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We undertake a dielectric breakdown failure analysis of thin hexagonal boron nitride (h-BN) by conduction atomic force microscopy. The breakdown field is 21 MV cm–1 for 3 nm-thick h-BN, and the breakdown voltage statistics follows a tight monomodal Weibull distribution, indicating the material suitability as a gate dielectric. Breakdown effects extend over an area of ∼100 nm diameter and evolve by defect generation in the h-BN, with increasing conductance under repeated stressing; but the breakdown current–voltage (I–V) curves differ from conventional ultrathin SiO2 and HfO2 films. Specifically, there are indications that 2D layering is influencing the breakdown as follows: (i) Fowler–Nordheim fitting of successive I–V curves after stressing often proceeds in discrete monolayer thickness values of ∼0.3 nm, an effect that we propose arises from electrical "shorting" between adjacent layers, and (ii) the Weibull slope decreases as film thickness increases, indicating that the defect generation is not random but occurs preferentially at specific locations.

Graphene shows a strong promise for detection of terahertz (THz) radiation due to its high carrier mobility, compatibility with on-chip waveguides and transistors, and small heat capacitance. At the same time, weak reaction of graphene's physical properties on the detected radiation can be traced down to the absence of band gap. Here, we study the effect of electrically-induced band gap on THz detection in graphene bilayer with split-gate p-n junction. We show that gap induction leads to simultaneous increase in current and voltage responsivities. At operating temperatures of ~25 K, the responsivity at 20 meV band gap is from 3 to 20 times larger than that in the gapless state. The maximum voltage responsivity of our devices at 0.13 THz illumination exceeds 50 kV/W, while the noise equivalent power falls down to 36 fW/Hz^0.5. These values set new records for semiconductor-based cryogenic terahertz detectors, and pave the way for efficient and fast terahertz detection.

Abstract Hydrogen bonding plays a crucial role in biology and technology, yet it remains poorly understood and quantified despite its fundamental importance. Traditional models, which describe hydrogen bonds as electrostatic interactions between electropositive hydrogen and electronegative acceptors, fail to quantitatively capture bond strength, directionality, or cooperativity, and cannot predict the properties of complex hydrogen-bonded materials. Here, we introduce a concept of hydrogen bonds as elastic dipoles in an electric field, which captures a wide range of hydrogen bonding phenomena in various water systems. Using gypsum, a hydrogen bond heterostructure with two-dimensional structural crystalline water, we calibrate the hydrogen bond strength through an externally applied electric field. We show that our approach quantifies the strength of hydrogen bonds directly from spectroscopic measurements and reproduces a wide range of key properties of confined water reported in the literature. Using only the stretching vibration frequency of confined water, we can predict hydrogen bond strength, local electric field, O-H bond length, and dipole moment. Our work also introduces hydrogen bond heterostructures – a class of electrically and chemically tunable materials that offer stronger, more directional bonding compared to van der Waals heterostructures, with potential applications in areas such as catalysis, separation, and energy storage.

ABSTRACT The selective, rapid, and sensitive detection of deoxyribonucleic acid (DNA) nucleobases is critical for applications in genetic diagnostics, forensic analysis, and molecular biology research. Conventional detection techniques often require sophisticated instrumentation and complex sample preparation, which limit their use in point‐of‐care settings. Advances in 2D nanomaterials, particularly graphene oxide (GO), have enabled the development of highly sensitive DNA sensors; however, challenges in achieving selectivity, simplicity, and speed remain. In this work, we present a simple and cost‐effective transistor‐based memristive DNA sensor that exploits the specific interactions between GO and double‐stranded DNA. The platform enables direct, label‐free quantification of DNA sequences across a guanine–cytosine (GC) content range of 37%–55%, with strong linear calibration (coefficient of determination, R 2 = 0.9785). The measurement process is rapid, with electrical signals acquired within 2–5 min, and does not require denaturation, fluorescent labeling, or polymerase chain reaction (PCR) amplification. The slow relaxation of current decay following electrical pulse stimulation correlates strongly with GC content, yielding a robust analytical signal. These findings establish a pathway for DNA composition analysis, genetic screening, and taxonomic fingerprinting using memristive GO biosensors.

Functional graphene optical sensors are now viable due to the recent developments in hand‐held Raman spectroscopy and the chemical vapor deposition (CVD) of graphene films. Herein, the strain in graphene/poly (methyl methacrylate) sensor coatings is followed using Raman band shifts. The performance of an “ideal” mechanically‐exfoliated single crystal graphene flake is compared to a scalable CVD graphene film. The dry‐transferred mechanically exfoliated sample has no residual stresses, whereas the CVD sample is in compression following the solvent evaporation during its transfer. The behavior of the sensors under cyclic deformation shows an initial breakdown of the graphene‐polymer interface with the interface then stabilizing after several cycles. The Raman 2D band shift rates per unit strain of the exfoliated graphene are ≈35% higher than CVD graphene making the former more strain sensitive. However, for practical wide‐area applications, CVD graphene coatings are still viable candidates as a Raman system can be used to read the strain in any 5 μm diameter spot in the coating to an absolute accuracy of ≈0.01% strain and resolution of ≈27 microstrains (μs), which compares favorably to commercial photoelastic systems.

