Andre Geim
Degree: PhD
Position: Distinguished Visiting Professor
Affiliation: University of Manchester
Research Type: Experiment
Email: geim@manchester.ac.uk
Website: http://www.condmat.physics.manchester.ac.uk/people/academic/geim/
CA2DM Publications:
2024 |
Ronceray, Nathan; Spina, Massimo; Chou, Vanessa Hui Yin; Lim, Chwee Teck; Geim, Andre K; Garaj, Slaven Elastocapillarity-driven 2D nano-switches enable zeptoliter-scale liquid encapsulation Journal Article NATURE COMMUNICATIONS, 15 (1), 2024. @article{ISI:001158425400020, title = {Elastocapillarity-driven 2D nano-switches enable zeptoliter-scale liquid encapsulation}, author = {Nathan Ronceray and Massimo Spina and Vanessa Hui Yin Chou and Chwee Teck Lim and Andre K Geim and Slaven Garaj}, doi = {10.1038/s41467-023-44200-3}, times_cited = {0}, year = {2024}, date = {2024-01-02}, journal = {NATURE COMMUNICATIONS}, volume = {15}, number = {1}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Biological nanostructures change their shape and function in response to external stimuli, and significant efforts have been made to design artificial biomimicking devices operating on similar principles. In this work we demonstrate a programmable nanofluidic switch, driven by elastocapillarity, and based on nanochannels built fromlayered two-dimensional nanomaterials possessing atomically smooth surfaces and exceptional mechanical properties. We explore operational modes of the nanoswitch and develop a theoretical framework to explain the phenomenon. By predicting the switchingreversibility phase diagram-based on material, interfacial and wetting properties, as well as the geometry of the nanofluidic circuit-we rationally design switchable nano-capsules capable of enclosing zeptoliter volumes of liquid, as small as the volumes enclosed in viruses. The nanoswitch will find useful application as an active element in integrated nanofluidic circuitry and could be used to explore nanoconfined chemistry and biochemistry, or be incorporated into shape-programmable materials.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Biological nanostructures change their shape and function in response to external stimuli, and significant efforts have been made to design artificial biomimicking devices operating on similar principles. In this work we demonstrate a programmable nanofluidic switch, driven by elastocapillarity, and based on nanochannels built fromlayered two-dimensional nanomaterials possessing atomically smooth surfaces and exceptional mechanical properties. We explore operational modes of the nanoswitch and develop a theoretical framework to explain the phenomenon. By predicting the switchingreversibility phase diagram-based on material, interfacial and wetting properties, as well as the geometry of the nanofluidic circuit-we rationally design switchable nano-capsules capable of enclosing zeptoliter volumes of liquid, as small as the volumes enclosed in viruses. The nanoswitch will find useful application as an active element in integrated nanofluidic circuitry and could be used to explore nanoconfined chemistry and biochemistry, or be incorporated into shape-programmable materials. |
2021 |
Xu, Shuigang; Ezzi, Mohammed Al M; Balakrishnan, Nilanthy; Garcia-Ruiz, Aitor; Tsim, Bonnie; Mullan, Ciaran; Barrier, Julien; Xin, Na; Piot, Benjamin A; Taniguchi, Takashi; Watanabe, Kenji; Carvalho, Alexandra; Mishchenko, Artem; Geim, A K; Fal'ko, Vladimir I; Adam, Shaffique; Neto, Antonio Helio Castro; Novoselov, Kostya S; Shi, Yanmeng Tunable van Hove singularities and correlated states in twisted monolayer-bilayer graphene Journal Article NATURE PHYSICS, 17 (5), pp. 619-+, 2021, ISSN: 1745-2473. @article{ISI:000619417000001, title = {Tunable van Hove singularities and correlated states in twisted monolayer-bilayer graphene}, author = {Shuigang Xu and Mohammed Al M Ezzi and Nilanthy Balakrishnan and Aitor Garcia-Ruiz and Bonnie Tsim and Ciaran Mullan and Julien Barrier and Na Xin and Benjamin A Piot and Takashi Taniguchi and Kenji Watanabe and Alexandra Carvalho and Artem Mishchenko and A K Geim and Vladimir I Fal'ko and Shaffique Adam and Antonio Helio Castro Neto and Kostya S Novoselov and Yanmeng Shi}, doi = {10.1038/s41567-021-01172-9}, times_cited = {0}, issn = {1745-2473}, year = {2021}, date = {2021-02-18}, journal = {NATURE PHYSICS}, volume = {17}, number = {5}, pages = {619-+}, publisher = {NATURE RESEARCH}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Understanding and tuning correlated states is of great interest and importance to modern condensed-matter physics. The recent discovery of unconventional superconductivity and Mott-like insulating states in magic-angle twisted bilayer graphene presents a unique platform to study correlation phenomena, in which the Coulomb energy dominates over the quenched kinetic energy as a result of hybridized flat bands. Extending this approach to the case of twisted multilayer graphene would allow even higher control over the band structure because of the reduced symmetry of the system. Here we study electronic transport properties of twisted monolayer-bilayer graphene (a bilayer on top of monolayer graphene heterostructure). We observe the formation of van Hove singularities that are highly tunable by changing either the twist angle or external electric field and can cause strong correlation effects under optimum conditions. We provide basic theoretical interpretations of the observed electronic structure.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Understanding and tuning correlated states is of great interest and importance to modern condensed-matter physics. The recent discovery of unconventional superconductivity and Mott-like insulating states in magic-angle twisted bilayer graphene presents a unique platform to study correlation phenomena, in which the Coulomb energy dominates over the quenched kinetic energy as a result of hybridized flat bands. Extending this approach to the case of twisted multilayer graphene would allow even higher control over the band structure because of the reduced symmetry of the system. Here we study electronic transport properties of twisted monolayer-bilayer graphene (a bilayer on top of monolayer graphene heterostructure). We observe the formation of van Hove singularities that are highly tunable by changing either the twist angle or external electric field and can cause strong correlation effects under optimum conditions. We provide basic theoretical interpretations of the observed electronic structure. |
