Bridging the Gap between Reality and Ideal in Chemical Vapor Deposition Growth of Graphene

C-Me-graphene: an ideal two-dimensional nodal line semimetal with ultrahigh Young's modulus

Nodal line semimetal (NLSM) has become a captivating medium for studying varieties of novel quantum phenomena. Here, based on first-principles calculations, we identify a square compound lattice (SCL) structure, namely C-Me-graphene, featuring a NLSM, wherein the nodal line of this configuration resides precisely at the Fermi energy without any extraneous bands in the vicinity, manifesting the quintessential characteristics of an ideal NLSM. As a corollary, utilizing symmetry analysis, we propose that nodal lines can be generated by exploiting the two-dimensional (2D) SCL of carbon. This is because the SCL not only satisfies time-reversal symmetry and inversion symmetry but also conforms to glide mirror symmetry. Additionally, this structure reveals remarkable mechanical attributes, exemplifying the highest Young's modulus within the realm of 2D materials, second only to graphene. Our work not only identifies an ideal carbon-based NLSM but also advances a scheme for crafting NLSMs, which would greatly enrich topological materials with exotic properties.

Emerging Advances around Nanofluidic Transport and Mass Separation under Confinement in Atomically Thin Nanoporous Graphene

Membrane separation stands as an environmentally friendly, high permeance and selectivity, low energy demand process that deserves scientific investigation and industrialization. To address intensive demand, seeking appropriate membrane materials to surpass trade-off between permeability and selectivity and improve stability is on the schedule. 2D materials offer transformational opportunities and a revolutionary platform for researching membrane separation process. Especially, the atomically thin graphene with controllable porosity and structure, as well as unique properties, is widely considered as a candidate for membrane materials aiming to provide extreme stability, exponentially large selectivity combined with high permeability. Currently, it has shown promising opportunities to develop separation membranes to tackle bottlenecks of traditional membranes, and it has been of great interest for tremendously versatile applications such as separation, energy harvesting, and sensing. In this review, starting from transport mechanisms of separation, the material selection bank is narrowed down to nanoporous graphene. The study presents an enlightening overview of very recent developments in the preparation of atomically thin nanoporous graphene and correlates surface properties of such 2D nanoporous materials to their performance in critical separation applications. Finally, challenges related to modulation and manufacturing as well as potential avenues for performance improvements are also pointed out.

Controllable preparation of graphene glass fiber fabric towards mass production and its application in self-adaptive thermal management

Direct synthesis of graphene on nonmetallic substrates via chemical vapor deposition (CVD) has become a frontier research realm targeting transfer-free applications of CVD graphene. However, the stable mass production of graphene with a favorable growth rate and quality remains a grand challenge. Herein, graphene glass fiber fabric (GGFF) was successfully developed through the controllable growth of graphene on non-catalytic glass fiber fabric, employing a synergistic binary-precursor CVD strategy to alleviate the dilemma between growth rate and quality. The binary precursors consisted of acetylene and acetone, where acetylene with high decomposition efficiency fed rapid graphene growth while oxygen-containing acetone was adopted for improving the layer uniformity and quality. Notably, the bifurcating introducing-confluent premixing (BI-CP) system was self-built for the controllable introduction of gas and liquid precursors, enabling the stable production of GGFF. GGFF features solar absorption and infrared emission properties, based on which the self-adaptive dual-mode thermal management film was developed. This film can automatically switch between heating and cooling modes by spontaneously perceiving the temperature, achieving excellent thermal management performances with heating and cooling power of ∼501.2 and ∼108.6 W m-2, respectively. These findings unlock a new strategy for the large-scale batch production of graphene materials and inspire advanced possibilities for further applications.

Multispecies-coadsorption-induced rapid preparation of graphene glass fiber fabric and applications in flexible pressure sensor

Direct chemical vapor deposition (CVD) growth of graphene on dielectric/insulating materials is a promising strategy for subsequent transfer-free applications of graphene. However, graphene growth on noncatalytic substrates is faced with thorny issues, especially the limited growth rate, which severely hinders mass production and practical applications. Herein, graphene glass fiber fabric (GGFF) is developed by graphene CVD growth on glass fiber fabric. Dichloromethane is applied as a carbon precursor to accelerate graphene growth, which has a low decomposition energy barrier, and more importantly, the produced high-electronegativity Cl radical can enhance adsorption of active carbon species by Cl-CH2 coadsorption and facilitate H detachment from graphene edges. Consequently, the growth rate is increased by ~3 orders of magnitude and carbon utilization by ~960-fold, compared with conventional methane precursor. The advantageous hierarchical conductive configuration of lightweight, flexible GGFF makes it an ultrasensitive pressure sensor for human motion and physiological monitoring, such as pulse and vocal signals.

Progress in Advanced Infrared Optoelectronic Sensors

Infrared optoelectronic sensors have attracted considerable research interest over the past few decades due to their wide-ranging applications in military, healthcare, environmental monitoring, industrial inspection, and human-computer interaction systems. A comprehensive understanding of infrared optoelectronic sensors is of great importance for achieving their future optimization. This paper comprehensively reviews the recent advancements in infrared optoelectronic sensors. Firstly, their working mechanisms are elucidated. Then, the key metrics for evaluating an infrared optoelectronic sensor are introduced. Subsequently, an overview of promising materials and nanostructures for high-performance infrared optoelectronic sensors, along with the performances of state-of-the-art devices, is presented. Finally, the challenges facing infrared optoelectronic sensors are posed, and some perspectives for the optimization of infrared optoelectronic sensors are discussed, thereby paving the way for the development of future infrared optoelectronic sensors.

Toward the Production of Super Graphene

The quality requirements of graphene depend on the applications. Some have a high tolerance for graphene quality and even require some defects, while others require graphene as perfect as possible to achieve good performance. So far, synthesis of large-area graphene films by chemical vapor deposition of carbon precursors on metal substrates, especially on Cu, remains the main way to produce high-quality graphene, which has been significantly developed in the past 15 years. However, although many prototypes are demonstrated, their performance is still more or less far from the theoretical property limit of graphene. This review focuses on how to make super graphene, namely graphene with a perfect structure and free of contaminations. More specially, this study focuses on graphene synthesis on Cu substrates. Typical defects in graphene are first discussed together with the formation mechanisms and how they are characterized normally, followed with a brief review of graphene properties and the effects of defects. Then, the synthesis progress of super graphene from the aspects of substrate, grain size, wrinkles, contamination, adlayers, and point defects are reviewed. Graphene transfer is briefly discussed as well. Finally, the challenges to make super graphene are discussed and a strategy is proposed.

