Tailoring the degree of structural disorder in Ge-Sb-Te alloys is important for the development of non-volatile phase-change memory and neuro-inspired computing.Upon crystallization from the amorphous phase,these allo...Tailoring the degree of structural disorder in Ge-Sb-Te alloys is important for the development of non-volatile phase-change memory and neuro-inspired computing.Upon crystallization from the amorphous phase,these alloys form a cubic rocksalt-like structure with a high content of intrinsic vacancies.Further thermal annealing results in a gradual structural transition towards a layered structure and an insulator-to-metal transition.In this work,we elucidate the atomic-level details of the structural transition in crystalline GeSb_(2)Te_(4) by in situ high-resolution transmission electron microscopy experiments and ab initio density functional theory calculations,providing a comprehensive real-time and real-space view of the vacancy ordering process.We also discuss the impact of vacancy ordering on altering the electronic and optical properties of GeSb_(2)Te_(4),which is relevant to multilevel storage applications.The phase evolution paths in Ge-Sb-Te alloys and Sb_(2)Te_(3)are illustrated using a summary diagram,which serves as a guide for designing phase-change memory devices.展开更多
Compact nanophotonic elements exhibiting adaptable properties are essential components for the miniaturization of powerful optical technologies such as adaptive optics and spatial light modulators.While the larger cou...Compact nanophotonic elements exhibiting adaptable properties are essential components for the miniaturization of powerful optical technologies such as adaptive optics and spatial light modulators.While the larger counterparts typically rely on mechanical actuation,this can be undesirable in some cases on a microscopic scale due to inherent space restrictions.Here,we present a novel design concept for highly integrated active optical components that employs a combination of resonant plasmonic metasurfaces and the phase-change material Ge3Sb2Te6.In particular,we demonstrate beam switching and bifocal lensing,thus,paving the way for a plethora of active optical elements employing plasmonic metasurfaces,which follow the same design principles.展开更多
In thermoelectrics,phase engineering serves a crucial function in deter-mining the power factor by affecting the band degeneracy.However,for low-symmetry compounds,the mainstream one-step phase manipulation strategy,d...In thermoelectrics,phase engineering serves a crucial function in deter-mining the power factor by affecting the band degeneracy.However,for low-symmetry compounds,the mainstream one-step phase manipulation strategy,depending solely on the valley or orbital degeneracy,is inadequate to attain a high density-of-states effective mass and exceptional zT.Here,we employ a distinctive two-step phase manipulation strategy through stepwise tailoring chemical bonds in GeSe.Initially,we amplify the valley degeneracy via CdTe alloying,which elevates the crystal symmetry from a covalently bonded orthorhombic to a metavalently bonded rhombohedral phase by significantly suppressing the Peierls distortion.Subsequently,we incorporate Pb to trigger the convergence of multivalence bands and further enhance the density-of-states effective mass by moderately restraining the Peierls distortion.Additionally,the atypical metavalent bonding in rhombohedral GeSe enables a high Ge vacancy concentration and a small band effective mass,leading to increased carrier concentration and mobility.This weak chemical bond along with strong lattice anharmonicity also reduces lattice thermal conductivity.Consequently,this unique property ensemble contributes to an outstanding zT of 0.9 at 773 K for Geo.8oPbo.2oSe(CdTe)o.25.This work underscores the pivotal role of the two-step phase manipulation by stepwise tailoring of chemical bonds in improving the thermoelectric performance of p-bonded chalcogenides.展开更多
AgSbTe_(2)-based ternary chalcogenides show excellent thermoelectric performance at low-and middletemperature ranges,yet their practical applications are greatly limited by their intrinsic poor thermodynamic stability...AgSbTe_(2)-based ternary chalcogenides show excellent thermoelectric performance at low-and middletemperature ranges,yet their practical applications are greatly limited by their intrinsic poor thermodynamic stability.In this work,we demonstrate that AgSbTe_(2)-based ternary chalcogenides can be stabilized for service below their decomposition threshold.A series of AgxSb_(2-x)Te_(3-x)(x=1.0,0.9,0.8 and 0.7)samples have been prepared by the melt-quenching method.Among them,phase pure Ag0.9Sb1.1Te2.1 is verified by comprehensive structural characterizations from macroscale by X-ray diffraction to microscale by energy-dispersive spectroscopy and then to sub-nanometer scale by atom probe tomography.This composition is further chosen for the stability investigation.The decomposition threshold of Ag_(0.9)Sb_(1.1)Te_(2.1)appears around 473 K.Below this temperature,the chemical compositions and thermoelectric properties are barely changed even after 720 h annealing at 473 K.The figure-of-merit(zT)value of Ag_(0.9)Sb_(1.1)Te_(2.1)below the decomposition threshold is very competitive for real applications even compared with Bi_(2)Te_(3-)based alloys.The average zT of Ag_(0.9)Sb_(1.1)Te_(2.1)at 300e473 K reaches 0.84,which is higher than most other thermoelectric materials in a similar temperature range,promising applications in miniaturized refrigeration and power generation near room temperature.展开更多
