Browse through over scientific publications by CA2DM staff, students, collaborators, and partners.
2012 |
dos Santos, Lopes J M B; Peres, N M R; Neto, Castro A H Continuum model of the twisted graphene bilayer Journal Article PHYSICAL REVIEW B, 86 (15), 2012, ISSN: 1098-0121. @article{ISI:000310195900007, title = {Continuum model of the twisted graphene bilayer}, author = {J M B Lopes dos Santos and N M R Peres and A H Castro Neto}, doi = {10.1103/PhysRevB.86.155449}, issn = {1098-0121}, year = {2012}, date = {2012-10-01}, journal = {PHYSICAL REVIEW B}, volume = {86}, number = {15}, abstract = {The continuum model of the twisted graphene bilayer [Lopes dos Santos, Peres, and Castro Neto, Phys. Rev. Lett. 99, 256802 (2007)] is extended to include all types of commensurate structures. The essential ingredient of the model, the Fourier components of the spatially modulated hopping amplitudes, can be calculated analytically for any type of commensurate structures in the low-twist-angle limit. We show that the Fourier components that could give rise to a gap in the sublattice exchange symmetric (SE-even) structures discussed by Mele [Phys. Rev. B 81, 161405 (2010)] vanish linearly with angle, whereas the amplitudes that saturate to finite values, as theta -> 0, ensure that all low-angle structures share essentially the same physics. We extend our previous calculations beyond the validity of perturbation theory to discuss the disappearance of Dirac cone structure at angles below theta less than or similar to 1 degrees.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The continuum model of the twisted graphene bilayer [Lopes dos Santos, Peres, and Castro Neto, Phys. Rev. Lett. 99, 256802 (2007)] is extended to include all types of commensurate structures. The essential ingredient of the model, the Fourier components of the spatially modulated hopping amplitudes, can be calculated analytically for any type of commensurate structures in the low-twist-angle limit. We show that the Fourier components that could give rise to a gap in the sublattice exchange symmetric (SE-even) structures discussed by Mele [Phys. Rev. B 81, 161405 (2010)] vanish linearly with angle, whereas the amplitudes that saturate to finite values, as theta -> 0, ensure that all low-angle structures share essentially the same physics. We extend our previous calculations beyond the validity of perturbation theory to discuss the disappearance of Dirac cone structure at angles below theta less than or similar to 1 degrees. |
Patra, A K; Singh, S; Barin, B; Lee, Y; Ahn, J -H; del Barco, E; Mucciolo, E R; Oezyilmaz, B Dynamic spin injection into chemical vapor deposited graphene Journal Article APPLIED PHYSICS LETTERS, 101 (16), 2012, ISSN: 0003-6951. @article{ISI:000310669300046, title = {Dynamic spin injection into chemical vapor deposited graphene}, author = {A K Patra and S Singh and B Barin and Y Lee and J -H Ahn and E del Barco and E R Mucciolo and B Oezyilmaz}, doi = {10.1063/1.4761932}, issn = {0003-6951}, year = {2012}, date = {2012-10-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {101}, number = {16}, abstract = {We demonstrate dynamic spin injection into chemical vapor deposition (CVD) grown graphene by spin pumping from permalloy (Py) layers. Ferromagnetic resonance measurements at room temperature reveal a strong enhancement of the Gilbert damping at the Py/graphene interface, indeed exceeding that observed in Py/platinum interfaces. Similar results are also shown on Co/graphene layers. This enhancement in the Gilbert damping is understood as the consequence of spin pumping at the interface driven by magnetization dynamics. Our observations suggest a strong enhancement of spin-orbit coupling in CVD graphene, in agreement with earlier spin valve measurements. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4761932]}, keywords = {}, pubstate = {published}, tppubtype = {article} } We demonstrate dynamic spin injection into chemical vapor deposition (CVD) grown graphene by spin pumping from permalloy (Py) layers. Ferromagnetic resonance measurements at room temperature reveal a strong enhancement of the Gilbert damping at the Py/graphene interface, indeed exceeding that observed in Py/platinum interfaces. Similar results are also shown on Co/graphene layers. This enhancement in the Gilbert damping is understood as the consequence of spin pumping at the interface driven by magnetization dynamics. Our observations suggest a strong enhancement of spin-orbit coupling in CVD graphene, in agreement with earlier spin valve measurements. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4761932] |
You, Jhih-Shih; Lee, Hao; Fang, Shiang; Cazalilla, Miguel A; Wang, Daw-Wei Tuning the Kosterlitz-Thouless transition to zero temperature in anisotropic boson systems Journal Article PHYSICAL REVIEW A, 86 (4), 2012, ISSN: 1050-2947. @article{ISI:000309650800013, title = {Tuning the Kosterlitz-Thouless transition to zero temperature in anisotropic boson systems}, author = {Jhih-Shih You and Hao Lee and Shiang Fang and Miguel A Cazalilla and Daw-Wei Wang}, doi = {10.1103/PhysRevA.86.043612}, issn = {1050-2947}, year = {2012}, date = {2012-10-01}, journal = {PHYSICAL REVIEW A}, volume = {86}, number = {4}, abstract = {We study the two-dimensional Bose-Hubbard model with anisotropic hopping. Focusing on the effects of anisotropy on superfluid properties such as the helicity modulus and the normal-to-superfluid [Berezinskii-Kosterlitz-Thouless (BKT)] transition temperature, two different approaches are compared: large-scale quantum Monte Carlo simulations and the self-consistent harmonic approximation (SCHA). For the latter, two different formulations are considered, one applying near the isotropic limit and the other applying in the extremely anisotropic limit. Thus we find that the SCHA provides a reasonable description of superfluid properties of this system provided the appropriate type of formulation is employed. The accuracy of the SCHA in the extremely anisotropic limit, where the BKT transition temperature is tuned to zero (i.e., at a quantum critical point) and therefore quantum fluctuations play a dominant role, is particularly striking.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the two-dimensional Bose-Hubbard model with anisotropic hopping. Focusing on the effects of anisotropy on superfluid properties such as the helicity modulus and the normal-to-superfluid [Berezinskii-Kosterlitz-Thouless (BKT)] transition temperature, two different approaches are compared: large-scale quantum Monte Carlo simulations and the self-consistent harmonic approximation (SCHA). For the latter, two different formulations are considered, one applying near the isotropic limit and the other applying in the extremely anisotropic limit. Thus we find that the SCHA provides a reasonable description of superfluid properties of this system provided the appropriate type of formulation is employed. The accuracy of the SCHA in the extremely anisotropic limit, where the BKT transition temperature is tuned to zero (i.e., at a quantum critical point) and therefore quantum fluctuations play a dominant role, is particularly striking. |
Liu, S; Xu, X F; Xie, R G; Zhang, G; Li, B W Anomalous heat conduction and anomalous diffusion in low dimensional nanoscale systems Journal Article EUROPEAN PHYSICAL JOURNAL B, 85 (10), 2012, ISSN: 1434-6028. @article{ISI:000310646100014, title = {Anomalous heat conduction and anomalous diffusion in low dimensional nanoscale systems}, author = {S Liu and X F Xu and R G Xie and G Zhang and B W Li}, doi = {10.1140/epjb/e2012-30383-8}, issn = {1434-6028}, year = {2012}, date = {2012-10-01}, journal = {EUROPEAN PHYSICAL JOURNAL B}, volume = {85}, number = {10}, abstract = {Heat conduction is an important energy transport process in nature. Phonon is the major energy carrier for heat in semiconductors and dielectric materials. In analogy to Ohm's law of electrical conduction, Fourier's law is the fundamental law of heat conduction in solids. Although Fourier's law has received great success in describing macroscopic heat conduction in the past two hundred years, its validity in low dimensional systems is still an open question. Here we give a brief review of the recent developments in experimental, theoretical and numerical studies of heat conduction in low dimensional systems, including lattice models and low dimensional nanostructures such as nanowires, nanotubes and graphene. We will demonstrate that phonons transport in low dimensional systems superdiffusively, which leads to a size dependent thermal conductivity. In other words, Fourier's law is not applicable in low dimensional structures.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Heat conduction is an important energy transport process in nature. Phonon is the major energy carrier for heat in semiconductors and dielectric materials. In analogy to Ohm's law of electrical conduction, Fourier's law is the fundamental law of heat conduction in solids. Although Fourier's law has received great success in describing macroscopic heat conduction in the past two hundred years, its validity in low dimensional systems is still an open question. Here we give a brief review of the recent developments in experimental, theoretical and numerical studies of heat conduction in low dimensional systems, including lattice models and low dimensional nanostructures such as nanowires, nanotubes and graphene. We will demonstrate that phonons transport in low dimensional systems superdiffusively, which leads to a size dependent thermal conductivity. In other words, Fourier's law is not applicable in low dimensional structures. |
Alexandre, Simone S; Lucio, A D; Neto, Castro A H; Nunes, R W Correlated Magnetic States in Extended One-Dimensional Defects in Graphene Journal Article NANO LETTERS, 12 (10), pp. 5097-5102, 2012, ISSN: 1530-6984. @article{ISI:000309615000006, title = {Correlated Magnetic States in Extended One-Dimensional Defects in Graphene}, author = {Simone S Alexandre and A D Lucio and A H Castro Neto and R W Nunes}, doi = {10.1021/nl3017434}, issn = {1530-6984}, year = {2012}, date = {2012-10-01}, journal = {NANO LETTERS}, volume = {12}, number = {10}, pages = {5097-5102}, abstract = {Ab initio calculations indicate that while the electronic states introduced by tilt grain boundaries in graphene are only partially confined to the defect core, a translational grain boundary introduces states near the Fermi level that are very strongly confined to the core of the defect, and display a ferromagnetic instability. The translational boundary lies along a graphene zigzag direction and its magnetic state is akin to that which has been theoretically predicted to occur on zigzag edges of graphene ribbons. Unlike ribbon edges, the translational grain boundary is fully immersed within the bulk of graphene, hence its magnetic state is protected from the contamination and reconstruction effects that have hampered experimental detection of the magnetic ribbon states. Moreover, our calculations suggest that charge transfer between grain boundaries and the bulk in graphene is short ranged, with charge redistribution confined to similar to 5 angstrom from the geometric center of the 1D defects.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Ab initio calculations indicate that while the electronic states introduced by tilt grain boundaries in graphene are only partially confined to the defect core, a translational grain boundary introduces states near the Fermi level that are very strongly confined to the core of the defect, and display a ferromagnetic instability. The translational boundary lies along a graphene zigzag direction and its magnetic state is akin to that which has been theoretically predicted to occur on zigzag edges of graphene ribbons. Unlike ribbon edges, the translational grain boundary is fully immersed within the bulk of graphene, hence its magnetic state is protected from the contamination and reconstruction effects that have hampered experimental detection of the magnetic ribbon states. Moreover, our calculations suggest that charge transfer between grain boundaries and the bulk in graphene is short ranged, with charge redistribution confined to similar to 5 angstrom from the geometric center of the 1D defects. |
Hipolito, F; Chaves, A J; Ribeiro, R M; Vasilevskiy, M I; Pereira, Vitor M; Peres, N M R Enhanced optical dichroism of graphene nanoribbons Journal Article PHYSICAL REVIEW B, 86 (11), 2012, ISSN: 1098-0121. @article{ISI:000308866700007, title = {Enhanced optical dichroism of graphene nanoribbons}, author = {F Hipolito and A J Chaves and R M Ribeiro and M I Vasilevskiy and Vitor M Pereira and N M R Peres}, doi = {10.1103/PhysRevB.86.115430}, issn = {1098-0121}, year = {2012}, date = {2012-09-01}, journal = {PHYSICAL REVIEW B}, volume = {86}, number = {11}, abstract = {The optical conductivity of graphene nanoribbons is analytical and exactly derived. It is shown that the absence of translational invariance along the transverse direction allows considerable intraband absorption in a narrow frequency window that varies with the ribbon width, and lies in the THz range domain for ribbons 10-100 nm wide. In this spectral region the absorption anisotropy can be as high as two orders of magnitude, which renders the medium strongly dichroic, and allows for a very high degree of polarization (up to similar to 85%) with just a single layer of graphene. Using a cavity for impedance enhancement, or a stack of few layer nanoribbons, these values can reach almost 100%. This opens a potential prospect of employing graphene ribbon structures as efficient polarizers in the far IR and THz frequencies.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The optical conductivity of graphene nanoribbons is analytical and exactly derived. It is shown that the absence of translational invariance along the transverse direction allows considerable intraband absorption in a narrow frequency window that varies with the ribbon width, and lies in the THz range domain for ribbons 10-100 nm wide. In this spectral region the absorption anisotropy can be as high as two orders of magnitude, which renders the medium strongly dichroic, and allows for a very high degree of polarization (up to similar to 85%) with just a single layer of graphene. Using a cavity for impedance enhancement, or a stack of few layer nanoribbons, these values can reach almost 100%. This opens a potential prospect of employing graphene ribbon structures as efficient polarizers in the far IR and THz frequencies. |
