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Nanomaterials with a large chiroptical response and high structural stability are desirable for advanced miniaturized optical and optoelectronic applications. One-dimensional (1D) nanotubes are robust crystals with inherent and continuously tunable chiral geometries. However, their chiroptical response is typically weak and hard to control, due to the diverse structures of the coaxial tubes. Here we demonstrate that as-grown multiwalled boron nitride nanotubes (BNNTs), featuring coherent-stacking structures including near monochirality, homo-handedness and unipolarity among the component tubes, exhibit a scalable nonlinear chiroptical response. This intrinsic architecture produces a strong nonlinear optical response in individual multiwalled BNNTs, enabling second-harmonic generation (SHG) with a conversion efficiency up to 0.01% and output power at the microwatt level—both excellent figures of merit in the 1D nanomaterials family. We further show that the rich chirality of the nanotubes introduces a controllable nonlinear geometric phase, producing a chirality-dependent SHG circular dichroism with values of −0.7 to +0.7. We envision that our 1D chiral platform will enable novel functions in compact nonlinear light sources and modulators.

The Boltzmann Tyranny, set by thermionic statistics, dictates the lower limit of switching slope (SS) of a MOSFET to be 60 mV/dec, the fundamental barrier for low-dissipative electronics. The large SS leads to nonscalable voltage, significant leakage, and power consumption, particularly at short channels, making transistor scaling an intimidating challenge. In recent decades, an array of steep-slope transistors has been proposed; none is close to an ideal switch with ultimately abrupt switching (SS ∼ 0 mV/dec) between the binary logic states. We demonstrated an all-2D-materials van-der-Waals-heterostructure (vdW)-based FET that exhibits ultrasteep switching (0.33 mV/dec), a large on/off current ratio (∼107), and an ultralow off current (∼0.1 pA). The “Subthreshold-Free” operation achieved by the collective behavior of functional materials enables FET switching directly from the OFF-state to the ON-state with entirely eliminated subthreshold region, behaving as the ideal logic switch. Two-inch wafer-scale device fabrication is demonstrated. Boosted by device innovation and emerging materials, the research presents an advancement in achieving the “beyond-Boltzmann” transistors, overcoming one of the CMOS electronics’ most infamous technology barriers that have plagued the research community for decades.

The exceptional physical properties of two-dimensional (2D) van der Waals (vdW) materials have been extensively researched, driving advances in material synthesis. Epitaxial growth, a prominent synthesis strategy, enables the production of large-area, high-quality 2D films compatible with advanced integrated circuits. Typical 2D single crystals, such as graphene, transition metal dichalcogenides and hexagonal boron nitride, have been epitaxially grown at a wafer scale. A systematic summary is required to offer strategic guidance for the epitaxy of emerging 2D materials. Here we focus on the epitaxy methodologies for 2D vdW materials in two directions: the growth of in-plane single-crystal monolayers and the fabrication of out-of-plane homostructures. We first discuss nucleation control of a single domain and orientation control over multiple domains to achieve large-scale single-crystal monolayers. We analyse the defect levels and measures of crystalline quality of typical 2D vdW materials with various epitaxial growth techniques. We then outline technical routes for the growth of homogeneous multilayers and twisted homostructures. We further summarize the current strategies to guide future efforts in optimizing on-demand fabrication of 2D vdW materials, as well as subsequent device manufacturing for their industrial applications.

Monolayer transition metal dichalcogenides (TMDs) are considered promising building blocks for next-generation photonic and optoelectronic devices, owing to their fascinating optical properties. However, their inherent weak light absorption and low quantum yield severely hinder their practical applications. Here, we report up to 18000-fold photoluminescence (PL) enhancement in a monolayer WSe2-coupled plasmonic nanocavity. A spectroscopy-assisted nanomanipulation technique enables the assembly of a nanocavity with customizable resonances to simultaneously enhance the excitation and emission processes. In particular, precise control over the magnetic cavity mode facilitates spectral and spatial overlap with the exciton, resulting in plasmon–exciton intermediate coupling that approaches the maximum emission rate in the hybrid system. Meanwhile, the cavity mode exhibits high radiation directivity, which overwhelmingly directs surface-normal PL emission and leads to a 17-fold increase in the collection efficiency. Our approach opens up a new avenue to enhance the PL intensity of monolayer TMDs, facilitating their implementation in highly efficient optoelectronic devices.

Within the family of two-dimensional dielectrics, rhombohedral boron nitride (rBN) is considerably promising owing to having not only the superior properties of hexagonal boron nitride1–4—including low permittivity and dissipation, strong electrical insulation, good chemical stability, high thermal conductivity and atomic flatness without dangling bonds—but also useful optical nonlinearity and interfacial ferroelectricity originating from the broken in-plane and out-of-plane centrosymmetry5–23. However, the preparation of large-sized single-crystal rBN layers remains a challenge24–26, owing to the requisite unprecedented growth controls to coordinate the lattice orientation of each layer and the sliding vector of every interface. Here we report a facile methodology using bevel-edge epitaxy to prepare centimetre-sized single-crystal rBN layers with exact interlayer ABC stacking on a vicinal nickel surface. We realized successful accurate fabrication over a single-crystal nickel substrate with bunched step edges of the terrace facet (100) at the bevel facet (110), which simultaneously guided the consistent boron–nitrogen bond orientation in each BN layer and the rhombohedral stacking of BN layers via nucleation near each bevel facet. The pure rhombohedral phase of the as-grown BN layers was verified, and consequently showed robust, homogeneous and switchable ferroelectricity with a high Curie temperature. Our work provides an effective route for accurate stacking-controlled growth of single-crystal two-dimensional layers and presents a foundation for applicable multifunctional devices based on stacked two-dimensional materials.

We proposed a unique wire-production process by rolling up and drawing chemical vapor deposition copper/graphene (Cu/Gr) foils, and a good strength-conductivity trade-off was achieved originating from the dispersed Gr in Cu matrix and the high-quality heterointerfaces. The 1.14 mm cold-drawn composite wire exhibited a tensile strength of 455 ± 5 MPa and a conductivity of 98.18 ± 0.16 % of the International Annealed Copper Standard (IACS), and the tensile strength was 250 ± 2 MPa with a satisfied electrical conductivity of 101.68 ± 0.52 % IACS upon annealing. The microstructure involution during the preparing process was revealed, and the reinforcement mechanisms in the yield strength and conductivity due to the introduced Gr were clarified. The results indicated that the Gr plays a role in pinning dislocations and preventing grain boundary movement during deformation and the subsequent annealing, thereby enhancing the strength of the Cu matrix. Meanwhile, the Cu-Gr coupling interfaces exhibited an electronic doping effect, enhancing the conductive properties. Our work presented a feasible method for preparing Cu/Gr composite wire with comprehensive electrical conductivity and strength optimization.

