We report on the analysis of nonlinear current-voltage characteristics exhibited by a set of blocking metal/SnO(2)/metal. Schottky barrier heights in both interfaces were independently extracted and their dependence on the metal work function was analyzed. The disorder-induced interface states effectively pinned the Fermi level at the SnO(2) surface, leading to the observed Schottky barriers. The model is useful for any two-terminal device which cannot be described by a conventional diode configuration.

In this work we report on structural and Raman spectroscopy measurements of pure and Sn-doped In 2 O 3 nanowires. Both samples were found to be cubic and high quality single crystals. Raman analysis was performed to obtain the phonon modes of the nanowires and to confirm the compositional and structural information given by structural characterization. Cubic-like phonon modes were detected in both samples and their distinct phase was evidenced by the presence of tin doping. As a consequence, disorder effects were detected evidenced by the break of the Raman selection rules.

The study of structures based on nonstoichiometric SnO 2−x compounds, besides experimentally observed, is a challenging task taking into account their instabilities. In this paper, we report on single crystal Sn 3 O 4 nanobelts, which were successfully grown by a carbothermal evaporation process of SnO 2 powder in association with the well known vapor-solid mechanism. By combining the structural data and transport properties, the samples were investigated. The results showed a triclinic semiconductor structure with a fundamental gap of 2.9 eV. The semiconductor behavior was confirmed by the electron transport data, which pointed to the variable range hopping process as the main conduction mechanism, thus giving consistent support to the mechanisms underlying the observed semiconducting character.

Over the last two decades, oxide nanostructures have been continuously evaluated and used in many technological applications. The advancement of the controlled synthesis approach to design desired morphology is a fundamental key to the discipline of material science and nanotechnology. These nanostructures can be prepared via different physical and chemical methods; however, a green and ecofriendly synthesis approach is a promising way to produce these nanostructures with desired properties with less risk of hazardous chemicals. In this regard, ZnO and TiO2 nanostructures are prominent candidates for various applications. Moreover, they are more efficient, non-toxic, and cost-effective. This review mainly focuses on the recent state-of-the-art advancements in the green synthesis approach for ZnO and TiO2 nanostructures and their applications. The first section summarizes the green synthesis approach to synthesize ZnO and TiO2 nanostructures via different routes such as solvothermal, hydrothermal, co-precipitation, and sol-gel using biological systems that are based on the principles of green chemistry. The second section demonstrates the application of ZnO and TiO2 nanostructures. The review also discusses the problems and future perspectives of green synthesis methods and the related issues posed and overlooked by the scientific community on the green approach to nanostructure oxides.

Using low-resistance indium contacts, we measured some transport properties of undoped vapor-liquid-solid grown tin oxide monocrystals with a belt shape. From the transport measurements, the two following conduction mechanisms were investigated: thermal activation and variable range hopping. An energy gap of 3.8 eV was found. The energy gap was confirmed by thermally activated measurements in the range between 10 and 300 K. For high temperatures (T>300 K), the influence of the disorder caused by the superficial ions layer is measurable. The electron transport in this case was found to be governed by the well known variable range hopping mechanism and the spatial extension of carrier’s wavelength was calculated to be 4 nm.

LaNiO 3 thin films were deposited on SrLaAlO 4 (1 0 0) and SrLaAlO 4 (0 0 1) single crystal substrates by a chemical solution deposition method and heat-treated in oxygen atmosphere at 700 1C in tube oven. Structural, morphological, and electrical properties of the LaNiO 3 thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and electrical resistivity as temperature function (Hall measurements). The X-ray diffraction data indicated good crystallinity and a structural preferential orientation. The LaNiO 3 thin films have a very flat surface and no droplet was found on their surfaces. Samples of LaNiO 3 grown onto (1 0 0) and (0 0 1) oriented SrLaAlO 4 single crystal substrates reveled average grain size by AFM approximately 15-30 nm and 20-35 nm, respectively. Transport characteristics observed were clearly dependent upon the substrate orientation which exhibited a metal-to-insulator transition. The underlying mechanism is a result of competition between the mobility edge and the Fermi energy through the occupation of electron states which in turn is controlled by the disorder level induced by different growth surfaces.

In this work we report on the transition from metal to insulator conduction of individual single crystalline In2O3 wires induced by different oxygen concentration during their growth. The transport measurements revealed that the metallic conduction was mainly governed by the acoustic phonon scattering and the insulating character was addressed by the variable range hopping mechanism, which in turn can be considered as a first evidence of the occurrence of an Anderson-like metal-insulator-transition (MIT). The experimental data provided the critical carrier density to be 8×1018 cm-3 corresponding to a critical impurities spacing of 2.5 nm, which was found to be in agreement with previous reported data on polycrystalline indium oxide samples and with our recent finding on In2O3 semiconducting samples. The approach presented here can be used to grow other metal oxide systems in which oxygen vacancies play a fundamental role for the electron transport features.

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