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Under cyclic loading, while graphene can suffer from catastrophic brittle fatigue failure, graphene oxide (GO) can be engineered to improve fatigue response and possibly ductile failure. Herein, we study the fatigue response of atomically thin GO using atomistic simulations complemented by atomic force microscopy-based experiments. Analysis of the damage and failure mechanisms demonstrated a notable role of functionalization degree and ratio on the fatigue resistance of GO. In the presence of defects, GO with a low functionalization degree (

The rapid development of two-dimensional (2D) materials has significantly broadened the scope of 2D science in both fundamental scientific interests and emerging technological applications, wherein the mechanical properties play an indispensably key role. Nevertheless, particularly challenging is the ultrathin nature of 2D materials that makes their manipulations and characterizations considerably difficult. Herein, thanks to the excellent flexibility of vanadium disulfide (VS2) sheets, their susceptibility to out-of-plane deformation is exploited to realize the controllable loading and enable the accurate measurements of mechanical properties. In particular, the Young's modulus is estimated to be 44.4 ± 3.5 GPa, approaching the lower limit for 2D transition metal dichalcogenides (TMDs). We further report the first measurement of thickness-dependent bending rigidity of VS2, which deviates from the prediction of the classical continuum mechanics theory. Additionally, a deeper understanding of the mechanics within two dimensions also facilitates the modulation of strain-coupled physics at the nanoscale. Our Raman measurements showed the Gruneisen parameters for VS2 were determined for the first time to be γE2g1 ≈ 0.83 and γA1g ≈ 0.32.

Semiconducting polymer nanoparticles (SPNs) possess many special photophysical and chemical properties. However, little research has been done on the potential of SPNs in laser technology. In this work, we present the ultrafast pulses generation at 1.5 and 2 μm through proposing the deposition of SPNs onto a side-polished fiber (SPF) platform as the nonlinear optical modulator. SPNs are designed and prepared through a combination of density functional theory and nanoreprecipitation method. The prepared SPNs not only exhibit strong linear absorption but also has nonlinear saturable absorption characteristics. Once SPF-SPNs saturable absorber (SA) is integrated into the laser cavity, ultrafast lasers of 1.5 and 2 μm can be achieved with high performance. Our results show that SAs based on the SPNs and SPF are promising nonlinear optical modulators for broadband ultrafast pulse generation.

Polymer single crystals continue to infiltrate emerging technologies such as flexible organic field-effect transistors because of their excellent translational symmetry and chemical purity. However, owing to the methodological challenges, direct imaging of the polymer chains folding direction resulting in sectorization of single crystals has rarely been investigated. Herein, we directly image the sectorization of polymer single crystals through anisotropic elastic deformation on the surface of macromolecular single crystals. A variant of friction force microscopy, in which the scanning direction of the probe tip is parallel with the cantilever axis, allows for high contrast imaging of the sectorization in polymer single crystals. The lateral deflection of the cantilever resulting from shear forces transverse to the scan direction shows a close connection with the in-plane components of the elastic tensor of the polymer single crystals, which is of a fundamentally different origin than the friction forces. This allows for fast, facile, and nondestructive characterization of the microstructure and in-plane elastic anisotropy of compliant crystalline materials such as polymers.

Assembling monolayers into a bilayer system unlocks the rotational free degree of van der Waals (vdW) homo/heterostructure, enabling the building of twisted bilayer graphene (tBLG) which possesses novel electronic, optical, and mechanical properties. Previous methods for preparation of homo/heterstructures inevitably leave the polymer residue or hexagonal boron nitride (h-BN) mask, which usually obstructs the measurement of intrinsic mechanical and surface properties of tBLG. Undoubtedly, to fabricate the designable tBLG with clean interface and surface is necessary but challenging. Here, we propose a simple and handy method to prepare atomically clean twisted bilayer graphene with controllable twist angles based on wetting-induced delamination. This method can transfer tBLG onto a patterned substrate, which offers an excellent platform for the observation of physical phenomena such as relaxation of moire pattern in marginally tBLG. These findings and insight should ultimately guide the designable packaging and atomic characterization of the two-dimensional (2D) materials.

