High-temperature Annealing In Air Research Articles

Single-Photon Emission from Point Defects in Hexagonal Boron Nitride Induced by Plasma Treatment.

Solid-state quantum emitters are gaining significant attention for many quantum information applications. Hexagonal boron nitride (h-BN) is an emerging host material for generating bright, stable, and tunable single-photon emission with narrow line widths at room temperature. In this work, we present a facile and efficient approach to generate high-density single-photon emitters (SPEs) in mechanically exfoliated h-BN through H- or Ar-plasma treatment followed by high-temperature annealing in air. It is notable that the postannealing is essential to suppress the fluorescence background in photoluminescence spectra and enhance emitter stability. These quantum emitters exhibit excellent optical properties, including high purity, brightness, stability, polarization degree, monochromaticity, and saturation intensity. The effects of process parameters on the quality of quantum emitters were systematic investigated. We find that there exists an optimal plasma power and h-BN thickness to achieve a high SPE density. This work offers a practical avenue for generating SPEs in h-BN and holds promise for future research and applications in quantum photonics.

Neuromorphic memristor based on amorphous InAlZnO film for synaptic behavior simulation

Neuromorphic computing that emulates brain behaviors can address the challenge of von Neumann bottleneck and is one of the crucial compositions of next-generation computing. Here, the polynary oxide of amorphous InAlZnO (a-IAZO)-based memristor is employed as electronic synapse with essential properties of biological synapse, including spiking timing-dependent plasticity, paired-pulse facilitation, long-term depression/potentiation, and Pavlov associative memory. Especially, the a-IAZO memristor properties are quite sensitive to the oxygen vacancy content, which exhibit stable switching and narrow distribution of Set/Reset voltage due to the oxygen vacancy content decrease after high-temperature annealing in air, showing promise for memristor performance enhancement. This work promotes the development of high-performance memristors with polynary oxide for neuromorphic computing and opens a path for a-IAZO film application in optoelectronics.

Effects of surface conditions on the visible luminescence of ZnO

The effects of surface conditions on photo-induced-carrier (PIC) diffusion are studied by solving one-dimensional continuity equation. Using various forms of ZnO samples with different surface conditions, the PICs lost at sample surface are substantiated to have important contributions to the visible luminescence. For unpassivated ZnO nanorods and single-crystal samples that undergo a high-temperature annealing in air, the visible luminescence originating from the PICs diffused to the surface is estimated more than 99.8 % and 70 % at room temperature, respectively, and more than 99.99 % and 97 % at low temperature. The structureless luminescence caused by PICs, such as the green, yellow, and orange luminescence bands are well fitted under the framework of tail-state luminescence, while the structured green band is suggested to be in association with a specific type of surface states formed during high-temperature annealing in oxidizing atmosphere and can be fitted with Huang-Rhys model by taking into account tail-state luminescence.

Synergistic Catalytic Effect of Ag and MgO Nanoparticles Supported on Defective BN Surface in CO Oxidation Reaction.

Micron-sized supports of catalytically active nanoparticles (NPs) can become a good alternative to nanocarriers if their structure is properly tuned. Here, we show that a combination of simple and easily scalable methods, such as defect engineering and polyol synthesis, makes it possible to obtain Ag and MgO nanoparticles supported on defective hexagonal BN (h-BN) support with high catalytic activity in the CO oxidation reaction. High-temperature annealing in air of Mg-containing (<0.2 at.%) h-BN micropellets led to surface oxidation, the formation of hexagonal-shaped surface defects, and defect-related MgO NPs. The enhanced catalytic activity of Ag/MgO/h-BN materials is attributed to the synergistic effect of h-BN surface defects, ultrafine Ag and MgO NPs anchored at the defect edges, and MgO/Ag heterostructures. In addition, theoretical simulations show a shift in the electron density from metallic Ag towards MgO and the associated decrease in the negative charge of oxygen adsorbed on the Ag surface, which positively affects the catalytic activity of the Ag/MgO/h-BN material.

