Growth of WS2 Nanotubes Phases

The geometric structure of single-walled nanotubes

In this paper, we survey a number of existing geometric structures which have been proposed by the authors as possible models for various nanotubes. Atoms assemble into molecules following the laws of quantum mechanics, and in general computational approaches to predicting the molecular structure can be arduous and involve considerable computing time. Fortunately, nature favours minimum energy structures which tend to be either very symmetric or very unsymmetric, and which therefore can be analyzed from a geometrical perspective. The conventional rolled-up model of nanotubes completely ignores any effects due to curvature and the present authors have proposed a number of exact geometric models. Here we review a number of these recent developments relating to the geometry of nanotubes, including both the traditional rolled-up models and some exact polyhedral constructions. We review a number of formulae for four materials, carbon, silicon, boron and boron nitride, and we also include results for the case when the bond lengths may take on distinct values.

WS2 nanobuds as a new hybrid nanomaterial

We report on the first inorganic nanobuds: WS2 nanotubes decorated with fullerene-like particles. They were synthesized by sulfurization of W5O14 nanowires. The fullerene-like particles nucleate in surface corrugations of the nanowires and grow by a diffusion process simultaneously with the transformation of nanowires into hollow multiwall nanotubes. Electron microscopy data are correlated with details of the transformation process revealing the possible mechanism of the formation of these new complex nanomaterials.

Single-walled MoTe(2) nanotubes

The structural, electronic, and mechanical properties of single-walled MoTe(2) nanotubes are investigated using density functional theory. All large-diameter MoTe(2) nanotubes are found to be narrow-gap semiconductors, whereas small-diameter nanotubes are found to be less stable compared to large-diameter nanotubes. Notably, the armchair MoTe(2) nanotubes exhibit an indirect band gap, whereas the zigzag nanotubes exhibit a direct band gap. The band gap decreases with decreasing diameter of the tube or if the tube is under compression or elongation in the axial direction. Young's modulus of MoTe(2) nanotubes is calculated and is found to be dependent on the diameter and chirality of the tubes. The armchair nanotubes are stiffer than the zigzag nanotubes with the same diameter. Compared to the homologous MoTe(2) nanotubes, the MoTe(2) nanotubes are softer due to less strain-energy cost in forming the nanotube structures.

Facile Hydrogen Evolution Reaction on WO3Nanorods

Tungsten trioxide nanorods have been generated by the thermal decomposition (450 °C) of tetrabutylammonium decatungstate. The synthesized tungsten trioxide (WO₃) nanorods have been characterized by XRD, Raman, SEM, TEM, HRTEM and cyclic voltammetry. High resolution transmission electron microscopy and X-ray diffraction analysis showed that the synthesized WO₃nanorods are crystalline in nature with monoclinic structure. The electrochemical experiments showed that they constitute a better electrocatalytic system for hydrogen evolution reaction in acid medium compared to their bulk counterpart.

Novel Route to WOx Nanorods and WS2 Nanotubes from WS2 Inorganic Fullerenes

WO(x) (2 < x < 3) and WS(2) nanostructures have been widely praised due to applications as catalysts, solid lubricants, field emitters, and optical components. Many methods have been developed to fabricate these nanomaterials; however, most attention was focused on the same dimensional transformation from WO(x) nanoparticles or nanorods to WS(2) nanoparticles or nanotubes. In a solid-vapor reaction, by simply controlling the quantity of water vapor and reaction temperature, we have realized the transformation from quasi-zero-dimensional WS(2) nanoparticles to one-dimensional W(18)O(49) nanorods, and subsequent sulfuration reactions have further converted these W(18)O(49) nanorods into WS(2) nanotubes. The reaction temperature, quantity of water vapor, and pretreatment of the WS(2) nanoparticle precursors are important process parameters for long, thin, and homogeneous W(18)O(49) nanorods growth. The morphologies, crystal structures, and circling transformation mechanisms of sulfide-oxide-sulfide are discussed, and the photoluminescence properties of the resulting nanorods are investigated using a Xe lamp under an excitation of 270 nm.

