Detection of H2S, SO2, and NO2 using electrostatic sprayed tungsten oxide films

doi:10.1016/j.mssp.2010.01.001

Materials Science in Semiconductor Processing

Volume 13, Issue 1, February 2010, Pages 1-8

https://doi.org/10.1016/j.mssp.2010.01.001 Get rights and content

Abstract

This paper presents the electrostatic spray deposition of tungsten oxide (WO₃) films for the detection of different pollutant gases. The influence of several types of precursors on the structure and morphology of the films was studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. This preliminary study allowed to select the proper precursor for the preparation of pure and porous WO₃ films which offer high gas response (R_air/R_gas=1200) to low concentrations of H₂S (10 ppm) at low operating temperature (200 °C). The gas response to NO₂ and SO₂ is low at this temperature suggesting no possible interference with these two gases during the H₂S detection. Furthermore, the films are able to detect very low concentrations of NO₂ (less than 1 ppm) at 150 °C.

Introduction

Due to its negative impacts on the health and on the environment a great attention has been paid to the air pollution caused by different pollutant gases released from industrial processes and vehicles. Usually, conventional techniques like chromatography or electrochemistry are used to detect and monitor these gases. To overcome their disadvantages in terms of high price, large volume and time consuming, semiconductor metal oxide gas sensors can be employed.

The tungsten trioxide gas sensor was first reported by Shaver [1], who observed the modification of the WO₃ film resistance upon hydrogen exposure. Over the time, WO₃ proved to be an attractive material for gas sensor applications, mainly used for the detection of NO₂ [2], [3], [4] but also employed for the detection of other gases, such as H₂S [5], SO₂ [6], O₂ [7], etc.

Teoh et al. [8] prepared mesoporous WO₃ films which showed very high gas response at low concentration of NO₂ and at low operating temperature. The authors suggested that WO₃ excellent sensing properties are due to its high surface area which allows high quantities of gas to be adsorbed. Tamaki et al. [9] found a correlation between NO₂ gas response and the thickness of the WO₃ films and that of the electrodes: when the film thickness is higher than the electrode one, the gas response improves with the film thickness decrease. Furthermore, when the film thickness is lower than the substrate one, the gas response proved to be independent of the film thickness. The influence of the annealing atmosphere on the WO₃ gas response has been studied by Lozzi et al. [10]. They showed that the vacuum treated films have a lower gas response to NO₂ comparing with those annealed in air. Hence, the decrease in the gas response was explained by the decrease in the film oxygen concentration.

The film substrate can have an influence on the gas response as showed by Lee et al. [11]. The authors found that the substrates with high degree of surface roughness induce the formation of highly porous films with small particle size, increasing in this way the gas response. Several authors have improved the gas sensor properties by doping with different kinds of metals or metal oxides. The most employed dopant to increase the WO₃ gas response to NO₂ is TiO₂, and, this improvement is usually correlated with the inhibition of the WO₃ grain growth during the doping process [12], [13].

Concerning the H₂S detection, Barrett et al. [14] was one of the first authors who investigated the gas response of WO₃ to H₂S. Solis et al. [5] detected H₂S with a very high gas response (four orders of magnitude) at room temperature and this remarkable performance was related to the formation of tetragonal WO₃ phase. The inconvenience of these sensors was the resistance recovery obtained only by applying a heat treatment at 250 °C. Noble metals as activator layers or dopants were also used to improve the gas response to H₂S. Tao et al. [15] have chosen Pt as an activator layer to improve the gas response to H₂S and the selectivity to other reducing gases like CH₄, CO, and H₂. Stankova et al. [16] studied the influence of the electrode geometry on the WO₃ gas response to H₂S. It was found that smaller the gap between the electrodes is, higher the sensor gas response is. Hoel et al. [17] have detected H₂S at room temperature using Al doped WO₃ films. The films proved to detect H₂S, NO₂ and CO at different operating temperatures (i.e., 400, 525, and 700 K). The use of a sensor array operating at different temperatures was proposed to improve the selectivity.

It is obvious that various methods have been used to improve the gas response of WO₃, including especially the modification of the morphology and the microstructure (i.e., grain size, film thickness, phase) by using different deposition techniques [18], [19], [20], [21], by doping with different compounds [12], [13], [22], [23] or by modifying the sensor geometry [16], [24].

