Estudio de nanomateriales modificados basados en Au mediante espectroscopía de resonancia de plasmones de superficie

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 14-03-2014In this work, surface plasmon resonance (SPR) spectroscopy has been employed as a probe to study modifications in nanostructured systems based on Au. Those modifications include a) structural and morphological changes induced by annealing and b) electronic modifications upon X-ray irradiation. The use of SPR spectroscopy to follow the evolution of modifications in nanostructures (especially, in situ and in real time) has been scarcely explored and its study results interesting and relevant for the plasmonic technology. In this first part of the work, we have grown nanostructures from Au films and Au/Fe bilayers which have been later annealed under different conditions. These nanostructures have been characterized morphologically and analyzed by SPR spectroscopy, in order to follow the morphological changes of the systems varying the sample features (i.e., initial thickness) and the annealing conditions. With the purpose of studying changes induced upon X-ray irradiation using SPR as a probe, we have designed and developed a SPR system based on the Kretschmann-Raether configuration compatible with a X-ray absorption spectroscopy (XAS) beamline (SPR-XAS setup). Using this device, a study of the effects of the X-rays on glasses and Co-Phthalocyanines (CoPcs) has been carried out. For the study on glasses, two different types are analyzed: soda-lime and silica substrates, and for the case of the CoPcs, these have been grown varying the film thickness and the growth conditionsEn este trabajo se ha empleado la espectroscopía de resonancia de plasmones de superficie (SPR) para estudiar modificaciones en sistemas nanoestructurados basados en Au. Estas modificaciones incluyen a) cambios estructurales y morfológicos inducidos mediante tratamientos térmicos y b) modificaciones electrónicas bajo irradiación con rayos X. El uso de la espectroscopía de SPR para seguir la evolución de modificaciones en nanoestructuras (especialmente, in situ y en tiempo real) ha sido escasamente explorado y su estudio resulta interesante y relevante para el campo de la plasmónica. En la primera parte de este trabajo se ha llevado a cabo la fabricación de nanoestructuras a partir de películas de Au y bicapas Au/Fe tratadas térmicamente bajo diferentes condiciones. Estas nanoestructuras han sido caracterizadas morfológicamente y analizadas mediante espectroscopía de SPR con el fin de estudiar los cambios estructurales inducidos en las muestras al variar parámetros como el espesor y las condiciones del tratamiento térmico. Con el objetivo de estudiar modificaciones inducidas en la materia bajo irradiación con rayos X usando la SPR como sonda, se ha diseñado y desarrollado un sistema experimental de SPR basado en la configuración de Kretschmann-Raether y compatible con la espectroscopía de absorción de rayos X (dispositivo SPR-XAS). Mediante este montaje experimental se han analizado los efectos inducidos por los rayos X en vidrios y en Ftalocianinas de Co (CoPcs), in situ y en tiempo real. Para el caso de los vidrios, dos tipos diferentes han sido empleados como substratos: sodicocálcicos y de sílice. Por otro lado, las CoPcs estudiadas han sido crecidas variando su espesor y las condiciones de crecimientoDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEunpu

Modified Au-based nanomaterials studied by surface plasmon resonance spectroscopy

Tesis Doctoral realizada por Aída Serrano Rubio en la Universidad Complutense de Madrid (Facultad de Ciencias Físicas. Departamento de Física de Materiales) y el CSIC - Instituto de Cerámica y Vidrio (ICV).[EN]: In this work, surface plasmon resonance (SPR) spectroscopy has been employed as a probe for studying modifications in nanostructured systems based on Au. Those modifications include: a) structural and morphological changes induced by annealing and b) electronic modifications upon X-ray irradiation. The use of SPR spectroscopy to follow the evolution of modifications in nanostructures (especially, in situ and in real time) has been scarcely explored and its study results interesting and relevant for the plasmonic technology. For that, different experiments have been planned and performed.[ES]: En este trabajo se ha empleado la espectroscopía de resonancia de plasmones de superficie (SPR) para estudiar modificaciones en sistemas nanoestructurados basados en Au. Estas modificaciones incluyen: a) cambios estructurales y morfológicos inducidos mediante tratamientos térmicos y b) modificaciones electrónicas bajo irradiación con rayos X. El uso de la espectroscopía de SPR para seguir la evolución de modificaciones en nanoestructuras (especialmente, in situ y en tiempo real) ha sido escasamente explorado y su estudio resulta interesante y relevante para el campo de la plasmónica. Para llevar a cabo la realización de este trabajo, varios experimentos han sido planteados y realizados.La realización de este trabajo de tesis doctoral ha sido posible gracias a la fianciación de los proyectos de investigación BONSAI (LSHB-CT-2006-037639) and MAGNYFICO (NMP4-SL-2009-228622) financiados por la Unión Europea. El Ministerio de Economía y Competitividad y el Consejo Superior de Investigaciones Cientifícas son también agradecidos por la financiación y la provisión de las instalaciones de radiación sincrotrón en BM25-Spline, en el ESRF. Aída Serrano Rubio agradece la financiación otorgada por el Consejo Superior de Investigaciones Científicas con una Beca JAE (JAEPre096) de cuatro años de duración para desarrollar la tesis doctoral en el Instituto de Cerámica y Vidrio.Peer Reviewe

