Ultrathin Thickness Research Articles

Large-area ultrathin 2D Co(OH)2 nanosheets: a bifunctional electrode material for supercapacitor and water oxidation

Ultrathin film of active materials having thickness <5 nm emerged as a promising candidate for miniaturized energy storage and conversion devices. However, the small lateral size restricts its real device applications. Herein, we report large area, 2D, ultrathin (thickness: 4.3 ± 0.3 nm) Co(OH)2 nanosheets as bifunctional electrode material for supercapacitor and oxygen evolution reaction developed by ionic layer epitaxy method at the water-air interface. The symmetric supercapacitor device exhibited excellent volumetric capacitance of 2313 F/cm3 at 0.4 mA/cm2 current density. Additionally, it exhibited a remarkable volumetric energy density of 0.205 Wh/cm3 at a power density of 0.145 W/cm3, which is better than reported 2D electrode materials. Furthermore, the cobalt hydroxide (Co(OH)2) ultrathin-film electrodes showed improved oxygen evolution reaction electrocatalytic activity with low overpotential (ƞ10, 330 mV) and Tafel slope (47 mV/dec). The structural and morphological investigations after long-term operations show substantial stability of the electrode material. The theoretical investigations of electronic structures, quantum capacitance, and free energy profiles for the oxygen evolution reaction mechanism corroborate the experimental results.

Axially slow-variation microbubble resonators fabricated by an improved arc discharge method for strain sensing applications

In this paper, we proposed an axially slow-variation microbubble resonator fabricated by an improved arc discharge method and applied to axial strain sensing. The prepared resonators are characterized by ultra-thin wall thickness and axial slow-variation. The wall thickness was experimentally measured to reach 938 nm and maintain a quality factor of an optical mode as large as 7.36 ×107. The main factors affecting the strain sensitivity of the microbubble resonators are investigated theoretically and experimentally. Experimentally, the maximum sensitivity measured was 13.08pm/µε, which is three times higher than the microbubble resonators without this method. The device is simple to prepare and possesses ultra-thin wall thickness. It is promising for applications in high-precision sensing, such as single molecule and biological sensing.

Optimizing the electromagnetic wave absorption properties of core-shell Fe/FeN/Fe3C@GN nanoparticles by low-temperature NH3 plasma

Surface modification via low-temperature plasma has an extensive application prospect in different engineering fields due to its comprehensive merits in facilitating the introduction of functional groups and creating more heterogeneous interfaces. Herein, a simple high-temperature plasma method is developed to get novel multiple-phase nanocomposites of core-shell Fe/FeN/Fe3C@GN nanoparticles with bifunctional characteristics of microwave absorption (MA) and anti-corrosion. And then, we further investigate the MA properties of Fe/FeN/Fe3C@GN nanoparticles after low-temperature NH3 plasma etching. It is found that surface modification of Fe/FeN/Fe3C@GN nanoparticles can generate remarkable changes in specific surface areas, Raman features and MA properties of these nanocomposites. The Fe/FeN/Fe3C@GN nanoparticles after NH3 plasma etching possess excellent MA properties with an optimal reflection loss (RL) of −51.0 dB at an ultra-thin thickness of 1.9 mm with a low filling content of 30 wt% and the corresponding effective absorption bandwidth (EAB < −10 dB) up to 4.7 GHz (13.3–18.0 GHz). The fascinating MA properties of etched Fe/FeN/Fe3C@GN nanoparticles may be attributed to the cooperative effect of several points: (i) The NH3 plasma etch introduces a large number of polar functional groups, which can be regarded as the polarization center to produce more polarization loss; (ii) The appropriate dielectric loss and impedance matching achieve a good balance, and the abundant heterogeneous interface significantly enhances the polarization relaxation loss; (iii) The existence of hetero-nanostructure further improves the multiple reflections and scattering of the propagating microwaves. In addition, this work provides a new strategy for the design and fabrication of core-shell MA materials.

