Materials Physics Center EHU

Donostia / San Sebastián, Spain

Materials Physics Center EHU

Donostia / San Sebastián, Spain

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Arandia I.,University of the Basque Country | Mugica A.,University of the Basque Country | Zubitur M.,University of the Basque Country | Arbe A.,Materials Physics Center EHU | And 6 more authors.
Macromolecules | Year: 2015

The structure, morphology, and thermal properties of biobased and biodegradable poly(butylene succinate-ran-butylene azelate) random copolyesters with a wide composition range were studied. These PBS-ran-PBAz copolymers can crystallize in the entire composition range despite being random, displaying a eutectic point when their melting point is plotted as a function of composition. Wide angle X-ray scattering (WAXS) studies confirmed isodimorphic behavior where PBS-rich copolymers crystallize with PBS type unit cells with some PBAz repeating unit inclusions and vice versa for PBAz-rich copolymers. Away from eutectic compositions the copolymers exhibit only one crystalline phase (PBS-rich or PBAz-rich crystalline phases) while at the eutectic point both phases can crystallize. The only double crystalline copolymer among those prepared had a composition close to the eutectic point of 45 mol % PBS (and 55 mol % PBAz). The crystallization of the two phases occurred in the same temperature range upon cooling from the melt at 10 °C/min in a DSC (i.e., coincident crystallization). Self-nucleation (SN) studies of the PBS-rich phase were performed. After SN, the separate crystallization of each phase was clearly observed during cooling from the self-nucleation temperature (i.e., PBS and PBAz-rich phases). Small angle X-ray scattering (SAXS) experiments were performed for the first time for these types of isodimorphic copolymers. The results show that the lamellar long period is a strong function of composition. While limited inclusions of PBAz units within the crystal lattice only cause a slight expansion of the PBS component unit cell, the increase of comonomer content produces an unexpected synergistic increase in long periods and lamellar thickness values. In the case of the only double crystalline copolymer examined, the PBS-rich phase forms space filling spherulites (observed by polarized light optical microscopy, PLOM) at higher temperatures that template the superstructural morphology of the copolymer. These PBS-rich phase spherulites contain radial lamellar stacks whose long period was determined by SAXS. Upon further cooling, the PBAz-rich phase crystallizes in the intraspherulitic amorphous regions with newly formed lamellae that have their own distinct long period according to SAXS results. AFM observations of the PBS-rich crystalline lamellae confirmed the lamellar thickness and long spacings determined by SAXS. A schematic morphological model of the mixed spherulites produced by this double crystalline diblock copolymer is proposed based on the experimental evidence collected by SAXS, PLOM, and AFM. © 2014 American Chemical Society.


Schmidt M.K.,Materials Physics Center EHU | Schmidt M.K.,Donostia International Physics Center | Esteban R.,Donostia International Physics Center | Gonzalez-Tudela A.,Max Planck Institute of Quantum Optics | And 4 more authors.
ACS Nano | Year: 2016

Plasmon-enhanced Raman scattering can push single-molecule vibrational spectroscopy beyond a regime addressable by classical electrodynamics. We employ a quantum electrodynamics (QED) description of the coherent interaction of plasmons and molecular vibrations that reveal the emergence of nonlinearities in the inelastic response of the system. For realistic situations, we predict the onset of phonon-stimulated Raman scattering and a counterintuitive dependence of the anti-Stokes emission on the frequency of excitation. We further show that this QED framework opens a venue to analyze the correlations of photons emitted from a plasmonic cavity. © 2016 American Chemical Society.


Stradi D.,Autonomous University of Madrid | Stradi D.,IMDEA Madrid Institute for Advanced Studies | Barja S.,IMDEA Madrid Institute for Advanced Studies | Barja S.,Autonomous University of Madrid | And 17 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

The interpretation of scanning tunneling spectroscopy (STS) and scanning tunneling microscopy measurements of epitaxial graphene on lattice-mismatched substrates is a challenging problem, because of the spatial modulation in the electronic structure imposed by the formation of a moiré pattern. Here we describe the electronic structure of graphene adsorbed on Ru(0001) by means of density functional theory calculations that include van der Waals interactions and are performed on a large 11×11 unit cell to account for the observed moiré patterns. Our results show the existence of localized electronic states in the high and low areas of the moiré at energies close to and well above the Fermi level, respectively. Localization is due to the spatial modulation of the graphene-Ru(0001) interaction and is at the origin of the various peaks observed in STS spectra. © 2012 American Physical Society.


Stradi D.,Autonomous University of Madrid | Stradi D.,IMDEA Madrid Institute for Advanced Studies | Barja S.,IMDEA Madrid Institute for Advanced Studies | Barja S.,Autonomous University of Madrid | And 17 more authors.
Physical Review Letters | Year: 2011

Elaborate density functional theory (DFT) calculations that include the effect of van der Waals (vdW) interactions have been carried out for graphene epitaxially grown on Ru(0001). The calculations predict a reduction of structural corrugation in the observed moiré pattern of about 25% (∼0.4Å) with respect to DFT calculations without vdW corrections. The simulated STM topographies are close to the experimental ones in a wide range of bias voltage around the Fermi level. © 2011 American Physical Society.