Chen, Jie; Zhang, Gang; Li, Baowen Thermal contact resistance across nanoscale silicon dioxide and silicon interface Journal Article JOURNAL OF APPLIED PHYSICS, 112 (6), 2012, ISSN: 0021-8979. @article{ISI:000309423200137, title = {Thermal contact resistance across nanoscale silicon dioxide and silicon interface}, author = {Jie Chen and Gang Zhang and Baowen Li}, doi = {10.1063/1.4754513}, issn = {0021-8979}, year = {2012}, date = {2012-09-01}, journal = {JOURNAL OF APPLIED PHYSICS}, volume = {112}, number = {6}, abstract = {Silicon dioxide and silicon (SiO2/Si) interface plays a very important role in semiconductor industry. However, at nanoscale, its interfacial thermal properties have not been well understood so far. In this paper, we systematically study the interfacial thermal resistance (Kapitza resistance) of a heterojunction composed of amorphous silicon dioxide and crystalline silicon by using molecular dynamics simulations. Numerical results have shown that Kapitza resistance at SiO2/Si interface depends on the interfacial coupling strength remarkably. In the weak interfacial coupling limit, Kapitza resistance depends on both the detailed interfacial structure and the length of the heterojunction, showing large fluctuation among different samples. In contrast, it is almost insensitive to the detailed interfacial structure or the length of the heterojunction in the strong interfacial coupling limit, giving rise to a nearly constant value around 0.9 x 10(-9) m(2)KW(-1) at room temperature. Moreover, the temperature dependent Kapitza resistance in the strong interfacial coupling limit has also been examined. Our study provides useful guidance to the thermal management and heat dissipation across nanoscale SiO2/Si interface, in particular, for the design of silicon nanowire based nano electronics and photonics devices. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754513]}, keywords = {}, pubstate = {published}, tppubtype = {article} } Silicon dioxide and silicon (SiO2/Si) interface plays a very important role in semiconductor industry. However, at nanoscale, its interfacial thermal properties have not been well understood so far. In this paper, we systematically study the interfacial thermal resistance (Kapitza resistance) of a heterojunction composed of amorphous silicon dioxide and crystalline silicon by using molecular dynamics simulations. Numerical results have shown that Kapitza resistance at SiO2/Si interface depends on the interfacial coupling strength remarkably. In the weak interfacial coupling limit, Kapitza resistance depends on both the detailed interfacial structure and the length of the heterojunction, showing large fluctuation among different samples. In contrast, it is almost insensitive to the detailed interfacial structure or the length of the heterojunction in the strong interfacial coupling limit, giving rise to a nearly constant value around 0.9 x 10(-9) m(2)KW(-1) at room temperature. Moreover, the temperature dependent Kapitza resistance in the strong interfacial coupling limit has also been examined. Our study provides useful guidance to the thermal management and heat dissipation across nanoscale SiO2/Si interface, in particular, for the design of silicon nanowire based nano electronics and photonics devices. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754513] |
Gogoi, Pranjal Kumar; Santoso, Iman; Saha, Surajit; Wang, Sihao; Neto, Antonio Castro H; Loh, Kian Ping; Venkatesan, T; Rusydi, Andrivo Optical conductivity study of screening of many-body effects in graphene interfaces Journal Article EPL, 99 (6), 2012, ISSN: 0295-5075. @article{ISI:000309773700028, title = {Optical conductivity study of screening of many-body effects in graphene interfaces}, author = {Pranjal Kumar Gogoi and Iman Santoso and Surajit Saha and Sihao Wang and Antonio H Castro Neto and Kian Ping Loh and T Venkatesan and Andrivo Rusydi}, doi = {10.1209/0295-5075/99/67009}, issn = {0295-5075}, year = {2012}, date = {2012-09-01}, journal = {EPL}, volume = {99}, number = {6}, abstract = {Theoretical studies have shown that electron-electron (e-e) and electron-hole (e-h) interactions play important roles in many observed quantum properties of graphene making this an ideal system to study many-body effects. In this report we show that spectroscopic ellipsometry can enable us to measure this interactions quantitatively. We present spectroscopic data in two extreme systems of graphene on quartz (GOQ), an insulator, and graphene on copper (GOC), a metal which show that for GOQ, both e-e and e-h interactions dominate while for GOC e-h interactions are screened. The data further enables the estimation of the strength of the many-body interaction through the effective fine-structure constant, alpha*(g). The alpha*(g) for GOQ indicates a strong correlation with an almost energy-independent value of about 1.37. In contrast, the alpha*(g) value of GOC is photon energy dependent and is almost two orders of magnitude lower at low energies indicating very weak correlation. Copyright (C) EPLA, 2012}, keywords = {}, pubstate = {published}, tppubtype = {article} } Theoretical studies have shown that electron-electron (e-e) and electron-hole (e-h) interactions play important roles in many observed quantum properties of graphene making this an ideal system to study many-body effects. In this report we show that spectroscopic ellipsometry can enable us to measure this interactions quantitatively. We present spectroscopic data in two extreme systems of graphene on quartz (GOQ), an insulator, and graphene on copper (GOC), a metal which show that for GOQ, both e-e and e-h interactions dominate while for GOC e-h interactions are screened. The data further enables the estimation of the strength of the many-body interaction through the effective fine-structure constant, alpha*(g). The alpha*(g) for GOQ indicates a strong correlation with an almost energy-independent value of about 1.37. In contrast, the alpha*(g) value of GOC is photon energy dependent and is almost two orders of magnitude lower at low energies indicating very weak correlation. Copyright (C) EPLA, 2012 |
Qiu, Xue Peng; Shin, Young Jun; Niu, Jing; Kulothungasagaran, Narayanapillai; Kalon, Gopinadhan; Qiu, Caiyu; Yu, Ting; Yang, Hyunsoo Disorder-free sputtering method on graphene Journal Article AIP ADVANCES, 2 (3), 2012. @article{ISI:000309388800021, title = {Disorder-free sputtering method on graphene}, author = {Xue Peng Qiu and Young Jun Shin and Jing Niu and Narayanapillai Kulothungasagaran and Gopinadhan Kalon and Caiyu Qiu and Ting Yu and Hyunsoo Yang}, doi = {10.1063/1.4739783}, year = {2012}, date = {2012-09-01}, journal = {AIP ADVANCES}, volume = {2}, number = {3}, abstract = {Deposition of various materials onto graphene without causing any disorder is highly desirable for graphene applications. Especially, sputtering is a versatile technique to deposit various metals and insulators for spintronics, and indium tin oxide to make transparent devices. However, the sputtering process causes damage to graphene because of high energy sputtered atoms. By flipping the substrate and using a high Ar pressure, we demonstrate that the level of damage to graphene can be reduced or eliminated in dc, rf, and reactive sputtering processes. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4739783]}, keywords = {}, pubstate = {published}, tppubtype = {article} } Deposition of various materials onto graphene without causing any disorder is highly desirable for graphene applications. Especially, sputtering is a versatile technique to deposit various metals and insulators for spintronics, and indium tin oxide to make transparent devices. However, the sputtering process causes damage to graphene because of high energy sputtered atoms. By flipping the substrate and using a high Ar pressure, we demonstrate that the level of damage to graphene can be reduced or eliminated in dc, rf, and reactive sputtering processes. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4739783] |
Luo, Zhiqiang; Cong, Chunxiao; Zhang, Jun; Xiong, Qihua; Yu, Ting The origin of sub-bands in the Raman D-band of graphene Journal Article CARBON, 50 (11), pp. 4252-4258, 2012, ISSN: 0008-6223. @article{ISI:000306824100032, title = {The origin of sub-bands in the Raman D-band of graphene}, author = {Zhiqiang Luo and Chunxiao Cong and Jun Zhang and Qihua Xiong and Ting Yu}, doi = {10.1016/j.carbon.2012.05.008}, issn = {0008-6223}, year = {2012}, date = {2012-09-01}, journal = {CARBON}, volume = {50}, number = {11}, pages = {4252-4258}, abstract = {In Raman spectroscopy investigations of defective suspended graphene, splitting in the D band is observed. Four double resonance Raman scattering processes: the outer and inner scattering processes, as well as the scattering processes with electrons first scattered by phonons (''phonon-first'') or by defects (''defect-first''), are found to be responsible for these features of the D band. The D sub-bands associated with the outer and inner processes merge with increasing defect concentration. However a Stokes/anti-Stokes Raman study indicates that the splitting of the D band due to the separate ``phonon-first'' and ``defect-first'' processes is valid for suspended graphene. For graphene samples on a SiO2/Si substrate, the sub-bands of D band merge due to the increased Raman broadening parameter resulting from the substrate doping. Moreover, the merging of the sub-bands shows excitation energy dependence, which can be understood by considering the energy dependent lifetime and/or scattering rate of photo-excited carriers in the Raman scattering process. (C) 2012 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In Raman spectroscopy investigations of defective suspended graphene, splitting in the D band is observed. Four double resonance Raman scattering processes: the outer and inner scattering processes, as well as the scattering processes with electrons first scattered by phonons (''phonon-first'') or by defects (''defect-first''), are found to be responsible for these features of the D band. The D sub-bands associated with the outer and inner processes merge with increasing defect concentration. However a Stokes/anti-Stokes Raman study indicates that the splitting of the D band due to the separate ``phonon-first'' and ``defect-first'' processes is valid for suspended graphene. For graphene samples on a SiO2/Si substrate, the sub-bands of D band merge due to the increased Raman broadening parameter resulting from the substrate doping. Moreover, the merging of the sub-bands shows excitation energy dependence, which can be understood by considering the energy dependent lifetime and/or scattering rate of photo-excited carriers in the Raman scattering process. (C) 2012 Elsevier Ltd. All rights reserved. |
Wang, Yu; Lee, Wong Cheng; Manga, Kiran Kumar; Ang, Priscilla Kailian; Lu, Jiong; Liu, Yan Peng; Lim, Chwee Teck; Loh, Kian Ping Fluorinated Graphene for Promoting Neuro-Induction of Stem Cells Journal Article ADVANCED MATERIALS, 24 (31), pp. 4285+, 2012, ISSN: 0935-9648. @article{ISI:000307163000008, title = {Fluorinated Graphene for Promoting Neuro-Induction of Stem Cells}, author = {Yu Wang and Wong Cheng Lee and Kiran Kumar Manga and Priscilla Kailian Ang and Jiong Lu and Yan Peng Liu and Chwee Teck Lim and Kian Ping Loh}, doi = {10.1002/adma.201200846}, issn = {0935-9648}, year = {2012}, date = {2012-08-01}, journal = {ADVANCED MATERIALS}, volume = {24}, number = {31}, pages = {4285+}, abstract = {Surface engineering of substrates offers the possibility of controlling the physiological functions of cells at the molecular level. Fluorinated graphene promotes the differentiation of MSCs towards neuronal lineages. Cell alignment using printed polydimethylsiloxane channel arrays on fluorinated graphene further enhances the neuro-induction of MSCs even in the absence of chemical inducers.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Surface engineering of substrates offers the possibility of controlling the physiological functions of cells at the molecular level. Fluorinated graphene promotes the differentiation of MSCs towards neuronal lineages. Cell alignment using printed polydimethylsiloxane channel arrays on fluorinated graphene further enhances the neuro-induction of MSCs even in the absence of chemical inducers. |
Tang, Lena Ai Ling; Wang, Junzhong; Lim, Teck Kwang; Bi, Xuezhi; Lee, Wong Cheng; Lin, Qingsong; Chang, Young-Tae; Lim, Chwee Teck; Loh, Kian Ping High-Performance Graphene-Titania Platform for Detection of Phosphopeptides in Cancer Cells Journal Article ANALYTICAL CHEMISTRY, 84 (15), pp. 6693-6700, 2012, ISSN: 0003-2700. @article{ISI:000307159200061, title = {High-Performance Graphene-Titania Platform for Detection of Phosphopeptides in Cancer Cells}, author = {Lena Ai Ling Tang and Junzhong Wang and Teck Kwang Lim and Xuezhi Bi and Wong Cheng Lee and Qingsong Lin and Young-Tae Chang and Chwee Teck Lim and Kian Ping Loh}, doi = {10.1021/ac301119r}, issn = {0003-2700}, year = {2012}, date = {2012-08-01}, journal = {ANALYTICAL CHEMISTRY}, volume = {84}, number = {15}, pages = {6693-6700}, abstract = {Phosphopeptides play a crucial role in many biological processes and constitute some of the most powerful biomarkers in disease detection. However they are often present in very low concentration, which makes their detection highly challenging. Here, we demonstrate the use of a solution-dispersible graphene-titania platform for the selective extraction of phosphopeptides from peptide mixtures. This is followed by direct analysis by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS). The efficient charge and energy exchange between graphene and TiO2 during laser irradiation in SELDI-TOF MS promotes the soft ionization of analytes and affords a detection limit in the attomole range, which is 10(2)-10(5) more sensitive than conventional platforms. The graphene-titania platform can also be used for detecting phosphopeptides in cancer cells (HeLa cells), where it shows high specificity (94%). An expanded library of 967 unique phosphopeptides is detected using significantly reduced loading of extraction matrixes compared to conventional TiO2 bead-based assays.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Phosphopeptides play a crucial role in many biological processes and constitute some of the most powerful biomarkers in disease detection. However they are often present in very low concentration, which makes their detection highly challenging. Here, we demonstrate the use of a solution-dispersible graphene-titania platform for the selective extraction of phosphopeptides from peptide mixtures. This is followed by direct analysis by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS). The efficient charge and energy exchange between graphene and TiO2 during laser irradiation in SELDI-TOF MS promotes the soft ionization of analytes and affords a detection limit in the attomole range, which is 10(2)-10(5) more sensitive than conventional platforms. The graphene-titania platform can also be used for detecting phosphopeptides in cancer cells (HeLa cells), where it shows high specificity (94%). An expanded library of 967 unique phosphopeptides is detected using significantly reduced loading of extraction matrixes compared to conventional TiO2 bead-based assays. |
