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Tungsten oxide has drawn widespread attention due to its outstanding physical properties; however, the use of high temperature, low pressure, and expensive catalysts has been challenging in the synthesis of tungsten oxide nanowires. In this study, we developed a single step thermal evaporation process without any catalyst to synthesize WO3−x nanowires on silicon substrates and indium tin oxide glass substrate safely and economically. We utilized the Taguchi method to design experiments for the synthesis of tungsten oxide nanowires and analyze the effect of processing parameters. The growth mechanism of nanowires is proposed to be a vapor–solid mechanism. Confirmed to be oxygen-vacancy-rich WO3−x nanowires through high-resolution transmission electron microscopy studies, the nanowires have a great morphology with a high aspect ratio of around 700. The electrical resistivity of a single WO3−x nanowire at 300 K was measured to be 2.32 × 10−5 Ω M, which is relatively low due to rich oxygen vacancies. We synthesized WO3−x nanowires on an indium tin oxide glass substrate and assembled electrochromic devices with LiClO4/PC as the electrolyte. The devices were demonstrated to have fast coloring and bleaching rates of less than one second at low voltage; at high voltage, the color of the devices could change to a deeper color but take more than 2 seconds to react. Compared with previous works, the electrochromic devices from this study exhibit superior response time and stability. These significant results make WO3−x nanowires promising materials for applications in semiconductors, nanodevices, display and green technology. [ABSTRACT FROM AUTHOR]

Single-crystalline iron silicide nanowires were synthesized via an original approach, pre-deposition method (PDM), with significantly improved morphologies and physical characteristics as compared with those fabricated by conventional chemical vapor deposition. In the pre-deposition method, combining rapid thermal annealing (RTA) and chemical vapor deposition (CVD), iron silicide nanowires grew from the heterogeneous nucleation sites on the surface of the thin film without a catalyst or Al2O3 template. The morphology of the nanowires has been considerably improved in terms of alignment and aspect ratio. HRTEM analysis confirms that the nanowires were β-FeSi2 with a crystal direction of [111]. Physical property measurements indicate that compared with CVD β-FeSi2 nanowires, β-FeSi2 nanowires synthesized by the PDM performed better in both the field emission and magnetic properties. Magnetic property measurements show that the coercive field of PDM nanowires increased from 249 Oe to 900 Oe. Field emission studies reveal that the average β value of the CVD β-FeSi2 nanowires was 1060, while that of the PDM nanowires became 1892. Notably, with a furnace, few researchers can successfully synthesize nanowires of β-FeSi2, which is one of the most fascinating silicides for its important applications. [ABSTRACT FROM AUTHOR]

High quality single-crystalline NiSi2, Ni2Si and Ni31Si12 nanowire arrays coated with amorphous silicon dioxide were synthesized in high quantity by a nickel transport chemical vapor deposition (CVD) method. The morphological changes with various reaction temperatures, ambient pressures and reaction times, were observed and studied. At 750 °C and 850 °C, cone-shaped nanowire arrays were formed, composed of dense and oriented Ni31Si12 and Ni2Si nanowires with lengths of over 60 μm. The growth mechanisms of the nickel silicide nanowires have been proposed and identified with microscopy studies. Field emission measurements show that the as-grown NiSi2, Ni2Si and Ni31Si12 nanowires were of remarkable field enhancement factors, 2532, 4822 and 4099, respectively, and magnetic property measurements show ferromagnetic characteristics for the Ni2Si and Ni31Si12 nanowires, demonstrating promising potential applications for field emitters, magnetic storage, and biological cell separation. [ABSTRACT FROM AUTHOR]