Uniform Films Research Articles

Dioctyl-substituted dibenzotetracyanonaphthoquinodimethane for air-stable n-channel organic semiconductor

Abstract In this study, a novel n-channel 11,11,12,12-tetracyanonaphtho-2,6-quinodimethane-based organic semiconductor C8-DBTNAP was synthesized. C8-DBTNAP had good solubility and low-lying lowest unoccupied molecular orbital level (−4.41 eV). The good thin-film formability of C8-DBTNAP made it produce continuous, strip-shaped and uniform crystalline films. C8-DBTNAP organic thin-film transistors demonstrated high electron mobility up to 0.4 cm2/Vs under air conditions. These findings revealed that DBTNAP skeleton can be expected as a potential building block for developing high-performance, air-stable n-channel organic semiconductors.

L-tryptophanium picrate as novel anticorrosion agent for mild steel in 5% HCl: A detailed experimental and in silico investigation

Acidizing in petroleum recovery often leads to severe corrosion of mild steel, necessitating the development of highly effective corrosion inhibitors. In this study, L-tryptophanium picrate ( [Trp][Pic]), an amino acid derivative synthesised by one-step synthesis involving two-component acid–base reaction between L-tryptophan and picric acid, is investigated as a novel corrosion inhibitor for mild steel in 5% HCl. A comprehensive experimental and theoretical approach was employed to evaluate its performance. Weight loss measurements, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) were used to determine the inhibition efficiency. At 30°C, [Trp][Pic] significantly increased the polarization resistance from 81.08 Ω cm² in the uninhibited solution to 462.15 Ω cm² in the presence of 100 ppm of [Trp][Pic], achieving an inhibition efficiency of 82.46%. PDP results confirmed its mixed-type behavior, reducing both anodic and cathodic reactions. Surface analysis through SEM and AFM demonstrated the formation of a uniform protective film of [Trp][Pic] that shielded the steel surface. X-ray photoelectron spectroscopy (XPS) supported the role of donor-acceptor interactions between heteroatoms and Fe atoms in the chemisorption mechanism. Molecular dynamics (MD) simulations identified key binding sites responsible for the strong adsorption of [Trp][Pic], providing insight into the molecular-level mechanism of inhibition. These findings highlight the potential of [Trp][Pic] as a promising corrosion inhibitor for industrial applications.

Investigations on the thermal stability and oxidation of exfoliated PdTe2 using Raman spectroscopy

Layered superconductive PdTe2, a promising thermoelectric material of high ZT values, has garnered considerable interest in the electronics and quantum computing domains. In this work, the thermal stability and oxidation of as-exfoliated PdTe2 flakes under different conditions were investigated through Raman spectroscopy, optical microscopy (OM), atom force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), showing high thermal stability up to 720 K (under rough vacuum conditions) and 573 K (under ambient conditions). With increased annealing temperature from 573 to 648 K, the as-exfoliated PdTe2 undergoes oxidation in air, forming uniform γ-TeO2 films on the flake surfaces. At 673 K, the flake surfaces clearly exhibit randomly distributed α-TeO2 nanoparticles in SEM images, indicating the transformation from the γ- to the α- phase. The AFM analysis conclusively demonstrates the morphology evolution of surface oxidation during different annealing periods, revealing an increase in oxidation from the edge to the surface center as a function of the annealing duration. Nanobubbles formed in PdTe2 but did not show observable enhancement on the surface oxidations. These results offer an essential understanding of the thermal surface stability and reactivity of PdTe2 in ambient, thus for the expected performance in future PdTe2-based thermoelectric device applications.

Janus Electronic Devices with Ultrathin High-κ Gate Dielectric Directly Integrated on 1T'-MoTe2.