Graphene with fascinating properties has been deemed as an excellent reinforcement for cementitious composites, enabling construction materials to be smarter, stronger, and more durable. However, some challenges such as dispersion issues and high costs, hinder the direct incorporation of graphene-based reinforcement fillers into cementitious composites for industrial production. The combination of graphene with conventional fibers to reinforce cement hence appears as a more promising pathway especially towards the commercialization of graphene for cementitious materials. In this review paper, a critical and synthetical overview on recent research findings of the implementation of graphene in fiber-reinforced cementitious composites was conducted. The preparation and characterization methods of hybrid graphene-fiber fillers are first introduced. Mechanical reinforcing mechanisms are subsequently summarized, highlighting the main contribution of nucleation effect, filling effect, interfacial bonding effect, and toughening effect. The review further presents in detail the enhancements of multifunctional properties of graphene-fiber reinforced cementitious composites, involving the interfacial properties, mechanical properties, durability, electrical conductivity, and electromagnetic interference shielding. The main challenges and future prospects are finally discussed to provide constructive ideas and guidance to assist with relevant studies in future.

This work combines experimental atomic force microscopy (AFM) and density functional theory (DFT) simulations to study oxidized-metal (oxidized copper & titanium) and 2D-material (graphene & MoS2) interfaces. Combining AFM and DFT allowed identifying the interfacial interaction and established a correlation between tribological behavior, interfacial charge distribution, and variations in the potential energy profile with sliding along the metal/2D-materials interfaces. The TiO2 (rutile) and CuO (cupric oxide) metal oxides were mostly found to chemisorb along the interface with the 2D-materials. Both the metal-oxide counter-surfaces (TiO2 and CuO) exhibited higher friction force and adhesion on graphene than on MoS2. The CuO surface was inferred to be copper rich based on comparison with DFT simulations. The interfacial electronic charge distribution and relative energy change were identified to strongly influence sliding and adhesive behavior between oxidized-metal/2D-material contacts when considering only electronic effects in the DFT simulations. More homogenous interfacial charge distribution/sharing and lower surface energy variation, as found on the MoS2 surfaces, were identified to lower friction and adhesion. Non-electronic effects not captured by simulations were found to likely dominate interfacial shear strength measurements experimentally. Therefore, MoS2 should be used in interfacial applications involving TiO2 and copper-rich CuO surfaces requiring lower adhesion and friction.

Silver nanoparticles (Ag NPs) have promising plasmonic properties, however, they are rarely used in biomedical applications because of their potent toxicity. Herein, an electron compensation effect from Au to Ag was applied to design safe Au@Ag core-shell NPs. The Ag shell thickness was precisely regulated to enable the most efficient electron enrichment in Ag shell of Au@Ag

Though pristine graphene exhibits remarkable mechanical and electronic properties, many electromechanical applications may come from chemically doping it with heteroatoms. The goal is to tune the atomic lattice and, in turn, modulate the electronic band structure of graphene – that may also affect the mechanical responses of the graphene sheet. Particularly essential for both practical applications and fundamental interests is to characterize the effect of chemical doping on the mechanical properties of graphene. Here we report graphene can maintain a large fraction of its pristine strength and stiffness after substituting boron for carbon atoms. Counter-intuitively, boron doping can ameliorate the brittle nature of the original lattice by deflecting the cracks and enabling damage-tolerant behaviors. We further offer a direct mapping between the Raman spectra and the measured mechanical performances that can show the relationship between doping structure and mechanical properties of graphene. This work offers important implications for the rational design of graphene-based systems that require chemical modifications and also utilize the mechanics of graphene.

As an essential component of flexible optoelectronic devices, transparent conductive films made of silver nanowire (AgNW) have attracted wide attention due to the extraordinary optical, electrical and mechanical properties. However, the application of AgNW coating still faces some challenges to be overcome including large contact resistance and poor durability. Here, we induce insulating graphene oxide over silver nanowire network through solution process to modify the electrical property and provide a protective layer. Strong interaction with substrates reducing the contact resistance of AgNW junctions and extra conductive channels of graphene oxide sheets contributes to the dramatic enhancement in electric property as well as durability. The resulting coating exhibits superior and uniform optoelectronic performances (sheet resistance of ~ 38 Ω·sq−1 with 91% transmittance at 550 nm), outstanding stability in harsh environments, strong adhesion, and excellent mechanical flexibility after 3,000 bending cycles at a bending radius of 2.0 mm, which imply the promising application prospects in flexible optoelectronics.

High filler loading in polymer alone cannot meet the increasing requirements of the electronic industry, so the hybrid fillers with unique advantages have been developed. In this work, chemical exfoliation and mechanical mixing are combined to disperse hybrid fillers of graphene nanoplatelets (GNPs) and boron nitride (BN) nanoplatelets inside short carbon fibers (SCF) based epoxy matrix. Such surface modified hybrid fillers/epoxy nanocomposites exhibit a high thermal conductivity of ca. 0.8 W m−1 K−1 and an electrical volume resistivity of ca. 6.41 × 1015 Ω cm at a low filler loading of 3 wt% SCF + 5 wt% modified GNP-BN. Furthermore, the thermal stability, heat dissipation and absorption properties are enhanced for the ternary hybrid fillers/epoxy nanocomposites. Overall, such a system offers an outstanding approach for the electronic industry to enhance the thermal conductivity without compromising the electrical insulation property of epoxy materials.

