Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subje...Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subjected to atomic-level structural engineering by doping with transition metals(M=Fe,Co,or Ni),which simultaneously induced the formation of metal-N active sites in the g-C_(3)N_(4)framework and modulated the bandgap of g-C_(3)N_(4).Experiments and density functional theory calculations further verified that the as-formed metal-N bonds in M-doped g-C_(3)N_(4)acted as an"electron transfer bridge",where the migration of photo-generated electrons along the bridge enhanced the efficiency of separation of the photogenerated charges,and the optimized bandgap of g-C_(3)N_(4)afforded stronger reduction ability and wider light absorption.As a result,doping with either Fe,Co,or Ni had a positive effect on the HER activity,where Co-doped g-C_(3)N_(4)exhibited the highest performance.The findings illustrate that this atomic-level structural engineering could efficiently improve the HER activity and inspire the design of powerful photocatalysts.展开更多
Mn_(3)TeO_(6)(MTO) has been experimentally found to adopt a P2_(1)/In structure under high pressure,which exhibits a significantly smaller band gap compared to the atmospheric R3 phase.In this study,we systematically ...Mn_(3)TeO_(6)(MTO) has been experimentally found to adopt a P2_(1)/In structure under high pressure,which exhibits a significantly smaller band gap compared to the atmospheric R3 phase.In this study,we systematically investigate the magnetism,structural phase transition,and electronic properties of MTO under high pressure through first-principles calculations.Both R3 and P2_(1)/n phases of MTO are antiferromagnetic at zero temperature.The R3 phase transforms to the P2_(1)/n phase at 7.5 8 GPa,accompanied by a considerable volume collapse of about 6.47%.Employing the accurate method that combines DFT+U/and GW,the calculated band gap of R3 phase at zero pressure is very close to the experimental values,while that of the P2_(1)/n phase is significantly overestimated.The main reason for this difference is that the experimental study incorrectly used the Kubelka-Munk plot for the indirect band gap to obtain the band gap of the P2_(1)/n phase instead of the Kubelka-Munk plot for the direct band gap.Furthermore,our study reveals that the transition from the R3 phase to the P2_(1)/n phase is accompanied by a slight reduction in the band gap.展开更多
Strain is a powerful tool to modify the optical properties of semiconducting transition metal dichalcogenides like MoS_(2),MoSe_(2),WS_(2) and WSe_(2).In this work we provide a thorough description of the technical de...Strain is a powerful tool to modify the optical properties of semiconducting transition metal dichalcogenides like MoS_(2),MoSe_(2),WS_(2) and WSe_(2).In this work we provide a thorough description of the technical details to perform uniaxial strain measurements on these two-dimensional semiconductors and we provide a straightforward calibration method to determine the amount of applied strain with high accuracy.We then employ reflectance spectroscopy to analyze the strain tunability of the electronic properties of single-,bi-and tri-layer MoS_(2),MoSe_(2),WS_(2) and WSe_(2).Finally,we quantify the flake-to-flake variability by analyzing 15 different single-layer MoS_(2) flakes.展开更多
From the recent experimentally observed conduction band offset and previously reported band gaps,one may deduce that the valence band offset between rutile SnO2 and TiO2 is around 1 eV,with TiO2 having a higher valenc...From the recent experimentally observed conduction band offset and previously reported band gaps,one may deduce that the valence band offset between rutile SnO2 and TiO2 is around 1 eV,with TiO2 having a higher valence band maximum.This implication sharply contradicts the fact that the two compounds have the same rutile structure and the Γ3^+ VBM state is mostly an oxygen p state with a small amount of cation d character,thus one would expect that SnO2 and TiO2 should have small valence band offset.If the valence band offset between SnO2 and TiO2 is indeed small,one may question the correctness of the previously reported band gaps of SnO2 and TiO2.In this paper,using first-principles calculations with different levels of computational methods and functionals within the density functional theory,we reinvestigate the long-standing band gap problem for SnO2.Our analysis suggests that the fundamental band gap of SnO2 should be similar to that of TiO2,i.e.,around 3.0 eV.This value is significantly smaller than the previously reported value of about 3.6 eV,which can be attributed as the optical band gap of this material.Similar to what has been found in In2O3,the discrepancy between the fundamental and optical gaps of SnO2 can be ascribed to the inversion symmetry of its crystal structure and the resultant dipole-forbidden transitions between its band edges.Our results are consistent with most of the optical and electrical measurements of the band gaps and band offset between SnO2 and TiO2,thus provide new understanding of the band structure and optical properties of SnO2.Experimental tests of our predictions are called for.展开更多