Integrating high-quality dielectrics with two-dimensional (2D) transition metal chalcogenides (TMDCs) is crucial for high-performance electronics. However, the lack of dangling bonds on 2D material surfaces complicates direct dielectric deposition. We propose using atomic layer deposition (ALD) to integrate ultrathin high-κ dielectric directly on 1T'-MoTe2 surfaces, facilitating the creation of high-performance back-gated field-effect transistors (FETs). Exploiting 1T'-MoTe2's natural oxidation in ambient conditions, we directly deposit dense and uniform HfO2 dielectric films below 5 nm, achieving an equivalent oxide thickness (EOT) of 0.97 nm. The resulting back-gate transistors, with a monolayer MoSSe on HfO2/1T'-MoTe2, show a current on/off ratio over 105 and operate at low voltages (<1 V), indicating high gating efficiency and a charge carrier mobility of 2.93 cm2V-1s-1. Additionally, we demonstrate a 6 × 5 bottom-gated array of MoSSe transistors using all-1T'-MoTe2 electrodes, achieving an 86.7% sample yield. Our approach also enables the creation of various integrated logic circuits such as inverters, NAND, and NOR gates. This research offers a feasible method for integrating high-κ dielectric films using industrially compatible ALD processes, providing excellent thickness control, uniformity, and scalability for 2D electronic devices.

Chiral optical properties of metasurfaces comprised of chiral media: effects of geometric and material chirality

We deconvolute the distinct and sometimes competing effects of geometric and material chirality in metastructures created from materials that are intrinsically chiral. We find that overlapping Mie-like resonances in nanodisk arrays leads to 6-fold CD enhancement compared to a uniform film. Furthermore, making the medium chiral does not necessarily increase CD; enhancement depends on the magnitude of the Pasteur parameter and its real and imaginary components. Finally, to demonstrate how geometric and material chirality can be combined, we design a geometrically chiral meta-atom out of chiral media and observe over 9-fold enhancement in both CD and g-factor compared to a metasurface comprised of achiral material.

Formation mechanisms of product film on high corrosion resistant EW75 Mg alloy: The effect of corrosive media

Compact and uniform product films with the similar microstructure as magnesium substrate are formed on EW75 alloy in both NaCl and Na2SO4 solution, and the film growth rate in Na2SO4 was even faster than that in the higher corrosive NaCl. This special phenomenon was investigated by electrochemical measurements, transmission electron microscopy (TEM) observation and X-ray diffraction (XRD) analysis, experimental design of corrosive media with different conductivity and concentration was used, and the corrosion process of Mg matrix and Mg-RE precipitates was explored, respectively. The results show that compared with Cl-, SO42- exhibits the stronger binding trend with Mg2+/RE3+, resulting in the faster charge transfer of the anodic metal in SO42- containing solution. And the higher dissolution rate of Mg substrate in Na2SO4 solution promotes the formation of the product film.

Simulation and optimization of reactor airflow and magnetic field for enhanced thin film uniformity in physical vapor deposition

Planar magnetron sputtering reactors are widely utilized in the semiconductor industry due to their high deposition rate, low substrate temperature, and capability for large-area coating. Careful control of the reactor's flow field and magnetic field is essential to ensure appropriate thickness uniformity of the thin film and uniform etching of the target. Utilizing finite element analysis software, simulations were conducted to obtain numerical solutions for the airflow and magnetic field. An increase in the inlet diameter from 4 mm to 5 mm resulted in a 63.4 % decrease in the gas distribution unevenness coefficient. Conversely, increasing the outlet diameter from 1 mm to 2 mm led to a 636.6 % increase in the coefficient. At a pitch of 11.7 mm, the horizontal magnetic field component on the target surface peaked at 0.24 T, covering a larger area. A dual-runway structure reduced the circumferential component of the horizontal magnetic field by more than half. Analysis of the results precipitated the optimization of key component structures, resulting in an optimal solution: an air ring diameter of 5 mm, an outlet diameter of 1 mm, outlet spacing of 12 mm, double inlets, and 38 outlets on each side of the air ring. Further optimization determined the optimal magnet-to-target surface spacing of 11.7 mm, with the dual-runway structure effectively improving the uniformity of the radial magnetic field distribution and increasing the target etching area. This study provides a theoretical basis for optimizing planar magnetron sputtering reactors.

