Temperature-Dependent Paracrystalline Nucleation in Atomically Disordered Diamonds.

Atomically disordered diamonds with medium-range order realized in recent experiments extend our knowledge of atomic disorder in materials. However, the current understanding of amorphous carbons cannot answer why paracrystalline diamond (p-D) can be formed inherently different from other tetrahedral amorphous carbons (ta-Cs), and the emergence of p-D seems to be easily hindered by inappropriate temperatures. Herein, we performed atomistic-based simulations to shed light on temperature-dependent paracrystalline nucleation in atomically disordered diamonds. Using metadynamics and two carefully designed collective variables, reversible phase transitions among different ta-Cs can be presented under different temperatures, evidenced by corresponding local minima on the free energy surface and reaction path along the free energy gradient. We found that p-D is preferred in a narrow range of temperatures, which is comparable to real experimental temperatures under the Arrhenius framework. The insights and related methods should open up a perspective for investigating other amorphous carbons.

Strain Engineering of Ion-Coordinated Nanochannels in Nanocellulose.

Expanding the interlayer spacing plays a significant role in improving the conductivity of a cellulose-based conductor. However, it remains a challenge to regulate the cellulose nanochannel expanded by ion coordination. Herein, starting from multiscale mechanics, we proposed a strain engineering method to regulate the interlayer spacing of the cellulose nanochannels. First-principles calculations were conducted to select the most suitable ions for coordination. Large-scale molecular dynamics simulations were performed to reveal the mechanism of interlayer spacing expansion by the ion cross-linking. Combining the shear-lag model, we established the relationship between interfacial cross-link density and interlayer spacing of an ion-coordinated cellulose nanochannel. Consequently, fast ion transport and current regulation were realized via the strain engineering of nanochannels, which provides a promising strategy for the current regulation of a cellulose-based conductor.

Anisotropic Fracture of Two-Dimensional Ta2NiSe5.

Anisotropic two-dimensional materials present a diverse range of physical characteristics, making them well-suited for applications in photonics and optoelectronics. While mechanical properties play a crucial role in determining the reliability and efficacy of 2D material-based devices, the fracture behavior of anisotropic 2D crystals remains relatively unexplored. Toward this end, we herein present the first measurement of the anisotropic fracture toughness of 2D Ta2NiSe5 by microelectromechanical system-based tensile tests. Our findings reveal a significant in-plane anisotropic ratio (∼3.0), accounting for crystal orientation-dependent crack paths. As the thickness increases, we observe an intriguing intraplanar-to-interplanar transition of fracture along the a-axis, manifesting as stepwise crack features attributed to interlayer slippage. In contrast, ruptures along the c-axis surprisingly exhibit persistent straightness and smoothness regardless of thickness, owing to the robust interlayer shear resistance. Our work affords a promising avenue for the construction of future electronics based on nanoribbons with atomically sharp edges.

Biomimetic Ultratough, Strong, and Ductile Artificial Polymer Fiber Based on Immovable and Slidable Cross-links.

It remains a challenge to artificially fabricate fibers with the macroscopic mechanical properties and characteristics of spider silk. Herein, a covalently cross-linked double-network strategy was proposed to disrupt the inverse relation of strength and toughness in the fabrication of ultratough and superstrong artificial polymer fibers. Our design utilized a strong fishnet-like structure based on immovable cellulose nanocrystal cross-links to mimic the function of the ß-sheet nanocrystallites and a slidable mechanically interlocked network based on polyrotaxane to imitate the dissipative stick-slip motion of the ß-strands in spider silk. The resultant fiber exhibited superior mechanical properties, including gigapascal tensile strength, a ductility of over 60%, and a toughness exceeding 420 MJ/m3. The fibers also showed robust biological functions similar to those of spider silks, demonstrating mechanical enhancement, energy absorption ability, and shape memory. A composite with our artificial fibers as reinforcing fibers exhibited remarkable tear and fatigue resistance.