Synergistic polarization engineering of dielectric towards low-voltage high-mobility solution-processed ultraflexible organic transistors

The emerging wearable skin-like electronics require the ultra-flexible organic transistor to operate at low voltage for electrical safety and energy efficiency and simultaneously enable high field-effect mobility to ensure the carrier migration ability and the switching speed of circuits. However, the currently reported low-voltage organic transistors generally present low mobility, originating from the trade-off between molecular polarity and surface polarity of the dielectrics. In this work, the orientation polarization of the dielectric is enhanced by introducing a flexible quaternary ammonium side chain, and the surface polarity is weakened by the shielding effect of the nonpolar methyl groups on the polar nitrogen atom. The resulting antisolvent QPSU dielectric enables the high-dielectric constant up to 18.8 and the low surface polarity with the polar component of surface energy only at 2.09 mJ/m2. Such a synergistic polarization engineering between orientation polarization and surface polarity makes the solution-processed ultraflexible transistors present the ultralow operational voltage down to −3 V, the ultrahigh charge-carrier mobility up to 8.28 cm2 V−1 s−1 at 1 Hz, excellent cyclic operational stability and long-term air stability. These results combined with the ultrathin thickness of transistor as low as 135 nm, the ultralight mass of 0.5 g/m2, the conformal adherence capability on human skin and 1-μm blade edge, and the strong mechanical robustness with stable electrical properties for 30,000 bending cycles, open up an available strategy to successfully realize low-voltage high-mobility solution-processed organic transistor, and presents the potential application of QPSU dielectric for the next-generation wearable imperceptible skin-like electronics.

Evaporation-induced self-assembled ultrathin AgNW networks for highly conformable wearable electronics

The flexibility and stability of transparent electrodes play a crucial role in the growing popularity of flexible devices, especially in potential wearable electronics. To date, various solution-coating techniques have been developed for fabricating silver nanowire (AgNW) flexible bioelectronics. However, achieving the orderly distributed patterns of AgNW without undesirable aggregations still poses a grand challenge. Here, an approach to realize regular patterned ultrathin AgNW networks on a freestanding electrospun PVDF-TrFE frame by evaporation-induced self-assembly is proposed. The patterning mechanism of evaporating AgNW colloidal suspension is investigated from experimental and theoretical analysis. The influence of evaporation-induced flow inside colloidal freestanding membranes on forming regular square hole-shaped arrays, selective deposition of AgNW, and aligning them along the artificial pinning array are addressed. Owing to the orderly arrangement of AgNW networks, the resultant flexible electrode achieves ultrathin thickness (about 5 μm), high optical transmittance (87.8%), and low sheet resistance (8.4 Ω·sq−1) with a relatively low dosage of AgNW (9 μg·cm−2). The electrode exhibits excellent durability during cyclic bending (50,000 times) and stretching (50% strain). The resistance remains virtually unchanged during 200 days in everyday environments. Furthermore, the excellent conformability and breathability of the flexible transparent electrode attached to the human skin demonstrates its potential application as an e-skin sensor. Our findings reliably urge a simple approach to underscore better outcomes with effective patterns by self-assembly of AgNW for highly conformal wearable electronics.

High performance CH3NH3PbI3 perovskite photodetector functionalized by T-Ag plasmonic nanostructure

Photodetectors with ultrathin thickness and high efficiency are increasingly needed in the developing of wearable devices. However, the very limited active layer thickness has seriously restricted the photoelectric conversion efficiency. Here, the optical nanostructure fabricated with the assistance of self-assembly polystyrene mask layer has been integrated to increase the light absorption capacity by simultaneously utilizing the local surface plasma resonance, gap plasma, and the microcavity resonance effect. With the incorporation of triangular silver (T-Ag) nanostructure, the photogenerated current and response speed have significantly enhanced 481.25% and 26.30%, respectively. This strategy provides a viable way to design high-efficiency ultra-thin photodetectors.

Rapid construction of nickel phyllosilicate with ultrathin layers and high performance for CO2 methanation

