2D nanomaterials offer unique functional properties when combined with metal powder feedstock, enabling advanced composites for engineering and energy applications1. Scalable fabrication of nanosheet-reinforced metal matrix composites (2DMMCs) remains challenging. In this study, we first exfoliate 2D materials using a solvent-free ball milling approach, using graphene and hexagonal boron nitride (hBN) as demonstrators, and then attach the resulting 2D nanoplatelets onto a wide range of metal powders, including copper (Cu), titanium (Ti-6Al-4V), aluminum (AlSi10Mg), and stainless steel (SS316L). To provide a mechanistic understanding of exfoliation, we use density functional theory (DFT) and discrete element method (DEM) simulations, offering new insights into the forces that drive nanosheet exfoliation. The resulting 2DMMC powders combine excellent scalability and effectiveness. After consolidation, titanium alloy/graphene systems reaching thermal conductivity values of 17 W·m⁻¹·K⁻¹, comparable or superior to previous reports. Finally, we showcase their printability, confirming compatibility with large-scale manufacturing techniques and highlighting their potential for next-generation thermal applications.
Current progress in two-dimensional (2D) materials explorations leads to constant specie enrichments of possible advanced materials down to two dimensions. The metal chalcogenide-based 2D materials are promising grounds where many adjacent territories are waiting to be explored. Here, a stable monolayer Ni3TeO6 (NTO) structure was computationally predicted and its stacked 2D nanosheets experimentally synthesized. Theoretical design undergoes featuring coordination of metalloid chalcogen, slicing the bulk structure, geometrical optimizations and stability study. The predicted layered NTO structure is realized in nanometer-thick nanosheets via a one-pot shape-controlled hydrothermal synthesis. Compared to the bulk, the 2D NTO own a lowered bandgap energy, more sensitive wavelength selectivity and an emerging photocatalytic hydrogen evolution ability under visible light. Beside a new 2D NTO with the optoelectrical and photocatalytic merits, its existing polar space group, structural specification, and design route are hoped to benefit 2D semiconductor innovations both in species enrichment and future applications.
Nanopores in two-dimensional (2D) membranes hold immense potential in single-molecule sensing, osmotic power generation, and information storage. Recent advances in 2D nanopores, especially on single-layer MoS2, focus on the scalable growth and manufacturing of nanopore devices. However, there still remains a bottleneck in controlling the nanopore stability in atomically thin membranes. Here, we evaluate the major factors responsible for the instability of the monolayer MoS2 nanopores. We identify chemical oxidation and delamination of monolayers from their underlying substrates as the major reasons for the instability of MoS2 nanopores. Surface modification of the substrate and reducing the oxygen from the measurement solution improves nanopore stability and dramatically increases their shelf-life. Understanding nanopore growth and stability can provide insights into controlling the pore size, shape and can enable long-term measurements with a high signal-to-noise ratio and engineering durable nanopore devices.
Although chromium trihalides are widely regarded as a promising class of two-dimensional magnets for next-generation devices, an accurate description of their electronic structure and magnetic interactions has proven challenging to achieve. Here, we quantify electronic excitations and spin interactions in CrX 3 (X = Cl, Br, I) using embedded many-body wavefunction calculations and fully generalized spin Hamiltonians. We find that the three trihalides feature comparable d-shell excitations, consisting of a high-spin 4 A 2 ( t 2 g 3 e g 0 ) ground state lying 1.5-1.7 eV below the first excited state 4 T 2 ( t 2 g 2 e g 1 ). CrCl3 exhibits a single-ion anisotropy A sia = - 0.02 meV, while the Cr spin-3/2 moments are ferromagnetically coupled through bilinear and biquadratic exchange interactions of J 1 = - 0.97 meV and J 2 = - 0.05 meV, respectively. The corresponding values for CrBr3 and CrI3 increase to A sia = -0.08 meV and A sia= - 0.12 meV for the single-ion anisotropy, J 1 = -1.21 meV, J 2 = -0.05 meV and J 1 = -1.38 meV, J 2 = -0.06 meV for the exchange couplings, respectively. We find that the overall magnetic anisotropy is defined by the interplay between A sia and A dip due to magnetic dipole-dipole interaction that favors in-plane orientation of magnetic moments in ferromagnetic monolayers and bulk layered magnets. The competition between the two contributions sets CrCl3 and CrI3 as the easy-plane (A sia + A dip >0) and easy-axis (A sia + A dip <0) ferromagnets, respectively. The differences between the magnets trace back to the atomic radii of the halogen ligands and the magnitude of spin-orbit coupling. Our findings are in excellent agreement with recent experiments, thus providing reference values for the fundamental interactions in chromium trihalides.
