The influences of the spacer-layer Ta on the structures and magnetic properties of NdFeB/NdCeFeB multilayer films are investigated via DC sputtering under an Ar pressure of 1.2 Pa. An obvious （00l） texture of the ha...The influences of the spacer-layer Ta on the structures and magnetic properties of NdFeB/NdCeFeB multilayer films are investigated via DC sputtering under an Ar pressure of 1.2 Pa. An obvious （00l） texture of the hard phase is observed in each of the films, which indicates that the main phase of the film does not significantly change with Ta spacer-layer thickness. As a result, both the remanence and the saturation magnetization of the magnet first increase and then decrease, and the maximum values of 4π Mr and Hcj are 10.4 kGs （1 Gs=10^-4 T） and 15.0 kOe （1 Oe=79.5775 A·m^-1） for the film with a 2-nm-thick Ta spacer-layer, respectively, where the crystalline structures are columnar shape particles. The measured relationship between irreversible portion D （H）=-△ Mirr/2Mr and H indicates that the nucleation field of the film decreases with spacer layer thickness increasing, owing to slightly disordered grains near the interface between different magnetic layers.展开更多
We theoretically study the influence of spacer layer thickness fluctuation（SLTF） on the mobility of a twodimensional electron gas（2DEG） in the modulation-doped Al x Ga 1 x As/GaAs/Al x Ga 1 x As quantum well.The d...We theoretically study the influence of spacer layer thickness fluctuation（SLTF） on the mobility of a twodimensional electron gas（2DEG） in the modulation-doped Al x Ga 1 x As/GaAs/Al x Ga 1 x As quantum well.The dependence of the mobility limited by SLTF scattering on spacer layer thickness and donor density are obtained.The results show that SLTF scattering is an important scattering mechanism for the quantum well structure with a thick well layer.展开更多
Different than covalently bonded magnetic multilayer systems,high-quality interfaces without dangling bonds in van der Waals(vd W)junctions of two-dimensional(2D)layered magnetic materials offer opportunities to reali...Different than covalently bonded magnetic multilayer systems,high-quality interfaces without dangling bonds in van der Waals(vd W)junctions of two-dimensional(2D)layered magnetic materials offer opportunities to realize novel functionalities.Here,we report the fabrication of multi-state vertical spin valves without spacer layers by using vd W homo-junctions in which exfoliated Fe3GeTe2 nanoflakes act as ferromagnetic electrodes and/or interlayers.We demonstrate the typical behavior of two-state and threestate magnetoresistance for devices with two and three Fe3GeTe2 nanoflakes,respectively.Distinct from traditional spin valves with sandwich structures,our novel homo-junction-based spin-valve structure allows the straightforward realization of multi-state magnetic devices.Our work demonstrates the possibility of extend multi-state,non-volatile spin information to 2 D magnetic homo-junctions,and it emphasizes the utility of vd W interface as a fundamental building block for spintronic devices.展开更多
A novel structure of 4H-SiC MESFETs is proposed that focuses on surface trap suppression.Characteristics of the device have been investigated based on physical models for material properties and improved trap models.B...A novel structure of 4H-SiC MESFETs is proposed that focuses on surface trap suppression.Characteristics of the device have been investigated based on physical models for material properties and improved trap models.By comparing with the performance of the well-utilized buried-gate incorporated with a field-plate （BG-FP） structure,it is shown that the proposed structure improves device properties in comprehensive aspects. A p-type spacer layer introduced in the channel layer suppresses the surface trap effect and reduces the gate-drain capacitance（C_（gd）） under a large drain voltage.A p-type spacer layer incorporated with a field-plate improves the electric field distribution on the gate edge while the spacer layer induces less C_（gd） than a conventional FP.For microwave applications,4H-SiC MESFET for the proposed structure has a larger gate-lag ratio in the saturation region due to better surface trap isolation from the conductive channel.For high power applications,the proposed structure is able to endure higher operating voltage as well.The maximum saturation current density of 460 mA/mm is yielded.Also,the gate-lag ratio under a drain voltage of 20 V is close to 90%.In addition,5%and 17.8%improvements in f_T and f_（max） are obtained compared with a BG-FP MESFET in AC simulation,respectively.Parameters and dimensions of the proposed structure are optimized to make the best of the device for microwave applications and to provide a reference for device design.展开更多