Two-dimensional transition metal dichalcogenides(TMDs)have intriguing physic properties and offer an exciting platform to explore many features that are important for future devices.In this work,we synthesized monolay...Two-dimensional transition metal dichalcogenides(TMDs)have intriguing physic properties and offer an exciting platform to explore many features that are important for future devices.In this work,we synthesized monolayer WS_(2)as an example to study the optical response with hydrostatic pressure.The Raman results show a continuous tuning of the lattice vibrations that is induced by hydrostatic pressure.We further demonstrate an efficient pressure-induced change of the band structure and carrier dynamics via transient absorption measurements.We found that two time constants can be attributed to the capture process of two kinds of defect states,with the pressure increasing from 0.55 GPa to 2.91 GPa,both of capture processes were accelerated,and there is an inflection point within the pressure range of 1.56 GPa to 1.89 GPa.Our findings provide valuable information for the design of future optoelectronic devices.展开更多
High-voltage LiCoO_(2)(LCO)offers a prelude to breaking the bottleneck of the energy density of lithium-ion batteries,however,LiCoO_(2)is subject to serious structural and interfacial degradation above voltages>4.5...High-voltage LiCoO_(2)(LCO)offers a prelude to breaking the bottleneck of the energy density of lithium-ion batteries,however,LiCoO_(2)is subject to serious structural and interfacial degradation above voltages>4.55 V(vs.Li/Li^(+)).Herein,an in-situ Li_(6.25)La_(3)Zr_(2)A_(l0.25)O_(12)(LLZAO)layer is constructed on the LCO surface to achieve operating voltage at 4.6 V.The detailed characterizations(ex-situ XRD,ex-situ Raman,DFT,etc.)reveal that the LLZAO layer greatly enhances Li+conductivity attributed to the ionconducting layer on the surface/interface,and closely combines with LiCoO_(2)particle to ensure stable cathode/electrolyte interface,thus suppressing the highly reactive Co^(4+)and O^(-)triggered surface side reactions at high-voltage.Moreover,the introduction of La^(3+)/Zr^(4+)/Al^(3+)with a larger ionic radius(La^(3+)/Zr^(4+)are larger than Co^(3+))and weaker electronegativity(La/Zr/Al are weaker than Co)into Co^(3+)sites readjusts the electron cloud density between Co–O–Li,which reinforces the Co–O bond and widens the band-center gap of Co 3d and O 2p,thus restraining the detrimental phase transition(from H3 to H1-3 phase)and the formation of Co_(3)O_(4)spinel phase(attributed to lattice oxygen release),subsequently alleviating the particle cracking and structural collapse during repeated Li^(+)de/intercalation.Therefore,after 100 cycles at 3.0–4.6 V,LCO@1.0LLZAO exhibits a superior discharge capacity of 188.5 m A h g^(-1),with a capacity retention of 85.1%.The above research has brought about meaningful guidance for the evolution of cathode materials with high voltage.展开更多
The electronic density of states and band structures of doped and un-doped anatase TiO2 were studied by the Linearized Augmented Plane Wave method based on the density functional theory. The calculation shows that the...The electronic density of states and band structures of doped and un-doped anatase TiO2 were studied by the Linearized Augmented Plane Wave method based on the density functional theory. The calculation shows that the band structures of TiO2 crystals doped with transition metal atoms become narrower. Interesting, an excursion towards high energy level with increasing atomic number in the same element period could be observed after doping with transition metal atoms.展开更多
Time-resolved photoluminescence (TRPL) was applied to investigate the transient process in GaP1-xNx (x = 0.12%) alloy. The filling, transferring and decay processes among nitrogen pairs are directly observed. The ...Time-resolved photoluminescence (TRPL) was applied to investigate the transient process in GaP1-xNx (x = 0.12%) alloy. The filling, transferring and decay processes among nitrogen pairs are directly observed. The NN4 pair, either not present or only a small obscure peak under a proper excitation condition in the steady-state photoluminescence spectrum, is well resolved by TRPL.展开更多
