We report on the unusually high optical transmitivity of silver coated two-dimensional colloidal crystals. Our sample consists
of a 50 nm silver film deposited on top of a regular two-dimensional array of polystyrene spheres of 400 nm diameter. Two-dimensional
colloidal crystals were prepared according to the drop-coating technique, and subsequently covered in a silver
film by thermal evaporation. Morphology of the crystal was checked by means of scanning electron microscopy. We
measured transmission through the composite metallo-dielectric films at normal and also oblique incidence. Additional
reflectance spectra and surface enhanced Raman scattering are used to understand the optical/plasmonic properties of the
prepared nanostructure. Dependence of the spectral features on incident angle suggests highly localized optical/plasmonic
modes are involved in the mechanism of transmission.
The objective of this study is to develop a procedure for controlling the deposition of colloidal crystal coatings from
nanoparticle suspensions. We experimentally deposited polystyrene nanospheres on glass plates by dragging a small
volume of liquid over the substrates. The mechanism governing the deposition is convective assembly. It has been
observed that the number of deposited nanosphere layers can be influenced by the deposition speed and the nanosphere
volume fraction, as predicted by theory. Crystal coatings of a few square centimeters were deposited in minutes from
suspensions of 5 - 20 μL. Our computer simulations of the phenomena generated structures similar to those from
experimental films, proving the validity of the model elaborated for the assembly process.
A chemical system consisting of a metallic salt, a water-soluble polymeric matrix and a photosensitive specie absorbing
at two-photon, has been used to produce metal deposition upon exposure to a femtosecond laser. We show that this
technique can be used to fabricate 2D and 3D metallic structures with gold and silver. We illustrate the potential use of
this technique for the fabrication of optical diffractive structures and we report on the first observations of spectral
filtering effects in the near vicinity of micro/nano structures.
We are using the technique of two-photon induced photoprecipitation to fabricate gold and silver nanostructures. Gold and silver nanoparticles are produced in solution as well as in thin films. In both cases an absorption peak associated with the plasmon resonance is clearly observed and is found to vary as particles grow. In addition, we show that this technique also permits the fabrication of 2D and 3D metallic nanostructures with a good quality. The potential for optical applications is discussed and illustrated on some examples. In particular, we observe high efficiency luminescence and strong tunable diffusion.
Zero-order transmission silver gratings of very narrow and deep enough slits exhibit exceptional transmission properties in visible and near-IR light. By using a rigorous electromagnetic analysis of light diffraction, we show that the transmission enhancement occurs as a result of a resonant interaction of the incident light with surface plasmons located inside the grating slits.
We study from a theoretical point of view the electromagnetic enhancement related to the surface enhanced Raman scattering on silver gratings. The local field is obtained by means of numerical calculations based on the rigorous coupled-wave analysis. Enhancements of up to 106 in the Raman signal of molecules adsorbed on these gratings could be obtained at the excitation wavelength (lambda) equals 514 nm.
Optical excitation at low temperature of pentacene guest molecules in benzoic acid crystals leads to the appearance of a great variety of defect structures. The reaction mechanism proposed is the transfer of a proton from the matrix to the dye forming a very unstable hydrogenated complex of pentacene which relaxes to ground state pentacene and a proton in a defect position of matrix. These results may serve as model for the study of spectral holeburning and spectral diffusion processes in amorphous solids.
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