Ultrasmall Thickness Research Articles

Ultrathin, Mechanically Durable, and Scalable Polymer-in-Salt Solid Electrolyte for High-Rate Lithium Metal Batteries.

Polymer-in-salt solid-state electrolytes (PIS SSEs) are emerging for high room-temperature ionic conductivity and facile handling, but suffer from poor mechanical durability and large thickness. Here, Al2O3-coated PE (PE/AO) separators are proposed as robust and large-scale substrates to trim the thickness of PIS SSEs without compromising mechanical durability. Various characterizations unravel that introducing Al2O3 coating on PE separators efficiently improves the wettability, thermal stability, and Li-dendrite resistance of PIS SSEs. The resulting PE/AO@PIS demonstrates ultra-small thickness (25µm), exceptional mechanical durability (55.1MPa), high decomposition temperature (330°C), and favorable ionic conductivity (0.12 mS cm-1 at 25°C). Consequently, the symmetrical Li cells remain stable at 0.1mA cm-2 for 3000 h, without Li dendrite formation. Besides, the LiFePO4|Li full cells showcase excellent rate capability (131.0 mAh g-1 at 10C) and cyclability (93.6% capacity retention at 2C after 400 cycles), and high-mass-loading performance (7.5mg cm-2). Moreover, the PE/AO@PIS can also pair with nickel-rich layered oxides (NCM811 and NCM9055), showing a remarkable specific capacity of 165.3 and 175.4 mAh g-1 at 0.2C after 100 cycles, respectively. This work presents an effective large-scale preparation approach for mechanically durable and ultrathin PIS SSEs, driving their practical applications for next-generation solid-state Li-metal batteries.

RuAl intermetallic compound of low resistivity scaling and high thermal stability as potential interconnect metallization

Thin films of single-phase ruthenium aluminide (RuAl) intermetallic compound were deposited by magnetron co-sputtering. An ordered B2 body-centered cubic structure of high crystallinity was formed after rapid thermal annealing at 800 °C for 1 min. Data fittings using the Fuchs–Sondheimer and Mayadas–Shatzkes models suggested the very short mean free path of electrons of below 5 nm and the high specularity parameter of 0.9. The short mean free path and the much reduced diffuse scattering of electrons at the interface effectively suppressed the resistivity scaling of the B2 RuAl intermetallic compound as compared to ruthenium metal. At an ultra-small film thickness of below 5 nm, the reflection of electrons by grain boundaries or domain walls might alternatively dominate the increase in resistivity. The RuAl intermetallic compound with an ordered B2 structure and a high cohesive energy (a large negative mixing enthalpy) also demonstrated a superior thermal stability at an extreme temperature up to 900 °C. It could be a promising candidate for potential use as the next-generation interconnect metallization without the need of a diffusion barrier.

Heterogeneous burr-like CoNiO2/Ti3C2Tx MXene nanospheres for ultralow microwave absorption and satellite skin application

Nowadays, it is still a challenging task to exploit electromagnetic wave absorption (EMA) materials with superior EMA performance under an ultrasmall thickness (approximately 1 mm). In this study, heterogeneous CoNiO2/Ti3C2Tx MXene hybrid absorbers were successfully synthesized by using a simple and convenient self-assembly process. Benefiting from the increased porosity, heterogeneous interfaces, and multiple polarization processes, the unique burr-like CoNiO2/Ti3C2Tx MXene nanospheres (CNO/MXene-S) exhibited a remarkable EMA capacity with a minimum reflection loss (RLmin) value of −60.61 dB at an ultrasmall thickness of 1.069 mm and −66.79 dB at a matching thickness of 2.565 mm, respectively. The density functional theory (DFT) calculations were utilized to analyze the EMA mechanisms. Furthermore, the satellite radar cross-section (RCS) simulations demonstrated that compared with a non-stealth satellite, a stealth satellite with the CNO/MXene-S absorber exhibited decreased surface reflection of radar waves and a shortened radar detection distance. Therefore, the as-prepared CNO/MXene-S absorber with an ultrasmall matching thickness can be highly promising for the electromagnetic protection of spacecraft and electromagnetic communication devices.

