X-ray Photoelectron Spectroscopy Depth Profiling Research Articles

Impact of interfacial engineering on MgO-based resistive switching devices for low-power applications

In this work, the resistive switching characteristics of MgO/Al2O3-based resistive random-access memory (ReRAM) devices have been reported. Analysis shows the change in dominant conduction mechanism from space-charge-limited conduction to Schottky emission owing to the incorporation of an Al2O3 insertion layer. The MgO/Al2O3 bilayer ReRAM devices exhibit lower power operation (50.6% reduction) and better switching uniformity as compared to single-layer devices, depending on the stack configuration. This can be attributed to the lower oxygen vacancy accumulation and filament confinement at the MgO/Al2O3 interface, resulting in a more controllable switching operation. Further X-ray photoelectron spectroscopy (XPS) depth profile analysis of the bilayer device reveals that the switching dynamics are correlated directly with the oxygen vacancy concentrations. These findings indicate the importance of interfacial layer engineering in improving the resistive switching properties of MgO-based memory devices, thus allowing for low-power applications.

The pervasive presence of oxygen in ZrC

Based on the recent interest in oxy-carbide materials in catalysis, we employ a thin film model concept to highlight that variation of key reaction parameters in the reactive magnetron sputtering of zirconium carbide films (sputtering power, template temperature or reactive plasma environment) under realistic preparation and application conditions often results in zirconium oxy-carbide films of varying stoichiometry. The composition of the films grown on silicon wafers and in vacuo - cleaved NaCl (001) single crystal facets was confirmed by depth profiling X-ray photoelectron spectroscopy and electron microscopy analysis. A correlation between methane-to-argon ratio, excess carbon and template temperature with elemental composition emphasizes the exclusive presence of oxygen-containing zirconium carbides. To generalize the approach, we also show that embedding of highly ordered Cu particles with uniform sizes in zirconium oxy-carbide matrices yields well-defined metal / oxy-carbide interfaces. As the presence of an oxy-carbide and its reactivity has been inextricably linked to enhanced activity and selectivity in a variety of processes, including hydrogenation, oxidation or reduction reactions, our model thin film approach provides the necessary well-defined catalysts to derive mechanistic details and to study the decomposition/re-carburization cycles of oxy-carbides. We have exemplified the concept for zirconium oxy-carbide, but deliberate extension to similar systems is easily possible.

On the presence of oxyphosphorus bonds in TOPCon solar cell polycrystalline silicon films

The presence of silicon oxyphosphorus bonds in the heavily phosphorus (P)-doped n+-type polycrystalline silicon film (n+-poly Si) of TOPCon solar cell has been mainly revealed through a depth-profile X-ray photoelectron spectroscopy (XPS) characterization of chemical components. X-ray diffraction (XRD) pattern is applied to the verification of recrystallized phases in the n+-poly Si film, while high-resolution transmission electron microscopy (HR-TEM) with energy dispersive X-ray (EDX) pattern is used for distinguishing the crystallinity and the elemental segregation. The test sample is of a typical rear passivation contact stacks of c-Si/SiOx/n+-poly Si/SiO2, in which the n+-poly Si layer is heavily phosphorus-doped by ion implantation of as-deposited intrinsic thin film through low-pressure chemical vapor deposition (LPCVD) and recrystallization at 900 °C afterward. In the whole n+-poly Si layer, XPS P 2p electronic states at 129.8, 133.4 and 136.8 eV have been detected and assigned to be Si–P (or P–P), O–P and P–O–P bonds, respectively. In addition, the thermodynamic functions, such as the Gibbs free energy and mole formation energy of likely chemical bonds under the lowest energy as well as temperature-composition fraction (T-CF) phase diagram, are also implemented in the verification of the derivatives of phosphorus oxides.

Cu-Mg-O thin films by RF magnetron co-sputtering: Their band offsets with CdS in heterojunction solar cells

We report on Cu-Mg.O thin films of 100 - 300 nm in thickness produced by radio frequency (RF) reactive sputtering fromCu and Mg-metal targets in an argon-oxygen ambient. The amount of Mg in the thin films was varied through changingthe RF power applied at the Mg target. When the Mg content in the Cu-Mg-O film changed from 0 to 0.3, the opticalbandgap increased from 1.73 eV to 2.13 eV, and the electrical conductivity decreased from 9 x 10-3 Ω-1 cm-1(CuxO) to 6.7x 10-5 Ω-1 cm-1(Cuo7/Mg0.30). Solar cells of these films, FTO/ CdS/Cu0.85Mg0.15O/C-Ag, showed a short circuit current density of 2.86 mA/cm2 an open circuit voltage of 378 mV, and power conversion efficiency of 0.25%. X-ray photo-electron spectroscopy depth profile analyses of the interfaces suggest a negative conduction band offset in CdS/Cu0.85Mg0.15O( — 0.74 eV) as well as in CdS/CuxO (0.9 eV) solar cells.

