A new two-dimensional atomic crystal,monolayer cuprous telluride(Cu2Te)has been fabricated on a grapheneSi C(0001)substrate by molecular beam epitaxy(MBE).The low-energy electron diffraction(LEED)characterization show...A new two-dimensional atomic crystal,monolayer cuprous telluride(Cu2Te)has been fabricated on a grapheneSi C(0001)substrate by molecular beam epitaxy(MBE).The low-energy electron diffraction(LEED)characterization shows that the monolayer Cu2Te forms a √3×√3superstructure with respect to the graphene substrate.The atomic structure of the monolayer Cu2Te is investigated through a combination of scanning tunneling microscopy(STM)experiments and density functional theory(DFT)calculations.The stoichiometry of the Cu2Te sample is verified by x-ray photoelectron spectroscopy(XPS)measurement.The angle-resolved photoemission spectroscopy(ARPES)data present the electronic band structure of the sample,which is in good agreement with the calculated results.Furthermore,air-exposure experiments reveal the chemical stability of the monolayer Cu2Te.The fabrication of this new 2D material with a particular structure may bring new physical properties for future applications.展开更多
Binary Cu-based chalcogenide thermoelectric materials have attracted a great deal of attention due to their outstanding physical properties and fascinating phase sequence.However,the relatively low figure of merit z T...Binary Cu-based chalcogenide thermoelectric materials have attracted a great deal of attention due to their outstanding physical properties and fascinating phase sequence.However,the relatively low figure of merit z T restricts their practical applications in power generation.A general approach to enhancing z T value is to produce nanostructured grains,while one disadvantage of such a method is the expansion of grain size in heating-up process.Here,we report a prominent improvement of z T in Cu2Te（0.2）Se（0.8）,which is several times larger than that of the matrix.This significant enhancement in thermoelectric performance is attributed to the formation of abundant porosity via cold press.These pores with nano-to micrometer size can manipulate phonon transport simultaneously,resulting in an apparent suppression of thermal conductivity.Moreover,the Se substitution triggers a rapid promotion of power factor,which compensates for the reduction of electrical properties due to carriers scattering by pores.Our strategy of porosity engineering by phonon scattering can also be highly applicable in enhancing the performances of other thermoelectric systems.展开更多
We report on the fabrication and characterization of multi-leg bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thermoelectric devices. The two materials were deposited, on top of SiO2/Si substrates, using P...We report on the fabrication and characterization of multi-leg bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thermoelectric devices. The two materials were deposited, on top of SiO2/Si substrates, using Pulsed Laser Deposition (PLD). The SiO2 layer was used to provide insulation between the devices and the Si wafer. Copper was used as an electrical connector and a contact for the junctions. Four devices were built, where the Bi2Te3 and Sb2Te3 were deposited at substrate temperatures of 100°C, 200°C, 300°C and 400°C. The results show that the device has a voltage sensitivity of up to 146 μV/K and temperature sensitivity of 6.8 K/mV.展开更多
The effects of annealing process on the electrical conductivity and mechanical properties of Cu-Te alloys were studied via AG-10TA electronic universal machine, SB2230 digital electric bridge, SEM and EDS. The results...The effects of annealing process on the electrical conductivity and mechanical properties of Cu-Te alloys were studied via AG-10TA electronic universal machine, SB2230 digital electric bridge, SEM and EDS. The results show that recrystallization and precipitation occur simultaneously during the annealing process of Cu-Te alloys. Tellurium precipitates as Cu2Te second phase. The grain size increases with the increasing of annealing temperature and time. The electrical conductivity increases monotonously. The tensile strength of Cu-Te alloy is higher than that of pure copper.展开更多
Topological phase transition in a single material usually refers to transitions between a trivial band insulator and a topological Dirac phase, and the transition may also occur between different classes of topologica...Topological phase transition in a single material usually refers to transitions between a trivial band insulator and a topological Dirac phase, and the transition may also occur between different classes of topological Dirac phases.It is a fundamental challenge to realize quantum transition between Z_2 nontrivial topological insulator（TI） and topological crystalline insulator（TCI） in one material because Z_2 TI and TCI have different requirements on the number of band inversions. The Z_2 TIs must have an odd number of band inversions over all the time-reversal invariant momenta, whereas the newly discovered TCIs, as a distinct class of the topological Dirac materials protected by the underlying crystalline symmetry, owns an even number of band inversions. Taking PbSnTe_2 alloy as an example, here we demonstrate that the atomic-ordering is an effective way to tune the symmetry of the alloy so that we can electrically switch between TCI phase and Z_2 TI phase in a single material. Our results suggest that the atomic-ordering provides a new platform towards the realization of reversibly switching between different topological phases to explore novel applications.展开更多
