Person: Cremades RodrÃguez, Ana Isabel
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First Name
Ana Isabel
Last Name
Cremades RodrÃguez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias FÃsicas
Department
Area
Ciencia de los Materiales e IngenierÃa Metalúrgica
Identifiers
10 results
Search Results
Now showing 1 - 10 of 10
Item Cathodoluminescence from nanocrystalline silicon films in the scanning electron microscope(Solided State phenomena, 1998) Méndez MartÃn, Bianchi; Piqueras de Noriega, Javier; Plugaru, R; Craciun, G.; Nastase, N.; Cremades RodrÃguez, Ana Isabel; Nogales DÃaz, EmilioLuminescence emission of nanocrystalline silicon films has been studied by cathodoluminescence (CL) in the scanning electron microscope. As deposited films show visible luminescence with dominant blue band as well as a red band. The evolution of CL bands after implantation and anodization treatments is investigated. Our results suggest that the dominant blue band has a complex character with a component at 400 nm which appears related to quantum size effects.Item The controlled transition-metal doping of SnO_2 nanoparticles with tunable luminescence(CrystEngComm, 2014) Peche Herrero, M. A.; Maestre Varea, David; Ramirez Castellanos, J.; Cremades RodrÃguez, 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.Item Optical properties and defect structure of MOVPE InGaN films(Optical Microestructuras Characterization of Semiconductors, Optical Microstructural Characterization of Semiconductors, 2000) Cremades RodrÃguez, Ana Isabel; Albrecht, M.; Ulloa, J.M.; Piqueras de Noriega, Javier; Strunk, H.P.; Hanser, D.; Davis, R. F.A series of 100 nm thick InGaN films with In content up to 14% has been grown by MOVPE on SiC substrates. Optical characterization was carried out by means of reflectance spectrometry, photoluminescence and cathodoluminescence. Optical properties of the samples have been correlated with the microstructural properties measured by atomic force microscopy, transmission electron microscopy and X-ray diffraction data. Results indicate a dependence of the optical properties on the In content in the sample, as well as on the residual stress in the films induced by Indium incorporation. Part of the strain is reduced elastically by formation of pinholes which reach the InGaN/GaN interface, where first misfit dislocations are observed to form. Our results show that luminescence is directly correlated with the strain distribution in the layers. Pinholes are observed to act as nonradiative recombination sites for carriers, while strain relaxation around pinholes may enhance luminescence emission. We discuss the influence of strain with respect to In incorporation, the appearance of piezoelectric fields and effects due to strain induced band bending.Item Thermal growth, luminescence and whispering gallery resonance modes of indium oxide microrods and microcrystals(Journal of marerials chemistry C, 2013) Bartolomé VÃlchez, Javier; Cremades RodrÃguez, Ana Isabel; Piqueras de Noriega, JavierIndium oxide microcrystals with shapes of truncated cubes and pyramids as well as microrods with square, triangular or hexagonal cross-sections are grown by a catalyst free evaporation deposition method. Size and shape control of the crystals as a function of the treatment parameters is discussed. Their luminescence properties are investigated and some features in the cathodoluminescence images are suggested to be related to the possible formation of a core dislocation. The waveguiding behaviour of the rods as well as whispering gallery resonances with improved Q-factor are demonstrated for hexagonal and square cross-section rods. The effect of tapering of the rods on the resonance wavelength is also studied and fitted to a theoretical model.Item Growth and luminescence of N doped TiO_2 nanowires(Journal of Neuroscience and Nanotechnology, 2008) Maestre Varea, David; Cremades RodrÃguez, Ana Isabel; Gregoratti, Luca; Piqueras de Noriega, JavierTitanium oxide nanowires have been grown by thermal treatment of pressed TiN powder under argon or N-2 flow. It has been found that two-step treatments at two different temperatures, 400 degrees C and 800 degrees C, lead to the growth of nanowires all over the sample surface. The nanowires are of single crystalline rutile structure. Energy dispersive X-ray spectroscopy and photoelectron spectroscopy measurements show that the oxide nanostructures contain N from the starting nitride. The mechanism of N incorporation into the oxide and its possible effect on the luminescence are discussed.Item Minority carrier diffusion length in AlGaN: A combined electron beam induced current and transmission microscopy(Solid State Phenomena, 1998) Cremades RodrÃguez, Ana Isabel; Albrecht, M.; Voigt, A.; Krinke, J.; Dimitrov, R.; Ambacher, O.; Stutzmann, M.Combined electron beam induced current and transmission electron microscopy measurements have been performed on both undoped and Si-doped AlGaN epitaxial films with aluminium contents x ranging from x=0 to x=0.79. TEM analysis shows the distribution and type of structural defects, the