1,721,123 research outputs found
Dataset Figures paper entitled "Grain Boundaries and the Photoresponse of Epitaxial LaFeO3 films"
No full textJ/V, STEM, 4D-STEM, EELS, XRD and AFM Raw data.-
Los archivos .dat se pueden abrir con Origin, Excel, Numbers. Los archivos .xrdml, se pueden abrir con X'pert Highscore. Los archivos.mi se pueden abrir con Gwyddion, Mountains. Los archivos .dm4 Digital MicrographDataset Description: Grain Boundaries and the Photoresponse of Epitaxial LaFeO3 films
The dataset associated with the study ""Grain Boundaries and the Photoresponse of Epitaxial LaFeO3 films"" show that grain boundary engineering in narrow band-gap oxide thin films is a suited strategy to enhance their photoresponse.
Motivation
Centrosymmetric LaFeO3 (LFO) shows photovoltaic effect when sandwiched between asymmetric electrodes, which stems from the built-in potential induced by the different work functions of the top and bottom electrodes, interfacial polar discontinuity or even flexoelectric fields. However, the complex microstructure of epitaxial LFO film contributes to its photoresponse differently depending on the crystallographic domain landscape and the nature of the grain boundaries originating between them.
Dataset Content and Structure
The dataset includes the following categories of data:
Photoresponse measurements – J/V curves.
High resolution HAADF-STEM images.
4D-STEM for the study of the cristallographic domains within the thin films.
EELS measurements.
AFM images.
XRD measurements - Reciprocal Space Maps.Raw data for all FiguresN
Unravelling and controlling hidden imprint fields in ferroelectric capacitors
Full text linkFerroelectric materials have a spontaneous polarization that can point along energetically equivalent, opposite directions. However, when ferroelectric layers are sandwiched between different metallic electrodes, asymmetric electrostatic boundary conditions may induce the appearance of an electric field (imprint field, E imp) that breaks the degeneracy of the polarization directions, favouring one of them. This has dramatic consequences on functionality of ferroelectric-based devices such as ferroelectric memories or photodetectors. Therefore, to cancel out the E imp, ferroelectric components are commonly built using symmetric contact configuration. Indeed, in this symmetric contact configuration, when measurements are done under time-varying electric fields of relatively low frequency, an archetypical symmetric single-step switching process is observed, indicating E imp ∼ 0. However, we report here on the discovery that when measurements are performed at high frequency, a well-defined double-step switching is observed, indicating the presence of E imp. We argue that this frequency dependence originates from short-living head-to-head or tail-to-tail ferroelectric capacitors in the device. We demonstrate that we can modulate E imp and the life-time of head-to-head or tail-to-tail polarization configurations by adjusting the polarization screening charges by suitable illumination. These findings are of relevance to understand the effects of internal electric fields on pivotal ferroelectric properties, such as memory retention and photoresponse
Selecting Steady and Transient Photocurrent Response in BaTiO3 Films
Full text linkThe ferroelectric polarization and short-circuit photocurrent in BaTiO3 thin films are studied for different contact configurations that allow to measure the photoresponse and polarization under the presence of large or negligible imprint field. It is found that in all cases, the direction of the photocurrent is dictated by the depolarizing field and ultimately by the film polarization, with a negligible contribution of the imprint electric field. However, dramatic differences are found in their time-dependent photoresponse. Whereas in presence of imprint, steady photocurrents are observed under suitable illumination, transient photocurrents are generated in absence of imprint. It is argued that this distinct behavior is determined by the different Schottky barrier height at electrodes which thus offers a simple way to tune the film photoresponse. These findings can be exploited for electro-optic read-out and writing of ferroelectric memories
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Large room-temperature electroresistance in dual-modulated ferroelectric tunnel barriers
Full text linkPt/BaTiO3/La0.7Sr0.3MnO3 tunnel junctions, at negative voltage bias, for two polarization directions are represented. It is demonstrated that reversing the polarization direction of a ferroelectric barrier in a tunnel junction leads to a change of junction conductance and capacitance, with concomitant variations on the barrier height and effective thickness, both contributing to produce larger electroresistance
Strain and interface-induced charge, orbital and spin orderings in transition-me tal oxide perovskites
Full text linkPremi Extraordinari de Doctorat concedit pels programes de doctorat de la UAB per curs acadèmic 2017-201
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Electrical properties of BaTiO3, CoFe2O4 and La1/2(Ca, Sr)1/2MnO3 thin films and their importance for active barriers in tunnel transport