Two Birds with One Stone: Concurrent Ligand Removal and Carbon Encapsulation Decipher Thickness-Dependent Catalytic Activity.

A carbon shell encapsulating a transition metal-based core has emerged as an intriguing type of catalyst structure, but the effect of the shell thickness on the catalytic properties of the buried components is not well known. Here, we present a proof-of-concept study to reveal the thickness effect by carbonizing the isotropic and homogeneous oleylamine (OAm) ligands that cover colloidal MoS2. A thermal treatment turns OAm into a uniform carbon shell, while the size of MoS2 monolayers remains identical. When evaluated toward an acidic hydrogen evolution reaction, the calcined MoS2 catalysts deliver a volcano-type activity trend that depends on the calcination temperature. Rutherford backscattering spectrometry and depth-profiling X-ray photoelectron spectroscopy consistently provide an accurate quantification of the carbon shell thickness. The same variation pattern of catalytic activity and carbon shell thickness, aided by kinetic studies, is then persuasively justified by the respective limitations of electron and proton conductivities on the two branches of the volcano curve.

Mo-doped Cr-Ti-Mo ternary o-MAX with ultra-low wear at elevated temperatures

In this work, the Cr-Ti-Mo ternary o-MAX ceramics based on the Cr2TiAlC2 phase are synthesized, and their tribological performance at elevated temperatures up to 800 ºC in the air is evaluated. With Si3N4 as a tribocouple, an unexpected ultra-low wear rate reaching 6.1 × 10−8 mm3 N−1 m−1 is observed in Cr1.9Ti0.9Mo0.2AlC2 at 800 ºC, accompanied by a stable coefficient of friction (COF) around 0.33 in a wide temperature range. X-ray photoelectron spectroscopy (XPS) depth profiling confirms a tribofilm with gradient composition, which simultaneously offers fluid lubricating at elevated temperatures and self-healing after cooling. Particularly, confirmed by the theoretical simulations, the doping of Mo improves the interlayer binding as well as alters the oxidation behaviors of Cr2TiAlC2. With an optimal interlayer binding strength and oxidation rate, the Cr1.9Ti0.9Mo0.2AlC2 can generate a tribofilm possessing ideal composition, which simultaneously promotes lubrication and anti-wear performance at elevated temperatures.

XPS investigation of 5N purity Al thin foils for MEMS devices

Thin Al foils are promising materials for applications in devices of microelectromechanical systems (MEMS). In this work, three foils of high purity (5N) Al with different thickness (10, 50, and 125 μm) were analyzed by means of X‐ray photoelectron spectroscopy (XPS), before and after annealing (720 K for 30 min). XPS surface analysis and depth profiling of chemical composition were performed to investigate the distribution of Al oxide. Electron energy loss spectroscopy (EELS) measurements were also carried out in order to identify the plasmon losses and chemical state of Al. The loss peaks in the 5N‐Al thin foils were compared with those of an Al foil of commercial purity (99.95 wt%). The thickness of the oxide layer on the sample surface of all the samples is not constant and oxide is thicker in the samples of high purity than in those of commercial quality. Moreover, the thinnest foils of 5N‐Al (10 μm) exhibit the thinnest oxide layer. These findings have been discussed by considering the size effect, that is, mechanical properties of thin foils are improving as the thickness decreases. The complex morphology of the metal‐oxide interface may contribute to enhance the mechanical performances of Al foils with a thickness below ~50 μm, because the free dislocations pile up against the interface which represents an obstacle for their motion hindering plastic deformation. Obtained results suggest that Al foils to be used in MEMS devices should be of high purity and annealed to get a surface completely covered by the oxide layer.

