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35 results on '"Tollan, Christopher"'

3. Unveiling the mechanisms of the spin Hall effect in Ta

Author

Sagasta, Edurne, Omori, Yasutomo, Vélez, Saül, Llopis, Roger, Tollan, Christopher, Chuvilin, Andrey, Hueso, Luis E., Gradhand, Martin, Otani, YoshiChika, and Casanova, Fèlix

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Spin-to-charge current interconversions are widely exploited for the generation and detection of pure spin currents and are key ingredients for future spintronic devices including spin-orbit torques and spin-orbit logic circuits. In case of the spin Hall effect, different mechanisms contribute to the phenomenon and determining the leading contribution is peremptory for achieving the largest conversion efficiencies. Here, we experimentally demonstrate the dominance of the intrinsic mechanism of the spin Hall effect in highly-resistive Ta. We obtain an intrinsic spin Hall conductivity for $\beta$-Ta of -820$\pm$120 ($\hbar$/e) $\Omega^{-1}cm^{-1}$ from spin absorption experiments in a large set of lateral spin valve devices. The predominance of the intrinsic mechanism in Ta allows us to linearly enhance the spin Hall angle by tuning the resistivity of Ta, reaching up to -35$\pm$3%, the largest reported value for a pure metal., Comment: 9 pages and 4 figures + Supplemental Material (2 pages, 3 figures)

Published
2018
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6. Spin transport enhancement by controlling the Ag growth in lateral spin valves

Author

Isasa, Miren, Villamor, Estitxu, Fallarino, Lorenzo, Idigoras, Olatz, Suszka, Anna K., Tollan, Christopher, Berger, Andreas, Hueso, Luis E., and Casanova, Fèlix

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

The role of the growth conditions in the spin transport properties of silver (Ag) have been studied by using lateral spin valve structures. By changing the deposition conditions of Ag from polycrystalline to epitaxial growth, we have observed a considerable enhancement of the spin diffusion length, from $\lambda_{Ag}$ = 449 $\pm$ 30 to 823 $\pm$ 59 nm. This study shows that diminishing the grain boundary contribution to the spin relaxation mechanism is an effective way to improve the spin diffusion length in metallic nanostructures., Comment: 6 pages, 3 figures

Published
2014
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7. Toward sub-second solution exchange dynamics in flow reactors for liquid-phase transmission electron microscopy

Author

Eusko Jaurlaritza, Diputación Foral de Gipuzkoa, Ministerio de Economía y Competitividad (España), Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Ciencia e Innovación (España), PON Ricerca e Innovazione, Consejo Superior de Investigaciones Científicas [https://ror.org/02gfc7t72], Merkens, Stefan, Tollan, Christopher, De Salvo, Giuseppe, Bejtka, Katarzyna, Fontana, Marco, Chiodoni, Angelica, Kruse, Joscha, Iriarte-Alonso, Maiara A., Grzelczak, Marek, Chuvilin, Andrey, Eusko Jaurlaritza, Diputación Foral de Gipuzkoa, Ministerio de Economía y Competitividad (España), Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Ciencia e Innovación (España), PON Ricerca e Innovazione, Consejo Superior de Investigaciones Científicas [https://ror.org/02gfc7t72], Merkens, Stefan, Tollan, Christopher, De Salvo, Giuseppe, Bejtka, Katarzyna, Fontana, Marco, Chiodoni, Angelica, Kruse, Joscha, Iriarte-Alonso, Maiara A., Grzelczak, Marek, and Chuvilin, Andrey

Abstract

Liquid-phase transmission electron microscopy is a burgeoning experimental technique for monitoring nanoscale dynamics in a liquid environment, increasingly employing microfluidic reactors to control the composition of the sample solution. Current challenges comprise fast mass transport dynamics inside the central nanochannel of the liquid cell, typically flow cells, and reliable fixation of the specimen in the limited imaging area. In this work, we present a liquid cell concept – the diffusion cell – that satisfies these seemingly contradictory requirements by providing additional on-chip bypasses to allow high convective transport around the nanochannel in which diffusive transport predominates. Diffusion cell prototypes are developed using numerical mass transport models and fabricated on the basis of existing two-chip setups. Important hydrodynamic parameters, i.e., the total flow resistance, the flow velocity in the imaging area, and the time constants of mixing, are improved by 2-3 orders of magnitude compared to existing setups. The solution replacement dynamics achieved within seconds already match the mixing timescales of many ex-situ scenarios, and further improvements are possible. Diffusion cells can be easily integrated into existing liquid-phase transmission electron microscopy workflows, provide correlation of results with ex-situ experiments, and can create additional research directions addressing fast nanoscale processes.

