Search

Role of "O" defects in sensing pollutant with nanostructured SnO2 is not well understood, especially at low temperatures. SnO2 nanoparticles were grown by soft chemistry route followed by subsequent annealing treatment under specific conditions. Nanowires were grown by chemical vapor deposition technique. A systematic photoluminescence (PL) investigation of "O" defects in SnO2 nanostructures revealed a strong correlation between shallow donors created by the in-plane and the bridging "O" vacancies and gas sensing at low temperatures. These SnO2 nanostructures detected methane (CH4), a reducing and green house gas at a low temperature of 50 °C. Response of CH4 was found to be strongly dependent on surface defect in comparison to surface to volume ratio. Control over "O" vacancies during the synthesis of SnO2 nanomaterials, as supported by X-ray photoelectron spectroscopy and subsequent elucidation for low temperature sensing are demonstrated. [ABSTRACT FROM AUTHOR]

Ultrathin films of Al2O3 prepared by atomic layer deposition have been subjected to local electrical stress analysis using conducting atomic force microscopy. The loss of local dielectric integrity through current leakage in these extremely thin films is studied using scanning spreading resistance imaging. Our experimental results shows that repeated voltage stress progressively increases number of leakage spots. While the density of leakage spots increase with higher applied bias for thin oxide films, initial increase and reduction in leakage spots are observed for thick films. [ABSTRACT FROM AUTHOR]

Nanoparticles of Zn0.95-xCo0.05InxO (x=0.0 to 0.07) were synthesized by the pyrolitic reaction of sol-gels obtained from respective metal precursors. X-ray diffraction and high-resolution transmission electron microscopy studies confirm the formation of impurity-free wurtzite type ZnO structure for all the compositions. While pristine ZnO is diamagnetic, Zn0.95Co0.05O nanoparticles show weak paramagnetic behavior at room temperature. When 'In.' is codoped with Co with x=0.0 to 0.07 in Zn0.95-xCo0.05InxO, a systematic increase in magnetic moment is observed up to x=0.07. First-principles modeling supports that the ferromagnetic phase become more favorable at higher indium doping concentrations. [ABSTRACT FROM AUTHOR]

We report an extraordinary coexistence of sign reversal of both magnetization and exchange bias field in the La0.2Ce0.8CrO3 nanoparticles. From the high resolution transmission electron microscopy image, and field dependence of thermoremanent and isothermoremanent magnetization measurements, the nanoparticles are found to be of core-shell nature. The core-shell configuration with an antiferromagnetic core of the Cr3+ and Ce3+ spins and a disordered shell with the uncompensated spins, explains the sign reversal of both magnetization and exchange bias field. The present study shows an excellent way of tuning the sign of both magnetization and exchange bias field in a single magnetic system. [ABSTRACT FROM AUTHOR]

Ba and Mn doped BiFeO3 prepared through the pyrolysis of xerogel precursors are characterized by powder x-ray diffraction, high resolution transmission electron microscopy, superconducting quantum interference device magnetometry, and polarization measurements. Structural studies by x-ray diffraction and transmission electron microscopy show a tetragonal lattice for Ba substituted BiFeO3 and a rhombohedral lattice for Mn substituted BiFeO3. A large ferromagnetic hysteresis loop is observed for Ba doped BiFeO3. Coexistence of distorted rhombohedral and tetragonal phases is observed in Ba and Mn codoped BiFeO3, where enhanced ferroelectric and ferromagnetic properties are produced by the internal strain. Density functional calculations are used to substantiate the results. [ABSTRACT FROM AUTHOR]

SnO2:Eu3+ nanoparticles uniformly dispersed in TiO2 matrix were prepared at 185 °C in ethylene glycol. Unlike in SnO2:Eu3+, significant improvement in the exciton mediated energy transfer between SnO2 and Eu3+ ions was observed when SnO2:Eu3+ nanoparticles are dispersed in TiO2 matrix, and this is attributed to effective shielding of surface Eu3+ ions present in SnO2:Eu3+ nanoparticles from the vibrations of stabilizing ligand by TiO2 matrix. Annealing the samples at high temperatures leads to formation of Sn1-xTixO2, without significantly affecting the energy transfer process between Eu3+ ions and semiconductor host. [ABSTRACT FROM AUTHOR]

Pressure dependent synchrotron x-ray diffraction studies on Pb0.70Ca0.30TiO3 (PCT30) ferroelectric ceramic reveal a crossover in the nature of phase transition from first order nature observed at ambient pressures to second order at high pressures. It is shown that Ca2+ doping affects the transition temperature but does not change the transition pressure of PbTiO3 significantly. The values of bulk modulus and its pressure derivative are also given in this letter. [ABSTRACT FROM AUTHOR]

The nature of charge transport across rough, insulating layers of TiO2 on TiSi2 is investigated using conducting atomic force microscopy. The conducting tip, the insulating layer, and the metallic TiSi2 layer constitute a metal-insulator-metal system. This system exhibits a strong correlation between the topographic image and the current image. Based on this observation, the dependence of current-voltage characteristics on the local thickness of the TiO2 layer is examined and analyzed on the basis of the Fowler-Nordheim tunneling mechanism. This analysis indicates that both field emission and trap assisted tunneling contribute to the conduction mechanism. Evidence of switching due to detrapping of charges is also seen in the I-V characteristics, confirming the role of trap states. [ABSTRACT FROM AUTHOR]

Ba and Mn doped BiFeO3 prepared through the pyrolysis of xerogel precursors are characterized by powder x-ray diffraction, high resolution transmission electron microscopy, superconducting quantum interference device magnetometry, and polarization measurements. Structural studies by x-ray diffraction and transmission electron microscopy show a tetragonal lattice for Ba substituted BiFeO3 and a rhombohedral lattice for Mn substituted BiFeO3. A large ferromagnetic hysteresis loop is observed for Ba doped BiFeO3. Coexistence of distorted rhombohedral and tetragonal phases is observed in Ba and Mn codoped BiFeO3, where enhanced ferroelectric and ferromagnetic properties are produced by the internal strain. Density functional calculations are used to substantiate the results. [ABSTRACT FROM AUTHOR]

The nature of charge transport across rough, insulating layers of TiO2 on TiSi2 is investigated using conducting atomic force microscopy. The conducting tip, the insulating layer, and the metallic TiSi2 layer constitute a metal-insulator-metal system. This system exhibits a strong correlation between the topographic image and the current image. Based on this observation, the dependence of current-voltage characteristics on the local thickness of the TiO2 layer is examined and analyzed on the basis of the Fowler-Nordheim tunneling mechanism. This analysis indicates that both field emission and trap assisted tunneling contribute to the conduction mechanism. Evidence of switching due to detrapping of charges is also seen in the I-V characteristics, confirming the role of trap states. [ABSTRACT FROM AUTHOR]