Epitaxial growth and air-stability of monolayer Cu2Te

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 ■ superstructure 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.

Se substitution and micro-nano-scale porosity enhancing thermoelectric Cu2Te

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.

CuTe,Cu_2和Cu_2Te的结构与势能函数

在Cu和Te的RECP(Relativistic Effective Core Potential)近似下,运用B3LYP方法,在LANL2DZ基组水平上对CuTe,Cu2和Cu2Te分子体系的结构进行优化计算.结果表明,CuTe和Cu2分子的基电子状态分别为2Π和1∑g+,Cu2Te分子的基态为单重态的C2V构型,其电子状态为1A1.同时还计算了Cu2Te分子基态的离解能、力常数和振动频率.采用最小二乘法拟合出CuTe和Cu2分子Murrell-Sorbie势能函数参数.在此基础上,运用多体展式理论方法导出Cu2Te分子基态势能函数的解析表达式,其势能面准确复现了平衡态的结构特征.

Effects of annealing process on electrical conductivity and mechanical property of Cu-Te alloys

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.

Cu-Te合金的退火工艺

研究了退火工艺对Te含量分别为0.02%、0.07%、0.10%的3种Cu-Te合金的力学与导电性能及组织的影响,测试了不同退火温度和不同退火时间下合金的力学性能和导电性能,使用扫描电镜(SEM)研究了Cu-Te合金在不同退火温度下拉伸断口的形貌变化。结果表明:Cu-Te合金断裂属于韧性断裂,断裂形成的韧窝随着退火温度的上升,尺寸变得越大、越深,形状变得更加圆整;随着退火温度与退火时间的增加,Cu-Te合金的导电率持续增加,抗拉强度在350~390℃退火1 h时变化不大,合金处于回复阶段,400℃退火1 h后,抗拉强度大幅度下降,合金处于再结晶阶段;Cu-Te合金经过冷变形(ε=96.5%)后,在400℃退火1 h,获得最佳的综合性能。