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81 results on '"Agulló-López, Fernando"'

7. Light and Thermally Induced Charge Transfer and Ejection of Micro‐/Nanoparticles from Ferroelectric Crystal Surfaces.

Author

Sebastián‐Vicente, Carlos, García‐Cabañes, Angel, Agulló‐López, Fernando, and Carrascosa, Mercedes

Subjects
FERROELECTRIC crystals, CHARGE transfer, CRYSTAL surfaces, ELECTRIC fields, SURFACE charges
Abstract

During real‐time operation of photovoltaic optoelectronic tweezers, a novel intriguing phenomenon has been recently observed, namely, silver nanoparticles previously deposited on ferroelectric LiNbO3:Fe surfaces are ejected from them by illumination. Here, it is shown that this phenomenon results from the electrical charging of the micro‐/nanoparticles previously trapped on the LiNbO3:Fe surfaces and the subsequent Coulomb repulsion. Specific experiments are performed to determine the sign of the transferred charges, which is negative/positive for the +c/−c sample face, i.e., it coincides with that of the stored charges on each surface. The charging/ejection process is proved to occur regardless of the illuminated crystal surface, the dielectric or metallic nature of the particles, and in different surrounding media. Besides, the role of the excitation light intensity is also explored. Next, to assess the generality of the ejection phenomenon, similar experiments based on the pyroelectric effect are performed, i.e., generating the electric fields by changing the crystal temperature instead of illuminating it. Thereby, thermally driven particle ejection is demonstrated using different ferroelectric crystals. The similarities found for the two approaches throw light on the charge transfer and ejection mechanism and remark the universality of the phenomenon for ferroelectrics, which can find many technological applications. [ABSTRACT FROM AUTHOR]

Published
2022
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26. Massive ordering and alignment of cylindrical micro-objects by photovoltaic optoelectronic tweezers

Author

Elvira, Iris, Muñoz-Martínez, Juan F., Barroso, Álvaro, Denz, Cornelia, Ramiro, José B., García-Cabañes, Angel, Agulló-López, Fernando, and Carrascosa, Mercedes

Abstract

Optical tools for manipulation and trapping of micro- and nano-objects are a fundamental issue for many applications in nano- and biotechnology. This work reports on the use of one such method, known as photovoltaic optoelectronics tweezers, to orientate and organize cylindrical microcrystals, specifically elongated zeolite L, on the surface of Fe-doped LiNbO_3 crystal plates. Patterns of aligned zeolites have been achieved through the forces and torques generated by the bulk photovoltaic effect. The alignment patterns with zeolites parallel or perpendicular to the substrate surface are highly dependent on the features of light distribution and crystal configuration. Moreover, dielectrophoretic chains of zeolites with lengths up to 100 μm have often been observed. The experimental results of zeolite trapping and alignment have been discussed and compared together with theoretical simulations of the evanescent photovoltaic electric field and the dielectrophoretic potential. They demonstrate the remarkable capabilities of the optoelectronic photovoltaic method to orientate and pattern anisotropic microcrystals. The combined action of patterning and alignment offers a unique tool to prepare functional nanostructures with potential applications in a variety of fields such as nonlinear optics or plasmonics.

Published
2018

28. Photovoltaic versus optical tweezers

Author

Villarroel, Javier, primary, Burgos, Héctor, additional, García-Cabañes, Ángel, additional, Carrascosa, Mercedes, additional, Blázquez-Castro, Alfonso, additional, and Agulló-López, Fernando, additional

Published
2011
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33. Novel Push−Pull Phthalocyanines as Targets for Second-Order Nonlinear Applications

Author

Maya, Eva M., primary, García-Frutos, Eva M., additional, Vázquez, Purificación, additional, Torres, Tomás, additional, Martín, Guillermo, additional, Rojo, Gema, additional, Agulló-López, Fernando, additional, González-Jonte, Raúl H., additional, Ferro, Victor R., additional, García de la Vega, José M., additional, Ledoux, Isabelle, additional, and Zyss, Joseph, additional

Published
2003
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43. Synthesis, structure and second-order nonlinear optical properties of highly functionalized 6-aminopentafulvenes

Author

Piniella, Joan F., primary, Alvarez-larena, Angel, additional, Díaz-garcía, María A., additional, Agulló-lópez, Fernando, additional, Ledoux, Isabelle, additional, Zyss, Joseph, additional, Kato, Midori, additional, Kiguchi, Masashi, additional, Miranda, M. Mar, additional, Muñoz, Montserrat, additional, Soler, Elena, additional, Sorribes, Silvia, additional, and Germain, Gabriel, additional

Published
1998
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48. Real-Time Identification of Oxygen Vacancy Centers in LiNbO 3 and SrTiO 3 during Irradiation with High Energy Particles.

Author

Crespillo, Miguel L., Graham, Joseph T., Agulló-López, Fernando, Zhang, Yanwen, Weber, William J., and Jackson, Robert A.

