Showing papers on "Bilayer graphene published in 2017"
TL;DR: It is demonstrated that at small twist angles, the electronic properties of bilayer graphene moiré crystals are strongly altered by electron–electron interactions.
Abstract: According to electronic structure theory, bilayer graphene is expected to have anomalous electronic properties when it has long-period moire patterns produced by small misalignments between its individual layer honeycomb lattices. We have realized bilayer graphene moire crystals with accurately controlled twist angles smaller than 1° and studied their properties using scanning probe microscopy and electron transport. We observe conductivity minima at charge neutrality, satellite gaps that appear at anomalous carrier densities for twist angles smaller than 1°, and tunneling densities-of-states that are strongly dependent on carrier density. These features are robust up to large transverse electric fields. In perpendicular magnetic fields, we observe the emergence of a Hofstadter butterfly in the energy spectrum, with fourfold degenerate Landau levels, and broken symmetry quantum Hall states at filling factors ±1, 2, 3. These observations demonstrate that at small twist angles, the electronic properties of bilayer graphene moire crystals are strongly altered by electron-electron interactions.
479 citations
TL;DR: In this article, the lattice relaxation in the twisted bilayer graphene (TBG) and its effect on the electronic band structure was theoretically studied and an effective continuum theory was developed to obtain the optimized structure to minimize the total energy.
Abstract: We theoretically study the lattice relaxation in the twisted bilayer graphene (TBG) and its effect on the electronic band structure. We develop an effective continuum theory to describe the lattice relaxation in general TBGs and obtain the optimized structure to minimize the total energy. At small rotation angles $l{2}^{\ensuremath{\circ}}$, in particular, we find that the relaxed lattice drastically reduces the area of the AA stacking region and forms a triangular domain structure with alternating AB and BA stacking regions. We then investigate the effect of the domain formation on the electronic band structure. The most notable change from the nonrelaxed model is that an energy gap of up to 20 meV opens at the superlattice subband edges on the electron and hole sides. We also find that the lattice relaxation significantly enhances the Fermi velocity, which was strongly suppressed in the nonrelaxed model.
363 citations
TL;DR: Graphene nanoribbons on highly porous 3D graphene foam as the binder-free cathode for flexible Al-ion batteries exhibit low charge voltage, high capacity, excellent cycling ability, and fast charging and slow discharging performance.
Abstract: Graphene nanoribbons on highly porous 3D graphene foam as the binder-free cathode for flexible Al-ion batteries exhibit low charge voltage, high capacity, excellent cycling ability (even after 10 000 cycles there is no capacity decay), and fast charging and slow discharging performance (the battery can be fully charged in 80 s and discharged in more than 3100 s).
307 citations
TL;DR: Two-dimensional hexagonal boron nitride (h-BN) has similar lattice structure to graphene and has a lattice mismatch with graphene of less than 1.7%. At the same time, h-BN has an atomic level of flat surface, B atoms and N atoms saturated into the bond, which was considered the highest among the insulating substrates as discussed by the authors.
289 citations
TL;DR: A critical review of recent results in the graphene thermal field focusing on phonon dispersion, specific heat, thermal conductivity, and comparison of different models and computational approaches is provided in this article.
Abstract: A discovery of the unusual thermal properties of graphene stimulated experimental, theoretical and computational research directed at understanding phonon transport and thermal conduction in two-dimensional material systems. We provide a critical review of recent results in the graphene thermal field focusing on phonon dispersion, specific heat, thermal conductivity, and comparison of different models and computational approaches. The correlation between the phonon spectrum in graphene-based materials and the heat conduction properties is analyzed in details. The effects of the atomic plane rotations in bilayer graphene, isotope engineering, and relative contributions of different phonon dispersion branches are discussed. For readers' convenience, the summaries of main experimental and theoretical results on thermal conductivity as well as phonon mode contributions to thermal transport are provided in the form of comprehensive annotated tables.
255 citations
TL;DR: In this article, the authors have successfully prepared macro-size atomically flat monolayer NbSe2 films on bilayer graphene terminated surface of 6H-SiC(0001) substrates by a molecular beam epitaxy (MBE) method.
