2D materials: increscent quantum flatland with immense potential for applications

Amorphous boron nitride: synthesis, properties and device application

Amorphous boron nitride (a-BN) exhibits remarkable electrical, optical, and chemical properties, alongside robust mechanical stability, making it a compelling material for advanced applications in nanoelectronics and photonics. This review comprehensively examines the unique characteristics of a-BN, emphasizing its electrical and optical attributes, state-of-the-art synthesis techniques, and device applications. Key advancements in low-temperature growth methods for a-BN are highlighted, offering insights into their potential for integration into scalable, CMOS-compatible platforms. Additionally, the review discusses the emerging role of a-BN as a dielectric material in electronic and photonic devices, serving as substrates, encapsulation layers, and gate insulators. Finally, perspectives on future challenges, including defect control, interface engineering, and scalability, are presented, providing a roadmap for realizing the full potential of a-BN in next-generation device technologies.

Experimental Realization of Fluoroborophene

Borophene, an anisotropic metallic Dirac material exhibits superlative physical and chemical properties. While the lack of bandgap restricts its electronic chip applications, insufficient charge carrier density and electrochemical/catalytically active sites, restricts its energy storage and catalysis applications. Fluorination of borophene can induce bandgap and yield local electron injection within its crystallographic lattice. Herein, a facile synthesis of fluoroborophene with tunable fluorine content through potassium fluoride-assisted solvothermal-sonochemical combinatorial approach is reported. Fluoroborophene monolayers with lateral dimension 50 nm-5 µm are synthesized having controlled fluorine content (12-35%). Fluoroborophene exhibits inter-twinned crystallographic structure, with fluorination-tunable visible-range bandgap ≈1.5-2.5 eV, and density functional theory calculations also corroborate it. Fluoroborophene is explored for electrocatalytic oxygen evolution reaction in an alkaline medium and bestow a good stability. Tunable bandgap, electrophilicity and molecular anchoring capability of fluoroborophene will open opportunities for novel electronic/optoelectronic/spintronic chips, energy storage devices, and in numerous catalytic applications.

Li-ion transport in two-dimensional nanofluidic membranes

The growing demand for lithium, driven by its critical role in lithium-ion batteries (LIBs) and other applications, has intensified the need for efficient extraction methods from aqua-based resources such as seawater. Among various approaches, 2D channel membranes have emerged as promising candidates due to their tunable ion selectivity and scalability. While significant progress has been made in achieving high Li+/Mg2+ selectivity, enhancing Li+ ion selectivity over Na+ ion, the dominant monovalent cation in seawater, remains a challenge due to their similar properties. This review provides a comprehensive analysis of the fundamental mechanisms underlying Li+ selectivity in 2D channel membranes, focusing on the dehydration and diffusion processes that dictate ion transport. Inspired by the principles of biological ion channels, we identify key factors-channel size, surface charge, and binding sites-that influence energy barriers and shape the interplay between dehydration and diffusion. We highlight recent progress in leveraging these factors to enhance Li+/Na+ selectivity and address the challenges posed by counteracting effects in ion transport. While substantial advancements have been made, the lack of comprehensive principles guiding the interplay of these variables across permeation steps represents a key obstacle to optimizing Li+/Na+ selectivity. Nonetheless, with their inherent chemical stability and fabrication scalability, 2D channel membranes offer significant potential for lithium extraction if these challenges can be addressed. This review provides insights into the current state of 2D channel membrane technologies and outlines future directions for achieving enhanced Li+ ion selectivity, particularly in seawater applications.

Topological surface states of semimetal TaSb2

Topological surface states, protected by the global symmetry of the materials, are the keys to understanding various novel electrical, magnetic, and optical properties. TaSb2 is a newly discovered topological material with unique transport phenomena, including negative magnetoresistance and resistivity plateau, whose microscopic understanding is yet to be reached. In this study, we investigate the electronic band structure of TaSb2 using angle-resolved photoemission spectroscopy and density functional theory. Our analyses reveal distinct bulk and surface states in TaSb2, providing direct evidence of its topological nature. Notably, surface states predominate the electronic contribution near the Fermi level, while bulk bands are mostly located at higher binding energies. Our study underlines the importance of systematic investigations into the electronic structures of topological materials, offering insights into their fundamental properties and potential applications in future technologies.

