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.

[1]  S. K. Gupta,et al.  Room temperature operated ammonia gas sensor using polycarbazole Langmuir–Blodgett film , 2005 .

[2]  A. Ivaska,et al.  Spectroelectrochemical study on the charging reactions of electrochemically synthesized films from 2-methoxynaphthalene , 2006 .

[3]  Ashok Mulchandani,et al.  Single Polypyrrole Nanowire Ammonia Gas Sensor , 2007 .

[4]  Helmut Neugebauer,et al.  Processable Multipurpose Conjugated Polymer for Electrochromic and Photovoltaic Applications , 2010 .

[5]  J. Bernède,et al.  Comparison of polycarbazole obtained by oxidation of carbazole either in solution or in thin film form , 1997 .

[6]  Jingkun Xu,et al.  Low-potential electrochemical polymerization of carbazole and its alkyl derivatives , 2006 .

[7]  R. F. Nelson,et al.  Anodic Oxidation Pathways of Carbazoles I . Carbazole and N‐Substituted Derivatives , 1968 .

[8]  A. T. Johnson,et al.  Fabrication and electrical characterization of polyaniline-based nanofibers with diameter below 30 nm , 2003 .

[9]  V. Saxena,et al.  A study on Langmuir–Blodgett films of conducting polycarbazole , 2005 .

[10]  Hua Bai,et al.  Gas Sensors Based on Conducting Polymers , 2007, Sensors (Basel, Switzerland).

[11]  C. R. Martin,et al.  Effect of reagent concentrations used to synthesize polypyrrole on the chemical characteristics and optical and electronic properties of the resulting polymer , 1992 .

[12]  K. Hoshino,et al.  Nanostructured Hybrid Materials Formed by Cell Reaction between Polycarbazole and Metals , 2006 .

[13]  Wu Chun-Guey,et al.  Room temperature dedoping of conducting poly-3-alkylthiophenes , 1998 .