We have investigated the electronic and structural properties of inorganic nanoribbons （BN, AIN, GaN, SiC, and ZnO） with unpassivated zigzag edges using density functional theory calculations. We find that, in gener...We have investigated the electronic and structural properties of inorganic nanoribbons （BN, AIN, GaN, SiC, and ZnO） with unpassivated zigzag edges using density functional theory calculations. We find that, in general, the unpassivated zigzag edges can lead to spin-splitting of energy bands. More interestingly, the inorganic nanoribbons A1N and SiC with either one or two edges unpassivated are predicted to be half metallic. Possible structural reconstruction at the unpassivated edges and its effect on the electronic properties are investigated. The unpassivated N edge in the BN nanoribbon and P edge in the AlP nanoribbon are energetically less stable than the corresponding reconstructed edge. Hence, edge reconstruction at the two edges may occur at high temperatures. Other unpassivated edges of the inorganic nanoribbons considered in this study are all robust against edge reconstruction.展开更多
Connecting three zigzag graphene nanoribbons（ZGNRs） together through the sp^3 hybrid bonds forms a star-like ZGNR（S-ZGNR）. Its band structure shows that there are four edge states at k = 0.5, in which the three el...Connecting three zigzag graphene nanoribbons（ZGNRs） together through the sp^3 hybrid bonds forms a star-like ZGNR（S-ZGNR）. Its band structure shows that there are four edge states at k = 0.5, in which the three electrons distribute at three outside edge sites, and the last electron is shared equally（50%） by two sites near the central site. The lowest conductance step in the valley is 2, two times higher than that of monolayer ZGNR（M-ZGNR）. Furthermore, in one quasithree-dimensional hexagonal lattice built, both of the Dirac points and the zero-energy states appear in the band structure along the z-axis for the fixed zero k-point in the x-y plane. In addition, it is an insulator in the x-y plane due to band gap 4 eV, however, for any k-point in the x-y plane the zero-energy states always exist at kz = 0.5.展开更多
Analytical studies of the effect of edge decoration on the energy spectrum of semi-infinite one-dimensional （1D） model and zigzag edged graphene （ZEG） are presented by means of transfer matrix method, in the frame...Analytical studies of the effect of edge decoration on the energy spectrum of semi-infinite one-dimensional （1D） model and zigzag edged graphene （ZEG） are presented by means of transfer matrix method, in the frame of which the conditions for the existence of edge states are determined. For 1D model, the zero-energy surface state occurs regardless of whether the decorations exist or not, while the non-zero-energy surface states can be induced and manipulated through adjusting the edge decoration. On the other hand, the case for the semi-infinite ZEG model with nearestneighbour interaction is discussed in the analogous way. The non-zero-energy surface states can be induced by the edge decoration and moreover, the ratio between the edge hopping and the bulk hopping amplitudes should be within a certain threshold.展开更多
The atomic edge structure of graphene governs its unique electronic properties with applications in nanoscale electronics and optoelectronics.To fully realize its potential,it is critical to develop a precision etchin...The atomic edge structure of graphene governs its unique electronic properties with applications in nanoscale electronics and optoelectronics.To fully realize its potential,it is critical to develop a precision etching process producing graphene edges along desired directions.Here,we present a novel approach utilizing scanning probe lithography(SPL)facilitated by a mechanochemical atomic attrition process.This technique enables the fabrication of nanopatterns in single-layer graphene from graphene edges,precisely along the crystallographic orientation of zigzag(ZZ)and armchair(AC)edges,without inducing mechanical damage to the surrounding area.Density functional theory(DFT)calculations revealed that the dissociation of CC bonds by the SPL probe is mediated by the formation of interfacial bridge bonds between the graphene edge and the reactive silica surface.This SPL-based mechanochemical etching method enables the construction of various nanodevice structures with specific edge orientations,which allows the exploitation of their electronic properties.展开更多
