Post-annealing Treatment Research Articles

The BaCeO3-based composite protonic conductors prepared by Spark Plasma Sintering (SPS) and free-sintering methods

The poor chemical stability and unsatisfactory electrical conductivity of the BaCeO3-based protonic conductors may be improved by doping, by the creation of solid solutions (e.g. with BaZrO3) or by the formation of composite materials. In this work, the latter approach was used and the BaCe0·9Y0·1O3 – (Ba–Ce–Y–Si–P–O) composites were synthesized and investigated. The BaCe0·9Y0·1O3 host material and the modifier phase (6 wt%) powders were mixed by mechanical homogenization. The sintering of compacted powders was done using Spark Plasma Sintering (SPS) and the free-sintering (FS) methods, followed by the post-annealing of some samples. The influence of the sintering method and the presence of the modifier phase on the phase composition, crystallographic structure, microstructure and electrical properties were investigated. A strong influence of the sintering method on these properties was found. Also, the introduction of the modifier phase leads to considerable changes in phase composition, which are dependent on the sintering method and the post-annealing treatment. The electrical properties, determined in different gas atmospheres using the Electrochemical Impedance Spectroscopy (EIS) technique, were correlated with the phase composition and microstructure changes. The minor increase of electrical conductivity due to the introduction of the modifier phase was observed only in the case of SPS sintered samples. A detailed discussion of the observed correlations including the possible chemical composition and structural changes, mutual reactivity, amorphization, the removal of residual stress and the detailed analysis of the EIS results was done. The formation of BaCe0·9Y0·1O3 – (Ba–Ce–Y–Si–P–O) composite materials using the Spark Plasma Sintering method was found to be a promising approach towards ceramic protonic conductors with improved properties.

Electrocatalytic performance investigation of NiCo2O4 nanostructures prepared by hydrothermal method and thermal post-annealing treatment

Nickel-cobalt oxide (NiCo2O4), also known as nickel–cobalt ore, is a spinel-structured mixed oxide. It is more environmentally friendly, abundant in nature, has better electrical conductivity, and has higher electrochemical activity than two single-component oxides, nickel oxide and cobalt oxide. Here, NiCo2O4 is synthesized using a simple hydrothermal method and then annealed in the air for 3 h at 300, 350, 400 and 450 °C. The resulting materials were characterized using X-ray diffraction (XRD), Fourier-Transform-Infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), ultraviolet–visible (UV–vis) spectroscopy and electrochemical techniques. A single-phase face-centered cubic spinel structure with a nanorod-like morphology is obtained at 350 °C, and samples above this temperature show mixed phases consisting of nanowires and nanorods.. The sample annealed at 350 °C demonstrated excellent electrochemical performance for hydrogen evolution reaction (HER), with an overpotential of 435 mV at a current density of 10 mA/cm2, a pseudo-capacitance of 0.287 mF/cm2, a Tafel slope of 71 mV/dec, an exchange current density of 3.5 × 10-3 mA/cm2, and a minimum charge transfer resistance of 98 O. The study thus demonstrated the efficacy of the hydrothermal method and thermal post-annealing treatment in producing NiCo2O4 nanostructures with excellent electrocatalytic performance for energy conversion and storage applications.

Control of inhomogeneity and magnetic properties of ZnO:Co films grown by magnetron sputtering using nitrogen

We experimentally report the control of structural inhomogeneity and magnetic properties of Co-doped ZnO films using nitrogen mediated-crystallization. The ZnO:CoN were grown on a silicon substrate at room temperature by RF-magnetron sputtering using nitrogen and followed by a post-annealing treatment for 3 hours at 400 °C, 600 °C, 800 °C and 1000 °C in the air. This method induces changes in inhomogeneity properties comprised by microstructure and stoichiometry of each film, which are confirmed by X-ray diffraction, thermal desorption, and X-ray fluorescence measurements. The difference in inhomogeneity has led to the transformation in the magnetic properties. Films annealed at 400 °C, which showed the highest inhomogeneity, exhibited superparamagnetic-ferromagnetic properties. In contrast, all the other films exhibited diamagnetic properties. Increasing the post-annealing temperature above 400 °C reduces inhomogeneities indicated by improved grain size, decreased impurities, and lattice parameters and stoichiometry of ZnO:CoN films approached those of pure ZnO. Our present results will contribute to control the inhomogeneity of ZnO:Co films to improve magnetic properties at room temperature.

