Over 19% Efficiency Perovskite Solar Modules by Simultaneously Suppressing Cation Deprotonation and Iodide Oxidation

Perovskite solar cells (PSCs) based on sputtered nickel oxide (NiOx) hole transport layer have emerged as promising configuration due to their good stability, cost-effectiveness, and scalability. However, the adverse chemical redox reaction at the NiOx/perovskite interface remains an ever-present problem that has not yet been well solved. To address this issue before, the problems that cation deprotonation and iodide oxidation that occurred in precursor solution easily result in the interfacial chemical reaction should be prevented. Hence, we report an efficient strategy to simultaneously suppress the interfacial reaction and stabilize the precursor solution by incorporating a reducing and weakly acidic stabilizer, l-ascorbic acid (l-AA). l-AA can reduce I2 generated in the precursor solution and during the interfacial reaction to I-. Furthermore, the protons ionized by adjacent enol hydroxyl groups in l-AA effectively impede the deprotonation of organic cations in the precursor solution as well as at the NiOx/perovskite interface resulting from the chemical reaction. Attributing to the improved crystallization of the perovskite film and the suppression of the interfacial reaction by l-AA, the inverted PSC based on such good light absorber achieves an impressive power conversion efficiency (PCE) of 22.72% along with a high open-circuit voltage of 1.19 V. Notably, further introducing l-AA into the large-area solar modules by the slot-die coating method in air enables a remarkable PCE of 19.17%, which reaches one of the highest PCEs reported for inverted perovskite solar modules (PSMs) (active area >50 cm2) to date. l-AA located at the buried interface also forms a barrier layer that can prevent undesirable chemical reactions at the NiOx/perovskite interface, significantly enhancing the device stability of solar cells and PSMs. These findings in our work provide important guidance for improving the NiOx/perovskite interface and the fabrication of highly efficient, low-cost, and large-area PSMs.

Trigger of the Highly Resistive Layer Formation at the Cathode-Electrolyte Interface in All-Solid-State Lithium Batteries Using a Garnet-Type Lithium-Ion Conductor

Interfacial materials design is critical in the development of all-solid-state lithium batteries. We must develop an electrode-electrolyte interface with low resistance and effectively utilize the energy stored in the battery system. Here, we investigated the highly resistive layer formation process at the interface of a layered cathode: LiCoO2, and a garnet-type solid-state electrolyte: Li6.4La3Zr1.4Ta0.6O12, during the cosintering process using in situ/ex situ high-temperature X-ray diffraction. The onset temperature of the reaction between a lithium-deficient LixCoO2 and Li6.4La3Zr1.4Ta0.6O12 is 60 °C, while a stoichiometric LiCoO2 does not show any reaction up to 900 °C. The chemical potential gap of lithium first triggers the lithium migration from the garnet phase to the LixCoO2 below 200 °C. The lithium-extracted garnet gradually decomposes around 200 °C and mostly disappears at 500 °C. Since the interdiffusion of the transition metal is not observed below 500 °C, the early-stage reaction product is the decomposed lithium-deficient garnet phase. Electrochemical impedance spectroscopy results showed that the highly resistive layer is formed even below 200 °C. The present work offers that the origin of the highly resistive layer formation is triggered by lithium migration at the solid-solid interface and decomposition of the lithium-deficient garnet phase. We must prevent spontaneous lithium migration at the cathode-electrolyte interface to avoid a highly resistive layer formation. Our results show that the lithium chemical potential gap should be the critical parameter for designing an ideal solid-solid interface for all-solid-state battery applications.

Advancing Inorganic Microcapsule Fabrication through Frozen-Assisted Interfacial Reactions Utilizing Liquid Marbles

Inorganic microcapsules (IMs) have gained significant attention as versatile platforms for delivering functional agents in various fields. Traditional template-dependent methods employing hard templates often involve complex and harsh template removal processes. Achieving IMs with diverse composition and structure remains challenging with current preparation strategies. Therefore, in this work, we have for the first time demonstrated an extremely facile and efficient liquid-marbles-based template approach for fabricating pure inorganic microcapsules via interfacial reaction in a mild aqueous solution. The water-water reaction interface is created by changing the wettability of the liquid marble (LM) surface through the icing-melting process. The composition and function of the inorganic shell could be easily adjusted by varying the inorganic reagent species of the interfacial reaction, the hydrophobic particle of the shell, and the reaction environment according to the specific requirements of the application field. Such an approach provides a flexible platform for material preparation.

Construction of an OCP-ATR-FTIR Spectroscopy Device to In Situ Monitor the Interfacial Reaction of Contaminants: Competitive Adsorption of Cr(VI) and Oxalate on Hematite

The comprehensive understanding of contaminant interfacial behavior strongly depends on the in situ characterization technique, which is still a great challenge. In this study, we constructed a device integrated with open-circuit potentialand attenuated total reflectance Fourier transform infrared (OCP-ATR-FTIR) spectroscopy to simultaneously monitor the electrochemical and infrared spectral information on the interfacial reaction for the process analysis, taking the competitive adsorption of hexavalent chromium (Cr(VI)) and oxalate on hematite nanocubes (HNC) as an example. The synchronous OCP and infrared results revealed that Cr(VI) interacted with HNC via bidentate binuclear inner-sphere coordination, accompanied by electron transfer from HNC to Cr(VI), while oxalate was adsorbed on HNC through bidentate mononuclear side-on inner-sphere coordination with electron transfer from HNC to oxalate, and also outer-sphere coordination with negative charge accumulation. When oxalate was added to HNC with preadsorbed Cr(VI), oxalate would occupy the inner-sphere adsorption sites and thus cause the detaching of preadsorbed Cr(VI) from HNC. This study provides a promising in situ characterization technique for real-time interfacial reaction monitoring and also sheds light on the competitive adsorption mechanism of oxalate and Cr(VI) on the mineral surface.

Long-Term Aging Study on the Solid State Interfacial Reactions of In on Cu Substrate

Indium is considered a candidate low-temperature solder because of its low melting temperature and excellent mechanical properties. However, the solid-state microstructure evolution of In with different substrates has rarely been studied due to the softness of In. To overcome this difficulty, cryogenic broad Ar+ beam ion polishing was used to produce an artifact-free Cu/In interface for observation. In this study, we accomplished phase identification and microstructure investigation at the Cu/In interface after long-term thermal aging. CuIn2 was observed to grow at the Cu/In interface and proved to be a stable phase in the Cu-In binary system. The peritectoid temperature of the Cu11In9 + In → CuIn2 reaction was confirmed to be between 100 and 120 °C. In addition, the growth rate of CuIn2 was discovered to be dominated by the curvature of the reactant Cu11In9/In phase and the temperature difference with the peritectoid temperature. Finally, a comprehensive microstructural evolution mechanism of the Cu/In solid-state interfacial reaction was proposed.

A Study on the Interfacial Reactions between Gallium and Cu/Ni/Au(Pd) Multilayer Metallization

This research introduces low-temperature soldering of Ga with practical metallization structures, namely, Cu/Ni/Pd and Cu/Ni/Au, applied to contemporary microelectronic packages. Through these multilayer configurations, the study investigates the stability of the Ni diffusion barrier by examining changes in the interfacial microstructure as Ni is consumed. The interfacial reactions are conducted across a temperature spectrum of 160, 200, 240, and 280 °C, with reaction durations ranging from 30 to 270 min. Valuable insights for low-temperature soldering with Ga are extracted from the data. At lower reaction temperatures, the presence of Ga-rich intermetallic compounds (IMCs), specifically GaxNi (x = 89 to 95 at%), on the Ga7Ni3 layer is notably confirmed. As the reaction temperature and duration increase, the gradual consumption of the Ni layer occurs. This gives rise to the formation of Ga-Cu IMCs, specifically CuGa2 and γ3-Cu9Ga4, beneath the Ga-Ni IMC layer. Concurrently, the gap between the Ga-Ni and Ga-Cu IMC layers widens, allowing molten Ga to infiltrate. The rate of Ga7Ni3 growth follows a time exponent ranging approximately from 1.1 to 1.7. This highlights the significant influence of interface reaction-controlled kinetics on Ga7Ni3 IMC growth. The activation energy for Ga7Ni3 growth is determined to be 61.5 kJ/mol. The growth of Ga7Ni3 is believed to be primarily driven by the diffusion of Ga atoms along grain boundaries, with the porous microstructure inherent in the Ga7Ni3 layer providing additional diffusion pathways.