Abstract: Two-dimensional (2D) transition metal dichalcogenides (TMDs) have a range of unique physics properties and could be used in the development of electronics, photonics, spintronics, and quantum computing devices. The mechanical exfoliation technique of microsize TMD flakes has attracted particular interest due to its simplicity and cost effectiveness. However, for most applications, large-area and high-quality films are preferred. Furthermore, when the thickness of crystalline films is down to the 2D limit (monolayer), exotic properties can be expected due to the quantum confinement and symmetry breaking. In this paper, we have successfully prepared macro-size atomically flat monolayer NbSe2 films on bilayer graphene terminated surface of 6H-SiC(0001) substrates by a molecular beam epitaxy (MBE) method. The films exhibit an onset superconducting critical transition temperature (Tconset) above 6 K and the zero resistance superconducting critical transition temperature (Tczero) up to 2.40 K. Simultaneously, t...
242 citations
TL;DR: In this paper, a large volume, high-concentration, plane-defect-free, few-layer graphene dispersion is fast produced from graphite at high yield through ball milling.
Abstract: Due to low density, extremely high electrical and thermal conductivities, graphene has great potential to construct lightweight thermal conductive paper for high-power electric devices. However, the remarkable properties of graphene are on a molecular level and difficult to achieve when processed into macroscopic paper. Here, an effective route to construct ultrahigh conductive graphene paper is developed. First, large-volume, high-concentration, plane-defect-free, few-layer graphene dispersion is fast produced from graphite at high yield through ball milling. The exfoliated graphene dispersion is further processed into graphene paper through fast filtration, thermal treatment, and mechanical compression. The electrical and thermal conductivities of the resultant graphene paper are as high as 2231 S cm−1 and 1529 W m−1 K−1, superior to previously reported graphene papers. Structural analyses confirm that the ultrahigh conductivities are attributed to high quality of graphene sheets, their compact ordered stacking, and large graphitic crystalline domain size, which improve electron and phonon transport within basal plane of graphene sheet and between graphene sheets.
235 citations
TL;DR: Graphene is established as a pristine and tunable experimental platform for studying the interplay between topology and quantum criticality, and for detecting non-Abelian qubits.
Abstract: Non-Abelian anyons are a type of quasiparticle with the potential to encode quantum information in topological qubits protected from decoherence. Experimental systems that are predicted to harbour non-Abelian anyons include p-wave superfluids, superconducting systems with strong spin-orbit coupling, and paired states of interacting composite fermions that emerge at even denominators in the fractional quantum Hall (FQH) regime. Although even-denominator FQH states have been observed in several two-dimensional systems, small energy gaps and limited tunability have stymied definitive experimental probes of their non-Abelian nature. Here we report the observation of robust even-denominator FQH phases at half-integer Landau-level filling in van der Waals heterostructures consisting of dual-gated, hexagonal-boron-nitride-encapsulated bilayer graphene. The measured energy gap is three times larger than observed previously. We compare these FQH phases with numerical and theoretical models while simultaneously controlling the carrier density, layer polarization and magnetic field, and find evidence for the paired Pfaffian phase that is predicted to host non-Abelian anyons. Electric-field-controlled level crossings between states with different Landau-level indices reveal a cascade of FQH phase transitions, including a continuous phase transition between the even-denominator FQH state and a compressible composite fermion liquid. Our results establish graphene as a pristine and tunable experimental platform for studying the interplay between topology and quantum criticality, and for detecting non-Abelian qubits.
205 citations
TL;DR: In this article, strongly interacting bosons have been predicted to display a transition into a superfluid ground state, similar to Bose-Einstein condensation, in a double bilayer graphene structure with excitons as the bosonic particles.
Abstract: Strongly interacting bosons have been predicted to display a transition into a superfluid ground state, similar to Bose–Einstein condensation. This effect is now observed in a double bilayer graphene structure, with excitons as the bosonic particles.
199 citations
TL;DR: Theoretical calculations were used to elucidate the effects of individual chemical forms of nitrogen on magnetic properties, and showed that magnetic effects were triggered by graphitic nitrogen, whereas pyridinic and chemisorbed nitrogen contributed much less to the overall ferromagnetic ground state.