Eda, Goki; Fujita, Takeshi; Yamaguchi, Hisato; Voiry, Damien; Chen, Mingwei; Chhowalla, Manish Coherent Atomic and Electronic Heterostructures of Single-Layer MoS2 Journal Article ACS NANO, 6 (8), pp. 7311-7317, 2012, ISSN: 1936-0851. @article{ISI:000307988900091, title = {Coherent Atomic and Electronic Heterostructures of Single-Layer MoS2}, author = {Goki Eda and Takeshi Fujita and Hisato Yamaguchi and Damien Voiry and Mingwei Chen and Manish Chhowalla}, doi = {10.1021/nn302422x}, issn = {1936-0851}, year = {2012}, date = {2012-08-01}, journal = {ACS NANO}, volume = {6}, number = {8}, pages = {7311-7317}, abstract = {Nanoscale heterostructures with quantum dots, nanowires, and nanosheets have opened up new routes toward advanced functionalities and implementation of novel electronic and photonic devices in reduced dimensions. Coherent and passivated heterointerfaces between electronically dissimilar materials can be typically achieved through composition or doping modulation as in GaAs/AlGaAs and Si/NiSi or heteroepitaxy of lattice matched but chemically distinct compounds. Here we report that single layers of chemically exfoliated MoS2 consist of electronically dissimilar polymorphs that are lattice matched such that they form chemically homogeneous atomic and electronic heterostructures. High resolution scanning transmission electron microscope (STEM) imaging reveals the coexistence of metallic and semiconducting phases within the chemically homogeneous two-dimensional (2D) MoS2 nanosheets. These results suggest potential for exploiting molecular scale electronic device designs in atomically thin 2D layers.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Nanoscale heterostructures with quantum dots, nanowires, and nanosheets have opened up new routes toward advanced functionalities and implementation of novel electronic and photonic devices in reduced dimensions. Coherent and passivated heterointerfaces between electronically dissimilar materials can be typically achieved through composition or doping modulation as in GaAs/AlGaAs and Si/NiSi or heteroepitaxy of lattice matched but chemically distinct compounds. Here we report that single layers of chemically exfoliated MoS2 consist of electronically dissimilar polymorphs that are lattice matched such that they form chemically homogeneous atomic and electronic heterostructures. High resolution scanning transmission electron microscope (STEM) imaging reveals the coexistence of metallic and semiconducting phases within the chemically homogeneous two-dimensional (2D) MoS2 nanosheets. These results suggest potential for exploiting molecular scale electronic device designs in atomically thin 2D layers. |
Kotov, Valeri N; Uchoa, Bruno; Pereira, Vitor M; Guinea, F; Neto, Castro A H Electron-Electron Interactions in Graphene: Current Status and Perspectives Journal Article REVIEWS OF MODERN PHYSICS, 84 (3), pp. 1067-1125, 2012, ISSN: 0034-6861. @article{ISI:000306549100001, title = {Electron-Electron Interactions in Graphene: Current Status and Perspectives}, author = {Valeri N Kotov and Bruno Uchoa and Vitor M Pereira and F Guinea and A H Castro Neto}, doi = {10.1103/RevModPhys.84.1067}, issn = {0034-6861}, year = {2012}, date = {2012-07-01}, journal = {REVIEWS OF MODERN PHYSICS}, volume = {84}, number = {3}, pages = {1067-1125}, abstract = {The problem of electron-electron interactions in graphene is reviewed. Starting from the screening of long-range interactions in these systems, the existence of an emerging Dirac liquid of Lorentz invariant quasiparticles in the weak-coupling regime is discussed, as well as the formation of strongly correlated electronic states in the strong-coupling regime. The analogy and connections between the many-body problem and the Coulomb impurity problem are also analyzed. The problem of the magnetic instability and Kondo effect of impurities and/or adatoms in graphene is also discussed in analogy with classical models of many-body effects in ordinary metals. Lorentz invariance is shown to play a fundamental role and leads to effects that span the whole spectrum, from the ultraviolet to the infrared. The effect of an emerging Lorentz invariance is also discussed in the context of finite size and edge effects as well as mesoscopic physics. The effects of strong magnetic fields in single layers and some of the main aspects of the many-body problem in graphene bilayers are briefly reviewed. In addition to reviewing the fully understood aspects of the many-body problem in graphene, a plethora of interesting issues are shown to remain open, both theoretically and experimentally, and the field of graphene research is still exciting and vibrant.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The problem of electron-electron interactions in graphene is reviewed. Starting from the screening of long-range interactions in these systems, the existence of an emerging Dirac liquid of Lorentz invariant quasiparticles in the weak-coupling regime is discussed, as well as the formation of strongly correlated electronic states in the strong-coupling regime. The analogy and connections between the many-body problem and the Coulomb impurity problem are also analyzed. The problem of the magnetic instability and Kondo effect of impurities and/or adatoms in graphene is also discussed in analogy with classical models of many-body effects in ordinary metals. Lorentz invariance is shown to play a fundamental role and leads to effects that span the whole spectrum, from the ultraviolet to the infrared. The effect of an emerging Lorentz invariance is also discussed in the context of finite size and edge effects as well as mesoscopic physics. The effects of strong magnetic fields in single layers and some of the main aspects of the many-body problem in graphene bilayers are briefly reviewed. In addition to reviewing the fully understood aspects of the many-body problem in graphene, a plethora of interesting issues are shown to remain open, both theoretically and experimentally, and the field of graphene research is still exciting and vibrant. |
Yan, Yonghong; Liang, Qi-Feng; Zhao, Hui; Wu, Chang-Qin; Li, Baowen Thermoelectric properties of one-dimensional graphene antidot arrays Journal Article PHYSICS LETTERS A, 376 (35), pp. 2425-2429, 2012, ISSN: 0375-9601. @article{ISI:000306624600019, title = {Thermoelectric properties of one-dimensional graphene antidot arrays}, author = {Yonghong Yan and Qi-Feng Liang and Hui Zhao and Chang-Qin Wu and Baowen Li}, doi = {10.1016/j.physleta.2012.06.010}, issn = {0375-9601}, year = {2012}, date = {2012-07-01}, journal = {PHYSICS LETTERS A}, volume = {376}, number = {35}, pages = {2425-2429}, abstract = {We investigate the thermoelectric properties of one-dimensional (1D) graphene antidot arrays by nonequilibrium Green's function method. We show that by introducing antidots to the pristine graphene nanoribbon the thermal conductance can be reduced greatly while keeping the power factor still high, thus leading to an enhanced thermoelectric figure of merit (ZT). Our numerical results indicate that ZT values of 1D antidot graphene arrays can be up to unity, which means the 1D graphene antidot arrays may be promising for thermoelectric applications. (C) 2012 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We investigate the thermoelectric properties of one-dimensional (1D) graphene antidot arrays by nonequilibrium Green's function method. We show that by introducing antidots to the pristine graphene nanoribbon the thermal conductance can be reduced greatly while keeping the power factor still high, thus leading to an enhanced thermoelectric figure of merit (ZT). Our numerical results indicate that ZT values of 1D antidot graphene arrays can be up to unity, which means the 1D graphene antidot arrays may be promising for thermoelectric applications. (C) 2012 Elsevier B.V. All rights reserved. |
Fei, Z; Rodin, A S; Andreev, G O; Bao, W; McLeod, A S; Wagner, M; Zhang, L M; Zhao, Z; Thiemens, M; Dominguez, G; Fogler, M M; Neto, Castro A H; Lau, C N; Keilmann, F; Basov, D N Gate-tuning of graphene plasmons revealed by infrared nano-imaging Journal Article NATURE, 487 (7405), pp. 82-85, 2012, ISSN: 0028-0836. @article{ISI:000305982900054, title = {Gate-tuning of graphene plasmons revealed by infrared nano-imaging}, author = {Z Fei and A S Rodin and G O Andreev and W Bao and A S McLeod and M Wagner and L M Zhang and Z Zhao and M Thiemens and G Dominguez and M M Fogler and A H Castro Neto and C N Lau and F Keilmann and D N Basov}, doi = {10.1038/nature11253}, issn = {0028-0836}, year = {2012}, date = {2012-07-01}, journal = {NATURE}, volume = {487}, number = {7405}, pages = {82-85}, abstract = {Surface plasmons are collective oscillations of electrons in metals or semiconductors that enable confinement and control of electromagnetic energy at subwavelength scales(1-5). Rapid progress in plasmonics has largely relied on advances in device nano-fabrication(5-7), whereas less attention has been paid to the tunable properties of plasmonic media. One such medium-graphene-is amenable to convenient tuning of its electronic and optical properties by varying the applied voltage(8-11). Here, using infrared nano-imaging, we show that common graphene/SiO2/Si back-gated structures support propagating surface plasmons. The wavelength of graphene plasmons is of the order of 200 nanometres at technologically relevant infrared frequencies, and they can propagate several times this distance. We have succeeded in altering both the amplitude and the wavelength of these plasmons by varying the gate voltage. Using plasmon interferometry, we investigated losses in graphene by exploring real-space profiles of plasmon standing waves formed between the tip of our nano-probe and the edges of the samples. Plasmon dissipation quantified through this analysis is linked to the exotic electrodynamics of graphene(10). Standard plasmonic figures of merit of our tunable graphene devices surpass those of common metal-based structures.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Surface plasmons are collective oscillations of electrons in metals or semiconductors that enable confinement and control of electromagnetic energy at subwavelength scales(1-5). Rapid progress in plasmonics has largely relied on advances in device nano-fabrication(5-7), whereas less attention has been paid to the tunable properties of plasmonic media. One such medium-graphene-is amenable to convenient tuning of its electronic and optical properties by varying the applied voltage(8-11). Here, using infrared nano-imaging, we show that common graphene/SiO2/Si back-gated structures support propagating surface plasmons. The wavelength of graphene plasmons is of the order of 200 nanometres at technologically relevant infrared frequencies, and they can propagate several times this distance. We have succeeded in altering both the amplitude and the wavelength of these plasmons by varying the gate voltage. Using plasmon interferometry, we investigated losses in graphene by exploring real-space profiles of plasmon standing waves formed between the tip of our nano-probe and the edges of the samples. Plasmon dissipation quantified through this analysis is linked to the exotic electrodynamics of graphene(10). Standard plasmonic figures of merit of our tunable graphene devices surpass those of common metal-based structures. |
Peres, N M R; Ferreira, Aires; Bludov, Yu V; Vasilevskiy, M I Light scattering by a medium with a spatially modulated optical conductivity: the case of graphene Journal Article JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (24), 2012, ISSN: 0953-8984. @article{ISI:000304874900017, title = {Light scattering by a medium with a spatially modulated optical conductivity: the case of graphene}, author = {N M R Peres and Aires Ferreira and Yu V Bludov and M I Vasilevskiy}, doi = {10.1088/0953-8984/24/24/245303}, issn = {0953-8984}, year = {2012}, date = {2012-06-01}, journal = {JOURNAL OF PHYSICS-CONDENSED MATTER}, volume = {24}, number = {24}, abstract = {We describe light scattering from a graphene sheet having a modulated optical conductivity. We show that such modulation enables the excitation of surface plasmon polaritons by an electromagnetic wave impinging at normal incidence. The resulting surface plasmon polaritons are responsible for a substantial increase of electromagnetic radiation absorption by the graphene sheet. The origin of the modulation can be due either to a periodic strain field or to adatoms (or absorbed molecules) with a modulated adsorption profile.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We describe light scattering from a graphene sheet having a modulated optical conductivity. We show that such modulation enables the excitation of surface plasmon polaritons by an electromagnetic wave impinging at normal incidence. The resulting surface plasmon polaritons are responsible for a substantial increase of electromagnetic radiation absorption by the graphene sheet. The origin of the modulation can be due either to a periodic strain field or to adatoms (or absorbed molecules) with a modulated adsorption profile. |
