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1 to 18 of 18 results
  • Hopping conductivity and polarization effects in a fullerene derivative salt

     Macovez, Roberto; Zachariah, Manesh; Romanini, Michela; Zygouri, Panagiota; Gournis, Dimitrios; Tamarit Mur, Jose Luis
    The journal of physical chemistry. Part C, nanomaterials and interfaces
    Vol. 118, num. 23, p. 12170-12175
    DOI: 10.1021/jp503298e
    Date of publication: 2014-06-12
    Journal article

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    Impedance spectroscopy is employed to probe the frequency-dependent conductivity and dielectric response of the C60O24Na 24 fulleride. The conduction properties of this organic material match the so-called universal behavior of the ac conductivity in disordered media [Dyre, J. C.; Schroder, T. B. Rev. Mod. Phys. 2000, 72, 873-892]. In the whole temperature range studied, electrical conduction is due to intermolecular hopping processes of electronic charge carriers, characterized by an effective activation energy ranging between 0.7 eV at room temperature and 0.9 eV at 475 K. A single dielectric loss feature is observed, associated with the hopping of charge carriers surrounded by a polarization cloud. The polarizability of the material is mainly due to the distortion of the ionic O-Na bonds of the fullerene derivative, which are tight enough that no ionic contribution to the conductivity is observed up to the highest temperature probed (550 K). © 2014 American Chemical Society.

  • Ultraslow dynamics of water in organic molecular solids

     Macovez, Roberto; Mitsari, Efstratia; Zachariah, Manesh; Romanini, Michela; Zygouri, Panagiota; Gournis, Dimitrios; Tamarit Mur, Jose Luis
    The journal of physical chemistry. Part C, nanomaterials and interfaces
    Vol. 118, num. 9, p. 4941-4950
    DOI: 10.1021/jp4097138
    Date of publication: 2014-03-06
    Journal article

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    The relaxation dynamics of water in hygroscopic molecular solids is probed by broadband dielectric spectroscopy in the temperature range from 200 to 450 K. Evidence is found for three types of dynamic processes. The intermediate process is common to all probed materials and is associated with the reorientation of bound water molecules that are attached directly onto organic molecules and counterions. A faster process is observed in rhodamine chloride and fullerol, which is the dynamic signature of water in higher hydration layers, either at grain boundaries (rhodamine) or in interstitial clusters (fullerol). All these processes are observed near room temperature and exhibit nonmonotonic temperature dependence and decreasing spectral strength upon heating. In fullerol a third, ultraslow relaxation is observed at high temperature, which may be due to the reorientation of water-fullerol complexes or to the diffusion of water vapor through intermolecular voids.

  • Transicions de fase, polimorfisme i dinàmica de la metastabilitat

     Crespo Artiaga, Daniel; Pradell Cara, Trinitat; Buti Papiol, Salvador; Del Barrio Casado, Maria; Pardo Soto, Luis Carlos; Pineda Soler, Eloy; Bruna Escuer, Pere; Salvado Cabre, Nativitat; Ruiz Martin, Maria Dolores; Macovez, Roberto; Rojas Gregorio, Jose Ignacio; Lloveras Muntane, Pol Marcel; Beltran Sanchidrian, Victòria; Ye, Jin; Liu, Chaoren; Madinehei, Seyed Milad; Mitsari, Efstratia; Molina Giralt, Gloria; Romanini, Michela; Rovira Esteva, Muriel; Tripathi, Pragya; Vispa, Alessandro; Vallés Sales, Araceli; Zachariah, Manesh; Zhai, Fuqiang; Tamarit Mur, Jose Luis
    Competitive project

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  • Intrinsic and water-induced relaxation dynamics and conductivity of organic nanoporous materials and thin films

     Macovez, Roberto; Zachariah, Manesh; Mitsari, Efstratia; Tripathi, Pragya; Romanini, Michela; Zygouri, Panagiota; Gournis, Dimitrios; Del Barrio Casado, Maria; Tamarit Mur, Jose Luis
    International Conference on Broadband Dielectric Spectroscopy and its Applications
    p. 62
    Presentation's date: 2014-09-16
    Presentation of work at congresses

