Mechanism of Gas Sensing

When a freshly prepared sol-gel derived nanocrystalline SnO2 semiconductor thin film is exposed to air, physisorbed oxygen molecules pick up electrons from the conduction band of SnO2 and change to O—ds or O—^^ species. Consequently, a positive space-charge layer forms just below the surface of SnO2 particles, which creates a potential barrier between the particles increasing the electrical resistance of the nanocrystalline SnO2 film, Figure 11 [82].

However, when a reducing gas comes in contact with the nanocrystalline SnO2 film, it gets oxidized via reaction with


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