Simultaneously Strengthening and Toughening All-Natural Structural Materials via 3D Nanofiber Network Interfacial Design.

Constructing structural materials from sustainable raw materials is considered an efficient way to reduce the potential threat posed by plastics. Nevertheless, challenges remain regarding combining excellent mechanical and thermal properties, especially the balance of strength and toughness. Here, we report a 3D nanofiber network interfacial design strategy to strengthen and toughen all-natural structural materials simultaneously. The introduced protonated chitosan at the interface between the surface oxidized 3D nanonetwork of bacterial cellulose forms the interfacial interlocking structure of nanonetworks, achieving a robust physical connection and providing enough physical contact sites for chemical crosslinking. The obtained sustainable structural material successfully integrates excellent mechanical and thermal properties on the nanoscale of cellulose nanofibers, such as light weight, high strength, and superior thermal expansion coefficient. The relationship between structural design and comprehensive mechanical property improvement is analyzed in detail, providing a universal perspective to design sustainable high-performance structural materials from nanoscale building blocks.

Bioinspired Impact-Resistant and Self-Monitoring Nanofibrous Composites.

Lightweight and impact-resistant materials with self-monitoring capability are highly desired for protective applications, but are challenging to be artificially fabricated. Herein, a scalable-manufactured aramid nanofiber (ANF)-based composite combining these key properties is presented. Inspired by the strengthening and toughening mechanisms relying on recoverable interfaces commonly existing in biological composites, mechanically weak but dense hydrogen bonds are introduced into the ANF interfaces to achieve simultaneously enhanced tensile strength (300 MPa), toughness (55 MJ m-3 ), and impact resistance of the nanofibrous composite. The achieved mechanical property combination displays attractive advantages compared with that of most of previously reported nanocomposites. Additionally, the nanofibrous composite is designed with a capability for real-time self-monitoring of its structural safety during both quasi-static tensile and dynamic impact processes, based on the strain/damage-induced resistance variations of a conductive nanowire network inside it. These comprehensive properties enable the present nanofibrous composite with promising potential for protective applications.

Micromechanical Landscape of Three-Dimensional Disordered Graphene Networks.

Disordered carbons can be considered under the modeling framework of disordered graphene networks (DGNs) due to the continuous three-dimensional connectivity and high graphitization. Correlating microstructures and mechanical behaviors of DGNs to their topology is pivotal to revealing more intrinsic features hidden by disorder. Herein, starting from basic deformations and topology, we investigate DGNs with various densities to explore their micromechanical landscape. Both the tension and shear of DGNs exhibit prolonged plastic platforms through local tearing of microstructures. However, compression displays special plastic damages of forming kinklike puckers and sp3-bonded carbon, resulting in a tension-compression asymmetry of DGNs. Out-of-plane topological defects contribute to the main negative-curvature topology in deformed DGNs. Moreover, there are novel scaling laws where both the Young's modulus and strength (logarithms) follow an inversely proportional scaling with respect to average angular defects. Ashby charts demonstrate that the mechanical properties of DGNs can reach the theoretical limit region, surpassing those of most conventional materials.

Bio-Inspired Lotus-Fiber-like Spiral Hydrogel Bacterial Cellulose Fibers.

Hydrogel materials with high water content and good biocompatibility are drawing more and more attention now, especially for biomedical use. However, it still remains a challenge to construct hydrogel fibers with enough strength and toughness for practical applications. Herein, we report a bio-inspired lotus-fiber-mimetic spiral structure hydrogel bacterial cellulose fiber with high strength, high toughness, high stretchability, and energy dissipation, named biomimetic hydrogel fiber (BHF). The spiral-like structure endows BHF with excellent stretchability through plastic deformation and local failure, assisted by the breaking-reforming nature of the hydrogen bonding network among cellulose nanofibers. With the high strength, high stretchability, high energy dissipation, high hydrophilicity, porous structure, and excellent biocompatibility, BHF is a promising hydrogel fiber for biomedicine. The outstanding stretchability and energy dissipation of BHF allow it to absorb energy from the tissue deformation around a wound and effectively protect the wound from rupture, which makes BHF an ideal surgical suture.