Chiral nanographenes (NGs) have garnered significant interest as optoelectronic materials in recent years. While helically chiral NGs have been extensively studied, axially chiral NGs have only witnessed limited examples, with no prior reports of axially chiral nonbenzenoid NGs. Herein we report an axially chiral nonbenzenoid nanographene featuring six pentagons and four heptagons. This compound, denoted as 2, was efficiently synthesized via an efficient Pd-catalyzed aryl silane homocoupling reaction. The presence of two bulky 3,5-di-tert-butylphenyl groups around the axisconnecting the two nonbenzenoid PAH (AHR) segments endows 2with atropisomeric chirality and high racemization energy barrier, effectively preventing racemization of both R- and S-enantiomers at room temperature. Optically pure R-2and S-2were obtained by chiral HPLC separation, and they exhibit circular dichroism (CD) activity at wavelengths up to 660 nm, one of the longest wavelengths with CD responses reported for the chiral NGs. Interestingly, racemic 2forms a homoconfiguration p-dimer in the crystal lattice, belonging to the I222chiral space group. Consequently, this unique structure renders crystals of 2with a second harmonic generation (SHG) response, distinguishing it from all the reported axially chiral benzenoid NGs. Moreover, R-2and S-2also exhibit SHG-CD properties.

The permeability and selectivity of biological and artificial ion channels correlate with the specific hydration structure of single ions. However, fundamental understanding of the effect of ion–ion interaction remains elusive. Here, via non-contact atomic force microscopy measurements, we demonstrate that hydrated alkali metal cations (Na+and K+) at charged surfaces could come into close contact with each other through partial dehydration and water rearrangement processes, forming one-dimensional chain structures. We prove that the interplay at the nanoscale between the water–ion and water–water interaction can lead to an effective ion–ion attraction overcoming the ionic Coulomb repulsion. The tendency for different ions to become closely packed follows the sequence K+> Na+> Li+, which is attributed to their different dehydration energies and charge densities. This work highlights the key role of water molecules in prompting close packing and concerted movement of ions at charged surfaces, which may provide new insights into the mechanism of ion transport under atomic confinement.

• Single-crystal electrolytic copper foils, with thickness up to 500 µm and facets including both low and high index ones, are first obtained through facet copy from a single-crystal template. • Crystallographic characterizations clearly visualize the facet copy process, where a seed that copy the orientation of the template first grow vertically, and then spread out. • The single-crystal electrolytic Cu foils exhibit remarkably improved mechanical properties than the original ones (elongation-to-fracture: 105% vs. 24%, average numbers of cycles to failure: 1600 vs. 200, and electrical conductivity of 102.6% of the international annealed copper standard (IACS) vs. 98.5%). Depending on the production process, copper (Cu) foils can be classified into two types, i.e., rolled copper (r-Cu) foils and electrolytic copper (e-Cu) foils. Owing to their high electrical conductivity and ductility at low cost, e-Cu foils are employed extensively in modern industries and account for more than 98% of the Cu foil market share. However, industrial e-Cu foils have never been single-crystallized due to their high density of grain boundaries, various grain orientations and vast impurities originating from the electrochemical deposition process. Here, we report a methodology of transforming industrial e-Cu foils into single crystals by facet copy from a single-crystal template. Different facets of both low and high indices are successfully produced, and the thickness of the single crystal can reach 500 µm. Crystallographic characterizations directly recognized the single-crystal copy process, confirming the complete assimilation impact from the template. The obtained single-crystal e-Cu foils exhibit remarkably improved ductility (elongation-to-fracture of 105% vs. 25%), fatigue performance (the average numbers of cycles to failure of 1600 vs. 200) and electrical property (electrical conductivity of 102.6% of the international annealed copper standard (IACS) vs. 98.5%) than original ones. This work opens up a new avenue for the preparation of single-crystal e-Cu foils and may expand their applications in high-speed, flexible, and wearable devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Platinum (Pt) oxides are vital catalysts in numerous reactions, but research indicates that they decompose at high temperatures, limiting their use in high-temperature applications. In this study, we identify a two-dimensional (2D) crystalline Pt oxide with remarkable thermal stability (1,200 K under nitrogen dioxide) using a suite of in situ methods. This 2D Pt oxide, characterized by a honeycomb lattice of Pt atoms encased between dual oxygen layers forming a six-pointed star structure, exhibits minimized in-plane stress and enhanced vertical bonding due to its unique structure, as revealed by theoretical simulations. These features contribute to its high thermal stability. Multiscale in situ observations trace the formation of this 2D Pt oxide from α-PtO2, providing insights into its formation mechanism from the atomic to the millimetre scale. This 2D Pt oxide with outstanding thermal stability and distinct surface electronic structure subverts the previously held notion that Pt oxides do not exist at high temperatures and can also present unique catalytic capabilities. This work expands our understanding of Pt oxidation species and sheds light on the oxidative and catalytic behaviours of Pt oxide in high-temperature settings.

Copper-based nanomaterials are compelling for high-efficient, low-cost electrocatalytic CO2reduction reaction (CO2RR) due to their exotic electronic and structural properties. However, controllable preparation of copper-based two-dimensional (2D) materials with abundant catalytically active sites, that guarantee high CO2RR performance, remains challenging, especially on a large scale. Here, an in situvertical growth of scalable metallic 2D Cu2Te nanosheet arrays on commercial copper foils is demonstrated for efficient CO2-to-CH4electrocatalysis. The edge-oriented growth of Cu2Te nanosheets with tunable sizes and thicknesses is facilely attained by a two-step process of chemical etching and chemical vapor deposition. These active sites abounding on highly exposed edges of Cu2Te nanosheets greatly promote the electroreduction of CO2into CH4at a potential as low as −0.4 V (versus the reversible hydrogen electrode), while suppressing hydrogen evolution reaction. When a flow cell is employed to accelerate the mass transfer, the faradaic efficiency reaches ∼63% at an applied current density of 300 mA cm–2. These findings will provide great possibilities for developing scalable, energy-efficient Cu-based CO2RR electrocatalysts.