Thermally Induced Irreversible Disorder in Interlayer Stacking of γ-GeSe

The interlayer stacking shift in van der Waals (vdW) crystals represents an important degree of freedom to control various material properties, including magnetism, ferroelectricity, and electrical properties. On the other hand, the structural phase transitions driven by interlayer sliding in vdW crystals often exhibit thickness-dependent, sample-specific behaviors with significant hysteresis, complicating a clear understanding of their intrinsic nature. Here, the stacking configuration of the recently identified vdW crystal, γ-GeSe, is investigated, and the disordering manipulation of stacking sequence is demonstrated. It is observed that the well-ordered AB' stacking configuration in as-synthesized samples undergoes irreversible disordering upon Joule heating via electrical biasing or thermal treatment, as confirmed by atomic resolution scanning transmission electron microscopy (STEM). Statistical analysis of STEM data reveal the emergence of stacking disorder, with samples subjected to high electrical bias reaching the maximum levels of disorder. The energies of various stacking configurations and energy barriers for interlayer sliding are examined using first-principles calculation and a parameterized model to elucidate the key structural parameters related to stacking shift. The susceptibility of interlayer stacking to disorder through electrical or thermal treatments should be carefully considered to fully comprehend the structural and electrical properties of vdW crystals.

Two-Dimensional CNPs Superstructures Derived from Metal-Organic Frameworks for Electromagnetic Wave Absorption

Carbon nanoparticles (CNPs) derived from metal-organic frameworks (ZIF-8) are synthesized, which are further self-assembled into mono- or bilayer superstructures for electromagnetic (EM) wave absorption. Furthermore, the effect of ZIF-8 morphology (cubic or rhombic dodecahedral) on the superstructure and EM absorption performance of CNPs is investigated. The as-prepared cubic bilayer superstructure exhibits a higher BET surface area of 526.1 m2/g and a higher pore volume of 0.232 cm3/g than the rhombic dodecahedral monolayer superstructure (30.0 m2/g and 0.051 cm3/g, respectively). As a result, the two-dimensional CNPs with a bilayer structure are able to deliver the highest EM absorption performance with an effective absorption bandwidth of 6.2 GHz at a thickness of merely 2.4 mm. This work provides a new approach to designing and preparing high-performance EM wave absorption materials.

Graphene via Microwave Expansion of Graphite Followed by Cryo-Quenching and its Application in Electrostatic Droplet Switching

Monoelemental atomic sheets (Xenes) and other 2D materials offer record electronic mobility, high thermal conductivity, excellent Young's moduli, optical transparency, and flexural capability, revolutionizing ultrasensitive devices and enhancing performance. The ideal synthesis of these quantum materials should be facile, fast, scalable, reproducible, and green. Microwave expansion followed by cryoquenching (MECQ) leverages thermal stress in graphite to produce high-purity graphene within minutes. MECQ synthesis of graphene is reported at 640 and 800 W for 10 min, followed by liquid nitrogen quenching for 5 and 90 min of sonication. Microscopic and spectroscopic analyses confirmed the chemical identity and phase purity of monolayers and few-layered graphene sheets (200-12 µm). Higher microwave power yields thinner layers with enhanced purity. Molecular dynamics simulations and DFT calculations support the exfoliation under these conditions. Electrostatic droplet switching is demonstrated using MECQ-synthesized graphene, observing electrorolling of a mercury droplet on a BN/graphene interface at voltages above 20 V. This technique can inspire the synthesis of other 2D materials with high purity and enable new applications.