Woods, C R; Ares, P; Nevison-Andrews, H; Holwill, M J; Fabregas, R; Guinea, F; Geim, A K; Novoselov, K S; Walet, N R; Fumagalli, L Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride Journal Article NATURE COMMUNICATIONS, 12 (1), 2021, ISSN: 2041-1723. @article{ISI:000662813400002, title = {Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride}, author = {C R Woods and P Ares and H Nevison-Andrews and M J Holwill and R Fabregas and F Guinea and A K Geim and K S Novoselov and N R Walet and L Fumagalli}, doi = {10.1038/s41467-020-20667-2}, times_cited = {6}, issn = {2041-1723}, year = {2021}, date = {2021-01-12}, journal = {NATURE COMMUNICATIONS}, volume = {12}, number = {1}, publisher = {NATURE RESEARCH}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {When two-dimensional crystals are brought into close proximity, their interaction results in reconstruction of electronic spectrum and crystal structure. Such reconstruction strongly depends on the twist angle between the crystals, which has received growing attention due to interesting electronic and optical properties that arise in graphene and transitional metal dichalcogenides. Here we study two insulating crystals of hexagonal boron nitride stacked at small twist angle. Using electrostatic force microscopy, we observe ferroelectric-like domains arranged in triangular superlattices with a large surface potential. The observation is attributed to interfacial elastic deformations that result in out-of-plane dipoles formed by pairs of boron and nitrogen atoms belonging to opposite interfacial surfaces. This creates a bilayer-thick ferroelectric with oppositely polarized (BN and NB) dipoles in neighbouring domains, in agreement with our modeling. These findings open up possibilities for designing van der Waals heterostructures and offer an alternative probe to study moire-superlattice electrostatic potentials.}, keywords = {}, pubstate = {published}, tppubtype = {article} } When two-dimensional crystals are brought into close proximity, their interaction results in reconstruction of electronic spectrum and crystal structure. Such reconstruction strongly depends on the twist angle between the crystals, which has received growing attention due to interesting electronic and optical properties that arise in graphene and transitional metal dichalcogenides. Here we study two insulating crystals of hexagonal boron nitride stacked at small twist angle. Using electrostatic force microscopy, we observe ferroelectric-like domains arranged in triangular superlattices with a large surface potential. The observation is attributed to interfacial elastic deformations that result in out-of-plane dipoles formed by pairs of boron and nitrogen atoms belonging to opposite interfacial surfaces. This creates a bilayer-thick ferroelectric with oppositely polarized (BN and NB) dipoles in neighbouring domains, in agreement with our modeling. These findings open up possibilities for designing van der Waals heterostructures and offer an alternative probe to study moire-superlattice electrostatic potentials. |
2020 |
Yang, Yaping; Li, Jidong; Yin, Jun; Xu, Shuigang; Mullan, Ciaran; Taniguchi, Takashi; Watanabe, Kenji; Geim, Andre K; Novoselov, Konstantin S; Mishchenko, Artem In situ manipulation of van der Waals heterostructures for twistronics Journal Article SCIENCE ADVANCES, 6 (49), 2020, ISSN: 2375-2548. @article{ISI:000596477400035, title = {In situ manipulation of van der Waals heterostructures for twistronics}, author = {Yaping Yang and Jidong Li and Jun Yin and Shuigang Xu and Ciaran Mullan and Takashi Taniguchi and Kenji Watanabe and Andre K Geim and Konstantin S Novoselov and Artem Mishchenko}, doi = {10.1126/sciadv.abd3655}, times_cited = {0}, issn = {2375-2548}, year = {2020}, date = {2020-12-01}, journal = {SCIENCE ADVANCES}, volume = {6}, number = {49}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, address = {1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA}, abstract = {In van der Waals heterostructures, electronic bands of two-dimensional (2D) materials, their nontrivial topology, and electron-electron interactions can be markedly changed by a moire pattern induced by twist angles between different layers. This process is referred to as twistronics, where the tuning of twist angle can be realized through mechanical manipulation of 2D materials. Here, we demonstrate an experimental technique that can achieve in situ dynamical rotation and manipulation of 2D materials in van der Waals heterostructures. Using this technique, we fabricated heterostructures where graphene is perfectly aligned with both top and bottom encapsulating layers of hexagonal boron nitride. Our technique enables twisted 2D material systems in one single stack with dynamically tunable optical, mechanical, and electronic properties.