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Selim Ciraci - One of the best experts on this subject based on the ideXlab platform.
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armchair Nanoribbons of silicon and germanium honeycomb structures
Physical Review B, 2010Co-Authors: Seymur Cahangirov, M. Topsakal, Selim CiraciAbstract:We present a first-principles study of bare and hydrogen passivated armchair Nanoribbons of the puckered single layer honeycomb structures of silicon and germanium. Our study includes optimization of atomic structure, stability analysis based on the calculation of phonon dispersions, electronic structure and the variation of band gap with the width of the ribbon. The band gaps of silicon and germanium Nanoribbons exhibit family behavior similar to those of graphene Nanoribbons. The edges of bare Nanoribbons are sharply reconstructed, which can be eliminated by the hydrogen termination of dangling bonds at the edges. Periodic modulation of the nanoribbon width results in a superlattice structure which can act as a multiple quantum wells. Specific electronic states are confined in these wells. Confinement trends are qualitatively explained by including the effects of the interface. In order to investigate wide and long superlattice structures we also performed empirical tight binding calculations with parameters determined from \textit{ab initio} calculations.
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elastic and plastic deformation of graphene silicene and boron nitride honeycomb Nanoribbons under uniaxial tension a first principles density functional theory study
Physical Review B, 2010Co-Authors: M. Topsakal, Selim CiraciAbstract:Department of Physics, Bilkent University Ankara 06800, Turkey(Dated: January 26, 2010)This study of elastic and plastic deformation of graphene, silicene and boron nitride (BN) honey-comb Nanoribbons under uniaxial tension determines their elastic constants and reveals interestingfeatures. In the course of stretching in the elastic range, the electronic and magnetic properties canbe strongly modi ed. In particular, it is shown that the band gap of a speci c armchair nanoribbonis closed under strain and highest valance and lowest conduction bands are linearized. This way,the massless Dirac fermion behavior can be attained even in a semiconducting nanoribbon. Un-der plastic deformation, the honeycomb structure changes irreversibly and o ers a number of newstructures and functionalities. Cage like structures, even suspended atomic chains can be derivedbetween two honeycomb akes. Present work elaborates on the recent experiments by Jin et al.,Phys. Rev. Lett. 102, 205501 (2009) deriving carbon chains from graphene. Furthermore, thesimilar formations of atomic chains from BN and Si Nanoribbons are predicted.
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Elastic and plastic deformation of graphene, silicene, and boron nitride honeycomb Nanoribbons under uniaxial tension: A first-principles density-functional theory study
Physical Review B - Condensed Matter and Materials Physics, 2010Co-Authors: M. Topsakal, Selim CiraciAbstract:This study of elastic and plastic deformation of graphene, silicene, and boron nitride (BN) honeycomb Nanoribbons under uniaxial tension determines their elastic constants and reveals interesting features. In the course of stretching in the elastic range, the electronic and magnetic properties can be strongly modified. In particular, it is shown that the band gap of a specific armchair nanoribbon is closed under strain and highest valance and lowest conduction bands are linearized. This way, the massless Dirac fermion behavior can be attained even in a semiconducting nanoribbon. Under plastic deformation, the honeycomb structure changes irreversibly and offers a number of new structures and functionalities. Cagelike structures, even suspended atomic chains can be derived between two honeycomb flakes. Present work elaborates on the recent experiments [C. Jin, H. Lan, L. Peng, K. Suenaga, and S. Iijima, Phys. Rev. Lett. 102, 205501 (2009)] deriving carbon chains from graphene. Furthermore, the similar formations of atomic chains from BN and Si Nanoribbons are predicted.
