Elevated Annealing Temperatures Research Articles

Preparation of SrVO3 by annealing of Sr2V2O7 in a reducing atmosphere

This study focuses on the synthesis of SrVO3 through the reduction of Sr2V2O7 by annealing in a reducing atmosphere. The effects of annealing temperature and annealing duration on Sr2V2O7 were investigated. The X-ray powder diffraction pattern showed that stoichiometric changes to Sr2V2O7 were achieved only at an elevated annealing temperature of 1000 °C in a reducing atmosphere, and that the desired SrVO3 was obtained only after 144 h of annealing. Further investigation of SrVO3 was performed using X-ray photoelectron spectroscopy, which confirmed that the reduction of V5+ found in Sr2V2O7 to V4+ found in SrVO3 was achieved.

Microstructural transformation and failure mechanism of CrN/CrTiSiN coatings experienced annealing post-treatment

There are great efforts for enhancing the characteristics of PVD multilayered coatings and one solution could be heat treating the coated part. The current research analyzed the effect of annealing temperatures on the microstructural transformation and failure mechanism of CrN/CrTiSiN multilayered coatings. The coatings were annealed in air at temperatures ranging from 500 °C to 1000 °C for 1 h. The characterization methods included XRD, XPS, FESEM, EDS, and Rockwell-C adhesion tests. The findings indicated that the as-deposited coating exhibited a consistent structure of the CrN phase. During the process of annealing from 500 to 700 °C, the CrN phase transforms into the Cr2N phase. At 800 °C, the structure is fully composed of Cr2N. At 900 °C, the elevated annealing temperature causes the Cr2N phase to change into the Cr2O3 phase. The volume fraction of the Cr2O3 phase increases until the temperature reaches 1000 °C. The results showed that the transition of Cr2N → Cr2O3 within the coating's thickness would lead to peeling off the coating due to an increase in the lattice volume. The EDS mapping shows that raising the annealing temperature for a constant time will result in more oxygen infiltration into the coating's thickness.

Interfacial molecular structure and orientation evolution of the polystyrene under confinement during annealing revealed by sum frequency generation vibrational spectroscopy

The geometrical confinement directly affects many crucial properties of polymer thin films by interfacial interactions. A key to understanding the role of these interfacial interactions is to specifically probe the confined interface at the molecular level and in situ. However, the direct and nondestructive detection of interfacial polymer structures under confinement is very difficult. In this study, specific interface-sensitive sum frequency generation (SFG) spectroscopy was applied to study the deuterated PS (d8-PS) film confined between hydrogenated poly (methyl methacrylate) (PMMA) films at the molecular level and in situ. The results showed that the ordering/orientation of the PS chain (backbone and phenyl group) evolved at the buried d8-PS/PMMA interface during annealing. The tilt angle of the PS phenyl group increased while the twist angle decreased with elevated annealing temperature. Both overall SFG ssp and ppp intensities decreased after annealing at 433 K for 24 h, indicating that PS chains entangled with or penetrated the PMMA chains at the confined interface. This study qualitatively and quantitatively revealed the interfacial structure and structural evolution of the PS chain confined between PMMA films in situ during annealing, which is beneficial to the molecular-level understanding of the interfacial chain conformational relaxation of polymers under confinement.

High yield stress and narrow phase transformation hysteresis of thermomechanical-processing NiTiCu shape memory alloy

NiTiCu shape memory alloy is subjected to thermomechanical processing which deals with local canning compression followed by annealing at 300, 450 and 600 °C, respectively. Transformation temperatures of annealed NiTiCu specimens increase with elevating annealing temperature. Following annealing at 300 °C, NiTiCu specimen exhibits high yield stress of about 2000 MPa due to the existence of nanocrystalline grains. NiTiCu sample annealed at 600 °C possesses an extremely narrow phase transformation hysteresis width of about 1 °C. Nanotwins are found in NiTiCu sample annealed at 300 °C, while a large number of twin variants appear in NiTiCu samples annealed at 450 and 600 °C. Nanocrystalline grains contribute to suppressing the occurrence of twin variants. Furthermore, nanocrystalline grains are not beneficial to the formation of martensite variants. In the case of compressive loading, martensite reorientation and detwinning take place more readily in NiTiCu samples annealed at 450 and 600 °C.