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In van der Waals heterostructures, electronic bands of two-dimensional (2D) materials, their nontrivial topology, and electron-electron interactions can be markedly changed by a moire pattern induced by twist angles between different layers. This process is referred to as twistronics, where the tuning of twist angle can be realized through mechanical manipulation of 2D materials. Here, we demonstrate an experimental technique that can achieve in situ dynamical rotation and manipulation of 2D materials in van der Waals heterostructures. Using this technique, we fabricated heterostructures where graphene is perfectly aligned with both top and bottom encapsulating layers of hexagonal boron nitride. Our technique enables twisted 2D material systems in one single stack with dynamically tunable optical, mechanical, and electronic properties. |
Shi, Yanmeng; Xu, Shuigang; Yang, Yaping; Slizovskiy, Sergey; Morozov, Sergey V; Son, Seok-Kyun; Ozdemir, Servet; Mullan, Ciaran; Barrier, Julien; Yin, Jun; Berdyugin, Alexey I; Piot, Benjamin A; Taniguchi, Takashi; Watanabe, Kenji; Fal'ko, Vladimir I; Novoselov, Kostya S; Geim, A K; Mishchenko, Artem Electronic phase separation in multilayer rhombohedral graphite Journal Article NATURE, 584 (7820), pp. 210-+, 2020, ISSN: 0028-0836. @article{ISI:000559831500011, title = {Electronic phase separation in multilayer rhombohedral graphite}, author = {Yanmeng Shi and Shuigang Xu and Yaping Yang and Sergey Slizovskiy and Sergey V Morozov and Seok-Kyun Son and Servet Ozdemir and Ciaran Mullan and Julien Barrier and Jun Yin and Alexey I Berdyugin and Benjamin A Piot and Takashi Taniguchi and Kenji Watanabe and Vladimir I Fal'ko and Kostya S Novoselov and A K Geim and Artem Mishchenko}, doi = {10.1038/s41586-020-2568-2}, times_cited = {0}, issn = {0028-0836}, year = {2020}, date = {2020-08-13}, journal = {NATURE}, volume = {584}, number = {7820}, pages = {210-+}, publisher = {NATURE RESEARCH}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Of the two stable forms of graphite, hexagonal and rhombohedral, the former is more common and has been studied extensively. The latter is less stable, which has so far precluded its detailed investigation, despite many theoretical predictions about the abundance of exotic interaction-induced physics(1-6). Advances in van der Waals heterostructure technology(7)have now allowed us to make high-quality rhombohedral graphite films up to 50 graphene layers thick and study their transport properties. Here we show that the bulk electronic states in such rhombohedral graphite are gapped(8)and, at low temperatures, electron transport is dominated by surface states. Because of their proposed topological nature, the surface states are of sufficiently high quality to observe the quantum Hall effect, whereby rhombohedral graphite exhibits phase transitions between a gapless semimetallic phase and a gapped quantum spin Hall phase with giant Berry curvature. We find that an energy gap can also be opened in the surface states by breaking their inversion symmetry by applying a perpendicular electric field. Moreover, in rhombohedral graphite thinner than four nanometres, a gap is present even without an external electric field. This spontaneous gap opening shows pronounced hysteresis and other signatures characteristic of electronic phase separation, which we attribute to emergence of strongly correlated electronic surface states.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Of the two stable forms of graphite, hexagonal and rhombohedral, the former is more common and has been studied extensively. The latter is less stable, which has so far precluded its detailed investigation, despite many theoretical predictions about the abundance of exotic interaction-induced physics(1-6). Advances in van der Waals heterostructure technology(7)have now allowed us to make high-quality rhombohedral graphite films up to 50 graphene layers thick and study their transport properties. Here we show that the bulk electronic states in such rhombohedral graphite are gapped(8)and, at low temperatures, electron transport is dominated by surface states. Because of their proposed topological nature, the surface states are of sufficiently high quality to observe the quantum Hall effect, whereby rhombohedral graphite exhibits phase transitions between a gapless semimetallic phase and a gapped quantum spin Hall phase with giant Berry curvature. We find that an energy gap can also be opened in the surface states by breaking their inversion symmetry by applying a perpendicular electric field. Moreover, in rhombohedral graphite thinner than four nanometres, a gap is present even without an external electric field. This spontaneous gap opening shows pronounced hysteresis and other signatures characteristic of electronic phase separation, which we attribute to emergence of strongly correlated electronic surface states. |
