High Air Stability Research Articles

Liquid Metal Mediated Heterostructure Fluoride Solid Electrolytes of High Conductivity and Air Stability for Sustainable Na Metal Batteries.

Fluoride-based solid electrolytes (SEs) have emerged as a promising component for high-energy-density rechargeable solid-state batteries (SSBs) in view of their wide electrochemical window, high air stability, and interface compatibility, but they still face the challenge of low ion conductivity and the lack of a desired structure for sodium metal SSBs. Here, we report a sodium-rich heterostructure fluoride SE, Na3GaF6-Ga2O3-NaCl (NGFOC-G), synthesized via in situ oxidation of liquid metal gallium and in situ chlorination using low-melting GaCl3. The distinctive features of NGFOC-G include single-crystal Na3GaF6 domains within an open-framework structure, composite interface decoration of Ga2O3 and NaCl with a concentration gradient, exceptional air stability, and high electrochemical oxidation stability. By leveraging the penetration of gallium at NaF grain boundaries and the in situ self-oxidation to form Ga2O3 nanodomains, the solid-phase reaction kinetics of NaF and GaF3 is activated for facilitating the synthesis of main component Na3GaF6. The introduction of a small amount of a chlorine source during synthesis further softens and modifies the boundaries of Na3GaF6 along with Ga2O3. Benefiting from the enhanced interface ion transport, the optimized NGFOC-G exhibits an ionic conductivity up to 10-4 S/cm at 40 °C, which is the highest level reported among fluoride-based sodium-ion SEs. This SE demonstrates a "self-protection" mechanism, where the formation of a high Young's modulus transition layer rich in NaF and Na2O under electrochemical driving prevents the dendrite growth of sodium metal. The corresponding Na/Na symmetric cells show minimal voltage hysteresis and stable cycling performance for at least 1000 h. The Na/NGFOC-G/Na3V2(PO4)3 cell demonstrates stable capacity release around 100 mAh/g at room temperature. The Na/NGFOC-G/FeF3 cell delivers a high capacity of 461 mAh/g with an excellent stability of conversion reaction cycling.

A Durable and High-Voltage Mn-Graphite Dual-Ion Battery Using Mn-Based Hybrid Electrolytes.

Rechargeable Mn-metal batteries (MMBs) can attract considerable attention because Mn has the intrinsic merits including high energy density (976mAhg-1), high air stability, and low toxicity. However, the application of Mn in rechargeable batteries is limited by the lack of proper cathodes for reversible Mn2+ intercalation/de-intercalation, thus leading to low working voltage (<1.8V) and poor cycling stability (≤200cycles). Herein, a high-voltage and durable MMB with graphite as the cathode is successfully constructed using a LiPF6-Mn(TFSI)2 hybrid electrolyte, which shows a high discharge voltage of 2.34V and long-term stability of up to 1000cycles. Mn(TFSI)2 can reduce the plating/stripping overpotential of Mn ions, while LiPF6 can efficiently improve the conductivity of the electrolyte. Electrochemical in-situ characterization implies the dual-anions intercalation/de-intercalation at the cathode and Mn2+ plating/stripping reaction at the anode. Theoretical calculations unveil the top site of graphite is the energetically favorable for anions intercalation and TFSI- shows the low migration barrier. This work paves an avenue for designing high-performance rechargeable MMBs towards electricity storage.

