By creating defects via oxygen plasma treatment, we demonstrate optical properties variation of single-layer MoS 2 . We found that, with increasing plasma exposure time, the photoluminescence (PL) evolves from very high intensity to complete quenching, accompanied by gradual reduction and broadening of MoS 2 Raman modes, indicative of distortion of the MoS 2 lattice after oxygen bombardment. X-ray photoelectron spectroscopy study shows the appearance of Mo 6+ peak, suggesting the creation of MoO 3 disordered regions in the MoS 2 flake. Finally, using band structure calculations, we demonstrate that the creation of MoO 3 disordered domains upon exposure to oxygen plasma leads to a direct to indirect bandgap transition in single-layer MoS 2 , which explains the observed PL quenching. KEYWORDS 2D materials, defect engineering, optical properties, bandgap tuning, molybdenum trioxide INTRODUCTIONThe ability to controllably tailor the properties of a material is a key factor in the development of many novel applications. In the case of bulk semiconductors, creating and manipulating defects constitutes an essential element in controlling the electrical, magnetic, and optical properties of the host material. 1 Although the role of defects is well understood in bulk semiconductors, it has received little attention in emerging two-dimensional (2D) layered semiconductors, preventing their full exploitation for tailored 2D nanoelectronic and photonic devices. Graphene and graphene oxide are examples of the impact that defects can have on 2D materials. Pristine graphene, which contains no intrinsic defect, is well known for its extraordinary high mobility, and is of great importance for high frequency device applications. 2, 3 However, its inherent lack of bandgap and low absorption of solar photons greatly limit its use in electronic and photonic devices. On the other hand, its solution processed counterparts, graphene oxide and reduced graphene oxide, have a large amount of defects, which lead to formation of a bandgap and open the way to many other applications in photodetectors, sensors, catalysis, and solar cell. [4][5][6][7][8] Recently, layered transition metal dichalcogenides (TMDs) have emerged as important materials for 2D device engineering. 9-11 Molybdenum disulfide (MoS 2 ), composed of weak van der Waals bonded S-Mo-S units, offers a large intrinsic bandgap that is strongly dependent on the number of layers, with an indirect bandgap (1.2 eV) in bulk MoS 2 transitioning to a direct

We demonstrate that the electrical property of a single layer molybdenum disulfide (MoS 2 ) can be significantly tuned from semiconducting to insulating regime via controlled exposure to oxygen plasma. The mobility, on-current and resistance of single layer MoS 2 devices were varied up to four orders of magnitude by controlling the plasma exposure time. Raman spectroscopy, X-ray photoelectron spectroscopy and density functional theory studies suggest that the significant variation of electronic properties is caused by the creation of insulating MoO 3 -rich disordered domains in the MoS 2 sheet upon oxygen plasma exposure, leading to an exponential variation of resistance and mobility as a function of plasma exposure time. The resistance variation calculated using an effective medium model is in excellent agreement with the measurements. The simple approach described here can be used for the fabrication of tunable two dimensional nanodevices on MoS 2 and other transition metal dichalcogenides.

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Hollow microporous organic networks (H-MONs) were prepared by a template method using silica spheres. The shell thickness was delicately controlled by changing the synthetic conditions. The H-MONs were used as a template for the synthesis of nanoparticulate Co3O4 hollows which showed excellent catalytic performance in H2O2 oxidation.

Tubes from tubes: Microporous organic nanotubes were prepared by Sonogashira coupling between tetrakis(4‐ethynylphenyl)methane and N,N′‐di(4‐iodophenyl)‐4,4′‐bipyridinium dichloride. These nanotubes were used as a template for secondary inorganic materials, namely Fe2O3 nanotubes with a high discharge capacity and excellent stability.