Oxygen-deficient Defects Research Articles

Rapid Synthesis and Characterization of an Oxygen-Deficient Defect Perovskite La4BaCu5O13+δ Phase

Oxygen-deficient defect perovskite La4BaCu5O13+δ phase has been synthesized by the nitrate-citrate gel combustion method at 950°C for 2 h. Structural parameters were refined by the Rietveld refinement method using room-temperature powder XRD data. The La4BaCu5O13+δ crystallizes in the tetragonal structure with space group P4/m (no. 83) and having the lattice parameters a=8.6508(1) Å and c=3.8606(2) Å, respectively. Oxygen content was determined by the iodometric titration. Low-temperature resistivity result reveals that La4BaCu5O13+δ compound exhibit metallic behavior up to 15 K.

Study of the excitation properties of the Si3O2 cluster under an external electric field

The structure of the Si3Ox (x = 2, 3) cluster is investigated; we find that the geometry of Si3O2 is similar to that of Si3O3 except for the oxygen-deficient defect structure (Si-Si band) which exists only in the Si3O2 cluster. It is known that oxygen-deficient defects are used to explain visible luminescence (especially blue, purple and ultraviolet light) from silicon-based materials, which are directly bound up with the excited states of the molecules. Therefore the excitation properties of the two clusters are also studied. Our results show that the absorption spectrum of Si3O2 is concentrated in the visible light region. In contrast, the absorption spectrum of Si3O3 is mainly located in the ultraviolet light region. The calculations are perfectly consistent with experimental data and also support the theory of oxygen-deficient defects.

Flexible Resistive Switching Memory Device Based on Amorphous InGaZnO Film With Excellent Mechanical Endurance

Semitransparent flexible resistive-switching memory devices, using amorphous InGaZnO as the switching layer, are fabricated on plastic substrates at room temperature. The device shows high performance, excellent flexibility, and mechanical endurance in bending tests. No performance degradation occurs, and the stored information is not lost after bending the device to different angles and up to 105 times. Studies on the temperature-dependent electrical properties reveal that the conducting channels of the low-resistance state are composed of oxygen-deficient defects, and partial oxidation of these defects switches the device to the high-resistance state. The unique electronic structure and flexible mechanical properties of amorphous InGaZnO ensure stable device performance in flexible applications.

Electrical Characterization of Hydrothermally Grown ZnO Annealed in Different Atmospheres

Hydrothermally grown ZnO crystals were investigated by capacitance techniques, such as deep level transient spectroscopy (DLTS) and thermal admittance spectroscopy (TAS). N-type ZnO samples were treated by high-temperature annealing in different gas ambients, followed by Pd Schottky contact formation on the zinc-polar surface. The DLTS measurements show three main levels in the band gap with the position of Ec−0.19, −0.30, and −0.54 eV, labelled E2, E3, and E4, respectively (Ec denotes the conduction band edge). The TAS measurements reveal the E2 and E3 levels in the 70–120 K range, and demonstrate complete carrier freeze-out at 50 K corresponding to a shallow donor at 30 meV below Ec. The data are consistent with an assignment of the E2 and E3 levels to oxygen deficient defects while the E4 level appears to originate from a zinc-deficient defect. Further, the role of residual impurities on the observed defects cannot be excluded and this holds especially for E2 and E3.

Effect of calcination atmosphere on photoluminescence properties of nanocrystalline ZrO 2 thin films prepared by sol–gel dip coating method

Highly transparent and homogeneous nanocrystalline ZrO 2 thin films were prepared by the sol–gel dip coating method. The X-ray diffraction (XRD) pattern of ZrO 2 thin films calcined in air, O 2 or N 2 shows the formation of tetragonal phase with varying crystallite size. X-ray photoelectron spectroscopy (XPS) gives Zr 3d and O 1s spectra of thin film annealed in air, which reveal zirconium suboxide component (ZrO x , 0< x<2), Zr–O bond and surface defects. An average transmittance greater than 85% (in UV–vis region) is observed in all calcined samples. Photoluminescence (PL) reveals an intense emission peak at 379 nm and weak peaks at 294, 586 and 754 nm for ZrO 2 film calcined in air. An enhancement of PL intensity and red-shift is observed in films calcined in O 2 and N 2 atmosphere. This is due to the reconstruction of zirconium nanocrystal interfaces and vacancies, which help passivate the non-radiative defects. The oxygen deficient defect, which is due to the distorted Zr–O bond, is suggested to be responsible for photoluminescence. The defect states in the nanocrystalline zirconia thin films play an important role in the energy transfer process. The luminescence defects in the film make it suitable for gas sensors development and tunable lasers.

