The structure of a heterojunction made up of an （8, 0） carbon nanotube and an （8, 0） boron nitride nanotube is achieved through geometry optimization implemented in the CASTEP package. Based on the optimized geome...The structure of a heterojunction made up of an （8, 0） carbon nanotube and an （8, 0） boron nitride nanotube is achieved through geometry optimization implemented in the CASTEP package. Based on the optimized geometry, the model of the heterojunction is established. Its transport properties are investigated by combining the nonequilibrium Green＇s function with density functional theory. Results show that both the lowest unoccupied molecular orbital and the highest occupied molecular orbital mainly locate on the carbon nanotube section. In the current-voltage characteristic of the heterojunction, a rectification feature is revealed.展开更多
A two-probe system of the heterojunction formed by an （8, 0） carbon nanotube （CNT） and an （8, 0） silicon carbide nanotube （SiCNT） was established based on its optimized structure. By using a method combining n...A two-probe system of the heterojunction formed by an （8, 0） carbon nanotube （CNT） and an （8, 0） silicon carbide nanotube （SiCNT） was established based on its optimized structure. By using a method combining nonequilibrium Green＇s function （NEGF） with density functional theory （DFF）, the transport properties of the het-erojunction were investigated. Our study reveals that the highest occupied molecular orbital （HOMO） has a higher electron density on the CNT section and the lowest unoccupied molecular orbital （LUMO） mainly concentrates on the interface and the SiCNT section. The positive and negative threshold voltages are ＋1.8 and -2.2 V, respectively.展开更多
The electronic transport properties of the armchair silicon carbide nanotube（SiCNT） are investigated by using the combined nonequilibrium Green＇s function method with density functional theory.In the equilibrium tr...The electronic transport properties of the armchair silicon carbide nanotube（SiCNT） are investigated by using the combined nonequilibrium Green＇s function method with density functional theory.In the equilibrium transmission spectrum of the nanotube,a transmission valley of about 2.12 eV is discovered around Fermi energy,which means that the nanotube is a wide band gap semiconductor and consistent with results of first principle calculations. More important,negative differential resistance is found in its current voltage characteristic.This phenomenon originates from the variation of density of states caused by applied bias voltage.These investigations are meaningful to modeling and simulation in silicon carbide nanotube electronic devices.展开更多
We investigate atomic and electronic structures of boron nanotubes （BNTs） by using the density functional theory （DFT）. The transport properties of BNTs with different diameters and chiralities are studied by the ...We investigate atomic and electronic structures of boron nanotubes （BNTs） by using the density functional theory （DFT）. The transport properties of BNTs with different diameters and chiralities are studied by the Keldysh nonequilibrium Green function （NEGF） method. It is found that the cohesive energies and conductances of BNTs decrease as their diameters decrease. It is more difficult to form （N, 0） tubes than （M, M） tubes when the diameters of the two kinds of tubes are comparable. However, the （N, 0） tubes have a higher conductance than the （M, M） tubes. When the BNTs are connected to gold electrodes, the coupling between the BNTs and the electrodes will affect the transport properties of tubes significantly.展开更多
Using the nonequilibrium Green＇s function method combined with the tight-binding Hamiltonian, we theoretically investigate the spin-dependent transmission probability and spin Seebeck coefficient of a crossed armchai...Using the nonequilibrium Green＇s function method combined with the tight-binding Hamiltonian, we theoretically investigate the spin-dependent transmission probability and spin Seebeck coefficient of a crossed armchair-edge graphene nanoribbon （AGNR） superl＇attice p-n junction under a perpendicular magnetic field with a ferromagnetic insulator, where junction widths Wi of 40 and 41 are considered to exemplify the effect of semiconducting and metallic AGNRs, respectively. A pristine AGNR system is metallic when the transverse layer m = 3j ＋ 2 with a positive integer j and an insulator otherwise. When stubs are present, a semiconducting AGNR junction with width W1= 40 always shows metallic behavior regardless of the potential drop magnitude, magnetization strength, stub length, and per- pendicular magnetic field strength. However, metallic or semiconducting behavior can be obtained from a metallic AGNR junction with Wi = 41 by adjusting these physical parameters. Furthermore, a metal-to-semiconductor transition can be obtained for both superlattice p-n junctions by adjust- ing the number of periods of the superlattice. In addition, the spin-dependent Seebeck coefficient and spin Seebeck coefficient of the two systems are of the same order of magnitude owing to the appearance of a transmission gap, and the maximum absolute value of the spin Seebeck coefficient reaches 370 μV/K when the optimized parameters are used. The calculated results offer new possi- bilities for designing electronic or heat-spintronic nanodevices based on the graphene superlattice p-n junction.展开更多