Recent Advances in Nanomaterials for Modulation of Stem Cell Differentiation and Its Therapeutic Applications

Challenges in directed differentiation and survival limit the clinical use of stem cells despite their promising therapeutic potential in regenerative medicine. Nanotechnology has emerged as a powerful tool to address these challenges and enable precise control over stem cell fate. In particular, nanomaterials can mimic an extracellular matrix and provide specific cues to guide stem cell differentiation and proliferation in the field of nanotechnology. For instance, recent studies have demonstrated that nanostructured surfaces and scaffolds can enhance stem cell lineage commitment modulated by intracellular regulation and external stimulation, such as reactive oxygen species (ROS) scavenging, autophagy, or electrical stimulation. Furthermore, nanoframework-based and upconversion nanoparticles can be used to deliver bioactive molecules, growth factors, and genetic materials to facilitate stem cell differentiation and tissue regeneration. The increasing use of nanostructures in stem cell research has led to the development of new therapeutic approaches. Therefore, this review provides an overview of recent advances in nanomaterials for modulating stem cell differentiation, including metal-, carbon-, and peptide-based strategies. In addition, we highlight the potential of these nano-enabled technologies for clinical applications of stem cell therapy by focusing on improving the differentiation efficiency and therapeutics. We believe that this review will inspire researchers to intensify their efforts and deepen their understanding, thereby accelerating the development of stem cell differentiation modulation, therapeutic applications in the pharmaceutical industry, and stem cell therapeutics.

Emergence of two distinct phase transitions in monolayer CoSe2 on graphene

Dimensional modifications play a crucial role in various applications, especially in the context of device miniaturization, giving rise to novel quantum phenomena. The many-body dynamics induced by dimensional modifications, including electron-electron, electron-phonon, electron-magnon and electron-plasmon coupling, are known to significantly affect the atomic and electronic properties of the materials. By reducing the dimensionality of orthorhombic CoSe2 and forming heterostructure with bilayer graphene using molecular beam epitaxy, we unveil the emergence of two types of phase transitions through angle-resolved photoemission spectroscopy and scanning tunneling microscopy measurements. We disclose that the 2 × 1 superstructure is associated with charge density wave induced by Fermi surface nesting, characterized by a transition temperature of 340 K. Additionally, another phase transition at temperature of 160 K based on temperature dependent gap evolution are observed with renormalized electronic structure induced by electron-boson coupling. These discoveries of the electronic and atomic modifications, influenced by electron-electron and electron-boson interactions, underscore that many-body physics play significant roles in understanding low-dimensional properties of non-van der Waals Co-chalcogenides and related heterostructures.

Spin-orbit-splitting-driven nonlinear Hall effect in NbIrTe4

The Berry curvature dipole (BCD) serves as a one of the fundamental contributors to emergence of the nonlinear Hall effect (NLHE). Despite intense interest due to its potential for new technologies reaching beyond the quantum efficiency limit, the interplay between BCD and NLHE has been barely understood yet in the absence of a systematic study on the electronic band structure. Here, we report NLHE realized in NbIrTe4 that persists above room temperature coupled with a sign change in the Hall conductivity at 150 K. First-principles calculations combined with angle-resolved photoemission spectroscopy (ARPES) measurements show that BCD tuned by the partial occupancy of spin-orbit split bands via temperature is responsible for the temperature-dependent NLHE. Our findings highlight the correlation between BCD and the electronic band structure, providing a viable route to create and engineer the non-trivial Hall effect by tuning the geometric properties of quasiparticles in transition-metal chalcogen compounds.

An elementary review on basic principles and developments of qubits for quantum computing

An elementary review on principles of qubits and their prospects for quantum computing is provided. Due to its rapid development, quantum computing has attracted considerable attention as a core technology for the next generation and has demonstrated its potential in simulations of exotic materials, molecular structures, and theoretical computer science. To achieve fully error-corrected quantum computers, building a logical qubit from multiple physical qubits is crucial. The number of physical qubits needed depends on their error rates, making error reduction in physical qubits vital. Numerous efforts to reduce errors are ongoing in both existing and emerging quantum systems. Here, the principle and development of qubits, as well as the current status of the field, are reviewed to provide information to researchers from various fields and give insights into this promising technology.

