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Future applications of single‐molecular and large‐surface area molecular devices require a thorough understanding and control of molecular junctions, interfacial phenomena, and intermolecular interactions. In this contribution the concept of single‐molecule junction and host‐guest complexation to sheath a benchmark molecular wire–namely 4,4′‐(1,4‐phenylenebis(ethyne‐2,1‐diyl))dianiline – with an insulating cage, pillar[5]arene 1,4‐diethoxy‐2‐ethyl‐5‐methylbenzene is presented. The insertion of one guest molecular wire into one host pillar[5]arene is probed by 1H‐NMR (nuclear magnetic resonance), whilst the self‐assembly capabilities of the amine‐terminated molecular wire remain intact after complexation as demonstrated by XPS (X‐ray photoelectron spectroscopy) and AFM (atomic force microscopy). Encapsulation of the molecular wire prevents the formation of π‐ π stacked dimers and permits the determination of the true single molecule conductance with increased accuracy and confidence, as demonstrated here by using the STM–BJ technique (scanning tunneling microscopy– break junction). This strategy opens new avenues in the control of single‐molecule properties and demonstrates the pillararenes capabilities for the future construction of arrays of encapsulated single‐molecule functional units in large‐surface area devices. Encapsulation of molecular wires: determination of ‘true’ single molecule conductance // formation of large area molecular devices composed of extended arrays of single‐molecules.

For the past three decades, the coordination-driven self-assembly of three-dimensional structures has undergone rapid progress; however, parallel efforts to create large discrete two-dimensional architectures—as opposed to polymers—have met with limited success. The synthesis of metallo-supramolecular systems with well-defined shapes and sizes in the range of 10–100 nm remains challenging. Here we report the construction of a series of giant supramolecular hexagonal grids, with diameters on the order of 20 nm and molecular weights greater than 65 kDa, through a combination of intra- and intermolecular metal-mediated self-assembly steps. The hexagonal intermediates and the resulting self-assembled grid architectures were imaged at submolecular resolution by scanning tunnelling microscopy. Characterization (including by scanning tunnelling spectroscopy) enabled the unambiguous atomic-scale determination of fourteen hexagonal grid isomers.Metal-mediated self-assembly in solution typically leads to small two- and three-dimensional architectures on scales smaller than 10 nm, but now a series of large, discrete, two-dimensional supramolecular hexagonal grids have been prepared through a combination of intra- and intermolecular coordination interactions. These 20-nm-wide grids have been imaged at submolecular resolution using scanning tunnelling microscopy.

The cuprate high-temperature superconductors have been the focus of unprecedentedly intense and sustained study not only because of their high superconducting transition temperatures, but also because they represent the most exquisitely investigated examples of highly correlated electronic materials. In particular, the pseudogap regime of the phase diagram exhibits a variety of mysterious emergent behaviors. In the last few years, evidence from NMR and scanning tunneling microscopy (STM) studies, as well as from a new generation of X-ray scattering experiments, has accumulated, indicating that a general tendency to short-range– correlated incommensurate charge density wave (CDW) order is \"intertwined\" with the superconductivity in this regime. Additionally, transport, STM, neutron-scattering, and optical experiments have produced evidence—not yet entirely understood—of the existence of an associated pattern of long-range–ordered point-group symmetry breaking with an electron-nematic character. We have carried out a theoretical analysis of the Landau– Ginzburg–Wilson effective field theory of a classical incommensurate CDW in the presence of weak quenched disorder. Although the possibilities of a sharp phase transition and long-range CDW order are precluded in such systems, we show that any discrete symmetry-breaking aspect of the charge order—nematicity in the case of the unidirectional (stripe) CDW we consider explicitly— generically survives up to a nonzero critical disorder strength. Such \"vestigial order,\" which is subject to unambiguous macroscopic detection, can serve as an avatar of what would be CDW order in the ideal, zero disorder limit. Various recent experiments in the pseudogap regime of the hole-doped cuprates are readily interpreted in light of these results.

