The selective functionalization of graphene edges is driven by the chemical reactivity of its carbon atoms. The chemical reactivity of an edge, as an interruption of the honeycomb lattice of graphene, differs from the relative inertness of the basal plane. In fact, the unsaturation of the pz orbitals and the break of the π conjugation on an edge increase the energy of the electrons at the edge sites, leading to specific chemical reactivity and electronic properties. Given the relevance of the chemistry at the edges in many aspects of graphene, the present Review investigates the processes and mechanisms that drive the chemical functionalization of graphene at the edges. Emphasis is given to the selective chemical functionalization of graphene edges from theoretical and experimental perspectives, with a particular focus on the characterization tools available to investigate the chemistry of graphene at the edge.

Charged molecules can translocate through the nanopore. The instant passage of the molecule momentarily impacts the conductance by locally reducing the aperture size of the channel. The resulting variations of the ionic conductance depends on the local topology of the translocating molecule; particularly, portions of long chain molecules such as polymers, proteins or DNA mark the electronic readout with specific conductance blockade fingerprints, and ultimately allow for reconstructing the sequence of monomers composing the translocating strands. [10] Consequently, thinner pores, i.e., capillaries with shorter channels, are capable of resolving shorter portions of molecules, leading for instance toward highresolution sequencing devices. [1] Thus, the challenge toward high-resolution sequencing has driven the development of ultrashort channel nanopores. Historically, two major classes of nanopores, i.e., biological and solid state nanopores, have been considered. The thickness of these nanopores varies from a few nanometers, as for α-hemolysin biological nanopores, [11,12] up to tens of nanometers for solid-state nanopores. [13] A revolutionary breakthrough aiming at reducing the capillary length of nanopores was achieved by the introduction of 2D materials such as graphene, [14][15][16] hexagonal boron nitride, [17] and molybdenum disulfide. [18][19][20][21] Indeed, the monoatomic capillary length of 2D nanopores is expected to offer sequencing capabilities, [2] but has not been realized yet. Inferior mechanical stability is one of the downsides of thin membranes inherently limiting the sustainability of 2D nanopores. Moreover, the complex fabrication process, involving cleanroom facilities and electron beam lithography, [22][23][24] can be demanding to scale up to industrial production. The noise levels in such devices are also orders of magnitude higher than those for long capillary-based nanopores, thus hindering their application for sequencing. [25] To address these issues, we introduce the concept of interfacial nanopores, generated at the crossing of two trenches, as illustrated in Figure 1. Fundamentally, the cross-section of two 1D straight lines is a zero-dimensional entity defined as a point (Figure 1a). The addition of a second dimensionality implies the overlap of two components to become a surface (Figure 1b). Similarly, in a 3D space, the interface shared between two tangent rectangular parallelepipeds is a surface, hence mathematically 2D (Figure 1c). Unlike nanopores commonly fabricated in 2D materials-which notwithstanding still possess a finite thickness-the surface defined by the crossing parallelepipeds is strictly 2D and thus does not exhibit any thickness. A High-fidelity analysis of translocating biomolecules through nanopores demands shortening the nanocapillary length to a minimal value. Existing nanopores and capillaries, however, inherit a finite length from the parent membranes. Here, nanocapillaries of zero depth are formed by dissolving two superimposed and crossing metallic nanoro...

We report the selective functionalization of an edge of graphene via the electrografting of 4-nitrobenzene diazonium tetrafluoroborate. The edge - a single line of carbon atoms - forms during the process of cutting a graphene monolayer with an atomically sharp microtome knife. Embedded in a polymeric matrix, the just cut bare graphene edge efficiently transfers electrons to a ferricyanide probe in solution. By monitoring the electron exchange reactions of the edge upon functionalization, we observe an annihilation of the reduction and oxidation peaks of the ferricyanide probe, characteristic of the formation of a nitroaryl passivation layer on the edge of graphene. For the first time, the chemical state of a single line of carbon atoms is influenced and monitored using an electrochemical cell, therefore bypassing the usual requirements of atomic resolution characterization techniques, which often demand very clean graphene samples and vacuum processing.

The investigation of the transport properties of single molecules by flowing tunneling currents across extremely narrow gaps is relevant for challenges as diverse as the development of molecular electronics and sequencing of DNA. The achievement of well-defined electrode architectures remains a technical challenge, especially due to the necessity of high precision fabrication processes and the chemical instability of most bulk metals. Here, we illustrate a continuously adjustable tunneling junction between the edges of two twisted graphene sheets. The unique property of the graphene electrodes is that the sheets are rigidly supported all the way to the atomic edge. By analyzing the tunneling current characteristics, we also demonstrate that the spacing across the gap junction can be controllably adjusted. Finally, we demonstrate the transition from the tunneling regime to contact and the formation of an atomic-sized junction between the two edges of graphene.

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