BICs-enhanced active terahertz wavefront modulator enabled by laser-cut graphene ribbons

Graphene-based terahertz (THz) metasurfaces combined with metallic antennas have the advantages of ultra-small thickness, electrical tunability, and fast tuning speed. However, their tuning ability is limited by non-independently tunable pixels and low modulation depth due to the ultra-small thickness of graphene. Here, we demonstrate a reconfigurable THz phase modulator with 5×5 independently tunable units enabled by switching the voltages applied on 10 graphene ribbons prepared by laser cutting. In addition, by introducing quasi-bound states in the continuum resonance through a designed double C-shaped antenna, the efficiency of the device is enhanced by 2.7–3.6 times under different graphene chemical potentials. Experimental results demonstrate that a focus can be formed, and the focal length is changed from 14.3 mm to 22.6 mm. This work provides potential for compact THz spatial light modulators that may be applied in THz communication, detection, and imaging.

Fabrication of binary to quaternary PVDF based flexible composite films and ultrathin sandwich structured quaternary PVDF/CB/g-C3N4/BaFe11.5Al0.5O19 composite films for efficient EMI shielding performance

This work reports the facile fabrication of binary, ternary, and quaternary polymer composite films using combinations of Polyvinylidene fluoride (PVDF), Carbon Black (CB), Graphitic carbon nitride (g-C3N4), and Aluminum doped Barium hexaferrite (BaFe11.5Al0.5O19) nanoplatelets for application as EMI shielding materials at X-band frequency. The excellent total EMI-SE of 47.39 dB in X-band for ultra-small thickness of 0.193 mm was observed for the quaternary PVDF/CB/g-C3N4/BaFe11.5Al0.5O19 composite film. The quaternary composite film was further hot pressed into sandwich-structured two-layer and three-layer composite films. The sandwich and/or multi-layered structure of the PVDF/CB/g-C3N4/BaFe11.5Al0.5O19 composite film improved the EMI shielding performance through multiple reflection loss. With the addition of intact conduction of fillers and multiple-reflection-absorption effect, the multi-layered composite structure attained the best shielding efficiency (SE) of 64.54 dB.

Ultrathin metal-mesh Janus membranes with nanostructure-enhanced hydrophobicity for high-efficiency fog harvesting

Fog harvesting has been reckoned to be one of the most facile and economical approaches to alleviating the ever-increasing global water scarcity . Janus membranes, especially metallic ones, outperform other fog collectors in terms of fog harvesting efficiencies , and they are the selection for sustainable water production as passive devices. However, there is a lack of metallic Janus membranes with ultrasmall feature sizes due to the limitation of the laser ablation fabrication method , which restrains parameter optimization for highly efficient fog collectors. In this work, photolithography , electroplating , and nanoimprint lithography processes are employed to enable ultrasmall membrane thickness and nanopatterning on the membrane surface . A 4-μm-thick ultrathin hierarchical metal-mesh Janus membrane with a pitch of 60 μm is fabricated, which achieves a record-high water collection rate of 233 mg cm −2 ·min −1 with nanostructure-enhanced hydrophobicity . The morphology of the membrane is characterized by scanning electron microscopy, while the fog collection process is observed under a high-speed camera and a microscope. Experimental measurement and finite-element numerical modeling unveil that a smaller membrane thickness and a more hydrophobic water-collecting surface contribute to higher water collection rates by accelerating water transport and reducing water re-evaporation. • Photolithography and electroplating replace laser ablation for metallic JM fabrication. • Metallic JMs with unprecedented thickness down to 4 μm are fabricated. • Nanopatterning on JMs changes surface wettability and boosts WCR. • A record-high WCR of 233 mg cm −2 ·min −1 is achieved.

Bioinspired MXene/polyurethane plastic films with exceptional flexibility and toughness for electromagnetic interference shielding

Conductive materials with good mechanical performance are desired for electromagnetic interference (EMI) shielding. MXene (Ti3C2Tx), as a new 2D material, shows great potential due to its outstanding conductivity. The rigid nature and hydrophilic surface of MXene indicate its similarity to minerals, leading to the possibility of forming a conductive artificial nacre shell. Herein, highly flexible and tough MXene nanosheet/polyurethane composite films with a nacre-like structure are reported. The hydrogen bonding between MXene nanosheets and polyurethane chains endows an internal plasticization process and results in exceptional flexibility and toughness of 21.0 MJ m−3. Meanwhile, the MXene nanosheet/polyurethane composite film exhibits high electrical conductivity (126 S cm−1) and excellent specific EMI shielding efficiency (11312 dB cm2 g−1) at an ultra-small thickness (12.5 μm) and high polymer content (45.6 wt%). The nacre-inspired conductive composite film in this work offers a new strategy for the design and preparation of tough and flexible conductive materials.

