We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

We uncover the interlayer shear mode of multi-layer graphene samples, ranging from bilayergraphene (BLG) to bulk graphite, and show that the corresponding Raman peak measures the interlayer coupling. This peak scales from∼43cm −1 in bulk graphite to∼31cm −1 in BLG. Its low energy makes it a probe of near-Dirac point quasi-particles, with a Breit-Wigner-Fano lineshape due to resonance with electronic transitions. Similar shear modes are expected in all layered materials, providing a direct probe of interlayer interactions.Single Layer Graphene (SLG) has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability [1,2]. As the knowledge of the basic properties of SLG increases, an ever growing effort is being devoted to a deeper understanding of Few Layer Graphene (FLG) samples [3][4][5], and to their application in useful devices. For example, since SLG absorbs 2.3% of the incident light [6], FLG can be used to beat the transmittance of Indium Tin Oxide(∼90%) [2], and to engineer near-market transparent conductors [7], exploiting the lower sheet resistance afforded by combining more than one SLG [2,7]. Bilayer graphene (BLG) is a tunable band gap semiconductor [8], tri-layer graphene (TLG) has a unique electronic structure consisting, in the simplest approximation, of massless SLG and massive BLG subbands [9][10][11]. FLG with less than 10 layers do each show a distinctive band structure [11]. The layers can be stacked as in graphite, or have any orientation. This gives rise to a wealth of electronic properties, such as the appearance of a Dirac spectrum even in FLG [12].There is thus an increasing interest in the physics and applications of FLG. Optical microscopy can count the number of layers [13,14], but does not offer the insights of Raman spectroscopy, being this sensitive to quasiparticle interactions [15]. Raman spectroscopy is one of the most useful and versatile tools to probe graphene samples [15,16]. The measurement of the SLG, BLG, and FLG Raman spectra[15] triggered a huge effort to understand phonons, electron-phonon, magneto-phonon and electron-electron interactions, and the influence on the Raman process of number and orientation of layers, electric or magnetic fields, strain, doping, disorder, edges, and functional groups [16].The SLG phonon dispersions comprise three acoustic and three optical branches. A necessary, but not sufficient, condition for a phonon mode to be Raman active is to satisfy the Raman fundamental selection rule, i.e. to be at the Brillouin Zone centre, Γ, with wavevector q ≈ 0 [17]. SLG has six normal modes at Γ: [18]. There are two degenerate in-plane optical modes, E 2g , and one out-of-plane optical mode B 2g [18]. E 2g modes are Raman active, while B 2g is neither Raman nor IR active [18]. In the case of graphite there are 4 atoms per unit cell, and only half of them have fourth neighbors that either lie directly above or below in adjacent layers. Therefore the two atoms of the unit cell in each layer are now inequivalent. ...

Crumpled graphene films are broadly used, for instance in electronics1, energy storage2, 3, composites4, 5, and biomedicine6. Although it is known that the degree of crumpling affects graphene's properties and the performance of graphene-based devices and materials3, 5, 7, the controlled folding and unfolding of crumpled graphene films has not been demonstrated. Here we report an approach to reversibly control the crumpling and unfolding of large-area graphene sheets. We show with experiments, atomistic simulations and theory that, by harnessing the mechanical instabilities of graphene adhered on a biaxially pre-stretched polymer substrate and by controlling the relaxation of the pre-strains in a particular order, graphene films can be crumpled into tailored self-organized hierarchical structures that mimic superhydrophobic leaves. The approach enables us to fabricate large-area conductive coatings and electrodes showing superhydrophobicity, high transparency, and tunable wettability and transmittance. We also demonstrate that crumpled graphene-polymer laminates can be used as artificial-muscle actuators.

Hippo effectors YAP/TAZ act as on–off mechanosensing switches by sensing modifications in extracellular matrix (ECM) composition and mechanics. The regulation of their activity has been described by a hierarchical model in which elements of Hippo pathway are under the control of focal adhesions (FAs). Here we unveil the molecular mechanism by which cell spreading and RhoA GTPase activity control FA formation through YAP to stabilize the anchorage of the actin cytoskeleton to the cell membrane. This mechanism requires YAP co-transcriptional function and involves the activation of genes encoding for integrins and FA docking proteins. Tuning YAP transcriptional activity leads to the modification of cell mechanics, force development and adhesion strength, and determines cell shape, migration and differentiation. These results provide new insights into the mechanism of YAP mechanosensing activity and qualify this Hippo effector as the key determinant of cell mechanics in response to ECM cues.

Heterostructures formed by stacking layered materials require atomically clean interfaces. However, contaminants are usually trapped between the layers, aggregating into randomly located blisters, incompatible with scalable fabrication processes. Here we report a process to remove blisters from fully formed heterostructures. Our method is over an order of magnitude faster than those previously reported and allows multiple interfaces to be cleaned simultaneously. We fabricate blister-free regions of graphene encapsulated in hexagonal boron nitride with an area ~ 5000 μm2, achieving mobilities up to 180,000 cm2 V−1 s−1 at room temperature, and 1.8 × 106 cm2 V−1 s−1 at 9 K. We also assemble heterostructures using graphene intentionally exposed to polymers and solvents. After cleaning, these samples reach similar mobilities. This demonstrates that exposure of graphene to process-related contaminants is compatible with the realization of high mobility samples, paving the way to the development of wafer-scale processes for the integration of layered materials in (opto)electronic devices.

