Substitutional doping has been proven to be an effective route to engineer band gap, transport characteristics, and magnetism in transition metal dichalcogenides. Herein, we demonstrate substitutional doping of monolayer tungsten disulfide (WS2) with Nb via the chemical vapor deposition technique. Scanning transmission electron microscopy confirms that Nb successfully substituted the W atom in the WS2 lattice. Moreover, photoluminescence indicates a significant red shift when different concentrations of Nb are introduced, in agreement with density functional theory calculations. Electrical measurements reveal the degenerate p-type semiconductor behavior of Nb-doped WS2 field-effect transistors. The successful synthesis of p-type WS2 in this study provides a promising method to expand the electronic and photonic engineering of two-dimensional materials.

Geckos have the extraordinary ability to prevent their sticky feet from fouling while running on dusty walls and ceilings. Understanding gecko adhesion and self-cleaning mechanisms is essential for elucidating animal behaviours and rationally designing gecko-inspired devices. Here we report a unique self-cleaning mechanism possessed by the nano-pads of gecko spatulae. The difference between the velocity-dependent particle-wall adhesion and the velocity-independent spatula-particle dynamic response leads to a robust self-cleaning capability, allowing geckos to efficiently dislodge dirt during their locomotion. Emulating this natural design, we fabricate artificial spatulae and micromanipulators that show similar effects, and that provide a new way to manipulate micro-objects. By simply tuning the pull-off velocity, our gecko-inspired micromanipulators, made of synthetic microfibers with graphene-decorated micro-pads, can easily pick up, transport, and drop-off microparticles for precise assembling. This work should open the door to the development of novel self-cleaning adhesives, smart surfaces, microelectromechanical systems, biomedical devices, and more.

Growth of large-area, uniform, and high-quality monolayer transition-metal dichalcogenides (TMDs) for practical and industrial applications remains a long-standing challenge. The present study demonstrates a modified predeposited chemical vapor deposition (CVD) process by employing an annealing procedure before sulfurization, which helps in achieving large-area, highly uniform, and high-quality TMDs on various substrates. The annealing procedure resulted in a molten liquid state of the precursors in the CVD process, which not only facilitated a uniform redistribution of the precursor on the substrate (avoid the aggregation) because of the uniform redistribution of the liquid precursor on the substrate but more importantly avoided the undesired multilayer growth via the selflimited lateral supply precursors mechanism. A 2 in. uniform and continuous monolayer WS 2 film has been synthesized on the SiO 2 /Si substrate. Moreover, uniform monolayer WS 2 single crystals can be prepared on more general and various substrates including sapphire, mica, quartz, and Si 3 N 4 using the same growth procedure. Besides, this growth mechanism can be generalized to synthesize other monolayer TMDs such as MoS 2 and MoS 2 /WS 2 heterostructures. Hence, the present method provides a generalized attractive strategy to grow large-area, uniform, single-layer two-dimensional (2D) materials. This study has significant implications in the advancement of batch production of various 2D-material-based devices for industrial and commercial applications.

Shape engineering plays a crucial role in the application of two-dimensional (2D) layered metal dichalcogenide (LMD) crystalline materials in terms of physical and chemical property modulation. However, controllable growth of 1T phase tin disulfide (SnS2) with multifarious morphologies has rarely been reported and remains challenging. Herein, we report a direct synthesis of large-size, uniform, and atomically thin 1T-SnS2 with multiple morphologies by adding potassium halides via a facile chemical vapor deposition process. A variety of morphologies, i.e., from hexagon, triangle, windmill, and dendritic to coralloid, corresponding to fractal dimensions from 1.01 to 1.81 are accurately controlled by growth conditions. Moreover, the Sn concentration controls the morphology change of SnS2. The edge length of the SnS2 dendritic flake can grow larger than 500 μm in 5 min. Potassium halides can significantly reduce the surface migration barrier of the SnS2 cluster and enhance the SnS2 adhesion force with substrate to facilitate efficient high in-plane growth of monolayer SnS2 compared to sodium halides by density functional theory calculations. More branched SnS2 with higher fractal dimension provides more active sites for enhancing hydrogen evolution reactions. Importantly, we prove that potassium halides are preferable for 1T-phase LMDs structures, while sodium halides are more suitable for 2H-phase materials. The growth mechanism proposed here provides a general approach for controllable-phase synthesis of 2D LMD crystals and related heterostructures. Shape engineering of 2D materials also provides a strategy to tune LMD properties for demanding applications.

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