Band offset in semiconductors is a fundamental physical quantity that determines the performance of optoelectronic devices.However,the current method of calculating band offset is difficult to apply directly to the la...Band offset in semiconductors is a fundamental physical quantity that determines the performance of optoelectronic devices.However,the current method of calculating band offset is difficult to apply directly to the large-lattice-mismatched and heterovalent semiconductors because of the existing electric field and large strain at the interfaces.Here,we proposed a modified method to calculate band offsets for such systems,in which the core energy level shifts caused by heterovalent effects and lattice mismatch are estimated by interface reconstruction and the insertion of unidirectional strain structures as transitions,respectively.Taking the Si and III-V systems as examples,the results have the same accuracy as what is a widely used method for small-lattice-mismatched systems,and are much closer to the experimental values for the large-lattice-mismatched and heterovalent systems.Furthermore,by systematically studying the heterojunctions of Si and III-V semiconductors along different directions,it is found that the band offsets of Si/InAs and Si/InSb systems in[100],[110]and[111]directions belong to the type I,and could be beneficial for silicon-based luminescence performance.Our study offers a more reliable and direct method for calculating band offsets of large-lattice-mismatched and heterovalent semiconductors,and could provide theoretical support for the design of the high-performance silicon-based light sources.展开更多
Heterovalent doped(K_(0.48-0.07)xNa_(0.52-0.43)xBi_(0.5)x)(Nb_(0.95-0.95x)Sb_(0.05-0.05x)Zrx)O_(3)ceramics were fabricated using conventional solid-state reaction.Then,the phase structures,dielectric,ferroelectric,and...Heterovalent doped(K_(0.48-0.07)xNa_(0.52-0.43)xBi_(0.5)x)(Nb_(0.95-0.95x)Sb_(0.05-0.05x)Zrx)O_(3)ceramics were fabricated using conventional solid-state reaction.Then,the phase structures,dielectric,ferroelectric,and electricstrain properties were investigated.The compositions were tuned to be located at polymorphic phase boundary with increasing heterovalent Bi3t and Zr4t doping levels.A large strain of 0.19%was obtained at relatively low electric fields of 30 kV/cm in the composition of x=0.04.The normalized large-signal d33*values were approximately 633 pm/V under a low driving electric field of 30 kV/cm,which were comparable or larger than the values reported for other lead-free families.The large strains obtained can be attributed to the formation of nanodomains and high-density domain walls,which were confirmed by the observations of domain morphology using transmission electron microscopy(TEM)technique.Excellent temperature stability of the strain properties of the x=0.04 sample could be ascribed to the sluggish behaviour for the local structural heterogeneity in heterovalent-ion doped KNN ceramic.Theoretical simulations revealed that the Zr^(4t)produce the local stress at the BO6 octahedra and Bi3t could yield off-centering of AO12 ployhedron due to the nature of Bi 6s lone pair electrons,which induced lattice expansion and local distortions in the sample.The local displacements are strongly anisotropic in heterovalent-ion doped system.It is believed that random local fields exist in these compositions owing to the eixstence of charge distribution.Such heterovalent doping of Bi^(3t)and Zr^(4t)could destory simultaneously the orthorhombic symmetry and the short-range ferroelecctric order,leading to the formation of complex nanodomains and local structral hetergenenity.Heterovalent doping may,therefore,offer a new avenve to design novel K0.5Na0.5NbO3(KNN)-based materials for their mutifunctional applications.展开更多
Surface modification of different functional molecules onto NaREF_(4)(RE=rare earth)upconversion nanoparticles(UCNPs)impart their multiple functionalities.Functional molecules can be loaded onto NaREF_(4) UCNPs throug...Surface modification of different functional molecules onto NaREF_(4)(RE=rare earth)upconversion nanoparticles(UCNPs)impart their multiple functionalities.Functional molecules can be loaded onto NaREF_(4) UCNPs through the formation of coordination bonds between the surface-exposed RE^(3+) ions and the appropriate chemical groups of functional molecules.The density of surface RE^(3+) ions directly determines the loading efficiency of Na REF4 UCNPs.However,NaREF_(4) is a binary cation system,rendering the surface-distributed Na;and RE^(3+) ions remains a mystery.Here,we develop an effective strategy to significantly enhance the density of surface RE^(3+) ions,thus maximizing the loading capacity of NaREF_(4) UCNPs.This strategy is based on a heterovalent cation exchange(HCE)reaction in the surface region in which Na^(+)ions are replaced by RE^(3+) ions.The density of surface ligands enhances from 3.6 to 8.8 molecules/nm^(2) after reaction,suggesting that the loading efficiency increases by approximately 150%.Benefiting from the improved loading capacity,we demonstrate such surface-RE-rich nanoparticles have the ability to offer higher colloidal stability and more desirable photodynamic therapy(PDT)efficacy.This work not only advances our understanding of cation exchange reactions in RE-based nanoparticles,but also provides significant value for considerable applications such as sensing,bioimaging,and therapy.展开更多