Finite-sized graphene sheets, such as graphene nanoislands （GNIs）, are promising candidates for practical applications in graphene-based nanoelectronics. GNIs with well-defined zigzag edges are predicted to have spi...Finite-sized graphene sheets, such as graphene nanoislands （GNIs）, are promising candidates for practical applications in graphene-based nanoelectronics. GNIs with well-defined zigzag edges are predicted to have spin-polarized edge-states similar to those of zigzag-edged graphene nanoribbons, which can achieve graphene spintronics. However, it has been reported that GNIs on metal substrates have no edge states because of interactions with the substrate. We used a combination of scanning tunneling microscopy, spectroscopy, and density functional theory calculations to demonstrate that the edge states of GNIs on an Ir substrate can be recovered by intercalating a layer of Si atoms between the GNIs and the substrate. We also found that the edge states gradually shift to the Fermi level with increasing island size. This work provides a method to investigate spin-polarized edge states in high-quality graphene nanostructures on a metal substrate.展开更多
The formation and control of a room-temperature magnetic order in two- dimensional （2D） materials is a challenging quest for the advent of innovative magnetic- and spintronic-based technologies. To date, edge magnet...The formation and control of a room-temperature magnetic order in two- dimensional （2D） materials is a challenging quest for the advent of innovative magnetic- and spintronic-based technologies. To date, edge magnetism in 2D materials has been experimentally observed in hydrogen （H）-terminated graphene nanoribbons （GNRs） and graphene nanomeshes （GNMs）, but the measured magnetization remains far too small to allow envisioning practical applications. Herein, we report experimental evidences of large room-temperature edge ferromagnetism （FM） obtained from oxygen （O）-terminated zigzag pore edges of few-layer black phosphorus （P） nanomeshes （BPNMs）. The magnetization values per unit area are -100 times larger than those reported for H-terminated GNMs, while the magnetism is absent for H-terminated BPNMs. The magnetization measurements and the first-principles simulations suggest that the origin of such a magnetic order could stem from ferromagnetic spin coupling between edge P with O atoms, resulting in a strong spin localization at the edge valence band, and from uniform oxidation of full pore edges over a large area and interlayer spin interaction. Our findings pave the way for realizing high-efficiency 2D flexible magnetic and spintronic devices without the use of rare magnetic elements.展开更多
The structure and edge states of two-dimensional few-layer Bi(110)films grown on a graphene/SiC substrate were studied by low-temperature scanning tunneling microscopy and spectroscopy.We found that the local density ...The structure and edge states of two-dimensional few-layer Bi(110)films grown on a graphene/SiC substrate were studied by low-temperature scanning tunneling microscopy and spectroscopy.We found that the local density of states of few-layer Bi(110)films are layer-dependent and that the films transition from exhibiting semiconducting characteristics to metallic ones as the number of layers increases.The in-plane lattice structure has numerous displacements and inversions,which implies that the atomic arrangement and atomic buckling in ultrathin Bi(110)films are flexible.The edges formed between 4-monolayer Bi(110)and graphene are reconstructed and distorted,and the corresponding edge states are topographically dependent.Steps from the substrate and domain boundaries also modify the electronic structures and induce additional defect-dependent states.We also found that the zigzag-shaped step edges in few-layer Bi(110)films are nonreconstructed and possess layer-dependent homogeneous edge states,providing a very likely platform for further research on quantum interference of the edge mode in order to confirm the topology in Bi(110).展开更多
Peri-annulation is recognized as an influential structural motif in accessing functional molecular materials.However,efficient synthetic access to peri-annulated structures remains challenging.Herein,we show that mech...Peri-annulation is recognized as an influential structural motif in accessing functional molecular materials.However,efficient synthetic access to peri-annulated structures remains challenging.Herein,we show that mechanochemistry is a valuable synthetic tool to achieve this goal.It is comparatively better than activation through microwave irradiation and conventional solution-phase reactions.The synthesized materials are molecularly curved nanographenes containing sulfur and selenium atoms.The curvature comes from the use of corannulene as the central building block,upon which the benzothiophene or benzoselenophene are peri-annulated through the palladium-catalyzed direct arylation reactions.Peri-annulation endows the nanographene structures with better optical properties as compared to other annulation chemistries.展开更多
