Resonance phenomena of π-mode forming in multi-element gratings

An analysis of resonances of scattering from multi-element grating formed by a finite number of resonant elements is presented. It has been shown that gratings with three and more elements on its period can support the π-mode. The π-mode of a grating is characterized by the existence of the regions in the vicinity of the grating and along its period where the electromagnetic field has opposite phases. The existence and excitation of the π-mode in finite gratings with resonant cells formed by several scatterers having open cavities have been studied. The particular case of the grating with cells formed by three identical slotted cylinders has been considered in detail. An application of gratings which support the π-mode in electron-vacuum oscillators of millimeter waves for efficient deceleration of electrons and extracting energy from electron beam is discussed.     

Concentration dependence of thermodynamic interaction parameters in a polymer-polymer-solvent system

Summary The concentration dependence of Thermodynamic Interaction Parameters is reported for the system Polystyrene (PS, M_{W 3}=4.4 · 10⁵) — Polybutylmethacrylate (PBMA, M_{W 2}=2.7 · 10⁵) — CCl₄.     

On manifestation & physics of the Kurdjumov and spillover effects in carbon nanostructures,under intercalation of high density hydrogen

Abstract

Some experimental evidences and the physics (thermodynamics) of the nanoscale self-intercalation of high-density gaseous molecular hydrogen (ρ?≈?0.045?g/cm³, T?≈?300?K) into surface nanoclusters in highly oriented pyrolytic graphite and epitaxial graphene, as well as the nanoscale self-intercalation of high density solid molecular hydrogen (ρ?≈?0.5?g/cm³, T?≈?300?K, the compressed pressure ～ 0.5 Mbar) into graphite nanofibers are considered, with regard to the problem of compact and efficient hydrogen on-board storage and other clean energy applications. Perspectives of further developments of these results are considered, as well.     

Sodium storage properties of thin phosphorus-doped graphene layers developed on the surface of nanodiamonds under hot pressing conditions

Abstract

Phosphorus-doped graphene layers have been formed on the surface of nanodiamond (ND) particles by hot pressing of a mixture of purified detonation ND powder and triphenylphosphine (TPP) at 1000?°C and 100?bar. X-ray photoelectron spectroscopy detected about 1.7 at.% of phosphorus in the product, most of which was in the oxidized form. The same treatment conditions of the ND powder without the addition of TPP resulted in the only partial covering of some ND particles by sp²-hybridized carbon layers. The tests in Na-ion half-cells found that the pure carbon sample can reversibly sustain 42 mAh g^?1 at a current density of 0.1?A g^?1. For the phosphorus-doped sample, this value increases up to 54 mAh g^?1 due to mainly accumulation of sodium at various defects created in the graphitic layers as a result of phosphorus incorporation. Taking into account inertness of inner diamond cores, specific capacity values are 417 mAh g^?1 for phosphorus-doped graphene layers and 587 mAh g^?1 for non-doped ones.     

MXene Composite and Coaxial Fibers with High Stretchability and Conductivity for Wearable Strain Sensing Textiles

The integration of nanomaterials with high conductivity into stretchable polymer fibers can achieve novel functionalities such as sensing physical deformations. With a metallic conductivity that exceeds other solution‐processed nanomaterials, 2D titanium carbide MXene is an attractive material to produce conducting and stretchable fibers. Here, a scalable wet‐spinning technique is used to produce Ti₃C₂T_x MXene/polyurethane (PU) composite fibers that show both conductivity and high stretchability. The conductivity at a very low percolation threshold of ≈1 wt% is demonstrated, which is lower than the previously reported values for MXene‐based polymer composites. When used as a strain sensor, the MXene/PU composite fibers show a high gauge factor of ≈12900 (≈238 at 50% strain) and a large sensing strain of ≈152%. The cyclic strain sensing performance is further improved by producing fibers with MXene/PU sheath and pure PU core using a coaxial wet‐spinning process. Using a commercial‐scale knitting machine, MXene/PU fibers are knitted into a one‐piece elbow sleeve, which can track various movements of the wearer's elbow. This study establishes fundamental insights into the behavior of MXene in elastomeric composites and presents strategies to achieve MXene‐based fibers and textiles with strain sensing properties suitable for applications in health, sports, and entertainment.     

