Cathodoluminescence of defects in sintered tin oxide

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

Cathodoluminescence and REBIC study of defects in tin oxide

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

CL study of blue and UV emissions in ß-Ga_2O_3 nanowires grown by thermal evaporation of GaN

We report a cathodoluminescence (CL) study of ß-Ga_2O_3 nanowires grown by thermal evaporation of GaN on Si(100) and Au/Si(00) substrates. Condensation and subsequent oxidation of metallic Ga is suggested as the growth mechanism of ß-Ga_2O_3 nanowires. The ß-Ga_2O_3 nanowires grown on Si(100) show multiple bends or undulations, together with a strong UV emission at 3.31 eV and a weak blue emission centered at 2.8 eV as a band component. The ß-Ga_2O_3 nanowires grown on Au/Si(100) substrates recorded a lower CL intensity of a well-defined blue emission of 2.8 eV. A thermal treatment on these samples produced an increase of the UV emission and quenching of the blue band. Thermal annealing of oxygen vacancies is proposed as the responsible mechanism for the observed behavior of these samples

Effect of total pressure on the formation and size evolution of silicon quantum dots in silicon nitride films

The size of silicon quantum dots (Si QDs) embedded in silicon nitride (SiN(x)) has been controlled by varying the total pressure in the plasma-enhanced chemical vapor deposition (PECVD) reactor. This is evidenced by transmission electron microscopy and results in a shift in the light emission peak of the quantum dots. We show that the luminescence in our structures is attributed to the quantum confinement effect. These findings give a strong indication that the quality (density and size distribution) of Si QDs can be improved by optimizing the deposition parameters which opens a route to the fabrication of an all-Si tandem solar cell

Temperature-dependent photoluminescence of anatase Li-doped TiO_(2) nanoparticles

TiO_(2) is currently one of the most employed material in photocatalysis and optoelectronic applications. By doping with different elements, tailored luminescent and optoelectronic properties can be obtained, which further enhances its applicability. The achievement of deeper knowledge and control on the recombination processes via light-metal doping engineering promises a wider use in optoelectronic applications. In this work, the luminescent properties of undoped and Li-doped anatase TiO_(2) nanoparticles obtained by hydrolysis process are studied, by means of photoluminescence (PL) measurements from 10 K to room-temperature. TiO_(2) presents a wide emission which covers the visible range, while Li-doping quenches the emission on the low visible region. By terms of time-resolved luminescence (TR-PL), lifetime of the recombination processes can be obtained, in which a decrease on lifetime values can be observed for the doped samples

Synthesis of In_2S_3 and In_6S_7 microcolumns and nanowires by a vapor-solid method

Indium sulfide (In_2S_3) is a promising candidate for the replacement of CdS buffer layers in solar cell devices, while hexaindium heptasulfide (In_6S_7) presents interesting properties for its use as absorber material. In this work the fabrication of In_2S_3 microcolumns as well as novel In_6S_7 nanowires with diameters of about 70-120nm is reported. The structures are grown following a thermal evaporation-deposition method at temperatures between 900 and 1000º C. Control of the phase and morphology of the structures is achieved through both the evaporation and deposition temperatures, which can be tuned separately. Energy dispersive spectroscopy shows no traces of residual oxygen, while X-ray photoelectron spectroscopy indicates the presence of small amounts of oxygen incorporated at the surface of the structures. The In_6S_7 nanowires are found to be degenerated n-type semiconductors, with the Fermi level above the conduction band minimum. The origin of this n-type degeneracy is discussed in terms of S vacancies

An approach to emerging optical and optoelectronic applications based on NiO micro- and nanostructures

Nickel oxide (NiO) is one of the very few p-type semiconducting oxides, the study of which is gaining increasing attention in recent years due to its potential applicability in many emerging fields of technological research. Actually, a growing number of scientific works focus on NiO-based electrochromic devices, high-frequency spintronics, fuel cell electrodes, supercapacitors, photocatalyst, chemical/gas sensors, or magnetic devices, among others. However, less has been done so far in the development of NiO-based optical devices, a field in which this versatile transition metal oxide still lags in performance despite its potential applicability. This review could contribute with novelty and new forefront insights on NiO micro and nanostructures with promising applicability in optical and optoelectronic devices. As some examples, NiO lighting devices, optical microresonators, waveguides, optical limiters, and neuromorphic applications are reviewed and analyzed in this work. These emerging functionalities, together with some other recent developments based on NiO micro and nanostructures, can open a new field of research based on this p-type material which still remains scarcely explored from an optical perspective, and would pave the way to future research and scientific advances

Growth and characterization of SnO_2 micro- and nanotubes

Micro- and nanotubes, and other elongated structures of SnO_2 as wires and rods, were grown after sintering in argon flow at temperatures ranging from 1350 degrees C to 1500 degrees C. The morphology and luminescence properties of these structures have been investigated by means of the secondary electron and the cathodoluminescence (CL) modes of the scanning electron microscope (SEM)

Photochromic mechanism in oxygen-containing yttrium hydride thin films: An optical perspective

Oxygen-containing yttrium hydride thin films exhibit photochromic behavior: Transparent thin films reversibly switch from a transparent state to a photodarkened state after being illuminated with UV or blue light. From optical spectrophotometry and ellipsometry measurements of the transparent state and photodarkened state, it is concluded that the photochromic effect can be explained by the gradual growth, under illumination, of metallic domains within the initial wide-band-gap semiconducting lattice. This conclusion is supported by Raman measurements

Oxygen vacancy related distortions in rutile TiO_2 nanoparticles: a combined experimental and theoretical study

The effects of doubly ionized oxygen vacancies [(V_O)ˆ(2+)]on the electronic structure and charge distribution in rutile TiO_2 are studied by combining first-principles calculations based on density functional theory and experimental results from x-ray photoelectron and x-ray absorption measurements carried out in synchrotron facilities on rutile TiO_2 nanoparticles. The generalized gradient approximation of the Perdew-Burke-Ernzerhof functional has demonstrated its suitability for the analysis of the [(V_O)ˆ(2+)]defects in rutile TiO_2. It has been found that the presence of empty electronic states at the conduction band shifted ̴1 eV from t_(2g) and e_(g) states can be associated with local distortions induced by [(V_O)ˆ(2+)]defects, in good agreement with Gauss-Lorentzian band deconvolution of experimental O K-edge spectra. The asymmetry of t(2g) and e(g) bands at the O-K edge has been associated with [(V_O)ˆ(2+)], which can enrich the understanding of studies where the presence of these defects plays a key role, as in the case of doped TiO_2