Browse through over scientific publications by CA2DM staff, students, collaborators, and partners.
2013 |
Schmidt, H; Rode, J C; Belke, C; Smirnov, D; Haug, R J Mixing of edge states at a bipolar graphene junction Journal Article PHYSICAL REVIEW B, 88 (7), 2013, ISSN: 1098-0121. @article{ISI:000323154400003, title = {Mixing of edge states at a bipolar graphene junction}, author = {H Schmidt and J C Rode and C Belke and D Smirnov and R J Haug}, doi = {10.1103/PhysRevB.88.075418}, issn = {1098-0121}, year = {2013}, date = {2013-08-01}, journal = {PHYSICAL REVIEW B}, volume = {88}, number = {7}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {An atomic force microscope is used to locally manipulate a single layer graphene sheet. Transport measurements in this region as well as in the unmanipulated part reveal different charge carrier densities, while mobilities stay in the order of 10(4) cm(2)(V s)(-1). With a global backgate, the system is tuned from a unipolar n-n' or p-p' junction with different densities to a bipolar p-n junction. Magnetotransport across this junction verifies its nature, showing the expected quantized resistance values as well as the switching with the polarity of the magnetic field. Measurements at higher magnetic fields show a suppression of the mixing of edge states with different polarity at the p-n junction.}, keywords = {}, pubstate = {published}, tppubtype = {article} } An atomic force microscope is used to locally manipulate a single layer graphene sheet. Transport measurements in this region as well as in the unmanipulated part reveal different charge carrier densities, while mobilities stay in the order of 10(4) cm(2)(V s)(-1). With a global backgate, the system is tuned from a unipolar n-n' or p-p' junction with different densities to a bipolar p-n junction. Magnetotransport across this junction verifies its nature, showing the expected quantized resistance values as well as the switching with the polarity of the magnetic field. Measurements at higher magnetic fields show a suppression of the mixing of edge states with different polarity at the p-n junction. |
Zheng, Yi; Su, Chenliang; Lu, Jiong; Loh, Kian Ping Room-Temperature Ice Growth on Graphite Seeded by Nano-Graphene Oxide Journal Article ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 52 (33), pp. 8708-8712, 2013, ISSN: 1433-7851. @article{ISI:000322835700047, title = {Room-Temperature Ice Growth on Graphite Seeded by Nano-Graphene Oxide}, author = {Yi Zheng and Chenliang Su and Jiong Lu and Kian Ping Loh}, doi = {10.1002/anie.201302608}, issn = {1433-7851}, year = {2013}, date = {2013-08-01}, journal = {ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, volume = {52}, number = {33}, pages = {8708-8712}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Lin, Jiadan; Zhong, Jianqiang; Zhong, Shu; Li, Hai; Zhang, Hua; Chen, Wei Modulating electronic transport properties of MoS2 field effect transistor by surface overlayers Journal Article APPLIED PHYSICS LETTERS, 103 (6), 2013, ISSN: 0003-6951. @article{ISI:000322908300067, title = {Modulating electronic transport properties of MoS2 field effect transistor by surface overlayers}, author = {Jiadan Lin and Jianqiang Zhong and Shu Zhong and Hai Li and Hua Zhang and Wei Chen}, doi = {10.1063/1.4818463}, issn = {0003-6951}, year = {2013}, date = {2013-08-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {103}, number = {6}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {In situ bottom-gated molybdenum disulfide (MoS2) field effect transistors (FETs) device characterization and in situ ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy measurements were combined to investigate the effect of surface modification layers of C-60 and molybdenum trioxide (MoO3) on the electronic properties of single layer MoS2. It is found that C-60 decoration keeps MoS2 FET performance intact due to the very weak interfacial interactions, making C-60 as an ideal capping layer for MoS2 devices. In contrast, decorating MoO3 on MoS2 induces significant charge transfer at the MoS2/MoO3 interface and largely depletes the electron charge carriers in MoS2 FET devices. (C) 2013 AIP Publishing LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In situ bottom-gated molybdenum disulfide (MoS2) field effect transistors (FETs) device characterization and in situ ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy measurements were combined to investigate the effect of surface modification layers of C-60 and molybdenum trioxide (MoO3) on the electronic properties of single layer MoS2. It is found that C-60 decoration keeps MoS2 FET performance intact due to the very weak interfacial interactions, making C-60 as an ideal capping layer for MoS2 devices. In contrast, decorating MoO3 on MoS2 induces significant charge transfer at the MoS2/MoO3 interface and largely depletes the electron charge carriers in MoS2 FET devices. (C) 2013 AIP Publishing LLC. |
Xia, Minggang; Su, Zhidan; Song, Yang; Han, Jinyun; Zhang, Shengli; Li, Baowen Localized vibrational, edges and breathing modes of graphene nanoribbons with topological line defects Journal Article EUROPEAN PHYSICAL JOURNAL B, 86 (8), 2013, ISSN: 1434-6028. @article{ISI:000323742400007, title = {Localized vibrational, edges and breathing modes of graphene nanoribbons with topological line defects}, author = {Minggang Xia and Zhidan Su and Yang Song and Jinyun Han and Shengli Zhang and Baowen Li}, doi = {10.1140/epjb/e2013-40068-5}, issn = {1434-6028}, year = {2013}, date = {2013-08-01}, journal = {EUROPEAN PHYSICAL JOURNAL B}, volume = {86}, number = {8}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {Peculiar vibrational modes of graphene nanoribbons (GNRs) with topological line defects were presented. We find that phonon dispersion relations of the topological defective GNRs are more similar to those of perfect armchair-edge GNR than to zigzag-edge GNR in spite of their zigzag edge. All vibrational modes at G point are assigned in detail by analyzing their eigenvectors and are presented by video. Three types of characteristic vibrational modes, namely, localized vibrational modes in defect sites, edges, and breathing modes, are observed. Five localized vibrational modes near the defect sites are found to be robust against the width of the topological line-defective GNR. The Raman D' band just originates from one localized mode, 1622 cm(-1). The vibrational mode is sensitive to symmetry. The edge modes are related with structural symmetry but not with widths. Two edge modes are asymmetrical and only one is symmetrical. The breathing modes are inversely proportional to the width for wide-defect GNRs, and inversely proportional to the square root of the width for narrow-defect GNRs. The breathing mode frequencies of defective GNRs are slightly higher than those of perfect GNRs. These vibrational modes may be useful in the manipulation of thermal conductance and implementation of single phonon storage.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Peculiar vibrational modes of graphene nanoribbons (GNRs) with topological line defects were presented. We find that phonon dispersion relations of the topological defective GNRs are more similar to those of perfect armchair-edge GNR than to zigzag-edge GNR in spite of their zigzag edge. All vibrational modes at G point are assigned in detail by analyzing their eigenvectors and are presented by video. Three types of characteristic vibrational modes, namely, localized vibrational modes in defect sites, edges, and breathing modes, are observed. Five localized vibrational modes near the defect sites are found to be robust against the width of the topological line-defective GNR. The Raman D' band just originates from one localized mode, 1622 cm(-1). The vibrational mode is sensitive to symmetry. The edge modes are related with structural symmetry but not with widths. Two edge modes are asymmetrical and only one is symmetrical. The breathing modes are inversely proportional to the width for wide-defect GNRs, and inversely proportional to the square root of the width for narrow-defect GNRs. The breathing mode frequencies of defective GNRs are slightly higher than those of perfect GNRs. These vibrational modes may be useful in the manipulation of thermal conductance and implementation of single phonon storage. |
Burson, Kristen M; Cullen, William G; Adam, Shaffique; Dean, Cory R; Watanabe, K; Taniguchi, T; Kim, Philip; Fuhrer, Michael S Direct Imaging of Charged Impurity Density in Common Graphene Substrates Journal Article NANO LETTERS, 13 (8), pp. 3576-3580, 2013, ISSN: 1530-6984. @article{ISI:000323241000020, title = {Direct Imaging of Charged Impurity Density in Common Graphene Substrates}, author = {Kristen M Burson and William G Cullen and Shaffique Adam and Cory R Dean and K Watanabe and T Taniguchi and Philip Kim and Michael S Fuhrer}, doi = {10.1021/nl4012529}, issn = {1530-6984}, year = {2013}, date = {2013-08-01}, journal = {NANO LETTERS}, volume = {13}, number = {8}, pages = {3576-3580}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Kelvin probe microscopy in ultrahigh vacuum is used to image the local electrostatic potential fluctuations above hexagonal boron nitride (h-BN) and SiO2, common substrates for graphene. Results are compared to a model of randomly distributed charges in a two-dimensional (2D) plane. For SiO2, the results are well modeled by 2D charge densities ranging from 0.24 to 2.7 X 10(11) cm(-2), while h-BN displays potential fluctuations 1-2 orders of magnitude lower than SiO2, consistent with the improvement in charge carrier mobility for graphene on h-BN compared to SiO2. Electron beam exposure of SiO2 increases the charge density fluctuations, creating long-lived metastable charge populations of similar to 2 x 10(11) cm(-2) at room temperature, which can be reversed by heating.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Kelvin probe microscopy in ultrahigh vacuum is used to image the local electrostatic potential fluctuations above hexagonal boron nitride (h-BN) and SiO2, common substrates for graphene. Results are compared to a model of randomly distributed charges in a two-dimensional (2D) plane. For SiO2, the results are well modeled by 2D charge densities ranging from 0.24 to 2.7 X 10(11) cm(-2), while h-BN displays potential fluctuations 1-2 orders of magnitude lower than SiO2, consistent with the improvement in charge carrier mobility for graphene on h-BN compared to SiO2. Electron beam exposure of SiO2 increases the charge density fluctuations, creating long-lived metastable charge populations of similar to 2 x 10(11) cm(-2) at room temperature, which can be reversed by heating. |
Lee, Jong Hak; Koon, Gavin Kok Wai; Shin, Dong Wook; Fedorov, V E; Choi, Jae-Young; Yoo, Ji-Beom; Oezyilmaz, Barbaros Property Control of Graphene by Employing ``Semi-Ionic'' Liquid Fluorination Journal Article ADVANCED FUNCTIONAL MATERIALS, 23 (26), pp. 3329-3334, 2013, ISSN: 1616-301X. @article{ISI:000327489200010, title = {Property Control of Graphene by Employing ``Semi-Ionic'' Liquid Fluorination}, author = {Jong Hak Lee and Gavin Kok Wai Koon and Dong Wook Shin and V E Fedorov and Jae-Young Choi and Ji-Beom Yoo and Barbaros Oezyilmaz}, doi = {10.1002/adfm.201202822}, issn = {1616-301X}, year = {2013}, date = {2013-07-01}, journal = {ADVANCED FUNCTIONAL MATERIALS}, volume = {23}, number = {26}, pages = {3329-3334}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Semi-ionically fluorinated graphene (s-FG) is synthesized with a one step liquid fluorination treatment. The s-FG consists of two different types of bonds, namely a covalent C-F bond and an ionic C-F bond. Control is achieved over the properties of s-FG by selectively eliminating ionic C-F bonds from the as prepared s-FG film which is highly insulating (current < 10(-13) A at 1 V). After selective elimination of ionic C-F bonds by acetone treatment, s-FG recovers the highly conductive property of graphene. A 10(9) times increase in current from 10(-13) to 10(-4)A at 1 V is achieved, which indicates that s-FG recovers its conducting property. The properties of reduced s-FG vary according to the number of layers and the single layer reduced s-FG has mobility of more than 6000 cm(2) V-1 s(-1). The mobility drastically decreases with increasing number of layers. The bi-layered s-FG has a mobility of 141cm(2) V-1 s(-1) and multi-layered s-FG film showed highly p-type doped electrical property without Dirac point. The reduction via acetone proceeds as 2C(2)F((semi-ionic)) + CH3C(O)CH3(l) HF + 2C((s)) + C2F(covalent) + CH3C(O)CH2(l). The fluorination and reduction processes permit the safe and facile non-destructive property control of the s-FG film.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Semi-ionically fluorinated graphene (s-FG) is synthesized with a one step liquid fluorination treatment. The s-FG consists of two different types of bonds, namely a covalent C-F bond and an ionic C-F bond. Control is achieved over the properties of s-FG by selectively eliminating ionic C-F bonds from the as prepared s-FG film which is highly insulating (current < 10(-13) A at 1 V). After selective elimination of ionic C-F bonds by acetone treatment, s-FG recovers the highly conductive property of graphene. A 10(9) times increase in current from 10(-13) to 10(-4)A at 1 V is achieved, which indicates that s-FG recovers its conducting property. The properties of reduced s-FG vary according to the number of layers and the single layer reduced s-FG has mobility of more than 6000 cm(2) V-1 s(-1). The mobility drastically decreases with increasing number of layers. The bi-layered s-FG has a mobility of 141cm(2) V-1 s(-1) and multi-layered s-FG film showed highly p-type doped electrical property without Dirac point. The reduction via acetone proceeds as 2C(2)F((semi-ionic)) + CH3C(O)CH3(l) HF + 2C((s)) + C2F(covalent) + CH3C(O)CH2(l). The fluorination and reduction processes permit the safe and facile non-destructive property control of the s-FG film. |
Singh, Simranjeet; Patra, Ajit Kumar; Barin, Brett; del Barco, Enrique; Oezyilmaz, Barbaros Spin Pumping in Permalloy/Graphene and Permalloy/Graphite Interfaces Journal Article IEEE TRANSACTIONS ON MAGNETICS, 49 (7), pp. 3147-3150, 2013, ISSN: 0018-9464, (12th Joint MMM-Intermag Conference, Chicago, IL, JAN 14-18, 2013). @article{ISI:000322483200019, title = {Spin Pumping in Permalloy/Graphene and Permalloy/Graphite Interfaces}, author = {Simranjeet Singh and Ajit Kumar Patra and Brett Barin and Enrique del Barco and Barbaros Oezyilmaz}, doi = {10.1109/TMAG.2013.2244067}, issn = {0018-9464}, year = {2013}, date = {2013-07-01}, journal = {IEEE TRANSACTIONS ON MAGNETICS}, volume = {49}, number = {7}, pages = {3147-3150}, publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC}, address = {445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA}, organization = {AIP Publishing; IEEE Magnet Soc}, abstract = {This article reports a comparative study of the spin pumping induced by graphite and graphene layers adjacent to an extended ferromagnetic Permalloy film. The corresponding enhancement of the Gilbert damping in the ferromagnet is determined by analyzing the frequency dependence of the ferromagnetic resonance linewidth in experiments done with a broad band microwave spectrometer. The results show that a single graphene layer is more efficient than a thick graphite film in absorbing the angular momentum pumped away from the Permalloy during the resonant precession of its magnetization. We associate this effect to an enhancement of the spin-orbit coupling in the graphene layer due to Copper adatoms residual from the chemical vapor deposition process used to synthesize the graphene used in the experiments.}, note = {12th Joint MMM-Intermag Conference, Chicago, IL, JAN 14-18, 2013}, keywords = {}, pubstate = {published}, tppubtype = {article} } This article reports a comparative study of the spin pumping induced by graphite and graphene layers adjacent to an extended ferromagnetic Permalloy film. The corresponding enhancement of the Gilbert damping in the ferromagnet is determined by analyzing the frequency dependence of the ferromagnetic resonance linewidth in experiments done with a broad band microwave spectrometer. The results show that a single graphene layer is more efficient than a thick graphite film in absorbing the angular momentum pumped away from the Permalloy during the resonant precession of its magnetization. We associate this effect to an enhancement of the spin-orbit coupling in the graphene layer due to Copper adatoms residual from the chemical vapor deposition process used to synthesize the graphene used in the experiments. |
