Browse through over scientific publications by CA2DM staff, students, collaborators, and partners.
2012 |
Ochoa, H; Neto, Castro A H; Guinea, F Elliot-Yafet Mechanism in Graphene Journal Article PHYSICAL REVIEW LETTERS, 108 (20), 2012, ISSN: 0031-9007. @article{ISI:000304176300002, title = {Elliot-Yafet Mechanism in Graphene}, author = {H Ochoa and A H Castro Neto and F Guinea}, doi = {10.1103/PhysRevLett.108.206808}, issn = {0031-9007}, year = {2012}, date = {2012-05-01}, journal = {PHYSICAL REVIEW LETTERS}, volume = {108}, number = {20}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {The differences between spin relaxation in graphene and in other materials are discussed. For relaxation by scattering processes, the Elliot-Yafet mechanism, the relation between the spin and the momentum scattering times, acquires a dependence on the carrier density, which is independent of the scattering mechanism and the relation between mobility and carrier concentration. This dependence puts severe restrictions on the origin of the spin relaxation in graphene. The density dependence of the spin relaxation allows us to distinguish between ordinary impurities and defects which modify locally the spin-orbit interaction.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The differences between spin relaxation in graphene and in other materials are discussed. For relaxation by scattering processes, the Elliot-Yafet mechanism, the relation between the spin and the momentum scattering times, acquires a dependence on the carrier density, which is independent of the scattering mechanism and the relation between mobility and carrier concentration. This dependence puts severe restrictions on the origin of the spin relaxation in graphene. The density dependence of the spin relaxation allows us to distinguish between ordinary impurities and defects which modify locally the spin-orbit interaction. |
Ferreira, Aires; Peres, N M R; Neto, Castro A H Confined magneto-optical waves in graphene Journal Article PHYSICAL REVIEW B, 85 (20), 2012, ISSN: 1098-0121. @article{ISI:000304081900013, title = {Confined magneto-optical waves in graphene}, author = {Aires Ferreira and N M R Peres and A H Castro Neto}, doi = {10.1103/PhysRevB.85.205426}, issn = {1098-0121}, year = {2012}, date = {2012-05-01}, journal = {PHYSICAL REVIEW B}, volume = {85}, number = {20}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {The electromagnetic mode spectrum of single-layer graphene subjected to a quantizing magnetic field is computed taking into account intraband and interband contributions to the magneto-optical conductivity. We find that a sequence of weakly decaying quasi-transverse-electric modes, separated by magnetoplasmon polariton modes, emerge due to the quantizing magnetic field. The characteristics of these modes are tunable by changing the magnetic field or the Fermi energy.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The electromagnetic mode spectrum of single-layer graphene subjected to a quantizing magnetic field is computed taking into account intraband and interband contributions to the magneto-optical conductivity. We find that a sequence of weakly decaying quasi-transverse-electric modes, separated by magnetoplasmon polariton modes, emerge due to the quantizing magnetic field. The characteristics of these modes are tunable by changing the magnetic field or the Fermi energy. |
Niu, Jing; Truong, Viet Giang; Huang, Han; Tripathy, Sudhiranjan; Qiu, Caiyu; Wee, Andrew T S; Yu, Ting; Yang, Hyunsoo Study of electromagnetic enhancement for surface enhanced Raman spectroscopy of SiC graphene Journal Article APPLIED PHYSICS LETTERS, 100 (19), 2012, ISSN: 0003-6951. @article{ISI:000304108000017, title = {Study of electromagnetic enhancement for surface enhanced Raman spectroscopy of SiC graphene}, author = {Jing Niu and Viet Giang Truong and Han Huang and Sudhiranjan Tripathy and Caiyu Qiu and Andrew T S Wee and Ting Yu and Hyunsoo Yang}, doi = {10.1063/1.4712054}, issn = {0003-6951}, year = {2012}, date = {2012-05-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {100}, number = {19}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {The electromagnetic enhancement for surface enhanced Raman spectroscopy (SERS) of graphene is studied by inserting a layer of Al2O3 between epitaxial graphene and Au nanoparticles. Different excitation lasers are utilized to study the relationship between laser wavelength and SERS. The theoretical calculation shows that the extinction spectrum of Au nanoparticles is modulated by the presence of graphene. The experimental results of the relationship between the excitation laser wavelength and the enhancement factor fit well with the calculated results. An exponential relationship is observed between the enhancement factor and the thickness of the spacer layer. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712054]}, keywords = {}, pubstate = {published}, tppubtype = {article} } The electromagnetic enhancement for surface enhanced Raman spectroscopy (SERS) of graphene is studied by inserting a layer of Al2O3 between epitaxial graphene and Au nanoparticles. Different excitation lasers are utilized to study the relationship between laser wavelength and SERS. The theoretical calculation shows that the extinction spectrum of Au nanoparticles is modulated by the presence of graphene. The experimental results of the relationship between the excitation laser wavelength and the enhancement factor fit well with the calculated results. An exponential relationship is observed between the enhancement factor and the thickness of the spacer layer. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712054] |
Lu, Jiong; Neto, Castro A H; Loh, Kian Ping Transforming moire blisters into geometric graphene nano-bubbles Journal Article NATURE COMMUNICATIONS, 3 , 2012, ISSN: 2041-1723. @article{ISI:000304611400019, title = {Transforming moire blisters into geometric graphene nano-bubbles}, author = {Jiong Lu and A H Castro Neto and Kian Ping Loh}, doi = {10.1038/ncomms1818}, issn = {2041-1723}, year = {2012}, date = {2012-05-01}, journal = {NATURE COMMUNICATIONS}, volume = {3}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Strain engineering has been proposed as an alternative method for manipulating the electronic properties of graphene. However, the bottleneck for strain engineering in graphene has been the ability to control such strain patterns at the nanoscale. Here we show that high level of control can be accomplished by chemically modifying the adherence of graphene on metal. Using scanning tunnelling microscopy, the shape evolution of graphene Moire blisters towards geometrically well-defined graphene bubbles was studied during the controlled, sub-layer oxidation of the ruthenium substrate. Understanding the dynamics of the oxidation process and defects generation on the Ru substrate allows us to control the size, shape and the density of the bubbles and its associated pseudo-magnetism. We also show that a modification of the same procedure can be used to create antidots in graphene by catalytic reaction of the same nanobubbles.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Strain engineering has been proposed as an alternative method for manipulating the electronic properties of graphene. However, the bottleneck for strain engineering in graphene has been the ability to control such strain patterns at the nanoscale. Here we show that high level of control can be accomplished by chemically modifying the adherence of graphene on metal. Using scanning tunnelling microscopy, the shape evolution of graphene Moire blisters towards geometrically well-defined graphene bubbles was studied during the controlled, sub-layer oxidation of the ruthenium substrate. Understanding the dynamics of the oxidation process and defects generation on the Ru substrate allows us to control the size, shape and the density of the bubbles and its associated pseudo-magnetism. We also show that a modification of the same procedure can be used to create antidots in graphene by catalytic reaction of the same nanobubbles. |
Bao, Qiaoliang; Loh, Kian Ping Graphene Photonics, Plasmonics, and Broadband Optoelectronic Devices Journal Article ACS NANO, 6 (5), pp. 3677-3694, 2012, ISSN: 1936-0851. @article{ISI:000304231700006, title = {Graphene Photonics, Plasmonics, and Broadband Optoelectronic Devices}, author = {Qiaoliang Bao and Kian Ping Loh}, doi = {10.1021/nn300989g}, issn = {1936-0851}, year = {2012}, date = {2012-05-01}, journal = {ACS NANO}, volume = {6}, number = {5}, pages = {3677-3694}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Graphene has been hailed as a wonderful material in electronics, and recently, it is the rising star in photonics, as well. The wonderful optical properties of graphene afford multiple functions of signal emitting, transmitting, modulating, and detection to be realized in one material. In this paper, the latest progress in graphene photonics, plasmonics, and broadband optoelectronic devices is reviewed. Particular emphasis is placed on the ability to integrate graphene photonics onto the silicon platform to afford broadband operation In light routing and amplification, which involves components like polarizer, modulator, and photodetector. Other functions like saturable absorber and optical limiter are also reviewed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene has been hailed as a wonderful material in electronics, and recently, it is the rising star in photonics, as well. The wonderful optical properties of graphene afford multiple functions of signal emitting, transmitting, modulating, and detection to be realized in one material. In this paper, the latest progress in graphene photonics, plasmonics, and broadband optoelectronic devices is reviewed. Particular emphasis is placed on the ability to integrate graphene photonics onto the silicon platform to afford broadband operation In light routing and amplification, which involves components like polarizer, modulator, and photodetector. Other functions like saturable absorber and optical limiter are also reviewed. |
Ni, Guang-Xin; Zheng, Yi; Bae, Sukang; Tan, Chin Yaw; Kahya, Orhan; Wu, Jing; Hong, Byung Hee; Yao, Kui; Oezyilmaz, Barbaros Graphene-Ferroelectric Hybrid Structure for Flexible Transparent Electrodes Journal Article ACS NANO, 6 (5), pp. 3935-3942, 2012, ISSN: 1936-0851. @article{ISI:000304231700032, title = {Graphene-Ferroelectric Hybrid Structure for Flexible Transparent Electrodes}, author = {Guang-Xin Ni and Yi Zheng and Sukang Bae and Chin Yaw Tan and Orhan Kahya and Jing Wu and Byung Hee Hong and Kui Yao and Barbaros Oezyilmaz}, doi = {10.1021/nn3010137}, issn = {1936-0851}, year = {2012}, date = {2012-05-01}, journal = {ACS NANO}, volume = {6}, number = {5}, pages = {3935-3942}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Graphene has exceptional optical, mechanical, and electrical properties, making it an emerging material for novel optoelectronics, photonics, and flexible transparent electrode applications. However, the relatively high sheet resistance of graphene is a major constraint for many of these applications. Here we propose a new approach to achieve low sheet resistance in large-scale CVD monolayer graphene using nonvolatile ferroelectric polymer gating. In this hybrid structure, large-scale graphene is heavily doped up to 3 x 10(13) cm(-2) by nonvolatile ferroelectric dipoles, yielding a low sheet resistance of 120 Omega/square at ambient conditions. The graphene-ferroelectric transparent conductors (GFeTCs) exhibit more than 95% transmittance from the visible to the near-infrared range owing to the highly transparent nature of the ferroelectric polymer. Together with its excellent mechanical flexibility, chemical inertness, and the simple fabrication process of ferroelectric polymers, the proposed GFeTCs represent a new route toward large-scale graphene-based transparent electrodes and optoelectronics.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene has exceptional optical, mechanical, and electrical properties, making it an emerging material for novel optoelectronics, photonics, and flexible transparent electrode applications. However, the relatively high sheet resistance of graphene is a major constraint for many of these applications. Here we propose a new approach to achieve low sheet resistance in large-scale CVD monolayer graphene using nonvolatile ferroelectric polymer gating. In this hybrid structure, large-scale graphene is heavily doped up to 3 x 10(13) cm(-2) by nonvolatile ferroelectric dipoles, yielding a low sheet resistance of 120 Omega/square at ambient conditions. The graphene-ferroelectric transparent conductors (GFeTCs) exhibit more than 95% transmittance from the visible to the near-infrared range owing to the highly transparent nature of the ferroelectric polymer. Together with its excellent mechanical flexibility, chemical inertness, and the simple fabrication process of ferroelectric polymers, the proposed GFeTCs represent a new route toward large-scale graphene-based transparent electrodes and optoelectronics. |
