Chemical Annealing Research Articles

Highly‐Sensitive and High Operating Range Fully‐Printed Humidity Sensors Based on BiFeO3/BiOCl Heterojunctions

AbstractFully‐printed humidity sensors based on BiFeO3/BiOCl heterojunctions fabricated using a two‐step process with serigraphic printing are reported. Most importantly, this unique sensor architecture provides a broader relative humidity sensing range compared to pristine BFO sensors due to a synergistic effect between dense networks of BiOCl nanosheets synthetized atop BFO powders. With surface‐to‐weight ratios reaching 7.75 m2 g−1, these heterostructures increase the sensitivity and operating range of BFO‐based humidity sensors. While previously reported BFO humidity sensors only detect relative humidities above 30%, The BFO/BiOCl heterojunctions can measure relative humidities as low as 15% due to their increased surface area. Optimal growth and packing of the BiOCl nanosheet/BFO powder heterostructure are achieved by tuning the loading of the BFO powder and simultaneously forming the BiOCl sheets by chemical etching and annealing of the BFO powder. Excellent performance of optimized sensors including tracking and monitoring different types of breathing are demonstrated while mounted on an oxygen mask.

Chemical Annealing Restructures RNA for Nanopore Detection.

RNA is a key biochemical marker, yet its chemical instability and complex secondary structure hamper its integration into DNA nanotechnology-based sensing platforms. Relying on the denaturation of the native RNA structure using urea, we show that restructured DNA/RNA hybrids can readily be prepared at room temperature. Using solid-state nanopore sensing, we demonstrate that the structures of our DNA/RNA hybrids conform to the design at the single-molecule level. Employing this chemical annealing procedure, we mitigate RNA self-cleavage, enabling the direct detection of restructured RNA molecules for biosensing applications.

High-sensitivity NH3 gas detection at room temperature using In2O3 nanoparticles-modified VO2(B) nanorods heterojunction

In2O3 nanoparticles-modified VO2(B) nanorods heterojunction was proposed to improve the NH3 sensing performance at room temperature (25 ℃). VO2(B) nanorods were prepared by hydrothermal method and modified with In2O3 nanoparticles through chemical deposition and annealing. The effect of annealing temperature on microstructure and NH3 sensing performance was investigated. The morphology and crystal structure of the composite structure were characterized using SEM, TEM, and XRD. The results show that In2O3 nanoparticles with a diameter of 20–25 nm were uniformly distributed on the surface of VO2(B) nanorods when the annealing temperature was 400 ℃. Room temperature NH3 sensing performance was tested for six concentrations (1–100 ppm). Results showed that samples annealed at 400 ℃ exhibited the highest sensitivity, with a response value of up to 92 for 100 ppm NH3. This excellent sensing performance can be attributed to the excitation of electrons in narrow bandgap semiconductor VO2(B) at room temperature and the surface modification by In2O3 nanoparticles, which promote the adsorption of surface oxygen. Density functional theory indicated the composite structure has lower NH3 adsorption energy compared to VO2(B) and In2O3. A possible sensing mechanism combined heterojunction effect with hydroxylization effect was proposed to explain the sensing enhancement for composite structure.

Review of Single Crystal Synthesis of 11 Iron-Based Superconductors.

The 11 system in the iron-based superconducting family has become one of the most extensively studied materials in the research of high-temperature superconductivity, due to their simple structure and rich physical properties. Many exotic properties, such as multiband electronic structure, electronic nematicity, topology and antiferromagnetic order, provide strong support for the theory of high-temperature superconductivity, and have been at the forefront of condensed matter physics in the past decade. One noteworthy aspect is that a high upper critical magnetic field, large critical current density and lower toxicity give the 11 system good application prospects. However, the research on 11 iron-based superconductors faces numerous obstacles, mainly stemming from the challenges associated with producing high-quality single crystals. Since the discovery of FeSe superconductivity in 2008, researchers have made significant progress in crystal growth, overcoming the hurdles that initially impeded their studies. Consequently, they have successfully established the complete phase diagrams of 11 iron-based superconductors, including FeSe1-xTex, FeSe1-xSx and FeTe1-xSx. In this paper, we aim to provide a comprehensive summary of the preparation methods employed for 11 iron-based single crystals over the past decade. Specifically, we will focus on hydrothermal, chemical vapor transport (CVT), self-flux and annealing methods. Additionally, we will discuss the quality, size, and superconductivity properties exhibited by single crystals obtained through different preparation methods. By exploring these aspects, we can gain a better understanding of the advantages and limitations associated with each technique. High-quality single crystals serve as invaluable tools for advancing both the theoretical understanding and practical utilization of high-temperature superconductivity.

