Using a stiffness matrix method, we in- vestigate the propagation behaviors of elastic waves in one-dimensional （1D） piezoelectric/piezomagnetic （PE/PM） phononic crystals （PCs） with line defects by calculating e...Using a stiffness matrix method, we in- vestigate the propagation behaviors of elastic waves in one-dimensional （1D） piezoelectric/piezomagnetic （PE/PM） phononic crystals （PCs） with line defects by calculating energy reflection/transmittion coefficients of quasi-pressure and quasi-shear waves. Line defects are created by the re- placement of PE or PM constituent layer. The defect modes existing in the first gap are considered and the influences on defect modes of the material properties and volume fraction of the defect layers, the type of incident waves, the location of defect layer and the number of structural layers are discussed in detail. Numerical results indicate that defect modes are the most obvious when the defect layers are inserted in the middle of the perfect PCs; the types of incidence wave and material properties of the defect layers have important effects on the numbers, the location of frequencies and the peaks of defect modes, and the defect modes are strongly de- pendent on volume fraction of the defect layers. We hope this paper will be found useful for the design of PE/PM acoustic filters or acoustic transducer with PCs structures.展开更多
We investigate in detail the influence of line defects on focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens. Through simulations, we find that a focusing can always be observed when a l...We investigate in detail the influence of line defects on focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens. Through simulations, we find that a focusing can always be observed when a line defect in the lens is introduced along the light transmission direction and the width of the line defect is less than λ/2. However, there appear two focusings when the width of the line defect is more than λ/2. When the line defect is introduced along the direction perpendicular to the transmission, there is always one focusing.展开更多
This paper presents a photonic crystal(PhC)line-defect slow-light waveguide modified by resonant rings.We introduce resonant rings into the line defect,constructing a slow-light waveguide with high normalized delay ba...This paper presents a photonic crystal(PhC)line-defect slow-light waveguide modified by resonant rings.We introduce resonant rings into the line defect,constructing a slow-light waveguide with high normalized delay bandwidth product(NDBP)and low group velocity dispersion(GVD).We simulate,analyze,and optimize the structural parameters of this slow-light waveguide using the finite difference time domain(FDTD)method,theoretically achieving a maximum group index of 3.7,maximum bandwidth of 15.6 nm,and maximum NDBP of 0.4416 for slow-light effect.The resonant ring-modified PhC slow-light waveguide designed in this paper exhibits GVD lower than the order of 10^(−20)s^(2)/m over a normalized frequency range from 0.3554 to 0.4175.This study is expected to provide theoretical references for the study of slow-light buffering devices based on PhCs with high NDBP values.展开更多
Miniaturization of efficient thermoelectric(TE)devices has long been hindered by the weak mechanical strength and insufficient heat-to-electricity conversion efficiency of zone-melted(ZM)ingots.Here,we successfully pr...Miniaturization of efficient thermoelectric(TE)devices has long been hindered by the weak mechanical strength and insufficient heat-to-electricity conversion efficiency of zone-melted(ZM)ingots.Here,we successfully prepared a robust high-performance p-type Bi_(0.4)Sb_(1.6)Te_(3.72)bulk alloy by combining an ultrafast thermal explosion reaction with the spark plasma sintering(TER-SPS)process.It is observed that the introduced excess Te not only enhances the(00l)-oriented texture to ensure an outstanding power factor(PF)of 5 mW m^(−1)K^(−2),but also induces extremely high-density line defects of up to 10^(11)–10^(12)cm^(−2).Benefiting from such heavily dense line defects,the enhancement of the electronic thermal conductance from the increased electron mobility is fully compensated by the stronger phonon scattering,leading to an evident net reduction in total thermal conductivity.As a result,a superior ZT value of~1.4 at 350 K is achieved,which is 40%higher than that of commercial ZM ingots.Moreover,owing to the strengthening of grain refinement and highdensity line defects,the mechanical compressive stress reaches up to 94 MPa,which is 154%more than that of commercial single crystals.This research presents an effective strategy for the collaborative optimization of the texture,TE performance,and mechanical strength of Bi2Te3-based materials.As such,the present study contributes significantly to the future commercial development of miniature TE devices.展开更多