Optical Properties of MoS2 , MoSe2 , WS2 , and WSe2 under External Electric Field

The combination of finite semiconductor band gap and ultrasmall thickness makes few-layer transition-metal dichalcogenides (TMDCs) promising materials for use in optoelectronics devices. Here, we use density-functional theory to investigate the photon-energy-dependent optical properties of two-layer (2L), three-layer, four-layer, and five-layer ${\mathrm{Mo}\mathrm{S}}_{2}$, ${\mathrm{Mo}\mathrm{Se}}_{2}$, ${\mathrm{WS}}_{2}$, and ${\mathrm{W}\mathrm{Se}}_{2}$ TMDCs. We find that the values of the dielectric constant and the refractive index always increase with the number of layers as well as with external electric field in the static region. However, in the visible region (400--600 nm), the values of the dielectric constant and the refractive index decrease with increasing external electric field. Among these TMDCs, ${\mathrm{Mo}\mathrm{Se}}_{2}$ shows the strongest response under electric field. We find that in contrast to a small electro-optic response in the weak-field limit, a large change in the refractive index is applied under large applied fields, with the increasing response obtained for thinner TMDC films. The magnitude and even the sign of the electro-optic response changes with the photon frequency and reaches the peak values in the 1.5--2.5 eV range. The position of the peak electro-optic response can be tuned by both changing the number of layers and the TMDC composition. 2L ${\mathrm{Mo}\mathrm{Se}}_{2}$ exhibits the highest response of 8.8 pm/V at 2.3 eV that is comparable to the response of typical oxide electro-optic ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_{3}$. Analysis of the sensitivity trends of these TMDC systems shows that compared to the changes in the band gap, the changes of the onset of strong absorption under electric field and change in the number of layers show better correlation with the changes in the electro-optic response. Our results provide guidance for the possible use of these materials in optical micro- or nanocavities for devices such as tunable optical filters and fast optical switches.

Ultrathin 2D nanosheets of transition metal (hydro)oxides as prospective materials for energy storage devices: A short review

The ultrathin two-dimensional (2D) transition metal oxides and hydroxides (TMO and TMH) nanosheets are attractive for creating high-performance energy storage devices due to a set of unique physical and chemical properties. Flat 2D structure of such materials provides a sufficient number of active adsorption centers, and the ultra-small thickness, on the order of several nanometers, provides fast charge transfer, which significantly improves electronic conductivity. This brief review summarizes recent progress in the synthesis of materials based on ultrathin 2D nanosheets for energy storage applications, including pseudocapacitors, lithium-ion batteries, and other rechargeable devices. The review also presents examples of representative work on the synthesis of ultrathin 2D nanomaterials based on TMO and TMH for various power sources. In conclusion, the article discusses possible prospects and directions for further development of methods and routes for the synthesis of ultrathin two-dimensional transition metal oxides and hydroxides.

A High‐Capacity, Long‐Cycling All‐Solid‐State Lithium Battery Enabled by Integrated Cathode/Ultrathin Solid Electrolyte

AbstractCurrent all‐solid‐state lithium battery (ASSLB) manufacturing typically involves laborious fabrication and assembly of individual electrodes and solid electrolyte, which inevitably result in large interfacial resistances. Moreover, due to the unfavorable mechanical strength, most solid electrolytes are fabricated to be overly thick and are incapable of retarding lithium dendrite formation. These factors limit the attainable energy density and cyclability of ASSLBs. Here, a novel integrated cathode/solid electrolyte for scalable ASSLB manufacturing is reported by directly fabricating an ultrathin yet robust fiber network reinforced solid electrolyte on the cathode. The integrated design allows continuous ion conduction at both the interface and the entire cathode, thereby considerably reducing interfacial resistance and enabling higher cathode loading. Meanwhile, the strong fiber network endows the solid electrolyte with an ultrasmall thickness and superior dendrite suppression capability. As a result, the newly‐developed Li/LiFePO4 ASSLB achieves a high capacity of 155.2 mAh g–1 at 0.5 C and 45 °C with capacity retention of 84.3% after 500 cycles. Even with a cathode loading of 13 mg cm–2, the battery still delivers a capacity of 124.1 mAh g–1. Additionally, a pouch cell with this integrated design displays good electrochemical performance and safety, showing great promise for practical applications.

