| 摘要 |
The concentration of NOx in a gaseous mixture is measured using a solid state sensor comprising a surface thin film of semiconductive material. In a preferred embodiment, the thin film semiconductor comprises tin oxide having an oxygen to tin atomic ratio of between 1.5 and 1.95, preferably between 1.8 and 1.9, and is formed by reactive sputtering from a tin or tin oxide target in an argon-oxygen atmosphere. The electrical resistance of the tin oxide thin film is highly sensitive to NOx species, but is essentially unaffected by the presence of other common gases such as CO, H2, O2, SO2, NH3 and hydrocarbons. Water vapor present in the mixture has a small effect upon the resistance of the film. The thin film tin oxide sensor may be used to measure NOx in air and, in one particularly advantageous aspect of this invention, is employed to measure NOx emissions in automotive exhaust gas.
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