Many three-dimensional (3D) nanomaterial-based assemblies need incorporation with elastomers to attain stretchability-that also compromises their pristine advantages for functional applications. Here, we show the design of elastomer-free, highly deformable silver nanowire (AgNW) conductors through dip-coating AgNWs on a 3D polymeric scaffold and following a simple triaxial compression approach. The resulting 3D AgNW conductors exhibit good stability of resistance under multimodal deformation, such as stretching, compressing, and bending as well as comparable conductivity with those elastomer-based ones. Moreover, the buckled structures endow our 3D conductors with novel negative Poisson's ratio behavior, which can offer good comfortability to curvilinear surfaces. The combination of mechanical properties, conductive performance, and unique deformation characteristics can satisfy multiscale conformal mechanics with a soft, curvilinear human body.

As one typical representative of van der Waals structures, multilayered graphene sheets (MLGSs) have attracted much attention in recent years due to their unusual properties and new phenomena. Due to the ultralow interlayer interaction, these materials may easily encounter mechanical failure and subsequently the malfunction of devices. It becomes essential to clarify failure modes and the beneath mechanism. Through an inverse blister test, bending induced failure (local buckling) of MLGSs is observed experimentally. Theoretical modeling and molecular dynamics simulations are then conducted to investigate the bending behavior of MLGSs without any edge constrain. We demonstrate three failure modes, including interlayer shearing, rippling and kink buckling/delamination. Compared with previous studies, we find the occurrence of failure is length and thickness dependent. Short sheets prefer to continuous interlayer shearing, long and thin/thick sheets prefer to snap-through sliding, while long and medium-thick sheets prefer to kink buckling. We propose failure criteria and draw a phase diagram to predict the failure modes. Furthermore, we analytically deduce the bending stiffness of MLGSs before the failure which is also found to be length dependent that below a critical length (∼9.7 nm), it decreases dramatically. Our results not only shed new light for understanding the bending behavior of MLGS, but also extend to other heterostructures, paving the way for potential implications of 2-dimensional materials.

Cyclic loading leads to interfacial fatigue of a graphene/polymer contact and multimode fracture of the graphene., Graphene is often in contact with other materials through weak van der Waals (vdW) interactions. Of particular interest is the graphene-polymer interface, which is constantly subjected to dynamic loading in applications, including flexible electronics and multifunctional coatings. Through in situ cyclic loading, we directly observed interfacial fatigue propagation at the graphene-polymer interface, which was revealed to satisfy a modified Paris’ law. Furthermore, cyclic loading through vdW contact was able to cause fatigue fracture of even pristine graphene through a combined in-plane shear and out-of-plane tear mechanism. Shear fracture was found to mainly initiate at the fold junctions induced by cyclic loading and propagate parallel to the loading direction. Fracture mechanics analysis was conducted to explain the kinetics of an exotic self-tearing behavior of graphene during cyclic loading. This work offers mechanistic insights into the dynamic reliability of graphene and graphene-polymer interface, which could facilitate the durable design of graphene-based structures.

Biocompatible neural interfaces hold great promise for treating neurological disorders and enhancing the mental and physical ability of human beings. Most of the currently available neural interfaces are made from rigid, dense inorganic materials that cause tissue damage. We present supersoft multichannel electrodes by depositing gold layers on thin bacterial cellulose (BC) (Au-BC electrodes). The Young’s modulus of BC (EBC = 120 kPa) is between those of the brain tissue (Ebrain = 2.7–3.1 kPa) and the peripheral neural tissues (Eperipheral nerve = 580–840 kPa). The bending stiffness of the Au-BC electrodes corresponds to 1/5200 of Au-polyimide electrodes with the same layout. Furthermore, the Au-BC electrodes are highly durable (conductivity >95% after 100 cycles of 180° bending). In vivo recording of brain electric activity demonstrates the great potential of the Au-BC electrodes for neural interfacing applications.

