Scalable Manufacturing of Free-Standing,Strong Ti3C2Tx MXene Films with Outstanding Conductivity

Free-standing films that display high strength and high electrical conductivity are critical for flexible electronics, such as electromagnetic interference (EMI) shielding coatings and current collectors for batteries and supercapacitors. 2D Ti₃C₂T_x flakes are ideal candidates for making conductive films due to their high strength and metallic conductivity. It is, however, challenging to transfer those outstanding properties of single MXene flakes to macroscale films as a result of the small flake size and relatively poor flake alignment that occurs during solution-based processing. Here, a scalable method is shown for the fabrication of strong and highly conducting pure MXene films containing highly aligned large MXene flakes. These films demonstrate record tensile strength up to ≈570 MPa for a 940 nm thick film and electrical conductivity of ≈15 100 S cm⁻¹ for a 214 nm thick film, which are both the highest values compared to previously reported pure Ti₃C₂T_x films. These films also exhibit outstanding EMI shielding performance (≈50 dB for a 940 nm thick film) that exceeds other synthetic materials with comparable thickness. MXene films with aligned flakes provide an effective route for producing large-area, high-strength, and high-electrical-conductivity MXene-based films for future electronic applications.     

High-temperature superconducting dual-mode resonator on (100) MgO substrate

We report, for the first time to our knowledge, a clear resonant peak split in the range of 7.7–9.7 GHz in a perturbed dual-mode disk-type resonator (DMDR) made of YBa₂Cu₃O_7–x (YBCO) superconducting thin film on MgO substrate. Epitaxial YBCO superconducting thin films were grown on (100) MgO substrates by pulsed laser deposition technique. The critical temperature of superconducting thin film on MgO substrate was 85 K. Superconducting dualmode disk resonators were designed by microwave design software, EEsof, and patterned by photolithography and a wet-etch process. The unloaded quality factor (Q_UL) of the superconducting DMDR was found to be 1,312 at 77 K. We believe this type of DMDR can be utilized for dual-mode resonator-based filters for satellite communications.     

Bath Electrospinning of Continuous and Scalable Multifunctional MXene‐Infiltrated Nanoyarns

Electroactive yarns that are stretchable are desired for many electronic textile applications, including energy storage, soft robotics, and sensing. However, using current methods to produce these yarns, achieving high loadings of electroactive materials and simultaneously demonstrating stretchability is a critical challenge. Here, a one‐step bath electrospinning technique is developed to effectively capture Ti₃C₂T_x MXene flakes throughout continuous nylon and polyurethane (PU) nanofiber yarns (nanoyarns). With up to ≈90 wt% MXene loading, the resulting MXene/nylon nanoyarns demonstrate high electrical conductivity (up to 1195 S cm^?1). By varying the flake size and MXene concentration, nanoyarns achieve stretchability of up to 43% (MXene/nylon) and 263% (MXene/PU). MXene/nylon nanoyarn electrodes offer high specific capacitance in saturated LiClO₄ electrolyte (440 F cm^?3 at 5 mV s^?1), with a wide voltage window of 1.25 V and high rate capability (72% between 5 and 500 mV s^?1). As strain sensors, MXene/PU yarns demonstrate a wide sensing range (60% under cyclic stretching), high sensitivity (gauge factor of ≈17 in the range of 20–50% strain), and low drift. Utilizing the stretchability of polymer nanofibers and the electrical and electrochemical properties of MXene, MXene‐based nanoyarns demonstrate potential in a wide range of applications, including stretchable electronics and body movement monitoring.     

Effective microwave surface impedance of superconducting films inthe mixed state

The effective microwave surface impedance of multilayer structures made of high-T_c superconducting films in the mixed state, lossy dielectrics, and normal metals are theoretically calculated. The linear response of the superconductor to a microwave field is analyzed within both transmission line theory and the framework of a self-consistent treatment of vortex dynamics reported by Coffey and Clem (1991). The microwave properties are investigated as a function of static field and film thickness for nonresonant structures. The effect of substrate thickness on the resonant phenomenon is carefully studied as well. Numerical results reveal that the substrate resonance in the Meissner state behaves like a parallel lumped-parameter resonator, while in the vortex state it behaves as a series lumped resonant circuit. The basic distinction suggests that care should be taken in microwave applications when using superconducting films in the vortex state     

