Person: Fernández Sánchez, Paloma
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First Name
Paloma
Last Name
Fernández Sánchez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
Area
Ciencia de los Materiales e Ingeniería Metalúrgica
Identifiers
35 results
Search Results
Now showing 1 - 10 of 35
Item Porosity-induced gain of luminescence in CdSe(Semiconductor Science and Technology, 2004) Monaico, E.; Ursaki, V. V.; Urbieta Quiroga, Ana Irene; Fernández Sánchez, Paloma; Piqueras De Noriega, Francisco Javier; Boyd, R. W.; Tiginyanu, I. M.Porous CdSe layers have been produced by anodic etching of crystalline substrates in a HCl solution. Anodization under in situ. UV illumination resulted in the formation of uniformly distributed parallel pores with a diameter of 30 nm, stretching perpendicularly to the initial surface. At the same time, pronounced nonuniformities in the spatial distribution of pores were evidenced in samples subjected to anodic etching in the dark. Gain of luminescence was observed in some porous regions and attributed to the formation of ring microcavities for light in the porous network.Item Fabrication and characterization of ZnO:CuO electronic composites for their application in sensing processes(IEEE sensors journal, 2021) Ramos Ramos, D.J.; Sotillo Buzarra, Belén; Urbieta Quiroga, Ana Irene; Fernández Sánchez, PalomaSensing behaviour of samples belonging to the system ZnO:CuO has been investigated. Samples with different proportions of ZnO and CuO have been sintered and exposed to a reducing agent as ethanol (C_2H_5OH). All the samples have been characterized not only from the point of view of the sensing properties but also regarding morphology, composition, crystallinity and luminescent properties in order to correlate these properties to the sensing behaviour. Sensitivity, response times, recovery and stability have been measured under exposure to ethanol vapour in concentrations 800, 4700 and 16000 ppm. Sensing cycles have been performed at three different temperatures: 25, 50 and 100 degrees C.Item Effect of plastic deformation on the luminescence of ZnSe crystals(Solid State Phenomena, 1998) Fernández Sánchez, Paloma; Piqueras De Noriega, Francisco Javier; Urbieta Quiroga, Ana Irene; Rebane, Y. T.; Shreter, Y. G.The electronic recombination properties of defects in ZnSe is a subject of interest related to the application of this material in optoelectronic devices operating in the blue-green range. In this work the influence of defects, in particular the deformation induced defects, on the luminescence of bulk ZnSe single crystals has been investigatd by cathodoluminescence in the SEM. The crystals were compressed along [100] direction wih plastic strains of 3% and 6.4% respectively. Deformation has been found to cause a reduction of the total CL intensity of the sample. CL images of deformed samples reveal dark slip bands. The CL spectrum of an undeformed crystal at 85K shows the near band edge emission at 2.8eV and a broad band peaked at 2.2eV with a shoulder at about 2eV. Deformation at the low strain causes only slight spectral changes while in the heavily deformed crystal a strong relative enhancement of the deep level band in the range 2-2.2eV is observed. The relation of these spectral changes with the deformation induced defects is discussed.- Project number: 30
Item Creación de un portal para gamificación en la enseñanza universitaria(2018) López Orozco, José Antonio; Fernández Sánchez, Paloma; Urbieta Quiroga, Ana Irene; Hidalgo Alcalde, Pedro; Besada Portas, Eva; Garrido Díaz, Esther; Solís Fernández, Fernando; Pellejero Cuevas, NoeliaSe propone la creación de un portal de servicios para facilitar la creación y el uso de herramientas de gamificación. - Project number: 104
Item Diseño de herramientas de dinamización del aula adaptables a distintos escenarios de docencia (presenciales o en línea)(2022) Fernández Sánchez, Paloma; Arroyo Bujase, Alex Miguel; Díaz-Guerra Viejo, Carlos; Fernández Jiménez, Rubén; Garrido Díaz, Esther; Hidalgo Alcalde, Pedro; Panis Maramba, Carlo Dexter; Romero Izquierdo, Carlos; Sotillo Buzarra, Belén; Urbieta Quiroga, Ana Irene Item Growth of Zr/ZrO_(2) core-shell structures by fast thermal oxidation(Applied sciences-basel, 2023) Ramos Justicia, Juan Francisco; Ballester Andújar, José Luis; Urbieta Quiroga, Ana Irene; Fernández Sánchez, PalomaThis research has been conducted to characterize and validate resistive heating as a synthesis method for zirconium oxides (ZrO_(2)). A wire of Zr has been oxidized to form a core-shell structure, in which the core is a metal wire, and the shell is an oxide layer that is around 10 mu m thick. The characterization of the samples has been performed by means of several techniques based on Scanning Electron Microscopy (SEM). The topography images show that thermal gradient appears to have little influence on morphology, unlike time, which plays an important role. The chemical composition was analyzed by X-ray spectroscopy (EDX) and X-ray diffraction (XRD), and Raman spectroscopy has been used to assess crystallinity and crystal structure. The oxide layer is mainly formed by monoclinic ZrO_(2), alongside other, less significant, phases. Photoluminescence (PL) and cathodoluminescence (CL) measurements have allowed us to study the distribution of defects along the shell and to confirm the degree of uniformity. The oxygen vacancies, either as isolated defects or forming complexes with impurities, play a determinant role in the luminescent processes. Color centers, mainly electron centers such as F, F-A and F-AA, give rise to several visible emissions extending from blue to green, with main components at around 2 eV, 2.4-2.5 eV and 2.7 eV. The differences between PL and CL in relation to distinct recombination paths are also discussed.Item ZnO nanoparticles with controllable Ce content for efficient photocatalytic degradation of MB synthesized by the Polyol method(Catalysts, 2021) Flores Carrasco, Gregorio; Rodríguez Peña, Micaela; Urbieta Quiroga, Ana Irene; Fernández