Showing papers by "Chandran Sudakar published in 2008"
TL;DR: In this paper, the structural and optical properties of xSnO2 and yFe2O3 composite thin films are reported. And the bandgap for these composites continuously increases from 2.3 to 3.89 eV.
Abstract: We report the structural and optical properties of xSnO2–yFe2O3 nanocrystalline composite thin films. SnO2 and Fe2O3 exhibit strong phase separation instability and their particle size and crystallinity are tunable by changing their composition and annealing temperature. The bandgap for these composites continuously increases from 2.3 to 3.89 eV. We discuss the increasing bandgap values in terms of the quantum confinement effect manifested by the decreasing size of Fe2O3 crystallites. The method provides a generic approach for the tuning of the bandgap in nanocomposite systems.
72 citations
TL;DR: It is proposed that the time evolution of the scattering patterns, which is very fast at short times and significantly slower at long times, can be explained using a model based on a two-stage chain formation and coarsening processes.
Abstract: We report an experimental investigation of time dependent anisotropic light scattering by an aqueous suspension of tetramethyl ammonium hydroxide coated ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ nanoparticles $(\ensuremath{\sim}6\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ under the ON-OFF transient of an external dc magnetic field. The study employs the synchronized recording and measurement of the two magnetic-field-induced light-scattering patterns produced by two identical orthogonal He-Ne laser beams passing through the ferrofluid sample and propagating parallel and perpendicular to the applied field, respectively. From these patterns, we extract the time dependence of the induced optical anisotropy, which provides a measure of the characteristic time scale and kinematic response for field-induced structure formation in the sample. We propose that the time evolution of the scattering patterns, which is very fast at short times and significantly slower at long times, can be explained using a model based on a two-stage chain formation and coarsening processes.
68 citations
TL;DR: In this article, the structural properties of pure TiO2 have been investigated using Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) and the results suggest that ferromagnetism in the vacuum-annealed sputtered samples is mediated by surface defects or interfacial effects.
63 citations
TL;DR: In this article, a series of Sn and Eu doped TiO 2 (Ti 1−( x +0.001) Eu 0.05 O 2− δ) nanoparticles have been synthesized by polyol method.
61 citations
TL;DR: In this article, a co-precipitation technique was used to synthesize tetramethyl ammonium hydroxide as a surfactant for tetrameric nanoparticles.
35 citations
TL;DR: In this article, composite nanoparticles of aerosol OT-alginate hydrogel loaded with Fe3O4 and rhodamine 6G in average diameter between 25 nm and 50 nm were synthesized by emulsification-cross-linking process and characterized by transmission electron microscopy (TEM) and SQUID magnetometery measurements.
Abstract: Composite nanoparticles of aerosol OT-alginate hydrogel loaded with Fe3O4 and rhodamine 6G (R6G) in average diameter between 25 nm and 50 nm were synthesized by emulsification-cross-linking process and characterized by transmission electron microscopy (TEM) and SQUID magnetometery measurements. TEM measurements show that the Fe3O4 particles are uniformly distributed within AOT-alginate nanoparticles. The Ca2+ cross-linked AOT-alginate nanoparticles loaded with Fe3O4 and rhodamine showed superparamagnetic behavior at room temperature with saturation magnetization of ~50 emu/g of Fe3 O4. Similar behavior was exhibited by Fe2+ cross-linked AOT-alginate nanoparticles loaded with Fe3O4 and rhodamine except it showed twice the magnetization of Ca2+ crosslinked counterpart. A decrease in the amount of rhodamine loading for the composite nanoparticle systems as compared to the bare AOT-alginate nanoparticles was found.
20 citations
TL;DR: In this article, the structural and magnetic properties of spin coated Co3−yZnyO4 thin films were investigated and shown to exhibit a crystalline Zn:CoO core with a disordered oxygen deficient amorphous Co:ZnO surface.
Abstract: We report on the structural and the magnetic properties of spin coated Co3−yZnyO4 thin films. The microstructure of high vacuum annealed films exhibit a crystalline Zn:CoO core with a disordered oxygen deficient amorphous Co:ZnO surface. Weak ferromagnetism (m∼15mμB∕Co) and an exchange bias (HE∼500Oe) are observed at 10K despite the absence of any Co metal clusters. HE is smaller for samples with smaller Zn fractions (for Co3O4-HV, HE∼250Oe). Adding Zn significantly enhances HE. The exchange anisotropy in an antiferromagnetic material due to surface disordered weak ferromagnetism and its overall implications to dilute magnetic semiconducting oxides are discussed.
18 citations
TL;DR: In this paper, a polyol-mediated approach was employed to obtain nanoparticles of vanadia-zirconia (∼10nm) and Ti 4+ -modified ZIRconia catalyst for the selective oxidative dehydrogenation reaction of propane to propene.
Abstract: A polyol-mediated route was employed to obtain nanoparticles of vanadia–zirconia (∼10 nm) and Ti 4+ -modified zirconia catalyst for the selective oxidative dehydrogenation reaction of propane to propene. The catalytic activity and selectivity of samples thus prepared were compared with the values for the sample synthesized by the conventional impregnation method. More dispersed amorphous vanadia species on zirconia support could be obtained by polyol method compared to those obtained by conventional impregnation route, as discerned from transmission electron microscopy (TEM) and Raman studies. Raman spectra of samples prepared by polyol method indicated the presence of monovanadate and polyvanadate species on the zirconia support surface, whereas the impregnated sample showed the existence of aggregated vanadia besides mono and polyvanadate species though the vanadia loading was the same on all samples. XPS studies revealed that vanadia existed as both V 5+ and V 4+ in the samples prepared by the polyol method, whereas only V 5+ state was seen in the impregnated sample. The catalysts prepared by polyol method exhibited enhanced selectivity for propene formation compared to the sample prepared by impregnation method. The enhanced selectivity is attributed to the presence of dispersed vanadia species with lower valence state of vanadium. The present results demonstrate that the polyol-mediated synthesis is an efficient method for the preparation of supported vanadia catalysts containing such active species.
