Abstract: A multilayer ultrathin filmof poly(3,4-ethylene dioxythiophene) (PEDOT) was first prepared by a modified Langmuir-Blodgett (LB) technique. The polymerization of EDOT monomer occured in a multilayer as-prepared LB film by exposing the filmto EDOTvapor. The formation of PEDOTparticles in the LBfilmwas confirmed by UV-Vis-near IR (UV-Vis-NIR) absorption spectrumand X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) investigation of the filmsurface exhibited small PEDOTparticles distributed in stearic acid (SA) LBfilms. Secondary ion mass spectrometry (SIMS) was employed to analyze the location of PEDOT formed and the results showed that PEDOT was well confined in the multilayer structure. A 60-layer PEDOT LB film had higher conductivity (2.6 S·cm-1) than a conventional PEDOT film, and exhibited excellent doping/dedoping characteristics. An investigation of the relationship between film conductivity and exposure time on EDOT ambience revealed that the film obtained steady conductivity after 120 min and it was concluded that the lower oxidizer density in LB film might slow the polymerization speed of EDOT. In a study of sensitive characteristics, the PEDOT film showed faster and nonlinear responses to analyte gas in a lower concentration (φ<30×10^-6), and exhibited a linear response to analyte in a higher concentration (φ=(30-120)^10-6). The result of gas sensitivity also showed that the film had excellent reversible and reproducible response to HCl vapor. The mechanismof conductivity and gas sensitivity of composite LB films were also included.

Key words: Langmuir-Blodgett film, Conducting polymer, Conductivity, Gas sensitivity, Ultrathin film