Monolayer MnTe_(2)stabilized as 1 T structure has been theoretically predicted to be a two-dimensional(2 D)ferromagnetic metal and can be tuned via strain engineering.There is no naturally van der Waals(vdW)layered Mn...Monolayer MnTe_(2)stabilized as 1 T structure has been theoretically predicted to be a two-dimensional(2 D)ferromagnetic metal and can be tuned via strain engineering.There is no naturally van der Waals(vdW)layered MnTe_(2)bulk,leaving mechanical exfoliation impossible to prepare monolayer MnTe_(2).Herein,by means of molecular beam epitaxy(MBE),we successfully prepared monolayer hexagonal MnTe_(2)on Si(111)under Te rich condition.Sharp reflection high-energy electron diffraction(RHEED)and low-energy electron diffraction(LEED)patterns suggest the monolayer is atomically flat without surface reconstruction.The valence state of Mn^(4+)and the atom ratio of([Te]:[Mn])further confirm the MnTe_(2)compound.Scanning tunneling spectroscopy(STS)shows the hexagonal MnTe_(2)monolayer is a semiconductor with a large bandgap of~2.78 eV.The valence-band maximum(VBM)locates at theΓpoint,as illustrated by angle-resolved photoemission spectroscopy(ARPES),below which three hole-type bands with parabolic dispersion can be identified.The successful synthesis of monolayer MnTe_(2)film provides a new platform to investigate the 2D magnetism.展开更多
Semiconducting manganese ditelluride(MnTe_(2))crystalizes in a high symmetry cubic structure with sufficient band gap and consists of nontoxic elements only,therefore is focused on in this work for its potential therm...Semiconducting manganese ditelluride(MnTe_(2))crystalizes in a high symmetry cubic structure with sufficient band gap and consists of nontoxic elements only,therefore is focused on in this work for its potential thermoelectric applications.This material intrinsically comes with a very low hole concentration of 10^(19)cm^(-3),which can be successfully increased to 4×10^(20)cm^(-3)through Ag-doping at Mn site.Such a broad carrier concentration enables an effective optimization on thermoelectric power factor,and the doping process effectively reduces the lattice thermal conductivity down to~0.5 W/m-K due to the phonons scattered by additional point defects.As a result,a peak zT of~0.7 is obtained in p-type conduction.Moreover,the SPB model with acoustic scattering estimates the electronic properties well,which also enables insight into the underlying physical parameters related to the thermoelectric performance.Importantly,band structure calculation suggests a potentially higher thermoelectric performance for n-type conduction due to both higher band degeneracy and lower band effective mass.This work reveals MnTe_(2)is a novel promising thermoelectric material.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11604366,11634007,21872099,and 22072102)the National Natural Science Foundation of Jiangsu Province,China(Grant No.BK 20160397)support from the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2017370)。
文摘Monolayer MnTe_(2)stabilized as 1 T structure has been theoretically predicted to be a two-dimensional(2 D)ferromagnetic metal and can be tuned via strain engineering.There is no naturally van der Waals(vdW)layered MnTe_(2)bulk,leaving mechanical exfoliation impossible to prepare monolayer MnTe_(2).Herein,by means of molecular beam epitaxy(MBE),we successfully prepared monolayer hexagonal MnTe_(2)on Si(111)under Te rich condition.Sharp reflection high-energy electron diffraction(RHEED)and low-energy electron diffraction(LEED)patterns suggest the monolayer is atomically flat without surface reconstruction.The valence state of Mn^(4+)and the atom ratio of([Te]:[Mn])further confirm the MnTe_(2)compound.Scanning tunneling spectroscopy(STS)shows the hexagonal MnTe_(2)monolayer is a semiconductor with a large bandgap of~2.78 eV.The valence-band maximum(VBM)locates at theΓpoint,as illustrated by angle-resolved photoemission spectroscopy(ARPES),below which three hole-type bands with parabolic dispersion can be identified.The successful synthesis of monolayer MnTe_(2)film provides a new platform to investigate the 2D magnetism.
基金This work is supported by the National Natural Science Foundation of China(Grant No.11474219 and 51772215)the National Recruitment Program of Global Youth Experts(1000 Plan)and the Fok Ying Tung Education Foundation(Grant No.20170072210001)CW and YC acknowledge the financial support from the Early Career Scheme of RGC under Project Number 27202516 and the research computing facilities offered by ITS,HKU.
文摘Semiconducting manganese ditelluride(MnTe_(2))crystalizes in a high symmetry cubic structure with sufficient band gap and consists of nontoxic elements only,therefore is focused on in this work for its potential thermoelectric applications.This material intrinsically comes with a very low hole concentration of 10^(19)cm^(-3),which can be successfully increased to 4×10^(20)cm^(-3)through Ag-doping at Mn site.Such a broad carrier concentration enables an effective optimization on thermoelectric power factor,and the doping process effectively reduces the lattice thermal conductivity down to~0.5 W/m-K due to the phonons scattered by additional point defects.As a result,a peak zT of~0.7 is obtained in p-type conduction.Moreover,the SPB model with acoustic scattering estimates the electronic properties well,which also enables insight into the underlying physical parameters related to the thermoelectric performance.Importantly,band structure calculation suggests a potentially higher thermoelectric performance for n-type conduction due to both higher band degeneracy and lower band effective mass.This work reveals MnTe_(2)is a novel promising thermoelectric material.