Improving the co and ch4 gas sensor response at room temperature of alpha-fe2o3(0001) epitaxial thin films grown on srtio3(111) incorporating au(111) islands

In this work, the functional character of complex -Fe2O3(0001)/SrTiO3(111) and Au(111) islands/ -Fe2O3(0001)/SrTiO3(111) heterostructures has been proven as gas sensors at room temperature. Epitaxial Au islands and -Fe2O3 thin film are grown by pulsed laser deposition on SrTiO3(111) substrates. Intrinsic parameters such as the composition, particle size and epitaxial character are investigated for their influence on the gas sensing response. Both Au and -Fe2O3 layer show an island-type growth with an average particle size of 40 and 62 nm, respectively. The epitaxial and incommensurate growth is evidenced, confirming a rotation of 30 between the in-plane crystallographic axes of -Fe2O3(0001) structure and those of SrTiO3(111) substrate and between the in-plane crystallographic axes of Au(111) and those of -Fe2O3(0001) structure. -Fe2O3 is the only phase of iron oxide identified before and after its functionalization with Au nanoparticles. In addition, its structural characteristics are also preserved after Au deposition, with minor changes at short-range order. Conductance measurements of Au(111)/ -Fe2O3(0001)/SrTiO3(111) system show that the incorporation of epitaxial Au islands on top of the -Fe2O3(0001) layer induces an enhancement of the gas-sensing activity of around 25% under CO and 35% under CH4 gas exposure, in comparison to a bare -Fe2O3(0001) layer grown on SrTiO3(111) substrates. In addition, the response of the heterostructures to CO gas exposure is around 5–10% higher than to CH4 gas in each case.This work has been supported by the Ministerio Español de Ciencia e Innovación (MICINN) and the Consejo Superior de Investigaciones Cientificas (CSIC) through the projects PIE-2010-OE-013- 200014, PIE 2021-60-E-030 and RTI2018-095303-A-C52. The ESRF, MICINN and CSIC are acknowledged for the provision of synchrotron radiation facilities. A.S. acknowledges financial support from Comunidad de Madrid for an “Atracción de Talento Investigador” Contract (2017-t2/IND5395)

Interlayer-Confined Cu(II) Complex as an Efficient and Long-Lasting Catalyst for Oxidation of H2S on Montmorillonite

Removal of highly toxic H2S for pollution control and operational safety is a pressing need. For this purpose, a montmorillonite intercalated with Cu(II)-phenanthroline complex [Cu[(Phen)(H2O)2]2+ (Mt-CuPhen) was prepared to capture gaseous H2S under mild conditions. This hybrid material was simple to obtain and demonstrated an outstanding ability to entrap H2S at room temperature, retaining high efficiency for a very long time (up to 36.8 g of S/100 g Mt-CuPhen after 3 months of exposure). Sorbent and H2S uptake were investigated by elemental analysis, X-ray powder diffraction measurements, diffuse reflectance (DR) UV–Vis and infrared spectroscopy, thermal analysis and evolved gas mass spectrometry, scanning electron microscopy equipped with energy-dispersive X-ray spectrometer, and X-ray absorption spectroscopy. The H2S capture was studied over time and a mechanism of action was proposed. The entrapping involves a catalytic mechanism in which [Cu[(Phen)(H2O)2]2+ acts as catalyst for H2S oxidation to S0 by atmospheric oxygen. The low cost and the long-lasting performance for H2S removal render Mt-CuPhen an extremely appealing trap for H2S removal and a promising material for many technological applications

Thermal route for the synthesis of maghemite/hematite core/shell nanowires

Nowadays, iron oxide-based nanostructures are key materials in many technological areas. Their physical and chemical properties can be tailored by tuning the morphology. In particular, the possibility of increasing the specific surface area has turned iron oxide nanowires (NWs) into promising functional materials in many applications. Among the different possible iron oxide NWs that can be fabricated, maghemite/hematite iron oxide core/shell structures have particular importance since they combine the magnetism of the inner maghemite core with the interesting properties of hematite in different technological fields ranging from green energy to biomedical applications. However, the study of these iron oxide structures is normally difficult due to the structural and chemical similarities between both iron oxide polymorphs. In this work, we propose a route for the synthesis of maghemite/hematite NWs based on the thermal oxidation of previously electrodeposited iron NWs. A detailed spectroscopic analysis based on Raman, Mossbauer, and X-ray absorption shows that the ratio of both oxides can be controlled during fabrication. Transmission electron microscopy has been used to check the core/shell structure of the NWs. The biocompatibility and capability of internalization of these NWs have also been proven to show the potential of these NWs in biomedical applications

A combined micro-Raman, X-ray absorption and magnetic study to follow the glycerol-assisted growth of epsilon-iron oxide sol-gel coatings

