Annealing In Air Research Articles

Reactively grown Al/Si-based top coatings protecting TM-diborides (TM = W, Ti, Hf) against high-temperature oxidation

Architectural designs involving Al- and/or Si-containing top coatings present an effective approach to protect oxidation-sensitive materials such as binary transition metal (TM) diborides against high-temperature oxidation. Using reactive arc evaporation, Al-Si-N, Al-Si-O, and Si-O top coatings were applied on sputter-deposited WB1.9, TiB2.7, and HfB2.4 thin films, respectively. A pure Si adhesion layer was introduced prior to the deposition of both oxide-based top coatings (Al-Si-O & Si-O) to prevent in-situ oxidation of the diboride base layers. During thermal annealing up to 1200 °C, Al-Si-O and Si-O provided outstanding oxidation resistance on top of TiB2.7 and HfB2.4, while limited adhesion was observed on WB1.9 at elevated temperatures. Contrary, Al-Si-N protected architectures suffered from accelerated oxidation beyond 800 to 1000 °C. Isothermal annealing in ambient air at 1200 °C for 30 h confirmed the long-term stability of the oxide-based top coatings, revealing no decohesion or oxygen inward diffusion beyond the Si interlayer. Complementary TEM analysis showed that the Si-O top coating forms a dense SiO2 scale above the columnar HfB2.4, while the formation of a mullite scale (3Al2O3·2SiO2) and pronounced recrystallization is recorded for the Al-Si-O protected HfB2.4. In summary, the Al-Si-O- and Si-O-based top coatings demonstrated exceptional high-temperature oxidation resistance, fully protecting the TM-diborides from oxidative attack.

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.

Effect of annealing on the exchange coupling between magnetic phases and the exchange bias effect in Co/CoO nanocomposite

In this study, Co particles were synthesized by a polyol method, and the subsequent annealing in air was performed to prepare Co/CoO nanocomposites. Samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and magnetic measurements. SEM images of a typical nanocomposite sample pointed out the agglomeration of about 20 nm particles into micrometer-sized spheres. XRD analysis showed an increased content of the CoO phase with annealing time. The main focus was given to the effect of annealing on the exchange coupling between the Co ferromagnetic phase and the CoO antiferromagnetic phase, which in turn affects the exchange bias effect (EB) in this material. It was shown that annealing enhanced the exchange coupling between two phases leading to an increase of the exchange bias field (Heb) as compared to the unannealed sample. A value of Heb = 155 Oe was attained with annealing at a temperature of 300 °C for 90 min. The dependence of Heb on the exchange coupling between phases was discussed using a 1D-Heisenberg-model Monte Carlo simulation. Besides, the simulation also underpined the experimental data on temperature dependence of the EB and coercivity.

Enhanced performance of Cu2ZnSnS4 based bifacial solar cells with FTO and W/FTO back contacts through absorber air annealing and Na incorporation

This study reports on the influence of air annealing and Na incorporation into the absorber on the performance of Cu2ZnSnS4 (CZTS) bifacial solar cells with FTO and W/FTO back contacts. Na was incorporated by depositing ∼12 nm thick NaF on the CZTS precursors prior to the sulfurization process via thermal evaporation. After sulfurization, some of the samples were annealed in air at 300 °C for 90 s and subsequently at 200 °C for 600 s. Transmission electron microscopy confirmed sulfurization of the W interlayer to form WS2 which improves the FTO ohmicity. Na incorporation improved grain size of the absorber as revealed by scanning electron microscopy. Non-annealed samples had the unwanted SnS2 phase while the air annealed samples, particularly those with both W interlayer and Na incorporation, were exempt from SnS2 phase, as was confirmed through grazing incident X-ray diffraction and Raman spectroscopy. These results suggest that absorber air annealing and Na incorporation enhance absorber crystal growth which is advantageous in reducing bulk carrier recombination. As a result, the efficiency was significantly improved from 3.0% for solar cells fabricated directly on FTO to 5.2% for those whose absorbers were air annealed, incorporated with Na and made on W/FTO. The latter also exhibits the highest external quantum efficiency response and calculated short circuit current density for both sides illumination. This indicates that the air annealing, Na incorporation and W interlayer are enhancing the performance of bifacial CZTS solar cells with FTO back contact for both back side and front side illumination.