The controllable synthesis of complicated nanostructures in advanced two-dimensional(2D)semiconductors,such as periodic regular hole arrays,is essential and remains immature.Here,we report a green,facile,highly contro...The controllable synthesis of complicated nanostructures in advanced two-dimensional(2D)semiconductors,such as periodic regular hole arrays,is essential and remains immature.Here,we report a green,facile,highly controlled synthetic method to efficiently pattern 2D semiconductors,such as periodic regular hexagonal-shaped hole arrays(HHA),in 2D-TMDs.Combining the production of artificial defect arrays through laser irradiation with anisotropic annealing etching,we created HHA with different arrangements,controlled hole sizes,and densities in bilayer WS_(2).Atomic force microscopy(AFM),Raman,photoluminescence(PL),and scanning transmission electron microscopy(STEM)characterization show that the 2D semiconductors have high quality with atomical clean and sharp edges as well as undamaged crystals in the unetched region.Furthermore,other nanostructures,such as nanoribbons and periodic regular triangular-shaped 2D-TMD arrays,can be fabricated.This kind of 2D semiconductors fabrication strategy is general and can be extended to a series of 2D materials.Density functional theory(DFT)calculations show that one WS_(2)molecule from the edges of the laser-irradiated holed region exhibits a robust etching activation,making selective etching at the artificial defects and the fabrication of regular 2D semiconductors possible.展开更多
文摘We have investigated the electronic and structural properties of inorganic nanoribbons （BN, AIN, GaN, SiC, and ZnO） with unpassivated zigzag edges using density functional theory calculations. We find that, in general, the unpassivated zigzag edges can lead to spin-splitting of energy bands. More interestingly, the inorganic nanoribbons A1N and SiC with either one or two edges unpassivated are predicted to be half metallic. Possible structural reconstruction at the unpassivated edges and its effect on the electronic properties are investigated. The unpassivated N edge in the BN nanoribbon and P edge in the AlP nanoribbon are energetically less stable than the corresponding reconstructed edge. Hence, edge reconstruction at the two edges may occur at high temperatures. Other unpassivated edges of the inorganic nanoribbons considered in this study are all robust against edge reconstruction.
基金Project supported by the National Natural Science Foundation of China(Grant No.10947004)the Jiangsu Government Scholarship for Overseas Studies,China
文摘Connecting three zigzag graphene nanoribbons（ZGNRs） together through the sp^3 hybrid bonds forms a star-like ZGNR（S-ZGNR）. Its band structure shows that there are four edge states at k = 0.5, in which the three electrons distribute at three outside edge sites, and the last electron is shared equally（50%） by two sites near the central site. The lowest conductance step in the valley is 2, two times higher than that of monolayer ZGNR（M-ZGNR）. Furthermore, in one quasithree-dimensional hexagonal lattice built, both of the Dirac points and the zero-energy states appear in the band structure along the z-axis for the fixed zero k-point in the x-y plane. In addition, it is an insulator in the x-y plane due to band gap 4 eV, however, for any k-point in the x-y plane the zero-energy states always exist at kz = 0.5.
基金supported by the National Natural Science Foundation of China (Grant No.10847001)the National Basic Research Program of China (Grant Nos.2009CB929204 and 2011CB921803)
文摘Analytical studies of the effect of edge decoration on the energy spectrum of semi-infinite one-dimensional （1D） model and zigzag edged graphene （ZEG） are presented by means of transfer matrix method, in the frame of which the conditions for the existence of edge states are determined. For 1D model, the zero-energy surface state occurs regardless of whether the decorations exist or not, while the non-zero-energy surface states can be induced and manipulated through adjusting the edge decoration. On the other hand, the case for the semi-infinite ZEG model with nearestneighbour interaction is discussed in the analogous way. The non-zero-energy surface states can be induced by the edge decoration and moreover, the ratio between the edge hopping and the bulk hopping amplitudes should be within a certain threshold.