We present a tunable phononic crystal which can be switched from a mechanically insulating to a mechanically conductive (transmissive) state. Specifically, in our simulations for a phononic lattice under biaxial tension (σ xx = σ yy = 0.01 N m-1), we find a bandgap for out-of-plane phonons in the range of 48.8-56.4 MHz, which we can close by increasing the degree of tension uniaxiality (σ xx/σ yy) to 1.7. To manipulate the tension distribution, we design a realistic device of finite size, where σ xx/σ yy is tuned by applying a gate voltage to a phononic crystal made from suspended graphene. We show that the bandgap closing can be probed via acoustic transmission measurements and that the phononic bandgap persists even after the inclusion of surface contaminants and random tension variations present in realistic devices. The proposed system acts as a transistor for MHz-phonons with an on/off ratio of 105 (100 dB suppression) and is thus a valuable extension for phonon logic applications. In addition, the transition from conductive to isolating can be seen as a mechanical analogue to a metal-insulator transition and allows tunable coupling between mechanical entities (e.g. mechanical qubits).
DNA methylation is an epigenetic modification involving the addition of a methyl group to DNA, which is heavily involved in gene expression and regulation, thereby critical to the progression of diseases such as cancer. In this work we show that detection and localization of DNA methylation can be achieved with nanopore sensors made of two-dimensional (2D) materials such as graphene and molybdenum di-sulphide (MoS2). We label each DNA methylation site with a methyl-CpG binding domain protein (MBD1), and combine molecular dynamics simulations with electronic transport calculations to investigate the translocation of the methylated DNA-MBD1 complex through 2D material nanopores under external voltage biases. The passage of the MBD1-labeled methylation site through the pore is identified by dips in the current blockade induced by the DNA strand, as well as by peaks in the transverse electronic sheet current across the 2D layer. The position of the methylation sites can be clearly recognized by the relative positions of the dips in the recorded ionic current blockade with an estimated error ranging from 0% to 16%. Finally, we define the spatial resolution of the 2D material nanopore device as the minimal distance between two methylation sites identified within a single measurement, which is 15 base pairs by ionic current recognition, but as low as 10 base pairs by transverse electronic conductance detection, indicating better resolution with this latter technique. The present approach opens a new route for precise and efficient profiling of DNA methylation.
We demonstrate Andreev pair injection across Nb-WS2 junction evident as Andreev reflection in differential conductivity spectra below Nb critical temperature T c . The superconducting- 2D semiconducting junction defined by a focused ion beam, shaped Nb pads, and semi-dry transfer of single layer CVD-grown WS2 crystals ensured the mechanical integrity of the 2D TMD film, reduced contamination and defects at Nb-WS2 junction, enabling the pristine study of the interface and facilitating Andreev pair injection. We observed enhanced conductivity in dI / dV spectra for junction voltages smaller than the corresponding Nb superconducting gap, which vanishes as the device temperature is increased above the T c . The position and the temperature dependence of the conductivity peaks suggest proximity effect-related phenomena explained by developed modified BTK theory. The presented results are crucial for the future implementation of proximity-based 2D hybrid devices including quantum light sources and superconducting field-effect transistors based on superconductor-semiconductor junctions.
Two-dimensional (2D) Ruddlesden-Popper (RP) metal halides present unique and tunable properties. However, direct and oriented synthesis is challenging due to low formation energies that lead to rapid, uncontrolled growth during solution-based processing. Here, we report the solvent-free growth of oriented n = 1 (PEA)2PbI4 RP films by pulsed laser deposition (PLD). In situ photoluminescence (PL) during deposition reveals the formation of the n = 1 phase at the early stages of growth. X-ray diffraction (XRD) and grazing-incidence wide-angle scattering (GIWAXS) confirm a single oriented n = 1 phase, independent of the substrate. Co-localized spatially resolved PL and AFM further validate the conformal growth. While oriented growth is substrate-independent, film stability is not. (PEA)2PbI4 films grown on strained epitaxial MAPbI3 remain stable for over 184 days without any sign of cation exchange. This work highlights the potential of PLD for direct, room-temperature synthesis of 2D (PEA)2PbI4 RP films and stable 2D/3D heterostructures.
