Fulvio Ratto

PHD Student

Université du Québec
Institut national de la recherche scientifique
Énergie, Matériaux et Télécommunications
1650, boulevard Lionel-Boulet
Varennes, Québec, Canada
J3X 1S2

Telephone: +1 (450) 929-8206
Fax: +1 (450) 929-8102
ratto@emt.inrs.ca
www.emt.inrs.ca

Fulvio Ratto Curriculum Vitae (11/2004)

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The current optoelectronic technology is ever more suffering from major drawbacks, which are prompting the quest for alternative solutions. Aspects of major concern touch on the incompatibility of opto- and microelectronic components, as well as the growing difficulties in shrinking the dimensions of transistors. The self-assembly of Ge(Si) quantum dots (QDs) on Si surfaces represents an ideal solution to both problems. Indeed, the carrier confining nano-islands resulting by deposition of Ge on Si substrates may be exploited for applications as diverse as Si-based lasers, quantum computers or biosensors. For these reasons, these systems have been widely investigated in the past. Still, the shortage of experimental techniques allowing for a dynamic characterization of the relevant evolution processes has always been hindering a unique picture of the atomistic phenomena leading to the QDs self-assembly. Characterizing all the diffusion and inter-diffusion processes at the surface may allow for a comprehensive understanding of the optoelectronic behaviour of individual nano-islands and of the kinetic pathways that trigger their nucleation and evolution. The goal of the project is that of gaining such an insight, in order to achieve control over the overall system properties.

Quantum confinement in nanostructured materials often stems from chemical and strain gradients at the nanoscale. Our group has recently developed a novel approach for mapping the stoichiometry of compound semiconductors with resolution in the nanorange. It consists of a new analytical procedure for gaining quantitative information from sequences of energy–filtered X–Ray Photoemission Electron Microscopy images. As a non–destructive tool for accessing the nanoscale spectroscopically, the experimental technique offers substantial advantages with respect to competitive methods presently in use.

Left panel: a Low Energy Electron Microscopy image of a Ge(Si) island obtained by depositing 10 ML Ge on an as–cleaned Si(111) substrate at 450 °C. Right panel: corresponding surface Si concentration map obtained by processing sequences of synchrotron X–Ray Photoemission Electron Microscopy images and spectra. The center is clearly depleted in silicon, i.e. enriched in germanium, pointing to the overwhelming role of kinetic diffusion dynamics in determining the intermixing phenomena (from: F. Ratto, A. Locatelli, S. Fontana, S. Kharrazi, S. Ashtaputre, S.K. Kulkarni, S. Heun, F. Rosei, ‘Chemical mapping of individual semiconductor nanostructures’, Small 2, 401 (2006)).