Publications
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Cooling and self-oscillation in a nanotube electromechanical resonator
Urgell C., Yang W., De Bonis S.L., Samanta C., Esplandiu M.J., Dong Q., Jin Y., Bachtold A. Nature Physics; 16 (1): 32 - 37. 2020. 10.1038/s41567-019-0682-6. IF: 19.256
Nanomechanical resonators are used with great success to couple mechanical motion to other degrees of freedom, such as photons, spins and electrons1,2. The motion of a mechanical eigenmode can be efficiently cooled into the quantum regime using photons2–4, but not other degrees of freedom. Here, we demonstrate a simple yet powerful method for cooling, amplification and self-oscillation using electrons. This is achieved by applying a constant (d.c.) current of electrons through a suspended nanotube in a dilution refrigerator. We demonstrate cooling to 4.6 ± 2.0 quanta of vibrations. We also observe self-oscillation, which can lead to prominent instabilities in the electron transport through the nanotube. We attribute the origin of the observed cooling and self-oscillation to an electrothermal effect. This work shows that electrons may become a useful resource for cooling the mechanical vibrations of nanoscale systems into the quantum regime. © 2019, The Author(s), under exclusive licence to Springer Nature Limited.
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Electrophoretic origin of long-range repulsion of colloids near water/Nafion interfaces
Esplandiu M.J., Reguera D., Fraxedas J. Soft Matter; 16 (15): 3717 - 3726. 2020. 10.1039/d0sm00170h. IF: 3.140
One of the most striking properties of Nafion is the formation of a long-range solute exclusion zone (EZ) in contact with water. The mechanism of formation of this EZ has been the subject of a controversial and long-standing debate. Previous studies by Schurr et al. and Florea et al. root the explanation of this phenomenon in the ion-exchange properties of Nafion, which generates ion diffusion and ion gradients that drive the repulsion of solutes by diffusiophoresis. Here we have evaluated separately the electrophoretic and chemiphoretic contributions to multi-ionic diffusiophoresis using differently charged colloidal tracers as solutes to identify better their contribution in the EZ formation. Our experimental results, which are also supported by numerical simulations, show that the electric field, built up due to the unequal diffusion coefficients of the exchanged ions, is the dominant parameter behind such interfacial phenomenon in the presence of alkali metal chlorides. The EZ formation depends on the interplay of the electric field with the zeta potential of the solute and can be additionally modulated by changing ion diffusion coefficients or adding salts. As a consequence, we show that not all solutes can be expelled from the Nafion interface and hence the EZ is not always formed. This study thus provides a more detailed description of the origin and dynamics of this phenomenon and opens the door to the rational use of this active interface for many potential applications. This journal is © The Royal Society of Chemistry.
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Highly reduced ecotoxicity of ZnO-based micro/nanostructures on aquatic biota: Influence of architecture, chemical composition, fixation, and photocatalytic efficiency
Serrà A., Zhang Y., Sepúlveda B., Gómez E., Nogués J., Michler J., Philippe L. Water Research; 169 (115210) 2020. 10.1016/j.watres.2019.115210. IF: 9.130
Developing efficient sunlight photocatalysts with enhanced photocorrosion resistance and minimal ecotoxicological effects on aquatic biota is critical to combat water contamination. Here, the role of chemical composition, architecture, and fixation on the ecotoxicological effects on microalgae of different ZnO and ZnO@ZnS based water decontamination photocatalysts was analyzed in depth. In particular, the ecotoxicological effects of films, nanoparticles and biomimetic micro/nano-ferns were carefully assessed by correlating the algae's viability to the Zn(II) release, the photocatalyst–microalgae interaction, and the production of reactive oxygen species (ROS). The results showed a drastic improvement in algal viability for supported ZnO@ZnS core@shell micro/nanoferns, as their ecotoxicity after 96 h light exposure was significantly lower (3.7–10.0% viability