Abstract: Nitrogen doping opens possibilities for tailoring the electronic properties and band gap of graphene toward its applications, e.g., in spintronics and optoelectronics. One major obstacle is development of magnetically active N-doped graphene with spin-polarized conductive behavior. However, the effect of nitrogen on the magnetic properties of graphene has so far only been addressed theoretically, and triggering of magnetism through N-doping has not yet been proved experimentally, except for systems containing a high amount of oxygen and thus decreased conductivity. Here, we report the first example of ferromagnetic graphene achieved by controlled doping with graphitic, pyridinic, and chemisorbed nitrogen. The magnetic properties were found to depend strongly on both the nitrogen concentration and type of structural N-motifs generated in the host lattice. Graphenes doped below 5 at. % of nitrogen were nonmagnetic; however, once doped at 5.1 at. % of nitrogen, N-doped graphene exhibited transition to a ferr...
182 citations
TL;DR: The first measurement of the interlayer shear stress of bilayer graphene based on pressurized microscale bubble loading devices is reported, and an experimental method for characterizing the fundamental inter layer shear properties of the emerging 2D materials is established for potential applications in multilayer systems.
Abstract: Monolayer two-dimensional (2D) crystals exhibit a host of intriguing properties, but the most exciting applications may come from stacking them into multilayer structures. Interlayer and interfacial shear interactions could play a crucial role in the performance and reliability of these applications, but little is known about the key parameters controlling shear deformation across the layers and interfaces between 2D materials. Herein, we report the first measurement of the interlayer shear stress of bilayer graphene based on pressurized microscale bubble loading devices. We demonstrate continuous growth of an interlayer shear zone outside the bubble edge and extract an interlayer shear stress of 40 kPa based on a membrane analysis for bilayer graphene bubbles. Meanwhile, a much higher interfacial shear stress of 1.64 MPa was determined for monolayer graphene on a silicon oxide substrate. Our results not only provide insights into the interfacial shear responses of the thinnest structures possible, but also establish an experimental method for characterizing the fundamental interlayer shear properties of the emerging 2D materials for potential applications in multilayer systems.
28 Nov 2017
TL;DR: X-ray diffraction peak at around 10° and broad D band peak at 1350 cm–1 in Raman spectra confirm the presence of oxygen-rich functional groups on the surface of GOQDs, which show tunable oxygen functional groups, which are confirmed by X-ray photoelectron spectroscopy.
Abstract: In this study, we present the preparation of graphene quantum dots (GQDs) and graphene oxide quantum dots (GOQDs). GQDs/GOQDs are prepared by an easy electrochemical exfoliation method, in which two graphite rods are used as electrodes. The electrolyte used is a combination of citric acid and alkali hydroxide in water. Four types of quantum dots, GQD1–GQD4, are prepared by varying alkali hydroxide concentration in the electrolyte, while keeping the citric acid concentration fixed. Variation of alkali hydroxide concentration in the electrolyte results in the production of GOQDs. Balanced reaction of citric acid and alkali hydroxide results in the production of GQDs (GQD3). However, three variations in alkali hydroxide concentration result in GOQDs (GQD1, GQD2, and GQD4). GOQDs show tunable oxygen functional groups, which are confirmed by X-ray photoelectron spectroscopy. GQDs/GOQDs show absorption in the UV region and show excitation-dependent photoluminescence behavior. The obtained average size is 2–3 nm...
TL;DR: B graphene is reported on as a single-phase mixed conductor that demonstrates Li diffusion faster than in graphite and even surpassing the diffusion of sodium chloride in liquid water.
Abstract: Time-dependent Hall measurements show lithium ions diffuse faster inside bilayer graphene than in graphite by an order of magnitude.
TL;DR: In this article, the photonic valley-hall effect with valley-chirality locked beam splitting, and topological valley-polarized edge states, are demonstrated for the first time on a photonic platform.
Abstract: The valley Hall effect and topological valley edge states are two fundamental properties in gapped valleytronic materials, such as MoS${}_{2}$ and biased bilayer graphene. Such properties have paved the way for applications in valleytronics. Here, the authors experimentally demonstrate a valley surface-wave photonic crystal on a single metal surface, as the photonic analog of the valley-Hall topological insulator phase. The photonic valley-Hall effect with valley-chirality locked beam splitting, and topological valley-polarized edge states, are demonstrated for the first time on a photonic platform.
TL;DR: This work shows that interaction effects may induce either an antiferromagnetic or a ferromagnetic polarization of AA regions under bias, depending on the electrical bias between layers, which could turn twisted bilayer graphene into an ideal system to study frustrated magnetism in two dimensions.
