Isabel Romero

Donostia International Physics Center, San Sebastián, Basque Country, Spain

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Publications (9)31.62 Total impact

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    Isabel Romero · F Javier García de Abajo
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    ABSTRACT: We study the optical properties of metamaterials formed by layers of metallic nanoparticles. The effective optical constants of these materials are retrieved from the calculated angle-dependent Fresnel reflection coefficients for s and p incident-light polarization. We investigate the degree of anisotropy in the effective permittivity as a function of inter-layer spacing, particle size, filling fraction of the metal, and particle shape. For layers of spherical particles periodically arranged in a hexagonal lattice, the anisotropy disappears for the three inter-layer spacings corresponding to simple cubic (sc), bcc, and fcc volume symmetry. For non-spherical particles, an isotropic response can be still obtained with other values of the inter-layer spacing. Finally, we provide a quantitative answer to the question of how many layers are needed to form an effectively homogeneous metamaterial slab. Surprisingly, only one layer can be enough, except in the spectral range close to the particle plasmon resonances.
    Full-text · Article · Nov 2009 · Optics Express
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    ABSTRACT: We identify weak and strong coupling regimes between a near-field probing tip and a plasmonic sample by imaging plasmon-resonant gold nanodisks with scattering-type scanning near-field optical microscopy s-SNOM. By means of rigorous electrodynamical calculations based on a model system, we find that in the weak coupling regime, s-SNOM can be applied for direct mapping of plasmonic nanoantenna modes, while in the strong coupling regime, the near-field probe allows for high-precision opto-mechanical control of the antenna response.
    Full-text · Article · Mar 2009 · Physical review. B, Condensed matter
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    ABSTRACT: Imaging plasmon-resonant gold nanodisks acting as optical nanoantennas by scattering-type near-field optical microscopy (s-SNOM), we identify weak and strong coupling regimes between the near-field probe and the plasmonic nanoantenna sample. By means of rigorous electrodynamical calculations based on a model system, we find that in the weak coupling regime, s-SNOM can be applied for direct mapping of plasmonic nanoantenna modes, while in the strong coupling regime, the near-field probe allows for high-precision opto-mechanical control of the antenna response.
    No preview · Article · Mar 2009
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    ABSTRACT: Plasmonic nanoparticle pairs known as "dimers" embody a simple system for generating intense nanoscale fields for surface enhanced spectroscopies and for developing an understanding of coupled plasmons. Individual nanoshell dimers in directly adjacent pairs and touching geometries show dramatically different plasmonic properties. At close distances, hybridized plasmon modes appear whose energies depend extremely sensitively on the presence of a small number of molecules in the interparticle junction. When touching, a new plasmon mode arising from charge transfer oscillations emerges. The extreme modification of the overall optical response due to minute changes in very reduced volumes opens up new approaches for ultrasensitive molecular sensing and spectroscopy.
    Full-text · Article · May 2008 · Nano Letters
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    ABSTRACT: Plasmon propagation is investigated in arrays of silica particles buried in gold. Long propagation distances are obtained, thus providing a realistic scenario for plasmonic circuits based upon buried structures.
    No preview · Conference Paper · Sep 2007
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    ABSTRACT: The dielectric properties of metamaterials consisting of periodically arranged metallic nanoparticles of spherical shape are calculated by rigorously solving Maxwell's equations. Effective dielectric functions are obtained by comparing the reflectivity of planar surfaces limiting these materials with Fresnel's formulas for equivalent homogeneous media, showing mixing and splitting of individual-particle modes due to inter-particle interaction. Detailed results for simple cubic and fcc crystals of aluminum spheres in vacuum, silver spheres in vacuum, and silver spheres in a silicon matrix are presented. The filling fraction of the metal f is shown to determine the position of the plasmon modes of these metamaterials. Significant deviations are observed with respect to Maxwell-Garnett effective medium theory for large f, and multiple plasmons are predicted to exist in contrast to Maxwell-Garnett theory. Comment: 6 pages, 4 figures
    Full-text · Article · Aug 2007 · Physical review. B, Condensed matter
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    ABSTRACT: Plasmons in structured metallic systems have attracted considerable attention over the last few years as promising candidates to realize plasmon guiding, plasmon amplification, and in general, optical components at the nanoscale. Examples of these systems are chains of nanoparticles, where
    No preview · Article · Jun 2007
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    ABSTRACT: The response of gold nanoparticle dimers is studied theoretically near and beyond the limit where the particles are touching. As the particles approach each other, a dominant dipole feature is observed that is pushed into the infrared due to interparticle coupling and that is associated with a large pileup of induced charge in the interparticle gap. The redshift becomes singular as the particle separation decreases. The response weakens for very small separation when the coupling across the interparticle gap becomes so strong that dipolar oscillations across the pair are inhibited. Lowerwavelength, higher-order modes show a similar separation dependence in nearly touching dimers. After touching, singular behavior is observed through the emergence of a new infrared absorption peak, also accompanied by huge charge pileup at the interparticle junction, if initial interparticle-contact is made at a single point. This new mode is distinctly different from the lowest mode of the separated dimer. When the junction is made by contact between flat surfaces, charge at the junction is neutralized and mode evolution is continuous through contact. The calculated singular response explains recent experiments on metallic nanoparticle dimers and is relevant in the design of nanoparticle-based sensors and plasmon circuits.
    Full-text · Article · Nov 2006 · Optics Express

  • No preview · Article · Jan 2006 · Physical Review B