Artifact-Free Microstructures in the Interfacial Reaction between Eutectic In-48Sn and Cu Using Ion Milling

Eutectic In-48Sn was considered a promising candidate for low-temperature solder due to its low melting point and excellent mechanical properties. Both Cu₂(In,Sn) and Cu(In,Sn)₂ formation were observed at the In-48Sn/Cu interface after 160 °C soldering. However, traditional mechanical polishing produces many defects at the In-48Sn/Cu interface, which may affect the accuracy of interfacial reaction investigations. In this study, cryogenic broad Ar⁺ beam ion milling was used to investigate the interfacial reaction between In-48Sn and Cu during soldering. The phase Cu₆(Sn,In)₅ was confirmed as the only intermetallic compound formed during 150 °C soldering, while Cu(In,Sn)₂ formation was proven to be caused by room-temperature aging after soldering. Both the Cu₆(Sn,In)₅ and Cu(In,Sn)₂ phases were confirmed by EPMA quantitative analysis and TEM selected area electron diffraction. The microstructure evolution and growth mechanism of Cu₆(Sn,In)₅ during soldering were proposed. In addition, the Young's modulus and hardness of Cu₆(Sn,In)₅ were determined to be 119.04 ± 3.94 GPa and 6.28 ± 0.13 GPa, respectively, suggesting that the doping of In in Cu₆(Sn,In)₅ has almost no effect on Young's modulus and hardness.

A Fluid Multivalent Magnetic Interface for High-Performance Isolation and Proteomic Profiling of Tumor-Derived Extracellular Vesicles

Isolation and analysis of tumor-derived extracellular vesicles (T-EVs) are important for clinical cancer management. Here, we develop a fluid multivalent magnetic interface (FluidmagFace) in a microfluidic chip for high-performance isolation, release, and protein profiling of T-EVs. The FluidmagFace increases affinity by 105-fold with fluidity-enhanced multivalent binding to improve isolation efficiency by 13.9% compared with a non-fluid interface. Its anti-adsorption property and microfluidic hydrodynamic shear minimize contamination, increasing detection sensitivity by two orders of magnitude. Moreover, its reversibility and expandability allow high-throughput recovery of T-EVs for mass spectrometric protein analysis. With the chip, T-EVs are detected in all tested cancer samples with identification of differentially expressed proteins compared with healthy controls. The FluidmagFace opens a new avenue to isolation and release of targets for cancer diagnosis and biomarker discovery.

Beneficial Role of Inherently Formed Residual Lithium Compounds on the Surface of Ni-Rich Cathode Materials for All-Solid-State Batteries

This study validates the beneficial role of residual Li compounds on the surface of Ni-rich cathode materials (LiNi_xCo_yMn_zO₂, NCM). Residual Li compounds on Ni-rich NCM are naturally formed during the synthesis procedure, which degrades the initial Coulombic efficiency and generates slurry gelation during electrode fabrication in Li-ion batteries (LIBs) using liquid electrolytes. To solve this problem, washing pretreatment is usually introduced to remove residual Li compounds on the NCM surface. In contrast to LIBs, we found that residual Li compounds can serve as a functional layer that suppresses the interfacial side reactions of the NCM in all-solid-state batteries (ASSBs). The formation of resistive phosphate-based compounds from the undesirable side reaction during the initial charging step is suppressed by the residual Li compounds on the surface of the NCM, thereby reducing polarization growth in ASSBs and enhancing rate performances. The advantageous effects of the intrinsic residual Li compounds on the NCM surface suggest that the essential washing process of the NCM for the liquid-based LIB system should be reconsidered for ASSB systems.

Near-Ideal Top-Gate Controllability of InGaZnO Thin-Film Transistors by Suppressing Interface Defects with an Ultrathin Atomic Layer Deposited Gate Insulator

An ultrathin atomic-layer-deposited (ALD) AlO_x gate insulator (GI) was implemented for self-aligned top-gate (SATG) amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs). Although the 4.0-nm thick AlO_x exhibited ideal insulating properties, the interaction between ALD AlO_x and predeposited a-IGZO caused a relatively defective interface, thus giving rise to hysteresis and bias stress instabilities. As analyzed using high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and the Hall measurement, the chemical reaction between the ALD precursor and a-IGZO is revealed. This was effectively prevented by preoxidizing a-IGZO with nitrous oxide (N₂O) plasma. With 4 nm-AlO_x GI and low-defect interfaces, high performance and stability were simultaneously achieved on SATG a-IGZO TFTs, including a near-ideal record-low subthreshold swing of 60.8 mV/dec, a low operation voltage below 0.4 V, a moderate mobility of 13.3 cm²/V·s, a low off-current below 10^-13 A, a large on/off ratio over 10⁹, and negligible threshold-voltage shifts less than 0.04 V against various bias-temperature stresses. This work clarifies the vital interfacial reaction between top-gate high-k dielectrics and amorphous oxide semiconductors (AOSs) and further provides a feasible way to remove this obstacle to downscaling SATG AOS TFTs.

Aging Interfacial Structure and Abnormal Tensile Strength of SnAg3Cu0.5/Cu Solder Joints

In this study, the interfacial structure and abnormal long-term increase of tensile strength in the interfacial intermetallic compounds (IMCs) between SnAg3Cu0.5 solder and Cu substrates during isothermal aging were investigated. After reflow soldering, the IMC layer at the interface was thin and scallop-type. The interfacial layer became thicker with the increase in aging time. After 200 h of aging at 150 °C, the thickness of the interface gradually increased to 3.93 μm and the interface became smooth. Compared with the unaged Cu-Sn interface, the aged joint interface contained more Cu₃Sn. The top of the IMC being reflown was relatively smooth, but became denser and prismatic in shape after 200 h of aging at 150 °C. The tensile strength of the joint, immediately after the reflow, reached 81.93 MPa. The tensile properties of the solder joints weakened and then strengthened as they aged. After 200 h of aging at 150 °C, the tensile strength was 83.86 MPa, which exceeded that of the unaged solder joint interface, because the fracture mode of the solder joints changed during aging.

Diffusion Barrier Properties of the Intermetallic Compound Layers Formed in the Pt Nanoparticles Alloyed Sn-58Bi Solder Joints Reacted with ENIG and ENEPIG Surface Finishes

Pt-nanoparticle (NP)-alloyed Sn-58Bi solders were reacted with electroless nickel-immersion gold (ENIG) and electroless nickel-electroless palladium-immersion gold (ENEPIG) surface finishes. We investigated formation of intermetallic compounds (IMCs) and their diffusion barrier properties at reaction interfaces as functions of Pt NP content in the composite solders and duration of solid-state aging at 100 °C. At Sn-58Bi-xPt/ENIG interfaces, typical Ni₃Sn₄/Ni₃P(P-rich layer) microstructure was formed. With the large consumption of the Ni-P layer, the Ni-P and Cu layers were intermixed and Cu atoms spread over the composite solder after 500 h of aging. By contrast, a (Pd,Ni)Sn₄/thin Ni₃Sn₄ microstructure was observed at the Sn-58Bi-xPt/ENEPIG interfaces. The (Pd,Ni)Sn₄ IMC effectively suppressed the consumption of the Ni-P layer and Ni₃Sn₄ growth, functioning as a good diffusion barrier. Therefore, the Sn-58Bi-xPt/ENEPIG joint survived 500 h of aging without microstructural degradation. Based on the experimental results and analysis of this study, Sn-58Bi-0.05Pt/ENEPIG is suggested as the optimum combination for future low-temperature soldering systems.

