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The numerous grainboundaries solid electrolyte interface, whether naturally occurring or artificially designed, leads to non-uniform Li metal deposition and consequently results in poor full-battery performance. Herein, a lithium-ion selective transport layer is reported to achieve a highly efficient and dendrite-free lithium metal anode. The layer-by-layer assembled protonated carbon nitride nanosheets present uniform macroscopical structure without grainboundaries. The carbon nitride with ordered pores in basal plane provides high-speed lithium-ion transport channels with low tortuosity. Consequently, the assembled 324 Wh kg -1 pouch cell exhibits 300 stable cycles with a capacity retention of 90.0% and an average Coulombic efficiency up to 99.7%. The ultra-dense Li metal anode makes current collector-free anode possible, achieving high energy density and long cycle life of a 7 Ah cell (506 Wh kg -1 , 160 cycles). Thus, it is proved that a macroscopically uniform interface layer with lithium-ion conductive channels could achieve Li metal battery with promising application potential., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Epitaxial growth of two-dimensional (2D) materials with uniform orientation has been previously realized by introducing a small binding energy difference between the two locally most stable orientations. However, this small energy difference can be easily disturbed by uncontrollable dynamics during the growth process, limiting its practical applications. Herein, we propose a quasi-equilibrium growth (QEG) strategy to synthesize inch-scale monolayer α-In 2 Se 3 single crystals, a semiconductor with ferroelectric properties, on fluor-phlogopite substrates. The QEG facilitates the discrimination of small differences in binding energy between the two locally most stable orientations, realizing robust single-orientation epitaxy within a broad growth window. Thus, single-crystal α-In 2 Se 3 film can be epitaxially grown on fluor-phlogopite, the cleavage surface atomic layer of which has the same 3-fold rotational symmetry with α-In 2 Se 3 . The resulting crystalline quality enables high electron mobility up to 117.2 cm 2 V -1 s -1 in α-In 2 Se 3 ferroelectric field-effect transistors, exhibiting reliable nonvolatile memory performance with long retention time and robust cycling endurance. In brief, the developed QEG method provides a route for preparing larger-area single-crystal 2D materials and a promising opportunity for applications of 2D ferroelectric devices and nanoelectronics., (© 2024. The Author(s).)

Two-dimensional (2D) layered materials have been studied in depth during the past two decades due to their unique structure and properties. Transition metal (TM) intercalation of layered materials have been proven as an effective way to introduce new physical properties, such as tunable 2D magnetism, but the direct growth of atomically thin heteroatoms-intercalated layered materials remains untapped. Herein, we directly synthesize various ultrathin heteroatoms-intercalated 2D layered materials (UHI-2DMs) through flux-assisted growth (FAG) approach. Eight UHI-2DMs (V 1/3 NbS 2 , Cr 1/3 NbS 2 , Mn 1/3 NbS 2 , Fe 1/3 NbS 2 , Co 1/3 NbS 2 , Co 1/3 NbSe 2 , Fe 1/3 TaS 2 , Fe 1/4 TaS 2 ) were successfully synthesized. Their thickness can be reduced to the thinnest limit (bilayer 2D material with monolayer intercalated TM), and magnetic ordering can be induced in the synthesized structures. Interestingly, due to the possible anisotropy-stabilized long-range ferromagnetism in Fe 1/3 TaS 2 with weak interlayer coupling, the layer-independent magnetic ordering temperature of Fe 1/3 TaS 2 was revealed by magneto-transport properties. This work establishes a general method for direct synthesis of heteroatom-intercalated ultrathin 2D materials with tunable chemical and physical properties., (© 2024. The Author(s).)

Domain boundaries have been intensively investigated in bulk ferroelectric materials and two-dimensional materials. Many methods such as electrical, mechanical and optical approaches have been utilized to probe and manipulate domain boundaries. So far most research focuses on the initial and final states of domain boundaries before and after manipulation, while the microscopic understanding of the evolution of domain boundaries remains elusive. In this paper, we report controllable manipulation of the domain boundaries in two-dimensional ferroelectric In 2 Se 3 with atomic precision using scanning tunneling microscopy. We show that the movements of the domain boundaries can be driven by the electric field from a scanning tunneling microscope tip and proceed by the collective shifting of atoms at the domain boundaries. Our density functional theory calculations reveal the energy path and evolution of the domain boundary movement. The results provide deep insight into domain boundaries in two-dimensional ferroelectric materials and will inspire inventive applications of these materials., (© 2024. The Author(s).)

