The on-surface synthesis method allows the fabrication of atomically precise narrow graphene nanoribbons(GNRs),which bears great potential in electronic applications.Here,we synthesize armchair graphene nanoribbons(AG...The on-surface synthesis method allows the fabrication of atomically precise narrow graphene nanoribbons(GNRs),which bears great potential in electronic applications.Here,we synthesize armchair graphene nanoribbons(AGNRs)and chevron-type graphene nanoribbons(CGNRs)array on a vicinal Au(111112)surface using 10,10′-dibromo-9,9′-bianthracene(DBBA)and 6,12-dibromochrysene(DBCh)as precursors,respectively.This process creates spatially wellaligned GNRs,as characterized by scanning tunneling microscopy.AGNRs show strong Raman linear polarizability for application in optical modulation devices.Different from the distinct polarization of AGNRs,only weak polarization exists in CGNRs polarized Raman spectrum,which suggests that the presence of the zigzag boundary in the nanoribbon attenuates the polarization rate as an important factor affecting the polarization.We analyze the Raman activation mode of CGNRs using the peak polarization to expand the application of the polarization Raman spectroscopy in nanoarray analysis.展开更多
We study the valley-dependent electron transport in a four-terminal mesoscopic device of the two monolayer graphene nanoribbons vertically stacked together, where the intersection forms a bilayer graphene lattice with...We study the valley-dependent electron transport in a four-terminal mesoscopic device of the two monolayer graphene nanoribbons vertically stacked together, where the intersection forms a bilayer graphene lattice with a controllable twist angle. Using a tight-binding lattice model, we show that the longitudinal and transverse conductances exhibit significant valley polarization in the low energy regime for small twist angles. As the twist angle increases, the valley polarization shifts to the high energy regime. This arises from the regrouping effect of the electron band in the twisted bilayer graphene region. But for relatively large twist angles, no significant valley polarization is observed. These results are consistent with the spectral densities of the twisted bilayer graphene.展开更多
We calculated the room-temperature phonon thermal conductivity and phonon spectrum of alkyl group-functionalized zigzag graphene nanoribbons(ZGNRs) with molecular dynamics simulations. The increase in both chain lengt...We calculated the room-temperature phonon thermal conductivity and phonon spectrum of alkyl group-functionalized zigzag graphene nanoribbons(ZGNRs) with molecular dynamics simulations. The increase in both chain length and concentration of alkyl groups caused remarkable reduction of phonon thermal conductivity in functionalized ZGNRs. Phonon spectra analysis showed that functionalization of ZGNR with alkyl functional groups induced phonon–structural defect scattering, thus leading to the reduction of phonon thermal conductivity of ZGNR. Our study showed that surface functionalization is an effective routine to tune the phonon thermal conductivity of GNRs, which is useful in graphene thermal-related applications.展开更多
We present a study of electronic properties of zigzag graphene nanoribbons (ZGNRs) substitutionally doped with nitrogen atoms at a single edge by first principle calculations. We find that the two edge states near t...We present a study of electronic properties of zigzag graphene nanoribbons (ZGNRs) substitutionally doped with nitrogen atoms at a single edge by first principle calculations. We find that the two edge states near the Fermi level sepa- rate due to the asymmetric nitrogen-doping. The ground states of these systems become ferromagnetic because the local magnetic moments along the undoped edges remain and those along the doped edges are suppressed. By controlling the charge-doping level, the magnetic moments of the whole ribbons are modulated. Proper charge doping leads to interest- ing half-metallic and single-edge conducting ribbons which would be helpful for designing graphene-nanoribbon-based spintronic devices in the future.展开更多