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first principles study of zinc oxide honeycomb structures
Physical Review B, 2009Co-Authors: M. Topsakal, Seymur Cahangirov, E. Bekaroglu, Selim CiraciAbstract:We present a first-principles study of the atomic, electronic, and magnetic properties of two-dimensional (2D), single and bilayer ZnO in honeycomb structure and its armchair and zigzag Nanoribbons. In order to reveal the dimensionality effects, our study includes also bulk ZnO in wurtzite, zincblende, and hexagonal structures. The stability of 2D ZnO, its Nanoribbons and flakes are analyzed by phonon frequency, as well as by finite temperature ab initio molecular-dynamics calculations. 2D ZnO in honeycomb structure and its armchair Nanoribbons are nonmagnetic semiconductors but acquire net magnetic moment upon the creation of zinc-vacancy defect. Zigzag ZnO Nanoribbons are ferromagnetic metals with spins localized at the oxygen atoms at the edges and have high spin polarization at the Fermi level. However, they change to nonmagnetic metal upon termination of their edges with hydrogen atoms. From the phonon calculations, the fourth acoustical mode specified as twisting mode is also revealed for armchair nanoribbon. Under tensile stress the Nanoribbons are deformed elastically maintaining honeycomblike structure but yield at high strains. Beyond yielding point honeycomblike structure undergo a structural change and deform plastically by forming large polygons. The variation in the electronic and magnetic properties of these Nanoribbons have been examined under strain. It appears that plastically deformed Nanoribbons may offer a new class of materials with diverse properties.
M. Topsakal - One of the best experts on this subject based on the ideXlab platform.
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armchair Nanoribbons of silicon and germanium honeycomb structures
Physical Review B, 2010Co-Authors: Seymur Cahangirov, M. Topsakal, Selim CiraciAbstract:We present a first-principles study of bare and hydrogen passivated armchair Nanoribbons of the puckered single layer honeycomb structures of silicon and germanium. Our study includes optimization of atomic structure, stability analysis based on the calculation of phonon dispersions, electronic structure and the variation of band gap with the width of the ribbon. The band gaps of silicon and germanium Nanoribbons exhibit family behavior similar to those of graphene Nanoribbons. The edges of bare Nanoribbons are sharply reconstructed, which can be eliminated by the hydrogen termination of dangling bonds at the edges. Periodic modulation of the nanoribbon width results in a superlattice structure which can act as a multiple quantum wells. Specific electronic states are confined in these wells. Confinement trends are qualitatively explained by including the effects of the interface. In order to investigate wide and long superlattice structures we also performed empirical tight binding calculations with parameters determined from \textit{ab initio} calculations.
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elastic and plastic deformation of graphene silicene and boron nitride honeycomb Nanoribbons under uniaxial tension a first principles density functional theory study
Physical Review B, 2010Co-Authors: M. Topsakal, Selim CiraciAbstract:Department of Physics, Bilkent University Ankara 06800, Turkey(Dated: January 26, 2010)This study of elastic and plastic deformation of graphene, silicene and boron nitride (BN) honey-comb Nanoribbons under uniaxial tension determines their elastic constants and reveals interestingfeatures. In the course of stretching in the elastic range, the electronic and magnetic properties canbe strongly modi ed. In particular, it is shown that the band gap of a speci c armchair nanoribbonis closed under strain and highest valance and lowest conduction bands are linearized. This way,the massless Dirac fermion behavior can be attained even in a semiconducting nanoribbon. Un-der plastic deformation, the honeycomb structure changes irreversibly and o ers a number of newstructures and functionalities. Cage like structures, even suspended atomic chains can be derivedbetween two honeycomb akes. Present work elaborates on the recent experiments by Jin et al.,Phys. Rev. Lett. 102, 205501 (2009) deriving carbon chains from graphene. Furthermore, thesimilar formations of atomic chains from BN and Si Nanoribbons are predicted.
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Elastic and plastic deformation of graphene, silicene, and boron nitride honeycomb Nanoribbons under uniaxial tension: A first-principles density-functional theory study
Physical Review B - Condensed Matter and Materials Physics, 2010Co-Authors: M. Topsakal, Selim CiraciAbstract:This study of elastic and plastic deformation of graphene, silicene, and boron nitride (BN) honeycomb Nanoribbons under uniaxial tension determines their elastic constants and reveals interesting features. In the course of stretching in the elastic range, the electronic and magnetic properties can be strongly modified. In particular, it is shown that the band gap of a specific armchair nanoribbon is closed under strain and highest valance and lowest conduction bands are linearized. This way, the massless Dirac fermion behavior can be attained even in a semiconducting nanoribbon. Under plastic deformation, the honeycomb structure changes irreversibly and offers a number of new structures and functionalities. Cagelike structures, even suspended atomic chains can be derived between two honeycomb flakes. Present work elaborates on the recent experiments [C. Jin, H. Lan, L. Peng, K. Suenaga, and S. Iijima, Phys. Rev. Lett. 102, 205501 (2009)] deriving carbon chains from graphene. Furthermore, the similar formations of atomic chains from BN and Si Nanoribbons are predicted.
