Supramolecular Multilayered Templates for Fabricating Nanometer-Precise Spacings: Implications for the Next-Generation of Devices Integrating Nanogap/Nanochannel Components.

Molecular transistors, electromagnetic waveguides, plasmonic devices, and novel generations of nanofluidic channels comprise precisely separated gaps of nanometric and subnanometric spacing. Nonetheless, fabricating a nanogap/nanochannel is a technological challenge, currently tackled by several approaches such as breakdown electromigration and lithography. The aforementioned techniques, though, are limited, respectively, in terms of gap stability and ultimate resolution. Here, nanogaps/nanochannels are templated via the microtomy of metallic thin films embedded in a polymer matrix and precisely separated by a nanometric, sacrificial layer of polyelectrolytes grown via the layer-by-layer (LbL) approach. The versatility of the LbL technique, both in terms of the number of layers and composition of polyelectrolytes, allows to finely tune the spacing across the gap; the LbL template can further be removed by plasma etching. Our findings pave the path toward the realization of molecularly defined functional spacings at the nanometer-scale for the modular implementation of devices integrating nanogap/nanochannel components.

Electrophilic radical coupling at the edge of graphene.

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.

Dynamic Tunneling Junctions at the Atomic Intersection of Two Twisted Graphene Edges.

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.

Zero-Depth Interfacial Nanopore Capillaries.

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 nanorods, molded in polymeric slabs. In an electrolyte, the interface shared by the crossing fluidic channels is mathematically of zero thickness and defines the narrowest constriction in the stream of ions through the nanopore device. This novel architecture provides the possibility to design nanopore fluidic channels, particularly with a robust 3D architecture maintaining the ultimate zero thickness geometry independently of the thickness of the fluidic channels. With orders of magnitude reduced biomolecule translocation speed, and lowered electronic and ionic noise compared to nanopores in 2D materials, the findings establish interfacial nanopores as a scalable platform for realizing nanofluidic systems, capable of single-molecule detection.

Chemistry at the Edge of Graphene.

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.