Passivating Polycrystalline Copper with an Ultrathin Samarium Layer

Herein, it is reported that how a layer of samarium (Sm) with a thickness equivalent to ≈2 atoms (0.8 nm) deposited by thermal evaporation is remarkably effective at passivating polycrystalline copper (Cu) toward oxidation in ambient air. To monitor the rate of Cu oxidation in real time, slablike Cu films with a thickness of 9 nm are fabricated on glass modified with a layer of 3‐mercaptopropyl silatrane, which immobilizes condensing Cu atoms by reaction with the thiol moiety, promoting slablike film formation at very low thickness. Upon exposure to ambient air the rate of increase in electrical resistance due to reaction with oxygen and water is slowed by more than an order of magnitude when the Cu film is capped with the ultrathin Sm layer. After 1 year, the resistance increases by ≈30% as compared to ≈190% for Cu films without an ultrathin Sm layer. Photoelectron spectroscopy, atomic force microscopy, and Kelvin probe measurements shed light on the underlying mechanism of passivation. Additionally, the ultrathin Sm layer is greatly lowering the work function of polycrystalline Cu films making this approach attractive for applications requiring a low‐work‐function electrode with high stability in air.

Li8P2S9 solid electrolyte with high ionic conductivity and air stability by Bi2Se3 co-doping

Excellent ionic conductivity and electronic insulation are core properties of solid electrolytes. In this study, we use high-energy ball milling and high-temperature sintering heat treatment to prepare a solid electrolyte, and its ionic conductivity (1.57 × 10−4 S⋅cm−1) is comparable with that of Li8P2S9 in the glass–ceramic state. On this basis, we modify the prepared LPS solid-state electrolyte through Bi2Se3 doping. First-principles computations based on density functional theory (DFT) indicate that Bi2Se3 doping can broaden lithium-ion transport channels and increase the lithium-ion conduction rate. With a doping ratio of 4 %, the ion conductivity reaches 3.02 × 10−3 S⋅cm−1, which offers good insulation to electrons and a stable −0.5 to 5 V (vs. Li/Li+) high-voltage platform. Additionally, Bi2Se3 doping significantly improved the air stability of the LPS solid electrolyte, reducing its adsorption energy to water and preventing the replacement of S by O from H2O.

Asymmetric contact-induced selective doping of CVD-grown bilayer WS2 and its application in high-performance photodetection with an ultralow dark current.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are excellent candidates for high-performance optoelectronics due to their high carrier mobility, air stability and strong optical absorption. However, photodetectors made with monolayer TMDs often exhibit a high dark current, and thus, there is a scope for further improvement. Herein, we developed a 2D bilayer tungsten disulfide (WS2) based photodetector (PD) with asymmetric contacts that exhibits an exceptionally low dark current and high specific detectivity. High-quality and large-area monolayer and bilayer WS2 flakes were synthesized using a thermal chemical vapor deposition system. Compared to conventional symmetric contact electrodes, utilizing metal electrodes with higher and lower work functions relative to bilayer WS2 aids in achieving asymmetric lateral doping in the WS2 flakes. This doping asymmetry was confirmed through the photoluminescence spectral profile and Raman mapping analysis. With the asymmetric contacts on bilayer WS2, we find evidence of selective doping of electrons and holes near the Ti and Au contacts, respectively, while the WS2 region away from the contacts remains intrinsic. When compared with the symmetric contact case, the dark current in the WS2 PD with asymmetric (Au, Ti) contact decreases by an order of magnitude under reverse bias with a concomitant increase in the photocurrent, resulting in an improved on/off ratio of ∼105 and overall improved device performance under identical illumination conditions. We explained this improved performance based on the energy band alignment showing a unidirectional charge flow under light illumination. Our results indicate that the planar device structure and compatibility with current nanofabrication technologies can facilitate its integration into advanced chips for futuristic low-power optoelectronic and nanophotonic applications.

SiSe2 for Superior Sulfide Solid Electrolytes and Li-Ion Batteries.

