Javier Piqueras - Academia.edu (original) (raw)

Papers by Javier Piqueras

Research paper thumbnail of Defect assessment of Mg-doped GaN by beam injection techniques

Journal of Applied Physics, 2003

The electronic recombination properties of Mg-doped GaN have been investigated by steady state an... more The electronic recombination properties of Mg-doped GaN have been investigated by steady state and time-resolved cathodoluminescence (TRCL) in the scanning electron microscope, photocurrent (PC) spectroscopy, and optical beam induced current (OBIC). CL and OBIC maps reveal an inhomogeneous recombination activity in the investigated material. Deep levels giving rise to level-to-band transitions were detected by PC spectroscopy. A large PC quenching observed upon illumination with light of (2.65–2.85) eV is tentatively attributed to metastable traps within the band gap. CL spectra reveal the existence of emission bands centered at 85 K at 3.29, 3.20, 3.15, and 3.01 eV, respectively. Both time-resolved and steady-state CL measurements carried out under different excitation conditions indicate that the 3.15 and 3.01 eV emissions are likely related to donor-acceptor pair transitions. TRCL measurements also reveal different recombination kinetics for these bands and suggest that deep dono...

Research paper thumbnail of Cathodoluminescence from mechanically cracked porous silicon

Materials Science and Engineering: B, 1999

Cathodoluminescence of porous silicon after mechanical damage with a tip has been studied in the ... more Cathodoluminescence of porous silicon after mechanical damage with a tip has been studied in the scanning electron microscope. Mechanical damage results in the exposure of new surfaces related to fracture and to small particles appearing over the porous silicon layer. The freshly generated surfaces caused an increase of several orders of magnitude in the luminescence efficiency.

Research paper thumbnail of Cathodoluminescence study of ytterbium doped GaSb

Materials Science and Engineering: B, 2005

Thermal treatment of compacted GeO 2 powder under argon flow leads to the growth of a dense distr... more Thermal treatment of compacted GeO 2 powder under argon flow leads to the growth of a dense distribution of microwires and nanowires on the sample surface. Extended treatment causes the formation of more complex structures, including arrays of nanoneedles. Enhanced cathodoluminescence emission is associated with the wires and needles, which show a component at 2.72 eV not observed for the untreated material.

Research paper thumbnail of Shape-controlled synthesis and cathodoluminescence properties of elongated α-Fe2O3 nanostructures

Journal of Applied Physics, 2008

α -Fe 2 O 3 (hematite) nanostructures with various morphologies have been grown by thermal oxidat... more α -Fe 2 O 3 (hematite) nanostructures with various morphologies have been grown by thermal oxidation of compacted iron powder at temperatures between 700 and 900 °C. Different thermal treatments have been found to induce the growth of single-crystalline nanowires, nanobelts, nanoplates and featherlike structures, free and caped nanopillars, and pyramidal microcrystals or cactuslike microstructures. The experimental conditions leading to the different morphologies have been systematically investigated, as well as the possible growth mechanisms. The obtained nanostructures have been characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy, x-ray diffraction, and cathodoluminescence (CL) spectroscopy in the SEM. The formation of the nanostructures induces changes in the intensity and spectral distribution of the CL emission, as compared with the bulk material. Ligand to metal charge transfer transitions as well as Fe3+ ligand field transitio...

Research paper thumbnail of Cathodoluminescence of Ga1-xInxAsySb1-y epitaxial layers

Research paper thumbnail of Study of the defect structure, compositional and electrical properties of Er2O3-doped n-type GaSb:Te crystals grown by the vertical Bridgman technique

Materials Science and Engineering: B, 2002

The defect structure of Te-doped GaSb samples co-doped with Er 2 O 3 and grown by the vertical Br... more The defect structure of Te-doped GaSb samples co-doped with Er 2 O 3 and grown by the vertical Bridgman technique has been analysed. This study was carried out for different Er and Te concentrations. The defect structure of the samples has been analysed by means of cathodoluminescence (CL), scanning electron microscopy (SEM) and wavelength dispersive X-ray microanalysis (WDX). The effect of the defect structure and sample composition on the electrical properties of the material has been established taking into account the results obtained by means of the van der Pauw technique.

