ppb level detection of NO<sub>2</sub> using a WO<sub>3</sub> thin film-based sensor: material optimization, device fabrication and packaging

Prajapati, Chandra Shekhar; Bhat, Navakanta

doi:10.1039/c7ra13659e

Cited by 40 publications

(35 citation statements)

References 56 publications

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“…Furthermore, the NO 2 interaction in the upper film layers had less impact on the total resistance change than if the same reaction would occur in the lower layers, where also electrode effects might play a role [69]. The observed optimum (1.9-3.1 μm, Figure 4) for these flame-made and highly porous films occurred at a significantly larger thickness than for sputtered WO3 films (i.e., 85 nm) [23]. For the latter, however, crystal size depended on film thickness due to nucleation and growth during deposition [70] that influenced sensitivity [71].…”

Section: Film Characterizationmentioning

confidence: 89%

“…Consequently, film thickness, porosity, pore size, and available surface area affect analyte's penetration depth and interaction probability and, thus, sensor sensitivity. In fact, for sputtered WO 3 films, the optimum NO 2 response has been reported at~85 nm thickness in the range of 40 to 200 nm [23]. Besides, the NO 2 sensitivity of WO 3 lamella stacks prepared by precipitation increase with porosity by adding hydrothermally-made SnO 2 nanoparticles as spacers [29], though, chemical sensitization by SnO 2 might also play a role.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, layer-by-layer inkjet printing has been used to obtain different thicknesses of Cu 2 O and CuO films for NO 2 sensing; however, the effect of film thickness on sensor sensitivity and selectivity was not investigated [30]. Changes in film morphology (e.g., thickness, porosity), however, are accompanied typically by process-related changes, for instance, altered crystal size (e.g., during sputtering [23]) or additives [29]. As a result, also the transducer function in the sensing nanoparticles may be altered, making it difficult to associate increasing sensor performance unambiguously to film thickness.…”

Section: Introductionmentioning

confidence: 99%

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Thickness Optimization of Highly Porous Flame-Aerosol Deposited WO3 Films for NO2 Sensing at ppb

et al. 2020

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Nitrogen dioxide (NO2) is a major air pollutant resulting in respiratory problems, from wheezing, coughing, to even asthma. Low-cost sensors based on WO3 nanoparticles are promising due to their distinct selectivity to detect NO2 at the ppb level. Here, we revealed that controlling the thickness of highly porous (97%) WO3 films between 0.5 and 12.3 μm altered the NO2 sensitivity by more than an order of magnitude. Therefore, films of WO3 nanoparticles (20 nm in diameter by N2 adsorption) with mixed γ- and ε-phase were deposited by single-step flame spray pyrolysis without affecting crystal size, phase composition, and film porosity. That way, sensitivity and selectivity effects were associated unambiguously to thickness, which was not possible yet with other sensor fabrication methods. At the optimum thickness (3.1 μm) and 125 °C, NO2 concentrations were detected down to 3 ppb at 50% relative humidity (RH), and outstanding NO2 selectivity to CO, methanol, ethanol, NH3 (all > 105), H2, CH4, acetone (all > 104), formaldehyde (>103), and H2S (835) was achieved. Such thickness-optimized and porous WO3 films have strong potential for integration into low-power devices for distributed NO2 air quality monitoring.

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Section: Film Characterizationmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thickness Optimization of Highly Porous Flame-Aerosol Deposited WO3 Films for NO2 Sensing at ppb

et al. 2020

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“…Semiconductor gas sensors were firstly commercialized as gas leak detectors in the 1960s [1], and additional studies have been carried out in order to detect various gases such as alcohol and volatile organic compounds (VOCs) [2][3][4]. The inhalation of even low concentration of NO 2 causes serious damage to the respiratory system [5][6][7]. Therefore, the United States Environmental Protection Agency (EPA) sets the regulatory value of 0.053 ppm NO 2 as an air quality standard [8].…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, the development of highly sensitive semiconductor NO 2 sensors has been expected all over the world. Among the various semiconducting metal oxides, SnO 2 [11][12][13], WO 3 [5,14,15], In 2 O 3 [16][17][18][19][20][21][22][23][24][25][26], and ZnO [27][28][29] are well known as semiconducting NO 2 -sensing materials. In addition, the structural modification of the sensing layer is one of important techniques in order to enhance the sensing properties.…”

Section: Introductionmentioning

confidence: 99%

Enhanced NO2-Sensing Properties of Au-Loaded Porous In2O3 Gas Sensors at Low Operating Temperatures

et al. 2020

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NO2-sensing properties of semiconductor gas sensors using porous In2O3 powders loaded with and without 0.5 wt% Au (Au/In2O3 and In2O3 sensors, respectively) were examined in wet air (70% relative humidity at 25 °C). In addition, the effects of Au loading on the increased NO2 response were discussed on the basis of NO2 adsorption/desorption properties on the oxide surface. The NO2 response of the Au/In2O3 sensor monotonically increased with a decrease in the operating temperature, and the Au/In2O3 sensor showed higher NO2 responses than those of the In2O3 sensor at a temperature of 100 °C or lower. In addition, the response time of the Au/In2O3 sensor was much shorter than that of the In2O3 sensor at 30 °C. The analysis based on the Freundlich adsorption mechanism suggested that the Au loading increased the adsorption strength of NO2 on the In2O3 surface. Moreover, the Au loading was also quite effective in decreasing the baseline resistance of the In2O3 sensor in wet air (i.e., increasing the number of free electrons in the In2O3), which resulted in an increase in the number of negatively charged NO2 species on the In2O3 surface. The Au/In2O3 sensor showed high response to the low concentration of NO2 (ratio of resistance in target gas to that in air: ca. 133 to 0.1 ppm) and excellent NO2 selectivity against CO and ethanol, especially at 100 °C.

