Person: Fernández Sánchez, Paloma
Universidad Complutense de Madrid
Faculty / Institute
Física de Materiales
Ciencia de los Materiales e Ingeniería Metalúrgica
Now showing 1 - 10 of 110
PublicationCathodoluminescence of In doped ZnS nanostructures grown by vapor-solid method(Elsevier Science SA, 2013-06-25) Piqueras de Noriega, Javier; Sotillo Buzarra, Belén; Fernández Sánchez, PalomaVapor–solid (VS) growth method at temperatures in the range from 1000 °C to 1200 °C has been used to obtain In doped ZnS micro- and nanostructures. The morphologies of the synthesized structures depend strongly on the deposition temperature, consisting on nano- and microswords, nanoribbons and nanoplates, with a major presence of nanoplates and strongly hierarchical structures at the higher In contents. The degree of impurity incorporation and the influence of the dopant on the luminescence properties have been studied. While in pure ZnS the main deep level bands are peaked in the blue-green region, In doped samples show an orange-red emission. PublicationComposition dependence of cathodoluminescence emission of Al_xGa_(1−x)P(Pergamon-Elsevier Science LTD, 1990-10) Fernández Sánchez, Paloma; Domínguez-Adame Acosta, Francisco; Piqueras de Noriega, Javier; Armelles, G.Cathodoluminescence of AlxGa1−xP has been investigated for x between 0.10 and 0.53. A band corresponding to the 610 nm band of pure GaP has been found to shift to higher energies with increasing x. The position of a red band centred at 690 nm is independent of x. PublicationObtention and characterization of ferrous chloride FeCl_2•4H_2O from water pickling liquors(MDPI, 2021-09) Alcaraz, Lorena; Sotillo Buzarra, Belén; Marco, Jose F.; Alguacil, Francisco J.; Fernández Sánchez, Paloma; López, Félix A.As a hazardous waste, water pickling liquors must be properly treated. An alternative consists of promoting the formation of ferrous salts from this residue due to their higher ferrous content. Since FeCl_2•4H_2O is widely used in several applications, obtaining pure crystals of this material appears to be an interesting prospect. However, this compound has scarcely been investigated. In the present work, FeCl_2•4H_2O crystals were obtained from water pickling liquors. Their structural and morphological characteristics were investigated by X-ray diffraction, scanning electron microscopy as well as Mossbauer spectroscopy. In addition, the photoluminescence study of the obtained samples was also assessed. It was observed that after some aging time, the obtained crystals changed in colour from green to more yellowish. As such, the aged sample was also evaluated, and their structural characteristics were compared with the original crystals. Despite this, the obtained crystals exhibit a FeCl_2•4H_2O structure, which is not modified with the aging of the sample. PublicationResults of the verification of the NIR MOS EMIR(SPIE, the international society for optics and photonics, 2014) Garzón, F.; Castro Rodríguez, N.; Insausti, M.; López Martín, L.; Hammersley, Peter; Barreto, M.; Fernández Sánchez, Paloma; Joven, E.; López, P.; Mato, A.; Moreno, H.; Nuñez, M.; Patrón, J.; Rasilla, J. L.; Redondo, P.; Rosich, J.; Pascual Ramírez, Sergio; Grange, R.EMIR is one of the first common user instruments for the GTC, the 10 meter telescope operating at the Roque de los Muchachos Observatory (La Palma, Canary Islands, Spain). EMIR is being built by a Consortium of Spanish and French institutes led by the Instituto de Astrofisica de Canarias (IAC). EMIR is primarily designed to be operated as a MOS in the K band, but offers a wide range of observing modes, including imaging and spectroscopy, both long slit and multiobject, in the wavelength range 0.9 to 2.5 μm. This contribution reports on the results achieved so far during the verification phase at the IAC prior to its shipment to the GTC for being commissioned, which is due by mid 2015. After a long period of design and fabrication, EMIR finally entered into its integration phase by mid 2013. Soon after this, the verification phase at the IAC was initiated aimed at configuring and tuning the EMIR functions, mostly the instrument control system, which includes a sophisticated on line data reduction pipeline, and demonstrating the fulfillment of the top level requirements. We have designed an ambitious verification plan structured along the three kind of detectors at hand: the MUX and the engineering and scientific grade arrays. The EMIR subsystems are being integrated as they are needed for the purposes of the verification plan. In the first stage, using the MUX, the full optical system, but with a single dispersive element out of the three which form the EMIR suite, the two large wheels mounting the filters and the pseudo-grisms, plus the detector translation unit holding the MUX, were mounted. This stage was mainly devoted to learn about the capabilities of the instrument, define different settings for its basic operation modes and test the accuracy, repeatability and reliability of the mechanisms. In the second stage, using the engineering Hawaii2 FPA, the full set of pseudo-grisms and band filters are mounted, which means that the instrument is fully assembled except for the cold slit unit, a robotic reconfigurable multislit mask system capable of forming multislit pattern of 55 different slitlets in the EMIR focal plane. This paper will briefly describe the principal units and features of the EMIR instrument as the main results of the verification performed so far are discussed. The development and fabrication of EMIR is funded by GRANTECAN and the Plan Nacional de Astronomia y Astrofisica (National Plan for Astronomy and Astrophysics, Spain). PublicationOrigin of yellow luminescence