Two-dimensional(2D)transition metal dichalcogenides(TMDCs)showed great potentials in 2D nanoelectronic devices due to their abundant and unique properties.The performance stability of the 2D TMDCs devices turns into o...Two-dimensional(2D)transition metal dichalcogenides(TMDCs)showed great potentials in 2D nanoelectronic devices due to their abundant and unique properties.The performance stability of the 2D TMDCs devices turns into one of the keys for their practical applications but has been rarely explored.Here,we investigated stability of MoS_(2)devices in ambient condition and contributed the device performance degradation to the surface oxidation of the contact metals with low work function,which increased the contact barrier and hindered the electron injection.We developed a new approach to recover the performance of the aged devices through the selective doping of contacts with organolithium,which prolonged the lifetime of MoS_(2)devices.Our work not only provides important insights into the stability of 2D TMDCs devices,but also opens up a new avenue for optimizing the performance of 2D MoS_(2)devices.展开更多
Background Ecoenzymatic stoichiometry models(EEST)are often used to evaluate microbial nutrient use efficiency,but the validity of these models under exogenous nitrogen(N)input has never been clarified.Here,we investi...Background Ecoenzymatic stoichiometry models(EEST)are often used to evaluate microbial nutrient use efficiency,but the validity of these models under exogenous nitrogen(N)input has never been clarified.Here,we investigated the effects of long-term N addition(as urea)on microbial N use efficiency(NUE),compared EEST and^(18)O-labeling methods for determining NUE,and evaluated EEST’s theoretical assumption that the ratios of standard ecoenzymatic activities balance resource availability with microbial demand.Results We found that NUE estimated by EEST ranged from 0.94 to 0.98.In contrast,estimates of NUE by the^(18)O-labeling method ranged from 0.07 to 0.30.The large differences in NUE values estimated by the two methods may be because the sum ofβ-N-acetylglucosaminidase and leucine aminopeptidase activities in the EEST model was not limited to microbial N acquisition under exogenous N inputs,resulting in an overestimation of microbial NUE by EEST.In addition,the acquisition of carbon by N-acquiring enzymes also likely interferes with the evaluation of NUE by EEST.Conclusions Our results demonstrate that caution must be exercised when using EEST to evaluate NUE under exogenous N inputs that may skew standard enzyme assays.展开更多
Single-crystal graphene domains grown by chemical vapor deposition （CVD） intrinsically tend to have a six-fold symmetry; however, several factors can influence the growth kinetics, which can in turn lead to the form...Single-crystal graphene domains grown by chemical vapor deposition （CVD） intrinsically tend to have a six-fold symmetry; however, several factors can influence the growth kinetics, which can in turn lead to the formation of graphene with different shapes. Here we report the growth of oriented large-area pentagonal single-crystal graphene domains on Cu foils by CVD. We found that high-index Cu planes contributed selectively to the formation of pentagonal graphene. Our results indicated that lattice steps present on the crystalline surface of the underlying Cu promoted graphene growth in the direction perpendicular to the steps and finally led to the disappearance of one of the edges forming a pentagon. In addition, hydrogen promoted the formation of pentagonal domains. This work provides new insights into the mechanism of graphene growth.展开更多
Optical channel waveguides with depressed cladding configurations have been produced in Nd,Gd∶CaF_(2)laser crystals by using ultrafast laser inscription.Waveguide properties are investigated in terms of guiding behav...Optical channel waveguides with depressed cladding configurations have been produced in Nd,Gd∶CaF_(2)laser crystals by using ultrafast laser inscription.Waveguide properties are investigated in terms of guiding behaviors and localized laserinduced lattice damages.Under an optical pump of 808 nm light,continuous-wave waveguide lasing at 1.06μm is achieved,with a single-mode operation and a minimum lasing threshold of 98.8 m W.Furthermore,the visible emissions of Nd^(3+)with short wavelengths ranging from 415 nm to 550 nm and long wavelengths from 550 nm to 625 nm are observed upon 808 nm laser excitation via the up-converted process.The intensity ratios of two wavelength ranges are proved to be tunable through changing the pumping polarizations.展开更多
