Showing papers by "Gérard Tourillon published in 1990"
TL;DR: In this article, the x-ray absorption fine structure of polyacrylonitrile (PAN) thin films electrochemically deposited on Ni have been studied by near edge x−ray absorption, as a function of the film thickness and annealing treatment.
Abstract: Polyacrylonitrile (PAN) thin films electrochemically deposited on Ni have been studied by near edge x‐ray absorption fine structure, as a function of the film thickness and annealing treatment. For 20A thick films, the polymer chains are oriented perpendicular to the surface with the C≡N groups parallel to it. Below a few angstroms, no polymerization occurs but molecules are adsorbed perpendicular to the surface. Annealing at 300°C results in the loss of the majority part of the N content of the film in contrast with the admitted mechanism for bulk PAN.
23 citations
TL;DR: In this article, the C 1s oscillator strength spectra were compared to the NEXAFS spectra of electropolymerized thin films of the same materials, showing that the width and peak intensity of the c 1s {yields} {pi}{sup *} excitation are essentially unchanged on alkylation.
Abstract: Oscillator strengths for C 1s and S2p excitation have been derived from gas-phase electron energy loss spectra of a series of 3-alkyl-substituted thiophenes. The C 1s oscillator strength spectra are compared to the C 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of electropolymerized thin films of the same materials. In the gas-phase-monomer spectra the width and peak intensity of the C 1s {yields} {pi}{sup *} excitation are essentially unchanged on alkylation.
18 citations
TL;DR: In this article, the electronic properties and orientation of films of poly−3−alkylselenophenes electrochemically deposited onto Pt have been studied by NEXAFS.
Abstract: The electronic properties and orientation of films of poly‐3‐alkylselenophenes electrochemically deposited onto Pt have been studied by NEXAFS. The C—K edge characteristics reveal that several major effects occur when n is increased from 0 to 9: (i) In the undoped semiconducting form, a continuous decrease in the polymeric 1s → π* intensity is observed due to an overlap between the π* antibonding band from the polymer and the band which develop when the alkyl chain length increases. (ii) The doping to the conducting state proceeds via a narrowing of the bandgap causing the appearance of metallic‐like behavior. However, the changes in the unoccupied antibonding π* band become less pronounced for a long alkyl chain length. (iii) The orientation of the selenophene ring structure switches from a "lying‐down" to an "on‐edge" configuration with the long alkyl chain being oriented perpendicular to the Pt surfaces.
15 citations
01 Sep 1990-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a plastic scintillator is used for both X-ray absorption near-edge structure (XANES) and extended Xray absorption fine-structure (EXAFS) spectroscopy.
Abstract: A fluorescence detection system based on a plastic scintillator is presented that can be used for both X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Its counting rate is limited by the pulsation frequency of the synchrotron radiation (3.16×10 6 counts s −1 ), and can be theoretically extended to roughly 5×10 7 counts s −1 if used on a multibunch storage ring synchrotron radiation source. Its physical characteristics (fluorescence decay time and fast electronics) are such that the dead-time correction is entirely defined by the revolution period of the charged particles in the storage ring. It shows a broad spectral response and is particularly well adapted to the measurement of hard X-rays (from 6 to 25 keV). Its volume is small (diameter 60 mm; height 240 mm), and filters of small dimensions are used to preferentially remove the scattered radiation. The entrance window of the detector is placed at 2–3 mm above the top of the sample, and a solid angle of collection of nearly 50% of 2π sr is achieved. The shape of the plastic scintillator can be easily modified to fit various geometries. It operates in both horizontal and vertical planes. It is about ten times less expensive than an energy-dispersive detection system based on a single Ge solid-state detector. The detector presents a high sensitivity. It is possible to obtain the entire EXAFS spectrum of an electrochemically (under potential deposition) deposited monolayer of Cu atoms on gold, with acquisition time of less than one hour (compared to 25 h for a Ge solid-state detector). Orientation-dependent X-ray absorption spectroscopy was performed on thin (800 A) copper phthalocyanine film, and the spectra of diluted Cu 2+ ions in aqueous solution (18 ppm) and Co atoms in YBa 2 Cu 3 O 7 powder (230 ppm) were also measured to assess the sensitivity of the detector.
14 citations
TL;DR: In this article, the NEXAFS spectra reveal that the polymeric chains are well ordered on the metallic surface: in its undoped state, the layers lie flat on Pt with strong interactions between the electron states of the metal and the antibonding π* band of the polymer.
Abstract: NEXAFS spectroscopy is a technique well suited to probing metal/organic molecule or metal/polymer interfaces. Two systems, related to the Pt/organic conducting polymer and Ni/polyacrylonitrile interfaces, are discussed in detail.For poly-3-alkylthiophene (and selenophene) thin films electrochemically deposited onto Pt, the C K-edge characteristics reveal that (i) the polymeric chain unit is composed of the same architecture as the monomer and (ii) the doping proceeds via a narrowing of the band gap with the appearance of metallic-like behaviour. The same tendencies are observed by varying the structure of the monomer, the nature of the dopant and the film thickness, which evidences a similar conduction mechanism for these five-membered polyheterocycles. The NEXAFS spectra reveal that the polymeric chains are well ordered on the metallic surface: in its undoped state, the layers lie flat on Pt with strong interactions between the electron states of the metal and the antibonding π* band of the polymer; when doped, the NEXAFS characteristics exhibit changes as a function of thickness. The first layer lies flat on the Pt surface while the other ones are randomly oriented, due to the intercalation of anions during the oxidation process. Finally, the orientation of the polymeric chain switches from a ‘lying-down’ to an ‘on-edge’ configuration when a long alkyl chain is added on the ring, this alkyl chain is oriented perpendicular to the Pt surface.Polyacrylonitrile (PAN) thin films electrochemically deposited on Ni have been studied by NEXAFS as a function of the film thickness and annealing treatment. For 20 A thick films, the polymer chains are oriented perpendicular to the surface with the CN groups parallel to it. Below a few A, no polymerization occurs, but molecules are adsorbed perpendicular to the surface. Annealing at 300 °C results in the loss of the majority of the N content of the film in contrast to the admitted mechanism for bulk PAN.
12 citations
TL;DR: In this paper, a comparative in situ time-resolved X-ray absorption study of the electrochemical inclusion of copper and iron species in poly(3-methyl-thiophene) is reported.
Abstract: A comparative in situ time-resolved X-ray absorption study of the electrochemical inclusion of copper and iron species in poly(3-methyl-thiophene)(PMeT) is reported For both treatments, incorporation of metallic ion and complexation with sulphur atoms of the polymer backbone lead to a significant increase of the ex situ macroscopic conductivity However, the detailed mechanisms and kinetics of the various processes are specific to the metallic ion incorporated in the polymer
9 citations