The traditional techniques for the synthesis of nickel phyllosilicates usually time-consuming and energy-intensive, which often lead to the formation of layers with excessive thickness due to uncontrolled crystal growth. In order to overcome these challenges, this work introduces a microwave-assisted synthesis strategy to facilitate the synthesis of Ni-phyllosilicate-based catalysts within an exceptionally short duration of only five minutes, attaining a peak temperature of merely 102 °C. To enhance the specific surface area and to increase the exposure of active sites, an investigation was conducted involving three surfactants. The employment of hexadecyl trimethyl ammonium bromide (CTAB) has yielded remarkable results, with an ultrahigh specific surface area reaching 535 m2 g−1 and an ultrathin lamellar thickness of 1.43 nm. The catalyst exhibited an impressive CO2 conversion of 81.7 % at 400 °C, 60 L g−1 h−1, 0.1 MPa. It also demonstrated a substantial turnover frequency for CO2 (TOFCO2) of 5.4 ± 0.1 × 10−2 s−1, alongside a relatively low activation energy (Ea) of 80.74 kJ·mol−1. Moreover, the catalyst maintained its high stability over a period of 100 h and displayed high resistance to sintering. To further elucidate growth temperature gradient of the catalyst and concentration gradient of the materials involved, COMSOL Multiphysics (COMSOL) simulations were effectively utilized. In conclusion, this work breaks the limitation associated with traditional, laborious synthesis methods for Ni-phyllosilicates, which can produce materials with high surface area and thin-layer characteristics.

Solution-Processed Monolayer Molecular Crystals: From Precise Preparation to Advanced Applications.

Emerging monolayer molecular crystals (MMCs) have become prosperous in recent decades due to their numerous advantages. First, downsizing the active layer thickness to monolayer in organic field-effect transistors (OFETs) is beneficial to elucidate the intrinsic charge-transport behavior. Next, the ultrathin conducting channel can reduce bulk injection resistance to extract mobility accurately. Then, direct exposure of the conducting channel can enhance the sensing performance. Finally, MMCs combine the merits of ultrathin thickness and high crystallization, which will improve the optoelectronic performance and realize complex device architectures for future advanced optoelectronic applications. In this Review, recent research progress in precise preparations and advanced applications of solution-processed MMCs are summarized. We present the current challenges related to MMCs with specific structures and desired performances, and an outlook regarding their application in next-generation integrated organic optoelectronics is provided.

Multifunctional Ultrathin Metasurface with a Low Radar Cross Section and Variable Infrared Emissivity.

The development of stealth devices that are compatible with both infrared (IR) and radar systems remains a significant challenge, as the material properties required for effective IR and radar stealth are often contradictory. In this work, based on an IR electrochromic device (IR-ECD), concepts of metamaterial manipulating electromagnetic waves are applied to develop a multifunctional ultrathin metasurface with a low radar cross section (RCS) and variable infrared emissivity. This paper presents a linear-to-linear polarization conversion metasurface (PCM) designed by hollowing the IR-ECD. In this way, the IR-ECD based on polyaniline (PANI) can also modulate the reflection waves in the microwave band without affecting its features in the infrared region. Thus, the proposed metasurface integrates both microwave stealth and variable infrared emissivity through a single layer. The measured results show that a 10 dB RCS reduction is achieved in the band of 8.46-9.5 GHz, and the infrared emissivity can be adjusted from 0.870 to 0.513 in the infrared stealth band of 8-14 μm. Due to the ultrathin thickness (only 0.081λ0 at 9 GHz), low RCS in the X-band, and variable infrared emissivity, the designed multifunctional stealth metasurface has promising applications on military platforms with various surrounding environments.

Synthesis of the 2D Ternary Topological Insulator Bi2‐xSbxSe3 with a Low Carrier Concentration and Ultrahigh Carrier Mobility

AbstractHighcarrier concentration and low mobility in Bi2Se3 hide thetopological surface states (TSS). In the 2D ternary topological insulator (TI) Bi2–xSbxSe3,compensatory Sb doping regulates the carrier concentration and mobility withambipolar performance, together with the ultrathin thickness; these factorsmake the TSS in the 2D ternary TI Bi2–xSbxSe3 more observable. Here, a chemical vapor deposition (CVD) method is provided for synthesizing ultrathin Sb‐doped Bi2Se3 nanoplates with dimensions of 2–126 nm in thickness, 3–100 µm in lateral size, and an average Sb doping ranging from 0.15 ≤ x ≤ 0.75. Bi2–xSbxSe3 field effect transistors and Hall devices are manufactured to determine the carrier concentration and mobility of the obtained Bi2–xSbxSe3 nanoplates. These findings demonstrate that the 2D carrier concentration for Bi2–xSbxSe3 nanoplates can decrease up to 1.6 × 1012 cm–2. Furthermore, field‐effect mobility and Hall mobility of up to 3411 cm2 V–1s–1 and 6462 cm2 V–1 s–1, respectively, are realized. A strong ambipolar field effect is found in low‐carrier‐density Bi2–xSbxSe3 nanoplates, proving that these nanostructures may be freely controlled in terms of carrier type and concentration. The synthesis of high‐quality Bi2–xSbxSe3 nanoplates with low‐carrier concentration and high‐mobility provides a platform for investigating TI characteristics more clearly.