Recent trends in the transfer of graphene films

Recent years have witnessed advances in chemical vapor deposition growth of graphene films on metal foils with fine scalability and thickness controllability. However, challenges for obtaining wrinkle-free, defect-free and large-area uniformity remain to be tackled. In addition, the real commercial applications of graphene films still require industrially compatible transfer techniques with reliable performance of transferred graphene, excellent production capacity, and suitable cost. Transferred graphene films, particularly with a large area, still suffer from the presence of transfer-related cracks, wrinkles and contaminants, which would strongly deteriorate the quality and uniformity of transferred graphene films. Potential applications of graphene films include moisture barrier films, transparent conductive films, electromagnetic shielding films, and optical communications; such applications call different requirements for the performance of transferred graphene, which, in turn, determine the suitable transfer techniques. Besides the reliable transfer process, automatic machines should be well developed for the future batch transfer of graphene films, ensuring the repeatability and scalability. This mini-review provides a summary of recent advances in the transfer of graphene films and offers a perspective for future directions of transfer techniques that are compatible for industrial batch transfer.

Silicon Radical-Induced CH4 Dissociation for Uniform Graphene Coating on Silica Surface

Due to the manufacturability of highly well-defined structures and wide-range versatility in its microstructure, SiO2 is an attractive template for synthesizing graphene frameworks with the desired pore structure. However, its intrinsic inertness constrains the graphene formation via methane chemical vapor deposition. This work overcomes this challenge by successfully achieving uniform graphene coating on a trimethylsilyl-modified SiO2 (denote TMS-MPS). Remarkably, the onset temperature for graphene growth dropped to 720 °C for the TMS-MPS, as compared to the 885 °C of the pristine SiO2. This is found to be mainly from the Si radicals formed from the decomposition of the surface TMS groups. Both experimental and computational results suggest a strong catalytic effect of the Si radicals on the CH4 dissociation. The surface engineering of SiO2 templates facilitates the synthesis of high-quality graphene sheets. As a result, the graphene-coated SiO2 composite exhibits a high electrical conductivity of 0.25 S cm-1. Moreover, the removal of the TMP-MPS template has released a graphene framework that replicates the parental TMS-MPS template on both micro- and nano- scales. This study provides tremendous insights into graphene growth chemistries as well as establishes a promising methodology for synthesizing graphene-based materials with pre-designed microstructures and porosity.

Advancements in Transparent Conductive Oxides for Photoelectrochemical Applications

Photoelectrochemical cells (PECs) are an important technology for converting solar energy, which has experienced rapid development in recent decades. Transparent conductive oxides (TCOs) are also gaining increasing attention due to their crucial role in PEC reactions. This review comprehensively delves into the significance of TCO materials in PEC devices. Starting from an in-depth analysis of various TCO materials, this review discusses the properties, fabrication techniques, and challenges associated with these TCO materials. Next, we highlight several cost-effective, simple, and environmentally friendly methods, such as element doping, plasma treatment, hot isostatic pressing, and carbon nanotube modification, to enhance the transparency and conductivity of TCO materials. Despite significant progress in the development of TCO materials for PEC applications, we at last point out that the future research should focus on enhancing transparency and conductivity, formulating advanced theories to understand structure-property relationships, and integrating multiple modification strategies to further improve the performance of TCO materials in PEC devices.

Modulation of transport at the interface in the microporous layer for high power density proton exchange membrane fuel cells

The proton exchange membrane (PEM) fuel cell is a device that demonstrates a significant potential for environmental sustainability, since it efficiently converts chemical energy into electrical energy. The microporous layer (MPL) in PEM fuel cells promotes gas transport and eliminates water. Nevertheless, the power density of PEM fuel cells is restricted by ohmic losses and mass transport losses in conventional MPLs. In this study, we enhanced the power density of proton exchange membrane (PEM) fuel cells through the identification of appropriate materials and the mitigation of mass transport losses occurring at the interface between the microporous layer and the catalyst layer. The incorporation of high electron conductivity, slip behavior at the interface between graphene and water, and rapid water evaporation facilitated by nanoporous graphene effectively address transport-related challenges. We evaluated two types of graphene as potential substitutes for carbon black in the microporous layer (MPL). The enhanced power density (up to 1.1 W cm-2) under all humidity conditions and reduced mass transport resistance (a 75 % reduction compared to carbon black MPL) make them promising candidates for next-generation PEM fuel cells. Furthermore, these findings provide guidance for controlling interfacial mass transport in colloidal systems.

Magnetoresistance properties in nickel-catalyzed, air-stable, uniform, and transfer-free graphene

A transfer-free graphene with high magnetoresistance (MR) and air stability has been synthesized using nickel-catalyzed atmospheric pressure chemical vapor deposition. The Raman spectrum and Raman mapping reveal the monolayer structure of the transfer-free graphene, which has low defect density, high uniformity, and high coverage (>90%). The temperature-dependent (from 5 to 300 K) current-voltage (I-V) and resistance measurements are performed, showing the semiconductor properties of the transfer-free graphene. Moreover, the MR of the transfer-free graphene has been measured over a wide temperature range (5-300 K) under a magnetic field of 0 to 1 T. As a result of the Lorentz force dominating above 30 K, the transfer-free graphene exhibits positive MR values, reaching ∼8.7% at 300 K under a magnetic field (1 Tesla). On the other hand, MR values are negative below 30 K due to the predominance of the weak localization effect. Furthermore, the temperature-dependent MR values of transfer-free graphene are almost identical with and without a vacuum annealing process, indicating that there are low density of defects and impurities after graphene fabrication processes so as to apply in air-stable sensor applications. This study opens avenues to develop 2D nanomaterial-based sensors for commercial applications in future devices.

Physically Exfoliating 2D Materials: A Versatile Combination of Different Materials into a Layered Structure

Improving the properties of the existing two-dimensional (2D) materials is a major concern for many researchers today. Synergistic coupling of single-phase 2D material species with secondary functional materials has resulted in 2D nanohybrids with significantly enhanced properties beyond the sum of their individual components. In particular, nanohybrids created by alternatingly integrating different material species in the confined 2D nanometer regime have the potential to meet the needs of a wide variety of applications, particularly the many important energy-related applications that are of interest. However, scaling up production of 2D nanohybrids is still challenging, which is a major barrier to their practical application. Delamination and exfoliation by physical means separate the weakly bound 2D nanosheets into kinetically stable single- or few-layers. Herein, we provide a concise overview of recent achievements in the physical exfoliation-based fabrication of 2D nanohybrids featuring controlled heterolayered structures. Several strategies to efficiently produce heterolayered 2D nanohybrids in large quantities are described, such as (i) coexfoliation of different 2D species, (ii) aqueous-phase synthesis, and (iii) gas-phase synthesis. The versatility of the 2D nanohybrids was also illustrated by remarkable research examples, especially in energy-related applications.