Thermal Stability between Sulfide Solid Electrolytes and Oxide Cathode

In pursuit of high-energy/power density, lithium-ion batteries suffer from increasing safety risks that need to be urgently solved. These safety problems promisingly might be solved by replacing liquid electrolytes (LEs) with inorganic solid electrolytes (SEs), because of their high thermal stability and nonflammability. However, thermal stability studies on sulfide SEs have been rarely reported, due to their extremely high reactivity, strong corrosiveness, instability to air, toxic gas release, etc. To fill this gap, thermal stability performances of sulfide SEs are verified from the perspectives of essential combustion elements in this work. Simple and effective experimental devices/approaches have been developed to systematically study the thermodynamic and kinetic properties of thermal stability between typical sulfide SEs (Li₃PS₄, Li₇P₃S₁₁, Li₆PS₅Cl, LSPSCl, Li₄SnS₄) and oxide cathode Li_1-xCoO₂ with different delithiation states. Practical improved methods are realized to block the thermochemical interfacial reaction for enhanced thermal stability between sulfide SEs and oxide cathodes.

Interfacial Reaction Mechanism between Ceramic Mould and Single Crystal Superalloy for Manufacturing Turbine Blade

Single crystal superalloys are the preferred materials for manufacturing turbine blades of advanced aero-engines, due to their excellent high temperature comprehensive performance. The interfacial reaction between alloys and ceramic mould are an important factor to influence the surface quality and service performance of the turbine blade. It is very important to reveal the interfacial reaction mechanism to improve turbine blade quality and yield rate. In this paper, the interfacial reactions between DD6 single crystal superalloy and ceramic mould were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The results show that the main reaction products were HfO₂, Al₂O₃ and Y₃Al₅O₁₂ when the yttrium oxide powders were the prime coat materials, while alloy surface suffered undesirable sand fusion; the thicknesses of the reaction layers were over 20 μm. The reaction layer can be divided into two layers, the layer close to the alloy was mainly composed of Al₂O₃ and Y₃Al₅O₁₂, and the layer close to the mould was composed of SiO₂, Al₂O₃ and Y₃Al₅O₁₂. Avoiding the formation of Y₂O₃-Al₂O₃-SiO₂ ternary low-melts can solve the interfacial reaction between DD6 alloy and yttrium oxide mould.

Exploring the Interfacial Reaction of Nano Al/CuO Energetic Films through Thermal Analysis and Ab Initio Molecular Dynamics Simulation

The effect of the interface layer on energy release in nanoenergetic composite films is important and challenging for the utilization of energy. Nano Al/CuO composite films with different modulation periods were prepared by magnetron sputtering and tested by differential scanning calorimetry. With the increase in the modulation period of the nano Al/CuO energetic composite films, the interface layer contained in the energetic composite film decreased meaningfully, increasing the total heat release meaningfully. Ab initio molecular dynamics (AIMD) simulation were carried out to study the preparation process changes and related properties of the nano Al/CuO energetic composite films under different configurations at 400 K. The results showed that the diffusion of oxygen atoms first occurred at the upper and lower interfaces of CuO and Al, forming AlO_x and Cu_xAl_yO_z. The two-modulation-period structure changed more obviously than the one-modulation-period structure, and the reaction was faster. The propagation rate and reaction duration of the front end of the diffusion reaction fronts at the upper and lower interfaces were different. The Helmholtz free energy loss of the nano Al/CuO composite films with a two-modulation-period configuration was large, and the number of interfacial layers had a great influence on the Helmholtz free energy, which was consistent with the results of the thermal analysis. Current molecular dynamics studies may provide new insights into the nature and characteristics of fast thermite reactions in atomic detail.

Electrode Engineering in Halide Perovskite Electronics: Plenty of Room at the Interfaces

Contact engineering is a prerequisite for achieving desirable functionality and performance of semiconductor electronics, which is particularly critical for organic-inorganic hybrid halide perovskites due to their ionic nature and highly reactive interfaces. Although the interfaces between perovskites and charge-transporting layers have attracted lots of attention due to the photovoltaic and light-emitting diode applications, achieving reliable perovskite/electrode contacts for electronic devices, such as transistors and memories, remains as a bottleneck. Herein, a critical review on the elusive nature of perovskite/electrode interfaces with a focus on the interfacial electrochemistry effects is presented. The basic guidelines of electrode selection are given for establishing non-polarized interfaces and optimal energy level alignment for perovskite materials. Furthermore, state-of-the-art strategies on interface-related electrode engineering are reviewed and discussed, which aim at achieving ohmic transport and eliminating hysteresis in perovskite devices. The role and multiple functionalities of self-assembled monolayers that offer a unique approach toward improving perovskite/electrode contacts are also discussed. The insights on electrode engineering pave the way to advancing stable and reliable perovskite devices in diverse electronic applications.

Modified Breath Figure Methods for the Pore-Selective Functionalization of Honeycomb-Patterned Porous Polymer Films

Recent developments in the field of the breath figure (BF) method have led to renewed interest from researchers in the pore-selective functionalization of honeycomb-patterned (HCP) films. The pore-selective functionalization of the HCP film gives unique properties to the film which can be used for specific applications such as protein recognition, catalysis, selective cell culturing, and drug delivery. There are several comprehensive reviews available for the pore-selective functionalization by the self-assembly process. However, considerable progress in preparation technologies and incorporation of new materials inside the pore surface for exact applications have emerged, thus warranting a review. In this review, we have focused on the pore-selective functionalization of the HCP films by the modified BF method, in which the self-assembly process is accompanied by an interfacial reaction. We review the importance of pore-selective functionalization, its applications, present limitations, and future perspectives.

Fabrication and Excellent Performances of Bismuth Telluride-Based Thermoelectric Devices

The barrier layer between thermoelectric (TE) legs and electrodes has crucial impact on the electrothermal conversion efficiency of the TE device; however, the interfacial reaction of the Ni metal barrier layer with TE legs in traditional Bi₂Te₃-based devices is harmful to the device performance. Herein, a high-quality barrier layer of a Ni-based alloy has been fabricated on both n-type and p-type Bi₂Te₃-based TE legs by the electroplating method. The in situ XRD results indicate that the as-prepared Bi₂Te₃-based TE legs with a Ni-based alloy barrier layer remain stable even at 300 °C. The high-resolution high-angle annular dark field scanning transmission electron microscopy images reveal that the Ni-based alloy barrier layer has more excellent stability than that of the Ni metal barrier layer. The Bi₂Te₃-based TE devices with excellent structural and performance stabilities were assembled with the as-grown high-performance n-type and p-type Bi₂Te₃-based leg with a Ni-based alloy barrier layer, which have lower internal resistance and higher cooling and power generation performances. A maximum cooling temperature difference over 65 K and a maximum cooling capacity of 55 W were obtained for the high-performance Bi₂Te₃-based TE devices. This work provides a new strategy for high-temperature applications of commercial Bi₂Te₃-based TE devices.