Electroconductive biomaterials are gaining significant consideration for regeneration in tissues where electrical functionality is of crucial importance, such as myocardium, neural, musculoskeletal, and bone tissue. In this work, conductive biohybrid platforms were engineered by blending collagen type I and 2D MXene (Ti3C2Tx) and afterwards covalently crosslinking; to harness the biofunctionality of the protein component and the increased stiffness and enhanced electrical conductivity (matching and even surpassing native tissues) that two-dimensional titanium carbide provides. These MXene platforms were highly biocompatible and resulted in increased proliferation and cell spreading when seeded with fibroblasts. Conversely, they limited bacterial attachment (Staphylococcus aureus) and proliferation. When neonatal rat cardiomyocytes (nrCMs) were cultured on the substrates increased spreading and viability up to day 7 were studied when compared to control collagen substrates. Human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were seeded and stimulated using electric-field generation in a custom-made bioreactor. The combination of an electroconductive substrate with an external electrical field enhanced cell growth, and significantly increased cx43 expression. This in vitro study convincingly demonstrates the potential of this engineered conductive biohybrid platform for cardiac tissue regeneration.
We investigate the properties of momentum-dark excitons and trions formed in two-dimensional (2D) materials that exhibit an inverted Mexican hat-shaped-dispersion relation, taking as an example monolayer InSe. We employ variational techniques to obtain the momentum-dark ground state and bright state (non-zero and zero quasiparticle momenta, respectively). These states are particularly relevant due to their peaks in the quasiparticle density of states, where for the momentum-dark ground state, the contribution here is largest due to the presence of a van Hove singularity (VHS). The momentum-dark systems require a brightening procedure to provide the necessary momentum to become bright. We study the brightening through coupling to phonons and compute the photoluminescence spectrum. This work opens new avenues of research, such as exploiting dark excitons in solar cells and other semiconductor-based optoelectronic devices.
The development of high-precision large-area optical coatings and devices comprising low-dimensional materials hinges on scalable solution-based manufacturability with control over exfoliation procedure-dependent effects. As such, it is critical to understand the influence of technique-induced transition metal dichalcogenide (TMDC) optical properties that impact the design, performance, and integration of advanced optical coatings and devices. Here, we examine the optical properties of semiconducting MoS2 films from the exfoliation formulations of four prominent approaches: solvent-mediated exfoliation, chemical exfoliation with phase reconversion, redox exfoliation, and native redox exfoliation. The resulting MoS2 films exhibit distinct refractive indices (n), extinction coefficients (k), dielectric functions (ε1 and ε2), and absorption coefficients (α). For example, a large index contrast of Δn ≈ 2.3 is observed. These exfoliation procedures and related chemistries produce different exfoliated flake dimensions, chemical impurities, carrier doping, and lattice strain that influence the resulting optical properties. First-principles calculations further confirm the impact of lattice defects and doping characteristics on MoS2 optical properties. Overall, incomplete phase reconfiguration (from 1T to mixed crystalline 2H and amorphous phases), lattice vacancies, intraflake strain, and Mo oxidation largely contribute to the observed differences in the reported MoS2 optical properties. These findings highlight the need for controlled technique-induced effects as well as the opportunity for continued development of, and improvement to, liquid phase exfoliation methodologies. Such chemical and processing-induced effects present compelling routes to engineer exfoliated TMDC optical properties toward the development of next-generation high-performance mirrors, narrow bandpass filters, and wavelength-tailored absorbers.
