Good quality ZnO nanostructures were obtained by the microwave-assisted hydrothermal synthesis, at low reaction temperatures, using zinc acetate as the starting precursor. X-ray diffraction confirmed the crystallinity of the ZnO nanostructures, which resulted free of impurities. Field emission gun scanning electron microscopy analysis revealed that the ZnO nanostructures crystallized at 120 1C were more homogeneous and had a constant diameter along the entire wire length, exhibiting an ideal defect density that favors the gas sensing response. A new ozone gas sensor based on these nanostructures was evaluated at low exposure times (15 s) by recording the change in the film resistance. The ZnO nanostructures showed good sensitivity even at low ozone concentration (100 ppb), and fast response and short recovery time at 200 1C, demonstrating great potential for a variety of applications. Two main effects were observed: the first one is intrinsic to that of the sample, while the second is a consequence of the surface and interface complex cluster defects, which produce extrinsic defects.
Perovskite structured oxides are important functional materials often used for the development of modern devices. To extend their applicability, these materials need to be scalably and efficiently grown in the form of thin films. In this work, perovskite structured thin films of nanograined LaFeO 3 (LFO) were chemically grown using polymeric precursors on Pt substrates. The thin films were characterized by X-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The electrical properties of the films were also measured. The homogeneous LFO thin films synthesized at a sintering temperature of 500 1C in 2 h contained grains with lateral dimensions of about 68 nm and 356 nm in thickness. The dielectric permittivity and dielectric loss measurements of the sample indicated only a slight dispersion in the frequency because of the lower two-dimensional stress in the plane of the film. The nanograined LFO semiconductor thin films showed a room temperature magnetic coercive field, which rendered them magnetically soft. The electrical characterization of the films, including temperature-dependent conductivity and thermopower confirmed p-type conduction and the mobility activation energy was measured to be 0.96 eV. A strong magnetization with a remnant magnetization of $60 emu/g was observed in the LFO films, indicating the uncompensated spin magnets moments of the Fe 3 þ ions.
Heterostructured thin films of lanthanum ferrite (LFO) and bismuth ferrite (BFO) with different thicknesses were successfully obtained by a soft chemical method. The films were deposited by spin-coating and annealed at 500°C for 2 h. The XRD pattern confirmed the purity of the thin films, where no additional peaks associated with impurity phases were present. The morphology analysis showed spherical grains with a random size distribution. The grain sizes increased with the number of BFO layers. The average grain size varied from 43 nm to 68 nm. The best dielectric results were obtained for the film with 6 LFO sublayers and 4 BFO top layers, in which the dielectric constant showed low dispersion. Since the capacitance-voltage curve for the film 6-LFO/4-BFO is symmetrical around null voltage, it can be inferred that this heterostructure has few mobile ions and accumulated charges on the film-substrate interface. In this film, polarization remains almost constant during 10 12 cycles before the onset of degradation, which shows the very high resistance of the films to fatigue. Magnetoelectric coefficient measurements of the films revealed the formation of hysteresis loops, and a maximum value of 12 V/cmOe was obtained for the magnetoelectric coefficient in the longitudinal direction; this value is much higher than that previously reported for pure BFO thin films.
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