Abstract: Twisted graphene bilayers develop highly localized states around $AA$-stacked regions for small twist angles. We show that interaction effects may induce either an antiferromagnetic or a ferromagnetic (FM) polarization of said regions, depending on the electrical bias between layers. Remarkably, FM-polarized $AA$ regions under bias develop spiral magnetic ordering, with a relative 120\ifmmode^\circ\else\textdegree\fi{} misalignment between neighboring regions due to a frustrated antiferromagnetic exchange. This remarkable spiral magnetism emerges naturally without the need of spin-orbit coupling, and competes with the more conventional lattice-antiferromagnetic instability, which interestingly develops at smaller bias under weaker interactions than in monolayer graphene, due to Fermi velocity suppression. This rich and electrically controllable magnetism could turn twisted bilayer graphene into an ideal system to study frustrated magnetism in two dimensions.
TL;DR: Spectroscopic evidence for the formation of diamondene is provided by performing Raman spectroscopy of double-layer graphene under high pressure and is explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix.
Abstract: Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectroscopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens. The synthesis of two-dimensional diamond is the ultimate goal of diamond thin-film technology. Here, the authors perform Raman spectroscopy of bilayer graphene under pressure, and obtain spectroscopic evidence of formation of diamondene, an atomically thin form of diamond.
08 Nov 2017
TL;DR: In this article, a structural transformation of the moire pattern inherent to twisted bilayer graphene taking place at twist angles θ below a crossover angle is revealed by a change in the functional form of the twist energy density.
Abstract: Experiments on bilayer graphene unveiled a fascinating realization of stacking disorder where triangular domains with well-defined Bernal stacking are delimited by a hexagonal network of strain solitons. Here we show by means of numerical simulations that this is a consequence of a structural transformation of the moire pattern inherent to twisted bilayer graphene taking place at twist angles θ below a crossover angle . The transformation is governed by the interplay between the interlayer van der Waals interaction and the in-plane strain field, and is revealed by a change in the functional form of the twist energy density. This transformation unveils an electronic regime characteristic of vanishing twist angles in which the charge density converges, though not uniformly, to that of ideal bilayer graphene with Bernal stacking. On the other hand, the stacking domain boundaries form a distinct charge density pattern that provides the STM signature of the hexagonal solitonic network.
TL;DR: In this paper, density functional theory calculations have been carried out to study the adsorption of varous gas molecules (H2O, NH3, CO, NO2 and NO) on pristine graphene and Ga-doped graphene in order to explore the feasibility of Ga-Doped graphene based gas sensor.
TL;DR: In this paper, the authors reported the observation of excitons in bilayer graphene using photocurrent spectroscopy of high-quality BLG encapsulated in hexagonal boron nitride and observed two prominent excitonic resonances with narrow line widths that are tunable from the mid-infrared to the terahertz range.
Abstract: Excitons, the bound states of an electron and a hole in a solid material, play a key role in the optical properties of insulators and semiconductors. Here, we report the observation of excitons in bilayer graphene (BLG) using photocurrent spectroscopy of high-quality BLG encapsulated in hexagonal boron nitride. We observed two prominent excitonic resonances with narrow line widths that are tunable from the mid-infrared to the terahertz range. These excitons obey optical selection rules distinct from those in conventional semiconductors and feature an electron pseudospin winding number of 2. An external magnetic field induces a large splitting of the valley excitons, corresponding to a g-factor of about 20. These findings open up opportunities to explore exciton physics with pseudospin texture in electrically tunable graphene systems.
TL;DR: Applying an external transverse electric field of some 1 V/nm, countering the built-in field of the heterostructure, completely reverses this effect and allows, instead of holes, electrons to be spin valley locked with 2 meV spin-orbit splitting.
Abstract: Proximity orbital and spin-orbit effects of bilayer graphene on monolayer ${\mathrm{WSe}}_{2}$ are investigated from first principles. We find that the built-in electric field induces an orbital band gap of about 10 meV in bilayer graphene. Remarkably, the proximity spin-orbit splitting for holes is 2 orders of magnitude---the spin-orbit splitting of the valence band at $K$ is about 2 meV---more than for electrons. Effectively, holes experience spin valley locking due to the strong proximity of the lower graphene layer to ${\mathrm{WSe}}_{2}$. However, applying an external transverse electric field of some $1\text{ }\text{ }\mathrm{V}/\mathrm{nm}$, countering the built-in field of the heterostructure, completely reverses this effect and allows, instead of holes, electrons to be spin valley locked with 2 meV spin-orbit splitting. Such a behavior constitutes a highly efficient field-effect spin-orbit valve, making bilayer graphene on ${\mathrm{WSe}}_{2}$ a potential platform for a field-effect spin transistor.
