Thermopower measurements on pentacene transistors

We present the first thermoelectric measurements on pentacene field effect transistors. We report high values of the Seebeck coefficient at room temperature between 240 and 500 micro V/K depending on the dielectric surface treatment. These values are independent of the thickness of the channel and of the applied gate voltage. Two contributions to the Seebeck coefficient are clearly identified: the expected contribution that is dependent on the position of the transport level and reflects the activated character of carrier generation, and an unexpected intrinsic contribution of 265 plus minus 40 micro V/K that is independent of the temperature and the treatment of the oxide surface. This value corresponds to an unusually large lattice vibrational entropy of 3 kB per carrier. We demonstrate that this intrinsic vibrational entropy arises from lattice hardening induced by the presence of the charge-carrier. Our results provide direct evidence of the importance of electronic polarization effects on charge transport in organic molecular semiconductors.Comment: 7 pages, 8 figures, LaTe

Low-loss polymer waveguides on nanoporous layers

Multimode planar polymer waveguides were fabricated on hybrid polymer nanoporous layers with a fast industrial aqueous-based method well adapted to coat large-surface plastic substrates and easily scalable up to economical mass production volumes. Using a fiber probe internal light source technique, we were able to measure quantitatively the modal propagation losses. In particular, attenuation coefficients lower than 0.5 dB/cm were found for the fundamental modes, thus showing the potential of our polymer nanoporous layers as optical isolation layers in waveguiding applications

Counterion effects in cyanine heterojunction photovoltaic devices

We investigated cyanine heterojunction photovoltaic devices using carbocyanine dyes as donors and buckminsterfullerene (C60) as acceptor. In particular, we focused on the influence of cyanine counterions on the photovoltaic device characteristics. It was found that counterions can be displaced in the applied electric field and give rise to important hystereses in the current-voltage characteristics, which are related to charge injection processes at electrode and organic heterointerfaces. Mobile counterions have also a drastic effect on the photocurrent spectrum and are responsible for an important C60 contribution at the organic heterojunction between cyanine and C60. If the counterion is covalently linked to the cyanine dye, the C60 contribution in the blue spectral domain can not be observed

Quantum Yield Measurement of Fluorescent Zeolite Nanopigments

Organic fluorescent molecules are infiltrated in the channels of zeolite L nanocrystals, thus creating organic-inorganic fluorescent nanoparticles. Combined with dielectric matrices, these fluorescent nanopigments open the way to the realization of novel optical devices. In this paper, the optical measurement of the quantum yield of fluorescent zeolites by means of a precise and reliable diffuse reflectance technique is presented. Several possible factors that may affect the fluorescence quantum yield are also investigated

Lumière et matière.

L’avatar de la lumière qui se révèle dans ce chapitre est à la fois le plus concret, puisque c’est dans son interaction avec la matière que la lumière acquiert tout son éclat, et le plus mystérieux, car, après vingt-cinq siècles de recherches, seules les théories un peu difficiles du 20 e siècle ont pu en éclairer tous les aspects. C’est particulièrement dans ses échanges avec la matière que la lumière se révèle source d’énergie et source de vie. Lorsqu’elle met ..