Multiplexed monitoring of wound biomarkers is essential for early detection of infection, inflammation, and assessment of healing. However, existing biosensors lack the sensitivity, specificity, and integration required for clinical needs. We developed a portable multimodal sensing chip to simultaneously detect multiple wound-relevant biomarkers. Specifically, the device integrates laser-induced graphene (LIG) electrodes for differential pulse voltammetry-based detection of uric acid and phenazine-1-carboxylic acid (a biomarker of Pseudomonas aeruginosa), open-circuit potential reading of pH using polyaniline-modified LIG, and a LIG-based extended-gate field effect transistor for detecting interleukin-6. We validated the devices in phosphate-buffered saline and wound simulating medium and demonstrated accurate, multiplexed detection in clinical ranges. Furthermore, in vitro experiments with an agar-based wound model highlighted the system's promise for wound monitoring. The sensing chip was integrated with a wireless analyzer for real-time data acquisition. This minimally invasive platform could support continuous wound assessment by monitoring infection and inflammation for future smart wound dressings.
Conventional Coulomb engineering, through controlled manipulation of the environment, offers an effective route to tune the correlation properties of atomically thin van der Waals materials via static screening. Here we present tunable dynamical screening as a method for precisely tailoring bosonic modes to optimize many-body properties. We show that "bosonic engineering" of plasmon modes can be used to enhance plasmon-induced superconducting critical temperatures of layered superconductors in metallic environments by up to an order of magnitude, due to the formation of interlayer hybridized plasmon modes with enhanced superconducting pairing strength. We determine optimal properties of the screening environment to maximize critical temperatures. We show how bosonic engineering can aid the search for experimental verification of plasmon mediated superconductivity.
Isotope-enriched bulk hexagonal boron nitride (hBN) crystals have enhanced properties that improve the performance of nanophotonic and quantum technologies. Developing methods to deposit epitaxial layers on such crystals enables the exciting prospects of producing isotope-engineered hBN layers and heterostructures. Here, we demonstrate the homoepitaxial growth of hBN with phase-separated 10B and 11B isotopes by high-temperature molecular beam epitaxy (HT-MBE). Controlled nucleation, improved surface uniformity, and step-flow growth of an h10BN epilayer were achieved by etching the h11BN bulk crystals with molecular hydrogen. The alignment of the h10BN epilayer and host h11BN lattices was confirmed by lattice-resolved atomic force microscopy. Micro-Raman spectroscopy and scattering-type scanning near-field optical microscopy show that the bulk h11BN and h10BN epilayer have distinct phonon energies, with no intermixing of the van der Waals layers, thus enabling the different boron isotopes to be spatially separated in the heterostructure. This work demonstrates the potential of HT-MBE to produce isotopic heterostructures of hBN to advance future nanophotonic and quantum technologies.
Single-layer semiconducting transition-metal dichalcogenides, lacking point inversion symmetry, provide an efficient platform for valleytronics, where the electronic, orbital, magnetic, valley, and lattice degrees of freedom can be selectively manipulated by using polarized light. This task is, however, thought to be impeded in parent bulk compounds where the point inversion symmetry is restored. Exploiting the underlying quantum physics in bulk materials is thus one of the biggest paradigmatic challenges. Here we show that a sizable optical Kerr rotation can be efficiently generated without breaking point-inversion symmetry in a wide energy range on ultrafast timescales in bulk WSe2, by means of circularly-polarized light. We rationalize this finding as a result of the hidden spin/layer/orbital/valley order. The spectral analysis reveals distinct A-, B-, and C-exciton features, which we show to stem from a selective Pauli blocking effect on top of the hidden-order pseudospin order and of the spin Berry curvature. The Kerr response lifetime (τ ~ 500 fs), common to all the peaks, suggests that excitonic dynamics dominate over single-particle decay. The present report demonstrates that the hidden order at play in bulk centrosymmetric layered materials can stem out in macroscopical bulk features, opening the way for an effective exploitation of bulk WSe2 in novel optoelectronic and orbitronics applications.
