Direct growth of ultrafast transparent single-layer graphene defoggers

Atomic engineering of two-dimensional materials via liquid metals

Two-dimensional (2D) materials, known for their distinctive electronic, mechanical, and thermal properties, have attracted considerable attention. The precise atomic-scale synthesis of 2D materials opens up new frontiers in nanotechnology, presenting novel opportunities for material design and property control but remains challenging due to the high expense of single-crystal solid metal catalysts. Liquid metals, with their fluidity, ductility, dynamic surface, and isotropy, have significantly enhanced the catalytic processes crucial for synthesizing 2D materials, including decomposition, diffusion, and nucleation, thus presenting an unprecedented precise control over material structures and properties. Besides, the emergence of liquid alloy makes the creation of diverse heterostructures possible, offering a new dimension for atomic engineering. Significant achievements have been made in this field encompassing defect-free preparation, large-area self-aligned array, phase engineering, heterostructures, etc. This review systematically summarizes these contributions from the aspects of fundamental synthesis methods, liquid catalyst selection, resulting 2D materials, and atomic engineering. Moreover, the review sheds light on the outlook and challenges in this evolving field, providing a valuable resource for deeply understanding this field. The emergence of liquid metals has undoubtedly revolutionized the traditional nanotechnology for preparing 2D materials on solid metal catalysts, offering flexible possibilities for the advancement of next-generation electronics.

Fabrication of Single-Crystal Violet Phosphorus Flakes For Ultrasensitive Photodetection

Violet phosphorus (VP) has attracted a lot of attention for its unique physicochemical properties and emerging potential in photoelectronic applications. Although VP has a van der Waals (vdW) structure similar to that of other 2D semiconductors, direct synthesis of VP on a substrate is still challenging. Moreover, optoelectronic devices composed of transfer-free VP flakes have not been demonstrated. Herein, a bismuth-assisted vapor phase transport technique is designed to grow uniform single-crystal VP flakes on the SiO2/Si substrate directly. The size of the crystalline VP flakes is an order of magnitude larger than that of previous liquid-exfoliated samples. The photodetector fabricated with the VP flakes shows a high responsivity of 12.5 A W-1 and response/recovery time of 3.82/3.03 ms upon exposure to 532 nm light. Furthermore, the photodetector shows a small dark current (<1 pA) that is beneficial to high-sensitivity photodetection. As a result, the detectivity is 1.38 × 1013 Jones that is comparable with that of the vdW p-n heterojunction detector. The results reveal the great potential of VP in optoelectronic devices as well as the CVT technique for the growth of single-crystal semiconductor thin films.

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.

Recent advances in batch production of transfer-free graphene

Large-area transfer-free graphene films prepared via chemical vapor deposition have proved appealing for various applications, with exciting examples in electronics, photonics, and optoelectronics. To achieve their commercialisation, batch production is a prerequisite. Nevertheless, the prevailing scalable synthesis strategies that have been reported are still obstructed by production inefficiencies and non-uniformity. There has also been a lack of reviews in this realm. We present herein a comprehensive and timely summary of recent advances in the batch production of transfer-free graphene. Primary issues and promising approaches for improving the graphene growth rate are first addressed, followed by a discussion of the strategies to guarantee in-plane and batch uniformity for graphene grown on planar plates and wafer-scale substrates, with the design of the target equipment to meet productivity requirements. Finally, potential research directions are outlined, aiming to offer insights into guiding the scalable production of transfer-free graphene.

Night-time radiative warming using the atmosphere

Night-time warming is vital for human production and daily life. Conventional methods like active heaters are energy-intensive, while passive insulating films possess restrictions regarding space consumption and the lack of heat gain. In this work, a nanophotonic-based night-time warming strategy that passively inhibits thermal radiation of objects while actively harnessing that of atmosphere is proposed. By using a photonic-engineered thin film that exhibits high reflectivity (~0.91) in the atmospheric transparent band (8-14 μm) and high absorptivity (~0.7) in the atmospheric radiative band (5-8 and 14-16 μm), temperature rise of 2.1 °C/4.4 °C compared to typical low-e film and broadband absorber is achieved. Moreover, net heat loss as low as 9 W m-2 is experimentally observed, compared to 16 and 39 W m-2 for low-e film and broadband absorber, respectively. This strategy suggests an innovative way for sustainable warming, thus contributes to addressing the challenges of climate change and promoting global carbon neutrality.

Recent advances in prevailing antifogging surfaces: structures, materials, durability, and beyond

In past decades, antifogging surfaces have drawn more and more attention owing to their promising and wide applications such as in aerospace, traffic transportation, optical devices, the food industry, and medical and other fields. Therefore, the potential hazards caused by fogging need to be solved urgently. At present, the up-and-coming antifogging surfaces have been developing swiftly, and can effectively achieve antifogging effects primarily by preventing fog formation and rapid defogging. This review analyzes and summarizes current progress in antifogging surfaces. Firstly, some bionic and typical antifogging structures are described in detail. Then, the antifogging materials explored thus far, mainly focusing on substrates and coatings, are extensively introduced. After that, the solutions for improving the durability of antifogging surfaces are explicitly classified in four aspects. Finally, the remaining big challenges and future development trends of the ascendant antifogging surfaces are also presented.

