Gold-Doped Tin Oxide Film for Highly Sensitive Carbon Monoxide Sensing
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https://doi.org/10.1007/s11664-020-08613-w Ó 2020 The Minerals, Metals & Materials Society
ORIGINAL RESEARCH ARTICLE
Gold-Doped Tin Oxide Film for Highly Sensitive Carbon Monoxide Sensing RAHUL PRAJESH,1,2,3 MOHD NAHID,1 VIKAS SAINI,1 VINAY GOYAL,1,2 ASHOK SHARMA,1 JITENDRA BHARGAVA,1 and AJAY AGARWAL1,2 1.—CSIR-Central Electronics Engineering Institute, Pilani, Rajasthan 333031, India. 2.—Academy of Scientifice and Innovative Research (AcSIR), Ghaziabad, India. 3.—e-mail: [email protected]
This paper presents the development of gold-doped tin oxide (SnO2) film, realized by radiofrequency (RF) sputtering, which is highly sensitive for carbon monoxide (CO) gas. According to the Occupational Safety and Health Administration (OSHA), human exposure to 50 ppm CO is safe up to 8 h (as permissible exposure limit), but inhalation of higher concentrations of CO can cause headache, dizziness, nausea, etc. Hence, it is imperative to detect CO gas in low concentrations. The receptor films were prepared via reactive cosputtering of high-purity Sn and Au targets and characterized by x-ray diffraction (XRD), which confirmed the presence of SnO2 and gold. The thin films of pristine SnO2 and gold-doped SnO2 were also examined through field emission scanning electron microscopy (FESEM) images, showing the distinction in their structures. A reasonably enhanced response of 56.4% was exhibited by gold-doped SnO2 compared to 15.5% for pristine SnO2 for 50 ppm CO at operating temperature of each film. Key words: Reactive sputtering, XRD, FESEM, gas sensor, gold doping, SnO2
INTRODUCTION Carbon monoxide (CO) is a colorless, odorless and tasteless gas, and humans are unable to detect it without a detector. The density of CO (1.14 kg/m3) is slightly less than that of air. CO is a non-irritating gas and known as a silent killer. The main source of its production is partial combustion of carboncontaining materials such as propane, kerosene, gasoline and coal.1 CO is a toxic gas, and when carbon-containing materials burn with a reduced amount of oxygen, the carbon atoms react with oxygen atoms and form CO molecules. These CO molecules cannot react further with oxygen atoms (due to scarcity of oxygen) to form carbon dioxide (CO2). For instance, this phenomenon occurs when
(Received April 21, 2020; accepted November 6, 2020) Rahul Prajesh and Mohd Nahid have contributed equally to this work.
operating a stove or an internal combustion engine in an enclosed space with limited oxygen supply, resulting in CO production. Carbon dioxide is produced by complete combustion of CO with a blue flame. Iron smelting in a blast furnace also produces CO as a byproduct. This toxic gas enters the body by inhalation through the lungs and binds to the oxygen-carrying component ‘‘hemoglobin’’. CO binds to the iron atom 200–250 times more readily than oxygen, which results in decrement of oxygencarrying capacity of hemoglobin (also known as the ‘‘Halden effect’’).2 Common metal oxides for CO sensing include Bi2O3, CeO2, Co3O4, CuO, Fe2O3, Ga2O3, MoO3,
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