Miguel A.,University of the Basque Country | Al-Saleh M.,University of the Basque Country | Azkargorta J.,University of the Basque Country | Morea R.,CSIC - Institute of Optics | And 8 more authors.
Optical Materials | Year: 2013

In this work we report the spectroscopic properties of Er 3+-doped fluorotellurite glasses in the 46.6TeO2-18.2ZnO- 35.2ZnF2 system for different ErF3 concentrations between 0.5 and 3 wt%. Absorption and emission spectra and lifetimes have been measured in the visible and near infrared regions. Judd-Ofelt analysis has been performed to estimate the radiative transition probabilities. The high content of ZnF2 in this glass decreases the covalency degree in rare-earth site and results in a lower value of Ω2 if compared with zinc tellurite glasses. The infrared emissions at 1532 nm are broader by nearly 30 nm in these glasses if compared to silica glass. This broad emission together with the high values of the stimulated emission cross-section and lifetime of level 4I13/2 make these glasses attractive for broadband amplifiers. The decays from level 4I13/2 are single exponentials for all concentrations which indicates a fast energy diffusion between Er3+ ions. Similar values for the critical radius and energy transfer microparameter are obtained for the different concentrations, which supports the dipole-dipole transfer hypothesis. © 2012 Elsevier B.V. All rights reserved.


Schmidt M.K.,Materials Physics Center EHU | Schmidt M.K.,Donostia International Physics Center | Aizpurua J.,Materials Physics Center EHU | Aizpurua J.,Donostia International Physics Center | And 5 more authors.
Physical Review Letters | Year: 2015

The polarization of the light scattered by an optically dense and random solution of dielectric nanoparticles shows peculiar properties when the scatterers exhibit strong electric and magnetic polarizabilities. While the distribution of the scattering intensity in these systems shows the typical irregular speckle patterns, the helicity of the incident light can be fully conserved when the electric and magnetic polarizabilities of the scatterers are equal. We show that the multiple scattering of helical beams by a random dispersion of "dual" dipolar nanospheres leads to a speckle pattern exhibiting a perfect isotropic constant polarization, a situation that could be useful in coherent control of light as well as in lasing in random media. © 2015 American Physical Society.


Esteban R.,Materials Physics Center EHU | Esteban R.,Donostia International Physics Center | Zugarramurdi A.,CNRS Institute of Molecular Sciences | Zugarramurdi A.,Aalto University | And 9 more authors.
Faraday Discussions | Year: 2015

The optical response of plasmonic nanogaps is challenging to address when the separation between the two nanoparticles forming the gap is reduced to a few nanometers or even subnanometer distances. We have compared results of the plasmon response within different levels of approximation, and identified a classical local regime, a nonlocal regime and a quantum regime of interaction. For separations of a few Ångstroms, in the quantum regime, optical tunneling can occur, strongly modifying the optics of the nanogap. We have considered a classical effective model, so called Quantum Corrected Model (QCM), that has been introduced to correctly describe the main features of optical transport in plasmonic nanogaps. The basics of this model are explained in detail, and its implementation is extended to include nonlocal effects and address practical situations involving different materials and temperatures of operation. This journal is © The Royal Society of Chemistry.


Mertens J.,University of Cambridge | Eiden A.L.,University of Cambridge | Sigle D.O.,University of Cambridge | Huang F.,University of Cambridge | And 9 more authors.
Nano Letters | Year: 2013

Graphene is used as the thinnest possible spacer between gold nanoparticles and a gold substrate. This creates a robust, repeatable, and stable subnanometer gap for massive plasmonic field enhancements. White light spectroscopy of single 80 nm gold nanoparticles reveals plasmonic coupling between the particle and its image within the gold substrate. While for a single graphene layer, spectral doublets from coupled dimer modes are observed shifted into the near-infrared, these disappear for increasing numbers of layers. These doublets arise from charger-transfer-sensitive gap plasmons, allowing optical measurement to access out-of-plane conductivity in such layered systems. Gating the graphene can thus directly produce plasmon tuning. © 2013 American Chemical Society.


PubMed | Materials Physics Center EHU
Type: | Journal: Faraday discussions | Year: 2015

The optical response of plasmonic nanogaps is challenging to address when the separation between the two nanoparticles forming the gap is reduced to a few nanometers or even subnanometer distances. We have compared results of the plasmon response within different levels of approximation, and identified a classical local regime, a nonlocal regime and a quantum regime of interaction. For separations of a few ngstroms, in the quantum regime, optical tunneling can occur, strongly modifying the optics of the nanogap. We have considered a classical effective model, so called Quantum Corrected Model (QCM), that has been introduced to correctly describe the main features of optical transport in plasmonic nanogaps. The basics of this model are explained in detail, and its implementation is extended to include nonlocal effects and address practical situations involving different materials and temperatures of operation.


PubMed | Donostia International Physics Center, Macquarie University and Materials Physics Center EHU
Type: Journal Article | Journal: Physical review letters | Year: 2015

The polarization of the light scattered by an optically dense and random solution of dielectric nanoparticles shows peculiar properties when the scatterers exhibit strong electric and magnetic polarizabilities. While the distribution of the scattering intensity in these systems shows the typical irregular speckle patterns, the helicity of the incident light can be fully conserved when the electric and magnetic polarizabilities of the scatterers are equal. We show that the multiple scattering of helical beams by a random dispersion of dual dipolar nanospheres leads to a speckle pattern exhibiting a perfect isotropic constant polarization, a situation that could be useful in coherent control of light as well as in lasing in random media.

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