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Molybdenum disulfide (MoS2) is back in the spotlightbecause of the indirect-to-direct bandgap tunability and valley relatedphysics emerging in the monolayer regime. However, rigorous controlof the monolayer thickness is still a huge challenge for commonlyutilized physical exfoliation and chemical synthesis methods. Herein,we have successfully grown predominantly monolayer MoS2on an inert and nearly lattice-matching mica substrate by usinga low-pressure chemical vapor deposition method. The growth is proposedto be mediated by an epitaxial mechanism, and the epitaxial monolayerMoS2is intrinsically strained on mica due to a small adlayer-substratelattice mismatch (∼2.7%). Photoluminescence (PL) measurementsindicate strong single-exciton emission in as-grown MoS2and room-temperature PL helicity (circular polarization ∼0.35)on transferred samples, providing straightforward proof of the highquality of the prepared monolayer crystals. The homogeneously strainedhigh-quality monolayer MoS2prepared in this study couldcompetitively be exploited for a variety of future applications. [ABSTRACT FROM AUTHOR]

The atomic layer of hybridized hexagonalboron nitride (h-BN) andgraphene has attracted a great deal of attention after the pioneeringwork of P. M. Ajayan et al. on Cu foils because of their unusual electronicproperties (Ci, L. J.; et al. Nat. Mater.2010, 9, 430−435). However,many fundamental issues are still not clear, including the in-planeatomic continuity as well as the edge type at the boundary of hybridizedh-BN and graphene domains. To clarify these issues, we have successfullygrown a perfect single-layer h-BN-graphene (BNC) patchwork on a selectedRh(111) substrate, via a two-step patching growth approach. With theideal sample, we convinced that at the in-plane linking interface,graphene and h-BN can be linked perfectly at an atomic scale. Moreimportantly, we found that zigzag linking edges were preferably formed,as demonstrated by atomic-scale scanning tunneling microscopy images,which was also theoretically verified using density functional theorycalculations. We believe the experimental and theoretical works areof particular importance to obtain a fundamental understanding ofthe BNC hybrid and to establish a deliberate structural control targetinghigh-performance electronic and spintronic devices. [ABSTRACT FROM AUTHOR]

Kagome materials have recently garnered substantial attention due to the intrinsic flat band feature and the stimulated magnetic and spin-related many-body physics. In contrast to their bulk counterparts, two-dimensional (2D) kagome materials feature more distinct kagome bands, beneficial for exploring novel quantum phenomena. Herein, we report the direct synthesis of an ultrathin kagome-structured Co-telluride (Co 9 Te 16 ) via a molecular beam epitaxy (MBE) route and clarify its formation mechanism from the Co-intercalation in the 1T-CoTe 2 layers. More significantly, we unveil the flat band states in the ultrathin Co 9 Te 16 and identify the real-space localization of the flat band states by in situ scanning tunneling microscopy/spectroscopy (STM/STS) combined with first-principles calculations. A ferrimagnetic order is also predicted in kagome-Co 9 Te 16 . This work should provide a novel route for the direct synthesis of ultrathin kagome materials via a metal self-intercalation route, which should shed light on the exploration of the intriguing flat band physics in the related systems.

Recently, two-dimensional (2D) atomic sheets have inspired new ideas in nanoscience including topologically protected charge transport,1,2 spatially separated excitons,3 and strongly anisotropic heat transport.4 Here, we report the intriguing observation of stable nonvolatile resistance switching (NVRS) in single-layer atomic sheets sandwiched between metal electrodes. NVRS is observed in the prototypical semiconducting (MX 2 , M = Mo, W; and X = S, Se) transitional metal dichalcogenides (TMDs),5 which alludes to the universality of this phenomenon in TMD monolayers and offers forming-free switching. This observation of NVRS phenomenon, widely attributed to ionic diffusion, filament, and interfacial redox in bulk oxides and electrolytes,6-9 inspires new studies on defects, ion transport, and energetics at the sharp interfaces between atomically thin sheets and conducting electrodes. Our findings overturn the contemporary thinking that nonvolatile switching is not scalable to subnanometre owing to leakage currents.10 Emerging device concepts in nonvolatile flexible memory fabrics, and brain-inspired (neuromorphic) computing could benefit substantially from the wide 2D materials design space. A new major application, zero-static power radio frequency (RF) switching, is demonstrated with a monolayer switch operating to 50 GHz.

Monolayer MoS2 prepared by chemical vapor deposition (CVD) has a highly polycrystalline nature largely because of the coalescence of misoriented domains, which severely hinders its future applications. Identifying and even controlling the orientations of individual domains and understanding their merging behavior therefore hold fundamental significance. In this work, by using single-crystalline sapphire (0001) substrates, we designed the CVD growth of monolayer MoS2 triangles and their polycrystalline aggregates for such purposes. The obtained triangular MoS2 domains on sapphire were found to distributively align in two directions, which, as supported by density functional theory calculations, should be attributed to the relatively small fluctuations of the interface binding energy around the two primary orientations. Using dark-field transmission electron microscopy, we further imaged the grain boundaries of the aggregating domains and determined their prevalent armchair crystallographic orientations with respect to the adjacent MoS2 lattice. The coalescence of individual triangular flakes governed by unique kinetic processes is proposed for the polycrystal formation. These findings are expected to shed light on the controlled MoS2 growth toward predefined domain orientation and large domain size, thus enabling its versatile applications in next-generation nanoelectronics and optoelectronics.