Continuous wafer-scale graphene on cubic-SiC（O01）

The atomic and electronic structure of graphene synthesized on commercially available cubic-SiC（001）/Si（001） wafers have been studied by low energy electron microscopy （LEEM）, scanning tunneling microscopy （STM）, low energy electron diffraction （LEED）, and angle resolved photoelectron spectroscopy （ARPES）. LEEM and STM data prove the wafer-scale continuity and uniform thickness of the graphene overlayer on SIC（001）. LEEM, STM and ARPES studies reveal that the graphene overlayer on SIC（001） consists of only a few monolayers with physical properties of quasi-freestanding graphene. Atomically resolved STM and micro-LEED data show that the top graphene layer consists of nanometer-sized domains with four different lattice orientations connected through the 〈110〉-directed boundaries. ARPES studies reveal the typical electron spectrum of graphene with the Dirac points close to the Fermi level. Thus, the use of technologically relevant SiC（001）/Si（001） wafers for graphene fabrication repre-sents a realistic way of bridging the gap between the outstanding properties of graphene and their applications.     

Effects of Pb Intercalation on the Structural and Electronic Properties of Epitaxial Graphene on SiC

The effects of Pb intercalation on the structural and electronic properties of epitaxial single‐layer graphene grown on SiC(0001) substrate are investigated using scanning tunneling microscopy (STM), noncontact atomic force microscopy, Kelvin probe force microscopy (KPFM), X‐ray photoelectron spectroscopy, and angle‐resolved photoemission spectroscopy (ARPES) methods. The STM results show the formation of an ordered moiré superstructure pattern induced by Pb atom intercalation underneath the graphene layer. ARPES measurements reveal the presence of two additional linearly dispersing π‐bands, providing evidence for the decoupling of the buffer layer from the underlying SiC substrate. Upon Pb intercalation, the Si 2p core level spectra show a signature for the existence of Pb? Si chemical bonds at the interface region, as manifested in a shift of 1.2 eV of the bulk SiC component toward lower binding energies. The Pb intercalation gives rise to hole‐doping of graphene and results in a shift of the Dirac point energy by about 0.1 eV above the Fermi level, as revealed by the ARPES measurements. The KPFM experiments have shown that decoupling of the graphene layer by Pb intercalation is accompanied by a work function increase. The observed increase in the work function is attributed to the suppression of the electron transfer from the SiC substrate to the graphene layer. The Pb intercalated structure is found to be stable in ambient conditions and at high temperatures up to 1250 °C. These results demonstrate that the construction of a graphene‐capped Pb/SiC system offers a possibility of tuning the graphene electronic properties and exploring intriguing physical properties such as superconductivity and spintronics.     

Nanostructuring Confinement for Controllable Interfacial Charge Transfer

Carbon nanostructures supported semiconductors are common in photocatalytic and photoelectrochemical applications, as it is expected that the nanoconductors can improve the spatial separation and transport of photogenerated charge carriers. Transfer of charge carriers through the carbon‐semiconductor interface is the key electronic process, which determines the role of charge separation channels, and is sensitively influenced by band structures of the semiconductor near the contacts. Usually, this electronic process suffers from excessive energy dissipation by thermionic emission, which will undesirably prevent the interfacial charge transfer and eventually aggravate the recombination of photogenerated charge carriers. Unfortunately, this critical issue has hardly been consciously considered. Here, ultrathin dopant‐free tunneling interlayers coated on the surface of graphene and sandwiched between the carbon sheets and the semiconductor nanostructures are adopted as a model system to demonstrate energy saving for the interfacial charge transfer. The nanostructuring confinement of band bending within the ultrathin interlayers in contact with the graphene sheets effectively narrows the width of the potential barriers, which enables tunneling of a substantial number of photogenerated electrons to the co‐catalysts without unduly consuming energy. Besides, the dopant‐free tunneling interlayers simultaneously block the transferred electrons in the sandwiched graphene sheets from leakage.     

Imaging of resonant quenching of surface plasmons by quantum dots

In scanning tunneling microscopy (STM), confinement of surface plasmons to the optical cavity formed at the metallic tunneling gap stimulates the emission of light. We demonstrate that quantum dots (QDs) found in such a cavity give rise to discrete, observable transitions in the tunneling luminescence spectrum due to the resonant extinction of the plasmon. The observed resonances represent a fingerprint of the QD and occur at the optical band gap owing to the nearly simultaneous transfer of carriers from both sides of the tunneling gap to the QD. The resonant quenching of surface plasmons enables a new imaging technique, dubbed plasmon resonance imaging, with a spatial resolution potentially similar to that of STM and the energy resolution of optical spectroscopies. This detection and imaging strategy is not restricted to QDs, being of great interest to an entire spectrum of nanostructures, from molecular assemblies and biomolecules to carbon nanotubes.     