Two-dimensional(2D)materials with defects are desired for catalysis after the adsorption of monodispersed noble metal atoms.High-performance catalysts with the absolute value of Gibbs free energy(|△GH|)close to zero,...Two-dimensional(2D)materials with defects are desired for catalysis after the adsorption of monodispersed noble metal atoms.High-performance catalysts with the absolute value of Gibbs free energy(|△GH|)close to zero,is one of the ultimate goals in the catalytic field.Here,we report the formation of monolayer titanium selenide(TiSe2)with line defects.The low-temperature scanning tunneling microscopy/spectroscopy(STM/S)measurements revealed the structure and electronic states of the line defect.Density functional theory(DFT)calculation results confirmed that the line defects were induced by selenium vacancies and the STM simulation was in good agreement with the experimental results.Further,DFT calculations show that monolayer TiSe_(2) with line defects have good catalytic activity for hydrogen evolution reaction(HER).If the defects are decorated with single Pt atom,the HER catalytic activity will be enhanced dramatically(|△GH|=0.006 eV),which is much better than Pt metal(|△GH|=0.09 eV).Line defects in monolayer TiSe_(2)/Au(111)provide a wonderful platform for the design of high-performance catalysts.展开更多
Aluminum metallization using the sprayed coating for exhaust mild steel （MS） pipes of tractors is a standard practice for avoiding rusting. Patches of thin metal coats are prone to rusting and are thus considered as...Aluminum metallization using the sprayed coating for exhaust mild steel （MS） pipes of tractors is a standard practice for avoiding rusting. Patches of thin metal coats are prone to rusting and are thus considered as defects in the surface coating. This paper reports a novel configuration of the fiber optic sensor for on-line checking the aluminum metaUization uniformity and hence for defect detection. An optimally chosen high bright 440 nm BLUE LED （light-emitting diode） launches light into a transmitting fiber inclined at the angle of 60° to the surface under inspection placed adequately. The reflected light is transported by a receiving fiber to a blue enhanced photo detector. The metallization thickness on the coated surface results in visually observable variation in the gray shades. The coated pipe is spirally inspected by a combination of linear and rotary motions. The sensor output is the signal conditioned and monitored with RISHUBH DAS. Experimental results show the good repeatability in the defect detection and coating non-uniformity measurement.展开更多
The realization of Majorana zero modes in condensed matter have been attracting enormous interests from fundamental science such as topological quantum computation.Recently iron based superconductors were identified a...The realization of Majorana zero modes in condensed matter have been attracting enormous interests from fundamental science such as topological quantum computation.Recently iron based superconductors were identified as a high-temperature platform for realizing topological superconductivity and Majorana modes.As unconventional superconductors,one of the most important characteristics of them is that they are in the vicinity of magnetic states due to the strong Hund’s coupling in iron atoms.Here we propose that the line defects with missing Te/Se anions in Fe(Se,Te)superconductors provide the realization of intrinsic antiferromagnetic(AFM)chains with Rashba spin-orbit coupling.Against conventional wisdom,Majorana zero modes(MZMs)can be robustly generated at these AFM chain ends.These results can consistently explain the recent experimental observation of zero-energy end states in line defects of monolayer Fe(Te,Se)/SrTiO_(3) by scanning tunneling microscopy(STM)measurements.Our research not only demonstrates an unprecedented interplay among native line defect,emergent magnetism and topological superconductivity but also explores a high-temperature platform for Majorana fermions.展开更多
Defects play vital roles in tailoring structures and properties of materials including the atomically thin two-dimensional(2D)materials,and increasing demands are requested to find effective ways to realize the defect...Defects play vital roles in tailoring structures and properties of materials including the atomically thin two-dimensional(2D)materials,and increasing demands are requested to find effective ways to realize the defect engineering,i.e.,tuning the defects and thus the materials’structure–property in a well-controlled way.Herein,we propose a novel method to tune the structures and configurations of one-dimensional(1D)line defects in monolayer MoS2 via mass transport induced structural transformation.By using atomic-resolved annular dark-field scanning transmission electron microscopy(ADF-STEM),we demonstrate in situ that sulfur vacancy line defect can be healed locally into defect-free MoS_(2)lattice via the desorption of Mo atoms from vacancy lines and adsorption into a moving Mo cluster.Furthermore,directional transport of Mo atoms(or Mo cluster)along the sulfur vacancy lines can induce the formation of Mo chains.Such a mass transport induced defect tuning provides more operational routes for the rational defect designing and property tuning in MoS_(2)as well as other related 2D materials.展开更多