A sharply transected spinal cord has been shown to be fused under the accelerating influence of membrane fusogens such as polyethylene glycol (PEG) (GEMINI protocol). Previous work provided evidence that this is i...A sharply transected spinal cord has been shown to be fused under the accelerating influence of membrane fusogens such as polyethylene glycol (PEG) (GEMINI protocol). Previous work provided evidence that this is in fact possible. Other fusogens might improve current results. In this study, we aimed to assess the effects of PEGylated graphene nanoribons (PEG-GNR, and called "TexasPEG" when prepared as lwt% dispersion in PEG600) versus placebo (saline) on locomotor function recovery and cellular level in a rat model of spinal cord transection at lumbar segment 1 (L1) level. In vivo and in vitro experiments (n -- 10 per experiment) were designed. In the in vivo experiment, all rats were submitted to full spinal cord transection at L1 level. Five weeks later, behavioral assessment was performed using the Basso Beattie Bresnahan (BBB) locomotor rating scale. Immunohistochemical staining with neuron marker neurofilament 200 (NF200) antibody and astrocyt- ic scar marker glial fibrillary acidic protein (GFAP) was also performed in the injured spinal cord. In the in vitro experiment, the effects of TexasPEG application for 72 hours on the neurite outgrowth of SH-SYSY cells were observed under the inverted microscope. Results of both in vivo and in vitro experiments suggest that TexasPEG reduces the formation of glial scars, promotes the regeneration of neurites, and thereby contributes to the recovery of locomotor function of a rat model of spinal cord transfection.展开更多
We have performed density-functional calculations of the transport properties of the zigzag graphene nanoribbon (ZGNR) adsorbed with a single iron atom. Two adsorption configurations are considered, i.e., iron adsor...We have performed density-functional calculations of the transport properties of the zigzag graphene nanoribbon (ZGNR) adsorbed with a single iron atom. Two adsorption configurations are considered, i.e., iron adsorbed on the edge and on the interior of the nanoribbon. The results show that the transport features of the two configurations are similar. However, the transport properties are modified due to the scattering effects induced by coupling of the ZGNR band states to the localized 3d-orbital state of the iron atom. More importantly, one can find that several dips appear in the transmission curve, which is closely related to the above mentioned coupling. We expect that our results will have potential applications in graphene-based spintronic devices,展开更多
By using first-principles calculations and nonequilibrium Green's function technique, we study elastic transport properties of crossed graphene nanoribbons. The results show that the electronic transport properties o...By using first-principles calculations and nonequilibrium Green's function technique, we study elastic transport properties of crossed graphene nanoribbons. The results show that the electronic transport properties of molecular junctions can be modulated by doped atoms. Negative differential resistance (NDR) behaviour can be observed in a certain bias region, when crossed graphene nanoribbons are doped with nitrogen atoms at the shoulder, but it cannot be observed for pristine crossed graphene nanoribbons at low biases. A mechanism for the negative differential resistance behaviour is suggested.展开更多
The transport properties of hexagonal boron-nitride nanoribbons under the uniaxial strain are investigated by the Green's function method. We find that the transport properties of armchair boron-nitride nanoribbon st...The transport properties of hexagonal boron-nitride nanoribbons under the uniaxial strain are investigated by the Green's function method. We find that the transport properties of armchair boron-nitride nanoribbon strongly depend on the strain. In particular, the features of the conductance steps such as position and width are significantly changed by strain. As a strong tensile strain is exerted on the nanoribbon, the highest conductance step disappears and subsequently a dip emerges instead. The energy band structure and the local current density of armchair boron nitride nanoribbon under strain are calculated and analysed in detail to explain these characteristics. In addition, the effect of strain on the conductance of zigzag boron-nitride nanoribbon is weaker than that of armchair boron nitride nanoribbon.展开更多