Neutral Silicon Vacancy Centers in Undoped Diamond via Surface Control.

Neutral silicon vacancy centers (SiV^{0}) in diamond are promising candidates for quantum applications; however, stabilizing SiV^{0} requires high-purity, boron-doped diamond, which is not a readily available material. Here, we demonstrate an alternative approach via chemical control of the diamond surface. We use low-damage chemical processing and annealing in a hydrogen environment to realize reversible and highly stable charge state tuning in undoped diamond. The resulting SiV^{0} centers display optically detected magnetic resonance and bulklike optical properties. Controlling the charge state tuning via surface termination offers a route for scalable technologies based on SiV^{0} centers, as well as charge state engineering of other defects.

(Si)GeSn Isothermal Multilayer Growth for Specific Applications Using GeH4 and Ge2H6

The experimental demonstration of Ge1-xSnx alloys lasers opened group-IV materials towards high-performance electronic and photonic devices that can be easily integrated with the current Si semiconductor technology. In recent years, GeSn-based optoelectronic devices including light-emitting and detectors, modulators, and CMOS have been proven.The major challenges for the Ge1-xSnx epitaxy arise from the low solid solubility of Sn in Ge, the large lattice mismatch, and the reduced thermal stability between Ge and Sn. All these are becoming extremely critical at higher Sn contents. Non-equilibrium conditions offered by molecular beam epitaxy (MBE), chemical vapor deposition (CVD), flash lamp, or laser annealing have been lately investigated. Between them, CVD is to date the preferred growth technique for its current development compatible with the industry offering micron-thick layers with the highest crystal quality.While Tin-tetrachloride (SnCl4) becomes the standard Sn precursor, for Ge different gasses, like germane (GeH4) and digermane (Ge2H6) are used attempting to archive high Sn incorporation and high material quality. While Ge1-xSnx films with the same high Sn content can be obtained regardless of the used precursor, the advantages and disadvantages of each precursor are discussed in this work. The use of Ge2H6 is accompanied by high growth rates, being favorable in applications where relatively thick films are needed, such as laser structures. On the other hand, with a relatively low growth rate, GeH4 provides a greater thickness control, achieving clear and sharp interfaces in heterostructures. For this reason, GeH4 is the appropriate precursor for quantum transport or spintronic.The biggest challenge in heterostructure designs is going up and down in Sn content. The growth of a Ge1-ySny on a Ge1-xSnx, y<x, or SiGeSn layer cannot be performed by increasing the growth temperature. Post-annealing processes lead to strong crystallinity degradation of the already grown layer by strong Sn diffusion or Sn segregation due to the limited thermal stability of Ge1-xSnx alloys.In this work, we address simple methodologies to enhance the gradient or step Sn content without changing the process temperature. Controlling only the carrier gas flow while keeping the standard growth parameters constant, high-quality Ge1-xSnx alloys with uniform Sn content up to 15 at.% are obtained. The proposed method acts as guidance to produce Ge1-xSnx heterostructures that can be extended to any CVD reactor, independently of the used precursor, GeH4 or Ge2H6. Different devices structures are presented proving the applicability of the isothermal multilayer growth. Figure 1