Pattern-Dependent Radio Frequency Heating of Laser-Induced Graphene Flexible Heaters

Graphene is an excellent choice for heating applications due to its high thermal conductivity and is considered an interesting candidate for application in flexible heaters. The major challenge, though, is the costly and chemical-intensive pathways to produce graphene on a large scale. Laser ablation of polymeric substrates is a relatively recent technique for a facile, single-step, chemical-free fabrication of graphene, referred to as laser-induced graphene (LIG). This work demonstrates the fabrication of patterned LIG-based flexible heaters and their response to radio frequency (RF) electromagnetic waves. Polymeric substrates were scribed with laser patterns in both raster and vector modes and subjected to RF electromagnetic fields to test their heating response. We confirmed different graphene morphologies of the lased patterns through various materials characterization methods. The maximum steady-state temperature observed for the LIG heater was approximately 500 °C. Unprecedented heating rates, as high as 502 °C/s, were observed when LIG heaters were exposed to RF fields at 200 MHz frequency and 4.6 W power. Mechanical and thermal stability tests for the best heater were also performed showing a stable thermal response for 1000 bending cycles and 20 cycles of the heating test for 8.5 h, respectively. Our work suggests that LIG heaters produced in vector mode lasing outperformed those lased in raster mode which can be attributed to the improved graphene quality for RF absorbance.

Transfer-Free CVD Growth of High-Quality Wafer-Scale Graphene at 300 °C for Device Mass Fabrication

Direct chemical vapor deposition of graphene on semiconductors and insulators provides high feasibility for integration of graphene devices and semiconductor electronics. However, the current methods typically rely on high temperatures (>1000 °C), which can damage the substrates. Here, a growth method for high-quality large-area graphene at 300 °C is introduced. A multizone furnace with gradient temperature control was designed according to a computational fluid dynamics model. The crucial roles of the chamber pressure in the film continuity and hydrogen composition in the graphene defect density at low temperature were revealed. As a result, a uniform graphene film with the Raman ratio I_D/I_G = 0.08 was obtained. Furthermore, a technique of laminating single-crystal Cu foil as a sacrificial layer on the substrate was proposed to realize transfer-free growth, and a wafer-scale graphene transistor array was demonstrated with good performance consistency, which paves the way for mass fabrication of graphene devices.

Copper acetate-facilitated transfer-free growth of high-quality graphene for hydrovoltaic generators

Direct synthesis of high-quality graphene on dielectric substrates without a transfer process is of vital importance for a variety of applications. Current strategies for boosting high-quality graphene growth, such as remote metal catalyzation, are limited by poor performance with respect to the release of metal catalysts and hence suffer from a problem with metal residues. Herein, we report an effective approach that utilizes a metal-containing species, copper acetate, to continuously supply copper clusters in a gaseous form to aid transfer-free growth of graphene over a wafer scale. The thus-derived graphene films were found to show reduced multilayer density and improved electrical performance and exhibited a carrier mobility of 8500 cm2 V−1 s−1. Furthermore, droplet-based hydrovoltaic electricity generator devices based on directly grown graphene were found to exhibit robust voltage output and long cyclic stability, in stark contrast to their counterparts based on transferred graphene, demonstrating the potential for emerging energy harvesting applications. The work presented here offers a promising solution to organize the metal catalytic booster toward transfer-free synthesis of high-quality graphene and enable smart energy generation.

Robust photothermal anti-icing/deicing via flexible CMDSP carbon nanotube films

Photothermal anti-icing/deicing technology is an environmentally friendly surface technology that can be applied to the surface of aircraft, vehicles or ships. However, it is still a huge challenge to develop a strong and stable flexible film that can efficiently convert light to heat. Here, based on a simple electrochemical method to construct a zinc oxide (ZnO) nanoneedles structure on the surface of the carbon nanotube film, a film with the function of condensed micro-droplet self-propelling (CMDSP) was successfully prepared. The prepared film has excellent light absorption capacity and high energy transfer efficiency (76.71%). The film has strong photothermal anti-icing/deicing performance. Under 4406 Lux light irradiation, even under low temperature conditions of -5 °C, the icing delay time exceeds 4 h. This novel characteristic is attributed to the CMDSP function on the surface and the ultra-fast evaporation mechanism, which can remove water droplets on the surface as quickly as possible. This function helps to design energy-saving equipment that requires high-power heating and deicing.

Fast Peel-Off Ultrathin, Transparent, and Free-Standing Films Assembled from Low-Dimensional Materials Using MXene Sacrificial Layers and Produced Bubbles

Ultrathin, transparent, and free-standing films assembled from low-dimensional nanomaterials (LDMs) are promising for various applications, including transparent heaters and membranes. However, the intact separation of the assembled films, especially those with controlled ultrathin thickness from deposited substrates, is a tremendous challenge, particularly for fast peeling off via self-detaching. Herein, we propose a versatile method to rapidly peel off ultrathin assembled LDM films, including three types of carbon nanotubes, vermiculite, Ag nanowires, and carbon nanotube@graphene, by dissolving the MXene interlayer from the layer-by-layer filtered MXene/LDM Janus films using diluted H₂ O₂ . The MXene sacrificial interlayers play dual roles, including physical isolation of LDM films from filter membranes and the production of bubbles that buoy ultrathin LDM films, making them free-standing. The integrality and self-detaching rate of the LDM films are determined by the loading and reactivity of the MXene interlayers. The intact LDM films can self-detach in 80 s by dissolving the optimized MXene interlayer and producing bubbles. The as-made free-standing ultrathin LDM films can be transferred to arbitrary substrates and exhibit outstanding performance as transparent heaters. This scalable method provides an efficient and versatile method to produce ultrathin, transparent, and free-standing LDM films and finds new applications for the growing MXene family.