Discovery of Real-Space Topological Ferroelectricity in Metallic Transition Metal Phosphides

Ferroelectric metals—with coexisting ferroelectricity and structural asymmetry—challenge traditional perceptions because free electrons screen electrostatic forces between ions, the driving force of breaking the spatial inversion symmetry. Despite ferroelectric metals having been unveiled one after another, topologically switchable polar objects with metallicity have never been identified so far. Here, the discovery of real-space topological ferroelectricity in metallic and non-centrosymmetric Ni₂P is reported. Protected by the rotation–inversion symmetry operation, it is found that the balanced polarity of alternately stacked polyhedra couples intimately with elemental valence states, which are verified using quantitative electron energy-loss spectroscopy. First-principles calculations reveal that an applied in-plane compressive strain creates a tunable bilinear double-well potential and reverses the polyhedral polarity on a unit-cell scale. The dual roles of nickel cations, including polar displacement inside polyhedral cages and a 3D bonding network, facilitate the coexistence of topological polarity with metallicity. In addition, the switchable in-plane polyhedral polarity gives rise to a spin–orbit-coupling-induced spin texture with large momentum-dependent spin splitting. These findings point out a new direction for exploring valence–polarity–spin correlative interactions via topological ferroelectricity in metallic systems with structural asymmetry.     

Additive-Free Aqueous MXene Inks for Thermal Inkjet Printing on Textiles

Direct printing of functional inks onto flexible substrates allows for scalable fabrication of wearable electronics. However, existing ink formulations for inkjet printing require toxic solvents and additives, which make device fabrication more complex, limit substrate compatibility, and hinder device performance. Even water-based carbon or metal nanoparticle inks require supplemental surfactants, binders, and cosolvents to produce jettable colloidal suspensions. Here, a general approach is demonstrated for formulating conductive inkjet printable, additive-free aqueous Ti₃C₂T_x MXene inks for direct printing on various substrates. The rheological properties of the MXene inks are tuned by controlling the Ti₃C₂T_x flake size and concentration. Ti₃C₂T_x-based electrical conduits and microsupercapacitors (MSCs) are printed on textile and paper substrates by optimizing the nozzle geometry for high-resolution inkjet printing. The chemical stability and electrical properties of the printed devices are also studied after storing the devices for six months under ambient conditions. Current collector-free, textile-based MSCs show areal capacitance values up to 294 mF cm⁻² (2 mV s⁻¹) in poly(vinyl alcohol)/sulfuric acid gel electrolyte, surpassing reported printed MXene-based MSCs and inkjet-printed MSCs using other 2D nanomaterials. This work is an important step toward increasing the functional capacity of conductive inks and simplifying the fabrication of wearable textile-based electronics.     

Solution‐Processed Ti3C2Tx MXene Antennas for Radio‐Frequency Communication

Highly integrated, flexible, and ultrathin wireless communication components are in significant demand due to the explosive growth of portable and wearable electronic devices in the fifth‐generation (5G) network era, but only conventional metals meet the requirements for emerging radio‐frequency (RF) devices so far. Here, it is reported on Ti₃C₂T_x MXene microstrip transmission lines with low‐energy attenuation and patch antennas with high‐power radiation at frequencies from 5.6 to 16.4 GHz. The radiation efficiency of a 5.5 µm thick MXene patch antenna manufactured by spray‐coating from aqueous solution reaches 99% at 16.4 GHz, which is about the same as that of a standard 35 µm thick copper patch antenna at about 15% of its thickness and 7% of the copper weight. MXene outperforms all other materials evaluated for patch antennas to date. Moreover, it is demonstrated that an MXene patch antenna array with integrated feeding circuits on a conformal surface has comparable performance with that of a copper antenna array at 28 GHz, which is a target frequency in practical 5G applications. The versatility of MXene antennas in wide frequency ranges coupled with the flexibility, scalability, and ease of solution processing makes MXene promising for integrated RF components in various flexible electronic devices.