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Characterizing materials to atomic resolution and first-principles structure-property prediction are two pillars for accelerating functional materials discovery. However, we are still lacking a rapid, noise-robust framework to extract multilevel atomic structural motifs from complex materials to complement, inform, and guide our first-principles models. Here, we present a machine learning framework that rapidly extracts a hierarchy of complex structural motifs from atomically resolved images. We demonstrate how such motif hierarchies can rapidly reconstruct specimens with various defects. Abstracting complex specimens with simplified motifs enabled us to discover a previously unidentified structure in a Mo─V─Te─Nb polyoxometalate (POM) and quantify the relative disorder in a twisted bilayer MoS2. In addition, these motif hierarchies provide statistically grounded clues about the favored and frustrated pathways during self-assembly. The motifs and their hierarchies in our framework coarse-grain disorder in a manner that allows us to understand a much broader range of multiscale samples with functional imperfections and nontrivial topological phases. Nanyang Technological University Published version S.J.P. acknowledges funding from the Singapore Ministry of Education Tier 1 grant R-284-000-172-114 and Tier 2 grant R-284-000-175-112 and from the National University of Singapore. N.D.L. acknowledges funding support from the National Research Foundation (Competitive Research Programme grant number NRF-CRP16-2015-05), as well as the National University of Singapore Early Career Research Award. Q.H. would also like to acknowledge the support by the National Research Foundation (NRF) Singapore, under its NRF Fellowship (NRF-NRFF11-2019-0002). X.Z. thanks the support from the Presidential Postdoctoral Fellowship, Nanyang Technological University, Singapore via grant 03INS000973C150.

The ability to precisely engineer the doping of sub-nanometer bimetallic clusters offers exciting opportunities for tailoring their catalytic performance with atomic accuracy. However, the fabrication of singly dispersed bimetallic cluster catalysts with atomic-level control of dopants has been a long-standing challenge. Herein, we report a strategy for the controllable synthesis of a precisely doped single cluster catalyst consisting of partially ligand-enveloped Au4Pt2 clusters supported on defective graphene. This creates a bimetal single cluster catalyst (Au4Pt2/G) with exceptional activity for electrochemical nitrogen (N2) reduction. Our mechanistic study reveals that each N2 molecule is activated in the confined region between cluster and graphene. The heteroatom dopant plays an indispensable role in the activation of N2 via an enhanced back donation of electrons to the N2 LUMO. Moreover, besides the heteroatom Pt, the catalytic performance of single cluster catalyst can be further tuned by using Pd in place of Pt as the dopant., The fabrication of singly dispersed metal cluster catalysts with atomic-level control of dopants is a long-standing challenge. Here, the authors report a strategy for the synthesis of a precisely doped single cluster catalyst which shows exceptional activity for electrochemical dinitrogen reduction.

We report a simple procedure to fabricate single crystals 3D C60 having an FCC structure on silicon substrates using a vapour–solid set-up in vacuum conditions. The morphology of the deposited film can be tuned by controlling the temperature and position of the substrate. The as-fabricated samples are extensively characterised by transmission electron microscopy, scanning electron microscope, X-ray powder diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and nano-indentation, which allow us to shed light on the recrystallization process of the C60. In addition, the growth mechanism of the formation of crystalline 3D structure of the C60 film is discussed in detail. Based on the newly gained knowledge of mechanism and its unique properties, fullerene has shown huge potential as a solid lubricant on various kinds of substrates.

Simple strain enhancement Piezoelectric materials are important as sensors and transducers for applications such as ultrasonics. Liu et al. discovered nanopillar regions in a sodium-niobium-oxide film that substantially improve the piezoelectric properties (see the Perspective by Bassiri-Gharb). These nanopillar regions reverse where the cations and anions are located in the crystal structure, with a distinctive boundary in between. This difference in structure results in a strain-sensitive polarity that enhances the piezoelectric properties in a chemically simple material. Science this issue p. 292 ; see also p. 252

Two-dimensional (2D) materials1–5 offer a unique platform from which to explore the physics of topology and many-body phenomena. New properties can be generated by filling the van der Waals gap of 2D materials with intercalants6,7; however, post-growth intercalation has usually been limited to alkali metals8–10. Here we show that the self-intercalation of native atoms11,12 into bilayer transition metal dichalcogenides during growth generates a class of ultrathin, covalently bonded materials, which we name ic-2D. The stoichiometry of these materials is defined by periodic occupancy patterns of the octahedral vacancy sites in the van der Waals gap, and their properties can be tuned by varying the coverage and the spatial arrangement of the filled sites7,13. By performing growth under high metal chemical potential14,15 we can access a range of tantalum-intercalated TaS(Se)y, including 25% Ta-intercalated Ta9S16, 33.3% Ta-intercalated Ta7S12, 50% Ta-intercalated Ta10S16, 66.7% Ta-intercalated Ta8Se12 (which forms a Kagome lattice) and 100% Ta-intercalated Ta9Se12. Ferromagnetic order was detected in some of these intercalated phases. We also demonstrate that self-intercalated V11S16, In11Se16 and FexTey can be grown under metal-rich conditions. Our work establishes self-intercalation as an approach through which to grow a new class of 2D materials with stoichiometry- or composition-dependent properties.

