Néon | EPFL Graph Search

Le néon est l'élément chimique de numéro atomique 10, de symbole Ne. Son nom est tiré du grec , « nouveau ». Dans le tableau périodique des éléments, il se trouve dans le groupe principal, ou le groupe de l'UICPA, et appartient donc aux gaz nobles. Comme les autres gaz rares, c'est un gaz incolore, extrêmement inerte et monoatomique. Pour de nombreuses propriétés telles que le point de fusion et d'ébullition ou la masse volumique, il se situe entre l'hélium, plus léger, et l'argon, plus lourd. Le néon est l'un des éléments les plus abondants de l'univers, mais il est relativement rare sur Terre, car, comme l'hélium, une grande partie du gaz s'est échappée dans l'espace. On le trouve principalement dans l'atmosphère terrestre dont il est un des gaz à l'état de traces ; seules de petites quantités sont piégées dans les roches. Comme le krypton et le xénon, le néon est découvert en 1898 par William Ramsay et Morris William Travers par distillation fractionnée de l'air liquide. Les a

Spectroscopy of 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) attached to rare gas samples: Clusters vs. bulk matrices. I. Absorption spectroscopy

Matthieu Dvorak, Wolfgang Harbich, Stefan Minniberger, Alexandre Rydlo

The interaction between 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) and rare gas or para-hydrogen samples is studied by means of laser-induced fluorescence excitation spectroscopy. The comparison between spectra of PTCDA embedded in a neon matrix and spectra attached to large neon clusters shows that these large organic molecules reside on the surface of the clusters when doped by the pick-up technique. PTCDA molecules can adopt different conformations when attached to argon, neon, and para-hydrogen clusters which implies that the surface of such clusters has a well-defined structure without liquid or fluxional properties. Moreover, a precise analysis of the doping process of these clusters reveals that the mobility of large molecules on the cluster surface is quenched, preventing agglomeration and complex formation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4759443]

American Institute of Physics2012

Spectroscopy of 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) attached to rare gas samples: Clusters vs. bulk matrices. II. Fluorescence emission spectroscopy

Matthieu Dvorak, Wolfgang Harbich, Stefan Minniberger, Alexandre Rydlo

The interaction between 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) molecules and solid rare gas samples is studied by means of fluorescence emission spectroscopy. Laser-excited PTCDA-doped large argon, neon, and para-hydrogen clusters along with PTCDA embedded in helium nanodroplets are spectroscopically characterized with respect to line broadening and shifting. A fast non-radiative relaxation is observed before a radiative decay in the electronic ground state takes place. In comparison, fluorescence emission studies of PTCDA embedded in bulk neon and argon matrices result in much more complex spectral signatures characterized by a splitting of the different emission lines. These can be assigned to the appearance of site isomers of the surrounding matrix lattice structure. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4759445]

American Institute of Physics2012

Study of the Optical UV-Visible Electron Induced Luminescence of Small Size Selected Metal Clusters in Rare Gas Solids

Alexandre Rydlo

The optical properties of small size selected metal clusters have been studied by fluorescence spectroscopy. Cun (n = 1-5, 8), Agn (n = 1-5, 8, 9, 20), Aun (n = 1-5, 8) and Nin (n = 1-3) clusters embedded in condensed neon are photoionized by VUV photons in the solid, and the fluorescence originating from the reneutralization of the transient cluster ions is recorded. The VUV photons result from the radiative decay of excitons which are generated by the impact of electrons of variable energy on the solid. A new experimental setup has been developed, which permits the excitation of the rare gas solid by electrons with an energy between 0 and 200 eV. A field emission electron source based on carbon nanotubes provides an intense electron beam without any light generation. A custom built cryopumped gas purification system allows the production of rare gas solids with a purity in the order of up to 10-5. The characteristics and a physical descriptive model of electron induced luminescence is presented. The measurement of electron currents through the solid are thoroughly analyzed. Based on localized exciton production and radiative deexcitation of the host rare gas atoms near the surface of the solid, the excitation can be spread over distances as large as 20-30 µm by high energy photons which excite the species contained in the solid. Quenching and amplification effects on the luminescence intensities are observed depending on the material and the size of the dopants contained in the rare gas solids. These effects are believed to originate from the local enhanced electric field induced by the metal clusters which act as antennas. The analysis of the luminescence spectra reveals rich spectroscopic signatures from the UV to the near IR. A certain amount of fluorescent transitions could be identified from conventional excitation fluorescence spectroscopy. This proves that this new method is sensitive and reliable. The so far reported new transitions await interpretation on the basis of sophisticated quantum calculations.

EPFL2010

Study of the Optical UV-Visible Electron Induced Luminescence of Small Size Selected Metal Clusters in Rare Gas Solids

Alexandre Rydlo

EPFL2010