Among the various existing layered compounds, silicon diselenide (SiSe2) possesses diverse chemical and physical properties, owing to its large interlayer spacing and interesting atomic arrangements. Despite the unique properties of layered SiSe2, it has not yet been used in energy applications. Herein, we introduce the synthesis of layered SiSe2 through a facile solid-state synthetic route and demonstrate its versatility as a sulfide solid electrolyte (SE) additive for all-solid-state batteries (ASSBs) and as an anode material for Li-ion batteries (LIBs). Li-argyrodites with various compositions substituted with SiSe2 are synthesized and evaluated as sulfide SEs for ASSBs. SiSe2-substituted Li-argyrodites exhibit high ionic conductivities, low activation energies, and high air stabilities. In addition, when using a sulfide SE, the ASSB full cell exhibits a high discharge/charge capacity of 202/169 mAh g-1 with a high initial Coulombic efficiency (ICE) of 83.7% and stable capacity retention at 1C after 100 cycles. Furthermore, the Li-storage properties of SiSe2 as an anode material for LIBs are evaluated, and its Li-pathway mechanism is explored by using various cutting-edge ex situ analytical tools. Moreover, the SiSe2 nanocomposite anode exhibits a high Li- insertion/extraction capacity of 950/775 mAh g-1, a high ICE of 81.6%, a fast rate capability, and stable capacity retention after 300 cycles. Accordingly, layered SiSe2 and its versatile applications as a sulfide SE additive for ASSBs and an anode material for LIBs are promising candidates in energy storage applications as well as myriad other applications.

Liquid Metal Powders Wrapped with Robust Shell by Bimetallic Ions Chelation Strategy for Energy Harvesting and Flexible Electronics

AbstractExcellent electrical and fluidic properties render liquid metal (LM) a promising material for flexible electronics, soft robotics, and stretchable circuits. Although producing LM micro/nano droplets by nanometerization addresses the tricky issue of the processing result from high surface tension, it still remains challenging to obtain stable LM droplets because of their dynamic surfaces. In this study, LM powders wrapped with robust shells are fabricated by bimetallic ions chelation strategy. During sonicating LM (e.g., EGaIn) in an alginate solution, a microgel shell is first formed by the coordination of Ga3+ and carboxyl groups. Subsequently, LM powders are achieved by introducing Ca2+ as secondary metal ions to chelate with redundant carboxyl groups. Besides high chemical stability in water and air, these nonstick LM powders also exhibit superior photothermal effects for energy harvesting, being capable of recovering electrical conductivity by mechanical sintering for flexible electronics. These conductive circuits based on LM powders not only work as electro‐thermal heaters, and electromagnetic interference shielding material but also can be designed as smart actuators. Thus, this bimetallic ions chelation strategy may start a pathway to produce stable, transportable LM powders with multifunctional properties, applicable in stretchable electronics, smart actuators, and electric skins.

Air- and photo-stable luminescent carbodicarbene-azaboraacenium ions.

Substitution of a C=C bond by an isoelectronic B-N bond is a well-established strategy to alter the electronic structure and stability of acenes. BN-substituted acenes that possess narrow energy gaps have attractive optoelectronic properties. However, they are susceptible to air and/or light. Here we present the design, synthesis and molecular structures of fully π-conjugated cationic BN-doped acenes stabilized by carbodicarbene ligands. They are luminescent in the solution and solid states and show high air and moisture stability. Compared with their neutral BN-substituted counterparts as well as the parent all-carbon acenes, these species display improved quantum yields and small optical gaps. The electronic structures of the azabora-anthracene and azabora-tetracene cations resemble higher-order acenes while possessing high photo-oxidative resistance. Investigations using density functional theory suggest that the stability and photo-physics of these conjugated systems may be ascribed to their cationic nature and the electronic properties of the carbodicarbene.

Iridium Catalysts with f-Amphbinol Ligands: Highly Stereoselective Hydrogenation of a Variety of Ketones.

A series of novel and modular ferrorence-based amino-phosphine-binol (f-amphbinol) ligands have been successfully synthesized. The f-amphbinol ligands exhibited extremely high air stability and catalytic efficiency in the Ir-catalyzed stereoselective hydrogenation of various ketones to afford corresponding stereodefined alcohols with excellent results (full conversions, cis/trans >99:1, and 83% → 99% ee, TON up to 500 000). Control experiments have shown that -OH and -NH groups played a key role in this stereoselective hydrogenation.