Background:Freeze–thaw events are common in boreal and temperate forest ecosystems and are increasingly infuenced by climate warming.Soil microorganisms play an important role in maintaining ecosystem stability,but t...Background:Freeze–thaw events are common in boreal and temperate forest ecosystems and are increasingly infuenced by climate warming.Soil microorganisms play an important role in maintaining ecosystem stability,but their responses to freeze–thaw cycles(FTCs)are poorly understood.We conducted a feld freeze–thaw experiment in a natural Korean pine and broadleaf mixed forest in the Changbai Mountain Nature Reserve,China,to determine the dynamic responses of soil microbial communities to FTCs.Results:Bacteria were more sensitive than fungi to FTCs.Fungal biomass,diversity and community composition were not signifcantly afected by freeze–thaw regardless of the stage.Moderate initial freeze–thaw resulted in increased bacterial biomass,diversity,and copiotrophic taxa abundance.Subsequent FTCs reduced the bacterial biomass and diversity.Compared with the initial FTC,subsequent FTCs exerted an opposite efect on the direction of change in the composition and function of the bacterial community.Soil water content,dissolved organic carbon,ammonium nitrogen,and total dissolved phosphorus were important factors determining bacterial community diversity and composition during FTCs.Moreover,the functional potentials of the microbial community involved in C and N cycling were also afected by FTCs.Conclusions:Diferent stages of FTCs have diferent ecological efects on the soil environment and microbial activities.Soil FTCs changed the soil nutrients and water availability and then mainly infuenced bacterial community composition,diversity,and functional potentials,which may disturb C and N states in this temperate forest soil.This study also improves our understanding of microbial communities regulating their ecological functions in response to climate change.展开更多
Edge effects are predicted to significantly impact the properties of low dimensional materials with layered structures. The synthesis of low dimensional materials with copious edges is desired for exploring the effect...Edge effects are predicted to significantly impact the properties of low dimensional materials with layered structures. The synthesis of low dimensional materials with copious edges is desired for exploring the effects of edges on the band structure and properties of these materials. Here we developed an approach for synthesizing MoS2 nanobelts terminated with vertically aligned edges by sulfurizing hydrothermally synthesized MoO3 nanobelts in the gas phase through a kinetically driven process; we then investigated the electrical and magnetic properties of these metastable materials. These edge-terminated MoS2 nanobelts were found to be metallic and ferromagnetic, and thus dramatically different from the semiconducting and nonmagnetic two-dimensional （2D） and three-dimensional （3D） 2H-MoS2 materials. The transitions in electrical and magnetic properties elucidate the fact that edges can tune the properties of low dimensional materials. The unique structure and properties of this one-dimensional （1D） MoS2 material will enable its applications in electronics, spintronics, and catalysis.展开更多
Depressed cladding waveguides are fabricated in Pr:LiYF_(4)(YLF)crystal by femtosecond laser inscription following a helical scheme.With the optimized parameters,the propagation loss of the waveguide is around 0.12 dB...Depressed cladding waveguides are fabricated in Pr:LiYF_(4)(YLF)crystal by femtosecond laser inscription following a helical scheme.With the optimized parameters,the propagation loss of the waveguide is around 0.12 dB/cm for multimode guiding.Under optical pumping with InGaN laser diodes at 444 nm,efficient waveguide lasers in the orange around604 nm(π-polarized)are achieved with minimum lasing threshold of 119.8 mW,maximum slope efficiency of 16.6%,and maximum output power of 120.6 mW.Benefiting from their optimized performances,the waveguides produced in this work are promising for applications as compact orange laser sources.展开更多
Chirality-specific growth of single-walled carbon nanotubes(SWNTs) remains a challenge for their practical applications in electronics. Here, we explored the surface growth of SWNTs by utilizing the atomic-precise sil...Chirality-specific growth of single-walled carbon nanotubes(SWNTs) remains a challenge for their practical applications in electronics. Here, we explored the surface growth of SWNTs by utilizing the atomic-precise silver cluster complex [Ag_(15){1,3,5–(C:C)_3–C_6H_3}_2(Py[8])_3–(CF_3SO_3)_3](CF_3SO_3)_6(Py[8] is abbreviation for octamethylazacalix[8]pyridine) as a catalyst precursor. The diameters of most acquired SWNTs distributed in the range of 1.2–1.4 nm, which is suitable for making high performance field-effect transistors. The high quality of the obtained SWNTs was evidenced by Raman spectroscopy and electrical measurements. Successful growth of high quality SWNTs in this study foresees that rational design of metal-organic complexes as growth catalysts can open up a new avenue for the controllable synthesis of SWNTs.展开更多
基金L.J.acknowledges the National Natural Science Foundation of China(No.21925504)Tsinghua Toyota Joint Research Fund.Z.H.C.acknowledges the National Natural Science Foundation of China(Nos.61674045,61911540074)Fundamental Research Funds for the Central Universities and the Research Funds of Renmin University of China(Nos.21XNLG27,22XNH097).
