A Novel Heteronanostructure System: Hierarchical W Nanothorn Arrays on WO₃ Nanowhiskers

Abstract

The assembly of 1D nanostructures in the fabrication of nanoelectronic and nanophotonic devices is currently attracting significant attention. In particular, semiconductor and metal nanowires or nanorods are considered to be important building blocks in the fabrication of future nanodevices. Various types of nanowire heterostructures have been reported, including core/shell [1] and core/multishell nanocable structures, [2] coaxial nanowire heterojunctions, [3] epitaxial nanorod heterostructures, [4] and hierarchical heterostructures.[ [5g]Nanorods of transition metal oxides, such as WO 3, which have large surface areas and a high-aspect-ratio structure, are promising candidates for a vast range of applications including gas sensors, [6] photocatalysts, [7] electrochromic devices, [8] field-emission devices, [9] and solar-energy devices.[10] Because of the distinctive and promising properties of WO 3 , as-synthesized nanorods may also serve as functional building blocks in the fabrication of 3D nanostructures or multifunctional heteronanostructures. Recently Zhou et al. demonstrated the 3D growth of WO 3 nanowire networks using a thermal evaporation method.[11]W is a metal with a fairly low resistivity and a near-ideal midgap work function, and can be produced with a high refractivity through high-temperature processes. W can be used in metal gates in applications of complementary metal oxide semiconductor (CMOS) technology in nanodevices smaller than 100 nm.[12] W materials can be produced with various dimensions; 1D W nanowires have been found in particular to have useful electrical properties, such as efficient field-electron emission in a moderate electric field.[13] Although 1Dnanostructures of W and WO 3 have been studied extensively, few studies of W/WO 3 heteronanostructures have been reported.In this communication, we report the fabrication of a novel hierarchical heteronanostructure: single-crystal W nanothorns grown on WO 3 nanowhiskers (hereafter these heteronanostructures will be referred to as WWOs). In this WWO nanostructure, the WO 3 nanowhiskers were coated with thin W layers and W nanothorns grew on them. We used a two-step evaporation process to fabricate the hierarchical WWOs.In the first step, WO 3 nanowhiskers were deposited on a W plate by heating WO 3 powder at 1100°C on the substrate. Then, a mixture of WO 3 and graphite powder was used as the source material for the growth of the W nanothorns on the asprepared WO 3 nanowhiskers. Si powder was also heated with the substrate at 1100°C. We used the carbothermal reduction of WO 3 (WO 3 + C → WO x + CO 3-x ; x = 1-2) [14] and were able to expedite the further reduction of WO x species by using Si (WO x + Si → W + SiO x ) to produce W vapor. It is well known that W can be grown by Si reduction of W compounds.[15] The resulting W vapor was deposited on the WO 3 nanowhiskers to produce the WWO heteronanostructure. Our method for growing W nanomaterials is different to that used in previous studies: the thermal-heating of W films was the previ...

ZnS nanostructures: From synthesis to applications

“…For a given material, it has been demonstrated that the field-emission performance, including emission current, field-enhancement factor, etc., can be enhanced through increasing its aspect ratio (length to thickness ratio), assembling it into arrays, or decorating its surface with a lower work function materialunder keeping a low turn-on field [360][361][362][363]. For example, Ye and co-workers proposed two alternative approaches to enhance FE performance of standard ZnO nanorods with a diameter of $150 nm: The first one is to decrease the tip radius of ZnO nanorods by controlling the growth processes, and the second one is to lower the work function of ZnO by modifying it with metal particles (such as Pt and Ag nanoparticles) with a lower work function.…”

Hierarchical WO3 Hollow Shells: Dendrite, Sphere, Dumbbell, and Their Photocatalytic Properties

“…[11][12][13] Nanostructured tungsten oxide (WO 3 ) is of great interest due to its broad range of applications, such as in gas sensors, photocatalysts, electrochromic devices, field-emission devices, and solar-energy devices. [14][15][16][17][18] Much effort has been made to synthesize tungsten oxide nanostructures [19][20][21][22][23][24] (nanowires, nanotubes, nanobelts, nanoplatelets, hollow shperes and mesoporous). However, these nanostructures are usually obtained under high temperature, long reaction time and/or on special substrates, it is still challenging to organize WO 3 nanoscaled building blocks into well-defined 2D and 3D nanostructures under mild experimental conditions.…”

Field-Emission Performance of Wormhole-Like Mesoporous Tungsten Oxide Nanowires

“…The wormhole-like mesoporous tungsten oxide nanowires of 20 nm diameter also exhibit an extremely low threshold field (for an emission current density of 10 mA/cm 2 ) of 1.75 V/lm. These turn-on fields of wormhole-like mesoporous tungsten oxide nanowires are lower than those reported for a carbon film (7 V/lm), 17 needle-shaped SiC nanorods (5 V/lm), 5 as-synthesized b-SiC nanoneedles (1.8 V/lm), 7 single-crystal W nanothorns grown on WO 3 nanowhiskers (6.2 V/lm), 18 and W 18 O 49 nanowires (2.6 V/lm), 9 demonstrating that the prepared sample of wormhole-like mesoporous tungsten oxide nanowires is an excellent field emitter.…”