Nano-estructuras tridimensionales funcionales (alúmina 3D y redes de nanohilos interconectados en las 3 direcciones del espacio)

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 09-03-2022This Thesis has been focused on the development of functional nanostructures for a variety of applications, from structural coloring to magnetic nanostructures with tailored properties and highly efficient thermoelectric metamaterials. In all cases, the fabrication of such nanostructures has been based on two processes: aluminum anodization and electrochemical growth. Both are chemical processes, which need no vacuum and that are well known at the industrial level. The results that are presented in this manuscript represent the state of the art of both techniques, which is well endorsed by the publications that have resulted from it.In brief, the main objective pursued in this Ph.D. Thesis has been to prove the versatility of a recent kind of alumina membranes, consisting of longitudinal pores that are transversely perforated by smaller pore channels, in the development of future nanotechnology applications. These 3D-Anodic alumina templates (3D AAO) have been studied by themselves, but also used as templates to grow different materials and tune their properties...Este trabajo de tesis se centra en el desarrollo de nanoestructuras funcionales interconectadas para diversas aplicaciones, desde la obtención de color estructural a la fabricación de metamateriales magnéticos con propiedades modificadas, así como metamateriales termoeléctricos de alta eficiencia. En todos estos casos, la fabricación de estas nanoestructuras se ha basado en dos procesos: anodización de aluminio y crecimiento electroquímico. Ambos son procesos químicos que no requieren de vacío y que son muy conocidos a nivel industrial. Los resultados que se presentan en este manuscrito muestran el estado del arte en ambas técnicas, lo que queda patente por las publicaciones científicas a las que este trabajo ha dado lugar. Brevemente, el objetivo principal de esta Tesis ha sido probar la versatilidad de un tipo de membranas de alúmina desarrolladas recientemente para el desarrollo de futuras aplicaciones nanotecnológicas. Estas membranas consisten en poros longitudinales que están unidos por poros transversales más pequeños que forman canales que los conectan. Estas membranas de alúmina tridimensionales (3D-AAO, del inglés 3D Anodic Aluminum Oxide) se han estudiado, por un lado, como plataformas para la generación de dispositivos en sí mismas, y, por otro lado, como plantillas para crecer en su estructura porosa distintos materiales y nanoestructurarlos, modificando de este modo sus propiedades...Fac. de Ciencias FísicasTRUEunpu

Tailoring magnetic anisotropy at will in 3d interconnected nanowire networks

The control of magnetic anisotropy has been the driving force for the development of magnetic applications in a wide range of technological fields from sensing to spintronics. In recent years, the possibility of tailoring the magnetic properties goes together with a need for new 3D materials to expand the applications to a new generation of devices. Herein, the possibility of designing the magnetic anisotropy of 3D magnetic nanowire networks is shown just by modifying the geometry of the structure or by composition. It is also shown that this is possible when the magnetic properties of the structure are governed by magnetostatic anisotropy. The present approach can guide systematic tuning of the magnetic easy axis and coercivity in the desired direction at the nanoscale. Importantly, this can be achieved on virtually any magnetic material, alloy, or multilayers that can be prepared inside porous alumina. These results are promising for engineering novel magnetic devices that exploit tailored magnetic anisotropy using metamaterials concept

Cylindrical Three-Dimensional Porous Anodic Alumina Networks

The synthesis of a conformal three-dimensional nanostructure based on porous anodic alumina with transversal nanopores on wires is herein presented. The resulting three-dimensional network exhibits the same nanostructure as that obtained on planar geometries, but with a macroscopic cylindrical geometry. The morphological analysis of the nanostructure revealed the effects of the initial defects on the aluminum surface and the mechanical strains on the integrity of the three-dimensional network. The results evidence the feasibility of obtaining 3D porous anodic alumina on non-planar aluminum substrates.The European Research Council and the EU-H2020 program are gratefully acknowledged for co-funding this work through the projects Tonality (ERC-2014-PoC) and Marie Skłodowska-Curie Fellow (706094–TONSOPS). We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

Antibacterial activity of a chitosan-PVA-Ag+-Tobermorite composite for periodontal repair

A polymer-mineral composite was prepared by solvent casting a mixture of chitosan, poly(vinyl alcohol), and Ag+-exchanged tobermorite in dilute acetic acid and characterised by scanning electron microscopy and Fourier transform infrared spectroscopy. The in vitro bioactivity of the CPTAg membrane was confirmed by the formation of hydroxyapatite on its surface in simulated body fluid. The alkaline dissolution products of the tobermorite lattice buffered the acidic breakdown products of the chitosan polymer and the presence of silver ions resulted in marked antimicrobial action against S. aureus, P. aeruginosa, and E. coli. The in vitro cytocompatibility of the CPTAg membrane was confirmed using MG63 osteosarcoma cells. The findings of this preliminary study have indicated that chitosan-poly(vinyl alcohol)-Ag+-tobermorite composites may be suitable materials for guided tissue regeneration applications