Full text linkLa miniaturización ha sido el concepto relevante de la tecnología basada en silicio. No obstante, el escalamiento de su elemento pilar (el transistor de efecto de campo por apilamiento de metal/óxido/semiconductor) pronto llevará a la capa óxido de silicio a un espesor de 2 nm, donde la eficiencia de los dispositivos es afectada por el incremento de las corrientes de fuga debida al efecto túnel. Por lo tanto, la substitución del óxido de silicio parece inminente. La implementación de óxidos que presentan orden ferroico puede ser vista como una nueva ruta a seguir en el campo tecnológico. Por ejemplo, en memorias de acceso aleatorio (en inglés RAMs). Memorias ferroelectricas (RAMs), en las cuales la información es codificada a través de polarización ferroelectrica, ya están siendo usadas en dispositivos comerciales. Materiales ferroelectricos están siendo usados en investigaciones sobre celdas solares. Aislantes magnéticos han sido importantes en espintrónica. El control del magnetismo mediante campos eléctricos es otro tópico que resulta prometedor. Aquí, la corriente de fuga asociada al transporte túnel no es vista como un problema sino como una herramienta para leer información en dispositivos eléctricos o magnéticos y memorias. No obstante la física de las capas delgadas y ultradelgadas de ciertos óxidos ferroicos a un no está completamente entendida. Esta tesis está encaminada a investigar materiales con propiedades ferroicas a nanoescala. En el primer bloque, materiales magnéticos como CoFe2O4 y La0.5A0.5MnO3 (con A = Sr, Ca) han sido estudiados y la variación de sus propiedades bajo estrés han sido monitoreadas y explicadas. En el caso de CoFe2O4 medidas de impedancia en función de la frecuencia y bias DC han sido realizadas. La constante dieléctrica hallada es correlacionada con el estrés. Con respecto a La0.5A0.5MnO3, capas nanométricas han sido crecidas sobre diferentes substratos para imponer un estado de estrés mediante el crecimiento coherente de las películas. El orden magnético y el carácter eléctrico de las películas de La0.5A0.5MnO3 es explicado en términos de ordenamiento orbital. El segundo bloque trata sobre la descripción de algunos experimentos preliminares sobre el efecto de la luz en las propiedades ferroelectricas. Fotocorriente es medida en películas de BaTiO3. También se ha encontrado que la polarización y campo coercitivo pueden ser reducidos mediante iluminación. El último bloque es dedicado a la caracterización de junturas ferroelectricas de túnelamiento (en inglés FTJs). BaTiO3 es usado como barrera ferroelectrica mientras que La0.7Sr0.3MnO3 y Pt son usados como electrodos inferior y superior respectivamente. El control eléctrico de estados de resistencia de remanencia en FTJs de gran área muestran 3x104% electroresistencia túnel (en inglés TER) a temperatura ambiente. Medidas de capacitancia en función del voltaje DC presentan similitud con aquellas encontradas en metal-óxido-semiconductor. Posteriormente, capas ultradelgadas de La0.5A0.5MnO3 han sido insertadas entre el electrodo metálico y la capa ferroelectrica con el propósito de explorar una posible transición metal-aislante en estas capas como una forma de mejorar el valor de TER. Se encuentra que, para una composición particular el valor de TER, puede crecer hasta 5 veces. En relación a las capas ultradelgadas de CoFe2O4 se han observado contribución túnel y contribución tipo no túnel.Shrinking has been the relevant concept of silicon-based technology. However the scaling of its cornerstone (metal oxide semiconductor field effect transistor) will lead to the silicon oxide layer to the scale of 2 nm, where the efficiency of the devices is affected due to the increase of leakage current by tunnel effect. Therefore, the replacement of silicon oxides will be imminent. The implementation of oxides materials with ferroic order can be seen as new avenue in the technology. For instance, in random accesses memories (RAMs). Ferroelectric RAMs (FeRAMs), in which information is encoded through the ferroelectric polarization, they are already commercially available. Ferrolectrics implemented in solar cells has been recently investigated. Magnetic insulators have been also attractive in spintronics. The control of magnetism by electric field also seems promising. Here, leakage current associated to the tunnel transport is view not as a problem but as tool to read information in electric or magnetic devices and memories. Nevertheless the physics of thin and ultrathin layers of some relevant ferroic oxides is not yet complete understood. This thesis is aimed to investigate oxides materials with ferroic character. In the first block, magnetic materials as CoFe2O4 and La0.5A0.5MnO3 (with A = Sr, Ca) have been investigated and the variation of their properties under strain has been monitored and explained. In the case of CoFe2O4 impedance measurements as a function of frequency and DC bias were done; the determined electrical permittivity is correlated with strain. Regarding La0.5A0.5MnO3, nanometric films were grown on different substrates to impose different strain states by the coherent growth of the films. The magnetic and electric character was monitored and explained in terms of orbital ordering. The second block concerns the description of some preliminary experiments on the effects of the visible light on the ferroelectric properties. Photocurrent is measured in BaTiO3 films. It is found that polarization and coercive field can be depressed by illumination. The last block is mainly devoted to the characterization of ferroelectric tunnel junctions (FTJs). BaTiO3 is used as ferroelectric barrier while La0.7Sr0.3MnO3 and Pt are the bottom and top electrode respectively. The electric field control of the remanent resistance states of large area FTJs displaying values of 3_104% tunnel electroresistance room temperature. Capacitance vs. bias measurements in these junctions present similarities to those found in metal-oxide-semiconductor. Next, ultrathin layers of La0.5A0.5MnO3 have been inserted between ferroelectric layer and metallic electrode aiming to explore possible metal-to-insulator transition in these layers as a way to enhance the tunnel electroresistance of the device. It is found that for some particular composition is seen that the room temperature electroresistance can increase up to five times. In relation to CoFe2O4 ultrathin films it has been observed tunnel and non-tunnel channels. A methodology to study the transport in ultrathin films of this type is proposed
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