A comparison of different carbon filaments on the nanometer and atomic scales by scanning tunneling microscopy

Scanning tunneling microscopy (STM) has been employed as a tool to elucidate the structural differences between carbon nanotubes (CNTs) and carbon nanofibers (CNFs) at the nanometer and atomic scales. As opposed to the seamless, virtually defect-free structure of CNTs that was visualized by STM at both scales, CNFs displayed a fragmented graphitic conformation (nanographites), where the nanographitic domains were below 2-3 nm in lateral size. Thus, STM is proposed as a suitable technique to discriminate these two types of carbon nanostructures.     

Graphene Acoustic Phonon‐Mediated Pseudo‐Landau Levels Tailoring Probed by Scanning Tunneling Spectroscopy

Graphene has attracted great interests in various areas including optoelectronics, spintronics, and nanomechanics due to its unique electronic structure, a linear dispersion with a zero bandgap around the Dirac point. Shifts of Dirac cones in graphene creates pseudo‐magnetic field, which generates an energy gap and brings a zero‐magnetic‐field analogue of the quantum Hall effect. Recent studies have demonstrated that graphene pseudo‐magnetic effects can be generated by vacancy defects, atom adsorption, zigzag or armchair edges, and external strain. Here, a larger than 100 T pseudo‐magnetic field is reported that generated on the step area of graphene; and with the ultrahigh vacuum scanning tunneling microscopy, the observed Landau levels can be effectively tailored by graphene phonons. The zero pseudo‐Landau level is suppressed due to the phonon‐mediated inelastic tunneling, and this is observed by the scanning tunneling spectroscopy spectrum and confirmed by the Vienna ab initio simulation package calculation, where graphene phonons modulate the flow of tunneling electrons and further mediate pseudo‐Landau levels. These observations demonstrate a viable approach for the control of pseudo‐Landau levels, which tailors the electronic structure of graphene, and further ignites applications in graphene valley electronics.     

Fabrication of Millimeter‐Scale,Single‐Crystal One‐Third‐Hydrogenated Graphene with Anisotropic Electronic Properties

Periodically hydrogenated graphene is predicted to form new kinds of crystalline 2D materials such as graphane, graphone, and 2D C_xH_y, which exhibit unique electronic properties. Controlled synthesis of periodically hydrogenated graphene is needed for fundamental research and possible electronic applications. Only small patches of such materials have been grown so far, while the experimental fabrication of large‐scale, periodically hydrogenated graphene has remained challenging. In the present work, large‐scale, periodically hydrogenated graphene is fabricated on Ru(0001). The as‐fabricated hydrogenated graphene is highly ordered, with a √3 × √3/R30° period relative to the pristine graphene. As the ratio of hydrogen and carbon is 1:3, the periodically hydrogenated graphene is named “one‐third‐hydrogenated graphene” (OTHG). The area of OTHG is up to 16 mm². Density functional theory calculations demonstrate that the OTHG has two deformed Dirac cones along one high‐symmetry direction and a finite energy gap along the other directions at the Fermi energy, indicating strong anisotropic electrical properties. An efficient method is thus provided to produce large‐scale crystalline functionalized graphene with specially desired properties.     

Dirac Fermion Kinetics in 3D Curved Graphene

3D integration of graphene has attracted attention for realizing carbon-based electronic devices. While the 3D integration can amplify various excellent properties of graphene, the influence of 3D curved surfaces on the fundamental physical properties of graphene has not been clarified. The electronic properties of 3D nanoporous graphene with a curvature radius down to 25–50 nm are systematically investigated and the ambipolar electronic states of Dirac fermions are essentially preserved in the 3D graphene nanoarchitectures, while the 3D curvature can effectively suppress the slope of the linear density of states of Dirac fermion near the Fermi level are demonstrated. Importantly, the 3D curvature can be utilized to tune the back-scattering-suppressed electrical transport of Dirac fermions and enhance both electron localization and electron–electron interaction. As a result, nanoscale curvature provides a new degree of freedom to manipulate 3D graphene electrical properties, which may pave a new way to design new 3D graphene devices with preserved 2D electronic properties and novel functionalities.     