Two-dimensional(2D)layered silicon telluride(SizTes)nanocrystals were compressed to 12 GPa using diamond anvil cell techniques.Optical measurements show a color change from transparent red to opaque black indicating a...Two-dimensional(2D)layered silicon telluride(SizTes)nanocrystals were compressed to 12 GPa using diamond anvil cell techniques.Optical measurements show a color change from transparent red to opaque black indicating a semiconductor-to-metal phase transition.Raman scattering was used to observe the stiffening of the crystal lattice and subsequent phase behavior.A possible phase transition was observed.at 9.5±0.5 GPa evidenced by the disappearance of the Atg stretching mode.SizTes was intercalated with elemental manganese to^1 at.%.Intercalation lowers the pressure of the proposed phase transition to 7.5±1 GPa.Raman modes show both phonon stiffening and phonon softening,suggesting negative linear compressibility.These results provide fundamental insight into the high-pressure optical phonon behavior of silicon telluride and illuminate how a specific electron-donating intercalant can chemically alter pressure-dependent optical phonon behavior.展开更多
Bismuth teUuride （Bi2Te3） is one of the most important commercial thermoelectric materials. In recent years, the discovery of topologically protected surface states in Bi chalcogenides has paved the way for their ap...Bismuth teUuride （Bi2Te3） is one of the most important commercial thermoelectric materials. In recent years, the discovery of topologically protected surface states in Bi chalcogenides has paved the way for their application in nanoelectronics. Determination of the fracture toughness plays a crucial role for the potential application of topological insulators in flexible electronics and nanoelectro- mechanical devices. Using depth-sensing nanoindentation tests, we investigated for the first time the fracture toughness of bulk single crystals of Bi2Te3 topological insulators, grown using the Bridgmantockbarger method. Our results highlight one of the possible pitfalls of the technology based on topological insulators.展开更多
基金Project supported by the National Key Research&Development Program of China(Grant Nos.2016YFA0202300 and 2018YF A0305800)the National Natural Science Foundation of China(Grant Nos.61888102,11604373,61622116,and 51872284)+2 种基金the CAS Pioneer Hundred Talents Program,China,the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB30000000 and XDB28000000)Beijing Nova Program,China(Grant No.Z181100006218023)the University of Chinese Academy of Sciences
文摘A new two-dimensional atomic crystal,monolayer cuprous telluride(Cu2Te)has been fabricated on a grapheneSi C(0001)substrate by molecular beam epitaxy(MBE).The low-energy electron diffraction(LEED)characterization shows that the monolayer Cu2Te forms a √3×√3superstructure with respect to the graphene substrate.The atomic structure of the monolayer Cu2Te is investigated through a combination of scanning tunneling microscopy(STM)experiments and density functional theory(DFT)calculations.The stoichiometry of the Cu2Te sample is verified by x-ray photoelectron spectroscopy(XPS)measurement.The angle-resolved photoemission spectroscopy(ARPES)data present the electronic band structure of the sample,which is in good agreement with the calculated results.Furthermore,air-exposure experiments reveal the chemical stability of the monolayer Cu2Te.The fabrication of this new 2D material with a particular structure may bring new physical properties for future applications.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51771126 and 11774247)the Youth Foundation of Science and Technology Department of Sichuan Province,China(Grant No.2016JQ0051)+2 种基金Sichuan University Outstanding Young Scholars Research Funding(Grant No.2015SCU04A20)the World First-Class University Construction Fundingthe Fundamental and Frontier Research Project in Chongqing(Grant No.CSTC2015JCYJBX0026)
文摘Binary Cu-based chalcogenide thermoelectric materials have attracted a great deal of attention due to their outstanding physical properties and fascinating phase sequence.However,the relatively low figure of merit z T restricts their practical applications in power generation.A general approach to enhancing z T value is to produce nanostructured grains,while one disadvantage of such a method is the expansion of grain size in heating-up process.Here,we report a prominent improvement of z T in Cu2Te（0.2）Se（0.8）,which is several times larger than that of the matrix.This significant enhancement in thermoelectric performance is attributed to the formation of abundant porosity via cold press.These pores with nano-to micrometer size can manipulate phonon transport simultaneously,resulting in an apparent suppression of thermal conductivity.Moreover,the Se substitution triggers a rapid promotion of power factor,which compensates for the reduction of electrical properties due to carriers scattering by pores.Our strategy of porosity engineering by phonon scattering can also be highly applicable in enhancing the performances of other thermoelectric systems.