Until now, the deposition of WO₃ films has been done by several techniques as chemical vapour deposition [25], sol–gel [2], [26], sputtering [18], [27], and spray pyrolysis [19], [20]. In this work the electrostatic spray deposition technique is selected for the preparation of WO₃ films considering that it allows an easy control of the morphology and the composition of the films. Firstly, the influence of the precursor solution on the structure and the morphology of the films are presented. Secondly, the performance of WO₃ films in the detection of different pollutant gases (H₂S, SO₂, and NO₂) is evaluated as a function of the operating temperature, and also as a function of the gas concentration.

Section snippets

Sensor fabrication

For the fabrication of the sensors, alumina pellets (99.7%, Gimex Technische Keramiek B.V., The Netherlands), with a dimension of 10×20 mm² and a thickness of 1 mm were used. Platinum electrodes (1–5 μm in thickness) were applied by coating a platinum paste (Engelhard Clal, model 6082A) followed by a thermal treatment at 800 °C for 2 h in air. A distance of 1 mm was maintained between the two electrodes. Then the WO₃ sensing film was deposited on this Pt-coated alumina substrate using a stainless

Gas-sensing measurements

The experimental set-up used to evaluate the WO₃ gas sensing performances is described in Fig. 1. The films were placed in a closed quartz tube furnace where the measurements were carried out at different operating temperatures (50–300 °C). The temperature was measured using a K type thermocouple (placed close to the sensor) which was controlled by a PID temperature regulator (JUMO dTRON 16.1). The resistance of the films was measured with an electrometer (KEITHLEY 6514) by using Pt wires and

Structure and morphology characterization

The relevant parameters influencing the sensor performance are mainly connected with their morphology and their microstructure. The porous structure is preferable because it enhances the adsorption of the gas molecules improving in this way the gas response. In the same way, the small particle size also plays a very important role for a gas response improvement. Hence, tailoring these parameters is of great interest.

The structure of the films prepared using different types of precursors has

Conclusions

In this paper it is demonstrated that a simple and cost-effective deposition technique, i.e., electrostatic spray deposition can be used for the fabrication of WO₃ sensors which are able to detect different pollutant gases. The films are obtained with different types of precursors and the most convenient one (tungsten ethoxide) has been selected for the fabrication of good quality films in terms of microstructure and morphology.

The films are able to detect very small quantities of NO₂ (less

References (53)

M. Blo et al.
Synthesis of pure and loaded powders of WO₃ for NO₂ detection through thick film technology
Sensors Actuators B
(2004)
X. He et al.
NO₂ sensing characteristics of WO₃ thin film microgas sensor
Sensors Actuators B
(2003)
J.L. Solis et al.
Nanocrystalline tungsten oxide thick-film with high sensitivity to H₂S at room temperature
Sensors Actuators B
(2001)
Y. Shimizu et al.
Improvement of SO₂ sensing properties of WO₃ by noble metal loading
Sensors Actuators B
(2001)
H. Nakagawa et al.
A room-temperature operated hydrogen leak sensor
Sensors Actuators B
(2003)
L.G. Teoh et al.
Sensitivity properties of a novel NO₂ gas sensor based on mesoporous WO₃ thin film
Sensors Actuators B
(2003)
J. Tamaki et al.
Detection of dilute nitrogen dioxide and thickness effect of tungsten oxide thin films sensors
Sensors Actuators B
(2003)
L. Lozzi et al.
The influence of air and vacuum thermal treatments on the NO₂ gas sensitivity of WO₃ thin films prepared by thermal evaporation
Thin Solid Films
(2001)
D.-S. Lee et al.
Effect of substrate on NO₂-sensing properties of WO₃ thin film gas sensors
Thin Solid Films
(2000)
D.-S. Lee et al.
The TiO₂-adding effects in WO₃-based NO₂ sensors prepared by coprecipitation and precipitation method
Sensors Actuators B
(2000)

K. Nishio et al.

Electrochromic thin films prepared by sol–gel process

Sol Energy Mater Sol Cells

(2001)

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