High-sensitivity fiber-tip acoustic sensor with ultrathin gold diaphragm

Miniature acoustic sensors with high sensitivity are highly desired for applications in medical photoacoustic imaging, acoustic communications and industrial nondestructive testing. However, conventional acoustic sensors based on piezoelectric, piezoresistive and capacitive detectors usually require a large element size on a millimeter to centimeter scale to achieve a high sensitivity, greatly limiting their spatial resolution and the application in space-confined sensing scenarios. Herein, by using single-crystal two-dimensional gold flakes (2DGFs) as the sensing diaphragm of an extrinsic Fabry-Perot interferometer on a fiber tip, we demonstrate a miniature optical acoustic sensor with high sensitivity. Benefiting from the ultrathin thickness (∼8 nm) and high reflectivity of the 2DGF, the fiber-tip acoustic sensor gives an acoustic pressure sensitivity of ∼300 mV/Pa in the frequency range from 100 Hz to 20 kHz. The noise-equivalent pressure of the fiber-tip acoustic sensor at the frequency of 13 kHz is as low as 62.8 µPa/Hz1/2, which is one or two orders of magnitude lower than that of reported optical acoustic sensors with the same size.

A sub-10 nm polyamide nanofiltration membrane from polyvinylpyrrolidone-mediated interfacial polymerization

In conventional interfacial polymerization (IP) for thin-film composite nanofiltration membranes, the separation layer is typically thick (∼100 nm), which limits its water permeance. In this study, we successfully synthesized an ultrathin polyamide layer (∼8.6 nm) from polyvinylpyrrolidone (PVP)-mediated IP. With the surfactant concentration over its critical micelle concentration, PVP not only formed a monolayer at the water-heptane interface, but also stayed in the aqueous solution. The CO groups of PVP formed the N–H⋯O hydrogen bond interactions with N–H bonds of piperazine (PIP) monomers in the aqueous phase to slow down the diffusion of PIP monomers. Besides, PVP with amphiphilic groups minimized the interfacial tension at the water-heptane interface to regulate IP processes. By adjusting the concentration of PVP, we obtained a sub-10 nm polyamide nanofiltration membrane. Moreover, hydrophilic PVP macromolecules improved the membrane surface hydrophilicity. Due to the ultrathin thickness and improved hydrophilicity, the optimized polyamide membrane demonstrated a threefold increase in permeance compared to that of the pristine polyamide membrane without PVP addition, and maintained 98.4% rejection for 1000 ppm Na2SO4 solution. This study provides a new insight into fabricating sub-10 nm polyamide membranes for nanofiltration processes.

Efficient Protection of Paper‐Based Cultural Relics via In Situ Synthesis of Carbon Dots/Layered Double Hydroxide

AbstractPaper‐based cultural relics are of great value and have been facing irreversible damage caused by multiple factors, among which acid hydrolysis and ultraviolet photodegradation are the main processes leading to paper deterioration. Paper protection highly relies on a limited range of materials with single functions, and the design of new materials that ensure long‐term safety and efficiency by simultaneously addressing the issues of acidification and UV degradation in paper is highly desired. In this study, the introduction of carbon dots (CDs)‐enhanced layered double hydroxides (LDH) 0D/2D nanohybrids (CDs/Mg‐Al LDH) &amp;nbsp;is proposed as novel dual‐functional materials for paper protection against UV degradation and acidification. Through a CDs‐assisted in situ growth strategy, CDs/Mg‐Al LDH with ultrathin thickness (≈9.1 nm) and CDs‐intercalated structure are achieved. The CDs/Mg‐Al LDH nanohybrids demonstrate high dispersibility, strong UV absorption, and remarkable photostability, resulting in protected‐paper with decelerated acidification, oxidation, and yellowing degradation processes under both accelerated UV‐aging and dry‐heat conditions. Additionally, the protected‐paper can emit uniform blue light under 365 nm UV excitation allows for easy identification of the distributed CDs/Mg‐Al LDH within the paper, marking a unique and practical feature. This research paces a new direction for the protection of paper‐based relics with emerging carbon dots‐based 0D/2D nanomaterials.