Indium selenide(InSe),as a wide-bandgap semiconductor,has received extensive attention in the flexible electronics field in recent years due to its exceptional plasticity and promising thermoelectric performance.Howev...Indium selenide(InSe),as a wide-bandgap semiconductor,has received extensive attention in the flexible electronics field in recent years due to its exceptional plasticity and promising thermoelectric performance.However,the low carrier concentration severely limits its thermoelectric performance improvement.In this work,we conducted contrasting strategies that can be employed to increase the carrier concentration of InSe,including bandgap narrowing and heterovalent doping.Specifically,the carrier concentration initially increases as a result of the reduced bandgap upon Te alloying and then slightly decreases due to the weak electronegativity of Te.Whereas Br doping realizes high carrier concentration by pushing the Fermi level into the conduction bands and activating the multiple bands.On the other hand,both Te and Br obviously suppress the thermal conductivity due to the point defect scattering.By contrast,Br doping realizes a higher thermoelectric performance with a maximum ZT of~0.13 at 773 K benefiting from the better optimization of carrier concentration.This work elucidates the strategies for enhancing carrier concentration at anion sites and demonstrates the high efficiency of halogen doping in InSe.Moreover,the carrier concentration of InSe is promising to be further optimized,and future work should focus on employing approaches such as cation doping or secondphase compositing.展开更多
In the early-stage diagnosis of lung cancer,the low-concentration(<5 ppm)volatile organic compounds(VOCs)are extensively identified to be the biomarkers for breath analysis.Herein,the urchin-like sodium(Na)-doped z...In the early-stage diagnosis of lung cancer,the low-concentration(<5 ppm)volatile organic compounds(VOCs)are extensively identified to be the biomarkers for breath analysis.Herein,the urchin-like sodium(Na)-doped zinc oxide(ZnO)nanoneedles were synthesized through a hydrothermal strategy with the addition of different contents of citric acid.The Na-doped ZnO gas sensor with a 3:1 molar ratio of Na^(+)and citric acid showed outstanding sensing properties with an optimal selectivity to various VOCs(formaldehyde(HCOH),isopropanol,acetone,and ammonia)based on working temperature regulation.Specifically,significantly enhanced sensitivity(21.3@5 ppm)compared with pristine ZnO(~7-fold),low limit of detection(LOD)(298 ppb),robust humidity resistance,and long-term stability of formaldehyde sensing performances were obtained,which can be attributed to the formation of a higher concentration of oxygen vacancies(20.98%)and the active electron transitions.Furthermore,the improved sensing mechanism was demonstrated by the exquisite band structure and introduction of the additional acceptor level,which resulted in the narrowed bandgap of ZnO.展开更多
Applying mixed oxygen ionic and electronic conducting(MIEC)oxides as the cathode offers a promis-ing solution to enhance the performance of solid oxide fuel cells(SOFCs).However,the phase instability in CO_(2)-contain...Applying mixed oxygen ionic and electronic conducting(MIEC)oxides as the cathode offers a promis-ing solution to enhance the performance of solid oxide fuel cells(SOFCs).However,the phase instability in CO_(2)-containing air and sluggish oxygen reduction activity of MIEC cathodes remain a long-term chal-lenge for optimizing the electrochemical performance of SOFCs.Herein,a heterovalent co-doping strategy is proposed to enhance the oxygen reduction activity and CO_(2)tolerance of SOFCs cathodes,which can be demonstrated by developing a novel BaCo_(0.6)Fe_(0.4)O_(3)-δ(BCF)-based MIEC oxide,BaCo_(0.6)Fe_(0.2)Sn_(0.1) Y_(0.1)O_(3-δ)(BCFSY).In addition to improving the stability of BCF-based perovskites,this strategy achieves an opti-mized balance of ionic mobility and oxygen vacancies due to the synergies between the effects of the co-dopants.Compared with single-doped materials,BCFSY exhibits improved CO_(2)tolerance and consider-ably higher ORR activity,which is reflected in a significantly lower polarization resistance of 0.15Ωcm^(2) at 600℃.The results of this work provide an efficient tactic for designing electrode materials for SOFCs.展开更多
基金This work was supported by the National Key Research and Development Program of China(Grant No.2018YFB2200100)the Key Research Program of the Chinese Academy of Sciences(Grant No.XDPB22)+1 种基金the National Natural Science Foundation of China(Grant No.118764347,11614003,11804333)H.X.D.was also supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2017154).