Very recently,experimental evidence showed that the hydrogen is retained in dithiol-terminated single-molecule junction under the widely adopted preparation conditions,which is in contrast to the accepted view[Nat.Che...Very recently,experimental evidence showed that the hydrogen is retained in dithiol-terminated single-molecule junction under the widely adopted preparation conditions,which is in contrast to the accepted view[Nat.Chem.11351(2019)].However,the hydrogen is generally assumed to be lost in the previous physical models of single-molecule junctions.Whether the retention of the hydrogen at the gold-sulfur interface exerts a significant effect on the theoretical prediction of spin transport properties is an open question.Therefore,here in this paper we carry out a comparative study of spin transport in M-tetraphenylporphyrin-based(M=V,Cr,Mn,Fe,and Co;M-TPP)single-molecule junction through Au-SR and Au-S(H)R bondings.The results show that the hydrogen at the gold-sulfur interface may dramatically affect the spin-filtering efficiency of M-TPP-based single-molecule junction,depending on the type of transition metal ions embedded into porphyrin ring.Moreover,we find that for the Co-TPP-based molecular junction,the hydrogen at the gold-sulfur interface has no obvious effect on transmission at the Fermi level,but it has a significant effect on the spin-dependent transmission dip induced by the quantum interference on the occupied side.Thus the fate of hydrogen should be concerned in the physical model according to the actual preparation condition,which is important for our fundamental understanding of spin transport in the single-molecule junctions.Our work also provides guidance in how to experimentally identify the nature of gold-sulfur interface in the single-molecule junction with spin-polarized transport.展开更多
基金Project supported by the Chinese Defence Advance Research Program of Science and Technology,China (GrantNo. 9140A08060407DZ0103)
文摘The structure of a heterojunction made up of an （8, 0） carbon nanotube and an （8, 0） boron nitride nanotube is achieved through geometry optimization implemented in the CASTEP package. Based on the optimized geometry, the model of the heterojunction is established. Its transport properties are investigated by combining the nonequilibrium Green＇s function with density functional theory. Results show that both the lowest unoccupied molecular orbital and the highest occupied molecular orbital mainly locate on the carbon nanotube section. In the current-voltage characteristic of the heterojunction, a rectification feature is revealed.
基金supported by the Pre-Research Foundation from the National Ministries and Commissions(No.51308040203)
文摘A two-probe system of the heterojunction formed by an （8, 0） carbon nanotube （CNT） and an （8, 0） silicon carbide nanotube （SiCNT） was established based on its optimized structure. By using a method combining nonequilibrium Green＇s function （NEGF） with density functional theory （DFF）, the transport properties of the het-erojunction were investigated. Our study reveals that the highest occupied molecular orbital （HOMO） has a higher electron density on the CNT section and the lowest unoccupied molecular orbital （LUMO） mainly concentrates on the interface and the SiCNT section. The positive and negative threshold voltages are ＋1.8 and -2.2 V, respectively.
基金Project supported by the National Pre-Research Foundation of China(No.51308030201)
文摘The electronic transport properties of the armchair silicon carbide nanotube（SiCNT） are investigated by using the combined nonequilibrium Green＇s function method with density functional theory.In the equilibrium transmission spectrum of the nanotube,a transmission valley of about 2.12 eV is discovered around Fermi energy,which means that the nanotube is a wide band gap semiconductor and consistent with results of first principle calculations. More important,negative differential resistance is found in its current voltage characteristic.This phenomenon originates from the variation of density of states caused by applied bias voltage.These investigations are meaningful to modeling and simulation in silicon carbide nanotube electronic devices.
