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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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Experimental setup for sensitivity measurements.
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f1-sensors-12-02598: Experimental setup for sensitivity measurements.

Mentions: Thin films of SnO2 mixed CeO2 were prepared by co-evaporation using physical vapor deposition. For this purpose CeO2 was evaporated by e-beam while SnO2 was evaporated by thermal evaporation simultaneously. Ratios of the two materials were controlled by quartz crystal monitor. The evaporation rates of CeO2 and SnO2 were fixed at 3.2 Ǻ/s and 0.8 Ǻ/s respectively (75% CeO2 and 25% SnO2), with the total rate of 4 Ǻ/s. The films were prepared in a Leybold L560 box coater pumped by a turbomolecular pump. The system was initially pumped to a base pressure of 1 × 10−4 Pa. Before deposition, the materials were slowly outgassed, with a shutter blocking the vapors from reaching the substrate. The films were deposited on unheated substrates. The substrates were rotating during the deposition, and the source-to-substrate distance was 40 cm. The evaporation rates and thickness of the films were controlled by a quartz crystal thickness monitor. For different purposes of film characterization, the films were simultaneously deposited on tantalum substrates (for X-ray photoelectron spectroscopy, XPS), fused silica substrates (for optical measurements), and alumina substrates (for gas sensing measurements). After the films were deposited, they were removed from the coating chamber and exposed to the ambient atmosphere. Subsequently, all samples were annealed in air at 500 °C for two hours in order to thermally stabilize the films prior to sensing measurements. XPS was performed using a VG Scientific MKII spectrometer with an Al Kα (1,486.6 eV) X-ray source. The instrumental resolution was 1.2 eV, with a slit width of 0.6 cm. Prior to the XPS analysis; the samples were transferred in air to the XPS analysis chamber. The C 1s peak of hydrocarbon contamination, at a binding energy of 284.5 eV, was used as an energy reference. During the XPS analysis, the samples were maintained at ambient temperature at a pressure of 5 × 10−7 Pa. Normal-incidence transmittance and reflectance, over the wavelength range 300–1,200 nm, were measured using a Jasco V-570 double beam spectrophotometer. The thicknesses of the annealed films were measured using a surface profilometer (AMBIOS XP-2), and was found to be 220 nm. The AFM images of the sample were acquired using tapping mode of Digital Instrument’s (VEECO) Innova SPM and Nano-Drive Controller system. For these images the Phosphorus (n) doped Silicon probes were used. These probes have the nominal tip radius of less than 10 nm, tip height of 15 to 20 μm and the resonant frequency of about 300 kHz. The AFM images were processed using Digital Instruments SPMLab Version 7.0 software for leveling and noise removal. The gas-sensing measurements were made on the films deposited on top of alumina substrates with platinum interdigitated electrodes (for electrical measurements). A platinum heater was printed on the backside of the substrate. The gas-sensing measurements were carried out in the environmental test chamber shown in Figure 1.


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)

Experimental setup for sensitivity measurements.
© Copyright Policy
Related In: Results  -  Collection

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

f1-sensors-12-02598: Experimental setup for sensitivity measurements.
Mentions: Thin films of SnO2 mixed CeO2 were prepared by co-evaporation using physical vapor deposition. For this purpose CeO2 was evaporated by e-beam while SnO2 was evaporated by thermal evaporation simultaneously. Ratios of the two materials were controlled by quartz crystal monitor. The evaporation rates of CeO2 and SnO2 were fixed at 3.2 Ǻ/s and 0.8 Ǻ/s respectively (75% CeO2 and 25% SnO2), with the total rate of 4 Ǻ/s. The films were prepared in a Leybold L560 box coater pumped by a turbomolecular pump. The system was initially pumped to a base pressure of 1 × 10−4 Pa. Before deposition, the materials were slowly outgassed, with a shutter blocking the vapors from reaching the substrate. The films were deposited on unheated substrates. The substrates were rotating during the deposition, and the source-to-substrate distance was 40 cm. The evaporation rates and thickness of the films were controlled by a quartz crystal thickness monitor. For different purposes of film characterization, the films were simultaneously deposited on tantalum substrates (for X-ray photoelectron spectroscopy, XPS), fused silica substrates (for optical measurements), and alumina substrates (for gas sensing measurements). After the films were deposited, they were removed from the coating chamber and exposed to the ambient atmosphere. Subsequently, all samples were annealed in air at 500 °C for two hours in order to thermally stabilize the films prior to sensing measurements. XPS was performed using a VG Scientific MKII spectrometer with an Al Kα (1,486.6 eV) X-ray source. The instrumental resolution was 1.2 eV, with a slit width of 0.6 cm. Prior to the XPS analysis; the samples were transferred in air to the XPS analysis chamber. The C 1s peak of hydrocarbon contamination, at a binding energy of 284.5 eV, was used as an energy reference. During the XPS analysis, the samples were maintained at ambient temperature at a pressure of 5 × 10−7 Pa. Normal-incidence transmittance and reflectance, over the wavelength range 300–1,200 nm, were measured using a Jasco V-570 double beam spectrophotometer. The thicknesses of the annealed films were measured using a surface profilometer (AMBIOS XP-2), and was found to be 220 nm. The AFM images of the sample were acquired using tapping mode of Digital Instrument’s (VEECO) Innova SPM and Nano-Drive Controller system. For these images the Phosphorus (n) doped Silicon probes were used. These probes have the nominal tip radius of less than 10 nm, tip height of 15 to 20 μm and the resonant frequency of about 300 kHz. The AFM images were processed using Digital Instruments SPMLab Version 7.0 software for leveling and noise removal. The gas-sensing measurements were made on the films deposited on top of alumina substrates with platinum interdigitated electrodes (for electrical measurements). A platinum heater was printed on the backside of the substrate. The gas-sensing measurements were carried out in the environmental test chamber shown in Figure 1.

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