Biaxial compressive strain has been used to markedly enhance the ferroelectric properties of BaTiO3 thin films. This strain, imposed by coherent epitaxy, can result in a ferroelectric transition temperature nearly 500 degrees C higher and a remanent polarization at least 250% higher than bulk BaTiO3 single crystals. This work demonstrates a route to a lead-free ferroelectric for nonvolatile memories and electro-optic devices.

Photoluminescent and gas-sensing properties of ZnO nanowires prepared by an ionic liquid assisted vapor transfer approach

Using in situ high-resolution synchrotron x-ray scattering, the Curie temperature T C has been determined for ultrathin c-axis epitaxial PbTiO 3 films on conducting substrates (SrRuO 3 on SrTiO 3 ), with surfaces exposed to a controlled vapor environment. The suppression of T C was relatively small, even for the thinnest film (1.2 nm). We observe that 180 stripe domains do not form, indicating that the depolarizing field is compensated by free charge at both interfaces. This is confirmed by ab initio calculations that find polar ground states in the presence of ionic adsorbates.

In this article, we review gas sensor application of one-dimensional (1D) metal-oxide nanostructures with major emphases on the types of device structure and issues for realizing practical sensors. One of the most important steps in fabricating 1D-nanostructure devices is manipulation and making electrical contacts of the nanostructures. Gas sensors based on individual 1D nanostructure, which were usually fabricated using electron-beam lithography, have been a platform technology for fundamental research. Recently, gas sensors with practical applicability were proposed, which were fabricated with an array of 1D nanostructures using scalable micro-fabrication tools. In the second part of the paper, some critical issues are pointed out including long-term stability, gas selectivity, and room-temperature operation of 1D-nanostructure-based metal-oxide gas sensors.

We fabricated a nanowire-based gas sensor using a simple method of growing SnO(2) nanowires bridging the gap between two pre-patterned Au catalysts, in which the electrical contacts to the nanowires are self-assembled during the synthesis of the nanowires. The gas sensing capability of this network-structured gas sensor was demonstrated using a diluted NO(2). The sensitivity, as a function of temperature, was highest at 200 °C and was determined to be 18 and 180 when the NO(2) concentration was 0.5 and 5 ppm, respectively. Our sensor showed higher sensitivity compared to different types of sensors including SnO(2) powder-based thin films, SnO(2) coating on carbon nanotubes or single/multiple SnO(2) nanobelts. The enhanced sensitivity was attributed to the additional modulation of the sensor resistance due to the potential barrier at nanowire/nanowire junctions as well as the surface depletion region of each nanowire.

Novel SnO(2)-In(2)O(3) heterostructured nanowires were produced via a thermal evaporation method, and their possible nucleation/growth mechanism is proposed. We found that the electronic conductivity of the individual SnO(2)-In(2)O(3) nanowires was 2 orders of magnitude better than that of the pure SnO(2) nanowires, due to the formation of Sn-doped In(2)O(3) caused by the incorporation of Sn into the In(2)O(3) lattice during the nucleation and growth of the In(2)O(3) shell nanostructures. This provides the SnO(2)-In(2)O(3) nanowires with an outstanding lithium storage capacity, making them suitable for promising Li ion battery electrodes.

Highly efficient planar perovskite optoelectronic devices are realized by amine-based solvent treatment on compact TiO2 and by optimizing the morphology of the perovskite layers. Amine-based solvent treatment between the TiO2 and the perovskite layers enhances electron injection and extraction and reduces the recombination of photogenerated charges at the interface.

SrRuO 3 (SRO) is widely used as an electrode in oxide electronic device applications due to its excellent material properties such as metallic conductivity, chemical stability, good lattice match with multifunctional oxides, and atomically smooth and welldefined surfaces. [1][2][3][4][5][6] Especially in the fabrication of epitaxial thin-film heterostructures, the crystal symmetry and domain structure of the overlayer thin film are strongly dependent on those of the bottom electrode. Thus, it is critical to investigate the crystal symmetry and domain structure of the bottom electrode at the growth temperature and during cooling of the epitaxial heterostructures to room temperature if the bottom electrode undergoes structural transitions.In ABO 3 perovskite materials, the ideal cubic symmetry can be distorted by several mechanisms such as distortions of the octahedra, cation displacements within the octahedra, and tilting of the octahedra. The first two mechanisms are driven by electronic instabilities of the octahedral metal ion as exemplified by the Jahn-Teller distortion in KCuF 3 or the ferroelectric displacement of titanium in BaTiO 3 . [7,8] The third and most common mechanism, octahedral tilting, can be realized by tilting essentially rigid BO 6 octahedra while maintaining their corner-sharing connectivity. This type of distortion is typically observed when the A cation is too small for the cubic BO 3 corner-sharing octahedral network.At room temperature bulk SRO exhibits orthorhombic symmetry (Pbnm).[9] Figure 1 shows the sequence of phase transitions in unstrained bulk SRO from orthorhombic to tetragonal and then cubic symmetry with increasing temperature.[10] According to the Glazer notation, octahedral tilting in orthorhombic SRO is described by a À a À c þ , implying that RuO 6 octahedra are rotated in opposite directions by equivalent magnitude along [100] and [010] and in the same direction about [001]. [11,12] Tetragonal SRO is a one-tilt system, where RuO 6 octahedra are rotated only about the [001] direction (a 0 a 0 c À ). The tetragonal phase of SRO is stable within the very narrow temperature range from 547 to 677 8C and, finally, high-symmetry cubic perovskite (Pm3m) becomes stable above 677 8C.[10]Enormous strains exist in thin films when one material is deposited onto a substrate due to differences in crystal symmetry, lattice parameters, and thermal expansion coefficients between the film and the underlying substrate. [2,14] As a result, the properties of thin films can be differ widely from the intrinsic properties of the unstrained bulk counterparts. For example, recent experiments have shown strain-induced ferroelectricity in SrTiO 3 (STO) films at room temperature [15] and huge changes in the ferroelectric transition temperature in both BaTiO 3 . [16] Several groups have reported on the structural phase transition of SRO in thin-film form. The structural transition temperature of an epitaxial SRO thin film on (001) STO substrates, investigated using in situ transmission electron micro...