Research paper thumbnail of Luminescence properties of transition-metal-doped GaSb

Physical Review B, 1998

The luminescence properties of transition-metal ͑Cr, V, and Ru͒-doped GaSb single crystals have b... more The luminescence properties of transition-metal ͑Cr, V, and Ru͒-doped GaSb single crystals have been studied by a cathodoluminescence ͑CL͒ technique in a scanning electron microscope. Spatial segregation of impurities along the longitudinal direction of the crystals grown by the Bridgman method has been investigated. These dopants suppress the native acceptor concentration to varying extent. The behavior of Ru has been found to be different from the behavior of V and Cr. In particular the complete disappearance of the 777 meV ͑band A͒ emission has been observed in GaSb:Ru with a low doping level. A peak at 767 meV is also seen in this sample which, to the best of our knowledge, has not been previously observed in GaSb. The CL results have been complemented by x-ray-microanalysis measurements to ascertain the effect of doping level on the luminescence properties. ͓S0163-1829͑98͒05608-2͔

Research paper thumbnail of Nature of compensating luminescence centers in Te-diffused and -doped GaSb

Journal of Applied Physics, 1996

Diffusion of tellurium in undoped p-GaSb has been carried out. Using the cathodoluminescence and ... more Diffusion of tellurium in undoped p-GaSb has been carried out. Using the cathodoluminescence and photoluminescence techniques, the luminescence centers in Te-diffused samples have been identified and compared with the Te-doped bulk GaSb. Fundamental differences in the radiative levels are observed between the diffused and the as-grown doped samples. Evidence for self-compensating acceptor complexes are seen in diffused samples. With short and moderate diffusion times, a compensating acceptor complex VGaGaSbTeSb is observed. For long diffusion times, the dominant acceptor center has been attributed to the antisite defect GaSb or related complex. The reasons for the formation of various acceptor centers have been discussed.

Research paper thumbnail of Spatial distribution of recombination centers in GaAs:Te: Effects of the doping level

Journal of Applied Physics, 1994

The distribution in liquid-encapsulated-Czochralski (LEC) GaAs:Te wafers of point and complex def... more The distribution in liquid-encapsulated-Czochralski (LEC) GaAs:Te wafers of point and complex defects has been investigated together with their influence on the minority-carrier diffusion length L. Three wafers with different Te-doping concentration (2.2×1017, 4.5×1017, and 1.5×1018 cm−3) have been studied by means of the electron-beam-induced-current (EBIC) mode of scanning electron microscopy and of the surface photovoltage (SPV) method. The morphology and electrical activity of the defects observed across each wafer have been correlated to the formation and distribution of deep electronic levels, which are significantly affected by the tellurium concentration. The diffusion length has been found to be mainly controlled by deep levels associated with dislocations. EBIC localized measurements of L and of the net ionized free-carrier concentration provide evidence for the influence of Te concentration on impurity segregation at complex defects.

Research paper thumbnail of Red luminescence of Cr in-Ga 2 O 3 nanowires

Related Articles Reduced temperature sensitivity of the polarization properties of hydrogenated I... more Related Articles Reduced temperature sensitivity of the polarization properties of hydrogenated InGaAsN V-groove quantum wires Appl. Phys. Lett. 101, 151114 (2012) Diameter dependent optical emission properties of InAs nanowires grown on Si Appl. Phys. Lett. 101, 053103 (2012) Quantitative absorption spectra of quantum wires measured by analysis of attenuated internal emissions Appl. Phys. Lett. 100, 112101 (2012) Localization effects on recombination dynamics in InAs/InP self-assembled quantum wires emitting at 1.5μm J. Appl. Phys. 110, 103502 (2011) Isotropic Hall effect and “freeze-in” of carriers in the InGaAs self-assembled quantum wires J. Appl. Phys. 110, 083714 (2011)

