In situ spectroscopic studies to investigate uncharacteristic NH3 sensing behavior of polycarbazole Langmuir-Blodgett films

The polycarbazole films deposited by Langmuir-Blodgett (LB) technique exhibit a decrease in resistance on exposure to NH3, which is exactly opposite to the usual response (i.e. increase in resistance) observed for p-type conducting polymers We have investigated the mechanism of this uncharacteristic NH3 sensing behavior of polycarbazole LB films by carrying out in situ Fourier transform infrared and ultraviolet-visible absorption spectroscopy. The results are compared with electropolymerized (EP) films. It is shown that EP film is p-doped, which gets reduced by interacting with NH3, and as a result, its resistance increases On the other hand. LB film is found to be intrinsically undoped. Interaction with NH3 makes LB film n-doped, which results in a decrease of its resistance The n-doping of LB film has independently been confirmed by electrochemical reduction process (C) 2010 Elsevier B V All rights reserved