Two-dimensional (2D) materials, such as molybdenum disulfide (MoS 2 ), have been shown to exhibit excellent electrical and optical properties. The semiconducting nature of MoS 2 allows it to overcome the shortcomings of zero-bandgap graphene, while still sharing many of graphene's advantages for electronic and optoelectronic applications. Discrete electronic and optoelectronic components, such as field-effect transistors, sensors and photodetectors made from few-layer MoS 2 show promising performance as potential substitute of Si in conventional electronics and of organic and amorphous Si semiconductors in ubiquitous systems and display applications. An important next step is the fabrication of fully integrated multi-stage circuits and logic building blocks on MoS 2 to demonstrate its capability for complex digital logic and high-frequency ac applications. This paper demonstrates an inverter, a NAND gate, a static random access memory, and a five-stage ring oscillator based on a direct-coupled transistor logic technology. The circuits comprise between two to twelve transistors seamlessly integrated side-byside on a single sheet of bilayer MoS 2 . Both enhancement-mode and depletion-mode transistors were fabricated thanks to the use of gate metals with different work functions. Keywords: molybdenum disulfide (MoS 2 ), transition metal dichalcogenides (TMD), Two-dimensional (2D)electronics, integrated circuits, ring oscillator.2 Two-dimensional (2D) materials, such as molybdenum disulfide (MoS 2 ) 1 and other members of the transition metal dichalcogenides family, represents the ultimate scaling of material dimension in the vertical direction. Nano-electronic devices built on 2D materials offer many benefits for further miniaturization beyond Moore's Law 2,3 and as a high-mobility option in the emerging field of large-area and low-cost electronics that is currently dominated by low-mobility amorphous silicon 4 and organic semiconductors 5,6 . MoS 2 , a 2D semiconductor material, is also attractive as a potential complement to graphene 7,8,9 for constructing digital circuits on flexible and transparent substrates, while its 1.8 eV bandgap 10,11 is advantageous over silicon for suppressing the source-to-drain tunneling at the scaling limit of transistors 12 . Molybdenum disulfide (MoS 2 ) is a layered semiconductor from the transition metal dichalcogenides material family (TMD), MX 2 (M=Mo, W; X=S, Se, Te) 10,11,19,20 . A single molecular layer of MoS 2 consists of a layer of Mo atoms sandwiched between two layers of sulfur atoms by covalent bonds 10 . The strong intra-layer covalent bonds confer MoS 2 crystals excellent mechanical strength, thermal stability up to 1090 C in inert environment 21 , and a surface free of dangling bonds. On the other hand, the weak inter-layer Van der Waal's force allows single-or fewlayer MoS 2 thin films to be created through micro-mechanical cleavage technique 22 and through anisotropic 2D 3 growth by chemical vapor deposition 23,24 . This unique property of MoS 2 , and 2D ...

Hexagonal boron nitride (h-BN) is very attractive for many applications, particularly, as protective coating, dielectric layer/substrate, transparent membrane, or deep ultraviolet emitter. In this work, we carried out a detailed investigation of h-BN synthesis on Cu substrate using chemical vapor deposition (CVD) with two heating zones under low pressure (LP). Previous atmospheric pressure (AP) CVD syntheses were only able to obtain few layer h-BN without a good control on the number of layers. In contrast, under LPCVD growth, monolayer h-BN was synthesized and time-dependent growth was investigated. It was also observed that the morphology of the Cu surface affects the location and density of the h-BN nucleation. Ammonia borane is used as a BN precursor, which is easily accessible and more stable under ambient conditions than borazine. The h-BN films are characterized by atomic force microscopy, transmission electron microscopy, and electron energy loss spectroscopy analyses. Our results suggest that the growth here occurs via surface-mediated growth, which is similar to graphene growth on Cu under low pressure. These atomically thin layers are particularly attractive for use as atomic membranes or dielectric layers/substrates for graphene devices.

In this contribution we demonstrate a method of synthesizing a hexagonal boron nitride (h-BN) thin film by ambient pressure chemical vapor deposition on polycrystalline Ni films. Depending on the growth conditions, the thickness of the obtained h-BN film is between ∼5 and 50 nm. The h-BN grows continuously on the entire Ni surface and the region with uniform thickness can be up to 20 μm in lateral size which is only limited by the size of the Ni single crystal grains. The hexagonal structure was confirmed by both electron and X-ray diffraction. X-ray photoelectron spectroscopy shows the B/N atomic ratio to be 1:1.12. A large optical band gap (5.92 eV) was obtained from the photoabsorption spectra which suggest the potential usage of this h-BN film in optoelectronic devices.