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first principles study of zinc oxide honeycomb structures
Physical Review B, 2009Co-Authors: M. Topsakal, Seymur Cahangirov, E. Bekaroglu, Selim CiraciAbstract:We present a first-principles study of the atomic, electronic, and magnetic properties of two-dimensional (2D), single and bilayer ZnO in honeycomb structure and its armchair and zigzag Nanoribbons. In order to reveal the dimensionality effects, our study includes also bulk ZnO in wurtzite, zincblende, and hexagonal structures. The stability of 2D ZnO, its Nanoribbons and flakes are analyzed by phonon frequency, as well as by finite temperature ab initio molecular-dynamics calculations. 2D ZnO in honeycomb structure and its armchair Nanoribbons are nonmagnetic semiconductors but acquire net magnetic moment upon the creation of zinc-vacancy defect. Zigzag ZnO Nanoribbons are ferromagnetic metals with spins localized at the oxygen atoms at the edges and have high spin polarization at the Fermi level. However, they change to nonmagnetic metal upon termination of their edges with hydrogen atoms. From the phonon calculations, the fourth acoustical mode specified as twisting mode is also revealed for armchair nanoribbon. Under tensile stress the Nanoribbons are deformed elastically maintaining honeycomblike structure but yield at high strains. Beyond yielding point honeycomblike structure undergo a structural change and deform plastically by forming large polygons. The variation in the electronic and magnetic properties of these Nanoribbons have been examined under strain. It appears that plastically deformed Nanoribbons may offer a new class of materials with diverse properties.
Xinliang Feng - One of the best experts on this subject based on the ideXlab platform.
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Graphene nanoribbon heterojunctions
Nature Nanotechnology, 2014Co-Authors: Jinming Cai, Pascal Ruffieux, Carlo A Pignedoli, Xinliang Feng, Leopold Talirz, Hajo Söde, Liangbo Liang, Vincent Meunier, Reinhard Berger, Klaus MüllenAbstract:p–n junctions are formed in heterostructures made of pristine and nitrogen-doped graphene Nanoribbons. Despite graphene's remarkable electronic properties^ 1 , 2 , the lack of an electronic bandgap severely limits its potential for applications in digital electronics^ 3 , 4 . In contrast to extended films, narrow strips of graphene (called graphene Nanoribbons) are semiconductors through quantum confinement^ 5 , 6 , with a bandgap that can be tuned as a function of the nanoribbon width and edge structure^ 7 , 8 , 9 , 10 . Atomically precise graphene Nanoribbons can be obtained via a bottom-up approach based on the surface-assisted assembly of molecular precursors^ 11 . Here we report the fabrication of graphene nanoribbon heterojunctions and heterostructures by combining pristine hydrocarbon precursors with their nitrogen-substituted equivalents. Using scanning probe methods, we show that the resulting heterostructures consist of seamlessly assembled segments of pristine (undoped) graphene Nanoribbons (p-GNRs) and deterministically nitrogen-doped graphene Nanoribbons (N-GNRs), and behave similarly to traditional p–n junctions^ 12 . With a band shift of 0.5 eV and an electric field of 2 × 10^8 V m^–1 at the heterojunction, these materials bear a high potential for applications in photovoltaics and electronics.
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intraribbon heterojunction formation in ultranarrow graphene Nanoribbons
ACS Nano, 2012Co-Authors: Stephan Blankenburg, Rached Jaafar, Roman Fasel, Pascal Ruffieux, Daniele Passerone, Xinliang Feng, Klaus Müllen, Carlo A PignedoliAbstract:Graphene Nanoribbons—semiconducting quasi-one-dimensional graphene structures—have great potential for the realization of novel electronic devices. Recently, graphene nanoribbon heterojunctions—interfaces between Nanoribbons with unequal band gaps—have been realized with lithographic etching techniques and via chemical routes to exploit quantum transport phenomena. However, standard fabrication techniques are not suitable for ribbons narrower than ∼5 nm and do not allow to control the width and edge structure of a specific device with atomic precision. Here, we report the realization of graphene nanoribbon heterojunctions with lateral dimensions below 2 nm via controllable dehydrogenation of polyanthrylene oligomers self-assembled on a Au(111) surface from molecular precursors. Atomistic simulations reveal the microscopic mechanisms responsible for intraribbon heterojunction formation. We demonstrate the capability to selectively modify the heterojunctions by activating the dehydrogenation reaction on sin...
