Urban smog issue has become more and more heated topic in China in recent years.Vehicle pollution is one of the main reasons for smog and haze in most large and medium-sized cities in the country.Maybe it is not surpr...Urban smog issue has become more and more heated topic in China in recent years.Vehicle pollution is one of the main reasons for smog and haze in most large and medium-sized cities in the country.Maybe it is not surprising now that the nation drives 95 million cars,second only to the United States with 240 million.Therefore,China has released a series of policies to alleviate the increasingly severe urban smog issues and accelerate upgrading of oil products quality.展开更多
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-radi...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.展开更多
文摘Urban smog issue has become more and more heated topic in China in recent years.Vehicle pollution is one of the main reasons for smog and haze in most large and medium-sized cities in the country.Maybe it is not surprising now that the nation drives 95 million cars,second only to the United States with 240 million.Therefore,China has released a series of policies to alleviate the increasingly severe urban smog issues and accelerate upgrading of oil products quality.
文摘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.
