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Investigation of the carbon monoxide gas sensing characteristics of tin oxide mixed cerium oxide thin films.

Durrani SM, Al-Kuhaili MF, Bakhtiari IA, Haider MB - Sensors (Basel) (2012)

Bottom Line: The films were investigated for the detection of carbon monoxide, and were found to be highly sensitive.We found that 430 °C was the optimum operating temperature for sensing CO gas at concentrations as low as 5 ppm.Our sensors exhibited fast response and recovery times of 26 s and 30 s, respectively.

View Article: PubMed Central - PubMed

Affiliation: Physics Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia. smayub@kfupm.edu.sa

ABSTRACT
Thin films of tin oxide mixed cerium oxide were grown on unheated substrates by physical vapor deposition. The films were annealed in air at 500 °C for two hours, and were characterized using X-ray photoelectron spectroscopy, atomic force microscopy and optical spectrophotometry. X-ray photoelectron spectroscopy and atomic force microscopy results reveal that the films were highly porous and porosity of our films was found to be in the range of 11.6-21.7%. The films were investigated for the detection of carbon monoxide, and were found to be highly sensitive. We found that 430 °C was the optimum operating temperature for sensing CO gas at concentrations as low as 5 ppm. Our sensors exhibited fast response and recovery times of 26 s and 30 s, respectively.

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Normal-incidence transmittance (T) and reflectance (R) spectra of a deposited film of thickness 220 nm.
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f4-sensors-12-02598: Normal-incidence transmittance (T) and reflectance (R) spectra of a deposited film of thickness 220 nm.

Mentions: The normal-incidence reflectance and transmittance spectra, in the wavelength range λ = 250 – 850 nm, are shown in Figure 4. The transmittance spectra are obtained by dividing the measured transmittance by that of a fused silica substrate. The optical properties of the films can be used to estimate their porosity. The columnar microstructure of the films indicates the presence of voids within the films, which results in the films being porous. These voids (pores) may be filled with moisture (water) or air. The average packing density (p) is defined as the volume occupied by the solid part divided by the total volume occupied by the solid and voids. In the transparent region (λ > 500 nm), the refractive index of a film (nf) can be estimated from the minima in the transmittance spectra. The relation between the refractive index of the film (nf) and the packing density is given by [18]:(1)nf2=(1−p)nv4+(1+p)nv2 ns2(1+p)nv2+(1−p)ns2where ns is the bulk refractive index of the solid material, and nv is the refractive index of the voids (nv = 1.33 if the voids are filled with water or 1.0 if they are filled with air). The refractive index of the mixture film (nf = 2.012) was obtained from the minimum in the transmittance (at λ = 572 nm) using the equation for the transmittance of a thin film on a transparent substrate [19]. The bulk refractive index of CeO2 and SnO2 is 2.5 and 2.0 respectively [20,21]. The bulk refractive index of CeO2 and SnO2 along with the XPS results were used to calculated the bulk refractive index of the mixture and found to be 2.305. Using these values in Equation (1), the packing density of the mixture was found to be 0.783 (for water-filled pores) or 0.884 (for air-filled pores). The porosity (P) is defined as: P = 1 – p. Thus, the porosity was in the range 11.6–21.7%. While porosity for pure CeO2 [8] reported earlier was 32%.


Investigation of the carbon monoxide gas sensing characteristics of tin oxide mixed cerium oxide thin films.

Durrani SM, Al-Kuhaili MF, Bakhtiari IA, Haider MB - Sensors (Basel) (2012)

Normal-incidence transmittance (T) and reflectance (R) spectra of a deposited film of thickness 220 nm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3376601&req=5

f4-sensors-12-02598: Normal-incidence transmittance (T) and reflectance (R) spectra of a deposited film of thickness 220 nm.
Mentions: The normal-incidence reflectance and transmittance spectra, in the wavelength range λ = 250 – 850 nm, are shown in Figure 4. The transmittance spectra are obtained by dividing the measured transmittance by that of a fused silica substrate. The optical properties of the films can be used to estimate their porosity. The columnar microstructure of the films indicates the presence of voids within the films, which results in the films being porous. These voids (pores) may be filled with moisture (water) or air. The average packing density (p) is defined as the volume occupied by the solid part divided by the total volume occupied by the solid and voids. In the transparent region (λ > 500 nm), the refractive index of a film (nf) can be estimated from the minima in the transmittance spectra. The relation between the refractive index of the film (nf) and the packing density is given by [18]:(1)nf2=(1−p)nv4+(1+p)nv2 ns2(1+p)nv2+(1−p)ns2where ns is the bulk refractive index of the solid material, and nv is the refractive index of the voids (nv = 1.33 if the voids are filled with water or 1.0 if they are filled with air). The refractive index of the mixture film (nf = 2.012) was obtained from the minimum in the transmittance (at λ = 572 nm) using the equation for the transmittance of a thin film on a transparent substrate [19]. The bulk refractive index of CeO2 and SnO2 is 2.5 and 2.0 respectively [20,21]. The bulk refractive index of CeO2 and SnO2 along with the XPS results were used to calculated the bulk refractive index of the mixture and found to be 2.305. Using these values in Equation (1), the packing density of the mixture was found to be 0.783 (for water-filled pores) or 0.884 (for air-filled pores). The porosity (P) is defined as: P = 1 – p. Thus, the porosity was in the range 11.6–21.7%. While porosity for pure CeO2 [8] reported earlier was 32%.

Bottom Line: The films were investigated for the detection of carbon monoxide, and were found to be highly sensitive.We found that 430 °C was the optimum operating temperature for sensing CO gas at concentrations as low as 5 ppm.Our sensors exhibited fast response and recovery times of 26 s and 30 s, respectively.

View Article: PubMed Central - PubMed

Affiliation: Physics Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia. smayub@kfupm.edu.sa

ABSTRACT
Thin films of tin oxide mixed cerium oxide were grown on unheated substrates by physical vapor deposition. The films were annealed in air at 500 °C for two hours, and were characterized using X-ray photoelectron spectroscopy, atomic force microscopy and optical spectrophotometry. X-ray photoelectron spectroscopy and atomic force microscopy results reveal that the films were highly porous and porosity of our films was found to be in the range of 11.6-21.7%. The films were investigated for the detection of carbon monoxide, and were found to be highly sensitive. We found that 430 °C was the optimum operating temperature for sensing CO gas at concentrations as low as 5 ppm. Our sensors exhibited fast response and recovery times of 26 s and 30 s, respectively.

Show MeSH