Griffin, Eoin; Mogg, Lucas; Hao, Guang-Ping; Kalon, Gopinadhan; Bacaksiz, Cihan; Lopez-Polin, Guillermo; Zhou, T Y; Guarochico, Victor; Cai, Junhao; Neumann, Christof; Winter, Andreas; Mohn, Michael; Lee, Jong Hak; Lin, Junhao; Kaiser, Ute; Grigorieva, Irina; Suenaga, Kazu; Ozyilmaz, Barbaros; Cheng, Hui-Min; Ren, Wencai; Turchanin, Andrey; Peeters, Francois M; Geim, Andre K; Lozada-Hidalgo, Marcelo Proton and Li-Ion Permeation through Graphene with Eight-Atom-Ring Defects Journal Article ACS NANO, 14 (6), pp. 7280-7286, 2020, ISSN: 1936-0851. @article{ISI:000543744100086, title = {Proton and Li-Ion Permeation through Graphene with Eight-Atom-Ring Defects}, author = {Eoin Griffin and Lucas Mogg and Guang-Ping Hao and Gopinadhan Kalon and Cihan Bacaksiz and Guillermo Lopez-Polin and T Y Zhou and Victor Guarochico and Junhao Cai and Christof Neumann and Andreas Winter and Michael Mohn and Jong Hak Lee and Junhao Lin and Ute Kaiser and Irina Grigorieva and Kazu Suenaga and Barbaros Ozyilmaz and Hui-Min Cheng and Wencai Ren and Andrey Turchanin and Francois M Peeters and Andre K Geim and Marcelo Lozada-Hidalgo}, doi = {10.1021/acsnano.0c02496}, times_cited = {0}, issn = {1936-0851}, year = {2020}, date = {2020-06-23}, journal = {ACS NANO}, volume = {14}, number = {6}, pages = {7280-7286}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Defect-free graphene is impermeable to gases and liquids but highly permeable to thermal protons. Atomic-scale defects such as vacancies, grain boundaries, and Stone-Wales defects are predicted to enhance graphene's proton permeability and may even allow small ions through, whereas larger species such as gas molecules should remain blocked. These expectations have so far remained untested in experiment. Here, we show that atomically thin carbon films with a high density of atomic-scale defects continue blocking all molecular transport, but their proton permeability becomes similar to 1000 times higher than that of defect-free graphene. Lithium ions can also permeate through such disordered graphene. The enhanced proton and ion permeability is attributed to a high density of eight-carbon-atom rings. The latter pose approximately twice lower energy barriers for incoming protons compared to that of the six-atom rings of graphene and a relatively low barrier of similar to 0.6 eV for Li ions. Our findings suggest that disordered graphene could be of interest as membranes and protective barriers in various Li-ion and hydrogen technologies.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Defect-free graphene is impermeable to gases and liquids but highly permeable to thermal protons. Atomic-scale defects such as vacancies, grain boundaries, and Stone-Wales defects are predicted to enhance graphene's proton permeability and may even allow small ions through, whereas larger species such as gas molecules should remain blocked. These expectations have so far remained untested in experiment. Here, we show that atomically thin carbon films with a high density of atomic-scale defects continue blocking all molecular transport, but their proton permeability becomes similar to 1000 times higher than that of defect-free graphene. Lithium ions can also permeate through such disordered graphene. The enhanced proton and ion permeability is attributed to a high density of eight-carbon-atom rings. The latter pose approximately twice lower energy barriers for incoming protons compared to that of the six-atom rings of graphene and a relatively low barrier of similar to 0.6 eV for Li ions. Our findings suggest that disordered graphene could be of interest as membranes and protective barriers in various Li-ion and hydrogen technologies. |
Velicky, Matej; Hu, Sheng; Woods, Colin R; Toth, Peter S; Zolyomi, Viktor; Geim, Andre K; Abruna, Hector D; Novoselov, Kostya S; Dryfe, Robert A W Electron Tunneling through Boron Nitride Confirms Marcus-Hush Theory Predictions for Ultramicroelectrodes Journal Article ACS NANO, 14 (1), pp. 993-1002, 2020, ISSN: 1936-0851. @article{ISI:000510531500088, title = {Electron Tunneling through Boron Nitride Confirms Marcus-Hush Theory Predictions for Ultramicroelectrodes}, author = {Matej Velicky and Sheng Hu and Colin R Woods and Peter S Toth and Viktor Zolyomi and Andre K Geim and Hector D Abruna and Kostya S Novoselov and Robert A W Dryfe}, doi = {10.1021/acsnano.9b08308}, times_cited = {0}, issn = {1936-0851}, year = {2020}, date = {2020-01-01}, journal = {ACS NANO}, volume = {14}, number = {1}, pages = {993-1002}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Marcus-Hush theory of electron transfer is one of the pillars of modern electrochemistry with a large body of supporting experimental evidence presented to date. However, some predictions, such as the electrochemical behavior at disk ultramicroelectrodes, remain unverified. Herein, we present a study of electron tunneling across a hexagonal boron nitride acting as a barrier between a graphite electrode and redox mediators in a liquid solution. This was achieved by the fabrication of disk ultramicroelectrodes with a typical diameter of 5 pm. Analysis of voltammetric measurements, using two common outer-sphere redox mediators, yielded several electrochemical parameters, including the electron transfer rate constant, limiting current, and transfer coefficient. They depart significantly from the Butler-Volmer kinetics and instead show behavior previously predicted by the Marcus-Hush theory of electron transfer. In addition, our system provides a noteworthy experimental platform, which could be applied to address a number of scientific problems such as identification of reaction mechanisms, surface modification, or long-range electron transfer.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Marcus-Hush theory of electron transfer is one of the pillars of modern electrochemistry with a large body of supporting experimental evidence presented to date. However, some predictions, such as the electrochemical behavior at disk ultramicroelectrodes, remain unverified. Herein, we present a study of electron tunneling across a hexagonal boron nitride acting as a barrier between a graphite electrode and redox mediators in a liquid solution. This was achieved by the fabrication of disk ultramicroelectrodes with a typical diameter of 5 pm. Analysis of voltammetric measurements, using two common outer-sphere redox mediators, yielded several electrochemical parameters, including the electron transfer rate constant, limiting current, and transfer coefficient. They depart significantly from the Butler-Volmer kinetics and instead show behavior previously predicted by the Marcus-Hush theory of electron transfer. In addition, our system provides a noteworthy experimental platform, which could be applied to address a number of scientific problems such as identification of reaction mechanisms, surface modification, or long-range electron transfer. |