Crystallization features and physical properties of the thin-film heterostructure of lead zirconate titanate – lead oxide

Various diagnostic techniques aimed at studying the structure and physical properties (synchronous thermal analysis, atomic force microscopy operating in the current measurement mode, electron-probe X-ray spectral microanalysis, dynamic method for determining the pyroelectric response) were used to study the crystallization features and physical properties of the thin-film heterostructure PZT – PbO1+x formed by a two-stage technique of RF magnetron sputtering of a ceramic target. During the first stage, amorphous films were deposited on a “cold” platinized silicon substrate, while the second stage involved high-temperature annealing in air. It was shown that annealing of amorphous films and crystallization of the intermediate pyrochlore phase are accompanied by additional oxidation of the structure resulting in the formation of lead orthoplumbate and lead dioxide and additional oxidation of organic inclusions. The presence of a liquid phase of lead oxide contributes to the formation of the pyrochlore phase. It was found that lead oxide layers have significantly higher through conductivity than perovskite blocks. It was assumed that the increased conductivity of lead oxide layers is associated with lead dioxide, which has high conductive properties. Self-polarized thin films were detected to have an abnormal electrical response to the strobing thermal exposure, including the typical pyroelectric response, local photoconductivity shunted by layers of the perovskite phase, and through photoconductivity. The presence of photoconductivity is also associated with the conductive properties of lead dioxide

Study of the Structural, Electrical, and Mechanical Properties and Morphological Features of Y-Doped CeO2 Ceramics with Porous Structure

In this work, ceramic samples of cerium oxide doped with yttrium were investigated. The concentration of a dopant Y(NO3)3 varied from 5 to 25 wt% in the initial charge. In the course of the experiment, a simple method was developed to obtain ceramics with a porosity of ~20% via one-step annealing in air in a muffle furnace. For comparison, samples with two annealings were also synthesized to determine the effects of pores on electrical, structural, and mechanical characteristics. The obtained samples were examined via X-ray powder diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, Raman spectroscopy, dielectric spectroscopy, and Vickers microhardness measurements. The substitution of Ce4+ ions with Y3+ ions led to a significant decrease in the lattice parameter, average crystallite size, and average grain size, with a simultaneous increase in the lattice defectivity, dielectric constant, electrical conductivity, and microhardness values. It is shown that samples with a dopant weight fraction of 0.05–0.15 and one-step annealing have favorable electrical and mechanical characteristics for energy applications as porous materials with ionic conductivity.

Investigation of the Effect of Vacuum and Air Annealing on the Structural, Optical and Electrical Properties of Radio Frequency Sputtered WO<sub>3</sub> Thin Films

Thin films of tungsten oxide were deposited on glass substrates by the radio frequency (RF) reactive sputtering from a high purity tungsten metal target (99.9%) with a diameter of 10 cm. The reactive sputtering was carried out in an argon-oxygen gas mixture containing 20% of O2 and 80% of Ar. The used RF power is 200 W while fixing the deposition time at 120 min. Finally, the prepared films were annealed at different temperatures (350 °C, 400 °C, 450 °C, 500°C and 550 °C) for 1 hour under air and under vacuum. X-ray diffractograms showed that the deposited thin films crystallized in Hexagonal/Monoclinic WO3 phase. It was found that the crystallite size varies with the annealing temperature and the lattice parameters is a= 7.3064Å, b = 7.5292Å, c = 7.6875Å and a=b= 7.3242Å, c= 7.6624 Å, for h-WO3 and m-WO3 structures, respectively. Scanning Electron Microscopy (SEM), Raman spectra confirmed the formation of WO3 thin films. In addition, optical transmittance data revealed that the optical bandgap of the films decreases with increasing the annealing temperature. Electrical measurements revealed that annealing in air results in more resistive samples, which should be taken into account in future investigations, especially as buffer layers for efficient photovoltaic solar cells. Keywords: Vacuum, Tungsten oxide, Raman spectroscopy, RF Sputtering method, RF Power, Annealing temperature.

