Mechanisms of resonant low frequency Raman scattering from metallic nanoparticle Lamb modes

International audienceThe low frequency Raman scattering from gold nanoparticle bimodal assemblies with controlled size distributions has been studied. Special care has been paid to determining the size dependence of the Raman intensity corresponding to the quadrupolar Lamb mode. Existing models based on a microscopic description of the scattering mechanism in small particles (bond polarizability, dipole induced dipole models) predict, for any Raman-active Lamb modes, an inelastic intensity scaling as the volume of the nanoparticle. Surprisingly experimental intensity ratios are found to be anomalously much greater than theoretical ones, calling into question this scaling law. To explain these discrepancies, a simple mechanism of Raman scattering, based on the density fluctuations in the nanoparticles induced by the Lamb modes, is introduced. This modeling, in which the nanoparticle is described as an elastic isotropic continuous medium-as in Lamb theory, successfully explains the major features exhibited by low frequency Raman modes. Moreover this model provides a unified picture for any material, suitable for handling both small and large size ranges, as well as non-resonant and resonant excitation conditions in the case of metallic species. Published by AIP Publishing

Enhanced Raman Scattering of amorphous matrices for Fiber Optics Sensor

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Surface-enhanced Raman spectroscopy of the endothelial cell membrane

We applied surface-enhanced Raman spectroscopy (SERS) to cationic gold-labeled endothelial cells to derive SERS-enhanced spectra of the bimolecular makeup of the plasma membrane. A two-step protocol with cationic charged gold nanoparticles followed by silver-intensification to generate silver nanoparticles on the cell surface was employed. This protocol of post-labelling silver-intensification facilitates the collection of SERS-enhanced spectra from the cell membrane without contribution from conjugated antibodies or other molecules. This approach generated a 100-fold SERS-enhancement of the spectral signal. The SERS spectra exhibited many vibrational peaks that can be assigned to components of the cell membrane. We were able to carry out spectral mapping using some of the enhanced wavenumbers. Significantly, the spectral maps suggest the distribution of some membrane components are was not evenly distributed over the cells plasma membrane. These results provide some possible evidence for the existence of lipid rafts in the plasma membrane and show that SERS has great potential for the study and characterization of cell surfaces

Laser treatment of Ag@ZnO nanorods as long-life-span SERS surfaces.

This is the accepted manuscript. The final version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/am506622x.UV nanosecond laser pulses have been used to produce a unique surface nanostructuration of Ag@ZnO supported nanorods (NRs). The NRs were fabricated by plasma enhanced chemical vapor deposition (PECVD) at low temperature applying a silver layer as promoter. The irradiation of these structures with single nanosecond pulses of an ArF laser produces the melting and reshaping of the end of the NRs that aggregate in the form of bundles terminated by melted ZnO spherical particles. Well-defined silver nanoparticles (NPs), formed by phase separation at the surface of these melted ZnO particles, give rise to a broad plasmonic response consistent with their anisotropic shape. Surface enhanced Raman scattering (SERS) in the as-prepared Ag@ZnO NRs arrays was proved by using a Rhodamine 6G (Rh6G) chromophore as standard analyte. The surface modifications induced by laser treatment improve the stability of this system as SERS substrate while preserving its activity.We thank the Junta de Andalucía (TEP8067, FQM-6900 and P12-FQM-2265) and the Spanish Ministry of Economy and Competitiveness (Projects CONSOLIDER-CSD 2008-00023, MAT2011-28345-C02-02, MAT2013-40852-R, MAT2013-42900-P and RECUPERA 2020) for financial support. The authors also thank the European Union Seventh Framework Programme under Grant Agreements 312483-ESTEEM2 (Integrated Infrastructure Initiative-I3) and REGPOT-CT-2011-285895-Al-NANOFUNC, and the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC grant agreement 291522 - 3DIMAGE. R. J. Peláez acknowledges the grant JCI-2012_13034 from the Juan de la Cierva program

Size dispersion effects on the low-frequency Raman scattering of quasispherical silver nanoparticles: Experiment and theory