Developing efficient (co-)catalysts with optimized interfacial mass and charge transport properties is essential for enhanced oxygen evolution reaction (OER) via electrochemical water splitting. Here we report one-atom-thick hexagonal boron nitride (hBN) as an attractive co-catalyst with enhanced OER efficiency. Various electrocatalytic electrodes are encapsulated with centimeter-sized hBN films which are dense and impermeable so that only the hBN surfaces are directly exposed to reactive species. For example, hBN covered Ni-Fe (oxy)hydroxide anodes show an ultralow Tafel slope of ~30 mV dec -1 with improved reaction current by about 10 times, reaching ~2000 mA cm -2 (at an overpotential of ~490 mV) for over 150 h. The mass activity of hBN co-catalyst is found exceeding that of commercialized catalysts by up to five orders of magnitude. Using isotope experiments and simulations, we attribute the results to the adsorption of oxygen-containing intermediates at the insulating co-catalyst, where localized electrons facilitate the deprotonation processes at electrodes. Little impedance to electron transfer is observed from hBN film encapsulation due to its ultimate thickness. Therefore, our work also offers insights into mechanisms of interfacial reactions at the very first atomic layer of electrodes., (© 2023. The Author(s).)

Single-atom catalysts provide efficiently utilized active sites to improve catalytic activities while improving the stability and enhancing the activities to the level of their bulk metallic counterparts are grand challenges. Herein, we demonstrate a family of single-atom catalysts with different interaction types by confining metal single atoms into the van der Waals gap of two-dimensional SnS 2 . The relatively weak bonding between the noble metal single atoms and the host endows the single atoms with more intrinsic catalytic activity compared to the ones with strong chemical bonding, while the protection offered by the layered material leads to ultrahigh stability compared to the physically adsorbed single-atom catalysts on the surface. Specifically, the trace Pt-intercalated SnS 2 catalyst has superior long-term durability and comparable performance to that of commercial 10 wt% Pt/C catalyst in hydrogen evolution reaction. This work opens an avenue to explore high-performance intercalated single-atom electrocatalysts within various two-dimensional materials., (© 2022. The Author(s).)

Electrochemical reduction of CO 2 to multi-carbon fuels and chemical feedstocks is an appealing approach to mitigate excessive CO 2 emissions. However, the reported catalysts always show either a low Faradaic efficiency of the C 2+ product or poor long-term stability. Herein, we report a facile and scalable anodic corrosion method to synthesize oxygen-rich ultrathin CuO nanoplate arrays, which form Cu/Cu 2 O heterogeneous interfaces through self-evolution during electrocatalysis. The catalyst exhibits a high C 2 H 4 Faradaic efficiency of 84.5%, stable electrolysis for ~55 h in a flow cell using a neutral KCl electrolyte, and a full-cell ethylene energy efficiency of 27.6% at 200 mA cm -2 in a membrane electrode assembly electrolyzer. Mechanism analyses reveal that the stable nanostructures, stable Cu/Cu 2 O interfaces, and enhanced adsorption of the *OCCOH intermediate preserve selective and prolonged C 2 H 4 production. The robust and scalable produced catalyst coupled with mild electrolytic conditions facilitates the practical application of electrochemical CO 2 reduction., (© 2022. The Author(s).)

Emerging two-dimensional (2D) layered materials have been attracting great attention as sensing materials for next-generation high-performance biological and chemical sensors. The sensor performance of 2D materials is strongly dependent on the structural defects as indispensable active sites for analyte adsorption. However, controllable defect engineering in 2D materials is still challenging. In the present work, we propose exploitation of controllably grown polycrystalline films of 2D layered materials with high-density grain boundaries (GBs) for design of ultra-sensitive ion sensors, where abundant structural defects on GBs act as favorable active sites for ion adsorption. As a proof-of-concept, our fabricated surface plasmon resonance sensors with GB-rich polycrystalline monolayer WS 2 films have exhibited high selectivity and superior attomolar-level sensitivity in Hg 2+ detection owing to high-density GBs. This work provides a promising avenue for design of ultra-sensitive sensors based on GB-rich 2D layered materials.