A facile method for fabrication of large area graphene nanostructures

In this study, we introduce a novel method to produce large area interconnected graphene nanostructures. A single layer CVD (Chemical Vapor Deposition) grown graphene was nanostructured by employing dewetted Ni thin film as an etching mask for the underlying graphene. As a result, a network of graphene nanostructures with irregular shapes and widths down to 10 nm is obtained. The FET (field effect transistor) devices fabricated employing the nanostructured graphene as channel material exhibit increased on/off current ratio compared to pristine graphene indicating a slight band gap opening due to the quantum confinement effect in such narrow graphene nanostructures. This technique can be useful for the large scale fabrication of graphene based electronic devices such as FETs and sensors.     

Topographic and spectroscopic characterization of electronic edge states in CVD grown graphene nanoribbons

We used scanning tunneling microscopy and spectroscopy (STM/S) techniques to analyze the relationships between the edge shapes and the electronic structures in as-grown chemical vapor deposition (CVD) graphene nanoribbons (GNRs). A rich variety of single-layered graphene nanoribbons exhibiting a width of several to 100 nm and up to 1 μm long were studied. High-resolution STM images highlight highly crystalline nanoribbon structures with well-defined and clean edges. Theoretical calculations indicate clear spin-split edge states induced by electron-electron Coulomb repulsion. The edge defects can significantly modify these edge states, and different edge structures for both sides of a single ribbon produce asymmetric electronic edge states, which reflect the more realistic features of CVD grown GNRs. Three structural models are proposed and analyzed to explain the observations. By comparing the models with an atomic resolution image at the edge, a pristine (2,1) structure was ruled out in favor of a reconstructed edge structure composed of 5-7 member rings, showing a better match with experimental results, and thereby suggesting the possibility of a defective morphology at the edge of CVD grown nanoribbons.     

Rapid Low‐Temperature 3D Integration of Silicon Nanowires on Flexible Substrates

The vertical integration of 1D nanostructures onto the 2D substrates has the potential to offer significant performance gains to flexible electronic devices due to high integration density, large surface area, and improved light absorption and trapping. A simple, rapid, and low temperature transfer bonding method has been developed for this purpose. Ultrasonic vibration is used to achieve a low temperature bonding within a few seconds, resulting in a polymer‐matrix‐free, electrically conducting vertical assembly of silicon nanowires (SiNWs) with a graphene/PET substrate. The microscopic structure, and mechanical and electrical characteristics of the interface between the transferred SiNW array and graphene layer are subsequently investigated, revealing that this creates a mechanically robust and electrically Ohmic contact. This newly developed ultrasonic transfer bonding technique is also found to be readily adaptable for diverse substrates of both metal and polymer. It is therefore considered as a valuable technique for integrating 1D vertical nanostructures onto the 2D flexible substrates for flexible photovoltaics, energy storage, and water splitting systems.     

In‐Plane Electrical Connectivity and Near‐Field Concentration of Isolated Graphene Resonators Realized by Ion Beams

Graphene plasmons provide great opportunities in light–matter interactions benefiting from the extreme confinement and electrical tunability. Structured graphene cavities possess enhanced confinements in 3D and steerable plasmon resonances, potential in applications for sensing and emission control at the nanoscale. Besides graphene boundaries obtained by mask lithography, graphene defects engineered by ion beams have shown efficient plasmon reflections. In this paper, near‐field responses of structured graphene achieved by ion beam direct‐writing are investigated. Graphene nanoresonators are fabricated easily and precisely with a spatial resolution better than 30 nm. Breathing modes are observed in graphene disks. The amorphous carbons around weaken the response of edge modes in the resonators, but meanwhile render the isolated resonators in‐plane electrical connections, where near‐fields are proved gate‐tunable. The realization of gate‐tunable near‐fields of graphene 2D resonators opens up tunable near‐field couplings with matters. Moreover, graphene nonconcentric rings with engineered near‐field confinement distributions are demonstrated, where the quadrupole plasmon modes are excited. Near‐field mappings reveal concentrations at the scale of within certain zones which can be engineered. The realization of electrically tunable graphene nanoresonators by ion beam direct‐writing is promising for active manipulation of emission and sensing at the nanoscale.     