High‐performance perovskite/silicon heterojunction solar cells enabled by industrially compatible postannealing

AbstractIn recent years, developing dopant‐free carrier‐selective contacts, instead of heavily doped Si layer (either externally or internally), for crystalline silicon (c‐Si) solar cells have attracted considerable interests with the aim to reduce parasitic light absorption and fabrication cost. However, the stability still remains a big challenge for dopant‐free contacts, especially when thermal treatment is involved, which limits their industrial adoption. In this study, a perovskite material ZnTiO3 combining with an ultrathin (~1 nm) SiO2 film and Al layer is used as an electron‐selective contact, forming an isotype heterojunction with n‐type c‐Si. The perovskite/c‐Si heterojunction solar cells exhibit a performance‐enhanced effect by postmetallization annealing when the annealing temperature is 200–350°C. Thanks to the postannealing treatment, an impressive efficiency of 22.0% has been demonstrated, which is 3.5% in absolute value higher than that of the as‐fabricated solar cell. A detailed material and device characterization reveal that postannealing leads to the diffusion of Al into ZnTiO3 film, thus doping the film and reducing its work function. Besides, the coverage of SiO2 is also improved. Both these two factors contribute to the enhanced passivation effect and electron selectivity of the ZnTiO3‐based contact and hence improve the cell performance.

Donor:Acceptor Janus Nanoparticle-Based Films as Photoactive Layers: Control of Assembly and Impact on Performance of Devices.

Water-processable organic semiconductor nanoparticles (NPs) are considered promising materials for the next-generation of optoelectronic applications due to their controlled size, internal structure, and environmentally friendly processing. Reasonably, the controllable assembly of donor:acceptor (D:A) NPs on large areas, quality, and packing density of deposited films, as well as layer morphology, will influence the effectiveness of charge transfer at an interface and the final performance of designed optoelectronic devices.This work represents an easy and effective approach for designing self-assembled monolayers of D:A NPs. In this self-assembly procedure, the NP arrays are prepared on a large scale (2 × 2 cm2 ) at the air/water interface with controlled packing density and morphology. Due to the unique structure of individual D:A Janus particles and their assembled arrays, the Janus nanoparticle (JNP)-based device exhibits an 80% improvement of electron mobility and more balanced charge extraction compared to the conventional core-shell NP-based device. An outstanding performance of polymer solar cells with over 5% efficiency is achieved after post-annealing treatment of assembled arrays, representing one of the best results for NP-based organic photovoltaics. Ultimately, this work provides a new protocol for processing water-processable organic semiconductor colloids and future optoelectronic fabrication.

Effect of the Annealing Conditions on the Strain Responses of Lead-Free (Bi0.5Na0.5)TiO3–BaZrO3 Ferroelectric Thin Films

Bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT)–based thin films have attracted large attention for the production of modern precise micro–devices due to their outstanding strain responses. However, obtaining good electrical properties and low leakage current in BNT-based thin films is still a great challenge. In this work, 0.945(Bi0.5Na0.5)TiO3–0.055BaZrO3 (BNT–5.5BZ) thin films were deposited by the chemical solution deposition (CSD) method and annealed under two different conditions. This work describes a careful research study on the influence of the annealing conditions on the crystalline structure, morphology, and electrical performance of the BNT–5.5BZ thin films. The films exhibited a dense structure and excellent electrical properties following an optimized thermal treatment process. An ultra–high strain response of 1.5% with a low dielectric loss of ~0.03 was obtained in the BNT–5.5BZ thin films after post-annealing in an O2 atmosphere. The results of this work show that the enhanced strain response was mainly due to a reversible field-induced phase transition between the ferroelectric phase and the relaxation state. The post-annealing treatment is an effective method to optimize the electrical properties of BNT–based films, providing many opportunities for the application of ferroelectric devices.