Jahan, Maryam; Bao, Qiaoliang; Loh, Kian Ping Electrocatalytically Active Graphene-Porphyrin MOF Composite for Oxygen Reduction Reaction Journal Article JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 134 (15), pp. 6707-6713, 2012, ISSN: 0002-7863. @article{ISI:000302887300033, title = {Electrocatalytically Active Graphene-Porphyrin MOF Composite for Oxygen Reduction Reaction}, author = {Maryam Jahan and Qiaoliang Bao and Kian Ping Loh}, doi = {10.1021/ja211433h}, issn = {0002-7863}, year = {2012}, date = {2012-04-01}, journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, volume = {134}, number = {15}, pages = {6707-6713}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Pyridine-functionalized graphene (reduced graphene oxide) can be used as a building block in the assembly of metal organic framework (MOF). By reacting the pyridine-functionalized graphene with iron-porphyrin, a graphene-metalloporphyrin MOF with enhanced catalytic activity for oxygen reduction reactions (ORB) is synthesized. The structure and electrochemical property of the hybrid MOF are investigated as a function of the weight percentage of the functionalized graphene added to the iron-porphyrin framework. The results show that the addition of pyridine-functionalized graphene changes the crystallization process of iron-porphyrin in the MOF, increases its porosity, and enhances the electrochemical charge transfer rate of iron-porphyrin. The graphene-metalloporphyrin hybrid shows facile 4-electron ORR and can be used as a promising Pt-free cathode in alkaline Direct Methanol Fuel Cell.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Pyridine-functionalized graphene (reduced graphene oxide) can be used as a building block in the assembly of metal organic framework (MOF). By reacting the pyridine-functionalized graphene with iron-porphyrin, a graphene-metalloporphyrin MOF with enhanced catalytic activity for oxygen reduction reactions (ORB) is synthesized. The structure and electrochemical property of the hybrid MOF are investigated as a function of the weight percentage of the functionalized graphene added to the iron-porphyrin framework. The results show that the addition of pyridine-functionalized graphene changes the crystallization process of iron-porphyrin in the MOF, increases its porosity, and enhances the electrochemical charge transfer rate of iron-porphyrin. The graphene-metalloporphyrin hybrid shows facile 4-electron ORR and can be used as a promising Pt-free cathode in alkaline Direct Methanol Fuel Cell. |
Cresti, Alessandro; Fogler, Michael M; Guinea, Francisco; Neto, Castro A H; Roche, Stephan Quenching of the Quantum Hall Effect in Graphene with Scrolled Edges Journal Article PHYSICAL REVIEW LETTERS, 108 (16), 2012, ISSN: 0031-9007. @article{ISI:000302957000011, title = {Quenching of the Quantum Hall Effect in Graphene with Scrolled Edges}, author = {Alessandro Cresti and Michael M Fogler and Francisco Guinea and A H Castro Neto and Stephan Roche}, doi = {10.1103/PhysRevLett.108.166602}, issn = {0031-9007}, year = {2012}, date = {2012-04-01}, journal = {PHYSICAL REVIEW LETTERS}, volume = {108}, number = {16}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Edge nanoscrolls are shown to strongly influence transport properties of suspended graphene in the quantum Hall regime. The relatively long arclength of the scrolls in combination with their compact transverse size results in formation of many nonchiral transport channels in the scrolls. They short circuit the bulk current paths and inhibit the observation of the quantized two-terminal resistance. Unlike competing theoretical proposals, this mechanism of disrupting the Hall quantization in suspended graphene is not caused by ill-chosen placement of the contacts, singular elastic strains, or a small sample size.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Edge nanoscrolls are shown to strongly influence transport properties of suspended graphene in the quantum Hall regime. The relatively long arclength of the scrolls in combination with their compact transverse size results in formation of many nonchiral transport channels in the scrolls. They short circuit the bulk current paths and inhibit the observation of the quantized two-terminal resistance. Unlike competing theoretical proposals, this mechanism of disrupting the Hall quantization in suspended graphene is not caused by ill-chosen placement of the contacts, singular elastic strains, or a small sample size. |
Manga, Kiran Kumar; Wang, Junzhong; Lin, Ming; Zhang, Jie; Nesladek, Milos; Nalla, Venkatram; Ji, Wei; Loh, Kian Ping High-Performance Broadband Photodetector Using Solution-Processible PbSe-TiO2-Graphene Hybrids Journal Article ADVANCED MATERIALS, 24 (13), pp. 1697-1702, 2012, ISSN: 0935-9648. @article{ISI:000302014400004, title = {High-Performance Broadband Photodetector Using Solution-Processible PbSe-TiO2-Graphene Hybrids}, author = {Kiran Kumar Manga and Junzhong Wang and Ming Lin and Jie Zhang and Milos Nesladek and Venkatram Nalla and Wei Ji and Kian Ping Loh}, doi = {10.1002/adma.201104399}, issn = {0935-9648}, year = {2012}, date = {2012-04-01}, journal = {ADVANCED MATERIALS}, volume = {24}, number = {13}, pages = {1697-1702}, publisher = {WILEY-V C H VERLAG GMBH}, address = {PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY}, abstract = {Highly sensitive, multicomponent broadband photodetector devices are made from PbSe/ graphene/ TiO2. TiO2 and PbSe nanoparticles act as light harvesting photoactive materials from the UV to IR regions of the electromagnetic spectrum, while the graphene acts as a charge collector for both photogenerated holes and electrons under an applied electric field.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Highly sensitive, multicomponent broadband photodetector devices are made from PbSe/ graphene/ TiO2. TiO2 and PbSe nanoparticles act as light harvesting photoactive materials from the UV to IR regions of the electromagnetic spectrum, while the graphene acts as a charge collector for both photogenerated holes and electrons under an applied electric field. |
Ferreira, Aires; Peres, N M R; Ribeiro, R M; Stauber, T Graphene-based photodetector with two cavities Journal Article PHYSICAL REVIEW B, 85 (11), 2012, ISSN: 2469-9950. @article{ISI:000301916100008, title = {Graphene-based photodetector with two cavities}, author = {Aires Ferreira and N M R Peres and R M Ribeiro and T Stauber}, doi = {10.1103/PhysRevB.85.115438}, issn = {2469-9950}, year = {2012}, date = {2012-03-01}, journal = {PHYSICAL REVIEW B}, volume = {85}, number = {11}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We present an efficient graphene-based photodetector with two Fabri-Perot cavities. It is shown that the absorption can reach almost 100% around a given frequency, which is determined by the two-cavity lengths. It is also shown that hysteresis in the absorbance is possible, with the transmittance amplitude of the mirrors working as an external driving field. The role of nonlinear contributions to the optical susceptibility of graphene is discussed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present an efficient graphene-based photodetector with two Fabri-Perot cavities. It is shown that the absorption can reach almost 100% around a given frequency, which is determined by the two-cavity lengths. It is also shown that hysteresis in the absorbance is possible, with the transmittance amplitude of the mirrors working as an external driving field. The role of nonlinear contributions to the optical susceptibility of graphene is discussed. |
Kitt, Alexander L; Pereira, Vitor M; Swan, Anna K; Goldberg, Bennett B Lattice-corrected strain-induced vector potentials in graphene Journal Article PHYSICAL REVIEW B, 85 (11), 2012, ISSN: 2469-9950. @article{ISI:000301837400006, title = {Lattice-corrected strain-induced vector potentials in graphene}, author = {Alexander L Kitt and Vitor M Pereira and Anna K Swan and Bennett B Goldberg}, doi = {10.1103/PhysRevB.85.115432}, issn = {2469-9950}, year = {2012}, date = {2012-03-01}, journal = {PHYSICAL REVIEW B}, volume = {85}, number = {11}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {The electronic implications of strain in graphene can be captured at low energies by means of pseudovector potentials which can give rise to pseudomagnetic fields. These strain-induced vector potentials arise from the local perturbation to the electronic hopping amplitudes in a tight-binding framework. Here we complete the standard description of the strain-induced vector potential, which accounts only for the hopping perturbation, with the explicit inclusion of the lattice deformations or, equivalently, the deformation of the Brillouin zone. These corrections are linear in strain and are different at each of the strained, inequivalent Dirac points, and hence are equally necessary to identify the precise magnitude of the vector potential. This effect can be relevant in scenarios of inhomogeneous strain profiles, where electronic motion depends on the amount of overlap among the local Fermi surfaces. In particular, it affects the pseudomagnetic field distribution induced by inhomogeneous strain configurations, and can lead to new opportunities in tailoring the optimal strain fields for certain desired functionalities.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The electronic implications of strain in graphene can be captured at low energies by means of pseudovector potentials which can give rise to pseudomagnetic fields. These strain-induced vector potentials arise from the local perturbation to the electronic hopping amplitudes in a tight-binding framework. Here we complete the standard description of the strain-induced vector potential, which accounts only for the hopping perturbation, with the explicit inclusion of the lattice deformations or, equivalently, the deformation of the Brillouin zone. These corrections are linear in strain and are different at each of the strained, inequivalent Dirac points, and hence are equally necessary to identify the precise magnitude of the vector potential. This effect can be relevant in scenarios of inhomogeneous strain profiles, where electronic motion depends on the amount of overlap among the local Fermi surfaces. In particular, it affects the pseudomagnetic field distribution induced by inhomogeneous strain configurations, and can lead to new opportunities in tailoring the optimal strain fields for certain desired functionalities. |
Huang, Han; Wong, Swee Liang; Sun, Jiatao; Chen, Wei; Wee, Andrew Thye Shen Trapping Single Polar Molecules in SiC Nanomesh via Out-of-Plane Dipoles Journal Article ACS NANO, 6 (3), pp. 2774-2778, 2012, ISSN: 1936-0851. @article{ISI:000301945900096, title = {Trapping Single Polar Molecules in SiC Nanomesh via Out-of-Plane Dipoles}, author = {Han Huang and Swee Liang Wong and Jiatao Sun and Wei Chen and Andrew Thye Shen Wee}, doi = {10.1021/nn300258b}, issn = {1936-0851}, year = {2012}, date = {2012-03-01}, journal = {ACS NANO}, volume = {6}, number = {3}, pages = {2774-2778}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The self-assembly of nonplanar chloroaluminum phthalocyanine (ClAlPc) molecules as well-ordered single-molecule dipole arrays on the silicon carbide (SiC) nanomesh substrate was investigated using low temperature scanning tunneling microscopy. ClAlPc exclusively adsorbs in the center of the SiC nanomesh holes with its inherent dipole (from Cl to Al) pointing toward the substrate. The dipole can be inverted by a positively biased tip with a threshold tip voltage of 3.3 V. We deduce that the interaction between the intrinsic dipole of ClAlPc and the periodic out-of-plane component of the surface dipole on the SiC nanomesh plays a significant role in the dipole array formation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The self-assembly of nonplanar chloroaluminum phthalocyanine (ClAlPc) molecules as well-ordered single-molecule dipole arrays on the silicon carbide (SiC) nanomesh substrate was investigated using low temperature scanning tunneling microscopy. ClAlPc exclusively adsorbs in the center of the SiC nanomesh holes with its inherent dipole (from Cl to Al) pointing toward the substrate. The dipole can be inverted by a positively biased tip with a threshold tip voltage of 3.3 V. We deduce that the interaction between the intrinsic dipole of ClAlPc and the periodic out-of-plane component of the surface dipole on the SiC nanomesh plays a significant role in the dipole array formation. |