Rationally Designed Ag@polymer@2-D LDH Nanoflakes for Bifunctional Efficient Electrochemical Sensing of 4-Nitrophenol and Water Oxidation Reaction

The rational design and demonstration of a facile sequential template-mediated strategy to construct noble-metal-free efficient bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and electrocatalytic detection of hazardous environmental 4-nitrophenol (4-NP) have continued as a major challenging task. Herein, we construct a novel Ag@polymer/NiAl LDH (designated as APL) nanohybrid as an efficient bifunctional electrocatalyst by a simple hydrolysis method. The well-fabricated APL/GCE exhibited an extensive linear range from 0.1 to 100 μM in optimized conditions. It showed a detection limit (LOD) of 0.0096 μM (9.6 nM) (S/N = 3) for 4-NP in pH 6 by differential pulse voltammetry (DPV). Meanwhile, the newly fabricated APL exhibited outstanding OER activity with a very low overpotential of 259 mV to deliver 10 mA cm^-2 current density (J) at a scan rate of 5 mV/s. The Tafel plot value of APL is low (97 mV/dec) compared to that of the benchmark RuO₂ due to a fast kinetic reaction. Besides, the durability of the electrocatalyst was assessed by a chronoamperometry test (CA) for 36 h at 1.55 mV vs RHE, and the long-term cycling stability was analyzed by using cyclic voltammetry (CV); after 5000 cycles, the electrocatalyst was highly stable. These demonstrated results could lead to an alternative electrocatalyst construction for the bifunctionally efficient electrochemical sensing of 4-nitrophenol and oxygen evolution reaction.

Direct Visualization of Dynamic Mobility of Li2O2 in Li-O2 Batteries: A Differential Interference Microscopy Study

The reversibility and the discharge/charge performance in nonaqueous lithium-oxygen (Li-O₂) batteries are critically dependent on the kinetics of interfacial reactions. However, the interfacial reaction dynamic behaviors, especially the quantitative analysis, are still far from deep understanding. Using the method of laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM), we monitored the Li-O₂ interfacial reaction and in situ traced the Li₂O₂ migration processes promoted by the solution catalyst. Different dynamic behaviors exist when regulating the concentration of the redox mediator. Quantitative analysis of the discharged Li₂O₂ particles shows high mobility at the early discharge stage and decayed motion in the subsequent process, indicating the solution-mediated pathway participating Li₂O₂ formation in the low-concentration redox mediator addition, while particles/aggregates confined into the amorphous film demonstrate simultaneous solution and surface route-mediated pathway participation in the high-concentration case. These distinctive observations of Li₂O₂ formation and decomposition processes present the advantage of LCM-DIM to fundamentally understand the dynamic evolution in Li-O₂ batteries.

Vacuum Brazing of Metallized YSZ and Crofer Alloy Using 72Ag-28Cu Filler Foil

The study focused on dissimilar brazing of metallized YSZ (Yttria-Stabilized Zirconia) and Crofer alloy using BAg-8 (72Ag-28Cu, wt%) filler foil. The YSZ substrate was metallized by sequentially sputtering Ti (0.5/1 μm), Cu (1/3 μm), and Ag (1.5/5 μm) layers, and the Crofer substrate was coated with Ag layers with a thickness of 1.5 and 5 μm, respectively. The BAg-8 filler demonstrated excellent wettability on both metallized YSZ and Crofer substrates. The brazed joint primarily consisted of Ag-Cu eutectic. The metallized Ti layer dissolved into the braze melt, and the Ti preferentially reacted with YSZ and Fe from the Crofer substrate. The globular Fe₂Ti intermetallic compound was observed on the YSZ side of the joint. The interfacial reaction of Ti was increased when the thickness of the metallized Ti layer was increased from 0.5 to 1 μm. Both brazed joints were crack free, and no pressure drop was detected after testing at room temperature for 24 h. In the YSZ/Ti(0.5μ)/Cu(1μ)/Ag(1.5μ)/BAg-8(50μ)/Ag(1.5μ)/Crofer joint tested at 600 °C, the pressure of helium decreased from 2.01 to 1.91 psig. In contrast, the helium pressure of the YSZ/Ti(1μ)/Cu(3μ)/Ag(5μ)/BAg-8(50μ)/Ag(5μ)/Crofer joint slightly decreased from 2.02 to 1.98 psig during the cooling cycle of the test. The greater interfacial reaction between the metallized YSZ and BAg-8 filler due to the thicker metallized Ti layer on the YSZ substrate was responsible for the improved gas-tight performance of the joint.

Drastic Reduction of the Solid Electrolyte-Electrode Interface Resistance via Annealing in Battery Form

The origin of electrical resistance at the interface between the positive electrode and solid electrolyte of an all-solid-state Li battery has not been fully determined. It is well known that the interface resistance increases when the electrode surface is exposed to air. However, an effective method of reducing this resistance has not been developed. This report demonstrates that drastic reduction of the resistance is achievable by annealing the entire battery cell. Exposing the LiCoO₂ positive electrode surface to H₂O vapor increases the resistance by more than 10 times (to greater than 136 Ω cm²). The magnitude can be reduced to the initial value (10.3 Ω cm²) by annealing the sample in a battery form. First-principles calculations reveal that the protons incorporated into the LiCoO₂ structure are spontaneously deintercalated during annealing to restore the low-resistance interface. These results provide fundamental insights into the fabrication of high-performance all-solid-state Li batteries.

Metal Emulsion-Based Synthesis, Characterization, and Properties of Sn-Based Microsphere Phase Change Materials

A comparative study of the metal emulsion-based synthesis of Sn-based materials in two different types of molten salts (namely LiCl–KCl–CsCl and LiNO₃-NaNO₃-KNO₃ eutectics) is presented, and the properties of Sn, Sn-Cu and Sn-Cu-Zn microsphere phase change materials prepared in chloride salts are evaluated by differential scanning calorimetry (DSC) to understand the effect of element doping. Despite a high ultrasonic power (e.g., 600 W or above) being required for dispersing liquid Sn in the chloride system, well-shaped Sn microspheres with a relatively narrow size range, e.g., about 1 to 15 µm or several micrometers to around 30 µm, can be prepared by adjusting the ultrasonic power (840–1080 W), sonication time (5–10 min) and the volume ratio of salts to metal (25:1–200:1). Such a method can be extended to the synthesis of Sn-based alloy microspheres, e.g., Sn-Cu and Sn-Cu-Zn microspheres. In the nitrate system, however, a very low ultrasonic power (e.g., 12 W) can be used to disperse liquid Sn, and the particles obtained are much smaller. At low ultrasonic power (e.g., 12 W), the particle size is generally less than 10 or 4 µm when the sonication time reaches 2 or 5 min, and at high ultrasonic power, it is typically in the range of hundreds of nanometers to 2 µm, regardless of the change in ultrasonic power (480–1080 W), irradiation time (5–10 min), or volume ratio of salts to metal (25:1–1000:1). In addition, the appearance of a SnO phase in the products prepared under different conditions hints at the occurrence of a reaction between Sn droplets and O₂ in situ generated by the ultrasound-induced decomposition of nitrates, and such an interfacial reaction is believed to be responsible for these differences observed in two different molten salt systems. A DSC study of Sn, Sn-Cu, and Sn-Cu-Zn microspheres encapsulated in SiO₂ reveals that Cu (0.3–0.9 wt.%) or Cu-Zn (0.9 wt.% Cu and 0.6% Zn) doping can raise the onset freezing temperature and thus suppress the undercooling of Sn, but a broad freezing peak observed in these doped microspheres, along with a still much higher undercooling compared to those of reported Sn-Cu or Sn-Cu-Zn solders, suggests the existence of a size effect, and that a low temperature is still needed for totally releasing latent heat. Since the chloride salts can be recycled by means of the evaporation of water and are stable at high temperature, our results indicate that the LiCl–KCl–CsCl salt-based metal emulsion method might also serve as an environmentally friendly method for the synthesis of other metals and their alloy microspheres.