Imaging of biomolecules guides our understanding of their diverse structures and functions 1 , 2 . Real-space imaging at sub-nanometre resolution using cryo-electron microscopy has provided key insights into proteins and their assemblies 3 , 4 . Direct molecular imaging of glycans—the predominant biopolymers on Earth, with a plethora of structural and biological functions 5 —has not been possible so far 6 . The inherent glycan complexity and backbone flexibility require single-molecule approaches for real-space imaging. At present, glycan characterization often relies on a combination of mass spectrometry and nuclear magnetic resonance imaging to provide insights into size, sequence, branching and connectivity, and therefore requires structure reconstruction from indirect information 7 – 9 . Here we show direct imaging of single glycan molecules that are isolated by mass-selective, soft-landing electrospray ion beam deposition and imaged by low-temperature scanning tunnelling microscopy 10 . The sub-nanometre resolution of the technique enables the visualization of glycan connectivity and discrimination between regioisomers. Direct glycan imaging is an important step towards a better understanding of the structure of carbohydrates. An imaging method combining soft-landing electrospray ion beam deposition and low-temperature scanning tunnelling microscopy resolves the structures of glycans at sub-nanometre resolution, revealing the connectivity of glycan chains and the types of linkages.

One-dimensional (1D) interacting electrons are often described as a Luttinger liquid 1 – 4 having properties that are intrinsically different from those of Fermi liquids in higher dimensions 5 , 6 . In materials systems, 1D electrons exhibit exotic quantum phenomena that can be tuned by both intra- and inter-1D-chain electronic interactions, but their experimental characterization can be challenging. Here we demonstrate that layer-stacking domain walls (DWs) in van der Waals heterostructures form a broadly tunable Luttinger liquid system, including both isolated and coupled arrays. We have imaged the evolution of DW Luttinger liquids under different interaction regimes tuned by electron density using scanning tunnelling microscopy. Single DWs at low carrier density are highly susceptible to Wigner crystallization consistent with a spin-incoherent Luttinger liquid, whereas at intermediate densities dimerized Wigner crystals form because of an enhanced magneto-elastic coupling. Periodic arrays of DWs exhibit an interplay between intra- and inter-chain interactions that gives rise to new quantum phases. At low electron densities, inter-chain interactions are dominant and induce a 2D electron crystal composed of phased-locked 1D Wigner crystal in a staggered configuration. Increased electron density causes intra-chain fluctuation potentials to dominate, leading to an electronic smectic liquid crystal phase in which electrons are ordered with algebraical correlation decay along the chain direction but disordered between chains. Our work shows that layer-stacking DWs in 2D heterostructures provides opportunities to explore Luttinger liquid physics. Layer-stacking domain walls in van der Waals heterostructures form a broadly tunable Luttinger liquid system, including both isolated and coupled arrays.

In recent years, correlated insulating states, unconventional superconductivity, and topologically non-trivial phases have all been observed in several moiré heterostructures. However, understanding of the physical mechanisms behind these phenomena is hampered by the lack of local electronic structure data. Here, we use scanning tunnelling microscopy and spectroscopy to demonstrate how the interplay between correlation, topology, and local atomic structure determines the behaviour of electron-doped twisted monolayer–bilayer graphene. Through gate- and magnetic field-dependent measurements, we observe local spectroscopic signatures indicating a quantum anomalous Hall insulating state with a total Chern number of ±2 at a doping level of three electrons per moiré unit cell. We show that the sign of the Chern number and associated magnetism can be electrostatically switched only over a limited range of twist angle and sample hetero-strain values. This results from a competition between the orbital magnetization of filled bulk bands and chiral edge states, which is sensitive to strain-induced distortions in the moiré superlattice. Twisted moiré heterostructures offer a highly tunable solid-state platform for exploring fundamental condensed matter physics. Here, the authors use scanning tunnelling microscopy to investigate the local electronic structure of the gate-controlled quantum anomalous Hall insulator state in twisted monolayer–bilayer graphene.