基金Project supported by the National Natural Science Foundation of China (Grant No 10774176)the National Basic Research Program of China (Grant Nos 2006CB806202 and 2006CB921305)the Shanghai Supercomputing Center,Chinese Academyof Sciences
文摘We investigate atomic and electronic structures of boron nanotubes （BNTs） by using the density functional theory （DFT）. The transport properties of BNTs with different diameters and chiralities are studied by the Keldysh nonequilibrium Green function （NEGF） method. It is found that the cohesive energies and conductances of BNTs decrease as their diameters decrease. It is more difficult to form （N, 0） tubes than （M, M） tubes when the diameters of the two kinds of tubes are comparable. However, the （N, 0） tubes have a higher conductance than the （M, M） tubes. When the BNTs are connected to gold electrodes, the coupling between the BNTs and the electrodes will affect the transport properties of tubes significantly.
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 11704118, 11774085, and 11404230）, the Scientific Research Fund of Hu- nan Provincial Education Department （Grant Nos. 17A193 and17C0946）, the Hunan Provincial Natural Science Foundation of China （Grant No. 2017JJ3210）, and the Foundation of Science and Technology Bureau of Sichuan Province （No. 2013JY0085）.
文摘Using the nonequilibrium Green＇s function method combined with the tight-binding Hamiltonian, we theoretically investigate the spin-dependent transmission probability and spin Seebeck coefficient of a crossed armchair-edge graphene nanoribbon （AGNR） superl＇attice p-n junction under a perpendicular magnetic field with a ferromagnetic insulator, where junction widths Wi of 40 and 41 are considered to exemplify the effect of semiconducting and metallic AGNRs, respectively. A pristine AGNR system is metallic when the transverse layer m = 3j ＋ 2 with a positive integer j and an insulator otherwise. When stubs are present, a semiconducting AGNR junction with width W1= 40 always shows metallic behavior regardless of the potential drop magnitude, magnetization strength, stub length, and per- pendicular magnetic field strength. However, metallic or semiconducting behavior can be obtained from a metallic AGNR junction with Wi = 41 by adjusting these physical parameters. Furthermore, a metal-to-semiconductor transition can be obtained for both superlattice p-n junctions by adjust- ing the number of periods of the superlattice. In addition, the spin-dependent Seebeck coefficient and spin Seebeck coefficient of the two systems are of the same order of magnitude owing to the appearance of a transmission gap, and the maximum absolute value of the spin Seebeck coefficient reaches 370 μV/K when the optimized parameters are used. The calculated results offer new possi- bilities for designing electronic or heat-spintronic nanodevices based on the graphene superlattice p-n junction.
基金the National Natural Science Foundation of China(Grant Nos.11674092,11804093,and 61764005)the Natural Science Foundation of Hunan Province,China(Grant No.2019JJ40006)+2 种基金the Scientific Research Fund of the Education Department of Hunan Province,China(Grant No.18B368)the Science and Technology Development Plan Project of Hengyang City,China(Grant No.2018KJ121)the Science and Technology Plan Project of Hunan Province,China(Grant No.2016TP1020).
文摘Very recently,experimental evidence showed that the hydrogen is retained in dithiol-terminated single-molecule junction under the widely adopted preparation conditions,which is in contrast to the accepted view[Nat.Chem.11351(2019)].However,the hydrogen is generally assumed to be lost in the previous physical models of single-molecule junctions.Whether the retention of the hydrogen at the gold-sulfur interface exerts a significant effect on the theoretical prediction of spin transport properties is an open question.Therefore,here in this paper we carry out a comparative study of spin transport in M-tetraphenylporphyrin-based(M=V,Cr,Mn,Fe,and Co;M-TPP)single-molecule junction through Au-SR and Au-S(H)R bondings.The results show that the hydrogen at the gold-sulfur interface may dramatically affect the spin-filtering efficiency of M-TPP-based single-molecule junction,depending on the type of transition metal ions embedded into porphyrin ring.Moreover,we find that for the Co-TPP-based molecular junction,the hydrogen at the gold-sulfur interface has no obvious effect on transmission at the Fermi level,but it has a significant effect on the spin-dependent transmission dip induced by the quantum interference on the occupied side.Thus the fate of hydrogen should be concerned in the physical model according to the actual preparation condition,which is important for our fundamental understanding of spin transport in the single-molecule junctions.Our work also provides guidance in how to experimentally identify the nature of gold-sulfur interface in the single-molecule junction with spin-polarized transport.