Correlating atomic configurations—specifically, degree of disorder (DOD)—of an amorphous solid with properties is a long-standing riddle in materials science and condensed matter physics, owing to difficulties in determining precise atomic positions in 3D structures1–5. To this end, 2D systems provide insight to the puzzle by allowing straightforward imaging of all atoms6,7. Direct imaging of amorphous monolayer carbon (AMC) grown by laser-assisted depositions has resolved atomic configurations, supporting the modern crystallite view of vitreous solids over random network theory8. Nevertheless, a causal link between atomic-scale structures and macroscopic properties remains elusive. Here we report facile tuning of DOD and electrical conductivity in AMC films by varying growth temperatures. Specifically, the pyrolysis threshold temperature is the key to growing variable-range-hopping conductive AMC with medium-range order (MRO), whereas increasing the temperature by 25 °C results in AMC losing MRO and becoming electrically insulating, with an increase in sheet resistance of 109times. Beyond visualizing highly distorted nanocrystallites embedded in a continuous random network, atomic-resolution electron microscopy shows the absence/presence of MRO and temperature-dependent densities of nanocrystallites, two order parameters proposed to fully describe DOD. Numerical calculations establish the conductivity diagram as a function of these two parameters, directly linking microstructures to electrical properties. Our work represents an important step towards understanding the structure–property relationship of amorphous materials at the fundamental level and paves the way to electronic devices using 2D amorphous materials.

Monolayer transition metal dichalcogenides have high nonlinear optical susceptibility but are limited by atomic thickness. Zhou et al. found that MoS2superlattice thin films enhance second harmonic generation efficiency, retaining nonlinear susceptibilities and offering tunable optical cross sections for improved light-matter interaction.

Copper-based bimetallic heterostructures have recently gained extensive attention because of their promising capability to steer the selectivity of electrochemical CO2reduction into high-valued multicarbon products. However, a thorough mechanistic understanding toward the CO2reduction pathway and the influence of interfacial atomic configuration has not yet been unveiled. Herein, we rationally engaged facet engineering to construct a Au/Cu heterostructure viaan epitaxial growth and observed that Au(110)/Cu(110) exhibited the highest yield rate toward multicarbon alcohols, compared with results for Au(111)/Cu(111) and Au(100)/Cu(100). According to electrochemical analysis, the enhanced activity was attributed to high-conversion capabilities of both CO2-to-CO and *CO-to-C2+alcohols. Moreover, we confirmed that the buildup of *CO is more crucial than the atomic arrangement of Cu surface for multicarbon production. Our work demonstrates a benchmark tandem CO2electroreduction system to explicitly link the interfacial atomic configuration to the electrocatalytic performance and sheds light on the facet engineering of bimetallic electrodes in electrolysis.

Interfacial atomic configuration and its evolution play critical roles in the structural stability and functionality of mixed zero-dimensional (0D) metal nanoparticles (NPs) and two-dimensional (2D) semiconductors. In situobservation of the interface evolution at atomic resolution is a vital method. Herein, the directional migration and structural evolution of Au NPs on anisotropic ReS2were investigated in situby aberration-corrected transmission electron microscopy. Statistically, the migration of Au NPs with diameters below 3 nm on ReS2takes priority with greater probability along the b-axis direction. Density functional theory calculations suggest that the lower diffusion energy barrier enables the directional migration. The coalescence kinetics of Au NPs is quantitatively described by the relation of neck radius (r) and time (t), expressed as r2=Kt. Our work provides an atomic-resolved dynamic analysis method to study the interfacial structural evolution of metal/2D materials, which is essential to the study of the stability of nanodevices based on mixed-dimensional nanomaterials.

Pentagonal cyclization at the bay positions of armchair-edged graphenic cores can build molecular bowls without the destruction of hexagonal lattices. However, this synthesis remains challenging due to unfavorable strain and the multiple reactions required. Here, we show that a new type of graphenic molecular bowl with a depth of 1.7 Å and a diameter of 1.2 nm is constructed by sextuple Se annulation at the bay positions of armchair-edged hexa-peri-hexabenzocoronene. This graphenic bowl is functionalized with phenylseleno groups that stack into a discrete bilayer dimer in solution. Such a dimer exhibits high stability and survives in the gas phase after laser ablation. Strikingly, the asymmetric one-dimensional supramolecular columns of graphenic bowl with coherent stacking configuration are observed in the solid state, which results in a strong second harmonic generation with prominent polarization dependence. Our findings present a concise synthesis of a giant molecular bowl with a graphenic core and demonstrate the unique supramolecular assembly of extended graphenic bowls.

The essence of connection in vehicle network is the social relationship between people, and thus Vehicular Social Networks (VSNs), characterized by social aspects and features, can be formed. The information collected by VSNs can be used for context prediction of autonomous vehicles. Multivariate relations are common in square connected relations caused by geographic characteristics in VSNs. They can effectively reflect the high-order structural features of the network dataset. It is necessary to exploit the multivariate relations of VSNs to improve the performance of context prediction. However, The representation of entity-relationes in the network often adopts a binary form, and the existing graph learning methods rely on the neighborhood information of nodes to achieve the aggregation or diffusion of information. Using this to represent multivariate relations will result in partial omissions or even complete loss of valuable information, which ultimately affects the learning effect of learning methods. In order to better understand the social behavior of the VSNs, this paper uses the network motif to implement the representation of the multivariate relations in the network, and proposes the graPh learnIng with moTif mAtrix (PITA) method. This method can be used as a preprocessing step for the measurement strategy of the relations in VSNs and the graph learning, which can mine the information in VSNs and improve the accuracy of the original graph learning method by the multivariate relation information. We performed experiments on 6 network datasets. The experimental results show that in the node classification task, the baseline method modified by the PITA method has a higher classification accuracy than the original method.

The properties of two-dimensional (2D) van der Waals materials can be tuned through nanostructuring or controlled layer stacking, where interlayer hybridization induces exotic electronic states and transport phenomena. Here we describe a viable approach and underlying mechanism for the assisted self-assembly of twisted layer graphene. The process, which can be implemented in standard chemical vapour deposition growth, is best described by analogy to origami and kirigami with paper. It involves the controlled induction of wrinkle formation in single-layer graphene with subsequent wrinkle folding, tearing and re-growth. Inherent to the process is the formation of intertwined graphene spirals and conversion of the chiral angle of 1D wrinkles into a 2D twist angle of a 3D superlattice. The approach can be extended to other foldable 2D materials and facilitates the production of miniaturized electronic components, including capacitors, resistors, inductors and superconductors.