Park, Hyoungki; Wadehra, Amita; Wilkins, John W; Neto, Antonio Castro H Magnetic states and optical properties of single-layer carbon-doped hexagonal boron nitride Journal Article APPLIED PHYSICS LETTERS, 100 (25), 2012, ISSN: 0003-6951. @article{ISI:000305676400084, title = {Magnetic states and optical properties of single-layer carbon-doped hexagonal boron nitride}, author = {Hyoungki Park and Amita Wadehra and John W Wilkins and Antonio H Castro Neto}, doi = {10.1063/1.4730392}, issn = {0003-6951}, year = {2012}, date = {2012-06-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {100}, number = {25}, abstract = {We show that carbon-doped hexagonal boron nitride (h-BN) has extraordinary properties with many possible applications. We demonstrate that the substitution-induced impurity states, associated with carbon atoms, and their interactions dictate the electronic structure and properties of C-doped h-BN. Furthermore, we show that stacking of localized impurity states in small C clusters embedded in h-BN forms a set of discrete energy levels in the wide gap of h-BN. The electronic structures of these C clusters have a plethora of applications in optics, magneto-optics, and opto-electronics. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730392]}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show that carbon-doped hexagonal boron nitride (h-BN) has extraordinary properties with many possible applications. We demonstrate that the substitution-induced impurity states, associated with carbon atoms, and their interactions dictate the electronic structure and properties of C-doped h-BN. Furthermore, we show that stacking of localized impurity states in small C clusters embedded in h-BN forms a set of discrete energy levels in the wide gap of h-BN. The electronic structures of these C clusters have a plethora of applications in optics, magneto-optics, and opto-electronics. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730392] |
Luo, Zhiqiang; Cong, Chunxiao; Zhang, Jun; Xiong, Qihua; Yu, Ting Direct observation of inner and outer G ` band double-resonance Raman scattering in free standing graphene Journal Article APPLIED PHYSICS LETTERS, 100 (24), 2012, ISSN: 0003-6951. @article{ISI:000305269200065, title = {Direct observation of inner and outer G ` band double-resonance Raman scattering in free standing graphene}, author = {Zhiqiang Luo and Chunxiao Cong and Jun Zhang and Qihua Xiong and Ting Yu}, doi = {10.1063/1.4729407}, issn = {0003-6951}, year = {2012}, date = {2012-06-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {100}, number = {24}, abstract = {In contrary to the widely reported single and symmetric peak feature of G' band in Raman spectrum of graphene, we herein report the observation of splitting in G' band in free standing graphene. Our experimental findings provide a direct and strong support for the previous theoretical prediction that the coexistence of the outer and inner processes in the double-resonance Raman scattering would cause the splitting of G' mode. The investigation of the influence of trigonal warping effect on the spectral features of G' subbands further verified the theoretical interpretation established on the anisotropic electronic structure of graphene. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729407]}, keywords = {}, pubstate = {published}, tppubtype = {article} } In contrary to the widely reported single and symmetric peak feature of G' band in Raman spectrum of graphene, we herein report the observation of splitting in G' band in free standing graphene. Our experimental findings provide a direct and strong support for the previous theoretical prediction that the coexistence of the outer and inner processes in the double-resonance Raman scattering would cause the splitting of G' mode. The investigation of the influence of trigonal warping effect on the spectral features of G' subbands further verified the theoretical interpretation established on the anisotropic electronic structure of graphene. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729407] |
Reus, William F; Thuo, Martin M; Shapiro, Nathan D; Nijhuis, Christian A; Whitesides, George M The SAM, Not the Electrodes, Dominates Charge Transport in Metal-Monolayer//Ga2O3/Gallium-Indium Eutectic Junctions Journal Article ACS NANO, 6 (6), pp. 4806-4822, 2012, ISSN: 1936-0851. @article{ISI:000305661300028, title = {The SAM, Not the Electrodes, Dominates Charge Transport in Metal-Monolayer//Ga2O3/Gallium-Indium Eutectic Junctions}, author = {William F Reus and Martin M Thuo and Nathan D Shapiro and Christian A Nijhuis and George M Whitesides}, doi = {10.1021/nn205089u}, issn = {1936-0851}, year = {2012}, date = {2012-06-01}, journal = {ACS NANO}, volume = {6}, number = {6}, pages = {4806-4822}, abstract = {The liquid-metal eutectic of gallium and indium (EGaln) is a useful electrode for making soft electrical contacts to self-assembled monolayers (SAMs). This electrode has, however, one feature whose effect on charge transport has been incompletely understood: a thin (approximately 0.7 nm) film-consisting primarily of Ga2O3-that covers its surface when in contact with air. SAMs that rectify current have been measured using this electrode in Ag-TS-SAM//Ga2O3/EGaln (where Ag-TS = template-stripped Ag surface) junctions. This paper organizes evidence, both published and unpublished, showing that the molecular structure of the SAM (specifically, the presence of an accessible molecular orbital asymmetrically located within the SAM), not the difference between the electrodes or the characteristics of the Ga2O3 film, causes the observed rectification. By examining and ruling out potential mechanisms of rectification that rely either on the Ga2O3 film or on the asymmetry of the electrodes, this paper demonstrates that the structure of the SAM dominates charge transport through Ag-TS-SAM//Ga2O3/EGaln junctions, and that the electrical characteristics of the Ga2O3 film have a negligible effect on these measurements.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The liquid-metal eutectic of gallium and indium (EGaln) is a useful electrode for making soft electrical contacts to self-assembled monolayers (SAMs). This electrode has, however, one feature whose effect on charge transport has been incompletely understood: a thin (approximately 0.7 nm) film-consisting primarily of Ga2O3-that covers its surface when in contact with air. SAMs that rectify current have been measured using this electrode in Ag-TS-SAM//Ga2O3/EGaln (where Ag-TS = template-stripped Ag surface) junctions. This paper organizes evidence, both published and unpublished, showing that the molecular structure of the SAM (specifically, the presence of an accessible molecular orbital asymmetrically located within the SAM), not the difference between the electrodes or the characteristics of the Ga2O3 film, causes the observed rectification. By examining and ruling out potential mechanisms of rectification that rely either on the Ga2O3 film or on the asymmetry of the electrodes, this paper demonstrates that the structure of the SAM dominates charge transport through Ag-TS-SAM//Ga2O3/EGaln junctions, and that the electrical characteristics of the Ga2O3 film have a negligible effect on these measurements. |
Chen, Jie; Zhang, Gang; Li, Baowen Impacts of Atomistic Coating on Thermal Conductivity of Germanium Nanowires Journal Article NANO LETTERS, 12 (6), pp. 2826-2832, 2012, ISSN: 1530-6984. @article{ISI:000305106400030, title = {Impacts of Atomistic Coating on Thermal Conductivity of Germanium Nanowires}, author = {Jie Chen and Gang Zhang and Baowen Li}, doi = {10.1021/nl300208c}, issn = {1530-6984}, year = {2012}, date = {2012-06-01}, journal = {NANO LETTERS}, volume = {12}, number = {6}, pages = {2826-2832}, abstract = {By using nonequilibrium molecular dynamics simulations, we demonstrated that thermal conductivity of germanium nanowires can be reduced more than 25% at room temperature by atomistic coating. There is a critical coating thickness beyond which thermal conductivity of the coated nanowire is larger than that of the host nanowire. The diameter-dependent critical coating thickness and minimum thermal conductivity are explored. Moreover, we found that interface roughness can induce further reduction of thermal conductivity in coated nanowires. From the vibrational eigenmode analysis, it is found that coating induces localization for low-frequency phonons, while interface roughness localizes the high-frequency phonons. Our results provide an available approach to tune thermal conductivity of nanowires by atomic layer coating.}, keywords = {}, pubstate = {published}, tppubtype = {article} } By using nonequilibrium molecular dynamics simulations, we demonstrated that thermal conductivity of germanium nanowires can be reduced more than 25% at room temperature by atomistic coating. There is a critical coating thickness beyond which thermal conductivity of the coated nanowire is larger than that of the host nanowire. The diameter-dependent critical coating thickness and minimum thermal conductivity are explored. Moreover, we found that interface roughness can induce further reduction of thermal conductivity in coated nanowires. From the vibrational eigenmode analysis, it is found that coating induces localization for low-frequency phonons, while interface roughness localizes the high-frequency phonons. Our results provide an available approach to tune thermal conductivity of nanowires by atomic layer coating. |
Ochoa, H; Neto, Castro A H; Guinea, F Elliot-Yafet Mechanism in Graphene Journal Article PHYSICAL REVIEW LETTERS, 108 (20), 2012, ISSN: 0031-9007. @article{ISI:000304176300002, title = {Elliot-Yafet Mechanism in Graphene}, author = {H Ochoa and A H Castro Neto and F Guinea}, doi = {10.1103/PhysRevLett.108.206808}, issn = {0031-9007}, year = {2012}, date = {2012-05-01}, journal = {PHYSICAL REVIEW LETTERS}, volume = {108}, number = {20}, abstract = {The differences between spin relaxation in graphene and in other materials are discussed. For relaxation by scattering processes, the Elliot-Yafet mechanism, the relation between the spin and the momentum scattering times, acquires a dependence on the carrier density, which is independent of the scattering mechanism and the relation between mobility and carrier concentration. This dependence puts severe restrictions on the origin of the spin relaxation in graphene. The density dependence of the spin relaxation allows us to distinguish between ordinary impurities and defects which modify locally the spin-orbit interaction.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The differences between spin relaxation in graphene and in other materials are discussed. For relaxation by scattering processes, the Elliot-Yafet mechanism, the relation between the spin and the momentum scattering times, acquires a dependence on the carrier density, which is independent of the scattering mechanism and the relation between mobility and carrier concentration. This dependence puts severe restrictions on the origin of the spin relaxation in graphene. The density dependence of the spin relaxation allows us to distinguish between ordinary impurities and defects which modify locally the spin-orbit interaction. |
Ferreira, Aires; Peres, N M R; Neto, Castro A H Confined magneto-optical waves in graphene Journal Article PHYSICAL REVIEW B, 85 (20), 2012, ISSN: 1098-0121. @article{ISI:000304081900013, title = {Confined magneto-optical waves in graphene}, author = {Aires Ferreira and N M R Peres and A H Castro Neto}, doi = {10.1103/PhysRevB.85.205426}, issn = {1098-0121}, year = {2012}, date = {2012-05-01}, journal = {PHYSICAL REVIEW B}, volume = {85}, number = {20}, abstract = {The electromagnetic mode spectrum of single-layer graphene subjected to a quantizing magnetic field is computed taking into account intraband and interband contributions to the magneto-optical conductivity. We find that a sequence of weakly decaying quasi-transverse-electric modes, separated by magnetoplasmon polariton modes, emerge due to the quantizing magnetic field. The characteristics of these modes are tunable by changing the magnetic field or the Fermi energy.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The electromagnetic mode spectrum of single-layer graphene subjected to a quantizing magnetic field is computed taking into account intraband and interband contributions to the magneto-optical conductivity. We find that a sequence of weakly decaying quasi-transverse-electric modes, separated by magnetoplasmon polariton modes, emerge due to the quantizing magnetic field. The characteristics of these modes are tunable by changing the magnetic field or the Fermi energy. |
Niu, Jing; Truong, Viet Giang; Huang, Han; Tripathy, Sudhiranjan; Qiu, Caiyu; Wee, Andrew T S; Yu, Ting; Yang, Hyunsoo Study of electromagnetic enhancement for surface enhanced Raman spectroscopy of SiC graphene Journal Article APPLIED PHYSICS LETTERS, 100 (19), 2012, ISSN: 0003-6951. @article{ISI:000304108000017, title = {Study of electromagnetic enhancement for surface enhanced Raman spectroscopy of SiC graphene}, author = {Jing Niu and Viet Giang Truong and Han Huang and Sudhiranjan Tripathy and Caiyu Qiu and Andrew T S Wee and Ting Yu and Hyunsoo Yang}, doi = {10.1063/1.4712054}, issn = {0003-6951}, year = {2012}, date = {2012-05-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {100}, number = {19}, abstract = {The electromagnetic enhancement for surface enhanced Raman spectroscopy (SERS) of graphene is studied by inserting a layer of Al2O3 between epitaxial graphene and Au nanoparticles. Different excitation lasers are utilized to study the relationship between laser wavelength and SERS. The theoretical calculation shows that the extinction spectrum of Au nanoparticles is modulated by the presence of graphene. The experimental results of the relationship between the excitation laser wavelength and the enhancement factor fit well with the calculated results. An exponential relationship is observed between the enhancement factor and the thickness of the spacer layer. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712054]}, keywords = {}, pubstate = {published}, tppubtype = {article} } The electromagnetic enhancement for surface enhanced Raman spectroscopy (SERS) of graphene is studied by inserting a layer of Al2O3 between epitaxial graphene and Au nanoparticles. Different excitation lasers are utilized to study the relationship between laser wavelength and SERS. The theoretical calculation shows that the extinction spectrum of Au nanoparticles is modulated by the presence of graphene. The experimental results of the relationship between the excitation laser wavelength and the enhancement factor fit well with the calculated results. An exponential relationship is observed between the enhancement factor and the thickness of the spacer layer. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712054] |