Influence of ex-situ annealing on the friction and wear performance of multi-layer Ti3C2Tx coatings

2D materials have gained momentum for lubrication purposes, which holds specifically true under more severe conditions such as elevated temperatures. Among them, MXenes are a new family of 2D materials, which offer an excellent electrical conductivity, tunable surface functionality, and outstanding mechanical properties. In the past five years, MXenes have been significantly studied for tribological applications due to their ability to form easy-to-shear tribofilms with excellent wear resistance. However, little is known regarding MXenes’ tribological performance at elevated temperatures. Therefore, we systematically studied the tribological performance of spray-coated Ti3C2Tx coatings after thermal annealing at temperatures between 50 and 400 °C using linear-reciprocating ball-on-disc tribometry. Advanced materials characterization demonstrated that thermal annealing of MXenes results in the release of superficial and intercalated water, the removal of surface terminations, and the oxidation of Ti3C2Tx to TiO2. Consequently, the tribological performance of the annealed coatings deteriorated, which is particularly pronounced for thin coatings, high normal loads, and elevated annealing temperatures. Our results provide insight into the thermal stability of Ti3C2Tx coatings as well as the implications on their tribological performance.

Thermal annealing of DC sputtered Nb3Sn and V3Si thin films for superconducting radio-frequency cavities

Nb 3 Sn and V3Si thin films are promising candidates for the next generation of superconducting radio-frequency (SRF) cavities. However, sputtered films often suffer from stoichiometry and strain issues. This exploratory study investigates the structural and chemical effects of thermal annealing, both in−situ and post-sputtering, on DC-sputtered Nb3Sn and V3Si films with varying thicknesses, deposited on Nb or Cu substrates. Building upon our initial studies [Howard et al., Proceedings of the SRF’21, East Lansing, MI (JACoW, 2021), p. 82.], we provide fundamental insights into recrystallization, phase changes, and the issues of stoichiometry and strain. Through annealing at 950 °C, we have successfully enabled the recrystallization of 100 nm thin Nb3Sn films on Nb substrates, yielding stoichiometric and strain-free grains. For 2 μm thick films, elevated annealing temperatures led to the removal of internal strain and a slight increase in grain size. Moreover, annealing enabled a phase transformation from an unstable to a stable structure in V3Si films, while we observed significant Sn loss in 2 μm thick Nb3Sn films after high-temperature annealing. Similarly, annealing films atop Cu substrates resulted in notable Sn and Si loss due to the generation of Cu–Sn and Cu–Si phases, followed by evaporation. These results encourage us to refine our process to obtain high-quality sputtered films for SRF use.

Synchronization of theoretical and experimental studies on the enriched optical and dielectric properties of size modulated CoCr2O4 quantum dots

This work focused on the influence of annealing temperature on CoCr2O4 nanoceramics synthesized through a co-precipitation method without the aid of surfactants or templates. The study for the first time correlated the electrical and optical properties of this nanomaterial and investigated the underlying physical concepts through probable theoretical demonstrations. Structural analysis using X-Ray diffractometry, Rietveld Refinement, and FTIR spectroscopy revealed a cubic crystal structure (space group Fd-3m) and the evolution of spinel-type AB2O4 phase. The crystallite size, determined via the Debye-Scherrer method, exhibited growth from 5.2 nm to 23.7 nm due to an increase in annealing temperature from 400 °C to 600 °C. Moreover, FESEM images exhibited an increase in grain size due to nanoparticle agglomeration at elevated annealing temperatures. The direct bandgap decreased from 2.55 eV to 2.40 eV as the annealing temperature escalated. The semi-conducting nature was also verified from Band structure, DOS, and I–V analysis. Crystallinity-mediated behaviour of various optical properties and emission spectra were carefully scrutinized. Frequency and calcination temperature-dependent dielectric properties and Nyquist plot revealed MWS-type polarization and semiconducting arc-like behaviour. The Coats and Redfern model computed activation energy of the system was 24.69 kJ/mol. These findings supported the suitability of this nanomaterial in optoelectronic applications.