Growth of Vertical Graphene Sheets on Silicon Nanoparticles Well-Dispersed on Graphite Particles for High-Performance Lithium-Ion Battery Anode

With rapidly increasing demand for high energy density, silicon (Si) is greatly expected to play an important role as the anode material of lithium-ion batteries (LIBs) due to its high specific capacity. However, large volume expansion for silicon during the charging process is still a serious problem influencing its cycling stability. Here, a Si/C composite of vertical graphene sheets/silicon/carbon/graphite (VGSs@Si/C/G) is reported to address the electrochemical stability issues of Si/graphite anodes, which is prepared by adhering Si nanoparticles on graphite particles with chitosan and then in situ growing VGSs by thermal chemical vapor deposition. As a promising anode material, due to the buffering effect of VGSs and tight bonding between Si and graphite particles, the composite delivers a high reversible capacity of 782.2 mAh g-1 after 1000 cycles with an initial coulombic efficiency of 87.2%. Furthermore, the VGSs@Si/C/G shows a diffusion coefficient of two orders higher than that without growing the VGSs. The full battery using VGSs@Si/C/G anode and LiNi0.8 Co0.1 Mn0.1 O2 cathode achieves a high gravimetric energy density of 343.6 Wh kg-1 , a high capacity retention of 91.5% after 500 cycles and an excellent average CE of 99.9%.

Recent Advances in Transfer-Free Synthesis of High-Quality Graphene

High-quality graphene obtained by chemical vapor deposition (CVD) technique holds significant importance in constructing innovative electronic and optoelectronic devices. Direct growth of graphene over target substrates readily eliminates cumbersome transfer processes, offering compatibility with practical application scenarios. Recent years have witnessed growing strategic endeavors in the preparation of transfer-free graphene with favorable quality. Nevertheless, timely review articles on this topic are still scarce. In this contribution, a systematic summary of recent advances in transfer-free synthesis of high-quality graphene on insulating substrates, with a focus on discussing synthetic strategies designed by elevating reaction temperature, confining gas flow, introducing growth promotor and regulating substrate surface is presented.

A novel electrochemical aptasensor based on eco-friendly synthesized titanium dioxide nanosheets and polyethyleneimine grafted reduced graphene oxide for ultrasensitive and selective detection of ciprofloxacin

Developing a rapid, sensitive, and efficient analytical method for the trace-level determination of highly concerning antibiotic ciprofloxacin (CIP) is desirable to guarantee the safety of human health and ecosystems. In this work, a novel electrochemical aptasensor based on polyethyleneimine grafted reduced graphene oxide and titanium dioxide (rGO/PEI/TiO2) nanocomposite was constructed for ultrasensitive and selective detection of CIP. Through the in-situ electrochemical oxidation of Ti3C2Tx nanosheets, TiO2 nanosheets with good electrochemical response were prepared in a more convenient and eco-friendly method. The prepared TiO2 nanosheets promote charge transferring on electrode interface, and [Fe(CN)6]3-/4- as electrochemical active substance can be electrostatically attracted by rGO/PEI. Thus, electrochemical detection signal of the aptasensor variates a lot after specific binding with CIP, achieving working dynamic range of 0.003-10.0 μmol L-1, low detection limit down to 0.7 nmol L-1 (S/N = 3) and selectivity towards other antibiotics. Additionally, the aptasensor exhibited good agreement with HPLC method at 95% confidence level, and achieved good recoveries (96.8-106.3%) in real water samples, demonstrating its suitable applicability of trace detection of CIP in aquatic environment.

Effect of Ambient Environment on Laser Reduction of Graphene Oxide for Applications in Electrochemical Sensing

Electrochemical sensors play an important role in a variety of applications. With the potential for enhanced performance, much of the focus has been on developing nanomaterials, in particular graphene, for such sensors. Recent work has looked towards laser scribing technology for the reduction of graphene oxide as an easy and cost-effective option for sensor fabrication. This work looks to develop this approach by assessing the quality of sensors produced with the effect of different ambient atmospheres during the laser scribing process. The graphene oxide was reduced using a laser writing system in a range of atmospheres and sensors characterised with Raman spectroscopy, XPS and cyclic voltammetry. Although providing a slightly higher defect density, sensors fabricated under argon and nitrogen atmospheres exhibited the highest average electron transfer rates of approximately 2 × 10-3 cms-1. Issues of sensor reproducibility using this approach are discussed.

Graphene-Based Wearable Temperature Sensors: A Review

Flexible sensing electronics have received extensive attention for their potential applications in wearable human health monitoring and care systems. Given that the normal physiological activities of the human body are primarily based on a relatively constant body temperature, real-time monitoring of body surface temperature using temperature sensors is one of the most intuitive and effective methods to understand physical conditions. With its outstanding electrical, mechanical, and thermal properties, graphene emerges as a promising candidate for the development of flexible and wearable temperature sensors. In this review, the recent progress of graphene-based wearable temperature sensors is summarized, including material preparation, working principle, performance index, classification, and related applications. Finally, the challenges and future research emphasis in this field are put forward. This review provides important guidance for designing novel and intelligent wearable temperature-sensing systems.

Fast synthesis of large-area bilayer graphene film on Cu

Bilayer graphene (BLG) is intriguing for its unique properties and potential applications in electronics, photonics, and mechanics. However, the chemical vapor deposition synthesis of large-area high-quality bilayer graphene on Cu is suffering from a low growth rate and limited bilayer coverage. Herein, we demonstrate the fast synthesis of meter-sized bilayer graphene film on commercial polycrystalline Cu foils by introducing trace CO₂ during high-temperature growth. Continuous bilayer graphene with a high ratio of AB-stacking structure can be obtained within 20 min, which exhibits enhanced mechanical strength, uniform transmittance, and low sheet resistance in large area. Moreover, 96 and 100% AB-stacking structures were achieved in bilayer graphene grown on single-crystal Cu(111) foil and ultraflat single-crystal Cu(111)/sapphire substrates, respectively. The AB-stacking bilayer graphene exhibits tunable bandgap and performs well in photodetection. This work provides important insights into the growth mechanism and the mass production of large-area high-quality BLG on Cu.

