Xingfang Luo

Horizontal growth of MoS2 nanowires by chemical vapour deposition

We describe a single step route for the synthesis of MoS2 wires using a chemical vapour deposition (CVD) method. By tuning the CVD growth parameters, the horizontally oriented MoS2 nanowires on SiO2/Si substrate can be synthesized successfully. The MoS2 nanowire has height of about 93 nm and width of about 402 nm with multilayer structure. Good local photoluminescence (PL) properties can be observed for these horizontal MoS2 nanowires. The successful fabrication and prominent PL effect of the horizontal MoS2 nanowires provide potential applications for the MoS2-based in planar devices.

Monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes with enhanced photoluminescence

The precise control of the morphology and crystal shape of MoS2 nanostructures is of particular importance for their application in nanoelectronic and optoelectronic devices. Here, we describe a single step route for the synthesis of monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes using a chemical vapor deposition method. First-principles calculations demonstrated that the bandgap of the pyramid-like MoS2 nanodot is a direct bandgap. Enhanced local photoluminescence emission was observed in the pyramid-like MoS2 nanodot, in comparison with monolayered MoS2 flakes. The findings presented here provide new opportunities to tailor the physical properties of MoS2via morphology-controlled synthesis.

Tuning strain and photoluminescence of confined Au nanoparticles by hydrogen passivation

Au nanoparticles confined in an Al2O3 matrix are synthesized using pulsed laser deposition method and rapid thermal annealing technique. The confined Au nanoparticles experience a compressive strain during the growth process. It is demonstrated that hydrogen passivation can be used to enhance and tailor the optical properties of confined Au nanoparticles by engineering the strain and defect states of the confined Au nanoparticles. The findings provide an insight and useful methodology to improve the emission efficiency of noble metal nanoparticle based materials for potential application in optoelectronic and photonic devices.

Work function variation of monolayer MoS2 by nitrogen-doping

Monolayer MoS2 films with substantial sulfur vacancies are obtained using the laser molecular beam epitaxy (L-MBE) technique benefitted by high substrate temperature and ultrahigh vacuum growth conditions. The intrinsic sulfur vacancies present an excellent opportunity for varying the work function of monolayer MoS2 films by nitrogen doping. The in-plane doping of nitrogen atoms on L-MBE-synthesized monolayer MoS2 films is realized on the basis of rapid thermal annealing in a nitrogen environment. The as-grown and nitrogen-doped monolayer MoS2 films are evaluated by using Raman and photoluminescence spectroscopies. In accordance with the X-ray photoelectron spectroscopy results, the ultraviolet photoelectron spectroscopy investigation shows that the work function of the monolayer MoS2 films increases by 0.29 eV after covalent nitrogen doping. Nitrogen doping on monolayer MoS2 is further treated theoretically using first-principles calculations. Based on theoretical calculations and experimental validations, it is illustrated that nitrogen is a promising in-plane heteroatom dopant for work function variation of monolayer MoS2.

Matrix-Dependent Strain Distributions of Au and Ag Nanoparticles in a Metal-Oxide-Semiconductor-Based Nonvolatile Memory Device

The matrix-dependent strain distributions of Au and Ag nanoparticles in a metal-oxide-semiconductor based nonvolatile memory device are investigated by finite element calculations. The simulation results clearly indicate that both Au and Ag nanoparticles incur compressive strain by high-k Al2O3 and conventional SiO2 dielectrics. The strain distribution of nanoparticles is closely related to the surrounding matrix. Nanoparticles embedded in different matrices experience different compressive stresses, which provide opportunities for tailoring the microstructure of Au and Ag nanoparticles. This opens up ways for exploring strain effects on physical properties and further tunes the charge storage properties of nanoparticles.