content of cubic phase and the decomposition phenomena strongly to depend on the Al content of the layers. The influence of the cubic phase on the electronic properties of the samples is discussed taking into account the high piezoelectric effect present in these alloys. The diffusion length of minority carriers has been determined by EBIC measurements and a lower limit of the lifetime has been estimated.Item Cr doped titania microtubes and microrods synthesized by a vapor-solid method(CrystEngComm, 2013) Cristian Vasquez, G.; Andrea Peche-Herrero, M.; Maestre Varea, David; Cremades RodrÃguez, Ana Isabel; Ramirez-Castellanos, Julio; Gonzalez-Calbet, José M.; Piqueras de Noriega, JavierCr doped TiO_2 rutile nanoparticles have been used as precursor of microrods and microtubes grown by a vapor-solid method. The grown microstructures have nearly square cross-sections of a few microns wide and lengths of up to about 100 microns. By longer thermal treatments or higher growth temperatures, the ratio of microrods to microtubes increases. The presence of partially filled openings with growth steps in the internal faces of the tubes indicates that the tubes transform into rods by extended or intense thermal treatments, which enables to control the nature of the microstructures, tubes or rods, by varying the parameters of the thermal treatment. Cr incorporation has been found to be homogeneous along the growth axis, with amounts in the range from 1.2 to 2.8% of cationic fraction, which depend on the Cr content in the precursor and on the growth parameters. Optical activation of the Cr ions has been demonstrated by cathodoluminescence in the scanning electron microscopy, and crystallographic assessment of the structures has been carried out using Raman spectroscopy and electron backscattered diffraction.Item Characterization of flame grown diamond films by luminescence and EPR(Optical Microestructuras Characterization of Semiconductors, Microcrystalline and nanocrystalline semiconductors, 1995) Pereira, L.; Pereira, E.; Tavares, C.; Neto, M.; Cremades RodrÃguez, Ana Isabel; Piqueras de Noriega, Javier; Jiménez, J.; MartÃn, P.Item Effect of thermal and mechanical treatments on the cathodoluminescence of tin and titanium oxides(Spatially resolved characterization of local phenomena in materials and nanostructures, 2003) Maestre Varea, David; Plugaru, R; Cremades RodrÃguez, Ana Isabel; Piqueras de Noriega, JavierThe luminescence of titanium oxide and tin oxide has been investigated by cathodoluminescence in the SEM, as a function of the structural changes induced by thermal treatments. The evolution of the luminescence of TiO2 rutile, anatase and mixture phase with the annealing temperature is related to the process of thermal induced grain texture and to transition of metastables phases to the stable rutile. The emission band is peaked at 480 nm for the composite phase and at 580 nm for anatase and rutile phases respectively. A broad band in the 520-560 nm region is present in the spectra of both anatase and rutile phase. Thermal annealing leads to a red shift of the luminescence emission, with the emission band peaked at around 820 nm. In sintered tin oxide the main emission bands appear centered at about 480 nm and 630 nm. The intensity of these bands increases with annealing temperature up to 1200degreesC, whereas for samples annealed at 1500degreesC these emissions are quenched. Mechanical ball milling has been used to produce nanocrystalline SnO_2 grains to investigate the influence of the presence of nanocrystals on the CL emission.Item Cathodoluminescence study of GaN-infilled opal nanocomposites(Physica Status Solidi A-Applied Research, 2003) Cremades RodrÃguez, Ana Isabel; Sanchez, M.; Piqueras de Noriega, Javier; Golubev, VG.In this study, three-dimensional ordered synthetic opals formed by spheres of 230 nm impregnated with GaN have been investigated. In some of the samples gold and platinum were also introduced. The potential applications of GaN-opal assemblies include use in large surface area (of the order of 10 m_2/cm_3 GaN-based light-emitting devices at a high density of elements. Also, the photonic crystal properties of perfect opal-GaN composites, characterized by the presence of a photonic band gap in the visible range, allow a substantial modification of the emitting properties of GaN-based nanodevices in this spectral region. The optical properties of GaN synthesized within interconnected opal voids have been investigated by cathodoluminescence (CL) in a scanning electron microscope. X-ray spectra have been obtained in order to test the quality of the GaN inside the voids. All CL spectra of the samples show a predominant emission centered at about 2.7 eV which is attributed to the opal matrix. CL spectra also reveal some differences in the spectral distribution of the luminescence which depends on the electron beam-sample orientation. Inhibition of the band edge emission of GaN has been observed in most of the samples. A possible correlation of this effect with the existence of a photonic band gap in the samples is discussed.