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This paper addresses the heating/cooling-induced formation, dissociation and phase separation during thermal oxidation of Sm 2 (Co, Fe, Cu, Zr) 17 alloys at 298.15 K-973 K, using real-time and room-temperature measurements. Whereas, Fe 3 O 4 forms at 673 K ≤ T ≤ 773 K, it transforms to CuFe 2 O 4 at 823 K ≤ T ≤ 973 K because of the incorporation of Cu+2 into the octahedral Fe+2 lattice sites in Fe 3 O 4. CuFe 2 O 4 dissociates instantaneously upon cooling, and separates into layered structure of Cu-oxides at oxide-surface and Fe 3 O 4 underneath. A detailed discussion on possible reaction pathways leading to these phenomena during the heating/cooling cycle is presented here. [Display omitted] • Real-time, in-situ x-ray diffractograms are recorded during oxidation of Sm 2 Co 17. • Fe 3 O 4 transforms to CuFe 2 O 4 in 823 K ≤ T ≤ 973 K due to Cu+ 2 inclusion in Fe 3 O 4. • Upon cooling from 973 K, CuFe 2 O 4 dissociates instantaneously into Fe 3 O 4 and CuO. • Phase separation happens forming Cu oxides at the surface and Fe 3 O 4 in interior. • Increased bulk copper content leads to dense, compact copper oxide surface layer. [ABSTRACT FROM AUTHOR]

Solar-driven hydrogen generation is one of the promising technologies developed to address the world's growing energy demand in an sustainable way. While, for hydrogen generation (otherwise water splitting), photocatalytic, photoelectrochemical, and PV-integrated water splitting systems employing conventional semiconductor oxides materials and their electrodes have been under investigation for over a decade, lead (Pb)- halide perovskites (HPs) made their debut in 2016. Since then, the exceptional characteristics of these materials, such as their tunable optoelectronic properties, ease of processing, high absorption coefficients, and long diffusion lengths, have positioned them as a highly promising material for solar-driven water splitting. Like in solar photovoltaics, a solar-driven water splitting field is also dominated by Pb-HPs with ongoing efforts to improve material stability and hydrogen evolution/generation rate (HER). Despite this, with the unveiling potential of various Pb-free HP compositions in photovoltaics and optoelectronics researchers were inspired to explore the potential of these materials in water splitting. In this current review, we outlined the fundamentals of water splitting, provided a summary of Pb HPs in this field, and the associated issues are presented. Subsequently, Pb-free HP compositions and strategies employed for improving the photocatalytic and/or electrochemical activity of the material are discussed in detail. Finally, this review presents existing issues and the future potential of lead-free HPs, which show potential for enhancing productivity of solar-to-hydrogen conversion technologies. [ABSTRACT FROM AUTHOR]

Solution‐processable perovskite‐based devices are potentially very interesting because of their relatively cheap fabrication cost but outstanding optoelectronic performance. However, the solution spin‐coating process involves complicated processes, including perovskite solution droplets, nucleation of perovskite, and formation of intermediate perovskite films, resulting in complicated crystallization pathways for perovskite films under annealing. Understanding and therefore controlling the fabrication process of perovskites is difficult. Recently, synchrotron radiation‐based in situ grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) techniques, which possess the advantages of high collimation, high resolution, and high brightness, have enabled to bridge complicated perovskite structure information with device performance by revealing the real‐time crystallization pathways of perovskites during the spin‐coating process. Herein, the developments of synchrotron radiation‐based in situ GIWAXS are discussed in the study of the crystallization process of perovskites, especially revealing the important crystallization mechanisms of state‐of‐the‐art perovskite optoelectronic devices with high performance. At the end, several potential applications and challenges associated with in situ GIWAXS techniques for perovskite‐based devices are highlighted. [ABSTRACT FROM AUTHOR]

