Mingxiao Fu

Raman spectroscopic evidence of thickness dependence of the doping level of electrochemically deposited polypyrrole film

In this paper, we present resonance Raman spectroscopic studies on as-grown thin polypyrrole (PPy) films electrochemically deposited on flat platinum electrode surfaces by direct oxidation of pyrrole in acetonitrile. It was found that the overall features of the Raman spectra depend strongly on film thickness, mainly due to that the doping level of PPy increases during film growth process. Electrochemical and X-ray photoelectron spectroscopic (XPS) examinations have confirmed this discovery. The doping level of PPy film with a given thickness also depends on the property of supporting electrolyte.

Raman spectroscopic studies on the structural changes of electrosynthesized polythiophene films during the heating and cooling processes

Abstract Polythiophene (PT), poly (3-chlorothiophene) and poly (3-methylthiophene) have been electrochemically synthesized by direct oxidative polymerization of corresponding monomers at stainless steel electrode and in boron trifluoride diethyl etherate solution. The as-grown PT films have been peeled off from the electrode surfaces and characterized by resonance Raman spectroscopy in the temperature scale of 78–573 K. During the heating process, the Raman bands related to the oxidized species decreased gradually, mainly due to the effects of oxygen and moisture in air. Finally, the polymers changed into the neutral states and then decomposed. During the cooling process, the polymer chain segments of the neutral species changed from a disordered (coil-like) to an ordered (rod-like) structure and caused the elongation of conjugated chain length. This led to the dramatic decrease of the Raman intensities of the bands related to the neutral species. On the other hand, the Raman intensities of the bands associated with the oxidized species are nearly independent of temperature. This is mainly because the oxidized species have quinoidic structures and their conformation does not change during the cooling process.

Doping level change of polythiophene film during its electrochemical growth process

Polythiophene (Pth) films have been electrochemically deposited on mirror-like stainless steel (SS) (or gold) electrode surfaces by direct oxidation of thiophene in boron trifluoride diethyl etherate (BFEE) solutions at a constant applied potential of 1.3 V (vs. Ag/AgCl). The Raman spectra of Pth films have been investigated by excitation with a 514, 633 or 785 nm laser beam. The 633 nm laser beam was found to be the best among the three excitation lights tried for studying the doping level change of Pth film. The overall features of 633 nm excited resonance Raman spectra of as-grown Pth films depend strongly on film thickness. Raman and X-ray photoelectron energy spectroscopic (XPS) results and electrochemical studies demonstrated that the doping level of the Pth film increased with the increase of film thickness. Furthermore, successive cyclic voltammetric scanning was found to be a more effective approach than applying a constant positive potential for doping a thin compact conducting polymer film.

Electrochemical fabrication of aligned microtubular heterojunctions of poly(p-phenylene) and polythiophene

Aligned microtubular heterojunctions of poly(p-phenylene) (PPP) and polythiophene (PTh) were fabricated by successive electrochemical oxidations of benzene and thiophene in freshly distilled boron trifluoride–diethyl ether (BFEE) solution and using a microporous alumina membrane with pores of 200 nm diameter as the template. The morphology and chain structure of the microtubular heterojunctions were studied by scanning and transmission electron microscopies and Raman spectroscopy. The current (I)–voltage (V) curves revealed that the aligned microtubular heterojunctions had a better rectification effect than that of the normal PPP/PTh bilayer heterojunction.

Electrochemical fabrication of polythiophene film coated metallic nanowire arrays

Metallic gold (Au) and silver (Ag) nanowire arrays coated with polythiophene (PTh) films were fabricated by successive electrochemical depositions of PTh and metal into the pores of a microporous alumina membrane. The diameter of the composite nanowires was 200 nm and that of the metallic nanowires was about 100 nm. They are adhered to a thin gold film and aligned in a high density of ca. 1010 wires/cm2. The morphology of the composite nanowires has been characterized by an optical microscope, Raman spectroscopy, scanning and transmission electron microscopies. Their electrochemical property has also been investigated.

Aligned polythiophene coated gold nanowires

Metallic gold (Au) nanowire arrays coated with polythiophene (PTh) films were fabricated by successive electrochemical depositions of PTh and the metal into the pores of a microporous alumina membrane. The diameter of the composite nanowires was 200 nm and that of the Au nanowires was about 100 nm. They are adhered to a thin gold film and aligned in a high density of 10 10 wires / cm 2 . The morphology of the composite nanowires has been characterized by an optical microscope, Raman spectroscopy, scanning and transmission electron microscopies.

Raman spectroscopic studies on the structural changes of poly(3-methylthiophene) during heating and cooling processes

Poly(3-methylthiophene) (PMeT) electrosynthesized by direct oxidation of 3-methylthiophene in boron trifluoride diethyl etherate (BFEE) has been studied by Raman spectroscopy in the temperature scale of 123–458 K. Experimental results demonstrate that the thermal stability of PMeT in the oxidized state is much lower than that of the polymer in the neutral state. Furthermore, during the cooling process, the conformation of neutral species changes from a coil-like state into a rod-like state, while the conformation of the oxidized species does not change.

High-quality polyene prepared by liquid/solid two-phase dehydrochlorination of poly(vinyl chloride)

Polyvinyl chloride) (PVC) can be dehydrochlorinated extensively in a liquid/solid two-phase system by the catalyzation of poly(ethylene glycol) (PEG). The product, dehydrochlorinated poly(vinyl chloride) (DPVC), is polyacetylene-like and has the longest polyene sequences so far and a narrow dispersity of polyene sequences according to its FT-infrared and Raman spectra.