Resistive switching and artificial synapses performance of co-evaporated Cs3Cu2I5 films

Perovskite memristors have garnered significant interest for their potential simulating artificial synapses; however, the presence of the toxic lead-based perovskites has hindered advancements in this field. In this work, a nontoxic, thickness-controllable Cs3Cu2I5 perovskite functional layer is synthesized through a dual-source vapor deposition for the Ag/Cs3Cu2I5/ITO memristor. The co-evaporation method shows advantages of various element, controllable atomic ratio and thickness, free impurity, and continuously uniform film. This device demonstrates an operating voltage of 1.2 V, a low power consumption of 0.013 W, a retention time exceeding 104 s, and an endurance of over 400 cycles. The synaptic behavior is emulated using the memristor, focusing on phenomena such as short-term potentiation and depression, paired-pulse facilitation, and spike-time-dependent plasticity. The migration of Na+ and Cl− ions, which occurs between the synaptic cleft and the postsynaptic membrane in biological synapses, is analogously represented by the movement of Ag+ ions between functional layer and the bottom electrode of the memristor. This process is further analyzed using the Hodgkin–Huxley neuron model. The Cs3Cu2I5-based memristor shows considerable promise for applications in storage systems and artificial synapses.

Toward Sustainable Poly(lactic acid)/Poly(propylene carbonate) Blend Films with Balanced Mechanical Properties, High Optical Transmittance, and Gas Barrier Performance via Reactive Compatibilization and Biaxial Stretching.

Sustainable poly(lactic acid) (PLA)/poly(propylene carbonate) (PPC) blends were compatibilized by the environmentally friendly epoxidized soybean oil (ESO) through the chemical reaction of epoxy functional groups on ESO with the terminated carboxyl and hydroxyl groups of PLA/PPC. The compatibilization effect of ESO was confirmed by Fourier transform infrared spectroscopy, rheological property testing, differential scanning calorimetry, and morphological observations. It was revealed that the molecular chain entanglement between PLA and PPC was significantly enhanced and the dispersed PPC phase size was decreased, which endowed the blend with high viscosity modulus, low tan δ, and great stretchability, especially for the blend containing 1.0 wt % ESO. The compatibilization effect dramatically reinforced the toughening modification of PPC on PLA, resulting in a great ductility with a fracture strain up to 187.3%, more than 20 times that of the pristine PLA, while maintaining a high strength of 44.5 MPa. Compared to the neat PLA and the PLA/PPC blend, the compatibilized blend showed a much larger draw ratio of up to 6.5 × 6.5 during biaxial stretching, producing a uniform film with balanced mechanical properties, high optical transparency, and good oxygen barrier performance. This work will be of vital importance for guiding the preparation of PLA-based films with superior comprehensive properties.

Fully hot Air-Processed All-Inorganic CsPbI2Br perovskite solar cells for outdoor and indoor applications

The all-inorganic α-CsPbI2Br perovskite has emerged as a promising material for photovoltaic applications due to its superior optoelectronic properties and thermal stability. However, achieving a defect-free, crystalline CsPbI2Br perovskite film remains challenging due to the rapid crystal growth induced via high-temperature hot plate processing, which causes surface defects including pinholes and voids. This study introduces a novel hot plate-free methodology in which the perovskite film is fully processed using a dynamic hot air treatment under ambient conditions. Crystallographic and microscopic analyses reveal that hot air-assisted method produces highly crystalline, uniform, and compact perovskite film. The controlled crystal growth mechanism facilitated by the hot air process involves the formation of an intermediate phase (CsI-DMSO:PbX2), followed by gradual solvent evaporation, resulting in improved film quality. The resulting perovskite solar cells (PSCs) exhibited a champion power conversion efficiency (PCE) of 13.74 % and maintained around 51.60 % of its initial PCE after thermal aging at 85 ℃ under ambient conditions over 1440 h. Furthermore, under indoor white LED illumination (3200 K, 1000 lx), the optimized PSC achieved an impressive PCE of 22.50 %. These findings demonstrate that the dynamic hot air process is a viable and scalable technique for producing high-performance, stable PSCs under ambient conditions.

The Molecular Additive N-Acetyl-L-Phenylalanine Delays the Crystallization and Suppresses the Phase Impurity for Achieving Triple-Cation Perovskite Solar Cells with Efficiency Over 25.