The discovery of ferromagnetic two-dimensional van der Waals materials has opened up opportunities to explore intriguing physics and to develop innovative spintronic devices. However, controllable synthesis of these 2D ferromagnets and enhancing their stability under ambient conditions remain challenging. Here, we report chemical vapor deposition growth of air-stable 2D metallic 1T-CrTe 2 ultrathin crystals with controlled thickness. Their long-range ferromagnetic ordering is confirmed by a robust anomalous Hall effect, which has seldom been observed in other layered 2D materials grown by chemical vapor deposition. With reducing the thickness of 1T-CrTe 2 from tens of nanometers to several nanometers, the easy axis changes from in-plane to out-of-plane. Monotonic increase of Curie temperature with the thickness decreasing from ~130.0 to ~7.6 nm is observed. Theoretical calculations indicate that the weakening of the Coulomb screening in the two-dimensional limit plays a crucial role in the change of magnetic properties.

Valley pseudospin in transition metal dichalcogenides monolayers intrinsically provides additional possibility to control valley carriers, raising a great impact on valleytronics in following years. The spin-valley locking directly contributes to optical selection rules which allow for valley-dependent addressability of excitons by helical optical pumping. As a binary photonic addressable route, manipulation of valley polarization states is indispensable while effective control methods at deep-subwavelength scale are still limited. Here, we report the excitation and control of valley polarization in h-BN/WSe 2 /h-BN and Au nanoantenna hybrid structure by electron beam. Near-field circularly polarized dipole modes can be excited via precise stimulation and generate the valley polarized cathodoluminescence via near-field interaction. Effective manipulation of valley polarization degree can be realized by variation of excitation position. This report provides a near-field excitation methodology of valley polarization, which offers exciting opportunities for deep-subwavelength valleytronics investigation, optoelectronic circuits integration and future quantum information technologies.

The electronic, optical and chemical properties of two-dimensional transition metal dichalcogenides strongly depend on their three-dimensional atomic structure and crystal defects. Using Re-doped MoS 2 as a model system, here we present scanning atomic electron tomography as a method to determine three-dimensional atomic positions as well as positions of crystal defects such as dopants, vacancies and ripples with a precision down to 4 pm. We measure the three-dimensional bond distortion and local strain tensor induced by single dopants. By directly providing these experimental three-dimensional atomic coordinates to density functional theory, we obtain more accurate electronic band structures than derived from conventional density functional theory calculations that relies on relaxed three-dimensional atomic coordinates. We anticipate that scanning atomic electron tomography not only will be generally applicable to determine the three-dimensional atomic coordinates of two-dimensional materials, but also will enable ab initio calculations to better predict the physical, chemical and electronic properties of these materials.

To date, effective control over the electrochemical reduction of CO 2 to multicarbon products (C ≥ 2) has been very challenging. Here, we report a design principle for the creation of a selective yet robust catalytic interface for heterogeneous electrocatalysts in the reduction of CO 2 to C 2 oxygenates, demonstrated by rational tuning of an assembly of nitrogen-doped nanodiamonds and copper nanoparticles. The catalyst exhibits a Faradaic efficiency of ~63% towards C 2 oxygenates at applied potentials of only -0.5 V versus reversible hydrogen electrode. Moreover, this catalyst shows an unprecedented persistent catalytic performance up to 120 h, with steady current and only 19% activity decay. Density functional theory calculations show that CO binding is strengthened at the copper/nanodiamond interface, suppressing CO desorption and promoting C 2 production by lowering the apparent barrier for CO dimerization. The inherent compositional and electronic tunability of the catalyst assembly offers an unrivalled degree of control over the catalytic interface, and thereby the reaction energetics and kinetics.

The original version of this Article omitted an affiliation of Xiewen Wen: 'College of Chemistry and Molecular Engineering, Beijing National Laboratory for Molecular Sciences, Peking University, Beijing 100871, China'. This has been corrected in both the PDF and HTML versions of the Article.