Liquid-Metal-Assisted Deposition and Patterning of Molybdenum Dioxide at Low Temperature

Molybdenum dioxide (MoO2), considering its near-metallic conductivity and surface plasmonic properties, is a great material for electronics, energy storage devices and biosensing. Yet to this day, room-temperature synthesis of large area MoO2, which allows deposition on arbitrary substrates, has remained a challenge. Due to their reactive interfaces and specific solubility conditions, gallium-based liquid metal alloys offer unique opportunities for synthesizing materials that can meet these challenges. Herein, a substrate-independent liquid metal-based method for the room temperature deposition and patterning of MoO2 is presented. By introducing a molybdate precursor to the surrounding of a eutectic gallium-indium alloy droplet, a uniform layer of hydrated molybdenum oxide (H2MoO3) is formed at the interface. This layer is then exfoliated and transferred onto a desired substrate. Utilizing the transferred H2MoO3 layer, a laser-writing technique is developed which selectively transforms this H2MoO3 into crystalline MoO2 and produces electrically conductive MoO2 patterns at room temperature. The electrical conductivity and plasmonic properties of the MoO2 are analyzed and demonstrated. The presented metal oxide room-temperature deposition and patterning method can find many applications in optoelectronics, sensing, and energy industries.

Formation and Growth of Intermetallic Compounds during Reactions between Liquid Gallium and Solid Nickel

Liquid metals, such as Ga and eutectic Ga-In, have been extensively studied for various applications, including flexible and wearable devices. For applying liquid metal to electronic devices, interconnection with the various metal electrodes currently in use, and verifying their mechanical reliability are essential. Here, detailed investigations of the formation and growth of intermetallic compounds (IMCs) during the reactions between liquid Ga and solid nickel were conducted. Ga and Ni were reacted at 250, 300, and 350 °C for 10-240 min. The IMC double layer observed after the reactions contained a Ga7Ni3 bottom layer formed during the reactions, and a GaxNi top layer (with 89-95 at.% of Ga) precipitated during cooling. Numerous empty channels exist between the rod-type Ga7Ni3 IMCs. Ga7Ni3 growth occurred only in the vertical direction, without lateral coarsening and merging between the rods. The time exponents were measured at 1.1-1.5, implying that the reaction kinetics were near-interface reaction-controlled. The activation energy for Ga7Ni3 growth was determined as 49.1 kJ/mol. The experimental results of the Ga-Ni reaction study are expected to provide important information for incorporating liquid metals into electronic devices in the future.

Understanding the Origin of Metal Gate Work Function Shift and Its Impact on Erase Performance in 3D NAND Flash Memories

We studied the metal gate work function of different metal electrode and high-k dielectric combinations by monitoring the flat band voltage shift with dielectric thicknesses using capacitance-voltage measurements. We investigated the impact of different thermal treatments on the work function and linked any shift in the work function, leading to an effective work function, to the dipole formation at the metal/high-k and/or high-k/SiO₂ interface. We corroborated the findings with the erase performance of metal/high-k/ONO/Si (MHONOS) capacitors that are identical to the gate stack in three-dimensional (3D) NAND flash. We demonstrate that though the work function extraction is convoluted by the dipole formation, the erase performance is not significantly affected by it.

Incorporating Electro-Epoxidation into Electrospray Ionization Mass Spectrometry for Simultaneous Analysis of Negatively and Positively Charged Unsaturated Glycerophospholipids

In this study, we develop an alternating current (AC)-induced electro-epoxidation reaction and incorporate it into nanoelectrospray ionization for locating carbon-carbon double-bonds in positively and negatively charged forms of lipids simultaneously. An AC voltage plays multiple roles in this method, including initiation of the electro-epoxidation of carbon-carbon double-bonds in both charged states of lipids and protonation/deprotonation of lipids for detection in both ion modes. Moreover, the rapid switch between native lipids and their electro-epoxidation products can be achieved at different AC voltages. The efficacy of the present method was demonstrated in mixtures of lipid standards and in a biological polar lipid extract. The advantages of simultaneous detection of negatively and positively charged unsaturated lipids, the low sample consumption, and on-demand electro-epoxidation should allow its wide applications in lipid-related research.

pH-Responsive Capsule Polymer Particles Prepared by Interfacial Photo-Cross-Linking: Effect of the Alkyl Chain Length of the pH-Responsive Monomer

pH-responsive capsule particles have immense potential for use in various advanced fields, such as microreactors and drug delivery. Moreover, the interfacial photo-cross-linking of spherical polymer particles is a promising strategy to create various functional capsule particles. In this study, pH-responsive capsule polymer particles were prepared by interfacial photo-cross-linking with photo-reactive polymers possessing different pH-responsive monomer units of different alkyl chain lengths, namely, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, and 2-diisopropylaminoethyl methacrylate. Using these different pH-responsive monomers, regulation of the controlled release properties of pH-responsive capsule particles was achieved. All capsule particles prepared from these three different polymers released encapsulated molecules under acidic conditions; however, more acidic conditions were necessary for releasing encapsulated molecules with the increasing alkyl chain length. The afforded results indicated that pH-responsive monomers of different alkyl chain lengths could be successfully employed to regulate the pH-responsive controlled release property of the capsule particles prepared by interfacial photo-cross-linking.

Using TOF-SIMS Spectrometry to Study the Kinetics of the Interfacial Retro Diels-Alder Reaction

In this work, the use of Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was explored as a technique for monitoring the interfacial retro Diels–Alder (retro DA) reaction occurring on well-controlled self-assembled monolayers (SAMs). A molecule containing a Diels–Alder (DA) adduct was grafted on to the monolayers, then the surface was heated at different temperatures to follow the reaction conversion. A TOF-SIMS analysis of the surface allowed the detection of a fragment from the molecule, which is released from the surface when retro DA reaction occurs. Hence, by monitoring the decay of this fragment’s peak integral, the reaction conversion could be determined in function of the time and for different temperatures. The viability of this method was then discussed in comparison with the results obtained by ¹H NMR spectroscopy.

Effect of Cu Content on Performance of Sn-Zn-Cu Lead-Free Solder Alloys Designed by Cluster-Plus-Glue-Atom Model

The mechanical properties of solder alloys are a performance that cannot be ignored in the field of electronic packaging. In the present study, novel Sn-Zn solder alloys were designed by the cluster-plus-glue-atom (CPGA) model. The effect of copper (Cu) addition on the microstructure, tensile properties, wettability, interfacial characterization and melting behavior of the Sn-Zn-Cu solder alloys were investigated. The Sn₂₉Zn_4.6Cu_0.4 solder alloy exhibited a fine microstructure, but the excessive substitution of the Cu atoms in the CPGA model resulted in extremely coarse intermetallic compound (IMC). The tensile tests revealed that with the increase in Cu content, the tensile strength of the solder alloy first increased and then slightly decreased, while its elongation increased slightly first and then decreased slightly. The tensile strength of the Sn₂₉Zn_4.6Cu_0.4 solder alloy reached 95.3 MPa, which was 57% higher than the plain Sn-Zn solder alloy, which is attributed to the fine microstructure and second phase strengthening. The spreadability property analysis indicated that the wettability of the Sn-Zn-Cu solder alloys firstly increased and then decreased with the increase in Cu content. The spreading area of the Sn₂₉Zn_0.6Cu_0.4 solder alloy was increased by 27.8% compared to that of the plain Sn-Zn solder due to Cu consuming excessive free state Zn. With the increase in Cu content, the thickness of the IMC layer decreased owing to Cu diminishing the diffusion force of Zn element to the interface.

Interfacial Reaction Induced Disruption and Dissolution of Dynamic Polymer Networks

The reaction of amine-terminated polystyrene (PS-NH₂ ) with an epoxy-based dynamic polymer networks (DPNs) above the topology freezing transition temperature of the DPN, results in the disruption of the network by the formation of graft copolymers at the interface between the linear homopolymer and the network. The rate of the disruption decreases with annealing time and is strongly dependent on the molecular weight of the PS-NH₂ , with the lower molecular weight PS-NH₂ reacting much more rapidly than the higher molecular weight PS-NH₂ . A higher catalyst concentration in the DPN also promotes the interfacial reaction, indicating a reaction-rate-controlled process.

