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One-dimensional polycrystallineTa2O5nanostructures are synthesized by the annealing of theSiO2nanowires at 950°C in a reductive Ta vapor ambiance. The formation mechanism ofTa2O5nanostructures is discussed and illustrated in detail. The nucleation and grain growth ofTa2O5crystals were investigated during the formation of theSiO2/Ta2O5core-shelled structures. The diffusion-controlled growth is suggested to be the rate-determining step for the diffusion of the Ta atoms through the ash layer to react with O atoms and substitute Si atoms.

Coaxial metal-oxide-semiconductor (MOS) Au-Ga2O3-GaN heterostructure nanowires were successfully fabricated by an in situ two-step process. The Au-Ga2O3 core-shell nanowires were first synthesized by the reaction of Ga powder, a mediated Au thin layer, and a SiO2 substrate at 800 degrees C. Subsequently, these core-shell nanowires were nitridized in ambient ammonia to form a GaN coating layer at 600 degrees C. The GaN shell is a single crystal, an atomic flat interface between the oxide and semiconductor that ensures that the high quality of the MOS device is achieved. These novel 1D nitride-based MOS nanowires may have promise as building blocks to the future nitride-based vertical nanodevices.

1-D tungsten oxide nanowires exhibiting distinctive electrochromic, gaschromic properties; in this study, we demonstrate an innovative way to fabricate the tungsten oxide nanowires on silicon substrate. The suggested growth mechanism is Vapor-Solid (VS) growth, while, the nitrogen-doping tungsten oxide nanowires were fabricated via the ammonia decomposition during the formation process. Their nano-devices were successful fabricated and the variety devices characteristics were reported.

Half-metallic materials, such as CrO2, La0.7Sr0.3MnO3 (LSMO), and Fe3O4 are highly attractive for spintronics applications because of their high spin polarization. Among these materials, magnetite (Fe3O4) is superior to others because of its high Curie temperature (Tc) of 858 K, which is crucial for thermal stability in device applications. In addition, magnetite has proven to be a ferromagnetic material with a high spin polarization (ca. 100 %) at the Fermi level, which results in a metallic minority spin channel and a semiconductor majority spin channel. Besides the utilization of spin electronics, magnetite can also be used as catalyst and in tunneling magnetoresistance (TMR) and giant magnetoresistive (GMR) devices. Previously, various studies in electron transport and magnetoresistance (MR) of magnetite have mainly focused on 2D structures, such as epitaxial thin films, polycrystalline films, and nanoclusters. Recently, the electronic characteristics of 1D magnetite nanostructures have received much attention because of their unique electron-transport behaviors, which may be different from those of the bulk. In addition, low-dimensional Fe3O4 nanoparticles are particularly promising in biomedical applications, such as drug transport/delivery, cell separation and imaging, and therapeutic in vivo technologies. In this study, a simple vapor–solid growth method was applied to grow a-Fe2O3 NWs in an oxygen-deficient environment; magnetite NWs were then formed by converting the vertically aligned a-Fe2O3 NWs template in a reductive atmosphere. An extensive investigation on the mechanism of transforming a-Fe2O3 NWs to Fe3O4 NWs has been published elsewhere. Electrical measurements were performed by fabricating nanodevices in which the NWs were laid on top of the designed Si chips. The Verwey temperature-transition phenomenon was observed in low-temperature measurements of the nanodevices. The magnetic behavior of the NWs was investigated by superconducting quantum interference device (SQUID) measurements. In addition, a magnetic flux map was acquired by electron holography, which revealed the magnetic microstructure of the 1D magnetite nanowires. Figure 1A and B shows a top-view morphology image of a-Fe2O3 and Fe3O4 NWs, respectively. After the reduction process, the morphology of the Fe3O4 NWs was very similar to that of the a-Fe2O3 template. Figure 1C shows a transmission electron microscopy (TEM) image of the magnetite NWs; the high-resolution TEM (HRTEM) image of the modulated a-Fe2O3 NW due to the oxygen deficiency and the magnetite diffraction pattern (DP) are shown in the insets of the image. The HRTEM image in Figure 1D reveals the single-crystalline structure of the NWs, without linear or planar defects. The two d-spacings of 0.29 nm were identified as Fe3O4 {022} planes. The diffraction pattern, shown in the inset in Figure 1D, also illustrates the single-crystal nature of the NWs at the [111] zone axis. Figure 2A shows a scanning electron microscopy (SEM) image of the nanodevices; an enlarged image of one of the devices in Figure 2A is shown in Figure 2B. The two-point I–V measurements were performed at room temperature in a LabView controlled measurement system under ambient conditions. The linear I–V curves (shown in Fig. 2C) indicate that the characteristics fit well to Ohm’s law. The zero-field resistivities of the nanodevices were estimated by the following equation: R = qL/A (R: resistance, q: resistivity, A: cross-section area, L: NW length). The diameter and length of the measured NWs were 25 nm and 0.7526 lm, respectively. Assuming that the Fe3O4 NWs were of a circular cross-section, the obtained resistivity was 10.30 X cm; approximately three orders of magnitude larger than that of bulk magnetite crystal (19 000 lX cm). The large measured difference between the NWs and the single crystal may be due to contact resistance and surface scattering, resulting from the high surface ratio. However, the surface-scattering mechanism, based on the Fuchs–Sonderheimer (FS) theory, indicates that the aspect ratio is an important factor to the total resistance of nanostructures. According to FS theory, when surface scattering is the dominant mechanism the resistivity of a nanowire deC O M M U N IC A TI O N