基金supported by the National Natural Science Foundation of China(Nos.52122507,52350411,and 12002289)the National Key R&D Program of China-Young Scientist Program(No.2023YFB3405500)+1 种基金The Independent Project of State Key Laboratory of Rail Transit Vehicle System(No.2023TPL-T04)Seong H.Kim was supported by the National Science Foundation of the USA(No.CMMI-1912199).
文摘The atomic edge structure of graphene governs its unique electronic properties with applications in nanoscale electronics and optoelectronics.To fully realize its potential,it is critical to develop a precision etching process producing graphene edges along desired directions.Here,we present a novel approach utilizing scanning probe lithography(SPL)facilitated by a mechanochemical atomic attrition process.This technique enables the fabrication of nanopatterns in single-layer graphene from graphene edges,precisely along the crystallographic orientation of zigzag(ZZ)and armchair(AC)edges,without inducing mechanical damage to the surrounding area.Density functional theory(DFT)calculations revealed that the dissociation of CC bonds by the SPL probe is mediated by the formation of interfacial bridge bonds between the graphene edge and the reactive silica surface.This SPL-based mechanochemical etching method enables the construction of various nanodevice structures with specific edge orientations,which allows the exploitation of their electronic properties.
基金This work is supported by the National Key Research and Development Projects of China （No. 2016YFA0202300）, the National Basic Research Program of China （Nos. 2013CBA01600 and 2015CB921103）, the National Natural Science Foundation of China （Nos. 61390501, 51325204, 51210003, and 61622116）, and the CAS Pioneer Hundred Talents Program. Work at Yanderbilt is partially supported by the Department of Energy grant DE- FG02-09ER46554 and by the McMinn Endowment. Y. Y. Z and S. T. P acknowledge the National Energy Research Scientific Computing Center （NERSC）, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and the Extreme Science and Engineering Discovery Environment （XSEDE）, which is supported by the National Science Foundation Grant ACI-1053575.
文摘Finite-sized graphene sheets, such as graphene nanoislands （GNIs）, are promising candidates for practical applications in graphene-based nanoelectronics. GNIs with well-defined zigzag edges are predicted to have spin-polarized edge-states similar to those of zigzag-edged graphene nanoribbons, which can achieve graphene spintronics. However, it has been reported that GNIs on metal substrates have no edge states because of interactions with the substrate. We used a combination of scanning tunneling microscopy, spectroscopy, and density functional theory calculations to demonstrate that the edge states of GNIs on an Ir substrate can be recovered by intercalating a layer of Si atoms between the GNIs and the substrate. We also found that the edge states gradually shift to the Fermi level with increasing island size. This work provides a method to investigate spin-polarized edge states in high-quality graphene nanostructures on a metal substrate.
文摘The formation and control of a room-temperature magnetic order in two- dimensional （2D） materials is a challenging quest for the advent of innovative magnetic- and spintronic-based technologies. To date, edge magnetism in 2D materials has been experimentally observed in hydrogen （H）-terminated graphene nanoribbons （GNRs） and graphene nanomeshes （GNMs）, but the measured magnetization remains far too small to allow envisioning practical applications. Herein, we report experimental evidences of large room-temperature edge ferromagnetism （FM） obtained from oxygen （O）-terminated zigzag pore edges of few-layer black phosphorus （P） nanomeshes （BPNMs）. The magnetization values per unit area are -100 times larger than those reported for H-terminated GNMs, while the magnetism is absent for H-terminated BPNMs. The magnetization measurements and the first-principles simulations suggest that the origin of such a magnetic order could stem from ferromagnetic spin coupling between edge P with O atoms, resulting in a strong spin localization at the edge valence band, and from uniform oxidation of full pore edges over a large area and interlayer spin interaction. Our findings pave the way for realizing high-efficiency 2D flexible magnetic and spintronic devices without the use of rare magnetic elements.