We study the local density of states （LDOS） for electrons scattering off the line edge of an atomic step defect on the surface of a three-dimensional （3D） topological insulator （TI） and the line edge of a finite...We study the local density of states （LDOS） for electrons scattering off the line edge of an atomic step defect on the surface of a three-dimensional （3D） topological insulator （TI） and the line edge of a finite 3D TI, where the front surface and side surface meet with different Fermi velocities, respectively. By using a S-function potential to model the edges, we find that the bound states existed along the step line edge significantly contribute to the LDOS near the edge, but do not modify the exponential behavior away from it. In addition, the power-law decaying behavior for LDOS oscillation away from the step is understood from the spin rotation for surface states scattering off the step defect with magnitude depending on the strength of the potential. Furthermore, the electron refraction and total reflection analogous to optics occurred at the line edge where two surfaces meet with different Fermi velocities, which leads to the LDOS decaying behavior in the greater Fermi velocity side similar to that for a step line edge. However, in the smaller velocity side the LDOS shows a different decaying behavior as x-1/2, and the wavevector of LDOS oscillation is no longer equal to the diameter of the constant energy contour of surface band, but is sensitively dependent on the ratio of the two Fermi velocities. These effects may be verified by STM measurement with high precision.展开更多
基金supported by the National Natural Science Foundation of China(11102122)
文摘Using a stiffness matrix method, we in- vestigate the propagation behaviors of elastic waves in one-dimensional （1D） piezoelectric/piezomagnetic （PE/PM） phononic crystals （PCs） with line defects by calculating energy reflection/transmittion coefficients of quasi-pressure and quasi-shear waves. Line defects are created by the re- placement of PE or PM constituent layer. The defect modes existing in the first gap are considered and the influences on defect modes of the material properties and volume fraction of the defect layers, the type of incident waves, the location of defect layer and the number of structural layers are discussed in detail. Numerical results indicate that defect modes are the most obvious when the defect layers are inserted in the middle of the perfect PCs; the types of incidence wave and material properties of the defect layers have important effects on the numbers, the location of frequencies and the peaks of defect modes, and the defect modes are strongly de- pendent on volume fraction of the defect layers. We hope this paper will be found useful for the design of PE/PM acoustic filters or acoustic transducer with PCs structures.
基金Project supported by the National Natural Science Foundation of China (Grant No.10704006)
文摘We investigate in detail the influence of line defects on focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens. Through simulations, we find that a focusing can always be observed when a line defect in the lens is introduced along the light transmission direction and the width of the line defect is less than λ/2. However, there appear two focusings when the width of the line defect is more than λ/2. When the line defect is introduced along the direction perpendicular to the transmission, there is always one focusing.
基金supported by the Graduate Student Innovation Fund of Xi’an Shiyou University(No.YCS21211087).
文摘This paper presents a photonic crystal(PhC)line-defect slow-light waveguide modified by resonant rings.We introduce resonant rings into the line defect,constructing a slow-light waveguide with high normalized delay bandwidth product(NDBP)and low group velocity dispersion(GVD).We simulate,analyze,and optimize the structural parameters of this slow-light waveguide using the finite difference time domain(FDTD)method,theoretically achieving a maximum group index of 3.7,maximum bandwidth of 15.6 nm,and maximum NDBP of 0.4416 for slow-light effect.The resonant ring-modified PhC slow-light waveguide designed in this paper exhibits GVD lower than the order of 10^(−20)s^(2)/m over a normalized frequency range from 0.3554 to 0.4175.This study is expected to provide theoretical references for the study of slow-light buffering devices based on PhCs with high NDBP values.