Lu, Jiong; Neto, Castro A H; Loh, Kian Ping Transforming moire blisters into geometric graphene nano-bubbles Journal Article NATURE COMMUNICATIONS, 3 , 2012, ISSN: 2041-1723. @article{ISI:000304611400019, title = {Transforming moire blisters into geometric graphene nano-bubbles}, author = {Jiong Lu and A H Castro Neto and Kian Ping Loh}, doi = {10.1038/ncomms1818}, issn = {2041-1723}, year = {2012}, date = {2012-05-01}, journal = {NATURE COMMUNICATIONS}, volume = {3}, abstract = {Strain engineering has been proposed as an alternative method for manipulating the electronic properties of graphene. However, the bottleneck for strain engineering in graphene has been the ability to control such strain patterns at the nanoscale. Here we show that high level of control can be accomplished by chemically modifying the adherence of graphene on metal. Using scanning tunnelling microscopy, the shape evolution of graphene Moire blisters towards geometrically well-defined graphene bubbles was studied during the controlled, sub-layer oxidation of the ruthenium substrate. Understanding the dynamics of the oxidation process and defects generation on the Ru substrate allows us to control the size, shape and the density of the bubbles and its associated pseudo-magnetism. We also show that a modification of the same procedure can be used to create antidots in graphene by catalytic reaction of the same nanobubbles.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Strain engineering has been proposed as an alternative method for manipulating the electronic properties of graphene. However, the bottleneck for strain engineering in graphene has been the ability to control such strain patterns at the nanoscale. Here we show that high level of control can be accomplished by chemically modifying the adherence of graphene on metal. Using scanning tunnelling microscopy, the shape evolution of graphene Moire blisters towards geometrically well-defined graphene bubbles was studied during the controlled, sub-layer oxidation of the ruthenium substrate. Understanding the dynamics of the oxidation process and defects generation on the Ru substrate allows us to control the size, shape and the density of the bubbles and its associated pseudo-magnetism. We also show that a modification of the same procedure can be used to create antidots in graphene by catalytic reaction of the same nanobubbles. |
Bao, Qiaoliang; Loh, Kian Ping Graphene Photonics, Plasmonics, and Broadband Optoelectronic Devices Journal Article ACS NANO, 6 (5), pp. 3677-3694, 2012, ISSN: 1936-0851. @article{ISI:000304231700006, title = {Graphene Photonics, Plasmonics, and Broadband Optoelectronic Devices}, author = {Qiaoliang Bao and Kian Ping Loh}, doi = {10.1021/nn300989g}, issn = {1936-0851}, year = {2012}, date = {2012-05-01}, journal = {ACS NANO}, volume = {6}, number = {5}, pages = {3677-3694}, abstract = {Graphene has been hailed as a wonderful material in electronics, and recently, it is the rising star in photonics, as well. The wonderful optical properties of graphene afford multiple functions of signal emitting, transmitting, modulating, and detection to be realized in one material. In this paper, the latest progress in graphene photonics, plasmonics, and broadband optoelectronic devices is reviewed. Particular emphasis is placed on the ability to integrate graphene photonics onto the silicon platform to afford broadband operation In light routing and amplification, which involves components like polarizer, modulator, and photodetector. Other functions like saturable absorber and optical limiter are also reviewed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene has been hailed as a wonderful material in electronics, and recently, it is the rising star in photonics, as well. The wonderful optical properties of graphene afford multiple functions of signal emitting, transmitting, modulating, and detection to be realized in one material. In this paper, the latest progress in graphene photonics, plasmonics, and broadband optoelectronic devices is reviewed. Particular emphasis is placed on the ability to integrate graphene photonics onto the silicon platform to afford broadband operation In light routing and amplification, which involves components like polarizer, modulator, and photodetector. Other functions like saturable absorber and optical limiter are also reviewed. |
Ni, Guang-Xin; Zheng, Yi; Bae, Sukang; Tan, Chin Yaw; Kahya, Orhan; Wu, Jing; Hong, Byung Hee; Yao, Kui; Oezyilmaz, Barbaros Graphene-Ferroelectric Hybrid Structure for Flexible Transparent Electrodes Journal Article ACS NANO, 6 (5), pp. 3935-3942, 2012, ISSN: 1936-0851. @article{ISI:000304231700032, title = {Graphene-Ferroelectric Hybrid Structure for Flexible Transparent Electrodes}, author = {Guang-Xin Ni and Yi Zheng and Sukang Bae and Chin Yaw Tan and Orhan Kahya and Jing Wu and Byung Hee Hong and Kui Yao and Barbaros Oezyilmaz}, doi = {10.1021/nn3010137}, issn = {1936-0851}, year = {2012}, date = {2012-05-01}, journal = {ACS NANO}, volume = {6}, number = {5}, pages = {3935-3942}, abstract = {Graphene has exceptional optical, mechanical, and electrical properties, making it an emerging material for novel optoelectronics, photonics, and flexible transparent electrode applications. However, the relatively high sheet resistance of graphene is a major constraint for many of these applications. Here we propose a new approach to achieve low sheet resistance in large-scale CVD monolayer graphene using nonvolatile ferroelectric polymer gating. In this hybrid structure, large-scale graphene is heavily doped up to 3 x 10(13) cm(-2) by nonvolatile ferroelectric dipoles, yielding a low sheet resistance of 120 Omega/square at ambient conditions. The graphene-ferroelectric transparent conductors (GFeTCs) exhibit more than 95% transmittance from the visible to the near-infrared range owing to the highly transparent nature of the ferroelectric polymer. Together with its excellent mechanical flexibility, chemical inertness, and the simple fabrication process of ferroelectric polymers, the proposed GFeTCs represent a new route toward large-scale graphene-based transparent electrodes and optoelectronics.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene has exceptional optical, mechanical, and electrical properties, making it an emerging material for novel optoelectronics, photonics, and flexible transparent electrode applications. However, the relatively high sheet resistance of graphene is a major constraint for many of these applications. Here we propose a new approach to achieve low sheet resistance in large-scale CVD monolayer graphene using nonvolatile ferroelectric polymer gating. In this hybrid structure, large-scale graphene is heavily doped up to 3 x 10(13) cm(-2) by nonvolatile ferroelectric dipoles, yielding a low sheet resistance of 120 Omega/square at ambient conditions. The graphene-ferroelectric transparent conductors (GFeTCs) exhibit more than 95% transmittance from the visible to the near-infrared range owing to the highly transparent nature of the ferroelectric polymer. Together with its excellent mechanical flexibility, chemical inertness, and the simple fabrication process of ferroelectric polymers, the proposed GFeTCs represent a new route toward large-scale graphene-based transparent electrodes and optoelectronics. |
Jahan, Maryam; Bao, Qiaoliang; Loh, Kian Ping Electrocatalytically Active Graphene-Porphyrin MOF Composite for Oxygen Reduction Reaction Journal Article JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 134 (15), pp. 6707-6713, 2012, ISSN: 0002-7863. @article{ISI:000302887300033, title = {Electrocatalytically Active Graphene-Porphyrin MOF Composite for Oxygen Reduction Reaction}, author = {Maryam Jahan and Qiaoliang Bao and Kian Ping Loh}, doi = {10.1021/ja211433h}, issn = {0002-7863}, year = {2012}, date = {2012-04-01}, journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, volume = {134}, number = {15}, pages = {6707-6713}, abstract = {Pyridine-functionalized graphene (reduced graphene oxide) can be used as a building block in the assembly of metal organic framework (MOF). By reacting the pyridine-functionalized graphene with iron-porphyrin, a graphene-metalloporphyrin MOF with enhanced catalytic activity for oxygen reduction reactions (ORB) is synthesized. The structure and electrochemical property of the hybrid MOF are investigated as a function of the weight percentage of the functionalized graphene added to the iron-porphyrin framework. The results show that the addition of pyridine-functionalized graphene changes the crystallization process of iron-porphyrin in the MOF, increases its porosity, and enhances the electrochemical charge transfer rate of iron-porphyrin. The graphene-metalloporphyrin hybrid shows facile 4-electron ORR and can be used as a promising Pt-free cathode in alkaline Direct Methanol Fuel Cell.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Pyridine-functionalized graphene (reduced graphene oxide) can be used as a building block in the assembly of metal organic framework (MOF). By reacting the pyridine-functionalized graphene with iron-porphyrin, a graphene-metalloporphyrin MOF with enhanced catalytic activity for oxygen reduction reactions (ORB) is synthesized. The structure and electrochemical property of the hybrid MOF are investigated as a function of the weight percentage of the functionalized graphene added to the iron-porphyrin framework. The results show that the addition of pyridine-functionalized graphene changes the crystallization process of iron-porphyrin in the MOF, increases its porosity, and enhances the electrochemical charge transfer rate of iron-porphyrin. The graphene-metalloporphyrin hybrid shows facile 4-electron ORR and can be used as a promising Pt-free cathode in alkaline Direct Methanol Fuel Cell. |
Cresti, Alessandro; Fogler, Michael M; Guinea, Francisco; Neto, Castro A H; Roche, Stephan Quenching of the Quantum Hall Effect in Graphene with Scrolled Edges Journal Article PHYSICAL REVIEW LETTERS, 108 (16), 2012, ISSN: 0031-9007. @article{ISI:000302957000011, title = {Quenching of the Quantum Hall Effect in Graphene with Scrolled Edges}, author = {Alessandro Cresti and Michael M Fogler and Francisco Guinea and A H Castro Neto and Stephan Roche}, doi = {10.1103/PhysRevLett.108.166602}, issn = {0031-9007}, year = {2012}, date = {2012-04-01}, journal = {PHYSICAL REVIEW LETTERS}, volume = {108}, number = {16}, abstract = {Edge nanoscrolls are shown to strongly influence transport properties of suspended graphene in the quantum Hall regime. The relatively long arclength of the scrolls in combination with their compact transverse size results in formation of many nonchiral transport channels in the scrolls. They short circuit the bulk current paths and inhibit the observation of the quantized two-terminal resistance. Unlike competing theoretical proposals, this mechanism of disrupting the Hall quantization in suspended graphene is not caused by ill-chosen placement of the contacts, singular elastic strains, or a small sample size.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Edge nanoscrolls are shown to strongly influence transport properties of suspended graphene in the quantum Hall regime. The relatively long arclength of the scrolls in combination with their compact transverse size results in formation of many nonchiral transport channels in the scrolls. They short circuit the bulk current paths and inhibit the observation of the quantized two-terminal resistance. Unlike competing theoretical proposals, this mechanism of disrupting the Hall quantization in suspended graphene is not caused by ill-chosen placement of the contacts, singular elastic strains, or a small sample size. |
Manga, Kiran Kumar; Wang, Junzhong; Lin, Ming; Zhang, Jie; Nesladek, Milos; Nalla, Venkatram; Ji, Wei; Loh, Kian Ping High-Performance Broadband Photodetector Using Solution-Processible PbSe-TiO2-Graphene Hybrids Journal Article ADVANCED MATERIALS, 24 (13), pp. 1697-1702, 2012, ISSN: 0935-9648. @article{ISI:000302014400004, title = {High-Performance Broadband Photodetector Using Solution-Processible PbSe-TiO2-Graphene Hybrids}, author = {Kiran Kumar Manga and Junzhong Wang and Ming Lin and Jie Zhang and Milos Nesladek and Venkatram Nalla and Wei Ji and Kian Ping Loh}, doi = {10.1002/adma.201104399}, issn = {0935-9648}, year = {2012}, date = {2012-04-01}, journal = {ADVANCED MATERIALS}, volume = {24}, number = {13}, pages = {1697-1702}, abstract = {Highly sensitive, multicomponent broadband photodetector devices are made from PbSe/ graphene/ TiO2. TiO2 and PbSe nanoparticles act as light harvesting photoactive materials from the UV to IR regions of the electromagnetic spectrum, while the graphene acts as a charge collector for both photogenerated holes and electrons under an applied electric field.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Highly sensitive, multicomponent broadband photodetector devices are made from PbSe/ graphene/ TiO2. TiO2 and PbSe nanoparticles act as light harvesting photoactive materials from the UV to IR regions of the electromagnetic spectrum, while the graphene acts as a charge collector for both photogenerated holes and electrons under an applied electric field. |
