Showing papers by "Chandran Sudakar published in 2009"
TL;DR: In this paper, a polyol-based synthesis of mixed oxide nanoparticles for hydrogen generation from water using methanol as sacrificial reagent was studied under sunlight type radiation and the results indicate that mixed oxides have better activity compared to pure TiO 2 synthesized by the same method and the activity decreases with increasing SnO 2 concentration in TiO2.
154 citations
TL;DR: No evidence is found for any systematic variation of the electric or magnetic properties of BiFeO(3) depending on the transition metal dopant, suggesting that these properties are determined mainly by extrinsic effects arising from defects or grain boundaries.
Abstract: We have synthesized a range of transition-metal-doped BiFeO3 thin films on conducting silicon substrates using a spin-coating technique from metal–organic precursor solutions. Bismuth, iron and transition-metal–organic solutions were mixed in the appropriate ratios to produce 3% transition-metal-doped samples. X-ray diffraction studies show that the samples annealed in a nitrogen atmosphere crystallize in a rhombohedrally distorted BiFeO3 structure with no evidence for any ferromagnetic secondary phase formation. We find evidence for the disappearance of the 404 cm−1 Raman mode for certain dopants indicative of structural distortions. The saturation magnetization of these BiFeO3 films has been found to increase on doping with transition metal ions, reaching a maximum value of 8.5 emu cm−3 for the Cr-doped samples. However, leakage current measurements find that the resistivity of the films typically decreases with transition metal doping. We find no evidence for any systematic variation of the electric or magnetic properties of BiFeO3 depending on the transition metal dopant, suggesting that these properties are determined mainly by extrinsic effects arising from defects or grain boundaries.
134 citations
TL;DR: In this article, the authors used point contact Andreev reflection measurements to directly determine the spin polarization, which was found to be approximately $50% ± 1.5% for both compositions.
Abstract: We present evidence for spin-polarized charge carriers in ${\text{In}}_{2}{\text{O}}_{3}$ films. Both ${\text{In}}_{2}{\text{O}}_{3}$ and Cr doped ${\text{In}}_{2}{\text{O}}_{3}$ films exhibit room-temperature ferromagnetism after vacuum annealing, with a saturation moment reaching approximately $0.5\text{ }\text{emu}/{\text{cm}}^{3}$ for the Cr doped samples. We used point contact Andreev reflection measurements to directly determine the spin polarization, which was found to be approximately $50%\ifmmode\pm\else\textpm\fi{}5%$ for both compositions. These results are consistent with suggestions that the ferromagnetism observed in certain oxide semiconductors may be carrier mediated.
81 citations
TL;DR: In this paper, the photocatalytic property of self-doped TiO 2 nanoparticles was modified by synthesizing through different routes, such as Solvothermal (T-Sol), T-Son, and polyol (T -Pol).
63 citations
TL;DR: In this paper, structural, optical, and electrical properties of both as-grown and vacuum annealed In2O3 thin films were investigated for optical spectroscopy measurements.
Abstract: We have investigated the structural, optical, and electrical properties of both as-grown and vacuum annealed In2O3 thin films. In contrast to the insulating as-prepared samples, vacuum annealed In2O3 films exhibit a metallic electrical conductivity with increased carrier concentration and mobility. We attribute the excess carriers to an oxygen deficiency introduced during vacuum annealing. Remarkably, these carrier densities seem to be stable under ambient conditions for at least two years. Optical spectroscopy measurements show a large optical transparency, greater than 80%, for both the as-prepared and vacuum annealed In2O3 films.
43 citations
TL;DR: In this paper, the effect of surfactant treatment on the structural and magnetic properties of Mn-doped ZnO bulk (Zn 0.978Mn0.03Li 0.01O) was investigated.
Abstract: We report the effect of surfactant treatment on the structural and magnetic properties of Mn-doped ZnO bulk (Zn 0.978Mn 0.022O) and Mn- and Li-codoped ZnO nanoparticles (Zn 0.96Mn 0.03Li 0.01O) prepared by low-temperature reaction. X-ray diffraction and transmission electron microscopy analyses of these samples showed the formation of impurity-free crystals with wurtzite ZnO structure. XPS data revealed that Mn exists in the 2+ oxidation state. TEM and HRTEM studies of sodium bis-2-ethylhexyl sulfosuccinate (AOT)-treated Zn 0.978Mn 0.022O showed predominantly rodlike microstructures developing into platelets and sizes in the range of 50-500 nm, whereas the AOT-treated Zn 0.96Mn 0.03Li 0.01O sample showed nearly spherical particles in the nanometer regime (20-30 nm). DC magnetization measurements as a function of field showed enhanced room temperature ferromagnetism for the surfactant-treated Zn 0.978Mn 0.022O and Zn 0.96Mn 0.03Li 0.01O. We discuss the possible role of surfactant and Li ion on the magnetic properties of Mn-doped ZnO.
36 citations
TL;DR: In this paper, Fe3O4 magnetic nanoparticles having diameters of approximately 12 nm were prepared by chemical coprecipitation, which were coated with three different fatty acid surfactants: oleic acid, lauric acid and myristic acid.