Multilayer van der Waals (vdW) film materials have attracted extensive interest from the perspective of both fundamental research1–3and technology4–7. However, the synthesis of large, thick, single-crystal vdW materials remains a great challenge because the lack of out-of-plane chemical bonds weakens the epitaxial relationship between neighbouring layers8–31. Here we report the continuous epitaxial growth of single-crystal graphite films with thickness up to 100,000 layers on high-index, single-crystal nickel (Ni) foils. Our epitaxial graphite films demonstrate high single crystallinity, including an ultra-flat surface, centimetre-size single-crystal domains and a perfect AB-stacking structure. The exfoliated graphene shows excellent physical properties, such as a high thermal conductivity of ~2,880 W m−1K−1, intrinsic Young’s modulus of ~1.0 TPa and low doping density of ~2.2 × 1010cm−2. The growth of each single-crystal graphene layer is realized by step edge-guided epitaxy on a high-index Ni surface, and continuous growth is enabled by the isothermal dissolution–diffusion–precipitation of carbon atoms driven by a chemical potential gradient between the two Ni surfaces. The isothermal growth enables the layers to grow at optimal conditions, without stacking disorders or stress gradients in the final graphite. Our findings provide a facile and scalable avenue for the synthesis of high-quality, thick vdW films for various applications.

The production of large-area twisted bilayer graphene (TBG) with controllable angles is a prerequisite for proceeding with its massive applications. However, most of the prevailing strategies to fabricate twisted bilayers face great challenges, where the transfer methods are easily stuck by interfacial contamination, and direct growth methods lack the flexibility in twist-angle design. Here we develop an effective strategy to grow centimetre-scale TBG with arbitrary twist angles (accuracy, <1.0°). The success in accurate angle control is realized by an angle replication from two prerotated single-crystal Cu(111) foils to form a Cu/TBG/Cu sandwich structure, from which the TBG can be isolated by a custom-developed equipotential surface etching process. The accuracy and consistency of the twist angles are unambiguously illustrated by comprehensive characterization techniques, namely, optical spectroscopy, electron microscopy, photoemission spectroscopy and photocurrent spectroscopy. Our work opens an accessible avenue for the designed growth of large-scale two-dimensional twisted bilayers and thus lays the material foundation for the future applications of twistronics at the integration level.

The synergistic interaction between terraces and step sites plays a key role to enhance the production of C2+fuels from electrochemical CO2reduction.

Confined nanospaces provide a new platform to promote catalytic reactions. However, the mechanism of catalytic enhancement in the nanospace still requires insightful exploration due to the lack of direct visualization. Here, we report operandoinvestigations on the etching and growth of graphene in a two-dimensional (2D) confined space between graphene and a Cu substrate. We observed that the graphene layer between the Cu and top graphene layer was surprisingly very active in etching (more than 10 times faster than the etching of the top graphene layer). More strikingly, at a relatively low temperature (∼530 °C), the etched carbon radicals dissociated from the bottom layer, in turn feeding the growth of the top graphene layer with a very high efficiency. Our findings reveal the in situdynamics of the anomalous confined catalytic processes in 2D confined spaces and thus pave the way for the design of high-efficiency catalysts.

Missing second-order nonlinearity in centrosymmetric graphene overshadows its intriguing optical attribute. Here, we report redox-governed charge doping could effectively break the centrosymmetry of bilayer graphene (BLG), enabling a strong second harmonic generation (SHG) with a strength close to that of the well-known monolayer MoS2. Verified from control experiments with in situelectrical current annealing and electrically gate-controlled SHG, the required centrosymmetry breaking of the emerging SHG arises from the charge-doping on the bottom layer of BLG by the oxygen/water redox couple. Our results not only reveal that charge doping is an effective way to break the inversion symmetry of BLG despite its strong interlayer coupling but also indicate that SHG spectroscopy is a valid technique to probe molecular doping on two-dimensional materials.

Over the past 70 years, the semiconductor industry has undergone transformative changes, largely driven by the miniaturization of devices and the integration of innovative structures and materials. Two-dimensional (2D) materials like transition metal dichalcogenides (TMDs) and graphene are pivotal in overcoming the limitations of silicon-based technologies, offering innovative approaches in transistor design and functionality, enabling atomic-thin channel transistors and monolithic 3D integration. We review the important progress in the application of 2D materials in future information technology, focusing in particular on microelectronics and optoelectronics. We comprehensively summarize the key advancements across material production, characterization metrology, electronic devices, optoelectronic devices, and heterogeneous integration on silicon. A strategic roadmap and key challenges for the transition of 2D materials from basic research to industrial development are outlined. To facilitate such a transition, key technologies and tools dedicated to 2D materials must be developed to meet industrial standards, and the employment of AI in material growth, characterizations, and circuit design will be essential. It is time for academia to actively engage with industry to drive the next 10 years of 2D material research.

Gapless Dirac fermions in monolayer graphene give rise to an abundance of peculiar physical properties, including exceptional broadband nonlinear optical responses. By tuning the chemical potential, stacking order, and photonic structures, the effective modulation of nonlinear optical phenomena in graphene has been demonstrated in recent years. Here, we demonstrate that optical helicity can be used as an extra tuning knob for four-wave mixing in gated graphene. Our results reveal the helicity selection rule for four-wave mixing in monolayer graphene, revealing nearly perfect circular polarization. Corresponding theoretical interpretations of the helicity selection rule that are also applicable to other nonlinear optical processes and materials are presented.

Plasmonic radial breathing mode (RBM), featured with radially oscillating charge density, arises from the surface plasmon waves confined in the flat nanoparticles. The zero net dipole moment endows the RBM with an extremely low radiation yet a remarkable intense local field. On the other hand, owing to the dark mode nature, the RBMs routinely escape from the optical measurements, severely preventing their applications in optoelectronics and nanophotonics. Here, we experimentally demonstrate the existence of RBM in a hexagonal Au nanoplate-on-mirror nanocavity using a far-field linear-polarized light source. The polarization-resolved scattering measurements cooperated with the full-wave simulations elucidate that the RBM originates from the standing plasmon waves residing in the Au nanoplate. Further numerical analysis shows the RBM possesses the remarkable capability of local field enhancement over the other dark modes in the same nanocavity. Moreover, the RBM is sensitive to the gap and nanoplate size of the nanocavity, providing a straightforward way to tailor the wavelength of RBM from the visible to near-infrared region. Our approach provides a facile optical path to access to the plasmonic RBMs and may open up a new route to explore the intriguing applications of RBM, including surface-enhanced Raman scattering, enhanced nonlinear effects, nanolasers, biological and chemical sensing.