文摘Band offset in semiconductors is a fundamental physical quantity that determines the performance of optoelectronic devices.However,the current method of calculating band offset is difficult to apply directly to the large-lattice-mismatched and heterovalent semiconductors because of the existing electric field and large strain at the interfaces.Here,we proposed a modified method to calculate band offsets for such systems,in which the core energy level shifts caused by heterovalent effects and lattice mismatch are estimated by interface reconstruction and the insertion of unidirectional strain structures as transitions,respectively.Taking the Si and III-V systems as examples,the results have the same accuracy as what is a widely used method for small-lattice-mismatched systems,and are much closer to the experimental values for the large-lattice-mismatched and heterovalent systems.Furthermore,by systematically studying the heterojunctions of Si and III-V semiconductors along different directions,it is found that the band offsets of Si/InAs and Si/InSb systems in[100],[110]and[111]directions belong to the type I,and could be beneficial for silicon-based luminescence performance.Our study offers a more reliable and direct method for calculating band offsets of large-lattice-mismatched and heterovalent semiconductors,and could provide theoretical support for the design of the high-performance silicon-based light sources.
基金supported by National Science Foundation of China(NSFC No.52172125),the CSS project(YK2015-0602006),the Natural Science Foundation of Shandong Province of China(Grant No.ZR2018BA028),Quzhou Science and Technology Plan Project(2022K108)and General Research Project of Zhejiang Provincial Department of Education(Y202249978).
文摘Heterovalent doped(K_(0.48-0.07)xNa_(0.52-0.43)xBi_(0.5)x)(Nb_(0.95-0.95x)Sb_(0.05-0.05x)Zrx)O_(3)ceramics were fabricated using conventional solid-state reaction.Then,the phase structures,dielectric,ferroelectric,and electricstrain properties were investigated.The compositions were tuned to be located at polymorphic phase boundary with increasing heterovalent Bi3t and Zr4t doping levels.A large strain of 0.19%was obtained at relatively low electric fields of 30 kV/cm in the composition of x=0.04.The normalized large-signal d33*values were approximately 633 pm/V under a low driving electric field of 30 kV/cm,which were comparable or larger than the values reported for other lead-free families.The large strains obtained can be attributed to the formation of nanodomains and high-density domain walls,which were confirmed by the observations of domain morphology using transmission electron microscopy(TEM)technique.Excellent temperature stability of the strain properties of the x=0.04 sample could be ascribed to the sluggish behaviour for the local structural heterogeneity in heterovalent-ion doped KNN ceramic.Theoretical simulations revealed that the Zr^(4t)produce the local stress at the BO6 octahedra and Bi3t could yield off-centering of AO12 ployhedron due to the nature of Bi 6s lone pair electrons,which induced lattice expansion and local distortions in the sample.The local displacements are strongly anisotropic in heterovalent-ion doped system.It is believed that random local fields exist in these compositions owing to the eixstence of charge distribution.Such heterovalent doping of Bi^(3t)and Zr^(4t)could destory simultaneously the orthorhombic symmetry and the short-range ferroelecctric order,leading to the formation of complex nanodomains and local structral hetergenenity.Heterovalent doping may,therefore,offer a new avenve to design novel K0.5Na0.5NbO3(KNN)-based materials for their mutifunctional applications.
基金financially supported by the National Natural Science Foundation of China(Nos.61805083,31801968,and 51802281)。
文摘Surface modification of different functional molecules onto NaREF_(4)(RE=rare earth)upconversion nanoparticles(UCNPs)impart their multiple functionalities.Functional molecules can be loaded onto NaREF_(4) UCNPs through the formation of coordination bonds between the surface-exposed RE^(3+) ions and the appropriate chemical groups of functional molecules.The density of surface RE^(3+) ions directly determines the loading efficiency of Na REF4 UCNPs.However,NaREF_(4) is a binary cation system,rendering the surface-distributed Na;and RE^(3+) ions remains a mystery.Here,we develop an effective strategy to significantly enhance the density of surface RE^(3+) ions,thus maximizing the loading capacity of NaREF_(4) UCNPs.This strategy is based on a heterovalent cation exchange(HCE)reaction in the surface region in which Na^(+)ions are replaced by RE^(3+) ions.The density of surface ligands enhances from 3.6 to 8.8 molecules/nm^(2) after reaction,suggesting that the loading efficiency increases by approximately 150%.Benefiting from the improved loading capacity,we demonstrate such surface-RE-rich nanoparticles have the ability to offer higher colloidal stability and more desirable photodynamic therapy(PDT)efficacy.This work not only advances our understanding of cation exchange reactions in RE-based nanoparticles,but also provides significant value for considerable applications such as sensing,bioimaging,and therapy.