Oxidization-Temperature-Triggered Rapid Preparation of Large-Area Single-Crystal Cu(111) Foil

The controlled preparation of single-crystal Cu(111) is intensively investigated owing to the superior properties of Cu(111) and its advantages in synthesizing high-quality 2D materials, especially graphene. However, the accessibility of large-area single-crystal Cu(111) is still hindered by time-consuming, complicated, and high-cost preparation methods. Here, the oxidization-temperature-triggered rapid preparation of large-area single-crystal Cu(111) in which an area up to 320 cm² is prepared within 60 min, and where low-temperature oxidization of polycrystalline Cu foil surface plays a vital role, is reported. A mechanism is proposed, by which the thin Cu_x O layer transforms to a Cu(111) seed layer on the surface of Cu to induce the formation of a large-area Cu(111) foil, which is supported by both experimental data and molecular dynamics simulation results. In addition, a large-size high-quality graphene film is synthesized on the single-crystal Cu(111) foil surface and the graphene/Cu(111) composites exhibit enhanced thermal conductivity and ductility compared to their polycrystalline counterpart. This work, therefore, not only provides a new avenue toward the monocrystallinity of Cu with specific planes but also contributes to improving the mass production of high-quality 2D materials.

Precursor-mediated in situ growth of hierarchical N-doped graphene nanofibers confining nickel single atoms for CO2 electroreduction

Despite the various strategies for achieving metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) with different microenvironments for electrochemical carbon dioxide reduction reaction (CO2RR), the synthesis-structure-performance correlation remains elusive due to the lack of well-controlled synthetic approaches. Here, we employed Ni nanoparticles as starting materials for the direct synthesis of nickel (Ni) SACs in one spot through harvesting the interaction between metallic Ni and N atoms in the precursor during the chemical vapor deposition growth of hierarchical N-doped graphene fibers. By combining with first-principle calculations, we found that the Ni-N configuration is closely correlated to the N contents in the precursor, in which the acetonitrile with a high N/C ratio favors the formation of Ni-N3, while the pyridine with a low N/C ratio is more likely to promote the evolution of Ni-N2. Moreover, we revealed that the presence of N favors the formation of H-terminated edge of sp2 carbon and consequently leads to the formation of graphene fibers consisting of vertically stacked graphene flakes, instead of the traditional growth of carbon nanotubes on Ni nanoparticles. With a high capability in balancing the *COOH formation and *CO desorption, the as-prepared hierarchical N-doped graphene nanofibers with Ni-N3 sites exhibit a superior CO2RR performance compared to that with Ni-N2 and Ni-N4 ones.

Increasing coverage of mono-layer graphene grown on hexagonal boron nitride

Graphene sitting on hexagonal boron nitride (h-BN) always exhibits excellent electrical properties. And the properties of graphene onh-BN are often dominated by its domain size and boundaries. Chemical vapor deposition (CVD) is a promising approach to achieve large size graphene crystal. However, the CVD growth of graphene onh-BN still faces challenges in increasing coverage of monolayer graphene because of a weak control on nucleation and vertical growth. Here, an auxiliary source strategy is adapted to increase the nucleation density of graphene onh-BN and synthesis continuous graphene films. It is found that both silicon carbide and organic polymer e.g. methyl methacrylate can assist the nucleation of graphene, and then increases the coverage of graphene onh-BN. By optimizing the growth temperature, vertical accumulation of graphitic materials can be greatly suppressed. This work provides an effective approach for preparing continuous graphene film onh-BN, and may bring a new sight for the growth of high quality graphene.

A carbon allotrope with twisted Dirac cones induced by grain boundaries composed of pentagons and octagons

The grain boundaries (GBs) composed of pentagons and octagons (558 GBs) have been demonstrated to induce attractive transport properties such as Van Hove singularity (VHS) and quasi-one-dimensional metallic wires. Here, we propose a monolayer carbon allotrope which is formed from the introduction of periodic 558 GBs to decorate intact graphene, termed as PHO-graphene. The calculated electronic properties indicate that PHO-graphene not only inherits the previously superior characteristics such as Van Hove singularity and quasi-one-dimensional metallic wires, but also possesses two twisted Dirac cones near the Fermi level. Further calculation finds that the Berry phase is quantized to ± π at the two Dirac points, which is consistent with the distribution of the corresponding Berry curvature. The parity argument uncovers that PHO-graphene hosts a nontrivial band topology and the edge states connecting the two Dirac points are clearly visible. Our findings not only provide a reliable avenue to realize the abundant and extraordinary properties of carbon allotropes, but also offer an attractive approach for designing all carbon-based devices.

Layer-Structured Anisotropic Metal Chalcogenides: Recent Advances in Synthesis, Modulation, and Applications

The unique electronic and catalytic properties emerging from low symmetry anisotropic (1D and 2D) metal chalcogenides (MCs) have generated tremendous interest for use in next generation electronics, optoelectronics, electrochemical energy storage devices, and chemical sensing devices. Despite many proof-of-concept demonstrations so far, the full potential of anisotropic chalcogenides has yet to be investigated. This article provides a comprehensive overview of the recent progress made in the synthesis, mechanistic understanding, property modulation strategies, and applications of the anisotropic chalcogenides. It begins with an introduction to the basic crystal structures, and then the unique physical and chemical properties of 1D and 2D MCs. Controlled synthetic routes for anisotropic MC crystals are summarized with example advances in the solution-phase synthesis, vapor-phase synthesis, and exfoliation. Several important approaches to modulate dimensions, phases, compositions, defects, and heterostructures of anisotropic MCs are discussed. Recent significant advances in applications are highlighted for electronics, optoelectronic devices, catalysts, batteries, supercapacitors, sensing platforms, and thermoelectric devices. The article ends with prospects for future opportunities and challenges to be addressed in the academic research and practical engineering of anisotropic MCs.

Uniform thin ice on ultraflat graphene for high-resolution cryo-EM

Cryo-electron microscopy (cryo-EM) visualizes the atomic structure of macromolecules that are embedded in vitrified thin ice at their close-to-native state. However, the homogeneity of ice thickness, a key factor to ensure high image quality, is poorly controlled during specimen preparation and has become one of the main challenges for high-resolution cryo-EM. Here we found that the uniformity of thin ice relies on the surface flatness of the supporting film, and developed a method to use ultraflat graphene (UFG) as the support for cryo-EM specimen preparation to achieve better control of vitreous ice thickness. We show that the uniform thin ice on UFG improves the image quality of vitrified specimens. Using such a method we successfully determined the three-dimensional structures of hemoglobin (64 kDa), α-fetoprotein (67 kDa) with no symmetry, and streptavidin (52 kDa) at a resolution of 3.5 Å, 2.6 Å and 2.2 Å, respectively. Furthermore, our results demonstrate the potential of UFG for the fields of cryo-electron tomography and structure-based drug discovery.