Sánchez, Paloma; Rabanal, María EugeniaThis paper reports on the synthesis of Ce-doped ZnO (CZO) nanoparticles (NPs) by an alternative polyol method at low temperature. The method, facile and rapid, uses acetate-based precursors, ethylene glycol as solvent, and polyvinylpyrrolidone as capping agent. The effects of the Ce-doping concentration (ranging from 0 to 8.24 atomic%) on the structural, morphological, compositional, optical, luminescence, and photocatalytic properties of the NPs were investigated by several techniques. The structural findings confirmed that the CZO NPs have a typical hexagonal wurtzite-type structure with a preferred orientation along the (101) plane. The results obtained by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) revealed that the NPs size decreased (from similar to 30 to similar to 16 nm) with an increase in the Ce-doping concentration. Energy Dispersive X-Ray Spectroscopy (EDS) and High Resolution Transmission Microscopy (HRTEM) results confirmed the incorporation of Ce ions into the ZnO lattice. Ce-doping influences the photoluminescence (PL) emission compared to that of pure ZnO. The PL emission is related to the presence of different kinds of defects, which could take part in charge transfer and/or trapping mechanisms, hence playing an essential role in the photocatalytic activity (PCA). In fact, in this work we report an enhancement of PCA as a consequence of Ce-doping. In this sense, the best results were obtained for samples doped with 3.24 atomic%, that exhibited a photocatalytic degradation efficiency close to 99% after 60 min ultraviolet (UV) illumination, thus confirming the viability of Ce-doping for environmental applications.Item Cathodoluminescence and scanning tunnelling spectroscopy of ZnO single crystals(Materials Science and Engineering B-Solid State Materials for Advanced Technology, 2002) Urbieta Quiroga, Ana Irene; Fernández Sánchez, Paloma; Hardalo, C.; Piqueras De Noriega, Francisco Javier; Sekiguchi, T.Bulk ZnO single crystals grown by the hydrothermal (HTT) and alkali flux methods have been investigated by means of scanning tunnelling spectroscopy (STS) and time resolved cathodoluminescence (CL). Measurements were performed in the different crystalline faces. The results from these measurements show that both, surface electrical properties and luminescent characteristics depend on the face studied. Polar O-terminated surfaces show an intrinsic conduction behaviour with a surface band gap ranging from 0.4 to 0.8 eV. Zn-terminated surfaces show mainly n-type conduction. The non-polar faces present either intrinsic or p-type behaviour. CL spectra show that the relative intensity of the different components of the deep level band also depends on the atomic structure of the face under study. This complex behaviour is clearly revealed from the time resolved spectra. The differences observed are attributed to the nature of the defects present in each case and, in particular, to different impurity incorporation processes that could be mainly controlled by the atomic configuration and polarity of the planes.Item LTA zeolite particles functionalized with nanomagnetite for effective recovery of dysprosium from liquid solutions(Microporous and Mesoporous Materials, 2024) Alcaraz, Lorena; Sotillo Buzarra, Belén; Iglesias, Carlos; López, Félix A.; Fernández Sánchez, Paloma; Belviso, Claudia; Urbieta Quiroga, Ana IreneRare earth elements (REEs) as Dysprosium (Dy) are critical elements for the fabrication of components in many green energy technologies, from electric vehicles to wind turbines. Consequently, there is an increasing interest in creating sustainable and effective materials for the recovery and recycling of these elements. Zeolite materials have demonstrated a high affinity and selectivity for REEs. Thus, this paper aims to study the use of a synthetic LTA zeolite functionalized with nanomagnetite for Dy absorption, including a complete characterization of the synthetic zeolite, the kinetics and the factors affecting the adsorption efficiency. The maximum adsorption capacity reaches a value around 35 mg of Dy per gram of zeolite. The results from the adsorption isotherms and kinetic study revealed a good agreement with both Langmuir and Temkin models and pseudo-second-order kinetics. Furthermore, the thermodynamic analysis suggests that the adsorption of Dy onto the zeolite is a spontaneous and favorable process. The findings from this work could provide insights into the design and optimization of zeolite-based processes for REE recovery and recycling, contributing to the development of a more sustainable and circular economy.Item Dysprosium removal from water using active carbons obtained from spent coffee ground(Nanomaterials, 2019) Alcaraz, Lorena; Escudero, María Esther; Alguacil, Francisco José; Llorente, Irene; Urbieta Quiroga, Ana Irene; Fernández Sánchez, Paloma; López, Félix AntonioThis paper describes the physicochemical study of the adsorption of dysprosium (Dy^(3+)) in aqueous solution onto two types of activated carbons synthesized from spent coffee ground. Potassium hydroxide (KOH)-activated carbon is a microporous material with a specific Brunauer-Emmett-Teller (BET) surface area of 2330 m^2.g^-1 and pores with a diameter of 3.2 nm. Carbon activated with water vapor and N_2 is a solid mesoporous, with pores of 5.7 nm in diameter and a specific surface of 982 m^2.g^-1. A significant dependence of the adsorption capacity on the solution pH was found, but it does not significantly depend on the dysprosium concentration nor on the temperature. A maximum adsorption capacity of 31.26 mg.g^-1 and 33.52 mg.g^-1 for the chemically and physically activated carbons, respectively, were found. In both cases, the results obtained from adsorption isotherms and kinetic study were better a fit to the Langmuir model and pseudo-second-order kinetics. In addition, thermodynamic results indicate that dysprosium adsorption onto both activated carbons is an exothermic, spontaneous, and favorable process.