Research paper thumbnail of Study of pinholes and nanotubes in AlInGaN films by cathodoluminescence and atomic force microscopy

Journal of Applied Physics, 2004

Cathodoluminescence (CL) in the scanning electron microscope and atomic force microscopy (AFM) ha... more Cathodoluminescence (CL) in the scanning electron microscope and atomic force microscopy (AFM) have been used to study the formation of pinholes in tensile and compressively strained AlInGaN films grown on Al2O3 substrates by plasma-induced molecular beam epitaxy. Nanotubes, pits, and V-shaped pinholes are observed in a tensile strained sample. CL images show an enhanced emission around the pits and a lower intensity at the V-shaped pinholes. Rounded pinholes appear in compressively strained samples in island-like regions with higher In concentration. The grain structure near the pinholes is resolved by AFM.

Research paper thumbnail of Cathodoluminescence of defects in sintered tin oxide

Journal of Applied Physics, 2004

Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to investigate t... more Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to investigate the luminescence 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 analyzed by CL microscopy and spectroscopy. The main emission bands appear centered at about 2.58, 2.25, and 1.94 eV depending on the sintering treatment. CL images reveal that the 2.25 and the 2.58 eV bands are associated at specific crystal faces. The evolution of the luminescence bands with mechanical milling shows a complex evolution of the 1.94 and 2.58 eV emissions which is explained by formation and recovery of defects during milling.

Research paper thumbnail of Growth and luminescence properties of micro- and nanoneedles in sintered CdSe

Applied Physics Letters, 2004

Sintering CdSe powder under argon flow at temperatures in the range 800-900°C produces the format... more Sintering CdSe powder under argon flow at temperatures in the range 800-900°C produces the formation of needles on the sample surface. Bundles of parallel needles of a diameter of about 50 nm give rise to a domain-like appearance in the sample. In addition, rods and needles with a wide range of dimensions up to several microns appear distributed in the surface. The influence of ball milling of the starting powder on the formation of the needles is investigated. Cathodoluminescence in the scanning electron microscope has been used to characterize the sintered samples.

Research paper thumbnail of Spatially resolved characterization of local phenomena in materials and nanostructures : symposium held December 2-5, 2002, Boston, Massachusetts, U.S.A

A primary driver of progress in nanoscience and technology is the continuing advances in the abil... more A primary driver of progress in nanoscience and technology is the continuing advances in the ability to measure structure, and particularly properties, at spatially localized scales. From the point of view of characterization, it is worth mentioning advances in the interpretation of processes in semiconductors, the ability to observe and manipulate metal, carbon and silicon nanowires and nanodots, and studies in molecular self-assembly. The papers in this book fall into two categories - those addressing classes of characterization techniques that emphasize how the combination of theoretical, experimental, and instrumentational developments lead to new capabilities in nanoscale characterization, and those focused on the use of various spatially localized approaches on a single phenomenon or materials issue. Topics include: characterization with electron optics; novel measurements of nanoscale properties; size-dependent behavior of nanoparticles; biological systems at the nanoscale; p...

Research paper thumbnail of Growth and characterization of Cr doped SnO2 microtubes with resonant cavity modes

Journal of Materials Chemistry C, 2016

Cr doped SnO2 microtubes have been fabricated by a thermal evaporation–deposition method.

Research paper thumbnail of Effect of Erbidum on the Luminescence Properties of GaSb Crystals

Solid State Phenomena, 1998

The interest of rare earth doping of semiconductors has increased in the last years due to its po... more The interest of rare earth doping of semiconductors has increased in the last years due to its possible applications in optical devices requiring temperature stability. Advantages of these systems are the presence of a sharp temperature independent rare-earth luminescence and the possibility of activation of the emitting rare-earth centers by minority carrier injection. In this work the effect of erbium doping on the luminescence and on the native accepters of GaSb crystals has been investigated by CL-SEM. Er doping has been found to increase the total CL intensity and to produce spectral changes that depend on the erbium concentration. At moderate doping the native acceptor concentration, as detected by the luminescence band A, decreases. At high Er concentrations Er-Sb precipitates form and doping appears not to be efficient in the suppression of accepters. X-ray microanalysis reveals that the composition of the precipitates is Er-5 Sb-3. Emission from intraionic transitions of Er is observed in highly doped crystals.