Flexible Optical Synapses Based on In2Se3/MoS2 Heterojunctions for Artificial Vision Systems in the Near-Infrared Range

Near-infrared (NIR) synaptic devices integrate NIR optical sensitivity and synaptic plasticity, emulating the basic biomimetic function of the human visual system and showing great potential in NIR artificial vision systems. However, the lack of semiconductor materials with appropriate band gaps for NIR photodetection and effective strategies for fabricating devices with synaptic behaviors limit the further development of NIR synaptic devices. Here, a two-terminal NIR synaptic device consisting of the In₂Se₃/MoS₂ heterojunction has been constructed, and it exhibits fundamental synaptic functions. The reduced band gap and potential barrier of In₂Se₃/MoS₂ heterojunctions are essential for NIR synaptic plasticity. In addition, the NIR synaptic properties of In₂Se₃/MoS₂ heterojunctions under strain have been studied systematically. The ΔEPSC of the In₂Se₃/MoS₂ synaptic device can be improved from 38.4% under no strain to 49.0% under a 0.54% strain with a 1060 nm illumination for 1 s at 100 mV. Furthermore, the artificial NIR vision system consisting of a 10 × 10 In₂Se₃/MoS₂ device array has been fabricated, exhibiting image sensing, learning, and storage functions under NIR illumination. This research provides new ideas for the design of flexible NIR synaptic devices based on 2D materials and presents many opportunities in artificial intelligence and NIR vision systems.

Integrating Dual-Interfacial Liquid Metal Based Nanodroplet Architectures and Micro-Nanostructured Engineering for High Efficiency Solar Energy Harvesting

Broadband strong absorption of solar light over a wide range of angles, low heat loss, and excellent structural reliability are of significance for enhancing solar harvesting of photothermal materials; however, it remains a challenge to achieve these attributes simultaneously. Herein, a tailored photothermal composite nanodroplet (LMP-rGO) featured with dual-interface, which comprises liquid metal (LM) core with polydopamine (PDA) photothermal middle layer of tunable thickness and reduced graphene oxide (rGO) shell, is particularly prepared. Thermal-insulating PDA coating and light-absorbing carbonaceous shell allow it to synergistically suppress heat loss and reinforce photon absorptivity. To maximize photothermal conversion and photon harvesting yield on solar light, inspired by light trapping architecture, a three-dimensional (3D) stepped micropyramid grating array framework is tactfully designed to ameliorate light coupling. Utilizing the scalability and cost-effectiveness of the poly(vinyl alcohol) (PVA), the flexible 3D-structured PVA/LMP-rGO absorbers are successfully constructed via a controllable casting molding strategy. As a proof-of-concept, the developed micrograting absorber exhibits a desirable combination of strong broadband selective light absorption (94.9% for parallel to the grating direction and 97.3% for perpendicular to the grating direction), superior photothermal conversion effect (89.4%), high heat flux density, and fascinating mechanical properties. Also, an efficient and steady solar-driven thermoelectric generator (STEG) system for real-time solar-heat-electric conversion, with its high peak power density of 245.9 μW cm^-2 under one sun irradiation, is further displayed, making an important step to rationally design LM-based nanocomposite droplets for solar energy harvesting.

Direct-Chemical Vapor Deposition-Enabled Graphene for Emerging Energy Storage: Versatility, Essentiality, and Possibility

The direct chemical vapor deposition (CVD) technique has stimulated an enormous scientific and industrial interest to enable the conformal growth of graphene over multifarious substrates, which readily bypasses tedious transfer procedure and empowers innovative materials paradigm. Compared to the prevailing graphene materials (i.e., reduced graphene oxide and liquid-phase exfoliated graphene), the direct-CVD-enabled graphene harnesses appealing structural advantages and physicochemical properties, accordingly playing a pivotal role in the realm of electrochemical energy storage. Despite conspicuous progress achieved in this frontier, a comprehensive overview is still lacking by far and the synthesis-structure-property-application nexus of direct-CVD-enabled graphene remains elusive. In this topical review, rather than simply compiling the state-of-the-art advancements, the versatile roles of direct-CVD-enabled graphene are itemized as (i) modificator, (ii) cultivator, (iii) defender, and (iv) decider. Furthermore, essential effects on the performance optimization are elucidated, with an emphasis on fundamental properties and underlying mechanisms. At the end, perspectives with respect to the material production and device fabrication are sketched, aiming to navigate the future development of direct-CVD-enabled graphene en-route toward pragmatic energy applications and beyond.

High Performance Hall Sensors Built on Chemical Vapor Deposition-Grown Bilayer Graphene

Graphene has been considered as an excellent channel material for constructing magnetic sensors or Hall elements with high sensitivity and linearity. Compared to intensively reported graphene Hall elements (GHEs) fabricated on monolayer graphene, the exploration on bilayer graphene-based Hall elements is very rare. Here, we first investigate the performance and potential of Hall elements built on chemical vapor deposition-grown bilayer graphene. Without applying any gate voltage, the bilayer GHEs exhibit a typical voltage sensitivity of 119 mV/VT and current sensitivity of 397 V/AT, which are higher than those in the monolayer GHEs, indicating the better performance in practical applications. Moreover, the bilayer GHEs present obviously lower noise and then the minimum detection magnetic field compared to the monolayer ones. Hall elements built on bilayer graphene show certain unique advantages and can be used as an important supplement to mainstreaming monolayer GHEs.

Complementary Chemical Vapor Deposition Fabrication for Large-Area Uniform Graphene Glass Fiber Fabric

The lightweight, flexible, high-performance electrothermal material is in high demand in object thermal management. Graphene glass fiber fabric (GGFF) is characterized by excellent electrical conductivity, light weight, and high flexibility, showing superiorities as an electrothermal material. However, the traditional single-carbon-precursor chemical vapor deposition (CVD) graphene growth strategy commonly suffers from the severe thickness nonuniformity of the large-sized graphene film along the gas-flowing direction. Herein, a complementary CVD graphene growth strategy based on the simultaneous introduction of high- and low-decomposition-energy-barrier mixed carbon precursors is developed. In this way, the large-area uniform GGFF with a dramatically decreased nonuniformity coefficient is fabricated (0.260 in 40 cm × 4 cm). GGFF-based heater presents a widely tunable temperature range (20-170 °C) at low working voltage (<10 V) and uniform large-area heating temperature (171.4 ± 3.6 °C in 20 cm × 15 cm), which realizes remarkable anti/deicing performances under the low energy consumption (fast ice melting rate of 79 s mm^-1 under a low energy consumption of 0.066 kWh mm^-1 m^-2 ). The large-area uniform GGFF possesses substantial advantages for applications in thermal management, and the complementary CVD fabrication strategy shows reliable scalability and universality, which can be extended to the synthesis of various materials.