Electromagnetic wave absorption mechanism and wear corrosion characteristics of Ti3SiC2 MAX phase-doped Ni/AlN composite coating with core-shell structure based on laser cladding-induced pitaya-like multi-level heterogeneous interface

To satisfy the service requirements of wave-absorbing materials in harsh environments, it is important to design and manufacture corrosion-resistant composite-absorbing materials. According to the strategy of impedance matching and the dissipation behaviour of nickel-based alloys, AlN ceramics, and MAX-phase Ti3SiC2 multicomponent composite-regulated materials were studied. As an additive manufacturing technology, multilevel heterointerface composites with core–shell structures were obtained by laser cladding. The construction of a unique core–shell structure of a metal–ceramic and ceramic (core)–ceramic (shell) multi-level heterogeneous interface increased the interfacial relaxation and multiple dissipation and improved the impedance matching. The results enabled the N20M3 cladding coating to exhibit excellent microwave absorption characteristics, with a reflection loss of −32.84 dB at the ultra-thin thickness of 1.8 mm. Additionally, the composites exhibited excellent corrosion resistance, high hardness, and relatively good resistance to erosion wear. This work promotes the durability of wave-absorbing materials under severe conditions, as well as the integration of the efficient manufacturing of wave-absorbing materials.

High-enhancement photoluminescence of monolayer MoS2 in hybrid plasmonic systems.

Monolayer molybdenum disulfide (M o S 2) has a weak light-matter interaction due to ultrathin thickness, which limits its potential application in lasing action. In this study, we propose a hybrid structure consisting of a nanocavity and Au nanoparticles to enhance the photon emission efficiency of monolayer M o S 2. Numerical simulations show that photoluminescence (PL) emission is significantly enhanced by introducing localized surface plasmon resonance (LSPR) to the proposed structure. Furthermore, an exciton energy band system is proposed to elucidate the physical mechanism of the PL process. By optimizing the spacer thickness, a high Purcell enhancement factor of 95 can be achieved. The results provided by this work pave the way to improve the PL efficiency of two-dimensional (2D) material, which constitutes a significant step towards the development of nanodevices such as nanolasers and sensors.

Ternary-coordination-regulated polyamide nanofiltration membranes for Li+/Mg2+ separation

Thin-film composite (TFC) membranes prepared by the interfacial polymerization (IP) of amines and trimesoyl chloride (TMC) have been widely utilized for Li+/Mg2+ separation from salt-lake brine. The relatively high lithium rejection hinders the achievement of high lithium extraction efficiency. In this study, a polyphenol-metal-assisted method was designed to regulate the structure of polyethylenimine (PEI)-based polyamide nanofiltration (NF) membranes. Tannic acid (TA) was first deposited onto the substrate, followed by the impregnation of the Cu2+ ions-incorporated aqueous PEI monomer solution to establish ternary interactions among PEI, TA, and Cu2+ ions. Based on the synergistic effect of ternary interactions, the resultant PA-TA-Cu membrane possesses ultrathin thickness (≈11 nm), high positive charge, and relatively loose structure. It exhibited a high MgCl2 rejection (95.9 %) and a low LiCl rejection (17.1 %), with a pure water permanence of 4.87 L m−2 h−1 bar−1. Furthermore, the NF membrane exhibits a high Li+/Mg2+ separation factor (26.5) and excellent long-term stability. This study provides an efficient strategy for fabricating an excellent NF membrane for lithium extraction from salt-lake brines.