Britnell, Liam; Gorbachev, Roman V; Jalil, Rashid; Belle, Branson D; Schedin, Fred; Katsnelson, Mikhail I; Eaves, Laurence; Morozov, Sergey V; Mayorov, Alexander S; Peres, Nuno M R; Neto, Antonio Castro H; Leist, Jon; Geim, Andre K; Ponomarenko, Leonid A; Novoselov, Kostya S Electron Tunneling through Ultrathin Boron Nitride Crystalline Barriers Journal Article NANO LETTERS, 12 (3), pp. 1707-1710, 2012, ISSN: 1530-6984. @article{ISI:000301406800102, title = {Electron Tunneling through Ultrathin Boron Nitride Crystalline Barriers}, author = {Liam Britnell and Roman V Gorbachev and Rashid Jalil and Branson D Belle and Fred Schedin and Mikhail I Katsnelson and Laurence Eaves and Sergey V Morozov and Alexander S Mayorov and Nuno M R Peres and Antonio H Castro Neto and Jon Leist and Andre K Geim and Leonid A Ponomarenko and Kostya S Novoselov}, doi = {10.1021/nl3002205}, issn = {1530-6984}, year = {2012}, date = {2012-03-01}, journal = {NANO LETTERS}, volume = {12}, number = {3}, pages = {1707-1710}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel. |
Mao, Jinhai; Huang, Li; Pan, Yi; Gao, Min; He, Junfeng; Zhou, Haitao; Guo, Haiming; Tian, Yuan; Zou, Qiang; Zhang, Lizhi; Zhang, Haigang; Wang, Yeliang; Du, Shixuan; Zhou, Xingjiang; Neto, Castro A H; Gao, Hong-Jun Silicon layer intercalation of centimeter-scale, epitaxially grown monolayer graphene on Ru(0001) Journal Article APPLIED PHYSICS LETTERS, 100 (9), 2012, ISSN: 0003-6951. @article{ISI:000301504800048, title = {Silicon layer intercalation of centimeter-scale, epitaxially grown monolayer graphene on Ru(0001)}, author = {Jinhai Mao and Li Huang and Yi Pan and Min Gao and Junfeng He and Haitao Zhou and Haiming Guo and Yuan Tian and Qiang Zou and Lizhi Zhang and Haigang Zhang and Yeliang Wang and Shixuan Du and Xingjiang Zhou and A H Castro Neto and Hong-Jun Gao}, doi = {10.1063/1.3687190}, issn = {0003-6951}, year = {2012}, date = {2012-02-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {100}, number = {9}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION & FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {We develop a strategy for graphene growth on Ru(0001) followed by silicon-layer intercalation that not only weakens the interaction of graphene with the metal substrate but also retains its superlative properties. This G/Si/Ru architecture, produced by silicon-layer intercalation approach (SIA), was characterized by scanning tunneling microscopy/spectroscopy and angle resolved electron photoemission spectroscopy. These experiments show high structural and electronic qualities of this new composite. The SIA allows for an atomic control of the distance between the graphene and the metal substrate that can be used as a top gate. Our results show potential for the next generation of graphene-based materials with tailored properties. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3687190]}, keywords = {}, pubstate = {published}, tppubtype = {article} } We develop a strategy for graphene growth on Ru(0001) followed by silicon-layer intercalation that not only weakens the interaction of graphene with the metal substrate but also retains its superlative properties. This G/Si/Ru architecture, produced by silicon-layer intercalation approach (SIA), was characterized by scanning tunneling microscopy/spectroscopy and angle resolved electron photoemission spectroscopy. These experiments show high structural and electronic qualities of this new composite. The SIA allows for an atomic control of the distance between the graphene and the metal substrate that can be used as a top gate. Our results show potential for the next generation of graphene-based materials with tailored properties. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3687190] |
Britnell, L; Gorbachev, R V; Jalil, R; Belle, B D; Schedin, F; Mishchenko, A; Georgiou, T; Katsnelson, M I; Eaves, L; Morozov, S V; Peres, N M R; Leist, J; Geim, A K; Novoselov, K S; Ponomarenko, L A Field-Effect Tunneling Transistor Based on Vertical Graphene Heterostructures Journal Article SCIENCE, 335 (6071), pp. 947-950, 2012, ISSN: 0036-8075. @article{ISI:000300931800040, title = {Field-Effect Tunneling Transistor Based on Vertical Graphene Heterostructures}, author = {L Britnell and R V Gorbachev and R Jalil and B D Belle and F Schedin and A Mishchenko and T Georgiou and M I Katsnelson and L Eaves and S V Morozov and N M R Peres and J Leist and A K Geim and K S Novoselov and L A Ponomarenko}, doi = {10.1126/science.1218461}, issn = {0036-8075}, year = {2012}, date = {2012-02-01}, journal = {SCIENCE}, volume = {335}, number = {6071}, pages = {947-950}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, address = {1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA}, abstract = {An obstacle to the use of graphene as an alternative to silicon electronics has been the absence of an energy gap between its conduction and valence bands, which makes it difficult to achieve low power dissipation in the OFF state. We report a bipolar field-effect transistor that exploits the low density of states in graphene and its one-atomic-layer thickness. Our prototype devices are graphene heterostructures with atomically thin boron nitride or molybdenum disulfide acting as a vertical transport barrier. They exhibit room-temperature switching ratios of approximate to 50 and approximate to 10,000, respectively. Such devices have potential for high-frequency operation and large-scale integration.}, keywords = {}, pubstate = {published}, tppubtype = {article} } An obstacle to the use of graphene as an alternative to silicon electronics has been the absence of an energy gap between its conduction and valence bands, which makes it difficult to achieve low power dissipation in the OFF state. We report a bipolar field-effect transistor that exploits the low density of states in graphene and its one-atomic-layer thickness. Our prototype devices are graphene heterostructures with atomically thin boron nitride or molybdenum disulfide acting as a vertical transport barrier. They exhibit room-temperature switching ratios of approximate to 50 and approximate to 10,000, respectively. Such devices have potential for high-frequency operation and large-scale integration. |
Zhang, L M; Andreev, G O; Fei, Z; McLeod, A S; Dominguez, G; Thiemens, M; Castro-Neto, A H; Basov, D N; Fogler, M M Near-field spectroscopy of silicon dioxide thin films Journal Article PHYSICAL REVIEW B, 85 (7), 2012, ISSN: 2469-9950. @article{ISI:000300566200010, title = {Near-field spectroscopy of silicon dioxide thin films}, author = {L M Zhang and G O Andreev and Z Fei and A S McLeod and G Dominguez and M Thiemens and A H Castro-Neto and D N Basov and M M Fogler}, doi = {10.1103/PhysRevB.85.075419}, issn = {2469-9950}, year = {2012}, date = {2012-02-01}, journal = {PHYSICAL REVIEW B}, volume = {85}, number = {7}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We analyze the results of scanning near-field infrared spectroscopy performed on thin films of a-SiO2 on Si substrate. The measured near-field signal exhibits surface-phonon resonances whose strength has a prominent thickness dependence in the range from 2 to 300 nm. These observations are compared with calculations in which the tip of the near-field infrared spectrometer is modeled either as a point dipole or an elongated spheroid. The latter model accounts for the antenna effect of the tip and gives a better agreement with the experiment. Possible applications of the near-field technique for depth profiling of layered nanostructures are discussed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We analyze the results of scanning near-field infrared spectroscopy performed on thin films of a-SiO2 on Si substrate. The measured near-field signal exhibits surface-phonon resonances whose strength has a prominent thickness dependence in the range from 2 to 300 nm. These observations are compared with calculations in which the tip of the near-field infrared spectrometer is modeled either as a point dipole or an elongated spheroid. The latter model accounts for the antenna effect of the tip and gives a better agreement with the experiment. Possible applications of the near-field technique for depth profiling of layered nanostructures are discussed. |
Tang, Lena A L; Lee, Wong Cheng; Shi, Hui; Wong, Ethel Y L; Sadovoy, Anton; Gorelik, Sergey; Hobley, Jonathan; Lim, Chwee Teck; Loh, Kian Ping Highly Wrinkled Cross-Linked Graphene Oxide Membranes for Biological and Charge-Storage Applications Journal Article SMALL, 8 (3), pp. 423-431, 2012, ISSN: 1613-6810. @article{ISI:000299621500013, title = {Highly Wrinkled Cross-Linked Graphene Oxide Membranes for Biological and Charge-Storage Applications}, author = {Lena A L Tang and Wong Cheng Lee and Hui Shi and Ethel Y L Wong and Anton Sadovoy and Sergey Gorelik and Jonathan Hobley and Chwee Teck Lim and Kian Ping Loh}, doi = {10.1002/smll.201101690}, issn = {1613-6810}, year = {2012}, date = {2012-02-01}, journal = {SMALL}, volume = {8}, number = {3}, pages = {423-431}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Inspired by the amphiphilicity of graphene oxide (GO), the surface of water is used as a template for the assembly of a GO film. Methacrylate-functionalized GO sheets can be cross-linked instantaneously at the waterair interface to form a highly wrinkled membrane spreading over an extended area. The multiple covalent linkages amongst the GO sheets enhances the in-plane stiffness of the film compared to noncovalently bonded GO films. The highly convoluted GO membrane can be used in two applications: the promoting of spontaneous stem-cell differentiation towards bone cell lineage without any chemical inducers, and for supercapacitor electrodes. Due to reduced van der Waals restacking, capacitance values up to 211 F g-1 can be obtained. The scalable and inexpensive nature of this assembly route enables the engineering of membranes for applications in regenerative medicine and energy-storage devices where secondary structures like nanotopography and porosity are important performance enhancers.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Inspired by the amphiphilicity of graphene oxide (GO), the surface of water is used as a template for the assembly of a GO film. Methacrylate-functionalized GO sheets can be cross-linked instantaneously at the waterair interface to form a highly wrinkled membrane spreading over an extended area. The multiple covalent linkages amongst the GO sheets enhances the in-plane stiffness of the film compared to noncovalently bonded GO films. The highly convoluted GO membrane can be used in two applications: the promoting of spontaneous stem-cell differentiation towards bone cell lineage without any chemical inducers, and for supercapacitor electrodes. Due to reduced van der Waals restacking, capacitance values up to 211 F g-1 can be obtained. The scalable and inexpensive nature of this assembly route enables the engineering of membranes for applications in regenerative medicine and energy-storage devices where secondary structures like nanotopography and porosity are important performance enhancers. |
Wang, Yu; Jaiswal, Manu; Lin, Ming; Saha, Surajit; Oezyilmaz, Barbaros; Loh, Kian Ping Electronic Properties of Nanodiamond Decorated Graphene Journal Article ACS NANO, 6 (2), pp. 1018-1025, 2012, ISSN: 1936-0851. @article{ISI:000300757900005, title = {Electronic Properties of Nanodiamond Decorated Graphene}, author = {Yu Wang and Manu Jaiswal and Ming Lin and Surajit Saha and Barbaros Oezyilmaz and Kian Ping Loh}, doi = {10.1021/nn204362p}, issn = {1936-0851}, year = {2012}, date = {2012-02-01}, journal = {ACS NANO}, volume = {6}, number = {2}, pages = {1018-1025}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The electronic properties of graphene sheets decorated with nanodiamond (ND) particles have been investigated. The chemical fusion of ND to the graphene lattice creates pockets of local defects with robust interfacial bonding. At the ND-bonded regions, the atoms of graphene lattice follow sp(3)-like bonding, and such regions play the role of conduction bottlenecks for the percolating sp(2) graphene network. The low-temperature charge transport reveals an insulating behavior for the disordered system associated with Anderson localization for the charge carriers in graphene. A large negative magnetoresistance is observed in this insulating regime, and its origin is discussed in the context of magnetic correlations of the localized charge carriers with local magnetic domains and extrinsic metal impurities associated with the ND.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The electronic properties of graphene sheets decorated with nanodiamond (ND) particles have been investigated. The chemical fusion of ND to the graphene lattice creates pockets of local defects with robust interfacial bonding. At the ND-bonded regions, the atoms of graphene lattice follow sp(3)-like bonding, and such regions play the role of conduction bottlenecks for the percolating sp(2) graphene network. The low-temperature charge transport reveals an insulating behavior for the disordered system associated with Anderson localization for the charge carriers in graphene. A large negative magnetoresistance is observed in this insulating regime, and its origin is discussed in the context of magnetic correlations of the localized charge carriers with local magnetic domains and extrinsic metal impurities associated with the ND. |
