84 research outputs found
High-resolution microscopy of plasmon field distributions by scanning tunneling luminescence and photoemission electron microscopies
Experimental study of hot spots in gold/glass nanocomposites films by photoemission electron microscopy
International audienceIn this paper, an experimental study of hot spots in gold/dielectric films using photoemission electron microscopy is reported. This technique allows a characterization of the statistical optical properties with unprecedented accuracy in the 800- to 1040-nm range. Theoretical predictions of the scaling theory on the number and intensity wavelength dependences of hot spots in the near-infrared are confirmed. Statistical properties of the intensity distribution, spectral behavior, and spatial localization of the hot spots are reported
Two-photon luminescence of single colloidal gold nanorods: revealing the origin of plasmon relaxation in small nanocrystals
The two-photon luminescence (TPL) of small 10 nm x 40 nm colloidal gold
nanorods (GNR) is investigated at the single object level, combining
polarization resolved TPL and simultaneously acquired topography. A very high
dependence of the TPL signal with both the nanorods longitudinal axis and the
incident wavelength is observed confirming the plasmonic origin of the signal
and pointing the limit of the analogy between GNRs and molecules. The spectral
analysis of the TPL evidences two emission bands peaks: in the visible (in
direct connection with the gold band structure), and in the infrared. Both
bands are observed to vary quadradically with the incident excitation beam but
exhibit different polarization properties. The maximum two-photon brightness of
a single GNR is measured to be a few millions higher than the two-photon
brightness of fluorescein molecules. We show that the important TPL observed in
these small gold nanorods results from resonance effects both at the excitation
and emission level : local field enhancement at the longitudinal surface
plasmon resonances (LSPR) first results in an increase of the electron-hole
generation. Further relaxation of electron-hole pairs then mostly leads to the
excitation of the GNR transverse plasmon mode and its subsequent radiative
relaxation
Diffraction d'Ă©lectrons lents - DEL. Diffraction d'Electrons Lents DEL, Low Energy Electron Diffraction LEED, Low Energy Electron Microscopy LEEM
MasterDiffraction Ă©lastique d'Ă©lectrons lents par la surface d'un Ă©chantillon cristallin - DEL, LEED. Reconstructions de surface. Niveau Master 2. Univ. Paris Sacla
Nanostructures, de l'élaboration aux propriétés
The work presented in this memorandum sums up a significant part of my research activity in surfacescience. The adopted central theme belongs to the nanoscience research area, from the fabrication ofstructures of interest to their physical properties. Nanoscience and nanotechnology manipulate elementary entities, such as atoms and molecules, tofabricate coherent structures of specific functional properties. This objective is achieved through two differentapproaches, either a descending top down or an ascending bottom-up way. The top-down approach proceedsby continuous down scaling of objects and structures validated at macro and mesoscopic scales. On theopposite the ascending bottom-up route seeks to have elementary bricks built up into increasingly complexassemblies. This work aims at an illustration of the ascending way. In a first part, I report a series of works dedicated to the fabrication of nanostructures of interesttaking advantage of spontaneous physical processes leading to spatial self-organization. Particular emphasis isgiven to two surface structuration methods (i) the growth kinetic instabilities and (ii) the supramolecular selfassemblingprocesses. A growth instability is an out of equilibrium process intrinsic to the growth of a crystal. These morphological instabilities result from the interplay between antagonist forces and are responsible forthe efficient in-plane nanostructuration of the growth interface on a 10-nanometer scale. For stepped surfaces,also known as vicinal surfaces, the morphological growth instabilities at work close to the room temperatureare the meandering and the step bunching instabilities. For their parts self-assembling processes arespontaneous processes responsible for the reversible organization of molecular units into ordered structures bynon-covalent interactions at a solid surface. Precise handling of the latter allows for direct driving of theordering pattern. This method needs a clear understanding of supramolecular architectures and makes use ofmolecular engineering capabilities. The use of surface reconstructions and light matter interaction are alsobriefly mentioned. Beyond purely dimensional aspects, this work aims at the investigation and development of specificfunctional aspects of the fabricated nanostructures. In a second part of the manuscript, I so focus on someresults on the physical properties of supramolecular architectures (molecular sieve) and the plasmonics ofnano-objects. For the latter a particular emphasis is given to an efficient near field mapping technique, thephotoemission electron microscopy.Ce travail de synthèse reprend une part significative de mon activité de recherche en physique dessurfaces. Le fil conducteur adopté relève de la thématique nanoscience, de l’élaboration de structuresd’intérêt à leurs propriétés physiques. Nanoscience et nanotechnologie envisagent la manipulation et l’agencement d’entités élémentaires(atomes, molécules) sous forme de structures cohérentes à usages fonctionnels. Cet objectif est accessible viadeux voies distinctes, une voie descendante top-down et une voie ascendante bottom-up. La voie descendanteprocède par miniaturisation progressive d’objets et de structures validés aux échelles macro- et mésoscopique. La voie ascendante consiste à assembler des composants élémentaires (atomes, molécules) pour fabriquer desstructures fonctionnelles de complexité croissante. Ce travail de synthèse constitue une illustration de la voieascendante. Dans une première partie, je rapporte une série de travaux consacrés à l’élaboration de structuresd’intérêt par la mise à profit de phénomènes physiques spontanés d’auto-organisation spatiale. Deux outils denanostructuration des surfaces sont plus particulièrement traités. Il s’agit des instabilités cinétiques decroissance et des processus d’autoassemblage supramoléculaire. Le premier désigne un processus horsd’équilibre intrinsèque à la croissance par épitaxie d’un cristal. Ces instabilités morphologiques, issues de lacompétition entre forces antagonistes, structurent efficacement l’interface de croissance à l’échelle de ladizaine de nanomètres. Dans le cas de surfaces à marches, surfaces dites vicinales, les instabilités à l’oeuvre auvoisinage de la température ambiante sont les instabilités de méandre et de mise en paquets des fronts demarche. Le second outil vise au pilotage de la physique d’assemblage de molécules à la surface d’un solide autravers de la maîtrise des interactions molécule\substrat. Ce travail s’appuie sur un effort de compréhensiondes architectures supramoléculaires et une étape d’ingénierie amont des molécules cibles. En complément,l’emploi de reconstructions de surface et de processus d’interaction lumière matière sont également abordés. Au–delà des aspects purement dimensionnels, ce travail s’attache à l’étude et la mise en valeur decertains aspects fonctionnels des nanostructures obtenues. Dans une seconde partie de ce document, j’abordeainsi quelques résultats liés aux propriétés physiques des assemblages supramoléculaires (fonctions detamis moléculaires) et à la plasmonique de nano-objets métalliques via la mise à profit d’une alternative auxoutils d’investigation usuels, à savoir la microscopie de photoémission d’électrons
Spectrométrie des électrons Auger - Auger Electron Spectroscopy AES
MasterSpectrométrie des électrons Auger. Auger Electron Spectroscopy AES, AES-X (X-ray excitation), AES-E (Electron excitation), Scanning Auger Microscopy SAM
Microscopies Ă force atomique AFM, DFM, MFM, EFM, LFM
MasterMicroscopie à force atomique. Imager une surface via la mesure des forces d’interaction qui s’exercent entre les atomes d’une surface et ceux d’une pointe sonde
- …