Supported Cu/W/Mo/Ni—Liquid Metal Catalyst with Core-Shell Structure for Photocatalytic Degradation

Room-temperature liquid metal is a very ideal material for the design of catalytic materials. At low temperatures, the liquid metal enters the liquid state. It provides an opportunity to utilize the liquid phase in the catalysis, which is far superior to the traditional solid-phase catalyst. Aiming at the low performance and narrow application scope of the existing single-phase liquid metal catalyst, this paper proposed a type of liquid metal/metal oxide core-shell composite multi-metal catalyst. The Ga2O3 core-shell heterostructure was formed by chemical modification of liquid metals with different nano metals Cu/W/Mo/Ni, and it was applied to photocatalytic degrading organic contaminated raw liquor. The effects of different metal species on the rate of catalytic degradation were explored. The selectivity and stability of the LM/MO core-shell composite catalytic material were clarified, and it was found that the Ni-LM catalyst could degrade methylene blue and Congo red by 92% and 79%, respectively. The catalytic mechanism and charge transfer mechanism were revealed by combining the optical band gap value. Finally, we provided a theoretical basis for the further development of liquid metal photocatalytic materials in the field of new energy environments.

Bioinspired adhesive coatings from polyethylenimine and tannic acid complexes exhibiting antifogging, self-cleaning, and antibacterial capabilities

In this work, we develop a simple yet robust method to fabricate a bioinspired adhesive coating based on polyethyleneimine (PEI) and tannic acid (TA) complexes, exhibiting excellent antifogging, self-cleaning, and antibacterial properties. The polyethyleneimine-tannic acid (PEI-TA) complexes coating combined with the bioinspired adhesive property from TA can be effectively and stably coated onto various substrates through a one-step deposition process, and the hydrophilicity of the coated substrates can be significantly enhanced with their water contact angle less than 10°. The bioinspired adhesive coating endows the coated substrates with outstanding antifogging and self-cleaning performance. Moreover, it is found that the PEI-TA coated safety goggles display excellent durability and antifogging capability compared to the commercial antifogging safety goggles and commercial antifogging agents coated safety goggles under 65 ℃ vapor condition for 2 h. Furthermore, the PEI-TA coatings show superior antibacterial activities for Gram-negative Escherichiak coli and Gram-positive Staphylococcus aureus. The antifogging, self-cleaning, and antibacterial coating provides widely potential application prospects in optical and medical devices.

Study on Fast Cold Start-Up Method of Proton Exchange Membrane Fuel Cell Based on Electric Heating Technology

In order to realize the low temperature and rapid cold start-up of a proton exchange membrane fuel cell stack, a dynamic model containing 40 single proton exchange membrane fuel cells is established to estimate the melting time of the proton exchange membrane fuel cell stack as well as to analyze the melting process of the ice by using the obtained liquid–solid boundary. The methods of proton exchange membrane electric heating and electrothermal film heating are utilized to achieve cold start-up of the proton exchange membrane fuel cell (PEMFC). The fluid simulation software fluent is used to simulate and analyze the process of melting ice. The solidification and melting model and multi-phase flow model are introduced. The pressure-implicit with splitting of operators algorithm is also adopted. The results show that both the proton exchange membrane electric heating technology and the electrothermal film heating method can achieve rapid cold start-up. The interior ice of the proton exchange membrane fuel cell stack melts first, while the first and 40th pieces melt afterwards. The ice melting time of the proton exchange membrane fuel cell stack is 32.5 s and 36.5 s with the two methods, respectively. In the end, the effect of different electrothermal film structures on cold start-up performance is studied, and three types of pore diameter electrothermal films are established. It is found that the electrothermal film with small holes melts completely first, and the electrothermal film with large holes melts completely last.

Wafer-scale 2D PtTe2 layers for high-efficiency mechanically flexible electro-thermal smart window applications

Two-dimensional (2D) transition metal dichalcogenide (TMD) layers have gained increasing attention for a variety of emerging electrical, thermal, and optical applications. Recently developed metallic 2D TMD layers have been projected to exhibit unique attributes unattainable in their semiconducting counterparts; e.g., much higher electrical and thermal conductivities coupled with mechanical flexibility. In this work, we explored 2D platinum ditelluride (2D PtTe2) layers - a relatively new class of metallic 2D TMDs - by studying their previously unexplored electro-thermal properties for unconventional window applications. We prepared wafer-scale 2D PtTe2 layer-coated optically transparent and mechanically flexible willow glasses via a thermally-assisted tellurization of Pt films at a low temperature of 400 °C. The 2D PtTe2 layer-coated windows exhibited a thickness-dependent optical transparency and electrical conductivity of >106 S m-1 - higher than most of the previously explored 2D TMDs. Upon the application of electrical bias, these windows displayed a significant increase in temperature driven by Joule heating as confirmed by the infrared (IR) imaging characterization. Such superior electro-thermal conversion efficiencies inherent to 2D PtTe2 layers were utilized to demonstrate various applications, including thermochromic displays and electrically-driven defogging windows accompanying mechanical flexibility. Comparisons of these performances confirm the superiority of the wafer-scale 2D PtTe2 layers over other nanomaterials explored for such applications.

Laser-Induced Graphene Paper Heaters with Multimodally Patternable Electrothermal Performance for Low-Energy Manufacturing of Composites

Low-energy manufacturing of polymeric composites through two-dimensional electrothermal heaters is a promising strategy over the traditional autoclave and oven. Laser-induced graphene paper (LIGP) is a recent emergent multifunctional material with the merits of one-step computer aided design and manufacturing (CAD/CAM) as well as a flexible thin nature. To fully explore its capabilities of in situ heating, herein, we adventurously propose and investigate the customizable manufacture and modulation of LIGP enabled heaters with multimodally patternable performance. Developed by two modes (uniform and nonuniform) of laser processing, the LIGP heaters (LIGP-H) show distinctively unique characteristics, including high working range (>600 °C), fast stabilization (<8 s), high temperature efficiency (∼370 °C·cm²/W), and superb robustness. Most innovatively, the nonuniform processing could section LIGP-H into subzones with independently controlled heating performance, rendering various designable patterns. The above unique characteristics guarantee the LIGP-H to be highly reliable for in situ curing composites with flat, curved, and even inhomogeneous structures. With enormous energy-savings (∼85%), superb curing accuracy, and comparable mechanical strength, the proposed device is advantageous for assuring high-quality and highly efficient manufacturing.

