Silicene,silicon analogue to graphene which possesses a two-dimensional(2D)hexagonal lattice,has attracted increasing attention in the last few years due to predicted unique properties.However,silicon naturally posses...Silicene,silicon analogue to graphene which possesses a two-dimensional(2D)hexagonal lattice,has attracted increasing attention in the last few years due to predicted unique properties.However,silicon naturally possesses a three-dimensional(3D)diamond structure,so there seems to be not any natural solid phase of silicon similar to graphite.Here we report the synthesis of new silicene structure with a unique rectangular lattice by using a coherent electron beam to irradiate amorphous silicon nanofilm produced by pulsed laser deposition(PLD).Under the irradiation of coherent electron beam with proper kinetic energy,the surface layer of silicon nanofilm can be crystallized into silicene.The dynamic stability and the energy band properties of this new silicene structure are investigated by using first-principle calculations and density function theory(DFT)with the help of the observed crystalline structure and lattice constant.The new silicene structure has a real direct bandgap of 0.78 eV.Interestingly,the simulating calculation shows that the convex bond angle is 118°in the new silicene structure with rectangular lattices.The DFT simulations reveal that this new silicene structure has a Dirac-cone-like energy band.The experimental realization of silicene and the theoretically predicted properties shed light on the silicon material with potential applications in new devices.展开更多
The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces,for example,a Si-O-Si bridge bond on curved surface provides the localized le...The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces,for example,a Si-O-Si bridge bond on curved surface provides the localized levels in band gap and its bonding energy is shallower than that on facet.The red-shifting of PL spectra on smaller silicon quantum dots can be explained by curved surface effect.Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided in curved surface effect.展开更多
A new conception of nano-laser is proposed in which depending on the size of nano-clusters(silicon quantum dots(QD)),the pumping level of laser can be tuned by the quantum confinement(QC)effect,and the population inve...A new conception of nano-laser is proposed in which depending on the size of nano-clusters(silicon quantum dots(QD)),the pumping level of laser can be tuned by the quantum confinement(QC)effect,and the population inversion can be formed between the valence band and the localized states produced from the surface bonds.The nano-laser belongs to the emission of typeⅡ.The peaks of stimulated emission are observed at 605 nm and 693 nm.Through the micro-cavity of nano-laser,a full width at half maximum of the peak at 693 nm can reach to 0.5 nm.The theoretical model and the experimental results indicate that it is a necessary condition for setting up nano-laser that the smaller size of nano-clusters(d<3 nm)can make the localized states into band gap below the conduction band opened and the states of conduction band become the pumping level of nano-laser.The emission energy of nano-laser will be limited in the range of 1.7~2.3 eV generally due to the position of the localized states in gap,which is good in agreement between the experiments and the theory.展开更多
Dynamics of photoluminescence(PL) and electroluminescence(EL) on nanosilicon deposited by Yb is investigated.The sharper PL peaks near 700 nm are observed on silicon quantum dots (Si QDs) coated by Yb.The enhanced EL ...Dynamics of photoluminescence(PL) and electroluminescence(EL) on nanosilicon deposited by Yb is investigated.The sharper PL peaks near 700 nm are observed on silicon quantum dots (Si QDs) coated by Yb.The enhanced EL peaks in the wavelength region from 1 200 nm to 1 600 nm are measured on silicon film deposited by Yb.It is discovered that the EL intensity enhances and the peaks number increases with increasing number of Si-Yb layers.The emission wavelength could be manipulated into the window of optical communication by SiYb bonding on nanosilicon.Si-Yb quantum cascade and PIN hybrid light-emitting diode is designed to apply in optical communicating,which is suitable to be integrated on silicon chip.展开更多
Both the photosynthetic light curves and CO2 curves of Juglans regia L. and Ziziphus jujuba Mill. var. spinosa in three seasons were measured using a LI-6400 portable photosynthesis system. The maximal net photosynthe...Both the photosynthetic light curves and CO2 curves of Juglans regia L. and Ziziphus jujuba Mill. var. spinosa in three seasons were measured using a LI-6400 portable photosynthesis system. The maximal net photosynthetic rate （Amax）, apparent quantum efficiency（φ）, maximal carboxylation rate （Vcmax） and water use efficiency （WUE） of the two species were calculated based on the curves. The results showed that Amax of J. regia reached its maximum at the late-season, while the highest values of Amax of Z. jujuba occurred at the mid-season. The Amax of J. regia was more affected by relative humidity （RH） of the atmosphere, while that of Z. jujuba was more affected by the air temperature. Light saturation point （LSP） and Light compensation point （LCP） of J. regia had a higher correlation with RH of the atmosphere, those of Z. jujuba, however, had a higher correlation with air temperature. Vcmax of both J. regia and Z. jujuba had negative correlation with RH of the atmosphere. WUE of J. regia would decrease with the rise of the air temperature while that of Z. jujuba increased. Thus it could be seen that RH, temperature and soil moisture had main effect on photosynthesis and WUE of J. regia and Z. jujuba. Incorporating data on the physiological differences among tree species into forest carbon models will greatly improve our ability to predict alterations to the forest carbon budgets under various environmental scenarios such as global climate change, or with differing species composition.展开更多
This paper addresses a box transport problem that requires the cooperation of multiple mobile robots. A geometric-based distributed formation control strategy is proposed for robots to push the box to the target, whic...This paper addresses a box transport problem that requires the cooperation of multiple mobile robots. A geometric-based distributed formation control strategy is proposed for robots to push the box to the target, which might be static or dynamic. Velocity and hardware constraints are considered in the advanced planning of the trajectory. Information sharing is included because the robots used as box pushers cannot acquire the required environmental information from their local sensors. Simulation results show the effectiveness of the proposed distributed cooperation strategy.展开更多
基金the Science and Technology Program of Guizhou Province,China(Grant Nos.[2018]5781 and[2020]1Y022)the Open Project of State Key Laboratory of Surface Physics and Department of Physics,Fudan University,Shanghai,China(Grant No.KF201903)the National Natural Science Foundation of China(Grant No.11847084)。
文摘Silicene,silicon analogue to graphene which possesses a two-dimensional(2D)hexagonal lattice,has attracted increasing attention in the last few years due to predicted unique properties.However,silicon naturally possesses a three-dimensional(3D)diamond structure,so there seems to be not any natural solid phase of silicon similar to graphite.Here we report the synthesis of new silicene structure with a unique rectangular lattice by using a coherent electron beam to irradiate amorphous silicon nanofilm produced by pulsed laser deposition(PLD).Under the irradiation of coherent electron beam with proper kinetic energy,the surface layer of silicon nanofilm can be crystallized into silicene.The dynamic stability and the energy band properties of this new silicene structure are investigated by using first-principle calculations and density function theory(DFT)with the help of the observed crystalline structure and lattice constant.The new silicene structure has a real direct bandgap of 0.78 eV.Interestingly,the simulating calculation shows that the convex bond angle is 118°in the new silicene structure with rectangular lattices.The DFT simulations reveal that this new silicene structure has a Dirac-cone-like energy band.The experimental realization of silicene and the theoretically predicted properties shed light on the silicon material with potential applications in new devices.
