Maestre Varea, David

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First Name
Last Name
Maestre Varea
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Física de Materiales
Ciencia de los Materiales e Ingeniería Metalúrgica
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Now showing 1 - 10 of 66
  • Publication
    Electrical and optical properties of composite PEDOT: PSS-based thin films with NiO nanoparticles
    (Elsevier, 2020-05-08) Moldarev, D.; Taeño González, María; Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Karazhanov, Smagul Zh; Marstein, E.
    Due to the combination of low cost materials deposition and device fabrication methods as well as competitive efficiency compared to the other Si solar cell architectures, the hybrid organic-silicon solar cells have attracted attention of the scientific community. It has recently been demonstrated that spin-coated poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (hereafter PEDOT:PSS) on a silicon wafer is a promising material due to its good optical and electrical properties. However, degradation caused by atmospheric exposure and relatively poor passivation properties limits implementation of PEDOT:PSS- silicon devices. Functionalization of PEDOT:PSS by inorganic nanoparticles might provide a possible solution as was shown for TiO_2 and SnO_2 nanoparticles. In this contribution, we present our results on spincoated PEDOT:PSS thin-films with NiO nanoparticles. We show that PEDOT:PSS mixed with Triton X-100 and dimethyl sulfoxide (DMSO) or ethylene glycol (EG) form a homogenous film and passivates the Si surface with charge carrier lifetimes of 300-400 ms with good reproducibility. Time-resolved measurements revealed continuous degradation of the passivation properties in air, however saturation of the degradation at approximately 150 ms was observed in N_2 atmosphere. The influence of the NiO nanoparticles on the optical properties of PEDOT:PSS is negligible, whereas the surface passivation properties are worsened due probably to the formation of large size agglomerates exceeding thickness of PEDOT:PSS film.
  • Publication
    In situ local oxidation of SnO induced by laser irradiation: a stability study
    (MDPI, 2021-04-10) Vázquez López, Antonio; Maestre Varea, David; Ramírez Castellanos, Julio; Cremades Rodríguez, Ana Isabel
    In 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.
  • Publication
    Direct observation of potential barrier formation at grain boundaries of SnO_2 ceramics
    (Iop Publishing Ltd, 2004-11) Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier
    Remote electron beam induced current (REBIC) and cathodoluminescence (CL) modes in the scanning electron microscope (SEM) have been used to investigate SnO2 sintered samples. The study of the electrically active boundaries present in the oxide shows a characteristic peak and trough (PAT) contrast after thermal treatments in oxygen. Temperature-dependent measurements of the REBIC contrast show the presence of a shallow defect level 60 meV below the conduction band. This level is asigned to oxygen species adsorbed on the defect-rich boundaries. Evolution of REBIC contrast of the grain boundaries with excitation density enabled us to perform local measurements of minority carrier diffusion length.
  • Publication
    Unravelling the role of lithium and nickel doping on the detect structure and phase transition of anatase TIO2 nanoparticles
    (Springer, 2022-04) Vázquez López, Antonio; Maestre Varea, David; Martínez Casado, Ruth; Ramírez Castellanos, Julio; Pís, Igor; Nappini, Silvia; Cremades Rodríguez, Ana Isabel
    Anatase TiO_2 nanoparticles doped either with Li or Ni have been synthesized via hydrolysis in variable concentrations. Microstructural analysis confirms the high crystallinity of the doped nanoparticles with sizes around 7 nm, while compositional analysis shows low doping below 2% at. Despite the low concentration of dopants, variations in the Raman and Photoluminescence signals were observed in the doped nanoparticles, mainly due to non-stoichiometry and oxygen deficiency promoted by Li or Ni doping. Doping effects associated with Li and Ni were observed by photoelectron spectroscopy and first principle calculations, which associate the appearance of states in the valence band region to oxygen deficiency and Li or Ni doping and lower n-type character induced by Ni doping. Finally, changes in the thermally induced anatase-to-rutile transition (ART) have been also observed in the doped samples, leading to a dopant-promoted faster ART which occurs at lower temperature boosted due to the dopant effect.