Tailored Synthesis of Heterogenous 2D TMDs and Their Spectroscopic Characterization

Two-dimensional (2D) vertical van der Waals heterostructures (vdWHs) show great potential across various applications. However, synthesizing large-scale structures poses challenges owing to the intricate growth parameters, forming unexpected hybrid film structures. Thus, precision in synthesis and thorough structural analysis are essential aspects. In this study, we successfully synthesized large-scale structured 2D transition metal dichalcogenides (TMDs) via chemical vapor deposition using metal oxide (WO3 and MoO3) thin films and a diluted H2S precursor, individual MoS2, WS2 films and various MoS2/WS2 hybrid films (Type I: MoxW1-xS2 alloy; Type II: MoS2/WS2 vdWH; Type III: MoS2 dots/WS2). Structural analyses, including optical microscopy, Raman spectroscopy, transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy, and cross-sectional imaging revealed that the A1g and E2g modes of WS2 and MoS2 were sensitive to structural variations, enabling hybrid structure differentiation. Type II showed minimal changes in the MoS2's A1g mode, while Types I and III exhibited a ~2.8 cm-1 blue shift. Furthermore, the A1g mode of WS2 in Type I displayed a 1.4 cm-1 red shift. These variations agreed with the TEM-observed microstructural features, demonstrating strain effects on the MoS2-WS2 interfaces. Our study provides insights into the structural features of diverse hybrid TMD materials, facilitating their differentiation through Raman spectroscopy.

Electronic Structure of Above-Room-Temperature van der Waals Ferromagnet Fe3GaTe2

Fe3GaTe2, a recently discovered van der Waals ferromagnet, demonstrates intrinsic ferromagnetism above room temperature, necessitating a comprehensive investigation of the microscopic origins of its high Curie temperature (TC). In this study, we reveal the electronic structure of Fe3GaTe2 in its ferromagnetic ground state using angle-resolved photoemission spectroscopy and density functional theory calculations. Our results establish a consistent correspondence between the measured band structure and theoretical calculations, underscoring the significant contributions of the Heisenberg exchange interaction (Jex) and magnetic anisotropy energy to the development of the high-TC ferromagnetic ordering in Fe3GaTe2. Intriguingly, we observe substantial modifications to these crucial driving factors through doping, which we attribute to alterations in multiple spin-splitting bands near the Fermi level. These findings provide valuable insights into the underlying electronic structure and its correlation with the emergence of high-TC ferromagnetic ordering in Fe3GaTe2.

Dielectric Constant in Nanoscale Bubbles on MoS2

Nanoscale bubbles form inevitably during the transfer of two-dimensional (2D) materials on a target substrate due to their van der Waals interaction. Despite a large number of studies based on nanobubble structures with localized strain, the dielectric constant (κ) in nanobubbles of MoS2 is poorly understood. Here, we report κ measurements for nanobubbles on MoS2 by probing the polarization forces based on electrostatic force microscopy. Remarkably, higher κ values of 6-8 independent of the nanobubble size are observed for the nanobubbles as compared to flat regions with a κ of ≈3. We find that the charge carrier increase owing to the strain-induced bandgap reduction is responsible for the enhanced κ of the nanobubbles, where the measured κ is in good agreement with the calculations based on the Clausius-Mossotti relation. Our results provide fundamental information about the strain-induced local dielectric properties of 2D materials and a guide for the design and fabrication of high-performance optoelectrical devices based on 2D materials.

Laterally gated ferroelectric field effect transistor (LG-FeFET) using α-In2Se3 for stacked in-memory computing array

In-memory computing is an attractive alternative for handling data-intensive tasks as it employs parallel processing without the need for data transfer. Nevertheless, it necessitates a high-density memory array to effectively manage large data volumes. Here, we present a stacked ferroelectric memory array comprised of laterally gated ferroelectric field-effect transistors (LG-FeFETs). The interlocking effect of the α-In2Se3 is utilized to regulate the channel conductance. Our study examined the distinctive characteristics of the LG-FeFET, such as a notably wide memory window, effective ferroelectric switching, long retention time (over 3 × 104 seconds), and high endurance (over 105 cycles). This device is also well-suited for implementing vertically stacked structures because decreasing its height can help mitigate the challenges associated with the integration process. We devised a 3D stacked structure using the LG-FeFET and verified its feasibility by performing multiply-accumulate (MAC) operations in a two-tier stacked memory configuration.

