Academic literature on the topic 'Transport/transfert de charge'

There is a need for monolithic devices capable of spatial resolution in imaging and ionizing radiation detection. In this thesis, a GaAs acoustic charge transport device (ACT) was studied for this purpose. A new method of charge injection has been demonstrated for the ACT. Using near-infrared optical pulses incident through thin semi-transparent chromium windows, electron-hole-pairs were separated by the electric field in a depleted n-type channel region of the device. For light penetration less than the depth of the electron potential minimum, and for small injection levels, calculations indicated that electrons and holes were separated at their saturation velocities. Holes moving toward the surface of the substrate could recombine with electrons at an evaporated Schottky metal plate. Electrons moving toward the channel centre were bunched and transported by the electric field coupled to a <110> propagating surface acoustic wave (SAW) on (100) cut GaAs. Quantum efficiency, defined as the number of electrons collected at the output per incident photon on the GaAs surface, was greater than 9% at an optical wavelength of 730 nm. When compensation was made for the loss and reflection due to the chromium windows, the quantum efficiency was in excess of 24%. Charge transfer efficiency was greater than 0.992 with the ACT clocked at 360 MHz. The demonstrated optical injection technique may be of use in future ACT imaging devices.<br>Applied Science, Faculty of<br>Electrical and Computer Engineering, Department of<br>Graduate

In this thesis, we model electronic states, charge transfer and charge transport in organic semiconductors (OSCs). We are interested in the effect of chemical structure, molecular packing and different types of disorder on the charge transport in these materials, which is an important factor determining the efficiencies of devices made with OSCs. This is an intrinsically multiscale problem, and we use computational methods than span length and time-scales. We investigate the effect of molecular packing and crystal structure on charge carrier mobility in molecular crystals. We also model the electron mobility in disordered small molecules containing different defects to find the effect of these defects on the performance of devices. We perform electronic structure calculations to investigate the HOMO and LUMO levels in the presence of different defects, as well as to generate absorption, photoluminescence and infrared spectra to compare to experimental spectra. We develop a computationally efficient method for modelling polarons in organic semiconductors within a tight-binding framework. We apply the method to large assemblies of fullerene molecules generated with coarse-grained molecular dynamics. The method allows us to explore the effect of energetic and configurational disorder, as well as polaron formation, on the density of states and size of charge states in these systems. We further develop a method for calculating transfer integrals between molecules or molecular fragments, based on performing calculations of molecular orbitals in a counterpoise basis set. We apply it to calculating intramolecular transfer integrals and transfer integrals between donor and acceptor molecules at interfaces in organic photovoltaics, and between dopant and host molecules.