Automated Assembly of Wafer-Scale 2D TMD Heterostructures of Arbitrary Layer Orientation and Stacking Sequence Using Water Dissoluble Salt Substrates

We report a novel strategy to assemble wafer-scale two-dimensional (2D) transition metal dichalcogenide (TMD) layers of well-defined components and orientations. We directly grew a variety of 2D TMD layers on "water-dissoluble" single-crystalline salt wafers and precisely delaminated them inside water in a chemically benign manner. This manufacturing strategy enables the automated integration of vertically aligned 2D TMD layers as well as 2D/2D heterolayers of arbitrary stacking orders on exotic substrates insensitive to their kind and shape. Furthermore, the original salt wafers can be recycled for additional growths, confirming high process sustainability and scalability. The generality and versatility of this approach have been demonstrated by developing proof-of-concept "all 2D" devices for diverse yet unconventional applications. This study is believed to shed a light on leveraging opportunities of 2D TMD layers toward achieving large-area mechanically reconfigurable devices of various form factors at the industrially demanded scale.

Graphene-Based Thermoacoustic Sound Source

Thermoacoustic (TA) effect has been discovered for more than 130 years. However, limited by the material characteristics, the performance of a TA sound source could not be compared with magnetoelectric and piezoelectric loudspeakers. Recently, graphene, a two-dimensional material with the lowest heat capacity per unit area, was discovered to have a good TA performance. Compared with a traditional sound source, graphene TA sound sources (GTASSs) have many advantages, such as small volume, no diaphragm vibration, wide frequency range, high transparency, good flexibility, and high sound pressure level (SPL). Therefore, graphene has a great potential as a next-generation sound source. Photoacoustic (PA) imaging can also be applied to the diagnosis and treatment of diseases using the photothermo-acoustic (PTA) effect. Therefore, in this review, we will introduce the history of TA devices. Then, the theory and simulation model of TA will be analyzed in detail. After that, we will talk about the graphene synthesis method. To improve the performance of GTASSs, many strategies such as lowering the thickness and using porous or suspended structures will be introduced. With a good PTA effect and large specific area, graphene PA imaging and drug delivery is a promising prospect in cancer treatment. Finally, the challenges and prospects of GTASSs will be discussed.

Metal-Free Synthesis of Boron-Doped Graphene Glass by Hot-Filament Chemical Vapor Deposition for Wave Energy Harvesting

Property modulation of graphene glass by heteroatom doping such as boron (B) and nitrogen (N) is important to extend its practical applications. However, unlike N doping, research studies about the metal-free synthesis of B-doped graphene on glass through the chemical vapor deposition (CVD) method are rarely reported. Herein, we report a hot-filament CVD approach to prepare B-doped graphene glass using diborane (B₂H₆) as the B dopant. The synthesized B-doped graphene was uniform on a large-scale and composed of nanocrystalline graphene grains. By raising the B₂H₆ flow from 0 to 15 sccm, the B content of graphene was facilely modulated from 0 to 5.3 at. %, accompanied with the improvement of both transparency and conductivity. The B-doped graphene prepared on glass at 15 sccm B₂H₆ flow presented the optimal transparent conductive performance superior to those of most reported graphene glass fabricated by other state-of-the-art approaches. Furthermore, for the first time, the performance of graphene glass for wave energy harvesting has been elaborated. It was found that the output power produced by inserting graphene glass into 0.6 M sodium chloride (NaCl) solution could be improved by more than 6 times through B doping. The significant enhancement resulted from the higher waving voltage and smaller resistance of B-doped graphene on glass than the pristine ones. In addition, the waving voltage inversed the polarity after B doping, which was due to the opposite variation of surface potential of pristine and B-doped graphene after NaCl immersion. This work would pave ways for the metal-free preparation and expand the energy-harvesting applications of B-doped graphene materials.

Transparent Electrothermal Film Defoggers and Antiicing Coatings based on Wrinkled Graphene

Fog, frost, ice, and other natural phenomena can inevitably affect human life and the function of equipment. Therefore, removal or prevention is an urgent problem to be solved. As a new type of 2D material, graphene possesses great application potential in defogging and antiicing. In this work, a graphene film with intentionally increased defects and uniformly distributed wrinkles is synthesized on copper-zinc alloy substrates by chemical vapor deposition, and transparent electrothermal film defoggers are prepared based on such material. The defoggers can completely remove fog within 5 s when supplying a safe voltage of 28 V. The surface resistance of the defoggers is sensitive to humidity and it can monitor the defogging process in real time. Such outstanding performance is attributed to the ultrafast evaporation mechanism, which can prevent excessive water accumulation. The antiicing performance of wrinkled graphene (WG) is further studied. The antiicing coatings can delay freezing for 1.25 h at -15 °C or 2.8 h at -10 °C. The superior performance of WG can be explained by its unique surface structure and nanoscale roughness. Taken together, WG is expected to be used in antifog glass, rearview mirror defogging, aircraft surface deicing, and other applications.

Properties of Undoped Few-Layer Graphene-Based Transparent Heaters

In many applications like sensors, displays, and defoggers, there is a need for transparent and efficient heater elements produced at low cost. For this reason, we evaluated the performance of graphene-based heaters with from one to five layers of graphene on flexible and transparent polyethylene terephthalate (PET) substrates in terms of their electrothermal properties like heating/cooling rates and steady-state temperatures as a function of the input power density. We found that the heating/cooling rates followed an exponential time dependence with a time constant of just below 6 s for monolayer heaters. From the relationship between the steady-state temperatures and the input power density, a convective heat-transfer coefficient of 60 W·m^-2·°C^-1 was found, indicating a performance much better than that of many other types of heaters like metal thin-film-based heaters and carbon nanotube-based heaters.

