Aerosol-Assisted CVD-Grown WO₃ Nanoneedles Decorated with Copper Oxide Nanoparticles for the Selective and Humidity-Resilient Detection of H₂S

Abstract

A gas-sensitive hybrid material consisting of Cu2O nanoparticle-decorated WO3 nanoneedles is successfully grown for the first time in a single step via aerosol-assisted chemical vapor deposition. Morphological, structural, and composition analyses show that our method is effective for growing single-crystalline, n-type WO3 nanoneedles decorated with p-type Cu2O nanoparticles at moderate temperatures (i.e., 380 °C), with cost effectiveness and short fabrication times, directly onto microhot plate transducer arrays with the view of obtaining gas sensors. The gas-sensing studies performed show that this hybrid nanomaterial has excellent sensitivity and selectivity to hydrogen sulfide (7-fold increase in response compared with that of pristine WO3 nanoneedles) and a low detection limit (below 300 ppb of H2S), together with unprecedented fast response times (2 s) and high immunity to changes in the background humidity. These superior properties arise because of the multiple p-n heterojunctions created at the nanoscale in our hybrid nanomaterial.

Smart control of chemical gas sensors for the reduction of their time response

“…The WO 3 nanoneedles functionalized with gold have been grown in a single step using localized aerosol-assisted chemical vapor deposition (AACVD), of tungsten hexacarbonyl (20 mg, W(CO) 6 , SigmaAldrich, ≥97%) with tetrachloroauric acid trihydrate ((1 mg, HAuCl 4 ·3H 2 O, SigmaAldrich, 99.9%). These active sensing layers were grown on top of silicon MEMS membranes that comprise a pair of interdigitated gold electrodes and an embedded polysilicon resistor that performs the function of sensor heater, [13,14]. The membrane has an area of 450×450 µm 2 and the interdigitated electrode gap is 50 µm.…”

Chemical Vapour Deposition of Gas Sensitive Metal Oxides

“…This relative value (i.e., Response/Concentration) was used as a quantitative factor to compare the sensitivity of the most common CVD-deposited tungsten oxide morphologies reported in the literature, although it is worth noting that strictly sensitivity is defined as the slope of the calibration curve (calibration curves were not available in most of the reports summarized in Table 1). It is apparent from Figure 2 that tungsten oxide has a notable sensitivity to NO 2 and this characteristic is generally observed for tungsten oxide making it a good candidate to selectively detect NO 2 in the presence of gases such as C 2 H 5 OH, CH 4 , CO, NH 3 , H 2 , C 6 H 6 and H 2 S [21,24]. Table 1 for each morphology/gas combination).…”

“…These materials are typically monoclinic or tetragonal phases with a variety of morphologies reported including films, particles and low dimensional structures, with the formation of nanostructures (NS) demonstrated below 600˝C for AACVD [15] and at 800˝C for hot filament CVD. The starting materials reported in the production of gas sensitive tungsten oxide include metallic W [16,17], WO 3 (powder, pellet) [18,19], WCl 6 [20], W(OCl 4 ) [21], W(CO) 6 [22][23][24] [20,21,26,27], silicon- [16,22,23,25] or polymer-based [28] gas sensing devices. The localized CVD of tungsten oxide nanostructures on Si-based microhotplates ( Figure 1) via heating provided from the sensor platform itself, rather than from the reactor chamber, has also been demonstrated as a viable method for the fabrication of gas sensors based on tungsten oxide [23], which provides interesting new possibilities for sensor processing.…”

Gas Sensing Approaches Based on WO3 Nanowire-Back Gated Devices

“…Gas sensors based on single crystalline metal oxide nanostructures (SMOx) offer many advantages in sensor performance such as high stability at typical operating temperatures, high surface to volume ratio, and tailored surface chemistry via functionalization [1][2][3]. At a given high operating temperature, the surface of the sensing material gives rise to high concentration of adsorbed oxygen species, which modulates the electron density at the surface and its electronic state.…”