A 2D Titanium Carbide MXene Flexible Electrode for High-Efficiency Light-Emitting Diodes

Although several transparent conducting materials such as carbon nanotubes, graphene, and conducting polymers have been intensively explored as flexible electrodes in optoelectronic devices, their insufficient electrical conductivity, low work function, and complicated electrode fabrication processes have limited their practical use. Herein, a 2D titanium carbide (Ti₃C₂) MXene film with transparent conducting electrode (TCE) properties, including high electrical conductivity (≈11 670 S cm⁻¹) and high work function (≈5.1 eV), which are achieved by combining a simple solution processing with modulation of surface composition, is described. A chemical neutralization strategy of a conducting-polymer hole-injection layer is used to prevent detrimental surface oxidation and resulting degradation of the electrode film. Use of the MXene electrode in an organic light-emitting diode leads to a current efficiency of ≈102.0 cd A⁻¹ and an external quantum efficiency of ≈28.5% ph/el, which agree well with the theoretical maximum values from optical simulations. The results demonstrate the strong potential of MXene as a solution-processable electrode in optoelectronic devices and provide a guideline for use of MXenes as TCEs in low-cost flexible optoelectronic devices.     

Investigation of space charge at pentacene/Au interface with UV/ozone treatment by a near-field microwave microprobe

The near-field microwave microprobe (NFMM) and Kelvin-probe measurements were performed to evaluate the conductivity in terms of surface potential of pentacene films on Au electrode. The UV/ozone treated and untreated Au electrodes were prepared to reveal the relationship between the electrical conductivity and interfacial electrostatic charging phenomena. For the pentacene film deposited on the Au electrode with UV/ozone treatment, holes were displaced from Au electrode to pentacene film, resulting the accumulation of apparent positive charges in the interfacial region of pentacene film around Au electrode. The NFMM measurement revealed that the reflection coefficient of microwave, S₁₁ increased with UV/ozone treatment, indicating the resistance decrease of the surface. Accumulation of positive charge in the interfacial region of Au electrode/pentacene film is one of the essential reasons for the increase of the conductivity of pentacene film.     

Humidity sensing characteristics of hydrotungstite thin films

Thin films of the hydrated phase of tungsten oxide, hydrotungstite (H₂WO₄·H₂O), have been grown on glass substrates using a dip-coating technique. The b-axis oriented films have been characterized by X-ray diffraction and scanning electron microscopy. The electrical conductivity of the films is observed to vary with humidity and selectively show high sensitivity to moisture at room temperature. In order to understand the mechanism of sensing, the films were examined by X-ray diffraction at elevated temperatures and in controlled atmospheres. Based on these observations and on conductivity measurements, a novel sensing mechanism based on protonic conduction within the surface layers adsorbed onto the hydrotungstite film is proposed.     

Investigation and Modeling Nonlinear Characteristics of High-Tc Superconducting Resonators

The high-quality resonators and pass-band filters based on high-T _c superconducting (HTS) films are of the most interest for practical applications. The industrial application of the devices is retarded by nonlinearity of the film surface impedance under microwave power of a high level. The phenomenological model of nonlinear characteristics of HTS resonators was developed and applied to different kinds of planar resonators: disk, parallel plate, and micro-strip resonator. A comparison of experimental and modeled characteristics of the resonators revealed the distinctive difference in the model parameters. Some limiting characteristics are discussed.     

Nonlinear Microwave Response of Epitaxial YBaCuO Films of Varying Oxygen Content on MgO Substrates

We have investigated the nonlinear microwave properties of electron-beam coevaporated YBa₂Cu₃O_7–x films on MgO, using stripline resonators at 2.3 GHz and temperatures 1.7–80 K. The oxygen content of the films ranged from strongly underdoped to overdoped. Above 20 K, the nonlinear response of the resonators was dominated by the superconductor. We could establish clear correlations between the nonlinear surface resistance, two-tone intermodulation (IMD), and oxygen content of the films, which indicate that the superconducting order parameter is important for the nonlinearities. A power-law representation of the nonlinear current-voltage relation would not be appropriate to explain our results phenomenologically. Below 20 K, the dielectric loss tangent of MgO dominated the nonlinear response of the resonators. With increasing power, the dissipation losses decreased markedly, accompanied by enhanced IMD. The surface reactance passed through a shallow minimum at about 5 K, independent of power. We attribute these effects to resonant absorption by impurity states in MgO.     