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atomically precise bottom up fabrication of graphene Nanoribbons
Nature, 2010Co-Authors: Pascal Ruffieux, Stephan Blankenburg, Rached Jaafar, Marco Bieri, Thomas Braun, Matthias Muoth, Ari P Seitsonen, Moussa Saleh, Xinliang FengAbstract:Graphene Nanoribbons, narrow straight-edged strips of the single-atom-thick sheet form of carbon, are predicted to exhibit remarkable properties, making them suitable for future electronic applications. Before this potential can be realized, more chemically precise methods of production will be required. Cai et al. report a step towards that goal with the development of a bottom-up fabrication method that produces atomically precise graphene Nanoribbons of different topologies and widths. The process involves the deposition of precursor monomers with structures that 'encode' the topology and width of the desired ribbon end-product onto a metal surface. Surface-assisted coupling of the precursors into linear polyphenylenes is then followed by cyclodehydrogenation. Given the method's versatility and precision, it could even provide a route to more unusual graphene nanoribbon structures with tuned chemical and electronic properties. Graphene Nanoribbons (GNRs) have structure-dependent electronic properties that make them attractive for the fabrication of nanoscale electronic devices, but exploiting this potential has been hindered by the lack of precise production methods. Here the authors demonstrate how to reliably produce different GNRs, using precursor monomers that encode the structure of the targeted nanoribbon and are converted into GNRs by means of surface-assisted coupling. Graphene Nanoribbons—narrow and straight-edged stripes of graphene, or single-layer graphite—are predicted to exhibit electronic properties that make them attractive for the fabrication of nanoscale electronic devices1,2,3. In particular, although the two-dimensional parent material graphene4,5 exhibits semimetallic behaviour, quantum confinement and edge effects2,6 should render all graphene Nanoribbons with widths smaller than 10 nm semiconducting. But exploring the potential of graphene Nanoribbons is hampered by their limited availability: although they have been made using chemical7,8,9, sonochemical10 and lithographic11,12 methods as well as through the unzipping of carbon nanotubes13,14,15,16, the reliable production of graphene Nanoribbons smaller than 10 nm with chemical precision remains a significant challenge. Here we report a simple method for the production of atomically precise graphene Nanoribbons of different topologies and widths, which uses surface-assisted coupling17,18 of molecular precursors into linear polyphenylenes and their subsequent cyclodehydrogenation19,20. The topology, width and edge periphery of the graphene nanoribbon products are defined by the structure of the precursor monomers, which can be designed to give access to a wide range of different graphene Nanoribbons. We expect that our bottom-up approach to the atomically precise fabrication of graphene Nanoribbons will finally enable detailed experimental investigations of the properties of this exciting class of materials. It should even provide a route to graphene nanoribbon structures with engineered chemical and electronic properties, including the theoretically predicted intraribbon quantum dots21, superlattice structures22 and magnetic devices based on specific graphene nanoribbon edge states3.
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atomically precise bottom up fabrication of graphene Nanoribbons
Nature, 2010Co-Authors: Pascal Ruffieux, Stephan Blankenburg, Rached Jaafar, Marco Bieri, Thomas Braun, Matthias Muoth, Ari P Seitsonen, Moussa Saleh, Xinliang FengAbstract:Graphene Nanoribbons (GNRs) have structure-dependent electronic properties that make them attractive for the fabrication of nanoscale electronic devices, but exploiting this potential has been hindered by the lack of precise production methods. Here the authors demonstrate how to reliably produce different GNRs, using precursor monomers that encode the structure of the targeted nanoribbon and are converted into GNRs by means of surface-assisted coupling.
Alex Zettl - One of the best experts on this subject based on the ideXlab platform.