2019 |
Wang, Zihao; Wang, Yi Bo; Yin, J; Tovari, E; Yang, Y; Lin, L; Holwill, M; Birkbeck, J; Perello, D J; Xu, Shuigang; Zultak, J; Gorbachev, R V; Kretinin, A V; Taniguchi, T; Watanabe, K; Morozov, S V; Andelkovic, M; Milovanovic, S P; Covaci, L; Peeters, F M; Mishchenko, A; Geim, A K; Novoselov, K S; Fal'ko, Vladimir I; Knothe, Angelika; Woods, C R Composite super-moire lattices in double-aligned graphene heterostructures Journal Article SCIENCE ADVANCES, 5 (12), 2019, ISSN: 2375-2548. @article{ISI:000505069600089, title = {Composite super-moire lattices in double-aligned graphene heterostructures}, author = {Zihao Wang and Yi Bo Wang and J Yin and E Tovari and Y Yang and L Lin and M Holwill and J Birkbeck and D J Perello and Shuigang Xu and J Zultak and R V Gorbachev and A V Kretinin and T Taniguchi and K Watanabe and S V Morozov and M Andelkovic and S P Milovanovic and L Covaci and F M Peeters and A Mishchenko and A K Geim and K S Novoselov and Vladimir I Fal'ko and Angelika Knothe and C R Woods}, doi = {10.1126/sciadv.aay8897}, times_cited = {0}, issn = {2375-2548}, year = {2019}, date = {2019-12-01}, journal = {SCIENCE ADVANCES}, volume = {5}, number = {12}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, address = {1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA}, abstract = {When two-dimensional (2D) atomic crystals are brought into close proximity to form a van der Waals heterostructure, neighbouring crystals may influence each other's properties. Of particular interest is when the two crystals closely match and a moire pattern forms, resulting in modified electronic and excitonic spectra, crystal reconstruction, and more. Thus, moire patterns are a viable tool for controlling the properties of 2D materials. However, the difference in periodicity of the two crystals limits the reconstruction and, thus, is a barrier to the low-energy regime. Here, we present a route to spectrum reconstruction at all energies. By using graphene which is aligned to two hexagonal boron nitride layers, one can make electrons scatter in the differential moire pattern which results in spectral changes at arbitrarily low energies. Further, we demonstrate that the strength of this potential relies crucially on the atomic reconstruction of graphene within the differential moire super cell.}, keywords = {}, pubstate = {published}, tppubtype = {article} } When two-dimensional (2D) atomic crystals are brought into close proximity to form a van der Waals heterostructure, neighbouring crystals may influence each other's properties. Of particular interest is when the two crystals closely match and a moire pattern forms, resulting in modified electronic and excitonic spectra, crystal reconstruction, and more. Thus, moire patterns are a viable tool for controlling the properties of 2D materials. However, the difference in periodicity of the two crystals limits the reconstruction and, thus, is a barrier to the low-energy regime. Here, we present a route to spectrum reconstruction at all energies. By using graphene which is aligned to two hexagonal boron nitride layers, one can make electrons scatter in the differential moire pattern which results in spectral changes at arbitrarily low energies. Further, we demonstrate that the strength of this potential relies crucially on the atomic reconstruction of graphene within the differential moire super cell. |
Yang, Yaping; Zou, Yi-Chao; Woods, Colin R; Shi, Yanmeng; Yin, Jun; Xu, Shuigang; Ozdemir, Servet; Taniguchi, Takashi; Watanabe, Kenji; Geim, Andre K; Novoselov, Kostya S; Haigh, Sarah J; Mishchenko, Artem Stacking Order in Graphite Films Controlled by van der Waals Technology Journal Article NANO LETTERS, 19 (12), pp. 8526-8532, 2019, ISSN: 1530-6984. @article{ISI:000502687500023, title = {Stacking Order in Graphite Films Controlled by van der Waals Technology}, author = {Yaping Yang and Yi-Chao Zou and Colin R Woods and Yanmeng Shi and Jun Yin and Shuigang Xu and Servet Ozdemir and Takashi Taniguchi and Kenji Watanabe and Andre K Geim and Kostya S Novoselov and Sarah J Haigh and Artem Mishchenko}, doi = {10.1021/acs.nanolett.9b03014}, times_cited = {0}, issn = {1530-6984}, year = {2019}, date = {2019-12-01}, journal = {NANO LETTERS}, volume = {19}, number = {12}, pages = {8526-8532}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {In graphite crystals, layers of graphene reside in three equivalent, but distinct, stacking positions typically referred to as A, B, and C projections. The order in which the layers are stacked defines the electronic structure of the crystal, providing an exciting degree of freedom which can be exploited for designing graphitic materials with unusual properties including predicted high-temperature superconductivity and ferromagnetism. However, the lack of control of the stacking sequence limits most research to the stable ABA form of graphite. Here, we demonstrate a strategy to control the stacking order using van der Waals technology. To this end, we first visualize the distribution of stacking domains in graphite films and then perform directional encapsulation of ABC-rich graphite crystallites with hexagonal boron nitride (hBN). We found that hBN encapsulation, which is introduced parallel to the graphite zigzag edges, preserves ABC stacking, while encapsulation along the armchair edges transforms the stacking to ABA. The technique presented here should facilitate new research on the important properties of ABC graphite.