We report on a strong photoluminescence (PL) enhancement of monolayer MoS2 through defect engineering and oxygen bonding. Micro-PL and Raman images clearly reveal that the PL enhancement occurs at cracks/defects formed during high-temperature annealing. The PL enhancement at crack/defect sites could be as high as thousands of times after considering the laser spot size. The main reasons of such huge PL enhancement include the following: (1) the oxygen chemical adsorption induced heavy p doping and the conversion from trion to exciton; (2) the suppression of nonradiative recombination of excitons at defect sites, which was verified by low-temperature PL measurements. First-principle calculations reveal a strong binding energy of ∼2.395 eV for an oxygen molecule adsorbed on a S vacancy of MoS2. The chemically adsorbed oxygen also provides a much more effective charge transfer (0.997 electrons per O2) compared to physically adsorbed oxygen on an ideal MoS2 surface. We also demonstrate that the defect engineering and oxygen bonding could be easily realized by mild oxygen plasma irradiation. X-ray photoelectron spectroscopy further confirms the formation of Mo-O bonding. Our results provide a new route for modulating the optical properties of two-dimensional semiconductors. The strong and stable PL from defects sites of MoS2 may have promising applications in optoelectronic devices.

We study by Raman scattering the shear and layer breathing modes in multilayer MoS2. These are identified by polarization measurements and symmetry analysis. Their positions change with the number of layers, with different scaling for odd and even layers. A chain model explains the results, with general applicability to any layered material, and allows one to monitor their thickness.

Hollow particle-based N-doped carbon nanofibers synthesized via a facile electrospinning and carbonization method exhibit enhanced supercapacitive performance.

The development of high-performance anode materials for next-generation lithium-ion batteries (LIBs) is vital to meeting the requirements for large-scale applications ranging from electric vehicles to power grids. Conversion-type transition-metal compounds are attractive anodes for next-generation LIBs because of their diverse compositions and high theoretical specific capacities. Here, we provide an overview of the recent development of some representative conversion-type anode materials (CTAMs) in LIBs. In this review, we start with an introduction to typical CTAMs and their lithium storage mechanisms. Then, we present the obstacles to their widespread implementation and the corresponding nanoengineering strategies for high-performance CTAMs, including the use of low-dimensional nanostructures, hierarchical porous nanostructures, hollow structures, and hybridization with various carbonaceous materials. Particularly, we highlight the relationship between these nanostructures and the lithium storage properties. Lastly, we present some perspectives on the current challenges and possible research directions for nanostructured CTAMs.

We report polarization resolved photoluminescence from monolayer MoS2, a two-dimensional, non-centrosymmetric crystal with direct energy gaps at two different valleys in momentum space. The inherent chiral optical selectivity allows exciting one of these valleys and close to 90% polarized emission at 4K is observed with 40% polarization remaining at 300K. The high polarization degree of the emission remains unchanged in transverse magnetic fields up to 9T indicating robust, selective valley excitation.

We demonstrate rational design and fabrication of hierarchical InS-CdInS heterostructured nanotubes as efficient and stable photocatalysts for visible light CO reduction. The novel self-templated strategy, including sequential anion- and cation-exchange reactions, integrates two distinct sulfide semiconductors into hierarchical tubular hybrids with homogeneous interfacial contacts and ultrathin two-dimensional (2D) nanosheet subunits. Accordingly, the hierarchical heterostructured nanotubes facilitate separation and migration of photoinduced charge carriers, enhance the adsorption and concentration of CO molecules, and offer rich active sites for surface redox reactions. Benefiting from these structural and compositional features, the optimized hierarchical InS-CdInS nanotubes without employing noble metal cocatalysts in the catalytic system manifest remarkable performance for deoxygenative reduction of CO with high CO generation rate (825 μmol h g) and outstanding stability under visible light irradiation.

Exploring effective electrocatalysts is a crucial requirement for boosting the efficiency of water splitting to obtain clean fuels. Here, a self-templating strategy is reported to synthesize Ni-Fe mixed diselenide cubic nanocages for the electrocatalytic oxygen evolution reaction (OER). The diselenide nanocages are derived from corresponding Prussian-blue analog nanocages, which are first obtained by treating the nanocube precursor with a site-selective ammonia etchant. The resulting Ni-Fe mixed diselenide nanocages perform as a superior OER electrocatalyst, which affords a current density of 10 mA cm at a small overpotential of 240 mV; a high current density, mass activity, and turnover frequency of 100 mA cm , 1000 A g , and 0.58 s , respectively, at the overpotential of 270 mV; a Tafel slope as small as 24 mV dec ; and excellent stability in alkaline medium.

The oxygen evolution reaction (OER) is involved in various renewable energy systems,such as water-splitting cells and metal-air batteries.N i-Fel ayered double hydroxides (LDHs) have been reported as promising OER electrocatalysts in alkaline electrolytes.T he rational design of advanced nanostructures for Ni-FeLDHs is highly desirable to optimize their electrocatalytic performance.H erein, we report af acile self-templated strategy for the synthesis of novel hierarchical hollown anoprisms composed of ultrathin Ni-FeL DH nanosheets.T etragonal nanoprisms of nickel precursors were first synthesized as the self-sacrificing template.A fterwards, these Ni precursors were consumed during the hydrolysis of iron(II) sulfate for the simultaneous growth of al ayer of Ni-FeL DH nanosheets on the surface.T he resultant Ni-FeL DH hollow prisms with large surface areas manifest high electrocatalytic activity towards the OER with lowo verpotential, small Tafel slope,and remarkable stability.