Tang, Wei; Zhu, Yusong; Hou, Yuyang; Liu, Lili; Wu, Yuping; Loh, Kian Ping; Zhang, Hanping; Zhu, Kai Aqueous rechargeable lithium batteries as an energy storage system of superfast charging Journal Article ENERGY & ENVIRONMENTAL SCIENCE, 6 (7), pp. 2093-2104, 2013, ISSN: 1754-5692. @article{ISI:000320779700008, title = {Aqueous rechargeable lithium batteries as an energy storage system of superfast charging}, author = {Wei Tang and Yusong Zhu and Yuyang Hou and Lili Liu and Yuping Wu and Kian Ping Loh and Hanping Zhang and Kai Zhu}, doi = {10.1039/c3ee24249h}, issn = {1754-5692}, year = {2013}, date = {2013-07-01}, journal = {ENERGY & ENVIRONMENTAL SCIENCE}, volume = {6}, number = {7}, pages = {2093-2104}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {Due to the energy crisis within recent decades, renewable energies such as solar, wind and tide energies have received a lot of attention. However, these renewable energies are dependent on the time and season. Consequently, energy storage systems are needed to fully utilize these energies including their connection with smart grids. Aqueous rechargeable lithium batteries (ARLBs) may be an ideal energy storage system due to its excellent safety and reliability. However, since the introduction of ARLBs in 1994, the progress on improving their performance has been very limited. Recently, their rate performance, especially superfast charging performance, reversible capacity and cycling life of their electrode materials were markedly improved. The present work reviews the latest advances in the exploration of the electrode materials and the development of battery systems. Also the main challenges in this field are briefly commented on and discussed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Due to the energy crisis within recent decades, renewable energies such as solar, wind and tide energies have received a lot of attention. However, these renewable energies are dependent on the time and season. Consequently, energy storage systems are needed to fully utilize these energies including their connection with smart grids. Aqueous rechargeable lithium batteries (ARLBs) may be an ideal energy storage system due to its excellent safety and reliability. However, since the introduction of ARLBs in 1994, the progress on improving their performance has been very limited. Recently, their rate performance, especially superfast charging performance, reversible capacity and cycling life of their electrode materials were markedly improved. The present work reviews the latest advances in the exploration of the electrode materials and the development of battery systems. Also the main challenges in this field are briefly commented on and discussed. |
Eda, Goki; Maier, Stefan A Two-Dimensional Crystals: Managing Light for Optoelectronics Journal Article ACS NANO, 7 (7), pp. 5660-5665, 2013, ISSN: 1936-0851. @article{ISI:000322417400003, title = {Two-Dimensional Crystals: Managing Light for Optoelectronics}, author = {Goki Eda and Stefan A Maier}, doi = {10.1021/nn403159y}, issn = {1936-0851}, year = {2013}, date = {2013-07-01}, journal = {ACS NANO}, volume = {7}, number = {7}, pages = {5660-5665}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Semiconducting two-dimensional (2D) crystals such as MoS2 and WSe2 exhibit unusual optical properties that can be exploited for novel optoelectronics ranging from flexible photovoltaic cells to harmonic generation and electro-optical modulation devices. Rapid progress of the field, particularly in the growth area, is beginning to enable ways to implement 2D crystals into devices with tailored functionalities. For practical device performance, a key challenge is to maximize light matter interactions in the material, which is inherently weak due to its atomically thin nature. Light management around the 2D layers with the use of plasmonic nanostructures can provide a compelling solution.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Semiconducting two-dimensional (2D) crystals such as MoS2 and WSe2 exhibit unusual optical properties that can be exploited for novel optoelectronics ranging from flexible photovoltaic cells to harmonic generation and electro-optical modulation devices. Rapid progress of the field, particularly in the growth area, is beginning to enable ways to implement 2D crystals into devices with tailored functionalities. For practical device performance, a key challenge is to maximize light matter interactions in the material, which is inherently weak due to its atomically thin nature. Light management around the 2D layers with the use of plasmonic nanostructures can provide a compelling solution. |
Li, Xiuqiang; Chen, Jie; Yu, Chenxi; Zhang, Gang Comparison of isotope effects on thermal conductivity of graphene nanoribbons and carbon nanotubes Journal Article APPLIED PHYSICS LETTERS, 103 (1), 2013, ISSN: 0003-6951. @article{ISI:000321497200038, title = {Comparison of isotope effects on thermal conductivity of graphene nanoribbons and carbon nanotubes}, author = {Xiuqiang Li and Jie Chen and Chenxi Yu and Gang Zhang}, doi = {10.1063/1.4813111}, issn = {0003-6951}, year = {2013}, date = {2013-07-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {103}, number = {1}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {By using molecular dynamics simulation, we explore the isotope effect on thermal conductivity of graphene nanoribbons (GNRs) and carbon nanotubes (CNTs). For both GNRs and CNTs, the lattice thermal conductivity decreases when isotope concentration increases from 0% to 30%. The thermal conductivity reduction ratio in GNRs is less than that in CNTs. For example, thermal conductivity of CNT with 5% C-13 concentration is 25% lower than that of pure CNTs; however, the reduction in thermal conductivity of GNRs with the same isotope concentration is only about 12%. Lattice dynamics analysis reveals that these phenomena are related to the phonon localization. (C) 2013 AIP Publishing LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } By using molecular dynamics simulation, we explore the isotope effect on thermal conductivity of graphene nanoribbons (GNRs) and carbon nanotubes (CNTs). For both GNRs and CNTs, the lattice thermal conductivity decreases when isotope concentration increases from 0% to 30%. The thermal conductivity reduction ratio in GNRs is less than that in CNTs. For example, thermal conductivity of CNT with 5% C-13 concentration is 25% lower than that of pure CNTs; however, the reduction in thermal conductivity of GNRs with the same isotope concentration is only about 12%. Lattice dynamics analysis reveals that these phenomena are related to the phonon localization. (C) 2013 AIP Publishing LLC. |
O'Mahony, S; O'Dwyer, C; Nijhuis, C A; Greer, J C; Quinn, A J; Thompson, D Nanoscale Dynamics and Protein Adhesivity of Alkylamine Self-Assembled Mono layers on Graphene Journal Article LANGMUIR, 29 (24), pp. 7271-7282, 2013, ISSN: 0743-7463. @article{ISI:000320748200014, title = {Nanoscale Dynamics and Protein Adhesivity of Alkylamine Self-Assembled Mono layers on Graphene}, author = {S O'Mahony and C O'Dwyer and C A Nijhuis and J C Greer and A J Quinn and D Thompson}, doi = {10.1021/la304545n}, issn = {0743-7463}, year = {2013}, date = {2013-06-01}, journal = {LANGMUIR}, volume = {29}, number = {24}, pages = {7271-7282}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Atomic-scale molecular dynamics computer simulations are used to probe the structure, dynamics, and energetics of alkylamine self-assembled monolayer (SAM) films on graphene and to model the formation of molecular bilayers and protein complexes on the films. Routes toward the development and exploitation of functionalized graphene structures are detailed here, and we show that the SAM architecture can be tailored for use in emerging applications (e.g., electrically stimulated nerve fiber growth via the targeted binding of specific cell surface peptide sequences on the functionalized graphene scaffold). The simulations quantify the changes in film physisorption on graphene and the alkyl chain packing efficiency as the film surface is made more polar by changing the terminal groups from methyl (-CH3) to amine (-NH2) to hydroxyl (-OH). The mode of molecule packing dictates the orientation and spacing between terminal groups on the surface of the SAM, which determines the way in which successive layers build up on the surface, whether via the formation of bilayers of the molecule or the immobilization of other (macro)molecules (e.g., proteins) on the SAM. The simulations show the formation of ordered, stable assemblies of monolayers and bilayers of decylamine-based molecules on graphene. These films can serve as protein adsorption platforms, with a hydrophobin protein showing strong and selective adsorption by binding via its hydrophobic patch to methyl-terminated films and binding to amine-terminated films using its more hydrophilic surface regions. Design rules obtained from modeling the atomic-scale structure of the films and interfaces may provide input into experiments for the rational design of assemblies in which the electronic, physicochemical, and mechanical properties of the substrate, film, and protein layer can be tuned to provide the desired functionality.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Atomic-scale molecular dynamics computer simulations are used to probe the structure, dynamics, and energetics of alkylamine self-assembled monolayer (SAM) films on graphene and to model the formation of molecular bilayers and protein complexes on the films. Routes toward the development and exploitation of functionalized graphene structures are detailed here, and we show that the SAM architecture can be tailored for use in emerging applications (e.g., electrically stimulated nerve fiber growth via the targeted binding of specific cell surface peptide sequences on the functionalized graphene scaffold). The simulations quantify the changes in film physisorption on graphene and the alkyl chain packing efficiency as the film surface is made more polar by changing the terminal groups from methyl (-CH3) to amine (-NH2) to hydroxyl (-OH). The mode of molecule packing dictates the orientation and spacing between terminal groups on the surface of the SAM, which determines the way in which successive layers build up on the surface, whether via the formation of bilayers of the molecule or the immobilization of other (macro)molecules (e.g., proteins) on the SAM. The simulations show the formation of ordered, stable assemblies of monolayers and bilayers of decylamine-based molecules on graphene. These films can serve as protein adsorption platforms, with a hydrophobin protein showing strong and selective adsorption by binding via its hydrophobic patch to methyl-terminated films and binding to amine-terminated films using its more hydrophilic surface regions. Design rules obtained from modeling the atomic-scale structure of the films and interfaces may provide input into experiments for the rational design of assemblies in which the electronic, physicochemical, and mechanical properties of the substrate, film, and protein layer can be tuned to provide the desired functionality. |
Britnell, L; Ribeiro, R M; Eckmann, A; Jalil, R; Belle, B D; Mishchenko, A; Kim, Y -J; Gorbachev, R V; Georgiou, T; Morozov, S V; Grigorenko, A N; Geim, A K; Casiraghi, C; Neto, Castro A H; Novoselov, K S Strong Light-Matter Interactions in Heterostructures of Atomically Thin Films Journal Article SCIENCE, 340 (6138), pp. 1311-1314, 2013, ISSN: 0036-8075. @article{ISI:000320320200039, title = {Strong Light-Matter Interactions in Heterostructures of Atomically Thin Films}, author = {L Britnell and R M Ribeiro and A Eckmann and R Jalil and B D Belle and A Mishchenko and Y -J Kim and R V Gorbachev and T Georgiou and S V Morozov and A N Grigorenko and A K Geim and C Casiraghi and A H Castro Neto and K S Novoselov}, doi = {10.1126/science.1235547}, issn = {0036-8075}, year = {2013}, date = {2013-06-01}, journal = {SCIENCE}, volume = {340}, number = {6138}, pages = {1311-1314}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, address = {1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA}, abstract = {The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum efficiency of above 30%).}, keywords = {}, pubstate = {published}, tppubtype = {article} } The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum efficiency of above 30%). |
Qi, Zenan; Bahamon, D A; Pereira, Vitor M; Park, Harold S; Campbell, D K; Neto, Castro A H Resonant Tunneling in Graphene Pseudomagnetic Quantum Dots Journal Article NANO LETTERS, 13 (6), pp. 2692-2697, 2013, ISSN: 1530-6984. @article{ISI:000320485100060, title = {Resonant Tunneling in Graphene Pseudomagnetic Quantum Dots}, author = {Zenan Qi and D A Bahamon and Vitor M Pereira and Harold S Park and D K Campbell and A H Castro Neto}, doi = {10.1021/nl400872q}, issn = {1530-6984}, year = {2013}, date = {2013-06-01}, journal = {NANO LETTERS}, volume = {13}, number = {6}, pages = {2692-2697}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Realistic relaxed configurations of triaxially strained graphene quantum dots are obtained from unbiased atomistic mechanical simulations. The local electronic structure and quantum transport characteristics of y-junctions based on such dots are studied, revealing that the quasi-uniform pseudomagnetic field induced by strain restricts transport to Landau level- and edge state-assisted resonant tunneling. Valley degeneracy is broken in the presence of an external field, allowing the selective filtering of the valley and chirality of the states assisting in the resonant tunneling. Asymmetric strain conditions can be explored to select the exit channel of the y-junction.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Realistic relaxed configurations of triaxially strained graphene quantum dots are obtained from unbiased atomistic mechanical simulations. The local electronic structure and quantum transport characteristics of y-junctions based on such dots are studied, revealing that the quasi-uniform pseudomagnetic field induced by strain restricts transport to Landau level- and edge state-assisted resonant tunneling. Valley degeneracy is broken in the presence of an external field, allowing the selective filtering of the valley and chirality of the states assisting in the resonant tunneling. Asymmetric strain conditions can be explored to select the exit channel of the y-junction. |