Modulating p-type doping of two dimensional material palladium diselenide

The van der Waals heterostructures have evolved as novel materials for complementing the Si-based semiconductor technologies. Group-10 noble metal dichalcogenides (e.g., PtS2, PtSe2, PdS2, and PdSe2) have been listed into two-dimensional (2D) materials toolkit to assemble van der Waals heterostructures. Among them, PdSe2 demonstrates advantages of high stability in air, high mobility, and wide tunable bandgap. However, the regulation of p-type doping of PdSe2 remains unsolved problem prior to fabricating p–n junction as a fundamental platform of semiconductor physics. Besides, a quantitative method for the controllable doping of PdSe2 is yet to be reported. In this study, the doping level of PdSe2 was correlated with the concentration of Lewis acids, for example, SnCl4, used for soaking. Considering the transfer characteristics, the threshold voltage (the gate voltage corresponding to the minimum drain current) increased after SnCl4 soaking treatment. PdSe2 transistors were soaked in SnCl4 solutions with five different concentrations. The threshold voltages from the as-obtained transfer curves were extracted for linear fitting to the threshold voltage versus doping concentration correlation equation. This study provides in-depth insights into the controllable p-type doping of PdSe2. It may also push forward the research of the regulation of conductivity behaviors of 2D materials.

High Reactivity of Supermolecular Nanoentities of a Vitamin B12 Derivative in Langmuir-Schaefer Films Toward Gaseous Toxins.

Recently, we have described the first supermolecular nanoentities (SMEs) of a vitamin B12 derivative, viz., a monocyano form of heptabutyl cobyrinate ((CN-)BuCby), unique nanoparticles with strong noncovalent intermolecular interactions, and emerging optical and redox properties. In this work, the fast response of thin films based on the SMEs of the B12 derivative to gaseous toxins (viz., hydrogen cyanide, ammonia, sulfur dioxide, and hydrogen sulfide) particularly dangerous for humans was demonstrated. The reaction between SMEs of (CN-)BuCby in Langmuir-Schaefer (LS) films and HCN generates dicyano species and proceeds ca. 5-fold more rapidly than the process involving drop-coated films that contain (CN-)BuCby in molecular form. The highest sensitivity toward HCN was achieved by using thicker LS films. The reaction proceeds reversibly: upon exposure to air, the dicyano complex undergoes partial decyanation. The decyanated complex retains reactivity toward HCN for at least four subsequent cycles. The processes involving SMEs of (CN-)BuCby and NH3, SO2, and H2S are irreversible, and the sensitivity of the films toward these gases is lower in comparison with HCN. Presented data provides mechanistic information on the reactions involving solid vitamin B12 derivatives and gaseous toxins. In the case of NH3, deprotonation of the coordinated Co(III)-ion water molecule occurs, and the generated hydroxocyano species exhibit high air stability. After binding of SO2, a mixture of sulfito and dicyano species is produced, and the regenerated film contains aquacyano and diaqua or aquahydroxo species, which possess high reactivity toward gaseous toxins. Reaction with H2S produces a mixture of the Co(III)-dicyano form and Co(II)-species containing sulfide oxidation products, which are resistant to aerobic oxidation. Our findings can be used for the development of naked-eye, electronic optic, and chemiresistive sensors toward gaseous toxins with improved reactivity for prompt cyanide detection in air, blood, and plant samples and for analysis of exhaled gases for the diagnosis of diseases.