Atmospheric Pressure Chemical Vapor Deposition: An Alternative Route to Large-Scale MoS2 and WS2 Inorganic Fullerene-like Nanostructures and Nanoflowers

Large-scale MoS2 and WS2 inorganic fullerene-like (IF) nanostructures (onionlike nanoparticles, nanotubes) and elegant three-dimensional nanoflowers (NF) have been selectively prepared through an atmospheric pressure chemical vapor deposition (APCVD) process with the reaction of chlorides and sulfur. The morphologies were controlled by adjusting the deposition position, the deposition temperature, and the flux of the carrier gas. All of the nanostructures have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A reaction mechanism is proposed based on the experimental results. The surface area of MoS2 IF nanoparticles and the field-emission effect of as-prepared WS2 nanoflowers is reported.

FUNCTIONAL OXIDE NANOBELTS: Materials, Properties and Potential Applications in Nanosystems and Biotechnology

Nanobelt is a quasi-one-dimensional structurally controlled nanomaterial that has well-defined chemical composition, crystallographic structure, and surfaces (e.g., growth direction, top/bottom surface, and side surfaces). This article reviews the nanobelt family of functional oxides, including ZnO, SnO2, In2O3, Ga2O3, CdO, and PbO2 and the relevant hierarchical and complex nanorods and nanowires that have been synthesized by a solid-vapor process. The nanobelts are single crystalline and dislocation free, and their surfaces are atomically flat. The oxides are semiconductors that have been used for fabrication of nanosize functional devices of key importance for nanosystems and biotechnology, such as field-effect transistors, gas sensors, nanoresonators, and nanocantilevers. The structurally controlled ZnO nanobelts that exhibit piezoelectric properties are also reviewed. By controlling growth kinetics, we show the success of growing nanobelt-based novel structures whose surfaces are dominated by the polarized +-(0001) facets. Owing to the positive and negative ionic charges on the zinc- and oxygen-terminated +-(0001) surfaces, respectively, a spontaneous polarization is induced across the nanobelt thickness. As a result, helical nanostructures and nanorings are formed by rolling up single-crystal nanobelts; this phenomenon is a consequence of minimizing the total energy contributed by spontaneous polarization and elasticity. The polar surface-dominated ZnO nanobelts are likely to be an ideal system for understanding piezoelectricity and polarization-induced ferroelectricity at nano-scale and they could have applications as one-dimensional nano-scale sensors, transducers, and resonators.

Synthesis and optical properties of colloidal tungsten oxide nanorods

Thermal decomposition of W(CO)6 in oleylamine in the presence of mild oxidant Me3NO.2H2O produces tungsten oxide nanorods with diameters ranging from 3 to 6 nm. The size of nanorods can be easily varied by the employed surfactant ratio or reaction temperature. The prepared tungsten oxide nanorods exhibit strong photoluminescence (PL) peaks in 300-500 nm, which show a weak size dependency.

Large-scale synthesis of tungsten oxide nanowires with high aspect ratio

Through the controlled removal of surfactant from the presynthesized mesolamellar precursor (WO-L) at elevated temperature, tungsten oxide nanowires with diameters ranging from 10 to 50 nm and lengths up to several micrometers were obtained on a large scale. The structure, morphology, and composition of the nanowires were characterized by the XRD, TEM, HRTEM, EDX, and Raman spectra.

Growth and structure evolution of novel tin oxide diskettes

The novel SnO diskettes have been synthesized by evaporating either SnO or SnO(2) powders at elevated temperature. Disregard the source material being SnO or SnO(2), the SnO diskettes are formed at a low-temperature region of 200-400 degrees C. Two types of diskette shapes have been identified: the solid-wheel shape with a drop center rim (type I) and the diskette with cone peak(s) and spiral steps (type II). The diskettes are determined to be tetragonal SnO structure (P4/nmm), with their flat surfaces being (001). The formation of the SnO diskettes is suggested to result from a solidification process. The structural evolution from SnO diskettes to SnO(2) diskettes has been investigated by oxidizing at different temperatures. The result shows that the phase transformation from SnO to SnO(2) occurs in two processes of decomposition and oxidization, and the decomposition process consists of two steps: first from SnO to Sn(3)O(4) and then from Sn(3)O(4) to SnO(2).