Synthesis and properties of epitaxial oxide thin films prepared by polymer assisted deposition

This thesis describes the most relevant aspects in PAD method as well the process of optimization to obtain high quality epitaxial thin films of multicationic oxides. For this we have analyzed the structure and the behavior of polymers both in solution and under thermal degradation, and it has been determined the degree of retention for different metals in combination with various chelating agents. The synthesis and characterization of thin films have been applied to a set of oxides with different compositions and properties, controlling the thickness, stoichiometry, etc. The effect of growth conditions was studied by comparison with films prepared by classical physical methods. Furthermore, two different materials were combined in the same structure in the form of bilayers with a clear interface between the two individual layers. All this progress over single-crystal substrates was used to deposit functional oxides integrated on silicon at the end of this thesis

High quality thin films of thermoelectric misfit cobalt oxides prepared by a chemical solution method

Misfit cobaltates ([Bi/Ba/Sr/Ca/CoO]nRS[CoO2]q) constitute the most promising family of thermoelectric oxides for high temperature energy harvesting. However, their complex structure and chemical composition makes extremely challenging their deposition by high-vacuum physical techniques. Therefore, many of them have not been prepared as thin films until now. Here we report the synthesis of high-quality epitaxial thin films of the most representative members of this family of compounds by a water-based chemical solution deposition method. The films show an exceptional crystalline quality, with an electrical conductivity and thermopower comparable to single crystals. These properties are linked to the epitaxial matching of the rock-salt layers of the structure to the substrate, producing clean interfaces free of amorphous phases. This is an important step forward for the integration of these materials with complementary n-type thermoelectric oxides in multilayer nanostructuresThis research was supported by the European Research Council (ERC StG-2DTHERMS), Ministerio de Economía y Competitividad of Spain (MAT2010-16157 & MAT2013-44673-R) and Xunta de Galicia (2012-CP071). J.M.V-F acknowledges the MINECO for support with a PhD grant of the FPI programS

Magnetic hyperthermia enhancement in iron-based materials driven by carbon support interactions

Magnetic hyperthermia (MH) shows great potential in clinical applications because of its very localized action and minimal side effects. Because of their high saturation magnetization values, reduced forms of iron are promising candidates for MH. However, they must be protected in order to overcome their toxicity and instability (i. e., oxidation) under biological conditions. In this work, a novel methodology for the protection of iron nanoparticles through confinement within graphitic carbon layers after thermal treatment of preformed nanoparticles supported on carbon is reported. We demonstrate that the size and composition of the nascent confined iron nanoparticles, as well as the thickness of their protective carbon layer can be controlled by selecting the nature of the carbon support. Our findings reveal that a higher nanoparticle–carbon interaction, mediated by the presence of oxygen-containing groups, induces the formation of small and well-protected α-Fe-based nanoparticles that exhibit promising results towards MH based on their enhanced specific absorption rate valuesAgencia Estatal de Investigación. Grant Numbers: RTI2018-101097-A-I00, RyC-2016-20258, PID2021-127341OB-I00. European Research Council. Grant Numbers: 679124, 966743. Consellería de Cultura, Educación e Ordenación Universitaria, Xunta de Galicia. Grant Numbers: 2019-2022, ED431G 2019/03, ED431B 2021/13. Ministerio de Ciencia, Innovación y Universidades. Grant Number: FPU2020S

High-yield halide-assisted synthesis of metal–organic framework UiO-based nanocarriers

The synthesis of nanosized metal–organic frameworks (NMOFs) is requisite for their application as injectable drug delivery systems (DDSs) and other biorelevant purposes. Herein, we have critically examined the role of different synthetic parameters leading to the production of UiO-66 crystals smaller than 100 nm. Of note, we demonstrate the co-modulator role conferred by halide ions, not only to produce NMOFs with precise morphology and size, but also to significantly improve the reaction yield. The resulting NMOFs are highly crystalline and exhibit sustained colloidal stability in different biologically relevant media. As a proof of concept, these NMOFs were loaded with Rhodamine 6G (R6G), which remained trapped in most common biologically relevant media. When incubated with living mammalian cells, the R6G-loaded NMOFs were efficiently internalized and did not impair cell viability even at relatively high doses.The authors acknowledge the financial support of the MCIN/AEI (PID2019-108624RB-I00, RYC-2017-23457, RYC-2019-028238-I), the Xunta de Galicia (ED431F 2017/02, ED431F 2020/11, 2021-CP090, Centro Singular de Investigación de Galicia Accreditation 2019–2022, ED431G 2019/03), the European Union (European RegionalDevelopment Fund – ERDF; H2020-MSCA-ITN grant agreement no. 860942; H2020-FET-Open grant agreement no. 899612; H2020-ICT grant agreement no. 10101694 and INTERREG V-A Spain–Portugal, project 0624_2IQBIONEURO_6_E), and the European Research Council (starting grant no. 950421). M.C.-M. thanks the AEI (FPU19/03155). The authors are grateful for the use of RIAIDT-USC analytical facilities.S

