Bioinspired stretchable molecular composites of 2D-layered materials and tandem repeat proteins.

Protein based composites, such as nacre and bone, show astounding evolutionary capabilities, including tunable physical properties. Inspired by natural composites, we studied assembly of atomistically thin inorganic sheets with genetically engineered polymeric proteins to achieve mechanically compliant and ultra-tough materials. Although bare inorganic nanosheets are brittle, we designed flexible composites with proteins, which are insensitive to flaws due to critical structural length scale (∼2 nm). These proteins, inspired by squid ring teeth, adhere to inorganic sheets via secondary structures (i.e., ß-sheets and α-helices), which is essential for producing high stretchability (59 ± 1% fracture strain) and toughness (54.8 ± 2 MJ/m3). We find that the mechanical properties can be optimized by adjusting the protein molecular weight and tandem repetition. These exceptional mechanical responses greatly exceed the current state-of-the-art stretchability for layered composites by over a factor of three, demonstrating the promise of engineering materials with reconfigurable physical properties.

Experimental Decoding and Tuning Electronic Friction of Si Nanotip Sliding on Graphene.

Due to the coupled contributions of adhesion and carrier to friction typically found in previous research, decoupling the electron-based dissipation is a long-standing challenge in tribology. In this study, by designing and integrating a graphene/h-BN/graphene/h-BN stacking device into an atomic force microscopy, the carrier density dependent frictional behavior of a single-asperity sliding on graphene is unambiguously revealed by applying an external back-gate voltage, while maintaining the adhesion unaffected. Our experiments reveal that friction on the graphene increases monotonically with the increase of carrier density. By adjusting the back-gate voltage, the carrier density of the top graphene layer can be tuned from -3.9 × 1012 to 3.5 × 1012 cm-2, resulting in a ∼28% increase in friction. The mechanism is uncovered from the consistent dependence of the charge density redistribution and sliding barrier on the carrier density. These findings offer new perspectives on the fundamental understanding and regulation of friction at van der Waals interfaces.

High-Sensitive Spatiotemporal Distribution Imaging of Compression Stresses Based on Time-Evolutional Responsiveness.

Mechanoresponsive materials have been studied to visualize and measure stresses in various fields. However, the high-sensitive and spatiotemporal imaging remain a challenging issue. In particular, the time evolutional responsiveness is not easily integrated in mechanoresponsive materials. In the present study, high-sensitive spatiotemporal imaging of weak compression stresses is achieved by time-evolutional controlled diffusion processes using conjugated polymer, capsule, and sponge. Stimuli-responsive polydiacetylene (PDA) is coated inside a sponge. A mechanoresponsive capsule is set on the top face of the sponge. When compression stresses in the range of 6.67-533 kPa are applied to the device, the blue color of PDA is changed to red by the diffusion of the interior liquid containing a guest polymer flowed out of the disrupted capsule. The applied strength (F/N), time (t/s), and impulse (F·t/N s) are visualized and quantified by the red-color intensity. When a guest metal ion is intercalated in the layered structure of PDA to tune the responsivity, the device visualizes the elapsed time (τ/min) after unloading the stresses. PDA, capsule, and sponge play the important roles to achieve the time evolutional responsiveness for the high-sensitive spatiotemporal distribution imaging through the controlled diffusion processes.

Elucidating Structural Disorder in Ultra-Thin Bi-Rich Bismuth Oxyhalide Photocatalysts.

Advancing the field of photocatalysis requires the elucidation of structural properties that underpin the photocatalytic properties of promising materials. The focus of the present study is layered, Bi-rich bismuth oxyhalides, which are widely studied for photocatalytic applications yet poorly structurally understood, due to high levels of disorder, nano-sized domains, and the large number of structurally similar compounds. By connecting insights from multiple scattering techniques, utilizing electron-, X-ray- and neutron probes, the crystal phase of the synthesized materials is allocated as layered Bi24O31X10 (X = Cl, Br), albeit with significant deviation from the reported 3D crystalline model. The materials comprise anisotropic platelet-shaped crystalline domains, exhibiting significant in-plane ordering in two dimensions but disorder and an ultra-thin morphology in the layer stacking direction. Increased synthesis pH tailored larger, more ordered crystalline domains, leading to longer excited state lifetimes determined via femtosecond transient absorption spectroscopy (fs-TAS). Although this likely contributes to improved photocatalytic properties, assessed via the photooxidation of benzylamine, increasing the overall surface area facilitated the most significant improvement in photocatalytic performance. This study, therefore, enabled both phase allocation and a nuanced discussion of the structure-property relationship for complicated, ultra-thin photocatalysts.