Dielectric and room temperature ferromagnetism in vacuum annealed Bi(Zn0.5Zr0.5)O3 modified PbTiO3 ceramics

Polycrystalline solid solutions of (1-x)PbTiO3-(x)Bi(Zn0.5Zr0.5)O3[x = 0.10, 0.20, 0.30] have been synthesized by using solid state reaction method and followed by air annealing (AA)/ vacuum annealing (VA). All the samples show single phase perovskite structure with tetragonal symmetry (P4mm). Structural parameters are calculated using the Rietveld refinement technique. With the help of Scanning Electron Microscope (SEM), the surface morphology of all the samples is recorded at room temperature. The influence of VA on dielectric parameters such as dielectric constant and tangent loss of the synthesized samples are studied and compared with that of AA samples. These results unfold superior dielectric properties of VA samples as compared to AA samples. Intriguingly, the VA samples exhibit exotic ferromagnetism in non-magnetic PbTiO3–Bi(Zn0.5Zr0.5)O3 samples, transforming these into room temperature magneto-electric multiferroics. Besides, both the ferroelectric and ferromagnetic order parameters were found to increase with the increase in Bi(Zn0.5Zr0.5)O3 doping in PbTiO3. The enhanced physical properties witnessed in VA PbTiO3–Bi(Zn0.5Zr0.5)O3 samples localized hopping of charge carriers confined to the grain.

La(Ca)CrO3-Filled SiCN Precursor Thin Film Temperature Sensor Capable to Measure up to 1100 °C High Temperature.

Thin-film sensors are regarded as advanced technologies for in situ condition monitoring of components operating in harsh environments, such as aerospace engines. Nevertheless, these sensors encounter challenges due to the high-temperature oxidation of materials and intricate manufacturing processes. This paper presents a simple method to fabricate high temperature-resistant oxidized SiCN precursor and La(Ca)CrO3 composite thin film temperature sensors by screen printing and air annealing. The developed sensor demonstrates a broad temperature response ranging from 200 °C to 1100 °C with negative temperature coefficients (NTC). It exhibits exceptional resistance to high-temperature oxidation and maintains performance stability. Notably, the sensor's resistance changes by 3% after exposure to an 1100 °C air environment for 1 h. This oxidation resistance improvement surpasses the currently reported SiCN precursor thin-film sensors. Additionally, the sensor's temperature coefficient of resistance (TCR) can reach up to -7900 ppm/°C at 200 °C. This strategy is expected to be used for other high-temperature thin-film sensors such as strain gauges, heat flux sensors, and thermocouples. There is great potential for applications in high-temperature field monitoring.

Regulation of optical, thermal, and electrical properties of GaNbO4 crystal by Mg2+ doping

In this paper, GaNbO4 crystal properties were regulated by Mg2+ doping. The refractive indexes, optical properties, and thermal properties were characterized, the influence of Mg2+ doping and air annealing on the conductivity and photoluminescence properties of GaNbO4 was systematically studied. The Mg2+ doping causes the ultraviolet absorption edge of GaNbO4 crystal blue shift, and the band gap of Mg: GaNbO4 crystal is 3.463 eV. The thermal expansion coefficient in b-direction was presented, which is -0.977 × 10−6 K−1; the high-temperature resistivity of the Mg: GaNbO4 crystal decreases from 1.7 × 109 to 3.0 × 106 W·cm in the temperature range of 500 to 800 °C, decreasing by about an order of magnitude after air annealing. The photoluminescence spectrum shows an enhanced blue emission in Mg: GaNbO4 crystals, and x-ray photoelectron spectroscopy was measured, the element's chemical states and oxygen vacancies in the crystal were analyzed. The regulation mechanism of the crystal properties was discussed in detail.