Electron transport layer of tin dioxide deposited by reactive plasma and its application in perovskite solar cells

The electron transport layer is very important for the device efficiency and stability of perovskite solar cells. Tin dioxide is a common electron transport layer in high-efficiency solar cells and has good carrier extraction and transport capability. However, using the solution method to prepare tin dioxide, a large number of defects are generated on its surface during high-temperature annealing in air, which can degrade the electrical properties of the film, so the solution method is not conducive to preparing large-area film. In this paper, the reactive plasma deposition method is used to prepare tin dioxide thin film, and the performance of the thin film is optimized by adjusting the glow discharge time and working current. The film is applied to small-area N-I-P type perovskite solar cells, the efficiency reaching to 21.24%. The hysteresis of the device is improved by introducing stannous isooctanoate and tin dioxide as a double electron transport layer, the open circuit voltage of the solar cell increases from 1.11 to 1.15 V, the efficiency rises from 21.27% to 22.15%, and the hysteresis factor decreases from 24.04% to 3.69%. This work presents a new preparation method and effective optimization strategy to prepare tin dioxide electron transport layer, which will promote the development of planar heterojunction perovskite solar cells and provide a new research idea for preparing high-efficiency and stable perovskite solar cells.

Comprehensive microstructural and optical characterization of the thermal stability of aluminum-titanium oxynitride thin films after high temperature annealing in air

The thermal stability of two AlyTi1-y(OxN1-x) layers prepared by cathodic vacuum arc deposition with different oxygen content was studied after high temperature annealing of the samples in air. These layers were designed to be part of solar-selective coating (SSC) stacks. Compositional and microstructural characterization of the thin films was performed before and after the thermal treatment by elastic recoil detection (ERD), transmission electron microscopy, and Raman spectroscopy. AlyTi1-yN sample was stable after 2 h of annealing at 450 °C. Initial stages of the formation of a surface oxide layer after annealing at 650 °C were observed both by ERD and Raman analysis. Contrarily, no changes were found after 2 h annealing treatment either at 450 and 650 °C in the composition and microstructure of AlyTi1-y(OxN1-x) sample. In both samples, the formation of a surface anatase TiO2 film was reported after 2 h annealing at 800 °C. These compositional and microstructural changes were correlated with the optical properties determined by spectroscopic ellipsometry. A transition from metallic to dielectric behavior with increasing annealing temperature was observed. These results complete the durability studies on the designed SSC based on AlyTi1-y(OxN1-x) materials, confirming that these stacks withstand breakdown at 600 °C in air.

Microstructure and Performance Analysis of Low-Temperature Solid Oxide Fuel Cells Synthesized on Inert Al2O3 Substrates

Low-temperature solid oxide fuel cells (LT-SOFC) are usually fabricated using ultra-thin yttria-stabilized zirconia electrolyte films and Pt electrodes. This paper studies the possibility of creating LT-SOFCs using the traditional ceramic materials such as the NiO/GDC (GDC - gadolinium doped ceria) anode, GDC electrolyte, and La0.6Sr0.4CoO3 (LSC) cathode. The anode/electrolyte bilayer structure is prepared on porous anodic aluminium oxide substrates using magnetron sputtering. The microstructure of the obtained bilayer structure is investigated before and after high-temperature annealing in air. The fuel cells are fabricated with the LSC cathode; their current-voltage characteristic and electrochemical impedance spectra are measured in the temperature range of 450–600°C.

Оптическая керамика MgF2

The results of studies of the luminescent properties of ceramics of MgF2 and MgF2, doped with tungsten trioxide, synthesized in air under the influence of a pulsed electron beam are presented. The photo- and cathodoluminescence spectra and the photoluminescence excitation spectra were studied at 300 K both in as-prepared samples and in the samples after high-temperature annealing in air. The presence of two types of luminescent centers in ceramics ware discovered: electron color centers with parameters similar to those in the crystal structure of MgF2, emitting centers of the impurity type W-O-Va, and the formation of an MgO phase in annealed ceramics.

Thermal Transformation of the Surface of Mn-, W-Containing Plasma Electrolytic Oxide Coatings on Titanium

Thermal behavior of the surface of coatings formed on titanium specimens by plasma electrolytic oxidation (PEO) in phosphate—borate—tungstate electrolyte containing manganese acetate as a precursor was studied. High-temperature annealing in air allows directional obtaining of ensembles of nano- and microcrystals of definite composition and geometry on the surface of specimens with multicomponent PEO coatings.

The Influence of Thermal Treatment and Solar Radiation on the Optical Characteristics of Zinc Oxide Nanostructures

The luminescence properties of ZnO nanorods and nanocrystals after high-temperature annealing in air and exposure to strong solar radiation were studied. Under UV radiation, as-prepared nanorods and nanocrystals exhibit the luminescence spectra with maxima at 380–384 and 560–570 nm. The thermal treatment and high-intensity solar radiation of both nanostructures results in an increase in the intensity of short-wave length luminescence bands. Moreover, the long-wave luminescence band (LB) vanishes in the spectra of nanorods, and a new band at 520 nm appears in the luminescence spectra of nanocrystals. The effect of solar radiation on the properties of nanorods is more pronounced than in the case of nanocrystals, it is possible due to predominately ray heating (annealing) of nanorods than nanocrystals.