Stable two-dimensional tin-based perovskites for warm-white light emitters

Two-dimensional (2D) Sn-based organic-inorganic hybrid perovskites are useful materials for white light emitters due to their super high fluorescence efficiency and higher stability when compared to their three-dimensional (3D) counterparts. Herein, 2D Ruddlesden-Popper (RP) perovskites (BA)2Sn(Br1-x Ix)4 (BA = n-butylammonium, x: 0–1) were prepared and regulated using halogen doping. As iodine content increased, the band gap of (BA)2Sn(Br1-xIx)4 was finely regulated from 2.35 eV to 2.0 eV, thereby tuning the photoluminescence from yellow to red with relatively high PLQY exceeding 40 %. The use of small amounts of Pb2+ to stabilize Sn2+ through the addition of PbO in the precursor solution resulted in high air- and photo stable (BA)2Pb0.1Sn0.9(Br–I)4 phosphors with bright yellow to red light. The mixture with (BA)2PbBr4 (blue light phosphor) followed by excitement by UV LED chips (285 nm) resulted in cold and warm white Sn–Br–I perovskite LEDs. The CIE coordinates and correlated color temperature (CCT) indicated Br0.4I0.6 LED as an ideal warm-white emitter with suitable CIE (0.352, 0.330) and CCT (4376.3 K). The prepared white LEDs showed high photo and air stability without significant luminescence decay (<5 % relative) under continuous UV light excitation over 200 min and exposure to air for 3 months.

Highly Stable Protonic Ceramic Electrolysis Cells Based on Air Electrodes with Finger-Like Pores Current Collection Layers Running in High-Steam-Content Air.

The steam content in the air electrode is one of the major factors determining the efficiency and stability of protonic ceramic electrolysis cells (PCECs). In this work, the La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) current collection layer (CCL) film with unique finger-like pores was successfully prepared by the phase-inversion tape-casting technique (PT), which promoted the gas diffusion inside the electrode and effectively improved the stability of the single cell in high-humidity air. A screen-printed LSCF-BaCe0.7Zr0.1Y0.1Yb0.1O3 catalytic active layer (CAL) was also applied to match the thermal expansion coefficient (TEC) values and improve the interface combination. The electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) studies of the symmetric cells showed that when the film was used to match different CALs as an air electrode, the gas diffusion inside the electrode was no longer restricted by the increasing steam content in air. The single cell exhibited a high electrolysis current density of 1 A cm-2 (1.25 V) at 650 °C; furthermore, no performance degradation was observed in this high current density when electrolyzed in air with 40 and 60% humidity for more than 250 h. These results present a simplified and economical scheme to develop air electrodes with high stability in wet air with a high steam content.

Highly sensitive, super high stretchable hydrogel strain sensor with underwater repeated adhesion and rapid healing

Traditional hydrogel-based strain sensors do not work well under water due to extreme swelling and poor adhesion to substrates in water-rich conditions. Inspired by the jellyfish tentacles, a super stretchable dual crosslinked hydrogel was prepared as a motion sensor underwater. The hydrogel contained a cationic surfactant, hexadecyl trimethyl ammonium bromide (CTAB), that crosslinked with hydrophobic lauryl methacrylate (LMA) units in an AA-LMA copolymer. Al3+ ions also coordinated with carboxyl groups in PAA chains and amino groups on chitosan (CS) to form ionic crosslink points. The formed hydrogel exhibited excellent anti-swelling characteristics, superior tensile properties (≈3000%), and rapid self-healing performance. Due to the complementary effects of electrostatic interactions and dynamic chemical bond formation, the hydrogel efficiently and repeatably adhered to various biological tissues, such as hogskin and shrimp, in aquatic environments. Moreover, the hydrogel-based strain sensor showed high sensitivity (GF = 2.04) over a wide sensing range from 0 to 1000% strain with high stability in air and water. The prepared materials' unique performance further expands their application prospects in flexible wearable devices, anti-counterfeiting recognition, and other fields in environmental conditions.