Multi-dimensional characterizations of washing durable ZnO/phosphazene-siloxane coated fabrics via ToF-SIMS and XPS

The poor washing durability of nylon fabric coating hinders their applications. Here, by spray coating zinc oxide (ZnO) and APESP siloxane on the surface of nylon 6, we find that the washing durability of the coated fabric could be enhanced dramatically. To reveal its mechanism, the microstructure of the fabric was investigated via Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), respectively. It was found that the ratio of ZnO and APESP can significantly influent the acquired fabric morphology. XPS depth profiling results further suggest the crosslinked network of the ZnO/APESP on the fabric surface. Moreover, the formation of Si–O–Zn bonds confirmed by the modified auger parameter can enhance the washing durability of the fabric coating. Moreover, the characterization methods introduced in this paper, in particular the UB mode, which can be applied into ToF-SIMS measurements to obtain 2D mapping and model construction results with higher spatial resolution, thus providing guidelines for future nanoscale researches.

In2S3-Gr and In2S3-CNT nanocomposite thin films as gas sensors

The present work reports the response of the In2S3-Gr and In2S3-CNT nanocomposite thin film sensors in the presence of interfering vapours such as alcohols like ethanol and methanol, ketone like acetone and inorganic gas like ammonia. We also investigated the variation in gas sensing properties with change in thickness of the nanocomposite thin films. The structural, topological, compositional and optical analysis of samples are performed using X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and UV–Vis-NIR spectroscopy. The lattice strain, the crystallite size and dislocation density of as-deposited films were obtained from XRD analysis. The thickness of the films and surface roughness are determined by AFM analysis. The XPS depth profile affirms the presence of In, S, C and O in all the samples. From optical absorption studies, bandgap was determined and this is compared with thickness of the films. As the thickness increases, the bandgap energy of the In2S3-Gr/In2S3-CNT nanocomposite thin film decreases from 2.52/2.75 eV to 2.05/2.42 eV. The gas sensing parameters such as sensitivity, response time and recovery time of all the samples are determined. From the experiment, it is obtained that the triple dip In2S3-Gr nanocomposite thin film with the highest root mean square roughness and the lowest bandgap energy shows the highest gas sensing efficiency and have better sensitivity to ethanol vapour.

Interfacial bonding flame retarded coating of nylon 6: Anti-dropping, self-extinguishment and water-proof

Melt-dripping is one of the key focuses for flame retardant modification research of nylon 6 (PA6). In this paper, amine-activated cyclotriphosphazene containing siloxane (N-APESP) was prepared via two-step synthesis of cyclotriphosphazene, KH550 and 1,3-propane diamine. Then, Si-O-Si crosslinking structure containing cyclotriphosphazene, called Si-CP structure, was formed on the PA6 surface by interfacial bonding and hydrolytic condensation of N-APESP. The interfacial bonding among Si-CP structure, melamine (MA) and PA6 via the reaction of aldehyde and amino, was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was verified that there was 2–5 μm Si-CP coating containing on the PA6 surface by means of XPS depth profiling. The test results showed that the interfacial bonding Si-CP coating improved the anti-dropping, self-extinguishment and water-proof of PA6 plates. The water proof of the specimens were retained, especially for MA/PA6, with water contact angle of more than 90°. Compared with the UL-94 V-2 rating of the contrast specimens, the interfacial bonding made Si-CP@(10%MA/PA6) reach V-0 rating because of anti-dropping and after-flame time reduction. Meanwhile, the after-flame time of Si-CP@PA6 and Si-CP@(5%MA/PA6) was reduced by 76.34% and 77.56%, respectively. The flame-retardancy mechanism of the Si-CP coating was explored by thermogravimetry, cone calorimetry and char residue characterization. It was Si-CP coating that played an important role in the formation of strengthened expanded bubbly structure with rich P and Si during heating and combustion, so that the barrier effect was enhanced and the melting droplet problem was solved.

Effects of mineral surface silanization and bitumen coating on its filtration from an aqueous slurry