This work presents an investigation of nanoribbons cut from β_(12)-borophene sheets by applying the density functional theory. In particular, the electronic and magnetic properties of borophene nanoribbons(BNR) are s...This work presents an investigation of nanoribbons cut from β_(12)-borophene sheets by applying the density functional theory. In particular, the electronic and magnetic properties of borophene nanoribbons(BNR) are studied. It is found that all the ribbons considered in this work behave as metals, which is in good agreement with the recent experimental results. β_(12)-BNR has significant diversity due to the existence of five boron atoms in a unit cell of the sheet. The magnetic properties of the ribbons are strongly dependent on the cutting direction and edge profile. It is interesting that a ribbon with a specific width can behave as a normal or a ferromagnetic metal with magnetization at just one edge or two edges. Spin anisotropy is observed in some ribbons, and the magnetic moment is not found to be the same in both edges in an antiferromagnetic configuration. This effect stems from the edge asymmetry of the ribbons and results in the breaking of spin degeneracy in the band structure. Our findings show that β_(12) BNRs are potential candidates for next-generation spintronic devices.展开更多
Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well wi...Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix. The complex band structure gives extra information on carrier's decay behaviour. The imaginary loop connects the conduction and valence band, and can profoundly affect the characteristics of nanoscale electronic device made with graphene nanoribbons. In this work, the complex band structure calculation includes not only the first nearest neighbour interaction, but also the effects of edge bond relaxation and the third nearest neighbour interaction. The band gap is classified into three classes. Due to the edge bond relaxation and the third nearest neighbour interaction term, it opens a band gap for N = 3M- 1. The band gap is almost unchanged for N =3M + 1, but decreased for N = 3M. The maximum imaginary wave vector length provides additional information about the electrical characteristics of graphene nanoribbons, and is also classified into three classes.展开更多
One-dimensional Cr2NO2 nanoribbons cut from the oxygen-passivated Cr2NO2 MXene were investigated by using density functional theory. The wide nanoribbons have ferromagnetic ground states and are intrinsic half-metals,...One-dimensional Cr2NO2 nanoribbons cut from the oxygen-passivated Cr2NO2 MXene were investigated by using density functional theory. The wide nanoribbons have ferromagnetic ground states and are intrinsic half-metals, independent of their chirality. The half-metallic band gaps of wide nanoribbons are larger than 1 eV, which are large enough for avoiding thermally activated spin flip. The magnetism does not rely on the edge states but originates from all the Cr atoms. Furthermore, the half-metallicity is still robust in an electronic device even if the bias is up to 1 V. Therefore, one-dimensional Cr2NO2 nanoribbons are good candidates for spintronics.展开更多
The electric field effect in ultrathin zigzag graphene nanoribbons containing only three or four zigzag carbon chains is studied by first-principles calculations, and the change of conducting mechanism is observed wit...The electric field effect in ultrathin zigzag graphene nanoribbons containing only three or four zigzag carbon chains is studied by first-principles calculations, and the change of conducting mechanism is observed with increasing in-plane electric field perpendicular to the ribbon. Wider zigzag graphene nanoribbons have been predicted to be spin-splitted for both valence band maximum(VBM) and conduction band minimum(CBM) with an applied electric field and become half-metal due to the vanishing band gap of one spin with increasing applied field. The change of VBM for the ultrathin zigzag graphene nanoribbons is similar to that for the wider ones when an electric field is applied. However, in the ultrathin zigzag graphene nanoribbons, there are two kinds of CBMs, one is spin-degenerate and the other is spin-splitted, and both are tunable by the electric field. Moreover, the two CBMs are spatially separated in momentum space. The conducting mechanism changes from spin-degenerate CBM to spin-splitted CBM with increasing applied electric field. Our results are confirmed by density functional calculations with both LDA and GGA functionals, in which the LDA always underestimates the band gap while the GGA normally produces a bigger band gap than the LDA.展开更多
Based on non-equilibrium Green’s function method combined with the density functional theory, we have studied the electronic properties of a graphene nanoribbon (GNR) which is composed of two GNRs with different widt...Based on non-equilibrium Green’s function method combined with the density functional theory, we have studied the electronic properties of a graphene nanoribbon (GNR) which is composed of two GNRs with different widths. The results show that the electron transmission is greatly modulated by the applied bias. The current of the system displays negative differential resistance effect, which is attributed to the broadening of the transmission gap with the increase of the bias around the Fermi level.展开更多