Research paper thumbnail of Structural and luminescence properties of Eu and Er implanted Bi 2O3 nanowires for optoelectronic applications

Journal of Materials Chemistry C, 2013

ABSTRACT Effective Er and Eu doping of α-Bi2O3 nanowires has been achieved by ion implantation. T... more ABSTRACT Effective Er and Eu doping of α-Bi2O3 nanowires has been achieved by ion implantation. The nanostructures exhibit stable and efficient photoluminescence emission at room temperature after adequate annealing. X-ray photoelectron and X-ray absorption spectroscopy measurements reveal the incorporation of Er and Eu ions only in the desired trivalent charge state. The structural recovery of the implantation damage after thermal treatments was monitored by micro-Raman spectroscopy. Nanowires implanted with 300 keV ions and fluences in the range of 2 × 1015 to 8 × 1015 cm−2 show luminescence emission after annealing at 450 °C and 550 °C. Samples implanted with Eu ions show Eu3+ emission lines at 543 nm (5D1–7F1 transition), 587 nm (5D1–7F3 transition), 613 and 622 nm (5D0–7F2 transitions). Er-implanted nanowires show luminescence in the red range between 650 and 680 nm, corresponding to Er3+ 2F9/2–4I15/2 transitions. High angle annular dark field scanning transmission electron microscopy observations combined with energy dispersive X-ray microanalysis measurements reveal the formation of dopant-rich regions at higher fluences, leading to a reduced optical signal.

Research paper thumbnail of Study of Laser Annealed Ferromagnetic Amorphous Ribbons by Scanning Electron-Acoustic Microscopy

Acoustical Imaging, 1993

Scanning Electron Acoustic Microscopy (SEAM) was developped in 1980 (l)(2) and has been mainly us... more Scanning Electron Acoustic Microscopy (SEAM) was developped in 1980 (l)(2) and has been mainly used in the last few years in the characterization of metals and semiconductors. SEAM has been also applied to the observation of different surface and subsurface features in ceramics (3) and domain walls in amorphous ferromagnetic alloys (4).

Research paper thumbnail of Luminescence and waveguiding behavior in Tb doped ZnO micro and nanostructures

Journal of Alloys and Compounds, 2014

ABSTRACT Tb doped ZnO micro- and nanostructures have been grown by a catalyst free vapor-solid me... more ABSTRACT Tb doped ZnO micro- and nanostructures have been grown by a catalyst free vapor-solid method. Luminescence properties and waveguiding behavior of the diverse nanostructures have been investigated by cathodoluminescence (CL) and micro-photoluminescence (μ-PL). Luminescence spectra of nanobelts and nanowires show the Tb3+ emission lines. Efficient waveguiding behavior has been observed for both ZnO and Tb3+ luminescence bands in the microwires. Optical resonant modes have been also observed in nanotriangles and tapered nanowires opening the possibility of their use in a wide variety of optical devices.

Research paper thumbnail of Luminescence and Raman study of Zn4In2O7 nanobelts and plates

Superlattices and Microstructures, 2013

Luminescence of Zn 4 In 2 O 7 nanobelts and microplates synthesized by a thermal evaporation-depo... more Luminescence of Zn 4 In 2 O 7 nanobelts and microplates synthesized by a thermal evaporation-deposition method, has been investigated by photoluminescence (PL) and cathodoluminescence (CL) in the scanning electron microscope (SEM). Time resolved and temperature dependent CL measurements show that an emission at 2.37 eV appears to be characteristic of the Indium-Zinc-Oxide (IZO) compound investigated. PL and waveguiding behavior of the microplates is described. Raman spectra of the structures as a function of In content has been studied.