Formation and topological structure of three-dimensional disordered graphene networks.

Disordered graphene networks (DGNs) can be regarded as the three-dimensional (3D) assembly of graphene-like fragments at the nanoscale, in which some intrinsic topological features are usually hidden in these formless fragments without clear understanding. Although some high-resolution structural patterns have been observed in pyrolytic carbons and flash graphene experimentally, it is still hard to characterize the topology and texture of DGNs considering continuous 3D connectivity. Toward this end, starting from the annealing process, we herein performed molecular dynamics simulations to investigate the formation and topological structure of DGNs. Three typical stages are found during the formation of DGNs, that is, the formation of polyaromatic fragments, formation of a disordered framework, and further graphitization. The topology of the obtained DGNs was then investigated, including topological defects, stacking behavior, and global curvature. Several typical in-plane and out-of-plane topological defects are found to connect the 3D network of graphene-like layers. The computed X-ray diffraction and angular defects demonstrate that a high-density DGN tends to form a randomly stacked structure with more connections, while a low-density DGN exhibits more bowl-shaped layers and a less distorted curvature. At low annealing temperatures, the local curvature of DGNs is highly distorted, and the structure seems to lack graphitization compared to high-temperature ones.

Anomalously low friction of confined monolayer water with a quadrilateral structure.

In this work, we explored how the structure of monolayer water confined between two graphene sheets is coupled to its dynamic behavior. Our molecular dynamics simulations show that there is a remarkable interrelation between the friction of confined water with two walls and its structure under extreme confinement. When the water molecules formed a regular quadrilateral structure, the friction coefficient is dramatically reduced. Such a low-friction coefficient can be attributed to the formation of long-range ordered hydrogen bond network, which not only decreases the structure corrugation in the direction perpendicular to the walls but also promotes the collective motion of the confined water. The regular quadrilateral structure can be formed only if the number density of confined water falls within a certain range. Higher number density results in larger structure corrugations, which increases the friction, while smaller number density leads to an irregular hydrogen bond network in which the collective motion cannot play the role. We demonstrated that there are four distinct stages in the diagram of the friction coefficient vs the number density of confined water. This research clearly established the connection between the dynamic characteristics of confined monolayer water and its structure, which is beneficial to further understand the mechanism of the high-speed water flow through graphene nanocapillaries observed in recent experiments.

Structural and dynamic characteristics in monolayer square ice.

When water is constrained between two sheets of graphene, it becomes an intriguing monolayer solid with a square pattern due to the ultrahigh van der Waals pressure. However, the square ice phase has become a matter of debate due to the insufficient experimental interpretation and the slightly rhomboidal feature in simulated monolayer square-like structures. Here, we performed classical molecular dynamics simulations to reveal monolayer square ice in graphene nanocapillaries from the perspective of structure and dynamic characteristics. Monolayer square-like ice (instantaneous snapshot), assembled square-rhombic units with stacking faults, is a long-range ordered structure, in which the square and rhombic units are assembled in an order of alternative distribution, and the other rhombic unit forms stacking faults (polarized water chains). Spontaneous flipping of water molecules in monolayer square-like ice is intrinsic and induces transformations among different elementary units, resulting in the structural evolution of monolayer square ice in dynamics. The existence of stacking faults should be attributed to the spontaneous flipping behavior of water molecules under ambient temperature. Statistical averaging results (thermal average positions) demonstrate the inherent square characteristic of monolayer square ice. The simulated data and insight obtained here might be significant for understanding the topological structure and dynamic behavior of monolayer square ice.

Superheating of monolayer ice in graphene nanocapillaries.

