WO3 thin film sensor prepared by sol–gel technique and its low-temperature sensing properties to trimethylamine

FABRICATION AND CHARACTERIZATION OF Fe-DOPED TUNGSTEN TRIOXIDE PHOTOELECTRODES IN AQUEOUS MEDIUM USING TUNGSTIC ACID AND FERROCENE AS STARTING MATERIALS

“…The band gap of the thin films was estimated by plotting (-InT) 1/2 against energy (hν) for undoped and Fe-doped WO 3 thin films, assuming the materials are indirect semiconductors. The band gap of the undoped WO 3 is 2.74 eV and it is in agreement with previous studies [22][23][24][25][26]. Meanwhile, the band gap of the doped thin films was decreased to 2.60 eV as the concentration of Fe increased up to 20%.…”

“…In order to reduce the band gap, WO 3 was synthesized via different methods [18][19][20][21]. The narrow band gap of 2.20 -2.80 eV helps in absorption of ultraviolet region and blue region of visible light in solar spectrum [22][23][24][25]. Furthermore, WO 3 has been investigated with the aim of improving catalyst activity and stability in the irradiated aqueous environment [26][27][28][29].…”

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.…”

“…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. As with other metal oxides, tungsten oxide deposited via CVD has been used in resistive mode, with demonstrated sensitivity to NO 2 [16,21,26], N 2 O [17], C 2 H 5 OH [20,27], CO [23,25], NH 3 [18], H 2 [22], humidity [19] and aromatic compounds such as benzene [29] and toluene [30] (Table 1). The relative sensor response (R) to ppm concentrations (C) of CO, C 2 H 5 OH and NO 2 (Table 1) are plotted in Figure 2.…”