Patterning nanoroads and quantum dots on fluorinated graphene

Using ab initio methods we have investigated the fluorination of graphene and find that different stoichiometric phases can be formed without a nucleation barrier, with the complete “2D-Teflon” CF phase being thermodynamically most stable. The fluorinated graphene is an insulator and turns out to be a perfect matrix-host for patterning nanoroads and quantum dots of pristine graphene. The electronic and magnetic properties of the nanoroads can be tuned by varying the edge orientation and width. The energy gaps between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO) of quantum dots are size-dependent and show a confinement typical of Dirac fermions. Furthermore, we study the effect of different basic coverage of F on graphene (with stoichiometries CF and C₄F) on the band gaps, and show the suitability of these materials to host quantum dots of graphene with unique electronic properties.     

Facile synthesis of three-dimensional porous graphene nanostructures from coordination complexes for supercapacitor electrode

Fabrication of hierarchical nanostructures is an important way for performance improvement and application expansion of nanomaterials. It is still a great challenge to synthesize three dimensional hierarchical graphene nanostructures with controlled secondary structures and primary building units, because it is difficult to realize effective control of graphene layer morphology and necessary arrangement of graphene. In this work, a “complex-directed” strategy has been successfully developed for the synthesis of three dimensional graphene nanostructures. Especially, the obtained three dimensional graphene nanostructures are quite regular in morphology, they can be nanorods or regular particles, composed of hollow graphene nanospheres with different layers. The morphology and the structure of these nanostructures, including primary building units and secondary structures are strongly dependent on the amount of HCl solution. The obtained three-dimensional graphene nanostructure can serve as an excellent candidate for electrode material of electric double layer capacitors (EDLCs) and present outstanding electrochemical behaviors. This is mainly due to the excellent electrical conductivity of graphene hollow nanospheres and the porous structures conducive to ion diffusion and electron transport.     

A Simple Route to Porous Graphene from Carbon Nanodots for Supercapacitor Applications

A facile method to convert biomolecule‐based carbon nanodots (CNDs) into high‐surface‐area 3D‐graphene networks with excellent electrochemical properties is presented. Initially, CNDs are synthesized by microwave‐assisted thermolysis of citric acid and urea according to previously published protocols. Next, the CNDs are annealed up to 400 °C in a tube furnace in an oxygen‐free environment. Finally, films of the thermolyzed CNDs are converted into open porous 3D turbostratic graphene (3D‐ts‐graphene) networks by irradiation with an infrared laser. Based upon characterizations using scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, Fourier‐transform infrared spectroscopy, and Raman spectroscopy, a feasible reaction mechanism for both the thermolysis of the CNDs and the subsequent laser conversion into 3D‐ts‐graphene is presented. The 3D‐ts‐graphene networks show excellent morphological properties, such as a hierarchical porous structure and a high surface area, as well as promising electrochemical properties. For example, nearly ideal capacitive behavior with a volumetric capacitance of 27.5 mF L ^{? 1} is achieved at a current density of 560 A L ^{? 1}, which corresponds to an energy density of 24.1 mWh L ^{? 1} at a power density of 711 W L ^{? 1}. Remarkable is the extremely fast charge–discharge cycling rate with a time constant of 3.44 ms.     

Substrate Phonon‐Mediated Plasmon Hybridization in Coplanar Graphene Nanostructures for Broadband Plasmonic Circuits

The mode hybridization between adjacent graphene nanoribbons determines the integration density of graphene‐based plasmonic devices. Here, plasmon hybridization in graphene nanostructures is demonstrated through the characterization of the coupling strength of plasmons in graphene nanoribbons as a function of charge density and inter‐ribbon spacing using Fourier transform infrared microscopy. In combination with numerical simulations, it is shown that the plasmon coupling is strongly mediated by the substrate phonons. For polar substrates, the plasmon coupling strength is limited by the plasmon–phonon interactions. In contrast, a nonpolar substrate affects neither the energy distribution of the original plasmon modes in graphene nanostructures nor their plasmon interactions, which increases exponentially as the inter‐ribbon spacing decreases. To further explore the potential of graphene broadband plasmonics on nonpolar substrates, a scheme is proposed that uses a metal–dielectric heterostructure to prevent the overlap of plasmons between neighboring graphene nanoribbons. The device structures retain the plasmon resonance frequency of the graphene ribbons and maximally isolate the plasmonic components from the surrounding electromagnetic environment, allowing modular design in integrated plasmonic circuits.     