Research paper thumbnail of Defect assessment of Mg-doped GaN by beam injection techniques

Journal of Applied Physics, 2003

The electronic recombination properties of Mg-doped GaN have been investigated by steady state an... more The electronic recombination properties of Mg-doped GaN have been investigated by steady state and time-resolved cathodoluminescence (TRCL) in the scanning electron microscope, photocurrent (PC) spectroscopy, and optical beam induced current (OBIC). CL and OBIC maps reveal an inhomogeneous recombination activity in the investigated material. Deep levels giving rise to level-to-band transitions were detected by PC spectroscopy. A large PC quenching observed upon illumination with light of (2.65–2.85) eV is tentatively attributed to metastable traps within the band gap. CL spectra reveal the existence of emission bands centered at 85 K at 3.29, 3.20, 3.15, and 3.01 eV, respectively. Both time-resolved and steady-state CL measurements carried out under different excitation conditions indicate that the 3.15 and 3.01 eV emissions are likely related to donor-acceptor pair transitions. TRCL measurements also reveal different recombination kinetics for these bands and suggest that deep dono...

Research paper thumbnail of Cathodoluminescence from mechanically cracked porous silicon

Materials Science and Engineering: B, 1999

Cathodoluminescence of porous silicon after mechanical damage with a tip has been studied in the ... more Cathodoluminescence of porous silicon after mechanical damage with a tip has been studied in the scanning electron microscope. Mechanical damage results in the exposure of new surfaces related to fracture and to small particles appearing over the porous silicon layer. The freshly generated surfaces caused an increase of several orders of magnitude in the luminescence efficiency.

Research paper thumbnail of Cathodoluminescence study of ytterbium doped GaSb

Materials Science and Engineering: B, 2005

Thermal treatment of compacted GeO 2 powder under argon flow leads to the growth of a dense distr... more Thermal treatment of compacted GeO 2 powder under argon flow leads to the growth of a dense distribution of microwires and nanowires on the sample surface. Extended treatment causes the formation of more complex structures, including arrays of nanoneedles. Enhanced cathodoluminescence emission is associated with the wires and needles, which show a component at 2.72 eV not observed for the untreated material.

Research paper thumbnail of Shape-controlled synthesis and cathodoluminescence properties of elongated α-Fe2O3 nanostructures

Journal of Applied Physics, 2008

α -Fe 2 O 3 (hematite) nanostructures with various morphologies have been grown by thermal oxidat... more α -Fe 2 O 3 (hematite) nanostructures with various morphologies have been grown by thermal oxidation of compacted iron powder at temperatures between 700 and 900 °C. Different thermal treatments have been found to induce the growth of single-crystalline nanowires, nanobelts, nanoplates and featherlike structures, free and caped nanopillars, and pyramidal microcrystals or cactuslike microstructures. The experimental conditions leading to the different morphologies have been systematically investigated, as well as the possible growth mechanisms. The obtained nanostructures have been characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy, x-ray diffraction, and cathodoluminescence (CL) spectroscopy in the SEM. The formation of the nanostructures induces changes in the intensity and spectral distribution of the CL emission, as compared with the bulk material. Ligand to metal charge transfer transitions as well as Fe3+ ligand field transitio...

Research paper thumbnail of Cathodoluminescence of Ga1-xInxAsySb1-y epitaxial layers

Research paper thumbnail of Study of the defect structure, compositional and electrical properties of Er2O3-doped n-type GaSb:Te crystals grown by the vertical Bridgman technique

Materials Science and Engineering: B, 2002

The defect structure of Te-doped GaSb samples co-doped with Er 2 O 3 and grown by the vertical Br... more The defect structure of Te-doped GaSb samples co-doped with Er 2 O 3 and grown by the vertical Bridgman technique has been analysed. This study was carried out for different Er and Te concentrations. The defect structure of the samples has been analysed by means of cathodoluminescence (CL), scanning electron microscopy (SEM) and wavelength dispersive X-ray microanalysis (WDX). The effect of the defect structure and sample composition on the electrical properties of the material has been established taking into account the results obtained by means of the van der Pauw technique.