The blister test has been extensively used as a simple and effective approach to measure the elastic modulus and the interface adhesion energy of two-dimensional nanomembrane. However, the conventional blister test model is commonly based on the Hencky solution in which the clamped boundary is assumed without consideration of sliding, and consequently, it can hardly obtain the stress distribution outside the blister region. Therefore, in this paper, the clamped boundary condition is removed, and the Hencky solution is extended based on the Lame solution to account for both the sliding displacement and the stress and strain fields outside the blister region. The expression of the extended Hencky solution is as simple as the original one, but it provides a more accurate description for both the blister configuration and the stress and strain fields of nanomembrane, which are proved by molecular dynamics (MD) simulations of graphene blister test. Our theoretical model is further validated by the experimental results regarding the blister test of a monolayer graphene membrane, where a higher accuracy can be observed in the interpretation of the data.

Due to their extraordinary mechanical properties, nanocarbon materials (e.g. carbon nanotube and graphene) are attracting great interests in the field of nanocomposites. One unique feature in nanocarbon-based nanocomposites is their intrinsically rich interface, allowing them to adapt the microstructures in response to external loading and, in turn, to stiffen themselves. This mechanical behavior, called responsive stiffening, was usually observed in biological materials such as bones and muscles. The mechanically responsive behaviors of nanocarbon-based materials are particularly exciting because the nanocarbon-enabled huge interface area offers opportunities to tune such stiffening performance while this interface advantage is not fully exploited yet. Here, we demonstrate stiffening behaviors in graphene oxide (GO)-based film materials in response to dynamic oscillations. Through a facile method of polymer content alteration and alkali treatment, the microstructure and interlayer interaction of GO films are modified, along with the resulted responsively stiffening performance. Based on polarized Raman spectra characterizations, we attribute the stiffening mechanism to the microstructural evolution of GO films during dynamic tension as well as the polymer chains alignment. Finally, we highlight the significantly improved static mechanical properties of GO film after a simple stiffening process. Our results not only aid in the development of biomimetic, adaptive materials, but provide a mechanical way for the design of high-performance nanocarbon-based nanocomposites.

As the world’s space agencies look to long duration spaceflight beyond low earth orbit, engineering materials in deep space flight will endure galactic cosmic ray irradiation, of which 85% is protons. Characterization of proton irradiation damage near the threshold displacement energy is required to understand the mechanisms behind performance degradation and the fluence dependent effects of a thermalized spectrum on surface sensitive tribological characteristics. Here, tribological degradation of a space-grade molybdenum disulfide lubricant exposed to low energy (500 eV) protons is investigated as a function of fluence. A 21% increased coefficient of friction and 86% increase in wear rate is measured at 1020 H / m 2 , and 170% increased CoF and 465% increased wear rate at 3·1023 H / m 2 . Associated softening and decreased stiffness is measured by nanoindentation. X-ray photoelectron spectroscopy and Raman spectroscopy identify the mechanism of tribological degradation as being the preferential removal of sulfur leading to a disordered and reactive non-stoichiometric MoS2-x surface with compromised tribological properties. Missions beyond low-earth orbit will be required to withstand GCR radiation, and it is not suggested that the density of radiation damage sustained will be acutely detrimental to MoS2 lubricants. Still, research missions should plan to characterize the magnitude of radiation damage effects.

In order to reduce the fiber crosstalk for the space division multiplexing (SDM), this paper proposes a novel multi-core few-mode fiber of composite refractive index profile and dual assistance structure. On the one hand, by adopt dual assistance of air-hole embedment and trench wrapping around all the seven cores, inter-core crosstalk is greatly reduced. On the other hand, a non-circularly symmetrical refractive index (RI) profile is innovatively proposed for the six outer-ring cores, which not only weakens the inter-mode coupling but also has a suppression effect on inter-core crosstalk. The finite element method (FEM) is used to analyze the fiber structure. In the case of transmitting six spatial modes, the minimum inter-mode effective RI difference ( Δ neff) between the linear polarization (LP) modes of the center core and between the spatial modes of the outer-ring core are greater than 0.5 × 10−3, the inter-core crosstalk of the sixth mode LP02 at 1550 nm is less than -66dB/100km, and the relative core multiplexing factor reaches 29.24. The characteristics of this structure are significantly better than that of current commercial optical fibers, promising broad application prospects in large-capacity SDM optical communication system.

It is fundamentally important to understand how the interlayer interaction of neighboring graphene sheets is influenced by chemical doping. Here we investigate the interlayer coupling of multilayer graphene doped with controlled boron content via the Raman-active in-plane shear mode. The experimental results reveal a remarkable decline in the interlayer shear modulus as boron content increases, which is a direct consequence of the enlarged interlayer spacing, further supported by the molecular dynamic (MD) simulations. Nanoindentation tests were conducted to clarify the influence of interlayer coupling behaviors on nanomechanical behaviors of boron-doped bilayer graphene. As the interlayer slippage is induced under shear deformations, the weakened shear resistance would lead to the reduced energy dissipation during sliding process. Our results provide valuable insight into fundamental mechanical properties of boron-doped graphene and its interfaces and potentially allows tailoring of interlayer coupling f...