Armchair graphene nanoribbons with different proportions of edge oxygen atoms are analyzed in this study using the crystal orbital method,which is based on density functional theory.Although buckled edges are present,...Armchair graphene nanoribbons with different proportions of edge oxygen atoms are analyzed in this study using the crystal orbital method,which is based on density functional theory.Although buckled edges are present,all the nanoribbons are energetically favorable.Unlike the adjacent edge oxygen atoms,the isolated edge oxygen atoms cause semiconductor-metal transitions by introducing edge states.For graphene nanoribbons with all oxygen atoms on the edges,band gap and carrier mobility vary with ribbon width.Furthermore,this behavior is different from that of hydrogen-passivated graphene nanoribbons because of different effective widths,which are pictorially presented with crystal orbitals.The carrier mobilities are as 18%~65% magnitude as those of hydrogen-passivated nanoribbons and are of the order of 10^3 cm^2·V^-1·s^-1.展开更多
The first principles density-functional theoretical calculations of U adatom adsorption and diffusion on a planar graphene and quasi-one-dimensional graphene nanoribbons(GNRs) are performed. An energetic preference ...The first principles density-functional theoretical calculations of U adatom adsorption and diffusion on a planar graphene and quasi-one-dimensional graphene nanoribbons(GNRs) are performed. An energetic preference is found for U adatom diffusing to the hollow sites of both graphene and GNRs surface. A number of U distinctive diffusion paths either perpendicular or parallel to the ribbon growth direction are examined. The edge effects are evidenced by the calculated energy barriers of U adatom diffusion on armchair and zigzag nanoribbons surfaces. The calculation results indicate that the diffusion of U adatom from the inner site toward the edge site is a feasible process, particularly in zigzagGNR. It is viable to control the initial morphology of nuclear carbon material to retard the diffusion and concentration of nuclides.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.61901200)the Yunnan Fundamental Research Projects(Grant Nos.2019FD041,202101AU070043,202101AV070008+2 种基金202101AW070010)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.NXDB30010000)the Dongguan Innovation Research Team Program。
文摘The on-surface synthesis method allows the fabrication of atomically precise narrow graphene nanoribbons(GNRs),which bears great potential in electronic applications.Here,we synthesize armchair graphene nanoribbons(AGNRs)and chevron-type graphene nanoribbons(CGNRs)array on a vicinal Au(111112)surface using 10,10′-dibromo-9,9′-bianthracene(DBBA)and 6,12-dibromochrysene(DBCh)as precursors,respectively.This process creates spatially wellaligned GNRs,as characterized by scanning tunneling microscopy.AGNRs show strong Raman linear polarizability for application in optical modulation devices.Different from the distinct polarization of AGNRs,only weak polarization exists in CGNRs polarized Raman spectrum,which suggests that the presence of the zigzag boundary in the nanoribbon attenuates the polarization rate as an important factor affecting the polarization.We analyze the Raman activation mode of CGNRs using the peak polarization to expand the application of the polarization Raman spectroscopy in nanoarray analysis.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12174051 and 11874221)。
文摘We study the valley-dependent electron transport in a four-terminal mesoscopic device of the two monolayer graphene nanoribbons vertically stacked together, where the intersection forms a bilayer graphene lattice with a controllable twist angle. Using a tight-binding lattice model, we show that the longitudinal and transverse conductances exhibit significant valley polarization in the low energy regime for small twist angles. As the twist angle increases, the valley polarization shifts to the high energy regime. This arises from the regrouping effect of the electron band in the twisted bilayer graphene region. But for relatively large twist angles, no significant valley polarization is observed. These results are consistent with the spectral densities of the twisted bilayer graphene.