We present a method for synthesizing MoS(2)/Graphene hybrid heterostructures with a growth template of graphene-covered Cu foil. Compared to other recent reports, (1, 2) a much lower growth temperature of 400 °C is required for this procedure. The chemical vapor deposition of MoS(2) on the graphene surface gives rise to single crystalline hexagonal flakes with a typical lateral size ranging from several hundred nanometers to several micrometers. The precursor (ammonium thiomolybdate) together with solvent was transported to graphene surface by a carrier gas at room temperature, which was then followed by post annealing. At an elevated temperature, the precursor self-assembles to form MoS(2) flakes epitaxially on the graphene surface via thermal decomposition. With higher amount of precursor delivered onto the graphene surface, a continuous MoS(2) film on graphene can be obtained. This simple chemical vapor deposition method provides a unique approach for the synthesis of graphene heterostructures and surface functionalization of graphene. The synthesized two-dimensional MoS(2)/Graphene hybrids possess great potential toward the development of new optical and electronic devices as well as a wide variety of newly synthesizable compounds for catalysts.

Photoluminescence (PL) properties of single-layer MoS2 are indicated to have strong correlations with the surrounding dielectric environment. Blue shifts of up to 40 meV of exciton or trion PL peaks were observed as a function of the dielectric constant of the environment. These results can be explained by the dielectric screening effect of the Coulomb potential; based on this, a scaling relationship was developed with the extracted electronic band gap and exciton and trion binding energies in good agreement with theoretical estimations. It was also observed that the trion/exciton intensity ratio can be tuned by at least 1 order of magnitude with different dielectric environments. Our findings are helpful to better understand the tightly bound exciton properties in strongly quantum-confined systems and provide a simple approach to the selective and separate generation of excitons or trions with potential applications in excitonic interconnects and valleytronics.

he ongoing global pandemic of the novel SARS-CoV-2 coronavirus presents an urgent need for the development of effective preventative and treatment therapies. The viral spike (S)-protein is a prime target for such therapies because of its critical role in the virus life cycle. The transmembrane CoV S-protein spike trimer is composed of interwoven protomers that include an N-terminal receptor-binding S1 subunit and a C-terminal S2 subunit that contains the fusion elements (Fig. 1a,b) 1. The S1 subunit is subdivided into the N-terminal domain (NTD) followed by the receptor-binding domain (RBD) and two structurally conserved subdomains (SD1 and SD2). Together, these domains cap the S2 subunit, protecting the conserved fusion machinery. Binding to the host receptor via the RBD in S1 is followed by proteolytic cleavage of the spike by host proteases 2. Large conformational changes in the S-protein result in S1 shedding and exposure of the fusion machinery in S2. Class I fusion proteins, such as the CoV-2 S-protein, undergo large conformational changes during the fusion process and must, by necessity, be highly flexible and dynamic. Indeed, cryo-EM structures of the SARS-CoV-2 spike reveal considerable flexibility and dynamics in the S1 subunit 1,2 , especially around the RBD, which exhibits two discrete conformational states-a 'down' state that is shielded from receptor binding and an 'up' state that is receptor-accessible. The wealth of structural information for β-CoV S-proteins, including the recently determined cryo-EM structures of the SARS-CoV-2 spike 1-11 , has provided a rich source of detailed geometric information from which to begin precise examination of the macromolecular transitions underlying triggering of this fusion machine. Several structures of soluble ectodomain constructs that retain the complete S1 subunit and the surface-exposed S2 subunit have been determined. These include SARS-CoV-2 1,3 , SARS 4-8 , MERS 4,9 and other human 1,10 and murine 11 β-CoV S-proteins.

Hexagonal boron nitride (h-BN) is a promising material as a dielectric layer or substrate for two-dimensional electronic devices. In this work, we report the synthesis of large-area h-BN film using atmospheric pressure chemical vapor deposition on a copper foil, followed by Cu etching and transfer to a target substrate. The growth rate of h-BN film at a constant temperature is strongly affected by the concentration of borazine as a precursor and the ambient gas condition such as the ratio of hydrogen and nitrogen. h-BN films with different thicknesses can be achieved by controlling the growth time or tuning the growth conditions. Transmission electron microscope characterization reveals that these h-BN films are polycrystalline, and the c-axis of the crystallites points to different directions. The stoichiometry ratio of boron and nitrogen is close to 1:1, obtained by electron energy loss spectroscopy. The dielectric constant of h-BN film obtained by parallel capacitance measurements (25 μm(2) large areas) is 2-4. These CVD-grown h-BN films were integrated as a dielectric layer in top-gated CVD graphene devices, and the mobility of the CVD graphene device (in the few thousands cm(2)/(V·s) range) remains the same before and after device integration.

Transient receptor potential melastatin member 8 (TRPM8) is a calcium ion (Ca2+)–permeable cation channel that serves as the primary cold and menthol sensor in humans. Activation of TRPM8 by cooling compounds relies on allosteric actions of agonist and membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2), but lack of structural information has thus far precluded a mechanistic understanding of ligand and lipid sensing by TRPM8. Using cryo–electron microscopy, we determined the structures of TRPM8 in complex with the synthetic cooling compound icilin, PIP2, and Ca2+, as well as in complex with the menthol analog WS-12 and PIP2. Our structures reveal the binding sites for cooling agonists and PIP2in TRPM8. Notably, PIP2binds to TRPM8 in two different modes, which illustrate the mechanism of allosteric coupling between PIP2and agonists. This study provides a platform for understanding the molecular mechanism of TRPM8 activation by cooling agents.