Mechano-thermo-chromic device with supersaturated salt hydrate crystal phase change

Active control of transparency/color is the key to many functional optoelectric devices. Applying an electric field to an electrochromic or liquid crystal material is the typical approach for optical property control. In contrast to the conventional electrochromic method, we developed a new concept of smart glass using new driving mechanisms (based on mechanical stimulus and thermal energy) to control optical properties. This mechano-thermo-chromic smart glass device with an integrated transparent microheater uses a sodium acetate solution, which shows a unique marked optical property change under mechanical impact (mechanochromic) and heat (thermochromic). Such mechano-thermo-chromic devices may provide a useful approach in future smart window applications that could be operated by external environment conditions.

Flexible and transparent graphene/silver-nanowires composite film for high electromagnetic interference shielding effectiveness

Herein, an efficient approach to prepare flexible, transparent, and lightweight films based on graphene nanosheets (GNS) and silver nanowires (AgNWs) for high electromagnetic interference (EMI) shielding effectiveness (SE) has been explained. High-conductive GNS were fabricated by liquid phase stripping and composited with AgNWs by a two-step spin-coating method. Owing to the high transparency, good conductivity, and homogeneous distribution of both GNS and AgNWs, the obtained GNS/AgNWs film exhibits superb EMI SE and light transmittance, yielding a significantly high EMI SE up to 26 dB in both Ku-band and K-band and light transmittance higher than 78.4%. Moreover, this GNS/AgNWs film shows good flexibility and excellent structural stability. The obtained flexible, light and transparent film could have a great potential for transparent EMI shielding and smart electronics.

Atomic-Scale Structural Modification of 2D Materials

2D materials have attracted much attention since the discovery of graphene in 2004. Due to their unique electrical, optical, and magnetic properties, they have potential for various applications such as electronics and optoelectronics. Owing to thermal motion and lattice growth kinetics, different atomic-scale structures (ASSs) can originate from natural or intentional regulation of 2D material atomic configurations. The transformations of ASSs can result in the variation of the charge density, electronic density of state and lattice symmetry so that the property tuning of 2D materials can be achieved and the functional devices can be constructed. Here, several kinds of ASSs of 2D materials are introduced, including grain boundaries, atomic defects, edge structures, and stacking arrangements. The design strategies of these structures are also summarized, especially for atomic defects and edge structures. Moreover, toward multifunctional integration of applications, the modulation of electrical, optical, and magnetic properties based on atomic-scale structural modification are presented. Finally, challenges and outlooks are featured in the aspects of controllable structure design and accurate property tuning for 2D materials with ASSs. This work may promote research on the atomic-scale structural modification of 2D materials toward functional applications.

Direct CVD Growth of Graphene on Traditional Glass: Methods and Mechanisms

Chemical vapor deposition (CVD) on catalytic metal surfaces is considered to be the most effective way to obtain large-area, high-quality graphene films. For practical applications, a transfer process from metal catalysts to target substrates (e.g., poly(ethylene terephthalate) (PET), glass, and SiO₂ /Si) is unavoidable and severely degrades the quality of graphene. In particular, the direct growth of graphene on glass can avoid the tedious transfer process and endow traditional glass with prominent electrical and thermal conductivities. Such a combination of graphene and glass creates a new type of glass, the so-called "super graphene glass," which has attracted great interest from the viewpoints of both fundamental research and daily-life applications. In the last few years, great progress has been achieved in pursuit of this goal. Here, these growth methods as well as the specific growth mechanisms of graphene on glass surfaces are summarized. The typical techniques developed include direct thermal CVD growth, molten-bed CVD growth, metal-catalyst-assisted growth, and plasma-enhanced growth. Emphasis is placed on the strategy of growth corresponding to the different natures of glass substrates. A comprehensive understanding of graphene growth on nonmetal glass substrates and the latest status of "super graphene glass" production are provided.

Controllable Growth of Graphene on Liquid Surfaces

Controllable fabrication of graphene is necessary for its practical application. Chemical vapor deposition (CVD) approaches based on solid metal substrates with morphology-rich surfaces, such as copper (Cu) and nickel (Ni), suffer from the drawbacks of inhomogeneous nucleation and uncontrollable carbon precipitation. Liquid substrates offer a quasiatomically smooth surface, which enables the growth of uniform graphene layers. The fast surface diffusion rates also lead to unique growth and etching kinetics for achieving graphene grains with novel morphologies. The rheological surface endows the graphene grains with self-adjusted rotation, alignment, and movement that are driven by specific interactions. The intermediary-free transfer or the direct growth of graphene on insulated substrates is demonstrated using liquid metals. Here, the controllable growth process of graphene on a liquid surface to promote the development of attractive liquid CVD strategies is in focus. The exciting progress in controlled growth, etching, self-assembly, and delivery of graphene on a liquid surface is presented and discussed in depth. In addition, prospects and further developments in these exciting fields of graphene growth on a liquid surface are discussed.

