Gas sensing of colloidal polyaniline in a chemoresistor consisting of nanometer electrodes

The high conductivity of colloid-conducting polymers is explained by the networking structures and the hopping mechanisms of the metallic particles [1,2,4]. To observe how the metallic region and the networking structures differ in sensing NH 3 gas, E-beam lithography and electromigration were used to make chemoresistors with nanometer-gap electrodes. Colloid Pani was coated on a nanometer gap as a reaction matrix for the gas. The I– V curves were measured in a vacuum and the NH 3 gas was nonlinear. In sensors with a gap of less than 10 nm, there was a two- or threefold increase in the conductivity, and the work function decreased from 600 meV in a vacuum to 250 meV in NH 3 gas. In contrast, the conductivity of sensors with gaps of 200 and 500 nm decreased to 1/1000 in the NH 3 gas environment. The decrease of the conductivity can be explained by electron–hole annihilation, which appears to occur on the surface of the secondary particles. With comb-type electrodes, the operating voltage can be decreased by three orders of magnitude. In electrodes with 200 and 500 nm gaps, the I– V has a step-type response to NH 3 gas.