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In graphite crystals, layers of graphene reside in three equivalent, but distinct, stacking positions typically referred to as A, B, and C projections. The order in which the layers are stacked defines the electronic structure of the crystal, providing an exciting degree of freedom which can be exploited for designing graphitic materials with unusual properties including predicted high-temperature superconductivity and ferromagnetism. However, the lack of control of the stacking sequence limits most research to the stable ABA form of graphite. Here, we demonstrate a strategy to control the stacking order using van der Waals technology. To this end, we first visualize the distribution of stacking domains in graphite films and then perform directional encapsulation of ABC-rich graphite crystallites with hexagonal boron nitride (hBN). We found that hBN encapsulation, which is introduced parallel to the graphite zigzag edges, preserves ABC stacking, while encapsulation along the armchair edges transforms the stacking to ABA. The technique presented here should facilitate new research on the important properties of ABC graphite. |
2018 |
Hamer, Matthew; Tovari, Endre; Zhu, Mengjian; Thompson, Michael D; Mayorov, Alexander; Prance, Jonathon; Lee, Yongjin; Haley, Richard P; Kudrynskyi, Zakhar R; Patane, Amalia; Terry, Daniel; Kovalyuk, Zakhar D; Ensslin, Klaus; Kretinin, Andrey; Geim, Andre; Gorbachev, Roman Gate-Defined Quantum Confinement in InSe-Based van der Waals Heterostructures Journal Article NANO LETTERS, 18 (6), pp. 3950-3955, 2018, ISSN: 1530-6984. @article{ISI:000435524300089, title = {Gate-Defined Quantum Confinement in InSe-Based van der Waals Heterostructures}, author = {Matthew Hamer and Endre Tovari and Mengjian Zhu and Michael D Thompson and Alexander Mayorov and Jonathon Prance and Yongjin Lee and Richard P Haley and Zakhar R Kudrynskyi and Amalia Patane and Daniel Terry and Zakhar D Kovalyuk and Klaus Ensslin and Andrey Kretinin and Andre Geim and Roman Gorbachev}, doi = {10.1021/acs.nanolett.8b01376}, times_cited = {2}, issn = {1530-6984}, year = {2018}, date = {2018-06-01}, journal = {NANO LETTERS}, volume = {18}, number = {6}, pages = {3950-3955}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Indium selenide, a post-transition metal chalco-genide, is a novel two-dimensional (2D) semiconductor with interesting electronic properties. Its tunable band gap and high electron mobility have already attracted considerable research interest. Here we demonstrate strong quantum confinement and manipulation of single electrons in devices made from few-layer crystals of InSe using electrostatic gating. We report on gate-controlled quantum dots in the Coulomb blockade regime as well as one-dimensional quantization in point contacts, revealing multiple plateaus. The work represents an important milestone in the development of quality devices based on 2D materials and makes InSe a prime candidate for relevant electronic and optoelectronic applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Indium selenide, a post-transition metal chalco-genide, is a novel two-dimensional (2D) semiconductor with interesting electronic properties. Its tunable band gap and high electron mobility have already attracted considerable research interest. Here we demonstrate strong quantum confinement and manipulation of single electrons in devices made from few-layer crystals of InSe using electrostatic gating. We report on gate-controlled quantum dots in the Coulomb blockade regime as well as one-dimensional quantization in point contacts, revealing multiple plateaus. The work represents an important milestone in the development of quality devices based on 2D materials and makes InSe a prime candidate for relevant electronic and optoelectronic applications. |
2017 |
Esfandiar, A; Radha, B; Wang, F C; Yang, Q; Hu, S; Garaj, S; Nair, R R; Geim, A K; Gopinadhan, K Size effect in ion transport through angstrom-scale slits Journal Article SCIENCE, 358 (6362), pp. 511-513, 2017, ISSN: 0036-8075. @article{ISI:000413757500042, title = {Size effect in ion transport through angstrom-scale slits}, author = {A Esfandiar and B Radha and F C Wang and Q Yang and S Hu and S Garaj and R R Nair and A K Geim and K Gopinadhan}, doi = {10.1126/science.aan5275}, times_cited = {0}, issn = {0036-8075}, year = {2017}, date = {2017-10-27}, journal = {SCIENCE}, volume = {358}, number = {6362}, pages = {511-513}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, address = {1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA}, abstract = {In the field of nanofluidics, it has been an ultimate but seemingly distant goal to controllably fabricate capillaries with dimensions approaching the size of small ions and water molecules. We report ion transport through ultimately narrow slits that are fabricated by effectively removing a single atomic plane from a bulk crystal. The atomically flat angstrom-scale slits exhibit little surface charge, allowing elucidation of the role of steric effects. We find that ions with hydrated diameters larger than the slit size can still permeate through, albeit with reduced mobility. The confinement also leads to a notable asymmetry between anions and cations of the same diameter. Our results provide a platform for studying the effects of angstrom-scale confinement, which is important for the development of nanofluidics, molecular separation, and other nanoscale technologies.