By direct numerical simulations of the plane Couette flow (PCF) in a large computational domain, it is shown that an isolated turbulent band decays monotonically at low Reynolds numbers but experiences transient growt...By direct numerical simulations of the plane Couette flow (PCF) in a large computational domain, it is shown that an isolated turbulent band decays monotonically at low Reynolds numbers but experiences transient growth before the eventual relaminarization at moderate Reynolds numbers. The lower bound Reynolds number of the transient-growth regime is determined as 286. The width, length, and tilt angle of the iso- lated band structure are defined based on the disturbance kinetic energy in the mid-plane, and the geometric characteristics of the band can be described with a tilted rectangle. It is illustrated that before its eventual fragmentation, the isolated turbulent band decays in a style of longitudinal contraction, where the center, width, and tilt angle of the band keep almost constant but the band length contracts with a statistically constant velocity.展开更多
Band structure and bonding properties have been investigated in terms of periodic density functional theory(DFT) method,and two-photon absorption(TPA) spectra have been simulated by two-band model for ZnGeP2 and A...Band structure and bonding properties have been investigated in terms of periodic density functional theory(DFT) method,and two-photon absorption(TPA) spectra have been simulated by two-band model for ZnGeP2 and AgGaS2 crystals.It has been predicted that the AgGaS2 crystal has a wider window of nonlinear transmission,and the laser pumping energy larger than 1.02 and 1.35 eV will lead to deleterious TPA of higher nonlinear effect for ZnGeP2 and AgGaS2 crystals,respectively.Electron origin of TPA for them is also discussed.展开更多
To investigate the band structure is one of the key approaches to study the fundamental properties of a novel material.We report here the precision band mapping of a 2-dimensional(2D) spin-orbit(SO) coupling in an opt...To investigate the band structure is one of the key approaches to study the fundamental properties of a novel material.We report here the precision band mapping of a 2-dimensional(2D) spin-orbit(SO) coupling in an optical lattice.By applying the microwave spin-injection spectroscopy, the band structure and spin-polarization distribution are achieved simultaneously.The band topology is also addressed with observing the band gap close and re-open at the Dirac points.Furthermore, the lattice depth and the Raman coupling strength are precisely calibrated with relative errors in the order of 10^(-3).Our approach could also be applied for exploring the exotic topological phases with even higher dimensional system.展开更多
In this study, we theoretically investigate the strain effect on the orientation-dependent high-order harmonic generation(HHG) of monolayer aluminum nitride(Al N) by solving the multiband semiconductor Bloch equations...In this study, we theoretically investigate the strain effect on the orientation-dependent high-order harmonic generation(HHG) of monolayer aluminum nitride(Al N) by solving the multiband semiconductor Bloch equations in strong laser fields. Our simulations denote that the efficiency of the orientation-dependent HHG is considerably enhanced when a 15% biaxial tensile strain is applied to Al N, which is attributed to the downshifting energy level of the conduction band. Furthermore, the odd-even feature in the orientation-dependent high harmonic spectra owing to the strain is considerably different when compared with that in the case without strain. The enhanced quantum interference between different energy bands in strained Al N around the Γ-M direction is responsible for the observed odd-even distributions of the orientation-dependent HHG. This study helps to better understand the HHG in solids by tuning their electronic structures.展开更多
文摘Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subjected to atomic-level structural engineering by doping with transition metals(M=Fe,Co,or Ni),which simultaneously induced the formation of metal-N active sites in the g-C_(3)N_(4)framework and modulated the bandgap of g-C_(3)N_(4).Experiments and density functional theory calculations further verified that the as-formed metal-N bonds in M-doped g-C_(3)N_(4)acted as an"electron transfer bridge",where the migration of photo-generated electrons along the bridge enhanced the efficiency of separation of the photogenerated charges,and the optimized bandgap of g-C_(3)N_(4)afforded stronger reduction ability and wider light absorption.As a result,doping with either Fe,Co,or Ni had a positive effect on the HER activity,where Co-doped g-C_(3)N_(4)exhibited the highest performance.The findings illustrate that this atomic-level structural engineering could efficiently improve the HER activity and inspire the design of powerful photocatalysts.