Polytypism in transition metal dichalcogenides (TMDs) introduces an additional degree of freedom for tailoring the electronic properties of layered van der Waals materials. Polytypes with larger unit cells, spanning four or six layers, can be viewed as natural homostructures, since their atomic composition remains identical across the layers. The resultant crystalline environments can potentially give rise to exotic electronic states, earning these materials recent attention. In this study, we examine structural and charge transport properties of metallic and superconducting 4Ha-NbSe2. We find that the compound has a highly disordered stacking of layers, which impedes interlayer coherence, as demonstrated by detailed out-of-plane resistivity measurements, and effectively tunes the bulk system towards an atomically thin limit. The disordered structure largely accounts for the enhanced resistivity anisotropy and superconducting upper critical field, when compared to 2Ha-NbSe2. This phenomenon can be exploited to promote quasi-two-dimensional physics in bulk crystals, and our study also underscores the importance of thorough structural characterization when investigating large-unit-cell polytypes of TMDs.
Sunlight is widely seen as one of the most abundant forms of renewable energy, with photovoltaic cells based on pn junctions being the most commonly used platform attempting to harness it. Unlike in conventional photovoltaic cells, the bulk photovoltaic effect (BPVE) allows for the generation of photocurrent and photovoltage in a single material without the need to engineer a pn junction and create a built-in electric field, thus offering a solution that can potentially exceed the Shockley-Queisser efficiency limit. However, it requires a material with no inversion symmetry and is therefore absent in centrosymmetric materials. Here, we demonstrate that breaking the inversion symmetry by structural disorder can induce BPVE in ultrathin PtSe2, a centrosymmetric semiconducting van der Waals material. Homogenous illumination of defective PtSe2 by linearly and circularly polarized light results in a photoresponse termed as linear photogalvanic effect (LPGE) and circular photogalvanic effect (CPGE), which is mostly absent in the pristine crystal. First-principles calculations reveal that LPGE originates from Se vacancies that act as asymmetric scattering centers for the photo-generated electron-hole pairs. Our work emphasizes the importance of defects to induce photovoltaic functionality in centrosymmetric materials and shows how the range of materials suitable for light sensing and energy-harvesting applications can be extended.
Mechanical cantilevers are central to nanotechnology, where low bending rigidity makes stability the fundamental challenge. Here, we introduce a wrinkle-induced stiffening approach that enhances the bending rigidity of monolayer graphene by several orders of magnitude, enabling the fabrication of mechanically robust graphene cantilevers. When suspended over microcavities, these wrinkled membranes exhibit significant increases in both in-plane and out-of-plane stiffness, as confirmed by nanoindentation and resonance measurements, which also reveal that enhanced bending rigidity strongly influences their vibrational response. This behavior marks a transition from tension-dominated mechanics to a regime where bending effects become prominent, even in a single atomic layer. By sculpting these structures, we realize graphene cantilevers with measured bending rigidities between 106-107 eV, while maintaining femtogram-scale mass. These findings establish a mechanical stabilization mechanism for realizing ultrathin cantilevers and highlight their potential for applications where high compliance is of importance.
Two-dimensional materials can be strongly influenced by their surroundings. A dielectric environment screens and reduces the Coulomb interaction between electrons in the two-dimensional material. Since in Mott materials the Coulomb interaction is responsible for the insulating state, manipulating the dielectric screening provides direct control over Mottness. Our many-body calculations reveal the spectroscopic fingerprints of such Coulomb engineering: we demonstrate eV-scale changes to the position of the Hubbard bands and show a Coulomb engineered insulator-to-metal transition. Based on our proof-of-principle calculations, we discuss the (feasible) conditions under which our scenario of Coulomb engineering of Mott materials can be realized experimentally.
Thermoelectric materials are of great interest for heat energy harvesting applications. One such promising material is TlGaSe2, a 2D-layered, p-type semiconducting ternary chalcogenide. Recent reports show it can be processed as a thin film, opening the door for large-scale commercialization. However, TlGaSe2 is prone to stacking faults along the [001] stacking direction and their role in its thermoelectric properties has not yet been understood. Herein, TlGaSe2 is investigated via (scanning) transmission electron microscopy and first-principles calculations. Stacking faults are found to be present throughout the material, as density functional theory calculations reveal a low stacking fault energy of ~12 mJ m-2. Electron transport calculations show an enhancement of thermoelectric power factors when stacking faults are present. This implies the presence of stacking faults is key to the material's excellent thermoelectric properties along the [001] stacking direction, which can be further enhanced by doping the material to carrier concentrations of ~1019 cm-3.