The crystallization process plays an important role in the formation of high-quality perovskite film for achieving efficient perovskite solar cells (PSCs), especially in the formation of mixed-cation perovskite film, as there are normally more phase impurities than in pure CH(NH2)2PbI3 (FAPbI3) film. Herein, a molecular additive strategy, i.e., introducing non-planar molecule N-acetyl-L-phenylalanine (APO) into the lead iodide (PbI2) precursor solution, is proposed to modulate crystallization kinetics and inhibit the generation of phase impurities of metastable pretreated perovskite film. The delayed crystallization process promotes a sufficient reaction between organic salts solution and inorganic Pb-I framework, and perovskite phase decomposition is prevented by forming strong hydrogen bonds between ─NH and I, resulting in the formation of uniform film with large-size crystal grains and high-purity crystalline phase. Ultimately, the target PSC devices achieve an impressive power conversion efficiency (PCE) of 25.05%, which is among the highest values of triple-cation (FAMACs) PSCs. Meanwhile, PSC modules with 10.8 cm2 obtain a PCE of 20.35%. Furthermore, the unencapsulated PSCs retain 94% of the initial efficiency after 40 days of storage under ambient conditions with 20% RH and also yield superior operational stability under light soaking at maximum power point tracking (MPPT) in nitrogen (N2) atmosphere.

Improving Uniformity of Electroplated Co Thin Film on SOFC Interconnector by Controlling Electrochemical Behavior and Microstructure

Solid oxide fuel cells (SOFC), a third-generation ultra-clean fuel cell, operate at a higher temperature of 600°C and have high energy conversion efficiency. SOFC is capable of a combined power generation system and produces water as a by-product, therefore is attracting attention as one of the eco-friendly power sources. As the SOFC interconnect material, ferritic stainless steel containing Cr is dominant, however it has the problem of durability which originates from the sublimation of Cr on the interconnect surface during high temperature operation. To suppress the Cr sublimation, research is being extensively conducted and the coating of a thin passivation material is thought as a promising solution. In this study, we selected Co thin film as a passivation layer and developed an electroplating technique where the uniformity of Co thin film in an air channel pattern is controlled using organic additives and current densities. The difference in thickness of electroplated Co thin film according to the position of the pattern were measured. In addition, the microstructure of the Co thin film was observed using an EBSD (electron backscatter diffraction) system, and the corresponding electrochemical behavior was analyzed. The uniformity of the Co thin film improved as the current density decreased, which is the result of the increase of Co ions reaching the bottom of the pattern. Furthermore, the combination of thiourea and saccharin led to the decrease in the grain size, resulting in enhancing the uniformity.

Fabrication of Uniform Porous Anodic Aluminum Oxide by Anodizing Aluminum in Trisodium Phosphate with Higher pH Values

Anodizing of aluminum is an electrochemical process of surface oxidation to form an alumina layer. Porous anodic aluminum oxide (PAAO) possessing self-organized nanopores can be obtained by anodizing aluminum in several acidic electrolyte solutions, and it has been widely used to develop emerging applications, such as nano-filters and optical devices. Recently, we found that anodizing in several alkaline solutions caused the formation of PAAOs with unique nanostructures such as an extremely high porosity and ultra-flat barrier layer. However, the anodizing process in alkaline solutions with higher pH values produced a slightly non-uniform film due to the active dissolution environment of alumina. Herein, we report the fabrication of uniform PAAO film by anodizing aluminum in alkaline solutions and their unique nanostructures.High-purity aluminum specimens were electropolished in 78 vol% CH3COOH/ 22 vol% - 70% HClO4. The electropolished specimens, then, were anodized in a 0.3 M trisodium phosphate (Na3PO4) solution at 274 K (pH = 13.1) and a constant voltage of 2-100 V. A platinum plate was used as the cathode, and the aluminum specimen was placed parallel to and 22 mm from the platinum plate. We investigated the effect of various operating conditions on the formation of PAAO film. The growth behavior and internal structure of anodized specimens were examined by optical microscopy (OM), field-emission scanning electron microscopy (FE-SEM), and scanning transmission electron microscopy (STEM).Figure 1a shows the OM images of the aluminum specimen anodized in a 0.3 M Na3PO4 solution at 274 K and a constant voltage of 20 V for 60 min with and without stirring the solution. A non-uniform appearance with both weak white and metallic luster areas was obtained on the specimen anodized with stirring, whereas a uniform metallic luster can be observed without stirring. The SEM images of four different surface positions (2 mm intervals) of each anodized specimen are shown in Figure 1b. In the case of the stirring condition, the surface of PAAO on the left was dissolved due to the high pH value of the Na3PO4 solution and higher dissolution rate caused by stirring. On the other hand, a uniform PAAO film possessing similar nanoscale pores was successfully fabricated by suppressing non-uniform dissolution without stirring. The PAAO film grew by anodizing in the Na3PO4 solution at extremely low applied voltages less than 10 V. Figure 1