Electronic and structural disorder of NiCo2O4 nanostructures using phytochemicals from desert gourd offered efficient asymmetric supercapacitor and oxygen evolution reaction

In this study, we have utilized the raw material of desert gourd fruit juice which distributed in the wide range of desert areas of the world. The desert gourd juice carries a significant content of acidic compounds which can slightly decrease the pH of growth solution, hence it could impart a significant role in the morphological transformation. Also, the purpose of using desert gourd fruit juice was the availability of rich amount of green reducing, capping and stabilizing agents for obtaining the short range and closely packed nanoparticles of NiCo2O4. The preparation of nanostructured NiCo2O4 materials was carried out by using desert gourd fruit juice through hydrothermal process followed by thermal annealing in air. The morphology, crystalline structure, surface chemical composition and localized atomic investigations were performed by several analytical techniques. The role of desert gourd fruit juice on the structural and functional features of NiCo2O4 was also explored. The desert gourd juice through the decrease in the pH of growth solution and carrying green reducing, capping and stabilizing agents originating closely packed NiCo2O4 nanoparticles instead of nanorod like morphology. The oxygen evolution reaction (OER) half-cell characterization demonstrated overpotential of 260 mV@10 mAcm−2, Tafel slope of 62 mV dec−1 and durability of 40 h using NiCo2O4 nanostructures prepared with 2 mL of desert gourd juice. Moreover, energy storage aspects of NiCo2O4 nanostructures prepared with desert gourd juice were studied for supercapacitor application and an asymmetric supercapacitor (ASC) was developed. The findings of presented study revealed a high specific capacitance (Cs) 1958.17 F/g for newly developed ASC and high retention percentage of 99–90 % during cycling stability was also notice. The enhanced performance of as prepared NiCo2O4 nanostructures are attributed from the formation of unique architecture, surface oxygen vacancies, high ionic diffusion, high exposure of surface active sites, fast electron communication, swift charge transport at the interface between electrode and electrolyte.

Pure-Phase, Large-Grained Wide-Band-Gap Perovskite Films for High-Efficiency, Four-Terminal Perovskite/Silicon Tandem Solar Cells.

High-quality, stable perovskite films with a wide band gap between 1.65 and 1.80 eV are highly suitable for efficient and cost-competitive silicon-based tandem solar cells. Herein, we demonstrate that the combined strategies of the Pb(SCN)2 additive and air annealing can enable the Cs0.22FA0.78Pb(I0.85Br0.15)3 films with a wide band gap of 1.65 eV and favored properties including pure composition, high crystallinity, micro-sized grains, and reduced defects. With these desired films, the average efficiencies of semitransparent perovskite solar cells (PSCs) are boosted from (18.13 ± 0.31) to (20.35 ± 0.28)%. Further, the semitransparent PSC is used to assemble the four-terminal perovskite/TOPCon tandem solar cell. Benefiting from its excellent performance and preferred optical properties, the obtained tandem solar cell yields a milestone efficiency of 30.32%.

Performance optimization of nanometer-thin indium-tin oxide transistors by two-step air annealing

In this study, the influence of air annealing on nanometer-thin indium tin oxide (ITO) transistors was investigated. Compared with unannealed devices, the field-effect mobility and subthreshold swing of ultrathin ITO transistors with pre-annealing, post-annealing, and two-step annealing were greatly improved. Under a pre-annealing temperature at 200 °C and post-annealing temperature at 100 °C, the ultra-thin ITO transistors showed field-effect mobility of 34.2 cm2/Vs, steep subthreshold swing of 1.95 V/decade, and high Ion/Ioff ratio of 2.46 × 107. X-ray photoelectron spectroscopy revealed that the performance changes could be ascribed to the changes in the oxygen vacancies in the ITO channel under different annealing conditions. The dependence of subthreshold swing on the annealing process may be related to the absorption and release of water molecules from the ultrathin ITO surface. Overall, these results emphasize the importance of the annealing procedures for nanometer-thin ITO transistors.