Chemically grown Bi2S3 nanorod films for hydrogen evolution

Bi2S3 nanorod films were grown on ITO-coated glass substrates through chemical bath deposition (CBD) and annealing in a sulfur atmosphere. The as-deposited films were amorphous/nanocrystalline, with a particle size of 20 nm and a direct optical band gap of 1.87 eV. Upon annealing at 350 °C, the films exhibited a nanorod morphology with a length of 300 nm. Further increasing the temperature from 400 to 450 °C resulted in an increased diameter of nanorods. The direct optical band gap decreased from 1.68 to 1.47 eV upon increasing the annealing temperature from 350 to 400 °C. Photoelectrochemical (PEC) measurements showed that the nanorod films grown on ITO-coated glass substrates exhibited significantly increased PEC activity owing to their nanorod structures. The Bi2S3 nanorod films formed at 400 °C exhibited a maximum photocurrent density of 6.1 mA/cm2 at 1 V, which was 2.5 times higher than that of the as-deposited films. The enhancement in the photocurrent density could be due to the effective visible-light absorption of Bi2S3 nanorods as a result of the increased crystallinity and decreased band gap. This study demonstrates the synthesis route involving a simple and inexpensive CBD method of Bi2S3 nanorod films for the optimized PEC water-splitting applications.

Annealing Engineering in the Growth of Perovskite Grains

Perovskite solar cells (PSCs) are a promising and fast-growing type of photovoltaic cell due to their low cost and high conversion efficiency. The high efficiency of PSCs is closely related to the quality of the photosensitive layer, and the high-quality light absorbing layer depends on the growth condition of the crystals. In the formation of high-quality crystals, annealing is an indispensable and crucial part, which serves to evaporate the solvent and drive the crystallization of the film. Various annealing methods have different effects on the promotion of the film growth process owing to the way they work. Here, this review will present a discussion of the growth puzzles and quality of perovskite crystals under different driving forces, and then explain the relationship between the annealing driving force and crystal growth. We divided the main current annealing methods into physical and chemical annealing, which has never been summarized before. The main annealing methods currently reported for crystal growth are summarized to visualize the impact of annealing design strategies on photovoltaic performance, while the growth mechanisms of thin films under multiple annealing methods are also discussed. Finally, we suggest future perspectives and trends in the industrial fabrication of PSCs in the future. The review promises industrial manufacturing of annealed PSCs. The review is expected to facilitate the industrial fabrication of PSCs.

Thin film formation of wet chemically deposited NiOx and parasitic oxides at NiOx/Si interfaces during high-temperature annealing of selective contacts in perovskite/Si tandem solar cells

Wet chemically deposited NiOx is a promising hole-transport material in perovskite/Si tandem solar cells due to its high work function, chemical stability, and low cost. However, it requires subsequent annealing that may lead to the formation of SiOz at the Si interface to the bottom cell. These layers of nm thickness exhibit non-stoichiometric chemical composition and are detrimental for charge transport and passivation. In this contribution, we investigate the atomic and electronic structure as well as chemical properties of NiOx layers on Si after wet chemical deposition and annealing in air between 200 °C and 600 °C. For this purpose, photoelectron spectroscopy, X-ray diffraction, differential thermal analysis/thermogravimetric analysis coupled with Fourier transform infrared spectroscopy, time-of-flight secondary ion mass spectrometry, and electron-energy loss spectroscopy in a scanning transmission electron microscope are applied. After deposition and annealing at 200 °C, a mixed bulk phase consisting of NiOxHy is found which transforms to pure NiOx above 300 °C. A parasitic SiOz layer is observed at the NiOx/Si interface after this process, with a thickness of 3–4 nm after annealing at 500 °C. The impact of this interfacial layer for electrical current transport will be discussed concerning optimized performance and integrability in perovskite/silicon tandems.

Optical Printing of Conductive Silver on Ultrasmooth Nanocellulose Paper for Flexible Electronics

The nanofibrillated cellulose paper (nanocellulose paper or nanopaper), which is flexible, transparent, ultrasmooth, and biodegradable, has emerged as a new substrate material for the next generation of paper‐based flexible electronics. Herein a visible light‐induced printing technique for depositing highly conductive silver (Ag) patterns on nanopaper is reported. The optical Ag printing process is simple to implement at room temperature and only requires nontoxic, low‐cost aqueous chemical solutions and an inexpensive light projection setup. The abundant carboxyl groups on the nanopaper enable efficient absorption of Ag+ions on the nanopaper surface for light‐induced reduction of Ag+into a thin film of densely packed silver nanoparticles (AgNPs). Chemical annealing of the deposited AgNPs further enhances the conductivity of the printed Ag patterns. The mechanical and electrical properties of the printed Ag patterns on nanopaper are characterized, and the application of the optical Ag printing technique fabricating the nanopaper‐based flexible circuits and electrochemical biosensors is also demonstrated. The optical printing technique will enable new designs and applications of nanopaper‐based flexible electronics.