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nanoimaging of low loss plasmonic waveguide modes in a graphene nanoribbon
Nano Letters, 2021Co-Authors: Wenyu Zhao, Alex Zettl, Xiao Xiao, Yue Jiang, Kenji Watanabe, Takashi Taniguchi, Feng WangAbstract:Graphene Nanoribbons are predicted to support low-loss and tunable plasmonic waveguide modes with an ultrasmall mode area. Experimental observation of the plasmonic waveguide modes in graphene Nanoribbons, however, is challenging because conventional wet lithography has difficulty creating a clean graphene nanoribbon with a low edge roughness. Here, we use a dry lithography method to fabricate ultraclean and low-roughness graphene Nanoribbons, which are then encapsulated in hexagonal boron nitride (hBN). We demonstrate low-loss plasmon propagation with a quality factor up to 35 in the ultraclean nanoribbon waveguide using cryogenic infrared nanoscopy. In addition, we observe both the fundamental and the higher-order plasmonic waveguide modes for the first time. All the plasmon waveguide modes can be tuned through electrostatic gating. The observed tunable plasmon waveguide modes in ultraclean graphene Nanoribbons agree well with the finite-difference time-domain (FDTD) simulation results. They are promising for reconfigurable photonic circuits and devices at a subwavelength scale.
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Coronene-Based Graphene Nanoribbons Insulated by Boron Nitride Nanotubes: Electronic Properties of the Hybrid Structure
2018Co-Authors: Eduardo Gracia-espino, Hamid Reza Barzegar, Alex ZettlAbstract:We present a theoretical study on the formation of graphene Nanoribbonsvia polymerization of coronene moleculesinside the inner cavity of boron nitride nanotubes. We examine the electronic property of the hybrid system, and we show that the boron nitride nanotube does not significantly alter the electronic properties of the encapsulated graphene nanoribbon. Motivated by previous experimental works, we examine graphene Nanoribbons with two different widths and investigate probable scenarios for defect formation and/or twisting of the resulting graphene Nanoribbons and their effect on the electronic properties of the hybrid system
Yongwei Zhang - One of the best experts on this subject based on the ideXlab platform.
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polarity reversed robust carrier mobility in monolayer mos2 Nanoribbons
Journal of the American Chemical Society, 2014Co-Authors: Yongqing Cai, Gang Zhang, Yongwei ZhangAbstract:Using first-principles calculations and deformation potential theory, we investigate the intrinsic carrier mobility (μ) of monolayer MoS2 sheet and Nanoribbons. In contrast to the dramatic deterioration of μ in graphene upon forming Nanoribbons, the magnitude of μ in armchair MoS2 Nanoribbons is comparable to its sheet counterpart, albeit oscillating with ribbon width. Surprisingly, a room-temperature transport polarity reversal is observed with μ of hole (h) and electron (e) being 200.52 (h) and 72.16 (e) cm2 V–1 s–1 in sheet, and 49.72 (h) and 190.89 (e) cm2 V–1 s–1 in 4 nm nanoribbon. The high and robust μ and its polarity reversal are attributable to the different characteristics of edge states inherent in MoS2 Nanoribbons. Our study suggests that width reduction together with edge engineering provide a promising route for improving the transport properties of MoS2 nanostructures.
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polarity reversed robust carrier mobility in monolayer mos2 Nanoribbons
arXiv: Materials Science, 2013Co-Authors: Yongqing Cai, Gang Zhang, Yongwei ZhangAbstract:Using first-principles calculations and deformation potential theory, we investigate the intrinsic carrier mobility ({\mu}) of monolayer MoS2 sheet and Nanoribbons. In contrast to the dramatic three orders of magnitude of deterioration of {\mu} in graphene upon forming Nanoribbons, the magnitude of {\mu} in armchair MoS2 Nanoribbons is comparable to that in monolayer MoS2 sheet, albeit oscillating with width. Surprisingly, a room-temperature transport polarity reversal is observed with {\mu} of hole (h) and electron (e) being 200.52 (h) and 72.16 (e) cm2V-1s-1 in sheet, and 49.72 (h) and 190.89 (e) cm2V-1s-1 in 4 nm-wide nanoribbon. The robust magnitudes of {\mu} and polarity reversal are attributable to the different characteristics of edge states inherent in MoS2 Nanoribbons. Our study suggests that width-reduction together with edge engineering provide a promising route for improving the transport properties of MoS2 nanostructures.