Direct characterization of intrinsic defects in monolayer ReSe2 on graphene

Understanding the characteristics of intrinsic defects in crystals is of great interest in many fields, from fundamental physics to applied materials science. Combined investigations of scanning tunneling microscopy/spectroscopy (STM/S) and density functional theory (DFT) are conducted to understand the nature of Se vacancy defects in monolayer (ML) ReSe2 grown on a graphene substrate. Among four possible Se vacancy sites, we identify the Se4 vacancy close to the Re layer by registry between STM topography and DFT simulated images. The Se4 vacancy is also thermodynamically favored in formation energy calculations, supporting its common observation via STM. dI/dV spectroscopy shows that the Se4 vacancy has a defect state at around -1.0 V, near the valence band maximum (EVBM). DOS calculations done for all four Se vacancies indicate that only the Se4 vacancy presents such a defect state near EVBM, confirming experimental observations. Our work provides valuable insights into the behavior of ML ReSe2/graphene heterojunctions containing naturally occurring Se vacancies, which may have strong implications in electronic device applications.

Lattice modulation strategies for 2D material assisted epitaxial growth

As an emerging single crystals growth technique, the 2D-material-assisted epitaxy shows excellent advantages in flexible and transferable structure fabrication, dissimilar materials integration, and matter assembly, which offers opportunities for novel optoelectronics and electronics development and opens a pathway for the next-generation integrated system fabrication. Studying and understanding the lattice modulation mechanism in 2D-material-assisted epitaxy could greatly benefit its practical application and further development. In this review, we overview the tremendous experimental and theoretical findings in varied 2D-material-assisted epitaxy. The lattice guidance mechanism and corresponding epitaxial relationship construction strategy in remote epitaxy, van der Waals epitaxy, and quasi van der Waals epitaxy are discussed, respectively. Besides, the possible application scenarios and future development directions of 2D-material-assisted epitaxy are also given. We believe the discussions and perspectives exhibited here could help to provide insight into the essence of the 2D-material-assisted epitaxy and motivate novel structure design and offer solutions to heterogeneous integration via the 2D-material-assisted epitaxy method.

Enhanced thermoelectric performance of SnSe by controlled vacancy population

The thermoelectric performance of SnSe strongly depends on its low-energy electron band structure that provides high density of states in a narrow energy window due to the multi-valley valence band maximum (VBM). Angle-resolved photoemission spectroscopy measurements, in conjunction with first-principles calculations, reveal that the binding energy of the VBM of SnSe is tuned by the population of Sn vacancy, which is determined by the cooling rate during the sample growth. The VBM shift follows precisely the behavior of the thermoelectric power factor, while the effective mass is barely modified upon changing the population of Sn vacancies. These findings indicate that the low-energy electron band structure is closely correlated with the high thermoelectric performance of hole-doped SnSe, providing a viable route toward engineering the intrinsic defect-induced thermoelectric performance via the sample growth condition without an additional ex-situ process.

Ultra-thin grating coupler for guided exciton-polaritons in WS2 multilayers

An ultra-thin transition metal dichalcogenide (TMDC) layer can support guided exciton-polariton modes due to the strong coupling between excitons and photons. Herein, we report the guided mode resonance in an ultra-thin TMDC grating structure. Owing to the strong exciton resonances in TMDCs, a TMDC grating structure shows guided-mode resonance even at a thickness limit of ∼10 nm and is capable of realizing polaritonic dispersion in a monolithic grating structure. We investigated the polarization and thickness dependence of the optical dispersion relations of the tungsten disulfide (WS2) grating structure. In addition, we confirmed that the monolithic WS2 grating coupler can be used to couple the near-field guided exciton-polariton out into the far field. We believe that ultra-thin TMDC layers can facilitate sub-wavelength nanophotonic applications.