Ferreira, Aires; Peres, N M R; Ribeiro, R M; Stauber, T Graphene-based photodetector with two cavities Journal Article PHYSICAL REVIEW B, 85 (11), 2012, ISSN: 2469-9950. @article{ISI:000301916100008, title = {Graphene-based photodetector with two cavities}, author = {Aires Ferreira and N M R Peres and R M Ribeiro and T Stauber}, doi = {10.1103/PhysRevB.85.115438}, issn = {2469-9950}, year = {2012}, date = {2012-03-01}, journal = {PHYSICAL REVIEW B}, volume = {85}, number = {11}, abstract = {We present an efficient graphene-based photodetector with two Fabri-Perot cavities. It is shown that the absorption can reach almost 100% around a given frequency, which is determined by the two-cavity lengths. It is also shown that hysteresis in the absorbance is possible, with the transmittance amplitude of the mirrors working as an external driving field. The role of nonlinear contributions to the optical susceptibility of graphene is discussed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present an efficient graphene-based photodetector with two Fabri-Perot cavities. It is shown that the absorption can reach almost 100% around a given frequency, which is determined by the two-cavity lengths. It is also shown that hysteresis in the absorbance is possible, with the transmittance amplitude of the mirrors working as an external driving field. The role of nonlinear contributions to the optical susceptibility of graphene is discussed. |
Kitt, Alexander L; Pereira, Vitor M; Swan, Anna K; Goldberg, Bennett B Lattice-corrected strain-induced vector potentials in graphene Journal Article PHYSICAL REVIEW B, 85 (11), 2012, ISSN: 2469-9950. @article{ISI:000301837400006, title = {Lattice-corrected strain-induced vector potentials in graphene}, author = {Alexander L Kitt and Vitor M Pereira and Anna K Swan and Bennett B Goldberg}, doi = {10.1103/PhysRevB.85.115432}, issn = {2469-9950}, year = {2012}, date = {2012-03-01}, journal = {PHYSICAL REVIEW B}, volume = {85}, number = {11}, abstract = {The electronic implications of strain in graphene can be captured at low energies by means of pseudovector potentials which can give rise to pseudomagnetic fields. These strain-induced vector potentials arise from the local perturbation to the electronic hopping amplitudes in a tight-binding framework. Here we complete the standard description of the strain-induced vector potential, which accounts only for the hopping perturbation, with the explicit inclusion of the lattice deformations or, equivalently, the deformation of the Brillouin zone. These corrections are linear in strain and are different at each of the strained, inequivalent Dirac points, and hence are equally necessary to identify the precise magnitude of the vector potential. This effect can be relevant in scenarios of inhomogeneous strain profiles, where electronic motion depends on the amount of overlap among the local Fermi surfaces. In particular, it affects the pseudomagnetic field distribution induced by inhomogeneous strain configurations, and can lead to new opportunities in tailoring the optimal strain fields for certain desired functionalities.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The electronic implications of strain in graphene can be captured at low energies by means of pseudovector potentials which can give rise to pseudomagnetic fields. These strain-induced vector potentials arise from the local perturbation to the electronic hopping amplitudes in a tight-binding framework. Here we complete the standard description of the strain-induced vector potential, which accounts only for the hopping perturbation, with the explicit inclusion of the lattice deformations or, equivalently, the deformation of the Brillouin zone. These corrections are linear in strain and are different at each of the strained, inequivalent Dirac points, and hence are equally necessary to identify the precise magnitude of the vector potential. This effect can be relevant in scenarios of inhomogeneous strain profiles, where electronic motion depends on the amount of overlap among the local Fermi surfaces. In particular, it affects the pseudomagnetic field distribution induced by inhomogeneous strain configurations, and can lead to new opportunities in tailoring the optimal strain fields for certain desired functionalities. |
Huang, Han; Wong, Swee Liang; Sun, Jiatao; Chen, Wei; Wee, Andrew Thye Shen Trapping Single Polar Molecules in SiC Nanomesh via Out-of-Plane Dipoles Journal Article ACS NANO, 6 (3), pp. 2774-2778, 2012, ISSN: 1936-0851. @article{ISI:000301945900096, title = {Trapping Single Polar Molecules in SiC Nanomesh via Out-of-Plane Dipoles}, author = {Han Huang and Swee Liang Wong and Jiatao Sun and Wei Chen and Andrew Thye Shen Wee}, doi = {10.1021/nn300258b}, issn = {1936-0851}, year = {2012}, date = {2012-03-01}, journal = {ACS NANO}, volume = {6}, number = {3}, pages = {2774-2778}, abstract = {The self-assembly of nonplanar chloroaluminum phthalocyanine (ClAlPc) molecules as well-ordered single-molecule dipole arrays on the silicon carbide (SiC) nanomesh substrate was investigated using low temperature scanning tunneling microscopy. ClAlPc exclusively adsorbs in the center of the SiC nanomesh holes with its inherent dipole (from Cl to Al) pointing toward the substrate. The dipole can be inverted by a positively biased tip with a threshold tip voltage of 3.3 V. We deduce that the interaction between the intrinsic dipole of ClAlPc and the periodic out-of-plane component of the surface dipole on the SiC nanomesh plays a significant role in the dipole array formation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The self-assembly of nonplanar chloroaluminum phthalocyanine (ClAlPc) molecules as well-ordered single-molecule dipole arrays on the silicon carbide (SiC) nanomesh substrate was investigated using low temperature scanning tunneling microscopy. ClAlPc exclusively adsorbs in the center of the SiC nanomesh holes with its inherent dipole (from Cl to Al) pointing toward the substrate. The dipole can be inverted by a positively biased tip with a threshold tip voltage of 3.3 V. We deduce that the interaction between the intrinsic dipole of ClAlPc and the periodic out-of-plane component of the surface dipole on the SiC nanomesh plays a significant role in the dipole array formation. |
Britnell, Liam; Gorbachev, Roman V; Jalil, Rashid; Belle, Branson D; Schedin, Fred; Katsnelson, Mikhail I; Eaves, Laurence; Morozov, Sergey V; Mayorov, Alexander S; Peres, Nuno M R; Neto, Antonio Castro H; Leist, Jon; Geim, Andre K; Ponomarenko, Leonid A; Novoselov, Kostya S Electron Tunneling through Ultrathin Boron Nitride Crystalline Barriers Journal Article NANO LETTERS, 12 (3), pp. 1707-1710, 2012, ISSN: 1530-6984. @article{ISI:000301406800102, title = {Electron Tunneling through Ultrathin Boron Nitride Crystalline Barriers}, author = {Liam Britnell and Roman V Gorbachev and Rashid Jalil and Branson D Belle and Fred Schedin and Mikhail I Katsnelson and Laurence Eaves and Sergey V Morozov and Alexander S Mayorov and Nuno M R Peres and Antonio H Castro Neto and Jon Leist and Andre K Geim and Leonid A Ponomarenko and Kostya S Novoselov}, doi = {10.1021/nl3002205}, issn = {1530-6984}, year = {2012}, date = {2012-03-01}, journal = {NANO LETTERS}, volume = {12}, number = {3}, pages = {1707-1710}, abstract = {We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel. |
Mao, Jinhai; Huang, Li; Pan, Yi; Gao, Min; He, Junfeng; Zhou, Haitao; Guo, Haiming; Tian, Yuan; Zou, Qiang; Zhang, Lizhi; Zhang, Haigang; Wang, Yeliang; Du, Shixuan; Zhou, Xingjiang; Neto, Castro A H; Gao, Hong-Jun Silicon layer intercalation of centimeter-scale, epitaxially grown monolayer graphene on Ru(0001) Journal Article APPLIED PHYSICS LETTERS, 100 (9), 2012, ISSN: 0003-6951. @article{ISI:000301504800048, title = {Silicon layer intercalation of centimeter-scale, epitaxially grown monolayer graphene on Ru(0001)}, author = {Jinhai Mao and Li Huang and Yi Pan and Min Gao and Junfeng He and Haitao Zhou and Haiming Guo and Yuan Tian and Qiang Zou and Lizhi Zhang and Haigang Zhang and Yeliang Wang and Shixuan Du and Xingjiang Zhou and A H Castro Neto and Hong-Jun Gao}, doi = {10.1063/1.3687190}, issn = {0003-6951}, year = {2012}, date = {2012-02-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {100}, number = {9}, abstract = {We develop a strategy for graphene growth on Ru(0001) followed by silicon-layer intercalation that not only weakens the interaction of graphene with the metal substrate but also retains its superlative properties. This G/Si/Ru architecture, produced by silicon-layer intercalation approach (SIA), was characterized by scanning tunneling microscopy/spectroscopy and angle resolved electron photoemission spectroscopy. These experiments show high structural and electronic qualities of this new composite. The SIA allows for an atomic control of the distance between the graphene and the metal substrate that can be used as a top gate. Our results show potential for the next generation of graphene-based materials with tailored properties. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3687190]}, keywords = {}, pubstate = {published}, tppubtype = {article} } We develop a strategy for graphene growth on Ru(0001) followed by silicon-layer intercalation that not only weakens the interaction of graphene with the metal substrate but also retains its superlative properties. This G/Si/Ru architecture, produced by silicon-layer intercalation approach (SIA), was characterized by scanning tunneling microscopy/spectroscopy and angle resolved electron photoemission spectroscopy. These experiments show high structural and electronic qualities of this new composite. The SIA allows for an atomic control of the distance between the graphene and the metal substrate that can be used as a top gate. Our results show potential for the next generation of graphene-based materials with tailored properties. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3687190] |
Britnell, L; Gorbachev, R V; Jalil, R; Belle, B D; Schedin, F; Mishchenko, A; Georgiou, T; Katsnelson, M I; Eaves, L; Morozov, S V; Peres, N M R; Leist, J; Geim, A K; Novoselov, K S; Ponomarenko, L A Field-Effect Tunneling Transistor Based on Vertical Graphene Heterostructures Journal Article SCIENCE, 335 (6071), pp. 947-950, 2012, ISSN: 0036-8075. @article{ISI:000300931800040, title = {Field-Effect Tunneling Transistor Based on Vertical Graphene Heterostructures}, author = {L Britnell and R V Gorbachev and R Jalil and B D Belle and F Schedin and A Mishchenko and T Georgiou and M I Katsnelson and L Eaves and S V Morozov and N M R Peres and J Leist and A K Geim and K S Novoselov and L A Ponomarenko}, doi = {10.1126/science.1218461}, issn = {0036-8075}, year = {2012}, date = {2012-02-01}, journal = {SCIENCE}, volume = {335}, number = {6071}, pages = {947-950}, abstract = {An obstacle to the use of graphene as an alternative to silicon electronics has been the absence of an energy gap between its conduction and valence bands, which makes it difficult to achieve low power dissipation in the OFF state. We report a bipolar field-effect transistor that exploits the low density of states in graphene and its one-atomic-layer thickness. Our prototype devices are graphene heterostructures with atomically thin boron nitride or molybdenum disulfide acting as a vertical transport barrier. They exhibit room-temperature switching ratios of approximate to 50 and approximate to 10,000, respectively. Such devices have potential for high-frequency operation and large-scale integration.}, keywords = {}, pubstate = {published}, tppubtype = {article} } An obstacle to the use of graphene as an alternative to silicon electronics has been the absence of an energy gap between its conduction and valence bands, which makes it difficult to achieve low power dissipation in the OFF state. We report a bipolar field-effect transistor that exploits the low density of states in graphene and its one-atomic-layer thickness. Our prototype devices are graphene heterostructures with atomically thin boron nitride or molybdenum disulfide acting as a vertical transport barrier. They exhibit room-temperature switching ratios of approximate to 50 and approximate to 10,000, respectively. Such devices have potential for high-frequency operation and large-scale integration. |
Zhang, L M; Andreev, G O; Fei, Z; McLeod, A S; Dominguez, G; Thiemens, M; Castro-Neto, A H; Basov, D N; Fogler, M M Near-field spectroscopy of silicon dioxide thin films Journal Article PHYSICAL REVIEW B, 85 (7), 2012, ISSN: 2469-9950. @article{ISI:000300566200010, title = {Near-field spectroscopy of silicon dioxide thin films}, author = {L M Zhang and G O Andreev and Z Fei and A S McLeod and G Dominguez and M Thiemens and A H Castro-Neto and D N Basov and M M Fogler}, doi = {10.1103/PhysRevB.85.075419}, issn = {2469-9950}, year = {2012}, date = {2012-02-01}, journal = {PHYSICAL REVIEW B}, volume = {85}, number = {7}, abstract = {We analyze the results of scanning near-field infrared spectroscopy performed on thin films of a-SiO2 on Si substrate. The measured near-field signal exhibits surface-phonon resonances whose strength has a prominent thickness dependence in the range from 2 to 300 nm. These observations are compared with calculations in which the tip of the near-field infrared spectrometer is modeled either as a point dipole or an elongated spheroid. The latter model accounts for the antenna effect of the tip and gives a better agreement with the experiment. Possible applications of the near-field technique for depth profiling of layered nanostructures are discussed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We analyze the results of scanning near-field infrared spectroscopy performed on thin films of a-SiO2 on Si substrate. The measured near-field signal exhibits surface-phonon resonances whose strength has a prominent thickness dependence in the range from 2 to 300 nm. These observations are compared with calculations in which the tip of the near-field infrared spectrometer is modeled either as a point dipole or an elongated spheroid. The latter model accounts for the antenna effect of the tip and gives a better agreement with the experiment. Possible applications of the near-field technique for depth profiling of layered nanostructures are discussed. |