A NiCrAlTi coating combining the tough nano-grained matrix and the soft nano-precipitate with outstanding cavitation-resistant performance

To resist the cavitation erosion occurring in the hydrodynamic system, a NiCrAlTi nanocrystalline coating was prepared by the magnetron sputtering and post-annealing treatment. The coating was composed of the tough nano-grained matrix, a large amount of soft B19′-NiTi, a few η-Ni3Ti precipitates, as well as abundant dispersed nano-twins. It showed outstanding cavitation-resistant properties compared to almost all anti-cavitation-erosion materials. Its superior cavitation-resistant property could be attributed to the tough nano-grained matrix and the soft nano-precipitates B19′. The former absorbed the cavitation energy through the high hardness and the enhanced work-hardening ability. The latter rebounded the cavitation energy through the elastic deformation and rotation behaviors.

Defect recombination suppression and carrier extraction improvement for efficient CsPbBr3/SnO2 heterojunction photodetectors

Perovskite materials with excellent optical and electronic properties have huge potential in the research field of photodetectors. Constructing heterojunctions and promoting carrier transportation are significant for the development of perovskite-based optoelectronics devices with high performances. Herein, we demonstrated a CsPbBr3/SnO2 heterojunction photodetector and improved the device performances through post-annealing treatment of SnO2 film. The results indicated that the electrical properties of SnO2 films will make an important impact on carrier extraction, especially for type-II heterojunction. As the electrons transfer layer in CsPbBr3/SnO2 type-II heterojunction, defects related to oxygen vacancy should be the key factor to affect carrier concentration, induce carriers’ limitation and recombination rate. Under proper annealing temperature for SnO2 layer, the recombination rate can decrease to 1.37 × 1021 cm3 s and the spectral responsivity will be highly increased. This work can enhance the understanding on the photoresponse of perovskite photodetectors, and will be helpful for the further optimization and design of optoelectronic devices based on the perovskite heterojunction.

Spray‐pyrolyzed Cd‐substituted kesterite thin‐films for photovoltaic applications: Post annealing conditions and property studies

Kesterite materials were investigated for their suitability as absorber layers for thin‐film photovoltaic cells. Thin-films of copper cadmium zinc tin sulfide (Cu2CdxZn1‐xSnS4) were prepared by spray pyrolysis on soda‐lime glass. The obtained thin‐films were subjected to post annealing treatment at 525 °C in a sulfur atmosphere to study the effects on morphology, stoichiometry, phase formation and optical properties by scanning electron microscopy (SEM), energy‐dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and ultraviolet visible spectroscopy (UV–Vis). The XRD patterns revealed the presence of prominent kesterite peaks in the unannealed and annealed thin‐films, with enhanced crystallinity in the annealed thin‐films. The crystal sizes of the unannealed and annealed thin‐films were estimated from the XRD data and ranged from 5 nm to 27 nm for unannealed thin‐films and 13 nm–25 nm for annealed thin‐films. The unannealed thin‐films exhibited a non‐uniformly shaped morphology, which was a mixture of cube‐shaped and rod‐shaped nanoparticles, while the annealed thin‐films exhibited a uniformly shaped morphology of flake‐shaped nanoparticles, indicating enhanced crystallinity. Chemical composition analyses revealed a divergent stoichiometry with high Cu content and deficient S content for the unannealed thin‐films, while the annealed thin‐films exhibited the desired stoichiometry, compensated by the sulfur atmosphere during the post‐annealing treatment. The UV–Vis absorption spectra showed a high absorption coefficient of more than 104 cm−1 for both the unannealed and annealed thin‐films. The bandgap energies for the unannealed thin‐films deviated from the optimum bandgap value for PV application and ranged from 2.38 eV to 1.46 eV with increasing Cd ratio, while the annealed thin‐films exhibited bandgap energies of about 1.77 eV–1.28 eV with increasing Cd ratio, indicating red‐shift absorption. Although other optical properties such as refractive index and dielectric properties were improved with the addition of Cd for unannealed thin‐films, these properties were better in the annealed thin‐films. The enhanced properties of the spray pyrolyzed Cd‐substituted thin‐films and their treatment after annealing can be explored as absorber layer deposition method and treatments to improve the performance and commercialization of kesterite thin‐film photovoltaic devices.