Published
2024

8. Synthesis characterisation and photophysical properties of [60]fullerene containing polymers

Author

Tollan, Christopher Mark

Subjects
546.68124254
Abstract

A range of acrylic polymers incorporating azafulleroids and aziridinofullerenes have been prepared. This was achieved through the synthesis of 3-bromopropyl acrylate. which was subsequently copolymerised with other acrylic monomers. Nucleophilic substitution of the bromine atom using sodium azide afforded the corresponding azido substituted acrylic copolymer. The azido group is capable of forming a triazoline derivative with [60]fullerene, which after extrusion of nitrogen, leads to the formation of iminofullerene monoadducts attached to the acrylic polymer backbone. Various fulleropyrrolidine monoadducts have been prepared by [3+2] cycloaddition of azomethine ylides to [60]fullerene through use ofN-substituted and unsubstituted a-amino acids in conjunction with benzaldehyde derivatives. Fulleropyrrolidine and azafulleroid acrylic monomers have been prepared. The fulleropyrrolidine monomer was formed by the creation of an amide bond between acryloyl chloride and the pyrrolidine ring nitrogen of 2-phenylfulleropyrrolidine. For the azafulleroid acrylic monomer an acrylic azide was reacted directly with [60] fullerene. An investigation of the conditions required to polymerise the above monomers has been carried out using a variety of cationic initiators. An investigation into the reaction of an acid chloride containing polymer with 2- phenylfulleropyrrolidine in a similar fashion to the formation of the acrylic fulleropyrrolidine monomer above has also been performed. This has lead to the formation of various soluble fullerene/acrylic polymers. Various synthetic routes were investigated in order to form a fullerene functionalised with an alcohol group. It was hoped that such an alcoholic fullerene might provide a useful precursor to an acrylic monomer. While attempting to form an alcoholic fullerene it was found that (5,6)-open 3-iminofulleropropyl benzoate forms three products on addition of a molar ratio of a methanolic sodium hydroxide solution in sunlight. Similar products are absent in the same reaction with (6,6)-open 3-iminofulleropropyl benzoate. The relatively rapid formation of such well-defined products in the presence of sodium hydroxide is intriguing. Characterisation of these products is also included in this study.

Published
2007

12. Quantification of reagent mixing in liquid flow cells for Liquid Phase-TEM

Author

Eusko Jaurlaritza, Ministerio de Economía y Competitividad (España), Diputación Foral de Gipuzkoa, Merkens, Stefan, De Salvo, Giuseppe, Kruse, Joscha, Modin, Evgenii, Tollan, Christopher, Grzelczak, Marek, Chuvilin, Andrey, Eusko Jaurlaritza, Ministerio de Economía y Competitividad (España), Diputación Foral de Gipuzkoa, Merkens, Stefan, De Salvo, Giuseppe, Kruse, Joscha, Modin, Evgenii, Tollan, Christopher, Grzelczak, Marek, and Chuvilin, Andrey

Abstract

Liquid-Phase Transmission Electron Microscopy (LP-TEM) offers the opportunity to study nanoscale dynamics of phenomena related to materials and life science in a native liquid environment and in real time. Until now, the opportunity to control/induce such dynamics by changing the chemical environment in the liquid flow cell (LFC) has rarely been exploited due to an incomplete understanding of hydrodynamic properties of LP-TEM flow systems. This manuscript introduces a method for hydrodynamic characterization of LP-TEM flow systems based on monitoring transmitted intensity while flowing a strongly electron scattering contrast agent solution. Key characteristic temporal indicators of solution replacement for various channel geometries were experimentally measured. A numerical physical model of solute transport based on realistic flow channel geometries was successfully implemented and validated against experiments. The model confirmed the impact of flow channel geometry on the importance of convective and diffusive solute transport, deduced by experiment, and could further extend understanding of hydrodynamics in LP-TEM flow systems. We emphasize that our approach can be applied to hydrodynamic characterization of any customized LP-TEM flow system. We foresee the implemented predictive model driving the future design of application-specific LP-TEM flow systems and, when combined with existing chemical reaction models, to a flourishing of the planning and interpretation of experimental observations.