Phase transitions of electron-hole pairs on semiconductor/conductor interfaces determine fundamental properties of optoelectronics. To investigate interfacial dynamical transitions of charged quasiparticles, however, remains a grand challenge. By employing ultrafast mid-infrared microspectroscopic probes to detect excitonic internal quantum transitions and two-dimensional atomic device fabrications, we are able to directly monitor the interplay between free carriers and insulating interlayer excitons between two atomic layers. Our observations reveal unexpected ultrafast formation of tightly bound interlayer excitons between conducting graphene and semiconducting MoSe 2 . The result suggests carriers in the doped graphene are no longer massless, and an effective mass as small as one percent of free electron mass is sufficient to confine carriers within a 2D hetero space with energy 10 times larger than the room-temperature thermal energy. The interlayer excitons arise within 1 ps. Their formation effectively blocks charge recombination and improves charge separation efficiency for more than one order of magnitude.

Doped semiconductors are the most important building elements for modern electronic devices 1 . In silicon-based integrated circuits, facile and controllable fabrication and integration of these materials can be realized without introducing a high-resistance interface 2,3 . Besides, the emergence of two-dimensional (2D) materials enables the realization of atomically thin integrated circuits 4-9 . However, the 2D nature of these materials precludes the use of traditional ion implantation techniques for carrier doping and further hinders device development 10 . Here, we demonstrate a solvent-based intercalation method to achieve p-type, n-type and degenerately doped semiconductors in the same parent material at the atomically thin limit. In contrast to naturally grown n-type S-vacancy SnS 2 , Cu intercalated bilayer SnS 2 obtained by this technique displays a hole field-effect mobility of ~40 cm 2  V -1  s -1 , and the obtained Co-SnS 2 exhibits a metal-like behaviour with sheet resistance comparable to that of few-layer graphene 5 . Combining this intercalation technique with lithography, an atomically seamless p-n-metal junction could be further realized with precise size and spatial control, which makes in-plane heterostructures practically applicable for integrated devices and other 2D materials. Therefore, the presented intercalation method can open a new avenue connecting the previously disparate worlds of integrated circuits and atomically thin materials.

Van der Waals heterostructures composed of two-dimensional transition-metal dichalcogenides layers have recently emerged as a new family of materials, with great potential for atomically thin opto-electronic and photovoltaic applications. It is puzzling, however, that the photocurrent is yielded so efficiently in these structures, despite the apparent momentum mismatch between the intralayer/interlayer excitons during the charge transfer, as well as the tightly bound nature of the excitons in 2D geometry. Using the energy-state-resolved ultrafast visible/infrared microspectroscopy, we herein obtain unambiguous experimental evidence of the charge transfer intermediate state with excess energy, during the transition from an intralayer exciton to an interlayer exciton at the interface of a WS2/MoS2 heterostructure, and free carriers moving across the interface much faster than recombining into the intralayer excitons. The observations therefore explain how the remarkable charge transfer rate and photocurrent generation are achieved even with the aforementioned momentum mismatch and excitonic localization in 2D heterostructures and devices.

Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid-base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti(4+) to form planar p-type [Ti(4+)n(InSe)] coordination complexes. Using this strategy, we fabricate planar p-n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B(3+), Al(3+) and Sn(4+)) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid-base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.

The isolation of the two-dimensional semiconductor molybdenum disulphide introduced a new optically active material possessing a band gap that can be facilely tuned via elastic strain. As an atomically thin membrane with exceptional strength, monolayer molybdenum disulphide subjected to biaxial strain can embed wide band gap variations overlapping the visible light spectrum, with calculations showing the modified electronic potential emanating from point-induced tensile strain perturbations mimics the Coulomb potential in a mesoscopic atom. Here we realize and confirm this 'artificial atom' concept via capillary-pressure-induced nanoindentation of monolayer molybdenum disulphide from a tailored nanopattern, and demonstrate that a synthetic superlattice of these building blocks forms an optoelectronic crystal capable of broadband light absorption and efficient funnelling of photogenerated excitons to points of maximum strain at the artificial-atom nuclei. Such two-dimensional semiconductors with spatially textured band gaps represent a new class of materials, which may find applications in next-generation optoelectronics or photovoltaics.