Natural materials are renowned for their exquisite designs that optimize function, as illustrated by the elasticity of blood vessels, the toughness of bone and the protection offered by nacre 1,2,3,4,5 . Particularly intriguing are spider silks, with studies having explored properties ranging from their protein sequence 6 to the geometry of a web 7 . This highly adapted material system 8 , which is wellknown to meet a spider's many needs, exhibits exemplary mechanical properties 9,10,11,12,13,14,15 . It thus comes as no surprise that there has been much interest in the molecular design underpinning the outstanding performance of silk fibres 1,6,10,13,19,20 , and in the mechanical characteristics of web-like structures 16,17,18,21 . Yet it remains unknown how the mechanical characteristics of spider silk contribute to the integrity and performance of a spider web. Here we report web deformation experiments and simulations that identify the nonlinear response of silk threads to stress-involving softening at a yield point and dramatic stiffening at large strain until failure-as crucial for localizing the load-induced deformation and hence for endowing spider webs with robustness. Control simulations confirm that a nonlinear stress response results in superior resistance to defects compared to linear elastic or elastic-plastic (softening) material behaviour. We further show that under distributed loads, such as exerted by wind, the behaviour of silk under small-deformation is essential in maintaining the web's structural integrity. The superior performance of silk in webs is therefore not merely due to its exceptional ultimate strength and strain, but more importantly arises from the nonlinear response of silk threads to strain and their geometrical arrangement in a web.While spider silk is employed in a myriad of functions from wrapping prey to lining retreats 22,23 , here we focus on silk's structural role in aerial webs and on how silk's material properties relate to web function. The mechanical behaviour of silk, like that of other biological materials, is determined by the nature of its constituent molecules and their hierarchical assembly into fibres 13,19,20,24,25,26 (Fig. S1). Spider webs themselves are characterized by a highly organized geometry that optimizes their function 7,8,16,17,18 . To explore the contribution of the material characteristics to web function, we develop a web model with spiral and radial threads based on the geometry commonly found in orb webs 1 . The silk material behaviour is parameterized from atomistic simulations of dragline silk from the species Nephila clavipes (Model A) 19,20 ( Fig. 1a-b) and validated against experiments 10 (Methods Summary). As properties of silk can vary across evolutionary lineages by over 100% 9,27,28 (SI Section S1), we avoid species-specific silk properties and use instead a representative model to reflect the characteristic nonlinear stress-strain behaviour of silk found in a web. The mechanical performance of individual silk threads has been...

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We present an overview of the main techniques for production and processing of graphene and related materials (GRMs), as well as the key characterization procedures. We adopt a ‘hands-on’ approach, providing practical details and procedures as derived from literature as well as from the authors’ experience, in order to enable the reader to reproduce the results. Section is devoted to ‘bottom up’ approaches, whereby individual constituents are pieced together into more complex structures. We consider graphene nanoribbons (GNRs) produced either by solution processing or by on-surface synthesis in ultra high vacuum (UHV), as well carbon nanomembranes (CNM). Production of a variety of GNRs with tailored band gaps and edge shapes is now possible. CNMs can be tuned in terms of porosity, crystallinity and electronic behaviour. Section covers ‘top down’ techniques. These rely on breaking down of a layered precursor, in the graphene case usually natural crystals like graphite or artificially synthesized materials, such as highly oriented pyrolythic graphite, monolayers or few layers (FL) flakes. The main focus of this section is on various exfoliation techniques in a liquid media, either intercalation or liquid phase exfoliation (LPE). The choice of precursor, exfoliation method, medium as well as the control of parameters such as time or temperature are crucial. A definite choice of parameters and conditions yields a particular material with specific properties that makes it more suitable for a targeted application. We cover protocols for the graphitic precursors to graphene oxide (GO). This is an important material for a range of applications in biomedicine, energy storage, nanocomposites, etc. Hummers’ and modified Hummers’ methods are used to make GO that subsequently can be reduced to obtain reduced graphene oxide (RGO) with a variety of strategies. GO flakes are also employed to prepare three-dimensional (3d) low density structures, such as sponges, foams, hydro- or aerogels. The assembly of flakes into 3d structures can provide improved mechanical properties. Aerogels with a highly open structure, with interconnected hierarchical pores, can enhance the accessibility to the whole surface area, as relevant for a number of applications, such as energy storage. The main recipes to yield graphite intercalation compounds (GICs) are also discussed. GICs are suitable precursors for covalent functionalization of graphene, but can also be used for the synthesis of uncharged graphene in solution. Degradation of the molecules intercalated in GICs can be triggered by high temperature treatment or microwave irradiation, creating a gas pressure surge in graphite and exfoliation. Electrochemical exfoliation by applying a voltage in an electrolyte to a graphite electrode can be tuned by varying precursors, electrolytes and potential. Graphite electrodes can be either negatively or positively intercalated to obtain GICs that are subsequently exfoliated. We also discuss the materials that can be amenable to exfoliation, by ...