Nair, R R; Tsai, I-L; Sepioni, M; Lehtinen, O; Keinonen, J; Krasheninnikov, A V; Neto, Castro A H; Katsnelson, M I; Geim, A K; Grigorieva, I V Dual origin of defect magnetism in graphene and its reversible switching by molecular doping Journal Article NATURE COMMUNICATIONS, 4 , 2013, ISSN: 2041-1723. @article{ISI:000323625200007, title = {Dual origin of defect magnetism in graphene and its reversible switching by molecular doping}, author = {R R Nair and I-L Tsai and M Sepioni and O Lehtinen and J Keinonen and A V Krasheninnikov and A H Castro Neto and M I Katsnelson and A K Geim and I V Grigorieva}, doi = {10.1038/ncomms3010}, issn = {2041-1723}, year = {2013}, date = {2013-06-01}, journal = {NATURE COMMUNICATIONS}, volume = {4}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Control of magnetism by applied voltage is desirable for spintronics applications. Finding a suitable material remains an elusive goal, with only a few candidates found so far. Graphene is one of them and attracts interest because of its weak spin-orbit interaction, the ability to control electronic properties by the electric field effect and the possibility to introduce paramagnetic centres such as vacancies and adatoms. Here we show that the magnetism of adatoms in graphene is itinerant and can be controlled by doping, so that magnetic moments are switched on and off. The much-discussed vacancy magnetism is found to have a dual origin, with two approximately equal contributions; one from itinerant magnetism and the other from dangling bonds. Our work suggests that graphene's spin transport can be controlled by the field effect, similar to its electronic and optical properties, and that spin diffusion can be significantly enhanced above a certain carrier density.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Control of magnetism by applied voltage is desirable for spintronics applications. Finding a suitable material remains an elusive goal, with only a few candidates found so far. Graphene is one of them and attracts interest because of its weak spin-orbit interaction, the ability to control electronic properties by the electric field effect and the possibility to introduce paramagnetic centres such as vacancies and adatoms. Here we show that the magnetism of adatoms in graphene is itinerant and can be controlled by doping, so that magnetic moments are switched on and off. The much-discussed vacancy magnetism is found to have a dual origin, with two approximately equal contributions; one from itinerant magnetism and the other from dangling bonds. Our work suggests that graphene's spin transport can be controlled by the field effect, similar to its electronic and optical properties, and that spin diffusion can be significantly enhanced above a certain carrier density. |
Radchenko, T M; Shylau, A A; Zozoulenko, I V; Ferreira, Aires Effect of charged line defects on conductivity in graphene: Numerical Kubo and analytical Boltzmann approaches Journal Article PHYSICAL REVIEW B, 87 (19), 2013, ISSN: 2469-9950. @article{ISI:000319802900006, title = {Effect of charged line defects on conductivity in graphene: Numerical Kubo and analytical Boltzmann approaches}, author = {T M Radchenko and A A Shylau and I V Zozoulenko and Aires Ferreira}, doi = {10.1103/PhysRevB.87.195448}, issn = {2469-9950}, year = {2013}, date = {2013-05-01}, journal = {PHYSICAL REVIEW B}, volume = {87}, number = {19}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Charge carrier transport in single-layer graphene with one-dimensional charged defects is studied theoretically. Extended charged defects, considered an important factor for mobility degradation in chemically vapor-deposited graphene, are described by a self-consistent Thomas-Fermi potential. A numerical study of electronic transport is performed by means of a time-dependent real-space Kubo approach in honeycomb lattices containing millions of carbon atoms, capturing the linear response of realistic size systems in the highly disordered regime. Our numerical calculations are complemented with a kinetic transport theory describing charge transport in the weak scattering limit. The semiclassical transport lifetimes are obtained by computing scattered amplitudes within the second Born approximation. The transport electron-hole asymmetry found in the semiclassical approach is consistent with the Kubo calculations. In the strong scattering regime, the conductivity is found to be a sublinear function of electronic density and weakly dependent on the Thomas-Fermi screening wavelength. We attribute this atypical behavior to the extended nature of one-dimensional charged defects. Our results are consistent with recent experimental reports.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Charge carrier transport in single-layer graphene with one-dimensional charged defects is studied theoretically. Extended charged defects, considered an important factor for mobility degradation in chemically vapor-deposited graphene, are described by a self-consistent Thomas-Fermi potential. A numerical study of electronic transport is performed by means of a time-dependent real-space Kubo approach in honeycomb lattices containing millions of carbon atoms, capturing the linear response of realistic size systems in the highly disordered regime. Our numerical calculations are complemented with a kinetic transport theory describing charge transport in the weak scattering limit. The semiclassical transport lifetimes are obtained by computing scattered amplitudes within the second Born approximation. The transport electron-hole asymmetry found in the semiclassical approach is consistent with the Kubo calculations. In the strong scattering regime, the conductivity is found to be a sublinear function of electronic density and weakly dependent on the Thomas-Fermi screening wavelength. We attribute this atypical behavior to the extended nature of one-dimensional charged defects. Our results are consistent with recent experimental reports. |
Reddy, M V; Yu, Cai; Jiahuan, Fan; Loh, Kian Ping; Chowdari, B V R Li-Cycling Properties of Molten Salt Method Prepared Nano/Submicrometer and Micrometer-Sized CuO for Lithium Batteries Journal Article ACS APPLIED MATERIALS & INTERFACES, 5 (10), pp. 4361-4366, 2013, ISSN: 1944-8244. @article{ISI:000319551200052, title = {Li-Cycling Properties of Molten Salt Method Prepared Nano/Submicrometer and Micrometer-Sized CuO for Lithium Batteries}, author = {M V Reddy and Cai Yu and Fan Jiahuan and Kian Ping Loh and B V R Chowdari}, doi = {10.1021/am400579q}, issn = {1944-8244}, year = {2013}, date = {2013-05-01}, journal = {ACS APPLIED MATERIALS & INTERFACES}, volume = {5}, number = {10}, pages = {4361-4366}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {We report the synthesis of CuO material by molten salt method at a temperature range, 280 to 950 degrees C for 3 h in air. This report includes studies on the effect of morphology, crystal structure and electrochemical properties of CuO prepared at different temperatures Obtained CuO was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area methods. Samples prepared at >= 410 degrees C showed a single-phase material with a lattice parameter value of a = 4.69 angstrom}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report the synthesis of CuO material by molten salt method at a temperature range, 280 to 950 degrees C for 3 h in air. This report includes studies on the effect of morphology, crystal structure and electrochemical properties of CuO prepared at different temperatures Obtained CuO was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area methods. Samples prepared at >= 410 degrees C showed a single-phase material with a lattice parameter value of a = 4.69 angstrom |
Lin, Jiadan; Li, Hai; Zhang, Hua; Chen, Wei Plasmonic enhancement of photocurrent in MoS2 field-effect-transistor Journal Article APPLIED PHYSICS LETTERS, 102 (20), 2013, ISSN: 0003-6951. @article{ISI:000320619300071, title = {Plasmonic enhancement of photocurrent in MoS2 field-effect-transistor}, author = {Jiadan Lin and Hai Li and Hua Zhang and Wei Chen}, doi = {10.1063/1.4807658}, issn = {0003-6951}, year = {2013}, date = {2013-05-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {102}, number = {20}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {The two-dimensional material, molybdenum disulfide (MoS2), has attracted considerable attention for numerous applications in optoelectronics. Here, we demonstrate a plasmonic enhancement of photocurrent in MoS2 field-effect-transistor decorated with gold nanoparticles, with significantly enhanced photocurrent peaked at the plasmon resonant wavelength around 540 nm. Our findings offer a possibility to realize wavelength selectable photodetection in MoS2 based phototransistors. (C) 2013 AIP Publishing LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The two-dimensional material, molybdenum disulfide (MoS2), has attracted considerable attention for numerous applications in optoelectronics. Here, we demonstrate a plasmonic enhancement of photocurrent in MoS2 field-effect-transistor decorated with gold nanoparticles, with significantly enhanced photocurrent peaked at the plasmon resonant wavelength around 540 nm. Our findings offer a possibility to realize wavelength selectable photodetection in MoS2 based phototransistors. (C) 2013 AIP Publishing LLC. |
Sushkov, O P; Neto, Castro A H Topological Insulating States in Laterally Patterned Ordinary Semiconductors Journal Article PHYSICAL REVIEW LETTERS, 110 (18), 2013, ISSN: 0031-9007. @article{ISI:000319021100011, title = {Topological Insulating States in Laterally Patterned Ordinary Semiconductors}, author = {O P Sushkov and A H Castro Neto}, doi = {10.1103/PhysRevLett.110.186601}, issn = {0031-9007}, year = {2013}, date = {2013-05-01}, journal = {PHYSICAL REVIEW LETTERS}, volume = {110}, number = {18}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We propose that ordinary semiconductors with large spin-orbit coupling, such as GaAs, can host stable, robust, and tunable topological states in the presence of quantum confinement and superimposed potentials with hexagonal symmetry. We show that the electronic gaps which support chiral spin edge states can be as large as the electronic bandwidth in the heterostructure miniband. The existing lithographic technology can produce a topological insulator operating at a temperature of 10-100 K. Improvement of lithographic techniques will open the way to a tunable room temperature topological insulator.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We propose that ordinary semiconductors with large spin-orbit coupling, such as GaAs, can host stable, robust, and tunable topological states in the presence of quantum confinement and superimposed potentials with hexagonal symmetry. We show that the electronic gaps which support chiral spin edge states can be as large as the electronic bandwidth in the heterostructure miniband. The existing lithographic technology can produce a topological insulator operating at a temperature of 10-100 K. Improvement of lithographic techniques will open the way to a tunable room temperature topological insulator. |
Balakrishnan, Jayakumar; Koon, Gavin Kok Wai; Jaiswal, Manu; Neto, Castro A H; Oezyilmaz, Barbaros Colossal enhancement of spin-orbit coupling in weakly hydrogenated graphene Journal Article NATURE PHYSICS, 9 (5), pp. 284-287, 2013, ISSN: 1745-2473. @article{ISI:000318550200018, title = {Colossal enhancement of spin-orbit coupling in weakly hydrogenated graphene}, author = {Jayakumar Balakrishnan and Gavin Kok Wai Koon and Manu Jaiswal and A H Castro Neto and Barbaros Oezyilmaz}, doi = {10.1038/nphys2576}, issn = {1745-2473}, year = {2013}, date = {2013-05-01}, journal = {NATURE PHYSICS}, volume = {9}, number = {5}, pages = {284-287}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Graphene's extremely small intrinsic spin-orbit (SO) interaction(1) makes the realization of many interesting phenomena such as topological/quantum spin Hall states(2,3) and the spin Hall effect(4) (SHE) practically impossible. Recently, it was predicted(1,5-7) that the introduction of adatoms in graphene would enhance the SO interaction by the conversion of sp(2) to sp(3) bonds. However, introducing adatoms and yet keeping graphene metallic, that is, without creating electronic (Anderson) localization(8), is experimentally challenging. Here, we show that the controlled addition of small amounts of covalently bonded hydrogen atoms is sufficient to induce a colossal enhancement of the SO interaction by three orders of magnitude. This results in a SHE at zero external magnetic fields at room temperature, with non-local spin signals up to 100 Omega; orders of magnitude larger than in metals(9). The non-local SHE is, further, directly confirmed by Larmor spin-precession measurements. From this and the length dependence of the non-local signal we extract a spin relaxation length of similar to 1 mu m, a spin relaxation time of similar to 90 ps and a SO strength of 2.5 meV.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene's extremely small intrinsic spin-orbit (SO) interaction(1) makes the realization of many interesting phenomena such as topological/quantum spin Hall states(2,3) and the spin Hall effect(4) (SHE) practically impossible. Recently, it was predicted(1,5-7) that the introduction of adatoms in graphene would enhance the SO interaction by the conversion of sp(2) to sp(3) bonds. However, introducing adatoms and yet keeping graphene metallic, that is, without creating electronic (Anderson) localization(8), is experimentally challenging. Here, we show that the controlled addition of small amounts of covalently bonded hydrogen atoms is sufficient to induce a colossal enhancement of the SO interaction by three orders of magnitude. This results in a SHE at zero external magnetic fields at room temperature, with non-local spin signals up to 100 Omega; orders of magnitude larger than in metals(9). The non-local SHE is, further, directly confirmed by Larmor spin-precession measurements. From this and the length dependence of the non-local signal we extract a spin relaxation length of similar to 1 mu m, a spin relaxation time of similar to 90 ps and a SO strength of 2.5 meV. |
Sharma, Anand; Kotov, Valeri N; Neto, Antonio Castro H Effect of uniaxial strain on ferromagnetic instability and formation of localized magnetic states on adatoms in graphene Journal Article PHYSICAL REVIEW B, 87 (15), 2013, ISSN: 1098-0121. @article{ISI:000318177600002, title = {Effect of uniaxial strain on ferromagnetic instability and formation of localized magnetic states on adatoms in graphene}, author = {Anand Sharma and Valeri N Kotov and Antonio H Castro Neto}, doi = {10.1103/PhysRevB.87.155431}, issn = {1098-0121}, year = {2013}, date = {2013-04-01}, journal = {PHYSICAL REVIEW B}, volume = {87}, number = {15}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We investigate the effect of an applied uniaxial strain on the ferromagnetic instability due to long-range Coulomb interaction between Dirac fermions in graphene. In the case of undeformed graphene the ferromagnetic exchange instability occurs at sufficiently strong interaction within the Hartree-Fock approximation. In this work we show that using the same theoretical framework but with an additional applied uniaxial strain, the transition can occur for much weaker interaction, within the range in suspended graphene. We also study the consequence of strain on the formation of localized magnetic states on adatoms in graphene. We systematically analyze the interplay between the anisotropic (strain-induced) nature of the Dirac fermions in graphene, onsite Hubbard interaction at the impurity, and the hybridization between the graphene and impurity electrons. The polarization of the electrons in the localized orbital is numerically calculated within the mean-field self-consistent scheme. We obtain a complete phase diagram containing nonmagnetic as well as magnetic regions, and our results can find prospective application in the field of carbon-based spintronics. DOI: 10.1103/PhysRevB.87.155431}, keywords = {}, pubstate = {published}, tppubtype = {article} } We investigate the effect of an applied uniaxial strain on the ferromagnetic instability due to long-range Coulomb interaction between Dirac fermions in graphene. In the case of undeformed graphene the ferromagnetic exchange instability occurs at sufficiently strong interaction within the Hartree-Fock approximation. In this work we show that using the same theoretical framework but with an additional applied uniaxial strain, the transition can occur for much weaker interaction, within the range in suspended graphene. We also study the consequence of strain on the formation of localized magnetic states on adatoms in graphene. We systematically analyze the interplay between the anisotropic (strain-induced) nature of the Dirac fermions in graphene, onsite Hubbard interaction at the impurity, and the hybridization between the graphene and impurity electrons. The polarization of the electrons in the localized orbital is numerically calculated within the mean-field self-consistent scheme. We obtain a complete phase diagram containing nonmagnetic as well as magnetic regions, and our results can find prospective application in the field of carbon-based spintronics. DOI: 10.1103/PhysRevB.87.155431 |