Tang, Lena A L; Lee, Wong Cheng; Shi, Hui; Wong, Ethel Y L; Sadovoy, Anton; Gorelik, Sergey; Hobley, Jonathan; Lim, Chwee Teck; Loh, Kian Ping Highly Wrinkled Cross-Linked Graphene Oxide Membranes for Biological and Charge-Storage Applications Journal Article SMALL, 8 (3), pp. 423-431, 2012, ISSN: 1613-6810. @article{ISI:000299621500013, title = {Highly Wrinkled Cross-Linked Graphene Oxide Membranes for Biological and Charge-Storage Applications}, author = {Lena A L Tang and Wong Cheng Lee and Hui Shi and Ethel Y L Wong and Anton Sadovoy and Sergey Gorelik and Jonathan Hobley and Chwee Teck Lim and Kian Ping Loh}, doi = {10.1002/smll.201101690}, issn = {1613-6810}, year = {2012}, date = {2012-02-01}, journal = {SMALL}, volume = {8}, number = {3}, pages = {423-431}, abstract = {Inspired by the amphiphilicity of graphene oxide (GO), the surface of water is used as a template for the assembly of a GO film. Methacrylate-functionalized GO sheets can be cross-linked instantaneously at the waterair interface to form a highly wrinkled membrane spreading over an extended area. The multiple covalent linkages amongst the GO sheets enhances the in-plane stiffness of the film compared to noncovalently bonded GO films. The highly convoluted GO membrane can be used in two applications: the promoting of spontaneous stem-cell differentiation towards bone cell lineage without any chemical inducers, and for supercapacitor electrodes. Due to reduced van der Waals restacking, capacitance values up to 211 F g-1 can be obtained. The scalable and inexpensive nature of this assembly route enables the engineering of membranes for applications in regenerative medicine and energy-storage devices where secondary structures like nanotopography and porosity are important performance enhancers.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Inspired by the amphiphilicity of graphene oxide (GO), the surface of water is used as a template for the assembly of a GO film. Methacrylate-functionalized GO sheets can be cross-linked instantaneously at the waterair interface to form a highly wrinkled membrane spreading over an extended area. The multiple covalent linkages amongst the GO sheets enhances the in-plane stiffness of the film compared to noncovalently bonded GO films. The highly convoluted GO membrane can be used in two applications: the promoting of spontaneous stem-cell differentiation towards bone cell lineage without any chemical inducers, and for supercapacitor electrodes. Due to reduced van der Waals restacking, capacitance values up to 211 F g-1 can be obtained. The scalable and inexpensive nature of this assembly route enables the engineering of membranes for applications in regenerative medicine and energy-storage devices where secondary structures like nanotopography and porosity are important performance enhancers. |
Wang, Yu; Jaiswal, Manu; Lin, Ming; Saha, Surajit; Oezyilmaz, Barbaros; Loh, Kian Ping Electronic Properties of Nanodiamond Decorated Graphene Journal Article ACS NANO, 6 (2), pp. 1018-1025, 2012, ISSN: 1936-0851. @article{ISI:000300757900005, title = {Electronic Properties of Nanodiamond Decorated Graphene}, author = {Yu Wang and Manu Jaiswal and Ming Lin and Surajit Saha and Barbaros Oezyilmaz and Kian Ping Loh}, doi = {10.1021/nn204362p}, issn = {1936-0851}, year = {2012}, date = {2012-02-01}, journal = {ACS NANO}, volume = {6}, number = {2}, pages = {1018-1025}, abstract = {The electronic properties of graphene sheets decorated with nanodiamond (ND) particles have been investigated. The chemical fusion of ND to the graphene lattice creates pockets of local defects with robust interfacial bonding. At the ND-bonded regions, the atoms of graphene lattice follow sp(3)-like bonding, and such regions play the role of conduction bottlenecks for the percolating sp(2) graphene network. The low-temperature charge transport reveals an insulating behavior for the disordered system associated with Anderson localization for the charge carriers in graphene. A large negative magnetoresistance is observed in this insulating regime, and its origin is discussed in the context of magnetic correlations of the localized charge carriers with local magnetic domains and extrinsic metal impurities associated with the ND.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The electronic properties of graphene sheets decorated with nanodiamond (ND) particles have been investigated. The chemical fusion of ND to the graphene lattice creates pockets of local defects with robust interfacial bonding. At the ND-bonded regions, the atoms of graphene lattice follow sp(3)-like bonding, and such regions play the role of conduction bottlenecks for the percolating sp(2) graphene network. The low-temperature charge transport reveals an insulating behavior for the disordered system associated with Anderson localization for the charge carriers in graphene. A large negative magnetoresistance is observed in this insulating regime, and its origin is discussed in the context of magnetic correlations of the localized charge carriers with local magnetic domains and extrinsic metal impurities associated with the ND. |
Ni, Guang-Xin; Zheng, Yi; Bae, Sukang; Kim, Hye Ri; Pachoud, Alexandre; Kim, Young Soo; Tan, Chang-Ling; Im, Danho; Ahn, Jong-Hyun; Hong, Byung Hee; Oezyilmaz, Barbaros Quasi-Periodic Nanoripples in Graphene Grown by Chemical Vapor Deposition and Its Impact on Charge Transport Journal Article ACS NANO, 6 (2), pp. 1158-1164, 2012, ISSN: 1936-0851. @article{ISI:000300757900021, title = {Quasi-Periodic Nanoripples in Graphene Grown by Chemical Vapor Deposition and Its Impact on Charge Transport}, author = {Guang-Xin Ni and Yi Zheng and Sukang Bae and Hye Ri Kim and Alexandre Pachoud and Young Soo Kim and Chang-Ling Tan and Danho Im and Jong-Hyun Ahn and Byung Hee Hong and Barbaros Oezyilmaz}, doi = {10.1021/nn203775x}, issn = {1936-0851}, year = {2012}, date = {2012-02-01}, journal = {ACS NANO}, volume = {6}, number = {2}, pages = {1158-1164}, abstract = {The technical breakthrough in synthesizing graphene by chemical vapor deposition methods (CVD) has opened up enormous opportunities for large-scale device applications. To improve the electrical properties of CVD graphene grown on copper (Cu-CVD graphene), recent efforts have focused on increasing the grain size of such polycrystalline graphene films to 100 mu m and larger. While an increase in grain size and, hence, a decrease of grain boundary density is expected to greatly enhance the device performance, here we show that the charge mobility and sheet resistance of Cu-CVD graphene Is already limited within a single grain. We find that the current high-temperature growth and wet transfer methods of CVD graphene result in quasi-periodic nanoripple arrays (NRAs). Electron-flexural phonon scattering in such partially suspended graphene devices Introduces anisotropic charge transport and sets limits to both the highest possible charge mobility and lowest possible sheet resistance values. Our findings provide guidance for further improving the CVD graphene growth and transfer process.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The technical breakthrough in synthesizing graphene by chemical vapor deposition methods (CVD) has opened up enormous opportunities for large-scale device applications. To improve the electrical properties of CVD graphene grown on copper (Cu-CVD graphene), recent efforts have focused on increasing the grain size of such polycrystalline graphene films to 100 mu m and larger. While an increase in grain size and, hence, a decrease of grain boundary density is expected to greatly enhance the device performance, here we show that the charge mobility and sheet resistance of Cu-CVD graphene Is already limited within a single grain. We find that the current high-temperature growth and wet transfer methods of CVD graphene result in quasi-periodic nanoripple arrays (NRAs). Electron-flexural phonon scattering in such partially suspended graphene devices Introduces anisotropic charge transport and sets limits to both the highest possible charge mobility and lowest possible sheet resistance values. Our findings provide guidance for further improving the CVD graphene growth and transfer process. |
Reddy, M V; Yu, Cai; Jiahuan, Fan; Loh, Kian Ping; Chowdari, B V R Molten salt synthesis and energy storage studies on CuCo2O4 and CuO center dot Co3O4 Journal Article RSC ADVANCES, 2 (25), pp. 9619-9625, 2012, ISSN: 2046-2069. @article{ISI:000312061000042, title = {Molten salt synthesis and energy storage studies on CuCo2O4 and CuO center dot Co3O4}, author = {M V Reddy and Cai Yu and Fan Jiahuan and Kian Ping Loh and B V R Chowdari}, doi = {10.1039/c2ra21033a}, issn = {2046-2069}, year = {2012}, date = {2012-01-01}, journal = {RSC ADVANCES}, volume = {2}, number = {25}, pages = {9619-9625}, abstract = {CuCo2O4 and CuO center dot Co3O4 compounds were prepared by a one-pot simple molten salt method (MSM) at 280 degrees C to 750 degrees C. Changes in morphology, crystal structure and electrochemical properties of CuCo2O4 as a function of preparation temperatures were investigated using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer-Emmett- Teller absorption isotherm. XRD patterns of the sample prepared at 280 degrees C show a crystalline cubic structure with a lattice parameter value of a = 8.131 angstrom and a surface area value of 9.8 m(2) g(-1). The sample prepared at temperatures >510 degrees C shows the presence of CuO center dot Co3O4 phases. Energy storage properties are evaluated using cyclic voltammetry (CV) and galvanostatic cycling studies. CV studies show a main anodic peak at similar to 2.1 V and cathodic peak at similar to 1.2 V. At a current rate of 60 mA g(-1) and in the voltage range of 0.005-3.0 V vs. Li, CuCo2O4 composite prepared at 510 degrees C shows a high and stable capacity of similar to 680 (quenched) and 740 (slow cooling) mAh g(-1) at the end of the 40th cycle.}, keywords = {}, pubstate = {published}, tppubtype = {article} } CuCo2O4 and CuO center dot Co3O4 compounds were prepared by a one-pot simple molten salt method (MSM) at 280 degrees C to 750 degrees C. Changes in morphology, crystal structure and electrochemical properties of CuCo2O4 as a function of preparation temperatures were investigated using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer-Emmett- Teller absorption isotherm. XRD patterns of the sample prepared at 280 degrees C show a crystalline cubic structure with a lattice parameter value of a = 8.131 angstrom and a surface area value of 9.8 m(2) g(-1). The sample prepared at temperatures >510 degrees C shows the presence of CuO center dot Co3O4 phases. Energy storage properties are evaluated using cyclic voltammetry (CV) and galvanostatic cycling studies. CV studies show a main anodic peak at similar to 2.1 V and cathodic peak at similar to 1.2 V. At a current rate of 60 mA g(-1) and in the voltage range of 0.005-3.0 V vs. Li, CuCo2O4 composite prepared at 510 degrees C shows a high and stable capacity of similar to 680 (quenched) and 740 (slow cooling) mAh g(-1) at the end of the 40th cycle. |
Lu, Jiong; Yeo, Pei Shan Emmeline; Zheng, Yi; Yang, Zhiyong; Bao, Qiaoliang; Gan, Chee Kwan; Loh, Kian Ping Using the Graphene Moire Pattern for the Trapping of C-60 and Homoepitaxy of Graphene Journal Article ACS NANO, 6 (1), pp. 944-950, 2012, ISSN: 1936-0851. @article{ISI:000299368300112, title = {Using the Graphene Moire Pattern for the Trapping of C-60 and Homoepitaxy of Graphene}, author = {Jiong Lu and Pei Shan Emmeline Yeo and Yi Zheng and Zhiyong Yang and Qiaoliang Bao and Chee Kwan Gan and Kian Ping Loh}, doi = {10.1021/nn204536e}, issn = {1936-0851}, year = {2012}, date = {2012-01-01}, journal = {ACS NANO}, volume = {6}, number = {1}, pages = {944-950}, abstract = {The graphene Moire superstructure offers a complex landscape of humps and valleys to molecules adsorbing and diffusing on it. Using C-60 molecules as the classic hard sphere analogue, we examine its assembly and layered growth on this corrugated landscape. At the monolayer level, the cohesive interactions of C-60 molecules adsorbing on the Moire lattice freeze the molecular rotation of C-60 trapped in the valley sites, resulting in molecular alignment of all similarly trapped C-60 molecules at room temperature. The hierarchy of adsorption potential well on the Moire lattice causes diffusion-limited dendritic growth of C-60 films, as opposed to isotropic growth observed on a smooth surface like graphite. Due to the strong binding energy of the C-60 film, part of the dentritic C-60 films polymerize at 850 K and act as solid carbon sources for graphene homoepitaxy. Our findings point to the possibility of using periodically corrugated graphene in molecular spintronics due to its ability to trap and align organic molecules at room temperature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The graphene Moire superstructure offers a complex landscape of humps and valleys to molecules adsorbing and diffusing on it. Using C-60 molecules as the classic hard sphere analogue, we examine its assembly and layered growth on this corrugated landscape. At the monolayer level, the cohesive interactions of C-60 molecules adsorbing on the Moire lattice freeze the molecular rotation of C-60 trapped in the valley sites, resulting in molecular alignment of all similarly trapped C-60 molecules at room temperature. The hierarchy of adsorption potential well on the Moire lattice causes diffusion-limited dendritic growth of C-60 films, as opposed to isotropic growth observed on a smooth surface like graphite. Due to the strong binding energy of the C-60 film, part of the dentritic C-60 films polymerize at 850 K and act as solid carbon sources for graphene homoepitaxy. Our findings point to the possibility of using periodically corrugated graphene in molecular spintronics due to its ability to trap and align organic molecules at room temperature. |
