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We report a general synthetic strategy for highly robust growth of diverse lateral heterostructures, multiheterostructures, and superlattices from two-dimensional (2D) atomic crystals. A reverse flow during the temperature-swing stage in the sequential vapor deposition growth process allowed us to cool the existing 2D crystals to prevent undesired thermal degradation and uncontrolled homogeneous nucleation, thus enabling highly robust block-by-block epitaxial growth. Raman and photoluminescence mapping studies showed that a wide range of 2D heterostructures (such as WS-WSe and WS-MoSe), multiheterostructures (such as WS-WSe-MoS and WS-MoSe-WSe), and superlattices (such as WS-WSe-WS-WSe-WS) were readily prepared with precisely controlled spatial modulation. Transmission electron microscope studies showed clear chemical modulation with atomically sharp interfaces. Electrical transport studies of WSe-WS lateral junctions showed well-defined diode characteristics with a rectification ratio up to 10.

The splitting of water photoelectrochemically into hydrogen and oxygen represents a promising technology for converting solar energy to fuel. The main challenge is to ensure that photogenerated holes efficiently oxidize water, which generally requires modification of the photoanode with an oxygen evolution catalyst (OEC) to increase the photocurrent and reduce the onset potential. However, because excess OEC material can hinder light absorption and decrease photoanode performance, its deposition needs to be carefully controlled--yet it is unclear which semiconductor surface sites give optimal improvement if targeted for OEC deposition, and whether sites catalysing water oxidation also contribute to competing charge-carrier recombination with photogenerated electrons. Surface heterogeneity exacerbates these uncertainties, especially for nanostructured photoanodes benefiting from small charge-carrier transport distances. Here we use super-resolution imaging, operated in a charge-carrier-selective manner and with a spatiotemporal resolution of approximately 30 nanometres and 15 milliseconds, to map both the electron- and hole-driven photoelectrocatalytic activities on single titanium oxide nanorods. We then map, with sub-particle resolution (about 390 nanometres), the photocurrent associated with water oxidation, and find that the most active sites for water oxidation are also the most important sites for charge-carrier recombination. Site-selective deposition of an OEC, guided by the activity maps, improves the overall performance of a given nanorod--even though more improvement in photocurrent efficiency correlates with less reduction in onset potential (and vice versa) at the sub-particle level. Moreover, the optimal catalyst deposition sites for photocurrent enhancement are the lower-activity sites, and for onset potential reduction the optimal sites are the sites with more positive onset potential, contrary to what is obtainable under typical deposition conditions. These findings allow us to suggest an activity-based strategy for rationally engineering catalyst-improved photoelectrodes, which should be widely applicable because our measurements can be performed for many different semiconductor and catalyst materials.

Epitaxial growth of A-A and A-B stacking MoS2 on WS2 via a two-step chemical vapor deposition method is reported. These epitaxial heterostructures show an atomic clean interface and a strong interlayer coupling, as evidenced by systematic characterization. Low-frequency Raman breathing and shear modes are observed in commensurate stacking bilayers for the first time; these can serve as persuasive fingerprints for interfacial quality and stacking configurations.

Recently, 2D materials exhibit great potential for humidity sensing applications due to the fact that almost all atoms are at the surface. Therefore, the quality of the material surface becomes the key point for sensitive perception. This study reports an integrated, highly sensitive humidity sensors array based on large-area, uniform single-layer molybdenum disulfide with an ultraclean surface. Device mobilities and on/off ratios decrease linearly with the relative humidity varying from 0% to 35%, leading to a high sensitivity of more than 10 . The reversible water physisorption process leads to short response and decay times. In addition, the device array on a flexible substrate shows stable performance, suggesting great potential in future noncontact interface localization applications.

Two-dimensional materials with intrinsic magnetism have recently drawn intense interest for both the fundamental studies and potential technological applications. However, the studies to date have been largely limited to mechanically exfoliated materials. Herein, an atmospheric pressure chemical vapor deposition route to ultrathin group VB metal telluride MTe (M = V, Nb, Ta) nanoplates with thickness as thin as 3 nm is reported. It is shown that the resulting nanoplates can be systematically evolved from mostly thicker hexagonal domains to thinner triangular domains with an increasing flow rate of the carrier gas. X-ray diffraction and transmission electron microscopy studies reveal MTe (M = V, Nb, Ta) nanoplates are high-quality single crystals. High-resolution scanning transmission electron microscope imaging reveals the VTe and NbTe nanoplates adopt the hexagonal 1T phase and the TaTe nanoplates show a monoclinic distorted 1T phase. Electronic transport studies show that MTe single crystals exhibit metallic behavior. Magnetic measurements show that VTe and NbTe exhibit ferromagnetism and TaTe shows paramagnetic behavior. The preparation of ultrathin few-layered MTe nanoplates will open up exciting opportunities for the burgeoning field of spintronics, sensors, and magneto-optoelectronics.

2D semiconductors are promising channel materials for field-effect transistors (FETs) with potentially strong immunity to short-channel effects (SCEs). In this paper, a grain boundary widening technique is developed to fabricate graphene electrodes for contacting monolayer MoS . FETs with channel lengths scaling down to ≈4 nm can be realized reliably. These graphene-contacted ultrashort channel MoS FETs exhibit superior performances including the nearly Ohmic contacts and excellent immunity to SCEs. This work provides a facile route toward the fabrication of various 2D material-based devices for ultrascaled electronics.

The effective capture of radioiodine, produced or released from nuclear-related activities, is of paramount importance for the sustainable development of nuclear energy. Here, a series of zirconium-based metal−organic frameworks (Zr-MOFs), with a Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 cluster and various carboxylate linkers, were investigated for the capture of volatile iodine. Their adsorption kinetics and recyclability were investigated in dry and humid environments. The structural change of Zr-MOFs during iodine trapping was studied using powder X-ray diffraction and pore structure measurements. Experimental spectra (Raman and X-ray photoelectron spectroscopy) and density functional theory (DFT) calculations for the linkers and Zr clusters were performed to understand the trapping mechanism of the framework. When interacting with iodine molecules, MOF-808, NU-1000, and UiO-66, with highly connected and/or rigid linkers, have better structural stability than UiO-67 and MOF-867, which have flexible linkers with less connectivity. Particularly, MOF-808, with a rigid and tritopic benzenetricarboxylate linker, has the highest iodine adsorption capacity (2.18 g/g, 80 °C), as well as the largest pore volume after iodine elution. In contrast, UiO-67, with long linear ditopic linkers, exhibits the weakest stability and lowest adsorption capacity (0.53 g/g, 80 °C) because of its most serious collapse of pore structures. After incorporating with strong electron-donating imidazole/pyridine ligands, both the stability and adsorption capacity of MOF-808/NU-1000 decrease. DFT calculations verify that the N-heterocycle groups could enhance the affinity toward iodine by strong charge transfer. DFT calculations also suggest that the terminal −OH in MOF-808 has a strong affinity toward iodine (−54 kJ/mol I 2 ) and water (−63 kJ/mol H 2 O) and a weak affinity toward NO 2 (−27 kJ/mol NO 2 ). With high adsorption capacity and excellent stability, MOF-808 shows great potential for the sustainable removal of radioiodine.