Electrocatalytic N_(2) reduction reaction(NRR)represents an appealing solution for sustainable ammonia production,whereas exploring high-efficiency NRR catalysts is highly desired but extremely challenging.Herein,we c...Electrocatalytic N_(2) reduction reaction(NRR)represents an appealing solution for sustainable ammonia production,whereas exploring high-efficiency NRR catalysts is highly desired but extremely challenging.Herein,we combine Ti_(3) C_(2)T_(x)-MXene quantum dots(MQDs)with porous Cu nanosheets to design a novel heterostructured MQDs/Cu as an effective and durable NRR catalyst.Impressively,MQDs/Cu showed a synergistically enhanced NRR activity with an NH_(3) yield of 78.5 lg h^(-1) mg^(-1)(-0.5 V)and a Faradaic efficiency of 21.3%(-0.4 V),far superior to pure MQDs and Cu,and outperforming the majority of the state-of-the-art NRR catalysts.Density function theory computations demonstrated that the synergy of MQDs and Cu enabled the creation of interfacial Cu-Ti dimer as dual-active-centers to strongly activate the absorbed N 2 and promote the*N_(2)H formation,consequently resulting in the much reduced energy barriers and greatly enhanced NRR performance.展开更多
Solar-driven photocatalytic CO_(2) reduction to produce valuable chemicals and fuels offers an attractive strategy in alleviating the energy crisis.Pt quantum dots(PtQDs)with TiO_(2) nanowire(TiO_(2)NW)/Ti_(3)C_(2) MX...Solar-driven photocatalytic CO_(2) reduction to produce valuable chemicals and fuels offers an attractive strategy in alleviating the energy crisis.Pt quantum dots(PtQDs)with TiO_(2) nanowire(TiO_(2)NW)/Ti_(3)C_(2) MXene heterostructures(Pt-TiO_(2)NW/Ti_(3)C_(2)) with tight interfacial contacts between the various components were prepared at room temperature via oxidation reactions.The incorporated PtQDs played crucial roles as electron conduction bridges supported by the cocatalyst effect,effectively enhancing the separation efficiencies of photoinduced electron/hole pairs and improving CO_(2) reduction under simulated solar light irradiation.The Pt-TiO_(2)NW/Ti_(3)C_(2) heterostructures exhibited remarkable carbon monoxide(CO)and methane(CH_(4)) production at respective rates of 38.14 and 36.15μmol g^(-1)after 10 h of simulated solar light irradiation,an apparent quantum yield of 1.68%,and 79.2%selectivity for CH4.The photocatalytic activities of the Pt-TiO_(2) NW/Ti_(3)C_(2) heterostructures for CO_(2) reduction were significantly enhanced compared to those of TiO_(2)NW/Ti_(3)C_(2) and the single-component photocatalysts,and they exhibited remarkable stabilities even after five cycles.In addition,the densities of states and electronic characteristics of Ti_(3)C_(2) MXene and Pt-TiO_(2)NW/Ti_(3)C_(2) were studied using density functional theory,and a synergistic mechanism of the improvement in CO_(2) photoreduction is proposed.展开更多
Systematic investigation of InAs quantum dot(QD) growth using molecular beam epitaxy has been carried out, focusing mainly on the InAs growth rate and its effects on the quality of the InAs/GaAs quantum dots.By optimi...Systematic investigation of InAs quantum dot(QD) growth using molecular beam epitaxy has been carried out, focusing mainly on the InAs growth rate and its effects on the quality of the InAs/GaAs quantum dots.By optimizing the growth rate, high quality InAs/GaAs quantum dots have been achieved.The areal quantum dot density is 5.9× 1010 cm-2, almost double the conventional density(3.0 × 1010 cm-2).Meanwhile, the linewidth is reduced to 29 meV at room temperature without changing the areal dot density.These improved QDs are of great significance for fabricating high performance quantum dot lasers on various substrates.展开更多
According to geographic possibilism,environment does not determine socio-economic development.However,the environment sets certain constraints and limitations for development.How do natural settings influence populati...According to geographic possibilism,environment does not determine socio-economic development.However,the environment sets certain constraints and limitations for development.How do natural settings influence population dynamics?In this study,we examine this question using the example of?ibenik-Knin County,which includes Krka National Park(NP)with a GIS-based statistical approach.The following parameters represent natural factors:elevation,slope,distance from water,and proportion of karst areas.In addition,distance from Krka NP was also added as an independent seminatural factor(despite the fact that it is a social construction).The dependent social parameters are population density for selected historical dates,population change,year of maximum population,natural increase,migration,and age