Novoselov, K S; Neto, Castro A H Two-dimensional crystals-based heterostructures: materials with tailored properties Journal Article PHYSICA SCRIPTA, T146 , 2012, ISSN: 0031-8949, (Nobel Symposium on Graphene and Quantum Matter, Saltsjobaden, SWEDEN, MAY 27-31, 2010). @article{ISI:000300504800007, title = {Two-dimensional crystals-based heterostructures: materials with tailored properties}, author = {K S Novoselov and A H Castro Neto}, doi = {10.1088/0031-8949/2012/T146/014006}, issn = {0031-8949}, year = {2012}, date = {2012-01-01}, journal = {PHYSICA SCRIPTA}, volume = {T146}, abstract = {Graphene is just one example of a large class of two-dimensional crystals. These crystals can either be extracted from layered three-dimensional materials or grown artificially by several different methods. Furthermore, they present physical properties that are unique because of the low dimensionality and their special crystal structure. They have potential for semiconducting behavior, magnetism, superconductivity, and even more complex many-body phenomena. Two-dimensional crystals can also be assembled in three-dimensional heterostructures that do not exist in nature and have tailored properties, opening an entirely new chapter in condensed matter research.}, note = {Nobel Symposium on Graphene and Quantum Matter, Saltsjobaden, SWEDEN, MAY 27-31, 2010}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene is just one example of a large class of two-dimensional crystals. These crystals can either be extracted from layered three-dimensional materials or grown artificially by several different methods. Furthermore, they present physical properties that are unique because of the low dimensionality and their special crystal structure. They have potential for semiconducting behavior, magnetism, superconductivity, and even more complex many-body phenomena. Two-dimensional crystals can also be assembled in three-dimensional heterostructures that do not exist in nature and have tailored properties, opening an entirely new chapter in condensed matter research. |
2011 |
e Lopes, P L S; Neto, Castro A H; Caldeira, A O Chiral filtering in graphene with coupled valleys Journal Article PHYSICAL REVIEW B, 84 (24), 2011, ISSN: 1098-0121. @article{ISI:000298116400011, title = {Chiral filtering in graphene with coupled valleys}, author = {P L S e Lopes and A H Castro Neto and A O Caldeira}, doi = {10.1103/PhysRevB.84.245432}, issn = {1098-0121}, year = {2011}, date = {2011-12-01}, journal = {PHYSICAL REVIEW B}, volume = {84}, number = {24}, abstract = {We analyze the problem of electronic transmission through different regions of a graphene sheet that are characterized by different types of connections between the Dirac points. These valley symmetry breaking Hamiltonians might arise from electronic self-interaction mediated by the dielectric environment of distinct parts of the substrate on which the graphene sheet is placed. We show that it is possible to have situations in which we can use these regions to select or filter states of one desired chirality.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We analyze the problem of electronic transmission through different regions of a graphene sheet that are characterized by different types of connections between the Dirac points. These valley symmetry breaking Hamiltonians might arise from electronic self-interaction mediated by the dielectric environment of distinct parts of the substrate on which the graphene sheet is placed. We show that it is possible to have situations in which we can use these regions to select or filter states of one desired chirality. |
Ang, Priscilla Kailian; Li, Ang; Jaiswal, Manu; Wang, Yu; Hou, Han Wei; Thong, John T L; Lim, Chwee Teck; Loh, Kian Ping Flow Sensing of Single Cell by Graphene Transistor in a Microfluidic Channel Journal Article NANO LETTERS, 11 (12), pp. 5240-5246, 2011, ISSN: 1530-6984. @article{ISI:000297950200024, title = {Flow Sensing of Single Cell by Graphene Transistor in a Microfluidic Channel}, author = {Priscilla Kailian Ang and Ang Li and Manu Jaiswal and Yu Wang and Han Wei Hou and John T L Thong and Chwee Teck Lim and Kian Ping Loh}, doi = {10.1021/nl202579k}, issn = {1530-6984}, year = {2011}, date = {2011-12-01}, journal = {NANO LETTERS}, volume = {11}, number = {12}, pages = {5240-5246}, abstract = {The electronic properties of graphene are strongly influenced by electrostatic forces arising from long-range charge scatterers and by changes in the local dielectric environment. This makes graphene extremely sensitive to the surface charge density of cells interfacing with it Here, we developed a graphene transistor array integrated with microfluidic flow cytometry for the ``flow-catch-release'' sensing of malaria-infected red blood cells at the single-cell level. Malaria-infected red blood cells induce highly sensitive capacitively coupled changes in the conductivity of graphene. Together with the characteristic conductance dwell times, specific microscopic information about the disease state can be obtained.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The electronic properties of graphene are strongly influenced by electrostatic forces arising from long-range charge scatterers and by changes in the local dielectric environment. This makes graphene extremely sensitive to the surface charge density of cells interfacing with it Here, we developed a graphene transistor array integrated with microfluidic flow cytometry for the ``flow-catch-release'' sensing of malaria-infected red blood cells at the single-cell level. Malaria-infected red blood cells induce highly sensitive capacitively coupled changes in the conductivity of graphene. Together with the characteristic conductance dwell times, specific microscopic information about the disease state can be obtained. |
Ferreira, Aires; Viana-Gomes, J; Bludov, Yu. V; Pereira, V; Peres, N M R; Neto, Castro A H Faraday effect in graphene enclosed in an optical cavity and the equation of motion method for the study of magneto-optical transport in solids Journal Article PHYSICAL REVIEW B, 84 (23), 2011, ISSN: 2469-9950. @article{ISI:000297551600027, title = {Faraday effect in graphene enclosed in an optical cavity and the equation of motion method for the study of magneto-optical transport in solids}, author = {Aires Ferreira and J Viana-Gomes and Yu. V Bludov and V Pereira and N M R Peres and A H Castro Neto}, doi = {10.1103/PhysRevB.84.235410}, issn = {2469-9950}, year = {2011}, date = {2011-12-01}, journal = {PHYSICAL REVIEW B}, volume = {84}, number = {23}, abstract = {We show that by enclosing graphene in an optical cavity, giant Faraday rotations in the infrared regime are generated and measurable Faraday rotation angles in the visible range become possible. Explicit expressions for the Hall steps of the Faraday rotation angle are given for relevant regimes. In the context of this problem we develop an equation of motion (EOM) method for calculation of the magneto-optical properties of metals and semiconductors. It is shown that properly regularized EOM solutions are fully equivalent to the Kubo formula.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show that by enclosing graphene in an optical cavity, giant Faraday rotations in the infrared regime are generated and measurable Faraday rotation angles in the visible range become possible. Explicit expressions for the Hall steps of the Faraday rotation angle are given for relevant regimes. In the context of this problem we develop an equation of motion (EOM) method for calculation of the magneto-optical properties of metals and semiconductors. It is shown that properly regularized EOM solutions are fully equivalent to the Kubo formula. |
Lee, Dong Su; Riedl, Christian; Beringer, Thomas; Neto, Castro A H; von Klitzing, Klaus; Starke, Ulrich; Smet, Jurgen H Quantum Hall Effect in Twisted Bilayer Graphene Journal Article PHYSICAL REVIEW LETTERS, 107 (21), 2011, ISSN: 0031-9007. @article{ISI:000297136400005, title = {Quantum Hall Effect in Twisted Bilayer Graphene}, author = {Dong Su Lee and Christian Riedl and Thomas Beringer and A H Castro Neto and Klaus von Klitzing and Ulrich Starke and Jurgen H Smet}, doi = {10.1103/PhysRevLett.107.216602}, issn = {0031-9007}, year = {2011}, date = {2011-11-01}, journal = {PHYSICAL REVIEW LETTERS}, volume = {107}, number = {21}, abstract = {We address the quantum Hall behavior in twisted bilayer graphene transferred from the C face of SiC. The measured Hall conductivity exhibits the same plateau values as for a commensurate Bernal bilayer. This implies that the eightfold degeneracy of the zero energy mode is topologically protected despite rotational disorder as recently predicted. In addition, an anomaly appears. The densities at which these plateaus occur show a magnetic field dependent offset. It suggests the existence of a pool of localized states at low energy, which do not count towards the degeneracy of the lowest band Landau levels. These states originate from an inhomogeneous spatial variation of the interlayer coupling.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We address the quantum Hall behavior in twisted bilayer graphene transferred from the C face of SiC. The measured Hall conductivity exhibits the same plateau values as for a commensurate Bernal bilayer. This implies that the eightfold degeneracy of the zero energy mode is topologically protected despite rotational disorder as recently predicted. In addition, an anomaly appears. The densities at which these plateaus occur show a magnetic field dependent offset. It suggests the existence of a pool of localized states at low energy, which do not count towards the degeneracy of the lowest band Landau levels. These states originate from an inhomogeneous spatial variation of the interlayer coupling. |
Fei, Zhe; Andreev, Gregory O; Bao, Wenzhong; Zhang, Lingfeng M; McLeod, Alexander S; Wang, Chen; Stewart, Margaret K; Zhao, Zeng; Dominguez, Gerardo; Thiemens, Mark; Fogler, Michael M; Tauber, Michael J; Castro-Neto, Antonio H; Lau, Chun Ning; Keilmann, Fritz; Basov, Dimitri N Infrared Nanoscopy of Dirac Plasmons at the Graphene-SiO2 Interface Journal Article NANO LETTERS, 11 (11), pp. 4701-4705, 2011, ISSN: 1530-6984. @article{ISI:000296674700036, title = {Infrared Nanoscopy of Dirac Plasmons at the Graphene-SiO2 Interface}, author = {Zhe Fei and Gregory O Andreev and Wenzhong Bao and Lingfeng M Zhang and Alexander S McLeod and Chen Wang and Margaret K Stewart and Zeng Zhao and Gerardo Dominguez and Mark Thiemens and Michael M Fogler and Michael J Tauber and Antonio H Castro-Neto and Chun Ning Lau and Fritz Keilmann and Dimitri N Basov}, doi = {10.1021/nl202362d}, issn = {1530-6984}, year = {2011}, date = {2011-11-01}, journal = {NANO LETTERS}, volume = {11}, number = {11}, pages = {4701-4705}, abstract = {We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding 2 orders of magnitude increase in the value of in-plane component of incident wavevector q compared to free space propagation. At these high wavevectors, the Dirac plasmon is found to dramatically enhance the near-field interaction with mid-IR surface phonons of SiO2 substrate. Our data augmented by detailed modeling establish graphene as a new medium supporting plasmonic effects that can be controlled by gate voltage.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding 2 orders of magnitude increase in the value of in-plane component of incident wavevector q compared to free space propagation. At these high wavevectors, the Dirac plasmon is found to dramatically enhance the near-field interaction with mid-IR surface phonons of SiO2 substrate. Our data augmented by detailed modeling establish graphene as a new medium supporting plasmonic effects that can be controlled by gate voltage. |
Rodrigues, J N B; Goncalves, P A D; Rodrigues, N F G; Ribeiro, R M; dos Santos, Lopes J M B; Peres, N M R Zigzag graphene nanoribbon edge reconstruction with Stone-Wales defects Journal Article PHYSICAL REVIEW B, 84 (15), 2011, ISSN: 1098-0121. @article{ISI:000296290000014, title = {Zigzag graphene nanoribbon edge reconstruction with Stone-Wales defects}, author = {J N B Rodrigues and P A D Goncalves and N F G Rodrigues and R M Ribeiro and J M B Lopes dos Santos and N M R Peres}, doi = {10.1103/PhysRevB.84.155435}, issn = {1098-0121}, year = {2011}, date = {2011-10-01}, journal = {PHYSICAL REVIEW B}, volume = {84}, number = {15}, abstract = {In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge states. They are dispersive, with nonzero amplitudes in both sublattices; furthermore, the amplitudes have two components that decrease with different decay lengths with the distance from the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero-energy Landau level is no longer degenerate with edge states as in the case of the pristine zigzag ribbon.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge states. They are dispersive, with nonzero amplitudes in both sublattices; furthermore, the amplitudes have two components that decrease with different decay lengths with the distance from the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero-energy Landau level is no longer degenerate with edge states as in the case of the pristine zigzag ribbon. |
Rappoport, T G; Godoy, M; Uchoa, B; Santos, Dos R R; Neto, Castro A H Magnetic exchange mechanism for electronic gap opening in graphene Journal Article EPL, 96 (2), 2011, ISSN: 0295-5075. @article{ISI:000295974600033, title = {Magnetic exchange mechanism for electronic gap opening in graphene}, author = {T G Rappoport and M Godoy and B Uchoa and R R Dos Santos and A H Castro Neto}, doi = {10.1209/0295-5075/96/27010}, issn = {0295-5075}, year = {2011}, date = {2011-10-01}, journal = {EPL}, volume = {96}, number = {2}, abstract = {We show within a local self-consistent mean-field treatment that a random distribution of magnetic adatoms can open a robust gap in the electronic spectrum of graphene. The electronic gap results from the localization of the charge carriers that arises from the interplay between the graphene sublattice structure and the exchange interaction between the adatoms. The size of the gap depends on the strength of the exchange interaction between carriers and localized spins and can be controlled by both temperature and external magnetic field. Furthermore, we show that an external magnetic field creates an imbalance of spin-up and spin-down carriers at the Fermi level, making doped graphene suitable for spin injection and other spintronic applications. Copyright (C) EPLA, 2011}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show within a local self-consistent mean-field treatment that a random distribution of magnetic adatoms can open a robust gap in the electronic spectrum of graphene. The electronic gap results from the localization of the charge carriers that arises from the interplay between the graphene sublattice structure and the exchange interaction between the adatoms. The size of the gap depends on the strength of the exchange interaction between carriers and localized spins and can be controlled by both temperature and external magnetic field. Furthermore, we show that an external magnetic field creates an imbalance of spin-up and spin-down carriers at the Fermi level, making doped graphene suitable for spin injection and other spintronic applications. Copyright (C) EPLA, 2011 |