Interface failure is a common phenomenon for conventional composite materials when subjected to repeated mechanical loads, and it tends to be critical for nanocomposites due to several orders of magnitude enhancement in interfacial area. Herein, the graphene/poly(methyl methacrylate) (PMMA) interface when subjected to cyclic loading conditions exhibits obvious mechanical degradation through interfacial sliding, which has received little attention yet. Through a joint study of experimental tests and molecular dynamics simulations, the interface weakening is attributed to the formation of graphene buckles that not only reduces the interfacial contact area but also impairs the overall interfacial load transfer. However, reminiscent of the shape memory effect that is commonly triggered by temperature, conformational transition at the interfaces exhibits remarkable mechanical recovery under a moderate thermal stimulus, manifested by the interface reconstruction activated by van der Waals (vdW) forces. These findings elucidate the complex interactions between matrix and nanostructures in composite materials under cyclic loading conditions, and control over this mechanism could provide guidelines upon chemical design through tailoring the interfacial adhesion for specific applications.

We studied the influence of sp2 clustering on resistive switching uniformity in Cu/amorphous carbon/Pt electrochemical metallization memory. Herein, a simple method was utilized to adjust the degree of sp2 clustering by changing compliance currents (CCs). The small sp2 clusters within the a-C layer were found to condense into larger clusters with increasing CCs because of the CC-dependent Joule heating effect. Raman spectra experimentally verified the increase of sp2 cluster diameter with increasing CCs. Importantly, a switching uniformity improvement can be obtained by increasing the degree of sp2 clustering. The enhanced local electric field around sp2 clusters can account for the reduction of the Cu conductive filament randomness and corresponding improvement of memory performance.

The development of electromagnetic interference (EMI) shielding materials is moving forward towards being lightweight and showing high-performance. Here, we report on lightweight silver nanowire (AgNW)/MXene hybrid sponges featuring hierarchical structures that are fabricated by a combination of dip-coating and unidirectional freeze-drying methods. The commercial melamine formaldehyde sponges (MF), designed with a buckled structure, are chosen as the template for coating with the AgNW layer (BMF/AgNW). Furthermore, the additional irregular honeycomb architecture composed of MXene assembled cell walls is introduced inside the BMF cell-matrix through unidirectional freeze-drying of MXene aqueous suspensions. Consequently, the BMF/AgNW presents a better EMI shielding effectiveness of 40.0 dB contributed by the conductive network and multiple reflections and scattering compared with the MF/AgNW. Eventually, the resulting AgNW/MXene hybrid sponge exhibits a higher EMI shielding effectiveness of 52.6 dB with a low density of 49.5 mg cm-3 compared with the BMF/AgNW due to synergetic effects of the AgNW and MXene both in conductivity and hierarchical structure. These results also provide a novel way to fabricate lightweight and conductive sponges as high-performance EMI shielding materials.

At micro- and nanoscales, the gas pressure load is generally simulated by the thermal motion of gas molecules. However, the pressure load can hardly be produced or controlled accurately, because the effects of the wall thickness and the atomic weight of the gas molecules are not taken into account. In this paper, we propose a universal gas molecules model for simulating the pressure load accurately at micro- and nanoscales, named mock gas molecules model. Six scale-independent parameters are established in this model, thus the model is applicable at both micro- and nanoscales. To present the validity and accuracy of the model, the proposed model is applied into the coarse-grained molecular dynamics simulation of graphene blister, and the simulation results agree well with experimental observations from the graphene blister test, indicating that the model can produce and control the pressure load accurately. Furthermore, the model can be easily implemented into many simulators for problems about the solid–gas interaction, especially for membrane gas systems.

Graphene exhibits properties of atomic thickness, high transparency, and high carrier mobility, which is highly desirable for a flexible transparent conductive material. However, the electronic properties of large-area chemical vapor deposition grown graphene film suffer from insulated polymer contaminations introduced by the transfer process and the easily cracked nature. Here, we report a preparation method of a transfer-medium-free large-area nanofiber-reinforced graphene (a-PAN/G) film simply by annealing the electrostatically spun polyacrylonitrile (PAN) nanofibers on the graphene film. The film could be free-standing on water and suspended in air with high transparency and enhanced electrical and mechanical properties compared to that of a monolayer graphene film. The flexible transparent a-PAN/G films were demonstrated as active materials for sensitive pressure sensors. The obtained pressure sensors demonstrate high sensitivity (44.5 kPa-1 within 1.2 kPa), low operating voltage (0.01-0.5 V), and excellent stability for 5500 loading-unloading cycles, revealing promising potential applications in wearable electronics.

