Low-toxic chemical solution deposition methods for the preparation of multi-functional (Pb1-xCax)TiO3 thin films

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid. Facultad de Ciencias. Departamento de Química Inorgánica. Fecha de lectura: 18-09-200

Influence of excesses of volatile elements on structure and composition of solution derived lead-free (Bi0.50Na0.50)1xBaxTiO3 thin films

The preparation of (Bi0.50Na0.50)1−xBaxTiO3 films requires a compositional/structural control, as they determine the functionality of these materials. We report a systematic compositional and structural analysis on (Bi0.50Na0.50)1−xBaxTiO3 films fabricated by chemical solution deposition. The effects of incorporating Na(I) and Bi(III) excesses are analyzed through the comparison of the compositional depth profiles of stoichiometric films (BNBT) and films containing excesses (BNBTxs). Heterogeneous compositional profiles with larger bismuth content close to the substrate and thicker film-substrate interfaces are observed in BNBTxs, unlike stoichiometric films, which show atomic concentrations that correspond to the nominal composition of the precursor solution. Excesses induce structural differences in depth, observing a shift of the region of coexistence of rhombohedral and tetragonal phases (morphotropic phase boundary) toward higher x values and the formation of thick film-substrate interfaces. In contrast, stoichiometric films have homogeneous compositional and structural profiles with the MPB placed close to that described for bulk ceramics.This work was financed by Spanish Project MAT2013-40489-P. D. Pérez-Mezcua acknowledges the financial support of the FPU Spanish program (AP2012-0639). A portion of this research was carried out at the Stanford Synchrotron Radiation Lightsource, a national user facility operated by Stanford University. D. Chateigner acknowledges the Conseil Régional de Basse Normandie for its partial financial of the four-circles X-ray diffractometer.Peer reviewe

Photoferroelectric thin films for flexible systems by a three-in-one solution-based approach

The effective incorporation of (multi)functional oxides into next-generation flexible electronics systems requires novel fabrication technologies that enable the direct integration of crystalline oxide layers in them. Unfortunately, this is considerably challenging due to the thermal incompatibility between the crystallization temperatures of metal oxides (>600 degrees C) and the thermal stability of the flexible polymer substrates conventionally used (<400 degrees C). Here, it is shown that BiFeO(3)thin films can be grown on flexible plastic by solution processing involving three different but complementary strategies to induce the crystallization of the perovskite phase at a lower temperature limit of 325 degrees C. This "three-in-one" approach is based on the synthesis of tailored metal precursors i) with a molecular structure resembling the crystalline structure of the oxide phase, which additionally allows both ii) photochemical and iii) internal combustion reactions taking place in the thin films. The flexible BiFeO(3)thin films obtained from a specifically designed molecular complex withN-methyldiethanolamine yield a large remnant polarization of 17.5 mu C cm(-2), also showing photovoltaic and photocatalytic effects. This result paves the way for the direct integration of an interesting class of oxides with photoferroelectric properties in flexible devices with multiple applications in information and communication technology, and energy

Photochemical solution processing of films of metastable phases for flexible devices: the beta-Bi2O3 polymorph

The potential of UV-light for the photochemical synthesis and stabilization of non-equilibrium crystalline phases in thin films is demonstrated for the beta-Bi2O3 polymorph. The pure beta-Bi2O3 phase is thermodynamically stable at high temperature (450-667 degrees C), which limits its applications in devices. Here, a tailored UV-absorbing bismuth(III)-N-methyldiethanolamine complex is selected as an ideal precursor for this phase, in order to induce under UV-light the formation of a -Bi-O-Bi- continuous network in the deposited layers and the further conversion into the beta-Bi2O3 polymorph at a temperature as low as 250 degrees C. The stabilization of the beta-Bi2O3 films is confirmed by their conductivity behavior and a thorough characterization of their crystal structure. This is also supported by their remarkable photocatalytic activity. Besides, this processing method has allowed us for the first time the preparation of beta-Bi2O3 films on flexible plastic substrates, which opens new opportunities for using these materials in potential applications not available until now (e.g., flexible photocatalytic reactors, self-cleaning surfaces or wearable antimicrobial fabrics). Therefore, photochemical solution deposition (PCSD) demonstrates to be not only an efficient approach for the low temperature processing of oxide films, but also an excellent alternative for the stabilization of metastable phases