loss) compared to the ZnO films (18.4–35.5% loss), ZnO micro/nanoferns (28.5–53.5% loss), ZnO nanoparticles (48.3–91.7% loss) or ZnO@ZnS nanoparticles (8.6–19.2% loss) for catalysts concentrations ranging from 25 mg L−1 to 400 mg L−1. In particular, the ZnO@ZnS micro/nanoferns with a concentration of 400 mg L−1 exhibited excellent photocatalytic efficiency to mineralize a multi-pollutant solution (81.4 ± 0.3% mineralization efficiency after 210 min under UV-filtered visible light irradiation) and minimal photocorrosion (<5% of photocatalyst dissolution after 96 h of UV-filtered visible light irradiation). Remarkably, the ZnO@ZnS micro/nanoferns showed lower loss of algal viability (9.8 ± 1.1%) after 96 h of light exposure, with minimal reduction in microalgal biomass (9.1 ± 1.0%), as well as in the quantity of chlorophyll-a (9.5 ± 1.0%), carotenoids (8.6 ± 0.9%) and phycocyanin (5.6 ± 0.6%). Altogether, the optimized ZnO@ZnS core@shell micro/nanoferns represent excellent ecofriendly photocatalysts for water remediation in complex media, as they combine enhanced sunlight remediation efficiency, minimal adverse effects on biological microorganisms, high reusability and easy recyclability. © 2019 Elsevier Ltd
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Hybrid Ni@ZnO@ZnS-Microalgae for Circular Economy: A Smart Route to the Efficient Integration of Solar Photocatalytic Water Decontamination and Bioethanol Production
Serrà A., Artal R., García-Amorós J., Sepúlveda B., Gómez E., Nogués J., Philippe L. Advanced Science; 7 (3, 1902447) 2020. 10.1002/advs.201902447. IF: 15.840
Water remediation and development of carbon-neutral fuels are a priority for the evermore industrialized society. The answer to these challenges should be simple, sustainable, and inexpensive. Thus, biomimetic-inspired circular and holistic processes combing water remediation and biofuel production can be an appealing concept to deal with these global issues. A simple circular approach using helical Spirulina platensis microalgae as biotemplates to synthesize Ni@ZnO@ZnS photocatalysts for efficient solar water decontamination and bioethanol production during the recycling process is presented. Under solar irradiation, the Ni@ZnO@ZnS-Spirulina photocatalyst exhibits enhanced activity (mineralization efficiency >99%) with minimal photocorrosion and excellent reusability. At the end of its effective lifetime for water remediation, the microalgae skeleton (mainly glycogen and glucose) of the photocatalyst is recycled to directly produce bioethanol by simultaneous saccharification and fermentation process. An outstanding ethanol yield of 0.4 L kg−1, which is similar to the highest yield obtained from oxygenic photosynthetic microorganisms, is obtained. Thus, the entire process allows effective solar photocatalytic water remediation and bioethanol production at room temperature using simple and easily scalable procedures that simultaneously fixes carbon dioxide, thereby constituting a zero-carbon-emission circular process. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Local manipulation of metamagnetism by strain nanopatterning
Foerster M., Menéndez E., Coy E., Quintana A., Gómez-Olivella C., Esqué De Los Ojos D., Vallcorba O., Frontera C., Aballe L., Nogués J., Sort J., Fina I. Materials Horizons; 7 (8): 2056 - 2062. 2020. 10.1039/d0mh00601g. IF: 12.319
Among metamagnetic materials, FeRh alloys are technologically appealing due to their uncommon antiferromagnetic-to-ferromagnetic metamagnetic transition which occurs at a temperature T∗ just above room temperature. Here, a controlled increase of T∗ (ΔT∗ ∼ 20 °C) is induced in pre-selected regions of FeRh films via mechanical strain nanopatterning. Compressive stresses generated at the vicinity of pre-defined nanoindentation imprints cause a local reduction of the FeRh crystallographic unit cell parameter, which leads to an increase of T∗ in these confined micro-/nanometric areas. This enhances the stability of the antiferromagnetic phase in these localized regions. Remarkably, generation of periodic arrays of nanopatterned features also allows modifying the overall magnetic and electric transport properties across large areas of the FeRh films. This approach is highly appealing for the design of new memory architectures or other AFM-spintronic devices. © The Royal Society of Chemistry.
