Laser induced enhancement of dichroism in supported silver nanoparticles deposited by evaporation at glancing angles.

Silver nanoparticles (NPs) depicting well defined surface plasmon resonance (SPR) absorption were deposited on flat substrates by physical vapor deposition in a glancing angle configuration. The particles were characterized by scanning electron microscopy and atomic force microscopy and their optical properties examined by UV-vis absorption spectroscopy using linearly polarized light. It was found that, depending on the amount of deposited silver and the evaporation angle, part of the 'as-prepared' samples present NPs characterized by an anisotropic shape and a polarization dependent SPR absorption and different colors when using polarized white light at 0° and 90°. Low-power irradiation of these materials with an infrared Nd-YAG nanosecond laser in ambient conditions produced an enhancement in such dichroism. At higher powers, the dichroism was lost and the SPR bands shifted to lower wavelengths as a result of the reshaping of the silver NPs in the form of spheres. The possible factors contributing to the observed changes in dichroism are discussed.

Anisotropic In-Plane Conductivity and Dichroic Gold Plasmon Resonance in Plasma-Assisted ITO Thin Films e-Beam-Evaporated at Oblique Angles.

ITO thin films have been prepared by electron beam evaporation at oblique angles (OA), directly and while assisting their growth with a downstream plasma. The films microstructure, characterized by scanning electron microscopy, atomic force microscopy, and glancing incidence small-angle X-ray scattering, consisted of tilted and separated nanostructures. In the plasma assisted films, the tilting angle decreased and the nanocolumns became associated in the form of bundles along the direction perpendicular to the flux of evaporated material. The annealed films presented different in-depth and sheet resistivity as confirmed by scanning conductivity measurements taken for the individual nanocolumns. In addition, for the plasma-assisted thin films, two different sheet resistance values were determined by measuring along the nanocolumn bundles or the perpendicular to it. This in-plane anisotropy induces the electrochemical deposition of elongated gold nanostructures. The obtained Au-ITO composite thin films were characterized by anisotropic plasmon resonance absorption and a dichroic behavior when examined with linearly polarized light.

Bending induced self-organized switchable gratings on polymeric substrates.

We present a straightforward procedure of self-surface patterning with potential applications as large area gratings, invisible labeling, optomechanical transducers, or smart windows. The methodology is based in the formation of parallel micrometric crack patterns when polydimethylsiloxane foils coated with tilted nanocolumnar SiO2 thin films are manually bent. The SiO2 thin films are grown by glancing angle deposition at room temperature. The results indicate that crack spacing is controlled by the film nanostructure independently of the film thickness and bending curvature. They also show that the in-plane microstructural anisotropy of the SiO2 films due to column association perpendicular to the growth direction determines the anisotropic formation of parallel cracks along two main axes. These self-organized patterned foils are completely transparent and work as customized reversible diffraction gratings under mechanical activation.