Showing papers by "Gilles Horowitz published in 1995"

Growth and Characterization of Sexithiophene Single Crystals

Abstract: Single crystals of unsubstituted sexithiophene (6T) were produced by a sublimation technique. X-ray structure shows that the molecule has a quasi-planar all-trans configuration, the torsional angles between adjacent rings being lower than their respective standard deviation. The unit cell belongs to space group P21h and presents the herringbone packing common to a great deal of planar molecules. Owing to the well-defined orientation of the molecules in single crystals, the polarization of vibration modes and coupling due to crystalfield effects could be unambiguously determined from polarized light IR spectroscopy. Raman spectra of the single crystals are also presented and compared to that of polycrystalline evaporated films.

Temperature Dependence of the Field-Effect Mobility of Sexithiophene. Determination of the Density of Traps

Abstract: La conductivite et la mobilite d'effet de champ du sexithiopheme non substitue (6T) et du di-alkyl-sexithiophene substitue en bout de chaine (DH6T) ont ete mesurees en fonction de la temperature. Pour des temperatures superieures a 150 K, on trouve une conductivite thermiquement activee, alors que la mobilite montre une energie d'activation dependante de la tension de grille. A forte tension et a haute temperature, on observe une saturation de la mobilite d'effet de champ. Les donnees ont ete analysees dans le cadre d'un modele de piegeages et depiegages multiples. On a ainsi determine la distribution des niveaux localises pres de la bande de transport pour les deux produits. Cette distribution a ete ajustee a une double exponentielle, par analogie avec celle du silicium amorphe hydrogene (a-Si:H). Les pieges profonds dans 6T et DH6T sont associes aux joints de grain. La mobilite plus faible de 6T est attribuee a sa plus grande concentration de defauts. Pour les temperatures inferieures a 150 K, le transport par sauts thermiquement actives entre etats localises devient le mecanisme dominant. Cependant, le transport par piegeages et depiegeages multiples peut de nouveau se manifester dans la couche d'accumulation d'un transitor a effet de champ fortement polarise

Exciton Coupling Effects in the Absorption and Photoluminescence of Sexithiophene Derivatives

Abstract: published in Advance ACS Abstracts, May 1, 1995. du Markcha1 Joffre, 92002 Nantene, France. 0022-365419512099-9155$09.00/0 SCHEME 1: Chemical Structure of Sexithiophene Derivatives 6T DH6T ClOH21 ClOH21 DD6T have been widely discussed in the literature, and particularly in the case of sexithiophene (6T), very little work has been carried out on the optical characteristics of 6T, and the energetic diagram of this compound is still an object of debate. From photoluminescence measurements under one- and two-photon excitation on a polycrystalline thin film of 6T, an electronic level ordering has been proposed by Taliani et al. in which it is suggested that the lowest Ag exciton level lies at 898 cm-’ above the lowest one-photon-allowed lB, exciton leveL4 Athouel et al. have reported that the n-n* transition in p-sexiphenyl is affected by orientation of these molecules in a thin film.5 Hamano et al. have fabricated molecular oriented thin films of 6T by organic molecular beam deposition.

Etude de l'orientation et de la structure de films de sexithiophène (6T) déposés sur les surfaces de SiO2 et de SiH/Si

Abstract: L'influence de la surface du subtrat vis a vis de l'orientation et de lan structure de films de 6T a ete etudiee par spectroscopie UV-VIS et par diffraction de rayons X rasants. Les spectres contiennent trois structures correspondant a trois populations de molecules ayant des environnements differents. La structure des films sur SiO 2 revele de faibles interactions avec le substrat alors que le substrat SiH/Si induit une organisation mesoscopique specifique en relation avec la qualite de la surface initiale