2D Ultrathin Titanium Nitride Nanosheets as Separator Coatings for Li-S Batteries.

Transition metal nitrides (TMNs) are affirmed to be an appealing candidate for boosting the performance of lithium-sulfur (Li-S) batteries due to their excellent conductivity, strong interaction with sulfur species, and the effective catalytic ability for conversion of polysulfides. However, the traditional bulk TMNs are difficult to achieve large active surface area and fast transport channels for electrons/ions simultaneously. Here, a 2D ultrathin geometry of titanium nitride (TiN) is realized by a facile topochemical conversion strategy, which can not only serve as an interconnected conductive platform but also expose abundant catalytic active sites. The ultrathin TiN nanosheets are coated on a commercial separator, serving as a multifunctional interlayer in Li-S batteries for hindering the polysulfide shuttle effect by strong capture and fast conversion of polysulfides, achieving a high initial capacity of 1357 mAh g-1 at 0.1 C and demonstrating a low capacity decay of only 0.046% per cycle over 1000 cycles at 1 C.

Novel Polytype of III-VI Metal Chalcogenides Nano Crystals Realized in Epitaxially Grown InTe.

III-VI metal chalcogenides have garnered considerable research attention as a novel group of layered van der Waals materials because of their exceptional physical properties and potential technological applications. Here, the epitaxial growth and stacking sequences of InTe is reported, an essential and intriguing material from III-VI metal chalcogenides. Aberration-corrected scanning transmission electron microscopy (STEM) is utilized to directly reveal the interlayer stacking modes and atomic structure, leading to a discussion of a new polytype. Furthermore, correlations between the stacking sequences and interlayer distances are substantiated by atomic-resolution STEM analysis, which offers evidence for strong interlayer coupling of the new polytype. It is proposed that layer-by-layer deposition is responsible for the formation of the unconventional stacking order, which is supported by ab initio density functional theory calculations. The results thus establish molecular beam epitaxy as a viable approach for synthesizing novel polytypes. The experimental validation of the InTe polytype here expands the family of materials in the III-VI metal chalcogenides while suggesting the possibility of new stacking sequences for known materials in this system.

Superlubric Sliding of Graphene Auto-Kirigami with Interfaces Containing Self-Assembled Stripe-Pattern Adsorbates.

Van der Waals heterostructures formed by stacked 2D materials show exceptional electronic, mechanical, and optical properties. Superlubricity, a condition where atomically flat, incommensurate planes of atoms result in ultra-low friction, is a prime example enabling, for example, self-assembly of optically visible graphene nanostructures in air via a sliding auto-kirigami process. Here, it is demonstrated that a subtle but ubiquitous adsorbate stripe structure found on graphene and graphitic surfaces in ambient conditions remains stable within the interface between twisted graphene layers as they slide over each other. Despite this contamination, the interface retains an exceptional superlubricious state with an estimated upper bound frictional shear strength of 10 kPa, indicating that direct atomic incommensurate contact is not required to achieve ambient superlubricity for 2D materials. The results suggest that any phenomena depending on 2D heterostructure interfaces such as exotic electronic behavior may need to consider the presence of stripe adsorbate structures that remain intercalated.

Black Phosphorus Molybdenum Disulfide Midwave Infrared Photodiodes with Broadband Absorption-Increasing Metasurfaces.

Black phosphorus (BP) has been established as a promising material for room temperature midwave infrared (MWIR) photodetectors. However, many of its attractive optoelectronic properties are often observable only at smaller film thicknesses, which inhibits photodetector absorption and performance. In this work, we show that metasurface gratings increase the absorption of BP-MoS2 heterojunction photodiodes over a broad range of wavelengths in the MWIR. We designed, fabricated, and characterized metasurface gratings that increase absorption at selected wavelengths or broad spectral ranges. We evaluated the broadband metasurfaces by measuring the room temperature responsivity and specific detectivity of BP-MoS2 photodiodes at multiple MWIR wavelengths. Our results show that broadband metasurface gratings are a scalable approach for boosting the performance of BP photodiodes over large spectral ranges.

Ultrahigh Lubricity between Two-Dimensional Ice and Two-Dimensional Atomic Layers.