基金Project supported by the National Natural Science Foundation of China(Grant No.11504418)China Scholarship Council Scholarship Program(Grant No.201706425053)the Fundamental Research Funds for the Central Universities of China(Grant No.2015XKMS075)
文摘We calculated the room-temperature phonon thermal conductivity and phonon spectrum of alkyl group-functionalized zigzag graphene nanoribbons(ZGNRs) with molecular dynamics simulations. The increase in both chain length and concentration of alkyl groups caused remarkable reduction of phonon thermal conductivity in functionalized ZGNRs. Phonon spectra analysis showed that functionalization of ZGNR with alkyl functional groups induced phonon–structural defect scattering, thus leading to the reduction of phonon thermal conductivity of ZGNR. Our study showed that surface functionalization is an effective routine to tune the phonon thermal conductivity of GNRs, which is useful in graphene thermal-related applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.10834012 and 11374342)National Key Basic Research and Development Program of China(Grant No.2009CB930700)the Knowledge Innovation Foundation of the Chinese Academy of Sciences(Grant No.KJCX2-YW-W35)
文摘We present a study of electronic properties of zigzag graphene nanoribbons (ZGNRs) substitutionally doped with nitrogen atoms at a single edge by first principle calculations. We find that the two edge states near the Fermi level sepa- rate due to the asymmetric nitrogen-doping. The ground states of these systems become ferromagnetic because the local magnetic moments along the undoped edges remain and those along the doped edges are suppressed. By controlling the charge-doping level, the magnetic moments of the whole ribbons are modulated. Proper charge doping leads to interest- ing half-metallic and single-edge conducting ribbons which would be helpful for designing graphene-nanoribbon-based spintronic devices in the future.
基金supported by a grant from the National Research Foundation(NRF)funded by the Korean government(NRF-2015M3A9C7030091 and NRF-2015R1C1A1A02037047)
文摘A sharply transected spinal cord has been shown to be fused under the accelerating influence of membrane fusogens such as polyethylene glycol (PEG) (GEMINI protocol). Previous work provided evidence that this is in fact possible. Other fusogens might improve current results. In this study, we aimed to assess the effects of PEGylated graphene nanoribons (PEG-GNR, and called "TexasPEG" when prepared as lwt% dispersion in PEG600) versus placebo (saline) on locomotor function recovery and cellular level in a rat model of spinal cord transection at lumbar segment 1 (L1) level. In vivo and in vitro experiments (n -- 10 per experiment) were designed. In the in vivo experiment, all rats were submitted to full spinal cord transection at L1 level. Five weeks later, behavioral assessment was performed using the Basso Beattie Bresnahan (BBB) locomotor rating scale. Immunohistochemical staining with neuron marker neurofilament 200 (NF200) antibody and astrocyt- ic scar marker glial fibrillary acidic protein (GFAP) was also performed in the injured spinal cord. In the in vitro experiment, the effects of TexasPEG application for 72 hours on the neurite outgrowth of SH-SYSY cells were observed under the inverted microscope. Results of both in vivo and in vitro experiments suggest that TexasPEG reduces the formation of glial scars, promotes the regeneration of neurites, and thereby contributes to the recovery of locomotor function of a rat model of spinal cord transfection.