Abstract: We prepared Fe3O4 magnetic nanoparticles having diameters of approximately 12 nm by chemical coprecipitation, which were coated with three different fatty acid surfactants: oleic acid, lauric acid, and myristic acid. From x-ray diffraction, transmission electron microscopy, and Mossbauer spectroscopy measurements we confirmed that Fe3O4 is the only phase present in the samples. The zero field cooled magnetization curves for the nanoparticles exhibit broad peaks, consistent with superparamagnetic blocking for the polydisperse samples, and a saturation magnetization smaller than that for bulk Fe3O4. Although there are minimal differences in the magnetic properties of the nanoparticles having different surfactants, we find significant changes in the hydrodynamic response depending on chain length. Hyperthermia measurements show considerably larger response for oleic acid-coated samples, while magneto-optical studies indicate that these samples have slower dynamics of aggregation under the influence of a dc f...
35 citations
TL;DR: In this article, the effects of UV irradiation on the electrical and optical properties of polycrystalline In2O3 films were investigated, and it was shown that UV illumination at a peak wavelength of 365 nm leads to a sharp drop in resistance and increase in carrier concentration.
Abstract: We have investigated the effects of UV irradiation on the electrical and optical properties of polycrystalline In2O3 films. We found that UV illumination at a peak wavelength of 365 nm leads to a sharp drop in resistance and increase in carrier concentration. This highly conductive state persists for a timescale of hours in air at room temperature after illumination. We observe distinct changes in the optical absorption spectra and the associated change in carrier concentration, which is consistent with a Burstein–Moss shift of ∼0.1 eV. The relaxation rate of this persistent conducting state depends strongly on temperature. We find that the conductance relaxation in an oxygen-free environment can be described by a stretched exponential while the behavior of the samples in air is better described by a logarithmic relaxation, both of which may be associated with glassy behavior.
34 citations
TL;DR: In this article, a morphological control and transformation of ZnO nanorods to spherical particles induced by Co substitution is reported. And the morphology completely reverts back to rod shape by Li incorporation.
Abstract: 1D nanostructures of Zn1−xCoxO (x = 0, 0.03 and 0.05) and Co and Li codoped ZnO (Zn0.85Li0.10Co0.05O) were prepared by a soft chemical method. We report a very interesting observation of morphological control and transformation of ZnO nanorods to spherical particles induced by Co substitution. It is also remarkable to note that the morphology completely reverts back to rod shape by Li incorporation. In addition to this unusual observation, the Li incorporation enhances the room-temperature ferromagnetic (RTFM) properties. These experimental observations are well-supported by theory work as well. These results are significant, as the 1D RTFM will have implications in spintronic devices.
30 citations
TL;DR: In this article, the effect of 5% Ti incorporation on lithium intercalation capacity of V 2 O 5 thin films prepared by spin coating using metalorganic (MO) and inorganic sol-gel (SG) precursors on indium tin oxide coated glass substrates have been investigated.
29 citations
TL;DR: In this article, a rf magnetron sputtering from an indium (In) metal target was used to construct thin InN thin films using rf magnetic sputtering.
Abstract: We have fabricated InN thin films using rf magnetron sputtering from an indium (In) metal target. Optical and electrical measurements show that these as-grown films are n-type with carrier concentrations ranging from 1020 to 1021 cm−3. This variation in carrier density is produced by controlling the conditions during the deposition. We used Rutherford backscattering spectrometry to identify possible sources for n-type carriers. We found that in addition to strong direct bandgap optical absorption ranging from 1.4 to 2.0 eV, a large plasmon absorption peak in the infrared region (0.45–0.8 eV) is also observed. This tunable IR absorption suggests that these highly degenerate InN films could be used for a number of applications, including optical filters and infrared devices.
TL;DR: In this paper, the electric field tuning of a magnetic phase transition temperature (TL) in multiferroic Ni3V2O8 thin films is reported. But the authors do not consider the effect of magnetic and ferroelectric correlation functions.
Abstract: We report on the electric-field tuning of a magnetic phase transition temperature (TL) in multiferroic Ni3V2O8 thin films. The simultaneous magnetic and ferroelectric transition in Ni3V2O8 exhibits a clear dielectric anomaly; we monitored TL under applied electric and magnetic fields using dielectric measurements. The transition temperature increases by 0.2 K±0.05 K when the sample is biased approximately 25 MV/m compared to zero bias. This electric-field control of the magnetic transition can be qualitatively understood using a mean-field model incorporating a tri-linear coupling between the magnetic order parameters and spontaneous polarization. The shape of the electric field-temperature phase boundary is consistent with the proper order parameter for the multiferroic phase in Ni3V2O8 being a linear combination of the magnetic and ferroelectric correlation functions.
TL;DR: This work presents a quick and easy thin film deposition technique to coat the end of a single optical fiber by dip-coating a metal-organic precursor, which is then decomposed in a propane flame, and yields results that are comparable or better than can be achieved with sputtering or thermal evaporation.
Abstract: Fiber-optic based interferometers are used to detect small displacements, down to the subnanometer range. Coating the end of the optical fiber with a partially reflecting thin film greatly improves the resolution of interferometers by increasing the multiple reflections between the fiber end and the measured object. In this work, we present a quick and easy thin film deposition technique to coat the end of a single optical fiber by dip-coating a metal-organic precursor, which is then decomposed in a propane flame. The coated fiber was tested for morphology and usefulness for interferometric application. We found that this coating technique is much faster and easier than conventional thin coating techniques, and yields results that are comparable or better than can be achieved with sputtering or thermal evaporation.