Ni, Guang-Xin; Zheng, Yi; Bae, Sukang; Kim, Hye Ri; Pachoud, Alexandre; Kim, Young Soo; Tan, Chang-Ling; Im, Danho; Ahn, Jong-Hyun; Hong, Byung Hee; Oezyilmaz, Barbaros Quasi-Periodic Nanoripples in Graphene Grown by Chemical Vapor Deposition and Its Impact on Charge Transport Journal Article ACS NANO, 6 (2), pp. 1158-1164, 2012, ISSN: 1936-0851. @article{ISI:000300757900021, title = {Quasi-Periodic Nanoripples in Graphene Grown by Chemical Vapor Deposition and Its Impact on Charge Transport}, author = {Guang-Xin Ni and Yi Zheng and Sukang Bae and Hye Ri Kim and Alexandre Pachoud and Young Soo Kim and Chang-Ling Tan and Danho Im and Jong-Hyun Ahn and Byung Hee Hong and Barbaros Oezyilmaz}, doi = {10.1021/nn203775x}, issn = {1936-0851}, year = {2012}, date = {2012-02-01}, journal = {ACS NANO}, volume = {6}, number = {2}, pages = {1158-1164}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The technical breakthrough in synthesizing graphene by chemical vapor deposition methods (CVD) has opened up enormous opportunities for large-scale device applications. To improve the electrical properties of CVD graphene grown on copper (Cu-CVD graphene), recent efforts have focused on increasing the grain size of such polycrystalline graphene films to 100 mu m and larger. While an increase in grain size and, hence, a decrease of grain boundary density is expected to greatly enhance the device performance, here we show that the charge mobility and sheet resistance of Cu-CVD graphene Is already limited within a single grain. We find that the current high-temperature growth and wet transfer methods of CVD graphene result in quasi-periodic nanoripple arrays (NRAs). Electron-flexural phonon scattering in such partially suspended graphene devices Introduces anisotropic charge transport and sets limits to both the highest possible charge mobility and lowest possible sheet resistance values. Our findings provide guidance for further improving the CVD graphene growth and transfer process.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The technical breakthrough in synthesizing graphene by chemical vapor deposition methods (CVD) has opened up enormous opportunities for large-scale device applications. To improve the electrical properties of CVD graphene grown on copper (Cu-CVD graphene), recent efforts have focused on increasing the grain size of such polycrystalline graphene films to 100 mu m and larger. While an increase in grain size and, hence, a decrease of grain boundary density is expected to greatly enhance the device performance, here we show that the charge mobility and sheet resistance of Cu-CVD graphene Is already limited within a single grain. We find that the current high-temperature growth and wet transfer methods of CVD graphene result in quasi-periodic nanoripple arrays (NRAs). Electron-flexural phonon scattering in such partially suspended graphene devices Introduces anisotropic charge transport and sets limits to both the highest possible charge mobility and lowest possible sheet resistance values. Our findings provide guidance for further improving the CVD graphene growth and transfer process. |
Reddy, M V; Yu, Cai; Jiahuan, Fan; Loh, Kian Ping; Chowdari, B V R Molten salt synthesis and energy storage studies on CuCo2O4 and CuO center dot Co3O4 Journal Article RSC ADVANCES, 2 (25), pp. 9619-9625, 2012, ISSN: 2046-2069. @article{ISI:000312061000042, title = {Molten salt synthesis and energy storage studies on CuCo2O4 and CuO center dot Co3O4}, author = {M V Reddy and Cai Yu and Fan Jiahuan and Kian Ping Loh and B V R Chowdari}, doi = {10.1039/c2ra21033a}, issn = {2046-2069}, year = {2012}, date = {2012-01-01}, journal = {RSC ADVANCES}, volume = {2}, number = {25}, pages = {9619-9625}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {CuCo2O4 and CuO center dot Co3O4 compounds were prepared by a one-pot simple molten salt method (MSM) at 280 degrees C to 750 degrees C. Changes in morphology, crystal structure and electrochemical properties of CuCo2O4 as a function of preparation temperatures were investigated using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer-Emmett- Teller absorption isotherm. XRD patterns of the sample prepared at 280 degrees C show a crystalline cubic structure with a lattice parameter value of a = 8.131 angstrom and a surface area value of 9.8 m(2) g(-1). The sample prepared at temperatures >510 degrees C shows the presence of CuO center dot Co3O4 phases. Energy storage properties are evaluated using cyclic voltammetry (CV) and galvanostatic cycling studies. CV studies show a main anodic peak at similar to 2.1 V and cathodic peak at similar to 1.2 V. At a current rate of 60 mA g(-1) and in the voltage range of 0.005-3.0 V vs. Li, CuCo2O4 composite prepared at 510 degrees C shows a high and stable capacity of similar to 680 (quenched) and 740 (slow cooling) mAh g(-1) at the end of the 40th cycle.}, keywords = {}, pubstate = {published}, tppubtype = {article} } CuCo2O4 and CuO center dot Co3O4 compounds were prepared by a one-pot simple molten salt method (MSM) at 280 degrees C to 750 degrees C. Changes in morphology, crystal structure and electrochemical properties of CuCo2O4 as a function of preparation temperatures were investigated using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer-Emmett- Teller absorption isotherm. XRD patterns of the sample prepared at 280 degrees C show a crystalline cubic structure with a lattice parameter value of a = 8.131 angstrom and a surface area value of 9.8 m(2) g(-1). The sample prepared at temperatures >510 degrees C shows the presence of CuO center dot Co3O4 phases. Energy storage properties are evaluated using cyclic voltammetry (CV) and galvanostatic cycling studies. CV studies show a main anodic peak at similar to 2.1 V and cathodic peak at similar to 1.2 V. At a current rate of 60 mA g(-1) and in the voltage range of 0.005-3.0 V vs. Li, CuCo2O4 composite prepared at 510 degrees C shows a high and stable capacity of similar to 680 (quenched) and 740 (slow cooling) mAh g(-1) at the end of the 40th cycle. |
Lu, Jiong; Yeo, Pei Shan Emmeline; Zheng, Yi; Yang, Zhiyong; Bao, Qiaoliang; Gan, Chee Kwan; Loh, Kian Ping Using the Graphene Moire Pattern for the Trapping of C-60 and Homoepitaxy of Graphene Journal Article ACS NANO, 6 (1), pp. 944-950, 2012, ISSN: 1936-0851. @article{ISI:000299368300112, title = {Using the Graphene Moire Pattern for the Trapping of C-60 and Homoepitaxy of Graphene}, author = {Jiong Lu and Pei Shan Emmeline Yeo and Yi Zheng and Zhiyong Yang and Qiaoliang Bao and Chee Kwan Gan and Kian Ping Loh}, doi = {10.1021/nn204536e}, issn = {1936-0851}, year = {2012}, date = {2012-01-01}, journal = {ACS NANO}, volume = {6}, number = {1}, pages = {944-950}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The graphene Moire superstructure offers a complex landscape of humps and valleys to molecules adsorbing and diffusing on it. Using C-60 molecules as the classic hard sphere analogue, we examine its assembly and layered growth on this corrugated landscape. At the monolayer level, the cohesive interactions of C-60 molecules adsorbing on the Moire lattice freeze the molecular rotation of C-60 trapped in the valley sites, resulting in molecular alignment of all similarly trapped C-60 molecules at room temperature. The hierarchy of adsorption potential well on the Moire lattice causes diffusion-limited dendritic growth of C-60 films, as opposed to isotropic growth observed on a smooth surface like graphite. Due to the strong binding energy of the C-60 film, part of the dentritic C-60 films polymerize at 850 K and act as solid carbon sources for graphene homoepitaxy. Our findings point to the possibility of using periodically corrugated graphene in molecular spintronics due to its ability to trap and align organic molecules at room temperature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The graphene Moire superstructure offers a complex landscape of humps and valleys to molecules adsorbing and diffusing on it. Using C-60 molecules as the classic hard sphere analogue, we examine its assembly and layered growth on this corrugated landscape. At the monolayer level, the cohesive interactions of C-60 molecules adsorbing on the Moire lattice freeze the molecular rotation of C-60 trapped in the valley sites, resulting in molecular alignment of all similarly trapped C-60 molecules at room temperature. The hierarchy of adsorption potential well on the Moire lattice causes diffusion-limited dendritic growth of C-60 films, as opposed to isotropic growth observed on a smooth surface like graphite. Due to the strong binding energy of the C-60 film, part of the dentritic C-60 films polymerize at 850 K and act as solid carbon sources for graphene homoepitaxy. Our findings point to the possibility of using periodically corrugated graphene in molecular spintronics due to its ability to trap and align organic molecules at room temperature. |
Novoselov, K S; Neto, Castro A H Two-dimensional crystals-based heterostructures: materials with tailored properties Journal Article PHYSICA SCRIPTA, T146 , 2012, ISSN: 0031-8949, (Nobel Symposium on Graphene and Quantum Matter, Saltsjobaden, SWEDEN, MAY 27-31, 2010). @article{ISI:000300504800007, title = {Two-dimensional crystals-based heterostructures: materials with tailored properties}, author = {K S Novoselov and A H Castro Neto}, doi = {10.1088/0031-8949/2012/T146/014006}, issn = {0031-8949}, year = {2012}, date = {2012-01-01}, journal = {PHYSICA SCRIPTA}, volume = {T146}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {Graphene is just one example of a large class of two-dimensional crystals. These crystals can either be extracted from layered three-dimensional materials or grown artificially by several different methods. Furthermore, they present physical properties that are unique because of the low dimensionality and their special crystal structure. They have potential for semiconducting behavior, magnetism, superconductivity, and even more complex many-body phenomena. Two-dimensional crystals can also be assembled in three-dimensional heterostructures that do not exist in nature and have tailored properties, opening an entirely new chapter in condensed matter research.}, note = {Nobel Symposium on Graphene and Quantum Matter, Saltsjobaden, SWEDEN, MAY 27-31, 2010}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene is just one example of a large class of two-dimensional crystals. These crystals can either be extracted from layered three-dimensional materials or grown artificially by several different methods. Furthermore, they present physical properties that are unique because of the low dimensionality and their special crystal structure. They have potential for semiconducting behavior, magnetism, superconductivity, and even more complex many-body phenomena. Two-dimensional crystals can also be assembled in three-dimensional heterostructures that do not exist in nature and have tailored properties, opening an entirely new chapter in condensed matter research. |
2011 |
e Lopes, P L S; Neto, Castro A H; Caldeira, A O Chiral filtering in graphene with coupled valleys Journal Article PHYSICAL REVIEW B, 84 (24), 2011, ISSN: 1098-0121. @article{ISI:000298116400011, title = {Chiral filtering in graphene with coupled valleys}, author = {P L S e Lopes and A H Castro Neto and A O Caldeira}, doi = {10.1103/PhysRevB.84.245432}, issn = {1098-0121}, year = {2011}, date = {2011-12-01}, journal = {PHYSICAL REVIEW B}, volume = {84}, number = {24}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We analyze the problem of electronic transmission through different regions of a graphene sheet that are characterized by different types of connections between the Dirac points. These valley symmetry breaking Hamiltonians might arise from electronic self-interaction mediated by the dielectric environment of distinct parts of the substrate on which the graphene sheet is placed. We show that it is possible to have situations in which we can use these regions to select or filter states of one desired chirality.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We analyze the problem of electronic transmission through different regions of a graphene sheet that are characterized by different types of connections between the Dirac points. These valley symmetry breaking Hamiltonians might arise from electronic self-interaction mediated by the dielectric environment of distinct parts of the substrate on which the graphene sheet is placed. We show that it is possible to have situations in which we can use these regions to select or filter states of one desired chirality. |