This dataset contains data from the paper "Out-of-equilibrium criticalities in graphene superlattices"

The inherent crystal anisotropy of hexagonal boron nitride (hBN) provides the ability to support hyperbolic phonon polaritons, that is, polaritons that can propagate with very large wave vectors within the material volume, thereby enabling optical confinement to exceedingly small dimensions. Indeed, previous research has shown that nanometer-scale truncated nanocone hBN cavities, with deep subdiffractional dimensions, support three-dimensionally confined optical modes in the mid-infrared. Because of optical selection rules, only a few of the many theoretically predicted modes have been observed experimentally via far-field reflection and scattering-type scanning near-field optical microscopy (s-SNOM). The photothermal induced resonance (PTIR) technique probes optical and vibrational resonances overcoming weak far-field emission by leveraging an atomic force microscope (AFM) probe to transduce local sample expansion caused by light absorption. Here we show that PTIR enables the direct observation of previously unobserved, dark hyperbolic modes of hBN nanostructures. Leveraging these optical modes and their wide range of angular and radial momenta could provide a new degree of control over the electromagnetic near-field concentration, polarization in nanophotonic applications.

We report a stoichiometric derivative of graphene with a fluorine atom attached to each carbon. Raman, optical, structural, micromechanical and transport studies show that the material is qualitatively different from the known graphene-based nonstoichiometric derivatives. Fluorographene is a high-quality insulator (resistivity >10^12 Ohm per square) with an optical gap of 3 eV. It inherits the mechanical strength of graphene, exhibiting Young's modulus of 100 N/m and sustaining strains of 15%. Fluorographene is inert and stable up to 400C even in air, similar to Teflon.

Electrically induced $p-n$ junctions in graphene bilayer (GBL) have shown superior performance for detection of sub-THz radiation at cryogenic temperatures, especially upon electrical induction of the band gap $E_g$. Still, the upper limits of responsivity and noise equivalent power (NEP) at very large $E_g$ remained unknown. Here, we study the cryogenic performance of GBL detectors at $f=0.13$ THz by inducing gaps up to $E_g \approx 90$ meV, a value close to the limits observed in recent transport experiments. High value of the gap is achieved by using high-$\kappa$ bottom hafnium dioxide gate dielectric. The voltage responsivity, current responsivity and NEP optimized with respect to doping do not demonstrate saturation with gap induction up to its maximum values. The NEP demonstrates an order-of-magnitude drop from $\sim450$ fW/Hz$^{1/2}$ in the gapless state to $\sim30$ fW/Hz$^{1/2}$ at the largest gap. At largest induced band gaps, plasmonic oscillations of responsivity become visible and important for optimization of sub-THz response.

<title>Abstract</title> Water molecules at the solid-liquid interface display intricate behaviours sensitive to small changes. The presence of different interfacial components, such as cations or functional groups, shape the physical and chemical properties of the hydrogen bond network. Understanding such interfacial hydrogen-bond networks is essential for a large range of applications and scientific questions. To probe the interfacial hydrogen-bond network, atmospheric water capture is a powerful tool. Here, we experimentally observe that a calcium ion on a calcium-intercalated graphene oxide aerogel (Ca-GOA) surface captures 2.7 times more water molecules than in its freestanding state. From density functional theory (DFT) calculations, we uncover the synergistically enhanced hydrogen-bond network of the calcium ion-epoxide complex due to significantly larger polarizations and hydrogen bond enthalpies. This study reveals valuable insights into the interfacial water hydrogen-bond network on functionalized carbon-cation complexed surfaces and potential pathways for future atmospheric water generation technologies.

Higher-order exchange interactions and quantum effects are widely known to play an important role in describing the properties of low-dimensional magnetic compounds. Here we identify the recently discovered two-dimensional (2D) van der Waals (vdW) CrI3 as a quantum non-Heisenberg material with properties far beyond an Ising magnet as initially assumed. We find that biquadratic exchange interactions are essential to quantitatively describe the magnetism of CrI3 but requiring quantum rescaling corrections to reproduce its thermal properties. The quantum nature of the heat bath represented by discrete electron-spin and phonon-spin scattering processes induced the formation of spin fluctuations in the low temperature regime. These fluctuations induce the formation of metastable magnetic domains evolving into a single macroscopic magnetization or even a monodomain over surface areas of a few micrometers. Such domains display hybrid characteristics of Neel and Bloch types with a narrow domain wall width in the range of 3-5 nm. Similar behaviour is expected for the majority of 2D vdW magnets where higher-order exchange interactions are appreciable.

Two‐dimensional materials (2DMs), especially graphene derivatives, have attracted a wide range of interest in science and technology because of their exceptional physical and chemical properties and large potential application areas in electrochemistry, photonics, bioengineering, electronics and membrane separation fields. Our review focuses on recent advances in the construction of new functional composites using graphene oxide (GO), reduced graphene oxide (rGO) and bio‐based macromolecules. The incorporation of bio‐based polymers into GO and rGO nanolayers provides a novel way to tailor the properties of 2DMs. Meanwhile, 2DMs/bio‐based polymer composites are sustainable and biocompatible. Benefiting from the combination of superior properties of both materials, they are endowed with new functions and new application areas. Here, we compare existing fabrication approaches for 2DMs/bio‐based polymer composites. Then, we highlight the properties of composites such as ionic conductivity, molecular transport, mechanical properties, biocompatibility and sustainability. Finally, we discuss recent progress in applications of 2DMs/bio‐based polymer composites for efficient ionic and molecular separation technologies, the construction of energy‐related devices including fuel cells and transistors, and biomedical engineering. © 2020 Society of Industrial Chemistry