Uncapped double stacked In0.5Ga0.5As quantum dots（QDs） with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition（MOCVD）.The precursors used for the growth of the GaAs layer ...Uncapped double stacked In0.5Ga0.5As quantum dots（QDs） with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition（MOCVD）.The precursors used for the growth of the GaAs layer and In0.5Ga0.5As QDs were trimethylgallium（TMGa）,trimethylindium（TMIn）,and arsine（AsH3）.The morphology and optical properties of the self-assembled In0.5Ga0.5As QDs were investigated and characterized using atomic force microscopy（AFM） and photoluminescence（PL）.The AFM images revealed that the sizes of the dots on the topmost were not uniformly distributed.The average size of the dots fluctuated as the GaAs spacer layer thickness increased.A room temperature PL measurement was used to establish the quality and quantity of the stacked QDs.The PL peak position remained at 1148 nm for all samples of QDs;however,the PL intensity increased as spacer layer thickness increased.The structure of the spacer layer in the stacked QD affected the morphology of the topmost surface of the QDs.The PL measurement coherently reflected the AFM characterization,in which the strong PL spectra were caused by the uniformity and high density of the QDs.The surface morphology,structure,and optical properties of the stacked QDs are attributed to seed-layer（first layer） formation of dots and spacer layer structures.展开更多
Iron-based superconductors include pnictides and chalcogenides.So far,the chalcogenides are much fewer in number[1],thus it is particularly valuable to find new superconductors in iron chalcogenides,for the'ultima...Iron-based superconductors include pnictides and chalcogenides.So far,the chalcogenides are much fewer in number[1],thus it is particularly valuable to find new superconductors in iron chalcogenides,for the'ultimate'understanding of iron-based superconductivity.The tetragonal binary iron selenide(β-Fe1+δSe)is the structurally simplest iron-based superconductor with a superconducting critical temperature(Tc)of 8.5 K at ambient pressure[2].By intercalation of alkali metal ions into展开更多
基金supported by the Major State Basic Research Development Program of China(Grant No.2014CB643701)the General Program of the National Natural Science Foundation of China(Grant No.51571064)
文摘The influences of the spacer-layer Ta on the structures and magnetic properties of NdFeB/NdCeFeB multilayer films are investigated via DC sputtering under an Ar pressure of 1.2 Pa. An obvious （00l） texture of the hard phase is observed in each of the films, which indicates that the main phase of the film does not significantly change with Ta spacer-layer thickness. As a result, both the remanence and the saturation magnetization of the magnet first increase and then decrease, and the maximum values of 4π Mr and Hcj are 10.4 kGs （1 Gs=10^-4 T） and 15.0 kOe （1 Oe=79.5775 A·m^-1） for the film with a 2-nm-thick Ta spacer-layer, respectively, where the crystalline structures are columnar shape particles. The measured relationship between irreversible portion D （H）=-△ Mirr/2Mr and H indicates that the nucleation field of the film decreases with spacer layer thickness increasing, owing to slightly disordered grains near the interface between different magnetic layers.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60976008,61006004,61076001,and10979507)the National Basic Research Program of China (Grant No. A000091109-05)the National High Technology Research and Development Program of China (Grant No. 2011AA03A101)
文摘We theoretically study the influence of spacer layer thickness fluctuation（SLTF） on the mobility of a twodimensional electron gas（2DEG） in the modulation-doped Al x Ga 1 x As/GaAs/Al x Ga 1 x As quantum well.The dependence of the mobility limited by SLTF scattering on spacer layer thickness and donor density are obtained.The results show that SLTF scattering is an important scattering mechanism for the quantum well structure with a thick well layer.