State-of-the-art chemical sensors based on covalent organic frameworks (COFs) are restricted to the transduction mechanism relying on luminescence quenching and/or enhancement. Herein, we present an alternative methodology via a combination of in situ-grown COF films with interdigitated electrodes utilized for capacitive benzene detection. The resultant COF-based sensors exhibit highly sensitive and selective detection at room temperature toward benzene vapor over carbon dioxide, methane, and propane. Their benzene detection limit can reach 340 ppb, slightly inferior to those of the metal oxide semiconductor-based sensors, but with reduced power consumption and increased selectivity. Such a sensing behavior can be attributed to the large dielectric constant of the benzene molecule, distinctive adsorptivity of the chosen COF toward benzene, and structural distortion induced by the custom-made interaction pair, which is corroborated by sorption measurements and density functional theory (DFT) calculations. This study provides new perspectives for fabricating COF-based sensors with specific functionality targeted for selective gas detection.

In recent years, two‐dimensional (2D) ternary materials have attracted wide attention due to their novel properties which can be achieved by regulating their chemical composition with a very great degree of freedom and adjustable space. However, as for the precise synthesis of 2D ternary materials, great challenges still lie ahead that hinder their further development. In this work, we demonstrated a simple and reliable approach to synthesize 2D ternary‐layered BiOCl crystals through a microwave‐assisted space‐confined process in a short time (

Nanoscale phase mixtures in transition-metal oxides (TMOs) often render these materials susceptible to external stimuli (electric field, mechanical stress, etc.), which can lead to rich functional properties and device applications. Here, direct observation and multifield manipulation of a nanoscale mixture of brownmillerite SrFeO

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) have emerged as attractive platforms in next-generation nanoelectronics and optoelectronics for reducing device sizes down to a 10 nm scale. To achieve this, the controlled synthesis of wafer-scale single-crystal TMDs with high crystallinity has been a continuous pursuit. However, previous efforts to epitaxially grow TMD films on insulating substrates (e.g., mica and sapphire) failed to eliminate the evolution of antiparallel domains and twin boundaries, leading to the formation of polycrystalline films. Herein, we report the epitaxial growth of wafer-scale single-crystal MoS2 monolayers on vicinal Au(111) thin films, as obtained by melting and resolidifying commercial Au foils. The unidirectional alignment and seamless stitching of the MoS2 domains were comprehensively demonstrated using atomic- to centimeter-scale characterization techniques. By utilizing onsite scanning tunneling microscope characterizations combined with first-principles calculations, it was revealed that the nucleation of MoS2 monolayer is dominantly guided by the steps on Au(111), which leads to highly oriented growth of MoS2 along the ⟨110⟩ step edges. This work, thereby, makes a significant step toward the practical applications of MoS2 monolayers and the large-scale integration of 2D electronics.

The ability to tune both local and global environments of a single-metal active center on a support is crucial for the development of highly robust and efficient single-atom electrocatalysts (SAECs...

Developing highly active oxygen evolution reaction (OER) catalysts with fast OER kinetics is crucial for disruptively changing the energy technology, where unlocking of the catalytic origin is the ...

Crystalline SnSe has been revealed as an efficient thermoelectric candidate with outstanding performance. Herein, record-high thermoelectric performance is achieved among SnSe crystals via simply introducing a small amount of SnSe2 as a kind of extrinsic defect dopant. This excellent performance mainly arises from the largely enhanced power factor by increasing the carrier concentration high as 6.55 × 1019 cm-3, which was surprisingly promoted by introducing extrinsic SnSe2 even though pristine SnSe2 is an n-type conductor. The optimized carrier concentration promotes a deeper Fermi level and activates more valence bands, leading to an extraordinary room-temperature power factor ∼54 μW cm-1 K-2 through enlarging the band effective mass and Seebeck coefficient. As a result, on the basis of simultaneously depressed thermal conductivity induced from both Sn vacancies and SnSe2 microdomains, maximum ZT values ∼0.9-2.2 and excellent average ZT > 1.7 among the working temperature range are achieved in Na doped SnSe crystals with 2% extrinsic SnSe2. Our investigation illustrates new approaches on improving thermoelectric performance through introducing defect dopants, which might be well-implemented in other thermoelectric systems.

To provide alternative battery technologies to lithium ion battery, multivalent metal ion batteries with their high theoretical capacities and ease of preparation have gradually gained attention from both academia and industries. In this work, we report bismuth ion battery (BIB) as a promising trivalent metal ion battery, next to the only known aluminum ion battery. Our BIB successfully demonstrates battery behavior with discharge plateaus at 0.5 and 0.2 V. Gravimetric capacity of 300 mAh g-1 at current density of 0.2 A g-1 was obtained with ca. 98% coulombic efficiency. In addition, stable cyclic life was achieved after 100 cycles at 0.3 A g-1 which further suggests its suitability as potential trivalent metal ion battery.