Water drop-surface interactions as the basis for the design of anti-fogging surfaces: Theory, practice, and applications trends

Glass- and polymer-based materials have become essential in the fabrication of a multitude of elements, including eyeglasses, automobile windshields, bathroom mirrors, greenhouses, and food packages, which unfortunately mist up under typical operating conditions. Far from being an innocuous phenomenon, the formation of minute water drops on the surface is detrimental to their optical properties (e.g., light-transmitting capability) and, in many cases, results in esthetical, hygienic, and safety concerns. In this context, it is therefore not surprising that research in the field of fog-resistant surfaces is gaining in popularity, particularly in recent years, in view of the growing number of studies focusing on this topic. This review addresses the most relevant advances released thus far on anti-fogging surfaces, with a particular focus on coating deposition, surface micro/nanostructuring, and surface functionalization. A brief explanation of how surfaces fog up and the main issues of interest linked to fogging phenomenon, including common problems, anti-fogging strategies, and wetting states are first presented. Anti-fogging mechanisms are then discussed in terms of the morphology of water drops, continuing with a description of the main fabrication techniques toward anti-fogging property. This review concludes with the current and the future perspectives on the utility of anti-fogging surfaces for several applications and some remaining challenges in this field.

Controllable Fabrication of Graphene and Related Two-Dimensional Materials on Liquid Metals via Chemical Vapor Deposition

Due to the confinement of the charge, spin, and heat transport in the plane, graphene and related two-dimensional (2D) materials have been demonstrated to own many unique and excellent properties and witnessed many breakthroughs in physics. They show great application potential in many fields, especially for electronics and optoelectronics. However, a bottleneck to widespread applications is precise and reliable fabrication, in which the control of the layer number and domain assembly is the most basic and important since they directly determine the qualities and properties of 2D materials. The chemical vapor deposition (CVD) strategy was regarded as the frontrunner to achieve this target, and the design of the catalytic substrate is of great significance since it has the most direct influence on the catalysis and mass transfer, which can be the most essential elemental steps. In recent years, as compared to traditional solid metal catalysts, the emergence of liquid metal catalysts has brought a brand-new perspective and contributes to a huge change and optimization in the fabrication of 2D materials. On one hand, strictly self-limited growth behavior is discovered and is robust to the variation of the growth parameters. The atoms in the liquid metal tend to move intensely and arrange in an amorphous and isotropic way. The liquid surface is smooth and isotropic, and the vacancies in the fluidic liquid phase enable the embedding of heteroatoms. The phase transition from liquid to solid will facilitate the unique control of the mass-transfer path, which can trigger new growth mechanisms. On the other hand, the excellent rheological properties of liquid metals allow us to explore self-assembly of the 2D materials grown on the surface, which can activate new applications based on the derived collective properties, such as the integrated devices. Indeed, liquid metals show many unique behaviors in the catalytic growth and assembly of 2D materials. Thus, this Account aims to highlight the controllable fabrication of graphene and related 2D materials on liquid metals. By utilizing the phase transition of liquid metals, the segregation of precursors in the bulk can be controlled, leading to self-limited growth. By utilizing the fluidity of the liquid metals, 2D material crystals can achieve self-assembly on their surface, including oriented stitching, ordered assembly, and heterostacking, which enables the creation of new multilevel or hybrid structures, leading to property and function extension and even the emergence of new physics. Finally, the unique liquid characteristic of liquid metals can also offer us new ideas about the transfer process. By utilizing the shear transformation of liquid metals, the direct sliding transfer of 2D materials onto arbitrary substrates can be realized. The research concerning the self-limited growth, self-assembly, and sliding transfer of 2D materials on liquid metals is just raising the curtain on the behavioral study of 2D materials on liquid metals. We believe these primary technology developments revealed by liquid metals will establish a solid foundation for both fundamental research and practical application of 2D materials.

Highly Conductive Nitrogen-Doped Graphene Grown on Glass toward Electrochromic Applications

The direct synthesis of low sheet resistance graphene on glass can promote the applications of such intriguing hybrid materials in transparent electronics and energy-related fields. Chemical doping is efficient for tailoring the carrier concentration and the electronic properties of graphene that previously derived from metal substrates. Herein, we report the direct synthesis of 5 in. uniform nitrogen-doped (N-doped) graphene on the quartz glass through a designed low-pressure chemical vapor deposition (LPCVD) route. Ethanol and methylamine were selected respectively as precursor and dopant for acquiring predominantly graphitic-N-doped graphene. We reveal that by a precise control of growth temperature and thus the doping level the sheet resistance of graphene on glass can be as low as one-half that of nondoped graphene, accompanied by relative high crystal quality and transparency. Significantly, we demonstrate that this scalable, 5 in. uniform N-doped graphene glass can serve as excellent electrode materials for fabricating high performance electrochromic smart windows, featured with a much simplified device structure. This work should pave ways for the direct synthesis and application of the new type graphene-based hybrid material.

Flourishing Bioinspired Antifogging Materials with Superwettability: Progresses and Challenges

Antifogging (AF) structure materials found in nature have great potential for enabling novel and emerging products and technologies to facilitate the daily life of human societies, attracting enormous research interests owing to their potential applications in display devices, traffics, agricultural greenhouse, food packaging, solar products, and other fields. The outstanding performance of biological AF surfaces encourages the rapid development and wide application of new AF materials. In fact, AF properties are inextricably associated with their surface superwettability. Generally, the superwettability of AF materials depends on a combination of their surface geometrical structures and surface chemical compositions. To explore their general design principles, recent progresses in the investigation of bioinspired AF materials are summarized herein. Recent developments of the mechanism, fabrication, and applications of bioinspired AF materials with superwettability are also a focus. This includes information on constructing superwetting AF materials based on designing the topographical structure and regulating the surface chemical composition. Finally, the remaining challenges and promising breakthroughs in this field are also briefly discussed.

Stretchable and Energy-Efficient Heating Carbon Nanotube Fiber by Designing a Hierarchically Helical Structure

Inspired by the hierarchically helical structure of classical thermal insulation material-wool, a stretchable heating carbon nanotube (CNT) fiber is created with excellent mechanical and heating properties. It can be stretched by up to 150% with high stability and reversibility, and a good thermal insulation is achieved from a large amount of formed hierarchically helical voids inside. Impressively, it exhibits ultrafast thermal response over 1000 °C s^-1 , low operation voltage of several volts, and high heating stability over 5000 cycles. These hierarchically helical CNT fibers, for the first time, are demonstrated as monofilaments to produce soft and lightweight textiles at a large scale with high heating performances.

