets, MoS2@SnO2, and TiO2@MoS2 heterostructure-based field emitters. The orthodoxy test confirms the viability of the field emission measurements, specifically field enhancement factor (βFE) of the MoS2@TiO2/Si emitters. The enhanced FE behavior of the MoS2@TiO2/Si emitter can be attributed to the modulation of the electronic properties due to heterostructure and interface effects, in addition to the high aspect ratio of the vertically aligned TiO2 nanorods. Furthermore, these MoS2@TiO2/Si emitters exhibit better emission stability. The results obtained herein suggest that the heteroarchitecture of MoS2@β-TiO2 nanorods holds the potential for their applications in FE-based nanoelectronic devices such as displays and electron sources. Moreover, the strategy employed here to enhance the FE behavior via rational design of heteroarchitecture structure can be further extended to improve other functionalities of various nanomaterials.

PEROVSKITE-BASED COLOSSAL MAGNETORESISTANCE MATERIALS AND THEIR IRRADIATION STUDIES: A REVIEW

Recent technologies have developed appreciably over the last few years to maneuver the materials properties in the desirable range of performances. Swift heavy ion (SHI) irradiation has been utilized for modifying the properties of various materials to a great degree; SHI is used in various systems such as in mixing two different materials and in hightemperature superconductors, ferrites, manganites, etc. In this chapter, we focus our attention to the manganite materials. We will first provide an overview of the electrical and magnetic properties of manganites, then discuss the various modes of interaction of swift heavy ions with materials, and finally provide information about available reports on the effects of SHI irradiation on the structural, electrical, and magnetic properties of manganites.

Spitzer shaped ZnO nanostructures for enhancement of field electron emission behaviors

We observed enhanced field emission (FE) behavior for spitzer shaped ZnO nanowires synthesized via a hydrothermal approach. The spitzer shaped and pointed tipped 1D ZnO nanowires of average diameter 120 nm and length ∼5–6 μm were randomly grown over an ITO coated glass substrate. The turn-on field (Eon) of 1.56 V μm−1 required to draw a current density of 10 μA cm−2 from these spitzer shaped ZnO nanowires is significantly lower than that of pristine and doped ZnO nanostructures, and MoS2@TiO2 heterostructure based FE devices. The orthodoxy test that was performed confirms the feasibility of a field enhancement factor (βFE) of 3924 for ZnO/ITO emitters. The enhancement in FE behavior can be attributed to the spitzer shaped nanotips, sharply pointed nanotips and individual dispersion of the ZnO nanowires. The ZnO/ITO emitters exhibited very stable electron emission with average current fluctuations of ±5%. Our investigations suggest that the spitzer shaped ZnO nanowires have potential for further improving in electron emission and other functionalities after forming tunable nano-hetero-architectures with metal or conducting materials.

MnFe2O4: Synthesis, morphology and electrochemical properties

MnFe2O4 has been synthesized by simple ammonia assisted co-precipitation method to obtain nanocrystalline powder. X-ray diffraction studies confirmed its crystallinity and phase purity. The MnFe2O4 calcined at 1000°C for 4 h has spinel crystal structure with Fd3m space group and lattice constant 8.511 A. The electrode was prepared by dip coating method on stainless steel substrate and fired at 600°C for 2 h. Random shape grains of 0.2 to 1.5 micron with pores of 1-2 micron dimensions were observed in SEM images. The electrochemical studies of MnFe2O4 were carried out with 1 mole Na2SO4 electrolyte. The MnFe2O4 electrode shows highest specific capacitance of 27.53 F.g−1 and interfacial capacitance of 0.83 F.cm−2.

Electronic Structure of Visible Light-Driven Photocatalyst δ-Bi11VO19 Nanoparticles Synthesized by Thermal Plasma

Size confinement for tailoring of electronic structures can in principle be explored for enhancement of photocatalytic properties. In the present work, vanadium-doped bismuth oxide nanoparticles, with an average particle size of 36 nm, are synthesized for the first time, using the thermal plasma method, in large scale with high yield to explore for photocatalytic applications. The electronic and crystallographic structures of the sample are studied experimentally and theoretically. Systematic investigations of the electronic structure of the fluorite type cubic phase of Bi11VO19 nanoparticles are reported for the first time. Enhancement is observed in the photocatalytic activity as compared to other delta phases of bismuth vanadate. The valence band is found to comprise mainly of O 2p states, whereas the conduction band arises from V 3d states giving rise to a band gap value of 2.26 eV. Absence of excess O in δ-Bi2O3 results in shrinking of the band gap because of O 2p, Bi 6s and 6p states from the surrounding atoms at doping sites. Bi11VO19 nanoparticles show an efficient visible light absorption and exhibit excellent photodegradation properties of methylene blue solution under visible light irradiation.