Valley pseudospin in two-dimensional (2D) transition-metal dichalcogenides (TMDs) allows optical control of spin-valley polarization and intervalley quantum coherence. Defect states in TMDs give rise to new exciton features and theoretically exhibit spin-valley polarization; however, experimental achievement of this phenomenon remains challenges. Here, we report unambiguous valley pseudospin of defect-bound localized excitons in CVD-grown monolayer MoS2; enhanced valley Zeeman splitting with an effective g-factor of -6.2 is observed. Our results reveal that all five d-orbitals and the increased effective electron mass contribute to the band shift of defect states, demonstrating a new physics of the magnetic responses of defect-bound localized excitons, strikingly different from that of A excitons. Our work paves the way for the manipulation of the spin-valley degrees of freedom through defects toward valleytronic devices.

The breaking of multiple symmetries by periodic lattice distortion at a commensurate charge density wave (CDW) state is expected to give rise to intriguing interesting properties. However, accessing the commensurate CDW state on bulk TaS2 crystals typically requires cryogenic temperatures (77 K), which precludes practical applications. Here, we found that heteroepitaxial growth of a 2H-tantalum disulfide bilayer on a hexagonal-boron nitride (h-BN) substrate produces a robust commensurate CDW order at room temperature, characterized by a Moire superlattice of 3 × 3 TaS2 on a 4 × 4 h-BN unit cell. The CDW order is confirmed by scanning transmission electron microscopy and Raman measurements. Theoretical calculations reveal that the stabilizing energy for the CDW phase of the monolayer and bilayer 2H-TaS2-on-h-BN substrates arises primarily from interfacial electrostatic interactions and, to a lesser extent, interfacial strain. Our work shows that engineering interfacial electrostatic interactions in an ultrathin van der Waals heterostructure constitutes an effective way to enhance CDW order in two-dimensional materials.

Regulating the temperature of buildings has the highest expenditure of energy (35–40%); thus, transparent heat reflectors (THRs) have been at the forefront of passive cooling technology due to its ability to reflect near-infrared (NIR) wavelengths without compromising optical transmission. Current designs like metallic thin films and dielectric–metal–dielectric are expensive and face complications with material incompatibility, oxidation, and interdiffusion, which hamper their performance. A cost-effective THR using a single-layer coating has not yet been achieved due to the susceptibility of metals to oxidation. In this work, a layer of CuS was fabricated onto flexible polyethylene terephthalate (PET) via radio frequency magnetron sputtering (RFMS), a high throughput method known for its conformal large-area fabrication. The 150 nm-thick CuS-PET films demonstrated a visible transmission T550 nm of 64.1% and NIR reflectance of 50% that resulted in 8 °C passive cooling. Additionally, wetting the surface re...

The metallic elements with a small atomic radius can not only compensate for the intrinsic vacancies to improve the carrier mobility, but also can form interstitials to reduce lattice thermal conductivity. In this work, we investigate the contrasting roles of three different metallic elements with small atomic radius on the thermoelectric properties of n-type PbM0.01Se (M = Cu, Zn, Ni). We find that all the metallic elements can increase the carrier concentration as electron donors and improve the electrical transport properties. In addition, the lattice thermal conductivity of PbSe can be significantly decreased through the formation of interstitials by the incorporated extra metallic elements. We also find that the PbCu0.01Se sample exhibits a unique and complex behavior compared with the other samples due to the diffusion and the thermally activated oxidation of Cu+ ions. When the temperature increased to 673 K, the carrier concentration of PbCu0.01Se sample increases suddenly and continues to increase by nearly two folds, which we ascribe to the release of 3d orbital electrons in Cu+ ions. This results in a strong decoupling of the charge and heat transport in the material, which can be manifested by the overestimation of the electronic thermal conductivity when assuming strong electron–phonon coupling in Wiedemann–Franz law. A maximum ZT of ∼1.6 can be reached at 773 K and the average ZT of ∼0.96 can be achieved in PbCu0.01Se. Our results demonstrate the exceptional contrasting behavior of Cu in PbSe by comparing with Zn and Ni, and the thermoelectric performance of n-type PbSe can be enhanced through the introduction of extra metallic elements with small radius.

The electrochemical oxygen reduction reaction (ORR) is one of the key processes for various energy storage and conversion systems. To date, transition metal-based nitrogen–carbon systems (M/NC) have been demonstrated as promising low-cost catalysts. However, their low content of metals and the lack of coupling among multimetal atoms still affect the ORR kinetics. Herein, we develop a hierarchical N-doped carbon structure to house isolated trimetal (Co, Fe and Zn) atoms via pyrolysis of doped amorphous ZIF-90. Owing to the versatile compositional and structural design of its precursors, the resultant catalyst has a high metal loading (5.5 wt%) and a highly open structure with abundant mesopores, which significantly increase the population of effective active sites. Moreover, charge transfer among these three metals (Co, Fe and Zn) is found, which leads to the promotion of the oxidation state of Co species (primary active sites). Benefiting from the openly accessible active sites and the promotion effect, the catalyst exhibits remarkable ORR activity and stability, outperforming its bimetallic/single metal counterparts and commercial Pt/C.