Inhibiting in Situ Phase Transition in Ruddlesdenpopper Perovskite Via Tailoring Bond Hybridization for Oxygen Ion Conduction

Owing to the excellent physical and chemical properties, mixed ionic-electronic conducting (MIEC) oxide materials, especially Ruddlesden-Popper (RP) perovskite oxides with the chemical formula of An+1BnO3n+1, are interesting materials for gas separation, solid oxide fuel/electrolysis cells, polymer electrolyte fuel cells, lithium-ion battery, sodium-ion battery, zinc ion battery and metal-air battery. The in-situ phase transition at different temperatures is a common phenomenon for these MIEC oxide materials, which generally exerts a great influence on the properties and functionalities of these materials and finally determines their performance in various applications. However, the in-depth understanding of the mechanism of phase transitions is still limited so far. Element-doping has been recognized as a facile and efficient strategy to improve the oxygen ionic or electronic conductivity or to stabilize the crystal phase structure (inhibiting both ex-situ and in-situ phase transitions) favorable for oxygen ion conduction. Herein, the ex-situ collapse at room temperature of crystal structure together with the generation of impurities in orthorhombic Pr2NiO4 through Mo doping are observed as the rearrangement of praseodymium atoms-based lattice deformation, which could be attributed to the Mo-induced destabilization of the Pr2NiO4 systems. Noteworthy is that, such effect can be prohibited by controlling the doping contents, and the resultant materials would give rise to the inhibition of in-situ phase transition (high temperature) from low order Pr2NiO4 (An+1BnO3n+1 (n=1)) to high order Pr4Ni3O10 (An+1BnO3n+1 (n=3)) by adjusting bond hybridization at the phase interface. Mo-doping can influence the covalent interaction between praseodymium and oxygen and then promotes the mobility of interstitial oxygen. Pr2Ni1-xMoxO4+ δ were further developed as oxygen separation membrane to help further evaluate the performance of oxygen ion conductivity. In Pr2Ni1-xMoxO4+ δ, Mo doping level of x = 0.05 resulted in an oxygen permeation flux of 3.35 mL min-1 cm-2 at 1000 °C, comparing favorably with the literature. Furthermore, membranes made with Pr2Ni0.95Mo0.05O4+ δ showed high permeation stability in air or helium, and exhibits high CO2 tolerance without obvious decline of the oxygen permeation flux during 500 hours at round 900 °C. This work advances our understanding of the ex-situ and in-situ phase transitions of Pr2NiO4-based RP perovskite materials and shows how Mo doping can stabilizes the in-situ phase structure and improves the mobility of interstitial oxygen. Figure 1

Designing high-efficiency electrode contacts to two-dimensional semiconductor Cu2Se

High-efficiency electrode contact plays a pivotal role in achieving 2D material-based high performance nano devices. Recently, monolayer semiconducting Cu2Se with high stability in air and high carrier mobility of about 103 cm2 V−1 s−1 have been experimentally fabricated. Herein, to design high-efficiency electrode contacts for Cu2Se monolayer, the contact properties between Cu2Se monolayer and a series of experimentally fabricated 2D metals (MX2 in T-phase or H-phase, M = Ni, Nb, Ti, V, Co, Zr, and Ta, X = S, Se and Te) are systematically investigated based on first-principles calculations. Considering both Schottky barriers and tunneling barriers of these metal–semiconductor junctions (MSJs), H-NbSe2 is screened out as the most adaptable electrode for monolayer Cu2Se. Moreover, the fermi level pinning effects are discovered in these MSJs due to the potential steps contributed by the interface dipoles. Our work not only provides useful instruction for the design of high-performance 2D nano devices based on Cu2Se monolayer but also offers insights for prospection into the fundamental electronic properties of MSJs.