Published
2023

18. In-plane anisotropic and ultra-low-loss polaritons in a natural van der Waals crystal

Author

Taboada-Gutiérrez, Javier, Weiliang, Ma, Li, Shaojuan, Nikitin, Alexey Y., Yuan, Jian, Martín-Sánchez, Javier, Amenabar, Iban, Li, Peining, Vélez, Saul, Tollan, Christopher, Dai, Zhigao, Zhang, Yupeng, Sriram, Sharath, Kalantar-Zadeh, Kourosh, Lee, Shuit-Tong, Hillenbrand, Rainer, Alonso-González, Pablo, Bao, Qiaoliang, Taboada-Gutiérrez, Javier, Weiliang, Ma, Li, Shaojuan, Nikitin, Alexey Y., Yuan, Jian, Martín-Sánchez, Javier, Amenabar, Iban, Li, Peining, Vélez, Saul, Tollan, Christopher, Dai, Zhigao, Zhang, Yupeng, Sriram, Sharath, Kalantar-Zadeh, Kourosh, Lee, Shuit-Tong, Hillenbrand, Rainer, Alonso-González, Pablo, and Bao, Qiaoliang

Published
2019

20. Unveiling the mechanisms of the spin Hall effect in Ta

Author

Sagasta, Edurne, primary, Omori, Yasutomo, additional, Vélez, Saül, additional, Llopis, Roger, additional, Tollan, Christopher, additional, Chuvilin, Andrey, additional, Hueso, Luis E., additional, Gradhand, Martin, additional, Otani, YoshiChika, additional, and Casanova, Fèlix, additional

Published
2018
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23. Conductive Polymer–Inorganic Hybrid Materials through Synergistic Mutual Doping of the Constituents

Author

Wang, Weike, Chen, Chaoqiu, Tollan, Christopher, Yang, Fan, Beltrán, Mikel, Qin, Yong, and Knez, Mato

Abstract

Polymer-matrix-based inorganic–organic hybrid materials are at the cutting edge of current research for their great promise of merging properties of soft and hard solids in one material. Infiltration of polymers with vapors of reactive metal organics is a pathway for postsynthetic blending of the polymer with inorganic materials. Here, we show that this process is also an excellent method for fabricating conductive hybrid materials. Polyaniline (PANI) was infiltrated with ZnO and the initially insulating polymer was converted to a PANI/ZnO hybrid with conductivities as high as 18.42 S/cm. The conductivity is based on a synergistic effect of the constituting materials, where the inorganic and the polymeric fractions mutually act as dopants for the counterpart. The process temperature is a very important factor for successful infiltration, and the number of applied infiltration cycles allows tuning the level of conductivity of the resulting PANI/ZnO.

Published
2024
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33. Functionalization of Defect Sites in Graphene with RuO2for High Capacitive Performance

Author

Yang, Fan, Zhang, Lianbing, Zuzuarregui, Ana, Gregorczyk, Keith, Li, Le, Beltrán, Mikel, Tollan, Christopher, Brede, Jens, Rogero, Celia, Chuvilin, Andrey, and Knez, Mato

Abstract

Graphene is an attractive material for its physicochemical properties, but for many applications only chemically synthesized forms such as graphene oxide (GO) and reduced graphene oxide (rGO) can be produced in sufficient amounts. If considered as electrode material, the intrinsic defects of GO or rGO may have negative influence on the conductivity and electrochemical properties. Such defects are commonly oxidized sites that offer the possibility to be functionalized with other materials in order to improve performance. In this work, we demonstrate how such ultimately efficient functionalization can be achieved: namely, through controlled binding of very small amount of materials such as RuO2to rGO by atomic layer deposition (ALD), in this way substituting the native defect sites with RuO2defects. For the example of a supercapacitor, we show that defect functionalization results in significantly enhanced specific capacitance of the electrode and that its energy density can be stabilized even at high consumption rates.

Published
2015
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35. Irreversible Thermochromic Behavior in Gold and Silver Nanorod/Polymeric Ionic Liquid Nanocomposite Films

Author

Tollan, Christopher M., Marcilla, Rebeca, Pomposo, Jose A., Rodriguez, Javier, Aizpurua, Javier, Molina, Jon, and Mecerreyes, David

Abstract

The novel application of gold and silver nanorods as irreversible thermochromic dyes in polymeric ionic liquid (PIL) nanocomposites is proposed here. These materials have been synthesized by anion exchange of an imidazolium-based PIL in a solution that also contained gold nanorods. This resulted in the entrapment of the nanoobjects within a solid polymer precipitate. In this article, the effect of the temperature was studied in relation to the change of shape and, consequently, color of the gold or silver nanorods within the films. For the nanocomposites studied here, a maximum of two visual thermochromic transitions was observed for gold nanorods and up to three transitions were observed for silver nanorods.

Published
2009
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