Synergistic Control of Molecular Self-Assembly and Orientation to Enhance the Performance of Organic Field-Effect Transistors Utilizing Solution-Processable Organic Semiconductors

Introduction: Fast development of solution-processable organic semiconductors and their utilization as active components of organic electronic devices has gained momentum in the recent past aiming towards the practical realization of low-cost flexible and printable electronics. The past decade has witnessed significant scientific efforts to improve the charge transport characteristics of organic semiconductors by tuning their chemical structure or by varying the film fabrication techniques to enhance the macromolecular ordering. Due to the quasi-one-dimensional nature of organic conjugated polymers (CPs), their backbone orientation and self-assembly have been extensively explored to improve the optoelectronic characteristics of organic electronic devices. Organic electronic devices quite often need multilayer fabrication of devise components, where control of their morphology along with the various interfaces critically controls the overall performance of the devices. Therefore, there is an urge for the facile fabrication of large-area uniform films with controllable film morphology and minimal interference to the underlying layers. Our group has developed and improvised a novel method of thin film fabrication known as the floating-film transfer method (FTM), which provides not only large-area uniform thin films but also these films exhibit directional molecular orientation. Control of molecular orientation is highly desired to control the extent and directionality (vertical or in-plane) of the charge transport, which needs to be amicably utilized to harness the full potentiality of the device performance under investigation. Results and Discussion: The uniqueness of the FTM lies in 1st of all the fabrication of floating films of solution-processable CPs on an orthogonal liquid substrate followed by its transfer on any desired substrate by stamping, which has been schematically represented in Fig.1(a). Thanks to the isolation of film fabrication and transfer, it is possible to fabricate multilayers of the same or different CPs without having any adverse effect on the underlying layers, which is one of the intriguing issues for thin film fabrication using solution processing. We have demonstrated that controlling the parameters for thin film fabrication using NR-P3HT under FTM led to not only macroscopically oriented thin films but also there was a remarkable enhancement in the field effect mobility (>100 times) of organic field-effect transistors (OFETs) as compared to their spin-coated thin film device counterparts. One of the well-studied CPs, PBTTT-C14 possesses a rigid-rod-like polymeric backbone with liquid-crystalline behaviour, which is rather difficult to orient, and has been reported to impart enhanced carrier mobility when its thin film was annealed at its liquid-crystalline temperature of 180oC. Utilizing highly edge-on oriented thin films of this CP processed by FTM, we have not only demonstrated a very high optical dichroism of >10 but also an OFET mobility of 1.24 cm2/Vs, which is one of the highest reported mobility for this class of CPs as shown in Fig. 1(b). Despite the enhancement in solubility as a function of increasing alkyl-chain length in the P3AT class of CPs, there is a drastic fall in carrier mobility up to 4-5 orders of magnitude. We have recently demonstrated that FTM is capable of solving this issue amicably, where the detrimental influence of alkyl chain length for planer charge carrier transport was not observed making the freedom for the selection of any of P3ATs for OFET applications. Fabrication of a large-area ≈40 cm2 film with uniform orientation was recently reported for poly(3,3‴-dialkylquaterthiophene) (PQT) using FTM. An array of bottom-gate top contact OFETs fabricated along the length of a single large-area (≈15 × 2.5 cm2) thin film demonstrated the average field-effect mobility of 0.03 cm2/V s with a very narrow standard deviation of 12%. It has been found that the pre-conceived notion of the orientation of the FTM thin films is perpendicular to the direction of the flow of thin films is not completely true and the viscous force of not only the liquid substrate but also the CP solution plays a vital role in determining the direction of orientation as shown schematically in Fig. 1(c). Based on combined theoretical and experimental approaches, we have demonstrated the control of the extent and direction of molecular orientation using DPP-TTT, a rigid rod-like donor-acceptor type CP, which is rather difficult to orient owing to its molecular rigidity. Harnessing the synergy of orientation and molecular orientation under FTM using DPP-TTT, a very high field-effect mobility of 12.4 cm2V-1s-1 was recently demonstrated, which is one of the highest values reported for solution-processable organic semiconducting polymers. Results pertaining to the film fabrication by FTM, orientation mechanism, film uniformity and anisotropy along with the application of FTM-processed films towards their suitability of OFETs will be discussed in detail. Figure 1