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In the field of nanofluidics, it has been an ultimate but seemingly distant goal to controllably fabricate capillaries with dimensions approaching the size of small ions and water molecules. We report ion transport through ultimately narrow slits that are fabricated by effectively removing a single atomic plane from a bulk crystal. The atomically flat angstrom-scale slits exhibit little surface charge, allowing elucidation of the role of steric effects. We find that ions with hydrated diameters larger than the slit size can still permeate through, albeit with reduced mobility. The confinement also leads to a notable asymmetry between anions and cations of the same diameter. Our results provide a platform for studying the effects of angstrom-scale confinement, which is important for the development of nanofluidics, molecular separation, and other nanoscale technologies. |
2015 |
Gopinadhan, Kalon; Shin, Young Jun; Jalil, Rashid; Venkatesan, Thirumalai; Geim, Andre K; Neto, Antonio Castro H; Yang, Hyunsoo Extremely large magnetoresistance in few-layer graphene/boron-nitride heterostructures Journal Article NATURE COMMUNICATIONS, 6 , 2015, ISSN: 2041-1723. @article{ISI:000363021700001, title = {Extremely large magnetoresistance in few-layer graphene/boron-nitride heterostructures}, author = {Kalon Gopinadhan and Young Jun Shin and Rashid Jalil and Thirumalai Venkatesan and Andre K Geim and Antonio Castro H Neto and Hyunsoo Yang}, doi = {10.1038/ncomms9337}, times_cited = {0}, issn = {2041-1723}, year = {2015}, date = {2015-09-01}, journal = {NATURE COMMUNICATIONS}, volume = {6}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Understanding magnetoresistance, the change in electrical resistance under an external magnetic field, at the atomic level is of great interest both fundamentally and technologically. Graphene and other two-dimensional layered materials provide an unprecedented opportunity to explore magnetoresistance at its nascent stage of structural formation. Here we report an extremely large local magnetoresistance of similar to 2,000% at 400 K and a non-local magnetoresistance of 490,000% in an applied magnetic field of 9 T at 300 K in few-layer graphene/boron-nitride heterostructures. The local magnetoresistance is understood to arise from large differential transport parameters, such as the carrier mobility, across various layers of few-layer graphene upon a normal magnetic field, whereas the non-local magnetoresistance is due to the magnetic field induced Ettingshausen-Nernst effect. Non-local magnetoresistance suggests the possibility of a graphene-based gate tunable thermal switch. In addition, our results demonstrate that graphene heterostructures may be promising for magnetic field sensing applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Understanding magnetoresistance, the change in electrical resistance under an external magnetic field, at the atomic level is of great interest both fundamentally and technologically. Graphene and other two-dimensional layered materials provide an unprecedented opportunity to explore magnetoresistance at its nascent stage of structural formation. Here we report an extremely large local magnetoresistance of similar to 2,000% at 400 K and a non-local magnetoresistance of 490,000% in an applied magnetic field of 9 T at 300 K in few-layer graphene/boron-nitride heterostructures. The local magnetoresistance is understood to arise from large differential transport parameters, such as the carrier mobility, across various layers of few-layer graphene upon a normal magnetic field, whereas the non-local magnetoresistance is due to the magnetic field induced Ettingshausen-Nernst effect. Non-local magnetoresistance suggests the possibility of a graphene-based gate tunable thermal switch. In addition, our results demonstrate that graphene heterostructures may be promising for magnetic field sensing applications. |
2014 |
Kretinin, A V; Cao, Y; Tu, J S; Yu, G L; Jalil, R; Novoselov, K S; Haigh, S J; Gholinia, A; Mishchenko, A; Lozada, M; Georgiou, T; Woods, C R; Withers, F; Blake, P; Eda, G; Wirsig, A; Hucho, C; Watanabe, K; Taniguchi, T; Geim, A K; Gorbachev, R V Electronic Properties of Graphene Encapsulated with Different Two-Dimensional Atomic Crystals Journal Article NANO LETTERS, 14 (6), pp. 3270-3276, 2014, ISSN: 1530-6984. @article{ISI:000337337100045, title = {Electronic Properties of Graphene Encapsulated with Different Two-Dimensional Atomic Crystals}, author = {A V Kretinin and Y Cao and J S Tu and G L Yu and R Jalil and K S Novoselov and S J Haigh and A Gholinia and A Mishchenko and M Lozada and T Georgiou and C R Woods and F Withers and P Blake and G Eda and A Wirsig and C Hucho and K Watanabe and T Taniguchi and A K Geim and R V Gorbachev}, doi = {10.1021/nl5006542}, times_cited = {0}, issn = {1530-6984}, year = {2014}, date = {2014-06-01}, journal = {NANO LETTERS}, volume = {14}, number = {6}, pages = {3270-3276}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Hexagonal boron nitride is the only substrate that has so far allowed graphene devices exhibiting micrometer-scale ballistic transport. Can other atomically flat crystals be used as substrates for making quality graphene heterostructures? Here we report on our search for alternative substrates. The devices fabricated by encapsulating graphene with molybdenum or tungsten disulfides and hBN are found to exhibit consistently high carrier mobilities of about 60 000 cm(2) V-1 s(-1). In contrast, encapsulation with atomically flat layered oxides such as mica, bismuth strontium calcium copper oxide, and vanadium pentoxide results in exceptionally low quality of graphene devices with mobilities of similar to 1000 cm(2) V-1 s(-1). We attribute the difference mainly to self-cleansing that takes place at interfaces between graphene, hBN, and transition metal dichalcogenides. Surface contamination assembles into large pockets allowing the rest of the interface to become atomically clean. The cleansing process does not occur for graphene on atomically flat oxide substrates.