Nanostructuring Nickel–Zinc–Boron/Graphitic Carbon Nitride as the Positive Electrode and BiVO4-Immobilized Nitrogen-Doped Defective Carbon as the Negative Electrode for Asymmetric Capacitors

Rationally designed compounds with exceptional surface functionalities are greatly necessary for efficient energy-storage technologies. Herein an aqueous battery-type hybrid supercapacitor device is fabricated based on amorphous nickel–zinc–boron/graphitic carbon nitride (Ni–Zn–B/g-C3N4) nanosheet network structures as the cathode and a bismuth vanadate-anchored carbon nanotube matrix with nitrogen dopants and defect sites (BiVO4/NC) as the anode. Interconnected nanosheet-assembled Ni–Zn–B/g-C3N4 porous networks are developed via a scalable liquid-phase reduction method, while the BiVO4/NC nanocomposite frameworks are prepared by a simple chemical precipitation route and annealing treatment. Because of the unique compositional and structural features as well as enhanced electrochemical properties, the as-assembled Ni–Zn–B/g-C3N4//BiVO4/NC aqueous alkaline device with a large working potential of 1.6 V exhibits a remarkable energy-storage capability with a high energy density of 78.4 Wh kg–1 and a power density of 907.7 W kg–1 together with a good cyclic performance (85.3% retention after 8000 cycles). Considering the intriguing results and reasonable design of the cathode and anode materials, this work provides a significant prospect for designing a high-performance energy-storage system. The intrinsically enhanced electrochemical performances of heterostructured Ni–Zn–B/g-C3N4 and BiVO4/NC demonstrate their potential utilization in energy-storage systems.

Growth and characteristics of β-Ga2O3 thin films on sapphire (0001) by low pressure chemical vapour deposition

Monoclinic β phase Ga2O3 has been considered as a promising candidate for next generation radio frequency and high-power devices because of its ultrawide bandgap and high breakdown field. The development of epitaxial growth techniques and the synthesis of high quality β-Ga2O3 thin films are crucial for the device applications. In this work, the heteroepitaxial β-Ga2O3 thin films were grown on sapphire (0001) substrates by low pressure chemical vapor deposition. The influence of growth parameters such as the source/substrate temperatures, the oxygen/Ar gas flow rates, and the surface morphology of substrate on the resultant crystallinity and surface roughness of the β-Ga2O3 films were investigated. The β-Ga2O3 heteroepitaxial layer on sapphire exhibits an RMS roughness of 1.82 nm, an XRD rocking curve of 1.18°, and a growth rate of 0.72 μm/h. The β-Ga2O3 film grown on the buffer layer exhibit a smoother surface, whereas the chemical etching and annealing lead to an improved crystallinity and a rough surface. However, there is a trade-off between the crystallization and the surface roughness.

Characterisation of High Temperature Oxidation Phenomena during AISI 430 Stainless Steel Manufacturing under a Controlled H2 Atmosphere for Bright Annealing

Localised-in-the-edge oxidation of four AISI 430 alloys was investigated after an industrial bright annealing process. The oxidised surface of each specimen was characterised by X-ray photoelectron spectroscopy (XPS), Raman-spectroscopy and SEM. The results showed that the selective oxidation of Cr and Mn took place at the coil edges of AISI 430. This led to the formation of an oxide scale based on Cr2O3 and MnCr2O4. On the other hand, the formation of Cr(OH)3 and MnOOH in the outer part of the oxide scale was related to the effect of the H2–N2 environment on the annealing furnace. The results concluded that the composition of Cr and Mn in the alloy determined the composition of the oxidation products. However, the effect of annealing time was minor in this oxidation mechanism, which slightly contributed to an increase in the cation diffusion from the steel to the oxide. Finally, the results obtained indicate that the colouration of the coil edges displayed in each studied material varies according to the alloy chemical composition and annealing time.

