Realization of wafer-scale single-crystal films of transition metal dichalcogenides (TMDs) such as WS 2 requires epitaxial growth and coalescence of oriented domains to form a continuous monolayer. The domains must be oriented in the same crystallographic direction on the substrate to inhibit the formation of inversion domain boundaries (IDBs), which are a common feature of layered chalcogenides. Here we demonstrate fully coalesced unidirectional WS 2 monolayers on 2 in. diameter c-plane sapphire by metalorganic chemical vapor deposition using a multistep growth process to achieve epitaxial WS 2 monolayers with low in-plane rotational twist (0.09°). Transmission electron microscopy analysis reveals that the WS 2 monolayers are largely free of IDBs but instead have translational boundaries that arise when WS 2 domains with slightly offset lattices merge together. By regulating the monolayer growth rate, the density of translational boundaries and bilayer coverage were significantly reduced. The unidirectional orientation of domains is attributed to the presence of steps on the sapphire surface coupled with growth conditions that promote surface diffusion, lateral domain growth, and coalescence while preserving the aligned domain structure. The transferred WS 2 monolayers show neutral and charged exciton emission at 80 K with negligible defect-related luminescence. Back-gated WS 2 field effect transistors exhibited an I ON / OFF of ∼10 7 and mobility of 16 cm 2 /(V s). The results demonstrate the potential of achieving wafer-scale TMD monolayers free of inversion domains with properties approaching those of exfoliated flakes.

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been reported as potential electrodes for energy storage. These 2D materials demonstrate unique properties, including high electronic conductivity, high capacity, flexibility, strength, and electrochemical stability. However, all of these materials have limitations in energy storage, such as the low electronic conductivity of oxides and the limited redox activity of graphene-based materials, and limiting charge storage capacity. [1a,7] The challenge, therefore, is to fabricate electrodes that will combine all of the aforementioned characteristics in one structure. Due to this challenge, efforts have been devoted to build heterostructures by stacking different 2D sheets to mitigate the weaknesses of each component. [1a] For example, heterostructures of graphene/TMD, [8] graphene/TMO, [9] graphene/phosphorene, [3a,b] etc., have been fabricated and exhibit enhanced energy storage capability compared to their individual building blocks.In recent years, 2D transition metal carbides, nitrides, and carbonitrides, known as MXenes, have emerged as an attractive class of materials due to their combined properties of metallic conductivity, good mechanical strength, and pseudocapacitive charge storage. [6,10] A variety of MXene-based electrodes have been developed and shown promising performance in supercapacitors, [11] Li-ion, [12] Li-S, [13] and other batteries. [14] Like other 2D materials, the restacking of MXene nanosheets decreases the performance of MXene-based electrodes by hindering electrolyte accessibility and ion transport. Additionally, the electrochemical properties of MXenes strongly depend on the surface chemistry; their surface terminations need to be well controlled to minimize irreversible capacity. [15] To fully utilize the energy storage capability of MXenes, one of the most promising strategies is to combine MXene nanosheets with other nanomaterials to form a hybrid/heterostructured architecture, which would inherit the advantages of individual building blocks while eliminating their shortcomings. [6,10,16] For example, numerous carbon nanomaterials, [11c,17] oxide nanoparticles, [18] and polymer molecules [19] have been incorporated Stacking different 2D materials is a promising strategy to fabricate heterostructures that combine the advantages and eliminate the associated shortcomings of individual building blocks. When used for energy storage, 2D heterostructures provide the opportunity to manufacture flexible and conductive paper electrodes, which require no binders, conductive additives, or current collectors. Here, 2D MXene/graphene heterostructured papers are manufactured by alternately stacking Ti 3 C 2 T x MXene and reduced graphene oxide (rGO) nanosheets using spray-assisted layer-by-layer assembly. Up to letter paper-sized free-standing films can be manufactured within half an hour of spraying. When used directly as anodes for Na-ion storage, the MXene/ rGO heterostructured films exhibit improved electrochemical performance compared to pure MXene and rGO films in terms of capacity, ...

In the emerging era of the internet of things (IoT), ubiquitous sensors continuously collect, consume, store, and communicate a huge volume of information which is becoming increasingly vulnerable to theft and misuse. Modern software cryptosystems require extensive computational infrastructure for implementing ciphering algorithms, making them difficult to be adopted by IoT edge sensors that operate with limited hardware resources and at low energy budgets. Here we propose and experimentally demonstrate an “all-in-one” 8 × 8 array of robust, low-power, and bio-inspired crypto engines monolithically integrated with IoT edge sensors based on two-dimensional (2D) memtransistors. Each engine comprises five 2D memtransistors to accomplish sensing and encoding functionalities. The ciphered information is shown to be secure from an eavesdropper with finite resources and access to deep neural networks. Our hardware platform consists of a total of 320 fully integrated monolayer MoS2-based memtransistors and consumes energy in the range of hundreds of picojoules and offers near-sensor security.