Research paper thumbnail of Luminescence properties of transition-metal-doped GaSb

Physical Review B, 1998

The luminescence properties of transition-metal ͑Cr, V, and Ru͒-doped GaSb single crystals have b... more The luminescence properties of transition-metal ͑Cr, V, and Ru͒-doped GaSb single crystals have been studied by a cathodoluminescence ͑CL͒ technique in a scanning electron microscope. Spatial segregation of impurities along the longitudinal direction of the crystals grown by the Bridgman method has been investigated. These dopants suppress the native acceptor concentration to varying extent. The behavior of Ru has been found to be different from the behavior of V and Cr. In particular the complete disappearance of the 777 meV ͑band A͒ emission has been observed in GaSb:Ru with a low doping level. A peak at 767 meV is also seen in this sample which, to the best of our knowledge, has not been previously observed in GaSb. The CL results have been complemented by x-ray-microanalysis measurements to ascertain the effect of doping level on the luminescence properties. ͓S0163-1829͑98͒05608-2͔

Research paper thumbnail of Nature of compensating luminescence centers in Te-diffused and -doped GaSb

Journal of Applied Physics, 1996

Diffusion of tellurium in undoped p-GaSb has been carried out. Using the cathodoluminescence and ... more Diffusion of tellurium in undoped p-GaSb has been carried out. Using the cathodoluminescence and photoluminescence techniques, the luminescence centers in Te-diffused samples have been identified and compared with the Te-doped bulk GaSb. Fundamental differences in the radiative levels are observed between the diffused and the as-grown doped samples. Evidence for self-compensating acceptor complexes are seen in diffused samples. With short and moderate diffusion times, a compensating acceptor complex VGaGaSbTeSb is observed. For long diffusion times, the dominant acceptor center has been attributed to the antisite defect GaSb or related complex. The reasons for the formation of various acceptor centers have been discussed.

Research paper thumbnail of Spatial distribution of recombination centers in GaAs:Te: Effects of the doping level

Journal of Applied Physics, 1994

The distribution in liquid-encapsulated-Czochralski (LEC) GaAs:Te wafers of point and complex def... more The distribution in liquid-encapsulated-Czochralski (LEC) GaAs:Te wafers of point and complex defects has been investigated together with their influence on the minority-carrier diffusion length L. Three wafers with different Te-doping concentration (2.2×1017, 4.5×1017, and 1.5×1018 cm−3) have been studied by means of the electron-beam-induced-current (EBIC) mode of scanning electron microscopy and of the surface photovoltage (SPV) method. The morphology and electrical activity of the defects observed across each wafer have been correlated to the formation and distribution of deep electronic levels, which are significantly affected by the tellurium concentration. The diffusion length has been found to be mainly controlled by deep levels associated with dislocations. EBIC localized measurements of L and of the net ionized free-carrier concentration provide evidence for the influence of Te concentration on impurity segregation at complex defects.

Research paper thumbnail of Red luminescence of Cr in-Ga 2 O 3 nanowires

Related Articles Reduced temperature sensitivity of the polarization properties of hydrogenated I... more Related Articles Reduced temperature sensitivity of the polarization properties of hydrogenated InGaAsN V-groove quantum wires Appl. Phys. Lett. 101, 151114 (2012) Diameter dependent optical emission properties of InAs nanowires grown on Si Appl. Phys. Lett. 101, 053103 (2012) Quantitative absorption spectra of quantum wires measured by analysis of attenuated internal emissions Appl. Phys. Lett. 100, 112101 (2012) Localization effects on recombination dynamics in InAs/InP self-assembled quantum wires emitting at 1.5μm J. Appl. Phys. 110, 103502 (2011) Isotropic Hall effect and “freeze-in” of carriers in the InGaAs self-assembled quantum wires J. Appl. Phys. 110, 083714 (2011)