Defect-mediated ferroelectric domain depinning of polycrystalline BiFeO3 multiferroic thin films

The ferroelectric domain depinning in a polycrystalline BiFeO3 film is studied by a defect-mediated diffusion mechanism driven by a secondary re-oxidation anneal. The presence of defect complexes (oxygen-vacancy-associated dipoles) responsible for pinning is discussed from the current-voltage (I-V) characteristics of the film. Dissociation of these complexes by re-oxidation anneal produces the effective depinning of domains in the material. The released oxygen vacancies would be compensated at the re-oxidized state due to the valence change of Fe2+ to Fe3+. Improvement on domain mobility results in a larger contribution to ferroelectric switching, showing a room-temperature remanent polarization of 67 μC cm-2. © 2014 AIP Publishing LLC.This work was financed by Spanish Project No. MAT2010-15365. I.B. acknowledges the financial support of the Juan de la Cierva Spanish program. C.G.-L. acknowledges the financial support of the JAE-Tec (CSIC) Spanish program.Peer Reviewe

Dielectric properties of Pb0.5Ca0.5TiO3 thin films

6 pages, 9 figures.A dielectric study is carried out on chemical solution-deposited calcium lead titanate (Pb,Ca)TiO3 thin films, with calcium contents of 50 at. %, by measuring capacitance versus voltage as a function of temperature. A moderate ferroelectric activity is observed that remains in a broad temperature range, and that depends on the applied voltage and thickness of the films. This behavior is associated with the built-in fields generated as result of the space charge inside the films. From the diffusivity of dielectric constant versus temperature (K′−T) curves, the relaxorlike nature of the films is also demonstrated. The feasibility of these films for fabrication of voltage tuneable capacitors and charge store devices (dynamic random access memories) is confirmed.This work has been supported by the Spanish Project No. MAT2001-1564. One of the authors (R.J.) recognizes the support of Ramon y Cajal contract of the Ministerio de Educación y Ciencia.Peer reviewe

Enhanced ferroelectric and ferromagnetic properties in lead-free multilayer composite films based on ferroelectric (Bi0.5Na0.5)0.945Ba0.055TiO3 and multiferroic BiFeO3

The study of the functional properties of the multilayer composite films of ferroelectric (Bi0.5Na0.5)0.945Ba0.055TiO3 (BNBT) and multiferroic BiFeO3 (BF) obtained by chemical solution deposition has been performed in this work. First, it has been observed a significant improvement of the remnant polarization of the multilayer composite with respect to the single phase film of BNBT: Pr = 32 μC × cm−2, which is comparable with the values reported for bulk BNBT. This is a consequence of the stabilization of the ferroelectric domains of BNBT, although the relaxor character is still present. The leakage currents, which prevent the full exploitation of the properties of BF films, are reduced thanks to the combination with insulator BNBT layers. Besides, the magnetic behavior shows values of remnant magnetization at room temperature that makes this multilayer composites promising for multiferroic applications.This work has been funded by the Spanish Project MAT2010-15365, MAT2013-40489-P, and MAT2011-C02-02. A. Perez-Rivero acknowledges the funding of his Spanish FPI Ph.D. grant. Dr. I. Bretos is a postdoctoral fellow of the Spanish Juan de la Cierva programme.Peer Reviewe

Polarization switching at room temperature of undoped BiFeO3 thin films crystallized at temperatures between 400 ≤ T ≤ 500 °C