Investigation and Modeling Nonlinear Characteristics of High-Tc Superconducting Resonators

The high-quality resonators and pass-band filters based on high-T _c superconducting (HTS) films are of the most interest for practical applications. The industrial application of the devices is retarded by nonlinearity of the film surface impedance under microwave power of a high level. The phenomenological model of nonlinear characteristics of HTS resonators was developed and applied to different kinds of planar resonators: disk, parallel plate, and micro-strip resonator. A comparison of experimental and modeled characteristics of the resonators revealed the distinctive difference in the model parameters. Some limiting characteristics are discussed.     

Enhanced Thermoelectric Performance of Rare-Earth-Free n-Type Oxide Perovskite Composite with Graphene Analogous 2D MXene

Here, the first experimental demonstration on the effect of incorporating new generation 2D material, MXene, on the thermoelectric performance of rare-earth-free oxide perovskite is reported. The charge localization phenomenon is predominant in the electron transport of doped SrTiO₃ perovskites, which deters from achieving a higher thermoelectric power factor in these oxides. In this work, it is shown that incorporating Ti₃C₂T_x MXene in a matrix of SrTi_0.85Nb_0.15O₃ (STN) facilitates the delocalization of electrons resulting in better than single-crystal-like electron mobility in polycrystalline composites. A 1851% increase in electrical conductivity and a 1000% enhancement in power factor are attained. Besides, anharmonicity caused by MXene in the STN matrix has led to enhanced Umklapp scattering giving rise to lower lattice thermal conductivity. Hence, 700% ZT enhancement is achieved in this composite. Further, a prototype of thermoelectric generator (TEG) using only n-type STN + MXene is fabricated and a power output of 38 mW is obtained, which is higher than the reported values for oxide TEG.     

Superhigh Electromagnetic Interference Shielding of Ultrathin Aligned Pristine Graphene Nanosheets Film

Ultrathin, lightweight, high-strength, and thermally conductive electromagnetic interference (EMI) shielding materials with high shielding effectiveness (SE) are highly desired for next-generation portable and wearable electronics. Pristine graphene (PG) has a great potential to meet all the above requirements, but the poor processability of PG nanosheets hinders its applications. Here, efficient synthesis of highly aligned laminated PG films and nacre-like PG/polymer composites with a superhigh PG loading up to 90 wt% by a scanning centrifugal casting method is reported. Due to the PG-nanosheets-alignment-induced high electrical conductivity and multiple internal reflections, such films show superhigh EMI SE comparable to the reported best synthetic material, MXene films, at an ultralow thickness. An EMI SE of 93 dB is obtained for the PG film at a thickness of ≈100 µm, and 63 dB is achieved for the PG/polyimide composite film at a thickness of ≈60 µm. Furthermore, such PG-nanosheets-based films show much higher mechanical strength (up to 145 MPa) and thermal conductivity (up to 190 W m⁻¹ K⁻¹) than those of their MXene counterparts. These excellent comprehensive properties, along with ease of mass production, pave the way for practical applications of PG nanosheets in EMI shielding.     

Hydrophobic,Flexible, and Lightweight MXene Foams for High‐Performance Electromagnetic‐Interference Shielding

Ultrathin, lightweight, and flexible electromagnetic‐interference (EMI) shielding materials are urgently required to manage increasingly serious radiation pollution. 2D transition‐metal carbides (MXenes) are considered promising alternatives to graphene for providing excellent EMI‐shielding performance due to their outstanding metallic electrical conductivity. However, the hydrophilicity of MXene films may affect their stability and reliability when applied in moist or wet environments. Herein, for the first time, an efficient and facile approach is reported to fabricate freestanding, flexible, and hydrophobic MXene foam with reasonable strength by assembling MXene sheets into films followed by a hydrazine‐induced foaming process. In striking contrast to well‐known hydrophilic MXene materials, the MXene foams surprisingly exhibit hydrophobic surfaces and outstanding water resistance and durability. More interestingly, a much enhanced EMI‐shielding effectiveness of ≈70 dB is achieved for the lightweight MXene foam as compared to its unfoamed film counterpart (53 dB) due to the highly efficient wave attenuation in the favorable porous structure. Therefore, the hydrophobic, flexible, and lightweight MXene foam with an excellent EMI‐shielding performance is highly promising for applications in aerospace and portable and wearable smart electronics.     