Low temperature and high humidity conditions significantly degrade the performance of solid-state lubricants consisting of van der Waals (vdW) atomic layers, owing to the liquid water layer attached/intercalated to the vdW layers, which greatly enhances the interlayer friction. However, using low temperature in situ atomic force microscopy (AFM) and friction force microscopy (FFM), we unveil the unexpected ultralow friction between two-dimensional (2D) ice, a solid phase of water confined to the 2D space, and the 2D molybdenum disulfides (MoS2). The friction of MoS2 and 2D ice is reduced by more than 30% as compared to bare MoS2 and the rigid surface. The phase transition of liquid water into 2D ice under mechanical compression has also been observed. These new findings can be applied as novel frictionless water/ice transport technology in nanofluidic systems and promising high performance lubricants for operating in low temperature and high humidity environments.

2D Layered Materials for Fast-Charging Lithium-Ion Battery Anodes.

The development of electric vehicles has received worldwide attention in the background of reducing carbon emissions, wherein lithium-ion batteries (LIBs) become the primary energy supply systems. However, commercial graphite-based anodes in LIBs currently confront significant difficulty in enduring ultrahigh power input due to the slow Li+ transport rate and the low intercalation potential. This will, in turn, cause dramatic capacity decay and lithium plating. The 2D layered materials (2DLMs) recently emerge as new fast-charging anodes and hold huge promise for resolving the problems owing to the synergistic effect of a lower Li+ diffusion barrier, a proper Li+ intercalation potential, and a higher theoretical specific capacity with using them. In this review, the background and fundamentals of fast-charging for LIBs are first introduced. Then the research progress recently made for 2DLMs used for fast-charging anodes are elaborated and discussed. Some emerging research directions in this field with a short outlook on future studies are further discussed.

Comprehensive Insights into the Family of Atomically Thin 2D-Materials for Diverse Photocatalytic Applications.

2D materials with their fascinating physiochemical, structural, and electronic properties have attracted researchers and have been used for a variety of applications such as electrocatalysis, photocatalysis, energy storage, magnetoresistance, and sensing. In recent times, 2D materials have gained great momentum in the spectrum of photocatalytic applications such as pollutant degradation, water splitting, CO2 reduction, NH3 production, microbial disinfection, and heavy metal reduction, thanks to their superior properties including visible light responsive band gap, improved charge separation and electron mobility, suppressed charge recombination and high surface reactive sites, and thus enhance the photocatalytic properties rationally as compared to 3D and other low-dimensional materials. In this context, this review spot-lights the family of various 2D materials, their properties and their 2D structure-induced photocatalytic mechanisms while giving an overview on their synthesis methods along with a detailed discussion on their diverse photocatalytic applications. Furthermore, the challenges and the future opportunities are also presented related to the future developments and advancements of 2D materials for the large-scale real-time photocatalytic applications.

Interlayer Sodium Plating/Stripping in Van der Waals-Layered Quantum Dot Superstructure.

Assembling quantum dots (QDs) into van der Waals (vdW)-layered superstructure holds great promise for the development of high-energy-density metal anode. However, designing such a superstructure remains to be challenging. Here, a chemical-vapor Oriented Attachment (OA) growth strategy is proposed to achieve the synthesis of vdW-layered carbon/QDs hybrid superlattice nanosheets (Fe7 S8 @CNS) with a large vdW gap of 3 nm. The Fe7 S8 @CNS superstructure is assembled by carbon-coated Fe7 S8 (Fe7 S8 @C) QDs as building blocks. Interestingly, the Fe7 S8 @CNS exhibits two kinds of edge dislocations similar to traditional atom-layered materials, suggesting that Fe7 S8 @C QDs exhibit quasi-atomic growth behavior during the OA process. More interestingly, when used as host materials for sodium metal anodes, the Fe7 S8 @CNS shows the interlayer sodium plating/stripping behavior, which well suppresses Na dendrite growth. As a result, the cell with Fe7 S8 @CNS anode can keep stable cycling for 1000 h with a high Coulombic efficiency (CE) of ≈99.5% at 3.0 mA cm-2 and 3.0 mAh cm-2 . Noticeably, the Na@Fe7 S8 @CNS||Na3 V2 (PO4 )3 full cells can attain a capacity of 88.8 mAh g-1 with a retention of 97% after 1000 cycles at 1.0 A g-1 (≈8 C), showing excellent cycle stability for practical applications. This work enriches the vdW-layered QDs superstructure family and their application toward energy storage.

