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Description
$SnO_2$, a n-type metal oxide semiconductor with a wide band gap of 3.6 eV has emerged as a potent gas sensing material. The gas sensing properties of $SnO_2$ can be further enhanced by doping it with foreign metals, noble elements and metal oxides in addition to reducing it to nanometer size. In this work we have studied the gas sensing performance of tin oxide by reducing it to nanometer scale and doping it with Cu. Further we have used Raman Spectroscopy as the sensing tool, instead of the conventional electrical method. Due to the band bending phenomenon in $SnO_2$, a charge depleted region is developed at the conduction band leading to decrease in conductivity. If this surface is exposed to reducing gases like CO or $H_2$, they would react with the ionosorbed oxygen and donate electrons to the conduction band, thus replenishing the otherwise charge depleted region of the conduction band. This results in the increase of conduction of the sensor. We had proceeded on the basis of the fact that due to this replenishment of charges, there would be a change in shape, size or orientation in the electron cloud when the surface of the sensor is exposed $NH_3$, another reducing gas. This change would produce a change in the polarizability ellipsoid and that would be reflected as an intensity variation of the classical Raman modes which was observed in our study.