Ang, Priscilla Kailian; Li, Ang; Jaiswal, Manu; Wang, Yu; Hou, Han Wei; Thong, John T L; Lim, Chwee Teck; Loh, Kian Ping Flow Sensing of Single Cell by Graphene Transistor in a Microfluidic Channel Journal Article NANO LETTERS, 11 (12), pp. 5240-5246, 2011, ISSN: 1530-6984. @article{ISI:000297950200024, title = {Flow Sensing of Single Cell by Graphene Transistor in a Microfluidic Channel}, author = {Priscilla Kailian Ang and Ang Li and Manu Jaiswal and Yu Wang and Han Wei Hou and John T L Thong and Chwee Teck Lim and Kian Ping Loh}, doi = {10.1021/nl202579k}, issn = {1530-6984}, year = {2011}, date = {2011-12-01}, journal = {NANO LETTERS}, volume = {11}, number = {12}, pages = {5240-5246}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The electronic properties of graphene are strongly influenced by electrostatic forces arising from long-range charge scatterers and by changes in the local dielectric environment. This makes graphene extremely sensitive to the surface charge density of cells interfacing with it Here, we developed a graphene transistor array integrated with microfluidic flow cytometry for the ``flow-catch-release'' sensing of malaria-infected red blood cells at the single-cell level. Malaria-infected red blood cells induce highly sensitive capacitively coupled changes in the conductivity of graphene. Together with the characteristic conductance dwell times, specific microscopic information about the disease state can be obtained.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The electronic properties of graphene are strongly influenced by electrostatic forces arising from long-range charge scatterers and by changes in the local dielectric environment. This makes graphene extremely sensitive to the surface charge density of cells interfacing with it Here, we developed a graphene transistor array integrated with microfluidic flow cytometry for the ``flow-catch-release'' sensing of malaria-infected red blood cells at the single-cell level. Malaria-infected red blood cells induce highly sensitive capacitively coupled changes in the conductivity of graphene. Together with the characteristic conductance dwell times, specific microscopic information about the disease state can be obtained. |
Ferreira, Aires; Viana-Gomes, J; Bludov, Yu. V; Pereira, V; Peres, N M R; Neto, Castro A H Faraday effect in graphene enclosed in an optical cavity and the equation of motion method for the study of magneto-optical transport in solids Journal Article PHYSICAL REVIEW B, 84 (23), 2011, ISSN: 2469-9950. @article{ISI:000297551600027, title = {Faraday effect in graphene enclosed in an optical cavity and the equation of motion method for the study of magneto-optical transport in solids}, author = {Aires Ferreira and J Viana-Gomes and Yu. V Bludov and V Pereira and N M R Peres and A H Castro Neto}, doi = {10.1103/PhysRevB.84.235410}, issn = {2469-9950}, year = {2011}, date = {2011-12-01}, journal = {PHYSICAL REVIEW B}, volume = {84}, number = {23}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We show that by enclosing graphene in an optical cavity, giant Faraday rotations in the infrared regime are generated and measurable Faraday rotation angles in the visible range become possible. Explicit expressions for the Hall steps of the Faraday rotation angle are given for relevant regimes. In the context of this problem we develop an equation of motion (EOM) method for calculation of the magneto-optical properties of metals and semiconductors. It is shown that properly regularized EOM solutions are fully equivalent to the Kubo formula.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show that by enclosing graphene in an optical cavity, giant Faraday rotations in the infrared regime are generated and measurable Faraday rotation angles in the visible range become possible. Explicit expressions for the Hall steps of the Faraday rotation angle are given for relevant regimes. In the context of this problem we develop an equation of motion (EOM) method for calculation of the magneto-optical properties of metals and semiconductors. It is shown that properly regularized EOM solutions are fully equivalent to the Kubo formula. |
Lee, Dong Su; Riedl, Christian; Beringer, Thomas; Neto, Castro A H; von Klitzing, Klaus; Starke, Ulrich; Smet, Jurgen H Quantum Hall Effect in Twisted Bilayer Graphene Journal Article PHYSICAL REVIEW LETTERS, 107 (21), 2011, ISSN: 0031-9007. @article{ISI:000297136400005, title = {Quantum Hall Effect in Twisted Bilayer Graphene}, author = {Dong Su Lee and Christian Riedl and Thomas Beringer and A H Castro Neto and Klaus von Klitzing and Ulrich Starke and Jurgen H Smet}, doi = {10.1103/PhysRevLett.107.216602}, issn = {0031-9007}, year = {2011}, date = {2011-11-01}, journal = {PHYSICAL REVIEW LETTERS}, volume = {107}, number = {21}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We address the quantum Hall behavior in twisted bilayer graphene transferred from the C face of SiC. The measured Hall conductivity exhibits the same plateau values as for a commensurate Bernal bilayer. This implies that the eightfold degeneracy of the zero energy mode is topologically protected despite rotational disorder as recently predicted. In addition, an anomaly appears. The densities at which these plateaus occur show a magnetic field dependent offset. It suggests the existence of a pool of localized states at low energy, which do not count towards the degeneracy of the lowest band Landau levels. These states originate from an inhomogeneous spatial variation of the interlayer coupling.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We address the quantum Hall behavior in twisted bilayer graphene transferred from the C face of SiC. The measured Hall conductivity exhibits the same plateau values as for a commensurate Bernal bilayer. This implies that the eightfold degeneracy of the zero energy mode is topologically protected despite rotational disorder as recently predicted. In addition, an anomaly appears. The densities at which these plateaus occur show a magnetic field dependent offset. It suggests the existence of a pool of localized states at low energy, which do not count towards the degeneracy of the lowest band Landau levels. These states originate from an inhomogeneous spatial variation of the interlayer coupling. |
Fei, Zhe; Andreev, Gregory O; Bao, Wenzhong; Zhang, Lingfeng M; McLeod, Alexander S; Wang, Chen; Stewart, Margaret K; Zhao, Zeng; Dominguez, Gerardo; Thiemens, Mark; Fogler, Michael M; Tauber, Michael J; Castro-Neto, Antonio H; Lau, Chun Ning; Keilmann, Fritz; Basov, Dimitri N Infrared Nanoscopy of Dirac Plasmons at the Graphene-SiO2 Interface Journal Article NANO LETTERS, 11 (11), pp. 4701-4705, 2011, ISSN: 1530-6984. @article{ISI:000296674700036, title = {Infrared Nanoscopy of Dirac Plasmons at the Graphene-SiO2 Interface}, author = {Zhe Fei and Gregory O Andreev and Wenzhong Bao and Lingfeng M Zhang and Alexander S McLeod and Chen Wang and Margaret K Stewart and Zeng Zhao and Gerardo Dominguez and Mark Thiemens and Michael M Fogler and Michael J Tauber and Antonio H Castro-Neto and Chun Ning Lau and Fritz Keilmann and Dimitri N Basov}, doi = {10.1021/nl202362d}, issn = {1530-6984}, year = {2011}, date = {2011-11-01}, journal = {NANO LETTERS}, volume = {11}, number = {11}, pages = {4701-4705}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding 2 orders of magnitude increase in the value of in-plane component of incident wavevector q compared to free space propagation. At these high wavevectors, the Dirac plasmon is found to dramatically enhance the near-field interaction with mid-IR surface phonons of SiO2 substrate. Our data augmented by detailed modeling establish graphene as a new medium supporting plasmonic effects that can be controlled by gate voltage.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding 2 orders of magnitude increase in the value of in-plane component of incident wavevector q compared to free space propagation. At these high wavevectors, the Dirac plasmon is found to dramatically enhance the near-field interaction with mid-IR surface phonons of SiO2 substrate. Our data augmented by detailed modeling establish graphene as a new medium supporting plasmonic effects that can be controlled by gate voltage. |
Rodrigues, J N B; Goncalves, P A D; Rodrigues, N F G; Ribeiro, R M; dos Santos, Lopes J M B; Peres, N M R Zigzag graphene nanoribbon edge reconstruction with Stone-Wales defects Journal Article PHYSICAL REVIEW B, 84 (15), 2011, ISSN: 1098-0121. @article{ISI:000296290000014, title = {Zigzag graphene nanoribbon edge reconstruction with Stone-Wales defects}, author = {J N B Rodrigues and P A D Goncalves and N F G Rodrigues and R M Ribeiro and J M B Lopes dos Santos and N M R Peres}, doi = {10.1103/PhysRevB.84.155435}, issn = {1098-0121}, year = {2011}, date = {2011-10-01}, journal = {PHYSICAL REVIEW B}, volume = {84}, number = {15}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge states. They are dispersive, with nonzero amplitudes in both sublattices; furthermore, the amplitudes have two components that decrease with different decay lengths with the distance from the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero-energy Landau level is no longer degenerate with edge states as in the case of the pristine zigzag ribbon.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge states. They are dispersive, with nonzero amplitudes in both sublattices; furthermore, the amplitudes have two components that decrease with different decay lengths with the distance from the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero-energy Landau level is no longer degenerate with edge states as in the case of the pristine zigzag ribbon. |
Rappoport, T G; Godoy, M; Uchoa, B; Santos, Dos R R; Neto, Castro A H Magnetic exchange mechanism for electronic gap opening in graphene Journal Article EPL, 96 (2), 2011, ISSN: 0295-5075. @article{ISI:000295974600033, title = {Magnetic exchange mechanism for electronic gap opening in graphene}, author = {T G Rappoport and M Godoy and B Uchoa and R R Dos Santos and A H Castro Neto}, doi = {10.1209/0295-5075/96/27010}, issn = {0295-5075}, year = {2011}, date = {2011-10-01}, journal = {EPL}, volume = {96}, number = {2}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {We show within a local self-consistent mean-field treatment that a random distribution of magnetic adatoms can open a robust gap in the electronic spectrum of graphene. The electronic gap results from the localization of the charge carriers that arises from the interplay between the graphene sublattice structure and the exchange interaction between the adatoms. The size of the gap depends on the strength of the exchange interaction between carriers and localized spins and can be controlled by both temperature and external magnetic field. Furthermore, we show that an external magnetic field creates an imbalance of spin-up and spin-down carriers at the Fermi level, making doped graphene suitable for spin injection and other spintronic applications. Copyright (C) EPLA, 2011}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show within a local self-consistent mean-field treatment that a random distribution of magnetic adatoms can open a robust gap in the electronic spectrum of graphene. The electronic gap results from the localization of the charge carriers that arises from the interplay between the graphene sublattice structure and the exchange interaction between the adatoms. The size of the gap depends on the strength of the exchange interaction between carriers and localized spins and can be controlled by both temperature and external magnetic field. Furthermore, we show that an external magnetic field creates an imbalance of spin-up and spin-down carriers at the Fermi level, making doped graphene suitable for spin injection and other spintronic applications. Copyright (C) EPLA, 2011 |