Rodrigues, J N B; Goncalves, P A D; Santos, Jaime E; Neto, Castro A H Thermodynamics of a Potts-like model for a reconstructed zigzag edge in graphene nanoribbons Journal Article PHYSICAL REVIEW B, 87 (13), 2013, ISSN: 2469-9950. @article{ISI:000317821400002, title = {Thermodynamics of a Potts-like model for a reconstructed zigzag edge in graphene nanoribbons}, author = {J N B Rodrigues and P A D Goncalves and Jaime E Santos and A H Castro Neto}, doi = {10.1103/PhysRevB.87.134204}, issn = {2469-9950}, year = {2013}, date = {2013-04-01}, journal = {PHYSICAL REVIEW B}, volume = {87}, number = {13}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We construct a three-color Potts-like model for the graphene zigzag edge reconstructed with Stone-Wales carbon rings in order to study its thermal equilibrium properties. We consider two cases which have different ground states: the edge with nonpassivated dangling carbon bonds and the edge fully passivated with hydrogen. We study the concentration of defects perturbing the ground-state configuration as a function of the temperature. The defect concentration is found to be exponentially dependent on the effective parameters that describe the model at all temperatures. Moreover, we analytically compute the domain-size distribution of the defective domains and conclude that it does not have fat tails. In an appendix, we show how the exchange parameters of the model can be estimated using density functional theory results. Such equilibrium mechanisms place a lower bound on the concentration of defects in zigzag edges since the formation of such defects is due to nonequilibrium kinetic mechanisms. DOI: 10.1103/PhysRevB.87.134204}, keywords = {}, pubstate = {published}, tppubtype = {article} } We construct a three-color Potts-like model for the graphene zigzag edge reconstructed with Stone-Wales carbon rings in order to study its thermal equilibrium properties. We consider two cases which have different ground states: the edge with nonpassivated dangling carbon bonds and the edge fully passivated with hydrogen. We study the concentration of defects perturbing the ground-state configuration as a function of the temperature. The defect concentration is found to be exponentially dependent on the effective parameters that describe the model at all temperatures. Moreover, we analytically compute the domain-size distribution of the defective domains and conclude that it does not have fat tails. In an appendix, we show how the exchange parameters of the model can be estimated using density functional theory results. Such equilibrium mechanisms place a lower bound on the concentration of defects in zigzag edges since the formation of such defects is due to nonequilibrium kinetic mechanisms. DOI: 10.1103/PhysRevB.87.134204 |
Bludov, Yu V; Ferreira, Aires; Peres, N M R; Vasilevskiy, M I A PRIMER ON SURFACE PLASMON-POLARITONS IN GRAPHENE Journal Article INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 27 (10, SI), 2013, ISSN: 0217-9792. @article{ISI:000318176400002, title = {A PRIMER ON SURFACE PLASMON-POLARITONS IN GRAPHENE}, author = {Yu V Bludov and Aires Ferreira and N M R Peres and M I Vasilevskiy}, doi = {10.1142/S0217979213410014}, issn = {0217-9792}, year = {2013}, date = {2013-04-01}, journal = {INTERNATIONAL JOURNAL OF MODERN PHYSICS B}, volume = {27}, number = {10, SI}, publisher = {WORLD SCIENTIFIC PUBL CO PTE LTD}, address = {5 TOH TUCK LINK, SINGAPORE 596224, SINGAPORE}, abstract = {We discuss the properties of surface plasmons-polaritons in graphene and describe four possible ways of coupling electromagnetic radiation in the terahertz (THz) spectral range to this type of surface waves: (i) the attenuated total reflection (ATR) method using a prism in the Otto configuration, (ii) graphene micro-ribbon arrays or monolayers with modulated conductivity, (iii) a metal stripe on top of the graphene layer, and (iv) graphene-based gratings. The text provides a number of original results along with their detailed derivation and discussion.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We discuss the properties of surface plasmons-polaritons in graphene and describe four possible ways of coupling electromagnetic radiation in the terahertz (THz) spectral range to this type of surface waves: (i) the attenuated total reflection (ATR) method using a prism in the Otto configuration, (ii) graphene micro-ribbon arrays or monolayers with modulated conductivity, (iii) a metal stripe on top of the graphene layer, and (iv) graphene-based gratings. The text provides a number of original results along with their detailed derivation and discussion. |
Ponomarenko, L A; Belle, B D; Jalil, R; Britnell, L; Gorbachev, R V; Geim, A K; Novoselov, K S; Neto, Castro A H; Eaves, L; Katsnelson, M I Field-effect control of tunneling barrier height by exploiting graphene's low density of states Journal Article JOURNAL OF APPLIED PHYSICS, 113 (13), 2013, ISSN: 0021-8979. @article{ISI:000317238000069, title = {Field-effect control of tunneling barrier height by exploiting graphene's low density of states}, author = {L A Ponomarenko and B D Belle and R Jalil and L Britnell and R V Gorbachev and A K Geim and K S Novoselov and A H Castro Neto and L Eaves and M I Katsnelson}, doi = {10.1063/1.4795542}, issn = {0021-8979}, year = {2013}, date = {2013-04-01}, journal = {JOURNAL OF APPLIED PHYSICS}, volume = {113}, number = {13}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {We exploit the low density of electronic states of graphene to modulate the tunnel current flowing perpendicular to the atomic layers of a multi-layer graphene-boron nitride device. This is achieved by using the electric field effect to raise the Fermi energy of the graphene emitter layer and thereby reduce the effective barrier height for tunneling electrons. We discuss how the electron charge density in the graphene layers and the properties of the boron nitride tunnel barrier determine the device characteristics under operating conditions and derive expressions for carrier tunneling in these highly anisotropic layered heterostructures. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795542]}, keywords = {}, pubstate = {published}, tppubtype = {article} } We exploit the low density of electronic states of graphene to modulate the tunnel current flowing perpendicular to the atomic layers of a multi-layer graphene-boron nitride device. This is achieved by using the electric field effect to raise the Fermi energy of the graphene emitter layer and thereby reduce the effective barrier height for tunneling electrons. We discuss how the electron charge density in the graphene layers and the properties of the boron nitride tunnel barrier determine the device characteristics under operating conditions and derive expressions for carrier tunneling in these highly anisotropic layered heterostructures. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795542] |
Bae, Sang-Hoon; Kahya, Orhan; Sharma, Bhupendra K; Kwon, Junggou; Cho, Hyoung J; Ozyilmaz, Barbaros; Ahn, Jong-Hyun Graphene-P(VDF-TrFE) Multilayer Film for Flexible Applications Journal Article ACS NANO, 7 (4), pp. 3130-3138, 2013, ISSN: 1936-0851. @article{ISI:000318143300026, title = {Graphene-P(VDF-TrFE) Multilayer Film for Flexible Applications}, author = {Sang-Hoon Bae and Orhan Kahya and Bhupendra K Sharma and Junggou Kwon and Hyoung J Cho and Barbaros Ozyilmaz and Jong-Hyun Ahn}, doi = {10.1021/nn400848j}, issn = {1936-0851}, year = {2013}, date = {2013-04-01}, journal = {ACS NANO}, volume = {7}, number = {4}, pages = {3130-3138}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {A flexible, transparent acoustic actuator and nanogenerator based on graphene/P(VDF-TrFE)/graphene multilayer film is demonstrated. P(VDF-TrFE) is used as an effective doping layer for graphene and contributes significantly to decreasing the sheet resistance of graphene to 188 ohm/sq. The potentiality of graphene/P(VDF-TrFE)/graphene multilayer film is realized in fabricating transparent, flexible acoustic devices and nanogenerators to represent its functionality. The acoustic actuator shows good performance and sensitivity over a broad range of frequency. The output voltage and the current density of the nanogenerator are estimated to be similar to 3 V and similar to 0.37 mu Acm(-2), respectively, upon the application of pressure. These values are comparable to those reported earlier for Zn0- and PIT-based nanogenerators. Finally, the possibility of rollable devices based on graphene/P(VDF-TrfE)/graphene structure is also demonstrated under a dynamic mechanical loading condition.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A flexible, transparent acoustic actuator and nanogenerator based on graphene/P(VDF-TrFE)/graphene multilayer film is demonstrated. P(VDF-TrFE) is used as an effective doping layer for graphene and contributes significantly to decreasing the sheet resistance of graphene to 188 ohm/sq. The potentiality of graphene/P(VDF-TrFE)/graphene multilayer film is realized in fabricating transparent, flexible acoustic devices and nanogenerators to represent its functionality. The acoustic actuator shows good performance and sensitivity over a broad range of frequency. The output voltage and the current density of the nanogenerator are estimated to be similar to 3 V and similar to 0.37 mu Acm(-2), respectively, upon the application of pressure. These values are comparable to those reported earlier for Zn0- and PIT-based nanogenerators. Finally, the possibility of rollable devices based on graphene/P(VDF-TrfE)/graphene structure is also demonstrated under a dynamic mechanical loading condition. |
Chhowalla, Manish; Shin, Hyeon Suk; Eda, Goki; Li, Lain-Jong; Loh, Kian Ping; Zhang, Hua The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets Journal Article NATURE CHEMISTRY, 5 (4), pp. 263-275, 2013, ISSN: 1755-4330. @article{ISI:000317182900009, title = {The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets}, author = {Manish Chhowalla and Hyeon Suk Shin and Goki Eda and Lain-Jong Li and Kian Ping Loh and Hua Zhang}, doi = {10.1038/NCHEM.1589}, issn = {1755-4330}, year = {2013}, date = {2013-04-01}, journal = {NATURE CHEMISTRY}, volume = {5}, number = {4}, pages = {263-275}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Ultrathin two-dimensional nanosheets of layered transition metal dichalcogenides (TMDs) are fundamentally and technologically intriguing. In contrast to the graphene sheet, they are chemically versatile. Mono-or few-layered TMDs - obtained either through exfoliation of bulk materials or bottom-up syntheses - are direct-gap semiconductors whose bandgap energy, as well as carrier type (n- or p-type), varies between compounds depending on their composition, structure and dimensionality. In this Review, we describe how the tunable electronic structure of TMDs makes them attractive for a variety of applications. They have been investigated as chemically active electrocatalysts for hydrogen evolution and hydrosulfurization, as well as electrically active materials in opto-electronics. Their morphologies and properties are also useful for energy storage applications such as electrodes for Li-ion batteries and supercapacitors.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Ultrathin two-dimensional nanosheets of layered transition metal dichalcogenides (TMDs) are fundamentally and technologically intriguing. In contrast to the graphene sheet, they are chemically versatile. Mono-or few-layered TMDs - obtained either through exfoliation of bulk materials or bottom-up syntheses - are direct-gap semiconductors whose bandgap energy, as well as carrier type (n- or p-type), varies between compounds depending on their composition, structure and dimensionality. In this Review, we describe how the tunable electronic structure of TMDs makes them attractive for a variety of applications. They have been investigated as chemically active electrocatalysts for hydrogen evolution and hydrosulfurization, as well as electrically active materials in opto-electronics. Their morphologies and properties are also useful for energy storage applications such as electrodes for Li-ion batteries and supercapacitors. |
Peres, N M R; Bludov, Yu V; Ferreira, Aires; Vasilevskiy, M I Exact solution for square-wave grating covered with graphene: surface plasmon-polaritons in the terahertz range Journal Article JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (12), 2013, ISSN: 0953-8984. @article{ISI:000315598400007, title = {Exact solution for square-wave grating covered with graphene: surface plasmon-polaritons in the terahertz range}, author = {N M R Peres and Yu V Bludov and Aires Ferreira and M I Vasilevskiy}, doi = {10.1088/0953-8984/25/12/125303}, issn = {0953-8984}, year = {2013}, date = {2013-03-01}, journal = {JOURNAL OF PHYSICS-CONDENSED MATTER}, volume = {25}, number = {12}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {We provide an analytical solution to the problem of scattering of electromagnetic radiation by a square-wave grating with a flat graphene sheet on top. We show that for deep groves there is a strong plasmonic response, with light absorption in the graphene sheet reaching more than 45% due to the excitation of surface plasmon-polaritons. The case of a grating with a graphene sheet presenting an induced periodic modulation of the conductivity is also discussed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We provide an analytical solution to the problem of scattering of electromagnetic radiation by a square-wave grating with a flat graphene sheet on top. We show that for deep groves there is a strong plasmonic response, with light absorption in the graphene sheet reaching more than 45% due to the excitation of surface plasmon-polaritons. The case of a grating with a graphene sheet presenting an induced periodic modulation of the conductivity is also discussed. |
Lobos, Alejandro M; Cazalilla, Miguel A Easy-axis ferromagnetic chain on a metallic surface Journal Article JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (9), 2013, ISSN: 0953-8984. @article{ISI:000314823600009, title = {Easy-axis ferromagnetic chain on a metallic surface}, author = {Alejandro M Lobos and Miguel A Cazalilla}, doi = {10.1088/0953-8984/25/9/094008}, issn = {0953-8984}, year = {2013}, date = {2013-03-01}, journal = {JOURNAL OF PHYSICS-CONDENSED MATTER}, volume = {25}, number = {9}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {The phases and excitation spectrum of an easy-axis ferromagnetic chain of S = 1/2 magnetic impurities built on the top of a clean metallic surface are studied. As a function of the (Kondo) coupling to the metallic surface and at low temperatures, the spin chain exhibits a quantum phase transition from an Ising ferromagnetic phase with long-range order to a paramagnetic phase where quantum fluctuations destroy the magnetic order. In the paramagnetic phase, the system consists of a chain of Kondo singlets where the impurities are completely screened by the metallic host. In the ferromagnetic phase, the excitations above the Ising gap are damped magnons, with a finite lifetime arising due to the coupling to the substrate. We discuss the experimental consequences of our results to spin-polarized electron energy loss spectroscopy, and we finally analyze possible extensions to spin chains with S > 1/2.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The phases and excitation spectrum of an easy-axis ferromagnetic chain of S = 1/2 magnetic impurities built on the top of a clean metallic surface are studied. As a function of the (Kondo) coupling to the metallic surface and at low temperatures, the spin chain exhibits a quantum phase transition from an Ising ferromagnetic phase with long-range order to a paramagnetic phase where quantum fluctuations destroy the magnetic order. In the paramagnetic phase, the system consists of a chain of Kondo singlets where the impurities are completely screened by the metallic host. In the ferromagnetic phase, the excitations above the Ising gap are damped magnons, with a finite lifetime arising due to the coupling to the substrate. We discuss the experimental consequences of our results to spin-polarized electron energy loss spectroscopy, and we finally analyze possible extensions to spin chains with S > 1/2. |