Initial Nucleation Approach for Large Grain-Size and High-Quality Microcrystalline Silicon Active Layer in Thin Film Transistors

High mobility and stability are critical factors for thin film transistor (TFT) device quality. These parameters are directly dependent on the crystalline structure of the active layer materials. In this paper, the early nucleation approach was performed for increasing the crystalline grain size of microcrystalline silicon (μc-Si:H) active layer for TFT device quality. The crystalline nucleation is delicately regulated in an intense hydrogen plasma environment using the plasma enhanced chemical vapor deposition (PECVD). When compared to μc-Si:H deposition without the nucleation approach, the crystalline volume factor of μc-Si:H increased from 60% to over 80% by using the nucleation technique. The nucleation increases the crystalline grain size by five orders of magnitude. Furthermore, the surface roughness of μc-Si:H is decreased from 13.7 nm to 7.1 nm. A forming-gas post-annealing treatment (≤400 °C) is used to minimize defect density. With a low microstructural factor, thermal-treated film quality improves dramatically. Nucleation approach is to be a simple and efficient for producing high-quality TFT devices.

The Multiplicity of π-π Interactions of Fused-Ring Electron Acceptor Polymorphs on the Exciton Migration and Charge Transport.

Efficient long-range exciton migration and charge transport are the key parameters for organic photovoltaic materials, which strongly depend on the molecular stacking modes. Herein, we extracted the stacked structures of the archetype fused-ring electron acceptor molecule, ITIC, based on the information on four polymorphic crystals and investigated the relationship between molecular stacking modes and exciton migration/charge transport properties through the intermolecular Coulomb coupling and charge transfer integral calculation. Experimentally, the thin film texture is crystallized through a post-annealing treatment through grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements, which lead to the enhanced exciton migration through exciton-exciton annihilation in the femtosecond transient absorption (fs-TA) measurements. This work demonstrates the relationship between the molecular arrangement and the exciton migration and electron transport and highlights the significance of optimizing molecular stacking for the development of high-performance electron acceptor materials.

Electrical characterization of sol-gel La2Ti2O7 films for resistive random access memory applications

The bipolar resistive switching (BRS) devices were investigated for RRAM applications in a MIM structure based on sol-gel derived amorphous La2Ti2O7 (LTO) thin films. The influences on the resistive switching (RS) properties according to the film thickness, electrode, annealing temperature and post metal annealing (PMA) treatment were also discussed. Moreover, RS performance of the RRAMs is affected by the work functions of electrodes. The RS characteristics of the devices are controlled by oxygen vacancies and the content of oxygen vacancies was seriously reduced after annealing, which led to a significant decrease of the endurance. In addition, PMA treatment increased the content of oxygen vacancies attributed to the forming of AlOx interface layer and made Al ions diffuse into the films to form bridges, which improved the RS performance of the devices. Consequently, the sample with 300 °C PMA exhibits the optimized RS properties with maximum switching cycles of 2674, a Ron/Roff ratio of 102, low operating voltages (VSet/VReset = 1.32 V/−1.21 V), and a retention time of over 104 s at room temperature and 85 °C, indicating the promising potential for practical RRAM applications. Conduction mechanism of all devices with Al top electrode were described by trap-controlled space-charge limited current (SCLC) and ohmic conduction.