Effect of calcium precursor on the bioactivity and biocompatibility of sol-gel-derived glasses

This study investigated the impact of different calcium reagents on the morphology, composition, bioactivity and biocompatibility of two-component (CaO-SiO2) glasses produced by the Stöber process with respect to their potential application in guided tissue regeneration (GTR) membranes for periodontal repair. The properties of the binary glasses were compared with those of pure silica Stöber particles. The direct addition of calcium chloride (CC), calcium nitrate (CN), calcium methoxide (CM) or calcium ethoxide (CE) at 5 mol % with respect to tetraethyl orthosilicate in the reagent mixture gave rise to textured, micron-sized aggregates rather than monodispersed ~500 nm spheres obtained from the pure silica Stöber synthesis. The broadening of the Si-O-Si band at ~1100 cm-1 in the infrared spectra of the calcium-doped glasses indicated that the silicate network was depolymerised by the incorporation of Ca2+ ions and energy dispersive X-ray analysis revealed that, in all cases, the Ca:Si ratios were significantly lower than the nominal value of 0.05. The distribution of Ca2+ ions was also found to be highly inhomogeneous in the methoxide-derived glass. All samples released soluble silica species on exposure to simulated body fluid, although only calcium-doped glasses exhibited in vitro bioactivity via the formation of hydroxyapatite. The biocompatibilities of model chitosan-glass GTR membranes were assessed using human MG63 osteosarcoma cells and were found to be of the order: CN < pure silica ~ CC << CM ~ CE. Calcium nitrate is the most commonly reported precursor for the sol-gel synthesis of bioactive glasses; however, the incomplete removal of nitrate ions during washing compromised the cytocompatibility of the resulting glass. The superior bioactivity and biocompatibility of the alkoxide-derived glasses is attributed to their ease of dissolution and lack of residual toxic anions. Overall, calcium ethoxide was found to be the preferred precursor with respect to extent of calcium-incorporation, homogeneity, bioactivity and biocompatibility

Unveiling the Complex Magnetization Reversal Process in 3D Nickel Nanowire Networks

Understanding the interactions among magnetic nanostructures is one of the key factors to predict and control the advanced functionalities of Three-Dimensional (3D) integrated magnetic nanostructures. In this work, we focus on different interconnected Ni nanowires forming an intricate, but controlled, and ordered magnetic system: Ni 3D Nanowire Networks. These self-ordered systems present striking anisotropic magnetic responses, depending on the interconnections' position between nanowires. To understand their collective magnetic behavior, we studied the magnetization reversal processes within different Ni 3D Nanowire Networks compared to the 1D nanowire array counterparts. We characterized the systems at different angles using first magnetization curves, hysteresis loops, and First Order Reversal Curves techniques, which provided information about the key features that enable macroscopic tuning of the magnetic properties of the 3D nanostructures. In addition, micromagnetic simulations endorsed the experiments, providing an accurate modeling of their magnetic behavior. The results revealed a plethora of magnetic interactions, neither evident nor intuitive, which are the main role players controlling the collective response of the system. The results pave the way for the design and realization of 3D novel metamaterials and devices based on the nucleation and propagation of ferromagnetic domain walls both in 3D self-ordered systems and future nano-lithographied devices

Synthesis and characterization 3D Modulated and smooth TiO2 nanotubes for energy applications

Trabajo presentado en el International Conference on Hybrid and Organic Photovoltaics (HOPV16), celebrado en Swansea (Reino Unido), del 29 de junio al 1 de julio de 2016For more than a decade anodic TiO2 nanotubes layers (TNTL) have attracted the attention of many research groups, with more than 5000 publications in the 2009-14 period[1]. This interest bases on their optimal characteristics for different fields of applications ranging from biomaterials to water remediation and solar cells, and also due to their fast and easy synthesis processing. Pulsed galvanostatic anodization allows the modulation of the shape of TiO2 nanotubes resulting in a 3D nanostructure[2]. This 3D nanostructure can be tuned in order to control their optical properties[3][4]. In this contribution, we will present the obtained results on the synthesis and characterization of smooth TNTL and 3D modulated TNTL by potentiostatic and pulsed galvanostatic methods. The morphology (SEM), electrical and thermal properties by Kelvin probe and scanning thermal microscopy of the samples depending on their nanostructure will be discussed.This work was supported by the Marie Skłodowska-Curie Individual Fellowship 2015 grant 706094 “TONSOPS”.Peer reviewe