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  • Ultra-slow dynamics of water in organic molecular solids

     Mitsari, Efstratia; Macovez, Roberto; Zachariah, Manesh; Tripathi, Pragya; Romanini, Michela; Zygouri, Panagiota; Gournis, Dimitrios; Tamarit Mur, Jose Luis
    WaterEurope
    p. 48
    Presentation's date: 2014-06-14
    Presentation of work at congresses

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  • Water-dependent conductivity of fullerene derivatives

     Zachariah, Manesh; Mitsari, Efstratia; Romanini, Michela; Tamarit Mur, Jose Luis; Zygouri, Panagiota; Gournis, Dimitrios; Macovez, Roberto
    International Discussion Meeting on Relaxation in Complex Systems
    p. 206
    Presentation's date: 2013-07-23
    Presentation of work at congresses

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  • Ultra-slow dynamics of water in hygroscopic molecular solids

     Macovez, Roberto; Mitsari, Efstratia; Zachariah, Manesh; Romanini, Michela; Capaccioli, Simone; Zygouri, Panagiota; Gournis, Dimitrios; Tamarit Mur, Jose Luis
    International Discussion Meeting on Relaxation in Complex Systems
    p. 383
    Presentation's date: 2013-07-22
    Presentation of work at congresses

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  • Dinámica en sólidos desordenados

     Romanini, Michela; Macovez, Roberto; Ruiz Martin, Maria Dolores; Levit Valenzuela, Rafael; Pardo Soto, Luis Carlos; Del Barrio Casado, Maria; Vispa, Alessandro; Tamarit Mur, Jose Luis
    Competitive project

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  • Surfaces and thin films of fullerenes

     Macovez, Roberto; RUDOLF, PETRA
    DOI: 10.4032/9789814267885
    Date of publication: 2012-03-30
    Book chapter

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  • Molecular conformation in organic films from quantum chemistry ab initio calculations and second harmonic spectroscopy

     Macovez, Roberto; López, Núria; Mariano, Marina; Maymò, Marc; Martorell Pena, Jordi
    The journal of physical chemistry. Part C, nanomaterials and interfaces
    Vol. 116, num. 51, p. 26784-26790
    DOI: 10.1021/jp3075018
    Date of publication: 2012-11-30
    Journal article

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    Identifying molecular species and conformations at surfaces is of interest for both catalytic and biointerfacial research. Here, we present an extinction and second harmonic spectroscopy study of films of crystal violet together with quantum chemistry ab initio calculations on several conformation geometries of this dye. By comparing experimental and theoretical data, we identify the molecular species responsible for the spectral resonances, and we ascribe the nonlinear optical generation to pyramidal conformers with nonzero dipolar hyperpolarizability. Our results, which are consistent with recent findings on alcohol solutions of the same dye, help to settle a long-standing debate and demonstrate that nonlinear second harmonic spectroscopy is a valuable tool for identifying and probing molecular conformation in interfacial systems.

  • Ultra-slow relaxation dynamics of water in molecular hygroscopic salts

     Macovez, Roberto; Mitsari, Efstratia; Zachariah, Manesh; Romanini, Michela; Capaccioli, Simone; Tamarit Mur, Jose Luis
    Congrés Internacional de Materials Moleculars
    p. 299
    Presentation's date: 2012-07-06
    Presentation of work at congresses

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  • Large Optical-Frequency Shift of Molecular Radiation via Coherent Coupling to an Off-Resonance Plasmon

     Macovez, Roberto; Mariano, Marina; Di Finizio, Sergio; Kozyreff, Gregory; Martorell Pena, Jordi
    Physical review letters
    Vol. 107, num. 7, p. 1-5
    DOI: 10.1103/PhysRevLett.107.073902
    Date of publication: 2011-08-09
    Journal article

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  • Surface hubbard U of alkali fullerides

     Macovez, Roberto
    Journal of electron spectroscopy and related phenomena
    Vol. 183, num. 1-2, p. 94-100
    Date of publication: 2011
    Journal article