Research paper thumbnail of Study of pinholes and nanotubes in AlInGaN films by cathodoluminescence and atomic force microscopy

Journal of Applied Physics, 2004

Cathodoluminescence (CL) in the scanning electron microscope and atomic force microscopy (AFM) ha... more Cathodoluminescence (CL) in the scanning electron microscope and atomic force microscopy (AFM) have been used to study the formation of pinholes in tensile and compressively strained AlInGaN films grown on Al2O3 substrates by plasma-induced molecular beam epitaxy. Nanotubes, pits, and V-shaped pinholes are observed in a tensile strained sample. CL images show an enhanced emission around the pits and a lower intensity at the V-shaped pinholes. Rounded pinholes appear in compressively strained samples in island-like regions with higher In concentration. The grain structure near the pinholes is resolved by AFM.

Research paper thumbnail of Cathodoluminescence of defects in sintered tin oxide

Journal of Applied Physics, 2004

Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to investigate t... more Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to investigate the luminescence 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 analyzed by CL microscopy and spectroscopy. The main emission bands appear centered at about 2.58, 2.25, and 1.94 eV depending on the sintering treatment. CL images reveal that the 2.25 and the 2.58 eV bands are associated at specific crystal faces. The evolution of the luminescence bands with mechanical milling shows a complex evolution of the 1.94 and 2.58 eV emissions which is explained by formation and recovery of defects during milling.

Research paper thumbnail of Growth and luminescence properties of micro- and nanoneedles in sintered CdSe

Applied Physics Letters, 2004

Sintering CdSe powder under argon flow at temperatures in the range 800-900°C produces the format... more Sintering CdSe powder under argon flow at temperatures in the range 800-900°C produces the formation of needles on the sample surface. Bundles of parallel needles of a diameter of about 50 nm give rise to a domain-like appearance in the sample. In addition, rods and needles with a wide range of dimensions up to several microns appear distributed in the surface. The influence of ball milling of the starting powder on the formation of the needles is investigated. Cathodoluminescence in the scanning electron microscope has been used to characterize the sintered samples.

Research paper thumbnail of Spatially resolved characterization of local phenomena in materials and nanostructures : symposium held December 2-5, 2002, Boston, Massachusetts, U.S.A

A primary driver of progress in nanoscience and technology is the continuing advances in the abil... more A primary driver of progress in nanoscience and technology is the continuing advances in the ability to measure structure, and particularly properties, at spatially localized scales. From the point of view of characterization, it is worth mentioning advances in the interpretation of processes in semiconductors, the ability to observe and manipulate metal, carbon and silicon nanowires and nanodots, and studies in molecular self-assembly. The papers in this book fall into two categories - those addressing classes of characterization techniques that emphasize how the combination of theoretical, experimental, and instrumentational developments lead to new capabilities in nanoscale characterization, and those focused on the use of various spatially localized approaches on a single phenomenon or materials issue. Topics include: characterization with electron optics; novel measurements of nanoscale properties; size-dependent behavior of nanoparticles; biological systems at the nanoscale; p...

Research paper thumbnail of Growth and characterization of Cr doped SnO2 microtubes with resonant cavity modes

Journal of Materials Chemistry C, 2016

Cr doped SnO2 microtubes have been fabricated by a thermal evaporation–deposition method.

Research paper thumbnail of Effect of Erbidum on the Luminescence Properties of GaSb Crystals

Solid State Phenomena, 1998

The interest of rare earth doping of semiconductors has increased in the last years due to its po... more The interest of rare earth doping of semiconductors has increased in the last years due to its possible applications in optical devices requiring temperature stability. Advantages of these systems are the presence of a sharp temperature independent rare-earth luminescence and the possibility of activation of the emitting rare-earth centers by minority carrier injection. In this work the effect of erbium doping on the luminescence and on the native accepters of GaSb crystals has been investigated by CL-SEM. Er doping has been found to increase the total CL intensity and to produce spectral changes that depend on the erbium concentration. At moderate doping the native acceptor concentration, as detected by the luminescence band A, decreases. At high Er concentrations Er-Sb precipitates form and doping appears not to be efficient in the suppression of accepters. X-ray microanalysis reveals that the composition of the precipitates is Er-5 Sb-3. Emission from intraionic transitions of Er is observed in highly doped crystals.