Subjects
ALKALI metal halides, NUCLEAR engineering, OXYGEN, CRYSTAL lattices, OPTOELECTRONIC devices
Abstract

Oxygen vacancies are known to play a central role in the optoelectronic properties of oxide perovskites. A detailed description of the exact mechanisms by which oxygen vacancies govern such properties, however, is still quite incomplete. The unambiguous identification of oxygen vacancies has been a subject of intense discussion. Interest in oxygen vacancies is not purely academic. Precise control of oxygen vacancies has potential technological benefits in optoelectronic devices. In this review paper, we focus our attention on the generation of oxygen vacancies by irradiation with high energy particles. Irradiation constitutes an efficient and reliable strategy to introduce, monitor, and characterize oxygen vacancies. Unfortunately, this technique has been underexploited despite its demonstrated advantages. This review revisits the main experimental results that have been obtained for oxygen vacancy centers (a) under high energy electron irradiation (100 keV–1 MeV) in LiNbO3, and (b) during irradiation with high-energy heavy (1–20 MeV) ions in SrTiO3. In both cases, the experiments have used real-time and in situ optical detection. Moreover, the present paper discusses the obtained results in relation to present knowledge from both the experimental and theoretical perspectives. Our view is that a consistent picture is now emerging on the structure and relevant optical features (absorption and emission spectra) of these centers. One key aspect of the topic pertains to the generation of self-trapped electrons as small polarons by irradiation of the crystal lattice and their stabilization by oxygen vacancies. What has been learned by observing the interplay between polarons and vacancies has inspired new models for color centers in dielectric crystals, models which represent an advancement from the early models of color centers in alkali halides and simple oxides. The topic discussed in this review is particularly useful to better understand the complex effects of different types of radiation on the defect structure of those materials, therefore providing relevant clues for nuclear engineering applications. [ABSTRACT FROM AUTHOR]

Published
2021
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49. Supramolecular organization of subphthalocyanines in Langmuir and Langmuir-Blodgett films

Author

Victoria Martínez-Díaz, M., del Rey, Belén, Torres, Tomás, Agricole, Beatrice, Mingotaud, Christophe, Cuvillier, Nicolas, Rojo, Gema, and Agulló-López, Fernando

Abstract

Interfacial studies of a series of subphthalocyanine (SubPc) macrocycles 1-3, 5 and 6, differently substituted either in the periphery (with polar and donor groups) or in the axial position of the macrocycle (with a chlorine atom or a trihexylsiloxy group), have been carried out. Remarkable changes in the orientation of the macrocycles at the air/water interface have been observed by varying the number of polar groups in the periphery or adding a bulky group in the axial position. The morphology of the monolayers has been carefully studied by Brewster angle microscopy. Monolayers made of compounds 1-3 could be efficiently transferred onto hydrophobic substrates. LB films of SubPc 1 were characterized in detail by UV-VIS and IR spectroscopies, and X-ray diffraction and ellipsometry experiments. These studies indicate that the LB films of SubPc 1 are surely Y-type, formed by layers of a well-defined average thickness of ca. 16 Å. Preliminary studies on the nonlinear optical (NLO) properties of these materials have been carried out. In particular, second harmonic generation (SHG) experiments have been performed on LB films of SubPc 1.

Published
1999
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50. Second-order non-linear optical properties of ‘bent’ ferrocenyl derivatives

Author

A. Campo, José, Cano, Mercedes, V. Heras, José, López-Garabito, Carolina, Pinilla, Elena, Torres, Rosario, Rojo, Gema, and Agulló-López, Fernando

Abstract

The organometallic compounds [4-O2NC6H3(2-CH3)N=NC6H3(5′-CH3)-2′-(η5-C5H4)Fe(η5-C5H5)] 1 and [Mo(Cl)(TpAn)(NO){NHC6H3(3-CH3)[N=NC6H3(5-CH3)-2-(η5-C5H4)Fe(η5-C5H5)]-4}] 2 {TpAn=hydrotris[3-(p-methoxyphenyl)pyrazol-1-yl]borate} have been synthesized, characterized and their second-order non-linear optical (NLO) properties studied. In both cases the location of the ferrocenyl donor group at the ortho position of the aryl group with respect to the N}}n2N group breaks the ‘molecular linearity’ defined by the bridging axis between the donor and acceptor groups. The crystal structure of 1 has been determined to be non-centrosymmetric, by contrast to the centrosymmetric related ‘linear’ compound [4-O2NC6H3(2-CH3)N}}n2NC6H4-4′-(η5-C5H4)Fe(η5-C5H5)] having the ferrocenyl group at the para position of the aryl group. The three non-zero components of the second-harmonic susceptibility χij(2) (2ω;ω,ω) tensor have been determined for poled poly(methyl methacrylate) films containing compounds 1 and 2; χ31(2)>χ33(2), suggesting a tilted (non-parallel) optical transition moment in relation to the permanent dipole moment. This also may account for the breaking of Kleinman's symmetry under near-resonant conditions, i.e. χ15(2)≠χ31(2). Moreover, by comparing the results with those of related compounds having the ferrocenyl group in the para position of the aryl group, it has been concluded that molecular ‘bending’ strongly reduces the second-order NLO response, but it maintains strong off-diagonal (χ31(2)) components of the χij(2) tensor.

Published
1999
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