Optimizing Photonic Annealing Technique for High-k Dielectric of Full-Solution-Processed Oxide Thin Film Transistor

In this article, it is demonstrated that the photonic annealing process of ultraviolet (UV) irradiation or rapid thermal annealing (RTA)-assisted LA technique can effectively enhance the bias and illumination stability of full-solution-processed oxide thin film transistor (TFT). Although both post-annealing treatments have comparable effects, UV irradiation has relatively less heat loss and time consumption of only 3 min, compared to the RTA process that heats at a temperature of 400 °C and holds 10 min. Depending on the laser annealing (LA)/UV technique, the amorphous hafnium-aluminum oxide (HAO) dielectric thin film exhibits a smooth surface with an rms value of 0.293 nm, a high optical bandgap of 6.19 eV, and good dielectric performance with high dielectric constants of 12.9, low leakage current densities, and high breakdown field of about 4 MV/cm. Moreover, full-solution-processed indium-tin-oxide (ITO)–HAO–tungsten-zinc-tin-oxide (WZTO) TFT shows excellent overall properties with the mobility ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> ) of 10.65 cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{2}}\cdot \text{V}^{-{1}}\cdot \text{s}^{-{1}}$ </tex-math></inline-formula> , subthreshold swing (SS) of 198 mV/dec. And the device has good bias and illumination stability, especially the threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{T}$ </tex-math></inline-formula> ) shifts are all less than 3 V under positive bias illumination stress (PBIS) and negative bias illumination stress (NBIS) testing for 10000 s. These indicate the potential for the photonic annealing process of the UV-assisted LA technique on improving the stability of the full-solution-processed TFTs, which is attributed to high-throughput fabrication for large-area, transparent, and flexible electronics.

Modifying crystallinity and mechanical properties of (CoCrNi)95.8Ce4.2 medium entropy alloy films by post-annealing treatment

In this work, (CoCrNi)95.8Ce4.2 medium entropy alloy films with amorphous and nanocrystalline phases were deposited on 304 steel substrates via radio frequency magnetron co-sputtering. The post-annealing treatment was conducted to investigate the effects of different annealing temperatures (250, 350, 450 and 500 °C) on the microstructures and mechanical properties of the films. The crystallinity increased with the increasing annealing temperature. When the films were annealed at 250 and 350 °C, some nanocrystals were formed in the amorphous matrix. Interestingly, plenty of stacking faults were observed in 450 and 500 °C annealed films because of the low stacking fault energy and annealing process. The hardness and Young's modulus were measured by nanoindentation. Both hardness and Young's modulus increased and then decreased with the increasing annealing temperature. The hardness and Young's modulus reached the maxima of 12.60 and 231.24 GPa, respectively, due to the increasing crystallinity and the formation of stacking faults at 450 °C annealing. However, in the annealing temperature range from 450 to 500 °C, hardness and Young's modulus decreased because of the grain growth. Therefore, the results of this work suggested that the moderate post-annealing treatment was beneficial to promote the formation of stacking faults and strengthen the mechanical properties.

Effect of post-annealing treatment on the thermoelectric properties of Ag2Se flexible thin film prepared by magnetron sputtering method