Lim, Candy Haley Yi Xuan; Sorkin, Anastassia; Bao, Qiaoliang; Li, Ang; Zhang, Kai; Nesladek, Milos; Loh, Kian Ping A hydrothermal anvil made of graphene nanobubbles on diamond Journal Article NATURE COMMUNICATIONS, 4 , 2013, ISSN: 2041-1723. @article{ISI:000318873900010, title = {A hydrothermal anvil made of graphene nanobubbles on diamond}, author = {Candy Haley Yi Xuan Lim and Anastassia Sorkin and Qiaoliang Bao and Ang Li and Kai Zhang and Milos Nesladek and Kian Ping Loh}, doi = {10.1038/ncomms2579}, issn = {2041-1723}, year = {2013}, date = {2013-03-01}, journal = {NATURE COMMUNICATIONS}, volume = {4}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {The hardness and virtual incompressibility of diamond allow it to be used in high-pressure anvil cell. Here we report a new way to generate static pressure by encapsulating single-crystal diamond with graphene membrane, the latter is well known for its superior nano-indentation strength and in-plane rigidity. Heating the diamond-graphene interface to the reconstruction temperature of diamond (similar to 1,275 K) produces a high density of graphene nanobubbles that can trap water. At high temperature, chemical bonding between graphene and diamond is robust enough to allow the hybrid interface to act as a hydrothermal anvil cell due to the impermeability of graphene. Superheated water trapped within the pressurized graphene nanobubbles is observed to etch the diamond surface to produce a high density of square-shaped voids. The molecular structure of superheated water trapped in the bubble is probed using vibrational spectroscopy and dynamic changes in the hydrogen-bonding environment are observed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The hardness and virtual incompressibility of diamond allow it to be used in high-pressure anvil cell. Here we report a new way to generate static pressure by encapsulating single-crystal diamond with graphene membrane, the latter is well known for its superior nano-indentation strength and in-plane rigidity. Heating the diamond-graphene interface to the reconstruction temperature of diamond (similar to 1,275 K) produces a high density of graphene nanobubbles that can trap water. At high temperature, chemical bonding between graphene and diamond is robust enough to allow the hybrid interface to act as a hydrothermal anvil cell due to the impermeability of graphene. Superheated water trapped within the pressurized graphene nanobubbles is observed to etch the diamond surface to produce a high density of square-shaped voids. The molecular structure of superheated water trapped in the bubble is probed using vibrational spectroscopy and dynamic changes in the hydrogen-bonding environment are observed. |
Huang, Yuan; Wu, Jing; Xu, Xiangfan; Ho, Yuda; Ni, Guangxin; Zou, Qiang; Koon, Gavin Kok Wai; Zhao, Weijie; Neto, Castro A H; Eda, Goki; Shen, Chengmin; Oezyilmaz, Barbaros An innovative way of etching MoS2: Characterization and mechanistic investigation Journal Article NANO RESEARCH, 6 (3), pp. 200-207, 2013, ISSN: 1998-0124. @article{ISI:000316087300006, title = {An innovative way of etching MoS2: Characterization and mechanistic investigation}, author = {Yuan Huang and Jing Wu and Xiangfan Xu and Yuda Ho and Guangxin Ni and Qiang Zou and Gavin Kok Wai Koon and Weijie Zhao and A H Castro Neto and Goki Eda and Chengmin Shen and Barbaros Oezyilmaz}, doi = {10.1007/s12274-013-0296-8}, issn = {1998-0124}, year = {2013}, date = {2013-03-01}, journal = {NANO RESEARCH}, volume = {6}, number = {3}, pages = {200-207}, publisher = {TSINGHUA UNIV PRESS}, address = {B605D, XUE YAN BUILDING, BEIJING, 100084, PEOPLES R CHINA}, abstract = {We report a systematic study of the etching of MoS2 crystals by using XeF2 as a gaseous reactant. By controlling the etching process, monolayer MoS2 with uniform morphology can be obtained. The Raman and photoluminescence spectra of the resulting material were similar to those of exfoliated MoS2. Utilizing this strategy, different patterns such as a Hall bar structure and a hexagonal array can be realized. Furthermore, the etching mechanism was studied by introducing graphene as an etching mask. We believe our technique opens an easy and controllable way of etching MoS2, which can be used to fabricate complex nanostructures, such as nanoribbons, quantum dots, and transistor structures. This etching process using XeF2 can also be extended to other interesting two-dimensional crystals.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report a systematic study of the etching of MoS2 crystals by using XeF2 as a gaseous reactant. By controlling the etching process, monolayer MoS2 with uniform morphology can be obtained. The Raman and photoluminescence spectra of the resulting material were similar to those of exfoliated MoS2. Utilizing this strategy, different patterns such as a Hall bar structure and a hexagonal array can be realized. Furthermore, the etching mechanism was studied by introducing graphene as an etching mask. We believe our technique opens an easy and controllable way of etching MoS2, which can be used to fabricate complex nanostructures, such as nanoribbons, quantum dots, and transistor structures. This etching process using XeF2 can also be extended to other interesting two-dimensional crystals. |
Reddy, M V; Tung, Bui Dang; Yang, Lu; Minh, Nguyen Dang Quang; Loh, K P; Chowdari, B V R Molten salt method of preparation and cathodic studies on layered-cathode materials Li(Co0.7Ni0.3)O-2 and Li(Ni0.7Co0.3)O-2 for Li-ion batteries Journal Article JOURNAL OF POWER SOURCES, 225 , pp. 374-381, 2013, ISSN: 0378-7753. @article{ISI:000313923400054, title = {Molten salt method of preparation and cathodic studies on layered-cathode materials Li(Co0.7Ni0.3)O-2 and Li(Ni0.7Co0.3)O-2 for Li-ion batteries}, author = {M V Reddy and Bui Dang Tung and Lu Yang and Nguyen Dang Quang Minh and K P Loh and B V R Chowdari}, doi = {10.1016/j.jpowsour.2012.07.009}, issn = {0378-7753}, year = {2013}, date = {2013-03-01}, journal = {JOURNAL OF POWER SOURCES}, volume = {225}, pages = {374-381}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {Layered compounds, Li(Co0.7Ni0.3)O-2 (I) and Li(Ni0.7Co0.3)O-2 (II) were prepared by molten salt method in temperature ranging from 650 to 950 degrees C. The effect of morphology, crystal structure and electrochemical properties of materials were evaluated by X-Ray Diffraction (XRD), Scanning Electron Microscopy and Brunauer-Emmett-Teller surface area, cyclic voltammetry (CV) and galvanostatic cycling. XRD pattern shows a hexagonal type structure with lattice parameters of a similar to 2.828 angstrom, c similar to 14.096 angstrom for I and a similar to 2.851 angstrom, c similar to 14.121 angstrom for II prepared in oxygen flow. The surface area of the compounds, I and II are 1.74 and 0.75 m(2) g(-1) respectively. CV studies show a main anodic peak occur at similar to 3.8-3.94 V vs. Li and a cathodic peak occur at similar to 3.6-3.7 V vs. Li. Galvanostatic cycling studies are carried out at a current rate of 30 mA g(-1) in the voltage range of 2.5-4.3 V, at room temperature. Li(Co0.7Ni0.3)O-2 prepared at 750 degrees C in air show a reversible capacity of 145 mAh g(-1) at the 1st discharge cycle and 13% capacity fading between 2 and 56 cycles, whereas Li(Ni0.7Co0.3)O-2 reheated in the presence of oxygen deliver a high and stable reversible capacity of 165 mAh g(-1) at the end of 60th cycle. (C) 2012 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Layered compounds, Li(Co0.7Ni0.3)O-2 (I) and Li(Ni0.7Co0.3)O-2 (II) were prepared by molten salt method in temperature ranging from 650 to 950 degrees C. The effect of morphology, crystal structure and electrochemical properties of materials were evaluated by X-Ray Diffraction (XRD), Scanning Electron Microscopy and Brunauer-Emmett-Teller surface area, cyclic voltammetry (CV) and galvanostatic cycling. XRD pattern shows a hexagonal type structure with lattice parameters of a similar to 2.828 angstrom, c similar to 14.096 angstrom for I and a similar to 2.851 angstrom, c similar to 14.121 angstrom for II prepared in oxygen flow. The surface area of the compounds, I and II are 1.74 and 0.75 m(2) g(-1) respectively. CV studies show a main anodic peak occur at similar to 3.8-3.94 V vs. Li and a cathodic peak occur at similar to 3.6-3.7 V vs. Li. Galvanostatic cycling studies are carried out at a current rate of 30 mA g(-1) in the voltage range of 2.5-4.3 V, at room temperature. Li(Co0.7Ni0.3)O-2 prepared at 750 degrees C in air show a reversible capacity of 145 mAh g(-1) at the 1st discharge cycle and 13% capacity fading between 2 and 56 cycles, whereas Li(Ni0.7Co0.3)O-2 reheated in the presence of oxygen deliver a high and stable reversible capacity of 165 mAh g(-1) at the end of 60th cycle. (C) 2012 Elsevier B.V. All rights reserved. |
Park, Hyoungki; Wadehra, Amita; Wilkins, John W; Neto, Antonio Castro H Spin-polarized electronic current induced by sublattice engineering of graphene sheets with boron/nitrogen Journal Article PHYSICAL REVIEW B, 87 (8), 2013, ISSN: 2469-9950. @article{ISI:000315482900004, title = {Spin-polarized electronic current induced by sublattice engineering of graphene sheets with boron/nitrogen}, author = {Hyoungki Park and Amita Wadehra and John W Wilkins and Antonio H Castro Neto}, doi = {10.1103/PhysRevB.87.085441}, issn = {2469-9950}, year = {2013}, date = {2013-02-01}, journal = {PHYSICAL REVIEW B}, volume = {87}, number = {8}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {We show that spin-polarized electron transport can be achieved by the substitutional doping of only one sublattice of graphene by nitrogen or boron atoms. The bipartite character via two sublattices remains persistent in the electronic structures of graphene doped with low concentrations of nitrogens (borons). The delocalized spin-densities induced by the unpaired electrons at substitutional sites permeate only through the sublattice where the nitrogen (boron) atoms belong. For interacting nitrogen (boron) atoms located along the ``zigzag'' direction and in the same sublattice, the ferromagnetic spin-ordering is favorable, and substitution-induced localized impurity states selectively disturb the spin-polarized pi orbital of that same sublattice. The bipartite character of graphene lattice governs the unique properties of two-dimensional hybrid graphene-boron nitride nanostructures. DOI: 10.1103/PhysRevB.87.085441}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show that spin-polarized electron transport can be achieved by the substitutional doping of only one sublattice of graphene by nitrogen or boron atoms. The bipartite character via two sublattices remains persistent in the electronic structures of graphene doped with low concentrations of nitrogens (borons). The delocalized spin-densities induced by the unpaired electrons at substitutional sites permeate only through the sublattice where the nitrogen (boron) atoms belong. For interacting nitrogen (boron) atoms located along the ``zigzag'' direction and in the same sublattice, the ferromagnetic spin-ordering is favorable, and substitution-induced localized impurity states selectively disturb the spin-polarized pi orbital of that same sublattice. The bipartite character of graphene lattice governs the unique properties of two-dimensional hybrid graphene-boron nitride nanostructures. DOI: 10.1103/PhysRevB.87.085441 |
Bosman, Michel; Ye, Enyi; Tan, Shu Fen; Nijhuis, Christian A; Yang, Joel K W; Marty, Renaud; Mlayah, Adnen; Arbouet, Arnaud; Girard, Christian; Han, Ming-Yong Surface Plasmon Damping Quantified with an Electron Nanoprobe Journal Article SCIENTIFIC REPORTS, 3 , 2013, ISSN: 2045-2322. @article{ISI:000315154900001, title = {Surface Plasmon Damping Quantified with an Electron Nanoprobe}, author = {Michel Bosman and Enyi Ye and Shu Fen Tan and Christian A Nijhuis and Joel K W Yang and Renaud Marty and Adnen Mlayah and Arnaud Arbouet and Christian Girard and Ming-Yong Han}, doi = {10.1038/srep01312}, issn = {2045-2322}, year = {2013}, date = {2013-02-01}, journal = {SCIENTIFIC REPORTS}, volume = {3}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Fabrication and synthesis of plasmonic structures is rapidly moving towards sub-nanometer accuracy in control over shape and inter-particle distance. This holds the promise for developing device components based on novel, non-classical electro-optical effects. Monochromated electron energy-loss spectroscopy (EELS) has in recent years demonstrated its value as a qualitative experimental technique in nano-optics and plasmonic due to its unprecedented spatial resolution. Here, we demonstrate that EELS can also be used quantitatively, to probe surface plasmon kinetics and damping in single nanostructures. Using this approach, we present from a large (>50) series of individual gold nanoparticles the plasmon Quality factors and the plasmon Dephasing times, as a function of energy/frequency. It is shown that the measured general trend applies to regular particle shapes (rods, spheres) as well as irregular shapes (dendritic, branched morphologies). The combination of direct sub-nanometer imaging with EELS-based plasmon damping analysis launches quantitative nanoplasmonics research into the sub-nanometer realm.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Fabrication and synthesis of plasmonic structures is rapidly moving towards sub-nanometer accuracy in control over shape and inter-particle distance. This holds the promise for developing device components based on novel, non-classical electro-optical effects. Monochromated electron energy-loss spectroscopy (EELS) has in recent years demonstrated its value as a qualitative experimental technique in nano-optics and plasmonic due to its unprecedented spatial resolution. Here, we demonstrate that EELS can also be used quantitatively, to probe surface plasmon kinetics and damping in single nanostructures. Using this approach, we present from a large (>50) series of individual gold nanoparticles the plasmon Quality factors and the plasmon Dephasing times, as a function of energy/frequency. It is shown that the measured general trend applies to regular particle shapes (rods, spheres) as well as irregular shapes (dendritic, branched morphologies). The combination of direct sub-nanometer imaging with EELS-based plasmon damping analysis launches quantitative nanoplasmonics research into the sub-nanometer realm. |