Band anisotropy and effective mass renormalization in strained metallic VO2 (101) thin films

We explore how strain impacts the band structure of metallic-phase VO2 thin films deposited on TiO2(101) substrates. Employing a combination of X-ray absorption linear dichroism and valence band measurements, we demonstrate that strain can alter the intrinsic band structure anisotropy of metallic VO2. Our findings reveal that reducing the thickness of VO2 films leads to a more isotropic band structure. This observation is further supported by an analysis of the electronic population redistribution in the d||−π*\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{{||}}{-}{\\pi }^{* }$$\\end{document} bands, which affects the screening length and induces effective mass renormalization. Overall, our results underscore the potential of strain manipulation in tailoring the electronic structure uniformity of thin films, thereby expanding the scope for engineering VO2 functionalities.

Engineering High-Color Purity Photonic Crystal Strain Sensors via Melt-Shear Process

Non-close-packed colloidal photonic crystals (CPhCs) are a class of optical materials characterized by their ability to reflect specific wavelengths of light, determined by the arrangement of constituent particles. The manipulation of particle spacing enables precise control over the reflected color, offering versatile coloration capabilities via mechanical or electrical means. This property renders CPhCs highly promising for diverse applications across various fields.In this investigation, our focus lies on developing a method for fabricating uniform photonic crystal films with exceptional color purity through a uniform melt-shear process. Leveraging polystyrene@poly(methylmethacrylate)@poly(ethyl acrylate) (PS@PMMA@PEA) core-intermediate-shell (CIS) particles with polydopamine (PDA), we crafted stretchable films with tailored optical properties. By subjecting the amorphous CIS particles to high shear force, we induced alignment and crystallization during the melt shear process, yielding films with enhanced crystallinity. The superior color purity exhibited by these films stems from the absorption of scattered light by the PDA coating, which effectively suppresses unwanted reflections. To optimize the active reflection layers, we systematically varied parameters including process temperature, shear rate, pressure, thickness, and stacking method of films. This comprehensive optimization strategy culminated in photonic crystal films capable of seamless color transitions from red to blue. Such remarkable color-changing properties hold significant promise for applications in biomimetic strain and stress sensing, where precise and responsive color variations are desirable indicators.

(Invited) Emerging Two-Dimensional Materials for Device Applications

Two-dimensional (2D) materials, such as Graphene, h-BN and MoS2, are promising candidates in a number of advanced device applications, owing to their exceptional electrical, optical and mechanical properties. Scalable growth of high quality 2D materials is crucial for their adoption in technological applications the same way the arrival of high-quality silicon single crystals was to the semiconductor industry. While CVD growth of wafer-scale monolayer graphene and TMDs has been demonstrated, considerable challenges still remain. In this talk, we first report a CVD method to grow fluorine rich 2D polymer (2DP-F) on varies substrates for low-k dielectrics in 2D TMDs based devices. Using precursors with low vaporize temperature, a uniform and ultra-flat 2DP-F film with controlled thickness can be deposited on silicon oxide wafer, glass, sapphire and mica substrates. Dielectric properties and relevant mechanical properties were carefully characterized. These 2DP-F films were then used as the substrate for transition metal dichalcogenides (TMDs) based devices, and significant improvements in device performances were found, possibly owing to the ultra-smooth and dangling bond free surface of 2DP-F that can significantly reduce the interfacial scattering of carriers.Next, we show that atomically thin Cs3Bi2I9, an all-inorganic lead-free perovskite derivative with strong optical activity can be successfully synthesized by vapor growth method. Reducing the dimensionality of such perovskites could utilize the materials’ advantages for solid-state information devices like valleytronics. By breaking the inversion symmetry, 2D Cs3Bi2I9 flakes with odd-layer number exhibited persistent, optically addressable valley polarization. This study potentially opens generalizable CVD method for growing a broad range of 2D perovskites towards cost-effective and energy-efficient integrated device applications. Finally, we report a two-step vapor phase growth process for the creation of high-quality vdW heterostructures based on perovskites and TMDCs, such as 2D Cs3Bi2I9/MoSe2, with a large lattice mismatch. Supported by experimental and theoretical investigations, we discover that the Cs3Bi2I9/MoSe2 vdW heterostructure possesses hybrid band alignments consisting of type-I and type-II heterojunctions because of the existence of defect energy levels in Cs3Bi2I9. More importantly, we demonstrate that the type-II heterojunction in the Cs3Bi2I9/MoSe2 vdW heterostructure not only shows a higher interlayer exciton density, but also exhibits a longer interlayer exciton lifetime than traditional 2D TMDCs based type-II heterostructures. Such vdW heterostructures provide promising platforms for exploring novel physics and cutting-edge optoelectronics and valleytronics applications.