The effects of residual bitumen on oil sands tailings filtration have rarely been examined. In the present work, the filtration of bitumen-coated minerals, including quartz, rutile, kaolinite, and montmorillonite, was studied. Bitumen-coated quartz was compared with silanized quartz to decouple the effects of surface hydrophobicity and adsorbed bitumen layer on filtration. The minerals were treated in bitumen-toluene solutions with different bitumen concentrations. The treated minerals were subjected to vaccum filtration and their wettability was measured by sessile drop contact angle method. It was found that the filtration rate of silanized quartz was linearly correlated with contact angle. It was also observed that at low bitumen concentration, the contact angle and filtration rate of all tested minerals were increased. However, at high bitumen concentration, the filtration rates were reduced drastically despite the high contact angle. CHNS elemental analyses, and X-ray photoelectron spectroscopy surface composition and depth profile analyses showed that the minerals had higher C, N, S contents and thicker bitumen layer when they were treated at higher bitumen concentration. It was hypothesized that under the pressure gradient during filtration, the thick and patchy bitumen coating layers could inter-penetrate when the mineral particles were pushed together, to form a inter-locked film to close off the pores in the filter cake. Indeed, mineral-bitumen aggregates were observed by X-ray microscope/nanoCT imaging of the filter cake. It was concluded that a thin layer of bitumen coating helped filtration due to the induced hydrophobicity, but a thick (and patchy) bitumen coating impeded filtration.

Quantification of the Activator and Sensitizer Ion Distributions in NaYF4 :Yb3+ , Er3+ Upconverting Nanoparticles Via Depth-Profiling with Tender X-Ray Photoemission.

The spatial distribution and concentration of lanthanide activator and sensitizer dopant ions are of key importance for the luminescence color and efficiency of upconverting nanoparticles (UCNPs). Quantifying dopant ion distributions and intermixing, and correlating them with synthesis methods require suitable analytical techniques. Here, X-ray photoelectron spectroscopy depth-profiling with tender X-rays (2000-6000eV), providing probe depths ideally matched to UCNP sizes, is used to measure the depth-dependent concentration ratios of Er3+ to Yb3+ , [Er3+ ]/[Yb3+ ], in three types of UCNPs prepared using different reagents and synthesis methods. This is combined with data simulations and inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurements of the lanthanide ion concentrations to construct models of the UCNPs' dopant ion distributions. The UCNP sizes and architectures are chosen to demonstrate the potential of this approach. Core-only UCNPs synthesized with XCl3 ·6H2 O precursors (β-phase) exhibit a homogeneous distribution of lanthanide ions, but a slightly surface-enhanced [Er3+ ]/[Yb3+ ] is observed for UCNPs prepared with trifluroacetate precursors (α-phase). Examination of Yb-core@Er-shell UCNPs reveals a co-doped, intermixed region between the single-doped core and shell. The impact of these different dopant ion distributions on the UCNP's optical properties is discussed to highlight their importance for UCNP functionality and the design of efficient UCNPs.

The oxidation behaviors of high-purity niobium for superconducting radio-frequency cavity application in vacuum heat treatment

To explore the impact mechanism of vacuum heat treatment on the performance of Superconducting Radio-Frequency (SRF) Cavities, especially in the medium temperature range (300–400 °C), the chemical composition on the surfaces and the impurities distribution along the depth of the high-purity niobium (Nb) samples heat-treated at 250–800 °C in Ultra High Vacuum (UHV) were investigated using X-ray photoelectron spectroscopy (XPS). The XPS results on the surface showed that the surface oxide composition varied with the different heat-treatment temperatures. Among the range of 250–600 °C, Nb2O5 gradually reduces and suboxide such as NbO, Nb2O, and NbOx gradually enhances with the increasing of heat-treatment temperature. However, an elevated proportion of Nb2O5 was shown on the sample heat-treated at 800 °C. The XPS depth profiles acquired by different times of Ar+ etching revealed that the oxygen concentration in depths increased after heat treatment in UHV and presented a temperature dependence, while the nitrogen was not precisely identified. This work might also contribute to understanding the effect of material properties on the RF performance and help to optimize the surface-treatment process for SRF Nb cavities.

Surface chemical and geometrical properties of pure copper powder intended for binder jetting and sintering

One novel important application of sinter‐based additive manufacturing involving binder jetting is copper‐based products. Three different variants of nominally pure copper powder having particle size distributions with D90 < 16, 22, or 31 μm were investigated in this study. The packing behavior and the flow properties using dynamic test and shear cell, as well as specific surface area were evaluated. The analyses employed illustrate the multidimensional complexity. Because different measurements capture different aspect of the powder, it is imperative to apply a characterization approach involving different methods. Surface chemical analysis by means of X‐ray photoelectron spectroscopy (XPS) showed that all powder variants were covered by Cu2O, CuO, and Cu (OH)2, with Cu2O being dominant in all cases. The finest powder with D90 < 16 μm tended to have higher relative amount of copper in divalent state. The average apparent oxide thickness estimated by XPS depth profiling showed that the two coarser variants had similar overall average oxide thickness, whereas the finest one possessed smaller oxide thickness. The surface chemistry of the powder grades is found to be related to their rheological behavior in dynamic condition. Considering the specific surface areas in combination with the average oxide thicknesses, the amount of surface bound oxygen was estimated to be about ~220 ppm for all three variants. Specific concerns need to be taken during the sintering of powder to keep oxygen level below that of electrolytic pitch copper (400 ppm).