[EN] Epsilon iron oxide (ε-FeO) coatings on Si(100) substrates are obtained by an easy one-pot sol-gel recipe assisted by glycerol in an acid medium. Glycerol, given its small dimensions, enables the formation of ε-FeO nanoparticles with a size of a few nanometers and the highest purity is reached in coatings after a densification treatment at 960 °C. The structural and compositional evolution up to 1200 °C is studied by confocal Raman microscopy and X-ray absorption spectroscopy techniques, correlating the existing magnetic properties. We report a novel characterization method, which allows monitoring the evolution of the precursor micelles as well as the intermediate and final phases formed. Furthermore, the inherent industrial technology transfer of the sol-gel process is also demonstrated with the ε-FeO polymorph, impelling its application in the coatings form.This work has been supported by the Ministerio de Ciencia e Innovación (MCINN, Spain) through the projects PIE: 2021-60-E-030, PIE: 2010-6-OE-013, PID2019-104717RB-I00 (2020–2022), MAT2017-86540-C4-1-R, RTI2018-095856-B-C21 (2019–2021), RTI2018-097895-B-C43 and RTI2018-095303-A-C52. The authors are grateful to The ESRF (France), MCINN and Consejo Superior de Investigaciones Científicas (CSIC, Spain) for the provision of synchrotron radiation facilities and to the BM25-SpLine Staff for their valuable help. A.S.and A.M.-N acknowledge financial support from Comunidad de Madrid (Spain) for an “Atracción de Talento Investigador” Contract 2017-t2/IND5395 and 2018-T1/IND-10360, respectivel

Correction: A feasible pathway to stabilize monoclinic and tetragonal phase coexistence in barium titanate-based ceramics

Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu

Dense strontium hexaferrite-based permanent magnet composites assisted by cold sintering process

[EN] The use of rare-earth-based permanent magnets is one of the critical points for the development of the current technology. On the one hand, industry of the rare-earths is highly polluting due to the negative environmental impact of their extraction and, on the other hand, the sector is potentially dependent on China. Therefore, investigation is required both in the development of rare-earth-free permanent magnets and in sintering processes that enable their greener fabrication with attractive magnetic properties at a more competitive price. This work presents the use of a cold sintering process (CSP) followed by a post-annealing at 1100 °C as a new way to sinter composite permanent magnets based on strontium ferrite (SFO). Composites that incorporate a percentage ≤ 10% of an additional magnetic phase have been prepared and the morphological, structural and magnetic properties have been evaluated after each stage of the process. CSP induces a phase transformation of SFO in the composites, which is partially recovered by the post-thermal treatment improving the relative density to 92% and the magnetic response of the final magnets with a coercivity of up to 3.0 kOe. Control of the magnetic properties is possible through the composition and the grain size in the sintered magnets. These attractive results show the potential of the sintering approach as an alternative to develop modern rare-earth-free composite permanent magnets.This work has been supported by the Ministerio Español de Ciencia e Innovación (MICINN), Spain, through the projects MAT2017-86540-C4-1-R and RTI2018-095303-A-C52, and by the European Commission through Project H2020 No. 720853 (Amphibian). C.G.-M. and A.Q. acknowledge financial support from MICINN through the “Juan de la Cierva” program (FJC2018-035532-I) and the “Ramón y Cajal” contract (RYC-2017-23320). S. R.-G. gratefully acknowledges the financial support of the Alexander von Humboldt foundation, Germany. A.S. acknowledges the financialsupport from the Comunidad de Madrid, Spain, for an “Atracción de Talento Investigador” contract (No. 2017-t2/IND5395)

Reversible temperature-driven domain transition in bistable Fe magnetic nanostrips grown on Ru(0001)

© 2015 American Physical Society. High-aspect-ratio Fe nanostrips are studied with real-space micromagnetic imaging methods. We experimentally demonstrate reversible switching from essentially homogeneous single-domain states at room temperature to multidomain diamond states at elevated temperature. This temperature-dependent magnetic bistability can be understood and modeled by accounting for the temperature dependence of the magnetocrystalline, shape, and magnetoelastic anisotropies. These results show how the transition temperature between two magnetic domain states can be tailored by controlling epitaxial strain and particle geometry, which may generate new opportunities for magnetic memory and logic device design.Peer Reviewe

A feasible pathway to stabilize monoclinic and tetragonal phase coexistence in barium titanate-based ceramics

Multiphase coexistence has attracted significant interest in recent years because its control has entailed a significant breakthrough for the piezoelectric activity enhancement of lead-free piezoelectric oxides. However, the comprehension of phase coexistence still has many controversies including an adequate synthesis process and/or the role played by crystalline phases in functional properties. In this study, functional barium titanate [BaTiO_(3), (BTO)]-based materials with tunable functional properties were obtained by compositional modification via Bismuth (Bi) doping. Towards this aim, we systematically synthesized BTO-based materials by a sol-gel method, focusing on the control of Bi substitution in the BaTiO_(3) structure. In particular, we found that the substitution of Bi^(+3) leads to the stabilization of a monoclinic-tetragonal (M-T) phase boundary close to room temperature, which facilities the polarization process of the system. As a surprising result, we believe that the simple and cost-effective strategy and design principles described in this work open up the possibility of obtaining BTO-based lead-free ceramics with enhanced properties induced by the stabilization of the phase coexistence, expanding their application range