A super flexible and custom-shaped graphene heater

In this paper, we fabricate a graphene film heater through laser reduction on graphene oxide, which is a two-step process. The electrothermal performance of the graphene heater can be adjusted by the laser energy density. While the applied voltage is 18 V, the graphene heater reaches a steady-state temperature of 247.3 °C within 20 s. After the graphene heater is folded in half 100 times, its output temperature remains to be precisely controlled by the input power and the temperature distribution is uniform. In addition, the flexibility of the graphene heater is superior to a heater based on a commercial indium tin oxide film. It's worth noting that the graphene heater can be fabricated with desired shapes directly and easily, which is rare among the reported film heaters. In consideration of the high performance of the graphene film heater, we demonstrate its three application scenarios: portable warmers applied in medical infusion apparatus, flexible custom-shaped heaters for special requirements and displays.

Controlled Chemical Synthesis in CVD Graphene

Due to the unique properties of graphene, single layer, bilayer or even few layer graphene peeled off from bulk graphite cannot meet the need of practical applications. Large size graphene with quality comparable to mechanically exfoliated graphene has been synthesized by chemical vapor deposition (CVD). The main development and the key issues in controllable chemical vapor deposition of graphene has been briefly discussed in this chapter. Various strategies for graphene layer number and stacking control, large size single crystal graphene domains on copper, graphene direct growth on dielectric substrates, and doping of graphene have been demonstrated. The methods summarized here will provide guidance on how to synthesize other two-dimensional materials beyond graphene.

Graphene: An Outstanding Multifunctional Coating for Conventional Materials

As the most significant facilitator of human civilization, materials are eternal jewels in the view of researchers whose brilliance never faded. However, simple conventional materials, which are most commonly used and indispensable today, seem too primitive and insufficiently functional to meet the demands of the future intelligent and informational applications, urging more functions to be integrated. The ideal strategy to achieve the transformations of conventional materials non-destructively is functionalizing the surface and retaining the original properties at the same time. Graphene, a two-dimensional material with only atomic-thickness, has come into the view of the researchers, attributed to its various outstanding properties. In recent years, a large amount of research has been devoted to "wearing" graphene to functionalize the conventional materials, booming a huge "graphene-X" family. In this concept, representative members are illustrated and their improved functions are demonstrated. Also, the prospects and challenges for this dazzling family are discussed.

Self-Terminating Confinement Approach for Large-Area Uniform Monolayer Graphene Directly over Si/SiOx by Chemical Vapor Deposition

To synthesize graphene by chemical vapor deposition (CVD) both in large area and with uniform layer number directly over Si/SiO_x has proven challenging. The use of catalytically active metal substrates, in particular Cu, has shown far greater success and therefore is popular. That said, for electronics applications it requires a transfer procedure, which tends to damage and contaminate the graphene. Thus, the direct fabrication of uniform graphene on Si/SiO_x remains attractive. Here we show a facile confinement CVD approach in which we simply "sandwich" two Si wafers with their oxide faces in contact to form uniform monolayer graphene. A thorough examination of the material reveals it comprises faceted grains despite initially nucleating as round islands. Upon clustering, they facet to minimize their energy. This behavior leads to faceting in polygons, as the system aims to ideally form hexagons, the lowest energy form, much like the hexagonal cells in a beehive, which requires the minimum wax. This process also leads to a near minimal total grain boundary length per unit area. This fact, along with the high graphene quality, is reflected in its electrical performance, which is highly comparable with graphene formed over other substrates, including Cu. In addition, the graphene growth is self-terminating. Our CVD approach is easily scalable and will make graphene formation directly on Si wafers competitive against that from metal substrates, which suffer from transfer. Moreover, this CVD route should be applicable for the direct synthesis of other 2D materials and their van der Waals heterostructures.

Fast Growth and Broad Applications of 25-Inch Uniform Graphene Glass

A unique ethanol-precursor-based LPCVD route is developed for the fast (4 min, improved 20 times) and scalable (25 inch, improved six times) growth of high-quality graphene glass. The obtained graphene glass presents high uniformity across large areas and is demonstrated to be an excellent material for constructing switchable windows and biosensor devices, owing to its excellent transparency and conductivity.

High-performance graphene-based flexible heater for wearable applications

A graphene-based flexible heater with low driving voltage and ultrafast response time.

Graphene Glass from Direct CVD Routes: Production and Applications

Recently, direct chemical vapor deposition (CVD) growth of graphene on various types of glasses has emerged as a promising route to produce graphene glass, with advantages such as tunable quality, excellent film uniformity and potential scalability. Crucial to the performance of this graphene-coated glass is that the outstanding properties of graphene are fully retained for endowing glass with new surface characteristics, making direct-CVD-derived graphene glass versatile enough for developing various applications for daily life. Herein, recent advances in the synthesis of graphene glass, particularly via direct CVD approaches, are presented. Key applications of such graphene materials in transparent conductors, smart windows, simple heating devices, solar-cell electrodes, cell culture medium, and water harvesters are also highlighted.

