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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 study, indium oxide nanowires of high-density were synthesized by chemical vapor deposition (CVD) through a vapor–liquid–solid (VLS) mechanism without carrier gas. The indium oxide nanowires possess great morphology with an aspect ratio of over 400 and an average diameter of 50 nm; the length of the nanowires could be over 30 μm, confirmed by field-emission scanning electron microscopy (SEM). Characterization was conducted with X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence spectrum (PL). High-resolution TEM studies confirm that the grown nanowires were single crystalline c-In2O3 nanowires of body-centered cubic structures. The room temperature PL spectrum shows a strong peak around 2.22 eV, originating from the defects in the crystal structure. The electrical resistivity of a single indium oxide nanowire was measured to be 1.0 × 10−4 Ω⋅cm, relatively low as compared with previous works, which may result from the abundant oxygen vacancies in the nanowires, acting as unintentional doping. [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]

In this study, an efficient method to synthesize CuO-CuS core-shell nanowires by two-step annealing process was reported. CuO nanowires were prepared on copper foil via thermal oxidation in a three-zone horizontal tube furnace. To obtain larger surface area for photocatalytic applications, we varied four processing parameters, finding that growth at 550 °C for 3 h with 16 °C/min of the ramping rate under air condition led to CuO nanowires of appropriate aspect ratio and number density. The second step, sulfurization process, was conducted to synthesize CuO-CuS core-shell nanowires by annealing with sulfur powder at 250 °C for 30 min under lower pressure. High-resolution transmission electron microscopy studies show that a 10 nm thick CuS shell formed and the growth mechanism of the nanowire heterostructure has been proposed. With BET, the surface area was measured to be 135.24 m2·g−1. The photocatalytic properties were evaluated by the degradation of methylene blue (MB) under visible light irradiation. As we compared CuO-CuS core-shell nanowires with CuO nanowires, the 4-hour degradation rate was enhanced from 67% to 89%. This could be attributed to more effective separation of photoinduced electron and hole pairs in the CuO-CuS heterostructure. The results demonstrated CuO-CuS core-shell nanowires as a promising photocatalyst for dye degradation in polluted water. [ABSTRACT FROM AUTHOR]

In this paper, we report the synthesis of iron silicide and β-iron disilicide nanowires with chemical vapor deposition; remarkably, the latter has drawn much attention but has seldom been achieved. We also propose the formation mechanisms for the two phases. To investigate the effects of the growth parameters on compositions and morphologies of the iron silicide nanowires, we changed and studied the reaction time, substrate temperature, position of samples, and pressure. The reaction concentration was found to be altered by all of the parameters; thus, we observed different nanowires in terms of morphologies and compositions with scanning electron microscopy. To confirm the growth direction and crystal structure of the nanowires, we conducted x-ray diffraction and high-resolution transmission electron microscopy studies. With the potential of being utilized as circuit elements in electronic devices for Schottky barriers, ohmic contacts, and interconnection among silicon-based transistors, the silicide work at nanoscale is beneficial for nanoelectronics. Understanding the effects of these growth parameters facilitates the control of nanowire growth with better quality. [ABSTRACT FROM AUTHOR]

Two-dimensional antimonene has attracted much attention because of its excellent stability and remarkable physical properties. Understanding the growth mechanism of antimonene by investigating processing parameters and structural properties is necessary for developing reliable fabrication methods. In this study, NaCl-assisted van der Waals epitaxy, one of the methods for scale-up fabrication, is employed to achieve atomic layer antimonene with high coverage rate. Furthermore, high-resolution images of atomic structure are presented with the powerful transmission electron microscopy, helping us confirm the exact configuration of antimonene. Meanwhile, we studied the effect of electron beam irradiation on antimonene; it was found that the stacking structure of antimonene would change under electron beam irradiation, and the moiré patterns of twisted few-layered antimonene were also observed. These results provide comprehensive study of growth mechanisms and in-depth knowledge of antimonene nanostructure, which are expected to facilitate the development of controllable fabrication for future device applications. The different reaction pathways induced by electron beam irradiation with the in situ TEM imaging of the evolution of the microstructure of antimonene: knock-on effects and formation of Moiré patterns. [Display omitted] [ABSTRACT FROM AUTHOR]

