Person:
Fernández Sánchez, Paloma

First Name

Paloma

Last Name

Fernández Sánchez

URI

https://hdl.handle.net/20.500.14352/74998

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física de Materiales

Area

Ciencia de los Materiales e Ingeniería Metalúrgica

Identifiers

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Search Results

Now showing 1 - 10 of 114

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.
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, Paloma
Sensing 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.
Dual regimes of ion migration in high repetition rate femtosecond laser inscribed waveguides
(IEEE Photonics technology letters, 2015) Teddy Fernández, Toney; Sotillo Buzarra, Belén; del Hoyo, Jesús; Valles, Juan Antonio; Martínez Vázquez, Rebeca; Fernández Sánchez, Paloma; Solis, Javier
Ion migration in high repetition rate femtosecond laser inscribed waveguides is currently being reported in different optical glasses. For the first time, we discuss and experimentally demonstrate the presence of two regimes of ion migration found in laser written waveguides. Regime-I corresponds to the initial waveguide formation mainly via light element migration (in our case atomic weight < 31 u), whereas regime-II majorly corresponds to the movement of heavy elements. This behavior brings attention to a problem which has never been analyzed before and that affects the laser written active waveguides, in which active ions migrate changing their local spectroscopic properties. The migration of active ions may in fact detune the predesigned optimal values of active photonic devices. This letter experimentally demonstrate this problem and provides solutions to avert it.
Control of waveguide properties by tuning femtosecond laser induced compositional changes
(Applied physics letters, 2014) Del Hoyo Muñoz, Jesús; Martínez Vázquez, Rebeca; Sotillo Buzarra, Belén; Teddy Fernández, Toney; Siegel, Jan; Fernández Sánchez, Paloma; Osellame, Roberto; Solís Céspedes, Francisco Javier
Local compositional changes induced by high repetition rate fs-laser irradiation can be used to produce high performance optical waveguides in phosphate-based glasses. The waveguide refractive index contrast is determined by the local concentration of La, which can be changed by the action of the writing laser pulses. In this work, we have investigated the degree of control that can be exerted using this waveguide writing mechanism over the cross-section of the guiding region, and the local refractive index and compositional changes induced. These variables can be smoothly controlled via processing parameters using the slit shaping technique with moderate Numerical Aperture (NA 0.68) writing optics. The combined use of X-ray microanalysis and near field refractive index profilometry evidences a neat linear correlation between local La content and refractive index increase over a broad Δn interval (>3 x 10^2). This result further confirms the feasibility of generating efficient, integrated optics elements via spatially selective modification of the glass composition.
Pulsed laser annealing of CdTe single crystals
(Journal of Optoelectronics and Advanced Materials, 2000) Fernández Sánchez, Paloma; Solís, J.; Piqueras De Noriega, Francisco Javier
Pulsed laser treatments in air and in vacuum have been performed in CdTe wafers. The laser induced changes have been monitored by emissive mode and cathodoluminescence (CL) in a scanning electron microscope. Remarkable differences between the effects of both types of treatment have been found. In particular, while the irradiation in vacuum appears as a suitable technique for rapid annealing, irradiations in air can be accompanied by strong degradation of the sample surface.
Dense vertical nanoplates arrays and nanobelts of indium doped ZnO grown by thermal treatment of ZnS-In_2O_3 powders
(Journal of Crystal Growth, 2010) Alemán, A.; Fernández Sánchez, Paloma; Piqueras De Noriega, Francisco Javier
Dense vertical arrays of indium doped ZnO nanoplates have been grown by thermal treatment of compacted ZnS-In_2O_3 powders with 0.35 at% of In. The distribution of nanoplates is related to the grain structure of the substrate. Only a small content of In has been detected in the plates by energy dispersive X-ray spectroscopy, but comparison with previous works shows that its presence in the precursor determines the growth of the nanoplates. Increase in the amount of In in the precursor leads to the growth of long indium doped ZnO nanobelts. Cathodoluminescence spectra of the nanobelts show a 23 meV blue shift of the band edge emission.
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.
Competition effects during femtosecond laser induced element redistribution in Ba- and La-migration based laser written waveguides
(Materials, 2021) Macías Montero, Manuel; Moreno Zárate, Pedro; Muñoz, Francisco; Sotillo Buzarra, Belén; García Pardo, Marina; Serna, Rosalia; Fernández Sánchez, Paloma; Solís, Javier
Fs-laser induced element redistribution (FLIER) has been a subject of intensive research in recent years. Its application to various types of glasses has already resulted in the production of efficient optical waveguides, tappers, amplifiers and lasers. Most of the work reported on FLIER-based waveguides refers to structures produced by the cross-migration of alkali (Na, K) and lanthanides (mostly La). The latter elements act as refractive index carrying elements. Herein, we report the production of Ba-based, FLIER-waveguides in phosphate glass with an index contrast > 10^(-2). Phosphate glasses modified with the same amount of Na_2O and K_2O, and variable amounts of BaO and/or La_2O_3 were used to produce the FLIER-waveguides with Ba and or La acting as index carriers. Ba-only modified glasses show a waveguide writing threshold and light guiding performance comparable to that of La-based structures. However, mixed Ba-La glasses show a much higher element migration threshold, and much smaller compositionally modified regions. This behavior is consistent with a competition effect in the cross-migration of both elements (Ba and La) against the alkalis. Such an effect can be applied to inhibit undesired element redistribution effects in fs-laser processing applications in multicomponent glasses.
Search for isotropic γ-radiation in the cosmological window between 65-tev and 200-tev
(Physics letters B, 1995) Martínez Pabón, María Beatriz; Arqueros Martínez, Fernando; Fernández Sánchez, Paloma; Fonseca, V.
Electromagnetic energy injected into the universe above a few hundred TeV is expected to pile up as γ radiation in a relatively narrow energy interval below 100 TeV due to its interaction with the 2.7°K background radiation. We present an upper limit (90% C.L.) on the ratio of primary γ to charged cosmic rays in the energy interval 65-160 TeV (80- 200 TeV) of 10.3 . 10¯³(7.8 . 10¯³). Data from the HEGRA cosmic-ray detector complex consisting of a wide angle Cerenkov array (AIROBICC) measuring the lateral distribution of air Čerenkov light and a scintillator array, were used with a novel method to discriminate γ-ray and hadron induced air showers. If the presently unmeasured universal far infrared background radiation is not too intense, the result rules out a topological-defect origin of ultrahigh energy cosmic rays for masses of the X particle released by the defects equal to or larger than about 10_(16) GeV.
Luminescence properties of mechanically milled and laser irradiated ZnO
(Nanotechnology, 2003) Radoi, R.; Fernández Sánchez, Paloma; Piqueras De Noriega, Francisco Javier; Wiggins, M. S.; Solís, J.
The effect of mechanical milling on the luminescence properties of ZnO microcrystalline samples has been studied by means of cathodoluminescence in a scanning electron microscope. The samples consisted of pressed pellets of commercially available ZnO powder which were ball milled to investigate the possibility of nanocrystalline ZnO formation. Changes observed in the relative intensities of the characteristic ultraviolet and green band of ZnO are discussed in terms of defects generated during milling. The effect of nano- and picosecond pulsed laser irradiation on the particle size and luminescence of the milled samples has been also investigated.