Wet‐Spun Superelastic Graphene Aerogel Millispheres with Group Effect

Graphene aerogel has attracted great attention due to its unique properties, such as ultralow density, superelasticity, and high specific surface area. It shows huge potential in energy devices, high‐performance pressure sensors, contaminates adsorbents, and electromagnetic wave absorbing materials. However, there still remain some challenges to further promote the development and real application of graphene aerogel including cost‐effective scalable fabrication and miniaturization with group effect. This study shows millimeter‐scale superelastic graphene aerogel spheres (GSs) with group effect and multifunctionality. The GSs are continuously fabricated on a large scale by wet spinning of graphene oxide liquid crystals followed by facile drying and thermal annealing. Such GS has an unusual core–shell structure with excellent elasticity and specific strength. Significantly, both horizontally and vertically grouped spheres exhibit superelasticity comparable to individual spheres, enabling it to fully recover at 95% strain, and even after 1000 compressive cycles at 70% strain, paving the way to wide applications such as pressure‐elastic and adsorbing materials. The GS shows a press‐fly behavior with an extremely high jump velocity up to 1.2 m s^?1. For the first time, both free and oil‐adsorbed GSs are remotely manipulated on water by electrostatic charge due to their ultralow density and hydrophobic properties.     

Gate‐Controlled Graphene–Silicon Schottky Junction Photodetector

Various photodetectors showing extremely high photoresponsivity have been frequently reported, but many of these photodetectors could not avoid the simultaneous amplification of dark current. A gate‐controlled graphene–silicon Schottky junction photodetector that exhibits a high on/off photoswitching ratio (≈10⁴), a very high photoresponsivity (≈70 A W⁻¹), and a low dark current in the order of µA cm⁻² in a wide wavelength range (395–850 nm) is demonstrated. The photoresponsivity is ≈100 times higher than that of existing commercial photodetectors, and 7000 times higher than that of graphene‐field‐effect transistor‐based photodetectors, while the dark current is similar to or lower than that of commercial photodetectors. This result can be explained by a unique gain mechanism originating from the difference in carrier transport characteristics of silicon and graphene.     

Gate‐Tunable Graphene–WSe2 Heterojunctions at the Schottky–Mott Limit

Metal–semiconductor interfaces, known as Schottky junctions, have long been hindered by defects and impurities. Such imperfections dominate the electrical characteristics of the junction by pinning the metal Fermi energy. Here, a graphene–WSe₂ p‐type Schottky junction, which exhibits a lack of Fermi level pinning, is studied. The Schottky junction displays near‐ideal diode characteristics with large gate tunability and small leakage currents. Using a gate electrostatically coupled to the WSe₂ channel to tune the Schottky barrier height, the Schottky–Mott limit is probed in a single device. As a special manifestation of the tunable Schottky barrier, a diode with a dynamically controlled ideality factor is demonstrated.     

Graphene‐Based Electrodes

Graphene, the thinnest two dimensional carbon material, has become the subject of intensive investigation in various research fields because of its remarkable electronic, mechanical, optical and thermal properties. Graphene‐based electrodes, fabricated from mechanically cleaved graphene, chemical vapor deposition (CVD) grown graphene, or massively produced graphene derivatives from bulk graphite, have been applied in a broad range of applications, such as in light emitting diodes, touch screens, field‐effect transistors, solar cells, supercapacitors, batteries, and sensors. In this Review, after a short introduction to the properties and synthetic methods of graphene and its derivatives, we will discuss the importance of graphene‐based electrodes, their fabrication techniques, and application areas.     

Nanopatched Graphene with Molecular Self‐Assembly Toward Graphene–Organic Hybrid Soft Electronics

Increasing the mechanical durability of large‐area polycrystalline single‐atom‐thick materials is a necessary step toward the development of practical and reliable soft electronics based on these materials. Here, it is shown that the surface assembly of organosilane by weak epitaxy forms nanometer‐thick organic patches on a monolayer graphene surface and dramatically increases the material's resistance to harsh postprocessing environments, thereby increasing the number of ways in which graphene can be processed. The nanopatched graphene with the improved mechanical durability enables stable operation when used as transparent electrodes of wearable strain sensors. Also, the nanopatched graphene applied as an electrode modulates the molecular orientation of deposited organic semiconductor layers, and yields favorable nominal charge injection for organic transistors. These results demonstrate the potential for use of self‐assembled organic nanopatches in graphene‐based soft electronics.     

Hollow‐Structured Graphene–Silicone‐Composite‐Based Piezoresistive Sensors: Decoupled Property Tuning and Bending Reliability

A versatile flexible piezoresistive sensor should maintain high sensitivity in a wide linear range, and provide a stable and repeatable pressure reading under bending. These properties are often difficult to achieve simultaneously with conventional filler–matrix composite active materials, as tuning of one material component often results in change of multiple sensor properties. Here, a material strategy is developed to realize a 3D graphene–poly(dimethylsiloxane) hollow structure, where the electrical conductivity and mechanical elasticity of the composite can be tuned separately by varying the graphene layer number and the poly(dimethylsiloxane) composition ratio, respectively. As a result, the sensor sensitivity and linear range can be easily improved through a decoupled tuning process, reaching a sensitivity of 15.9 kPa^?1 in a 60 kPa linear region, and the sensor also exhibits fast response (1.2 ms rising time) and high stability. Furthermore, by optimizing the density of the graphene percolation network and thickness of the composite, the stability and repeatability of the sensor output under bending are improved, achieving a measurement error below 6% under bending radius variations from ?25 to +25 mm. Finally, the potential applications of these sensors in wearable medical devices and robotic vision are explored.     

Graphene–Graphene Oxide Floating Gate Transistor Memory

A novel transparent, flexible, graphene channel floating‐gate transistor memory (FGTM) device is fabricated using a graphene oxide (GO) charge trapping layer on a plastic substrate. The GO layer, which bears ammonium groups (NH₃⁺), is prepared at the interface between the crosslinked PVP (cPVP) tunneling dielectric and the Al₂O₃ blocking dielectric layers. Important design rules are proposed for a high‐performance graphene memory device: i) precise doping of the graphene channel, and ii) chemical functionalization of the GO charge trapping layer. How to control memory characteristics by graphene doping is systematically explained, and the optimal conditions for the best performance of the memory devices are found. Note that precise control over the doping of the graphene channel maximizes the conductance difference at a zero gate voltage, which reduces the device power consumption. The proposed optimization via graphene doping can be applied to any graphene channel transistor‐type memory device. Additionally, the positively charged GO (GO–NH₃⁺) interacts electrostatically with hydroxyl groups of both UV‐treated Al₂O₃ and PVP layers, which enhances the interfacial adhesion, and thus the mechanical stability of the device during bending. The resulting graphene–graphene oxide FGTMs exhibit excellent memory characteristics, including a large memory window (11.7 V), fast switching speed (1 μs), cyclic endurance (200 cycles), stable retention (10⁵ s), and good mechanical stability (1000 cycles).