Optical Thin Films Fabrication Techniques-Towards a Low-Cost Solution for the Integrated Photonic Platform: A Review of the Current Status

In the past few decades, several methods concerning optical thin films have been established to facilitate the development of integrated optics. This paper provides a brief depiction of different techniques for implementing optical waveguide thin films that involve chemical, physical, and refractive index modification methods. Recent advances in these fabrication methods are also been presented. Most of the methods developed for the realization of the thin-films are quite efficient, but they are expensive and require sophisticated equipment. The major interest of the scientists is to develop simple and cost-effective methods for mass production of optical thin films resulting in the effective commercialization of the waveguide technology. Our research group is focused on developing a silica-titania optical waveguide platform via the sol-gel dip-coating method and implementing active and passive optical elements via the wet etching method. We are also exploring the possibility of using nanoimprint lithography (NIL) for patterning these films so that the fabrication process is efficient and economical. The recent developments of this platform are discussed. We believe that silica-titania waveguide technology developed via the sol-gel dip-coating method is highly attractive and economical, such that it can be commercialized for applications such as sensing and optical interconnects.

Combinatorial Cu-Ni Alloy Thin-Film Catalysts for Layer Number Control in Chemical Vapor-Deposited Graphene

We synthesized a combinatorial library of CuxNi1−x alloy thin films via co-sputtering from Cu and Ni targets to catalyze graphene chemical vapor deposition. The alloy morphology, composition, and microstructure were characterized via scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and X-ray diffraction (XRD), respectively. Subsequently, the CuxNi1−x alloy thin films were used to grow graphene in a CH4-Ar-H2 ambient at atmospheric pressure. The underlying rationale is to adjust the CuxNi1−x composition to control the graphene. Energy dispersive x-ray spectroscopy (EDS) analysis revealed that a continuous gradient of CuxNi1−x (25 at. % < x < 83 at.%) was initially achieved across the 100 mm diameter substrate (~0.9%/mm composition gradient). The XRD spectra confirmed a solid solution was realized and the face-centered cubic lattice parameter varied from ~3.52 to 3.58 A˙, consistent with the measured composition gradient, assuming Vegard’s law. Optical microscopy and Raman analysis of the graphene layers suggest single layer growth occurs with x > 69 at.%, bilayer growth dominates from 48 at.% < x < 69 at.%, and multilayer (≥3) growth occurs for x < 48 at.%, where x is the Cu concentration. Finally, a large area of bi-layer graphene was grown via a CuxNi1−x catalyst with optimized catalyst composition and growth temperature.

Preparation of a Vertical Graphene-Based Pressure Sensor Using PECVD at a Low Temperature

Flexible pressure sensors have received much attention due to their widespread potential applications in electronic skins, health monitoring, and human-machine interfaces. Graphene and its derivatives hold great promise for two-dimensional sensing materials, owing to their superior properties, such as atomically thin, transparent, and flexible structure. The high performance of most graphene-based pressure piezoresistive sensors relies excessively on the preparation of complex, post-growth transfer processes. However, the majority of dielectric substrates cannot hold in high temperatures, which can induce contamination and structural defects. Herein, a credibility strategy is reported for directly growing high-quality vertical graphene (VG) on a flexible and stretchable mica paper dielectric substrate with individual interdigital electrodes in plasma-enhanced chemical vapor deposition (PECVD), which assists in inducing electric field, resulting in a flexible, touchable pressure sensor with low power consumption and portability. Benefitting from its vertically directed graphene microstructure, the graphene-based sensor shows superior properties of high sensitivity (4.84 KPa^-1) and a maximum pressure range of 120 KPa, as well as strong stability (5000 cycles), which makes it possible to detect small pulse pressure and provide options for preparation of pressure sensors in the future.

Two-Dimensional Field-Effect Transistor Sensors: The Road toward Commercialization

The evolutionary success in information technology has been sustained by the rapid growth of sensor technology. Recently, advances in sensor technology have promoted the ambitious requirement to build intelligent systems that can be controlled by external stimuli along with independent operation, adaptivity, and low energy expenditure. Among various sensing techniques, field-effect transistors (FETs) with channels made of two-dimensional (2D) materials attract increasing attention for advantages such as label-free detection, fast response, easy operation, and capability of integration. With atomic thickness, 2D materials restrict the carrier flow within the material surface and expose it directly to the external environment, leading to efficient signal acquisition and conversion. This review summarizes the latest advances of 2D-materials-based FET (2D FET) sensors in a comprehensive manner that contains the material, operating principles, fabrication technologies, proof-of-concept applications, and prototypes. First, a brief description of the background and fundamentals is provided. The subsequent contents summarize physical, chemical, and biological 2D FET sensors and their applications. Then, we highlight the challenges of their commercialization and discuss corresponding solution techniques. The following section presents a systematic survey of recent progress in developing commercial prototypes. Lastly, we summarize the long-standing efforts and prospective future development of 2D FET-based sensing systems toward commercialization.

3D Continuously Porous Graphene for Energy Applications

Constructing bulk graphene materials with well-reserved 2D properties is essential for device and engineering applications of atomically thick graphene. In this article, the recent progress in the fabrications and applications of sterically continuous porous graphene with designable microstructures, chemistries, and properties for energy storage and conversion are reviewed. Both template-based and template-free methods have been developed to synthesize the 3D continuously porous graphene, which typically has the microstructure reminiscent of pseudo-periodic minimal surfaces. The 3D graphene can well preserve the properties of 2D graphene of being highly conductive, surface abundant, and mechanically robust, together with unique 2D electronic behaviors. Additionally, the bicontinuous porosity and large curvature offer new functionalities, such as rapid mass transport, ample open space, mechanical flexibility, and tunable electric/thermal conductivity. Particularly, the 3D curvature provides a new degree of freedom for tailoring the catalysis and transport properties of graphene. The 3D graphene with those extraordinary properties has shown great promises for a wide range of applications, especially for energy conversion and storage. This article overviews the recent advances made in addressing the challenges of developing 3D continuously porous graphene, the benefits and opportunities of the new materials for energy-related applications, and the remaining challenges that warrant future study.

Progress on Optical Fiber Biochemical Sensors Based on Graphene

Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing has also been a hotspot in cross-research in biology, materials, medicine, and micro-nano devices in recent years, owing to prospective benefits, such as high sensitivity, small size, and strong anti-electromagnetic interference capability and so on. Here, the progress of optical fiber biochemical sensors based on graphene is reviewed. The fabrication of graphene materials and the sensing mechanism of the graphene-based optical fiber sensor are described. The typical research works of graphene-based optical fiber biochemical sensor, such as long-period fiber grating, Bragg fiber grating, no-core fiber and photonic crystal fiber are introduced, respectively. Finally, prospects for graphene-based optical fiber biochemical sensing technology will also be covered, which will provide an important reference for the development of graphene-based optical fiber biochemical sensors.

