Influence of Molecular Organization on the Electrical Characteristics of {\pi}-conjugated Self-assembled Monolayers

Two new thiol compounds with {\sigma}-{\pi}-{\sigma} structure were synthesized and self-assembled on gold substrates. The morphology and the structural characterization of SAMs assessed by infrared spectroscopy, contact angle, XPS, electrochemistry and scanning tunneling microscopy (STM) show the formation of monolayers. SAMs with a terthiophene (3TSH) core as conjugated system are much better organized compared to those with a naphthalene carbodiimide (NaphSH) core as demonstrated by the cyclic voltammetry and STM studies. The surface concentration of 3TSH and NaphSH is respectively three and six times lower than ordered SAMs of pure alkyl chains. A large number of I/V characteristics have been studied either by STS measurements on gold substrates or by C-AFM on gold nanodots. Transition Voltage Spectroscopy (TVS) was used to clearly identify the transport in these partially organized monolayers. The chemical nature of the conjugated system, donor for 3TSH and acceptor for NaphSH, involves an opposite rectification associated to the asymmetrical coupling of the molecular orbitals and the electrodes. The conductance histograms show that the 3TSH junctions are less dispersed than those of NaphSH junctions. This is explained by a better control of the molecular organization in the molecular junctions.Comment: Full paper with supporting informatio

A bridged low band gap A-D-A quaterthiophene as efficient donor for organic solar cells

International audience[small alpha],[small omega]-Bis(dicyanovinyl)quaterthiophene 1 with a median 4,4-diethyl-4H-cyclopenta[2,1-b:3,4-b[prime or minute]]dithiophene has been synthesized. UV-Vis absorption data show that the covalent bridging of the inner 2,2[prime or minute]-bithiophene leads to a significant reduction of the HOMO-LUMO gap essentially due to an increase of the HOMO level as confirmed by electrochemical and theoretical results. X-ray diffraction analysis of a single crystal of 1 shows that except for the out-of-plane ethyl groups, the conjugated system displays a quasi-planar geometry while the molecular packing exhibits strong [small pi]-stacking interactions and multiple short intermolecular contacts. Quaterthiophene 1 has been used as active donor material in organic solar cells of various architectures including bi-layer planar hetero-junctions and hybrid co-evaporated bulk hetero-junctions with C60 as electron acceptor material. A maximum conversion efficiency of 4.30% is obtained with a hybrid co-evaporated device. These results are discussed in terms of structure-properties relationships with reference to the open-chain parent [small alpha],[small omega]-bis(dicyanovinyl)quaterthiophene 2

Etude électrochimique de molécules aminées aliphatiques et hétéroaromatiques. Application aux microcapteurs de pH.

The first part describes the state of the art (electrochemical synthesis, developed applications and electrochemical reaction mechanisms) of the molecules used in his work: pyrrole and ethylenediamine. A second part is dedicated to the evolution of pH measurement processes. Thus, after an explanation of the pH concept, a presentation of both conventional pH measurement technique and of recent pH measurements methods is given.Then, thin polymer films are deposited on platinum surfaces by anodic electropolymerization of pyrrole and ethylenediamine. Then, we tested different electrolyte composition to determine the influence of solvent, salt and monomer concentrations on the electro-oxidation of pyrrole and ethylenediamine solutions. After that, several spectroscopic (IR and XPS) and microscopic (AFM and SEM) techniques were used to characterize the modified surfaces.Finally, pH sensors were elaborated by “lift-off” process then modified by anodic electrooxidization of pyrrole and ethylenediamine. This method was proved to be a good alternative to standard pH probes since these sensors can be both miniaturized and used in the clinical field if biocompatible polymers are selected as active layers. The sensitivity, reversibility and stability of these pH sensors were estimated for pH values between 4.5 and 9.0.Dans un premier chapitre, je développerai l’état de l’art des molécules que nous avons choisies d’utiliser : le pyrrole et l’éthylènediamine : historique des travaux publiés, premiers travaux de synthèse électrochimique, applications développées et étude des mécanismes réactionnels électrochimiques possibles. Une seconde partie sera dédiée à l’essor des procédés de mesures du pH. Ceci débutera par une explication de la notion de pH, suivie d’une présentation des techniques de mesure du pH par des appareillages conventionnels, jusqu’aux nouvelles méthodes développées dernièrement.Puis, nous tenterons de déposer en couches minces des polymères en utilisant le fait que le pyrrole et l’éthylènediamine électropolymérisent par oxydation anodique à la surface d’une électrode. Nous électro-oxydons alors différentes solutions de pyrrole et d’éthylènediamine en modifiant la composition des électrolytes : nature du solvant et concentrations en sel de fond et en monomère. Nous caractériserons ensuite les surfaces modifiées, au moyen de techniques spectroscopiques (IR et XPS) et microscopiques (AFM et MEB).Finalement, nous présenterons des surfaces de platine fabriquées par « lift-off » puis modifiées par électro-oxydation du pyrrole ou de l’éthylènediamine et ainsi servir de couches sensibles de capteurs de pH. Cette méthode semble être une bonne alternative car ces capteurs sont à la fois miniaturisables et utilisables dans le milieu clinique si des polymères biocompatibles sont choisis comme couches actives. La sensibilité, la réversibilité et la stabilité de détection aux variations de pH des capteurs sont ensuite estimées pour des valeurs de pH comprises entre 4,5 et 9

