High Sensitivity Semiconductor NO[sub 2] Gas Sensor Based on Mesoporous WO[sub 3] Thin Film

Teoh, Lay Gaik; Hung, I‐Ming; Shieh, Jiann; Wei, Lai; Hon, Min–Hsiung

doi:10.1149/1.1585252

Cited by 67 publications

(44 citation statements)

References 20 publications

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“…The most important factors that influence the tungsten oxide sensor characteristics are microstructure and surface area. Mesoporous tungsten oxide with porous structure and higher surface area means more surface adsorption sites available to react with the NO 2 gas, inducing a lower operating temperature and a higher sensitivity of the sensor as reported by Teoh et al [26]. However, the tungsten oxide also has a good sensitivity for NO gas as reported in this paper.…”

Section: Gas-sensing Measurement For Mesoporous Tungsten Oxidesupporting

confidence: 61%

Effect of copolymer and additive concentrations on the behaviors of mesoporous tungsten oxide

Wei¹,

Shieh²,

Teoh³

et al. 2005

Journal of Alloys and Compounds

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Section: Gas-sensing Measurement For Mesoporous Tungsten Oxidesupporting

confidence: 61%

Effect of copolymer and additive concentrations on the behaviors of mesoporous tungsten oxide

Wei¹,

Shieh²,

Teoh³

et al. 2005

Journal of Alloys and Compounds

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“…[1][2][3][4] Thus, various methods used to fabricate WO 3 are reported, such as evaporation, [5][6][7] spray pyrolysis, 8 pulsed layer deposition 9,10 and electrodeposition. 11,12 However, the electrochemical anodization method adopted in this work provides a simple and economic way of synthesizing targeted morphologies such as nanoporous or nanotube structures.…”

mentioning

confidence: 99%

Electrochromic Enhancement of WO₃-TiO₂Composite Films Produced by Electrochemical Anodization

Gui

Blackwood

2014

J. Electrochem. Soc.

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An enhancement of the electrochromic properties of WO 3 thin films by the incorporation of TiO 2 is presented. The composite films are obtained by anodizing co-sputtered tungsten / titanium on conductive glass substrates in 1 M H 2 SO 4 solution containing 0.3 wt% NaF. As the titanium content is increased from 0 to 15 at.% a morphology evolution occurs, from nano-porous to nano-flakes and finally to nano-blocks interweaved with nano-pores. The nano-flakes, obtained at 10 at% Ti, proved to be the most conducive structure for the insertion and removal of Li + ions such that this composition exhibits transmittance regulation abilities of 58.5%, 72% and 77.7% at 550 nm, 632.8 nm and 800 nm respectively, which are more than a 25% improvement at all wavelengths over a pure WO 3 film formed in the same way. The WO 3 /TiO 2 film with addition of 10 at.% Ti also has faster coloration/bleaching times, especially in the critical near infrared region with values of 10 s / 64 s at 800 nm compared with 32 s / 90 s of a pure WO 3 thin film, as well as improved stability losing less than 5% of its capacity after 1000 switching cycles. and electrodeposition. 11,12 However, the electrochemical anodization method adopted in this work provides a simple and economic way of synthesizing targeted morphologies such as nanoporous or nanotube structures. Unfortunately there are still drawbacks when compared to vacuum deposited films, for instance the electrochemically prepared WO 3 has poorer reversibility and stability as well as a shorter optical modulation range. This has led to interest in mixed metal oxide composite systems to compensate for these eficiencies. [13][14][15][16][17][18][19] To date, there are many reports on the doping or mixing other oxides with WO 3 to improve its electrochromic properties, with oxides of barium, 20 cobalt, 21 nickel, 22 molybdenum 23 and most successfully titanium.24 Even a small quantity of the guest oxide has a profound effect on the host's optical properties. Hashimoto and Matsuoka first reported in 1991 that an amorphous WO 3 -TiO 2 film, produced by electron beam deposition method, exhibits a longer life-time than a pure tungsten oxide film. 24 Subsequently, in 1993, Gottsche et al. 25 compared the electrochromic properties of mixed WO 3 -TiO 2 thin films fabricated by sputtering and sol-gel techniques. These authors point out that the addition of TiO 2 with molar percentages ranging from 10% to 15% reduced the crystallinity of WO 3 host and led to significant structural changes. Later, Wang and Hu successfully composed a TiO 2 -doped WO 3 film by spin coating and found that the Ti-addition stabilized the peroxotungstic acid in the spin coating solutions. 26 In 2005, Patil et al. 27 prepared WO 3 -TiO 2 films via a spray pyrolysis method and discussed the improved electrochromic reversibility and coloration efficiency.However, in these earlier works the coloration efficiency has not improved significantly to the level where it can be used in a practical smart window. Indeed, in some cases cert...