基金Project supported by National Key Research and Development Program of China(Grant No.2021YFB3802300)the Natural Science Foundation of China Academy of Engineering Physics(Grant Nos.U1730248 and U1830101)the National Natural Science Foundation of China(Grant Nos.12202418,11872056,11904282,12074274,and 12174356)。
文摘Mn_(3)TeO_(6)(MTO) has been experimentally found to adopt a P2_(1)/In structure under high pressure,which exhibits a significantly smaller band gap compared to the atmospheric R3 phase.In this study,we systematically investigate the magnetism,structural phase transition,and electronic properties of MTO under high pressure through first-principles calculations.Both R3 and P2_(1)/n phases of MTO are antiferromagnetic at zero temperature.The R3 phase transforms to the P2_(1)/n phase at 7.5 8 GPa,accompanied by a considerable volume collapse of about 6.47%.Employing the accurate method that combines DFT+U/and GW,the calculated band gap of R3 phase at zero pressure is very close to the experimental values,while that of the P2_(1)/n phase is significantly overestimated.The main reason for this difference is that the experimental study incorrectly used the Kubelka-Munk plot for the indirect band gap to obtain the band gap of the P2_(1)/n phase instead of the Kubelka-Munk plot for the direct band gap.Furthermore,our study reveals that the transition from the R3 phase to the P2_(1)/n phase is accompanied by a slight reduction in the band gap.
基金This project has received funding from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation programme(grant agreement no 755655,ERC-StG 2017 project 2D-TOPSENSE)R.F.acknowledges the support from the Spanish Ministry of Economy,Industry and Competitiveness through a Juan de la Cierva-formación fellowship 2017 FJCI-2017-32919.H.L.acknowledges the grant from China Scholarship Council(CSC)under No.201907040070.
文摘Strain is a powerful tool to modify the optical properties of semiconducting transition metal dichalcogenides like MoS_(2),MoSe_(2),WS_(2) and WSe_(2).In this work we provide a thorough description of the technical details to perform uniaxial strain measurements on these two-dimensional semiconductors and we provide a straightforward calibration method to determine the amount of applied strain with high accuracy.We then employ reflectance spectroscopy to analyze the strain tunability of the electronic properties of single-,bi-and tri-layer MoS_(2),MoSe_(2),WS_(2) and WSe_(2).Finally,we quantify the flake-to-flake variability by analyzing 15 different single-layer MoS_(2) flakes.