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Hexagonal boron nitride is the only substrate that has so far allowed graphene devices exhibiting micrometer-scale ballistic transport. Can other atomically flat crystals be used as substrates for making quality graphene heterostructures? Here we report on our search for alternative substrates. The devices fabricated by encapsulating graphene with molybdenum or tungsten disulfides and hBN are found to exhibit consistently high carrier mobilities of about 60 000 cm(2) V-1 s(-1). In contrast, encapsulation with atomically flat layered oxides such as mica, bismuth strontium calcium copper oxide, and vanadium pentoxide results in exceptionally low quality of graphene devices with mobilities of similar to 1000 cm(2) V-1 s(-1). We attribute the difference mainly to self-cleansing that takes place at interfaces between graphene, hBN, and transition metal dichalcogenides. Surface contamination assembles into large pockets allowing the rest of the interface to become atomically clean. The cleansing process does not occur for graphene on atomically flat oxide substrates. |
2013 |
Britnell, L; Ribeiro, R M; Eckmann, A; Jalil, R; Belle, B D; Mishchenko, A; Kim, Y -J; Gorbachev, R V; Georgiou, T; Morozov, S V; Grigorenko, A N; Geim, A K; Casiraghi, C; Neto, Castro A H; Novoselov, K S Strong Light-Matter Interactions in Heterostructures of Atomically Thin Films Journal Article 2081 SCIENCE, 340 (6138), pp. 1311-1314, 2013, ISSN: 0036-8075. @article{ISI:000320320200039, title = {Strong Light-Matter Interactions in Heterostructures of Atomically Thin Films}, author = {L Britnell and R M Ribeiro and A Eckmann and R Jalil and B D Belle and A Mishchenko and Y -J Kim and R V Gorbachev and T Georgiou and S V Morozov and A N Grigorenko and A K Geim and C Casiraghi and Castro A H Neto and K S Novoselov}, doi = {10.1126/science.1235547}, times_cited = {2081}, issn = {0036-8075}, year = {2013}, date = {2013-06-14}, journal = {SCIENCE}, volume = {340}, number = {6138}, pages = {1311-1314}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, address = {1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA}, abstract = {The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum efficiency of above 30%).}, keywords = {}, pubstate = {published}, tppubtype = {article} } The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum efficiency of above 30%). |
Nair, R R; Tsai, I-L; Sepioni, M; Lehtinen, O; Keinonen, J; Krasheninnikov, A V; Neto, Castro A H; Katsnelson, M I; Geim, A K; Grigorieva, I V Dual origin of defect magnetism in graphene and its reversible switching by molecular doping Journal Article NATURE COMMUNICATIONS, 4 , 2013, ISSN: 2041-1723. @article{ISI:000323625200007, title = {Dual origin of defect magnetism in graphene and its reversible switching by molecular doping}, author = {R R Nair and I-L Tsai and M Sepioni and O Lehtinen and J Keinonen and A V Krasheninnikov and Castro A H Neto and M I Katsnelson and A K Geim and I V Grigorieva}, doi = {10.1038/ncomms3010}, times_cited = {0}, issn = {2041-1723}, year = {2013}, date = {2013-06-01}, journal = {NATURE COMMUNICATIONS}, volume = {4}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Control of magnetism by applied voltage is desirable for spintronics applications. Finding a suitable material remains an elusive goal, with only a few candidates found so far. Graphene is one of them and attracts interest because of its weak spin-orbit interaction, the ability to control electronic properties by the electric field effect and the possibility to introduce paramagnetic centres such as vacancies and adatoms. Here we show that the magnetism of adatoms in graphene is itinerant and can be controlled by doping, so that magnetic moments are switched on and off. The much-discussed vacancy magnetism is found to have a dual origin, with two approximately equal contributions; one from itinerant magnetism and the other from dangling bonds. Our work suggests that graphene's spin transport can be controlled by the field effect, similar to its electronic and optical properties, and that spin diffusion can be significantly enhanced above a certain carrier density.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Control of magnetism by applied voltage is desirable for spintronics applications. Finding a suitable material remains an elusive goal, with only a few candidates found so far. Graphene is one of them and attracts interest because of its weak spin-orbit interaction, the ability to control electronic properties by the electric field effect and the possibility to introduce paramagnetic centres such as vacancies and adatoms. Here we show that the magnetism of adatoms in graphene is itinerant and can be controlled by doping, so that magnetic moments are switched on and off. The much-discussed vacancy magnetism is found to have a dual origin, with two approximately equal contributions; one from itinerant magnetism and the other from dangling bonds. Our work suggests that graphene's spin transport can be controlled by the field effect, similar to its electronic and optical properties, and that spin diffusion can be significantly enhanced above a certain carrier density. |