Efficient production of ligand-free microscintillators at gram-scale for high-resolution X-ray luminescence imaging

The efficient production of high-quality scintillators with long radioluminescence afterglow is crucial for high-performance X-ray luminescence extension imaging. However, scaling-up the synthesis of ligand-free scintillators to fabricate large-area X-ray imaging screens for industrial applications remains a challenge. In this study, we report an efficient method to synthesize ligand-free, lanthanide-doped microscintillators by a one-pot reaction via the concentrated hydrothermal method. The as-synthesized microscintillators exhibit prolonged persistent radioluminescence for up to 30 days after X-ray exposure and remain high stability in air or water for more than 18 months without deterioration. Monte Carlo simulations indicate that the size effect is responsible for the excellent afterglow performance of the microscintillators. We employ these high-quality lanthanide-doped microscintillators to fabricate a large-area X-ray imaging detector using a blade-coating method, a spatial resolution of 24.9 lp/mm for X-ray imaging. Our study offers a solution for scaling-up the synthesis of low-cost microscintillators for practical applications.

Fabrication of large columnar grains composed CsPbBr3 films for efficient solar cells through ligand engineering

All inorganic perovskite of CsPbBr3 based perovskite solar cells (PSCs) have attracted increasingly attentions in the hot topics for research of PSCs owing to their high stability in air. Fabrication of columnar CsPbBr3 grains spanning the whole films is strongly desired for fabrication of highly efficient solar cells. Here, we introduce a polymer of polyethylene oxide (PEO) into PbBr2 solution as a ligand to modify the formation of CsPbBr3 films, and then promote the microstructure of CsPbBr3 films, which evolves from small grains to equiaxed large grains with preferred crystallographic orientation. The improved quality of CsPbBr3 films contributes to low defect density and prolonged life time of carriers. As a result, the efficiency of carbon-based hole transportation layer (HTL) free solar cell boosts from 5.92 % to 8.12 % by optimizing the volume fraction of PEO in PbBr2 solution.

Synergistic Effect of Calcination and Sintering on the Reduction of Grain Boundary Resistance of LATP Solid Electrolyte.

The NASICON-type Li1.4Al0.4Ti1.6(PO4)3 (LATP) solid electrolyte is a promising candidate for next-generation lithium-ion batteries due to its high stability in air and moisture, as well as high bulk ion conductivity. However, the grain boundary resistance of LATP limits its overall ionic conductivity, which remains a major obstacle to the commercialization of all-solid-state batteries. In this study, we made efforts to solve the problem by promoting the minimization of voids and the formation of well-defined grain boundaries by controlling the temperature of two heat treatments during the synthesis process. The crystallization temperature was confirmed through thermogravimetric analysis/DTA analysis, and the degree of crystallization was confirmed using XRD analysis. The formation of grain boundaries and the presence of voids were evaluated by cross-sectional SEM images after sintering. After sintering, the LA_900 °C sample, characterized by a high degree of crystallization and well-formed grain boundaries without voids, demonstrated a low bulk and grain boundary resistance, which was confirmed by electrochemical impedance spectroscopy analysis. The result was an ionic conductivity of 1.72 × 10-4 S/cm. These results provide valuable insights into the facile synthesis of LATP.

P-Type Conversion of WS2 and WSe2 by Position-Selective Oxidation Doping and Its Application in Top Gate Transistors.

For the complementary operation of two-dimensional (2D) material-based field-effect transistors (FETs), high-performance p-type FETs are essential. In this study, we applied surface charge-transfer doping from WOx, which has a large work function of ∼6.5 eV, selectively to the access region of WS2 and WSe2 by covering the channel region with h-BN. By reducing the Schottky barrier width at the contact and injecting holes into the valence band, the p-type conversion of intrinsically n-type trilayer WSe2 FET was successfully achieved. However, trilayer WS2 did not show clear p-type conversion because its valence band maximum is 0.66 eV lower than that of trilayer WSe2. Although inorganic WOx boasts high air stability and fabrication process compatibility due to its high thermal budget, the trap sites in WOx cause large hysteresis during back gate operation of WSe2 FETs. However, by using top gate (TG) operation with an h-BN protection layer as a TG insulator, a high-performance p-type WSe2 FET with negligible hysteresis was achieved.