Interfacial Photo-Cross-Linking: Simple but Powerful Approach for Fabricating Capsule Polymer Particles with Tunable pH-Responsive Controlled Release Capability

Herein, we describe capsule polymer particles with precisely controlled pH-responsive release properties prepared directly via the interfacial photo-cross-linking of spherical poly(2-diethylaminoethyl methacrylate-co-2-cinnamoylethyl methacrylate) (P(DEAEMA-CEMA)) particles. In the interfacial photo-cross-linking, photoreactive cinnamoyl groups in the polymer particles were cross-linked via [2π + 2π] cycloaddition reactions at the polymer/water interface, showing that the shell-cross-linked hollow polymer particles can be directly prepared from spherical polymer particles. The approach has fascinating advantages such as using minimal components, simplicity, and not requiring sacrificial template particles and toxic solvents. The following important observations are made: (I) encapsulated materials were stably retained in the capsule particles under neutral pH conditions; (II) encapsulated materials were released from the capsule particles under acidic pH conditions; (III) the release kinetics of encapsulated materials were controlled by the pH conditions; i.e., immediate and sustained release was achieved by varying the acidity of the aqueous media; (IV) the photoirradiation time did not significantly affect the release kinetics under different pH conditions; and (V) the pH-responsive release properties were regulated by changing the polymer composition in P(DEAEMA-CEMA). Furthermore, by exploiting the pH-responsiveness, capsule particles are successfully obtained via an all-aqueous process from spherical polymer particles. The advantages of the all-aqueous encapsulation process allowed the water-soluble biomacromolecules such as DNA and saccharides to be successfully encapsulated in the P(DEAEMA-CEMA) hollow particles. With this simple interfacial photo-cross-linking strategy, we envision the ready synthesis of sophisticated particulate materials for broad application in advanced research fields.

Estradiol Removal by Adsorptive Coating of a Microfiltration Membrane

This work demonstrates the enhancement of the adsorption properties of polyethersulfone (PES) microfiltration membranes for 17β-estradiol (E2) from water. This compound represents a highly potent endocrine-disrupting chemical (EDC). The PES membranes were modified with a hydrophilic coating functionalized by amide groups. The modification was performed by the interfacial reaction between hexamethylenediamine (HMD) or piperazine (PIP) as the amine monomer and trimesoyl chloride (TMC) or adipoyl chloride (ADC) as the acid monomer on the surface of the membrane using electron beam irradiation. The modified membranes and the untreated PES membrane were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), water permeance measurements, water contact angle measurements, and adsorption experiments. Furthermore, the effects of simultaneous changes in four modification parameters: amine monomer types (HMD or PIP), acid monomer types (TMC or ADC), irradiation dosage (150 or 200 kGy), and the addition of toluene as a swelling agent, on the E2 adsorption capacity were investigated. The results showed that the adsorption capacities of modified PES membranes toward E2 are >60%, while the unmodified PES membrane had an adsorption capacity up to 30% for E2 under similar experimental conditions, i.e., an enhancement of a factor of 2. Next to the superior adsorption properties, the modified PES membranes maintain high water permeability and no pore blockage was observed. The highlighted results pave the way to develop efficient low-cost, stable, and high-performance adsorber membranes.

Interfacial Reactions and Mechanical Properties of Sn-58Bi Solder Joints with Ag Nanoparticles Prepared Using Ultra-Fast Laser Bonding

The effects of Ag nanoparticle (Ag NP) addition on interfacial reaction and mechanical properties of Sn–58Bi solder joints using ultra-fast laser soldering were investigated. Laser-assisted low-temperature bonding was used to solder Sn–58Bi based pastes, with different Ag NP contents, onto organic surface preservative-finished Cu pads of printed circuit boards. The solder joints after laser bonding were examined to determine the effects of Ag NPs on interfacial reactions and intermetallic compounds (IMCs) and high-temperature storage tests performed to investigate its effects on the long-term reliabilities of solder joints. Their mechanical properties were also assessed using shear tests. Although the bonding time of the laser process was shorter than that of a conventional reflow process, Cu–Sn IMCs, such as Cu₆Sn₅ and Cu₃Sn, were well formed at the interface of the solder joint. The addition of Ag NPs also improved the mechanical properties of the solder joints by reducing brittle fracture and suppressing IMC growth. However, excessive addition of Ag NPs degraded the mechanical properties due to coarsened Ag₃Sn IMCs. Thus, this research predicts that the laser bonding process can be applied to low-temperature bonding to reduce thermal damage and improve the mechanical properties of Sn–58Bi solders, whose microstructure and related mechanical properties can be improved by adding optimal amounts of Ag NPs.

Interfacial Reaction-Induced Defect Engineering: Enhanced Visible and Near-Infrared Absorption of Wide Band Gap Metal Oxides with Abundant Oxygen Vacancies

Modified metal oxides with narrow band gaps have attracted great interest in photothermal applications because of their wide optical absorption range. To tune wide band gap metal oxides into visible and near-infrared responsive materials, we deploy a unique interfacial reaction-induced defect engineering approach, which enables us to effectively modify the electronic structure of metal oxides by introducing oxygen vacancy defects. This approach reduced the band gap of zirconia from 5.47 to 1.38 eV, accompanied by a color change to black. More importantly, it is not limited by the size of the metal oxides, and bulk black zirconia was successfully obtained for the first time. It has been demonstrated that the prepared black zirconia can be applied as an effective photothermal therapy agent in vitro. Additionally, the interfacial reaction-induced defect engineering approach has been successfully extended to enhance the optical absorption of other metal oxides.

Effect of SiO2-Al2O3 Glass Composite Coating on the Oxidation Behavior of Ti60 Alloy

A SiO₂–Al₂O₃ glass composite coating was prepared on Ti60 alloy via air spraying slurry and then a suitable baking process. It was composed of potassium silicate glass, alumina and quartz powders. The high temperature oxidation performance of the alloy with and without coating was evaluated in static air at both 800 °C and 900 °C. The results show that catastrophic oxidation occurs for Ti60 bare alloy. It had a mass gain of about 2 mg/cm² after oxidation at 800 °C and 17 mg/cm² at 900 °C for 100 h. On the contrary, the oxidation resistance of alloy coated with composite coating was much improved with the mass gain about 0.36 mg/cm² and 0.95 mg/cm² at 800 °C and at 900 °C, respectively. The microstructure evolution of the composite coating and the alloy was analyzed by scanning electron microscope and electron probe microanalyzer. The effect of the composite coating on the oxidation performance of the alloy is discussed especially in terms of oxygen diffusion and interfacial reaction.

Advanced Functional Hierarchical Nanoporous Structures with Tunable Microporous Coatings Formed via an Interfacial Reaction Processing

It is challenging, but constructing hierarchical nanoporous structures with microporous coatings for various important applications, such as entrapment of homogeneous catalysts, size/shape selective catalysis, and so forth, is an urgent need. Moreover, microporous inorganic coatings are particularly desirable because of their excellent stability in organic solvents and at elevated temperatures and pressures. In this study, we design a novel liquid phase interfacial reaction process to form a defect-free, hybrid coating, which can be subsequently converted into microporous coatings, with tunable pore size, on nanoporous materials. As an example to entrap functional materials, tetrakis(triphenylphosphine) palladium (Pd(PPh₃)₄) was in situ synthesized in the mesoporous channels and encapsulated by the microporous coating shell. The encapsulated Pd(PPh₃)₄ catalyst exhibited negligible Pd leaching, providing a promising solution for the challenging catalyst separation problem in homogeneous catalysis. These results suggest that this novel strategy might be an effective way of forming microporous inorganic coatings on nanoporous materials for entrapping functional materials for wide applications.