Santos, Jaime E; Peres, Nuno M R; dos Santos, Joao Lopes M B; Neto, Antonio Castro H Electronic doping of graphene by deposited transition metal atoms Journal Article PHYSICAL REVIEW B, 84 (8), 2011, ISSN: 2469-9950. @article{ISI:000294325400014, title = {Electronic doping of graphene by deposited transition metal atoms}, author = {Jaime E Santos and Nuno M R Peres and Joao M B Lopes dos Santos and Antonio H Castro Neto}, doi = {10.1103/PhysRevB.84.085430}, issn = {2469-9950}, year = {2011}, date = {2011-08-01}, journal = {PHYSICAL REVIEW B}, volume = {84}, number = {8}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We perform a phenomenological analysis of the problem of the electronic doping of a graphene sheet by deposited transition metal atoms, which aggregate in clusters. The sample is placed in a capacitor device such that the electronic doping of graphene can be varied by the application of a gate voltage and such that transport measurements can be performed via the application of a (much smaller) voltage along the graphene sample, as reported in the work of Pi et al. [Phys. Rev. B 80, 075406 (2009)]. The analysis allows us to explain the thermodynamic properties of the device, such as the level of doping of graphene and the ionization potential of the metal clusters, in terms of the chemical interaction between graphene and the clusters. We are also able, by modeling the metallic clusters as perfectly conducting spheres, to determine the scattering potential due to these clusters on the electronic carriers of graphene and hence the contribution of these clusters to the resistivity of the sample. The model presented is able to explain the measurements performed by Pi et al. on Pt-covered graphene samples at the lowest metallic coverages measured, and we also present a theoretical argument based on the above model that explains why significant deviations from such a theory are observed at higher levels of coverage.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We perform a phenomenological analysis of the problem of the electronic doping of a graphene sheet by deposited transition metal atoms, which aggregate in clusters. The sample is placed in a capacitor device such that the electronic doping of graphene can be varied by the application of a gate voltage and such that transport measurements can be performed via the application of a (much smaller) voltage along the graphene sample, as reported in the work of Pi et al. [Phys. Rev. B 80, 075406 (2009)]. The analysis allows us to explain the thermodynamic properties of the device, such as the level of doping of graphene and the ionization potential of the metal clusters, in terms of the chemical interaction between graphene and the clusters. We are also able, by modeling the metallic clusters as perfectly conducting spheres, to determine the scattering potential due to these clusters on the electronic carriers of graphene and hence the contribution of these clusters to the resistivity of the sample. The model presented is able to explain the measurements performed by Pi et al. on Pt-covered graphene samples at the lowest metallic coverages measured, and we also present a theoretical argument based on the above model that explains why significant deviations from such a theory are observed at higher levels of coverage. |
Neto, Castro A H; Novoselov, K New directions in science and technology: two-dimensional crystals Journal Article REPORTS ON PROGRESS IN PHYSICS, 74 (8), 2011, ISSN: 0034-4885. @article{ISI:000293225900001, title = {New directions in science and technology: two-dimensional crystals}, author = {A H Castro Neto and K Novoselov}, doi = {10.1088/0034-4885/74/8/082501}, issn = {0034-4885}, year = {2011}, date = {2011-08-01}, journal = {REPORTS ON PROGRESS IN PHYSICS}, volume = {74}, number = {8}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {Graphene is possibly one of the largest and fastest growing fields in condensed matter research. However, graphene is only one example in a large class of two-dimensional crystals with unusual properties. In this paper we briefly review the properties of graphene and look at the exciting possibilities that lie ahead.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene is possibly one of the largest and fastest growing fields in condensed matter research. However, graphene is only one example in a large class of two-dimensional crystals with unusual properties. In this paper we briefly review the properties of graphene and look at the exciting possibilities that lie ahead. |
de Gail, R; Goerbig, M O; Guinea, F; Montambaux, G; Neto, Castro A H Topologically protected zero modes in twisted bilayer graphene Journal Article PHYSICAL REVIEW B, 84 (4), 2011, ISSN: 1098-0121. @article{ISI:000292825100016, title = {Topologically protected zero modes in twisted bilayer graphene}, author = {R de Gail and M O Goerbig and F Guinea and G Montambaux and A H Castro Neto}, doi = {10.1103/PhysRevB.84.045436}, issn = {1098-0121}, year = {2011}, date = {2011-07-01}, journal = {PHYSICAL REVIEW B}, volume = {84}, number = {4}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We show that a twisted graphene bilayer can reveal unusual topological properties at low energies, as a consequence of a Dirac-point splitting. These features rely on a symmetry analysis of the electron hopping between the two layers of graphene and we derive a simplified effective low-energy Hamiltonian which captures the essential topological properties of a twisted graphene bilayer. The corresponding Landau levels peculiarly reveal a degenerate zero-energy mode which cannot be lifted by strong magnetic fields.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show that a twisted graphene bilayer can reveal unusual topological properties at low energies, as a consequence of a Dirac-point splitting. These features rely on a symmetry analysis of the electron hopping between the two layers of graphene and we derive a simplified effective low-energy Hamiltonian which captures the essential topological properties of a twisted graphene bilayer. The corresponding Landau levels peculiarly reveal a degenerate zero-energy mode which cannot be lifted by strong magnetic fields. |
Peres, N M R; dos Santos, Lopes J M B; Neto, Castro A H Coulomb drag and high-resistivity behavior in double-layer graphene Journal Article EPL, 95 (1, SI), 2011, ISSN: 0295-5075. @article{ISI:000291990600030, title = {Coulomb drag and high-resistivity behavior in double-layer graphene}, author = {N M R Peres and J M B Lopes dos Santos and A H Castro Neto}, doi = {10.1209/0295-5075/95/18001}, issn = {0295-5075}, year = {2011}, date = {2011-07-01}, journal = {EPL}, volume = {95}, number = {1, SI}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {We show that Coulomb drag in ultra-clean graphene double layers can be used for controlling the on-and-off ratio for current flow by tuning the external gate voltage. Hence, although graphene remains semi-metallic, the double-layer graphene system can be tuned from conductive to a highly resistive state. We show that our results explain previous data of Coulomb drag in double-layer graphene samples in disordered SiO2 substrates. Copyright (C) EPLA, 2011}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show that Coulomb drag in ultra-clean graphene double layers can be used for controlling the on-and-off ratio for current flow by tuning the external gate voltage. Hence, although graphene remains semi-metallic, the double-layer graphene system can be tuned from conductive to a highly resistive state. We show that our results explain previous data of Coulomb drag in double-layer graphene samples in disordered SiO2 substrates. Copyright (C) EPLA, 2011 |
Nayak, Tapas R; Andersen, Henrik; Makam, Venkata S; Khaw, Clement; Bae, Sukang; Xu, Xiangfan; Ee, Pui-Lai R; Ahn, Jong-Hyun; Hong, Byung Hee; Pastorin, Giorgia; Oezyilmaz, Barbaros Graphene for Controlled and Accelerated Osteogenic Differentiation of Human Mesenchymal Stem Cells Journal Article ACS NANO, 5 (6), pp. 4670-4678, 2011, ISSN: 1936-0851. @article{ISI:000292055200049, title = {Graphene for Controlled and Accelerated Osteogenic Differentiation of Human Mesenchymal Stem Cells}, author = {Tapas R Nayak and Henrik Andersen and Venkata S Makam and Clement Khaw and Sukang Bae and Xiangfan Xu and Pui-Lai R Ee and Jong-Hyun Ahn and Byung Hee Hong and Giorgia Pastorin and Barbaros Oezyilmaz}, doi = {10.1021/nn200500h}, issn = {1936-0851}, year = {2011}, date = {2011-06-01}, journal = {ACS NANO}, volume = {5}, number = {6}, pages = {4670-4678}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Current tissue engineering approaches combine different scaffold materials with living cells to provide biological substitutes that can repair and eventually improve tissue functions. Both natural and synthetic materials have been fabricated for transplantation of stem cells and their specific differentiation Into muscles, bones, and cartilages. One of the key objectives for bone regeneration therapy to be successful Is to direct stem cells' proliferation and to accelerate their differentiation in a controlled manner through the use of growth factors and osteogenic inducers. Here we show that graphene provides a promising biocompatible scaffold that does not hamper the proliferation of human mesenchymal stem cells (hMSCs) and accelerates their specific differentiation into bone cells. The differentiation rate Is comparable to the one achieved with common growth factors, demonstrating graphene's potential for stem cell research.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Current tissue engineering approaches combine different scaffold materials with living cells to provide biological substitutes that can repair and eventually improve tissue functions. Both natural and synthetic materials have been fabricated for transplantation of stem cells and their specific differentiation Into muscles, bones, and cartilages. One of the key objectives for bone regeneration therapy to be successful Is to direct stem cells' proliferation and to accelerate their differentiation in a controlled manner through the use of growth factors and osteogenic inducers. Here we show that graphene provides a promising biocompatible scaffold that does not hamper the proliferation of human mesenchymal stem cells (hMSCs) and accelerates their specific differentiation into bone cells. The differentiation rate Is comparable to the one achieved with common growth factors, demonstrating graphene's potential for stem cell research. |
Avsar, Ahmet; Yang, Tsung-Yeh; Bae, Sukang; Balakrishnan, Jayakumar; Volmer, Frank; Jaiswal, Manu; Yi, Zheng; Ali, Syed Rizwan; Guentherodt, Gernot; Hong, Byung Hee; Beschoten, Bernd; Oezyilmaz, Barbaros Toward Wafer Scale Fabrication of Graphene Based Spin Valve Devices Journal Article NANO LETTERS, 11 (6), pp. 2363-2368, 2011, ISSN: 1530-6984. @article{ISI:000291322600029, title = {Toward Wafer Scale Fabrication of Graphene Based Spin Valve Devices}, author = {Ahmet Avsar and Tsung-Yeh Yang and Sukang Bae and Jayakumar Balakrishnan and Frank Volmer and Manu Jaiswal and Zheng Yi and Syed Rizwan Ali and Gernot Guentherodt and Byung Hee Hong and Bernd Beschoten and Barbaros Oezyilmaz}, doi = {10.1021/nl200714q}, issn = {1530-6984}, year = {2011}, date = {2011-06-01}, journal = {NANO LETTERS}, volume = {11}, number = {6}, pages = {2363-2368}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {We demonstrate injection, transport, and detection of spins in spin valve arrays patterned in both copper based chemical vapor deposition (Cu-CVD) synthesized wafer scale single layer and bilayer graphene. We observe spin relaxation times comparable to those reported for exfoliated graphene samples demonstrating that chemical vapor deposition specific structural differences such as nanoripples do not limit spin transport in the present samples. Our observations make Cu-CVD graphene a promising material of choice for large scale spintronic applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We demonstrate injection, transport, and detection of spins in spin valve arrays patterned in both copper based chemical vapor deposition (Cu-CVD) synthesized wafer scale single layer and bilayer graphene. We observe spin relaxation times comparable to those reported for exfoliated graphene samples demonstrating that chemical vapor deposition specific structural differences such as nanoripples do not limit spin transport in the present samples. Our observations make Cu-CVD graphene a promising material of choice for large scale spintronic applications. |
