Effect of ferrous/ferric ions molar ratio on reaction mechanism for hydrothermal synthesis of magnetite nanoparticlesMizutani, N.; Iwasaki, T.; Watano, S.; Yanagida, T.; Tanaka, H.; Kawai, T.
doi: 10.1007/s12034-008-0112-3pmid: N/A
Magnetite nanoparticles were prepared by hydrothermal synthesis under various initial ferrous/ferric molar ratios without adding any oxidizing and reducing agents in order to clarify effects of the molar ratio on the reaction mechanism for the formation of magnetite nanoparticles. The magnetite nanoparticles prepared were characterized by a scanning electron microscope, powder X-ray diffractometer, and superconducting quantum interference device (SQUID). At the molar ratio corresponding to the stoichiometric ratio in the synthesis reaction of magnetite from ferrous hydroxide and goethite, the nucleation of magnetite crystals progressed rapidly in an initial stage of the hydrothermal synthesis, resulting in formation of the magnetite nanoparticles having a smaller size and a lower crystallinity. On the other hand, at higher molar ratios, the particle size and crystallinity increased with increasing molar ratio because using surplus ferrous hydroxide the crystallites of magnetite nanoparticles grew up slowly under hydrothermal conditions according to the Schikorr reaction. The magnetite nanoparticles prepared under various molar ratios had good magnetic properties regardless of the molar ratio.
Synthesis, characterization, sintering and dielectric properties of nanostructured perovskite-type oxide, Ba 2 GdSbO 6Vijayakumar, C.; Padma Kumar, H.; Solomon, Sam; Thomas, J.; Warriar, P.; Koshy, J.
doi: 10.1007/s12034-008-0113-2pmid: N/A
Nanoparticles of barium gadolinium antimonate (Ba 2 GdSbO 6 ), a complex perovskite-type oxide, has been synthesized using an auto ignition combustion process for the first time. The nanoparticles thus obtained have been characterized by powder X-ray diffraction, thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy and transmission electron microscopy. The XRD studies have shown that the as-prepared powder is phase pure Ba 2 GdSbO 6 and has a complex cubic perovskite (A 2 BB′O 6 ) crystalline structure with lattice constant, a = 8·449 Å. The TEM image reveals that the particle size of the as-prepared nano powder was in the range 30–60 nm. The nanocrystals of Ba 2 GdSbO 6 synthesized by the combustion technique could be sintered to 96% of the theoretical density by heating at a temperature of 1560°C for a short duration of 3 h. The surface morphology of the sintered pellet has been studied by scanning electron microscope (SEM). The dielectric constant ( ɛ r ) was 20 and the loss factor (tan δ ) was 0·03 at 3 MHz. By the present combustion technique a phase pure nanopowder of Ba 2 GdSbO 6 could be obtained by a single step process without the need of any calcination step.
Thermodynamic analysis of growth of iron oxide films by MOCVD using tris( t -butyl-3-oxo-butanoato)iron(III) as precursorDhar, Sukanya; Shalini, K.; Shivashankar, S.
doi: 10.1007/s12034-008-0114-1pmid: N/A
Thermodynamic calculations, using the criterion of minimization of total Gibbs free energy of the system, have been carried out for the metalorganic chemical vapour deposition (MOCVD) process involving the β -ketoesterate complex of iron (tris( t -butyl-3-oxo-butanoato)iron(III) or Fe(tbob) 3 ) and molecular oxygen. The calculations predict, under different CVD conditions such as temperature and pressure, the deposition of carbon-free pure Fe 3 O 4 , mixtures of different proportions of Fe 3 O 4 and Fe 2 O 3 , and pure Fe 2 O 3 . The regimes of these thermodynamic CVD parameters required for the deposition of these pure and mixed phases have been depicted in a ‘CVD phase stability diagram’. In attempts at verification of the thermodynamic calculations, it has been found by XRD and SEM analysis that, under different conditions, MOCVD results in the deposition of films comprising pure and mixed phases of iron oxide, with no carbonaceous impurities. This is consistent with the calculations.
Electroless deposition, post annealing and characterization of nickel films on siliconSabharwal, Subir; Palit, Siddharth; Tokas, R.; Poswal, A.; Sangeeta, A.
doi: 10.1007/s12034-008-0115-0pmid: N/A
Electroless deposition of nickel (EN) films on n -type silicon has been investigated under different process conditions. The interface between the film and substrate has been characterized for electrical properties by probing the contact resistances. X-ray diffraction and atomic force microscopy have been performed to obtain information about the structural and morphological details of the films. As a comparative study, nickel films have also been sputter deposited on silicon substrates. An as-deposited electroless film is observed to form non-ohmic contact while in a sputtered film prepared without the application of substrate heating, the formation of metal-insulating-semiconductor type junction is seen.