The influence of Ni on the contributions of the superplastic deformation mechanisms of the Al–Zn–Mg–Cr alloys

The Ni influence on the superplastic characteristics, the microstructure evolution and the contributions of the superplastic deformation mechanisms for Al-Zn-Mg-Cr-based alloys have been investigated. The alloys contained dispersoids enriched with Cr, Mg and a minor of Zn of a mean size of 140 nm and in addition the Al3Ni phase in the alloy with nickel. Al3Ni phase increased homogeneity and stablity grain structure during elevated annealing temperature and during superplastic deformation at 440°C. The mean grain size decreases from 7.7 to 7.3 µm before the onset of the deformation and from 10 to 8.6 µm after straining of 0.69. The dislocations aggregations near Al3Ni particles were revealed. The microstructure evolution was compared at the testing condition providing a similar value of the strain rate sensitivity coefficient m≈0.6. The grain boundary sliding contribution is twofold larger and the intragranular dislocation slip is three times smaller in the alloy with Al3Ni particles compared to nickel-free alloy. Al3Ni particles leads to more equiaxed finegrain structure and an increase elongation to failure.

InP-based quantum dot lasers emitting at 1.3 µm

In this paper, we report on InP-based quantum dot (QD) lasers with InAs QDs emitting at the telecom O-band. A molecular beam epitaxy (MBE) based novel growth technique was implemented by using strained islands allowing the formation of smaller QDs by still keeping a high QD density. The laser structure is lattice matched to InP except for the active region. The active layer consists of a few monolayers (ML) thick InAs QDs which were grown on a thin GaAs nucleation layer, which enables tuning the size of the QDs. The impact of different nucleation layer structures and of the InAs growth rate on the QD formation process was investigated, with results indicating that the surface roughness of the nucleation layer and the availability of nucleation sites strongly influence adatom diffusion and the resulting QD size and uniformity. Broad area lasers were processed and exhibited a high modal gain of 78 cm−1 for 6 QD layers and an internal quantum efficiency of 0.68 for the laser treated with rapid thermal annealing (RTA) at 680 °C. A further improvement in laser performance was obtained at an elevated annealing temperature of 766 °C.

Effect of heat treatment on coupled magnetostructural transition and magnetocaloric effect of MnNiGe system

Material with coupled magnetic and structural transition is of significant interest in the field of energy-efficient technology. In this work, a sharp first-order magneto-structural transition (MST) from a ferromagnetic orthorhombic TiNiSi-type martensite phase to a paramagnetic hexagonal Ni2In-type austenite phase is observed in hexagonal Mn0.85Fe0.15NiGe compound through the heat treatment technique. Through heat treatment, the first-order MST for Mn0.85Fe0.15NiGe sample is observed to decrease drastically from 279.1 K to 211.8 K for the elevated annealing temperatures from 873 K to 1173 K. Furthermore, total entropy change (ΔS) is synergistically associated with the magnetic and structural entropy change in this system. This synergic feature governs a large ΔS ∼ 62.7 Jkg-1K−1, while magnetic entropy change is about 31.3 Jkg-1K−1 (∼52.1%) and the lattice part contributes the remaining ∼48.7% for the sample annealed at 1073 K due to the field change of 5T. In addition, a large effective refrigerant capacity reaches 226.7 Jkg−1 at 226 K for the sample due to the field change of 5T. Henceforth, this work shows an effective and efficient scheme to control the MST temperature of hexagonal phase-transition families using heat treatment method without changing the chemical composition of the sample. Our results based on heat treatment methodology provide a feasible platform for tuning MST and the associated caloric properties.