文摘We report on the fabrication and characterization of multi-leg bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thermoelectric devices. The two materials were deposited, on top of SiO2/Si substrates, using Pulsed Laser Deposition (PLD). The SiO2 layer was used to provide insulation between the devices and the Si wafer. Copper was used as an electrical connector and a contact for the junctions. Four devices were built, where the Bi2Te3 and Sb2Te3 were deposited at substrate temperatures of 100°C, 200°C, 300°C and 400°C. The results show that the device has a voltage sensitivity of up to 146 μV/K and temperature sensitivity of 6.8 K/mV.
基金Project(50201010) supported by the National Natural Science Foundation of China Project(20010610013) supported by Dectoral Subject Foundation of Ministry of Eduction
文摘The effects of annealing process on the electrical conductivity and mechanical properties of Cu-Te alloys were studied via AG-10TA electronic universal machine, SB2230 digital electric bridge, SEM and EDS. The results show that recrystallization and precipitation occur simultaneously during the annealing process of Cu-Te alloys. Tellurium precipitates as Cu2Te second phase. The grain size increases with the increasing of annealing temperature and time. The electrical conductivity increases monotonously. The tensile strength of Cu-Te alloy is higher than that of pure copper.
基金Supported by the Major State Basic Research Development Program of China under Grant No 2016YFB0700700the National Natural Science Foundation of China(NSFC)under Grants Nos 11634003,11474273,61121491 and U1530401+1 种基金supported by the National Young 1000 Talents Plansupported by the Youth Innovation Promotion Association of CAS(2017154)
文摘Topological phase transition in a single material usually refers to transitions between a trivial band insulator and a topological Dirac phase, and the transition may also occur between different classes of topological Dirac phases.It is a fundamental challenge to realize quantum transition between Z_2 nontrivial topological insulator（TI） and topological crystalline insulator（TCI） in one material because Z_2 TI and TCI have different requirements on the number of band inversions. The Z_2 TIs must have an odd number of band inversions over all the time-reversal invariant momenta, whereas the newly discovered TCIs, as a distinct class of the topological Dirac materials protected by the underlying crystalline symmetry, owns an even number of band inversions. Taking PbSnTe_2 alloy as an example, here we demonstrate that the atomic-ordering is an effective way to tune the symmetry of the alloy so that we can electrically switch between TCI phase and Z_2 TI phase in a single material. Our results suggest that the atomic-ordering provides a new platform towards the realization of reversibly switching between different topological phases to explore novel applications.
文摘Two-dimensional(2D)layered silicon telluride(SizTes)nanocrystals were compressed to 12 GPa using diamond anvil cell techniques.Optical measurements show a color change from transparent red to opaque black indicating a semiconductor-to-metal phase transition.Raman scattering was used to observe the stiffening of the crystal lattice and subsequent phase behavior.A possible phase transition was observed.at 9.5±0.5 GPa evidenced by the disappearance of the Atg stretching mode.SizTes was intercalated with elemental manganese to^1 at.%.Intercalation lowers the pressure of the proposed phase transition to 7.5±1 GPa.Raman modes show both phonon stiffening and phonon softening,suggesting negative linear compressibility.These results provide fundamental insight into the high-pressure optical phonon behavior of silicon telluride and illuminate how a specific electron-donating intercalant can chemically alter pressure-dependent optical phonon behavior.
文摘Bismuth teUuride （Bi2Te3） is one of the most important commercial thermoelectric materials. In recent years, the discovery of topologically protected surface states in Bi chalcogenides has paved the way for their application in nanoelectronics. Determination of the fracture toughness plays a crucial role for the potential application of topological insulators in flexible electronics and nanoelectro- mechanical devices. Using depth-sensing nanoindentation tests, we investigated for the first time the fracture toughness of bulk single crystals of Bi2Te3 topological insulators, grown using the Bridgmantockbarger method. Our results highlight one of the possible pitfalls of the technology based on topological insulators.