Layer-by-layer stacking or lateral interfacing of atomic monolayers has opened up unprecedented opportunities to engineer two-dimensional heteromaterials. Fabrication of such artificial heterostructures with atomically clean and sharp interfaces, however, is challenging. Here, we report a one-step growth strategy for the creation of high-quality vertically stacked as well as in-plane interconnected heterostructures of WS2/MoS2 via control of the growth temperature. Vertically stacked bilayers with WS2 epitaxially grown on top of the MoS2 monolayer are formed with preferred stacking order at high temperature. A strong interlayer excitonic transition is observed due to the type II band alignment and to the clean interface of these bilayers. Vapour growth at low temperature, on the other hand, leads to lateral epitaxy of WS2 on MoS2 edges, creating seamless and atomically sharp in-plane heterostructures that generate strong localized photoluminescence enhancement and intrinsic p-n junctions. The fabrication of heterostructures from monolayers, using simple and scalable growth, paves the way for the creation of unprecedented two-dimensional materials with exciting properties.

Perfect graphene is believed to be the strongest material. However, the useful strength of large-area graphene with engineering relevance is usually determined by its fracture toughness, rather than the intrinsic strength that governs a uniform breaking of atomic bonds in perfect graphene. To date, the fracture toughness of graphene has not been measured. Here we report an in situ tensile testing of suspended graphene using a nanomechanical device in a scanning electron microscope. During tensile loading, the pre-cracked graphene sample fractures in a brittle manner with sharp edges, at a breaking stress substantially lower than the intrinsic strength of graphene. Our combined experiment and modelling verify the applicability of the classic Griffith theory of brittle fracture to graphene. The fracture toughness of graphene is measured as the critical stress intensity factor of and the equivalent critical strain energy release rate of 15.9 J m(-2). Our work quantifies the essential fracture properties of graphene and provides mechanistic insights into the mechanical failure of graphene.

Graphene and hexagonal boron nitride are typical conductor and insulator, respectively, while their hybrids hexagonal boron carbonitride are promising as a semiconductor. Here we demonstrate a direct chemical conversion reaction, which systematically converts the hexagonal carbon lattice of graphene to boron nitride, making it possible to produce uniform boron nitride and boron carbonitride structures without disrupting the structural integrity of the original graphene templates. We synthesize high-quality atomic layer films with boron-, nitrogen- and carbon-containing atomic layers with full range of compositions. Using this approach, the electrical resistance, carrier mobilities and bandgaps of these atomic layers can be tuned from conductor to semiconductor to insulator. Combining this technique with lithography, local conversion could be realized at the nanometre scale, enabling the fabrication of in-plane atomic layer structures consisting of graphene, boron nitride and boron carbonitride. This is a step towards scalable synthesis of atomically thin two-dimensional integrated circuits.

Graphene and hexagonal boron nitride (h-BN) have similar crystal structures with a lattice constant difference of only 2%. However, graphene is a zero-bandgap semiconductor with remarkably high carrier mobility at room temperature, whereas an atomically thin layer of h-BN is a dielectric with a wide bandgap of ∼5.9 eV. Accordingly, if precise two-dimensional domains of graphene and h-BN can be seamlessly stitched together, hybrid atomic layers with interesting electronic applications could be created. Here, we show that planar graphene/h-BN heterostructures can be formed by growing graphene in lithographically patterned h-BN atomic layers. Our approach can create periodic arrangements of domains with size ranging from tens of nanometres to millimetres. The resulting graphene/h-BN atomic layers can be peeled off the growth substrate and transferred to various platforms including flexible substrates. We also show that the technique can be used to fabricate two-dimensional devices, such as a split closed-loop resonator that works as a bandpass filter.

Hexagonal boron nitride is a two-dimensional layered material that can be stable at 1,500 °C in air and will not react with most chemicals. Here we demonstrate large-scale, ultrathin, oxidation-resistant coatings of high-quality hexagonal boron nitride layers with controlled thicknesses from double layers to bulk. We show that such ultrathin hexagonal boron nitride films are impervious to oxygen diffusion even at high temperatures and can serve as high-performance oxidation-resistant coatings for nickel up to 1,100 °C in oxidizing atmospheres. Furthermore, graphene layers coated with a few hexagonal boron nitride layers are also protected at similarly high temperatures. These hexagonal boron nitride atomic layer coatings, which can be synthesized via scalable chemical vapour deposition method down to only two layers, could be the thinnest coating ever shown to withstand such extreme environments and find applications as chemically stable high-temperature coatings.