Особенности изменения интенсивностей основных полос фотолюминесценции ионов Tb-=SUP=-3+-=/SUP=- и их сателлитов в поликристаллическом люминофоре Gd-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-:Tb(3 mol%)

Samples of Gd2O3:Tb(3 mol%) phosphor were obtained by sol-gel method followed by annealing at 800oC and 1200oC in air. At high annealing temperature, the intensities of the main emission bands 484 and 541 nm increase, but the ratio of the intensities of these emission bands to their satellites 493 and 549 nm respectively decreases. Based on the analysis of X-ray diffractometry, radiation spectra, far-infrared and Raman spectroscopy, as well as diffuse reflectance spectroscopy, we established: the increase in the crystallinity of the samples with a significant reduction of the lattice strain stress at elevated annealing temperatures, changes in the structure of the bandgap with degenerated acceptor and donor zones of impurities Tb4+ and Tb3+ respectively. The diffuse reflection spectra of the sample after annealing at 800oC under optical excitation showed a direct charge transition through the bandgap with Eg = 2.56 eV. After elevated annealing temperature the concentration of Tb4+ ions decreases due to reduction to Tb3+. As a result, at low excitation energies the degeneracy of the acceptor zone is still preserved and there is a direct transition of charges through the bandgap with Eg = 2.55 eV. At high excitation energies the degeneracy of the acceptor zone is removed and there is a direct transition through the bandgap with Eg = 3.39 eV. These effects are accompanied by a relatively large increase in the emission intensity of the satellites, especially at the 549 nm.

Peculiarities of changes in the intensities of the main photoluminescence bands of Tb-=SUP=-3+-=/SUP=- ions and their satellites in polycrystalline Gd-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- : Tb(3 mol%)

Samples of Gd2O3 : Tb(3 mol%) phosphor were obtained by sol-gel method followed by annealing at 800oC and 1200oC in air. At high annealing temperature, the intensities of the main emission bands 484 and 541 nm increase, but the ratio of the intensities of these emission bands to their satellites 493 and 549 nm respectively decreases. Based on the analysis of X-ray diffractometry, emission spectra, far-infrared and Raman spectroscopy, as well as diffuse reflectance spectroscopy, we established: the increase in the crystallinity of the samples with a significant reduction of the lattice strain stress at elevated annealing temperatures, changes in the structure of the bandgap with degenerated acceptor and donor zones of impurities Tb4+ and Tb3+ respectively. The diffuse reflection spectra of the sample after annealing at 800oC under optical excitation showed a direct charge transition through the bandgap with Eg=2.56 eV. After elevated annealing temperature the concentration of Tb4+ ions decreases due to reduction to Tb3+. As a result, at low excitation energies the degeneracy of the acceptor zone is still preserved and there is a direct transition of charges through the bandgap with Eg=2.55 eV. At high excitation energies the degeneracy of the acceptor zone is removed and there is a direct transition through the bandgap with Eg=3.39 eV. These effects are accompanied by a relatively large increase in the emission intensity of the satellites, especially at the 549 nm. Keywords: Gd oxide, Tb3++ photoluminescence spectra, far infrared and Raman spectroscopy spectra, structure of the bandgape, distribution of Tb3+ and Tb4+ in cation sublattice.

Tailoring the structural and magnetic properties of self-ordered nickel nanowires created by template-assisted electrodeposition route

Thin films of vertically oriented self-ordered nickel nanowires were fabricated using the template-assisted electrodeposition method. Magnetic measurements of as-formed nanowires revealed the presence of an axial easy magnetization direction due to the shape of the nanowires. At moderate annealing temperatures, the magnetic anisotropy changed from positive to negative. This indicated easy magnetization direction flipping from axial to radial configuration. A nickel oxide phase started to grow at higher annealing temperatures with a distinct reduction in saturation magnetization due to its antiferromagnetic character. In addition, an exchange bias was observed owing to the coexistence of ferromagnetic and antiferromagnetic phases. Single-phase nickel oxide nanowires were generated at elevated annealing temperatures and exhibited an unexpected ferromagnetic behavior attributed to the incorporation of nickel ions and oxygen vacancies as suggested by ferromagnetic resonance measurements. Diffuse reflection measurements indicated an effective energy gap of 4.2 eV for nickel oxide nanowires.