Kajen, R S; Chandrasekhar, N; Pey, K L; Vijila, C; Jaiswal, M; Saravanan, S; Ng, Andrew M H; Wong, C P; Loh, K P Charge transport in lightly reduced graphene oxide: A transport energy perspective Journal Article JOURNAL OF APPLIED PHYSICS, 113 (6), 2013, ISSN: 0021-8979. @article{ISI:000315054000043, title = {Charge transport in lightly reduced graphene oxide: A transport energy perspective}, author = {R S Kajen and N Chandrasekhar and K L Pey and C Vijila and M Jaiswal and S Saravanan and Andrew M H Ng and C P Wong and K P Loh}, doi = {10.1063/1.4792042}, issn = {0021-8979}, year = {2013}, date = {2013-02-01}, journal = {JOURNAL OF APPLIED PHYSICS}, volume = {113}, number = {6}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION & FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {Significant variation in the charge transport behaviour in graphene oxide (GO) ranging from Schottky to Poole-Frenkel and to space charge limited transport exists. These have been extensively reported in the literature. However, the validity of such conventional charge transport models meant for delocalized carriers, to study charge transport through localised states in GO, a disordered semiconductor is open to question. In this work, we use the concept of transport energy (TE) to model charge transport in lightly reduced GO (RGO) and demonstrate that the TE calculations match well with temperature dependent experimental I-V data on RGO. We report on a temperature dependent TE ranging from a few 10meV to 0.1 eV in slightly reduced GO. Last, we point out that, despite the success of several delocalised charge transport models in estimating barrier heights that resemble the TE level, they remain largely accidental and lack the insight in which the TE concept provides in understanding charge transport in RGO. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792042]}, keywords = {}, pubstate = {published}, tppubtype = {article} } Significant variation in the charge transport behaviour in graphene oxide (GO) ranging from Schottky to Poole-Frenkel and to space charge limited transport exists. These have been extensively reported in the literature. However, the validity of such conventional charge transport models meant for delocalized carriers, to study charge transport through localised states in GO, a disordered semiconductor is open to question. In this work, we use the concept of transport energy (TE) to model charge transport in lightly reduced GO (RGO) and demonstrate that the TE calculations match well with temperature dependent experimental I-V data on RGO. We report on a temperature dependent TE ranging from a few 10meV to 0.1 eV in slightly reduced GO. Last, we point out that, despite the success of several delocalised charge transport models in estimating barrier heights that resemble the TE level, they remain largely accidental and lack the insight in which the TE concept provides in understanding charge transport in RGO. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792042] |
Lu, Jiong; Yeo, Pei Shan Emmeline; Zheng, Yi; Xu, Hai; Gan, Chee Kwan; Sullivan, Michael B; Neto, Castro A H; Loh, Kian Ping Step Flow Versus Mosaic Film Growth in Hexagonal Boron Nitride Journal Article JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135 (6), pp. 2368-2373, 2013, ISSN: 0002-7863. @article{ISI:000315080100058, title = {Step Flow Versus Mosaic Film Growth in Hexagonal Boron Nitride}, author = {Jiong Lu and Pei Shan Emmeline Yeo and Yi Zheng and Hai Xu and Chee Kwan Gan and Michael B Sullivan and A H Castro Neto and Kian Ping Loh}, doi = {10.1021/ja3117735}, issn = {0002-7863}, year = {2013}, date = {2013-02-01}, journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, volume = {135}, number = {6}, pages = {2368-2373}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Many emerging applications of hexagonal boron nitride (h-BN) in graphene-based nanoelectronics require high-quality monolayers as the ultrathin dielectric. Here, the nucleation and growth of h-BN monolayer on Ru(0001) surface are investigated using scanning tunneling microscopy with a view toward understanding the process of defect formation on a strongly interacted interface. In contrast to homoelemental bonding in graphene, the heteroelemental nature of h-BN gives rise to growth fronts with elemental polarity. This can have consequences in the different stages of film growth, from the nucleation of h-BN magic clusters and their sintering to form compact triangular islands to the growth of patchwork mosaic monolayer with a high density of misfit boundaries. The parallel alignment of triangular islands on the same terrace produces translational fault lines when growth fronts merge, while antiparallel alignment of islands on adjacent terraces produces non-bonded fault lines between domains terminated by like atoms. With these insights into the generation of void defects and fault lines at grain boundaries, we demonstrate a strategy to obtain high-quality h-BN monolayer film based on step flow growth.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Many emerging applications of hexagonal boron nitride (h-BN) in graphene-based nanoelectronics require high-quality monolayers as the ultrathin dielectric. Here, the nucleation and growth of h-BN monolayer on Ru(0001) surface are investigated using scanning tunneling microscopy with a view toward understanding the process of defect formation on a strongly interacted interface. In contrast to homoelemental bonding in graphene, the heteroelemental nature of h-BN gives rise to growth fronts with elemental polarity. This can have consequences in the different stages of film growth, from the nucleation of h-BN magic clusters and their sintering to form compact triangular islands to the growth of patchwork mosaic monolayer with a high density of misfit boundaries. The parallel alignment of triangular islands on the same terrace produces translational fault lines when growth fronts merge, while antiparallel alignment of islands on adjacent terraces produces non-bonded fault lines between domains terminated by like atoms. With these insights into the generation of void defects and fault lines at grain boundaries, we demonstrate a strategy to obtain high-quality h-BN monolayer film based on step flow growth. |
Zou, Xingquan; Shang, Jingzhi; Leaw, Jianing; Luo, Zhiqiang; Luo, Liyan; La-o-Vorakiat, Chan; Cheng, Liang; Cheong, S A; Su, Haibin; Zhu, Jian-Xin; Liu, Yanpeng; Loh, Kian Ping; Neto, Castro A H; Yu, Ting; Chia, Elbert E M Terahertz Conductivity of Twisted Bilayer Graphene Journal Article PHYSICAL REVIEW LETTERS, 110 (6), 2013, ISSN: 0031-9007. @article{ISI:000314770600024, title = {Terahertz Conductivity of Twisted Bilayer Graphene}, author = {Xingquan Zou and Jingzhi Shang and Jianing Leaw and Zhiqiang Luo and Liyan Luo and Chan La-o-Vorakiat and Liang Cheng and S A Cheong and Haibin Su and Jian-Xin Zhu and Yanpeng Liu and Kian Ping Loh and A H Castro Neto and Ting Yu and Elbert E M Chia}, doi = {10.1103/PhysRevLett.110.067401}, issn = {0031-9007}, year = {2013}, date = {2013-02-01}, journal = {PHYSICAL REVIEW LETTERS}, volume = {110}, number = {6}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Using terahertz time-domain spectroscopy, the real part of optical conductivity [sigma(1)(omega)] of twisted bilayer graphene was obtained at different temperatures (10-300 K) in the frequency range 0.3-3 THz. On top of a Drude-like response, we see a strong peak in sigma(1)(omega) at similar to 2.7 THz. We analyze the overall Drude-like response using a disorder-dependent (unitary scattering) model, then attribute the peak at 2.7 THz to an enhanced density of states at that energy, which is caused by the presence of a van Hove singularity arising from a commensurate twisting of the two graphene layers. DOI: 10.1103/PhysRevLett.110.067401}, keywords = {}, pubstate = {published}, tppubtype = {article} } Using terahertz time-domain spectroscopy, the real part of optical conductivity [sigma(1)(omega)] of twisted bilayer graphene was obtained at different temperatures (10-300 K) in the frequency range 0.3-3 THz. On top of a Drude-like response, we see a strong peak in sigma(1)(omega) at similar to 2.7 THz. We analyze the overall Drude-like response using a disorder-dependent (unitary scattering) model, then attribute the peak at 2.7 THz to an enhanced density of states at that energy, which is caused by the presence of a van Hove singularity arising from a commensurate twisting of the two graphene layers. DOI: 10.1103/PhysRevLett.110.067401 |
Liu, Liwei; Yang, Kai; Jiang, Yuhang; Song, Boqun; Xiao, Wende; Li, Linfei; Zhou, Haitao; Wang, Yeliang; Du, Shixuan; Ouyang, Min; Hofer, Werner A; Neto, Antonio Castro H; Gao, Hong-Jun Reversible Single Spin Control of Individual Magnetic Molecule by Hydrogen Atom Adsorption Journal Article SCIENTIFIC REPORTS, 3 , 2013, ISSN: 2045-2322. @article{ISI:000314401900005, title = {Reversible Single Spin Control of Individual Magnetic Molecule by Hydrogen Atom Adsorption}, author = {Liwei Liu and Kai Yang and Yuhang Jiang and Boqun Song and Wende Xiao and Linfei Li and Haitao Zhou and Yeliang Wang and Shixuan Du and Min Ouyang and Werner A Hofer and Antonio H Castro Neto and Hong-Jun Gao}, doi = {10.1038/srep01210}, issn = {2045-2322}, year = {2013}, date = {2013-02-01}, journal = {SCIENTIFIC REPORTS}, volume = {3}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {The reversible control of a single spin of an atom or a molecule is of great interest in Kondo physics and a potential application in spin based electronics. Here we demonstrate that the Kondo resonance of manganese phthalocyanine molecules on a Au(111) substrate have been reversibly switched off and on via a robust route through attachment and detachment of single hydrogen atom to the magnetic core of the molecule. As further revealed by density functional theory calculations, even though the total number of electrons of the Mn ion remains almost the same in the process, gaining one single hydrogen atom leads to redistribution of charges within 3d orbitals with a reduction of the molecular spin state from S = 3/2 to S = 1 that directly contributes to the Kondo resonance disappearance. This process is reversed by a local voltage pulse or thermal annealing to desorb the hydrogen atom.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The reversible control of a single spin of an atom or a molecule is of great interest in Kondo physics and a potential application in spin based electronics. Here we demonstrate that the Kondo resonance of manganese phthalocyanine molecules on a Au(111) substrate have been reversibly switched off and on via a robust route through attachment and detachment of single hydrogen atom to the magnetic core of the molecule. As further revealed by density functional theory calculations, even though the total number of electrons of the Mn ion remains almost the same in the process, gaining one single hydrogen atom leads to redistribution of charges within 3d orbitals with a reduction of the molecular spin state from S = 3/2 to S = 1 that directly contributes to the Kondo resonance disappearance. This process is reversed by a local voltage pulse or thermal annealing to desorb the hydrogen atom. |
Yang, Huanping; Hu, Hailong; Wang, Yingying; Yu, Ting Rapid and non-destructive identification of graphene oxide thickness using white light contrast spectroscopy Journal Article CARBON, 52 , pp. 528-534, 2013, ISSN: 0008-6223. @article{ISI:000314192700058, title = {Rapid and non-destructive identification of graphene oxide thickness using white light contrast spectroscopy}, author = {Huanping Yang and Hailong Hu and Yingying Wang and Ting Yu}, doi = {10.1016/j.carbon.2012.10.005}, issn = {0008-6223}, year = {2013}, date = {2013-02-01}, journal = {CARBON}, volume = {52}, pages = {528-534}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {By white light contrast spectroscopy, we have successfully identified number of graphene oxide (GO) layers (<= 10 layers) and obtained a new refractive index of GO sheets (<= 10 layers) of n(GO) = 1.2-0.24i. For few layers (<= 10 layers) GO sheets, both the contrast at similar to 580 nm wavelength and the Raman intensity of G band linearly increase with the increase of the layer numbers. However, due to the laser induced heating effects and the requirement of a reference Raman spectrum in Raman spectroscopy measurements, contrast spectroscopy is non-destructive and more efficient. Simulations based on the Fresnel's equations agree well with evolution of the contrast and G band intensity as a function of number of layers. The precise refractive index of GO obtained in this work can be widely used in further study of GO. Therefore, our experimental contrast values can be directly used as a standard to identify the thickness of GO on Si substrate with 300 nm SiO2 capping layer, which paves a novelty way towards future fundamental research and applications of graphene-based materials. (c) 2012 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } By white light contrast spectroscopy, we have successfully identified number of graphene oxide (GO) layers (<= 10 layers) and obtained a new refractive index of GO sheets (<= 10 layers) of n(GO) = 1.2-0.24i. For few layers (<= 10 layers) GO sheets, both the contrast at similar to 580 nm wavelength and the Raman intensity of G band linearly increase with the increase of the layer numbers. However, due to the laser induced heating effects and the requirement of a reference Raman spectrum in Raman spectroscopy measurements, contrast spectroscopy is non-destructive and more efficient. Simulations based on the Fresnel's equations agree well with evolution of the contrast and G band intensity as a function of number of layers. The precise refractive index of GO obtained in this work can be widely used in further study of GO. Therefore, our experimental contrast values can be directly used as a standard to identify the thickness of GO on Si substrate with 300 nm SiO2 capping layer, which paves a novelty way towards future fundamental research and applications of graphene-based materials. (c) 2012 Elsevier Ltd. All rights reserved. |
Nerngchamnong, Nisachol; Yuan, Li; Qi, Dong-Chen; Li, Jiang; Thompson, Damien; Nijhuis, Christian A The role of van der Waals forces in the performance of molecular diodes Journal Article NATURE NANOTECHNOLOGY, 8 (2), pp. 113-118, 2013, ISSN: 1748-3387. @article{ISI:000315178800019, title = {The role of van der Waals forces in the performance of molecular diodes}, author = {Nisachol Nerngchamnong and Li Yuan and Dong-Chen Qi and Jiang Li and Damien Thompson and Christian A Nijhuis}, doi = {10.1038/NNANO.2012.238}, issn = {1748-3387}, year = {2013}, date = {2013-02-01}, journal = {NATURE NANOTECHNOLOGY}, volume = {8}, number = {2}, pages = {113-118}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {One of the main goals of organic and molecular electronics is to relate the performance and electronic function of devices to the chemical structure and intermolecular interactions of the organic component inside them, which can take the form of an organic thin film, a self-assembled monolayer or a single molecule(1-7). This goal is difficult to achieve because organic and molecular electronic devices are complex physical-organic systems that consist of at least two electrodes, an organic component and two (different) organic/inorganic interfaces. Singling out the contribution of each of these components remains challenging. So far, strong pi-pi interactions have mainly been considered for the rational design and optimization of the performances of organic electronic devices(8-10), and weaker intermolecular interactions have largely been ignored. Here, we show experimentally that subtle changes in the intermolecular van der Waals interactions in the active component of a molecular diode dramatically impact the performance of the device. In particular, we observe an odd-even effect as the number of alkyl units is varied in a ferrocene-alkanethiolate self-assembled monolayer. As a result of a more favourable van der Waals interaction, junctions made from an odd number of alkyl units have a lower packing energy (by,similar to 0.4-0.6 kcal mol(-1)), rectify currents 10 times more efficiently, give a 10% higher yield in working devices, and can be made two to three times more reproducibly than junctions made from an even number of alkyl units.}, keywords = {}, pubstate = {published}, tppubtype = {article} } One of the main goals of organic and molecular electronics is to relate the performance and electronic function of devices to the chemical structure and intermolecular interactions of the organic component inside them, which can take the form of an organic thin film, a self-assembled monolayer or a single molecule(1-7). This goal is difficult to achieve because organic and molecular electronic devices are complex physical-organic systems that consist of at least two electrodes, an organic component and two (different) organic/inorganic interfaces. Singling out the contribution of each of these components remains challenging. So far, strong pi-pi interactions have mainly been considered for the rational design and optimization of the performances of organic electronic devices(8-10), and weaker intermolecular interactions have largely been ignored. Here, we show experimentally that subtle changes in the intermolecular van der Waals interactions in the active component of a molecular diode dramatically impact the performance of the device. In particular, we observe an odd-even effect as the number of alkyl units is varied in a ferrocene-alkanethiolate self-assembled monolayer. As a result of a more favourable van der Waals interaction, junctions made from an odd number of alkyl units have a lower packing energy (by,similar to 0.4-0.6 kcal mol(-1)), rectify currents 10 times more efficiently, give a 10% higher yield in working devices, and can be made two to three times more reproducibly than junctions made from an even number of alkyl units. |