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    Wereport a combined photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES) study of distilled, phase pure films of C60 and the monomeric fullerides Cs6C60, Cs4C60 and fcc RbC60. The separation between the highest energy PES and lowest energy IPES features, which is a measure of the barrier to hopping, is 1.45 eV in Cs4C60 and 0.7 eV in RbC60. This difference is large enough to explain, in a correlated electron picture, the reported differences in electronic mobility between the two stoichoimetries. From the PES-IPES energy separation, the value of the Hubbard U is estimated to be 1.5 eV in closed-shell C60 and Cs6C60, while in Cs4C60 and RbC60 such value is reduced to∼1 and 0.7 eV, respectively. This trend can be only partially understood taking into account the different molecular polarizability and crystal structure of the various stoichiometries. The relatively low values found for open-shell compounds indicate that the bulk Hubbard U is smaller in open-shell fullerides than usually believed, which might help explain superconductivity and the observation of spin-singlets in odd-stoichiometry fullerides.

  • Molecular X(2) gratings via electron-beam lithography

     Domínguez Juárez, Jorge Luis; Macovez, Roberto; Ujue González, María; Martorell Pena, Jordi
    Applied physics letters
    Vol. 97, num. 3, p. 1-3
    DOI: 10.1063/1.3464161
    Date of publication: 2010-07-14
    Journal article

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    We show that the nonlinear optical activity of an organic molecule may be quenched by electron irradiation. Exploiting this effect, we inscribe periodic χ(2) patterns in the molecular films by means of a scanning electron microscope. The second harmonic diffraction efficiency of the resulting χ(2) gratings is measured. The relative intensity of the diffraction orders observed agrees with the expectations for a sheet of nonlinear dipoles with a periodic modulation. No linear diffraction is seen. The present method allows realizing any type of two-dimensional χ(2) pattern with a resolution only limited by the electron beam patterning capabilities.

  • DINÁMICA DE SOLIDOS ORIENTACIONALMENTE DESORDENADOS

     Levit Valenzuela, Rafael; Rovira Esteva, Muriel; Martinez Garcia, Julio Cesar; Del Barrio Casado, Maria; Ruiz Martin, Maria Dolores; Pardo Soto, Luis Carlos; Macovez, Roberto; Veglio, Nestor Raul; Romanini, Michela; Tamarit Mur, Jose Luis
    Competitive project

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    Measurement of the dispersion of air and of refractive index anomalies by wavelength- dependent nonlinear interferometry  Open access

     Macovez, Roberto; Mariano, Marina; Di Finizio, Sergio; Martorell Pena, Jordi
    Optics express
    Vol. 17, num. 16, p. 13881-13888
    Date of publication: 2009-07-27
    Journal article

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    We carry out wavelength-dependent second harmonic interference experiments using thin films of an organic dye as nonlinear optical sources. While the measured difference of refractive index between the fundamental and second harmonic wavelengths follows the theoretical expectation for air in a wide spectral region, anomalous dispersion is observed when the second harmonic light lies in the absorption band of the dye. The sensitivity of the technique to small refractive index variations may prove useful for sensing applications as well as for testing models of light dispersion in weakly dispersing and absorbing media.

  • New approaches for the fabrication of photonic structures of nonlinear optical materials

     Carvajal, J J; Peña, A; Kumar, R.; Pujol, M. C.; Mateos, X.; Aguiló, M; Díaz, F; Vázquez De Aldana, J. R.; Méndez, C.; Moreno, P; Roso, L; Trifonov, T; Rodriguez Martinez, Angel; Alcubilla Gonzalez, Ramon; Král, Z; Ferré Borrull, J.; Pallarès Marzal, Josep; Marsal, L F; Finizio, Sergio Di; Martorell, J; Macovez, Roberto
    Journal of luminescence
    Vol. 129, num. SI:12, p. 1441-1447
    DOI: 10.1016/j.jlumin.2009.03.035
    Date of publication: 2009-12
    Journal article

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  • Nonlinear Optics in the Nano and Micro Dimensions

     Di Finizio, Sergio; Vidal Asensio, Xavier; Domínguez Juárez, Jorge Luis; Botey Cumella, Muriel; Macovez, Roberto; Martorell Pena, Jordi
    Annual International Laser Physics Workshop
    Presentation's date: 2008-07-04
    Presentation of work at congresses

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