Ge–Sb–Se–Te chalcogenides, namely Se-substituted Ge–Sb–Te, have been developed as an alternative optical phase change material (PCM) with a high figure-of-merit. A need for the integration of such new PCMs onto a variety of photonic platforms has necessitated the development of fabrication processes compatible with diverse material compositions as well as substrates of varying material types, shapes, and sizes. This study explores the application of chemical solution deposition as a method capable of creating conformally coated layers and delves into the resulting modifications in the structural and optical properties of Ge–Sb–Se–Te PCMs. Specifically, we detail the solution-based deposition of Ge–Sb–Se–Te layers and present a comparative analysis with those deposited via thermal evaporation. We also discuss our ongoing endeavor to improve available choice of processing-material combinations and how to realize solution-derived high figure-of-merit optical PCM layers, which will enable a new era for the development of reconfigurable photonic devices. [ABSTRACT FROM AUTHOR]

The black phase of formamidinium lead iodide (FAPbI3) perovskite shows huge promise as an efficient photovoltaic, but it is not favoured energetically at room temperature, meaning that the undesirable yellow phases are always present alongside it during crystallization1–4. This problem has made it difficult to formulate the fast crystallization process of perovskite and develop guidelines governing the formation of black-phase FAPbI3 (refs. 5,6). Here we use in situ monitoring of the perovskite crystallization process to report an oriented nucleation mechanism that can help to avoid the presence of undesirable phases and improve the performance of photovoltaic devices in different film-processing scenarios. The resulting device has a demonstrated power-conversion efficiency of 25.4% (certified 25.0%) and the module, which has an area of 27.83 cm2, has achieved an impressive certified aperture efficiency of 21.4%.The black phase of formamidinium lead iodide perovskite is used to make highly efficient solar cells, and a technique to improve its purity and stability by controlling crystal nucleation could make them even better. [ABSTRACT FROM AUTHOR]

Metal halide perovskite materials have demonstrated significant potential in various optoelectronic applications, such as photovoltaics, light emitting diodes, photodetectors, and lasers. However, the stability issues of perovskite materials continue to impede their widespread use. Many studies have attempted to understand the complex degradation mechanism and dynamics of these materials. Among them, in situ and/or operando approaches have provided remarkable insights into the degradation process by enabling precise control of degradation parameters and real-time monitoring. In this review, we focus on these studies utilizing in situ and operando approaches and demonstrate how these techniques have contributed to reveal degradation details, including structural, compositional, morphological, and other changes. We explore why these two approaches are necessary in the study of perovskite degradation and how they can be achieved by upgrading the corresponding ex situ techniques. With recent stability improvements of halide perovskite using various methods (compositional engineering, surface engineering, and structural engineering), the degradation of halide perovskite materials is greatly retarded. However, these improvements may turn into new challenges during the investigation into the retarded degradation process. Therefore, we also highlight the importance of enhancing the sensitivity and probing range of current in situ and operando approaches to address this issue. Finally, we identify the challenges and future directions of in situ and operando approaches in the stability research of halide perovskites. We believe that the advancement of in situ and operando techniques will be crucial in supporting the journey toward enhanced perovskite stability. [ABSTRACT FROM AUTHOR]

Electrons can enhance SiO2 atomic layer deposition (ALD) at low temperatures using disilane (Si2H6) and either ozone (O3/O2) or water (H2O) as reactants. SiO2 electron-enhanced ALD (EE-ALD) was demonstrated at 35 °C by exposing the sample to sequential electron, oxygen reactant, and Si2H6 exposures. The reaction sequence was electron beam exposure for 3 s, purge for 5 s, O3/O2 or H2O exposure at 0.5–1.0 Torr for 3 s, purge for 10 s, Si2H6 exposure at 100 mTorr for 1 s, and purge for 15 s. The electron exposure was an electron current of ∼150 mA for 3 s. The electrons were produced by a hollow cathode plasma electron source typically operating with a grid bias of ≈−300 V. These electrons could irradiate a sample area of ∼2 × 2 cm2. In situ spectroscopic ellipsometry measurements determined that SiO2 EE-ALD films nucleated rapidly and deposited linearly versus number of EE-ALD cycles. The SiO2 EE-ALD growth rate was 0.89 Å/cycle using O3/O2 and 0.88 Å/cycle using H2O. The SiO2 growth rate was also self-limiting at higher electron and Si2H6 exposures. In addition, SiO2 EE-ALD films were grown by changing the reaction sequence or codosing the electrons with the oxygen reactant. The SiO2 EE-ALD films could be grown on conducting silicon wafers or insulating SiO2 films. SiO2 EE-ALD is believed to be possible on insulating SiO2 films because the secondary electron yield for SiO2 at electron energies of ∼100–300 eV is greater than unity. Under these conditions, the SiO2 film charges positive during electron exposure and then pulls back secondary electrons to maintain charge neutrality. The SiO2 EE-ALD films had properties that were comparable with thermal SiO2 oxides. The refractive indices of the SiO2 EE-ALD films were similar at n = 1.44 ± 0.02 for various process conditions and equivalent to the refractive index of a wet thermal SiO2 oxide film. In addition, all the SiO2 EE-ALD films yielded etch rates in dilute buffered oxide etch solution that were only slightly higher than the etch rate of a thermal SiO2 oxide film. SiO2 EE-ALD should be useful to deposit high-quality SiO2 films for various applications at low temperatures. [ABSTRACT FROM AUTHOR]

