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San Sebastián de los Reyes, Spain

Teperik T.V.,University Paris - Sud | Nordlander P.,Rice University | Aizpurua J.,Material Physics Center EHU | Aizpurua J.,Donostia International Physics Center | And 2 more authors.
Optics Express | Year: 2013

Using a fully quantum mechanical approach we study the optical response of a strongly coupled metallic nanowire dimer for variable separation widths of the junction between the nanowires. The translational invariance of the system allows to apply the time-dependent density functional theory (TDDFT) for nanowires of diameters up to 10 nm which is the largest size considered so far in quantum modeling of plasmonic dimers. By performing a detailed analysis of the optical extinction, induced charge densities, and near fields, we reveal the major nonlocal quantum effects determining the plasmonic modes and field enhancement in the system. These effects consist mainly of electron tunneling between the nanowires at small junction widths and dynamical screening. The TDDFT results are compared with results from classical electromagnetic calculations based on the local Drude and non-local hydrodynamic descriptions of the nanowire permittivity, as well as with results from a recently developed quantum corrected model. The latter provides a way to include quantum mechanical effects such as electron tunneling in standard classical electromagnetic simulations. We show that the TDDFT results can be thus retrieved semi-quantitatively within a classical framework. We also discuss the shortcomings of classical non-local hydrodynamic approaches. Finally, the implications of the actual position of the screening charge density at the gap interfaces are discussed in connection with plasmon ruler applications at subnanometric distances. © 2013 Optical Society of America.

Barroso-Bujans F.,Material Physics Center EHU | Alegria A.,Material Physics Center EHU | Alegria A.,University of the Basque Country | Colmenero J.,Material Physics Center EHU | And 2 more authors.
Journal of Physical Chemistry C | Year: 2010

The mechanisms involved in the thermal reduction of graphite oxide (GO) are not yet clear. In the present study, the thermal reduction of GO, obtained by a Brodie-based method, is monitored by means of time- and temperature-resolved X-ray diffraction (XRD), thermogravimetric analysis (TGA), and TGA/mass spectrometry (MS) in dynamic (nonisothermal) and static (isothermal) modes. Two distinct mechanisms were well resolved by the fitting of isothermal TGA data to 2D diffusion and autocatalytic models, which provides new insights on the thermal behavior of GO. The combined TGA and XRD results in isothermal mode suggest that the 2D diffusion mechanism mainly occurs in the interlayer, whereas the autocatalytic mechanism occurs in the external surface. The latter overcomes the former when GO has lost about 10 wt %. The results are compared to previous studies on the thermal reduction of GO. The differences found could be attributed to the synthetic method used to obtain GO. © 2010 American Chemical Society.

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