基金support from the Beijing Computational Science Research Center (CSRC)supported by the Science Challenge Project (No.TZ2016003)+1 种基金the National Key Research and Development Program of China (No.2016YFB0700700)the Nature Science Foundation of China (No.11634003,51672023,U1930402 )
文摘From the recent experimentally observed conduction band offset and previously reported band gaps,one may deduce that the valence band offset between rutile SnO2 and TiO2 is around 1 eV,with TiO2 having a higher valence band maximum.This implication sharply contradicts the fact that the two compounds have the same rutile structure and the Γ3^+ VBM state is mostly an oxygen p state with a small amount of cation d character,thus one would expect that SnO2 and TiO2 should have small valence band offset.If the valence band offset between SnO2 and TiO2 is indeed small,one may question the correctness of the previously reported band gaps of SnO2 and TiO2.In this paper,using first-principles calculations with different levels of computational methods and functionals within the density functional theory,we reinvestigate the long-standing band gap problem for SnO2.Our analysis suggests that the fundamental band gap of SnO2 should be similar to that of TiO2,i.e.,around 3.0 eV.This value is significantly smaller than the previously reported value of about 3.6 eV,which can be attributed as the optical band gap of this material.Similar to what has been found in In2O3,the discrepancy between the fundamental and optical gaps of SnO2 can be ascribed to the inversion symmetry of its crystal structure and the resultant dipole-forbidden transitions between its band edges.Our results are consistent with most of the optical and electrical measurements of the band gaps and band offset between SnO2 and TiO2,thus provide new understanding of the band structure and optical properties of SnO2.Experimental tests of our predictions are called for.
基金This work was supported by Shenzhen Science and Technology Innovation Commission(JCYJ20220530153004010).
文摘Two-dimensional transition metal dichalcogenides(TMDs)have intriguing physic properties and offer an exciting platform to explore many features that are important for future devices.In this work,we synthesized monolayer WS_(2)as an example to study the optical response with hydrostatic pressure.The Raman results show a continuous tuning of the lattice vibrations that is induced by hydrostatic pressure.We further demonstrate an efficient pressure-induced change of the band structure and carrier dynamics via transient absorption measurements.We found that two time constants can be attributed to the capture process of two kinds of defect states,with the pressure increasing from 0.55 GPa to 2.91 GPa,both of capture processes were accelerated,and there is an inflection point within the pressure range of 1.56 GPa to 1.89 GPa.Our findings provide valuable information for the design of future optoelectronic devices.
基金supported by the Chongzuo Science and Technology Program Project Fund(No.FA20210713)。
文摘High-voltage LiCoO_(2)(LCO)offers a prelude to breaking the bottleneck of the energy density of lithium-ion batteries,however,LiCoO_(2)is subject to serious structural and interfacial degradation above voltages>4.55 V(vs.Li/Li^(+)).Herein,an in-situ Li_(6.25)La_(3)Zr_(2)A_(l0.25)O_(12)(LLZAO)layer is constructed on the LCO surface to achieve operating voltage at 4.6 V.The detailed characterizations(ex-situ XRD,ex-situ Raman,DFT,etc.)reveal that the LLZAO layer greatly enhances Li+conductivity attributed to the ionconducting layer on the surface/interface,and closely combines with LiCoO_(2)particle to ensure stable cathode/electrolyte interface,thus suppressing the highly reactive Co^(4+)and O^(-)triggered surface side reactions at high-voltage.Moreover,the introduction of La^(3+)/Zr^(4+)/Al^(3+)with a larger ionic radius(La^(3+)/Zr^(4+)are larger than Co^(3+))and weaker electronegativity(La/Zr/Al are weaker than Co)into Co^(3+)sites readjusts the electron cloud density between Co–O–Li,which reinforces the Co–O bond and widens the band-center gap of Co 3d and O 2p,thus restraining the detrimental phase transition(from H3 to H1-3 phase)and the formation of Co_(3)O_(4)spinel phase(attributed to lattice oxygen release),subsequently alleviating the particle cracking and structural collapse during repeated Li^(+)de/intercalation.Therefore,after 100 cycles at 3.0–4.6 V,LCO@1.0LLZAO exhibits a superior discharge capacity of 188.5 m A h g^(-1),with a capacity retention of 85.1%.The above research has brought about meaningful guidance for the evolution of cathode materials with high voltage.