Grain boundaries could exhibit exceptional electronic structure and exotic properties, which are determined by a local atomic configuration and stoichiometry that differs from the bulk. However, optical and plasmonic properties at the grain boundaries in metallic oxides have rarely been discussed before. Here, we show that non-stoichiometric grain boundaries in the newly discovered metallic SrNbO3 photocatalyst show exotic electronic, optical and plasmonic phenomena in comparison to bulk. Aberration-corrected scanning transmission electron microscopy and first-principles calculations reveal that a Nb-rich grain boundary exhibits an increased carrier concentration with quasi-1D metallic conductivity, and newly induced electronic states contributing to the broad energy range of optical absorption. More importantly, dielectric function calculations reveal extended and enhanced plasmonic excitations compared with bulk SrNbO3. Our results show that non-stoichiometric grain boundaries might be utilized to control the electronic and plasmonic properties in oxide photocatalysis.

Development of efficient and durable oxygen evolution reaction (OER) catalysts has a direct impact on the water splitting efficiency and cost effectiveness. In this work, we report the successful synthesis of a new Ni(OH)2 structure, strain-stabilized Ni(OH)2 nanoribbons (NR-Ni(OH)2) two to three layers thick, with widths of 2–5 nm, via an electro-oxidation route. Conventional Ni(OH)2 usually has negligible OER activity, while NR-Ni(OH)2 shows high activity for the oxygen evolution reaction and an overpotential of 162 millivolts and furthermore exhibits long-term stability in alkaline electrolyte. The substantial reduction in the overpotential of NR-Ni(OH)2 is due to its easier OOH* adsorption by the active four-coordinated Ni edge sites. The enhanced catalytic activity of NR-Ni(OH)2 makes it an excellent candidate for industrial applications.

Hollow-structuring of active components is among the most effective strategies for improving the kinetics of oxygen electrode catalysts, benefiting from the much-improved active surface area, enhanced accessible active sites, and formation of the desired defects on the exposed surface. Integration of active hollow nanostructures with functionalized carbon nanofibers synergizes the electrochemical performance and mechanical flexibility, which are particularly of interest for all-solid-state zinc–air batteries (FASS ZABs). In the present work, we demonstrate that the electrospinning of Prussian blue analogs can give rise to hollow FeCo alloy nanoparticles assembled in nitrogen-doped carbon nanofibers (h-FeCo alloy/N-CNFs). The h-FeCo alloy/N-CNFs thus derived exhibit superior bifunctional activities for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), and impressive performance in rechargeable Zn–air batteries. When integrated into a rechargeable FASS ZAB, they exhibit a high open circuit voltage of 1.335 V and a stable discharge–charge plateau around 1.1 V to 2.0 V, together with a large voltage efficiency of 63.5%, under bending conditions.

Scanning transmission electron microscopy (STEM) has emerged as a uniquely powerful tool for structural and functional imaging of materials on the atomic level. Driven by advances in aberration correction, STEM now allows the routine imaging of structures with single-digit picometre-level precision for localization of atomic units. This Primer focuses on the opportunities emerging at the interface between STEM and machine learning (ML) methods. We review the primary STEM imaging methods, including structural imaging, electron energy loss spectroscopy and its momentum-resolved modalities and 4D-STEM. We discuss the quantification of STEM structural data as a necessary step towards meaningful ML applications and its analysis in terms of the relevant physics and chemistry. We show examples of the opportunities offered by structural STEM imaging in elucidating the chemistry and physics of complex materials and how the latter connect to first-principles and phase-field models to yield consistent interpretation of generative physics. We present the critical infrastructural needs for the broad adoption of ML methods in the STEM community, including the storage of data and metadata to allow the reproduction of experiments. Finally, we discuss the application of ML to automating experiments and novel scanning modes.