基金U.S.Air Force Office of Scientific Research Grants FA9550-15-1-0236 and FA9550-20-1-0068,the T.L.L.Temple Foundation,the John J.and Rebecca Moores Endowment,and the State of Texas through the Texas Center for Superconductivity at the University of Houston.
文摘The structure and edge states of two-dimensional few-layer Bi(110)films grown on a graphene/SiC substrate were studied by low-temperature scanning tunneling microscopy and spectroscopy.We found that the local density of states of few-layer Bi(110)films are layer-dependent and that the films transition from exhibiting semiconducting characteristics to metallic ones as the number of layers increases.The in-plane lattice structure has numerous displacements and inversions,which implies that the atomic arrangement and atomic buckling in ultrathin Bi(110)films are flexible.The edges formed between 4-monolayer Bi(110)and graphene are reconstructed and distorted,and the corresponding edge states are topographically dependent.Steps from the substrate and domain boundaries also modify the electronic structures and induce additional defect-dependent states.We also found that the zigzag-shaped step edges in few-layer Bi(110)films are nonreconstructed and possess layer-dependent homogeneous edge states,providing a very likely platform for further research on quantum interference of the edge mode in order to confirm the topology in Bi(110).
基金supported by the Ministry of Education Singapore under the AcRF Tier 2(MOE-T2EP10221-0002)the Ministry of Research,Innovation and Digitalization under Romania's National Recovery and Resilience Plan PNRR-Ⅲ-C9-2022-I8 Program with Project code 167/15.11.22。
文摘Peri-annulation is recognized as an influential structural motif in accessing functional molecular materials.However,efficient synthetic access to peri-annulated structures remains challenging.Herein,we show that mechanochemistry is a valuable synthetic tool to achieve this goal.It is comparatively better than activation through microwave irradiation and conventional solution-phase reactions.The synthesized materials are molecularly curved nanographenes containing sulfur and selenium atoms.The curvature comes from the use of corannulene as the central building block,upon which the benzothiophene or benzoselenophene are peri-annulated through the palladium-catalyzed direct arylation reactions.Peri-annulation endows the nanographene structures with better optical properties as compared to other annulation chemistries.
基金National Key R&D Program of the Ministry of Science and Technology of China,Grant/Award Number:2022YFA1203801The National Natural Science Foundation of China,Grant/Award Numbers:51991340,51991343,52221001,62174051+1 种基金The Hunan Key R&D Program Project,Grant/Award Number:2022GK2005Ningbo Natural Science Foundation,Grant/Award Number:2023J023。
文摘The controllable synthesis of complicated nanostructures in advanced two-dimensional(2D)semiconductors,such as periodic regular hole arrays,is essential and remains immature.Here,we report a green,facile,highly controlled synthetic method to efficiently pattern 2D semiconductors,such as periodic regular hexagonal-shaped hole arrays(HHA),in 2D-TMDs.Combining the production of artificial defect arrays through laser irradiation with anisotropic annealing etching,we created HHA with different arrangements,controlled hole sizes,and densities in bilayer WS_(2).Atomic force microscopy(AFM),Raman,photoluminescence(PL),and scanning transmission electron microscopy(STEM)characterization show that the 2D semiconductors have high quality with atomical clean and sharp edges as well as undamaged crystals in the unetched region.Furthermore,other nanostructures,such as nanoribbons and periodic regular triangular-shaped 2D-TMD arrays,can be fabricated.This kind of 2D semiconductors fabrication strategy is general and can be extended to a series of 2D materials.Density functional theory(DFT)calculations show that one WS_(2)molecule from the edges of the laser-irradiated holed region exhibits a robust etching activation,making selective etching at the artificial defects and the fabrication of regular 2D semiconductors possible.