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Self-Assembly of Mechanoplasmonic Bacterial Cellulose–Metal Nanoparticle Composites
Eskilson O., Lindström S.B., Sepulveda B., Shahjamali M.M., Güell-Grau P., Sivlér P., Skog M., Aronsson C., Björk E.M., Nyberg N., Khalaf H., Bengtsson T., James J., Ericson M.B., Martinsson E., Selegård R., Aili D. Advanced Functional Materials; 30 (40, 2004766) 2020. 10.1002/adfm.202004766. IF: 16.836
Nanocomposites of metal nanoparticles (NPs) and bacterial nanocellulose (BC) enable fabrication of soft and biocompatible materials for optical, catalytic, electronic, and biomedical applications. Current BC–NP nanocomposites are typically prepared by in situ synthesis of the NPs or electrostatic adsorption of surface functionalized NPs, which limits possibilities to control and tune NP size, shape, concentration, and surface chemistry and influences the properties and performance of the materials. Here a self-assembly strategy is described for fabrication of complex and well-defined BC–NP composites using colloidal gold and silver NPs of different sizes, shapes, and concentrations. The self-assembly process results in nanocomposites with distinct biophysical and optical properties. In addition to antibacterial materials and materials with excellent senor performance, materials with unique mechanoplasmonic properties are developed. The homogenous incorporation of plasmonic gold NPs in the BC enables extensive modulation of the optical properties by mechanical stimuli. Compression gives rise to near-field coupling between adsorbed NPs, resulting in tunable spectral variations and enhanced broadband absorption that amplify both nonlinear optical and thermoplasmonic effects and enables novel biosensing strategies. © 2020 The Authors. Published by Wiley-VCH GmbH
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Simultaneous individual and dipolar collective properties in binary assemblies of magnetic nanoparticles
Sánchez E.H., Vasilakaki M., Lee S.S., Normile P.S., Muscas G., Murgia M., Andersson M.S., Singh G., Mathieu R., Nordblad P., Ricci P.C., Peddis D., Trohidou K.N., Nogués J., De Toro J.A. Chemistry of Materials; 32 (3): 969 - 981. 2020. 10.1021/acs.chemmater.9b03268. IF: 9.567
Applications based on aggregates of magnetic nanoparticles are becoming increasingly widespread, ranging from hyperthermia to magnetic recording. However, although some uses require collective behavior, others need a more individual-like response, the conditions leading to either of these behaviors are still poorly understood. Here, we use nanoscale-uniform binary random dense mixtures with different proportions of oxide magnetic nanoparticles with low/high anisotropy as a valuable tool to explore the crossover from individual to collective behavior. Two different anisotropy scenarios have been studied in two series of binary compacts: M1, comprising maghemite (γ-Fe2O3) nanoparticles of different sizes (9.0 nm/11.5 nm) with barely a factor of 2 between their anisotropy energies, and M2, mixing equally sized pure maghemite (low-anisotropy) and Co-doped maghemite (high-anisotropy) nanoparticles with a large difference in anisotropy energy (ratio > 8). Interestingly, while the M1 series exhibits collective behavior typical of strongly coupled dipolar systems, the M2 series presents a more complex scenario where different magnetic properties resemble either "individual-like"or "collective", crucially emphasizing that the collective character must be ascribed to specific properties and not to the system as a whole. The strong differences between the two series offer new insight (systematically ratified by simulations) into the subtle interplay between dipolar interactions, local anisotropy and sample heterogeneity to determine the behavior of dense assemblies of magnetic nanoparticles. © 2020 American Chemical Society.
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Voltage-driven motion of nitrogen ions: a new paradigm for magneto-ionics
de Rojas J., Quintana A., Lopeandía A., Salguero J., Muñiz B., Ibrahim F., Chshiev M., Nicolenco A., Liedke M.O., Butterling M., Wagner A., Sireus V., Abad L., Jensen C.J., Liu K., Nogués J., Costa-Krämer J.L., Menéndez E., Sort J. Nature Communications; 11 (1, 5871) 2020. 10.1038/s41467-020-19758-x. IF: 12.121
Magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions. Here, we demonstrate room-temperature voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a CoN film. Nitrogen magneto-ionics in CoN is compared to oxygen magneto-ionics in Co3O4. Both materials are nanocrystalline (face-centered cubic structure) and show reversible voltage-driven ON-OFF ferromagnetism. In contrast to oxygen, nitrogen transport occurs uniformly creating a plane-wave-like migration front, without assistance of diffusion channels. Remarkably, nitrogen magneto-ionics requires lower threshold voltages and exhibits enhanced rates and cyclability. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. These results may open new avenues in applications such as brain-inspired computing or iontronics in general. © 2020, The Author(s).