Interlayer electronic coupling in two-dimensional materials enables tunable and emergent properties by stacking engineering. However, it also results in significant evolution of electronic structures and attenuation of excitonic effects in two-dimensional semiconductors as exemplified by quickly degrading excitonic photoluminescence and optical nonlinearities in transition metal dichalcogenides when monolayers are stacked into van der Waals structures. Here we report a van der Waals crystal, niobium oxide dichloride (NbOCl

Accurate geometrical calibration between the scan coordinates and the camera coordinates is critical in four-dimensional scanning transmission electron microscopy (4D-STEM) for both quantitative imaging and ptychographic reconstructions. For atomic-resolved, in-focus 4D-STEM datasets, we propose a hybrid method incorporating two sub-routines, namely a J-matrix method and a Fourier method, which can calibrate the uniform affine transformation between the scan-camera coordinates using raw data, without a priori knowledge of the crystal structure of the specimen. The hybrid method is found robust against scan distortions and residual probe aberrations. It is also effective even when defects are present in the specimen, or the specimen becomes relatively thick. We will demonstrate that a successful geometrical calibration with the hybrid method will lead to a more reliable recovery of both the specimen and the electron probe in a ptychographic reconstruction. We will also show that, although the elimination of local scan position errors still requires an iterative approach, the rate of convergence can be improved, and the residual errors can be further reduced if the hybrid method can be firstly applied for initial calibration. The code is made available as a simple-to-use tool to correct affine transformations of the scan-camera coordinates in 4D-STEM experiments.

Amorphization is an efficient strategy to activate intrinsically inert catalysts. However, the low crystallinity of amorphous catalysts often causes high solubility and poor electrochemical stability in aqueous solution. Here, a different mechanism is developed to simultaneously stabilize and activate the water-soluble amorphous MoSx Oy via a charge-balancing strategy, which is induced by different electronegativity between the co-dopants Rh (2.28) and Sn (1.96). The electron-rich Sn prefers to stabilize the unstable apical O sites in MoSx Oy through charge transfer, which can prevent the H from attacking. Meanwhile, the Rh, as the charge regulator, shifts the main active sites on the basal plane from inert Sn to active apical Rh sites. As a result, the amorphous RhSn-MoSx Oy exhibits drastic enhancement in electrochemical stability (η10 increases only by 12 mV) after 1000 cycles and a distinct activity (η10 : 26 mV and Tafel: 30.8 mV dec-1 ) for the hydrogen evolution reaction in acidic solution. This work paves a route for turning impracticably water-soluble catalysts into treasure and inspires new ideas to design high-performance amorphous electrocatalysts. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University H.J.F. and Y.Z. thank the financial support from Agency for Science, Technology and Research (A*STAR), Singapore by AME Individual Research Grants (A1983c0026), and from Singapore Ministry of Education by Tier 2 grant (MOE2017-T2-1-073). Y.Z. appreciates the support from Science and Technology Commission of Shanghai Municipality (19ZR1465100). S.Z.L. and H.W. appreciate the financial support from Singapore Ministry of Education by Tier 1 (RG8/20). X.X.Z. thanks the support from the Presidential Postdoctoral Fellowship, NTU, Singapore. Z.L., J.D.Z., and X.X.Z. thank the support from Singapore Ministry of Education via AcRF Tier 2 (MOE2019-T2-2-105 and MOE2016-T2-1-131) and AcRF Tier 1 (RG7/18).

A large electromechanical response in ferroelectrics is highly desirable for developing high-performance sensors and actuators. Enhanced electromechanical coupling in ferroelectrics is usually obtained at morphotropic phase boundaries requiring stoichiometric control of complex compositions. Recently it was shown that giant piezoelectricity can be obtained in films with nanopillar structures. Here, we elucidate its origin in terms of atomic structure and demonstrate a different system with a greatly enhanced response. This is in non-stoichiometric potassium sodium niobate epitaxial thin films with a high density of self-assembled planar faults. A giant piezoelectric coefficient of ∼1900 picometer per volt is demonstrated at 1 kHz, which is almost double the highest ever reported effective piezoelectric response in any existing thin films. The large oxygen octahedral distortions and the coupling between the structural distortion and polarization orientation mediated by charge redistribution at the planar faults enable the giant electric-field-induced strain. Our findings demonstrate an important mechanism for realizing the unprecedentedly giant electromechanical coupling and can be extended to many other material functions by engineering lattice faults in non-stoichiometric compositions.

Description, Role of charged defects in resistance fatigue of ferroelectric tunnel junctions has been revealed at atomic scale., Ferroelectric tunnel junctions (FTJs) are promising candidates for next-generation memories due to fast read/write speeds and low-power consumptions. Here, we investigate resistance fatigue of FTJs, which is performed on Pt/BaTiO3/Nb:SrTiO3 devices. By direct observations of the 5–unit cell–thick BaTiO3 barrier with high-angle annular dark-field imaging and electron energy loss spectroscopy, oxygen vacancies are found to aggregate at the Pt/BaTiO3 interface during repetitive switching, leading to a ferroelectric dead layer preventing domain nucleation and growth. Severe oxygen deficiency also makes BaTiO3 lattices energetically unfavorable and lastly induces a destruction of local perovskite structure of the barrier. Ferroelectric properties are thus degraded, which reduces barrier contrast between ON and OFF states and smears electroresistance characteristics of Pt/BaTiO3/Nb:SrTiO3 FTJs. These results reveal an atomic-scale fatigue mechanism of ultrathin ferroelectric barriers associated with the aggregation of charged defects, facilitating the design of reliable FTJs and ferroelectric nanoelectronic devices for practical applications.