Characterization and photocatalytic activity of boron-doped TiO 2 thin films prepared by liquid phase deposition techniqueBegum, Noor; Farveez Ahmed, H.; Hussain, O.
doi: 10.1007/s12034-008-0117-ypmid: N/A
Boron doped TiO 2 thin films have been successfully deposited on glass substrate and silicon wafer at 30°C from an aqueous solution of ammonium hexa-fluoro titanate and boron trifluoride by liquid phase deposition technique. The boric acid was used as an F − scavenger. The resultant films were characterized by XRD, EDAX, UV and microstructures by SEM. The result shows the deposited film to be amorphous which becomes crystalline between 400 and 500°C. The EDAX and XRD data confirm the existence of boron atom in TiO 2 matrix and a small peak corresponding to rutile phase was also found. Boron doped TiO 2 thin films can be used as photocatalyst for the photodegradation of chlorobenzene which is a great environmental hazard. It was found that chlorobenzene undergoes degradation efficiently in presence of boron doped TiO 2 thin films by exposing its aqueous solution to visible light. The photocatalytic activity increases with increase in the concentration of boron.
Effects of Ni doping on photocatalytic activity of TiO 2 thin films prepared by liquid phase deposition techniqueBegum, Noor; Farveez Ahmed, H.; Gunashekar, K.
doi: 10.1007/s12034-008-0118-xpmid: N/A
The TiO 2 thin films doped by Ni uniformly and non-uniformly were prepared on glass substrate from an aqueous solution of ammonium hexa-fluoro titanate and NiF 2 by liquid phase deposition technique. The addition of boric acid as an F − scavenger will shift the equilibrium to one side and thereby deposition of the film is progressed. The rate of the reaction and the nature of deposition depend on growing time and temperature. The resultant films were characterized by XRD, EDAX, UV and SEM. The result shows that the deposited films have amorphous background, which becomes crystalline at 500°C. The EDAX data confirms the existence of Ni atoms in TiO 2 matrix. XRD analysis reveals the peaks corresponding to Ni but no peak of crystalline NiO was found. The transmittance spectra of Ni uniformly and non-uniformly doped TiO 2 thin films show ‘blue shift and red shift’, respectively. Ni-doped TiO 2 thin films can be used as photocatalyst for the photodegradation of methyl orange dye. It was found that, organic dye undergoes degradation efficiently in presence of non-uniformly Ni-doped TiO 2 thin films when compared to uniformly doped films and pure TiO 2 films under visible light. The photocatalytic activity increases with increase in the concentration of Ni in case of nonuniformly doped thin films but decreases with the concentration when uniformly doped thin films were used.
p -AgCoO 2 / n -ZnO heterojunction diode grown by rf magnetron sputteringVanaja, K.; Bhatta, Umananda; Ajimsha, R.; Jayalekshmi, S.; Jayaraj, M.
doi: 10.1007/s12034-008-0119-9pmid: N/A
P -type transparent semiconducting AgCoO 2 thin films were deposited by rf magnetron sputtering of sintered AgCoO 2 target. The AgCoO 2 films grown by rf sputtering were highly c -axis oriented showing only (001) reflections in the X-ray diffraction pattern unlike in the case of amorphous films grown by pulsed laser deposition (PLD). The bulk powder of AgCoO 2 was synthesized by hydrothermal process. The optical bandgap was estimated as 4·15 eV and has a transmission of about 50% in the visible region. The temperature dependence of conductivity shows a semiconducting behaviour. The positive sign of Seebeck coefficient (+220 μVK −1 ) indicates p -type conductivity. Transparent p-n heterojunction on glass substrate was fabricated by rf magnetron sputtering of p -AgCoO 2 and n -type ZnO: Al thin films. The structure of the diode was glass/ITO/ n -ZnO/ p -AgCoO 2 . The junction between p -AgCoO 2 and n -ZnO was found to be rectifying.
Strain induced anomalous red shift in mesoscopic iron oxide prepared by a novel techniqueNarayanan, T.; Sakthi Kumar, D.; Yoshida, Yasuhiko; Anantharaman, M.
doi: 10.1007/s12034-008-0120-3pmid: N/A
Nano magnetic oxides are promising candidates for high density magnetic storage and other applications. Nonspherical mesoscopic iron oxide particles are also candidate materials for studying the shape, size and strain induced modifications of various physical properties viz. optical, magnetic and structural. Spherical and nonspherical iron oxides having an aspect ratio, ∼2, are synthesized by employing starch and ethylene glycol and starch and water, respectively by a novel technique. Their optical, structural, thermal and magnetic properties are evaluated. A red shift of 0·24 eV is observed in the case of nonspherical particles when compared to spherical ones. The red shift is attributed to strain induced changes in internal pressure inside the elongated iron oxide particles. Pressure induced effects are due to the increased overlap of wave functions. Magnetic measurements reveal that particles are superparamagnetic. The marked increase in coercivity in the case of elongated particles is a clear evidence for shape induced anisotropy. The decreased specific saturation magnetization of the samples is explained on the basis of weight percentage of starch, a nonmagnetic component and is verified by TGA and FTIR studies. This technique can be modified for tailoring the aspect ratio and these particles are promising candidates for drug delivery and contrast enhancement agents in magnetic resonance imaging.