Cong, Chunxiao; Li, Kun; Zhang, Xi Xiang; Yu, Ting Visualization of arrangements of carbon atoms in graphene layers by Raman mapping and atomic-resolution TEM Journal Article SCIENTIFIC REPORTS, 3 , 2013, ISSN: 2045-2322. @article{ISI:000314400000009, title = {Visualization of arrangements of carbon atoms in graphene layers by Raman mapping and atomic-resolution TEM}, author = {Chunxiao Cong and Kun Li and Xi Xiang Zhang and Ting Yu}, doi = {10.1038/srep01195}, issn = {2045-2322}, year = {2013}, date = {2013-02-01}, journal = {SCIENTIFIC REPORTS}, volume = {3}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {In-plane and out-of-plane arrangements of carbon atoms in graphene layers play critical roles in the fundamental physics and practical applications of these novel two-dimensional materials. Here, we report initial results on the edge/crystal orientations and stacking orders of bi- and tri-layer graphene (BLG and TLG) from Raman spectroscopy and transmission electron microscopy (TEM) experiments performed on the same sample. We introduce a new method of transferring graphene flakes onto a normal TEM grid. Using this novel method, we probed the BLG and TLG flakes that had been previously investigated by Raman scattering with high-resolution (atomic) TEM.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In-plane and out-of-plane arrangements of carbon atoms in graphene layers play critical roles in the fundamental physics and practical applications of these novel two-dimensional materials. Here, we report initial results on the edge/crystal orientations and stacking orders of bi- and tri-layer graphene (BLG and TLG) from Raman spectroscopy and transmission electron microscopy (TEM) experiments performed on the same sample. We introduce a new method of transferring graphene flakes onto a normal TEM grid. Using this novel method, we probed the BLG and TLG flakes that had been previously investigated by Raman scattering with high-resolution (atomic) TEM. |
Malard, Leandro M; Mak, Kin Fai; Neto, Castro A H; Peres, N M R; Heinz, Tony F Observation of intra- and inter-band transitions in the transient optical response of graphene Journal Article NEW JOURNAL OF PHYSICS, 15 , 2013, ISSN: 1367-2630. @article{ISI:000313910400001, title = {Observation of intra- and inter-band transitions in the transient optical response of graphene}, author = {Leandro M Malard and Kin Fai Mak and A H Castro Neto and N M R Peres and Tony F Heinz}, doi = {10.1088/1367-2630/15/1/015009}, issn = {1367-2630}, year = {2013}, date = {2013-01-01}, journal = {NEW JOURNAL OF PHYSICS}, volume = {15}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {The transient optical conductivity of freely suspended graphene was examined by femtosecond time-resolved spectroscopy using pump excitation at 400 nm and probe radiation at 800 nm. The optical conductivity (or, equivalently, absorption) changes abruptly upon excitation and subsequently relaxes to its initial value on the time scale of 1 ps. The form of the induced change in the optical conductivity varies strongly with excitation conditions, exhibiting a crossover from enhanced to decreased optical conductivity with increasing pump fluence. We describe the graphene response in terms of transient heating of the electrons, with the characteristic relaxation time of the transient conductivity reflecting the cooling of the electron system and the strongly coupled optical phonons through emission of lower energy phonons. The change in the optical conductivity is attributed to a combination of induced absorption from intra-band transitions of the photo-generated carriers and bleaching of the inter-band transitions by Pauli blocking. The former effect, which corresponds to the high-frequency wing of the Drude response, dominates at low pump fluence. In this regime of a limited rise in the electron temperature, an increase in the optical conductivity is observed. At high pump fluence, elevated electron temperatures are achieved. The decrease in the inter-band bleaching then dominates the transient response, the intra-band contribution being overwhelmed despite an increase in the Drude scattering rate with temperature. The temporal evolution of the optical conductivity in all the regimes can be described within a model including the intra- and inter-band contributions with a time-varying electronic temperature. An increased Drude scattering rate is inferred for high electron temperature and mechanisms for this enhancement are considered. The calculated scattering rate for interactions of the carriers with zone-center and zone-edge optical phonons agrees well with the rates obtained from experiment.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The transient optical conductivity of freely suspended graphene was examined by femtosecond time-resolved spectroscopy using pump excitation at 400 nm and probe radiation at 800 nm. The optical conductivity (or, equivalently, absorption) changes abruptly upon excitation and subsequently relaxes to its initial value on the time scale of 1 ps. The form of the induced change in the optical conductivity varies strongly with excitation conditions, exhibiting a crossover from enhanced to decreased optical conductivity with increasing pump fluence. We describe the graphene response in terms of transient heating of the electrons, with the characteristic relaxation time of the transient conductivity reflecting the cooling of the electron system and the strongly coupled optical phonons through emission of lower energy phonons. The change in the optical conductivity is attributed to a combination of induced absorption from intra-band transitions of the photo-generated carriers and bleaching of the inter-band transitions by Pauli blocking. The former effect, which corresponds to the high-frequency wing of the Drude response, dominates at low pump fluence. In this regime of a limited rise in the electron temperature, an increase in the optical conductivity is observed. At high pump fluence, elevated electron temperatures are achieved. The decrease in the inter-band bleaching then dominates the transient response, the intra-band contribution being overwhelmed despite an increase in the Drude scattering rate with temperature. The temporal evolution of the optical conductivity in all the regimes can be described within a model including the intra- and inter-band contributions with a time-varying electronic temperature. An increased Drude scattering rate is inferred for high electron temperature and mechanisms for this enhancement are considered. The calculated scattering rate for interactions of the carriers with zone-center and zone-edge optical phonons agrees well with the rates obtained from experiment. |
Shin, Young Jun; Gopinadhan, Kalon; Narayanapillai, Kulothungasagaran; Kalitsov, Alan; Bhatia, Charanjit S; Yang, Hyunsoo Stochastic nonlinear electrical characteristics of graphene Journal Article APPLIED PHYSICS LETTERS, 102 (3), 2013, ISSN: 0003-6951. @article{ISI:000314032600065, title = {Stochastic nonlinear electrical characteristics of graphene}, author = {Young Jun Shin and Kalon Gopinadhan and Kulothungasagaran Narayanapillai and Alan Kalitsov and Charanjit S Bhatia and Hyunsoo Yang}, doi = {10.1063/1.4788737}, issn = {0003-6951}, year = {2013}, date = {2013-01-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {102}, number = {3}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION & FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {A stochastic nonlinear electrical characteristic of graphene is reported. Abrupt current changes are observed from voltage sweeps between the source and drain with an on/off ratio up to 10(3). It is found that graphene channel experiences the topological change. Active radicals in an uneven graphene channel cause local changes of electrostatic potential. Simulation results based on the self-trapped electron and hole mechanism account well for the experimental data. Our findings illustrate an important issue of reliable electron transports and help for the understanding of transport properties in graphene devices. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4788737]}, keywords = {}, pubstate = {published}, tppubtype = {article} } A stochastic nonlinear electrical characteristic of graphene is reported. Abrupt current changes are observed from voltage sweeps between the source and drain with an on/off ratio up to 10(3). It is found that graphene channel experiences the topological change. Active radicals in an uneven graphene channel cause local changes of electrostatic potential. Simulation results based on the self-trapped electron and hole mechanism account well for the experimental data. Our findings illustrate an important issue of reliable electron transports and help for the understanding of transport properties in graphene devices. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4788737] |
Neto, Silva M B; Neto, Castro A H; Kim, J S; Stewart, G R d-f hybridization and quantum criticality in weakly-itinerant ferromagnets Journal Article JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (2), 2013, ISSN: 0953-8984. @article{ISI:000312106700013, title = {d-f hybridization and quantum criticality in weakly-itinerant ferromagnets}, author = {M B Silva Neto and Castro A H Neto and J S Kim and G R Stewart}, doi = {10.1088/0953-8984/25/2/025601}, issn = {0953-8984}, year = {2013}, date = {2013-01-01}, journal = {JOURNAL OF PHYSICS-CONDENSED MATTER}, volume = {25}, number = {2}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {We investigate the unusual magnetic, thermodynamic and transport properties of nearly-critical, weakly-itinerant fenomagnets with the general formula UTX, where T = Rh, Co and X = Ge, Si. As a unique feature of these systems, we show how changes in the V-df hybridization, which controls their proximity to a ferromagnetic instability, determine the evolution of the ground state magnetization, M-0, the Curie temperature, T-C, the density of states at the Fermi level, N(E-F), the T-2 resistivity coefficient, A, and the specific heat coefficient, gamma. The universal aspect of our findings comes from the dependence on only two parameters: the transition metal T-d bandwidth, W-d, and the distance between the T-d and U-f band centers, C-Td - C-Uf. We discuss our results in connection to data for URh1-xCoxGe.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We investigate the unusual magnetic, thermodynamic and transport properties of nearly-critical, weakly-itinerant fenomagnets with the general formula UTX, where T = Rh, Co and X = Ge, Si. As a unique feature of these systems, we show how changes in the V-df hybridization, which controls their proximity to a ferromagnetic instability, determine the evolution of the ground state magnetization, M-0, the Curie temperature, T-C, the density of states at the Fermi level, N(E-F), the T-2 resistivity coefficient, A, and the specific heat coefficient, gamma. The universal aspect of our findings comes from the dependence on only two parameters: the transition metal T-d bandwidth, W-d, and the distance between the T-d and U-f band centers, C-Td - C-Uf. We discuss our results in connection to data for URh1-xCoxGe. |
Guo, Zhengang; Reddy, M V; Goh, Bee Min; San, Angela Koh Phei; Bao, Qiaoliang; Loh, Kian Ping Electrochemical performance of graphene and copper oxide composites synthesized from a metal-organic framework (Cu-MOF) Journal Article RSC ADVANCES, 3 (41), pp. 19051-19056, 2013, ISSN: 2046-2069. @article{ISI:000325408300046, title = {Electrochemical performance of graphene and copper oxide composites synthesized from a metal-organic framework (Cu-MOF)}, author = {Zhengang Guo and M V Reddy and Bee Min Goh and Angela Koh Phei San and Qiaoliang Bao and Kian Ping Loh}, doi = {10.1039/c3ra43308k}, issn = {2046-2069}, year = {2013}, date = {2013-01-01}, journal = {RSC ADVANCES}, volume = {3}, number = {41}, pages = {19051-19056}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {A composite made from copper oxide (CuO) and exfoliated graphene (G) was synthesized by sintering a Cu-based metal-organic framework (Cu-MOF) embedded with exfoliated G. The G-embedded Cu-MOF was first synthesized by the self-assembly process of Cu(NO3)(2)center dot 6H(2)O and DMTA (2,5-imethoxyterephthalatic acid) in the presence of exfoliated, few-layer G in the range of 2-5 mu m. 5 wt% exfoliated G was incorporated into the MOF as an impurity. The X-Ray diffraction studies of the composite show that the characteristics of the few-layer G can be observed along with (hkl) lines of Cu-MOF. Upon heating, the Cu-MOF-G system decomposes to form a conductive composite consisting of sheet-like CuO and G sheets. Due to the ability of G to act as conductive additive, the CuO-G composite delivers improved electrochemical properties and stable cycling compared to pure CuO, the Cu-MOF or physically mixed Cu-MOF-G composites.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A composite made from copper oxide (CuO) and exfoliated graphene (G) was synthesized by sintering a Cu-based metal-organic framework (Cu-MOF) embedded with exfoliated G. The G-embedded Cu-MOF was first synthesized by the self-assembly process of Cu(NO3)(2)center dot 6H(2)O and DMTA (2,5-imethoxyterephthalatic acid) in the presence of exfoliated, few-layer G in the range of 2-5 mu m. 5 wt% exfoliated G was incorporated into the MOF as an impurity. The X-Ray diffraction studies of the composite show that the characteristics of the few-layer G can be observed along with (hkl) lines of Cu-MOF. Upon heating, the Cu-MOF-G system decomposes to form a conductive composite consisting of sheet-like CuO and G sheets. Due to the ability of G to act as conductive additive, the CuO-G composite delivers improved electrochemical properties and stable cycling compared to pure CuO, the Cu-MOF or physically mixed Cu-MOF-G composites. |
Prabu, M; Reddy, M V; Selvasekarapandian, S; Admas, S; Loh, K P; Rao, Subba G V; Chowdari, B V R Effect of LLT Coating on Elevated Temperature Cycle Life Performance of LiMn2O4 Cathode Material Journal Article JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 160 (5), pp. A3144-A3147, 2013, ISSN: 0013-4651. @article{ISI:000320202800024, title = {Effect of LLT Coating on Elevated Temperature Cycle Life Performance of LiMn2O4 Cathode Material}, author = {M Prabu and M V Reddy and S Selvasekarapandian and S Admas and K P Loh and Subba G V Rao and B V R Chowdari}, doi = {10.1149/2.021305jes}, issn = {0013-4651}, year = {2013}, date = {2013-01-01}, journal = {JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, volume = {160}, number = {5}, pages = {A3144-A3147}, publisher = {ELECTROCHEMICAL SOC INC}, address = {65 SOUTH MAIN STREET, PENNINGTON, NJ 08534 USA}, abstract = {LiMn2O4 compound are synthesized by polymer precursor method using polyvinyl pyrrolidone (PVP) at temperatures (T), 650,750 and 850 degrees C which was coated by a thin La0.61Li0.17TiO3 (LLT). The structure and the morphology of the compounds are studied by the Rietveld refined X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques, respectively. To investigate the effect of LLT coating galvanostatic charge discharge cycling (60 mA g(-1)) studies are made in the voltage range of 3.5-4.3 V vs. Li at elevated temperature (55 deg. C). The high-temperature electrochemical performance of the LiMn2O4 was significantly improved by the LLT coating. (C) 2013 The Electrochemical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } LiMn2O4 compound are synthesized by polymer precursor method using polyvinyl pyrrolidone (PVP) at temperatures (T), 650,750 and 850 degrees C which was coated by a thin La0.61Li0.17TiO3 (LLT). The structure and the morphology of the compounds are studied by the Rietveld refined X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques, respectively. To investigate the effect of LLT coating galvanostatic charge discharge cycling (60 mA g(-1)) studies are made in the voltage range of 3.5-4.3 V vs. Li at elevated temperature (55 deg. C). The high-temperature electrochemical performance of the LiMn2O4 was significantly improved by the LLT coating. (C) 2013 The Electrochemical Society. |
