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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]

In this work, we report a novel and efficient silicidation method to synthesize higher manganese silicide (HMS) nanowires with interesting characterization and physical properties. High density silicon nanowire arrays fabricated by chemical etching reacted with MnCl2 precursor through a unique double tube chemical vapor deposition (CVD) system, where we could enhance the vapor pressure of the precursor and provide stable Mn vapor with a sealing effect. It is crucial that the method enables the efficient formation of high quality higher manganese silicide nanowires without a change in morphology and aspect ratio during the process. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize the HMS nanowires. High-resolution TEM studies confirm that the HMS nanowires were single crystalline Mn27Si47 nanowires of Nowotny Chimney Ladder crystal structures. Magnetic property measurements show that the Mn27Si47 nanowire arrays were ferromagnetic at room temperature with a Curie temperature of over 300 K, highly depending on the relationship between the direction of the applied electric field and the axial direction of the standing nanowire arrays. Field emission measurements indicate that the 20 μm long nanowires possessed a field enhancement factor of 3307. The excellent physical properties of the HMS nanowires (NWs) make them attractive choices for applications in spintronic devices and field emitters. [ABSTRACT FROM AUTHOR]

Abstract Transition metal silicide nanowires exhibit low resistivity, great thermal stability and excellent mechanical strength, contributing to their applications as interconnection and contact materials for future integrated circuits devices. In this work, we successfully fabricated two kinds of chromium silicide/silicon heterostructure nanowires through solid state reactions — bare Si/Cr 3 Si nanowires and Si/Cr 5 Si 3 -Al 2 O 3 core-shell nanowires. The growth behaviors and diffusion mechanisms of the two silicide heterostructure nanowires were investigated with in-situ TEM at 700 °C. During the growth of chromium silicide nanowires, unique amorphous Si phase would form first in front of silicide nanowires. Also, we found that oxide-shell could control the diffusion process in silicon nanowires. With oxide-shell, compression stress would restrain the growth of chromium silicide in the radial direction but accelerate its growth rate in the axial direction. Additionally, Al 2 O 3 shell reduced the radial expansion of chromium silicide nanowires and hindered Cr-rich phases with Cr 5 Si 3 appearing as the first phase. The crystal structures of the nanowires have been identified to be single-crystalline A15 and D8m type structure of the intrinsic Cr 3 Si nanowires and Cr 5 Si 3 nanowires, respectively. In addition to fundamental science, the significant study is beneficial for future processing techniques in nanotechnology and related applications. Graphical abstract With in-situ transmission electron microscopy (TEM), we successfully transformed single crystalline Si nanowires to chromium silicide/Si nanowire heterostructures. Also, during the solid state phase transformation process, we observed unique structures at the interface, demonstrated to be amorphous Si phase after Si Si bond breaking, which led the chromium silicide nanowire growth by interface-reaction control. Unlabelled Image Highlights • We utilized solid state reactions to fabricate controllable and unique Cr 3 Si/Si and Cr 5 Si/Si nanowire heterostructures. • With in-situ transmission electron microscopy (TEM), we observed a special interfacial reaction during the silicidation. • The design of Si-Al 2 O 3 core-shell effectively improved the morphology and crystallinity of the nanowire heterostructures. • We used distinctive methods and results to systematically investigate the kinetics of the nanowire heterostructures. [ABSTRACT FROM AUTHOR]