Author
Francis Lévy
Other affiliations: École Normale Supérieure, ETH Zurich, École Polytechnique ...read more
Bio: Francis Lévy is an academic researcher from École Polytechnique Fédérale de Lausanne. The author has contributed to research in topics: Thin film & Sputtering. The author has an hindex of 51, co-authored 241 publications receiving 11643 citations. Previous affiliations of Francis Lévy include École Normale Supérieure & ETH Zurich.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this article, the metastable phase anatase has been shown to have a wider optical absorption gap than rutile thin films, which is consistent with the high mobility, bandlike conduction observed in anatase crystals.
Abstract: Electrical and optical spectroscopic studies of TiO2 anatase thin filmsdeposited by sputtering show that the metastable phase anatase differs in electronic properties from the well‐known, stable phase rutile. Resistivity and Hall‐effect measurements reveal an insulator–metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self‐trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.
1,560 citations
TL;DR: In this paper, the experimental density of states (DOS) was found to be in agreement with the theoretical DOS reported in the literature for anatase crystals, and shows some characteristics similar to the experimental DOS reported for rutile crystals.
Abstract: Photoemission spectromicroscopy was used to investigate the electronic structure of TiO2 anatase single crystals and polycrystalline thin films The stoichiometry and the degree of oxidation of as-grown crystals, as-deposited films, as well as of thermally annealed samples in different atmospheres, were analyzed, based on the Ti 2p and O 1s core levels, with an energy resolution of 04 eV The experimental density of states (DOS) was found to be in agreement with the theoretical DOS reported in the literature for anatase crystals, and shows some characteristics similar to the experimental DOS reported for rutile crystals In reduced samples, the experimental DOS is characterized by intense emission in the region of O 2p bonding orbitals, and does not exhibit an appreciable density of states in the band gap As-grown crystals exhibit small band gap emission (a few percent of the valence band VB signal) at about 08 eV, which is attributed to Ti3+ (3d) defect states Annealing the crystals at high temperatures in O2 or subsequent thermal reduction in an Ar-H2 Mixture (95%-5%) produces nearly stoichiometric surfaces with smaller or undetectable density of Ti3+ States In addition, some redistribution of the spectral weight is observed in the VB spectra
664 citations
TL;DR: The synthesis, structure, and self-assembly of single-wall subnanometer-diameter molybdenum disulfide tubes are reported on, using a novel type of catalyzed transport reaction including C60 as a growth promoter.
Abstract: We report on the synthesis, structure, and self-assembly of single-wall subnanometer-diameter molybdenum disulfide tubes. The nanotubes are up to hundreds of micrometers long and display diverse self-assembly properties on different length scales, ranging from twisted bundles to regularly shaped "furry" forms. The bundles, which contain interstitial iodine, can be readily disassembled into individual molybdenum disulfide nanotubes. The synthesis was performed using a novel type of catalyzed transport reaction including C(60) as a growth promoter.
483 citations
TL;DR: In this article, resistivity, thermopower, and Hall-effect measurements on large single crystals of the anatase form of TiO2 all indicate high mobility n-type carriers that are produced by thermal excitation from a density of ∼1018 cm−3 putatively present shallow donor states.
Abstract: Resistivity, thermopower, and Hall‐effect measurements on large single crystals of the anatase form of TiO2 all indicate high mobility n‐type carriers that are produced by thermal excitation from a density of ∼1018 cm−3 putatively present shallow donor states. The decrease of the mobility with increasing temperature is consistent with the scattering of carriers by the optical phonons of TiO2.
462 citations
TL;DR: The drive to develop detectors capable of counting the number of photons in a weak optical pulse is motivated by potential applications in quantum computing as discussed by the authors, where superconducting nanostructures are one exciting approach: offering high sensitivity and operate at repetition rates up to 80 MHz.
Abstract: The drive to develop detectors capable of counting the number of photons in a weak optical pulse is motivated by potential applications in quantum computing. Superconducting nanostructures are one exciting approach: offering high sensitivity and operate at repetition rates up to 80 MHz.
415 citations
Cited by
More filters
TL;DR: Because monolayer MoS(2) has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors, and could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting.
Abstract: Two-dimensional materials are attractive for use in next-generation nanoelectronic devices because, compared to one-dimensional materials, it is relatively easy to fabricate complex structures from them. The most widely studied two-dimensional material is graphene, both because of its rich physics and its high mobility. However, pristine graphene does not have a bandgap, a property that is essential for many applications, including transistors. Engineering a graphene bandgap increases fabrication complexity and either reduces mobilities to the level of strained silicon films or requires high voltages. Although single layers of MoS(2) have a large intrinsic bandgap of 1.8 eV (ref. 16), previously reported mobilities in the 0.5-3 cm(2) V(-1) s(-1) range are too low for practical devices. Here, we use a halfnium oxide gate dielectric to demonstrate a room-temperature single-layer MoS(2) mobility of at least 200 cm(2) V(-1) s(-1), similar to that of graphene nanoribbons, and demonstrate transistors with room-temperature current on/off ratios of 1 × 10(8) and ultralow standby power dissipation. Because monolayer MoS(2) has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors. Monolayer MoS(2) could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting.
12,477 citations
9,432 citations
TL;DR: Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency as mentioned in this paper, and many DSC research groups have been established around the world.
Abstract: Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...
8,707 citations
TL;DR: This observation shows that quantum confinement in layered d-electron materials like MoS(2), a prototypical metal dichalcogenide, provides new opportunities for engineering the electronic structure of matter at the nanoscale.
Abstract: Novel physical phenomena can emerge in low-dimensional nanomaterials. Bulk MoS2, a prototypical metal dichalcogenide, is an indirect bandgap semiconductor with negligible photoluminescence. When the MoS2 crystal is thinned to monolayer, however, a strong photoluminescence emerges, indicating an indirect to direct bandgap transition in this d-electron system. This observation shows that quantum confinement in layered d-electron materials like MoS2 provides new opportunities for engineering the electronic structure of matter at the nanoscale.
7,886 citations
TL;DR: The field of photocatalysis can be traced back more than 80 years to early observations of the chalking of titania-based paints and to studies of the darkening of metal oxides in contact with organic compounds in sunlight as discussed by the authors.
5,729 citations