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“…According to a report by Teoh et al 29 higher symmetry may result from static disorder, which can be ascribed to the presence of clusters of edge-sharing octahedral randomly distributed in the lattice. Indeed, the tendency to form edge-sharing octahedral is found in oxygen deficient tungsten oxides phase and the titanium substitution for tungsten will induce the same effect of oxygen substoichiometry.…”

Section: Resultsmentioning

confidence: 99%

Honey-Comb Structured WO₃/TiO₂Thin Films with Improved Electrochromic Properties

Gui

Blackwood

2015

J. Electrochem. Soc.

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The electrochromic properties of 90:10 WO 3 /TiO 2 thin films produced by anodizing co-sputtered W/Ti films in a fluorinated ethylene glycol solution are investigated in relation to corresponding pure WO 3 films. SEM images revealed that the TiO 2 content resulted in a more open honey-comb structure that increased the charge accommodation ability by 250%. The superior charge storage property of the WO 3 /TiO 2 meant that it had a better light modulation range, with transmittance of <1% at 800 nm in the colored state. The electrochromic kinetic processes associated with coloration and bleaching are also much faster in the presence of TiO 2 , with data generated by electrochemical impedance spectroscopy revealing that this is due to a reduction in the resistance to the insertion of Li + ions. Materials characterization techniques revealed that the WO 3 /TiO 2 composite maintains the monoclinic structure of the WO 3 and that the Ti atoms are substituted into the WO 3 matrix, rather than forming discrete 8 This especially important in the tropics where air-conditioning usage is high, in part due to architects making extensive use of aesthetically pleasing glass.However, unless the WO 3 is made via expensive high vacuum techniques, some of its properties, such electrochromic reversibility, stability or optical modulation, fall short of those required for a practical smart window. Since these drawbacks have proven difficult to overcome in a pure WO 3 system there have been a number of attempts to solve them by doping or mixing with other electrochromic materials, usually another transition metal oxide. [9][10][11][12][13][14][15][16] In 2005, Patil et al.17 investigated the effect of TiO 2 additions on the electrochromic properties of tungsten trioxide films prepared through spray pyrolysis, finding improved electrochromic reversibility, but not any real enhancement of the coloration efficiency. 17One possible way to improve electrochromic efficiency is to tailor the morphology of the oxide to have spacious channels that can aid charge/ion injection into and transport within the film.18-20 One approach to achieve this is by electrochemical anodization. In 2009 Zheng et al., 7 successfully formed a macro-porous WO 3 thin film by anodizing pure tungsten, which had been deposited onto conductive fluorine doped tin oxide (FTO) glass by a magnetron sputtering method, in NH 4 F aqueous electrolyte. This success provides and broadens the application of electrochromic WO 3 thin films on "Smart Windows" where the transparent substrate is essential. However, these authors only focused on the fabrication of WO 3 thin film with macro-porous structure on FTO glass, giving neither details nor further exploration of the electrochromic properties.Besides efforts have been directed at improving electrochromic properties by producing mixed transition metal oxide films, most notably WO 3 /TiO 2 , by techniques such as electron beam deposition, sputtering, hydrothermal and the sol-gel method. 17,[21][22][23] Although the synthesized film...

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High Sensitivity Semiconductor NO[sub 2] Gas Sensor Based on Mesoporous WO[sub 3] Thin Film

Cited by 67 publications

References 20 publications

Effect of copolymer and additive concentrations on the behaviors of mesoporous tungsten oxide

Effect of copolymer and additive concentrations on the behaviors of mesoporous tungsten oxide

Electrochromic Enhancement of WO₃-TiO₂Composite Films Produced by Electrochemical Anodization

Honey-Comb Structured WO₃/TiO₂Thin Films with Improved Electrochromic Properties

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High Sensitivity Semiconductor NO[sub 2] Gas Sensor Based on Mesoporous WO[sub 3] Thin Film

Cited by 67 publications

References 20 publications

Effect of copolymer and additive concentrations on the behaviors of mesoporous tungsten oxide

Effect of copolymer and additive concentrations on the behaviors of mesoporous tungsten oxide

Electrochromic Enhancement of WO3-TiO2Composite Films Produced by Electrochemical Anodization

Honey-Comb Structured WO3/TiO2Thin Films with Improved Electrochromic Properties

Contact Info

Product

Resources

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Electrochromic Enhancement of WO₃-TiO₂Composite Films Produced by Electrochemical Anodization

Honey-Comb Structured WO₃/TiO₂Thin Films with Improved Electrochromic Properties