Mechanisms for Graphene Growth on SiO2 Using Plasma-Enhanced Chemical Vapor Deposition: A Density Functional Theory Study

Plasma-enhanced chemical vapor deposition (PE-CVD) of graphene layers on dielectric substrates is one of the most important processes for the incorporation of graphene in semiconductor devices. Graphene is moving rapidly from the laboratory to practical implementation; therefore, devices may take advantage of the unique properties of such nanomaterial. Conventional approaches rely on pattern transfers after growing graphene on transition metals, which can cause nonuniformities, poor adherence, or other defects. Direct growth of graphene layers on the substrates of interest, mostly dielectrics, is the most logical approach, although it is not free from challenges and obstacles such as obtaining a specific yield of graphene layers with desired properties or accurate control of the growing number of layers. In this work, we use density-functional theory (DFT) coupled with ab initio molecular dynamics (AIMD) to investigate the initial stages of graphene growth on silicon oxide. We select C₂H₂ as the PE-CVD precursor due to its large carbon contribution. On the basis of our simulation results for various surface models and precursor doses, we accurately describe the early stages of graphene growth, from the formation of carbon dimer rows to the critical length required to undergo dynamical folding that results in the formation of low-order polygonal shapes. The differences in bonding with the functionalization of the silicon oxide also mark the nature of the growing carbon layers as well as shed light of potential flaws in the adherence to the substrate. Finally, our dynamical matrix calculations and the obtained infrared (IR) spectra and vibrational characteristics provide accurate recipes to trace experimentally the growth mechanisms described and the corresponding identification of possible stacking faults or defects in the emerging graphene layers.

Green Carbon Nanostructures for Functional Composite Materials

Carbon nanostructures are widely used as fillers to tailor the mechanical, thermal, barrier, and electrical properties of polymeric matrices employed for a wide range of applications. Reduced graphene oxide (rGO), a carbon nanostructure from the graphene derivatives family, has been incorporated in composite materials due to its remarkable electrical conductivity, mechanical strength capacity, and low cost. Graphene oxide (GO) is typically synthesized by the improved Hummers’ method and then chemically reduced to obtain rGO. However, the chemical reduction commonly uses toxic reducing agents, such as hydrazine, being environmentally unfriendly and limiting the final application of composites. Therefore, green chemical reducing agents and synthesis methods of carbon nanostructures should be employed. This paper reviews the state of the art regarding the green chemical reduction of graphene oxide reported in the last 3 years. Moreover, alternative graphitic nanostructures, such as carbons derived from biomass and carbon nanostructures supported on clays, are pointed as eco-friendly and sustainable carbonaceous additives to engineering polymer properties in composites. Finally, the application of these carbon nanostructures in polymer composites is briefly overviewed.

Intrinsic Wettability in Pristine Graphene

The wettability of graphene remains controversial owing to its high sensitivity to the surroundings, which is reflected by the wide range of reported water contact angle (WCA). Specifically, the surface contamination and underlying substrate would strongly alter the intrinsic wettability of graphene. Here, the intrinsic wettability of graphene is investigated by measuring WCA on suspended, superclean graphene membrane using environmental scanning electron microscope. An extremely low WCA with an average value ≈30° is observed, confirming the hydrophilic nature of pristine graphene. This high hydrophilicity originates from the charge transfer between graphene and water molecules through H-π interaction. The work provides a deep understanding of the water-graphene interaction and opens up a new way for measuring the surface properties of 2D materials.

Toward Epitaxial Growth of Misorientation-Free Graphene on Cu(111) Foils

The epitaxial growth of single-crystal thin films relies on the availability of a single-crystal substrate and a strong interaction between epilayer and substrate. Previous studies have reported the roles of the substrate (e.g., symmetry and lattice constant) in determining the orientations of chemical vapor deposition (CVD)-grown graphene, and Cu(111) is considered as the most promising substrate for epitaxial growth of graphene single crystals. However, the roles of gas-phase reactants and graphene-substrate interaction in determining the graphene orientation are still unclear. Here, we find that trace amounts of oxygen is capable of enhancing the interaction between graphene edges and Cu(111) substrate and, therefore, eliminating the misoriented graphene domains in the nucleation stage. A modified anomalous grain growth method is developed to improve the size of the as-obtained Cu(111) single crystal, relying on strongly textured polycrystalline Cu foils. The batch-to-batch production of A3-size (∼0.42 × 0.3 m²) single-crystal graphene films is achieved on Cu(111) foils relying on a self-designed pilot-scale CVD system. The as-grown graphene exhibits ultrahigh carrier mobilities of 68 000 cm² V^-1 s^-1 at room temperature and 210 000 cm² V^-1 s^-1 at 2.2 K. The findings and strategies provided in our work would accelerate the mass production of high-quality misorientation-free graphene films.

Lattice Orientation Heredity in the Transformation of 2D Epitaxial Films

The ability to control lattice orientation is often an essential requirement in the growth of both 2D van der Waals (vdW) layered and nonlayered thin films. Here, a unique and universal phenomenon termed "lattice orientation heredity" (LOH) is reported. LOH enables product films (including 2D-layered materials) to inherit the lattice orientation from reactant films in a chemical conversion process, excluding the requirement on the substrate lattice order. The process universality is demonstrated by investigating the lattice transformations in the carbonization, nitridation, and sulfurization of epitaxial MoO₂ , ZnO, and In₂ O₃ thin films. Their resultant compounds all inherit the mono-oriented crystal feature from their precursor oxides, including 2D vdW-layered semiconductors (e.g., MoS₂ ), metallic films (e.g., MXene-like Mo₂ C and MoN), wide-bandgap semiconductors (e.g., hexagonal ZnS), and ferroelectric semiconductors (e.g., In₂ S₃ ). Using LOH-grown MoN as a seeding layer, mono-oriented GaN is achieved on an amorphous quartz substrate. The LOH process presents a universal strategy capable of growing epitaxial thin films (including 2D vdW-layered materials) not only on single-crystalline but also on noncrystalline substrates.

Graphene Transfer: Paving the Road for Applications of Chemical Vapor Deposition Graphene

Owing to the fascinating properties of graphene, fulfilling the promising characteristics of graphene in applications has ignited enormous scientific and industrial interest. Chemical vapor deposition (CVD) growth of graphene on metal substrates provides tantalizing opportunities for the large-area synthesis of graphene in a controllable manner. However, the tedious transfer of graphene from metal substrates onto desired substrates remains inevitable, and cracks of graphene membrane, transfer-induced doping, wrinkles as well as surface contamination can be incurred during the transfer, which highly degrade the performance of graphene. Furthermore, new issues can arise when moving to large-scale transfer at an industrial scale, thus cost-efficient and environment-friendly transfer techniques also become imperative. The aim of this review is to provide a comprehensive understanding of transfer-related issues and the corresponding experimental solutions and to provide an outlook for future transfer techniques of CVD graphene films on an industrial scale.