Organometal halide perovskites have recently emerged as an appealing candidate in photovoltaic devices due to their excellent properties. Therefore, intense efforts have been devoted to find the ideal organics for perovskite solar cells. In response, we investigate the doping effect of CH3SH organic on the structure and related performance of a CH3NH3PbI3 perovskite solar cell, via in situ synchrotronbased grazing incidence X-ray diffraction (GIXRD), together with scanning electron microscopy (SEM). In situ GIXRD investigations clearly illustrated the transformation and modification of the perovskite structure induced by the organic dopant, which subsequently led to the enhancement of the power conversion efficiency of fabricated solar cells. Notably, nanoporous morphology and nanocrystalline structures were discovered in the perovskite film by SEM; they were also confirmed by the increase in broadening peaks/features in the GIXRD measurements. Overall, our study may ultimately result in an attractive strategy for the fabrication of high performance perovskite solar cells. [ABSTRACT FROM AUTHOR]

Thin, porous films of WO3 were fabricated by solution-based synthesis via spin-coating using polyethylene glycol (PEG), a block copolymer (PIB50-b-PEO45), or a combination of PEG and PIB50-b-PEO45 as structure-directing agents. The influence of the polymers on the composition and porosity of WO3 was investigated by microwave plasma atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and gas sorption analysis. The electrochromic performance of the WO3 thin films was characterized with LiClO4 in propylene carbonate as electrolyte. To analyze the intercalation of the Li+ ions, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy were performed on films in a pristine or reduced state. The use of PEG led to networks of micropores allowing fast reversible electrochromic switching with a high modulation of the optical transmittance and a high coloration efficiency. The use of PIB50-b-PEO45 provided isolated spherical mesopores leading to an electrochromic performance similar to compact WO3, only. Optimum characteristics were obtained in films which had been prepared in the presence of both, PEG and PIB50-b-PEO45, since WO3 films with mesopores were obtained that were interconnected by a microporous network and showed a clear progress in electrochromic switching beyond compact or microporous WO3. [ABSTRACT FROM AUTHOR]

The addition of molten alkali metal salts drastically accelerates the kinetics of CO2 capture by MgO through the formation of MgCO3. However, the growth mechanism, the nature of MgCO3 formation, and the exact role of the molten alkali metal salts on the CO2 capture process remain elusive, holding back the development of more-effective MgO-based CO2 sorbents. Here, we unveil the growth mechanism of MgCO3 under practically relevant conditions using a well-defined, yet representative, model system that is a MgO(100) single crystal coated with NaNO3. The model system is interrogated by in situ X-ray reflectometry coupled with grazing incidence X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. When bare MgO(100) is exposed to a flow of CO2, a noncrystalline surface carbonate layer of ca. 7-Å thickness forms. In contrast, when MgO(100) is coated with NaNO3, MgCO3 crystals nucleate and grow. These crystals have a preferential orientation with respect to the MgO(100) substrate, and form at the interface between MgO(100) and the molten NaNO3. MgCO3 grows epitaxially with respect to MgO(100), and the lattice mismatch between MgCO3 and MgO is relaxed through lattice misfit dislocations. Pyramid-shaped pits on the surface of MgO, in proximity to and below the MgCO3 crystals, point to the etching of surface MgO, providing dissolved [Mg2+...O2-] ionic pairs for MgCO3 growth. Our studies highlight the importance of combining X-rays and electron microscopy techniques to provide atomic to micrometer scale insight into the changes occurring at complex interfaces under reactive conditions. [ABSTRACT FROM AUTHOR]