Understanding the 2D-material and substrate interaction during epitaxial growth towards successful remote epitaxy: a review

Remote epitaxy, which was discovered and reported in 2017, has seen a surge of interest in recent years. Although the technology seemed to be difficult to reproduce by other labs at first, remote epitaxy has come a long way and many groups are able to consistently reproduce the results with a wide range of material systems including III-V, III-N, wide band-gap semiconductors, complex-oxides, and even elementary semiconductors such as Ge. As with any nascent technology, there are critical parameters which must be carefully studied and understood to allow wide-spread adoption of the new technology. For remote epitaxy, the critical parameters are the (1) quality of two-dimensional (2D) materials, (2) transfer or growth of 2D materials on the substrate, (3) epitaxial growth method and condition. In this review, we will give an in-depth overview of the different types of 2D materials used for remote epitaxy reported thus far, and the importance of the growth and transfer method used for the 2D materials. Then, we will introduce the various growth methods for remote epitaxy and highlight the important points in growth condition for each growth method that enables successful epitaxial growth on 2D-coated single-crystalline substrates. We hope this review will give a focused overview of the 2D-material and substrate interaction at the sample preparation stage for remote epitaxy and during growth, which have not been covered in any other review to date.

Modelling the structural disorder in trigonal-prismatic coordinated transition metal dichalcogenides

The structural disorder in trigonal-prismatic coordinated transition metal layered dichalcogenides is investigated. The structural model taking into account stacking faults, correlated displacement of atoms and average crystallite size is assessed by fitting to the X-ray diffraction pattern of an exfoliated–restacked MoS₂ sample.

Trigonal-prismatic coordinated transition metal dichalcogenides (TMDCs) are formed from stacked (chalcogen)–(transition metal)–(chalcogen) triple layers, where the chemical bond is covalent within the triple layers and van der Waals (vdW) forces are effective between the layers. Bonding is at the origin of the great interest in these compounds, which are used as 2D materials in applications such as catalysis, electronics, photoelectronics, sensors, batteries and thermoelectricity. This paper addresses the issue of modelling the structural disorder in multilayer TMDCs. The structural model takes into account stacking faults, correlated displacement of atoms and average crystallite size/shape, and is assessed by simulation of the X-ray diffraction pattern and fitting to the experimental data relative to a powdered sample of MoS₂ exfoliated and restacked via lithiation. From fitting, an average crystallite size of about 50 Å, nearly spherical crystallites and a definite probability of deviation from the fully eclipsed atomic arrangement present in the ordered structure are determined. The increased interlayer distance and correlated intralayer and interlayer atomic displacement are attributed to the presence of lithium intercalated in the vdW gap between triple layers (Li/Mo molar ratio of about 0.06). The model holds for the whole class of trigonal-prismatic coordinated TMDCs, and is suitably flexible to take into account different preparation routes.

Machine-learning-assisted analysis of transition metal dichalcogenide thin-film growth

In situ reflective high-energy electron diffraction (RHEED) is widely used to monitor the surface crystalline state during thin-film growth by molecular beam epitaxy (MBE) and pulsed laser deposition. With the recent development of machine learning (ML), ML-assisted analysis of RHEED videos aids in interpreting the complete RHEED data of oxide thin films. The quantitative analysis of RHEED data allows us to characterize and categorize the growth modes step by step, and extract hidden knowledge of the epitaxial film growth process. In this study, we employed the ML-assisted RHEED analysis method to investigate the growth of 2D thin films of transition metal dichalcogenides (ReSe₂) on graphene substrates by MBE. Principal component analysis (PCA) and K-means clustering were used to separate statistically important patterns and visualize the trend of pattern evolution without any notable loss of information. Using the modified PCA, we could monitor the diffraction intensity of solely the ReSe₂ layers by filtering out the substrate contribution. These findings demonstrate that ML analysis can be successfully employed to examine and understand the film-growth dynamics of 2D materials. Further, the ML-based method can pave the way for the development of advanced real-time monitoring and autonomous material synthesis techniques.