MOF-derived ZnCo2O4@NiCo2S4@PPy core–shell nanosheets on Ni foam for high-performance supercapacitors

The ZnCo2O4@NiCo2S4@PPy core–shell nanosheets material is prepared by directly growing leaf-like ZnCo2O4 nanosheets derived from the metal-organic framework (MOF) on Ni foam (NiF) via chemical bath deposition and annealing methods and then combining with NiCo2S4 and PPy via electrodeposition methods. The special core–shell structure formed by MOF-derived ZnCo2O4, NiCo2S4 and PPy creates a bi-interface, which could significantly promote the contact between electrode and electrolyte, provide more active sites and accelerate electron/ion transfer. And the combination of these three materials also produces a strong synergistic effect, which could further improve the capacitive performance of the electrode. Therefore, the ZnCo2O4@NiCo2S4@PPy/NiF electrode exhibits the maximum areal capacitance (3.75 F cm−2) and specific capacitance (2507.0 F g−1) at 1 mA cm−2 and 0.5 A g−1, respectively. Moreover, its capacitance retention rate is still 83.2% after 5000 cycles. In addition, a coin-type hybrid supercapacitor is assembled and displays a high energy density of 44.15 Wh kg−1 and good cycling performance.

Binder-free CuO nanoneedle arrays based tube-type sensor for H2S gas sensing

CuO nanoneedle arrays were directly prepared on the commercial ceramic tubes by magnetron sputtering and subsequent wet chemical etching and annealing. This brand-new fabrication of the tube-type gas sensor retains the high specific surface area of nanoneedle and avoids using binders that are generally used for coating gas-sensitive materials on the surface of the ceramic tube. The as-fabricated binder-free CuO nanoneedle arrays sensor exhibits a decent response of 76.50 % to 10 ppm H2S at a low temperature of 150 °C. The response decreases to 20.27 % as the relative humidity increases from 40 % to 80 %. Moreover, the sensor shows good selectivity, reproducibility, and long-term stability to a low concentration of 10 ppm H2S. This superior sensing performance can be attributed to the abundant surface reactive adsorption sites provided by CuO nanoneedle arrays and the sensitization effect of p-p nano-homojunctions that arose from the interlaced CuO nanoneedles.

Chemical passivation of the perovskite layer and its real-time effect on the device performance in back-contact perovskite solar cells

The back-contact architecture for perovskite solar cells (PSCs) offers the possibility of positioning both electrodes on one side of the absorber layer and shining light directly on the perovskite photoactive layer. This helps us to avoid the occurrence of transmission losses caused by the charge collecting transparent conductive oxide electrode in the conventional sandwich structure for PSCs. The back-contact device architecture is also useful for conducting fundamental studies as it has an exposed photoactive area, permitting in situ measurements on the effects of chemical treatment, passivation, and annealing. A successful application of back-contact PSCs in studying the effect of chemical passivation of the perovskite photo-absorber layer trap states with pyridine and its influence on the device performance have been studied. The real-time effect of pyridine vapor treatment on the device performance is visualized by monitoring the maximum power output of the devices under operation conditions. The device performance enhancement by ∼12% owing to the surface passivating effect of pyridine is demonstrated.

In situ forming microporous gelatin methacryloyl hydrogel scaffolds from thermostable microgels for tissue engineering.