  • Publication
    Growth and luminescence properties of micro- and nanotubes in sintered tin oxide
    (American Institute of Physics, 2005-02-15) Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier
    Sintering SnO_2 under argon flow at temperatures in the range of 1350-1500 degreesC causes the formation of wires, rods, and tubes on the sample surface. At high temperatures of the mentioned range, microwires with lengths of hundreds of microns are formed. At lower temperatures the formation of micro- and nanorods as well as micro- and nanotubes takes place. The influence of ball milling of the starting powder on the formation of tubes is investigated. The local cathodoluminescence measurements show a different defect structure in the tubes than in the sample background.
  • Publication
    Indium sulfide and ternary In-S-O nanowires for optoelectronic applications
    (Cambridge Univ. Press, 2012-08) Bartolomé Vílchez, Javier; Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier
  • Publication
    I.amAble: El aprendizaje en ciencias al servicio de la inclusión educativa
    (2019-08-20) 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 Paloma
    I.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.
  • Publication
    The controlled transition-metal doping of SnO_2 nanoparticles with tunable luminescence
    (RSC Royal Society of Chemistry, 2014) Peche Herrero, M. A.; Maestre Varea, David; Ramirez Castellanos, J.; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier; González Calvet, J. M.
    SnO_2 nanoparticles doped with transition metals (V, Cr, Mn) have been synthesized by both the hydrothermal method (HDT) in a basic media and the liquid mixed method (LQM) based on the Pechini method. Nanocrystalline particles obtained via a liquid mixed technique show a well-defined chemical composition and an average size of 6 nm, with a high degree of both crystallinity and chemical homogeneity. Nanoparticles prepared via a hydrothermal method exhibit a high dispersion in size as well as agglomeration effects. As the LQM demonstrates advantages with respect to the HDT, a more detailed investigation has been carried out on the SnO_2 nanoparticles doped with V, Cr and Mn grown by this method. The microstructure of the materials was elucidated by means of X-ray Diffraction (XRD), Selected-Area Electron Diffraction (SAED), and High-Resolution Transmission Electron Microscopy (HRTEM). Luminescence from undoped and doped SnO_2 nanoparticles was characterized by cathodoluminescence (CL). The luminescence studies demonstrate a strong dependence of CL signals with transition metal doping, thus inducing red, green or orange emissions when doping with Cr, V or Mn respectively.
  • Publication
    Composition-dependent electronic properties of indium-zinc-oxide elongated microstructures
    (Pergamon-Elsevier Science LTD, 2013-04) Bartolomé Vílchez, Javier; Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Amatti, M.; Piqueras de Noriega, Javier
    Microrods and hierarchical structures of indium-zinc-oxide (IZO) with different compositions were grown by thermal treatments of mixtures of InN and ZnO powders. In long rods, an increase in Zn content along the growth axis is revealed by energy dispersive spectroscopy. The structures obtained range from Zn-doped indium oxide with a few atomic per cent of Zn, to IZO compounds of the type Zn_kIn_2O_k+3. X-ray photoelectron spectroscopy measurements with spatial resolution show that IZO microstructures degenerate at room temperature, with carrier concentration of the order of 10^20 cm^-3. Electron accumulation has been found for undoped (1 0 0) and (1 1 1) surfaces, whereas depletion of carriers at the surface is observed in IZO samples. The Fermi level position correlates with the Zn concentration at the surface which, taking into account the surface dependence of the ionization potentials, work functions and band gaps, could lead to tunable material properties for device applications. Cathodoluminescence emission intensity is enhanced by the presence of Zn, which induces spectral changes and broadening of the emission band compared with undoped material. The results are discussed in terms of the charge neutrality level and the band structure of the material.
  • Publication
    MADRID (Marco Activo De Recursos de Innovación Docente). Madrid - Comunidad
    (Universidad Complutense, 2018-02-21) Baratas Díaz, Luis Alfredo; Becerra García, Nieves; Rodríguez López, Blanca María; Negro Alousque, Isabel; Cuervo Calvo, Laura; Rouanne, Laurence Louise Marcelle; González González, Juán Jesús; Maestre Varea, David; García Norro, Juán José; Ruiz Tendero, Germán; Pala Paul, Jesús; Ranchal Sánchez, Rocio; Rovira Madrid, Rogelio; Álvarez Serrano, Inmaculada; Cipres Palacín, María Ángeles; Reol Merino, Milagros; García Leal, María del Carmen