Investigation of the mechanism of the anomalous Hall effects in Cr2Te3/(BiSb)2(TeSe)3 heterostructure

The interplay between ferromagnetism and the non-trivial topology has unveiled intriguing phases in the transport of charges and spins. For example, it is consistently observed the so-called topological Hall effect (THE) featuring a hump structure in the curve of the Hall resistance (Rxy) vs. a magnetic field (H) of a heterostructure consisting of a ferromagnet (FM) and a topological insulator (TI). The origin of the hump structure is still controversial between the topological Hall effect model and the multi-component anomalous Hall effect (AHE) model. In this work, we have investigated a heterostructure consisting of BixSb2-xTeySe3-y (BSTS) and Cr2Te3 (CT), which are well-known TI and two-dimensional FM, respectively. By using the so-called "minor-loop measurement", we have found that the hump structure observed in the CT/BSTS is more likely to originate from two AHE channels. Moreover, by analyzing the scaling behavior of each amplitude of two AHE with the longitudinal resistivities of CT and BSTS, we have found that one AHE is attributed to the extrinsic contribution of CT while the other is due to the intrinsic contribution of BSTS. It implies that the proximity-induced ferromagnetic layer inside BSTS serves as a source of the intrinsic AHE, resulting in the hump structure explained by the two AHE model.

Intermetallic Nanoarchitectures for Efficient Electrocatalysis

Intermetallic structures whose regular atomic arrays of constituent elements present unique catalytic properties have attracted considerable attention as efficient electrocatalysts for energy conversion reactions. Further performance enhancement in intermetallic catalysts hinges on constructing catalytic surfaces possessing high activity, durability, and selectivity. In this Perspective, we introduce recent endeavors to boost the performance of intermetallic catalysts by generating nanoarchitectures, which have well-defined size, shape, and dimension. We discuss the beneficial effects of nanoarchitectures compared with simple nanoparticles in catalysis. We highlight that the nanoarchitectures have high intrinsic activity owing to their inherent structural factors, including controlled facets, surface defects, strained surfaces, nanoscale confinement effects, and a high density of active sites. We next present notable examples of intermetallic nanoarchitectures, namely, facet-controlled intermetallic nanocrystals and multidimensional nanomaterials. Finally, we suggest the future research directions of intermetallic nanoarchitectures.

Novel Approach to High κ (∼59) and Low EOT (∼3.8 Å) near the Morphotrophic Phase Boundary with AFE/FE (ZrO2/HZO) Bilayer Heterostructures and High-Pressure Annealing

We present herewith a novel approach of equally thick AFE/FE (ZrO₂/HZO) bilayer stack heterostructure films for achieving an equivalent oxide thickness (EOT) of 4.1 Å with a dielectric constant (κ) of 56 in complementary metal-oxide semiconductor (CMOS) compatible metal-ferroelectric-metal (MFM) capacitors using a high-pressure annealing (HPA) technique. The low EOT and high κ values were achieved by careful optimization of AFE/FE film thicknesses and HPA conditions near the morphotropic phase boundary (MPB) after field cycling effects. Stable leakage current density (J < 10^-7 A/cm² at ±0.8 V) was found at 3/3 nm bilayer stack films (κ = 56 and EOT = 4.1 Å) measured at room temperature. In comparison with previous work, our remarkable achievement stems from the interfacial coupling between FE and AFE films as well as a high-quality crystalline structure formed by HPA. Kinetically stabilized hafnia films result in a small grain size in bilayer films, leading to reducing the leakage current density. Further, a higher κ value of 59 and lower EOT of 3.4 Å were found at 333 K. However, stable leakage current density was found at 273 K with a high κ value of 53 and EOT of 3.85 Å with J < 10^-7 A/cm². This is the lowest recorded EOT employing hafnia and TiN electrodes that are compatible with CMOS, and it has important implications for future dynamic random access memory (DRAM) technology.