SnO₂ Nanoslab as NO₂ Sensor: Identification of the\nNO₂ Sensing Mechanism on a SnO₂ Surface

Abstract

Among\nthe various metal oxides, SnO₂ has been most widely exploited\nas a semiconductor gas sensor for its excellent functionalities. Models\nillustrating the sensing mechanism of SnO₂ have been proposed\nand tested to explain experimentally derived “power laws”.\nThe models, however, are often based on somewhat simplistic assumptions;\nfor instance, the net charge transfer from an adsorbate to a sensor\nsurface site is assumed to occur only by integer values independent of the\ncrystallographic planes. In this work, we use layer-shaped SnO₂ crystallites with one nanodimension (1ND-crystallites) as\nNO₂ gas sensing elements under flat band conditions, and\nderive appropriate “power laws” by combining the dynamics\nof gas molecules on the sensor surface with a depletion theory of\nsemiconductor. Our experimentally measured sensor response as a function\nof NO₂ concentration when compared with the theoretically\nderived power law indicates that sensing occurs primarily through\nthe chemisorption of single NO₂ molecules at oxygen vacancy\nsites on the sensor surface.