We elucidate the role of subsurface oxygen on the production of C2 products from CO2 reduction over Cu electrocatalysts using the newly developed grand canonical potential kinetics density functional theory method, which predicts that the rate of C2 production on pure Cu with no O is ∼500 times slower than H2 evolution. In contrast, starting with Cu2O, the rate of C2 production is >5,000 times faster than pure Cu(111) and comparable to H2 production. To validate these predictions experimentally, we combined time-dependent product detection with multiple characterization techniques to show that ethylene production decreases substantially with time and that a sufficiently prolonged reaction time (up to 20 h) leads only to H2 evolution with ethylene production ∼1,000 times slower, in agreement with theory. This result shows that maintaining substantial subsurface oxygen is essential for long-term C2 production with Cu catalysts. [ABSTRACT FROM AUTHOR]

Surface and interface play critical roles in energy storage devices, calling for operando characterization techniques to probe the electrified surfaces/interfaces. In this work, surface science methodology, including electron spectroscopy and scanning probe microscopy, has been successfully applied to visualize electrochemical processes at operating electrode surfaces in an Al/graphite model battery. Intercalation of anions together with cations is directly observed in the surface region of a graphite electrode with tens of nanometers thickness, the concentration of which is one order higher than that in bulk. An intercalation pseudocapacitance mechanism and a double specific capacity in the electrode surface region are expected based on the super-dense intercalants and anion/cation co-intercalation, which are in sharp contrast to the battery-like mechanism in the electrode bulk. The distinct electrochemical mechanism at the electrode surface is verified by performance tests of real battery devices, showing that a surface-dominant, nanometer-thick graphite cathode outperforms a bulk-dominant, micrometer-thick graphite cathode. Our findings highlight the important surface effect of working electrodes in charge storage systems. [ABSTRACT FROM AUTHOR]

This study aims to evaluate various polymorphs of Fe2O3 (γ- and α-types) as anode material for sodium-ion batteries and their conversion mechanisms. In this work, pulsed laser deposition (PLD) was used to successfully fabricate Fe2O3 (both γ- and α-types) thin film followed by the electrochemical investigation as anode material for a sodium-ion battery. The γ-Fe2O3 shows high reversibility than α-Fe2O3 while discharging at a deep discharge voltage of 0.01 V. The α-Fe2O3 changes to Fe3O4 during sodium extraction, while the γ-Fe2O3 remains unaltered upon cycling. The γ-Fe2O3 shows high electrochemical performance regarding cycle life and discharge capacity than α-Fe2O3 (considering up to 80 cycles). The discharge capacity of γ-Fe2O3 is 335.2 mAh g−1 and of α-Fe2O3 is 248.7 mAh g−1 for the 1st cycle at a current rate of 475 mA g−1. The achieved superior performance of γ-Fe2O3 is credited to the reversible reaction path and binder-free nature of the thin film. [ABSTRACT FROM AUTHOR]

Antireflective (AR) coatings with photocatalytic activity for solar cover glasses are extensively investigated at present, mostly in multilayer systems including titania. In this study, bifunctional single coats from porous silica in combination with up to 33 mol % ceria were prepared by sol-gel dip-coating on low-iron soda-lime float glass. After heat treatment for one hour at 350 °C, the coated glasses were characterized. Solar transmittance decreased with increasing ceria content, whereas photocatalytic activity increases. Crystallization of cubic ceria was detected by grazing incidence X-ray diffraction. Chemical depth profiling by secondary neutral mass spectrometry revealed the enrichment of cerium at the coating surface as well as at the interface to the glass substrate. Self-assembled ceria crystallization at the interfaces resulted in a three-layered mesostructure of the coating, which was verified by field-emission scanning electron spectroscopy. Cubic ceria crystals at the interface act as a barrier for the sodium diffusion from the substrate, which prevents the poisoning of the photocatalyst, while those crystals at the surface act as an electron donor for photooxidation processes, both enabling adequate photocatalytic activity. The triple-layer architecture with the sequence of high/low/high refractive index materials allows for optical interference sustaining the AR-function. [ABSTRACT FROM AUTHOR]