The funnelling of energy within multichromophoric assemblies is at the heart of the efficient conversion of solar energy by plants. The detailed mechanisms of this process are still actively debated as they rely on complex interactions between a large number of chromophores and their environment. Here we used luminescence induced by scanning tunnelling microscopy to probe model multichromophoric structures assembled on a surface. Mimicking strategies developed by photosynthetic systems, individual molecules were used as ancillary, passive or blocking elements to promote and direct resonant energy transfer between distant donor and acceptor units. As it relies on organic chromophores as the elementary components, this approach constitutes a powerful model to address fundamental physical processes at play in natural light-harvesting complexes.Energy funnelling within multichromophoric assemblies is key to the conversion of solar energy by plants. Now, energy transport between phthalocyanine-based chromophores has been monitored at the submolecular level using scanning tunnelling microscopy, focusing on the role of ancillary, passive and blocking chromophores in promoting and directing energy transfer between distant donor and acceptor units.

Molecular tips in scanning tunneling microscopy can directly detect intermolecular electron tunneling between sample and tip molecules and reveal the tunneling facilitation through chemical interactions that provide overlap of respective electronic wave functions, that is, hydrogen-bond, metal-coordination-bond, and charge-transfer interactions. Nucleobase molecular tips were prepared by chemical modification of underlying metal tips with thiol derivatives of adenine, guanine, cytosine, and uracil and the outmost single nucleobase adsorbate probes intermolecular electron tunneling to or from a sample nucleobase molecule. We found that the electron tunneling between a sample nucleobase and its complementary nucleobase molecular tip was much facilitated compared with its noncomplementary counterpart. The complementary nucleobase tip was thereby capable of electrically pinpointing each nucleobase. Chemically selective imaging using molecular tips may be coined \"intermolecular tunneling microscopy\" as its principle goes and is of general significance for novel molecular imaging of chemical identities at the membrane and solid surfaces.

Scanning probe microscopy techniques, such as atomic force microscopy and scanning tunnelling microscopy, are harnessed to image nanoscale structures with an exquisite resolution, which has been of significant value in a variety of areas of nanotechnology. These scanning probe techniques, however, are not generally suitable for high-throughput imaging, which has, from the outset, been a primary challenge. Traditional approaches to increasing the scalability have involved developing multiple probes for imaging, but complex probe design and electronics are required to carry out the detection method. Here, we report a probe-based imaging method that utilizes scalable cantilever-free elastomeric probe design and hierarchical measurement architecture, which readily reconstructs high-resolution and high-throughput topography images. In a single scan, we demonstrate imaging with a 100-tip array to obtain 100 images over a 1-mm 2 area with 10 6 pixels in less than 10 min. The potential for large-scale tip integration and the advantage of a simple probe array suggest substantial promise for our approach to high-throughput imaging far beyond what is currently possible. High-throughput imaging has generally been challenging for scanning probe microscopy techniques. Here, the authors introduce binary-state scanning probe microscopy, which uses a cantilever-free elastomeric probes and a hierarchical measurement architecture for parallel topography imaging.

To advance meaningful guidelines in the design of electrocatalytically active catalysts, a knowledge of the nature of active sites is the starting point. However, multiple factors such as material composition, site coordination, electrolyte effects, the support material, surface strain, and others influence catalytic behavior. Therefore, the identification of active sites can be complex. A substantial contributor can be in-situ experiments, which are able to identify active centers in a specific system while the reaction takes place. An example of such a technique is electrochemical scanning tunneling microscopy (EC-STM), which relates locally confined noise features to local electrocatalytic activity. In this work, we spotlight recent achievements of this technique with respect to palladium (Pd) surfaces for the hydrogen reduction reaction, where strain due to hydride formation comes into play in addition to surface coordination. Secondly, we demonstrate the high resolution of the technique on graphite-based surfaces. Here, edge sites are particularly active. Thus, with the EC-STM technique, we take strain effects (like on Pd) or effects of coordination (like on carbon) into account. Therefore, we can determine active sites with great accuracy under reaction conditions.