基金supported by the National Science Fund for Distinguished Young Scholars(No.51925101)the Tencent Xplorer Prize,the National Natural Science Foundation of China(Nos.52371208,52250090,52002042,51772012,51571007and 12374023)+1 种基金Beijing Municipal Natural Science Foundation(JQ18004)the 111 Project(B17002)。
文摘Indium selenide(InSe),as a wide-bandgap semiconductor,has received extensive attention in the flexible electronics field in recent years due to its exceptional plasticity and promising thermoelectric performance.However,the low carrier concentration severely limits its thermoelectric performance improvement.In this work,we conducted contrasting strategies that can be employed to increase the carrier concentration of InSe,including bandgap narrowing and heterovalent doping.Specifically,the carrier concentration initially increases as a result of the reduced bandgap upon Te alloying and then slightly decreases due to the weak electronegativity of Te.Whereas Br doping realizes high carrier concentration by pushing the Fermi level into the conduction bands and activating the multiple bands.On the other hand,both Te and Br obviously suppress the thermal conductivity due to the point defect scattering.By contrast,Br doping realizes a higher thermoelectric performance with a maximum ZT of~0.13 at 773 K benefiting from the better optimization of carrier concentration.This work elucidates the strategies for enhancing carrier concentration at anion sites and demonstrates the high efficiency of halogen doping in InSe.Moreover,the carrier concentration of InSe is promising to be further optimized,and future work should focus on employing approaches such as cation doping or secondphase compositing.
基金the Outstanding Youth Foundation of Jiangsu Province of China(No.BK20211548)the Yangzhou Science and Technology Plan Project(No.YZ2023246)the Qinglan Project of Yangzhou University,and the Research Innovation Plan of Graduate Education Innovation Project in Jiangsu Province(No.KYCX23_3530).
文摘In the early-stage diagnosis of lung cancer,the low-concentration(<5 ppm)volatile organic compounds(VOCs)are extensively identified to be the biomarkers for breath analysis.Herein,the urchin-like sodium(Na)-doped zinc oxide(ZnO)nanoneedles were synthesized through a hydrothermal strategy with the addition of different contents of citric acid.The Na-doped ZnO gas sensor with a 3:1 molar ratio of Na^(+)and citric acid showed outstanding sensing properties with an optimal selectivity to various VOCs(formaldehyde(HCOH),isopropanol,acetone,and ammonia)based on working temperature regulation.Specifically,significantly enhanced sensitivity(21.3@5 ppm)compared with pristine ZnO(~7-fold),low limit of detection(LOD)(298 ppb),robust humidity resistance,and long-term stability of formaldehyde sensing performances were obtained,which can be attributed to the formation of a higher concentration of oxygen vacancies(20.98%)and the active electron transitions.Furthermore,the improved sensing mechanism was demonstrated by the exquisite band structure and introduction of the additional acceptor level,which resulted in the narrowed bandgap of ZnO.
基金supported by the National Natural Science Foundation of China (No. 22078022)China Postdoctoral Science Foundation (No.2021M690379)
文摘Applying mixed oxygen ionic and electronic conducting(MIEC)oxides as the cathode offers a promis-ing solution to enhance the performance of solid oxide fuel cells(SOFCs).However,the phase instability in CO_(2)-containing air and sluggish oxygen reduction activity of MIEC cathodes remain a long-term chal-lenge for optimizing the electrochemical performance of SOFCs.Herein,a heterovalent co-doping strategy is proposed to enhance the oxygen reduction activity and CO_(2)tolerance of SOFCs cathodes,which can be demonstrated by developing a novel BaCo_(0.6)Fe_(0.4)O_(3)-δ(BCF)-based MIEC oxide,BaCo_(0.6)Fe_(0.2)Sn_(0.1) Y_(0.1)O_(3-δ)(BCFSY).In addition to improving the stability of BCF-based perovskites,this strategy achieves an opti-mized balance of ionic mobility and oxygen vacancies due to the synergies between the effects of the co-dopants.Compared with single-doped materials,BCFSY exhibits improved CO_(2)tolerance and consider-ably higher ORR activity,which is reflected in a significantly lower polarization resistance of 0.15Ωcm^(2) at 600℃.The results of this work provide an efficient tactic for designing electrode materials for SOFCs.