Graphene-enabled active terahertz focusing with wide tuning range

Tunable terahertz (THz) metalenses using graphene have the advantages of good tunability, fast tuning speed, and ultra-small thickness for compact THz photonic systems. However, it is still a great challenge to realize such an active metalens with a large tuning range of focal length. Here, we propose a reflective metamirror with a graphene-coated metallic antenna array. Using an algorithm to find the C-shaped antennas with large phase changes when the graphene is gated, the metamirror with a wide tuning range is designed. The simulation results indicate that the focal length is able to be continuously changed by 96λ when the graphene chemical potential increases from 0.04 eV to 0.52 eV at 1 THz. The full width at half maximum of the focus is close to the diffraction limit. This method is anticipated to open up a new way for designing graphene-based widely tunable THz metasurfaces.

MATHEMATICAL MODEL FOR MEASURING THE CONCENTRATION OF NANOPARTICLES IN A LIQUID DURING SEDIMENTATION

Expanding the application areas of polymer composite materials with dispersed filler requires the development of technologies providing the required mechanical characteristics. One of these methods is based on forming a thin polymer shell on the surfaces of particles. At the same time, it is impossible to take into account the mechanical characteristics of a thin polymer shell due to its ultra-small thickness. The mechanical properties of the polymer shell can be determined only by indirect methods, and prior information can improve the adequacy of the properties determination. The method, which allows reducing the requirements for composite sample preparation, is proposed. This method is based on the sedimentation approach. It is suggested to evaluate the sedimentation time (or velocity) by measuring the optical density of the solution, consisting of nanoparticles and polymer macromolecules. The nanoparticle and polymer macromolecules parameters are defined using sedimentation time. The mathematical model for simulation of the photo sedimentation velocity of particles in a solvent is developed. The model considers the sedimentation process under the influence of gravity, hydrostatic lift, and drag forces. The model takes into account also the influence of the Brownian motion of the solvent on the particle movements based on elastic collision as well as the effect of the inelastic collision of particles with each other. The particle concentration is estimated based on beam light scattering modeling. The results of the mathematical model investigation and the experimental results confirm the feasibility of the proposed method. The results and estimations allow both to determine the sedimentation time and to formulate the method requirements for measuring particles of various sizes and densities. The proposed approach can be used to create equipment for nanoparticle parameters (mass, density) measuring.

Electrochemically Controlled Synthesis of Ultrathin Nickel Hydroxide Nanosheets for Electrocatalytic Oxygen Evolution.

The development of oxygen evolution reaction (OER) catalysts with high activity and high stability through convenient and economical methods is greatly important for the promotion of hydrogen energy based on electrolysis technology. Herein, by using an unconventional high electrodeposition potential, novel petal-like clusters constructed by cross-linking ultrathin nickel hydroxide nanosheets were controllably synthesized on nickel foam (or copper foam or carbon cloth) and the effect of electrodeposition conditions on their OER performance was carefully explored. Due to the abundant catalytically active sites, promoting electron conduction/mass transmission from the specific micro-nano structure, as well as the ultrasmall thickness of ∼3.0 nm, the optimized α-Ni(OH)2/NF self-supporting electrode exhibits excellent electrocatalytic performance for OER, merely requiring low overpotentials of 192 and 240 mV to yield current densities of 10 and 100 mA cm-2 in 1.0 M KOH, respectively, which surpassed those of all of the reported nickel hydroxide/oxides and the benchmark RuO2. Moreover, α-Ni(OH)2/NF can drive the high-current density (500-1000 mA cm-2) OER at low overpotentials, meeting the requirements of potential industrial applications.