Pure BiFeO3 perovskite thin films have been prepared on Pt-coated silicon substrates by chemical solution deposition at temperatures below 500 °C. Precursor solutions with and without Bi(III) excess have been used. Perovskite films without crystalline secondary phases, as detected by X-ray diffraction analysis, are obtained at the lowest temperature limit of 400 °C. However, the scanning electron micrographs of these films show surface microstructures formed by well defined grains surrounded by a fine grained phase, suggesting the appearance of a volume fraction of crystals in an early stage of crystallization. The films prepared with Bi(III) excess have better defined ferroelectric hysteresis loops than those without any excess, especially for the films annealed at 400 °C, which can be attributed to an improved connectivity of the ferroelectric phase. This together with the fact that leakage current densities in the films decrease with decreasing the processing temperature, make that the BiFeO3 films prepared with Bi(III) excess and annealed at 400 and 450 °C can be poled at room temperature, obtaining an effective switching of the ferroelectric polarization with the electric field. Remanent polarization values of PR ~ 10 and ~60 μC/cm2 with coercive fields of EC ~ 205 and 235 kV/cm were obtained for the films prepared at 400 and 450 °C, respectively. The demonstration of the functionality at room temperature of these low temperature processed undoped BiFeO3 thin films increases the interest in these materials for their integration in multiferroic devices.This work has been funded by the COST-Action IC1208 and the Spanish Projects MAT2010-15365 and MAT2013-40489-P. A. Perez-Rivero acknowledges the support of the FPI Spanish program and I. Bretos of “Juan de la Cierva” Spanish program.Peer reviewe

Los asquerosos. Miedo [Reseña]

Reseña crítica de dos obras: Lorenzo, S.; Tió, G., Il. (2018). Los asquerosos. Madrid, España, Blackie Books. y Zweig, S.; Bravo de la Varga, R., trad. (2018). Miedo. En Colección: Cuadernos del acantilado; 85 Madrid, España, Acantilado.. Esta reseña forma parte de la colección «Lecturas indultadas», con motivo de la celebración del Día del Libro, 2020. Madrid. 21 de abril de 2020. Sujeta a licencia Reconocimiento 4.0 Internacional (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/deed.es_ES[ES] Dos libros en los que sus protagonistas se ven encerrados en casa por distintos motivos. Y dos formas distintas de enfrentarse al confinamiento. ¿Con cuál te quedas?N

Ferroeléctricos sobre silicio preparados por métodos de depósito químico de disoluciones: de la lámina delgada a los sistemas auto-ensamblados.

[EN] The work of the authors during the last years on ferroelectric thin and ultra-thin films deposited by Chemical Solution Deposition (CSD) onto silicon based substrates is reviewed in this paper. Ferroelectric layers integrated with silicon substrates have potential use in the new micro/nanoelectronic devices. Two hot issues are here considered: 1) the use of low processing temperatures of the ferroelectric film, with the objective of not producing any damage on the different elements of the device heterostructure, and 2) the downscaling of the ferroelectric material with the aim of achieving the high densities of integration required in the next generation of nanoelectronic devices. The UV-assisted Rapid Thermal Processing has successfully been used in our laboratory for the fabrication of ferroelectric films at low temperatures. Preliminary results on the CSD preparation of nanosized ferroelectric structures are shown.[ES] Este artículo revisa el trabajo realizado por los autores durante los últimos años sobre lámina delgada y ultra-delgada ferroeléctrica preparada mediante el depósito químico de disoluciones (CSD) sobre substratos de silicio. Las películas ferroeléctricas integradas con silicio tienen potenciales usos en los nuevos dispositivos micro/nanoelectrónicos. Dos aspectos claves son aquí considerados: 1) el uso de bajas temperaturas de procesado de la lámina ferroeléctrica, con el fin de no dañar los diferentes elementos que forman la heteroestructura del dispositivo y 2) la disminución de tamaño del material ferroeléctrico con el fin de conseguir las altas densidades de integración requeridas en la próxima generación de dispositivos nanoelectróncos. Los procesos térmicos rápidos asistidos con irradiación UV se están usando en nuestro laboratorio para conseguir la fabricación del material ferroeléctrico a temperaturas bajas compatibles con la tecnología del silicio. Se muestran resultados preliminares sobre estructuras ferroeléctricas nanométricas preparadas por CSD.This work has been supported by the Spanish project CICTY MAT-2004-02014.Peer reviewe