Kajen, R S; Chandrasekhar, N; Pey, K L; Vijila, C; Jaiswal, M; Saravanan, S; Ng, Andrew M H; Wong, C P; Loh, K P Trap Levels in Graphene Oxide: A Thermally Stimulated Current Study Journal Article ECS SOLID STATE LETTERS, 2 (2), pp. M17-M19, 2013, ISSN: 2162-8742. @article{ISI:000318342500002, title = {Trap Levels in Graphene Oxide: A Thermally Stimulated Current Study}, author = {R S Kajen and N Chandrasekhar and K L Pey and C Vijila and M Jaiswal and S Saravanan and Andrew M H Ng and C P Wong and K P Loh}, doi = {10.1149/2.006302ssl}, issn = {2162-8742}, year = {2013}, date = {2013-01-01}, journal = {ECS SOLID STATE LETTERS}, volume = {2}, number = {2}, pages = {M17-M19}, publisher = {ELECTROCHEMICAL SOC INC}, address = {65 SOUTH MAIN STREET, PENNINGTON, NJ 08534 USA}, abstract = {We report thermally stimulated current (TSC) experiments on graphene oxide ( GO) to study the effects of various defect levels near the GO Fermi level. The TSC peaks are ascribed to detrapping from defect levels to the GO hopping transport energy level, and are found to be in agreement with the GO density of states reported in the literature. This work will be useful in evaluating the use of GO in memory/dielectric/barrier applications. (C) 2012 The Electrochemical Society. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report thermally stimulated current (TSC) experiments on graphene oxide ( GO) to study the effects of various defect levels near the GO Fermi level. The TSC peaks are ascribed to detrapping from defect levels to the GO hopping transport energy level, and are found to be in agreement with the GO density of states reported in the literature. This work will be useful in evaluating the use of GO in memory/dielectric/barrier applications. (C) 2012 The Electrochemical Society. All rights reserved. |
Reddy, M V; Beichen, Zhang; Loh, K P; Chowdari, B V R Facile synthesis of Co3O4 by molten salt method and its Li-storage performance Journal Article CRYSTENGCOMM, 15 (18), pp. 3568-3574, 2013, ISSN: 1466-8033. @article{ISI:000317594600010, title = {Facile synthesis of Co3O4 by molten salt method and its Li-storage performance}, author = {M V Reddy and Zhang Beichen and K P Loh and B V R Chowdari}, doi = {10.1039/c3ce26985j}, issn = {1466-8033}, year = {2013}, date = {2013-01-01}, journal = {CRYSTENGCOMM}, volume = {15}, number = {18}, pages = {3568-3574}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {We synthesized Co3O4 compounds using different molten salts such as LiNO3:LiOH, LiNO3: LiCl, NaNO3: KNO3, KCl and studied their morphology and Li-storage properties. Eleven samples were prepared at various temperatures ranging from 180 degrees C to 710 degrees C and evaluated the effect of different Co-salts such as Co-sulphate, Co-acetate and Co-hydroxide on crystal growth and Li-storage performance. The obtained Co3O4 powders were characterized by a variety of techniques. Li-storage performance studies on Co3O4 prepared by different Co-salts show reversible capacity values in the range, 778 to 1090 mA h g(-1) at a current rate of 60 mA g(-1) and at the end of the 40th cycle. Among the effects of preparation temperature, Co3O4 prepared at 510 degrees C showed the best combination of capacity and sustainability. Co3O4 prepared from different cobalt sources among Co-sulphate delivered the highest and most stable capacity with the smallest fading. We report the growth, reaction mechanism and storage performance of different Co3O4.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We synthesized Co3O4 compounds using different molten salts such as LiNO3:LiOH, LiNO3: LiCl, NaNO3: KNO3, KCl and studied their morphology and Li-storage properties. Eleven samples were prepared at various temperatures ranging from 180 degrees C to 710 degrees C and evaluated the effect of different Co-salts such as Co-sulphate, Co-acetate and Co-hydroxide on crystal growth and Li-storage performance. The obtained Co3O4 powders were characterized by a variety of techniques. Li-storage performance studies on Co3O4 prepared by different Co-salts show reversible capacity values in the range, 778 to 1090 mA h g(-1) at a current rate of 60 mA g(-1) and at the end of the 40th cycle. Among the effects of preparation temperature, Co3O4 prepared at 510 degrees C showed the best combination of capacity and sustainability. Co3O4 prepared from different cobalt sources among Co-sulphate delivered the highest and most stable capacity with the smallest fading. We report the growth, reaction mechanism and storage performance of different Co3O4. |
Shen, Xiaonan; Wang, Haomin; Yu, Ting How do the electron beam writing and metal deposition affect the properties of graphene during device fabrication? Journal Article NANOSCALE, 5 (8), pp. 3352-3358, 2013, ISSN: 2040-3364. @article{ISI:000316959500033, title = {How do the electron beam writing and metal deposition affect the properties of graphene during device fabrication?}, author = {Xiaonan Shen and Haomin Wang and Ting Yu}, doi = {10.1039/c3nr33460k}, issn = {2040-3364}, year = {2013}, date = {2013-01-01}, journal = {NANOSCALE}, volume = {5}, number = {8}, pages = {3352-3358}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {Electron beam exposure and metallic contact formation are commonly used processes for fabrication of graphene-based devices. We report a detailed Raman study on the influence of medium energy electron irradiation and metal atoms on defectivity and doping on monolayer and bilayer graphene. It is found that the electron beam could induce disorder into graphene layers mainly by three ways: knocking-off carbon atoms, reaction with substrate and deposition of amorphous carbon. We observe that bilayer graphene exhibits higher stability under e-beam irradiation than monolayer graphene. Our study on the formation process of metallic contacts reveals that evaporation of Ti normally cannot induce any defects into graphene while deposition of Au can introduce a large amount of damage. This work could be valuable for further development of processes in the fabrication of graphene-based devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electron beam exposure and metallic contact formation are commonly used processes for fabrication of graphene-based devices. We report a detailed Raman study on the influence of medium energy electron irradiation and metal atoms on defectivity and doping on monolayer and bilayer graphene. It is found that the electron beam could induce disorder into graphene layers mainly by three ways: knocking-off carbon atoms, reaction with substrate and deposition of amorphous carbon. We observe that bilayer graphene exhibits higher stability under e-beam irradiation than monolayer graphene. Our study on the formation process of metallic contacts reveals that evaporation of Ti normally cannot induce any defects into graphene while deposition of Au can introduce a large amount of damage. This work could be valuable for further development of processes in the fabrication of graphene-based devices. |
Zhao, Weijie; Ghorannevis, Zohreh; Chu, Leiqiang; Toh, Minglin; Kloc, Christian; Tan, Ping-Heng; Eda, Goki Evolution of Electronic Structure in Atomically Thin Sheets of WS2 and WSe2 Journal Article ACS NANO, 7 (1), pp. 791-797, 2013, ISSN: 1936-0851. @article{ISI:000314082800085, title = {Evolution of Electronic Structure in Atomically Thin Sheets of WS2 and WSe2}, author = {Weijie Zhao and Zohreh Ghorannevis and Leiqiang Chu and Minglin Toh and Christian Kloc and Ping-Heng Tan and Goki Eda}, doi = {10.1021/nn305275h}, issn = {1936-0851}, year = {2013}, date = {2013-01-01}, journal = {ACS NANO}, volume = {7}, number = {1}, pages = {791-797}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Geometrical confinement effect in exfoliated sheets of layered materials leads to significant evolution of energy dispersion in mono- to few-layer thickness regime. Molybdenum disulfide (MoS2) was recently found to exhibit indirect-to-direct gap transition when the thickness is reduced to a single monolayer. Emerging photoluminescence (PL) from monolayer MoS2 opens up opportunities for a range of novel optoelectronic applications of the material. Here we report differential reflectance and PL spectra of mono- to few-layer WS2 and WSe2 that indicate that the band structure of these materials undergoes similar indirect-to-direct gap transition when thinned to a single monolayer. The transition is evidenced by distinctly enhanced PL peak centered at 630 and 750 nm in monolayer WS2 and WSe2, respectively. Few-layer flakes are found to exhibit comparatively strong indirect gap emission along with direct gap hot electron emission, suggesting high quality of synthetic crystals prepared by a chemical vapor transport method. Fine absorption and emission features and their thickness dependence suggest a strong effect of Se p-orbitals on the d electron band structure as well as interlayer coupling in WSe2.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Geometrical confinement effect in exfoliated sheets of layered materials leads to significant evolution of energy dispersion in mono- to few-layer thickness regime. Molybdenum disulfide (MoS2) was recently found to exhibit indirect-to-direct gap transition when the thickness is reduced to a single monolayer. Emerging photoluminescence (PL) from monolayer MoS2 opens up opportunities for a range of novel optoelectronic applications of the material. Here we report differential reflectance and PL spectra of mono- to few-layer WS2 and WSe2 that indicate that the band structure of these materials undergoes similar indirect-to-direct gap transition when thinned to a single monolayer. The transition is evidenced by distinctly enhanced PL peak centered at 630 and 750 nm in monolayer WS2 and WSe2, respectively. Few-layer flakes are found to exhibit comparatively strong indirect gap emission along with direct gap hot electron emission, suggesting high quality of synthetic crystals prepared by a chemical vapor transport method. Fine absorption and emission features and their thickness dependence suggest a strong effect of Se p-orbitals on the d electron band structure as well as interlayer coupling in WSe2. |
King, Laurie A; Zhao, Weijie; Chhowalla, Manish; Riley, Jason D; Eda, Goki Photoelectrochemical properties of chemically exfoliated MoS2 Journal Article JOURNAL OF MATERIALS CHEMISTRY A, 1 (31), pp. 8935-8941, 2013, ISSN: 2050-7488. @article{ISI:000321864300031, title = {Photoelectrochemical properties of chemically exfoliated MoS2}, author = {Laurie A King and Weijie Zhao and Manish Chhowalla and Jason D Riley and Goki Eda}, doi = {10.1039/c3ta11633f}, issn = {2050-7488}, year = {2013}, date = {2013-01-01}, journal = {JOURNAL OF MATERIALS CHEMISTRY A}, volume = {1}, number = {31}, pages = {8935-8941}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {Group 6 transition metal dichalcogenides (TMD) such as MoS2 are promising candidates for photocatalysis and photoelectrochemical applications. Despite their promise, scalable deposition of thin films remains a challenge for TMD-based photoanodes. Here we investigate the photoelectrochemical properties of ultrathin films of chemically exfoliated MoS2 and its composites with TiO2 nanoparticles. We show that MoS2 monolayer films exhibit photoelectrochemical properties similar to bulk materials, generating photocurrent at excitation wavelengths above the direct band gap edge at similar to 660 nm (similar to 1.9 eV). We also demonstrate that MoS2 monolayers adsorbed on TiO2 behave as effective photosensitizers. We find that in TiO2-MoS2 composite photoanodes, photoexcited hot electrons in MoS2 are able inject into TiO2 whilst holes are removed by the electrolyte so as to generate electrical current from incident light. Our results demonstrate the potential of solution-processed MoS2 monolayers for photoelectrochemical applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Group 6 transition metal dichalcogenides (TMD) such as MoS2 are promising candidates for photocatalysis and photoelectrochemical applications. Despite their promise, scalable deposition of thin films remains a challenge for TMD-based photoanodes. Here we investigate the photoelectrochemical properties of ultrathin films of chemically exfoliated MoS2 and its composites with TiO2 nanoparticles. We show that MoS2 monolayer films exhibit photoelectrochemical properties similar to bulk materials, generating photocurrent at excitation wavelengths above the direct band gap edge at similar to 660 nm (similar to 1.9 eV). We also demonstrate that MoS2 monolayers adsorbed on TiO2 behave as effective photosensitizers. We find that in TiO2-MoS2 composite photoanodes, photoexcited hot electrons in MoS2 are able inject into TiO2 whilst holes are removed by the electrolyte so as to generate electrical current from incident light. Our results demonstrate the potential of solution-processed MoS2 monolayers for photoelectrochemical applications. |
Shang, Jingzhi; Cong, Chunxiao; Zhang, Jun; Xiong, Qihua; Gurzadyan, Gagik G; Yu, Ting Observation of low-wavenumber out-of-plane optical phonon in few-layer graphene Journal Article JOURNAL OF RAMAN SPECTROSCOPY, 44 (1), pp. 70-74, 2013, ISSN: 0377-0486. @article{ISI:000313595500011, title = {Observation of low-wavenumber out-of-plane optical phonon in few-layer graphene}, author = {Jingzhi Shang and Chunxiao Cong and Jun Zhang and Qihua Xiong and Gagik G Gurzadyan and Ting Yu}, doi = {10.1002/jrs.4141}, issn = {0377-0486}, year = {2013}, date = {2013-01-01}, journal = {JOURNAL OF RAMAN SPECTROSCOPY}, volume = {44}, number = {1}, pages = {70-74}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {Few-layer graphene grown by chemical vapor deposition has been studied by Raman and ultrafast laser spectroscopy. A low-wavenumber Raman peak of similar to 120 cm-1 and a phonon-induced oscillation in the kinetic curve of electronphonon relaxation process have been observed, respectively. The Raman peak is assigned to the low-wavenumber out-of-plane optical mode in the few-layer graphene. The phonon band shows an asymmetric shape, a consequence of so-called Breit-Wigner-Fano resonance, resulting from the coupling between the low-wavenumber phonon and electron transitions. The obtained oscillation wavenumber from the kinetic curve is consistent with the detected low-wavenumber phonon by Raman scattering. The origin of this oscillation is attributed to the generation of coherent phonons and their interactions with photoinduced electrons. Copyright (C) 2012 John Wiley & Sons, Ltd.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Few-layer graphene grown by chemical vapor deposition has been studied by Raman and ultrafast laser spectroscopy. A low-wavenumber Raman peak of similar to 120 cm-1 and a phonon-induced oscillation in the kinetic curve of electronphonon relaxation process have been observed, respectively. The Raman peak is assigned to the low-wavenumber out-of-plane optical mode in the few-layer graphene. The phonon band shows an asymmetric shape, a consequence of so-called Breit-Wigner-Fano resonance, resulting from the coupling between the low-wavenumber phonon and electron transitions. The obtained oscillation wavenumber from the kinetic curve is consistent with the detected low-wavenumber phonon by Raman scattering. The origin of this oscillation is attributed to the generation of coherent phonons and their interactions with photoinduced electrons. Copyright (C) 2012 John Wiley & Sons, Ltd. |