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Optoelectronic Gas Sensing Platforms: From Metal Oxide Lambda Sensors to Nanophotonic Metamaterials

Perkins

Gholipour

2021

Advanced Photonics Research

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Gas sensing technology platforms have allowed for the improvement of crucial industrial processes and the decreased emissions of environmentally harmful gases that have led to deleterious outcomes. Industries where gas control has become critical are petrochemical, refinery, food and beverage, and power generation. These industries utilize gases such as ethylene, sulfur, carbon dioxide (CO 2 ), and oxygen (O 2 ) to produce gasoline, carbonated beverages, and electricity. [1] During various processes, harmful gases such as carbon monoxide (CO), CO 2 , sulfur dioxide (SO 2 ), and nitrogen dioxide (NO 2 ) and volatile organic compounds (VOCs) such as ethanol (C 2 H 5 OH), acetone (CH 3 COCH 3 ), toluene (C 7 H 8 ), and acetylene (C 2 H 2 ) can be emitted. [2][3][4][5][6] The emission of these environmentally toxic gases and VOCs from both industrial processes and automobiles has been linked to the nitrous oxides (NO x ), CO, and hydrocarbon emissions responsible for acid rain in the 1960s. Legislation was introduced to address and mitigate this acidic precipitation and the emission of environmentally toxic gasses by requiring the use of gas sensors and catalytic converters. [2] Gas sensing technology can be found in two leading commercial platforms: electronic (lambda sensors) and optical (nondispersive infrared (NDIR) sensors and optrodes). Lambda sensors are made with electrolytes or gas-sensitive films that exploit the ionic conductivity of electrolytes or the adsorption of gases and bonding of hydroxyl groups on metal oxide (MO) materials. State-of-the-art, automotive lambda sensors, also known as "automotive oxygen sensors," use a solid yttria-stabilized zirconia (YSZ) electrolyte in wideband sensor design geometries. The wideband sensor design was adapted from the early narrowband YSZ sensor design that utilized a simple Nernst cell. The wideband sensor design offers improved sensor linearity when compared to the narrowband designs across a wide range of air-to-fuel ratio values. Though the electrolytic lambda sensors' physical design has changed in previous years, the sensor has not seen an improvement in terms of electrolytic materials.Lambda sensors have also been based on gas-sensitive oxide films, instead of electrolytes, that employ the use of MO materials. MO materials include a wide range of oxidized transitional metals. These MOs undergo electronic changes when gases or VOCs are chemisorbed or bound to hydroxyl groups on the material's surface, thereby increasing or decreasing the MO's resistivity. The gas-material interaction only occurs at high temperatures, called the "activation temperatures," required by the MO.High activation temperatures are common in both electrolytic and MO gas sensors. Bringing the electrolytic and MO gas sensors to these high temperatures requires electronic heater elements. The reduction of the activation temperature of a lambda sensor can be achieved by using promoter materials and catalytic metals. Some material platforms, such as metal-organic frameworks (MOFs), are als...

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ppb level detection of NO₂ using a WO₃ thin film-based sensor: material optimization, device fabrication and packaging

Abstract: In this study, we have investigated the thickness-dependent nitrogen dioxide (NO2) sensing characteristics of a reactive-ion magnetron sputtered tungsten trioxide (WO3) film, followed by morphological and electrical characterizations.

Cited by 40 publications

References 56 publications

Thickness Optimization of Highly Porous Flame-Aerosol Deposited WO3 Films for NO2 Sensing at ppb

Thickness Optimization of Highly Porous Flame-Aerosol Deposited WO3 Films for NO2 Sensing at ppb

Enhanced NO2-Sensing Properties of Au-Loaded Porous In2O3 Gas Sensors at Low Operating Temperatures

Optoelectronic Gas Sensing Platforms: From Metal Oxide Lambda Sensors to Nanophotonic Metamaterials

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ppb level detection of NO2 using a WO3 thin film-based sensor: material optimization, device fabrication and packaging

Abstract: In this study, we have investigated the thickness-dependent nitrogen dioxide (NO2) sensing characteristics of a reactive-ion magnetron sputtered tungsten trioxide (WO3) film, followed by morphological and electrical characterizations.

Cited by 40 publications

References 56 publications

Thickness Optimization of Highly Porous Flame-Aerosol Deposited WO3 Films for NO2 Sensing at ppb

Thickness Optimization of Highly Porous Flame-Aerosol Deposited WO3 Films for NO2 Sensing at ppb

Enhanced NO2-Sensing Properties of Au-Loaded Porous In2O3 Gas Sensors at Low Operating Temperatures

Optoelectronic Gas Sensing Platforms: From Metal Oxide Lambda Sensors to Nanophotonic Metamaterials

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ppb level detection of NO₂ using a WO₃ thin film-based sensor: material optimization, device fabrication and packaging