Smoothing the surface roughness of aluminum nitride films obtained by magnetron sputtering

When producing aluminum nitride films used in radio electronic devices on bulk (BAW) and surface acoustic waves (SAW), such as resonators, filters, sensors, by magnetron sputtering, a problem arises due to the large surface roughness of the films, as a result of which acoustic waves scatter on irregularities and, as a result, deterioration of the resonance characteristics of the devices. In this paper, we study the possibility of improving the surface quality of aluminum nitride films by smoothing the surface roughness upon irradiation with a beam of cluster argon ions. It is shown that the effect of low-energy (10 V/atom) argon cluster ions leads to surface modification, removal of residual chemical contaminants in the near-surface layer, and additional smoothing of the film surface at an ultra-small thickness of the etched layer (<100 nm).

Enhanced terahertz focusing for a graphene-enabled active metalens.

Graphene-based terahertz (THz) metasurfaces have the advantages of ultra-small thickness, electrical tunability, and fast tuning speed. However, many such structures suffer low efficiency, especially for transmissive devices. Here we propose a hybrid structure for focusing THz waves with tunability and enhanced focusing efficiency, which is composed of a graphene-loaded metallic metasurface sandwiched by two mutually orthogonal gratings. Experimental results show that due to the multi-reflection between the metasurface layer and the grating layer, the focusing efficiency is enhanced by 1.8 times, and the focal length of the metalens is increased by 0.61 mm when the applied gate voltage on the graphene is increased from 0 V to 1.4 V. We hope the proposed structure may open a new avenue for reconfigurable THz metasurfaces with high efficiencies.

Recent Progress of Two‐Dimensional Metal‐Organic Frameworks and Their Derivatives for Oxygen Evolution Electrocatalysis

AbstractThe development of high‐performance transition metal−based electrocatalysts for the oxygen evolution reaction (OER) is paramount for electrochemical secondary metal‐air batteries and water splitting. Two‐dimensional (2D) metal‐organic framework (MOF) nanosheets have recently emerged as a novel class of efficient electrocatalysts for OER, due to a high specific surface area, ultrasmall thickness and abundance of active sites. Here, we summarize recent progress in the preparation and characterization of 2D transition metal−based MOFs (e. g. Ni, Co and Cu), as well as their composites and derivatives, including metals/alloys, metal oxides/chalcogenides and metal phosphides/hydroxides, as OER electrocatalysts reported over the past several years. Design principles and preparation routes are presented. The performance of the electrocatalysts is directly compared in terms of overpotential (η) (thermodynamics) and electrocatalytic current density (kinetics), as well as operational stability (economics). Many of these materials exhibit superior catalytic activity compared to the noble metal−based catalysts such as RuO2 (η&lt;300 mV at 10 mA cm−2), and considerable stability with negligible decay with operation over several hours to days. Challenges and perspectives of applying 2D MOFs and their derivatives for OER electrocatalysis are also discussed.

One-step scalable preparation of graphene nanosheets and high-thermal-conductivity flexible graphene films

It is well known that graphene nanosheets (GNSs) have many excellent properties. However, it has been a difficult thing to exfoliate graphite into GNSs in a controllable and scalable manner. In this research, a new strategy named xylitol-assisted ball milling exfoliation (XABME) was developed for the scalable preparation of GNSs. The experimental results characterized by a series of measurements showed that GNSs were successfully exfoliated by the XABME strategy. The structure of the prepared nanosheets was featured by large lateral size and ultra-small thickness. Furthermore, the prepared GNSs easily achieved high production yield (≈54%). Lastly, the as-obtained GNSs and cellulose nanofibers (CNF) were compounded to form some nanomaterial films. The prepared films exhibited excellent flexibility and higher thermal conductivity, with the in-plane thermal conductivity of 90 wt% GNS film (8.0 W/(m·K)) being 11.4 times higher than that of the film without GNSs. This shows that GNSs could effectively enhance the thermal conductivity of the CNF matrix and indicate that these prepared films have great potentials in the thermal management of portable mobile devices.