Nanoblisters such as nanobubbles and nanotents formed by two-dimensional (2D) materials have been extensively exploited for strain engineering purposes as they can produce self-sustained, nonuniform in-plane strains through out-of-plane deformation. However, deterministic measure and control of strain fields in these systems are challenging because of the atomic thinness and unconventional interface behaviors of 2D materials. Here, we experimentally characterize a simple and unified power law for the profiles of a variety of nanobubbles and nanotents formed by 2D materials such as graphene and MoS_{2} layers. Using membrane theory, we analytically unveil what sets the in-plane strains of these blisters regarding their shape and interface characteristics. Our analytical solutions are validated by Raman spectroscopy measured strain distributions in bulged graphene bubbles supported by strong and weak shear interfaces. We advocate that both the strain magnitudes and distributions can be tuned by 2D material-substrate interface adhesion and friction properties.

Deterministic design of surface patterns has seen a surge of interests because of their wide applications in flexible and stretchable electronics, microfluidics, and optical devices. Recently, instability of bilayer systems has been extensively utilized by which micro-/nano-patterns of a film can be easily achieved through macroscopically deforming the underlying substrate. For a bilayer system with traditional thermostable substrates, the pattern morphology is only determined by initial strain mismatch of the two layers, and the realization of localized patterns appears to be particularly challenging because of the difficulties associated with manipulating inhomogeneous deformations. In this work, we exploit cross-linked polyethylene ( cPE), a shape memory polymer (SMP), as the flexible substrate for building micro-/nano-structures of sputtered gold films. We find that the shape memory effect can offer new dimensions for designing diverse and hierarchical surface structures by harnessing film thickness orheating time and by globally or locally controlling the thermal field. By combining those strategies, we further demonstrate versatile hierarchical, superimposed, and local surface patterns based on this cPE/gold (Au) system. Piezoresistive pressure sensors are assembled with the obtained patterned surface, which have high sensitivity, operational range, and cyclic stability. These results highlight the unique advantages of SMPs for building arbitrary surface patterns.

Carbon nanomaterials (e.g., carbon nanotubes and graphene) have been deemed as versatile building blocks to create a novel generation of nanocomposites desired for a variety of commercial applications. Different from that of the conventional fiber-based composites, the enormous interfacial areas, van der Waals forces dominated interface interactions as well as multiple scale load transfer mechanism would greatly impact the mechanical behaviors of carbon nanomaterials-based composites. Besides the widely concerned nanofiller-matrix interface, the filler-filler interface has to be considered in nanocomposites. The main challenge is how to monitor the load transfer process and evaluate load-bearing capability of fillers in composites. Here, we summarize the recent progress in experimental characterization of atomic-scale interface mechanics, and clarify its importance on the reinforcement of nanocomposites. We also highlight the significance of competed mechanism between intrinsic mechanical strength of nanofillers and interfacial shear effect, allowing the delicate design of nanocomposites that deliver desired properties.

Raman spectroscopy has been widely utilized to investigate the properties of graphene materials and defect effects due to external injection. We presented a detailed Raman spectroscopy study of boron-doped single-layer to six-layer graphene with three different concentrations of substitutional boron atoms as ∼0.16 wt. %, ∼0.48 wt. %, and ∼0.76 wt. %. The Raman signatures of G, 2D, and defect-dependent modes were illustrated. The properties of these modes were revealed with enhanced boron contents and increased layer number. The behaviors of defect-dependent modes reached a plateau when boron content was larger than 0.48 wt. % to show the saturation of interaction between boron and carbon atoms. These modes upshifted with increasing layer number because boron defects in diff ;erent layers interacted with each other by the cascade quenching. Our study provides a detailed investigation of how boron doping changed the properties of graphene layers by defect effects. The results will induce great potential for applications in optoelectronic devices.

There is increasing evidence in literature for significant improvements in both toughness and strength of graphene-based nanocomposites through engineering their nano-interfaces with hydrogen bonds (H-bonds). However, the underlying mechanical behaviors and properties of these H-bonded interfaces at the microscopic level were still not experimentally clarified and evaluated. Herein, this work reports a study on the interfacial stress transfer between a monolayer graphene and a commonly used poly(methyl methacrylate) (PMMA) matrix under pristine vdW and modified H-bonding interactions. A nonlinear shear-lag model considering friction beyond linear bonding was proposed to understand evolution of interfacial stresses and further identify key interfacial parameters (such as interfacial stiffness, strength, frictional stress and adhesion energy) with the aid of in situ Raman spectroscopy and atomic force microscopy. The present study can provide fundamental insight into the reinforcing mechanism and unique mechanical behavior of chemically modified graphene nano-interfaces and develop further a basis for interfacial optimal design of graphene-based high-performance nanocomposites.

