na powder (P172SB, PØchiney) with a specific area of 10.2 m 2 g ±1 , a refractive index of 1.70, and a mean diameter of 0.5 lm. A dispersant (phosphoric ester) is also used to decrease the viscosity and to increase the stability of the suspension. The final mixture is prepared with 80 wt.-% (50 vol.-%) of alumina, dispersant (1.5 wt.-% with respect to alumina) and photoinitiator (5.56 wt.-% with respect to the monomer) mixed in a ball mill for 20 min at 350 rpm.The scraper is based on a 10 mm long scalpel. It is moved at a speed of 1.2 mm s ±1, which corresponds to a shear rate varying from 60 to 24 s ±1 , depending on the layer thickness (from 20 to 50 lm, respectively).The debinding step consists of several heating steps. First, the sample is heated to 120 C (degradation temperature of the polymer) at 60 C h ±1. A slower second temperature gradient of 6 C h ±1 is applied up to 500 C and the temperature is maintained for 30 min. The quick heating of the sintering step is applied by increasing the temperature at 900 C h ±1 to 1550 C. The object to be sintered is kept at this temperature for 5 h, and is then cooled to ambient temperature. Detection of CO and O 2 Using Tin Oxide Nanowire Sensors** By Andrei Kolmakov, Youxiang Zhang, Guosheng Cheng, and Martin Moskovits* Solid-state gas sensors play a major role in semiconductor processing, medical diagnosis, environmental sensing, personal safety, and national security, with economic impact in agriculture, medicine, and in the automotive and aerospace industries.[1±3] Most sensors operate on the basis of the modification of the electrical properties of an active element, normally a metal oxide film, brought about by the adsorption of an analyte on the surface of the sensor. A current major goal in gas sensing is massive parallelism, wherein many sensors, each with its unique chemical properties, are operated together and their outputs processed simultaneously, perhaps using learning strategies like neural networks, so that the overall device operates ªintelligentlyº, mimicking, for example, the complex operation of a mammalian nose and its corresponding brain function. [4] This task implies the need for further miniaturization of the active elements with the simultaneous sensitivity increase to compensate for surface area loss. Here, conventional thin film technology faces its fundamental limits. Promising strategies for achieving the above goal of using many sensing elements restricted to a small volume will likely come out of nanoscience and technology and, specifically, out of a subset of technologies amenable to parallelism and array fabrication that do not sacrifice sensitivity and selectivity. This challenge necessitates several design features to be achieved simultaneously, including the development of new materials, innovation in structure and architecture, and the development of highly sensitive, responsive, and selective, yet ultra-small active elements arranged so as to minimize inter-element cross-talk. [5,6] The high surface-to-volume ratio of nano...

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This letter discusses Mg incorporation in GaN nanowires with diameters ϳ35 nm, fabricated by vapor-liquid-solid synthesis in p-type nanowires. Turning on the Mg doping halfway through the synthesis produced nanowires with p-n junctions that showed excellent rectification properties down to 2.6 K. The nanowires are shown to possess good-quality, crystalline, hexagonal GaN inner cores surrounded by an amorphous GaN outer layer. Most wires grow such that the crystalline c axis is normal to the long axis of the nanowire. The temperature dependence of the current-voltage characteristics is consistent with electron tunneling through a voltage-dependent barrier.

An easily generalizable method is reported for converting metal nanowires topotactically to their stoichiometric oxides. Because many such metal oxides are the active semiconductor elements in sensors, this method is potentially useful in preparing nanowire-based sensor elements. The process is illustrated by converting Sn nanowires fabricated electrochemically in porous alumina templates to SnO2 in a manner that preserves the wire's nanostructure. The kinetically controlled oxidation process, which is initially fed by molten tin at the nanowire's core, gives rise to a number of distinct, coaxial core−shell metastable phases. The process can easily be extended to fabricate free-standing arrays of parallel metal oxide nanowires with possible sensor and optoelectronic applications that are structurally compatible with planar technologies.

Among the Li-rich layered oxides LiMnO has significant theoretical capacity as a cathode material for Li-ion batteries. Pristine LiMnO generally has to be electrochemically activated in the first charge-discharge cycle which causes very low Coulombic efficiency and thus deteriorates its electrochemical properties. In this work, we show that low-temperature reduction can produce a large amount of structural defects such as oxygen vacancies, stacking faults, and orthorhombic LiMnO in LiMnO. The Rietveld refinement analysis shows that, after a reduction reaction with stearic acid at 340 °C for 8 h, pristine LiMnO changes into a LiMnO-LiMnO (0.71/0.29) composite, and the monoclinic LiMnO changes from LiMnO in the pristine LiMnO (P-LiMnO) to LiMnO in the reduced LiMnO (R-LiMnO), indicating the production of a large amount of oxygen vacancies in the R-LiMnO. High-resolution transmission electron microscope images show that a high density of stacking faults is also introduced by the low-temperature reduction. When measured as a cathode material for Li-ion batteries, R-LiMnO shows much better electrochemical properties than P-LiMnO. For example, when charged-discharged galvanostatically at 20 mA·g in a voltage window of 2.0-4.8 V, R-LiMnO has Coulombic efficiency of 77.1% in the first charge-discharge cycle, with discharge capacities of 213.8 and 200.5 mA·h·g in the 20th and 30th cycles, respectively. In contrast, under the same charge-discharge conditions, P-LiMnO has Coulombic efficiency of 33.6% in the first charge-discharge cycle, with small discharge capacities of 80.5 and 69.8 mA·h·g in the 20th and 30th cycles, respectively. These materials characterizations, and electrochemical measurements show that low-temperature reduction is one of the effective ways to enhance the performances of LiMnO as a cathode material for Li-ion batteries.