18 citations
TL;DR: In this article, the magnetic properties of CuO-ZnO heterostructures were investigated to elucidate the origin of the ferromagnetic signature in Cu doped ZnO.
Abstract: We investigated the magnetic properties of CuO–ZnO heterostructures to elucidate the origin of the ferromagnetic signature in Cu doped ZnO. The CuO and ZnO layer thickness were varied from 15 to 150 nm and from 70to350nm, respectively. Rutherford backscattering experiments showed no significant diffusion of either Cu in ZnO or Zn in CuO layers. Magnetic measurements indicate ferromagnetism at 300K, which depends on the CuO particle size, but not on the CuO–ZnO interfacial area. Polarized neutron reflectometry measurements show that the observed magnetization cannot be accounted for solely by spins localized near the CuO–ZnO interface or in the CuO layer.
17 citations
TL;DR: In this article, the properties of sputter deposited InN thin films prepared from an InN-MT and an In2O3 target (InN-OT) were investigated.
Abstract: We have investigated the properties of sputter deposited InN thin films prepared from an In-metal (InN-MT) and an In2O3 target (InN-OT) The excess oxygen present in the InN-OT films alters the microstructure by introducing additional disorder Depth dependent x-ray photoelectron spectroscopy measurements indicate the presence of higher concentrations of oxygen in InN-OT Raman spectra show evidence for the presence of an In2O3 secondary phase in both samples Although the InN-OT film has a higher oxygen concentration, both films show similar electrical and optical properties
12 citations
TL;DR: In this article, the effect of surfactant treatment on the structural and magnetic properties of Co-doped ZnO (Zn0.95Co0.05Li0.10O), prepared by a low-temperature solid-state pyrolitic reaction was investigated.
TL;DR: In this paper, the authors investigated the aggregation and dissociation dynamics of 6-nm size Fe3O4 nanoparticles coated by tetra methyl ammonium hydroxide (TMAH) and the same size γ-Fe2O3 nanoparticles precipitated inside an alginate hydrogel matrix, both in aqueous suspensions, using dc magnetic-field-induced time-dependent light scattering patterns.
Abstract: We have investigated the aggregation and dissociation dynamics of
6-nm size Fe3O4 nanoparticles coated by tetra methyl ammonium hydroxide (TMAH) and the same size γ-Fe2O3 nanoparticles precipitated inside an alginate hydrogel matrix, both in aqueous suspensions, using dc magnetic-field-induced time-dependent light scattering patterns.
For the Fe3O4 ferrofluid, a strong anisotropy in light scattering was observed for light propagating perpendicular to the magnetic field. This behavior is attributed to the aggregation of the nanoparticles into chain-like and column-like structures oriented parallel to the magnetic field. A significantly different behavior is observed for the aqueous suspension of
γ-Fe2O3 nanoparticles precipitated in alginate hydrogel, for which the application of the dc magnetic field
produced little to no change in the light scattering patterns. We attribute this difference to the constrained random distribution of
γ-Fe2O3 nanoparticles precipitated in the alginate matrix. Correlating the results from this investigation with our previous study of magneto-thermal measurements in ac fields [Vaishnava et al., J. Appl. Phys. 102, 063914 (2007)], we conclude that for a ferrofluid to exhibit significant thermal effects under an ac magnetic field, it should exhibit optical anisotropy by developing a chain like structure under the influence of a dc magnetic field.
TL;DR: Under certain situations with known known nanoparticle concentrations, the static dephasing theory can be used to quantify the susceptibility or concentration of nanoparticles in either a static or dynamic flow environment at a given time point.
Abstract: This work compares the measured $${{R}_{2}^*}$$
of magnetic nanoparticles to their corresponding theoretical values in both gel phantoms and dynamic water flows on the basis of the static dephasing theory. The magnetic moment of a nanoparticle solution was measured by a magnetometer. The $${{R}_{2}^*}$$
of the nanoparticle solution doped in a gel phantom was measured at both 1.5 and 4.7 T. A total of 12 non-steady state flow experiments with different nanoparticle concentrations were conducted. The $${{R}_{2}^*}$$
at each time point was measured. The theoretical $${{R}_{2}^*}$$
on the basis of the magnetization of nanoparticles measured by the magnetometer agree within 11% of MRI measurements in the gel phantom study, a significant improvement from previous work. In dynamic flow experiments, the total $${{R}_{2}^*}$$
calculated from each experiment agrees within 15% of the theoretical $${{R}_{2}^*}$$
for 10 of the 12 cases. The MRI phase values are also reasonably predicted by the theory. The diffusion effect does not seem to contribute significantly. Under certain situations with known $${{R}_{2}^*}$$
, the static dephasing theory can be used to quantify the susceptibility or concentration of nanoparticles in either a static or dynamic flow environment at a given time point. This approach may be applied to in vivo studies.