The freezing and melting of low-dimensional materials, either via a first-order phase transition or without any discontinuity in thermodynamic, still remain a matter of debate. Melting (superheating) in two-dimensional (2D) ice is fundamentally different from that in bulk counterpart. Here, we perform comprehensive molecular dynamics simulations of the superheating of monolayer ice in graphene nanocapillaries to understand the nature of melting transition in 2D water/ice. We find four different superheating (melting) scenarios can happen in the superheating of monolayer square-like ice, which are closely related to the lateral pressure and the channel width. The anomalous two-stage melting transition with arisen coexistence phase is found, which reveals the unknown extraordinary characteristics of melting in 2D water/ice. Under ultrahigh lateral pressure, the intermediate monolayer triangular amorphous ice will be formed during the superheating of monolayer square-like ice with both continuous-like and first-order phase transitions. Whereas, under low lateral pressure, the melting in monolayer square-like ice manifests typical discontinuity with notable hysteresis-loop in potential energy during the heating/cooling process. Moreover, we also find that highly puckered monolayer square-like ice can transform into bilayer AB-stacked amorphous ice with square pattern in the superheating process. The superheating behavior under high lateral pressure can be partly regarded as the compression limit of superheated monolayer water. The intrinsic phenomena in our simulated superheating of monolayer ice may be significant for understanding the melting behavior in 2D water/ice.

Shape-Controlled Deterministic Assembly of Nanowires.

Large-scale, deterministic assembly of nanowires and nanotubes with rationally controlled geometries could expand the potential applications of one-dimensional nanomaterials in bottom-up integrated nanodevice arrays and circuits. Control of the positions of straight nanowires and nanotubes has been achieved using several assembly methods, although simultaneous control of position and geometry has not been realized. Here, we demonstrate a new concept combining simultaneous assembly and guided shaping to achieve large-scale, high-precision shape controlled deterministic assembly of nanowires. We lithographically pattern U-shaped trenches and then shear transfer nanowires to the patterned substrate wafers, where the trenches serve to define the positions and shapes of transferred nanowires. Studies using semicircular trenches defined by electron-beam lithography yielded U-shaped nanowires with radii of curvature defined by inner surface of the trenches. Wafer-scale deterministic assembly produced U-shaped nanowires for >430,000 sites with a yield of ∼90%. In addition, mechanistic studies and simulations demonstrate that shaping results in primarily elastic deformation of the nanowires and show clearly the diameter-dependent limits achievable for accessible forces. Last, this approach was used to assemble U-shaped three-dimensional nanowire field-effect transistor bioprobe arrays containing 200 individually addressable nanodevices. By combining the strengths of wafer-scale top-down fabrication with diverse and tunable properties of one-dimensional building blocks in novel structural configurations, shape-controlled deterministic nanowire assembly is expected to enable new applications in many areas including nanobioelectronics and nanophotonics.

AB-stacked square-like bilayer ice in graphene nanocapillaries.

Water, when constrained between two graphene sheets and under ultrahigh pressure, can manifest dramatic differences from its bulk counterparts such as the van der Waals pressure induced water-to-ice transformation, known as the metastability limit of two-dimensional (2D) liquid. Here, we present result of a new crystalline structure of bilayer ice with the AB-stacking order, observed from molecular dynamics simulations of constrained water. This AB-stacked bilayer ice (BL-ABI) is transformed from the puckered monolayer square-like ice (pMSI) under higher lateral pressure in the graphene nanocapillary at ambient temperature. BL-ABI is a proton-ordered ice with square-like pattern. The transition from pMSI to BL-ABI is through crystal-to-amorphous-to-crystal pathway with notable hysteresis-loop in the potential energy during the compression/decompression process, reflecting the compression/tensile limit of the 2D monolayer/bilayer ice. In a superheating process, the BL-ABI transforms into the AB-stacked bilayer amorphous ice with the square-like pattern.