A facile, effective and environmental friendly route was presented to prepare lipophilic graphene oxide (GO) derivates via the esterification reaction of the carboxylate salt of GO and 1-bromohexadecane in the presence of a phase-transfer reagent in water. The resultant long alkyl chains modified graphene oxide sheets (GO-HD) show the long-term and stable dispersion capability in many organic solvents. Successful grafting of long alkyl chains onto GO surfaces was confirmed through FTIR, XPS, TGA, UV–vis spectrum techniques. Moreover, we utilized the GO-HD as a reinforcing filler to prepare GO-HD/thermoplastic polyurethane (TPU) nanocomposites through solution casting method. The uniform distribution and good interfacial adhesion are expected for the GO-HD based nanocomposites due to the good compatibility between long alkyl chains of GO-HD fillers and TPU chains. Notably, tensile mechanical tests demonstrated that the GO-HD/TPU nanocomposites at low filler contents (≤2 wt%) exhibit higher modulus, ultimate tensile strength without compromising the intrinsic extensibility of TPU matrix as compared with the GO/TPU nanocomposites with same filler content. Further, in situ tensile-micro Raman spectroscopy tests were employed to monitor the load transfer process at a microscopic level, and revealed the improved load transfer efficiency in the GO-HD/TPU nanocomposites.

The van der Waals (vdW) force dominated interface between graphene and polymer matrix creates weak points in the mechanical sense. Chemical functionalization was expected to be an effective approach in transfer of the outstanding performance of graphene across multiple length scales up to the macroscopic level, due to possible improvements in the interfacial adhesion. However, published works showed the contradiction that improvements, insensitivity, or even worsening of macro-mechanical performance have all been reported in graphene-based polymer nanocomposites. Particularly central cause of such discrepancy is the variations in graphene/polymer interfacial chemistry, which is critical in nanocomposites with vast interfacial area. Herein, O3/H2O gaseous mixture was utilized to oxidize monolayer graphene sheet with controlled functionalization degrees. Hydrogen bonds (H bonds) are expected to form between oxidized graphene sheet/poly(methyl methacrylate) (PMMA) at the interface. On the basis of in situ tensile-micro Raman spectroscopy, the impacts of bonding types (vdW and H-bonds) on both key interfacial parameters (such as interfacial shear strength and critical length) and failure modes of graphene/PMMA nanocomposite were clarified for the first time at the microscopic level. Our results show that owing to improved interfacial interaction via H bonds, the interface tends to be stiffening and strengthening. Moreover, the mechanical properties of the functionalized graphene/PMMA interface will be set by the competition between the enhanced interfacial adhesion and the degraded elastic modulus of graphene, which was caused by structural defects in the graphene sheet during the functionalization process and could lead to catastrophic failure of graphene sheets in our experimental observation. Our results will be helpful to design various nanofiller-based nanocomposites with high mechanical performance.

ZnPc single-crystal nanobelts were grown by a physical vapor transport process with the length ranging from 20 to 150 μm and the width ranging from several tens of nanometers to several micrometers. Based on high crystalline ZnPc nanobelts, its single-crystal nanobelt transistors were realized. The field-effect mobility is as high as 0.75 cm2V−1s−1 with OTS modified SiO2 as dielectric, which is the highest value for the reported ZnPc devices. In addition, ZnPc nanobelt transistors show the excellently photosensitive properties with the high photoswitching ratio (|Ilight/Idark|) of 7.34 × 103 and the high photoresponsivity at 1.57 × 104 AW−1. These results indicate the future potential of ZnPc single-crystal transistors in organic electronic and optoelectronic applications.

The commercialized, low-cost, and lightweight glass fiber microwires have been shown as a new mask to simplify the fabrication of organic single-crystal nanowire transistors based on copper phthalocyanine (CuPc). The glass fiber is light weight so that the van der Waals force is capable of resisting the effect of gravity when the substrate is flipped over. In this case, the glass fiber mask need not be artificially fixed onto the substrate during metal deposition for electrode fabrication, so the device fabrication process can be simplified. With such a facile method, multiple organic single-crystal nanowire transistors can be fabricated at the same time, and the high mobility up to 0.7 cm $^{2}\text{V}^{{-1}}\text{s}^{{-1}}$ has been realized for CuPc nanowire transistors. Good stability has been also demonstrated. This method effectively improves the efficiency of devices preparation, showing the potential in large-scale fabrication of organic nanowire transistors. Meanwhile, it is favorable for the fundamental electrical studies of 1-D organic nanomaterials.