Fe-doped V2O5layered nanowire cathode material with high lithium storage performance.

As a lithium-ion battery cathode material with high theoretical capacity, the application of V2O5is limited by its unstable structure and low intrinsic conductivity. In this paper, we report a Fe doped V2O5nanowire with a layered structure of 200-300 nm diameter prepared by electrostatic spinning technique. The 3Fe-V2O5electrode exhibited a superb capacity of 436.9 mAh g-1in the first cycle when tested in the voltage range of 2.0-4.0 V at current density of 100 mA g-1, far exceeding its theoretical capacity (294 mAh g-1), and the high capacity of 312 mAh g-1was still maintained after 50 cycles. The superb performance is mainly attributed to its unique layered nanowire structure and the enhanced electrical conductivity as well as optimized structure brought by Fe-doping. This work made the homogeneous doping and nanosizing of the material easily achieved through electrostatic spinning technology, leading to an increase in the initial capacity of the V2O5cathode material and the cycling stability compared to the pure V2O5, which is an extremely meaningful exploration.

Structural and thermodynamic properties of quasi-2D Mo(1-x)Wx(S, Se, Te)2monolayer alloys: a statistical first principle study.

In this work, we report anab initiostudy of the structural and thermodynamic properties of two-dimensional transition-metal dichalcogenides (2D-TMDC) alloys, Mo(1-x)Wx(S, Se, Te)2, using the cluster expansion framework to compute the Helmholtz free energy of alloys as a function of alloy composition and temperature, in the framework of the generalized quasi-chemical approximation. We consider alloying only on the metal sublayer. Our results indicate a weak dependence of the structural properties (lattice constants, nearest-neighbor bond lengths, and layer width) on the alloy composition (i.e. concentrations of W and Mo atoms), in line with the very similar values of the atomic radii of Mo and W atoms. A stronger dependence on the chalcogen is obtained, a trend that reflects the larger variations in atomic radii among the three chalcogen species. As a function of composition, the structural parameters we examined show similar trends, with negligible bowing (i.e. deviations from a Vegard's law interpolation between end compounds), for the three alloys. Moreover, already at 300 K the behavior of these structural features as a function of composition is very similar to that of the standard-regular-solution (SRS) high-temperature limit. In contrast, the electronic band gaps of the the three alloys as a function of composition show small but significant bowing, as high as -1% to -2% near thex= 0.5 alloy composition. Similarly to the structural features, the band gaps attain the high-temperature SRS limit already at 300 K. Regarding thermodynamic properties, we obtain negative values of the internal energy of mixing for the three alloys over the full range of compositions. Therefore, the theoretical alloying phase diagram for the three alloys is featureless, with stability of a fully-mixed alloy at all temperatures and compositions, with no miscibility gap (hence no bimodal nor spinodal decomposition lines). The thermodynamic potentials (mixing internal energy, mixing entropy, and mixing free energy) reach the high-temperature limit at ∼1000 K, the temperature range of synthesis of 2D-TMDC alloys. These trends of structural and electronic properties of the 2D-TMDC alloys are due to the very similar atomic radii and the nearly identical coordination chemistry of Mo and W. Our results are in agreement with experimental work on the alloying of Mo and W atoms, for samples of Mo(1-x)WxS2monolayer alloys, that found that the random mixed alloy is the thermodynamically stable state for this alloy, with no segregation or phase separation.

Molecular beam epitaxy growth and scanning tunneling microscopy study of 2D layered materials on epitaxial graphene/silicon carbide.

Since the advent of atomically flat graphene, two-dimensional (2D) layered materials have gained extensive interest due to their unique properties. The 2D layered materials prepared on epitaxial graphene/silicon carbide (EG/SiC) surface by molecular beam epitaxy (MBE) have high quality, which can be directly applied without further transfer to other substrates. Scanning tunneling microscopy and spectroscopy (STM/STS) with high spatial resolution and high-energy resolution are often used to study the morphologies and electronic structures of 2D layered materials. In this review, recent progress in the preparation of various 2D layered materials that are either monoelemental or transition metal dichalcogenides on EG/SiC surface by MBE and their STM/STS investigations are introduced.

Heat Conductor-Insulator Transition in Electrochemically Controlled Hybrid Superlattices.