基金financially supported by the National Key Research and Development Program of China (2018YFB0703600)the National Natural Science Foundation of China (51772232)+1 种基金the 111 Project of China (B07040)Wuhan Frontier Project on Applied Research Foundation (2019010701011405)
文摘Miniaturization of efficient thermoelectric(TE)devices has long been hindered by the weak mechanical strength and insufficient heat-to-electricity conversion efficiency of zone-melted(ZM)ingots.Here,we successfully prepared a robust high-performance p-type Bi_(0.4)Sb_(1.6)Te_(3.72)bulk alloy by combining an ultrafast thermal explosion reaction with the spark plasma sintering(TER-SPS)process.It is observed that the introduced excess Te not only enhances the(00l)-oriented texture to ensure an outstanding power factor(PF)of 5 mW m^(−1)K^(−2),but also induces extremely high-density line defects of up to 10^(11)–10^(12)cm^(−2).Benefiting from such heavily dense line defects,the enhancement of the electronic thermal conductance from the increased electron mobility is fully compensated by the stronger phonon scattering,leading to an evident net reduction in total thermal conductivity.As a result,a superior ZT value of~1.4 at 350 K is achieved,which is 40%higher than that of commercial ZM ingots.Moreover,owing to the strengthening of grain refinement and highdensity line defects,the mechanical compressive stress reaches up to 94 MPa,which is 154%more than that of commercial single crystals.This research presents an effective strategy for the collaborative optimization of the texture,TE performance,and mechanical strength of Bi2Te3-based materials.As such,the present study contributes significantly to the future commercial development of miniature TE devices.
基金We thank Guangchao Chen for his help.This work was supported by the National Key R&D Program of China(Nos.2019YFA0308500 and 2018YFA0305800)the National Natural Science Foundation of China(Nos.61925111 and 61888102)+1 种基金Strategic Priority Research Program of Chinese Academy of Sciences(Nos.XDB28000000 and XDB30000000)the Fundamental Research Funds for the Central Universities,and CAS Key Laboratory of Vacuum Physics.
文摘Two-dimensional(2D)materials with defects are desired for catalysis after the adsorption of monodispersed noble metal atoms.High-performance catalysts with the absolute value of Gibbs free energy(|△GH|)close to zero,is one of the ultimate goals in the catalytic field.Here,we report the formation of monolayer titanium selenide(TiSe2)with line defects.The low-temperature scanning tunneling microscopy/spectroscopy(STM/S)measurements revealed the structure and electronic states of the line defect.Density functional theory(DFT)calculation results confirmed that the line defects were induced by selenium vacancies and the STM simulation was in good agreement with the experimental results.Further,DFT calculations show that monolayer TiSe_(2) with line defects have good catalytic activity for hydrogen evolution reaction(HER).If the defects are decorated with single Pt atom,the HER catalytic activity will be enhanced dramatically(|△GH|=0.006 eV),which is much better than Pt metal(|△GH|=0.09 eV).Line defects in monolayer TiSe_(2)/Au(111)provide a wonderful platform for the design of high-performance catalysts.
文摘Aluminum metallization using the sprayed coating for exhaust mild steel （MS） pipes of tractors is a standard practice for avoiding rusting. Patches of thin metal coats are prone to rusting and are thus considered as defects in the surface coating. This paper reports a novel configuration of the fiber optic sensor for on-line checking the aluminum metaUization uniformity and hence for defect detection. An optimally chosen high bright 440 nm BLUE LED （light-emitting diode） launches light into a transmitting fiber inclined at the angle of 60° to the surface under inspection placed adequately. The reflected light is transported by a receiving fiber to a blue enhanced photo detector. The metallization thickness on the coated surface results in visually observable variation in the gray shades. The coated pipe is spirally inspected by a combination of linear and rotary motions. The sensor output is the signal conditioned and monitored with RISHUBH DAS. Experimental results show the good repeatability in the defect detection and coating non-uniformity measurement.
基金funding provided by Shanghai Jiao Tong Universitysupported by the National Natural Science Foundation of China(grant no.12047503)+2 种基金supported by the Ministry of Science and Technology(grant no.2022YFA1403901)the National Natural Science Foundation of China(grant no.NSFC-11888101)the New Cornerstone Foundation.