Mechanisms of cation-induced superlubricity transition of poly(vinylphosphonic acid) coatings

Water-based superlubricity systems have unique advantages, such as low friction and environmental friendliness. While control of water-based superlubricity is highly attractive, it is also challenging. The superlubricity transition behavior of poly(vinylphosphonic acid) (PVPA) lubricated using a NaCl solution when mixed with multiple lubricants was investigated in this study. The mechanisms of superlubricity transition were investigated by exploring the internal structural changes of a PVPA coating and the molecular behaviors at the PVPA interface affected by cations through X-ray photoelectron spectroscopy (XPS) depth profiling, quartz crystal microbalance with dissipation (QCM-D), and molecular dynamics simulation. The type and magnitude of the superlubricity transition caused by cations with different valence states are clearly different. The introduced monovalent cation that can stably adsorb on the PVPA surface, exhibits a strong attraction toward the surrounding water molecules, instantaneously strengthening the lubrication at the PVPA interface. These changes at the interface are reversible and would cause a sudden decrease in the coefficient of friction (COF). Adsorbing an introduced divalent cation on the PVPA molecular chain leads to the transformation of the PVPA coating from a stable network structure to an unstable bridging structure. The sudden increase in the COF, caused by the altered internal structure of the coating, is irreversible. This study provides theoretical support for the adaptive control of water-based superlubricity and intelligent lubrication.

Etch mechanism of an Al2O3 hard mask in the Bosch process

The etching of high aspect ratio structures in silicon via the Bosch process is essential in modern technologies such as microelectromechanical systems (MEMS) and through‑silicon vias (TSV) fabrication. The process can be very demanding on the mask selectivity due to long etching times, and it has been shown that an Al 2 O 3 hard mask is very suitable in this regard, as it offers significantly higher selectivity compared to the conventional SiO 2 or resist masks. In this work, we employ a combination of Scanning Electron Microscopy (SEM), Spectroscopic Ellipsometry (SE) and X-Ray Photoelectron Spectroscopy (XPS) depth profiling to scrutinize the Al 2 O 3 mask etching mechanism and therefore the origin of the extraordinary high selectivity. We demonstrate that by increasing the passivation step time, a thicker fluorocarbon polymer layer is formed on the Al 2 O 3 , and Al 2 O 3 is then removed with a minuscule average etch rate of ~0.01 nm/min. XPS depth profiling reveals that during Deep Reactive Ion Etching (DRIE) using the Bosch process, an AlF x layer is formed between the polymer and Al 2 O 3 . As AlF x is non-volatile, it requires sputtering to be removed. If the polymer layer is thick enough to attenuate the incoming ions such that their energy is not sufficient to lead to desorption of AlF x , such as when using a longer passivation time, the mask is not eroded. By investigating the surface after different amounts of DRIE cycles, we also obtained information about the formation rate of AlF x and the changes in the Al 2 O 3 and polymer thicknesses over the course of a DRIE process. These findings further expand the knowledge of DRIE and can help process engineers to tailor the processes accordingly. • Selectivity of an Al 2 O 3 mask in the Bosch process becomes practically infinite with longer passivation step time • XPS depth profiling reveals that an AlF x layer is formed during DRIE between Al 2 O 3 and the fluorocarbon polymer on top • This non-volatile AlF x cannot be removed by sputtering if the polymer is thick enough, i.e. with longer passivation time • The dynamics of AlF x formation during DRIE was observed with time resolved measurements

In-situ release of phosphorus combined with rapid surface reconstruction for Co–Ni bimetallic phosphides boosting efficient overall water splitting