Chemically Integrated Inorganic‐Graphene Two‐Dimensional Hybrid Materials for Flexible Energy Storage Devices

State‐of‐the‐art energy storage devices are capable of delivering reasonably high energy density (lithium ion batteries) or high power density (supercapacitors). There is an increasing need for these power sources with not only superior electrochemical performance, but also exceptional flexibility. Graphene has come on to the scene and advancements are being made in integration of various electrochemically active compounds onto graphene or its derivatives so as to utilize their flexibility. Many innovative synthesis techniques have led to novel graphene‐based hybrid two‐dimensional nanostructures. Here, the chemically integrated inorganic‐graphene hybrid two‐dimensional materials and their applications for energy storage devices are examined. First, the synthesis and characterization of different kinds of inorganic‐graphene hybrid nanostructures are summarized, and then the most relevant applications of inorganic‐graphene hybrid materials in flexible energy storage devices are reviewed. The general design rules of using graphene‐based hybrid 2D materials for energy storage devices and their current limitations and future potential to advance energy storage technologies are also discussed.     

Enhanced Peltier Effect in Wrinkled Graphene Constriction by Nano‐Bubble Engineering

Inspired by the promising applications in thermopower generation from waste heat and active on‐chip cooling, the thermoelectric and electrothermal properties of graphene have been extensively pursued by seeking ingeniously designed structures with thermoelectric conversion capability. The graphene wrinkle is a ubiquitous structure formed inevitably during the synthesis of large‐scale graphene films but the corresponding properties for thermoelectric and electrothermal applications are rarely investigated. Here, the electrothermal Peltier effect from the graphene wrinkle fabricated on a germanium substrate is reported. Peltier cooling and heating across the wrinkle are visualized unambiguously with polarities consistent with p‐type doping and in accordance with the wrinkle spatial distribution. By direct patterning of the nano‐bubble structure, the current density across the wrinkle can be boosted by current crowding to enhance the Peltier effect. The observed Peltier effect can be attributed to the nonequilibrium charge transport by interlayer tunneling across the van der Waals barrier of the graphene wrinkle. The graphene wrinkle in combination with nano‐bubble engineering constitutes an innovative and agile platform to design graphene and other more general two‐dimensional (2D) thermoelectrics and opens the possibility for realizing active on‐chip cooling for 2D nanoelectronics with van der Waals junctions.     

Dirac Semimetal Heterostructures: 3D Cd3As2 on 2D Graphene

Dirac semimetal is an emerging class of quantum matters, ranging from 2D category, such as, graphene and surface states of topological insulator to 3D category, for instance, Cd₃As₂ and Na₃Bi. As 3D Dirac semimetals typically possess Fermi‐arc surface states, the 2D–3D Dirac van der Waals heterostructures should be promising for future electronics. Here, graphene–Cd₃As₂ heterostructures are fabricated through direct layer‐by‐layer stacking. The electronic coupling results in a notable interlayer charge transfer, which enables us to modulate the Fermi level of graphene through Cd₃As₂. A planar graphene p–n–p junction is achieved by selective modification, which demonstrates quantized conductance plateaus. Moreover, compared with the bare graphene device, the graphene–Cd₃As₂ hybrid device presents large nonlocal signals near the Dirac point due to the charge transfer from the spin‐polarized surface states in the adjacent Cd₃As₂. The results enrich the family of van der Waals heterostructure and should inspire more studies on the application of Dirac/Weyl semimetals in spintronics.     

Monolayer Graphene Coupled to a Flexible Plasmonic Nanograting for Ultrasensitive Strain Monitoring

Plasmonically coupled graphene structures have shown great promise for sensing applications. Their complex and cumbersome fabrication, however, has prohibited their widespread application and limited their use to rigid, planar surfaces. Here, a plasmonic sensor based on gold nanowire arrays on an elastomer with an added graphene monolayer is introduced. The stretchable plasmonic nanostructures not only significantly enhance the Raman signal from graphene, but can also be used by themselves as a sensor platform for 2D strain sensing. These nanowire arrays on an elastomer are fabricated by template‐stripping based nanotransfer printing, which enables a simple and fast production of stable nanogratings. The ultrasmooth surfaces of such transferred structures facilitate reliable large‐area transfers of graphene monolayers. The resulting coupled graphene‐nanograting construct exhibits ultrahigh sensitivity to applied strain, which can be detected by shifts in the plasmonic‐enhanced Raman spectrum. Furthermore, this sensor enables the detection of adsorbed molecules on nonplanar surfaces through graphene‐assisted surface enhanced Raman spectroscopy (SERS). The simple fabrication of the plasmonic nanowire array platform and the graphene‐coupled devices have the potential to trigger widespread SERS applications and open up new opportunities for high‐sensitivity strain sensing applications.