Ellipsometric study of the porous silicon: The impact of decoration and oxidation on porosity depth profiling

The multiple-angle-of-incidence ellipsometric studies of the decoration by isopropyl alcohol of porous silicon (PSi) have been performed. The existence of a subsurface thin film of modified PSi with 5–7 % higher porosity contrary to the initial PSi layer was established. The refractive index and thickness of the film were calculated in the single-layer reflective system model. It was found that empty pores of the film after the sample was kept in isopropyl alcohol for 24 h were filled by its molecules. Thus, the effective refractive index of the modified film decreased while its thickness slightly increased. The refractive index decrease of the film over time during several months of observation is the result of the continuation of the PSi oxidation in atmospheric conditions. The work also presents the results of the PSi samples' oxidation degree by the ellipsometric method after high-temperature annealing in dry air (T = 1000 °C).

MICROSTRUCTURE OF A CrSi2 TRANSITION LAYER PRODUCED BY HOT PRESSING OF Cr AND Si

Hot pressing of a Si single crystal in the bulk of electrolytic Cr powder at 1213 K, with subsequent annealing in air, leads to the formation of an intermediate polycrystalline silicide layer at the interface between the initial components. The phase composition and microstructure of the transition layer and its vicinity were investigated by scanning electron microscopy, X-ray energy-dispersive microanalysis, and electron backscatter diffraction. The transition layer has a crystal structure of the hexagonal phase of chromium disilicide (sp. gr. P6222). An additional annealing up to 120 h leads to insignificant recrystallization of small grains into larger ones.

Synthesis, Ionic, and Phase Compositions of Ferrogarnet Y2.5Ce0.5Fe2.5Ga2.5O12

X-ray powder diffraction, X-ray photoelectron, and Mössbauer spectroscopy are used to study the ionic and phase compositions of samples of powdered ferrogarnet Y2.5Ce0.5Fe2.5Ga2.5O12 obtained by gel combustion followed by crystallization in vacuum and additional annealing in air at 750°С. According to X-ray photoelectron and Mössbauer spectroscopy data, the iron and cerium cations in the homogeneous ferrogarnet structure are stabilized in the formal oxidation state Fe3+. At the same time, along with Ce3+, the surface of Y2.5Ce0.5Fe2.5Ga2.5O12 particles contains Ce4+ ions. The results obtained can be used to create functional materials for a new generation of magnetooptical devices.

Effects of annealing environments on structural, surface topological and optical properties of Gd-doped ZnO films: a comparative study of argon and air annealing

Effects of annealing environments on structural, surface topological and optical properties of Gd-doped ZnO films: a comparative study of argon and air annealing

Investigation of the processing effect parameters on the spectroscopic properties of ZnSe nanocrys-tals for hot-pressed ceramics of the Cleartran and Multispectral classes