Effects of post metallization annealing on Al2O3 atomic layer deposition on n-GaN

The chemical, physical and electrical properties and the robustness of post metallization annealed Al2O3 atomic layers deposited on n-type GaN are investigated in this work. Planar metal insulator capacitors are used to demonstrate a gate-first with following ohmic contacts formation at elevated temperature up to 600 °C process flow. X-ray photoelectron spectroscopy indicates that no new bonds in the Al2O3 layer are formed due to exposure to the elevated annealing temperature. X-ray diffraction measurements show no crystallization of the oxide layer. Atomic force microscopy shows signs of degradation of the sample annealed at 600 °C. Electrical measurements indicate that the elevated annealing temperature results in an increase of the oxide depletion and the deep depletion capacitances simultaneously, that results in a reduction of the flat band voltage to zero, which is explained by fixed oxide charges curing. A forward bias step stress capacitance measurement shows that the total number of induced trapped charges are not strongly affected by the elevated annealing temperatures. Interface trap density of states analysis shows the lowest trapping concentration for the capacitor annealed at 500 °C. Above this temperature, the interface trap density of states increases. When all results are taken into consideration, we have found that the process thermal budget allows for an overlap between the gate oxide post metallization annealing and the ohmic contact formation at 500 °C.

Effect of Al content on microstructure and mechanical properties of atmosphere plasma sprayed AlxCoCrFeNi high-entropy alloy coatings under post-annealing

In this work, AlxCoCrFeNi (x = 0.2, 0.5, 1.0) high-entropy alloy (HEA) coatings were fabricated by atmosphere plasma spraying (APS) and then annealed at 600, 800, 1000 °C under Ar atmosphere. The as-sprayed HEAs exhibited lamellar microstructure of alloy phase with oxide strips. The Al content showed a positive and negative correlation with the formation of BCC (A2/B2) and FCC (A1) in the coatings, respectively. A symbiotic relationship between FCC and oxides was first proposed. During annealing, the transformation from mixed BCC to A2/B2 in HEA coatings was dominated by Al content, thus leading to unique microstructure at different temperatures. The hardness of as-annealed HEAs was determined by the morphology and distribution of Al-rich BCC phase. The HEA coating with higher Al content (x = 1.0) could keep high hardness under elevated annealing temperatures. While the coating with lower Al content (x = 0.2) showed stability both in microstructure and mechanical properties.

Direct PCR with the CDC 2019 SARS-CoV-2 assay: optimization for limited-resource settings

PCR-based diagnostics generally require nucleic acid extraction from patient specimens prior to amplification. As highlighted early in the COVID-19 pandemic, extraction steps may be difficult to scale during times of massive demand and limited reagent supply. Forgoing an extraction step, we previously reported that the N1 primer/probe-set of the widespread CDC COVID-19 assay maintains high categorical sensitivity (95%) and specificity (100%) with direct inoculation of viral transport media (VTM) into qRT-PCR reactions. In contrast, the N2 set demonstrated a prominent Ct delay and low sensitivity (33%) without extraction. In the current study, we have improved the performance of this modified CDC assay (in particular the N2 set) by incorporating N1/N2/RNase P multiplexing and dissecting the effects of annealing temperature, VTM interference, and inoculum volume. The latter two factors exerted a more prominent effect on the performance of N2 than N1, although these effects were largely overcome through elevated annealing temperature. This unextracted/multiplex protocol was evaluated with 41 SARS-CoV-2 positive and 43 negative clinical samples, demonstrating a categorical sensitivity of 92.7% and specificity of 100% versus the unmodified CDC methodology. Overall, this work offers a generalizable strategy to maximize testing capabilities for COVID-19 or other emerging pathogens when resources are constrained.