Understanding the mechanisms underpinning the charge carrier scattering at grain boundaries is crucial to design thermoelectrics and other electronic materials.Yet,this is a very challenging task due to the complex ch...Understanding the mechanisms underpinning the charge carrier scattering at grain boundaries is crucial to design thermoelectrics and other electronic materials.Yet,this is a very challenging task due to the complex characteristics of grain boundaries and the resulting difficulties in correlating grain boundary structures to local properties.Recent advances in characterizing charge transport across grain boundaries are reviewed,demonstrating how the microstructure,composition,chemical bonding and electrical properties of the same individual grain boundary can be correlated.A much higher potential barrier height is observed in high-angle grain boundaries.This can be ascribed to the larger number density of deep trapping states caused by the local collapse of metavalent bonding.A novel approach to study the influence of the local chemical bonding mechanism around defects on the resulting local properties is thus developed.The results provide insights into the tailoring of electronic properties of metavalently bonded compounds by engineering the characteristics of grain boundaries.展开更多
基金support of National Natural Science Foundation of China(61774123)support of National Natural Science Foundation of China(52150710545)+4 种基金support of their work at CAID.J.-J.W.and M.W.acknowledges financial support from Alexander von Humboldt Foundationfunding from Deutsche Forschungsgemeinschaft within SFB 917“Nanoswitches”support of 111 Project 2.0(BP2018008)the International Joint Laboratory for Micro/Nano Manufacturing and Measurement Technologies of Xi'an Jiaotong Universityprovided by the HPC platform of Xi'an Jiaotong University and the Hefei Advanced Computing Center,and the National Supercomputing Center in Xi'an.
文摘Tailoring the degree of structural disorder in Ge-Sb-Te alloys is important for the development of non-volatile phase-change memory and neuro-inspired computing.Upon crystallization from the amorphous phase,these alloys form a cubic rocksalt-like structure with a high content of intrinsic vacancies.Further thermal annealing results in a gradual structural transition towards a layered structure and an insulator-to-metal transition.In this work,we elucidate the atomic-level details of the structural transition in crystalline GeSb_(2)Te_(4) by in situ high-resolution transmission electron microscopy experiments and ab initio density functional theory calculations,providing a comprehensive real-time and real-space view of the vacancy ordering process.We also discuss the impact of vacancy ordering on altering the electronic and optical properties of GeSb_(2)Te_(4),which is relevant to multilevel storage applications.The phase evolution paths in Ge-Sb-Te alloys and Sb_(2)Te_(3)are illustrated using a summary diagram,which serves as a guide for designing phase-change memory devices.
基金support by the ERC Advanced Grant(COMPLEXPLAS)BMBF(13N9048 and 13N10146)+3 种基金the Baden Württemberg Stiftung(Internationale Spitzenforschung II)DFG(SPP1391,FOR730 and GI 269/11-1)SFB 917(Resistive Nanoswitches)support by the Carl-Zeiss-Stiftung。
文摘Compact nanophotonic elements exhibiting adaptable properties are essential components for the miniaturization of powerful optical technologies such as adaptive optics and spatial light modulators.While the larger counterparts typically rely on mechanical actuation,this can be undesirable in some cases on a microscopic scale due to inherent space restrictions.Here,we present a novel design concept for highly integrated active optical components that employs a combination of resonant plasmonic metasurfaces and the phase-change material Ge3Sb2Te6.In particular,we demonstrate beam switching and bifocal lensing,thus,paving the way for a plethora of active optical elements employing plasmonic metasurfaces,which follow the same design principles.
基金National Natural Science Foundation of China(52071218)National Key R&D Program of China(2021YFB1507403)+2 种基金Shenzhen University 2035 Pro-gram for Excellent Research( 00000218)China Postdoctoral Science Foundation(2022M722170)Y.Y.and M.W.acknowledge support from the German Research Founda tion(Deutsche Forchungsgemeinschaft,DFG)within project SFB917.Y.Y.acknowledges financial support under the Excellence Strategy of the Federal Govemment and the L ander within the ERS RWTH StartUp grant(Grant No.StUpPD_392-21).The authors also appre-ciate the Instrumental Analysis Center of Shenzhen University.