文摘The realization of Majorana zero modes in condensed matter have been attracting enormous interests from fundamental science such as topological quantum computation.Recently iron based superconductors were identified as a high-temperature platform for realizing topological superconductivity and Majorana modes.As unconventional superconductors,one of the most important characteristics of them is that they are in the vicinity of magnetic states due to the strong Hund’s coupling in iron atoms.Here we propose that the line defects with missing Te/Se anions in Fe(Se,Te)superconductors provide the realization of intrinsic antiferromagnetic(AFM)chains with Rashba spin-orbit coupling.Against conventional wisdom,Majorana zero modes(MZMs)can be robustly generated at these AFM chain ends.These results can consistently explain the recent experimental observation of zero-energy end states in line defects of monolayer Fe(Te,Se)/SrTiO_(3) by scanning tunneling microscopy(STM)measurements.Our research not only demonstrates an unprecedented interplay among native line defect,emergent magnetism and topological superconductivity but also explores a high-temperature platform for Majorana fermions.
基金This work done in Hangzhou was financially supported by the National Natural Science Foundation of China(Nos.51772265,5171165024 and 61721005)Zhejiang Provincial Nature Science Foundation(No.D19E020002)+5 种基金the Program of the Ministry of Education of China for Introducing Talents of Discipline to Universities(No.B16042)This work done in Beijing was financially supported by the Ministry of Science and Technology(MOST)of China(No.2018YFE0202700)the National Natural Science Foundation of China(Nos.11974422,61674171,11622437,and 61761166009)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB30000000)the Fundamental Research Funds for the Central Universities of China and the Research Funds of Renmin University of China(Nos.16XNLQ01,19XNLG11,19XNQ025(W.J.))We thank Chunxia Yang for kindly providing us high-quality CVD-grown MoS2 samples.Calculations were performed at the Physics Lab of High-Performance Computing of Renmin University of China and Shanghai Supercomputer Center.The work on electron microscopy was done at the Center for Electron Microscopy of Zhejiang University.
文摘Defects play vital roles in tailoring structures and properties of materials including the atomically thin two-dimensional(2D)materials,and increasing demands are requested to find effective ways to realize the defect engineering,i.e.,tuning the defects and thus the materials’structure–property in a well-controlled way.Herein,we propose a novel method to tune the structures and configurations of one-dimensional(1D)line defects in monolayer MoS2 via mass transport induced structural transformation.By using atomic-resolved annular dark-field scanning transmission electron microscopy(ADF-STEM),we demonstrate in situ that sulfur vacancy line defect can be healed locally into defect-free MoS_(2)lattice via the desorption of Mo atoms from vacancy lines and adsorption into a moving Mo cluster.Furthermore,directional transport of Mo atoms(or Mo cluster)along the sulfur vacancy lines can induce the formation of Mo chains.Such a mass transport induced defect tuning provides more operational routes for the rational defect designing and property tuning in MoS_(2)as well as other related 2D materials.
基金Project supported by the National Natural Science Foundation of China(Grant No.11274108)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20114306110008)the Hunan Provincial Innovation Foundation for Postgraduates(Grant No.CX2012B204)
文摘We study the local density of states （LDOS） for electrons scattering off the line edge of an atomic step defect on the surface of a three-dimensional （3D） topological insulator （TI） and the line edge of a finite 3D TI, where the front surface and side surface meet with different Fermi velocities, respectively. By using a S-function potential to model the edges, we find that the bound states existed along the step line edge significantly contribute to the LDOS near the edge, but do not modify the exponential behavior away from it. In addition, the power-law decaying behavior for LDOS oscillation away from the step is understood from the spin rotation for surface states scattering off the step defect with magnitude depending on the strength of the potential. Furthermore, the electron refraction and total reflection analogous to optics occurred at the line edge where two surfaces meet with different Fermi velocities, which leads to the LDOS decaying behavior in the greater Fermi velocity side similar to that for a step line edge. However, in the smaller velocity side the LDOS shows a different decaying behavior as x-1/2, and the wavevector of LDOS oscillation is no longer equal to the diameter of the constant energy contour of surface band, but is sensitively dependent on the ratio of the two Fermi velocities. These effects may be verified by STM measurement with high precision.