Влияние термической обработки и солнечной радиации на оптические характеристики наноструктур оксида цинка

Emission properties of ZnO nanorods and nanocrystals after high-temperature annealing in air and irradiation with high-intensity solar radiation have been studied. As-synthesized nanorods and nanocrystals under UV radiation exhibit a luminescence with maxima at around 380-384 and 560-570 nm. In both nanostructures, after heat treatment and irradiation with high-intensity solar radiation, an increase in the intensities of the short-wavelength luminescence bands is observed. In addition, after heat treatment and irradiation, in nanorods the long-wavelength luminescence band vanishes, while a new band at 520 nm appears in the luminescence spectrum of the nanocrystals. Irradiation with solar radiation has a greater effect on the emission properties of nanorods than nanocrystals and it is possible, caused by predominantly radiation heating (annealing) of nanorods than nanocrystals.

Red-emitting Lu3Al5O12: Mn transparent ceramic phosphors: valence state evolution studies of Mn ions

A red-emitting Lu3Al5O12: Mn (LuAG: Mn) transparent ceramic phosphor was successfully prepared via a two-step process: vacuum sintering and further high-temperature annealing in air. The LuAG: Mn ceramics with a transmittance of ~40% in visible light were obtained after vacuum sintering. Through the transmittance spectra, electron spin resonance measurement, cathodoluminescence technology and photoluminescence spectra, valence state evolution of Mn ions in LuAG ceramics before and after annealing were elaborately demonstrated. It's proved that part of Mn2+ were oxidized to Mn4+ during the annealing process, which is responsible for the bright red emission of the annealed sample under ultraviolet light excitation. The red-emitting LuAG: Mn transparent ceramic phosphor is a promising candidate to help make white light-emitting diodes (WLEDs) with high color rendering index.

Down-shifting emission by charge transfer band in porous silicon infiltrated with Eu3+ and Gd3+ ions

Down-shifting emission properties of europium (Eu3+) and gadolinium (Gd3+) ions incorporated in porous silicon (PS) layers are presented. Different samples were prepared by electrochemical etching of p+-type crystalline silicon wafers followed by simple impregnation with rare earth ions from nitrate solutions of europium and gadolinium and subsequent high temperature annealing in air. The samples exhibited room temperature photoluminescence (PL) and the excitation spectra present a wide excitation band around 233 nm which can be associated to the charge transfer band transitions. This band is attributed to O2−(2p)→Eu3+(4f) ligand-to-metal charge transfer. The down-shifting emission for Gd+3:Eu3+ was analyzed by a simple rate equation model to study the interaction between the O2− ions and Eu3+ ions. The exact solution of this model agrees very well with the experimental results.

Rapid low-temperature synthesis of perovskite/carbon nanocomposites as superior electrocatalysts for oxygen reduction in Zn-air batteries

The conventional ceramic synthesis of perovskite oxides involves extended high-temperature annealing in air and is unfavorable to the in situ hybridization of the conductive agent, thus resulting in large particle sizes, low surface area and limited electrochemical activities. Here we report a rapid gel auto-combustion approach for the synthesis of a perovskite/carbon hybrid at a low temperature of 180 °C. The energy-saving synthetic strategy allows the formation of small and homogeneously dispersed LaxMnO3±δ/C nanocomposites. Remarkably, the synthesized La0.99MnO3.03/C nanocomposite exhibits comparable oxygen reduction reaction (ORR) activity (with onset and peak potentials of 0.97 and 0.88 V, respectively) to the benchmark Pt/C due to the facilitated charge transfer, optimal eg electron filling of Mn, and coupled C–O–Mn bonding. Furthermore, the nanocomposite efficiently catalyzes a Zn-air battery that delivers a peak power density of 430 mW·cm−2, an energy density of 837 W·h·kgZn−1 and 340 h stability at a current rate of 10 mA·cm−2.

Effect of high-temperature annealing in air and N2 atmosphere on the mechanical properties of Si3N4 fibers

Continuous silicon nitride (Si3N4) fibers are considered as one of the most promising high-temperature wave-transparent fibers, the high-temperature performance of which need to be investigated. The Si3N4 fibers were heat-treated at elevated temperatures for different duration times in air and N2 atmosphere, respectively. The compositions, microstructures and mechanical properties were investigated by XRD, XPS, SEM and tensile strength analysis. The results show that the heat-treatment temperature, exposure time and atmosphere all have effects on the performance of the fibers. And the decrease in strength of the Si3N4 fibers annealed in N2 is due to the thermal decomposition of SixNyO and grain growth of Si3N4, while the degradation of the fibers annealed in air is mainly owing to the oxidation reactions.