Organic-Organic Composite Electrolyte Enables Ultralong Cycle Life in Solid-State Lithium Metal Batteries

Ionic conducting polymer electrolytes for solid-state lithium-ion batteries have attracted ever-increasing attention because of their decent ionic conductivity, flexibility, no liquid leakage, and good processability. Poly(vinylidene fluoride) (PVDF)-based polymer electrolytes have recently stood out among the polymer electrolytes due to their high room temperature ionic conductivity. However, the interface between PVDF-based polymer electrolytes and lithium metal decays over time until the batteries break down. Here, we introduce a small amount of poly(acrylic acid) (PAA) into a PVDF-based polymer electrolyte and synthesize an organic-organic composite electrolyte that alleviates the interfacial reaction with lithium metal, which shows great superiority over other modification methods such as coating. The cycle life of lithium symmetric cells is prolonged from 130 to 850 h at 0.44 mA cm^-2 due to the effective suppression of interfacial reaction. The much more stable interface also enables excellent cycle performance in a solid-state LiCoO₂||Li cell at 30 °C with a capacity decay of 0.03% per cycle for 1000 cycles, which is much lower than that of a cell without blending PAA (0.13% per cycle for only 450 cycles). The results would shed light on the applications of PVDF-based polymer electrolytes in solid-state lithium metal batteries.

Microstructure Characterization and Interfacial Reactions between Au-Sn Solder and Different Back Metallization Systems of GaAs MMICs

GaAs monolithic microwave integrated circuits (MMICs) with different back metallization systems (TiW/Au and Au/Ti/Au) exhibit different problems in the automatic Au-Sn eutectic bonding process, such as edge breakage or excessive voids. In this study, the formation mechanism of the edge breakage and excessive voids were investigated to prevent the damage of the MMICs in mass production scenarios. The microstructure and elemental distribution were studied using a scanning electron microscope and energy-dispersive spectroscopy. The void contents of the brazed region were measured with three-dimensional computed tomography. The top Au layer of the TiW/Au metallization partially dissolved in the melting An-Sn solder. Consequently, liquidus temperature of the solder increased, leading to isothermal solidification with the formation of ζ-Au₅Sn in the scrubbing process, which was the reason for the edge breakage. The terminal Au film of the Au/Ti/Au metallization completely dissolved in the melting An-Sn solder. The metallurgical combination was achieved by the formation of the TiAu₄ intermetallic compound between the Au-Sn solder and the Ti layer. The wettability of Au-Sn solder on Ti layer should be improved to prevent the formation of the excessive voids.

Effect of Metal Electrodes on Aging-Induced Performance Recovery in Perovskite Solar Cells

For commercialization of perovskite solar cells (PSCs), it is important to substitute the alternative electrode for Au to decrease the unit cost. From the early stage, Ag exhibits a potential to be a good counter electrode in PSCs; however, there is an abnormal s-shaped J-V curve with the Ag electrode, and it is recovered as time passes. The perception of the aging-induced recovery process and refutation of the raised stability issues are required for commercial application of Ag electrodes. Herein, we compared the aging effect of PSCs with Ag and Au electrodes and found that only devices with Ag electrodes have a dramatical aging-induced recovery process. We observed the change of photoelectronic properties only in the devices with Ag electrodes as time passes, which mainly contributes to recovery of the s-shaped J-V curve. We verified the work function change of an aged Ag electrode and its mechanism by photoelectron spectroscopy analysis. By comparing the light stability under 1 sun intensity illumination, we can assure the practical stability of Ag electrodes in case of being encapsulated. This work suggests the profound understanding of the aging-induced recovery process of PSCs and the possibility of commercial application of Ag electrodes.

Interfacial Reactions and Mechanical Properties Studies of C-Coated and C/B4C Duplex-Coated SiC Fiber-Reinforced Ti2AlNb Composites

Continuous SiC fiber-reinforced Ti2AlNb matrix composites have a great potential for high-temperature aviation structure applications, and their properties strongly depend on the microstructure of the interfacial reaction layer. Notably, introducing diffusion barrier coatings has still been a popular strategy for optimizing the interfacial structure and interfacial properties of SiCf/Ti. In this work, C coating and C/B4C duplex coating were successfully fabricated onto SiC fibers via chemical vapor deposition (CVD), then consolidated into the SiCf/C/Ti2AlNb and the SiCf/C/B4C/Ti2AlNb composites, respectively, via hot isostatic pressing (HIP) under the condition of 970 °C, 150 MPa, 120 min, and finally furnace cooled to room temperature. The C- and C/B4C-dominated interfacial reactions in the SiCf/C/Ti2AlNb and the SiCf/C/B4C/Ti2AlNb were explored, revealing two different reaction products sequences: The different-sized TiC and the coarse-grained (Ti,Nb)C + AlNb3 for the SiCf/C/Ti2AlNb; and the fine-grained TiB2 + TiC, the needle-shaped (Ti,Nb)B2/NbB + (Ti,Nb)C, the coarse-grained (Ti,Nb)C + AlNb2 for the SiCf/C/B4C/Ti2AlNb. Annealing experiments were further carried out to verify the different reaction kinetics caused by C coating and C/B4C duplex coating. The reaction layer (RL)-dominated interfacial strength and tensile strength estimations showed that higher interface strength and tensile strength occurred in the SiCf/C/Ti2AlNb instead of the SiCf/C/B4C/Ti2AlNb, when the same failure mode of fiber push-out took place.

Infrared Brazed Joints of Ti50Ni50 Shape Memory Alloy and Ti-15-3 Alloy Using Two Ag-Based Fillers

The wettability, microstructures, and bonding strength of infrared brazing Ti-15-3 and Ti₅₀Ni₅₀ shape memory alloy using 72Ag-28Cu (wt.%) and 68.8Ag-26.7Cu-4.5Ti (wt.%) filler metals have been investigated. Only Ticusil^® active braze readily wets both Ti₅₀Ni₅₀ and Ti-15-3 substrates. Wetting of eutectic 72Ag-28Cu melt on Ti₅₀Ni₅₀ base metal is greatly ameliorated by adding 4.5 wt.% Ti into the alloy. The brazed Ti-15-3/BAg-8/Ti₅₀Ni₅₀ joint consists of Cu-Ti intermetallics in the Ag-rich matrix. The formation of interfacial Cu(Ti,V) and (Cu_xNi_1-x)₂Ti intermetallics next to Ti-15-3 and Ti₅₀Ni₅₀ substrates, respectively, is attributed to the wetting of both substrates. The brazed Ti-15-3/Ticusil^®/Ti₅₀Ni₅₀ joint shows a vigorous reaction, which results in the formation of a large amount of Ti₂Ni intermetallics in the joint. The maximum joint strengths using BAg-8 and Ticusil^® filler metals are 197 MPa and 230 MPa, respectively.

Interfacial Microstructure in W/2024Al Composite and Inhibition of W-Al Direct Reaction by CeO₂ Doping: Formation and Crystallization of Al-Ce-Cu-W Amorphous Layers

In this work, interfacial microstructure in W/2024Al composite and inhibition of the W-Al direct reaction by CeO₂ doping were investigated. The composites were prepared through powder sintering, and after preparation the composites were treated by annealing at 823 K. For the prepared W/2024Al composite, a multi-phase thin layer composed of WAl₁₂ and WAl₅ compounds were formed at the interface due to the W-Al direct reaction. While doping CeO₂ in the composite, Al-Ce-Cu-W amorphous substituting of W-Al compounds were formed at the interfacial reaction layer. In an annealed state, the composite with CeO₂ doping shows a significant inhibitory effect on W-Al compounds, which was attributed to the crystallized layer that evolved from Al-Ce-Cu-W amorphous as an interfacial obstacle. The crystallization product for Al-Ce-Cu-W amorphous layer was identified as bcc-structure Al-Ce-Cu-W phase without any binary/ternary Ce-containing phases. Therefore, by doping CeO₂ in W/2024Al composite, W-Al direct reaction was markedly inhibited during both preparation and annealing.

