Gas-sensing properties of oxide semiconductors improves by using then in
nanocrystalline forms. The sensitivity of gas-sensor has also been
modified by adding metals or metal oxides as catalytic agents. Using the
In2O3 and Ag nanoparticles as the precursor; In2O3: Ag composite
nanoparticle layers have been grown. It has been demonstrated that a
decreasing particle size leads to an increased sensitivity and a
decreased response time. At C2H5OH concentration of 1000 ppm in air and
at an operating temperature of 400°C, sensitivity and response time of
325 and 8 s, respectively have been achieved in case of In2O3
nanoparticles with a size of 14 nm. With the addition of 15% silver,
response time of 6 s and sensitivity of 436 has been obtained for 1000
ppm ethanol at 400°C. Ag2O nanoparticle draws electrons from the In2O3
layer and enhances the formation of electron-depleted layer. On exposure
to a reducing gas, interfacial Ag2O is reduced to Ag, with a decrease or
disappearance of the space-charge layer. Gas sensing response thus
depends on the change in depletion layer in interface from Ag2O-In2O3 to
accumulation layer in Ag-In2O3.