Manifestation of the Sapphire Crystal Structure in the Surface Nanopattern and Its Application in the Nitride Film Growth

The “quenching” technique was used to investigate the initial stage of the formation of a terracestep nanostructure on the R-cut surface of sapphire crystal upon high-temperature annealing in air. The morphological features of the formation of A- and R-sapphire planes are experimentally shown in dependence on the misorientation direction and qualitatively interpreted with allowance for the surface energy density for the main sapphire faces. The possibilities of forming AlN layers on the R-sapphire surface with a terrace-step nanostructure under thermochemical effect and high-temperature substrate annealing in a mixture of nitrogen and reducing gases are considered.

Formation of new structural states in compressed BaTiO3 nanopowders

The structural changes in BaTiO3 nanocrystal powder and tablets have been probed via X-ray diffraction, scanning electron and transmission microscopy, and differential calorimetry after successive hightemperature annealing in air. It is shown that, beginning with the annealing temperature of 1200°C, significant amount of the Ba2TiO4 phase forms in the tablets together with the BaTiO3 phase. This phase is equilibrium one; it practically vanishes when the annealing temperature decreases to 700–600°C; and this phase practically restored to the initial state when the annealing temperature is again increased to 1200°C. Annealing the powders causes no formation of new phases, but an increase in their crystallite sizes. A probable reason of the emergence of Ba2TiO4 phase in tablets and its absence in free powder is discussed, as well.

A mixed mechanochemical-ceramic solid-state synthesis as simple and cost effective route to high-performance LiNi0.5Mn1.5O4 spinels.

The implementation of high potential materials as positive electrodes in high energy Li-ion batteries requires to develop scalable and smart synthetic routes. In the case of the LiNi0.5Mn1.5O4 (LNMO) spinel material, a successful preparation strategy must drive the phase formation in order to obtain structural, morphological and surface properties capable to boost performances in lithium cells and minimize the electrolyte degradation. Here we discuss a novel simple and easily scalable mechanochemical synthetic route, followed by a high temperature annealing in air, to prepare LMNO materials starting from oxides. A synergic doping with chromium and iron has been incorporated, resulting in the spontaneous segregation of a CrOx-rich surface layer. The effect of the annealing temperature on the physico-chemical properties of the LMNO material has been investigated as well as the effect on the performances in Li-cells.

Buried Charge at the TiO2/SrTiO3 (111) Interface and Its Effect on Photochemical Reactivity

High-temperature annealing in air is used to produce SrTiO3 (111) surfaces with two types of atomically flat terraces: those that promote photoanodic reactions and those that promote photocathodic reactions. Surface potential measurements show that the photocathodic terraces have a relatively more positive surface potential than the photoanodic terraces. After depositing thin TiO2 films on the surface, from 1 to 13 nm thick, the surface of the film above the photocathodic terraces also has photocathodic properties, similar to those of the bare surface. While a more positive surface potential can be detected on the surface of the thinnest TiO2 films (1 nm thick), it is undetectable for thicker films. The persistence of the localized photocathodic properties on the film surface, even in the absence of a measurable difference in local potential, indicates that the charge associated with specific terraces on the bare SrTiO3 (111) surface remains localized at the TiO2/SrTiO3 interface and that the buried charge influences the motion of photogenerated carriers.

Origin of polychromatic emission and defect distribution within annealed ZnO nanoparticles

Defects distribution in ZnO nano-particles is introduced by high temperature annealing in air and corresponding visible emission are comprehensively analyzed. Grain size initially increases with increasing annealing temperature until 800°C and decreases after that. Higher temperature annealing alters defect distribution and initiates formation of OZn (Zinc at oxygen site). Formation of OZn, and presence of conventional defects is confirmed by Electron Paramagnetic Resonance spectra. Spatial distribution of polychromatic emission centers in annealed sample is estimated by diffusion mediated growth and confirmed by florescence imaging. Blue emission centre is found to be located on surface of particle/grain which gets modified by surface capping using PEG and PVA. These visible emissions exhibit strong excitation dependence, and can be excited below the bad gap energy. Based on XRD, EPR, emission by low energy excitation, and florescence imaging schematic of defect distribution within particle/grain and their corresponding emission is proposed.