Effect of intersection annealing on the microstructure and compressive properties of pure Mg processed by four-pass ambient ECAP

Intersection annealing (different time and temperature) was carried out on Fe-clad pure Mg bars processed by four-pass ambient equal channel angular pressing (ECAP). Microstructures, textures and compressive properties of the as-annealed samples were investigated in detail. The results indicate that average grain size is the finest after intersection annealing at 150 °C × 30 min. Texture intensity after intersection annealing at 200 °C × 30 min is the strongest due to preferred grain growth. Compressive yield strength (CYS) is the best after intersection annealing at 150 °C × 30 min, ultimate compressive strength (UCS) and compressive strains (CS) all decrease with increasing grain size due to elevated annealing temperatures.

Enhanced structural and morphological properties of ZnO nanorods using plant extract-assisted solution immersion method

Zinc oxide nanorods were successfully synthesized via a modified biosynthesis approach using plant extract. It consisted of two sections: first, the deposition of biosynthesized zinc oxide seed layer’s solution on a glass substrate using the spin-coat method. (using zinc nitrate hexahydrate and Pandanus amaryllifolius as a precursor and stabilizer). Second, the growth of zinc oxide nanorods on deposited biosynthesized zinc oxide seed layer using the solution immersion method. All samples were annealed at a temperature of 100 °C, 200 °C, 300 °C, 400 °C and 500 °C to observe the effect of annealing temperature on structural and morphological properties of the samples. The hexagonal wurtzite structure of zinc oxide was evident. A primary three peaks occur at 2θ = 31.78, 34.47, and 36.26, which resemble the (100), (002), and (101) zinc oxide crystallographic planes, respectively using X-ray diffraction (XRD) characterization. By using field emission scanning electron microscopy (FESEM), the smallest diameter (290 nm) of zinc oxide nanorods were demonstrated when annealed at 400 °C compared to other annealing temperatures. In addition, uniform dense rods structures were developed as annealing temperatures were increased. This study is the first to report on the ability of Pandanus amaryllifolius as an alternative stabilizer to investigate thedevelopment ofa highly crystalline and dense zinc oxide nanorods structure. It reveals that zinc oxide nanorods successfully synthesized on the biosynthesized zinc oxide seed layer. An elevated annealing temperature have demonstrated the enhancement of the structural and morphological properties of the samples. The advantages from the findings would be towards the optoelectronic applications such as ultra-violet sensors.

Appearance of inverted hysteresis, pinning effect in amorphous FeCoB ribbon with annealing: A Kerr microscopy investigation

A systematic investigation has been carried out on the magnetic domain evolution and local hysteresis behavior in iron based amorphous ribbons (FeCoB) by Kerr microscopy with annealing. Explicitly, we have studied the ‘stress’ magnetic domain structure at the strained region of the ribbon, which is likely to be caused by local residual stress present in the ribbon. It is observed that the stress magnetic domain pattern gradually vanishes at elevated annealing temperature due to thermally relieving of compressive stress. Interestingly, in the same region of the ribbon, but at different ranges of temperature annealing, we have encountered different magnetic domains mechanisms and hysteresis behavior, namely domain wall pinning, inverted hysteresis behavior, and domain wall propagation. The results are explained in terms of competition between different source of anisotropy in the ribbon emerging at different annealing temperature.

Solution processed Al-doped ZnO and its performance in dye sensitized solar cells

Al-doped ZnO rods of nanometer to sub-micrometer size range have been successfully synthesized by a simple yet cost-effective solution processed sonochemical technique. Systematic XRD analysis established the solid solubility limit for Al in the ZnO lattice to be ca. 3 mol% at an elevated annealing temperature of 800 °C. The secondary ZnAl2O4 phase appears with increasing dopant concentrations and at lower annealing temperatures. Significant variations in the optoelectronic properties are induced by modifications in the surface defects of ZnO rods as a result of Al doping. As a consequence, an improved fill factor (FF) of 74.78 and 75.76% with a conversion efficiency (η) of 1.59 and 1.79% have been achieved for the fabricated DSSC devices made of the 800 °C annealed ZnO rods doped by 1 and 3 mol% Al, respectively.