SnO₂ nanoslab as NO₂ sensor: Identification of the NO₂ sensing mechanism on a SnO₂ surface

Among the various metal oxides, SnO₂ has been most widely exploited as a semiconductor gas sensor for its excellent functionalities. Models illustrating the sensing mechanism of SnO₂ have been proposed and tested to explain experimentally derived "power laws". The models, however, are often based on somewhat simplistic assumptions; for instance, the net charge transfer from an adsorbate to a sensor surface site is assumed to occur only by integer values independent of the crystallographic planes. In this work, we use layer-shaped SnO₂ crystallites with one nanodimension (1ND-crystallites) as NO₂ gas sensing elements under flat band conditions, and derive appropriate "power laws" by combining the dynamics of gas molecules on the sensor surface with a depletion theory of semiconductor. Our experimentally measured sensor response as a function of NO₂ concentration when compared with the theoretically derived power law indicates that sensing occurs primarily through the chemisorption of single NO₂ molecules at oxygen vacancy sites on the sensor surface.