Problem. The problem is unavailability of inexpensive ZnSe nanocrystals for hot-pressed ceramics of the Cleartran or Multispectral classes. Goal. The goal is to investigate and improve the structural features of ZnSe nanocrystals obtained by combustion synthesis during annealing in air or nitrogen. Methodology. ZnSe nanocrystals were characterized by combustion synthesis using electron scanning microscopy, X-ray diffraction analysis, electron paramagnetic resonance, and photoluminescence analysis. Results. To improve the spectroscopic properties of ZnSe nanocrystals were synthesized by combustion synthesis method (self-propagating high-temperature synthesis) with different initial current pulses, a series of thermal annealing was carried out in the temperature range Т = 200 ÷ 800 °С with a step of Т = 100 °С at atmospheric pressure, in air or in nitrogen. The developed approach makes it possible to obtain the investigated ZnSe nanocrystals with specified properties by controlling their crystal structure. The dependences of the structure, characteristics of the magnetic field, and hyperfine structure of electron paramagnetic resonance, photoluminescence spectra during annealing in air or nitrogen from temperatures of annealing were obtained. In comparison with the initial charge, the size of nanocrystals grows by ~ 20 %, the fraction of the cubic phase increases, the parameters of nanocrystals lattice grows, and the number of dislocations and microstress decrease after annealing. It is recommended to use a current pulse of ~ 40 A, and then perform annealing at a temperature of T = 800 °C in nitrogen for the synthesis of ZnSe nanocrystals with a more perfect structure. Originality. The annealing of ZnSe nanocrystals obtained by combustion synthesis in air or nitrogen was studied. Practical value. The obtained results allow using the synthesized ZnSe nanocrystals by combustion synthesis method for various optoelectronic devices or for obtaining hot-pressed ceramics of the Cleartran or Multispectral classes.

Post deposition annealing effect on properties of CdS films and its impact on CdS/Sb2Se3 solar cells performance

Antimony selenide (Sb2Se3) is one of the emerging photovoltaic absorber materials possessing abundance and non-toxicity as the main attributes. Following CdTe technology, CdS is a widely used partner layer for Sb2Se3 solar cells. Related to CdS/Sb2Se3 device configuration, a number of studies reported findings and challenges regarding the intermixing phenomenon at the main interface and suitability of various annealing for CdS (and related interface) and still, significant room remains in developing strategies for interface optimization and understanding of the physiochemistry behind. In this perspective, this work provides a systematic investigation of the effect of vacuum and air annealing at temperatures between 200 and 400°C on the properties of CdS deposited by chemical bath deposition and combined with Sb2Se3 absorber obtained by close-spaced sublimation the direct impact of the CdS annealing on the device performance is illustrated. It is found that by varying the annealing temperature from 200 to 400°C in both, vacuum and air ambient, the morphology of CdS changes from highly dispersed small grain structure to sintered dense grains, the band gap decreases from 2.43 to 2.35 eV and the electron density drops from ∼1018 to ∼1011 cm−3. These changes were correlated with the changes in the CdS lattice and connected with the mobility of the OH group and the presence of secondary phases in CdS layers. 200°C air annealing of CdS was found as an optimal treatment resulting in 2.8% Sb2Se3/CdS cell efficiency - a 60% boost compared to the 1.8% performance of the device with as-deposited CdS. Material and device characterization analysis is performed, providing complementary insights on the interrelation between the physicochemical mechanism of the CdS annealing processes and device functionality.

Chemical Bath Deposition of α-GaOOH with Tunable Morphology on Silicon Using the pH Adjustment

The growth of GaOOH by chemical bath deposition has received great attention over the past years as a first step to form Ga2O3 with the α- or β-phases by combining a wet chemical route with thermal annealing in air. By using gallium nitrate and sodium hydroxide in aqueous solution, we show that the structural morphology of GaOOH deposits is thoroughly tunable in terms of both dimensions, density, and nature by varying the initial pH value from acidic to basic conditions. In the low-pH region associated with a low supersaturation level and where Ga3+ ions represent the dominant Ga(III) species, GaOOH microrods with a low aspect ratio and low density prevail. In the intermediate-pH region associated with a high supersaturation level and where GaOH2+ ions represent the dominant Ga(III) species, GaOOH prismatic nanorods with a high aspect ratio and high density are preferentially formed. In the high-pH region where Ga(OH)4- complexes are predominantly formed, the growth of partially crystallized GaOOH thin films with a typical thickness of about 1 μm proceeds. These findings show the correlation between the characteristics of the chemical bath and the resulting structural morphology of GaOOH deposits. They further open great perspectives to grow GaOOH and hence Ga2O3-based materials on silicon with a dedicated structural morphology using chemical bath deposition for engineering devices in the fields of gas sensing, solar-blind UV-C photodetection, and power electronics.