文摘The electronic density of states and band structures of doped and un-doped anatase TiO2 were studied by the Linearized Augmented Plane Wave method based on the density functional theory. The calculation shows that the band structures of TiO2 crystals doped with transition metal atoms become narrower. Interesting, an excursion towards high energy level with increasing atomic number in the same element period could be observed after doping with transition metal atoms.
基金Supported by the National Natural Science Foundation of China under Grant No 60276002.
文摘Time-resolved photoluminescence (TRPL) was applied to investigate the transient process in GaP1-xNx (x = 0.12%) alloy. The filling, transferring and decay processes among nitrogen pairs are directly observed. The NN4 pair, either not present or only a small obscure peak under a proper excitation condition in the steady-state photoluminescence spectrum, is well resolved by TRPL.
基金Project supported by the National Natural Science Foundation of China(Nos.91752203,11490553,and 11602148)
文摘By direct numerical simulations of the plane Couette flow (PCF) in a large computational domain, it is shown that an isolated turbulent band decays monotonically at low Reynolds numbers but experiences transient growth before the eventual relaminarization at moderate Reynolds numbers. The lower bound Reynolds number of the transient-growth regime is determined as 286. The width, length, and tilt angle of the iso- lated band structure are defined based on the disturbance kinetic energy in the mid-plane, and the geometric characteristics of the band can be described with a tilted rectangle. It is illustrated that before its eventual fragmentation, the isolated turbulent band decays in a style of longitudinal contraction, where the center, width, and tilt angle of the band keep almost constant but the band length contracts with a statistically constant velocity.
基金Supported by the National Natural Science Foundation of China (No. 20373073)the National Basic Research Program of China (No. 2007CB815307)+1 种基金the Funds of Chinese Academy of Sciences (KJCX2-YW-H01)Fujian Key Laboratory of Nanomaterials (No. 2006L2005)
文摘Band structure and bonding properties have been investigated in terms of periodic density functional theory(DFT) method,and two-photon absorption(TPA) spectra have been simulated by two-band model for ZnGeP2 and AgGaS2 crystals.It has been predicted that the AgGaS2 crystal has a wider window of nonlinear transmission,and the laser pumping energy larger than 1.02 and 1.35 eV will lead to deleterious TPA of higher nonlinear effect for ZnGeP2 and AgGaS2 crystals,respectively.Electron origin of TPA for them is also discussed.
基金supported by the National Key R&D Program of China (2016YFA0301601 and 2016YFA0301604)the National Natural Science Foundation of China (11674301, 11761161003, and 11625522)the Thousand-Young-Talent Program of China
文摘To investigate the band structure is one of the key approaches to study the fundamental properties of a novel material.We report here the precision band mapping of a 2-dimensional(2D) spin-orbit(SO) coupling in an optical lattice.By applying the microwave spin-injection spectroscopy, the band structure and spin-polarization distribution are achieved simultaneously.The band topology is also addressed with observing the band gap close and re-open at the Dirac points.Furthermore, the lattice depth and the Raman coupling strength are precisely calibrated with relative errors in the order of 10^(-3).Our approach could also be applied for exploring the exotic topological phases with even higher dimensional system.
基金supported by the National Natural Science Foundation of China(Grant Nos.11974185,11704187,11774175,and 11834004)the Natural Science Foundation of Jiangsu Province(Grant No.BK20170032)。
文摘In this study, we theoretically investigate the strain effect on the orientation-dependent high-order harmonic generation(HHG) of monolayer aluminum nitride(Al N) by solving the multiband semiconductor Bloch equations in strong laser fields. Our simulations denote that the efficiency of the orientation-dependent HHG is considerably enhanced when a 15% biaxial tensile strain is applied to Al N, which is attributed to the downshifting energy level of the conduction band. Furthermore, the odd-even feature in the orientation-dependent high harmonic spectra owing to the strain is considerably different when compared with that in the case without strain. The enhanced quantum interference between different energy bands in strained Al N around the Γ-M direction is responsible for the observed odd-even distributions of the orientation-dependent HHG. This study helps to better understand the HHG in solids by tuning their electronic structures.