Polycrystalline pyrochlore Lu2Ti2O7 pellets are irradiated with 600-keV Kr^3＋ions up to a fluence of 1.45 ×10^16Kr^3＋/cm^2. Irradiation induced structural modifications are examined by using grazing incidence x...Polycrystalline pyrochlore Lu2Ti2O7 pellets are irradiated with 600-keV Kr^3＋ions up to a fluence of 1.45 ×10^16Kr^3＋/cm^2. Irradiation induced structural modifications are examined by using grazing incidence x-ray diffraction（GIXRD） and cross-sectional transmission electron microscopy（TEM）. The GIXRD reveals that amorphous fraction increases with the increase of fluences up to 2 × 10^15Kr^3＋/cm^2, and the results are explained with a direct-impact model.However, when the irradiation fluence is higher than 2 × 10^15Kr^3＋/cm^2, the amorphous fraction reaches a saturation of-80%. Further TEM observations imply that nano-crystal is formed with a diameter of -10 nm within the irradiation layer at a fluence of 4 × 10^15Kr^3＋/cm^2. No full amorphization is achieved even at the highest fluence of 1.45 × 10^16Kr^3＋/cm^2（-36 displacement per atom）. The high irradiation resistance of pyrochlore Lu2Ti2O7 at higher fluence is explained on the basis of enhanced radiation tolerance of nano-crystal structure.展开更多
Three-dimensional(3 D)topological insulators(TIs)are candidate materials for various electronic and spintronic devices due to their strong spin-orbit coupling and unique surface electronic structure.Rapid,low-cost pre...Three-dimensional(3 D)topological insulators(TIs)are candidate materials for various electronic and spintronic devices due to their strong spin-orbit coupling and unique surface electronic structure.Rapid,low-cost preparation of large-area TI thin films compatible with conventional semiconductor technology is the key to the practical applications of TIs.Here we show that wafer-sized Bi2Te3 family TI and magnetic TI films with decent quality and well-controlled composition and properties can be prepared on amorphous SiO2/Si substrates by magnetron cosputtering.The SiO2/Si substrates enable us to electrically tune(Bi1-xSbx)2Te3 and Cr-doped(Bi1-xSbx)2 Te3 TI films between p-type and n-type behavior and thus study the phenomena associated with topological surface states,such as the quantum anomalous Hall effect(QAHE).This work significantly facilitates the fabrication of TI-based devices for electronic and spintronic applications.展开更多
The valley splitting has been realized in the graphene/Ni heterostructure with the splitting value of 14 meV,and the obtained valley injecting efficiency from the heterostructure into graphene was 6.18%[Phys.Rev.B 921...The valley splitting has been realized in the graphene/Ni heterostructure with the splitting value of 14 meV,and the obtained valley injecting efficiency from the heterostructure into graphene was 6.18%[Phys.Rev.B 92115404(2015)].In this paper,we report a way to improve the valley splitting and the valley injecting efficiency of the graphene/Ni heterostructure.By intercalating an Au monolayer between the graphene and the Ni,the split can be increased up to 50 meV.However,the valley injecting efficiency is not improved because the splitted valley area of graphene moves away from the Fermi level.Then,we mend the deviation by covering a monolayer of Cu on the graphene.As a result,the valley injecting efficiency of the Cu/graphene/Au/Ni heterostructure reaches 10%,which is more than 60%improvement compared to the simple graphene/Ni heterostructure.Then we theoretically design a valley-injection device based on the Cu/graphene/Au/Ni heterostructure and demonstrate that the valley injection can be easily switched solely by changing the magnetization direction of Ni,which can be used to generate and control the valley-polarized current.展开更多
A well-established method is highly desirable for growing topological insulator thin films with low carrier density on a wafer-level scale. Here, we present a simple, scalable method based on magnetron sputtering to o...A well-established method is highly desirable for growing topological insulator thin films with low carrier density on a wafer-level scale. Here, we present a simple, scalable method based on magnetron sputtering to obtain high-quality Bi_(2) Te_(3) films with the carrier density down to 4.0 × 10^(13) cm^(-2). In contrast to the most-used method of high substrate temperature growth, we firstly sputtered Bi_(2) Te_(3) thin films at room temperature and then applied post-annealing. It enables the growth of highly-oriented Bi_(2) Te_(3) thin films with larger grain size and smoother interface. The results of electrical transport show that it has a lower carrier density as well as a larger coherent length(~ 228 nm, 2 K). Our studies pave the way toward large-scale, cost-effective production of Bi_(2) Te_(3) thin films to be integrated with other materials in wafer-level scale for electronic and spintronic applications.展开更多
基金Project sponsored by the National Natural Science Foundation of China(Grant No.11205128)the Fundamental Research Funds for the Central UniversitiesChina(Grant No.2012121034)
文摘Polycrystalline pyrochlore Lu2Ti2O7 pellets are irradiated with 600-keV Kr^3＋ions up to a fluence of 1.45 ×10^16Kr^3＋/cm^2. Irradiation induced structural modifications are examined by using grazing incidence x-ray diffraction（GIXRD） and cross-sectional transmission electron microscopy（TEM）. The GIXRD reveals that amorphous fraction increases with the increase of fluences up to 2 × 10^15Kr^3＋/cm^2, and the results are explained with a direct-impact model.However, when the irradiation fluence is higher than 2 × 10^15Kr^3＋/cm^2, the amorphous fraction reaches a saturation of-80%. Further TEM observations imply that nano-crystal is formed with a diameter of -10 nm within the irradiation layer at a fluence of 4 × 10^15Kr^3＋/cm^2. No full amorphization is achieved even at the highest fluence of 1.45 × 10^16Kr^3＋/cm^2（-36 displacement per atom）. The high irradiation resistance of pyrochlore Lu2Ti2O7 at higher fluence is explained on the basis of enhanced radiation tolerance of nano-crystal structure.