Human-Like Sensing and Reflexes of Graphene-Based Films

Humans have numerous senses, wherein vision, hearing, smell, taste, and touch are considered as the five conventionally acknowledged senses. Triggered by light, sound, or other physical stimulations, the sensory organs of human body are excited, leading to the transformation of the afferent energy into neural activity. Also converting other signals into electronical signals, graphene-based film shows its inherent advantages in responding to the tiny stimulations. In this review, the human-like senses and reflexes of graphene-based films are presented. The review starts with the brief discussions about the preparation and optimization of graphene-based film, as where as its new progress in synthesis method, transfer operation, film-formation technologies and optimization techniques. Various human-like senses of graphene-based film and their recent advancements are then summarized, including light-sensitive devices, acoustic devices, gas sensors, biomolecules and wearable devices. Similar to the reflex action of humans, graphene-based film also exhibits reflex when under thermal radiation and light actuation. Finally, the current challenges associated with human-like applications are discussed to help guide the future research on graphene films. At last, the future opportunities lie in the new applicable human-like senses and the integration of multiple senses that can raise a revolution in bionic devices.

Direct CVD Graphene Growth on Semiconductors and Dielectrics for Transfer-Free Device Fabrication

Graphene is the most broadly discussed and studied two-dimensional material because of its preeminent physical, mechanical, optical, and thermal properties. Until now, metal-catalyzed chemical vapor deposition (CVD) has been widely employed for the scalable production of high-quality graphene. However, in order to incorporate the graphene into electronic devices, a transfer process from metal substrates to targeted substrates is inevitable. This process usually results in contamination, wrinkling, and breakage of graphene samples - undesirable in graphene-based technology and not compatible with industrial production. Therefore, direct graphene growth on desired semiconductor and dielectric substrates is considered as an effective alternative. Over the past years, there have been intensive investigations to realize direct graphene growth using CVD methods without the catalytic role of metals. Owing to the low catalytic activity of non-metal substrates for carbon precursor decomposition and graphene growth, several strategies have been designed to facilitate and engineer graphene fabrication on semiconductors and insulators. Here, those developed strategies for direct CVD graphene growth on semiconductors and dielectrics for transfer-free fabrication of electronic devices are reviewed. By employing these methods, various graphene-related structures can be directly prepared on desired substrates and exhibit excellent performance, providing versatile routes for varied graphene-based materials fabrication.

Highly Stable and Conductive Microcapsules for Enhancement of Joule Heating Performance

Nanocarbons show great promise for establishing the next generation of Joule heating systems, but suffer from the limited maximum temperature due to precociously convective heat dissipation from electrothermal system to surrounding environment. Here we introduce a strategy to eliminate such convective heat transfer by inserting highly stable and conductive microcapsules into the electrothermal structures. The microcapsule is composed of encapsulated long-chain alkanes and graphene oxide/carbon nanotube hybrids as core and shell material, respectively. Multiform carbon nanotubes in the microspheres stabilize the capsule shell to resist volume-change-induced rupture during repeated heating/cooling process, and meanwhile enhance the thermal conductance of encapsulated alkanes which facilitates an expeditious heat exchange. The resulting microcapsules can be homogeneously incorporated in the nanocarbon-based electrothermal structures. At a dopant of 5%, the working temperature can be enhanced by 30% even at a low voltage and moderate temperature, which indicates a great value in daily household applications. Therefore, the stable and conductive microcapsule may serve as a versatile and valuable dopant for varieties of heat generation systems.

Graphene Coating of Silicon Nanoparticles with CO2 -Enhanced Chemical Vapor Deposition

Understanding the growth of graphene over Si species is becoming ever more important as the huge potential for the combination of these two materials becomes more apparent, not only for device fabrication but also in energy applications, particularly in Li-ion batteries. Thus, the drive for the direct fabrication of graphene over Si is crucial because indirect approaches, by their very nature, require processing steps that, in general, contaminate, damage, and are costly. In this work, the direct chemical vapor deposition growth of few-layer graphene over Si nanoparticles is systematically explored through experiment and theory with the use of a reducer, H2 or the use of a mild oxidant, CO2 combined with CH4 . Unlike the case of CH4 , with the use of CO2 as a mild oxidant in the reaction, the graphene layers form neatly over the surface and encapsulate the Si particles. SiC formation is also prevented. These structures show exceptionally good electrochemical performance as high capacity anodes for lithium-ion batteries. Density functional theory studies show the presence of CO2 not only prevents SiC formation but helps enhance the catalytic activity of the particles by maintaining an SiOx surface. In addition, CO2 can enhance graphitization.

Transparent flexible electrodes based on a AgNW network reconstructed by salt

Pre-coated NaCl could result in a reshaped AgNW network and reduce junction resistance significantly.

A study of the growth-time effect on graphene layer number based on a Cu–Ni bilayer catalyst system

Graphene layer number is controlled by changing Cu–Ni ratio and growth time. Single- and few-layer graphene are formed separately on Cu- and Ni-rich catalysts. The growth of bilayer graphene is attributed to the synergic effect of Cu and Ni (1 : 1).

Growing Uniform Graphene Disks and Films on Molten Glass for Heating Devices and Cell Culture

The direct growth of uniform graphene disks and their continuous film is achieved by exploiting the molten state of glass. The use of molten glass enables highly uniform nucleation and an enhanced growth rate (tenfold) of graphene, as compared to those scenarios on commonly used insulating solids. The obtained graphene glasses show promising application potentials in daily-life scenarios such as smart heating devices and biocompatible cell-culture mediums.

Reduced graphene oxide-wrapped MoO3 composites prepared by using metal-organic frameworks as precursor for all-solid-state flexible supercapacitors

Reduced graphene oxide-wrapped MoO3M (rGO/MoO3 ) is prepared by a novel and simple method that is developed by using a metal-organic framework as the precursor. After a two-step annealing process, the obtained rGO/MoO3 composite is used for a high-performance supercapacitor electrode. Moreover, an all-solid-state flexible supercapacitor is fabricated based on the rGO/MoO3 composite, which shows stable performance under different bending states.