We demonstrate a novel solution-based assembly method using a writing brush to realize the controllable fabrication of highly-oriented and large-scale TCNQ single-crystal microwire arrays. The arrays can not only be grown on conventional rigid substrates, such as Si, Si/SiO2 and low-cost glass, but also on nonconventional substrates, which include flexible polyethylene terephthalate (PET), curved glass hemispheres and commercially available plastic contact lenses. Their morphology is optimized by tuning solution concentration, substrate temperature, brush type, inclination angles and pressure of the brush. The length of the microwire arrays can extend to the millimeter level, and their preferential orientation is perpendicular to the lengthwise direction of the brush hair. The coverage area of microwire arrays with a consistent orientation can reach 1.5 × 2.0 mm2 and the success ratio is as high as 93%. Based on these microwire arrays, devices on different substrates, including rigid Si/SiO2 and flexible PET, can be easily realized in one step. The anisotropic transport of TCNQ crystals is studied with respect to the concentration controlled morphology. All these results illustrate the broad application prospects of this facile writing-brush method in the growth of large-scale, high-quality organic micro/nanowires for integration into flexible organic semiconductor devices and circuits.

MXene-based materials have been widely studied recently for effective electromagnetic interference (EMI) shielding due to the prominent intrinsic electrical conductivity. Nevertheless, the poor mechanical performance of pure MXene films limits the practical application in EMI shielding. Thus, we integrate MXene with aramid nanofiber (ANF) to develop a composite film with layered structure through a simple vacuum-assisted filtration method. The resulting ANF/MXene (20/80) composite exhibits a high electrical conductivity of 879.0 S/cm, EMI shielding effectiveness (SE) of 40.6 dB and specific SE (SSE/t, SE divided by the density and thickness) of 50,491 dB∙cm2∙g−1 with an ultrathin thickness of 3.2 μm. Furthermore, the ANF/MXene (60/40) realizes a balance between mechanical properties and EMI shielding performance with the strength of 201.3 MPa and SE of 28.1 dB, which enables the ANF/MXene composite films as promising EMI shielding materials with excellent mechanical robustness.

Sputter deposited molybdenum disulfide coatings are one of the most common lubricants for extreme environments. However, their performance predictability remains limited by the complexity of van der Waals wear and shear mechanics in bulk materials resulting in unexpected premature failure. In the present study, two nanostructured MoS2 coatings of similar macroscopic properties are shown to exhibit entirely different wear and shear mechanics due to their nanostructure. Friction force microscopy with steel-beaded cantilevers is used to measure the per-cycle evolution of friction, wear, and topography in situ over the lubricant lifetime under an inert nitrogen environment. Molecular dynamics simulations confirm the subsurface structural failure mechanisms of the coatings under shear stress and AFM phase imaging and Raman spectroscopy are used to identify tribofilm formation mechanics. The nanocrystal amorphous composite structure shows improved wear resistance but at the cost of limited stress relaxation which creates high-stress failure and fracture-dominated wear. The purely nanocrystalline coating exhibits lower shear resistance but consistent stress relaxation by van der Waals cleavage and triple junction fracture which results in higher wear rates with predictable abrasion-dominated failure. The contrast in nanoscale performance of the coatings allows for the lubricant nanostructure to be tuned for ideal applications for extreme environments.

Monolayer two-dimensional (2D) crystals exhibit a host of intriguing properties, but the most exciting applications may come from stacking them into multilayer structures. Interlayer and interfacial shear interactions could play a crucial role in the performance and reliability of these applications, but little is known about the key parameters controlling shear deformation across the layers and interfaces between 2D materials. Herein, we report the first measurement of the interlayer shear stress of bilayer graphene based on pressurized microscale bubble loading devices. We demonstrate continuous growth of an interlayer shear zone outside the bubble edge and extract an interlayer shear stress of 40 kPa based on a membrane analysis for bilayer graphene bubbles. Meanwhile, a much higher interfacial shear stress of 1.64 MPa was determined for monolayer graphene on a silicon oxide substrate. Our results not only provide insights into the interfacial shear responses of the thinnest structures possible, but also establish an experimental method for characterizing the fundamental interlayer shear properties of the emerging 2D materials for potential applications in multilayer systems.