Apparent auxetic to non-auxetic crossover driven by Co2+ redistribution in CoFe2O4 thin films

Oxide spinels of general formula AB2O4 (A = Mg2+, Fe2+; B = Al3+, Cr3+, etc.) constitute one of the most abundant crystalline structures in mineralogy. In this structure, cations distribute among octahedral and tetrahedral sites, according to their size and the crystal-field stabilization energy. The cationic arrangement determines the mechanical, magnetic, and transport properties of the spinel and can be influenced by external parameters like temperature, pressure, or epitaxial stress in the case of thin films. Here, we report a progressive change in the sign of the Poisson ratio, ν, in thin films of CoFe2O4, defining a smooth crossover from auxetic (ν 0) behavior in response to epitaxial stress and temperature. Microstructural and magnetization studies, as well as ab initio calculations, demonstrate that such unusual elastic response is actually due to a progressive redistribution of Co2+ among the octahedral and tetrahedral sites of the spinel structure. The results presented in this work clarify a long standing controversy about the magnetic and elastic properties of Co-ferrites and are of general applicability for understanding the stress-relaxation mechanism in complex crystalline structures.This work has received financial support from Ministerio de Economía y Competitividad (Spain) under Project No. MAT2016-80762-R and MAT2017-82970-C2-R, Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016-2019, No. ED431G/09), the European Union (European Regional Development Fund-ERDF), and the European Commission through the Horizon H2020 funding by H2020-MSCA-RISE-2016-Project No. 734187–SPICOLOST. I.L.d.P. and B.R.-M. thank the funding under the ESTEEM2 project and the researchers L.A. Rodríguez and E. Snoeck for preliminary Lorentz Microscopy (L.M.) and electron holography (EH) studies in CoFe2O4 samples synthesized by PAD method performed at CEMES (Toulouse)S

Crystal engineering and ferroelectricity at the nanoscale in epitaxial 1D manganese oxide on silicon

Ferroelectric oxides have attracted much attention due to their wide range of applications, particularly in electronic devices such as nonvolatile memories and tunnel junctions. As a result, the monolithic integration of these materials into silicon technology and their nanostructuration to develop alternative cost-effective processes are among the central points in the current technology. In this work, we used a chemical route to obtain nanowire thin films of a novel Sr1+δMn8O16 (SMO) hollandite-type manganese oxide on silicon. Scanning transmission electron microscopy combined with crystallographic computing reveals a crystal structure comprising hollandite and pyrolusite units sharing the edges of their MnO6 octahedra, resulting in three types of tunnels arranged along the c axis, where the ordering of the Sr atoms produces natural symmetry breaking. The novel structure gives rise to ferroelectricity and piezoelectricity, as revealed by local direct piezoelectric force microscopy measurements, which confirmed the ferroelectric nature of the SMO nanowire thin films at room temperature and showed a piezoelectric coefficient d33 value of 22 ± 6 pC N−1. Moreover, we proved that flexible vertical SMO nanowires can be harvested providing an electrical output energy through the piezoelectric effect, showing excellent deformability and high interface recombination. This work indicates the possibility of engineering the integration of 1D manganese oxides on silicon, a step which precedes the production of microelectronic devices.A. C.-G., C. J., R. G.-B. and J. M. V.-F. acknowledge the financial support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (No. 803004) and the French Agence Nationale de la Recherche (ANR), project Q-NOSS ANR ANR-16-CE09-0006-01. This project has received funding from the EU-H2020 research and innovation program under grant agreement no 654360 having benefitted from the access provided by ICMAB-CSIC in Barcelona within the framework of the NFFA-Europe Transnational Access Activity. This project has received funding from the European's Union Horizon 2020 research and innovation programme under Grant No. 823717-ESTEEM3, the Spanish Ministry of Economy and Competitivity through Project MAT2017-82970-C2-2-R, and the Aragon Regional Government through Project No. E13_20R (with European Social Fund). We acknowledge SOLEIL for provision of synchrotron radiation facilities, and we would like to thank Pierre Fertey for assistance in using beamline Cristal. J. G. also acknowledges the Ramon y Cajal program (RYC-2012-11709). The authors thank D. Montero for providing the FEGSEM images. N. M. acknowledges the Spanish Ministry of Science, Innovation and Universities through Severo Ochoa FUNFUTURE (CEX2019-000917-S) and SUMATE (RTI2018-095853-B-C21) projects, co-financed by the European Regional Development Fund. The FEGSEM instrumentation was facilitated by the Institut des Matériaux de Paris Centre (IMPC FR2482). The authors thank Frederic Pichot for his expertise and advice during the nanowire lithographic process. The STEM microscopy work was conducted in the Laboratorio de Microscopias Avanzadas (LMA) at Instituto de Nanociencia de Aragon (INA) at the University of Zaragoza.Peer reviewe

Polymer assisted deposition of epitaxial oxide thin films

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Semiconducting Films: Electric and Mechanical Switching of Ferroelectric and Resistive States in Semiconducting BaTiO 3- δ Films on Silicon (Small 39/2017)

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