Person: Fernández Sánchez, Paloma
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First Name
Paloma
Last Name
Fernández Sánchez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
Area
Ciencia de los Materiales e Ingeniería Metalúrgica
Identifiers
11 results
Search Results
Now showing 1 - 10 of 11
Item Voids, nanochannels and formation of nanotubes with mobile Sn fillings in Sn doped ZnO nanorods(Nanotechnology, 2010) Ortega Villafuerte, Yanicet; Dieker, Ch; Jaeger, W.; Piqueras de Noriega, Javier; Fernández Sánchez, PalomaZnO nanorods containing different hollow structures have been grown by a thermal evaporation-deposition method with a mixture of ZnS and SnO(2) powders as precursor. Transmission electron microscopy shows rods with rows of voids as well as rods with empty channels along the growth axis. The presence of Sn nanoprecipitates associated with the empty regions indicates, in addition, that these are generated by diffusion processes during growth, probably due to an inhomogeneous distribution of Sn. The mechanism of forming voids and precipitates appears to be based on diffusion processes similar to the Kirkendall effect, which can lead to void formation at interfaces of bulk materials or in core-shell nanostructures. In some cases the nanorods are ZnO tubes partially filled with Sn that has been found to melt and expand by heating the nanotubes under the microscope electron beam. Such metal-semiconductor nanostructures have potential applications as thermal nanosensors or as electrical nanocomponents.Item Al doped ZnO nanoplate arrays and microbox structures grown by thermal deposition(Journal of Applied Physics, 2009) 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.Item Growth and luminescence of oriented nanoplate arrays in tin doped ZnO(Nanotechnology, 2007) Ortega Villafuerte, Yanicet; Fernández Sánchez, Paloma; Piqueras de Noriega, JavierSintering of a ZnO-SnO_2 mixture under argon flow leads to the growth of microrods on the sample surface, which are formed by oriented stacks of nanoplates. Energy dispersive spectroscopy and cathodoluminescence ( CL) in the scanning electron microscope show that the stacks of nanoplates consist of Sn doped ZnO. The stacks of nanoplates have well defined orientations relative to the growth axis of the rod. The formation of the nanoplates, which is not observed when undoped ZnO is used in the same process, is attributed to the stresses generated by the presence of Sn atoms in the rods.Item Complex hierarchical arrangements of stacked nanoplates in Al-doped ZnO(Physica Status Solidi A-Applications and Materials Science, 2012) Piqueras de Noriega, Javier; Ortega Villafuerte, Yanicet; Fernández Sánchez, Paloma; Jäger, Wolfgang; Häußler , DietrichAl-doped micro- and nanostructures have been grown by an evaporation–deposition method with a mixture of ZnS and Al_2O_3 powders as precursor. It has been found that the presence of Al is the cause of the growth of complex morphologies, as rods formed by stacks of nanoplates and other complex hierarchical structures. The role of Al in the growth process has been investigated by electron microscopy techniques. Al-rich particles in specific sites of a central rod lead to hierachical growth. Transmission electron microscopy shows that in some cases the Al-rich zones are clusters of spinel ZnAl_2O_4 nanoparticles adhered to ZnO nanorods. Al incorporation into the structures and the dopant effect on the luminescence behavior of the ZnO structures were investigated by energy dispersive spectroscopy and by cathodoluminescence.Item Influence of Indium doping in the morphology of ZnS nanostructures grown by a vapor-solid method(CrystEngComm, 2013) Sotillo Buzarra, Belén; Ortega Villafuerte, Yanicet; Fernández Sánchez, Paloma; Piqueras De Noriega, Francisco JavierPure and In-doped ZnS structures have been grown using a VS method. Thermal treatments have been performed at temperatures ranging from 1000 to 1200 °C, during 15 to 17 hours in a N2 overpressure environment. Nanowires and nanoribbons are the main kind of structures obtained for pure ZnS, depending on the deposition temperature. In the case of ZnS:In, nano- and microswords, nanoribbons, hierarchical structures and nanoplates are obtained, depending on the In content in the starting material and on the deposition temperature. Nanoplates are the dominant structures for the higher In content. The influence of the impurity incorporation on the morphology of the structures has been studied by transmission electron microscopy. While in pure ZnS wires and ribbons two main growth directions are observed ([0001] and [10-10]), indium doped structures show a greater variety of morphologies associated with different growth behavior.Item Sn and Mg doped ZnO nanowires and nanoplates(Physics, chemistry and application of nanostructures: reviews and short notes, 2007) Piqueras de Noriega, Javier; Ortega Villafuerte, Yanicet; Urbieta Quiroga, Ana Irene; Fernández Sánchez, PalomaSintering of ZnO-SnO_2 and ZnO-MgO mixtures, with few at. % of Sn or Mg at 1280 C under argon flaw leads to the growth of microrods on the sample surface, which