Three primary colors emitting from Er 3+–Eu 3+ co-doped oxygen-deficient glasses

Three individual primary colors were generated from only one piece of Er 3+–Eu 3+ co-doped oxygen-deficient germanate glass under UV light irradiation. Blue, green, and red emissions were originated from Ge-related oxygen-deficient defect centers (GODCs), Er 3+ ions, and Eu 3+ ions, respectively. Detailed photoluminescence spectra, decay curve analyses, and electron paramagnetic resonance measurements were carried and the results indicate the existence of energy transfer between Er 3+ and Eu 3+ ions, GODCs and Eu 3+ ions.

Si3O cluster: excited properties under external electric field and oxygen-deficient defect models

This paper investigates the excited states of Si3O molecule by using the single-excitation configuration interaction and density functional theory. It finds that the visible light absorption spectrum of Si3O molecule comprises the yellow and the purple light without external electric field, however all the visible light is included except the green light under the action of external electric field. Oxygen-deficient defects, which also can be found in Si3O molecule, have been used to explain the luminescence from silicon-based materials but the microstructures of the materials are still uncertain. Our results accord with the experimental values perfectly, this fact suggests that the structure of Si3O molecule is expected to be one of the main basic structures of the materials, so the oxygen-deficient defect structural model for Si3O molecule also has been provided to research the structures of materials.

Thickness Impacts of Vacancy Defects in Epitaxial La0.7Sr0.3MnO3 Thin Films Using Slow Positron Beam

Thickness effects of thin La0.7Sr0.3MnO3 (LSMO) films on (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates were examined by a slow positron beam technique. Doppler-broadening line shape parameter S was measured as a function of thickness and differnt annealing conditions. Results reveal there could be more than one mechanism to induce vacancy-like defects. It was found that strain-induced defects mainly influence the S value of the in situ oxygen-ambience annealing LSMO thin films and the strain could vanish still faster along with the increase of thickness, and the oxygen-deficient induced defects mainly affect the S value of post-annealing LSMO films.

Synthesis of nanoparticles in laser ablation of aluminum in liquid

We report the synthesis of aluminum nanoparticles using pulsed laser ablation in water confined plasma. Nanoparticles have spherical shape and size distribution depends on laser fluence. Strong blue photoluminescence peaks at 405 nm (3.06 eV) and 430 nm (2.89 eV) due to oxygen deficient defects (F, F+, and F++ centers) is reported with different UV excitations. A comparative study of plasma in deionized water and air ambient reveals enhanced line broadening and higher electron density in water confined plasma compared to that in air, in agreement with radiative recombination model. The temporal dependence of spectral radiant energy density of plasma is also discussed.

Structure and electronic properties of step edges in the aluminum oxide film on NiAl(110)

Thin film aluminum oxide has been investigated at step edges of the NiAl(110) substrate by means of low temperature scanning tunneling microscopy and atomic force microscopy. A preference of the step edges for certain orientations and a restructuring of the substrate step edges during the oxidation were shown. The surface unit cell of the oxide film at the step edge is similarly extended as at the antiphase domain boundaries (APDBs), which are oxygen deficient defects with ${\text{F}}^{2+}$-like centers. The local electronic structure and the local work function at the step edges resemble that of the APDBs. Therefore, an oxide film structure at the step edge which is similar to the APDB as well as a carpetlike coverage of the substrate steps is concluded. This means there are ${\text{F}}^{2+}$-like centers at step edges.

Oxygen deficiency defects in amorphous Al2O3

In the electron energy loss spectra for amorphous, atomic layer deposited (ALD) Al2O3 film, a peak at 6.4 eV was observed. First principle quantum chemical simulation shows that it relates to excitation of neutral oxygen vacancy in Al2O3. The 2.91 eV luminescence excited in a band near 6.0 eV in amorphous Al2O3 is similar to that in bulk crystals which is associated with neutral oxygen vacancy. Thus, the amorphous ALD Al2O3 film is oxygen deficient and the oxygen vacancy parameters are similar in crystalline and amorphous Al2O3.

