Photoluminescence (PL) of transition metal dichalcogenides (TMDs) can be engineered by controlling the density of defects, which provide active sites for electron-hole recombination, either radiatively or non-radiatively. However, the implantation of defects by external stimulation, such as uniaxial tension and irradiation, tends to introduce local damages or structural non-homogeneity, which greatly degrades their luminescence properties and impede their applicability in constructing optoelectronic devices. In this paper, we present a strategy to introduce a controllable level of defects into the MoS2 monolayers by adding a hydrogen flow during the chemical vapor deposition, without sacrificing their luminescence characteristics. The density of the defect is controlled directly by the concentration of hydrogen. For an appropriate hydrogen flux, the monolayer MoS2 sheets have three times stronger PL emission at the excitonic transitions, compared with those samples with nearly perfect crystalline structure. The defect-bounded exciton transitions at lower energies arising in the defective samples and are maximized when the total PL is the strongest. However, the B exciton, exhibits a monotonic decline as the defect density increases. The Raman spectra of the defective MoS2 reveal a redshift (blueshift) of the in-plane (out-of-plane) vibration modes as the hydrogen flux increases. All the evidence indicates that the generated defects are in the form of sulfur vacancies. This study renders the high-throughput synthesis of defective MoS2 possible for catalysis or light emitting applications.
Using plasma build-up welding technology, Ni60, WC, Cr3C2, and TiC composite powders were clad on the surface of the substrate in a certain proportion according to the metallurgical bonding method to increase the bond strength between the coating and the substrate. Scanning electron microscopy and energy dispersive spectroscopy were used to observe the microstructure of the surfacing layer and the chemical composition of the sample. The hardness and wear resistance of the surfacing layer were tested and analyzed by the HV-1000 hardness tester and the impact wear device. The results showed that in the microstructure, fishbone, spider-web, and floral-like structures appeared in the surfacing layer. When the micro-hardness was tested, the depth of the indentation reflected the hardness of the surfacing layer. When analyzing wear resistance, the amount of wear increases with time. 相似文献