A Catalyzed-Growth Route to Directly Form Micropatterned WO₂ and WO₃ Nanowire Arrays with Excellent Field Emission Behaviors at Low Temperature

Abstract

By adjusting the type of catalysts, the controlled growth of micropatterned WO 2 and WO 3 nanowire arrays has been first accomplished at low temperature (450-600 °C). The as-prepared WO 2 and WO 3 nanowires are proven to be single crystalline structures with a single phase by Raman and transmission electron microscopy (TEM) techniques. Their formation mechanisms are attributed to the vapor-liquid-solid (VLS) mechanism. It is found that both micropatterned WO 2 and WO 3 nanowire arrays have very excellent field emission (FE) properties with quite low turn-on field (1.36 V/μm) and threshold field (2.38 V/μm), which is very similar to carbon nanotubes (CNTs) with best FE behaviors. In addition, the physical properties of an individual WO 2 and individual WO 3 nanowire are compared to probe the determinant factor for their different FE behaviors and understand their FE mechanism. Their very excellent FE performance suggests that this novel growth method is a useful technique for low-temperature preparation of micropatterned nanoemitter cathode arrays.

Highly conductive vertically aligned molybdenum nanowalls and their field emission property

“…Taking the average values of a height of 3.5 μm, width of 1 μm, thickness of 50 nm, and R equal to 35.49 and 36 Ω, we can obtain the conductivity of a single molybdenum nanowall: ${\sigma }_{\text{forward}}=1.97\times {10}^4{\Omega }^{-1}{\text{cm}}^{-1};\text{and}{\sigma }_{\text{reverse}}=1.94\times {10}^4{\Omega }^{-1}{\text{cm}}^{-1}$. Table 3 lists the calculated conductivities of molybdenum nanowall samples grown on different substrates, showing that these values, ranging from 0.88 × 10 4 Ω −1 cm −1 to 5.23 × 10 4 Ω −1 cm −1 , are usually about one to four orders of magnitude higher than those of other reported nanostructures [6,26,28,31-34]. We should like to note that most of the conductivity values of the Mo nanowall on different substrates are about an order of magnitude less than the value of the molybdenum bulk material (approximately 19.46 × 10 4 Ω −1 cm −1 ) [35].…”

Temperature and acidity effects on WO3 nanostructures and gas-sensing properties of WO3 nanoplates

“…However, so far, no reference has been found concerning the effects of both hydrothermal temperature and the amount of acid on crystal phases and morphologies of WO 3 nanostructures. WO 3 nanostructures could be extensively applied in electrochromic and photochromic devices [6,[17][18][19][20], lithium ion batteries [21][22], photoelectrodes [23], photocatalysts [24][25][26], solar energy devices [27][28], field electron emission [29][30] and gas sensors [1,10,13,14,16,[31][32][33][34][35][36][37][38][39][40][41][42] etc. Being one of the important gas-sensor materials, more and more WO 3 nanomaterials with new structures or morphologies have been synthesized because the gas-sensing properties could be tuned by the structures and morphologies of the materials.…”

Growth mechanism of planar or nanorod structured tungsten oxide thin films deposited via aerosol assisted chemical vapour deposition (AACVD)

“…In general, deposition of thin films usually proceeds via nucleation and growth stages which include three modes: Frank van-der-Merwe (FM) (layer-by-layer), Stranski-Krastanov (SK) (layer plus island) and VolmerWeber (VM) (island) [16]. For synthesis of 1D tungsten oxide NR structures, both vapour-solid (VS) and vapourliquid-solid (VLS) growth mechanisms have been reported [17,18]. Recently, a planar defect driven growth mechanism was proposed in which oxygen defects parallel to the NR growth direction [010] compress the growth direction along the [100] and [001] directions resulting in anisotropic growth [19].…”