The growth of wafer-scale single-crystal two-dimensional transition metal dichalcogenides (TMDs) on insulating substrates is critically important for a variety of high-end applications1–4. Although the epitaxial growth of wafer-scale graphene and hexagonal boron nitride on metal surfaces has been reported5–8, these techniques are not applicable for growing TMDs on insulating substrates because of substantial differences in growth kinetics. Thus, despite great efforts9–20, the direct growth of wafer-scale single-crystal TMDs on insulating substrates is yet to be realized. Here we report the successful epitaxial growth of two-inch single-crystal WS2monolayer films on vicinal a-plane sapphire surfaces. In-depth characterizations and theoretical calculations reveal that the epitaxy is driven by a dual-coupling-guided mechanism, where the sapphire plane–WS2interaction leads to two preferred antiparallel orientations of the WS2crystal, and sapphire step edge–WS2interaction breaks the symmetry of the antiparallel orientations. These two interactions result in the unidirectional alignment of nearly all the WS2islands. The unidirectional alignment and seamless stitching of WS2islands are illustrated via multiscale characterization techniques; the high quality of WS2monolayers is further evidenced by a photoluminescent circular helicity of ~55%, comparable to that of exfoliated WS2flakes. Our findings offer the opportunity to boost the production of wafer-scale single crystals of a broad range of two-dimensional materials on insulators, paving the way to applications in integrated devices.

Electrocatalytic conversion of carbon dioxide (CO2) to methane (CH4) has drawn great attention for solving the problem of global warming by reducing greenhouse gases and recycling carbon resources. Among reported Cu-based catalysts, Cu nanosheets (Cu NSs) with a highly exposed (111) facet are beneficial for converting CO2to CH4. However, the stability issue of Cu NSs, due to their dissolution, severely limits their performance and practical application in electrocatalytic CO2reduction. Here, we report a method to effectively passivate the dissolution of Cu NSs by adding an appropriate amount of Cu2+in the electrolyte, which improves the selectivity and stability of CO2reduction to CH4. Structural characterization and CO2reduction tests indicate that the Cu NSs maintain the exposed (111) facet and thus maintain the efficient reduction of CO2to CH4in the electrolyte containing an appropriate Cu2+concentration. The Cu NSs exhibit a high CH4selectivity of ∼70% and a high stability of ∼60% for ∼10 h. This work indicates that a moderate amount of Cu2+in the electrolyte can passivate the Cu dissolution and increase the stability of Cu electrodes, providing a new perspective for achieving better stability of catalysts in the future.

Graphical Abstract:

Hydrogen peroxide (H2O2) solution and its aerosols are common disinfectants, especially for urgent reuse of personal protective equipment during the COVID-19 pandemic. Highly sensitive and selective evaluation of the H2O2concentration is key to customizing the sufficient disinfection process and avoiding disinfection overuse. Amperometric electrochemical detection is an effective means but poses challenges originated from the precarious state of H2O2. Here, an atomic Co–Nx–C site anchored neuronal-like carbon modified amperometric sensor (denoted as the CoSA-N/C@rGO sensor) is designed, which exhibits a broad detection range (from 250 nM to 50 mM), superior sensitivity (743.3 μA mM−1cm−2, the best among carbon-based amperometric sensors), strong selectivity (no response to interferents), powerful reliability (only 2.86% decay for one week) and fast response (just 5 s) for residual H2O2detection. We validated the accuracy and practicability of the CoSA-N/C@rGO sensor in the actual H2O2disinfection process of personal protective equipment. Further characterization verifies that the electrocatalytic activity and selective reduction of H2O2is determined by the atomically dispersed Co–Nx–C sites and the high oxygen content of CoSA-N/C@rGO, where the response time and reliability of H2O2detection is determined by the neuronal-like structure with high nitrogen content. Our findings pave the way for developing a sensor with superior sensitivity, selectivity and stability, rendering promising applications such as medical care and environmental treatment.

The breakdown of translational symmetry at heterointerfaces leads to the emergence of new phonon modes localized at the interface1. These modes have an essential role in thermal and electrical transport properties in devices, especially in miniature ones wherein the interface may dominate the entire response of the device2. Although related theoretical work began decades ago1,3–5, experimental research is totally absent owing to challenges in achieving the combined spatial, momentum and spectral resolutions required to probe localized modes. Here, using the four-dimensional electron energy-loss spectroscopy technique, we directly measure both the local vibrational spectra and the interface phonon dispersion relation for an epitaxial cubic boron nitride/diamond heterointerface. In addition to bulk phonon modes, we observe modes localized at the interface and modes isolated from the interface. These features appear only within approximately one nanometre around the interface. The localized modes observed here are predicted to substantially affect the interface thermal conductance and electron mobility. Our findings provide insights into lattice dynamics at heterointerfaces, and the demonstrated experimental technique should be useful in thermal management, electrical engineering and topological phononics.

Non-invasive, high-throughput spectroscopic techniques can identify chiral indices (n,m) of carbon nanotubes down to the single-tube level1–6. Yet, for complete characterization and to unlock full functionality, the handedness, the structural property associated with mirror symmetry breaking, also needs to be identified accurately and efficiently7–14. So far, optical methods fail in the handedness characterization of single nanotubes because of the extremely weak chiroptical signals (roughly 10−7) compared with the excitation light15,16. Here we demonstrate the complete structure identification of single nanotubes in terms of both chiral indices and handedness by Rayleigh scattering circular dichroism. Our method is based on the background-free feature of Rayleigh scattering collected at an oblique angle, which enhances the nanotube’s chiroptical signal by three to four orders of magnitude compared with conventional absorption circular dichroism. We measured a total of 30 single-walled carbon nanotubes including both semiconducting and metallic nanotubes and found that their absolute chiroptical signals show a distinct structure dependence, which can be qualitatively understood through tight-binding calculations. Our strategy enables the exploration of handedness-related functionality of single nanotubes and provides a facile platform for chiral discrimination and chiral device exploration at the level of individual nanomaterials.