Effect of VO2/Graphene Heterojunction on Terahertz Wave Electromagnetic Absorption

In the past two decades, metamaterial design has been applied to terahertz wave detection research, which is very important because metamaterial has the advantages of high absorption, ultra-thin device thickness, design flexibility and frequency selectivity. In this paper, the VO2/Graphene heterostructures were designed on the silicon dioxide layer, and the terahertz wave absorption bandwidth was tuned by adjusting the size and conductivity of VO2 and the Fermi level of graphene. According to the simulation results, the VO2/Graphene heterostructures has a substantial absorption bandwidth of more than 7 THz and an absorption peak intensity that is continuously tuned between 2.8% and 98% by adjusting temperature change the conductivity of VO2. Meanwhile, the heterojunctions also have high absorption ability for terahertz waves incident at different polarization angles. The new idea is provided by our research results for the design of heterojunction terahertz absorption devices.

Cylindrical metalens for multidimensional control of terahertz waves

Metalens, consisting of planar micro/nanostructure arrays, has shown great potentials in beam steering, subwavelength focusing and high-resolution imaging. Taking the advantages of ultrathin thickness and compact design, it can be integrated with a photonic chip to improve the collection efficiency of optoelectronic systems. However, it remains challenging to realize the multidimensional control of terahertz (THz) waves by using a metalens, although the convergence properties have been widely studied. Here, we design and experimentally demonstrate a multifunctional cylindrical metalens by using a tri-layer metallic metasurface. By modulating the amplitude, phase and polarization states of terahertz waves independently, the cylindrical metalens can generate two focal lines at different positions for transmitted x- and y- polarized terahertz waves with varying amplitude distribution. Importantly, up to 64.7% focusing efficiency has been obtained at the frequency of 0.34 THz with a numerical aperture (NA) of 0.75. Our study offers a novel method for implementing multifunctional cylindrical metalens which lays the foundation of advanced integration with arrayed terahertz detection chips.

Nano FeCoNi-based high-entropy alloy for microwave absorbing with high magnetic loss and corrosion resistance

With the development of modern communication and military technology, the protection of electromagnetic wave pollution and radar stealth technology have been widely concerned. In this background, the magnetic metals were widely used due to the strong ferromagnetism, which can induce strong magnetic loss to the electromagnetic wave. However, it remains challenging to precisely control the wave-absorbing performance of individual magnetic metals, and there are issues with poor corrosion resistance and high temperature resistance. Therefore, the alloy powders based on Fe, Co, and Ni in this work were prepared by wet chemical method at room temperature. Different from most of the traditional powder metallurgy methods, the wet chemical method enables us to obtain binary, ternary and quaternary alloys with a nanometer-scale and uniform distribution, all products have a microscopic morphology of 300–500 nm spheres. The FeCoNi alloy powder shows an effective absorption band (RL<-10 dB) of 7 GHz in the high frequency electromagnetic wave range at an ultrathin thickness of 1.5 mm, which has a high temperature magnetism (Tc >900 K) and excellent corrosion resistance. Further doping of Cu to form a quaternary alloy can improve the corrosion resistance and maintain the original wave-absorbing properties, while doping of Mo and Sn can adjust the position of the effective absorption bandwidth.

Atomic-Scale Imaging of Clay Mineral Nanosheets and Their Supramolecular Complexes through Electron Microscopy: A Supramolecular Chemist's Perspective.

Recent advancements in electron microscopy techniques have revolutionized the ability to directly visualize and understand the intricate world of supramolecular chemistry. This paper provides a concise overview of a study delving into the atomic-scale imaging of monolayer clay mineral nanosheets and their associated supramolecular complexes. The imaging is conducted by harnessing the power of aberration-corrected scanning transmission electron microscopy (STEM). Clay mineral nanosheets, with their anionic charge and ultrathin thickness (of 1 nm), serve as a stable Coulombic host material for cationic guest molecules through electrostatic interactions, facilitating exceptional stability and control during observation. By incorporation of heavy-metal atom markers coordinated within the target molecules, high-angle annular dark field STEM enables a clear visualization of these supramolecular complexes. This approach helps to overcome the limitations of graphene-based systems and expands the possibilities of atomic-scale imaging of nonperiodic molecular assemblies formed by weak supramolecular interactions. The fusion of electron microscopy techniques with the principles of supramolecular and material chemistry offers exciting opportunities for studying the structure, behavior, and properties of complex supramolecular systems. It sheds light on the intricate molecular architectures and design principles governing these systems. This study showcases the immense potential of electron microscopy in supramolecular chemistry and invites researchers from various disciplines to explore the transformative possibilities of atomic-scale imaging in the field.