基金Support from the National Natural Science Foundation of China(Grant No.60966002,11264007)the National Key Laboratory of Surface Physics in Fudan University
文摘The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces,for example,a Si-O-Si bridge bond on curved surface provides the localized levels in band gap and its bonding energy is shallower than that on facet.The red-shifting of PL spectra on smaller silicon quantum dots can be explained by curved surface effect.Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided in curved surface effect.
基金Support from the National Natural Science Foundation of China(Grant No.10764002,60966002,11264007)the National Key Laboratory of Surface Physics in Fudan University
文摘A new conception of nano-laser is proposed in which depending on the size of nano-clusters(silicon quantum dots(QD)),the pumping level of laser can be tuned by the quantum confinement(QC)effect,and the population inversion can be formed between the valence band and the localized states produced from the surface bonds.The nano-laser belongs to the emission of typeⅡ.The peaks of stimulated emission are observed at 605 nm and 693 nm.Through the micro-cavity of nano-laser,a full width at half maximum of the peak at 693 nm can reach to 0.5 nm.The theoretical model and the experimental results indicate that it is a necessary condition for setting up nano-laser that the smaller size of nano-clusters(d<3 nm)can make the localized states into band gap below the conduction band opened and the states of conduction band become the pumping level of nano-laser.The emission energy of nano-laser will be limited in the range of 1.7~2.3 eV generally due to the position of the localized states in gap,which is good in agreement between the experiments and the theory.
基金National Natural Science Foundation of China(Grant No.11264007)
文摘Dynamics of photoluminescence(PL) and electroluminescence(EL) on nanosilicon deposited by Yb is investigated.The sharper PL peaks near 700 nm are observed on silicon quantum dots (Si QDs) coated by Yb.The enhanced EL peaks in the wavelength region from 1 200 nm to 1 600 nm are measured on silicon film deposited by Yb.It is discovered that the EL intensity enhances and the peaks number increases with increasing number of Si-Yb layers.The emission wavelength could be manipulated into the window of optical communication by SiYb bonding on nanosilicon.Si-Yb quantum cascade and PIN hybrid light-emitting diode is designed to apply in optical communicating,which is suitable to be integrated on silicon chip.
基金the State Key Basic Research and Development Plan of China(2002CB111504)the Project of Turning Cropland to Forest of State Forestry Administration and the Distinguished Young Scientist Fund of the NationalNatural Science Foundation of China (2002002002).
文摘Both the photosynthetic light curves and CO2 curves of Juglans regia L. and Ziziphus jujuba Mill. var. spinosa in three seasons were measured using a LI-6400 portable photosynthesis system. The maximal net photosynthetic rate （Amax）, apparent quantum efficiency（φ）, maximal carboxylation rate （Vcmax） and water use efficiency （WUE） of the two species were calculated based on the curves. The results showed that Amax of J. regia reached its maximum at the late-season, while the highest values of Amax of Z. jujuba occurred at the mid-season. The Amax of J. regia was more affected by relative humidity （RH） of the atmosphere, while that of Z. jujuba was more affected by the air temperature. Light saturation point （LSP） and Light compensation point （LCP） of J. regia had a higher correlation with RH of the atmosphere, those of Z. jujuba, however, had a higher correlation with air temperature. Vcmax of both J. regia and Z. jujuba had negative correlation with RH of the atmosphere. WUE of J. regia would decrease with the rise of the air temperature while that of Z. jujuba increased. Thus it could be seen that RH, temperature and soil moisture had main effect on photosynthesis and WUE of J. regia and Z. jujuba. Incorporating data on the physiological differences among tree species into forest carbon models will greatly improve our ability to predict alterations to the forest carbon budgets under various environmental scenarios such as global climate change, or with differing species composition.
基金Project supported by the National Natural Science Foundation of China (No. 60675043) the Science and Technology Project of Zhejiang Province of China (No. 2007C21051)
文摘This paper addresses a box transport problem that requires the cooperation of multiple mobile robots. A geometric-based distributed formation control strategy is proposed for robots to push the box to the target, which might be static or dynamic. Velocity and hardware constraints are considered in the advanced planning of the trajectory. Information sharing is included because the robots used as box pushers cannot acquire the required environmental information from their local sensors. Simulation results show the effectiveness of the proposed distributed cooperation strategy.
