Person:
Maestre Varea, David

First Name

David

Last Name

Maestre Varea

URI

https://hdl.handle.net/20.500.14352/75109

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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Now showing 1 - 10 of 29

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.
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.
Indium Tin Oxide micro- and nanostructures grown by thermal treatment of InN/SnO2
(Journal of Physical Chemistre C, 2010) Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Gregorati, Luca; Piqueras de Noriega, Javier
Mixtures of InN and SnO2 powders, with it weight ratio of 10:1, have been used as precursors for the thermal growth of arrow-shaped and other elongated micro- and nanostructures of indium-tin oxide (ITO) containing about 2.6 atom % of Sit. The temperatures used in the process, in the range 650-750 degrees C, favor the decomposition of InN and oxidation of In, with it limited incorporation of Sit in the resulting compound. Arrow-shaped indium-tin oxide structures are obtained and formation of stannates during the process is avoided. X-ray photoelectron spectroscopy indicates that tin incorporates into the In2O3 lattice mainly as Sn4+. Luminescence of the ITO microstructures has been studied by cathodoluminescence in the scanning electron microscope.
Two-dimensional Zn_k In_2O_(k+3) nanostructures: synthesis, growth mechanism, self-assembly, and luminescence
(Journal of Nanoparticle Research, 2013) Bartolomé Vílchez, Javier; Maestre Varea, David; Amati, Mateo; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier
Indium-zinc oxide nanostructures, such as nanosheets, nanobelts, and wires formed by oriented stacks of nanoplates have been grown by a controlled thermal evaporation method without the use of a foreign catalyst. Surface features in the stacked hexagonal nanoplates suggest a dislocation-driven growth mechanism for these structures. A growth model for these stacks is proposed based on changes in velocity growth rate between the outer and the inner part of the plates. Zn incorporation has been investigated by means of energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and selected area electron diffraction. The formation of Zn_k In_2O_(k+3) ternary compounds has been demonstrated. Cathodoluminescence emission and its correlation with the morphology of the structures and Zn content have been studied.
Indium sulfide and ternary In-S-O nanowires for optoelectronic applications
(Microscopy and Microanalysis, 2012) Bartolomé Vílchez, Javier; Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier
Growth and luminescence properties of micro- and nanotubes in sintered tin oxide
(Journal of Applied Physics, 2005) Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier
Sintering SnO_2 under argon flow at temperatures in the range of 1350-1500 degreesC causes the formation of wires, rods, and tubes on the sample surface. At high temperatures of the mentioned range, microwires with lengths of hundreds of microns are formed. At lower temperatures the formation of micro- and nanorods as well as micro- and nanotubes takes place. The influence of ball milling of the starting powder on the formation of tubes is investigated. The local cathodoluminescence measurements show a different defect structure in the tubes than in the sample background.
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 Rodríguez, 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.
Composition-dependent electronic properties of indium-zinc-oxide elongated microstructures
(Acta Materialia, 2013) Bartolomé Vílchez, Javier; Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Amatti, M.; Piqueras de Noriega, Javier
Microrods and hierarchical structures of indium-zinc-oxide (IZO) with different compositions were grown by thermal treatments of mixtures of InN and ZnO powders. In long rods, an increase in Zn content along the growth axis is revealed by energy dispersive spectroscopy. The structures obtained range from Zn-doped indium oxide with a few atomic per cent of Zn, to IZO compounds of the type Zn_kIn_2O_k+3. X-ray photoelectron spectroscopy measurements with spatial resolution show that IZO microstructures degenerate at room temperature, with carrier concentration of the order of 10^20 cm^-3. Electron accumulation has been found for undoped (1 0 0) and (1 1 1) surfaces, whereas depletion of carriers at the surface is observed in IZO samples. The Fermi level position correlates with the Zn concentration at the surface which, taking into account the surface dependence of the ionization potentials, work functions and band gaps, could lead to tunable material properties for device applications. Cathodoluminescence emission intensity is enhanced by the presence of Zn, which induces spectral changes and broadening of the emission band compared with undoped material. The results are discussed in terms of the charge neutrality level and the band structure of the material.
Direct observation of potential barrier formation at grain boundaries of SnO_2 ceramics
(Semiconductor Science and Technology, 2004) Maestre Varea, David; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier
Remote electron beam induced current (REBIC) and cathodoluminescence (CL) modes in the scanning electron microscope (SEM) have been used to investigate SnO2 sintered samples. The study of the electrically active boundaries present in the oxide shows a characteristic peak and trough (PAT) contrast after thermal treatments in oxygen. Temperature-dependent measurements of the REBIC contrast show the presence of a shallow defect level 60 meV below the conduction band. This level is asigned to oxygen species adsorbed on the defect-rich boundaries. Evolution of REBIC contrast of the grain boundaries with excitation density enabled us to perform local measurements of minority carrier diffusion length.
Indium Zinc Oxide pyramids with pinholes and nanopipes
(Journal of Physical Chemistry C, 2011) Bartolomé Vílchez, Javier; Maestre Varea, David; Amati, Mateo; Cremades Rodríguez, Ana Isabel; Piqueras de Noriega, Javier
Micropyramids of zinc-doped indium oxide have been grown by thermal treatments of compacted InN and ZnO powders at temperatures between 700:and 900 degrees C Under argon flow. X-ray diffraction (XRD) measurements and energy-dispersive X-ray (EDS) mappings as well as local EDS spectra enable the identification of rough surfaces of the pyramids with the nucleation of a shell of nanocrystallites with high Zn/In ratio because of the formation of Zn(k)In(2)O(k+3). Some of the pyramids have a truncated tip with pinholes with regular crystalline facets. The apexes of these pinhole's present a hollow core or nanopipe The possible relation of the nanopipes with a dislocation driven growth is discussed. A growth model is proposed from the morphology evolution of the pyramids during the formation of the In(2)O(3)-ZnO (IZO) compound X-ray photoelectron spectroscopy and microscopy (XPS-ESCA) Measurements are used to discuss the Zn incorporation as a dopant and the formation of Zn(k)In(2)O(k+3) ternaries. Cathodoluminescence (CL) in the scanning electron microscopy (SEM) shows a dependence of the luminescence of the microstructures on the Zn concentration and the growth temperature.