Plasmon | EPFL Graph Search

Dans un métal, un plasmon est une oscillation de plasma quantifiée, ou un quantum d'oscillation de plasma. Le plasmon est une quasiparticule résultant de la quantification de fréquence plasma, tout comme le photon et le phonon sont des quantifications de vibrations respectivement lumineuses et mécaniques. Ainsi, les plasmons sont des oscillations collectives d'un gaz d'électrons, par exemple à des fréquences optiques. Le couplage d'un plasmon et d'un photon crée une autre quasiparticule dite plasma polariton. Depuis que les plasmons sont définis comme la quantification des oscillations de plasma classique, la plupart de leurs propriétés peuvent être calculées directement à partir des équations de Maxwell. Éléments de théorie Les oscillations de plasma d'un métal peuvent être comprises dans le cadre d'une théorie classique. Si on suppose que les ions sont fixes, et que les électrons peuvent se déplacer en bloc, et que x est la position du centre de masse

Nanoparticle on mirror plasmonic nanostructure for molecular cavity optomechanics

Aqeel Ahmed, Christophe Marcel Georges Galland, Nils Kipfer, Tianqi Zhu

The plasmonic response of gold can be utilized to enhance the incident electromagnetic (EM) field by several orders of magnitude. When a gold nanoparticle is placed in close proximity to a gold film, the incident field can excite a deeply confined plasmon, strongly enhancing the Raman interaction with molecules placed within the gap. Recent theoretical predictions suggest the suitability of such arrangements to optically amplify the internal vibrations of molecules. This paper presents the fabrication and characterization of such plasmonic nanocavities.

IEEE2018

Optical properties of small metal clusters

Chongqi Yu

This thesis is devoted to the study of the optical properties of small metal clusters and metal cluster organic compounds. For this purpose a ultra-high vacuum (UHV) experimental apparatus has been built which allows for the deposition of mass selected neutral clusters in a size range up to 16,000 amu which corresponds to Ag150 or Au80. Cluster cations are produced in a gas aggregation cluster source, steered in an ion optics device and co-deposited with electrons and excess rare gas on a cryogenic deposition head. Neutral mono dispersed clusters are analyzed by optical absorption, fluorescence and excitation spectroscopy in the UV-visible energy range. A novel custom-made conical octupole combined to an organic molecule injector has been built, serving as a generator of metal cluster-organic compounds. These are atomically precise model systems which permit to study surface-enhanced Raman scattering (SERS) in order to test the theoretical models and better understand the mechanism of SERS. Optical absorption on size-selected silver clusters of Agn (n= 20 â 120) embedded in neon solid matrix was investigated. The spectra show plasmon-like absorption profiles around a photon energy of 4.0 eV which match in energy molecular like absorption spectra for the smallest Ag clusters but are sensitively higher than what would be expected for the dipolar absorption for bulk silver of about 3.3 eV. The central absorption peak, i.e. the plasmon energy as a function of cluster size is presented. The data fall in a transition between a blueshift of the plasmon resonance with decreasing size to a superimposed red shift for the very smallest sizes. Superimposed, we observe a distinct structure where clusters with atom number of 8,18,34,58,92 show a localized maximum value of the plasmon energy. These numbers correspond perfectly to the fully filled states of 1p, 1d, 1f, 1g and 1h according to the electronic shell model, manifesting a clear sub-shell effect. Optical absorption, fluorescence and excitation spectroscopy on size-selected small gold clusters of Aum (m= 19,20,21) embedded in solid neon were measured. These are the first optical data on ligand free neutral atomically precise Au clusters. Au20, the famous tetraedic structure, shows a rich structured absorption spectrum, superimposed on a continuous background increasing to the UV part of the spectrum. Au21 and Au19 show the same tendency, however without any superimposed structure. Very interestingly, all three Au clusters show strong fluorescence centered at around 1.85 eV, here again Au20 being the prominent species. Comparison to ligand protected Au clusters clearly proves that the fluorescence comes from the Au cluster itself and is only weakly influenced by the ligands. For the first time, size-selected small metal-organic compounds of silver-pyridine AgaPyb (a= 1,3; b= 1,2) which are prototypes for surface enhanced Raman scattering (SERS) have been produced and isolated in a solid Ne matrix. Optical absorption and fluorescence spectra have been measured. Raman scattering cross sections with an enhancement factor of 103 have been found in fair agreement with recent high level time-dependent density functional theory (TDDFT) calculations.

EPFL2015

Programmable chiral nanocolloids

Hyeonho Jeong

Nanoparticles promise a variety of application in energy, medicine, and biology. However, most nanoparticlesâ material composition and shape cannot be tuned and so functions have thus far been limited. Moreover they are often also chemically unstable in solution. Therefore, the overall goal of this thesis is to develop nanoparticles whose function and shape can be programmed and that can be corrosion protected, and to then apply these nanoparticles to sensing tasks in complex biological fluids. A special focus of this thesis is chiral nanostructures. A promising technique to address this is physical vapour shadow growth, namely nano glancing angle depo-sition (nanoGLAD). This scheme allows the design of new three-dimensional (3D) hybrid nanoparticles as it permits the control over both the shape and material composition of the nanoparticles. Although this method offers the possibility to grow nanoparticles that are functionally programmed, it has so far not al-lowed the use of many materials that are chemically unstable in solution, which limits the scope of poten-tial applications. This thesis starts with describing the nanoGLAD growth procedure. A first application is the wafer-scale patterning of unconventional nanoshapes, e.g. tri-layer particles, holes, rings, and hollow domes, which are not possible using state of the art 3D nanofabrication methods (chapter 2). Then, in conjunction with atom-ic layer deposition (ALD), this thesis shows how the nanoGLAD scheme can be adapted for the fabrication of â3D core-shell nanoparticles and nanocolloidsâ using unstable and reactive materials. The key concept here is that the core consists of the unstable material which is grown such that the shell contains no voids or defects (chapter 3). Notably, the shapes that can be grown include symmetry-broken chiral nanoparti-cles, which possess unique spectral properties that make them useful for sensing applications. This thesis uses chiral nanocolloids to realise extremely sensitive plasmonic nanosensors and nanocolloids that can also be used as a nanomechanical probes for active nanorheology. By forming a composite of two materials during growth â one that gives a strong plasmonic response and the other to tune the compositeâs dielec-tric function â plasmonic nanoparticles are presented that show record local surface plasmon resonance (LSPR) sensitivities to date (chapter 4). With the same alloying principle a plasmonic and a ferromagnetic material are combined. The resulting âchiral + plasmonic + ferromagneticâ particles can be actuated using a magnetic field and this is used to measure the viscosity of blood plasma in the presence of blood cells. The viscosity of blood serum is an important disease indicator, but the measurement using commercial rheome-ters requires the separation of the blood cells. This is not needed in the nanorheological measurements shown in this thesis (chapter 5).

EPFL2017