TL;DR: An atomic scale study of heteroepitaxial growth and relationship of a single-atom-thick ZnO layer on graphene using atomic layer deposition can lead to a new class of atomically thin two-dimensional heterostructures of semiconducting oxides formed by highly controlled epitaxial Growth.
Abstract: Atomically thin semiconducting oxide on graphene carries a unique combination of wide band gap, high charge carrier mobility, and optical transparency, which can be widely applied for optoelectronics. However, study on the epitaxial formation and properties of oxide monolayer on graphene remains unexplored due to hydrophobic graphene surface and limits of conventional bulk deposition technique. Here, we report atomic scale study of heteroepitaxial growth and relationship of a single-atom-thick ZnO layer on graphene using atomic layer deposition. We demonstrate atom-by-atom growth of zinc and oxygen at the preferential zigzag edge of a ZnO monolayer on graphene through in situ observation. We experimentally determine that the thinnest ZnO monolayer has a wide band gap (up to 4.0 eV), due to quantum confinement and graphene-like structure, and high optical transparency. This study can lead to a new class of atomically thin two-dimensional heterostructures of semiconducting oxides formed by highly controlled...
TL;DR: In this article, the sensing performances of Fe embedded graphene sheets (including monolayer Fe-MG and bilayer FeBG) toward toxic gases (NO, CO, HCN and SO2) are comparably investigated.
Abstract: Based on the first-principles calculations, the sensing performances of Fe embedded graphene sheets (including monolayer Fe-MG and bilayer Fe-BG) toward toxic gases (NO, CO, HCN and SO2) are comparably investigated. Compared with the Fe-MG, the stable configuration of Fe-BG sheet exhibits the stronger affinity toward the gas molecules. The adsorbed NO has the largest energy difference between Fe-MG and Fe-BG substrate as compared with the other gases, as well as inducing the change in electronic structure and magnetic property of Fe-graphene systems. In addition, the supported Pt(111) substrate can effectively regulate the strength of interaction between gas molecule and Fe-graphene substrates. As a result, the increased layer of graphene substrate can be utilizing as good sensor for toxic gas molecules, yet the metal Pt supported substrate can enhance the magnetic property of adsorbed gas on the Fe-graphene systems. These results could provide important information for controlling the adsorption sensoring of gas molecules, which opens up a new avenue for the design and fabrication of the graphene-based gas sensors or spintronic devices.
TL;DR: In this paper, the authors reported transport measurements of a robust sequence of even-denominator FQH in dual-gated bilayer graphene (BLG) devices.
Abstract: The distinct Landau level spectrum of bilayer graphene (BLG) is predicted to support a non-abelian even-denominator fractional quantum Hall (FQH) state similar to the 5 2 state first identified in GaAs However, the nature of this state has remained difficult to characterize Here, we report transport measurements of a robust sequence of even-denominator FQH in dual-gated BLG devices Parallel field measurement confirms the spin-polarized nature of the ground state, which is consistent with the Pfaffian/anti-Pfaffian description The sensitivity of the even-denominator states to both filling fraction and transverse displacement field provides new opportunities for tunability Our results suggest that BLG is a platform in which topological ground states with possible non-abelian excitations can be manipulated and controlled
TL;DR: In this article, a tunable Y-branch graphene plasmonic switch operating at the wavelength of 1.55μm is proposed in which graphene is placed on white graphene.
TL;DR: In this paper, a large-area, sub-10-nm single and bilayer graphene nanomeshes from block copolymer self-assembly was fabricated and the authors measured the thermal conductivity, thermoelectric and electrical transport properties to experimentally verify the effect of quantum confinement, phonon-edge scattering and crossplane coupling.
TL;DR: It is demonstrated that spin dependent scatterings at the contact/graphene interfaces affect the spin injection efficiencies and hence prevent the material from achieving its full potential, and that such signal is absent if graphene is contacted to bilayer WSe2 where the inversion symmetry is restored.