Manipulation of electron beam irradiation using TEM determines the selective region with a particular size and depth to conduct the subsequent process for nanopore formation. • Recording the effect of e-beam irradiation on Mo 5 O 14 nanowires by in situ TEM. • Manipulating e-beam to define the anticipated region and the size of nanoporosity. • Atom removal and crystallinity degradation resulting in structural transformation. • The formation of nanopores due to the numerous broken bonds in crystalline Mo 5 O 14. • Revealing the mechanism of selective nanopore formation in nanoscale modification. The Mo 5 O 14 -type structure is representative of the MoO-based catalyst in the selective oxidation process. Single-crystalline Mo 5 O 14 nanowires can be synthesized in a controlled manner by chemical vapor deposition (CVD). A nanowire catalyst with a porous structure combines the advantages of both nanoparticles and nanowires, leading to a substantial increase in the specific surface area. Therefore, we aim to manipulate the e-beam irradiation process on Mo 5 O 14 nanowires to induce the nanoporous structures in selected regions. In situ transmission electron microscopy (TEM) enabled us to visualize the structural transformation through gradual e-beam irradiation. The e-beam irradiation process removes oxygen atoms and renders the internal structure unstable. After the irradiated region is exposed to air, atoms tend to escape to decrease the internal energy. This results in the formation of nanopores because of the irradiation effect. By nanoscale modification method, the irradiated region is controlled by the electron beam size, which determines the nanopore distribution in the selected region. The study is beneficial for increasing the surface area of Mo 5 O 14 -type catalysts with variable nanopore densities and for modifying nanomaterials using a convenient method. [ABSTRACT FROM AUTHOR]

The atomic scale Silicidation of Ni-Si System by In-situ TEM Investigation could be divide into three steps. At the first step (250 °C), Ni would diffuse into Si substrate to synthesize triangular Ni 2 Si. Afterwards, continuous NiSi thin films would be synthesized at 400 °C. At last, trapezoid NiSi would react with Si to form NiSi 2 at third step (600 °C). Furthermore, the electric electrical properties of Ni-Si system were identified by four-point probe measurements; the resistivities of NiSi, Ni 2 Si and NiSi 2 were 14.13 µΩ∙cm, 22.80 µΩ∙cm and 37.77 µΩ∙cm, respectively. • The diffusion behaviour of Ni-Si system was investigated through in situ HRTEM. • Ni 2 Si and NiSi were diffusion controlled and NiSi 2 was nucleation controlled. • The resistivities of NiSi, Ni 2 Si and NiSi 2 were 14.1, 22.8, and 37.7 µΩ∙cm, respectively. • The diffusion rate could be calculated by in-situ TEM observation. • This work provides a novel method to obtain low resistivity silicide for IC devices. Nickel silicide has many advantages, such as low resistivity and low formation temperature; therefore, it has been widely used in the fields of solar cells, transistors and complementary metal-oxidesemiconductor (CMOS) devices. To obtain high-quality nickel-silicide thin film, solid-state reaction is a convenient and efficient fabrication method. For better understanding of the dynamic formation mechanism, we used in-situ transmission electron microscopy (TEM) to record the diffusion behavior during the heating process. In this work, three-steps annealing process to synthesize different nickel silicides corresponding to the various formation temperatures were investigated systematically. At 250 °C, the product of the first-step annealing was inverted-triangle Ni 2 Si, embedded in the Si substrate. Then, well-distributed NiSi thin film was synthesized, having the lowest resistivity among Ni-Si system at 400 °C. Finally, NiSi 2 , a Si-rich product, would form during the third-step annealing at 600 °C. NiSi 2 product and Si substrate have small lattice mismatch; thus, the epitaxial relationship would be observed. We provide the evidence of diffusion behaviors and structural identification of Ni-Si system. Furthermore, these results are beneficial for the formation of specific nickel silicides, which is expected to optimize the fabrication of microelectronics. [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]