index.The analysis units are the 199 settlements found in the county,and the 20 local administrative units(LAU2).The study period can be divided into five phases:from the first census in 1857 to 1921,there was a slow increase in most settlements;then a relatively constant phase up to 1961(some settlements began shrinking in this period);a slow decrease until 1991;arapid decrease during the next decade;and relative stabilisation to present day.These processes were also accompanied by significant inner and outer migrations.As for the relationships between natural and demographic factors,we found that although the coastal-inland area dichotomy is dominant in the study area,elevation has the highest correlation with most population parameters.However,distance from water is also significantly correlated with population change and migration in certain periods.In the inland areas,there are statistically significant differences between the demographic processes of fully-karstic and partially-karstic areas,while in the coastal zone,the karst effect is overshadowed by other social processes.The impact of Krka NP on the demographic characteristics of the surrounding settlements was statistically not detectable.Our final conclusion is that correlations between natural and population parameters are low or moderately strong but statistically significant in many cases,thus the basic principles of geographic possibilism are valid for the area.展开更多
Electrocatalytic N_(2) fixation through N_(2) reduction reaction(NRR)has been regarded as a promising route for sustainable NH_(3) synthesis,while exploring high-performing NRR catalysts is pivotal yet challenging.Her...Electrocatalytic N_(2) fixation through N_(2) reduction reaction(NRR)has been regarded as a promising route for sustainable NH_(3) synthesis,while exploring high-performing NRR catalysts is pivotal yet challenging.Herein,BN quantum dots/Ti_(3)C_(2)T_(x)-MXene(BNQDs/Ti_(3)C_(2)T_(x))heterostructure is demonstrated as an efficient and durable NRR catalyst,exhibiting a high NH_(3) yield of 52.8±3.3μg h^(-1) mg^(-1) with an FE of 19.1±1.6%at0.4 V(vs.RHE),which stand at the high level among all reported BN-and MXene-based NRR catalysts.Theoretical computations reveal that the electronic interactions between BNQDs and Ti_(3)C_(2)T_(x) enrich the electron density of B atoms at the heterointerface and endow them with enhanced electron-donating capability for N_(2) activation and protonation.Meanwhile,the decorated BNQDs can block the active sites of Ti_(3)C_(2)T_(x) for hydrogen evolution,rendering a high N_(2)-to-NH_(3) selectivity.展开更多
This paper investigates theoretically the electronic structure and transport of a two-level quantum dot irradiated under a strong laser field at low temperatures. Using the method of Keldysh equation of motion for non...This paper investigates theoretically the electronic structure and transport of a two-level quantum dot irradiated under a strong laser field at low temperatures. Using the method of Keldysh equation of motion for nonequilibrium Green functions, it examines the time-averaged density of states and conductance for the system with photon polarization parallel with and perpendicular to the tunnelling current direction respectively. It is demonstrated that, by analysing some numerical examples, more photon sidebands resonance states and multi-and single-photon transitions are found when diagonal matrix elements dominate the interaction, while the electronic transitions due to multiphoton absorption are more or less suppressed when off-diagonal interaction dominates.展开更多
Using an equation-of-motion technique, we theoretically study the Fano-Kondo effect in the T-shaped double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. We calculate the density of state...Using an equation-of-motion technique, we theoretically study the Fano-Kondo effect in the T-shaped double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. We calculate the density of states in this system with both parallel and antiparaIlel lead-polarization alignments, and our results reveal that the interdot coupling, the spin-polarized strength and the energy level of the side coupled quantum dot greatly influence the density of states of the central quantum dot. This system is a possible candidate for spin valve transistors and may have potential applications in the spintronics.展开更多
基金This work is supported by the National Natural Science Foundation of China(51761024,52161025)Natural Sci-ence Foundation of Gansu Province(20JR10RA241,21JR1RA247)+1 种基金Longyuan Youth Innovative and Entrepreneurial Talents Project([2021]17)the Foundation of A Hundred Youth Talents Training Program of Lanzhou Jiaotong University.
