Person:
Cremades Rodríguez, Ana Isabel

First Name

Ana Isabel

Last Name

Cremades Rodríguez

URI

https://hdl.handle.net/20.500.14352/75041

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Area

Ciencia de los Materiales e Ingeniería Metalúrgica

Identifiers

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Now showing 1 - 10 of 89

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, Manuel
Electrical 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.
Electron beam induced current and remote electron beam induced current assessment of chemical vapor deposited diamond films
(Journal of Applied Physics, 1999) Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier
In the present work, electron beam induced current (EBIC) has been applied to characterize several kinds of chemical vapor deposition diamond films. Regions of enhanced carrier recombination are detected in plan-view observations of thin films as well as in cross sections of thick films. Remote EBIC (REBIC) has been applied to obtain information about charged defects present in the samples. The dependence of EBIC and REBIC contrast on the contact configuration used, and on the observation conditions has been analyzed. Cathodoluminescence images of the same samples have been recorded for comparison.
Caracterización microestructural de láminas de diamante por técnicas de inyección de haces
(2002) Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Francisco Javier
En el trabajo de investigación desarrollado en esta tesis doctoral se han caracterizado láminas de diamante crecidas mediante deposición química a partir de fase vapor (cvd) mediante catadoluminiscencia (cl), fotoluminiscencia con resolución temporal (trpl), raman, electroluminiscencia (el), y corriente inducida por el haz de electrones de un microscopio electrónico de barrido (ebic). Se han estudiado en detalle láminas sin tratar, correlacionando los resultados de las medidas con los parámetros de la deposición y la estructura de defectos de las láminas. Asimismo, se ha prestado atención al efecto de la irradiación con láser sobre la luminiscencia de las láminas. Con ebic y el se han estudiado las propiedades de recombinación de portadores. Como complemento al estudio del diamante, se han incluido algunos resultados sobre la luminiscencia de laminas epitaxiales de gan.
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 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.
Luminescence Study of Structural-Changes Induced by Laser Cutting in Diamond Films
(Journal of Applied Physics, 1995) Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier
The effect of laser cutting on the structure of a chemical vapor deposited diamond film has been investigated by cathodoluminescence (CL) in the scanning electron microscope. The variation of particle morphology and CL spectra as a function of the distance to the cutting edge is described and possible laser induced structural changes are discussed. At the damaged region total CL emission increases and nitrogen-vacancy centers are detected.
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, Javier
Cathodoluminescence (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.
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 Isabel
Anatase 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.
Luminescence study of thermal treated and laser irradiated Bi_12GeO_20 and Bi_12SiO_20 crystals
(Journal of Applied Physics, 1998) Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier; Remón, A.; García, J. A.; Santos, M. T.; Dieguez, E.
Changes on the defect structure of Bi12GeO20 (BGO) and Bi12SiO20 (BSO) crystals induced by thermal treatments and laser irradiation have been studied by means of cathodoluminescence in the scanning electron microscope. The results have been compared to those previously reported for untreated and electron irradiated samples and recombination mechanisms responsible for some of the observed luminescence bands are discussed. Annealing of EGO samples causes the appearance of a new luminescence band at about 390 nm. The centers responsible for this band decorate the deformation slip bands in quenched EGO as observed in the cathodoluminescence images. The emission observed in BSO in the same spectral range is quenched during the annealing treatment. The annealing induced reduction of Bi ions to metallic Bi appears to be related to the quenching of a band at 640 nm observed in untreated samples.
Characterisation of different habits in torch-flame-grown diamond and diamond-like films
(Diamond and Related Materials, 1999) Pereira, L..; Pereira, E.; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier; Jimenez, J.; Bielza, J.M.
Diamond and diamond-like films grown by the torch flame method have been analysed by different techniques, namely scanning electron microscopy, Raman spectroscopy, electron paramagnetic resonance and catholuminescence microscopy, in order to investigate the main structural features of the different habits present in the films. A correlation between the observed crystal habits, the defect structure and the formation of diamond and/or diamond-like phases has been established. This enables a general quality assessment of the deposits and their correlation with some features usually observed in carbon films
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, Javier
Rutile 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.