Neto, Antonio Castro H Another Spin on Graphene Journal Article SCIENCE, 332 (6027), pp. 315-316, 2011, ISSN: 0036-8075. @article{ISI:000289516600033, title = {Another Spin on Graphene}, author = {Antonio H Castro Neto}, doi = {10.1126/science.1204496}, issn = {0036-8075}, year = {2011}, date = {2011-04-01}, journal = {SCIENCE}, volume = {332}, number = {6027}, pages = {315-316}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, address = {1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Neto, Castro A H; Novoselov, K Two-Dimensional Crystals: Beyond Graphene Journal Article MATERIALS EXPRESS, 1 (1), pp. 10-17, 2011, ISSN: 2158-5849. @article{ISI:000311866900002, title = {Two-Dimensional Crystals: Beyond Graphene}, author = {A H Castro Neto and K Novoselov}, doi = {10.1166/mex.2011.1002}, issn = {2158-5849}, year = {2011}, date = {2011-03-01}, journal = {MATERIALS EXPRESS}, volume = {1}, number = {1}, pages = {10-17}, publisher = {AMER SCIENTIFIC PUBLISHERS}, address = {26650 THE OLD RD, STE 208, VALENCIA, CA 91381-0751 USA}, abstract = {Human progress and development has always been marked by breakthroughs in the control of materials. Since pre-historic times, through the stone, bronze, and iron ages, humans have exploited their environment for materials that can be either used directly or can be modified for their benefit, to make their life more comfortable, productive, or to give them military advantage. One age replaces another when the material that is the basis for its sustainability runs its course and is replaced by another material which presents more qualities. Multi-tasking, speed, versatility, and flexibility are at the heart of modern technology. In recent years a new class of materials that can fulfill these needs have emerged: two-dimensional (2D) crystals. Graphene is probably the most famous example, but there are numerous other examples with amazing electronic and structural properties. In this paper we look into the possible routes for exploration of this new field that presents new venues in basic science as well as in applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Human progress and development has always been marked by breakthroughs in the control of materials. Since pre-historic times, through the stone, bronze, and iron ages, humans have exploited their environment for materials that can be either used directly or can be modified for their benefit, to make their life more comfortable, productive, or to give them military advantage. One age replaces another when the material that is the basis for its sustainability runs its course and is replaced by another material which presents more qualities. Multi-tasking, speed, versatility, and flexibility are at the heart of modern technology. In recent years a new class of materials that can fulfill these needs have emerged: two-dimensional (2D) crystals. Graphene is probably the most famous example, but there are numerous other examples with amazing electronic and structural properties. In this paper we look into the possible routes for exploration of this new field that presents new venues in basic science as well as in applications. |
2010 |
Pereira, Vitor M; Ribeiro, R M; Peres, N M R; Neto, Castro A H Optical properties of strained graphene Journal Article EPL, 92 (6), 2010, ISSN: 0295-5075. @article{ISI:000287023900021, title = {Optical properties of strained graphene}, author = {Vitor M Pereira and R M Ribeiro and N M R Peres and A H Castro Neto}, doi = {10.1209/0295-5075/92/67001}, issn = {0295-5075}, year = {2010}, date = {2010-12-01}, journal = {EPL}, volume = {92}, number = {6}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {The optical conductivity of graphene strained uniaxially is studied within the Kubo-Greenwood formalism. Focusing on inter-band absorption, we analyze and quantify the breakdown of universal transparency in the visible region of the spectrum, and analytically characterize the transparency as a function of strain and polarization. Measuring transmittance as a function of incident polarization directly reflects the magnitude and direction of strain. Moreover, direction-dependent selection rules permit the identification of the lattice orientation by monitoring the van Hove transitions. These photoelastic effects in graphene can be explored towards atomically thin, broadband optical elements. Copyright (C) EPLA, 2010}, keywords = {}, pubstate = {published}, tppubtype = {article} } The optical conductivity of graphene strained uniaxially is studied within the Kubo-Greenwood formalism. Focusing on inter-band absorption, we analyze and quantify the breakdown of universal transparency in the visible region of the spectrum, and analytically characterize the transparency as a function of strain and polarization. Measuring transmittance as a function of incident polarization directly reflects the magnitude and direction of strain. Moreover, direction-dependent selection rules permit the identification of the lattice orientation by monitoring the van Hove transitions. These photoelastic effects in graphene can be explored towards atomically thin, broadband optical elements. Copyright (C) EPLA, 2010 |
1994 |
WU, SX; MAI, YW; COTTERELL, B DUCTILE-BRITTLE FRACTURE TRANSITION AS A RESULT OF INCREASING IN-PLANE CONSTRAINT IN A MEDIUM CARBON STEEL Inproceedings {Landes, JD; McCabe, DE; Boulet, JAM} (Ed.): FRACTURE MECHANICS: TWENTY-FOURTH VOLUME, pp. 376-386, AMER SOC TESTING & MAT, COMM E8 FATIGUE & GRACTRUE; UNIV TENNESSEE; OAK RIDGE NATL LAB AMERICAN SOCIETY TESTING AND MATERIALS, 100 BARR HARBOR DRIVE, W CONSHOHOCKEN, PA 19428-2959, 1994, ISSN: 1071-5827, (24th National Symposium on Fracture Mechanics, GATLINBURG, TN, JUN 30-JUL 02, 1992). @inproceedings{ISI:A1994BC72V00020, title = {DUCTILE-BRITTLE FRACTURE TRANSITION AS A RESULT OF INCREASING IN-PLANE CONSTRAINT IN A MEDIUM CARBON STEEL}, author = {SX WU and YW MAI and B COTTERELL}, editor = {JD {Landes and DE McCabe and JAM} Boulet}, doi = {10.1520/STP13716S}, issn = {1071-5827}, year = {1994}, date = {1994-01-01}, booktitle = {FRACTURE MECHANICS: TWENTY-FOURTH VOLUME}, volume = {1207}, pages = {376-386}, publisher = {AMERICAN SOCIETY TESTING AND MATERIALS}, address = {100 BARR HARBOR DRIVE, W CONSHOHOCKEN, PA 19428-2959}, organization = {AMER SOC TESTING & MAT, COMM E8 FATIGUE & GRACTRUE; UNIV TENNESSEE; OAK RIDGE NATL LAB}, series = {AMERICAN SOCIETY FOR TESTING AND MATERIALS SPECIAL TECHNICAL PUBLICATION}, note = {24th National Symposium on Fracture Mechanics, GATLINBURG, TN, JUN 30-JUL 02, 1992}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } |
0000 |
Chua, Rebekah; Yang, Jing; He, Xiaoyue; Yu, Xiaojiang; Yu, Wei; Bussolotti, Fabio; Wong, Ping Kwan Johnny; Loh, Kian Ping; Breese, Mark B H; Goh, Kuan Eng Johnson; Huang, Yu Li; Wee, Andrew T S Can Reconstructed Se-Deficient Line Defects in Monolayer VSe2 Induce Magnetism? Journal Article ADVANCED MATERIALS, 0000, ISSN: 0935-9648. @article{ISI:000530864700001, title = {Can Reconstructed Se-Deficient Line Defects in Monolayer VSe2 Induce Magnetism?}, author = {Rebekah Chua and Jing Yang and Xiaoyue He and Xiaojiang Yu and Wei Yu and Fabio Bussolotti and Ping Kwan Johnny Wong and Kian Ping Loh and Mark B H Breese and Kuan Eng Johnson Goh and Yu Li Huang and Andrew T S Wee}, doi = {10.1002/adma.202000693, Early Access Date = MAY 2020}, issn = {0935-9648}, journal = {ADVANCED MATERIALS}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {There have been several recent conflicting reports on the ferromagnetism of clean monolayer VSe2. Herein, the controllable formation of 1D defect line patterns in vanadium diselenide (VSe2) monolayers initiated by thermal annealing is presented. Using scanning tunneling microscopy and q-plus atomic force microscopy techniques, the 1D line features are determined to be 8-member-ring arrays, formed via a Se deficient reconstruction process. The reconstructed VSe2 monolayer with Se-deficient line defects displays room-temperature ferromagnetism under X-ray magnetic circular dichroism and magnetic force microscopy, consistent with the density functional theory calculations. This study possibly resolves the controversy on whether ferromagnetism is intrinsic in monolayer VSe2, and highlights the importance of controlling and understanding the atomic structures of surface defects in 2D crystals, which could play key roles in the material properties and hence potential device applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } There have been several recent conflicting reports on the ferromagnetism of clean monolayer VSe2. Herein, the controllable formation of 1D defect line patterns in vanadium diselenide (VSe2) monolayers initiated by thermal annealing is presented. Using scanning tunneling microscopy and q-plus atomic force microscopy techniques, the 1D line features are determined to be 8-member-ring arrays, formed via a Se deficient reconstruction process. The reconstructed VSe2 monolayer with Se-deficient line defects displays room-temperature ferromagnetism under X-ray magnetic circular dichroism and magnetic force microscopy, consistent with the density functional theory calculations. This study possibly resolves the controversy on whether ferromagnetism is intrinsic in monolayer VSe2, and highlights the importance of controlling and understanding the atomic structures of surface defects in 2D crystals, which could play key roles in the material properties and hence potential device applications. |
Li, Chen; Lin, Wang; Yue, Peng; Xuewei, Feng; Sarkar, Soumya; Sifan, Li; Bochang, Li; Liang, Liu; Kaizhen, Han; Xiao, Gong; Jingsheng, Chen; Yan, Liu; Genquan, Han; Ang, Kah-Wee A van der Waals Synaptic Transistor Based on Ferroelectric Hf0.5Zr0.5O2 and 2D Tungsten Disulfide Journal Article ADVANCED ELECTRONIC MATERIALS, 0000, ISSN: 2199-160X. @article{ISI:000530860500001, title = {A van der Waals Synaptic Transistor Based on Ferroelectric Hf0.5Zr0.5O2 and 2D Tungsten Disulfide}, author = {Chen Li and Wang Lin and Peng Yue and Feng Xuewei and Soumya Sarkar and Li Sifan and Li Bochang and Liu Liang and Han Kaizhen and Gong Xiao and Chen Jingsheng and Liu Yan and Han Genquan and Kah-Wee Ang}, doi = {10.1002/aelm.202000057, Early Access Date = MAY 2020}, issn = {2199-160X}, journal = {ADVANCED ELECTRONIC MATERIALS}, publisher = {WILEY}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {Neuromorphic computing on the hardware level is promising for performing ever-increasing data-centric tasks owing to its superiority to conventional von Neumann architecture in terms of energy efficiency and learning ability. One key aspect to its implementation is the development of artificial synapses that can effectively emulate the multiple functionalities exhibited by their biological counterparts. Here, building on an inorganic ferroelectric gate stack integrated with a 2D layered semiconductor (WS2), a new type of ferroelectricity-based synaptic transistor that differs from those relying on interface traps or floating gate configuration is reported. By virtue of a 6 nm thick ferroelectric hafnium zirconium oxide by atomic layer deposition and postannealing treatment, the device shows a channel resistance change ratio above 10(5) corresponding to opposite ferroelectric polarization direction. Furthermore, by applying electrical stimulus to the gate, it demonstrates good capability to mimic various synaptic behaviors including long-term potentiation, long-term depression, spike-amplitude-dependent plasticity, and spike-rate-dependent plasticity. Given the inherent compatibility of the ferroelectric gate stack with existing fabrication technology, and the reliability of ferroelectricity engineering, this work paves the way toward practical implementation of synaptic devices in neuromorphic circuits.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Neuromorphic computing on the hardware level is promising for performing ever-increasing data-centric tasks owing to its superiority to conventional von Neumann architecture in terms of energy efficiency and learning ability. One key aspect to its implementation is the development of artificial synapses that can effectively emulate the multiple functionalities exhibited by their biological counterparts. Here, building on an inorganic ferroelectric gate stack integrated with a 2D layered semiconductor (WS2), a new type of ferroelectricity-based synaptic transistor that differs from those relying on interface traps or floating gate configuration is reported. By virtue of a 6 nm thick ferroelectric hafnium zirconium oxide by atomic layer deposition and postannealing treatment, the device shows a channel resistance change ratio above 10(5) corresponding to opposite ferroelectric polarization direction. Furthermore, by applying electrical stimulus to the gate, it demonstrates good capability to mimic various synaptic behaviors including long-term potentiation, long-term depression, spike-amplitude-dependent plasticity, and spike-rate-dependent plasticity. Given the inherent compatibility of the ferroelectric gate stack with existing fabrication technology, and the reliability of ferroelectricity engineering, this work paves the way toward practical implementation of synaptic devices in neuromorphic circuits. |