文摘Two-dimensional(2D)transition metal dichalcogenides(TMDCs)showed great potentials in 2D nanoelectronic devices due to their abundant and unique properties.The performance stability of the 2D TMDCs devices turns into one of the keys for their practical applications but has been rarely explored.Here,we investigated stability of MoS_(2)devices in ambient condition and contributed the device performance degradation to the surface oxidation of the contact metals with low work function,which increased the contact barrier and hindered the electron injection.We developed a new approach to recover the performance of the aged devices through the selective doping of contacts with organolithium,which prolonged the lifetime of MoS_(2)devices.Our work not only provides important insights into the stability of 2D TMDCs devices,but also opens up a new avenue for optimizing the performance of 2D MoS_(2)devices.
基金funded by the National Key Research and Development Program of China(2020YFA0608100)the National Natural Science Foundation of China(32001174 and 32101378)+2 种基金the Major Program of Institute of Applied Ecology,Chinese Academy of Sciences(IAEMP202201)Key Research Program of Frontier Sciences,Chinese Academy of Sciences(ZDBS-LY-DQC019)Project funded by China Postdoctoral Science Foundation(2022M710004).
文摘Background Ecoenzymatic stoichiometry models(EEST)are often used to evaluate microbial nutrient use efficiency,but the validity of these models under exogenous nitrogen(N)input has never been clarified.Here,we investigated the effects of long-term N addition(as urea)on microbial N use efficiency(NUE),compared EEST and^(18)O-labeling methods for determining NUE,and evaluated EEST’s theoretical assumption that the ratios of standard ecoenzymatic activities balance resource availability with microbial demand.Results We found that NUE estimated by EEST ranged from 0.94 to 0.98.In contrast,estimates of NUE by the^(18)O-labeling method ranged from 0.07 to 0.30.The large differences in NUE values estimated by the two methods may be because the sum ofβ-N-acetylglucosaminidase and leucine aminopeptidase activities in the EEST model was not limited to microbial N acquisition under exogenous N inputs,resulting in an overestimation of microbial NUE by EEST.In addition,the acquisition of carbon by N-acquiring enzymes also likely interferes with the evaluation of NUE by EEST.Conclusions Our results demonstrate that caution must be exercised when using EEST to evaluate NUE under exogenous N inputs that may skew standard enzyme assays.
基金This work was supported by the National Natural Science Foundation of China （Nos. 51422204 and 51372132） and the National Basic Research Program of China （No. 2013CB228506）.
文摘Single-crystal graphene domains grown by chemical vapor deposition （CVD） intrinsically tend to have a six-fold symmetry; however, several factors can influence the growth kinetics, which can in turn lead to the formation of graphene with different shapes. Here we report the growth of oriented large-area pentagonal single-crystal graphene domains on Cu foils by CVD. We found that high-index Cu planes contributed selectively to the formation of pentagonal graphene. Our results indicated that lattice steps present on the crystalline surface of the underlying Cu promoted graphene growth in the direction perpendicular to the steps and finally led to the disappearance of one of the edges forming a pentagon. In addition, hydrogen promoted the formation of pentagonal domains. This work provides new insights into the mechanism of graphene growth.
基金supported by the National Key Research and Development Project of China(No.2019YFA0705000)the National Natural Science Foundation of China(NSFC)(Nos.11874243,11525418,91750201,and 11974218)+1 种基金the Innovation Group of Jinan(No.2018GXRC010)the Local Science and Technology Development Project of the Central Government(No.YDZX20203700001766)。
文摘Optical channel waveguides with depressed cladding configurations have been produced in Nd,Gd∶CaF_(2)laser crystals by using ultrafast laser inscription.Waveguide properties are investigated in terms of guiding behaviors and localized laserinduced lattice damages.Under an optical pump of 808 nm light,continuous-wave waveguide lasing at 1.06μm is achieved,with a single-mode operation and a minimum lasing threshold of 98.8 m W.Furthermore,the visible emissions of Nd^(3+)with short wavelengths ranging from 415 nm to 550 nm and long wavelengths from 550 nm to 625 nm are observed upon 808 nm laser excitation via the up-converted process.The intensity ratios of two wavelength ranges are proved to be tunable through changing the pumping polarizations.
基金The National Natural Science Foundation of China(31770531,32001174)the Key Research Program of Frontier Sciences,CAS(QYZDB-SSW-DQC006)+1 种基金the Key Laboratory of Geographical Processes and Ecological Security of Changbai Mountains,Ministry of Education(GPES201902)the Youth Innovation Promotion Association CAS to Chao Wang(2018231).