Majorana zero modes (MZMs) obey non-Abelian statistics and are considered building blocks for constructing topological qubits. Iron-based superconductors with topological band structures have emerged as promising hosting materials, since isolated candidate MZMs in the quantum limit have been observed inside the topological vortex cores. However, these materials suffer from issues related to alloying-induced disorder, uncontrolled vortex lattices and a low yield of topological vortices. Here, we report the formation of an ordered and tunable MZM lattice in naturally-strained stoichiometric LiFeAs by scanning tunneling microscopy/spectroscopy (STM/S). We observe biaxial charge density wave (CDW) stripes along the Fe-Fe and As-As directions in the strained regions. The vortices are pinned on the CDW stripes in the As-As direction and form an ordered lattice. We detect more than 90 percent of the vortices to be topological and possess the characteristics of isolated MZMs at the vortex center, forming an ordered MZM lattice with the density and the geometry tunable by an external magnetic field. Remarkably, with decreasing the spacing of neighboring vortices, the MZMs start to couple with each other. Our findings provide a new pathway towards tunable and ordered MZM lattices as a platform for future topological quantum computation.

Two-dimensional (2D) Fe-chalcogenides (e.g., FeS, FeSe, and FeTe, etc.) have sparked extensive interest due to their rich phase diagrams including superconductivity, magnetism, and topological state, as well as versatile applications in electronic devices and energy related fields. However, the phase-tunable synthesis and green transfer of such fascinating materials still remain challenging. Herein, we develop a temperature-mediated chemical vapor deposition (CVD) approach to grow ultrathin nonlayered hexagonal and layered tetragonal FeTe nanosheets on mica substrates, with their thicknesses down to ∼2.3 and ∼4.0 nm, respectively. Interestingly, we have observed exciting ferromagnetism with the Curie temperature approaching ∼300 K and high conductivity (∼1.96 × 105 S m-1) in 2D hexagonal FeTe. More significantly, we have designed a swift, high-efficiency, and etching-free method for the transfer of 2D FeTe nanosheets onto arbitrary substrates, and such a transfer strategy enables the cyclic utilization of growth substrates. These results should propel the further development of phase-tunable synthesis and green transfer of 2D Fe-chalcogenides, as well as their potential applications in spintronic devices.

Clean water and sanitation are the sixth goal of the United Nation’s sustainable development goals by 2030. Thus, research into expanding clean water supply has been steadily growing. Photothermal vaporization is a technique that utilizes light-to-heat conversion and proper thermal insulation to localize heat and produce steam at accelerated rates at temperatures below 100 °C. Covellite (CuS) has been investigated for this application as it possesses localized surface plasmon resonance (LSPR) in the near-infrared (IR) wavelengths, converting light into heat. However, recent studies on CuS have been limited to preparation via wet chemical methods to achieve nanoscale structures. These methods require an extra step of material transfer, leading to adhesion issues with the working substrate. In this work, we report the growth of polycrystalline CuS nanopillars using rf magnetron sputtering, a high-throughput physical vapor deposition process. By introduction of N2 gas, an etchant, in the plasma, a balance of...

To date, thermoelectric performance has been enhanced through improving the power factor and/or reducing the lattice thermal conductivity. Here, we report an effective method of boosting thermoelec...

Integrating multiple properties in a single system is crucial for the continuous developments in electronic devices. However, some physical properties are mutually exclusive in nature. Here, we report the coexistence of two seemingly mutually exclusive properties-polarity and two-dimensional conductivity-in ferroelectric Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ thin films at the LaAlO$_3$/Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ interface at room temperature. The polarity of a ~3.2 nm Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ thin film is preserved with a two-dimensional mobile carrier density of ~0.05 electron per unit cell. We show that the electronic reconstruction resulting from the competition between the built-in electric field of LaAlO$_3$ and the polarization of Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ is responsible for this unusual two-dimensional conducting polar phase. The general concept of exploiting mutually exclusive properties at oxide interfaces via electronic reconstruction may be applicable to other strongly-correlated oxide interfaces, thus opening windows to new functional nanoscale materials for applications in novel nanoelectronics., Comment: Main text: 25 pages, 4 figures Supplementary note: 19 pages, 11 figures

Artificial nitrogen fixation through the nitrogen reduction reaction (NRR) under ambient conditions is a potentially promising alternative to the traditional energy-intensive Haber–Bosch process. F...

Thermoelectric technology allows conversion between heat and electricity. Many good thermoelectric materials contain rare or toxic elements, so developing low-cost and high-performance thermoelectric materials is warranted. Here, we report the temperature-dependent interplay of three separate electronic bands in hole-doped tin sulfide (SnS) crystals. This behavior leads to synergistic optimization between effective mass (m*) and carrier mobility (μ) and can be boosted through introducing selenium (Se). This enhanced the power factor from ~30 to ~53 microwatts per centimeter per square kelvin (μW cm−1 K−2 at 300 K), while lowering the thermal conductivity after Se alloying. As a result, we obtained a maximum figure of merit ZT (ZTmax) of ~1.6 at 873 K and an average ZT (ZTave) of ~1.25 at 300 to 873 K in SnS0.91Se0.09 crystals. Our strategy for band manipulation offers a different route for optimizing thermoelectric performance. The high-performance SnS crystals represent an important step toward low-cost, Earth-abundant, and environmentally friendly thermoelectrics.