Abstract: The observation of micrometer size spin relaxation makes graphene a promising material for applications in spintronics requiring long-distance spin communication However, spin dependent scatterings at the contact/graphene interfaces affect the spin injection efficiencies and hence prevent the material from achieving its full potential While this major issue could be eliminated by nondestructive direct optical spin injection schemes, graphene’s intrinsically low spin–orbit coupling strength and optical absorption place an obstacle in their realization We overcome this challenge by creating sharp artificial interfaces between graphene and WSe2 monolayers Application of circularly polarized light activates the spin-polarized charge carriers in the WSe2 layer due to its spin-coupled valley-selective absorption These carriers diffuse into the superjacent graphene layer, transport over a 35 μm distance, and are finally detected electrically using Co/h-BN contacts in a nonlocal geometry Polarization-depen
TL;DR: In this article, a structural transformation of the moire pattern inherent of twisted bilayer graphene taking place at twist angles below a crossover angle is shown. But the transformation is governed by the interplay between the interlayer van der Waals interaction and the in-plane strain field, and is revealed by a change in the functional form of the twist energy density.
Abstract: Experiments on bilayer graphene unveiled a fascinating realization of stacking disorder where triangular domains with well-defined Bernal stacking are delimited by a hexagonal network of strain solitons. Here we show by means of numerical simulations that this is a consequence of a structural transformation of the moire pattern inherent of twisted bilayer graphene taking place at twist angles $\theta$ below a crossover angle $\theta^{\star}=1.2^{\circ}$. The transformation is governed by the interplay between the interlayer van der Waals interaction and the in-plane strain field, and is revealed by a change in the functional form of the twist energy density. This transformation unveils an electronic regime characteristic of vanishing twist angles in which the charge density converges, though not uniformly, to that of ideal bilayer graphene with Bernal stacking. On the other hand, the stacking domain boundaries form a distinct charge density pattern that provides the STM signature of the hexagonal solitonic network.
TL;DR: In this paper, a room-temperature gas sensor based on bilayer graphene fabricated by an interfacial transfer of chemical vapor deposited graphene onto nickel interdigitated electrodes is presented.
TL;DR: It is demonstrated that thermally induced spin-state switching of spin-crossover nanoparticle thin films can be monitored through the electrical transport properties of graphene lying underneath the films, and this graphene sensor approach can be applied to a wide class of systems with tunable electronic polarizabilities.
Abstract: Future multifunctional hybrid devices might combine switchable molecules and 2D material-based devices. Spin-crossover compounds are of particular interest in this context since they exhibit bistability and memory effects at room temperature while responding to numerous external stimuli. Atomically thin 2D materials such as graphene attract a lot of attention for their fascinating electrical, optical, and mechanical properties, but also for their reliability for room-temperature operations. Here, we demonstrate that thermally induced spin-state switching of spin-crossover nanoparticle thin films can be monitored through the electrical transport properties of graphene lying underneath the films. Model calculations indicate that the charge carrier scattering mechanism in graphene is sensitive to the spin-state dependence of the relative dielectric constants of the spin-crossover nanoparticles. This graphene sensor approach can be applied to a wide class of (molecular) systems with tunable electronic polariz...
TL;DR: By identifying the original lattice orientation of the monolayer graphene on Cu foil, or establishing the relation between the fold angle and twist angle, this folding technique allows for the preparation of twisted bilayer graphene films with defined stacking orientations and may also be extended to create folded structures of other two-dimensional nanomaterials.
Abstract: Folded graphene in which two layers are stacked with a twist angle between them has been predicted to exhibit unique electronic, thermal, and magnetic properties. We report the folding of a single crystal monolayer graphene film grown on a Cu(111) substrate by using a tailored substrate having a hydrophobic region and a hydrophilic region. Controlled film delamination from the hydrophilic region was used to prepare macroscopic folded graphene with good uniformity on the millimeter scale. This process was used to create many folded sheets each with a defined twist angle between the two sheets. By identifying the original lattice orientation of the monolayer graphene on Cu foil, or establishing the relation between the fold angle and twist angle, this folding technique allows for the preparation of twisted bilayer graphene films with defined stacking orientations and may also be extended to create folded structures of other two-dimensional nanomaterials.