Colloidal quantum dots are promising photoactive materials that enable plentiful photonic and optoelectronic applications ranging from lasers, displays and photodetectors to solar cells1–9. However, these applications mainly utilize the linear optical properties of quantum dots, and their great potential in the broad nonlinear optical regime is still waiting for full exploration10–12. Here, we demonstrate that a simple coating of a sub-200-nm-thick quantum dot film on two-dimensional materials can significantly enhance their nonlinear optical responses (second, third and fourth harmonic generation) by more than three orders of magnitude. Systematic experimental results indicate that this enhancement is driven by a non-trivial mechanism of multiphoton-excitation resonance energy transfer, where the quantum dots directly deliver their strongly absorbed multiphoton energy to the adjacent two-dimensional materials by a remote dipole–dipole coupling. Our findings could expand the applications of quantum dots in many exciting areas beyond linear optics, such as nonlinear optical signal processing, multiphoton imaging and ultracompact nonlinear optical elements.

The electrochemical conversion of CO2to valuable fuels is a plausible solution to meet the soaring need for renewable energy sources. However, the practical application of this process is limited by its poor selectivity due to scaling relations. Here we introduce the rational design of the monolayer hexagonal boron nitride/copper (h-BN/Cu) interface to circumvent scaling relations and improve the electrosynthesis of CH4. This catalyst possesses a selectivity of >60% toward CH4with a production rate of 15 μmol·cm–2·h–1at −1.00 V vs RHE, along with a much smaller decaying production rate than that of pristine Cu. Both experimental and theoretical calculations disclosed that h-BN/Cu interfacial perimeters provide specific chelating sites to immobilize the intermediates, which accelerates the conversion of *CO to *CHO. Our work reports a novel Cu catalyst engineering strategy and demonstrates the prospect of monolayer h-BN contributing to the design of heterostructured CO2reduction electrocatalysts for sustainable energy conversion.

A wide range of biomedical devices are being used to treat cardiovascular diseases, and thus they routinely come into contact with blood. Insufficient hemocompatibility has been found to impair the functionality and safety of these devices through the activation of blood coagulation and the immune system. Numerous attempts have been made to develop surface modification approaches of the cardiovascular devices to improve their hemocompatibility. However, there are still no ideal “blood-friendly” coating materials, which possess the desired hemocompatibility, tissue compatibility, and mechanical properties. As a novel multifunctional material, graphene has been proposed for a wide range of biomedical applications. The chemical inertness, atomic smoothness, and high durability make graphene an ideal candidate as a surface coating material for implantable devices. Here, we evaluated the hemocompatibility of a graphene film prepared on quartz glasses (Gra-glasses) from a direct chemical vapor deposition process. We found that the graphene coating, which is free of transfer-mediating polymer contamination, significantly suppressed platelet adhesion and activation, prolonged coagulation time, and reduced ex vivothrombosis formation. We attribute the excellent antithrombogenic properties of the Gra-glasses to the low surface roughness, low surface energy (especially the low polar component of the surface energy), and the negative surface charge of the graphene film. Given these excellent hemocompatible properties, along with its chemical inertness, high durability, and molecular impermeability, a graphene film holds great promise as an antithrombogenic coating for next-generation cardiovascular devices.

Phonon polaritons enable light confinement at deep subwavelength scales, with potential technological applications, such as subdiffraction imaging, sensing and engineering of spontaneous emission. However, the trade-off between the degree of confinement and the excitation efficiency of phonon polaritons prevents direct observation of these modes in monolayer hexagonal boron nitride (h-BN), where they are expected to reach ultrahigh confinement. Here, we use monochromatic electron energy-loss spectroscopy (about 7.5?meV energy resolution) in a scanning transmission electron microscope to measure phonon polaritons in monolayer h-BN, directly demonstrating the existence of these modes as the phonon Reststrahlen band (RS) disappears. We find phonon polaritons in monolayer h-BN to exhibit high confinement (>487 times smaller wavelength than that of light in free space) and ultraslow group velocity down to about 10-5c. The large momentum compensation provided by electron beams additionally allows us to excite phonon polaritons over nearly the entire RS band of multilayer h-BN. These results open up a broad range of opportunities for the engineering of metasurfaces and strongly enhanced light–matter interactions.

Properly cutting graphene into certain high-quality micro-/nanoscale structures in a cost-effective way has a critical role. Here, we report a novel approach to pattern graphene films by H2O-based magnetic-assisted ultraviolet (UV) photolysis under irradiation at 184.9 nm. By virtue of the paramagnetic characteristic, the photo-dissociated hydroxyl [OH(X2Π)] radicals are magnetized and have their oxidation capability highly enhanced through converting into an accelerated directional motion. Meanwhile, the precursor of H2O(X̃1A1) molecules distributes uniformly thanks to its weak diamagnetic characteristic, and there exists no instable diamagnetic intermediate to cause lateral oxidation. Possessing these unique traits, the H2O-based magnetic-assisted UV photolysis has the capability of making graphene microscale patterns with the linewidth down to 8.5 μm under a copper grid shadow mask. Furthermore, it is feasible to pattern graphene films into 40 nm-wide ribbons under ZnO nanowires and realize hybrid graphene/ZnO nanoribbon field-effect transistors with a hole mobility up to 7200 cm2·V–1·s–1. The X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analyses reveal that OH(X2Π) radicals act as a strong oxidant and that another product of H(12S) adsorbs weakly on graphene.

Nonlinear optical fibres have been employed for a vast number of applications, including optical frequency conversion, ultrafast laser and optical communication1–4. In current manufacturing technologies, nonlinearity is realized by the injection of nonlinear materials into fibres5–7or the fabrication of microstructured fibres8–10. Both strategies, however, suffer from either low optical nonlinearity or poor design flexibility. Here, we report the direct growth of MoS2, a highly nonlinear two-dimensional material11, onto the internal walls of a SiO2optical fibre. This growth is realized via a two-step chemical vapour deposition method, where a solid precursor is pre-deposited to guarantee a homogeneous feedstock before achieving uniform two-dimensional material growth along the entire fibre walls. By using the as-fabricated 25-cm-long fibre, both second- and third-harmonic generation could be enhanced by ~300 times compared with monolayer MoS2/silica. Propagation losses remain at ~0.1?dB?cm–1for a wide frequency range. In addition, we demonstrate an all-fibre mode-locked laser (~6?mW output, ~500?fs pulse width and ~41?MHz repetition rate) by integrating the two-dimensional-material-embedded optical fibre as a saturable absorber. Initial tests show that our fabrication strategy is amenable to other transition metal dichalcogenides, making these embedded fibres versatile for several all-fibre nonlinear optics and optoelectronics applications.

