Poly (3-dodecylthiophene) Langmuir–Blodgett films: Preparation and characterization

Poly(3-dodecylthiophene) (P3DDT)/stearic acid (SA) monolayer and multilayers have been successfully deposited onto indium tin oxide (ITO) substrates through Langmuir–Blodgett (LB) technique. Surface pressure–mean molecular area (π–A) isotherms, X-ray diffraction (XRD) pattern, absorption spectrum, fluorescence spectrum, atomic force microscope (AFM), and photo-assistant conducting AFM (PC-AFM) have been used for characterization. The AFM topographic images of P3DDT/SA LB film showed high coverage morphology with some aggregated islands dispersed uniformly in the film when deposited at surface pressure of 40 mN/m. Compared with the absorption and fluorescence spectra of P3DDT in toluene, the spectra of P3DDT/SA LB films showed an obvious red-shift phenomena, which were due to the formation of P3DDT aggregates in LB films. It was confirmed by XRD measurement that P3DDT/SA LB films formed an ordered structure with an average thickness of 2.9 nm. The results from PC-AFM measurements showed that the P3DDT/SA LB films had much higher conductivity under UV light irradiation, which indicated that P3DDT molecules had a good photocurrent response in such ordered structure.