Characteristics of Cu/C films on polymer substrates prepared by ECR–MOCVD

Cu/C films were prepared at ambient temperature under a Cu(hfac)₂-Ar-H₂ atmosphere in order to obtain metallized polymer by using electron cyclotron resonance metal organic chemical vapor deposition(ECR-MOCVD) coupled with a direct current (DC) bias system. DC bias selectively attracts the positively charged copper ions and then makes them deposit on the polymer substrate. Structural analysis of the films by ECR showed that fine copper grains were embedded in an amorphous polymer matrix. The electrical properties of the films were closely related to the process parameters such as microwave power, magnet current, H₂/Ar mole ratio and periodic negative voltage. The increase in H₂ contents, microwave power, magnet current and the negative voltage brought on copper-rich film formation with low electrical resistance. On the other hand carbon-rich films with low sheet electrical resistance were prepared with lower values for process parameters described above. Formation of Cu/C films depends strongly on the periodic negative pattern of DC bias and the electrical sheet resistance of the films was controlled in the 10⁸–10⁰ ohm/sq range by process parameters of the ECR-MOCVD system.     

Dielectric resonator as a possible standard for characterization of high temperature superconducting films for microwave applications

The performance of several designs of dielectric resonators used for microwave characterization of FITS films has been analyzed from the point of view of accuracy, sensitivity, and range. Designs discussed include Hakki-Coieman shielded types as well as open-ended resonators with sapphire, rutile and (ZrSn)TiO₃ dielectrics. The best dielectric resonators have proved to have an uncertainty in surface resistance measurements only twice the uncertainty in theQ-factor. high sensitivity, and ability to measure a wide range of surface resistances. Hence the dielectric resonator technique can be considered as a standard for measurements of surface resistance of HTS films for wireless and PCS communication systems applications provided that adequate measurement procedures of theQ ₀-factor are followed.     

Multifunctional Nanocomposites with High Strength and Capacitance Using 2D MXene and 1D Nanocellulose

The family of two‐dimensional (2D) metal carbides and nitrides, known as MXenes, are among the most promising electrode materials for supercapacitors thanks to their high metal‐like electrical conductivity and surface‐functional‐group‐enabled pseudocapacitance. A major drawback of these materials is, however, the low mechanical strength, which prevents their applications in lightweight, flexible electronics. A strategy of assembling freestanding and mechanically robust MXene (Ti₃C₂T_x ) nanocomposites with one‐dimensional (1D) cellulose nanofibrils (CNFs) from their stable colloidal dispersions is reported. The high aspect ratio of CNF (width of ≈3.5 nm and length reaching tens of micrometers) and their special interactions with MXene enable nanocomposites with high mechanical strength without sacrificing electrochemical performance. CNF loading up to 20%, for example, shows a remarkably high mechanical strength of 341 MPa (an order of magnitude higher than pristine MXene films of 29 MPa) while still maintaining a high capacitance of 298 F g^?1 and a high conductivity of 295 S cm^?1. It is also demonstrated that MXene/CNF hybrid dispersions can be used as inks to print flexible micro‐supercapacitors with precise dimensions. This work paves the way for fabrication of robust multifunctional MXene nanocomposites for printed and lightweight structural devices.     

