Surface ionization (SI) gas detection experiments have been performed on platinum (Pt) and metal oxide (MOX) films. The probability of surface ion emission varies with temperature in an Arrhenius-type manner. Among all hydrocarbons studied so far those with amine functional groups exhibited the lowest activation energies allowing detection in the ppm concentration range at emitter operation temperatures of about 400 C. All other kinds of hydrocarbons could not be detected under these same conditions, not even if their concentrations were as high as 1% or 2%. Under high-temperature conditions ( 800 C), this kind of selectivity breaks down and solid-state SI emitters start to behave in a similar way as flame ionization detectors, allowing detection of a much wider range of hydrocarbon species. Emitter materials with surface morphologies in the nanometer range were found to form much more efficient ion emitters than emitters with smooth surfaces.Index Terms-Charge transfer process, functional hydrocarbons, gas sensing mechanism, proton affinity, surface ionization (SI).

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