文摘Electrocatalytic N_(2) reduction reaction(NRR)represents an appealing solution for sustainable ammonia production,whereas exploring high-efficiency NRR catalysts is highly desired but extremely challenging.Herein,we combine Ti_(3) C_(2)T_(x)-MXene quantum dots(MQDs)with porous Cu nanosheets to design a novel heterostructured MQDs/Cu as an effective and durable NRR catalyst.Impressively,MQDs/Cu showed a synergistically enhanced NRR activity with an NH_(3) yield of 78.5 lg h^(-1) mg^(-1)(-0.5 V)and a Faradaic efficiency of 21.3%(-0.4 V),far superior to pure MQDs and Cu,and outperforming the majority of the state-of-the-art NRR catalysts.Density function theory computations demonstrated that the synergy of MQDs and Cu enabled the creation of interfacial Cu-Ti dimer as dual-active-centers to strongly activate the absorbed N 2 and promote the*N_(2)H formation,consequently resulting in the much reduced energy barriers and greatly enhanced NRR performance.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the South Korean Ministries of Education(NRF-2021R1I1A3059469,NRF2018R1A6A1A03024962)Science and ICT(NRF-2020R1A2C2100746)。
文摘Solar-driven photocatalytic CO_(2) reduction to produce valuable chemicals and fuels offers an attractive strategy in alleviating the energy crisis.Pt quantum dots(PtQDs)with TiO_(2) nanowire(TiO_(2)NW)/Ti_(3)C_(2) MXene heterostructures(Pt-TiO_(2)NW/Ti_(3)C_(2)) with tight interfacial contacts between the various components were prepared at room temperature via oxidation reactions.The incorporated PtQDs played crucial roles as electron conduction bridges supported by the cocatalyst effect,effectively enhancing the separation efficiencies of photoinduced electron/hole pairs and improving CO_(2) reduction under simulated solar light irradiation.The Pt-TiO_(2)NW/Ti_(3)C_(2) heterostructures exhibited remarkable carbon monoxide(CO)and methane(CH_(4)) production at respective rates of 38.14 and 36.15μmol g^(-1)after 10 h of simulated solar light irradiation,an apparent quantum yield of 1.68%,and 79.2%selectivity for CH4.The photocatalytic activities of the Pt-TiO_(2) NW/Ti_(3)C_(2) heterostructures for CO_(2) reduction were significantly enhanced compared to those of TiO_(2)NW/Ti_(3)C_(2) and the single-component photocatalysts,and they exhibited remarkable stabilities even after five cycles.In addition,the densities of states and electronic characteristics of Ti_(3)C_(2) MXene and Pt-TiO_(2)NW/Ti_(3)C_(2) were studied using density functional theory,and a synergistic mechanism of the improvement in CO_(2) photoreduction is proposed.
基金Project supported by the National Key Technology Research and Development Program of China(Grant No.2018YFA0306101)the National Natural Science Foundation of China(Grant No.61505196)+1 种基金the Scientific Instrument Developing Project of the Chinese Academy of Sciences(Grant No.YJKYYQ20170032)the Guangdong Science and Technology Project,China(Grant No.20180329)
文摘Systematic investigation of InAs quantum dot(QD) growth using molecular beam epitaxy has been carried out, focusing mainly on the InAs growth rate and its effects on the quality of the InAs/GaAs quantum dots.By optimizing the growth rate, high quality InAs/GaAs quantum dots have been achieved.The areal quantum dot density is 5.9× 1010 cm-2, almost double the conventional density(3.0 × 1010 cm-2).Meanwhile, the linewidth is reduced to 29 meV at room temperature without changing the areal dot density.These improved QDs are of great significance for fabricating high performance quantum dot lasers on various substrates.