Very dense and uniformly distributed nitrogen-doped tungsten oxide (WO(3)) nanowires were synthesized successfully on a 4-inch Si(100) wafer at low temperature. The nanowires were of lengths extending up to 5 mum and diameters ranging from 25 to 35 nm. The highest aspect ratio was estimated to be about 200. An emission peak at 470 nm was found by photoluminescence measurement at room temperature. The suggested growth mechanism of the nanowires is vapor-solid growth, in which gaseous ammonia plays a significant role to reduce the formation temperature. The approach has proved to be a reliable way to produce nitrogen-doped WO(3) nanowires on Si in large quantities. The direct fabrication of WO(3)-based nanodevices on Si has been demonstrated.

Functional 1D metal oxides have attracted much attention because of their unique applications in electronic, optoelectronic, and spintronic devices. For semiconducting oxide nanowires (NWs) (e.g., ZnO, In2O3, and SnO2 NWs), field-effect transistors and light-emitting diodes have been demonstrated. Metallic oxide nanoscale materials, such as nanoscale RuO2, can be good candidates as interconnects in electronic applications. RuO2 nanomaterials have been produced by chemical vapor deposition (CVD) and through chemical reaction. Recently, RuO2 NWs have been synthesized using pure Ru as metal target under different flux ratios of O2/Ar in a reactive sputtering system. [5]

Low-temperature synthesis of GaN nanowires is successfully achieved by silica-enhanced processes. GaN nanowires were synthesized by reaction of metal gallium vapor with ammonia and hydrogen gases at the temperature of 700 °C on the amorphous SiO2 substrate. From scanning electron microscopy images, the morphologies of GaN nanowires are wirelike with a length up to 5μm and the average diameter of GaN nanowires measured by transmission electron microscopy (TEM) is about 25 nm. The x-ray diffraction analysis of as-synthesized products indicates that the nanowires have the hexagonal wurtzite structure of GaN crystal. The corresponding electron diffraction pattern also indicates that the as-synthesized GaN nanowires exhibited a single-crystal feature with uniform oxygen doping characterized by electron energy loss spectroscopy. The compositional line profile of TEM analysis reveals that GaN nanowires are terminated by Au nanoparticles, which infer an evidence that the vapor-liquid-solid model is the major grow...

CuOx nanowires were synthesized by a low-cost and large-scale electrochemical process with AAO membranes at room temperature and its resistive switching has been demonstrated. The switching characteristic exhibits forming-free and low electric-field switching operation due to coexistence of significant amount of defects and Cu nanocrystals in the partially oxidized nanowires. The detailed resistive switching characteristics of CuOx nanowire systems have been investigated and possible switching mechanisms are systematically proposed based on the microstructural and chemical analysis via transmission electron microscopy.

One-dimensional metal oxide nanomaterials have attracted much attention due to their semiconducting behavior and applications in nanodevices such as gas sensors, photoA field-effect transistors (FETs), and light-emitting diodes. [1] The control of electrons and holes, that is, n- or ptype nature, inside the functional metal oxide is of vital importance in the application of nanodevices. In general, ntype metal oxide nanomaterials are easily formed due to oxygen deficiencies (vacancies), which result in a donor level below but close to the conduction band. By contrast, p-type behavior is hard to achieve except in cases where the material is naturally p type. The common way to form the p type is through diffusion during the growth process or implantation into an as-grown sample, followed by post-annealing at high temperatures in order to eliminate defects. [2] By contrast, by using a reductive ambient, the direct transition between the n and p types of a metal oxide can be A through a change of dominant carriers on the surface, namely, those of electrons or holes. This n–p switch was first found in Cr2O3 under a treatment of ethanol vapor. [3] In addition, the n–p switch was found in other functional metal oxides, such as SnO2, MoO3, and In2O3, under certain kinds of reductive ambient. [4] However, the details of the n–p transition are still under investigation.

An approach to investigate the electric field distribution and field-emission property of a single crystal tungsten oxide (WO3) nanowire by electron holography technique is presented, which solves the problems encountered in the traditional reconstruction of the holograms, the so-called perturbed reference wave. We proposed this unique method to meticulously illustrate the status of the surroundings of a single crystal nanowire under biased conditions. This paves the way to precisely quantifying the electric and magnetic field distributions for nanostructures as well as nanodevices.

GaN nanowires were synthesized by reaction of metal gallium vapor with ammonia and hydrogen gases at the temperature of 700 °C on the amorphous SiO2 substrate. The morphologies of GaN nanowires are wirelike with a length up to 5 μm and the average diameter of GaN nanowires measured by transmission electron microscopy (TEM) is about 25 nm. The x-ray diffraction analysis of as-synthesized products indicates that the nanowires have the hexagonal wurtzite structure of GaN crystal. The corresponding electron diffraction pattern also indicates that the as-synthesized GaN nanowires exhibited a single-crystal feature with uniform oxygen doping characterized by electron energy loss spectroscopy.