Francis Lévy | EPFL Graph Search

Après sa formation secondaire à La Chaux-de-Fonds, Francis Lévy étudie à l'Ecole Polytechnique Fédérale de Zurich où il obtient le diplôme de physicien (1963). Assistant au Laboratoire de physique des corps solides de l'ETHZ, il publie sa thèse de doctorat sur les propriétés structurales et magnétiques de composés des terres rares (1969). A l'Institut de physique appliquée de l'EPFL, ses recherches concernent la croissance de cristaux et la physique des semi-conducteurs. De 1974 à 1975, au Laboratoire Cavendish de l'Université de Cambridge (UK), il étudie les matériaux à structures cristallines de basse dimensionnalité et leurs propriétés électroniques. De retour à l'EPFL, ses recherches portent sur de nombreux composés des métaux de transition. Il crée un groupe de recherche sur la physique et les technologies pour les couches minces. Ses travaux visent à comprendre les propriétés physique et chimiques de couches minces fonctionnelles en relation avec des caractéristiques structurales et électroniques ainsi qu'avec des paramètres de dépôt.

Avec le titre de professeur (1987), il enseigne la physique générale, la physique du solide et des semi-conducteurs. Il est l'auteur du volume 18 du Traité des Matériaux: Physique et Technologie des Semi-conducteurs (PPUR) ainsi que auteur ou coauteur de plus de 460 publications scientifiques originales.

Influence of gold particle size on the photocatalytic activity for acetone oxidation of Au/TiO2 catalysts prepared by dc-magnetron sputtering

Francis Lévy

Two series of Au/TiO2 materials with different gold content have been prepared by dc-magnetron sputtering on ceramic shaped pure anatase or Degussa P25 TiO2. The time of deposition was varied between 1 and 20 min in order to obtain different thickness and nanoparticle size of the gold films. For comparison samples with Au loadings in the range 0.3-0.9 wt% were prepared using the deposition-precipitation methodology. The obtained materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). DR-UV-Vis and atomic force and scanning electron microscopy techniques. The photocatalytic activity was checked in the photo-oxidation of acetone under both UV and visible irradiation conditions. Several factors were found to influence the photoactivity. An optimal Au content corresponding to a maximum activity is observed and attributed to the occurrence of adequate titania surface coverage and Au particle size. The support plays an important role and it was found that pristine anatase on which gold (average particle size 7.7 nm) was deposed by dc-reactive sputtering exhibits the maximum of the activity. Samples prepared by dc-sputtering were more active than samples prepared by deposition-precipitation method. Also, the photocatalysts prepared using dc-reactive sputtering showed activity under both UV and visible light irradiation, while those prepared using the deposition-precipitation technique are active only under UV light. The most likely mechanism of gold activation of titania is that upon light absorption, gold nanoparticles inject electrons into the titania conduction band. (C) 2011 Elsevier B.V. All rights reserved.

2011

Nanoscale Optical Detector with Single-Photon and Multiphoton Sensitivity

Alessandro Gaggero, Francis Lévy, Francesco Marsili

We present the first nanoscale (down to approximate to 50 x 50 nm(2)) detector displaying single-photon sensitivity and a nanosecond response. This type of nanodetector can also be operated in multiphoton mode, where the detection threshold can be set at N = 1, 2, 3, or 4 photons, thus allowing the mapping of photon number statistics on the nanoscale. Its operation principle based on that of hot-spot formation in superconducting nanowires allies the temporal resolution and sensitivity of superconducting single-photon detectors with subwavelength resolution and photon number discrimination. Such detectors can be of great interest for the study of nanophotonic devices at low temperature.

2010

High quality superconducting NbN thin films on GaAs

Alessandro Gaggero, Francis Lévy, Francesco Marsili, Alessandro Surrente

A very promising way to increase the detection efficiency of nanowire superconducting single-photon detectors (SSPDs) consists in integrating them with advanced optical structures such as distributed Bragg reflectors (DBRs) and optical waveguides. This requires transferring the challenging SSPD technology from the usual substrates, i.e. sapphire and MgO, to an optical substrate like GaAs, on which DBRs and waveguides can be easily obtained. Therefore, we optimized the deposition process of few-nm thick superconducting NbN films on GaAs and AlAs/GaAs-based DBRs at low temperatures (substrate temperature T-S = 400 degrees C), in order to prevent As evaporation. NbN films ranging from 150 to 3 nm in thickness were then deposited on single-crystal MgO, GaAs, MgO-buffered GaAs and DBRs by current-controlled DC magnetron sputtering (planar, circular, balanced configuration) of Nb in an Ar + N-2 plasma. 5.5 nm thick NbN films on GaAs exhibit T-C = 10.7 K, Delta T-C = 1.1 K and RRR = 0.7. The growth of such high quality thin NbN films on GaAs and DBRs has never been reported before.

2009