Person: Maestre Varea, David
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First Name
David
Last Name
Maestre Varea
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
Area
Ciencia de los Materiales e Ingeniería Metalúrgica
Identifiers
62 results
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Now showing 1 - 10 of 62
Item Crecimiento y caracterización mediante técnicas de microscopía, de nano-y microestructuras de SnO2 y TiO2(2007) Maestre Varea, David; Cremades Rodríguez, Ana; Piqueras de Noriega, JavierEn la presente tesis doctoral se exponen y discuten los principales resultados extraídos de la investigación realizada sobre muestras de SnO2 y TiO2 sinterizado, o en forma de micro- y nanoestructuras alargadas. Ambos materiales se encuentran entre los óxidos semiconductores más destacados, debido a sus interesantes propiedades físico-químicas y sus extendidas aplicaciones en dispositivos optoelectrónicos, sensores de gases o catalizadores. Las diferentes técnicas de caracterización empleadas en este trabajo permiten describir la estructura y composición de las muestras, así como analizar sus propiedades eléctricas y de luminiscencia a escala micro- y nanométrica. En primer lugar se ha realizado un completo análisis de la evolución microestructural, así como de las propiedades ópticas y electrónicas de muestras de SnO2 en función de los parámetros que definen el proceso de sinterizado, prestando especial atención al comportamiento de las fronteras de grano. Asimismo hemos analizado las propiedades y evolución morfológica de nano- y microestructuras alargadas de SnO2 y TiO2 crecidas mediante un original método de evaporación-solidificación desarrollado en presencia de un flujo continuo de gas. En este caso las estructuras crecen sobre la propia superficie de la muestra, que actúa como fuente y sustrato, sin necesidad de emplear ningún catalizador o sustrato externo. De este modo hemos conseguido crecer y caracterizar micro- y nanoestructuras de SnO2 en forma de varillas y tubos. En el caso del TiO2, además de estructuras alargadas y escalonadas, hemos crecido y caracterizado micro- y nanoestructuras dopadas con nitrógeno. Las propiedades específicas que presentan estas estructuras de dimensiones micro- y nanométricas permiten ampliar y mejorar las aplicaciones del SnO2 y el TiO2.Item Surface dielectric tunnel barrier induced by Mn doping in SnO_2 micro- and nanostructures(Physica status solidi A-applications and materials science, 2018) Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Herrera, ManuelElectrical properties of undoped and Mn doped SnO2 microplates and rods are studied by electron beam induced current (EBIC) in a scanning electron microscope (SEM), and I-V curves acquired at room temperature. AFM measurements reveal the formation of numerous terraces at the (-101) surface of the analyzed Mn-doped SnO2 microplates, which also exhibit high carrier recombination processes at their central region, as confirmed by combined EBIC and cathodoluminescence (CL) measurements. A diffusion length for minority carriers about 205nm is obtained by EBIC measurements. Different electrical conduction mechanisms, such as Fowler-Nordheim, direct tunneling and Poole-Frenkel, are evaluated in the electrical analysis of the samples. Mn doped microplates show lower conductivity than the undoped microds. Moreover the height of the surface tunnel barrier is increased by Mn doping, as confirmed by the analysis of the I-V curves acquired under transversal configuration. A value of the relative dielectric constant E-r about 7.3 is estimated for the probed SnO2 microstructures.Item In situ local oxidation of SnO induced by laser irradiation: a stability study(Nanomaterials, 2021) Vázquez López, Antonio; Maestre Varea, David; Ramírez Castellanos, Julio; Cremades Rodríguez, Ana IsabelIn this work, semiconductor tin oxide (II) (SnO) nanoparticles and plates were synthesized at room conditions via a hydrolysis procedure. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the high crystallinity of the as-synthesized romarchite SnO nanoparticles with dimensions ranging from 5 to 16 nm. The stability of the initial SnO and the controlled oxidation to SnO_2 was studied based on either thermal treatments or controlled laser irradiation using a UV and a red laser in a confocal microscope. Thermal treatments induced the oxidation from SnO to SnO2 without formation of intermediate SnO_x, as confirmed by thermodiffraction measurements, while by using UV or red laser irradiation the transition from SnO to SnO_2 was controlled, assisted by formation of intermediate Sn3O4, as confirmed by Raman spectroscopy. Photoluminescence and Raman spectroscopy as a function of the laser excitation source, the laser power density, and the irradiation duration were analyzed in order to gain insights in the formation of