Améliorer notre compréhension des mécanismes de transport/transfert de charges et de stockage de charges dans les films d'oxyde métallique semi-conducteur mésoporeux transparents (fonctionnalisés ou non par des chromophores redox-actifs) dans des électrolytes aqueux est d'une importance fondamentale pour le développement et l'optimisation d'une large gamme de dispositifs de production ou de stockage d'énergie éco-compatibles et/ou éco-durables (cellules solaires à colorants, batteries, photoélectrolyseurs, ….). Dans ce but, des films de TiO2 semi-conducteur mésoporeux préparés par dépôt sous incidence rasante (GLAD-TiO2) ont été sélectionnés pour leur grande surface spécifique, leur morphologie bien contrôlée, leur transparence élevée dans le visible et leur semiconductivité bien définie qui peut être facilement ajustée par l’application d’un potentiel externe, autorisant ainsi leur caractérisation aisée par spectroélectrochimie en temps réel. Nous avons d'abord étudié le transfert et transport de charges dans des électrodes GLAD-ITO et GLAD-TiO2 fonctionnalisées par une porphyrine de manganèse redox-active jouant à la fois le rôle de chromophore et de catalyseur. Nous avons démontré que la réponse électrochimique des électrodes ainsi modifiées, enregistrée en l'absence ou en présence du substrat O2, dépend fortement de la conductivité du film mésoporeux. En utilisant la voltamétrie cyclique couplée à la spectroscopie d'absorption UV-visible, nous avons pu extraire des informations clés telles que la vitesse du transfert d'électrons hétérogène entre le chromophore redox immobilisé et le matériau semi-conducteur, et aussi pu rationaliser le comportement électrochimique spécifique obtenu sur un film GLAD-TiO2 modifié par la porphyrine en condition catalytique. En parallèle, nous avons développé un procédé de fonctionnalisation de ces films d'oxyde métallique mésoporeux (en l’occurrence des films GLAD-ITO) par électrogreffage de sels d'aryldiazonium générés in situ, permettant d'obtenir des électrodes fonctionnalisées avec un taux de recouvrement surfacique élevé et une stabilité dans le temps particulièrement bonne en conditions hydrolytiques. Nous avons également étudié le stockage de charges au sein d’électrodes GLAD-TiO2 dans divers électrolytes aqueux. Nous avons notamment démontré pour la première fois qu’une insertion rapide, massive et réversible de protons peut être effectuée dans des films de TiO2 nanostructurés amorphes immergés dans un tampon aqueux neutre, le donneur de protons étant alors la forme acide faible du tampon. Nous avons également démontré que ce processus de stockage d’électrons couplé à l’insertion de protons peut se produire sur toute la gamme de pH et pour un vaste panel d'acides faibles organiques ou inorganiques, mais aussi de complexes aqueux d'ions métalliques multivalents, à condition que le potentiel appliqué et le pKa de l'acide faible soient correctement ajustés<br>Better understanding of the mechanisms of charge transport/transfer and charge storage in transparent mesoporous semiconductive metal oxide films (either functionalized or not by redox-active chromophores) in aqueous electrolytes is of fundamental importance for the development and optimization of a wide range of safe, eco-compatible and sustainable energy producing or energy storage devices (e.g., dye-sensitized solar cells, batteries, photoelectrocatalytic cells, …). To address this question, mesoporous semiconductive TiO2 films prepared by glancing angle deposition (GLAD-TiO2) were selected for their unique high surface area, well-controlled morphology, high transparency in the visible, and well-defined semiconductivity that can be easily adjusted through an external bias, allowing thus their characterization by real-time spectroelectrochemistry. We first investigated charge transfer/transport at GLAD-ITO and GLAD-TiO2 electrodes functionalized by a redox-active manganese porphyrin that can play both the role of chromophore and catalyst. We demonstrate that the electrochemical response of the modified electrodes, recorded either in the absence or presence of O2 as substrate, is strongly dependent on the mesoporous film conductivity. By using cyclic voltammetry coupled to UV-visible absorption spectroscopy, we were able to recover some key information such as the heterogeneous electron transfer rate between the immobilized redox-active dye and the semiconductive material, and also to rationalize the specific electrochemical behavior obtained at a porphyrin-modified GLAD TiO2 film under catalytic turnover. In parallel, we developed a new functionalization procedure of mesoporous metal oxide films (GLAD-ITO in the present case) by electrografting of in-situ generated aryldiazonium salts, allowing for modified electrodes characterized by both a high surface coverage and a particularly good stability over time under hydrolytic conditions. Also, we investigated charge storage at GLAD-TiO2 electrodes under various aqueous electrolytic conditions. We notably evidenced for the first time that fast, massive, and reversible insertion of protons can occur in amorphous nanostructured TiO2 films immersed in near neutral aqueous buffer, with the proton donor being the weak acid form of the buffer but not water. We also demonstrated that this proton-coupled electron charge storage process can occur over the entire range of pH and for a wide range of organic or inorganic weak acids, but also of multivalent metal ion aquo complexes, as long as the applied potential and pKa of weak acid are properly adjusted

Using fluorescein isothiocyanate-dextran filled inside-out vesicles derived from 4$ sp prime$,4-diisothiocyano-2$ sp prime$,2-disulfonic stilbene treated human red blood cells, we investigated the mechanistic basis for the decrease in the Na:Rb(K) stoichiometry of the Na,K-ATPase observed when the cytoplasmic sodium concentration is decreased below 0.4 mM (Blostein, R., 1983, J. Biol. Chem. 258: 12228-12232). First, we considered the possibility of H$ sp{+}$ replacing Na$ sp{+}$ and/or K$ sp{+}$. It was found that in the absence of Na$ sp{+}$, a decrease in pH from 7.4 to 6.0 effected an increase in ATPase activity $( upsilon)$, an increase in phosphoenzyme intermediate (EP) and a strophanthidin-sensitive ATP-dependent H/K exchange. Conversely, in the absence of K$ sp{+}$, a decrease in pH from 7.4 to 6.0 effected an increase in $ upsilon$, a decrease in EP and a strophanthidin-sensitive ATP-dependent Na/H exchange. These results suggest that protons can substitute for sodium and potassium in the sodium pump reaction. Second, it was shown that under conditions where H$ sp{+}$ do not replace Na$ sp{+}$ or K$ sp{+}$, the membrane potential $( Delta Psi)$ effected by the sodium pump is cytoplasmic side-negative at (Na$ sb{ rm cyt}$) $>$ 1 mM and extracellular side-negative at (Na$ sb{ rm cyt}$) 7.8. Our results are consistent with the notion that protons, sodium and potassium ions are transported by a similar mechanism in P-type ATPases.