基金supported by the National Natural Science Foundation of China(Grant Nos.11374162 and 51032002)the Key Project of the National High Technology Research and Development Program of China(Grant No.2011AA050526)
文摘We have performed density-functional calculations of the transport properties of the zigzag graphene nanoribbon (ZGNR) adsorbed with a single iron atom. Two adsorption configurations are considered, i.e., iron adsorbed on the edge and on the interior of the nanoribbon. The results show that the transport features of the two configurations are similar. However, the transport properties are modified due to the scattering effects induced by coupling of the ZGNR band states to the localized 3d-orbital state of the iron atom. More importantly, one can find that several dips appear in the transmission curve, which is closely related to the above mentioned coupling. We expect that our results will have potential applications in graphene-based spintronic devices,
基金supported by the National Natural Science Foundation of China (Grant Nos.10325415 and 50504017)the Natural Science Foundation of Hunan Province,China (Grant No.07JJ3102)the Science Develop Foundation of Central South University,China (Grant Nos.08SDF02 and 09SDF09)
文摘By using first-principles calculations and nonequilibrium Green's function technique, we study elastic transport properties of crossed graphene nanoribbons. The results show that the electronic transport properties of molecular junctions can be modulated by doped atoms. Negative differential resistance (NDR) behaviour can be observed in a certain bias region, when crossed graphene nanoribbons are doped with nitrogen atoms at the shoulder, but it cannot be observed for pristine crossed graphene nanoribbons at low biases. A mechanism for the negative differential resistance behaviour is suggested.
基金Project supported by the Cultivation Fund of the Key Scientific and Technical Innovation Project,Ministry of Education of China(Grant No.708068)the Specialized Research Fund for the Doctoral Program of Higher Education,Ministry of Education of China(Grant No.200805301001)the Open Fund based on Innovation Platform of Hunan Colleges and Universities,China (Grant No.09K034)
文摘The transport properties of hexagonal boron-nitride nanoribbons under the uniaxial strain are investigated by the Green's function method. We find that the transport properties of armchair boron-nitride nanoribbon strongly depend on the strain. In particular, the features of the conductance steps such as position and width are significantly changed by strain. As a strong tensile strain is exerted on the nanoribbon, the highest conductance step disappears and subsequently a dip emerges instead. The energy band structure and the local current density of armchair boron nitride nanoribbon under strain are calculated and analysed in detail to explain these characteristics. In addition, the effect of strain on the conductance of zigzag boron-nitride nanoribbon is weaker than that of armchair boron nitride nanoribbon.
文摘This work presents an investigation of nanoribbons cut from β_(12)-borophene sheets by applying the density functional theory. In particular, the electronic and magnetic properties of borophene nanoribbons(BNR) are studied. It is found that all the ribbons considered in this work behave as metals, which is in good agreement with the recent experimental results. β_(12)-BNR has significant diversity due to the existence of five boron atoms in a unit cell of the sheet. The magnetic properties of the ribbons are strongly dependent on the cutting direction and edge profile. It is interesting that a ribbon with a specific width can behave as a normal or a ferromagnetic metal with magnetization at just one edge or two edges. Spin anisotropy is observed in some ribbons, and the magnetic moment is not found to be the same in both edges in an antiferromagnetic configuration. This effect stems from the edge asymmetry of the ribbons and results in the breaking of spin degeneracy in the band structure. Our findings show that β_(12) BNRs are potential candidates for next-generation spintronic devices.
基金Project supported by the Fundamental Research Funds for the Central Universities (Grant No. YWF-10-02-040)
文摘Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix. The complex band structure gives extra information on carrier's decay behaviour. The imaginary loop connects the conduction and valence band, and can profoundly affect the characteristics of nanoscale electronic device made with graphene nanoribbons. In this work, the complex band structure calculation includes not only the first nearest neighbour interaction, but also the effects of edge bond relaxation and the third nearest neighbour interaction. The band gap is classified into three classes. Due to the edge bond relaxation and the third nearest neighbour interaction term, it opens a band gap for N = 3M- 1. The band gap is almost unchanged for N =3M + 1, but decreased for N = 3M. The maximum imaginary wave vector length provides additional information about the electrical characteristics of graphene nanoribbons, and is also classified into three classes.
