Browsing by Author "Bernede, JC"

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    Comparison of polycarbazole obtained by oxidation of carbazole either in solution or in thin film form
    (1997) Taoudi, H; Bernede, JC; Bonnet, A; Morsli, M; Godoy, A
    A comparative characterization of polycarbazole obtained either by electrochemical oxidation of carbazole in solution or vacuum evaporated carbazole films is described. The first method starts with conducting electrodes in an electrolyte solution containing the carbazole monomer. In the second, the oligomer source consists of thin films deposited under vacuum on conducting SnO2 coated glass substrate. The polymerization is corroborated by the red shift in the threshold absorption edge and the appearance of features in the visible-to-near ultraviolet (UV) domain. After oxidation, thin films obtained by the second method are amorphous while some crystallites with carbazole structure are present in thr other. The electrical conductivity and the spin density of the polycarbazole obtained by oxidation of predeposited thin films are higher and thermogravimetric measurements shaw that it is more stable. These results could be attributed to a longer averaged chain length in agreement with X-ray diffraction spectra which shows that probably some monomers and/or oligomers art effectively present in the polycarbazole obtained from carbazole in solution, (C) 1997 Elsevier Science S.A.
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    Degradation of the electrical properties of chlorine-doped poly(seleno-p-arylen diamine)s
    (1996) MHarzi, H; Safoula, G; Conan, A; Bernede, JC; Diaz, F; Godoy, A; Molinie, P; Spiesser, M
    The changes in the conductivity of chlorine-doped poly(seleno-p-arylen diamine)s have been studied with temperature, storage time and ambient atmosphere, The samples have also been studied using X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR). The conductivity of the polymers with carbonyl in their backbone decreases with storage time but is insensitive to oxygen, The decrease in conductivity with time is attributed to the breaking of the Se-N bonds by chlorine attack, which induces polymer degradation as shown by XPS. The conductivity of the polymers without carbonyl in their backbone was increased by oxygen. This increase can be attributed to oxidation of these polymers and to bipolaron formation as shown by ESR measurements. (C) 1996 Elsevier Science Limited
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    Evaporated thin films of insulating poly-(tetrabromo-p-phenylenediselenide)
    (PERGAMON-ELSEVIER SCIENCE LTD, 2002) D'Almeida, K; Bernede, JC; Godoy, A; Diaz, FR; Mevellec, JY; Molinie, P
    It has been shown that thin insulating film at the interface transparent conductive oxide/organic electroluminescent film could improve the performance of organic electroluminescent diodes (OLED). Such insulating film can be inorganic or organic. Poly-(tetrabromo-p-phenylenediselenide) (FBrPDSe) has been proved to be an efficient insulating film in OLED. The properties of these evaporated PBrPDSe thin films have been systematically studied by IR absorption, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electron spin resonance and optical transmission measurements. It is shown that, when the deposition temperature is kept below the decomposition temperature of the polymer, tetrabromo-p-phenylenediselenide molecule is preserved during the deposition process. However the polymer, which is insoluble in powder form, becomes soluble after deposition. It can be concluded that films are mainly composed of oligomers of tetrabromo-p-phenylenediselenide.
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    Poly(p-phenylene-diselenocarbonate) and poly(p-phenylene-diselenothiocarbonate): New semiconducting polymers
    (1996) Diaz, FR; Godoy, A; Tagle, LH; Valdebenito, N; Bernede, JC
    New polymers which contain selenium in the main chain have been synthesized. Poly(p-phenylene-diselenocarbonate) and poly(p-phenylene-diselenothiocarbonate) have been studied by X-ray photoelectron spectroscopy (XPS). Electrical conductivity was measured on samples without dopant agent and on samples doped with AlCl3, FeCl3, SbF5 and I-2. The morphology of these compounds was studied using a scanning electron microscope (SEM). Copyright (C) 1996 Elsevier Science Ltd
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    Synthesis and characterization of polyarylureas. I. Potentially semiconducting polymers
    (WILEY-BLACKWELL, 2001) Diaz, FR; Godoy, A; Moreno, J; Bernede, JC; Sanchez, CO; Opazo, A; Gargallo, L
    Polyarylureas were synthesized from the reaction between phosgene with aromatic diamines. Depending on the pH, the polyarylureas presented different colors when the solvent used was pyridine. The polyarylureas were characterized by IR spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy (XPS). To study the thermal stability of the polymers, a thermal degradation was performed between 35 and 700 degreesC. The polyarylureas decomposed above 350 degreesC. Without doping, polyarylureas are considered as semiconductors [sigma = 10(-9) (Omega cm)(-) (1)]; after doping with I-2, their electrical conductivity increases by several orders of magnitude. (C) 2001 John Wiley & Sons, Inc.
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    The influence of microcrystalline inhomogeneities embedded in amorphous InxSe100-x films on their electrical and optical properties
    (1996) Bernede, JC; Marsillac, S; Conan, A; Godoy, A
    In the past, InxSe100-x amorphous layers have been described as n or p type according to their majority carriers. The majority carrier type varies from one study to another, even with films of the same composition, which is a very serious problem. In this paper we explain this discrepancy by demonstrating that microcrystallite inhomogeneities are present in the amorphous InxSe100-x. While x-ray diffraction patterns are typical of amorphous samples, the selected-area diffraction obtained using a transmission electron microscope depends on the area studied. It is shown that the layers are constituted of microcrystallites embedded in an amorphous matrix. Therefore the majority carrier type changes when the p-type nature of the amorphous matrix is masked by the n-type nature of the crystallites at the percolation threshold. Of course this percolation threshold depends not only on the composition of the layer but also on the deposition process, which explains the different majority carrier types found for identical composition The two critical temperatures measured from the conductivity curves can be attributed to the phase transition alpha-In2Se3 --> beta-In2Se3 of the microcrystallites (the first one) and the overall crystallization of the layer (the second one). The typical optical absorption and differential thermal analysis properties are explained in the same way.