Devices operating with excitons have promising prospects for overcoming the dilemma of response time and integration in current generation of electron- or/and photon-based elements and devices. Although the intrinsic properties including edges, grain boundaries, and defects of atomically thin semiconductors have been demonstrated as a powerful tool to adjust the bandgap and exciton energy, investigating the intrinsic modulation of spatiotemporal dynamics still remains challenging on account of the short exciton diffusion length. Here, we achieve the attractive remote lightening phenomenon, in which the emission region could be far away (up to 14.6 μm) from the excitation center, by utilizing a femtosecond laser with ultrahigh peak power as excitation source and the edge region with high photoluminescence efficiency as a bright emitter. Furthermore, the ultrafast transition between exciton and trion is demonstrated, which provides insight into the intrinsic modulation on populations of exciton and trion states. The complete cascaded physical scenario of exciton spatiotemporal dynamics is eventually established. This work can refresh our perspective on the spatial nonuniformities of CVD-grown atomically thin semiconductors and provide important implications for developing durable and stable excitonic devices in the future.

Quartz fiber, a widely used reinforcer with high tensile strength and excellent heat resistance, can have more attractive electrical applications such as electromagnetic interference shielding, static dissipation, and strain sensing if it becomes conductive. Many attempts have been made to increase the electrical conductivity of quartz fiber by surface coating of conductive polymers or plating of metal films, but suffers from sacrificing flexibility and causing heavy metal pollution. Here we designed and massively produced a hybrid structure of graphene quartz fiber (GQF) by a forced-flow chemical vapor deposition (CVD) method, which combines the excellent conductivity of graphene and the extraordinary properties of quartz fiber. The as-fabricated flexible GQF exhibited high sensitivity, fast response (<0.5 s) and good durability (∼5000 cycles) to organic solvent vapor, suitable as a real-time biomimetic gas sensor. Furthermore, the massively produced GQFs can be knitted into meter-scale fabrics with tunable conductivity (sheet resistances of 0.2–10 kΩ/sq) and superior electrothermal conversion efficiency (up to 980 °C within a few seconds at 24 V), thus propelling its promising application in industrial electric heaters. We expect this hybrid GQF material will greatly expand the applications of traditional quartz fiber into an infusive multifunctional regime.

The production of large single-crystal metal foils with various facet indices has long been a pursuit in materials science owing to their potential applications in crystal epitaxy, catalysis, electronics and thermal engineering1–5. For a given metal, there are only three sets of low-index facets ({100}, {110} and {111}). In comparison, high-index facets are in principle infinite and could afford richer surface structures and properties. However, the controlled preparation of single-crystal foils with high-index facets is challenging, because they are neither thermodynamically6,7nor kinetically3favourable compared to low-index facets6–18. Here we report a seeded growth technique for building a library of single-crystal copper foils with sizes of about 30 × 20 square centimetres and more than 30 kinds of facet. A mild pre-oxidation of polycrystalline copper foils, followed by annealing in a reducing atmosphere, leads to the growth of high-index copper facets that cover almost the entire foil and have the potential of growing to lengths of several metres. The creation of oxide surface layers on our foils means that surface energy minimization is not a key determinant of facet selection for growth, as is usually the case. Instead, facet selection is dictated randomly by the facet of the largest grain (irrespective of its surface energy), which consumes smaller grains and eliminates grain boundaries. Our high-index foils can be used as seeds for the growth of other Cu foils along either the in-plane or the out-of-plane direction. We show that this technique is also applicable to the growth of high-index single-crystal nickel foils, and we explore the possibility of using our high-index copper foils as substrates for the epitaxial growth of two-dimensional materials. Other applications are expected in selective catalysis, low-impedance electrical conduction and heat dissipation.

Defects exist ubiquitously in crystal materials, and usually exhibit a very different nature from the bulk matrix. Hence, their presence can have significant impacts on the properties of devices. Although it is well accepted that the properties of defects are determined by their unique atomic environments, the precise knowledge of such relationships is far from clear for most oxides because of the complexity of defects and difficulties in characterization. Here, we fabricate a 36.8° SrRuO3grain boundary of which the transport measurements show a spin-valve magnetoresistance. We identify its atomic arrangement, including oxygen, using scanning transmission electron microscopy and spectroscopy. Based on the as-obtained atomic structure, the density functional theory calculations suggest that the spin-valve magnetoresistance occurs because of dramatically reduced magnetic moments at the boundary. The ability to manipulate magnetic properties at the nanometer scale via defect control allows new strategies to design magnetic/electronic devices with low-dimensional magnetic order.We manipulate the local magnetic properties of SrRuO3at a grain boundary, providing new strategies to design atomic-sized magnetic/electronic devices with low-dimensional magnetic order via defect engineering.

Wafer-scale monocrystalline two-dimensional (2D) materials can theoretically be grown by seamless coalescence of individual domains into a large single crystal. Here we present a concise study of the coalescence behavior of crystalline 2D films using a combination of complementary in situmethods. Direct observation of overlayer growth from the atomic to the millimeter scale and under model- and industrially relevant growth conditions reveals the influence of the film–substrate interaction on the crystallinity of the 2D film. In the case of weakly interacting substrates, the coalescence behavior is dictated by the inherent growth kinetics of the 2D film. It is shown that the merging of coaligned domains leads to a distinct modification of the growth dynamics through the formation of fast-growing high-energy edges. The latter can be traced down to a reduced kink-creation energy at the interface between well-aligned domains. In the case of strongly interacting substrates, the lattice mismatch between film and substrate induces a pronounced moiré corrugation that determines the growth and coalescence behavior. It furthermore imposes additional criteria for seamless coalescence and determines the structure of grain boundaries. The experimental findings, obtained here for the case of graphene, are confirmed by theory-based growth simulations and can be generalized to other 2D materials that show 3- or 6-fold symmetry. Based on the gained understanding of the relation between film–substrate interaction, shape evolution, and coalescence behavior, conditions for seamless coalescence and, thus, for the optimization of large-scale production of monocrystalline 2D materials are established.