are formed by oriented stacks of nanoplates. Energy dispersive spectroscopy and cathodoluminescence (CL) in the scanning electron microscope show that the stacks of nanoplates consist of Sn doped and Mg doped ZnO respectively. The stacks of nanoplates have well defined orientations relative to the growth axis of the rod. In the case of Sri the formation of the nanoplates is attributed to the stresses generated by the presence of Sri atoms in the rods.Item Self-assembled three-dimensional Al-doped ZnO nanorod networks(Semiconductor Science and Technology, 2011) Piqueras de Noriega, Javier; Fernández Sánchez, Paloma; Ortega Villafuerte, YanicetAl-doped ZnO nanorod networks and other microstructures have been grown by a thermal evaporation–deposition method with a mixture of ZnS and Al_2O_3 powders as precursor. Some of the grown structures consist of star-like arrays of nanorods arranged around a central axis with nearly four-fold symmetry. Scanning electron microscopy (SEM) observations indicate that these arrays are the origin of large well-ordered three-dimensional networks of nanorods resulting from the perpendicular growth of lateral branches in every nanorod. CL in SEM has been used to study the influence of Al doping on the emission. Regions with high Al content, about 1 at%, show a luminescence band at about 1.98 eV.Item In situ TEM and analytical STEM studies of ZnO nanotubes with Sn cores and Sn nanodrops(Journal of Physics D: Applied Physics, 2013) Piqueras de Noriega, Javier; Ortega Villafuerte, Yanicet; Fernández Sánchez, Paloma; Häußler, Dietrich; Jäger, WolfgangZnO nanorods with Sn core regions grown by a thermal evaporation–deposition method from a mixture of SnO_2 and ZnS powders as precursors, are used to study the behaviour of liquid metal in the nanotubes' core regions and the formation of liquid metal nanodrops at the tube ends by in situ TEM experiments. The compositions of the core materials and of the nanodrops were assessed by employing HAADF-STEM imaging and spatially resolved EDXS measurements. By applying variable thermal load through changing the electron-beam flux of the electron microscope, melting of the metallic core can be induced and the behaviour of the liquid metal of the nanorods can be monitored locally. Within the nanorod core, melting and reversible thermal expansion and contraction of Sn core material is reproducibly observed. For nanotubes with core material near-tip regions, a nanodrop emerges from the tip upon melting the core material, followed by reabsorption of the melt into the core and re-solidification upon decreasing the heat load, being reminiscent of a 'soldering nanorod'. The radius of the liquid nanodrop can reach a few tens of nanometres, containing a total volume of 10^20 up to 10^18 l of liquid Sn. In situ TEM confirms that the radius of the nanodrop can be controlled via the thermal load: it increases with increasing temperature and decreases with decreasing temperature. In addition, some phenomena related to structure modifications during extended electron-beam exposure are also described.Item Self-assembled tin-doped ZnO nanowire and nanoplate structures grown by thermal treatment of ZnS powder(Journal of Crystal Growth, 2009) Ortega Villafuerte, Yanicet; Fernández Sánchez, Paloma; Piqueras de Noriega, JavierSintering of a ZnS-SnO(2) mixture under argon flow leads to the growth of columnar nanoplate arrays as well as arrays of nanowires, nanorods and nanoplates with six-fold symmetry. The six-fold nanoplate structures correspond to a more advanced stage of growth than the nanowire structures. Cathodoluminescence (CL) in the scanning electron microscope (SEM) shows that the structures contain Sri, but the amount of this element is normally under the detection limit of X-ray energy-dispersive spectroscopy (EDS). The formation of branches in the hierarchical structures depends on the presence of Sri and on defects in the Mixture powder.Item Influence of indium doping on the morphology of ZnS nanostructures grown by a vapor-solid method(CrystEngComm, 2013) Piqueras de Noriega, Javier; Sotillo Buzarra, Belén; Ortega Villafuerte, Yanicet; Fernández Sánchez, PalomaPure and In-doped ZnS structures have been grown using a VS method. Thermal treatments have been performed at temperatures ranging from 1000 to 1200 °C, during 15 to 17 hours in a N_2 overpressure environment. Nanowires and nanoribbons are the main kind of structures obtained for pure ZnS, depending on the deposition temperature. In the case of ZnS:In, nano- and microswords, nanoribbons, hierarchical structures and nanoplates are obtained, depending on the In content in the starting material and on the deposition temperature. Nanoplates are the dominant structures for the higher In content. The influence of the impurity incorporation on the morphology of the structures has been studied by transmission electron microscopy. While in pure ZnS wires and ribbons two main growth directions are observed ([0001] and [10[1 with combining macron]0]), indium doped structures show a greater variety of morphologies associated with different growth behavior.