SnO_2 from SnO. Finally, a tailored spatial SnO/SnO_2 micropatterning was achieved by controlled laser irradiation with potential applicability in optoelectronics and sensing devices.Item Cathodoluminescence and REBIC study of defects in tin oxide(24th International Conference on Microelectronics (MIEL 2004), 2004) Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, JavierCathodoluminescence (CL) and remote electron beam induced current (REBIC) in the scanning electron microscope (SEM) has been used to investigate the electron recombination mechanisms in tin oxide. Sintered material prepared from high purity powder has been found to show a strong dependence of the CL emission on the thermal treatments applied during sample preparation. SEM images show the presence of nano and microcrystalline grains. The correlation of the grain size and morphology with the optical emission is analysed by CL microscopy and spectroscopy. The evolution of the luminescence bands with mechanical milling shows a complex evolution of the 1.94 eV and 2.58 eV emissions which is explained by formation and recovery of defects during milling. REBIC measurements and imaging are used to characterize the formation of a potential barrier at the grain boundaries.Item Fe-TiO_2 nanoparticles synthesized by green chemistry for potential application in waste water photocatalytic treatment(Journal of nanatechnology, 2019) Solano, Ricardo A.; Herrera, Adriana P.; Maestre Varea, David; Cremades Rodríguez, Ana IsabelAnatase TiO_2 nanoparticles doped with iron ions have been synthesized via the green chemistry method using aqueous extract of lemongrass (Cymbopogon citratus) obtained from Soxhlet extraction and doped by wet impregnation. The TiO_2 anatase phase has been doped with Fe^3+ (0.05, 0.075, and 0.1 Fe^3+ : Ti molar ratio) at 550 degrees C and 350 degrees C, respectively. The scanning electron microscopy with energy-dispersive X-ray (SEM-EDS) shows nanoparticle clusters and efficiencies of impregnations between 66.5 and 58.4% depending on the theoretical dopant amount. The electron transmission microscopy (TEM) reveals final particle sizes ranging between 7 and 26 nm depending on the presence or not of the dopant. The cathodoluminescence (CL) and photoluminescence (PL) studies of the doped and undoped nanoparticles show a luminescence signal attributed to surface oxygen vacancies (visible CL emission 380-700 nm and PL emission 350-800 nm); additionally, a decrease in emission intensity is observed due the inhibition of the recombination of the photogenerated electron-holes pairs; moreover, nanopowders were analyzed by UV-Vis spectrophotometry of diffuse reflectance, and the absorption edge of the Fe-TiO_2 in comparison to undoped TiO_2 is extended greatly toward the visible light. The six bands (A_1g + 2B_1g + 3E_g) found by Raman spectroscopy and the x-ray diffraction pattern (XRD) confirm that synthesized TiO_2 is only anatase phase, which is commonly used as a catalyst in waste water treatment, specifically in heterogeneous photocatalytic processes.Item Effects of transition metal doping on the growth and properties of Rutile TiO_2 nanoparticles(Journal of Physical Chemistry C, 2013) Cristian Vasquez, G.; Andrea Peche-Herrero, M.; Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Ramirez-Castellanos, Julio; María Gonzalez-Calbe, José; Piqueras de Noriega, JavierRutile TiO_2 nanoparticles doped with V, Cr, or Mn ions have been synthesized via a modified Pechini method using polymeric precursors. The final particle sizes range between 20 and 500 nm depending on the selected dopant. The TiO_2 rutile phase has been stabilized in the doped nanoparticles at 650 degrees C. Microstructural analysis shows a good crystallinity and cationic homogeneity of the doped nanoparticles. The cathodoluminescence study of the doped and undoped nanoparticles shows a luminescence signal related to the structural defects of the samples and the presence of dopants. In particular, an intense 1.52 eV emission associated with Ti^3+ interstitials dominates the luminescence of undoped nanoparticles, which also exhibit less intense emissions extending from 2 to 3.4 eV. The presence of V, Cr, or Mn in the rutile TiO_2 nanoparticles induces variations in the associated cathodoluminescence signal which would be useful in order to achieve a deeper understanding of the doping process and spread future optical applications. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ti^3+ in the near-surface region of the nanoparticles, the concentration of which decreases when doping. The presence of Ti^3+ interstitials related states in the band gap is discussed.Item Synergetic improvement of stability and conductivity of hybrid composites formed by PEDOT:PSS and SnO nanoparticles(Molecules, 2020) Vázquez López, Antonio; Yaseen, Anisa; Maestre Varea, David; Ramírez Castellanos, Julio; Marstein, Erik S; Karazhanov, Smagul Zh; Cremades Rodríguez, Ana IsabelIn this work, layered hybrid composites formed by tin oxide (SnO) nanoparticles synthesized by hydrolysis and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) have been analyzed. Prior to the composite study, both SnO and PEDOT:PSS counterparts were characterized by diverse techniques, such as X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), photoluminescence (PL), atomic force microscopy (AFM), optical absorption and Hall effect measurements. Special attention was given to the study of the stability of the polymer under laser illumination, as well as the analysis of the SnO to SnO_2 oxidation assisted by laser irradiation, for which different laser sources and neutral filters were employed. Synergetic effects were observed in the hybrid composite, as the addition of SnO nanoparticles improves the stability and electrical conductivity of the polymer, while the polymeric matrix in which the nanoparticles are embedded hinders formation of SnO_2. Finally, the Si passivation behavior of the hybrid composites was studied.Item Indium Tin Oxide micro- and nanostructures grown by thermal treatment of InN/SnO2(Journal of Physical Chemistre C, 2010) Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Gregorati, Luca; Piqueras de Noriega, JavierMixtures of InN and SnO2 powders, with it weight ratio of 10:1, have been used as precursors for the thermal growth of arrow-shaped and other elongated micro- and nanostructures of indium-tin oxide (ITO) containing about 2.6 atom % of Sit. The temperatures used in the process, in the range 650-750 degrees C, favor the decomposition of InN and oxidation of In, with it limited incorporation of Sit in the resulting compound. Arrow-shaped indium-tin oxide structures are obtained and formation of stannates during the process is avoided. X-ray photoelectron spectroscopy indicates that tin incorporates into the In2O3 lattice mainly as Sn4+. Luminescence of the ITO microstructures has been studied by cathodoluminescence in the scanning electron microscope.Item Two-dimensional Zn_k In_2O_(k+3) nanostructures: synthesis, growth mechanism, self-assembly, and luminescence(Journal of Nanoparticle Research, 2013) Bartolomé Vílchez, Javier; Maestre Varea, David; Amati, Mateo; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, JavierIndium-zinc oxide nanostructures, such as nanosheets, nanobelts, and wires formed by oriented stacks of nanoplates have been grown by a controlled thermal evaporation method without the use of a foreign catalyst. Surface features in the stacked hexagonal nanoplates suggest a dislocation-driven growth mechanism for these structures. A growth model for these stacks is proposed based on changes in velocity growth rate between the outer and the inner part of the plates. Zn incorporation has been investigated by means of energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and selected area electron diffraction. The formation of Zn_k In_2O_(k+3) ternary compounds has been demonstrated. Cathodoluminescence emission and its correlation with the morphology of the structures and Zn content have been studied.- Project number: 52
Item I.amAble: El aprendizaje en ciencias al servicio de la inclusión educativa(2019) Herrero Domínguez, Santiago; Corrales Castellanos, María Eugenia; Sobrino Díaz, María Lourdes; Cilleros Prados, Olga; Barba Fernández, Carmen; Azor Lafarga, Alberto Eduardo; Hernández Díaz, María Yolanda; Martínez del Pozo, Álvaro; Ranchal Sánchez, Rocío; Maestre Varea, David; Méndez Pozo, Gonzalo Rubén; Gervás Gómez-Navarro, Pablo; Pastor Gil, Lorena; Taravillo Corralo, Mercedes; Guerrero Martínez, Andrés; Sánchez Benítez, Francisco Javier; Martín Conde, María; Priego Bermejo, José Luis; González Prieto, Rodrigo; Jiménez Aparicio, Reyes; Álvarez Serrano, Inmaculada; Cortés Gil, Raquel; Osío Barcina, José de Jesús; Mancheño Real, María José; Arribas Fernández, Paula; Lobato Fernández, Álvaro; Sánchez Arroyo, Antonio José; Torrecilla Manresa, Sofía; Cárdenas Bonett, Marlón Félix; Desvoyes, Benedicte; Bárcena Espelleta, Araceli; Nacenta Torres, Pablo; Rubio Lago, Luis; Bautista Blasco, Susana; Julián Cortés, Alvaro; Arancibia Llaneza, Julieta Noelia; Lombraña Pascual, Rodrigo; Catalán Torrecilla, Cristina; Gutiérrez Franco, Yanna María; Mártínez Ruiz, María PalomaI.amAble es un proyecto que nació con una filosofía centrada en la utilización de acciones de solidaridad como método de aprendizaje. Se diseñan y organizan talleres científicos inclusivos para realizarlos en parejas formadas por personas con discapacidad cognitiva y de educación secundaria ordinaria. Se pretende aprender a la vez que se da un servicio a la universidad y a la sociedad, y ese es el espíritu que se ha seguido manteniendo durante esta tercera edición del curso 2018-2019.