Interrelation between External Pressure, SEI Structure and Electrodeposit Morphology in an Anode-Free Lithium Metal Battery

We explore the interrelation between external pressure (0.1, 1, 10 MPa), solid electrolyte interphase (SEI) structure/morphology, and lithium metal plating/stripping behavior. To simulate anode-free lithium metal batteries (AF-LMBs) analysis was performed on “empty” Cu current collectors in standard carbonate electrolyte. Lower pressure promotes organic-rich SEI and macroscopically heterogeneous, filament-like Li electrodeposits interspersed with pores. Higher pressure promotes inorganic F-rich SEI with more uniform and denser Li film. A “seeding layer” of lithiated pristine graphene (pG@Cu) favors an anion-derived F-rich SEI and promotes uniform metal electrodeposition, enabling extended electrochemical stability at a lower pressure. State-of-the-art electrochemical performance is achieved at 1MPa: pG-enabled half-cell is stable after 300 hrs (50 cycles) at 1 mA cm-2 rate - 3 mAh cm-2 capacity (17.5 mm plated/stripped), with cycling Coulombic efficiency (CE) of 99.8%. AF-LMB cells with high mass loading NMC622 cathode (21 mg cm-2) undergo 200 cycles with a CE of 99.4% at C/5-charge and C/2-discharge (1C = 178 mAh/g). Density functional theory (DFT) highlights the differences in the adsorption energy of solvated-Li+ onto various crystal planes of Cu (100), (110), and (111), versus lithiated/delithiated (0001) graphene, giving insight regarding the role of support surface energetics in promoting SEI heterogeneity.

Dependence of Cation Structures on Electrochemical Polymerization of Aniline in Phosphonium Ionic Liquids

Ionic liquids (ILs) are known to possess unique physicochemical and abundant design properties. When ILs are used as electrolytes in the electropolymerization reactions of aromatic compounds to form conducting polymers, the grown film properties are significantly dependent of the combination of cations and anions. Typical researches on the IL-based electrolytes have been described for nitrogen-based ILs;1) on the other hand, phosphonium-based ILs have also attracted attention in recent years. We have reported the preliminary electrochemical investigation for electropolymerization of aniline (ANi), indicating that the phosphonium ILs were able to be employed as potential electrolytes.2) In this work, various phosphonium ILs ( Fig. 1) including typical two phosphonium ILs such as triethylpenthylphosphonium bis(trifluoromethanesulfonyl)amide (P2225-TFSA) and tributylmethylphosphonium bis(trifluoromethanesulfonyl)amide (P4441-TFSA) 3) are selected for the electrooxidative polymerization of ANi, in order to investigate the influence of the physicochemical properties of the phosphonium ILs on the electropolymerization processes and the grown polyaniline (PANi) films.The phosphonium ILs were synthesized and purified according to a previously published paper.3) The electrolytes were prepared by adding 2.0 M of ANi monomer and 1.0 M of 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide (HTFSA) as a proton source. The electropolymerization was carried out by cyclic voltammetry (CV) using a three-electrode cell with a platinum disc or an indium tin oxide (ITO) as a working electrode, a Ag/Ag+ as a reference electrode and a platinum wire as a counter electrode (potential sweep rate: 0.1 V s-1, potential range: -0.5~+1.5 V). The morphology of the electropolymerized PANi films on the ITO electrode were observed by scanning electron microscopy (SEM).Fig. 2 shows the cyclic voltammograms for electrooxidative polymerization of ANi in typical P2225-TFSA and P4441-TFSA. It was found that the P4441-TFSA based electrolyte tended to give relatively low oxidation currents, forming the uniform PANi film on the electrode surface as shown in Fig. 3. The voltammograms for the electropolymerization measured in various phosphonium ILs will be discussed, demonstrating the influence of the transport property of the phosphonium IL electrolytes.