Buckling failure of square ice-nanotube arrays constrained in graphene nanocapillaries.

Graphene confinement provides a new physical and mechanical environment with ultrahigh van der Waals pressure, resulting in new quasi-two-dimensional phases of few-layer ice. Polymorphic transition can occur in bilayer constrained water/ice system. Here, we perform a comprehensive study of the phase transition of AA-stacked bilayer water constrained within a graphene nanocapillary. The compression-limit and superheating-limit (phase) diagrams are obtained, based on the extensive molecular-dynamics simulations at numerous thermodynamic states. Liquid-to-solid, solid-to-solid, and solid-to-liquid-to-solid phase transitions are observed in the compression and superheating of bilayer water. Interestingly, there is a temperature threshold (∼275 K) in the compression-limit diagram, which indicates that the first-order and continuous-like phase transitions of bilayer water depend on the temperature. Two obviously different physical processes, compression and superheating, display similar structural evolution; that is, square ice-nanotube arrays (BL-VHDI) will bend first and then transform into bilayer triangular AA stacking ice (BL-AAI). The superheating limit of BL-VHDI exhibits local maxima, while that of BL-AAI increases monotonically. More importantly, from a mechanics point of view, we propose a novel mechanism of the transformation from BL-VHDI to BL-AAI, both for the compression and superheating limits. This structural transformation can be regarded as the "buckling failure" of the square-ice-nanotube columns, which is dominated by the lateral pressure.

Discontinuous phase diagram of amorphous carbons.

The short-range order and medium-range order of amorphous carbons demonstrated in experiments allow us to rethink whether there exist intrinsic properties hidden by atomic disordering. Here we presented six representative phases of amorphous carbons (0.1-3.4 g/cm3), namely, disordered graphene network (DGN), high-density amorphous carbon (HDAC), amorphous diaphite (a-DG), amorphous diamond (a-D), paracrystalline diamond (p-D), and nano-polycrystalline diamond (NPD), respectively, classified by their topological features and microstructural characterizations that are comparable with experiments. To achieve a comprehensive physical landscape for amorphous carbons, a phase diagram was plotted in the sp3/sp2 versus density plane, in which the counterintuitive discontinuity originates from the inherent difference in topological microstructures, further guiding us to discover a variety of phase transitions among different amorphous carbons. Intriguingly, the power law, log(sp3/sp2) ∝ ρn, hints at intrinsic topology and hidden order in amorphous carbons, providing an insightful perspective to reacquaint atomic disorder in non-crystalline carbons.

Necklace-like Te-Au reticula platform with three dimensional hotspots Surface-Enhanced Raman Scattering (SERS) sensor for food hazards analysis.

In this work, we combined three-dimensional (3D) necklace-like Te-Au reticula as novel surface-enhanced Raman scattering (SERS) active substrates with oxidation-reduction displacement reactions to construct a molecular machine for SERS detection. The structurally tunable 3D necklace-like spatial structures generated more active 'hot spots' and thus enhanced the sensitivity of SERS signals. Besides, layers of ultrathin nanowires showed high sequence dependence that ensure the repeatability and abundant hotspots at interparticle gaps and guarantee the high SERS performance of the substrate. A better-localized surface plasmon resonance (LSPR) effect of the sensor was verified by finite-difference time-domain (FDTD) analysis in both Raman intensities and electromagnetic field distributions compared to the citrate-stabilized AuNPs and CTAB-protected AuNRs. The proposed strategy can also serve as a universally amplified and sensitive detection platform for monitoring different molecules, thus achieving an amplification detection of 3,3'-diethylthiatricarbocyanine iodide (DTTCI) are 1 nM and R6G with a low limit of detection of 1 pM. Especially, the intensity of the main vibration of R6G from 30 spots of SERS data with excellent reproducibility (relative standard deviation of 6.25 %). High selectivity and accuracy of the SERS sensor were proved by practical analysis melamine (MM) in milk with a linear calibration curve (R2 = 0.9962) and a limit of detection of 0.75 mg/kg. Our research provides a new perspective to construct 3D SERS sensor from integrated structural design.