OH-Radical Oxidation of Lung Surfactant Protein B on Aqueous Surfaces

Air pollutants generate reactive oxygen species on lung surfaces. Here we report how hydroxyl radicals (·OH) injected on the surface of water react with SP-B_1-25, a 25-residue polypeptide surrogate of human lung surfactant protein B. Our experiments consist of intersecting microjets of aqueous SP-B_1-25 solutions with O₃/O₂/H₂O/N₂(g) gas streams that are photolyzed into ·OH(g) in situ by 266 nm laser nanosecond pulses. Surface-sensitive mass spectrometry enables us to monitor the prompt (<10 μs) and simultaneous formation of primary O _n -containing products/intermediates (n≤5) triggered by the reaction of ·OH with interfacial SP-B_1-25. We found that O-atoms from both O₃ and ·OH are incorporated into the reactive cysteine Cys₈ and Cys₁₁ and tryptophan Trp₉ components of the hydrophobic N-terminus of SP-B_1-25 that lies at the topmost layers of the air-liquid interface. Remarkably, these processes are initiated by ·OH additions rather than by H-atom abstractions from S-H, C-H, or N-H groups. By increasing the hydrophilicity of the N-terminus region of SP-B_1-25, these transformations will impair its role as a surfactant.

Quantum Dots: Origin of Positive Aging in Quantum‐Dot Light‐Emitting Diodes (Adv. Sci. 10/2018)

In the movie “The Curious Case of Benjamin Button”, Benjamin Button becomes younger and younger as time passes by. He experiences a “positive aging” life, which seems impossible in human beings, but becomes a reality in quantum‐dot light‐emitting diodes (QLEDs). In article number https://doi.org/10.1002/advs.201800549 , Shuming Chen and co‐workers report positive aging in QLEDs, i.e., efficiency increased with time. They disclose the origin of positive aging and provide a new insight into the exciton quenching mechanisms, which would be useful for constructing efficient QLED devices.

Origin of Positive Aging in Quantum-Dot Light-Emitting Diodes

The phenomenon of positive aging, i.e., efficiency increased with time, is observed in quantum-dot light-emitting diodes (QLEDs). For example, the external quantum efficiency (EQE) of blue QLEDs is significantly improved from 4.93% to 12.97% after storage for 8 d. The origin of such positive aging is thoroughly investigated. The finding indicates that the interfacial reaction between Al cathode and ZnMgO electron transport layer accounts for such improvement. During shelf-aging, the Al slowly reacts with the oxygen from ZnMgO, and consequently, leads to the formation of AlO x and the production of oxygen vacancies in ZnMgO. The AlO x interlayer reduces the electron injection barrier while the oxygen vacancies increase the conductivity of ZnMgO and, as a result, the electron injection is effectively enhanced. Moreover, the AlO x can effectively suppress the quenching of excitons by metal electrode. Due to the enhancement of electron injection and suppression of exciton quenching, the aged blue, green, and red QLEDs exhibit a 2.6-, 1.3-, and 1.25-fold efficiency improvement, respectively. The studies disclose the origin of positive aging and provide a new insight into the exciton quenching mechanisms, which would be useful for further constructing efficient QLED devices.

Interfacial Reaction of Fulleropyrrolidines Affecting Organic Photovoltaic Performance

Fulleropyrrolidine derivatives are intrinsically basic owing to the amino group within the pyrrolidine structure. It can be predicted that the basicity of fulleropyrrolidine may affect the photovoltaic devices containing an acidic layer (e.g.

, PEDOT

PSS). To clarify the effect of basic fulleropyrrolidine derivatives, we synthesized compounds with an N-benzyl substituent group and fabricated organic photovoltaic (OPV) cells using this N-benzyl fulleropyrrolidine. A device structure with the ITO/PEDOT:PSS/organic layer (PTB7:fulleropyrrolidine)/Ca/Al showed high series resistance, short-circuit current density (J_sc), and low fill factor (FF) values. However, OPV cells having an inverted structure, without the PEDOT:PSS layer, contributed good device performance. We were able to reproduce the high series resistance in a model experiment using aqueous ammonia vapor to treat the PEDOT:PSS layer. Our results indicated that the activity of the PEDOT:PSS layer was affected by the basicity of the fulleropyrrolidines. These results also explain why this phenomenon does not occur at the interface of OPV devices when conventional [6,6]-phenyl C₆₁ butyric acid methyl ester is used as an acceptor material. This finding would contribute to enhancing the OPV device performances from a chemical view point of designing a new compound.

Al2O3 Passivation Effect in HfO2·Al2O3 Laminate Structures Grown on InP Substrates

The passivation effect of an Al₂O₃ layer on the electrical properties was investigated in HfO₂-Al₂O₃ laminate structures grown on indium phosphide (InP) substrate by atomic-layer deposition. The chemical state obtained using high-resolution X-ray photoelectron spectroscopy showed that interfacial reactions were dependent on the presence of the Al₂O₃ passivation layer and its sequence in the HfO₂-Al₂O₃ laminate structures. Because of the interfacial reaction, the Al₂O₃/HfO₂/Al₂O₃ structure showed the best electrical characteristics. The top Al₂O₃ layer suppressed the interdiffusion of oxidizing species into the HfO₂ films, whereas the bottom Al₂O₃ layer blocked the outdiffusion of In and P atoms. As a result, the formation of In-O bonds was more effectively suppressed in the Al₂O₃/HfO₂/Al₂O₃/InP structure than that in the HfO₂-on-InP system. Moreover, conductance data revealed that the Al₂O₃ layer on InP reduces the midgap traps to 2.6 × 10¹² eV^-1 cm^-2 (compared to that of HfO₂/InP, that is, 5.4 × 10¹² eV^-1 cm^-2). The suppression of gap states caused by the outdiffusion of In atoms significantly controls the degradation of capacitors caused by leakage current through the stacked oxide layers.

Parasitic Reactions in Nanosized Silicon Anodes for Lithium-Ion Batteries

When designing nano-Si electrodes for lithium-ion batteries, the detrimental effect of the c-Li₁₅Si₄ phase formed upon full lithiation is often a concern. In this study, Si nanoparticles with controlled particle sizes and morphology were synthesized, and parasitic reactions of the metastable c-Li₁₅Si₄ phase with the nonaqueous electrolyte was investigated. The use of smaller Si nanoparticles (∼60 nm) and the addition of fluoroethylene carbonate additive played decisive roles in the parasitic reactions such that the c-Li₁₅Si₄ phase could disappear at the end of lithiation. This suppression of c-Li₁₅Si₄ improved the cycle life of the nano-Si electrodes but with a little loss of specific capacity. In addition, the characteristic c-Li₁₅Si₄ peak in the differential capacity (dQ/dV) plots can be used as an early-stage indicator of cell capacity fade during cycling. Our findings can contribute to the design guidelines of Si electrodes and allow us to quantify another factor to the performance of the Si electrodes.

Soldering Characteristics and Mechanical Properties of Sn-1.0Ag-0.5Cu Solder with Minor Aluminum Addition

Driven by the trends towards miniaturization in lead free electronic products, researchers are putting immense efforts to improve the properties and reliabilities of Sn based solders. Recently, much interest has been shown on low silver (Ag) content solder SAC105 (Sn-1.0Ag-0.5Cu) because of economic reasons and improvement of impact resistance as compared to SAC305 (Sn-3.0Ag-0.5Cu. The present work investigates the effect of minor aluminum (Al) addition (0.1-0.5 wt.%) to SAC105 on the interfacial structure between solder and copper substrate during reflow. The addition of minor Al promoted formation of small, equiaxed Cu-Al particle, which are identified as Cu₃Al₂. Cu₃Al₂ resided at the near surface/edges of the solder and exhibited higher hardness and modulus. Results show that the minor addition of Al does not alter the morphology of the interfacial intermetallic compounds, but they substantially suppress the growth of the interfacial Cu₆Sn₅ intermetallic compound (IMC) after reflow. During isothermal aging, minor alloying Al has reduced the thickness of interfacial Cu₆Sn₅ IMC but has no significant effect on the thickness of Cu₃Sn. It is suggested that of atoms of Al exert their influence by hindering the flow of reacting species at the interface.