Push-Pull Triphenylamine Chromophore Syntheses and Optoelectronic Characterizations

Article de revue (Article scientifique dans une revue à comité de lecture)International audienceA series of push–pull molecules combining a diarylamine donor block with various electron-acceptor units through phenylthienyl (PT) and bithienyl (TT) π-conjugating spacers have been synthesized. Optical and electrochemical results, supported by theoretical calculations, show that the electronic properties of the molecules can be modulated by varying the strength of the acceptor group and/or the structure of the conjugating spacer. As a first evaluation of the potential of these compounds as donors in organic solar cells (OSC), simple planar heterojunction (PHJ) prototypes using fullerene C60 as electron acceptor have been fabricated. Most OSCs exhibit analogous photoconversion efficiencies in the 1.5–2 % range. Their characteristics are discussed in terms of structure–properties relationships.</p

Effect of electrolyte solvent on the morphology of polypyrrole films. Application of the use of polypyrrole in pH sensors

International audienceElectrochemical and morphological characteristics of polypyrrole (PPy) films electro-deposited from three different electrolyte solutions (acetonitrile, water and acetonitrile + water) have been investigated using atomic force microscopy and scanning electron microscopy. Experimental parameters including the electrolyte and the deposition time were shown to affect the morphologies of polypyrrole films. After characterization of the polypyrrole film morphologies, these polymer films were successfully tested as sensitive layers in pH sensors since the pH sensor responses were fast, linear and sensitive to pH changes. More, these responses of the pH sensors were dependent on the experimental conditions of the electro-deposition (thickness and solvent)

Electro-grafted organic thin films in Nano-memristor device

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Towards organic film passivation of germanium wafers using diazonium salts: mechanism and ambient stability

International audienceGermanium is well-known for its good electronic properties but also the poor passivation quality of its natural or thermally-grown oxide layer. The robust passivation of Ge surfaces is thus a crucial step on the way to its integration in electronics at nanoscale. Before passivation, the natural oxide layer must be removed from the surface. Different methods were investigated and compared. The surfaces were analyzed by X-ray photoelectron spectroscopy and by atomic force microscopy to determine the impact of the etching on the roughness. Oxide-free Cl-terminated surfaces were chosen and functionalized with various arenediazonium salts. The grafting is a fast reaction (less than 30 minutes) and proceeds in soft conditions (room temperature in acetonitrile solutions). The functionalization was found to proceed even at low temperature (-18°C). The modified surfaces were mainly studied by XPS and AFM. The morphology of the organic layer was influenced by the temperature and duration of the grafting as well as by the presence of substituents on the aromatic ring. We demonstrated that smooth oxide-free Ge surfaces could be prepared by a cyclic oxidation- rinsing- etching procedure and could be functionalized with various arenediazonium salts. The stability of the organic layer was compared to the stability of a self-assembled monolayer of alkanethiolates. The absolute coverage was also determined. This constitutes a first step towards Ge crystal passivation by organic thin films

Spirobifluorene based small push-pull molecules for organic photovoltaic applications

International audienceFour analogous push-pull systems have been synthesized. If the latter all involve the same electron rich diphenylamine termination (D) and π-conjugating spacer (p) they differ from their electron withdrawing groups (A) and more importantly by their linear or 3D structure. Indeed, two push-pull spirobifluorene derivatives, which present two perpendicular D-p-A systems by molecule, are compared to their linear analogues. After description of their syntheses, spectroscopic and electrochemical properties, comforted by theoretical calculations, are discussed and compared. Then, a preliminary evaluation of compounds as active materials in organic solar cells is presented and demonstrates the potential interest of spiro-based derivatives for organic photovoltaics

Electrografted organic memristors: scaling study yusing carbon nanotube electrodes and prospects for artificial neural networks

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Small Molecular conjugated systems for organic solar cells

Date du colloque : 06/2013</p