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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. This soft confinement allows the low-loss lateral ultra-confinement of graphene plasmons, scaling up their resonance frequency from the native terahertz to the commercially relevant visible range. Visible graphene plasmons localized into nanocorrugations mediate much stronger light–matter interactions (Raman enhancement) than previously achieved with graphene, enabling the detection of specific molecules from femtomolar solutions or ambient air. Moreover, nanocorrugated graphene sheets also support propagating visible plasmon modes, as revealed by scanning near-field optical microscopy observation of their interference patterns.

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 (Pt2HgSe3) is a candidate QSH material, realizing the long sought-after Kane–Mele insulator. Using scanning tunneling microscopy, we measure a band gap in excess of 100 meV and identify the hallmark edge states. By calculating the Z2invariant, we confirm the topological nature of the gap. Jacutingaite is stable in air, and we demonstrate exfoliation down to at least two layers and show that it can be integrated into heterostructures with other two-dimensional materials. This adds a topological insulator to the 2D quantum material library.

Despite their application potential, the structure of CVD grown MoSe2single layers remained relatively unexplored. Here we report the rotationally aligned CVD growth of MoSe2single layers on graphite. Such MoSe2layers are characterized by grain boundary structures with significantly reduced disorder and display a much lower grain boundary density compared to samples grown by MBE. We show that the grain boundaries of CVD MoSe2on graphite are predominantly mirror twin boundaries (MTBs) and distinguish two classes of such MTBs based on their orientation relative to the zigzag directions of the MoSe2lattice. By combining atomic resolution scanning tunneling microscopy (STM) and spectroscopy measurements with DFT calculations, we demonstrate that the predominantly present MTBs running along zigzag directions only slightly perturb the electronic structure of the MoSe2sheet. This enables the CVD growth of large-area MoSe2layers with high structural and electronic quality. Atomic resolution STM investigations also revealed a high density (1012cm–2) of native point defects identified as Mo vacancies. Our DFT calculations predict that Mo vacancies in MoSe2are magnetic, and their magnetic moment can be efficiently controlled electrically by tuning the Fermi level position.

The chemical inertness of the defect-free basal plane confers environmental stability to MoS2single layers, but it also limits their chemical versatility and catalytic activity. The stability of pristine MoS2basal 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 MoS2single 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 MoS2-xOxcrystals. Oxygen substitution sites present all over the basal plane act as single-atom reaction centres, substantially increasing the catalytic activity of the entire MoS2basal plane for the electrochemical H2evolution reaction.