Super-Stretchable and High-Energy Micro-Pseudocapacitors Based on MXene Embedded Ag Nanoparticles.

The advancement of aqueous micro-supercapacitors offers an enticing prospect for a broad spectrum of applications, spanning from wearable electronics to micro-robotics and sensors. Unfortunately, conventional micro-supercapacitors are characterized by low capacity and slopy voltage profiles, limiting their energy density capabilities. To enhance the performance of these devices, the use of 2D MXene-based compounds has recently been proposed. Apart from their capacitive contributions, these structures can be loaded with redox-active nanowires which increase their energy density and stabilize their operation voltage. However, introducing rigid nanowires into MXene films typically leads to a significant decline in their mechanical properties, particularly in terms of flexibility. To overcome this issue, super stretchable micro-pseudocapacitor electrodes composed of MXene nanosheets and in situ reconstructed Ag nanoparticles (Ag-NP-MXene) are herein demonstrated, delivering high energy density, stable operation voltage of ≈1 V, and fast charging capabilities. Careful experimental analysis and theoretical simulations of the charging mechanism of the Ag-NP-MXene electrodes reveal a dual nature charge storage mechanism involving ad(de)sorption of ions and conversion reaction of Ag nanoparticles. The superior mechanical properties of synthesized films obtained through in situ construction of Ag-NP-MXene structure show an ultra stretchability, allowing the devices to provide stable voltage and energy output even at 100% elongation.

Biomimetic Multimodal Receptors for Comprehensive Artificial Human Somatosensory System.

Electronic skin (e-skin) capable of acquiring environmental and physiological information has attracted interest for healthcare, robotics, and human-machine interaction. However, traditional 2D e-skin only allows for in-plane force sensing, which limits access to comprehensive stimulus feedback due to the lack of out-of-plane signal detection caused by its 3D structure. Here, a dimension-switchable bioinspired receptor is reported to achieve multimodal perception by exploiting film kirigami. It offers the detection of in-plane (pressure and bending) and out-of-plane (force and airflow) signals by dynamically inducing the opening and reclosing of sensing unit. The receptor's hygroscopic and thermoelectric properties enable the sensing of humidity and temperature. Meanwhile, the thermoelectric receptor can differentiate mechanical stimuli from temperature by the voltage. The development enables a wide range of sensory capabilities of traditional e-skin and expands the applications in real life.

Highly Regular Layered Structure via Dual-Spatially-Confined Alignment of Nanosheets Enables High-Performance Nanocomposites.

Assembling ultrathin nanosheets into layered structure represents one promising way to fabricate high-performance nanocomposites. However, how to minimize the internal defects of the layered assemblies to fully exploit the intrinsic mechanical superiority of nanosheets remains challenging. Here, a dual-scale spatially confined strategy for the co-assembly of ultrathin nanosheets with different aspect ratios into a near-perfect layered structure is developed. Large-aspect-ratio (LAR) nanosheets are aligned due to the microscale confined space of a flat microfluidic channel, small-aspect-ratio (SAR) nanosheets are aligned due to the nanoscale confined space between adjacent LAR nanosheets. During this co-assembly process, SAR nanosheets can flatten LAR nanosheets, thus reducing wrinkles and pores of the assemblies. Benefiting from the precise alignment (orientation degree of 90.74%) of different-sized nanosheets, efficient stress transfer between nanosheets and interlayer matrix is achieved, resulting in layered nanocomposites with multiscale mechanical enhancement and superior fatigue durability (100 000 bending cycles). The proposed co-assembly strategy can be used to orderly integrate high-quality nanosheets with different sizes or diverse functions toward high-performance or multifunctional nanocomposites.