Jinlan Wang

Hopping transport through defect-induced localized states in molybdenum disulphide

Molybdenum disulphide is a novel two-dimensional semiconductor with potential applications in electronic and optoelectronic devices. However, the nature of charge transport in back-gated devices still remains elusive as they show much lower mobility than theoretical calculations and native n-type doping. Here we report a study of transport in few-layer molybdenum disulphide, together with transmission electron microscopy and density functional theory. We provide direct evidence that sulphur vacancies exist in molybdenum disulphide, introducing localized donor states inside the bandgap. Under low carrier densities, the transport exhibits nearest-neighbour hopping at high temperatures and variable-range hopping at low temperatures, which can be well explained under Mott formalism. We suggest that the low-carrier-density transport is dominated by hopping via these localized gap states. Our study reveals the important role of short-range surface defects in tailoring the properties and device applications of molybdenum disulphide.

Strong Photoluminescence Enhancement of MoS2 through Defect Engineering and Oxygen Bonding

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.

Density-functional study of Au n ( n = 2 – 2 0 ) clusters: Lowest-energy structures and electronic properties

We have investigated the lowest-energy structures and electronic properties of the

Towards intrinsic charge transport in monolayer molybdenum disulfide by defect and interface engineering

{\mathrm{Au}}_{n}(n=2--20)

Recent Progress and Challenges in Graphene Nanoribbon Synthesis

clusters based on density-functional theory with local density approximation. The small

Two-dimensional quasi-freestanding molecular crystals for high-performance organic field-effect transistors

{\mathrm{Au}}_{n}

High-Temperature Ferroelectricity and Photoluminescence in a Hybrid Organic–Inorganic Compound: (3-Pyrrolinium)MnCl3

clusters adopt planar structures up to

Light-Induced Ambient Degradation of Few-Layer Black Phosphorus: Mechanism and Protection.

n=6.

Tailoring band gap in GaN sheet by chemical modification and electric field: Ab initio calculations

Flat cage structures are preferred in the range of

Geometric and electronic properties of titanium clusters studied by ultrasoft pseudopotential

n=10--14