Research paper thumbnail of Structural and luminescence properties of Eu and Er implanted Bi 2O3 nanowires for optoelectronic applications

Journal of Materials Chemistry C, 2013

ABSTRACT Effective Er and Eu doping of α-Bi2O3 nanowires has been achieved by ion implantation. T... more ABSTRACT Effective Er and Eu doping of α-Bi2O3 nanowires has been achieved by ion implantation. The nanostructures exhibit stable and efficient photoluminescence emission at room temperature after adequate annealing. X-ray photoelectron and X-ray absorption spectroscopy measurements reveal the incorporation of Er and Eu ions only in the desired trivalent charge state. The structural recovery of the implantation damage after thermal treatments was monitored by micro-Raman spectroscopy. Nanowires implanted with 300 keV ions and fluences in the range of 2 × 1015 to 8 × 1015 cm−2 show luminescence emission after annealing at 450 °C and 550 °C. Samples implanted with Eu ions show Eu3+ emission lines at 543 nm (5D1–7F1 transition), 587 nm (5D1–7F3 transition), 613 and 622 nm (5D0–7F2 transitions). Er-implanted nanowires show luminescence in the red range between 650 and 680 nm, corresponding to Er3+ 2F9/2–4I15/2 transitions. High angle annular dark field scanning transmission electron microscopy observations combined with energy dispersive X-ray microanalysis measurements reveal the formation of dopant-rich regions at higher fluences, leading to a reduced optical signal.

Research paper thumbnail of Study of Laser Annealed Ferromagnetic Amorphous Ribbons by Scanning Electron-Acoustic Microscopy

Acoustical Imaging, 1993

Scanning Electron Acoustic Microscopy (SEAM) was developped in 1980 (l)(2) and has been mainly us... more Scanning Electron Acoustic Microscopy (SEAM) was developped in 1980 (l)(2) and has been mainly used in the last few years in the characterization of metals and semiconductors. SEAM has been also applied to the observation of different surface and subsurface features in ceramics (3) and domain walls in amorphous ferromagnetic alloys (4).

Research paper thumbnail of Luminescence and waveguiding behavior in Tb doped ZnO micro and nanostructures

Journal of Alloys and Compounds, 2014

ABSTRACT Tb doped ZnO micro- and nanostructures have been grown by a catalyst free vapor-solid me... more ABSTRACT Tb doped ZnO micro- and nanostructures have been grown by a catalyst free vapor-solid method. Luminescence properties and waveguiding behavior of the diverse nanostructures have been investigated by cathodoluminescence (CL) and micro-photoluminescence (μ-PL). Luminescence spectra of nanobelts and nanowires show the Tb3+ emission lines. Efficient waveguiding behavior has been observed for both ZnO and Tb3+ luminescence bands in the microwires. Optical resonant modes have been also observed in nanotriangles and tapered nanowires opening the possibility of their use in a wide variety of optical devices.

Research paper thumbnail of Luminescence and Raman study of Zn4In2O7 nanobelts and plates

Superlattices and Microstructures, 2013

Luminescence of Zn 4 In 2 O 7 nanobelts and microplates synthesized by a thermal evaporation-depo... more Luminescence of Zn 4 In 2 O 7 nanobelts and microplates synthesized by a thermal evaporation-deposition method, has been investigated by photoluminescence (PL) and cathodoluminescence (CL) in the scanning electron microscope (SEM). Time resolved and temperature dependent CL measurements show that an emission at 2.37 eV appears to be characteristic of the Indium-Zinc-Oxide (IZO) compound investigated. PL and waveguiding behavior of the microplates is described. Raman spectra of the structures as a function of In content has been studied.