Hydrogen evolution driven by heteroatoms of bidentate N-heterocyclic ligands in iron(II) complexes.

While Pt is considered the best catalyst for the electrocatalytic hydrogen evolution reaction (HER), it is evident that non-noble metal alternatives must be explored. In this regard, it is well known that the binding sites for non-noble metals play a pivotal role in facilitating efficient catalysis. Herein, we studied Fe(II) complexes with bidentate 2-(2'-pyridyl)benzoxazole (LO), 2-(2'-pyridyl)benzthiazole (LS), 2-(2'-pyridyl)benzimidazole (LNH), and 2-2'-bipyridyl (Lpy) ligands - by adding trifluoroacetic acid (TFA) to their acetonitrile solution - in order to examine how their reactivity towards protons under reductive conditions could be impacted by the non-coordinating heteroatoms (S, O, N, or none).

The composition and structure of the ubiquitous hydrocarbon contamination on van der Waals materials.

The behavior of single layer van der Waals (vdW) materials is profoundly influenced by the immediate atomic environment at their surface, a prime example being the myriad of emergent properties in artificial heterostructures. Equally significant are adsorbates deposited onto their surface from ambient. While vdW interfaces are well understood, our knowledge regarding atmospheric contamination is severely limited.

Observation of competing, correlated ground states in the flat band of rhombohedral graphite.

In crystalline solids, the interactions of charge and spin can result in a variety of emergent quantum ground states, especially in partially filled, topological flat bands such as Landau levels or in "magic angle" graphene layers. Much less explored is rhombohedral graphite (RG), perhaps the simplest and structurally most perfect condensed matter system to host a flat band protected by symmetry. By scanning tunneling microscopy, we map the flat band charge density of 8, 10, 14, and 17 layers and identify a domain structure emerging from a competition between a sublattice antiferromagnetic insulator and a gapless correlated paramagnet.

Large-area nanoengineering of graphene corrugations for visible-frequency graphene plasmons.

Quantum confinement of the charge carriers of graphene is an effective way to engineer its properties. This is commonly realized through physical edges that are associated with the deterioration of mobility and strong suppression of plasmon resonances. Here, we demonstrate a simple, large-area, edge-free nanostructuring technique, based on amplifying random nanoscale structural corrugations to a level where they efficiently confine charge carriers, without inducing significant inter-valley scattering.

Signature of Large-Gap Quantum Spin Hall State in the Layered Mineral Jacutingaite.

Quantum spin Hall (QSH) insulators host edge states, where the helical locking of spin and momentum suppresses backscattering of charge carriers, promising applications from low-power electronics to quantum computing. A major challenge for applications is the identification of large gap QSH materials, which would enable room temperature dissipationless transport in their edge states. Here we show that the layered mineral jacutingaite (PtHgSe) is a candidate QSH material, realizing the long sought-after Kane-Mele insulator.

Transition Metal Chalcogenide Single Layers as an Active Platform for Single-Atom Catalysis.

Among the main appeals of single-atom catalysts are the ultimate efficiency of material utilization and the well-defined nature of the active sites, holding the promise of rational catalyst design. A major challenge is the stable decoration of various substrates with a high density of individually dispersed and uniformly active monatomic sites. Transition metal chalcogenides (TMCs) are broadly investigated catalysts, limited by the relative inertness of their pristine basal plane.

Spontaneous doping of the basal plane of MoS single layers through oxygen substitution under ambient conditions.

The chemical inertness of the defect-free basal plane confers environmental stability to MoS single layers, but it also limits their chemical versatility and catalytic activity. The stability of pristine MoS basal plane against oxidation under ambient conditions is a widely accepted assumption however, here we report single-atom-level structural investigations that reveal that oxygen atoms spontaneously incorporate into the basal plane of MoS single layers during ambient exposure. The use of scanning tunnelling microscopy reveals a slow oxygen-substitution reaction, during which individual sulfur atoms are replaced one by one by oxygen, giving rise to solid-solution-type 2D MoSO crystals.

Highly wear-resistant and low-friction SiN composites by addition of graphene nanoplatelets approaching the 2D limit.

Graphene nanoplatelets (GNPs) have emerged as one of the most promising filler materials for improving the tribological performance of ceramic composites due to their outstanding solid lubricant properties as well as mechanical and thermal stability. Yet, the addition of GNPs has so far enabled only a very limited improvement in the tribological properties of ceramics, particularly concerning the reduction of their friction coefficient. This is most likely due to the challenges of achieving a continuous lubricating and protecting tribo-film through a high GNP coverage of the exposed surfaces.

Preparing local strain patterns in graphene by atomic force microscope based indentation.

Patterning graphene into various mesoscopic devices such as nanoribbons, quantum dots, etc. by lithographic techniques has enabled the guiding and manipulation of graphene's Dirac-type charge carriers. Graphene, with well-defined strain patterns, holds promise of similarly rich physics while avoiding the problems created by the hard to control edge configuration of lithographically prepared devices.

The intrinsic defect structure of exfoliated MoS2 single layers revealed by Scanning Tunneling Microscopy.

MoS2 single layers have recently emerged as strong competitors of graphene in electronic and optoelectronic device applications due to their intrinsic direct bandgap. However, transport measurements reveal the crucial role of defect-induced electronic states, pointing out the fundamental importance of characterizing their intrinsic defect structure. Transmission Electron Microscopy (TEM) is able to image atomic scale defects in MoS2 single layers, but the imaged defect structure is far from the one probed in the electronic devices, as the defect density and distribution are substantially altered during the TEM imaging.

Nanomesh-Type Graphene Superlattice on Au(111) Substrate.

The adherence of graphene to various crystalline substrates often leads to a periodic out-of-plane modulation of its atomic structure due to the lattice mismatch. While, in principle, convex (protrusion) and concave (depression) superlattice geometries are nearly equivalent, convex superlattices have predominantly been observed for graphene on various metal surfaces. Here we report the STM observation of a graphene superlattice with concave (nanomesh) morphology on Au(111).

Exfoliation of large-area transition metal chalcogenide single layers.

Isolating large-areas of atomically thin transition metal chalcogenide crystals is an important but challenging task. The mechanical exfoliation technique can provide single layers of the highest structural quality, enabling to study their pristine properties and ultimate device performance. However, a major drawback of the technique is the low yield and small (typically < 10 μm) lateral size of the produced single layers.

Room-temperature magnetic order on zigzag edges of narrow graphene nanoribbons.

The possibility that non-magnetic materials such as carbon could exhibit a novel type of s-p electron magnetism has attracted much attention over the years, not least because such magnetic order is predicted to be stable at high temperatures. It has been demonstrated that atomic-scale structural defects of graphene can host unpaired spins, but it remains unclear under what conditions long-range magnetic order can emerge from such defect-bound magnetic moments. Here we propose that, in contrast to random defect distributions, atomic-scale engineering of graphene edges with specific crystallographic orientation--comprising edge atoms from only one sub-lattice of the bipartite graphene lattice--can give rise to a robust magnetic order.

Tailoring the atomic structure of graphene nanoribbons by scanning tunnelling microscope lithography.

The practical realization of nanoscale electronics faces two major challenges: the precise engineering of the building blocks and their assembly into functional circuits. In spite of the exceptional electronic properties of carbon nanotubes, only basic demonstration devices have been realized that require time-consuming processes. This is mainly due to a lack of selective growth and reliable assembly processes for nanotubes.