Organometal halide perovskites have recently emerged as an appealing candidate in photovoltaic devices due to their excellent properties. Therefore, intense efforts have been devoted to find the ideal organics for perovskite solar cells. In response, we investigate the doping effect of CH3SH organic on the structure and related performance of a CH3NH3PbI3 perovskite solar cell, via in situ synchrotron- based grazing incidence X-ray diffraction (GIXRD), together with scanning electron microscopy (SEM). In situ GIXRD investigations clearly illustrated the transformation and modification of the perovskite structure induced by the organic dopant, which subsequently led to the enhance‐ ment of the power conversion efficiency of fabricated solar cells. Notably, nanoporous morphology and nanocrystal‐ line structures were discovered in the perovskite film by SEM; they were also confirmed by the increase in broad‐ ening peaks/features in the GIXRD measurements. Overall, our study may ultimately result in an attractive strategy for the fabrication of high performance perovskite solar cells.

The air/liquid interface is an excellent platform to assemble two-dimensional (2D) sheets of materials by enhancing spontaneous organizational features of the building components and encouraging large length scale in-plane growth. We have grown 2D molecularly-thin crystalline metal-organic-framework (MOF) nanosheets composed of porphyrin building units and metal-ion joints (NAFS-13) under operationally simple ambient conditions at the air/liquid interface. In-situ synchrotron X-ray diffraction studies of the formation process performed directly at the interface were employed to optimize the NAFS-13 growth protocol leading to the development of a post-injection method -post-injection of the metal connectors into the water subphase on whose surface the molecular building blocks are pre-oriented- which allowed us to achieve the formation of large-surface area morphologically-uniform preferentially-oriented single-layer nanosheets. The growth of such large-size high-quality sheets is of interest for the understanding of the fundamental physical/chemical properties associated with ultra-thin sheet-shaped materials and the realization of their use in applications. [ABSTRACT FROM AUTHOR]

The effects of the thermal processing and iron doping on RF magnetron co-sputtered barium strontium titanate thin film properties have been investigated. X-ray diffraction and Raman spectroscopy have been used to determine the structural evolution of the films as a function of the annealing temperature and the amount of iron dopant. X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy were employed to gain information about the chemical binding states and the defect structure. The enhancement of the quality factor Q, as well as the decreasing permittivity and tunability due to iron acceptor doping are demonstrated. [ABSTRACT FROM AUTHOR]

Using poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as hole conductor, a series of inverted planar CH3NH3PbI3−xClx perovskite solar cells (PSCs) were fabricated based on perovskite annealed by an improved time-temperature dependent (TTD) procedure in a flowing nitrogen atmosphere for different time. Only after an optimum annealing time, an optimized power conversion efficiency of 14.36% could be achieved. To understand their performance dependence on annealing time, an in situ real-time synchrotron-based grazing incidence X-ray diffraction (GIXRD) was used to monitor a step-by-step gradual structure transformation from distinct mainly organic-inorganic hybrid materials into highly ordered CH3NH3PbI3 crystal during annealing. However, a re-crystallization process of perovskite crystal was observed for the first time during such an annealing procedure, which helps to enhance the perovskite crystallization and preferential orientations. The present GIXRD findings could well explain the drops of the open circuit voltage (Voc) and the fill factor (FF) during the ramping of temperature as well as the optimized power conversion efficiency achieved after an optimum annealing time. Thus, the present study not only illustrates clearly the decisive roles of post-annealing in the formation of solution-processed perovskite to better understand its formation mechanism, but also demonstrates the crucial dependences of device performance on the perovskite microstructure in PSCs. [ABSTRACT FROM AUTHOR]

Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co3+/4+ ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions. [ABSTRACT FROM AUTHOR]