Monolayer molybdenum disulfide (MoS₂) has emerged as one of the most promising channel materials for next-generation nanoelectronics and optoelectronics owing to its atomic thickness, dangling-bond-free flat surface, and high electrical quality. Currently, high-quality monolayer MoS₂ wafers are primarily grown on sapphire substrates incompatible with conventional device fabrication, and thus transfer processes to a suitable substrate are typically required before the device can be processed. Here, we demonstrate the batch production of transfer-free MoS₂ top-gate devices directly on sapphire growth substrates via step engineering. By introducing substrate steps on growth substrate sapphire, high-κ dielectric layers with superior quality and uniform can be directly deposited on the epitaxially grown monolayer MoS₂. For the substrate with a maximum step density of 100 μm⁻¹, the gate capacitance can reach ~ 1.87 μF∙cm⁻², while the interface trap state density (D_it) can be as low as ~ 7.6 × 10¹⁰ cm⁻²∙eV⁻¹. The direct deposition of high-quality dielectric layers on grown monolayer MoS₂ enables the batch fabrication of top-gate devices devoid of transfer and thus excellent device yield of > 96%, holding great promise for large-scale two-dimensional (2D) integrated circuits.

Photodetectors and optoelectronic synapses are vital for construction of artificial visual perception system. However, the hardware implementations of optoelectronic-neuromorphic devices based on conventional architecture usually suffer from poor scalability, light response range, and limited functionalities. Here, large-scale flexible monolayer MoS₂ devices integrating photodetectors and optoelectronic synapses over the entire visible spectrum in one device have been realized, which can be used in photodetection, optical communication, artificial visual perception system, and optical artificial neural network. By modulating gate voltages, we enable MoS₂-based devices to be photodetectors and also optoelectronic synapses. Importantly, the MoS₂-based optoelectronic synapses could implement many synaptic functions and neuromorphic characteristics, such as short-term memory (STM), long-term memory (LTM), paired-pulse facilitation (PPF), long-term potentiation (LTP)/long-term depression (LTD), and “learning-experience” behavior. Furthermore, an associative learning behavior (the classical conditioning Pavlov’s dog experiment) was emulated using paired stimulation of optical and voltage pulses. These results facilitate the development of MoS₂-based multifunctional optoelectronic devices with a simple device structure, showing great potential for photodetection, optoelectronic neuromorphic computing, human visual systems mimicking, as well as wearable and implantable electronics.

As an emerging two-dimensional (2D) semiconductor material, monolayer MoS₂ has recently attracted considerable attention. Various promising applications of this material have been proposed for electronics, optoelectronics, sensing, catalysis, energy storage, and so on. To realize these practical applications, high-quality and large-area MoS₂ with controllable properties is required. Among the many different synthesis techniques, epitaxy provides a promising route for producing MoS₂ monolayers. Here, we review the epitaxial growth of monolayer MoS₂ on various substrates, with a particular focus on large-scale films with large domain sizes and high domain alignments. Finally, we offer perspectives and challenges for future research and applications of this technology.

Two-dimensional semiconducting transition-metal dichalcogenides have attracted considerable interest owing to their unique physical properties and future device applications. In particular, grain boundaries (GBs) have been often observed in single-layer MoS2 grown via chemical vapor deposition, which can significantly influence the material properties. In this study, we examined the electronic structures of various GBs in single-layer MoS₂ grown on highly oriented pyrolytic graphite using low-temperature scanning tunneling microscopy/spectroscopy. By measuring the local density of states of a series of GBs with tilt angles ranging from 0° to 25°, we found that the bandgaps at the GBs can be either broadened or narrowed with respect to the intrinsic single-layer MoS₂. The bandgap broadening shows that the GBs can become more insulating, which may directly influence the transport properties of nanodevices based on polycrystalline single-layer MoS₂ and be useful for optoelectronics.

All-graphene devices are new class of graphene devices with simple layouts and low contact resistances. Here we report a clean fabrication strategy for all-graphene devices via a defect-assisted anisotropic etching. The as-fabricated graphene is free of contamination and retains the quality of pristine graphene. The contact resistance at room temperature (RT) between a bilayer graphene channel and a multilayer graphene electrode can be as low as ~5 Ω·μm, the lowest ever achieved experimentally. Our results suggest the feasibility of employing such all-graphene devices in high performance carbon-based integrated circuits.