Intra-gap Absorption in Superconducting Ba(Fe1−x Co x )2As2 Thin Films Studied by a Fabry–Pérot Resonant Technique

For superconducting films, the optical intra-gap conductivity provides valuable information on the superconductivity mechanism, in particular on the gap symmetry, quasiparticles, and superconducting carrier dynamics. Experimentally, however, it is extracted with rather large uncertainty caused by the huge negative value of the dielectric constant. We have performed systematic numerical analysis of Fabry–Pérot resonators, which consist of two identical superconducting iron pnictide thin films on dielectric substrates that are positioned face-to-face to each other and are separated by a spacer. We demonstrate that such a Fabry–Pérot arrangement can significantly enhance the accuracy to the dynamical conductivity σ ₁ of the films, as the efficiency of interaction of the probing radiation with the superconducting films is improved. Using a coherent source terahertz spectrometer (4–45 cm^?1) with a Mach–Zehnder interferometer, we have measured the complex transmissivity of three Fabry–Pérot resonators composed by identical pairs of Ba(Fe_0.9Co_0.1)₂As₂ films with the thicknesses: 25, 30, and 50 nm. We show that the experimental spectra can be well described by a corresponding five-layer model based on Fresnel’s equations and analyze the advantages and challenges of the Fabry–Pérot resonant technique for iron pnictide films.     

Cold Sintered Ceramic Nanocomposites of 2D MXene and Zinc Oxide

Nanocomposites containing 2D materials have attracted much attention due to their potential for enhancing electrical, magnetic, optical, mechanical, and thermal properties. However, it has been a challenge to integrate 2D materials into ceramic matrices due to interdiffusion and chemical reactions at high temperatures. A recently reported sintering technique, the cold sintering process (CSP), which densifies ceramics with the assistance of transient aqueous solutions, provides a means to circumvent the aforementioned problems. The efficacious co‐sintering of Ti₃C₂T_x (MXene), a 2D transition carbide, with ZnO, an oxide matrix, is reported. Using CSP, the ZnO–Ti₃C₂T_x nanocomposites can be sintered to 92–98% of the theoretical density at 300 °C, while avoiding oxidation or interdiffusion and showing homogeneous distribution of the 2D materials along the ZnO grain boundaries. The electrical conductivity is improved by 1–2 orders of magnitude due to the addition of up to 5 wt% MXene. The hardness and elastic modulus show an increase of 40–50% with 0.5 wt% MXene, and over 150% with 5 wt% of MXene. The successful densification of ZnO–MXene nanocomposite demonstrates that the cold sintering of ceramics with 2D materials is a promising processing route for designing new nanocomposites with a diverse range of applications.     

Electromagnetic Shielding of Monolayer MXene Assemblies

Miniaturization of electronics demands electromagnetic interference (EMI) shielding of nanoscale dimension. The authors report a systematic exploration of EMI shielding behavior of 2D Ti₃C₂T_x MXene assembled films over a broad range of film thicknesses, monolayer by monolayer. Theoretical models are used to explain the shielding mechanism below skin depth, where multiple reflection becomes significant, along with the surface reflection and bulk absorption of electromagnetic radiation. While a monolayer assembled film offers ≈20% shielding of electromagnetic waves, a 24-layer film of ≈55 nm thickness demonstrates 99% shielding (20 dB), revealing an extraordinarily large absolute shielding effectiveness (3.89 × 10⁶ dB cm² g⁻¹). This remarkable performance of nanometer-thin solution processable MXene proposes a paradigm shift in shielding of lightweight, portable, and compact next-generation electronic devices.     

Characterization of Superconductor Coplanar Resonators Deposited on Different Substrates by Thermal Coevaporation

This study is based on two commercially available YBCO thin films deposited by the thermal coevaporation method on different substrates (MgO and LaAlO₃). Those films should be optimized for microwave applications. The structure and microstructure of the film deposited on LaAlO₃ have been investigated, respectively by XRD and SEM. These characterizations showed the high quality of the films concerning the c-axis orientation and the smooth and homogenous morphology. The films have then been etched into two different coplanar line resonators by ionic method (YBCO/LaAlO₃) and chemical one (YBCO/MgO) and their microwave properties have been characterized in two different cryogenic experimental set-ups. Despite the differences between these coplanar resonators, we have obtained the same intrinsic parameters (λ₀ = 190 nm, T _c=87 K with γ = 3) corresponding to the data provided by THEVA and a very low surface resistance (R _s=0.4 m Ω at 31 K and 10 GHz).