Catalytic Properties of FeCoNi Alloy Electrode for Alkaline Water Electrolysis Prepared by Anodizing

1.Introduction Alkaline water splitting, a low-cost and simple hydrogen production method, has been attracting attention to the realization of a sustainable society. However, the overpotential of the oxygen evolution reaction (OER) on the anode is high and the hydrogen production efficiency is low. Catalysts containing Fe, Co, and Ni are expected to be promising candidates for electrodes materials [1]. Recently, we succeeded in fabricating FeNi and FeNiCo alloy electrodes covered with a porous metal fluoride film by anodizing, which exhibited better OER activity and durability than OER catalysts [2]. We reported that the metal fluoride films synthesized by anodizing in fluoride-containing organic electrolytes converted to metal oxyhydroxide during OER in KOH aqueous solution. However, the physical properties of the films and electrode characteristics, which are the factors responsible for the high OER activity of this electrode, remain unclear.In this study, various commercial FeNiCo and FeNi alloys (Kovar: Fe-17 mass% Co-29 mass% Ni, 42-Invar: Fe-42 mass% Ni, 45-Permalloy: Fe-45 mass% Ni, 78-Permalloy: Fe-78 mass% Ni) were anodized to fabricate highly active OER electrodes and applied to in-situ Raman spectroscopic characterization to understand the activation mechanism of the anodized alloy electrodes.2.Experimental Commercial FeCoNi and FeNi alloys were used for electrode preparation. The electrolytes used for anodizing were ethylene glycol containing 0.54 M NH4F and 2.5 M H2O for Kovar, 45-Permalloy, and 42-Invar, and ethylene glycol containing 0.08 M NH4F and 0.02 M H2O for 78-Permalloy. The anodizing process was performed at 10 V for 60 min at 293 K in an ethylene glycol-based electrolyte, and platinum was used as the counter electrode. The surface morphology and composition of the OER electrodes were measured using field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. In-situ Raman measurements were conducted using laboratory-made cells. The measurement was performed using a three-electrode system with a platinum counter electrode and an Hg/HgO electrode as the reference electrode under a flow of 1 M KOH aqueous solution at 24.0 mL min-1. In-situ Raman spectra were measured under potentiostatic conditions every 0.2 V from 1.13 V vs. RHE.3.Results and discussion【morphology and compositional characterization】 The surface morphology of the films was highly dependent on the composition of the FeCoNi and FeNi alloys. A uniform and smooth film with an average thickness of 200 nm was observed in the anodized 78-Permalloy electrode, and non-uniform films with an average thickness of 1 µm were observed in the anodized 45-Permalloy and 42-Invar electrodes. The anodized Kovar electrode exhibited a non-uniform and wide crack film with an average thickness of 2.5 µm. The cationic composition of the films was also dependent on the composition of the commercial FeCoNi and FeNi alloys. The anodized 78-Permalloy electrode showed the lowest Fe content in the film.【Raman measurement】 The ex-situ Raman measurements revealed the presence of mixed phases of spinel oxide and metal oxyhydroxide for all electrodes after OER, indicating that the metal fluoride films were completely converted to metal oxide and metal oxyhydroxide. Then, in-situ Raman measurements were conducted under the controlled potential in 1 M KOH aqueous solution. The peak intensity of spinel oxides decreased and that of metal oxyhydroxides increased with increasing applied potential. Because the spinel oxide peaks disappeared and those of metal oxyhydroxide were only observed at the OER onset potential for all electrodes, the in-situ measurements revealed that metal oxyhydroxide is an active phase for OER in the electrolysis system. Interestingly, when the electrode potential was returned to negative, the film structure reverted to the mixed phases of spinel oxide and metal oxyhydroxide. Therefore, we confirmed that the anodized electrodes possess structural reversibility. However, since no trend was observed in the correlation between structural change behaviors and the order of OER activities of the electrodes, other factors would also contribute to OER activities in addition to the formation of the metal-oxyhydroxide structure.