Converting biopolymers to extracellular matrix (ECM)‐mimetic hydrogel‐based scaffolds has provided invaluable opportunities to design in vitro models of tissues/diseases and develop regenerative therapies for damaged tissues. Among biopolymers, gelatin and its crosslinkable derivatives, such as gelatin methacryloyl (GelMA), have gained significant importance for biomedical applications due to their ECM‐mimetic properties. Recently, we have developed the first class of in situ forming GelMA microporous hydrogels based on the chemical annealing of physically crosslinked GelMA microscale beads (microgels), which addressed several key shortcomings of bulk (nanoporous) GelMA scaffolds, including lack of interconnected micron‐sized pores to support on‐demand three‐dimensional‐cell seeding and cell–cell interactions. Here, we address one of the limitations of in situ forming microporous GelMA hydrogels, that is, the thermal instability (melting) of their physically crosslinked building blocks at physiological temperature, resulting in compromised microporosity. To overcome this challenge, we developed a two‐step fabrication strategy in which thermostable GelMA microbeads were produced via semi‐photocrosslinking, followed by photo‐annealing to form stable microporous scaffolds. We show that the semi‐photocrosslinking step (exposure time up to 90 s at an intensity of ~100 mW/cm2 and a wavelength of ~365 nm) increases the thermostability of GelMA microgels while decreasing their scaffold forming (annealing) capability. Hinging on the tradeoff between microgel and scaffold stabilities, we identify the optimal crosslinking condition (exposure time ~60 s) that enables the formation of stable annealed microgel scaffolds. This work is a step forward in engineering in situ forming microporous hydrogels made up from thermostable GelMA microgels for in vitro and in vivo applications at physiological temperature well above the gelatin melting point.

Phase change on stainless-steel mesh for promoting sulfate radical formation via peroxymonosulfate oxidation

Surface-etched and N2-annealed stainless-steel mesh (NESS) was fabricated by a chemical etching and annealing treatment under a nitrogen atmosphere of a cheap stainless-steel mesh, and employed to degrade organic pollutants via peroxymonosulfate (PMS) activation. Extensive characterization showed that surface modification could bring about phase change and metal layer generation with a thickness of several nanometers. Excellent electron conductivity and the favorable morphology with coexisting Fe, Ni, and Cr species in NESS make an effective electron transfer between catalysts and PMS. The as-prepared NESS itself can induce the PMS activation, and oxygen vacancies can strengthen chemical bonding with PMS, providing active sites to activate PMS. As a result, NESS possessed a superior activity in PMS activation for mineralization of organic compounds. Electron paramagnetic resonance and quenching experiments demonstrated SO4•−, HO•, O2•− and 1O2 were the dominant reactive species. Considering the procedure simplicity, NESS is an effective and low-cost catalyst for environmental applications.

Nanosphere lithography: the effect of chemical etching and annealing sequence on the shape and spectrum of nano-metal arrays

In this paper, it is shown that the sequence of chemical etching of the template and annealing has a significant effect on the shape and spectrum of the nano-metal arrays fabricated by nanosphere lithography (NSL). Higher nanoparticles with sharp edges are fabricated as a consequence of annealing the metal coated template, which is a 2d colloidal crystal, before chemical etching. Consequently, the absorption spectra of the fabricated sample become much sharper, in comparison with the one that is fabricated with the reversed order and also a shift is observed in the peak wavelength. The achieved result has practical importance for the applications of these nano-metal arrays in localized surface plasmon resonance (LSPR) based sensors.

Large improvement of CNT yarn electrical conductivity by varying chemical doping and annealing treatment

High conductive carbon nanotube (CNT) yarns are a near challenge to be an alternative to metal in electrical wiring. In this work, we largely improve carbon nanotube yarn electrical conductivity by chemical doping, annealing treatments (above 2000 °C) and combination of both. We present a new efficient CNT p-type dopant based on platinum chloride IV. It decreases the resistivity by a factor of 3 and is stable over half a year. The annealing treatments above 2000 °C dramatically improve the CNT structural quality by a decade. In addition, we show that the CNT yarn electrical resistivity decreases linearly with the CNT structural quality increase and we report the world record resistivity for an undoped CNT yarn spun from CNT array (0.76 mΩ cm). We reveal that the CNT structural quality is not the only factor needed to reach high electrical conductivities. The increase in CNT structural quality significantly improves the doping efficiency by a factor of 2. By systematic measurements of the CNT yarn and web resistance from 3 K to 300 K, we are able to explain the influence of the doping, annealing, compaction and CNT length on the electrical charge transport.