Luminescence properties of reduced SrO–Al 2O 3–GeO 2 glasses

We report on the luminescence properties of reduced SrO–Al 2O 3–GeO 2 glasses. Metal Al instead of corresponding oxide (Al 2O 3) is added into SrO–Al 2O 3–GeO 2 glasses in order to control the oxygen-deficient defects. The obtained transparent glass samples, in which Ge 2+ defects are stable, emit bright blue, white, and red light when excited by 300, 335 and 370 nm ultraviolet light, respectively. Quantities of the defects can be controlled by adjusting the amount of metal Al, resulting in tunable luminescence from blue to white and to red. The origins of different luminescence centers are discussed and the color coordinates of the photoluminescence spectra are also calculated.

Electroluminescence of as-sputtered silicon-rich SiO x films

Si-rich oxide films (SiO x, 0 < x < 2) were synthesized by reactive magnetron sputtering of a single Si target in a gas mixture of argon and oxygen. Intense visible electroluminescence was observed from the as-deposited SiO x film. The microstructure of the as-sputtered SiO x films was characterized by Raman and X-ray photoelectron spectroscopy techniques. Nanoscale amorphous Si clusters formed in the as-sputtered films. The electroluminescence was attributed to the oxygen-deficient defect luminescent centres and the formation of the amorphous Si nanoclusters.

Characterization of the anomalous luminescence properties from self-ordered porous anodic alumina with oxalic acid electrolytes

The pore height and diameter of the nanoscale structure of porous anodic alumina (PAA) film produced by the anodization technique are controllable. The structures can be applied for the fabrication of visible spectral range optical devices. In this study we characterized the luminescence properties of self-ordered PAA films evaporated onto silicon substrates. Anomalous luminescence properties produced by carrier confinement were observed in PAA films fabricated with the introduction of oxalic acid electrolytes during the anodization process. The recombination mechanisms were characterized by measuring the temperature-dependent photoluminescence (PL) spectra. The PL spectra of PAA films show an asymmetrical luminescence profile in the blue emission region. The Gaussian function divides these into two subbands. The subbands originate from two different kinds of oxygen-deficient defect centers, namely, F+ (oxygen vacancy with only one electron) and F (oxygen vacancy with two electrons) centers. The F centers are densest at the surface but show a gradual decrease with an increase in the pore wall depth and electrolyte concentration. However, the reverse trend is observed for the F+ centers. In strong contrast to the commonly expected trend of a uniform reduction in non-radiative recombination with decreasing lattice temperature, we observed an anomalous low-temperature PL growth and decline between the F and F+ centers. Theoretical models corroborate the anomalous temperature behavior. All the calculations are in agreement with the experimental observations.

In situ passivation and blue luminescence of silicon clusters using a cluster beam/H2O codeposition production method

Si clusters are produced in a gas aggregation source and fly through ultrahigh vacuum onto a cold target where they are codeposited with water vapor. Melting of the ice yields immediately a suspension of nanoparticles that emits intense, nondegrading luminescence in the blue wavelength range. Spectroscopic analysis reveals a Si/SiO core-shell structure where the luminescence stems from oxygen deficient defects. The main advantage of our production method is that it yields the luminescent Si nanoparticles in one step.

PHOTOLUMINESCENCE OF NON-CRYSTALLINE ALUMINA NANOWIRES SYNTHESIZED BY DIRECT ANODIZATION OF ALUMINUM

Alumina nanowires have been synthesized by a simple electrochemical route, by tailoring the anodization process of aluminum. Two-stage anodization of pure aluminum foils were carried out in 0.3 M oxalic acid electrolyte by maintaining a constant current density of 250 A/m2 and suitably controlling the other anodization parameters: anodization voltage, bath temperature and anodization time. The fabricated alumina nanowires were investigated by field-emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Moreover, the X-ray diffraction (XRD) study on the prepared nanowires shows that they are non-crystalline in nature. The photoluminescence (PL) spectra of alumina nanowires exhibit two stable emission bands at 438 and 581 nm. The blue luminescence behavior of the alumina nanowires are attributed to the oxygen-deficient defect centers. PL study of alumina nanowires shows that they have potential applications in light emission devices.

