Contains full texts of Diffusion Fundamentals II conference volume

A selection of papers presented at the Eighth International Bologna Conference on Magnetic Resonance in Porous Media, 10-14 September 2006, University of Bologna, Italy

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Contains the extended versions of selected abstracts of the Proceedings of Diffusion Fundamentals I and further conference contributions.

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Scope of the conference: As a ubiquitous process of random movement, ranging from molecular up to macroscopic and even cosmic scales, diffusion is key to spreading phenomena in quite diverse areas. Bringing together scientists from disciplines as different as archaeology, ecology, epidemics, ethnology, linguistics and sociology with biologists, chemists, physicists, mathematicians and engineers, Diffusion Fundamentals VI is scheduled to highlight the astonishingly similar patterns of spreading phenomena in Humanities, Natural Sciences and Engineering.

Scope of the conference: As a ubiquitous process of random movement, ranging from molecular up to macroscopic and even cosmic scales, diffusion is key to spreading phenomena in quite diverse areas. Bringing together scientists from disciplines as different as archaeology, ecology, epidemics, ethnology, linguistics and sociology with biologists, chemists, physicists, mathematicians and engineers, Diffusion Fundamentals VI is scheduled to highlight the astonishingly similar patterns of spreading phenomena in Humanities, Natural Sciences and Engineering.

L’objectif de ce travail de thèse est d’étudier certaines propriétés locales de structures contenant des nanocristaux de Ge sur leur surface par utilisation de la technique nano-EBIC(courant induit par bombardement électronique et collecté par un nano-contact). La particularité de cette technique qui utilise le même principe que la technique EBIC classique est l’utilisation d’une pointe conductrice d’un AFM (microscope à force atomique) à la place d’une électrode standard. Nous nous sommes intéressés à la détermination de la longueur de diffusion effective (Leff) et l’étude de sa variation en fonction de paramètres tels que l’énergie primaire et la taille des nanocristaux. Leff augmente pour les faibles énergies primaires, passe par un maximum qui dépend de la taille des nanocristaux, puis diminue pour les énergies élevées. Ce comportement de l’évolution de Leff a été expliqué en chapitre 2. Cependant, ce résultat n’a jamais été observé auparavant. C’est pourquoi, nous avons complété ce travail par une étude basée sur la simulation Monte-Carlo, où l’effet de plusieurs paramètres a été analysé. Parmi les paramètres étudiés, on cite la taille et la forme du nano-contact (ou plus précisément la taille de la nano-zone de déplétion qui se forme sous le contact), la vitesse de recombinaison en surface et l’énergie primaire. La simulation donne le même comportement de variation de Leff que dans le cas expérimental. / The objective of this work is to study certain local properties of structures containing on their surface Ge nanocrystals by using the nano-EBIC (Electron beam induced current collected by a nano-contact). The peculiarity of this technique which uses the same principle as the classical EBIC technique is the use of a conductive AFM (atomic force microscope) tip instead of a standard electrode. We were interested in the determination of the effective diffusion length (Leff) and the study of its variation according to parameters such as the primary energy and the size of nanocrystals. Leff increases for weak energies, reaches a maximum which depends on the nanocrystal size, then decreases for high energies. This behavior of the evolution of Leff was explained in chapter 2. However, this result has never been reported previously. That is why we completed this work by a study based on the Monte-Carlo simulation, where the effect of several parameters was analyzed. Among the parameters studied, we quote the size and the shape of the nano-contact (or more exactly the size of the depletion nano-zone formed under the contact), the surface recombination velocity and the primary energy. The simulation gives the same behavior of Leff variation than the experimental case.