Leng, Kai; Fu, Wei; Liu, Yanpeng; Chhowalla, Manish; Loh, Kian Ping From bulk to molecularly thin hybrid perovskites Journal Article NATURE REVIEWS MATERIALS, 0000, ISSN: 2058-8437. @article{ISI:000522380500001, title = {From bulk to molecularly thin hybrid perovskites}, author = {Kai Leng and Wei Fu and Yanpeng Liu and Manish Chhowalla and Kian Ping Loh}, doi = {10.1038/s41578-020-0185-1, Early Access Date = MAR 2020}, issn = {2058-8437}, journal = {NATURE REVIEWS MATERIALS}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Owing to their layered structure, the properties of 2D perovskites can be controlled by tuning their thickness. This Review surveys how fine-tuning the thickness of 2D perovskites from the sub-micrometre to the molecularly thin regime helps to optimize their electrical and optical properties for use in different applications. Organic-inorganic hybrid perovskites have been intensively researched in the past decade for their optoelectronic properties. The emergence of Ruddlesden-Popper perovskites, which have mixed dimensionality, has heralded new opportunities for tailor-made semiconductors that combine enhanced stability with useful properties between those of 2D and 3D systems. Inspired by advances in 2D materials research, there is growing interest in molecularly thin versions of these hybrid perovskites, owing to their ease of incorporation into electronic devices. There is, thus, a need to understand thickness-dependent electrical, excitonic and phononic properties that go beyond quantum-confinement effects. Recent studies have shown that, apart from tuning the dimensionality of the system, fine-tuning its thickness also helps to optimize performance in different applications, ranging from third-harmonic generation to photodetectors and spintronics.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Owing to their layered structure, the properties of 2D perovskites can be controlled by tuning their thickness. This Review surveys how fine-tuning the thickness of 2D perovskites from the sub-micrometre to the molecularly thin regime helps to optimize their electrical and optical properties for use in different applications. Organic-inorganic hybrid perovskites have been intensively researched in the past decade for their optoelectronic properties. The emergence of Ruddlesden-Popper perovskites, which have mixed dimensionality, has heralded new opportunities for tailor-made semiconductors that combine enhanced stability with useful properties between those of 2D and 3D systems. Inspired by advances in 2D materials research, there is growing interest in molecularly thin versions of these hybrid perovskites, owing to their ease of incorporation into electronic devices. There is, thus, a need to understand thickness-dependent electrical, excitonic and phononic properties that go beyond quantum-confinement effects. Recent studies have shown that, apart from tuning the dimensionality of the system, fine-tuning its thickness also helps to optimize performance in different applications, ranging from third-harmonic generation to photodetectors and spintronics. |
Xiong, Ting; Zhu, Mingke; Zhang, Yaoxin; Lee, Wee Siang Vincent; Yu, Zhi Gen; Xue, Junmin Interlayer Engineering of MnO2 with High Charge Density Bi3+ for High Rate and Stable Aqueous Supercapacitor Journal Article BATTERIES & SUPERCAPS, 0000. @article{ISI:000526099200001, title = {Interlayer Engineering of MnO2 with High Charge Density Bi3+ for High Rate and Stable Aqueous Supercapacitor}, author = {Ting Xiong and Mingke Zhu and Yaoxin Zhang and Wee Siang Vincent Lee and Zhi Gen Yu and Junmin Xue}, doi = {10.1002/batt.202000007, Early Access Date = FEB 2020}, journal = {BATTERIES & SUPERCAPS}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Two-dimensional delta-MnO2 has attracted considerable attention as supercapacitor electrode due to its ability to incorporate foreign ions into its interlayer spacing which suggests the possibility of capacitance enhancement through interlayer engineering. Incorporating high charge density cation such as Bi3+ into the MnO2 interlayer becomes an attractive strategy that not only serves to stabilize the layer structure, it is also an important prelude towards the weakening of the chemical bonding between the O from MnO2 and the intercalating electrolyte species. This in turn leads to higher reversibility while ensuring excellent structural stability that is portrayed in enhanced cyclic stability and rate performance. Herein, the Bi3+-modified delta-MnO2 delivered a reversible specific capacity of 421 F g(-1) at 1 A g(-1), which is higher than that of the previously reported mono/divalent cation-intercalant modified MnO2 systems. Using the N-doped carbon nanosheets as the negative electrode, the assembled asymmetric supercapacitor achieved a high capacitance of 77 F g(-1) at 1 Ag-1. Furthermore, the high energy density of 20 Wh kg(-1) was recorded at a high-power density of 39 kW kg(-1), while simultaneously demonstrating excellent cycle performance of 82 % capacitance retention after 40 000 cycles. This work has shown that interlayer engineering of layered MnO2 could potentially provide new insight into the development of high-performance supercapacitor electrode.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Two-dimensional delta-MnO2 has attracted considerable attention as supercapacitor electrode due to its ability to incorporate foreign ions into its interlayer spacing which suggests the possibility of capacitance enhancement through interlayer engineering. Incorporating high charge density cation such as Bi3+ into the MnO2 interlayer becomes an attractive strategy that not only serves to stabilize the layer structure, it is also an important prelude towards the weakening of the chemical bonding between the O from MnO2 and the intercalating electrolyte species. This in turn leads to higher reversibility while ensuring excellent structural stability that is portrayed in enhanced cyclic stability and rate performance. Herein, the Bi3+-modified delta-MnO2 delivered a reversible specific capacity of 421 F g(-1) at 1 A g(-1), which is higher than that of the previously reported mono/divalent cation-intercalant modified MnO2 systems. Using the N-doped carbon nanosheets as the negative electrode, the assembled asymmetric supercapacitor achieved a high capacitance of 77 F g(-1) at 1 Ag-1. Furthermore, the high energy density of 20 Wh kg(-1) was recorded at a high-power density of 39 kW kg(-1), while simultaneously demonstrating excellent cycle performance of 82 % capacitance retention after 40 000 cycles. This work has shown that interlayer engineering of layered MnO2 could potentially provide new insight into the development of high-performance supercapacitor electrode. |
Guo, Rui; Zheng, Yue; Hu, Zehua; Zhang, Jialin; Han, Cheng; Longhi, Elena; Barlow, Stephen; Marder, Seth R; Chen, Wei CHEMISTRY-A EUROPEAN JOURNAL, 0000, ISSN: 0947-6539. @article{ISI:000513994300001, title = {Surface Functionalization of Black Phosphorus with a Highly Reducing Organoruthenium Complex: Interface Properties and Enhanced Photoresponsivity of Photodetectors}, author = {Rui Guo and Yue Zheng and Zehua Hu and Jialin Zhang and Cheng Han and Elena Longhi and Stephen Barlow and Seth R Marder and Wei Chen}, doi = {10.1002/chem.201905173, Early Access Date = FEB 2020}, issn = {0947-6539}, journal = {CHEMISTRY-A EUROPEAN JOURNAL}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {In this work, a heterostructure obtained by vacuum evaporation of a strong molecular n-dopant, [RuCp*(mes)](2), onto black phosphorus (BP) is reported, along with the systematic investigation of the interfacial structure and properties by various in situ characterization techniques. Ultraviolet photoelectron spectra (UPS) showed a large decrease in the work function of BP and a new peak within the bandgap, which is attributed to electron transfer from dopants to the underlying BP. The electrons trapped at the interface act as hole traps and induce photogating effect so that a photodetector based on BP-organoruthenium complex heterostructure demonstrates a photoresponsivity of 5.5 mA W-1 and an EQE of 1.3 % at 515 nm, a tenfold improvement compared to the pristine BP device.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this work, a heterostructure obtained by vacuum evaporation of a strong molecular n-dopant, [RuCp*(mes)](2), onto black phosphorus (BP) is reported, along with the systematic investigation of the interfacial structure and properties by various in situ characterization techniques. Ultraviolet photoelectron spectra (UPS) showed a large decrease in the work function of BP and a new peak within the bandgap, which is attributed to electron transfer from dopants to the underlying BP. The electrons trapped at the interface act as hole traps and induce photogating effect so that a photodetector based on BP-organoruthenium complex heterostructure demonstrates a photoresponsivity of 5.5 mA W-1 and an EQE of 1.3 % at 515 nm, a tenfold improvement compared to the pristine BP device. |
Feng, Xuewei; Li, Yida; Wang, Lin; Chen, Shuai; Yu, Zhi Gen; Tan, Wee Chong; Macadam, Nasiruddin; Hu, Guohua; Huang, Li; Chen, Li; Gong, Xiao; Chi, Dongzhi; Hasan, Tawfique; Thean, Aaron Voon-Yew; Zhang, Yong-Wei; Ang, Koh-Wee A Fully Printed Flexible MoS2 Memristive Artificial Synapse with Femtojoule Switching Energy Journal Article ADVANCED ELECTRONIC MATERIALS, 0000, ISSN: 2199-160X. @article{ISI:000486813700001, title = {A Fully Printed Flexible MoS2 Memristive Artificial Synapse with Femtojoule Switching Energy}, author = {Xuewei Feng and Yida Li and Lin Wang and Shuai Chen and Zhi Gen Yu and Wee Chong Tan and Nasiruddin Macadam and Guohua Hu and Li Huang and Li Chen and Xiao Gong and Dongzhi Chi and Tawfique Hasan and Aaron Voon-Yew Thean and Yong-Wei Zhang and Koh-Wee Ang}, doi = {10.1002/aelm.201900740, Early Access Date = SEP 2019}, issn = {2199-160X}, journal = {ADVANCED ELECTRONIC MATERIALS}, publisher = {WILEY}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {Realization of memristors capable of storing and processing data on flexible substrates is a key enabling technology toward ``system-on-plastics''. Recent advancements in printing techniques show enormous potential to overcome the major challenges of the current manufacturing processes that require high temperature and planar topography, which may radically change the system integration approach on flexible substrates. However, fully printed memristors are yet to be successfully demonstrated due to the lack of a robust printable switching medium and a reliable printing process. An aerosol-jet-printed Ag/MoS2/Ag memristor is realized in a cross-bar structure by developing a scalable and low temperature printing technique utilizing a functional molybdenum disulfide (MoS2) ink platform. The fully printed devices exhibit an ultra-low switching voltage (0.18 V), a high switching ratio (10(7)), a wide range of tuneable resistance states (10-10(10) omega) for multi-bit data storage, and a low standby power consumption of 1 fW and a switching energy of 4.5 fJ per transition set. Moreover, the MoS2 memristor exhibits both volatile and non-volatile resistive switching behavior by controlling the current compliance levels, which efficiently mimic the short-term and long-term plasticity of biological synapses, demonstrating its potential to enable energy-efficient artificial neuromorphic computing.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Realization of memristors capable of storing and processing data on flexible substrates is a key enabling technology toward ``system-on-plastics''. Recent advancements in printing techniques show enormous potential to overcome the major challenges of the current manufacturing processes that require high temperature and planar topography, which may radically change the system integration approach on flexible substrates. However, fully printed memristors are yet to be successfully demonstrated due to the lack of a robust printable switching medium and a reliable printing process. An aerosol-jet-printed Ag/MoS2/Ag memristor is realized in a cross-bar structure by developing a scalable and low temperature printing technique utilizing a functional molybdenum disulfide (MoS2) ink platform. The fully printed devices exhibit an ultra-low switching voltage (0.18 V), a high switching ratio (10(7)), a wide range of tuneable resistance states (10-10(10) omega) for multi-bit data storage, and a low standby power consumption of 1 fW and a switching energy of 4.5 fJ per transition set. Moreover, the MoS2 memristor exhibits both volatile and non-volatile resistive switching behavior by controlling the current compliance levels, which efficiently mimic the short-term and long-term plasticity of biological synapses, demonstrating its potential to enable energy-efficient artificial neuromorphic computing. |