from reduced pressure grown bulk GaN crystals(Springer, 2000-07) Herrera Zaldiva, M.; Fernández Sánchez, Paloma; Piqueras de Noriega, Javier; Sukhoveyev, W.; Ivantsov, V. A.; Shreter, Y. G.Cathodoluminescence (CL) in the scanning electron microscope has been applied to study the luminescence emission of GaN single crystals grown by LPE methods. CL spectra show the presence of near band edge and of yellow emissions. The latter has been found to be mainly related to rows of hillocks formed at the growth steps. The origin of the yellow luminescence is discussed PACS: 78.60Hk; 71.55Eq. PublicationStudy of electronic deep levels in CdTe and CdTe:V by cathodoluminescence microscopy(Editions Physique, 1994) Pal, U.; Piqueras de Noriega, Javier; Fernández Sánchez, Paloma; Serrano, M. D.; Diéguez, E. PublicationCathodoluminescence and scanning tunnelling spectroscopy of ZnO single crystals(Elsevier Science Sa, 2002-04-30) Urbieta Quiroga, Ana Irene; Fernández Sánchez, Paloma; Hardalo, C.; Piqueras de Noriega, Javier; Sekiguchi, T.Bulk ZnO single crystals grown by the hydrothermal (HTT) and alkali flux methods have been investigated by means of scanning tunnelling spectroscopy (STS) and time resolved cathodoluminescence (CL). Measurements were performed in the different crystalline faces. The results from these measurements show that both, surface electrical properties and luminescent characteristics depend on the face studied. Polar O-terminated surfaces show an intrinsic conduction behaviour with a surface band gap ranging from 0.4 to 0.8 eV. Zn-terminated surfaces show mainly n-type conduction. The non-polar faces present either intrinsic or p-type behaviour. CL spectra show that the relative intensity of the different components of the deep level band also depends on the atomic structure of the face under study. This complex behaviour is clearly revealed from the time resolved spectra. The differences observed are attributed to the nature of the defects present in each case and, in particular, to different impurity incorporation processes that could be mainly controlled by the atomic configuration and polarity of the planes. PublicationZnO nanoparticles with controllable Ce content for efficient photocatalytic degradation of MB synthesized by the Polyol method(MDPI, 2021-01) Flores Carrasco, Gregorio; Rodríguez Peña, Micaela; Urbieta Quiroga, Ana Irene; Fernández Sánchez, Paloma; Rabanal, María EugeniaThis paper reports on the synthesis of Ce-doped ZnO (CZO) nanoparticles (NPs) by an alternative polyol method at low temperature. The method, facile and rapid, uses acetate-based precursors, ethylene glycol as solvent, and polyvinylpyrrolidone as capping agent. The effects of the Ce-doping concentration (ranging from 0 to 8.24 atomic%) on the structural, morphological, compositional, optical, luminescence, and photocatalytic properties of the NPs were investigated by several techniques. The structural findings confirmed that the CZO NPs have a typical hexagonal wurtzite-type structure with a preferred orientation along the (101) plane. The results obtained by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) revealed that the NPs size decreased (from similar to 30 to similar to 16 nm) with an increase in the Ce-doping concentration. Energy Dispersive X-Ray Spectroscopy (EDS) and High Resolution Transmission Microscopy (HRTEM) results confirmed the incorporation of Ce ions into the ZnO lattice. Ce-doping influences the photoluminescence (PL) emission compared to that of pure ZnO. The PL emission is related to the presence of different kinds of defects, which could take part in charge transfer and/or trapping mechanisms, hence playing an essential role in the photocatalytic activity (PCA). In fact, in this work we report an enhancement of PCA as a consequence of Ce-doping. In this sense, the best results were obtained for samples doped with 3.24 atomic%, that exhibited a photocatalytic degradation efficiency close to 99% after 60 min ultraviolet (UV) illumination, thus confirming the viability of Ce-doping for environmental applications. PublicationDeep energy levels in CdTe and CdZnTe(American Institute of Physics, 1998-02-15) Castaldini, A.; Cavallini, A.; Fraboni, B; Fernández Sánchez, Paloma; Piqueras de Noriega, JavierThe deep levels present in semiconducting CdTe and semi-insulating CdTe:Cl and Cd0.8Zn0.2Te have been investigated by means of cathodoluminescence, deep level transient spectroscopy (DLTS), photo-induced current transient spectroscopy, and photo-DLTS. The latter two methods, which can be applied to semi-insulating materials, allow to characterize the deep traps located up to midgap and can determine whether they are hole or electron traps. We have identified 12 different traps, some common to all the investigated samples, some peculiar to one of them. A comparison of the results obtained from the various materials is given and the status of defect models is reviewed. PublicationAl doped ZnO nanoplate arrays and microbox structures grown by thermal deposition(American Institute of Physics, 2009-03-01) Ortega Villafuerte, Yanicet; Fernández Sánchez, Paloma; Piqueras de Noriega, JavierAl doped ZnO arrays of nanoplates and of ordered nanoneedles have been grown by a thermal evaporation-deposition method. The nanoplates, which have mainly triangular shape. Interpenetrating triangles and crossing of the triangles with other planar arrangements form a structure consisting of arrays of microboxes. The influence of Al on the luminescence of the nanostructures has been studied by cathodoluminescence (CL) in the scanning electron microscope. Intense CL emission from the internal faces of the microboxes is related to the presence of deep level defects.