基金supported by the National Research,Development and Innovation Office Hungary(NKFIH)K124497 Project。
文摘According to geographic possibilism,environment does not determine socio-economic development.However,the environment sets certain constraints and limitations for development.How do natural settings influence population dynamics?In this study,we examine this question using the example of?ibenik-Knin County,which includes Krka National Park(NP)with a GIS-based statistical approach.The following parameters represent natural factors:elevation,slope,distance from water,and proportion of karst areas.In addition,distance from Krka NP was also added as an independent seminatural factor(despite the fact that it is a social construction).The dependent social parameters are population density for selected historical dates,population change,year of maximum population,natural increase,migration,and age index.The analysis units are the 199 settlements found in the county,and the 20 local administrative units(LAU2).The study period can be divided into five phases:from the first census in 1857 to 1921,there was a slow increase in most settlements;then a relatively constant phase up to 1961(some settlements began shrinking in this period);a slow decrease until 1991;arapid decrease during the next decade;and relative stabilisation to present day.These processes were also accompanied by significant inner and outer migrations.As for the relationships between natural and demographic factors,we found that although the coastal-inland area dichotomy is dominant in the study area,elevation has the highest correlation with most population parameters.However,distance from water is also significantly correlated with population change and migration in certain periods.In the inland areas,there are statistically significant differences between the demographic processes of fully-karstic and partially-karstic areas,while in the coastal zone,the karst effect is overshadowed by other social processes.The impact of Krka NP on the demographic characteristics of the surrounding settlements was statistically not detectable.Our final conclusion is that correlations between natural and population parameters are low or moderately strong but statistically significant in many cases,thus the basic principles of geographic possibilism are valid for the area.
基金supported by the National Natural Science Foundation of China(51761024)Natural Science Foundation of Gansu Province(20JR10RA241)+2 种基金Longyuan Youth Innovative and Entrepreneurial Talents Project([2021]17)Central Government Guides Local Science and Technology Development Project(206Z1003G)Key Project of Education Department of Hebei Province(ZD2020339).
文摘Electrocatalytic N_(2) fixation through N_(2) reduction reaction(NRR)has been regarded as a promising route for sustainable NH_(3) synthesis,while exploring high-performing NRR catalysts is pivotal yet challenging.Herein,BN quantum dots/Ti_(3)C_(2)T_(x)-MXene(BNQDs/Ti_(3)C_(2)T_(x))heterostructure is demonstrated as an efficient and durable NRR catalyst,exhibiting a high NH_(3) yield of 52.8±3.3μg h^(-1) mg^(-1) with an FE of 19.1±1.6%at0.4 V(vs.RHE),which stand at the high level among all reported BN-and MXene-based NRR catalysts.Theoretical computations reveal that the electronic interactions between BNQDs and Ti_(3)C_(2)T_(x) enrich the electron density of B atoms at the heterointerface and endow them with enhanced electron-donating capability for N_(2) activation and protonation.Meanwhile,the decorated BNQDs can block the active sites of Ti_(3)C_(2)T_(x) for hydrogen evolution,rendering a high N_(2)-to-NH_(3) selectivity.
基金Project supported by the National Natural Science Foundation of China （Grant No 10574042） and the Guizhou Provincial Science and Technology Foundation of China （Grant No 20052088）.
文摘This paper investigates theoretically the electronic structure and transport of a two-level quantum dot irradiated under a strong laser field at low temperatures. Using the method of Keldysh equation of motion for nonequilibrium Green functions, it examines the time-averaged density of states and conductance for the system with photon polarization parallel with and perpendicular to the tunnelling current direction respectively. It is demonstrated that, by analysing some numerical examples, more photon sidebands resonance states and multi-and single-photon transitions are found when diagonal matrix elements dominate the interaction, while the electronic transitions due to multiphoton absorption are more or less suppressed when off-diagonal interaction dominates.
基金supported by the Scientific Research Funds of Education Department of Sichuan Province (Grant No 2006A069)the Major Basic Research Project of Sichuan Province (Grant No 2006J13-155)the Scientific Research Innovation for Postgraduates of Sichuan Normal University
文摘Using an equation-of-motion technique, we theoretically study the Fano-Kondo effect in the T-shaped double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. We calculate the density of states in this system with both parallel and antiparaIlel lead-polarization alignments, and our results reveal that the interdot coupling, the spin-polarized strength and the energy level of the side coupled quantum dot greatly influence the density of states of the central quantum dot. This system is a possible candidate for spin valve transistors and may have potential applications in the spintronics.