Enabling Ultrathin Metamaterial Absorbers with Narrow Slits

AbstractMetamaterial absorbers (MAs) consisting of subwavelength units offer flexible design freedom and prominent advantages over traditional absorbers. Here, it is found that narrow slits provide the MAs a significant passageway to control the absorption behavior and obtain an ultrasmall thickness. As narrowing the slits in an MA gradually, two effects appear in turn, of which the former is that the slits help the localized energy leak away from the resonant units to balance the material absorption and radiation leakage rates and sustain perfect absorption, and the latter is that acting as a capacitor, the slits red‐shift the absorption peak. A record ultrathin microwave MA with a thickness of only 1/474 of the working wavelength is demonstrated. Colossal electric field is excited inside ultranarrow slits by the assistance of localized resonance in collecting the incident wave. The finding can be extended to other frequencies, and is fascinating for some areas requiring ultrathin absorption structures or strong interaction between waves and matters.

Potentiometric Hydrogen Sensing of Ultrathin Highly-Ordered SnO2 Films

Introduction The sensing performance of mixed-potential gas sensors is highly dependent on the electrode microstructure. Recently, much effort has been made to improve the sensor performance by engineering of the electrode microstructure [1, 2]. Nevertheless, the different microstructure parameters, such as thickness, porosity, and three phase boundary (TPB), contribute jointly to the sensing response, and their respective contributions are usually difficult to identify. In order to shed light on the role of TPB, it is crucial to minimize the influence of the diffusion-reaction process occurring inside the electrode, which could be achieved by using a very thin electrode. Moreover, a highly-ordered electrode morphology may help obtain well-defined TPB. Herein, we fabricated sub-micron thick ordered SnO2 sensing electrodes on YSZ substrate by employing a Polystyrene (PS) sphere-template method [3]. Three sensors were obtained by using PS spheres of different diameters in order to vary the TPB density. The gas sensing characteristics of the sensors were systematically studied. The sensing behavior was discussed in relation to the electrode microstructure. Sensor fabrication and characterization As depicted in Figure 1, ultrathin highly-ordered porous film sensors were prepared by using PS sphere templates in 200 nm, 500 nm and 1000 nm diameters. SEM, TEM and AFM images of SnO2 porous film electrodes were presented in Figure 2. Periodically ordered films of inverse opal structure were observed, with uniform circular pore openings and interconnected walls as the skeleton. Each film was porous and a homogenous assembly of 10-20 nm sized particles. The wall height was roughly half of the PS sphere size, which increased from 121 nm to 248 nm and 448 nm for the three PF film electrodes. Sensing performance Figure 3a and b show the response values and response time of the three PF sensors as a function of hydrogen concentration at 500°C. Obviously, the response significantly increased, i.e., became more negative, with decreasing template diameters, while the response time of the three sensors was generally rather close to each other, with a value of 4.5 s-6 s for 500 ppm H2 at 500°C. Figure 3c displays the cross-sensitivities of the PF sensors to 100 ppm various gases at 450°C. The PF sensors exhibited much poorer H2 selectivity than regular thick film sensors [4].The ultra-small film thickness and porous nature of the PF SE are highly favorable for the gas transport from the gas phase to the TPB. The three PF sensors exhibited very close response time despite their minor difference in the film thickness (in the order of hundreds of nanometer), suggesting absence of significant electrode process and of large H2 concentration reduction. This may allow us to study the effect of the TPB density on the sensing response. The TPB length was thus estimated for the PF sensors. Clearly, the TPB density values increased with the decrease of the PS template diameter. It can also be seen that for each H2 concentration, the response indeed increased (became more negative) monotonically with increasing TPB density (Figure 4). It should be noted, however, that the ultra-thin film electrode was disadvantageous to the selectivity. To achieve good overall sensing performance, e.g., fast response kinetics, large response, and high selectivity, careful tuning of the film thickness and TPB density would be demanded.

Microscale Generation of Entangled Photons without Momentum Conservation.

We report, for the first time, the observation of spontaneous parametric down-conversion (SPDC) free of phase matching (momentum conservation). We alleviate the need to conserve momentum by exploiting the position-momentum uncertainty relation and using a planar geometry source, a 6 μm thick layer of lithium niobate. Nonphase-matched SPDC opens up a new platform on which to investigate fundamental quantum effects but it also has practical applications. The ultrasmall thickness leads to a frequency spectrum an order of magnitude broader than that of phase-matched SPDC. The strong two-photon correlations are still preserved due to energy conservation. This results in ultrashort temporal correlation widths and huge frequency entanglement. The studies we make here can be considered as the initial steps into the emerging field of nonlinear quantum optics on the microscale and nanoscale.