基金supported by the National Natural Science Foundation of China(No.21203127)the Scientific Research Base Development Program of the Beijing Municipal Commission of Education
文摘One-dimensional Cr2NO2 nanoribbons cut from the oxygen-passivated Cr2NO2 MXene were investigated by using density functional theory. The wide nanoribbons have ferromagnetic ground states and are intrinsic half-metals, independent of their chirality. The half-metallic band gaps of wide nanoribbons are larger than 1 eV, which are large enough for avoiding thermally activated spin flip. The magnetism does not rely on the edge states but originates from all the Cr atoms. Furthermore, the half-metallicity is still robust in an electronic device even if the bias is up to 1 V. Therefore, one-dimensional Cr2NO2 nanoribbons are good candidates for spintronics.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11204201 and 11147142)the Natural Science Foundation for Young Scientists of Shanxi Province,China(Grant No.2013021010-1)
文摘The electric field effect in ultrathin zigzag graphene nanoribbons containing only three or four zigzag carbon chains is studied by first-principles calculations, and the change of conducting mechanism is observed with increasing in-plane electric field perpendicular to the ribbon. Wider zigzag graphene nanoribbons have been predicted to be spin-splitted for both valence band maximum(VBM) and conduction band minimum(CBM) with an applied electric field and become half-metal due to the vanishing band gap of one spin with increasing applied field. The change of VBM for the ultrathin zigzag graphene nanoribbons is similar to that for the wider ones when an electric field is applied. However, in the ultrathin zigzag graphene nanoribbons, there are two kinds of CBMs, one is spin-degenerate and the other is spin-splitted, and both are tunable by the electric field. Moreover, the two CBMs are spatially separated in momentum space. The conducting mechanism changes from spin-degenerate CBM to spin-splitted CBM with increasing applied electric field. Our results are confirmed by density functional calculations with both LDA and GGA functionals, in which the LDA always underestimates the band gap while the GGA normally produces a bigger band gap than the LDA.
文摘Based on non-equilibrium Green’s function method combined with the density functional theory, we have studied the electronic properties of a graphene nanoribbon (GNR) which is composed of two GNRs with different widths. The results show that the electron transmission is greatly modulated by the applied bias. The current of the system displays negative differential resistance effect, which is attributed to the broadening of the transmission gap with the increase of the bias around the Fermi level.
基金supported by the National Natural Science Foundation of China(No.21203127)the Beijing Higher Education Young Elite Teacher Project(YETP1629)the Scientific Research Base Development Program of the Beijing Municipal Commission of Education
文摘Armchair graphene nanoribbons with different proportions of edge oxygen atoms are analyzed in this study using the crystal orbital method,which is based on density functional theory.Although buckled edges are present,all the nanoribbons are energetically favorable.Unlike the adjacent edge oxygen atoms,the isolated edge oxygen atoms cause semiconductor-metal transitions by introducing edge states.For graphene nanoribbons with all oxygen atoms on the edges,band gap and carrier mobility vary with ribbon width.Furthermore,this behavior is different from that of hydrogen-passivated graphene nanoribbons because of different effective widths,which are pictorially presented with crystal orbitals.The carrier mobilities are as 18%~65% magnitude as those of hydrogen-passivated nanoribbons and are of the order of 10^3 cm^2·V^-1·s^-1.
基金supported by the International S&T Cooperation Program of China(Grant No.2014DFG60230)the National Natural Science Foundation of China(Grant Nos.91326105,21306220,and 21501189)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA02040104)
文摘The first principles density-functional theoretical calculations of U adatom adsorption and diffusion on a planar graphene and quasi-one-dimensional graphene nanoribbons(GNRs) are performed. An energetic preference is found for U adatom diffusing to the hollow sites of both graphene and GNRs surface. A number of U distinctive diffusion paths either perpendicular or parallel to the ribbon growth direction are examined. The edge effects are evidenced by the calculated energy barriers of U adatom diffusion on armchair and zigzag nanoribbons surfaces. The calculation results indicate that the diffusion of U adatom from the inner site toward the edge site is a feasible process, particularly in zigzagGNR. It is viable to control the initial morphology of nuclear carbon material to retard the diffusion and concentration of nuclides.