The electrocaloric effect in ferroelectric materials has drawn much attention due to its potential applications in integrated circuit cooling and novel cooling devices. In contrast to the widely researched positive electrocaloric effect, the negative electrocaloric effect has received much less attention due to the lack of any effective methods for significant enhancement. In this work, we fabricated PbZrO3 thin film on a Pt/Si substrate by the sol-gel method. By controlling the interface conditions between the thin film and substrate, we induced defects into the interface and stabilized a transient ferroelectric phase in the PbZrO3 thin film. The emergence of the transient ferroelectric phase postpones the antiferroelectric-ferroelectric phase transition. As a result, a negative electrocaloric effect up to -18.5 K is estimated near room temperature, the highest one ever reported in this temperature range. This result suggests a new strategy to enhance the negative electrocaloric effect and may benefit the application of PbZrO3 thin films in cooling devices.

Piezocatalysis, converting mechanical vibration into chemical energy, has emerged as a promising candidate for water-splitting technology. However, the efficiency of the hydrogen production is quite limited. We herein report well-defined 10 nm BaTiO3 nanoparticles (NPs) characterized by a large electro-mechanical coefficient which induces a high piezoelectric effect. Atomic-resolution high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and scanning probe microscopy (SPM) suggests that piezoelectric BaTiO3 NPs display a coexistence of multiple phases with low energy barriers and polarization anisotropy which results in a high electro-mechanical coefficient. Landau free energy modeling also confirms that the greatly reduced polarization anisotropy facilitates polarization rotation. Employing the high piezoelectric properties of BaTiO3 NPs, we demonstrate an overall water-splitting process with the highest hydrogen production efficiency hitherto reported, with a H2 production rate of 655 μmol g-1 h-1 , which could rival excellent photocatalysis system. This study highlights the potential of piezoelectric catalysis for overall water splitting.

Controlled substitutional doping of two-dimensional transition-metal dichalcogenides (TMDs) is of fundamental importance for their applications in electronics and optoelectronics. However, achievin...

Extrinsically controlling the intrinsic activity and stability of two-dimensional (2D) semiconducting materials by substitutional doping is crucial for energy-related applications. However, an in s...

Enabled by the advances in aberration‐corrected scanning transmission electron microscopy (STEM), atomic‐resolution real space imaging of materials has allowed a direct structure‐property investigation. Traditional ways of quantitative data analysis suffer from low yield and poor accuracy. New ideas in the field of computer vision and machine learning have provided more momentum to harness the wealth of big data and sophisticated information in STEM data analytics, which has transformed STEM from a localized characterization technique to a macroscopic tool with intelligence. In this review article, we discuss the prime significance of defect topology and density in two‐dimensional (2D) materials, which have proved to be a powerful means to tune a wide range of properties. Subsequently, we systematically review advanced data analysis methods that have demonstrated promising prospects in analyzing STEM data, particularly for identifying structural defects, with high throughput and veracity. A unified framework for atomic structure identification is also summarized.

Defects are commonly found in two-dimensional (2D) transition-metal dichalcogenide (TMD) materials. Such defects usually dictate the optical and electrical properties of TMDs. It is thus important ...

The development of both flexible solid-state Zn-air and Al-air batteries are challenged by the efficient and stable air cathodes with high catalytic activities in both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). In this work, we report the rational design of hollow N-doped carbon nanotube arrays embedded with confined Co nanoparticles (HCA-Co) through a facile solution-reaction and annealing process. Due to the unique integration of hollow carbon nanoarray with tiny cobalt nanoparticles, the obtained flexible HCA-Co electrode shows promising catalytic properties toward both ORR and OER that achieves a current density of 10 mA cm−2 at small overpotential of 290 mV in OER, and demonstrates an onset potential of 0.92 V in ORR. The HCA-Co can be applied as a binder-free air-cathode for flexible all-solid-state zinc-air batteries, which presents a relatively high open circuit potential (1.40 V) with better cycling stability than Pt/C based battery. The HCA-Co is also utilised as cathode for solid-state Al battery, which shows a high open circuit potential (1.966 V) with better mechanical flexibility than that of Pt/C-based battery. Such flexible electrode with excellent bifunctional catalytic properties hold great promise for the application in flexible electronics.