文摘In thermoelectrics,phase engineering serves a crucial function in deter-mining the power factor by affecting the band degeneracy.However,for low-symmetry compounds,the mainstream one-step phase manipulation strategy,depending solely on the valley or orbital degeneracy,is inadequate to attain a high density-of-states effective mass and exceptional zT.Here,we employ a distinctive two-step phase manipulation strategy through stepwise tailoring chemical bonds in GeSe.Initially,we amplify the valley degeneracy via CdTe alloying,which elevates the crystal symmetry from a covalently bonded orthorhombic to a metavalently bonded rhombohedral phase by significantly suppressing the Peierls distortion.Subsequently,we incorporate Pb to trigger the convergence of multivalence bands and further enhance the density-of-states effective mass by moderately restraining the Peierls distortion.Additionally,the atypical metavalent bonding in rhombohedral GeSe enables a high Ge vacancy concentration and a small band effective mass,leading to increased carrier concentration and mobility.This weak chemical bond along with strong lattice anharmonicity also reduces lattice thermal conductivity.Consequently,this unique property ensemble contributes to an outstanding zT of 0.9 at 773 K for Geo.8oPbo.2oSe(CdTe)o.25.This work underscores the pivotal role of the two-step phase manipulation by stepwise tailoring of chemical bonds in improving the thermoelectric performance of p-bonded chalcogenides.
基金supported by the National Natural Science Foundation of China(91963208 and 52122213)Shanghai Government(20JC1415100)+3 种基金Shanghai Pilot Program for Basic Research-Chinese Academy of Science,Shanghai Branch(JCYJ-SHFY-2022-002)the CAS-DOE Program of Chinese Academy of Sciences(121631KYSB20180060)the financial support from DFG SFB 917 projectthe financial support under the Excellence Strategy of the Federal Government and the Lander within the ERS RWTH Start-Up grant(Grant No.StUpPD_392e21).
文摘AgSbTe_(2)-based ternary chalcogenides show excellent thermoelectric performance at low-and middletemperature ranges,yet their practical applications are greatly limited by their intrinsic poor thermodynamic stability.In this work,we demonstrate that AgSbTe_(2)-based ternary chalcogenides can be stabilized for service below their decomposition threshold.A series of AgxSb_(2-x)Te_(3-x)(x=1.0,0.9,0.8 and 0.7)samples have been prepared by the melt-quenching method.Among them,phase pure Ag0.9Sb1.1Te2.1 is verified by comprehensive structural characterizations from macroscale by X-ray diffraction to microscale by energy-dispersive spectroscopy and then to sub-nanometer scale by atom probe tomography.This composition is further chosen for the stability investigation.The decomposition threshold of Ag_(0.9)Sb_(1.1)Te_(2.1)appears around 473 K.Below this temperature,the chemical compositions and thermoelectric properties are barely changed even after 720 h annealing at 473 K.The figure-of-merit(zT)value of Ag_(0.9)Sb_(1.1)Te_(2.1)below the decomposition threshold is very competitive for real applications even compared with Bi_(2)Te_(3-)based alloys.The average zT of Ag_(0.9)Sb_(1.1)Te_(2.1)at 300e473 K reaches 0.84,which is higher than most other thermoelectric materials in a similar temperature range,promising applications in miniaturized refrigeration and power generation near room temperature.
基金The authors acknowledge the financial support from DFG(Deutsche Forschungsgemeinschaft)SFB 917 project.
文摘Understanding the mechanisms underpinning the charge carrier scattering at grain boundaries is crucial to design thermoelectrics and other electronic materials.Yet,this is a very challenging task due to the complex characteristics of grain boundaries and the resulting difficulties in correlating grain boundary structures to local properties.Recent advances in characterizing charge transport across grain boundaries are reviewed,demonstrating how the microstructure,composition,chemical bonding and electrical properties of the same individual grain boundary can be correlated.A much higher potential barrier height is observed in high-angle grain boundaries.This can be ascribed to the larger number density of deep trapping states caused by the local collapse of metavalent bonding.A novel approach to study the influence of the local chemical bonding mechanism around defects on the resulting local properties is thus developed.The results provide insights into the tailoring of electronic properties of metavalently bonded compounds by engineering the characteristics of grain boundaries.