Designing materials with ultralow thermal conductivity has broad technological impact, from thermal protection to energy harvesting. Low thermal conductivity is commonly observed in anharmonic and strongly disordered materials, yet a microscopic understanding of the correlation to atomic motion is often lacking. Here we report that molecular insertion into an existing two-dimensional layered lattice structure creates a hybrid superlattice with extremely low thermal conductivity. Vibrational characterization and ab initio molecular dynamics simulations reveal strong damping of transverse acoustic waves and significant softening of longitudinal vibrations. Together with spectral correlation analysis, we demonstrate that the molecular insertion creates liquid-like atomic motion in the existing lattice framework, causing a large suppression of heat conduction. The hybrid materials can be transformed into solution-processable coatings and used for thermal protection in wearable electronics. Our work provides a generic mechanism for the design of heat insulators and may further facilitate the engineering of heat conduction based on understanding atomic correlations.

Resonant Grating-Enhanced Black Phosphorus Mid-Wave Infrared Photodetector.

Black phosphorus (BP) has emerged as a promising materials system for mid-wave infrared photodetection because of its moderate bandgap, high carrier mobility, substrate compatibility, and bandgap tunability. However, its uniquely tunable bandgap can only be taken advantage of with thin layer thicknesses, which ultimately limits the optical absorption of a BP photodetector. This work demonstrates an absorption-boosting resonant metal-insulator-metal (MIM) metasurface grating integrated with a thin-film BP photodetector. We designed and fabricated different MIM gratings and characterized their spectral properties. Then, we show that an MIM structure increased room temperature responsivity from 12 to 77 mA W-1 at 3.37 µm when integrated with a thin-film BP photodetector. Our results show that MIM structures simultaneously increase mid-wave infrared absorption and responsivity in a thin-film BP photodetector.

Atomic-Scale Mapping and Quantification of Local Ruddlesden-Popper Phase Variations.

The Ruddlesden-Popper (An+1BnO3n+1) compounds are highly tunable materials whose functional properties can be dramatically impacted by their structural phase n. The negligible differences in formation energies for different n can produce local structural variations arising from small stoichiometric deviations. Here, we present a Python analysis platform to detect, measure, and quantify the presence of different n-phases based on atomic-resolution scanning transmission electron microscopy (STEM) images. We employ image phase analysis to identify horizontal Ruddlesden-Popper faults within the lattice images and quantify the local structure. Our semiautomated technique considers effects of finite projection thickness, limited fields of view, and lateral sampling rates. This method retains real-space distribution of layer variations allowing for spatial mapping of local n-phases to enable quantification of intergrowth occurrence and qualitative description of their distribution suitable for a wide range of layered materials.

Maldistribution of Chemical Bond Strength Inducing Exceptional Anisotropy of Thermal Conductivity in Non-Layered Materials.

Currently, the efforts to find materials with high κ anisotropy ratios mainly focus on layered materials, however, the limited quantity and lower workability comparing to non-layered ones boost the exploration of non-layered materials with high κ anisotropy ratios. Here, taking PbSnS3 , a typical non-layered orthorhombic compound, as an example, we propose that maldistribution of chemical bond strength can lead to large anisotropy of κ in non-layered materials. Our result reveals that the maldistribution of Pb-S bonds lead to obvious collective vibrations of dioctahedron chain units, resulting in an anisotropy ratio up to 7.1 at 200 K and 5.5 at 300 K, respectively, which is one of the highest ever reported in non-layered materials and even surpasses many classical layered materials such as Bi2 Te3 and SnSe. Our findings can not only broaden the horizon for exploring high anisotropic κ materials but also provide new opportunities for the application of thermal management.

Encapsulating Metal Nanoparticles into a Layered Zeolite Precursor with Surface Silanol Nests Enhances Sintering Resistance.

Supported metal nanoparticles are used as heterogeneous catalysts but often deactivated due to sintering at high temperatures. Confining metal species into a porous matrix reduces sintering, yet supports rarely provide additional stabilization. Here, we used the silanol-rich layered zeolite IPC-1P to stabilize ultra-small Rh nanoparticles. By adjusting the IPC-1P interlayer space through swelling, we prepared various architectures, including microporous and disordered mesoporous. In situ scanning transmission electron microscopy confirmed that Rh nanoparticles are resistant to sintering at high temperature (750 °C, 6 hrs). Rh clusters strongly bind to surface silanol quadruplets at IPC-1P layers by hydrogen transfer to clusters, while high silanol density hinders their migration based on density functional theory calculations. Ultimately, combining swelling with long-chain surfactant and utilizing metal-silanol interactions resulted in a novel, catalytically active material-Rh@IPC_C22.