• Co-Ni bimetallic phosphides with a 2D/3D structure are developed for overall water splitting. • In-situ phosphorus diffusion from the substrate is confirmed. • CoOOH is rapid generated to achieve surface self-reconstruction. • The enhanced electrocatalytic activities are investigated by DFT calculations. Novel Co-Ni bimetallic phosphides with a 2D/3D structure were developed by in-situ phosphorization and rapid surface reconstruction strategies for use as an efficient electrocatalyst toward overall water splitting. In-situ phosphorus diffusion from the substrate was confirmed by high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) depth profiles. The generation of cobalt oxyhydroxide was also verified during electrochemical treatment, achieving surface self-reconstruction. The obtained materials revealed efficient and stable electrocatalytic performance, with HER and OER overpotentials of 117 mV and 272 mV, respectively. A low cell voltage of 1.59 V was achieved for overall water splitting with long-term stability. These properties were ascribed to the 2D/3D nanostructure with abundant interface defects. In-situ Raman spectroscopy and density functional theory (DFT) calculations were carried out to further understand the electrocatalytic activity and the promoted mechanism of reconstruction-derived CoOOH on OER performance.

An Evaluation of Nanoparticle Distribution in Solution-Derived YBa2Cu3O7−δ Nanocomposite Thin Films by XPS Depth Profiling in Combination with TEM Analysis

This work discusses the development of an analysis routine for evaluating the nanoparticle distribution in nanocomposite thin films. YBa2Cu3O7−δ (YBCO) nanocomposite films were synthesized via a chemical solution deposition approach starting from colloidal YBCO solutions with preformed nanoparticles. The distribution of the nanoparticles and interlayer diffusion are evaluated with X-ray photoelectron spectroscopy (XPS) depth profiling and compared with cross-sectional transmission electron microscopy (TEM) images. It is shown that the combination of both techniques deliver valuable information on the film properties as nanoparticle distribution, film thickness and interlayer diffusion.

High-Properties electrochromic device based on TiO2@Graphene/Prussian blue Core-Shell nanostructures

• A novel TNRA@G/PB core–shell nanostructure has been successfully prepared. • The evolution of PB growth layer were studied by XPS depth profiles. • Excellent performance depends on the porous structure and electron transpor. • A model of K + diffusion and e - transport at the interface was proposed. Herein, the successful preparation of a high-performance electrochromic device (ECD) with the TNRA@G/PB core–shell nanostructure as the electrode has been described. The core–shell nanostructure was formed by wrapping graphene (G) and growing Prussian blue (PB) on the TiO 2 nanorod array (TNRA) through the two-step hydrothermal and spin coating method. The existence state of elemental iron (Fe) and the evolution of the PB growth layer were studied by X-ray photoelectron spectroscopy (XPS) depth profiles. In addition, a model of K + diffusion and electron transport in the ECDs was proposed to explain the mechanism of the enhanced electrochromic property of the TNRA@G/PB core–shell nanostructures. The TNRA as a support template is conducive to electrolyte penetration and rapid ion replenishment to active sites. At the same time, the porous structure can alleviate the volume expansion during the electrical cycle which will increase the cycle stability of ECDs. G acts as a bridge between the conductive and active layer and can reduce the loss of electrons between interfaces in the transport process. It provides a fast transport channel for electrons and promotes the rapid response of electrochromism. Compared with ECDs based on the traditional PB film, TNRA@G/PB core–shell nanostructures achieve a higher optical modulation range (56.1%) and a shorter switching time (t c /t b = 1.0/2.8 s). In particular, the coloration efficiency (CE) has been significantly increased to 129.1 cm 2 /C at a wavelength of 700 nm, which shows a promising application in high-performance ECDs.

The chemical evolution of solid electrolyte interface in sodium metal batteries.

The solid electrolyte interface (SEI) formed on the anode is one of the key factors that determine the life span of sodium metal batteries (SMBs). However, the continuous evolution of SEI during charging/discharging processes complicates the fundamental understanding of its chemistry and structure. In this work, we studied the underlying mechanisms of the protection effect offered by the SEI derived from sodium difluoro(oxalato)borate (NaDFOB). In situ nuclear magnetic resonance (NMR) shows that the prior reduction of DFOB anion contributes to the SEI formation, and it suppresses the decomposition of carbonate solvents. Depth-profiling x-ray photoelectron spectroscopy and high-resolution solid-state NMR reveal that the DFOB anion is gradually turned into borate and fluoride-rich SEI with cycling. The protection effect of SEI reaches the optimum at 50 cycles, which triples the life span of SMB. The detailed investigations provide valuable guidelines for the SEI engineering.