Photosensitivity of SiO2–Al and SiO2–Na glasses under ArF (193nm) laser

Abstract Photosensitivity of SiO 2 –Al and SiO 2 –Na glass samples was probed by means of the induced optical absorption and luminescence as well as by electron spin-resonance (ESR) after irradiation with excimer-laser photons (ArF, 193 nm). Permanent visible darkening in the case of SiO 2 –Al and transient, life time about one hour, visible darkening in the case of SiO 2 –Na was found under irradiation at 290 K. No darkening was observed at 80 K for either kind of material. This investigation is dedicated to revealing the electronic processes responsible for photosensitivity at 290 and 80 K. The photosensitivity of both materials is related to impurity defects excited directly in the case of SiO 2 –Na and/or by recapture of self-trapped holes, which become mobile at high temperature in the case of SiO 2 –Al. Electrons remain trapped on the localized states formed by oxygen deficient defects.

Effect of carbon implantation on visible luminescence and composition of Si-implanted SiO 2 layers

Ion implantation is a convenient tool for synthesis of silicon nanocrystals in SiO 2 matrix which exhibit strong red/near-IR luminescence at room temperature. Ion beams can be successfully used also for controllable modification of the nanostructures by introducing defects or changing their phase composition. In the present work, both possibilities are tested by implantation of carbon into thermal SiO 2 films either containing pre-fabricated Si nanocrystals or as-implanted with Si. In the carbon-free SiO 2 films, Si nanocrystals were synthesized at typical Si excess of about 10 at.% and annealing temperatures of 1000 and 1100 °C. It is shown that carbon ion irradiation of the Si-implanted and then annealed SiO 2 films completely quenches a luminescence band at 650–850 nm related to Si nanocrystals and gives rise to emission in the range of 350–650 nm that originated from oxygen-deficient defects. The subsequent final thermal treatment reduces concentration of the matrix defects, but only partially recovers photoluminescence from Si nanocrystals depending on the C dose. The latter is explained by the hindering effect of implanted carbon on growth and crystallization of Si phase inclusions. Strong “white” emission in the spectral range of 350–800 nm is observed only for the equal Si and C concentrations, irrespective of the sequence of carbon introduction and Si nanocrystal formation. This broad spectral band consists of the three sub-bands at around 400, 500 and 620 nm attributed to inclusions of SiC, C and Si phases, respectively. Electron spectroscopy analysis of the annealed layers confirms the presence of silicon carbide phase and carbon precipitates showing the diamond-like sp 3, not the graphitic sp 2 hybridization. The Si- and C-rich nanoclusters with a size of 3–5 nm were identified in the co-implanted films by electron microscopy as amorphous nanoparticles.

A novel approach towards the production of luminescent silicon nanoparticles: sputtering, gas aggregation and co-deposition with H2O

Silicon clusters were produced by sputtering of a p-doped Si target and aggregation of the Si atoms in an argon gas atmosphere. The clusters were deposited in ultra high vacuum onto either (i) carbon transmission electron microscope (TEM) grids or (ii) a liquid nitrogen cooled finger on which a thick layer of ice was co-deposited during the exposure to the cluster beam. The ice layer containing the clusters was melted to form a liquid sample which showed luminescence peaking at 421 nm when excited at 307.5 nm. The luminescence is attributed to electron-hole recombination in oxygen deficient defects in the Si–SiO2 interface region. TEM images of the nanoparticles deposited on the carbon grids show spherical particles with diameters ranging from 4 to 50 nm, flake-like structures or nanotube-like shapes. Grids with higher deposited densities reveal clusters that are agglomerated into chains, TEM images of the dried liquid sample show a network of fibres indicating that growth into fibres is further promoted when the clusters gain mobility in the melted ice.

镱锡共掺光纤预制棒的光敏特性和发光特性研究

Sn/Yb codoped silica optical fiber preform is prepared by the modified chemical vapor deposition (MCVD) followed by the solution-doping method. Ultraviolet (UV) optical absorption, photoluminescence (PL) spectra under 978-nm laser diode (LD) pumping, and refractive index change after exposure to 266-nm laser pulses are obtained. There is only a little change in the PL spectra while a positive refractive index change up to 2\times10^{-4} is observed after 30-min exposure to 266-nm laser pulses. The results show that both of the peculiar photosensitivity of Sn-doped silica and the gain property of Yb-doped silica fiber are preserved in the Sn/Yb codoped silica optical fiber preform. The experimental data suggest that the photosensitivity of the fiber preform under high energy density laser irradiation should be mainly due to the bond-breaking of oxygen deficient defects, while under relatively low energy density laser irradiation, the refractive index change probably originates from the photoconversion of optically active defects.