基金supported by the National Key R&D Program of China (2017YFA0303400 and 2017YFB0405700)the National Natural Science foundation of China (61774144)+2 种基金Beijing Natural Science Foundation Key Program (Z190007)the Project from Chinese Academy of Sciences (QYZDY-SSW-JSC020, XDPB12, and XDB28000000)K C Wong Education Foundation。
文摘Different than covalently bonded magnetic multilayer systems,high-quality interfaces without dangling bonds in van der Waals(vd W)junctions of two-dimensional(2D)layered magnetic materials offer opportunities to realize novel functionalities.Here,we report the fabrication of multi-state vertical spin valves without spacer layers by using vd W homo-junctions in which exfoliated Fe3GeTe2 nanoflakes act as ferromagnetic electrodes and/or interlayers.We demonstrate the typical behavior of two-state and threestate magnetoresistance for devices with two and three Fe3GeTe2 nanoflakes,respectively.Distinct from traditional spin valves with sandwich structures,our novel homo-junction-based spin-valve structure allows the straightforward realization of multi-state magnetic devices.Our work demonstrates the possibility of extend multi-state,non-volatile spin information to 2 D magnetic homo-junctions,and it emphasizes the utility of vd W interface as a fundamental building block for spintronic devices.
基金Project supported by the Pre-research Foundation of China(No.51308030201)the Special Foundation,China(No.9140A080509DZ0106)the Fundamental Research Funds for the Central Universities,China
文摘A novel structure of 4H-SiC MESFETs is proposed that focuses on surface trap suppression.Characteristics of the device have been investigated based on physical models for material properties and improved trap models.By comparing with the performance of the well-utilized buried-gate incorporated with a field-plate （BG-FP） structure,it is shown that the proposed structure improves device properties in comprehensive aspects. A p-type spacer layer introduced in the channel layer suppresses the surface trap effect and reduces the gate-drain capacitance（C_（gd）） under a large drain voltage.A p-type spacer layer incorporated with a field-plate improves the electric field distribution on the gate edge while the spacer layer induces less C_（gd） than a conventional FP.For microwave applications,4H-SiC MESFET for the proposed structure has a larger gate-lag ratio in the saturation region due to better surface trap isolation from the conductive channel.For high power applications,the proposed structure is able to endure higher operating voltage as well.The maximum saturation current density of 460 mA/mm is yielded.Also,the gate-lag ratio under a drain voltage of 20 V is close to 90%.In addition,5%and 17.8%improvements in f_T and f_（max） are obtained compared with a BG-FP MESFET in AC simulation,respectively.Parameters and dimensions of the proposed structure are optimized to make the best of the device for microwave applications and to provide a reference for device design.
基金Supported by the Ministry of Science,Technology and Innovationof Malaysia
文摘Uncapped double stacked In0.5Ga0.5As quantum dots（QDs） with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition（MOCVD）.The precursors used for the growth of the GaAs layer and In0.5Ga0.5As QDs were trimethylgallium（TMGa）,trimethylindium（TMIn）,and arsine（AsH3）.The morphology and optical properties of the self-assembled In0.5Ga0.5As QDs were investigated and characterized using atomic force microscopy（AFM） and photoluminescence（PL）.The AFM images revealed that the sizes of the dots on the topmost were not uniformly distributed.The average size of the dots fluctuated as the GaAs spacer layer thickness increased.A room temperature PL measurement was used to establish the quality and quantity of the stacked QDs.The PL peak position remained at 1148 nm for all samples of QDs;however,the PL intensity increased as spacer layer thickness increased.The structure of the spacer layer in the stacked QD affected the morphology of the topmost surface of the QDs.The PL measurement coherently reflected the AFM characterization,in which the strong PL spectra were caused by the uniformity and high density of the QDs.The surface morphology,structure,and optical properties of the stacked QDs are attributed to seed-layer（first layer） formation of dots and spacer layer structures.
文摘Iron-based superconductors include pnictides and chalcogenides.So far,the chalcogenides are much fewer in number[1],thus it is particularly valuable to find new superconductors in iron chalcogenides,for the'ultimate'understanding of iron-based superconductivity.The tetragonal binary iron selenide(β-Fe1+δSe)is the structurally simplest iron-based superconductor with a superconducting critical temperature(Tc)of 8.5 K at ambient pressure[2].By intercalation of alkali metal ions into