Gas sensing technologies for smart cities require miniaturization, cost-effectiveness, low power consumption, and outstanding sensitivity and selectivity. On-chip, tailorable capacitive sensors integrated with metal-organic framework (MOF) films are presented, in which abundant coordinatively unsaturated metal sites are available for gas detection. The in situ growth of homogeneous Mg-MOF-74 films is realized with an appropriate metal-to-ligand ratio. The resultant sensors exhibit selective detection for benzene vapor and carbon dioxide (CO2 ) at room temperature. Postsynthetic modification of Mg-MOF-74 films with ethylenediamine decreases sensitivity toward benzene but increases selectivity to CO2 . The reduced porosity and blocked open metal sites caused by amine coordination account for a deterioration in the sensing performance for benzene (by ca. 60 %). The enhanced sensitivity for CO2 (by ca. 25 %) stems from a tailored amine-CO2 interaction. This study demonstrates the feasibility of tuning gas sensing properties by adjusting MOF-analyte interactions, thereby offering new perspectives for the development of MOF-based sensors.

Heterostructures comprising van der Waals (vdW) stacked transition metal dichalcogenide (TMDC) monolayers are a fascinating class of two-dimensional (2D) materials. The presence of interlayer excitons, where the electron and the hole remain spatially separated in the two layers due to ultrafast charge transfer, is an intriguing feature of these heterostructures. The optoelectronic functionality of 2D heterostructure devices is critically dependent on the relative rotation angle of the layers. However, the role of the relative rotation angle of the constituent layers on intralayer absorption is not clear yet. Here, we investigate MoS2/WSe2 vdW heterostructures using monochromated low-loss electron energy loss (EEL) spectroscopy combined with aberration-corrected scanning transmission electron microscopy and report that momentum conservation is a critical factor in the intralayer absorption of TMDC vdW heterostructures. The evolution of the intralayer excitonic low-loss EEL spectroscopy peak broadenings as a function of the rotation angle reveals that the interlayer charge transfer rate can be about an order of magnitude faster in the aligned (or anti-aligned) case than in the misaligned cases. These results provide a deeper insight into the role of momentum conservation, one of the fundamental principles governing charge transfer dynamics in 2D vdW heterostructures.

The Rashba effect plays important roles in emerging quantum materials physics and potential spintronic applications, entailing both the spin orbit interaction (SOI) and broken inversion symmetry. In this work, we devise asymmetric oxide heterostructures of LaAlO3//SrTiO3/LaAlO3 (LAO//STO/LAO) to study the Rashba effect in STO with an initial centrosymmetric structure, and broken inversion symmetry is created by the inequivalent bottom and top interfaces due to their opposite polar discontinuities. Furthermore, we report the observation of a transition from the cubic Rashba effect to the coexistence of linear and cubic Rashba effects in the oxide heterostructures, which is controlled by the filling of Ti orbitals. Such asymmetric oxide heterostructures with initially centrosymmetric materials provide a general strategy for tuning the Rashba SOI in artificial quantum materials., The two-dimensional electron gases that form at LaAlO3/SrTiO3 heterostructure interfaces feature strong spin-orbit interactions, leading to proposed spintronic applications. Lin et al. show that the design of asymmetric heterostructures enables the Rashba spin-orbit interaction to be tuned between two regimes.

Exploring efficient strategies to increase CO2 photoreduction performance is a key challenge in the energy conversion field. Herein, a cooperative role involving an ultrathin 2D structure and surface defects is employed to design defective Bi2MoO6 ultrathin nanosheets, to boost the CO2 photoreduction activity under water with no sacrificial agent, co-catalyst or extra photosensitizer. Bi2MoO6 ultrathin nanosheets with surface “Bi O″ vacancy pairs are grown via a template-directed strategy, as proved by STEM-ADF and positron annihilation spectroscopy. The engineered “Bi O″ vacancy pairs tune the local atomic structure, electronic structure of Bi2MoO6 and serve as charge separation centers to boost the electron-hole separation. Meanwhile, the defective ultrathin structure favors the CO2 adsorption, activation and CO desorption processes. With the merits of atomically-thin configuration and surface defects, the defective Bi2MoO6 ultrathin nanosheets display 2.55 times improved CO formation rate than their bulk counterpart under light irradiation.

Structural defects in two-dimensional transition-metal dichalcogenides can significantly modify the material properties. Previous studies have shown that chalcogen defects can be created by physical sputtering, but the energetic ions can potentially displace transition-metal atoms at the same time, leading to ambiguous results and in some cases, degradation of material quality. In this work, selective sputtering of S atoms in monolayer MoS2 without damaging the Mo sublattice is demonstrated with low-energy helium plasma treatment. Based on X-ray photoelectron spectroscopy analysis, wide-range tuning of S defect concentration is achieved by controlling the ion energy and sputtering time. Furthermore, characterization with scanning transmission electron microscopy confirms that by keeping the ion energy low, the Mo sublattice remains intact. The properties of MoS2 at different defect concentrations are also characterized. In situ device measurement shows that the flake can be tuned from a semiconducting to metallic-like behavior by introducing S defects due to the creation of mid-gap states. When the defective MoS2 is exposed to air, the S defects are soon passivated, with oxygen atoms filling the defect sites.