Recent Progress in Flexible Graphene-Based Composite Fiber Electrodes for Supercapacitors

Graphene has shown the world its fascinating properties, including high specific surface area, high conductivity, and extraordinary mechanical properties, which enable graphene to be a competent candidate for electrode materials. However, some challenges remain in the real applications of graphene-based electrodes, such as continuous preparation of graphene fibers with highly ordered graphene sheets as well as strong interlayer interactions. The combination of graphene with other materials or functional guests hence appears as a more promising pathway via post-treatment and in situ hybridism to produce composite fibers. This article firstly provides a full account of the classification of graphene-based composite fiber electrodes, including carbon allotropy, conductive polymer, metal oxide and other two-dimensional (2D) materials. The preparation methods of graphene-based composite fibers are then discussed in detail. The context further demonstrates the performance optimization of graphene-based composite fiber electrodes, involving microstructure design and surface modification, followed by the elaboration of the application of graphene-based composite fiber electrodes in supercapacitors. Finally, we present the remaining challenges that exist to date in order to provide meaningful guidelines in the development process and prospects of graphene-based composite fiber electrodes.

Graphene Biodevices for Early Disease Diagnosis Based on Biomarker Detection

The early diagnosis of diseases plays a vital role in healthcare and the extension of human life. Graphene-based biosensors have boosted the early diagnosis of diseases by detecting and monitoring related biomarkers, providing a better understanding of various physiological and pathological processes. They have generated tremendous interest, made significant advances, and offered promising application prospects. In this paper, we discuss the background of graphene and biosensors, including the properties and functionalization of graphene and biosensors. Second, the significant technologies adopted by biosensors are discussed, such as field-effect transistors and electrochemical and optical methods. Subsequently, we highlight biosensors for detecting various biomarkers, including ions, small molecules, macromolecules, viruses, bacteria, and living human cells. Finally, the opportunities and challenges of graphene-based biosensors and related broad research interests are discussed.

CVD Synthesis of 3D-Shaped 3D Graphene Using a 3D-Printed Nickel-PLGA Catalyst Precursor

Earlier, various attempts to develop graphene structures using chemical and nonchemical routes were reported. Being efficient, scalable, and repeatable, 3D printing of graphene-based polymer inks and aerogels seems attractive; however, the produced structures highly rely on a binder or an ice support to stay intact. The presence of a binder or graphene oxide hinders the translation of the excellent graphene properties to the 3D structure. In this communication, we report our efforts to synthesize a 3D-shaped 3D graphene (3D²G) with good quality, desirable shape, and structure control by combining 3D printing with the atmospheric pressure chemical vapor deposition (CVD) process. Direct ink writing has been used in this work as a 3D-printing technique to print nickel powder-PLGA slurry into various shapes. The latter has been employed as a catalyst for graphene growth via CVD. Porous 3D²G with high purity was obtained after etching out the nickel substrate. The conducted micro CT and 2D Raman study of pristine 3D²G revealed important features of this new material. The interconnected porous nature of the obtained 3D²G combined with its good electrical conductivity (about 17 S/cm) and promising electrochemical properties invites applications for energy storage electrodes, where fast electron transfer and intimate contact with the active material and with the electrolyte are critically important. By changing the printing design, one can manipulate the electrical, electrochemical, and mechanical properties, including the structural porosity, without any requirement for additional doping or chemical postprocessing. The obtained binder-free 3D²G showed a very good thermal stability, tested by thermo-gravimetric analysis in air up to 500 °C. This work brings together two advanced manufacturing approaches, CVD and 3D printing, thus enabling the synthesis of high-quality, binder-free 3D²G structures with a tailored design that appeared to be suitable for multiple applications.

Atomically Thin Bilayer Janus Membranes for Cryo-electron Microscopy

Cryo-electron microscopy (cryo-EM) has emerged as a vital tool to reveal the native structure of beam-sensitive biomolecules and materials. Yet high-resolution cryo-EM analysis is still limited by the poorly controlled specimen preparation and urgently demands a robust supporting film material to prepare desirable samples. Here, we developed a bilayer Janus graphene membrane with the top-layer graphene being functionalized to interact with target molecules on the surface, while the bottom layer being kept intact to reinforce its mechanical steadiness. The ultraclean and atomically thin bilayer Janus membrane prepared by our protocol on one hand generates almost no extra noise and on the other hand reduces the specimen motion during cryo-EM imaging, thus allowing the atomic-resolution characterization of surface functional groups. Using such Janus membranes in cryo-EM specimen preparation, we were able to directly image the lithium dendrite and reconstruct macromolecules at near-atomic resolution. Our results demonstrate the bilayer Janus design as a promising supporting material for high-resolution cryo-EM and EM imaging.

Biomass-Derived Carbon Materials: Controllable Preparation and Versatile Applications

Biomass-derived carbon materials (BCMs) are encountering the most flourishing moment because of their versatile properties and wide potential applications. Numerous BCMs, including 0D carbon spheres and dots, 1D carbon fibers and tubes, 2D carbon sheets, 3D carbon aerogel, and hierarchical carbon materials have been prepared. At the same time, their structure-property relationship and applications have been widely studied. This paper aims to present a review on the recent advances in the controllable preparation and potential applications of BCMs, providing a reference for future work. First, the chemical compositions of typical biomass and their thermal degradation mechanisms are presented. Then, the typical preparation methods of BCMs are summarized and the relevant structural management rules are discussed. Besides, the strategies for improving the structural diversity of BCMs are also presented and discussed. Furthermore, the applications of BCMs in energy, sensing, environment, and other areas are reviewed. Finally, the remaining challenges and opportunities in the field of BCMs are discussed.

In Situ Investigation of the Motion Behavior of Graphene on Liquid Copper

The in situ investigation of the dynamic growth process and novel assembly phenomena of graphene on liquid copper (Cu) is of great significance to deeply understand the special behavior of graphene and self-assembly mechanism. Here, the direct observation of the graphene growth and motion behavior on liquid Cu via in situ imaging is reported. Evidence of graphene movement on liquid Cu is offered and it is demonstrated that the translation and rotation behaviors of graphene are affected by the surface condition of liquid Cu. The self-assembly process of graphene array is also revealed by capturing the dynamic changes of graphene in real-time. Further analysis highlights the importance of surface energy of liquid Cu and the interaction between graphene building blocks during the self-assembling process. The growth parameters are also investigated to flexibly control the assembly configuration of graphene arrays. This work provides an insight into the mechanism of graphene motion and assembly behavior that can be used to guide the controllable manipulation of 2D materials and on-demand fabrication assembly structures with desired properties.