The coupling between surface plasmon polaritons and confined acoustic vibrations in embedded silver nanoparticles is studied both theoretically and experimentally. The inelastic light scattering spectra simulated assuming deformation potential and surface orientation mechanisms are quantitatively compared to Raman measurements. The effects of size distribution (width and profile) and excitation energy on the low-frequency Raman spectra are addressed in this work and used to provide a characterization tool of the size distribution of metal nanoparticles. The quantitative agreement between measured and simulated spectra supports the fact that the surface orientation mechanism gives the dominant contribution to the resonant Raman scattering mediated by surface plasmon polaritons. © 2007 The American Physical Society.This work was partially supported by MAT2005-06508- C02-01, MEC Spain. J.M. acknowledges financial support from the CSIC and the European Social Fund.Peer Reviewe

Comment on Manna et al. SARS-CoV-2 Inactivation in Aerosol by Means of Radiated Microwaves. Viruses 2023, 15, 1443

International audienceIn a recent article published in Viruses by Manna et al. [1], the authors estimate the resonant frequency of SARS-CoV-2 particles using elastic continuum theory of the vibrational modes of a sphere [2]. Unfortunately, the article provides an incorrect solution to the eigenvalue equation. Although this does not influence the validity of the experimental results, the error will be misleading if the solution is used to select frequencies for testing virus inactivation in other studies. This comment provides details on how to obtain a correct solution numerically

Sculpting nanometer-sized light landscape with plasmonic nanocolumns

Plasmonic structures are commonly used to both confine and enhance surface electromagnetic fields. In the past ten years, their peculiar optical properties have given rise to many promising applications ranging from high density data storage to surface optical trapping. In this context, we investigated both far-field and near-field optical response of a collection of densely packed silver nanocolumns embedded in amorphous aluminum oxide using the discrete dipole approximation. In the far field, a good fit of the calculated to the experimental absorption spectra can only be achieved when in addition to interaction between neighboring nanocolumns, a nanorod shape with periodic shrinks mimicking the experimental morphology of the nanocolumns is used. In the near field, modulated field intensities following the nanocolumns distribution and tunable with the incident wavelength are predicted outside the region occupied by the nanocolumns. This plasmonic image transfer has a resolution of approximately 1.8D where D is the diameter of the nanocolumns that in our case is 2.4 nm. © 2009 American Institute of Physics.Peer Reviewe

Elastic Moduli of Permanently Densified Silica Glasses

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Surface plasmons and vibrations of self-assembled silver nanocolumns

6 pags. ; 5 figs. 1 tab.Optical and vibrational properties of novel self-assembled silver nanocolumns are studied experimentally and theoretically. The split of the surface plasmon resonance into transverse and longitudinal modes verifies the one-dimensional character of the nanocolumns. In this work, we have identified the acoustic vibration modes of the nanocolumns using Raman scattering, as spheroid-like modes (l = 2, m = ±2) involving vibrations of the nanocolumns along their minor axes and the existence of surface plasmon-vibration coupling mechanisms.Acknowledgment. This work was partially supported by MAT2005-06508-C02-01, MEC (Spain), and by EU Network HPRN-CT-2002-00328. J.M. acknowledges an I3P fellowship from the CSIC and the European Social Fund. D.B.M. acknowledges support from NSERC.Peer reviewe

Production of self-aligned metal nanocolumns embedded in an oxide matrix film

3 pags. ; 4 figs.Self-aligned silver nanocolumns embedded in amorphous Al₂O₃ matrix are produced by alternate pulsed laser deposition at room temperature in a single step process. The morphology and the spatial distribution have been investigated by standard, high resolution, and scanning transmission electron microscopy. Polycrystalline nanocolumns having diameters close to 3 nm and heights up to 7 nm are all oriented perpendicular to the substrate surface. The self-alignment of the nanocolumns is the consequence of the deposition of consecutive layers of Ag nanoparticles using the first layer as template for the ordered growth of the nanocolumns. Control over the density, diameter and height of the nanocolumns is achievable by tailoring the deposition sequence.This work was partially supported by TIC2002-03235, CICYT (Spain) and by ESP2002-04509-C04-01, and EU Network HPRN-CT-2002-00328.Peer reviewe