Flexible thermoelectric power generation devices can help solve the power supply problem of wearable electronic devices. Herein, single-phase Ag2Se films with a thickness of less than 500 nm were deposited on flexible polyimide substrates via magnetron sputtering. The microstructure, chemical composition, and thermoelectric properties of the films were investigated at different annealing temperatures (523 K–673 K). After annealing, the X-ray diffraction (XRD) test showed that the film had obvious preferential growth in the (002) and (004) crystallographic directions. Scanning electron microscopy (SEM) showed that with increasing annealing temperature, the size of the grains initially increased and subsequently decreased. Finally, after annealing at 623 K for 20 min, the film obtained a peak power factor of 526.86 μW∙m−1∙K−2. A six-leg flexible generator comprising Ag2Se films has a maximum power density of 7.52 W∙m−2 (50 K temperature difference). After 1000 bending times, the resistivity of the device changed by only 14.11 %, and the actual application test revealed an output voltage of 12.3 mV and a power of 23.49 nW under a temperature difference of 22.2 K. This work demonstrates that thermal treatment of thin films prepared by magnetron sputtering is a remarkable approach to increase thermoelectric performance, providing an efficient fabrication scheme for the development of environmentally friendly and wearable flexible thermoelectric devices.

Enhanced tribological behavior of VAlN hard ceramic coating with intermittent amorphous carbon layer

Long-term lubricate coatings over a wide temperature range are prerequisite and still facing open challenge for aero-engines and sliding components in harsh conditions. In this work, DC magnetron sputtered VAlN hard ceramic coating was modified by the subsequently post-annealing treatment with graphite powder, where the intermittent amorphous carbon (a-C) top-layer was achieved under temperature of 800 °C and high vacuum. The tribological behavior of modified VAlN coatings was investigated and the results showed that displayed the high hardness of 34.4 GPa and the excellent self-adaptive lubrication from room temperature to 600 °C. Especially, due to the benefits of lamellar sliding interface between a-C top-layer and the a-C transfer film (30 nm–68 nm), the modified coating behaved the lowest friction coefficient of 0.11 at 300 °C. However, increasing the temperature to 600 °C led to the increased and stabilized friction coefficient at 0.36–0.41, which could be attributed to the formation of V2O5 lubricating phase. Further insight into the tribological behavior of the modified VAlN coating by a-C top-layer was discussed in terms of the microstructure evolution during friction test.

Tantalum oxide and silicon oxide mixture coatings deposited using microwave plasma assisted co-sputtering for optical mirror coatings in gravitational wave detectors.

This work presents the characterization of the optical and mechanical properties of thin films based on (T a 2 O 5)1-x (S i O 2)x mixed oxides deposited by microwave plasma assisted co-sputtering, including post-annealing treatments. The deposition of low mechanical loss materials (3×10-5) with a high refractive index (1.93) while maintaining low processing costs was achieved and the following trends were demonstrated: The energy band gap increased as the S i O 2 concentration was increased in the mixture, and the disorder constant decreased when the annealing temperatures increased. Annealing of the mixtures also showed positive effects to reduce the mechanical losses and the optical absorption. This demonstrates their potential as an alternative high-index material for optical coatings in gravitational wave detectors using a low-cost process.

In-situ crystalline TiNi thin films deposited by HiPIMS at a low substrate temperature

Magnetron sputtered TiNi thin films usually exhibit an amorphous structure and need a high substrate temperature (>450 °C) or a post-annealing treatment (>500 °C) to promote crystallization. However, these treatments could extremely limit the use of low melting point substrate materials. In this study, TiNi thin films were prepared by HiPIMS using different deposition parameters. The structure and phase transformation of TiNi films were investigated. Based on SEM, XRD, TEM, DSC and electrical resistivity analysis, results show that it is possible to deposit dense crystalline TiNi thin films at a low substrate temperature (230 °C). The crystallization mechanism was also discussed. Ions energy and substrate temperatures significantly affected the formation of crystalline structures.

Positive aging in InP-based QD-LEDs encapsulated with epoxy: the role of thiol molecules and post-annealing treatment

The diffusion of thiol molecules present in epoxy resin promotes positive aging in InP-based QD-LEDs. Subsequent annealing treatment enable thiol molecules migration into lower layers, leading to a remarkable performance enhancement.

Boride-mediated synthesis of a highly active cobalt-based electrocatalyst for alkaline hydrogen evolution reaction

A post-annealing treatment of Co2B/CoO/H3BO3 could dramatically improve the alkaline HER activity.