基金National Key R&D Plan Program of China(Grant No.2017YFF0206104)National Key Scien-tific Research Projects of China(Grant No.2015CB921502)+3 种基金National Natural Science Foundation of China(Grant Nos.61574169 and 51871018)Beijing Laboratory of Metallic Materials and Processing for Modern Transportation,the Opening Project of Key Laboratory of Microelectronics Devices&Integrated Technology,Institute of Microelectronics of Chinese Academy of SciencesBeijing Natural Science Foundation(Grant No.Z180014)Beijing Outstanding Young Scientists Projects(Grant No.BJJWZYJH01201910005018)。
文摘Three-dimensional(3 D)topological insulators(TIs)are candidate materials for various electronic and spintronic devices due to their strong spin-orbit coupling and unique surface electronic structure.Rapid,low-cost preparation of large-area TI thin films compatible with conventional semiconductor technology is the key to the practical applications of TIs.Here we show that wafer-sized Bi2Te3 family TI and magnetic TI films with decent quality and well-controlled composition and properties can be prepared on amorphous SiO2/Si substrates by magnetron cosputtering.The SiO2/Si substrates enable us to electrically tune(Bi1-xSbx)2Te3 and Cr-doped(Bi1-xSbx)2 Te3 TI films between p-type and n-type behavior and thus study the phenomena associated with topological surface states,such as the quantum anomalous Hall effect(QAHE).This work significantly facilitates the fabrication of TI-based devices for electronic and spintronic applications.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFF0206104)the National Natural Science Foundation of China(Grant No.51871018)+1 种基金Beijing Laboratory of Metallic Materials and Processing for Modern Transportation,the Opening Project of Key Laboratory of Microelec-tronics Devices&Integrated Technology,Institute of Microelectronics of Chinese Academy of Sciences,Beijing Natural Science Foundation,China(Grant No.Z180014)Beijing Outstanding Young Scientists Projects,China(Grant No.BJJWZYJH01201910005018).We gratefully acknowledge the Chinese Academy of Sciences for providing computation facilities.
文摘The valley splitting has been realized in the graphene/Ni heterostructure with the splitting value of 14 meV,and the obtained valley injecting efficiency from the heterostructure into graphene was 6.18%[Phys.Rev.B 92115404(2015)].In this paper,we report a way to improve the valley splitting and the valley injecting efficiency of the graphene/Ni heterostructure.By intercalating an Au monolayer between the graphene and the Ni,the split can be increased up to 50 meV.However,the valley injecting efficiency is not improved because the splitted valley area of graphene moves away from the Fermi level.Then,we mend the deviation by covering a monolayer of Cu on the graphene.As a result,the valley injecting efficiency of the Cu/graphene/Au/Ni heterostructure reaches 10%,which is more than 60%improvement compared to the simple graphene/Ni heterostructure.Then we theoretically design a valley-injection device based on the Cu/graphene/Au/Ni heterostructure and demonstrate that the valley injection can be easily switched solely by changing the magnetization direction of Ni,which can be used to generate and control the valley-polarized current.
基金supported by the National Natural Science Foundation of China (Grant Nos. 52072030, 52071025, and 51871018)the Beijing Outstanding Young Scientists Projects (Grant No. BJJWZYJH01201910005018)+2 种基金Beijing Natural Science Foundation,China (Grant No. Z180014)the Science and Technology Innovation Team Program of Foshan (Grant No. FSOAA-KJ919-4402-0087)Beijing Laboratory of Metallic Materials and Processing for Modern Transportation。
文摘A well-established method is highly desirable for growing topological insulator thin films with low carrier density on a wafer-level scale. Here, we present a simple, scalable method based on magnetron sputtering to obtain high-quality Bi_(2) Te_(3) films with the carrier density down to 4.0 × 10^(13) cm^(-2). In contrast to the most-used method of high substrate temperature growth, we firstly sputtered Bi_(2) Te_(3) thin films at room temperature and then applied post-annealing. It enables the growth of highly-oriented Bi_(2) Te_(3) thin films with larger grain size and smoother interface. The results of electrical transport show that it has a lower carrier density as well as a larger coherent length(~ 228 nm, 2 K). Our studies pave the way toward large-scale, cost-effective production of Bi_(2) Te_(3) thin films to be integrated with other materials in wafer-level scale for electronic and spintronic applications.