文摘Background:Freeze–thaw events are common in boreal and temperate forest ecosystems and are increasingly infuenced by climate warming.Soil microorganisms play an important role in maintaining ecosystem stability,but their responses to freeze–thaw cycles(FTCs)are poorly understood.We conducted a feld freeze–thaw experiment in a natural Korean pine and broadleaf mixed forest in the Changbai Mountain Nature Reserve,China,to determine the dynamic responses of soil microbial communities to FTCs.Results:Bacteria were more sensitive than fungi to FTCs.Fungal biomass,diversity and community composition were not signifcantly afected by freeze–thaw regardless of the stage.Moderate initial freeze–thaw resulted in increased bacterial biomass,diversity,and copiotrophic taxa abundance.Subsequent FTCs reduced the bacterial biomass and diversity.Compared with the initial FTC,subsequent FTCs exerted an opposite efect on the direction of change in the composition and function of the bacterial community.Soil water content,dissolved organic carbon,ammonium nitrogen,and total dissolved phosphorus were important factors determining bacterial community diversity and composition during FTCs.Moreover,the functional potentials of the microbial community involved in C and N cycling were also afected by FTCs.Conclusions:Diferent stages of FTCs have diferent ecological efects on the soil environment and microbial activities.Soil FTCs changed the soil nutrients and water availability and then mainly infuenced bacterial community composition,diversity,and functional potentials,which may disturb C and N states in this temperate forest soil.This study also improves our understanding of microbial communities regulating their ecological functions in response to climate change.
文摘Edge effects are predicted to significantly impact the properties of low dimensional materials with layered structures. The synthesis of low dimensional materials with copious edges is desired for exploring the effects of edges on the band structure and properties of these materials. Here we developed an approach for synthesizing MoS2 nanobelts terminated with vertically aligned edges by sulfurizing hydrothermally synthesized MoO3 nanobelts in the gas phase through a kinetically driven process; we then investigated the electrical and magnetic properties of these metastable materials. These edge-terminated MoS2 nanobelts were found to be metallic and ferromagnetic, and thus dramatically different from the semiconducting and nonmagnetic two-dimensional （2D） and three-dimensional （3D） 2H-MoS2 materials. The transitions in electrical and magnetic properties elucidate the fact that edges can tune the properties of low dimensional materials. The unique structure and properties of this one-dimensional （1D） MoS2 material will enable its applications in electronics, spintronics, and catalysis.
基金supported by the National Key Research and Development Program of China(No.2019YFA0705000)National Natural Science Foundation of China(NSFC)(Nos.11874243,12192254,91750201,and 11974218)+1 种基金Innovation Group of Jinan(No.2018GXRC010)Local Science and Technology Development Project of the Central Government(No.YDZX20203700001766)。
文摘Depressed cladding waveguides are fabricated in Pr:LiYF_(4)(YLF)crystal by femtosecond laser inscription following a helical scheme.With the optimized parameters,the propagation loss of the waveguide is around 0.12 dB/cm for multimode guiding.Under optical pumping with InGaN laser diodes at 444 nm,efficient waveguide lasers in the orange around604 nm(π-polarized)are achieved with minimum lasing threshold of 119.8 mW,maximum slope efficiency of 16.6%,and maximum output power of 120.6 mW.Benefiting from their optimized performances,the waveguides produced in this work are promising for applications as compact orange laser sources.
基金the National Natural Science Foundation of China (21322303, 51372134 and 21573125)the financial support from the National Natural Science Foundation of China (21132005, 21421064 and 21522206)+1 种基金the National Program for Thousand Young Talents of Chinathe National Basic Research Program of China (2013CB834501)
文摘Chirality-specific growth of single-walled carbon nanotubes(SWNTs) remains a challenge for their practical applications in electronics. Here, we explored the surface growth of SWNTs by utilizing the atomic-precise silver cluster complex [Ag_(15){1,3,5–(C:C)_3–C_6H_3}_2(Py[8])_3–(CF_3SO_3)_3](CF_3SO_3)_6(Py[8] is abbreviation for octamethylazacalix[8]pyridine) as a catalyst precursor. The diameters of most acquired SWNTs distributed in the range of 1.2–1.4 nm, which is suitable for making high performance field-effect transistors. The high quality of the obtained SWNTs was evidenced by Raman spectroscopy and electrical measurements. Successful growth of high quality SWNTs in this study foresees that rational design of metal-organic complexes as growth catalysts can open up a new avenue for the controllable synthesis of SWNTs.