Digital optical phase conjugation (DOPC) is a newly developed technique in wavefront shaping to control light propagation through complex media. Currently, DOPC has been demonstrated for the reconstruction of two- and three-dimensional targets and enabled important applications in many areas. Nevertheless, the reconstruction results are only phase conjugated to the original input targets. Herein, we demonstrate that DOPC could be further developed for creating structured light beams through a multimode fiber (MMF). By applying annular filtering in the virtual Fourier domain of the acquired speckle field, we realize the creation of the quasi-Bessel and donut beams through the MMF. In principle, arbitrary amplitude and/or phase circular symmetry filtering could be performed in the Fourier domain, thus generating the corresponding point spread functions. We expect that the reported technique can be useful for super-resolution endoscopic imaging and optical manipulation through MMFs.

The modulation of optical harmonic generation in two-dimensional (2D) materials is of paramount importance in nanophotonic and nano-optoelectronic devices for their applications in optical switching and communication. However, an effective route with ultrafast modulation speed, ultrahigh modulation depth, and broad operation wavelength range is awaiting a full exploration. Here, we report that an optical pump can dynamically modulate the third harmonic generation (THG) of a graphene monolayer with a relative modulation depth above 90% at a time scale of 2.5 ps for a broad frequency ranging from near-infrared to ultraviolet. Our observation, together with the real-time, time-dependent density functional theory (TDDFT) simulations, reveals that this modulation process stems from nonlinear dynamics of the photoexcited carriers in graphene. The superior performance of the nonlinear all-optical modulator based on 2D materials paves the way for its potential applications including nanolasers and optical communication circuits.

The defects in the ceria usually work as the active reaction sites in their industrial applications. In this article, we studied the formation and atomic process of the defects of ceria nanowires under heating by using in situaberration-corrected transmission electron microscopy (Cs-TEM) method. With the temperature elevating, ceria nanowires are reduced and defects begin to appear and grow up. When temperature reaches 1,023 K, the defect morphology exhibits the rhombus or hexagon patterns, which are surrounded by {111} and {200} planes with lower surface energy, and the heated ceria still maintain the same cubic fluorite structure as their parent. It is also indicated that the formation of defects originates from the release of lattice oxygen and the volatilization of surface Ce ions. This work provides an important insight into designing ceria-based catalysts and ionic conductors.

Van der Waals-coupled two-dimensional (2D) heterostructures have attracted great attention recently due to their high potential in the next-generation photodetectors and solar cells. The understanding of charge-transfer process between adjacent atomic layers is the key to design optimal devices as it directly determines the fundamental response speed and photon-electron conversion efficiency. However, general belief and theoretical studies have shown that the charge transfer behavior depends sensitively on interlayer configurations, which is difficult to control accurately, bringing great uncertainties in device designing. Here we investigate the ultrafast dynamics of interlayer charge transfer in a prototype heterostructure, the MoS2/WS2bilayer with various stacking configurations, by optical two-color ultrafast pump–probe spectroscopy. Surprisingly, we found that the charge transfer is robust against varying interlayer twist angles and interlayer coupling strength, in time scale of ∼90 fs. Our observation, together with atomic-resolved transmission electron characterization and time-dependent density functional theory simulations, reveals that the robust ultrafast charge transfer is attributed to the heterogeneous interlayer stretching/sliding, which provides additional channels for efficient charge transfer previously unknown. Our results elucidate the origin of transfer rate robustness against interlayer stacking configurations in optical devices based on 2D heterostructures, facilitating their applications in ultrafast and high-efficient optoelectronic and photovoltaic devices in the near future.

Large scale epitaxial growth and transfer of monolayer MoS2has attracted great attention in recent years. Here, we report the wafer-scale epitaxial growth of highly oriented continuous and uniform monolayer MoS2films on single-crystalline sapphire wafers by chemical vapor deposition (CVD) method. The epitaxial film is of high quality and stitched by many 0°, 60° domains and 60°-domain boundaries. Moreover, such wafer-scale monolayer MoS2films can be transferred and stacked by a simple stamp-transfer process, and the substrate is reusable for subsequent growth. Our progress would facilitate the scalable fabrication of various electronic, valleytronic, and optoelectronic devices for practical applications.

Excitonic devices operate based on excitons, which can be excited by photons as well as emitting photons and serve as a medium for photon-carrier conversion. Excitonic devices are expected to combine the advantages of both the high response rate of photonic devices and the high integration of electronic devices simultaneously. However, because of the neutral feature, exciton transport is generally achieved via diffusion rather than using electric fields, and the efficient control of exciton flux directionality has always been difficult. In this work, a precisely designed one-dimensional periodic nanostructure (1DPS) is used to introduce periodic strain field along with resonant mode to the WS2monolayer, achieving exciton oriented diffusion with a 7.6-fold exciton diffusion coefficient enhancement relative to that of intrinsic, while enhancing the excitonic emission intensity by a factor of 10 and reducing exciton saturation threshold power by 2 orders of magnitude. Based on the analysis of the density functional theory (DFT) and the finite-element method (FEM), we attribute the anisotropy of exciton diffusion to exciton funneling induced by periodic potentials, which do not require excessive potential height difference for an efficient oriented diffusion. As a result of resonant emission, the exciton diffusion is dragged into the nonlinear regime owing to the high exciton density close to saturation, which improves the exciton diffusion coefficient and diffusion anisotropy more appreciably.

The integration of photonic crystal fibre (PCF) with various functional materials has greatly expanded the application regimes of optical fibre1–12. The emergence of graphene (Gr) has stimulated new opportunities when combined with PCF, allowing for electrical tunability, a broadband optical response and all-fibre integration ability13–18. However, previous demonstrations have typically been limited to micrometre-sized samples, far behind the requirements of real applications at the metre-scale level. Here, we demonstrate a new hybrid material, Gr–PCF, with length up to half a metre, produced using a chemical vapour deposition method. The Gr–PCF shows a strong light–matter interaction with ~8?dB?cm-1attenuation. In addition, the Gr–PCF-based electro-optic modulator demonstrates a broadband response (1,150–1,600?nm) and large modulation depth (~20?dB?cm-1at 1,550?nm) under a low gate voltage of ~2?V. Our results could enable industrial-level graphene applications based on this Gr–PCF and suggest an attractive platform for two-dimensional material-PCF.